Patent GB-1105075-A (GB)
Title: Improvements in and relating to sewing machines
IPC: D05B69/22
Filed: 1966-02-24
Abstract: 1,105,075. Clutch and brake control. NECCHI S.p.A. 24 Feb., 1966 [5 March, 1965], No. 8070/66. Heading F2L. [Also in Division D1] A sewing machine comprises a driving motor, an electromagnetic clutch, an electromagnetic brake, a dynamo driven with the sewing machine and adapted to act on the clutch and brake for controlling the action thereof, and means for detecting the angular position of the driven shaft of the sewing machine and cooperating with the clutch and brake, when the machine reaches a predetermined reduced speed, for stopping the machine with its needle in a predetermined position, the reduction from normal to reduced speed being obtained by the use of a Zener diode acting as an automatic switch in the energizing circuits of the clutch and brake. The sewing machine is driven by a motor 11. The speed-control circuits are connected across the output lines 15, 16 of a bridge rectifier 14. Switch discs 21, 22, 23 rotate with the driving shaft. Disc 21 has a conducting sector 24 and co-operates with brushes 25, 26. Disc 22 is wholly conductive and co-operates with a brush 27. Disc 23 has a conducting sector 28 and co-operates with brushes 29, 30. Brushes 25, 26 are connected to the respective contacts of a selector switch 31, and the latter is connected via a normally closed switch 20 to line 15. Brushes 29, 30 are connected via a relay 19 to line 16. A contact 19<SP>1</SP> of relay 19 is inserted between brushes 27 and 30. The brake coil 33, a transistor 34 and a normally-closed contact 35<SP>1</SP> of a push-button switch 35 are connected in series between lines 15, 16. A contact l9<SP>11</SP> of relay 19, a Zener diode 41, a diode 40, a normally-closed contact 35<SP>11</SP> of switch 35, a tachymetric dynamo 37 rotating with the driven shaft, and a normally-closed contact 38<SP>1</SP> of a push-button switch 38 are connected in series between lines 15, 16. The base of transistor 34 is connected between contact 19<SP>11</SP> and Zener diode 41. Contact 35<SP>11</SP> is shunted by lines 43, 44 connected via variable resistances 45, 46 to the base of a transistor 47 which is in turn connected to the base of a transistor 48. The latter is connected in series with the clutch coil 51 and a contact 19<SP>111</SP> of relay 19 between lines 15, 16. Transistor 48 and contact 19<SP>111</SP> are shunted by a normally open contact 38<SP>111</SP> of switch 38. The arrangement is such that when the machine is stationary, relay 19 is energized via sectors 24 and 28, or via sector 24, disc 22 and contact 19<SP>1</SP>-sector 24 being wider than sector 28-and the closed contact of the selector switch 31. Contact 19<SP>11</SP> is closed to energize brake coil 33, and contact 19<SP>111</SP> is open to de-energize clutch coil 51. The machine is controlled by a treadle having three positions of adjustment. In the first position, switch 20 is opened to de-energize relay 19. Contact 19<SP>11</SP> then opens to de-energize brake coil 33 and contact 19<SP>111</SP> closes to energize close coil 51. The machine then runs at a speed of 150 r.p.m. controlled by the transistors 34, 47, 48. In the second treadle position, switch 35 is actuated to open contact 351 for isolating brake coil 33, and to open contact 35<SP>11</SP>, whereby the machine runs at an intermediate speed controlled by resistance 45. In the third treadle position, switch 38 is actuated for opening contact 38<SP>1</SP> to isolate dynamo 37, and to close contact 38<SP>11</SP> for connecting clutch coil 51 directly across lines 15, 16. The machine then runs at full speed. When the treadle is released, switches 20, 35 and 38 return to their initial positions. The voltage generated by dynamo 37 is sufficiently high to render Zener diode 41 conductive in the reverse direction, whereby brake coil 33 is energized, till the dynamo speed falls to the pre-set value of 150 r.p.m., when current flows through diode 41 ceases and the brake is released. The speed of 150 r.p.m. is sufficiently low to enable relay 19 to be energized, via the selected closed contact of switch 31, for stopping the machine with the needle either lowered or raised.