Magnetic Input Sensing Layout for Higher S/N Detection
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Solution Overview
Problem
In input devices using magnetic sensors to detect the state of a movable body, a low signal-to-noise (S/N) ratio occurs when the magnetic field component along a virtual plane crossing the virtual central line of the magnetic field is small, making it difficult to effectively detect the movement.
Innovation Solution
The input device incorporates a magnetic field generation means with a permanent magnet and a magnetic portion placed apart from the virtual central line, increasing the magnetic field component along the virtual plane. This configuration includes a yoke member with a ring-shaped magnetic portion that suppresses magnetic field leakage and enhances magnetic flux density in the detection area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the magnetic portion is placed on the virtual central line of the magnetic field, then the device structure is simplified, but the amount of magnetic field component along the virtual plane crossing the central line becomes small, resulting in low S/N ratio
Solution Approach 1:
The magnetic portion is intentionally positioned asymmetrically relative to the virtual central line of the magnetic field, specifically at a location where it does not coincide with the central line. This asymmetric placement creates a non-zero magnetic field component along the virtual plane crossing the central line, thereby improving the S/N ratio of the detected signal while maintaining a relatively simple device structure.
2Measurement precision
If the magnetic portion is placed apart from the virtual central line with space left between, then the S/N ratio is improved, but the device structure becomes more complex
Solution Approach 1:
The magnetic portion is positioned at a specific local region apart from the virtual central line, creating a localized magnetic field distribution that optimizes the magnetic field component in the detection direction. This localized placement strategy improves the S/N ratio without requiring comprehensive structural changes throughout the entire device, thus limiting the increase in overall device complexity.
3Reliability
If the yoke member with ring-shaped magnetic portion is used, then magnetic field leakage is suppressed and magnetic flux density is enhanced, but the manufacturing complexity increases
Solution Approach 1:
The magnetic field generation means employs a composite structure combining a yoke member made of magnetic material with a ring-shaped magnetic portion. This composite design concentrates and directs the magnetic flux effectively, suppressing leakage while enhancing the magnetic flux density in the detection area. The modular nature of this composite structure allows for relatively straightforward manufacturing processes.
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 increased magnetic field component along the virtual plane significantly improves the S/N ratio of the magnetic field components detected by the magnetic sensor, enabling effective detection of the movable body's state.
Implementation Method 1
a magnetic field generation means for generating a magnetic field oriented toward a lower side, which is another side in the direction of the normal, the magnetic field generation means being attached to the movable body
Implementation Method 2
a magnetic field direction detection means for detecting the direction of a magnetic field component along a virtual plane crossing the up-down direction
Implementation Method 3
first and second magneto-resistance elements with magnetism-sensing directions being orthogonal to each other
Data Source
AI summary
An input device has: a fixed base; a case positioned on the fixed base; a movable body supported on the fixed base by the case so as to be movable in a direction crossing the up-down direction; a magnetic field generation means, for generating a magnetic field downward, attached to the movable body; and a magnetic field direction detection means for detecting the direction of a magnetic field component along a virtual plane crossing the up-down direction, the magnetic field direction detection means being disposed, on the fixed base, at other than the position of a virtual central line of the magnetic field with the movable body being at a reference position. The magnetic field generation means includes a permanent magnet, one pole of which faces downward, and also includes a magnetic portion placed apart from the virtual central line of the magnetic field with space being left between them.