JPH0580590B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a shape memory alloy actuator using a shape memory alloy as a driving source, and more particularly to a shape memory alloy actuator that generates rotational force.

Prior Art FIG. 11 shows an example of a conventional shape memory alloy actuator. This actuator is Ti-Ni
(50-50 at%) alloy, and has a linear shape memory alloy 1 wound into a coil, and a bias spring 2, which is a tension coil spring. Remembers the shape.
One ends of the shape memory alloy 1 and the bias spring 2 are connected to each other (numeral 3 indicates the connection point), and the other ends of the shape memory alloy 1 and the bias spring 2 are respectively connected to the fixing member 4. Fixed.

In this conventional shape memory alloy actuator, when the shape memory alloy 1 is at a low temperature, the contraction force of the bias spring 2 deforms the alloy 1 into an elongated state. Therefore, shape memory alloy 1
The connection point 3 between the spring 2 and the spring 2 has been moved to the right in the figure. However, when the shape memory alloy 1 is heated above a certain temperature, the alloy 1 tries to return to its memorized shape due to the shape memory effect and contracts against the spring 2, so the bonding point 3 moves to the left in the figure. Moving.

Problems to be Solved by the Invention Next, the operation of the conventional shape memory alloy actuator will be examined in more detail. FIG. 12 shows an example of a load-displacement diagram during recovery and deformation of the shape memory alloy 1. In this figure, the solid line shows the relationship between load and displacement when the shape memory alloy 1 recovers its shape, and the broken line shows the relationship between the load and displacement when the shape memory alloy 1 deforms. As can be seen from this figure, the restoring force exceeds the force required for deformation over the entire range of deformation.

The load-displacement diagram of the bias spring 2 is shown by a dashed line in FIG.
That is, if the point of zero displacement of the spring 2 is O _s and the spring constant of the spring 2 is K, then the load-displacement line of the spring 2 becomes a straight line with an inclination K passing through the point O _s .

When the shape memory alloy 1 is in the low-temperature martensitic phase, it is deformed from the origin O (the point where the displacement of the shape memory alloy 1 is zero) to the point _C1 by the force _Fs of the spring 2.
This point C ₁ is the point where the force F _s of the spring 2 and the force F _d required to deform the shape memory alloy 1 are balanced,
In Fig. 12, on the left side, the force F _s of the spring 2 is greater than the force F _d required to deform the shape memory alloy 1.
This is an area that exceeds the above.

Moreover, when the shape memory alloy 1 is heated from such a state to a high temperature matrix state, ideally,
A shape recovery force F _r that far exceeds the force F _d required for deformation and reaches point C ₂ is generated, and shape memory alloy 1 becomes spring 2
, and its displacement x decreases. The shape is then recovered to a point _C3 where the shape recovery force F _r and the bias force F _s of the spring 2 are balanced (note that the shape recovery force F _r
becomes smaller as the displacement x of the shape memory alloy 1 decreases). The force F _ph that can be taken out to the outside in such a heating recovery state is F _ph = F _r −F _s (1). This change in F _ph is shown by the solid curve in FIG.

As is clear from this curve, the magnitude of F _ph depends on the displacement x, and has a maximum value at the displacement X ₁ of point C ₁ , F _ph(nax) = F _r (X ₁ ) − F _s (X ₁ ) ...(2), the minimum value F _ph(nio) = at the displacement X ₃ of point C ₃
It becomes 0.

Next, when the shape memory alloy 1 is cooled, it loses its shape recovery ability, so the alloy 1 is affected by the bias force of the spring 2.
It is deformed again to point C ₁ by F _s . Therefore, the force F _pc that can be extracted to the outside during this cooling is F _pc =F _s −F _d (3). This change in F _pc is shown by the dashed curve in FIG. As is clear from this curve, the point
This force F _pc takes the maximum value at the displacement X ₃ at C ₃ , F _pc(nax) = F _r (X ₃ ) − F _d (X ₃ )...(4), and becomes the minimum at the displacement X ₁ at the point C ₁ . value
F _pc(nio) = 0.

The F _ph(nax) and F _pc(nax) become larger as the spring constant K of the spring 2 becomes larger.

Also, if the heating-cooling process described above is repeated,
Ideally, the actuator of FIG.
The cycle of motion passing through the points C ₁ -C ₂ -C ₃ -C ₄ -C ₁ in Figure 2 will be repeated. And these points
The area surrounded by C ₁ −C ₂ −C ₃ −C ₄ −C ₁ is 1
The energy extracted in one movement cycle is Q _p . In addition _, the maximum displacement X _nax that can be taken out to the outside is X _nax = _{X 1 −} Spring constant K
The smaller the value, the larger the value.

