Lead screw efficiency - static and dynamic forces

[GeorgeEllwood]

Hello,
I've got a quick question about lead screw efficiencies. I've come across conflicting formulas to calculate the torque requirements for a load to be moved via a lead screw. The project I'm working on has low static and friction forces but high dynamic forces.
This issue seems to be whether to take into account the efficiency of the lead screw when calculating the dynamic forces, i.e. torque = J x angular acceleration. With an efficiency of ~0.3 this can make a big difference. I've seen conflicting formulas that do and don't include the efficiency.
The efficiency is taken into account when calculating the torque required to overcome friction and any static forces.
Many thanks
George

 

[desertfox]

Hi
Try this site

http://www.roymech.co.uk/Useful_Tables/Cams_Springs/Power_Screws_1.html

 

[GeorgeEllwood]

Thanks for the link. I couldn't find the answer there. The question I've got relates to the inertia of the load reflected onto the motor. Should this take into account the efficiency of the lead screw?

 

[desertfox]

Hi George

Your original post doesn't mention reflection of inertia to the motor but to answer your question, I think you work through all the inertia's (including reflected) and get the final torque required for the leadscrew, at that point you need to increase the motor torque to overcome the lack of 100% efficiency of the screw, so if the efficiency is 80% divide your calculated torque by 0.8.

 

[GeorgeEllwood]

Hi desertfox,
That is what I would have thought about reflection of inertia. But I've found formulas in a text book and a manufacturers catalogue that do not take the efficiency into account with the reflected inertia.
Thanks
George

 

[desertfox]

Hi George

Have a look at this link, this is how I would do it.

https://www.servo2go.com/support/attachments/sizinggearheads.pdf