Improved Control of Hydraulically Articulated Mining Booms

Abstract

The machines used for the removal of coal and mixed strata have hydraulically articulated booms. This project is concerned with one particular type of machine, that is, the boom-mounted ripper, which is used for the construction of roadways. These machines are presently open-loop controlled, with all control inputs originating from the machine operator. A dual microprocessor system has been developed which provides automatic and improved hand-controlled operation. Feedback is introduced to monitor the position of the boom for controlled positioning and continuous path operations. Multiprocessor system configuration, feedback systems, analogue-to-digital conversion and the microprocessor-based information retrieval system are developed and the results demonstrated. The hazardous environment of the coal mine required the electronic components of the system to have low-level current consumption, etc., in order to meet intrinsic safety requirements. Ergonomic and environmental considerations were involved in developing the machine operator interface. This led to a novel solution for tunnel profile definement to the system and limitation of hand-controlled movement of the boom. The tunnel profile can readily be changed and the system re-programmed, by unskilled personnel, in a mining environment. The hydraulic valves for control of direction and velocity of the boom movement are of the soft seat poppet design. This provides for high contamination tolerance of the dilute (5/95, oil in water) emulsion. These requirements were stipulated by the National Coal Board. Computerised simulations of inertia load control and valve response times with bench test confirmations are included, and a bang-bang (on/off) control philosophy has been adopted. Determination of boom velocity, required for optimal switching of the valves for boom positioning, is carried out using angular displacement transducers, a timer IC and software routines. The kinematic equations have been developed for referencing the boom, which is mounted on a free-ranging chassis, to the tunnel coordinates.