As can be seen from the above, even if the maximum displacement that can be completely recovered in the no-load state of the shape memory alloy 1 used is X _R and the recovery force at that time is F _R , the maximum displacement that can actually be taken out to the outside is Displacement X _nax and maximum force that can actually be extracted to the outside during heating
F _ph(nax) is a much smaller value than these.
Also, as mentioned above, X _nax , F _ph(nax) and F _pc(nax)
depends largely on the spring constant K of spring 2 and the installation position of the O _s point of spring 2. If the spring constant K and the installation position of the O _s point are changed to increase X _nax , F _{ph(nax )} , F _pc(nax) becomes significantly smaller, and conversely
By increasing F _ph(nax) and F _pc(nax) ,
X _nax becomes significantly smaller, and the fluctuations in the external forces (output) F _ph and F _pc become larger.

However, in actuators for robots, etc., it is possible to extract a certain amount of force to the outside during heating recovery and cooling deformation of the shape memory alloy, and the range of displacement can be widened. It is desirable that there be little variation in the magnitude of the force that can be extracted over a wide range of displacement.

Purpose of the Invention The present invention has been made in view of the above circumstances, and is capable of extracting a certain amount of torque to the outside during heating recovery and cooling deformation of a shape memory alloy, and suppressing the range of displacement. It is an object of the present invention to provide a shape memory alloy actuator that can be used over a wide range of displacement and has little variation in the magnitude of torque that can be taken out over this wide range of displacement.

Means for Solving the Problems The shape memory alloy actuator according to the present invention has the following features:
a rotatable winding member; a wire member having at least a portion made of a shape memory alloy, being wound around the winding member and having a portion fixed to the winding member; bias means for applying a bias torque in a predetermined direction to the winding member to apply a tensile force to the wire material through the winding member; Among them, the bias torque is made smaller as the rotation angle of the wrapping member becomes larger in the bias torque direction.

Effect In the present invention, since the bias means has the above-mentioned characteristics, for example, the curve shown in FIG.
Contrary to the case of conventional actuators, at least within a certain range, as shown by T _s ,
The smaller the elongation deformation of the shape memory alloy (that is, the more the shape recovery progresses), the smaller the tensile force acting on the wire material (in Fig. 1, the curve T _r represents the load when the shape memory alloy recovers its shape). The relationship between torque and displacement, and the curve _Td represents the relationship between load torque and displacement during deformation of shape memory alloy 1, respectively).

Therefore, as shown by the curves T _ph and T _pc in Fig. 2, a certain amount of torque can be extracted to the outside during heating recovery and cooling deformation of the shape memory alloy, and the displacement range is can be made over a wide range, and there is little variation in the magnitude of the torque that can be extracted over this wide displacement range, making it suitable for use as an actuator for a shoulder joint in a robot, for example.

Embodiments Hereinafter, the present invention will be described based on embodiments shown in the drawings.

3 to 7 show one embodiment of the present invention. In this embodiment, a rotating shaft 6 is rotatably supported by the box-shaped main body 5, and the tip of the rotating shaft 6 projects outside of the main body 5. A wrapping member 7 is fixed to the rotating shaft 6 inside the main body 5, as shown in FIGS. 4 and 5. The wrapping member 7 has a fan-shaped portion 7
a, and a pair of arm portions 7b that protrude in parallel to each other from this fan-shaped portion 7a.

The circular arc portion 7c of the fan-shaped portion 7a of the wrapping member 7
A linear shape memory alloy 8 made of a Ti-Ni alloy is wound around it. Note that the arc portion 7c of the wrapping member 7 forms an arc centered on the rotating shaft 6. This arc portion 7c has a seventh
As shown in the figure, a groove 7d is formed to prevent the shape memory alloy 8 from coming off the wrapping member 7. Moreover, the shape memory alloy 8 is
It memorizes a straight shape with length L (however,
In the present invention, the shape memory alloy 8 is operated by utilizing shape recovery from elongation deformation, so the shape memory alloy 8 may memorize a curved shape).

One end of the shape memory alloy 8 is attached to a wrapping member 7
The other end is fixed to the main body 5.

The pair of arms 7b are simply provided with a bias, which will be described later.
It is separated only to avoid mechanical interference with the spring 10, and essentially functions as one arm. Between the tips of these arms 7b is a spring support rod 9. attached. One end of a bias spring 10 made of a tension coil spring is attached to the spring support rod 9, and the other end of this spring 10 is attached to the main body 5 at a point Q. The spring 10 exerts a tensile force on the shape memory alloy 8 via the wrapping member 7.

