Hydraulic manipulator research at ORNL Page: 4 of 9
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phenomenon in hydraulic components that is
equivalent to the saturation and concomitant losses in
magnetic materials as is associated with electric
motors. Torque output from a hydraulic machine is
limited only by safe stress levels. Furthermore,
hydraulic actuators have a high stiffness compared to
other drive devices. In addition, they have a higher
speed of response as well as large torque-to-inertia
ratios, providing high acceleration capacity.
Hydraulic components may be operated in
continuous, intermittent, reversing, and stalled
conditions without damage. In addition, rotary and
linear hydraulic actuators are available for many
different sizes and power ranges?
Hydraulics technology is not without its
disadvantages. For example, hydraulic power is not
as readily available in most industrial settings as is
electric power, and most stationary applications must
have a hydraulic power supply installed. Hydraulic
components are expensive. Hydraulic fluids are
sometimes flammable and/or considered to be
hazardous waste. Hydraulic systems almost always
leak and are therefore considered messy. Hydraulic
fluids must be filtered and in some cases filtered
thoroughly for high-performance applications like
those found in servovalves. Contaminated oil is one
of the primary reasons for component failure in
hydraulic systems. Finally, hydraulic actuators are
not generally as flexible and easy to use for low-
power applications as are electric actuators.
II. RECENT HYDRAULIC MANIPULATOR
The recent focus on hydraulics and hydraulics
controls in the open literature highlights the
importance and relevance of hydraulics in today's
applications. Examples of current hydraulics-related
controls research and other hydraulics efforts relating
to automation can be found in recent literature.
Examples range from controllers for basic positioning
systems such as the work by Plummer and Vaughan3,
to system identification such as when Vossoughi and
Donath4 describe a globally linearizing feedback
controller for electrohydraulic servo systems, to work
done on the development of grasping control laws for
use with hydraulically actuated fingers in a robotic
hand by Pfeiffer.' In another example Conrad'
discusses the development of a mechatronic test
facility with a transputer controlled hydraulic robot.
Other less recent publications also highlight
hydraulics and hydraulics controls for automation
applications. Tsao and Tomizuka present the
development of a robust controller for an
electrohydraulic servo-actuator for machine tool
positioning. Jinghong, Zhaoneng, and Yuanzhang
present a short paper considering the variation of oil
effective bulk modulus with pressure in a hydraulic
system. They develop a model and compare it to
experimental results. Variation of bulk modulus is
one parameter that greatly affects the system
performance for hydraulic systems, which is one of
the topics of focus of ORNL hydraulics research.
III. PAST HYDRAULIC MANIPULATORS
AT OAK RIDGE NATIONAL
The applied nature of the projects at Oak Ridge
National Laboratory (ORNL) and the direct results of
the value of hydraulics have made hydraulics the
power source of choice in many ORNL projects.
Consequently, ORNL has had considerable experience
with hydraulic manipulators and movable systems
over the past decade. This section briefly describes
some of the hydraulic hardware systems developed at
Except for some very early work with
commercially available teleoperated manipulators, one
of the first hydraulic systems developed at ORNL was
the Soldier Robot Interface Platform (SRIP) vehicle
shown in Fig. i.
The SRIP vehicle was designed and built with
the. assistance of the Tooele Army Depot in Utah.
The SRIP has a hydrostatic-drive transmission and
was fitted with an electric arm and numerous sensor
systems. It was designed for two purposes; the
military developed it as a platform for research into
unexploded ordinance disposal, and the Department of
Energy (DOE) supported it for buried waste site
characterization and remediation. One of the
particularly challenging aspects of the SRIP
development was providing it with the ability to
maintain an accurate trajectory necessary for complete
coverage of an area during a waste characterization
survey in spite of limited accuracy wheel position
sensors and a hydrostatic transmission. At the time
of the development of SRIP, low-cost and accurate
Global Positioning System (GPS) sensors were not
Another hydraulic system developed at ORNL is
the Future Armor Rearm System (FARS), shown in
The FARS was designed and built with the
assistance of the Tooele Army Depot. The FARS
was developed to allow the Army to rearm its new
M1A1 tanks without exposing the soldier to the
hazards of the battlefield. The FARS hydraulically
actuated arm served several purposes: (1) to dock
with the empty tank; (2) to be a communication link
between the tank and the FARS rearm vehicle; and (3)
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Kress, R.L.; Jansen, J.F. & Love, L.J. Hydraulic manipulator research at ORNL, article, March 1, 1997; Tennessee. (digital.library.unt.edu/ark:/67531/metadc684548/m1/4/: accessed February 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.