Reflection Grating Angle Encoder for Eccentricity and Wobble Correction
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Solution Overview
Problem
Optical position-measuring devices face challenges in accurately determining the angle of rotation between two objects due to eccentricity and wobbling errors, especially when the graduated disk is not mounted correctly, leading to significant impairments in measuring accuracy, particularly in rotary optical position-measuring devices with incident light scanning.
Innovation Solution
An optical position-measuring device with a grating scale designed as a reflection grating, capable of generating position information for both azimuthal rotary movement and radial displacement, using a detection unit for radial and azimuthal scans, where the neutral axis of rotation for both scans lies in the same plane parallel to the non-tilted grating scale, allowing for correction of eccentricity and wobble errors through signal processing and calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the indexing disk is assembled separately by the customer, then the device is easier to assemble and transport, but the measuring accuracy deteriorates due to eccentricity errors
Solution Approach 1:
The patent performs preliminary calibration measurements during the assembly phase to detect and store correction values for eccentricity and wobble errors. By conducting the radial scan and determining correction values before actual measurement operations, the system prepares compensation data in advance, allowing accurate measurements even when the indexing disk is assembled separately by the customer with potential mounting errors.
2Measurement precision
If a second annular scale is added to correct eccentricity errors, then the measuring accuracy improves, but the device complexity increases
Solution Approach 1:
The patent makes the detection unit multi-functional by enabling it to perform both azimuthal scanning (for rotation angle measurement) and radial scanning (for eccentricity and wobble error detection). This single detection unit serves multiple purposes: measuring the primary rotation angle and simultaneously capturing error information needed for correction, thereby improving accuracy without adding a second complete detection system.
Solution Approach 2:
The patent introduces radial scanning as an additional dimension of measurement beyond the traditional azimuthal scanning. By adding radial scan capability to the detection unit, the system can detect eccentricity and wobble errors in the radial direction, enabling error correction without requiring a second annular scale, thus maintaining simplicity while improving accuracy.
3Measurement precision
If radial scanning is added to detect eccentricity and wobble, then the measuring accuracy improves, but the scanning time and device complexity increase
Solution Approach 1:
The patent performs radial scanning and correction value determination as a preliminary action during assembly or calibration, separate from the actual measurement operation. The correction values are stored in memory for later use, so during normal measurement only the azimuthal scan is needed, minimizing time loss while achieving accuracy improvement through the preliminary radial scan.
Solution Approach 2:
The patent implements radial scanning as a periodic calibration procedure rather than a continuous operation. The radial scan is performed at scheduled intervals (e.g., during assembly or maintenance), and the correction values are applied continuously during measurement operations. This periodic approach reduces overall scanning time while maintaining measurement accuracy through regular calibration.
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 device effectively corrects both eccentricity and wobble-related errors, enhancing the accuracy of angle-of-rotation measurements by storing angle-dependent correction values and applying them during the measuring operation, thereby improving the overall precision of the position-measuring device.
Implementation Method 1
a grating scale rotating about an axis of rotation, which is designed as a reflection grating
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2A~2B
AI summary
The present invention relates to an optical position measuring device for detecting the angle of rotation between two objects that rotate relative to each other. A grating scale rotating about an axis of rotation is designed as a reflection grating; position information regarding both an azimuthal rotation about the axis of rotation and a radial displacement of the grating scale is obtained from its scanning. At least one detection unit serves to scan the rotating grating scale in order to determine the azimuthal angle of rotation and any radial displacement of the grating scale. The neutral pivot points of the scans of the grating scale for determining the angle of rotation and displacement lie in the same plane, which is parallel to the grating scale. The neutral pivot point designates the location about which the grating scale or the detection unit can be tilted without positional displacement (Fig. 10B).