JPH02184830A - Camera shutter using electrostrictive element - Google Patents

Abstract

PURPOSE:To permit an electrostrictive element to possess enough driving power without being contrary to shutter miniaturization by displacing the electrostrictive element in the direction along an optical axis whose one end is installed on a shutter base board and the other end passes through the center of an exposure opening. CONSTITUTION:The plate shaped electrostrictive element 1, which is roughly round, is arranged so as to permit one end to be supported by a fixing member 2 and the other end to be displaced in the direction along the optical axis which passes through the center of the exposure opening. Therefore, the enough valid area is ensured with the shorter length in the optical axis direction. The length from a fixing point 2 to an application point 3 of the electrostrictive element provided with a hole in the center becomes the length along the arc and is longer compared with a short plate shaped one whose length is the same as that of the element 1 in the longer direction. Thus, the displacing amount at the application point becomes enough, and the big driving power is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a camera shutter that utilizes the electrostrictive action of an electrostrictive element as a driving force.

[Conventional technology]

Electrostrictive elements have been widely used in, for example, microphones and telephone receivers, but recently, as described in Japanese Patent Publication No. 45-15192, their application to blade drive means in camera shutters has also been proposed. There is.

In addition, the applicant of the present case also stated, for example, as described in Japanese Utility Model Application Publication No. 63-101925 and Japanese Utility Model Application Publication No. 63-105125,
An example of its application to a means for driving the blades of a camera shutter is proposed.

As shown in FIG. 10, this consists of a shutter base plate 21 having an exposure opening 21a, and a pair of shutter blades 23. 23, a fork portion 25a which is pivotally supported by a support shaft 24 on the surface of the base plate 21, has a fork portion 25a formed at one end thereof to engage with a tip of an electrostrictive element described later, and has arcuate holes 21b, 21b of the base plate 21 at the other end thereof. The bins 25b, 25 pass through and are pin-slot coupled to the slots 23a, 23a of the shutter blade 23.23, respectively.
b is fixedly attached to the opening/closing lever 25, and an elongated rectangular plate whose base is fixed and supported by a bracket 26 attached to the main plate 21 and whose tip is inserted and engaged with the fork part 25a of the opening/closing lever 25. 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 piezoelectric ceramic plates are stacked with insulating plates sandwiched between them, and when a voltage is applied to both insulated ceramic plates, , similar to a so-called parallel plate capacitor, charges are accumulated between the two insulated ceramic plates, and the capacitor has the property of being distorted in response to the potential difference between the two insulated ceramic plates. Even after the voltage application is stopped, the potential difference continues to be maintained due to the accumulated charge, so the above distorted state is maintained, and only when the two insulated ceramic plates are short-circuited, the charge is discharged and the distorted state is overcome. It has the property of returning to its initial state.

Here, the distortion characteristic of the electrostrictive element is shown by the following formula (1).

However, 1: Length of the electrostrictive element V: Drive voltage d: Electrostrictive constant Th: Thickness of the electrostrictive element And, in the above formula (1), formula (1) is converted to the following formula (2), It can be understood that the amount of displacement is directly proportional to the applied voltage.

Displacement = KV (2
) In this example, the amount of distortion of the electrostrictive element 27 is gradually increased by increasing the voltage applied to the electrostrictive element 27 at the same time as the shutter release.
Exposure aperture 2 by shutter blades 23 and 23 through
By gradually increasing the aperture diameter of the aperture 1a and shorting both terminals of the electrostrictive element 27 at a timing when an appropriate amount of exposure is given, the electrostrictive element 27 is returned to its initial state, and the exposed aperture 21a is instantly closed. I'm trying to close it.

Note that 28 is a photosensor that detects the small hole 23a of one shutter blade 23, detects the timing at which the shutter blade 23 starts to open, and sends this detection signal to the exposure time measuring means.

[Problem to be solved by the invention]

However, in the conventional example described above, in order to increase the driving force of the electrostrictive element 27, it is sufficient to increase the effective area of the electrostrictive element 27, but in order to meet the market demand for miniaturization of cameras, it is necessary to increase the electrostrictive element 27 needlessly. It was not possible to increase the size of the element 27. For example, in order to increase the effective area of the electrostrictive element 27, the width of the electrostrictive element 270 (length in the direction parallel to the optical axis)
Attempts to increase this would result in limitations due to the length of the lens barrel. Therefore, in a structure in which the displacement direction of the electrostrictive element 27 is set in a direction perpendicular to the optical axis as in the conventional example, miniaturization of the shutter and obtaining a large driving force are contradictory.

