Nexen HGP25 969053 - Manual (Page 5)

5 FORM NO. L-21277-B-1213
SYSTEM DESIGN OVERVIEW
The harmonic gearhead with integral pinion will hereafter be referred to within this manual as HGP. The pinion portion
of the HGP is part of the Nexen Roller Pinion System (RPS), which is comprised of rack(s) and a pinion. Therefore this
document will hereafter refer to those parts as RPS. For proper RPS operation, it is necessary for the user to adhere
to the general system requirements outlined below.
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• Unlike traditional rack and pinion drives, the RPS has zero mechanical clearance and requires a system preload
for proper operation. This preload must remain relatively consistent over the entire run to obtain optimal system
performance and life. Therefore it is crucial that the linear guiding system’s mounting surfaces are very parallel with
those of the RPS system, eliminating the potential for convergence or divergence at any point. If the guiding system
and RPS converge, preload will become excessive resulting in increased noise, reduction of life, and potential binding
within the RPS. If the guiding system and RPS diverge, preload will be lost resulting in backlash, loss of positional
accuracy, increased noise, and reduction of life. The main consideration when establishing guiding system and RPS
mounting surfaces within a machine is that they rise and fall together, at the same rate and position within the run
so that RPS preload remains within specifications. The best way to ensure minimal variation between the guiding
system and the RPS is to machine their mounting surfaces within the same machining operation. See Figures 3 and
4 for more details.
• Ensure that the machine bed and guiding system have sufficient rigidity, to prevent deflections that would affect RPS
preload and pinion alignment.
• The bottom and one side of the rack must be supported by a step in the machine bed. The height of this step should
be at least half of the rack thickness. The rack should not be solely supported by fasteners or pins. See Figure 5 for
specifications.
• For extremely long runs a single-piece machine bed will be impractical, requiring a segmented bed. When installing
the guiding system and RPS rack, advance planning of mounting hole positions should be done to ensure that the
machine bed’s joints are not in close proximity to the joints in the guiding system or RPS. Instead, span the machine
bed joints with the guiding system and RPS rack as much as possible.
• To achieve proper system preload, the recommended method is to mount the servo-driven components (motor and
HGP pinion) onto a sliding plate or bracket whose position can be adjusted such that the pinion rollers can adequately
slide into and out of engagement with the rack teeth.
o It is recommended that when establishing preload, the pinion should be moved into the rack instead of vice versa.
o If a sliding plate or bracket cannot be utilized, another possible preloading mechanism is to mount the servo-driven
components to a plate or bracket which has an eccentric mounting slot pattern.
As an accessory, Nexen offers a preloading system that can easily be integrated into an application, provided that a
suitable mounting surface and the correct mounting hole pattern can be added to the customer machine frame as
shown in Figure 14. Spring-loaded methods of achieving preload should not be used, as the spring force required
to counteract rack and pinion separation forces would be much higher than the allowed preloading force and would
therefore result in reduced product life and increased system noise.
• RPS should not be used in environments with temperatures outside of a -5° to 40° C (23° to 104° F) range or with
wide temperature variations within this range, as thermal expansion or contraction can affect RPS preload and meshing.
If you have an application with these temperature characteristics, consult Nexen.
• The HGP is available in a variety of corrosion resistant finishes. Consult Nexen for available options. Standard HGP
product finish includes an anodized aluminum motor adapter, black oxided gear housing and pinion body, and unfinished
bearing grade steel rollers. Pinion roller corrosion will lead to damage within the roller bearings, and eventual system
failure. Always protect the pinion from adverse environmental conditions. RPS rack finish varies by performance
grade, ranging from unfinished steel to stainless steel. Always review your requirements for corrosion resistance to
determine whether the HGP or RPS rack(s) have suitable finishes for the application, based on your familiarity with
the specified finishes and/or through relevant testing. Nexen makes no claims for HGP or RPS corrosion resistance
in any application.