Docstoc

Piezo_Actuator_Materials_Tutorial

Document Sample
Piezo_Actuator_Materials_Tutorial Powered By Docstoc
					Piezo Ceramic Actuators

   & Custom Subassemblies




                            +

                            +
                            +

                            +
                            +

                            +
                            +
                                                Piezoelectric Actuator Materials

                                            Introduction
                                            PI Ceramic piezoelectric actua-      Since the piezoelectric effect                (PZT), with improved proper-
                                            tors offer today’s motion engi-      exhibited by natural mono-                    ties have been developed.
                                            neer and scientist a practical       crystalline materials such as                 PZT ceramics are available
                                            way to achieve extremely high        quartz, tourmaline, Rochelle                  in many variations and
                                            positioning accuracy, shortest       salt, etc. is very small, poly-               are by far the most widely
                                            possible response times, best        crystalline piezoelectric cera-               used materials for piezo-
                                            dynamic operation and largest        mic materials, such as lead                   electric actuator applications
                                            forces in a wide variety of          (plumbum) zirconate titanate                  today.
                                            applications. Presently piezo-
                                            electric actuator based motion
                                            systems increasingly replace
                                            classical motion technolo-
                                            gies—improving products in
                                            terms of miniaturization, preci-
                                            sion and throughput. In addi-
                                            tion, the unique features of
                                            piezoelectric actuators will trig-
                                            ger the development of motion
                                            equipment that could not even
                                            exist without this technology.
                                            PI Ceramic, a member of the
                                                                                  The poling process in ferroelectric ceramics. Electric dipoles: (1) unpoled ferro-
                                            PI Group, offers the largest          electric ceramic, (2) during and (3) after poling (piezoelectric ceramic).
                                            selection worldwide of re-
                                            search- and industrial-reliability
                                            piezoelectric actuators. In addi-
                                            tion to the standard piezoelec-
PZT unit cell: 1) Perovskite-type lead      tric products presented in this
zirconate titanate (PZT) unit cell
in the symmetric cubic state above the      short catalog, we focus on cus-
Curie temperature.                          tom designs tailored to our
2) Tetragonally distorted unit cell below
the Curie temperature.                      customer’s requirements.
                                            The highly vertically integrated
                                            structure of the PI Group
                                            allows control of each manu-
                                            facturing step, beginning at the
                                            raw material up to finished                                                              Applications
                                            NanoPositioning systems, in-                                                             for Piezoelectric
                                            cluding electronic drivers,                                                              Actuators
                                            amplifiers and controllers. This                                                         s Optics and Photonics
                                            comprehensive development                                                                s Precision Mechanics
                                            and manufacturing know-how                                                               s Life Sciences, Medicine,
                                            of electromechanical compo-                                                                Biology
                                            nents and systems is unique in                                                           s Vibration Cancellation
                                            the world.                                                                               s Adaptronics
                                                                                                                                     s Mechanical Engineering
                                                                                                                                     s Measuring Technologies
                                                                                                                                     s Microelectronics
                                                                                                                                     s Disk Drive




                                                                                                                                                                       39
           Piezoelectric Actuator Materials (cont.)

     Below the so called Curie tem-                          taneous polarization in the
     perature TC (see Table 1) the                           direction of the poling field and
                                                                                                                 PIC 151      PIC 151 is a modified lead zirconate titanate (PZT)
     ionic lattice structure in the                          shows an overall piezoelectric
                                                                                                                              ceramic with high permittivity, coupling factor
     PZT crystallites becomes dis-                           effect. For some PZT ceram-
                                                                                                                              and charge constant. It is thus well-suited for
     torted and asymmetric (with                             ics, it is necessary to perform
                                                                                                                              PICA-Stack actuators and bender applications.
     an axis of polarity) and, addi-                         the poling process at elevated
                                                                                                                              Due to the high coupling factor and the low me-
     tionally, exhibits spontaneous                          temperatures.
                                                                                                                              chanical quality factor it is also recommended for
     polarization. One result is that                        Table 1 shows the specifica-                                     low frequency and pulsed ultrasonic applications.
     the discrete PZT crystallites                           tions of different PI Ceramic
     become piezoelectric. How-                              PZT piezoelectric materials.                        PIC 255      PIC 255 is a modified lead zirconate titanate (PZT)
     ever, the statistical distribution                                                                                       with a high Curie temperature, coupling factor
                                                             Ceramic types PIC 151 and PIC
     of the grain orientations in the                                                                                         and charge constant. The material is optimized
                                                             255 are the PI Ceramic stan-
     ceramic will cause the macro-                                                                                            for actuator application under dynamic or high-
                                                             dard actuator materials which
     scopic behavior to be non-                                                                                               temperature working conditions. Because of its
                                                             are used for the PICA-Stack
     piezoelectric.                                                                                                           high coercive field, PIC 255 can be used for bipo-
                                                             and PICA-Power actuators.
     An additional property, the fer-                        These materials show the                                         lar-driving-mode applications as well as for PICA-
     roelectric nature of the PZT                            highest piezoelectric deforma-                                   Shear actuators. Due to its high coupling effi-
     material, will help to solve this                       tion constants, d33, d31 and d15                                 ciency, low mechanical quality factor and low
     problem. When an intense                                (see Table 1) and, conse-                                        temperature coefficient, it is also well-suited for
     electric field is applied to the                        quently, the largest induced                                     low-power ultrasonic transducers, non-resonant
     ceramic, the different lattice                          strain values at comparable                                      broadband devices, sensors for load and sound
     orientations of the individual                          field strengths. These compo-                                    transducers and is preferred for vacuum applica-
     ceramic grains can be perma-                            sitions incorporate all our long-                                tions.
     nently altered. As a result of                          term experience in piezoelec-
     this “poling process” the                               tric actuator development,                          PIC 252      PIC 252 is a low-sintering modification of
     ceramic is accorded a net                               manufacturing and applica-                                       PIC 255, especially used for multilayer actuators.
     orientation of its internal, spon-                      tion.


