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R-l
MASTER SWITCH REVERSE
Fig. 5. Schematic of torque motor voltage controller.
as a rewind was obtained by using the motor at its rated output as a propulsion device. The electrical elements of this assembly are shown schematically in Fig. 5. From this, it will be noted that the use of a variable series resistance (R-l) in one leg of a single-phase motor, serves to vary the motor torque for either holdback tension or forward torque for take-up. The resistor (R-l) is varied by a commutator (S-l) by means of a follower arm in contact with the periphery of the film roll. Additionally, a relay (K-l) is used to vary the overall torque curve when the motor is functioning for a take-up instead of a holdback as in the case of reverse operation. This relay is normal in the holdback function and energized by the master control switch for the reverse or take-up function. As shown in Fig. 5, the commutator switch (S-l) is in its initial position at the maximum film roll diameter thus placing the least amount of R-l in series with a sec
ond resistor (R-2) and this combination being seen by one leg of the torque motor. As the commutator switch progresses with a decrease in film roll diameter, sections of R-l are automatically added, proportionally reducing the motor torque. As the last two steps are reached, R-l is opened allowing only the inherent load of the motor-drive assembly to serve as friction in the holdback function, these two steps being at diameters less than 5 in. When functioning as a take-up device, relay K-l becomes energized and shorts out R-2 to increase the overall torque range. Additionally, steps 1 and 2 of S-l are seen by R-l, thus giving a potential to the motor at the minimum or starting diameter of the take-up roll. Controlling the torque of each motor by the described method produced a film tension characteristic constant within 2 oz throughout the length of a 2000-ft reel using a 2-in. OD core.
Singer and Pettus: Magnetic Recording Equipment
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