Method and apparatus for compensating positional errors

• US 5,237,509 A
• Filed: 03/08/1991
• Issued: 08/17/1993
• Est. Priority Date: 03/09/1990
• Status: Expired due to Term

• Current Assignee: Toshiba Kikai Kabushiki Kaisha (Shibaura Machine Co., Ltd.)
• Original Assignee: Toshiba Kikai Kabushiki Kaisha (Shibaura Machine Co., Ltd.)
• Inventors: Shiozaki, Masahito, Fujita, Jun, Ueta, Toshihiro
• Primary Examiner(s): Smith, Jerry
• Assistant Examiner(s): GORDON, PAUL P
• Application Number:
  US07/666,783
• Time in Patent Office: 893 Days
• Field of Search: 364/167.01, 364/474.18, 364/474.28, 364/474.35, 318/561, 318/572, 318/569, 318/632
• US Class Current: 700/193
• CPC Class Codes: G05B 19/402 characterised by control arrangements for positioning, e.g. centring a tool relative to a hole in the workpiece, additional detection means to correct position G05B19/19 takes precedence
• CPC Class Codes: G05B 19/404 characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia G05B19/19, G05B19/41 take precedence
• CPC Class Codes: G05B 2219/35588 Pack, compress data efficiently in memory
• CPC Class Codes: G05B 2219/41036 Position error in memory, lookup table for correction actual position
• CPC Class Codes: G05B 2219/41055 Kind of compensation such as pitch error compensation

Abstract

In a numerical control of a machine tool, the relation between the total number of instructions, or the range of movement of the movable member of the machine tool and the actual amount of movement is not represented by a straight line but periodically change sinusoidally over substantially equal ranges of movement, due to a lead error of a ball screw used for moving the movable element. For the purpose of correctly compensate the position error in a short time, the total range of movement of the movable element is divided into a plurality of ranges, and start and end points of movement, types of movement of respective ranges and periods thereof are stored in memory means. The actual position of the movable element and the data stored in the memory means are used to correct the actual position of the movable member.

Claims

1. 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 a range of movement of said movable member into a plurality of sections corresponding to a plurality of types of repeating position error pattern;

a step of, in each of said sections, a configuration of a position error curve repeating in a same pattern;

a step of storing in memory means coordinates of a movement start point and end point and a length of one period of a pattern repeated in any one of said sections;

a step of dividing said pattern into small sections, each having a length shorter than a length of each period of respective patterns corresponding to types of respective patterns; and

a step of compensating for the position errors by using said small sections.

2. 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.

3. 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.

4. 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.

5. The apparatus according to claim 4 which further comprises a differentiator for producing a differentiated signal Vf to a third adder for applying its output signal Xcf to said position compensation quantity calculating unit for calculating a position error.

6. The apparatus according to claim 4 wherein one of said data memory means exchanges a position error quantity Cx between this data memory means and said position compensation quantity calculating unit.

7. The apparatus according to claim 4 wherein the other one of said data memory means exchanges a correction signal between this data memory means and said position compensation quantity calculating unit.

8. 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.