Patent Application
20090179948
The present invention relates to be field of printers and in particular pagewidth inkjet printers.
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.
Wiping the nozzle face of printhead is an effective way of removing paper dust, ink floods, dried ink or other contaminants. The ordinary worker will appreciate that countless different wiper configurations possible, the department or you will be unsuitable from the particular printer. The functional effectiveness of wiper (in terms of cleaning the printhead) must be weighed against the production costs, the intended operational life, the size and weight constraints and other considerations.
Accordingly, the present invention provides a printhead maintenance facility for an inkjet printer, the inkjet printer having a printhead with the nozzle face defining an array of nozzles, the printhead maintenance facility comprising:
a wiper member for wiping the nozzle face;
the maintenance drive for moving the wiper member across the array of nozzles in the nozzle face; wherein,
the wiper member has a single blade dimensioned to wipe all the nozzles in a single traverse across the nozzle face.
A single wiper blade extending the length of the nozzle array is a simple wiping arrangement with low production and assembly costs. In light of this, a single blade wiper is best suited to printers and the lower end of the price range. The higher production volumes demand cost efficient manufacturing techniques and straightforward assembly of the printer components. This may entail some compromise in terms of the operational life of the unit to all the speed and efficiency with which the wiper cleans the printhead. However the single blade design is compact and if it does not effectively clean the nozzle face in a single traverse, the maintenance drive can simply repeat the wiping operation until the printhead is clean.
Preferably, the printer has a media feed assembly for transporting sheets of media substrate past the printhead in a media feed direction, and the maintenance drive moves the wiper member across the nozzle face in the direction parallel to a media feed direction. In a further preferred form, the printhead is a pagewidth printhead and the single wiper blade extends the length of the nozzle array. Preferably the maintenance drive is configured to move the wiper member in the media feed direction and opposite to the media feed direction. In a particularly preferred form, the maintenance drive is configured to rotate the wiper member about the axis extending transverse to the media feed direction.
In some embodiments, the printhead maintenance facility further comprises a tubular chassis with a plurality of maintenance stations mounted to the chassis exterior, wherein the wiper member is one of the maintenance stations. Preferably, the chassis exterior has sockets in which the maintenance stations are mounted. In a particularly preferred form, the wiper member is a co-moulded polymer element with a hard plastic base for mounting in the socket, and the single blade being a soft elastomeric material extending from the hard plastic base.
In some embodiments, the single blade extends normal to the media feed direction. Optionally, the single blade extends at an angle to a line normal to the media feed direction.
Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which:
Briefly, the printer fluidic system has a printhead assembly 2 supplied with ink from an ink tank 4 via an upstream ink line 8. Waste ink is drained to a sump 18 via a downstream ink line 16. A single ink line is shown for simplicity. In reality, the printhead has multiple ink lines for full color printing. The upstream ink line 8 has a shut off valve 10 for selectively isolating the printhead assembly 2 from the pump 12 and or the ink tank 4. The pump 12 is used to actively prime or flood the printhead assembly 2. The pump 12 is also used to establish a negative pressure in the ink tank 4. During printing, the negative pressure is maintained by the bubble point regulator 6.
The printhead assembly 2 is 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 electromechanical) 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. 11/246687 (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.
Sheets of media are fed through the print engine by the main drive roller 186 and the exit feed roller 178. The main drive roller 186 is driven by the main drive pulley and encoder disk 188. The exit feed roller 178 is driven by the exit drive pulley 180 which is synchronized to the main drive pulley 188 by the media feed belt 182. The main drive pulley 188 is powered by the media feed motor 190 via the input drive belt 192.
The main drive pulley 188 has an encoder disk which is read by the drive pulley sensor 184. Data relating to the speed and number of revolutions of the drive shafts 186 and 178 is sent to the print engine controller (or PEC). The PEC (not shown) is mounted to the main PCB 194 (printed circuit board) and is the primary micro-processor for controlling the operation of the printer.
Reinforced bearing surfaces 128 are fixed to the pressed metal casing 196 of the print engine 3. These provide reference points for locating the printhead cartridge within the print engine. They are also positioned to provide a bearing surface directly opposite the compressive loads acting on the cartridge 2 when installed. The fluid couplings 120 push against the inlet and outlet manifolds of the cartridge when the manifold spouts (described below) open the shut off valves in the print engine (also described below). The pressure of the latch 126 on the cartridge 2 is also directly opposed by a bearing surface 128. Positioning the bearing surfaces 128 directly opposite the compressive loads in the cartridge 2, the flex and deformation in the cartridge is reduced. Ultimately, this assists the precise location of the nozzles relative to the media feed path. It also protects the less robust structures within the cartridge from damage.
