Reed D. Hanson

Periodic Sampling Interval Repetitive Control and Its Application to Variable Spindle Speed Noncircular Turning Process

This paper addresses discrete-time, repetitive control for linear, periodic, time-varying systems. A periodic, repetitive control design method based on gain scheduling is proposed and the necessary and sufficient condition for closed-loop stability is presented. Utilizing the special structure of the repetitive controller, an efficient method for evaluating the closed-loop stability is developed. The algorithm is applied to the control of a piezoelectric fast-tool stage for variable spindle speed noncircular turning process. The tool performs dynamic variable depth of cut machining to generate noncircular workpiece profiles while the spindle carrying the workpiece rotates at a variable speed to inhibit machining instability (chatter). Experimental machining results are presented that demonstrate the tracking performance of the period, time-varying controller design proposed, as well as the ability to increase machining stability using this approach.

Dynamic variable depth of cut machining using piezoelectric actuators

Abstract This paper describes the design of a piezoelectric actuated cutting tool and implementation of digital servo controls for machining surfaces with dynamically varying depth of cut. Through a flexure hinge, the tool holder could generate 50 μm travel at the tip of the cutting insert. Tool motion errors of less than 0.5 μm were achieved in tracking cyclic waveforms by employing a digital repetitive servo control. When applied to turning aluminum and steel workpieces with variable depth of cut using carbide tools, less than 5 μm machined surface errors were measured.

Design, Modeling, and Motion Control of the Noncircular Turning Process for Camshaft Machining

This paper presents the design, modeling, and motion control of the noncircular turning process for camshaft machining. The cam profile tracking performance requirements are first characterized to meet industry standards. Based on these requirements, a unique test fixture using state-of-the-art actuation and sensing technologies is designed for the noncircular turning process. Modeling of the electrohydraulic servo valve, actuator, and sensors is conducted based on their frequency responses. Digital motion control that achieves asymptotic cam profile tracking while maintaining system robust stability is designed and implemented on the turning test fixture. Spindle speed can be chosen depending on the required profile tracking accuracy with higher speed rendering higher machining rate for rough turning and lower speed rendering higher accuracy for finish turning. Experimental results of turning a variety of cam profiles show that the tracking error is less than 30 μm for spindle speed at 300 rpm and is less than 60 μm for spindle speed at 600 rpm or 1200 rpm.

Discrete-time Repetitive Control of LTI Systems Sampled at a Periodic Rate

Abstract In this paper, discrete-time repetitive control for linear systems sampled at a periodic time-varying rate is addressed. A necessary and sufficient condition for closed-loop stability is presented along with two control system design procedures. These methods are compared to previous methods developed for repetitive control of linear periodic systems.