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Home > Applications > How to apply a constant force on a moving object
Glass420

I would appreciate advice on how to solve the following issue.
I have a part that I am inserting into a 5C collet that has a spring loaded button that the part is pressed against. When the collet is closed pneumatically, it moves approximately 5 to 6 mm away from the robot gripper in the tool Z direction. What I need is a way to apply a force and move the robot while the collet closes. I have a FT 300 that I use to check if the part is aligned with the collet by measuring the insertion force as it is inserted. But, if I use the same method, as the collet closes I am not able to achieve consistent insert position.
David_Gariepy

Hi @Glass420

This can be done using the UR force mode wizard. Select tool as the feature, and enter the desired force in Newton.
In the force node, simply put a wait command.  It could be a wait time or wait for an input. It would look something like this: 

Force
  Wait DI[0] = HI

If you need lower force, you could do something similar using the FT-300:
The starting point is where you want to start to apply a force. Insert a loop with the required expression. For example, here it will loop until it receives a signal on DI1. Don't forget to tick the "check expression continuously". Then insert an if statement also with  "check expression continuously". in the example below, the movel will be executed as long as the force in z is below 5N. Insert a movel with a waypoint at the maximum distance at which you might need to move. 
As long as the signal isn't received, if the force drop below 5N, the robot will move toward the "lower_point" waypoint
 
MoveL
       starting_point
     Loop digital_in[1]≟ False 
       If norm(Fz)<5
         MoveL
           lower_point
       sync()
     sync()



Glass420

Hi David
I used the force wizard with the wait statement but the robot did not follow the collot closing.
Should I put a movel with a end point inside the force command then a wait?
The force is very generic but high (around 50 N) all that matters is the position is correct every time.
Also, with the force wizard, does the robot constantly adjust its position during the wait or does it stop when the froce is reached and maintain that current position?
Glass420

No need to reply to the above comment. I found my error. I had the wait command outside the force command.  I moved it inside and all is working.
Thanks for the help!