The field of the invention relates to the field of inkjet printing devices and, in particular, discloses an ink jet nozzle assembly that includes a displaceable ink pusher.
Many different types of printing have been invented, a large number of which are presently in use. The known forms of printing have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilisation of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electrostatic field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex
(see also U.S. Pat. No. 3,373,437 by Sweet et al).
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal inkjet printing has become an extremely popular form of inkjet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclose ink jet printing techniques that rely upon the activation of an electro-thermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Manufacturers such as Canon and Hewlett Packard manufacture printing devices utilizing the electro-thermal actuator.
A particular problem associated with thermal printers is that they are not suitable for pagewidth printheads capable of high definition printing. Such printheads require a very large number of densely packed nozzle arrangements that span a print medium. Applicant submits that operation of a required number of electro-thermal actuators would generate an unacceptable level of heat. This is the primary reason why the Applicant has developed MEMS-based printing technology. Such systems can be fabricated to define printhead chips having a large number of densely packed nozzle arrangements. In particular, Applicant has developed page width printheads that are capable of color printing over 20 pages per minute at resolution finer than 1200 dpi. Applicant has carried out many thousands of simulations in order to achieve an optimal design. In this work, Applicant has found that the ink pusher should move at least 1 micron in order to achieve effective drop ejection. Applicant has also found that certain problems arise with fabrication when an ink pusher is designed to move more than 5 microns. It follows that movement between 1 and 5 microns is most preferable.
As set out above, piezo-electric systems have been developed that act physically on the ink to eject the ink from the nozzle arrangements. In order to achieve ink drop ejection, the ink pusher is required to move through a particular range. Piezo-electric systems that use an ink pusher rely on the deflection of a plate or the like as a result of a force exerted in a direction that is generally at right angles to the direction of drop ejection. Applicant has found that a deflection of at least one micron would require a plate having a cross sectional area in excess of 100 square microns. This requirement precludes the fabrication of a printhead chip having the requisite number and density of nozzle arrangements.
A further problem with piezo-electric systems is that it is difficult to achieve an ink pusher that is capable of more than 100 nanometers of movement. This is largely due to the fact that such systems rely on buckling or deflection to achieve the necessary movement.
When creating a large number of inkjet nozzles which together form a printhead, it is necessary or desirable to ensure that the printhead is of a compact form so as to ensure that the printhead takes up as small a space as possible. Further, it is desirable that any construction of a printhead is as simple as possible and preferably; the number of steps in construction is extremely low, therefore ensuring simplicity of manufacture. Further, preferably each ink ejection nozzle is of a standard size and the ink forces associates with the ejection are regular across the nozzle.
Further, where the ink ejection mechanism is of a mechanical type attached to an actuator device, it is important to ensure that a substantial clearance is provided between an ink ejection nozzle and the surface of the paddle. Unless a large clearance is provided (of the order of 10 microns in the case of a 40 micron nozzle) a number of consequential problems may arise. For example, if a mechanical paddle ejection surface and nozzle chamber walls are too close, insufficient ink will be acted on by the paddle actuator so as to form a drop to be ejected. Further, high pressures and drag is likely to occur where movement of a paddle occurs close to nozzle chamber walls. Further, if the paddle is too close to the nozzle, there is a danger that an unwanted meniscus shape may occur after ejection of an ink drop with the ink meniscus surface attaching to the surface of the paddle.
Further, should the ink ejection mechanism be formed on a silicon wafer type device utilizing standard wafer processing techniques, it is desirable to minimize the thickness of any layer of material when forming the system. Due to differential thermal expansions, it is desirable to ensure each layer is of minimal thickness so as to reduce the likelihood of faults occurring during the fabrication of a printhead system due to thermal stress. Hence, it is desirable to construct a printhead system utilizing thin layers in the construction process.
This invention is based on the fact that the Applicant has achieved a generic MEMS structure that facilitates a particular range of movement of an ink pusher, which can be in the form of a paddle. The advantage of this is set out above.
According to a first aspect of the invention, there is provided an ink jet printhead chip that comprises
a substrate;
drive circuitry positioned in the substrate; and
a plurality of nozzle arrangements positioned on the substrate, each nozzle arrangement comprising
nozzle chamber walls and a roof wall that define a nozzle chamber and an ink ejection port in the roof wall in fluid communication with the nozzle chamber;
an ink pusher that is operatively positioned with respect to the nozzle chamber and is displaceable through a range of between 1 micron and 5 microns to eject ink from the ink ejection port; and
an actuator that is connected to the drive circuitry and the ink pusher to displace the ink pusher on receipt of an electrical signal from the drive circuitry.
