Coordinate Positioning Machine Calibration via Master Surface Contacts
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Solution Overview
Problem
Calibration of non-Cartesian coordinate positioning machines, such as articulated robots, is challenging due to the serial arrangement of axes that are not fixed relative to one another, leading to cumulative positional errors, and existing methods are cumbersome and costly.
Innovation Solution
A method involving contact between multiple reference surfaces of a tool and an artefact to determine and update model parameters, using a set of master separation values to recover or return to a known calibration state, allowing for quick and accurate recalibration of the tool centre point and tool frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If full recalibration procedures are performed on non-Cartesian machines, then manufacturing precision is maintained, but loss of time and productivity decrease significantly
Solution Approach 1:
The invention extracts only the essential calibration information needed to restore manufacturing precision by identifying and measuring specific feature-to-feature distances that characterize the tool frame. Instead of performing complete recalibration, the method isolates and updates only the critical parameters (tool centre point and tool frame orientation) that affect manufacturing accuracy, thereby reducing recalibration time while maintaining precision.
Solution Approach 2:
The method performs preliminary identification and recording of feature-to_feature distances during a master calibration stage. These pre-recorded distances serve as reference data that enables rapid recovery calibration without requiring time-consuming full recalibration procedures. The preliminary action of storing these characteristic distances allows for quick restoration of calibration accuracy when needed.
2Manufacturing precision
If comprehensive calibration methods are used to maintain accuracy, then manufacturing precision is improved, but device complexity and cost increase
Solution Approach 1:
The invention simplifies the calibration system by extracting only the essential measurements needed for accurate calibration - specifically, feature-to-feature distances between identifiable features on the tool and reference artefact. This extraction approach eliminates the need for complex comprehensive calibration systems while maintaining manufacturing precision through measurement of critical parameters only.
Solution Approach 2:
The method uses simple geometric features (such as spheres, cylinders, or planar surfaces) that can be easily manufactured and replicated on both the tool and reference artefact. These simplified feature copies enable accurate calibration without requiring complex calibration artifacts or measurement systems, thereby reducing device complexity while preserving calibration accuracy.
3Manufacturing precision
If frequent recalibration is performed to maintain precision, then manufacturing precision is maintained, but productivity and operational efficiency decrease
Solution Approach 1:
The invention performs preliminary recording of feature-to-feature distances during master calibration, creating a reference dataset that enables rapid recovery calibration. This preliminary action allows the system to maintain positioning accuracy through quick recalibration when drift is detected, rather than requiring frequent time-consuming full recalibration procedures, thereby preserving productivity.
Solution Approach 2:
The method extracts only the critical calibration parameters that need updating to maintain positioning accuracy. By identifying and updating only these essential parameters (tool centre point and tool frame orientation) rather than performing comprehensive recalibration, the system maintains manufacturing precision while minimizing disruption to operational efficiency and productivity.
Data Source
AI summary
A method of recovering a master calibration state of a coordinate positioning machine has a first member that is moveable relative to a second member, wherein the geometry of the machine is characterised by a set of model parameters. The machine is controlled to make point contact between multiple reference surfaces of a tool mounted on the first member and multiple reference surfaces of an artefact mounted on the second member. The separations between these contacting surfaces that would be expected from the current model parameters are determined, and these separations are recorded as a set of master separations. The contacting step is subsequently performed again in respect of at least some of the contacts for which master separations were recorded. At least one of the model parameters is updated to provide a closer correspondence between the expected separations and the master separations.