     Table 1: PI Ceramic Standard PZT Materials
     Parameter                             Unit                                PIC 151   PIC 155   PIC 255   PIC 181   PIC 241     PIC 300
     Density                                                  g/cm3            7.8       7.8       7.8       7.8       7.8         7.8
     Curie Temperature                     TC                 °C               250       345       350       330       270         370
     Relative Dielectric Permittivity       33
                                                    /
                                                    T
                                                         0
                                                                               2400      1450      1750      1200      1500        1050
                                            11
                                                    /
                                                    T
                                                         0
                                                                               1980      1400      1650      1500      1550        950
     Dielectric Dissipation Factor         tan                10-3             20        20        20        5         5           3
     Electromechanical Coupling Factor     kp                                  0.62      0.62      0.62      0.56      0.55        0.48
                                           kt                                  0.53      0.48                0.46      0.46        0.43
                                           k31                                 0.38      0.35      0.35      0.32      0.32        0.25
                                           k33                                 0.69      0.69      0.69      0.66      0.64        0.46
                                           k1   5
                                                                                                   0.xx      0.63      0.63        0.32
     Mechanical Quality Factor             Qm                                  100       80        80        2000      1200        1400
     Frequency Constant                    Np                 Hzm              1950      1960      2000      2270      2190        2350
                                           N1                 Hzm              1500      1500      1420      1640      1590        1700
                                           N3                 Hzm              1750      1780                2010      1550        1700
                                           Nt                 Hzm              1950      1990      2000      2110      2140        2100
     Piezoelectric Deformation             d31                pm/V             -210      -165      -180      -120      -130        -80
     (Charge) Coefficient                  d33                pm/V             500       360       400       265       290         155
                                           d15                pm/V                                 500       475       265         155
     Piezoelectric Voltage Coefficient     g31                10-3 Vm/N        -11.5     -12.9     -11.3     -11.2     -9.8        -9.5
                                           g33                10-3 Vm/N        22        27        25        25        21          16
     Elastic Compliance Coefficient        s11E               10-12 m2/N       15.0      15.6      16.1      11.8      12.6        11.1
                                           s33E               10-12 m2/N       19.0      19.7      20.7      14.2      14.3        11.8
     Elastic Stiffness Coefficient         c3 D 3
                                                              1010 N/m2        10.0      11.1      xx        16.6      13.8        16.4
     Temperature Coefficient               TC           33
                                                              10-3/K           6         6         4         3         3           2

     This data was measured according to EN50324 I/II.


                                                                       http://www.piceramic.com
40                                                                          info@piceramic.com
Layers in a stacked piezoelectric   Polymer coated stacked actuator (PICA-Stack) and ceramic insulated cofired     Layers in a cofired monolithic piezo-
actuator.                           actuator (PICMA™).                                                             electric actuator.


                                    PICMA™ and PICA:                            In contrast, PICMA™ actuators
                                    Cofired and Stacked                         are manufactured using a cofir-
                                    Piezoelectric Actuators                     ing technology. This advanced
                                    Two main types of piezo actua-              process allows for multilayer
                                    tors are available: cofired                 designs which have individual
                                    PICMA™ actuators requiring                  layer thicknesses of just 20 to
                                    about 100 volts for full motion,            100 µm. Hence PICMA™ actu-
                                    and glued PICA-Stack actua-                 ators require nominal voltages
                                    tors, requiring up to 1000 volts            of only 40 to 200 V.
                                    for full extension.                         Both types of piezoelectric
                                    The maximum electrical field                actuators can be used for
                                    which can be recommended                    many applications: PICMA™
                                    for reliable operation of PZT               actuators facilitate drive elec-
                                    ceramics is on the order of 1 to            tronics design and can be pro-
                                    2 kV/mm. To keep the operat-                duced at reasonable costs in
                                    ing voltage within practical lim-           standard sizes and large quan-
                                    its, actuators consist of thin              tities. Due to its manufactur-
                                    layers of electroactive ceramic             ing technology, PICA-Stack
                                    material which are electrically             actuators can be designed
                                    connected in parallel. The net              with larger cross-sections for
                                    positive displacement is the                high-load applications. They
                                    sum of the displacements of                 can easily lift weights of up to
                                    the individual layers. The thick-           several tons. Additionally, the
                                    ness of the individual layers               PICA-Stack technology is very
                                    determines the maximum ope-                 flexible in terms of special
                                    rating voltage of the actuator.             actuator shapes and sizes.
                                    Glued PICA-Stack piezoelectric
                                    actuators consist of separate
                                    ceramic discs with a thickness
                                    of 0.2 to 1.0 mm. These val-
                                    ues, which are limited by the
                                    manufacturing technology, re-
                                    sult in nominal driving voltages                                               Comparison of a long-travel, high-load
                                                                                                                   piezoelectric actuator and a compact
                                    of up to 1000 V.                                                               actuator for small loads.



