GB884589A - Improvements in or relating to electric control systems for sewing machines - Google Patents

Abstract

884,589. Sewing-machines. PFAFF A.G., G. M. May 21, 1958 [May 22, 1957], No. 16270/58. Class 112 A sewing machine has a control member having two fingers extending one each side of the needle in the stitching direction, the engagement of either of the fingers by the upper thread upon its failure to interlock with the lower thread causing stoppage of the machine. The control lever 9 is pivoted at 10 to an extension bar 5 carried on the presser bar. The two fingers 13, 14 are provided on the lower arm of the lever, the upper arm carrying a contact 17 urged, by a spring 18, towards an insulated contact 8, carried on the bar 5, either finger, according to the direction of stitching, being deflected by the slanting portion of the upper thread when the latter fails to interlock with the lower thread, the contacts 8 and 17 then parting to stop the machine. During the operation of the thread cutting knife the blade 23 contacts the bent tip 15 of the finger 14 to open the contacts and prevent the operation of the machine drive. A control circuit for the sewing machine, Fig. 4, includes both the normally closed contacts 8, 17 of the invention and also the normally open contacts 90 of a device, such as that described in Specification 826,488, for monitoring the upper thread. The machine is started by the momentary operation of a foot switch 69 to energize the starting lever solenoid 74, the movement of the lever first opening the contacts of switch 56 to de-energize the relay A and then closing the contacts to energize the oppositely wound, balanced relay coils 54, 76, the latter through the closed contacts 8, 17. Failure of the lower thread causes the upper thread to actuate one of the fingers 13, 14 to open contacts 8, 17, when coil 76 is de-energized and the now unbalanced coil 54 operates the relay A to close the contacts 3a, a relay hold-on circuit being established through relay contact 1a and hence light the warning lamp 84 and actuate the machine stop motion device solenoid 77 through the switch contacts 71, 83 and the switch 80 respectively both switches being closed when the machine is running. An interrupter switch 81 actuable by the stop motion device is provided to permit the solenoid 77 to actuate a stop motion device requiring two successive operations to stop the machine. Alternatively failure of the upper thread when the machine is running closes the switch 90, the capacitor 92 then being charged through the synchronous contact 91 and energizing the relay coil 58 to operate the relay A. The machine is stopped as before by the relay contacts 3a completing the circuit of the stop device and the capacitor is discharged through the relay contacts 4a.