The objective of this study is to develop a software of a microcomputer for application to retrofitting of conventional machine tools to NC machine tools. In the NC system for this study, the microcomputer acts as a machine control unit, stepping motors as drive units, and a Teletype as a tape reader.
The path control and the feedrate control are emphasized which are basic and important functions of the machine control unit in a contouring NC system. A 2-dimensional curve interpolation program is developed to interpolate circular, elliptic, and parabolic paths. To control the feedrates, RTC(real time clock) interrupts are used and a feedrate control routine is made. Also a 2-dimensional linear interpolation program is developed to interpolate straight lines, or to move the table to a desired position. In addition, a routine is made to provide a software interface between the microcomputer and a Teletype.
Simulation of the circular interpolation shows that the path error is less than or equal to 1/1000 in. which is the resolution of the NC system for this study.
With the execution of the software program, a milling machine could cut circular, elliptic, and parabolic paths accurately. Available feedrates are reciprocals of integers from 2 to 100, say 1/100, 1/99, 1/98,…, 1/3, 1/2 in/sec., and the cutting times agree with the expected times calculated from the theoretical feedrates.
