JP5029260B2 - Drive device - Google Patents

Description

  The present invention relates to a driving device and a lens driving device, and more particularly to a driving device and a lens driving device provided with a shape memory alloy wire.

  In recent years, attempts have been made to use shape memory alloy wires (hereinafter also referred to as SMA) for various driving devices. Such a drive device utilizes the property that even if the SMA is deformed at a temperature lower than the transformation temperature, it is restored to the original shape stored when heated to a temperature higher than the transformation temperature. Usually, SMA is formed in a string-like form, and can be operated as an actuator by expanding and contracting in the length direction by energization heating control.

  On the other hand, since the SMA is deformed only in the return direction to the memorized shape, in use, another actuator that deforms the SMA in the direction opposite to the return direction is required. For this reason, SMA is usually used in a configuration in which it is set with a biasing spring. By making the SMA an actuator with a set that is inexpensive and does not require control, the device can be simplified and reduced in price, and application to various devices is being studied.

For example, the lens support frame is provided with an SMA and a spring that urges the lens support frame so as to be movable in directions opposite to each other. Thus, a lens driving device that moves the lens support frame to a predetermined position is known (see Patent Document 1).
JP 2005-337262 A

  By the way, in such a device, SMA is used on the premise of an ideal property that does not deform at a temperature lower than the reaction temperature (transformation temperature) at all, and deforms in a straight line at a temperature higher than the reaction temperature. ing. However, in practice, SMA deforms slightly even at a temperature lower than the reaction temperature, and the deformation rate increases as the reaction temperature is approached.

  The lens driving device disclosed in Patent Document 1 does not consider such properties at temperatures lower than the reaction temperature of SMA. That is, even in a normal temperature region where the environmental temperature is lower than the reaction temperature of SMA, the SMA is slightly deformed due to a change in the environmental temperature, so that the position of the lens changes, and the lens cannot maintain a fixed position. Therefore, in particular, in lens driving such as control of the amount of extension from an infinite position used in an autofocus camera, there is a problem that the lens moves from the infinite position due to a change in environmental temperature and the photographing range is narrowed, greatly affecting AF performance.

  In addition, SMA has an austenite transformation start point (As point) at which a rapid reaction starts with heating, an austenite transformation end point (Af point) at which the reaction deteriorates at a higher temperature, and the reaction becomes saturated and becomes a memory state Thereafter, it has a martensitic transformation start point (Ms point) at which a rapid reverse reaction starts again as it cools, and a martensitic transformation end point (Mf point) at which the rapid reverse reaction is switched to a slow reaction. is doing. The relationship between the SMA temperature and the strain rate shows hysteresis, and the As point and the Mf point are similar in strain rate (slightly larger strain rate at the Mf point), but the temperature is higher at the As point. Similarly, the Af point and the Ms point have similar strain rates (slightly higher strain rate at the Ms point), but the temperature is higher at the Af point.

  Thus, since the relationship between the SMA temperature and the distortion rate shows hysteresis, when the environmental temperature is higher than the Mf point, the position of the lens before the SMA is energized and heated, the SMA is energized and heated, and then energized. The position of the lens when the SMA is stopped and the temperature of the SMA returns to the ambient temperature after cooling is greatly different. As a result, there is a problem that the AF performance is further lowered.

  The present invention has been made in view of the above problems, and provides a driving device and a lens driving device capable of performing position control of a driven body with high accuracy without being affected by environmental temperature. Objective.

The above object is achieved by the invention described in 1 or 2 below.

1. A shape memory alloy wire that contracts and expands by electric heating and deforms;
A driven body moved by deformation of the shape memory alloy wire;
A drive unit having
A lens supported by the driven body;
In a lens driving device comprising:
The lens driving device further includes:
A bias unit for applying a bias force in a direction opposite to the direction of movement by contraction due to heating of the shape memory alloy wire;
A restriction portion for restricting the driven body that the shape memory alloy wire extends and moves by the bias force when the shape memory alloy wire is not energized;
Have
One end of the effective movement range of the driven body is an infinite position of the lens, and the other end is a closest position of the lens,
When the energization to the shape memory alloy wire is turned off, the driven body is moved out of the effective movement range by the restricting portion at a predetermined upper limit temperature set as an upper limit value of the use environment temperature range of the lens driving device. Is in a regulated state,
The driven body is in contact with the restricting portion at a predetermined upper limit temperature set for a use environment temperature range of the lens driving device when extending the energization to the shape memory alloy wire, and the At the time of extension by cooling after the driven body leaves the restricting portion due to contraction due to energization heating to the shape memory alloy wire, the shape memory alloy wire is in contact with the restricting portion until the shape memory alloy wire falls to the predetermined upper limit temperature. The effective movement range is set so as not to
The effective movement range is set such that the distortion rate of the shape memory alloy wire corresponding to the effective movement range is smaller than the distortion rate at the time of non-energization in the operating environment temperature range. apparatus.

