Abstract:
An optical apparatus comprises a zoom lens for effecting magnification change, a focusing lens for effecting focus adjustment, a first motor for moving the focusing lens, a second motor for moving the zoom lens, and detecting mechanism for detecting the reference positions of the focusing lens and the zoom lens, the detecting mechanism being used in common to the two lenses.

Description:
This is a continuation application under 37 CFR 1.62 of prior application Ser. No. 791,869, filed Nov. 13, 1991 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an optical apparatus having a zoom lens for magnification change and a focusing lens for focus adjustment and having a motor for driving the two lens units. 
     2. Related Background Art 
     As a zoom lens barrel for a still camera or a zoom lens barrel for a video camera, there is known one of the type in which a focusing lens in the lens barrel is driven by a stepping motor. 
     Generally, to drive a moving object by a stepping motor, the so-called open loop control system is often adopted as a control system for the movement and positioning of the object. It is for the reason that in the case of the open loop control system, a detecting device for detecting the position of the moving object at every moment is unnecessary and the construction of the control system is simple and compact as compared with the control system of a closed loop control system. However, when effecting the positioning control of a moving object by an open loop control system using a stepping motor, it is necessary to return the moving object to a particular reference position before the starting of the positioning control in order to make the driving start position of the stepping motor and the driving start position of the moving object coincident with each other, and accordingly, reference position (reset position) detecting means for detecting whether the moving object has been positioned at the reference position (reset position) becomes necessary. 
     In a conventional zoom lens, only a focusing lens has been positioning-controlled by open loop control by stepping motor driving, while a zoom lens has been positioning-controlled by closed loop control using no stepping motor. The reason is that an attempt to effect the movement and positioning of the zoom lens by the open loop control using a stepping motor gives rise to the problem that the aforementioned reference position (reset position) detecting means becomes newly necessary for the zoom lens, but if another reference position detecting means is disposed in the narrow lens barrel, the lens barrel will become bulky or the design for preventing the lens barrel from becoming bulky becomes complicated. However, controlling the zoom lens unit by the open loop control system by a stepping motor has not only the utility that the movement of the zoom lens unit becomes digitally controllable, but also the utility that the simplification of the control system for the zoom lens unit and the compactness of the zoom lens barrel are made possible, and accordingly, it has been necessary to solve the above-noted problem. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is an optical apparatus characterized by the provision of a motor for driving a focusing lens, a motor for driving a zoom lens, and a common reference position detecting means for detecting the positions of the focusing lens and the zoom lens, respectively, and the necessity of providing discrete reference detecting positions for the respective lenses is eliminated, thus achieving the compactness of the optical apparatus. 
     One aspect of the invention is an optical apparatus characterized by the provision of a motor for driving a focusing lens and a motor for driving a zoom lens and in that the detections of the positions of the focusing lens and the zoom lens, respectively, are set so as to be effected substantially at the same location, and the detections of the reference positions of the respective lenses can be effected substantially at the same location, thus achieving the compactness of the optical apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view showing the structure of the essential portions of an optical apparatus such as a zoom lens barrel constructed in accordance with the present invention. 
     FIG. 2 is a flow chart of a control operation executed in the controller of the optical apparatus shown in FIG. 1. 
     FIG. 3 shows a partly modified embodiment of the optical apparatus shown in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Some embodiments of the present invention will hereinafter be described with reference to FIGS. 1 and 3. The embodiments which will hereinafter be described are those in a case where the present invention is applied to a zoom lens barrel for a camera, but as a matter of course, the present invention is also applicable to an optical apparatus for observation, etc. 
