Learning control method in numerical control machine tool

A learning control method for a numerical control machine tool which synchronously controls a rotational angle of a main shaft and a position of a feed shaft, said method comprising the steps of:

• (a) loading positional command values into a first data table, the positional command values being indicative of a desired position of the feed shaft relative to various rotational angles of the main shaft;
• (b) loading correction values into a second data table;
• (c) periodically detecting a position of the feed shaft at predetermined rotational angles of the main shaft to obtain actual positional values;
• (d) subtracting one of the positional command values and the actual positional values from the other of the positional command values and the actual positional values to obtain positional deviation values;
• (e) processing the positional deviation values in a predetermined manner to obtain processed positional deviation values;
• (f) adding the correction values to the processed positional deviation values to obtain new correction values;
• (g) loading the new correction values into the first data table;
• (h) repeating steps (c) through (g), which together constitute a correction value renewal cycle, until a deviation difference between the positional deviation values of an Nth correction value renewal cycle and the positional deviation values of an (N+1)th correction value renewal cycle decreases to less than a predetermined parameter value, N being a positive integer;
• and,
• (i) controlling the position of the feed shaft during operation of the machine tool according to the sum of the positional deviation values and the new correction values.