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The Center for Compact and Efficient Fluid Power.

The Center for Compact and Efficient Fluid Power (CCEFP) is an Engineering Research Center (ERC) supported by the National Science Foundation (Grant No. EEC-0540834). The center was started in 2006 and has overseen a revival of fluid power research at universities in the United States in the past few years. The CCEFP, headquartered at the University of Minnesota, is a network of seven universities and over 50 companies and non-profit institutions. Partnering universities are Georgia Institute of Technology, Milwaukee School of Engineering, North Carolina A&T State University, Purdue University, University of Illinois Urbana-Champaign and Vanderbilt University. The affiliated non-profit organizations include the National Fluid Power Association, Project Lead The Way, and the Science Museum of Minnesota.

Before CCEFP, university research in fluid power in the United States was confined to a few isolated research groups. It has now grown to an $8 million coordinated effort with funding from government, industry and universities. Our researchers work closely with industry and employ a systems approach to set research priorities. We are currently supporting 21 research projects that are demonstrated on four test beds.

The Center currently has 48 faculty and staff researchers, 81 graduate students, and 63 undergraduate researchers. Since its inception, one hundred and four bachelors, eighty masters and twenty-eight doctoral students have graduated. A recent survey showed that 61% of CCEFP graduates enter the fluid power field. Center researchers have been active in publishing research and patenting inventions. To date, research has resulted in seventy-eight publications in technical journals and two hundred and forty-eight publications in conference proceedings. Forty-three inventions have been disclosed, twenty-four patent applications filed, two patents awarded and two licenses issued to industry.

Fluid power is prevalent in many applications: agriculture, manufacturing, healthcare, transportation, renewable energy, etc. It is responsible for transmitting approximately 2 to 3 percent of all energy in the U.S. Figure 1 shows that the range of power and weight for fluid power applications spanning six orders of magnitude. Although fluid power is a relatively mature industry, it can be improved in three broad significant areas--efficiency (reducing energy losses and enabling energy efficient systems), compactness (enabling new untethered, portable human scale and sub-human scale applications) and effectiveness (leak-free, quiet and easy to use). This will benefit humanity by significantly reducing energy consumption and spawning whole new industries.

Research within the CCEFP are motivated and integrated in four major test bed systems:

1. Mobile Heavy Equipment (50 kW-500 kW): Excavator

2. Highway Vehicles (10 kW-100 kW): Hydraulic Hybrid Passenger Vehicle

3. Mobile Human Scale Equipment (100W-1 kW): Patient Handling Robot

4. Human Assist Devices (10W-100W): Orthosis

These test beds encompass current and future applications of fluid power, influence neighboring applications and solve important societal problems. Recent research initiatives at CCEFP are also addressing new fluid power applications in the larger and smaller scales: wind power (megawatts) and medical micro devices (less than one watt).

Strategic reviews of each test bed identified the technical barriers that must be overcome to achieve success. The nine most important fluid power technical barriers, of which three are deemed transformational, are listed in Table 1. There are currently about 20 core research projects within CCEFP that address these barriers.

Results from each research project will be incorporated into one of the four test beds, where certain barriers are targeted to be highlighted on certain test beds. For each test bed, the current state, the desired end state, the barriers and the targeted approach to overcome these barriers is described below.

Mobile Heavy Equipment (50 kW-500 kW): Excavator

This test bed demonstrates greatly improved efficiency in current fluid power applications. The excavator is an example of a large class of mobile equipment. The current fluid power systems on mobile heavy equipment are inefficient in their components, systems and control. The two largest sources of inefficiency are throttling control and hydraulic pumps and motors. Other sources of inefficiency include a lack of systematic approach to energy management for multi-axis systems and the lack of advances in hydraulic fluid properties. The desired end state would be equipment with an efficiency that is double current values. This would be achieved by creating more efficient pumps and motors, engineered fluids, more efficient human machine interfaces, displacement control and sophisticated energy management of multi-axis systems.

Highway Vehicles (10 kW-100 kW): Hydraulic Hybrid Passenger Vehicle

This test bed demonstrates greatly improved efficiency in transportation by developing a hydraulic hybrid passenger vehicle. This effort complements existing industry-based research on heavier hydraulic hybrid vehicles. The target mileage for the CCEFP hydraulic hybrid vehicle is seventy to one hundred miles per gallon, more than doubling current fleet averages. The barriers to achieving this goal are inefficient pumps and motors, low energy density for accumulators and noise. Important unknowns include what architecture to use, and how to implement energy management and control. CCEFP's approach is to use a hydro-mechanical transmission with regeneration.

