CN118613654A - Actuator assembly - Google Patents

Abstract

An actuator assembly includes: a support structure including a first friction surface; a movable component including a second friction surface engaging the first friction surface; one or more SMA wires arranged to move the movable component relative to the support structure to any position within a range of motion when contracted; a biasing device arranged to bias the first friction surface and the second friction surface against each other with a normal force, thereby generating a static friction force that constrains movement of the movable component relative to the support structure at any position within the range of motion when the one or more SMA wires are not contracted, wherein the one or more SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface when contracted.

Description

Actuator assembly

field

The present application relates generally to actuator assemblies, and in particular to shape memory alloy (SMA) actuator assemblies.

background

Shape memory alloy (SMA) actuators are used in camera assemblies to achieve a series of movements of a lens carriage or an image sensor. For example, WO 2013/175197 A1 describes a camera having an SMA actuator assembly having an SMA wire that is configured to move a movable component in a direction perpendicular to the optical axis when contracted to provide optical image stabilization (OIS). The actuator assembly includes a flexible arm that provides a lateral biasing force that biases the lens assembly toward a center position. However, in some cases where it is desired to maintain the lens assembly in a given position, such known actuator assemblies will rely on continuous energization of the SMA wire over a long period of time. This arrangement not only consumes energy during the holding period, but the stability of the lens carriage is also susceptible to sudden movement and other external factors.

WO2020/120997A1 discloses various devices for holding a lens holder in a given position by friction. In particular, when the SMA wire is not energized, the lens holder is biased against the surface of the support structure by a biasing element to hold the lens holder in any given position. When actuated, the SMA wire acts on the biasing element to reduce friction, thereby enabling the lens holder to be driven to a new position.

Overview

The present invention provides various means for maintaining a movable component in a desired position when the SMA wires in the SMA actuator assembly are not energized, thereby eliminating the need for the SMA actuator to be continuously energized as required by the known art.

According to the present invention, an actuator assembly is provided, the actuator assembly comprising: a support structure, the support structure comprising a first friction surface; a movable part, the movable part comprising a second friction surface engaging the first friction surface; one or more SMA wires, the one or more SMA wires being arranged to move the movable part relative to the support structure to any position within a range of motion when contracted; a biasing device, the biasing device being arranged to bias the first friction surface and the second friction surface against each other with a normal force, thereby generating a static friction force, which constrains the movement of the movable part relative to the support structure at any position within the range of motion when the one or more SMA wires are not contracted, wherein the movable part or the support structure comprises a biasing device so that the biasing device moves with the movable part or remains static relative to the support structure, and the biasing device is arranged to apply a normal force only in a direction perpendicular to the range of motion at any position within the range of motion; wherein the one or more SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface when contracted.

When the SMA wire is not energized, the friction force constrains the movement of the movable component relative to the support structure. The movable component can be maintained in place without power consumption, thereby reducing the overall power consumption of the actuator assembly. When the SMA wire contracts, the normal force between the first friction surface and the second friction surface is reduced, and therefore the friction force is also reduced. The reduction in friction helps to overcome the friction force so that the movable component can be moved by the SMA wire. The movable component or the support structure includes a biasing device so that the normal force is only applied in a direction perpendicular to the range of motion at any position within the range of motion. This ensures that the biasing device does not oppose the stress in the SMA wire used to move the movable component.

According to the present invention, an actuator assembly is also provided, which includes: a support structure, which includes a first friction surface; a movable part, which includes a second friction surface engaged with the first friction surface; a support device, which is used to support the movement of the movable part relative to the support structure within a range of movement; one or more SMA wires, which are arranged to move the movable part relative to the support structure to any position within the range of movement when contracted; a biasing device, which is arranged to bias the first friction surface and the second friction surface against each other with a normal force, thereby generating a static friction force, which constrains the movement of the movable part relative to the support structure at any position within the range of movement when the one or more SMA wires are not contracted, wherein the one or more SMA wires are arranged to lift the movable part away from the first friction surface when contracted, so that the movable part is supported on the support device.

When the SMA wire is not energized, the friction force constrains the movement of the movable component relative to the support structure. The movable component can be maintained in the proper position without power consumption, thereby reducing the overall power consumption of the actuator assembly. When the SMA wire contracts, the movable component is lifted off the first friction surface, thereby eliminating the friction force that holds the movable component in the proper position when the SMA wire is not energized. Therefore, the movable component can be more easily moved within the range of motion by the SMA wire. After lifting off from the first friction surface, the movable component is only supported on the support device, thereby ensuring that the movement of the movable component is guided by the support device. This makes the controlled movement of the movable component by the SMA wire more precise and reliable than the case where the movable component is suspended only by the SMA wire after lifting off.

According to the present invention, an actuator assembly is also provided, which includes: a support structure, the support structure including a first friction surface; a movable part, the movable part including a second friction surface engaging the first friction surface; one or more SMA wires, the one or more SMA wires being arranged to move the movable part relative to the support structure to any position within a range of movement when contracted; a biasing device, the biasing device being arranged to bias the first friction surface and the second friction surface against each other with a normal force, thereby generating a static friction force, which constrains the movement of the movable part relative to the support structure at any position within the range of movement when the one or more SMA wires are not contracted, wherein the one or more SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface when contracted.

According to the present invention, there is also provided an actuator assembly, which comprises: a support structure, which comprises a first friction surface; a movable part, which comprises a second friction surface engaging the first friction surface; a spiral support device, which supports the movable element on the support structure and is arranged to guide the spiral movement of the movable element relative to the support structure around the spiral axis, wherein the spiral support device is formed by the first friction surface and the second friction surface; and one or more SMA wires, which are arranged to drive the movable element to rotate around the spiral axis when contracted, and the spiral support device converts the rotation into the spiral movement; and a biasing device, which is configured to load the spiral support device so as to bias the first friction surface and the second friction surface against each other with a normal force and generate a static friction force, which constrains the movement of the movable part relative to the support structure at any position within the range of movement when the one or more SMA wires are not contracted, wherein the one or more SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface when contracted.

Further aspects of the invention are set out in the following dependent claims and clauses and in the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG1 is a schematic side view of a prior art actuator assembly;

2A-2D are schematic side views of an actuator assembly according to an embodiment of the present invention, wherein the movable member includes a biasing device;

3A-3C are schematic side views of an actuator assembly according to an embodiment of the present invention, wherein the support structure includes a biasing device;

4A-4D are schematic side views of an actuator assembly according to an embodiment of the present invention, wherein an end stop is provided;

5A-5D are schematic side views of other embodiments of actuator assemblies;

6A-6C are schematic diagrams of an embodiment of the present invention, wherein the actuator assembly may be used as an auto focus (AF) actuator assembly in a camera device;

7A and 7B are schematic diagrams of another embodiment of the present invention, wherein the actuator assembly can be used as an auto focus (AF) actuator assembly in a camera device;

8A and 8B are partial schematic diagrams of other embodiments of the present invention;

9A-9D are schematic diagrams of an actuator assembly that may be used as an auto focus (AF) actuator assembly in a camera device; and

10A-10D are schematic diagrams of an actuator assembly that may be used as an optical image stabilization (OIS) actuator assembly in a camera device;

11A-11B are schematic diagrams of another actuator assembly that may be used as an optical image stabilization (OIS) actuator assembly in a camera device; and

12A-12B are schematic diagrams of another actuator assembly that may be used as an optical image stabilization (OIS) actuator assembly in a camera device.

Detailed Description

The present invention provides various means for maintaining a movable component of an actuator assembly in a desired position when the SMA wire is not energized, thereby eliminating the need to continuously energize the SMA wire as required by the known art.

FIG1 schematically depicts a schematic diagram of an actuator assembly 100 as disclosed in WO 2020/120997 A1. The actuator assembly 100 comprises a static component 101 and a movable component 104. The movable component 104 is movable relative to the static component 100. The static component 101 comprises a body 102 and a surface 106, which is held in a fixed position relative to the body 106, for example by a connecting portion (not shown). A gap is provided between the body 101 and the surface 106.

The movable component 104 is located in the gap between the body 102 and the surface 106. The movable component 104 is movable on the surface 106 relative to the static component 101. In this example, the movable component 104 is movable on the surface 106 in any direction in two dimensions.

The actuator assembly 100 also includes a spring 110 connected between the static component 101 and the movable component 104 by being connected to the body 101 at one end and to the movable component 104 at the other end. In this example, the spring 110 extends orthogonally to the surface 104, however this is not required. The spring 110 is held in compression and is therefore an elastic biasing element that acts as a biasing means to bias the movable component 104 into contact with the surface 106. This generates a reaction force between the movable component 104 and the surface 106, and a friction force between the movable component 104 and the surface 106.

The first actuator assembly 100 also includes two SMA wires 108 connected at one end to the body 101 and at the other end to the movable member 104. Each SMA actuator wire 108 is inclined at an acute angle a greater than 0° relative to the surface 106 so that when the SMA actuator wire 108 contracts, it applies a force having a component normal to the surface 106 that biases the movable member 104 away from the surface 106 and having a component parallel to the surface 106. The control circuit 200 in use applies a drive signal to the SMA wire 108.

In the actuator assembly 100 of FIG1 , the spring 110 is connected between the static component 101 and the movable component 102. Therefore, when the movable component 102 moves away from the initial center position, the spring 110 can generate a lateral force, i.e., a force parallel to the direction of movement. This lateral force can make it more complicated to accurately and reliably control the movement of the movable component 102. The lateral force can also counteract the friction between the movable component 102 and the static component 101.

In the case where the movable part 102 is lifted out of contact with the surface 106 by the SMA wire 108, the movable part 102 is held only by the SMA wire 108 and the spring 110. It is difficult to achieve stable positioning of the movable part 102. Controlling the SMA wire 108 to reliably and accurately move the movable part 102 without contacting the surface 106 is complicated.

Embodiments of the present invention provide improvements over the prior art actuator assembly 100 of FIG. 1 .

Actuator Assembly Overview

The following describes an embodiment of the present invention with reference to the schematic diagrams of FIG. 2 to FIG. 5 .

The actuator assembly includes a support structure 10 and a movable part 20. The movable part 20 is movable relative to the support structure 10. Generally, the support structure 10 and the movable part 20 may be referred to as a first part and a second part, respectively, and the terms "support structure 10 and movable part 20" are used herein for purely illustrative purposes. The support structure 10 may also be referred to as a static part. In this regard, the support structure 10 is used herein as a reference structure. Unless otherwise stated, the movement of any part of the actuator assembly 1 is described as relative to the support structure 10. However, generally, the support structure 10 itself may be movable, for example within a larger device containing the actuator assembly 1. In some embodiments, the support structure 10 may be composed of parts that are movable relative to each other.

The movable part 20 can move within a range of motion relative to the support structure 10. The range of motion can define movement of any number of degrees of freedom (DOF). Preferably, the range of motion defines movement of up to three degrees of freedom, such as one or three degrees of freedom. For example, the movable part 20 can move within the range of motion in a plane of motion relative to the support structure 10, and/or move along a motion axis within the range of motion.

The actuator assembly 1 includes one or more SMA wires 40. Preferably, the actuator assembly 2 includes at least two SMA wires 40. The SMA wires 40 are arranged to move the movable part 20 relative to the support structure 10 when contracted. The SMA wires 40 move the movable part 20 to any position within the range of motion. For example, the SMA wires 40 can move the movable part 20 in one DOF, two DOF, or three DOF. Preferably, the actuator assembly 1 includes at least two opposing SMA wires 40, wherein one of the two SMA wires 40 is arranged to move the movable part 20 in one direction within the range of motion, and the other of the two SMA wires 40 is arranged to move the movable part 20 in another opposite direction within the range of motion.

Each SMA wire 40 can be connected to the support structure 10 at one end by a corresponding coupling element (not shown), and connected to the movable part 20 at the other end by a corresponding coupling element (not shown). For example, the coupling element can be a crimp. The coupling element can provide a mechanical connection and an electrical connection to the SMA wire 40. In general, any other mechanism or device for transferring stress in the SMA wire 40 to the movable part 20 to drive the movable part 20 to move can be used.

The SMA wires 40 can each be electrically connected (via coupling elements) to a control circuit (not shown), which can be implemented in an integrated circuit (IC) chip, for example. The control circuit applies a drive signal to the SMA actuator wire 40 in use, which resistively heats the SMA wire 40, causing the SMA wire to contract. Multiple SMA wires 40 can be driven independently or in other ways. The control circuit can also measure the resistance of the SMA wire 40 and use the measured resistance to calculate/determine the position of the movable part 20. However, in general, the SMA wire 40 can be heated to contract by any other suitable means, such as via an external heat source, radiant heating, or inductive heating.

In this regard, the range of motion includes any movement of the movable component 20 relative to the support structure 10 that can be achieved by selective contraction of the arrangement of SMA wires 40. The range of motion can be defined as the movement that can be achieved by selective contraction of the SMA wires 40. Optionally, the range of motion can be limited by end stops between the support structure 10 and the movable component 20, particularly when contraction of the SMA wires 40 causes the end stops between the support structure 10 and the movable component to engage. The range of motion can also be at least partially affected by a support device that defines the degrees of freedom in which the movable component 20 can move.

Thus, the range of motion may be defined as the set of positions and orientations to which the movable component 20 may be moved relative to the support structure 10 by the SMA wires 40. The range of motion may be affected by one or more of the following factors: i) the arrangement of the SMA wires 40 and the controls used to drive the SMA wires 40, ii) providing end stops between the movable component 20 and the support structure 10 that limit the range of motion, iii) providing a support device that defines the degrees of freedom of movement of the movable component 20 relative to the support structure 10. In some embodiments, the range of motion may define the movement of the movable component 20 relative to the support structure 10 in a plane of motion (in 2 or 3 degrees of freedom) or along a path of motion (in 1 degree of freedom).

Friction surface with zero holding power

The support structure 10 includes a first friction surface 10f. The movable component 20 includes a second friction surface 20f. The second friction surface 20f of the movable component 20 engages with the first friction surface 10f of the support structure 10. The first friction surface 10f and the second friction surface 20f can engage with each other throughout the entire range of movement. Therefore, in normal use (i.e., under the contraction of the SMA wire 40 used to move the movable component 20), the first friction surface 10f and the second friction surface 20f can remain engaged with each other.