     FIG. 1 is a schematic view of the essential portions of a zoom lens barrel according to a first embodiment of the present invention. In FIG. 1, the reference numeral 1 designates a reset switch as reference position (reset position) detecting means fixed to a stationary member, not shown. As shown, this reset switch 1 has a U-shaped body, and the upper horizontal piece portion 1a (hereinafter referred to as the top plate portion) and the lower horizontal piece portion 1b (hereinafter referred to as the bottom plate portion) of the body are disposed parallel to the optical axis of an optical system which will be described later, and a plate to be detected which is protruded from a lens holder which will be described later is designed to be capable of coming into the space between the top plate portion 1a and the bottom plate portion 1b. A light projecting element is attached to the underside of the top plate portion 1a and a light receiving element is attached to the upper surface of the bottom plate portion 1b in opposed relationship with the light projecting element. The light receiving element and the light projecting element together constitute a photointerrupter, and the light receiving element is electrically connected to a controller 10 on an electronic circuit substrate through an electric wire w1. The controller 10 performs all the electrical controls of a plurality of counters, a motor driving circuit, etc. 
     The reference numeral 2 denotes a focusing lens holder carrying a focusing lens unit thereon. On the outer periphery of the holder 2, there are projectedly provided a feed screw engaging piece (or a female helicoid member) 2b provided with a threaded hole threadably engaged with a feed screw 8, a sleeve-shaped sliding portion 2c axially slidably fitted to a first guide bar 6, a projection piece 2d with a U-shaped groove axially slidably fitted to a second guide bar 7, and a plate to be detected 2a capable of coming into the space between the top plate portion 1a and the bottom plate portion 1b of the reset switch 1. 
     The feed screw 8 extends parallel to the optical axis of the lens and is fixed to the shaft of the stepping motor 4 for driving a focusing lens. 
     The first guide bar 6 and the second guide bar 7 extend parallel to the optical axis of the lens and are fixed to a stationary member, not shown. 
     The reference numeral 3 designates a zoom lens holder carrying a zoom lens unit thereon and disposed coaxially with and at a predetermined interval from the focusing lens holder 2. On the outer periphery of the zoom lens holder 3, there are projectedly provided a feed screw engaging piece (or a female helicoid member) 3b having a threaded hole threadably engaged with a feed screw 9, a sleeve-shaped sliding portion 3c axially slidably fitted to the first guide bar 6, a projection piece 3d with a U-shaped groove axially slidably fitted to the second guide bar 7, and a plate to be detected 3a capable of coming into the space between the top plate portion 1a and the bottom plate portion 1b of the reset switch 1. 
     The feed screw 9 extends parallel to the optical axis of the lens and is fixed to the shaft of a stepping motor 5 for driving a zoom lens. The stepping motor 4 is connected to the controller 10 by a wire w2, and the stepping motor 5 is connected to the controller 10 by a wire w3. 
     The operation when the lens barrel of the present embodiment having the structure as described above is mounted on a camera and photographing is effected by the camera will now be described with reference to FIGS. 1 and 2. FIG. 2 is a flow chart of the control operation executed in the controller 10 at that time. 
     When a power source switch, not shown, is closed, the motor 5 begins to rotate and the feed screw 9 is rotated, whereby the zoom lens holder 3 is moved along the feed screw 9 toward the fore-end of the screw 9 (step 1). When the plate to be detected 3a comes into the space between the top plate portion 1a and the bottom plate portion 1b of the reset switch 1, the light beam from the light projecting element of the photo-reflector is intercepted by the plate to be detected 3a and therefore, the switch 1 becomes ON (step 2) and resets the zooming counter of the controller 10 (step 3). Further, the motor 5 is driven in a predetermined direction. In response to this, the zooming counter of the controller 10 drives the motor 5 while counting the step number (the driving pulse number for driving the motor 5), thereby moving the zoom lens holder 3 to its initial set position (step 4). The motor 4 is then rotated and the focusing lens holder 2 is moved toward the fore end of the feed screw 8 (step 5). When the plate to be detected 2a comes into the space between the top plate portion 1a and the bottom plate portion 1b of the reset switch 1 and intercepts the light from the light projecting element, the switch 1 becomes ON (step 6) and resets the focusing counter of the controller 10 (step 7). Further, the motor 4 is driven in a predetermined direction. In response to this, the zooming counter of the controller 10 drives the motor 4 while counting the step number (the driving pulse number for driving the motor 4), thereby moving the focusing lens holder 2 to its initial set position (step 8). Thereafter, normal photographing becomes possible (step 9). 
