1. Small, light rack-and-pinion drive saves energy Page 1 of 2
Published on Machine Design (http://machinedesign.com)
Small, light rack-and-pinion drive saves energy
by Stephen J. Mraz
Created 12/08/2011 - 11:36
In the past, rack-and-pinion drives were generally developed for
planetary-gear units, with pinions fitted to the output shafts and matching
gear racks. But the rack-and-pinion drive would put an overhung load on
the gear unit that limited the size of the drive. Thus, the drives could only
use 40 to 60% of the gear units’ torque.
[1]
Engineers at Stober [2], Maysville, Ky. wanted to solve this problem, so
they developed the ZTRS drive, a compact, highly efficient rack-and-pinion drive. They
developed the drive together with Atlanta [3], a gear-rack manufacturer based in
Farmingdale, N. J.
The ZTRS drives are based on the company’s PH and PHA planetary-gear units, which
are torsionally stiff and generate high torque. Ratios range from 4:1 to 121:1, and drives
are available in right-angle versions and with built-in motors. But the ZTRS can be
attached directly to any servomotor.
The output-bearing housing supports the rack-and-pinion drive, which relieves the load on
the flange-mounted planetary gear’s bearings. This reduces the tilting moment and frees
engineers to match the drive to the torque needed for their application. In general, this lets
engineers use gear units a size smaller than those used in the past. The device also uses
comparatively small-diameter pinions, so it takes more speed to get the required feed rate.
This means the gear ratio is lower and, in many cases, a single-stage planetary gear unit
can be used instead of a two-stage device.
The ZTRS reduces linear backlash by 50% to 3 arc-min, and increases linear stiffness by
up to 100% compared to standard PH and PHA units. The new mounting configuration
lets it use pinions with small pitch diameters.
Apart from improving linear stiffness and linear backlash, the pinion concentricity was
adjusted to less than 0.01 mm. The drive is lubricated using a felt pinion built into the
output-bearing housing. It can be manually relubed or hooked to an automated lubrication
subsystem.
The flange-mounted planetary-gear unit offers a choice between helical PH and PHA
versions. And the ZTRS-PH(A) rack-and-pinion drive comes in sizes 7, 8, and 9, and
modules 2 to 6, with gearing quality 5.
© 2011 Penton Media, Inc. [4]
Source URL: http://machinedesign.com/article/small-light-rack-and-pinion-drive-saves-energy-1208
http://machinedesign.com/print/89831 7/24/2012

2. Small, light rack-and-pinion drive saves energy Page 2 of 2
Links:
[1] http://machinedesign.com/content/rack-and-pinion-drive-1208
[2] http://www.stober.com
[3] http://www.atlantadrives.com
[4] http://www.penton.com/Pages/TermsOfUse.aspx
http://machinedesign.com/print/89831 7/24/2012