Patent GB-585210-A (GB)
Title: Improvements in or relating to optical-projection apparatus
IPC: G03B23/04
Filed: 1942-10-22
Abstract: 585,210. Changing signs. PECHKRANZ, R. Oct. 22, 1942, No. 14851. [A Specification was laid open to inspection under Sect. 91 of the Acts, April 29, 1943.] [Class 3 (i)] [Also in Group XX] In slide-changing apparatus wherein one of a number of parallel slides in a box is moved, through mechanism, from the box to a projection position and returned to the box after projection, the box being then moved to bring the next slide into position, the mechanism is driven by a motor through a coupling which is automatically disengaged when the slide is in projecting position and is later re-engaged either by closure of a switch by the operator or automatically. As shown, a shaft 9 driven by a motor 6 through a worm 8, worm wheel 20 and coupling elements 19, 21 carries cams 22, 24, 26, 27, respectively operating means for raising and lowering a shutter 23 for raising the slides to a holder 15 in projection position and lowering them therefrom, for feeding the slide box 14 intermittently, and for rendering the slide box &c. immovable during projection. The coupling element 21 is slidable on the shaft 9 by a fork 39 secured to a shaft 38 carrying a lever 37, and an armature on the lever 37 is raised to turn the lever 37 and engage the coupling elements when the circuit of an electromagnet 11 is closed by the operator. The operation cycle then continues until a slide is in projection position, and a stop 36, on a lever 28 in the linkage serving to operate the shutter 23, engages the lever 37 and uncouples the elements 19, 21 ; each closure of the operator's switch then causes one revolution of the shaft 9 and one complete cycle of operations to occur. Predetermined exposure periods may be obtained with the aid of a bar 121 urged downwards against the lift of a spring 126 by a pawl engaging a rack upon the bar ; the bar is moved one rack tooth per revolution of the shaft 9 by the action of a cam secured to the worm wheel 20 and actuating a bell-crank lever carrying the pawl. At the end of the desired period a projection 123 on the bar 121 automatically tilts the lever 37, and the fork 39, to recouple the elements 19, 21. Tilting of the lever 37 moves a bar 124 to render the pawl inoperative for the return movement of the bar 121. The starting position of the bar 121 may be varied by adjustment of a wedge engaged on its under surface by a pin on the bar 121 ; full adjustment of the wedge renders the pawl inoperative, so that projection continues till the operator's switch is again closed. The slide box 14 is movable on track bars 13 and is fed, in each cycle, through the distance separating two slides, by a pawl 57 engaging a rack on the box 14, against the pull of a spring in a grooved drum 74 and a cable 73 ; a detent 67, immobilized by a member 65 on a rod 64 raised and lowered by the cam 27, holds the box during projection periods. Removal of the box 14 through a front aperture 5a in a casing 5 enclosing the apparatus may be effected by first rotating a knob 75 operating means for immobilizing the pawl 57 and detent 67 and also freeing the box from the cable 73, and then by pulling on a second knob operating a pusher moving the box into a position such that it may be handled; a scaled bar attached to the second knob indicates which slide is in projection position, when the knob is pulled and the box is not first freed for removal. Return of the slide box to its starting position, for a repeat projection of all the slides, is effected by the spring and cable 73 when a feeler 63 carried by the rod 64 fails to engage a slide as the rod moves downwards; means for the purpose of immobilizing the detent 67 to permit the return movement is described in detail. The motor circuit is completed through contacts on a drum 25 in parallel with the main switch so that after the latter is broken the motor continues to run until the contacts break at the zero position, i.e., with the shutter 23 in the closed position. Further contacts on the drum 25 are arranged in series with contacts controlled by the feeler 68 to operate a second electromagnet to disengage the clutch members 19, 21, in the zero position of the apparatus after the projection of the last slide. The return movement of the slide box makes another contact controlling the magnet 11 which restarts the cycle. For cooling purposes, air is drawn through openings 135 by a fan 7 driven by the motor 6, and passes to one side of the slide holder 15 by a duct 134, and to the other side thereof by way of an opening 138 in the bottom of the slide box 14. An annular space around the socket of the projection lamp 17 also permits the passage of cooling air, and the heated air escapes by openings 136 light-shielded by a plate 137.