Redundant Force Torque Sensor Fault Detection
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Solution Overview
Problem
Conventional force/torque sensors in robotic applications are susceptible to faults such as strain gage failures, which can lead to inaccurate measurement and reporting of applied loads, posing a safety risk, especially if the fault occurs when the system is not powered on.
Innovation Solution
A force/torque sensor design with n≥4 deformable beams, where at least four beams are instrumented with strain gages, generating eight gage signals that are grouped into four sets of six, allowing for comparison of force and torque values using different calibration matrices to detect faults and ensure continued operation even if one beam or its instrumentation fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional force/torque sensors use standard strain gage instrumentation, then the device complexity is low, but the reliability is poor due to susceptibility to faults such as strain gage failures, wiring faults, and measurement circuit component failures
Solution Approach 1:
The patent applies preliminary action by performing fault detection before the sensor is needed for critical operation. The system continuously monitors strain gage signals and compares readings from multiple beams to detect faults early, allowing the robot to interrupt ongoing movement before damage occurs. This proactive approach improves reliability by preventing catastrophic failures rather than reacting to them after they occur.
Solution Approach 2:
The patent implements feedback by continuously comparing force and torque values derived from different sets of gage signals. The measurement circuit receives signals from multiple beams, processes them through calibration matrices, and compares the resulting force/torque values to detect discrepancies indicating faults. This closed-loop feedback mechanism enables real-time fault detection, significantly improving sensor reliability without requiring complete system redesign.
2Reliability
If the sensor uses redundant instrumentation with n≥4 beams and multiple calibration matrices, then the reliability improves through fault detection, but the device complexity increases due to additional instrumentation and processing requirements
Solution Approach 1:
The patent applies segmentation by dividing the measurement system into multiple independent measurement paths. Instead of using a single strain gage configuration, the system uses n≥4 deformable beams with strain gages on at least four beams, creating multiple parallel measurement channels. Each beam provides independent force/torque data that can be processed separately through calibration matrices, allowing the system to segment the measurement function to improve reliability through redundancy.
Solution Approach 2:
The patent implements parameter changes by modifying the instrumentation parameters to include redundant measurement channels. The system changes from a single-beam or few-beam configuration to n≥4 beams with multiple strain gages per beam, altering the fundamental measurement parameters. This parameter change enables the measurement circuit to process multiple sets of gage signals simultaneously, comparing results to detect faults while maintaining acceptable device complexity through systematic processing.
3Measurement precision
If strain gages are affixed to multiple beams with redundant instrumentation, then the measurement precision improves through cross-validation, but the manufacturing precision requirements increase due to additional gage placement and calibration needs
Solution Approach 1:
The patent applies self-service by using the redundant measurement channels to self-validate each other's accuracy. The measurement circuit automatically compares force and torque values derived from different sets of gage signals, allowing the system to self-diagnose measurement errors without external intervention. This self-service mechanism improves measurement precision by enabling cross-validation of readings from multiple beams, while the automated comparison process compensates for variations in gage placement precision through statistical analysis and calibration.
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 redundant instrumentation enables the detection of faults and continued accurate measurement of forces and torques, ensuring safety by signaling faults and maintaining operational capability even if one beam or its instrumentation fails, thus preventing unintended robot operation.
Implementation Method 1
Strain gages are typically affixed to all four surfaces of each beam, nominally in the center of each respective surface. The gages translate tensile and compressive strains at the beams' surfaces, caused by mechanical deformation of the beams, into electrical signals.
Data Source
AI summary
A force/torque sensor includes a number n of deformable beams connecting the TAP to the MAP, wherein n≥4. At least four of the n deformable beams are instrumented with strain gages affixed to surfaces of the beams, such that each beam outputs two gage signals. The eight gage signals are grouped into four sets of six gage signals, such that each set includes the gage signals from three of the four instrumented beams. Each set of six gage signals is multiplied by a calibration matrix to yield a set of six force and torque values. The four sets of force and torque values are compared. If one set disagrees with the other three by greater than a predetermined tolerance, a sensor fault is signaled.