Mechanism for detecting a rotation amount of a diaphragm for use in optical systems

Abstract: A mechanism for detecting a rotation amount of a diaphragm (3,3) for use in an optical system, such as a camera, including an actuator (6) mounted on a cover plate (8) secured on a base plate (2) in the optical system, diaphragm blades (3,3) pivotally mounted on the base plate (2), and a rotating ring (5) supported by the diaphragm blades (3,3). When the actuator (6) is energized, the rotating ring (5) is rotated so that the diaphragm blades (3,3) are rotatingly moved to open or close a center opening (2a) of the base plate (2). The mechanism includes a magnet (10) with a magnetic gradient fixed on an outer periphery of the rotating ring (5) and a magnetic leakage flux detecting means (11) secured in the cover plate (8) so as to be disposed opposite the magnet (10) and spaced at a given clearance apart therefrom. When the rotating ring (5) is rotated by the actuator (6), the magnet (10) passes over the magnetic leakage flux detecting means (11). The detecting means (11) detects change in an amount of magnetic leakage flux generated from the magnet (10) so that a rotation amount of the diaphragm blade (3,3) is determined.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a mechanism for detecting a rotation amount of a diaphragm for use in an optical system such as a camera. 2. Description of the Background Art A camera such as a still camera, a video camera and the like has a driving actuator which rotatably operates diaphragm blades through a rotating ring. Conventionally, the actuator is also used for detecting a rotation amount of the diaphragm blades of the camera. FIG. 5 depicts a conventional driving actuator which serves for detection of operation of the diaphragm blades. Referring to FIG. 5, a driving actuator 50 includes a rotor 51 and a stator 53. The rotor 51 consists of semi-circular north- and south-polar magnet halves 51a and 51b which are attached together symmetrically around an axis 52 so as to form a rotor of circular shape. The stator 53 is provided, on an inner surface thereof, with a Hall element 54. The Hall element 54 faces a boundary between the magnets 51a and 51b and detects change in leakage flux generated from the rotor 51, which is rotatingly driven by energization of a coil 55 disposed on the stator 53. When the rotor 51 rotates, the leakage flux traversing the Hall element 54 is altered. An amount of rotation of the diaphragm blades is ascertained by detecting change in an amount of the leakage flux which traverses the Hall element. However, the driving actuator 50 has a small diameter so that only a small peripheral surface area of the rotor 51 moves relative to the element 54. Accordingly, an accuracy of detection of the leakage flux is lowered. In case that an opening defined by the diaphragm blades has a considerably small diameter, it is difficult to determine the fine amount of rotation of the diaphragm blades since the detection can be made only within a limited range. JP-A-56 151917 describes a device for controlling aperture blades in a camera. The aperture blades are positioned using an aperture blade operating ring and an aperture diameter setting ring driven by motors. In order to smooth a resetting operation of the aperture blades, a magnet is provided on the aperture blade operating ring and magnetic material is provided on the aperture diameter setting ring, or vice versa, so as to produce a magnetic coupling having a smoothing effect. Another device for controlling the diaphragm aperture is disclosed in EP-A-0 114 404. SUMMARY OF THE INVENTION It is an object of the present invention to provide a mechanism for detecting a rotation amount of diaphragm for use in optical systems, which is operable over a wide range with high accuracy. In order to accomplish this object, there is provided a mechanism for detecting a rotation amount of a diaphragm for use in an optical system including an actuator mounted on a cover plate which is secured on a rear side of a base plate with respect to the front side of the optical system, and provided with a rotating axis projecting from a front end surface of the actuator to which an arm member is pivotably supported, said cover plate having a circular opening formed at the centre thereof and an annular projection extending from a periphery of the opening toward the front side of the optical system; diaphragm means comprising aperture blades pivotably supported around pins on the rear side of the base plate and having guide holes thereon; and rotating ring means provided, on an outer periphery thereof, with a notch into which an end of the arm member of the actuator is engaged, said rotating ring means having, on a rear side surface thereof, pins which are engaged into the guide holes of said aperture blades of the diaphragm means and an annular projection extending toward the rear side of the optical system to be engaged with the annular projection of the cover plate; said mechanism comprising: an arcuate magnet to be fixed on the outer periphery of said rotating ring means so that it extends along the circumferential direction of the rotating ring means wherein the magnet exhibits a single magnetic polarity to the exterior of the rotating ring means and has a gradient of magnetic force such that the magnetic force varies continuously along the circumferential direction of the rotating ring means; and detecting means for detecting magnetic leakage flux from said magnet and comprising a single Hall element to be secured in the cover plate so as to be disposed opposite said magnet and spaced at a given clearance apart therefrom, so that on the basis of the change in the amount of said magnetic flux detected by said Hall element, the rotation amount of the rotating ring means and the diaphragm blades can be determined. