A Miniature High-Resolution Tension Sensor Based on a Photo-Reflector for Robotic Hands and Grippers

2025-07-01

AI Summary

To address the lack of high-precision, miniaturized tension sensing in compact tendon-driven grippers, this paper proposes a miniature, high-resolution tension sensor based on optoreflective principles. The sensor employs a symmetric elastomer structure with flexure hinges—designed using Timoshenko beam theory and validated via finite element analysis—and integrates a VCNT2020 optoreflector for near-field displacement detection, eliminating the need for light-absorbing coatings or complex optical components. With a compact volume of 13 × 7 × 6.5 mm³, it achieves a 200 N measurement range, a resolution of 9.9 mN, and root-mean-square errors of 0.455 N (static) and 0.073 N (closed-loop force control), while significantly reducing nonlinearity and hysteresis. Compared to conventional optointerrupter-based approaches, its overall performance improves by over an order of magnitude. Featuring high accuracy, miniaturization, and high-speed data acquisition (5 kHz, 16-bit ADC + CAN-FD), the sensor provides a robust force feedback solution for lightweight dexterous hands.

Technology Category

• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Computer Vision: Learning & Optimization for CV
• Humans and AI: Brain-Sensing and Analysis

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

Abstract

This paper presents a miniature tension sensor using a photo-reflector, designed for compact tendon-driven grippers and robotic hands. The proposed sensor has a small form factor of 13~mm x 7~mm x 6.5~mm and is capable of measuring tensile forces up to 200~N. A symmetric elastomer structure incorporating fillets and flexure hinges is designed based on Timoshenko beam theory and verified via FEM analysis, enabling improved sensitivity and mechanical durability while minimizing torsional deformation. The sensor utilizes a compact photo-reflector (VCNT2020) to measure displacement in the near-field region, eliminating the need for light-absorbing materials or geometric modifications required in photo-interrupter-based designs. A 16-bit analog-to-digital converter (ADC) and CAN-FD (Flexible Data-rate) communication enable efficient signal acquisition with up to 5~kHz sampling rate. Calibration experiments demonstrate a resolution of 9.9~mN (corresponding to over 14-bit accuracy) and a root mean square error (RMSE) of 0.455~N. Force control experiments using a twisted string actuator and PI control yield RMSEs as low as 0.073~N. Compared to previous research using photo-interrupter, the proposed method achieves more than tenfold improvement in resolution while also reducing nonlinearity and hysteresis. The design is mechanically simple, lightweight, easy to assemble, and suitable for integration into robotic and prosthetic systems requiring high-resolution force feedback.

Problem

• Miniature tension sensor for robotic hands and grippers
• High-resolution force measurement up to 200N
• Improved sensitivity and durability with compact design

Innovation

• Miniature tension sensor using photo-reflector
• Symmetric elastomer structure with flexure hinges
• 16-bit ADC and CAN-FD for high-resolution feedback