JP2009271204A - Lens drive unit - Google Patents

Abstract

Provided is a lens driving unit that has excellent lens driving acceleration performance and can detect a lens position without using a position sensor.
A lens driving unit 1 includes a cylindrical lens holder 2 that holds a lens inside, a movable coil 4 having an octagonal cross section attached coaxially to the lens holder 2, and 8 of the movable coil 4. A magnet 5 composed of eight magnet pieces 5a arranged to face two outer peripheral side portions, a movable coil 4 and a yoke body 6 having a U-shaped cross section for accommodating the magnet 5 therein, and a lens holder 2 are elastically supported. A pair of springs 8 and 9 and a position detection circuit unit 20 for detecting the position of the movable coil 4 are provided. The position detection circuit unit 20 detects an inductance change generated in the movable coil 4 when the relative position of the movable coil 4 with respect to the yoke body 6 changes. From this inductance change, the position of the movable coil 4 and thus the lens holder is calculated.
[Selection] Figure 2

Description

  The present invention relates to a lens driving unit using a voice coil motor as a lens actuator, and more particularly to a lens driving unit suitable for a small camera.

  As an actuator for driving a lens in the optical axis direction, a so-called voice coil motor is widely used mainly for portable small cameras that require an autofocus function because of low noise and power consumption. (For example, refer to Patent Document 1).

  In addition, as a control method for specifying a focus position of a focus lens (hereinafter abbreviated as “lens”), a high-frequency signal component included in a video signal from an imaging element such as a complementary metal-oxide semiconductor (CMOS) image sensor is maximized. A so-called hill-climbing method in which the lens is moved is widely adopted. (For example, refer to Patent Document 2).

  A method of performing automatic focusing while detecting a lens position by a position sensor such as a photo interrupter when a focus position is specified by a hill-climbing method is mainly used for digital cameras.

JP 2007-65430 A Japanese Patent Laid-Open No. 11-252441

  The voice coil motor includes a cylindrical movable coil, a cylindrical magnet that applies a magnetic field to the movable coil from the outer peripheral side, and a yoke that holds the magnet and forms a magnetic path, and is arranged coaxially. It is constituted by doing. Due to the interaction between the current flowing through the movable coil and the magnetic field formed by the magnet, the lens holder held on the inner peripheral side of the movable coil can be linearly moved together with the movable coil in the optical axis direction.

  A voice coil motor as a camera actuator disclosed in Patent Document 1 is configured such that a yoke that holds a magnet has a polygonal shape in which a cross-sectional shape in a direction orthogonal to the optical axis is a hexagon or more. Thereby, a magnet can be comprised using a some flat magnet.

  Since a flat magnet can be manufactured at a lower cost than a magnet having an arcuate curved surface, the use of a flat magnet can reduce the cost of components. However, the voice coil motor has problems that it is required to improve the acceleration performance, reduce the power consumption, and reduce the size by constantly increasing the magnetic efficiency as well as reducing the component cost.

  On the other hand, as a control method for moving the lens holder to the in-focus position, a method in which position information from a position sensor such as a photo interrupter is referred to together with image information from an image sensor is used in a relatively short time. It is supposed that an accurate in-focus position can be specified. However, since the position sensor is required, it is necessary to secure a space for installing the position sensor in the package, and there is a problem that the cost of parts increases.

  The present invention has been made in view of such problems, and a first object is to provide a small lens driving unit that can obtain position information of a lens holder without using a position sensor. The second object is to improve the acceleration performance of the lens by improving the magnetic efficiency of the voice coil motor, thereby reducing the time required to move the lens to a predetermined position, reducing power consumption and reducing the size. It is to provide a lens driving unit that can be realized.

  Therefore, the inventor of the present application, as a result of repeated studies to solve the above problems, the structure derived from a mechanistic viewpoint is effective in detecting the position of the lens holder from an electromagnetic viewpoint. It came to the knowledge that it could utilize as a means. As a result of further studies, the inventors have completed the following inventions.

  In order to solve the above-mentioned problem, a lens driving unit according to claim 1 of the present invention is arranged on a lens holder for holding a lens and an outer peripheral side of the lens holder, and together with the lens holder, an optical axis direction (vertical direction) ) Movable movable coil, a magnet disposed on the outer peripheral side of the movable coil to form a magnetic field, a yoke outer wall portion holding the magnet on the inner peripheral surface, and an inner peripheral side of the movable coil. A yoke body having a yoke inner wall portion, a spring elastically supporting the lens holder, and a position detecting means for detecting the position of the lens holder, wherein the yoke inner wall portion is The lower end surface thereof is formed so as to be positioned above the lower end surface of the magnet, and the position detecting means is configured to displace the movable coil in the optical axis direction. From inductance change occurring in the moving coil by, and is characterized in that to detect the position of the lens holder.

