JPH0519911B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric actuator, and particularly to a piezoelectric actuator that serves as a drive source for drive devices such as printers and relays.

[Conventional technology]

Conventionally, electromagnetic actuators have been widely used as drive sources for printers, relays, and the like. This electromagnetic actuator generates a magnetic field by passing power through the coil, and uses that magnetic force to drive the movable parts, so it not only requires a large amount of energy due to copper loss and iron loss, but also generates heat. There were also problems such as magnetic interference. Therefore, in recent years, electrical/mechanical energy conversion efficiency has improved,
A printing hammer for printers as shown in Figure 5, which uses a piezoelectric element with low power consumption, low heat generation, and no magnetic interference, has been reported (IEICE Mechanical Components Study Group material)
EMC84−49).

FIG. 5 is a schematic side view of a printing hammer for a printer showing an example of a conventional piezoelectric actuator.

In the same figure, the printing hammer has a plate spring 32 at the tip of the piezoelectric element 31 in the direction of extension (direction of arrow A).
The flight hammers 33 supported by the two are arranged so as to be in contact with each other. The flight hammer 33 is provided with a printing wire 34 for printing dots.

In this printing hammer, when a voltage is applied to the piezoelectric element 31, the flight hammer 33
1 receives a force from the piezoelectric element 31 and is accelerated, leaves the piezoelectric element 31 and flies. Then, the printing wire 34 collides with the platen 37 via the ink ribbon 35 and paper 36 in front, and prints a dot on the paper 36. After that, the flight hammer 33 receives the repulsive force from the platen 37 and the leaf spring 32.
It returns to the piezoelectric element 31 due to the restoring force.
By repeating this action, characters and figures are expressed as a collection of dots.

[Problem that the invention seeks to solve]

In the conventional printing hammer for printers described above, in order to speed up the printing operation, a leaf spring 3 is used.
2, the flight hammer 33, and the printing hammer 34, it is necessary to increase the natural frequency of the vibration system, and for this purpose, the spring constant of the leaf spring 32 must be increased. However, when the spring constant of the leaf spring 32 is increased, the energy transmitted from the piezoelectric element 31 to the flight hammer 33 is absorbed by the leaf spring 32.
Since the proportion spent on the deformation of the dot 2 increases, the kinetic energy of the flight hammer 33 decreases, and the density of the printed dots becomes thinner.

Therefore, in order to achieve faster printing operations without reducing print density, it is necessary to increase the energy transmitted from the piezoelectric element 31 to the flight hammer 33. When this transmitted energy is increased,
By increasing the spring constant of the leaf spring 32, the speed can be increased and the required printing density can be ensured.

In order to increase the transmitted energy, the energy generated by the piezoelectric element 31 may be increased, and the printing voltage may be increased. However, when the applied voltage is increased, the acceleration of the piezoelectric element 31 increases, and the internal stress generated by the chronic force of the piezoelectric element 31 itself increases, reducing reliability and causing a problem that it may break.

An object of the present invention is to provide a piezoelectric actuator that solves these problems.

[Means for solving problems]

The piezoelectric actuator of the present invention includes a piezoelectric element;
and a frame made of a shape memory alloy material that surrounds part or all of the piezoelectric element, and the strain recovery action of the frame caused by raising the temperature of the frame to a temperature higher than the transformation temperature causes the piezoelectric element to change in the direction of expansion and contraction. Both ends are fixed inside the frame, and compressive stress is applied to the piezoelectric element.

[Effect]

Shape memory alloys have a unique transformation temperature depending on their alloy composition; below the transformation temperature, the alloy structure exhibits a martensitic phase, and above the transformation temperature, the alloy structure exhibits an austenite phase (matrix phase). When a shape memory alloy is subjected to elastic deformation, a huge elastic strain that is several to several tens of times greater than that of ordinary alloys can be obtained.
Above the alloy's transformation temperature, the strain returns to zero as soon as the load is removed. This is generally called superelasticity. However, when deformed below the transformation temperature, this elastic strain is almost permanently preserved. When heated from this state to above the transformation temperature, the strain becomes zero and the material returns to its original shape, similar to the superelastic state.

