Torque Sensor Fail-Safe Design for Robot Arm Collision Prevention
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Solution Overview
Problem
Existing torque sensors in robot arms face difficulties in detecting abnormalities, leading to potential collisions between robot arms, as they lack a fail-safe function to detect and respond to sensor or arm malfunctions.
Innovation Solution
A torque sensor design incorporating first and second bridge circuits with strain sensors, a detecting circuit, and a controller that compares output voltages to detect abnormalities and stops the respective circuits when thresholds are exceeded, utilizing thin-film resistive elements on metallic plates fixed to a structure, enabling early detection and prevention of collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a torque sensor is attached to a robot arm to detect torque, then torque measurement capability is improved, but the ability to detect sensor abnormalities and provide fail-safe function deteriorates
Solution Approach 1:
The torque sensor is divided into two independent measurement systems: a main measurement system using a first bridge circuit and a backup measurement system using a second bridge circuit. Each system independently measures torque through strain sensors, allowing the backup system to take over when the main system detects abnormalities, thus providing fail-safe functionality while maintaining measurement capability.
Solution Approach 2:
The controller continuously monitors the output voltages from both bridge circuits and compares them to detect abnormalities before they lead to collisions. By performing preliminary detection and comparison of both measurement systems, the system can identify sensor failures early and switch to the backup system, preventing harmful outcomes.
2Reliability
If dual bridge circuits are implemented for abnormality detection, then reliability is improved, but device complexity increases
Solution Approach 1:
Two bridge circuits are integrated into a single torque sensor housing, sharing common structural elements such as the first and second structures, third structures, and strain sensors. This merging approach allows dual measurement systems to coexist in a compact form factor, reducing overall device complexity while maintaining reliability through redundancy.
Solution Approach 2:
The strain sensors serve multiple functions: they are part of both the first bridge circuit and the second bridge circuit, enabling each sensor to contribute to both measurement systems. This multi-functionality reduces the total number of components needed and simplifies the overall device structure while providing redundant measurement capabilities.
3Measurement precision
If continuous monitoring of both bridge circuits is performed, then abnormality detection precision is improved, but energy consumption increases
Solution Approach 1:
The controller implements a feedback mechanism by continuously comparing the output voltages from both bridge circuits and detecting deviations. This feedback loop enables precise abnormality detection by monitoring the relationship between the two measurement systems, allowing the system to identify failures when voltage differences exceed a threshold while managing energy consumption through intelligent comparison logic.
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 torque sensor effectively detects abnormalities and provides a fail-safe function, preventing collisions by identifying and isolating faulty bridge circuits, ensuring continued operation and safe operation of the robot arm.
Implementation Method 1
each of the strain sensors is constituted of a thin-film resistive element provided on a metallic plate through an insulating film
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
An abnormality of the torque sensor itself and an abnormality of a robot arm can be detected, and the torque sensor which has a fail-safe function is provided. A first structure 11 to be coupled to an object to be measured, a second structure 12, a first bridge circuit B1 including a plurality of first strain sensors configured to detect force to be transmitted between the first structure 11 and the second structure 12, a second bridge circuit B2 including a plurality of second strain sensors configured to detect force to be transmitted between the first structure 11 and the second structure 12, and a controller 19 configured to output a signal indicating an abnormality when a difference between a first output voltage of the first bridge circuit B1 and a second output voltage of the second bridge circuit B2 is greater than a first threshold voltage.