Anisotropic Stop Spring Structure for MEMS Adherence
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Solution Overview
Problem
Micromechanical sensors face issues with mechanical robustness and adherence due to novel load profiles, particularly in z acceleration sensors, where the movable mass tends to stick to mechanical stops, and existing resilient stops may not adequately address shear loads and lateral accelerations.
Innovation Solution
A stop spring structure with distinct spring constants in different directions (Kz > Kx and Ky) is designed, featuring a combination of torsion and meander or spiral springs to provide high stiffness in the z direction while maintaining low stiffness in x and y directions, reducing shear loads and adherence risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard fixed stop is used for the movable mass, then the mechanical robustness is improved, but the tendency to adhere increases and particle formation occurs during frequent overload
Solution Approach 1:
The patent applies beforehand cushioning by introducing a resilient stop structure that cushions the impact between the movable mass and the fixed stop before actual contact occurs. The resilient stop absorbs impact energy and reduces mechanical damage to stop surfaces, preventing adherence and particle formation during frequent overload events.
2Force
If the spring stiffness in z direction is increased to provide a hard stop, then the restoring force is improved, but the shear loads and lateral movement increase causing more adherence
Solution Approach 1:
The patent applies local quality by designing the resilient stop with directionally selective spring constants. The spring structure has high stiffness (Kz) in the z direction to provide strong restoring force, while maintaining low stiffness (Kx, Ky) in lateral directions to minimize shear loads and lateral movement, thereby reducing adherence risk.
Solution Approach 2:
The patent applies parameter changes by explicitly defining different spring constant values for different spatial directions (Kz > Kx and Ky). This anisotropic spring constant configuration allows the stop to provide high restoring force vertically while being compliant laterally, reducing both adherence and mechanical damage.
3Stability of the object's composition
If the spring stiffness in x and y directions is increased to reduce lateral movement, then the stability is improved, but the shear loads on the stop increase causing more mechanical damage
Solution Approach 1:
The patent applies local quality by making the resilient stop soft in lateral directions (x and y) while maintaining high stiffness in the z direction. This directional differentiation allows the stop to accommodate lateral accelerations without generating excessive shear loads, thereby protecting the stop surfaces from mechanical damage.
Solution Approach 2:
The patent converts the potentially harmful effect of lateral accelerations into a beneficial outcome by designing the resilient stop to be compliant in lateral directions. The low lateral stiffness allows the stop to yield under lateral loads, converting what would be damaging shear forces into controlled lateral deflections that protect the stop surfaces.
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 enhances mechanical robustness and reduces adherence by allowing deflection in all spatial directions, minimizing lateral movement and mechanical damage, and enabling independent setting of spring constants for improved performance under various load conditions.
Implementation Method 1
the stop spring structure has a first spring constant Kz at the location of the stop in the z direction, has a second spring constant Kx in a x direction, in parallel to the main extension plane x, y, and has a third spring constant Ky in a y direction
Implementation Method 2
featuring a combination of torsion and meander or spiral springs
Data Source
AI summary
A micromechanical device including a substrate, a movable mass, and a stop spring structure, which includes a stop. The substrate includes a substrate surface in parallel to a main extension plane and the movable mass is situated movably above the substrate surface in relation to the substrate. The stop spring structure is connected to the movable mass. The stop is designed to strike against the substrate surface in the event of a deflection of the movable mass in a z direction, perpendicular to the main extension plane. The stop spring structure, at the location of the stop, includes a first spring constant, a second spring constant, in parallel to the main extension plane, and a third spring constant, in parallel to the main extension plane and perpendicular to the x direction. The first spring constant is greater than the second spring constant and/or is greater than the third spring constant.