Setpoint was asked to retrofit a two up pick and place to a four up pick and place on a leak check machine. This would be no problem, but due to space constraints we were only allowed to use one gripper. One gripper gripping four pars is not trivial due to the fact that the world is not perfect and every thing is not exactly the same size and shape. We quickly made a prototype to see if this was even going to be possible.
When we got the grippers in we tested them on some parts given to us by the customer. The test showed potential. We did, however, see that some parts if rotated became loose. To solve this, we made some UHMW inserts that would give some compliance to the grippers. After bench testing the UHMW gripper inserts on the parts given to us it looked as if the grippers would work. The machine that we were retrofitting ran parts with three different heights. After retrofitting the machine and running it we found that for the two taller parts the grippers worked fine, but for the smaller one the gripper did not work.
To make the grippers work on the smaller parts Warren suggested using O-rings. Instead of using O-rings we went one step further and made the UHMW gripper inserts out of polyurethane. The polyurethane were more compliant and we could shape it to hug the whole part unlike an O-ring. This gave us our best result yet. The only problem with the polyurethane is that it would wear too fast and the gripper inserts were being replaced every three days. This was unacceptable so we went back to the drawing board.
We decided to make the gripper a three-point gripper. This helped, but then we were told that we could not use polyurethane any more due to its poor wear properties. We were so close to making the grippers work, but if we could not use polyurethane then this 4 up gripper tooling was not going to work. Then it just so happened that I found an O-ring that worked perfectly with the current configuration of our gripper. I quickly put them on and found they worked great. I knew that I was going get an “I told you so” from Warren… and I did. I took the grippers up to the customer and put them on and they ran fine. I guess the moral of all this bla bla bla is listen to your shop guys.