Scanning Probe Tip Ball Displacement Correction for Quadrant Projection Error
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Solution Overview
Problem
Existing shape measuring apparatuses with scanning probes face measurement errors due to quadrant projection, particularly when the angle between the stylus axis and contact direction varies, as existing correction methods do not account for changes in frequency transfer characteristics with angle changes.
Innovation Solution
The method involves detecting the displacement of the scanning probe's tip ball and the moving mechanism, calculating the angle between the contact direction and stylus axis, correcting the displacement based on the varying frequency transfer characteristic, and outputting a corrected value by adding the product of the sinusoidal value and the inverse of the frequency transfer characteristic to the displacement, thereby improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed correction filter based on frequency transfer characteristic is used, then measurement error correction is simplified, but measurement accuracy deteriorates when the angle between stylus axis and contact direction varies
Solution Approach 1:
The patent applies dynamics by making the correction filter adaptive rather than fixed. The system dynamically adjusts the correction filter parameters based on the detected angle between the stylus axis and contact direction, allowing the measurement system to adapt to varying measurement conditions and maintain high accuracy across different angles
Solution Approach 2:
The patent changes the parameters of the correction filter based on the measurement angle. By detecting the angle and selecting or adjusting correction filter parameters accordingly, the system optimizes the frequency transfer characteristic correction for each specific measurement configuration, resolving the contradiction between fixed simplicity and variable accuracy
2Productivity
If the frequency transfer characteristic is assumed constant, then correction calculation is simplified, but measurement error correction becomes inaccurate when angle varies
Solution Approach 1:
The patent performs preliminary measurement of the angle between the stylus axis and contact direction before applying correction. By detecting the angle in advance and using it to select or adjust the correction filter parameters, the system prepares the appropriate correction characteristics beforehand, ensuring accurate correction without complex real-time calculations
Solution Approach 2:
The system changes the correction parameters based on the measured angle, selecting from pre-calculated correction characteristics or adjusting filter parameters accordingly. This approach maintains calculation efficiency by using pre-computed values while adapting to different measurement angles for accurate correction
3Loss of time
If a simple correction method is used, then measurement process is faster, but quadrant projection error is not properly corrected when angle varies
Solution Approach 1:
The patent performs preliminary angle detection and correction filter selection before the actual measurement correction. This preliminary action allows the system to quickly apply the appropriate correction without complex real-time computations during measurement, maintaining speed while improving accuracy
Solution Approach 2:
The system dynamically selects or adjusts correction parameters based on the detected angle, enabling accurate quadrant projection error correction for varying measurement configurations without requiring complex real-time calculations, thus maintaining measurement speed
Data Source
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AI summary
In a shape measuring apparatus having a scanning probe(10) to perform scanning measurement using a tip ball(14) provided at an end of a stylus(12) with the tip ball(14) being in contact with an object(B) to be measured, a tip ball displacement detector(11) detects a displacement of the tip ball(14) of the scanning probe(10), a displacement of a moving mechanism(2,3,8) that relatively moves the object(B) to be measured and the scanning probe(10) is detected, and an angle(9) formed by a contact direction of the tip ball(14) with the object(B) to be measured and an axial direction of the stylus(12) is calculated. The displacement of the tip ball(14) that is detected by the tip ball displacement detector(11) is corrected on the basis of the angle(8), and a corrected value of the displacement is outputted. The corrected value is added to the displacement of the moving mechanism(2,3,8) to calculate a measurement value.