Robot Ball Joint Clearance Detection Using Torque Variation
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Solution Overview
Problem
Conventional methods for detecting abnormal clearance in ball joints of delta-type parallel link robots are inadequate, as they fail to accurately identify which joint has an issue and cannot effectively detect increased clearance between the ball and housing, leading to decreased positional accuracy and increased vibration, which can cause production stoppages and reduced system performance.
Innovation Solution
An abnormality detecting device that simulates robot motion along predetermined paths to calculate scores based on collisions between pairing elements, measures drive torque or current values during specific motions, and calculates an index value to determine if an abnormal clearance exists between designated pairs of elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional abnormality detection methods are used, then general robot motion abnormalities can be detected, but abnormal clearances in ball joints cannot be accurately detected
Solution Approach 1:
The invention segments the detection problem by separating general motion abnormality detection from specific clearance detection. It divides the ball joint into pairing elements (ball and housing) and independently evaluates their relative positional relationships, allowing precise measurement of clearance between specific components rather than detecting only overall motion abnormalities.
Solution Approach 2:
The invention introduces an intermediary coordinate system (joint coordinate system) that moves with the passive link to evaluate positional relationships between pairing elements. This intermediary reference frame enables accurate measurement of clearance without being affected by overall robot motion, solving the limitation of conventional fixed-coordinate detection methods.
2Ease of manufacture
If ball and housing are geometrically separated with elastic biasing, then joint assembly is easy, but joint may disassemble during high speed motion or collision
Solution Approach 1:
The invention applies preliminary action by pre-loading the ball toward the housing using elastic biasing force before operation. This preliminary mechanical action ensures the ball remains firmly seated in the housing during high-speed motion or collision, preventing disassembly while maintaining ease of assembly through the same elastic biasing mechanism.
3Reliability
If link-ball structure with unified ball and housing is used, then joint connection is secure, but clearance is generated affecting positional accuracy
Solution Approach 1:
The invention replaces direct mechanical contact measurement with optical detection. By using an optical detector to measure the positional relationship between the ball and housing through the transparent housing, it can detect clearance without mechanical interference, thereby maintaining both secure connection and high positional accuracy.
4Productivity
If conventional detection methods are used, then general abnormalities can be identified, but specific joint clearance issues cannot be localized
Solution Approach 1:
The invention applies local quality by placing detection functionality specifically at the ball joint level rather than at the robot controller level. The optical detector is positioned to locally measure clearance between the ball and housing, enabling precise localization of joint-specific issues without requiring complex system-wide analysis.
Data Source
AI summary
A device and method for judging the presence or absence of an abnormal clearance between paring elements of a passive joint of a robot. The device has sections configured to: calculate a score for each motion path, wherein the score is increased when the paring elements of an objective pair collide with each other and is decreased when the paring elements of the other pair collide with each other; generate a robot motion for moving the robot along the motion path having the score not lower than a predetermined threshold; measure a drive torque or a current value of a motor when the robot is moved according to the generated robot motion; calculate an index value based on a magnitude of variation of the measured drive torque or current value; and judge as to whether the abnormal clearance exists in the objective pair, based on the index value.