The ball screw drive is an assembly that
converts rotary motion to linear motion
and vice versa. The ball screw drive
consists of a ball screw and a ball nut
with recirculating ball bearings (Fig.
1). The connection between the screw
and the nut is made by ball bearings
that roll in the matching forms in the
screw and ball nut. The forces transmitted
are distributed over a large number
of ball bearings, giving a comparatively
low relative load per ball. With rolling
elements the ball screw drive has a
very low friction coefficient. Ball screw
drives typically provide mechanical efficiency
of greater than 90%, so their
higher initial cost is often offset by reduced
power requirements. The features
of ball screws in relation to other
linear actuation devices are summarized
in Figure 2 and the important ball
screw specifications are summarized in
Figure 3.

Optional Inputs
Figure 4 provides an overview of the
parameters used in the ball screw selection
and sizing process. The optional
inputs make it possible for the designer
to specify basic preferences for a specific
type of ball screw early in the selection
process. It’s important to note
that specifying optional inputs may unnecessarily
restrict component selection.
As an example, if you select metric
product series you eliminate about half
of the possible ball screw alternatives
even though it’s possible that an inch
series ball screw might work just as well
in the application.