EP1827836B1

EP1827836B1 - Capping system for inkjet printers having arcuately moveable printheads

Info

Publication number: EP1827836B1
Application number: EP04801127A
Authority: EP
Inventors: Norman M. Silverbrook Research Pty Ltd. BERRY; Akira Silverbrook Research Pty Ltd. NAKAZAWA; Kia Silverbrook Research Pty Ltd Silverbrook
Original assignee: Silverbrook Research Pty Ltd
Current assignee: Silverbrook Research Pty Ltd
Priority date: 2004-12-06
Filing date: 2004-12-06
Publication date: 2009-09-02
Anticipated expiration: 2024-12-06
Also published as: CA2588621A1; CA2588621C; KR100959216B1; AU2004325542B2; KR20070086544A; EP1827836A1; ATE441528T1; EP1827836A4; AU2004325542A1; WO2006060840A1; JP2008522857A; DE602004023008D1

Abstract

A capping mechanism is disclosed for a printhead (51) having a plurality of nozzles arranged to deliver ink onto print media which is transported past the printhead. The capping mechanism comprises actuating means (84, 85) arranged to move the printhead (51) in an arcuate direction away from a transport plane of the print media, from a printing first position to a capping second position, and a capping member (82) which is arranged to engage in nozzle capping engagement (57) with the printhead when the printhead is in the second position.

Description

FIELD OF THE INVENTION

This invention relates in general terms to Inkjet printers and more particularly to a mechanism for and a method of capping a pagewidth printhead assembly for an Inkjet printer. By "pagewidth" printhead assembly is meant one having a printhead which has a length which extends across substantially the full width of (paper, card, textile or other) media to be printed and which, whilst remaining in a stationary position, is controlled to deposit printing ink across the full print width of advancing print media.

DEFINITIONS

The expressions "pagewidth printhead" and "pagewidth printhead assembly" are applicable to a printhead, and an assembly incorporating a printhead, that has a length which extends across substantially the full width of (paper, card, textile or other) media to be printed and which, whilst remaining in a stationary position, is controlled to deposit printing ink across the full print width of advancing print media.
The expression "reciprocating printhead" is applicable to a printhead of the type that normally is integrated with an ink cartridge, which is carried by a reciprocating carriage and which is controlled to deposit printing ink whilst scanning across incrementally advancing print media

BACKGROUND OF THE INVENTION

The printheads of Inkjet printers have a series of nozzles from which individual ink droplets are ejected to deposit on print media to form desired printed images. The nozzles are incorporated in various types of printheads and their proper functioning is critical to the creation of quality images. Thus, any partial or total blockage of even a single nozzle may have a significant impact on a printed image, particularly in the case of a pagewidth printer.
The nozzles are prone to blockage due to their exposure to ever-present paper dust and other particulate matter and due to the tendency of ink to dry in the nozzles during, often very short, idle periods. That is, ink which is awaiting delivery from a nozzle forms a meniscus at the nozzle mouth and, when exposed to (frequently warm) air, the ink solvent is evaporated to leave a nozzle blocking deposit
Servicing systems are conventionally employed for maintaining the functionality of printheads, such systems providing one or more of the functions of capping, purging and wiping. Capping involves the covering of idle nozzles to preclude exposure of ink to drying air. Purging is normally effected by evacuating a capping chamber, thereby sucking deposits from the printhead that block or have the potential to block the nozzles. Wiping is performed in conjunction with the capping and/or purging functions and involves gently sweeping a membrane across the face of the printhead.
The majority of conventional Inkjet printers, particularly so-called desk top printers, employ reciprocating printheads which, as above mentioned, are driven to traverse across the width of a momentarily stationary page or portion of print media. In these printers, service stations are provided at one side of the printing zone and, on command, the printhead is traversed to the service station where it is docked for such time as servicing is performed and/or the printer is idle. However, inclusion of the service stations increases the total width of the printers and this is recognised as a problem in the context of trends to minimise the size of desk-top printers.
Moreover, the above described servicing system cannot feasibly be employed in relation to pagewidth printers which, as above mentioned, have a stationary printhead assembly that extends across the full width of the printing zone. The printhead assembly effectively defines the print zone and it cannot be moved outside of that zone for servicing. Furthermore, a pagewidth printhead has a significantly larger surface area and contains a vastly greater number of nozzles than a conventional Inkjet print
head, especially in the case of a large format printer, all of which dictate an entirely different servicing approach from that which has conventionally been adopted.
JP05330037A discloses the preamble of claim 1: a printer having two pagewidth print heads in confronting relationship and two associated capping members, actuating mechanisms to move heads in an arcuate direction from the printing to the capping position and actuating mechanisms to move capping members to effect capping engagement with heads.

