Patent GB-824939-A (GB)
Title: Improvements relating to the control of electrically driven sewing machines
IPC: B23B3/10
Filed: 1956-03-05
Abstract: 824,939. Sewing machines. SCHWAB, B. March 5, 1956 [March 5, 1955], No. 6929/56. Class 112 [Also in Group XXXVII] A sewing machine shaft w is driven from a shaft y which is adapted to be coupled for high-speed operation to a main motor M through a clutch Z having an energizing winding Zw. Low-speed operation of the machine is obtained by means of an auxiliary motor HM which is coupled to the shaft y through a friction or dog clutch z. Relays and associated components controlling the main and auxiliary drives are arranged in a housing GH, these relays also controlling an electro-magnet FM for lifting the foot which presses the material to be sewn on to the table, and an electro-magnet PU for actuating a feeddevice Tr so that the material can be fed to the machine in reverse directions. A pedal-operated switch FS is held closed throughout the period of operation of the machine, and a programme disc Sch is driven from the shaft w through reduction gearing. The disc Sch is graduated, and programme-setting sliders RI...RIV are set in appropriate positions with the aid of these graduations. As the disc rotates, the sliders successively actuate contacts a, b and c. Before carrying out a programme of operations, the disc is released and turned back to the zero position in which contact nk is closed to energize a pilot light KL. Closure of the pedal switch engages the main clutch and the machine runs at high speed until the inclined edge a 0  of the slider RI closes contact a. The main drive is thereby disengaged and the auxiliary drive becomes effective, Fig. 2 (not shown), so that the machine sews at low speed as far as the point b 0 . The contacts b are then closed for immediate disconnection of the auxiliary motor drive. In addition, the magnets FM and PU are energized to lift the foot and to initiate backward feed of the material, after which the magnet FM is de-energized so that the work is again pressed on to the table. The main-motor clutch Z is then re-engaged so that the machine sews at high speed until the edge a 1  of the slider RII re-closes the contact a whereby the change to the auxiliary drive is initiated and further operations are thereafter repeated in the manner described. The slider RIII effects similar control, but the slider RIV projects sufficiently to close contact c and this action prepares for the stopping of the machine at the point b 3 . Instead of employing a high-speed and low-speed motor, use may be made of a two-speed polechanging motor. In another arrangement, Fig. 3 (not shown), the machine drives a slip-ring with an insert of insulating material which co-operates with a fixed brush for providing a number of currentpulses corresponding to the number of stitches performed by the machine. These pulses effect the step-by-step advance of an electromagnetically operated switch. When the position of this switch corresponds to that of a multi-position switch, which may be set manually at a point relating to the numbers of stitches that the machine is desired to perform, then the machine is stopped. The performance of a pre-set programme can be interrupted at any time and, up re-starting, continued from the point at which it was interrupted.