MEMS Micro-Mirror Position Sensing via Electromagnetic Induction
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Solution Overview
Problem
Existing MEMS micro-mirror devices lack a simple and effective method for precise control and position sensing of micro-mirror deflection, leading to inconsistent image projection quality and potential electrical risks due to the limitations of existing position sensing systems, which are often complex, space-consuming, and sensitive to fabrication variations.
Innovation Solution
The use of independent drive and sensing coils, in conjunction with a magnet, allows for continuous measurement of micro-mirror positions and deflection angles, enabling precise control and feedback loop management to adapt to internal and external changes, thereby improving image quality and ensuring safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodetectors are used to determine micro-mirror position, then position sensing capability is improved, but device volume increases
Solution Approach 1:
The patent combines the drive coil and sensing coil into a single integrated electromagnetic actuation system. The sensing coil is integrated with the drive coil structure, allowing position sensing to be performed without adding separate photodetector components. This merging of functions resolves the contradiction by maintaining position sensing capability while avoiding the volume increase that would result from adding discrete photodetector components to the device.
2Measurement precision
If resistive material is added to torsion arms for position sensing, then position measurement capability is improved, but fabrication complexity increases
Solution Approach 1:
The patent replaces the mechanical/resistive sensing approach with an electromagnetic sensing system. Instead of using resistive material on torsion arms that requires complex doping and fabrication processes, the invention uses a sensing coil that detects position through electromagnetic induction. This substitution of the sensing mechanism eliminates the need for complex resistive material fabrication while maintaining position measurement capability.
3Measurement precision
If resistive material is added to torsion arms for position sensing, then position measurement capability is improved, but sensing performance deteriorates due to noise
Solution Approach 1:
The patent replaces the resistive sensing system with an electromagnetic sensing system using a sensing coil. The sensing coil detects micro-mirror position through electromagnetic induction without the parasitic noise inherent in resistive measurements. This substitution improves sensing performance and reliability by eliminating the noise sources associated with resistive material while maintaining position measurement capability.
4Measurement precision
If fixed electrode dimension is increased to match deflection amplitude for capacitive sensing, then position sensing range is improved, but manufacturing difficulty increases
Solution Approach 1:
The patent replaces the capacitive sensing system with an electromagnetic sensing system using a sensing coil. This substitution eliminates the need for large-dimensioned fixed electrodes that would be required for capacitive sensing across large deflection ranges. The electromagnetic sensing approach maintains full sensing range capability while using standard-sized components that are easier to manufacture with conventional semiconductor equipment.
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 solution enhances the quality of projected images and videos by providing continuous position sensing and feedback control, preventing undesired changes and electrical risks, while simplifying assembly and reducing manufacturing costs.
Implementation Method 1
a sensing coil (202) measures a signal induced by the magnet (200)
Implementation Method 2
different actuation principles can be used, including electrostatic, thermal, electro-magnetic or piezo-electric
Data Source
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Figure 5~6a
AI summary
The present invention concerns a method and an apparatus for controlling a MEMS micro-mirror device. The invention enables the control of the micro-mirror deflection angle and of the micro-mirror scanning frequency, essential for the projection as it relates directly to the size of the projected image. The MEMS micro-mirror device has a fixed part (102) and a micro-mirror (100) that can oscillate along at least one oscillation axis, a magnet (200) either placed next to said fixed part (102) or on the said movable part (100) and a sensing coil (202) placed on said moving part (100) or on said fixed part (102). A detecting circuit detects at least one value (U?nd) of the inducted voltage in said sensing coil (202) for each period and for each oscillation axis, and a calculating circuit (404) calculates the amplitude of the movement of said micro-mirror (100) by means of said value (Umd)- Another independent electrical drive coil can be used in order to have two independent electrical coils respectively for driving the micro- mirror and for sensing its positions. The invention can prevent an unexpected default of the projection system.