Patent GB-737942-A (GB)
Title: Photographic shutters
Inventor: WILLCOX FREDERICK PRESTON
IPC: G03B9/08
Filed: 1953-05-05
Abstract: 737,942. Photographic pivoted blade shutters. FAIRCHILD CAMERA & INSTRUMENT CORPORATION. May 5, 1953, No. 12436/53. Class 98 (1). In a shutter having the pivots of its blades on a circle surrounding the exposure aperture, each sector-shaped element for driving each blade has its pivot outside said circle and extends outwardly from said pivot and links are connected between adjacent outer corners of successive sector-shaped elements while means are provided for driving one of these elements so that by means of the links all the moves are moved simultaneously to open and close the shutter. As shown in Fig. 2, each of four shutter blades 28 pivoted at 32 on a main supporting plate 10 is connected by a cranked link 34 to a sector-shaped plate 40 pivoted on the plate 10 at 42, each of the plates 40 being connected to its adjacent pair by links 44. One of the plates 40 is connected by a link 50 to a bell-crank lever 52 pivoted at 54 which is in turn connected by a link 56 to a cranked arm 24 carried by a spindle 21 having at its opposite end lugs 16 (Fig. 1, not shown), to which the movable end of a driving spring is attached. A second set of four shutter blades 30 (Figs. 1 and 3, not shown), is pivoted on the opposite side of the plate 10 and is similarly connected to a cranked arm 26 on a similarly spring-driven spindle 23. The arms 24, 26 are latched in the tensioned position shown, in which the blades 28 cover the shutter aperture while the blades 30 are located clear of it, by a trigger 58 and a latch 74, respectively. On moving the trigger anticlockwise against its spring 62, the arm 24 is released to open the blades 28, and subsequently a cam nose 70 on a sector-shaped plate 64 adjustably secured by a screw-and-slot connection 66, 68 to the arm 24 trips the latch 74 so that the arm 26 is released to close the blades 30. To produce a good characteristic, the links 34 are pivoted to the opening blades 28 at 36 and to the closing blades 30 at the tail of the blades while each pivot pin between the links 50 and the bell-crank levers 52 is slightly off dead-centre relatively to the pivot pins 48, 54 and each pivot pin between the links 56 and the arm 24 or 26 is at dead-centre between the spindle 21 or 23 and the pivot between the links 56 and the bell-crank levers 52 so as to impart rapid initial movements to the blades and gradually to decelerate them to rest, the blade-driving mechanism being finally brought to rest by the curved leading edge of each arm 24, 26 being engaged by a finger 82 on a bell-crank lever 84 which is thereby rotated outwardly and which has an arm 86 against the tip of which presses a fixed spring blade 88. To set the shutter, the shafts 21, 23 are successively rotated so as to move the blades in self-capping relation. Cover-plates 12 (Figs. 1 and 3, not shown), and 14 carries on opposite sides of the plate 10 are slotted and channelled to accommodate the pins 36 and the linkages connecting the sector-shaped plates 40. In the arrangement shown in Fig. 5, only one set of four shutter blades 124 and blade-connecting links are used, and one of the sector-shaped plates 122 of the blade linkage is oscillated to open and close the blades by a link 120 driven from an arm 110 on a spring-driven shaft which makes a complete revolution, said arm being latched in the rest position between a resilient strip 130 and the end of a braking spring 132 until, after the driving spring has been tensioned by rotating the end opposite to that driving the shaft carrying the arm 110, the end of the strip is displaced clear of the arm by a trigger-operated pin 138.