Electrically Tunable Lens Autofocusing for 3D Profilometry
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Solution Overview
Problem
High-resolution three-dimensional shape measurement using digital fringe projection methods faces challenges in automation and accuracy due to the need for precise focal length adjustment and limited working range, as existing autofocusing techniques are not suitable for handling large depth variations and light efficiency.
Innovation Solution
A method and system that utilize a continuous geometric parameter model and electrically tunable lenses to automatically determine optimal focal length settings for a digital fringe projection system, enabling accurate 3D profiling across an arbitrary depth range by calibrating geometric parameters and using a 2D autofocusing technique to detect focal plane adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If traditional 2D autofocusing methods are used, then the system can automatically adjust focal length, but the measurement precision deteriorates because traditional methods do not accurately track focal length changes required for 3D profilometry
Solution Approach 1:
The patent replaces traditional 2D autofocusing methods with a new approach that uses a calibrated geometric parameter model and continuous functions to determine focal length. Instead of relying on image sharpness metrics, the system uses the relationship between camera position, projector position, and focal length defined by calibration data to automatically and accurately determine the optimal focal length setting.
Solution Approach 2:
The patent changes the parameter determination method by using continuous functions that relate focal length to camera and projector geometric parameters. Rather than using discrete focal length steps or image-based metrics, the system calculates focal length as a continuous parameter derived from the calibrated geometric model, enabling both automation and precision.
2Device complexity
If the focal plane is fixed after system calibration, then the system structure remains simple, but the adaptability deteriorates when targets are not within the depth-of-field of the system
Solution Approach 1:
The patent makes the focal plane dynamic by enabling automatic adjustment of focal length based on the depth of the target object. The system uses the calibrated geometric parameter model to calculate the appropriate focal length setting for objects at different depths, allowing the focal plane to adapt dynamically while maintaining a simple overall system structure.
Solution Approach 2:
The patent creates a universal system that can handle targets at various depths by integrating automatic focal length adjustment into the existing calibration framework. The calibrated geometric parameter model serves multiple functions: it defines system geometry, enables depth calculation, and determines optimal focal length settings, making the system adaptable to different measurement scenarios without requiring separate configurations.
3Adaptability or versatility
If real DOF extending methods are used to increase physical depth-of-field, then the working range improves, but light transfer efficiency significantly attenuates or the device complexity increases
Solution Approach 1:
The patent avoids physical modifications to extend depth-of-field by changing the operational parameter (focal length) based on target depth. Instead of using optical elements that physically extend DOF (which attenuate light), the system dynamically adjusts focal length settings to match the depth of objects being measured, maintaining optimal light transfer efficiency while achieving extended working range.
4Adaptability or versatility
If real DOF extending methods modify camera or projector configuration to increase physical DOF, then the working range improves, but the device complexity increases making implementation difficult
Solution Approach 1:
The patent achieves extended working range through dynamic parameter adjustment rather than static configuration changes. The system uses the calibrated geometric model to calculate and adjust focal length settings in real-time based on object depth, avoiding the need for complex mechanical or optical modifications to the camera or projector while achieving adaptable depth-of-field coverage.
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 approach allows for precise and automatic focal length adjustment, enhancing the accuracy and working range of 3D shape measurement systems by ensuring in-focus images are captured, even with large depth variations, and maintaining light transfer efficiency.
Implementation Method 1
the camera having an electrically tunable lens
Data Source
AI summary
The disclosure provides an improvement to digital fringe projection techniques in which the optimal focal length settings are automatically determined for reconstructing a 3D profile. In a pre-calibration phase, geometric parameters of the system are calibrated using a few discrete focal length settings. These discretely calibrated geometric parameters are fitted onto a continuous function model. In a 3D autofocusing phase, a set of optimal focal length settings for a scene are determined using a 2D autofocusing technique. Calibrated geometric parameters for each optimal focal length setting are automatically calculated using the continuous geometric parameter model. Finally, a 3D profile of objects in the scene is reconstructed using the calibrated geometric parameters for each optimal focal length setting.