                                                                                                                                                           41
             Displacement Modes of Piezoelectric Actuators

     For small electric driving sig-                              Table 2 illustrates the different                        tric field, the poling direction as   actuator is of a longitudinal or
     nals the displacement L of a                                 piezoelectric actuator displace-                         well as the mechanical strain         transverse type depends only
     bulk ceramic material sample                                 ment modes for PZT ceramics.                             or displacement, have the             on the displacement which is
     can be calculated from the fol-                                                                                       same orientation. Keep in mind        used. The shear mode is differ-
                                                                  By convention, index 3 is
     lowing equation:                                                                                                      that the longitudinal deforma-        ent, because in it the electric
                                                                  always aligned in the poling
     (Equation 1)                                                                                                          tion is always accompanied by         field and the poling direction
                                                                  direction of the material. The
                                                                                                                           a transverse deformation.             are perpendicular to each
          Lj = Sj L0 = dij Ei L0                                  small-signal values of the rele-
                                                                                                                           When driven with a positive           other. The PICA-Shear actua-
                                                                  vant piezoelectric deformation
     where:                                                                                                                voltage, U3, the material             tors use the shear displace-
                                                                  coefficients d33, d31 and d15 for
     Sj    mechanical strain in direction j (strain is                                                                     expands in the longitudinal           ment in the poling direction.
           defined as relative length change,                     the different actuator materials
            L/L) [dimensionless]
                                                                                                                           direction while at the same           To get the displacements of
                                                                  can be found in Table 1.
     L0 material thickness in field direction [m]
                                                                                                                           time shrinking in the trans-          the individual layers in a multi-
     Ei    electrical field in direction i [V/m]
                                                                  The longitudinal mode is used                            verse direction, as can be seen       layer actuator to add while
     dij piezoelectric deformation coefficient
                                                                  for most linear actuators in this                        from the material deformation         using the appropriate electrical
         [pm/V]                                                   catalog. In this mode, the elec-                         figures in Table 1. Whether the       contact configuration, the pol-
                                                                                                                                                                 ing orientations of adjacent lay-
                                                                                                                                                                 ers have to alternate (see
                                                                                                                                                                 Table 2).

     Table 2: Piezoelectric actuator modes in PZT ceramics.                                                                                                      Equation 1 is applicable for
     Mode                        Material deformation                                    Multilayer actuator configuration              Remarks
                                                                                                                                                                 small electric signals only,
     Longitudinal                                                                                                                       The longitudinal         because the piezoelectric
                                                                                                                                 ∆L     mode is the most
                                                                                                                                        important. It is
                                                                                                                                                                 deformation coefficients, dij,
                                                                                                       E           P                    used for PICMA™-,        for PZT ceramics show strong
                                            -                                   ∆L           U
                                                                                                       E           P
                                                                                                                                        PICA-Stack-,
                                                                                                                                                                 electric field dependency. In
                                                                                                                                        PICA-Thru-,
                                        U                                      L0                                  P                    PICA-Power- and
                                                            E3    P                                    E
                                                                                                                                        the Z-axis of            fact, the coefficient value can
                                3           +                                            L             E           P                    PICA-Shear actua-
                                        2                                                                                                                        increase by a factor of 1.5 to 2
                                                                                                                                        tors.
                                                    i                                                  E           P
                                            1
                                                                                                                                                                 compared to the small-signal
                                                                                                       E           P
                                                                                                                                                                 value in Table 1 when the nom-
                                                                                                                                                                 inal voltage of the actuator is
                                 relevant deformation coefficient: d33
                                                                                                                                                                 applied. This increase leads to
     Transverse                                                                                                                         This mode is used
                                                                                                                                        for standard bending
                                                                                                                                                                 a very high large-signal de-
                                                                          ∆L                                                     ∆L     actuators (bimorphs
                                                                                                                                        or trimorphs) as
                                                                                                                                                                 formation coefficient d15 of
                                                                                                                                        well as for pure con-    1100 pm/V at an amplitude of
                                                                                                                                        tractors and tubes.
                                                -                                                           E          P                                         250 V for PICA-Shear actua-
                                            U                                                U
                                                             E3    P            L0                          E          P                                         tors, which are made of
                                    3       +
                                            2                                                               E          P                                         PIC 255.
                                                1       i                                                   E          P


                                 relevant deformation coefficient: d31

     Shear                                                                                                                              This mode is used
                                                                                                                               ∆L       for the X- and Y-axes
                                                                                                                                        of the PICA-Shear
                                                                           ∆L                                                           actuators.
                                                                                                               E           P
                                                -                                                U
                                                                                                            E          P
                                            U                                       L0
                                                            E1     P                                        E          P                                             where:
                                 1
                                        2
                                            +                                                              E           P
                                                                                                                                                                     Ei   vector component of the electric
                                                3   i                                                   E          P                                                      field
                                                                                                        E          P                                                 S    polarization direction

                                 relevant deformation coefficient: d15
                                                                                                                                                                     U    applied voltage
                                                                                                                                                                     i    current




                                                                        http://www.piceramic.com
42                                                                              info@piceramic.com
                                     Mechanical Considerations

