Institute of Energy Technology, Institute of Mechanical Engineering Aalborg University, Denmark


Location Aalborg, Denmark
Contact Persons Assoc. prof. Torben Andersen
Assoc. prof. Peder Pedersen
Assoc. prof. Michael R. Hansen
Address Institute of Energy Technology
Aalborg University
Pontoppidanstræde 101
9220 Aalborg Ø

Institute of Mechanical Engineering
Aalborg University
Pontoppidanstræde 105
9220 Aalborg Ø
Telephone number + 96 35 92 69 (Andersen)
+ 96 35 92 60 (Pedersen)
+ 96 35 93 21 (Hansen)
Email toa@iet.aau.dk
pp@iet.aau.dk
mrh@ime.aau.dk
Internet Site http://www.iet.aau.dk
http://www.ime.aau.dk

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


General Information

Aalborg University (AAU) was inaugurated in 1974 as the fifth Danish university. Since then the number of students has more than trebled, and at the beginning of the year 2001 more than 12,000 students are registered. AAU conducts teaching and research to the highest level in the fields of Humanities, Engineering, Natural Sciences and Social Sciences. In 1995 the Engineering College of Esbjerg became part of Aalborg University. Aalborg University’s annual budget is rapidly approaching one thousand million Danish kroner.
The Faculty of Engineering and Science at Aalborg University is an innovative faculty offering a wide range of educational programmes leading to degrees at bachelor, master and doctoral levels within the fields of engineering and sciences.
Our wide-ranging curriculum provides students with a high quality portfolio and allows opportunities for choice and flexibility of study.
Our unique study form has proved to be an essential innovation in higher education and is highly recognised by leading international industry. From day one until their graduation, students are accustomed to working in projects in groups and they are thus closely aligned to a problem-solving approach and have strong qualities in the fields of problem solving, co-operation and project work.

Fluid Power Research Group

The involved institutes: Energy of Technology (IET) and Mechanical Engineering (IME) are part of the Faculty of Engineering and Science at Aalborg University. The institutes have a comprehensive cooperation with industry and research institutions concerning PhD, co-financed positions, research projects, consultant work, etc. The total number of staff members of the institutes are estimated to 35 Faculty Members, 25 PhD Students, 10 Guest Researchers, 15 Research Assistants and 25 Technical and Administrative Personnel.
The fluid power systems group staff consist for the time being of 3 associate professors: Torben Andersen (IET), Peder Pedersen (IET) and Michael R. Hansen (IME) and 5 PhD-students (1 guest student). The group was founded 5 years ago and the world class laboratory facilities were established by aid of external funding. The group is co-working nationally with Professor Finn Conrad, Technical University of Denmark, Copenhagen and internationally through Fluid Power Net.

Research

The main research area is design of power mechatronic systems. Mechatronics is the synergistic combination of mechanical engineering, electronics, control systems, and computers. The key element in design of mechatronics is the integration of the mentioned areas. Adding the power term indicates that focus is on systems where the power utilization and transmission plays a key role in the performance assessment. Current fluid power related research topics within the above frame are:
Some examples of PhD-projects currently being carried out are:

Electronic Load Sensing and Power Management in Mobile Hydraulic Applications


Throughout the last three decades energy usage and system efficiency have become important design parameters for hydraulic systems, especially for mobile hydraulic systems, as power and cooling capacity is at limited disposal in these systems. However, there exist no methods and/or guidelines for how to design and control open circuit hydraulic system in the most energy efficient way, when also taking into account performance aspects and system cost. The design process is therefore highly dependent on the experience of the designer. Because of this lack of design methods, it is believed that there is an unexploited energy and cost saving potential in many hydraulic systems, which is due to poor system layout and utilisation. The objective of this project is therefore to develop guidelines for how to design and control (Electronic Load Sensing ELS) open circuit hydraulic systems, according to some optimality criteria, when also taking into account the possibilities arising by the increasing use of sensors and microcontrollers in hydraulic systems. The approach behind the project is to use numerically based optimisation routines, and the expected result will be a design tool in the form of a software program or framework of numerical routines and functions, which may be used in the development process to aid the system designer when designing or redesigning hydraulic open circuit systems. Besides these numerical routines, the objective is to develop the controller structure and algorithms for the overall system controller, so that the system is always operated in the most energy efficient way, when also handling saturation problems and ensuring the stability and performance of the system. The work is based on a number of industrial cases, with fork lifts being one of them, see Fig. 1. The work is ongoing and planned to finish in 2005.



Fig. 1: Industrial fork lift used in study

Multi Criteria Design Optimisation of Multibody Systems


The motivation for the project is the need for a systematic approach to the design process when de-signing a mechanical multibody system. Different op-timisation techniques are known and applied in tools to optimise a single structure in a given load situation. To some extent there also exist techniques to model multi-body systems including flexibility. When designing a complete mechanical system these two fields, optimi-sation and multibody dynamics, needs to be combined to maximize the performance of the system. In this context the performance function involves criteria such as energy consumption, payload, estimated life, re-sponse time, and net weight etc all related to a set of typical working cycles. The correlation between opti-misation and multibody dynamics has not been exam-ined as thoroughly as the two fields separately. There-fore, one of the main tasks of the project is to extract design guidelines from the work done on specific case studies, such as the mobile loader crane shown in Fig. 2.
The expected results of the project are computer tools that can assist in the design phase when designing systems of the same type as treated in the two cases. Most likely the tools consist of two main parts. One part is a multibody model of the mechanical system including the actuation and control systems. The second part is an optimisation routine that uses the first part for performance evaluation purposes. An important part of the project is experimental work carried out to test the models. The work is ongoing and planned to finish in 2006.



