Abstract:
A method for reducing a servicing noise is provided. In a measuring action, a servicing position is measured using a full pushing force of an actuator applied to a service station. In a disengaging action, the actuator is disengaged from the service station. In a reducing action, the pushing force is reduced to a minimum value. In an engaging action, the service station is engaged with the actuator. In a monitoring action, a position of the actuator is monitored during the engagement. In a comparing action, the actuator position is compared to the stored servicing position. In an increasing action, the pushing force is increased for future engagements if the servicing position has not been reached. A printing mechanism configured to employ such a method is also provided.

Description:
Printing mechanisms often include an inkjet printhead which is capable of forming an image on many different types of media. The inkjet printhead ejects droplets of colored ink through a plurality of orifices and onto a given media as the media is advanced through a printzone. As used herein, the term “media” may refer to one or more medium. The printzone is defined by the plane created by the printhead orifices and any scanning or reciprocating movement the printhead may have back-and-forth and perpendicular to the movement of the media. Methods for expelling ink from the printhead orifices, or nozzles, include piezo-electric and thermal techniques. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, the Hewlett-Packard Company. 
     A printing mechanism may have one or more inkjet printheads, corresponding to one or more colors, or “process colors” as they are referred to in the art. Many inkjet printing mechanisms contain a service station for maintenance of the inkjet printheads. The service station may include scrapers, ink-solvent applicators, primers, and/or caps to help keep the nozzles from drying out during periods of inactivity. 
     Some service stations are configured to minimize space and/or reduce cost by moving substantially in-line with the motion of the printheads, and by being activated into a servicing position by a carriage transporting the printheads. One such in-line service station can be found in U.S. Pat. No. 6,315,386. While in-line service stations can save space, the process of activating the service station into the servicing position can create an undesirable amount of noise. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-3 schematically illustrate one embodiment of a printing mechanism having an in-line service station. 
     FIG. 4 illustrates one embodiment of actions which adapt a servicing force for a service station. 
     FIG. 5 illustrates another embodiment of actions which adapt a servicing force for a service station. 
     FIG. 6 illustrates one embodiment of velocity and pulse width modulation curves for a printhead carriage. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 schematically illustrates one embodiment of a printing mechanism, here shown as an inkjet printer  20 , which may be used for printing on a variety of media, such as paper, transparencies, coated media, cardstock, photo quality papers, and envelopes in an industrial, office, home or other environment. A variety of inkjet printing mechanisms are commercially available. For instance, some of the printing mechanisms that may embody the concepts described herein include desk top printers, portable printing units, wide-format printers, hybrid electrophotographic-inkjet printers, copiers, video printers, and facsimile machines, to name a few. For convenience the concepts introduced herein are described in the environment of an inkjet printer. 
     While it is apparent that the printer components may vary from model to model, the typical inkjet printer  20  includes a printer controller  22  that receives instructions from a host device, such as a computer or personal data assistant (PDA) (not shown). A screen coupled to the host device may also be used to display visual information to an operator, such as the printer status or a particular program being run on the host device. Printer host devices, such as computers and PDA&#39;s, their input devices, such as a keyboards, mouse devices, stylus devices, and output devices such as liquid crystal display screens and monitors are all well known to those skilled in the art. 
     A print media handling system (not shown) may be used to advance a sheet of print media  24  through a printzone  26  for printing. A carriage guide rod  28  is positioned within the inkjet printer  20  to define a scanning axis  30 . In the case of FIG. 1, the scanning axis  30  is parallel to the X-axis. The guide rod  28  slidably supports an inkjet carriage  32  for travel back and forth, reciprocally, across the printzone. 26 . A carriage drive motor  34  is coupled to the carriage  32 , and may be used to propel the carriage  32  in response to an input  36  received from the controller  22 . To provide carriage position feedback information  38  to controller  22 , a conventional encoder strip (not shown) may be extended along the length of the printzone  26  and over a servicing region  40 . An optical encoder reader may be mounted on the back surface of printhead carriage  32  to read position information provided by the encoder strip, for example, as described in U.S. Pat. No. 5,276,970, also assigned to the Hewlett-Packard Company, the present assignee. Such an encoder is schematically illustrated as encoder block  42  in FIG.  1 . Position feedback  38  may be provided by other techniques familiar to those skilled in the art, for example, by connecting an encoder to the motor  36 , rather than to the printhead carriage  32  as illustrated in this embodiment. 
