Active suppression of machine tool chatter

Abstract

The aim of the work described in this thesis is to design, build, and test an active, chatter suppression system for use on a lathe. Many methods have been developed to minimise the effects of regenerative chatter in machine tools. These include machine redesign and stiffening, the inclusion of additional damping, and the use of passive and active control systems. The method described here is a development of two of these active methods, those of Comstock and Nachtigal, which control the relative position of the cutting tool. An on-line digital computer is used to monitor the cutting force, predict the relative tool-workpiece displacement, and drive the tool to suppress chatter build-up. The work is described in five main sections. After the introductary section, in which the problem is outlined and past work discussed, a theoretical analysis of chattering and its suppression is presented. Digital simulation is used to confirm and expand the theoretical results. The basic on-line identification method used to investigate the machine-workpiece structure is also presented. The third section describes the design and implementation of the experimental rigg especially the computer system and the tool positioner. Its use as a driver for a cheap, bolt-on CNC turning system is also discussed. The fourth section details the experimental work including calibration, cutting tests, suppressor validation and testing. Finally, the theory, simulation and experiments are discussed and related to past work. Suggestions are made for further reearch and development, including other applications of the system. Conclusions are drawn about the various techniques used during the work, with comments on the effectiveness of the suppression method.