Abstract:
A method is disclosed. The method includes monitoring a sensor for measured vacuum pressure within a print head, determining if the vacuum pressure measured at the sensor is less than a predetermined pressure threshold and indicating that the print head is ready to be decoupled from the maintenance station if the measured vacuum pressure is less than the predetermined pressure threshold.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to the field of ink jet printing systems. More particularly, the invention relates to maintaining a print head within an ink jet printing system. 
       BACKGROUND 
       [0002]    An ink jet printer is an example of a printing apparatus that ejects droplets of ink onto a recording medium, such as a sheet of paper, for printing an image on the recording medium. The ink jet printer includes a print engine having one or more ink jet print heads provided with an ink cartridge that accommodates the ink. In operation of the print engine, the ink is supplied from the ink cartridge to each ink jet print head having ejection nozzles, so that a printing operation is performed by ejection of the ink droplets from selected ejection nozzles. 
         [0003]    However, ink jet printers may suffer from one or more problems leading to nozzle clogging and the inability to fire an ink droplet under normal conditions. A clogged nozzle may not only result in diminished print quality, but may also require the expense of replacing the entire ink jet print head. Thus, ink jet print heads are regularly maintained to ensure usability. 
         [0004]    Maintenance of ink jet print heads typically involves a maintenance station, including an array of print head caps, hoses, manifolds, pumps, valves etc., that generate a vacuum that is used to pull ink through the print head to the maintenance station. Further, an ambient air system is implemented to relieve the vacuum prior to uncapping a capped print head after vacuum has been applied through the maintenance station. However, if the vacuum is not sufficiently relieved before releasing the print heads from the maintenance station, damage to the print head may occur (e.g., nozzle plates may be dislodged from the print head or the print head caps may be damaged resulting in costly part replacement and downtime). 
         [0005]    Current systems release the print heads after a predetermined time period. However, with the use of inks having different viscosities, the time period for the vacuum in the print head to become sufficiently relieved may vary. For instance low viscosity inks may take only several seconds for sufficient vacuum relief, while a higher viscosity ink may take several minutes. Thus, the predetermined time period must be set for the higher threshold, even if the actual relief time may be substantially less; or an ambient vacuum relief system and associated extra hardware is required to relieve the vacuum. 
         [0006]    Therefore, a system to monitor vacuum applied to a print head is desired. 
       SUMMARY 
       [0007]    In one embodiment, a method is disclosed. The method includes monitoring a sensor for measured vacuum pressure applied to a print head, determining if the vacuum pressure measured at the sensor is less than a predetermined pressure threshold and indicating that the print head is ready to be decoupled from the maintenance station if the measured vacuum pressure is less than the predetermined pressure threshold. 
         [0008]    In a further embodiment, a system is disclosed. The system includes a print engine having a sensor to measure vacuum pressure applied to the print head, a maintenance station coupled to pull ink from the print head via a vacuum, and a control to monitor the sensor and to determine if the vacuum pressure measured at the sensor is less than a predetermined pressure threshold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    A better understanding of the present invention can be obtained from the following detailed description in conjunction with the following drawings, in which: 
           [0010]      FIG. 1  illustrates one embodiment of a system; 
           [0011]      FIG. 2  illustrates one embodiment of a maintenance station; and 
           [0012]      FIG. 3  is a flow diagram illustrating one embodiment of vacuum relief. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    A mechanism to monitor vacuum for print head release is described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form to avoid obscuring the underlying principles of the present invention. 
         [0014]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0015]      FIG. 1  illustrates one embodiment of a system  100 . System  100  includes a print head  110  and a maintenance station  120 . In one embodiment, print head  110  is a component of an ink jet print engine that supplies ink from an ink cartridge to a medium via multitude of nozzles. In a further embodiment, print head  110  includes a vacuum sensor  115  that monitors vacuum pressure applied to print head  110  during maintenance. 
         [0016]    In such an embodiment, vacuum sensor  115  is an electronic vacuum gauge that is electrically coupled to maintenance station  120  to provide feedback signals. However in other embodiments, other types of pressure sensors may be implemented. 
