Patent GB-805582-A (GB)
Title: Improvements in and relating to photographic shutters
Inventor: WOODCOCK EDWARD CECIL
IPC: G03B17/42
Filed: 1955-03-25
Abstract: 805,582. Photographic cameras. WILLIAMSON MANUFACTURING CO., Ltd. March 25, 1955, No. 1668/57. Divided out of 805,581. Class 98(1) Crank mechanism for operating a photographic shutter, of the kind comprising a spring which is wound up to drive the crank and an escapement which permits the crank to rotate through half a revolution at a time, includes a braking mechanism which comes into operation after the crank has been released but before it comes to rest. As shown in Fig. 3, the shaft 46 carrying the crank has an escape tooth 47 co-operating with abutments 48, 49 on a rocking lever 51. When the spring driving the crank is stressed, the tooth 47 is checked by the abutment 48. When the lever 51 is rocked, the tooth 47 is freed and the crank makes half a revolution after which the tooth engages the opposite abutment 49. Rocking lever 51 in the opposite direction allows shaft 46 to turn through another half-revolution, so that tooth 47 again engages abutment 48. To lessen the blow of the tooth against the abutment, a surface 52 concentric with shaft 46 is formed behind the tooth and the lever 51 has corresponding braking surfaces 53, 54 which engage the surface 52 just before the tooth 47 engages one of the abutments to slow down the movement of the crank. To adjust the degree of braking, lever 51 is split and the parts can be drawn together by a screw 55. The shaft 46 is driven by two springs 59, 61, Fig. 2, the spring 59 being a light spring anchored to a rotatable sleeve 62 at one end and to a sleeve 63 fast on the shaft 46 at the other end. and the spring 61 being a heavy spring one end of which is anchored to sleeve 63 While the other end lies in a cut away part of the sleeve 62 so that it can freely rotate through 180 degrees in relation to this sleeve. The winding of the springs is effected from an electric motor 64, Fig. 1, which through worm gearing 65 and a pinion 66 rotates the wheel 58 which is integral with a bevel wheel 67 meshing with two further bevel wheels 68 carried on a spider 69. Wheels 68 mesh with a further bevel wheel 71 fast with a gear wheel 72 which, through an idler wheel 73 (see also Fig. 3) engages gear teeth formed on the periphery of the sleeve 62. A gear wheel 74 fast with spider 69 is driven by an electric motor 78 through a train of gearing 75 and two stages of worm gearing 76, 77, so that the springs may be pre-stressed to any desired extent. During the first half revolution of the shaft 46, only the light spring 59 is stressed, The springs, having been pre-stressed by action of the motor 78, are further stressed by action of the motor 64 driving the wheel 58. The wheel 58 turns the shaft 46 through half a revolution, whereupon a cam roller 56 (Fig. 3) engaging a cam groove 57 formed in the wheel 58 causes the lever 51 to rock, releasing the shaft 46 which turns through half a revolution. As shown in Fig. 2, the crank 42 on the shaft 46 is connected by a link 24 to a pin 23 which actuates a shutter mechanism of known type. The pin 23 engages a slot 43, Fig. 5, formed at the end of link 24 and consisting of two end portions of the same diameter as pin 23 joined by a part of somewhat less width, this part of the link being made resilient by two further slots 44 which end in round holes 45. At the end of the movement of crank 42, the moving parts of the shutter will still have considerable kinetic energy and will spring the sides of the slot 43 apart and move towards its other end. The friction exerted on the pin by the sides of the slot brings the shutter parts to rest before the pin reaches the end of the slot, even at the highest shutter speed.