Patent GB-759088-A (GB)
Title: Improvements in installations for motion-picture projection
IPC: G03B21/00
Filed: 1954-05-17
Abstract: 759,088. Control of several motors. DOWLING, R. W. May 17, 1954 [Aug. 27, 1953], No. 14381/54. Class 38(3) [Also in Group XX] The size of a projected motion picture is varied, as by means of a variable focal length objective, the size of the effective screen area being adjusted automatically, by a variable border, to correspond. Fig. 2 shows part of a system having pairs of masking members at the vertical and horizontal margins connected respectively to endless belts 23, 24 passing round pulleys 25, 26 on a shaft 27 so that rotation of the shaft produces equal and opposite movements of the members of each pair, the movements of the two pairs being in such a ratio that the ratio of the dimensions of the uncovered screen area remains constant. The shaft 27 is driven from a Selsyn receiver 37 connected to a transmitter 38 which is operated by one of the motors 34, 35, one for each direction of rotation, which also drives, through gearing 32, 33, a shaft 31 carrying pulleys 30 driving members 19 through endless cables 17 in tubular guides 18. The members 19 form parts of the projector lens mounts and their rotation adjusts the focal lengths of the lenses to suit the effective screen area. A normal objective 1, 2 (Fig. 4) is associated with an afocal system comprising a divergent member 3, rigid with 1, 2, a convergent member 4 and a divergent member 5. The members 3, 4, 5 are separately achromatized. The members 4 and 5 are carried in separate mounts with pins 13, 14 projecting through a longitudinal.slot 12 in a fixed tube 7 and through slots in a tube 15, rotated by the member 19, shaped to provide the required axial movements of the members 4, 5. The variation in brightness of the projected image with size may be compensated by a diaphragm operated by the member 19 or by a rheostat in the power supply to the light source similarly operated. Alternatively, the rheostat may be separately operated by a Selsyn receiver connected to the transmitter 38. Movements of the screen masks and focal length adjusting members, to produce an increase of picture size, are produced by the motor 34 energized through contacts 56 of a relay 54, the coil of which is connected to a supply 55 by closing contacts 44a, 44b or 44c. The relay has hold-on contacts 59 in series with a limit switch 61 and the motor may run until a projection 63 on a disc 63<SP>1</SP> on the shaft 31 opens this switch. A decrease of picture size is similarly produced by the motor 35 in association with the relay 57, motor contacts 58, hold-on contacts 60, a limit switch 62 and contacts 46a, 46b or 46c. Energization of either relay also energizes a coil 68, through contacts 66 or 67, to free a brake from a drum 71 on the motor shaft 36. Each relay has contacts 64 or 65 in series with the coil of the other to prevent simultaneous operation. Either change of picture size may be stopped by closing contacts 45a, 45b or 45c to energize a relay 70 and open normally-closed contacts 79 also in series with the relay hold-on contacts. The decrease of picture size is arranged to be somewhat slower than the increase. The contacts 44c, 45c, 46c are provided for manual control of the picture size. The contacts 44a, 45a, 46a are associated with one projector, and the contacts 44b, 45b, 46b with the other. The projector contacts are operated by the film itself or by a control band driven by the projector mechanism at reduced speed and provided with apertures, where required, co-operating with pivoted feelers which operate the contracts.