Patent GB-845557-A (GB)
Title: Improvements in or relating to motion picture projectors
IPC: G03B19/18
Filed: 1956-11-02
Abstract: 845,557. Kinematograph projectors. BAUER G.m.b.H., E. Nov. 2, 1956 [Nov. 5, 1955J, No. 33457/56, Class 97(1) A device for stopping a projector rapidly comprises an armature connected with the film feeding mechanism and selectivity acted upon by electromagnetic clutch coupling it to the driving means and by an electromagnetic brake, the brake and clutch being energized by a circuit including a contact breaker co-ordinated with the position of the film feeding mechanism and normally open contacts of a stop relay responsive to a stop pulse. The system shown comprises a main switch comprising simultaneously operated switches 33, 64, 86-88, 97-102. These switches each have an "off" position shown and two "on" positions corresponding respectively to operation at 16 and 24 frames per second and utilising the centre and right hand contacts of the different switches. In either "on" position the alternating current supply 27, 28 energizes, through the switch 33, the primary of a transformer 79, feeding the projection lamp 81 and a motor 78 driving a blower for the lamp as well as the primary of a transformer 32. At the same time a 3-phase supply 82 energizes, through the switches 86-88, a motor 89 driving a blower for the film. The centre contacts of the switches 97, 99, 101 energize the windings 106 of the motor 19 which cause it to drive the projector at 16 frames per second and the tight hand contacts of the switches 98, 100, 102 energize the windings 110 which drive at 24 frames per second. The motor is not started until the switch 93 is subsequently closed. The transformer 32 feeds a rectifier 35 which supplies various control relays. On switching on, the relay 58 is energized through a resistance 55 and normally closed switch 56, and closes switches 72, 86. The former energizes the relay 74 to close the motor switch 93: the latter energizes a solenoid 66 which holds a heat filter 71 out of the projection beam. At the same time current is fed to the winding 17 of a magnetic coupling between the driving motor and projector mechanism. To stop the projector, to show a stationary image, a switch 49 is closed, it need only be momentarily. This energizes a relay 51 which is then held on by a switch 53. The relay closes a switch 42 in series with a device comprising a slip ring 23 on the shaft of the intermittent feed mechanism and brushes 25, 26 which are bridged thereby at a particular point in the feed cycle. When this point is reached a relay 44 is energized and held on by switch 47. The relay 44 opens the switch 56 to de-energize the winding 17 to uncouple the motor from the projector and also to de-energize the relay 58 to stop the motor and allow the heat filter to drop into the projection beam. The relay 44 also closes the switch in the circuit of a magnetic brake 15 on the projector mechanism. This circuit is completed through resistances 61, 62 and a lamp 60 which assist the rapid initial rise in current. The resistance 61 is adjustable to provide the correct braking force and the resistance 62 is shorted by the switch 64, when operating at 24 frames per second, to increase the braking force. Normal projection is resumed by an inverse sequence of operation of the relays initiated by when the circuit of the relay 51 through the switch 53 is broken by opening one of the normally closed switches 39, 40, one of which may be on the projector, and one may be remote.