GB1317045A - Automatic control of mining machines - Google Patents

Abstract

1317045 Automatic speed and current control EICKHOFF MASCHINENFABRIK U EISENGIESSEREI mbH Gebr 4 June 1970 [20 June 1969] 26913/70 Heading G3R [Also in Division H2] A mining machine of the type having a variable speed electric winch motor and a cutting tool electric motor is automatically controlled so that the speed of the winch motor is maintained at a reduced value when the cutting tool motor is either idling or loaded beyond a desired maximum value, and attains a normal preselected higher value only when the tool motor is operating at its normal cutting load. The current taken by the cutting tool motor 2 is sensed by transformer 5 and applied to a limiter 22 which, at idling current levels of the motor, prevents a control member 24 from starting a servomotor 21 to adjust a potentiometer 20 to its position manually pre-set by a switch 10, the potentiometer setting determining the desired speed of the winch motor 3 under cutting conditions. When cutting commences, the tool current signal blocks the limiter 22 to allow operation of members 21, 24, the action being reversed when the motor 2 again idles to restore the servomotor 21 to its initial position. The current signal from transformer 5 and that from transformers 6 indicative of the winch motor current are applied to an OR gate 9 which passes the greater signal to a limiter 15 receiving the output of a member 14 supplied with the error signal of a comparator 11 fed with the desired speed signal of potentiometer 20 and an actual speed signal from a tachogenerator 12. When the output of gate 9 exceeds a pre-set value, it causes the limiter 15 to modify the output signal of member 14 and so control, via switch unit 17 and pulse generators 18, 18', the firing angle of thyristors 19 or 19' to reduce the winch motor current. Motor and thyristor temperature sensers 25, 25' also modify the signal supplied by member 14. If the winch motor speed exceeds the maximum attainable by its armature control system, a monitor 43 switches on to pass the combination of the output of member 14 and a reference signal 50 to a pulse generator 46 controlling a thyristor 47 in the field winding 48 of the motor 3. A limiter 32 and time delay unit 33 respond to overcurrent lasting longer than a predetermined time and cause the unit 17 to switch from members 18, 19 to 18', 19' to reverse the motor. During switchover the thyristors 19' are fired to allow the motor 3 to operate as a generator, voltage sensing resistors 34 controlling the unit 17 to ensure that switchover to the regenerating range occurs at the zero transition of the voltage half waves. An RC circuit 49 ensures that the motor drive current reduces gradually and another such circuit 38 causes member 24 to restore the servomotor 21 to its initial position and so provide reverse operation of motor 3 at reduced speed. Continued reversals of the motor 3 due to an overload on the winch causes a timer 39 and AND gate 40 to disengage the switch 10 and stop the machine.