JPH01264795A - Shape memory actuator - Google Patents

Abstract

PURPOSE:To prevent a shape memory alloy from losing the stored shape or deteriorating the shape recovery characteristic by providing a means to prevent the overheating of the shape memory alloy. CONSTITUTION:When a load is increased and the temperature T of an actuator 1 exceeds the upper limit T1 of the normal operating range, an excitation cutoff section 10 is deformed, the excitation cutoff section 1c is connected to a terminal 2. Both ends of the actuator 1 is short-circuited, the excitation is interrupted, the overheating of the actuator 1 made of a shape memory alloy is prevented. When the temperature T of this actuator 1 is returned to T1 or below, the excitation cutoff section 1c is separated from the terminal 2, the excitation is restarted.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to shape memory alloys (shape 1elor7).
The present invention relates to a shape memory actuator that drives a load by utilizing the deformation action of an errectalloy (hereinafter referred to as SMA) caused by temperature changes.

[Conventional technology]

The conventional general overheating prevention circuit was published in Japanese Patent Application Laid-Open No. 1608-1983.
It is described in Publication No. 04. An overview of this is shown in FIG. A thermistor 15 as a temperature sensor is attached in close contact with a transistor 13 as a heating element. The detection signal of the thermistor 15 is supplied to the temperature determination circuit 16,
It is determined whether the detected temperature is within the normal operating range of transistor 13. If the temperature is outside this operating range, an abnormality detection signal is supplied to the energization control circuit 11, and control such as cutting off the energization by the energization circuit 12 is performed.

In addition, a current detection circuit that detects the current flowing through the heating element,
A voltage detection circuit detects the voltage applied to the heating element, the electric power is determined from the detected current and voltage, the temperature is determined from these, the operation is controlled by the temperature judgment circuit, and the drive signal to the heating element is cut off. Conventional examples have also been devised.

Further, Japanese Patent Application No. 61-276089 filed by the applicant of the present application detects the resistance value of the SMA and converts it into the amount of curvature to control the amount of curvature.

[Problem to be solved by the invention]

However, the above-mentioned Japanese Patent Application No. 61-276089 did not give equivalent consideration to overheating of SMA. In general, when an SMA is overheated, its memorized shape recovery operation may deteriorate, and further overheating may cause the memorized shape to be lost and damage to other components of the actuator.

This invention was made to deal with the above-mentioned circumstances,
The purpose of this is to interrupt heating of the SMA in a shape memory actuator using SMA when the temperature of the SMA becomes higher than the normal operating range, thereby preventing performance deterioration or damage due to overheating of the SMA.

[Means to solve the problem]

The shape memory actuator according to the present invention includes means for detecting the temperature of the SMA, means for determining whether the detected temperature is within the normal operating range, and means for interrupting heating of the SMA when the detected temperature becomes higher than the normal operating range. Equipped with.

[Effect]

According to this invention, when the SMA becomes overheated, heating is interrupted, so that it is possible to prevent the SMA from losing its memorized shape or from deteriorating its shape recovery characteristics.

〔Example〕

An embodiment of the shape memory actuator according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the first embodiment. Same figure (a).

In (b) and (c), the temperature T is T<To, To≦T≦71,
It is a figure in the case of TI<T. Temperature To.

T1 is the lower and upper limits of the temperature range in which the SMA constituting the actuator normally operates. Figure 2 (a), (
b) and (c) are Fig. 1(a).

It is an equivalent circuit diagram of (b) and (c). Ro, R1゜R2
is the resistance value of the actuator 1, and ``is the resistance value of the current-carrying wire 3.

The actuator 1 made of SMA has a displacement part 1as which is deformed into a memorized shape by electrical heating and drives a load (not shown), a fixed part 1b which fixes the relative positional relationship of the entire actuator 1 to a terminal 2, and a fixed part 1b to prevent overheating of the actuator 1. It consists of an energization cutoff section 1c that cuts off energization. here,
The fixed portion 1b is fixed to a housing (not shown) or the like.

The displacement part 1a and the current cutoff part IC are subjected to different temperature treatments, and their shape recovery temperatures are different.

FIG. 3 is a diagram showing the relationship between temperature and displacement of the SMA, in which the displacement portion 1a has the characteristics shown by the solid line, and the current cutoff portion IC has the characteristics shown by the broken line. The temperature range To to T1 is the normal operating range, and the temperature range higher than T1 is the overheating range. The displaced portion 1a starts to deform when the temperature exceeds To, and recovers to the memorized shape when the temperature reaches T1. The current cutoff portion 1c starts deforming when the temperature exceeds TI.

