We currently use two 2 finger-140 grippers on a robot to move cup holders for a Toyota Rav4 in and out of a work station, The first side hands 2 cup holders to an operator who runs it through a clipping procedure, they are then placed in the other side of the work station and it checks the parts for completion. After the check passes the part slides back and the UR picks the parts from the inside of the cups. We had no problem until this week picking the cups and now the grippers have been polished smooth by the first station where the operator pulls the cups off of the grippers. 

When the UR enters the cups the grippers are in the closed position, it plunges to depth and opens the gripper to pick the cup holder. then lifts out of the nest and moves them to another location. As they lift one of the cups is falling off the gripper, and even setting the gripper force seems to have no impact.

I am now wondering if these grippers only account for gripping force on the closing motion and not the opening motion? If so is there any way to increase the opening force of the gripper?

@tylermartin the Gripper force is in effect in both opening and closing motion. Your issue is probably more about friction (contact point & finish). Can you send us some photos of your setup so we can advise ?

Robot picks from press and moves to hand part to operator, who pulls parts directly from grippers. When the grippers open to full open it signals that there are no parts and the robot can move out of work area.

Part has clips added in side A of workstation and is then placed in side B where app parts are checked. When parts pass the gantry slides back and the UR can come in to pick parts out and send them to a ramp where they slide to operators who assemble them onto the console base.

When UR picks cup holders from side B the larger cup holder is sometimes left in the nest because it slips out of the gripper. I had originally set the gripper force to 50 on Side B of the workstation and it has run like that for almost 1 year with no problem lifting parts. When the issue started I modified the program to set gripper force to 150 on side B, but the issue didn't change. This is why I wondered if the force was only accounted for on the closing motion. I will have to set gripper force to maximum for side B to see if it helps.

@tylermartin The force is also related to speed. The gripper can't reach full force if it is not at full speed. 
You can refer to the chart in the manual available here for the force applied according to force and speed setting : http://support.robotiq.com/pages/viewpage.action?pageId=8520171

Ok I will check my speed settings! Thank you. I didn't think of that fact.

Thanks @David_Gariepy for the speed relation tip. I have increased the speed of my gripper on the section of my program that picks the cups and I haven't had a dropped cup since! Much thanks!

@tylermartin Good, glad to hear this!