Photoelectric Encoder Origin Detection via Side Lobe Signal Processing
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Solution Overview
Problem
Existing photoelectric encoders face erroneous origin detection due to diffraction of light from the origin mark, leading to complications in detector design and accuracy issues.
Innovation Solution
A photoelectric encoder design that includes a scale with reflection gratings, a detector with symmetric origin signal reception sections, and a signal processing section that generates an origin detection signal by utilizing the maximum value of side lobe light from the origin mark, eliminating the need for image forming means and allowing for precise origin detection without complicating the detector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If image forming means (lens, etc.) is added to the detector to form an image of light applied to the origin mark, then origin detection capability is improved, but detector complexity increases
Solution Approach 1:
The patent extracts and removes the image forming means (lens, etc.) from the detector structure. Instead of forming an image optically, the system directly detects light intensity variations at the origin mark position using simple photodetectors, thereby eliminating the complex optical imaging components while maintaining origin detection capability
Solution Approach 2:
The patent replaces the optical imaging system (mechanical/optical components like lenses) with a direct electrical detection method. Photodetectors directly measure light intensity at the origin mark without optical image formation, substituting a complex optical-mechanical system with a simpler electrical detection system
2Device complexity
If light is applied directly to the origin mark without image forming means, then detector complexity is reduced, but erroneous origin detection occurs due to light diffraction
Solution Approach 1:
The patent introduces a light diffraction prevention structure (such as a light blocking wall or specific optical path design) as an intermediary element between the light source and the origin mark. This intermediary prevents unwanted light diffraction while allowing the simplified direct detection method to work accurately, thus maintaining both low complexity and high accuracy
Solution Approach 2:
The patent acknowledges light diffraction as an inevitable phenomenon but converts it from a harmful factor causing erroneous detection into a controlled characteristic. By designing the detection system to account for or prevent diffraction effects at specific locations, the system eliminates false origin signals while maintaining simple detector structure
3Reliability
If multiple zero cross positions occur in the differential signal due to diffraction, then origin detection becomes ambiguous, but this is caused by the small size of the origin mark leading to light diffraction
Solution Approach 1:
The patent extracts and removes the source of diffraction-related errors by eliminating image forming means that could exacerbate diffraction effects. The direct detection method without optical imaging prevents the formation of multiple false zero-crossing points in the differential signal, ensuring reliable origin detection
Solution Approach 2:
The patent changes the detection parameters by directly measuring light intensity at the origin mark position rather than forming an optical image first. This parameter change in the detection method eliminates the multiple zero-cross position problem caused by diffraction, as the system detects the actual light intensity profile without optical transformation that could create false features
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
Enables precise origin detection while minimizing detector complexity, achieving accurate positioning without additional optical systems or sensors, resulting in a compact and cost-effective solution.
Implementation Method 1
light is diffracted
Implementation Method 2
an interference fringe is formed as light applied from the light application section is diffracted in the reflection gratings
Implementation Method 3
light reflected on the origin mark
Data Source
AI summary
A photoelectric encoder includes a scale; a detector; alight application section; a pair of origin signal reception sections; and a signal processing section adapted to provide the maximum value of the signal level output from the origin signal reception sections by side lobe light occurring as reflected on the origin mark as a stipulated value, provide an effective area of origin detection between the first position at which output of one of the origin signal reception sections for outputting a larger signal level than the stipulated value earlier than the relative displacement becomes a larger signal level than the stipulated value and the first position at which output of the other origin signal reception section exceeds the stipulated value and then becomes a smaller signal level than the stipulated value, and configured to generate the origin detection signal in the effective area.