Universal Robots Forum

Screw loosening with high torque

Dear developers

I have an application where my UR16e needs to unscrew a bolt by rotating wrist 3 (the flange-joint). This bolt can need up to 40Nm to unscrew, while the motor of wrist 3 is rated to 56Nm.
My problem is that I can only get the joint to actuate 10-12 Nm on the bolt, by using the Force-node in Polyscope and specifying Rz in tool frame.
I have tried:

  • Specifying up to 50Nm on Rz in the Force-node

  • Changing speed limit of Rz

  • Setting the safety-configuration to “least restricted”

  • Increasing force_mode_gain and force_mode_damping

Bear in mind that my way of telling the torque is by get_joint_torques().
Does anyone know whether it is possible to get anywhere near 40Nm on wrist 3?

Thanks in advance,
Emil

I have now tried with an UR5e with the flange both close to and far away from the base. The result is the same, 10-12 Nm is the maximum torque that wrist 3 will exert. It may have something to do with the entire kinematic chain being under a lot of stress, but the other joints they don’t seem to be near their torque-limits. I’ve observed the shoulder-joint exert around 40 Nm in order to rotate the flange 12 Nm, but that’s nowhere near it’s limit of 150+ Nm.

Any ideas?

Hi Elars,

have you checked out Screw Tightening Application with High Torque?

and when yes, what is different between your and his application? (appart from the loosing and tightening part)

kind regards,

Corné

Hi Corne,

Yes my application is slightly different. In my application, the robot needs to apply 40Nm and turn the screw by the rotation of wrist 3, instead of just withstanding the forces caused by using a seperate tool that applies the torque.
Thanks for the input, I will post a reply to the linked thread asking for an update.

I am eager to hear any suggestions.

/Emil

You will not be able to loosen a 40Nm bolt with just wrist 3 joint. You will need to use some torque controlled tool like something from Atlas Copco or someone like that.