Rotary Encoder Calibration via Speed-Dependent Correction Factors
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Solution Overview
Problem
Rotary encoders in electrical machines face challenges in achieving precise angular resolution due to manufacturing tolerances, leading to amplitude, phase, and offset errors in sine and cosine tracks, which affect the accuracy of rotor position and speed measurement.
Innovation Solution
A method that regulates the electrical machine to a specific speed, determines the time profile of the rotor angle using the sine and cosine tracks, and applies correction factors to adjust the amplitude, phase, and offset of these tracks to minimize oscillations, thereby improving angular resolution and eliminating artifacts caused by sensor imperfections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manufacturing tolerances are reduced to improve measurement precision, then angular resolution improves, but manufacturing cost and complexity increase
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before final operation. The system conducts test runs at specific speeds to determine frequency-dependent errors, stores these correction values, and then uses them during normal operation to compensate for manufacturing tolerances without requiring tighter manufacturing tolerances.
Solution Approach 2:
The patent changes operational parameters by conducting calibration at specific speeds and using these to derive correction factors. The system measures errors at controlled speeds and frequencies, then applies these parameter-based corrections to compensate for manufacturing variations in the encoder tracks and sensors.
2Measurement precision
If calibration measurements are performed to improve measurement precision, then angular resolution improves, but time and complexity of operation increase
Solution Approach 1:
The calibration process is performed as a preliminary action during installation or setup, and the correction values are stored for reuse during normal operation. This one-time preliminary measurement eliminates the need for repeated calibration, reducing long-term time loss despite the initial calibration duration.
Solution Approach 2:
The system performs calibration at specific periodic intervals or under specific conditions (test runs at defined speeds), rather than continuously. This periodic approach balances the need for accuracy with time efficiency by calibrating only when necessary.
3Measurement precision
If correction factors are determined and applied to eliminate errors, then measurement precision improves, but device complexity increases
Solution Approach 1:
The system implements feedback by measuring actual encoder output during test runs, comparing it against expected values, determining correction factors based on the deviations, and then applying these corrections to subsequent measurements. This closed-loop feedback process systematically eliminates errors while maintaining manageable complexity through algorithmic correction.
Solution Approach 2:
The patent introduces correction factors as an intermediary element between the raw encoder signals and the final position calculation. These correction factors act as a mediator that compensates for manufacturing errors without requiring physical modification of the encoder hardware, thus improving precision while adding only software-based complexity.
4Measurement precision
If the number of lines in the encoder is increased to improve angular resolution, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
Instead of changing the physical parameter of the number of encoder lines, the patent changes the operational parameters by introducing speed-dependent correction factors. This allows the system to achieve improved effective resolution through software correction rather than hardware modification, avoiding the complexity and cost of higher-line encoders.
Data Source
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Figure 3a~3b
AI summary
The invention relates to a method (24) for calibrating a rotary encoder (8), in particular an incremental encoder, of an electrical machine (2), wherein said encoder has a number of reference marks (12) and outputs a sine track (14) and a cosine track (16). According to method (24) the electrical machine (2) is regulated to a specific speed (nsoll), an angle (38) of the electrical machine (2) is determined with the aid of the sine track (14) and/or the cosine track (16), from this an angular progression over time (22) is ascertained, an oscillation (44) in the angular progression over time (22) with a frequency of substantially one integral multiple of the product of the specific speed (nsoll) and the number of reference marks (12) is ascertained, and from this a correction factor (20) the sine track (14) and/or the cosine track (16) is derived, wherein the amplitude (A) of the oscillation (44) is less than or equal to a limiting value (48). The invention further relates to an encoder evaluation (18) and an electric motor (2) having a rotary encoder (8).