Differential Robot Joint Torque Diagnosis With Friction Wheels
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Solution Overview
Problem
Existing torque limiters for robot joints are not applicable to differential joint devices, leading to potential damage and safety risks due to excessive external forces, and existing methods for torque detection are either slow or not compact enough for use in wrist joints.
Innovation Solution
A differential joint device for robots incorporating friction wheels, encoders, and a processor to detect and adjust torque, with a method for diagnosing the joint state by comparing actual and expected output values of pitch and roll encoders, and controlling motors to compensate for errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a torque limiter is applied to a single axis joint, then torque detection and protection function is provided, but the joint becomes large and cannot be applied to compact wrist joints
Solution Approach 1:
The patent combines multiple friction wheels (first, second, and third friction wheels) into a single integrated differential joint device. The first and second friction wheels are disposed on opposite sides of the first shaft, while the third friction wheel is disposed at one end of the second shaft and contacts both the first and second friction wheels. This merging of multiple torque limitation functions into a compact differential structure enables the joint to provide comprehensive torque protection while maintaining a small size suitable for wrist joints.
Solution Approach 2:
The differential joint device performs multiple functions simultaneously: it provides torque limitation through friction wheels, detects torque through encoders (pitch output encoder and roll output encoder), and controls motor rotation. This multi-functionality allows a single compact structure to replace what would traditionally require separate torque limiters and sensors, thereby reducing overall joint size while maintaining protection capabilities.
2Reliability
If torque detection methods using torque sensors or current measurement are used, then torque detection function is provided, but the reaction speed is slow
Solution Approach 1:
The patent replaces electrical sensing methods (torque sensors and current measurement) with a mechanical friction wheel system that physically responds to external torque. The friction wheels are designed to slip or rotate in response to excessive torque, providing immediate mechanical feedback through the encoders. This mechanical substitution enables faster reaction speed while maintaining reliable torque detection.
3Speed
If friction wheels and encoders are used to detect torque, then fast response and compact size are achieved, but the device complexity increases
Solution Approach 1:
The patent employs a nested arrangement where the third friction wheel is disposed at one end of the second shaft and contacts both the first and second friction wheels. This nested configuration allows multiple friction wheels and encoders to be compactly arranged within a small volume, reducing spatial complexity while maintaining the fast response capability of the friction wheel system.
Solution Approach 2:
The patent uses encoders (pitch output encoder and roll output encoder) to detect the rotation angles of the friction wheels and provides feedback to the control system. This feedback mechanism enables the system to detect torque conditions and adjust motor rotation accordingly. While this adds control complexity, it also enables precise torque management and protection, justifying the increased complexity through improved reliability and response speed.
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 solution provides a compact and efficient way to detect and manage excessive torque in differential joints, preventing damage and ensuring safety by actively compensating for torque discrepancies, thus reducing the risk of accidents.
Implementation Method 1
a first friction wheel (30) rotatably disposed on one side of the first shaft (10), a second friction wheel (40) rotatably disposed on another side of the first shaft (10), a third friction wheel (50) rotatably disposed at one end of the second shaft (20), the third friction wheel (50) being in contact with the first friction wheel (30) and the second friction wheel (40)
Data Source
AI summary
A differential joint device for a robot includes a first shaft extending in a first direction, a second shaft connected to the first shaft and extending in a second direction vertical to the first direction, a first friction wheel rotatably disposed on one side of the first shaft, a second friction wheel rotatably disposed on another side of the first shaft, a third friction wheel rotatably disposed at one end of the second shaft, the third friction wheel being in contact with the first friction wheel and the second friction wheel, a pitch output encoder disposed to detect a rotation angle of the first shaft, a roll output encoder disposed to detect a rotation angle of the third friction wheel, a first driver configured to rotate the first friction wheel, and a second driver configured to rotate the second friction wheel.