Height Measurement Correction for Optical Aberration Error
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Solution Overview
Problem
Conventional height measurement methods using texture patterns and optical systems are prone to errors due to various aberrations, such as spherical aberration, which affect the accuracy of measured height values based on the inclination angle of the object's surface.
Innovation Solution
A method involving a height measuring apparatus with an imaging device and optical system that scans the object along its optical axis, calculates the inclination angle of the object's surface, and uses angle correction data to correct the measured height values, thereby reducing errors caused by optical aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional height measurement method using texture pattern and optical system is used, then height measurement can be performed, but measurement precision deteriorates due to optical aberrations such as spherical aberration affecting the measured height values
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values for various inclination angles before actual measurement. The system creates a lookup table of correction data that compensates for optical aberrations in advance, allowing rapid correction during measurement without real-time complex calculations.
Solution Approach 2:
The patent changes the parameter approach by shifting from direct height measurement to measuring inclination angle first, then using pre-stored correction data corresponding to that angle. This parameter transformation allows the system to compensate for optical aberrations by selecting appropriate correction values based on the measured inclination angle.
2Measurement precision
If height measurement is performed using degree of focus from images, then height value can be obtained, but error is introduced due to inclination angle of the object surface
Solution Approach 1:
The system performs preliminary measurement of the inclination angle and uses this information to select appropriate correction data before final height calculation. This preliminary action allows the system to account for inclination effects before they corrupt the height measurement.
Solution Approach 2:
The patent implements feedback by using the measured inclination angle to retrieve corresponding correction values, which are then applied to correct the height measurement. This feedback loop ensures that the measurement process automatically compensates for inclination-related errors based on the actual measured angle.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for more accurate height measurements by accounting for and correcting the errors introduced by optical aberrations, resulting in improved precision of the measured height values.
Implementation Method 1
an imaging device and an imaging optical system for forming an image of the object to an imaging plane of the image device
Implementation Method 2
images detected by an imaging device
Data Source
AI summary
There are provided a method for measuring a height by a height measuring apparatus including: obtaining, in advance, a height correction value depending on an inclination angle of a surface of the object as an angle correction data; obtaining, from the height value of each pixel of the imaging device, the inclination angle of the surface of the object which corresponds to each pixel position of the imaging device; obtaining the height correction value, which corresponds to the inclination angle obtained, from the angle correction data; and correcting the height value of the surface of the object, which corresponds to each pixel of the imaging device, by using the height correction value obtained.