FR3145616A1 - Accelerometer comprising a mass and an acceleration-sensitive device associated with the mass - Google Patents

Abstract

The invention relates to an accelerometer comprising a support (2), a seismic mass (1) with which an acceleration sensor is associated which has at least one acceleration sensitivity axis (As), the seismic mass being capable of being subjected to a force induced by an acceleration to be measured, and to a static force, such as the force of gravity or a force of inertia; an elastically deformable connecting device (3), which connects the seismic mass (1) to the support (2). The accelerometer also comprises a fixed stop system (5), and a movable stop device (34) which is fixed to the elastically deformable connecting device (3), or which forms part of the elastically deformable connecting device (3), and a displacement system (4) configured to move the movable stop device (34) against the fixed stop system (5), so as to elastically deform the elastically deformable connecting device (3) to apply a restoring force (FR) to the seismic mass (1). Figure for abstract: Fig.2

Description

Accelerometer comprising a mass and an acceleration-sensitive device associated with the mass FIELD OF THE INVENTION

The present invention relates generally to accelerometers. The invention relates more particularly to miniaturized accelerometers sensitive to gravity or more generally to any static force. More specifically, the invention is useful for accelerometers of the micro-electromechanical system type, also called MEMS (Micro Electro Mechanical Systems in English).

PRIOR ART

Generally speaking, a MEMS type accelerometer comprises a mass, called seismic mass or inertial mass, which is associated with at least one acceleration detection element (acceleration sensor).

The gravity force acting on the seismic mass generates an offset in the acceleration signal measured by the acceleration sensor which, if not compensated, requires a large measurement range for the acceleration sensor. In addition, when the accelerometer uses multiple acceleration sensors to suppress noise by differential measurement, the effect of the gravity force on the measured signals makes the noise suppression less effective.

To compensate for the effect of the force of gravity on the mass and therefore on the measurement made by the acceleration sensor, it is known, as illustrated in , to attach the seismic mass 1 to springs 3 connected to a support 2. The springs are configured to apply a restoring force to the mass to compensate for the gravity force to which the seismic mass is subjected.

Such a solution is for example described in patent FR2735580, in which gravity compensation uses pre-stressed springs. The stress (tension or compression) of the springs is obtained by depositing a layer of material on the spring. Such a solution cannot be dynamically modified to adapt to the orientation of the accelerometer which can be oriented vertically in the direction of the gravity force or in the opposite direction, or even be oriented horizontally.

Patent EP0886146 proposes an accelerometer comprising a mechanical system for adjusting the compression of the spring that connects the mass to the support, depending on the use made of the accelerometer. However, once the spring adjustment is defined, the compensation obtained is permanent.

Compensation for the gravity force on the mass can also be done as described in application WO2015/185222 by applying a compressive force to a beam that connects the seismic mass to the support, to bring said beam into bending. However, since this solution requires bending beams, the direction of the gravity compensation is predetermined by the bending direction of the beam, so that only two states are allowed for each beam: a state corresponding to an absence of bending and a compressive state corresponding to a bending of the beam in a predefined direction. Thus, it is necessary to provide two different sets of beams with opposite bending directions if it is desired to be able to compensate for the gravity force applied to the mass in one direction or the other depending on the orientation of the sensor. Furthermore, in the solution of application WO2015/185222, obtaining the bending state of the beam requires applying a significant compressive force since the direction of the compressive force is applied along the rigid axis of the beam.

In addition to these mechanical compensation solutions, developments have led to the use of dynamic compensation via the permanent adjustment of an external compensation force of the electrostatic or magnetic type.

US Patent 11401160 describes voltage pulses that apply electrostatic forces to a seismic mass to compensate for the effect of gravity. However, such a method requires a closed-loop system and a properly filtered voltage to maintain a low noise level, which significantly increases energy consumption.

The present invention aims to propose a new accelerometer making it possible to overcome all or part of the problems set out above. According to a particular aspect, the invention aims to improve the performance and in particular the precision of the acceleration measured by the accelerometer.

For this purpose, the invention relates to an accelerometer comprising:
- a support;
- a mass, called a seismic mass, with which is associated an acceleration sensor which has at least one acceleration sensitivity axis, the seismic mass being capable of being subjected to a force induced by an acceleration to be measured, and to a static force, such as the force of gravity or a force of inertia; and
- an elastically deformable connecting device, such as a spring, which connects the seismic mass to the support;
characterized in that the accelerometer also comprises:
- a fixed stop system, and a movable stop device which is fixed to the elastically deformable connecting device, or which forms part of the elastically deformable connecting device,
- a displacement system configured to move the movable stop device against the fixed stop system, so as to elastically deform the elastically deformable connecting device to apply a restoring force to the seismic mass.

