Control means for drive equipment

The circuit, which controls actuation of a clutch intermediate an electrical motor and a conveyor, is powered from a transformer which taps the power supply to the motor. The circuit contains a relay switch which is operable by a current sensor attached to the power supply line.

This invention relates to control means for drive equipment particularly to 
control means for controlling an hydraulically actuated clutch drivably 
connectable intermediate an electrical drive assembly and a driven 
assembly. 
In particular, though not exclusively, the present invention relates to 
control means for controlling a clutch drivably connectable intermediate 
an electric drive motor and a gearbox for a conveyor installed along a 
working face in an underground mine. 
The present invention relates particularly to an improvement in or a 
modification of, the invention described and claimed in U.S. Pat. No. 
4,039,057. 
An object of the present invention is to provide improved control means for 
drive equipment, which tends to be more responsive to operational modes of 
the electric drive motor. 
According to the present invention control means for controlling an 
hydraulically actuated clutch drivably connectible intermediate an 
electrical drive assembly and a driven assembly comprises, an electrical 
circuit including an electrical relay switch, a voltage transformer having 
a primary side connected to a power supply cable to the electrical drive 
assembly and a secondary side connected to solenoid means to control the 
clutch; sensor means connected to the power supply cable for sensing if an 
electrical current is being supplied to the drive assembly and adapted to 
derive an electrical signal indicative thereof and to actuate the relay 
switch to make or break the electrical circuit. 
Preferably, the control means comprises further sensor means for sensing 
operational modes of a brake associated with the driven assembly, the 
further sensor means being adapted to pass or prevent passage of an 
electrical signal dependent upon the sensed operational mode. 
Advantageously, the control means comprises indicator means to indicate 
when the relay switch is closed.

The present invention finds application, for example, in an underground 
mining installation. In such an installation conveyors are arranged along 
underground mineral working faces and along mine roadway tunnels. 
Referring to FIG. 1, such a conveyor (not shown) is powered by an 
electrical motor 2 which is drivably connected by means of an 
hydraulically actuated clutch 16 to a driven stage 7 of the conveyor 
gearbox. In steep or sloped mine working faces or roadway tunnels, the 
conveyor has a brake 14 associated therewith. It is necessary in mining 
installations of the kind described, that when the electrical motor power 
supply is switched on, then the clutch 16 is operable to ensure drivable 
engagement between the electrical motor 2 and the driven stage 7. It is 
also necessary, in steep or sloped mine working faces or roadway tunnels, 
that the brake is not actuated while the motor is energized so that 
driving by the electrical motor is not impeded. 
Referring now to FIG. 2, a power supply cable 1, comprising power supply 
lines 3, 4 and 5, is shown joining supply terminals 8, 9 and 10 and 
electrical motor terminals 11, 12 and 13. The supply lines 4, 5 are tapped 
at A and are connected to a primary side of a voltage transformer 15. The 
transformer 15 is protected by fuses 17, 18 connected between the supply 
lines and the transformer 15. 
The secondary side of the transformer is connected to solenoid means 20 via 
a relay switch RL1. A neon indicator N1 is connected in parallel with the 
solenoid means. The relay switch RL1 is connected so that when it is 
closed, a circuit including the transformer 15, the solenoid means 20 and 
the neon indicator is made and so that in consequence when the supply 
lines 4, 5 to the motor are live, the solenoid means 20 is actuated and 
the neon indicator N1 is energized. 
The solenoid means 20, is connected to hydraulic pressure fluid feed means 
21 (see FIG. 1) arranged to cause the clutch 16 to be actuated resulting 
in drivable engagement between the electrical motor 2 and the conveyor 
gearbox driven stage 7. 
Consequently, it will be understood that whenever the solenoid means 20 is 
actuated, then drivable engagement results between the electrical motor 
and the conveyor gearbox driven stage provided that the relay switch RL1 
remains closed. 
Unfortunately, as hereinbefore described, the solenoid means 20 would be 
actuated not only when the electrical motor is actuated, but also in the 
situation when power to the electrical motor has been recently removed and 
the electrical motor still continues to revolve due to the kinetic energy 
thereof which is not immediately dissipated. The solenoid means 20 remains 
actuated in this situation because back e.m.f. is generated by the motor. 
In order to remove this undesirable situation, it is necessary to provide 
sensor means 22 at B in the supply cable 1 to sense whether electrical 
current is being supplied to the electrical motor and to derive an 
electrical signal indicative thereof to control the relay switch RL1. It 
will be understood that the motor is unable to draw current from the power 
supply terminals 9, 10 after power supply to the electrical motor has been 
removed. 
For convenience, the relay switch RL1 is shown separately and differently 
in the two circuits including the transformer 15 and the sensor means 22, 
respectively. The circuit including the sensor means 22 comprises 
resistors R1, R2, R3, diode rectifying bridge D1; Zener diodes D2, D3; 
capacitor C1 and the previously mentioned control side of the relay switch 
RL1. 
The sensor means 22 comprises a current transformer of which the power 
supply line 5, acts as a single turn primary coil and a coil 25 acts as a 
secondary coil. Consequently, when the power to the motor is on, the motor 
current is sensed by the means 22 and a proportion is applied to the 
parallel burden resistors R1 and R2 by the current transformer. 
The voltage derived across the burden resistors R1, R2 is applied across 
points a, b of the rectifying bridge D1. The rectifying bridge D1 provides 
a full wave rectified output at points d, f. The output of the rectifying 
bridge D1 is smoothed by the capacitor C1. 
The smoothed output of the rectifying bridge D1 is connected across the 
relay switch RL1. Voltage across the relay switch RL1 is fixed at a 
desired level by a value chosen for the resistor R3. Zener diodes D2 and 
D3 are provided to limit the voltage across the relay switch RL1 to the 
desired value. 
In operation of the control means of the present invention, the solenoid 
means 20 is energized at all times when power is supplied to the motor, 
but is de-energized immediately when power is removed from the motor 
because the relay switch RL1 is opened immediately when the sensor 22 
fails to detect current in the power supply line 5 to the motor. 
Consequently, the motor will drivably engage the driven stage of the 
conveyor gearbox only when the clutch is actuated due to the solenoid 
means 20 being energized. 
A thermal switch 28 is provided in a pilot line 6 associated with the 
supply cable 1. The thermal switch 28 is mounted adjacent the previously 
mentioned brake associated with a conveyor usually installed in a steep or 
working face or mine roadway of the kind mentioned. The brake is 
resiliently biased towards its applied position and it is released 
hydraulically by the previously mentioned hydraulic pressure fluid feed 
means, when the solenoid means is energized. 
In operation, the thermal switch 28 is adapted to open if the brake starts 
to overheat. Such overheating is caused when the solenoid means 20 (which 
controls the feed of pressure to release the brake) is energized and the 
driven stage of the conveyor gearbox is driven while the brake is even so 
applied. 
The pilot line is connected to a trip switch 30 adapted to be thrown if the 
pilot line should not conduct, i.e. if the brake should overheat. Throwing 
of the trip switch has the effect of turning off the power supply to the 
motor and the motor is therefore stopped. 
Consequently, it can be seen that the motor is inoperable while the brake 
is overheated. 
From the above description, it can be seen that control means for 
controlling an hydraulically actuated clutch drivably connected 
intermediate an electrical drive assembly and a driven assembly is 
provided which is responsive to operation modes of the drive assembly.