                                Stiffness
                                When calculating force genera-          This narrow definition does        Since PZT ceramics are active
                                tion, resonant frequency, sys-          not apply for PZT ceramics         materials, they produce an
                                tem response, etc., piezo stiff-        because large- and small-signal    electrical response (charge)
                                ness is an important parame-            conditions, static and dynamic     when mechanically stressed
                                ter. In solid bodies stiffness          operation, open and shorted        (e.g. in dynamic operation).
                                depends on the Young’s modu-            electrodes must all be distin-     When the electric charge can-
                                lus, the ratio of stress (force         guished. The poling process of     not be drained from the ceram-
                                per unit area) to strain (change        PZT ceramics leaves a rema-        ics, it generates a counterforce
                                in length per unit length). It is       nent strain in the material        to the mechanical stress. This
                                generally described by the              which depends on the magni-        is why a piezoelectric ceramic
                                spring constant kT, relating the        tude of polarization. The polar-   with open electrodes appears
                                influence of an external force          ization is affected by both the    stiffer than one with shorted
                                to the dimensional change of            drive voltage and external         electrodes. With actuators
                                the body.                               forces. When an external force     (compound structures of dif-
                                                                        is applied to poled PZT ceram-     ferent active and passive
                                                                        ics, the dimensional change        materials) the scenario is even
                                                                        depends on the stiffness of        more complicated.
                                                                        the ceramic material and the
                                                                                                           The above discussion explains
                                                                        change of the remanent strain
                                                                                                           why the (dynamically meas-
                                                                        (caused by the polarization
                                                                                                           ured) resonant frequency of a
                                                                        change). The equation LN = F/kT
                                                                                                           piezo actuator differs from the
                                                                        is only valid for small forces
                                                                                                           statically measured stiffness
                                                                        and small signal conditions.
                                                                                                           using the equation
                                                                        For larger forces, an additional
                                                                        term describing the influence      (Equation 2)
                                                                        of the polarization changes,             1        kT
                                                                                                                          ___
                                                                        must be superimposed on            f0 = ___       meff
                                                                                                                2
                                                                        stiffness (kT).
                                                                                                           Since stiffness values of piezo
                                                                                                           actuators are not constants
                                                                                                           they can only be used to esti-
Quasi-static characteristic mechanical stress/strain curves for piezo
                                                                                                           mate the behavior under cer-
ceramic actuators and the derived stiffness values (note that
displacement is negative because the applied force is compressive).                                        tain conditions and to compare
Curve 1 is with the nominal operating voltage (voltage giving nominal
                                                                                                           different piezoelectric actua-
maximum displacement) on the electrodes, Curve 2 is with the elec-
trodes shorted (showing ceramics after depolarization).                                                    tors of one manufacturer.




                                                                                                                                        43
                             Mechanical Considerations . . . (cont.)

                         Load Capacity
                         PI Ceramic actuators can            Like any other actuator, a
                         withstand high pushing forces       piezoelectric actuator is com-
                         and carry loads to several          pressed when a force is
                         tons. Even when loaded, the         applied. Two cases must be
                         actuator will not lose any travel   considered when operating
                         as long as the maximum load         piezoelectric actuators with a
                         capacity is not exceeded. Load      load:
                         capacity and force generation
                                                             a) The load remains constant
                         must be distinguished.
                                                                during the motion process.
                                                             b) The load changes during the
                                                                motion process.




                         a   Constant Force                  b   Changing Force                        (Equation 4)
                                                                                                                       kT
                         Zero point is offset                (Force = Function of L, e.g. a             LR          (
                                                                                                                L0 1- ______
                                                                                                                      kT+kS      )
                                  A mass is installed        spring load):x4261}tbk{



     Case a,                                                                                           Maximum loss of displace-
                                  on the actuator which      Displacement is reduced
     zero-point offset                                                                     x426}tbk{
                                                                                                       ment due to external spring
     with constant                applies a force F =        For PZT operation with spring
     force (mass).                                                                                     force. In the case where the
                                  M · g (M: mass, g:         loads different rules apply. The          spring stiffness ks is     (infi-
                                  acceleration due to        “spring” could be an I-beam               nitely rigid restraint) the PZT
                                  gravity). With constant    or a single fiber, each with its          only acts as a force generator.
                   M              force the zero point       characteristic stiffness or
                                  will be offset by an       spring constant. Part of the
                                  amount LN          F/kT,   displacement ge-
                                  where kT equals the        nerated by the
                                  stiffness of the PZT       piezo effect is lost
                                  actuator. If this force    due to the elastic-
                         is within the specified load        ity of the piezo
                         limit (see technical data table),   element. The total
                         full displacement can be            available displace-
                         obtained at full operating volt-    ment can be
                         age.                                related to the                               Case b,
                                                             spring stiffness                             effective displacement of a piezo
                                                                                                          actuator acting against a spring
                                                             by the following                             load.
                                                             equations:
                                                             (Equation 3)
                                                                          kT
                                                               L      (
                                                                    L0 ______
                                                                        kT + kS        )
                                                             Maximum displacement of a
                                                             piezo actuator acting against a
                                                             spring load.

                               http://www.piceramic.com
44                                   info@piceramic.com
Force Generation
In most applications, PZT actu-
ators are used to produce dis-
placement. If used in a
restraint, they can generate
forces. Force generation is
always coupled with a reduc-
tion in displacement. The max-
imum force (blocked force) a
piezo actuator can generate
depends on its stiffness and
maximum displacement.
(Equation 5)
Fmax      kT L0
Maximum force that can be
generated in an infinitely rigid
restraint (infinite spring con-
stant). At maximum force gen-
eration, displacement is zero
where:
 L0    = max. nominal displacement with-
         out external force or restraint [m]
kT     = PZT actuator stiffness [N/m]          Force generation vs. displacement of a piezo actuator (displacement 30 µm,
                                               stiffness 200 N/µm) at various operating voltages. The points where the dashed
                                               lines (external spring curves) intersect the actuator force/displacement curves
In actual applications the load                determine the force and displacement for a given setup with an external spring.
                                               Maximum work can be done when the stiffness of the actuator and external
spring constant can be larger                  spring are identical.
or smaller than the actuator
spring constant. The force
Fmax eff generated by the actua-
tor working against an elastic
restraint is:   x4239}tbk{