  In this case, when the movable coil is moved over the entire movable range with respect to the optical axis direction, a part of the inner peripheral surface of the movable coil always faces the outer peripheral surface of the inner wall of the yoke. It is preferable that it is comprised.

  In this case, the position detecting means includes an input unit that applies a sinusoidal reference signal to the movable coil so as to be superimposed on the drive signal applied to the movable coil, and the movable coil corresponding to the reference signal. It is possible to use a position detection circuit unit that includes an output unit that detects an output signal from and a comparison unit that performs a difference between the reference signal and the output signal.

  According to this invention, the magnet and the yoke body are configured such that the lower end position of the yoke inner wall portion disposed on the inner peripheral side of the magnet is positioned higher than the lower end position of the magnet. As a result, a distribution (gradient) is generated in the magnetic field formed between the magnet and the inner wall of the yoke. This distribution is conspicuous below the position of the lower end surface of the yoke inner wall, and the magnetic flux from the magnet toward the inner wall of the yoke becomes lighter below the position of the lower end surface of the yoke inner wall. Tilt in the axial direction (vertical direction). Since the movable coil disposed between the magnet and the inner wall of the yoke moves in the optical axis direction, the direction and magnetic flux density of the magnetic flux that links the movable coil change continuously with the movement. The inductance of the moving coil changes as the interlinkage magnetic flux changes. Therefore, the relative position of the movable coil with respect to the yoke body is reflected in the inductance of the movable coil. Therefore, the position of the lens holder (lens) moving in the optical axis direction together with the movable coil can be detected by electrically detecting the inductance change of the movable coil. Thereby, the position of the lens holder can be accurately detected without using a position sensor. Since the position sensor becomes unnecessary, the installation space for the position sensor can be reduced, and the lens drive unit can be downsized. In addition, since the position of the lens can be detected, automatic focusing can be performed based on the position information of the lens holder together with the image information, and it can be expected that the time required to specify an accurate in-focus position is shortened. .

  According to a fourth aspect of the present invention, in the lens driving unit, the movable coil has a polygonal cross-sectional shape perpendicular to the optical axis, and the magnet is composed of a plurality of flat magnet pieces arranged adjacent to each other. In addition, each magnet piece is arranged so as to face each side portion constituting the polygonal outer peripheral surface of the coil.

  In this case, the coil preferably has an octagonal cross section perpendicular to the optical axis.

  According to this invention, the planar view shape (cross-sectional shape perpendicular to the optical axis) of the movable coil is a polygonal shape, and a plurality of plate-like magnet pieces are provided on each side surface portion constituting the outer peripheral surface of the movable coil. Are arranged opposite to each other. The plurality of flat magnet pieces are disposed adjacent to the magnet pieces on both sides in the circumferential direction. This improves the magnetic efficiency and increases the driving force generated in the movable coil as compared with the case where a movable coil having a circular shape in plan view is used. By increasing the driving force, the acceleration performance when the lens holder linearly moves to a predetermined position is improved, and the time required for moving the lens to the predetermined position is shortened. Therefore, the time required for specifying the in-focus position can be further shortened. Further, it is possible to realize low power consumption by improving magnetic efficiency and downsizing of components.

  The lens driving unit according to claim 6, wherein the spring includes a ring-shaped outer ring fixed to the yoke, and a ring-shaped inner ring disposed on the inner edge side of the outer ring and fixed to the lens holder. A ring, and a plurality of elastic connecting portions configured to connect the outer ring and the inner ring and be elastically deformable, and a damping agent is applied to a portion of the elastic connecting portion near the inner ring. It is characterized by that.

  According to this invention, since the damping agent is applied to the spring that elastically supports the lens holder, unnecessary vibration after the lens holder reaches the predetermined position can be quickly damped. As a result, it is possible to reduce image blurring during automatic focusing, and to further shorten the time required to specify the in-focus position. In addition, it can be expected that plastic deformation that may occur when an excessive external force such as a drop impact is applied to the spring is suppressed.

  Hereinafter, an example of a preferred embodiment of a lens driving unit according to the present invention will be described with reference to the drawings. 1 is an exploded perspective view showing a schematic configuration of a lens driving unit 1 according to an embodiment of the present invention, FIG. 2 is a longitudinal sectional view of the lens driving unit 1, and FIG. 3 is a transverse sectional view of the lens driving unit 1. It is.

