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An approach for combining transparency and motion assistance of a lower body exoskeleton

Jakob Ziegler, Bernhard Rameder, Hubert Gattringer, Andreas Mueller

TL;DR

The paper tackles robust gait assistance with a lower-limb exoskeleton by integrating a transparent operating mode and an adaptive-oscillator–driven motion-assistance mode. Transparency is achieved economically by exploiting actuator gear backlash, minimizing perceived interaction forces without extra sensors. Adaptive oscillators learn the quasi-periodic nature of gait to estimate future joint positions and generate a corresponding assistive torque, which is gated to ensure safety and robustness. Experimental results on a prototype with level-ground walking show promising, early evidence for smooth transition between stand and walk and for the feasibility of combining transparency with assistance, with future work aimed at objective performance metrics and more complex locomotion tasks.

Abstract

In this paper, an approach for gait assistance with a lower body exoskeleton is described. Two concepts, transparency and motion assistance, are combined. The transparent mode, where the system is following the user's free motion with a minimum of perceived interaction forces, is realized by exploiting the gear backlash of the actuation units. During walking a superimposed assistance mode applies an additional torque guiding the legs to their estimated future position. The concept of adaptive oscillators is utilized to learn the quasi-periodic signals typical for locomotion. First experiments showed promising results.

An approach for combining transparency and motion assistance of a lower body exoskeleton

TL;DR

The paper tackles robust gait assistance with a lower-limb exoskeleton by integrating a transparent operating mode and an adaptive-oscillator–driven motion-assistance mode. Transparency is achieved economically by exploiting actuator gear backlash, minimizing perceived interaction forces without extra sensors. Adaptive oscillators learn the quasi-periodic nature of gait to estimate future joint positions and generate a corresponding assistive torque, which is gated to ensure safety and robustness. Experimental results on a prototype with level-ground walking show promising, early evidence for smooth transition between stand and walk and for the feasibility of combining transparency with assistance, with future work aimed at objective performance metrics and more complex locomotion tasks.

Abstract

In this paper, an approach for gait assistance with a lower body exoskeleton is described. Two concepts, transparency and motion assistance, are combined. The transparent mode, where the system is following the user's free motion with a minimum of perceived interaction forces, is realized by exploiting the gear backlash of the actuation units. During walking a superimposed assistance mode applies an additional torque guiding the legs to their estimated future position. The concept of adaptive oscillators is utilized to learn the quasi-periodic signals typical for locomotion. First experiments showed promising results.

Paper Structure

This paper contains 8 sections, 6 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Setup
  3. Transparency
  4. Motion assistance
  5. Learning of periodic signals
  6. Assistive torque
  7. Experimental Results
  8. Conclusion

Figures (3)

  • Figure 1: Current setup of the exoskeleton and show-case of transparency mode
  • Figure 2: Adaption process with measured (solid) and estimated (dashed) signals on the top and torques according to calculated assistance (solid) and transparency (dashed) on the bottom (activated assistance dotted)
  • Figure 3: Adaption of the angular frequency (top) and the coefficients (bottom)