     As described above, in the present embodiment, the detections of the reset positions of the zoom lens and focusing lens can be accomplished by a reset switch common to the two lenses and therefore, without the apparatus being made bulky, the open loop control system of stepping motor driving can also be adopted for zoom lens control. 
     FIG. 3 shows a second embodiment of the present invention. This embodiment differs from the first embodiment in adopting a three-contact type leaf switch, instead of the photosensor as previously described, as the reset switch. Accordingly, in FIG. 3, portions similar in construction to those in the first embodiment are given similar reference characters and need not be described. 
     In FIG. 3, the reference numeral 11 designates a leaf switch having three contact pieces 11a-11c and electrically connected as the result switch to the controller 10 through a wire w1. 
     The plate to be detected 2a projectedly provided on the focusing lens holder 2 and the plate to be detected 3a projectedly provided on the zoom lens holder 3 are adapted to strike against the contact piece 11b of the leaf switch 11. 
     The operation of a photographing apparatus having the construction of FIG. 3 will now be described with reference to FIGS. 2 and 3. 
     When a power source switch, not shown, is closed, the motor 5 begins to rotate and the feed screw 9 is rotated, whereby the zoom lens holder 3 is moved along the feed screw 9 toward the fore-end of the screw 9 (step 1). When the plate to be detected 3a pushes the contact piece 11b of the leaf switch 11 and the contact piece 11b comes into contact with the contact piece 11a, the switch 11 becomes ON (step 2) and resets the zooming counter of the controller 10 (step 3). Further, the motor 5 is driven in a predetermined direction. In response to this, the zooming counter of the controller 10 drives the motor 5 while counting the step number (the driving pulse number for driving the motor), thereby moving the zoom lens holder 3 to its initial set position (step 4). The motor 4 is then rotated and the focusing lens holder 2 is moved toward the fore-end of the feed screw 8 (step 5). When the plate to be detected 2a pushes the contact piece 11b of the leaf switch 11 and the contact piece 11b comes into contact with the contact piece 11c, the switch 11 becomes ON (step 6) and resets the focusing counter of the controller 10 (step 7). Further, the motor 4 is driven in a predetermined direction. In response to this, the zooming counter of the controller 10 drives the motor 4 while counting the step number (the driving pulse number for driving the motor 4), thereby moving the focusing lens holder 2 to its initial set position (step 8). Thereafter, normal photographing becomes possible (step 9). 
     As described above, in the present embodiment, the detections of the reset positions of the zoom lens and focusing lens can be accomplished by a reset switch common to the two lenses and therefore, without the apparatus being made bulky, the open loop control system of stepping motor driving can also be adopted for zoom lens control. 
     As described above, in the above-described embodiments, design is made such that the initial set positions of the focusing lens unit and zoom lens unit can be detected by a reset switch and therefore, without the lens barrel being made bulky, the open loop control system can be adopted as the driving control system for the zoom lens unit and thus, according to the present invention, there can be provided an optical apparatus which is more compact and lower in manufacturing cost than the prior-art optical apparatus. Also, the detections of the initial set positions of the focusing lens unit and zoom lens unit are set so as to be effected substantially at the same location and therefore, without the lens barrel being made bulky, it has become possible to adopt the open loop control system as the driving control system for the zoom lens unit. 
     The foregoing embodiments have been described with respect to an optical apparatus in which the zoom lens is positioned on the more rearward side of the optical axis than the focusing lens, but a similar effect can also be obtained in an optical apparatus wherein the focusing lens is positioned on the more rearward side of the optical axis than the zoom lens, and this is covered by the scope of the present invention.