Both the channel molding 68 and the top cover molding 72 are molded from LCP (liquid crystal polymer) because of its stiffness and coefficient of thermal expansion that closely matches that of silicon. It will be appreciated that a relatively long structure such as a pagewidth printhead should minimize any thermal expansion differences between the silicon substrate of the printhead ICs 30 and their supporting structure.
Referring to
On the opposite side of the media feed path 22 is the printhead maintenance carousel 150 and its associated drive mechanisms. The printhead maintenance carousel 150 is mounted for rotation about the tubular drive shaft 156. The maintenance carousel 150 is also configured for movement towards and away from the printhead ICs 30. By raising the carousel 150 towards the printhead ICs 30, the various printhead maintenance stations on the exterior of the carousel are presented to the printhead. The maintenance carousel 150 is rotatably mounted on a lift structure 170 that is mounted to a lift structure shaft 156 such that it can pivot relative to the remainder of the print engine 3. The lift structure 170 includes a pair of lift arms 158 (only one lift arm is shown, the other being positioned at the opposite end of the lift structure shaft 156). Each lift arm 158 has a cam engaging surface 168, such as a roller or pad of low friction material. The cams (described in more detail below) are fixed to the carousel drive shaft 160 for rotation therewith. The lift arms 158 are biased into engagement with the cams on the carousel lift drive shaft 160, such that the carousel lift motor (described below) can move the carousel towards and away from the printhead by rotating the shaft 160.
The rotation of the maintenance carousel 150 about the tubular shaft 166 is independent of the carousel lift drive. The carousel drive shaft 166 engages the carousel rotation motor (described below) such that it can be rotated regardless of whether it is retracted from, or advanced towards, the printhead. When the carousel is advanced towards the printhead, the wiper blades 162 move through the media feed path 22 in order to wipe the printhead ICs 30. When retracted from the printhead, the carousel 150 can be repeatedly rotated such that the wiper blades 162 engage the doctor blade 154 and the cleaning pad 152. This is also discussed in more detail below.
Referring now to
With the lift arms 158 drawing the lift structure 170 downwards, the maintenance carousel 150 is retracted away from the printhead ICs 30. In this position, the carousel 150 can be rotated with none of the maintenance stations touching the printhead ICs 30. It does, however, bring the wiper blades 162 into contact with the doctor blade 154 and the absorbent cleaning pad 152.
The doctor blade 154 works in combination with the cleaning pad 152 to comprehensively clean the wiper blades 162. The cleaning pad 152 wipes paper dust and dried ink from the wiping contact face of the wiper blades 162. However, a bead of ink and other contaminants can form at the tip of the blades 162 where it does not contact the surface of the cleaning pad 152.
To dislodge this ink and dust, the doctor blade 154 is mounted in the print engine 3 to contact the blades 162 after they have wiped the printhead ICs 30, but before they contact the cleaning pad 152. Upon contact with the doctor blade 154, the wiper blades 162 flex into a curved shaped in order to pass. As the wiper blades 162 are an elastomeric material, they spring back to their quiescent straight shape as soon as they disengage from the doctor blade 154. Rapidly springing back to their quiescent shape projects dust and other contaminants from the wiper blade 162, and in particular, from the tip.
The ordinary worker will appreciate that the wiper blades 162 also flex when they contact the cleaning pad 152, and likewise spring back to their quiescent shapes once disengaged from the pad. However, the doctor blade 154 is mounted radially closer to the central shaft 166 of the carousel 150 than the cleaning pad 152. This bends the wiper blades 162 more as they pass, and so imparts more momentum to the contaminants when springing back to the quiescent shape. It is not possible to simply move the cleaning pad 152 closer to the carousel shaft 166 to bend the wiper blades 162 more, as the trailing blades would not properly wipe across the cleaning pad 152 because of contact with the leading blades.
The cleaning pad 152 is an absorbent foam body formed into a curved shape corresponding to the circular path of the wiper blades 162. The pad 152 cleans more effectively when covered with a woven material to provide a multitude of densely packed contacts points when wiping the blades. Accordingly, the strand size of the woven material should be relatively small; say less than 2 deniers. A microfiber material works particularly well with a strand size of about 1 denier.
The cleaning pad 152 extends the length of the wiper blades 162 which in turn extend the length of the pagewidth printhead. The pagewidth cleaning pad 152 cleans the entire length of the wiper blades simultaneously which reduces the time required for each wiping operation. Furthermore the length of the pagewidth cleaning pad inherently provides a large volume of the absorbent material for holding a relatively large amount of ink. With a greater capacity for absorbing ink, the cleaning pad 152 will be replaced less frequently.