The actuator assembly 1 further comprises a biasing device 30. The biasing device 30 is arranged to bias the first friction surface 10f and the second friction surface 20f against each other. The biasing device 30 applies a biasing force between the support structure 10 and the movable part 20. The biasing force comprises a component perpendicular to the first friction surface and the second friction surface, so the biasing device 30 applies a normal force N between the support structure 10 and the movable part 20. The normal force N is perpendicular to the range of movement and perpendicular to the friction surfaces 10f, 20f. Preferably, the biasing device 30 applies a biasing force in a direction perpendicular to the range of movement and perpendicular to the friction surfaces 10f, 20f. The biasing force of the biasing device may be equal to the normal force N. Therefore, the biasing force may not have a component parallel to the range of movement, and therefore does not affect the movement of the movable part 20 relative to the support structure 10.

The normal force N generates or produces a static friction force F between the first friction surface 10f and the second friction surface 20f. The static friction force F constrains the movement of the movable part 20 relative to the support structure 10, especially when the SMA wire 40 is not contracted. Such movement is constrained at any position and/or orientation within the range of movement of the movable part 20 relative to the support structure 10.

The SMA wire 40 can be used to move the movable member 20 to any position within the range of motion of the movable member 20 relative to the support structure 10. When powered (i.e., when a drive signal is applied to the SMA wire by the control circuit), the SMA wire 40 contracts and applies an actuation force for moving the movable member 20 in the corresponding direction. The actuation force is sufficient to overcome the friction force at the friction surfaces 10f, 20f (especially after the friction force is reduced or eliminated due to the contraction of the SMA wire) so as to drive the relative movement between the movable member 20 and the support structure 10. When the power supply to the SMA wire 40 is stopped, and therefore when the contraction of the SMA wire 40 is stopped, the movable member 20 is maintained at a position within its range of motion due to the friction force between the first friction surface 10f and the second friction surface 20f. In this state, the actuator assembly 1 holds the movable element 20 in place with zero power consumption, and thus the actuator assembly 1 can be referred to as a zero holding power actuator assembly, as can other actuator assemblies disclosed herein. Thus, the movable member 20 is held in position without the need to power the SMA wires 40 , reducing power consumption of the actuator assembly compared to a situation where the SMA wires 40 need to be powered to hold the movable member 20 in position.

The SMA wire 40 is arranged to reduce the normal force N between the first friction surface 10f and the second friction surface 20f when contracted. In other words, the composite force acting on the movable part 20 due to the stress in the SMA wire 40 has a component parallel to the normal force N but in the opposite direction to the normal force N. The stress in the SMA wire 40 affects (particularly reduces) the normal force N. In some embodiments, equal stress (or tension or strain) in the SMA wire 40 can reduce the normal force N without moving the movable part 20. Unequal strain in the SMA wire 40 can cause movement of the movable part 20.

This arrangement of reducing the normal force N by the SMA wire 40 allows the friction force to be selectively reduced by appropriate contraction of the SMA wire 40. This reduction in friction force helps to overcome the friction force, thereby allowing the movable component 20 to move within the range of motion. Therefore, the stress in the SMA wire 40 required to move the movable component 20 can be reduced compared to the case where the friction force is not reduced. In addition, in the case where the SMA wire 40 is not contracted, the friction force can be designed to be higher than the case where the friction force cannot be reduced, thereby reducing the risk of accidental movement of the movable component 20 without contraction of the SMA wire.

Friction characteristics

As described above, the normal force N generates or produces a static friction force F between the first friction surface 10f and the second friction surface 20f. The static friction force F constrains the movement of the movable component 20 relative to the support structure 20. Therefore, the magnitude of the static friction force F is large enough to constrain such movement. The magnitude of the static friction force F is proportional to the normal force N and the static friction coefficient μ, so F=μ*N. The static friction force F can be increased by increasing the normal force N (which is achieved by appropriately designing the biasing device 30) and/or increasing the static friction coefficient (which is achieved by appropriately designing the friction surfaces 10f, 20f).

The magnitude of the static friction force is large enough to constrain the movement of the movable part, especially before the static friction force is reduced due to the contraction of the SMA wire 40. The ratio of the static friction force to the weight of the movable part can be greater than 1. Therefore, the magnitude of the static friction force is greater than the weight of the movable part. This ensures that, for example, the movement of the movable part is constrained by the friction force even when the actuator assembly 1 is turned to one side. The weight of the movable part is considered to be equal to the mass of the movable part multiplied by the average gravitational acceleration of the earth (9.81m/ ^s2 ). Preferably, the ratio of the static friction force to the weight of the movable part is greater than 3, further preferably greater than 5, and further preferably greater than 10. This ensures that the movement of the movable part 20 is constrained even when the actuator assembly 1 is accelerated. The larger ratio of the static friction force to the weight of the movable part reduces the risk of the movable part moving due to acceleration of the actuator assembly 1 (e.g., impact event). In some cases, the higher friction force may also compensate for any lateral biasing force of the biasing device 30, such as when the biasing device is connected between the support structure 10 and the movable member 20 (as shown in Figure 4D).

The SMA wire can be arranged to reduce the normal force when it is contracted. In some embodiments, the normal force between the first friction surface and the second friction surface is reduced by at least 10%, preferably at least 20%, and most preferably at least 50%. The normal force N can be reduced by at least 90%. In some embodiments, the normal force N is reduced by 100%, i.e., the movable part 20 is lifted off the first friction surface 10f.

Similarly, the static friction F between the first friction surface and the second friction surface can be reduced by at least 10%, preferably at least 20%, and most preferably at least 50%. The static friction F can be reduced by at least 90%. In some embodiments, the static friction F is reduced by 100%, that is, the movable part 20 is lifted off from the first friction surface 10f. Therefore, the total friction between the movable part 20 and the support structure 10 can be reduced, for example, by at least 10%, at least 20%, at least 50% or at least 90%. Some residual friction can remain in any support device (if provided), even when the movable part is lifted off from the first friction surface 10f.

The magnitude of the static friction force is low enough to allow the SMA wire 40 to overcome the static friction force, thereby moving the movable part 20 relative to the support structure 10, especially after the static friction force is reduced due to the contraction of the SMA wire 40. Therefore, the magnitude of the reduced static friction force is less than the force applied to the movable part 20 in the moving direction by the SMA wire 40. The static friction force can be less than 50%, preferably less than 20%, and more preferably less than 10% of the force generated by the 200 MPa stress in the SMA wire 40 for moving the movable part 20 relative to the support structure 10.

The static friction coefficient between the first friction surface 10f and the second friction surface 20f directly affects the magnitude of the static friction force F. The static friction coefficient can be changed by appropriate processing or selection of the materials of the first friction surface 10f and the second friction surface 20f. The static friction coefficient can be in the range between 0.05 and 0.6. Preferably, the static friction coefficient is in the range between 0.1 and 0.4. Generally, a lower static friction coefficient can be compensated by a higher normal force N applied by the biasing device 30.

The requirements for the static friction force F between the first friction surface 10f and the second friction surface 20f have been described above. These requirements can ensure that once the movable part 20 is in place, the movable part 20 remains in place relative to the support structure 10. Preferably, the same requirements apply to the dynamic friction force or kinetic friction force between the first friction surface 10f and the second friction surface 20f, thereby ensuring that the movable part 20 is quickly stationary after being moved by the SMA wire 40. To this end, the ratio of the kinetic friction force to the weight of the movable part, the relationship between the kinetic friction force and the force due to the SMA wire 40, and the kinetic friction coefficient between the first friction surface 10f and the second friction surface 20f can be described relative to the static friction force F. Preferably, the static friction coefficient between the first friction surface 10f and the second friction surface 20f is substantially equal (e.g., varies by less than 5%, preferably less than 1%) to the kinetic friction coefficient between the first friction surface 10f and the second friction surface 20f. This makes the forces acting on the movable part more predictable and reduces the complexity of movement control.

Bias device

2A-2D and 3A-3C schematically depict embodiments of an actuator assembly 1. Compared to the prior art actuator assembly 100 of FIG. 1 , in which a spring 110 is connected between a static component 101 and a movable component 102, the movable component 20 in FIG. 2A-2D or the support structure 10 in FIG. 3A-3C comprises a biasing device 30 of the depicted actuator assembly 1. Thus, the biasing device 30 moves with the movable component 20 in FIG. 2A-2D or remains static relative to the support structure 10 in FIG. 3A-3C.

Therefore, the biasing device 30 is arranged to apply a normal force N in a direction perpendicular to the range of motion only at any position within the range of motion. Compared to the spring 110 of the prior art actuator assembly 100 of FIG. 1 , the biasing device 30 of the embodiment of FIGS. 2 and 3 does not generate a lateral force acting parallel to the range of motion when moving away from the initial center position. Therefore, there is no lateral force opposing the friction between the movable part 20 and the support structure 10, reducing the risk of accidental movement of the movable part 20 without contraction of the SMA wire 40. Due to the absence of varying lateral forces acting on the movable part 20, controlled and precise movement of the movable part 20 relative to the support structure 10 can be made simpler.

2A-2D depict an embodiment of the invention in which a biasing device 30 forms part of a movable part 20. The movable part 20 comprises a biasing device 30. The biasing device 30 moves together with the movable part 20 (in its entirety) relative to the support structure. In this arrangement, it is easier to ensure that the biasing force of the biasing arrangement 30 acts in a direction perpendicular to the range of movement. Although the support structure 10 is depicted as two parts 10 in the figures for ease of illustration, in reality the support structure 10 may be one part, i.e. the two parts 10 depicted in FIGS. 2A-2C are connected.

As shown, the movable member 20 includes two parts 20a, 20b. The biasing device 30 applies a biasing force between the two parts 20a, 20b. The two parts 20a, 20b can be coupled via the biasing device 30. One end of the biasing device 30 can be connected to one of the two parts 20a, 20b, and the other end of the biasing device 30 can be connected to the other of the two parts 20a, 20b.

For example, in the embodiment of FIG. 2A , the support device 50 is disposed between one of the sections 20 b and the support structure 10. The SMA wire 40 is connected between the other of the sections 20 a and the support structure 10. The second friction surface 20 f is disposed on the other of the sections 20 a. The SMA wire 40 is angled away from the friction surfaces 10 f, 20 f and is arranged to move the movable member in opposite directions. Therefore, upon equal contraction (or equal tension) of the SMA wire 40, the normal force N between the first friction surface 10 f and the second friction surface 20 f is reduced. The difference in contraction between the SMA wires 40 causes the movable member 20 to move on the support device 50 relative to the support structure 10.

FIG. 2B shows another embodiment of the present invention, in which the biasing device 30 is part of the movable part 20. Here, the biasing device 30 is an elastic element, in particular comprising a flexure. In the illustrated embodiment, a portion 20b of the movable part 20 is a body connected to the flexure, and another portion of the movable part 20 is formed integrally with the flexure. Generally, one or both portions of the movable part 20 may be formed integrally with the biasing device 30, whether the biasing device is in the form of an elastic element (e.g. one or more flexures) or in any other form. As described with respect to FIG. 2A, the support device 50 is arranged between a portion 20b of the movable part 20 and the support structure 10. The SMA wire 40 is connected between the other portion 20a of the movable part 20 and the support structure 10. The second friction surface 20f is formed on the other portion 20a. Therefore, the second friction surface 20f is formed integrally with the biasing device 30 (in the form of a flexure).

FIG. 2C shows another embodiment of the present invention, in which the biasing device 30 is part of the movable part 20. The movable part 20 includes two parts 20a, 20b. One of the SMA wires 40 is connected to one part 20a, and the other of the SMA wires 40 is connected to the other part 20b. The second friction surface 20f is formed between the support structure 10 and the two parts of the movable part 20. When the SMA wires 40 are isocontracted (or isotensoidal), the normal force N acting between the first friction surface 10f and the second friction surface 20f is reduced. The contraction difference between the SMA wires 40 causes the movable part 20 to move relative to the support structure. In the embodiment of FIG. 2C, the friction surfaces 10f, 20f are used as a bearing device 50, in particular a plain bearing, for guiding the movement of the movable part 20 relative to the support structure 10.

FIG. 2D shows another embodiment of the present invention, in which the biasing device 30 is part of the movable part 20. Compared with the embodiment shown in FIG. 2A-FIG. 2C, the biasing device 30 is a magnetic biasing device 30. The magnetic biasing device 30 provides a magnetic biasing force for biasing the first friction surface 10f against the second friction surface 20f. The magnetic biasing device includes a magnet (preferably a permanent magnet) located on a part 20a of the movable part 20 and a magnet (preferably a permanent magnet) or a ferromagnetic material located on another part 20b of the movable part 20. The biasing force of the biasing device 30 corresponds to the magnetic force between the magnetic parts. The support device 50 is arranged between one part 20b and the support structure 10. The SMA wire 40 is connected between the other part 20a and the support structure 10, and the second friction surface 20f is arranged on the other part 20a.

FIG. 2D also schematically depicts a support device 22 between the two parts 20a, 20b. In FIG. 2D, the support device 22 is a planar support, although in general the support device 22 may include any other form of support, such as a rolling support or a flexible support. The support device 22 may allow the two parts 20a, 20b to move relative to the support structure 10 in a direction perpendicular to any direction of movement of the movable part 20 within the range of movement. Therefore, the support device 22 may constrain the movement of the two parts 20a, 20b relative to the support structure 10 in a direction parallel to any direction of movement of the movable part 20 within the range of movement. Due to the relatively low lateral stiffness of the magnetic biasing device 30, the arrangement of the support device 22 may be particularly beneficial in an embodiment having a magnetic biasing device. However, in general, the support device 22 may be arranged between any two parts 20a, 20b of the movable part 20 or between any two parts 10a, 10b of the support structure 10.

3A-3C depict an embodiment of the invention in which the biasing arrangement 30 forms part of the support structure 10. The support structure 10 comprises the biasing arrangement 30. The biasing arrangement 30 (in its entirety) remains static relative to the support structure 10, and the movable part 20 moves relative to the biasing arrangement 30. In this arrangement, it is easier to ensure that the biasing force of the biasing arrangement 30 acts in a direction perpendicular to the range of movement.

As shown, the support structure 10 includes two parts 10a, 10b. The biasing device 30 applies a biasing force between the two parts 10a, 10b. The two parts 10a, 10b can be connected via the biasing device 30. One end of the biasing device 30 can be connected to one of the two parts 10a, 10b, and the other end of the biasing device 30 can be connected to the other of the two parts 10a, 10b.

