Patent GB-990931-A (GB)
Title: Improvements in or relating to electromagnetic clutch and brake control arrangements
IPC: D05B69/22
Filed: 1962-01-30
Abstract: 990, 931. Sewing machines. NECCHI S.p.A. Jan. 30, 1962 [Feb. 10, 1961], No. 3429/62. Heading D1G. [Also in Divisions F2 and G3] A drive for a machine such as a buttonhole sewing machine is controlled by an electromagnetic clutch and an electromagnetic brake, the energization current of the clutch being reduced to allow slipping for a slow speed drive, and a speed proportional voltage applied to the clutch or brake so varying as to maintain substantially constant the reduced speed, a machine-driven switch and a time-delay relay co-operating to apply the brake fully and bring the machine to rest in a predetermined position. As shown, an electromagnetic clutch B, Fig. 1, between an A.C. motor and a buttonhole sewing machine C, is fully engaged when current from a rectifier 12 flows through a circuit 5, S2, N5, L5, 5<SP>1</SP>, but is partly engaged to allow slipping when a resistor 54 is introduced into the circuit. At the same time, an output driven generator T supplies a speed proportional voltage through two potentiometers 75, 87 to the emitter of a transistor U and so varies the current supplied therethrough to brake D that the output shaft is driven at a substantially constant speed. To start an operating cycle of the machine, a pedal G is actuated to close contacts GH and open contacts GE. Closing the contacts GH connects A.C. lines 10 through a solenoid H to operate relay switches HO, H2, H3, H4, H7. Opening the contacts GE opens a circuit from the A. C. lines through a transformer 18, a rectifier 19 and an electromagnet E, immobilizing the upper thread cutting knife of the sewing machine and lowering the presser foot. Closing the contacts H2 energizes an electromagnet F to retract the lower threadcutting knife, and closing the contacts 113 energizes a relay W through the rectifier 12. The relay N now closes contacts N1, N3, the former energizing a relay I to open and close contacts 11,12 in circuits energizing the electromagnets E, F, to maintain these in their set condition. Closure of the contacts H4 energizes a relay L to close contacts L1, L4, L5, the first closing a holding circuit for the relay I, and closing of the contacts L5 energizing the clutch B through a switch N5, now conditioned to engage a contact a, and through a normally closed switch S2. The clutch B is accordingly fully engaged, thus causing the motor A to drive the sewing machine C. A cam K driven by the machine now closes a switch X so that the pedal G can be released, de-energizing the solenoid H and closing the contacts GE. The electromagnet F and the relays N, L remain energized. One completion of an operating cycle, the cam K opens the switch X to de-energize the relay N. The switch N5 then engages a contact b and introduces a resistor 54 into the clutch-engaging circuit, causing the clutch B to slip. At the same time, contacts N7 are closed to give partial energization of the brake D through the transistor U, so that the buttonhole sewing machine rotates at a reduced speed. The bias applied to the transistor U from the output shaft driven generator T and the potentiometers 75, 87 is fed through a resistor 78, the cam K having opened a switch Z, and so varies that the reduced speed of the driven shaft remains constant. In a modification, Fig. 2, the energization of the brake D is constant but variable slip of the clutch B to give a constant speed of the machine is obtained by connecting the emitter of the transistor U across a resistor 99 fed from the output shaft generator T and the potentiometers 75, 87. The resistor 99 is also fed through a transformer 100 and a rectifier 98, the arrangement being such that increasing speed of the output shaft and the generator T increases the bias on the transistor U, so that the clutch-energizing current is reduced and the clutch B slips. Correspondingly decreasing speed of the output shaft &c. causes the clutch B to be more firmly engaged. Accordingly output shaft speed remains constant. In either form, the cam K next mechanically actuates a knife to cut the buttonhole, and then closes the contacts Z to short the resistor 78, increasing the bias of the transistor U. In the Fig. 1 form, the brake D is more firmly engaged, while in Fig. 2 the clutch is less firmly engaged. In both cases, the speed of the output shaft is further reduced. The cam K now closes a switch Y to energize a time-delay relay M, through a sector-switch W rotating with the output shaft of the clutch. The relay M is energized a predetermined time after the circuit has been made through the sector-switch W, when the speed of the buttonhole sewing machine has been further reduced to its second value. The relay M actuates switches MI, M6, MD, Fig. 1, and also in Fig. 2 a switch M5. The switch M6 makes a holding circuit for the relay M, and the switch MD makes a circuit for full application of the brake D, this circuit also including a part of the sector switch W which completes the circuit at a particular point of the operating cycle. Thus the machine is always brought to rest in a predetermined position. The contacts M5 are opened by the relay M, and de-energize the relay I, thus energizing the electromagnet E to raise the presser foot of the buttonhole machine and to actuate the upper thread-cutting knife, and simultaneously de-energizing the electromagnet F to actuate the lower thread-cutting knife. In Fig. 2, opening the switch M5 de-energizes the clutch B. In either case, the machine is now ready to perform a new operating cycle, actuation of the pedal by de-energizing the relay M by energizing the relay H. To stop the machine at any moment, a pressbutton Q is actuated to energize a relay O, actuating switches including a switch 06 which energizes the relay M through the sector switch W, if the output shaft of the machine is correctly positioned, independently of the switch Y controlled by the cam K. A switch 03 de-energizes the relay N, so that the switch N5 connects the resistor 54 into the clutch circuit to allow slipping, and a switch 07 shorts the resistor 78 in the transistor bias circuit, further slowing the speed of the machine to permit energization of the relay M, following which the brake D is applied to stop the buttonhole sewing machine in its predetermined position. During this stopping, the electromagnet F is maintained energized to prevent the cutting of the lower thread, the electromagnet E is deenergized to prevent the lifting of the presser foot and operation of the upper thread cutting knife, and an electromagnet V is energized to prevent the buttonhole cutting knife from operating. To raise the presser foot, a press-button R is operated to energize a relay P, energizing the electromagnet E. To re-start after stopping, the pedal G is operated in the normal way. To operate the machine at all times at reduced speed, a switch S is actuated to open contacts S2 and close contacts S1, S3, introducing the resistor 54 into the clutch control circuit and engaging the brake D. To prevent actuation of the buttonhole cutting knife, a switch 5 is actuated to close contacts 103 and energize the electromagnet V.