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WO1998007183A9 - Actionneur piezo-electrique a coupe en serpentin - Google Patents

Actionneur piezo-electrique a coupe en serpentin

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Publication number
WO1998007183A9
WO1998007183A9 PCT/US1997/013135 US9713135W WO9807183A9 WO 1998007183 A9 WO1998007183 A9 WO 1998007183A9 US 9713135 W US9713135 W US 9713135W WO 9807183 A9 WO9807183 A9 WO 9807183A9
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WIPO (PCT)
Prior art keywords
actuator
ceramic
layers
accordance
cavities
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PCT/US1997/013135
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English (en)
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WO1998007183A2 (fr
WO1998007183A3 (fr
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Publication of WO1998007183A2 publication Critical patent/WO1998007183A2/fr
Priority to US09/041,278 priority Critical patent/US6107726A/en
Priority to PCT/US1998/005917 priority patent/WO1999005778A1/fr
Publication of WO1998007183A3 publication Critical patent/WO1998007183A3/fr
Publication of WO1998007183A9 publication Critical patent/WO1998007183A9/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Definitions

  • the present invention relates to low voltage, high displacement piezoelectric ceramic actuators. These actuators are useful for such military and commercial applica- tions as: vibration damping, noise suppression, acoustic camouflage, actuated structures and positioning. Additionally, these actuators may be grouped in multiple arrangements and operated simultaneously so that their force and strain outputs are additive, or grouped and operated indi- vidually, to achieve acoustic signal generation, e.g., in acoustic imaging or transmitting, or in acoustic communication.
  • piezoelectric actuators In order to meet the requirements presented by such applications, piezoelectric actuators must exhibit both moderate-to-high displacement and moderate-to-high force. Thus far, piezoelectric actuators have been limited by the need to balance displacement and force requirements in the device. For example, the choice has been between low displacement with high force (monolithic or multilayer piezo- electric ceramic actuators) or high displacement with low force (piezoelectric benders and strain amplifiers) . Little capability has existed for varying the force-displacement characteristics to suit a particular application.
  • piezoelectric bender devices can exhibit high bending strain levels of up to 10%, but their load carrying capabilities are only on the order of 10 "4 MPa.
  • the Inchworm motor can exhibit large lateral displacements and reasonable loads, but its speed is limited.
  • Flexten- sional actuators have been used as strain amplification devices for both single layer and multilayer piezoelectric materials, with typical strain amplification of about a factor of 5, but with about a 1000-fold decrease in load carrying capability.
  • more efficient actuators that combine high energy density (for compactness) with moderate strain amplification (for matching to moderate mechanical impedance loads) are required.
  • Figure 1 is a perspective view of a PZT blank used for fabrication of the devices described herein;
  • FIGS 2, 3, 4, and 5 are schematic perspective views of piezoelectric serpentine actuators in accordance with four different embodiments of the present invention.
  • Figures 6A and 6B are schematic elevation and cross- sectional perspective views, respectively, of a surface mounted sheet actuator in accordance with another embodiment of the invention
  • Figures 7A, 7B, 8A, 8B, 9, and 10 are schematic perspective views of actuators in accordance with other embodiments of the invention.
  • FIGS 11, 12, 13A, and 13B are schematic perspective views of actuators in accordance with still other embodi- ments of the invention.
  • Figures 14, 15, 16, and 17 are photomicrographs showing sheet actuators of different geometries.
  • the invention is a serpentine cross- section piezoelectric actuator.
  • the actuator includes a unitary piezoelectric or electrostrictive ceramic body, the body including a top, four sides generally normal to and interconnected with the top, a base generally normal to and interconnected with the sides, and two or more ceramic layers including a top ceramic layer providing the top, a bottom ceramic layer providing the bottom, and, optionally, one or more intermediate ceramic layers, the layers being disposed parallel to and superimposed over one another.
  • Each ceramic layer except the top ceramic layer is joined at a first side to one of the ceramic layers adjacent thereto by a first ceramic bridge and each ceramic layer except the bottom ceramic layer is joined at a second side opposite the first side to another of the ceramic layers adjacent thereto by a second ceramic bridge.
