Patent GB-1495116-A (GB)
Title: Forward-reverse multi-speed film transport mechanism
IPC: G03B1/18
Filed: 1976-09-02
Abstract: 1495116 Film projector drive mechanism BELL & HOWELL CO 2 Sept 1976 [2 Sept 1975] 36382/76 Heading G2E A motion picture projector has a drive mechanism which enables it to be driven in the forward or reverse direction at a number of different speeds. These are the normal rate, two different slow motion rates, and a still projection mode. The mechanism is driven from a shaft 10 rotating anticlockwise. A first gear 14 and a first (up and down) cam 11 are mounted on shaft 10. A shuttle 12, spring-urged upwards, has a portion 13 acting on a follower co-operating with cam 11. The cam has surfaces 23, 24 which cause the follower, and hence the shuttle, to move downwards (forward) and upwards (reverse) respectively. The shuttle is guided to move in a straight line by balls 25, 26 journalled in guide plates 27, 28, the ball mounting also allowing the shuttle to pivot so that its teeth 18, 19 can engage and disengage with the perforations in the film strip 20. Gear 14 meshes with a second gear 15 Fig. 1 (not shown) which carries teeth 32 meshing with teeth on a third gear 17, the gears being so related that the relative rotational speeds of gears 14 and 17 are in the ratio 9:1. Gear 17 has on its face a number of concentric cam tracks 35-38. Track 35 has nine dwelled portions, track 36 three dwelled portions, track 37 one dwelled portion, and track 38 none. A second (in and out) cam follower 16 is mounted at one end of an elongated member 40 which has a slot 41 enabling it to slide on an axle 30. Follower 16 is urged into engagement with the cam tracks on gear 17 by an extension 39 of shuttle 12, itself biased by a spring 78. The position of member 40 can be adjusted so as to bring follower 16 into engagement with any desired one of the cam tracks 35-38 by means of a cam 51 having a number of rounded portions 62-67. Cam 51 can be pivoted round an axis 61 by means of a handle (58), Fig. 1 (not shown) so as to bring any of the rounded surfaces into contact with member 40. In the position of Fig. 2, rounded portion 62 has engaged member 40 so as to bring follower 16 on to cam track 35, which has nine dwelled portions. Drive shaft 10 and hence cam 11 rotate at 18 revs/sec, so that gear 17 rotates at 2 revs/sec, giving a film transportation rate of 18 frames/sec. When either rounded portion 63 or 64 engages member 40, follower 16 engages cam track 36 for a film transportation rate of 6 frames/sec. Similarly engagement of rounded portions 65, 66 causes engagement with cam track 37 for a rate of 2 frames/sec, and engagement of portion 67 causes engagement with cam track 38 which has no dwells and thus causes the shuttle teeth to be continuously disengaged from the film, so producing still projection. For changing between forward and reverse projection, a lever 42 is displaced between a first and a second position. As shown in Fig. 2 the mechanism is set for forward projection. For reverse projection, lever 42 is pivoted clockwise, so that slot 43 in the lever, in which pin 44 on member 40 slides, causes member 40 to pivot correspondingly, into the position of Fig. 4 (not shown). In this position of follower 16, its angular displacement from the Fig. 2 position is such that the mechanism operates in the reverse mode, although the direction of rotation of shaft 10 is unaltered. Also mounted on shaft 10 is a multibladed shutter (70), Fig. 5 (not shown), and since its speed of rotation is unaltered even when the mechanism is in a slow motion or still mode, the gate aperture 21 will still be covered 54 times per sec, thus reducing flicker.