Vibration Sensor with Eddy Current Damping for Low-Frequency Detection
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Solution Overview
Problem
Existing vibration sensors face challenges in accurately detecting vibrations at low excitation frequencies due to poor signal-to-noise ratios and difficulties in producing high-precision optical gratings, making them unsuitable for active vibration isolation and imbalance detection in machine tools.
Innovation Solution
A vibration sensor with a mass block movably mounted by a spring, utilizing a position measuring device with a scanning head to detect displacements, and incorporating an eddy current brake for damping, allowing for precise measurement and control of vibrations down to low frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inductive speed sensors (geophones) are used to detect vibrations, then the sensor structure is simple and robust, but the signal-to-noise ratio becomes small at low oscillation frequencies
Solution Approach 1:
The patent replaces the inductive speed sensor (geophone) with a capacitive displacement sensor. This substitution changes the measurement principle from inductive voltage generation proportional to velocity to capacitive measurement of displacement. The capacitive sensor directly measures the position of the proof mass relative to the fixed electrode, enabling accurate detection of low-frequency vibrations without the signal-to-noise ratio degradation that plagues inductive sensors at frequencies below 4 Hz.
2Measurement precision
If optical gratings with periods of less than one micrometer are used for high-precision position measurement, then measurement precision improves, but manufacturing difficulty increases significantly
Solution Approach 1:
The patent transitions from using complex sub-micrometer optical gratings in the lateral dimension to using a capacitive sensor that measures displacement in the vertical dimension between two electrodes. This dimensional change allows high-precision measurement without requiring difficult-to-manufacture fine lateral structures. The capacitive gap can be precisely controlled through standard semiconductor fabrication techniques, avoiding the need for sub-micrometer grating patterns.
3Volume of moving object
If acceleration sensors optimized for mobile phones are used, then device miniaturization is achieved, but the frequency range and accuracy are unsuitable for active vibration damping
Solution Approach 1:
The patent modifies the parameters of the proof mass and spring constant to achieve a natural frequency of 0.6 Hz, which is specifically optimized for active vibration damping applications. Unlike mobile phone accelerometers designed for higher frequency ranges, this sensor's parameters are tuned to accurately measure low-frequency platform vibrations. The larger proof mass and softer spring enable detection of sub-4 Hz vibrations while maintaining a compact form factor suitable for integration into vibration isolation 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 solution enables effective detection and active damping of vibrations at frequencies as low as 0.4 Hz, improving signal quality and accuracy for applications like machine tool balancing and vibration isolation.
Implementation Method 1
a mass block 3, which is movably mounted relative to a frame 2 in a measuring direction X by means of at least one spring 5
Implementation Method 2
a displacement of the mass block 3 relative to the frame 2 being able to be detected by means of a position measuring device 6, 7
Implementation Method 3
incorporating an eddy current brake for damping
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A vibration sensor with a mass block (3) is described, which is movably mounted relative to a frame (2) in a measuring direction (X) by means of at least one spring (5), wherein a displacement in the measuring direction (X) of the mass block (3) relative to the frame (2) can be detected by means of a position measuring device. The position measuring device comprises a scale (7) and a scanning head (6) aligned with the scale (7). One of these two components is attached to the mass block (3), the other to the frame (2).