WO2003063262A2 - Actionneurs electro-actifs courbes - Google Patents

Actionneurs electro-actifs courbes Download PDF

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Publication number
WO2003063262A2
WO2003063262A2 PCT/GB2003/000201 GB0300201W WO03063262A2 WO 2003063262 A2 WO2003063262 A2 WO 2003063262A2 GB 0300201 W GB0300201 W GB 0300201W WO 03063262 A2 WO03063262 A2 WO 03063262A2
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WO
WIPO (PCT)
Prior art keywords
layer
electro
active
actuator
curvature
Prior art date
Application number
PCT/GB2003/000201
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English (en)
Other versions
WO2003063262A3 (fr
Inventor
Richard Topliss
Original Assignee
1...Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 1...Limited filed Critical 1...Limited
Priority to GB0416569A priority Critical patent/GB2399679B/en
Publication of WO2003063262A2 publication Critical patent/WO2003063262A2/fr
Publication of WO2003063262A3 publication Critical patent/WO2003063262A3/fr

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Classifications

    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
    • H10N30/204—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
    • H10N30/2041—Beam type
    • H10N30/2042—Cantilevers, i.e. having one fixed end

Definitions

  • This invention relates to curved elements of electro-active material. More particularly, the invention related to electro-active actuators displaying a movement when energized.
  • Electro-active materials are materials that deform or change their dimensions in response to applied electrical conditions or, vice versa, have electrical properties that change in response to applied mechanical forces.
  • the best-known and most used type of electro-active material is piezoelectric material, but other types of electro- active material include electrostrictive material.
  • piezoelectric device is a block of pre-poled, i.e., pre-oriented, piezoelectric material activated in an expansion-contraction mode by applying an activation voltage in direction of the poling.
  • piezoelectric devices are capacitive in nature, they exhibit a number of desirable mechanical and electrical characteristics. They have a very efficient coupling of energy from applied charge to mechanical strain, leading to a high bandwidth, a large force output and negligible resistive heating. Due to their capacitive nature, these devices draw their least current at zero rate of displacement.
  • the electro-active material which in general is crystalline, ceramic or polymer- based, determines the stiffness of electro-active devices.
  • the electro- active effects are extremely small, e.g. in the order of 1 nm/V, the change in dimensions is relatively small and requires high voltages. Therefore, more complicated electro-active structures have been developed to achieve larger displacements.
  • piezoelectric multilayer stacks can be fabricated by joining multiple piezoelectric rings or plates, such that the total displacement of the stack is the sum of the displacements of each individual plate. Inner electrodes separate adjacent plates. The stacks provide vertical displacement in accordance with their piezoelectric charge coefficients and the potential applied. Several hundred plates are necessary to provide total displacements of 10 or more micron.
  • a standard unimorph bender is made up of a flat piezoelectric strip bonded to a non-active, purely elastic layer, e.g. a metallic shim, from one side.
  • a voltage is applied across the thickness of the piezoelectric layer, longitudinal and transverse strain develop.
  • the elastic layer opposes the transverse strain, thus causing a bending deformation.
  • the non-active layer has a thickness in the same order of magnitude as the electro- active layer.
  • Bimorphs have at least two laminated piezoelectric layers, thus having at least one internal and two external electrodes to which voltages of opposite polarisation is applied.
  • the application of an electric field across the two outer layers causes one layer to expand while the other contracts. This results in a bending motion with relatively wide displacements at the tip of the cantilever beam.
  • the displacement of the tip is related to the length of the cantilever, the applied voltage and the thickness of the cantilever.
  • Cantilever-based piezoelectric actuators require lengths on the order of 25 mm or more to achieve a free deflection of 0.3 mm.
  • a reinforced bimorph i.e., a bimorph having a centre shim
  • a bimorph bender exhibits more displacement than a unimorph bender of equal dimensions.
  • bender-type electro-active structures have focussed more or less exclusively on bimorph structures while often referring in passing to unimorphs.
  • bimorphs, particularly curved bimorphs require at least one central electrode and are therefore difficult to manufacture.
