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A Novel 6-axis Force/Torque Sensor Using Inductance Sensors

Hyun-Bin Kim, Kyung-Soo Kim

TL;DR

The study introduces a novel six-axis force/torque sensor that uses inductance variation for non-contact sensing, enabling a compact, PCB-based architecture with onboard CAN-FD processing and up to ~4 kHz data throughput. By modeling the coil-target system as an LC resonator and calibrating with a rational-function fit, the sensor achieves high accuracy (RMSE ≈ $9\times10^{-4}$, $R^2=1.000$) and low linearity error (~$0.11\%$). Static tests show maximum errors around 0.64–0.75% full scale, with resolutions as fine as ~0.035 N for forces and ~1.6 mN·m for torques, and quantization levels exceeding 55k steps. The work demonstrates robust, low-noise performance with minimal crosstalk and highlights its potential for precision robotics requiring compact, non-contact sensing and integrated processing; future work includes coil optimization and environmental shielding to further enhance reliability.

Abstract

This paper presents a novel six-axis force/torque (F/T) sensor based on inductive sensing technology. Unlike conventional strain gauge-based sensors that require direct contact and external amplification, the proposed sensor utilizes non-contact inductive measurements to estimate force via displacement of a conductive target. A compact, fully integrated architecture is achieved by incorporating a CAN-FD based signal processing module directly onto the PCB, enabling high-speed data acquisition at up to 4~kHz without external DAQ systems. The sensing mechanism is modeled and calibrated through a rational function fitting approach, which demonstrated superior performance in terms of root mean square error (RMSE), coefficient of determination ($R^2$), and linearity error compared to other nonlinear models. Static and repeatability experiments validate the sensor's accuracy, achieving a resolution of 0.03~N and quantization levels exceeding 55,000 steps, surpassing that of commercial sensors. The sensor also exhibits low crosstalk, high sensitivity, and robust noise characteristics. Its performance and structure make it suitable for precision robotic applications, especially in scenarios where compactness, non-contact operation, and integrated processing are essential.

A Novel 6-axis Force/Torque Sensor Using Inductance Sensors

TL;DR

The study introduces a novel six-axis force/torque sensor that uses inductance variation for non-contact sensing, enabling a compact, PCB-based architecture with onboard CAN-FD processing and up to ~4 kHz data throughput. By modeling the coil-target system as an LC resonator and calibrating with a rational-function fit, the sensor achieves high accuracy (RMSE ≈ , ) and low linearity error (~). Static tests show maximum errors around 0.64–0.75% full scale, with resolutions as fine as ~0.035 N for forces and ~1.6 mN·m for torques, and quantization levels exceeding 55k steps. The work demonstrates robust, low-noise performance with minimal crosstalk and highlights its potential for precision robotics requiring compact, non-contact sensing and integrated processing; future work includes coil optimization and environmental shielding to further enhance reliability.

Abstract

This paper presents a novel six-axis force/torque (F/T) sensor based on inductive sensing technology. Unlike conventional strain gauge-based sensors that require direct contact and external amplification, the proposed sensor utilizes non-contact inductive measurements to estimate force via displacement of a conductive target. A compact, fully integrated architecture is achieved by incorporating a CAN-FD based signal processing module directly onto the PCB, enabling high-speed data acquisition at up to 4~kHz without external DAQ systems. The sensing mechanism is modeled and calibrated through a rational function fitting approach, which demonstrated superior performance in terms of root mean square error (RMSE), coefficient of determination (), and linearity error compared to other nonlinear models. Static and repeatability experiments validate the sensor's accuracy, achieving a resolution of 0.03~N and quantization levels exceeding 55,000 steps, surpassing that of commercial sensors. The sensor also exhibits low crosstalk, high sensitivity, and robust noise characteristics. Its performance and structure make it suitable for precision robotic applications, especially in scenarios where compactness, non-contact operation, and integrated processing are essential.
Paper Structure (10 sections, 14 equations, 8 figures, 8 tables)

This paper contains 10 sections, 14 equations, 8 figures, 8 tables.

Table of Contents

  1. Introduction
  2. Contribution
  3. Design of the Proposed Sensor
  4. Principle of the Proposed Sensor
  5. Elastomer and Printed Circuit Board Design
  6. Sensor Fabrication
  7. Sensor Evaluation
  8. Calibration
  9. Evaluation
  10. Discussion and Conclusion

Figures (8)

  • Figure 1: Principle of the proposed sensor (a). Inductance-to-digital converter with conductive target (b). Relative Inductance versus distance between coil and conductive target
  • Figure 2: Elastomer and printed circuit board design (a) Elastomer and T-beam structure (b) Sensing PCB with vertical sensing coil and horizontal sensing coil (c) Signal processing PCB design
  • Figure 3: Calculated graph of coils' inductance and conductive target distance (a) Horizontal coil (b) Vertical coil
  • Figure 4: Components of the proposed sensor; Five metallic components: Top part, elastomer, metal plate, support part and bottom part, two PCB components: Sensing PCB and Signal Processing PCB.
  • Figure 5: Calibration method with direct connecting along the $z$-axis with connection jig; F/T applied via handle for calibration.
  • ...and 3 more figures