SUMMARY OF THE INVENTION

Accordingly, a first embodiment of the invention provides a capping mechanism as detailed in claim 1. The invention also relates to a printer as detailed in claim 11. Advantageous embodiments are provided in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings-

Figure 1 shows a diagrammatic representation of a printer that incorporates a printhead assembly having two substantially identical printheads,
Figure 2 shows a perspective view of one of the printheads as seen in the direction of a printing zone of the printhead,
Figure 3 shows a sectional end view of one of the printheads,
Figure 4 shows a perspective view of an end portion of a channelled support member removed from the printhead of Figure 3 and fluid delivery lines connected to the support member,
Figure 5 shows an end view of connections made between the fluid delivery lines and the channelled support member of Figure 4,
Figure 6 shows a printed circuit board, with electronic components mounted to the board, when removed from a casing portion of the printhead of Figure 3,
Figures 7A, B and C show in block diagrammatic form capping mechanism according to the invention,
Figures 8A, B and C show in block diagrammatic form a second capping mechanism,
Figures 9A, B and C show in block diagrammatic form a third capping mechanism,
Figures 10A, B, C and D show in block diagrammatic form a fourth capping mechanism, being one that also includes a purging facility,
Figure 11 shows a perspective view of a capping member of a type suitable for use in the mechanisms shown in Figures 7 to10,
Figure 12 shows, in perspective, a sectional view of a portion a printhead chip that is mounted to the printhead and which incorporates printing fluid delivery nozzles and nozzle actuators,
Figure 13 shows a vertical section of a single nozzle in a quiescent state,
Figure 14 shows a vertical section of a single nozzle in an initial activation state,
Figure 15 shows a vertical section of a single nozzle in a later activation state,
Figure 16 shows a perspective view of a single nozzle in the activation state shown in Figure 15,
Figure 17 shows in perspective a sectioned view of the nozzle of Figure 16,
Figure 18 shows a sectional elevation view of the nozzle of Figure 16,
Figure 19 shows in perspective a partial sectional view of the nozzle of Figure 14,
Figure 20 shows a plan view of the nozzle of Figure 13,
Figure 21 shows a view similar to Figure 20 but with lever arm and moveable nozzle portions omitted,
Figure 22 illustrates data flow and functions performed by a print engine controller ("PEC") that forms one of the circuit components shown in Figure 6,
Figure 23 illustrates the PEC of Figure 22 in the context of an overall printing system architecture, and
Figure 24 illustrates the architecture of the PEC of Figure 23.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As illustrated in Figure 1, a pagewidth printhead assembly 50 composed of two substantially identical pagewidth printheads 51 is mounted within a printer 52. The printer is shown in outline because it may be constituted by any one of a large number of printer types; including desk-top, office, commercial and wide format printers. Also, the printer may incorporate a single sheet feed system or a roll-feed system for print media (not shown), and it may be arranged for printing alpha-numeric, graphical or decorative images, the latter being relevant to the printing of textiles and wall coverings. Various types of pagewidth printheads (including thermal or piezo-electric activated bubble jet printers) that are known in the art may alternatively be employed.
As illustrated in Figures 2 to 6 for exemplification purposes, each of the printheads 51 comprises four printhead modules 55, each of which in turn comprises a unitary arrangement of:

a) a plastics material support member 56,
b) four printhead micro-electro-mechanical system (MEMS) integrated circuit chips 57 (referred to herein simply as "printhead chips"),
c) a fluid distribution arrangement 58 mounting each of the printhead chips 57 to the support member 56, and
d) a flexible printed circuit connector 59 for connecting electrical power and signals to each of the printhead chips 57.

