Patent GB-912550-A (GB)
Title: Pivoted-blade photographic shutters
IPC: G03B9/64
Filed: 1959-12-31
Abstract: 912,550. Shutter retard mechanisms. AGFA A.G. Dec. 31, 1959 [Jan. 13, 1959; May 6, 1959], No. 44481/59. Class 98 (1). A retarding mechanism for a pivoted blade shutter comprises a ratchet escapement wheel and an escapement with or without a train of gear-wheels and pinions, and, for transmitting the retarding effect to a shutter master member, a pawl having a pivot linkage with said ratchet wheel or with one of said gear-wheels and adapted to engage a surface of said master member, during the running down thereof, for a period determined by the initial setting of the pawl by shutter speed setting means adapted to pivot the pawl, the pawl then disengaging the master member with guided escaping movement. As shown in Fig. 1, a retarding mechanism comprises an escapement 19 ratchet wheel 18 and a gear train 17, 15, 16 and 14, the wheel 14 having a pin 34 for engaging a cam 33 formed on the shutter speed setting disc 31, and a pivot pin 25 for a lever pawl 24 one end of which has a pin 29 for engaging a second cam 30 formed on disc 31 the two cams 30, 33 corresponding to different ranges of shutter speeds. The other end of pawl 24 is formed as a tooth 28 which, in dependence upon the amount of pivoting of the pawl 24 produced by pin 29 and cam 30 or upon the amount of rotation of wheel 14 by cam 33 acting on pin 34, will engage the surface 10 of a master member 7 at difference points along the line of travel of surface 10 with running down of the shutter so that the retarding effect is operative for variable intervals of time corresponding to different shutter speeds. The retarding effect is due to the inertia of the pawl and gear train and to the ratchet wheel 18 and also to the return spring 35 acting on a pin 26 on pawl 24, said spring, prior to engagement of tooth 28 with surface 10, serving to maintain positive contact of pin 29 with cam 30 and so to define the initial position of the pawl 24. As the master member runs down in the direction of the arrow 13, the surface 10 takes with it tooth 28 which moves along the line 37 as the pawl is pivoted and also moved bodily to cause rotation of wheel 14 by the cam action of a slot 27 in the housing engaging pin 26. On disengaging surface 10, tooth 28 rides on the peripheral portion 38 of the master member which, when retensioned in a direction opposite to 13 will allow the tooth 28 to regain its original position when it rides over the common edge of surfaces 38 and 10. In an embodiment including a fully-rotating master member having only one direction of rotation, the surface 38 is not required and surface 10 is formed on a small projection. The shutter speed setting disc may have only one cam for engaging the pawl, or when there are two cams, both of these may engage the pawl which is then supplied with an additional cam-follower pin, the two cams corresponding to different ranges of shutter speeds. In a further embodiment, the pawl is not pivoted on a gear-wheel of the retard mechanism, but on a disc 135 (Fig. 4) having a slot 122 through which projects a pin 143 fixed to a gear-wheel 137 mounted on the same spindle 122 as the disc (which acts as a flywheel) the initial orientation of gear-wheel 137 being defined by a cam 125 so as to bring pin 143 to varying distances from the slot extremity thereby providing a variable time-lag before the gear train engages the disc to add inertia to the pawl 112, or, in at least one setting of the pawl, to prevent any such engagement thereby effectively disconnecting the retard mechanism. In yet a further embodiment, the gear train is dispensed with, and the gear-wheel 137 of Fig. 4 is replaced by a ratchet wheel in engagement with an escapement.