Angular Encoder Index Correction via Read Head Runout
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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, leading to inaccuracies in distance and angle measurements.
Innovation Solution
A method is introduced to determine a reference correction value for the angular encoder using a processor, which involves obtaining incremental readings and index readings from multiple read heads to establish a stable absolute index position, accounting for eccentricity and ensuring the accuracy of angular positions over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an incremental encoder is used to measure angular positions, then the device complexity is reduced and ease of manufacture is improved, but the stability of absolute angular position over time deteriorates due to mechanical shocks and eccentricities
Solution Approach 1:
The system performs preliminary action by establishing a reference angular position at power-up and continuously monitoring the index mark position to detect drift caused by mechanical shocks or eccentricities. This preliminary reference establishment enables subsequent correction of angular position measurements, resolving the contradiction between using simple incremental encoders and maintaining stable absolute angular position over time.
2Measurement precision
If the index mark is used to establish absolute angular position, then measurement precision is improved, but reliability deteriorates because the absolute position may change over time due to mechanical shocks
Solution Approach 1:
The system implements feedback by continuously monitoring the index mark position and comparing it against the stored reference angular position. When drift is detected due to mechanical shocks or eccentricities, the system generates correction values that are applied to subsequent angular position measurements. This feedback mechanism maintains both measurement precision and reliability over time.
Solution Approach 2:
The system applies dynamics by making the reference angular position adaptive rather than static. The reference position is established at power-up and can be updated based on detected drift, allowing the system to dynamically adjust to mechanical changes while maintaining measurement accuracy. This dynamic approach resolves the contradiction between initial precision and long-term reliability.
3Measurement precision
If multiple read heads are used to determine reference position, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The system applies segmentation by using multiple read heads to independently measure angular position from different locations on the encoder disk. Each read head provides separate measurements that are processed to determine a comprehensive reference position. This segmentation approach improves measurement precision while keeping the added complexity manageable through systematic processing of multiple independent signals.
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 enhances the stability of the absolute angular position, improving the accuracy of distance and angle measurements by compensating for shifts caused by mechanical shocks and encoder eccentricities, thereby maintaining measurement precision.
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
Implementation Method 2
the read heads send out a beam of light that passes through the disk to be received by one or more optical detectors on the other side
Data Source
AI summary
A method is given for finding a reference correction value of an index mark of an angular encoder. The angular encoder includes a first read head, a second read head, and a patterned element having incremental marks and an index mark. In a first instance and in a second instance, the patterned element is rotated relative to the read heads to obtain incremental readings from the first read head and the second read head and an index mark from the first read head. Based on these readings, a processor determines, in the first instance, a first reference position and, in the second instance, a second reference position. The processor determines the reference correction value based at least in part on the first reference position and the second reference position.