For example, in the embodiment of FIG. 3A , the support device 50 is disposed between one of the sections 10 b and the movable member 20. The SMA wire 40 is connected between the other of the sections 10 a and the movable member 20. The first friction surface 10 f is disposed on the other of the sections 10 a. The SMA wire 40 is angled away from the friction surfaces 10 f, 20 f and is arranged to move the movable member in opposite directions. Therefore, upon isocontraction (or isotension) of the SMA wire 40, the normal force N between the first friction surface 10 f and the second friction surface 20 f is reduced. The difference in contraction between the SMA wires 40 causes the movable member 20 to move on the support device 50 relative to the support structure.

FIG. 3B depicts another embodiment in which the biasing device 30 is disposed between two portions 10a, 10b of the support structure 10. A support device 50 is disposed between one of the portions 10a and the movable component 20. An SMA wire 40 is connected between the other of the portions 10b and the movable component 20. A first friction surface 10f is disposed on the other of the portions 10b. The SMA wire 40 is angled away from the friction surfaces 10f, 20f and is arranged to move the movable component in opposite directions. Therefore, upon equal contraction (or equal tension) of the SMA wire 40, the normal force N between the first friction surface 10f and the second friction surface 20f is reduced. The difference in contraction between the SMA wires 40 causes the movable component 20 to move on the support device 50 relative to the support structure.

FIG. 3C depicts another embodiment in which the biasing device 30 is disposed between two portions 10a, 10b of the support structure 10. The embodiment of FIG. 3C is similar to the embodiment of FIG. 3B except for the arrangement of the SMA wire 40. In particular, in FIG. 3C, the SMA wire 40 is not angled relative to the friction surfaces 10f, 20f. The SMA wire 40 is connected between one portion 10a of the portions of the support structure 10 and the movable component 20. The SMA wire 40 is further bent around a portion of the other portion 10b of the support structure 10. Thus, the SMA wire 40 includes a first length of SMA wire extending between the portions of the support structure 10, and a second length of SMA wire extending between the other portion 10b of the support structure 10 and the movable component 20. Upon isocontraction (or isotension) of the SMA wire 40, the normal force N between the first friction surface 10f and the second friction surface 20f is reduced. The difference in contraction between the SMA wires 40 causes the movable component 20 to move relative to the support structure on the support device 50.

As shown in the embodiment of Figures 2B-2D, the support structure 10 may include a plurality of separated first friction surfaces 10f and/or the movable component 20 may include a plurality of separated second friction surfaces 20f. The normal force N acting between each of these friction surfaces may be reduced when the SMA wire 40 contracts, or the total normal force N may be reduced to reduce the total friction force. Generally, in any embodiment of the present invention, for example also in the embodiment of Figures 2A or 3A-3C, a plurality of separated first friction surfaces 10f and/or second friction surfaces 20f may be provided. For example, a plurality of separated friction surfaces may be arranged in different planes (as shown in Figure 2C), or may be arranged in the same plane (as shown in Figures 2B and 2D). The support structure and/or the movable component may optionally include one or more protrusions, on which the first friction surface 10f and/or the second friction surface 20f are formed, which allows the contact area between the first friction surface 10f and the second friction surface 20f to be defined.

In general, even though the biasing device 30 is schematically depicted as a spring element in FIGS. 2A-2C and 3A-3C , the biasing device 30 may include any component capable of applying a biasing force between the movable component 20 and the support structure 10. The biasing device 30 may, for example, include an elastic element, such as a flexure, a coil spring, a leaf spring, an elastomer, or any other suitable biasing element, such as a pair of magnets and a ferromagnetic element (as shown in FIG. 2D ).

In the device where the biasing device 30 includes a resilient element, the resilient element (e.g., a flexure) is preferably deformable (or only deformable) at least in a direction orthogonal to the friction surface 10f, 20f. Generally, the resilient element (e.g., a flexure) may also be deformable in directions other than perpendicular to the surface, particularly in embodiments where the biasing device is connected between the movable part 20 and the support structure 10. In embodiments where the movable part 20 or the support structure 10 includes a plurality of parts 10a, 10b, 20a, 20b, the parts 10a, 10b, 20a, 20b may be constrained from moving relative to each other in directions parallel to the range of movement. For example, with reference to FIGS. 2A-2C , the biasing device 30 may be relatively rigid in directions parallel to the range of movement. An additional support device 22 as described in FIG. 2D may optionally be provided to constrain the relative movement of the two parts 10a, 10b, 20a, 20b. An end stop 70 (as described with respect to FIGS. 4A-4D ) may also constrain such relative movement. Generally, the relative movement of the movable component 20 or two parts of the support structure 10 within the range of movement in a direction along the direction of movement or in a plane of movement may be constrained.

Although the biasing device 30 is schematically depicted as being arranged between the support structure 10 and the movable part 20 in the direction along the normal force N, in practice the biasing device 30 may be arranged in a lateral direction, i.e., in a direction from one side of the movable part 20 to one side of the support structure 10. For example, a bending spring or a leaf spring may extend generally in a direction parallel to the friction force F while applying the normal force N to the movable part 20. This may provide a more compact actuator assembly.

In some embodiments, the biasing device 30 may be arranged to also provide a biasing force to the support device 50. Thus, the biasing device 30 may be arranged to load the support device 50. The biasing device 30 may keep the support device 50 engaged. This is particularly advantageous when the support device 50 comprises a rolling bearing or a planar bearing.

Furthermore, even though in FIGS. 2A-2C and 3A-3C the biasing device 30 is depicted as pushing portions of the movable component 20 or support structure 10 apart (e.g., due to compression in the elastic element), the biasing device 30 may alternatively be arranged to pull these portions together (e.g., due to tension in the elastic element). Similarly, even though the magnetic biasing device 30 is depicted in FIG. 2D as pulling portions of the movable component 20 or support structure 10 together (e.g., due to attractive magnetic forces), the magnetic biasing device 30 may alternatively be arranged to pull these portions together.

The biasing device 30 may include a plurality of biasing elements that cooperate to provide a biasing force. Thus, the biasing device 30 may include any combination of the above-mentioned biasing devices.

Support device

In FIGS. 2A , 2B, 2D and 3A- 3C , a dedicated support device 50 is disposed between the support structure 10 and the movable component 20 , in particular, between the support structure 10 and a portion of the movable component 20 .

The bearing device 50 may be provided independently of the friction surfaces 10f, 20f. This may make the controlled movement of the movable part 20 relative to the support structure 10 by the SMA wire 40 simpler.

Unless the context requires otherwise, the support device 50 is used herein as follows. The support device 50 used herein includes the terms "sliding support" or "planar support", "rolling support" (including "ball support" or "roller support") and "flexible support". The term "support" used herein generally refers to any element or combination of elements used to constrain movement to only the desired movement. The term "sliding support" is used to mean a support in which a support element slides on a support surface, and includes a "planar support". The term "rolling support" is used to mean a support in which a rolling support element (such as a ball or roller) rolls on a support surface. In an embodiment, the support may be arranged on a nonlinear support surface or may include a nonlinear support surface. In some embodiments, more than one type of support device may be used in combination to provide a support function. Therefore, the term "support" used herein includes, for example, any combination of a planar support, a rolling support and a flexible support.

In the depicted embodiment, for example, the support device 50 includes a rolling bearing. For example, the rolling bearing is a roller bearing or a ball bearing. The rolling bearing includes a supporting bearing surface on the support structure 10, a movable bearing surface on the movable part 20, and a rolling bearing element (e.g., a roller or a ball) arranged between the supporting bearing surface and the movable bearing surface. In some embodiments, such as embodiments in which the range of movement is defined in a moving plane, the supporting bearing surface and the movable bearing surface are parallel to the first friction surface 10f and the second friction surface 20f.

In an alternative embodiment, the support device 50 includes a planar support or a sliding support. Therefore, the support device 50 in any embodiment described herein can be a planar support. The planar support is formed between the engagement surface on the support structure and the corresponding engagement surface on the movable part 20, and the engagement surface on the support structure engages with the corresponding engagement surface on the movable part 20. For example, in the case where the friction coefficient in the planar support is lower than the friction coefficient between the first friction surface 10f and the second friction surface 20f, for example, significantly lower (for example, less than 50% or less than 90%), the planar support can be considered to be separated from the friction surfaces 10f and 20f. To this end, the planar support can include a friction-reducing coating or material on the support structure 10 and/or the movable part 20, or a friction-reducing lubricant between the engagement surfaces. Such a planar support can, for example, include a polymer or a polymer coating. The static friction coefficient between the engagement surfaces of the planar support can be less than 5 times, preferably less than 10 times, of the static friction coefficient between the first friction surface 10f and the second friction surface 20f.

Alternatively, the support device 50 in any of the embodiments may include a flexible support (not shown). The flexible support includes one or more flexible members that resist deformation along their longitudinal length and are laterally deformable relative to their longitudinal length. The flexible members of the support device 50 can be maintained in tension, at least in part due to the biasing force of the biasing device 30. The flexible members allow the movable member 20 to move within the range of motion, but restrict movement outside the range of motion.

Typically, the actuator assembly 1 includes a support device 50 for supporting the movement of the movable component 20 relative to the support structure 10. The support device 50 can be separated from the first friction surface 10f and the second friction surface 20f (as shown in Figures 2A, 2B, 2D, 3A-3C). Alternatively, the support device 50 can be at least partially formed by the first friction surface 10f and the second friction surface 20f (as shown in Figure 2C).

The support device 50 constrains the movement of the movable part 20 within a range of movement. The support device 50 can constrain the movement of the movable part 20 relative to the support structure 10 within three degrees of freedom. For example, the support device 50 can constrain the movement of the movable part relative to the support structure to movement within a moving plane. The movement may include three DOFs, such as i) translation in a first direction in the moving plane, ii) translation in a second direction perpendicular to the first direction in the moving plane, and iii) rotation in the moving plane. Alternatively, the movement may include two degrees of freedom, such as i) translation in a first direction in the moving plane, ii) translation in a second direction perpendicular to the first direction in the moving plane. This can allow the actuator assembly to be used in applications that require such 3 DOF or 2 DOF movement, such as an optical image stabilization (OIS) actuator assembly that implements sensor-shift OIS or lens-shift OIS.

In other embodiments, the support device 50 can constrain the movement of the movable part 20 relative to the support structure 10 to movement in one degree of freedom. This can allow the actuator assembly to be used in applications that require such 1 DOF movement, such as an autofocus (AF) actuator assembly. An actuator assembly with 1 DOF movement can be easier to manufacture and control than an actuator assembly with more degrees of freedom. For example, the support device 50 can constrain the movement of the movable part relative to the support structure to a helical movement around a helical axis. Alternatively, the support device can constrain the movement of the movable part 20 relative to the support structure 10 to a translational movement along the axis of movement. Further alternatively, the support device 50 can constrain the movement of the movable part 20 relative to the support structure 10 to a rotational movement around a rotational axis.

Thus, there may be provided an actuator assembly comprising a support structure, the actuator assembly comprising the support structure comprising a first friction surface; a movable component comprising a second friction surface engaging the first friction surface; a helical bearing arrangement supporting the movable component on the support structure and arranged to guide helical movement of the movable component relative to the support structure about a helical axis, wherein the helical bearing arrangement is formed by the first friction surface and the second friction surface; and one or more SMA wires arranged to drive the movable component to rotate about the helical axis when contracted, the helical bearing arrangement converting the rotation into said helical movement; and a biasing arrangement configured to load the helical bearing arrangement so as to bias the first friction surface and the second friction surface against each other with a normal force and generate a static friction force that constrains movement of the movable component relative to the support structure at any position within the range of movement when the one or more SMA wires are not contracted, wherein the one or more SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface when contracted.

The first friction surface 10f and the second friction surface 20f can be arranged to allow the movable part 20 to move relative to the support structure 10 in the degrees of freedom allowed by the support device 50. For example, one or both of the first friction surface 10f and the second friction surface 20f are planar. This can allow movement in up to 3 degrees of freedom. In an embodiment that allows movement in one DOF, one of the first friction surface 10f and the second friction surface 20f can be set on a protrusion, and the other of the first friction surface 10f and the second friction surface 20f can be set on a guide channel of a shape complementary to the protrusion. Therefore, the range of movement of the movable part 20 relative to the support structure 10 can include movement along a line parallel to the guide channel.

End stops

As described above, the SMA wire 40 can reduce the normal force N between the first friction surface 10f and the second friction surface 20f. The first friction surface 10f and the second friction surface 20f can remain in contact when the SMA wire 40 is retracted. Alternatively, in any embodiment described herein, one or more SMA wires 40 can disengage the first friction surface 10f and the second friction surface 20f when retracted. Therefore, the first friction surface 10f and the second friction surface 20f can be separated when the SMA wire 40 is retracted. After the SMA wire 40 is retracted, the movable part 20 is not in direct contact with the first friction surface 10f.

Preferably, after separation of the first friction surface 10f and the second friction surface 20f, the movable part 20 is supported on the support device 50, preferably only on the support device 50. Therefore, the support device 50 continues to guide the movement of the movable part 20 relative to the support structure 10. This makes the controlled movement of the movable part 20 after being released from contact with the first friction surface 10f simpler than if no dedicated support device 50 is provided. The actuator assembly 1 in which the SMA wire 40 disengages the first friction surface and the second friction surface can also be referred to as a discrete friction actuator assembly 1, because the friction force between the movable part 20 and the support structure 10 can vary between two discrete values in use: a relatively high friction force that keeps the movable part 20 in place relative to the support structure 10 before the SMA wire 40 is retracted, and a relatively low (e.g., residual) friction force generated by the support device 50 after the SMA wire 40 is retracted.

Preferably, in embodiments where the first friction surface 10f and the second friction surface 20f are disengaged, an end stop 70 is provided. The end stop 70 engages when the SMA wire 40 contracts. The end stop 70 constrains the movement of the movable component 20 in a direction perpendicular to the range of movement when engaged. Therefore, the SMA wire 40 can more reliably and effectively drive the movement of the movable component 20. Once the end stop 70 engages, any strain in the SMA wire 40 can contribute to the movement of the movable component 20.

The end stop 70 may be implemented in any of the embodiments described herein. The end stop may be formed, for example, between two portions 20a, 20b of the movable component 20 or two portions 10a, 10b of the support structure 10. The end stop may constrain relative movement of the two portions 10a, 10b when engaged. The end stop may constrain relative movement of the two portions 10a, 10b in a direction perpendicular to any direction of movement of the movable component 20 relative to the support structure 10 when engaged.

