Patent GB-571669-A (GB)
Title: Improvements in or relating to electric motor controllers
IPC: H02P7/298
Filed: 1943-10-14
Abstract: 571,669. Master control of D.C. motors. IGRANIC ELECTRIC CO., Ltd., and NEWMAN, J. M. Oct. 14, 1943, No. 16876. Convention date, Oct. 14, 1942. [Class 38 (iii)] [Also in Group XXII] A control system for a D.C. motor provides for low speed operation under no-load conditions and for automatic acceleration to a selected maximum speed when load is applied. The system is particularly applicable to the control uf a compound motor M driving the chain 4 of a metal draw bench, and permits the carriage 2 which carries work holder 3 to be coupled to the chain by hook 5 when the chain is moving at a low speed to avoid jerking the work out of the holder, the load then imposed on the motor causing automatic acceleration of the chain to a desired drawing speed, determined by the setting of a regulator 7 for the shunt field SHF of the motor. If the imposed load is insufficient to cause acceleration, movement of the carriage away from the die 1 closes a limit switch LS1 which action also initiates acceleration. With the motor stopped and the carriage uncoupled, closure of knife switches KS1, KS2 and the " safe on " switch energises relay coils FA1, 1CT1, 2CT1 and 3CR1. Pressing of the " start " button then energises relays 1FA1, 2FA1 and UV1, causing short circuiting of shunt regulator 7 and the energisation of relay M1, the contacts M2 of which then connect the armature A and series field SF across the mains L1, L2 in series with resistance R1 and winding LR1 of a load relay. The motor then starts with full shunt field and with resistance R1 in the armature circuit but with the armature diverter resistance R7 disconnected. At a predetermined low armature EMF a voltage relay VR1 connected across the armature picks up, closing an energising circuit for a relay AS1 which connects the diverter resistance across the armature and limits further increase of speed to about 50 per cent full speed. Actuation of relay AS1 also prepares, over the " slow" button, a circuit for relay 1CR1 which is completed through limit switch LS2 when the carriage is in the start position. If now the carriage is coupled to the chain the drop in speed, and consequentially counter EMF of the motor, causes contacts of VR1 to drop out, the latter deenergising AS1 to disconnect diverting resistance R7 and energise relay 1A1, the contacts of which connect resistance R2 in parallel with R1 in the armature circuit. If the load imposed on the carriage is so light that VR1. does not drop out, 1A1 is energised to insert R2 by closure of limit switch LS1 as the carriage moves away from the die, contact 1A3 of relay 1A1 also de-energising AS1 to disconnect R7. Following actuation of 1A1, relays 2A1-5A1 pick up sequentially under the control of timing relays 1CT1 and 2CT1, inserting further resistances R3-R5 in parallel with, and finally short circuiting, R1 and R2. Relay FA1, which is of the delayed type, drops out after pick up of 5A1 and sequentially opens its contacts FA2, FA3 thereby de-energising 2FA1 and 1FA1 and so inserting the regulator 7 in the shunt field circuit to permit acceleration to the desired maximum speed. When the drawing operation is completed, or for some other reason, e.g., breakage of work, the motor becomes unloaded, low speed connections are re-established by the dropping out of the load relay. The latter has a series winding LR1 energised bv the armature current and a shunt winding LR2 energised from L3, L4, through a bridge circuit comprising potentiometers 9, 10, the former of which is ganged to the shunt regulator 7. Winding LR2, assists LR1 at low speed settings of regulator 7 and opposes it when the regulator is set for high speed, the setting of potentiometer 10 determining the armature current strength at which the effects of the two windings balance to bring about the drop out of the load relay contacts. When this occurs, the holding circuit of 1CR1 is opened at LR3, this relay dropping out and energising 1FA1 over contacts 1CR2 and thereby shorting section r1 of the shunt field regulator and de-energising relay FD1 which drops out after time delay and closes the circuit of 2FA1 for short circuiting section r2 of the regulator. The holding circuits of 1A1-4A1 are also interrupted at 1CR3 when 1CR1 drops out, causing armature resistances R2-R5 to be cut out. 3CR1 picks up as a consequence of de-energisation of FD1, thereby, reinstating resistance R1 in the armature circuit and energising AS1 to connect the diverter R7 across the armature. Acceleration to high speed, independent of load conditions, may be obtained by pressing the " fast" button, which provides an independent circuit for energising 1CR1. The slow speed conditions may be restored by operating the " slow " button, which interrupts the holding circuit of 1CR1.