O+P Fluidtechnik 6/2018

IFAS JUBILÄUM FORSCHUNG

IFAS JUBILÄUM FORSCHUNG UND ENTWICKLUNG RWTH and at rented locations in the vicinity of Aachen. Anyways, all collaborators involved experience a lot of extra work and everybody looks forward to the construction end by December 2018, latest. 1 ST DECADE – THE 1970 TH 02 Artificial heart and servovalve for pressure regulation Having started the research work in 1968 Prof. Backé needed to build up the first generation of researchers. It is a remarkable indication of a sound alumni team spirit that most former researchers still stay in contact with ifas, even with so many years having passed by. The fluid power network is something that bonds together and holds the whole working life and beyond. One example of research results of the first generation touches on hydrostatic drives. It is taken from the dissertation of Dr. Wolfgang Hahmann published in 1973 and shown in Fig. 1. Back then the dynamic performance was unknown and so typical step responses are shown. The drive speed is increased from standstill to 600 rpm and speed as well as pressure transients are plotted by changing the hydraulic capacity in the lines connecting pump and motor. A major finding was that natural frequency as well as damping decrease at the same time when the line volume e.g. the hydraulic capacity increases. The analytic model derived in the thesis provides the answer. With certain assumptions that can be taken from the thesis or today’s lecture materials, one can see that the hydraulic capacity appears in the denominator for the hydraulic frequency as well as for the damping ratio. So the lesson learnt is to bring pump and motor as closely together as possible to keep system dynamics high. Nobody questions this today and it reflects good engineering practice. The next example is taken from pneumatics research and deals with the development of an artificial heart. The institute was part of the collaborative research center SFB 109, where scientists from engineering and medicine worked closely together. The idea was to build a pneumatically operated pump as depicted in the left part of Fig. 2. The first prototypes were used in bypass operations and for experiments animals like pigs were used. The necessary control circuits are outlined and back than all controls were based on analog signals and analog process controls. A servo controlled pressure acted upon a membrane so shear stress in the blood flow was minimized. In order to precisely adjust the pressure a servo valve was researched and developed at IHP and Dr. Rolf Neuhaus took this as a challenge for his doctoral thesis which was published in 1981. The design used a sliding spool operating against a mechanical spring on one side and a flapper nozzle on the other side for pressure adjustment. Comparing set pressure and actual pressure on the spool face sides a precise servo pressure control was achieved. A cross sectional view can be taken from the right side of the figure. An awarding innovation was to use a voice coil actuator for the electromechanical drive to position the nozzle. Thus high precision met good bandwidth and let to remarkable research results with the center. Later the innovations were used as the birth of servopneumatic position drives and a spin-off company under the direction of Prof. Dr. Wolf Dieter Goedecke started in the former premises of Dual Company in the Black Forest. Prof. Goedecke was also continuously engaged in teaching in Aachen passing his knowledge on to next generations of students. The last example that originated in the 70 th and should be mentioned is the birth of 1D simulation with DSH. The abbreviation stands for Digital Simulation of Hydraulics. Meanwhile it covers hydraulics and pneumatics and can co-simulate with a whole range of other programs. Back than digital computers became more powerful and made the former analog computing obsolete. Fig. 3 shows the steps of the development until today. In the early 70 th Prof. René Schulz and Dr. Werner Hoffmann started their research on the subject and developed the DSH program structure as depicted in the left part of the figure. Both finished their doctoral thesis under the supervision of Prof. Backé. In 1986 the former DDR (German Democratic Republic) was interested in those developments and a spy with the informal name “Peter Lux” was sent to Aachen. He started with some research work and his pretended interest was to engage in research work leading to an external PhD thesis. Prof. Backé treated him honestly and that can be read in the Stasi material that is a teaching case today. Meanwhile the real person behind the name is known at ifas. Later in 1994 DSHplus was launched leading to the foundation of the spin-off company Fluidon which celebrated its 20 th birthday in 2015. Today, DSHplus is widely used in the fluid power industry and offers a lot of features that are not treated in this article because the information can be found on the homepage where also test versions are available for download. The research highlights from the 1980s until the first decade of the second millennium will be published in the upcoming issue of O+P Fluidtechnik. The issue after that will highlight the research of the current decade as well as the plans of the institute for the future. Prof. Dr.-Ing. Hubertus Murrenhoff, former Director of ifas, and Prof. Dr.-Ing. Katharina Schmitz, new Director of ifas since March 2018, Institute for Fluid Power Drives and Systems (ifas), RWTH Aachen University 40 O+P Fluidtechnik 6/2018

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