(Equation 6)
                      kT
F eff
 max
            kT L0 1- _____
                     kT+kS   (     )
Effective force a piezo actuator
can generate in a yielding
restraint
where:
 L0 = displacement (without external force
      or restraint) [m]
kT     = PZT actuator stiffness [N/m]
ks     = stiffness of external spring [N/m]




                                                                                                                                 45
                                                       Dynamic Behavior

                                                 How Fast Can a Piezo                 Resonant Frequency                           (Equation 8)
     For more information on                     Actuator Expand?
     advanced driving tech-                      Fast response is one of the
                                                                                      Piezoelectric actuators are not
                                                                                      designed to be driven at reso-
                                                                                                                                   f0 =   ( ___)
                                                                                                                                            2
                                                                                                                                             1            k  T
                                                                                                                                                         _______
                                                                                                                                                          meff
     niques such as Input-                       desirable features of piezo          nant frequency at the nominal                Resonant frequency of an ideal
     Shaping, Preshaping, and                    actuators. A rapid drive-voltage     voltage and load. This will                  spring/mass system
     Dynamic Linearization,                      change results in a rapid posi-      result in high dynamic forces                where:
     see the PI NanoPosition-                    tion change. This property is        which might damage the struc-                f0     = resonant frequency [Hz]
     ing Catalog, or website                     necessary in applications such       tural integrity of the ceramic               kT     = actuator stiffness [N/m]
     www.pi.ws.                                  as switching of valves/shut-         material (see Handling Pre-
                                                                                                                                   meff   = effective mass (about 1/3 of the
                                                 ters, generation of shock-           cautions p. 42).                                      mass of the ceramic stack plus any
                                                 waves, vibration cancellation                                                              installed end pieces) [kg]
                                                                                      In general, the resonant fre-
                                                 systems, etc. A piezo actuator
                                                                                      quency of any spring/mass                    Resonant frequencies of in-
                                                 can reach its nominal displace-
                                                                                      system is a function of its stiff-           dustrial-reliability piezoelec-
                                                 ment in approximately 1/3 of
                                                                                      ness and effective mass. The                 tric actuators range from
                                                 the period of the resonant fre-
                                                                                      resonant frequency given in                  100 kHz for actuators with a
                                                 quency.
                                                                                      the technical data tables                    total travel of a few microns to
                                                 (Equation 7)                         always refers to the unloaded                a few kilohertz for actuators
                                                 Tmin    1
                                                        ___                           actuators .                                  with a travel of more than
                                                         3f0                                                                       100 microns.
                                                 Rise times on the order of
                                                 microseconds and accelera-
                                                 tions of more than 10,000 g’s
                                                 are possible.




 Response of an undamped, lever-amplified PZT actuator (low resonant frequency)
 to a rapid drive-voltage change. Driving techniques such as InputShaping ®
 eliminate self generated ringing and allow settling in one period of the resonant
 frequency.



                                                                                       Effective mass of an actuator fixed at one end.




                                                         http://www.piceramic.com
46                                                               info@piceramic.com
                                                Driving Piezoelectric Actuators

                                            Piezoelectric actuators operate     maximum on the order of 10 %                   the nominal voltage, the loss
                                            as capacitive loads. The leak-      to 15% at nominal voltage. For                 factor becomes larger as well.
                                            age current values of PI            shear actuators these values                   It can increase up to 12 % to
                                            Ceramic actuators are very          can be even higher.                            15 % for longitudinal actuators
                                            low, because the effective          The same material mecha-                       or even more for shear actua-
                                            large-signal volume resistivity     nisms responsible for hystere-                 tors. The dielectric loss is
                                            of the materials used is very       sis are responsible for the                    closely related to the hystersis.
                                            large. Therefore, the actuators     creep phenomena in piezo-                      When considering the accom-
                                            consume almost no energy in         electric actuators. Driven by a                panying quadratic increase of
                                            static applications and conse-      step signal, the actuator will                 the power with the field, and,
                                            quently they produce virtually      follow the increasing voltage                  additionally, the increase in
                                            no heat.                            amplitude very closely, but it                 actuator capacitance with field
                                            In dynamic applications, the        will continue to change in                     by a factor of 1.5 to 2, self-
                                            power consumption increases         dimension slowly afterwards.                   heating effects can become
                                            linearly with the frequency         The creep rate decreases loga-                 significant during cycling with
                                            and the actuator capacitance.       rithmically with time. The over-               higher repetition rates at
                                            Note that actuator capacitance      all behavior is described by the               higher fields. Besides altering
                                            varies with respect to the          following equation:                            the performance specifica-
                                            applied voltage.                                                                   tions, this self-heating effect
                                                                                (Equation 9)                                   can possibly destroy the actua-
                                            Close contact with the manu-
                                            facturer will assure that
                                                                                 L(t)               [
                                                                                              Lt = 0.1 1+     ( )]
                                                                                                                t
                                                                                                            lg ___
                                                                                                               0.1
                                                                                                                               tor, should the temperature
                                                                                                                               increase above the allowed
                                            the right actuator design is        where:
                                                                                                                               maximum.
                                            chosen for your application!         L(t)     ... displacement as a function of
                                                                                              time [m]                         Because the actual maximum
                                                                                 Lt=0.1   ... displacement at 0.1 seconds      temperature increase inside
                                            Hysteresis and Creep                              after the voltage step is com-
                                                                                              plete [m]                        the actuator depends on sev-
                                            The displacement hysteresis                                                        eral factors like thermal cou-
                                                                                          ... creep factor, dependent on the
                                            and creep in piezoelectric actu-                  properties of the actuator (on   pling of the actuator to its
                                            ators can either be completely                    the order of 0.01 to 0.02)
                                                                                                                               mechanical environment, the
                                            eliminated by closed-loop           Again, the creep of the actua-                 geometry of the actuator itself,
                                            operation, or significantly         tor can be completely elimi-                   or whether it is driven with
                                            reduced by advanced open-           nated by closed-loop opera-                    forced convection or not, there
                                            loop driving techniques. Open-      tion.                                          is no general rule for the
                                            loop piezoelectric actuators                                                       driving power of a specific
Hysteresis curves of an open-loop piezo
actuator for various peak voltages.
                                            exhibit hysteresis in their         Actuator Self-Heating                          actuator.
The hysteresis is related to the distance   dielectric and electromechani-      When a piezoelectric actuator
moved.                                                                                                                         Close contact with the man-
                                            cal large signal-characteristics.   is driven by an AC voltage, the                ufacturer will help you to
                                            This hysteresis is mainly           apparent electric power con-                   find a reliable solution for
                                            caused by microscopic ferro-        sists primarily of reactive                    your application problem.
                                            electric polarization effects and   power, because of the capaci-
                                            is thus inherent to the materi-     tive nature of the actuator.
                                            als used.                           Even for small electric signals,
                                            Hysteresis increases with the       however, the dielectric loss
                                            electric field or voltage ampli-    factor, tan —the relation
                                            tude with which the actuator is     between true power and reac-
                                            driven. The “split” in the volt-    tive power—is on the order of
                                            age-displacement curves (see        2 % for actuators made of PZT
Creep of open-loop motion after a 60 µm
change in length as a function of time.     figure “Hysteresis curves”)         ceramics. When the signal
Creep is on the order of 1 % of the last    typically starts at 2 % for very    increases up to the peak-to-
commanded motion per time decade.
                                            small signals and reaches its       peak value corresponding to



