Patent GB-1274954-A (GB)
Title: An electrical drive
IPC: H02P29/00
Filed: 1969-08-13
Abstract: 1,274,954. Sewing machines; driving. QUICK-ROTAN BECKER & NOTZ K.G. 13 Aug., 1969 [23 Aug., 1968], No. 40543/69. Heading D1G. [Also in Division G3] The speed of a shaft is regulated by controlling the alternate energisation of an electromagnetic clutch and brake in response to a shaft speed signal when a bistable circuit connected to the regulator is in one condition, and the shaft is braked to a stop when the bistable circuit is in its other condition which is effected when the shaft speed is at a low "stopping" speed and when a pulse is produced which corresponds to a desired angular position of the shaft. The invention may be used in a machine tool coil winding machine or the like but is described in relation to an industrial sewing machine which is initially stopped with the needle down. For detecting the speed the shaft drives a magnet disc 14 associated with a pick-up coil 12 connected through a speed setting, pedal operated, variable coupling transformer 11 and a gate circuit 9 to the speed regulator 5. The gate 9 also rectifies the a.c. speed signal and applies a d.c. bias so that the input to 5 comprises a d.c., signal with an a.c. component, the magnitude of the peaks of which represent speed and control the conduction of transistors in the brake 1 and clutch 2 circuits alternately. (see Specification 1,263,540, Division G3). This signal is limited by a diode. A bistable circuit FF1 is switched to a condition in which the regulator 5 can operate by a switch S1 coupled to the pedal. To stop the shaft, the pedal is returned to open S1 and to adjust the speed signal to a valve corresponding to a "stopping" speed. The bistable FF1 and a second one FF2 are arranged so that the stopping speed is maintained until a pulse is applied to FF1 from an amplifier 19 which differentiates a pulse from a Hall device 18 when it is activated by a magnet 24 whose position on a disc 20 corresponds to "needle down". FF1 then causes the regulator 5 to block the speed signal and fully apply the brake for a time, determined by the charging rate of an R.C. circuit, sufficient for the shaft to come to rest. Backward movement of the pedal operates a switch S2 which, provided a gate G1 detects that the circuits correspond to the shaft having stopped in the needle down position, operates a thread drawing magnet 45 for a time determined by a monostable multivibrator M1. A second monostable circuit M3 prevents the shaft being started, even if S1 is closed. After a delay determined by an R.C. circuit 54 a third bistable circuit FF3 is changed over to change the polarity of the Hall device 21, and also to close gate 9 and open a gate 10 in a second pick up coil 13. The effect of this is for the shaft to be rotated at a speed determined by 13 until a second magnet 25, of opposite polarity to 24, produces a stopping pulse in the needle up position. When this condition is detected by a gate G2 another monostable circuit M2 energises a thread cutting magnet 46. A starting delay circuit 62 prevents spurise operation when the supply is switched on, and there is another safety circuit effective when the supply is switched off. A switch K provides manual means for changing from the needle down to the needle up position. All the circuits are described in detail (Figs. 2 .. 5, not shown).