The development of a depth control system for a peat milling machine, part II: System optimization and analysis

Optimization of the performance of a closed-loop, milling depth control system for a peat milling machine was undertaken. The system was optimized using a proportional-integral-derivative (PID) controller, set at a proportional gain of 50, and derivative and integral times of 0.5 and 0.89 s, respectively, giving a bandwidth of 66 rad s (- 1) with a response similar to a first-order system. The system was evaluated by comparison with the existing manual control method, and revealed large reductions in crop depth (yield) variation. The system allows the driver of the miller numerical control over peat crop depth (yield) in a way not previously feasible. The variance of depth produced by automatic control was at most a quarter (at 95% confidence) of that of manual control, on a depth-distance basis. Frequency domain comparison of the control methods, revealed a 71% reduction in the amplitudes of depth variation at frequencies below 45 rads(-1) for the automatic method. The significant advantages afforded by the system, give the peat production industry a tool, which if used in conjunction with application mapping technology, can lead to significant benefits in the quality control of peat production. (C) 2001 Silsoe Research Institute.