A Novel Means of Software Compensation for Robots and Machine Tools

Document Number: 2006-01-3167

Date Published: September 2006

Author(s):
Philip L. Freeman - Boeing Co.

Abstract:
Current methods of machine calibration and software compensation focus on either the joint motion errors (classic machine tool software compensation) or the geometric errors between the joints (robot calibration). However, both types of errors have a significant impact on the volumetric accuracy of a machine tool or robot. We have developed a calibration method that simultaneously identifies joint motion errors and geometric errors in a machine or robot with an arbitrary number and arrangement of links using a laser tracker. The simultaneous identification of all error sources decreases measurement time, with a typical calibration for a moderate-sized machine taking about four hours and 200-500 measurements.

The model presented is based on a mathematically minimal parametric model of the machine. Parameter identification is done in a statistically significant way, resulting in both the "best-fit" values for the parameters and the statistical confidence in those values. The results provide a very accurate assessment of the volumetric accuracy of the machine. Compensation is done through a simple, rapidly converging, iterative algorithm that is being implemented real time in the Siemens 840D controller. This paper covers the development of the model, identification of the parameters, and implementation of the software compensation scheme. Examples are given of implementation including: a high-speed, five-axis machine tool and a low-cost, five-axis drilling system. Both machines showed significant improvements to accuracy (approximately 80%) after software compensation, with volumetric accuracy approaching machine repeatability.

File Size: 453K
Product Status: In Stock

See other papers presented at Aerospace Manufacturing and Automated Fastening Conference and Exhibition, September 2006, Toulouse, FRANC, Session: Advanced Forming, Machining and Modeling Part 1 of 2

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