However, it will be understood that each of the printheads 51 may comprise substantially more than four modules 55 and/or that substantially more than four printhead chips 57 may be mounted to each module.
Each of the chips (as described in more detail later) has up to 7680 nozzles formed therein for delivering printing fluid onto the surface of the print media and, possibly, a further 640 nozzles for delivering pressurised air or other gas toward the print media.
The four printhead modules 55 are removably located in a channel portion 60 of a casing 61 by way of the support member 56 and the casing contains electrical circuitry 63 mounted on four printed circuit boards 62 (one for each printhead module 55) for controlling delivery of computer regulated power and drive signals by way of flexible PCB connectors 63a to the printhead chips 57. As illustrated in Figures 1 and 2, electrical power and print activating signals are delivered to one end of the two printheads 51 by way of conductors 64, and printing ink and air are delivered to the other end of the two printheads by fluid delivery lines 65. However, the ink and electrical power may both be delivered to one end of the printheads and alternative arrangements will exist when, as is contemplated, the printhead assembly 50 is integrated in an ink-supply cartridge.
The printed circuit boards 62 are carried by plastics material mouldings 66 which are located within the casing 61 and the mouldings also carry busbars 67 which in turn carry current for powering the printhead chips 57 and the electrical circuitry. A cover 68 normally closes the casing 61 and, when closed, the cover acts against a loading element 69 that functions to urge the flexible printed circuit connector 59 against the busbars 67.
The four printhead modules 55 may incorporate four conjoined support members 56 or, alternatively, a single support member 56 may be provided to extend along the full length of the printhead 51 and be shared by all four printhead modules. That is, a single support member 56 may carry all sixteen printhead chips 57.
As shown in Figures 3 and 4, the support member 56 comprises an extrusion that is formed with seven longitudinally extending closed channels 70, and the support member is provided in its upper surface with groups 71 of millimetric sized holes. Each group comprises seven separate holes 72 which extend into respective ones of the channels 70 and each group of holes is associated with one of the printhead chips 57. Also, the holes 72 of each group are positioned obliquely across the support member 56 in the longitudinal direction of the support member.
A coupling device 73 is provided for coupling fluid into the seven channels 70 from respective ones of the fluid delivery lines 65.
The fluid distribution arrangements 58 are provided for channelling fluid (printing ink and air) from each group 71 of holes to an associated one of the printhead chips 57. Printing fluids from six of the seven channel 70 are delivered to twelve rows of nozzles on each printhead chip 57 (ie, one fluid to two rows) and the millimetric-to-micrometric distribution of the fluids is effected by way of the fluid distribution arrangements 58. For a more detailed description of one arrangement for achieving this process reference may be made to the co-pending US Patent Applications referred to previously.
An illustrative embodiment of one printhead chip 57 is described in more detail, with reference to Figures 12 to 21, toward the end of this drawing-related description; as is an illustrative embodiment of a print engine controller for the printheads 51. The print engine controller is later described with reference to Figures 22 to 24.
A print media guide 74 is mounted to each of the printheads 51 and is shaped and arranged to guide the print media past the printing zone, as defined collectively by the printhead chips 57, in a manner to preclude the print media from contacting the nozzles of the printhead chips.
The fluids to be delivered to the printheads 51 will be determined by the functionality of the printer 52. However, as illustrated, provision is made for delivering six printing
fluids and air to the printhead chips 57 by way of the seven channels 70 in the support member 56. The six printing fluids may comprise:

Cyan printing ink
Magenta printing ink
Yellow printing ink
Black printing ink
Infrared ink
Fixative.

