WO2011016411A1

WO2011016411A1 - Drive device and lens drive device

Info

Publication number: WO2011016411A1
Application number: PCT/JP2010/063004
Authority: WO
Inventors: 篤広野田; 滋和田
Original assignee: コニカミノルタホールディングス株式会社
Priority date: 2009-08-06
Filing date: 2010-08-02
Publication date: 2011-02-10
Also published as: JPWO2011016411A1

Abstract

A drive device (La) is provided with a drive frame (22) which holds an object to be driven, guide sections (71, 72) which guide the drive frame (22) so that the guide frame (22) moves in a predetermined direction, and a shape memory alloy actuator (41) which applies a drive force. The drive device (La) is also provided with a movement direction changing section (25) which, when the drive frame (22) has moved to an end, makes contact with a movement limiting section (5) and moves, near the movement limiting section (5), the drive frame (22) in a direction different from the predetermined direction.

Description

Driving device and lens driving device

The present invention relates to a drive device that drives a driven body that requires a small and fine operation, such as a lens of a digital camera mounted on a mobile phone, a portable information terminal, or the like.

In many cases, a small mobile terminal such as a mobile phone, a personal digital assistant (PDA), or a portable music player is equipped with a digital camera for taking an image. In recent years, a digital camera mounted on the small mobile terminal is required not only to take an image but also to take a high-quality image. As one of methods for taking a high-quality image with the digital camera, a method of adding an optical function such as a focus function and a zoom function to the digital camera is used.

In order to add the optical function as described above, it is necessary to mount a driving device for driving the lens (and the lens support) provided in the digital camera. The digital camera is mounted in a limited space of the small portable terminal, and the driving device mounted on the digital camera needs to be small and light. As such a drive device that satisfies the requirements for small size and light weight, a drive device including a shape memory alloy (hereinafter referred to as SMA) actuator has been proposed.

Examples of the drive device provided with the SMA actuator include drive devices described in Japanese Patent Application Laid-Open Nos. 2007-58075, 2007-58076, and 2007-60530. In the drive devices described in these documents, a SMA wire (SMA actuator) is wound around a cantilever lever, an electric current is applied to the SMA actuator, and the lever is rotated by a temperature change caused by self-heating. Thus, the driven object is moved.

For example, when a highly accurate focus function or zoom function is added to the digital camera, it is necessary to stop the lens and the lens support (driven object) at an accurate position. As a method for controlling the position of the lens, it is known that lens position information is detected by a method such as conversion from a resistance value of a position sensor or an SMA actuator, and servo control is performed based on the position information.

In the driving device, the lens position is controlled as follows. The lens and the lens support are moved stepwise from one end to the other end of the movable range. Position information at each stage and information necessary for control are detected in advance. Information necessary for control in each stage is examined and servo control is performed based on the position information when it becomes the best, and the lens and the lens support are moved. For example, when the position control is autofocus control, a focus signal at each stage is detected as information necessary for control, and the best value of the focus signal is set as a focus position, based on position information at that position. Electric power is supplied to the SMA actuator to move the lens and the lens support to the in-focus position.

JP 2007-58075 A JP 2007-58076 A JP 2007-60530 A

When performing position control by the above-described method, a constant current may flow through the SMA actuator for a certain period of time when the driven object is in contact with the other end and stopped. In this case, the SMA actuator is supplied with a constant current for a certain period of time while the contraction is restricted. The SMA actuator has a characteristic that the temperature rapidly increases when a current of a predetermined value or more flows in a state where the contraction is limited. In addition, the SMA actuator has a characteristic that the stress rapidly increases as the temperature rises in a state where the length does not change (a state in which contraction is restricted).

When the driven object comes into contact with the other end and a constant current flows through the SMA actuator for a certain period of time, the SMA actuator accumulates the stress increased by the restriction of contraction and the stress increased by the temperature rise. Acted. That is, when contraction of the SMA actuator is restricted, when a constant current flows through the SMA actuator for a certain period of time, the acting stress rapidly increases. When high stress acts on the SMA actuator, it deteriorates even if the acting time is short.

When the SMA actuator deteriorates, the current value necessary for driving becomes larger than the current value before deterioration, and the accuracy of servo control is reduced. When the deterioration further progresses, the SMA actuator is broken (in the case of a line, it is disconnected), which becomes a fatal defect that makes it impossible to drive the driven object.

Therefore, an object of the present invention is to provide a drive device that can suppress deterioration of a shape memory alloy actuator and perform position control with high accuracy over a long period of time.

To achieve the above object, a driving apparatus according to the present invention includes a driving frame that holds a driven object, a guide portion that guides the driving frame to move in a predetermined direction, and a drive that moves the driving frame. A shape memory alloy actuator that applies force; and a movement restricting portion that contacts the drive frame and restricts the movement of the drive frame when the drive frame moves to an end of a movable range. The drive device is a delay that delays a time until the drive frame moves by the driving force of the shape memory alloy actuator and contacts the movement restriction unit immediately before the movement restriction unit restricts the movement. Department.

According to this configuration, the delay unit delays the time from when the drive frame approaches the movement restriction unit until it comes into contact with the movement restriction unit. Accordingly, it is possible to suppress a constant current from flowing through the shape memory alloy actuator for a certain period of time in a state where the contraction of the shape memory alloy actuator is regulated.

Thereby, it is possible to suppress the deterioration of the shape memory alloy actuator and to suppress the movement accuracy. Further, by suppressing the degradation, the life of the SMA actuator can be extended, and the drive device can be used stably over a long period of time.

In the above-described configuration, the delay unit may be a movement direction conversion unit that moves the movement direction of the drive frame in a direction different from the predetermined direction in the vicinity of the movement restriction unit.

