Patent GB-293381-A (GB)
Title: Improvements in and relating to methods of and means for driving films in sound recording or reproducing apparatus
IPC: G03B31/02
Filed: 1928-06-08
Abstract: 293,381. British Thomson-Houston Co., Ltd., (Assignees of Heisier, C. L.). July 5, 1927, [Convention date]. Film-feeding mechanism.-Relates to optical sound-recording and reproducing apparatus in which a film is fed through a machine by means of sprocket-wheels and one or more smooth-faced rollers or wheels, the latter type of driving means (referred to in the Specification as a belt-type. drive) operating in conjunction with the sprocket drive, but at a different position in the length of the film. According to the invention, in order to counteract inequalities in the relative speeds of the two drives, the speed of the belt-type drive is maintained constant, but that of the sprocketdrive is automatically varied when necessary in accordance with the rate of change which may occur in the length of film between the two driving-devices. The invention is shown as applied to a motion picture projecting and soundreproducing apparatus, in which a film 1 is fed between reels (not shown) by a sprocket-wheel 2, a smooth-faced drum 3, and a sprocket-wheel 4, the drum 3 serving to feed the film at a uniform speed past an optical sound-reproducing device. This consists of means 17 for directing a steady beam of light through the sound-record on the film on to a photo-electric cell located within the drum. Intead of using a rotary drum, the film may be fed past the optical device 17 by using one or more driven rollers coacting with a fixed support over which the film is drawn. After passing over the drum 3, the film forms a loop 24, and then moves through a guide 26 in the picture projector, in which is provided intermittent motion mechanism 28. A shaft 30 drives by means of gearing 31, 32 the sprocket. 2, and also drives through gearings at its lower end the mechanism 28 and the sprocket 4. The shaft 30 is itself driven through gears 35, 36 by a shaft 37, which is driven by the shaft 10 of a motor 11 through variable speed mechanism 38. This is controlled by a bell-crank lever 23 engaging a loop 21 in the film and actuating a brake 45, which coacts with a brake-drum 44 of the variable speed gear. The shaft 10 drives the drum 3 through a shaft 7 and gearing 6, 5. The arrangement is such that when the brake-drum 44 is unrestrained, the shaft 37 runs at the same speed as the motor shaft 10, but the gearing is preferably such that the sprockets 2, 4 tend to drive the film at a slightly greater speed than that of the belt-type drive 3. Thus the loop 21 increases in size until the bell-crank lever 23 applies the brake 45 to the drum 44, whereupon the speed of the shaft 37 is reduced until the loop 21 shortens sufficiently to release the brake. This action is repeated cyclically. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following subject-matter. Optical apparatus. - The construction of the drum 3, as adapted particularly for soundreproducing apparatus is shown in Fig. 3 (Cancelled). The drum, mounted on the face end of a shaft 49, comprises two spaced portions 50, 51, the part 50 having an inset tyre 55, preferably of rubber, to prevent the film 1 from slipping. Rubber idler-wheels engage the film opposite the tyre 55 and also, if desired, opposite the part 51. The space between the parts of the drum allows light to pass through the sound record 56 to a photoelectric cell 16 supported within the drum by a socket on a bracket 57. This subject-matter does not appear in the Specification as accepted.