Compliant MEMS Stops for Proof Mass PLL Stability
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Solution Overview
Problem
MEMS gyroscopes face instability due to abrupt changes in resonant frequency when the proof mass engages with hard stops, leading to potential damage and failure of the phase locked loop (PLL) circuit.
Innovation Solution
Implementing compliant or soft stop structures that are positioned adjacent to the proof mass suspension to smooth frequency changes, thereby maintaining the resonant frequency within the PLL stability range by increasing the stiffness of the proof mass suspension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hard stops are used to limit proof mass movement, then mechanical damage is prevented, but abrupt frequency changes occur causing PLL instability
Solution Approach 1:
A compliant stop structure is introduced as an intermediary element between the proof mass and the hard stop. This compliant stop acts as a mediator that gradually engages to limit proof mass movement while avoiding the abrupt frequency changes caused by direct hard stop engagement, thus maintaining PLL stability while still providing mechanical protection.
Solution Approach 2:
The stop structure's mechanical parameters are changed from rigid (hard stop only) to compliant (spring-based structure). This parameter change allows the stop to engage gradually rather than abruptly, smoothing out frequency transitions and preventing PLL instability while still limiting proof mass travel to protect against mechanical damage.
2Reliability
If over-travel stops are added to prevent damage, then device protection is improved, but manufacturing complexity increases
Solution Approach 1:
The compliant stop structure is merged with the existing hard stop architecture. The spring-based compliant stop is integrated into the same structural framework as the hard stop, allowing both protection functions to be combined in a single manufacturing process rather than requiring separate components and assembly steps.
3Stability of the object's composition
If compliant stops are used to smooth frequency changes, then PLL stability is improved, but device complexity increases
Solution Approach 1:
The compliant stop utilizes flexible spring structures (compliant beams) to achieve the desired frequency smoothing function. These flexible elements provide the necessary compliance to gradually engage with the proof mass while maintaining a relatively simple geometric form that does not significantly increase device complexity.
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 compliant stops reduce the likelihood of PLL circuit failure by minimizing abrupt frequency shifts, ensuring stable operation even under harsh conditions.
Implementation Method 1
positioned adjacent to the proof mass suspension to smooth frequency changes by increasing the stiffness of the proof mass suspension
Implementation Method 2
positioned adjacent to the proof mass suspension to physically engage with lateral oscillating movement of the proof mass suspension member
Data Source
AI summary
A MEMS inertial sensor device, method of operation, and fabrication process are described with a MEMS inertial sensor, drive actuation unit, drive measurement unit, and PLL circuit coupled together in operational engagement, where the MEMS inertial sensor includes a substrate, a proof mass positioned in spaced apart relationship above the substrate, a proof mass suspension member connected on a first end to the proof mass and connected on a second end to an anchor fixed to the substrate to enable the proof mass to laterally oscillate over the surface of the substrate, and a compliant stop structure positioned in relation to the proof mass suspension member to physically engage with lateral oscillating movement of the proof mass suspension member past a desired stroke travel distance without physically preventing lateral oscillating movement of the proof mass, thereby stiffening a spring stiffness measure of the proof mass suspension member.