Absolute Position Encoder Dirt Detection via Alternating Code Patterns
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Solution Overview
Problem
Conventional absolute position detection type photoelectric encoders are prone to false position detection due to dirt on the ABS scale, leading to increased calculation complexity and reduced resolution when attempting to mitigate this issue.
Innovation Solution
The ABS scale pattern is designed with alternating B and C patterns to represent '0' codes, ensuring that no more than three consecutive parts of the same type are used, allowing for dirt detection and preventing incorrect correlation calculations by identifying continuous sequences of four or more parts as dirt, thereby maintaining high resolution and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ABS scale patterns are used with standard correlation calculation, then the position detection system is simple to implement, but dirt on the scale causes false position detection and reduces reliability
Solution Approach 1:
The code elements on the ABS scale are segmented into pairs of adjacent parts (first and second parts), where each pair represents a binary value. This segmentation allows the system to detect dirt by identifying abnormal patterns in consecutive pairs, improving reliability without requiring complex additional hardware.
Solution Approach 2:
The scale pattern is designed in advance with specific constraints: at least three different pairs of neighboring parts encode the same binary value, and there are no more than two identical neighboring parts. This preliminary design enables the correlation calculation to inherently detect dirt conditions by recognizing when the expected pattern constraints are violated, eliminating the need for separate dirt detection mechanisms.
2Reliability
If the number of codes for correlation calculation is increased to avoid false detection, then position detection reliability improves, but calculation complexity and processing time increase
Solution Approach 1:
The invention changes the parameters of the scale pattern itself rather than increasing the number of codes used for calculation. By designing the pattern with specific constraints (at least three different pairs encoding the same binary value, no more than two identical neighboring parts), the system achieves dirt detection with the same calculation resources, avoiding increased processing time while maintaining reliability.
3Reliability
If division and shifting of the pattern is performed to mitigate dirt effects, then position detection reliability improves, but manufacturing complexity and cost increase
Solution Approach 1:
Instead of modifying the detection process to handle dirt (division and shifting), the invention inverts the approach by designing the scale pattern itself to be inherently resistant to dirt. The pattern constraints (at least three different pairs with same binary value, no more than two identical neighbors) are built into the manufacturing process, allowing standard correlation calculation to reliably detect position even in the presence of dirt, thereby maintaining manufacturing simplicity.
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 design enhances the robustness against dirt, preventing false position detection and improving the reliability of position detection while maintaining high resolution by distinguishing between clean and dirty patterns effectively.
Implementation Method 1
The light source 310 emits light toward the ABS scale 200
Implementation Method 2
The light is reflected at the reflecting part of the ABS scale 200
Implementation Method 3
transmitted at the transmitting part
Implementation Method 4
A photodiode array 340 is provided on the light receiving surface of the light receiving part 330
Data Source
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AI summary
There is provided an absolute position detection type photoelectric encoder which improves robustness to dirt while maintaining high resolution. A two-level code pattern according to a pseudo random code sequence is provided on a scale along a length measurement direction. Each code of the two-level code pattern indicates a code "1" or a code "0", and includes two bits. Each 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 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.