Method and apparatus for compensating positional errors

A method of compensating a position error of a numerical control apparatus that controls a movement of a movable member of a machine tool, comprising:

• a step of dividing said movement into a plurality of small sections in which a configuration of a position error is repeated;
• a step of detecting a present position of said movable member in any one of said small sections;
• a step of determining the present position of said movable member;
• a step of determining the present position of said movable member in any one of said small sections by using presorted data;
• and
• a step of determining a position error quantity and a position error quantity corresponding to each small sections.

A method of compensating a position error of a numerical control apparatus that controls a movement of a movable member of a machine tool, comprising:

• a step of dividing said movement into a plurality of small sections;
• a step of detecting a first present position of the movable element;
• a step of determining the first present position of the movable element;
• a step of determining a second present position of the movable element in a region in which position error patterns are repeated;
• a step of determining a third present position of the movable element in which one of the divided region, all of said determining being made in accordance with presorted data, determining a pattern of the position error and a position error quantity by using prestored data;
• a step of correcting a detected present position data using said position error quantity;
• and
• a step of positioning said movable member at a correct position by feeding back said corrected position data to said numerical control apparatus.

Apparatus for compensating a position error of numerical control apparatus that controls a movement of a movable member of a machine tool, comprising:

• an NC data reader for reading out an NC program;
• a keyboard;
• a main portion of said numerical control apparatus connected to receive an NC data read out by said NC data reader and an output of said keyboard;
• a program analyzer adapted in said main portion and for analyzing said NC program to be output;
• data memory means adapted in said main portion and having at least two kinds of memories, for receiving said NC program from said program analyzer and for storing a relation between an instructed position and an actual position of said movable member and a signal from said keyboard;
• a position compensation quantity calculating unit connected to said data memory means for producing a present position compensating signal Cx;
• a first adder for obtaining a difference between an output Xc of said program analyzer and a present position of said movable member;
• a servo control device connected to said program analyzer through said first adder for driving a motor for moving said movable member;
• means for detecting an actual position of said movable member for applying a feedback signal to said position compensation quantity calculating unit;
• and
• a second adder receiving said feedback signal from said calculating means for detecting an actual position of said movable member, and for calculating a difference between said feedback signal and said present position compensation signal Xc for applying a difference signal to said first adder.

Numerical control apparatus for controlling movement of a movable member of a machine tool comprising:

• first division means for dividing a range of movement into a plurality of sections corresponding to different types of patterns, a configuration of a position error curve repeating with same pattern;
• first memory means storing position coordinates of a start point and an end point in each divided section and a length of one period of a repeating pattern in said divided section;
• second division means for dividing each of said plurality of sections into a plurality of shorter sections with respect to a length of one period of each pattern;
• second memory means storing position error in one of said shorter sections obtained by dividing a length of one period of each pattern in accordance with types of respective patterns;
• means for supervising a present position of said movable member corresponding to an instructed position;
• means for judging whether a supervised position lies in one of divided sections by using data stored in said first and second memory means;
• means for judging whether said supervised position lies in one of said shorter sections in one period of said pattern;
• and
• a position compensation quantity calculating unit for calculating a position error in one shorter section in which said movable member is located by using a value of a position error stored corresponding to each shorter section of each pattern thereby compensating the position of said movable member by a calculated position compensating quantity.