Patent GB-737943-A (GB)
Title: Photographic shutter
Inventor: WILLCOX FREDERICK PRESTON
IPC: G03B9/22
Filed: 1953-05-05
Abstract: 737,943. Photographic pivoted blade shutters. FAIRCHILD CAMERA & INSTRUMENT CORPORATION. May 5, 1953, No. 12437/53. Class 98 (1). The shutter comprises a first set of pivoted blades arranged to open the exposure aperture, a second set of pivoted blades arranged subsequently to close the aperture, gear sectors each connected by a link to a separate blade of said sets, each gear sector meshing with a toothed element, the toothed elements of each set being connected by links to ensure simultaneous movement, separate driving means including a latchable crank connected by link mechanism to a shaft for driving the toothed elements of each set, and means responsive to movement of the driving means for the first set for initiating operation of the driving means of the second set. Preferably each driving means has its own driving spring and is wound by a separate lever, blocking means being provided to prevent winding of the spring for the second set of blades until that for the first set has been wound. As shown, each of five shutter blades 24 pivoted at 26 on a supporting plate 28 is connected by a cranked link 38 to a gear sector 42 meshing with a pivoted gear sector 44, each of the sectors 44 being connected to its adjacent pair by links 48. One sector 44 is secured to a shaft 49 which carries an arm 50 connected by a cranked link 51 to a latchable arm 54 secured to a shaft 56 to which is secured the centre of a driving spring 58 (Fig. 4), the outer end of which is secured to a fixed plate 57 (Fig. 8). A second set of five blades 34 is pivoted on a rear plate 32 and each is similarly connected to a shaft 80 having a driving spring 82. To set the shutter, separate levers 18 (Fig. 8) and 20 (Fig. 1, not shown), freely rotatable on the shafts 56, 86 are successively rotated clockwise against a return spring 61 so that an upstanding pin on each lever drives a lug rotationally secured to the shaft to tension the springs 58, 82. In so doing the blades are moved across the exposure aperture to the positions shown, the shutter being latched in the tensioned state by pivoted latch levers 66, 100 engaging the latchable arms 54, 88. To prevent unintentional exposures during tensioning, the tail 136 of a pivoted lever 130 normally blocks the path of a pin 63 on the lever 20 for tensioning the spring 82 for the blades 34 so that the lever 18 must be operated first to move the blades 24 over the exposure aperture. In so doing a pin 59 on the lever 18 engages a surface 133 on the lever 130 and rocks it clockwise to free the pin 63, a latch nose 132 retaining the pin 59 and so holding the shaft 56 still even if the trigger 22 which is connected by links 70, 68 to the latch 66 is operated. The lever 20 is then rotated clockwise, moving the blades 34 clear of the exposure aperture to tension the spring 82, the pin 63 sliding past a cam surface 138 on the lever 130. On releasing the lever 20 for spring return, its pin strikes the cam 138 and so frees the pin 59 from the nose 132 so that the lever 18 is spring-returned to rest. On now depressing the trigger 22, the latch 66 is tripped and the blades 24 are moved to open the shutter, and subsequently a cam nose 97 on a sector-shaped plate 91 adjustably secured for alteration during manufacture by a screw-and-slot connection 95 to the arm 54 trips the latch 100 so that the blades 34 close the shutter. Longer exposures may be used for a gear retard or like delay mechanism. To provide rapid movement of the blades the meshing sectors apply a speed step-up to the blades relatively to the linkages 48, 80, the pivotal connections of the blade-driving links 38, 74 with the gear sectors 42, 76 moving from one dead-centre position to the other. To decelerate the blades to rest gradually, the blade driving mechanism is arrested by the curved leading edge of each arm 54, 88 being engaged by a finger 106 on a bell-crank lever 110 which bears against an arm 112 of a bellcrank lever having a resilient arm 114 bearing against the shutter casing. On tensioning the shutter the arms 54, 88 engage another finger 104 on the lever 110 to return it to the position shown. For compactness the gear sectors 44, 78 are mounted coaxially while the idler gear sectors coaxial with the two power-driven gear sectors secured on the shafts 49, 93 are freely rotatable on these shafts. The outer supporting plates 30, 32 of the shutter may be channelled to accommodate the gear sector-connecting linkages.