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

Optimization of the performance of a closed-loop, milling depth control sys tem for a peat milling machine was undertaken. The system was optimized usi ng a proportional-integral-derivative (PID) controller, set at a proportion al gain of 50, and derivative and integral times of 0.5 and 0.89 s, respect ively, giving a bandwidth of 66 rad s (- 1) with a response similar to a fi rst-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 ove r 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% confiden ce) of that of manual control, on a depth-distance basis. Frequency domain comparison of the control methods, revealed a 71% reduction in the amplitud es of depth variation at frequencies below 45 rads(-1) for the automatic me thod. The significant advantages afforded by the system, give the peat prod uction industry a tool, which if used in conjunction with application mappi ng technology, can lead to significant benefits in the quality control of p eat production. (C) 2001 Silsoe Research Institute.