Method and apparatus for controlling a machine tool

Patent metadata

Field	Value
Publication number	US-9983563-B2
Application number	US-201514629925-A
Country	US
Kind code	B2
Filing date	Feb 24, 2015
Priority date	Mar 31, 2014
Publication date	May 29, 2018
Grant date	May 29, 2018

Abstract

A method for controlling a machine tool in which a main spindle on which a tool is mounted and a table holding a workpiece are moved relative to each other by two or more translation axes that are not perpendicular to each other and at least one rotation axis. In the method, an error in a position of the tool with respect to the workpiece due to a geometric error is corrected to calculate a command value for controlling the translation axis. The method includes a conversion step of converting the error and a correction value for correcting the error by performing a homogeneous coordinate transformation from a workpiece coordinate system to the imaginary Cartesian coordinate system, and a correction value calculation step of calculating a correction value in a command value coordinate system of the translation axis by performing a homogeneous coordinate transformation of the correction value.

First claim

What is claimed is:

1. A method for controlling a machine tool in which a main spindle on which a tool is mounted and a table that holds a workpiece are moved relative to each other by two or more machine tool translation axes and at least one machine tool rotation axis to machine the workpiece with the tool, at least two of the machine tool translation axes not perpendicular to each other, the method comprising:
obtaining a position of the tool in presence of a geometric error by performing a homogeneous coordinate transformation from a tool coordinate system to a workpiece coordinate system with the geometric error being taken into consideration,
obtaining an ideal position of the tool by performing the homogeneous coordinate transformation from the tool coordinate system to the workpiece coordinate system with the geometric error not being taken into consideration,
calculating an error in the position of the tool with respect to the workpiece due to the geometric error from the position of the tool in presence of the geometric error and the ideal position of the tool,
converting the error in the position of the tool with respect to the workpiece into an imaginary Cartesian coordinate system that comprises two or more Cartesian coordinate system axes that are perpendicular to each other, and converting a workpiece coordinate system correction value for correcting the error in the position of the tool with respect to the workpiece into an imaginary Cartesian coordinate system correction value in the imaginary Cartesian coordinate system by performing a homogeneous coordinate transformation from the workpiece coordinate system to the imaginary Cartesian coordinate system;
calculating a command value coordinate system correction value in a command value coordinate system by performing a homogeneous coordinate transformation of the imaginary Cartesian coordinate system correction value, converted into the imaginary Cartesian coordinate system in said converting the error, from the imaginary Cartesian coordinate system into the command value coordinate system;
calculating an updated command value by updating a command value for controlling the machine tool, by adding the command value coordinate system correction value, calculated in said calculating a correction value, to the command value; and
controlling the machine tool to perform the method based on the updated command value.

2. The method according to claim 1 , wherein
in said converting the error, the homogeneous coordinate transformation of the error in the position of the tool with respect to the workpiece and the workpiece coordinate system correction value for correcting the error in the position of the tool with respect to the workpiece from the workpiece coordinate system into the imaginary Cartesian coordinate system is performed in view of an inclination angle of the machine tool translation axis included in the two or more machine tool translation axes that are not perpendicular to each other with respect to a predetermined reference direction.

3. The method according to claim 1 , wherein the method further comprises:
selecting an arbitrary axis configuration, said arbitrary axis configuration comprising at least two arbitrary axis configuration translation axes that are perpendicular to each other, said arbitrary axis configuration comprising at least one arbitrary axis configuration translation axis selected from among the two or more machine tool translation axes and at least one arbitrary axis configuration rotation axis selected from among the at least one machine tool rotation axis, wherein
in said converting the error, the error in the position of the tool with respect to the workpiece and the workpiece coordinate system correction value are converted into an arbitrary imaginary Cartesian coordinate system that comprises two or more arbitrary imaginary Cartesian coordinate system axes that are among the at least two arbitrary axis configuration translation axes of the arbitrary axis configuration and that are perpendicular to each other, by performing the homogeneous coordinate transformation from the workpiece coordinate system to the arbitrary imaginary Cartesian coordinate system, and
in said calculating a command value coordinate system correction value, the command value coordinate system correction value is calculated by performing the homogeneous coordinate transformation of the imaginary Cartesian coordinate system correction value, converted into the arbitrary imaginary Cartesian coordinate system in said converting the error, from the arbitrary imaginary Cartesian coordinate system into the command value coordinate system.

4. The method according to claim 3 , wherein
said at least one arbitrary axis configuration translation axis selected from among the two or more machine tool translation axes is to be actually used to machine the workpiece, and said at least one arbitrary axis configuration rotation axis is to be actually used to machine the workpiece,
a used axis configuration that comprises only the one or more machine tool translation axes to be actually used to machine the workpiece and the one or more machine tool rotation axes to be actually used to machine the workpiece is selected as the arbitrary axis configuration, and
the imaginary Cartesian coordinate system comprises said at least two arbitrary axis configuration translation axes that are perpendicular to each other and that are included in the arbitrary imaginary Cartesian coordinate system.

5. The method according to claim 4 , wherein the method further comprises:
deciding that the error in the position of the tool with respect to the workpiece, in a first selectable axis configuration that comprises at least one machine tool translation axis and at least one machine tool rotation axis, is to retain a previous error or to be set to zero if it is determined that said first selectable axis configuration is not to be used to machine the workpiece.

6. The method according to claim 2 , wherein said method further comprises:
selecting an arbitrary axis configuration, said arbitrary axis configuration comprising at least two arbitrary axis configuration translation axes that are perpendicular to each other, said arbitrary axis configuration comprising at least one arbitrary axis configuration translation axis selected from among the two or more machine tool translation axes and at least one arbitrary axis configuration rotation axis selected from among the at least one machine tool rotation axis, wherein
in said converting the error, the error in the position of the tool with respect to the workpiece and the workpiece coordinate system correction value are converted into an arbitrary imaginary Cartesian coordinate system that comprises two or more arbitrary imaginary Cartesian coordinate system axes that are among the at least two arbitrary axis configuration translation axes of the arbitrary axis configuration and that are perpendicular to each other, by performing the homogeneous coordinate transformation from the workpiece coordinate system to the arbitrary imaginary Cartesian coordinate system, and
in said calculating a command value coordinate system correction value, the command value coordinate system correction value is calculated by performing the homogeneous coordinate transformation of the imaginary Cartesian coordinate system correction value, converted into the arbitrary imaginary Cartesian coordinate system in said converting the error, from the arbitrary imaginary Cartesian coordinate system into the command value coordinate system.

7. An apparatus for controlling a machine tool in which a main spindle on which a tool is mounted and a table that holds a workpiece are moved relative to each other by two or more machin

Assignees

• Okuma Machinery Works Ltd

Inventors

• Kondo Yasunori
• Matsushita Tetsuya

Classifications

• G05B2219/49202

  For point to point positioning · CPC title

• G05B2219/49194

  Structure error, in slide or screw · CPC title

• G05B19/402 Primary

  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 title

• G05B2219/49198

  Using lookup table, map, position and corresponding quasi static error · CPC title

• G05B19/404 Primary

  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 title