Patent Publication Number: US-9844944-B2

Title: Printing system servicing

Description:
RELATED DOCUMENTS 
     The present application is a continuation, and claims the benefit under 35 U.S.C. §120, of U.S. application Publication Ser. No. 14/427,566, filed Mar. 11, 2015 which is the national stage entry of International Patent Application No. PCT/US12/056264 filed Sep. 20, 2012. These applications are herein incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     Inkjet printheads may suffer from printhead nozzles becoming blocked or partially obstructed due to ink residue in proximity to the nozzles hardening. Blocked or obstructed printhead nozzles may lead to print quality issues, especially if ink drops are not ejected by a nozzle as planned during a printing operation. 
     In printing systems that use moveable printheads, such as printing systems that have printheads that are moveable over a print zone, a printhead may be moved out of a print zone and into a printhead service station. In the printhead service station printhead nozzles may be serviced, for example by being purged into a spittoon, or by being wiped with a mechanical wiping mechanism, before being returned to the print zone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples, or embodiments, of the invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a portion of a printing system according to one example; 
         FIG. 2  is section view of a nozzle wiping module according to one example; 
         FIG. 3  is a block diagram of a portion of a printing system according to one example; 
         FIGS. 4 a  to 4 d    are block diagrams showing a portion of a printing system according to one example; 
         FIG. 5  is a flow diagram outlining an example method according to one example; and 
         FIG. 6  is a block diagram of a controller according to one example. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1  there is shown a simplified block diagram of a printing system  100  according to one example. 
     The printing system  100  is a page-wide array printing system that has a print bar  102  on which are installable a plurality of inkjet printheads  104 . The printheads may be any kind of inkjet printhead, such as thermal inkjet printheads or piezo inkjet printheads. The printheads  104  are arranged in a longitudinal array configuration such that the printheads cover substantially the whole width of a print zone  106  in which printing may be performed. The printing system  100  may thus print along the whole width of a substrate  108  in the print zone  106  by advancing the substrate in a media advance direction  110  perpendicular to the print bar under the print bar  102 . In the example shown the printheads are arranged in a staggered configuration, although in other examples a non-staggered linear configuration could be used. 
     Operation of the printing system  100  is controlled by a printer controller  114 . 
     The printing system  100  comprises a nozzle control data generator  116  that generates printhead nozzle firing data based on data representing an image to be printed. In one example the nozzle control data generator  116  is integrated into the printer controller  114 , although in another example it is separate from the printer controller  114 . The generated nozzle control data is fed to the printheads  104  such that appropriate nozzles of the printheads  104  eject ink drops at specific times to recreate an image to be printed on the substrate  108  as the substrate  108  is advanced under print bar  102 . 
     The printing system  100  is arranged such that the print bar  102  is not moveable out of the print zone  106  during normal operation of the printing system  100 . In some examples, the printing system  100  may be a wide-format printing system in which case the print bar  106  may be in excess of 1 m in length. Accordingly, it is not generally practical to have such a print bar moveable out of the print zone  106  to perform nozzle servicing operations. 
     The printing system  100  additionally comprises a nozzle servicing module  112 , an example of which is shown in greater detail in  FIG. 2 . 
     The nozzle servicing module  112  is moveable along the length of the print bar  102  to perform nozzle servicing operations on the nozzles of printheads  104  installed on the print bar  102 . 
       FIG. 2  shows a section view of a nozzle servicing module  112  according to one example. 
     The nozzle servicing module  112  is supported on the print bar  102  by a pair of guide members  202 . The guide members  202  allow the nozzle servicing module  202  to move along the length of the print bar  102 . The print bar  102  may have shaped side members into which the guide members  202  fit or engage. The guide members  202  may include, for example, suitable bearings or bushes to reduce friction between the nozzle servicing module  112  and the print bar  102 . 
     Although not shown in  FIG. 2 , the nozzle servicing module  112  includes a drive system to enable the nozzle servicing module  112  to be moved along the length of the print bar  102  under control of the printer controller  114 . The drive system may include, for example, a motorized belt, a motor, or any other suitable drive mechanism. 
