Rotary Encoder Eccentricity Compensation via Code-Disc Image Analysis
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Solution Overview
Problem
Current rotary encoders, such as end-of-shaft and hollow-shaft encoders, face limitations in accurately determining the radial position of a rotating axis, leading to imprecise angular position measurements due to eccentricity, which is often corrected through expensive and complex methods involving multiple sensors or manual visual inspection.
Innovation Solution
A method using a fixed light source and sensor with an annular code-disc surrounding the rotating element, featuring a two-dimensional regular pattern interlaced with an absolute code, to determine and compensate for eccentricity, allowing for precise angular and radial position measurement without the need for high-cost multi-sensor arrangements or manual alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If manual visual inspection with microscope is used to align reference code-disc, then manufacturing precision of angular position is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The code disc automatically determines its own radial position and eccentricity by analyzing the image of its regular pattern captured by the sensor. The system performs self-alignment and self-correction without requiring manual intervention, microscopes, or external alignment tools. The computing means processes the image data to identify the actual rotation axis and compensate for eccentricity automatically.
2Measurement precision
If multiple sensor arrangements are used for eccentricity compensation, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The invention transitions from using multiple sensors arranged in specific geometric patterns to using a single sensor that captures two-dimensional image data. The code disc contains a regular pattern (such as a grid or array of features) that, when imaged, provides sufficient information in two dimensions to determine both radial position and angular position, as well as eccentricity, without requiring multiple separate sensing elements.
3Manufacturing precision
If code-disc is manually aligned and fixed with glue, then manufacturing precision is improved, but ease of manufacture deteriorates
Solution Approach 1:
The code disc automatically determines its own radial position and eccentricity by analyzing the image of its regular pattern captured by the sensor. The system performs self-alignment and self-correction without requiring manual intervention, microscopes, or external alignment tools. The computing means processes the image data to identify the actual rotation axis and compensate for eccentricity automatically.
Solution Approach 2:
The system changes from requiring precise physical alignment parameters (positioning the code disc exactly at a predetermined radial position) to using measured parameters. The radial position and angular position are determined based on the actual image captured by the sensor, and eccentricity is calculated from these measurements. This allows the system to accommodate manufacturing tolerances and assembly variations.
4Ease of operation
If theoretical resolution limit of optical microscope is used, then measurement precision is limited, but ease of operation is improved
Solution Approach 1:
The invention replaces the mechanical/optical microscope-based alignment system with an electronic image processing system. Instead of using a microscope to visually align the code disc, the system uses a sensor to capture an image of the code disc's regular pattern and processing means to automatically determine radial position, angular position, and eccentricity from the image data. This substitution enables higher precision while simplifying the operation.
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 approach enables highly accurate radial and angular position determination, achieving precision in the range of nanometers, reduces manufacturing and operational costs, and allows for automated compensation of positioning errors, making it suitable for various encoder applications.
Implementation Method 1
using at least one fixed light source emitting a beam of light in the direction of a fixed sensor
Implementation Method 2
arranging on the path of the beam of light an annular code-disc surrounding the rotating element and which is integral in rotation with the rotating element, said code-disc comprising a two dimensional regular pattern interlaced with an absolute code
Implementation Method 3
using at least one fixed sensor which is hit by the influenced beam of light
Data Source
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AI summary
The present invention concerns a method for working out at least the angular position of a rotating element which is mounted in a fixed frame, consisting in using at least one fixed light source emitting a beam of light in the direction of a fixed sensor, arranging the light source with respect to the rotating element and of the sensor in a way so as to induce an interaction between the beam of light and the sensor, which depends on the angular and the radial position of the rotating element and using computing and processing means for providing a value of the angular position dependent of the output signal of the sensor, characterized in that it consists in: a) arranging on the path of the beam of light a code-disc which presents a regular two dimensional pattern of transparent and opaque areas and an absolute code and which is integral in rotation with the rotating element, b) using the image casted by the code-disc on the sensor for determining the eccentricity of the code-disc in dependence of the angular position of the rotating element, c) using the eccentricity for compensating the value of the computed angular position, d) and computing a corrected angular position of the rotating element.