Patent GB-490210-A (GB)
Title: Improvements in or relating to apparatus for playing sound films
IPC: G11B15/22
Filed: 1937-02-04
Abstract: 490,210. Optical sound reproducing apparatus. BRITISH OZAPHANE, Ltd., and WENDER, E. J. Feb. 4, 1937, Nos. 3385 and 23423. [Class 40 (ii)] [Also in Groups XX and XL] Relates to apparatus for reproducing from sound-films having two parallel tracks running in opposite directions. According to the invention, the film drive is automatically reversed after the first track has been played, whilst means are automatically operated for changing over reproduction from the first track to the second, and the motor is automatically stopped when the playing of the second track is completed, such control being effected by means of conductive inserts provided in the film or in a " leader " attached thereto ; the inserts are adapted each to connect together two contacts which, when so connected, operate a switch so as to reverse the drive or to stop it, one or other of these operations being selected in accordance with the direction of movement of the film. In the apparatus shown, the film is drawn first from a spool 1 by a drive roller 3, past a sound gate 5, and thence to a take-up spool 9. The roller 3 is on the spindle of a flywheel pulley 28, Fig. 6, which is driven by a reversible motor 26. Attached to 28 is another pulley 29 which, by means of a belt 30 drives pulleys 31, 32, through which the spindles 39 of the spools 1, 9 are driven. The driving arrangements for the spindles 39 are alike, and are shown in Fig. 7. The pulley 31 (or 32) is coupled to a collar 38, fast on the spindle 39, through a friction clutch 46 and a one-way clutch 37, the collar being also connected through a second one-way clutch 41 to a pulley 40 on which acts a spring- actuated brake 42, Fig. 6. The clutches are so arranged that, for either direction of drive of the film, the take-up spool is positively driven and the associated brake-pulley 40 is inoperative, whilst the spindle of the other spool is declutched from its drive-pulley and its brake is in action. In order to allow the film to be rewound rapidly on to the spool 1, a lever 650 may be rotated by means of a knob 640, Fig. 1, to reduce the tension of both the brake springs 660. The spool 9 may be permanently fitted to the apparatus, and may consist of a transparent upper disc and a lower plate, separated by a spacer 65. The end of the film may be fastened in a radial slot in thespacer 65, by means of a cam-operated spring strip 67. The film preferably has a " leader " of rubberized cloth &c. at each end, which may have differently coloured sides to facilitate threading without twisting. The motor 26 is controlled by three switches, Fig. 14, a mercury switch 50, a switch 52 operated by a pivoted arm 53, Fig. 1, adapted to bear on the coil of film in the spool 9, and a third switch comprising a pair of fixed insulated contact strips 10, 11 constituting the sound gate 5, Figs. 1 and 2, and adapted to be bridged by one or other or a pair of conductive inserts in the film. The mercury switch 50 comprises a tiltable tube adapted to take any of three positions, the motor circuit being open when the tube is horizontal, Fig. 14. To start the machine, the switch 50 is tilted by means of a press-button, enabling the motor to feed the film from spool 1 on to spool 9. Before the end of the first run of the film, the arm 53 is so displaced that the switch 52 is moved over from the position shown in Fig. 14 to prepare a circuit through an electromagnet 49. This circuit is completed when, at the end of the playing of the first sound-track, one of the contacts inserted in the film bridges the contacts 10, 11. Thereupon the armature 34 of magnet 49 tilts the mercury switch 50 so as to reverse the motor, and the film begins to be rewound on the spool 1. Before the second track has been played completely, the arm 53 has moved inwardly sufficiently to shift the switch 52 back to prepare a circuit through a magnet 49<1>. This is energized when the second conductive insert in the film bridges the contacts 10, 11 at the end of the second run, and the armature 34<1> moves the mercury switch into the horizontal position, opening the motor circuit. The switch 50 may also be moved at any time into the reversing or stopping positions by manually-operable push-buttons. The optical system comprises a combined condenser and mirror unit 16 projecting light from a lamp (not shown) through an aperture 13, Fig. 2, in the gate 5 in contact with which the film runs, an image of the sound track being projected by an optical system 19 through a slit on to a light-sensitive device, preferably a selenium cell. In order to select the track to be played, in accordance with the direction of running of the film, there may be provided a movable mask which is in mechanical connection with the pulley 28. When the film begins to run, the mask is automatically moved in dependence on the direction of rotation of the pulley into one or other of two positions in which the sound-track to be played is exposed, and the other is covered. Alternatively, instead of such control of the light beam, a double selenium cell, as shown for example in Fig. 12, may be employed. The cell comprises two sensitized areas 61 on a common terminal formed by a metal backing 62. Each area 61 has its own terminal 63, and is separated from the other by an insulating gap 64. Both areas 61 are illuminated together by light passing through the respective sound-tracks, but only one or other of the active areas is brought into use as required, by means of a switch operated by mechanical connection with a film roller. A modified form of cell, in which the terminals 63 are at right-angles to the gap 64, is described.