Scanning Head Calibration Using Reference Artefact
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Solution Overview
Problem
Existing methods for calibrating motorized scanning heads require accurate alignment with calibrated rotary stages, which can introduce eccentricity errors and complicate the calibration process, limiting accuracy and ease of implementation.
Innovation Solution
A method involving a calibration artefact where a surface sensing device is rotated about the scanning head's axes in various orientations to measure properties, allowing for the creation of an error map that corrects measurement scale errors without requiring precise alignment with a calibrated rotary stage, thus eliminating eccentricity errors and simplifying the calibration process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a calibrated rotary stage is used to calibrate the scanning head, then the measurement scale can be calibrated, but accurate alignment between the scanning head and rotary stage is required which introduces eccentricity errors and complicates the calibration process
Solution Approach 1:
The patent introduces a calibration artefact as an intermediary object with known geometric properties (spheres or cylinders) that mediates between the scanning head and the calibration process. By measuring the artefact's known dimensions at multiple orientations, the system eliminates the need for direct alignment between the scanning head and a rotary stage, thereby removing eccentricity errors while maintaining calibration accuracy.
Solution Approach 2:
The patent creates a simplified calibration model using a calibration artefact that replicates the measurement function without requiring the complex alignment setup of a rotary stage. The artefact's known geometric properties serve as a copy of the reference standard, enabling calibration through measurement of the artefact itself rather than through direct comparison with a rotary stage.
2Measurement precision
If a calibrated rotary stage is used for calibration, then the measurement scale can be calibrated, but eccentricity errors arise from misalignment which limit measurement precision
Solution Approach 1:
The calibration artefact acts as an intermediary that eliminates eccentricity errors by providing a stable reference frame independent of the scanning head's alignment. The artefact's known geometric properties allow the system to measure and compensate for any alignment errors, thereby removing harmful eccentricity factors from the calibration process.
Solution Approach 2:
The patent converts the potential harm of alignment errors into a benefit by using the calibration artefact to measure and characterize these errors. By measuring the artefact at multiple orientations, the system can identify and compensate for eccentricity errors, transforming them from detrimental factors into correctable calibration parameters.
3Productivity
If the scanning head is directly coupled to a calibrated rotary stage, then calibration can be performed, but the calibration process becomes more time-consuming and complex
Solution Approach 1:
The patent extracts the calibration function from the complex rotary stage coupling and implements it independently through the calibration artefact. This allows the scanning head to be calibrated without being physically coupled to a rotary stage, significantly reducing calibration time and complexity while maintaining accuracy.
Solution Approach 2:
The calibration artefact provides a simplified copy of the calibration reference that can be quickly measured without the time-consuming alignment procedures required for rotary stage coupling. The artefact's fixed geometric properties enable rapid measurement at multiple orientations, improving calibration productivity.
Data Source
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AI summary
A method of calibrating an angular measurement scale in a motorised articulated scanning head (16) using a reference artefact (40; 60; 80) is described. The method comprises the step of rotating a surface sensing device, such as a scanning probe (28), mounted on the scanning head (16) about at least one axis (A1, A2) of the scanning head (16) to move the surface sensing device into a plurality of different angular orientations relative to the reference artefact (40; 60; 80). A step is then performed of measuring, with the surface sensing device, at least one property of the reference artefact (40; 60; 80) at each of the different angular orientations. An error map or function is then created for at least one measurement scale of the scanning head using the properties of the reference artefact (40; 60; 80) measured and optionally known or calibrated properties of that reference artefact (40; 60; 80). The method may comprise use of co-ordinate positioning apparatus, such as a co-ordinate measuring machine (14), to move the scanning head (16). The reference artefact (40; 60; 80) may comprise a single feature or an array of features (46; 66).