Rotary Encoder Calibration via Laser Speckle Analysis
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Solution Overview
Problem
Existing rotary encoders, such as those developed by HEIDENHAIN and ReniShaw, suffer from graduation errors due to tool machining and scanning errors resulting from dirt or damage, leading to inaccurate angle measurements.
Innovation Solution
A precision calibration method using a laser speckle image capturing module to capture frames of laser speckle images from an optical position surface, with image comparison libraries and mathematical equations to calculate image displacements, and a rotation matrix to enhance position precision, allowing for precise angle coordination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional tool machining is used to form gratings or barcodes on rotary encoders, then manufacturing process is simple, but graduation errors occur leading to poor measurement precision
Solution Approach 1:
The patent replaces traditional mechanical tool machining with a laser-based optical system. A laser beam is modulated to directly write gratings or barcodes on the rotary encoder disk, eliminating mechanical contact and associated machining errors. This substitution of mechanical fabrication with optical fabrication resolves the contradiction by achieving high manufacturing precision without the limitations of tool-based machining.
Solution Approach 2:
The patent changes the fabrication method from mechanical cutting to laser-induced material modification. By controlling laser parameters such as power, pulse duration, and scanning speed, precise gratings and barcodes can be formed directly on the disk surface. This parameter-based control enables high manufacturing precision and eliminates graduation errors inherent in traditional machining.
2Reliability
If barcodes are formed on circumferential surface through machining or etching, then initial positioning is achievable, but scanning errors occur during long-term use due to dirt and damage
Solution Approach 1:
The patent replaces mechanical reading systems with optical detection. Instead of physical contacts that can wear and generate scanning errors, the invention uses laser writing combined with optical sensors to read the encoded patterns. This non-contact optical system eliminates mechanical wear and reduces sensitivity to dirt and damage, improving long-term reliability.
Solution Approach 2:
The patent applies laser-based pre-calibration to write precise reference patterns on the rotary encoder disk before operation. These laser-written gratings and barcodes serve as stable reference markers that are less susceptible to degradation. The preliminary laser marking creates durable features that maintain accuracy over time, compensating for potential scanning errors.
3Measurement precision
If multiple optical sensors and complex cross-matching calculations are used, then absolute angle positioning is achieved, but device complexity increases
Solution Approach 1:
The patent uses laser writing to create precise optical copies or replicas of reference patterns directly on the rotary encoder disk. These laser-written patterns serve as stable reference copies that can be read by simpler sensors. The complex positioning information is encoded in the laser-written patterns themselves, reducing the need for multiple sensors and complex real-time calculations.
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 method effectively reduces graduation and scanning errors, enabling precise angle positioning and enhancing the accuracy of rotary encoders by calculating primary and secondary variation angles and image displacements.
Implementation Method 1
a laser speckle image capturing module to capture N frames of laser speckle image from an optical position surface of a rotary encoding body
Data Source
AI summary
The present invention mainly provides a precision calibration method for being applied in a high-precise rotary encoder system, wherein the primary technology feature of the precision calibration method is that: using a laser speckle image capturing module to capture N frames of laser speckle image from an optical position surface of a rotary encoding body, and then using image comparison libraries and particularly-designed mathematical equations to calculate N number of image displacements, so as to eventually calculate N number of primary variation angles and sub variation angles corresponding to the N frames of laser speckle image. Therefore, after the rotary encoding body is rotated by an arbitrary angle, an immediate angle coordinate can be precisely positioned according to the primary variation angles, the secondary variation angles and the N number of image displacements.