Automatic control of roadheader cutting head speed and load torque

Roadheaders are nowadays using both in mining engineering and in civil engineering (tunnelling). They often operate in hard rocks, so it is very important to optimize their performance by the full use of their power in different operating conditions. The coal seams are opened deeper and due to rock compactness and their uniaxial stress compression there increases serious problems with power demand and machine wear. The angular speed of cutting head should be adjusted to the rock hardness (the harder is the rock, the lower should be the speed) Nowadays, most of the produced roadheaders have constant speed driven cutting heads. In these cases, sometimes the rock cutting process is performed in conditions far from optimum. The paper presents a concept of the cutting head speed control system and selected results of research performed on laboratory stand equipped with a special R-130 roadheader with an inverter-fed cutting head drive. The closed-loop speed control is accomplished with a PI-controller. Optimum settings of this controller have been calculated using the model in the loop simulation and ITAE (Integral of Time multiplied by an Absolute value of Error) criterion. This criterion is widely used in electric drive technology. The application of the ITAE criterion for the selection of PI controller parameters usually provides a short settling time and an acceptable overshoot value. Results of the experiment show that the system is capable to maintain demanded speed and to follow commands from the master load controller. The drive operation parameters (motor power utilization and frequency of momentary overloads) are much better with automatic control of inverter frequency than with constant frequency drive operation. It should result in lowering power consumption and knife wear intensity.