Piezoelectric Vibration Damping of Rolling Contact

Abstract

Machines, which contain heavy rotating objects like rolls, are always sensitive to vibrations. These vibrations can usually be limited by a conservative design approach, by carefully balancing the rolls and by applying high precise manufacturing techniques. More critical are machines, in which rolls are in direct rolling contact and a web-like thin material is fed through this contact. Such material manipulation is used for example in manufacturing of paper, thin foils and metal sheets or in rotary printing machines. In the first case the rolls today are covered by polymer materials in order to <br/>make the contact zone larger. This produces non-classical delay type resonances, when the roll cover is deformed in the contact zone, and this penetration profile is entering the contact zone again before complete recovery. This type of self-excited nonlinear vibration is difficult to control with purely traditional damping methods. Active damping methods bring more possibilities to adapt to different running conditions. The knowledge of existing delay-resonance cases calls for methods, actuators and control circuits, which have the required performance to move rolls of 10 tons mass at frequency band 100 Hz and peak-amplitude level 0,01 mm. After closing out many other possibilities, piezoelectric actuators have been proposed to such damping task and the purpose of this thesis is to evaluate the feasibility of commercially available actuators in this service. <br/><br/> Piezoelectric actuators are very promising for vibration control applications, because of their easy controllability, high performance in producing large magnitude forces in combination with small magnitude motion outputs in an extremely fast response time. The control is straightforward by simply variating the input voltage of the actuator. Classical damping approaches are bringing the possibility to utilize large control gains in a wide stability domain. When control voltage is generated based on the vibration data measured from the system, which is the case in active damping approach, a counter-force driven by the piezoactuator can be fed in the opposite phase to the vibrating system. It is also possible to build a passive vibration damper by connecting an electric circuit to the electrodes of the piezoelectric actuator in order to harvest the electric energy originating from the oscillating mechanical part of the system. These electric circuits can consist of a resistor, an inductor and a capacitance in different serial or parallel layouts. In order to make such circuit adaptive one, sophisticated control electronics is needed to on-line modify the adjustable circuit parameters.