Basic Designs of Piezoelectric PositioningDrives/Syste m s

Tube Design When the outside industrial electrode ofa tube is separated into four90°segments, placing differen- tial drive voltages ±U on opposing electrodes will lead to bending of one end. Such scanner tubes that flex in X and Y are widely used in scanning- probe microscopes, such asscanning tunneling micro-scopes. The scanning range can beestimated as follows:(Equation 27) Monolithic ceramic tubes areyet another form of piezo actu-ator. Tubes are silvered inside and out and operate on the transversal piezo effect. When an electric voltage is applied between the outer and inner diameter of a thin-walled tube, the tube contracts axially and radially. Axial contraction canbe estimated by the followingequation:(Equation 26 a) where:d where:
31 = strain coefficient (dis-placement normal topolarization direction) [m/V]L = length of the piezoceramic tube [m]U = operating voltage [V]d = wall thickness [m] x = scan range in X and Y(for symmetrical electro- des) [m]d
31 = strain coefficient (dis-placement normal to polarization direction) [m/V]U = differential operatingvoltage [V]L = length [m]ID = inside diameter [m]d = wall thickness [m]
Fig. 43. Tube actuator design. The radial displacement is theresult of the superposition ofincrease in wall thickness(Equation 26 b) and the tangen- tial contraction:(Equation 26 b) Tube actuators cannot gener-ate or withstand large forces.Application examples: Micro- dosing, nanoliter pumping, scanning microscopy, industrial ink jet printers. Examples: PT120, PT130, PT140 (p. 1-26). r = tube radius (Equation 26 c) where: d = change in wall thickness[m] d
33 = strain coefficient (fieldand displacement inpolarization direction)[m/V]U = operating voltage [V]
Fig. 44. Piezo scanner tube working principle. © PI 1998-2005. Subject to change w/o notice. Cat 118 05/09.17 4-40