Geophone Mass Position Sensing via Capacitance
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Solution Overview
Problem
Existing geophone sensing elements face challenges in accurately determining the position of the inertial mass with respect to the support structure, leading to reduced effectiveness and quality due to displacement caused by changes in gravity or improper orientation, which complicates the manufacturing process and sensitivity issues.
Innovation Solution
A sensing element design incorporating a spring assembly with an electrically conductive member and a capacitor plate, where the distance between the capacitor plate and the electrically conductive member is variable, allowing for the estimation of the coil assembly's position using electrical capacitance, and optionally increasing the effective surface area with extended capacity plates or stationary capacitor plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the spring stiffness along the main axis is reduced to lower the resonant frequency and widen the frequency band, then the useful frequency band is widened, but the coil assembly becomes more susceptible to displacement due to gravity changes and improper orientation, reducing measurement precision
Solution Approach 1:
The patent replaces the mechanical spring suspension system with an electromagnetic suspension system. The coil assembly is suspended electromagnetically between two magnets, allowing precise position control through electromagnetic forces while maintaining a stiff mechanical support structure. This substitution enables both a wide frequency band and high position accuracy simultaneously.
Solution Approach 2:
The patent employs a feedback control system where the position of the coil assembly is continuously monitored and electromagnetic forces are adjusted to maintain the coil at its null position. This active feedback mechanism compensates for gravity changes and orientation variations, ensuring measurement precision is maintained across a wide frequency band.
2Measurement precision
If a displacement sensor is added to determine the relative position of the inertial mass, then position measurement capability is improved, but the device complexity increases and sensitivity is affected
Solution Approach 1:
The patent makes the coil assembly serve multiple functions: it acts as both the electromagnetic suspension element and the displacement sensing element. The coil's position, which is already critical for electromagnetic suspension, is simultaneously used for displacement measurement, eliminating the need for a separate displacement sensor and reducing overall device complexity.
Solution Approach 2:
The patent merges the suspension function and sensing function into a single integrated system. The coil assembly's electromagnetic interaction with the magnets provides both suspension and position information, combining what would traditionally be separate systems into one unified structure that reduces complexity while maintaining measurement precision.
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 solution enables precise estimation of the inertial mass position, improving the geophone's sensitivity and effectiveness by accurately determining displacement, thereby enhancing the geophone's frequency band and operational stability.
Implementation Method 1
A capacitor plate is disposed proximate the electrically conductive member and separated therefrom by a distance, the distance being variable by relative movement of the coil assembly and magnet. The capacitor plate and electrically conductive member form a variable capacitor that can be used to estimate the position of the coil assembly.
Implementation Method 2
The springs position the coil within the magnetic field so that the coil is centered laterally and along its axis within the magnetic field. The springs also form a suspension system having a predetermined resonant frequency.
Implementation Method 3
The movement of the coil assembly through a magnetic field causes a voltage to be generated at the output of the geophone.
Data Source
AI summary
A motion sensing element with position sensing includes a case, a magnet positioned within the case, a spring assembly having an electrically conductive member and a coil assembly coupled to the spring assembly. The coil assembly and magnet are moveable with respect to one another. A capacitor plate is proximate the electrically conductive member with a distance between the capacitor plate and electrically conductive member being variable as the magnet and coil assembly move. Leads connect the capacitor plate and electrically conductive member to a sensing circuit for estimating the relative positions of the magnet and coil assembly.