Displacement Detector Retroreflector Geometry
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Solution Overview
Problem
Conventional laser beam interference type displacement detectors face challenges in maintaining detection accuracy and stability due to changes in the relative posture between the scale and the detection head, particularly when the scale yaws, leading to fluctuations in optical path length and reduced interference signal intensity.
Innovation Solution
The displacement detector design includes a scale with a diffraction grating and a detection head that emits interference light perpendicular to the diffraction grating grooves, using retroreflectors to ensure incident and retroreflected light paths are perpendicular, thereby reducing changes in diffraction angles and enhancing detection accuracy by increasing the incident angle and maintaining high resolving power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the scale and detection head are arranged in a compact configuration with oblique incidence, then the device size is reduced, but the detection accuracy deteriorates due to posture changes
Solution Approach 1:
The patent changes the incidence angle parameter from oblique to perpendicular (0 degrees), which fundamentally alters the diffraction geometry. This parameter change makes the diffraction angle insensitive to posture variations while maintaining compact device size through optimized optical path design
2Reliability
If the incident angle is increased to reduce diffraction angle changes, then the stability improves, but the optical path length increases
Solution Approach 1:
The patent sets the incident angle to exactly 0 degrees (perpendicular incidence), which is the optimal parameter value that minimizes diffraction angle sensitivity to posture changes. This parameter optimization achieves maximum stability without unnecessarily increasing optical path length
3Measurement precision
If retroreflectors are added to ensure perpendicular incidence, then the detection accuracy improves, but the device complexity increases
Solution Approach 1:
The retroreflector is designed to automatically return diffracted light to the incident path without requiring external alignment or adjustment. This self-correcting feature maintains perpendicular incidence and detection accuracy while minimizing the complexity increase from adding the retroreflector component
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 stabilizes detection accuracy by minimizing changes in optical path length and diffraction efficiency, allowing for precise detection of relative displacement between the scale and detection head, even during yawing, and enhances signal efficiency and detection accuracy.
Implementation Method 1
a scale having a diffraction grating; and a detection head, which is arranged being capable of relatively moving with respect to the scale, emitting interference light to the scale and receiving diffracted light sent from the scale
Implementation Method 2
a retroreflector, which is arranged for each of the beams of diffracted light generated when the two beams of light incident upon the scale are diffracted by the diffraction grating, for retroreflecting the diffracted light
Implementation Method 3
a laser beam interference type displacement detector
Data Source
AI summary
The displacement detector includes: a light source 140; a beam splitter 170 for dividing the light, which is sent from the light source 140, into two beams of light; reflection mirrors 181, 182 provided for the two beams of light sent from the beam splitter 170, for reflecting these two beams of light and making them incident upon a scale 110; and corner cubes 191, 192 provided for the beams of diffracted light, which are generated when two beams of light incident upon the scale 110 are diffracted by the diffraction grating 111, wherein the corner cubes 191, 192 retroreflect the diffracted light and make the light incident upon the scale as retroreflected light. The incident angle to grating groove formed between the incident light and the normal line vector of the scale is larger than the diffraction angle formed between the retroreflected light and the normal line vector of the scale.