JP2019031962A - Controller and tactile feeling provision device - Google Patents

Abstract

To provide a technology capable of preventing change of output acceleration of an SMA actuator resulting from change of an environmental temperature.SOLUTION: A controller 16 of a shape memory alloy actuator 20 using a shape memory alloy-based expandable member 24 capable of expanding/contracting with temperature change, comprises: a temperature information acquisition unit 30 configured to acquire temperature information indicating an environmental temperature around the expandable member 24; and an electrification control unit 32 configured to set application voltage applied to the expandable member 24 based on the temperature information acquired by the temperature information acquisition unit 30, and electrify the expandable member 24 with the set application voltage. The electrification control unit 32 is configured to set the application voltage lower as the environmental temperature becomes higher.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a control device for a shape memory alloy actuator and a tactile sensation imparting device using them.

  2. Description of the Related Art Conventionally, a shape memory alloy actuator using a shape memory alloy (SMA) (hereinafter also simply referred to as an SMA actuator) is known as an actuator that can be miniaturized. The SMA actuator includes an expansion / contraction member made of a shape memory alloy, and can drive other driven elements by using expansion / contraction due to a temperature change of the expansion / contraction member.

  Patent Document 1 describes an energization control device that drives an expandable member by controlling energization of the expandable member. This energization control device drives a telescopic member by applying a constant voltage to the telescopic member.

JP 2006-183564 A

  When this inventor examined the indication technique of patent document 1, the following knowledge was acquired. When a constant voltage is applied to the expansion / contraction member regardless of the ambient temperature around the expansion / contraction member, the output acceleration, which is the acceleration of the driven element driven by the output of the SMA actuator, is greatly increased due to the change in the environmental temperature. It will change. Since it is not preferable that the output temperature of the SMA actuator is significantly changed by the environmental temperature, the improvement is desired.

  An aspect of the present invention is made in view of such a problem, and one of the objects is to provide a technique capable of suppressing a change in output acceleration of an SMA actuator caused by a change in environmental temperature.

  The first aspect of the present invention is a control device. The control device according to the first aspect is a control device for a shape memory alloy actuator using a shape memory alloy expansion / contraction member that can be expanded and contracted by a temperature change, and acquires temperature information indicating an ambient temperature around the expansion member. A temperature information acquisition unit; and an energization control unit configured to set an applied voltage to be applied to the elastic member based on the temperature information acquired by the temperature information acquisition unit, and to energize the elastic member by the set application voltage; The energization control unit sets the applied voltage to be lower as the environmental temperature is higher.

  According to this aspect, a large change in the output acceleration of the SMA actuator due to a change in the environmental temperature can be suppressed as compared with a case where a constant voltage is applied regardless of the environmental temperature.

It is a graph which shows the relationship between the output acceleration of a SMA actuator, and environmental temperature. It is a graph which shows the relationship between the electricity supply time with respect to an expansion-contraction member, and the output displacement amount of a SMA actuator. It is another graph which shows the relationship between the electricity supply time with respect to an expansion-contraction member, and the output displacement amount of a SMA actuator. It is a block diagram which shows the tactile sensation providing apparatus of 1st Embodiment. It is a schematic diagram which shows a part of electric equipment of 1st Embodiment. It is a side view which shows an example of the SMA actuator of 1st Embodiment. It is a figure which shows the resistance-temperature characteristic of the expansion-contraction member of 1st Embodiment. (A) is a figure which shows the correspondence of environmental temperature and applied voltage of 1st Embodiment, (b) is a figure which shows another correspondence. It is a block diagram which shows the tactile sensation providing apparatus of 2nd Embodiment.

First, the background of the present invention will be described. FIG. 1 is a graph showing the relationship between the output acceleration A of the SMA actuator and the environmental temperature Te. Here, the elastic member was energized under various conditions of the environmental temperature Te and under the following conditions. In this example, the reverse transformation start temperature _TAs is about 85 ° C., and the stretchable member is formed using a Ni—Ti-based shape memory alloy.
-The heating start temperature of the expansion / contraction member is the same as the environmental temperature Te-The applied voltage and energization time are constant regardless of the environmental temperature Te

  The output acceleration A of the SMA actuator in this specification is a driven period obtained within the measurement period when the period until it is restored to the original shape through contraction deformation due to current heating and expansion deformation due to heat radiation cooling is taken as the measurement period. It is defined by the difference value (peak peak value) between the maximum value and the minimum value of the acceleration of the element.

When a constant voltage is applied, the output acceleration A of the SMA actuator decreases when the environmental temperature Te is low in the temperature range below the reverse transformation start temperature _TAs (hereinafter referred to as the normal temperature range), and the environmental temperature Te is There is a tendency to increase at high temperatures. That is, the operating characteristics of the SMA actuator are significantly changed according to the environmental temperature Te. When the SMA actuator is incorporated in the tactile sensation imparting device, the tactile sensation imparted to the user by the tactile sensation imparting device is greatly changed due to the change in the output acceleration A of the SMA actuator, and there is a concern about the adverse effect on the feeling of use.

