Piezoelectric MEMS Mirror with Differential Arm Thickness
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Solution Overview
Problem
Microelectromechanical mirror devices with piezoelectric actuation are sensitive to spurious movements out of the plane and prone to shocks due to the length and thinness of driving arms, leading to multiple spurious modes at low frequencies and reduced robustness.
Innovation Solution
The microelectromechanical mirror device features a tiltable structure with elastic suspension elements and actuation arms of different thicknesses, where the driving arms have a smaller thickness than the elastic elements, and a reinforcement structure, optimizing the trade-off between displacement efficiency and robustness, with elastic decoupling elements positioned close to the axis of rotation to enhance the ratio of spurious mode frequencies and reduce shock sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If driving arms are made thin to increase displacement efficiency, then displacement efficiency is improved, but robustness against shocks deteriorates
Solution Approach 1:
The patent applies different thicknesses to different parts of the structure: driving arms have a first thickness optimized for displacement efficiency, while elastic suspension elements have a greater second thickness for robustness, and reinforcement structures have a third thickness for additional support. This local differentiation resolves the contradiction by optimizing each component's thickness for its specific function rather than using a uniform thickness throughout the structure.
2Length of moving object
If driving arms are made long to achieve wide rotation angles, then rotation angle is improved, but sensitivity to spurious movements increases
Solution Approach 1:
The patent introduces elastic suspension elements as intermediary components between the driving arms and the tiltable structure. These elements act as mediators that filter out spurious movements while transmitting the useful actuation forces, thereby allowing long driving arms to achieve wide rotation angles without being overly sensitive to spurious movements.
Solution Approach 2:
The patent employs composite structural design combining driving arms, elastic suspension elements, and reinforcement structures with different mechanical properties. This composite approach allows the system to simultaneously achieve the flexibility needed for wide rotation and the stiffness needed to reject spurious movements.
3Use of energy by moving object
If piezoelectric actuation is used to reduce power consumption, then power consumption is improved, but sensitivity to spurious movements worsens
Solution Approach 1:
The patent differentiates the thickness and mechanical properties of local components to address the sensitivity issue caused by piezoelectric actuation. By making elastic suspension elements thicker than driving arms, the structure locally enhances stiffness where needed to filter spurious movements while maintaining the low power consumption benefits of piezoelectric actuation.
4Volume of moving object
If device dimensions are reduced for portability, then compactness is improved, but robustness deteriorates
Solution Approach 1:
The patent employs a nested structural arrangement where reinforcement structures are positioned within or alongside the main device components. This nesting allows additional robustness-enhancing elements to be integrated into the compact device volume without significantly increasing the overall dimensions, thereby maintaining portability while improving robustness.
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 achieves wide angles of rotation with low biasing voltage, higher stiffness against spurious movements, reduced power consumption, and smaller device dimensions, while maintaining robustness against shocks, improving the overall performance and efficiency of the microelectromechanical mirror device.
Implementation Method 1
Each driving arm carries, at a top surface thereof, a respective piezoelectric structure... application of a biasing voltage V to the piezoelectric structure 33 of the first driving arm 32a... causes a rotation of a positive angle about the first axis of rotation
Implementation Method 2
Each driving arm is elastically coupled to the tiltable structure 22, by a respective first elastic decoupling element 34a... having a high stiffness in regard to movements out of the horizontal plane xy
Data Source
Figure 1A~1B
Figure 2A~3
Figure 4~6
AI summary
A microelectromechanical mirror device (200) has: a fixed structure (24) defining a cavity (23); a tiltable structure (22) carrying a reflecting surface (22'), elastically suspended above the cavity (23) and having a main extension in a horizontal plane (xy); elastic elements (26a-26b, 34a-34d) coupled to the tiltable structure (22); at least one first pair of driving arms (32a, 32b), which carry respective regions of piezoelectric material (33), that can be biased to cause rotation of the tiltable structure (22) about at least one first axis of rotation (X) parallel to a first horizontal axis (x) of the horizontal plane (xy), are elastically coupled to the tiltable structure on opposite sides of the first axis of rotation (X) and are interposed between the tiltable structure (22) and the fixed structure (24). The driving arms (32a, 32b) have, along an orthogonal axis (z) transverse to the horizontal plane (xy), a thickness smaller than that of at least some of the elastic elements (26a-26b, 34a-34d) coupled to the tiltable structure (22).