                                                                                                                                                             47
                                                        Open- and Closed-Loop Operation

                                                  Piezoelectric actuators have no      Piezoelectric actuators can be
                                                  “stick slip” effect and there-       operated in open-loop and
     For more information on
                                                  fore offer theoretically un-         closed-loop modes. In open-
     advanced driving tech-
                                                  limited resolution. In practice,     loop, displacement roughly
     niques, closed-loop oper-
                                                  actual resolution can be limited     corresponds to the drive volt-
     ation, controllers and
                                                  by a number of factors such as       age. This mode is ideal when
     nanopositioning sensors,
                                                  driving amplifier noise, sensor      the absolute position accuracy
     see the PI NanoPosition-
                                                  and control electronics quality,     is not critical. Open-loop piezo-
     ing Catalog, or website
                                                  which may exhibit noise and          electric actuators exhibit hys-
     www.pi.ws.
                                                  sensitivity to EMI, as well as       teresis and creep behavior, like
                                                  mechanical parameters such           other open-loop positioning
                                                  as mounting precision, preload-      systems.
                                                  ing, guiding and mechanical          Position servo-control elimi-
                                                  amplification mechanisms.            nates nonlinear behavior of
                                                                                       PZT ceramics and is the key to
                                                                                       highly repeatable motion.
                                                                                       PI offers the largest selection
                                                                                       of closed-loop piezo mecha-
                                                                                       nisms and control electronics
                                                                                       worldwide. The advantages of
                                                                                       position servo-control are:
                                                                                       s Very good linearity,
                                                                                         stability, repeatability
                                                                                         and accuracy
                                                                                       s Automatic compensation
                                                                                         for varying loads or forces
                                                                                       s Virtually infinite stiffness
                                                                                         (within load limits)
      Response of a PICA Stack piezo translator to a ± 1V, 200 Hz triangular drive
      signal. Note that one division is only 2 nanometers.                             s Elimination of hysteresis
                                                                                         and creep effects




                                                                                                                                   Ctrl Input / V

                                                                                        Open-loop vs. closed-loop performance graph of a typical
                                                                                        PI PZT actuator (supplied with each closed-loop system).




                                                           http://www.piceramic.com
48                                                                info@piceramic.com
                                                         Lifetime of PI Ceramic
                                                         Piezoelectric Actuators

                                                    The lifetime of a piezoelectric      after billions (1,000,000,000) of
                                                    actuator is not limited by wear      cycles. There is no generic
                                                                                                                             Please contact your PI
                                                    and tear. All PI Ceramic piezo       equation to determine the
                                                                                                                             sales & application engi-
                                                    actuators are specifically           lifetime because of the
                                                                                                                             neer for further infor-
                                                    designed for high-duty-cycle         many parameters such as
                                                                                                                             mation on lifetime and
                                                    applications. All materials used     temperature, humidity, volt-
                                                                                                                             handling issues.
                                                    are matched for robustness           age, acceleration, load, operat-
                                                    and lifetime. Endurance tests        ing    frequency,      insulation
                                                    on PI Ceramic actuators prove        materials, etc. which have an
                                                    consistent performance, even         influence.
                                                                                         PICMA™-type actuators have
                                                                                         advantages over other piezo
                                                                                         actuators, especially in humid
                                                                                         environments. Their mono-
                                                                                         lithic, ceramic-insulated design
                                                                                         blocks the diffusion of water
                                                                                         molecules into the insulation
                                                                                         layer, the major cause of
                                                                                         dielectric breakdown.
                                                                                         PI Ceramic invests consider-
                                                                                         able energy in investigating
                                                                                         and continually improving actu-
                                                                                         ator lifetime. The design of the
                                                                                         piezoelectric actuators in this
                                                                                         catalog reflect several decades
                                                                                         of experience in with thou-
PICMA™ piezo actuators (bottom curve) compared with conventional multilayer              sands of industrial piezo actua-
actuators with polymer insulation (top curve). PICMA™ Actuators are not affected         tor applications. Another result
by the high-humidity test conditions. Conventional piezo actuators exhibit in-
creased leakage current after only a few hours. Leakage current is an indication         of this experience is the
of insulation quality and expected lifetime. Test conditions: U = 100 VDC ; T = 25 °C;   “Handling Precautions” in the
Relative Humidity = 70%
                                                                                         following section.