The reason why the output acceleration A greatly changes according to the environmental temperature Te is that the amount of heat released per unit time (hereinafter referred to as the heat dissipation speed) from the elastic member changes according to the environmental temperature Te. it is conceivable that. That is, when the environmental temperature Te is low, when the expansion / contraction member is energized and heated to a temperature range between the reverse transformation start temperature _{TAs and the} reverse transformation end temperature _TAf (hereinafter referred to as the transformation temperature range), the member temperature of the expansion member The temperature difference between Tm and ambient temperature Te increases. As a result, the heat release rate of the expansion / contraction member is increased, the temperature increase rate of the expansion / contraction member in the transformation temperature range is excessively slow, and the shape recovery rate associated with reverse transformation is decreased, thereby reducing the output acceleration A. Is considered to be smaller. Further, when the environmental temperature Te is high, when the elastic member is energized and heated to the transformation temperature range, the temperature difference between the member temperature Tm of the elastic member and the environmental temperature Te becomes small. Due to this, the heat dissipation rate of the expansion / contraction member becomes slow, the temperature rise rate of the expansion / contraction member in the transformation temperature range becomes excessively fast, and the shape recovery speed associated with reverse transformation increases, so that the output acceleration A Is expected to increase.

  The present inventor examined this measure, and obtained the knowledge that it is effective to adjust the input heat amount per unit time by changing the applied voltage in accordance with the change in the environmental temperature Te. Specifically, when the environmental temperature Te is low, an excessive decrease in the temperature rise rate accompanying an increase in the heat dissipation rate can be achieved by energizing the expansion / contraction member with a relatively high applied voltage and increasing the amount of input heat per unit time. suppress. Further, when the environmental temperature Te is high, a relatively low applied voltage is applied to the expansion / contraction member to reduce the input heat amount per unit time, thereby suppressing an excessive increase in the temperature increase rate due to a decrease in the heat dissipation rate. .

  Thereby, compared with the case where a constant voltage is applied regardless of the environmental temperature Te, it is possible to suppress the change in the temperature increase rate in the transformation temperature range due to the change in the environmental temperature Te, and to greatly change the output acceleration A due to the change. It can be suppressed. Here, “a large change in the output acceleration can be suppressed” means that the difference value between the maximum value and the minimum value of the output acceleration that can be taken by the expansion / contraction member according to the environmental temperature Te can be reduced.

  FIG. 2 is a graph showing the relationship between the energization time for the expandable member and the output displacement amount of the SMA actuator. In this figure, unlike the condition described in FIG. 1, the elastic member is energized under conditions where the energization time is variously changed. Here, the output displacement amount is the displacement amount of the driven element driven by the output of the SMA actuator, and is the maximum displacement amount obtained within the above-described measurement period. As shown by line segments L0 to L2, the output displacement amount of the SMA actuator has a proportional relationship with the energization time for a while after the energization is started. The slope of the line segments L0 to L2, that is, the ratio of the change amount of the output displacement amount to the change amount of the energization time represents the output speed which is the change amount of the output displacement amount per unit time. It can be said that as the slopes of the line segments L0 to L2 increase, the output speed increases and the output acceleration obtained during the measurement period increases accordingly. From this, it can be said that the slopes of the line segments L0 to L2 represent the output acceleration.

  For example, assume that an output acceleration within a predetermined target range is obtained when the environmental temperature Te = 20 ° C. and the applied voltage Va = 15V. In the present embodiment, for example, when the ambient temperature Te is higher than 20 ° C., Te = 60 ° C., the applied voltage Va is set to 15V so that the slope of the line segment L1 approaches the slope of the line segment L0 (see direction Px). Set to a low 10V. For example, when the environmental temperature Te is Te = -40 ° C. lower than 20 ° C., the applied voltage Va is set to 20V higher than 15V so as to approach the slope of the line segment L0 from the line segment L2 (see direction Py). To do. By setting the applied voltage based on this idea, it is possible to control the output acceleration to be within the target range regardless of the environmental temperature Te.

  When the SMA actuator is incorporated in the tactile sensation imparting device, the output displacement amount affects the tactile sensation imparted to the user from the tactile sensation imparting device in addition to the output acceleration. In order to suppress a change in tactile sensation imparted to the user or to suppress an excessive distortion rate of the expansion / contraction member, the expansion / contraction member falls within an output displacement amount within a predetermined target range (for example, range Rb in FIG. 2). This controls the energization of the.