[Unit configuration]
The lens driving unit 1 includes a lens holder 2 that holds a lens (not shown), a magnetic circuit unit 3 that linearly moves the lens holder 2 in the vertical direction (the optical axis L direction shown in FIG. 2), and a magnetic circuit unit 3. A substantially ring-shaped frame 7 disposed on the lower side (imaging side), a pair of springs 8 and 9 that elastically support the lower side and the upper side (subject side) of the lens holder 2, respectively, and the magnetic circuit unit 3 2, a cover 11 that constitutes a package together with the base 10, and a position detection circuit unit 20 (shown by a broken line in FIG. 2) as position detection means for detecting the position of the lens holder.

  The lens holder 2 is formed using a resin such as polycarbonate, for example, and has a cylindrical portion 2a formed in a cylindrical shape, and a flange portion 2b formed to project outward from an outer peripheral surface near the lower portion of the cylindrical portion 2a. , And a step portion 2c formed on the upper surface side of the flange portion 2b.

  The cylindrical portion 2a has a lens disposed therein so that the optical axis coincides with the central axis of the cylinder. In addition, the cylindrical part 2a in this embodiment differs in the outer diameter by the upper part and lower part from the collar part 2b, and makes the outer diameter of a lower part smaller than the external shape of an upper part.

  The flange portion 2b is formed so that the outer edge forms an octagon shape corresponding to the shape of the movable coil 4 described later. Note that the collar portion 2b may be subjected to a hollow process for weight reduction.

  The staircase portion 2c is formed in a substantially rectangular parallelepiped shape at the boundary between the cylindrical portion 2a and the upper surface side of the flange portion 2b, and a plurality (four in this embodiment) are provided at equal intervals in the circumferential direction. Yes. As will be described later, the staircase portion 2 c serves as a positioning means for assembling the movable coil 4 to the lens holder 2 and serves as a means for regulating the upper limit of the limit movable range of the lens holder 2.

  The magnetic circuit unit 3 linearly moves the lens holder 2 in the optical axis direction based on a drive signal from a control circuit unit (not shown) arranged outside the package. The magnetic circuit unit 3 is composed of a movable coil 4 that allows current to flow, a magnet 5 that forms a magnetic field, and a yoke body 6 that forms a magnetic path, and is arranged coaxially around the lens holder 2. .

  The movable coil 4 is formed by winding a wire made of a conductive material such as copper into a substantially cylindrical shape. The cross-sectional shape perpendicular to the optical axis of the movable coil 4 (hereinafter referred to as a plan view shape or simply a cross-sectional shape) is an octagon for both the inner edge and the outer edge. That is, the movable coil 4 has an outer peripheral surface 4a and an inner peripheral surface 4b each consisting of eight side surfaces. The movable coil 4 is fixed to the outer edge side of the flange portion 2b with an adhesive, for example, in a state where the cylindrical portion 2a of the lens holder 2 is inserted on the inner peripheral side. At this time, the inner peripheral surface 4b near the lower end surface 4c of the movable coil 4 is opposed to the outer surfaces of the four stepped portions 2c, thereby positioning in the plane direction perpendicular to the optical axis.

  The magnet 5 is a rare earth sintered magnet, for example, and is composed of eight magnet pieces 5a having a rectangular flat plate shape. The eight magnet pieces 5a are magnetized in the thickness direction (magnetic pole surfaces are formed on both end surfaces in the thickness direction). The eight magnet pieces 5a are arranged opposite to the eight side surfaces constituting the outer peripheral surface 4a of the movable coil 4 with a predetermined interval therebetween. Further, the eight magnet pieces 5a are formed to have a width dimension that is adjacent to the magnet pieces 5a arranged on both sides of the circumferential direction. That is, the magnet 5 is configured so that the shape in plan view is an octagonal shape for both the inner edge and the outer edge when viewed throughout. Further, the magnet 5 is configured such that its height dimension is larger than the height dimension of the movable coil 4.

  The yoke body 6 is formed using a material that can easily pass a magnetic flux such as iron. The yoke body 6 is formed in a cylindrical shape as a whole, but as shown in FIG. 2, the longitudinal sectional shape of the side surface portion is formed in a U-shape. That is, the yoke body 6 includes a substantially cylindrical yoke outer wall portion 6a, a substantially cylindrical yoke inner wall portion 6b disposed on the inner peripheral side of the yoke outer wall portion 6a, and an upper end surface of the yoke outer wall portion 6a. And a substantially ring-shaped yoke coupling portion 6c that couples the upper end surface of the yoke inner wall portion 6b.

The yoke outer wall portion 6a is formed in an octagonal shape in plan view, and eight magnet pieces 5a are fixed to eight side portions constituting the inner peripheral surface 6aa by using, for example, an adhesive. Moreover, the height of the yoke outer wall 6 a is approximately the same as the height of the magnet 5. In this embodiment, the lower portion of the yoke outer wall portion 6a is slightly spaced from the lower end surface 5b of the magnet 5 (magnet piece 5a) with the upper end surface of the magnet 5 abutting against the lower surface of the yoke connecting portion 6c. It is formed in a height dimension that projects.

