Linear Motor Absolute Position Detection Without Additional Magnets
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Solution Overview
Problem
Existing methods for determining the absolute position of a rotor in a linear motor, especially in those with large ranges of motion or multiple rotors, require additional position magnets or closely arranged sensors, making them unsuitable for applications with extensive movement or multiple rotors.
Innovation Solution
The method involves detecting the edge areas of the drive magnets' arrangement using position sensors, allowing for coarse positioning without additional magnets or closely spaced sensors, and utilizing the known geometry to determine the specific drive magnet whose field is detected, enabling absolute positioning without referencing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional position magnets are arranged on the rotor to enable absolute position detection, then position detection accuracy is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The drive magnets on the rotor serve dual purposes: generating the magnetic field for linear motor operation and simultaneously enabling absolute position detection. By evaluating the magnetic field strength detected by position sensors and comparing it to reference values, the system determines rotor position without requiring separate position magnets, thus reducing device complexity while maintaining measurement precision.
Solution Approach 2:
The system uses its own operational components (drive magnets and drive coils) to perform the additional function of position detection. The drive magnets' magnetic fields are evaluated by position sensors to determine rotor position, allowing the motor system to self-diagnose its state without external辅助设备, thereby reducing overall system complexity.
2Measurement precision
If position sensors are arranged closely together to detect the magnetic field of position magnets, then measurement precision is improved, but the number of sensors and device complexity increase
Solution Approach 1:
The system evaluates the magnetic field strength parameter detected by position sensors and compares it against reference values to determine rotor position. By changing from a spatial arrangement approach (multiple closely-spaced sensors) to a parameter evaluation approach (comparing field strength values), the system achieves accurate position detection with fewer sensors spaced farther apart.
3Measurement precision
If a reference run (homing) is performed to determine the zero position before operation, then absolute position detection is enabled, but loss of time occurs during startup
Solution Approach 1:
Reference values for magnetic field strength are predetermined and stored during manufacturing or system setup. These pre-calculated reference values enable immediate position determination upon startup by direct comparison with current sensor readings, eliminating the need for time-consuming reference runs or homing procedures during each startup sequence.
4Adaptability or versatility
If the linear motor is designed for large range of motion, then adaptability is improved, but existing position detection methods become unsuitable
Solution Approach 1:
The rotor's magnetic field is evaluated in segments corresponding to different rotor positions. By dividing the evaluation into discrete position states based on magnetic field strength comparisons, the system can handle large ranges of motion using a straightforward comparison method rather than requiring complex continuous detection systems, thus maintaining simplicity while achieving high adaptability.
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 approach allows for accurate absolute positioning of the rotor without referencing or additional magnets, with position sensors that can be farther apart than the pole pitch, reducing the number of sensors needed and enabling precise positioning across large ranges of motion.
Implementation Method 1
a position sensor detecting a magnetic field of a drive magnet of the arrangement of drive magnets in the region of the position sensor
Implementation Method 2
a drive magnet (electromagnet or permanent magnet) is arranged on one of the two parts, which interacts with the magnetic field generated by an energized drive coil on the other part to generate a linear propulsion force
Data Source
Figure 1~3
Figure 4~5
Figure 6
AI summary
In order to determine the absolute position (xist) of a runner (3) of a linear motor, which is movable relative to a stationary part in a direction of movement (x), without moving the runner (3), without additional permanent magnets, without a close arrangement of position sensors (Sn-1, Sn, Sn+1) and even during large movements of the runner (3), it is provided that at least a boundary region (8) of the arrangement of drive magnets (4) is determined and a coarse position of the runner (3) is derived from this, based on which, with the known geometry of the runner (3), the specific drive magnet (4) of the arrangement of drive magnets (4) is determined whose magnetic field is detected by at least one of the position sensors (Sn-1, Sn, Sn+1) in the region of the arrangement of drive magnets (4), wherein the at least one position sensor (Sn-1, Sn, Sn+1) determines a relative position (xi) of the measured drive magnet (4) relative to the at least one position sensor (Sn-1, Sn,Sn+1) is determined and from the known installation position (ESn-1, ESn, ESn+1) of this at least one position sensor (Sn-1, Sn, Sn+1) and from the determined relative position (xi) the absolute position (xist) of the runner (3) is determined.