Photoelectric Encoder Signal Processing for Distorted Bright/Dark Patterns
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Solution Overview
Problem
Photoelectric encoders face challenges in accurately determining bright and dark parts in distorted light intensity distributions due to factors like light source distribution and lens distortion, leading to incorrect threshold settings and measurement reliability issues.
Innovation Solution
A signal processing method that classifies bright/dark images into image-forming and non-image-forming regions, calculates representative light intensities for non-image-forming regions, and performs Fourier transforms to establish a threshold line for accurate bright/dark determination, using a micro lens array to enhance measurement speed and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a fixedly-set threshold is applied to a distorted bright/dark image, then the processing is simple and fast, but the bright part and dark part cannot be correctly determined leading to measurement errors
Solution Approach 1:
The patent applies preliminary action by performing Fourier transform processing before threshold determination to remove long-period distortion from the bright/dark image. This preprocessing step corrects the distorted light intensity distribution caused by lens array boundary effects and light source non-uniformity, enabling subsequent threshold processing to accurately determine bright and dark parts without requiring complex adaptive thresholding during measurement
2Measurement precision
If Fourier transform filtering is applied to remove long-period distortion, then the bright/dark determination accuracy improves, but the processing complexity and time increase
Solution Approach 1:
The patent employs efficient Fourier transform algorithms that can be implemented with minimal computational resources, treating the complex signal processing as a disposable calculation that is performed once during measurement rather than requiring complex hardware modifications. The method uses standard Fourier transform techniques that are computationally efficient and can be implemented in software, avoiding the need for expensive specialized processing hardware
3Volume of moving object
If a lens array is used to miniaturize the detection head, then the detection region increases and focal distance decreases, but non-image-forming regions appear at lens boundaries causing distortion
Solution Approach 1:
The patent extracts and removes the harmful non-image-forming regions from the bright/dark image through Fourier transform processing. By identifying and eliminating the periodic distortion patterns caused by lens array boundaries, the method separates the useful image information from the harmful artifacts, allowing accurate bright/dark determination despite the presence of lens array structure in the optical path
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 method allows for correct determination of bright and dark parts in distorted light intensity distributions, improving measurement reliability and speed by using pre-processed images with representative light intensities, thereby enhancing the accuracy of position measurement in photoelectric encoders.
Implementation Method 1
a light-receiving detector that receives reflected light or transmitted light from the scale
Implementation Method 2
a light-receiving detector that receives reflected light or transmitted light from the scale
Implementation Method 3
a lens array 115 has a wider detection region and a shorter focal distance than those of a single lens
Implementation Method 4
a threshold can be calculated with filtering processing for removing long-period distortion using the Fourier transform
Data Source
AI summary
There is provided a signal processing method, for a photoelectric encoder, capable of correctly determining a bright part and a dark part of a bright/dark pattern having distorted light intensity distribution by setting an appropriate threshold. A detector unit includes a light source, a light-receiving detector that receives transmitted light from a scale to acquire a bright/dark image, and a lens arranged between the light source and the light-receiving detector. The detector unit classifies the bright/dark image acquired by the light-receiving detector into an image-forming region corresponding to a center region of the lens and a non-image-forming region corresponding to a region except for the center region of the lens, calculates a representative value reflecting a light intensity of the image-forming region, and obtains a pre-processed bright/dark image in which the light intensity of the non-image-forming region is replaced with the representative value.