Patent GB-517996-A (GB)
Title: Improvements relating to stentering machines
Filed: 1938-08-19
Abstract: 517,996. Control of two motors. MATHER & PLATT, Ltd., BARCLAY, S. F., and WHITELOCK, J. H. Aug. 19, 1938, No. 24425. [Class 38 (iii)] [Also in Group VIII] A stentering machine in which the two stenter chains are driven by individual motors of the induction type with electrically interconnected wound rotors and with rotor resistance to preserve synchronism is provided with automatic means to (1) vary the motor resistance in one or more stages inversely to the load, whereby a higher motor speed is maintained under heavy load (2) at starting-up, fully to establish the stator current prior to completion of the rotor circuit and (3) at stopping, to disconnect the rotor leads to the resistance while leaving the rotor slip rings interconnected and the stator circuit still established. The two motors a, b are mounted. one on each stenter rail, and are interconnected electrically and with a common connection to the resistance c when the switch d is closed. The sections c' of these resistances can be reduced in value for threading up the stenter, the sections c<2> are always in circuit and the sections c' can be cut out of circuit to prevent undue fall of motor speed due to increasing load. The stators are fed from the three-phase alternating current mains e when the switch f is closed. There is a current relay coil g inserted in one lead to the stators. When the load increases above a certain value, the rise in current closes a relay switch g<1>, thereby connecting coil h across the mains and causing the closure of a triple switch i associated therewith. This has the effect of short circuiting each section c<3> and preventing undue fall of motor speed as load increases. If desired the resistance in the rotor circuit may be reducd in steps by provision of several current relays set to operate at different current values and controlling a series of switches such as i. The motors are started and stopped by pushing buttons j, k respectively. Depressing button j closes switches m, n. Closure of switch m places coil p across the mains, causing the stator current switch f and an associated switch blade f<1> to close. One contact of the switch f<1> is connected to one end of coil p and the other contact is connected to one contact of a switch blade d<1> associated with the rotor switch d. Closure of switch n places a coil q across the mains via the switch o associated with push button k. One end of the coil q is connected to one contact of a switch blade d<2> associated with switch d and the other contact is connected to a point between switches n, o. Energizing the coil q causes closure of the switches d, d<1>, d<2>, but as the coil q is connected to the mains at the motor side of switch f current only passes thereto after this switch has closed. Owing to self inductance of the coil q, there is a slight time lag which prevents the switch d from closing until the stator current is fully established and thus the two rotors start in synchronism. When the button k is operated to stop the stentering machine the stator current is fully maintained until the motors have come to rest, so that the rotors slow down and stop in synchronism. This maintenance of stator current until the rotors stop is effected by the provision of a time delay device, of construction known per se, which prevents the switch d<1> from opening until a predetermined time after switches d, d<2>.