| 摘要 |
1463085 Automatic control of loop size POLAROID CORP 20 May 1974 [28 June 1973] 22445/74 Heading G3R [Also in Division H2] Speed control of a split-phase or shaded pole induction motor 80-82 is effected by providing a rectifier 88 between the A.C. input 85, 86 and the motor coils 81, 82 and an s.c.r. 89 in inverse parallel relationship therewith, triggering of the s.c.r. in appropriate (negative) half cycles of the source being effected by a means responsive to the A.C. voltage and comprising a potential divider 92, 91 connected across the A.C. input terminals 85, 86, and a diac 90 connected to the point between the two resistances. The motor has a further winding coupled with the stator core to act as a transformer to supply further loads. Control of the speed of the motor is obtained by causing a D.C. braking component to pass through the motor produced by retarding the firing angle of thyristor 90, this angle being controlled by variable resistance 91. The diac may be replaced by a S.U.S. and the resistance 92 by a capacitor. In a preferred embodiment, Fig. 1 the motor is used to move a photographic film and the variable resistor 64 is a photo-electric component arranged to detect the length of a loop of film 18 between a sound reproducing head and the optical gate, and to modify the motor speed to keep this length constant. |
