Patent GB-1271266-A (GB)
Title: A device for stopping a rotary body in a predetermined position
IPC: G01P3/487
Filed: 1969-06-03
Abstract: 1,271,266. Electromagnetic brakes; stopping at definite positions. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 3 June, 1969 [4 June, 1968; 12 May, 1969 (2)], No. 28096/69. Headings F2E and F2L. [Also in Divisions D1 and H2] A shaft position detecting device comprises two coils 11, 12 which co-operate with a flux generating means comprising a rotating magnet 22 to produce voltage pulses processed in a circuit, Fig. 2, to control the starting and stopping of the shaft. A second pair of positionally adjustable coils 13, 14, may be provided to allow the shaft to stop in one position before restarting to move to a second position. Clutch motor, high and low speed drive brake (Fig. 9).-A high speed motor M 1  and a low speed motor M 2  are provided, respectively connectible to a driving pulley shaft 49 by a clutch plate 53 slidable by a lever 56, pivoted at 57, into contact with either a lining 36 on the high speed motor flywheel 37 or a worm-wheel 45 driven by the motor M 2 . The lever 56 is biased in direction P by a spring 61 to contact a switch 68 and is provided with a lever cover 62 pivoted at 63 thereto and biased by spring 64 in direction Q. A plate 66 on the lever engages a microswitch 65 in the lever cover. The free end  of the lever cover is connected to a treadle (8, Fig. 1, not shown). The slow speed motor includes a brake comprising a brake disc 83 slidable on the motor shaft 76 and biased by a spring away from a brake lining 89 secured to a core 87 of an actuating coil 88. Operation, Fig. 2.-Main switch 94 energizes motor M 1 . Depression of treadle (8) pulls lever cover 62 in direction F 1  lever 56 engaging clutch plate 53 with flywheel 37 to drive the sewing machine at high speed. Microswitch 68 operates to energize relay coil L 1 , contacts S 18 , S 4  and S 6  closing to energize the low speed motor M 2 . Pulse voltages from coils 13 and 14 which pass to the bi-stable circuit T 3 , T 4  to interrupt the base current of transistor T 5 , but open contacts S 20  and S 16  prevent energization of relay coil L 2 . When the treadle is released the clutch connects shaft 49 to the slowly rotating wormwheel, microswitch 68 is released, current to coil L 1  now being controlled by transistor T 5  which is switched on and off by the bi-stable circuit due to the voltage pulses from the coil. Above a certain speed the interruption of the base current is short and L 1  is held on by capacitor C 1 ; below that speed the coil is deenergized, contacts S 18 , S 4  and S 6  open and S 1  closes, de-energizing motor M 2  and energizing brake coil 88 to stop the machine with needle lowered. Pivoting of the treadle in the opposite direction moves cover 62 and lever 56 in direction F 2  to release microswitch 65 and close contact S 20  to energize L 1  and consequently L 2 . The brake is released and M 2  energized, until a pulse from coil 13 interrupts the base current of transistor T 5  to de-energize L 1  and stop the machine with the needle raised. A further embodiment is described (Fig. 14, not shown) in which a further coil (L 3 ) is provided to actuate thread cutting mechanism not described. A third embodiment of the pulse generating device is described with reference to Figs. 15-18 wherein the magnet is stationary and a plate of non-uniform permeability is rotated and a modification is described for detecting more than two positions of the associated shaft.