     On guide member  202   a  is mounted an unwind roller  204 , and on guide member  202   b  is mounted a wind roller  206 . On the roller  204  is wound a length of nozzle wiping material  208 . In one example a textile material such as a microfiber cloth, may be used. The nozzle wiping material  208  feeds beneath the printheads  104  on the print bar  102  and is attached to the wind roller  206 . In one example the wind roller  206  is powered by an electric motor and the unwind roller  204  has a built-in resistance to unwinding, such that when the wind roller  206  rotates in a winding direction, the nozzle wiping material is held taught. In one example the unwind roller  204  is also powered to enable the nozzle wiping material  208  to wound back onto the unwind roller to allow a reciprocating wiping motion to be performed. 
     In one example the unwind roller  204  and wind roller  206  are positioned such that when the nozzle wiping material is held taught it exerts a pressure on printhead nozzles enabling them to be effectively wiped. In the present example the unwind and wind rollers are arranged such that wiping occurs in a direction orthogonal to the longitudinal axis of the print bar  102  when the wind roller is activated. In other examples, unwind and wind rollers are arranged such that wiping occurs in a direction oblique to the longitudinal axis of the print bar  102 . 
     Wiping may thus occur when the nozzle servicing module  112  is moved along the print bar, when the wind roller  206  winds nozzle wiping material  208  from the unwind roller  204 , or a combination of the two. 
     The thickness of the nozzle wiping material  208  is chosen such that it fits within the printhead-to-substrate gap  210  which may be in the order of between about 1 to 10 mm. In one example the width of the nozzle wiping material is less than or equal to the width of a printhead. 
     The nozzle servicing module  112  is controllable, by the printer controller  114 , to move along the length of the print bar  106  and also to cause a group of nozzles to be wiped by controlling the powered wind roller  206 . In this way, all of the nozzles of all of the printheads  104  may be serviced by the nozzle servicing module  112  without requiring the print bar to be moved to a service station, and, importantly, without requiring the print bar to be raised. In one example the nozzle servicing module  112  includes an encoder, such as an optical encoder, and the print bar  106  includes an encoder strip that is readable by the encoder, such that the position of the nozzle servicing module  112  is precisely determinable and precisely controllable. 
     Such a nozzle servicing module thus presents numerous advantages. However, performing a nozzle servicing operation does lead to interruption of a printing operation since the nozzles being services are unable to be used in a printing operation. 
     A further example, described below with reference to  FIGS. 3, 4 and 5 , aims to overcome the aforementioned shortcomings by providing a printing system  300  having an auxiliary carriage  302  on which is installable an auxiliary printhead  304 , in addition to a nozzle servicing module  112 . In one example the auxiliary printhead  304  has the same characteristics as the other printheads  104  on the print bar  102 . In other examples, multiple printheads may be installable on the carriage  302 . 
     The carriage  302  is moveable along a carriage bar  306  parallel to the print bar  108  under control of the printer controller  114 . In one example the carriage bar  306  is positioned upstream from the print bar  102 , although in another example the carriage bar  306  is positioned downstream from the print bar  102 . 
     The auxiliary printhead  304  selectively provides nozzle redundancy for a group of nozzles being serviced by the nozzle servicing module  112 , thereby enabling the nozzle servicing module  112  to perform a servicing operation on a group of printhead nozzles during a printing operation, such as printing a print job, without interruption of the printing operation. 
     Thus, as the nozzle servicing module  112  moves across the print bar  102  performing servicing operations on groups of printhead nozzles, printhead nozzles obscured by the nozzle servicing module  112  are replaced by nozzles on the auxiliary printhead  304 . Nozzle firing data for the replaced nozzles is diverted to the auxiliary printhead  304 , to enable the auxiliary printhead  304  to print those ink drops originally intended to be printed by those nozzles being serviced, as described further below. In one example, the nozzle firing data controls nozzle drive circuitry that causes a nozzle to eject ink drops. 
     In this manner, the printing system  300  is able to service printhead nozzles without interrupting a printing operation, such as a print job. In one example the speed at which media is advanced under the print bar  102  is the same during a printhead servicing operation as during a regular printing operation. In a further example the speed at which the media is advanced under the print bar  102  is reduced during a printhead servicing operation compared to the speed of a regular printing operation. 