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view illustrating a diaphragm-operating mechanism in which a mechanism for detecting a rotation amount of a diaphragm according to one embodiment of the present invention is incorporated; FIG. 2 is a rear view of the diaphragm-operating mechanism of FIG. 1; FIG. 3 is a schematic rear view of a mechanism for detecting a rotation amount of a diaphragm according to another embodiment of the present invention; FIG. 4 is a schematic side view of the mechanism of FIG. 3; and FIG. 5 is a schematic sectional view of a conventional driving actuator for a rotating ring for use in a camera. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of a mechanism for detecting a rotation amount of a diaphragm, for use in an optical system, according to the present invention will now be described with reference to the accompanying drawings. FIGS. 1 and 2 depict a diaphragm-operating mechanism for use in a camera such as a video camera. Referring to FIGS. 1 and 2, the diaphragm-operating mechanism 1 includes a square base plate 2 having a center opening 2a receiving a lens. On a rear side surface of the base plate 2, a pair of diaphragm blades 3, 3 are pivotably mounted around pins 4, 4 such that the opening 2a is closed or opened by rotating the diaphragm blades 3, 3. Each diaphragm blade 3 is provided with an arcuate guide hole 3a into which a pin Sa, protrudently formed on a front side face of the rotating ring 5, is engaged. The rotating ring 5 has a notch 5b on an outer periphery 5c thereof. Into the notch 5b is engaged an end portion of an arm member 6b which is rotatably mounted on a rotating axis 6a of an actuator 6. The actuator 6 is secured by screws 9, 9 to a cover plate 8 which is in turn fixedly secured to a rear side face of the base plate 2 by means of fastening members such as a screw 7a and a pin 7b. The cover plate 8 has a center opening 8a aligned with the opening 2a of the base plate 2. Along a front-side inner periphery of the cover plate 8 is formed an annular projection which engages a corresponding projection formed on the rear side of the rotating ring 5, whereby the rotating ring 5 is supportedly rotatable on the cover plate 8. In this configuration, when the actuator 6 is energized, the arm member 6b mounted on the rotating axis 6a forces the rotating ring 5 to rotate in a direction reverse to the rotational direction of the actuator 6, along the annular projection of the cover plate 8. The rotation of the rotating ring 5 causes the pins 5a, 5a to be moved along the guide holes 3a, 3a so that the diaphragm blades 3, 3 are urged to be pivotally moved around the pins 4, 4 so as to open or close the opening 2a of the base plate 2. The rotating ring 5 is provided, on the outer periphery 5c, with an arcuate protrudent portion 5d on a rear side surface of which an arcuate recess is formed, as illustrated in FIG. 1. Within the arcuate recess, attached by adhesives or the like a magnet plate 10 having a uniform thickness is provided. The magnet plate 10 has one polarity, e.g. north-polarity, and is tapered in a circumferential direction of the rotating ring 5 so that the magnet plate 10 is of an approximately triangular shape, such that a magnetic force of the magnet plate 10 gradually alters due to the tapered shape of the magnet plate 10. A Hall element 11 is secured to the cover plate 8 by press fitting or the like so as to be disposed opposite and apart at a given clearance from the magnet plate 10. In FIG. 1, numeral 12 represents a flexible substrate attached to the element 11. The mechanism for detecting a rotation amount of a diaphragm according to the preferred embodiment of the present invention includes the magnet plate 10 with gradually changed magnetic force which is attached to the rotating ring 5 for rotating the diaphragm blades 3, 3. When the rotating ring 5 is rotated by the actuator 6, the magnet plate 10 passes over the Hall element 11. The Hall element 11 opposite the magnet plate 10 detects change in an amount of magnetic leakage flux generated from the magnet plate 10. On the basis of the detected change in the amount of the magnetic flux, a rotation amount of the diaphragm blade 3 is determined. Since the magnet plate 10 is arranged at the arcuate protrudent portion 5d extending radially outwardly from the outer periphery 5c, an amount of movement of the magnet plate 10 in the circumferential direction of the rotating ring 5 is large. The mechanism according to the invention therefore can detect the rotation amount of the diaphragm blade 3 with high accuracy and fine detection capacity. Even in a case where the diaphragm blade has a relatively small diameter, the rotation amount of the diaphragm blade may be surely determined. Another preferred embodiment of