Piezoelectric Actuator Capacitance Sensing for Optical Power Control
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Solution Overview
Problem
Existing optical systems with tunable focal lengths, such as those used in augmented and virtual reality devices, face challenges in achieving high-speed and consistent tuning of focal lengths over a wide range, which has not been adequately addressed by current technologies.
Innovation Solution
A closed-loop control paradigm using capacitance sensing of a piezoelectric element to predictably and reproducibly manipulate the optical power of a lens, accounting for thermal and temporal variations to achieve a targeted focus condition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional optical tuning methods are used, then the system can achieve basic focal length adjustment, but the tuning speed and consistency over a wide range are insufficient
Solution Approach 1:
The patent implements a closed-loop feedback control system that continuously monitors the actual focal position and compares it with the target position. The controller adjusts the piezoelectric actuator input based on the measured error, ensuring accurate and consistent focal length tuning across the entire range while maintaining high tuning speed through real-time corrections.
Solution Approach 2:
The system dynamically changes multiple parameters including driving voltage amplitude and frequency, piezoelectric actuator positioning, and lens curvature based on real-time feedback. This multi-parameter adjustment enables the system to achieve wide focal length tuning range while maintaining precision and consistency throughout the tuning process.
2Speed
If higher driving voltages are applied to achieve faster focusing, then the tuning speed improves, but thermal variations and hysteresis effects worsen
Solution Approach 1:
The feedback control system continuously monitors focal position and compensates for thermal drift by adjusting the piezoelectric actuator input voltage. When thermal variations cause focal position deviations, the controller detects these changes and applies corrective voltage adjustments, maintaining focus accuracy despite high-speed operation and associated thermal effects.
Solution Approach 2:
The system applies periodic calibration sequences where the focal position is re-measured and corrected at regular intervals during operation. This periodic compensation counteracts cumulative thermal drift and hysteresis effects that occur during continuous high-speed tuning, ensuring long-term focus consistency.
3Adaptability or versatility
If the focal length tuning range is extended, then the versatility improves, but the precision and consistency of focus control deteriorate
Solution Approach 1:
The closed-loop feedback system maintains precision across the entire tuning range by continuously measuring the actual focal position and applying real-time corrections. The controller adjusts piezoelectric actuator inputs based on measured deviations, ensuring consistent focus precision whether operating at the extremes or center of the wide tuning range.
Solution Approach 2:
The system dynamically adapts its control parameters based on the current focal position within the tuning range. The controller adjusts voltage amplitude, frequency, and update rates according to the operating point, optimizing precision for each region of the tuning range while maintaining overall versatility across the full extent.
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 enables rapid and accurate focusing, allowing for the generation and maintenance of high-quality images in associated displays, while avoiding overshoot and excessive stress on lens components.
Implementation Method 1
a piezoelectric actuator assembly configured to deform the tunable lens in response to an applied voltage signal
Implementation Method 2
measuring a capacitance of the piezoelectric element
Data Source
AI summary
A method of operating a tunable lens includes determining a relationship between the optical power of a tunable lens and the capacitance of a piezoelectric element configured to deform the tunable lens, measuring the capacitance of the piezoelectric element, and applying a driving voltage to the piezoelectric element based on the measured capacitance to induce a desired optical power in the tunable lens.