     This system provides an important advantage, for example in commercial printers, as it helps increase the amount of time that a printing system is operational, since it becomes no longer necessary to stop printing operations to perform a printhead servicing operation. 
     To enable nozzles of the auxiliary printhead  304  to temporarily replace nozzles of one or multiple ones of the printheads  104  the printing system  300  additionally comprises a nozzle redundancy controller  310 . In one example the nozzle redundancy controller  310  is integrated into the printer controller  114 , although in another example the nozzle redundancy controller  310  is separate from the printer controllers  114 . 
     The nozzle redundancy controller  310  diverts printhead nozzle firing data generated by the nozzle control data generator  116  intended for nozzle circuitry of a printhead  104  on the print bar  106  to nozzle circuitry on the auxiliary printhead  302 . In this way nozzles of the auxiliary printhead  304  print a portion of the image to be printed instead of the portion of the image being printed by nozzles of printheads  104 . 
     Since the auxiliary printhead  302  is not located in the same vertical plane as the printheads  104  on the print bar  106 , appropriate modification to the timing of nozzle firing data is performed by the nozzle redundancy controller  310 , as will be described in greater detail below. The amount of modification may be based on the horizontal distance between printheads  104  on the print bar  106  and the printhead  304  on the carriage  306 . 
     A method of operating the printing system  100  will now be described in greater detail with reference to  FIG. 4  and  FIG. 5 . 
     The operation is controlled by the printer controller  114 , a more detailed illustration of which is shown in  FIG. 6 . 
     The printer controller  114  comprises a processor  602 , such as a microprocessor or microcontroller, and a memory  606  coupled to the processor  602  by a communications bus  604 . The memory  606  stores processor executable nozzle servicing module control instructions  608  that, when executed by the processor  602  cause the controller  114  to control the nozzle servicing module  112  as described herein. The memory  610  also stores processor executable auxiliary printhead control instructions  608  that, when executed by the processor  602  cause the controller  114  to control the auxiliary printhead  304 . 
     Turning now to  FIG. 4 a    is shown a portion of the printing system  300  in greater detail. A number of printheads  104  on a print bar are shown however, for reasons of clarity the print bar  102  is not shown. Each printhead  104  has a number of nozzles  402  through which ink or other fluid may be ejected in response to appropriate nozzle firing data being received by nozzle circuitry in the printhead. In  FIG. 4  only a small number of nozzles are shown on each printhead for clarity. However, it will be appreciated that a printhead  104  may comprise a many hundreds or thousands of nozzles. 
     When not used the nozzle wiping module  112  is parked in a parking area on the print bar  106  where it does not obstruct any nozzles. When a nozzle servicing operation is to be performed the nozzle wiping module  112  is moved, under control of the printer controller  114 , out of a first parking zone at one end of the print bar and along the print bar  106 . In one example the nozzle wiping module  112  is moved across the whole length of the print bar  102  to a second parking zone at the other end of the print bar. 
     In one example the auxiliary printhead is positioned such that nozzles on the auxiliary printhead extend laterally beyond the nozzle servicing module  112 , as shown in  FIG. 4 a   . In this way, as the nozzle servicing module  112  and the auxiliary printhead move across the print bar  102  the nozzles on auxiliary printhead  304  lead those nozzles on printheads  104  about to be obscured by the nozzle servicing module. This enables the end nozzles of the auxiliary printhead to replace corresponding nozzles on a printhead about to be serviced, before those nozzles are actually obscured by the nozzle servicing module  112 . 
     At block  502  the controller  114  starts moving the nozzle wiping module  112  and the auxiliary printhead  302  from a parking zone along the print bar  106 . 
     At block  504  the controller  114  determines whether any nozzles of any printheads, if any, are obscured by the nozzle wiping module  112 . 
     If the controller  114  determines that one or multiple nozzles are obscured by the nozzle wiping module  112 , the controller  114  transfers nozzle control data intended for nozzle circuitry of those obscured nozzles to nozzle circuitry of appropriate nozzles on the auxiliary printhead  304  which are aligned with those obscured nozzles. The controller also adjusts, as appropriate, the timing of the nozzle control data for the nozzles on the auxiliary printhead to compensate with the different horizontal position of the auxiliary printhead  304 . 
