Photoelectric Encoder Two-Level Code Pattern Dirt Robustness
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Solution Overview
Problem
Current photoelectric encoders face challenges in using common scale and electrical circuit components across both reflective and transmissive types due to differences in dirt sensitivity and image inversion requirements, leading to increased costs and part management complexity.
Innovation Solution
A photoelectric encoder design featuring a two-level code pattern on the scale with a detection head that includes a light source, image acquiring unit, inversion processing unit, and correlation calculation unit, allowing for adaptable operation between reflective and transmissive modes by adjusting inversion processing based on the detection method, and using pseudo random code sequences for robust position detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a scale pattern is designed for reflective type photoelectric encoders, then the chromium film reflects light to create bright/dark patterns, but the glass parts are more sensitive to dirt and scratches causing detection errors
Solution Approach 1:
The patent inverts the conventional scale pattern design by making the chromium film the dark part (code 0) and the glass part the bright part (code 1), opposite to the traditional design. This inversion allows the more durable glass parts to represent the bright codes, reducing sensitivity to dirt and scratches while maintaining detection accuracy.
2Adaptability or versatility
If inversion processing is added to commonly use electrical circuits in both reflective and transmissive types, then component compatibility improves, but device complexity and cost increase
Solution Approach 1:
The patent performs preliminary action by pre-inverting the scale pattern design during manufacturing rather than adding inversion processing during operation. The scale is designed with inverted patterns (chromium film as dark part, glass as bright part) so that no additional inversion processing is needed in the detection circuit, maintaining component compatibility while avoiding increased complexity.
3Measurement precision
If separate scale patterns are designed for reflective and transmissive types, then each type optimizes its detection performance, but part management complexity and costs increase
Solution Approach 1:
The patent achieves universality by designing a single inverted scale pattern that can be used in both reflective and transmissive photoelectric encoders. The chromium film serves as the dark part (code 0) and glass as the bright part (code 1) in both types, eliminating the need for separate scale patterns and reducing part management complexity while maintaining detection performance.
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 equivalent performance in both reflective and transmissive modes with improved robustness to dirt, reducing part counts and costs by allowing shared components and maintaining high accuracy in position detection.
Implementation Method 1
the light is reflected by the chromium film 22, and transmitted through the glass part 21
Implementation Method 2
the light transmitted through the scale 20 is received at the light receiving part
Data Source
AI summary
A scale is provided with a two-level code pattern according to a pseudo random code sequence along a length measurement direction. Each code of the two-level code pattern indicates a code “1” or “0”, each code includes two bits, and each bit of the two bits is L or H. The code “1” is represented by an A pattern which is a combination of L and H, and the code “0” is represented by a B pattern which is a combination of L and L or by a C pattern which is a combination of H and H. When the codes “0” are continued, the B pattern and the C pattern are alternately used. The scale is commonly used in a reflective type encoder or transmissive type encoder. A detection head part includes an inversion processing unit which performs inversion processing to a detection image of the scale as required.