Linear Motor Position Detection Using Magnetic Field Direction
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Solution Overview
Problem
Conventional magnetic encoders for linear motors require precise control of the gap between the magnetic scale and sensor, leading to increased complexity and cost, and existing solutions with additional sensors complicate the setup.
Innovation Solution
A position detection system using a magnetic sensor with a magneto-resistive element that outputs sine and cosine wave signals 90° phase shifted, allowing accurate position detection without strict gap control, combined with a position detecting circuit for digital data conversion and phase angle calculation, and a bearing for guiding the rod to maintain constant distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional magnetic encoder is used with a magnetic scale and magnetic sensor, then position detection is possible, but the gap between the magnetic scale and sensor must be controlled with high accuracy, increasing complexity and cost
Solution Approach 1:
The patent changes the detection parameter from magnetic field magnitude to magnetic field direction. The magnetic sensor detects the direction of the magnetic field vector rather than its magnitude, which allows accurate position detection without requiring precise gap control. This parameter change makes the system insensitive to gap variations while maintaining high measurement precision
Solution Approach 2:
The patent replaces the conventional magnetic encoder system with a magnetic sensor that directly detects the magnetic field generated by the linear motor's magnetic poles. This substitution eliminates the need for a separate magnetic scale and the complex gap control mechanism, simplifying the device while maintaining position detection capability
2Measurement precision
If the magnetic sensor is displaced from the optimal position, then the magnetic field acting on the sensor becomes small, but controlling the gap accurately increases manufacturing difficulty and cost
Solution Approach 1:
The patent changes from detecting magnetic field magnitude to detecting magnetic field direction. This parameter change makes the detection insensitive to the sensor's radial position (gap distance), allowing the sensor to be mounted at various distances from the magnetic poles while still achieving accurate position detection, thereby greatly easing manufacturing and assembly
Solution Approach 2:
The patent creates a detection system that is dynamically adaptive to gap variations. By detecting magnetic field direction rather than magnitude, the system automatically compensates for gap changes without requiring active control or adjustment mechanisms, simplifying manufacturing
3Measurement precision
If another magnetic sensor is provided at the opposite side to compensate displacement, then position detection accuracy is maintained, but the number of magnetic sensors increases
Solution Approach 1:
The patent merges the functions of multiple sensors into a single magnetic sensor. By using a vector magnetic sensor that can detect both the radial and axial components of the magnetic field, the system combines what would have required multiple sensors into one device, reducing component count while maintaining detection accuracy
Solution Approach 2:
The magnetic sensor performs multiple functions simultaneously: it detects position, and by detecting the direction of the magnetic field, it inherently compensates for gap variations without requiring additional sensors. This multi-functionality eliminates the need for extra compensation sensors
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
Facilitates accurate and inexpensive position detection with reduced complexity in mounting, enabling higher resolution and minimizing the impact of temperature variations and heat from coils on sensor output.
Implementation Method 1
a magnetic sensor having a magneto-resistive element of which a resistance varies depending on a direction of the magnetic field
Implementation Method 2
obtains thrust for linear movement by a magnetic field generated by the one and current passing through the coils of the other
Data Source
AI summary
A position detection system includes a linear motor having a rod in which magnetic poles of N pole and S pole are arranged alternately in an axial direction and a plurality of coils surrounding the rod a magnetic sensor for detecting change in the direction of the magnetic field of the rod caused by linear movement of the rod relative to the coils to output a sine wave signal and a cosine wave signal which are 90° phase shifted with respect to one another, and a position detecting circuit for detecting a position of the rod relative to the coils. As the magnetic sensor detects the change in the direction of the magnetic field of the rod, the sine wave signal and the cosine wave signal output from the magnetic sensor hardly vary even when the distance between the rod and the magnetic sensor is changed.