Abstract:
A system and method for sensing the positioning the printhead in one or more of a standby position, a wipe position, and a printing position uses electrical signals from a drive motor as an indicator of whether the printhead has properly moved to a desired position. As the printhead is tilted to a print position, a first position electrical signal is detected by sampling a resistance on the torque motor at a first time. A second position electrical signal is determined by sampling another resistance on the motor at a second time. A slope is calculated between the first position sample and the second position sample. The calculated slope is analyzed to determine whether the printhead is operating properly. Thus, the need for standalone sensors to determine the positioning of the printhead is eliminated.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     This invention generally relates to systems and methods for determining a printhead in a printing position.  
         [0003]     2. Description of Related Art  
         [0004]     A typical imaging apparatus, such as an ink-jet printer or a thermal printer, forms an image onto a recording medium, such as paper or film, by causing ink or the like to be deposited onto the recording medium. For example, an ink-jet printer performs printing by discharging ink through a printhead having nozzle(s) with an orifice and an electrothermal transducer which generates discharge energy for discharging ink from the orifice to form a pattern of ink dots on the recording medium. The printhead discharges the ink along a track by moving back and forth. Many printheads must also move toward and away from a printer&#39;s surface. However, the movement of the printhead may get trapped, jammed or wedged along the way. For example, in certain solid ink printing, the printhead is moved between printing, wiping and standby positions. If the printhead is not properly positioned, ink may be misdirected.  
         [0005]     Thus, in the past, a separate sensor was required to determine the position of the printhead so that the ink could be properly ejected onto the recording medium.  
         [0006]     For example, conventional printers use an optical sensor to ensure proper positioning of the printhead. However, separate sensors require numerous cablings and connectors to operate. Further, many printers typically have more than one sensor to determine positioning of the printhead, especially apparatus with color inks. Thus, the use of sensors becomes expensive, which drives the cost of manufacturing up. Moreover, because of the need for cables and connectors to operate the sensors, printing apparatus become large and bulky.  
       SUMMARY OF THE INVENTION  
       [0007]     Considering the above conventional drawbacks, it is desired to provide a printing apparatus control method which can efficiently determine the position of the printhead without the need of separate, standalone sensors.  
         [0008]     Accordingly, one aspect of the invention provides systems and methods for determining a printhead in a printing position without the use of standalone sensors.  
         [0009]     One exemplary embodiment according to the systems and methods of the invention include use of electrical signals from a motor while the printhead assembly moves over a head tilt cam to determine if the printhead has properly tilted to a print position.  
         [0010]     Another exemplary embodiment according to the systems and methods of the invention includes tilting the printhead from the standby position to the print position, sampling the electrical signal that measures torque from the motor that tilts the printhead at two positions, and calculating the slope of the signal between the two positions. The slope is then compared against a predetermined slope threshold to determine whether the printhead has properly tilted.  
         [0011]     In various exemplary embodiments of the systems and methods according to the invention, the first and second electrical signals measure resistance force on the motor.  
         [0012]     In various exemplary embodiments of the systems and methods according to the invention, the printhead is determined to operate properly when the calculated slope is above the predetermined threshold, for example, a positive slope.  
         [0013]     In further various exemplary embodiments of the systems and methods according to the invention, when the cam rotates and tilts the printhead, a resistance on the motor is sensed as the motor stops at two positions on the cam. A slope is then calculated between the two sampled electrical signals and compared against a predetermined threshold.  
         [0014]     In various exemplary embodiments of the systems and methods according to the invention, the first position samples the electrical signal at a low resistance area on the cam.  
         [0015]     In various exemplary embodiments of the systems and methods according to the invention, the second position error is samples the electrical signal at a position on the cam that is steep giving high resistance.  
         [0016]     In various exemplary embodiments of the systems and methods according to the invention, the slope is a calculation between the steepness of the two sampled electrical signals.  
         [0017]     In various exemplary embodiments of the systems and methods according to the invention, a tilting arm provides movement to the printhead in different positions.  
