Retroreflective Encoder Grating for Compact Displacement Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Retroreflection type photoelectric encoders face challenges in reducing the number of components and achieving downsizing due to complex configurations required for phase difference signal extraction, which complicates the device and hinders degree of integration.
Innovation Solution
A retroreflection type photoelectric encoder design that includes a scale diffraction grating and a detecting head unit with two retroreflecting units, each comprising a corner cube and a wedge prism, which deflects light by a predetermined angle to prevent interference and allow for interference fringe detection, reducing the need for multiple polarizers and phase plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple polarizers and phase plates are used to extract phase difference signals, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent combines the functions of multiple polarizers and phase plates into a single integrated optical system. The scale grating itself serves as the phase modulation element, while the object grating and illumination optics work together to generate and detect phase difference signals, eliminating the need for separate polarizing and phase-shifting components.
Solution Approach 2:
The scale grating performs multiple functions: it acts as both the diffraction element and the phase modulation element. The illumination optics system simultaneously generates the illumination light and serves as part of the detection path, reducing the need for separate dedicated components for each function.
2Measurement precision
If auxiliary diffraction gratings are added to extract phase signals, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the scale grating and object grating into a coordinated measurement system where the object grating is positioned on the measurement target. This combination allows phase difference extraction without requiring multiple auxiliary diffraction gratings, as the interference between light diffracted by the scale grating and light diffracted by the object grating provides the necessary phase information.
3Measurement precision
If complex optical systems are used to prevent beam interference, then measurement precision is improved, but ease of manufacture worsens
Solution Approach 1:
The patent employs a retroreflection configuration where the illumination light diffracted by the scale grating reflects off the object grating and returns through the same optical path. This self-service arrangement automatically maintains beam separation and phase relationship without requiring complex active control or precise real-time alignment, significantly improving ease of manufacture while maintaining measurement precision.
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 achieves a four-fold increase in optical resolution, allows for phase signal detection, and significantly reduces the number of components, enabling a more compact and cost-effective design with improved integration.
Implementation Method 1
Light is divided into two beams due to first diffraction by a scale diffraction grating
Implementation Method 2
These individual beams are retroreflected by retroreflective devices
Implementation Method 3
a light receiving unit that receives an interference fringe formed on the light receiving unit by the light retroreflected by the first retroreflecting unit and diffracted by the scale diffraction grating and the light retroreflected by the second retroreflecting unit and diffracted by the scale diffraction grating
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A displacement detecting device includes a scale diffraction grating (210) and a detecting head unit (300). The detecting head unit (300) includes a light source (320), a first retroreflecting unit (350) that retroreflectes positive first-order diffracted light of light diffracted by the scale diffraction grating, such that the retroreflected light enters the scale diffraction grating again, a second retroreflecting unit (360) that retroreflectes negative first-order diffracted light of the light diffracted by the scale diffraction grating, such that the retroreflected light enters the scale diffraction grating (210) again, and a light receiving unit (380) that receives an interference signal. Each of the first retroreflecting unit (350) and the second retroreflecting unit (360) has a deflecting function of deflecting light incident on the corresponding retroreflecting unit by a predetermined angle and then emitting the light.