DoF - a Robotiq Community
Warning sign
The Dof Community was shut down in June 2023. This is a read-only archive.
If you have questions about Robotiq products please reach our support team.

@steveB It depends on how fast you need to operate.  

If you have time to find the stack you could just always start from the same height and search the whole way down until you found a part.  This works well when you have a long machine cycle that gives the robot time to "find" the next part to work on.

I have written a couple that use the built-in force feedback to find the stack, it then records the current z-height of the stack to use as the start parameter on the next search loop.  This worked well in a sheet metal operation.  Once we reached a certain stack height it then notified the operator to add more parts, there was also a sensor under the stack to ensure that we knew there were parts there or not so that the robot didn't try to pick up the locating fixture the pieces were on.  This system used vacuum to pick up the metal pieces that were being assembled.

Another option is to install a distance sensor to the robot, like a Keyence laser or something like this, this would then be used to find the height to the parts from a known search location by giving you the distance from the location to the parts.  This could make the search faster by coming to a known starting location, finding the distance to the parts, rapidly moving close and then slowing to do the final search to the part maybe 10mm away from the part. 

Another option if you want to search but not use the force is to install a proximity sensor on the tool that can let you know when you are just a couple mm away from the part.