  • the bonding layer causes both an increase in hysteresis and a degradation of the displacement characteristics, in addition to delamination problems at the electrode interface layer. Also, the fabrication process, cutting, polishing, electroding, and bonding is rather laborious and costly. Any monolithic bender is expected to greatly reduce such - problems.
  • the known monolithic devices consist of a piezoelectrically active layer and a reduced passive layer formed in a high-temperature reduction treatment. An example of such a monolithic device is known as "rainbow" actuator.
  • Benders, stacks, tubes and other electro-active actuators are employed in a wide array of engineering systems, ranging from micro-positioning applications and acoustic wave processing to printing applications.
  • actuators are used in such applications to generate force and effect displacement, for example, to move levers or other force transmitting devices, pistons or diaphragms, to accurately position components, or to enable similar system functions.
  • Actuators employed for such functions are typically designed to provide a desired displacement or stroke over which a desired force is delivered to a given load.
  • electro-active actuators can generate a rotational or translational displacements or combinations of both movements.
  • a longitudinally extended layer of electro-active material bent to form a non-straight, curved line or contour of uniform or non-uniform curvature, having section with a small mean radius r to layer thickness t ratio.
  • the layer is preferably monolithic in the sense that it has no buried conductive layer or layers. Hence, electrodes to activate the electro-active layer are found exclusively on the surface of the layer. It will be appreciated by those skilled in the art that having a monolithic electro-active bender with displacement characteristics close to those of a bimorph of similar dimensions is advantageous in view of manufacturing such devices.
  • the radius of curvature is measured at a half-thickness point of the extended layer.
  • a practical limit to the ratio r/t appears to be closer to 0.6.
  • the value of r/t approaches infinity in the limit of a non-curved flat layer, the advantage offered by this invention reduces at a much higher values of r/t.
  • Preferable upper limits of the ratio r/t are hence 4, 3 or even only 2. Particularly advantageous are values of r/t in the region of 1.2.
  • the radius of curvature may change from point to point along the length of the layer.
  • the efficiency of the monolithic layer of is found to decrease with increasing value r/t, it is the design object of this invention to have low r/t values at as many points as possible, i.e. over as long stretches or sections of the layer as possible.
  • the parts where the ratio r/t is in the above range form a substantial amount of the curved actuator. It is particularly desirable to form a curved actuator with at least 50 % of its length being parts or sections wound such that the radius of curvature has a value close to the thickness of the layer. Practical devices are however likely to include straight sections or section with a large r/t ratio.
  • the layer will be curved in a direction perpendicular to the thickness of the layer that is with the axis of curvature perpendicular to the thickness direction.
  • any curve could be used.
  • the thickness of the layer of electro-active material may be measured in the direction along the radius of curvature, mat is perpendicular to me axis of curvature.
  • a very suitable form of generating long sections with small radii of curvature are wave-shaped benders and helical shaped benders.
  • a coiled helix exhibits large displacements compared to conventional benders.
  • the bender has an essentially linear but corrugated or wavy shape.
  • a corrugated linear bender may be folded or bent into an arc, a zigzag, serpentine or into circular or helical shapes.
  • Electro-active materials for use in the present invention are preferably piezoelectric materials such as PZT.
  • FIG. 1 A is a schematic cross-section of a known bimorph bender
  • FIG. IB is the bimorph bender of FIG. 1 A shown in an activated state;
  • FIG. 2 is a schematic cross-section of a known unimorph bender;
  • FIG. 3 A is a schematic cross-section of a bender illustrating features of the present invention;
  • FIG. 3B is a graph illustrating features of the present invention;
  • FIG. 4 is schematic cross-section of a corrugated bender
  • FIG. 5 is schematic cross-section of a coiled helical bender
  • FIG. 6A is a schematic perspective view of a first stage of an extrusion process suitable for manufacturing coiled helical benders
  • FIG. 6B is a schematic cross-section of the extrusion tool of FIG. 6A
  • FIG. 7 is a schematic perspective view of a second stage of an extrusion process suitable for manufachiring coiled helical benders
  • FIG. 8 is a schematic perspective view of a third stage of an extrusion process suitable for manufacturing coiled helical benders; and FIG. 9 is a flow chart summarizing the steps of FIG.6 to FIG.8.
