Levitated Mass Accelerometer Tether Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing force-balance accelerometers face measurement errors due to parasitic forces caused by parasitic electrostatic charge on levitated proof masses and mechanical hinge instability, which affects temperature and time stability, and results in cross-axis acceleration errors and fragility.
Innovation Solution
A levitated mass accelerometer with a flexible, electrically conductive tether provides a discharge path for parasitic electrostatic charge and maintains mechanical freedom, using force-balance loops for stabilization in all six axes, allowing for low resonant frequencies and robustness against shocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the spring constant K is reduced to improve temperature and time stability, then the natural frequency ω0 decreases, but the proof mass becomes more fragile and cannot survive shocks
Solution Approach 1:
The patent replaces the mechanical hinge suspension system with an electrostatic force balance system. The proof mass is suspended by electrostatic forces between capacitive plates rather than mechanical springs, eliminating the direct mechanical connection that limits both flexibility and shock resistance. This allows the system to achieve low resonant frequencies through electrical control while maintaining shock survivability.
Solution Approach 2:
The patent uses a flexible hinge made from composite materials with different properties in different regions. The hinge contains a weak section with lower stiffness for flexibility and a strong section with higher stiffness for shock resistance, combining the benefits of both soft and rigid structures in a single component.
2Speed
If the hinge is made thin and long to minimize spring constant, then the resonant frequency decreases, but the hinge becomes fragile and may not survive shocks
Solution Approach 1:
The hinge is segmented into multiple sections with different functional properties: a long, thin weak section that provides the necessary flexibility and low resonant frequency, and a shorter, thicker strong section that provides shock resistance. This segmentation allows each part to optimize for its specific function.
Solution Approach 2:
Different sections of the hinge have different local properties: the weak section has low stiffness (thin and long) for frequency control, while the strong section has high stiffness (thick and short) for mechanical strength. Each local region is optimized for its specific role in the overall system.
3Measurement precision
If there is an offset between electrical zero and mechanical zero, then measurement error occurs due to parasitic forces, but eliminating the offset is practically unavoidable due to temperature and material instability
Solution Approach 1:
The patent replaces the mechanical hinge that connects the proof mass to the frame with an electrostatic suspension system. This eliminates the mechanical zero reference that causes offset errors, as the electrostatic forces can be precisely controlled and balanced to maintain the proof mass at the electrical zero position regardless of temperature or material changes.
Solution Approach 2:
The system uses feedback control through force-balance loops that continuously monitor the position of the proof mass using capacitive position-pickoff plates and apply corrective electrostatic forces to maintain the mass at the electrical zero position. This active feedback compensates for any drift or offset, maintaining measurement accuracy over time and temperature.
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 effectively reduces measurement errors by neutralizing parasitic charges and enhancing stability, enabling accurate acceleration measurement across all axes with lower resonant frequencies and improved robustness.
Implementation Method 1
A levitated mass accelerometer with a flexible, electrically conductive tether provides a discharge path for parasitic electrostatic charge
Implementation Method 2
In accelerometers fabricated using MEMS—(Micro-Electro mechanical System) technologies the balancing force is electrostatic and is generated by means of capacitive plates and/or comb drives
Implementation Method 3
The proof mass movement is monitored by capacitive position-pickoff plates
Data Source
AI summary
A multi-axis force-balance accelerometer has a proof mass included within an enclosure. An electrically conductive tether, flexible in 6 degrees of freedom, provides a compliant electrically conductive link between the proof mass and the enclosure. Mechanical stops limit a range of motion of the proof mass. The enclosure includes captive plates and force balancing control loops for positioning the proof mass in a null position within the enclosure for each of the 3 rectilinear reference axes, and in a null position within the enclosure for each of 3 angular reference axes. The electrically conductive tether is sufficiently mechanically compliant that, on deactivation of the force balancing control loops for the rectilinear axes, the proof mass falls so as to rest on the mechanical stops.