Screwdriver mounting - which orientation is best?


I’m trying to understand what is the ideal orientation to mount a screwdriver on the robot flange, so that the robot can absorb the torque reaction in the safest and most effective manner.

I’ve seen this recommendation by user gba:

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.

This would suggest an orientation like this one. In this orientation, the torque reaction hits the tool flange because it is parallel to the screwdriver, and does not hit wrist 3:

However, in the UR Academy tutorials and in the icons shown in Screwdriving URCap, the orientation of the screwdriver is parallel to wrist 3, which goes contrary to the recommendation quoted above. In this orientation, the torque reaction hits wrist 3 because it is parallel to the screwdriver, and does not hit the tool flange:

Which of the two positions is best suited to absorb the torque reaction of the screwdriver, from the point of view of the robot joint longevity?
Is wrist 3 or the tool flange better suited to absorb the counter-torque from the screwdriver?
Is my analysis correct?

For this question, please assume that there’s no other spatial constraints that might make one orientation preferable to the other.

Thank you!

The second orientations is best.

In the first orientation, the reaction torque from the screwdriver is parallel to wrist 3. Wrist 3 and the tool flange share the same Z axis.

In the second orientation, the torque reaction is parallel to wrist 2, and the distance from wrist 2 rotation axis to screwdriver rotation axis creates some leverage to react to the screwdriver torque.

An even better mounting would be orientation 2, but with the screwdriver mounted so its rotation axis is angled and non parallel with wrist 2 rotation axis. This will allow multiple joints to take up the reactionary torque rather than whatever joint has a rotation axis parallel to the screwdriver’s rotation axis.

1 Like