Optical Encoder Moire Fringe Shadow Smoothing
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Solution Overview
Problem
Optical encoders using the moire detection method face issues with distortion and individual differences in incremental signals due to high-frequency grating pattern shadows, which are not effectively resolved by existing configurations that include large telecentric lenses, leading to reduced resolving power and increased complexity.
Innovation Solution
The optical encoder design incorporates a light source, first, second, and third grating patterns with different pitches, where the light receiving element array is positioned to receive light that forms moire fringes with a smoothed shadow of the third grating pattern, and includes a light receiving element array with multiple elements in different phases to combine signals and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a telecentric lens is included in the encoder to resolve the shadow of the high-frequency grating pattern, then the distortion and individual difference of the incremental signal are reduced, but the configuration becomes more complex and the size of the encoder increases
Solution Approach 1:
The patent extracts and removes the telecentric lens from the optical system, replacing it with a simplified configuration that uses only the scale pattern, grating pattern, and light receiving element. This eliminates the harmful effect of complex optical components while maintaining the ability to reduce shadow distortion through geometric arrangement.
Solution Approach 2:
The patent introduces a light receiving element that directly receives light from the grating pattern without requiring a telecentric lens as an intermediary. The light receiving element is positioned to receive light at specific angles, achieving shadow reduction through direct geometric relationships rather than optical components.
2Measurement precision
If a telecentric lens is included in the encoder to resolve the shadow of the high-frequency grating pattern, then the distortion and individual difference of the incremental signal are reduced, but the size of the encoder increases
Solution Approach 1:
The patent extracts and removes the telecentric lens from the optical system, replacing it with a simplified configuration that uses only the scale pattern, grating pattern, and light receiving element. This eliminates the harmful effect of complex optical components while maintaining the ability to reduce shadow distortion through geometric arrangement.
3Object-generated harmful factors
If the numerical aperture of the telecentric lens is reduced to prevent shadow resolution, then the shadow of the high-frequency grating pattern is not resolved, but the resolving power of the encoder is decreased
Solution Approach 1:
The patent changes the geometric parameters of the optical system by positioning the light receiving element to receive light at specific angles relative to the grating pattern. This geometric parameter change allows shadow reduction without requiring changes to lens aperture, thereby maintaining resolving power.
4Measurement precision
If the pitch of the moire fringes is made significantly larger than the pitch of the scale pattern to achieve high-resolution signals, then a large light receiving element is required, but the encoder size increases
Solution Approach 1:
The patent utilizes angular dimension by positioning the light receiving element to receive light at specific angles. This allows the system to achieve high resolution through angular separation rather than requiring large physical dimensions, effectively converting a one-dimensional size problem into an angular solution.
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 results in a compact optical encoder that decreases distortion and individual differences in incremental signals, maintaining high resolution without the need for large optical components like telecentric lenses.
Implementation Method 1
detecting moire fringes formed by disposing a grating pattern having a slightly different pitch from a pitch of a scale pattern between the scale pattern and a light receiving element
Implementation Method 2
first moire fringes including a shadow of the third grating pattern are formed on an exit plane of the third grating pattern due to a difference between the second pitch and the third pitch
Data Source
AI summary
An optical encoder includes a first grating pattern having a first pitch, a second grating pattern having a second pitch, a third grating pattern having a third pitch different from the second pitch, and a light receiving element configured to receive light from the third grating pattern in an order from a side of a light source, wherein first moire fringes including a shadow of the third grating pattern are formed on an exit plane of the third grating pattern due to a difference between the second pitch and the third pitch, and wherein the light receiving element receives light that forms second moire fringes in which the shadow of the third grating pattern is smoothed more than in the first moire fringes by placing the third grating pattern and the light receiving element away from each other.