a mechanism for detecting a rotation amount of a diaphragm according to the invention will be described with reference to the accompanying drawings, in which like numerals indicate like parts of the mechanism of the first embodiment described above, and therefore detailed explanations thereof are omitted hereinafter. As illustrated in FIG. 3, a magnet plate 10', which is of an arcuate shape having a uniform radial width, is attached to an outer periphery of the rear side of a rotating ring 5 so as to extend circumferentially and be disposed opposite a Hall element. Moreover, the magnet plate 10' is tapered in thickness circumferentially to thereby have triangular shape in the axial cross section, as shown in FIG. 4. Thus, the magnet plate 10' has a magnetic gradient along which a magnetic force of the magnet plate 10' is reduced in a circumferential direction. The second embodiment may achieve the same function and effect as the first embodiment. As is obvious from the aforementioned description of the preferred embodiments according to the invention, a mechanism for detecting a rotation amount of a diaphragm for use in an optical system includes a magnet having a gradient of magnetic force and a means for detecting magnetic leakage flux generated from the magnet. The magnet is fixedly arranged on an outer peripheral side of a rotating ring which rotates the diaphragm means of the optical system. The means for detecting magnetic flux is disposed opposite the magnet so as to be spaced at a given clearance apart from the magnet. To this end, an amount of movement of the magnet in a rotational direction is larger as compared with the conventional actuator in which both magnet and detecting means are incorporated. Accordingly, the amount of rotational movement of the diaphragm means may be detected with high accuracy and in a wide range. As described in the first and second embodiments mentioned above, the magnetic gradient is produced by changing the width or thickness of the magnetic plate. However, the magnet plate may otherwise have a gradient of magnetic force by changing a density of the magnetic flux. In addition, it will be noted that the detecting mechanism according to the invention is further applicable for detecting an amount of rotational movement of a lens barrel containing a zoom lens or the like.

Claims: A mechanism for detecting a rotation amount of a diaphragm (3, 3) for use in an optical system including an actuator (6) mounted on a cover plate (8) which is secured on a rear side of a base plate (2) with respect to the front side of the optical system, and provided with a rotating axis (6a) projecting from a front end surface of the actuator (6) to which an arm member (6b) is pivotably supported, said cover plate (8) having a circular opening (8a) formed at the centre thereof and an annular projection extending from a periphery of the opening toward the front side of the optical system; diaphragm means (3, 3) comprising aperture blades pivotably supported around pins (4, 4) on the rear side of the base plate (2) and having guide holes (3a, 3a) thereon; and rotating ring means (5) provided, on an outer periphery thereof, with a notch (5b) into which an end of the arm member (6b) of the actuator (6) is engaged, said rotating ring means (5) having, on a rear side surface thereof, pins (5a, 5a) which are engaged into the guide holes (3a, 3a) of said aperture blades of the diaphragm means (3, 3) and an annular projection (5d) extending toward the rear side of the optical system to be engaged with the annular projection of the cover plate (8); said mechanism comprising: an arcuate magnet (10) to be fixed on the outer periphery of said rotating ring means (5) so t a it extends along the circumferential direction of the rotating ring means, wherein the magnet exhibits a single magnetic polarity to the exterior of the rotating ring means and has a gradient of magnetic force such that the magnetic force varies continuously along the circumferential direction of the rotating ring means (5); and detecting means (11) for detecting magnetic leakage flux from said magnet and comprising a single Hall element to be secured in the cover plate (8) so as to be disposed opposite said magnet (10) and spaced at a given clearance apart therefrom, so that on the basis of the change in the amount of said magnetic flux detected by said Hall element, the rotation amount of the rotating ring means and the diaphragm blades can be determined. The mechanism according to claim 1, wherein said magnet (10) has a uniform thickness and is tapered in a circumferential direction of said rotating ring means (5). The mechanism according to claim 1, wherein said magnet (10) is of arcuate shape, has a constant radial width and is tapered in thickness outwardly from the rotating ring means. The mechanism according to claim 1, wherein said magnet (10) has a magnetic flux density varying in a circumferential direction of said rotating ring means (5) while having a constant thickness and width. The mechanism according to claim 1, wherein said rotating ring means (5) is mounted on a lens barrel containing a zoom lens.

Inventors: KAWAMURA HIROSHI, TSUJINAKA MASATO, KAWAMURA, HIROSHI, TSUJINAKA, MASATO
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: G03B9
IPC codes: G01D5, G03B9, G01B7