Patent GB-864955-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: H02P5/69
Filed: 1958-06-12
Abstract: 864,955. Control of several D.C. motors. IGRANIC ELECTRIC CO. Ltd. June 12, 1958 [June 14, 1957], No. 18799/58. Class 38 (3). [Also in Group XXXV] A printing-press has a plurality of motor-sections 4-10 adapted to be clutched to a common shaft 12 with means for declutching each section and operating it independently of the rest of the drive. The first section comprises a shuntwound motor M which is supplied with rectified current through power windings P of a magnetic amplifier MA1, the arrangement being such that the relative portions of the load to be shared by each motor is preselected, and, when one motor is disconnected from the drive for independent operation, the load is reapportioned among the remaining motors in accordance with the preselection. A transformer 18 supplies the magnetic amplifier MA1, a load-balancing amplifier MA2, and corresponding amplifiers in sections 6-10, as well as a further amplifier MA3 for comparing the current of each motor with the total load current. Amplifier MA1 is biased towards its on-condition by power windings P which are opposed by bias winding B. At the same time, speed reference windings SR are opposed by signal windings S which are fed from tachometer generator TG whereby the speed of the motor is kept at a value corresponding to the setting of rheostat 42. A change of load current of motor M in relation to the other drive motors is applied directly to the signal windings S of the amplifier MA2, and indirectly through amplifier MA3 to the reference windings R. The energization of the windings S predominates, so that the current in load-balancing windings LB of amplifier MA1 is modified to return the motor load current to the value determined by the setting of rheostat 46. This rheostat is adjusted to provide zero current-flow in the windings LB when the motor M is carrying the desired portion of the total load. When the load current of motor M changes to alter the energization of the reference windings R of amplifier MA2, a like change occurs in the load-balancing windings of sections 6-10. Thus, an increase in the load current of motor M, whilst decreasing the output of amplifier MA2, increases the outputs of the other load-balancing amplifiers provided that the energization of the signal windings of the latter remains constant. Thus sections 6-10 tend to take over some of the load of motor M until the load is rebalanced. If all four sections are connected in circuit to drive the common shaft 12, current-balancing windings CB1- CB4 of amplifier MA3 are energized, and the current in negative feedback winding FB has a value providing a predetermined output voltage for the amplifier. If the section 10 is disconnected, resistor 70c is included in circuit so that the current in the load-balancing amplifier reference windings of the other sections remains unchanged. Disconnection of section 10 deenergizes windings CB4 and connects resistor 84 in circuit with windings FB, the output voltage of the amplifier MA3 remaining constant. Similarly, when the second and third drive sections are disconnected, windings CB3 and CB2 are de-energized and resistors 82 and 80 are inserted to maintain the output of the amplifier MA3 substantially constant. Thus, when motors are disconnected from the system, the load is reapportioned among the remaining motors in a predetermined ratio, so that, if four motors share the total load equally, for example, disconnection of one motor causes the system to maintain the loads of the three remaining motors in balance. In another arrangement, the function of the amplifier MA3 is undertaken by a transformer, and the current-detecting device is a saturable reactor, Fig. 5 (not shown).