Machine Design

Rack-and-roller pinion eliminates positioning errors

The RPS line of rack-and-roller pinions from Nexen Group Inc. (nexengroup.com), Vadnais Hts., Minn., uses rollers supported by bearings for smooth motion along the face of each tooth on the rack. This reduces tooth-slap and ball-return noise common in other linear-motion systems. Teeth on the rack are designed so that the roller is always in contact with two or more teeth. This makes the system backlash-free in both directions, a characteristic traditional rack-and-pinion systems need complicated split and dual pinions to replicate. The tooth profile and needle-bearing rollers also eliminate thermal expansion and cumulative errors.

Speeds can be as high as 36 fps, and the nearly friction-free motion means even at these speeds the system experiences little wear and almost no heat is generated. Racks can be assembled from meter and half-meter segments to virtually any length.

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