  The yoke inner wall portion 6b is formed in an octagonal shape in plan view, and is predetermined between the cylindrical portion 2a (the portion above the flange portion 2b) constituting the lens holder 2 and the movable coil 4. It is arranged with an interval of. Further, the yoke inner side wall portion 6b is formed so that the height dimension relative to the yoke connecting portion 6c is smaller than the height dimension of the yoke outer wall portion 6a and the height dimension of the magnet 5. That is, the yoke inner wall portion 6 b is formed such that its lower end surface 6 ba is located above the lower end surface 5 b of the magnet 5. The yoke inner wall portion 6 b is disposed such that the lower end surface 6 ba is positioned above the upper surface 2 ca of the stepped portion 2 c formed on the lens holder 2. With this configuration, the lens holder 2 can be raised as much as possible until the upper surface 2ca of the stepped portion 2c contacts the lower end surface 6ba of the yoke inner wall portion 6b. In other words, the yoke inner wall 6b is configured to serve as a stopper that regulates the upper limit of the limit movable range of the lens holder 2 and restricts excessive movement of the lens holder 2.

When viewed from the upper surface side, the magnetic circuit unit 3 includes, on the outer peripheral side of the lens holder 2, a yoke inner wall 6b, a movable coil 4, a magnet 5, and a yoke outer wall 6a, as shown in FIG. The side surfaces corresponding to each other are opposed to each other, and are arranged symmetrically so that the center of each other substantially coincides with the optical axis L. As a result, the magnetic field formed by the magnet 5 is applied substantially vertically to the eight side surfaces of the movable coil 4 as viewed from above.

  The frame 7 is formed using a material that easily allows magnetic flux such as iron, for example, and is formed in a ring shape having an octagonal shape in plan view. The frame 7 is fixed using, for example, an adhesive along the entire circumference of the lower end surface 6ab of the yoke outer wall 6a. The frame 7 is for pressing and fixing the lower spring 8 to the base 10 side. However, by forming the frame 7 using a material that allows easy passage of magnetic flux, it serves as a yoke that forms a magnetic path. It has a function.

  The lower spring 8 is a double ring-shaped leaf spring made of a spring material such as beryllium copper. As shown in FIG. 4A, the lower spring 8 includes an outer ring 8a, an inner ring 8b arranged at a predetermined interval on the inner edge side of the outer ring 8a, an outer ring 8a and an inner ring 8b. And a plurality of (three in the present embodiment) elastic connecting portions 8c that are elastically deformed and arranged at equal intervals in the circumferential direction.

  As shown in FIG. 2, the outer ring 8 a is fixed using, for example, an adhesive while being sandwiched between the frame 7 and the base 10. The inner ring 8b is fixed to the lower surface side of the flange portion 2b constituting the lens holder 2 using, for example, an adhesive. The elastic connecting portion 8c is in a deformable state without being fixed to any member. In the present embodiment, the elastic connecting portion 8c has a smooth elasticity on the surface on the lens holder 2 side of the thin line portion (the portion surrounded by the broken line D shown in FIG. 4A) near the inner ring 8b. A damping agent is applied to the extent that deformation is not hindered.

  Similar to the lower spring 8, the upper spring 9 is a double ring-shaped plate spring made of a spring material such as beryllium copper. As shown in FIG. 4B, the upper spring 9 includes an outer ring 9a, an inner ring 9b disposed at a predetermined interval on the inner peripheral side of the outer ring 9a, an outer ring 9a and an inner ring 9b. , And a plurality (three in the present embodiment) of elastic connecting portions 9c arranged at equal intervals in the circumferential direction. As shown in FIG. 2, the outer ring 9a is fixed to the upper surface of the yoke connecting portion 6c using, for example, an adhesive. The inner ring 9b is fixed to the upper end surface of the cylindrical portion 2b of the lens holder 2 using, for example, an adhesive. The elastic connecting portion 9c is in a deformable state without being fixed to any member.

  Thereby, the lens holder 2 is held by the yoke body 6 movably in the optical axis direction by the pair of springs 8 and 9 (the lower spring 8 and the upper spring 9).

  The base 10 is formed of, for example, a resin such as polycarbonate, and includes a rectangular flat plate portion 10a and a column portion 10b having a substantially right-angled triangular cross section rising upward from the four corners of the flat plate portion 10a.

  The flat plate portion 10a has a circular through-hole 10c formed in the central portion, a ring-shaped protrusion 10d protruding upward along the outer edge of the through-hole 10c, and upward at the outer edge of the flat plate portion 10a. And a flat portion 10e protruding in a flat shape. A CMOS image sensor (not shown) as an image sensor is disposed below the through hole 10c.