  • FIGs. 1 and 2 Before referring to the novel configurations of benders, the salient features of known bender designs are illustrated in FIGs. 1 and 2.
  • a typical bimorph bender is shown in FIGs. 1 A and IB.
  • a bimorph bender 10 is known to include at least one pair of piezoelectric or piezo-ceramic plates 11 and 12, which may be elongated and are interposed between an inner electrode 13 or electrically conductive shim and outer electrodes 14.
  • the piezo-ceramic elements or plates 11 and 12 are shown electrically poled or polarized in a common direction, as represented by the arrows 111 and 121, respectively.
  • an electrical potential or voltage from a source 15 is applied across both of the piezo-ceramic elements 11 and 12 through the outer and inner electrodes 14, 13, as shown on FIG.
  • the element or plate 11 contracts and element or plate 12 expands, so that bimorph cantilever 10 bends in the direction perpendicular to its longitudinal axis.
  • the absolute displacement depends on the strength of the electric voltage applied to the bender and its material properties. If the polarity of the voltage applied from source 15 to bimorph leaf 10 is reversed, the direction of bending of the leaf will be opposite to that shown in FIG. IB.
  • the ummorph bender includes only one piezoelectric layer 21 having a top face electrode 22 and a bottom face electrode 23.
  • the lower electrode 23 is used to counter the strain in the piezoelectric layer when an electric field is applied across it. Therefore, the electrode 23 is shown to have a much greater thickness than the upper electrode 22 which is used solely as an electrically conductive layer.
  • An electrical power source 25 is used to supply the appropriate voltage to the electrodes. When energized the unimorph bends as shown.
  • FIG. 3 A The general features of a bender in accordance with the invention are shown in FIG. 3 A.
  • the bender of FIG. 3 A includes an electro-active layer 31 sandwiched between two electrode layers 32, 33.
  • both electrodes are used exclusively to shape the electrical field across the active layer 31.
  • the electro-active layer includes no passive layer, but forms a single homogeneous active layer. Therefore it appears appropriate to refer to a device in accordance with the invention as "monomorph".
  • the monomorphic structures of this invention are distinguishable from other monolithic devices by either its geometric features, in particular the r/t ratio as described below, or by the absence of a passive layer, i.e., a layer of material that is not electro-active.
  • the thickness of the electro-active layer is denoted as t.
  • a dashed curve 34 is shown.
  • This dashed circle 34 indicates the curvature at one point on the centre line of the layer 31. Its radius is denoted as the mean radius r.
  • the section of the bender has a semi-circular shape, all points located on the midpoint line or plane 34 of this example have an equal radius r of curvature. In general this is not the case and the curvature may change from point to point along the midplane.
  • the d33 effect has a predominant role in causing the displacement.
  • the d31 effect that contributes most to the displacement of the bender.
  • Both d33 and d31 are well known coefficients to describe the volume change of a piezoelectric material in relation to the electrical field applied to it. From the above general structure, there can be derived a number of geometrical configurations that firstly increase the curvature 1/r (given that increasing the thickness is straight-forward) and secondly increase the section of the layer exhibiting significant curvature.
  • FIG. 4 a wave shaped structure is shown.
  • Such structures per se are known for example as bimorphs with an apparently larger ratio r/t from the U.S. patent no. 3,816,774.
  • the piezoelectric layer made of PZT is interposed between two electrodes 42, 43.
  • the electrodes are at least one order, preferably two orders of magnitude thinner than the active layer 41.
  • the whole structure has a wave form assembled from semi-circular sections as shown in FIG.4 in a longitudinal cross-section. Both electrodes are connected to a voltage source (not shown). By applying an appropriate voltage across the layer 41, the free end of the wave shaped structure is displaced. Relative to its total active length, the bender of FIG. 4 has many sections that are strongly curved over more than 75 per cent of the length.
  • WO-01/47041 Another known geometry providing large sections of high curvature, i.e., small radii of curvature are described in the published international patent application WO-01/47041.
  • the devices of WO-01/47041 include what is referred to as "twice- coiled" structures having a helically wound piezoelectric tape with one (minor) helix being bend itself into a curve, spiral or (major) helix.
