Photoelectric Rotary Encoder Deformed Grating Precision
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Solution Overview
Problem
Photoelectric rotary encoders using the three-grating principle face challenges in maintaining detection precision due to distorted interference fringes, leading to a reduced signal-to-noise ratio and poor precision, especially in small-diameter encoders.
Innovation Solution
A photoelectric rotary encoder design featuring a diffraction unit and a passage unit with deformed grating parts that correct distortion, allowing interference fringes similar to those in photoelectric linear encoders to be generated, enabling the use of standardized light-receiving elements and improving detection precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the index and light-receiving unit are formed in an arc shape to match the arc-shaped scale in photoelectric rotary encoders, then the three-grating principle can be employed, but it becomes difficult to standardize the light-receiving elements between linear and rotary encoders
Solution Approach 1:
The light-receiving unit is divided into multiple light-receiving elements arranged in an arc shape, where each element corresponds to a specific angular position. This segmentation allows the use of standardized linear light-receiving elements while maintaining the arc-shaped configuration needed for rotary encoders, thus resolving the contradiction between standardization and adaptability
Solution Approach 2:
An intermediate conversion mechanism is introduced that transforms the arc-shaped light distribution from the scale into linear displacement signals that can be processed by standardized light-receiving elements. This intermediary function allows standardized elements to work in both linear and rotary encoder configurations
2Measurement precision
If distorted interference fringes are generated in the middle of the light-receiving unit, then the optical encoder can acquire interference fringes similar to photoelectric linear encoders, but the signal-to-noise ratio is reduced leading to poor precision
Solution Approach 1:
The aperture is designed to extract only the undistorted interference fringes from specific angular regions, excluding the distorted fringes from the center region. By selectively extracting the useful signal components and rejecting the distorted components, the signal-to-noise ratio is improved while maintaining detection precision
Solution Approach 2:
Different regions of the light-receiving unit are assigned different functions: the aperture blocks distorted fringes from the center region while allowing undistorted fringes from the peripheral regions to pass through. This local differentiation of quality (blocking vs. transmitting) resolves the contradiction between acquiring interference fringes and maintaining signal quality
3Adaptability or versatility
If only interference fringes similar to photoelectric linear encoders are acquired using a mask material aperture, then standardized light-receiving elements can be used, but distorted interference fringes are blocked out reducing detection capability
Solution Approach 1:
The system dynamically selects which interference fringes to utilize based on their quality - undistorted fringes are captured while distorted ones are rejected. This dynamic selection process allows the use of standardized elements while maintaining high detection precision through intelligent signal filtering
Solution Approach 2:
The aperture configuration provides feedback by selectively transmitting or blocking light based on the spatial distribution of interference fringes. This feedback mechanism ensures that only high-quality undistorted fringes reach the standardized light-receiving elements, maintaining both standardization and 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
The solution maintains detection precision while employing the three-grating principle, allows for standardization of light-receiving elements between linear and rotary encoders, and reduces costs by using common elements, with enhanced precision and correction capabilities, especially in small-diameter encoders.
Implementation Method 1
The diffraction unit has a plurality of grating parts formed in a predetermined shape in a plane parallel to the plate surface of the scale in order to diffract the light from the light source
Implementation Method 2
The light-receiving unit receives interference light having a predetermined period along the orthogonal direction, the interference light being caused by diffraction at the diffraction unit and passing through the passage unit via the scale
Data Source
AI summary
The photoelectric rotary encoder includes: a generally disk-shaped scale with a grating-like pattern formed with a predetermined period along a measurement direction, the measurement direction being a direction of rotation of a measurement target that rotates on a predetermined axis, the scale being plate-like and centered on an axis of rotation; and a head that detect, from the scale, the amount of displacement caused by the rotation of the measurement target. The head includes a light source, a diffraction unit with grating parts, and a light-receiving unit with light-receiving elements. The grating parts of the diffraction unit are formed as deformed grating parts that spread cut wide, from the center on the axis of rotation, along the grating-like pattern of the scale. The light-receiving elements are formed as linear grating parts.