Magnetic Position Sensor for Linear Motor
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Solution Overview
Problem
Existing position measurement systems for linear motors face challenges in achieving high-resolution, long-stroke, and temperature-stable absolute position sensing, particularly in varying magnetic field strengths and orientations, which affects motor commutation and control accuracy.
Innovation Solution
A low-cost, non-contact position sensor system using a combination of magnetic field direction sensors and Hall effect sensors to measure magnetic fields generated by armature magnets, compensating for variations in magnetic field strength and orientation, and utilizing a calibration lookup table to determine accurate armature positions, even at extreme temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetic field strength variations are used for position measurement, then position sensing capability is provided, but measurement precision deteriorates due to temperature changes and field strength variations
Solution Approach 1:
The patent transforms the problematic parameter (magnetic field strength) into a useful parameter by measuring magnetic field orientation instead. The system uses the orientation of magnetic field vectors, which remains stable despite temperature variations, to determine armature position. This parameter transformation resolves the contradiction by making measurements insensitive to temperature-induced field strength changes.
Solution Approach 2:
The patent introduces magnetic field orientation as an intermediary measurement approach. Rather than directly measuring magnetic field strength which varies with temperature, the system uses orientation information from multiple Hall effect sensors to indirectly determine position. This intermediary approach filters out temperature-related variations while preserving position information.
2Measurement precision
If magnetic sensors are placed close to the stator for accurate measurement, then position detection accuracy improves, but the system becomes sensitive to stator magnetic field interference
Solution Approach 1:
The patent extracts only the orientation information from the magnetic field while discarding the strength information that contains interference. By using multiple sensors to measure field orientation rather than total field strength, the system separates useful position information from harmful stator field interference.
Solution Approach 2:
The patent transitions from measuring magnetic field strength (one-dimensional magnitude) to measuring magnetic field orientation (angular dimension). This dimensional change allows the system to ignore radial field variations and focus on tangential field orientation, which correlates with armature position but is less affected by stator interference.
3Measurement precision
If high-resolution position sensing is implemented, then control accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent makes the existing armature magnets serve dual functions: force generation for motor operation and position sensing reference. The same magnets that produce motor force also create the magnetic field pattern used for position measurement, eliminating the need for separate sensing magnets or complex encoder structures.
Solution Approach 2:
The patent merges the force generation function and position sensing function into a single integrated system. The Hall effect sensors mounted on the stator simultaneously detect the magnetic field produced by armature magnets for both motor control and position measurement, reducing overall system complexity compared to separate sensing systems.
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
The system provides high-resolution, absolute position sensing over a wide temperature range, reducing manufacturing tolerances and assembly errors, and integrates position measurement with force generation, thereby enhancing motor control and stability in applications like vehicle suspension systems.
Implementation Method 1
The sensors can be digital sensors (such as Hall effect switches), analog sensors (such as magneto-resistive or giant magneto-resistive sensors), or a combination of both
Implementation Method 2
analog sensors (such as magneto-resistive or giant magneto-resistive sensors)
Data Source
AI summary
A position sensing system for positioning a linear motor that includes a stator and an armature having magnets, the armature moving relative to the stator along a path. A sensor determines a position of the armature based on measurements of a magnetic field generated by the magnets of the armature.