Encoder Sub-Divisional Error Self-Calibration Using Inspection Device
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Solution Overview
Problem
Existing encoder apparatuses face challenges in accurately determining and correcting for sub-divisional errors, which affect the precision of measurements in coordinate measuring machines and other applications, often requiring external calibration equipment.
Innovation Solution
A method to determine and correct for sub-divisional errors using measurements obtained during the inspection of an artefact, without the need for external calibration, by analyzing periodic variations in the encoder apparatus' output to generate an error map that can correct for these errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external calibration equipment (e.g., laser interferometer) is used to determine encoder sub-divisional error, then measurement precision is improved, but device complexity and loss of time increase
Solution Approach 1:
The measurement apparatus performs self-calibration by using its own inspection device to measure a calibration artefact and determine the encoder's sub-divisional error. The system uses measurements of a known calibration artefact (with known dimensional characteristics) to calculate error values without requiring external calibration equipment. This self-service approach eliminates the need for separate calibration devices while maintaining measurement precision.
Solution Approach 2:
A calibration artefact serves as an intermediary medium between the encoder system and the calibration process. The artefact has known dimensional characteristics that allow the inspection device to measure and compare against expected values, thereby determining encoder errors indirectly through the artefact's reference dimensions rather than requiring direct comparison with external calibration standards.
2Measurement precision
If external calibration equipment is used to determine encoder sub-divisional error, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The system performs self-calibration using its own inspection device and a calibration artefact, eliminating the need to schedule and perform separate calibration operations with external equipment. The calibration process is integrated into the normal measurement workflow, allowing the apparatus to calibrate itself without time loss associated with external calibration equipment availability and setup.
Solution Approach 2:
The calibration artefact is prepared in advance with known dimensional characteristics, allowing the calibration process to be performed quickly when needed. The artefact's pre-defined geometric features (such as spheres, cylinders, or other shapes with known dimensions) enable rapid measurement and error determination without requiring time-consuming setup or alignment procedures with external calibration equipment.
3Adaptability or versatility
If the inspection device measures a calibration artefact to determine encoder error, then self-calibration is achieved, but the artefact must have known dimensional characteristics
Solution Approach 1:
The system uses its own inspection device to measure the calibration artefact and determine encoder errors, making the calibration process self-contained. The inspection device that would normally be used for regular measurements is also employed for calibration, eliminating the need for separate calibration equipment and enabling the system to self-calibrate using readily available artefacts with known dimensions.
Data Source
AI summary
A method of determining sub-divisional error of an encoder apparatus, which is configured to measure relative position of relatively moveable parts of an apparatus on which an inspection device for inspecting an artefact is mounted, includes causing the inspection device to inspect a feature so as to obtain measurements of a surface of the feature by relatively moving the relatively moveable parts of the apparatus. The method also includes using the measurements of the surface of the feature obtained by the inspection device during the inspection of the feature to determine the sub-divisional error of the encoder apparatus.