Patent GB-707219-A (GB)
Title: Improvements in or relating to electrical apparatus
IPC: D05B65/00
Filed: 1949-10-28
Abstract: 707,219. Photo-electric control systems. SARGROVE ELECTRONICS Ltd., SARGROVE, J. A., and BALL, D. A. Oct. 17, 1950 [Oct. 28, 1949], No. 27704/49. Class 40 (3). [Also in Group VII] Photo-cell apparatus operating in conjunction with a counter is employed in a machine applying a continuous thread, tape or the like to a length of material to actuate a guillotine to sever the thread &c., a predetermined number of stitching actions behind the trailing edge of the material. The Figure shows apparatus for use with a "flat-lock" sewing machine producing a flat plaited thread chain in the working field, a guillotine 16 being provided near the outlet of this field to sever the chain. A pair of photocells 10 are mounted adjacent each other in the bottom arm of the machine and co-operates with a light projector 11 mounted close to the top working foot, the arrangement being such that the material obscures both cells whereas the chain due to its limited width may obscure only one. The cells energize a relay A through D.C. amplifier V1-V3, the voltage from the cells being such that the obscuring of a single cell has no effect. A safety switch 21 operates from the machine clutch and closes when the machine is operating. Contacts 18 are operated by cam 19 and complete the circuit for a high speed relay D at every stitch. With the machine stationary and no material in position, cells 10 are exposed and operate relay A. Contact a1 disconnects earth from the grid of normally cutoff stage V4 and allows the grid to travel positive as condenser C3 charges through very high resistance R5. When V4 conducts relay B operates and contacts bland b2 in changing over cause a pulse of current to pass through relay C from condenser C2. Contacts C1 are in the circuit of electromagnet 14 controlling the guillotine but fail to complete the circuit since the safety switch 21 is open with the machine stationary. If now the machine is started and material placed in position, photo-cells 10 remain exposed until the leading edge emerges from the working field whereupon relay A is released and with it relay B. The change over of contacts b1 and b2 pulses relay C which now energizes the guillotine electromagnet 14 and causes the thread chain preceding the leading edge to be severed. As the material proceeds through the machine photocells 10 remain obscured until the trailing edge emerges from the working field. At this point relay A is re-energized and contacts a1 remove the earth from V4 grid. Contact a2 connects with the circuit of a condenser C4 the charge on which is transferred to condenser C3 once per stitch through contact d1 of relay D. Condenser C4 has one tenth of the capacity of C3 so that C3 becomes fully charged after ten stiches. V4 thereupon conducts to operate relay B and through relay C causes the guillotine to sever the chain. The number of stitches may be varied by altering the ratio of C3 and C4, and by adjustment of potentiometer R2. Switch 28 permits the automatic operation to be stopped. Hand impulsing switch 25 operates the guillotine with the machine stationary.