Such an accelerometer architecture makes it possible to compensate for the effects of a static force that the seismic mass undergoes, in particular the effect of the force of gravity, with limited energy consumption. Indeed, the invention makes it possible to apply to the seismic mass a restoring force that is adjustable according to discrete values on a seismic mass. Because the adjustment of the restoring force is carried out by controlling the movement of a movable stop device against a fixed stop system, it is possible to apply to the movable stop device a displacement force of a given value towards a stop of the fixed stop system, which is greater than a given minimum value necessary to reach said stop of the fixed stop system, to bring the movable stop device into contact with the fixed stop and maintain it in contact with said fixed stop, without having to regulate the displacement force applied to the movable stop device to maintain it in position against the fixed stop.

This solution can be used effectively for any orientation between the sensitive axis of the accelerometer and the direction of the static force, such as gravity, since the movable stop device can be pulled in one direction or the opposite direction or left at rest. It can also be provided that the fixed stop system and the displacement system allow several movable stop devices to be moved in different directions.

In known solutions of the prior art that provide for canceling the measured signal shift resulting from gravity, using electrostatic compensation, it is often necessary to perform a closed-loop regulation of the applied electrostatic force, which increases the energy consumption. The solution according to the invention makes it possible to use an electrostatic force to compensate for the effect of the static force on the seismic mass without the disadvantage of significant energy consumption, thanks to the system of mechanical stops formed by the cooperation between the movable stop device and the fixed stop system.

According to one embodiment of the invention, the displacement system comprises an electrode system which makes it possible to generate an electrostatic force to move the movable stop device in different configurations against the fixed stop system, and thus stress the elastically deformable connecting device according to different configurations to obtain different values and directions of the resulting restoring force on the seismic mass. The resulting restoring force can thus be adjusted according to the static force(s) to be compensated that the seismic mass undergoes.

The invention makes it possible to benefit from the advantages of compensating for the effect of a static force that the seismic mass undergoes by applying an electrostatic force to the connecting device between the seismic mass and the support, because this electrostatic force is adjustable and reversible, with limited signal noise and without the disadvantage of significant electrical consumption that regulation of this electrostatic force would require.

The accelerometer may also include one or more of the following features taken in any technically admissible combination.

According to one embodiment, the movable stop device being electrically conductive, the movement system comprises an electrode system comprising at least one, preferably at least two electrodes, and a control unit configured to apply an electrical voltage to said at least one electrode to exert an electrostatic force on the movable stop device causing it to move into abutment against the fixed stop system.

According to one embodiment, the control unit is configured to control the electrode system to apply to said at least one electrode a given electrical voltage, generating an electrostatic force on the movable stop device which is greater than the minimum force necessary to maintain the movable stop device in contact with the fixed stop system.

According to one embodiment, the electrode system comprises a first and a second electrode distributed on either side of the elastically deformable connecting device, and the fixed stop system comprises two stops distributed on either side of the elastically deformable connecting device, such that energizing a first electrode to a given value causes the mobile stop device to move into abutment against a first stop of the fixed stop system, and energizing the second electrode to a given value causes the mobile stop device of the elastically deformable connecting device to move into abutment against the second stop of the fixed stop system.

According to one embodiment, the accelerometer comprising a control unit and the assembly of the elastically deformable connecting device, the movable stop device, the displacement system, and the fixed stop system forming an assembly, called a connecting assembly, the accelerometer comprises several connecting assemblies, the abutment movement of the movable stop device of the connecting device against the stop system of a connecting assembly being controllable by the control unit independently of the movement of the movable stop device of another connecting assembly.

According to one embodiment, the control unit is configured to control the connecting assemblies so as to apply a restoring force value on the seismic mass by the elastically deformable connecting device, which is different from the restoring force applied to the seismic mass by another connecting assembly.

According to one embodiment, wherein the elastically deformable connecting device of at least one connecting assembly has at least one physical characteristic, such as length and/or stiffness, which is different from the corresponding physical characteristic of the elastically deformable connecting device of another connecting assembly of the accelerometer.

According to one embodiment, the accelerometer is a micro-electromechanical system.

According to one embodiment, the fixed stop system is wholly or partly common with the electrode system.

According to one embodiment, the fixed stop system is formed in a single piece with the support.

According to one embodiment, the elastically deformable connecting device is formed in one piece with the support.

According to one embodiment, the accelerometer comprising a control unit for controlling the movement system, the control unit is configured to, preferably for each link assembly when the accelerometer comprises several link assemblies, allow selectively controlling the position of the movable stop device among a discrete set of positions.

According to one embodiment, the discrete set of positions of the movable stop device comprises the following positions:
- a so-called rest position of the elastically deformable connecting device corresponding to the absence of movement control of the movable stop device by the control unit;
- a first tension position in which the movable stop device is in abutment against the fixed stop system, so that the elastically deformable connecting device is in elastic tension and applies a first restoring force to the seismic mass;
- and, preferably, a second tension position in which the movable stop device abuts against the fixed stop system, such that the elastically deformable connecting device is in elastic tension and applies a second restoring force to the seismic mass, which is different from the first restoring force.

