Integrated process and control design for fast coordinate measuring machine

Abstract

Coordinate measuring machines (CMM) are widely used in manufacturing processes for accurate and rapid inspection of machine products. Accuracy and speed are two conflicting design requirements of the CMM control system which are dictated by the servo control loops and dynamics of the arms. The CMM considered here consists of three independent servo controlled orthogonal arms, a two degrees-of-freedom (DOF) probe, a granite table and a computer for the man-machine interface. The objective of this paper is to develop a computer-based design framework to optimize the CMM performance so that an optimal control solution to the probe positioning problem may be found. The control and optimization framework consist of the nonlinear mathematical model of the CMM implemented on the Boeing simulation package EASY5×, a test rig constructed to test and evaluate the controllers and a set of control and optimization algorithms developed specifically for the CMM application. The velocity loop is optimized for maximum bandwidth using the Sequential Quadratic Programing technique. A H ∞- based PI position controller is then developed to meet the control design performance requirements. The control tuning is made automatic by developing an autotuner which identifies the system dynamics and calculates a set of controller parameters for the optimal performance. Adaptive features are then introduced to compensate the effect of load and CMM design variations. Finally, simulation and experimental results are presented to evaluate the proposed integrated system and control design procedure.