Rack-and-pinion gearheads challenge ball screws

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Micromech says that rack-and-pinion technology is making a comeback, as more machine builders are turning to high-precision rack-and-pinion systems for precision motion with extremely high levels of rigidity.

For example, the Alpha gearhead, available from Micromech, combines a rack-and-pinion with a planetary gearhead, allowing feed rates of 60m/min to be achieved with acceleration rates of 5m/s/s. In fact Alpha is one of the few global companies to offer quality level 5 rack-and-pinion systems that have a repeatability of less than 2um and a cumulative pitch error less than two-thirds that of a ball screw. In addition to exceptional accuracy, these rack-and-pinion systems remain extremely rigid due to electronic preload.

Alpha gearheads offer superb quality, and these latest ranges are no exception. They have a weight- and space-saving mounting method through a compact gear reducer design with integrated pinion, and all mounting surfaces are ground to tight tolerances to give several mounting options. The gearheads run smoothly and with low noise due to the pre-assembled gear pinion units with helix angle 19 31' 42", pressure angle of 20deg and high concentricity (RTP version <10um). Maintenance is minimised having high reliability thanks to the use of a wear-resistant surface treatment and individually deburred gear teeth.

The compact design, with its low mass moments of inertia, results in high feed dynamics with short acceleration times. The engineers have maximised precision for lifting axes through the positive connection of the pinion, and an ultra-high linear accuracy due to a minimum total pitch error of 12um/500mm. The range also has high operational safety because of the high overload capacity.

Using the familiar Alpha gearheads TP and SP, the rack-and-pinion arrangement provides the following performances:

TP 004, 010, 025

maximum acceleration torque = 32-300Nm

maximum tangential force = 1160-8078N

TP 050

maximum acceleration torque = 500-650Nm

maximum tangential force = 7854-13174N

SP 060, 075, 100

maximum acceleration torque = 32-250Nm

maximum tangential force = 1675-10244N

SP 140

maximum acceleration torque = 400-450Nm

maximum tangential force = 10500-14100N

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