Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1991-01-28
1993-03-16
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
31856819, 318632, 901 42, 395 80, B25J 910, B25J 922, G05B 1918
Patent
active
051947927
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tool center point setting method in a robot, and more particularly, to a method capable of accurately and easily setting the tool center point without the need of removing a tool from a robot.
2. Description of the Related Art
Generally, during a robot operation, the target position and orientation of a robot tool, which are stated in a program created beforehand on an off-line basis and are represented by an orthogonal coordinate system, are converted into target values of joint angles of individual axes of the robot, and the joint angles are respectively controlled to these target joint angles. In this coordinate system conversion, various transformation matrices are used for the coordinate conversion between adjacent ones of various coordinate systems set for various sections of the robot. For example, employed is a transformation matrix for the coordinate conversion from a coordinate system set for the tool mounting surface into a tool coordinate system.
Conventionally, to determine the transformation matrix (i.e., to set the tool center point), at first, the distal end of a tool mounted to the tool mounting surface is positioned at a reference point whose coordinate position in a reference coordinate system is unknown, and a matrix P1" representing the position and orientation of the center of the tool mounting surface in the reference coordinate system at that time is derived. Then, after the tool is removed from the tool mounting surface, the center of the tool mounting surface is brought to the reference position, and a matrix P2" representing the position and orientation of the center of the tool mounting surface in the reference coordinate system at that time is derived. Assuming here that the transformation matrix is TCP" and an unknown matrix representing the coordinate position of the reference point in the reference coordinate system is P0", then the relationships represented by the following equations (1) and (2) stand between the matrices P0", P1" and TCP" and between the matrices P0" and P2", respectively. By eliminating the unknown matrix P0" from equation (1) using equation (2), the following equation (3) is derived. In equation (3), symbol P1".sup.-1 represents the inverse matrix of the matrix P1". In this manner, according to the conventional method, the transformation matrix TCP" is derived in accordance with equation (3).
In an actual working site, however, it is sometimes impossible to remove the tool from the tool mounting surface. In such a case, the conventional method cannot be used because it requires that the tool be removed to permit the center of the tool mounting surface to be positioned at the reference point.
Another tool center point setting method which does not require the removal of a tool is also known in the art. According to the method proposed in Japanese Patent Application No. 62-229820, for example, the operation of determining the center of the tool mounting surface while holding the distal end of the tool mounted to the tool mounting surface at the reference point is carried out with respect to at least four different orientations of the robot while the robot orientation is being changed. Then, the position of the tool center point is determined on the basis of the coordinate position of the center of a sphere passing through the at least four tool mounting surface centers thus determined.
According to this conventional method, however, in order to determine the position of the tool center point with a required accuracy, the operation of positioning the distal end of the tool at the reference point while the robot orientation is being changed must be repeatedly carried out a large number of times. This requires much labor. Moreover, the orientation of the tool cannot be determined.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method which is capable of accurately and easily setting the tool center point of a robot without the need o
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Fanuc Ltd.
Ip Paul
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