  Here, in energizing the expansion / contraction member, the control target includes energization time in addition to the applied voltage. When the environmental temperature Te is 60 ° C., if the energization time is shorter than when the environmental temperature Te is 20 ° C., the output displacement can be accommodated in the target range Rb, but the output acceleration that is the slope of the line segments L0 and L1. Does not change. That is, a desired output acceleration cannot be obtained even if the energization time for the elastic member is changed. In order to obtain a desired output acceleration according to the environmental temperature Te, it is effective to control the applied voltage rather than the energization time.

  In the example of FIG. 2, when the environmental temperature Te is in an excessively low temperature range such as −40 ° C., the output displacement amount does not change after a certain energization time (2.5 milliseconds) is exceeded. Even if the energization time is lengthened, the output displacement amount cannot be within the target range Rb. This is presumably because, as described above, the temperature difference between the member temperature Tm of the elastic member and the environmental temperature Te increases in the transformation temperature range, the heat dissipation rate of the elastic member becomes excessively high, and the temperature of the elastic member does not increase. . In this regard, even when the environmental temperature Te is excessively low, the control device of the present embodiment increases the amount of heat input to the elastic member by setting an appropriate applied voltage according to the environmental temperature Te. The temperature of the elastic member can be increased in the transformation temperature range, and the output displacement amount in the target range Rb can be obtained.

  Further, as described above, the control device of the present embodiment sets the applied voltage according to the environmental temperature Te so that the output acceleration of the SMA actuator is within a predetermined range. The present inventor has obtained the knowledge that there is the following problem in setting the applied voltage in this way.

  FIG. 3 is another graph showing the relationship between the energization time for the telescopic member and the output displacement amount of the SMA actuator. Controlling the applied voltage so that the output acceleration is in a predetermined range means, for example, controlling the applied voltage so that it falls within a range sandwiched between two straight lines La and Lb in the figure. . Here, for example, it is assumed that the output displacement amount of the target range Rb can be obtained when the energization time is 1.5 milliseconds. At this time, when the energization time for the expandable member is reduced (for example, when it is reduced from 1.5 milliseconds to 0.75 milliseconds), the output displacement amount range Rx1 decreases from the target range Rb along with the change. Resulting in. Similarly, when the energization time for the expansion / contraction member is increased (for example, from 1.5 milliseconds to 3.0 milliseconds), the output displacement range Rx2 increases from the target range Rb along with the change. Resulting in.

  As described above, when the energization time for the expandable member is changed in controlling the applied voltage so that the output acceleration is within the predetermined target range Rb, the output displacement amount of the SMA actuator is changed, and the target range is thus reached. The output displacement amount of Sb may not be obtained. Therefore, even if the output acceleration of the SMA actuator is controlled so as to be within the target range Rb, the tactile sensation imparted to the user changes due to the change in the output displacement amount, and there is a concern that the use feeling may be adversely affected.

  The present inventor has examined this measure, and finds that it is effective to stop energization when a certain energization time (for example, 1.5 milliseconds) elapses regardless of changes in the environmental temperature Te. Got. Thereby, in controlling the output acceleration to be within the target range, the change in the output displacement amount of the SMA actuator can be suppressed. As a result, it becomes easy to perform control so that both the output acceleration and the output displacement amount of the SMA actuator are within a predetermined range regardless of the change in the environmental temperature Te. Hereinafter, the technique made in such a background is demonstrated.

  Hereinafter, in the embodiment and the modification, the same reference numerals are given to the same components, and the duplicate description is omitted. In the drawings, for convenience of explanation, some of the components are omitted as appropriate, and the dimensions of the components are appropriately enlarged and reduced.

  FIG. 4 is a configuration diagram illustrating the tactile sensation imparting device 12 according to the first embodiment. FIG. 5 is a schematic diagram showing a part of the electric device 14 in which the tactile sensation imparting device 12 is used. The tactile sensation imparting device 12 can impart a tactile sensation to the user U in conjunction with the touch operation of the user U with respect to the operated portion 14 a of the electrical device 14. The electric device 14 of the present embodiment is a touch panel device, and the operated portion 14a that is touch-operated by the user is a touch panel. The tactile sensation imparting device 12 is incorporated in the electric device 14 as a part of the electric device 14. The tactile sensation imparting device 12 mainly includes a control device 16, a touch detection unit 18, an SMA actuator 20, and an urging unit 22. The control device 16 will be described later.

  The touch detection unit 18 can detect a touch operation on the operated unit 14 a of the electrical device 14. The touch detection unit 18 is, for example, a capacitive touch sensor incorporated in a touch panel.

  The SMA actuator 20 can drive the operated portion 14 a of the electric device 14 in a specific driving direction Pa by contraction deformation of the expansion member 24. The driving direction Pa is, for example, an in-plane direction or an out-of-plane direction of the touch panel.

  The urging unit 22 urges the operated portion 14a of the electric device 14 in the counter driving direction Pb opposite to the driving direction Pa. The urging portion 22 is an elastic body such as a coil spring.