Therefore, when fixing a piezoelectric element to a frame, the frame is made of a shape memory alloy, the inner length of the frame is memorized to be smaller than the length of the piezoelectric element, and the alloy structure constituting the frame is After applying force to the frame to deform it when it is in the martensitic phase and making the inner length of the frame larger than the length of the piezoelectric element, the piezoelectric element is inserted inside the frame, and then the alloy structure is changed to the austenite phase by raising the temperature above the transformation temperature. Then, the frame is deformed and the piezoelectric element is fixed inside the frame.

As a result, the piezoelectric element fixed inside the frame receives a compressive force from the frame. Further, even when the piezoelectric element is expanded by applying a voltage, the frame is elastically deformed, so a compressive force is always applied to the piezoelectric element.

Piezoelectric elements are strong against compressive stress but very weak against tensile stress. In the piezoelectric actuator of the present invention, by fixing the piezoelectric element inside the frame, a compressive force is always applied to the piezoelectric element, so the reliability of the piezoelectric element is greatly improved. Therefore, the applied voltage can be increased compared to the conventional case, and the output energy can be increased.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic side view showing a first embodiment of the present invention, and a piezoelectric actuator is composed of a piezoelectric element 11 and a U-shaped frame 12 made of a shape memory alloy. The inner length of the frame 12 is memorized to be smaller than the length of the piezoelectric element 11 in the direction of extension (direction of arrow A), and when the alloy structure constituting the frame 12 is in the martensitic phase below the transformation temperature, Apply force to frame 12 and frame 1
After deforming the deformed portion 12a of No. 2 to make the length of the inside of the frame 12 larger than the length of the piezoelectric element 11, the piezoelectric element 11 is inserted into the inside of the frame 12, and the alloy structure is changed to austenite at a temperature higher than the transformation temperature. The piezoelectric element 11 is fixed inside the frame 12 by restoring the deformation of the frame 12.

As a result, the piezoelectric element 11 fixed inside the frame 12 receives compressive stress from the frame 12, and the reliability of the piezoelectric element 11 is greatly improved. Furthermore, since the applied voltage can be increased, output energy can be increased.

FIG. 2 shows a second embodiment of the present invention, in which the piezoelectric actuator is composed of a piezoelectric element 23 and a square-shaped frame 28 made of a shape memory alloy. The inner length of the frame 28 is memorized to be smaller than the length of the piezoelectric element 23 in the direction of extension (direction of arrow A), and when the alloy structure constituting the frame 28 is in the martensitic phase below the transformation temperature, the frame 28 28 in the direction of arrow A to stretch the deformed portions 28a and 28b of the frame 28 to make the inner length of the frame 28 larger than the length of the piezoelectric element 23, and then insert the piezoelectric element 23 inside the frame 28. Thereafter, the temperature is raised to a temperature higher than the transformation temperature to change the alloy structure to an austenite phase, the deformation of the frame 28 is restored, and the piezoelectric element 23 is fixed inside the frame 28.

As a result, the piezoelectric element 23 fixed inside the frame 28 receives compressive stress from the frame 28, and the reliability of the piezoelectric element 23 is greatly improved. Furthermore, since the applied voltage can be increased, output energy can be increased.

FIG. 3 is a schematic side view of a printing hammer for a printer showing an example of use of the first embodiment shown in FIG.

In the figure, the piezoelectric actuator includes a piezoelectric element 11 and a U-shaped frame 12 made of a shape memory alloy.
The piezoelectric element 11 is fixed inside the frame 12 by the strain recovery operation of the frame 12. Further, the printing hammer is supported by a leaf spring 13, and a flight hammer 15 to which the printing wire 14 is connected is arranged so as to be in contact with the frame 12 at one end of the piezoelectric element 11 in the direction of extension (direction of arrow A). There is.

In this printing hammer, when a voltage is applied to the piezoelectric element 11, the flight hammer 15
1 is accelerated by the force from the piezoelectric element 11, and flies away from the frame 12. Then, the printing wire 14 collides with the platen 18 via the ink ribbon 16 and paper 17 in front, and prints dots on the paper 17. Thereafter, the flight hammer 15 returns to the frame 12 due to the repulsive force from the platen 18 and the return force of the leaf spring 13.