According to this configuration, even after the drive frame comes into contact with the movement restriction unit, the drive frame moves in a direction different from the predetermined direction, so that the drive frame does not stop at the moment when the drive frame comes into contact with the movement restriction unit. As a result, the shape memory alloy actuator continues to contract even if there is a time lag after the drive frame comes into contact with the movement restricting portion until the output of the driving force from the shape memory alloy actuator is stopped. And a sudden increase in stress can be suppressed.

Thereby, it is possible to suppress the deterioration of the shape memory alloy actuator and to suppress the movement accuracy. Further, by suppressing the deterioration, the life of the shape memory alloy actuator can be extended, and the drive device can be used stably over a long period of time.

In the above configuration, the position sensor that detects the position of the drive frame, and the supply of power applied to the shape memory alloy actuator based on the position information detected by the position sensor are controlled, and the drive is performed by the position sensor. And a controller that performs emergency stop control for stopping the supply of electric power to the shape memory alloy actuator when movement of the frame in a direction different from a predetermined direction is detected.

According to this configuration, it is possible to suppress an abrupt increase in the stress of the shape memory alloy actuator by performing the emergency stop control. Since the drive frame can be servo-controlled based on the position information, it is possible to improve the accuracy of position control of the drive frame.

In the above configuration, the position sensor may be a resistance detection unit that detects a change in electrical resistance of the shape memory alloy actuator. Thereby, it is not necessary to provide a position sensor separately, and it is possible to simplify the structure of a drive device.

In the above configuration, the controller may perform the emergency stop control when a predetermined maximum current or maximum voltage is applied to the shape memory alloy actuator for a predetermined time or more.

In the above configuration, the shape memory alloy actuator may be linear. Further, the shape is not limited to a linear shape, and a shape that can accurately move the drive frame in a predetermined direction, such as a rod shape, a belt shape, or a plate shape, can be widely employed.

In the above configuration, the guide portion may include a pair of flat plate springs arranged in parallel to each other to hold both ends of the drive frame in the moving direction. The guide portion is not limited to a pair of leaf springs arranged in parallel, and can guide movement of the drive frame in the predetermined direction, such as an engaging portion that engages with a rail shape extending in the predetermined direction. A device that can cope with movement of the drive frame in a direction other than a predetermined direction by the movement direction conversion unit can be widely used.

In the above configuration, the movement direction conversion unit may be formed such that a rotational moment acts on the drive frame when contacting the movement restriction unit. As the movement direction conversion unit that generates such a moment, for example, the movement direction conversion unit protrudes from the edge of the surface of the drive frame facing the movement restriction unit toward the movement restriction unit. Can be mentioned.

In the above configuration, the movement direction conversion unit is formed on a surface of the drive frame that faces the movement limitation unit, and the movement limitation unit includes a convex portion that contacts the movement direction conversion unit, and the movement At least one of the tip of the direction changing portion and the convex portion may be cut obliquely.

A lens driving device that drives an imaging lens of a digital camera can be used as the driving device described above.

According to the present invention, it is possible to provide a driving device capable of suppressing the deterioration of the shape memory alloy actuator and performing position control with high accuracy over a long period of time.

It is a schematic plan view of the lens drive device using an example of the drive device concerning this invention. It is the side view which looked at the lens drive device shown in FIG. 1 from the II side. It is a block diagram of the principal part of the lens drive device shown in FIG. It is a figure showing the relationship between the position of a lens and time when performing an autofocus process with the lens drive device shown in FIG. It is a flowchart which shows the process of performing an autofocus process with the lens drive device shown in FIG. It is a side view when the moving direction conversion part of the lens drive device shown in FIG. 2 contacts the movement restricting part. It is a side view when the lens drive frame of the lens drive device shown in FIG. 6 is rotating. It is a side view of the lens drive device using the other example of the drive device concerning the present invention. It is a side view which shows the state which the lens drive device shown in FIG. 8 contacted the movement control part. It is a top view of the lens drive device using the further another example of the drive device concerning the present invention. It is a side view of the lens drive device shown in FIG. It is a side view of the lens drive device using the other example of the drive device concerning the present invention.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic plan view of a lens driving device using an example of a driving device according to the present invention, and FIG. 2 is a side view of the lens driving device shown in FIG. In FIG. 1, for the sake of convenience, illustration of the movement limiting unit 5, the top plate unit 6, the upper plate spring 71, the lower plate spring 72, and the bias spring 8 is omitted.

As shown in FIGS. 1 and 2, the lens driving device La includes a base unit 1, a lens unit 2 that is an imaging optical system, and the lens unit 2 that is disposed on the base unit 1 and moves along the optical axis AX direction. A lever portion 3 to be driven, a drive portion 4 disposed on the base portion 1 to drive the lever portion 3, a movement restricting portion 5 (see FIG. 2) disposed so as to be parallel to the base portion 1, and the base portion 1 And a top plate portion 6 (see FIG. 2) disposed between the base plate 4 and the top plate portion 6, and an upper plate spring 71 and a lower plate spring 72 (which hold the lens unit 2). 2) and a bias spring 8 (see FIG. 2) for pressing the lens unit 1.

The base unit 1 constitutes the bottom of the lens driving device La, and is a member fixed to a member (for example, a frame of a mobile phone or a mount substrate) to which the lens driving device La is attached. The base portion 1 is a plate-like member having a square shape in plan view, but is not limited thereto. The base portion 1 may have a shape that matches a member to be attached, such as a circular shape or a polygonal shape in plan view. Further, the base portion 1 is a resin molded body, but is not limited thereto, and a plate-like one can be widely used.

