Computer observer for in-process measurement of lathe tool wear

Abstract

In the laboratory, tool wear is measured by direct visual observation of flank and crater wear dimensions using a tool maker's microscope. On the shop floor, the journeyman machinist uses chip appearance, sound, vibration, and surface finish to access tool condition. More precise information can be provided by between pass measurements of work piece dimensions. Although there is a body of research directed toward in-process measurement of tool wear, none has found practical application on the shop floor. This, despite the demands of unattended operation of machine tools in the automated factory. Two of the authors have developed a state space model of metal cutting on a lathe. Operation of that model was experimentally accessed using the Advanced Continuous Simulation Language (ACSL) [1]. The state space model embodied in the simulation is comprised of six state variables. In an actual lathe, four of those variables (spindle speed and torque, and cutting speed and force) would be directly measurable. The other two variables, flank and crater tool wear, would not be measurable. This paper describes a linear observer that reconstructs the two tool wear state variables based on system inputs and the four measurable state variables. In actual use the observer would be implemented using a microcomputer dedicated to the lathe. In this study, the previously developed ACSL model was substituted for the lathe, and the linear observer was incorporated as an extension to the simulation. Operation of the observer, including response to initial errors, is demonstrated.