Technical Briefs

Disturbance-Observer-Based Force Estimation for Haptic Feedback

[+] Author and Article Information
Abhishek Gupta

Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur, WB 721302 Indiaabhi@mech.iitkgp.ernet.in

Marcia K. O’Malley1

Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005omalleym@rice.edu


Corresponding author.

J. Dyn. Sys., Meas., Control 133(1), 014505 (Dec 02, 2010) (4 pages) doi:10.1115/1.4001274 History: Received November 17, 2008; Revised November 03, 2009; Published December 02, 2010; Online December 02, 2010

In this paper, we propose the use of a nonlinear disturbance-observer for estimation of contact forces during haptic interactions. Most commonly used impedance-type haptic interfaces employ open-loop force control under the assumption of pseudostatic interactions. Advanced force control in such interfaces can increase simulation fidelity through improvement of the transparency of the device. However, closed-loop force feedback is limited both due to the bandwidth limitations of force sensing and the associated cost of force sensors required for its implementation. Using a disturbance-observer, we estimate contact forces at the tool tip, then use these estimates for closed-loop control of the haptic interface. Simulation and experimental results, utilizing a custom single degree-of-freedom haptic interface, are presented to demonstrate the efficacy of the proposed disturbance-observer (DO)-based control approach. This approach circumvents the traditional drawbacks of force sensing while exhibiting the advantages of closed-loop force control in haptic devices. Results show that the proposed disturbance-observer can reliably estimate contact forces at the human-robot interface. The DO-based control approach is experimentally shown to improve haptic interface fidelity over a purely open-loop display while maintaining stable and vibration-free interactions between the human user and virtual environment.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Single degree-of-freedom haptic interface

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Figure 2

Measured (dashed) and estimated (solid) contact forces during free space interaction

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Figure 3

Measured (dashed) and estimated (solid) contact forces during virtual wall interaction (K=800 N/m)

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Figure 4

Transparency bandwidth for (a) open-loop, (b) closed-loop, and (c) disturbance-observer based controllers (wall stiffness=800 N/m)



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