GB799849A - Improvements in or relating to control arrangements for electric motors - Google Patents

Abstract

799,849. Control of D.C. motors; controllers. SQUARE D, CO. June 13, 1956 [June 24, 1955], No. 18220/56. Class 38 (3). Relates to a control system for rolling mills in which the next subsequent roll-spacing is preselected while the metal is between the rolls so that, immediately after the metal leaves the rolls, operation of a push-button causes the screw-down motor to rotate until the preselected roll-spacing is provided for the next successive pass. As shown, a screw-down motor 10, having armature 10a and series field winding 10f, is geared to mechanism associated with rolls 12. The motor 10 is linked through selsyn machines 14, 19, with the main driving gear 25 of a differential 26 which has a shaft 28 coupled through machines 30, 31, to an indicator 34. A coarse ponter 40 is associated with a graduated dial 41, and a fine pointer 38 co-operates with dial 39. The shaft 28 is also coupled to a set-up motor 46 having armature 46a and shunt field winding 46f. Another output shaft 29 of the differential is coupled to a face-plate controller 48 having arm 48a for fine control, and to a similar controller 52 having arm 52a for coarse control. The motor 46 is started, in the down direction for example, by means of a master switch 81, and drives the shaft 28 until the pointers 38, 40 indicate the desired spacing, the pointers being locked in the selected position during subsequent operations of the motor 10. The master switch 81 is then returned to the " off " position and the set-up motor stops. This operation of the motor 46 has driven the arms 48a, 52a from their neutral positions in a clockwise direction, whereby a relay 86 is energized to by-pass the controller 48. To operate the screw-down motor, a push-button 88 is closed to operate relays 89, 84, and " down contactor 62. At the same time, contactor 73 is closed, and the motor 10 runs in the down direction. The sequential closure of relays 66, 67, 68 removes resistor 65 and allows the screw-down motor to reach maximum speed. Operation of the motor 10 moves the rolls 12 toward each other and causes shaft 29 to drive the arm 52a towards its neitral position. In so moving, the arm effects operation of relays 91 and 85, whereby relay 68 is opened and contactor 70 is closed to complete an armature shunt circuit for the motor 10 so as to reduce its speed. A knife switch 92 permits the starting-point for slow-down of the motor to be adjusted. As the arm 52a further approaches its neutral position, the relay 86 is de-energized and the controller 48 is rendered effective to maintain the contactor 62 energized. Just before the arm 48a reaches its neutral position, contactor 72 is energized to reduce the value of shunt resistor 69; and, a short time later, contactor 71 further reduces the effective value of the resistor. When the arm 48a reaches its neutral position, the contactor 62 is opened to de-energize the motor 10 which is braked to a standstill. If it is now desired to separate the rolls, the master switch 81 is operated to cause the set-up motor 46 to run in the " up " direction. This moves the pointers 38, 40 on the indicator 34 to show the desired wider roll spacing and at the same time moves the arms 48a, 52a a comparable distance counterclockwise. When the push-button 88 is now closed, circuits similar to those described are set up. The screw-down motor 10 may be operated non-automatically by means of a multi-position, reversing, master controller 82. This controller is kept in its " off " position during automatic operation.