Robot Geometry Calibration

Present industrial robots require careful "teaching" before pick and place operations can be performed without the use of sophisticated sensors. Teaching a robot is a time consuming and tedious task. Its hand must be manually placed in each position needed to perform a task, and various measurements recorded. The process must be repeated for each operation and each time a robot is replaced or removed for repair. Teaching is necessary because each robot is slightly different from another due to manufacturing tolerances, so that the required motions cannot be calculated accurately. Direct measurement of the parameters for each robot is not precise enough to overcome this difficulty.

A technique was developed to estimate the actual parameters of each robot. The robot then can be automatically positioned anywhere in the workspace without "teaching' it first. The calibration technique is based on measuring the position of the robot hand accurately for a number of positions and then solving for all kinematics parameters that affect positioning. This calibration is performed once for each robot and is task independent. The main contribution of this work is the development of a general algorithm that can perform this calibration for any serial manipulator. The technique was validated through simulation studies for several manipulators and was tested at JPL's Telerobotics Testbed on a PUMA 560 robot. The tests showed that using this technique a positioning error of 6 mm can be reduced to less that 2 mm. This improved accuracy reduces the need for sophisticated sensors for pick-and-place robotic tasks. This technique was used to calibrate a PUMA 200 robot to perform a computer tomographic (CT) guided stereotactic brain surgery at Long Beach Memorial Hospital in the late 1980s.

Point of Contact:
Samad Hayati
Mail Stop 198-219
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
818-354-8273
hayati@telerobotics.jpl.nasa.gov

Telerobotics Program page

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Maintained by: Dave Lavery
Last updated: May 10, 1996