Capacitive Angle Encoder Error Compensation via Sensor Ring Segmentation
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Solution Overview
Problem
Capacitive angle encoders face challenges in achieving high precision due to manufacturing and assembly tolerances, which result in measurement errors and inaccuracies, particularly because existing compensation methods are insufficient for high precision requirements and do not account for all error sources such as deformations and external interference.
Innovation Solution
The use of multiple sensor rings with specifically designed coupling electrodes and phase permutations, where each sensor ring has a unique alpha interval total, allows for absolute angle determination by combining the signals from both rings, enabling comprehensive error self-compensation across both low-frequency and high-frequency components of the error spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If capacitive scanning is used instead of optical scanning, then power consumption is reduced and manufacturing cost is lowered, but measurement precision deteriorates due to sensitivity to manufacturing and assembly tolerances
Solution Approach 1:
The angle encoder is divided into multiple sensor rings (first sensor ring, second sensor ring, etc.), each with its own coupling electrodes and signal evaluation. By segmenting the measurement function across multiple independent rings, the system achieves both low power consumption (capacitive principle) and high precision (error compensation through multiple rings)
Solution Approach 2:
The invention changes the operational parameters by using multiple sensor rings with different alpha interval totals (first alpha interval total, second alpha interval total) that are relatively prime to each other. This parameter variation enables absolute angle determination and error compensation while maintaining the energy-efficient capacitive scanning approach
2Device complexity
If single sensor ring is used, then device complexity is reduced, but measurement precision deteriorates due to inability to compensate for manufacturing and assembly errors
Solution Approach 1:
The system uses multiple sensor rings (first sensor ring, second sensor ring) with different alpha interval configurations. Each ring provides independent measurement data that, when combined through signal evaluation, compensates for errors while maintaining manageable device complexity through modular architecture
Solution Approach 2:
The signal evaluation unit processes signals from multiple sensor rings and uses the relative primality of their alpha interval totals to determine absolute angular position. The system inherently compensates for manufacturing and assembly errors by comparing and combining measurements from multiple rings, providing self-correcting feedback
3Device complexity
If incremental angle determination is used, then device complexity is reduced, but reliability deteriorates due to requirement for reference position assumption after restart
Solution Approach 1:
Multiple sensor rings with different alpha interval totals are used to provide absolute position information. The first sensor ring and second sensor ring each contribute to determining the absolute angular position, eliminating the need for reference position assumption while keeping the system relatively simple
Solution Approach 2:
The angle encoder provides both incremental measurement capability and absolute position determination simultaneously through the combination of multiple sensor rings. This multi-functionality ensures reliability after restart without significantly increasing device complexity
4Measurement precision
If existing compensation methods are used, then some errors are reduced, but measurement precision deteriorates because not all error sources are compensated including deformations and external interference
Solution Approach 1:
Multiple sensor rings with different alpha interval configurations are deployed to cover different error spectra. Each ring compensates for specific types of errors, and the combination provides comprehensive error compensation including manufacturing tolerances, assembly errors, deformations, and external interference
Solution Approach 2:
The system uses a composite approach by combining measurements from multiple sensor rings with different alpha interval totals. This composite measurement strategy compensates for a broader range of errors than any single ring could achieve alone, including both low-frequency and high-frequency error components
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 significantly enhances measurement accuracy by eliminating ambiguities and compensating for a wide range of errors, including those caused by deviations in disk alignment and external interference, thereby improving precision and reducing manufacturing/assembly tolerance requirements.
Implementation Method 1
The distance between the first disk and the second disk is spaced apart from one another on a measuring axis in such a way that capacitive coupling causes coupling signals that change over time between the first and second coupling electrodes of a respective sensor ring to be transferable
Data Source
Figure 1~2b
Figure 2c~3
Figure 4a~4b
AI summary
A capacitive absolute angle encoder (100) with a first disk (1) rotatable relative to a second disk (2), and a first sensor ring (3) and a second sensor ring (4). The first and second sensor rings (3, 4) each have a plurality of capacitively coupled first coupling electrodes (5a, 5i, 5R-5U) and second coupling electrodes (6a, 6i, 6p, 6n). In at least one sensor ring (3, 4), coupling signals (7) from the second coupling electrodes (6a, 6i, 6p, 6n) of a type of sector (13a-13d) are combined sector by sector, so that by sector-related comparative evaluation of coupling signals (7) information about a deviation of the arrangement of the first and/or second disk (1, 2) from an ideal position relative to the measuring axis (50) can be determined.