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Impedance control of a cable-driven SEA with mixed H2/H synthesis

Ningbo Yu (Institute of Robotics and Automatic Information Systems, Nankai University, Tianjin, China and Tianjin Key Laboratory of Intelligent Robotics, Nankai University, Tianjin, China)
Wulin Zou (Institute of Robotics and Automatic Information Systems, Nankai University, Tianjin, China and Tianjin Key Laboratory of Intelligent Robotics, Nankai University, Tianjin, China)

Assembly Automation

ISSN: 0144-5154

Article publication date: 7 August 2017

Abstract

Purpose

This paper aims to present an impedance control method with mixed H2/H synthesis and relaxed passivity for a cable-driven series elastic actuator to be applied for physical human–robot interaction.

Design/methodology/approach

To shape the system’s impedance to match a desired dynamic model, the impedance control problem was reformulated into an impedance matching structure. The desired competing performance requirements as well as constraints from the physical system can be characterized with weighting functions for respective signals. Considering the frequency properties of human movements, the passivity constraint for stable human–robot interaction, which is required on the entire frequency spectrum and may bring conservative solutions, has been relaxed in such a way that it only restrains the low frequency band. Thus, impedance control became a mixed H2/H synthesis problem, and a dynamic output feedback controller can be obtained.

Findings

The proposed impedance control strategy has been tested for various desired impedance with both simulation and experiments on the cable-driven series elastic actuator platform. The actual interaction torque tracked well the desired torque within the desired norm bounds, and the control input was regulated below the motor velocity limit. The closed loop system can guarantee relaxed passivity at low frequency. Both simulation and experimental results have validated the feasibility and efficacy of the proposed method.

Originality/value

This impedance control strategy with mixed H2/H synthesis and relaxed passivity provides a novel, effective and less conservative method for physical human–robot interaction control.

Keywords

Acknowledgements

The authors would like to thank the responsible reviewers and editors for the careful review of the paper and the constructive comments, which have been of great help to improve the quality of the paper. This work was supported by the National Natural Science Foundation of China (61403215), the Natural Science Foundation of Tianjin (13JCYBJC36600) and the Fundamental Research Funds for the Central Universities.

Citation

Yu, N. and Zou, W. (2017), "Impedance control of a cable-driven SEA with mixed H2/H synthesis", Assembly Automation, Vol. 37 No. 3, pp. 296-303. https://doi.org/10.1108/AA-11-2016-150

Publisher

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Emerald Publishing Limited

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