GB1161115A - Improvements in or relating to Automatic Electrical Control Systems. - Google Patents

Abstract

1,161,115. Control of motors. W. R. C. DAWSON. 23 Aug., 1966 [23 Aug., 1965], No. 36173/65. Heading H2J. [Also in Division G3] An automatic control system for a cutting or like apparatus having a tool 11 driven by an A.C. electric motor 12 and a carriage 17 driven by an electric motor 25 for causing relative movement between a workpiece 16 and the tool 11 comprises a sensor 21 for sensing the load current fed to the motor 12, a comparator for comparing the current with a predetermined value, and power control means for controlling the power supplied to the feed motor which power control means is responsive to an output from the comparator and to the magnitude and phase of the voltage supplied to the motor 12 so as to automatically control the relative movement between the tool 11 and the workpiece 16 whereby the power absorbed by the motor 12 tends towards a desired valve. As shown in Fig. 2, the system includes a transistor 43 to the base of which is applied (a) a signal representative of load current exceeding a predetermined value, this signal being derived from the sensor 21 by way of a setting resistor 38 and a reference Zener diode 44, and (b) a signal derived from a transformer 26 having its primary winding connected to the supply for the motor 12, this signal rendering transistor 43 conductive in the absence of an output from the Zener diode 44. The output from the collector of transistor 43, which output is interrupted when the load current exceeds its predetermined value, is applied over a capacitor 45 to control a thyristor 40 in circuit with the armature 35 of the feed motor 25, this circuit being connected across the output from the transformer 26 and receiving a voltage representative of the magnitude and phase of the voltage supplied to the motor 12, and the motor 25 is thus controlled in such a manner that the carriage 17 is moved relative to the tool 11 at a rate sufficient to maintain the power absorbed by the motor 12 constant. A braking diode 46 may be connected across the armature 35, and the system may include limit switches to reverse the direction of the motor 25 when the carriage reaches the end of its travel towards the tool 11. A modified arrangement, including a sensitivity control circuit is described with reference to Fig. 4 (not shown).