                                                                                                                                                   49
                                   Lifetime of PI Ceramic
                                   Piezoelectric Actuators . . . (cont.)

                                                                   Handling Precautions                 they will damage the actua-
                                                                                                        tor. This can be ensured
                                                                   Piezoelectric actuators must         by the use of ball tips, fle-
                                                                   be handled with care because         xible tips, adequate guiding
                                                                   the internal ceramic materials       mechanisms etc. An excep-
                                                                   as well as ceramic end-plates        tion to this requirement is
                                                                   are fragile. Do not use metal        made for the PICA-Shear
                                                                   tools for actuator handling. Do      actuators, because they
                                                                   not scratch the coating on the       operate in the shear direc-
                                                                   side surfaces.                       tion. Do not exceed the
     No pulling force without preload.                                                                  maximum shear force spe-
                                                                   Besides these general instruc-
                                                                   tions the following precautions      cifications for these actua-
                                                                   have to be considered during         tors.
                                                                   handling of PI Ceramic piezo-      3. Piezoelectric stack actuators
                                                                   electric actuators:                   have to be mounted by glu-
                                                                   1. Piezoelectric stack actuators      ing them between even
                                                                      without axial preload are          metal or ceramic surfaces
                                                                      sensitive to pulling forces.       by a cold or hot curing
                                                                      A preload of half of the           epoxy, respectively. Ground
                                                                      blocking force is generally        surfaces are preferred.
                                                                      recommended (see data              Please, do not exceed the
                                                                      tables p. 13 to p. 27). This       specified working tempera-
     No lateral force or torque.
                                                                      recommendation is also             ture range of the actuator
                                                                      valid for PICA-Shear actua-        during curing.
                                                                      tors in axial direction, per-   4. The environment of all actu-
                                                                      pendicular to the shear            ators should be as dry as
                                                                      diplacement directions.            possible. While PICMA™
                                                                   2. Piezoelectric stack actuators      actuators    are    guarded
                                                                      may be stressed in the axial       against humidity by their
                                                                      direction only. The applied        ceramic coating, other actu-
                                                                      force must be centered very        ators must be protected by
                                                                      well. Tilting and shearing         other measures (hermetic
                                                                      forces, which can also             sealing, dry air flow, etc).
                                                                      be induced by parallelism
     Ball tips or flexures to decouple lateral forces or bending
     forces.
                                                                      errors of the endplates,
                                                                      have to be avoided because




                                    http://www.piceramic.com
50                                          info@piceramic.com
  The combination of long-         5. Should the stack become
  term high electric DC fields        charged, rapid discharging—
  and high relative humidity          especially without a pre-
  values should be avoided            load—might damage the
  with all piezoelectric ac-          stack. Therefore, it is appro-
  tuators. The electric field         priate to use a resistor for dis-
  attracts the water mole-            charging after any mistreat-
  cules or hydroxy ions from          ment. PI Ceramic delivers
  the environment to the sur-         PICA-Stack piezoelectric ac-
  face of the stack and leads         tuators with a shorting clamp.
  to a permanent increase in          We recommend use of                 Ball tips or flexures to decouple bending forces.
                                                                          }rfk




  its leakage current. This can       gloves and safety glasses
  finally result in damage            during handling.
  to the actuator. There is no
                                   6. The lateral (side) surfaces of
  polymer coating which can
                                      PICMA™ and PICA-Stack
  avoid the forced penetration
                                      actuators are not, or not fully,
  of these molecules.
                                      electrically insulated to allow
5. It is important to short-          a more compact design and
   circuit the piezoelectric          integration of the stack in
   stack actuators during any         the final assembly by the
   handling operation. The            customer. Therefore, the
   resulting loads will induce        customer is responsible for
                                                                           Bolting between plates is not recommended.
   charges on the stack elec-         designing in the required se-
   trodes which might result in       paration or suitable insulating
   high electric fields if the        materials, like polyamide foil
   leads are not shorted:             or PTFE tape, to insulate the
  a) changing temperatures,           stack from its surrounding.
     for example during curing
                                   7. Prevent any contamination
     or soldering processes,
                                      of the stack surfaces with
     induces charges by the
                                      conductive or corrosive sub-
     pyroelectric effect
                                      stances. Cleaning of the
  b) changing      mechanical         stacks should be done with
     loads, for example during        Isopropanol only. Do not use
     preload application, in-         acetone. Avoid excessive
     duces charges by the             ultrasonic cleaning at higher
     direct piezoelectric effect      temperatures.




                                                                                                                              51
             Piezoelectric Components

    Applications
    s   Actuators
    s   Sensors
    s   Ultrasonic Transducers
    s   Sonar Technology
    s   Ultrasonic Cleaning and
        Welding




                               mm
    Discs          OD          1 - 80
                   Thickness   min 0.2
    Rings          OD/ID       3 - 50
                   Thickness   0.2 - 15
    Tubes          OD/ID       1 - 80
                   L           max. 50
    Plates         L/W         1 - 70
                   TH          min 0.2
    Shear Plates   L/W         2 - 20
                   Thickness   max. 15




             http://www.piceramic.com
8                  info@piceramic.com
                                                   PICA-Stack Piezoelectric Actuators

                                             Applications
                                             s NanoPositioning
                                             s High-Load Positioning
                                             s Active Vibration
                                               Cancellation
                                             s Smart Structures
                                             s Precision Mechanics
                                             s Chip Manufacturing and
                                               Testing
                                             s Laser Tuning


                                             see PICA-Stack, PICA-Power and
                                             PICA-Thru datasheets,
                                             pages 16, 18, 20




                                                                                       Variety of piezo ceramic stacks.