  • First and second cavities extend into the ceramic body from the first and second sides, respectively, the first cavities alternating with the second cavities in the ceramic body, so that the ceramic body has a serpentine cross-section.
  • the body further includes a first electrode and a second electrode, each of an electrically conductive material. The first and second electrodes are disposed along and bonded to the first and second sides, respectively, of the body for activation of the actuator.
  • a piezoelectric ceramic actuator in accordance with the invention is a linear actua- tor including multiple lead zirconate titanate (PZT) ceramic layers with electrically conductive nickel electrodes, and has a cross-sectional footprint of about 0.1 x 0.1 to about 100 x 100 mm, and a length of about 0.1 - 1000 mm.
  • PZT lead zirconate titanate
  • the actuator may be fabricated from another piezo- electric or electrostrictive material including, but not limited to, a lead magnesium niobate; a lead zinc niobate; a lead nickel niobate; a titanate, tungstate, zirconate or niobate of lead, barium, bismuth, or strontium; or a derivative thereof.
  • piezoelectric materials materials of this type will be referred to as piezoelectric materials.
  • another known electrically conductive material may be used to fabricate the electrodes of the actuator.
  • Such electrically conductive materials include, but are not limited to, metals such as silver, palladium, or platinum, nickel, electroless nickel, vapor deposited or sputtered gold, chrome-gold, alloys of these metals, and conductive polymers or glasses.
  • the illustrative actuator is fabricated from a multilayer ceramic blank formed, e.g., molded, extruded, or diced from a piezoelectric material to have a serpentine cross section.
  • Figure 1 illustrates an example of such a blank, showing sintered PZT ceramic blank 1 of height H, width W, and length L (in the x, y, and z dimensions, respectively).
  • Blank 1 has multiple parallel ceramic layers 2 interconnected by bridging portions 3a and 3b at alternating ends of layers 2 to form a ceramic body of serpentine cross-section. Alternating slits or cavities 4a and 4b entering blank 1 from opposite side surfaces 5a and 5b of blank 1 are interposed between layers 2 to separate the layers.
  • Sides 6a and 6b have a serpentine cross-section, while top 7a and base 7b have a rectangular cross section.
  • Blank 1 is shown as having seven ceramic layers 2.
  • the layers in an individual actuator may vary from two to 1000, or even several thousand layers, while the thickness of each layer is typically about 10 - 10,000 ⁇ m and the length (z-dimension) of the transducer is typically about 0.1 - 1000 mm, depending on the application for which the transducer is designed.
  • the method described herein makes possible the net-shape molding of a transducer having several thousand, e.g., about 10,000 thin layers, each being, e.g., as thin as about 20 ⁇ m.
  • Cavities 4a and 4b define the thickness of the electrode layers in the finished transducer, typically 20 - 500 ⁇ m.
  • the outer dimensions, i.e., width W and length L of sintered blank 1 may be molded slightly oversize so that the width and length may be modified after sintering and electroding to fine-tune the device to a preselected resonance mode.
  • length L of sintered blank 1 may be sufficiently large to provide two or more individual devices, the blank being separated at a bridge 3a or 3b before or after the electroding and/or poling steps de- scribed below.
  • blank 1 may be of sufficient width W to provide two or more devices, the individual devices being separated from one another at a later stage in the fabrication process, as described below.
  • the ceramic blank shown in Figure 1 is net-shape molded by any of the techniques described in above-referenced U.S. Application 08/686,496.
  • blank 1 may be fabricated by injection molding a hot PZT-binder mixture into a chilled, closed mold, the mold being cooled to a temperature sufficient to solidify the mixture, then ejected from the mold.
  • the mold halves each have a number of longitudinal blade inserts projecting into the mold cavity to shape cavities 4a and 4b.
  • This molding method is performed in a manner similar to that described for injection molding of ceramic bodies in U.S. Patent No. 5,340,510, incorporated herein by reference.
  • the blank may be compression molded by placing a green ceramic preform between upper and lower mold halves of a heated compression molding apparatus.
  • the preform is fabricated using a mixture of a PZT ceramic powder and a thermoplastic organic binder, e.g., a wax.