2. The upper limit of the ambient temperature range, according to the 1, wherein the higher than corresponding temperatures martensite transformation finish point of the shape memory alloy wire was low Ku set than a temperature corresponding to a austenite transformation start point Drive device.

  According to the present invention, the effective movement range is set so that the distortion rate of the shape memory alloy wire corresponding to the effective movement range of the driven body is smaller than the distortion rate at the time of non-energization in the use environment temperature range. . That is, the configuration is such that the position of the driven body when not energized in the operating environment temperature range is located outside the effective movement range. Therefore, the effective movement range of the driven body is maintained within a predetermined range without being affected by the position change of the driven body due to a change in the environmental temperature or the positional deviation of the driven body at the environmental temperature before and after the energization heating due to hysteresis. Is done. As a result, the position of the driven body can be controlled with high accuracy.

  Further, since the lens is supported by the above-mentioned driven body, the focal position of the lens can be controlled with high accuracy, and the AF performance can be improved.

  Embodiments of a driving device and a lens driving device according to the present invention will be described below with reference to the drawings. In addition, although this invention is demonstrated based on embodiment of illustration, this invention is not limited to this embodiment.

Embodiment 1
First, the main configuration of the driving apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a schematic diagram illustrating a main configuration of a driving apparatus 10 according to the first embodiment.

  As shown in FIG. 1, the driving device 10 has a SMA 102 that reacts abruptly at a predetermined temperature and contracts in a predetermined direction (arrow Y1 direction), and loads in a direction opposite to the contraction direction of the SMA 102 (arrow Y2 direction). , The driven body 101 that is moved to a position where both forces are balanced, a drive circuit (not shown) that controls energization of the SMA 102, and the SMA 102 Is configured by a stopper 104 or the like that restricts the movement of the driven body 101 pulled by the bias spring 103 when the current is not energized.

  The temperature of the SMA 102 is controlled by its own Joule heat by energization. The SMA 102 exhibits superelasticity when it is not energized in a use environment, and is stretched with a light load. The driven body 101 is pressed against the stopper 104 by the tension of the bias spring 103. The tension of the bias spring 103 is set to be relatively large although it is smaller than the allowable stress of the SMA 102. The stress applied to the SMA 102 at the center temperature under the use environment is set to be less than the stress corresponding to the tension of the bias spring 103.

  Here, the relationship between the temperature and strain of the SMA 102 will be described with reference to FIG. FIG. 2 is a diagram showing the relationship between the temperature and strain rate of the SMA 102.

  As shown in FIG. 2, the SMA 102 is saturated with the austenite transformation start point (As point) at which a rapid reaction starts with heating and the austenite transformation end point (Af point) at which the reaction deteriorates at a higher temperature. After entering the memory state, the martensite transformation start point (Ms point) at which a rapid reverse reaction starts again with cooling, and the martensite transformation end point (Mf point) at which the rapid reverse reaction is switched to a slow reaction. ) And. Further, the relationship between the temperature and the strain rate of the SMA 102 shows hysteresis, and the As point and the Mf point have similar strain rates (slightly higher strain rate at the Mf point), but the temperature is higher at the As point. Similarly, the Af point and the Ms point have similar strain rates (slightly higher strain rate at the Ms point), but the temperature is higher at the Af point.

  The switching point (As point, Af point, Ms point, Mf point) of each reaction is ideally switched at an acute angle, but a Ti and Ni alloy in which a relatively rapid switching occurs, or Ti Even SMA made of an alloy of Ni and Cu shows a mild reaction. As shown in FIG. 2, each reaction switching point is determined by the intersection of the tangents of the linear reaction regions.

  Since the memory state of the SMA is determined, the distortion rate varies depending on the initial stress applied to the SMA. If the initial stress is large, the strain rate is large, and if it is small, the strain rate is small. Also, the reaction temperature increases with the distortion rate.

  That is, the reaction due to temperature differs depending on in which region the strain (stroke) used to drive the driven body 101 is used.