Mobile Human Scale Equipment (100W-1 kW): Patient-Handling Robot

This test bed demonstrates a compact patient-handling robot, an example of a portable, untethered human scale fluid power application. This project is a collaboration between the CCEFP and the Quality of Life Technology ERC led by Carnegie Mellon University and the University of Pittsburgh. The robot must operate autonomously for a reasonable length of time, navigate around obstacles in the hospital or nursing home environment, produce a required force with precision control and resulting dexterity and transport the patient safely. Barriers to this goal are a lack of compact power supplies, lack of miniature components and difficulty in operation and control. Safe and intuitive operation is an important requirement.

Human Assist Devices (10W-100W): Orthosis

By developing an orthosis, this test bed demonstrates a portable, un-tethered human-assist device requiring demanding miniaturization of fluid power systems that must operate in direct contact with humans. Current approaches are passive mechanical or tethered powered devices. The CCEFP will develop an active, portable fluid power assisted ankle-foot orthosis with appropriate power, forces and duration. Barriers include a lack of compact power supplies, compact integration and miniature components. The approach will be to use an HCCI miniature free-piston compressor to provide power to a highly integrated, miniaturized design.

The major technical goals of the center are:

1. Doubling fluid power efficiency in current applications and in new transportation applications.

2. Increasing fluid power energy storage density by an order of magnitude.

3. Developing new fluid power supplies that are one - two orders of magnitude smaller (10 W-1 kW) than anything currently available.

Doubling the efficiency in current off-road applications and future on-road applications will lead to a large reduction in energy consumption. Increasing the energy storage density is a requirement for hydraulic hybrid passenger vehicles to compete with electric hybrids. Developing new smaller fluid power supplies is a key enabling technology for mobile human scale devices and mobile human assist devices. Lastly, as a national Engineering Research Center it is important that the Center maintain its focus on fundamental research in the field of fluid power.

Dynamic systems and control play an important role in addressing many of the challenges outlined above. The papers included in this DSC Magazine issue are a sampling of these research activities:

* "Energy Management in Mobile Hydraulics" presents one of several energy management control strategies being developed in the center for hydraulic hybrid vehicles.

* "A Free-Liquid-Piston Engine Compressor for Compact Robot Power" presents a solution to the compact power supply barrier

* "Freeform Fluidics" addresses the compact integration issue using additive manufacturing;

* "Hydraulic Free Piston Engine Enabled by Active Motion Control" proposes a efficient hydraulic power source that can be used in a hydraulic hybrid vehicle.

* "MRI-Compatible Fluid Powered Medical Devices" illustrates how fluid power can be used in small and sensitive healthcare environments.


KIM A. STELSON is Director of the NSF-funded Engineering Research Center for Compact and Efficient Fluid Power. He is a Professor in the Department of Mechanical Engineering at the University of Minnesota where he has been since 1981. He received his B.S. from Stanford University in 1974 and his 5.M. and Sc.D. from M.I.T. in 1977 and 1982. Stelson has twice been awarded the Rudolf Kalman Best Paper Award of the ASME Journal of Dynamic Systems, Measurement and Control. He is a Fellow of the American Association for the Advancement of Science.

PERRY Y. LI received an M.A. from Cambridge University in 1987, an M.S. from Boston University in 1990 and a Ph.D. from the University of California, Berkeley in 1995. He is Professor of Mechanical Engineering and Deputy Director of the NSF Engineering Research Center for Compact and Efficient Fluid Power at the University of Minnesota, Minneapolis. From 1995-1997, he was with Xerox Corporation. His research in controls and fluid power include: energy storage, hydraulic hybrid vehicle, efficient fluid power components and human interactive robotics. He received the Young Investigator Award at the 2000 Japan-USA Symposium for Flexible Automation.

TABLE 1 Fluid Power Technical Barriers.


Efficient components
Efficient systems             Efficient components
Control and energy            Compact power supplies
management                    Compact energy storage
Compact power supplies
Compact energy storage
Compact integrated systems
Safe and easy to use
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Title Annotation:Focus on Dynamic Systems & Control
Author:Stelson, Kim A.; Li, Perry Y.
Publication:Mechanical Engineering-CIME
Article Type:Conference notes
Geographic Code:1USA
Date:Jun 1, 2013
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