This paper presents a concept for a micro‐assembly station and shows different possibilities for increasing the positioning accuracy. The main part of the station consists of a spatial parallel structure with three translational degrees of freedom. An additional rotational axis is integrated into the working platform. This structure is constructed with low friction joints, which are nearly free of backlash. The construction of these high precision joints is presented and the characteristics of the robot such as workspace and resolution are discussed. After this an approach for increasing the accuracy of parallel robots by integrating flexure hinges into the structure is described.
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.
Piezoelectric actuators are considered as standard structural elements in Microsystems Technology. A piezoelectric transducer conventionally works as a pure linear motor ͑piezotranslator͒. If a rotation is required from the piezoelectric transducer, a transmission mechanism must be designed. This article presents a study on the development of a novel two-degree-of-freedom piezoelectric rotary-linear actuator system, including ͑1͒ conceptual design, ͑2͒ dynamic modeling, ͑3͒ control, and ͑4͒ prototype. The experimental validation of these concepts was performed. The preliminary result of the experiment has shown that the proposed concept works very well; in particular, the system has achieved ͑1͒ the linear displacement resolutions: 26 nm, ͑2͒ the angular displacement resolution: 0.019°, ͑3͒ the maximum driving force: 2.09 N, and ͑4͒ the maximum driving torque: 12.20 N mm.
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