Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

A Feasibility Study of a Soft, Low-Cost, 6-Axis Load Cell for Haptics

Madison Veliky, Garrison L. H. Johnston, Ahmet Yildiz, Nabil Simaan

TL;DR

This study tackles the high cost barrier of 6-axis force/torque sensing for laparoscopic haptics by designing a soft, Hall-effect–based sensor that embeds magnets in silicone and uses an eight-sensor array to recover 6-DOF wrench measurements. The approach combines pose estimation of a deflecting center piece via Arun's method, extraction of a deflection twist, a linear b-field-to-twist mapping, and a stiffness-based force model to estimate wrenches, with calibration over 193 poses yielding a stiffness matrix $\mathbf{K}$ and a mapping $\mathbf{A}$, and validation achieving an RMS force error of $0.45\,\text{N}$ and a torque error of $0.014\,\text{Nm}$. The sensor costs approximately $32.74$ per unit, supports $\pm 50$ N lateral and $\pm 20$ N axial force ranges with $\pm 0.2$ Nm torque, and operates at roughly $100$ Hz, enabling practical haptic feedback in training devices. This feasibility work demonstrates that affordable, low-complexity F/T sensing is viable for soft-tissue surgical training, while acknowledging that non-linear magnetic-field/distortion effects and material hysteresis require future modeling for higher accuracy and broader deployment.

Abstract

Haptic devices have shown to be valuable in supplementing surgical training, especially when providing haptic feedback based on user performance metrics such as wrench applied by the user on the tool. However, current 6-axis force/torque sensors are prohibitively expensive. This paper presents the design and calibration of a low-cost, six-axis force/torque sensor specially designed for laparoscopic haptic training applications. The proposed design uses Hall-effect sensors to measure the change in the position of magnets embedded in a silicone layer that results from an applied wrench to the device. Preliminary experimental validation demonstrates that these sensors can achieve an accuracy of 0.45 N and 0.014 Nm, and a theoretical XY range of +/-50N, Z range of +/-20N, and torque range of +/-0.2Nm. This study indicates that the proposed low-cost 6-axis force/torque sensor can accurately measure user force and provide useful feedback during laparoscopic training on a haptic device.

A Feasibility Study of a Soft, Low-Cost, 6-Axis Load Cell for Haptics

TL;DR

This study tackles the high cost barrier of 6-axis force/torque sensing for laparoscopic haptics by designing a soft, Hall-effect–based sensor that embeds magnets in silicone and uses an eight-sensor array to recover 6-DOF wrench measurements. The approach combines pose estimation of a deflecting center piece via Arun's method, extraction of a deflection twist, a linear b-field-to-twist mapping, and a stiffness-based force model to estimate wrenches, with calibration over 193 poses yielding a stiffness matrix and a mapping , and validation achieving an RMS force error of and a torque error of . The sensor costs approximately per unit, supports N lateral and N axial force ranges with Nm torque, and operates at roughly Hz, enabling practical haptic feedback in training devices. This feasibility work demonstrates that affordable, low-complexity F/T sensing is viable for soft-tissue surgical training, while acknowledging that non-linear magnetic-field/distortion effects and material hysteresis require future modeling for higher accuracy and broader deployment.

Abstract

Haptic devices have shown to be valuable in supplementing surgical training, especially when providing haptic feedback based on user performance metrics such as wrench applied by the user on the tool. However, current 6-axis force/torque sensors are prohibitively expensive. This paper presents the design and calibration of a low-cost, six-axis force/torque sensor specially designed for laparoscopic haptic training applications. The proposed design uses Hall-effect sensors to measure the change in the position of magnets embedded in a silicone layer that results from an applied wrench to the device. Preliminary experimental validation demonstrates that these sensors can achieve an accuracy of 0.45 N and 0.014 Nm, and a theoretical XY range of +/-50N, Z range of +/-20N, and torque range of +/-0.2Nm. This study indicates that the proposed low-cost 6-axis force/torque sensor can accurately measure user force and provide useful feedback during laparoscopic training on a haptic device.
Paper Structure (18 sections, 26 equations, 8 figures, 2 tables)

This paper contains 18 sections, 26 equations, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Sensor Design
  3. Sensing Mechanism
  4. Mechanical Design
  5. Electrical Design
  6. Chip Configuration
  7. Force Estimation
  8. Center Piece Pose Estimation
  9. Deflection Twist
  10. Linear Estimation of Deflection Twists
  11. Force Sensing
  12. Sensitivity and Error Analysis
  13. Experiments
  14. Position Mapping
  15. Calibration
  16. ...and 3 more sections

Figures (8)

  • Figure 1: Integration of the proposed force sensor with a laparoscopic tool and haptic device.
  • Figure 2: (a) Picture of the assembled force/torque sensor. (b) Picture of the sensor with the top cover and top silicone layer removed. (c) Exploded view of sensor: top outer shell, silicone layer, MLX90393 Magnetometer, K&J Magnetics D101- N52 magnet, center piece, bottom outer shell.
  • Figure 3: Frame assignments for the nominal center frame {0}, the deformed center frame {C}, the sensor frames {$S_i$}, and the magnet frames {$M_i$}. See Multimedia Extension 1 for a visualization of how the center piece deforms under a load.
  • Figure 4: I2C wiring diagram. There exist 16 unique I2C addresses for the MLX90393 magnetometer which allows up to two F/T sensors on the same I2C bus.
  • Figure 5: Setup for sensitivity experiments
  • ...and 3 more figures