         [0018]     In further various exemplary embodiments of the systems and methods according to the invention, the different positions are a standby position, a wipe position, P 1 , P 2 , and a home/print position. P 1  and P 2  are two points on the cam where the electrical signals are sampled, from which the slope is calculated.  
         [0019]     In various exemplary embodiments of the systems and methods according to the invention, the sensed electrical signal is a measure of motor torque.  
         [0020]     These and other features and advantages of the invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     Various exemplary embodiments of the systems and methods of this invention will be described in detail, with reference to the following figures, wherein:  
         [0022]      FIG. 1  illustrates an exemplary embodiment of a printing apparatus that determines printhead position over a cam according to this invention;  
         [0023]      FIG. 2  is a chart of a slope for a position error when the printhead is in proper working condition;  
         [0024]      FIG. 3  is a chart of a slope for a position error when the printhead is not in proper working condition; and  
         [0025]      FIG. 4  is a flowchart outlining one exemplary embodiment of a method for determining the position of the printhead according to this invention. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0026]      FIG. 1  illustrates an exemplary embodiment of an apparatus that determines the printhead position tilting over a cam according to this invention. As shown in  FIG. 1 , the printing apparatus  100  includes a printhead  110 , a cam following arm  120 , a cam  130 , a rolling drum  140 , a gear train  150 , a motor  160 , and a processing means  180 , such as a controller, CPU, or ASIC.  
         [0027]     As an exemplary embodiment, the printing apparatus  100  is a solid-ink printer, for example, a Xerox 8400 printer. However, the invention is not limited to this and is applicable to any type of printing apparatus having a reciprocating or movable printhead.  
         [0028]     In solid-ink printing, the printhead  110  ejects an ink onto the rolling drum  140  that transfers the ink onto a recording medium, for example, but not limited to, paper, labels, transparencies, envelopes and business cards. The printhead  110  has an array of nozzles that can jet out a predetermined quantity of ink into the surface of drum  140  as known in the art.  
         [0029]     The cam following arm  120  provides movement to the printhead  110  enabling the printhead  110  to be positioned in various positions either closely adjacent to drum  140  or away from drum  140 . This is achieved by engagement with the cam  130 .  
         [0030]     In an exemplary embodiment, the different positions are a standby, a wipe, P 1 , P 2 , and a home/print position. In the standby position, the cam following arm  120  moves the printhead  110  in a position that is tilted away and farthest from the rolling drum  140 . In the wipe position, the cam following arm  120  moves the printhead  110  to a position where it can be engaged with a wiping device, such as, for example, a wiper blade. In the print/home position, the cam following arm  120  moves the printhead  110  close to the rolling drum  140  so that the ink can be applied on the drum  140 . Positions P 1  and P 2  are the locations on the cam where the electrical signals are read to calculate the slope.  
         [0031]     The cam  130  includes gear train  150  to drive the cam  130  via motor  160  having mating gear teeth. An exemplary motor is a servomotor. The print head tilt servomotor provides data to the controller that is related to the movement of the motor. If the torque is high or low the feedback gives the controller the information to make corrections, for example to keep a constant velocity. The positions on the cam where this feedback is read are designed to show a low and high resistance, from which the slope is calculated. This same feedback could be used in other cam designs, to show resistance and profile. Upon activation of drive motor  160 , cam  130  rotates, which causes cam following arm  120  to move relative to the cam  130  to cause printhead  110  to tilt from the shown standby position to either a wipe position or a print position. Electronic signals of the motor  160  are sampled at cam locations P 1  and P 2 . The position P 1  corresponds to a time when the cam following arm  120  should be in contact with an area on the cam  130  that is not steep. During the sampling at P 1 , there will not be much spring force. As such, resistance acting on the drive motor should be low. The sampling at P 2  corresponds to a time when the cam following arm  120  should be in contact with an area on the cam  130  that is steep. During the sampling at P 2 , there will be more spring force as higher resistance is needed to hold the tilt arm position on the cam. As such, resistance acting on the motor is higher. Processing means  180  then analyzes the electrical signals by calculating the slope between the two position samples to determine whether the printhead  110  is at a desired location.  
