GB824779A - Improvements in or relating to electrical controllers - Google Patents

Abstract

824,779. Control of A.C. motors; controllers. IGRANIC ELECTRIC CO. Ltd. May 2, 1956 [May 31, 1955], No. 13534/56. Class 38 (3). [Also in Group XXXV] An electric motor 12 driving a press 10 is started by closing push-button 54 to energize relay 52 which has a self-maintaining contact 52b. Upon closure of switch 34, relay 18 is energized to connect the motor to the supplylines and cause a contactor 24 to pick-up whereby contactor 22 is energized. To effect energization of solenoid 16, which releases the brake and clutches the motor to the press, both " run " buttons 36, 37, must be depressed. Such operation de-energizes contactor 24 but coil 22d remains energized through contact 22a so that current flows through the coil 20f of contactor 20. Contacts 20a, 20b, then complete a circuit to solenoid 16. The opening of contact 20e interrupts the circuit of coil 52a but contacts 52b, 52c are not immediately opened due to the time-delay feature of the relay 52. After the punch and die have closed so that a hand may not be inserted between them, limit switch 30 closes to complete a maintaining circuit for coil 20f. The " run " buttons 36, 37, may now be released and contactor 24 re-energized. A short time later in the cycle of press operation, limit switch 28 opens to de-energize coil 22d so that contact 22c normally closes to re-establish the maintaining circuit for coil 52a before contacts 52b can open. Somewhat later the limit switch 28 re-closes, but coil 22d is not energized. Near the end of the cycle of press operation, limit switch 30 opens to de-energize contactor 20 and stop the press when the ram reaches the top of its stroke, the motor continuing to operate whilst the press is stopped. The operator cannot cause the press to run continually by keeping the " run " buttons depressed since the opening of limit switch 28 will prevent the establishment of a circuit for the coil 20f. If the relay 22 fails to pick-up or drop-out the press will be prevented from starting or will stop, even if the operator does not release the " run " buttons during a press stroke. The failure of contactor 24 to pick-up or drop-out will cause the press to stop at the end of its stroke or prevent the initiation of a new cycle of operation. If the " run " buttons are fastened down, a new cycle of press operation cannot be started. The failure of contactor 20 to pick-up prevents energization of the solenoid 16 and starting of the press. If contactor 20 fails to drop-out it is impossible to re-energize coil 20f even though the " run " buttons are operated properly. The contactor 18 provides novoltage protection.