  FIG. 6 is a side view showing an example of the SMA actuator 20. The SMA actuator 20 of this embodiment includes a stator 26 and a mover 28 in addition to the elastic member 24.

  The stator 26 is attached to a casing (not shown) of the electric device 14, and the position of the electric device 14 with respect to the operated portion 14a is fixed. The mover 28 faces the stator 26 and is movable with the direction facing the stator 26 as the movable direction. The mover 28 can transmit the movement in the driving direction Pa to the operated portion 14a of the electric device 14 serving as a driven element, with one side of the moving direction as the driving direction Pa.

  The elastic member 24 is exemplified by a linear wire, but may be a belt-like belt or the like. The telescopic member 24 is electrically connected to an energization control unit 32 (described later) of the control device 16. The elastic member 24 is made of a shape memory alloy that can be expanded and contracted by a temperature change. The elastic member 24 made of shape memory alloy can be shrunk and deformed by reverse transformation (austenite transformation) by heating, and can be stretched and deformed by martensite transformation by cooling. The elastic member 24 can drive the movable element 28 in the driving direction Pa by contraction deformation.

FIG. 7 is a diagram showing resistance-temperature characteristics of the elastic member 24 of the present embodiment. The shape memory alloy constituting the elastic member 24 has a specific resistance-temperature characteristic in which the resistance value changes according to the member temperature Tm that is the temperature of the elastic member 24 in at least a part of the temperature range. The shape memory alloy of this embodiment is a Ni—Ti alloy. The shape memory alloy having this composition has a negative resistance-temperature in a temperature range Tra (hereinafter referred to as a transformation temperature range) not lower than the reverse transformation start temperature T _As (As point) and not higher than the reverse transformation end temperature T _Af (Af point). Has characteristics. Also, in the normal temperature range Trb below reverse transformation starting temperature T _As, positive resistance - it has a temperature characteristic. The negative resistance-temperature characteristic refers to a characteristic in which the resistance value decreases as the member temperature Tm increases, and the positive resistance-temperature characteristic refers to a characteristic in which the resistance value increases as the member temperature Tm increases.

  Returning to FIG. The control device 16 includes a temperature information acquisition unit 30 and an energization control unit 32. Each block of the control device 16 is realized in hardware by various electronic parts such as a CPU of a computer, mechanical parts, and the like, and is realized by a computer program and the like in software. Here, functional blocks realized by the cooperation are drawn. These functional blocks are realized by a combination of hardware elements and software elements, or only hardware elements.

  The temperature information acquisition unit 30 acquires temperature information indicating the environmental temperature Te based on the following idea. The expandable member 24 of the SMA actuator 20 has a very small volume and easily dissipates heat due to heat conduction between the stator 26 and the mover 28. Therefore, the member temperature Tm of the expansion / contraction member 24 is easily cooled to the environmental temperature Te very quickly, and becomes the same temperature as the environmental temperature Te except for a very short period after the energization heating of the expansion / contraction member 24. Therefore, in the present embodiment, it is considered that the environmental temperature Te is the same as the member temperature Tm.

Further, as described above, the elastic member 24, positive resistance at low normal temperature range Trb from the inverse transformation starting temperature T _As - has a temperature characteristic. Therefore, in the normal temperature range Trb, the member temperature Tm can be specified from the resistance value of the elastic member 24, and as a result, the environmental temperature Te can be specified. In the present embodiment, it is assumed that the elastic member 24 is used at such an environmental temperature Te in the normal temperature range Trb. Therefore, in the present embodiment, the resistance value of the expansion / contraction member 24 before starting energization is used as temperature information indicating the environmental temperature Te (member temperature Tm). Specifically, the temperature information acquisition unit 30 of the present embodiment detects a resistance value before starting the energization of the elastic member 24, and acquires the detected resistance value as temperature information indicating the environmental temperature Te. The temperature information acquisition unit 30 acquires temperature information based on the resistance value of the elastic member 24 in the normal temperature range Trb. The method for detecting the resistance value is not particularly limited, and for example, various known methods may be used. Note that the reverse transformation start temperature T _As of the shape memory alloy is, for example, about 85 ° C.

  The energization control unit 32 sets an applied voltage to be applied to the expansion / contraction member 24 based on the temperature information acquired by the temperature information acquisition unit 30, and supplies the expansion / contraction member 24 with the set application voltage. The energization control unit 32 according to the present embodiment stops energization of the expansion / contraction member 24 when a predetermined energization stop condition is satisfied after energization of the expansion / contraction member 24 is started. The energization stop condition of the present embodiment is that a predetermined energization time has elapsed since the energization of the elastic member 24 was started. The energization time of this embodiment is set to a constant value regardless of the environmental temperature Te.

