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Fluid Power Research Laboratory
The University of Manitoba
Winnipeg, Manitoba, Canada
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From Editor
International Journal of Fluid Power would like to introduce the fluid
power research and education centres with their expertise and
particular interests in this column. Jumping from continent to
continent we like to offer every research centre the opportunity to
present itself.
FLUID POWER RESEARCH CENTRES WORLD-WIDE
Introduction
The University of Manitoba is the first university in western Canada,
established in 1877. It remains the largest university in the province
and Manitoba’s only research intensive, medical/doctoral degree
granting institution. We have a multi-cultural campus with over 20
faculties. The student body exceeds 26,000 with approximately 2,600
international students from over 100 countries.
Manitoba is located in the geographical centre of Canada and North
America. Although our winters may be intimidating (we do have a tunnel
system at the University; so you can stay indoors if you prefer), our
spring, summer and fall seasons are very hospitable and there are
countless activities around the university and the city to keep
everybody active and entertained.
The Faculty of Engineering is the oldest engineering school in western
Canada, having celebrated 100 Years in 2007. Over 10,000 engineers have
graduated with at least one degree from our faculty. Much of our
success comes from our ability to adapt to the needs of the engineering
profession and engineeringstudents.
At the functional level, there are six undergraduate programs managed
by four departments: Biosystems Engineering (Environmental Engineering
Option), Civil Engineering (Environmental Engineering Option),
Electrical & Computer Engineering and, Mechanical &
Manufacturing Engineering (Aerospace Engineering Option). The Faculty
of Engineering at the University of Manitoba also offers minors in
Management, Arts, and Music.
The fluid power research laboratory was established
within the Department of Mechanical and Manufacturing Engineering in
1992. The goal was to conduct fundamental and applied research to
improve control and enhance reliability in fluid power actuation
systems. A wide range of applications are being considered: robotics
(underwater/mining hydraulic manipulators), manufacturing (injection
molding), aerospace (flight control actuators), off-highway (excavator
machines) and healthcare (pneumatic prostheses).
With supports from various granting agencies and
local industry, the laboratory is now equipped with approximately
$700,000 worth of equipment including a tele-operated UNIMATE hydraulic
robot, a hapticenabled seven degree-of-freedom open-control
architecture KODIAK hydraulic robot, a hardware-in-theloop flight
simulator consisting of a fault emulating hydraulic actuator coupled
with a loading actuator. We have also designed and built a single axis
hydraulic actuator for testing control algorithms applied to different
valving systems. A second high performance hydraulic test rig was also
constructed for studying contact transients and impact control research.
Fig. 3: Fluid Power Research Laboratory at the University of Manitoba houses essential equipment to gain indepth understanding
of the dynamics, and developadvanced tools and supporting theories for
robust control design and intelligent condition monitoring, of fluid power systems. Support for the infrastructure has come from many sources including Natural
Sciences and Engineering Research Council of Canada, NSERC. The facility has so far provided
an infrastructure for more than 40 graduate students and visiting scholars, and 45 undergraduate
students to perform world-class research
Fig. 4: Seven degree-of-freedom hydraulic robot,
interfaced with master arms- one with no force feedback, and one to
provide force feedback. Graphics display system and computer
interfacing allow operators move the robot in an interactive manner.
Fig. 5: Prototype of a seven degree-of-freedom humanoid
pneumatic arm designed and built in Fluid Power
Research Laboratory
The laboratory also houses a
pneumatic pick/place robot, a reconfigurable pneumatic test rig, a
smart pneumatic process valve and a muscle-like pneumatically-activated
arm. The test rigs, which are all interfaced with computers and
equipped with commercial and in-house developed software packages,
allow fundamental study of different control and condition monitoring
algorithms applied to hydraulic actuators ineither fully automated or tele-operated modes.
Recent Research Projects
Fault Diagnosis and Fault Tolerant Controls in Fluid Power Systems Hydraulic actuators,
as key components in many complex systems, must perform under all
circumstances and faulty conditions. Research is being conducted to
improve reliability, by understanding complex failure mechanisms in
hydraulic functions and, designing fault diagnosis and fault tolerant
controls for hydraulic actuators.
The most recent projects of this laboratory, involve
actuator leakage fault type and level detection using Volterra
nonlinear system theory and Extended Kalman Filtering and, design of
fixed-gain robust controllers to cope with hydraulic function
uncertainty, faulty actuator piston seal, incorrect pump pressure, and
malfunctioning position sensors. A hardware-in-the-loop simulator has
also been developed to support objective evaluation of fault tolerant
controllers within the context of the highly complex flight control
applications.
