Patent GB-827552-A (GB)
Title: Improvements in or relating to control systems for group stitch sewing machines
IPC: D05B69/20
Filed: 1957-02-26
Abstract: 827,552. Sewing machines. PFAFF A.G., G. M. Feb. 26, 1957 [Aug. 1, 1956], No. 6361/57. Class 112 A sewing machine having a starting member such as a lever arranged on operation to initiate a group of stitches, said group being repeated automatically during operation of the starting member, and restoration of the latter to its non-operated position causing the machine to stop at the end of the group then in progress, is provided with a control system comprising electrically actuable means for operating the starting member against a restoring force, and electrically operated timing control means for energizing the electrically actuable means to maintain the starting member operated during a period of presettable duration, whereby at the end of that period said force restores the starting member to its non-operated-position. In Fig. 2 energization of a control relay 6 closes a contact 5 to energize a solenoid 4 from a rectifier 7, whereby a pull rod 3<SP>1</SP> operates the spring-biased starting lever of the sewing machine. Double pole selector switches 18, 29, 30 are so arranged that only one can .remain closed at a given time. Contacts 34, 35, 36 of said switches are connected in series with respective lamps 31, 32, 33 and the power supply terminals 20, 21 of a rectified 12 in order to indicate which one of the switches is closed. A foot-operated switch 14 has a normally closed contact 22 connected by a lead to contact 17 of switch 18 and to a terminal 19 of rectifier 12. A normally open contact 15 of switch 14 is connected by a lead 13 to relay 6 and also to contacts 27, 28 of switches 29 and 30. Contacts 15 22 are also connected by a lead 16 to contact 17 of switches 18 and also to a capacitor 24. A terminal 11 of rectifier 12 is connected by a lead 10 to relay 6, also to a variable resistor 25 connected to contact 27 of switch 29, and to a variable resistor 26 connected to contact 28 of switch 30. With switch 18 closed, as shown, if switch 14 is depressed to close contact 15, relay 6 will remain energized to energize solenoid 4 as long as switch 14 is depressed. If switch 29 is closed and switch 14 is depressed, the charged capacitor 24 is shunted, together with resistor 25, across relay 6. The latter will thus be energized for a time period depending on the value of the resistor 25, and solenoid 4 will remain energized for the duration of this period. Closing of switch 30 and depression of switch 14 will similarly shunt the charged capacitor 24 and the resistor 26 across relay 6 to cause operation of the machine for a period of time determined by the value of resitor 26. In a modification, Fig. 3, the solenoid 4 is connected in series with a switch having a fixed contact 40 and a movable bimetallic contact 41 normally spring-biased to the closed position, and is also in series with a normally open contact 42 of a foot switch 14. The heating coil 44 of the bi-metallic contact is connected in series with a normally open contact 43 of the foot switch 14. The coil 44 may be connected by means of a switch 50, having respective arms 46 and 47, with any one of a series of resistors 45a, to 45e, the corresponding one of a series of indicator lamps 48a to 48e also being simultaneously connected in circuit. On closure of switch 14 therefore, the machine continues to operate until contact 41 is sufficiently heated to move away from contact 40, the duration of operating time thus depending on the value of the resistor in series therewith. Resistor 45e is preferably of zero resistance to short-circuit the coil 44 to produce a minimum period of operation.