Patent GB-393176-A (GB)
Title: Improvements in or relating to the recording and reproduction of sound
IPC: G11B7/24
Filed: 1932-10-28
Abstract: 393,176. Optical sound recording or reproducing apparatus. RADIO CORPORATION OF AMERICA, 570, Lexington Avenue, New York. U.S.A. Oct. 28, 1932, No. 30320. Convention date, Oct. 28, 1931. [Class 40 (ii).] Comprises optical sound recording or reproducing apparatus wherein a record film is moved at uniform speed by a friction drive and a light beam is moved transversely thereto at a speed which is proportional to that of the film, irrespective of film shrinkage. As shown by Fig. 3, a continuous loop film 11 is driven by a friction roller 12 on a drive shaft 13 and the recording or reproducing optical system 10 is coupled to the shaft 13 through gears 14, 15 and a lead screw 16 and nut 17. In this way the light beam is moved across the film at a speed proportional to that at which the film 11 is driven by the roller 12 to record, or to reproduce from, a helical sound record. Fig. 4 shows in side elevation a form of reproducing apparatus wherein a continuous film 112 is driven by a roller 111 mounted on a drive shaft 110 and is threaded around a split roller 113 at the translation point and around idler rollers 114, 115, the roller 115 being connected to a bell-crank 116 biased downwardly by a spring 118. Also mounted on the shaft 110, are a flywheel 123 and a worm 124 co-operating with a worm 125 on a shaft 126 which is coupled to a member 127 of a clutch through which the movement of the optical system is controlled. The other clutch member 136 is mounted on a shaft 137 provided with a gear 139 to co-operate with a gear 140 loosely mounted on a lead screw 149 which moves the optical system 134, as shown in perspective view by Fig. 10. Engagement of the clutch members is controlled by a lever 142 which can be moved by a control knob 145. The optical system 134 is supported upon a pair of rods 146, Fig. 6, arranged to move in sleeves 147 and connected to a member 148. Movement of the rods 146 in the sleeves 147 is effected by rotation of the lead screw 149 through a collar 164. The clutch member 127 is biased to its open position by a spring 151, Fig. 10, and is moved into closed position by a cam 152 on the shaft 153 of the control knob 145. Also mounted on the shaft 153 is a contact member 155 through which the electrical connections of the motor driving the main shaft 110 and of the amplifier 162, Fig. 4, are controlled. In operation, the control knob 145 is moved to engage the clutch members 127, 136 and close the circuits of the driving motor, the amplifier and the exciter lamp 156. During operation the optical system 134 moves transversely of the film 112 and the modulated light beam impinges upon a photo-electric cell 135. When the light beam reaches the end of a record the mechanism is stopped automatically by the opening of a switch 165, Fig. 10, through engagement with a member 166 mounted on the back of the support 129. The optical system is returned to its starting position by a spring 174, Fig. 6, within the gear 140 and the position at which it comes to rest is determined by a stop 167, Fig. 10, arranged to co-operate with a pivoted member 168 which is biased out of engagement during operation by a spring 171, but which at the end of operation is pulled into engaging position by a cable 172 attached to the member 148. The return of the optical system to starting position is controlled by a governor mechanism 141, Fig. 4. A recording apparatus according to the invention is described wherein the recording element is moved transversely of the film by means of a nut engaging with a lead screw which is connected through a clutch with the film-driving roller. Movement of the recording element is opposed by a powerful spring to eliminate the effect of any looseness between the lead screw and the nut, while the filmdriving roller is enclosed by a light-tight casing through which the optical system is inserted. The Specification as open to inspection under Sect. 91 describes also a special construction of a film-guiding roller and also of a pressure roller which prevents slippage of the film during its passage over a drum at the sound head. The guiding roller, Fig. 17 (Cancelled), comprises a member 253 mounted rotatably on a shaft 254. The edges of the film contact with supporting surfaces 257, 258 and are held between shoulders 259, 260 which are tapered except for a short distance above the film surface. The shoulder 259 is pressed by a spring 261 to allow for slight differences of film width. The spindle 254 may be adjusted endwise of a supporting plate by turning a nut 263. The pressure roller 247, Fig. 19 (Cancelled), is mounted on a shaft 264 having a bronze sleeve 265 over which are forced two further sleeves 266, 267 whereby rubber filmcontacting washers 269 are held in position. Fig. 6 (Cancelled) shows a modified means for supporting the film at the sound head wherein the film rests on a flanged drum 131<1> and on a similar member 132<1> which is spring-pressed by a spring 133<1>. This subject-matter does not appear in the Specification as accepted.