Monolithic Flexure Element for Inertial Sensor Noise Reduction
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Solution Overview
Problem
Existing inertial sensors face limitations in measuring low-frequency ground motion due to internal noise sources like creep and hysteresis noise, which are exacerbated by the dimensional stability of suspension mechanisms, leading to increased costs and complexity in design and assembly.
Innovation Solution
A long-period weak-motion inertial sensor is designed with a monolithic flexure element that has a stiff frame and movable mass integral clamps, a flexible region connecting them, and varying thickness along the length to minimize creep and hysteresis noise, while using materials with low loss angles and manufacturing processes that induce minimal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If flat metal leaf springs with separate clamp pieces are used to suspend the inertial mass, then the sensor can detect ground motion, but internal noise (hysteresis and creep) increases due to dimensional instability of the suspension mechanism
Solution Approach 1:
The patent merges the clamp pieces and flexure elements into a single monolithic suspension mechanism. This integration eliminates the interface between separate clamp and flexure components, removing the source of stick-slip hysteresis noise while maintaining the necessary suspension and restoring force functions for ground motion detection
Solution Approach 2:
The patent changes the geometric parameters of the suspension mechanism by designing a monolithic structure with specific thickness variations and contour shapes. This parameter optimization minimizes creep deformation and hysteresis loss, reducing internal noise to levels below the NLNM threshold while preserving measurement capability
2Ease of manufacture
If clamp pieces are used to attach flexure elements to the frame and movable mass, then assembly is possible, but assembly time increases due to alignment requirements and part count
Solution Approach 1:
The patent combines multiple separate components (clamp pieces and flexure elements) into a single monolithic suspension mechanism. This integration eliminates the need for separate assembly operations, removes alignment requirements between multiple parts, and reduces the total part count, thereby significantly reducing assembly time while maintaining manufacturability
3Measurement precision
If the suspension mechanism is made more compliant to reduce hysteresis noise, then measurement sensitivity improves, but creep noise increases due to spontaneous displacements
Solution Approach 1:
The patent optimizes the geometric parameters of the monolithic suspension mechanism, including thickness variations and contour shaping. These parameter changes create a structure that is compliant enough to minimize hysteresis loss and maximize sensitivity, while simultaneously maintaining sufficient structural integrity to suppress creep deformation and spontaneous displacements
Solution Approach 2:
The patent applies different local geometric qualities to different regions of the suspension mechanism. The monolithic structure features varying thickness and contour characteristics in different areas, creating locally optimized stiffness and compliance properties that collectively minimize both hysteresis and creep noise while enabling sensitive low-frequency detection
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 design reduces internal noise levels, enhancing the sensor's ability to detect small signals at low frequencies without the need for costly monolithic structures or complex geometries, thereby improving sensitivity and reducing assembly time and costs.
Implementation Method 1
a monolithic flexure element for suspending the movable mass in the frame... a stiffest flexible region for operatively connecting the frame integral clamp to the movable mass integral clamp
Implementation Method 2
Suspension hysteresis, also known as anelasticity, is quantified by measuring the phase shift between applied stress and resulting strain, called the loss angle
Implementation Method 3
wherein the variation in stiffness of the monolithic flexure element is controlled by varying thickness along the length of the monolithic flexure element
Implementation Method 4
a transducer for sensing displacements of the movable mass with respect to the frame
Data Source
AI summary
A long-period weak-motion inertial sensor includes a frame having a frame mounting surface, a movable mass having a movable mass mounting surface, a transducer for sensing displacements of the movable mass with respect to the frame, and a monolithic flexure element for suspending the movable mass in the frame. The monolithic flexure element includes: a stiff frame integral clamp attachable to the frame mounting surface of the frame, a stiff movable mass integral clamp attachable to the movable mass mounting surface of the movable mass, and a stiffest flexible region for operatively connecting the frame integral clamp to the movable mass integral clamp. The frame and movable mass mounting surfaces do not overlap the stiffest flexible region, thereby minimizing the generation of creep and hysteresis noise. The variation in stiffness of the monolithic flexure element is controlled by varying thickness along the length of the flexure element.