         [0032]      FIG. 2  is a chart comparing the motor torque (in/lbs) and slope between P 1  and P 2 , when the printhead  110  is in proper working condition. As shown in  FIG. 2 , the chart compares the resistance or torque (in/lbs) of the motor during the various tilt phases of the printhead  110 .  
         [0033]     As an exemplary embodiment, the various tilt phases are positions of the printhead  110  in relationship to the cam  130 . For example, the various tilting phases of the printhead  110  are a standby position, a wipe position and a home/print position, and various intermediate positions.  
         [0034]     As shown in  FIG. 2 , prior to the standby position, the printhead  110  assembly  100  engages with the cam  130 , which results in an increase of torque as the motor  160  produces a high resistance. As an exemplary embodiment, the resistance prior to standby position is 1.4 in/lbs and increases to 8.36 in/lbs. Next, as the printhead  110  assembly is moved from the standby position, the resistance reduces until the printhead  110  is in the wipe position. As an exemplary embodiment, the resistance decreases from 8.36 in/lbs to 4.33 in/lbs in the standby position. In the wipe position, a blade on the printhead  110  moves over the cam  130 . It is during the wipe position that the position errors at two spaced positions P 1  and P 2  of the motor  160  can be determined. As an exemplary embodiment, the resistance at P 1  is 2.5 in/lbs and the resistance at P 2  is 4.3 in/lbs. Reading the position errors P 1  and P 2  as the motor  160  moves over the cam  130  can determine whether the printhead  110  is in a proper working condition if P 2  is greater than P 1 . Finally, the printhead  110  returns to the print position. As an exemplary embodiment, the resistance at this print position is 1.3 in/lbs.  
         [0035]     In various exemplary embodiments, position P 1  occurs when the arm  120  is in contact with a flatter location on the cam  130  where there is not much resistance force (low torque), and position error P 2  occurs when the cam following arm  120  is in contact with the cam  130  right before a steeper part on the cam  130  so as to cause more resistance force (high torque). As shown in  FIG. 2 , the slope line between position errors P 1  and P 2  when operating properly is a positive slope and above some designated threshold (e.g., P 2  is higher than P 1 ) which indicates that the printhead  110  is rotating over the cam  130  properly and the printhead  110  is properly tilting to the home/print position. At this print position, the printhead  110  is ready to eject ink onto the drum to produce the image.  
         [0036]      FIG. 3  is a chart when the printhead  110  is not in proper working condition. The various tilting positions are the same as shown in  FIG. 2 .  
         [0037]     As shown in  FIG. 3 , the printhead  110  similarly engages the cam  130  as shown in  FIG. 2  until it reaches the wipe position. As an exemplary embodiment, the resistance prior to the standby position is 1.4 in/lbs, the same as the printhead  110  in proper working condition, and increases to 6.0 in/lbs. In this example, the print head was jammed in the standby position, therefore the cam following arm  120  could tilt with resistance to the standby position. Next, as the printhead  110  advances to the standby position, the resistance reduces until the printhead  110  is in a wipe position, which has the same resistance value as when the printhead  110  is operating properly. As an exemplary embodiment, the resistance decreases from 6.0 in/lbs to 4.33 in/lbs in the standby position. When tilting from the standby position towards the home/print position in  FIG. 3 , the resistance on the motor  160  is determined to be relatively low at both locations P 1  and P 2  since there is no resistance on the motor  160  going over the cam  130 . As an exemplary embodiment, the resistance during this move remains constant at 1.4 in/lbs. The low resistance can be attributed to the printhead  110  being stuck in the standby position or other obstruction that does not permit the printhead  110  to move over the cam  130  properly. Finally, during the return to the print position, the resistance remains relatively unchanged. As an exemplary embodiment, the resistance at this print position is 1.3 in/lbs.  