  In the protrusion 10d, a portion near the lower end surface of the cylindrical portion 2a of the lens holder 2 (a lower portion than the flange portion 2b) is movably inserted in the optical axis direction. Further, the protruding portion 10d is disposed so that the flange portion 2b of the lens holder 2 is positioned above the protruding portion 10d. With this configuration, the lens holder 2 can be lowered as much as possible until the lower surface of the flange portion 2b comes into contact with the upper end surface of the protrusion 10d. In other words, the protrusion 10d defines the lower limit of the limit movable range of the lens holder 2 (generally, a movable range wider than the actually permitted movable range), and the lens holder 2 is excessively moved downward. It is comprised so that it may play the role of the stopper which regulates. In the present embodiment, when the movable coil 4 is not energized, the lower surface of the flange portion 2b constituting the lens holder 2 is placed on the upper end surface of the protruding portion 10c. At this time, the upper end surface 4d of the movable coil 4 is located above the lower end surface 6ba of the yoke inner wall portion 6b.

  An outer ring 8a of the lower spring 8 is fixed to the upper surface of the flat portion 10e using, for example, an adhesive. Thereby, the outer ring 8 a of the lower spring 8, the frame 7, the yoke body 6, the magnet 5, and the outer ring 9 a of the upper spring 9 are integrated with the base 10.

  The cover 11 is formed using, for example, a sheet metal such as stainless steel, and has a flat plate portion 11a whose outer edge is rectangular, a leg portion 11b extending downward from four corners of the flat plate portion 11a, and a central portion of the flat plate portion 11a. And an opening 11c.

  The flat plate portion 11a is fixed on the yoke connecting portion 6c with an adhesive, for example, with the outer ring 9a of the upper spring 9 interposed therebetween. That is, the flat plate portion 11a serves as a presser that fixes the outer ring 9a of the upper spring 9 to the yoke connecting portion 6c. The four leg portions 11b are engaged and fixed with the corresponding four column portions 10b of the base 10, respectively. Thereby, the base 10 and the case 11 are integrated, and the package which accommodates the lens holder 2, the magnetic circuit part 3, etc. is comprised. The opening 11c is formed in a truncated conical shape, and a lighting opening 11ca is formed at the center of the upper surface. The opening 11ca is formed in a circular shape, and has a diameter smaller than the outer diameter on the upper end side of the cylindrical portion 2a of the lens holder 2 and larger than the inner diameter.

  Next, the position detection circuit unit 20 will be described. The position detection circuit unit 20 is a circuit that electrically detects the inductance (inductance change) of the movable coil 4 and is disposed outside the package in this embodiment. As shown together with the movable coil 4 in FIG. 5, the position detection circuit unit 20 includes an input unit 21, an output unit 22, a comparison unit 23, and an integration circuit unit 24.

  The input unit 21 superimposes a sinusoidal reference signal (a reference signal generated from the reference signal generation circuit unit) for detecting the inductance of the movable coil 4 on, for example, a pulsed drive signal for driving the movable coil 4. This circuit includes three resistors and an operational amplifier 21a as an adder. The drive signal and the reference signal superimposed by the operational amplifier 21 a are transmitted to the movable coil 4.

  The output unit 22 is a circuit for detecting an output signal corresponding to the reference signal from the movable coil 4, and includes a filter, three resistors, and an operational amplifier 22a as an amplifier. An output signal from the movable coil 4 is input to the filter, and an output component corresponding to the reference signal is filtered. The output component corresponding to the reference signal has a phase shift corresponding to the magnitude of the inductance of the movable coil 4 as compared with the reference signal input to the input unit 21. The detected output signal is amplified by the operational amplifier 22 a and transmitted to the comparison unit 23.

  The comparison unit 23 is a circuit for differentiating the output signal from the output unit 22 and the reference signal input to the input unit 21, and includes three resistors and an operational amplifier 23a as a comparator. Inductance of the movable coil 4 is reflected in the signal obtained by the operational amplifier 23a. The difference signal is transmitted to the integration circuit unit 24.

  The integration circuit unit 24 is a circuit that integrates the AC difference signal output from the comparison unit 23 and converts it into a direct current (DC) signal. The DC-converted signal is transmitted as a signal corresponding to the inductance of the movable coil 4 to a drive signal circuit unit (not shown) that generates a drive signal for the movable coil 4.

