Ball Screws: Back Calculating Torque

Look at a company called Nook Industries

www.nookindustries.com

They could help,Good Luck

Mark

Hi: I supposse you can do an energetic equation; that is; speed of lifting x weight=torque x angular speed.

As you told in your post, you know all the data, so you can calculate the torque.

Regards,

Gabriel

Torque = Force *pitch/(2*pi*eta)

Where eta is the efficiency of the ball screw (take it as 90% if you don't have a better figure). pi = 3.1416.

If pitch is in inches and force is in pounds force then torque is in lb-in.

Ball screws are just very efficient power screws for analysis. Notice that speed does not affect the torque. It does affect the power, though.

Power = torque * N * 2 *pi/(60 *8.79)

where torque is in lb-in, N is in RPM, and power is in Watts. (The figure 8.79 is required for the unit conversion - it really is much easier in metric units)

Greg

For back driving torque try to use the simple formula

T=.143 P*L

Where,

p=load (lbs)

L=Screw lead(inch/turn)

Go to FAG, Beaver, Saergeant, Shrillo web pages.

Remember that there is a rotary to linear work conversion relation.

Hence,

efficiency= (Force x linear distance per revolution)/Torque x 2 x Pi

Pi is there to keep the units pure, i.e., 2 Pi radians/revolution

linear disatnce per revolution = lead of the screw

Keep the units consistent.

The .143 factor is just the reciprocal using an assumed efficiency of 0.90 multiplied by 2 Pi. The assumption is far and appropriately conservative. Efficiency typically will increase slightly w/ speed. However, this is good enough for steady-state, i.e., constant velocity requirements.

For dynamic torque-the torque to accelerate, the inertias of the system need to be evaluated.

See the authors Juvinall & Mott mechanical engineering/design texts.