     In the printzone  26 , the media sheet  24  receives ink  44  from an inkjet cartridge, such as a black ink cartridge  46  or a color ink cartridge  48 . The illustrated printer  20  uses replaceable printhead cartridges where each cartridge has a reservoir that carries the entire ink supply as the printhead reciprocates across the printzone  26 . As used herein, the term “cartridge” may also refer to an “off-axis” ink delivery system, having main stationary reservoirs (not shown) for each ink located in an ink supply region. In an off-axis system, the cartridges may be replenished by ink conveyed through a flexible tubing system from the stationary main reservoirs which are located “off-axis” from the path of printhead travel, so only a small ink supply is propelled by carriage  32  across the printzone  26 . Other ink delivery or fluid delivery systems may also employ the systems and methods described herein, such as cartridges which have ink reservoirs that snap onto permanent or semi-permanent printheads. 
     The illustrated black ink cartridge  46  has a printhead  50 , and color ink cartridge  48  has a tri-color printhead  52  which ejects cyan, magenta, and yellow inks. In response to firing command control signals delivered from the controller  22  to the printhead carriage  32 , the printheads  50 ,  52  selectively eject ink  44  to form an image on a sheet of media  24  when in the printzone  26 . The printheads  50 ,  52  are thermal inkjet printheads, although other types of printheads may be used, such as piezoelectric printheads. 
     Between print jobs, the inkjet carriage  32  moves along the carriage guide rod  28  to the servicing region  40  where a service station  54  may perform various servicing functions known to those in the art, such as, priming, scraping, and capping for storage during periods of non-use to prevent ink from drying and clogging the inkjet printhead nozzles. For simplicity, the service station  54  is illustrated as a capping station. 
     The service station  54  has a frame  56  which defines a series of guide slots  58 . Two guide slots  58  are located on the front of the frame  56  as visible in FIG.  1 . Two similar guide slots  58  are located on the back of the frame  56  (not shown). A maintenance sled  60  is supported by the frame  56  on guide posts  62  which protrude from the maintenance sled  60  to slidably engage the guide slots  58 . A biasing spring  64  couples the sled  60  to the frame  56 , biasing the sled  60  in a negative X-axis direction and a negative Y-axis direction. As illustrated in FIG. 1, the maintenance sled  60  is in a retracted position. The maintenance sled  60  has a black printhead cap  66  and a color printhead cap  68  which are moveably coupled to the sled  60 , and biased in a positive Y-axis direction by capping springs  70 . The maintenance sled  60  also has an activation arm  72  protruding upwards from the sled  60 . The frame  56  is supported and held in a fixed position by a chassis (not shown) of the inkjet printer  20 . 
     As FIG. 2 illustrates, the printhead carriage  32  maybe moved along the carriage guide rod  28  in the positive X-axis direction until the carriage  32  contacts the activation arm  72 . After contacting the activation arm  72 , as the carriage  32  continues to move in the positive X-axis direction, the guide posts  62  move within the guide slots  58 , first up a ramp portion  74  and towards a top of the ramp portion  76 . The activation arm  72  is constructed to contact the carriage  32  when the printhead caps  66 ,  68  are horizontally aligned (along the X-axis) with their corresponding printheads  50 ,  52 . While there is horizontal alignment between the printhead caps  66 ,  68  and the printheads  50 ,  52  when the carriage  32  initially contacts the activation arm  72 , the caps  66 ,  68  do not contact the printheads  50 ,  52  until the carriage  32  continues to move the maintenance sled  60  further upwards as defined by the motion allowed by the guide slots  58  and the guide posts  62 . When the guide posts  62  move up the ramp  74  and approach the top of the ramp  76 , the caps  66 ,  68  will engage their respective printheads  50 ,  52 . As the carriage  32  continues to move along the carriage guide rod  28  in the positive X-axis direction, the maintenance sled  60  moves upwards relative to the printheads  50 ,  52 , causing the capping springs  70  to compress. Since the printheads  50 ,  52  are held in place by the printhead carriage  32 , the force in the positive Y-axis direction provided by the capping springs  70  tends to lift the carriage against the guide rod  28 , and may even cause a slight deflection of the guide rod  28 . 
