I check the rg_Grip_detected variable after picking up the part to confirm the part has been picked.
Generally I haven’t had a problem with this, even when switching between different fingers, without adjusting the fingertip offset.
However, I added a set of fingers for small parts, and am seeing the rg_Grip_detected variable fail when it is actually holding a part, so I think I need to work on my math a bit.
Does anyone know what the basic criteria are for that variable to be True? I’m assuming it’s plus/minus some value from the target diameter, and would vary somewhat depending on the force applied.
Also, is it possible to adjust the fingertip offset within a script rather than just through the URCap interface?
The manual doesn’t seem to give many details – I used to have a technical contact within Onrobot, but that email now bounces.
I could probably figure it out, but they’re trying to get production out so my access is limited. I just have the error check suppressed for now.
One thing I like to do for more information is to make sure to save the program, then either on a PC or right there on the pendent, open the filename’s .script extension. This will show you all the URScript that the robot is executing. It’s possible the CAP is doing all its execution through RPC calls, in which case you won’t see any of its code so you likely won’t be able to determine much, but maybe they are just writing straight script and you can decipher how they are determining the grip variable.
I’ve experienced issues with the OnRobot grip detection in the past, notably when using small parts, and the fingertips are only moving small distances, for example when changing grip distance by ~5mm. I’ve also had grip detection problems if only closing the gripper fingers to the distance required for the pick - I often will set the grip width to 0 for gripping to help the grip detection function correctly.
The grippers are starting from a closed position and opening enough that I don’t think there’s an issue of not enough stroke.
I did play with it a bit yesterday and found, at least for one part-finger combination, just how much over the actual bore size I had to target in order to detect the grip.
This will vary with the finger geometry and bore size – fingers touch in 4 places (2 per finger), so that overtravel distance and the fingertip offset which is set using the URCap setup page will really only apply to one configuration.
We have another system set up which tells the operator which finger set to use based on the bore diameter, and makes adjustments to the target dimension within the program. I’ll probably have to use this approach - just means some calculating and verifying with a bunch of different part-finger configurations.