Frequency scanning interferometry for accurate robot position measurement

Isa, Mohammed A; Khanesar, Mojtaba A; Leach, Richard; Branson, David; Piano, Samanta

Abstract

This paper presents a frequency scanning interferometry (FSI) shortwave infrared (IR) setup developed for position and orientation measurement of industrial robots. Within contemporary and future industrial frameworks, robots—in particular collaborative robots (cobots)—will play an important role in ensuring safe and coherent automation of manufacturing processes. Robots are generally regarded as a means to improve performance and reduce production costs through improved production efficiency, versatility and adaptability. However, due to high flexibility and compliance imposed for safety reasons, exact coordinate positions of robots during operation can vary significantly from desired positions. Systematic positioning errors are further exacerbated by backlash from wear and tear in motors and motion joints. Accurate measurement feedback is therefore required to satisfy performance requirements in high-accuracy applications. Common state-of-the-art solutions for high-accuracy applications involve the use of either costly laser tracking systems or less accurate photogrammetric systems. FSI can provide an alternative metrological solution for the measurement of position feedback for robots. Unlike conventional interferometry that measures relative displacements, FSI can be used for absolute distance measurement eliminating the need for continuous displacement of targets from reference positions during measurements. An optical fibre FSI setup has been developed to address requirements needed for measurement of robotic end-effector position and orientation. Some of the requirements considered include pose measurements, wide measurement field of view, sensitivity to moving targets and identification of multiple targets when displaced. Absolute distances of reflective targets mounted on the end-effector of a UR5 robot can be measured using frequency analysis of the interference intensity resulting from the interaction of frequency tuned IR light and the reflections of the light from the targets. Reflected light from each target interferes with a beat frequency that corresponds to the target distance. After target distances are determined from the beat frequencies, methods of determining robotic coordinate positions are investigated. Preliminary results indicate that real-time calibration of swept frequency using gas cell and frequency analysis of interference data are promising for robotic FSI position measurement. Future work will integrate the suitable elements of the FSI measurement systems for robotic tracking and comparative uncertainty analysis.

Citation

Isa, M. A., Khanesar, M. A., Leach, R., Branson, D., & Piano, S. (2022, May). Frequency scanning interferometry for accurate robot position measurement. Presented at 22nd International Conference & Exhibition, Geneva, Switzerland

• Presentation Conference Type: Edited Proceedings
• Conference Name: 22nd International Conference & Exhibition
• Start Date: May 30, 2022
• End Date: Jun 3, 2022
• Acceptance Date: Mar 18, 2022
• Online Publication Date: May 30, 2022
• Publication Date: May 30, 2022
• Deposit Date: Jun 8, 2022
• Publicly Available Date: Jun 20, 2022
• Series Title: euspen’s international conference and exhibition
• Book Title: Proceedings of 22nd International Conference & Exhibition
• Keywords: Frequency scanning interferometry; position measurement; uncertainty
• Public URL: https://nottingham-repository.worktribe.com/output/8394145
• Publisher URL: https://www.euspen.eu/euspen-knowledge-base/proceedings-search/#!/resource_title=accurate%20robot%20position%20measurement
• Related Public URLs: https://www.euspen.eu/euspen-knowledge-base/proceedings/#