Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/16—Production of nozzles
  • B41J2/1621—Manufacturing processes
  • B41J2/164—Manufacturing processes thin film formation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/14—Structure thereof only for on-demand ink jet heads
  • B41J2/14201—Structure of print heads with piezoelectric elements
  • B41J2/14209—Structure of print heads with piezoelectric elements of finger type, chamber walls consisting integrally of piezoelectric material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/16—Production of nozzles
  • B41J2/1607—Production of print heads with piezoelectric elements
  • B41J2/1609—Production of print heads with piezoelectric elements of finger type, chamber walls consisting integrally of piezoelectric material

Definitions

• the present invention relates to actuators and in particular actuators for droplet deposition apparatus.
• Droplet deposition apparatus or inkjet print heads are capable of placing small droplets of fluid onto a substrate.
• the apparatus which will be called an inkjet print head from now on - even though fluids other than ink may be ejected - force the fluid from nozzles which communicate with an ejection chamber.
• Actuators corresponding with the ejection chamber apply the force that ejects the fluid.
• These actuators take a number of different forms but tend to fall within one of two categories. The first of which is mechanical, where an electrical pulse causes the actuator to deform, and includes such technology as electrostatic, thermal bend or piezoelectric for example.
• the second category is thermal or bubble actuators, where heat is applied to bring the fluid to its nucleation point. The resultant bubble pressurises the ink in the chamber and forces some of it through the nozzle.
• a voltage with the same polarity as the poling voltage causes additional expansion along the poling axis and contraction perpendicular to the poling axis.
• a voltage with the opposite polarity has the opposite effect: contraction along the poling axis, and expansion perpendicular to the poling axis.
• the piezoelectric element returns to its poled dimensions when the voltage is removed from the electrodes.
• the piezoelectric element moves in thickness shear or face shear.
• one type of expansion is accompanied by another type of contraction which compensate each other resulting in no change of volume.
• the expansion of length of a plate may be compensated by an equal contraction of width or thickness.
• the compensating effects are not of equal magnitude and net volume change does occur. In all cases, the deformations are very small when amplification by mechanical resonance is not involved.
• Figure 1 describes the standard directions of piezoelectric material.
• the three orthogonal axis are termed 1 ,2 and 3.
• the polar, or 3 axis is always taken parallel to the direction of polarization within the ceramic.
• the indexes 4, 5 and 6 represent a shear movement around the 1 , 2 and 3 axis respectively.
• the direction of polarization is established during the poling process by a strong electrical field applied between two electrodes.
• double subscripts e.g. dij
• the first subscript gives the direction of the excitation, the second describes the direction of the system response. For example, d33 applies when the electric field is along the polarization axis (direction 3) and the strain (deflection) is along the same axis.
• the volume displaced in the pressure chambers also displaces a corresponding volume of fluid.
• the fluid is preferably in liquid form but may also be a gas.
• the coatings may have a functional feature other than simply stiffening portions of the wall such as, for example, a passivation function or an electrically conducting function.
• Two or more different coating materials may be provided on either or both sides of the wall in a layered arrangement.
• the same coating material, or materials may be provided on both sides of the wall in different thickness, the thickness on the or each side being selected to provide the relative difference in stiffness.
• the electrode means are preferably provided by electrodes located on opposing faces of the wall such that a field generated between them lies parallel to the array direction.
• the electrodes are of different thickness to provide the relative difference in stiffness.
• the electrodes may be formed by electroless plating.
• a seed layer can be deposited on one side of each wall using a directional technique eg. vacuum plating.
• the seed layer is then plated up with a suitable electroless process, resulting on a plated layer on one side of the wall but not on the other.
• a seed layer is then deposited on the ' other side of each wall, and the electroless plating process continued. Although both sides of the wall will now be plated, the initial layer on one side only will result in differential thicknesses being maintained.
• each pressure chamber may be of equal dimensions and comprise a nozzle through which fluid is ejected.
• some of the pressure chambers may be designated ejection chambers from which droplets are ejected through a nozzle whilst the remaining chambers are designated dummy chambers from which no fluid is ejected.
• the dummy chambers may comprise liquid or air.
• the cover may be stiff or preferably have a degree of flexibility to allow flexure of the displaceable walls, a flexible hinge may be provided by, for example a flexible glue layer may adhesively join the tops of the displaceable walls with the cover.
• Figures 6 and 7 illustrate the use of bending in actuation.
• Figure 8 shows an arrangement wherein channels can be actuate substantially independently.
• Figures 9 to 12 show alternative structures which allow simultaneous actuation of adjacent channels.
• an ink jet printhead 10 comprises a multiplicity of parallel ink channels 12 forming an array in which the channels are mutually spaced in an array direction perpendicular to the length of the channels.
• the channels are formed at a density of two or more channels per mm. in a laminated sheet 14 of piezo-electric material, suitably PZT, poled in the direction of arrows 15, 15' and are defined each by side walls 16 and a bottom surface, the thickness of the PZT being greater than the channel depth.
• the channels 12 are open topped and in the printhead are closed by a top sheet 20 of insulating material which is thermally matched to the sheet 14 and is disposed parallel to the bottom surfaces of the channels and bonded to the tops 22 of the walls 16.