The base unit 1, the movement limiting unit 5 and the top plate unit 6 may be connected via a support column or the like, or may be integrally formed. The base unit 1, the movement limiting unit 5, and the top plate unit 6 are fixed members that do not move when the lens unit 2 moves. Further, the movement restricting unit 5 can substitute a part of a member to be attached to which the lens driving device La is attached.

The lens unit 2 includes an imaging lens 21 which is a driven body, and a lens holding frame (driving frame) 22 on which the imaging lens 21 is held. The imaging lens 21 includes an objective lens, a focus lens, a zoom lens, and the like, and constitutes an imaging optical system for an imaging element (not shown). The imaging lens 21 is composed of a plurality of lenses, but may be composed of a single lens.

The lens drive frame 22 is a cylindrical frame (so-called ball frame) and is arranged so that the central axis and the optical axis AX overlap. A pair of support portions 23 protruding in the radial direction and having an angular difference of 180 degrees are formed on the side peripheral wall of the objective-side tip (tip on the movement restricting portion 5 side) of the lens drive frame 22.

The lens unit 2 is inserted into the opening formed in the top plate portion 6 and is disposed on the base portion 1 so that the pair of support portions 23 are positioned in the vicinity of the pair of diagonals of the base portion 1 in plan view. Has been. An upper leaf spring 71 and a lower leaf spring 72 are attached to the top plate portion 6 and the base portion 1 so as to be parallel to each other, and the lens unit 2 is held up and down by the upper leaf spring 71 and the lower leaf spring 72. ing. Thereby, the lens unit 2 is supported so as to be displaceable with respect to the base portion 1, the movement restricting portion 5 and the top plate portion 6, and the degree of freedom of the displacement is restricted in the direction along the optical axis AX. .

A spring receiver 24 for receiving the bias spring 8 is formed on the end surface of the lens drive frame 22 on the movement restricting portion 5 side. The spring receiver 24 has a cylindrical shape that protrudes in the axial direction from the edge of the end face of the lens driving frame 22 on the movement restricting portion 5 side. One end (lower end in the figure) of the bias spring 8 is fitted into the spring receiver 24, and the other end (upper end in the figure) is in contact with the movement restricting portion 5. The bias spring 8 is a coil spring, and biases a force (bias force) that pushes the lens unit 2 toward the base portion 1 along the optical axis AX.

The lens drive frame 22 is formed with a movement direction conversion section 25 that protrudes from the end of the spring receiver 24 on the movement restriction section 5 side. The movement direction conversion unit 25 is an example of a delay unit that delays the time from when the lens drive frame 22 approaches the movement restriction unit 5 until it comes into contact. When the lens unit 2 comes into contact with the movement restriction unit 5, the movement direction conversion unit 25 comes into contact first and converts the movement direction of the lens unit 2. The moving direction converting portion 25 is formed at a position having an angle difference of 90 degrees with each of the pair of supporting portions 23.

In the lens unit 2 shown in FIGS. 1 and 2, the moving direction conversion unit 25 is a rectangular parallelepiped shape, but is not limited thereto, and the movement limiting unit 5 side is formed in a curved surface shape. Or a pointed cone shape. Also, the connection surface with the spring receiver 24 is not limited to a rectangle, and a shape that can be connected to the spring receiver 24 such as a circle, an ellipse, or a polygon can be widely used.

The lever portion 3 engages with the lens unit 2 via a pair of support portions 23, and applies a driving force upward in the optical axis AX direction (direction toward the movement restriction portion 5) to the lens unit 2. The lever portion 3 includes an arm portion 31 having a circular arc shape in plan view, and an extending portion 32 formed so as to be orthogonal to the arm portion 31 from an intermediate base end portion of the arm portion 31. It is an L-shaped member rotated 180 degrees.

The arm portion 31 has a symmetrical shape across the base end portion, and is divided into two forks while being close to the outer peripheral surface of the lens unit 2, and is formed so as to surround one half of the lens unit 2. The distal ends (both ends) of the arm portion 31 reach positions where they overlap with the pair of support portions 23 of the lens unit 2 in plan view. A distal end of the arm part 31 is in contact with the support part 23, and a displacement output part 311 for applying a driving force to the support part 23 is formed.

The extended portion 32 is connected to the arm portion 31 at the upper end. The extended portion 32 is driven to drive the lens unit 2 via the lever portion 3 with the drive portion 4 engaged with a lower end portion (an end portion on the opposite side to which the arm portion 31 is connected). A displacement input unit 321 to which a force is applied is provided.

The lever portion 3 is disposed in the vicinity of the corner portion of the base portion 1 other than the corner portion where the pair of support portions 23 are located. In the vicinity of the corner portion where the lever portion 3 of the base portion 1 is disposed, a support leg portion 11 that is erected on the base portion 1 is provided. The support portion 111 of the support leg 11 has a cylindrical curved surface extending in a direction orthogonal to the optical axis AX direction and parallel to the base portion 1. A bent portion 33 which becomes a boundary between the arm portion 31 and the extending portion 32 of the lever portion 3 is in contact with the support portion 111, and thereby the lever portion 3 is supported so as to be swingable around the support portion 111. Yes.

The drive unit 4 includes a SMA actuator 41 in which a shape memory alloy (Shape Memory Alloy, hereinafter referred to as SMA) is linearly formed, and a pair of electrodes 42 for fixing both ends of the SMA actuator 41 and energizing the SMA actuator 41. And.

As the SMA actuator 41, for example, a Ni-Ti alloy or the like formed in a wire shape can be used. In addition, the SMA actuator is not limited to a wire-like one, and a shape (for example, a rod shape, a belt shape, a plate shape, etc.) that can move the arm portion can be widely adopted.