According to this usage example, the piezoelectric element 11 is
Since the piezoelectric element 11 receives compressive stress in advance from the piezoelectric element 2, the chronic force of the piezoelectric element 11 itself when the piezoelectric element 11 is expanding when a voltage is applied does not act on the piezoelectric element 11 as a tensile stress, resulting in highly reliable printing. It becomes a hammer. Further, since the output energy can be increased by increasing the voltage applied to the piezoelectric element 11, the speed can be increased.

Next, FIG. 4 is a schematic side view of a latch type relay showing an example of use of the second embodiment shown in FIG. 2.

In the figure, the piezoelectric actuator is composed of first and second piezoelectric elements 23 and 24 and square-shaped first and second frames 28 and 29 made of shape memory alloy. The elements 23 and 24 are fixed inside the first and second frames 28 and 29, respectively, by a strain recovery operation of the frames 28 and 29. In addition, the latch type relay is the flight member 2.
0 is inserted into the mounting parts 22a, 22b of the mounting member 22 and bent, and the flight member 20
First and second piezoelectric elements 23 and 24 are arranged on both sides of the reversing spring 21, respectively, and a movable contact 25 that is interlocked with the operation of the reversing spring 21 and a first and second fixed contact 26 opposite thereto. , 27 are connected to the mounting member 22. First and second piezoelectric elements 2
3 and 24 are the first and second frames 28, respectively.
29, and the first and second frames 2
8 and 29 are connected to the mounting member 22.

This latch-type relay flies the flying member 20 by the force generated by the first or second piezoelectric element 23 or 24, causes the reversing spring 21 to perform a reversing action, and moves the movable contact 25, from a to b or b in FIG. a
Switch to the state shown in

According to this usage example, the first and second piezoelectric elements 2
3 and 24 are the first and second frames 28, respectively.
Since compressive stress is previously received from the piezoelectric element 29, the inertial force of the piezoelectric element itself when the first or second piezoelectric element 23 or 24 is expanding when a voltage is applied does not act on the piezoelectric element as a tensile stress. , resulting in a highly reliable latch type relay. Moreover, by increasing the applied voltage, the first and second piezoelectric elements 2
Flight member 2 by increasing the generated energy of 3 and 24
Since the flight distance of 0 can be increased, the movable contact 25
A long stroke can be realized, making it a latch type relay for high power.

The shape memory alloy may be 65% copper Cu, 30% zinc Zn, 5% aluminum Al, or other shape memory alloys TiNi, CuAlNi, etc., and the composition of the alloy may be changed depending on the fixed conditions.

〔Effect of the invention〕

As explained above, by using the piezoelectric actuator of the present invention, it is possible to achieve high speed and long stroke, and there is an effect that a highly reliable printing hammer, relay, etc. can be obtained.

[Brief explanation of drawings]

1 and 2 are the first and second embodiments of the present invention, respectively.
FIG. 3 is a schematic side view of a printing hammer for a printer showing an example of the use of the first embodiment shown in FIG. FIG. 5 is a schematic side view of a latch type relay showing an example of use of the second embodiment, and FIG. 5 is a schematic side view of a printing hammer for a printer showing an example of a conventional piezoelectric actuator. 11, 23, 24, 31...piezoelectric element, 12,
28, 29... Frame, 13, 32... Leaf spring, 14, 34... Printing wire, 15, 33...
Flight hammer, 16,35...ink ribbon,
17,36...paper, 18,37...platen, 2
0... Flight member, 21... Reversing spring, 22... Mounting member, 25... Movable contact, 26, 27... Fixed contact.

Claims (1)

[Claims] 1 Consisting of a piezoelectric element and a frame made of a shape memory alloy material that surrounds part or all of the piezoelectric element, the piezoelectric element is A piezoelectric actuator, wherein both ends of the piezoelectric actuator in the direction of expansion and contraction are fixed inside the frame, and compressive stress is applied to the piezoelectric element.