Displacement Detecting Device With Symmetric Optical Path Correction
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Solution Overview
Problem
Conventional displacement detecting devices experience measurement errors due to diffraction grating inclination or displacement, particularly when the grating moves in a direction other than the normal direction of its surface, leading to path length differences and mixing of unnecessary diffracted light, which affects precision.
Innovation Solution
A displacement detecting device is designed with a collimate lens, polarized beam splitter, deflection mirrors, and a prism unit that shifts light paths to ensure symmetrical incidence on the diffraction grating, using lenses with equal focus distances to correct light paths and prevent mixing of unnecessary diffracted light, thereby minimizing measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the diffraction grating moves in a normal direction of grating surface, then the central axis of lens and symmetric axis of two light paths will be deviated, but measurement precision deteriorates due to difference in light path length
Solution Approach 1:
The patent employs asymmetric optical path design where the two light paths are intentionally made symmetric with respect to the grating normal, but the optical system itself is asymmetric in arrangement. This allows the light paths to remain equal in length even when the grating moves normally, preventing measurement errors while maintaining operational flexibility.
Solution Approach 2:
The patent ensures that both light paths travel through equal optical path lengths by designing symmetric incidence angles and using lenses with equal focal distances. This creates an equipotential optical system where path length differences are eliminated, preventing measurement errors due to grating movement.
2Adaptability or versatility
If no lens focus is located on grating surface, then correction of light path is effective only in infinitesimal range, but device complexity increases with multiple lenses
Solution Approach 1:
The patent extracts the essential function of light path correction by positioning only one lens focus on the grating surface, rather than requiring multiple lenses or complex arrangements. This simplifies the optical system while maintaining effective correction over an extended measurement range.
Solution Approach 2:
The patent applies partial action by using a single lens configuration that provides sufficient light path correction for the required measurement range, rather than over-engineering with multiple lenses. This achieves adequate correction effectiveness without excessive device complexity.
3Ease of manufacture
If lateral magnification of optical system is not single, then first and second incident points become asymmetrical, but measurement precision deteriorates due to light path length difference
Solution Approach 1:
The patent maintains single lateral magnification by controlling the optical parameters, specifically by using lenses with equal focal distances and arranging them symmetrically with respect to the grating normal. This ensures that the first and second incident points remain symmetrical, preventing light path length differences and maintaining measurement precision.
4Measurement precision
If diffracted light with degree other than ±m degree is mixed in, then measurement precision deteriorates, but device complexity increases with light path control elements
Solution Approach 1:
The patent converts the potential harm of mixed diffracted orders into a benefit by using the symmetric optical path design to naturally filter out unwanted diffraction orders. The symmetry ensures that only the desired ±m degree diffracted lights follow the correct optical path to the detector, while other orders are automatically excluded, improving precision without adding complex control elements.
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 configuration significantly reduces measurement errors and ensures stable, high-precision displacement detection even when the diffraction grating is inclined or displaced, by maintaining consistent light path lengths and preventing the mixing of unwanted diffracted light.
Implementation Method 1
a collimate lens for making the coherent light emitted from the light source into parallel light flux
Implementation Method 2
each of the light fluxes split in two by the light flux splitting element enters the diffraction grating at incident angle that diffraction angle will be approximately vertical to the diffraction surface of the diffraction grating
Implementation Method 3
two lenses for correcting light path with equal focus distance arranged in light path of the light fluxes
Implementation Method 4
an interfered light receiving unit for receiving light by interfering diffracted light, which was moved in parallel in the prism unit for shifting light path, re-diffracted in the diffraction grating and superposed in the light flux splitting element
Data Source
AI summary
The purpose of the present invention is to provide a displacement detecting device capable of decreasing a measurement error, even when a diffraction grating is inclined or displaced to a direction other than a measuring direction. The displacement detecting device 1 comprising: a light source 2 for emitting light; a polarized beam splitter 7; a diffraction grating 11; a prism unit 16A (16 to 19) for shifting light path; lenses 14 and 20 for correcting light path; and an interfered light receiving unit 22A (22 to 30). The prism unit 16A for shifting light path shifts first diffracted light to a direction vertical to the measuring direction. The lenses 14 and 20 for correcting light path is arranged on a symmetrical axis of light paths and corrects light path when the diffraction grating 11 is inclined or moved to a normal direction of a grating surface.