As shown in FIGS. 1 and 2, the SMA actuator 41 is wound around a displacement input portion 321 formed in the extending portion 32 of the lever portion 3, and is arranged in a V shape that is folded back by the extending portion 32. Yes. The pair of electrodes 42 are respectively disposed in the vicinity of the corner portion of the base portion 1 where the support portion 23 of the lens unit 2 is disposed. The pair of electrodes 42 energize the SMA actuator 41 and receive a force generated from the SMA actuator 41 during operation, and are firmly fixed to the base portion 1. Each of the pair of electrodes 42 is disposed so that the length from the V-shaped folding point (displacement input portion 321) of the SMA actuator 41 to each electrode 42 is equal. As a result, the amount of expansion / contraction on both sides of the displacement input portion 321 of the SMA actuator 41 becomes equal, and the tilt when the lever portion 3 is moved can be suppressed. In addition, friction (and wear) due to displacement between the SMA actuator 41 and the lever portion 3 during driving can be suppressed.

Further, the extending portion 321 is provided with a groove having a V-shaped cross section, and the SMA actuator 41 is bridged so as to fit into the V-shaped groove. Thereby, the SMA actuator 41 is not easily displaced in the direction along the side surface of the extended portion 321, and is stably suspended on the lever portion 3.

When the drive unit 4 is not driven, the bottom surface of the lens unit 2 is in contact with the base unit 1. At this time, the SMA actuator 41 is attached in a tensioned state, and the SMA actuator 41 pulls the displacement input unit 321. The displacement output part 311 of the lever part 3 is lifted, and the displacement output part 311 contacts the lower part of the support part 23.

SMA has a crystalline phase that changes with its own temperature. The SMA actuator 41 is a martensite phase when in a low temperature state, and an austenite phase when in a high temperature state. And the SMA actuator 41 can repeat a phase transformation reversibly by a temperature change. The SMA actuator 41 expands or contracts due to phase transformation. The SMA actuator 41 is a conductor having a predetermined electrical resistance, and Joule heat is generated when the SMA actuator 41 is energized. The SMA actuator 41 changes its temperature by this Joule heat and expands and contracts by phase transformation.

In the lens driving device La, when the driving unit 4 is not operating, that is, when the SMA actuator 41 is not energized, the lens unit 2 is biased by the bias spring 8 and is in contact with the base unit 1. Stopped at the origin (home position). At this time, the position of the lens unit 2 is determined by the lower end portion of the lens driving frame 22 coming into contact with the base portion 1.

When electric power is supplied through the electrode 42, the SMA actuator 41 generates Joule heat and the temperature rises. As the temperature of the SMA actuator increases, the SMA actuator undergoes phase transformation from the martensite phase to the austenite phase and contracts. As the SMA actuator 41 contracts, a tensile force F <b> 1 acts on the displacement input unit 321. The lever portion 3 swings around the support portion 111, and a displacement output portion 311 formed at the tip of the arm portion 31 pushes the support portion 23 in the direction opposite to the direction in which the bias force is applied. Thereby, the lens unit 2 moves toward the movement restricting unit 5 along the optical axis AX direction.

At this time, by adjusting the energization current to the SMA actuator 41, the amount of heat generation can be adjusted, and the amount of the tensile force F1 can be adjusted. The amount of displacement of the lens unit 2 can be adjusted by adjusting the tensile force F1.

When the energization to the SMA actuator 41 is stopped (or the voltage is reduced to a predetermined value), the amount of Joule heat generated by the SMA actuator 41 is reduced, and the temperature of the SMA actuator 41 is lowered. When the temperature of the SMA actuator 41 decreases, the austenite phase is transformed into the martensite phase. By this phase transformation, the SMA actuator 41 extends, the tensile force F1 acting on the displacement input unit 321 disappears, and the lens unit 2 returns to the home position by the bias force.

Thus, the drive unit 4 can displace the lens unit 2 along the optical axis AX by switching the energization ON / OFF to the SMA actuator 41. Further, by adjusting the magnitude of the energization current to the SMA actuator 41, the amount of the tensile force F1 can be adjusted, and the displacement amount of the lens unit 2 can also be adjusted.

SMA also has the characteristic that the resistance value changes according to the phase change. That is, there is a correlation between the resistance value of the SMA actuator 41 and the contraction amount, or the resistance value of the SMA actuator 41 and the position of the lens unit 2. Using this characteristic, the lens driving device La uses the resistance value of the SMA actuator 41 as the position information of the lens unit 2. Note that the SMA actuator 41 is controlled to be supplied with a predetermined current (constant current control). At that time, by measuring the voltage at both ends of the SMA actuator 41, the resistance value of the SMA actuator 41 can be detected from the current value and the voltage value.

Hereinafter, the position control of the lens unit in the lens driving device La will be described with reference to the drawings. FIG. 3 is a block diagram of a main part of the lens driving device shown in FIG. As illustrated in FIG. 3, the lens driving device La includes a driving power source (constant current source) Ps that supplies a driving current to the SMA actuator 41 and a control unit Cont that controls driving of the SMA actuator 41. In the following description, the control unit Cont is described as performing the drive control of the SMA actuator 41, but the present invention is not limited to this, and other controls may be performed.

First, the control unit Cont will be described. The control unit Cont includes an arithmetic processing unit such as a CPU. The control unit Cont detects the resistance value of the SMA actuator, the calculation unit C1, the processing program executed by the calculation unit C1, the storage unit M1 in which information such as information necessary for processing and information obtained by the processing is stored. A resistance detecting unit R1 for measuring time and a time measuring unit Tm for measuring time. In addition, although A / D ports, such as CPU, are utilized as resistance detection part R1 in control part Cont, it is not limited to it.

