Angular Encoder Index Mark Correction via Dual Read Heads
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Solution Overview
Problem
3D coordinate measurement devices face challenges in maintaining the stability of the absolute angular position of the rotating shaft over time due to mechanical shocks and eccentricities in the encoder disk, which can lead to errors in distance and angle measurements.
Innovation Solution
A method is introduced that uses two read heads to detect the index mark and generate analog signals, allowing a processor to determine a reference correction value based on these signals, thereby stabilizing the absolute index position and compensating for encoder eccentricity shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single read head is used to detect the index mark, then the device complexity is reduced, but the measurement precision deteriorates due to inability to compensate for encoder eccentricity
Solution Approach 1:
The encoder system is segmented into multiple independent read heads (at least two) that simultaneously detect the index mark from different angular positions. Each read head provides independent measurement data, allowing the system to segment the error sources and compensate for encoder eccentricity through comparative analysis of the multiple signals.
2Productivity
If mechanical shocks occur during operation, then the device remains compact and portable, but the stability of the absolute index position deteriorates due to encoder disk eccentricity shifts
Solution Approach 1:
The system continuously monitors the angular position of the index mark using multiple read heads and compares the measured position against the expected position. When deviations caused by mechanical shocks or eccentricity are detected, the system generates correction values that are fed back to compensate for the position drift, maintaining stability despite physical disturbances.
Solution Approach 2:
The system performs preliminary detection of the index mark position using multiple read heads to establish a reference state before normal operation begins. Correction values are pre-calculated based on the differential readings from the multiple read heads, allowing the system to proactively compensate for eccentricity effects before they accumulate during operation.
3Manufacturing precision
If incremental encoder lines are used for angular measurement, then the manufacturing precision is improved, but the reliability deteriorates due to lack of absolute position information
Solution Approach 1:
The index mark serves as an intermediary reference element that provides absolute position information. By detecting the angular position of this index mark relative to the incremental encoder lines using multiple read heads, the system bridges the gap between the incremental measurement system and the need for absolute position reference, enabling reliable initialization and shock detection.
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 ensures that the absolute index position remains stable over time, reducing measurement errors caused by mechanical shocks and encoder misalignment, and maintains accurate 3D coordinate determination.
Implementation Method 1
the read head sends out a beam of light that in some cases is reflected off the disk to one or more optical detectors that convert the received light into electrical signals
Data Source
AI summary
A method for finding a reference correction value of an angular encoder index mark is given. The angular encoder has a first read head, a second read head, and a patterned element that includes incremental marks and an index mark. In a first instance, the first read head detects the presence of the index mark and, in response, the second read head generates a first analog signal. In a second instance, the first read head detects the presence of the index mark and, in response, the second read head generates a second analog signal. A processor determines the reference correction value based at least in part on the first analog signal and the second analog signal.