In-Situ Calibration of Dexterous Robot Load Cells
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Solution Overview
Problem
Dexterous robots face challenges in calibrating miniature six-axis load cells integrated within their structure, as conventional external calibration jigs are impractical and calibration can drift due to mechanical changes, requiring an in-situ solution.
Innovation Solution
A method and apparatus for in-situ calibration of multi-axis load cells in a dexterous humanoid robot, where the robot automatically presses mating pairs of load cells together in various poses, processing joint angles and strain measurements to determine calibration matrices without an external jig, using a host machine connected to the load cells and angle sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional external calibration jigs are used to calibrate load cells, then calibration accuracy can be maintained, but the device complexity and impracticality increase for integrated robotic systems
Solution Approach 1:
The robot performs self-calibration by having its own load cells press against each other in mating pairs, eliminating the need for external calibration equipment. The system uses its inherent structure and sensors to generate calibration data through controlled self-contact operations
Solution Approach 2:
Instead of using external equipment to calibrate the load cells, the patent inverts the approach by using the load cells themselves to calibrate each other through mutual contact. The calibration source becomes the system's own components rather than external tools
2Device complexity
If load cells are integrated within the robot's architecture for compact design, then the robot structure is simplified, but calibration becomes difficult without external equipment
Solution Approach 1:
The integrated load cells perform self-calibration by pressing against each other, allowing the compact structure to maintain calibration capability without requiring disassembly or external equipment. The system calibrates itself while remaining in its integrated state
Solution Approach 2:
The load cells serve dual functions: they perform their primary measurement function and simultaneously serve as calibration sources for each other. This multi-functionality eliminates the need for separate calibration equipment while maintaining integration
3Measurement precision
If load cells are used for precise force and torque measurement, then measurement capability is improved, but calibration drift occurs over time due to mechanical changes
Solution Approach 1:
The system implements continuous or periodic self-calibration by repeatedly pressing mating load cells together and updating calibration matrices. This feedback mechanism corrects drift by comparing current measurements against the self-generated calibration reference, maintaining long-term accuracy
Solution Approach 2:
The system performs preliminary calibration actions by pressing load cells together before actual measurement tasks. This preparatory calibration ensures accurate measurements by correcting any drift that may have occurred, establishing a known reference state before operation
Data Source
AI summary
A robotic system includes a dexterous robot having robotic joints, angle sensors adapted for measuring joint angles at a corresponding one of the joints, load cells for measuring a set of strain values imparted to a corresponding one of the load cells during a predetermined pose of the robot, and a host machine. The host machine is electrically connected to the load cells and angle sensors, and receives the joint angle values and strain values during the predetermined pose. The robot presses together mating pairs of load cells to form the poses. The host machine executes an algorithm to process the joint angles and strain values, and from the set of all calibration matrices that minimize error in force balance equations, selects the set of calibration matrices that is closest in a value to a pre-specified value. A method for calibrating the load cells via the algorithm is also provided.