Next, the operation of this embodiment will be explained.

Since the shape memory alloy 8 is stretched by the contraction force of the bias spring 10, the alloy 8 undergoes an elongation displacement when the alloy 8 is at a low temperature. Therefore, the winding member 7 is rotated clockwise in the figure as shown in FIG. However, when the shape memory alloy 8 is heated to a certain temperature or higher (such heating can be achieved, for example, by applying electricity between both ends of the alloy 8), the alloy 8 retains its memorized shape due to the shape memory effect. Since it contracts against the spring 10 in an attempt to return to the length L, the wrapping member 7 and the rotating shaft 6 rotate counterclockwise.

Moreover, when the heating is stopped, the shape memory alloy 8 loses its shape recovery force, so the shape memory alloy 8 is again subjected to elongation deformation by the force of the spring 10, and the wrapping member 7 and the rotating shaft 6 are moved clockwise. Rotate.

Next, the operation of this embodiment will be explained in more detail. Assuming that the radius of the circular arc portion 7c of the wrapping member 7 is R, when the rotating shaft 6 rotates θ, the elongation x of the total length of the shape memory alloy 8 is approximately x=R・θ (6) (however, Here, the case where the shape memory alloy 8 has the length L of the memorized shape is assumed to be θ=0, and the direction of rotation in which the shape memory alloy 8 undergoes elongation deformation, that is, the clockwise rotation in the figure, is defined as the positive direction. do).

As a result, the torque T _r based on the elongation x and the shape recovery force of the shape memory alloy 1 and the force T _d required to deform the shape memory alloy 1 are
The results are as shown by the curves T _r and T _d in the figure, respectively.

On the other hand, as shown in FIG. 5, the distance between the fixing point Q of the spring 10 to the main body 5 and the rotation shaft 6 is A, the distance between the spring support rod 9 and the rotation shaft 6 is B, and the distance between the rotation shaft 6 and the rotation shaft 6 is Let α be the angle between the straight line connecting the point Q and the straight line connecting the rotating shaft 6 and the spring support rod 9, Y be the length of the spring 10 when no load is applied, and y be the elongation of the entire length of the spring 10. Then, (Y+y) ² =A ² +B ² +2ABcosα...(7).

Therefore, the elongation y of the spring 10 is y=√ ² + ² + 2− (8) Therefore, if the spring constant of the spring 10 is K, the bias force F _s of the spring 10 is F _s =K・y=(K√ ² + ² + 2
-Y)...(9) Also, if the distance (moment arm length) between the line of action of the force of the spring 10 and the rotating shaft 6 is C, then C=ABsinα/L...(10) Therefore, , bias torque due to spring 10
T _s is T _s = F _s・C=K(√ ² + ² + 2
−Y)・ABsinα/L…(11)

Then, when θ=0, if α=β, then α=β−θ, so equation (11) becomes T _s =K{√ ² + ² +2(−
)−Y}・ABsin(β−θ)/L (12).

The relationship between T _s and θ is shown in FIG. As is clear from the figure, in the case of this actuator, the line of action of the force of the spring 10 and the rotation axis 6
Since the distance C between θ decreases as θ becomes smaller, the bias torque T _s by the spring 10
also decreases as θ becomes smaller.

Therefore, if the unloaded length Y and spring constant K of the spring 10 are appropriately selected, the characteristics of the bias mechanism consisting of the spring 10 etc. as shown in FIG. 8 can be changed to the bias means shown in FIG. can have almost the same properties as the ideal property example, and therefore,
During heating recovery and cooling deformation of the shape memory alloy 8, a relatively large torque T _ph ′T _pc can be extracted to the outside, and the displacement range can be widened, and moreover, in this wide displacement range, the above-mentioned Fluctuations in the magnitude of the extractable torque T _ph ′T _pc can be reduced.

FIGS. 9 and 10 show another embodiment of the present invention, in which a shape memory alloy is used as the biasing means.

A rotating shaft 12 is rotatably supported by the box-shaped main body 11, and the tip of the rotating shaft 12 projects outside of the main body 11. A fan-shaped wrapping member 13 is fixed to the rotating shaft 12 inside the main body 11 .

Linear shape memory alloy made of Ti-Ni alloy 14
and 15 have one end fixed to the center of the circular arc portion 13a of the wrapping member 13 (numeral 16 indicates the fixing point), and the fixing point 16
A nearby portion is wrapped around the arc portion 13a. Note that the arc portion 13a of the wrapping member 13
As in the embodiment described above, the shape memory alloys 14 and 15 form a circular arc centered on the rotating shaft 12, and a groove is formed to prevent the shape memory alloys 14 and 15 from coming off from the circular arc portion 13a.