In some embodiments, the end stops, when engaged, may further constrain relative movement of the two parts 10a, 10b in a direction parallel to any direction of movement of the movable part 20 relative to the support structure 10. Such movement may be constrained, for example, due to friction between the surfaces of the end stops. The use of end stops to constrain such movement may avoid the need to provide any other arrangement (e.g., a resilient element having a relatively high stiffness in the direction of movement, or an additional support device 22 between the parts as shown in FIG. 2D ) to constrain such relative movement. The end stop surfaces may optionally be provided with complementary teeth (not shown) to constrain sliding between the end stop surfaces in a direction parallel to any direction of movement of the movable part 20 relative to the support structure 10.

4A-4D schematically depict various embodiments in which end stops 70 are provided.

FIG. 4A essentially depicts the actuator assembly 1 already described with reference to FIG. 2A , with the addition of an end stop 70. The end stop 70 is formed by an end stop surface located on one portion 20 a of the movable member 20 and an end stop surface located on another portion 20 b of the movable member 20. Upon contraction of the SMA wire 40, one portion 20 a of the movable member may move out of engagement with the first friction surface 10 f and engage with the end stop 70, as indicated by the arrow in FIG. 4A . In FIG. 4A , the end stop 70 is depicted as being provided by a protrusion on the other portion 20 b. Additionally or alternatively, the protrusion may be provided on one portion 20 a. Typically, no protrusion is required, and the end stop 70 may be formed between any corresponding surfaces on the first portion 20 a and the second portion 20 b of the movable member 20.

FIG. 4B essentially describes the actuator assembly 1 already described with reference to FIG. 3B , with the addition of an end stop 70. The end stop 70 is formed by an end stop surface on one portion 10a of the support structure 10 and an end stop surface on another portion 10b of the support structure 10. When the SMA wire 40 contracts, the other portion 20b of the support structure 10 can move out of engagement with the movable member 20, and the other portion 10b of the support structure 10 can move into engagement with the end stop 70, as indicated by the arrow in FIG. 4B . In FIG. 4B , the end stop 70 is depicted as being provided by a protrusion on one portion 10a. Additionally or alternatively, the protrusion can be provided on the other portion 10b. Typically, no protrusion needs to be provided, and the end stop 70 can be formed between any corresponding surfaces on the portions 10a, 10b.

FIG. 4C essentially depicts the actuator assembly 1 already described with reference to FIG. 3A , with the addition of an end stop 70. The end stop 70 is formed by an end stop surface on one portion 10a of the support structure 10 and an end stop surface on another portion 10b of the support structure 10. Upon contraction of the SMA wire 40, the movable member 20 may be moved out of engagement with one portion 10a of the support structure 10, and the other portion 10b of the support structure 10 may be moved into engagement with the end stop 70, as indicated by the arrows in FIG. 4C . In FIG. 4C , the end stop 70 is depicted as being provided by a protrusion on one portion 10a. Additionally or alternatively, the protrusion may be provided on the other portion 10b. Typically, no protrusion need be provided, and the end stop 70 may be formed between any corresponding surfaces on the portions 10a, 10b.

FIG4D depicts another embodiment of the present invention. Here, the biasing device 30 is arranged (e.g., connected) between the movable part 20 and the support structure 10. Thus, one end of the biasing device 30 is connected to the movable part 20, and the other end of the biasing device 30 is connected to the support structure 10. When a magnetic biasing device 30 is used, one part of the magnetic biasing device 30 is disposed on the support structure 10, and the other part is disposed on the movable part 20.

In the embodiment of FIG. 4D , an end stop 70 is formed between the movable part and the support device 50. In particular, when the SMA wire 40 is retracted, the movable part 20 can be moved out of engagement with the first friction surface 10 f and thus out of engagement with the support structure 10. As shown by the arrow in FIG. 4D , the movable part 20 can be moved into engagement with the end stop 70, in particular by moving into engagement with the support device 50. As a result, the movable part 20 is lifted off the first friction surface 10 f and moved onto the support element of the support device 50. In general, the SMA wire 40 can be arranged to release the movable part 20 from engagement with the first friction surface 10 f when retracted and to engage the movable part 20 with the support device 50 (for example, the support device 50 can include a rolling support, a planar support or a flexible support). When the power supply to the SMA wire 40 is stopped, the biasing device 30 can bias the movable part 20 out of engagement with the support device 50 and into engagement with the first friction surface 10 f.

SMA wire layout

In FIGS. 2A-2C , 3A-3C and 4A-4D , the SMA wire 40 is arranged at an angle away from the friction surface 10 f, 20 f. This is one way to ensure that the strain and/or stress in the SMA wire 40 can reduce the normal force N while driving the movement of the movable component 20 within the range of motion. This arrangement of the SMA wire 40 provides a relatively simple way to reduce the normal force N.

Typically, the one or more SMA wires 40 may be arranged to apply an actuation force to the movable component 20 relative to the support structure 10 when retracted, the actuation force being angled relative to (e.g., away from) the first friction surface 10f and the second friction surface 20f. The actuation force is not necessarily parallel to the SMA wires 40. In some embodiments (e.g., the embodiment of FIG. 3C ), the actuation force on the movable component 20 may even be parallel to the friction surfaces 10f, 20f.

For example, each SMA wire 40 may be a V-shaped wire. The V-shaped wire may be connected to the support structure 10 or the movable part 20 at both ends, and may be bent around the contact portion with the movable part 20 or the support structure 10. Therefore, the SMA wire 40 does not need to be directly connected between the movable part 20 and the support structure 10.

Optionally, a force modification mechanism (not shown) may be arranged between the SMA wire 40 and the movable component 20 or between the SMA wire 40 and the support structure 10. The force modification mechanism may change the direction of the stress in the SMA wire 40 to act on the movable component in the direction along the actuation force. Thus, even if the SMA wire 40 is arranged parallel to the friction surfaces 10f, 20f, the stress and/or strain in the SMA wire 40 may reduce the normal force N. Such a force modification mechanism may also achieve stroke or force amplification.

3C depicts a specific arrangement of the SMA wire 40, wherein the SMA wire 40 is connected at one end to a portion 10a of the support structure 10 and at the other end to the movable component 20. The SMA wire 40 is bent around another portion 10b of the support structure. Thus, the SMA wire 40 can apply an actuation force substantially parallel to the friction surfaces 10f, 20f to the movable component 20.

Generally, the SMA wire 40 is arranged to reduce the normal force between the first friction surface 10f and the second friction surface 20f when contracted. The SMA wire 40 can reduce the normal force due to equal stress and/or strain in the SMA wire 40. The SMA wire 40 is also arranged to move the movable part 20 relative to the support structure 10. Due to unequal stress and/or strain in the SMA wire 40, the SMA wire 40 can move the movable part 20.

Furthermore, the SMA wire 40 can be arranged to provide a biasing force to the support device 50 when retracted. Thus, the SMA wire 40 can help keep the support device 50 engaged.

Other Embodiments of the Actuator Assembly

Figures 5A-5D depict further embodiments of the actuator assembly 1, wherein the biasing means 30 is comprised by the movable part 20. The actuator assembly 1 of Figures 5A-5D is functionally similar to the actuator assembly 1 described with reference to Figures 2A and 2B.

Fig. 5A is one side view of the actuator assembly 1, and Fig. 5B is another side view of the actuator assembly 1. The movable member 20 moves in the left-right direction (movement direction M) in Fig. 5A, and enters and exits the page in Fig. 5B.

As shown in Fig. 5A, the actuator assembly 1 includes a flexure 30 having a first end fixedly attached to the movable member 20 and a free end forming a contact portion 32 to engage with and generate friction on the support structure 10. The contact portion 32 can be considered as a second portion of the movable member 20, wherein the flexure 30 acts as a biasing device 30 between the two portions of the movable member 20. Fig. 5B shows that one of the contact portions 32a is fully engaged with the first friction surface 10f of the support structure 10, while the other contact portion of the other flexure is disengaged from the surface.

The actuator assembly also includes an SMA wire 40 that is angled with respect to the direction of movement M and a direction normal to the surface of the support structure 10 and along the biasing force from the flexure. The SMA wire 40 is attached to the support structure and the end of the flexure 30 having the contact portion. When contracted, the SMA wire 40 applies an actuation force on the flexure 30, wherein a second force component normal to the surface of the support structure 10a causes the contact portion to retract from the surface, reducing the friction where it is located. The SMA wire 40 also applies a first force component in the direction of movement to drive movement of the movable member 20. Further contraction in the SMA wire 40 not only drives continued movement of the movable member 20, but also causes the contact portion 32 to disengage from the first friction surface 10f, eliminating the friction caused by the flexure 30. For example, the contact portion 32b is shown as being completely disengaged from the surface of the support structure 10 due to contraction of the corresponding SMA wire 40b.

When the supply of energy to the SMA wire 40 ceases, such as when the actuation force is withdrawn, the flexure 30 reengages the surface of the support structure 10 and applies a biasing force thereon to constrain free movement of the movable component 20 .

The movable component 20 also includes an end stop 70. The end stop defines the limit of movement of the contact portion 32 in a direction perpendicular to the friction surfaces 10f, 20f. As shown in FIG. 5B , when the SMA wire 40a is not energized, the contact portion 32a of the flexure 30 engages with the surface of the support structure 10, and the free end of the flexure 30 is spaced apart from the end stop 70. When the SMA wire 40b is energized, its actuation force causes the contact portion 32b to retreat until the free end of the flexure 30 abuts the end stop. Further contraction of the SMA wire 40b does not result in further retraction of the contact portion 32b. Instead, the actuation force is used only to drive the movement of the movable component 20, thereby allowing more precise position control of the movable component 20.

When the flexure 30 engages the end stop 70, the second actuation force from the SMA wire 40b applies a torque on the movable member 20. This resultant torque is counteracted by the other flexure 30 to prevent the movable member 20 from tilting. More specifically, the surface of the support structure 10 reacts to the torque through the contact portion 32a.

Preferably, the end stop 70 is arranged to protrude from the surface of the movable part to a height that leaves a minimum gap between the contact portion 32 and the surface of the support structure 10 when in contact with the free end of the flexure 30 .

FIG5C is a side cross-sectional view of another embodiment of the actuator assembly 1. The actuator assembly 1 has a flexure 30 and SMA wire 40 arranged in a manner similar to the embodiment of FIGS. 5A and 5B. Only a single SMA 40 is illustrated, although multiple SMA wires may be present. Similar features are not described again.

In this embodiment, the flexure 30 includes a lip extending upwardly toward its free end, which forms a contact portion 32 for engaging a surface of the support structure 10. Similar to the embodiment of Figure 5B, the movable member 20 includes an end stop 70 for limiting the displacement of the contact portion 32 during retraction of the SMA wire. Advantageously, the use of the upwardly extending lip reduces the degree of bending of the flexure 30 during wire retraction, thereby allowing the contact portion 32 to retract in a more efficient and precise manner.

In the absence of the second flexible member, the actuator assembly 6 further comprises a second support 50b for counteracting the torque caused by the second actuation force component, for example, a force component acting in a direction normal to the surface of the support structure 10. The second support 50b is shown as a ball support, but may be other suitable supports, such as a planar support. The second support 50b prevents tilting of the movable part 20, but allows relative movement between the support structure 10 and the movable part 20.

Fig. 5D is a side view of another embodiment of the actuator assembly 1. Features already described with reference to Figs. 5A and 5B are not described again.

As shown in Fig. 5D, the actuator assembly 1 includes a flexure 30 fixedly attached to the movable member 20 at an anchor point 34 by a flexure arm 38. The flexure arm 38 extends from a position along the length of the flexure 30 that is spaced apart from the free end of the flexure 30. In this way, the flexure 30 and the two free ends of the flexure 30 can pivot about the anchor point.

One of the free ends forms a contact portion 32 for engaging with the support structure 10 and generating friction thereat. That is, as shown in FIG5D , the contact portion 32 is shown to be fully engaged with the surface of the support structure 10.

The actuator assembly 1 also includes an SMA wire 40 that is angled with respect to the direction of movement (e.g., into the page in FIG. 5D ) and a direction normal to the surface of the support structure 10 (e.g., the bias force from the flexure). The SMA wire 40 is attached between the support structure and the other free end of the flexure 30. Thus, the flexure acts as a Class 1 lever.

When retracted, the SMA wire 40 exerts an actuation force on the flexure 30, wherein a second force component pulls downward on the end of the flexure 30 attached to the SMA wire 40, causing the flexure arm 38 to rotate about the anchor point 34. Thus, by leveraging, the free end of the flexure moves upward and thereby retracts the contact portion 32 from the surface, thereby reducing the friction where it is located. The SMA wire 40 also exerts a first force component in the direction of movement to drive movement of the movable member 20. Further retraction of the SMA wire 40 not only drives continued movement of the movable member 20, but also disengages the contact portion 32 from the surface of the support structure 10, eliminating the friction caused by the flexure 30. For example, due to the retraction of the SMA wire 40, the contact portion 32 is shown (along the dashed line) completely disengaging from the surface of the support structure 10.

5A and 5B , the movable member 20 also includes end stops 70 that define the limits of movement of the contact portion 32. Once the SMA wire 40 is energized, its actuation force causes the contact portion 32 to retract until the free end of the flexure 30 abuts the end stop 70. Further contraction of the SMA wire 40 does not cause further retraction of the contact portion 32. Instead, the actuation force is used only to drive movement of the movable member 20, thereby allowing for more precise positional control of the movable member 20.

In the embodiment shown in FIG. 5D , a force is applied at a distance closer to the fulcrum (e.g., anchor point 34) than the load, and the contact point 32 is arranged to displace by an amount greater than a given contraction in the SMA wire 40. Advantageously, this arrangement allows the contact point 32 to retract quickly. Alternatively, the force may be applied at the same distance as the load, or at a distance farther from the fulcrum than the load, so that the biasing force is overcome by a stiffer biasing element. More specifically, the flexure 30 is a force modification mechanism in which the ratio of input force to output force can be adapted for different applications.

Applications of actuator components

The actuator assembly 1 may generally be used in any application where it is desirable to move the movable member 20 within a range of motion using the SMA wire 40, and to maintain the movable member 20 at any position within the range of motion when power is removed from the SMA wire 20. The following description provides specific application examples of the present invention, but it should be understood that the actuator assembly 1 need not be used in these specific applications.

In some embodiments, the actuator assembly 1 can be a microactuator for a camera or mobile phone. For example, the actuator assembly can be configured to provide optical image stabilization (OIS) or autofocus (AF) in a camera device. For these purposes, the actuator assembly can achieve 3 DOF or 2 DOF movement (for OIS) or 1 DOF movement (for AF), as described above with respect to the support device 50.