[Operation and effect of unit]
Next, the operation of the lens driving unit 1 according to the embodiment of the present invention will be described with reference to the drawings. When a drive signal from a drive signal circuit unit arranged outside the package is input to the movable coil 4, an interaction between a current flowing through the movable coil 4 and a magnetic field applied from the magnet 5 to the movable coil 4 is caused. The movable coil 4 moves linearly in the optical axis direction. Since the lens holder 2 that holds the lens inside is integrated with the movable coil 4, the lens holder 2 also moves in the optical axis direction as the movable coil 4 moves.

  Light information from the subject is incident on a CMOS image sensor disposed on the lower side of the lens driving unit 1 while being condensed by the lens, and is converted into an image signal. The in-focus state is evaluated by analyzing the high-frequency component of the image signal. On the other hand, the position of the lens holder corresponding to the image signal whose focused state is evaluated is calculated from the inductance of the movable coil 4 detected by the position detection circuit unit 20.

  Here, the principle of deriving the position of the movable coil 4 in the optical axis direction from the inductance of the movable coil 4 detected by the position detection circuit unit 20 will be described with reference to FIGS. 6 (A), (B), and (C). I will explain. Note that a two-dot chain line with an arrow in the figure schematically shows a magnetic flux interlinking with the movable coil 4. Moreover, although the figure is sectional drawing, the hatching which shows that it is a cross section is abbreviate | omitted in order to make a figure legible.

  First, the positional relationship between the movable coil 4 and the yoke inner wall 6b will be described. As described above, the lower end surface 6ba of the yoke inner wall portion 6b is located above the upper surface 2ca of the stepped portion 2c formed on the lens holder 2 so as to define the upper limit of the limit movable range of the lens holder 2. (See FIG. 2). The movable coil 4 is configured such that its upper end surface 4d is positioned above the lower end surface 6ba of the yoke inner wall portion 6b. As a result, when viewed from a direction orthogonal to the optical axis, only the upper part of the movable coil 4 (the L1 part in FIG. 3A) overlaps the yoke inner wall 6b, and the lower part (the same figure). (L2 portion in (A)) does not overlap.

  Further, the lower end surface 4c of the movable coil 4 is positioned below the upper surface 2ca of the stepped portion 2c by the height of the stepped portion 2c formed in the lens holder 2. Therefore, even if the movable coil 4 is raised until the upper surface 2ca of the stepped portion 2c is brought into contact with the lower end surface 6ba of the yoke inner wall 6b, that is, the upper limit of the limit movable range, Only a part of the peripheral surface 4b overlaps with the yoke inner wall portion 6b. That is, the entire inner peripheral surface 4b of the movable coil 4 does not overlap with the yoke inner wall portion 6b. In other words, when the movable coil 4 is moved over the entire range of the limit movable range with respect to the optical axis direction, a part of the inner peripheral surface 4b of the movable coil 4 always faces the outer peripheral surface 6bb of the yoke inner wall portion 6b. Thus, the lens driving unit 1 is configured.

  Next, the magnetic flux that links the movable coil 4 will be described. As described above, the yoke inner wall portion 6b is configured such that its lower end surface 6ba is located above the lower end surface 5b of the magnet 5. As a result, the magnetic flux from the magnet 5 toward the yoke inner wall portion 6b is inclined upward as the lower portion of the magnet 5 (the angle formed with the optical axis in the cross section becomes smaller). This tendency is remarkable in the lower region from the height position of the lower end surface 6ba of the yoke inner wall 6b.

  Accordingly, as shown in FIGS. 6A, 6B, and 6C, when the movable coil 4 moves relative to the yoke inner wall portion 6b, the movable coil 4 and the yoke inner wall portion 6b overlap. Depending on the degree, the magnetic flux interlinking the movable coil 4 will be different. More specifically, as the movable coil 4 descends and the degree of overlap between the movable coil 4 and the yoke inner wall portion 6b decreases, the magnetic flux having a large inclination angle with respect to the normal line of the movable coil 4 increases. Conversely, as the movable coil 4 rises and the degree of overlap increases, the magnetic flux with a small inclination angle with respect to the normal line of the movable coil 4, that is, the perpendicular magnetic flux increases. If the movable coil 4 is raised until the entire movable coil 4 overlaps the yoke inner wall portion 6b, the ratio of the vertical magnetic flux increases, and even if the position of the movable coil 4 changes, the movable coil The magnetic flux interlinking 4 is almost unchanged.

  In this regard, as previously described, even when the movable coil 4 moves over the entire range of the limit movable range with respect to the optical axis direction, the entire movable coil 4 does not overlap with the yoke inner wall portion 6b. A part of the inner peripheral surface 4b of the coil 4 always faces the outer peripheral surface 6bb of the yoke inner side wall portion 6b. Therefore, when the movable coil 4 is moved over the entire range of the limit movable range, the magnetic flux component that is linked perpendicularly to the movable coil 4 continuously changes. (This is still the case when the movable coil 4 is moved over the entire range of the allowable movable range.)