The energization control unit 32 sets the applied voltage lower as the environmental temperature Te indicated by the temperature information is higher. FIG. 8 is a diagram illustrating a correspondence relationship between the environmental temperature Te and the applied voltage. As shown in FIG. 8A, the energization control unit 32 of the present embodiment sets the applied voltage so that the applied voltage continuously decreases as the environmental temperature Te increases. In addition to this, as shown in FIG. 8B, the applied voltage may be set so that the applied voltage decreases stepwise as the environmental temperature Te increases. The applied voltage, the minimum value becomes at transformation start temperature T _As to the upper limit temperature of usually a temperature range Trb, it envisaged lower limit temperature of usually a temperature range Trb (e.g., -40 ° C.) is set to be the maximum value The

Applied voltage, when the power supply stop condition is energized until satisfied, is set an elastic member 24 to the heatable sizes up to at least the inverse transformation starting temperature T _As above transformation temperature range Tra. The applied voltage has such a magnitude that the output acceleration A in the target range Ra as shown in FIG. 1 can be obtained regardless of the environmental temperature Te in the normal temperature range Trb when the energization stop condition is satisfied. Is set. The target range Ra of the output acceleration A is set so that, for example, the difference value between the maximum value and the minimum value of the output acceleration A that can be taken at the environmental temperature Te in the normal temperature range Trb is 5 Gpp or less.

  In setting the applied voltage that satisfies such conditions, the energization control unit 32 holds a table or expression that defines the correspondence between the temperature information indicating the environmental temperature Te and the applied voltage in the storage unit, and the table Or you may set an applied voltage based on temperature information using a type | formula. The correspondence between the temperature information and the applied voltage may be obtained by experiment, analysis, or the like.

The energization time is set in advance so as to obtain an output displacement amount in a predetermined target range Rb when an applied voltage is set so that an output acceleration in the target range Ra can be obtained. The upper limit value of the target range Rb is such that the distortion rate of the expansion / contraction member 24 from the start of energization to the expansion / contraction member 24 until the energization stop condition is satisfied does not exceed a predetermined allowable distortion rate. Is set to be The strain rate ε of the elastic member 24, as represented by the following formula (1), to the length L of the elastic member 24 when the elastic member 24 is in the transformation start temperature T _As, stretching in transformation temperature range Tra The ratio of the change amount λ of the length of the member 24 is shown.
ε = λ / L (1)

The strain rate of the expansion / contraction member 24 increases as the member temperature Tm of the expansion / contraction member 24 increases in the transformation temperature range Tra, and reaches the maximum strain rate at a temperature near the reverse transformation end temperature _TAf . As the strain rate of the elastic member 24 increases, there is a risk of promoting fatigue failure. Based on this, the allowable distortion rate is set so as to be, for example, half or less of the maximum distortion rate.

The operation of the tactile sensation imparting device 12 using the above control device 16 will be described.
When a touch operation on the operated portion 14a of the electrical device 14 is detected by the touch detection unit 18, the temperature information acquisition unit 30 acquires temperature information indicating the environmental temperature Te at that time. The temperature information acquisition unit 30 according to the present embodiment acquires temperature information when a touch operation is detected by detecting temperature information at a timing when the touch operation is detected. In addition, the temperature information acquisition unit 30 may acquire temperature information when a touch operation is detected by constantly monitoring the temperature information. The energization control unit 32 sets an applied voltage to be applied to the expansion / contraction member 24 based on the temperature information acquired by the temperature information acquisition unit 30, and supplies the expansion / contraction member 24 with the applied voltage. The energization control unit 32 of the present embodiment energizes the expansion and contraction member 24 without changing the set applied voltage from the start of energization until the energization stop condition is satisfied.

  When the energization control unit 32 energizes the expansion / contraction member 24, the expansion / contraction member 24 contracts and deforms. When the telescopic member 24 is contracted and deformed, the movable element 28 is driven in the driving direction Pa, and the movement of the movable element 28 is transmitted to the operated part 14a of the electric device 14, whereby the operated part 14a is also moved in the driving direction Pa. Driven. At this time, the operated portion 14 a of the electrical device 14 is driven in the driving direction Pa against the biasing force of the biasing portion 22.

  When energization of the expansion / contraction member 24 by the energization control unit 32 stops, the expansion / contraction member 24 expands and deforms so as to be restored to its original shape by heat radiation cooling. Along with this, transmission of force from the telescopic member 24 to the operated portion 14 a is released, and the operated portion 14 a is pushed back in the counter driving direction Pb by the urging force of the urging portion 22. The tactile sensation imparting device 12 vibrates the operated portion 14a by instantaneously causing the movement in the driving direction Pa and the counter driving direction Pb. Thereby, the vibration of the operated part 14a is transmitted to the user touching the operated part 14a, and a tactile sensation is given to the user.