SUMMARY OF THE INVENTION An object of the present invention is to provide a camera shutter in which an electrostrictive element has a sufficient driving force without contradicting the need to reduce the size of the shutter.

[Means to solve the problem]

In order to achieve the above object, in the camera shutter according to the present invention, the electrostrictive element has one end attached to the shutter substrate and the other end displaced in a direction along the optical axis passing through the center of the exposure aperture. configured or arranged substantially parallel to the shutter blades. Further, the electrostrictive element has a hole in the center thereof that is large enough not to block the light flux passing through the exposed aperture, and has a circular outer shape. Further, in another embodiment, the electrostrictive element has a rectangular shape.

[For production]

Since the electrostrictive element is arranged substantially parallel to the shutter blade, it is possible to secure a sufficiently large effective area while shortening the length in the optical axis direction, that is, to obtain a sufficiently large driving force. be able to. In addition, an electrostrictive element with a hole in the center has a length along an arc from the fixed point to the point of action, which is longer than a rectangular plate with the same length in the longitudinal direction. The amount of displacement at is sufficiently large.

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiments.

First, in FIGS. 1 to 3, 1 is a substantially circular electrostrictive plate whose one end is held by a fixing member 2 and whose other end is displaced in a direction along an optical axis passing through the center of an exposure aperture, which will be described later. Motoko, 3
4 is a point of application of the driving force to be provided at the free end of the plate-shaped electrostrictive element 1, and 4 is a hole formed in the center of the plate-shaped electrostrictive element 1 so as to taper from the fixed end toward the point of application 3. A teardrop-shaped hole 5 formed in is a driven member formed, for example, as a lever, which is engaged with the free end of the plate-shaped electrostrictive element 1. Reference numeral 6 holds one end of the plate-shaped electrostrictive element l in cooperation with the fixing member 2, and includes an exposure opening 6a and slots 6b, 6c, 6.
d, a pin 7 is implanted in the shutter substrate 6; bases 8 and 9 are rotatably fitted to the pin 7, respectively, and are formed to open and close the exposure opening 6a; A pair of shutter blades 10 are fixed to the shutter substrate 6 so as to form a space between which the shutter blades 8 and 9 can be accommodated, and are provided in an opening 10a aligned with the exposure opening 6a and slots 6b, 6c, and 6d, respectively. A cover plate 11 provided with matching slots 10b, 10c, and 10d is rotatably supported by a pin 12 on the back surface of the shutter board 6, and has a slot 11a at one end and slots 6c and 6d at the other end, respectively. The blade opening/closing lever has a pair of pins llb and llc extending upwardly therethrough and connected to the shutter blades 8 and 9 by pins and slots, respectively. The driven member 5 is configured as a crank lever rotatably supported by a bracket 13 mounted on a cover plate 10, and includes a fork portion 5a that holds the action point 3 of the plate-shaped electrostrictive element 1; Slots 10b, 6b
The arm portion 5b that passes through and hangs down, and the blade opening/closing lever 1
It has a spherical lower end portion 5c that fits into the slot lla of No. 1. In this embodiment, it is assumed that the free end of the plate-shaped electrostrictive element 1 is configured to curve downward when a voltage is applied.

Note that 14 is a photosensor that detects the small hole 8a of one shutter blade 8, detects the timing at which the shutter blade 8 starts opening, and sends this detection signal to the exposure time measuring means.

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 point of application 3 is displaced downward, and the driven member 5 is rotated to the left at the position shown in FIG. I am forced to do it. Therefore, the blade opening/closing lever 11 is rotated to the left from the position shown in FIG. 1 to the position shown in FIG. 3 using the pin 12 as a fulcrum.
The shutter blades 8 and 9 are opened. 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, and the driven member 5 is rotated to the right. As a result, the blade opening/closing lever 11 is again returned to the position shown in FIG. 1, and the shutter blades 8.9 are brought to the closed position, completing the - exposure operation.

In the case of this embodiment, the displacement direction of the plate-shaped electrostrictive element 1 is set parallel to the optical axis, that is, the plate-shaped electrostrictive element 1 is arranged substantially parallel to the shutter blade, so that the electrostrictive A sufficiently large effective area as an element can be secured, and as a result, a sufficiently large driving force can be obtained. According to experiments, when a plate-shaped electrostrictive element made of the same material and having the same length in the longitudinal direction was deformed under the same conditions, the driving force of the device of the present invention was increased by 70 to 1.50% compared to that of the conventional structure. Met.

