Optical Encoder Reference Detection Using Differential and Gate Signals
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Solution Overview
Problem
Conventional optical encoders face challenges in accurately detecting the reference position due to difficulties in distinguishing zero crossings, leading to inaccurate movement and potential damage to machine tools and processed goods.
Innovation Solution
An optical encoder design featuring a light source, a scale with periodic and reference position patterns, and a photodetector array with multiple elements that calculate differential signals and generate gate signals based on zero crossings to accurately output the reference position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional optical encoder uses two cell-photodetectors to detect reference position, then the structure is simple, but the reference position detection accuracy deteriorates due to inability to distinguish zero crossings
Solution Approach 1:
The photodetector is divided into multiple photodetector elements (at least three elements: first, second, and third photodetector elements) arranged in the movement direction of the scale. This segmentation allows the system to generate multiple differential signals and distinguish true zero crossings from false ones, thereby improving reference position detection accuracy while maintaining reasonable structural complexity.
Solution Approach 2:
Different regions of the photodetector are assigned different functions: the first and second photodetector elements generate a differential signal for zero crossing detection, while the second and third photodetector elements generate a gate signal for validation. This local differentiation enables accurate reference position detection by combining multiple signal types from different photodetector regions.
2Measurement precision
If the encoder uses multiple photodetector elements and signal processing, then reference position detection accuracy improves, but device complexity increases
Solution Approach 1:
The patent combines multiple signal generation functions into a single photodetector assembly with multiple elements. The first differential signal and gate signal are generated simultaneously from the same photodetector elements, merging detection and validation functions into one integrated component, which reduces overall device complexity despite improved accuracy.
Solution Approach 2:
The photodetector elements self-generate both the differential signal and gate signal without requiring external intervention. The signals are automatically produced based on light reception patterns, and the system self-validates zero crossings through the gate signal mechanism, reducing the need for complex external processing circuits.
3Speed
If conventional encoders detect zero crossings without validation, then detection speed is fast, but reliability deteriorates due to wrong detection
Solution Approach 1:
The gate signal is generated in advance based on the differential signal before final reference position determination. This preliminary signal validation ensures that only legitimate zero crossings are recognized, preventing wrong detections while maintaining fast detection speed through pre-computed validation criteria.
Solution Approach 2:
The gate signal provides feedback validation for the differential signal. When the gate signal indicates a valid state, the zero crossing is confirmed as accurate; when invalid, the system rejects the detection. This feedback mechanism ensures high reliability without significantly slowing down the detection process.
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 enables precise detection of the reference position, reducing errors and ensuring accurate movement, thus preventing damage to machine tools and improving the quality of processed goods.
Implementation Method 1
a photodetector for detecting the periodic pattern, which detects light which is irradiated from the light source and passed through the periodic optical pattern
Implementation Method 2
a photodetector for detecting the reference position, which includes a plurality of photodetector elements arranged one-dimensionally in a direction of movement of the scale, and which detects light passed through the reference position pattern
Data Source
AI summary
A photodetector group includes a plurality of photodetector elements which are arranged one-dimensionally in a direction of movement of a scale. An optical encoder includes a differential signal calculating member which calculates a first differential signal of an output signal from one photodetector element and an output signal from other photodetector element, and a gate signal forming member which generates a gate signal which includes an area of zero crossing by the first differential signal, near a position where light emitted from a light source is incident on the photodetector group upon passing through a reference position pattern formed on a scale. The optical encoder outputs a reference position signal based on a point of zero crossing of the first differential signal and the gate signal.