Active hydrostatic bearing with magnetorheological fluid

Abstract

Special bearings based on magnetic fluids are well known in literature. These bearings use the magnetic pressure inside a ferrofluid that is exposed to a magnetic field. The biggest disadvantage of this principle is the small load that can be supported. In one reference [B. M. Berkovsky, V. F. Medvedev, and M. S. Krakov, Magnetic Fluids, Engineering Applications (Oxford University Press, Oxford, 1993)], the specific load is specified as 1 N cm−2. To support heavy loads very large support areas are needed. We will present a completely different concept for bearings with magnetorheological fluids. Hydrostatic bearings get their load bearing capacity from the hydrostatic pressure produced by an external pump and should not be confused with hydrodynamic bearings presented in another reference [R. Patzwald, M. S. thesis, Institute für Werkzeugmaschinen und Fabrikbetrieb, Technische Universität, Berlin (2001)]. The main disadvantage of hydrostatic bearings is that the bearing gap varies with the payload. Conventional systems compensate for these variations with a change of the oil flow rate, that is done, for example, by external valves. Our contribution will present a hydrostatic bearing that uses magnetorheological fluids. Due to the fact that magnetorheological fluids change their rheological properties with the change of an external magnetic field, it is possible to achieve a constant bearing gap even if the payload changes. The great advantage of this system compared to valve based systems is the short response time to payload changes, because the active element (i.e., the fluid) acts directly inside the bearing gap, and not outside like in the case of valves.

C-code implementation of robust μ-synthesis-controllers for industry applications

“…the controller matrices are. For the designed µ-controllers the condition number κ is reduced from κ TMO =493 to κ TMO =78 for the TMO controller and from κ Z =1.33e 6 to κ Z =81 for the z-axis controller, by means of balancing the discrete controller in canonical, modal form (7) using (8). The used commands are ssbal and cond.…”

“…To implement the µ-controllers in C-Code it is useful to understand how the discrete state space representation (6) can be evaluated manually. Therefore at first the state vector x(k+1) is calculated recursively using x(k) (notation x k+1 and x k ) [1] by means of (6).…”

“…Applications of active hydrostatic bearings can be rarely found in literature [5], [6]. The application of µ-controllersynthesis in this technology is not known to the author's best knowledge.…”

Active vibration μ-synthesis-control of a hydrostatically supported flexible beam

“…Hesselbach et al (1999Hesselbach et al ( , 2002 describe the design of a novel actuator for the control of active hydrostatic bearings with electro-rheological and magneto-rheological fluids as active medium.…”

Load and stiffness of a planar ferrofluid pocket bearing

“…The planar ferrofluid bearing can be seen as a sort of hydrostatic bearing meaning that it does not need a relative movement between bearing faces to create a pressure field. Though the working principles are fundamentally different from the hydrostatic bearings of literature [22][23][24][25] that uses the magnetorheological effect and a pressure source to create a pressure field.…”