There is also provided a method for at least partially compensating for a static force, such as the force of gravity, experienced by the seismic mass of an accelerometer according to any one of the preceding embodiments, in which the method comprises moving the movable stop device against the fixed stop system so that the elastically deformable connecting device is in elastic tension and applies to the seismic mass a restoring force which at least partially compensates for said static force experienced by the seismic mass.

Other characteristics and advantages of the invention will emerge from the description which follows, which is purely illustrative and non-limiting and must be read in conjunction with the appended drawings, in which:

- there is a schematic view of an accelerometer according to an embodiment known from the state of the art;

- there is a schematic view of an accelerometer according to an embodiment of the invention, in a configuration for compensating for the gravity force experienced by the seismic mass using an electrode system generating an electrostatic force which moves movable stops against fixed stops;

- there is a block diagram illustrating different positions that an elastically deformable connecting device can take and in particular the three positions that the movable stop device can take between the stop elements of a fixed stop system, for an accelerometer according to one embodiment of the invention;

- there is a schematic view of the accelerometer of the , in the absence of electrostatic force applied to the elastically deformable connecting device;

- there is a schematic view of the accelerometer of the in a mode of operation where an electrostatic force is applied in one direction to each upper elastically deformable connecting device, and an electrostatic force is applied in the opposite direction to each lower elastically deformable connecting device;

- there is a schematic view of the accelerometer of the in a mode of operation where an electrostatic force is applied in the same direction to each of the elastically deformable connecting devices, in the sense of compensating for the force of gravity to which the seismic mass is subjected;

- there is a schematic view of an accelerometer according to another embodiment of the invention comprising several, for example four, elastically deformable connecting devices which connect the seismic mass to the support, on one side of the seismic mass, and several, for example four, other elastically deformable connecting devices which connect the seismic mass to the support, on the other side of the seismic mass;

- there is a schematic view of the accelerometer of the , in an operating mode where, for each of said sides of the seismic mass, an electrostatic force is applied in the same direction to a part of the elastically deformable connecting devices, in the sense of compensation for the gravity force to which the seismic mass is subjected, and where an electrostatic force is applied to another part of the elastically deformable connecting devices, in the same direction as that of the gravity force to which the seismic mass is subjected (considered in projection of the gravity force on the sensitivity axis of the sensor);

- there is a schematic view of an accelerometer according to another embodiment of the invention comprising several, for example four, elastically deformable connecting devices which connect the seismic mass to the support on one side of the seismic mass, and several, for example four other elastically deformable connecting devices which connect the seismic mass to the support on the other side of the seismic mass; a part of the elastically deformable connecting devices on each side having a length different from the other elastically deformable connecting devices located on the same side of the seismic mass;

- there is a schematic view of an accelerometer according to another embodiment of the invention for which the elastically deformable connecting devices comprise lever mechanisms for moving the movable stop device against the fixed stop system;

- there is a partial view of an accelerometer according to one embodiment of the invention, the electrode system and the fixed stop system with which the mobile stop device is able to cooperate not being shown,

- there is a detailed view of zone VII of the .

DETAILED DESCRIPTION

The inventive concept is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. In the drawings, the size and relative sizes of elements may be exaggerated for clarity. Like numerals refer to like elements throughout the drawings. However, this inventive concept may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this description is complete, and communicates the scope of the inventive concept to those skilled in the art.

A reference throughout the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the occurrence of the phrase "in an embodiment" at various locations throughout the specification does not necessarily refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any appropriate manner in one or more embodiments.

With reference to the figures, an accelerometer is shown comprising a support 2 and a seismic mass 1. The seismic mass 1 comprises a mass with which an acceleration sensor (not shown) is associated, i.e. a device that is sensitive to an acceleration in a given direction. The acceleration sensor thus makes it possible to measure, along its sensitivity axis, an acceleration to which it is subjected. The sensitivity axis of the sensor is denoted As. According to different embodiments of the invention, it may be provided that the acceleration-sensitive device is fixed or not to the mass. It may be provided that the acceleration-sensitive device is devoid of mechanical connection with the mass. For example, in the case of an optical, capacitive, or tunnel effect measurement, the acceleration measurement may be carried out without physical contact with the moving mass.

Seismic mass 1 is likely to be subjected to a force induced by an acceleration to be measured using the acceleration-sensitive device.

The seismic mass 1 is connected to the support 2 by an elastically deformable connecting device 3, such as a spring. According to a particular aspect, the elastically deformable character is reflected in the fact that the connecting device 3 is capable of bending and/or being elongated when it is stressed.

The connecting device 3 can be made of different materials, for example of the same material as the support 2. According to a particular aspect, the connecting device 3 has an elongated shape.

In the embodiments of the invention presented below, the seismic mass 1 is connected to the support 2 by several elastically deformable connecting devices 3. The description given for an elastically deformable connecting device 3 also applies to the other elastically deformable connecting devices 3 when they are present, except with regard to possible differences in particular characteristics between elastically deformable connecting devices 3 when this is indicated.

