Robot Joint Gap Detection Using Torque Simulation
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Solution Overview
Problem
In robot joint mechanisms, especially in delta-type parallel link robots, it is challenging to detect minute gaps between ball and housing components, which can lead to reduced positioning accuracy and increased vibration due to wear, and existing methods are difficult to implement during normal production operations without special robot motions or interfering with peripheral equipment.
Innovation Solution
A gap detection device and method that measures and simulates drive torque or current values during arbitrary motion trajectories, using feature calculation and gap estimation units to identify abnormal gaps based on measured and estimated variations, allowing for accurate detection of gaps in ball joints without requiring special robot motions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an integrated type ball joint with link ball structure is used, then the ball and housing are not easily separated due to mechanical connection, but a gap may be generated between the ball and housing due to wear, leading to deterioration in positioning accuracy and increase in vibration
Solution Approach 1:
The patent replaces direct mechanical sensing methods with torque-based detection. Instead of using mechanical sensors to directly measure the gap between ball and housing, the system uses torque measurements from the drive motor to indirectly detect gap abnormalities. This substitution allows for non-intrusive detection that does not interfere with the mechanical connection while still monitoring wear-induced gap changes.
Solution Approach 2:
The patent introduces torque as an intermediary parameter to detect gap changes. Rather than directly measuring the physical gap between ball and housing, the system measures the torque required to drive the joint and uses changes in torque characteristics as an indirect indicator of gap development. This intermediary approach enables detection without physical contact with the wear surfaces.
2Measurement precision
If a conventional sensor-based method is used to detect disengagement, then it works for separate type ball joints, but it is extremely difficult to detect minute gaps of about 0.1 to 0.2 mm in integrated type ball joints
Solution Approach 1:
The patent transitions from direct spatial measurement (attempting to measure the 0.1-0.2mm gap directly) to a different dimensional approach by measuring torque in the force domain. Instead of trying to resolve the minute physical distance between ball and housing surfaces, the system measures the rotational force required to overcome the gap, converting a difficult length measurement into a more measurable force parameter.
Solution Approach 2:
The patent replaces mechanical sensor-based detection with a torque-based detection system. Instead of using position sensors or displacement sensors that struggle to detect sub-millimeter gaps, the system uses torque sensors or motor current measurements to detect the mechanical effects of gap presence, achieving indirect measurement with higher sensitivity.
3Reliability
If a special robot motion is performed to identify joint with abnormal gap, then gap detection may be achieved, but it is difficult to perform such special robot motion due to interference between robot and peripheral equipment and layout constraints
Solution Approach 1:
The patent creates a detection system that serves multiple functions: it can detect gaps during normal production operations, during maintenance intervals, and under various operating conditions. The torque-based detection method works across different robot motions and configurations, eliminating the need for specialized detection movements while maintaining detection capability throughout the robot's operational envelope.
Solution Approach 2:
The patent enables continuous gap detection during normal robot operation rather than requiring periodic special detection motions. The torque measurement is continuously available during production operations, allowing for real-time monitoring of gap development without interrupting the robot's useful work or requiring it to move to specific detection positions.
4Productivity
If torque measurement and simulation method is used, then accurate gap detection can be achieved during normal production operations, but the device complexity increases due to measurement unit, simulation unit, and gap calculation unit
Solution Approach 1:
The patent makes the robot's existing drive system serve dual purposes: both driving the robot and providing torque measurement for gap detection. The motor that drives the joint also provides the torque signal needed for detection, eliminating the need for separate dedicated measurement hardware in many cases. The control system that already exists for motion control is also used for torque analysis.
Solution Approach 2:
The patent uses the existing control system and torque data as an intermediary between the motor and the gap detection function. Rather than adding complex dedicated hardware, the system processes torque information that is already available from the drive system, using software-based simulation and calculation units that leverage existing data streams to provide gap detection capability.
Data Source
AI summary
A gap detection device includes: a measurement unit measuring the driving torque or current value of a motor when the robot is actually being operated along an arbitrary motion trajectory; a simulation unit setting an arbitrary second gap amount between pairing elements of a plurality of pairing elements, performing a simulation in which the robot operates along the same arbitrary motion trajectory, and estimating the driving torque or the current value of the motor; a feature amount calculation unit calculating a first feature amount indicating fluctuations of a value related to the measured driving torque or current value, and a second feature amount indicating fluctuations of a value related to the estimated driving torque or current value; and a gap calculation unit calculating an index related to a first gap amount on the basis of the first feature amount, the second feature amount, and the second gap amount.