Universal Robots Forum

Screw Tightening Application with High Torque

Hello,

I am working on a project in which an UR16e Robot is implemented for screw tightening.
The torque value needed for this task is between 50-70 Nm.
According to this website Universal Robots - Max. joint torques , the maximum torque of wrist 1,2, and 3 on a UR16e is 56 Nm.
That means, the required torque to tighten the screws is over the maximum joint torque of the robot.
What i’m trying to do to solve this problem is to activate the brakes of wrist 1,2, and 3 during the tightening, so that the robot can withstand the counter torque from the screwdriver.
My question is, is it possible to activate the joint brakes through programming?
If not, is there any other solution to implement the UR16e for high torque application (up to 70 Nm)?
Any suggestions would be highly appreciated.

Have you tried applying this torque to the robot gradually when it isn’t moving to see if 70 Nm trips the safety? Could zero the ft_sensor() and display a readout variable using get_tcp_force() in a thread to see what it gets up to.

Hello @tanu, welcome to the Universal Robots community!

It is not possible to activate the joint brakes through programming.

However, the maximum torque of each of the joints is not strictly the limit of the possible torque that can be applied with an automatic screwdriver and withstood by the robot - it could be higher or lower, depending on several factors that include:

  • Tool mounting
  • Robot programming
  • Safety settings
  • Robot poses
  • Payload
  • Others not directly related with the robot, e.g., the tightening setup in the controller of the screwdriver that determines the strategy, torque, speed, angle, etc.

Screwdriving applications beyond 60 Nm usually require careful consideration of all the above factors, so I would encourage you to contact your Universal Robot distributor or a certified system integrator to help you achieve the require torque ensuring best possible performance and longest working life for the robot.

Some of the key points are:

  • Mount the automatic screwdriver or nut runner to the tool output flange of the robot in such way that the lever arm is maximized, thus the force required from the robot is minimized in order to maintain its position during the process; and avoid that the tightening axis is aligned, parallel or close to parallel with the Wrist 3 of the robot.
  • Define accurately the tool position, and the weight and center of gravity of the payload
  • Use the least restricted tool force limit value that the risk assessment permits.
  • Use the Screwdriving command in PolyScope with the option to Follow the screw using Force if the robot needs to move during the tightening process; or make sure that the robot is standing still before running the screwdriver - is_steady() == True
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Hello,

Thank you for your detailed answer.
This will help me a lot with the project.

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