JPH042796B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in actuators using shape memory alloys.

(Prior art and its problems) Various actuators are known that utilize the shape memory effect of Ni-Ti alloys. In many of these, shape memory alloys having unidirectional properties are used because if the shape memory alloy itself has two-way properties, it is not possible to accurately set the shapes on the high and low temperature sides. Methods for obtaining bidirectional characteristics using a unidirectional shape memory alloy include a bias method and a differential bidirectional element. These methods utilize the properties of being soft at low temperatures and hard at high temperatures, such as the bias method shown in FIG. 4.

That is, the shape memory alloy coil 5 and the coil spring 6
are arranged in parallel to the central axis 8 via the stopper 7.When the temperature is low, the shape memory coil is in a contracted shape due to the bias force of the coil spring, but when the shape memory coil is heated and becomes high temperature, The shape memory coil expands by overcoming the bias force of the coil spring, pushing the stopper to the right in the drawing, and the central axis moves to the right. When the heating is stopped and the temperature becomes low, the bias force of the coil spring becomes stronger, pushing back the shape memory coil and moving the stopper and central axis to the left. By repeating such operations, driving forces in two directions are applied to the central shaft. In addition, in the differential type, a shape memory coil is used instead of the coil spring 6 shown in Fig. 4, and the two left and right shape memory coils are alternately heated to obtain driving force in two directions in the same way as above. .

However, both the bias type and the differential type use the property of returning to the memorized shape when heated, so they return to the original position when the temperature becomes low. When maintaining the moved position, it is necessary to maintain that temperature for the period necessary to maintain shape memory. That is, in the bias type shown in FIG. 4, if the stopper is moved to the right and the temperature is to be maintained for a certain period of time, it is necessary to maintain the shape memory coil at a certain temperature for a certain period of time. Normally, methods for heating shape memory coils include heating the coil by directly applying electricity to the coil, heating with hot air, etc. However, current control devices, adjustment devices such as timers, and hot air heating devices are required. However, the cost is high, and there are also restrictions on the installation location, which pose major obstacles to the use of this type of drive device.

The inventor studied the above problems, made this improvement, and created it as an "actuator" on January 31, 1986.
A patent application was filed on the same day. As shown in Fig. 2, this invention allows a rectangular plate of shape memory alloy to memorize the shape of a rectangular shape as shown in Fig. 2 a, and then inverts this into a shape symmetrical to the memorized shape as shown in Fig. 2 b. The shape memory alloy plates are inserted into the shaft 4 through the stopper 3 in parallel with the shape memory alloy plate 2, and the upper and lower ends of the shape memory alloy plates are fixed. can be heated alternately. When the shape memory alloy plate 1 is heated to a predetermined temperature when it is stable at low temperatures in this state, the shape memory alloy plate 1 returns to its original memorized shape as shown in FIG. 2c. At this time, the shape memory alloy plate 2 also jumps from the memory shape of b to buckle and reverse as shown in c, and even if the shaft 4 is driven to the right and stops heating and is cooled, it remains stable in this state. Next, when the shape memory alloy plate 2 is heated in this state, the shape memory alloy plate 2 returns to the memorized original shape as shown in FIG. 1b, and the shape memory alloy plate 1 also jumps and buckles and reverses. The shaft 4 is driven to the left and remains stable in this state. By repeating the above operations, it becomes possible to provide intermittent or continuous drive in two directions to the shaft.

That is, since at least one of the shape memory alloy plates is inverted from its memorized shape and combined, it jumps and inverts during operation and becomes a buckled state, so that a stable stationary state can be maintained even during cooling.

(Problems to be Solved by the Invention) Although the above invention achieved the intended purpose, it was found that another problem arose. That is, when viewed microscopically, at low temperatures, the arc appears to be collapsed by a length b according to the stress distribution, as shown by the dotted line in FIG. 3, and the displacement decreases by that amount. This causes some play in the actuator itself, resulting in backlash.

To prevent this, it is extremely difficult to memorize a shape that corresponds to the stress distribution at low temperatures due to changes in plate thickness, heat treatment errors, etc. In order to prevent the above crash, it is necessary to apply a stopper to the shaft further before the position indicated by the dotted line, but this causes large strain on the alloy plate, causing fatigue to the alloy plate and reducing the number of operations. It was found that repeated use caused a decrease in service life. The present invention has been developed as a result of studying the above-mentioned problems, and has developed an actuator that prevents backlash and has a long life.

(Means and effects for solving the problem) The present invention stores a plurality of shape memory alloy plates in an arcuate or conical shape having a flat portion on the top plate, and stores one or more shape memory alloy plates among them. The shape memory alloy plate is reversed symmetrically with the shape and combined in parallel with the shaft, and the reversed shape memory alloy plate is returned to the memorized shape by heating, and the other shape memory alloy plate is reversed to drive the shaft in two directions. It is an actuator characterized by:

That is, as shown in FIG.
A rectangular plate of shape memory alloy made of
It is memorized in an arcuate shape with a flat part at the top as shown in . One of these sheets is inverted to be symmetrical to the memorized shape at room temperature as shown in 1 in Figure b, and the shape memory alloy sheet 2 with the same memorized shape is placed in parallel and inserted into the shaft 4 via the stopper 3. This is what I did. The upper and lower ends of the shape memory alloy plates 1 and 2 are fixed,
In addition, each can be heated separately,
The actuator is electrically and thermally insulated. To explain this operation, when the shape memory alloy plates 1 and 2 are stable at low temperatures in the state shown in Fig. 1b, when the shape memory alloy plate 1 is heated to a predetermined temperature, the shape memory alloy plates 1 and 2 change as shown in Fig. 1c. 1 returns to the memorized original shape. At this time, the shape memory alloy plate 2 jumps from the memorized shape of b to the shape of c, buckles and reverses, and even if the shaft 4 is driven to the right, stops heating, and is cooled, it remains stable in this state. Next, in this state, when the shape memory alloy plate 2 is heated with electricity, the shape memory alloy plate 2 returns to its original memorized shape as shown in Fig. 1b, and the shape memory alloy plate 1 jumps, buckles, and reverses itself. , shaft 4
is driven to the left and remains stable in this state. By repeating the above operations, it becomes possible to provide intermittent or continuous drive in two directions to the shaft.

However, the present invention provides at least one shape memory alloy plate.
The pieces are inverted from the memorized shape and combined, and this jumps and inverts during operation, resulting in a buckled state, so that a stable stationary state can be maintained during cooling.

In addition, in the present invention, since the shape memory alloy plate is memorized in an arcuate or conical shape with a flat portion at the top, it maintains the shape of a solid line at high temperatures as shown in Fig. Due to the stress, it takes on the shape approximately shown by the dotted line. That is, the displacement of the actuator increases by the length a.

However, if this actuator is constructed so that the moving point of the shaft can only move up to the position of the memorized shape, the stress generated by the strain a acts on the shaft as back pressure.

Therefore, it is possible to manufacture an actuator without crushing. It also acts as a key to the reversal when it is reversed.

The number of shape memory alloy plates used in the present invention can be two or more, and it is preferable in terms of force balance during operation that half of these plates are inverted from the memory shape and combined. Instead of a rectangular shape, a disc shaped like a cone may be used.

In addition to Ni-Ti alloys, shape memory alloys include
Ni-Ti alloys with added tertiary elements such as Fe and Co,
In addition to Cu-based alloys such as Cu-Al-Ni and Cu-Au-Zu, commonly used shape memory alloys can be used. Further, as a heating method for the shape memory alloy, in addition to current heating, ordinary heating methods such as hot air and gas flame can be used.

(Example) An embodiment of the present invention will be described below.

A rectangular plate made of a Ni-Ti alloy was shaped into an arcuate shape having a flat portion L at the top as shown in FIG. 1a, and then subjected to shape memory heat treatment.

Next, this plate was turned over at room temperature, and as shown in FIG. 1B, the shaft 4 was passed through the alloy plate 2 and the stopper 3 together with the alloy plate 2 in the memorized shape to form an actuator. Note that shape memory alloy plate 1,
2 can be heated separately by electricity or gas flame heating. The above-mentioned actuator remains stable and stationary in the state shown in FIG. 1b at room temperature, but when the shape memory alloy plate 1 is heated, this alloy plate returns to its memorized shape. At this time, the shape memory alloy plate 2 also jumps from the memorized shape of b as shown in c, reverses, and buckles, and the shaft 4 is driven rightward, stops heating, and remains stable in this state even after cooling. Next, when the shape memory alloy plate 2 is heated in this state, the shape memory alloy plate 2 is heated as shown in FIG.
returns to its original memorized shape, and the shape memory alloy plate 1
The shaft 4 also jumps, reverses and buckles, and the shaft 4 is driven to the left and comes to a stable standstill in this state. By repeating the above operations, it is possible to drive the shaft intermittently or continuously.

In the above, an example was explained in which the shape memory alloy plate 1 is inverted from the memorized shape and combined, but the alloy plate to be inverted may be either 1 or 2, and the initial heating may be applied to the inverted alloy. ,
As that alloy returns to its original shape, the force causes another alloy to go into an inverted buckled state, and then by alternately heating it, drive in two directions can be obtained.

(Effects) As explained above, according to the present invention, by alternately heating a plurality of shape memory alloy plates, the shape can be reversed and the shaft can be moved, giving reciprocating motion in two directions, and the heating can be stopped and maintain its position even in low temperatures. Moreover, it can select and maintain two required positions, has no backlash, has high accuracy of operation, and has a long cycle life, which is extremely effective.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the operating state of the actuator of the present invention, Fig. 2 is a schematic diagram showing the operating state of the actuator of the prior art, and Fig. 3 is a schematic diagram showing the operating state of the actuator of the prior art. FIG. 4 is a schematic diagram showing the operating state of a conventional actuator. 1... Shape memory alloy plate combined inverted, 2... Shape memory alloy plate, 3... Stopper, 4... Shaft,
5...Shape memory coil, 6...Coil spring, 7...Stopper, 8...Center shaft.

Claims (1)

[Claims] 1. A plurality of shape memory alloy plates are memorized into an arcuate or conical shape having a flat portion at the top, and one or more of the shape memory alloy plates are inverted symmetrically with the memorized shape and combined in parallel on a shaft, An actuator characterized by returning a shape memory alloy plate that has been inverted by heating to a memorized shape and inverting the other shape memory alloy plate to drive a shaft in two directions.