Both ends of the actuator 1 are connected to a current-carrying circuit 4 via a current-carrying wire 3.
It is also connected to the resistance value detection section 5 via the electric wire 3a for resistance value detection.

A terminal 2 is connected to the middle of the current-carrying wire 3 between the tip of the actuator 1 (the top of the displacement portion 1 a) and the current-carrying circuit 4 .

The terminal 2 is also fixed to the housing or the like.

The detection signal of the resistance value detection section 5 is input to the energization control section 6,
The output of the energization control section 6 controls the energization circuit 4. The energizing circuit 4 heats the actuator 1 via the energizing wire 3 using Joule heat.

The operation of the first embodiment will be explained.

When the actuator 1 is energized by the energizing circuit 4, it is heated by Joule heat. When the temperature reaches 10 or more,
As shown in FIG. 1(b), the displacement portion 1a starts deforming and drives the load. When the temperature is within the normal operating range of To-Tl, the displacement portion 1a can obtain a displacement corresponding to the amount of current supplied by the current supply circuit 4. Therefore, the amount of drive of the actuator 1 can be controlled by the amount of energization.

Here, since the current-carrying wire 3 is heated by electricity in the same way as the actuator 1, the resistance value changes depending on the temperature. However, since the electric wire 3a is not energized, its resistance value does not change. In this embodiment, the resistance value detection unit 5 detects the resistance value of the actuator 1 via the electric wire 3a, so that the resistance value of the actuator 1 can be accurately detected regardless of the resistance change of the current-carrying wire 3 due to temperature. . Since the resistance value of the SMA changes depending on the temperature, the resistance value detection section 5 calculates the amount of displacement of the displacement section 1a from the detected resistance value, and controls the amount of energization via the energization control section 6 so that the desired amount of displacement is obtained. Control. The energizing circuit 4 energizes the actuator 1 in a pulsed manner at a constant cycle,
The amount of energization is controlled by changing the duty ratio of the energization pulse.

However, when the load is large and the desired amount of displacement is attempted, the amount of energization becomes larger than usual. Then,
The temperature T of the actuator 1 exceeds the upper limit T1 of the normal operating range and enters the overheating range (T1 - T). Furthermore, if the current is continued, the shape memory of the actuator 1 will deteriorate or be lost, and surrounding components will also be affected.

However, in this example, when the temperature exceeds T1,
The current-carrying interrupter IC is deformed as shown in FIG. 1(C), and the current-carrying interrupter IC and the terminal 2 come into contact.

Therefore, as shown in FIG. 2(C), both ends of the actuator 1 are short-circuited, and the current supply is interrupted.

Therefore, the temperature of the actuator 1 is lowered and overheating is prevented. When the temperature returns to below T1, the energization interrupter IC separates from the terminal 2, and energization is resumed.

A second embodiment will be explained. The second embodiment differs from the first embodiment only in the characteristics of the actuator, and the block diagram is the same as that of the first embodiment.

FIG. 4 is a diagram showing the characteristics of the actuator of the second embodiment. The characteristics of the displacement section 1a shown by the solid line are the same as those of the first embodiment, but the current cutoff section 1c has a large hysteresis characteristic as shown by the broken line. It is characterized by being heat-treated to have the following properties. The temperature at which the current-carrying cutoff portion 1c starts its shape recovery operation is T1 as in the first embodiment, but the temperature at which the displacement returns to its original state is a temperature TI' lower than T1.

According to the second embodiment, as in the first embodiment, when the temperature exceeds T1, the energization cutoff portion 1c deforms and contacts the terminal 2, thereby interrupting energization. Thereafter, the interruption of energization is continued until the temperature is sufficiently lowered and becomes below Tl', which is within the normal operating range. In the first embodiment, the energization is interrupted when the temperature exceeds T1, but the energization is restarted immediately when the temperature falls below T1, so the temperature may repeatedly increase and decrease near T1.

However, in the second embodiment, the hysteresis of the energization interrupting part 1c is large, so that when the energization is interrupted by -degrees, the energization will not be restarted unless the temperature drops to a temperature lower than the temperature at which the energization was interrupted. Can be lowered.

