Stability and robustness of disturbance-observer-based motion control systems

Emre Sariyildiz, Kouhei Ohnishi

Research output: Contribution to journalArticlepeer-review

254 Citations (Scopus)


This paper analyzes the robustness and stability of a disturbance observer (DOB) and a reaction torque observer (RTOB)-based robust motion control systems. Conventionally, a DOB is analyzed by using an ideal velocity measurement that is obtained without using a low-pass filter (LPF); however, it is impractical due to noise constraints. An LPF of velocity measurement changes the robustness of a DOB significantly and puts a new design constraint on the bandwidth of a DOB. An RTOB, which is used to estimate environmental impedance, is an application of a DOB. The stability of an RTOB-based robust force control system has not been reported yet since its oversimplified model is derived by assuming that an RTOB has a feedforward control structure. However, in reality, it has a feedback control structure; therefore, not only the performance but also the stability is affected by the design parameters of an RTOB. A new practical stability analysis method is proposed for an RTOB-based robust force control system. In addition to that, novel and practical design methods, which improve the robustness of a DOB and the stability and performance of an RTOB-based robust force control system, are proposed by using the new analysis methods. The validity of the proposals is verified by simulation and experimental results.

Original languageEnglish
Article number6822593
Pages (from-to)414-422
Number of pages9
JournalIEEE Transactions on Industrial Electronics
Issue number1
Publication statusPublished - 2015 Jan 1
Externally publishedYes


  • Disturbance observer (DOB)
  • motion control systems
  • reaction torque observer (RTOB)
  • robustness and stability

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Electrical and Electronic Engineering


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