Piezoactuators Jiří Tůma 1
Domain Piezoelectric effect Direct piezoelectric effect discovered the brothers Pierre and Jacques Curie. They found that certain crystalline materials (ceramics) having the ability to polarize when subjected to an external force. Mechanical stress (compression and tension) generates electric charge and the electric field and external force in proportion. This phenomenon is used in sensors for dynamic forces. The inverse phenomenon lies in the fact that the electric field that is oriented parallel to the polarization direction, excites the mechanical expansion or contraction of the material. Piezoelectric effect is anisotropic, ie they act only in a certain direction. Dipole Mechanical stress - Electric voltage + Electric field Mechanical stress The behavior of the piezoelectric material in the unpolarized state (left) polarization after mechanical compression (middle), and after insertion of polarization of piezoelectric material to an electric field (right) 2
Piezoelectric coefficients and directions d ij : Strain coefficients [m/v]: strain developed (m/m) per electric field applied (V/m) or (due to the sensor / actuator properties of Piezo material). Charge output coefficients [C/N]: charge density developed (C/m²) per given stress (N/m²). g ij : Voltage coefficients or field output coefficients [Vm/N]: open circuit electric field developed (V/m) per applied mechanical stress (N/m²) or (due to the sensor / actuator properties of Piezo material) strain developed (m/m) per applied charge density (C/m²). k ij : Coupling coefficients [no Dimensionss]. The coefficients are energy ratios describing the conversion from mechanical to electrical energy or vice versa i strain direction j polarization direction http://www.physikinstrumente.com/tutorial/4_16.html polarization 1 4 3 Example: d 33 applies when the electric field is along the polarization axis (direction 3) and the strain (deflection) is along the same axis. d 31 applies if the electric field is in the same direction as before, but the strain is in the 1 axis (orthogonal to the polarization axis) 6 5 3 2
Piezoelectric materials The most popular material is a piezoelectric ceramic PZT (Lead-Zirconate-titanate) or polymer PVDF (Polyvinilidene fluoride). Material PZT PVDF Piezoelectric coefficients d 33 (10-12 C/N or m/v) d 31 (10-12 C/N or m/v) 300-150 -25 uniaxial d 31 =15 d 32 =3 biaxial d 31 =d 32 ==3 Maximum stress (MPa) Tensile stress Compression 600 80 200 200 Maximum intensity of the electric field (V/mm) 2000 5.10 5 Density (kg/m 3 ) 7600 1800 4
Piezoactuator types Three types of piezoelectric actuators are reported in literature Linear piezoelectric actuator Linear motor o Inchworm motors o Stick and slip actuators o Traveling wave ultrasonic motors Piezoelectric benders 5
Linear piezoelectric actuator Displacement of piezoelectric actuators L d33nu ΔL L E3L d 31 t n U L ΔL 2 1 U L Piezoelectric stack Laminar piezoactuator 6
Diamond piezoactuator Noliac piezo Free stroke [μm] 10000 Plate benders Ring benders Stacked actuator 1000 100 Wire 10 1 0.1 0.1 Single actuator 1 10 100 1000 10000 100000 Blocking force [N] Piezoelectric actuator Output member Fixed member Actuator pair Tension member 7
Application piezoactuator Active members in the Pratt truss with piezoactuators U Simple lever-arm mechanism 8
Piezoactuator design Stack actuator ceramic plates Thickness 0,1 mm.. 100 V, LVPZ - Low voltage piezo Thickness 1 mm.. 1000 V, HVPZ - High voltage piezo The maximum relative displacement is between 0,1 and 0,13 %, what means that the actuator of the 100 mm length has the absolute travel of 100 μm. The hysteresis of piezoactuators is up to 15%. Blocking force Direction of increasing voltage Two designs of piezoactuators: Some piezoactuator are designed for open-loop positioning tasks. They have only the voltage input Closed loop piezoactuator with the voltage input and the SGS-position sensors. Catalogue parameters 0 0 Travel travel (free stroke) force (blocking) 9
Products of Physic Instrument company Linear piezoelectric actuator E-504 Piezo Amplifier Module E-509 Signal Conditioner / Piezo Servo Module 10
Piezoactuators of the P-844 / P-845 type Outstanding Lifetime Due to PICMA Piezo Ceramic Stacks Travel Range to 90 µm Pushing Forces to 3000 N Pulling Forces to 700 N Sub-Millisecond Response, Sub-Nanometer Resolution Vacuum Version, Optional Water-Resistant Case 11
Technical Data 12
Movable bushing for a sleeve bearing Flexible tip 13
Y [micrometer] Active vibration control -100-150 -200-250 -100-300 0 5 10 15 20 25-300 -250-200-150 Time [s] X [micrometer] Bushing Load Rotor system Proximity probes Journal position Piezoelectric actuators Amplifier Controller dspace Reference 14
Piezo actuator drive (PAD) Noliac piezo Slow and precise motion /0 to 60 RPM) Kinematic principle with microtoothing Siemens 15
High-speed piezo motor actuator PI M-674 RodDrive: Integrated High- Speed Piezo Motor Actuator Drive-Component for Integration into Automation & Positioning Systems Flexible Choice of Travel Ranges to Several 100 mm Flexible Choice of Push/Pull Forces to Several 10 N Minimum Incremental Motion to 0.05 µm Velocity to 400 mm/s Self-Locking w/o Head Build Up 16
Inchworm motors 17
Stick and slip actuator Seismic mass Initial position piezo Moving object Starting position Jaws 80-Pitch Screw Seismic mass Slow extension piezo Moving object Slow rising Piezo Seismic mass Rapid contraction piezo Moving object Δx Quick return to starting position 18
Thank you for your attention 19