Eyewear Inspection Systems

Application: V200 Molded Safety Lens Inspection Systems
The Molded Safety Lens Inspection System (V200) is an automated vision system for inspecting cylindrical and toric safety lenses which contain no significant power. The system provides a highly reliable, quantitative screening for all types of optical defects, including internal inclusions, bubbles and stria, and surface defects such as waves, pits, scratches, and cracks. Lenses up to four inches (100 mm) high and eight inches (200 mm) wide can be accommodated.  The inspection time is typically three seconds per lens.

Introduction
The optical system resolution is typically 0.0018 inch (0.045 mm) and can be adjusted somewhat to meet customer needs. Defects are sized by calculating the maximum extent in any direction. The lens accept/reject decision is made on the basis of defect size, number, and location in the lens. Center viewing zones can have different acceptance specifications than the outside non-viewing zones. Defect statistics are collected and stored for all rejected lenses.

The lenses to be inspected are placed on a rotating carousel. A signal is then given to the computer via a foot switch or automation input to tell it that a lens is ready to inspect. The carousel rotates 180 degrees and stops for unloading and reloading. At the end of the rotation cycle, a decision for each lens is displayed on the CRT screen and an accept/reject output signal is provided for external automation.

The system keeps complete production statistics for the number of lenses inspected, the number rejected, and the reason for rejection by classification. An alarm is provided for excessive reject percentage, or for a repetitive defect which may occur at the same location on a high percentage of the lenses. In manual mode, a defect map of the lens can be placed up on the color monitor to assist the operator in locating and identifying  persistent defects. The graphical display can be zoomed in to show the size, shape, and contrast of any defect as seen by the camera system.

Optical Inspection Technique
Each visor is placed on a stage which rotates through the optical system. As it rotates, each visor is scanned in the vertical direction by a high speed 2048 pixel linear CCD camera using a white light telecentric optical system. The optical system converts the defects in the visor to light and dark areas in the image on the camera array. The camera array converts the image to a two-dimensional gray level map using 256 gray level increments. The pixel resolution and scan spacing is about 0.0018 inch which provides the capability to detect defects smaller than 0.00 1 inch.

Cleanliness
It is important that the lenses be kept clean from the time they leave the casting, coating, or polishing operation until they are loaded onto the inspection machine. Most types of dust, flash, or contamination are indistinguishable from defects if they are larger than the acceptable defect size.