Rotary Encoder Eccentricity Correction via Pre-Mounted Error Profiling
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Solution Overview
Problem
Highly accurate rotary encoders face accuracy issues due to eccentricity errors caused by imperfect mounting, which conventional methods struggle to fully correct, especially in space-constrained environments and require expensive solutions or master references.
Innovation Solution
A method involving measuring and centering the encoder scale blank about a second center during production, then matching this eccentricity during installation, allowing for the calculation and correction of sinusoidal errors using multiple angular orientations and markings, without needing a master reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the encoder scale blank is mounted as perfectly as possible about the same axis as the intended rotational axis, then manufacturing precision is improved, but absolutely perfect alignment is not possible so eccentricity errors may still occur
Solution Approach 1:
The patent applies preliminary action by measuring the eccentricity of the encoder scale blank during the manufacturing process itself, before installation. This allows the eccentricity characteristics to be captured and stored for later compensation, rather than waiting until installation to detect and correct the error.
Solution Approach 2:
The patent creates a copy of the encoder's eccentricity error characteristics by measuring the run-out at multiple angular positions and storing this data. This error profile is then used to compensate for the actual angular measurement errors during operation, effectively copying the error pattern to correct it.
2Measurement precision
If conventional error correction methods using three encoder readers or look-up tables are employed, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the error correction function from the physical encoder structure by measuring and storing the eccentricity characteristics separately. Instead of adding more readers or complex hardware, the solution extracts the error profile and handles correction through data processing and compensation calculations.
Solution Approach 2:
The patent changes the approach from physical correction (adding more readers or mechanical adjustments) to parameter-based correction. By measuring eccentricity at multiple angular positions and using these parameters to calculate compensation values, the system achieves error correction through mathematical parameter manipulation rather than physical modifications.
3Manufacturing precision
If the encoder is mounted with minimal eccentricity through careful adjustment, then manufacturing precision is improved, but space constraints and installation difficulty increase
Solution Approach 1:
The patent enables the encoder system to self-correct for eccentricity errors by measuring its own run-out characteristics during manufacturing and using this self-acquired data for compensation. This eliminates the need for complex installation procedures or external master references, allowing the system to handle its own alignment errors.
Data Source
AI summary
A method of determining the eccentricity of an encoder scale member of a rotary encoder includes taking an encoder scale blank having a geometric center and mounting the encoder scale blank centered about a second center. A scale can then be produced on the encoder scale blank thereby forming an encoder scale member. The scale of the encoder scale member is centered about the second center. Any eccentricity between the geometric center and the second center is measured by, for example, measuring any change in the apparent radius of the encoder scale member. The encoder scale member may then be mounted in a working location wherein it is rotated about a third axis. The eccentricity when mounted in the working location may be matched to that measured during manufacture thereof and/or the eccentricity errors arising from both manufacture and mounting of the encoder scale member may be determined.