Rack & Pinion vs. Ball Screw

Question

Rack & Pinion vs. Ball Screw

Tigerdawg (Mechanical)

(OP)

18 Dec 02 14:36

Can anyone give the pros and cons of using a rack and pinion versus a ball screw drive for a slide table?  The table may weigh as much as 1700lb fully loaded.  The design goal is a ~15 inch index in ~0.4 seconds.

With the rack and pinion I am primarily concerned with the backlash.  I do not want to spend the money on the typical 2 servo and 2 pinion drive to control the backlash.  Yet I am trying to avoid using a lock pin for precise positioning.

The ball screw can give the positioning I want, but I am unsure about the index speed.  I am also worried about the design life of the ball screw compared to the gear drive.

Thanks for any help you can provide.

SERVOCAM (Specifier/Regulator) · Answer 1 · 2002-12-23 23:43:30

The ballscrew is going to be rather large to handle the speeds, loads, and accelerations to give you good life. I have seen some 4 & 5 inch diameter screws moving some huge loads. Also look at a roller screw. Try www.exlar.com for them. Try NSK, Thomson, Nook, and Warner Linear, just to name a few, for some ballscrews.

The rack and pinion will can give you high accuracy positioning. You can machine them to tight tolerances or even run a linear scale along the system to position off of it. The speed & load of the rack & pinion can be very econimical.

With the 15 inches in 0.4 seconds spec, if using a 1/3 trap move, a Max Velocity of 56.25 in/sec and an Acceleration rate of 421.875 in/sec^2 or 1.1g's. Your ball screw is going to see thrusts close to 2000lbs. I can tell you that it is going to be a large screw if want life and the speeds. Call some screw mfgs and ask them what they think.

Cameron Anderson
Sales & Applications Engineer
Aerotech, Inc
St. Paul, MN
www.aerotech.com

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Rack & Pinion vs. Ball Screw