  According to the control device 16 described above, in the normal temperature range Trb, the applied voltage is set higher as the environmental temperature Te is lower, and the applied voltage is set lower as the environmental temperature Te is higher. Therefore, as described above, a large change in the output acceleration A caused by a change in the environmental temperature Te can be suppressed as compared with the case where a constant voltage is applied regardless of the environmental temperature Te.

  Further, the temperature information acquisition unit 30 acquires temperature information based on the resistance value of the elastic member 24. Therefore, a dedicated temperature measuring element is not required for acquiring temperature information indicating the environmental temperature, and the configuration of the control device 16 can be simplified.

  In addition, the energization control unit 32 stops energization based on the energization stop condition that a predetermined energization time has elapsed since the energization of the elastic member 24 was started. Therefore, the success or failure of the energization stop condition can be easily determined as compared with the case where the success or failure of the energization stop condition is determined based on the resistance value or the like of the elastic member 24.

  The predetermined energization time is set to a constant value regardless of the environmental temperature Te. Therefore, as described above, it becomes easy to control so that both the output acceleration and the output displacement amount of the SMA actuator 20 fall within a predetermined range regardless of the change in the environmental temperature Te.

(Second Embodiment)
FIG. 9 is a configuration diagram illustrating the tactile sensation imparting device 12 according to the second embodiment. The control device 16 of the present embodiment is different from the control device 16 of the first embodiment in the presence or absence of the resistance value acquisition unit 34 and the operation of the energization control unit 32.

  The resistance value acquisition unit 34 acquires the resistance value of the elastic member 24. In the present embodiment, the temperature information acquisition unit 30 also acquires the resistance value of the elastic member 24, and the temperature information acquisition unit 30 also serves as the resistance value acquisition unit 34. The resistance value acquisition unit 34 of the present embodiment acquires the resistance value of the elastic member 24 by detecting the resistance value of the elastic member 24. The method for detecting the resistance value is not particularly limited, and for example, various known methods may be used.

  The energization control unit 32 according to the present embodiment determines whether or not the energization stop condition is satisfied based on the resistance value acquired by the resistance value acquisition unit 34 after starting energization of the elastic member 24. The energization control unit 32 continues energization after energization is started until the energization stop condition is satisfied. The energization stop condition of this embodiment is set based on the following idea.

  As described above, in the transformation temperature range Tra, the strain rate of the elastic member 24 increases as the member temperature Tm of the elastic member 24 increases, and there is a risk of promoting fatigue failure as this increases. Therefore, as in the first embodiment, it is necessary to avoid an excessive increase in the member temperature Tm in the transformation temperature range Tra so as not to exceed the allowable strain rate.

  Here, as shown in FIG. 7, the elastic member 24 has a negative resistance-temperature characteristic in the transformation temperature range Tra. Therefore, the member temperature Tm of the expansion / contraction member 24 in the transformation temperature region Tr can be specified from the resistance value of the expansion / contraction member 24.

  Based on this, the energization stop condition of the present embodiment is that the resistance value acquisition unit 34 acquires the resistance value of the expansion / contraction member 24 equal to or higher than a predetermined reference resistance value Rr, and then the resistance value equal to or lower than the reference resistance value Rr. Is established when the resistance value acquisition unit 34 is acquired. The reference resistance value Rr is set so that the output displacement amount when heated to the member temperature Tm in the transformation temperature range Tra corresponding to the reference resistance value Rr falls within the target range Rb. As described above, the upper limit value of the target range Rb is set so that the distortion rate of the elastic member 24 does not exceed the allowable distortion rate. As a result, it is possible to avoid an excessive distortion rate due to excessive heating of the elastic member 24 in the transformation temperature range Tra, and to avoid a reduction in fatigue characteristics of the elastic member 24. One condition is that the resistance value acquisition unit 34 acquires a resistance value equal to or greater than the reference resistance value Rr for the following reason.

  As shown in FIG. 7, the shape memory alloy constituting the elastic member 24 of the present embodiment has a positive resistance-temperature characteristic in the normal temperature range Trb. Therefore, even when the expansion / contraction member 24 is in either the normal temperature range Trb or the transformation temperature range Tra, a situation in which the resistance value of the expansion / contraction member 24 falls below the reference resistance value Rr may occur. For this reason, when only the acquisition of the resistance value equal to or less than the reference resistance value Rr is set as the energization stop condition, the energization of the expansion / contraction member 24 is performed even when the member temperature Tm of the expansion / contraction member 24 is in the normal temperature range Trb. A situation of stopping can occur. When such a situation occurs, the elastic member 24 cannot be heated to the transformation temperature range Tra, and the driven element (the operated portion 14a) cannot be driven using the force generated by the contraction deformation.

