Optical Encoder Diffracted Light Error Reduction
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Solution Overview
Problem
Optical encoders face errors due to unwanted light interference when the number of functional light-receiving elements becomes odd, leading to unstable detection signals and increased complexity in shielding unwanted light, which complicates the encoder's structure and size.
Innovation Solution
The optical encoder is designed with a configuration where the number of light-receiving elements is set to minimize the number-of-elements-induced error, ensuring it remains below a predetermined allowable error, even if the total number of functional elements is odd, by adjusting the intensity of unwanted light rays and using a diffraction grating plate to efficiently collect diffracted light, thereby reducing the effect of unwanted light in a stable manner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a shielding object is provided to physically block unwanted light, then the effects of unwanted light are prevented, but the encoder increases in size and structural complexity
Solution Approach 1:
The patent extracts and eliminates the harmful unwanted light components (0-order and ±2-order light rays) from the optical path by configuring the diffraction grating plate to minimize their intensity, rather than using a physical shielding object. This removes the source of interference without adding complex shielding structures.
Solution Approach 2:
The patent changes the optical parameters by controlling the intensity distribution of diffracted light rays through the diffraction grating plate design, specifically ensuring that the 0-order light ray intensity is 50% or less and ±2-order light ray intensities are 14% or less relative to the ±1-order signal light, thereby reducing unwanted light effects without physical shielding.
2Reliability
If the number of light-receiving elements is set to an even number, then unwanted light effects are canceled out, but the detection becomes unstable when some elements become non-functional
Solution Approach 1:
The patent converts the harmful effect of unwanted light into a beneficial cancellation effect by carefully controlling the intensity parameters of diffracted light rays. By setting the 0-order light intensity to 50% or less and ±2-order light intensities to 14% or less, the unwanted light components naturally cancel out through interference, providing stable detection without requiring an even number of light-receiving elements.
3Measurement precision
If physical shielding is used to block unwanted light, then detection accuracy is improved, but the space required increases and the structure becomes more complex
Solution Approach 1:
The patent achieves improved detection accuracy by changing the optical parameters of the diffracted light through the diffraction grating plate configuration, specifically controlling the intensity ratios of different light rays, rather than using physical shielding that would increase encoder size.
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 allows for stable detection signals with reduced errors and improved accuracy, even with an odd number of functional light-receiving elements, by effectively managing the intensity of unwanted light and efficiently collecting diffracted light, thus maintaining performance without increasing the encoder's size or complexity.
Implementation Method 1
a scale with graduations; and a detection head provided, in a movable manner, relative to the scale... the graduations functioning as a diffraction grating for diffracting incident light
Implementation Method 2
The light-receiving means converts the light received at the light-receiving surface into detection signals that vary in a corresponding manner to the period of graduations
Implementation Method 3
The multiple diffracted light rays produce interference fringes with the same period as that of the graduations. The light-receiving means detects the detection signal by receiving such interference fringes
Data Source
AI summary
An optical encoder is provided that can reduce the effects of unwanted diffracted light in a stable manner. The optical encoder 1 comprises a scale 2 and a detection head 3. The detection head 3 includes a light source 4 and light-receiving means 6 with a light-receiving surface 60. The light-receiving surface 60 has an element row 7 with multiple light-receiving elements 70 arranged along the measurement direction with the same period as that of the interference fringes. Here, an error included in detection signals generated from the interference fringes, with such error being caused by the fact that the number of light-receiving elements 70 is an odd number, will be referred to as a number-of-elements-induced error, and a predetermined allowable error will be referred to as an allowable error. The number of light-receiving elements 70 in the element row 7 is set to be a number where the number-of-elements-induced error is smaller than the allowable error. Such number-of-elements-induced error is caused when there is an odd total number of light-receiving elements 70 and such odd total number of light-receiving elements 70 are functional, or when there is an even total number of light-receiving elements 70 but one less than such even total number of light-receiving elements are functional.