Tunable Acoustic Gradient Lens Amplitude Modulation for High-Speed Imaging
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Solution Overview
Problem
Precision machine vision inspection systems with tunable acoustic gradient (TAG) lenses face limitations in the amount of lighting that can be provided during image exposure for focus changes, necessitating improvements to enhance imaging capabilities.
Innovation Solution
A variable focal length (VFL) lens system incorporating a TAG lens, a controller, a light source, and a camera, where the TAG lens's optical power is periodically modulated at a resonant frequency using different amplitude driving signals to optimize exposure increments and focus positions, allowing for improved illumination and focus metric determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the TAG lens periodically modulates focus position at high speed, then the imaging speed and productivity are improved, but the amount of lighting energy available during each exposure is reduced
Solution Approach 1:
The patent applies periodic action by modulating the TAG lens at its resonant frequency to periodically sweep through different focal lengths. This allows the system to cycle through multiple focus positions rapidly, enabling high-speed imaging while using the periodic nature of the modulation to synchronize light source activation with specific phases of the focus sweep, thereby maximizing lighting energy utilization during each exposure window.
Solution Approach 2:
The patent implements preliminary action by pre-sweeping the focus position to a target Z-height before activating the light source for exposure. This ensures that the lens reaches the desired focal plane in advance, allowing the light source to provide maximum illumination energy during the exposure window without requiring continuous high-power lighting throughout the entire modulation cycle.
2Speed
If the exposure time is shortened to capture high-speed focus changes, then the imaging speed is improved, but the image brightness and illumination quality deteriorate
Solution Approach 1:
The system uses periodic modulation of the TAG lens at resonant frequencies (e.g., 400 kHz) to create repeated exposure opportunities. By synchronizing the light source activation with specific phases of this periodic cycle, the system can use short exposure times to capture high-speed focus changes while accumulating sufficient light energy through the repeated periodic cycles to maintain image brightness.
Solution Approach 2:
The patent applies preliminary action by pre-positioning the focus at the target Z-height before initiating the light source and camera exposure. This ensures that the lens is already at the correct focal plane when the short-duration exposure begins, eliminating the need for longer exposure times to accommodate focus traversal and thereby maintaining both high speed and adequate image brightness.
3Adaptability or versatility
If the focal length range is increased to cover more Z-heights, then the measurement range is improved, but the focus precision and image quality at each Z-height are reduced
Solution Approach 1:
The patent implements dynamics by using a tunable acoustic gradient lens that can rapidly and continuously adjust its focal length in response to applied voltages. This dynamic capability allows the system to sweep through a wide Z-height range quickly, then pause or dwell at specific target heights for precise measurements, thereby achieving both broad measurement range and high focus precision at each measured Z-height.
Solution Approach 2:
The system uses periodic modulation of the TAG lens to repeatedly sweep through the full focal length range. By synchronizing light source activation with specific phases of this periodic cycle, the system can capture images at multiple Z-heights during each sweep, providing both broad measurement coverage and sufficient image quality at each height through the accumulated light energy from the periodic cycling.
Data Source
AI summary
A variable focal length lens system includes a tunable acoustic gradient (TAG) lens; a TAG lens controller; and processor(s) configured to: (a) operate the TAG lens controller to drive a periodic modulation of the TAG lens optical power at a TAG lens resonant frequency, using a first amplitude driving signal that provides a first focal Z range extending between peak focus distances Z1max+ and Z1max−; and expose a first image using a first exposure increment approximately at the timing of Z1max+ or Z1max−; (b) adjust the TAG lens controller to drive the periodic modulation using a second amplitude driving signal that provides a second focal Z range extending between peak focus distances Z2max+ and Z2max−; and expose a second image using a second exposure increment approximately at the timing of Z2max+ or Z2max−; and (c) perform processing that includes determining focus metric values for the first and second images.