  In the driving apparatus 10 having the configuration shown in FIG. 1, since the stress of the SMA 102 is balanced with the tension of the bias spring 103 during driving, the relationship between the temperature and the strain rate of the SMA 102 is a solid curve shown in FIG. Although it moves up, it is located at the left end Po point on the reaction curve (dashed line) at the time of low stress at the time of deenergization. Note that the stress of the SMA 102 at this time is smaller than the tension of the bias spring 103, and the driven body 101 is pressed against the stopper 104. As the reaction progresses, the SMA 102 generates a force to return to the memory state, but if it is equal to or lower than the driving stress, the driven member 101 does not move and only the stress increases (arrow X1). The driven body 101 is finally moved when the stress of the SMA 102 exceeds a value that balances with the tension of the bias spring 103. The balanced position corresponds to the position Ps of the initial set strain on the reaction curve (solid line) at the time of driving stress.

  Here, the movement of the SMA 102 when the environmental temperature is higher than the Mf point, for example, at t1 shown in FIG. 2, will be described with reference to FIGS. When the SMA 102 is energized and heated, the stress of the SMA 102 increases as described above, and the SMA 102 contracts along the solid line from the Ps point toward the Af point. When the energization is stopped after contracting a predetermined amount, the SMA 102 is cooled and extended toward the Mf point along the solid line on the return side, and reaches equilibrium at the Pt1 point corresponding to the environmental temperature t1. That is, when the environmental temperature is higher than the Mf point, the distortion rate (elongation) of the SMA 102 is d1 as shown in FIG. A difference occurs, and the distortion rate corresponding to the Ps point before energization overheating does not return. That is, the reference position of the driven body 101 when the SMA 102 is not energized and heated changes. As a result, the use area of the driven body 101 shown in FIG. 2, that is, the effective movement range changes (narrows), and it becomes difficult to control the position of the driven body 101 with high accuracy.

  Therefore, in order to cope with such a problem, the driving apparatus 10 according to the first embodiment of the present invention has a distortion rate (elongation) of the SMA 102 corresponding to the effective movement range of the driven body 101 in the use environment temperature range. The effective movement range is set to be smaller than the distortion rate (elongation) at the time of non-energization. In other words, the configuration is such that the position of the driven body 101 when not energized in the operating environment temperature range is located outside the effective movement range.

  Specifically, as shown in FIG. 1, the reference position Pi point for driving and controlling the driven body 101 is set to a contraction direction (arrow Y1) of the SMA 102 more than the position Pt1 point of the driven body 101 at the temperature t1 described above. (Direction), that is, a position separated by a predetermined amount d2 in a direction in which the distortion rate (elongation) decreases, and the effective movement range D of the driven body 101 is set from the reference position Pi point to the Pn point. Here, the temperature t1 is the upper limit value of the operating temperature range, and is higher than the Mf point and lower than the As point.

  Thereby, the effective movement range D of the driven body 101 is not affected by the position change of the driven body 101 due to the change of the environmental temperature, the positional deviation of the driven body 101 at the environmental temperature before and after the energization heating due to the hysteresis, and the like. A predetermined range is maintained. As a result, the position of the driven body 101 can be controlled with high accuracy.

  In the driving apparatus 10 according to the present embodiment, the relationship between the temperature and the strain rate of the SMA 102 moves on a response curve (broken line) at low stress when not energized, and a response curve (solid line) at driving stress during driving. Although the configuration is such that it moves upward, the same effect can be obtained even when it is configured to move on the response curve (solid line) at the time of driving stress both during non-energization and during driving.

[Embodiment 2]
The main configuration of the lens driving device according to the second embodiment will be described with reference to FIG. FIG. 3 is a schematic diagram illustrating a main configuration of the lens driving device 1 according to the second embodiment.

  The lens driving device 1 is a camera focus adjusting device using the driving device 10 described above. The lens driving device 1 moves the lens 110 to the in-focus position based on distance information from a distance measuring unit (not shown).

  The lens 110 is fixed to a driven body 101 that is movably supported by the movement guide 106. The lens 110 is configured to be movable from a position Ps where the driven body 101 is pressed against the stopper 104 by the bias spring 103 to a closest position Pn indicated by a broken line. When the SMA 102 is energized from a drive circuit (not shown), the stress of the SMA 102 becomes equal to or greater than the stress of the bias spring 103 and the lens 110 is extended along the movement guide 106 in the direction of the arrow Y1.

  As in the case of the driving device 10 according to Embodiment 1 described above, the lens driving device 1 having such a configuration is greatly affected by hysteresis when the environmental temperature is higher than the Mf point, and the environmental temperature is the same t1. Regardless, the difference in d1 occurs in the distortion rate (elongation) of the SMA 102 before and after energization heating. As a result, the lens 110 does not return to the Ps point before energization heating, and balances at the Pt1 point. That is, the reference position of the driven body 101 when the SMA 102 is not energized and heated changes.

