Not all ball-screw makers spec products the same way.
This stiffness test rig uses a force sensor to measure axial thrust. A bracket clamped onto the drive journal prevents backdriving of the screw. The nut block has exchangeable inserts and hydraulically clamps to the cast-iron base. Three LVDT sensors measure relative motion between a shaft and nut. They attach to the unloaded portion of the screw and their tips touch the nut flange from behind. The arrangement averages all deformations of the nut body but does not include changes in shaft length. Forces in the rig can reach several thousand Newtons, though the shaft elastic displacement is only a few microns.
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