Dichroic Mirror Height Measurement for Color-Independent Wavelength Sensing
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Solution Overview
Problem
Existing height measurement methods using wavelength detection are affected by the color of the measurement object, leading to decreased accuracy in height measurement results.
Innovation Solution
A height measurement apparatus that irradiates the object with light fluxes of different wavelengths at an angle, using an optical element with varying transmittance and reflectance to separate light based on wavelength, and calculates height based on the ratio of reflected and transmitted light quantities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If wavelength of light from measurement object is obtained by color imaging element, then height measurement can be performed, but measurement accuracy decreases due to color of measurement object affecting wavelength derivation
Solution Approach 1:
The light detection is segmented into multiple channels (first light detector for reflected light, second light detector for transmitted light) to separately measure different light quantities. This segmentation allows independent measurement of reflection and transmission characteristics, eliminating the need to derive wavelength from color imaging and directly obtaining accurate wavelength information through ratio calculation.
Solution Approach 2:
An optical element with wavelength-dependent transmittance and reflectance characteristics is introduced as an intermediary between the measurement object and detectors. This optical element converts wavelength information into intensity ratios that can be measured by the detectors, serving as a mediator that transforms the measurement problem from direct color-based wavelength derivation to ratio-based wavelength determination.
2Manufacturing precision
If light intensity from color imaging element is used to derive wavelength, then height measurement is possible, but calculation accuracy cannot be guaranteed due to measurement object color influence
Solution Approach 1:
The harmful effect of measurement object color is extracted and isolated by using the ratio of reflected to transmitted light quantities. By taking the ratio, the color information (which affects both reflected and transmitted light equally) cancels out, leaving only the wavelength-dependent optical element characteristics. This extraction method removes the interference factor while preserving the measurement signal.
Solution Approach 2:
The measurement approach changes from using absolute light intensity parameters (which are affected by object color) to using ratio parameters (reflected light quantity divided by transmitted light quantity). This parameter transformation converts a color-sensitive measurement into a color-independent measurement, as the ratio eliminates the multiplicative effect of object color on the light signal.
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
The apparatus achieves high accuracy in height measurement by isolating wavelength information from the object's color influence, enabling precise calculation of object height and shape.
Implementation Method 1
an optical element of which a transmittance and a reflectance change according to a wavelength in a predetermined wavelength range and which separates the light from the measurement object by transmitting and reflecting the light
Data Source
AI summary
A height measurement apparatus includes: a light irradiation unit that irradiates a sample with irradiation light; a camera system that detects light from the sample irradiated with the irradiation light; and a control apparatus that calculates a height of the sample based on the wavelength information. The camera system includes an inclined dichroic mirror of which a transmittance and a reflectance change according to a wavelength in a predetermined wavelength range and which separates the light from the sample by transmitting and reflecting the light, a light detector that detects a reflected light quantity from light reflected by the inclined dichroic mirror, a light detector that detects a transmitted light quantity from light transmitted through the inclined dichroic mirror, and a processing unit that calculates the wavelength information based on a ratio between the reflected light quantity and the transmitted light quantity, to output the wavelength information.