Fig. 2: Loader crane used in study

Education

The study concept at AAU is problem-centred studies organised around projects with the students working in groups. The problem-oriented and project-based learning is that the students use half of their study time making projects and half the time taking courses. Half of those courses are study-unit courses, which give the student basic knowledge and the other half of the courses are project-oriented courses, which support the project. Study-unit courses are typically examined. One project is carried out at each semester. In their final project (thesis) the students spend all the time on the project work. Normally, 6 students work together in a project group except for the Bachelor or Master graduate project, where normally only two students work together.
The level within these areas is built up during the different semesters. For the technical curriculae until the 8th semester the courses (50%) are combined with project work (50%). During the 9th semester it is possible to attend project related courses, but generally the 9th and 10th semesters are based only on project work.
The fluid power research group is associated with the education within mechanical engineering. Particularly, it is heavily involved in two curriculae: Design of Mechanical Systems (DMS) and Electro-Mechanical System Design (EMSD) that stretches from the 6th to the 7th (B.Sc.) or the 10th semester (M.Sc.). For both curriculae focus is put on: design of machines and dynamic analysis with the DMS curriculum having a more classical mechanical engineering profile and the EMSD curriculum having a distinct mechatronic engineering profile, with both profiles being extremely well suited for the problem-oriented and project-based learning used at Aalborg University. In the following some examples are given of project themes for different semesters and curricula.6th semester project theme, DMS:

Design and Optimisation of Electro-Hydraulic-Mechanical System

A design task is formulated in detail, based on a working cycle where a payload of approximately 400 kg is to be positioned by a small vehicle. A number of standard components: Frequency converter, gearmotor, hydraulic pump station and hydraulic proportional valve are handed out to the students and they must use these in the design task. The design is manufactured and the student projects are compared with respect to: functionality, price, weight and efficiency. The outcome of a typical 6th semester project is shown in Fig. 3.



Fig. 3: CAD-model of the vehicle build

7th semester project theme, EMSD:

Servomechanisms and distributed loads

The project considers industrial servomechanisms with distributed load. The analysis and design of a position/velocity servo system on the basis of dynamic performance demands is wanted for the system. During the design work both an electrical and a hydraulic servomechanism is elected, and the designed control strategies are implemented digitally. As an example a hydraulically driven robot, as shown in Fig. 4, was modelled and simulated to test different control algorithms (incl. adaptive and learning control). It is a two-degrees-of-freedom rotary arm manipulator with a high-frequency servo valve controlled hydraulic cylinder driving each link. The robot was modelled including non-linearities and also used for the experi-mental evaluation and verification of the designed control algorithms.
The final thesis is often a continued investigation within the project area of the 9th semester. Thereby, the final thesis can get a character of industrial development work, further development or actual research, and in most cases include experimental work in laboratories, field measurements, measurements of existing systems or analytical and numerical model predictions. However, the final project can also include totally new subjects where the connection to the previous course of study is smaller. The possibility is given to gain international experience by having the development work carried out either in connection with a stay abroad or in surroundings with international relations.



Fig. 4: Hydraulic servo robot

A final project example from the EMSD curriculum is:

Analysis and Design of Controller for Electrical Load Sensing Pump

Traditionally load sensing control is made hydraulically. There are some well-established control methods, however, the many constraints related to the required functionality yields a non-trivial challenge. Electric load sensing control has the potential of removing some of these boundaries, however, this requires electrically actuated pumps. The objective of the project was to develop and test an electro-hydraulic actuator, including an internal controller strategy for controlling the displacement of the pump. In Fig. 5 is shown a part of the test facility. Important parameters in the design of the actuator module were low power consumption of the pilot supply, performance, cost and simplicity.



Fig. 5: Functional prototype of the ELS pump

The project outline included an analysis of the functional requirement for the pump actuator module, analysis of operation and dynamical requirements for the controlled pump, selection of the most promising topology and dimensioning of the actuator according to the functional requirements with emphasis on the actuator. See Fig. 6.



Fig. 6: The actuator module

A controller has been developed for swash plate angle (internal loop) and for controlling the pump pressure according to a load pressure (external loop). The controller enables the pump to follow a reference pressure under varying load conditions. Information to the controller is the pump pressure, diesel engine speed and reference pressure setting (LS pressure), and output of the controller is reference displacement of the pump.

Cooperation

Research and education are carried out in cooperation with a number of national industrial partners such as:

Facilities

There are a number of different test rigs and test equipment within the two institutes. Some have been designed and manufactured in-house and others are commercially available machinery. The latter has typically been made available from cooperation with the previously mentioned industrial partners. Examples of facilities are:
 

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