  Here, the inductance of the movable coil 4 increases as the magnetic flux interlinking perpendicularly to the movable coil 4 increases. Therefore, the inductance increases continuously as the movable coil 4 moves upward. Conversely, the inductance decreases continuously as the movable coil 4 moves downward. That is, the inductance of the movable coil 4 changes according to the position of the movable coil 4 with respect to the optical axis direction. Therefore, by detecting the inductance of the movable coil 4 (inductance change), the position of the movable coil 4 and, in turn, the position of the lens holder that moves integrally with the movable coil 4 can be calculated.

  In this way, the focus position is specified by the hill-climbing method from the position information of the lens holder detected by the position detection circuit unit 20 and the image information (high-frequency component of the image signal) by the CMOS image sensor. Specifically, the lens is moved in the optical axis direction in a predetermined step by first increasing or decreasing the drive current stepwise. At this time, the calculation processing unit of the drive signal circuit unit stores the image information for each step and the position information of the lens holder, and calculates the high frequency component of the image signal. Then, by moving the lens holder to the position where the maximum high frequency component is obtained, the automatic focusing of the lens is completed.

  As is clear from the above description of the operation, the lens driving unit 1 according to the present embodiment determines the position of the movable coil 4 and thus the position of the lens holder (lens held by the lens holder) without using a position sensor. It can be detected accurately. Since the position sensor becomes unnecessary, the installation space for the position sensor in the package can be reduced, and the lens drive unit 1 can be downsized. In addition, since the accurate position of the lens holder can be detected, it can be expected that the time required for specifying the in-focus position by the hill-climbing method is shortened.

  Further, in the lens driving unit 1, the movable coil 4 is formed so that the cross-sectional shape is an octagon. Then, eight flat magnet pieces 5a are arranged opposite to the eight side surfaces constituting the outer peripheral surface 4a of the movable coil 4. Further, the eight flat magnet pieces 5a are arranged adjacent to the magnet pieces 5a on both sides with respect to the circumferential direction, and when viewed as a whole, the shape of the top view is configured as an octagonal ring. With this configuration, the magnetic efficiency is improved and the driving force generated in the movable coil is increased as compared with the case where a movable coil having a circular shape in plan view is used.

  Here, the result of quantitatively examining the influence of the cross-sectional shape of the movable coil 4 on the magnetic efficiency by the static magnetic field analysis will be described. Table 1 shows that a magnet 5 constituted by arranging eight magnet pieces 5a in an octagonal shape, a movable coil 4 having an octagonal cross section (product of this embodiment), and a movable having a circular cross section. The Lorentz force generated in each movable coil 4 when combined with a coil (comparative product) is shown in comparison.

  As can be seen from Table 1, the Lorentz force for driving the movable coil 4 in the optical axis direction is increased by changing the cross-sectional shape of the movable coil 4 from a circular shape to an octagonal shape. This is because by making the cross-sectional shape of the movable coil 4 an octagonal shape, the gap with the magnet 5 is narrowed and made constant, and the effective magnetic flux that links the movable coil 4 increases.

  Thus, when the magnetic efficiency of the magnetic circuit unit is improved, the acceleration performance of the lens holder is improved. By improving the acceleration performance of the lens holder, the time required to move the lens to a predetermined position is shortened. As a result, the time required to specify the in-focus position can be further shortened. In addition, it is possible to reduce the drive current energized to the movable coil, and to realize low power consumption. Further, it is possible to reduce the size of components such as a moving coil.

  In the present embodiment, a damping agent is applied to a portion of the elastic coupling portion 8c of the lower spring 8 near the inner ring 8a. Thereby, the unnecessary vibration phenomenon which occurs after moving the lens holder 2 at high speed can be converged in a short time. As a result, the time required for searching for the in-focus position is further shortened. Moreover, it can be expected that plastic deformation at the elastic coupling portion 8c of the lower spring 8 that may occur when an external force such as a drop impact is applied is suppressed.

[Modification]
As mentioned above, although an example of preferable embodiment of this invention was demonstrated, about embodiment, it is not limited above, A various change and combination are possible.
For example, the position detection circuit unit 20 is not limited to the above embodiment, and an inductance change may be detected as a frequency change by applying a Colpitts oscillator circuit.

  In addition, when the lens driving unit 1 moves the movable coil 4 over the entire range of the limit movable range with respect to the optical axis direction, a part of the inner peripheral surface 4b of the movable coil 4 is the outer peripheral surface of the yoke inner wall portion 6b. Although it is configured to always face 6bb, it is not limited to this. For example, if a part of the outer peripheral surface of the movable coil 4 is opposed to the inner peripheral surface of the magnet 5, an inductance change can be detected.