Presently we aim at expanding the scope of the
previous work by covering more faults. Specifically, relative impact of
fault modes on the overall performance of hydraulic actuators is
currently being analyzed to gain an insight into the mechanism of
proper compensation through feedback control. Development of on-line
procedures for isolating faults in hydraulic systems taking into
account uncertain dynamics, dependency between fault types, and choice
of measurements is also underway.
Fig. 6: Hardware-in-the-loop (HIL) simulator test facility for research on condition monitoring and faulttolerant
control design of hydraulic actuators. The HIL simulator
integrates real hydraulic actuator hardware into the software
simulation of a highperformance jet aircraft. The experimental
hydraulic system consists of two independent circuits. One hydraulic
circuit, the fault simulator, is used to represent a flight control
actuator. The circuit is comprised of a servovalve controlled ram and
has been equipped with additional hardware elements that enable the
effects of various system faults to be simulated experimentally. The
second servovalve controlled hydraulic ram, is employed as a
dynamicload emulatorle
Control
Task of Interaction in Hydraulic Actuators Hydraulic actuators are
often used to cooperatively move an object, or individually interact
with environments. Thus, synchronization between the actuators and
controlled impact prior to maintaining contact is of great importance.
Contributions have been made to the development of control concepts for
hydraulic actuatorstargeting contact and cooperative tasks.
Fig. 7: Fully instrumented experimental test station for research
in contact task control of hydraulic actuators
A series of
projects were conducted focusing on key issues (such as impact
stabilization) that allow hydraulic actuators to come in contact with,
and exert a desired force on environments. Lyapunov-based position and
force controllers were combined, using a switching scheme and the
stability of the entire non-smooth system was studied using the concept
of Lyapunov exponents.
We have also designed controllers to allow multiple
hydraulic manipulators to cooperatively move an object along a desired
trajectory. Nonlinear hydraulic functions, parametric and model
uncertainties, friction, load sharing, internal force regulation,
measurement issues were all addressed. Our current interest is to
expand the previous work to allow multiple hydraulic arms to
cooperatively move a common object while controlling
the interaction force with the environment.
Impedance Control in Hydraulic/Pneumatic Manipulators
Position-based impedance control (PBIC) formulation has been
established as a suitable framework for considering both unconstrained
and constrained motion control problems in hydraulic robots. To meet
the demanding position-tracking requirements of PBIC, a nonlinear
PI-type position controller was developed first. Next, systematic
analyses supported by experiments were conducted which identified the
form of the PBIC-equivalent explicit force controller, and revealed an
important constraint for long-term static force regulation in PBIC
formulation.
Fig. 8: A very accurate (2 encoder resolution widths of error) position controller was developed, which
overcomes the control problems associated with deadband, stiction and saturation in hydraulic robots.
A position-based impedance technique incorporating the above position controller was implemented
on a Unimate hydraulic robot
Fig. 9: Simple and practical pneumatic devices have been constructed that are able to interact with a human upper limbs, wrists or fingers. These devices consist of various types of pneumatic actuators controlled by specialized valves via a computer and operate under the concept of position-based impedance control. The actuators are of low stiffness, by nature, enabling smooth compliant motion. They also offer good powerto-weight ratio. Provision for live video and audio with a remote computer is also possible. The forcedeformation
profiles are displayed on both computers with a built-in strip chart display. The goal is to develop portable devices capable of administering various forms of physiotherapy, tracking recovery, and communicating the information with a therapist
Current
research focuses on enabling pneumatic actuators to interact with
dynamic environments through the design of an appropriate PBIC scheme.
The current interest also lies in investigating how the property of
superposition in impedance control can be effectively utilized to
define a number of impedances, each correspondingto one objective in complex composite tasks.
Tip-Over Monitoring of Heavy-Duty Mobile Hydraulic
Machines
Excavators, forklifts and cranes are
extensively used in industry. Incorrect maneuvering the implements
would cause these machines to tip-over, causing potential hazard to the
operators and the people around. We have been studying heavy-duty
hydraulic machines to understand the mechanism of tip-over and
prevention in operation of such mobile machines. Software tools for
stability measure and tip-over simulations were developed.
Particularly, a complete simulation model of a crane carrying a
clamming device including tip-over dynamics was developed. Detailed
information about the effect of the flexibility between the base and
the ground, the effect of the friction between the tires and the
ground, and the interaction between the vehicle and the movements of
the crane links was considered. This work allows us to obtain further
insights into the necessary limits on loads, velocities and crane
configurations to
ensure sufficient stability in dynamic situations.
Fig. 10: Real-time simulator for clamming device mounted on a mobile crane. Users control the virtual machine
with a set of joysticks in the same way as they do on a real machine.
The users are placed in the loop of a real-time simulation, immersed in
a world
both autonomous of and responding to their actions
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