  • a twice-coiled helix is shown including a monolithic layer 51 firstly coiled into a minor helix with a radius to thickness ratio of under 2 and then bent into the three-quarter winding of the major helix 50.
  • the electro-active layer is activated using a first (outer) electrode 52 and a second (inner) electrode 53 to which a voltage is supplied in a manner well known and illustrated above.
  • a first (outer) electrode 52 and a second (inner) electrode 53 to which a voltage is supplied in a manner well known and illustrated above.
  • the other end of the actuator moves in direction of the axis of the major helix 50.
  • the three-quarter-turn major helix 50 is shown to better illustrate the device. However, adding more turns by selecting an appropriate pitch angle and radius of the major helix can produce devices exhibiting larger displacement.
  • the piezoelectric tape has a very small ratio of r/t for most of its length.
  • the present invention offers the possibility to efficiently build a variety of curved piezoelectric device that previously depended on bi-morph structures to generate sufficient displacement. In most cases, it is anticipated that redesigning the known device to one having smaller radii of curvature suffices for a transition to a monomorph device.
  • the devices according to this invention can therefore be built with a characteristic length (total diameter or length) of 1cm or less and layer thickness in the range of 0.3cm, even 0.1 cm and less.
  • a process of manufacturing such a device usually includes the step of a manufacturing a flat straight "green" tape having the desired thickness, width and length.
  • the tape in its green state is then wound round some plastically deformable former or mandrel.
  • the former with the tape is then wound round a second former having an outer diameter that matches the desired inner diameter of the major helix or bent of the device.
  • Extrusion can be designed as a continuous process, in which a plastically deformable rod is pulled off a reel at one end, PZT 'dough' that has been mixed with binders and/or plasticizer is fed into an Archimedes screw (or other ram) and is extruded onto the rod whilst at various points electrode ink and resinate are printed onto the rod and PZT and at the other end of the process the formed PZT/electrode combination tube is helically cut forming for example the minor helix of the double-wound actuator described above. After sfretching the minor coil it can be wound into a secondary coil and finally cut into single turn lengths and placed on a tray ready for sintering.
  • the individual stages are now described in more detail.
  • the first stage of the process as shown in FIG. 6 A requires a thermoplastic rod 61, used as the carrier on which the device is formed, to be pulled off a reel (not shown) at a constant speed.
  • a platinum resinate is then roller-printed using a drum 62 onto the surface of the rod.
  • the drum 62 rotates round the rod 61, covering the circumference in a thin layer of the resinate.
  • the rod 61 continues by passing through the centre of a conventional extrusion tool (generally 63). As the rod 61 passes through this extrusion tool, a layer of PZT dough 64 is co-extruded onto the surface of the rod 61.
  • the resinate being still wet (and inherently not adhering very well to the polyethylene rod material), is picked up onto the inner surface of the PZT layer 64, so that the rod now has a well-controlled layer of PZT with an inner electrode around it.
  • a further print roller 72 applies resinate to the outer surface of the PZT layer 64 to form thereon the outer electrode, as shown in Fig. 7.
  • the resulting cylinder of green elecfroded tape is then cut into a helix using a cutter 73 that rotates as the layered rod 61 advances.
  • the angle of the cutter 73 must be accurately set to correlate with the speed of the rod 61 and the rotational speed of the cutter to achieve the required helix pitch.
  • This stage produces a helically-cut tube 81; the next stage adjusts it and curves it, to make the required strongly curved and coiled monomorph.
  • the structure 81 is gently heated, to soften the thermoplastic PE rod 61, and is then stretched by means not shown to set the appropriate gap and pitch angle of the bimorph (the tensioning at this stage is also used to pull the structure through the machine). Then, whilst still warm, the stretched structure 81 is bent by winding it around a post 83 to form the secondary turn of the helix.
  • the thus strongly curved and coiled structure is then sliced to form the completed geometry - here depicted as a single turn of coiled PZT/electrode composite, and the individual coiled-coils thus formed are placed in a tray 84 for a subsequent sintering step (not illustrated). After sintering the devices are polarized applying a several hundred volts across the electrodes.
  • FIG. 9 the above steps are summarized as steps 91 to 98 in a flowchart.

