University of Twente Student Theses


Researching the effects of time-delay on admittance control

Euving, E.J. (2013) Researching the effects of time-delay on admittance control.

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Abstract:This research was done for haptic robots used in rehabilitation of stroke victims. The goal for these haptic robots is have the least possible impedance, commonly called zero impedance. Users should experience the lowest possible hindrance from the robot, which in practice means that the robot should have a low sensation (virtual) mass. Admittance Control is used to achieve this goal. When the goal is pursued problems are met in the form of system instability. There are two recognized situations where instability occurs: when the robots are free- oating and when they are in contact with a constraining environment. Many variables affect system stability. A goal of designers of haptic robots is to have enough knowledge about Admittance Control that a robot can be designed and any stability problems can be predicted in the design phase. This research focussed on one of these variables: pure time-delay in the controller of Admittance Control. The effects of time-delay on stability in both free- oating as constrained environment were examined and the possibility of using a Smith predictor as a solution was explored. This was researched using analytical and numerical models for both environments as well as experiments on a haptic robot set-up for a constrained environment. The results showed that time-delay decreases stability for free- oating environments and constrained environments, even at low values. A Smith predictor greatly negates the effects of time-delay and improves Admittance Control in constrained environment, but descreases haptic quality and stability in free- oating environments. Models and experiments are in agreement, suggesting that predictive models that capture the dominant effects can be used in the design phase of haptic robots.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering BSc (56966)
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