The filtered air will in use be delivered at a pressure slightly above atmospheric from a pressurised source (not shown) that is integrated in the printer.
Having identified the salient features of the pagewidth printheads, an embodiment of the capping mechanism that characterises the invention is now described with reference to the largely diagrammatic illustrations contained in Figure 7.
In the mechanism shown in Figure 7A, two (duplex) printheads 51 are located adjacent one another and together define a gap 80 through which print media is transported in the direction indicated by arrow 81. Two capping members 82 are located adjacent the printheads and are inclined at an angle of approximately 40 degrees to the direction of print media feed.
When capping is required, for example between successive print runs, the printheads 51 are turned in an arcuate direction through 40 degrees from a printing or non-capping first position to a nozzle capping second position as shown in Figure 7B. Thereafter, the capping members 82 are moved rectilinearly, in the directions of arrows 83, to the positions shown in Figure 7C where the capping members are located in nozzle capping engagement with the printhead chips 57 on each of the printheads 51.
Actuating mechanisms 84 and 85, as shown in block diagrammatic form in Figure 7C, are employed for effecting the described movements of the printheads 51 and capping members 82. These mechanisms may comprise geared motor drives, pneumatic actuators or other such mechanisms as are known in the art for effecting movement of relatively small mechanical devices.
With the mechanism as illustrated in Figures 7A to 7C, the print media may be maintained in position between the printheads 51 during the capping operation. Also, the capping members 82 are moved in directions normal to the respective printheads 51, thereby avoiding any potential for rubbing between the capping members and the printing zone of the printheads.
The mechanism as shown in Figures 8A to 8C is similar to that described above and like reference numerals are used to identify like parts. However, instead of moving the capping members 82 in a direction normal to the printing zones of the printheads 51, in this case the actuating mechanisms 85 effect rectilinear movement of the capping members 82 in a lateral direction with respect to the printing heads 51.
In the mechanism shown in Figure 9A, as in the case of that shown in Figure 7A, two printheads 51 are located adjacent one another and together define a gap 80 through which print media is transported in the direction indicated by arrow 81. Two capping members 82 are located adjacent the printheads and are inclined at an angle of approximately 80 degrees to the direction of print media feed.
When capping is required, for example between successive print runs, the printheads 51 are turned in an arcuate direction through 40 degrees from a non-capping first position to a nozzle capping second position as shown in Figure 9B. Thereafter, the capping members 82 are turned in an opposite arcuate direction through 40 degrees, in the directions of arrows 83, to the positions shown in Figure 9C where the capping members are located in nozzle capping engagement with the printhead chips 57 on each of the printheads 51.
The actuating mechanisms 84 and 85, as shown in block diagrammatic form in Figure 9C, are employed for effecting the described movements of the printheads 51 and capping members 82. As previously described these mechanisms may comprise geared motor drives, pneumatic actuators or other such mechanisms as are known in the art for effecting movement of relatively small mechanical devices.
Figures 10A, B, C and D illustrate a capping mechanism that is similar in construction and operation to that shown in Figures 9A, B and C, but one which also provides for purging of nozzles of the printhead 51. In this embodiment a capping member 86 doubles as a purging member and it incorporates a chamber 87 that is arranged to receive material that is purged from nozzles in the printing head chips 57. An extractor tube 88 extends into the chamber 87 and is connected to a suction pump or other such device 89 within the printer 50 for sucking material that is purged from the nozzle environment of the printhead.
When capping is required, the printheads 51 are turned in an arcuate direction through 40 degrees to the position shown in Figure 10B. Thereafter, the capping members 86 are turned in an opposite arcuate direction through 40 degrees, in the directions of arrows 83, to the positions shown in Figure 10C where the capping members are located in nozzle capping engagement with the printhead chips 57 on each of the printheads 51.
Thereafter, the printheads 51 are turned through a further angle of about 20 degrees, as shown in Figure 10D, to position the printhead chips 57 adjacent the chambers 87, and purging of the nozzles is effected.
If purging is required independently of capping, the printheads 51 will be turned though the full 60 degrees, and the capping members 86 will be turned through 40 degrees in the opposite direction so that the printhead chips 57 will align with the purging chambers 87.
As in the case of the mechanism that has been described with reference to Figures 7A to 7C, those that are illustrated in Figures 8, 9 and 10 may be actuated without interfering with the movement of print media.
The capping members 82 have a configuration as shown in Figure 11 and the capping members 86 have a configuration (not shown in detail) that comprises an adaptation of that shown in Figure 11. Thus the capping members comprise a body portion 100 and, moulded onto or otherwise secured to the body portion, a capping portion having an integrally formed lip portion 101 which surrounds a cavity 102. The body portion 100 is formed from a metal such as aluminium or from a rigid plastics material, and the capping portion (including the lip portion 101) is formed from an elastomeric material.
The lip portion 101 is peripherally configured to surround the printhead chips 57 collectively and the adjacent region of the printing zone of each or the printheads 51. Also, the cavity 102 may be provided or be lined with a hydrophobic material or a hydrophilic material, depending upon the function of the capping member and whether fluid that is purged from the printhead is to be expelled from or retained in the capping member
The capping members 82 and 86 may be formed, effectively, as one-piece members with a length that corresponds with that of a printhead to be capped or they may be formed from conjoined shorter-length portions that have an aggregate length corresponding to that of the printhead.
One of the printhead chips 57 is now described in more detail with reference to Figures 12 to 24.
As indicated above, each printhead chip 57 is provided with 7680 printing fluid delivery nozzles 150. The nozzles are arrayed in twelve rows 151, each having 640 nozzles, with an inter-nozzle spacing X of 32 microns. Adjacent rows are staggered by a distance equal to one-half of the inter-nozzle spacing so that a nozzle in one row is positioned mid-way between two nozzles in adjacent rows. Also, there is an inter-nozzle spacing Y of 80 microns between adjacent rows of nozzles.
Two adjacent rows of the nozzles 150 are fed from a common supply of printing fluid. This, with the staggered arrangement, allows for closer spacing of ink dots during printing than would be possible with a single row of nozzles and also allows for a level of redundancy that accommodates nozzle failure.
The printhead chips 57 are manufactured using an integrated circuit fabrication technique and, as previously indicated, they embody micro-electromechanical systems (MEMS). Each printhead chip 57 includes a silicon wafer substrate 152 and a 0.42 micron 1 P4M 12 volt CMOS micro-processing circuit is formed on the wafer. Thus, a silicon dioxide layer 153 is deposited on the substrate 152 as a dielectric layer and aluminium electrode contact layers 154 are deposited on the silicon dioxide layer 153. Both the substrate 152 and the layer 153 are etched to define an ink channel 155, and an aluminium diffusion barrier 156 is positioned about the ink channel 155.