As shown in
After dragging the wiper blades 162 past the doctor blade 154, any residual dust and contaminants stuck to the blades is removed by the absorbent cleaning pad 152. This step is shown in
During this process the print platen maintenance station 206 is directly opposite the printhead ICs 30. If desired, the carousel can be lifted by rotation of the lift cam 172 so that the nozzles can fire into the absorbent material 208. Any color mixing at the ink nozzles is immediately purged. Holes (not shown) drilled into the side of the tubular chassis 166 provides a fluid communication between the absorbent material 208 and the porous material 210 within the central cavity of the carousel shaft 166. Ink absorbed by the material 208 is drawn into, and retained by, the porous material 210. To drain the porous material 210, the carousel 150 can be provided with a vacuum attachment point (not shown) to draw the waste ink away.
With the wiper blades clean, the carousel 150 continues to rotate (see
At the end of the print job or prior to the printer going into standby mode, the carousel 150 is retracted away from the printhead ICs 30 in rotated so that the printhead capping maintenance station 198 is again presented to the printhead. As shown in
The maintenance carousel has four printhead maintenance stations; a print platen 206, a wiper member 162, a printhead capper 198 and a spittoon/blotter 220. Each of the maintenance stations is mounted to its own outer chassis component. The outer chassis components fit around the carousel tubular shaft 166 and interengage each other to lock on to the shaft. At one end of the tubular shaft 166 is a carousel encoder disk 204 and a carousel spur gear 212 which is driven by the carousel rotation motor (not shown) described below. The tubular shaft is fixed to the spur gear or rotation therewith. The printhead maintenance stations rotate together with the tubular shaft by virtue of their firm compressive grip on the shaft's exterior.
The wiper blade outer chassis component 214 is an aluminum extrusion (or other suitable alloy) configured to securely hold the wiper blades 162. Similarly, the other outer chassis components are metal extrusions for securely mounting the softer elastomeric and or absorbent porous material of their respective maintenance stations. The outer chassis components for the print platen 216 and the printhead capper 198 have a series of identical locking lugs 226 along each of the longitudinal edges. The wiper member outer chassis component 214 and the spittoon/blotter outer chassis component 218 have complementary bayonet style slots for receiving the locking lugs 226. Each of the bayonet slots has a lug access aperture 228 adjacent a lug locking slot 230. Inserting the locking lugs 226 into the lug access aperture 228 of the adjacent outer chassis component, and then longitudinally sliding the components relative to each other will lock them on to the chassis tubular shaft 166.
To improve the friction, and therefore the locking engagement, between each of the maintenance stations and the chassis chip shaft 166, each of the printhead maintenance stations have an element with a curved shaft engagement surface 234. The print platen 206 has an absorbent member 224 with a curved shaft engagement surface 234 formed on one side. The spittoon/blotter outer chassis component 218 has a relatively large absorbent spittoon/blotter member 220 which also has a curved shaft engagement surface 234 formed on its interior face. Likewise, the outer chassis component for the printhead capper 198, and the common base of the wiper blades 162 work has curved shaft engagement surfaces 234.
The ordinary worker will appreciate that clamping the outer chassis to the inner chassis with the use of interengaging locking formations minimizes the amount of machining and assembly time while maintaining fine tolerances for precisely mounting the maintenance station structures. Furthermore, the outer chassis components can be assembled in different configurations. The wiper blade outer chassis component 214 can change positions with the spittoon/blotter chassis component 218. Similarly, the printhead capper 198 can swap with the print platen 206. In this way the maintenance station can be assembled in a manner that is optimized for the particular printer in which it will be installed.
With the widespread popularity of digital photography, there is increasing demand for full bleed printing of color images. “Full bleed printing” is printing to the very edges of the media surface. This will usually cause some “over spray” where ejected ink misses the edge of the media substrate and deposits on the supporting print platen. This over spray ink can then smear onto subsequent sheets of media.
The arrangement shown in
Some printers in the Applicant's range use this to provide a printing gap 244 of 0.7 millimetres. However this can be further reduced by flattening the bead of encapsulant material 240 adjacent the printhead ICs 30. Power and data is transmitted to the printhead ICs 30 by the flex PCB 242 mounted to the exterior of the LCP molding 20. The contacts of the flex PCB 242 are electrically connected to the contacts of the printhead ICs 30 by a line of wire bonds (not shown). To protect the wire bonds, they are encapsulated in an epoxy material referred to as encapsulant. The Applicant has developed several techniques for flattening the profile of the wire bonds and the bead of encapsulant 240 covering them. This in turn allows the printing gap 244 to be further reduced.
