Magnetic Encoder Noise Rejection via Differential Signal Averaging
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Solution Overview
Problem
Magnetic encoders with multipole magnets face detection precision issues due to external magnetic noise, particularly from two-pole magnets and electromagnetic brakes, which introduce error components into the detection signals.
Innovation Solution
The magnetic encoder design features a multipole magnet with alternating N and S poles and strategically positioned magnetic detection units that output sinusoidal signals differing by 90°, allowing for noise component offset and averaging to remove external magnetic field influences, enabling precise rotational position detection without the need for distance between magnets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic detection elements are arranged facing the magnetized surface of a multipole magnet, then rotational position detection is enabled, but detection precision deteriorates due to magnetic noise from external sources such as two-pole magnets and electromagnetic brakes
Solution Approach 1:
The magnetic detection system is divided into multiple independent detection elements (first to fourth magnetic detection elements) arranged at different angular positions around the multipole magnet. Each detection element independently detects magnetic flux in its specific angular position, allowing the system to segment the detection field and process signals from multiple locations to identify and eliminate noise components.
Solution Approach 2:
The patent converts the harmful magnetic noise from external sources into a useful signal processing opportunity. By detecting the magnetic flux with multiple elements positioned at different angles, the system identifies that noise components appear identically in all detection signals while useful signal components differ by phase relationships. This allows the noise to be recognized and eliminated through differential processing, transforming the harmful interference into a means for noise rejection.
2Volume of moving object
If a multipole magnet and two-pole magnet are arranged in close proximity, then device compactness is improved, but detection precision deteriorates due to error components from the two-pole magnet
Solution Approach 1:
The detection system uses four magnetic detection elements segmented into two pairs: a first pair (first and second elements) positioned to detect signals from one region, and a second pair (third and fourth elements) positioned to detect signals from another region. This segmentation allows the system to process signals differentially, where the useful multipole magnet signals maintain proper phase relationships while the erroneous two-pole magnet signals are rejected through the differential processing.
Solution Approach 2:
The patent transforms the harmful magnetic field from the two-pole magnet into a rejectable noise component. By arranging detection elements at specific angular positions and processing the signals to exploit phase differences, the system identifies that genuine multipole magnet signals contain useful phase information while two-pole magnet interference appears as common-mode noise that can be eliminated through differential signal processing.
3Adaptability or versatility
If an electromagnetic brake is mounted on the actuator with the magnetic encoder, then braking function is added, but detection precision deteriorates due to leakage flux from the brake coil
Solution Approach 1:
The patent converts the harmful leakage flux from the electromagnetic brake coil into a rejectable noise component. The magnetic detection elements are positioned and configured to detect the multipole magnet's field while the brake coil's leakage flux appears as magnetic noise that can be identified and eliminated through differential signal processing of the multiple detection elements.
Solution Approach 2:
The patent introduces signal processing as an intermediary between the magnetic detection elements and the final position output. The processing unit receives signals from multiple detection elements, performs differential operations to eliminate common-mode noise from the brake coil, and produces a cleaned position signal. This intermediary processing stage separates the useful position information from the harmful brake interference.
4Measurement precision
If magnetic detection elements are positioned to detect leakage flux from a two-pole magnet, then absolute position detection capability is achieved, but detection precision deteriorates due to error components in the detection signal
Solution Approach 1:
The detection system segments the magnetic field detection into multiple spatial zones using four detection elements positioned at different angular locations. The first pair of elements detects signals from one angular region while the second pair detects from another region, allowing the system to process signals differentially to reject the error components generated by the two-pole magnet's leakage flux.
Solution Approach 2:
The patent transforms the error components from the two-pole magnet into identifiable noise that can be eliminated. By detecting magnetic flux with multiple elements and analyzing the phase relationships between their outputs, the system identifies that genuine absolute position signals from the multipole magnet contain specific phase characteristics while two-pole magnet interference appears as erroneous components that can be filtered out through differential processing.
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 configuration effectively removes detection errors caused by external magnetic noise, enhancing the precision of rotational position detection and allowing for a more compact design by enabling closer proximity of the encoder to the electromagnetic brake.
Implementation Method 1
a multipole magnet having a circular multipole magnetized surface in which magnetic N poles and S poles are formed in alternating fashion at equiangular intervals in a circumferential direction
Implementation Method 2
first to fourth magnetic detection units arranged in different angular positions in the circumferential direction of the multipole magnetized surface in order to detect changes in the magnetic field accompanying the rotation of the multipole magnet
Data Source
AI summary
First to fourth magnetic detection units (22-25) are arranged in opposition to a multipole magnetized surface (21a) of a multipole magnet (21) of a magnetic encoder (17). The first and second magnetic detection units (22, 23) are placed on positions separated from each other by 180 degrees on the periphery of the center of the multipole magnet and output an A-phase signal and a B-phase signal. The third and fourth magnetic detection units (24, 25) are placed on positions separated from each other by nearly 180 degrees on the periphery of the center of the multipole magnet and output an A-phase reverse signal and a B-phase reverse signal. Detection signals of the same phase are synthesized and averaged, and consequently a detection error generated by an outer magnetic flux extending in the diameter direction of the multipole magnet can be removed. The signal obtained by synthesizing the detection signals of the same phase and averaging the same and the reverse signal of a signal obtained by synthesizing reverse signals of the reverse phase and averaging the same are synthesized and averaged, and consequently the detection error generated by the outer magnetic flux radially extending in one direction along the radius direction of the multipole magnet can be removed.