  Here, once the resistance value of the expansion / contraction member 24 becomes equal to or higher than the reference resistance value Rr, the reference resistance value Rr is set not in the normal temperature range Trb but in the transformation temperature range Tra as long as the expansion / contraction member 24 is continuously energized and heated. A situation occurs. Therefore, one of the conditions is to obtain a resistance value equal to or higher than the reference resistance value Rr so that the energization can be stopped when the elastic member 24 is not in the normal temperature range Trb but in the transformation temperature range Tra. As a result, even when the shape memory alloy elastic member 24 having a positive temperature-temperature characteristic in the normal temperature region Trb is used, the elastic member 24 is electrically heated to the transformation temperature region Tra while the elastic member 24 is strained. It is possible to avoid the situation where there are too many.

  Note that the following energization stop condition may be set from the viewpoint of achieving the same purpose. When the expansion / contraction member 24 is heated from the normal temperature range Trb to the transformation temperature range Tra, the change amount per unit time of the resistance value of the expansion / contraction member 24 is switched from a positive value to a negative value. Utilizing this fact, the amount of change in the resistance value of the expansion / contraction member 24 is monitored, and the energization stop condition is that the amount of change is a negative value and obtaining a resistance value equal to or less than the reference resistance value Rr It may be set.

  In the above, the example of embodiment of this invention was demonstrated in detail. The above-described embodiments are merely specific examples for carrying out the present invention. The contents of the embodiments do not limit the technical scope of the present invention, and many design changes such as changes, additions, deletions, etc. of constituent elements are possible without departing from the spirit of the invention defined in the claims. Is possible. In the above-described embodiment, contents that can be changed in this way are emphasized with the notation of “embodiment”, “in the embodiment”, etc. Changes are allowed. Moreover, the hatching given to the cross section of drawing does not limit the material of the hatched object.

  Although the to-be-operated part 14a of the electric equipment 14 demonstrated the example which is a touchscreen, it is not limited to this. For example, a switch such as an on / off switch may be used. Moreover, although the to-be-operated part 14a and the touch detection part 18 of the electric equipment 14 demonstrated the example provided integrally as a part of touch panel, these may be provided separately.

  The specific structure of the SMA actuator 20 is not particularly limited as long as the movable element 28 can be driven in the driving direction Pa by contraction deformation of the elastic member 24. The composition of the shape memory alloy constituting the elastic member 24 is not particularly limited, and a Ni—Ti—Cu alloy may be used.

  When a Ni—Ti—Cu alloy is used as a shape memory alloy, there is no correlation between the member temperature Tm and the resistance value in the normal temperature range Trb. When the correlation is lost in this way, as described in the embodiment, temperature information indicating the environmental temperature Te in the normal temperature range Trb cannot be acquired from the resistance value of the expansion member 24. As an alternative, the temperature information acquisition unit 30 may acquire temperature information indicating the environmental temperature Te using a temperature measuring element such as a thermistor. In addition, the temperature information acquisition part 30 may acquire temperature information using a temperature measuring element irrespective of a composition of a shape memory alloy, and may acquire temperature information using another method.

  Although the energization control part 32 demonstrated the example which does not change the set applied voltage until it stops energizing with respect to the expansion-contraction member 24 after setting an applied voltage, it is not limited to this. For example, the energization control unit 32 may acquire the resistance value of the expansion / contraction member 24 even after energization of the expansion / contraction member 24 is started, and may change the applied voltage following the change of the resistance value during the energization.

  Although the example in which the predetermined energization time is a constant value has been described, a variable value set based on the temperature information acquired by the temperature information acquisition unit 30 may be used. For example, in the case of the high environmental temperature Te, the heat dissipation rate of the elastic member 24 is slower than in the case of the low environmental temperature Te. Therefore, if the energization time of the elastic member 24 is long, the elastic member 24 is easily heated excessively. There is a possibility that the distortion rate of the member 24 becomes excessive. In order to avoid this, the energization time may be set shorter as the environmental temperature Te becomes higher. The energization control unit 32 holds a table or an expression that defines the correspondence relationship between the energization time and the environmental temperature Te satisfying such conditions, and specifies the energization time from the environmental temperature Te using the table or expression. Also good.

  The method for controlling the applied voltage by the energization control unit 32 is not particularly limited. The energization control unit 32 may control the applied voltage applied to the expandable member 24 by generating a desired applied voltage based on the power supply voltage using, for example, a pulse width modulation circuit. In addition, for example, the power supply voltage may be lowered to a desired applied voltage by a dropper circuit.

  In addition, the applied voltage may be controlled using a plurality of capacitors having different capacitances. Specifically, the capacitor has a characteristic that as the capacitance increases, the rate of voltage drop due to discharge becomes slower and the voltage of the discharge current increases. Therefore, in supplying the discharge current of the capacitor to the expansion / contraction member 24, the applied voltage to the expansion / contraction member 24 increases when the capacitance of the capacitor is large, and the applied voltage to the expansion / contraction member 24 decreases when the capacitance is small.