  The lens driving unit 1 according to the present invention is not limited to the lens driving unit for autofocusing, but is a lens driving for the purpose of linearly moving the lens to a fixed position such as macro photography (close-up mode). It can also be applied as a unit.

  Further, the cross-sectional shape of the movable coil 4 is preferably an octagonal shape from the viewpoint of improving magnetic efficiency and ease of manufacturing, but is not limited to this, and is a polygonal shape other than an octagonal shape. May be. Moreover, the cross-sectional shape of the movable coil 4 is not limited to a polygonal shape, and may be a circular shape.

  Furthermore, the number of the flat magnet pieces 5a constituting the magnet 5 is not limited to eight, but may be an arbitrary number corresponding to the number of side portions constituting the outer peripheral surface 4a of the movable coil 4. be able to. In addition, the magnet 5 is not necessarily configured to be a polyhedron, and when the cross-sectional shape of the movable coil 4 is circular, the cross-sectional shape of the magnet 5 may be circular.

  Further, the application of the damping agent to the lower spring 8 is not limited to the above embodiment, and the damping agent may be applied to any of the pair of springs 8 and 9, or applied to both. You don't have to.

It is a disassembled perspective view which shows an example of the lens drive unit which concerns on embodiment of this invention. It is a longitudinal cross-sectional view which shows an example of the lens drive unit which concerns on embodiment of this invention. It is a cross-sectional view which shows an example of the lens drive unit which concerns on embodiment of this invention. It is a top view which shows an example of a pair of spring which concerns on embodiment of this invention. It is a figure which shows an example of a structure of the position detection circuit part which concerns on embodiment of this invention. It is a figure for demonstrating the method to detect the position of the lens holder of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens drive unit 2 Lens holder 2a Cylindrical part 2b Eaves part 2c Protrusion part 3 Magnetic circuit part 4 Movable coil 4a Outer peripheral surface 4b Inner peripheral surface 4c Lower end surface 4d Upper end surface 5 Magnet 5a Magnet piece 5b Lower end surface 6 York body 6a Yoke outer wall portion 6aa Inner peripheral surface 6ab Lower end surface 6b Yoke inner wall portion 6ba Lower end surface 6bb Outer peripheral surface 6c Yoke connecting portion 7 Frame 8 Upper spring 9 Lower spring 10 Base 11 Cover 20 Position detection circuit portion 21 Input portion 22 Output unit 23 Comparison unit 24 Integration circuit unit L Optical axis

Claims (6)

A lens holder for holding the lens;
A movable coil disposed on the outer peripheral side of the lens holder and movable in the optical axis direction (vertical direction) together with the lens holder;
A magnet that is arranged on the outer peripheral side of the movable coil and forms a magnetic field;
A yoke body having a yoke outer wall portion for holding the magnet on the inner peripheral surface, and a yoke inner wall portion disposed on the inner peripheral side of the movable coil;
A spring that elastically supports the lens holder;
A lens driving unit comprising: position detecting means for detecting the position of the lens holder;
The yoke inner wall portion is formed such that its lower end surface is located above the lower end surface of the magnet,
The lens driving unit, wherein the position detecting means detects the position of the lens holder from an inductance change generated in the movable coil when the movable coil is displaced in the optical axis direction.   When the movable coil is moved over the entire movable range with respect to the optical axis direction, a part of the inner peripheral surface of the movable coil is always opposed to the outer peripheral surface of the inner wall portion of the yoke. The lens driving unit according to claim 1, wherein: The position detecting means includes
An input unit that inputs a sine wave reference signal superimposed on a drive signal that drives the movable coil;
An output unit for detecting an output signal from the movable coil corresponding to the reference signal;
The lens driving unit according to claim 1, further comprising a comparison unit that makes a difference between the reference signal and the output signal. The movable coil has a polygonal cross-sectional shape perpendicular to the optical axis,
The magnet is composed of a plurality of flat magnet pieces arranged adjacent to each other, and is configured by disposing each magnet piece so as to face each side portion constituting the outer peripheral surface of the movable coil. The lens driving unit according to claim 1, wherein:   The lens driving unit according to claim 4, wherein the coil has an octagonal cross-sectional shape perpendicular to the optical axis. The spring is
A ring-shaped outer ring fixed to the yoke body;
A ring-shaped inner ring disposed on the inner edge side of the outer ring and fixed to the lens holder;
A plurality of elastic connecting portions configured to connect the outer ring and the inner ring and be elastically deformable;
The lens driving unit according to any one of claims 1 to 5, wherein a damping agent is applied to a portion of the elastic connecting portion near the inner ring.

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