Patent GB-994820-A (GB)
Title: Improvements in sewing machines
IPC: D05B69/22
Filed: 1963-04-18
Abstract: 994,820. Sewing-machines. GEORGII KOBOLD ELEKTRO-MOTOREN-APPARATEBAU G.m.b.H. April 18, 1963 [April 28, 1962], No. 15279/63. Heading D1G. [Also in Division H2] A sewing machine is driven by a motor having at least two separate windings, one having more poles than the other, the windings being separately energized to drive the motor at a low, or high speed respectively, a position indicator switch driven by the sewing machine being provided to allow the machine to be stopped by the motor brake with the needle in a particular position. The position indicator (see Fig. 5) comprises a bar magnet 28 which is rotated, by the needle driving shaft of the machine, adjacent two coils S 1 ,S 2 (see Fig. 6) either of which may be selectively energized. Two contact tongues are disposed in a tube E filled with an inert gas and are pressed together by the magnetic field of the energized coil and the permanent magnet when the latter is in a position in which it increases the field of the respective coil. The contacts are shown at e in Fig. 6. The driving motor 1 has a brake comprising a member 11 carrying a permanent magnet which presses the member 11 against a brake lining 8 except when the magnet's field is opposed by the energization of a coil L. The motor is cooled by a fan 19 driven by a continuously rotating motor 18. The motor is pivoted to the sewing machine table, to enable the motor to drive the machine by way of a Vee belt and stepped pulley. Operation. Contact t 1 of a pull switch are closed to energize relay D, which closes contact d and energizes coil L to release the motor brake, energize winding H 1 of relay H to close hold on contact h, throw over contact h 2  to de-energize coils 5 1 ,5 2 and close contact h 3 ,and energize relay A to close contacts a 1 ,a 2  to connect the three phase supply at R, S, T to the stator winding Ua, Va, Wa having the higher number of poles, the motor then running at its lower speed. Subsequent closing of contacts t 2 of the pull switch result in the energization of the second winding H 2 of relay H, which reinforces the effect of coil H 1 ,and of relay B whose contacts b 1 ,b 2 change over to switch the three phase supply to the winding U b , V b , W b having a low number of poles and the motor begins to run at maximum speed. If switch t 2 is then opened relay B is de-energized and the motor runs at low speed, condenser 36 discharging itself through coil H 2 .If thereafter t 1 is opened the short circuit of coils 5 1 ,5 2 is removed so that at the selected position of the needle shaft contact e will close to short circuit coil H 1 ,opening contacts h 1 ,h 2 h 3 .The subsequent opening of contacts e will de-energize relay A to switch off the motor and de-energize coil D to open contact d and apply the brake. If contacts t 2 and t 1 are switched off in immediate succession the relay H will not be immediately de-energized by the closing of contact e since coil  H 2 will be supplied by condenser 37 until the motor has decelerated. When the condenser has discharged the motor will be brought to rest as described above.