Variable magnification electrostatic copying apparatus

A variable magnification electrostatic copying apparatus comprising a transparent plate for placing thereon a document to be copied, an optical system for projecting an image of the document on an electrostatographic material at any desired projecting ratio selected from a plurality of projecting ratios in an exposure zone along the moving path of the electrostatographic material, said optical system including at least one optical element assembly adapted to be held at any one of a plurality of positions corresponding to the plurality of projecting ratios and remaining held at said position during the performance of said projection, and a projecting ratio changing means for moving said optical element assembly so as to change the projecting ratio of the optical system said optical system further including at least one exposure correcting plate mounted for free movement between an operating position at which it projects into a light path ranging from the document to the electrostatographic material and a non-operating position at which it deviates from the light path, spring means for elastically biasing the exposure correcting plate to one of the operating and non-operating positions, and moving means for moving the exposure correcting plate to the other of the operating and non-operating positions against the elastic biasing action of the spring means according to the position of the optical element assembly to be held at any one of the plurality of positions corresponding to the plurality of projecting ratios.

A variable magnification electrostatic copying apparatus comprising a transparent plate for placing thereon a document to be copied, an optical system for projecting an image of the document onto an electrostatographic material at any desired projecting ratio selected from a plurality of projecting ratios in an exposure zone along the moving path of the electrostatographic material, said optical system including at least one optical element assembly to be held at any one of a plurality of positions corresponding to the plurality of projecting ratios, and a projecting ratio changing means for moving the optical element assembly so as to change the projecting ratio of the optical system, said projecting ratio changing means including a stepping motor to be driven by supplying a pulse current, a power transmission system interposed between the stepping motor and the optical element assembly, a detecting means for detecting the optical element assembly when said optical element assembly is at a specified position at one extremity of the plurality of positions corresponding to the plurality of projecting ratios when viewed in the moving direction of the optical element assembly, and a control means for controlling the supply of a pulse current to the stepping motor on the basis of said specified position of the optical element assembly, said detecting means including a low-speed rotating plate drivingly connected to said stepping motor, a high-speed rotating plate drivingly connected to said stepping motor, a first detector for detecting the low-speed rotating plate when the low-speed rotating plate is at a predetermined angular position and a second detector for detecting the high-speed rotating plate when the high-speed rotating plate is at a predetermined angular position, whereby when the optical element assembly is moved from said specified position at one extremity of the plurality of positions to the other extremity, the low-speed rotating plate is rotated over a range not exceeding one turn and the high-speed rotating plate is rotated a plurality of turns, and when the optical element assembly is at said specified position, the low-speed rotating plate is at said predetermined angular position and is detected by the first detector and simultaneously the high-speed rotating plate is at said predetermined angular position and is detected by the second detector.

A variable magnification electrostatic copying apparatus comprising a transparent plate for placing thereon a document to be copied, an optical system for projecting an image of the document at any desired projecting ratio selected from a plurality of projecting ratios, said optical system including at least one optical element assembly to be held at any one of a plurality of positions corresponding to the plurality of projecting ratios, and a means for moving the optical element assembly so as to change the projecting ratio of the optical system, said projecting ratio changing means including drive source for changing the projecting ratio, a power transmission system interposed between said drive source and the optical element assembly, a detecting means for detecting the optical element assembly when the optical element assembly is at a specified position, and a control means for controlling the operation of said drive source according to an output signal of the detecting means;

• said detecting means including a low-speed rotating plate drivingly connected to said drive source, a high-speed rotating plate drivingly connected to said drive source, a first detector for detecting the low-speed rotating plate when said plate is at a predetermined angular position, and a second detector for detecting the high-speed rotating plate when said plate is at a predetermined angular position, and when the optical element assembly is moved from said specified position existing at said one extremity of the plurality of positions to a position existing at the other extremity end, the low-speed rotating plate is rotated through not more than one turn and the high-speed rotating plate is rotated through a plurality of turns, and when the optical element assembly reaches said specified position, the low-speed rotating plate is at the predetermined angular position and is detected by the first detector and the high-speed rotating plate is at the predetermined angular position and is detected by the second detector.