Patent Application
20090278876
This invention relates to inkjet nozzle assemblies. It has been developed primarily to improve the efficiency of thermal bend actuated inkjet nozzles.
The following application has been filed by the Applicant simultaneously with this application:
The disclosure of these co-pending application is incorporated herein by reference. The above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.
The following patents or patent applications filed by the applicant or assignee of the present invention are hereby incorporated by cross-reference.
The present Applicant has described previously a plethora of MEMS inkjet nozzles using thermal bend actuation. Thermal bend actuation generally means bend movement generated by thermal expansion of one material, having a current passing therethough, relative to another material. The resulting bend movement may be used to eject ink from a nozzle opening, optionally via movement of a paddle or vane, which creates a pressure wave in a nozzle chamber.
Some representative types of thermal bend inkjet nozzles are exemplified in the patents and patent applications listed in the cross reference section above, the contents of which are incorporated herein by reference.
The Applicant's U.S. Pat. No. 6,416,167 describes an inkjet nozzle having a paddle positioned in a nozzle chamber and a thermal bend actuator positioned externally of the nozzle chamber. The actuator takes the form of a lower active beam of conductive material (e.g. titanium nitride) fused to an upper passive beam of non-conductive material (e.g. silicon dioxide). The actuator is connected to the paddle via an arm received through a slot in the wall of the nozzle chamber. Upon passing a current through the lower active beam, the actuator bends upwards and, consequently, the paddle moves towards a nozzle opening defined in a roof of the nozzle chamber, thereby ejecting a droplet of ink. An advantage of this design is its simplicity of construction. A drawback of this design is that both faces of the paddle work against the relatively viscous ink inside the nozzle chamber.
The Applicant's U.S. Pat. No. 6,260,953 describes an inkjet nozzle in which the actuator forms a moving roof portion of the nozzle chamber. The actuator takes the form of a serpentine core of conductive material encased by a polymeric material. Upon actuation, the actuator bends towards a floor of the nozzle chamber, increasing the pressure within the chamber and forcing a droplet of ink from a nozzle opening defined in the roof of the chamber. The nozzle opening is defined in a non-moving portion of the roof. An advantage of this design is that only one face of the moving roof portion has to work against the relatively viscous ink inside the nozzle chamber. A drawback of this design is that construction of the actuator from a serpentine conductive element encased by polymeric material is difficult to achieve in a MEMS fabrication process.
The Applicant's U.S. Pat. No. 6,623,101 describes an inkjet nozzle comprising a nozzle chamber with a moveable roof portion having a nozzle opening defined therein. The moveable roof portion is connected via an arm to a thermal bend actuator positioned externally of the nozzle chamber. The actuator takes the form of an upper active beam spaced apart from a lower passive beam. By spacing the active and passive beams apart, thermal bend efficiency is maximized since the passive beam cannot act as heat sink for the active beam. Upon passing a current through the active upper beam, the moveable roof portion, having the nozzle opening defined therein, is caused to rotate towards a floor of the nozzle chamber, thereby ejecting through the nozzle opening. Since the nozzle opening moves with the roof portion, drop flight direction may be controlled by suitable modification of the shape of the nozzle rim. An advantage of this design is that only one face of the moving roof portion has to work against the relatively viscous ink inside the nozzle chamber. A further advantage is the minimal thermal losses achieved by spacing apart the active and passive beam members. A drawback of this design is the loss of structural rigidity in spacing apart the active and passive beam members.
There is a need to improve on the bend actuation efficiency of thermal bend actuators.
In a first aspect the present invention provides a thermal bend actuator, comprising:
said method comprising passing an electrical current through said active beam so as to cause thermoelastic expansion of said active beam relative to said passive beam and bending of said actuator resulting in ejection of ink from said nozzle chamber, wherein said current is delivered in an actuation pulse having a pulse width of less than 0.2 microseconds.
Optionally, the nozzle chamber comprises a floor and a roof having a moving portion, whereby actuation of said actuator moves said moving portion towards said floor.
Optionally, said moving portion comprises said actuator.