  • the molding temperature should be slightly greater than the softening temperature of the PZT-binder mixture.
  • the serpentine cross- section green body is made by forcing soft, heated thermoplastic PZT-binder mixture under pressure through a heated . die in the form of a negative of the desired serpentine shape.
  • a series of multiple extrusion process steps may be performed to gradually reduce the cross-section of the extruded serpentine blank to the desired fine dimensions.
  • Other piezoelectric ceramic materials, as described above, may also be used in any of the above-described methods.
  • the binder is removed from the blank by slow heating in a conventional manner, and the part is sintered to form sintered blank 1 described above, then prepared for use in a multilayer actuator as described below.
  • a serpentine ceramic body may be fabricated by machining and dicing of a sintered or green ceramic block, or other conventional method, the molding methods described above are greatly preferred, because of the repro- ducibility of the methods, the minute size of the ceramic bodies which may be made thereby, and the lower manufacturing cost.
  • Figure 2 illustrates a first type (Type I) of serpentine actuator, actuator 20, poled and electroded to operate in a first d 33 configuration.
  • Sintered serpentine blank 1 is poled in known manner, e.g., by using temporary electrodes, with the poling directions of each layer as indicated by arrows 10a and 10b.
  • Permanent electrodes 22a are applied to surfaces 8a of side 5a of the poled ceramic body, and perma- nent electrodes 22b are applied to surfaces 8b of side 5b.
  • Electrodes 22a and 22b cover only surfaces 8a and 8b, and do not extend into cavities 4a and 4b. Electrodes 22a and 22b are applied by conventional means, e.g., by abrading or stripping surfaces 5a and 5b to remove temporary electrodes then applying permanent electrodes 22a and 22b by masking non-coated surfaces and electroless plating with, e.g., nickel. Alternatively, the electrodes may be, e.g., vapor deposited or sputtered, e.g., with chrome-gold, or may be provided by fired silver frit or conductive polymers. Thus, actuator 20 is provided with separate electrodes 22a and 22b, electrically isolated from one another.
  • the poling directions and electrode placement are selected to provide a d 33 configuration for operation of the actuator.
  • the electrodes are then interconnected to a source of electrical power, as 25, for activation of the device, driving the device across its height with displacement and force applied in the direction shown by arrow 21.
  • FIG 3 illustrates a second type (Type II) of serpentine actuator, actuator 30 poled and electroded to operate in a d l5 configuration.
  • Sintered serpentine actuator 30 is poled in the same configuration as actuator 20 using, e.g., temporary electrodes, with the poling directions of each layer as indicated by arrows 10a and 10b.
  • Permanent electrode 32a is applied to surfaces 8a of side 6a of the poled ceramic body and extend into cavities 4a to cover the entire surfaces of each cavity 4a.
  • Permanent electrode 32b is applied to the surfaces 8b of side 5b and extend into cavities 4b to cover the entire surfaces of each cavity 4b. Electrodes 32a and 32b are applied as described above for electrodes 22a and 22b.
  • Gaps 34a and 34b separate elec- trodes 32a and 32b, electrically isolating the electrodes from one another.
  • the poling directions and electrode placement are selected to provide a d 15 configuration for operation of the actuator.
  • the electrodes are then interconnected to a source of electrical power, as 35, for acti- vation of the device, driving the device across its height with displacement and force applied in the direction shown by arrow 31.
  • Figure 4 illustrates a third type (Type III) of serpentine actuator, actuator 40, poled and electroded to operate in a d 31 configuration.
  • Sintered serpentine blank 1 is poled in known manner, e.g., by using temporary electrodes, with the poling directions of each layer as indicated by arrows 43a and 43b.
  • Permanent electrode 42a is applied to the entire surface of side 6a of the poled ceramic body, and permanent electrode 42b is applied to the entire surface of side 6b. Electrodes 42a and 42b cover only the surfaces of sides 6a and 6b, and do not extend into cavities 4a and 4b. Electrodes 42a and 42b are applied as described above for electrodes 22a and 22b.
  • actuator 40 is provided with separate electrodes 42a and 42b, electrically isolated from one another.
