GB933862A - Improvements in or relating to electric motor control arrangements for use in the transportation of web - Google Patents

Abstract

933,862. Control of several A.C. motors. ELECTRIC & MUSICAL INDUSTRIES Ltd. Nov. 30, 1959 [Nov. 28, 1958], No. 38498/58. Class 38 (3). When a switch SWA is closed, full power is applied to a take-up motor 10 for reeling magnetic tape, reduced power being supplied to the running winding 13 of capstan motor 12 through resistors R1, R2, in parallel. Full mains power is also applied to starting winding 14, the motor 11 coupled to the supply spool being de-energized. At a predetermined speed of the capstan roller, centrifugal switch 15 opens so that full power is now applied to the running winding 13 and the starting winding is disconnected. The take-up motor 10 receives reduced power through resistor R1, whilst the motor 11 is excited with D.C. braking current through resistor R3 to provide a back-tension. The tape thus reaches full speed and continues so to travel until the end of the tape is approached, whereupon a signal from photo-sensitive device P1 or P2 causes the starting winding 14 to receive full power in the reverse direction, the running winding 13 receiving reduced power. The capstan motor slows down, and simultaneously the motor driving the new take-up spool receives full power. The tape is accelerated until the centrifugal switch 15 opens whereupon the power supplies are changed to bring the tape to full speed. During the change-over it is necessary for relay RLF4 to be energized even though the centrifugal switch 15 is open and this is achieved by means of mercury switch 16 responsive to the direction of rotation of the capstan motor. Movement of the tape is stopped by opening switch SWA to de-energize the capstan motor, apply a small alternating-current to the take-up motor, and a direct braking current to the supply motor. After a predetermined period, both motors are de-energized. In the system described the tape is brought to rest due to the provision of transparent portions at the ends thereof, a switch SWB being operated when a spool is half full. With such an arrangement the length of transparent portions of the tape may be reduced. The photo-sensitive devices may be replaced by recorded signals at the ends of the tape. A switch 23 is coupled to switch 16 to ensure response to the signal from the photo-cell which occurs nearest to the end of the tape which is being approached and not to a signal which is received during acceleration of the tape. If the tape stops in the middle of its length due to power failure, the switch SWB ensures that, upon re-starting, the take-up spool is the one with the least amount of tape.