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Automatic Torque Controller for Torque Motors
By CARL E. HITTLE
The use of the automatic torque controller permits the full advantages of torque motors to be realized for film take-up and holdback duty without being handicapped by their inherent limitations when operated in the conventional
THE FIRST sound-on-film recording and reproducing units were made, many types of film-spool drives have been used on such apparatus. During the intervening years, film-spool drives ranging from the slipping belt to friction clutch, and, more recently, to torque-motor types have been used. When torque motors became available it was believed that they would provide the ultimate in performance, possessing more advantages than the previous types of drives and none of the disadvantages. Experience with these motors taught us that in the latter respect this was not true. As with the belt and the friction clutch drives, we found that torquemotor drives may also adversely affect the steadiness of film motion in the apparatus. Since the characteristics of
Presented on April 22, 1952, at the Society's Convention at Chicago, 111., by Edward P. Ancona, Jr., for the author, Carl E. Hittle, Radio Corporation of America, RCA Victor Div., Engineering Products Dept., 1560 N. Vine St., Hollywood 28, Calif.
torque-motor drives in connection with their use for take-up and feed spools in film-pulling mechanisms have been presented previously before the Society in a paper by A. L. Holcomb, * only the manner in which they may affect film motion will be reiterated. As stated in Mr. Holcomb's paper, these adverse effects may result from the following:
1. Sprocket-hole flutter (96 cycle/sec) due to high film tension at beginning or end of a reel.
2. Erratic shifting of the film with respect to the sprockets at "crossover" where the net tension on the film reverses.
3. Gear train chatter due to unloading the sprocket gears at crossover.
All of these contributing factors may be eliminated by maintaining constant film tension throughout the roll between each film spool and film sprocket with a differential in tension between
* A. L. Holcomb, "Film-spool drive with torque motor," Jour. SMPTE, 58: 28-35, Jan. 1952.
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July 1952 Journal of the SMPTE Vol. 59