Robot Load Deviation Calibration Using Tribological Contact
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Solution Overview
Problem
Existing methods for determining deviation of multi-jointed robots under load are cumbersome, expensive, and difficult to implement in production environments, particularly due to the need for external force applicators and deformation measurement equipment, which are invasive and require complex setup.
Innovation Solution
A method that uses the robot itself to generate solicitations by pressing it into contact with environmental constraints, such as tooling or workpieces, measuring positional variations during resisted movements, and associating these with force magnitudes, allowing for fully automated deviation determination without external clamping or reconfiguration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional calibration methods are used for multi-jointed robots, then initial positioning can be achieved, but deviation under load conditions deteriorates performance accuracy
Solution Approach 1:
The system performs preliminary actions by pre-calculating gravity compensation values and deviation correction values before actual operation. The gravity compensation is applied in advance to counteract gravitational effects, and the deviation correction values are pre-determined through calibration to compensate for load-induced inaccuracies during subsequent operations.
Solution Approach 2:
The system implements feedback by measuring actual robot position and orientation, comparing it with commanded values, and using the deviation information to correct positioning errors. The calibration process establishes feedback relationships between load conditions and positioning deviations, enabling continuous compensation during operation.
2Measurement precision
If gravity compensation is not applied, then system complexity remains low, but arm position accuracy under gravity deteriorates
Solution Approach 1:
The system replaces complex mechanical gravity compensation mechanisms with computational methods. Instead of using additional mechanical components or complex physical structures to counteract gravity, the invention uses software-based gravity compensation calculations that process joint position data and apply correction values, significantly reducing mechanical complexity while maintaining high positioning accuracy.
3Measurement precision
If detailed calibration procedures are performed, then positioning accuracy improves, but calibration time increases
Solution Approach 1:
The system applies partial calibration actions by focusing calibration efforts on the most critical deviation sources and load conditions. Rather than performing exhaustive calibration across all possible operating conditions, the method identifies and corrects the most significant error sources, achieving sufficient accuracy for practical applications while reducing overall calibration time.
Data Source
Figure 1~3d
Figure 4~5
Figure 6a~6c
AI summary
Determining deviation of a multi-jointed robot under load using a tribological contact between an end of the robot and any available hard constraint near the robot, involves pressing the end against the constraint, and then soliciting a movement of the end relative to the constraint in a tribologically resisted direction to apply a force that does not overbear the resistance. By measuring the force and a position encoded by the robot, a deviation of the robot under the corresponding load is determined. Correction terms may be required for deformation of the tribological surface and/or constraint. The constraint may be tooling or parts subjected to an intended process. The deviation at many measurement poses of the robot, each in multiple resisted directions, within the ordinary operating space of the robot, was used to derive compliances of the robot, and a kinetostatic model.