A passivation layer 157 of silicon nitride is deposited over the aluminium contact layers 154 and the layer 153. Portions of the passivation layer 157 that are positioned over the contact layers 154 have openings 158 therein to provide access to the contact layers.
Each nozzle 150 includes a nozzle chamber 159 which is defined by a nozzle wall 160, a nozzle roof 161 and a radially inner nozzle rim 162. The ink channel 155 is in fluid communication with the chamber 159.
A moveable rim 163, that includes a movable seal lip 164, is located at the lower end of the nozzle wall 160. An encircling wall 165 surrounds the nozzle and provides a stationery seal lip 166 that, when the nozzle 150 is at rest as shown in Figure 13, is adjacent the moveable rim 163. A fluidic seal 167 is formed due to the surface tension of ink trapped between the stationery seal 166 and the moveable seal lip 164. This prevents leakage of ink from the chamber whilst providing a low resistance coupling between the encircling wall 165 and a nozzle wall 160.
The nozzle wall 160 forms part of lever arrangement that is mounted to a carrier 168 having a generally U-shaped profile with a base 169 attached to the layer 157. The lever arrangement also includes a lever arm 170 that extends from the nozzle wall and incorporates a lateral stiffening beam 171. The lever arm 170 is attached to as pair of passive beams 172 that are formed from titanium nitride and are positioned at each side of the nozzle as best seen in figures 22 and 25. The other ends of the passive beams 172 are attached to the carriers 168.
The lever arm 170 is also attached to an actuator beam 173, which is formed from TiN. This attachment to the actuator beam is made at a point a small but critical distance higher than the attachments to the passive beam 172.
As can best be seen from Figures 16 and 19, the actuator beam 173 is substantially U-shaped in plan, defining a current path between an electrode 174 and an opposite electrode 175. Each of the electrodes 174 and 175 is electrically connected to a respective point in the contact layer 154. The actuator beam 173 is also mechanically secured to an anchor 176, and the anchor 176 is configured to constrain motion of the actuator beam 173 to the left of Figures 13 to 15 when the nozzle arrangement is activated.
The actuator beam 173 is conductive, being composed of TiN, but has a sufficiently high enough electrical resistance to generate self-heating when a current is passed between the electrodes 174 and 175. No current flows through the passive beams 172, so they do not experience thermal expansion.
In operation, the nozzle is filled with ink 177 that defines a meniscus 178 under the influence of surface tension. The ink is retained in the chamber 159 by the meniscus, and will not generally leak out in the absence of some other physical influence.
To fire ink from the nozzle, a current is passed between the contacts 174 and 175, passing through the actuator beam 173. The self-heating of the beam 173 causes the beam to expand, and the actuator beam 173 is dimensioned and shaped so that the beam expands predominantly in a horizontal direction with respect to Figures 13 to 15. The expansion is constrained to the left by the anchor 176, so the end of the actuator beam 173 adjacent the lever arm 170 is impelled to the right.
The relative horizontal inflexibility of the passive beams 172 prevents them from allowing much horizontal movement of the lever arm 170. However, the relative displacement of the attachment points of the passive beams and actuator beam respectively to the lever arm causes a twisting movement that, in turn, causes the lever arm 170 to move generally downwardly with a pivoting or hinging motion. However, the absence of a true pivot point means that rotation is about a pivot region defined by bending of the passive beams 172.
The downward movement (and slight rotation) of the lever arm 170 is amplified by the distance of the nozzle wall 160 from the passive beams 172. The downward movement of the nozzle walls and roof causes a pressure increase within the chamber 159, causing the meniscus 178 to bulge as shown in Figure 14, although the surface tension of the ink causes the fluid seal 167 to be stretched by this motion without allowing ink to leak out.
As shown in Figure 15, at the appropriate time the drive current is stopped and the actuator beam 173 quickly cools and contracts. The contraction causes the lever arm to commence its return to the quiescent position, which in turn causes a reduction in pressure in the chamber 159. The interplay of the momentum of the bulging ink and its inherent surface tension, and the negative pressure caused by the upward movement of the nozzle chamber 159 causes thinning, and ultimately snapping, of the bulging meniscus 178 to define an ink drop 179 that continues outwardly until it contacts passing print media.
Immediately after the drop 179 detaches, the meniscus 178 forms the concave shape shown in Figure 15. Surface tension causes the pressure in the chamber 159 to remain relatively low until ink has been sucked upwards through the inlet 155, which returns the nozzle arrangement and the ink to the quiescent situation shown in Figure 13.
As can best be seen from Figure 16, the printhead chip 57 also incorporates a test mechanism that can be used both post-manufacture and periodically after the prin head assembly has been installed. The test mechanism includes a pair of contacts 180 that are connected to test circuitry (not shown). A bridging contact 181 is provided on a finger 182 that extends from the lever arm 170. Because the bridging contact 181 is on the opposite side of the passive beams 172, actuation of the nozzle causes the bridging contact 181 to move upwardly, into contact with the contacts 180. Test circuitry can be used to confirm that actuation causes this closing of the circuit formed by the contacts 180 and 181. If the circuit is closed appropriately, it can generally be assumed that the nozzle is operative.
As stated previously the integrated circuits of the printhead chips 57 are controlled by the print engine controller (PEC) integrated circuits of the drive electronics 63. One or more PEC integrated circuits 100 is or are provided (depending upon the printing speed required) in order to enable page-width printing over a variety of different sized pages or continuous sheets. As described previously, each of the printed circuit boards 62 carried by the support moulding 66 carries one PEC integrated circuit 190 (Figure 22) which interfaces with four of the printhead chips 57, and the PEC integrated circuit 190 essentially drives the integrated circuits of the printhead chips 57 and transfers received print data thereto in a form suitable to effect printing.
An example of a PEC integrated circuit which is suitable for driving the printhead chips is described in the Applicant's co-pending US patent applications 09/575,108 (Docket No.PEC01US), 09/575,109 (Docket No.PEC02US), 09/575,110 (Docket No. PEC03US), 09/607,985 (Docket No.PEC04US), 09/607,990 (Docket No.PEC05US) and 09/606,999 (Docket No. PEC07US), which are incorporated herein by reference.
However, a brief description of the circuit is provided as follows with reference to Figures 22 to 24.
The data flow and functions performed by the PEC integrated circuit 190 are described for a situation where the PEC integrated circuit is provided for driving a printhead 51 having a plurality of printhead modules 55; that is four modules as described above. As also described above, each printhead module 55 provides for six channels of fluid for printing, these being:

Cyan, Magenta and Yellow (CMY) for regular colour printing;
Black (K) for black text and other black or greyscale printing;
Infrared (IR) for tag-enabled applications; and
Fixative (F) to enable printing at high speed.

Images are supplied to the PEC integrated circuit 190 by a computer which is programmed to perform the various processing steps 191 to 194 involved in printing an image prior to transmission to the PEC integrated circuit 190. These steps will typically involve receiving the image data (step 191) and storing this data in a memory buffer of the computer system (step 192) in which image layouts may be produced and any required objects may be added. Pages from the memory buffer are rasterized (step 193) and are then compressed, (step 194) prior to transmission to the PEC integrated circuit 190. Upon receiving the image data, the PEC integrated circuit 190 processes the data so as to drive the integrated circuits of the printhead chips 57.
Due to the page-width nature of the printhead assembly, each image should be printed at a constant speed to avoid creating visible artifacts. This means that the printing speed should be varied to match the input data rate. Document rasterization and document printing are therefore decoupled to ensure the printhead assembly has a constant supply of data. In this arrangement, an image is not printed until it is fully rasterized and, in order to achieve a high constant printing speed, a compressed version of each rasterized page image is stored in memory.
Because contone colour images are reproduced by stochastic dithering, but black text and line graphics are reproduced directly using dots, the compressed image format contains a separate foreground bi-level black layer and background contone colour layer. The black layer is composited over the contone layer after the contone layer is dithered. If required, a final layer of tags (in IR or black ink) is optionally added to the image for printout.
Dither matrix selection regions in the image description are rasterized to a contone-resolution bi-lev bitmap which is losslessly compressed to negligible size and which forms part of the compressed image. The IR layer of the printed page optionally contains encoded tags at a programmable density.
Each compressed image is transferred to the PEC integrated circuit 190 where it is then stored in a memory buffer 195. The compressed image is then retrieved and fed to an image expander 196 in which images are retrieved. If required, any dither may be applied to any contone layer by a dithering means 197 and any black bi-level layer may be composited over the contone layer by a compositor 198 together with any infrared tags which may be rendered by the rendering means 199. The PEC integrated circuit 190 then drives the integrated circuits of the printhead chips 57 to print the composite image data at step 200 to produce a printed image 201.
The process performed by the PEC integrated circuit 190 may be considered to consist of a number of distinct stages. The first stage has the ability to expand a JPEG-compressed contone CMYK layer. In parallel with this, bi-level IR tag data can be encoded from the compressed image. The second stage dithers the contone CMYK layer using a dither matrix selected by a dither matrix select map and, if required, composites a bi-level black layer over the resulting bi-level K layer and adds the IR layer to the image. A fixative layer is also generated at each dot position wherever there is a need in any of the C, M, Y, K, or IR channels. The last stage prints the bi-level CMYK+IR data through the printhead assembly 50.
Figure 23 shows the PEC integrated circuit 190 in the context of the overall printing system architecture. The various components of the architecture include:

The PEC integrated circuit 190 which is responsible for receiving the compressed page images for storage in a memory buffer 202, performing the page expansion, black layer compositing and sending the dot data to the printhead chips 57. The PEC integrated circuit 190 may also communicate with a master Quality Assurance (QA) integrated circuit 203 and with an ink cartridge Quality Assurance (QA) integrated circuit 204. The PEC integrated circuit 190 also provides a means of retrieving the printhead assembly characteristics to ensure optimum printing.
The memory buffer 202 for storing the compressed image and for scratch use during the printing of a given page. The construction and working of memory buffers is known to those skilled in the art and a range of standard integrated circuits and techniques for their use might be utilized.
The master integrated circuit 203 which is matched to the ink cartridge QA integrated circuit 204. The construction and working of QA integrated circuits is also known to those skilled in the art and a range of known QA processes might be utilized.