Support 2 is a reference structure, fixed to or forming all or part of an accelerometer housing or chassis.

The seismic mass 1, and therefore the acceleration sensor, is also sensitive to a static force, in particular the gravity force Fg. The static force can also be a constant inertial force, such as a constant centrifugal force.

According to a preferred embodiment of the invention, the accelerometer is a micro-electromechanical system (or MEMS for Micro Electro Mechanical Systems in English).

The acceleration sensitive device is configured to measure acceleration and may use different technologies, for example capacitive/capacitance, piezoelectricity, piezoresistivity, optical, tunnel effect or other.

In the remainder of the description, the static force considered is the gravity force Fg whose effect on the seismic mass 1 is sought to be compensated, but the invention and therefore the description which follows also applies to the case where the static force is a force other than the gravity force, such as a constant inertial force. When the sensitivity axis As of the acceleration sensor is parallel to the vertical, the acceleration sensor is subjected to the gravity force. When the acceleration sensor is oriented so that the sensitivity axis As is inclined, the acceleration sensor is subjected to a force corresponding to the projection onto the axis As of the gravity force.

The elastically deformable connecting device 3 is provided with a movable stop device 34, fixed to the elastically deformable connecting device 3, or forming part of the elastically deformable connecting device 3. The movable stop device 34 can thus be located between a part 32 of the elastically deformable connecting device 3 connected to the support 2 and a part 31 of the elastically deformable connecting device 3 connected to the mass 1.

The movable stop device 34 is movable by a displacement system 4 to come into abutment against a fixed stop system 5 so as to deform the elastically deformable connecting device 3 to oppose the force Fg exerted on the seismic mass 1 by gravity.

The movement system 4 makes it possible to move the movable stop device 34 in contact with the fixed stop system 5, and to maintain this contact to maintain said position as long as the movement is controlled by a control unit 100 as explained below.

The stop system 5 is fixed relative to the support 2 to which the elastically deformable connecting device 3 is connected. The stop system 5 can be made of the same material as the support 2 and can be made in one piece with the support 2. According to one embodiment of the invention, the support 2, the connecting device 3, and the stop system 5 can be obtained by etching a block of silicon.

Preferably, the elastically deformable connecting device 3 is movable in a direction transverse to the longitudinal direction of the elastically deformable connecting device 3 considered in an undeformed state of the elastically deformable connecting device 3 and in the absence of gravity force.

The accelerometer comprises a displacement system 4 configured to allow the elastically deformable connecting device 3 to be moved to come into abutment via a movable stop device 34, against the fixed stop system 5. The movement into abutment of the elastically deformable connecting device 3 against the fixed stop system 5 causes the elastically deformable connecting device 3 to apply a restoring force F _R to the seismic mass 1.

Preferably, the fixed stop system 5 comprises several stop elements 5A, 5B having different positions relative to the support 2.

The direction, sense and/or value of the restoring force can be defined according to the location of the stop element 5A, 5B of the fixed stop system 5 against which the movable stop device 34 is moved into abutment.

Thus, when the axis As of the sensor is oriented vertically, the restoring force F _R exerted by the elastically deformable connecting device 3 on the seismic mass 1 can be in the opposite direction to the gravity force to which the seismic mass 1 is subjected or in the same direction as said gravity force.

When the movable stop device 34 is in abutment against the fixed stop device 5, the elastically deformable connecting device 3 is under elastic tension. In particular, in the examples illustrated in the figures, the or each spring which forms an elastically deformable connecting device 3 is elongated.

Travel system

The displacement system 4 makes it possible to move the elastically deformable connecting device 3 in order to compensate in particular at least partially for the force of gravity experienced by the seismic mass.

According to different embodiments of the invention, and as illustrated in FIGS. 2 to 7A, the movement of the elastically deformable connecting device 3 is done by applying an electrostatic force Fe to the movable stop device 34 of the elastically deformable connecting device 3. The movable stop device 34 is electrically conductive. The movable stop device 34 can be fixed to the elastically deformable connecting device 3 or form a part of said elastically deformable connecting device 3.

According to an alternative embodiment, it can be provided that the movement of the elastically deformable connecting device 3 is done by application of a magnetic force or via a piezoelectric constraint to the movable stop device 34 of the elastically deformable connecting device 3.

Alternatively and/or in combination, the movement of the elastically deformable connecting device 3 can be carried out mechanically, for example using a pivot mechanism associated with a counterweight as illustrated in .

According to one embodiment of the invention and as illustrated more particularly in the , the displacement system 4 comprises an electrode system 40 and a control unit 100. The control unit 100 is configured to allow applying an electrical voltage, generated or supplied from an energy source, such as a battery included in the accelerometer, to at least one electrode of the electrode system to apply an electrostatic force Fe to the elastically deformable connecting device 3.

