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Soft Two-degree-of-freedom Dielectric Elastomer Position Sensor Exhibiting Linear Behavior

Alexandre Girard, Jean-Philippe Lucking Bigué, Benjamin M. O'Brien, Todd A. Gisby, Iain A. Anderson, Jean-Sébastien Plante

TL;DR

This work tackles the challenge of obtaining accurate end-effector position feedback for soft robots by introducing a pair of identical 2-DOF dielectric elastomer sensors that sense in-plane $x$ and $y$ displacements through a differential capacitance approach. The authors develop analytical one- and two-cell models, account for parasitic motions, and optimize the sensor geometry (e.g., $r_o=75$ mm, $r_i=20$ mm, $h_0=55$ mm) to achieve linear capacitance–displacement behavior. A handmade 2-DOF prototype demonstrates linear ΔC with displacement and, using calibration, achieves about $0.2$ mm accuracy on each DOF over a $30$ mm × $30$ mm range, corresponding to roughly $0.7 ext{%}$ error per DOF; a single sensor’s capacitance noise of ~10 pF translates to ~0.14 mm displacement uncertainty. The results showcase dielectric elastomer sensors as low-cost, soft, embedded multi-DOF position sensors with strong potential for MRI-guided soft robotics, and point to further improvements via silicone films, single-layer designs, increased pre-stretch, and multi-layer electrodes to boost bandwidth and sensitivity.

Abstract

Soft robots could bring robotic systems to new horizons, by enabling safe human-machine interaction. For precise control, these soft structures require high level position feedback that is not easily achieved through conventional one-degree-of-freedom (DOF) sensing apparatus. In this paper, a soft two-DOF dielectric elastomer (DE) sensor is specifically designed to provide accurate position feedback for a soft polymer robotic manipulator. The technology is exemplified on a soft robot intended for MRI-guided prostate interventions. DEs are chosen for their major advantages of softness, high strains, low cost and embedded multiple-DOF sensing capability, providing excellent system integration. A geometrical model of the proposed DE sensor is developed and compared to experimental results in order to understand sensor mechanics. Using a differential measurement approach, a handmade prototype provided linear sensory behavior and 0.2 mm accuracy on two-DOF. This correlates to a 0.7\% error over the sensor's 30 mm x 30 mm planar range, demonstrating the outstanding potential of DE technology for accurate multi-DOF position sensing.

Soft Two-degree-of-freedom Dielectric Elastomer Position Sensor Exhibiting Linear Behavior

TL;DR

This work tackles the challenge of obtaining accurate end-effector position feedback for soft robots by introducing a pair of identical 2-DOF dielectric elastomer sensors that sense in-plane and displacements through a differential capacitance approach. The authors develop analytical one- and two-cell models, account for parasitic motions, and optimize the sensor geometry (e.g., mm, mm, mm) to achieve linear capacitance–displacement behavior. A handmade 2-DOF prototype demonstrates linear ΔC with displacement and, using calibration, achieves about mm accuracy on each DOF over a mm × mm range, corresponding to roughly error per DOF; a single sensor’s capacitance noise of ~10 pF translates to ~0.14 mm displacement uncertainty. The results showcase dielectric elastomer sensors as low-cost, soft, embedded multi-DOF position sensors with strong potential for MRI-guided soft robotics, and point to further improvements via silicone films, single-layer designs, increased pre-stretch, and multi-layer electrodes to boost bandwidth and sensitivity.

Abstract

Soft robots could bring robotic systems to new horizons, by enabling safe human-machine interaction. For precise control, these soft structures require high level position feedback that is not easily achieved through conventional one-degree-of-freedom (DOF) sensing apparatus. In this paper, a soft two-DOF dielectric elastomer (DE) sensor is specifically designed to provide accurate position feedback for a soft polymer robotic manipulator. The technology is exemplified on a soft robot intended for MRI-guided prostate interventions. DEs are chosen for their major advantages of softness, high strains, low cost and embedded multiple-DOF sensing capability, providing excellent system integration. A geometrical model of the proposed DE sensor is developed and compared to experimental results in order to understand sensor mechanics. Using a differential measurement approach, a handmade prototype provided linear sensory behavior and 0.2 mm accuracy on two-DOF. This correlates to a 0.7\% error over the sensor's 30 mm x 30 mm planar range, demonstrating the outstanding potential of DE technology for accurate multi-DOF position sensing.
Paper Structure (20 sections, 20 equations, 21 figures, 3 tables)

This paper contains 20 sections, 20 equations, 21 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Background
  3. Approach and Results
  4. Design and modeling
  5. Robotic System
  6. Sensor Requirement
  7. Proposed Design
  8. Analysis
  9. One-cell Model
  10. Two-cell Model
  11. Parasitic Motion
  12. Geometrical Design
  13. Experiments
  14. Setup
  15. Protocol
  16. ...and 5 more sections

Figures (21)

  • Figure 1: Rigid robotics (a) vs. soft robotics (b)
  • Figure 2: DEs are flexible capacitors
  • Figure 3: Soft robot for MRI-guided interventions miron_design_2013
  • Figure 4: Robot six degrees-of-freedom. On top, translations and rotations of the needle guide, about the $x$ and $y$ axis, controlled by muscles inflations (active DOF). Below, translation and rotation, about the $z$ axis, which may be caused by external forces (passive DOF).
  • Figure 5: Four DOF sensing solution with two planar sensors
  • ...and 16 more figures