CoinFT: A Coin-Sized, Capacitive 6-Axis Force Torque Sensor for Robotic Applications

2025-03-25

AI Summary

To address the urgent need for miniaturized, lightweight, low-cost, and robust six-axis force/torque sensors in UAVs, robotic end-effectors, and wearable haptics, this paper introduces CoinFT—a coin-sized capacitive sensor. Our method employs a dual-layer rigid PCB stack integrated with a silicone micropillar array, combined with grouped-electrode scanning and time-division multiplexed readout to achieve high-sensitivity, fully decoupled six-degree-of-freedom measurement within an ultra-compact footprint. The design is fully open-source, covering hardware schematics, firmware, and fabrication protocols. Experimental evaluation demonstrates a force RMSE of 0.11 N (0–10 N range) and torque RMSE of 0.84 mN·m (corresponding to 0–4 N shear forces). CoinFT successfully enables closed-loop, pose-dependent fine contact force control on a UAV platform. This work establishes a high-performance, scalable sensing paradigm for contact-intensive robotic systems.

Technology Category

• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Machine Learning: Hardware-aware ML
• Computer Vision: Vision for Robotics & Autonomous Driving

Application Category

• Security and Privacy: Large-scale security measurements
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization

Abstract

We introduce CoinFT, a capacitive 6-axis force/torque (F/T) sensor that is compact, light, low-cost, and robust with an average mean-squared error of 0.11N for force and 0.84mNm for moment when the input ranges from 0~10N and 0~4N in normal and shear directions, respectively. CoinFT is a stack of two rigid PCBs with comb-shaped electrodes connected by an array of silicone rubber pillars. The microcontroller interrogates the electrodes in different subsets in order to enhance sensitivity for measuring 6-axis F/T. The combination of desirable features of CoinFT enables various contact-rich robot interactions at a scale, across different embodiment domains including drones, robot end-effectors, and wearable haptic devices. We demonstrate the utility of CoinFT on drones by performing an attitude-based force control to perform tasks that require careful contact force modulation. The design, fabrication, and firmware of CoinFT are open-sourced at https://hojung-choi.github.io/coinft.github.io/.

Problem

• Develop a compact, low-cost 6-axis force/torque sensor for robots
• Enhance sensitivity in measuring multi-axis forces and moments
• Enable precise force control in drones and wearable devices

Innovation

• Compact capacitive 6-axis force/torque sensor
• Comb-shaped electrodes with silicone pillars
• Subset electrode interrogation for sensitivity