MEMS Inertial Sensor Link Structure for Pivot Stiffness Balance
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Solution Overview
Problem
Existing micro-electro-mechanical gyrometers face challenges in achieving a balance between high stiffness for movements parallel to the frame's direction and flexibility for rotation about the detection axis, while minimizing stiffness that opposes rotation, leading to manufacturing difficulties and undesirable torque effects.
Innovation Solution
A micro-electromechanical device with a connection mechanism using a thin wall parallel to the support plane for high rigidity in the frame's direction and a retaining wall perpendicular to the support plane for minimal rotation stiffness, coupled with a symmetrical frame-mass assembly to compensate for torque effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a torsion beam link is used to connect the frame to the proof mass, then the link can allow the mass to pivot about its axis of rotation, but the link becomes difficult to manufacture with precise dimensions and control
Solution Approach 1:
The link is divided into two distinct functional elements: a first wall (parallel to support plane) for transmitting forces in the frame displacement direction, and a second wall (perpendicular to support plane) for defining the Z position and enabling rotation. This segmentation allows each element to be optimized independently for its specific function, improving both manufacturability and performance.
Solution Approach 2:
The solution transitions from a single three-dimensional torsion beam to a two-wall configuration where one wall extends in the X-direction (parallel to support plane) and the other extends in the Z-direction (perpendicular to support plane). This dimensional decomposition allows precise control of mechanical properties in different directions while simplifying manufacturing.
2Stability of the object's composition
If the link is made rigid in the Z direction to set the Z position of the proof mass, then the hinge function is fulfilled, but the link becomes less flexible for torsion about the Y axis
Solution Approach 1:
The link is segmented into two walls with different orientations: the first wall (parallel to support plane) provides rigidity in the X-direction for force transmission, while the second wall (perpendicular to support plane) provides rigidity in the Z-direction for position stability. This segmentation allows independent optimization of rigidity in different directions.
Solution Approach 2:
Different parts of the link structure have different mechanical properties tailored to their specific functions. The first wall is optimized for force transmission in the X-direction, while the second wall is optimized for position constraint in the Z-direction. This local differentiation of mechanical properties resolves the contradiction between rigidity and flexibility.
3Strength
If the link transmits forces parallel to the axis of displacement with high rigidity, then the frame can drive the mass effectively, but torque effects cause undesirable rotation of the mass
Solution Approach 1:
The harmful torque effect is extracted and isolated to a specific location: the intersection of the first and second walls. By carefully designing the connection geometry at this intersection point, the torque generated by force transmission can be compensated, allowing high rigidity force transmission while minimizing undesirable rotation.
Solution Approach 2:
The two walls are arranged asymmetrically in space (one parallel to support plane, one perpendicular) to create a geometric configuration that compensates for torque effects. This asymmetric arrangement allows the structure to transmit forces efficiently while the geometric relationship between the walls counteracts unwanted rotational moments.
4Manufacturing precision
If a thin wall parallel to the support plane is used for the link, then manufacturing precision is improved and torque effects are reduced, but the stiffness for rotation about the detection axis increases
Solution Approach 1:
The link is segmented into two walls with different orientations and functions. The first wall (parallel to support plane) provides manufacturing precision and reduces torque effects, while the second wall (perpendicular to support plane) provides the necessary rotation stiffness. This segmentation allows both requirements to be satisfied simultaneously by different structural elements.
Solution Approach 2:
The second wall (perpendicular to support plane) is specifically designed to provide local stiffness for rotation about the detection axis, while the first wall handles force transmission. This local differentiation of mechanical properties allows the structure to have low torque sensitivity while maintaining high rotation stiffness where needed.
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 provides a better compromise between stiffness and flexibility, enhancing the detection signal and reducing manufacturing variability, while effectively compensating for torque-induced rotation.
Implementation Method 1
a first wall (50), parallel to the mean plane (P) of the support (2), which allows the frame (3) to drive the mass (4) therewith, with high rigidity in a direction parallel to the axis of displacement (X)
Implementation Method 2
a second wall (61), perpendicular to the mean plane (P) of the support (2), which sets the position in a direction parallel to the axis (Z)
Implementation Method 3
each mass 4aa, 4aa′ then undergoes a Coriolis force, which is expressed as Fcor=2mcor(vx)∧(Ωy)
Implementation Method 4
This rotation of the lever is then measured, for example by virtue of strain gauges (piezoresistive, piezoelectric or resonant detection) to deduce the angular velocity Ω
Data Source
AI summary
A micro-electromechanical device of the inertial sensor type, includes a support, a movable frame, translationally guided along an axis of displacement parallel to the support, and including a proof mass which extends from a first end, connected to the support through a mechanical link, up to a second end, the mass being connected, on the side of the second end, to a member for detecting pivoting of the mass with respect to the frame. The link includes a thin, flexible wall which extends parallel to the support, from the frame to the first end of the proof mass, along a mean line which is parallel to the axis of displacement of the frame.