  • the poling directions and electrode placement are selected to provide a d configuration for operation of the actuator.
  • the electrodes are then interconnected to a source, as 45, of electrical power for activation of the de- vice, driving the device across its width with displacement and force applied in the direction shown by arrow 41.
  • Figure 5 illustrates a fourth type (Type IV) of serpentine actuator, actuator 50, poled and electroded to operate in a second d 33 configuration, different from that of actua- tor 20.
  • Sintered serpentine blank 1 is poled in known manner, e.g., by using temporary electrodes, with the poling directions of each layer as indicated by arrows 55a and 55b.
  • Permanent electrode 52a is applied to surfaces 8a of side 5a and extends into cavities 4a to cover all surfaces of each cavity 4a.
  • Permanent electrode 52b is applied to surfaces 8b of side 5b and extends into cavities 4b to cover all surfaces of each cavity 4b. Electrodes 52a and 52b are applied as described above for electrodes 22a and 22b.
  • Gaps 54a and 54b separate electrodes 52a and 52b, electrically isolating the electrodes from one another. If desired, poling can be accomplished using permanent electrodes 52a and 52b, since the configuration of these electrodes will produce the desired poling arrangement. However the poling is effected, the poling directions and electrode placement are selected to provide a d 33 configuration for operation of the actuator. The electrodes are then interconnected to a source, as 57, of electrical power for activation of the device, driving the device in the length direction across each ceramic layer thickness with displacement and force applied in the direction shown by arrow 56. In operation, serpentine actuators 20, 30, 40, and 50 as shown with open cavities in Figures 2, 3, 4, and 5, respectively, act as high compliance springs.
  • a force of about 0.2 - 20 MPa and strain of about 0.1 - 2% are typical of these spring actuators.
  • the dimensions and thickness of layers 2 and cavities 4a and 4b of blank 1 may be selected to adjust the spring constant of the elements. These actuators exhibit a high displacement/voltage ratio. In these actuators, the ends of oppositely poled piezoelectric element (layer) pairs are joined by stiff ceramic bridges.
  • the Type IV actuator, actuator 50 can be operated with open cavities 4a and 4b, as shown in Figure 5, in a manner similar to that shown for actuators 20, 30, and 40 in Figures 2, 3, and 4, respectively.
  • cavities 4a and 4b of a Type IV actuator would be filled with, e.g., polymer or metal, as described further below, to provide support and increase the force output of the device.
  • Cavities 4a and 4b of Type I, II, and III actuators may also be filled if desired, as described further below.
  • Type I actuator 20 Figure 2
  • Type III actuator 40 Figure 4
  • Type I actuator 20 is configured to operate in a slightly lower force/higher displacement regime than Type IV actuator 50 ( Figure 5) .
  • Type III actuator 40 requires only a low volt-
  • Type II actuator 30 ( Figure 3) generates bending in each layer by clamping of the mechanical d ls shear stress between elements (layers) by attachment of each element to elements on either side. The total displacement is the sum of these bending moments.
  • This actuator requires only a low drive voltage and can be configured to operate in a moderate force/moderate displacement regime because of its high piezoelectric coefficient and low stiffness.
  • Type IV actuator 50 exhibits a higher force/displacement ratio than actuators 20, 30, and 40.
  • Each ceramic layer of actuator 50 is subjected to a high electric field to yield strain levels perpendicular to the layers of up to about 0.1%.
  • cavities 4a and 4b open due to the bending at bridges 3a and 3b to increase overall strain levels of the device up to about 2%.
  • the thickness of ceramic layers 2, the thickness of cavities 4a and 4b, and the material filling the cavities may be selected to adjust the required voltage/current and the force/displacement ratios to a particular application.
  • These sheet actuators may be applied as surface mounted (patch) devices or as embedded devices.
  • Such sheet actuators are conformable to curved surfaces, and may be configured for unidirectional actuation, since the height component of the displacement is not significant in proportion to the length component.
  • the sheet actua- tor can exhibit higher displacement and higher force than prior art d 31 monolithic PZT plates.
