Copyright © IFAC Automation in Mining. Mineral and Metal Processing. Sun City. South Africa. 1995 THE MODELLING AND CONTROL OF A DEEP HOLE DRILLING RIG G P Hancke and G L van Harmelen Department of Electrical and Electronic Engineering University of Pretoria, PRETORIA 0002 South Africa Abstract: Drill bit performance in terms of average penetration rate and life has become extremely important because time dependant costs have become the major proportion of the total costs per meter drilled, due to the deep holes encountered, especially in the gold exploration drilling industry. This paper gives an overview of the important parameters influencing the drill bit performance. An instrumentation and control system has been implemented for controlling these parameters. An analysis and simulation done on an assumed model indicated that stable, well damped, closed loop control could be maintained over the wide range of system dynamics which were expected to be encountered in the system. Practical observational results agree well with the results obtained by the simulation. Keywords: Control applications; PID control; force control; power control; hydraulic systems; mining. 1. INTRODUCTION In the gold exploration drilling industry borehole depths of between 3000m and 5000m are a common requirement. In order to reach these depths, a larger capacity and higher capital cost drilling rig is required. Time-related costs, associated with the more expensive equipment, increasing labour costs and longer core retrieval and tripping times, have become the major proportion of the total costs per meter drilled, while the bit costs form a relatively minor proportion. Bit performance in terms of penetration rate and life expectancy has therefore become ,;xtremely important. It is apparent that the need exists for a reliable and practical method of achieving optimum bit performance over the wide range of operating parameters. This can best be accomplished by implementing a control system which will allow the rig to function at its optimum efficiency, throughout its entire operating range, measured in terms of factors such as specific energy (Heinz, 1985). 59 2. THE MECHANICAL FINE FEED SYSTEM The force on the drill bit and subsequent penetration rate and other parameters are controlled by means of the mechanical fine feed system of which a simplified schematic diagram is shown in Fig. 1. Fig. 1. The simplified fme feed mechanical system.