The resistance detector R1 measures the voltage across the SMA actuator 41 in a state where a predetermined current is flowing, and detects the resistance value of the SMA actuator 41 based on the current value and the voltage value. The calculation unit C1 calculates a drive current value for driving the lens unit 2 to the target position based on the resistance value of the SMA actuator 41 detected by the resistance detection unit R1. The calculation unit C1 instructs the drive power supply Ps to energize the calculated drive current value to the SMA actuator 41.

In order to detect the resistance value when the lens unit 2 is at the home position, a weak current that does not move the lens unit 2 is applied to the SMA actuator 41. The resistance value is detected based on the voltage values at both ends of the SMA actuator 41 at this time, and is set as the resistance value of the SMA actuator 41 when the lens unit 2 is at the home position. When the lens unit 2 is at the home position, the SMA actuator 41 is in the most extended state and the resistance value is the largest.

An autofocus process which is one of position controls in the lens driving device La will be described with reference to the drawings. FIG. 4 is a diagram showing the relationship between the lens position and time when autofocus processing is performed by the lens driving device shown in FIG. 1, and FIG. 5 shows the steps of performing autofocus processing by the lens driving device shown in FIG. It is a flowchart.

As shown in FIG. 4, the control unit Cont sends an instruction to the drive power supply Ps, and applies a current to the SMA actuator 41 so as to move the lens unit 2 stepwise from the home position. The controller Cont stores the resistance value (position information of the lens unit 2) of the SMA actuator 41 and the focus information at each stage, and determines the focus position based on the focus information. Then, the controller Cont energizes the SMA actuator 41 so that the resistance value of the SMA actuator 41 becomes the resistance value at the in-focus position. As a result, the lens unit 2 moves to the in-focus position.

In the autofocus process, as shown in FIG. 4, the lens unit 2 is moved in a plurality of stages to determine the in-focus position. The number of steps for measuring the focus information of the lens unit 2 is arbitrary, but in FIG. 4, the focus information is measured in 15 steps. Although the accuracy of autofocus increases as the number of steps increases, it goes without saying that it takes time to determine the in-focus position.

The details of the autofocus process will be described with reference to FIG. The calculation unit C1 needs to recognize from which stage in FIG. 4 the lens unit 2 is currently moving to the next stage. Therefore, in the autofocus process, an argument N for confirming from which stage the lens unit 2 has moved is used. When the autofocus process is started, the lens unit 2 moves from the home position to the first stage, and 1 is input to the argument N (step S01).

The calculation unit C1 calls the target resistance value R of the SMA actuator 41 from the storage unit M1 based on the argument N (step S02). The target resistance value R is the resistance value of the SMA actuator 41 when the lens unit 2 moves to the next stage position. For example, when the argument N is 1, it is the resistance value after the SMA actuator 41 has moved to the first stage position. At the start of control, the resistance value of the SMA actuator 41 is not detected, and the current value cannot be calculated. Therefore, it is necessary to distinguish between when the lens unit 2 starts from the home position (when control is started) and other times. In order to determine whether or not the focus control is immediately after the start, the calculation unit C1 determines whether or not the argument N is 1 (step S03).

When the argument N is 1 (YES in step S03), the calculation unit C1 recognizes that it is immediately after the driving of the lens unit 2 is started. At this time, the lens unit 2 is at the home position, and the SMA actuator 41 is not energized. The calculation unit C1 sets a predetermined current value for measuring the resistance value of the SMA actuator 41 when the lens unit 2 is at the home position (step S04). As described above, the predetermined current value is a weak current value such that the lens unit 2 does not move, and is called from the storage unit M1.

On the other hand, when the autofocus process is not immediately after starting, that is, when the argument N is not 1 (NO in step S03), the difference value dr of the resistance value calculated in step S08 described later is calculated at least once. . The calculation unit C1 calculates a current value applied to the SMA actuator 41 based on the difference value dr (step S05).

The current value calculated in step S05 is an optimal current value that does not heat the SMA actuator 41 excessively even when applied to the SMA actuator 41. That is, the current value calculated in step S05 generates Joule heat that is optimal for moving the lens unit 2 in the SMA actuator 41, and quickly brings the resistance value r of the SMA actuator 41 close to the target resistance value R (difference value). current value that brings dr close to 0).

The calculation unit C1 instructs the drive power supply Ps to apply the SMA actuator 41 to the SMA actuator 41 with the predetermined current value set in step S04 or the current value calculated in step S05 as the drive current value Ap. The received drive power supply Ps applies a current having a drive current value Ap to the SMA actuator 41 (step S06).

In step S06, after the drive current value Ap is supplied to the SMA actuator 41, the resistance detection unit R1 detects the resistance value r of the SMA actuator 41 (step S07). The method of detecting the resistance value r is as described above, and is performed using the voltage values at both ends of the SMA actuator 41.

The calculation unit C1 calculates a difference value dr between the resistance value r of the SMA actuator 41 detected by the resistance detection unit R1 in step S07 and the target resistance value R called in step S02 (step S08), and the difference value dr is calculated. It is determined whether or not the detected resistance value r is equal to the target resistance value R (step S09). When the difference value dr is 0 (YES in step S09), the calculation unit C1 recognizes that the lens unit 2 has moved to a predetermined position (a predetermined stage in FIG. 4), and at that time, an image sensor or the like is used. Then, focus information is detected (step S10).

Then, the focus information detected in step S10 and the resistance value r are stored in a database provided in the storage unit M1 (step S11). As the focus information, contrast information extracted from image information obtained from an image sensor or the like is used, but the focus information is not limited thereto. In step S11, after the focus information and the resistance value r are stored in the database, 1 is added to the current argument N as an argument to obtain a new argument N (step S12). Returning to step S02, using the new argument N, the calculation unit C1 repeats from the setting of the target resistance value R in the next stage.