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  • Micromachines (AREA)
  • General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)

Abstract

L'invention porte sur des actionneurs électro-actifs et sur leur procédé de fabrication. Lesdits actionneurs consistent en une couche s'étendant longitudinalement d'un matériau électro-actif recourbé de manière à former une ligne ou un dessin non rectiligne de courbure uniforme ou non uniforme et présentant une section dont le rapport (r/t) rayon de courbure moyen sur épaisseur est voisin de 0,5. Ladite couche, de préférence monolithique, ne comporte pas de couche électrode enfouie, ce qui en facilite la fabrication.
PCT/GB2003/000201 2002-01-23 2003-01-22 Actionneurs electro-actifs courbes WO2003063262A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0416569A GB2399679B (en) 2002-01-23 2003-01-22 Curved electro-active actuators

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GBGB0201458.7A GB0201458D0 (en) 2002-01-23 2002-01-23 Curved electro-active actuators
GB0201458.7 2002-01-23

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WO2003063262A2 true WO2003063262A2 (fr) 2003-07-31
WO2003063262A3 WO2003063262A3 (fr) 2004-03-04

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1717874A2 (fr) * 2005-04-28 2006-11-02 Brother Kogyo Kabushiki Kaisha Procédé de fabrication d'un actionneur piézo-électrique
US10570360B2 (en) 2012-11-27 2020-02-25 Cfd Research Corporation Multi-chambered cell culture device to model organ microphysiology

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3816774A (en) * 1972-01-28 1974-06-11 Victor Company Of Japan Curved piezoelectric elements
US4330730A (en) * 1980-03-27 1982-05-18 Eastman Kodak Company Wound piezoelectric polymer flexure devices
US4363993A (en) * 1979-12-12 1982-12-14 Sony Corporation Piezoelectric electro-mechanical bimorph transducer
EP0528279A1 (fr) * 1991-08-09 1993-02-24 Kureha Kagaku Kogyo Kabushiki Kaisha Dispositif piezoélectrique flexible
US5559387A (en) * 1994-05-13 1996-09-24 Beurrier; Henry R. Piezoelectric actuators
US5607535A (en) * 1993-05-20 1997-03-04 Fujitsu, Ltd. Method of manufacturing a laminated piezoelectric actuator
WO1998007183A2 (fr) * 1996-07-25 1998-02-19 Materials Systems Incorporated Actionneur piezo-electrique a coupe en serpentin
WO2001047041A2 (fr) * 1999-12-21 2001-06-28 1... Limited Dispositifs electro-actifs

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2375884B (en) * 2001-05-23 2005-01-05 1 Ltd Electro-active devices

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3816774A (en) * 1972-01-28 1974-06-11 Victor Company Of Japan Curved piezoelectric elements
US4363993A (en) * 1979-12-12 1982-12-14 Sony Corporation Piezoelectric electro-mechanical bimorph transducer
US4330730A (en) * 1980-03-27 1982-05-18 Eastman Kodak Company Wound piezoelectric polymer flexure devices
EP0528279A1 (fr) * 1991-08-09 1993-02-24 Kureha Kagaku Kogyo Kabushiki Kaisha Dispositif piezoélectrique flexible
US5607535A (en) * 1993-05-20 1997-03-04 Fujitsu, Ltd. Method of manufacturing a laminated piezoelectric actuator
US5559387A (en) * 1994-05-13 1996-09-24 Beurrier; Henry R. Piezoelectric actuators
WO1998007183A2 (fr) * 1996-07-25 1998-02-19 Materials Systems Incorporated Actionneur piezo-electrique a coupe en serpentin
WO2001047041A2 (fr) * 1999-12-21 2001-06-28 1... Limited Dispositifs electro-actifs

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1717874A2 (fr) * 2005-04-28 2006-11-02 Brother Kogyo Kabushiki Kaisha Procédé de fabrication d'un actionneur piézo-électrique
EP1717874A3 (fr) * 2005-04-28 2007-10-24 Brother Kogyo Kabushiki Kaisha Procédé de fabrication d'un actionneur piézo-électrique
US7793394B2 (en) 2005-04-28 2010-09-14 Brother Kogyo Kabushiki Kaisha Method of producing piezoelectric actuator
US10570360B2 (en) 2012-11-27 2020-02-25 Cfd Research Corporation Multi-chambered cell culture device to model organ microphysiology

Also Published As

Publication number Publication date
GB0201458D0 (en) 2002-03-13
GB0416569D0 (en) 2004-08-25
GB2399679B (en) 2005-06-22
WO2003063262A3 (fr) 2004-03-04
GB2399679A (en) 2004-09-22

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