  • FIGS. 6A and 6B illustrate a typical Type IV sheet- form d 33 actuator configured as shown in Figure 5 for actuator 50, mounted on a vibrating structure, e.g., an aircraft fuselage inside surface.
  • a vibrating structure e.g., an aircraft fuselage inside surface.
  • unidirec- tional operating Type IV sheet actuator 60 of width W and length L is mounted on surface 61 of vibrating structure 62.
  • Portion 64 shown in detailed cross-sectional view in Figure 8B, includes actuator 60, surface 61, and structure 62.
  • Activation of sheet actuator 60 expands the actuator in the direction of length L, allowing for detection and control of unacceptable vibration in the fuselage.
  • a similar device and mounting may be fabricated, using Type I, II, III, or IV serpentine actuator configurations, for other applications, e.g., to suppress noise and vibration in an aircraft cabin, transformer housing, air duct, or other vibration-prone equipment or noisy environment.
  • Type I, II, III, or IV actuators may be fabricated from the net-shape molded serpentine ceramic blank of Figure 1, or configurations similar to that shown in Figure 1.
  • Figure 7A illustrates bender actuator 70 configured as a Type IV actuator.
  • Actuator 70 includes serpentine piezoelectric ceramic body 71 having side surfaces 5a and 5b, side surfaces 6a and 6b, end surfaces 7a and 7b, and cavities 4a and 4b, similarly to blank 1 of Figure 1.
  • Body 71 is poled through the ceramic layer thickness dimension of parallel ceramic layers 72, as shown by arrows 73, and electrodes 74 and 75 are bonded to the ceramic body for actuation of the device as a Type IV actuator.
  • Side plate 78 of, e.g., stiff metal or stiff polymer is bonded to side surface 6b of body 71 by a suitable adhesive material such as an epoxy material or by glass frit, soldering, brazing, or direct thermo-bonding under heat and pressure.
  • suitable plate materials are metals such as aluminum, brass, or steel, or polymers such as a poly- imide, polyurethane, or fiber-reinforced epoxy material. If plate 78 is metal, a thin, non-conductive layer (not shown)
  • Type IV bender actuator 80 of Figure 7B is similar to actuator 70 of Figure 7A, and operates in a similar manner.
  • Piezoelectric ceramic body 81 includes serpentine portion 82 and solid portion 83. Body 81 is poled across the thickness of the ceramic layers and electrodes 84 and 85 applied in the same manner as is described above for actuator 70.
  • electrodes 84 and 85 may extend across solid portion 83 to edges 86 of the solid portion.
  • solid portion 8° serves the same function as side plate 78 of actuator 70, constraining side 6b of ser- pentine portion 82 adjacent to solid portion 83.
  • activation of Type IV actuator 80 causes bending of the device in the direction of arrows 89.
  • constraint may be effected in actuator 80 at a different side of serpentine portion 82 than that illustrated in Figure 7B.
  • actuators 70 and 80 are shown as Type IV actuators, either may be poled and electroded to operate as a Type I, II, or III actuator, depending on the application and the actuator characteristics required.
  • Figures 8A and 8B illustrate other alternative actuator configurations.
  • Figure 8A shows bender actuator 90 includ-
  • Electrodes 93a and 93b are applied to ceramic body 91 by plating or coating the surfaces with nickel or other electrically conducting material by conventional techniques, as described above for actuator 30. Electrode 93a extends continuously over surfaces 5a and 7a and within cavities 4a, while electrode 93b extends continuously over surfaces 5b and 7b and within cavities 4b. Electrodes 93a and 93b are electrically isolated from one another by gaps 94a and 94b.
  • Side plate 95 is bonded to body 91 via electrode 93b, and includes protrusions 96 extending into, filling, and bonded to gaps 4b.
  • Side plate 95 may be a polymer or metal materi- al, e.g., an epoxy or filled epoxy material, polyurethane, brass, or steel.
  • Side plate 95 may be fabricated by partial encapsulation of the plated ceramic body, or cavities 4b may be filled to form the protrusions and a separate plate bonded to the protrusions and the plated ceramic body.