The print platen 206 has an indentation or central recessed portion 248 which is directly opposite the nozzles of the printhead ICs 30. Any over spray ink will be in this region of the platen 206. Recessing this region away from the remainder of the platen ensures that the media substrate will not get smeared with wet over spray ink. The surface of the central recessed 248 is in fluid communication with an absorbent fibrous element 250. In turn, the fibrous element 250 is in fluid communication with porous material 254 in the centre of the chassis 236 by capillary tubes 252. Over sprayed ink is wicked into the fibrous element 250 and drawn into the porous material 254 by capillary action through the tubes 252.
Whenever the printhead cartridge 2 is replaced, it needs to be primed with ink. Priming is notoriously wasteful as the ink is typically forced through the nozzles until the entire printhead structure has purged any air bubbles. In the time it takes for the air to be cleared from the multitude of conduits extending through the printhead, a significant amount of ink has been wasted.
To combat this, the maintenance carousel 150 is raised so that the priming contact pad 258 covers the nozzles of the printhead ICs 30. Holding the contact pad 258 against the nozzle array as it is primed under pressure significantly reduces the volume of ink purged through the nozzles. The porous material partially obstructs the nozzles to constrict the flow of ink. However the flow of air out of the nozzles is much less constricted, so the overall priming process is not delayed because of the flow obstruction generated by the porous material. The elastomeric skirt 256 seals against the underside of the LCP molding 22 to capture any excess ink that may flow from the sides of the contact pad 258. Flow apertures 264 formed in the rigid polymer base 260 allows the ink absorbed by the pad 258 and any excess ink to flow to the absorbent fibrous element 250 (identical to that used by the print platen 206). As with the print platen 206, ink in the fibrous element 250 is drawn into the porous material 254 within the injection molded chassis 236 by the capillary tubes 252.
By using the printhead priming station 262, the amount of wasted ink is significantly reduced. Without the priming station, the volume of ink wasted when priming the pagewidth printhead is typically about two millilitres per color. With the priming station 262, this is reduced to 0.1 millilitres per color.
The priming contact pad 258 need not be formed of porous material. Instead, the pad can be formed from the same elastomeric material as the surrounding skirt 256. In this case, the contact pad 258 needs to have a particular surface roughness. The surface that engages the nozzle face of the printhead ICs 30, should be rough at the 2 to 4 micron scale, but smooth and compliant at the 20 micron scale. This type of surface roughness allows air to escape from between the nozzle face and contact pad, but only a small amount of ink.
In
The chassis 236 has four maintenance station mounting sockets 276 formed in its exterior surface. The sockets 276 are identical so that they can receive any one of the various maintenance stations (206, 266, 262, 272). In this way the maintenance stations become interchangeable modules and the order which the maintenance stations are presented to the printhead can be changed to suit different printers. Furthermore, if the maintenance stations themselves are modified, their standard sockets ensure they are easily incorporated into the existing production line with a minimum of retooling. The maintenance stations are secured in the sockets with adhesive but other methods such as an ultra sonic spot weld or mechanical interengagement would also be suitable.
As shown in
The five station maintenance carousel 150 adds a spittoon 284 to allow the printer to use major ink purges as part of the maintenance regime. The four station carousel of
The spittoon 284 has large apertures in its face 286 or a series of retaining ribs to hold the fibrous wicking material 250 in the hard plastic base. This keeps the fibrous element 250 very open to a potentially dense spray of ink. One face of the fibrous element 250 presses against the capillary tubes 252 to enhance the flow to the porous material 254 in the central cavity of the chassis 236.
The five socket chassis 236 is injection molded using five sliders configured at 72 degrees to each other, or six sliders at 60 degrees to each other. Similarly, a maintenance carousel with more than five stations is also possible. If the nozzle face is prone to collecting dried ink, it can be difficult to remove with a wiper alone. In these situations, the printer may require a station (not shown) for jetting ink solvent or other cleaning fluid onto the nozzle face. This can be incorporated instead of, or in addition to the spittoon.
With multiple parallel blades wiping across the nozzle face, a single traverse by the wiper member will collect more of the dust and contaminants. While a multiple blade design is less compact than a single blade, each wiping operation is quicker and more effective. Hence the printhead can be wiped between pages during the print job and any preliminary maintenance regime performed prior to a print job is completed in a short time.