On the other hand, the movement of the lens unit 2 is restricted by contact with the movement restriction unit 5 of the lens unit 2 while a current larger than a predetermined current value (current threshold value As) flows through the SMA actuator 41. As a result, the internal stress of the SMA actuator 41 increases. At this time, the temperature of the SMA actuator 41 also rises, and the stress further rises due to the temperature rise. When the stress of the SMA actuator 41 exceeds the limit stress, the SMA actuator 41 deteriorates, and when the deterioration progresses, it breaks.

Here, the current threshold value As is the maximum current value (maximum current) when the SMA actuator 41 is heated rapidly when applied to the SMA actuator 41 and the stress due to the temperature rise does not exceed the limit stress of the SMA actuator 41. In addition, the current value when the resistance value r becomes the target resistance value R does not become the current threshold value As, and the current that allows the displacement input unit 321 to continue to input the tensile force that can stop the lens unit 2. Value (smaller than the current threshold As).

The difference value dr between the resistance value r of the SMA actuator 41 and the target resistance value R does not become 0, and the duration time during which the drive current value Ap continuously exceeds the current threshold value As is acting on the SMA actuator 41. When the limit time set smaller than the sum of the times when the stress exceeds the limit stress is exceeded, it can be determined that the lens unit 2 is stopped. The controller Cont controls the SMA actuator 41 in accordance with this theory.

That is, when the difference value dr is not 0 in step 09 (that is, the detected resistance value r is different from the target resistance value R), the calculation unit C1 compares the drive current value Ap with a predetermined current threshold value As. (Step S13). When the drive current value Ap is smaller than the current threshold As (NO in step S13), the calculation unit C1 determines that the resistance value r of the SMA actuator 41 is larger than the target resistance value R and / or the current value is small. Recognize and return to step S05 to recalculate the current value.

When the drive current value Ap is greater than the current threshold value As (YES in step S13), the calculation unit C1 calls an elapsed time in which the drive current value Ap is continuously greater than the current threshold value As from the time measuring unit Tm, and the elapsed time. Is determined to exceed a predetermined time (limit time) (step S14). When the elapsed time does not exceed a predetermined time (limit time) (NO in step S14), the control unit Cont is in the middle of contracting operation of the SMA actuator 41 and the lens unit 2 is moving. Then, the process returns to step S07 while maintaining the energized state, and the resistance value r of the SMA actuator 41 is detected.

When the elapsed time exceeds the predetermined time (in the case of YES at step S14), the calculation unit C1 recognizes that the lens unit 2 is stopped (in contact with the movement limiting unit 5, etc.), and turns on the power source Ps. An instruction is sent to stop energization of the SMA actuator 41 (step S15), and driving of the SMA actuator 41 is stopped. Thereby, the heating of the SMA actuator 41 is stopped (cooled), the SMA actuator 41 extends, and the lens unit 2 returns to the home position.

As described above, the stage to which the movement shown in FIG. 4 is confirmed using the argument, and the target resistance value R is changed for each stage, thereby moving the lens unit 2 to the next stage. The target resistance value can be accurately called and the lens unit 2 can be moved accurately. The database of the storage unit M1 stores the resistance value and focus information of the SMA actuator 41 at each stage, and the calculation unit C1 determines the in-focus position based on each focus information, and the SMA actuator at that time A resistance value rp of 41 is determined.

The calculation unit C1 calculates a drive current value based on the resistance value rp at the in-focus position, and sends an instruction to the drive power supply Ps so as to energize the SMA actuator 41 with the drive current value. When the driving power source Ps energizes the SMA actuator 41 and the operation unit C1 confirms that the resistance value detected by the resistance detection unit R1 is the resistance value rp at the in-focus position, the lens driving device La is the lens unit. 41 is moved to the in-focus position, and the autofocus process is completed (see FIG. 4). After the subject image is picked up by the image pickup device at the in-focus position, the calculation unit C1 sends an instruction to the drive power source Ps and ends the energization of the SMA actuator 41. Thereby, the force from the SMA actuator 41 acting on the lens unit 2 is reduced, and the lens unit 2 returns to the home position. Note that the contents of the database storing the resistance value and the focus information in the storage unit M1 may be erased or kept after the imaging is completed.

As described above, in the lens driving device La, the resistance detection unit R1 serves as a position sensor for detecting the position of the lens unit, but detects the position of the lens unit 2 instead of the resistance detection unit R1. A position sensor may be provided. In that case, the calculation unit C1 uses the position information of the lens unit from the position sensor instead of the resistance value of the SMA actuator 41 to perform positioning control of the lens unit 2 (determination of the drive current value to the SMA actuator 41). Is possible. Further, both the resistance value and the position information may be detected, and the drive current value may be determined using both information. Since the resistance of the SMA actuator 41 increases, the degree of deterioration of the SMA actuator 41 can be confirmed by comparing the resistance value and the position information.

In the positioning control of the lens unit described above, the control (constant current control) is performed with the current value supplied to the SMA actuator 41, but the control (constant voltage control) is performed with the applied voltage. There may be.

When the contraction of the SMA actuator 41 is restricted in a state where a current exceeding a predetermined value flows, the temperature rapidly increases. The SMA actuator 41 also has a characteristic that stress increases as the temperature rises in a state where the length does not change. When the lens unit 2 comes into contact with the movement restricting unit 5 and stops moving in the lens driving device La, the increase in stress due to the inhibition of the contraction of the SMA actuator 41 and the increase in stress due to the temperature rise are integrated. . That is, when a current of a predetermined value or more flows through the SMA actuator 41 in a state where the movement of the lens unit 2 is stopped, the internal stress of the SMA actuator 41 rapidly increases even for a short time. The SMA actuator 41 is deteriorated by a sudden increase in internal stress.