According to one embodiment of the invention and as more particularly illustrated in the examples of Figures 2 to 6, the electrode system comprises a first and a second electrode distributed on either side of the elastically deformable connecting device 3 and the fixed stop system 5 comprises two stops 5A, 5B distributed on either side of the elastically deformable connecting device 3.

According to one embodiment of the invention, each electrode of the electrode system is said to be activatable/deactivatable in the sense that a given electrical voltage can or cannot be applied to said electrode via said control unit 100. Thus, the activation of a first electrode 4A (i.e. the application of a given voltage to said electrode by the control unit 100), while the second electrode 4B is deactivated (i.e. not subjected to a voltage from the control unit 100), causes the movement of the movable stop 34 of the elastically deformable connecting device 3 into abutment against the fixed stop 5A. The activation of the second electrode 4B (the first electrode 4A being deactivated), causes the movement of the movable stop 34 of the elastically deformable connecting device 3 into abutment against the fixed stop 5B.

It is also possible for the fixed stops 5A and 5B to be used as electrodes to attract the movable stop(s). To avoid too high a leakage current between a movable stop and a fixed stop during mechanical contact between them, it may be provided that an insulator is present on or around one or more fixed or movable stops, or that the contact surface between the stops is reduced.

The electrode system 40 can be controlled to apply the electrostatic force Fe to the movable stop device 34 in a given direction and sense, to cause the movement of the elastically deformable connecting device 3 against a part of the stop system 5, and thus the elastic tensioning/deformation of the elastically deformable connecting device 3.

The control unit 100 makes it possible to control the electrode system 40 to apply to the or each electrode of the electrode system, an electrical voltage to generate an electrostatic displacement force on the movable stop device 34 associated with the electrode system 40, towards a part of the fixed stop system 5 which is greater than the minimum force necessary to position the movable stop device 34 in contact with said part of the fixed stop system 5. The application of a constant electrical voltage adapted (i.e. sufficient) to move the elastically deformable connecting device 3 into abutment against the fixed stop system 5 means that it is not necessary to provide a loop system for regulating the electrical voltage applied to the electrodes.

According to one embodiment of the invention, the given voltage applied is said to be sufficient in the sense that, in the absence of a fixed stop system 5, the movable stop device 34 of the elastically deformable connecting device 3 would, from a rest position defined as being a position of the movable stop device 34 in the absence of electrical voltage applied to the electrode system and in the absence of static force experienced by the seismic mass, be moved due to the application of this electrical voltage to the electrode system over a distance greater than the distance over which the movable stop device 34 is moved when the movable stop device 34 is brought into abutment (and therefore blocked) against the fixed stop system 5 by the application of this electrical voltage.

Alternatively, it is possible to provide for applying a weaker force but to apply it sinusoidally at the resonance frequency of the system formed by the elastically deformable connecting device 3 and the corresponding movable stop device. Indeed, in a vacuum environment, the oscillation will cause an increasingly significant displacement of the movable stop device 34, and when the displacement brings the movable stop device 34 into contact with the fixed stop device, the space between the electrode and the elastically deformable connecting device 3 is reduced, so that the electrostatic force is greater for a given voltage. The electrostatic force applied when the movable stop device 34 is in abutment with the fixed stop system 5 must be greater than the restoring force of the entire elastically deformable connecting device 3 and the movable stop device 34 to allow the movable stop device 34 to remain in abutment against the fixed stop system 5 when the mass is further subjected to acceleration.

Such a combination of the electrode system 40 with the movable stop device 34 connected to the elastically deformable connecting device 3 and the fixed stop system 5 makes it possible to apply to the seismic mass 1 a restoring force which is adjustable according to discrete values by using an electrostatic force to pull the movable stop device 34 against the fixed stop system 5. This creates an adjustable restoring force (depending on the activated electrodes) on the mass 1 which makes it possible to compensate for the force of gravity.

The movable stop device 34 is mechanically stopped by the fixed stop system 5. The total noise of the accelerometer is not affected by the noise of the electrostatic force.

Depending on the direction and sense of the electrostatic traction, the restoring force can thus compensate for a static force that the mass undergoes and which can have different values and directions or senses. In particular, the restoring force can compensate for the gravity force that the mass and the acceleration sensor undergo when the sensitivity axis is oriented vertically. It is also possible to provide for applying a total restoring force of zero when the accelerometer is positioned so that the sensitivity axis of the sensor is oriented horizontally.

Preferably and as illustrated more particularly in Figures 2 to 6, the electrostatic force that the electrode system can generate is reversible, the resulting restoring force F _R that is applied to the mass 1 is reversible and can be modified subsequently if the orientation of the acceleration sensor relative to gravity is modified.

Linking sets

According to different embodiments of the invention and as illustrated and detailed below in Figures 2 to 6, the accelerometer can comprise several assemblies called connecting assemblies, each composed of an elastically deformable connecting device 3, an associated mobile stop device 34, a fixed stop system 5 and a displacement system 4. The connecting assemblies can comprise parts in common.

