Patent GB-844617-A (GB)
Title: Improvements in or relating to the positional control of movable devices of multiple-operation sewing or the like machines
Inventor: MYSKA GUENTER
IPC: D05B19/00
Filed: 1956-09-12
Abstract: 844,617. Photo-electric machine tool control. PFAFF A. G., G. M. Sept. 12, 1956, No. 27833/56. Class 40(3). [Also in Groups VII and XIX]  In a position control apparatus for advancing a workpiece through a plurality of successive predetermined distances, each of a series of incremental advance movements of the workpiece results in a photo-electrically produced pulse, and an electric pulse counter counts the pulses so produced and arrests movement of the workpiece when it reaches a predetermined limit number, the counter being preset by a programme control switch to a number below said limit number by an amount to cause the feed of the workpiece through the required distance, the programme control switch being automatically adjusted after the completion of the feed of the workpiece through a predetermined distance to preset the counter for controlling the next advance of the workpiece as required by the programme, or for arresting the driving means at the end of the last required advance. As described, the invention is applied to the control of a sewing machine having an electric motor 1 Fig. 1 which advances the work supporting carriage 17 with respect to the stitch forming tool 18. A photo-cell 20 and light source 21 are provided on opposite sides of a perforated light chopper disc 2 on a shaft 14 coupling the motor 1 to the work supporting carriage 17. The photo-cell is connected to the input of an electronic counter 3, which after a predetermined number of pulses from the photo-cell, closes a switch 41 which operates a control circuit to switch off the motor 1 and stop the advance of the workpiece and which through a delay circuit initiates operation of the stitching tool 18 to perform a stitching operation e.g. to form a button-hole. After the completion of the buttonhole the machine stops and the work clamp lever 35 is raised to close a contact 8 so that the control circuit is again operated, the motor 1 being thereby reconnected to further advance the workpiece until the motor 1 is again switched off by means of the electronic counter 3, so that a further button-hole can be formed. The cycle is repeated in accordance with the setting of a programme switch 4, by means of which the spacing of and the number of the button-holes is determined. The programme switch 4 comprises a plurality of banks of contacts and corresponding selector arms 45, 46, 47, 59 mounted upon a shaft 48. The contacts in the banks a, b, and c are connected to points in respective potentiometers, determined in accordance with the programme to be carried out, and the selector arms are connected to control electrodes of decade counting tubes 37, 38, 39, Fig. 2, such that for any given setting of the switch, the counters are preset to count a given number before operating the control circuit. The arms 45, 46, 47 and 59 are advanced clockwise by one contact upon energization of a magnet coil 52 each time the switch 41 of the counter 3 closes until upon the termination of the last sewing operation, the arm 59 bridges the contact 8, as shown when it reaches the contact 60, in order that the motor shall remain disconnected. An electronic counter 3 comprises three decade counting tubes 37, 38, 39, Fig. 2, which indicate digits from 0 to 9 by means of an electron beam controlled to assume ten stable positions indicated in co-operation with a digit scale upon a fluorescent screen of the tube. The flyback or resetting of the beam and the application of the counting pulses to the tubes 37, 38, 39 are effected by flip-flop connected double triodes 74, 73, 72 respectively and the counter is preceded by a pulse forming circuit comprising a flip-flop connected double triode 109 and an auxiliary double triode pulse former stage 113. The output stage consists of a flip-flop connected double triode 100 controlling the relay 101 which carries the contact 41 which serves to control the work feed and sewing operation. The control electrodes of the decade counting tubes 37, 38, 39 are connected to points on the voltage dividers 96, 95, 93 respectively through diodes 98, 97, 94 and selector arms 45, 46, 47 respectively of the programme switch 4. A double triode 99 serves to connect the left-hand ends of the voltage dividers 93, 95, 96 to the negative pole of the supply voltage for a short period to reset the counting tubes 37, 38, 39 to a number preselected by operation of the programme switch 4 prior to the starting of a new sewing cycle.