JPS6146477A - Actuator - Google Patents

Abstract

PURPOSE:To prevent overheat of a shape memory alloy and characteristics deterioration of the shape memory alloy, by using a positive-characteristics resistor as a heater for heating the shape memory alloy, and utilizing a self- temperature control function of the positive-characteristics resistor. CONSTITUTION:A plate-like shape memory alloy 1 such as Ti-Ni alloy and a positive-characteristics resistor 2 are sandwichedly combined with each other through a silicone resin 3 as an insulating material having good heat conductivity to form an actuator. The shape memory alloy 1 is engaged with a phosphor bronze leaf spring 4 for allowing bidirectional operation of the alloy 1. The actuator is integrally formed with a housing 5 made of Al. External terminals 6 are exposed from electrodes of the positive-characteristics resistor 2. When power is supplied to the external terminals 6, temperature of the positive-characteristics resistor 2 is increased to heat the shape memory alloy 1 through the silicon resin 3. As a result, the shape memory alloy 1 functions to return to a linear shape owing to its shape memory effect, thus operating as an actuator.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an actuator using a shape memory alloy.

Conventional Structure and Problems When a shape memory alloy (hereinafter referred to as SMA) is heated above its transformation temperature, it attempts to return to its memorized shape, causing displacement and generating force. In recent years, there has been active research and development into actuators that take advantage of this property.

Heating methods for operating this actuator include an indirect method and a direct method. The indirect method is a method in which SMAf is heated from outside using a heater or hot air. The direct method is a method that applies electricity to the SMA and utilizes self-heating due to the electrical resistance of the SMA.

Since the characteristics of SMA deteriorate when it is overheated, it is necessary to ensure that the maximum operating temperature is not exceeded in any heating method. The maximum operating temperature is generally about 150° C. when the SMA is a copper alloy, and about 200° C. when the SMA is a Ni-Ti alloy. If used at temperatures exceeding these temperatures, changes in transformation temperature and operational displacement may occur.
- This may occur, making it impossible to perform accurate control.

The following two methods are known to avoid overheating. One is a lock method. In this method, after the SMA is activated by heating, the movement of the SMA is immediately locked with a stopper and the heating is stopped.If you want to return the SMA to its original operation, move the stopper with another actuator. This is to release the lock. The others are energized power control methods.

In this method, the temperature of the heater or the temperature due to self-heating of the SMA is maintained at a constant temperature by controlling the current value or the interval between currents to be applied, respectively, using an electronic circuit.

These conventional methods have the following problems.

In the locking method, a locking actuator is required, resulting in a complicated structure, large size, and high cost. In the energized power control method, a separate electronic control circuit is required, which also increases the size of the system and increases the cost.

OBJECTS OF THE INVENTION The present invention is intended to solve such problems, and it is an object of the present invention to provide an actuator that has a simple structure and prevents overheating of the SMA.

Structure of the Invention To achieve this object, the present invention uses a positive characteristic resistor as a heater for heating the SMAe.

A positive characteristic resistor is a resistor whose electrical resistance suddenly increases by 3 to 7 orders of magnitude when the temperature rises to above the temperature of the material, and is also called a PTC resistor or a PTC thermistor. Due to this property, when a positive characteristic resistor is energized, it has a current (power) limiting effect at temperatures above one temperature, and can maintain its own temperature at a desired constant level.

Barium titanate ceramics are well known as positive characteristic resistors, and mixtures of carbon and polymer materials are also in practical use. The temperature can be changed by changing the composition and mixing ratio.

Therefore, by using a configuration in which a positive characteristic resistor is applied to the heater that heats SM/l, the self-temperature control function of the positive characteristic resistor prevents overheating above one temperature. It becomes possible to maintain. Therefore, deterioration of the characteristics of the SMA can be prevented.

Description of examples Hereinafter, the present invention will be explained by way of examples thereof.

FIG. 1 shows an embodiment of the present invention, and FIG. 1(a) is an external perspective view, and FIG. 1 (bl is a sectional configuration diagram thereof).

