Focusing device for automatic focusing camera
BACKGROUND OF THE INVENTION 
     This invention relates to a camera of the type in which focusing of the photographic lens is performed automatically. 
     There has already been provided a camera of the type which is capable of automatic focusing of the photographic lens by detecting object distance and generating an electric signal to cut off the electric current which is exciting an electromagnet used to displace the photographic lens, when the in-focus condition is detected. 
     It is the usual procedure for this type of camera that the automatic focusing electronic circuit is activated by closing a switch at the initial stage of shutter release operation to have the electromagnet excited and prepared for the focusing operation. Next the electromagnet is deenergized when a focus detection signal is generated. As a consequence, the battery is exhausted sooner due to extended excitation of the electromagnet. Furthermore, this type of camera has a disadvantage in that it requires a complex mechanism including a means for pushing the member which is actuated when the electromagnet is deenergized against the electromagnet so that it is difficult to reduce in size. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide an automatic focusing camera of a simple structure with less component parts and reduced dimensions, and also having a reduced battery consumption. 
     According to the present invention, an automatic focusing camera capable of automatic focusing of the photographic lens by detecting object distance is provided with an operating member, means for focus detection, a control member operated in connection with the operating member to stop the photographic lens at a focus matching position, and an electromagnet connected to the focus detecting means for detecting the focus matching position of the photographic lens. When the control member is shifted to a position corresponding to the focus matching position of the photographic lens interlocking with the operation of the operating member, the electromagnet attracts and holds the control member at the position corresponding to the focus matching position when a focus matching signal is given by the focus detecting means. The operating member may be adapted so as to be actuated in accordance with a shutter release operation or may be adapted so as to be released from detention in accordance with shutter release operation and to actuate the control member to perform focus detection while it is travelling. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic plan view of a first embodiment of the present invention in a charged state. 
     FIG. 2 is a schematic plan view of an essential part of a second embodiment of the present invention. 
     FIG. 3 is a schematic plan view of an essential part of a third embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, a base plate (1) has an aperture (1a) around which is rotatably fitted a cam ring (2) so as to be driven by a spring (2a). The cam ring (2) is coupled with the photographic lens and has a stopped cam part (2b) for adjusting the photographic lens to a focus matching position or in focus position. 
     An operating member (3) having a projecting pin (3d) protrusion (3e) and slots (3a) is slidably guided by pins (3b) fitted in the slots (3a) and is urged upwards by a spring (3c). 
     A control member (4), having an operating arm (4c), a retaining arm (4d) and a raised fixing end (4e), is rotatably fitted on a shaft (4a) and is urged clockwise by a spring (4b). The control member (4) is illustrated resting with the operating arm (4c) in contact with the pin (3d) while the retaining arm (4d) in contact with a fixed pin (4f). 
     An electromagnet (5) inclusing a coil (5b) connected to an automatic focus detecting electronic circuit, not shown, is fixed on the base plate (1) by means of screws (5a). An armature plate (5c) of a magnetic material is disposed adjacently to the electromagnet (5) and is slidably guided between the electromagnet (5) and a fixed pin (5d). The end of the retaining arm (4d) is fitted in a slot provided on one end of the armature plate (5c). 
     An initiating lever (6), having an extension (6d) to be engaged with the protrusion (3e) of the operating member (3) and an arm (6e) for starting the shutter, is rotatably fitted on a shaft (6a) and is urged counterclockwise by a spring (6b). The initiating lever (6) is illustrated resting retained by a fixed pin (6c) at the arm (6e). 
     A detecting lever (7) is rotatably fitted on the shaft (6a) and is urged clockwise by a spring (7a) while it is constrained from rotating clockwise by the inclined edge of the protrusion (3e) against which the projecting part (7b) rests. 
     The cam ring (2) is interlocked with the operating member (3) by a known means (8) so as to be operated in accordance with the reciprocation of the operating member (3). 
     The manner of operation of the mechanism will be explained hereinafter. Starting from the charged state as illustrated in FIG. 1, the automatic focus detecting electronic circuit is connected to the power source by a known means, not shown, and is activated when the operating member (3) is depressed against the spring (3c), being guided by pins (3b), for focus detection, while the detecting lever (7) is allowed to turn clockwise about the shaft (6a) being pulled by the spring (7a) as the projecting part (7b) follows the inclined edge of the protrusion (3e). 
     At the same time, the control member (4) is allowed to be turned about the shaft (4a) by the spring (4b) as the operating arm (4c) follows the downward movement of the pin (3d) so that the retaining arm (4d) pulls the armature plate (5c) leftwards and the raised fixing end (4e) approaches the step cam part (2b). 
     The clockwise movement of the detecting lever (7) is converted by a known means into electric signals, such as electric resistance, electric capacitance or electric pulses, and when an electric signal, equivalent to the focus matching signal given by the automatic focus detecting electronic circuit, is given, a electric current is fed to the coil (5b) of the electromagnet to magnetize the electromagnet (5) so that the armature plate (5c) is attracted and fixed by the electromagnet (5). Consequently, the raised fixing end (4e) is retained at the position corresponding to the focus matching or in focus position of the photo graphic lens and prepared for engaging with a step cam of the step cam part (2b). As the operating member (3) is depressed further, the cam ring (2) is allowed, through a known means (8), to be turned clockwise around the aperture (1a)being pulled by the spring (2a). The cam ring (2) is stopped when a step cam of the step cam part (2b) engages with the raised fixing end (4e) which has previously been retained at the position corresponding to the focus matching or in-focus postion of the photographic lens. 