• the channels 12 on their side wall and bottom surfaces are lined with a metallised electrode layer 24. It will be apparent therefore that when a potential difference of similar magnitude but opposite sign is applied to the electrodes on opposite faces of each of two adjacent walls 16, the walls will be subject to electric fields normal to the poling direction 15. The walls are in consequence deflected in shear mode, and are displaced to the positions indicated by the broken lines 28.
• the channels 12 comprise a forward part of uniform depth which is closed at its forward end by a nozzle plate 38 having formed therein a nozzle 40 from which droplets of ink in the channel are expelled by activation of the facing actuator walls 16 of the channel.
• the channel 12 also has a part of lesser depth extending from the tops of the walls 16.
• the metallised plating 24 which is on opposed surfaces of the walls 16 occupies the depth of the channel side walls but does not extend the length of the channel to minimise the capacitive load of the print head.
• a suitable electrode metal used is an alloy of nickel and chromium, i.e. nichrome or electroplated or electroless plated nickel.
• the electrodes are deposited by first using a plating angle to allow electrode deposition on the full depth of the side walls.
• a mask is used to prevent deposition on the walls in the manifold region.
• the step is repeated to allow electrodes to be formed on both sides of each wall.
• a third step is carried out with deposition perpendicular to the to the base of the channels, such that deposition occurs on the bottom of each channel and the channel run out in the manifold region.
• a droplet is ejected from each channel by applying a suitable waveform to the electrodes 24 on either side of the wall 16.
• a particularly preferred waveform is known as a draw-release-reinforce waveform.
• the volume of a selected channel is initially increased by drawing both walls bounding the chamber outwards and the walls are held in this position for a period of time. After the period of time has elapsed the walls are moved inwards to reduce the volume of the selected channel thereby ejecting a drop through the nozzle.
• each wall acts on neighbouring channels it is not possible to eject a droplet from both of the neighbouring channels simultaneously. Care must also be taken that droplets are not ejected from unselected channels.
• FIG. 4 Another form of an actuator is described with reference to Figure 4.
• a multiplicity of parallel channels are formed which are separated from one another by parallel walls of a piezoelectric ceramic.
• the direction of polarisation is, however, orthogonal to the direction of poling described with reference to Figure 2.
• the walls are polarised in the array direction and electrodes provided on either side of the wall apply a field across the wall in a direction parallel to the polarisation direction.
• Channels 12 are formed into one side of the PZT, and have nozzles 50 associated.
• Electrodes 24 are provided on the inside walls of the channels.
• the driving electrodes 24 are also used to apply the field which polarises the PZT as shown by arrows 15 in Figure 3.
• the electrodes on either side of the wall and base are of the same thickness.
• the wall 16 will thicken in d33 and contract in height in d31 as depicted by the dotted lines.
• the net displacement for a given channel in these directions is given the nomenclature ⁇ 3 i wa ⁇ and ⁇ 33Wa ⁇ .
• the total net displacement is therefore given by the equation:
• the stiffness of the base 18, however, can inhibit the bending movement of the wall and a design modification can be made to further improve the ejection efficiency.
• the poling direction within the base may be reversed, or the thickness of the base may be reduced.
• the structure should be sufficiently compliant at the top or the bottom (or both) of the wall to allow the necessary wall rotation there.
• the top plate 1114 may be made of a sufficiently compliant material.
• a mechanical hinge could be employed where the wall meets the top or bottom plates.
• the displacements in channel 1230 can be made to cancel each other, thereby causing substantially no net change in volume in channel 1230, while the displacements in channel 1220 reinforce to cause droplet ejection from that channel.
• actuation is effected by the application of a single field across the whole height of the wall.
• the direct mode wall portion 1202 it will be necessary for the direct mode wall portion 1202 to have increased activity, to balance the activity of portions 1204 and 1206. This can be achieved by using a greater electric field across this portion, higher activity piezoelectric material, a greater wall height for this portion, or any combination of these.
• direct mode operation could be applied to the base or roof of the channels. It can be seen though that the contraction in height of the wall portion acting in direct mode will tend to cause deflection of the base portion 1240 causing some displacement in both neighbouring channels.
• upper wall portions 1304 and 1306 act in the same way as described above in relation to Figure 9.
• the lower portion of the wall is formed of two pairs of chevron-like actuating portions 1308 and 1310, separated by a gap 1312.
• Figures 8 to 12 all employ two different modes of actuation, one causing displacements of the same sign in the two neighbouring channels (ie reducing the volume in both channels or increasing the volume in both channels) and one causing displacement of opposite sign in the two neighbouring channels (ie reducing the volume of one and increasing the volume of the other).
• the two different modes of actuation are superposed on the same wall portion, ie a single actuation surface undergoing two different modes of deflection.
• the two modes of actuation can be considered to derive from different wall portions having different actuation modes.
• upper and lower portions of the wall have different structures associated with different actuation modes, however there is some superposition of actuation modes in the lower portion as described above.
• each layer is conformal and cover the entire actuator.
• a nozzle is attached to the outer electrically conducting layer using an appropriate attach mechanism e.g. epoxy, thermocompressive, eutectic, anodic etc.