         [0017]    Maintenance station  120  is used to maintain print head  110  by pulling ink through and from print head  110  to maintenance station  120  via a vacuum source. Thus, maintenance station  120  is also coupled to print head  110  by caps  112 , which attach to print head  110 , and hoses  105 .  FIG. 2  illustrates one embodiment of maintenance station  200  corresponding to maintenance station  120  shown in  FIG. 1 . 
         [0018]    Maintenance station  200  includes a manifold  210  having fittings  211  for coupling to hoses  205 . Hoses  205  are coupled to print head caps, which are coupled to print head  110 , and are implemented to carry ink from print head  110  to manifold  210 . Maintenance station  200  also includes fittings  213  coupled at an end of manifold  210 . In one embodiment, each of fittings  213  are coupled to a valve and a vacuum source via a hose to provide the vacuum to manifold  210 . 
         [0019]    A vacuum is provided at each respective fitting  213 . Thus, the vacuum presented at fitting  213  enables ink to be pulled into manifold  210  from a print head via hoses  205  and fittings  211 , and out through fittings  213 . In other embodiments, separate ambient air ports may be provided to relieve the vacuum in order to prevent damage to the print head prior to removing a cap at the print head. According to one embodiment, all components of maintenance station  200  are composed of polypropylene. However in other embodiments, other materials are used for one or more of the components of maintenance station  200 . 
         [0020]    Referring back to  FIG. 1 , maintenance station  120  also includes a control  150 . Control  150  controls the print head  110  maintenance process by starting and stopping a vacuum cleaning sequence. According to one embodiment, control  150  receives feedback signals from vacuum sensor  115 . In such an embodiment, control  150  monitors the signals from vacuum sensor  115  once the cleaning sequence has ended in order to determine whether vacuum pressure measured at print head  110  by vacuum sensor  115  has been sufficiently relieved. Once the pressure is determined to be below a predetermined pressure threshold, caps  112  may be disconnected from print head  110 . For example, the print head caps may disengage when the vacuum is below 1 kPa. Although described above as included in maintenance station  120 , other embodiments may be implemented in which control  150  is external to maintenance station  120 . 
         [0021]      FIG. 3  is a flow diagram illustrating one embodiment of vacuum relief. At processing block  310 , the maintenance cycle in system  100  is completed. At processing block  320 , control  150  begins monitoring feedback signals received from vacuum sensor  115 . At decision block  330 , it is determined whether the signals indicate that the vacuum pressure measured by vacuum sensor  115  is less than the predetermined pressure threshold. 
         [0022]    If so, print head  110  is ready to be uncapped from maintenance station  120 , processing block  340 . In one embodiment, maintenance station  120  provides an audio and/or visual indication that the print head  110  is ready to be uncapped. In another embodiment, maintenance station  120  provides an indication internal to a print engine. For example, the print engine may cause print head  110  to uncap and continue with the cleaning cycle once the vacuum has reached the acceptable level, thereby producing a closed-loop system. 
         [0023]    If it is determined that the measured vacuum pressure is greater than the predetermined pressure threshold, control is returned to processing block  320 , where control  150  continues to monitor the signals from vacuum sensor  115  until the vacuum pressure falls below the predetermined pressure threshold. 
         [0024]    The above-described mechanism extends the life of print heads, and reduces service costs by ensuring that print heads are not uncapped prematurely. 
         [0025]    Embodiments of the invention may include various steps as set forth above. The steps may be embodied in machine-executable instructions. The instructions can be used to cause a general-purpose or special-purpose processor to perform certain steps. Alternatively, these steps may be performed by specific hardware components that contain hardwired logic for performing the steps, or by any combination of programmed computer components and custom hardware components. 
         [0026]    Elements of the present invention may also be provided as a machine-readable medium for storing the machine-executable instructions. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards, propagation media or other type of media/machine-readable medium suitable for storing electronic instructions. For example, the present invention may be downloaded as a computer program which may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) via a communication link (e.g., a modem or network connection). 
         [0027]    Throughout the foregoing description, for the purposes of explanation, numerous specific details were set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention may be practiced without some of these specific details. Accordingly, the scope and spirit of the invention should be judged in terms of the claims which follow.