Technical Data
Displacement                  up to 300 µm
Blocking force                up to 80 kN
Static load                   up to 100 kN
Operating voltage range       0 to1000 V
Operating temperature range   -20 to +85 °C (cryogenic and up to +150 °C on request)
Dynamic reliability           more than 10 9 cycles
Cross section shapes          cylindrical, tubular, rectangular
                                                                                       PZT Actuator for Structural Deformation / Vibration Damping in Aerospace Applications.
Length                        up to 300 mm




                                                                                                                                                                          9
                                   PICMA™ Monolithic Multilayer Actuators

                             Special Features
                             s Low Operating Voltage
                             s No Polymer Coating
                             s Ceramic Insulation
                             s 100 % Ultra-High Vacuum
                               Compatible
                             s Sub-nm Resolution
                             s Sub-ms Response Time


                             Applications
                             s NanoPositioning
                             s Precision Mechanics
                             s Semiconductor
                               Equipment
                             s Valves
                             s Laser Applications
                             s Telecommunication


                             see PICMA™ datasheets
                             pages 13, 14, 15




                                                                     PICMA™ Monolithic Actuators are the only ceramic insulated piezo actuators
                                                                     available. They provide higher reliability than other monolithic actuators and exhibit
                                                                     no measurable outgassing.
     Technical Data
     Cross section           2x2 to 10x10 mm2
     Displacement            up to 30 µm / segment
     Blocking force          up to 5 kN
     Operating voltage       max. 120 V
     Operating temperature   - 40 to +150 °C




                                      http://www.piceramic.com
10                                              info@piceramic.com
                              PICA-Shear Actuators (X, XY and XYZ)

                        Special Features
                        s Low Operating Voltage
                        s Special Polymer
                          Insulation
                        s 100 % UHV Compatible
                        s Sub-nm Resolution
                        s Sub-ms Response Time



                        Applications
                        s NanoPositioning
                        s Piezo-Motors
                        s Semiconductor
                          Equipment
                        s Laser Applications


                        see PICA Shear Actuators datasheet,
                        page 22




Technical Data
Cross section           3x3 to 10x10 mm2
Displacement            up to 10 µm
Operating voltage       max. +/- 375 V
Operating temperature   -40 to +150 °C (cryogenic on request)




                                                                     11
                               Piezoelectric Bender Actuators

                         Applications
                         s   Micropositioning
                         s   Pneumatic Valve Control
                         s   Telecommunication
                         s   Optical Switches
                         s   Ink Jet Printers



                         Special Features
                         s   Low Operating Voltage
                         s   No Polymer Coating
                         s   Full Ceramic Actuator
                         s   100 % UHV Compatible
                         s   µm Resolution
                         s   ms Response Time
                                                                  Variety of custom benders.


                         see PICMA™ Bender datasheet,
                         page 24




     Technical Data
     Displacement        up to 2 mm
     Blocking force      up to 2.5 N
     Operating voltage   max. 60 V / 300 V




                                                                  PI Ceramic Multilayer Benders are excellent actuators for pneumatic valves.




                                  http://www.piceramic.com
12                                           info@piceramic.com
Piezo Ceramic Actuators
& Custom Subassemblies
for Capital Equipment
Applications & Research

http://www.piceramic.com


    GERMANY                     USA                            UK
                                PI Physik Instrumente) L.P.    Lambda Photometrics Ltd.
                                Email: info@pi-usa.us          Tel: +44 (1582) 76 43 34
    PI Ceramic GmbH
                                http://www.pi-usa.us           Fax: +44 (1582) 71 20 84
    Lindenstrasse
                                USA East (Canada)              Email: info@lambdaphoto.co.uk
    07589 Lederhose
                                Tel: +1 (508) 832-3456         http://www.lambdaphoto.co.uk
    Germany
                                Fax: +1 (508) 832-0506
    Tel: +49 (36604) 882-0
                                USA West (Mexico)              FRANCE
    Fax: +49 (36604) 882-25
                                Tel: +1 (714) 850-9305         Polytec PI S.A.
    Email: info@piceramic.com
                                Fax: +1 (714) 850-9307         Tel: +33 (1) 48 10 39 30
    http://www.piceramic.com
                                                               Fax: +33 (1) 48 10 08 03
                                                               Email: pi.phot@polytec-pi.fr
    Physik Instrumente (PI)                                    http://www.polytec-pi.fr
    GmbH & Co.
    Auf der Römerstrasse 1                                     ITALY
    76228 Karlsruhe             JAPAN                          Physik Instrumente (PI) S. r. l.
    Tel: +49 (721) 4846-0       PI-Polytec Co. Ltd.            Tel: +39 (02) 665 011 01
    Fax: +49 (721) 4846-299     Email: info@pi-polytec.co.jp   Fax: +39 (02) 665 014 56
    Email: info@pi.ws           Tel: +81 (42) 526 7300         Email: info@pionline.it
    http://www.pi.ws            Fax: +81 (42) 526 7301         http://www.pionline.it

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:9
posted:11/24/2011
language:English
pages:20