Hydraulic machines have been widely used in a variety of high power applications. Typically these machines are operated by an operator. In past research the interaction safety between the operator and the machine was seldom investigated. This dissertation addressess the interaction stability issue by exploiting the safety guarantees offered by passive systems. The hydraulic machine considered in this dissertation is a 2-DOF hydraulic backhoe teleoperated by a 2-DOF, electro-mechanical, force-feedback capable joystick (master). Given a passive master and a passive slave, this dissertation proposes a systematic approach to design teleoperation control systems (based on bondgraphs) which ensure that the master and slave satisfy certain coordination and passivity requirements. Bondgraphs are used as they offer benefit of representing power flow in a dynamic system. Bondgraph based control is designed in three stages. In the first stage, a coordination control law is determined which ensures that the master and slave systems remain coordinated when teleoperated. In the second stage, desired dynamics of the coordinated teleoperated system are chosen based on the application. In the third stage, a passive control law is determined so as to ensure that the coordinated system behaves dynamically like the desired locked system hence in turn ensuring that the teleoperated system is passive with respect to a power supply rate. The proposed passive control ensures that the joystick teleoperated backhoe 1) is coordinated thus guaranteeing performance, 2) is passive with respect to an appropriate power input thus guaranteeing interaction safety and 3) can behave like 4th order system or a 2nd order system based on the choice of desired dynamics. The proposed passive control algorithms is experimentally verified and the benefits achieved by dynamically tuning the passive teleoperated system are documented. It is also shown that the proposed control design method can be extended to ensure passive teleoperation of arbitrary order passive master and passive slave systems.
This thesis is involved with the introduction of environmentally adapted lubricants (EALs) in hydro power plants. The work concerns environmental adaptation of journal bearings operating under boundary lubricated conditions with shaft oscillation.
To improve the environmentally adaption of the hydro power applications new EALs such as synthetic esters will be used to replace the existing mineral oils. New types of lubricants rise questions about their boundary lubrication performance and how they will affect machine/system design. This study aims to explore the potential for using EALs in slow sliding journal bearings with shaft oscillation as those supporting the Kaplan turbine blades. Oil lubricated bronze journal bearings have worked satisfactorily for many years. Journal bearings in water lubricated conditions have in recent years become a common design solution, but there is a lack of long term performance results for self-lubricated bearings.
In order to evaluate the performance of different lubricated environmentally adapted journal bearings a test rig was built. Test rig parameters were set to simulate water turbine conditions. Tests were performed with different bearing and shaft materials and different variants of a synthetic ester base lubricant suited for water turbine applications. The EALs were compared to the present used mineral oil reference. Self-lubricated bushings with water lubrication were compared to an EAL lubricated tin-bronze bearing. Tests were also conducted using identical materials in oscillating motion for a pin on disc. An additional test was performed with a roller on disc using a steel material combination found in a hydraulic system. All tests were performed with oscillating motion.
Results showed that synthetic esters affect the contact material to a larger extent than the tested mineral oil. Tin-bronze journal bearing and hardened steel shaft contact was transformed to a partly copper-copper and partly steel-copper contact due to dissolution of alloy elements from the bronze in to the lubricant. The formation of a copper layer affected the tribological performance. The synthetic esters were also sensitive to the selection of bearing and shaft material. Highly alloyed bronzes were more prone to corrosive wear. A coated shaft showed excellent performance with a low alloyed tin-bronze. Adhesion and abrasion in the contact had a large influence on performance. The comparison of self lubricated bearings with water lubrication to an EAL lubricated tin-bronze on stainless steel showed large performance differences between the water lubricated materials. They showed both better and worse friction and wear results than the EAL lubricated tin-bronze. The oscillating pin on disc can generate similar contact mechanisms as found in a journal bearing. This offers possibilities for faster and simpler studies of the tribological materiallubricant affect using spectroscopic techniques. The additional tests with roller on disc showed very low steel on steel friction and wear with the tested synthetic ester.
The principal conclusions of this work are that a synthetic ester lubricated tin-bronze journal bearing on hardened steel shaft can, under certain conditions, show excellent performance also outperforming mineral oil. A coated shaft/tin-bronze combination showed excellent performance and was not affected by load. It is possible to identify self-lubricated journal bearings better suited to shaft oscillation in water turbine applications than EAL lubricated bronze. Water lubrication is the most environmentally adapted solution. EALs such as synthetic esters tested have a promising future in the turbine hydraulic control system.
by M. Radhakrishnan
Publisher: ASME Press, New York
ISBN: 0791801845
Pages: 275
Hydraulic fluids are the most widely consumed of all industrial lubricants. Exploring a broad range of issues concerning the most widely consumed industrial lubricant, Hydraulic Fluids addresses engineers responsible for the selection, application, and maintenance of hydraulic fluids used in industrial machinery.
It demystifies the subject for mechanical engineers with little expertise in the chemistry of fluids.
Bringing together material unavailable in any other single source, this comprehensive, concise reference features detailed coverage of various hydraulic fluid properties, such as biodegradability and fire resistance, as well as relevant hydraulic fluid test procedures. It examines the re-refining, reclamation, and disposal of used hydraulic fluids.
Offering quick assistance in the diagnosis and solution of workplace problems, this handy guide provides ready access to essential data and guidelines for both inexperienced and seasoned technical professionals specializing in hydraulics, plant engineering, fluid power transmission, and other aspects of mechanical engineering.
Edited by Dresdner Verein zur Förderung der Fluidtechnik e.V. Dresden
Publisher: Dresdner Verein zur Förderung der Fluidtechnik e.V. Dresden
Vol. 1: 522 pages, Vol. 2: 544 pages
D. Merkle, B. Schrader, B. Thomes
Publisher: Springer, Berlin
ISBN: 3-540-21495-X
Language: German