Patent GB-1264385-A (GB)
IPC: G11B15/22
Filed: 1969-03-07
Abstract: 1,264,385. Differential switches. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 7 March, 1969 [11 March, 1968; 18 June, 1968], No. 12173/69. Heading H1N. A device for switching off or reversing the direction of movement of the drive of a tape in a recording and/or playback apparatus comprises a disc 7 constantly rotated by a motor and driving through friction coating 9 a winding disc 3 adapted to receive a tape on a spool, winding disc 3 being stopped if the tape stops such as by the end of the tape being reached. On the inside of disc 7 is a cam track 14 and a cam follower 19 on a lever 17, cam follower 19 being urged against the cam track by spring 18. Lever 17 is pivoted at 16 and one end 20 engages a switch 21 and the other end 24 carries a feeler 25 which rests against the periphery 28 of winding disc 3. When both discs 7 and 3 are rotating, lever 17 is reciprocated by cam 14 and periodically opens and closes switch 21, and feeler 25 is carried along by frictional contact between feeler 25 and periphery 28 against the action of spring 26 so that feeler 25 pivots to the right, Fig. 3 (not shown). When disc 3 stops rotating feeler 25 is no longer carried along by friction with periphery 28 and the next time cam 14 in disc 7, which is still rotating, moves lever 17 into the position shown in Fig. 2 with end 24 at a maximum distance from the centre of disc 3, feeler 25 is pulled by spring 26 against a stop 27 on lever 17 so that feeler 25 is radial to disc 3 and rests against it, thus holding lever 17 in the position shown so that it is no longer reciprocated by cam 14 and holds switch 21 closed. Switch 21 is connected to a capacitor 31, Fig. 3, and when switch 21 is being periodically opened and closed the capacitor cannot obtain a sufficient charge but when switch 21 is finally closed and remains closed capacitor 31 attains a sufficient charge to cause transistor 30, Fig. 3, to pass a current which causes a relay 22, Fig. 3, to respond so that the tape drive is switched off or changed over. In a second embodiment, Figs. 4, 5, 6 (not shown), lever 17 is replaced by a longitudinally displaceable slide 34 provided with two feelers, 25, 25<SP>1</SP>, effective for opposite directions of rotation of the disc with a changeover device 37 to ensure that the correct feeler for the direction of rotation is engaged with the periphery. In a third embodiment, Figs. 7, 8 (not shown), the cam follower 19 on lever 17 co-operates with a cam track on a flywheel 41. In a fourth embodiment, Fig. 9 (not shown), cam follower 19 co-operates with a cam on a flywheel 41 and there are two tape winding discs with a feeler 25, 25<SP>1</SP> for each and a change-over device to change over the drive and feelers to the winding disc being used. In a fifth embodiment, Figs. 10, 11, 12 (not shown), lever 17 is replaced by a straight operating member 15 having integral with it a cam follower 58 resting against a cam surface on the edge of disc 7 and a feeler 25 resting against the edge of disc 3. Member 15 is spring-urged in a direction to close switch 21 but is urged in the opposite direction by friction between feeler 25 and disc 3 so that member 15 reciprocates until disc 3 is stationary when the friction ceases and switch 21 is held closed. In a sixth embodiment, Figs. 13, 14, 15 (not shown), there are two levers 17, 17a co-operating with two cams 14, 14a on a common flywheel 41 and with two switches 21, 21a which are periodically actuated so that one switch is closed while the other is open until the tape winding disc 3 is stationary when both switches are held open. In a seventh embodiment, Figs 16, 17, 18 (not shown) two levers 17, 17a co-operate with a common cam 14 on a flywheel 41 and with a common switch 21 which is held closed by the levers alternately until tape winding disc 3 is stationary when the switch opens.