Measuring and testing – Instrument proving or calibrating – Displacement – motion – distance – or position
Reexamination Certificate
1997-09-25
2001-03-27
Noland, Thomas P. (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Displacement, motion, distance, or position
C073S001750, C318S568160, C318S568220, C901S046000, C901S047000
Reexamination Certificate
active
06205839
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for calibration of an industrial robot.
The invention also relates to equipment for calibration of the above-mentioned robot.
BACKGROUND OF THE INVENTION
An industrial robot may be viewed as a chain consisting of stiff links. Two links are joined to each other in such a way that they are rotatable in relation to each other around an axis of rotation, or displaceable in relation to each other along a linear movement path. An industrial robot usually has six axes of rotation. The last link in the chain may consist of a tool which, depending on the field of application, may be a gripper, a glue gun or a welding gun. In the following, the links in a robot will be referred to as arms, and their lengths will be referred to as arm's lengths.
For each of the axes of rotation or linear movement paths, servo equipment with a driving motor and a position transducer is provided, the transducer delivering a signal which is a measure of the angle of rotation of the actual axis in relation to a reference position. The servo system of each axis is supplied with a reference value of the angle of rotation or linear movement of the axis, and the driving motor of the axis causes the robot to move until the axis position indicated by the position transducer of the axis corresponds to the reference value supplied to the servo system. In order for the position and orientation of the tool to correspond to the desired values, the mechanical structure of the robot and the parameters, so-called kinematic parameters, which describe it must be known with a high accuracy. Since the kinematic parameters are not exactly the same for each robot, the individual deviations from an ideal robot, that is, the kinematic error parameters of the robot, must be known if a high accuracy is to be attained.
Examples of kinematic error parameters are variations in the lengths of the arms, so-called arm's length errors, obliquities in the axes of rotation in relation to each other, so-called axis-attitude errors, and lateral displacements of the axes in relation to each other, so-called axis-offset errors. These deviations arise during manufacture of the different mechanical components and during the assembly thereof. To this it is to be added the fact that the angle indicated by the position transducer of an axis must with great accuracy correspond to the actual angle of rotation of the arm which is controlled with the aid of the axis in question, so-called synchronizing errors.
For determining the deviation of an individual robot from an ideal robot, various forms of calibration methods are used. A large number of calibration methods are known. A disadvantage with certain of these methods is that they do not manage to make a complete calibration, that is, determine both arm's length errors, axis-attitude errors, axis-offset errors, synchronizing errors, transmission errors, and deflection errors for all of the axes of the robot. A disadvantage with the known methods which do manage to make a complete calibration is that they require expensive and delicate calibration equipment, for example theodolites.
SUMMARY OF THE INVENTION
The object of the invention is to provide a calibration method which
manages to calibrate all the axes of a six-axis robot, as well as the mounting of the tool and the mounting of the robot foot,
manages to calibrate arm's length errors, axis-attitude errors, axis-offset errors, synchronizing errors, transmission errors,
does not require expensive equipment,
provides high accuracy,
can be used under active-service conditions, for example in a production line for cars,
can be used without the robot-carried tool having to be dismantled,
can be used for fully-automatic calibration, for example during final testing of robots, and
is fast and can be performed without complicated adjustments of robot positions.
The invention also aims to provide calibration equipment to be used with the above-mentioned calibration method, wherein the equipment
is inexpensive,
is robust enough to endure a workshop environment,
is portable and hence easy to transport, and
does not need to be calibrated.
The configuration of the robot is defined by the angles of the axes of rotation thereof, and one configuration distinguishes from another if at least some of the angles of axes are changed.
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patent: 4804897 (1989-02-01), Gordon et al.
patent: 4883938 (1989-11-01), Sarugaku
patent: 5151007 (1992-09-01), Maruo
patent: 5239855 (1993-08-01), Schleifer et al.
patent: 5343397 (1994-08-01), Yoshino et al.
patent: 5404086 (1995-04-01), Takenaka et al.
patent: 5448146 (1995-09-01), Erlbacher
patent: 5668453 (1997-09-01), Muto et al.
patent: 44 19 909 A1 (1997-12-01), None
patent: 69911 (1989-03-01), None
Brogardh Torgny
Snell John-Erik
Asea Brown Bovreri AB
Noland Thomas P.
Pollock Vande Sande & Amernick
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