FIG. 5 is a block diagram of the third embodiment. Figure (a),
In (b) and (c), the temperature T is T<To, To≦T, respectively.
It is a figure in the case of ≦TI and TI<T. In the first embodiment, the displacement part 1a and the current cutoff part IC were subjected to different temperature treatments, but in the third embodiment, they are constructed of SMAs having the same characteristics and subjected to the same temperature treatment. Here, the distance p between the energization cutoff part IC and the terminal 2 is determined so that the energization cutoff part IC comes into contact with the terminal 2 when the temperature becomes T1 or higher.

According to the third embodiment, there is an advantage that the actuator 1 can be manufactured easily.

FIG. 6 is a block diagram of the fourth embodiment. The operation of the actuator 1 itself is the same as in the first to third embodiments, but the series circuit of the actuator 1 and the terminal 2 is connected to the current-carrying circuit 4 via the current-carrying wire 3, and the resistor is connected to the current-carrying circuit 4 via the current-carrying wire 3a. It is connected to the value detection section 5.

According to the fourth embodiment, the resistance value detection section 5 detects the sum of the resistance value of the actuator 1 and the resistance value of the current-carrying wire 3. The energization control unit 6 controls this combined resistance value R as shown in FIG. 2(C).
When becomes equal to the resistance value r of the energizing wire 3, it is determined that the temperature has entered the overheating range, and the energization is interrupted. Energization control section 6
causes the interruption of energization to continue for a certain period of time. By setting this interruption time to an arbitrary time, it is possible to obtain the same effect as when using an SMA with a large hysteresis as in the second embodiment. In this way, according to the fourth embodiment, double overheating prevention measures are taken, so safety is further ensured.

FIG. 7 is a block diagram of the fifth embodiment. The configuration of the actuator 1 is similar to that of the first embodiment.

Both ends of the actuator 1 are connected to a current-carrying circuit 4 via a current-carrying wire 3.
connected to. The terminal 2 is not inserted into the current-carrying wire 3, but is connected to the current-carrying wire 3 separately from the actuator 1, and is also connected to the resistance value detection section 5 via the wire 3a.

According to the fifth embodiment, the resistance value detection section 5 is the current cutoff section 1c.
When it is detected that the terminal 2 is in contact with the terminal 2, it is determined that the temperature has entered the overheating range, and the energization control section 6 interrupts the energization by the energization circuit 4.

FIG. 8 is a block diagram of the sixth embodiment. Contrary to the above embodiment, in the actuator 1, the current cutoff part IC is in contact with the terminal 2 as shown by the broken line in the normal temperature range. When the temperature reaches the overheating range, the current cutoff unit IC separates from the terminal 2 as shown by the solid line.

When the resistance value detection section 5 detects the non-contact between the energization cutoff section IC and the terminal 2, it determines that the temperature has entered the overheating range, and the energization control section 6 interrupts the energization by the energization circuit 4.

FIGS. 9(a), (b), and (c) are block diagrams of the seventh embodiment. In the seventh embodiment, in the first embodiment, the displacement part 1
A and the current cutoff part IC are constructed from separate SMAs, thereby eliminating the need for the fixed part 1b. Further, in this embodiment, the resistance value detection section 5 and the energization control section 6 are also unnecessary.

According to this embodiment, when the temperature reaches the overheating range, the ninth
As shown in Figure (c), the current cutoff portion 1c is deformed and comes into contact with the terminal 2. As a result, both ends of the actuator 1 are short-circuited, and power supply to the actuator 1 is cut off.

According to this embodiment, 1 corresponds to the displacement part and the current cutoff part.
This method has the advantage of being easy to manufacture, since it is sufficient to heat-treat the two SMAs at different temperatures without heat-treating both ends of one SMA at different temperatures. Furthermore, since there is no need to control the energizing circuit 4, the configuration is simple.

FIG. 10 is a block diagram of the eighth embodiment. In the eighth embodiment, the SMA of the seventh embodiment has a spiral shape. The displacement direction of the displacement part 1a is the horizontal direction in the drawing, the displacement direction of the energization interrupting part IC is the vertical direction in the drawing, and a movable terminal 8 that contacts the terminal 2 is connected to the rear end of the energization interrupting part 1c.

According to this embodiment, when the temperature reaches the overheating range, the current cutoff portion 1c contracts and the movable terminal 8 comes into contact with the terminal 2. As a result, both ends of the actuator 1 are short-circuited, and power supply to the actuator 1 is cut off.

In the first to eighth embodiments described above, since the temperature is detected from the amount of displacement using the deformation operation of the SMA, overheating can be reliably and accurately prevented. Furthermore, since the shape recovery temperature of the energization cutoff portion 1c can be arbitrarily set, the temperature at which energization is interrupted can be arbitrarily set.

