PCB VIsual Inspection

[Ahmed.Abdulbaky]

Dear all,

I need to do the Following Project:

I need to Visually Inspect on a SMD Line (the Requirements are: missing Components, Displacement or Shift and Inverse Placement ).

the Board size is 15x16 Cm, and the Pick and Place Machine Produce 4 Boards at a Time every 2 seconds( so we will inspect on a Board of Size 30x32 Cm Divided in 4 Similar Boards) and the minimum Size of Component to be inspected is 0.9mmx2mm.

so Please can you advice me with the Optimum Hardware Setup for this Project.

Best Regards

Ahmed Abdulbaky

[BruceAmmons]

Inspecting four boards in 2 seconds might be challenging.  Your inspection routines will need to be pretty efficient.  If one computer can't handle it, you could split it between two computers.  NI has a new quad core PXI that might be useful for this project.

I would probably set up two line scan cameras, one for each side of the 2x2 board.  This will minimize parallax errors, where a single camera would have significant distortion at the edges.  Each camera would need to be fairly high resolution.  The actual resolution would depend on the smallest detail you need to resolve.  If you need 0.1 mm resolution on a 15 cm board, you would want 1500 pixels on each camera.  If you need more detail than that, you will need higher resolution.

To control the resolution in the direction of travel, you need a high resolution encoder.  Each pulse of the encoder will capture one line of image.  You will want the encoder to pulse at a rate that will give you about the same resolution as in the other direction.

For the inspection, you will need to locate some fiducials on the board.  These are known reference points that don't move so you can locate all your inspection points relative to them.

Then you need to locate and inspect each item on the board.  Those algorithms will depend highly on what you are inspecting.

Hopefully this gives you a good starting point.

Bruce

[Ahmed.Abdulbaky]

 Dear Bruce,

What did you mean by Line Scan Camera, is this Similar to Smart Cameras, in my Setup I have a 1742 Smart Camera is it Suitable for my application?

Best Regards

Ahmed Abdulbaky

[Ahmed.Abdulbaky]

Dear Bruce,

i'd like to add further questions please,

why do i need a line camera , for example acquiring 2048X1 pixels , is it possible to do the processing using an Area scan camera ?

and do some Patern matching techniques after the proper image preprocessing ?

since i'm using a smart camera as i mentioned, i may calculate the field of vision and how much area from the board i'm aqcuiring at a time and do modify the camera position using stepper motors to switch to another portion from the board under inspection , and so on..

for example i may use 2 smart cameras, each camera is adjusted to view a single board from the 2X2 board frame, lets say each camera can see 1/4 from the single board area at a time, using stepper motors i can move the camera all over the single board , then switching to another board in the frame , and so on..

is this setup sufficient for my application ??

Thanks alot in advance.. 

[BruceAmmons]

You could use an area scan camera, but it would need to be high resolution, probably 2048x2048 or higher.  Those cameras get pretty expensive, and you would need four to be able to take pictures of the entire 2x2 board at once.

If you only have 2 seconds to inspect the board, you don't have time to move a lower resolution camera all over the boards.  It might be possible to move one high resolution camera over each of the 4 boards, but it would be tight.  You have to allow time for movement to stop, then allow the full exposure time of the camera.  Lighting a large area is fairly difficult, while using a line light with a line camera is cheap and easy and provides bright, even illumination.

The smart camera is probably not high enough resolution for this application.  The only way the resolution would work would be if you had enough time to move the camera to each point of interest, but that would take a significant amount of time.

I'm not sure what processing you will need to do.  Pattern matching will work well in most cases, but there are simpler methods for detecting presence/absence and other PCB checks.  Pattern matching requires high enough resolution to see the pattern and may require higher resolution than checking the average brightness of an area, for example.

Bruce

[Ahmed.Abdulbaky]

Thanks Bruce,

Can I use the Vision Builder and Vision Assistant with Line Cameras? and what is the Estimated Time for Line Camera to take pictures of our entire 2x2 board at once? 

Best Regards

Ahmed Abdulbaky

[BruceAmmons]

You could probably use Vision Builder, but VB is not known for being fast.  It has some overhead in the sequencing as far as I know.  I never use it, so I can't be sure.  You could use Vision Assistant to prototype your analysis algorithms.  I would suggest LabVIEW for more flexibility.  It would also be easier to set up parallel analysis for a multi-CPU processor.

You would need to capture about 4000 lines to get the complete image, based on our previous assumptions.  This could easily be done in two seconds, so you could analyze one image while capturing the next image.

Bruce

[Ahmed.Abdulbaky]

Thanks Dr.Bruce,

But we have a Modification now in an important Parameter, the Pick and Place Machine Produce the 2x2 Board every 2 minutes.

Can this Information help us in our Design with Area Cameras?

Best Regards

Ahmed Abdulbaky

[BruceAmmons]

2 minutes is much better than 2 seconds.  That gives a lot more time for the analysis side of things.

I still think the line scan camera is your best option.  It is cheaper and easier to light than any other options.  Line scan cameras just work very well on large flat objects like this.

You could probably move a lower resolution area camera around on the board, but that might still take longer than 2 minutes.  You also have issues of locating reference positions in each image, which is tedious.  I strongly recommend against it.

If you had two 2048x2048 area cameras side by side and had a good way to light the entire board evenly, you could have two triggers as the board moves past the cameras.  Each trigger would be positioned so the cameras would take a picture of a single board.

I would think a standard core 2 duo processor would handle this analysis just fine.  A quad processor would be overkill with 2 minutes of cycle time.

You technically could use Vision Builder for this project, but you would end up with a long string of analysis steps.  It could be difficult to figure out which one goes with which inspection when you are trying to edit them.  It would also be tedious to create the same inspection for similar components repeatedly.

Bruce

[JeffL]

You should be able to do these things in VBAI, but I'm not sure about efficiencies either. Vision Assistant with the Vision Development Module would also work, but requires a little more work at the gain of more control, of course.