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Application of Laser Feedback Metrology to a Hexapod Test Strut



M Schmidt-Lange, E Amatucci, Albert J. Wavering


A laser position feedback system has been designed to improve the accuracy of strut positioning for the prototype Ingersoll2 Octahedral Hexapod machine installed at National Institute of Standards and Technology (NIST) (Figure 1). Strut laser feedback metrology experiments are conducted on a test strut, which duplicates one of the Hexapod's struts but is positioned in a test stand. The Octahedral Hexapod machine is based on a Stewart platform [Ref. 1], with 6 ballscrew-driven struts that support and move a cutting spindle. The position and orientation of the spindle are determined by the lengths of the struts, which extend from 2150 mm to 3600 mm. For Hexapod machines; accurate, strut-length metrology is essential to achieving the accurate spindle platform motions necessary to take advantage of the Hexapod's speed and stiffness for various machining applications. Currently, a rotational resolver on the back of each direct drive motor is used for position feedback to the machine's controller. This configuration has significant disadvantages in measuring strut length due partly to leadscrew errors, backlash errors, friction in the spherical joints, and especially thermal errors. Therefore, there is ¿a need for closed-loop thermally invariant metrology that addresses the length of the total strut¿. [Ref. 2] Direct measurement of the strut length using laser interferometry seems a promising approach to significantly increase the accuracy of the machine. The goal of this project is to develop a laser strut length metrology system that is accurate to within 5 ¿m. In the Conclusions, we discuss other metrology techniques under investigation.
Proceedings Title
Proceedings of the 1998 ASPE Annual Meeting
Conference Dates
October 25-30, 1998
Conference Location
St. Louis, MO, US
Conference Title
1998 ASPE Annual Meeting


Metrology, Robotics & Intelligent Systems, Control, hexapod, interferometry, laser, metrology, position feedback, lateral transfer hollow


Schmidt-Lange, M. , Amatucci, E. and Wavering, A. (1998), Application of Laser Feedback Metrology to a Hexapod Test Strut, Proceedings of the 1998 ASPE Annual Meeting, St. Louis, MO, US, [online], (Accessed March 1, 2024)
Created September 30, 1998, Updated October 12, 2021