Patent GB-856141-A (GB)
Title: Visual training projector
IPC: G09B5/02
Filed: 1957-01-07
Abstract: 856,141. Optical projection apparatus. PERCEPTUAL DEVELOPMENT LABORATORIES Inc. Jan. 7, 1957 [April 13, 1956], No. 565/57. Class 97(1) Film strip feeding mechanism comprises a member reciprocated at a predetermined rate in the feed direction and another arranged to operate at any one of a plurality of rates which are fractions of the said predetermined rate to cause the member to engage the film and feed it. Preferably the reciprocating and engaging members are actuated by cams on the same shaft, two complete mechanisms being provided to feed separate films at different rates. The invention is described as applied to a device for testing visual perception comprising a projector for feeding and projecting in superposition a film 71, Fig. 26, having frames on which printed material is recorded, and a film 73 having frames which are opaque except for small transparent areas through which successive selected areas of the printed matter can be projected. This projector, Fig. 6, comprises a housing 15 closed at the top by a plate 13 which supports most of the parts of the film feed and projection system. A detachable cover may be secured by a catch 17. The motor 21 carries a blower 24 which supplies air to the tubular lamp housing and contains an eccentric type pump 28 which feeds air to the film gate assembly through the pipe 31. The motor drives the film feed mechanism through a pulley 23 and belt 82. The gate assembly, Fig. 22, comprises a plate 44 having a projection aperture 55 and formed on both sides with film guide channels 53 to accommodate the films 71, 73, the latter as an endless loop. Hinged gate members 45 carry resiliently mounted pressure pads each comprising an apertured plate 54 and a glass block 60. Air from the pipe 31 passes through channels 46 on either side of the plate 44 into channels formed in the faces of the blocks 60. Two intermittent feed mechanisms are provided, one for each film track. Each mechanism, Fig. 11, comprises a claw 69 at the upper end of an arm 64 which can pivot about, and slide along a rod 68. A cam 84, on a shaft 75, engages a follower on the claw arm and oscillates it along the rod, in the feed direction, the return movement being produced by a spring, not shown. Another spring normally holds the claw out of engagement with the film. A face cam 85 is driven from the shaft 75 by engagement of a dog with a collar 89 secured 'to the shaft. This permits axial movement of the cam effected by a fork 92 which may be pivoted about the rod 68 by energization of a solenoid CL1 (or CL2). This energisation closes a switch Sll (or S12) and moves the cam 85 to a position where it can bear on the arm 64 and produce film engaging and disengaging movements of the feed claw. The driving shaft 75 for each claw mechanism carries a cam which actuates a switch (shown in Fig. 28 as S7 or S13) which is utilised to ensure that the solenoid CL1 or CL2 can only be energised when the feed claw is in a position in its stroke aligned with a film perforation. A -spring loaded pivoted member 199 is provided at each film gate and moves into contact with the plate 44 when a film notch passes under it. These pivoted members thus form the switches shown in Fig. 28 as S9, S10. The control circuit shown in Fig. 28 is contained partly in the projector casing and partly in a remote control unit connected to it by a cable. The control unit includes a speed control variable resistance P1; a four position "function switch" Sl with separate banks S1AS1D and switches S2, S3, S4, S5, S6. Actuation of the switch S6 energizes a relay RY7 which connects the motor 21 and lamp 27 to the power supply. The switch also connects the power supply to the primary of a transformer T which has secondaries W2, W1 for energizing a relay RY1 and the heater of a thyratron V1, and to rectifiers SR1, SR2 which, with capacitors Cl, C2, provide positive and negative D.C. voltages B+ and B-, relatively to a return wire 113, at points 120, 121. The grid 122 of the thyratron is normally biassed negative from point 121 through normally closed contacts 125, 128 of relays RY3, RY4, normally closed contacts 130, 132 of switches S4, S5, which are double throw push buttons, a resistor R7 and a resistor R6 with a parallel capacitor C6. To feed the film 73 one frame at a time under manual control the switch S1 is placed in position 1 as shown and switch S4 depressed. The relay RY5 is then energized from the B- supply at point 121 through contacts 142, of switch S4, 125, of relay RY3, 128 and 146 of relay RY4. This closes contacts 148 to permit the capacitor C7, when the switch S13 closes to charge through resistor R9 from the B+ supply and apply a positive pulse