JPH078151B2 - Electrostrictive actuator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrostrictive actuator that uses the electrostrictive action of an electrostrictive element as a driving force.

[Conventional technology]

Conventionally, this type of electrostrictive actuator has been widely used, for example, in microphones, receivers, etc., but recently, as disclosed in Japanese Patent Publication No. 45-15192, for example, application to blade driving means in camera shutters has also been proposed. Has been done.

The applicant of the present application also proposes an example applied to a blade driving means of a camera shutter as described in, for example, Japanese Utility Model Laid-Open No. 63-101925 and Japanese Utility Model Laid-Open No. 63-105125.

As shown in FIG. 6, the shutter base plate 21 has an exposure opening 21a, and a pair of shutter blades 23 pivotally supported by a support shaft 22 on the back surface of the base plate 21 to open and close the exposure opening 21a. 23, and a fork portion 25a that is pivotally supported by a support shaft 24 on the surface of the main plate 21 and that engages with the tip of an electrostrictive element described later at one end side thereof and arc-shaped holes 21b, 21b of the main plate 21 at the other end side. Through the shutter blades 23,23 slot 23
Pins 25b and 2 that can be connected to a and 23a with pin slots, respectively
An elongated opening and closing lever 25 having a fixed 5b and a base portion fixed and supported by a bracket 26 attached to the main plate 21, and a distal end portion inserted into and engaged with a fork portion 25a of the opening and closing lever 25 and has a rectangular plate shape. It was composed of an electrostrictive element 27.

Here, to explain the structure and properties of the electrostrictive element 27, the electrostrictive element 27 has a structure in which a piezoelectric ceramic plate is laminated by sandwiching an insulating plate, and when a voltage is applied to both insulated ceramic plates. Like a so-called parallel plate capacitor, electric charges are accumulated between both insulated ceramic plates and have a property of being distorted according to a potential difference between both insulated ceramic plates.
Then, even after the voltage application is stopped, the potential difference is maintained by the accumulated electric charge, so the above-mentioned distorted state is maintained, and the electric charge is not discharged until the initial state from the distorted state when the two insulated ceramics are short-circuited. It has the property of returning to the state.

The distortion characteristic of the electrostrictive element is represented by the following formula (1).

Where l: length of electrostrictive element V: drive voltage d: electrostrictive constant Th: thickness of electrostrictive element Then, in the above equation (1), It is understood that the equation (1) is converted into the following equation (2), and the displacement amount is directly proportional to the applied voltage.

Displacement amount = KV (2) Therefore, in this example, the applied voltage to the electrostrictive element 27 is increased at the same time as the shutter release, so that the amount of distortion of the electrostrictive element 27 is gradually increased. By gradually increasing the aperture diameter of the exposure opening 21a by the shutter blades 23 and 23, and by short-circuiting both terminals of the electrostrictive element 27 at the timing when a proper exposure amount is given, the electrostrictive element 27 is initialized. Exposed opening 21a
Is closed instantly.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional example, the amount of displacement of the electrostrictive element 27 is increased by increasing the length of the electrostrictive element 27 as is apparent from the above formula (1), and the electrostrictive element 27 is increased by increasing the driving force. Although it is sufficient to increase the effective area of 27, it was impossible to unnecessarily increase the shape of the electrostrictive element 27 in order to satisfy the market demand for miniaturization of the camera. For example, electrostrictive element 27
When the length (length in the direction orthogonal to the optical axis) is increased, the width of the electrostrictive element 27 is increased in order to increase the effective area of the electrostrictive element 27 by limiting the size of the lens barrel diameter. The length in the direction parallel to the optical axis) is limited by the length of the lens barrel. Therefore, in the structure in which the displacement direction of the electrostrictive element 27 is set in the direction orthogonal to the optical axis as in the above-mentioned conventional example, miniaturization of the shutter and obtaining a large displacement amount and driving force are contrary to each other. .

On the other hand, if a substantially circular electrostrictive element having a plate-like shape and a circular hole formed in the substantially central portion is used, the above inconvenience can be solved. That is, by using a part of the electrostrictive element as a fixed point and a position facing the hole across the hole as an action point, the action point can be deformed in a direction substantially parallel to the central axis of the hole. Because you can. However, when the electrostrictive element is deformed in this way, the amount of displacement differs between the position near the inner circumference and the position near the outer circumference of the electrostrictive element, and the electrostrictive element deforms like a mortar. Therefore, there is a drawback that a displacement amount and a driving force are lost at the action point.

