Rack and pinion drives offer high power density and improved dynamics
21 July 2010
Generally, rack and pinion drives were developed from a planetary gear unit with a gearwheel fitted to the output shaft and the matching gear rack. But the overhung load on the gear unit from the rack and pinion combination is then so high that it actually determines the dimensioning. Gear unit torque availability is normally only in the 40 – 60 % range.
Stober and gear rack manufacturer, Atlanta have jointly developed a new concept for a super compact and highly efficient rack and pinion drive - the HighForce ZTRS-PH - featuring an integral output bearing housing and a highly stiff supporting assembly for the rack pinion, which relieves the load on the flange-mounted planetary gear unit bearings. The reduced tilting moment of this construction makes it possible to base the drive design on actual required torque and feed force.
As a rule this means that the gear unit can be a size smaller than normally used in the past. Due to the comparatively small pinions, a higher output speed is necessary to obtain the required feed rate, which means that the gear ratio is lower, and in many cases a single-stage planetary gear unit can be used instead of a two-stage. This results in outstanding power density.
Improved linear stiffness has not been forgotten in the new design, because the pinions do not now have to be flange-mounted directly on the gear flange shaft's bolt circle. The new mounting system makes it possible to use rack pinions with a very small number of pinion teeth, which increases linear stiffness by up to 100%.
Although the reduction in size was of central importance, other factors were also considered. Apart from the linear stiffness, the linear backlash was also improved through a 40% reduction, and the pinion concentricity is adjusted to ≤ 0.01 mm.
An optional pinion lubrication is integrated into the cast output bearing housing for manual operation or connection to a central lubrication system.
HighForce ZTRS-PH rack and pinion drives are available in sizes 7, 8 and 9, modules 2 to 6 and gearing quality 5.
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