     This process is repeated as the nozzle wiping module  112  is moved along the length of the print bar  102  to a second parking zone. 
     In  FIG. 4 a    is illustrated an example when the nozzle wiping module  112  has started to move from the first parking position. In this example, nozzles on the auxiliary printhead  304  are aligned with nozzles on a printhead  104  on the print bar  102  which are obscured by the nozzle wiping module  112 . 
     The printer controller  114  can accurately determine which nozzles are obscured by the nozzle wiping module  112  based, for example, on encoder or position detectors on the nozzle wiping module  112 . 
     A first set  406  of the nozzles  402  on printhead  104   a  are thus rendered inactive by the nozzle redundancy controller  310 , whilst the remaining nozzles remain active. Nozzle firing data generated by the nozzle control data generator  116  intended for the first set  406  of inactivated nozzles is diverted to the set  410  of nozzles on the auxiliary printhead  304  that are aligned with the inactivated set  406  of nozzles  402  on the printhead  104   a.    
     In one example the set of nozzles rendered inactive by the nozzle redundancy controller  310  covers more nozzles than are actually obscured by the nozzle wiping mechanism  112 . This allows for an additional safety margin of a predetermined number of nozzles. In other examples, however, just those nozzles obscured by the nozzle wiping mechanism  112  may be rendered inactive. In  FIG. 4 a   , it can be seen that a set  412  of nozzles of auxiliary printhead  304  are not aligned with any printhead nozzles, hence this set of nozzles are also rendered inactive. 
     In  FIG. 4 b   , the nozzle wiping mechanism  112  and auxiliary printhead  304  have advanced along the print bar  102 . The majority of the nozzles  402  of printhead  104   a  are obscured by the nozzle wiping mechanism  112 , and with the above-mentioned safety margin, a set  406  comprising all of the nozzles of printhead  104   a  are rendered inactive by the nozzle redundancy controller  310 , whilst a set  410  comprising all of the nozzles on auxiliary printhead  304  are activated. Nozzle firing data generated by the nozzle control data generator  116  intended for the inactivated nozzles of printhead  104   a  is diverted to the set  410  of active nozzles of the auxiliary printhead  304 . 
     In  FIG. 4 c   , the nozzle wiping mechanism  112  and auxiliary printhead  304  have further advanced along the print bar  102 , such that a first set  406   a  of nozzles of the printhead  104   a  are inactivated by the nozzle redundancy controller  310  along with a set  406   b  of nozzles of the printhead  104   b . Nozzle firing data generated by the nozzle control data generator  116  intended for the sets ( 406   a  and  406   b ) of inactivated nozzles of printhead  104   a  is diverted to the set  410  of active nozzles of the auxiliary printhead  304 . 
     In  FIG. 4 d   , the nozzle wiping mechanism  112  and auxiliary printhead  304  have still further advanced along the print bar  102 , such that a set  406  of nozzles of the printhead  104   b  are inactivated by the nozzle redundancy controller  310 . Nozzle firing data generated by the nozzle control data generator  116  intended for the set  406  of inactivated nozzles of printhead  104   b  is diverted to the set  410  of active nozzles of the auxiliary printhead  304 . 
     In the present example the nozzle wiping mechanism  112  and auxiliary printhead  304  are moved synchronously. In one example, the nozzle wiping mechanism  112  and auxiliary printhead  304  may be mounted on the same movable carriage, such as the auxiliary carriage  302 . In another example the nozzle wiping mechanism  112  and auxiliary printhead  304  may be moved substantially synchronously. 
     It will be appreciated that examples and embodiments of the present invention can be realized in the form of hardware, software or a combination of hardware and software. As described above, any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are examples of machine-readable storage that are suitable for storing a program or programs that, when executed, implement examples of the present invention. Examples of the present invention may be conveyed electronically via any medium such as a communication signal carried over a wired or wireless connection and examples suitably encompass the same. 
     All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. 
     Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.