Digital position control of a lathe tool

In this work a digital position control servomechanism, which had previously been developed by the author and a co-worker, has been fitted to the saddle of a copy turning lathe so that the positioning of the servo ram controls the setting of the lathe tool relative to the main spindle axis. In this way required workpiece diameters may be preset by means of the input to the digital servo, and it is intended to further develop the system to full numerical control of the machine.
The subject of the thesis is the analysis of the performance
of the digital servo, both theoretically and practically, the mounting of the servo on the lathe and subsequent accuracy checks on workpieces machined according to preset commands at the input to the servo. Analysis of the performance of the digital servo involved the use of a general purpose digital computer to simmulate the non-linear response characteristics of the system, and the performance tests were carried out using a data sampling technique which is fully described.
Since in operation the complete system involves the use of
two position servomechanisms in series, and since no overall
feedback link is provided, it was also necessary to investigate the performance of the hydraulic positioning system already fitted to the copying slide of the lathe. A series of experiments
was therefore set up to measure the lag and response of the hydraulic servo under typical working conditions, in order to establish that this lag could be ignored compared to the lag in the digital system in deciding the overall accuracy of the combined equipment. This work complete with the experimental results obtained is also included.

Laboratory facilities, and assistance and advice in the preparation of the computer programme which forms an essential part of the analysis, provided by Enfield College of Technology.