High-Stiffness Capacitive Torque Sensor Based on a Hybrid Scott-Russell and Parallelogram Mechanism
Jae Yoon Sim, Seung Yeon Lee, Dong-Yeop Seok, Yong Bum Kim, Hyouk Ryeol Choi
AI summary
Problem
Conventional joint torque sensors struggle to balance high structural stiffness with high sensing sensitivity, as insufficient rigidity degrades control bandwidth and positioning accuracy in high-performance robotic joints.
Approach
The design integrates a Scott-Russell flexure for mechanical displacement amplification with a parallelogram flexure to constrain electrode motion to pure translation, maximizing capacitance change without sacrificing structural rigidity.
Key results
- Achieved 2.2-fold mechanical displacement amplification via the Scott-Russell flexure
- Suppressed parasitic rotation to ensure pure translational electrode motion
- Maintained high torsional stiffness of 408 kNm/rad for robust joint integration
- Validated differential capacitance sensing through finite element analysis
Why it matters
This design enables high-bandwidth, high-precision torque control for advanced robotic joints and physical AI systems that demand both structural robustness and sensitive force feedback.
Abstract
While joint torque sensors enable precise robot interactions, insufficient structural stiffness significantly limits control bandwidth and accuracy by reducing overall system rigidity. This study proposes a high-stiffness torque sensor based on a hybrid Scott-Russell (SR) and parallelogram (PL) flexure mechanism. The SR structure performs mechanical displace- ment amplification, ensuring high sensitivity even within a rigid design. By integrating the PL mechanism, the inherent parasitic rotation typically observed in conventional SR structures is effectively suppressed, ensuring pure translational motion be- tween the capacitive electrodes. This hybrid flexure maximizes the capacitance change and achieves high sensing sensitivity while maintaining the high structural stiffness required for robust robotic joints. The proposed mechanism is validated through simulation, demonstrating its potential to ensure both system-level rigidity and high-resolution torque sensing.