Patent GB-376225-A (GB)
Title: Improvements in and relating to apparatus for recording or reproducing sound
IPC: G11B15/46
Filed: 1930-12-29
Abstract: 376,225. Driving sound films. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Heisler, C. L. ; 1443, Glenwood Boulevard, Schenectady, New York, U.S.A.) Dec. 29, 1930, No. 39089. Convention date, Dec. 28, 1929. Void [Published under Sect. 91 of the Acts]. [Class 40 (ii).] Film-driving means for optical sound-recording or reproducing apparatus comprises a sprocket and a drum arranged to engage the film, the speed of the drum being regulated in accordance with the speed of the sprocket-fed film by means of a controlling lever movable in response to changes in the length of the film between the sprocket and the drum, the controlling lever being weighted to render it substantially unresponsive to sudden small variation in the speed of the film. Means are also provided to prevent slippage of the film on the drum by applying tension to the film as it approaches the drum and by engaging the film as it leaves the drum by a roller which tends to move the film at a speed in excess of that at which the film is moved by the drum. A film 1 is held against the driving sprocket 3 by pressure rollers 4, 5 and passes successively in a tension loop over a control roller 6, over a pressure and guide roller 7, around a drum 8, over a pressure roller 9 and then in a free loop to a pressure roller 5 and the sprocket 3. The drum shaft is journalled in bearings one of which is shown at 12, and comprises two coaxial portions 14, 15 through the annular gap between which the photo-electric cell 20 is illuminated by light from a source 22 after passage through the sound record on the film. Both the sprocket 3 and drum 8 are driven from a common source of power through a compensator 23 of the type described in Specifi. cations 293,381, 295,378, [both in Class 40 (ii), Phonographs &c.], 346,149 and 355,236, which is designed to regulate the speed of the drum so that it moves the film at exactly the same Speed as does the sprocket. The compensator comprises essentially a mechanism by means of which the movement of a worm wheel 24 driven by a worm 25 on the driving-motor shaft rotates the drum shaft 10 at a slightly varying speed depending upon the pressure of a brake 26 on a brake wheel 27. Through a gear 24a movement is transmitted to the sprocket 3. The brake 26 is mounted on a lever 28 to which a spring 29 is attached, and engaging the lever 28 is a roller 30 mounted on an arm 31 secured to a shaft 32 to which also is secured a lever 33 carrying the control roller 6. A mass 35 is applied to the lever 33 to cause the latter to rotate counterclockwise in response to an increase in size of the film loop to operate the brake lever 28 to release the brake against the tension of the spring 29. The mass 35 also functions as an inertia device to steady the movement of the film. Where the film leaves the drum 8 it passes over the pressure roller 9 whose shaft is journalled in aT-shaped member 43, which is swivelled upon a rightangle extension 42 of a pivotally mounted arm 40. The shaft of the roller 9 has mounted at its other end a roller 44 of slightly less diameter than the roller 9, the faces of the rolls 9, 44 being conical, and the roller 44 engages the drum beyond the edge of the film. The roller 9 has a tyre of soft resilient material such as rubber while the roller 44 has a hard face adapted to resist wear. Roller 9 tends to move the film faster than it is moved by the drum, but since the diameter and coefficient of friction of the roll 9 is greater than that of the roller 44 slipping occurs only between roller 44 and the drum. By this means the film is constantly urged forward and is caused to hug the drum firmly.