Tracking Performances of Cascade and Sliding Mode Controllers with Application to a XY Milling Table Z.Jamaludin, H. van Brussel, J. Swevers K.U.Leuven, Department Mechanical Engineering Celestijnenlaan 300 B, B-3001, Heverlee, Belgium email: zamberi.jamaludin@student.kuleuven.be Abstract Design and implementation of robust tracking controllers for linear feed drive high speed machine tools are the primary objectives of this work. Cutting forces and friction forces limit tracking accuracy and their influences are minimised through robust controller design. This paper discusses the design and tracking performances of a traditional cascade and a sliding mode controller for a X-Y milling table. Circular tests are performed at selected tracking speeds and circle radii for tracking performance analysis. The tracking error for cascade P/PI controller is proportional to the reference tracking speed and is inversely proportional to the velocity gain value of the position loop controller. Speed and acceleration feedforward further reduce this tracking error. Quadrant glitches, a product of nonlinear friction at the points of velocity reversal, are observed. Sliding mode controller exhibits better tracking accuracy and dynamic stiffness and yields a significant reduction of the quadrant glitches. 1 Introduction Most electromechanical feed drives of table positioning systems rely on the ball screw mechanism for the rotational to linear motion conversion. According to Pritschow [1], the presence of a lead screw in the transmission mechanism gives rise to several performance limitations, namely: (1) backlash, (2) transmission errors from pitch tolerances of the leadscrew and (3) compliance yield a low first mechanical natural frequency of the system, resulting in smaller system’s bandwidth. On the other hand, direct linear drives, in the absent of any mechanical transmission element, eliminate the limitations associated with the ball screw drives. Figure 1 illustrates the opposing mechanical structure of the two drives systems with application to positioning control. linear motor encoder position measurement motor encoder position measurement lead screw milling table (a) (b) Figure 1: (a) ball screw feed drive and (b) linear drive controller milling table controller 81