  • cavities 4a and 4b my be filled by permitting the adhesive to flow into and fill the cavities. Constraint of one side of actuator 90 by side plate 95 during activation of the device causes bending of the device in the direction shown by arrows 97.
  • Another alternate device which may be derived from
  • Type II actuator 90 is shown in Figure 8B.
  • Type II actuator 100 includes piezoelectric ceramic body 91, electrodes 93a and 93b, and, e.g., metal or polymer side plate 95, as described above.
  • protrusions 96 of plate 95 have been shaped, e.g., by machining, casting, molding, spraying, plating, or other similar means to include cavities 101 extending into and parallel to cavities 4b.
  • Activation of spring actuator 100 causes bending of the device in the direction shown by arrow 102.
  • actuators 90 and 100 are shown as Type II actuators, either may be poled and electroded to operate as
  • Type I, III, or IV actuator depending on the application and the actuator characteristics required.
  • Type II bender actuator 110 fabricated in a similar manner to bender actuator 90, is shown in Figure 9.
  • Actua- tor 110 includes a pair of electroded piezoelectric bodies, Ilia and 111b which are each poled and electroded to operate as a Type II bender, as shown and described for ceramic body 91 of actuator 90, and are mirror images of one another.
  • Piezoelectric ceramic bodies Ilia and 111b are operated so that one expands while the other contracts upon applying voltages of suitable polarity to each, thereby causing bending of the device in the direction shown by arrows 114a and 114b.
  • Bodies Ilia and 111b are joined by central plate 112, which is bonded to each ceramic body.
  • Central plate 112 optionally includes protrusions 113a and 113b which extend into and fill cavities 4b of each body.
  • plate 112 and, optionally, protrusions 113a and 113b may be provided by an adhesive directly joining bodies Ilia and 111b.
  • actuator 110 is shown as a Type II actuator, it may be poled and electroded to operate as a Type I, III, or IV actuator, depending on the application and the actuator characteristics required.
  • actuator 120 which is an adaptation of a Type II actuator, is shown in Figure 10.
  • Actuator 120 includes serpentine piezoelectric ceramic body 121.
  • Body 121 is poled with pairs of adjacent layers having the same polarity, as shown in Figure 10, but with each pair having the opposite polarity to the pair or pairs adjacent thereto, so as to provide alternating pairs of bender layers.
  • the poling directions of each layer pair are indicated by arrows 122a and 122b.
  • Coatings 123a and 123b are applied and bonded to ceramic body 121 by coating surfaces 5a, 5b, 7a, and 7b and filling cavities 4a and 4b with an electri- cally conducting material more compliant and compressible that the piezoelectric material of body 121 (e.g., a porous
  • Coating 123a extends continuously over surfaces 5a, 7a, and 7b and within cavities 4a, while coating 123b extends continuously over surface 5b within cavities 4b. Coatings 123a and 123b are electrically isolated from one another by gaps 124a and 124b.
  • body 121 may be plated as described for actuator 110, and coatings 123a and 123b may be formed from a nonconductive material, e.g., a polyimid or epoxy material, by vapor deposition, by electrostatic powder deposition followed by fusion, or by dipping.
  • cavities similar to cavities 101 of actuator 100 can be formed between the coated layers to allow more room for bending and increase the actuator compliance.
  • Activation of the device by alternating voltages causes bending of the device in the directions shown by arrows 125a and 125b.
  • actuator 120 is shown as a Type II actuator, it may be poled and electroded to operate as a Type I, III, or IV actuator, depending on the application and the actuator characteristics required.
  • FIG. 11 illustrates Type IV actuator 50a, which includes Type IV actuator 50, as described above, and also includes filler portions 58a and 58b of a conductive stiff material, e.g., a silver-epoxy material, filling cavities 4a and 4b.
  • the silver-epoxy filler material is more flexible and compressible than the ceramic material of the body.
  • more flexible, e.g., elasto eric materials may be used as the filler material of filler portions 58a and 58b.
  • a polyurethane or rubber may be used as a flexible filler, or the polyurethane or rubber may be ad- mixed with polymer microballons to render the filler even more flexible.