The PEC integrated circuit 190 effectively performs four basic levels of functionality:

Receiving compressed pages via a serial interface such as an IEEE 1394.
Acting as a print engine for producing an image from a compressed form. The print engine functionality includes expanding the image, dithering the contone layer, compositing the black layer over the contone layer, optionally adding infrared tags, and sending the resultant image to the integrated circuits of the printhead chips.
Acting as a print controller for controlling the printhead chips 57 and the stepper motors 102, 108 and 111 of the printing system.
Serving as two standard low-speed serial ports for communication with the two QA integrated circuits. In this regard, two ports are used, and not a single port, so as to ensure strong security during authentication procedures.

These functions are now described in more detail with reference to Figure 24, which provides a more specific, exemplary illustration of the PEC integrated circuit architecture.
The PEC integrated circuit 190 incorporates a simple micro-controller CPU core 204 to perform the following functions:

Perform QA integrated circuit authentication protocols via a serial interface 205 between print images.
Run stepper motors of the printing system via a parallel interface 206 during printing to control delivery of print media to the printer for printing.
Synchronize the various components of the PEC integrated circuit 190 during printing.
Provide a means of interfacing with external data requests (programming registers, etc).
Provide a means of interfacing with the printhead assemblies' low-speed data requests (such as reading characterization vectors and writing pulse profiles).
Provide a means of writing portrait and landscape tag structures to an external DRAM 207.

In order to perform the image expansion and printing process, the PEC integrated circuit 190 includes a high-speed serial interface 208 (such as a standard IEEE 1394 interface), a standard JPEG decoder 209, a standard Group 4 Fax decoder 210, a custom half-toner/compositor (HC) 211, a custom tag encoder 212, a line loader/formatter (LLF) 213, and a printhead interface 214 (PHI) which communicates with the printhead chips 57. The decoders 209 and 210 and the tag encoder 212 are buffered to the HC 211. The tag encoder 212 allocates infrared tags to images.
The print engine function works in a double-buffered manner. That is, one image is loaded into the external DRAM 207 via a DRAM interface 215 and a data bus 216 from the high-speed serial interface 208, while the previously loaded image is read from the DRAM 207 and passed through the print engine process. When the image has been printed, the image just loaded becomes the image being printed, and a new image is loaded via the high-speed serial interface 208.
At the aforementioned first stage, the process expands any JPEG-compressed contone (CMYK) layers, and expands any of two Group 4 Fax-compressed bi-level data streams. The two streams are the black layer and a matte for selecting between dither matrices for contone dithering. At the second stage, in parallel with the first, any tags are encoded for later rendering in either IR or black ink.
Finally, in the third stage the contone layer is dithered, and position tags and the bi-level spot layer are composited over the resulting bi-level dithered layer. The data stream is ideally adjusted to create smooth transitions across overlapping segments in the printhead assembly and ideally it is adjusted to compensate for dead nozzles in the printhead assemblies. Up to six channels of bi-level data are produced from this stage.
However, it will be understood that not all of the six channels need be activated. For example, the printhead modules 55 may provide for CMY only, with K pushed into the CMY channels and IR ignored.
Alternatively, the position tags may be printed in K if IR ink is not employed. The resultant bi-level CMYK-IR dot-data is buffered and formatted for printing with the integrated circuits of the printhead chips 57 via a set of line buffers (not shown). The majority of these line buffers might ideally be stored on the external DRAM 207. In the final stage, the six channels of bi-level dot data are printed via the PHI 214.
The HC 211 combines the functions of half toning the contone (typically CMYK) layer to a bi-level version of the same, and compositing the spot1 bi-level layer over the appropriate half-toned contone layer(s). If there is no K ink, the HC 211 functions to map K to CMY dots as appropriate. It also selects between two dither matrices on a pixel-by-pixel basis, based on the corresponding value in the dither matrix select map. The input to the HC 211 is an expanded contone layer (from the JPEG decoder 205) through a buffer 217, an expanded bi-level spotl layer through a buffer 218, an expanded dither-matrix-select bitmap at typically the same resolution as the contone layer through a buffer 219, and tag data at full dot resolution through a buffer (FIFO) 220.
The HC 211 uses up to two dither matrices, read from the external DRAM 207. The output from the HC 211 to the LLF 213 is a set of printer resolution bi-level image lines in up to six colour planes. Typically, the contone layer is CMYK or CMY, and the bi-level spot1 layer is K Once started, the HC 211 proceeds until it detects an "end-of-image" condition, or until it is explicitly stopped via a control register (not shown).
The LLF 213 receives dot information from the HC 211, loads the dots for a given print line into appropriate buffer storage (some on integrated circuit (not shown) and some in the external DRAM 207) and formats them into the order required for the integrated circuits of the printhead chips 57. More specifically, the input to the LLF 213 is a set of six 32-bit words and a Data Valid bit, all generated by the HC 211.
As previously described, the physical location of the nozzles 150 on the printhead chips is in two offset rows 151, which means that odd and even dots of the same colour are for two different lines. In addition, there is a number of lines between the dots of one colour and the dots of another. Since the six colour planes for the same dot position are calculated at one time by the HC 211, there is a need to delay the dot data for each of the colour planes until the same dot is positioned under the appropriate colour nozzle. The size of each buffer line depends on the width of the printhead assembly. A single PEC integrated circuit 190 may be employed to generate dots for up to 16 printhead chips 57 and, in such case, a single odd or even buffer line is therefore 16 sets of 640 dots, for a total of 10,240 bits (1280 bytes).
The PHI 214 is the means by which the PEC integrated circuit 190 loads the printhead chips 57 with the dots to be printed, and controls the actual dot printing process. It takes input from the LLF 213 and outputs data to the printhead chips 57. The PHI 214 is capable of dealing with a variety of printhead assembly lengths and formats.
A combined characterization vector of each printhead assembly 50 and 51 can be read back via the serial interface 205. The characterization vector may include dead nozzle information as well as relative printhead module alignment data. Each printhead module can be queried via a low-speed serial bus 221 to return a characterization vector of the printhead module.
The characterization vectors from multiple printhead modules can be combined to construct a nozzle defect list for the entire printhead assembly and allows the PEC integrated circuit 190 to compensate for defective nozzles during printing. As long as the number of defective nozzles is low, the compensation can produce results indistinguishable from those of a printhead assembly with no defective nozzles.
Some of the features of a pagewidth printhead that incorporates the chip and the print engine controller which, have been described above
are summarised as follows:

1. The printhead will normally have at least four color channels.
2. The printhead will normally incorporate at least 1400 ink delivery nozzles per inch of print width for each color.
3. The printhead may incorporate a total of at least 50,000 nozzles.
4. The dot printing processing rate and the drop deposition rate of the printhead may be of the order of 10⁹ sec^-1 or greater.
5. The volume deposited per drop may be of the order of 2x10^-12 l or less.
6. The energy level expenditure per drop ejection may be of the order of 200x10^-9 J. or less.

It will be understood that the constructional and operating principles of the capping mechanism of the present invention may be realised in various embodiments. Thus,
variations and modifications may be made in respect of the embodiments as specifically described above by way of example.

Claims

A capping mechanism connected to a pagewidth printhead assembly (50) having-
a) two pagewidth printheads (51) disposed in contionting relationship when in a first printing position and

b) a plurality of nozzles located along the printheads (51) and arranged in use to deliver ink onto print media as it is transported past the printheads (51);
the capping mechanism comprising-
i) two capping members (82, 86) each associated with a corresponding one of the printheads, each capping member having a length corresponding substantially to that of the corresponding printhead (51), and

ii) actuating means (84, 85) arranged to move the printheads in an arcuate direction away from the transport plane of the print media, from the printing first position to a second position at which the capping members engage in nozzle capping engagement with the corresponding printheads (51),
characterized in that:
the capping members are located adjacent to one side of the printheads when the printheads are in the first printing position, the printheads (51) being moved in an arcuate direction when moving from said first position to said second position, one of the printheads being rotated in a clockwise direction while the other one of the printheads being rotated in an anti-clockwise direction when moving from said first position to said second position.
The capping mechanism as claimed in claim 1 wherein each capping member (82, 86) is formed effectively as a one-piece member.
The capping mechanism as claimed in claim 1 wherein each capping member (82, 86) comprises conjoined capping member portions having an aggregate length corresponding substantially to that of the associated printhead (51).
The capping mechanism as claimed in claim 1 wherein each capping member (82, 86) comprises a body portion formed from a rigid material and a capping portion having a) an integrally formed elastomeric material lip portion and b) a cavity surrounded by the lip portion, and wherein the lip portion is peripherally configured to surround the nozzles collectively of the associated printhead (51).
The capping mechanism as claimed in claim 1 wherein each capping member (82, 86) is arranged to be connected to a suction device whereby material may be sucked from the nozzle environment of the associated printhead (51).
The capping mechanism as claimed in claim 1 wherein a purging chamber (87) is located within each capping member (82, 86) and is arranged to be connected to a suction device (89) whereby material may be sucked from the nozzle environment of the associated printhead (51).
The capping mechanism as claimed in claim 1 wherein a further actuating mechanism is provided to effect movement of each capping member from a non-capping position to the second position.
The capping mechanism as claimed in claim 7 wherein the further actuating mechanism is arranged to impart linear movement to each capping member.
The capping mechanism as claimed in claim 7 wherein the further actuating mechanism is arranged to impart arcuate movement to each capping member.
The capping mechanism as claimed in claim 8 wherein each capping member is positioned in confronting relationship with the associated printhead when the associated printhead is in the second position and wherein the further actuating mechanism is arranged to move each capping member in a direction normal to the nozzle face of the associated printhead when effecting linear movement of each capping member from the non-capping position to the second position.
The capping mechanism as claimed in claim 1, wherein each capping member is inclined at an angle of approximately 40 degrees relative to the direction of print media feed.