Optical device in variable magnification electrostatic copying apparatus

Claim 1

Optical device for a variable magnification electrostatic copying apparatus, comprising - first reflecting mirror assembly (3) - mounted for reciprocal movement - along a stationary transparent plate (2) for a document (A) to be copied, and - being drivably connected to a driving power source - so that it is moved at a predetermined speed selected according to a magnification of copying, - second reflecting mirror assembly (5) -mounted for reciprocal movement - substantially parallel to the reciprocating direction of the first reflecting mirror assembly (3), - speed-reduction interlocking mechanism -for moving the second reflecting mirror assembly (5) at half speed with respect to the speed of the first reflecting mirror assembly (3), and including - pair of stationary pulleys (38, 40) - mounted rotatably in spaced-apart relationship in the reciprocating direction of the first and second reflecting mirror assemblies (3, 5), - a movable pulley (44) - mounted rotatably on the second reflecting mirror assembly (5), and - a rope (46) -wrapped about the pair of stationary pulleys (38, 40) and the movable pulley (44) and fixed to the first reflecting mirror assembly (3), and - a magnification setting mechanism (52) -for changing the position of the second reflecting mirror assembly (5) relative to the first reflecting mirror assembly (3) according to the magnification value; characterised in that -the magnification setting mechanism (52) includes ―a setting cam (53) - having a plurality of active portions (54a, 54b, 54c, 54d) corresponding to a plurality of magnification values, and - a setting member (56) - mounted for movement substantially parallel to the reciprocating direction of the first and second reflecting mirror assemblies (3, 5) and - adapted to be held by the setting cam (53) at any one of a plurality of setting positions corresponding to the plurality of magnification values, - both free end portions (48b, 48c) of the rope (46) of the reduction interlocking mechanism - are wrapped over the movable pulley (44) in mutually opposite directions and then fixed to the setting member (56), and -when the setting member (56) is moved, -the movable pulley (44) is correspondingly moved together with the second reflecting mirror assembly (5).