     As the operating member (3) is depressed further, the protrusion (3e) pushes the extension (6d) exposure initiating lever (6) so that the exposure initiating lever (6) is turned clockwise about the shaft (6a) against the spring (6b) to actuate the shutter for exposure. 
     Although the electromagnet (5) is unmagnetized after one of the step cams of the cam part (2b) has engaged with the raised fixing end (4e) as the cam ring (2) is turned clockwise by the spring (2a), the photographic lens remains focused. 
     When the depression on the operating member (3) is terminated the operating member (3) is pulled upwards by the spring (3c), being guided by the pins (3b) to the charged position as illustrated in FIG. 1. During the upward travel of the operating member (3), the protrusion (3e) separates from the extension (6d), the pin (3d) pushes the operating arm (4c) to turn the control member (4) counterclockwise about the shaft (4a) against the spring (4b) so that the raised fixing end (4e) is disengaged from the step cam part (2b), the retaining arm (4d) pushes the armature plate (5c) rightwards between the fixed pin (5d) and the electromagnet (5), and the inclined edge of the protrusion (3e) pushes the projecting part (7b) to turn the detecting lever (7) counterclockwise about the shaft (6a) against the spring (7a). Thus, the mechanism is restored to the charged state as illustrated in FIG. 1. 
     The cam ring (2) also is restored to the starting position as illustrated in FIG. 1 through the means (8) in accordance with the return travel of the operating member (3) so that the photographic lens also is restored to the starting position. Thus, the series of steps comprising the exposure operation is completed. 
     FIG. 2 illustrates an essential part of a second embodiment according to the present invention wherein those parts equivalent to corresponding parts of the first embodiment are indicated a like reference numeral and explanation on those parts will be omitted to avoid duplication. 
     Referring to FIG. 2, the control member (4) does not have a raised fixing end, but is provided with a pin (24g) and a push arm (24h). 
     A fixing lever (9), having a pin (9c) engaged with the push arm (24h) and a raised fixing end (9d) which is to be engaged with the step cam part (2b), is rotatably fitted on a shaft (9a) being urged clockwise by a spring (9b) and is illustrated resting retained at the pin (9c) by the push arm (24h). 
     An actuating member (10), having an arm (10c) which is to be engaged with the pin (24g), is rotatably fitted on a shaft (10a), urged clockwise by a spring (10b) and is illustrated resting on a fixed pin (10d). 
     In explaining the operation of the second embodiment, explanation will be omitted of the operation of those parts equivalent to those of the first embodiment. 
     In operation, as the operating member (3) is depressed, the operating arm (4c) follows the downward movement of the pin (3d) so that the control member (4) is allowed to be turned clockwise about the shaft (4a) by the spring (4b), consequently, the push arm (24h) separates from the pin (9c) to allow the fixing lever (9) to be turned about the shaft (9a) by the spring (9b) so that the fixing raised end (9d) advances into the step cam part (2b) operating range. Then in the similar procedure to that of the first embodiment, the electromagnet (5) is magnetized to attract and fix the armature plate (5c) so that the control member (4) and the fixing lever (9) are fixed at the position corresponding to the focus matching position of the photographic lens and the photographic lens is adjusted to the focus matching position. 
     When the detection of the focus matching position is impossible or the focus detecting electronic circuit fails to function due to circuit failure or exhaution of the battery, the actuating member (10) works to adjust the photographic lens to the pan-focus position where the photographic lens is focused to the practically acceptable extent for general use. Detailed explanation on the function of the actuating member (10) will be omitted. 
     The device according to the present invention can be adapted so as to perform automatic focus detection when the electromagnet (5) is magnetized and then initiate or complete exposure operation when the electromagnet (5) is unmagnetized by interlocking the actuating member (10) the exposure operation of the shutter. In this case, the automatic focus detecting circuit and an exposure controlling electronic circuit are required to be constructed so as to control the electromagnet (5). 
     FIG. 3 illustrates an essential part of a third embodiment according to the present invention. Explanation on the third embodiment will be made in contrast with the first embodiment of FIG. 1. 
     An operating member (33), slots (33a), pins (33b), a pin (33d) and a protrusion (33e) of FIG. 3 correspond to (3), (3a) , (3b), (3d) and (3e) of FIG. 1, respectively. The operating member (33) is urged downwards by a spring (33c) and is retained at the charged position by a hook (30b) of a detent (30) at the shoulder (33f). 
     The detent (30) having an arm (30c) is rotatably fitted on a shaft (30a) and is urged clockwise by a spring, not shown. 
     In operation, when the detent (30) is turned counterclockwise about the shaft (30a) against the spring by being pushed at the arm (30c) in accordance with shutter release operation, the retention at the shoulder (33f) by the hook (30b) is released so that the operating member (33) starts travelling downwards being guided by the pins (33b) fitted in the slots (33a) and pulled by the spring (33c). Then, in procedure similar to that of the first embodiment, the photographic lens is adjusted to the focus matching position and exposure operation of the shutter is performed, and thus, a series of photographing operation steps is completed. 
     In re-charging the device, the operating member (33) is raised against the spring (33c) as far as the charged position where the operating member (33) is retained by the hook (30b) of the detent (30) at the shoulder (33f). 
     It will be well understood that this invention provides an automatic focusing device of simple structure, of less trouble and of reduced dimensions for reduced manufacturing costs. Consumption of the battery is limited because the exciting coil (5b) of the electromagnet (5) is required to be excited only for a short period of time and the device requires no mechanism for pushing the armature plate against the electromagnet, while the device which is composed so as to determined the focus matching position of the photographic lens by unmagnetizing the electromagnet requires an extra mechanism.