Therefore, the lens driving device La using the driving device of the present invention is provided with a moving direction converting portion 25 protruding in the axial direction from the spring receiver 24 in order to suppress a rapid increase in internal stress of the SMA actuator 41. Yes. The operation after the lens driving device using the driving device according to the present invention comes into contact with the movement limiting unit will be described with reference to the drawings. 6 is a side view when the moving direction conversion unit of the lens driving device shown in FIG. 1 comes into contact with the movement restricting unit, and FIG. 7 is when the lens driving frame of the lens driving device shown in FIG. 6 rotates. FIG.

In the lens driving device La, the moving direction converting portion 25 protrudes toward a movement restricting portion 5 from a part of the spring receiver 24 (a position having an angle difference of 90 degrees with each of the pair of supporting portions 23). When the movement direction conversion unit 25 contacts the movement restriction unit 5, the movement of the lens drive frame 22 in the direction along the optical axis AX is restricted. At this time, the maximum current (or current exceeding it) flows through the SMA actuator 41. Here, as described above, the maximum current is a maximum current value at which when the SMA actuator 41 is suddenly heated when applied to the SMA actuator 41, the stress due to the temperature rise does not exceed the limit stress of the SMA actuator 41. . When a force from the displacement output unit 311 is applied to the support unit 23 in a state where the movement direction conversion unit 25 is in contact with the movement restriction unit 5, the lens driving frame 22 has a spring bearing around the movement direction conversion unit 25. A moment Mt that rotates the other part of the 24 in a direction in contact with the movement restriction unit 5 acts (see FIG. 6).

At this time, the lens driving frame 22 can be rotated around the moving direction conversion unit 25, and the lens driving frame 22 moves while elastically deforming the upper leaf spring 71 and the lower leaf spring 72 by the action of the moment Mt. It rotates around the direction changer 25 (see FIG. 7). Although the SMA actuator 41 is in a state where a maximum current (or a current exceeding it) flows, the SMA actuator 41 can contract while the lens driving frame 22 rotates, and the stress is prevented from increasing rapidly. be able to. During this rotation, the control unit Cont can detect that the lens unit 2 is in contact with the movement limiting unit 5 and the lens unit 2 is stopped. And since the control part Cont can stop electricity supply before a limit stress acts on the SMA actuator 41, degradation of the SMA actuator 41 can be suppressed. It should be noted that the shape and size of the movement direction conversion unit 25 is determined so that the lens drive frame 22 is rotated for a predetermined time after the movement direction conversion unit 25 contacts the movement restriction unit 5 (in step S14 in FIG. 5). The predetermined time is preferably exceeded.

Since the deterioration of the SMA actuator 41 can be suppressed by using the driving device shown above, a driving device that can stably drive the driven object (lens unit 2) with high accuracy over a long period of time is provided. It is possible. In the above configuration, the SMA actuator 41 is controlled by the current value applied to the SMA actuator 41, but is not limited thereto, and may be performed by the voltage value.

A lens driving device using another example of the driving device according to the present invention will be described with reference to the drawings. FIG. 8 is a side view of a lens driving device using another example of the driving device according to the present invention, and FIG. 9 is a side view showing a state where the lens driving device shown in FIG. 8 is in contact with the movement restricting portion. The lens driving device Lb has one support portion 23b formed on the lens drive frame 22b, and the SMA actuator 41 is directly engaged with the support portion 23b. Other portions have the same configuration as the lens driving device La, and substantially the same portions are denoted by the same reference numerals. Detailed descriptions of substantially the same parts are omitted.

As shown in FIGS. 8 and 9, the SMA actuator 41 is inclined with respect to the moving direction of the lens driving frame 22b. As the SMA actuator 41 contracts, a driving force in the optical axis AX direction acts on the lens driving frame 22b.

The moving direction converting portion 25 is arranged side by side in the radial direction of the support portion 23b and the lens driving frame 22b in plan view. When the SMA actuator 41 contracts in a state where the movement direction conversion unit 25 is in contact with the movement restriction unit 5, a moment that rotates the lens drive frame 22b around the movement direction conversion unit 25 acts. By this moment, the lens driving frame 22b rotates while elastically deforming the upper leaf spring 71 and the lower leaf spring 72. Even during this rotation, the SMA actuator 41 can be contracted while a maximum current (or a current exceeding it) is applied. Therefore, a rapid increase in stress of the SMA actuator 41 can be suppressed, and deterioration of the SMA actuator 41 can be suppressed. It is possible.

A lens driving device using still another example of the driving device according to the present invention will be described with reference to the drawings. FIG. 10 is a plan view of a lens driving device using still another example of the driving device according to the present invention, and FIG. 11 is a side view of the lens driving device shown in FIG. The lens driving device Lc has the same configuration as the lens driving device Lb except that it includes a lens driving frame 22c and a guide shaft 26 extending in the optical axis AX direction as a guide for the lens driving frame 22c. The same parts are denoted by the same reference numerals. Detailed descriptions of substantially the same parts are omitted.