     As the printhead carriage  32  continues to move in the positive X-axis direction, the guide posts  62  reach the top of the ramp  76 . At this point, the capping force exerted by the capping springs  70  remains relatively constant, since the capping springs  70  will not compress further. As FIG. 3 illustrates, the printhead carriage  32  can continue moving in the positive X-axis direction until the guide posts  62  reach the top end  78  of the guide slots  58 . When the guide posts  62  have reached the top end  78  of the guide slots  58 , the maintenance sled  60  is considered to be in a servicing position. In other embodiments, the maintenance sled  60  can reach the servicing position when the guide posts  62  have not reached the top end  78  of the guide slots, for example, in a situation where there is an alternate physical stop which the carriage  32  or the ink cartridges  46 ,  48  contact to prevent further motion and therefore determine the servicing position. 
     When the printhead carriage  32  is moved back in the negative X-axis direction, the biasing spring  64  maintains contact between the activation arm  72  and the carriage  32 . As the carriage  32  moves in the negative X-axis direction, the guide posts  62  move within the guide slots  58 , back past the top of the ramp  76  and down the ramp portion  74  until the maintenance sled  60  is in the retracted position once again. When the maintenance sled  60  reaches the retracted position, the carriage  32  will disengage the activation arm  72  as the carriage is moved further in the negative X-axis direction. 
     Given the torque capabilities of the motor  34  which is moving the printhead carriage  32 , and the mass of the ink cartridges  46 ,  48 , as well as the carriage  32  itself, it is often not possible for the carriage  32  to slowly engage the activation arm  72  and move the maintenance sled  60  from the retracted position to the servicing position in a slow and steady manner. Instead, it is often necessary to move the printhead carriage  32  a distance away from the service station  54  in the negative X-axis direction, and provide an input  36  to the motor  34  which will accelerate the printhead carriage  32  to a desired velocity before contacting the activation arm  72 . The momentum achieved by doing this is sufficient to overcome the forces associated with the guide posts  62  climbing the ramp  74 , compressing the capping springs  70 , and lifting the carriage guide rod  28 . Since these forces may vary over time depending on the age of the system and the manufacturing tolerances involved, it may be desirable to use a “full force push” by the printhead carriage  32  to guarantee that the maintenance sled  60  reaches the servicing position under all conditions, regardless of the amount of ink in the ink cartridges, the number of ink cartridges present, positioning differences due to manufacturing tolerances, varying friction in the system from one inkjet printer  20  to another, or varying friction in the system over time due to use, aging, contamination, or part wear. The momentum achieved by a full force push is empirically determined to be adequate to move the maintenance sled  60  into the servicing position, regardless of the variable conditions which may exist. A “full force” push or a “full pushing force” is not necessarily as hard as the printhead carriage  32  can push. Rather, a full force push, as used herein and in the claims, is a push determined to be adequate to allow the maintenance sled  60  to reach the servicing position under a number of variable conditions. While this is a robust solution, there will be situations where the full force push will effectively slam the carriage  32  into the activation arm  72 , slam the caps  66 ,  68  into the printheads  50 ,  52 , and/or slam the guide posts  62  into the top end  78  of the guide slots  58 , creating undesirable noise from the inkjet printer  20 , or possibly unseating one or more of the ink cartridges  46 ,  48  from the carriage  32 . 