         [0038]     However, as shown in  FIG. 3 , the slope line between position P 1  and P 2  is less than the designated threshold. (e.g., P 2  is was not sampled high enough above P 1 ), which indicates the printhead  110  is not moving over the cam  130  in a proper manner. The sampling of electrical signals at P 2   160  indicates that there is no resistance when stopped at the steep part of the cam  130  that generally causes a high resistance. From experiments, this has been determined to be a reliable indicator that the printhead  110  is not being correctly positioned because it should have a positive slope above the designated threshold. This is an indication that the printhead  110  is not in the desired position.  
         [0039]     It should be appreciated that the resistance during the tilting of the printhead is generally higher when the printhead  110  is operating properly than when the printhead  110  is not operating properly. However, for different cam  130  profiles, the values can be changed. What is important is that there is a known slope threshold that signifies improper operation of the printhead assembly.  
         [0040]      FIG. 4  is a flowchart outlining an exemplary embodiment of a method for determining the position of the printhead  110  to this invention. As shown in  FIG. 4 , beginning in step S 100 , operation of the method continues to step S 200 , which determines whether tilt position of the printhead  110  is in the standby position and is it being tilted to the home (print) position.  
         [0041]     If it is determined at step S 200  that the printhead  110  is not tilted in the standby position, operation continues to step S 300  which terminates the checking of the position of the printhead  110 . On the other hand, if it is determined at step S 200  that the printhead  110  is at the standby position, operation proceeds to step S 400 .  
         [0042]     In step S 400 , the operation moves the headtilt of the printhead  110  from the standby position to the printing position. In various exemplary embodiments, the printing position is when the printhead  110  is properly positioned relative to a printing surface, such as rolling drum  140 .  
         [0043]     At step S 500 , the engaged printhead  110  stops the motor  160  to sample the electrical signal at P 1  on the cam  130 . In various exemplary embodiments, position P 1  is a flatter location on the cam  130  where there is not much resistance force. Operation then proceeds to step S 600 .  
         [0044]     In step S 600 , the operation samples the motor  160  electrical signal, such as motor torque, and saves the samples for P 1 . Operation then proceeds to step S 700 .  
         [0045]     At step S 700 , the operation restarts the motor  160  to tilt the printhead and stop at position P 2 . At step S 800 , the process samples the motor  160  electrical signal, such as motor torque, and saves the samples for P 2 . In various exemplary embodiments, position P 2  is the location on the cam  130  adjacent to the large steep part of the cam that causes a higher resistance force, in order for the printhead to keep its position. Operation then proceeds to step S 900 .  
         [0046]     At step S 900 , the operation finishes tilting the printhead  110  to the print/home position, and proceeds to step S 1000  to calculate the slope using P 1  and P 2  electrical signal samples. In various exemplary embodiments, the slope is calculated by calculating the difference between the two samples P 2  and P 1 .  
         [0047]     In various exemplary embodiment, if the slope is above or equal to the designated threshold, the operation indicates that the printhead  110  is tilting over the cam  130  in proper working order. In a further various exemplary embodiment, if the slope is below the designated threshold, the operation indicates that the printhead  110  is not tilting over the cam  130  in proper working order. For example, but not limited to, the printhead  110  is jammed and unable to tilt. If the calculated slope is below the threshold there is less resistance on the motor  160  than should be as the printhead  110  moves over the cam  130 .  
         [0048]     If it is determined at step S 1100  that the slope between P 1  and P 2  is above or equal to the designated threshold, the operation continues to step S 1200  which terminates the operation and indicates the tilting of the printhead  110  to the home/print position was successful. On the other hand, if it is determined at step S 100  that the slope between P 1  and P 2  is below the designated threshold, operation proceeds to step S 1300 .  
         [0049]     At step S 1300 , the operation determines that the printhead  110  did not properly tilt to the home/print position, and repeats the operation at step S 200 . An error or other indicator may be provided to alert the user to the problem.  
         [0050]     While the invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made to the invention without departing from the spirit and scope thereof.