Variable Focal Length Lens Autofocus via Exposure Timing
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Solution Overview
Problem
Existing machine vision inspection systems with high-speed variable focal length lenses face challenges in automatically determining and adjusting image focus positions accurately and quickly, limiting their ability to perform high-speed precision inspections due to phase offset errors and latency in focus position modulation.
Innovation Solution
A system comprising a high-speed periodically modulated variable focal length lens, a VFL lens controller, a VFL-projected light source, a focus determining portion, an exposure timing adjustment circuit, and an exposure strobe time controller, which periodically modulates the focus position and adjusts exposure timing to ensure accurate focus alignment with the workpiece surface, using optical detectors to provide focus deviation signals and control image exposure for precise focus determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high-speed periodically modulated variable focal length lens is used to rapidly adjust focus position, then the inspection rate and throughput are improved, but phase offset errors and latency prevent accurate focus alignment with the workpiece surface
Solution Approach 1:
The system employs a focus determination portion that continuously monitors the focus position and generates focus deviation signals. These signals provide real-time feedback to the exposure timing adjustment circuit, which adjusts the exposure timing to compensate for phase offset errors. This closed-loop feedback mechanism enables accurate focus alignment despite the high-speed modulation of the VFL lens, resolving the contradiction between high inspection rate and focus alignment accuracy.
Solution Approach 2:
The system performs preliminary calibration to establish the relationship between VFL lens drive signals and focus positions. By pre-determining phase offset values and storing them in a lookup table, the system prepares correction data in advance. This preliminary action allows the exposure timing to be adjusted proactively based on the current focus state, eliminating latency effects and ensuring accurate focus alignment at high inspection speeds.
2Ease of operation
If conventional autofocusing methods are used with high-speed VFL lenses, then the system structure remains simple, but the focusing speed and accuracy are limited by phase offset errors and latency
Solution Approach 1:
The system replaces mechanical focus adjustment mechanisms with an electronically controlled VFL lens that can be modulated at high speeds. The focus position is controlled by electrical signals rather than mechanical movement, enabling focusing speeds that exceed the capabilities of conventional mechanical systems. This substitution eliminates mechanical inertia and friction, achieving both high focusing speed and precise focus position control.
Solution Approach 2:
The system dynamically adjusts the exposure timing based on the real-time focus state of the VFL lens. By continuously monitoring focus deviation signals and adjusting exposure timing accordingly, the system adapts to the dynamic behavior of the high-speed modulated lens. This dynamic adjustment compensates for phase offset errors and latency, maintaining focus position accuracy despite the rapid changes in focal length.
3Productivity
If the exposure timing is not adjusted for phase offset errors, then the system operation is simple, but the focus position determination is inaccurate
Solution Approach 1:
The system introduces an exposure timing adjustment circuit as an intermediary between the VFL lens controller and the image capture process. This intermediary component receives focus deviation signals, determines appropriate exposure timing adjustments based on pre-stored phase offset values, and applies corrections to the exposure timing. This intermediary layer enables accurate Z-height measurements by compensating for phase offset errors without becoming a bottleneck to high inspection throughput.
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 system enables rapid and accurate autofocusing, enhancing the inspection rate and precision by eliminating phase offset errors and latency, allowing for high-speed, high-throughput inspections even with high-speed variable focus lenses like TAG lenses.
Implementation Method 1
a VFL lens configured to receive image light transmitted by the objective lens
Implementation Method 2
an optical detector configured to input reflected VFL-projected light and to provide at least one optical detector signal that is responsive to a difference between a focus Z height
Data Source
AI summary
A system for providing an automatically focused image comprises an imaging system including a high speed periodically modulated variable focal length (VFL) lens, a VFL lens controller, a VFL-projected light source, a focus determining portion, an exposure timing adjustment circuit, and an exposure strobe time controller. The focus determining portion comprises an optical detector that inputs reflected VFL-projected light that is projected to, and reflected from, a workpiece through the VFL lens, and provides a focus deviation signal. The exposure timing adjustment circuit provides an exposure timing adjustment signal based on the focus deviation signal, which indicates a time when the imaging system focus Z-height approximately coincides with the workpiece surface Z height. The exposure strobe time controller uses the exposure timing adjustment signal to adjust the image exposure time so the imaging system focus Z-height coincides with the workpiece surface Z height at the adjusted image exposure time.