     FIG. 4 illustrates one embodiment of actions which adapt a servicing force for a service station. Based on feedback from the encoder  42 , the controller  22  is able to know the position of the printhead carriage  32  as it moves along the carriage guide rod  28  in the positive and negative X-axis directions. Using a full force push as described above, the controller can measure and store  80  the servicing position in terms of carriage position. After measuring and storing  80  the servicing position in terms of carriage position by using a full force push, the carriage disengages  82  the service station, and the controller reduces  84  the pushing force to a minimum value and engages the service station. Recall that the force of the push is determined in part by the velocity of the printhead carriage  32  when it contacts the activation arm  72 . The velocity of the printhead carriage  32  is a function of the input  36  to the motor  34 , the resistance to movement provided by the mass of the carriage  32  and the ink cartridges  46 ,  48 , and the distance the carriage  32  has to travel before contacting the activation arm  72 . The motor input  36  will determine the power given to the motor  34 , and therefore will affect the acceleration of the printhead carriage  32 . If the carriage  32  is allowed to accelerate over a larger distance, it will reach a higher velocity, and will be capable of pushing the activation arm  72  with a greater force. Therefore, to reduce the pushing force to a minimum value, the controller can reduce the level of motor input  36  and/or start the carriage  32  closer to the activation arm so that the carriage  32  will not accelerate to as high of a velocity as it can with the full force push. The minimum force can be calculated or empirically determined based on best case scenarios. Best case scenarios for a minimum force include a broken-in motor, nearly empty print cartridges, cap springs  70  which have a low force, and well-lubricated parts with minimal friction. As used herein and in the appended claims, the term “minimal force” or “minimum value” does not necessarily refer to an absolute lowest amount or value. Rather, “minimum force” and/or “minimum value” can also refer to a reduced or smaller value as compared to another value. For example, a minimum force can be any force which is less than the full force, and not necessarily the lowest possible force. 
     During the reduced force push, the controller monitors  86  the position of the printhead carriage. The carriage position is compared  88  to the stored servicing position. The controller then determines  90  if the servicing position has been reached based on the encoder position. If the servicing position has not been reached  92 , the carriage is disengaged  94  from the service station, and the pushing force is increased  96  by a desired increment and the service station is engaged by the carriage. The controller again monitors  86  the position of the carriage, and compares  88  the position of the carriage to the stored servicing position. If the servicing position has been reached  98 , the force used during the push is stored  100  as an adaptive servicing force for use with subsequent servicing events. 
     The controller may monitor  102  to see if both printheads have been removed. If both printheads have been removed  104 , the pushing force is set  106  to a minimum empty carriage value. The carriage can then be monitored  86  during subsequent pushes, and the push force increased  96  if necessary as described above. If the controller determines that both printheads have not been removed  108 , the controller may also determine  110  whether one of the printheads has been removed. If one of the printheads has been removed  112 , the pushing force is set  114  to a minimum single printhead value. The carriage can then be monitored  86  during subsequent pushes, and the push force increased  96  if necessary as described above. If none of the printheads have been removed  116 , the controller may continue to monitor  86  the carriage position during subsequent pushes. Although the embodiment of FIG. 4 uses the example of a carriage  32  which is capable of holding a maximum of two printheads, a similar process could be used for a carriage with any number of printheads. Instead of setting  106  the pushing force to a minimum empty carriage value, or setting  114  the pushing force to a minimum single printhead value, the controller would reduce the pushing force to an alternate minimum value which corresponded to the number of printheads remaining in the carriage. It should be understood that in other embodiments, it may be preferable to determine if any printheads have been removed from the carriage prior to reducing  84  the pushing force to a minimum value and engaging the service station for the first time. 
     This adaptive servicing method allows the minimum force required to service the printheads  50 ,  52 , in this case the minimum force required to cap the printheads, to be used. This produces less noise and less part wear than a non-adaptive full-force approach. This minimum force can be referred to as the adaptive servicing force. The adaptive servicing force may be represented by a starting distance from the service station  54  and the level of the motor input  36  provided during the push. The motor input  36  is commonly provided using pulse-width-modulation (PWM). 
     FIG. 5 illustrates another embodiment of actions which adapt a servicing force for a service station. The actions in FIG. 5 make use of the adaptive servicing force determined in the previously discussed process of FIG.  4 . The servicing position was determined during the full force push. Based on a knowledge of the dimensions of the service station  54 , and the knowledge of the servicing position, an estimate can be made of the location where the caps  66 ,  68  will contact the pens and therefore, where the cap springs  70  start to compress, and the carriage guide rod  28  begins to deflect. An estimate can also be made of the position of the top of the ramp  76 . 
     Prior to moving the printhead carriage to the servicing position, the carriage is moved  118  to the starting position for the adaptive servicing force determined during the previous actions. The motor input is set  120  to a first level equal to a first percentage of the motor input which was determined to result in the adaptive servicing force. This first percentage is less than one-hundred percent, and this first motor input level is chosen to be sufficient to move the carriage, engage the activation arm  72 , and start the guide posts  62  moving up the ramp  74 . The motor input is then set  122  to a second level equal to a second percentage of the motor input which was determined to result in the adaptive servicing force. This second percentage is greater than one-hundred percent, and is chosen to be sufficient to overcome the opposing cap spring  70  compression force as well as the opposing force from the carriage guide rod  28  as it is deflected. When the guide posts  62  have reached the top of the ramp  76 , the motor input is set  124  to a third level equal to a third percentage of the motor input which was determined to result in the adaptive capping force. This third percentage is less than one-hundred percent, and is chosen to allow the maintenance sled  60  to reach the servicing position. The first and third percentages may be different or the same. 
