Multivariate adaptive control for CNC milling machines using a PC-based open architecture controller
Abstract
The majority of motion control systems in use today employ fixed controllers such as PID, which are tuned for nominal system conditions. Such systems suffer from performance degradation as the system dynamics vary from the nominal conditions. Adaptive control offers an alternative control design methodology that adjusts control parameters at each sampling period based on the current model of the system dynamics. The adaptive algorithms can maintain stability and performance over a wide range of time-varying system conditions. Two adaptive control systems are presented with experimental results. The first controller maintains a constant cutting force for a single axis milling machine by controlling the part feedrate into the machine. The controller is an Extended Model Reference Adaptive Control (MRAC) scheme which maintains stability and performance in the presence of minimum and nonminimum phase discrete system zeros. The scheme incorporates feedback to maintain tracking ability and disturbance rejection and a Zero Phase Error Tracking Controller (ZPETC) to cancel out discrete numerator dynamics of the machining system. Controller development and experimental results are presented. The second part of this work is the derivation of a multivariate adaptive control algorithm to reduce the tracking and contour error of a two-dimensional contour of a milling machine. Stability and convergence proofs are provided for controllers which maintain performance and stability for minimum phase and nonminimum phase systems. Simulations and experimental results are presented for the existing control system, a fixed cross-coupling control system, and the multivariate adaptive controllers. An open architecture controller is designed and implemented to obtain experimental results on a three-axis milling machine utilizing a 32-bit processor. Conclusions and recommendations are then presented.
Degree
Ph.D.
Advisors
Shin, Purdue University.
Subject Area
Mechanical engineering|Electrical engineering
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