Absolute Rotary Encoder Calibration for Eccentricity Error Reduction
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Solution Overview
Problem
Absolute rotary encoders face challenges in accurately detecting absolute rotational positions due to eccentricity errors, which can result in significant deviations and inaccuracies even after correction, especially when the deviation amount exceeds a threshold value.
Innovation Solution
The solution involves a processor that sets a standard position where the deviation of the scale from the rotation axis is within a threshold value, and uses this standard position to process output signals from detection units to obtain relative displacements, thereby accurately detecting the absolute position of the scale by averaging the positions obtained from multiple detection units to minimize eccentricity errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If correction values are stored in memory and used to correct position values, then manufacturing precision can be improved, but measurement precision deteriorates when deviation amount exceeds threshold
Solution Approach 1:
The system performs preliminary detection to identify when the deviation amount exceeds the threshold value, and only then acquires correction values. This preliminary check prevents using invalid correction values that would compromise measurement precision, while still allowing correction to be applied when conditions are appropriate.
Solution Approach 2:
The system dynamically changes the parameter being measured from the raw position value to a corrected position value, but only when the deviation amount is within the threshold. When deviation exceeds the threshold, the system switches to acquiring correction values instead, thus adapting the measurement approach based on the current state to maintain precision.
2Measurement precision
If multiple detection units are used to average positions, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent combines the outputs of multiple detection units by calculating the average of their respective position values. This merging approach cancels out eccentricity errors that affect individual units differently, thereby improving measurement precision while utilizing existing detection units without adding excessive complexity.
3Reliability
If correction values are acquired when deviation exceeds threshold, then reliability improves, but loss of time increases due to additional detection steps
Solution Approach 1:
The system performs a preliminary check of the deviation amount before deciding whether to acquire correction values. This preliminary action allows the system to quickly determine if correction is needed, minimizing unnecessary detection steps and reducing time loss while ensuring reliability when corrections are actually required.
Solution Approach 2:
The detection unit itself generates the correction values by detecting the eccentricity error, eliminating the need for external calibration equipment or additional measurement devices. This self-service approach reduces time loss compared to external calibration methods while maintaining high reliability through internally generated correction data.
Data Source
AI summary
An encoder apparatus includes a detection unit, a scale disposed to oppose the detection unit and relatively rotatable with respect to the detection unit, and a processor configured to process an output signal output from the detection unit to obtain a relative position of the scale with respect to a standard position and thus detect an absolute position of the scale. The processor is configured to execute a setting process in which a position where a deviation amount of the scale in a predetermined direction with respect to a rotation axis is equal to or smaller than a threshold value is set as the standard position, the deviation amount changing in accordance with relative rotation of the scale with respect to the detection unit.