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Variable Stiffness & Dynamic Force Sensor for Tissue Palpation

Abu Bakar Dawood, Zhenyu Zhang, Martin Angelmahr, Alberto Arezzo, Kaspar Althoefer

TL;DR

Minimally invasive surgery suffers from limited tactile feedback, hindering tissue palpation. The authors propose a soft, pneumatic-stiffness-adjustable sensor whose stiffness is tunable by pneumatic pressure and whose deformation is inferred from light reflection to estimate contact force. Force is computed by a combination of a 4th-order polynomial mapping from optical readout to displacement and Hooke's law $F = kx$. Results show stiffness increases with pressure (approximately 0 PSI: 1016 N/m, 0.5 PSI: 1134 N/m, 1 PSI: 1302 N/m) and calculated forces agree with measurements with RMSE in the order of 0.016–0.131 N and $R^2$ values from 0.949 to 0.989, indicating good accuracy at lower pressures. The work demonstrates a MIS-compatible palpation sensor with tunable force range and outlines a path toward miniaturization and data-driven force estimation.

Abstract

Palpation of human tissue during Minimally Invasive Surgery is hampered due to restricted access. In this extended abstract, we present a variable stiffness and dynamic force range sensor that has the potential to address this challenge. The sensor utilises light reflection to estimate sensor deformation, and from this, the force applied. Experimental testing at different pressures (0, 0.5 and 1 PSI) shows that stiffness and force range increases with pressure. The force calibration results when compared with measured forces produced an average RMSE of 0.016, 0.0715 and 0.1284 N respectively, for these pressures.

Variable Stiffness & Dynamic Force Sensor for Tissue Palpation

TL;DR

Minimally invasive surgery suffers from limited tactile feedback, hindering tissue palpation. The authors propose a soft, pneumatic-stiffness-adjustable sensor whose stiffness is tunable by pneumatic pressure and whose deformation is inferred from light reflection to estimate contact force. Force is computed by a combination of a 4th-order polynomial mapping from optical readout to displacement and Hooke's law . Results show stiffness increases with pressure (approximately 0 PSI: 1016 N/m, 0.5 PSI: 1134 N/m, 1 PSI: 1302 N/m) and calculated forces agree with measurements with RMSE in the order of 0.016–0.131 N and values from 0.949 to 0.989, indicating good accuracy at lower pressures. The work demonstrates a MIS-compatible palpation sensor with tunable force range and outlines a path toward miniaturization and data-driven force estimation.

Abstract

Palpation of human tissue during Minimally Invasive Surgery is hampered due to restricted access. In this extended abstract, we present a variable stiffness and dynamic force range sensor that has the potential to address this challenge. The sensor utilises light reflection to estimate sensor deformation, and from this, the force applied. Experimental testing at different pressures (0, 0.5 and 1 PSI) shows that stiffness and force range increases with pressure. The force calibration results when compared with measured forces produced an average RMSE of 0.016, 0.0715 and 0.1284 N respectively, for these pressures.

Paper Structure

This paper contains 4 sections, 4 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Materials and Methods
  3. Results
  4. Acknowledgments.

Figures (3)

  • Figure 1: Our proposed palpation sensor - a black silicone dome with an integrated plastic fibre to restrict ballooning.
  • Figure 2: The experimental setup showing a modified CNC Milling machine with an ATI Mini40, Syringe pump and Keyence.
  • Figure 3: Calculated and measured forces by force torque sensor at 0, 0.5 and 1 PSI, respectively. Error bars show the standard deviation. R-squared and RMSE between the calculated values and measured values are also shown.