A single wiper blade is a simple wiping arrangement with low production and assembly costs. Furthermore, by mounting the blade so that it is skew to the wiping direction, the nozzle face will be in contact with only one section of blade and any time during the traverse of the wiper member. With only one section in contact with the nozzle face, the blade does not buckle or curl because of inconsistent contact pressure along its full length. This ensures sufficient contact pressure between the wiper blade and all of the nozzle face without needing to precisely line the blade so that it is completely parallel to the nozzle face. This allows the manufacturing tolerances to be relaxed so that higher volume low-cost production techniques can be employed. This may entail some compromise in terms of increasing the distance that the wiper member must travel in order to clean the printhead, and therefore increasing the time required from each wiping operation. However the reduced manufacturing costs outweigh these potential disadvantages.
Wiping the nozzle face of pagewidth printhead with a single long blade can be ineffective. Inconsistent contact pressure between the blade and the nozzle face can cause the blade to buckle or curl at certain sections along its length. In these sections the contact pressure can be insufficient or there maybe no contact between the blade and the nozzle face. A wiper blade divided into individual blade sections can address this problem. Each section is capable of moving relative to its adjacent sections so any inconsistencies in the contact force, will not cause buckling or curling in other sections of blade. In this may contact pressure is maintained at the nozzle face is clean effectively.
In
In
Using a wiping surface that has been divided into an array 310 of individual contact pads allows each pad to move relative to its adjacent pads so any inconsistencies in the contact force will vary the amount each pad compresses and deforms individually. Relatively high compression of one pad will not necessarily transfer compressive forces to its adjacent pad. In this way, uniform contact pressure is maintained at the nozzle face is cleaned more effectively.
In the wiping maintenance station 266 shown in
Using a wiping blade that has a zigzag or sinusoidal shape wipes the nozzle face with a number wiper sections that are inclined to the media feed direction. This configuration also keeps the length of travel of the wiper member relative to the printhead small enough to remain accurate and compact.
By using a wiping surface that has an angled or curved shape so that the majority of the nozzle face is wiped with a wiper section that is inclined to the media feed direction while reducing the length of travel of the wiper member relative to the printhead. The ordinary worker will understand that the contact blade can have a shallow V-shape or U-shape. Furthermore if the leading edge of the blade 318 is the intersection of the two linear sections (or the curved section of the U-shaped blade), the Applicant has found that there is less blade wear because of the additional support provided to the initial point of contact with the nozzle face.
It will be appreciated that some printhead designs will be most effectively cleaned by a wiper that has a combination of the above wiping structures. For example a single blade in combination with a series of skew blades, or a series of parallel blades with a fibrous pad in between. The combination wiper maintenance station can be derived by choosing the specific wiping structures on the basis of their individual merits and strength.
The exploded perspective in
The carousel lift cams 172 contact respective carousel lift arms 158 via the cam engaging rollers 168 (it will be appreciated that the cam engaging rollers could equally be a surface of low friction material such as high density polyethylene-HDPE). As the cams 172 are identical and identically mounted to the carousel lift shaft 160 the displacement of the carousel lift arms 158 is likewise identical.
The carousel rotation drive is best illustrated in the enlarged exploded partial perspective of
As the carousel rotation and the carousel lift the controlled by a separate independent drives, each drive powered by a stepper motor that provides the PEC with with feedback as to motor speed and rotation, the printer has a broad range of maintenance procedures from which to choose. The carousel rotation motor 326 can be driven in either direction and at the variable speeds. Accordingly the nozzle face can be wiped in either direction and the wiper blades can be cleaned against the absorbent pad 152 in both directions. This is particularly useful if paper dust or other contaminants passed to the nozzle face because of a mechanical engagement with the surface irregularity on the nozzle face. Wiping in the opposite direction will often dislodge such mechanical engagements. It is also useful to reduce the speed of the wiper blades 162 as they come into contact with the nozzle face and then increase speed once the blades have disengaged the nozzle face. Indeed the wiper blades 162 can slow down for initial contact with the nozzle face and subsequently increase speed while wiping.
Similarly, the wiper blades 162 can be moved past the doctor blade 154 at a greater speed than the blades are moved over the cleaning pad 152. The blades 162 can be wiped in both directions with any number of revolutions in either direction. Furthermore the order in which the various maintenance stations are presented to the printhead can be easily programmed into the PEC and or left to the discretion of the user.
The present invention has been described herein by way of example only. The ordinary worker will readily recognize many variations and modifications which do not depart from the spirit and scope of the broad inventive concept.
