MEMS Mirror Precession via Piezoelectric Cantilevers
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Solution Overview
Problem
Conventional MEMS mirrors used in laser distance sensors have a limited in-plane scan range due to the fracture stress limit of silicon cantilevers, restricting their ability to achieve a wide in-plane scanning range and all-round rotational displacement.
Innovation Solution
An optical scanning device with a mirror part supported by N swingable cantilevers and N drive cantilevers arranged to surround it, where the drive cantilevers are bent and equipped with piezoelectric elements, applying AC voltage to achieve a wide in-plane scan range through precession by setting the frequency and phase of the voltage applied to the piezoelectric elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon cantilever is used to support the mirror part, then the device structure is simple and manufacturable, but the in-plane scan range is limited by the fracture stress limit of silicon
Solution Approach 1:
The support structure is divided into two independent parts: N support cantilevers that hold the mirror part and N drive cantilevers that provide driving force. This segmentation allows each component to be optimized for its specific function, with drive cantilevers designed for large deflection and support cantilevers designed for structural stability.
Solution Approach 2:
The drive cantilevers act as intermediary elements between the piezoelectric elements and the mirror part. They transmit and amplify the small deformation from piezoelectric elements into large deflection, enabling wide in-plane scan range without directly loading the support cantilevers to their fracture limit.
2Manufacturing precision
If piezoelectric elements are driven at resonance frequency, then a large deformation is achieved from minute piezoelectric deformation, but the in-plane scan range is still limited by the fracture stress limit of silicon
Solution Approach 1:
The drive cantilevers are designed with bent shapes and specific elastic properties to operate dynamically at resonance frequency. This dynamic operation amplifies the small piezoelectric deformation into large deflection, achieving wide in-plane scan range while keeping the support cantilevers within their stress limits.
Solution Approach 2:
The elastic modulus and geometric parameters of the drive cantilevers are specifically optimized to achieve resonance at the desired operating frequency. By changing these parameters, the system transforms minute piezoelectric deformation into large mirror deflection, expanding the in-plane scan range beyond silicon fracture limits.
3Device complexity
If electrostatic force is used to drive the mirror, then the device configuration is simple, but the generated driving force is small and a sufficient deflection angle is not ensured
Solution Approach 1:
The patent replaces electrostatic driving with piezoelectric driving. Piezoelectric elements convert electrical energy directly into mechanical deformation with high efficiency and large force output, providing sufficient driving force for wide-angle scanning while maintaining relatively simple device configuration.
Solution Approach 2:
The drive system uses composite structures combining piezoelectric elements with bent cantilever beams. This composite design leverages the high coupling coefficient of piezoelectric materials to generate large driving forces and deflections, overcoming the limitation of small driving force in electrostatic systems.
4Force
If electromagnetic force is used to drive the mirror, then sufficient driving force is achieved, but a permanent magnet must be arranged externally, making the device configuration complicated and downsizing difficult
Solution Approach 1:
The patent extracts and eliminates the permanent magnet component from the driving system. By using piezoelectric elements that generate force through material deformation rather than magnetic fields, the system achieves sufficient driving force without external magnets, simplifying the device configuration and enabling downsizing.
Solution Approach 2:
The patent replaces the electromagnetic driving mechanism with a piezoelectric mechanism. This substitution eliminates the need for permanent magnets and complex magnetic circuits, reducing device complexity and size while maintaining sufficient driving force through the high coupling efficiency of piezoelectric materials.
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 increases the in-plane scan range of the mirror part, enabling all-round rotational displacement and allowing for 360-degree information acquisition by optimizing the deflection angle and linearity of the mirror's displacement.
Implementation Method 1
a plurality of driving piezoelectric elements secured on the N drive cantilevers and a power supply unit configured to apply AC voltage to the piezoelectric elements
Implementation Method 2
The mirror part precesses by setting a frequency of AC voltage applied to each of the piezoelectric elements to a common value and setting a phase of AC voltage applied to each of the piezoelectric elements to a value determined according to a position of the piezoelectric element
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An optical scanning device (100) includes a mirror part (1) having a mirror surface (1B) configured to reflect light, N support cantilevers (2-1) to (2-4) supporting the mirror part (1) swingably, N drive cantilevers (3-1) to (3-4), and a plurality of driving piezoelectric elements (5-i-a to d (i = 1 to 4)) secured on N drive cantilevers. The mirror part (1) precesses by setting the frequency of AC voltage applied to each of a plurality of piezoelectric elements (5-i-a, b, c, d) to a determined common value and setting the phase of AC voltage applied to each of a plurality of piezoelectric elements (5-i-a, b, c, d) to a value determined according to the position of each piezoelectric element.