It is an object of the present invention to provide an electrostrictive actuator that eliminates such drawbacks, makes the amount of displacement at the point of action of the electrostrictive element sufficiently large, and allows a sufficiently large driving force to be obtained. And

[Means for Solving the Problems]

In order to achieve the above object, the present invention is an electrostrictive actuator configured to obtain a driving force by fixing and distorting one end of a substantially circular plate-shaped electrostrictive element provided with a hole in a substantially central portion, The hole has a teardrop shape that tapers toward the point of application of the driving force.

[Work]

The plate-shaped electrostrictive element molded as described above has a length from the fixed point to the point of action that is along the arc and is longer than a rectangular plate having the same length in the longitudinal direction. The displacement amount of is sufficiently large. Further, the plate-shaped electrostrictive element has a structure almost equal to that of two rectangular plate-shaped elements having the same longitudinal length and arranged side by side and connected at the action point, and as a result, an effective area of sufficient size. Can be ensured, so that a sufficiently large driving force can be obtained. Furthermore, because the holes are teardrop-shaped as described above, they do not deform like a mortar like the case of circular holes,
No loss in displacement or driving force.

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiments. First, in FIGS. 1 and 2, 1 is a substantially circular plate-shaped electrostrictive element whose one end is held by a fixing member 2, and 3 is a driving force to be provided at the free end of the plate-shaped electrostrictive element 1. Point of action of 4
Is a teardrop-shaped hole formed in the central portion of the plate-shaped electrostrictive element 1 so as to taper from the fixed end toward the point of action 3 and 5 is a free end of the plate-shaped electrostrictive element 1. A driven member formed as a lever, for example, which is engaged with.

Since the electrostrictive actuator according to the present invention is configured as described above, when a voltage is applied between the front and back surfaces of the plate-shaped electrostrictive element 1, the plate-shaped electrostrictive element 1 is, for example, as shown by a chain line in FIG. When the deformed member 5 is rotated by a predetermined amount in the direction of the arrow and the front and back surfaces are short-circuited, the plate-shaped electrostrictive element 1 returns to its original shape, and at the same time, the driven member 5 is also adjusted to its original shape. Return to position. In this case, the length from the fixed point to the action point becomes the length along the arc, which is longer than that of a rectangular plate having the same longitudinal length, so that the displacement amount D at the action point becomes sufficiently large. Further, since the hole 4 has a teardrop shape as described above, it does not deform like a mortar like the plate-shaped electrostrictive element 1 having a substantially circular hole, The amount of displacement D of the free end, that is, the point of action 3 is large compared to it. According to the experiment, when the plate-shaped electrostrictive element made of the same material and having the same longitudinal length was deformed under the same condition, the displacement amount D of the present invention was increased by about 50% as compared with the conventional structure. .

The plate-shaped electrostrictive element 1 has substantially the same structure as two rectangular plate-shaped elements having the same length in the longitudinal direction, which are arranged in parallel and connected at an action point, and as a result, an effective area having a sufficient size. Can be secured, so that a sufficiently large driving force can be obtained. According to an experiment, when a plate-shaped electrostrictive element made of the same material and having the same longitudinal length was deformed under the same condition, the driving force of the present invention was increased by 70 to 150% as compared with the conventional structure. .

Incidentally, if the plate-shaped electrostrictive element is deformed into a mortar shape, the driving force will be lost, which is not preferable. However, if some loss can be ignored, the plate-shaped electrostrictive element may have a substantially circular hole.

FIGS. 3 to 5 show an embodiment in which the electrostrictive actuator according to the present invention is used as a blade driving means of a camera shutter, but it is substantially the same as the embodiment shown in FIGS. 1 and 2. The same parts are designated by the same reference numerals in the following description. 6 cooperates with the fixing member 2 to hold one end of the plate-shaped electrostrictive element 1 and exposes the opening 6a and the slots 6b, 6c. A shutter substrate 6d is provided, 7 is a pin implanted in the shutter substrate 6, and 8 and 9 are formed such that the bases are rotatably fitted to the pins 7 so that the exposure opening 6a can be opened and closed. The pair of shutter blades 10 are fixed to the shutter substrate 6 so as to form a space between the shutter blades 8 and 9 so as to accommodate the shutter blades 8 and 9, and the slot 10a and the slot 6 are aligned with the exposure opening 6a.
Cover plates provided with slots 10b, 10c, 10d which are aligned with b, 6c, 6d, respectively, and 11 are pins 12 on the back surface of the shutter substrate 6.
Is rotatably supported by a slot 11a at one end.
Is a blade opening / closing lever having a pair of pins 11b, 11c which extend through the slots 6c, 6d at the other end and extend upward, and which are respectively pin-slot connected to the shutter blades 8, 9.
The driven member 5 is configured as a crank lever rotatably supported by a bracket 13 mounted on the cover plate 10, and has a fork portion 5a for sandwiching the action point 3 of the plate-shaped electrostrictive element 1, and a fork portion 5a. It has an arm portion 5b penetrating through the slots, 10b, 6b, and a spherical lower end portion 5c fitted into the slot 11a of the blade opening / closing lever 11. In this embodiment, unlike the embodiment shown in FIGS. 1 and 2,
It is assumed that the free end of the plate-shaped electrostrictive element 1 is configured to bend downward when a voltage is applied.

