Servomechanism fault detection based on load torque observer and discrete wavelet transform

Chung-Wei Cheng*, Wen Peng Tseng, Mi Ching Tsai

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Most existing techniques which employ DWT (discrete wavelet transform) to detect servomechanism fault events are based on the analysis of measured motor current signals. However, the outcomes of these techniques tend to be unreliable when the motor suddenly accelerates or generates a very high output torque. Accordingly, to reduce the occurrence of false alarms, this paper develops a fault detection procedure based on the PICTO (PI-type closed-loop torque observer) structure and the DWT method. The PICTO structure is used to estimate the external load torque exerted on the servomechanisms. Utilizing the estimated data obtained from PICTO, a fault detection procedure is proposed which computes a "fault index" using DWT coefficients. This fault index enables the exact degree of the fault to be determined. The experimental results verify the effectiveness of the proposed fault detection approach.

Original languageEnglish
Pages (from-to)418-425
Number of pages8
JournalJSME International Journal, Series C: Mechanical Systems, Machine Elements and Manufacturing
Issue number2
StatePublished - 15 Dec 2006


  • Discrete wavelet transform
  • Fault detection
  • Load torque observer

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