Thus, a camera device is provided, comprising an actuator assembly 1, an image sensor, and a lens assembly comprising at least one element. One of the image sensor and the at least one lens element may be fixed relative to the movable component 20, and/or one of the image sensor and the at least one lens element (e.g., the other) may be fixed relative to the support structure 10. When the SMA wire 40 contracts, moving the movable component 20 relative to the support structure 10 may affect relative movement between the lens element and the image sensor. Moving the lens element relative to the image sensor along the optical axis of the lens assembly may affect AF in the camera device. Moving the lens element relative to the image sensor in a direction perpendicular to the optical axis and/or rotating the image sensor may affect OIS in the camera device.

An actuator assembly 1 that can affect OIS is described in WO 2013 175197A1 or WO 2017 072525A1, which are incorporated herein by reference. The present invention can be applied to these actuator assemblies 1. For example, embodiments of such an actuator assembly 1 are shown in Figures 11 and 12. In this regard, the movable part 20 can move in a moving plane within a moving range. The actuator assembly 1 may include a total of four SMA wires 40 connected between the movable part 20 and the support structure 10, wherein these SMA wires 40 are in an arrangement in which none of the SMA wires 40 are colinear, and wherein the SMA wires 40 can be selectively driven to move the movable part 10 relative to the support structure to any position within the moving range without applying any net torque to the movable part 20 about a main axis perpendicular to the moving plane.

For example, two of the SMA wires 40 may be connected between the movable component 20 and the support structure 10 to each apply a torque to the movable component 20 in a first orientation about the main axis in the plane of movement about the main axis, and another two SMA wires 40 may be connected between the movable component 20 and the support structure 10 to each apply a torque to the movable component in an opposite second orientation about the main axis in the plane of movement about the main axis. Four SMA wires 40 may be arranged in a loop at different angular positions about the main axis, with continuous SMA wires about the main axis being connected to apply forces to the movable element in alternating orientations about the main axis.

Alternatively, the movable part 10 may include a camera module having both a lens assembly and an image sensor. Tilting the camera module when the SMA wire is contracted is another way to implement OIS.

6-11 describe in more detail specific embodiments of the actuator assembly 1, wherein the actuator assembly implements the movement of the movable part 20 along the movement axis. These specific embodiments can be used, for example, to implement AF or OIS in a camera device.

6A , 6B and 6C are respectively a plan view and a side cross-sectional view of the actuator assembly 1 according to an embodiment of the present invention.

The actuator assembly 1 comprises a support structure 10 on which an image sensor (not shown) is mounted. As described below, the support structure 10 serves as a mounting platform for various components and also defines any reference features required during assembly.

The actuator assembly 1 also includes a lens element, which in this example is part of the movable part. The lens element includes a lens holder 20 that holds a lens (not shown), although alternatively, there may be multiple lenses. The lens may be made of glass or plastic. The lens element has an optical axis O aligned with the image sensor 3 and is arranged to focus an image on the image sensor.

Alternatively, although not shown, the image sensor may be part of the movable component and the lens element may be fixed relative to the support structure.

Although in this example the actuator assembly 1 is a camera device, this is generally not required. In some examples, the actuator assembly 1 may be an optical device in which the movable component is a lens element, but there is no image sensor. In other examples, the actuator assembly 1 may be a device of a type that is not an optical device and in which the movable element is not a lens element and there is no image sensor. In some examples, the actuator assembly 1 may be an optical device in which the movable component is a bracket supporting an image sensor, in which the lens bracket may be driven by another actuator, or may not be movable at all.

The actuator assembly 1 also includes a support device 50 in the form of ball bearings 50 along a plurality of guides 52 that support the lens holder 20 on the support structure 10. The ball bearings 50 and guides are configured to guide movement of the lens holder 20 relative to the support structure 10 along the optical axis O (which is therefore the direction of movement in this example) while constraining movement of the lens holder 20 relative to the support structure 10 in other degrees of freedom.

The actuator assembly 1 also includes a pair of SMA wires 40a, 40b, which are arranged at an angle to each other and to the direction of movement. In operation, the SMA wires 40a, 40b drive the lens holder 20 to move along the optical axis O. Each of the SMA wires 40a, 40b is connected to the support structure 10 at a first end through a static crimping portion 42a fixed to the side wall of the support structure. The static crimping portion 42a crimps the corresponding SMA wire 40a, 40b to provide a mechanical connection and an electrical connection through a corresponding electrical connector 44a. The SMA wires 40a, 40b are also connected to a moving crimping portion 42b provided on the flexure 30, which is attached to the lens holder 20 at the connecting tab 34. The crimping portion 42b is typically connected to an electrical connector 44b via an electrical path 43. In the illustrated embodiment, the electrical path 43 is shown as a straight connector. In some other embodiments, the electrical path 43 may be replaced by a labyrinth path or spring similar to the crimp plate 43 shown in Figure 3B. As a result, each of the SMA wires 40 is connected to the support structure 10 at one end and to the lens holder 20 at the other end via the flexure 30.

When retracted, the SMA wire 40a drives the lens holder in an upward direction, while the SMA wire 40b drives the lens holder in the opposite direction. The actuation force of the SMA wire 40 also pulls the lens holder 20 toward the corresponding ball bearing assembly 50, and thus presses on the corresponding ball bearing assembly 50. Advantageously, this arrangement allows the actuation force from the SMA wire 40 to act directly on the ball bearing 50, thereby reducing the amount of noise between the lens holder 20 and the support structure 10.

The flexure 30 has two opposite ends, one of which is attached to the SMA wire 40 and the other of which forms a contact portion 32 for engaging a corresponding surface of the support structure 10. More specifically, the flexure 30 biases the contact portion 32 against the support structure 10, thereby generating a friction force that constrains the free movement of the lens holder 20.

Compared to the embodiment of Fig. 5D, the flexure 30 of the embodiment shown in Fig. 6B includes two pivots connected in series. This arrangement allows the contact portion 32 to retract in the same direction as the wire retraction.

The flexure 30 generally includes a set of inner flexure arms 33 nested within a set of outer flexure arms 35. The outer flexure arms 35 have static crimps 42b for connecting to the SMA wire 40. The outer flexure arms 35 include protrusions 31 at a first end that align with corresponding protrusions 22 of the lens holder 20. That is, the protrusions 31 are positioned further toward the first end of the outer flexure arms 35 than the crimps 42b.

The outer flexible arm 35 is pivotally connected to the corresponding inner flexible arm 33 by a link 36 at a position along the length of the inner flexible arm 33 toward the second end of the outer flexible arm. Therefore, the outer flexible arm 35 is pivotable about the link 36 relative to the inner flexible arm 33.

The inner flexible arm 33 is connected at a first end to the movable end of the connecting protrusion 34 by another link 38. Therefore, the inner flexible arm 33 is pivotable about the link 38 relative to the lens holder. The inner flexible arms 33 are connected at their second ends to form a contact portion 32, which is opposite to the first end of the outer flexible arm 35. Therefore, the link 36 and the link 38 are connected in series along the flexure 30 by the pivot axis between the protrusion 31 at the first end of the outer flexible arm 35 and the contact portion 32 toward the second end of the inner flexible arm 33.

When energized, the SMA wire 40 contracts and pulls the protrusion 31 of the outer flexible arm 35 toward the corresponding protrusion 32 on the lens holder 20 until they engage each other. Thus, a pivot is formed between the protrusions 31, 32, thereby allowing the actuation force to be transmitted through the outer flexible arm 35 to compress the inner flexible arm 33 at the link 36, and the inner flexible arm 33, through the pivoting movement at the link 38, causes the contact portion 32 to retract and disengage from the surface of the support structure 10.

In the illustrated embodiment of FIGS. 6A-6C , where the actuation force is applied at a distance closer to the fulcrum (e.g., link 36) than the load (e.g., contact point 32), the contact point 32 is arranged to displace an amount greater than a given contraction in the SMA wire 40. Advantageously, this arrangement allows the contact point 32 to retract quickly. Alternatively, the force may be applied at the same distance as the load, or at a distance further from the fulcrum than the load, so that the biasing force is overcome by a stiffer biasing element. More specifically, the flexure 30 is a force modification mechanism in which the ratio of input force to output force can be adapted for different applications.

In addition, the actuating force includes a force component along the moving direction, which is used to drive the movement of the lens holder 20.

The surface of the lens holder 20 forms an end stop 70 that defines the limit of movement in the contact portion 32. As shown in FIG6A , when the SMA wire 40 is energized, the actuation force causes the contact portion 32 to retract until the end of the inner flexible arm 33 (e.g., the portion adjacent the link 38) abuts or engages the end stop 70. Further contraction of the SMA wire 40 will not result in further retraction of the contact portion 32. Instead, the actuation force will only be used to drive movement of the lens holder 20, thereby allowing for more precise position control.

Typically, the friction force is sufficient to constrain the free movement of the lens holder 20, but the friction force is insufficient to prevent relative movement between the lens holder 20 and the support structure 10 when the SMA wire 40 is energized. In some embodiments, one or both of the contact portion 32 or the protrusion 22 of the support structure 10 can be provided with a material or coating.

7A and 7B are respectively a truncated plan view and a side cross-sectional view of an actuator assembly 1 according to an embodiment of the present invention.

The actuator assembly 1 is similar in structure and function to the actuator assembly 1 of Figures 6A to 6C. Similar features are not described again. In this embodiment, the flexure 30 is a planar flexure of a different design.

The flexure 30 includes two opposing ends, one of which is attached to the SMA wire 40 and the other of which forms a contact portion 32 for engaging a corresponding surface of the support structure 10. In this embodiment, the contact portion 32 of the flexure 30 is curved or bent inwardly, which corresponds to the curved or tapered surface profile on the support structure 10. More specifically, the flexure 30 biases the contact portion 32 against the support structure 10, thereby generating a friction force that constrains the free movement of the lens holder 20. Therefore, the biasing force is angled with the quadrilateral side of the support structure 10.

6A to 6C, the flexure 30 of this embodiment shown in Fig. 7B includes two pivots connected in series. This arrangement allows the contact portion 32 to retract in the same direction as the wire retraction.

The flexure 30 is generally formed by a set of inner flexible arms 33 nested within a set of outer flexible arms 35. As shown in FIG. 7A , the flexure 30 has a planar profile. The outer flexible arm 35 has a crimp 42 b for connecting to the SMA wire 40. The outer flexible arm 35 includes a protrusion 31 at a first end that engages with a corresponding protrusion 22 of the lens holder 20. Thus, the outer flexible arm can pivot about the protrusion 22 of the lens holder 20. That is, the protrusion 31 is positioned more toward the first end of the outer flexible arm 35 than the crimp 42 b.

The outer flexible arm 35 is pivotally connected to the corresponding inner flexible arm 33 by a link 36 at a position along the length of the inner flexible arm 33 toward the second end of the outer flexible arm. Therefore, the outer flexible arm 35 is pivotable about the link 36 relative to the inner flexible arm 33.

The inner flexible arm 33 is connected at a first end to the movable end of the connecting lug 34 by another link 38. Therefore, the inner flexible arm 33 is pivotable about the link 38 relative to the lens holder. The inner flexible arms 33 are connected at their second ends to form a contact portion 32, which is opposite to the first end of the outer flexible arm 35. Therefore, the link 36 and the link 38 are pivots connected in series along the flexible member 30, located between the protrusion 31 at the first end of the outer flexible arm 35 and the contact portion 32 toward the second end of the inner flexible arm 33.

Once energized, the SMA wire 40 contracts and the actuation force is transmitted through the outer flexible arm 35 via the pivot formed between the protrusions 31 and 32 to compress the inner flexible arm 33 at the link 36, and the inner flexible arm 33 moves via the pivot at the link 38, causing the contact portion 32 to retract and disengage from the surface of the support structure 10.

In the illustrated embodiment of FIGS. 7A and 7B , where the actuation force is applied at a distance closer to the fulcrum (e.g., link 36) than the load (e.g., contact point 32), the contact point 32 is arranged to displace an amount greater than a given contraction in the SMA wire 40. Advantageously, this arrangement allows the contact point 32 to retract quickly. Alternatively, the force may be applied at the same distance as the load, or at a distance further from the fulcrum than the load, so that the biasing force is overcome by a stiffer biasing element. More specifically, the flexure 30 is a force modification mechanism in which the ratio of input force to output force can be adapted for different applications.

In addition, the actuating force includes a force component along the moving direction, which is used to drive the movement of the lens holder 20.

The surface of the lens holder 20 forms an end stop 70 that limits the range of movement in the contact portion 32. As shown in FIG. 7A , when the SMA wire 40 is energized, the actuation force causes the contact portion 32 to retract until the end of the inner flexible arm 33 (e.g., the portion adjacent the link 38) abuts or engages the end stop 70. Further contraction in the SMA wire 40 does not result in further retraction in the contact portion 32. Instead, the actuation force is used only to drive movement of the lens holder 20, thereby allowing for more precise position control.

Fig. 8A is a truncated plan view of an actuator assembly 1 according to another embodiment of the present invention. Similar to the embodiment of Figs. 6A to 6C, the actuator assembly 1 comprises a movable part 20 supported on a ball bearing and movable along an optical axis O. For the sake of brevity, similar features are not shown again.

As shown in FIG8A , the actuator assembly 1 includes a pair of opposing SMA wires 40, each of which is attached to the support structure 10 at one end via a static crimp 42a and to the movable part 20 at the other end via a moving crimp 42b. More specifically, the moving crimp 42b is connected to the movable part 20 via a flexible element (e.g., a planar crimp plate) so as to allow a certain degree of relative movement between the moving crimp 42b and the movable part 20. The SMA wires 40 are angled with respect to the direction of movement, so that when contracted, the SMA wires 40 apply a corresponding first force component for moving the movable part 20 in the opposite direction of movement to drive movement along the optical axis O, and apply a corresponding second force component for moving in the opposite direction transverse to the optical axis O (as shown by the arrows in FIG8A ).

The actuator assembly 1 includes a flexure 30, the two ends of which are fixedly attached to the moving crimp 42b. The term flexure 30 herein generally refers to a flexible member having at least one kink 36 adjacent to a plurality of flexible arms. When subjected to a compressive force, the curvature of the kink 36 may increase, causing the two ends of the two flexure 30 to move toward each other. The flexible arms may stiffen under compression, or may bend.

Generally, the buckling flexure 30 can be used as a force modification mechanism in place of the pivot arrangement shown in Figures 5D, 6 and 7. More specifically, when the SMA wire 40 is not energized, the buckling flexure 30 is biased at its contact portion 32 against the corresponding protrusion 22 extending from the support structure 10, and thereby generates a friction force for constraining the free movement of the movable member 20.

