Aspherical Surface Measurement Correction Using Master Work Piece Calibration
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Solution Overview
Problem
Current shape measurement devices, particularly those using pivot-type styluses, face challenges in achieving high precision for aspherical surfaces due to limitations in calibration methods, which result in significant shape errors when measuring industrial products like lenses with design values in the range of several dozen nanometers.
Innovation Solution
A measurement value correction method that involves preparing multiple work pieces from the same design data, using one as a master to obtain reference measurement values, calculating calibration data based on design data, and applying this calibration to correct target measurement values using a model expression fitted to the relationship between design and correction values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional calibration methods using ideal spherical surfaces and cylindrical surfaces are used, then the calibration process is simple, but the measurement precision for aspherical surfaces deteriorates significantly
Solution Approach 1:
The invention changes the calibration approach by using multiple work pieces with different aspherical parameters (different design values) instead of conventional spherical/cylindrical references. This allows the calibration data to capture the specific arc motion characteristics of pivot-type styluses when measuring aspherical surfaces, thereby improving measurement precision for aspherical work pieces while maintaining practical calibration feasibility
Solution Approach 2:
The invention creates calibration data by measuring multiple work pieces that replicate the aspherical geometry characteristics. These work pieces serve as copies of the measurement target geometry, allowing the system to learn correction factors specific to aspherical surfaces without requiring an ideal reference sphere, thus resolving the contradiction between calibration simplicity and measurement precision
2Measurement precision
If multiple work pieces from the same design data are used for calibration, then the calibration data becomes optimum for the measurement target, but the calibration process complexity increases
Solution Approach 1:
The invention makes the calibration system universal by using multiple work pieces with different design values that all share the same aspherical geometry type. The calibration data obtained from these diverse work pieces can be applied to measure any work piece with similar aspherical characteristics, achieving broad applicability without requiring separate calibration for each specific measurement target
Solution Approach 2:
The invention performs preliminary calibration measurements on multiple work pieces before actual production measurements. By pre-establishing calibration data from multiple reference work pieces, the system prepares correction factors in advance that can be efficiently applied during subsequent measurements, reducing real-time computational complexity while maintaining high precision
Data Source
AI summary
A measurement value correction method according to the present invention is a measurement value correction method for correcting a measurement value obtained by tracing a surface of a work piece with a stylus, and including a step of preparing a plurality of work pieces made from same design data, a step of adopting one of the work pieces as a master work piece and obtaining a reference measurement value with the stylus, a step of obtaining calibration data based on a difference between the reference measurement value and the design data, a step of adopting one of the plurality of work pieces other than the master work piece as a measurement target work piece and obtaining a target measurement value with the stylus, and a step of obtaining a corrected measurement value by correcting the target measurement value by using the calibration data.