Method for monitoring flexural vibrations of a piezoactuator

#This patent application is a national phase filing under section 371 of PCT/EP2011/065238, filed Sep. 2, 2011, which claims the priority of German patent application 10 2010 036 257.3, filed Sep. 3, 2010, each of which is incorporated herein by reference in its entirety.

#The present invention relates to a method for monitoring flexural vibrations in a mounted piezoactuator, and/or for mounting piezoactuators, with the aid of which the occurrence of flexural vibrations in the piezoactuator is avoided as far as possible.

#A piezoelectric actuator, also denoted as piezoactuator, is constructed with the aid of piezoelectric material and serves as mechanical drive for producing a movement by varying a dimension, specifically the length, of the piezoactuator by means of an electric voltage. A piezoactuator is typically constructed as a piezostack in which layers of a piezoelectric material of alternating polarization directions alternate with metal electrodes. The electrodes are connected alternately to one of two outer electrodes in the sequence of their arrangement.

#There follows a more precise description of examples of the method with the aid of the attached figures, in which:

#FIG. 1 shows a schematic arrangement of a mounted piezoactuator;

#FIG. 2 shows a flowchart relating to an exemplary embodiment of the method that is used to mount a piezoactuator; and

#FIG. 1 shows a schematic side view of an arrangement of a mounted piezoactuator 1 between holders 2. The holders 2 can be, for example, parts of an apparatus. The piezoactuator 1 is aligned in a longitudinal direction 3 in which it is possible to excite the longitudinal vibrations 4, which are required for the intended application of the piezoactuator 1. Transverse vibrations 5 can occur transverse to the direction of the longitudinal vibrations and lead to undesired or deleterious deformations of the piezoactuator 1.

#In order to eliminate the transverse vibrations as far as possible, the method having the method steps in accordance with the flow chart of FIG. 2 is applied, particularly when mounting the piezoactuator. The piezoactuator is mounted in a first method step 6. In a second method step 7, the measurement and evaluation of a small-signal spectrum of the mounted piezoactuator are conducted in the range of transverse vibrations that may occur. In a third method step 8 following thereupon or carried out at the same time as the second method step 7, the mounting of the piezoactuator is changed in order to reduce the transverse vibrations, in particular mounting parameters are adjusted or corrected until a stipulated impedance spectrum is achieved. An optimization can be undertaken by the repetition 9 of the second method step 7 and the third method step 8 so that, finally, a tolerable minimum of flexural vibrations is achieved or, ideally, the flexural vibrations are eliminated completely.

#FIG. 3 shows a diagram of an impedance spectrum. Plotted herein against the frequency f in Hz (hertz) is the absolute value |z| of the impedance in Ω (ohm). An impedance curve 10 measured before the optimization shows a plurality of parallel resonances 12 and series resonances 13. In the impedance curve 11 recorded after an optimization of the mounting of the piezoactuator, resonances occur at a greater frequency spacing, and relatively large local maxima and minima of the impedance occur only at high frequencies. It may be gathered therefrom that the occurrence of flexural vibrations was substantially reduced in the course of the optimization.