Height Measurement Optics Using Dichroic Ratio 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 intersecting the optical axis and uses an optical element with varying transmittance and reflectance to separate and calculate wavelength information based on the ratio of reflected and transmitted light quantities, independent of the object's color.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If wavelength detection is performed using a color imaging element, then the measurement process is simple, but the measurement precision deteriorates due to color interference from the measurement object
Solution Approach 1:
The patent introduces a dichroic mirror as an intermediary optical element between the light source and the measurement object. This dichroic mirror separates incident light into reflected and transmitted components based on wavelength, enabling wavelength detection without direct color interference from the measurement object. The intermediary element allows the system to obtain wavelength information while eliminating the harmful color interference that would otherwise affect measurement precision.
Solution Approach 2:
The patent replaces the conventional color imaging element (which uses photodetectors sensitive to color) with an optical separation system using a dichroic mirror and line sensors. Instead of relying on the color sensitivity of imaging elements that are affected by object color, the system uses optical reflection and transmission properties to separate wavelengths, substituting a mechanical/optical separation mechanism for the color-detection mechanism.
2Measurement precision
If multiple light fluxes of different wavelengths are used, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent segments the incident light into multiple wavelength components using a dichroic mirror, separating reflected and transmitted light based on their wavelength characteristics. This segmentation allows the system to detect different wavelengths simultaneously using line sensors positioned at specific locations, achieving high measurement precision while maintaining relatively simple optical architecture through systematic light division.
Solution Approach 2:
The dichroic mirror serves multiple functions simultaneously: it separates wavelengths, directs reflected light to one sensor and transmitted light to another sensor, and enables wavelength-dependent measurement. This multi-functionality reduces the need for additional separate optical components, thereby managing device complexity while achieving high measurement precision through wavelength-multiplexed detection.
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 higher accuracy in height measurement by calculating wavelength information without color interference, using line sensors and parallel light for precise imaging and shape derivation.
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
Implementation Method 2
a light irradiation unit that irradiates a measurement object with irradiation light including a plurality of light fluxes arranged in a direction intersecting an optical axis direction and having different wavelengths, at an angle inclined with respect to a height direction of the measurement object
Implementation Method 3
a first line sensor that detects a reflected light quantity from light reflected by the optical element, and a second line sensor that detects a transmitted light quantity from light transmitted through the optical element
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.