Since this embodiment is constructed as described above, when a voltage is applied between the front and back surfaces of the plate-shaped electrostrictive element 1, the action point 3 is displaced downward, and the driven member 5 is rotated leftward at the position shown in FIG. Be punished. Therefore, the blade opening / closing lever 11 is rotated counterclockwise from the position shown in FIG. 3 to the position shown in FIG. 5 with the pin 12 as a fulcrum, thereby opening the shutter blades 8 and 9. In this state, if the front and back surfaces of the plate-shaped electrostrictive element 1 are short-circuited or a reverse voltage is applied, the plate-shaped electrostrictive element 1 returns to its original shape, so that the driven member 5 is rotated to the right, and as a result, the blade opening / closing lever 11 Is returned to the position shown in FIG. 3 again, the shutter blades 8 and 9 are brought to the closed position, and one exposure operation is completed.

Also in this embodiment, the plate-shaped electrostrictive element 1 has a substantially circular shape, and the hole 4 is substantially teardrop-shaped, though slightly different from the embodiments of FIGS. 1 and 2, and is electrostrictive. Since a sufficiently large effective area as an element can be ensured, a sufficiently large driving force can be obtained. The shape of the hole 4 is not limited to the above-described embodiment, and various modifications can be made according to the member shape of other mechanism.

Further, since the displacement direction of the plate-shaped electrostrictive element 1 is set in the direction parallel to the optical axis, that is, the plate-shaped electrostrictive element 1 is arranged in the plane orthogonal to the optical axis, the same driving force can be obtained. The length in the optical axis direction is shorter than that of the rectangular plate shape. Experiments have shown that the present invention requires about 2/3 of the length in the optical axis direction as compared with the conventional structure.

Further, since the present invention has a far greater degree of freedom in design as compared with the conventional rectangular plate-like one, it is possible to substantially obtain the above effects.

Needless to say, the driven member 5 may be provided outside the plate-shaped electrostrictive element 1 as shown in FIGS.
Further, it goes without saying that the applicable range of the present invention is not limited to the shutter for a camera and may be used for a lens driving mechanism or the like.

〔The invention's effect〕

As described above, according to the present invention, the displacement amount of the action point is significantly larger than that of the conventional one without contradicting the downsizing of the shutter, and the electric power capable of generating a strong driving force for its size is generated. A strain actuator can be provided, and the range of use thereof can be further expanded.

[Brief description of drawings]

1 is a plan view of an essential part of an embodiment of an electrostrictive actuator according to the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is a view of an electrostrictive actuator according to the present invention. FIG. 4 is a plan view of an essential part showing a normal state of a shutter for a camera incorporating another embodiment, FIG. 4 is an explanatory vertical sectional view showing a vertical relation of components shown in FIG. 3, and FIG. FIG. 6 is a plan view showing a shutter blade open state, and FIG. 6 is a plan view showing an arrangement state of a conventional electrostrictive actuator. 1 ... plate-like electrostrictive element, 2 ... fixing member, 3 ... action point,
4 ... hole, 5 ... driven member.

Front page continuation (72) Inventor Haruki Oe 2-16-20 Shimura, Itabashi-ku, Tokyo Copal Co., Ltd. (72) Inventor Kunio Matsumoto 2-16-20 Shimura, Itabashi-ku, Tokyo Copal Co., Ltd. (72 ) Inventor Nobuyoshi Inoue 2-16-20 Shimura, Itabashi-ku, Tokyo Copal Co., Ltd. (56) References: 59-107716 (JP, U)

Claims (1)

[Claims] 1. An electrostrictive actuator in which a driving force is obtained by fixing and distorting one end of a substantially circular plate-shaped electrostrictive element having a hole formed in a substantially central portion, wherein the hole acts as a driving force. An electrostrictive actuator characterized by having a teardrop shape that tapers toward a point.