In the lens driving device Lc shown in FIG. 10, a cylindrical guided portion 221c is formed on the outer periphery of the lens driving frame 22c, and the guide shaft 26 penetrates the guided portion 221c. The inner diameter of the guided portion 221 c is formed larger than the outer diameter of the guide shaft 26, and the guided portion 221 c is loosely fitted on the guide shaft 26. The bias spring 8c is externally fitted to the guide shaft 26. One end of the bias spring 8c is in contact with the guided portion 221c and the other end is in contact with the movement restricting portion 5, and the guided portion 221c is brought into contact with the base portion 1. A force is applied (downward in FIG. 11). Further, in the lens driving frame 22c, the support portion 23c is formed on the opposite side of the imaging lens with the guide shaft 26 of the guided portion 221c interposed therebetween.

The SMA actuator 41 is formed in a V shape that is folded back by the support portion 23c in plan view. Furthermore, both end portions of the SMA actuator 41 are fixed to the electrode 42 and are fixed at positions closer to the movement limiting portion 5 in the optical axis AX direction than the support portion 23c of the electrode 42. As a result, when the SMA actuator 41 contracts, a driving force toward the movement restricting portion 5 along the guide shaft 26 acts on the support portion 23c.

Further, in the lens driving frame 22c, the moving direction converting portion 25c is formed at a position where the central angle about the central axis of the guided portion 221c and the lens driving frame 22c is 90 degrees. As shown in FIG. 11, when the lens drive frame 22c comes into contact with the movement restriction unit 5, the lens driving frame 22c rotates around the movement direction conversion unit 25c. By forming the moving direction converting portion 25c so as to be 90 degrees with the guided portion 221c, even if the gap between the guided portion 221c and the guide shaft 26 is small, the rotation amount of the lens driving frame 22c may be increased. Is possible. In addition, the movement direction conversion part 25c is not limited to a 90 degree position with respect to the to-be-guided part 25c.

A lens driving device using another example of the driving mechanism according to the present invention will be described with reference to the drawings. FIG. 12 is a side view of a lens driving device using another example of the driving device according to the present invention. The lens drive device Ld shown in FIG. 12 has the same configuration as the lens drive device La except that the movement direction conversion unit 25d and the movement restriction unit 5d are different, and substantially the same parts are denoted by the same reference numerals. . Detailed descriptions of substantially the same parts are omitted.

As shown in FIG. 12, the movement direction conversion section 25d of the lens driving device Ld has an end face 251d on the movement limiting section 5d side formed obliquely. Further, the movement restricting portion 5d includes a convex portion 51d, and the tip portion of the convex portion 51d is formed to be parallel or substantially parallel to the end surface 251d of the moving direction converting portion 25d. When the lens driving frame 22d moves toward the movement restricting portion 5d and the end surface 251d of the moving direction converting portion 25d comes into contact with the convex portion 51d of the movement restricting portion 5d, the end surface 251d moves along the convex portion 51d. The moving direction of the frame 22d is changed in a direction along the movement restricting portion 5d. As a result, the SMA actuator 41 can continue to contract even after the lens drive frame 22d and the movement restricting portion 5d come into contact with each other, so that an abrupt increase in stress can be suppressed and deterioration can be suppressed.

The present invention can be used for a driving device that moves a minute member such as an imaging lens of a digital camera.

DESCRIPTION OF SYMBOLS 1 Base part 2 Lens unit 21 Imaging lens 22 Lens drive frame 23 Support part 24 Spring receiver 25 Movement direction conversion part 3 Lever part 31 Arm part 311 Displacement output part 32 Extension part 321 Displacement input part 4 Drive part 5 Movement restriction part 6 Top plate portion 71 Upper plate spring 72 Lower plate spring 8 Bias spring

Claims

A drive frame for holding a driven object;
A guide portion for guiding the drive frame to move in a predetermined direction;
A shape memory alloy actuator for applying a driving force for moving the driving frame;
A movement restriction unit that contacts the drive frame when the drive frame moves to an end of the movable range and restricts the movement of the drive frame;
The drive frame moves by the driving force of the shape memory alloy actuator, and includes a delay unit that delays the time until the movement limit unit comes into contact immediately before the movement limit unit restricts the movement. A drive device characterized by the above.
2. The drive device according to claim 1, wherein the delay unit is a movement direction conversion unit that moves a movement direction of the drive frame in a direction different from the predetermined direction in the vicinity of the movement restriction unit.
A position sensor for detecting the position of the drive frame;
The power supply applied to the shape memory alloy actuator is controlled based on the position information detected by the position sensor, and the movement of the drive frame in a direction different from the predetermined direction is detected by the position sensor. The drive device according to claim 2, further comprising: a controller that performs emergency stop control for stopping power supply to the shape memory alloy actuator.
The drive device according to claim 3, wherein the position sensor includes a resistance detection unit that detects a change in electrical resistance of the shape memory alloy actuator.
The drive unit according to claim 3, wherein the control unit performs the emergency stop control when a predetermined maximum current or maximum voltage is applied to the shape memory alloy actuator for a predetermined time or more.
The drive device according to claim 1, wherein the shape memory alloy actuator is linear.
The drive device according to claim 1, wherein the guide portion includes a pair of flat plate springs that hold both ends of the drive frame in the moving direction and are arranged in parallel to each other.
3. The driving device according to claim 2, wherein the moving direction converting portion is formed so that a rotational moment acts on the driving frame when the moving direction changing portion comes into contact with the movement restricting portion.
The driving device according to claim 8, wherein the moving direction conversion unit is a protruding portion that protrudes toward the movement limiting unit from an edge portion of a surface of the driving frame that faces the movement limiting unit.
The movement direction conversion part is formed on a surface of the drive frame that faces the movement restriction part, and the movement restriction part includes a convex part that contacts the movement direction conversion part,
The drive device according to claim 2, wherein at least one of the tip of the moving direction converting portion and the convex portion is cut obliquely.
A lens driving device for driving an imaging lens using the driving device according to claim 1.