Patent Application
20090179977
The present invention relates to the field of inkjet printing and in particular, inkjet printers with pagewidth printheads.
The following applications have been filed by the Applicant simultaneously with the present application:
The disclosures of these co-pending applications are 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 Applicant has developed a wide range of printers that employ pagewidth printheads instead of traditional reciprocating printhead designs. Pagewidth designs increase print speeds as the printhead does not traverse back and forth across the page to deposit a line of an image. The pagewidth printhead simply deposits the ink on the media as it moves past at high speeds. Such printheads have made it possible to perform full colour 1600 dpi printing at speeds in the vicinity of 60 pages per minute; speeds previously unattainable with conventional inkjet printers.
Printing at these speeds consumes ink quickly and this gives rise to problems with supplying the printhead with enough ink. Not only are the flow rates higher but distributing the ink along the entire length of a pagewidth printhead is more complex than feeding ink to a relatively small reciprocating printhead.
The high print speeds require a large ink supply flow rate. However, the ink flow needs to be filtered to protect the micron-scale nozzles from any ink borne contaminants. Ideally the filter pore size is relatively small to remove smaller, and therefore more particulate contaminants from the ink. Unfortunately, the smaller the filter pore size, the more it constricts the flow of ink. The area of the filter membrane can be increased so that the filter is not as much of a constriction to the flow. However, large filter membranes are generally counter to compact design.
Accordingly, the present invention provides a filter assembly for an inkjet printhead, the filter assembly comprising:
an inlet for connection to an ink supply;
an outlet for connection to an inkjet printhead;
a filter membrane for filtering ink flowing from the inlet to the outlet; and,
a chamber to house the filter membrane such that the filter membrane divides the chamber into an upstream portion for holding a quantity of the unfiltered ink, and a down stream portion for holding a quantity of the filtered ink; wherein,
the upstream portion tapers towards the outlet and the downstream portion tapers towards the inlet.
The invention recognizes that the flow rate of ink through the filter membrane is greatest at the points proximate the inlet and remote from the outlet. Therefore the high flow rate areas of the membrane need to be adjacent larger volumes of supply ink. Conversely, the areas of low flowrate do not need to be adjacent large volumes of supply ink. By tapering the upstream portion of the chamber towards the outlet, no-flow or low-flow zones are minimized. If the low-flow areas of the membrane are adjacent large volumes of ink, this is essentially a dead volume of nearly stagnant ink. Therefore, the invention maintains the filter area while reducing the chamber volume for more compact design.
Preferably, the chamber is elongate with the inlet adjacent one end of the chamber and the outlet adjacent the other end of the chamber such that the filter membrane extends diagonally across chamber. In another preferred form, the filter membrane extends in two intersecting planes within the housing. This configuration allows more membrane surface area within the same chamber volume. Preferably, the downstream portion of the chamber is between the two intersecting planes. In a further preferred form, the two intersecting planes meet at a line positioned centrally within the chamber adjacent one end. Preferably the outlet is positioned centrally within the chamber adjacent the other end. In particular embodiments, the membrane is mounted to a frame that defines the outlet to form a wedge-shaped cassette for insertion into the chamber wherein the membrane defines the sides tapering to the apex of the wedge. In a particularly preferred form, the outlet is at the base of the wedge shape.
In a particularly preferred form, the filter membrane is heat sealed to outer surfaces of the frame such that particulate contaminants generated by the heat sealing process remain on in the upstream or ‘dirty’ portion of the chamber.
Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:
The invention will now be described with reference to the Applicant's printhead cartridge and print engine shown in
The printhead assembly 2 has an LCP (liquid crystal polymer) molding 20 supporting a series of printhead ICs 30 secured with an adhesive die attach film (not shown). The printhead ICs 30 have an array of ink ejection nozzles for ejecting drops of ink onto the passing media substrate 22. The nozzles are MEMS (micro electro-mechanical) structures printing at true 1600 dpi resolution (that is, a nozzle pitch of 1600 npi), or greater. The fabrication and structure of suitable printhead IC's 30 are described in detail in U.S. Ser. No. 11/246,687 (our docket no. MNN001US) the contents of which are incorporated by reference. The LCP molding 20 has a main channel 24 extending between the inlet 36 and the outlet 38. The main channel 24 feeds a series of fine channels 28 extending to the underside of the LCP molding 20. The fine channels 28 supply ink to the printhead ICs 30 through laser ablated holes in the die attach film.
Above the main channel 24 is a series of non-priming air cavities 26. These cavities 26 are designed to trap a pocket of air during printhead priming. The air pockets give the system some compliance to absorb and damp pressure spikes or hydraulic shocks in the ink. The printers are high speed pagewidth printers with a large number of nozzles firing rapidly. This consumes ink at a fast rate and suddenly ending a print job, or even just the end of a page, means that a column of ink moving towards (and through) the printhead assembly 2 must be brought to rest almost instantaneously. Without the compliance provided by the air cavities 26, the momentum of the ink would flood the nozzles in the printhead ICs 30. Furthermore, the subsequent ‘reflected wave’ can generate a negative pressure strong enough to deprime the nozzles.
The outlet manifold 50 has a fluidic damper that resonates at a frequency selected to attenuate potentially problematic standing waves at any of the resonant frequencies of the main channel 24. The operation of the fluidic damper is explained in detail in the Applicant's co-pending US patent application, our docket no. RRE013US, the contents of which are incorporated herein by reference.
Flex PCB 70 is adhered to the side of the air cavity molding 72 and wraps around to the underside of the channel molding 68. The printer controller on the print engine connects to the line of contacts 33. At the other side of the flex PCB 70 is a line of wire bonds 64 to electrically connect the conductors in the flex 70 to each of the printhead ICs 31. The wire bonds 64 are covered in encapsulant 62 which is profiled to have a predominantly flat outer surface. On the other side of the air cavity molding 72 is a paper guide 74 to direct sheets of media substrate past the printhead ICs at a predetermined spacing.
As seen in
The stack of wedge-shaped filter cassettes 98 in the inlet manifold 48 give a large filter membrane area within a small volume. This helps to keep the printhead cartridge compact and prolongs the operational life of the nozzles.
The above embodiments are purely illustrative and not restrictive or limiting on the scope of the invention. The skilled worker will readily recognize many variations and modifications which do not depart from the spirit and scope of the broad inventive concept.