  Utilizing this, the energization control unit 32 is configured to be able to supply the discharge current of any of the plurality of capacitors to the expansion / contraction member 24. The higher the environmental temperature Te indicated by the temperature information, the lower the capacitance of the capacitor. You may make it supply a discharge current to the expansion-contraction member 24. FIG. Thereby, the applied voltage is set based on the temperature information so that the applied voltage becomes lower as the environmental temperature Te indicated by the temperature information is higher. This capacitor is, for example, an electrolytic capacitor.

If the invention embodied by the above embodiment and modification is generalized, it can be said that the invention described in the following items is included.
(item)
A shape memory alloy actuator control device using an elastic member made of a shape memory alloy that can be expanded and contracted by a temperature change,
A resistance value acquisition unit for acquiring a resistance value of the elastic member;
An energization control unit for energizing the expandable member,
The energization control unit determines success or failure of a predetermined energization stop condition based on the resistance value acquired by the resistance value acquisition unit, and stops energization when the energization stop condition is satisfied,
The energization stop condition is a control device that acquires a resistance value equal to or higher than a predetermined reference resistance value and then acquires a resistance value equal to or lower than the reference resistance value.

  The problems relating to the invention described in this item are as follows.

  When this inventor examined the indication technique of patent document 1, the following knowledge was acquired. When driving the driven element using the elastic member made of shape memory alloy, the force generated by the contraction deformation of the elastic member is used as the driving force, so that the transformation temperature range is from the reverse transformation start temperature to the reverse transformation end temperature. Energization control is required to energize and heat the elastic member. In addition, in the disclosed technique of Patent Document 1, in order to avoid a situation where the strain rate of the expansion / contraction member is excessive, the resistance value of the expansion / contraction member is obtained after using a shape memory alloy having a negative resistance-temperature characteristic in the transformation temperature range. The energization control is performed so that does not fall below the reference resistance value.

  Here, in the disclosed technique of Patent Document 1, the above-described energization control is performed using a shape memory alloy having no correlation between the resistance value and the member temperature in a normal temperature range lower than the reverse transformation start temperature. From the viewpoint of increasing the degree of freedom of the material used for the shape memory alloy, it is desirable that the same energization control can be performed even when a shape memory alloy having a positive resistance-temperature characteristic in the normal temperature range is used for the elastic member.

  The invention described in this item has been made in view of such problems, and one of its purposes is to provide a stretchable member even when a shape memory alloy having a positive resistance-temperature characteristic in a normal temperature range is used as the stretchable member. Provided is a technique capable of avoiding a situation in which the distortion rate of the expansion and contraction member is excessive while driving the driven element using.

DESCRIPTION OF SYMBOLS 12 ... Tactile feeling provision apparatus, 14a ... Operated part, 16 ... Control apparatus, 18 ... Touch detection part, 20 ... Shape memory alloy actuator (SMA actuator), 24 ... Elastic member, 30 ... Temperature information acquisition part, 32 ... Current supply control Department.

Claims (6)

A control device for a shape memory alloy actuator using an elastic member made of a shape memory alloy that can be expanded and contracted by a temperature change,
A temperature information acquisition unit that acquires temperature information indicating an ambient temperature around the expansion member;
An application control unit configured to set an applied voltage to be applied to the expansion and contraction member based on the temperature information acquired by the temperature information acquisition unit, and to energize the expansion and contraction member by the set application voltage;
The energization control unit is a control device that sets the applied voltage lower as the environmental temperature is higher. The elastic member has a specific resistance-temperature characteristic in a temperature range lower than the reverse transformation start temperature,
The control device according to claim 1, wherein the temperature information acquisition unit acquires the temperature information based on a resistance value of the elastic member in a temperature range lower than the reverse transformation start temperature.   3. The control device according to claim 1, wherein the energization control unit stops energization when a predetermined energization time has elapsed since the energization of the elastic member is started.   The control device according to claim 3, wherein the predetermined energization time is set to a constant value regardless of the environmental temperature. A resistance value acquisition unit for acquiring the resistance value of the elastic member;
The energization control unit determines success or failure of a predetermined energization stop condition based on the resistance value acquired by the resistance value acquisition unit, and stops energization when the energization stop condition is satisfied,
The control device according to any one of claims 1 to 4, wherein the energization stop condition is to acquire a resistance value equal to or higher than a predetermined reference resistance value and then to acquire a resistance value equal to or lower than the reference resistance value. . A control device according to any one of claims 1 to 5;
A touch detection unit capable of detecting a touch operation on the operated unit by a user;
A shape memory alloy actuator capable of driving the operated portion by contraction deformation of an elastic member made of shape memory alloy,
The energization control unit is a tactile sensation imparting device that sets the applied voltage and energizes the stretchable member with the set applied voltage when a touch operation is detected by the touch detection unit.

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