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Particle Formation And Scattering Control In Inkjet Printers (AREA)
• Reciprocating Pumps (AREA)
• Coating Apparatus (AREA)
• Fluid-Pressure Circuits (AREA)

Priority Applications (8)

Applications Claiming Priority (2)

Publications (2)

Family

ID=32865808

Family Applications (1)

Country Status (12)

Cited By (1)

Families Citing this family (6)

Family Cites Families (15)

• 2004
  • 2004-07-10 GB GBGB0415529.7A patent/GB0415529D0/en not_active Ceased
• 2005
  • 2005-07-11 EP EP05761560.1A patent/EP1809480B1/en not_active Expired - Lifetime
  • 2005-07-11 BR BRPI0513219-3A patent/BRPI0513219A/pt not_active IP Right Cessation
  • 2005-07-11 CA CA002573041A patent/CA2573041A1/en not_active Abandoned
  • 2005-07-11 AU AU2005261498A patent/AU2005261498A1/en not_active Abandoned
  • 2005-07-11 RU RU2007105101/12A patent/RU2007105101A/ru not_active Application Discontinuation
  • 2005-07-11 KR KR1020077003210A patent/KR20070032811A/ko not_active Withdrawn
  • 2005-07-11 US US11/631,909 patent/US7780273B2/en not_active Expired - Fee Related
  • 2005-07-11 WO PCT/GB2005/002746 patent/WO2006005952A2/en not_active Ceased
  • 2005-07-11 JP JP2007519890A patent/JP4801061B2/ja not_active Expired - Fee Related
  • 2005-07-11 CN CNA2005800232722A patent/CN101107128A/zh active Pending
• 2007
  • 2007-01-03 IL IL180533A patent/IL180533A0/en unknown

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