Single-Track Position Encoder for Nanoscale Absolute Measurement
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Solution Overview
Problem
Current one-dimension position encoders face challenges in achieving nanoscale resolution due to the size and cost of double-track rulers, alignment issues between absolute and regular tracks, noise sensitivity, and thermal expansion effects, which compromise precision and compactness.
Innovation Solution
A one-dimension position measurement system using a single binary code applied on a ruler, where each codeword is unique and processed to compute absolute position, with error correction and interpolation methods to enhance precision, and thermal and tilt compensation techniques to maintain accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a double-track ruler with absolute track and regular track is used to achieve nanoscale position resolution, then measurement precision is improved, but device complexity and size increase
Solution Approach 1:
The patent combines the absolute position encoding and precise interpolation functions into a single integrated ruler track. The binary code is applied on one continuous track that serves both for determining absolute position (like the absolute track) and for interpolation (like the regular track), eliminating the need for separate parallel tracks while maintaining nanoscale measurement precision.
Solution Approach 2:
The single ruler track performs multiple functions simultaneously: it provides absolute position reference through binary coding and enables precise position interpolation through code analysis. This multi-functional design replaces the specialized absolute track and regular track separation, reducing system complexity while achieving both absolute positioning and nanoscale resolution.
2Measurement precision
If a double-track ruler is used to achieve precise absolute position, then measurement precision is improved, but manufacturing precision requirements increase due to alignment difficulties
Solution Approach 1:
By merging the absolute positioning code and the interpolation code into a single continuous binary code track, the patent eliminates the alignment interface between two separate tracks. The single-track design removes the manufacturing challenge of precisely aligning multiple tracks while maintaining the ability to compute both absolute and interpolated positions from the same code structure.
3Measurement precision
If photodiodes with sine and cosine multiplication are used to achieve high resolution, then measurement precision is improved, but distortion occurs due to ruler tilting
Solution Approach 1:
The system uses a camera to capture the binary code pattern and processes the image data to determine position. By using digital image processing and analyzing the binary code transitions in the captured image, the system can compensate for tilt effects through software algorithms rather than relying on analog photodiode multiplications that are sensitive to geometric distortions from tilting.
Solution Approach 2:
The patent replaces the analog photodiode multiplication system with a digital image processing system. Instead of using optical multiplication by sine and cosine signals that are sensitive to ruler tilt, the system captures the binary code with a camera and performs digital analysis, which is more robust to geometric distortions and allows for post-capture correction of tilt effects.
4Device complexity
If only one CCD line per code track is used to reduce device complexity, then device complexity is reduced, but measurement precision decreases due to noise
Solution Approach 1:
The patent uses a single camera to capture the binary code pattern, combining the functionality of multiple CCD lines into one imaging device. The camera captures a two-dimensional image of the code, allowing digital processing to extract position information while inherently averaging noise across multiple pixels in the image, thus maintaining precision without requiring multiple separate CCD lines.
Solution Approach 2:
The system uses a camera to create a digital copy (image) of the binary code on the ruler. This digital image can be processed multiple times and analyzed in various ways without additional hardware, allowing noise reduction through digital filtering and averaging while maintaining the simplicity of a single camera-based sensing system.
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 system achieves precise nanoscale position measurement with improved compactness and cost-effectiveness by using a single track, correcting reading errors, and compensating for temperature and sensor tilt, thereby enhancing the overall precision and reliability of position encoding.
Implementation Method 1
a camera for acquiring a picture of a portion of the code
Implementation Method 2
a camera for acquiring a picture of a portion of the code
Data Source
Figure 1~2
Figure 3(a)~3(b)
Figure 4(a)~4(b)
AI summary
The present invention discloses a one-dimension position measurement system comprising: a first ruler, on which a first one-dimension binary code si is applied, a camera for acquiring a picture of a portion of said code si, said portion having a length of I bits, and some processing means. Each codeword of length I of the one-dimension code si is unique within the whole code si. A codeword ai is read from said acquired picture of said portion of code si, and the processing means are implemented for computing an absolute position p of said codeword ai of said code si from: (I). An ad-hoc interpolation method is used to obtain a precision way below the distance between two bits of the codewords. The code si may be applied on the ruler by using some geometric primitives, a geometric primitive for encoding a "1" being different from a geometric primitive for encoding a "0", both having the same horizontal projection. The horizontal projection is then used for fine interpolation, achieving nanometre-scale resolution.