The connecting assemblies are distributed at different positions relative to the mass 1 or the support 2, in order to be able to generate the desired resulting restoring force in terms of direction, sense and value, in particular depending on the orientation, sense and value of the static force, such as the force of gravity, to be compensated.

According to one embodiment of the invention and as illustrated more particularly in Figures 3A and 4A, the movement in abutment of the movable abutment device 34 of the connecting device 3 against the fixed abutment system 5 of a connecting assembly can be controlled by the control unit 100 separately from another connecting assembly, so as to adjust the resulting compensation force applied to the mass.

Control unit

The control unit 100 makes it possible to control the movement system 4 in order to be able to move the movable stop device 34 into abutment against the fixed stop system 5.

As schematically illustrated in the , the control unit 100 is configured to allow selective control of the position of the movable stop device 34 among a set of several discrete positions which include a rest position and one or more positions defined by one or more stops of the fixed stop system 5.

According to one embodiment of the invention, the discrete positions that the movable stop device 34 can take include:

- a rest position corresponding to the absence of any command to move the movable stop device 34 by the control unit 100. The rest position corresponds to the absence of any application of electrical voltage to the electrode system associated with the movable stop device 34 or to the application of a zero potential difference between the electrode system and the movable stop 34, which results in the absence of any application of any displacement force (electrostatic force) to the movable stop device 34 and therefore the absence of any application of an additional restoring force to the seismic mass by moving the movable stop device 34,

- a first position of elastic tensioning of the elastically deformable connecting device 3 in which the elastically deformable connecting device 3 applies a first restoring force to the seismic mass 1. The first position corresponds to the position obtained by the application of an electrical voltage to the electrode system which generates an electrostatic force in one direction on the movable stop device 34 and thus the application of a corresponding first restoring force to the seismic mass 1.

Preferably, the discrete positions that the movable stop device 34 can take include: also a second position of elastic tensioning of the elastically deformable connecting device 3 in which the elastically deformable connecting device 3 applies a second restoring force to the seismic mass 1. The second position corresponds to the position obtained by applying an electrical voltage to the electrode system which generates an electrostatic force in the opposite direction (relative to the direction corresponding to the first position) on the movable stop device 34 and thus the application of a corresponding second restoring force, in the opposite direction to the first restoring force, on the seismic mass 1.

The different discrete positions that the movable stop device 34 can take depend on the configuration of the fixed stop system 5.

The control unit 100 is then configured to allow selectively controlling the position of the movable stop device 34 of each connection assembly among said set of discrete positions. It is thus possible by controlling independently of each other the position of each movable stop device 34 to obtain one of the discrete positions available for the corresponding movable stop device 34, to apply (local) restoring forces to the seismic mass 1, some of which may have different characteristics (direction, value, orientation) so as to obtain an overall restoring force applied by all of the movable stop devices 34 to the seismic mass 1 which is adjustable according to the combination of positions of the movable stop devices 34 selected.

To the , the different positions that the movable stop device 34 can take are shown superimposed on the same diagram, but are of course obtained selectively.

The description given above, in particular in connection with the in the simplified case of a connecting assembly formed by a fixed stop system 5, an elastically deformable connecting device 3, a mobile stop device 34 and a displacement system 4 (not shown), is also applicable in the case where the accelerometer comprises several connecting assemblies distributed at different locations relative to the mass, as illustrated schematically more particularly in Figures 2 and 3 to 6.

The control unit 100 can thus be configured to control the connecting assemblies so as to apply a restoring force on the seismic mass 1 by the elastically deformable connecting device 3, which is different from the restoring force applied by another connecting assembly, by its direction, its sense and/or its value according to the configuration of the connecting assembly and of the stop of the fixed stop system against which the movable stop device is moved.

The difference between two restoring forces may be a difference in the direction of movement of the movable stop device against a stop of the fixed stop system and/or a difference in value depending on the configuration of the connecting assembly, such as the stiffness (which depends on the length, width, height and Young's modulus of the material used) of the elastically deformable connecting device 3 and/or the distance (considered in the rest position) between the movable stop device 34 and the fixed stop system 5 (in particular the distance between the movable stop device 34 and the stop(s) 5A, 5B of the fixed stop device 5).

The control of the connecting assemblies by the control unit 100 thus makes it possible to obtain different discrete values of overall restoring force resulting from the positions of the movable stop devices 34 controlled by the control unit.

Such a design of the accelerometer makes it possible to adapt the overall restoring force applied to the mass according to the orientation of the accelerometer. In particular, the accelerometer (more particularly the sensitivity axis of the acceleration sensor) can be oriented vertically downwards or upwards, or horizontally or even be inclined. When the acceleration sensor is inclined relative to the direction of the static force to be compensated, the direction of the static force to be compensated is for example vertical in the case of the gravity force. In this case, the static force value to be compensated corresponds to the value of the static force projected onto the sensitivity axis As.

