Patent GB-1082491-A (GB)
Title: Improvements relating to material cutting machines
Inventor: ADDISON GEORGE THOMAS
IPC: H02P29/00
Filed: 1964-01-15
Abstract: 1,082,491. Control of motors. BRITISH JEFFREY-DIAMOND Ltd. Jan. 12, 1965 [Jan. 15, 1964], No. 1877/64. Heading H2J. [Also in Divisions E1 and G1] A coal-cutter is driven by electric motor 1, and the machine is traversed by hydraulic capstan motor 2 associated with pump 4 whose output is controlled by a thrustor mounted in cylinder 5. Auxiliary pumps 8, 9, 10 are connected to the cylinder, operation of valve A increasing the advance speed whilst operation of valve B reduces this speed. During withdrawal of the machine, the roles of the valves are reversed. Opening of valve C returns the thrustor to a central position and operates isolating valve E. Valve D operates stop valve F in a by-pass for the capstan motor. The valves are controlled by apparatus 12 which regulates the speed of advance of the cutter subject to over-riding load control. A reference signal from potentiometer 13 in unit (400) is compared, in phase-sensitive rectifier unit (500), with a signal from differential transformer 14 in thrustor-position detector unit (200). Load control unit (700) comprises current transformer 15 in circuit with the motor 1. Unit (600) controls the valves A, B, in accordance with the error signal from unit (500). The transformer 14 is supplied from oscillator (300) wherein transistors (308), (309), switch transistor (310) on and off, so driving the output transistors (311), (312). A feed-back circuit comprises resistor (337) and capacitors (336). The transformer 14 varies the output signals along leads (205), (206), differentially so that, when the thrustor is in a central position, the signals are equal and opposite. The potentiometer control unit (400) has terminals (401), (402), connected to stop control unit (900). Reversing switches (409), (410), are interlocked with wiper arm (406) and stop switch 20. The unit provides a reversible error signal between the slider of potentiometer (508) and common line (124) so that either of the transistors (608), (609), is caused to conduct. If the error signal is negative, transistor (604) is switched off and transistor (605) becomes more conductive. Transistor (608) becomes less conductive and transistor (609) more conductive. Transistor (618A) is triggered to switch on transistor (622A) which fires silicon controlled rectifier (625A) connected to solenoid winding 11A. Thus, valve A is opened to increase the speed of advance of the machine until the position of the thrustor corresponds with the setting of the reference potentiometer. If the error signal is positive, reverse action takes place and valve B is opened to reduce the traverse speed. The valves C and D have similar controlled rectifiers and trigger circuits. When the current taken by the motor 1 exceeds the level set by resistor (713), transistor (718) is switched on to cut-off transistors (724) whereby transistors (728), (731), are rendered conductive. A positive signal is fed to unit (500) so that valve B operates to decrease the traverse speed. In the event of extreme overload, set by resistor (715), transistor (734) de-energizes the solenoid of valve C. When the cutter clears the coal face at the end of a cut, transistor (801) is turned on by the load control unit so that transistor (812) is switched on to open both valves C, D. The stop control circuit is broken by the reference potentiometer to turn off transistors (907), (913), and switch on transistor 921. This causes valves C, D to open. Transistor (934) is switched on for five seconds after the equipment has been stopped to prevent closure of valves C, D until this period had ended.