Optionally, the nozzle opening is defined in the moving portion, such that the nozzle opening is moveable relative to the floor.
Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:
Figure is a graph showing variation of energy inputs required to achieve a peak deflection velocity of 3 m/s using different actuation pulse widths.
The moving portion 108 comprises a thermal bend actuator having a pair of cantilever beams in the form of an upper active beam 114 fused to a lower passive beam 116. The lower passive beam 116 defines the extent of the moving portion 108 of the roof. The upper active beam 114 comprises a pair of arms 114A and 114B which extend longitudinally from respective electrode contacts 118A and 118B. The arms 114A and 114B are connected at their distal ends by a connecting member 115. The connecting member 115 comprises a titanium conductive pad 117, which facilitates electrical conduction around this join region. Hence, the active beam 114 defines a bent or tortuous conduction path between the electrode contacts 118A and 118B.
The electrode contacts 118A and 118B are positioned adjacent each other at one end of the nozzle assembly and are connected via respective connector posts 119 to a metal CMOS layer 120 of the substrate 102. The CMOS layer 120 contains the requisite drive circuitry for actuation of the bend actuator.
The passive beam 116 is typically comprised of any electrically/thermally-insulating material, such as silicon dioxide, silicon nitride etc. The thermoelastic active beam 114 may be comprised of any suitable thermoelastic material, such as titanium nitride, titanium aluminium nitride and aluminium alloys. As explained in the Applicant's copending U.S. application Ser. No. 11/607,976 filed on 4 Dec. 2006 (Attorney Docket No. IJ70US), vanadium-aluminium alloys are a preferred material, because they combine the advantageous properties of high thermal expansion, low density and high Young's modulus.
Referring to
When it is required to eject a droplet of ink from the nozzle chamber 122, a current flows through the active beam 114 between the electrode contacts 118. The active beam 114 is rapidly heated by the current and expands relative to the passive beam 116, thereby causing the moving portion 108 to bend downwards towards the substrate 102 relative to the stationary portion 110. This movement, in turn, causes ejection of ink from the nozzle opening 112 by a rapid increase of pressure inside the nozzle chamber 122. When current stops flowing, the moving portion 108 is allowed to return to its quiescent position, shown in
In the nozzle design shown in
However, there is still a need to improve the overall efficiency of the bend actuator. Electrical losses can occur in the connecting member 115 due to the sharp bend in the current flow path; and thermal losses can occur by transfer of heat from the active layer 114 to the passive layer 116.
Turning now to
The nozzle assembly 200 is at the same stage of fabrication as the nozzle assembly 100 shown in
In
The heating bars 117 together occupy a relatively small region of the moving part 108. Typically, less than 10% or less than 5% of the total area of the moving part 108 is occupied by the heating bars 117. The heating bars together occupy a relatively small volume of the active beam 114. Typically, less than 50%, less than 40% or less than 30% of the total volume (and/or area) of the active beam 114 is occupied by the heating bars 117. Typically, the heater bars 117 have a width or a height dimension of less than 3 microns, less than 2.5 microns or less than 2 microns.
This configuration of the active beam 114 provides a number of advantages over the configuration shown in
Secondly, the connecting member 115 of the active beam 114 can be made larger, which minimizes current losses due to the sharp bend (180 degree bend) in the current flow path, and may obviate the need for the conduction pad 117. The majority of the active beam 114 of nozzle assembly 200 is dedicated to maximizing current flow into the heating bars 117, which are responsible for thermoelastic actuation. Typically, the connecting member 115 occupies at least 30% or at least 40% of the total volume of the active beam 114.
The nozzle assembly shown in
Typically, the total amount of energy input required for actuation in the present invention is reduced to less than 200 nJ or less than 150 nJ. Usually, the total energy input is in the range of 100-200 nJ or 100-150 nJ.
The skilled person will readily appreciate the advantages of overall lower energy input into thermal bend actuators in order to generate a predetermined peak deflection velocity. Thermal bend-actuated inkjet printheads may be made more efficient and require less power, in accordance with the bend actuators and methods described herein.
It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.