To the , an embodiment of the accelerometer has been shown, in a simplified manner, in a configuration where the movable stop devices 34 are in the rest position corresponding to an absence of electrostatic force applied to the corresponding elastically deformable connecting device 3 and therefore to an absence of electrostatic force applied to the movable stop devices 34.

In the example of the , the accelerometer is in a configuration where the acceleration sensor is oriented horizontally, i.e. the axis As is horizontal. Thus, in the horizontal position of the accelerometer, it can be provided that the unit 100 is configured to control the displacement system 40 so that the movable stop devices 34 are pulled in opposite directions to maintain a zero overall restoring force on the seismic mass.

Depending on the configuration of the accelerometer, it can also be provided that some or all of the movable stop devices 34 remain in the rest position.

In the example of the , the accelerometer is in a configuration where the acceleration sensor is oriented vertically, i.e. the axis As is vertical. Thus, in the vertical position of the accelerometer, it can be provided that the unit 100 is configured to control the electrode system 40 so that the movable stops 34 are pulled in the same directions and in the opposite direction of the force of gravity which is applied to the seismic mass, to come against the fixed stops 5A.

According to one embodiment, the accelerometer comprises at least three connection assemblies, which makes it possible to apply several return force values depending on the position occupied by the mobile stop device 34 for each of the connection assemblies.

According to one embodiment of the invention, it is provided that each of two opposite sides of the seismic mass 1 is provided with at least three connecting assemblies, for example four assemblies as in the example of the .

As illustrated in the for an orientation of the accelerometer where the latter has a sensitivity axis As inclined relative to the gravity force g, so that only the value of the projected gravity force g on the direction As needs to be compensated, the control unit 100 can be configured to obtain an overall restoring force on the seismic mass compensating for gravity, by controlling for each side of the seismic mass 1, the displacement of a part of the movable stop devices 34 against a stop 5A of the fixed stop system 5, for example the three highest movable stop devices 34 and the displacement of another part of the movable stop devices 34, for example the lowest movable stop device 34, against a stop 5B of the fixed stop system 5.

The control unit 100 is, for example, in the form of a microprocessor and a data memory in which computer instructions executable by said microprocessor are stored, or in the form of a microcontroller.

In other words, the functions and steps described can be implemented in the form of a computer program or via hardware components (e.g. programmable gate arrays). In particular, the functions and steps performed by the control unit for controlling the movement system of the or each elastically deformable connecting device, or the processing unit for measuring the acceleration, can be performed by instruction sets or computer modules implemented in a processor or controller or be performed by dedicated electronic components or components of the programmable logic circuit type (or FPGA which is the acronym for field-programmable gate array) or of the application-specific integrated circuit type (or ASIC which is the acronym for application-specific integrated circuit). It is also possible to combine computer parts and electronic parts.

The control or processing unit is thus an electronic and/or computer unit. When it is specified that said unit is configured to perform a given operation, this means that the unit comprises computer instructions and the corresponding execution means which make it possible to perform said operation and/or that the unit comprises corresponding electronic components.

Special embodiments s

It may be provided that the elastically deformable connecting device 3 of a connecting assembly has at least one physical characteristic, such as the stiffness for a spring, which is different from that of the elastically deformable connecting device 3 of another connecting assembly. Thus, in the case where the elastically deformable connecting devices 3 are springs, it may be provided that one or more springs have different technical characteristics from one spring to another so as to obtain different local restoring force values resulting from the stress on these springs. Such a configuration makes it possible to obtain an even finer adjustment of the overall restoring force applied to the moving mass.

The restoring force F _R of a spring can be calculated as being equal to K*x, with K the stiffness of the spring and x the displacement of the movable stop 34 from the rest position until it comes into contact with a stop of the fixed stop system 5.

Thus, it can be provided according to embodiments of the invention that the restoring force F _R of each spring is adjusted by design modifications on the dimension of the springs (thickness/length/width/folded springs, etc.), or by adjusting the gap between a movable stop 34 and a stop of the fixed stop system 5 or by changing the material used for the springs. illustrates an example with a different length for a spring on each side of the mass so that the local restoring force F _R ' exerted by the longer spring on the seismic mass is smaller than the restoring force F _R exerted on the seismic mass by a shorter spring.

According to another embodiment of the solution and as for example illustrated in , it can be provided that the displacement system 4 comprises a lever system configured to allow the moving stop devices 34 to be moved against stops 5A or 5B of the fixed stop system 5 by using for each assembly connecting the mass 1 to the support 2, a counterweight 46 (such as a small mass compared to the seismic mass) fixed to a lever 36 itself connected to the moving stop device 34 so that, by releasing the movement of the counterweight by gravity, the lever 36 pivots about a pivot axis A36 by causing the moving stop device 34 to move against a fixed stop of the fixed stop system 5.

The invention is not limited to the embodiments illustrated in the drawings.

Furthermore, the term "comprising" does not exclude other elements or steps. Furthermore, features or steps that have been described with reference to one of the embodiments set forth above may also be used in combination with other features or steps of other embodiments set forth above.