Further, since the plate-shaped electrostrictive element 1 is arranged in a plane perpendicular to the optical axis, the length in the optical axis direction is shorter than that of a conventional structure that can obtain the same driving force. According to experiments, it was found that the length in the optical axis direction of the structure of the present invention is about 2/3 that of the structure of the conventional structure.

In addition, since the plate-shaped electrostrictive element 1 has a hole in the center, the length from the fixed point to the point of action is the length along the arc, which is longer than a rectangular plate-shaped element with the same length in the longitudinal direction. As a result, the amount of displacement at the point of application becomes sufficiently large. Further, since the hole 4 is in the shape of a teardrop as described above, it does not deform into a mortar shape around the hole, unlike the substantially circular plate-shaped electrostrictive element l in which the hole is substantially circular. , the amount of displacement of the free end, that is, the point of action 3 is large in comparison. According to experiments, the same material
When a longitudinal plate-shaped electrostrictive element was deformed under the same conditions, the amount of displacement of the element of the present invention was approximately 50% greater than that of the conventional structure.

4 and 5 show a second embodiment, in which a driven member 5 is provided outside the plate-shaped electrostrictive element 1. Then, when a voltage is applied between the front and back surfaces of the plate-shaped electrostrictive element 1, the point of action 3 is displaced upward, the driven member 5 is rotated to the right at the position shown in FIG. The shutter blades 8 and 9 are shown as a chain line from the position shown by the solid line to the position shown by the dashed dot line in the figure, and the shutter blades 8 and 9 are opened.

FIG. 6 shows a third embodiment, in which the plate-shaped electrostrictive element 1 has a rectangular outer shape.

FIG. 7 shows a fourth embodiment, in which the plate-shaped electrostrictive element 1 has a rectangular shape that does not have a hole in the center but is arranged substantially parallel to the shutter blade so as not to block the exposed opening 6a. It is made up of things.

FIG. 8 shows a fifth embodiment, in which the plate-shaped electrostrictive element 1 is made half of that of the third embodiment.

FIG. 9 shows a sixth embodiment, in which the plate-shaped electrostrictive element l is made half of that of the second embodiment.

Furthermore, in order to obtain even greater driving force, electrostrictive elements may be stacked, and in that case, if a common voltage application electrode plate is separated between adjacent electrostrictive elements, the thickness of the entire electrostrictive element can be reduced. That is, it is good because the length in the optical axis direction does not have to be very large.

〔Effect of the invention〕

As described above, the camera shutter according to the present invention has the practically important advantage that the electrostrictive element has a sufficiently large driving force, without contradicting the reduction in size of the shutter.

[Brief explanation of the drawing]

FIG. 1 is a plan view of essential parts showing the normal state of a first embodiment of a camera shutter according to the present invention, FIG. 2 is an explanatory vertical cross-sectional view showing the relationship of the components shown in FIG. FIG. 4 is a plan view of main parts of the second embodiment; FIG. 5 is an explanatory vertical sectional view showing the vertical relationship of the components shown in FIG. 4; 9 to 9 are perspective views of essential parts of the third to sixth embodiments, respectively, and FIG. 10 is a plan view of the conventional example. ■... Plate electrostrictive element, 2... Fixing member, 3...
... Point of action, 4... Hole, 5... Driven member, 6...
...Shutter board, 7,12...Pin, 8,9
...Shutter blade, 10...Cover plate, 11...Blade opening/closing lever 13...Bracket, 14...Figure 1 1-3 Figure 1-4

Claims (3)

[Claims] (1) A shutter substrate having an exposure aperture, a shutter blade pivotally mounted on the shutter substrate to open and close the exposure aperture, and a shutter blade rotatably supported on the shutter substrate to open and close the shutter blade. In a camera shutter equipped with a lever member for driving the lever member, one end is attached to the shutter substrate and the other end is displaced in a direction along an optical axis passing through the center of the exposure aperture, as a driving source for driving the lever member. A camera shutter characterized by using an electrostrictive element. (2) The electrostrictive element is arranged substantially parallel to the shutter blade, has a hole in the center of a size that does not block the light flux passing through the exposure aperture, and has a circular outer shape. The camera shutter according to range (1). (3) The camera shutter according to claim (1), wherein the electrostrictive element is arranged substantially parallel to the shutter blades and has a rectangular shape.