| 摘要 |
992, 275. Sewing machines. O. B. SCHWAB, [trading as FRANKL & KIRCHNER]. Aug. 13, 1962 [Aug. 23, 1961], No. 30888/62. Heading D1G. [Also in Division H2] To stop a series commutator motor 7 driving a sewing machine, treadle 1 is released so that starting resistance 4 is increased until the motor is de-energized. Contacts 5, 6, are engaged before the motor comes to a standstill and a control circuit comprising transformer 12, 13 is energized. A transistor 16 is conductive, provided that centrifugal switch 11 is closed, so that electromagnetic brake 10 is excited to apply the brake and relay 17 responds so that the motor remains disconnected from the line during the braking operation. When the motor reaches a low speed, the centrifugal switch is opened whereby control of transistor 16 is taken over by photo-transistor 18. If the transistor receives light from source 14 by way of reflector 21 on balance wheel 22, its resistance is reduced and transistor 16 remains conductive so that the motor continues to be braked and may come to a standstill. The setting of reflector 21 corresponds to the dead centre position of the sewing machine needle. If the machine overruns this position, the motor is re-connected and continues to operate until the reflector again throws light upon the photo-transistor element whereupon the brake is re-applied. The brake comprises armature 27 coupled to rotor shaft 26, the brake coil being associated with non-magnetic disc 30 having a friction surface. A magnetic disc 32 is fixed to the armature 27. When the motor is energized, the brake is released due to axial movement of the rotor. The centrifugal switch 11 comprises insulating disc 34 supporting spring elements 35, 36, to which are fastened carbon brushes 37, 38. The rotating part of the switch comprises insulating plate 41 having slip-rings 42, 43. Weights 44, 45, are interconnected by a strap and are adapted to engage members 47, 48, connected to the sliprings. At low speeds, one or both weights hang down to interrupt the current. The control components except the photo-transistor 18 and light source 14 are accommodated within the motor housing. |