Upon contraction in the SMA wire 40, the second force component compresses the buckling flexure 30, further bending the kink 36 of the buckling flexure 30, thereby causing the contact portions 32 to retreat from their respective protrusions 22, such as along the arrows shown in Figure 8A. Advantageously, the use of the buckling arms 30 allows the contact portions 32 to be quickly retracted from the protrusions 22 of the support structure due to the bend in the kink 36.

The protrusion 22 also acts as an end stop that defines the limit of movement in the contact portion 32. As shown in FIG8A , when the SMA wire 40 is energized, the actuation force causes the contact portion 32 to retreat until the moving crimp 42 b abuts or engages the protrusion 22. Further contraction in the SMA wire 40 will not result in further retraction in the contact portion 32. Instead, the actuation force will only be used to drive movement of the lens holder 20, allowing for more precise position control.

Typically, the friction force is sufficient to constrain the free movement of the lens holder 20, but when the SMA wire 40 is energized, the friction force is insufficient to prevent relative movement between the lens holder 20 and the support structure 10. In some embodiments, one or both of the contact portion 32 or the protrusion 22 of the support structure 10 can be provided with the material or coating.

In some other embodiments, the flexure 30 can switch between a first configuration (e.g., when the contact portion 32 is engaged with the protrusion 22) and a second configuration (e.g., when the contact portion 32 is disengaged from the protrusion 22). More specifically, the flexure 30 can be stable only in the first configuration and the second configuration. Therefore, when the SMA wire 40 is energized, the flexure 30 can quickly switch toward the second configuration.

Fig. 8B is a truncated plan view of an actuator assembly 1 according to another embodiment of the present invention. Similar to the embodiment of Figs. 6A to 6C, the actuator assembly 1 comprises a movable part 20 supported on a ball bearing and movable along an optical axis O. For the sake of brevity, similar features are not shown again.

As shown in FIG8B , the actuator assembly 1 includes a pair of opposing SMA wires 40, one end of each wire 40 being attached to the support structure 10 via a static crimp 42a, and the other end being attached to the movable part 20 via a moving crimp 42b. More specifically, the moving crimp 42b is connected to the movable part 20 via a flexible element (e.g., a planar crimp plate) so as to allow a certain degree of relative movement between the moving crimp 42b and the movable part 20. The SMA wires 40 are angled with respect to the direction of movement, so that when contracted, the SMA wires 40 apply a corresponding first force component for moving the movable part 20 in the opposite direction of movement to drive movement along the optical axis O, and apply a corresponding second force component for moving in the opposite direction transverse to the optical axis O (as shown by the arrows in FIG8B ).

The actuator assembly 1 includes a flexure 30, the two ends of which are fixedly attached to the moving crimp 42b. The flexure 30 includes a plurality of kinks 36 adjoining a plurality of flexible arms. When subjected to a compressive force, the curvature of the kinks 36 may increase, causing the two ends of the two flexure 30 to move toward each other. The flexible arms may become stiff under compression, or may bend.

8A , the buckling flexure 30 can be used as a force correction mechanism. More specifically, when the SMA wire 40 is not energized, the buckling flexure 30 is biased against the corresponding protrusion 22 extending from the support structure 10 at its contact portion 32 (e.g., between the two kinks 36), and thereby generates a friction force for constraining the free movement of the movable component 20.

As the SMA wire 40 contracts, the second force component compresses the buckling flexure 30, further bending the kink 36 of the buckling flexure 30, thereby causing the contact portion 32 to move toward the movable member 20 and back away from the protrusion 22, such as along the arrows shown in FIG8B. Advantageously, the use of the buckling arm 30 allows the contact portion 32 to be quickly retracted from the protrusion 22 of the support structure due to the bend in the kink 36.

The surface of the moving portion 20 also acts as an end stop 70, which limits the movement of the contact portion 32. As shown in FIG8B, when the SMA wire 40 is energized, the actuation force causes the contact portion 32 to retreat until the flexure 30 abuts or engages the protrusion. Further contraction in the SMA wire 40 does not cause further retraction in the contact portion 32. Instead, the actuation force is used only to drive the movement of the lens holder 20, thereby allowing more precise position control.

In some other embodiments, the flexure 30 can switch between a first configuration (e.g., when the contact portion 32 is engaged with the protrusion 22) and a second configuration (e.g., when the contact portion 32 is disengaged from the protrusion 22). More specifically, the flexure 30 can be stable only in the first configuration and the second configuration. Therefore, when the SMA wire 40 is energized, the flexure 30 can quickly switch toward the second configuration.

9A and 9B are a plan view and a side cross-sectional view, respectively, of an actuator assembly 1 according to an embodiment of the present invention.

The SMA actuator 102 includes a support structure 10 and a movable part 20. The support structure 10 and the movable part 20 are flat parallel sheets facing each other. A suspension system including at least one or more flexures 30 supports the movable part 20 on the support structure 10 and guides the movable part 20 to move relative to the support structure 10 along the Z axis, which in this example is the moving axis O. More specifically, the flexure 30 supports the movable part 20 on the support structure and can therefore be considered as a support or the only support. As further described below, the suspension system constrains the translational movement of the movable part 20 relative to the support structure 10 along the X axis and the Y axis perpendicular to the Z axis.

Two SMA wires 40 are arranged as follows to drive the movement of the movable part 20 along the movement axis relative to the support structure 10. The SMA wires 40 are each connected to the support structure 10 at one end through a static crimping portion 42a, and connected to the movable part 20 at the other end through a movable crimping portion 42b. The static crimping portion 42a and the movable crimping portion 42b crimp the SMA wires 40 to provide mechanical and electrical connections.

The SMA wire 40 is tilted at a first acute angle θ relative to a plane normal to the Z-axis. The first acute angle θ is greater than 0 degrees, so that it applies a first force component to the support structure 10 and the movable member 10 along the Z-axis, and can thereby drive movement along the Z-axis. However, when the SMA wire 40 is contracted to drive relative movement, the tilting of the SMA wire 40 at the first acute angle θ provides a gain as the SMA wire 40 rotates, resulting in a relative movement along the Z-axis that is greater than the change in the length of the wire.

The two SMA wires 40 are under tension, and are opposite in the direction in which they apply forces to the movable part 20 with respective first force components in opposite directions parallel to the Z-axis. That is, as shown in FIG9B , the uppermost SMA wire 40 is connected to the movable part 20 at its upper end, thereby applying a force having a downward component along the Z-axis on the movable part 20, and the lowermost SMA wire 40 is connected to the movable part 20 at its lower end, thereby applying a force having an upward component along the Z-axis on the movable part 20. Therefore, the SMA wires 40 drive the movable part 20 to move in opposite directions along the Z-axis.

9A, where two SMA wires 40 are tilted from parallel and projected onto a plane normal to the Z axis as the axis of movement, the components of the force applied by the segments of the SMA wire 4 along the Y axis are in the same direction and therefore no coupling occurs.

In some embodiments, the suspension system does not include a conventional support member. That is, the flexible member 30 supports the movable member 20 on the support structure 10. Since the flexible member 30 is most easily deformed in the moving direction, the flexible member 30 can be considered as a support member for guiding the movable member 20 to move.

In the example shown, the suspension system also includes a support arrangement consisting of two supports 50 arranged as follows to allow the movable part 20 to move along the Z axis relative to the support structure 10. The supports 50 allow a certain degree of movement of the movable part 20 along the Y axis while constraining or limiting other undesirable movements that are not constrained by the flexure 30. The supports 50 can also be planar support elements. Each of the two supports 50 can extend along the Z axis, thereby allowing the movable part 20 to move along the Z axis relative to the support plate 10. There can be more than two supports, and preferably, they are spaced as far apart as possible within the range of the actuator.

9C and 9D are enlarged plan views and enlarged side cross-sectional views of the support 50 applicable to the embodiments of FIGS. 9A and 9B , respectively. The support 50 includes a ball bearing 52 running in a support race 54 extending along the Z axis so as to allow relative movement in the moving direction. The support race 54 is connected to the support structure 10 and the movable part 20 by an elastic element 56 that is deformable only in the Y direction. More specifically, the elastic element 56 is a sufficiently thin planar flexure (as shown in FIG. 13C ) to be deformable along the Y axis, thereby providing limited movement of the support race 54 orthogonal to the Z axis. Therefore, the flexure 30 can bias the movable part 20 against the protrusion 22 of the support structure 10 to generate a friction force.

The two supports 50 are spaced apart along the X-axis. As a result, the reaction forces generated within the supports 50 act together to restrict the rotational movement of the movable component 50 relative to the support structure 10 about the Z-axis.

As described above, the movable part 20 is supported by a pair of flexures 30 and a support 50. Figures 9A and 9B show only a single flexure 30, wherein another flexure 30 arranged in the opposite manner is not shown. The flexure 30 is attached to the support structure 10 and the movable part 20 by a first end 34 and a second end 36, respectively. The first end 34 and the second end 38 are connected by a flexible arm 38 and can move relative to each other along at least the Y-axis and the Z-axis. More specifically, the flexible arm 38 is deformable in the Y-direction and the Z-direction, which allows such relative movement.

As shown in the plan view of FIG9A , the flexible arm 38 is curved along its length. When the SMA wire 40a is not energized, the flexible member 30 is configured to bias the movable component 20 against the support structure 10. More specifically, the movable component 20 engages and is biased against a contact surface at a protrusion 22 formed on the side wall of the support structure. The biasing force from the flexible member 30 generates a friction force at the contact surface, which is sufficient to constrain the movement of the second component when one or more SMA wires are not energized.

When the SMA wire 40 is energized, the second force component of the actuation force opposes the biasing force applied by the flexure 30, causing the movable part 20 to retreat from the contact surface of the protrusion in a direction transverse to the optical axis. Therefore, when the SMA wire 40 is energized, the friction at the contact surface is reduced. This allows the first force component of the actuation force to drive the movable part 20 to move along the Z axis while being fully supported by the support 50.

In some embodiments, further contraction in the SMA wire 40 causes the movable component 20 to disengage from the protrusion 22 of the support structure 10 , thereby eliminating friction therebetween.

In contrast to the prior art embodiment 100, the contact surface on the protrusion 22 is different from the support 50 (if any) in the actuator assembly 1, but allows the movable component 20 to be fully supported and guided within the range of movement. In addition, the contact surface on the protrusion 22 is arranged on a different surface/side of the actuator assembly 1 than the support 50 (if any). Therefore, the friction force generated at the contact surface is disconnected from the support surface. Therefore, these two surfaces can be customized separately to meet their needs. Advantageously, compared to the prior art embodiment, when the second component is kept in place, the present invention provides more precise position control. In addition, because the contact surface does not need to be combined with a support, a wider range of surface profiles can be used to generate friction.

Figures 10A, 10B and 10C are respectively an exploded perspective view, an enlarged side cross-sectional view and a side schematic view of an actuator assembly 200 according to an embodiment of the present invention. The actuator assembly 200 is suitable for providing optical image stabilization (OIS) when incorporated into a camera device or other optical device. The actuator assembly 200 is arranged as described below, but generally has an arrangement and function similar to the actuator arrangement described in WO 2017/755788, except for some differences described below. Therefore, please refer to WO2017/755788.

The actuator assembly 200 comprises a support plate 250 and a movable member 260 , which in this example are a first member and a second member, respectively. The movable member 260 is movable relative to the support structure 260 .

The support structure 250 and the movable part 260 are a unitary sheet of metal, for example steel such as stainless steel. The support structure 250 is fixed to a support sheet 270 .

The movable part 260 supports the lens assembly 301. The support sheet 270 is fixed to the base 302, and the image sensor 303 is mounted on the base 302, however, the image sensor 303 may be omitted in other types of optical devices. In general, the movable part 260 may support the image sensor 303, and the lens assembly 301 may be mounted on the base 302. Each of the support structure 250 and the movable part 260 is provided with a central hole aligned with the optical axis O, allowing light to pass from the lens assembly 301 to the image sensor 303 to allow the image sensor 303 to capture an image formed by the lens assembly 301.

The actuator assembly 200 includes four planar supports 210 spaced apart around the optical axis O, each planar support having a structure shown in more detail in FIG. 10D . Each planar support 210 includes a support element 211 mounted on a support structure 250, for example, by an adhesive, and a support surface 212 as a surface of a movable part 260. The support element 211 is supported on the support surface 212. In particular, the outer surface 213 of the support element 211 contacts the support surface 212, and the outer surface 213 of the support element 211 and the support surface 212 conform to each other. The planar supports 210 can be arranged as described in further detail in WO 2017/755788.

Thus, the movable component 260 is able to move relative to the static plate 260 on the support surface 212 of the planar support 210 in any direction in two dimensions orthogonal to the optical axis O.

Alternatively, the planar support 210 may be reversed to include a support element mounted on the movable part 260 and a support surface that is a surface of the support structure 250. In this case, the support structure 250 would form the first component and the movable part 260 would form the second component. In this sense, the lens assembly 301 may be mounted on either the first component or the second component.

The actuator assembly 200 includes two flexures 267 connected between the support structure 250 and the movable member 260. In this example, the flexures 267 are integrally formed with the movable member 260 at one end thereof and mounted to the support structure 250 at the other end thereof, however the flexures 267 may be integrally formed with the support structure 250 and mounted to the movable member 260, or may be separate elements mounted to each of the support structure 250 and the movable member 260.

The flexure 267 is resilient and is therefore a resilient biasing element. The flexure 267 is arranged to act as a resilient biasing device that biases the support structure 250 into contact with the bearing surface 212 of the movable part 260. This can be achieved by configuring the flexure 267 so that the flexure 267 deflects from its relaxed state to provide a preload force that provides a bias. This creates a reaction between the movable part 260 and the bearing surface 212, and a friction force is generated between the movable part 260 and the bearing surface 212.

At the same time, the flexure 267 allows the movable component 260 to move orthogonally to the optical axis O relative to the support structure 250.

The flexure 267 is made of a suitable material that provides desired mechanical properties and is conductive, so that the flexure 267 can be electrically connected to the SMA wire 280 connected thereto for transmitting the drive current provided to the SMA wire 280. Typically, the material is a metal with a relatively high yield, such as steel, such as stainless steel.