  Therefore, as in the case of the driving device 10, as shown in FIG. 3, the reference position Pi point (infinite position) when driving the lens 110 is set to be SMA 102 more than the position Pt1 point of the lens 110 at the temperature t1. Is set at a position separated by a predetermined amount d2 in the shrinking direction (arrow Y1 direction), that is, in a direction in which the distortion rate (elongation) decreases, and the effective movement range D of the driven body 101 is recently set from the reference position Pi point (infinity position) The contact position Pn point is used.

  As a result, the effective movement range D of the lens 110 is maintained within a predetermined range without being influenced by the environmental temperature even when the environmental temperature is higher than the Mf point. As a result, the position of the lens 110 can be controlled with high accuracy between the infinite position Pi point and the closest position Pn point. In this embodiment, Pi and Pn are the infinite position and the closest position of the lens 110, respectively, but Pi and Pn may be the closest position and the infinite position of the lens 110, respectively.

  Here, driving control of the lens driving device 1 having such a configuration will be described with reference to FIG. FIG. 4 is a diagram illustrating the relationship between the movement amount of the lens 110 and the resistance value of the SMA 102.

  Normally, the resistance value of the SMA 102 decreases with transformation. Since the lens 110 is moved by contraction of the SMA 102, the resistance value decreases as the lens 110 moves. A drive circuit (not shown) and both ends of the SMA 102 are connected, and the SMA 102 is energized and heated. If the resistance value before energization is Ro at the position where the lens 110 is in contact with the stopper 104, the resistance value decreases as energization starts. When the lens 110 is heated to a temperature corresponding to the Ps point in FIG. 2, the lens 110 is separated from the stopper 104, and the resistance value at this time is Rs. As the heating continues, the lens 110 reaches the infinitely focused position Pi, and the resistance value becomes Ri. If the resistance value at the point P at which the subject is in focus is R, the drive circuit controls energization by a method such as feedback control so that the resistance value becomes R while detecting the resistance value of the SMA 102.

  Here, when the environmental temperature is the above-described t1, after the energization is stopped, the lens 110 does not return to the position Ps point of the stopper 104 but is positioned at the Pt1 point shown in FIG. Assuming that the resistance value at this time is Rt1, in the configuration of the present embodiment, since Rt1> Ri, the electric heating control is performed from this position Pi point to Ri (resistance value at the infinitely focused position Pi point). And Rn (the resistance value at the closest position Pn) can be moved to a position corresponding to an arbitrary resistance value. That is, even at the environmental temperature t1, the position control of the lens 110 can be performed with high accuracy between the infinite position Pi point and the closest position Pn point.

It is a schematic diagram which shows the principal part structure of the drive device which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between the temperature of SMA, and a distortion. It is a schematic diagram which shows the principal part structure of the lens drive device which concerns on Embodiment 2 of this invention. It is a figure which shows the relationship between the movement amount of a lens, and the resistance value of SMA.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens drive device 10 Drive device 101 Driven object 102 SMA
103 Bias spring 104 Stopper 105 Fixing member 106 Movement guide 110 Lens

Claims (2)

A shape memory alloy wire that contracts and expands by electric heating and deforms;
A driven body moved by deformation of the shape memory alloy wire;
A drive unit having
A lens supported by the driven body;
In a lens driving device comprising:
The lens driving device further includes:
A bias unit for applying a bias force in a direction opposite to the direction of movement by contraction due to heating of the shape memory alloy wire;
A restriction portion for restricting the driven body that the shape memory alloy wire extends and moves by the bias force when the shape memory alloy wire is not energized;
Have
One end of the effective movement range of the driven body is an infinite position of the lens, and the other end is a closest position of the lens,
When the energization to the shape memory alloy wire is turned off, the driven body is moved out of the effective movement range by the restricting portion at a predetermined upper limit temperature set as an upper limit value of the use environment temperature range of the lens driving device. Is in a regulated state,
The driven body is in contact with the restricting portion at a predetermined upper limit temperature set for a use environment temperature range of the lens driving device when extending the energization to the shape memory alloy wire, and the At the time of extension by cooling after the driven body leaves the restricting portion due to contraction due to energization heating to the shape memory alloy wire, the shape memory alloy wire is in contact with the restricting portion until the shape memory alloy wire falls to the predetermined upper limit temperature. The effective movement range is set so as not to
The effective movement range is set such that the distortion rate of the shape memory alloy wire corresponding to the effective movement range is smaller than the distortion rate at the time of non-energization in the operating environment temperature range. apparatus. The upper limit of the use environment temperature range is set higher than a temperature corresponding to a martensite transformation end point of the shape memory alloy wire and lower than a temperature corresponding to an austenite transformation start point. Drive device.

Images