GB595897A - Improvements in feeding arrangements for machine tools - Google Patents

Abstract

595,897. Control of motors. CROOKS, E., and d METROPOLITAN - VICKERS ELECTRICAL CO., Ltd., July 21, 1945, No. 18735. [Class 38(iii)] Travelling to predetermined limits.-An electric motor for effecting tool-feed motion in a machine tool is adapted to be operated or intermittently operated for periods which are determined by a controlled arcdischarge device which is normally non- conductive but is rendered conductive for a predetermined period following closure of a switch in response to the attainment of a predetermined relation between the positions of the tool and the work during a cutting or return-stroke. A three-phase squirrel cage induction motor M is connected to an alternating current supply through contacts f of a relay F. The motor is braked by the application of a direct current to the stator windings from a source S2 through contacts of a relay B which is controlled through a contact t of a timedelay relay T. During a normal working stroke a condenser C2 is charged from a transformer V through a rectifier Rff, and a grid-controlled arc-discharge valve Th is negatively biassed to maintain the starting relay F and a holding coil of a relay IR deenergised. When a switch FS is closed at one point during a cycle of operation of the machine, a pick-up coil IRP of the relay IR is energised to open contacts ir and ir1 and close contact ir2. The condenser C2 is discharged through resistors R4, R5, R6, and a portion of a potentiometer P, and the valve Th is positively biassed to energise the coils of relays F and IR. The motor is connected to the alternating current supply and contacts f3 of the relay F close to enargise the relay T. At the end of a predetermined period the valve Th is cut off due to discharge of the condenser C2 and the motor is disconnected from the alternating current supply, the contacts f2 being closed to energise the coil B which effects dynamic braking until the contact t opens. The control circuit is restored to its normal condition and the condenser C2 is recharged in preparation for another tool-feed movement. A switch RF enables the tool-feed movement to be repeated independently of the operation of the switch FS. A pushbutton Pb may be operated to by-pass the valve Th through a rectifier Rf for continuous operation of the tool-feed motor.