Rotary Encoder Index Pulse Detection via Symmetrical Photodiode Arrays
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Solution Overview
Problem
Existing rotary encoders face challenges in achieving accurate angle position detection due to temperature dependency, stray light interference, and increased diameter requirements, which affect signal strength and resolution, especially at high rotational speeds.
Innovation Solution
The device employs a single index track with a symmetrical light detector array, where non-inverting and inverting signals are generated using the same number of identical photodiodes, and a differential amplifier to minimize temperature-dependent interference, ensuring equal signal strength and capacitance between index and counting pulse channels, and uses a comparator with a threshold value adjusted for light intensity to maintain precise index pulse detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the index track is widened to generate stronger index signals, then the signal strength is improved, but the diameter of the encoder increases significantly
Solution Approach 1:
The patent combines the non-inverting and inverting index channel photodiodes into a single integrated circuit track, allowing both signals to be processed simultaneously in a compact radial space. This merging enables strong index signal generation without requiring separate wide tracks, thus avoiding encoder diameter increase while maintaining signal strength through coordinated photodiode arrangement and signal processing.
2Illumination intensity
If different amplification factors are used for count pulse signals and index signal, then the signal strength is equalized, but the temperature dependency of temporal association increases
Solution Approach 1:
The patent changes the photodiode area parameter to be equal for both index and counting pulse channels, rather than using different amplification factors. This parameter change ensures that both signal types have equal strength inherently, eliminating the need for differential amplification that would cause temperature-dependent temporal association issues. The equal area design maintains stable temporal relationships across temperature variations.
3Illumination intensity
If scattered light is present, then the index pulses become wider, but the position assignment accuracy decreases
Solution Approach 1:
The patent converts the harmful scattered light into a beneficial signal by using a differential evaluation method. The non-inverting and inverting index channel photodiodes are arranged to receive scattered light differently, and their differential signal processing cancels out the scattered light component while preserving the useful index pulse information. This transforms the harmful scattered light into a factor that does not degrade measurement precision.
4Speed
If the relative position of pulses shifts with increasing rotational speed, then high-speed operation is possible, but the counting results become incorrect
Solution Approach 1:
The patent changes the electrical capacitance parameter of the photodiodes to be equal between index and counting pulse channels. This parameter change ensures that pulse delay characteristics are matched, preventing relative position shifts even at high rotational speeds. The equal capacitance design maintains synchronous pulse timing, ensuring accurate counting results during high-speed operation.
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 approach results in precise and stable index pulse generation, maintaining signal integrity at high rotational speeds, reducing the influence of stray light, and allowing for narrower index pulses with high signal-to-noise ratios, thus enhancing the accuracy and efficiency of angle position measurement.
Implementation Method 1
a light source for emitting light and a coding mask arranged in the beam path of the light source for modulating the light... For receiving the light modulated by the coding mask and generating output signals dependent on the light intensity
Data Source
AI summary
The invention relates to a device for detecting angle or position changes, comprising a light source (4) for emitting light and a coding mask (9) arranged in the beam path of the light source for modulating the light. The coding mask (9) has a counting pulse track (10) and an index track (11), to each of which a light detector array (6A and 6B respectively) is assigned. The device also has an evaluation device (12) which evaluates the output signals of the light detector arrays, generates counting pulses from the output signals of the light detectors that are assigned to the counting pulse track, and generates an index pulse (16) to be assigned to the counting pulses from the output signals of the light detectors that are assigned to the index track. The evaluation device (12) has means (14) for forming a sum signal from non-inverted output signals of a first group Z of light detectors of the light detector array (6B) of the index channel and from inverted output signals of a second group Z' of light detectors of the light detector array (6B) of the index channel. The device is characterised in that the sum of the surfaces of the light detectors (7) of the first group Z of light detectors is equal to the sum of surfaces of the light detectors of the second group Z' of light detectors, the surface and quantity of light detectors preferably being equal.