Patent GB-295378-A (GB)
Title: Improvements in or relating to film driving mechanism for sound recording or reproducing apparatus
IPC: G03B31/02
Filed: 1928-07-13
Abstract: 295,378. British Thomson-Houston Co., Ltd., (Assignees of Heisler, C. L.). Aug. 11, 1927, [Convention date]. Feeding webs.-Relates to mechanism for driving a film in sound recording or reproducing apparatus, of the kind comprising a smooth feedwheel or drum (referred to in the Specification as a belt-type drive), and a sprocket-wheel or wheels, engaging the film at different points along its length. According to the invention, the sprocket or sprockets are driven at a substantially constant speed, but the speed of the belt-type drive is automatically varied in order to maintain the length of the film loop between the smooth feeddrum and an adjacent sprocket-wheel approximately constant. In the recording apparatus shown, the film 4 is drawn from a reel 5 by a sprocket-wheel 6 mounted on a shaft 7 which is coupled through a, fly-wheel 16 and a vibrationabsorbing disc 18 to a driving-shaft 17. The film is fed past the light-slit of the sound-recording device by a drum 21, against which it is pressed by rollers 55, 56. The drum 21, formed integrally with a fly-wheel 22, is fixed on a shaft 20. Friction-wheels 15, 23 are secured to the shafts 7, 20 respectively, and interengaging them is a frictionwheel 30, which is so mounted that it can engage different parts of the curved surfaces of the wheels 15, 23. By this means the speed at which the shaft 20 (and thereby the drum 21) is driven by the shaft 7 may be varied. This adjustment of the position of the wheel 30 is controlled by means of an arm 26, carrying a roller 25 which engages in a loop 4<a> of the film. The arm 26 is fixed on a shaft 27, which is acted upon by a spring 28, so that the arm 26 tends to rotate and hold the film in tension as it is fed to the drum 21. The wheel 30 is supported by a sleeve 32 which has a gimbal-joint mounting comprising a member 35 in which the sleeve 32 is trunnioned at 38, the member 35 being itself supported on trunnions 36 by the frame of the machine. Secured to one of the trunnions 38 is an arm 40, which is connected by a universal joint to a nut threaded on the end of the shaft 27. The speed of the friction-drive 15, 30, 23 is thus varied as rocking movements of the wheel 30 are caused by changes in the position of the arm 40 due to variations in the length of the film loop 4a. The Specification, as open to inspection under Sect. 91 (3) (a), comprises also the following subject-matter. In order to enable the film to be easily threaded through the machine, means are provided whereby movement of the door of the casing beyond a certain open position causes the wheels between which the film is held to be separated. For this purpose, two levers 52, 53 are mounted on a common pivot, one lever 53, pivotally supporting a plate 54 on which the pivot pins of the rollers 55, 56 are carried, while the lever 52 has an arm 59 on which the roller 60 is pivoted. The rollers are held down against the drum 21 and the sprocket 6 respectively by spring action on the levers 52, 53. The lever 52 also has an arm 63 linked to a pivoted plate 65 which carries the light-slit. When the door 2 is opened widely, a projection thereon (not shown) causes a wedge piece mounted on the casing to be thrust between the outer ends of the levers 52, 53. The movement of the levers thus caused shifts the rollers 55, 56, 60 away from the drum 21 and sprocket 6, and moves the member 65 away from the drum. This subject-matter does not appear in the Specification as accepted,