Power Screw
Cost
Size
Load
Capability
Load
Accuracy
Repeatability
Gear Box System:
~$1,000
Chain Drive
System: ~$600
Either option will
take up a
considerable
amount of space.
Gearbox
consolidates the
chain drive system
into a box, but will
still exceed space
requirements of
both the EHA and
Piezo systems.
User preset Static
Loading Only, will
fulfill PRP
requirements for
load magnitude.
Load accuracy will
depend directly on
gear reduction
through chain drive
or gearbox, and
operator ability.
Once preset, load
should be locked in
and remain the
same for test
duration.
Since this system
only delivers static
loading. Test
repeatability will be
a in direct relation
to load accuracy.
(see above)
Electrohydraulic
(EHA)
Pneumatics
Piezoelectric
~$2,500
~$1,000 (Static)
~$2,000 ( Dynamic)
>$20,000
EHA is selfcontained hydraulic
actuation unit, thus
having a much
smaller footprint
than the power
screw system.
The units will
require custom
mounting blocks and
spacers due to their
length. Larger than
piezos.
Can statically load to
PRP requirements.
Some minor (slow)
dynamic loading
may be possible with
proper control
system.
Load accuracy is
marginal at best just
in the nature of how
the units are
designed. They are
meant for tilt
displacement than
for accurate load
replication.
Oil heating during
testing could affect
load accuracy and
repeatability.
Monitored and
controlled through
the PLC. Proper
relief/check valve
calibration will be
critical.
Pneumatic cylinder
occupies roughly same
space as EHA units and
will require slightly larger
brackets. Mounting is
more ideal for load
application.
Smallest
footprint of all
load actuation
systems.
Will be able to statically
load to PRP requirements.
Load capability is in direct
relation to available air
pressure feed and piston
size. Some dynamic
ability if proportional
regulators added.
With a regulator, user
input and regulator
accuracy affect load
accuracy. Once set, load
will remain constant for
test duration.
Fast enough
reaction time to
replicate
simulated ESH-1
compressor load
profile. High
load magnitude
capabilities.
Highest load
accuracy of all
load actuation
systems in both
static and
dynamic load
profiles.
Again based on user-input
and regulator accuracy
and repeatability.
Regulator and actuator
calibration will be critical.
Highlight of the
piezoelectric
system is the
ability to provide
an accurate
dynamic load
profile at a high
level of
repeatability.
Manual level to
turn the gear box or
chain drive
assembly to load
Could be
Controls/User preset.
automated with
Interface
servo motor.
McMaster Carr
parts, high
availability.
Availability
Purely mechanical,
no additional power
system required
Power System (exception: servo
motor).
PLC (programmable
logic controller.)
Programming
(coding) will be the
challenge here.
Usability will be
simple inputs.
Would also allow for
a closed loop
feedback system.
Parker Hannifin.
Parts and service
readily available,
though not simple
McMaster Carr
items.
Power amplifier
necessary for Servo
motor (load based)
power needs.
No electronic user
interface. Manual
mechanical control via
knob on regulator and the
pressure dial gage make
up the entire control
system and user interface.
(Static case)
Dynamic option would
consist of a proportional
regulator.
Parker Hannifin. Parts and
service readily available,
Regulators available
through McMaster Carr.
Air feed line into room or
air compressor.
PLC. More
advanced coding
than EHA
option. Simple
user inputs.
Cutting edge
technology,
“made to order”
systems
contribute to
high costs and
long lead times.
Power amplifier
needed for
powering piezos
themselves as
well as necessary
control system.
Summary:
This project called for the design and build of a Dynamic Similarity Journal Bearing test rig. With the
available budget of $5,000 the dynamic aspect is not feasible. EHA were considered for their compact size and
self-contained design. They were later dismissed due to their lack of control, high power requirements, and high
cost. Remaining static options were a mechanical system in the form of a gearbox or chain drive power screw
systems, with the gear box and chain drive being implemented for gear reduction. Chain drive was dismissed
due to space requirements, leaving the gear box and pneumatic options. Pneumatics were chosen due to their
simple analysis, control, and low cost. The cheapest and simplest dynamic option would be an upgraded version
of the static pneumatic system, replacing the manual control air regulators with proportional regulator units.
This would provide dynamic load profiles but minimal control. The more load system control desired, the
higher the cost. This is evidenced by the ideal dynamic load system; piezoelectric, providing high load
capability and control, in both static and dynamic load profiles. The piezoelectric load actuation system was
dismissed due to system cost far exceeding the project budget.