Absolute Position Measurement Apparatus Using Dual Light Sources
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Solution Overview
Problem
Conventional laser interferometers lack accurate and reproducible origin position measurement due to wavelength variations and phase coincidence errors, leading to inferior reproducibility compared to the resolution of the first light source.
Innovation Solution
An absolute position measurement apparatus using a first light source and a second light source with lower coherence, where the origin position is defined by the point where the phases coincide or intensity is maximized, and the phase of the first light source is stored to redefine the origin position accurately, ensuring reproducibility and stability across wavelength variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the origin position is defined based on phase coincidence or maximum intensity of interference signals from two light sources, then the origin detection function is achieved, but the reproducibility of the origin position deteriorates due to wavelength variations and measurement inaccuracies
Solution Approach 1:
The patent performs preliminary measurement of the phase of the first light source at the origin position before wavelength variations occur. This pre-measured phase value is stored and used as a reference to compensate for subsequent wavelength changes, ensuring consistent origin position determination despite environmental variations.
Solution Approach 2:
The system uses the pre-measured phase of the first light source as a feedback reference. When wavelength variations occur, the system compares current measurements against this stored reference phase value to determine the correct origin position, creating a closed-loop compensation mechanism that maintains measurement consistency.
2Measurement precision
If the interferometer uses a first light source with high coherence for position measurement, then position measurement accuracy is improved, but the origin position measurement deteriorates due to sensitivity to wavelength variations and optical path differences
Solution Approach 1:
The patent introduces the phase information of the first light source at the origin position as an intermediary parameter. This phase value serves as a mediator that connects the high-precision position measurement capability with the stable origin detection requirement, allowing the system to leverage the strengths of the first light source while compensating for its weaknesses through the stored phase reference.
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 solution enables precise and reproducible origin position measurement, maintaining high accuracy and stability even with wavelength changes, improving reproducibility by redefining the origin based on stored phase values, thus enhancing the reliability of absolute position measurements.
Implementation Method 1
a point where the phases of each of the interference signals obtained from these two light sources coincide with each other or a point where an intensity of the interference signal obtained from the light source which has low coherency is maximized
Data Source
AI summary
An absolute position measurement apparatus measures an absolute position of an object to be measured using a first light source and a second light source which has coherency lower than that of the first light source. The absolute position measurement apparatus includes a measurement part which measures a point where phases of interference signals from the first and the second light sources coincide with each other or a point where an intensity of the interference signal from the second light source is maximized, an origin defining part which defines the point measured by the measurement part as an origin position, a phase storing part which stores the phase of the interference signal from the first light source at the origin position, an origin redefining part which redefines the origin position, and a position calculating part which calculates the absolute position of the object to be measured.