DoF - a Robotiq Community
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We did the same testing as above but with a fixed Cognex Camera. The Cognex camera has a really nice calibration feature built in its interface. This allows you to calibrate the robot with the vision system by simply moving the robot to 'calibration targets'. Once done, coordinate values output by the camera are in the robot's coordinate system. 
You will see in our video below that we are really repeatable when taking snapshots while leaving the white round piece at the same spot. We are 1-2mm off when we move the piece on the table. This is do to our calibration and our setup. We did not spend much time on the calibration since we simply wanted to run some testings rapidly. Furthermore, our touch tool was a Sharpie that could move a bit in its setup and the camera was installed on a stand that could vibrate a little. So our conclusion was that this setup worked well for repeatable results on these round object. To increase accuracy we would:

  1. Have the camera mounted on a more rigid and fixed pole. 
  2. Have a stiff point tool mounted on the robot as a tool that we would use in the calibration procedure. Have another stiff point tool on the table to perform TCP definition procedure on the UR such that we can define accurately the point tool on the robot arm.
  3. Have a small notch machined right in the middle of some target parts such that during the calibration procedure, we move with the robot and its point, right to the middle of the part with its point tool. That way we make sure that each target is pointed right in the middle during calibration.

Below is the video. Note that we can see two different part sizes in the video. The first one is about 1,25'' in diameter and the second one 0.5'' in diameter. Using blob tool we can easily switch between the two parts!