The main advantages of piezoelectrical actuators as compared with conventional actuation concepts are their high precision, unsurpassable resolution in motion (sub tm-range) and in particular their excellent dynamic behavior. Especially the very short response time of solid state actuators gives rise to new opportunities in developing high dynamical systems with unsurpassable characteristics. Very compact systems with parallel motion and high accuracy in high displacements can be realized by integration of piezoelectrical actuators into special mechanical frames with lever transmission systems made of solid state hinges. For the design of such dynamical actuation systems, the knowledge of significant parameters such as resonance frequency, stiffness and damping as a function of the additional load is important. This problem can be reduced to the determination of a few general system parameters, which is outlined in detail. As a result of the complexity of compact electromechanical actuation systems this determination is not a simple calculation by means of commonly given material specific parameters or by the actuator moved masses. Exact acquisition of the characteristics of the complete transducersystem requires the use of a known mathematical model of piezoelectrical transducers and appropriate measurements. Essential parameters and characteristic values of piezoelectrical actuators are presented in order to develop a suitable measuring technique for general characterization of system parameters.
Novel concepts have been developed for miniaturized fiber optic switches. They are based on transmittive microoptical components. Here, beam deflection is achieved by moving microprisms or microlenses with the use of miniaturized actuators, mainly piezoelectric actuators. The deflected beam is directed to a microlens array where each ofthe lenslets couples the beam into one of the output fibers. The latter are also used as a regular array (fibers embedded in V-grooves in silicon). Such miniaturized switches can be realized with quite good optical parameters (insertion loss, cross talk), and also short switchthg time in the order of 1 ms. For prototype fabrication and future production of such switches integration methods of the microoptical components and the actuators play an important role. hi the case that all components are adjusted and fixed separately a rather complex procedure and equipment is required and a special optomechanical design must be used to ensure sufficient system stability.In order to decrease considerably the effort for system integration we tested several approaches for building at first certath subassemblies. This was especially successful for the lens aimy/fiber array integration as the most critical in the switch configuration. By using a lens array substrate thickness slightly smaller than the lenslet focal length we were able to fix the fiber alTay by gluing directly to the substrate surface opposite to the lenslet surface. We also started to integrate other optical functions, such as deflection and collimation into one quasimonolithic component by replication techniques. Here, both microprism and microlens stmctures have been replicated onto SELFOC microlenses.
The main advantages of piezoelectrical actuators are their high resolution in motion and their excellent dynamic behavior. Especially the very short response time of solid state actuators presents new opportunities in developing high dynamical systems with unsurpassable characteristics. New concepts of piezoelectrically driven microoptical devices, e.g. optical fiber switches, intensity modulators and choppers, can be developed. Very compact systems with parallel motion and high accuracy can be realized by the integration of piezoelectrical actuators into special mechanical frames with solid state hinges. Due to the combination of piezoelectrical actuators and mechanical lever transmission systems decisive advantages compared with other actuation concepts can be obtained. Appropriate displacements can be reached with comparatively small sized and thus low capacitance actuators. Low capacitance actuators enable the use of efficient electrical amplifiers for high dynamics. The behavior of the mechanical system is equivalent to a spring-mass-oscillator with a high quality factor. Because of their high stiffness the resonance frequencies of piezoelectrical actuators are quite high, but parasitic oscillations can appear if the element is driven with unsteady electrical functions e.g. square-or triangle-functions. Unwanted oscillations can deteriorate the general characteristics of dynamic actuators or in worst cases they can cause mechanical break down. New hybrid piezoelectrical actuator systems for dynamical applications are presented. General aspects of improving the dynamics ofpiezoelectrical systems and different methods for adequate passive damping will be discussed in this paper.
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