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Stability and Performance Analysis of Human-Machine Interaction in Haptic Systems

Tajaddodianfar, Farid | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40365 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Ahmadian, Mohammad Taghi; Vossoughi, Gholamreza
  7. Abstract:
  8. Transparency is a measure of performance in haptic devices. In order to improve transparency and reduce the difference between the impedance transmitted to the user and the target impedance it is necessary to compensate for the dynamics of the haptic device. Due to stability reasons improvement of transparency is limited. Passivity as a stability criterion has been used widely in design and analysis of haptic devices. Since passivity is a conservative criterion, it acts as an obstacle in improving transparency of the haptic interfaces. In this project instead of passivity, robust stability of the interaction is studied in the presence of parametric uncertainties due to variations in user hand dynamics. Three design methods are implemented and their performance and stability are evaluated. The first strategy is based on H-infinity controller synthesis technique applied to a generalized control plant which involves the target impedance as a performance weighting function. Human hand dynamics is not present in the controller synthesis stage, because it does not affect the robot impedance and consequently has no effect on performance. The obtained results depend on the weighting function parameters. In the second approach a controller is designed based on the inverse model of the device. The advantage of the latter method is that it can reduce the device impedance in a wide frequency range and results in non-passive robot impedance which is much more transparent than the impedances obtained by passivity based methods. Simulation results confirm the effectiveness of the proposed methods. The third approach, proposes an algorithm which guarantees transparency of the haptic device in a stable manner. Assuming that the dynamics of the device is known, a certain compensatory structure is assigned. This special structure guarantees transparency of the device by compensating for dynamics of the device and its control loop. The design objective is to obtain a stabilizing controller which achieves robust interaction stability in the presence of parametric uncertainties of user hand dynamics and other sources of uncertainties. An iterative method is implemented, in conjunction with the D-K iteration algorithm, to derive controller dynamics. The algorithm is applied to a series elastic actuator based haptic device. This results in a widened frequency range of transparent impedance emulation. Simulation results confirm enhanced transparency and robust stability.
  9. Keywords:
  10. Haptic System ; Stability ; Robust Control ; Impedance Control ; Transparency

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