The Centre for
Power Transmission
and Motion Control

Location Bath, UK
Responsible Leader: Prof. Andrew R Plummer (Director)
Mrs Jane Phippen (Administrator)
Address Department of Mechanical Engineering,
University of Bath, Bath BA2 7AY, UK
Telephone number +44 (0) 1225 386371
Fax number +44 (0) 1225 386928
Email
Internet Site www.bath.ac.uk/mech-eng/ptmc

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




1 Background






The Centre




   The Centre for Power Transmission and Motion Control (PTMC) was founded as the Fluid Power Centre in 1968. It has a world-leading reputation as a centre of excellence in fluid power, power transmission and motion control. Its research activities are funded by government and industry at around £1m per annum. Short courses in hydraulic systems and electrical drives have attracted over 4000 delegates, and consultancy projects allow industry to access the Centre's expertise. The Centre is staffed by a Director, 9 academics, 3 support staff, and 25 researchers.






The Department





The Centre is linked to the Department of Mechanical Engineering. The Department's 900 undergraduate students take 4-year MEng degrees, and most of its 150 postgraduate students are undertaking PhD research projects. With 45 academic staff, and top ratings for teaching and research, it is one of the largest and most successful Mechanical Engineering departments in the UK.



The University





The University of Bath is currently celebrating its 40th anniversary. It has established an excellent reputation for teaching and research, with particular strengths in Science and Engineering. There are over 12 000 students taking first and higher degrees at the University.





Fig. 1:  The Centre for PTMC building




The role of the Centre



The Centre has specific objectives within the field of machine systems, namely:



The role of the Centre




2 Research



The Centre's major research fields are described below. An integrating theme has been the development of mathematical modelling and numerical solution techniques for fluid systems. This work has extended over several decades, and resulted in the Bathfp software package. As reflected by the change of name to PTMC, the Centre's scope has now grown beyond the original fluid power field, to include electro-magnetic systems and other technologies motivated particularly by challenges in automotive and aerospace engineering.



Fluid-borne noise





A prime source of noise in hydraulic systems is pump flow ripple, which produces fluid-borne noise or pressure ripple, resulting in vibration and air-borne noise. The Centre is well known for its research in this area, which has led to the development of International Standards for the measurement of flow ripple. A meth-odology has been developed to measure the noise-related characteristics of a wide range of fluid power components.

Current areas of investigation include:




Fig. 2:  Modelling fluid-borne noise

Two software packages have been developed to support this research and for commercial use:



Vehicle dynamics


   The Centre's major vehicle dynamics research activities include:


The narrow-track tilting vehicle research has included CLEVER (Compact Low Emission Vehicle for uRban transport), a multi-partner European project (Fig. 3). The prototype vehicle will be used as a test bed for further work on the challenging issues of tilting and steering dynamics, control and safety.







Fig. 3:  CLEVER: a narrow-track tilting 3-wheeler





Control of large flexible structures using hydraulic actuation



The movement of large structures, such as bridges, is often achieved using high pressure hydraulics. Although this approach has been used for many years, significant problems are still encountered due to inappropriate control, slip-stick motion and the flexibility of the structure.
The Gateshead Millennium Bridge in the UK has a unique rotating bridge design operated by hydraulic actuators at either side of river. The structure is large (100m wide x 45m high) and flexible (Fig. 4).
A simulation study was undertaken at the Centre to assist in the design of the actuation system; this included modelling the hydraulics, the controller and the flexibility of the structure.
Fundamental research into control of flexible structures continues, making use of a hydraulically-actuated flexible beam rig in the laboratory. The research includes application of robust control methods to achieve smooth and controlled lift-off and to minimise the vibration induced in a moving structure.




Fig. 4: Gateshead Millennium Bridge


Magnetic bearing Systems



Rotor/magnetic bearing systems possess many advantages over passive bearing systems. These include higher operating speeds, no wear under normal operation, the ability to control rotor position and transmitted force, and the elimination of lubrication supply systems. Disadvantages include the need for protective auxiliary bearings and the associated uncertain rotor dynamics, and the lack of a universal controller design method. Dynamic modelling and advanced control studies of these systems have included: Recent work at the Centre has focussed on the analysis and control of the contact dynamics with auxiliary bearings due to base motion or events such as sudden shaft unbalance.


Control of electrohydraulic servosystems



Research into adaptive and robust control of hydraulically actuated systems has been undertaken in many application areas. A recent project applied an adaptive control strategy to the Centre's MAST (Multi-axis shaker table), allowing improved tracking despite cross-axis interaction (Fig. 6). Other work includes use of adaptive control for improving the performance of injection moulding machines. It has been found that a simple proportional plus integral controller is adequate for closed-loop velocity control during the filling phase, but the adaptive controller is effective at compensating for significant non-linearities and disturbances during the packing phase.




