O+P Fluidtechnik 7-8/2018

FORSCHUNG UND

FORSCHUNG UND ENTWICKLUNG IFAS JUBILÄUM 50 YEARS OF FLUID POWER RESEARCH AT RWTH AACHEN UNIVERSITY – HIGHLIGHTS AND FUTURE CHALLENGES PART 2 – 1980-2009 Prof. Dr.-Ing. Hubertus Murrenhoff and Prof. Dr.-Ing. Katharina Schmitz The 11 th IFK 2018 took place from March 19 th through 21 st at the Eurogress in Aachen. During the concluding session on the last day of the event, Prof. Ernst Schmachtenberg, Rector of RWTH Aachen University, conducted the handover of the directorship at ifas. A talk followed with regard to the above title and for all readers of O+P Fluidtechnik that didn’t have the chance to attend the conference, the contents of that presentation are summarized in this three-part-series. This first part published in O+P Fluidtechnik 6/2018 gave an introduction describing the history of the Institute from its establishment in 1968 by Prof. Wolfgang Backé till today. Additionally, the research of the 1970s was highlighted. The following chapter will deal with research highlights of the 1980 th , 1990 th as well as 2000 th . The main projects of our current decade as well as an outlook on the future research contents and the new structure of the research groups will be given in the upcoming issue of O+P Fluidtechnik. 38 O+P Fluidtechnik 7-8/2018

IFAS JUBILÄUM 2 ND DECADE – THE 1980 TH This decade was characterized by a roaring development through the proportional technology. Servohydraulics was widely known from aircraft applications and originated for industrial use by developments known from MIT in Boston, Massachusetts. Names that stand for that development are Backburn, Reethof and Shearer along with their works documented in Fluid Power Control, MIT Press, 1960. These developments build the foundation for the first NC controlled machine tools being responsible for the start of multiple industrial revolutions. But there was a setback with regard to the costs involved for high performance and high precision continuously operating valves. The industrial answer was a heavy invest in proportional technology which started in the mid-1970 th and continued well into the next decades until today. In the lecture books of fluid power teaching in Aachen neither the word proportional-valve nor proportional technology was present until the early 80th. It all started with the intelligent design of the nonmagnetic 01 barrier in switching valves straightening the force characteristic. This laid the foundation for lots of developments to follow. An example is provided in Fig. 1. With components available using proportional technology, independent metering was born and the idea is displayed in the figure. Each chamber of the differential cylinder is connected to two cartridge valves; one to high pressure and one to return. The proportional control is incorporated into the pilot stages of the cartridge valves and allows onoff, checking as well as continuous functions like directional control, displacement, flow, force and pressure functions. Feedbacks are possible by specific sensors and internal feedback to the pilot offered lots of possibilities. First designs used barometric, mechanical or force feedback via levers, springs and specially shaped orifices. Later those feedbacks were more and more achieved by electric sensors. These multifunctional controls offered huge advantages compared to the use of single valves for each function. Lots of conferences addresses the development and the material can be found via a literature search in the GFPS literature base www.gfpsweb.org. It should not be covered here in detail because it would take a lot of space and might be subject for a later survey paper. Today the use of cartridge valves with mul- 02 Research of cavitation tiple functions is state of the art and it can be stated that it revolutionized fluid power drives and applications. One example is shown in the right hand side for typical press controls. The developments in industry were accompanied by lots of dissertations towards the subject which can be found in www.ifas.rwth-aachen.de looking at the years talked about here. Specific works are not named because it’s so easy to forget a good contribution. One specific work by Prof. Yung-Hsiang Lu can be mentioned published in 1981. Later in 2011 he became honorary citizen of RWTH Aachen University. Today lots of national and international research focuses again on independent metering with the focus of energy recuperation and regeneration. Here mobile applications offer a huge potential. A continuous companion of fluid power is the appearance of cavitation in its circuits and components. Damages are known from numerous text books and the phenomenon is also present in industrial use. This was the motivation for research in the 80th. The major Proportional technology and independent metering O+P Fluidtechnik 7-8/2018 39