High‐order variable‐structure disturbance estimators with applications to harmonic drive systems

Abstract

This paper describes the design of a high‐order variable‐structure disturbance estimator (VSDE) that provides asymptotic estimation of unknown disturbances described by polynomial functions of time with arbitrary degrees. In comparison with conventional VSDEs, the high‐order VSDE requires only a small switching gain for ensuring the existence of a sliding mode, thus alleviating the chattering problem. Moreover, the transfer function of a high‐order VSDE from an unknown disturbance to its estimate can have a high relative degree to enable the estimation of time derivatives of an unknown disturbance while providing adequate high‐frequency attenuation. Two high‐order VSDEs were implemented to simultaneously observe the motor‐side and the load‐side disturbances in a harmonic drive system. Experimental results show that the compensation offered by the high‐order VSDEs effectively deals with the disturbances induced by harmonic drive gearing.

Key words:

• disturbance estimator
• variable‐structure systems
• sliding mode
• harmonic drive

Notes

Corresponding author. (Tel: [phone] ext. 837; Fax: [phone]; Email: [email protected])

Additional information

Notes on contributors

Yu‐Sheng Lu

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