Some aspects of on-line computer control of a lathe

Abstract

A small lathe has been modified to work under microprocessor control to enhance the facilites which the lathe offers, and provide a wider operating range with relevant economic gains. As a result of these modifications the saddle motion is controlled by steppingmotors under closed-loop control giving better operating system characteristics as indicated below. An electrical circuit has been developed to monitor spindle torque and the mechanical link between the spindle motor and the screw has been replaced to give an " infinitely variable " gearbox, and this allows a variety of non-standard screws, helices and spirals to be manufactured. Software for the system includes control programs for implementation of the adaptive control function and monitoring of tool wear; linear and circular interpolation is implemented through the manipulation of Boolean functions, rather than by solving equations to optimise the performance of stepping motors when used for real-time control. Use o f low cost uncalibrated ball-screw s in conjunction with a calibration algorithm results in an overall accuracy better than the resolution of the system. It is concluded that it is practical to carry out a low-cost retrofit on existing machine tools to enhance their range of capabilities.