Piston Position Switch Using Dual Magnetic Field Discrimination
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Solution Overview
Problem
Existing position detection switches are susceptible to erroneous detection due to external magnetic fields, particularly in environments with welding magnetic fields, requiring sensors that detect magnetic fields in two orthogonal directions.
Innovation Solution
A position detection switch utilizing first and second sensors that sense magnetic fields in only one axial direction, with opposite output characteristics, and a cylinder magnetic field discrimination unit to distinguish between cylinder and external magnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensor that detects magnetic fields in two orthogonal directions is used, then the position detection can be performed, but the device complexity increases and susceptibility to external magnetic field interference worsens
Solution Approach 1:
The detection function is segmented into two separate sensors, each dedicated to detecting magnetic field changes in a specific direction. The first sensor detects changes when the piston moves in the +X direction, while the second sensor detects changes when the piston moves in the -X direction. This segmentation allows each sensor to be simple while collectively achieving accurate bidirectional position detection.
Solution Approach 2:
Each sensor is designed with localized detection characteristics optimized for its specific detection direction. The first sensor has its sensitive axis oriented to detect magnetic field changes in the +X direction, while the second sensor's sensitive axis is oriented to detect changes in the -X direction. This local optimization reduces the complexity that would arise from requiring a single sensor to handle all detection directions equally.
2Measurement precision
If sensors are arranged to detect magnetic fields in two orthogonal directions, then position detection is enabled, but the susceptibility to external magnetic field interference increases
Solution Approach 1:
The patent converts the potential harm of external magnetic field interference into a beneficial discrimination mechanism. By arranging the two sensors in opposite directions and comparing their output signals, the system can identify and reject external magnetic field interference that affects both sensors equally, while maintaining sensitivity to the differential magnetic field changes caused by piston movement.
Solution Approach 2:
The system uses feedback through signal comparison between the two sensors. The control unit continuously compares the output signals from the first and second sensors, and based on this comparison, determines the actual piston position while filtering out common-mode external magnetic field interference. This feedback mechanism enables real-time compensation for external interference.
3Measurement precision
If two MR sensors with orthogonal magnetoresistance element patterns are used, then position detection is achieved, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent employs standard, commercially available magnetic sensors that can be easily manufactured and replaced if needed. By using off-the-shelf sensors with known characteristics rather than custom-designed orthogonal MR sensors, the system achieves cost-effective manufacturing while maintaining adequate detection performance through the dual-sensor configuration.
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 switch effectively distinguishes between cylinder and external magnetic fields, reducing susceptibility to external interference and ensuring accurate piston position detection.
Implementation Method 1
a first sensor and a second sensor which each detect a magnetic field of a magnet that is mounted on a piston, and in which the first sensor and the second sensor are magnetic sensors that sense a magnetic field in only one axial direction
Data Source
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AI summary
A first sensor (28) and a second sensor (30), of this position detection switch (25) that detects the magnetic field of a magnet (22) attached to a piston (18), are magnetic sensors that sense only the magnetic field in a single axis direction, distinguish between forward and reverse directions, and output the results. The present invention comprises a cylinder magnetic field discrimination part (36) that compares the movement direction in an output (V1) of the first sensor and the movement direction in an output (V2) of the second sensor.