Articulated Robot Calibration Using Pivot Pose and Ballbar
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Solution Overview
Problem
Calibration of articulated robots with multiple rotary joints is challenging due to cumulative positional errors and uncertainties, and existing methods like laser tracking are expensive and slow, while other techniques require complex parametric modeling and multiple poses.
Innovation Solution
A method involving controlling the machine into a pivot pose, measuring errors at different target poses, and optimizing model parameters to minimize overall error, using a length-measuring device like a ballbar, with an adaptable pivot and spherical bearing surface for precise calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser tracking is used for calibration, then measurement precision is improved, but cost and calibration time increase
Solution Approach 1:
The patent replaces expensive laser tracking equipment with a simple, inexpensive ballbar device that can be easily manufactured and replaced. The ballbar uses basic spherical components and standard measurement techniques, eliminating the need for costly laser systems while maintaining adequate calibration precision for robotic applications.
Solution Approach 2:
The patent substitutes complex optical laser tracking systems with a simpler mechanical measurement approach using a ballbar. The ballbar relies on mechanical contact and basic geometric relationships rather than complex optical fields, reducing equipment cost and complexity while providing sufficient measurement capability for robot calibration.
2Measurement precision
If laser tracking is used for calibration, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent employs a simple ballbar device with basic spherical components instead of complex laser tracking equipment. This disposable-like approach uses inexpensive, easily manufactured parts that can be replaced if needed, dramatically reducing both cost and system complexity while maintaining functional adequacy for calibration tasks.
Solution Approach 2:
The patent replaces the complex optical and electronic systems of laser tracking with a straightforward mechanical measurement device. The ballbar uses simple mechanical contact between spherical surfaces and basic length measurement, eliminating the need for complex optical fields, sensors, and processing systems.
3Measurement precision
If traditional calibration techniques are used, then measurement precision is improved, but device complexity and number of required poses increase
Solution Approach 1:
The patent extracts and isolates the essential calibration function to a single, simple ballbar device, removing the need for complex parametric modeling and multiple calibration fixtures. By focusing on direct length measurement between two points, the method eliminates unnecessary procedural complexity while maintaining calibration accuracy.
Solution Approach 2:
Instead of using complex parametric models that require the machine to be moved through many different poses, the patent inverts the approach by using direct physical measurement with a ballbar. This reverses the traditional calibration paradigm, achieving accurate results through simple geometric measurement rather than complex mathematical modeling.
Data Source
AI summary
A method of calibrating a coordinate positioning machine is described. The machine is controlled into a pivot pose in which a target point associated with a moveable part of the machine and a pivot point associated with a fixed part of the machine are separated from one another by a known separation. An error value for that pose is determined based on the known separation and a separation expected for that pose from the existing model parameters of the machine. The machine is controlled into a plurality of different target poses, and for each target pose a separation between the target point and the pivot point is measured and an error value for that pose is determined based on the measured separation and a separation expected for that pose from the existing model parameters.