to the grid of the thyratron which conducts to energise the winding of solenoid CL1 and cause the cam 85 to engage the feed claw with the film. Actuation of the solenoid also closes the contacts 163, 164 of the switch S11 to energize the relay RY6 from the B- supply at 121 through the contact 142 of switch S4, now closed, contacts 125, 128 of relays RY3, RY4 and contact 163 of switch S11. When the relay RY6 is energised its contact 167 forms a holding-on circuit while the contact 169 re-establishes negative bias on the thyratron grid from point 121 through contacts 125 and resistors R6 and R7. The film is thus fed only one frame even if the switch S4 is held depressed. To feed the film 71 one frame under manual control the switch Sl is again placed in position 1 and the switch S5 depressed. The upper blade 132 of the switch S5 breaks from its upper contact to remove the negative bias from thyratron and closes on to its lower contact to charge the condenser C7 to apply a positive pulse to the thyratron as above. Also the lower blade 158 of the switch S4 breaks from its upper contact and closes on to its lower to insert the solenoid CL2 in the thyratron circuit instead of the solenoid CL1 so that the other feed mechanism is actuated. The remainder of the operation is as before. The film 73 may also be fed repetitively by pressing the "start" switch S2. Feeding continues at a rate determined by the setting of the resistance P1 until the "ston" switch S3 is depressed or until a marginal film notch N1, Fig. 26, passes under the contact 199, Fig. 11. Closure of the contacts 172 of the switch S2 energises the relay RY4 from the B+ supply at 120 through the contact 174 of relay RY2. The relay RY4 energizes the relay RY3 through its contacts 177, the switch S3 the contact 185 of relay RY1 and switch S1A, this relay then being held on by a circuit through its contact 191, the contact 185 of RY1 and the switches S3 and S1A, from the B+ supply. The relay RY4 also energizes the relay RY5 through its contact 187. This relay feeds a positive pulse to the thyratron grid as already described, the negative bias being removed by the opening of the contact 128, while closure of the contact 190 connects the B- supply at 121 to the contact 163 so that when the switch S11 is operated by closure of the solenoid CL1 the relay RY6 is energized. The energisation of the relay RY3 energizes, in turn, the relay RY2 from the B+ supply through the contact 192. The contact 174 is thereby opened and the relay RY4 drops out, but RY3 can be released only by opening the switch S3 or the contacts 185 of relay RY1. Operation of the relay RY5 and the feeding of a positive grid pulse to the thyratron have meanwhile energized the solenoid CL1 to feed the film. This also closes the contacts 164 of switch S11 to apply a negative bias to the thyratron grid from B- through resistor R5. When the frame is fed switch S7 is closed by rotation of the cam on shaft 75 to discharge capacitor C3 to apply a negative pulse to the thyratron anode and stop it conducting. Switches S7 and S11 now open and capacitor C5 begins to charge from B+ through resistor R8 and variable resistance P1. When the thyratron grid becomes sufficiently positive, depending on the setting of PI, the thyratron fires again and the cycle repeats. If a film notch N1 passes under the contact 199 this makes contact with the film-gate, thus closing the switch shown as S9. If the switch S14 is closed on to contact 198 the occurrence of the notch energises relay RY1 from the transformer secondary W2, thereby opening the contact 185 and allowing the relay RY3 to drop out and stop the feed sequence. It may also be stopped by depressing the switch S3. It may be restarted by depressing the switch S2 again. The film 71 may be controlled in an analogous manner with the switch S1 in position 3. It will be stopped automatically by the occurrence of a film notch, which, if the switch S14 is closed on to its contact 204, closes the switch S10. It may be desired to feed the film 71 by one frame at the conclusion of a sequence of frames of the film 73 identified by a notch N1. For this purpose the switch S1 is placed in position 2 and the switch S14 closed on to its contact 198. Now, when relay RY1 is energised by the occurrence of the notch, both solenoids CL1 and CL2 are connected into the thvratron circuit through the contacts 205. Both films are fed one frame and; the film notch having passed the contact 199, the feeding of the film 73 continues until it is stopped by the switch S3. The film 71 may be fed rapidly by moving the switch S1 to position 4 wherein the contact S1A energizes the solenoid CL2 continuously so that the film is fed at the maximum speed of reciprocation of the claw produced by the cam on shaft 75.