H
ere’s a little engineering
quiz for you: If an app
needs to move a 500 kN
axial load along a 1,500
mm stroke, is it best to use a roller screw
or ball screw?
If you instinctively said roller screw,
you may not be familiar with high-
capacity ball screws as an economical
and simplified alternative. Roller screws
have been promoted as the only choice
for handling large loads when size is a
constraint. But today, advances in ball
screws have led to improved versions
that can handle high-load applications.
This is important because high-load ball
screws typically cost 50% less than com-
parable roller screws.WHAT’S THE DIFFERENCE?
A ball screw consists of a threaded
metal shaft with a nut that rides along
its length as a motor turns the shaft. The
nut supports a table, arm, or other load
that needs to move in a straight line.
Re-circulating ball bearings within the
nut follow the shaft’s threads and dis-
tribute the load from the table or arm to
the bearings and then to the screw. The
bearings also let the nut move smoothly
along the screw with a low coefficient of
friction, allowing it to operate at greater
than 90% efficiency. Most of the motor’s
force goes into motion, not overcoming
friction.
The load capacity of the ball screw
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Roller screws consist of a set of recir-
culating rollers. Roller bearings with
grooved rolling elements have more
total surface contact area than balls. As
a result, service life and load-carrying
capacity increases.