Fig. 5:  Magnetic bearing research facility



Fluid systems



The Centre's expertise in modelling and simulation of fluid power has been applied to other fluid system fields. One is life support systems. Mathematical models have been developed for diving and submarine escape systems for British Royal Navy, and also for human respiratory and cardiovascular systems. The latter have been used in studies of artificially ventilated patients.
Fuel systems for future aircraft is another area. The current research will lead to the development of 'intelligent' components, such as pumps and valves, that will help to reduce system complexity, and ultimately give improved performance during both refuel and fuel-transfer operations.


Fig. 6: Adaptive control of a MAST




Fig. 7: Simulated flow through a ball valve






Synthesis and control of dynamic systems



   Work has been undertaken to develop a methodology for the automated generation and analysis of design variants of a dynamic system, given some desired dynamic specifications. The approach used takes advantage of the unified representation of dynamic systems provided by bond graph techniques combined with systems inversion and genetic algorithms.
Expertise in the dynamic simulation of multi-physics systems has resulted in the development of a software package, DYSIM. Inverse dynamic modelling for multi-body systems is being used for the synthesis of mechanisms, as well for real-time control of complex mechanical systems.


3 Teaching



   The Centre continues to offer short courses for industrial engineers. The regular 4-day courses are in the fields of fluid power and electrical drives: FP1: Introduction to Hydraulic Circuits & Components FP2: Component Selection for Hydraulic Systems FP3: Hydraulic System Design FP4: Introduction to Control for Electro-Hydraulic Systems ED1: Electrical Drives for Mechanical Engineers ED2: Servo-Electric Drive Performance and Control. Specialised courses tailored to particular companies' needs have also been run on many occasions.
An MSc in Fluid Power Systems has been offered since 1989. Students take the industrial short courses as well as a number of other taught modules, and also undertake a major project and dissertation. It can be undertaken either on a one-year full-time or a three-year part-time basis. Shorter Certificate and Diploma versions of the programme are also offered.
An MSc in Power Transmission and Motion Control was introduced in 1999. The course provides participants with the knowledge required to design the most appropriate motion control system to satisfy given performance requirements. The taught modules cover fluid power, electrical drives, mechanical drives and control systems.
The Centre does not have an organisational role in the delivery of undergraduate programmes, but Centre staff do deliver many courses in the machine systems field, and they also supervise student projects relevant to the needs of their industrial collaborators.




4 Consultancy and facilities



The Centre provides a consultancy service to industry in the following areas:
  • hydraulic system design, simulation and analysis,
  • hydraulic component testing,
  • contamination control,
  • fluid-borne noise measurement, analysis and control,
  • hydraulic and electric power-assisted steering systems,
  • aircraft systems,
  • control system design and analysis,
  • electric drives,
  • fluid bulk modulus measurement,
  • CFD and FE modelling,
  • test systems: actuation and control.
A range of laboratory facilities are available which are used in support of both industrial consultancy and research activities:
  • a state-of-the-art multi-axis shaker table for 6 DOF vibration testing with payloads up to 450kg (Fig.8),
  • a four-poster vehicle suspension test rig (Fig.9),
  • a range of hydraulic drives and test equipment,
  • a tilting-vehicle testbed prototype,
  • fluid-borne, structure-borne and air-borne noise test equipment,
  • magnetic bearing test equipment,
  • various shakers, modal analysis, and frequency analysis equipment,
  • virtual reality and video conferencing suites.
The Centre offers the following software packages for commercial use:
  • PC-Bathfp - fluid power system simulation software,
  • FBN - for measurement of fluid-borne noise,
  • Prasp - for modelling fluid borne noise.




Fig. 8: Multi-axis shaker table (MAST)






Fig. 9: Four-poster test rig


5 International links



Every year since 1988 the Centre has hosted an international symposium on Power Transmission and Motion Control, which has focussed on fluid power and related technologies. The 3-day event has established a reputation as a forum for presenting and discussing the latest technical developments from around the world. The Centre is a founder member of the Fluid Power Centres of Europe (FPCE), a grouping of the foremost research institutions in the field. It welcomes international visiting scholars, and has hosted many in the past from North America, Asia, Europe and elsewhere.

6 Industrial engagement



The Centre's activities are industry focussed. The Centre has had an Industrial Advisory Group since its inception to ensure that its research and teaching strategies remain relevant to industry. Recent collaborators on research and consultancy projects include: Ford Motor Company Jaguar Cars BMW Delphi John Deere Bosch Goodrich BOC Edwards Horstmann Defence Systems Molins Sterling Hydraulics Kvaerner Markham Airbus UK Parker Aerospace Parker Hannifin JATCO Instron Ltd Sun Hydraulics Aeroquip Eaton QinetiQ Ministry of Defence CarnaudMetalbox Engineering In addition, undergraduate and MSc projects are often industry-linked. Unusually, the majority of students spend at least one period on placement in industry during their first degree, and in turn this can ultimately help the company with graduate recruitment.



 

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