Patent GB-217292-A (GB)
Title: Improvements in and relating to cinematograph mechanism
IPC: G03B15/08
Filed: 1923-03-08
Abstract: 217,292. Redgrave, G. R., and Bowell, G. B. March 8, 1923. Kinematograph apparatus. - Constant tension is maintained in the section of film passing through the optical axis by means which is independent of the film surface, for example by means of a friction brake or clutch combined with one of the film drums, the drum, controlled by the film, and its spindle, rotated by the mechanism, being caused to rotate at different rates but with a substantially constant speed difference; the spring gate is omitted. Figs. 1, 2 and 3 show a projector of the type described in Specification 194,031 wherein the film passes continually from a spool 1, round a guide roller 2, upper toothless drum 3, rollers 4, 5, lower toothless drum 6, and roller 7, to a receiving spool, the rollers 4, 5 being reciprocated vertically so as to render the film intermittently stationary with respect to the optical axis. The drum 6 is mounted on its shaft 29 by a self aligning ball bearing 45, Fig. 4, and carries a disc 47 which, by means of a spring 51 and flange members 49, 50, is pressed against a friction disc 48 bearing on a flange member 46 secured to the, shaft, the friction being variable by adjustment of the member 50. The shaft 29 is rotated faster than the shaft 32 of the drum 3 so that the slip between the shaft 29 and the drum 6 produces the film tension. The transmission mechanism comprises a driving shaft 54 geared to a shaft 26 which is geared both to the shaft 29 and to a shaft 22. The shaft 22 drives the shutter 57 through bevel gearing, and also drives the drum 3 through a shaft 27, rotated 'at the same speed as the shaft 26, and carrying a tapered drum 30 engaging a friction disc 31 slidably mounted on the shaft 32 of the drum 3. Contact between the drum 30 and disc 31 is maintained by mounting the shaft 27 on a pivoted frame 33 pressed by springs 34. The shaft 22 carries a cam 16 which operates through a lever 17 to reciprocate a sliding spindle 13 carrying the spindles of the rollers 4, 5, the spindle 13 being carried in rotatable bushes 14, 15, and a spring 21 serving to keep the lever and cam in contact. The linear rate of feed of the film and the stroke of the rollers 4, 5 are adjusted simultaneously by rotating a handle 39 mounted on a shaft 38. The shaft 38 has a crank 37 carrying a blade 36 engaging a grooved boss 35 secured to the disc 31, and also has a crank connected bv a link 43 to a lever 42 projecting from a rotatable bush 41 carrying the bush 15 on an eccentric shank 40. Movement of the disc 31 on its shaft varies the ratio of the friction gear, and movement of the bush 15 alters the position of the spindle 13 so that the effective length of one arm of the lever 17 is varied. Means for taking up back lash may be provided. A constructional form of invention as applied to a maltese cross projector is described, a sprocket having a friction brake being provided above the optical axis and its spindle being rotated by means of a cam so that it always has a constant backward speed relatively to the sprocket. In another construction sprockets above and below the optical axis are driven through helical gears of different pitch on a longitudinally reciprocated vertical shaft driven through a helical gear slidable upon it. The reciprocation is such that the film is intermittently rendered stationary, and the gears are such that the upper spindle, which is connected to the upper sprocket by a friction brake, is rotated at a speed constantly different from that of the sprocket. According to one of the Provisional Specifications a cam mechanism for producing an oscillating movement between the brake surfaces may be provided.