This application is based on patent application No. 11-331162 filed in Japan, the contents of which are hereby incorporated by references.
This invention relates to a light image shift correcting device for optically correcting a shift of a light image on a focusing plane resulting from a shake of hands holding a camera, binocular, telescope or the like, and an optical device provided with a piezoelectric actuator.
Image shift correcting devices for optically correcting a shift of a light image in an optical apparatus have been known. For example, Japanese Unexamined Patent Publication 8-294287 discloses a light image shift correcting device shown in FIG. 24.
The light image shift correcting device is constructed as follows. A flange 502 is so mounted as to project from a cylindrical lens frame 501 for holding a lens 500 used to correct a light image shift, and a ring-shaped ultrasonic actuator 503 is mounted on the flange 502. The flange 502 is accommodated in a ring-shaped casing 504 having a U-shaped cross section, and the rear surface of the flange 502 is fixed to one inner surface 504a of the casing 504 via a spring 505 so that the ultrasonic actuator 503 is pressed into contact with the other inner surface 504b of the casing 504.
The ring-shaped ultrasonic actuator 503 used in this image shift correcting device is constructed by evenly adhering four fan-shaped piezoelectric devices 503b to a ring-shaped elastic member 503a as shown in FIG. 25. For instance, by driving a pair of piezoelectric devices 503b opposed to each other in Y-direction of FIG. 25, a distortion of making an elliptical motion in a plane (YZ-plane) including Y-axis and perpendicular to XY-plane is created on the upper surface of the elastic member 503a. On the other hand, by driving a pair of piezoelectric devices 503b opposed to each other in X-direction, a distortion of making an elliptical motion in a plane (XZ-plane) including X-axis and perpendicular to XY-plane is created on the upper surface of the elastic member 503a. 
In this image shift correcting device, contact points 503c to be held in contact with the inner surface 504b of the casing 504 project in specified positions with respect to X-direction and Y-direction of the elastic member 503a, and an elliptical motion in the XZ-plane or YZ-plane created on the elastic member 503a is transmitted via the contact points 503c to relatively move the flange 502 in X-direction or Y-direction with respect to the inner surface 504b of the casing 504. In this way, the lens 500 is moved in the plane (XY-plane) perpendicular to an optical axis L of a taking lens to correct a light image shift on a focusing plane.
In the light image shift correcting device disclosed in the above publication, distortions created on the upper surface of the elastic member differ depending on the shape, number and positions of the piezoelectric devices 503b adhered to the elastic member 503a, and transmitting positions of driving forces for effectively driving the flange 502 is restricted. This disadvantageously makes the construction of the ultrasonic actuator 503 complicated and causes the characteristic thereof to largely vary. Further, the driving force transmitting positions on the upper surface of the elastic member 503 are symmetrical with respect to Y-axis in the case of driving in X-direction, whereas they are symmetrical with respect to X-axis in the case of driving in Y-direction. Further, the phases of the driving forces outputted from these positions differ. Thus, it is necessary to effectively combine the driving forces at the two transmitting positions so as not to cause a loss of the driving forces, which presents the problem of a difficult drive control.
It is an object of the present invention to provide a light image shift correcting device and an optical device which are free from the problems residing in the prior art.
According to an aspect of the invention, a light image shift correcting device comprises a planar member having a reference surface perpendicular to an optical axis of a focusing optical system, a shift correcting optical member having a flange portion at its periphery, an urger for movably pressing the shift correcting optical member against the reference surface of the planar member at a plurality of parts of the flange portion, a torus type piezoelectric actuator pressed against the flange portion by a part of the urger, and a controller for controlling the torus type piezoelectric actuator.
According to another aspect of the invention, an optical device comprises an optical member, a holder for holding the optical member, the holder having a flat surface parallel with a specified direction, a guide for keeping the holder to move in the specified direction, and a torus type piezoelectric actuator which is in contact with the flat surface and moves the holder in the specified direction.
These and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed description and accompanying drawings.