Patent GB-959426-A (GB)
Title: Improvements in or relating to optical projectors
IPC: G03B23/04
Filed: 1962-05-28
Abstract: 959,426. Optical slide projectors. ERNST LEITZ G.m.b.H. May 28, 1962 [June 2, 1961] No. 20355/62. Heading G2J. [Also in Division G4] An optical projector comprises means for guiding a magazine of transparencies to be projected, means for moving the magazine in a step by step manner in the guiding means and automatically operable means for changing the transparencies, an indicating mechanism operable from the magazine moving means being provided for indicating the relative position of the magazine in the guiding means, the indicating mechanism having associated therewith a manually settable pre-selecting member which can be set to any one of a plurality of markings on the indicating mechanism, the particular marking to which the preselecting member has been set being indicative of a desired transparency to be projected, the preselecting member serving as a control member for a supplementary driving mechanism for the magazine, operable in dependence on the position of the transparency changing means, and actuatable by a release switch, the supplementary magazine driving mechanism enabling movement of the magazine into a position such as will bring the pre-selected transparency into the range of operation of the transparency changing means. The magazine slide changing mechanism of the illustrated embodiment (mechanically similar to that disclosed in Specification 925,474 and not therefore described here in great detail) comprises a crank plate 14, (Fig. 2,) coupled to a slide changing slider 5 (Fig. 3,) and couplable through a spring- urged pawl 25 on energization of an electromagnet 34 to a continuously rotating ratchet wheel 13 driven by a motor 7. Rotation of the plate 14 through one revolution from the position of Fig. 2, effects movement of the slider 5 from the projection position B into a position A straddling the magazine 3 and back to the projection position B. While the slide 5 is in the position A, a bar 45 on the plate 14 engages a toothed wheel 50 which is in engagement with a racked portion 2 of the magazine for advancing the same in step-by-step manner. The bar 45 is pivotally mounted at 47 and a deflecting member is provided at 43 (controlled by electromagnet 34 through linkage 42, 31) whereby the bar may be pivoted against a spring 48 into a position for reverse stepping movement of the magazine. A switch 65, operated through a bellcrank 23 by a cam 58a, is provided in circuit with a switch 158,161 (settable for forward or reverse magazine movement) to control automatically the direction of stepping movement regardless of how long a remote control switch 104 for the electromagnet 34 is depressed. If this switch 104, operated by a push button 100 is held closed sufficiently long, the crank plate 14 may be halted with the slider 5 in the position A, through engagement of the pawl 25 by a latching lever 37, in which position, the wheel 50 registers with a break 55 in a grooved track 54, whereby the magazine is free to be moved in or removed from its guide channel 1 as desired. The supplementary driving mechanism of the present invention is accommodated in a housing 129 releasably secured to the side of the projector casing whereas the indicating mechanism and pre-selecting member are mounted on a remote control unit 146. Rotatably connected with the shaft 50a of the wheel 50 is a cam disc 110 having the same number of lobes as the wheel 50 has teeth. Thus, as the magazine is moved stepby-step, a switch 111 is switched on and off and by way of one or other of two electromagnets 173, 174 (depending on the setting of said switch 158) and associated ratchet devices 172, 166, 179, 180 or 171, 167, 181, 182 an indicator plate 184 is rotated. This plate, which bears a scale of numbers cooperating with a stationary index 188 to indicate which slide is in position for projection is acted on by a spring-detent device (Fig. 5, not shown) to limit its rotation to whole steps only. To preselect the next slide to be projected a knob 187, rotatably mounted on the shaft 183 of the plate 184 but restrained from movement relative thereto by a spring-detent device (Fig. 5, not shown), is turned to register with the number corresponding to the desired slide and the switch 185 is set for forward or reverse movement as required. The button 100 is then depressed to close the switch 104 and is held down to render the latching lever 37 operative on the pawl 25. Further depression of the button 100 closes a switch 107 which energizes an electromagnet 121 which pivots the plate 120 mounting a reversible motor 114 to bring the gears 109, 118 into mesh whereby the magazine 3 is moved forwards or backwards depending on the setting of switch 158. This movement is accompanied by rotation of the cam disc 110 whereby the plate 184 and with it the knob 187 is also rotated. Magazine movement is terminated when a projection 186, rigid with the knob 187, engages and opens a switch 191. Deenergization of the electromagnet 34 by release of the button 100 then allows the plate 14 to complete its rotation and move the selected slide into position for projection. A switch 137, operable by a projection 138 on the slide 5 ensures that magazine movement by the motor 114 can only take place with the slide 5 in the position A. Indicating means operable in dependence on the position of switch 191 may be provided to signal when the selection process has been completed. In a modification, a single electromagnet may replace electromagnets 173, 174, friction wheels may replace gears 118, 109 and the reversible motor 114 may be replaced by a non-reversible motor with a reversing gear.