FIG. 11 is a block diagram of the ninth embodiment. A temperature sensor 9 such as a thermistor is attached to a part of the actuator 1,
Detect the temperature of actuator 1. The detected temperature is input to the temperature determination circuit 10, and it is determined whether it is within the normal operating range. If it is not within the normal operating range, the energization operation of the energization circuit 4 is interrupted via the energization control section 6.

In addition, although in the above description there is a single displacement section, a configuration may also be adopted in which there are a plurality of displacement sections and drives a plurality of loads.

Furthermore, since the actuator of the present invention can be made smaller, it can be applied to the curved tip of an endoscope. An example of application to an endoscope is shown in FIG. 12. Figure 12 is the first
This is a case where the embodiment is applied. Similarly, it is also possible to apply the second to ninth embodiments to an endoscope.

The endoscope 23 is formed by integrally connecting an operating section 18, an insertion section 20 having a curved section 17 at its tip, and a universal cord 19 having a light guide fiber (not shown). A pair of actuators 1 and a pair of terminals 2 each made of SMA are provided in the curved portion 17 . Actuator 1, terminal 2
are connected in series, and both ends of these series circuits are connected to a current-carrying circuit 4 via a current-carrying line 3. Energizing circuit 4
, the resistance value detection section 5, and the energization control section 6 are provided within the light source device 21. Although not shown, the light source device 21 includes a light source that supplies illumination light to the light guide fiber. Both ends of each actuator 1 are connected to a resistance value detection unit 5 via an electric wire 3a.
connected to. The detected value of the resistance of each actuator 1 is input to the energization control unit 6, which controls the energization of the actuator 1 by the energization circuit 4, and adjusts the amount of bending of the bending portion 17.

Here, also in this example, the resistance value detection unit 5 indicates that the amount of energization increases, the temperature of the shape memory actuator 1 reaches the overheating range, and one of the energization cutoff ICs deforms and comes into contact with the terminal 2. When detected, power supply to any actuator 1 is interrupted.

Note that instead of one pair of actuators, four actuators may be provided for bending in the vertical and horizontal directions. Further, the number of curved parts is not limited to one, and a plurality of curved parts may be connected in series. In this way, the amount of curvature can be increased.

〔Effect of the invention〕

As explained above, according to the present invention, the temperature is detected from the amount of displacement by utilizing the fact that the deformation operation of the SMA depends on temperature, and the current supply is interrupted when overheating occurs.
A shape memory actuator that can reliably prevent overheating of SMA is provided.

Alternatively, overheating can be reliably prevented by providing a temperature sensor or the like to determine the temperature of the SMA and interrupting the energization.

[Brief explanation of the drawing]

FIGS. 1(a), (b), and (c) are block diagrams of a first embodiment of a shape memory actuator according to the present invention, and FIG.
a), (b), (c) are Fig. 1 (a), (b), (e)
FIG. 3 is a diagram showing the characteristics of the SMA of the first embodiment, FIG. 4 is a diagram showing the characteristics of the SMA of the second embodiment, and FIG. 5(a). (b) and (C) are block diagrams of the third embodiment, FIG. 6 is a block diagram of the fourth embodiment, FIG. 7 is a block diagram of the fifth embodiment, and FIG. 8 is a block diagram of the sixth embodiment. Figure 9(a),
(b) and (c) are block diagrams of the seventh embodiment, Figure 10 is a block diagram of the eighth embodiment, Figure 11 is a block diagram of the ninth embodiment, and Figure 12 is adapted to the first embodiment. FIG. 13 is a block diagram of a conventional overheating prevention circuit. 1... Actuator, 1a... Displacement part, 1b...
・Fixed part, IC... Current cutoff part, 2... Terminal, 3.
... Current-carrying wire, 3a ... Electric wire, 4 ... Current-carrying circuit, 5.
... resistance value detection section, 6 ... energization control section, 8 ... movable terminal, 9 ... temperature sensor, 10 ... temperature determination circuit,
17...Bending portion, 18...Operation unit, one...Universal cord, 21...Light source device. Applicant's representative Patent attorney Atsushi Tsuboi Figure 4 1-51 Figure (a) (b) ζS2 figure 5 (a) (C) Figure 9 Figure 10 Figure 11 Figure 12 Toro Figure 13

Claims (1)

[Claims] A shape memory actuator using a shape memory alloy that deforms due to temperature changes, characterized in that the shape memory actuator is provided with means for preventing overheating of the shape memory alloy.