Assessing the usability of remote control servos for admittance-controlled haptic finger manipulators

Conference paper (2016)

Authors

H. A. Den Dekker University of Twente
N. W.M. Beckers University of Twente
Arvid Q.L. Keemink University of Twente
H. van der Kooij University of Twente, OLD Biorobotics
Arno H A Stienen University of Twente, Northwestern University
Research Group
Biomechatronics & Human-Machine Control (Mechanical, Maritime and Materials Engineering) (TU Delft)
Stability analysis Damping Admittance Bandwidth Torque Manipulators Servomotors
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Published Date

2016

Language

English

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Faculty

Mechanical, Maritime and Materials Engineering

Department

Biomechanical Engineering

Research Group

Biomechatronics & Human-Machine Control

Abstract

Robotic devices that are able to manipulate the fingers can support the study of robot-Assisted motor learning. Currently no devices are available that provide a transparent haptic environment and provide a platform to study motor learning. To cut down on costs it is proposed to use remote control (RC) servos with admittance control. In this study five RC servos are tested to evaluate their controller and passive dynamic properties. Frequency and step response are evaluated and passive dynamics are estimated using a model fit. With a fitted frequency response, system stability is evaluated for different human impedances. The high speed servos have lowest passive inertia (2 à 10-4 kgm2) and highest bandwidth (20 Hz). The communication protocol of RC servos causes a delay of more than 5 ms from change in setpoint to change in output. Stability analysis shows that the high speed servos have largest stability regions. Simulations show that reducing the virtual inertia and damping makes the system more susceptible to unstable behavior. At this moment however the passive dynamics of the setup are more transparent than the virtual inertia (1 · 10-3 kgm2) and damping that can be simulated with an admittance controller. A possible cause lies with the communication delay and high gearing present in RC servos.