The second actuator assembly 200 also includes four SMA wires 280 connected between the support structure 250 and the movable part 260. Specifically, the support structure 250 is formed with a crimping piece 251, and the movable part 260 is formed with a crimping piece 261, wherein the crimping pieces 251 and 261 crimp the four SMA wires 280 to connect them to the support structure 250 and the movable plate 260. In contrast to the arrangement of the SMA wires 280 extending perpendicular to the optical axis O disclosed in WO2017/755788, each SMA actuator wire 280 is inclined at an acute angle α greater than 0° relative to the support surface 212, so as to apply a force ("upper pressure") when the SMA actuator wire 280 contracts, the force having a component normal to the support surface 212 to bias the support structure 250 away from the support surface 212, and the force having a component parallel to the support surface 212.

The SMA wires 280 have an arrangement around the optical axis O, which is the same as the arrangement described in WO 2017/755788, so that each SMA wire 80 applies a component of force parallel to the support surface 212 in different directions, and the SMA wires 280 are capable of driving the movable part 260 to move in two dimensions on the support surface 212 relative to the support structure 250.

Because the SMA wires 280 are opposed, their average tension, and therefore upper pressure, can be controlled at least substantially independently of the movement.

The SMA wires 280 are each connected to a control circuit, which can be implemented in an integrated circuit chip. The control circuit applies a drive signal to the SMA actuator wires 280 in use, which resistively heats the SMA wires 280, causing the SMA wires to contract. In operation, the SMA wires 280 are selectively driven to move the movable component 260 along the movement axis relative to the support structure 250 in any direction orthogonal to the optical axis O. Such control can be used to move the lens assembly relative to the image sensor orthogonal to the optical axis O to provide OIS as described in WO 2017/755788.

In the absence of an applied drive signal, the SMA wire 280 does not contract, and thus the flexure 267 biases the movable member 260 against the support surface 212, generating a friction force sufficient to hold the movable member 260 in position on the support surface 212. In this state, the movable member 260 is held in position by the second actuator assembly 200 with zero power consumption.

When the SMA wire 280 is in an unpowered state, the flexure 267 can be designed to provide sufficient friction to reduce movement, thereby improving the stability of the second actuator assembly 200 and/or reducing the risk of audible noise. This is important because being able to turn off the OIS will reduce power consumption in situations where the OIS is ineffective (e.g., very high light levels). In this state, the friction should maintain the movable part 260 in place on the support surface 212 under typical forces acting on the second actuator assembly 200, including gravity (which can cause orientation dependence (attitude dependence)) and inertial impact forces. Otherwise, when the second actuator assembly 200 vibrates (e.g., due to tactile effects of a device such as a mobile phone (incorporating the second actuator assembly 200)), there is a risk that the second actuator assembly 200 is not stable enough and/or generates audible noise (e.g., between the movable part 260 and the support surface 212 or between the lens assembly 301 and the housing of the camera device 300). When the second actuator assembly 200 is not powered, the SMA wire 280 will relax and not exert much force. Therefore, the position of the lens assembly 301 will be determined by the interaction of the following forces:

The combined weight of the lens assembly 301 and the movable member 260;

The stiffness of the flexure 267 (in the plane of movement);

Friction; and

Inertia (when accelerating).

For example, when the camera arrangement is held with the optical axis O horizontal, the lens position will "sag" until the restoring force of the flexure 267 and the friction force balance the weight.

Generally, the strength of the friction force, and thus the biasing force from flexure 267, needs to increase as the mass of the camera lens assembly to be mounted on movable member 260 increases.

Additionally, as the camera accelerates, hard inertia can move the lens assembly 301 relative to the image sensor 303. Both of these effects are undesirable and can result in blur due to motion and potential interference with OIS. In order to achieve optimal OIS performance, a rigid, stable system is required. In the absence of contraction of the SMA wire 280, the friction generated between the movable component 260 and the support surface 212 can be less than the combined weight of the lens assembly 301 and the movable component 260. In this case, when the camera arrangement is held with the optical axis horizontal and other forces in the system are ignored, the movable component 260 is held in place on the support surface 212 by gravity.

This may hinder OIS performance if appropriate levels of friction to achieve these effects are encountered when driving the SMA wire 280. However, due to the tilt of the SMA wire 280, the force exerted by the SMA wire 280 on the support structure 250 has a component normal to the support surface 212, which biases the support structure 250 away from the support surface 212, thereby reducing the friction between the support structure 250 and the support surface 212 to reduce the impact on OIS performance.

To provide an appropriate degree of reduction, the ratio between the friction force generated when (i) the SMA wire 280 drives the maximum relative movement of the movable part 260 and (ii) the friction force generated when the SMA wire 280 is not contracted can be less than 0.9, more preferably less than 0.7. The inventors have found that this can be achieved with a practical set of design parameters, including, among other things, an angle α greater than 0.5°. In smaller actuators, angles of 0.5° or less are often associated with an impractically small height difference between the ends of the SMA wire 280, while in larger actuators, such small angles often do not provide sufficient upward force. Larger angles can be used, but generally result in taller actuators.

In order to constrain the free movement of the movable component 20 when the wire is not energized, the planar support 210 can be provided with a surface coating or material, etc. The coefficient of friction of the planar support 210, for example through surface roughness, is in the range of 0.05 to 0.6, or in the range of 0.1 to 0.4, or preferably in the range of 0.05 to 0.4. This arrangement can allow the biasing arrangement to generate sufficient friction to hold the second component in place when the SMA wire 280 is not energized, but will not generate significant resistance to the movement of the second component.

Figures 11 and 12 show further embodiments of the actuator assembly according to the present invention. The mechanical structure of these actuator assemblies 1 is described in, for example, WO 2013 175197A1 or WO 2017 072525A1, the above disclosures being incorporated herein by reference.

The actuator assembly 1 comprises a support structure 10 and a movable part 20. The movable part 20 is movable within a range of motion in a plane of motion. In particular, the movable part 20 is movable in translation and rotation in the plane of motion, i.e., has three DOFs in the plane of motion. The actuator assembly 1 comprises a total of four SMA wires 40 connected between the movable part 20 and the support structure 10, wherein the SMA wires 40 are in an arrangement in which none of the SMA wires 40 are co-linear, and wherein the SMA wires 40 can be selectively driven to move the movable part 10 relative to the support structure to any position within the range of motion without applying any net torque to the movable part 20 about a main axis perpendicular to the plane of motion.

For example, two of the SMA wires 40 may be connected between the movable component 20 and the support structure 10 to each apply a torque about the main axis in the plane of movement to the movable component 20 in a first orientation about the main axis, and another two SMA wires 40 may be connected between the movable component 20 and the support structure 10 to each apply a torque about the main axis in the plane of movement to the movable component in an opposite second orientation about the main axis. Four SMA wires 40 may be arranged in a loop at different angular positions about the main axis, with successive SMA wires about the main axis being connected to apply forces about the main axis in alternating orientations to the movable element.

Typically, fewer than four SMA wires 40 may be provided, such as two SMA wires 40 for driving translational movement of the movable member in a plane (and opposed by a resilient element, such as a spring), or three SMA wires 40 for driving translational movement of the movable member in a plane.

The lens assembly may be fixed relative to the movable part and the image sensor may be fixed relative to the support structure as described in WO 2013 175197A1. Alternatively, the image sensor may be fixed relative to the movable part and the lens assembly may be fixed relative to the support structure as described in WO 2017 072525A1. In either case, movement of the lens relative to the image sensor may affect OIS.

Fig. 11A shows a side view of the actuator assembly 1, and Fig. 11B shows a plan view of the actuator assembly 1. The support structure 10 comprises a biasing device 30. Thus, when the movable part 20 moves, the biasing device 30 remains static with the support structure 10. In other words, the support structure 10 comprises two parts coupled via an elastic element of the biasing device 30.

In particular, the biasing device 30 includes four elastic elements in the form of four flexible members. The first end of each flexible member is fixed relative to the support structure 10. The SMA wire 40 is connected to the second end of each flexible member. The second end of each flexible member includes a first friction surface 10f, which engages with a second friction surface 20f on the movable part 20. The flexible members are preloaded to bias the friction surfaces 10f, 20f together. The flexible members also provide a biasing force to push the support device 50, which is in the form of a ball bearing in the embodiment shown.

In the embodiment of FIG. 11 , the flexure is angled relative to the SMA wire. As a result, the flexure can deform (e.g., deform upward in FIG. 12B ) when the SMA wire 40 contracts. The friction force F between the friction surfaces 10 f, 20 f can thereby be reduced. In particular, in the opposite wire configuration of FIG. 11 , equal contraction of the SMA wire 40 can reduce the friction force F without moving the movable part 20, while differential contraction of the SMA wire 40 can result in movement of the movable part 20.

Fig. 12A shows a plan view of the actuator assembly 1, and Fig. 12B shows a side view of the actuator assembly 1. The support structure 10 partly includes the biasing device 30, and the movable part 20 partly includes the biasing device 30. Therefore, when the movable part 20 moves, a part of the biasing device 30 remains static with the support structure 10, and when the movable part 20 moves, a part of the biasing device 30 moves with the movable part 20. In particular, the biasing device 30 includes four pairs of elastic elements in the form of four pairs of flexible members, each pair of flexible members including a first flexible member and a second flexible member.

The first end of each first flexure is fixed relative to the support structure 10. The first end of each second flexure is fixed relative to the movable member 20. The SMA wire 40 is connected between the second ends of each pair of flexures. The second end of each flexure includes a first friction surface 10f, which engages with a corresponding second friction surface 20f on the movable member 20. The flexures are preloaded to bias the friction surfaces 10f, 20f together. The flexures can also provide a biasing force to load the support device 50.

In the embodiment of FIG. 12 , the SMA wire 40 is parallel to the flexure. However, the SMA wire is offset from a pair of flexures (i.e., spaced above the flexures in FIG. 12B ), i.e., the SMA wire 40 is not arranged in the same plane as the corresponding flexures. As a result, when the SMA wire 40 contracts, the flexures may be biased (e.g., biased upward in FIG. 12B ). The friction force F between the friction surfaces 10 f, 20 f may thereby be reduced.

Therefore, an actuator assembly is provided, the actuator assembly comprising a support structure and a movable part, the support structure comprising a first friction surface, the movable part comprising a second friction surface engaging the first friction surface, the actuator assembly further comprising one or more SMA wires, the one or more SMA wires being arranged to move the movable part relative to the support structure to any position within a range of motion when contracted, the actuator assembly further comprising a biasing device, the biasing device being arranged to bias the first friction surface and the second friction surface against each other with a normal force, thereby generating a static friction force, which constrains the movement of the movable part relative to the support structure at any position within the range of motion when the one or more SMA wires are not contracted. The movable part or the support structure may comprise the biasing device. This includes the movable part partially comprising the biasing device and the support structure partially comprising the biasing device. Therefore, the biasing device may move with the movable part or remain static relative to the support structure. The biasing device is arranged to apply a normal force only in a direction perpendicular to the range of motion at any position within the range of motion. The one or more SMA wires are arranged to reduce a normal force between the first friction surface and the second friction surface when contracted.

The actuator assembly 1 may include a total of four SMA wires 40. The SMA wires 40 may be arranged to drive the movable component 20 to move in three degrees of freedom in the moving plane. The friction surfaces 10f, 20f may be parallel to the moving plane. The biasing device includes an elastic element included by the movable component and/or an elastic element included by the supporting structure. Each elastic element is connected to one of the movable element or the supporting structure at one end, and each elastic element is connected to a corresponding SMA wire at the other end. The other end of the corresponding SMA wire is connected to another of the movable element or the supporting structure, or is connected to another elastic element, which is connected to another of the movable element or the supporting structure. Each elastic element may bias the friction surfaces 10f, 20f against each other. Each elastic element may load the supporting device included by the actuator assembly 1. The elastic element may be angled relative to the SMA wire. Optionally, the elastic element may be parallel to the SMA wire, but the SMA wire may not be coplanar with the elastic element.

The term "shape memory alloy (SMA) wire" may refer to any element containing SMA. SMA wires may generally be described as SMA elements. SMA elements may have any shape suitable for the purposes described herein. SMA elements may be elongated and may have a circular cross section or a cross section of any other shape. The cross section may vary along the length of the SMA element. SMA elements may have relatively complex shapes, such as a spiral spring shape. It is also possible that the length of the SMA element (however defined) may be similar to one or more of the other dimensions of the SMA element. The SMA element may be sheet-like, and such a sheet may be planar or non-planar. The SMA element may be pliant, or in other words, the SMA element may be flexible. In some examples, when connected in a straight line between two components, the SMA element can only apply tension that forces the two components together. In other examples, the SMA element may be bent around the component, and when the SMA element tends to straighten under tension, the SMA element may apply force to the component. The SMA element may be beam-like or rigid, and may be able to apply different forces (e.g., non-tension) to the element. The SMA wire element may or may not include non-SMA materials and/or components. For example, the SMA element may include a core of SMA and a coating of non-SMA material. Unless the context requires otherwise, the term "SMA element" may refer to any configuration of SMA material that acts as a single actuating element, for example, the single actuating element can be independently controlled to generate a force acting on the element. For example, the SMA element may include two or more parts of SMA material that are mechanically arranged in parallel and/or in series. In some arrangements, the SMA element may be a part of a larger SMA element. This larger SMA element may include two or more parts that can be individually controlled, thereby forming two or more SMA wires. The SMA element may include any other configuration of SMA wire, SMA foil, SMA film or SMA material. The SMA element may be manufactured using any suitable method, such as by methods involving stretching, rolling, or deposition and/or other forming processes. The SMA element may exhibit any shape memory effect, such as a thermal shape memory effect or a magnetic shape memory effect, and may be controlled in any suitable manner, such as by Joule heating, another heating technique, or by applying a magnetic field.

In general, although the present invention has been described with respect to SMA wires, actuator components other than SMA wires may also be used. For example, in any of the above embodiments, a voice coil motor (VCM), a piezoelectric element, or other actuator may be used in place of an SMA wire. Thus, any reference to an SMA wire above may be replaced with an actuator component, and any reference to contraction of an SMA wire may be replaced with actuation of an actuator component.

Various aspects of the invention are set out in the following clauses.The claims of the present application are further provided below under the heading "Claims".

1. An actuator assembly comprising:

a support structure comprising a first friction surface;

a movable member including a second friction surface engaging the first friction surface;

one or more SMA wires arranged to move the movable member relative to the support structure to any position within a range of motion when retracted;

a biasing device arranged to bias the first friction surface and the second friction surface against each other with a normal force so as to generate a static friction force which constrains movement of the movable component relative to the support structure at any position within the range of movement when the one or more SMA wires are not contracted,

wherein the movable part or the support structure comprises the biasing means so that the biasing means moves with the movable part or remains static relative to the support structure, and the biasing means is arranged to exert the normal force only in a direction perpendicular to the range of movement at any position within the range of movement;

Wherein the one or more SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface when contracted.

