Patent GB-655209-A (GB)
Title: Electrically operated photographic shutter
IPC: G03B9/58
Filed: 1948-07-21
Abstract: 655,209. Photographic shutters. GENERAL ANILINE & FILM CORPORATION. July 21, 1948, No. 19552. Convention date, Sept. 16, 1947. [Class 98 (i)] A photographic shutter having a number of movable shutter blades is provided with magnets disposed to present opposite polarities on opposite sides of each blade face and the blades are opened by passage of an electric current through said blades and are closed by reversal of said current. As shown, sliding plates 10, 11 of a non-magnetic material such as beryllium copper are guided in slideways 12 ... 17 of low friction material such as phenolic resins or other moulded plastics which may be impregnated with lubricant. The blade 11 has an overlapping stepped portion 18 which does not extend into the slideways so that the blades form a light-tight closure for the aperture 19. Two permanent magnets 22 lying in opposite senses parallel to the blades have polepieces close to the blades. Electromagnets supplied from the same D.C. source as the blade current may be employed, provision being made for saturation current to flow through them before the blade circuit is closed. The guideways which are provided with end members 20, 21 are apertured to allow spring blade brushes, connected to leads 25, 26 from a reversing switch 24, to engage the blades, and to accommodate the latch ends of pivoted bell-crank levers 63, 64 which are controlled by a link 65 directly operated by the release trigger 37 and which latch the blades against accidental movement. The reversing switch 24 comprises an insulated drum 27, provided with two conducting sectors 28, 29 and diametral pairs of lugs 30, 31 and 34, 35 on perpendicular diameters on opposite margins of the drum, brushes a, b connected to a D.C. supply such as the battery 23 and brushes c, d connected to the blade leads 25, 26. When the shutter is at rest after an exposure, the brushes a, b engage the insulated drum and the lug 30 is held stationary between the release 32 and a pivoted pawl engaging one of a diametral pair of pins on the setting knob which is spring- connected to the drum 27 freely mounted on the setting knob spindle. The shutter having been set by a half-turn of the setting knob to tension the spring, on depressing the trigger 37, the latches 63, 64 are released, the drum rotates, and current flows through brushes a, c and lead 25 to the blades and returns through lead 26 and brushes d, b, thus opening the shutter which remains open for a period determined by a conventional pallet and star wheel retard controlling a sector which has an arm 58 engaging the lug 34 and which is set for a chosen retard by a manually-operable cam 59 against which a pin 61 on the sector bears. When the lug 34 has slipped past the arm 58, the brushes c, d contact the insulated drum breaking the blade circuit which is remade by their contacting the sectors 28, 29 respectively as the drum rotates so reversing the current through the blades and closing the shutter, the drum being finally arrested by the trigger nose 43 engaging the lug 31 with the brushes a, b between the sectors 28, 29. To ensure that the shutter makes only a single exposure for each depression of the trigger, even if this is held depressed, a pivoted lever 33 is provided which bears against the trigger so that on depression thereof its nose 43 moves into the path of the lug 31 arresting the drum after a half-turn. Then on releasing the depressed trigger the lug 31 is held by the nose 39 of the trigger, the drum rotating insufficiently to close the supply circuit, the shutter then being ready for a further setting and releasing cycle.