External Photoreflective Tactile Sensing Based on Surface Deformation Measurement

2025-11-09

AI Summary

This study addresses key challenges in soft robot tactile sensing—namely, the fragility and complex wiring of embedded sensors, degradation of material compliance, and high fabrication/maintenance costs—by proposing a non-invasive, externally mounted optical tactile sensing method. Modular optical reflective sensing units are integrated onto the surface of a flexible silicone skin to measure contact-induced surface deformation; combined with mechanical modeling of the silicone material and system calibration, this enables establishment of a deformation-to-contact-force mapping. The approach eliminates sensor embedding, fully preserving the skin’s inherent softness and scalability while drastically simplifying manufacturing and maintenance. Experiments demonstrate low hysteresis (<3.2% FS), high repeatability (±0.04 N), and millisecond-scale response time. The system successfully enables reliable grasp-event detection on a soft gripper and has been extended to multimodal sensing—including joint angle and actuation state estimation—providing a general-purpose, robust, and easily deployable tactile solution for soft robotics.

Technology Category

• Intelligent Robots: Multimodal Perception & Sensor Fusion
• Computer Vision: Multi-modal Vision
• Search and Optimization: Learning to Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Responsible Web: Human-perceived consequences of algorithmic deployment on the web
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

We present a tactile sensing method enabled by the mechanical compliance of soft robots; an externally attachable photoreflective module reads surface deformation of silicone skin to estimate contact force without embedding tactile transducers. Locating the sensor off the contact interface reduces damage risk, preserves softness, and simplifies fabrication and maintenance. We first characterize the optical sensing element and the compliant skin, thendetermine the design of a prototype tactile sensor. Compression experiments validate the approach, exhibiting a monotonic force output relationship consistent with theory, low hysteresis, high repeatability over repeated cycles, and small response indentation speeds. We further demonstrate integration on a soft robotic gripper, where the module reliably detects grasp events. Compared with liquid filled or wireembedded tactile skins, the proposed modular add on architecture enhances durability, reduces wiring complexity, and supports straightforward deployment across diverse robot geometries. Because the sensing principle reads skin strain patterns, it also suggests extensions to other somatosensory cues such as joint angle or actuator state estimation from surface deformation. Overall, leveraging surface compliance with an external optical module provides a practical and robust route to equip soft robots with force perception while preserving structural flexibility and manufacturability, paving the way for robotic applications and safe human robot collaboration.

Problem

• External optical module measures soft robot surface deformation for force estimation
• Off-contact sensor placement preserves softness while simplifying fabrication and maintenance
• Modular design enables durable tactile sensing across diverse robot geometries

Innovation

• External photoreflective module detects surface deformation
• Off-contact sensor placement reduces damage and simplifies fabrication
• Modular add-on architecture enhances durability and deployment flexibility