Preloaded FSR Array Force Sensor for Low-Amplitude Tactile Sensing
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Solution Overview
Problem
Current force sensors, such as displacement sensors and strain gauges, face issues like unreliability, high cost, and sensitivity to temperature and humidity, while force sensitive resistor (FSR) sensors are slow and insensitive to low-amplitude forces, making them inadequate for providing reliable tactile feedback in robotic applications, particularly in surgeries where precise force measurements are crucial.
Innovation Solution
A low-cost, tri-axial force sensor utilizing an array of force sensitive resistors with a mechanically pre-loaded structure and built-in signal conditioning circuitry for on-board power regulation, programmable signal amplification, and analog to digital conversion, enabling high sensitivity to low-amplitude forces and multi-axis force vector decoding in a compact package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If force sensitive resistor sensors are used, then cost is reduced and robustness is improved, but sensitivity to low-amplitude forces deteriorates and response speed decreases
Solution Approach 1:
The sensor is divided into multiple independent FSR elements arranged in an array configuration. Each FSR element can be independently optimized and calibrated, allowing the system to achieve high sensitivity to low-amplitude forces while maintaining the cost advantages of FSR technology. The segmented structure enables parallel signal processing that compensates for individual element limitations.
Solution Approach 2:
The patent modifies the operating parameters of FSR sensors by implementing pre-loaded structures that apply initial mechanical stress to the FSR elements. This pre-loading changes the resistance characteristics and sensitivity curve of the FSR, enabling detection of low-amplitude forces (less than 1 N) that would otherwise be undetectable. The signal conditioning circuitry also adjusts electrical parameters to optimize sensitivity.
2Reliability
If force sensitive resistor sensors are used, then robustness to shock and temperature is improved, but response speed deteriorates
Solution Approach 1:
The sensor incorporates pre-loaded structures that apply initial mechanical force to the FSR elements before actual measurement begins. This preliminary action prepares the FSR in an optimal state for rapid response to incoming forces, reducing the mechanical rise time. The pre-loading also linearizes the response characteristics, enabling faster signal processing.
Solution Approach 2:
The patent replaces purely mechanical FSR response with an integrated electromechanical system. Signal conditioning circuitry converts mechanical deformation into electrical signals that can be processed and amplified rapidly, compensating for the inherently slow mechanical response of FSR materials. This substitution enables real-time force measurement despite the slow mechanical rise time of FSR elements.
3Measurement precision
If strain gauges are used, then measurement precision is improved, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent employs inexpensive FSR elements that can be easily replaced or recalibrated if needed. While individual FSR elements have limitations compared to strain gauges, their low cost and simplicity allow for array configurations that achieve comparable or superior overall precision. The simplicity of FSR fabrication eliminates the complex wiring and calibration procedures required for strain gauge systems.
Solution Approach 2:
The patent combines multiple FSR elements into an array structure with integrated signal conditioning circuitry. This merging of multiple simple elements achieves the measurement precision of complex strain gauge systems while maintaining the fabrication simplicity of FSR technology. The combined array provides redundancy and enables multi-axis force measurement capabilities.
4Measurement precision
If displacement sensors are used, then force sensing capability is provided, but reliability deteriorates due to mechanical friction and backlash
Solution Approach 1:
The patent replaces mechanical displacement sensing with direct electrical resistance measurement using FSR elements. This substitution eliminates mechanical linkages, friction, and backlash that plague displacement sensors. The FSR provides a direct electrical signal proportional to applied force, removing intermediate mechanical components that introduce errors and reduce reliability in robotic applications.
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 reliable, low-cost, and highly sensitive force readings, reducing tissue trauma in surgeries by offering precise tactile feedback, with improved sensitivity and accuracy in decoding force vectors, and is robust enough for adverse conditions.
Implementation Method 1
The force sensor comprises a force sensitive resistor secured by a preload structure
Data Source
AI summary
A force sensor comprising a force sensitive resistor having a common electrode and an electrode array separated by a force sensitive resistor material. The sensor includes a preload structure, where the preload structure imparts a force on the force sensitive resistor material. The sensor may also include a signal conditioning board to read a signal from the electrode array and convert it to a digital output.