Method for a grid projection lighting scheme to enable shape assessment of reflective material in 2-D images
Disclosed is a method for a grid projection lighting scheme to enable shape assessment of reflective material in 2-D images. Benefits include the capability to detect the shape of a reflective surface, faster inspection time, and compatibility with existing process equipment.
The disclosed method is a non-laser lighting scheme that uses a grid pattern projected towards a reflective 3-D shaped surface. The method enables 2-D vision systems using a fixed observation point to infer 3-D shape information.
Key elements
Two types of grid pattern lighting arrays comprise this method. Type A is a grid comprised of discrete points of light. Type B is a grid comprised of lines.
The lighting must be controlled carefully so that only these lights are visible. Shrouds/light curtains should be employed if stray, unwanted light interferes with the required effect.
The lighting scheme requires no moving parts like motor drives and does not require a laser.
Description
The disclosed method is demonstrated in a practical way when the reflection of an office cubicle grid layout is observed on corridor mirror balls. The office cubicles form a giant grid array that is projected onto the mirror ball surface. When viewed, the appearance of the reflection is warped, giving an indication of the shape of the mirror ball.
These mirror balls are similar in appearance to solder balls and joints. By comparing the grid warpage reflections for adjacent solder balls/joints, solder balls/joints can be identified when they are out of specification. In this case, solder balls/joints are the objects under inspection, but this technique can be used in inspecting other reflective 3-D surfaces as well.
This modification can be used on the following process equipment:
Solder ball inspection
Solder joint inspection
Other reflective material inspection
This method is somewhat similar to structured lighting inspection methods that utilize lasers and are mostly used for non-reflective surfaces. The disclosed technique employs the warpage measurement of a grid pattern (either points or lines) to measure shape without using a laser because the surface is known to be reflective.
Vision inspection systems conventionally build into process equipment often feature 2-D capability. Important measurements may not be performed because the third dimension is not detectible (see Figure 1). Conventional solutions involve the use of multiple cameras (see Figure 2). This solution is complicated and does not successfully indicate the correspondence of points to the shape of the surface. The disclosed method results in a mapped pattern that varies with a change of shape (see Figure 3).
Fig. 1
Fig. 2
Fig. 3
Disclosed anonymously
