GB956720A - - Google Patents

Abstract

956,720. Controlling clutch-brake combinations. QUICK-ELEKTROMOTORENWERK G.m.b.H. Oct. 21, 1960 [Oct. 31, 1959], No. 36095/60. Heading F2L. [Also in Division D1] A friction clutch mechanism drives a sewing-machine (see Division D1) selectively at high or low speed by the axial movement of a disc 21 under the control of a pedal 22 to engage either a highspeed clutch disc 10 or a low-speed clutch disc 16. The low-speed disc 16 is selectively driven through, or braked by, an electromagnetically-operated clutch having a control circuit which ensures that the sewing machine is stopped only when the arm shaft of the machine is in a particular angular position. The electromagnetic clutch comprises a shaft 13 drivably connected to a disc 39 journalled in a plunger 38, the disc and plunger being slidable axially within a magnet core 45. When a coil 47 is energized, a plunger 38 is moved against a spring 42 to engage the disc 39 with a driving disc 49 rotated by a slow-speed motor 50. When the coil is de-energized, the plunger 38 is returned by the spring 42, the disc 39 engaging a stationary part 41 to stop the shaft and the sewing machine. The control circuit includes an interrupted slip ring 5, 6, 7, driven directly by the arm shaft 3 of the sewing-machine, to ensure that de-energization of the coil and braking of the drive occurs only at the desired position of the arm shaft. Depression of the pedal 22 to start the machine by engaging the clutch discs 16, 21 also closes a switch 23 to energize a relay 24, of which the contact 26 is effective to control the electromagnetic clutch. On release of the pedal 22 to stop the machine, the low-speed drive 21, 16 is first engaged and the electromagnetic clutch drives through the worm &c. 14 to the arm shaft 3. On the next revolution of the latter, an insulating segment on one of the slip rings 5, 6, 7 breaks the circuit to the electromagnetic clutch 39 &c. and brings the machine to rest. In one modification, Fig. 1 (not shown), a tachometer generator on the driven shaft 20 delays braking of the machine until the speed of the parts has sufficiently decreased, and in another modification, Fig. 3 (also not shown), the clutch control circuit including a thyratron. Specification 750,686 is referred to.