The one in the figure is a 5M plate made of T i Ni alloy.
A1 and positive characteristic resistor 2 are sandwiched together with silicone resin 3, which is an insulator with good thermal conductivity, to form a 5MA1
This actuator has a configuration in which a bronze plate spring 4 is locked, an aluminum housing 5 is integrated, and an external terminal 6 is exposed from the electrode of a positive characteristic resistor 2 for two-way operation.

The operation of this actuator is as follows.

After cold rolling, 5MAl was held in a linear flat plate shape and subjected to memory heat treatment at 475° C. for 1 hour, so the memory shape is a flat plate. Figure 1 shows the low temperature state below the transformation temperature.
Since 5MA1 is easily deformed at low temperatures, it is bent by the leaf spring 4. When 0 current is applied to the external terminal 6, the temperature of the positive characteristic resistor 2 rises, and 5
When heat is transferred to MAl and the temperature exceeds the transformation temperature, 5MA1 moves in an attempt to return to its linear shape due to the shape memory effect. If the temperature of the positive characteristic resistor 2 is set to about 120° C., the SMA 1f4 always remains in a high temperature state in order to maintain that temperature.

When the current supply is stopped, the entire actuator cools down, and when the temperature drops below the transformation temperature, 5MA1 moves into a bent shape due to the force of the leaf spring 4.

In this way, it operates as an actuator when energized.

FIG. 2 shows another embodiment of the present invention, and FIG.
) is an external perspective view, and FIG. 2 fbl is a cross-sectional configuration diagram thereof.

The one in the figure is a coil-shaped SM made of T1Ni alloy.
The collar 10't of the movable rod 9 is placed between A7 and the bias spring 8.
- placed and placed inside the cylindrical positive characteristic resistor 11;
The actuator is sealed with a side cover 12, with external terminals 13 of a positive characteristic resistor 11 exposed and coated with silicone resin 14.

The operation of this actuator is as follows.

SMA7 was a cold drawn wire material kept in a fully compressed coil shape, that is, in an open pitch state, and subjected to memory heat treatment at 465° C. for 1 hour. FIG. 2 shows a high temperature state above the transformation temperature, where the temperature rises due to energization of the positive characteristic resistor 11, and the bias spring 8 of the compression coil spring is caused by the force that causes the SMA 7 to stretch due to the shape memory effect. This is the state in which the rod 9 is moved to the right by compressing it.

When the current supply is stopped, the entire actuator cools down, and when the temperature drops below the transformation temperature, the SMA 7 is compressed by the bias spring 8 because it is easily deformed, and the rod 9 moves to the left.

In the above embodiments, the SMA exhibiting unidirectional operating characteristics is
Because of this, a phosphor bronze plate spring or a complete combination of bias springs was used as a bias for bidirectional operation, but a bias is not necessary in the case of an SMA in which the alloy itself exhibits bidirectional operation.

Effects of the Invention Since the actuator of the present invention uses a positive characteristic resistor as a heater for the SMA, the SMA is maintained at a high temperature by heating, and even if the actuator is left in operation, the current flowing through it will not increase. This has excellent practical effects in that it does not cause overheating, requires less power in the heated state, and allows the actuator to be made smaller.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are an external perspective view and a cross-sectional configuration diagram of an actuator showing an embodiment of the present invention, and FIG. 2(a)
. (bl is an external perspective view and a sectional configuration diagram of an actuator showing another embodiment of the present invention. 1.7 Shape memory alloy (SMA), 2,1
1... Positive characteristic resistor, 4... Leaf spring,
8...Bias spring, 9...Movable rod.

Claims (3)

[Claims] (1) An actuator that uses a positive characteristic resistor as a heater to heat a shape memory alloy. (2) A positive characteristic resistor is placed in a shape memory alloy via an insulator with good thermal conductivity, and the shape memory alloy is displaced to a high temperature shape by applying electricity to the positive characteristic resistor, and then it is brought to a low temperature by stopping the electricity supply. The actuator according to claim 1, which causes displacement in a shape. (3) A patent claim in which a shape memory alloy is placed inside a tubular positive characteristic resistor, and the shape memory alloy is displaced into a high temperature shape by energizing the positive characteristic resistor, and is displaced into a low temperature shape by stopping the energization. The actuator according to the range 1 above.