  • the cavities may be filled with a rigid material such as a metal or conductive glass frit. If the filler is conductive, coating the surfaces of cavities 4a and 4b with a conductive coating, as described above, is optional.
  • actuator 50a is shown as a Type IV actuator, it may be poled and electroded to operate as a Type I, II, or III actuator, depending on the application and the actuator characteristics required.
  • An alternative geometry for the serpentine ceramic body of a serpentine actuator as described herein is illustrated in Figure 12A.
  • Serpentine actuator 130 includes ceramic body 131 and electrodes 132a and 132b. Ceramic body 131 includes bridges 133a and 133b which are narrower than bridges 3a and 3b of actuator 30 shown in Figure 3. Ceramic body 131 also includes ceramic layers 134a and 134b which are not parallel to one another.
  • Actuator 130 is poled and electroded to operate as a simple Type II actuator similar to that shown in Figure 3. However, it may be poled and electroded to operate as a Type I, III, or IV actuator, and may be adapted as descibed for any of the actuators of Figures 6A through 11, depending on the application and the actuator characteristics required.
  • FIG. 12B illustrates Type III actuator 40a including ceramic body 44, as described above, having layers 2a and 2b and bridges 3a and 3b. Outer edges 45a and inner edges 45c of bridges 3a, respectively and outer edges 45c and inner edges 45d of bridges 3b are radiused to avoid
  • actuator 40a is shown as a Type III actuator, it may be poled and electroded to operate as a Type I, II, or IV actuator, or to have ceramic layers at an angle to one another as shown in Figure 12A, depending on the application and the actuator characteristics required.
  • Another way to add to the robustness of the spring actuators described herein is to apply compression to the actuators in the direction of displacement during fabrication. Such a devices are illustrated in Figures 13A and 13B.
  • Figure 13A illustrates compressed actuator 20b, which includes actuator 20, as described above, and also includes end plates 24, threaded rods 25, and cap nuts 26. End plates 24 each include a bore at each corner through which threaded rods 25 extend. Alternatively, actuator 20 may be notched or otherwise shaped to acco odate rods 25. The degree of compression on actuator 20b may be adjusted by tightening or loosening nuts 26 on rods 25.
  • the plates, rods, and nuts are preferably of a metal such as steel, brass, or titanium, but may be of any suitable material known in the art.
  • Figure 13B illustrates an alternate way of compressing the actuators. Actuator 30b includes actuator 30, as described above, and fiberglass wrap 34.
  • wrap 34 is applied during fabrication of the actuator, and holds actuator 30 in compression. Compression may be applied, e.g., using a heat-shrink polymer in the wrap or by holding the actuator in compression with tooling while the wrap is applied.
  • actuators 20c and 30b are shown as Type I and
  • Type II actuators may be poled and
  • Type I, II, III or IV actuators may be fabricated from a serpentine- type blank, as described herein, of the piezoelectric materials mentioned above.
  • the blank may have a height of about 0.1 - 100 mm, a width of about 0.1 - 1000 mm and a length of about 0.1 - 1000 mm.
  • the devices may be electroded with any of the electrically conductive materials listed above.
  • the actuators described herein may be encapsulated in a conductive or non-conductive material, e.g., polyurethane or an epoxy material. Larger actuation strains and forces may be abtained by assembling together two or more of the single actuators described above, so that their force and/or strain outputs are additive.
  • a conductive or non-conductive material e.g., polyurethane or an epoxy material.
  • Samples 1 - 4 Four Type IV sheet actuators, Samples 1 - 4, were prepared by net-shape compression molding of a soft piezoelectric PZT (DoE type VI) as described above, having as- fired dimensions as follows:
  • the actuator pitch, ceramic layer thickness plus cavity thickness, was similar for the actuators of Samples 1 - 3, but the ceramic layer thickness/cavity thickness ratio was varied.
  • Sample 4 was similar to Sample 1, but differed in the height dimension.
  • Figures 14, 15, 16, and 17 illustrate the four sheet actuator electroded bodies, Samples 1, 2, 3, and 4, respectively.
  • Each of the actuators was poled and electroded in a Type IV configuration, as described above with reference to Figure 11.