Claims (14)

Accelerometer comprising:
- a support (2);
- a mass, called seismic mass (1) with which is associated an acceleration sensor which has at least one acceleration sensitivity axis (As), the seismic mass being capable of being subjected to a force induced by an acceleration to be measured, and to a static force, such as the force of gravity or a force of inertia; and
- an elastically deformable connecting device (3), such as a spring, which connects the seismic mass (1) to the support (2);
characterized in that the accelerometer also comprises:
- a fixed stop system (5), and a movable stop device (34) which is fixed to the elastically deformable connecting device (3), or which forms part of the elastically deformable connecting device (3),
- a displacement system (4) configured to move the movable stop device (34) against the fixed stop system (5), so as to elastically deform the elastically deformable connecting device (3) to apply a restoring force (F _R ) to the seismic mass (1). Accelerometer according to claim 1, wherein, the movable stop device (34) being electrically conductive, the displacement system (4) comprises an electrode system (40) comprising at least one, preferably at least two electrodes, and a control unit (100) configured to apply an electrical voltage to said at least one electrode to exert an electrostatic force (Fe) on the movable stop device (34) causing it to move into abutment against the fixed stop system (5). Accelerometer according to claim 2, wherein the control unit (100) is configured to control the electrode system (40) to apply to said at least one electrode a given electrical voltage, generating an electrostatic force on the movable stop device (34) which is greater than the minimum force necessary to maintain the movable stop device (34) in contact with the fixed stop system (5). Accelerometer according to any one of claims 2 or 3, in which the electrode system (40) comprises a first and a second electrode (4A, 4B) distributed on either side of the elastically deformable connecting device (3), and the fixed stop system (5) comprises two stops (5A, 5B) distributed on either side of the elastically deformable connecting device (3), such that energizing a first electrode to a given value causes the movement of the movable stop device (34) into abutment against a first stop (5A) of the fixed stop system (5), and energizing the second electrode (4B) to a given value causes the movement of the movable stop device (34) of the elastically deformable connecting device (3) into abutment against the second stop (5B) of the fixed stop system (5). Accelerometer according to any one of the preceding claims, wherein, the accelerometer comprising a control unit (100) and the assembly of the elastically deformable connecting device (3), the movable stop device (34), the displacement system (4), and the fixed stop system (5) forming an assembly, called a connecting assembly, the accelerometer comprises several connecting assemblies, the abutment movement of the movable stop device (34) of the connecting device (3) against the stop system (5) of a connecting assembly being controllable by the control unit (100) independently of the movement of the movable stop device (34) of another connecting assembly. Accelerometer according to claim 5, wherein the control unit (100) is configured to control the connecting assemblies (3) so as to apply a restoring force value on the seismic mass (1) by the elastically deformable connecting device (3), which is different from the restoring force applied to the seismic mass (1) by another connecting assembly. Accelerometer according to claim 6, wherein the elastically deformable connecting device (3) of at least one connecting assembly has at least one physical characteristic, such as length and/or stiffness, which is different from the corresponding physical characteristic of the elastically deformable connecting device (3) of another connecting assembly of the accelerometer. An accelerometer according to any preceding claim, wherein the accelerometer is a micro-electromechanical system. Accelerometer according to any one of the preceding claims, taken in combination with claim 2, in which the fixed stop system (5) is wholly or partly common with the electrode system (40). Accelerometer according to any one of the preceding claims, in which the fixed stop system (5) is formed in one piece with the support (2). Accelerometer according to any one of the preceding claims, in which the elastically deformable connecting device (3) is formed in one piece with the support (2). Accelerometer according to any one of the preceding claims, wherein, the accelerometer comprising a control unit (100) for controlling the displacement system (4), the control unit (100) is configured to, preferably for each link assembly when the accelerometer comprises several link assemblies, allow selectively controlling the position of the movable stop device (34) among a discrete set of positions. Accelerometer according to the preceding claim, in which the discrete set of positions of the movable stop device (34) comprises the following positions:
- a so-called rest position of the elastically deformable connecting device (3) corresponding to the absence of movement control of the movable stop device (34) by the control unit (100);
- a first tension position in which the movable stop device (34) is in abutment against the fixed stop system (5), so that the elastically deformable connecting device (3) is in elastic tension and applies a first restoring force to the seismic mass (1);
- and, preferably, a second tension position in which the movable stop device (34) abuts against the fixed stop system (5), so that the elastically deformable connecting device (3) is in elastic tension and applies to the seismic mass (1) a second restoring force, which is different from the first restoring force. Method for at least partially compensating for a static force, such as the force of gravity, experienced by the seismic mass (1) of an accelerometer according to any one of the preceding claims, in which the method comprises moving the movable stop device (34) against the fixed stop system (5) so that the elastically deformable connecting device (3) is in elastic tension and applies to the seismic mass (1) a restoring force (F _R ) which at least partially compensates for said static force experienced by the seismic mass (1).