     The actions of FIGS. 4 and 5 provide several advantages. The actions of FIG. 4 enable the determination of a minimum amount of force, referred to herein as the adaptive servicing force, required to move to the servicing position for a given printer under a given set of circumstances. By determining and using the adaptive servicing force, the amount of noise made while moving the printhead carriage to the servicing position is reduced as compared to servicing with a full force push. The actions of FIG. 5 may be used in combination with those of FIG.  4 . By taking a carriage starting position and a fixed motor input required to produce the adaptive servicing force, keeping the starting position, and varying the motor input based on percentages of the fixed input level, the amount of noise made during the movement to the servicing position can be further reduced. In addition to noise reductions, the actions of FIGS. 4 and 5 can also reduce part wear. Furthermore, the noise and part wear reductions are adaptable to each printing mechanism and for a given printing mechanism over time, as parts age and/or get contaminated and as the number of ink cartridges or amount of ink in the cartridges may vary. 
     FIG. 6 illustrates how the embodied actions of FIGS. 4 and 5 might look in terms of a motor input, carriage position, and resultant velocity curves. Full-force velocity curve  126  is illustrated for comparison purposes. The greater the velocity involved during the movement to the servicing position, the greater the noise will be. After completing the actions shown in FIG. 4, the controller will arrive at a fixed motor input as part of its adaptive servicing force. Here, the motor input is expressed in terms of PWM. Fixed motor input curve  128 , starting at a carriage position  130 , allows the carriage to reach a servicing position  132  with a substantially minimum force. The velocity curve associated with fixed motor input curve  128  is adaptive velocity curve  134 . Adaptive velocity curve  134  shows that the velocity while moving to the servicing position  132  is significantly less than the velocity during the full force velocity curve  126 . 
     Following the actions of FIG. 5, a fixed level  136  of the fixed motor input curve  128  is used to determine an optimized motor input curve  138 . During a first period  140 , a scaling percentage less than one-hundred percent is applied to the fixed level  136  to come up with the first period  140  of the optimized motor input curve  138 . During a second period  142 , a scaling percentage greater than one-hundred percent is applied to the fixed level  136  to come up with the second period  142  of the optimized motor input curve  138 . During a third period  144 , a scaling percentage less than one-hundred percent is applied to the fixed level  136  to come up with the third period  144  of the optimized motor input curve  138 . Optimized velocity curve  146  corresponds to the optimized motor input curve  138 , and is significantly lower than adaptive velocity curve  134 , thereby significantly reducing noise levels. 
     Performing adaptive printhead servicing actions and optimized servicing actions enables a printing mechanism to reliably cap or service printheads with a significantly reduced level of noise. Although capping has been used as an example of one possible servicing technique, the adaptive and optimizing actions described herein can also be applied to other types of printhead servicing, such as scrapping and wiping. The service station  54 , illustrated in the above embodiments, is not meant to be limiting in terms of the type of service station the adaptive printhead servicing actions and optimized servicing actions may be used with. Also, the actuator for the service station which contacts the activation arm  72  need not be a printhead carriage  32 . The printhead carriage  32  should be thought of more broadly as an actuator which is coupled to a motor and which comes into contact with the activation arm  72 . In the case where some other actuator is contacting the activation arm, the actuator would not need to move parallel or in-line with the scanning axis  30  of the printhead carriage. Regardless of the actuator used, the benefit of being able to reliably service the printheads while minimizing noise levels could still be realized and should fall within the scope of this disclosure. In discussing various components of the adaptive printhead servicing actions and optimized servicing actions, various benefits have been noted above. 
     It is apparent that a variety of other functionally and/or structurally equivalent modifications and substitutions may be made to perform adaptive printhead servicing actions and optimized servicing actions according to the concepts covered herein depending upon the particular implementation, while still falling within the scope of the claims below.