2. An actuator assembly according to clause 1, wherein the movable component comprises two parts connected via the biasing device, or wherein the support structure comprises two parts connected via the biasing device.

3. An actuator assembly according to clause 1 or 2, wherein the biasing means comprises a resilient element.

4. An actuator assembly according to clause 3, wherein the biasing means comprises one or more flexible members.

5. An actuator assembly according to any preceding clause, wherein the actuator assembly comprises support means for supporting the movable component for movement relative to the support structure.

Optionally, wherein the biasing means is arranged to load the support means.

6. An actuator assembly according to clause 2 and clause 5, wherein the bearing device is arranged on a part of the support structure or the movable part, and wherein the first friction surface or the second friction surface is arranged on another part of the support structure or the movable part.

7. An actuator assembly according to clause 6, wherein the one or more SMA wires are coupled to the support structure or the other portion of the movable component.

8. An actuator assembly according to clause 6 or 7, wherein the support structure or the other part of the movable component is formed integrally with the biasing means.

9. An actuator assembly according to any of clauses 5 to 8, wherein the one or more SMA wires are arranged to load the support means when contracted.

10. An actuator assembly according to any one of clauses 5 to 9, wherein the supporting device includes a rolling bearing member, the rolling bearing member including a supporting bearing surface on the supporting structure, a movable bearing surface on the movable part, and a rolling bearing element arranged between the supporting bearing surface and the movable bearing surface.

11. The actuator assembly of clause 10, wherein the support bearing surface and the movable bearing surface are parallel to the first friction surface and the second friction surface.

12. An actuator assembly according to any one of clauses 5 to 9, wherein the support device includes a planar support formed between a mating surface on the support structure and a corresponding mating surface on the movable part, and the mating surface on the support structure engages with the corresponding mating surface on the movable part.

13. An actuator assembly according to any of clauses 5 to 12, wherein the bearing arrangement is separate from the first friction surface and the second friction surface.

14. An actuator assembly according to any of clauses 5 to 13, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to movement in three degrees of freedom.

15. An actuator assembly according to clause 14, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to movement within a plane of movement.

16. An actuator assembly according to any of clauses 5 to 13, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to movement in one degree of freedom.

17. An actuator assembly according to clause 16, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to helical movement about a helical axis.

18. An actuator assembly according to clause 16, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to translational movement along an axis of movement or rotational movement about an axis of rotation.

19. An actuator assembly according to any preceding clause, wherein the one or more SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface by at least 10%, preferably at least 20%, most preferably at least 50% when contracted.

20. An actuator assembly according to any preceding clause, wherein the one or more SMA wires are arranged to disengage the first and second friction surfaces upon contraction.

21. An actuator assembly according to any preceding clause, wherein the one or more SMA wires are arranged to lift at least a portion of the movable component out of engagement with an end stop when retracted.

22. An actuator assembly according to clause 21, wherein the end stop is arranged on another part of the movable part.

23. An actuator assembly according to any preceding clause, wherein the ratio of static friction to weight of the movable part is greater than 1, preferably greater than 3, and further preferably greater than 5.

24. An actuator assembly according to any preceding clause, wherein the coefficient of static friction between the first friction surface and the second friction surface is in the range between 0.05 and 0.6, preferably in the range between 0.1 and 0.4.

25. An actuator assembly according to any of the preceding clauses, wherein the one or more SMA wires apply a force to the movable component that is angled relative to the first friction surface and the second friction surface.

26. An actuator assembly according to any of the preceding clauses, wherein the one or more SMA wires are angled relative to the first friction surface and the second friction surface.

27. An actuator assembly according to any of the preceding clauses, wherein the one or more SMA wires are angled relative to one or more directions of movement of the movable component relative to the support structure.

28. An actuator assembly according to any of the preceding clauses, wherein the one or more SMA wires include at least two opposing SMA wires, and the at least two opposing SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface when contracted, and move the movable part in opposite directions within the range of movement.

1a. An actuator assembly comprising:

a support structure comprising a first friction surface;

a movable member including a second friction surface engaging the first friction surface;

A support device for supporting the movement of the movable component relative to the support structure within a range of movement;

one or more SMA wires arranged to, when retracted, move the movable member relative to the support structure to any position within the range of movement;

a biasing device arranged to bias the first friction surface and the second friction surface against each other with a normal force so as to generate a static friction force which constrains movement of the movable component relative to the support structure at any position within the range of movement when the one or more SMA wires are not contracted,

Wherein the one or more SMA wires are arranged to lift the movable component away from the first friction surface when contracted such that the movable component is supported on the support means.

Optionally, wherein the biasing means is arranged to load the support means.

2a. An actuator assembly according to clause 1a, wherein the biasing means is connected between the movable member and the support structure.

3a. An actuator assembly according to clause 2a, wherein the one or more SMA wires are configured to lift the movable component away from the first friction surface and onto the support device when contracted.

4a. An actuator assembly according to claim 1a, wherein the movable part or the supporting structure includes the biasing device so that the biasing device moves with the movable part or remains static relative to the supporting structure, and the biasing device is arranged to apply the normal force only in a direction perpendicular to the moving range at any position within the moving range.

5a. An actuator assembly according to clause 1a or 4a, wherein the movable member comprises two parts coupled via the biasing means, or wherein the support structure comprises two parts coupled via the biasing means.

6a. An actuator assembly according to clause 5a, wherein the support device supports the movement of a part of the support structure or the movable component, and wherein the first friction surface or the second friction surface is arranged on another part of the support structure or the movable component.

7a. An actuator assembly according to clause 5a or 6a, comprising an end stop formed between the two parts of the movable component or between the two parts of the support structure.

8a. The actuator assembly of clause 7a, wherein the one or more SMA wires are configured to disengage the friction surface and engage the end stop when retracted.

9a. An actuator assembly according to any of clauses 5a to 8a, wherein the one or more SMA wires are connected to the support structure or the other part of the movable component.

10a. An actuator assembly according to any of clauses 5a to 9a, wherein the further portion of the movable member is formed integrally with the biasing means.

11a. An actuator assembly according to any of clauses 1a to 10a, wherein the biasing means comprises a resilient element.

12a. An actuator assembly according to clause 11, wherein the biasing means comprises one or more flexures.

13a. An actuator assembly according to any of clauses 1a to 12a, wherein the one or more SMA wires are arranged to load the support means when contracted.

14a. An actuator assembly according to any one of clauses 1a to 13a, wherein the support device includes a rolling support member, the rolling support member including a supporting support surface on the supporting structure, a movable supporting surface on the movable part, and a rolling support element arranged between the supporting support surface and the movable supporting surface.

15a. An actuator assembly according to clause 14a, wherein the support bearing surface and the movable bearing surface are parallel to the first friction surface and the second friction surface.

16a. An actuator assembly according to any one of clauses 1a to 13a, wherein the support device includes a planar support formed between a bonding surface on the support structure and a corresponding bonding surface on the movable part, and the bonding surface on the support structure engages with the corresponding bonding surface on the movable part.

17a. An actuator assembly according to any of clauses 1a to 17a, wherein the bearing arrangement is separate from the first friction surface and the second friction surface.

18a. An actuator assembly according to any of clauses 1a to 17a, wherein the ratio of static friction to weight of the movable part is greater than 1, preferably greater than 3, further preferably greater than 5.

19a. An actuator assembly according to any of clauses 1a to 18a, wherein the coefficient of static friction between the first friction surface and the second friction surface is in the range between 0.05 and 0.6, preferably in the range between 0.1 and 0.4.

20a. An actuator assembly according to any of clauses 1a to 19a, wherein the one or more SMA wires apply a force to the movable component that is angled relative to the first friction surface and the second friction surface.

21a. An actuator assembly according to any of clauses 1a to 20a, wherein the one or more SMA wires are angled relative to the first friction surface and the second friction surface.

22a. An actuator assembly according to any of clauses 1a to 21a, wherein the one or more SMA wires are angled relative to one or more directions of movement of the movable component relative to the support structure.

23a. An actuator assembly according to any one of clauses 1a to 22a, wherein the one or more SMA wires include at least two opposing SMA wires, and the at least two opposing SMA wires are arranged to reduce the normal force between the first friction surface and the second friction surface when contracted, and move the movable part in opposite directions within the movement range.

24a. An actuator assembly according to any of clauses 1a to 23a, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to movement in three degrees of freedom.

25a. An actuator assembly according to clause 24a, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to movement within a plane of movement.

26a. An actuator assembly according to any of clauses 1a to 23a, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to movement in one degree of freedom.

27a. An actuator assembly according to clause 26a, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to helical movement about a helical axis.

28a. An actuator assembly according to clause 26a, wherein the bearing arrangement constrains movement of the movable component relative to the support structure to translational movement along an axis of movement or rotational movement about an axis of rotation.

Claims (33)

1. An actuator assembly, comprising:

a support structure comprising a first friction surface;

a movable member including a second friction surface engaging the first friction surface;

one or more SMA wires arranged to move the movable part to any position within a range of movement relative to the support structure when contracted;

Biasing means arranged to bias the first and second friction surfaces against each other with a normal force, thereby generating a static friction force that constrains movement of the movable component relative to the support structure at any position within the range of movement when the one or more SMA wires are not contracted,

Wherein the one or more SMA wires are arranged to reduce the normal force between the first and second friction surfaces when contracted.

2. An actuator assembly according to claim 1, wherein the movable part or the support structure comprises the biasing means such that the biasing means moves with the movable part or remains stationary relative to the support structure, and the biasing means is arranged to apply the normal force only in a direction perpendicular to the range of movement at any position within the range of movement.

3. The actuator assembly of claim 1 or 2, wherein the movable member comprises two portions coupled via the biasing device, or wherein the support structure comprises two portions coupled via the biasing device.

4. The actuator assembly of claim 1, wherein the biasing device is connected between the movable member and the support structure.

5. An actuator assembly according to any preceding claim, wherein the biasing means comprises a resilient element.

6. The actuator assembly of claim 5, wherein the biasing means comprises one or more flexures.

7. An actuator assembly according to any preceding claim, wherein the actuator assembly comprises a support means for supporting the movable part for movement relative to the support structure, optionally wherein the biasing means is arranged to load the support means.

8. An actuator assembly according to claim 7, wherein the one or more SMA wires are arranged to lift the movable part off the first friction surface when contracted such that the movable part is supported on the support means.

9. The actuator assembly of claim 8, wherein the one or more SMA wires are configured to lift the movable component off the first friction surface onto the support device upon contraction.

10. An actuator assembly according to claim 3 and claim 7, wherein the bearing means is provided on a portion of the support structure or the moveable component, and wherein the first friction surface or the second friction surface is provided on another portion of the support structure or the moveable component.

11. An actuator assembly according to claim 10, wherein the one or more SMA wires are coupled to the support structure or the other portion of the movable component.

12. An actuator assembly according to claim 10 or 11, wherein the other part of the support structure or the moveable part is integrally formed with the biasing means.

13. An actuator assembly according to any one of claims 7 to 12, wherein the one or more SMA wires are arranged to load the support means upon contraction.

14. An actuator assembly according to any one of claims 7 to 13, wherein the bearing means comprises a rolling bearing comprising a support bearing surface on the support structure, a movable bearing surface on the movable part and a rolling bearing element arranged between the support bearing surface and the movable bearing surface.

15. The actuator assembly of claim 14, wherein the support bearing surface and the movable bearing surface are parallel to the first friction surface and the second friction surface.

16. An actuator assembly according to any one of claims 7 to 13, wherein the bearing means comprises a planar bearing formed between an engagement surface on the support structure and a corresponding engagement surface on the movable member, the engagement surface on the support structure engaging with the corresponding engagement surface on the movable member.

17. An actuator assembly according to any one of claims 7 to 14, wherein the support means is separate from the first and second friction surfaces.

18. An actuator assembly according to any one of claims 7 to 14, wherein the bearing means comprises the first and second friction surfaces.

19. An actuator assembly according to any one of claims 7 to 18, wherein the bearing means constrains movement of the moveable member relative to the support structure to movement in three degrees of freedom.

20. The actuator assembly of claim 19, wherein the bearing device constrains movement of the movable member relative to the support structure to movement in a plane of movement.

21. An actuator assembly according to claim 20, wherein the one or more SMA wires are arranged to move the movable part translationally and rotationally relative to the support structure within the plane of movement upon selective contraction, optionally wherein the one or more SMA wires comprise a total of four SMA wires.

22. An actuator assembly according to any one of claims 7 to 18, wherein the bearing means constrains movement of the moveable member relative to the support structure to movement in one degree of freedom.

23. The actuator assembly of claim 21, wherein the bearing device constrains movement of the movable member relative to the support structure to helical movement about a helical axis.

24. An actuator assembly according to claim 23, wherein the one or more SMA wires are arranged to drive rotation of the movable component about the helical axis, the support rotation translating rotation of the movable component into helical movement about the helical axis.

25. The actuator assembly of claim 22, wherein the bearing device constrains movement of the movable member relative to the support structure to translational movement along a movement axis or rotational movement about a rotation axis.

26. An actuator assembly according to claim 22, wherein the SMA wire is arranged to drive translational movement of the movable component along the movement axis or rotation of the movable component about the rotation axis.

27. An actuator assembly according to any preceding claim, wherein the one or more SMA wires are arranged to reduce the normal force between the first and second friction surfaces by at least 10%, preferably at least 20%, most preferably at least 50% upon contraction.

28. An actuator assembly according to any preceding claim, wherein the one or more SMA wires are arranged to disengage the first and second friction surfaces upon contraction.

29. An actuator assembly according to any preceding claim, wherein the one or more SMA wires are arranged to lift at least a portion of the movable part out of engagement with an end stop when contracted.

30. The actuator assembly of claim 29, wherein the end stop is disposed on another portion of the movable member.

31. An actuator assembly according to any preceding claim, wherein the ratio of static friction to weight of the movable member is greater than 1, preferably greater than 3, further preferably greater than 5.

32. An actuator assembly according to any of the preceding claims, wherein the static friction coefficient between the first and second friction surfaces is in the range between 0.05 and 0.6, preferably in the range between 0.1 and 0.4.

33. An actuator assembly according to any preceding claim, wherein the one or more SMA wires apply a force to the movable part that is angled relative to the first and second friction surfaces.