The other ends of the shape memory alloys 14 and 15 are fixed to the main body 11. Here, the shape memory alloys 14 and 15 are both straight and have a length L.
(However, as mentioned earlier, in the present invention, the shape memory alloys 14 and 15 mainly utilize the shape recovery force from elongation deformation, so the shape memory alloys 14 and 15 (The curved shape may be memorized.) When both shape memory alloys 14 and 15 are in a low temperature state, this actuator is in the state shown in FIG.
In this case, both shape memory alloys 14 and 15 are in a state of being subjected to elongation deformation due to the application of tensile force.

Next, the operation of this embodiment will be explained.

When one shape memory alloy 15 is kept in a low temperature state, the other shape memory alloy 14 is heated to a certain temperature or higher (such heating is performed, for example, when the shape memory alloy 14
(can be realized by passing current between both ends of the
The alloy 14 attempts to return to the length L of the original memorized shape due to the shape memory effect, and contracts against the shape memory alloy 15. Moreover, at this time, the shape memory alloy 15 undergoes a larger elongation deformation. Therefore,
The winding member 13 and the rotating shaft 12 are rotated counterclockwise in the figure.

In addition, contrary to the above case, when shape memory alloy 15 is heated to a certain temperature or higher while shape memory alloy 14 is kept at a low temperature, the shape memory effect causes the alloy 15 to change the length of the memorized shape. In an attempt to return to L, it contracts against the shape memory alloy 14. Also,
At this time, the shape memory alloy 14 undergoes greater elongation deformation. Therefore, the wrapping member 13
The rotating shaft 12 is rotated clockwise in the figure.

In this embodiment as well, the shape memory alloy 14 or 15 in the low temperature state functions as the biasing means.
The distance D between the line of action of the force that resists deformation and the rotating shaft 12 (the length of the moment arm) becomes smaller as the elongation deformation of the heated shape memory alloy becomes smaller (in other words, as the shape recovery progresses). ) become smaller.
Therefore, the tensile force that acts on the shape memory alloy that is heated by the shape memory alloy (biasing means) at the lower temperature becomes smaller as the elongation deformation of the latter shape memory alloy becomes smaller. The same effect can be obtained as in the case of .

In each of the above embodiments, the shape memory alloy itself is directly wrapped around the wrapping member, but it is also possible to connect a linear non-shape memory alloy to the shape memory alloy and wrap this non-shape memory alloy around the wrapping member. It may also be wrapped around the member.

Effects of the Invention As described above, the shape memory alloy actuator according to the present invention can extract a certain amount of torque to the outside during heating recovery and cooling deformation of the shape memory alloy, and can widen the range of displacement. Moreover, there is little variation in the magnitude of the torque that can be taken out over this wide displacement range, making it suitable for use as an actuator for a shoulder joint in a robot, for example.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between the displacement of the bias means and the bias force in the present invention, FIG. 2 is a characteristic diagram showing an example of the ideal output torque characteristic of the shape memory alloy actuator according to the present invention, and FIG. FIGS. 4 and 5 are perspective views showing one embodiment of the shape memory alloy actuator according to the invention; FIGS. 4 and 5 are sectional views showing said embodiment in different operating states, and FIG.
The figure is a view taken in the direction of arrow P in FIG. 5, FIG. 7 is a cross-sectional view of the circular arc portion of the wrapping member in the embodiment, and FIG. 8 is a load-displacement diagram of the shape memory alloy and the spring in the embodiment. 9 and 10 are cross-sectional views showing other embodiments of the present invention in different operating states, FIG. 11 is a front view showing a conventional shape memory alloy actuator, and FIG. 12 is a shape memory alloy actuator in the conventional example. Load-displacement diagrams for alloys and springs,
FIG. 13 is a characteristic diagram showing the output characteristics in the conventional example. 7... Wrap member, 8... Shape memory alloy, 1
0...Bias spring, 13...Wrap member,
14, 15...shape memory alloy.

Claims (1)

[Claims] 1. A rotatable winding member, and a wire member having at least a portion made of a shape memory alloy, which is wound around the winding member and partially fixed to the winding member. , bias means for applying a tensile force to the wire material through the winding member by applying a bias torque in a predetermined direction to the winding member, the biasing means having at least a predetermined direction. A shape memory alloy actuator characterized in that the bias torque decreases as the rotation angle of the wrapping member increases with respect to the bias torque direction within the range.