Cognex Vision Offset Equation

chintankAne

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Join Date
Apr 2014
Location
Surat
Posts
80
Hi
I am using Fanuc robot with Cognex camera for vision-guided robot application. In Spreadsheet I have following values.
Set X Found X
Set Y Found Y
Set R Found R

Now My question is how can I calculate Offset X, Y, R. ?? And Can I calculate Offsets number as accurate in IR Vision?
 
tarik1978, I check out that note. It is for a camera is directly connected to the robot. But, In our case camera is connected to PLC. and PLC does the math for offset. and It sends data to a robot in Group Input.
 
You dudn't mention that the robot must take the group inputs and use place them in a PR and use that PR as an offset to a position. Basically the same way as a VR is used to offset a position. Are you familiar with the elements of a PR? It would be something like this: (the syntax may not be totally correct)

PR[13]=PR[1]-PR[1] /* clears P[13]
PR[13].1 = GI[1] /* set X
PR[13].2 = GI[2] /* set Y
PR[13].6 = GI[3] /* set rotation about Z axis

PR[13] is now a offset that can be used on a base position
 
thank you for your reply.

In my GI[1], GI[2], GI[3] PLC will send the Offset value. But Camera Sending me Object Found X, Found Y and Found R.

My question is How can I calculate Offset X, Offset Y, and Offset R Value that I can send to GI[1],GI[2],GI[3].
 
You need some kind of mastering sequence. Here's what I would do, using a robot picking operation as an example:

1. Place the part in the pick position.

2. Measure the part and take the X,Y,R values and store them for later use (in the PLC).

3. Train the robot to pick the part at that part position. Say PR[2] is the pick position and you have the X,Y,R position for that position stored in the PLC.

For production use:

4. Take a part and put near the pick position and measure it.

5. Subtract from the new camera measurements the stored measurements you saved in step #2.

6. Transfer the resultant measurements as offsets via the group inputs to the robot. Use the group inputs as offsets to PR[2].

I don't know your application but that is what I do when picking parts out of dunnage when using a camera to offset for irregular position.
 
Last edited:
From within the Cagnex spreadsheet there is a calibration grid you print, place in front of the camera, it takes a picture and "learns" the distance each pixel is worth. This data is used by the camera to guide the robot to the part.
 
Offsets should be in Millimeters for offsetting linear moves, assuming the move command's frame is perpendicular to the camera. I haven't seen anyone offsetting joint moves.
 
""Those data are part found position. I do not think so those numbers are offset for robot.""

The data is the part found position AND the offset for the robot.

The PLC should not do any calculations nor should it store anything, the camera does all the offset calculations and passes the offset (in mm or inches) to the PLC that hands it to the robot as a group input. The robot uses the camera calculated position to offset the taught position that is stored in the robot.
 
I prefer my way because it works for any measurement device, be it a camera or LVDT, etc. But if the camera can do it and can be coordinated with the robot taught position, have at it.
 
""Those data are part found position. I do not think so those numbers are offset for robot.""

The data is the part found position AND the offset for the robot.

The PLC should not do any calculations nor should it store anything, the camera does all the offset calculations and passes the offset (in mm or inches) to the PLC that hands it to the robot as a group input. The robot uses the camera calculated position to offset the taught position that is stored in the robot.


I saw only data for Part found location. How can I see the offset data??
 

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