  • Low cost electroless nickel permanent electrodes were applied, as described above, and the cavities were filled with a silver-epoxy material. Electrical wires were attached to the electrodes in known manner.
  • Sample actuators 1, 2, and 4 were operated to evaluate the effect of device dimensions, i.e., height and ceramic/cavity thickness ratios, on compliance and actuation performance.
  • Table I shows the results as compared to solid, monolithic PZT (DoD type VI) ceramic control sample having the same piezoelectric properties as the ceramic used to form the actuators of Samples 1, 2, and 4.
  • Y E 33 is the Young's modulus
  • s' 3 is the compliance
  • d 33 is the piezoelectric constant of the solid PZT control sample and the actuators of Samples 1, 2, and 4.
  • the invention described herein presents to the art a novel piezoelectric actuator having a serpentine cross- section.
  • the actuator may be fabricated using net-shape forming processes, making possible the fabrication of a spring, stack multilayer, or spring or stack bender actuator.
  • the actuator is a reliable, low cost device exhibiting advantageous force/displacement characteristics which may be tailored to many applications.
  • the actuator is particularly useful for such applications as vibration damping, noise suppression, active surface control, actuated structures, positioning, acoustic transmitting, and acoustic signal generation.

Abstract

La présente invention concerne un actionneur piézo-électrique à coupe en serpentin. Cet actionneur est constitué d'un corps monobloc en céramique piézo-électrique ou électrostrictive, lequel corps comporte un dessus, quatre côtés généralement perpendiculaires au dessus auquel ils sont interconnectés, une base perpendiculaire aux côtés auxquels elle est interconnectée et au moins deux couches céramiques. En l'occurrence, on compte parmi les couches céramiques une couche céramique de dessus constituant le dessus, un couche céramique de fond constituant le fond, et de façon facultative, une ou plusieurs couches céramiques, ces couches étant disposées parallèlement les unes aux autres se superposant ainsi les unes sur les autres. Chaque couche céramique, sauf la couche céramique de dessus, se raccorde, par sa première face à l'une des couches céramiques qui lui fait suite, via un pont de céramique, et par sa seconde face, au verso de la première face, à l'une des couches céramiques qui lui fait suite, via un second pont de céramique. Une première cavité et une seconde cavité sont ménagées dans le corps de céramique, l'une à partir de la première face et l'autre à partir de la seconde face, de façon que le corps de céramique présente une coupe en serpentin. Le corps est pourvu en outre d'une première électrode et d'une seconde électrode en matière électroconductrice disposées, l'une le long de la première face et l'autre le long de la seconde faces, les électrodes adhérant à ces faces du corps de façon à provoquer le mouvement de l'actionneur.
PCT/US1997/013135 1996-07-25 1997-07-25 Actionneur piezo-electrique a coupe en serpentin Ceased WO1998007183A2 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US09/041,278 US6107726A (en) 1997-07-25 1998-03-11 Serpentine cross-section piezoelectric linear actuator
PCT/US1998/005917 WO1999005778A1 (fr) 1997-07-25 1998-03-24 Actionneur lineaire piezoelectrique a coupe en serpentin

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US2263496P 1996-07-25 1996-07-25
US60/022,634 1996-07-25

Publications (3)

Publication Number Publication Date
WO1998007183A2 WO1998007183A2 (fr) 1998-02-19
WO1998007183A3 WO1998007183A3 (fr) 1998-07-02
WO1998007183A9 true WO1998007183A9 (fr) 1998-08-06

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PCT/US1997/013135 Ceased WO1998007183A2 (fr) 1996-07-25 1997-07-25 Actionneur piezo-electrique a coupe en serpentin

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JP4220901B2 (ja) * 2001-10-30 2009-02-04 １．．．リミテッド 圧電デバイス
GB0126372D0 (en) 2001-11-02 2002-01-02 1 Ltd Curved electro-active actuators
GB0201458D0 (en) * 2002-01-23 2002-03-13 1 Ltd Curved electro-active actuators
US9294014B2 (en) * 2012-02-10 2016-03-22 Genziko Incorporated Power generator

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