Optimal Electro-Hydraulic Control of Mining Booms

Abstract

Mining boom rippers are used in the UK coal industry to drive tunnels, which provide ventilation and access to the coal seams. The present tunnelling machines are open-loop controlled; better positional control can be obtained by introducing feedback, and a microprocessor-based system provides automatic operation. A dual microprocessor system based on the 8085A 8-bit microprocessor has been built and tested on a boom ripper. Poppet valves are used in this system for their ease in interfacing to the microprocessor and their high dirt tolerance. A bang-bang (on-off) control philosophy is adopted to provide optimal positional control: the valves are fully opened to give the boom the maximum acceleration moving towards the desired position and will be closed completely to provide maximum deceleration when a pre-determined criterion has been satisfied. Two methods of providing the switching signals have been studied: the signals are determined by simply comparing the desired and the current boom positions in one method, or they can be determined by evaluating the switching function which accounts for the valve characteristics and other system properties. Both methods give a positional accuracy limited by the ADC (approximately ±1 cm at the cutter end, ±0.4% of the full range). However, the switching function evaluation method shortens the overall time to change the boom positions at high speed while increasing the complexity in the circuit and software design. It has been demonstrated that an APU can increase the speed and simplify the software in handling mathematical operations. An APU board has been developed, although it is not used in the simple comparison method. The APU will be particularly useful if the system is going to compensate for the machine chassis movement when the signals for the machine's position and orientation can be obtained.