Patent GB-1404095-A (GB)
Title: Electro-magnetic actuator devices
IPC: G03B9/08
Filed: 1973-04-19
Abstract: 1404095 Camera shutters POLAROID CORP 19 April 1973 [21 April 1972] 19005/73 Heading G2A [Also in Division H1] An actuator solenoid e.g. for controlling a camera shutter comprises a winding 42 on an insulant bobbin 44 positioned in a U-frame 46 forming part of the magnetic circuit. Within the winding a cylindrical armature 50 slidably cooperates with a fixed armature 52 within a non- magnetic liner 54 having a flux ring 56 surrounding the forward end of the liner in contact with the forward face of the frame. The fixed and movable armature faces have confronting faces with inter-engaging serrations; the major interface 90 being a right conical frustrum with a minor interface 94 extending in opposite sense thereto as a further conical frustrum of lesser diameter coaxial with the armatures; a working gap separating the conical surfaces which are surrounded by annular seating 96 between the fixed and movable armatures. A required flat force/displacement characteristic of the solenoid to retract the plunger 50 against the flat characteristic 100 of spring 62 Figs. 1, 2 is shown at 102 and serves to close a camera shutter in a prescribed time. The interface between the fixed and movable armatures is empirically shaped Figs. 6 to 8 (not shown) so that the force/stroke curve of the magnet on energization is given by 118 Fig. 5 wherein a high initial force is obtained at initial excitation, falling off to a constant level as displacement develops, rising towards the end of the stroke, and on termination of displacement falling off to a constant level sufficient to hold the plunger retracted against the spring loading with reduced power dissipation. The armatures may be of magnetic iron, or a ferrous alloy containing carbon, manganese, phosphorus, sulphur, lead and tellurium in stated proportions. The magnetic interfaces may be shaped as a single conic frustrum engaging a correspondingly shaped cavity Fig. 9 (not shown) giving the force/stroke curve 130, or narrower and more elongated inter-engaging frustra and corresponding cavities Fig. 10 (not shown) giving the curve 132, but these are less satisfactory. In a cycle of camera operation Fig. 3 (not shown) the shutter is initially open for viewing and focussing with the solenoid de-energized, and on switch actuation it is energized to retract plunger 50 and close the shutter fully. Reflex components are reorientated to set an exposure optical path, and the solenoid remains energized with a lowering of excitation current when the plunger 50 is fully seated for battery economy. Thereafter exposure is initiated by solenoid de-energization whereby the plunger 50 is driven outwards by spring 62 to open the shutter gradually, until light measurement circuitry determines a proper exposure, after which the solenoid is again energized to retract the plunger and close the shutter. When this is completed, the reflex components are reoriented to the viewing and focussing condition, while the solenoid remains energized at reduced power, and the exposed film is automatically processed. On completion, the solenoid is de-energized to open the shutter for viewing and focussing. For shutter operation the cap 58 of plunger 50 is movable outwardly to engage pin 60 extending from beam 22 under impulsion of helical spring 62, and the beam is rotatably mounted on stud 24 so that elongate slots 30, 32 in the ends engage pins 34, 36 of opposedly slidable shutter blades 12, 14 with teardrop shaped openings 16, 18 therein, which in conjunction define a variable aperture in the optical path of the camera. This is biased towards closure by a helical or spiral spring 38 surrounding stud 24, while the shutter is biased open by the solenoid spring 62 on deenergization and is closed on energization Figs. 1, 2.