Optical Tactile Sensor for Simultaneous Normal and Shear Load Sensing
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Solution Overview
Problem
Conventional tactile sensors are unable to effectively sense both normal and shear loads, which are essential for applications like robotic hands and prosthetic sockets, as they often require large and expensive multi-axis sensing solutions or are limited in differentiating between load types.
Innovation Solution
A tactile sensor design featuring an optically transparent layer bonded with an optically reflective layer, utilizing light emitters and detectors to measure changes in reflected light intensity due to normal and shear loads, allowing for simultaneous detection of both load types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional strain gauge-based load cells are used for multi-axis sensing, then both normal and shear loads can be sensed, but the device becomes large and expensive
Solution Approach 1:
The patent replaces traditional mechanical strain gauge-based load cells with an optical sensing system. Light emitters and photodetectors are used to detect deformations in the elastomer layer, substituting mechanical measurement with optical measurement to achieve multi-axis sensing with reduced size and cost
Solution Approach 2:
The sensor employs a composite structure consisting of an elastomer layer bonded to a rigid substrate. This composite design allows the elastomer to deform under load while the rigid substrate provides structural support, enabling both normal and shear load sensing in a compact configuration
2Difficulty of detecting and measuring
If conventional optical shear sensors are used, then shear load can be sensed, but normal load sensing is unable and axis differentiation is typically unable
Solution Approach 1:
The optical sensing system is designed to perform multiple functions: it can detect both normal loads (through vertical displacement of the elastomer surface) and shear loads (through lateral displacement of reflective boundaries). The same light emitter-photodetector pairs can sense deformations in different directions, providing universal sensing capability
Solution Approach 2:
The patent adds vertical dimension sensing capability to traditional optical shear sensors. By measuring light intensity changes caused by vertical elastomer deformation, the system can detect normal loads in addition to shear loads, transitioning from single-axis to multi-axis sensing
3Adaptability or versatility
If capacitive sensors or MEMS sensors are used for multi-axis sensing, then both normal and shear loads can be sensed, but the load capacity is relatively small and the sensors are commonly frail
Solution Approach 1:
The sensor uses a flexible elastomer layer as the sensing element. This thin film structure provides both sensitivity to small deformations and durability through material flexibility. The elastomer can withstand repeated loading cycles while maintaining its sensing capability, overcoming the fragility issue of MEMS sensors
Solution Approach 2:
The patent incorporates reflective boundaries with specific geometric configurations within the elastomer layer. These curved or angled reflective surfaces enhance the optical signal modulation in response to both normal and shear loads, improving sensitivity while maintaining structural integrity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The sensor provides accurate and simultaneous measurement of normal and shear loads, enhancing object manipulation and interface monitoring with a compact, cost-effective, and sensitive solution suitable for robotic skins and prosthetic sockets.
Implementation Method 1
When a normal load is applied, the optically transparent layer compresses, causing a change in reflected light intensity
Implementation Method 2
When shear load is applied, a boundary between optically reflective material and optically absorptive material is laterally displaced, causing a change in reflected light intensity
Implementation Method 3
light emitter(s) emit light that traverses through the optically transparent layer and reflects off optically reflective material of the first layer
Implementation Method 4
light detector(s) detect and measure intensity of reflected light
Data Source
AI summary
Various technologies described herein pertain to a tactile sensor that senses normal load and/or shear load. The tactile sensor includes a first layer and an optically transparent layer bonded together. At least a portion of the first layer is made of optically reflective material. The optically transparent layer is made of resilient material (e.g., clear silicone rubber). The tactile sensor includes light emitter/light detector pair(s), which respectively detect either normal load or shear load. Light emitter(s) emit light that traverses through the optically transparent layer and reflects off optically reflective material of the first layer, and light detector(s) detect and measure intensity of reflected light. When a normal load is applied, the optically transparent layer compresses, causing a change in reflected light intensity. When shear load is applied, a boundary between optically reflective material and optically absorptive material is laterally displaced, causing a change in reflected light intensity.