Preferably, each ink pusher is displaceable through a range of between 1.5 microns and 3 microns.
The ink jet printhead chip may be the product of a MEMS fabrication technique.
Each ink pusher may be in the form of a paddle member that is positioned in the nozzle chamber to span the nozzle chamber.
Each actuator may include an actuator arm that is fast with the substrate at one end and attached to the paddle member at an opposed end. The actuator arm may incorporate a thermal bend mechanism that is configured to deflect when heated by said electrical signal from the drive circuitry to displace the paddle member. Each thermal bend mechanism may include a portion of the actuator arm that is of a material having a coefficient of thermal expansion which is such that the material is capable of thermal expansion to an extent sufficient to perform work and an electrical heating circuit positioned on said portion of the actuator arm to heat a side of said portion so that said portion experiences differential thermal expansion resulting in deflection of the actuator arm and the displacement of the paddle member.
Alternatively, the roof wall may define the ink pusher. Each actuator may include an actuator arm that is fast with the substrate at one end and attached to the roof wall at an opposed end. The actuator arm may incorporate a thermal bend mechanism that is configured to deflect when heated by said electrical signal from the drive circuitry to displace the roof wall towards the substrate.
The actuator arm may be of a conductive material having a coefficient of thermal expansion that is such that the material is capable of thermal expansion to an extent sufficient to perform work. A portion of the actuator arm may define a heating circuit which is configured to expand thermally on receipt of said electrical signal, said portion of the actuator arm being positioned so that the actuator arm is deflected towards the substrate upon such deflection.
There is disclosed herein an ink jet nozzle assembly including a nozzle chamber containing ink to be ejected and a fluidic seal comprising a meniscus formed by said ink between two solid surfaces of said assembly that move relative to one another when the assembly is activated in use, and wherein at least one of said surfaces has a thin lip adjacent said fluidic seal to hinder wicking of said ink along said at least one surface.
Preferably said lip is less than or equal to about 1 micrometer thick.
There is further disclosed herein an ink jet nozzle assembly including:
a nozzle chamber having an inlet in fluid communication with an ink reservoir and a nozzle in fluid communication with a surrounding atmosphere;
the chamber including a fixed portion, a movable portion and a clearance space therebetween, relative movement between the fixed portion and the movable portion in an ejection phase reducing an effective volume of the chamber, and alternate relative movement in a refill phase enlarging the effective volume of the chamber;
the clearance space containing an ink/air interface, surface tension in ink across a meniscus at the interface forming a fluidic seal between the chamber and the atmosphere; wherein:
the clearance space, the nozzle and the inlet are dimensioned relative to one another such that ink is ejected preferentially form the chamber through the nozzle in droplet form in the ejection phase, and ink is alternately drawn preferentially into the chamber from the reservoir through the inlet in the refill phase without said fluidic seal breaking.
Preferably the chamber incorporates a rim extending outwardly adjacent at least a portion of the fluidic seal and is disposed to minimise wicking of ink from the chamber across the seal.
Preferably the movable portion includes the nozzle and the fixed portion is mounted on a substrate.
Preferably the fixed portion includes the nozzle mounted on a substrate and the movable portion includes an actuator.
Preferably a largest distance between the fixed portion and the movable portion across the clearance space is less than approximately 5 micrometers.
Preferably said distance is less than approximately 3 micrometers. Preferably said distance is less than approximately 1 micrometer.
Preferably said rim extends substantially around a periphery of the fluidic seal, immediately adjacent the clearance space.
Preferably a lower section of the rim includes a ledge portion overhanging a recess adapted to collect any residual ink wicking across the seal.
Preferably an outwardly protruding lip extends around the nozzle to minimise wicking of ink across an outer surface of the nozzle chamber.
Preferably at least one surface adjacent the clearance space includes a hydrophobic coating to enhance performance of the fluidic seal.
Preferably the hydrophobic coating is formed substantially from polytetrafluoroethylene (PTFE).
Preferably the ink jet nozzle assembly is manufactured using micro-electro-mechanical-systems (MEMS) techniques.