Patent Abstract:
A system and method for determining proper positioning of the printhead as it travels between first and second positions by sampling an electrical resistance signal of a motor during tilting of the printhead, calculating an average of specified samples at a time, and comparing the calculated average to a predetermined threshold to determine whether the printhead is operating properly. Thus, the need for sensors to determine the positioning of the printhead is eliminated.

Full 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 standby 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]     An exemplary embodiment according to the systems and methods of the invention includes the use of sampling of electrical signals showing the resistance force on the motor while the printhead assembly is rotated by a head tilt cam to determine if the printhead has properly moved to a standby position.  
         [0009]     According to the invention, an average sampling of electrical signals will be compared with a designated threshold. The signals are a measurement of resistance during a specified time, while tilting from the print position to the standby position. If the average is above the threshold, it is determined that the print head has properly tilted to the standby position.  
         [0010]     In various exemplary embodiments of the systems and methods according to the invention, the electrical signals correspond to the measure of resistance force on the motor.  
         [0011]     In various exemplary embodiments of the systems and methods according to the invention, the printhead is determined to operate properly when the calculated average value is above the predetermined threshold.  
         [0012]     In various exemplary embodiments of the systems and methods according to the invention, the printhead is determined to not be operating properly when the calculated average value is below the predetermined threshold.  
         [0013]     In further various exemplary embodiments of the systems and methods according to the invention, the predetermined threshold is a resistance value of 2.6  
         [0014]     In various exemplary embodiments of the systems and methods according to the invention, the calculated average value is measured a specified number of readings, such as 5.  
         [0015]     In various exemplary embodiments of the systems and methods according to the invention, the sampling of motor signals will be every 5 milliseconds after a specified start time.  
         [0016]     In various exemplary embodiments of the systems and methods according to the invention, the electrical motor signals are sampled over a predetermined time interval.  
         [0017]     In further various exemplary embodiments of the systems and methods according to the invention, the interval is 0.4 seconds.  
         [0018]     In various exemplary embodiments of the systems and methods according to the invention, a tilting arm provides movement to the printhead in different positions.  
         [0019]     In yet further various exemplary embodiments of the systems and methods according to the invention, the different positions include a standby position, a wipe position and a home/print position  
         [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 the position of a printhead rotated by a cam according to this invention;  
         [0023]      FIG. 2  illustrates in greater detail the components of the cam of  FIG. 1 ;  
         [0024]      FIG. 3  is a chart of sampled electrical motor signals when the printhead is in proper working condition;  
         [0025]      FIG. 4  is a chart of sampled electrical motor signals when the printhead is not in proper working condition; and  
         [0026]      FIG. 5  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  
       [0027]      FIG. 1  illustrates an exemplary embodiment of an apparatus that determines the printhead position as it is rotated by a cam according to this invention. As shown in  FIG. 1 , the printing apparatus  100  includes a printhead  110 , a tilting 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, custom ASCI or CPU.  
         [0028]     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.  
         [0029]     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.  
         [0030]     The cam  130  rotates and engages the tilt arm  120 , thereby rotating the printhead  110  into various positions, either closely adjacent to drum  140  or away from drum  140 . This is achieved by the engaged cam  130  being driven by motor  160 .  
         [0031]     In an exemplary embodiment, the different positions include a standby, a wipe and a home/print position. In moving to the standby position, the cam  130  rotates the tilt arm  120  to move the printhead  110  in a position that is tilted away and farthest from the rolling drum  140 . In the wipe position, the printhead  110  is at a position where it can be engaged with a wiping device, such as, for example, a wiper blade. In the print/home position, the printhead  110  is close to the rolling drum  140  so that the ink can be applied on the drum  140 .  
         [0032]     The cam  130  includes gear train  150  to drive the cam  130  via motor  160  having mating gear teeth. An exemplary motor is a servo motor. The printhead tilt motor 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, by increasing motor output force to compensate for the resistance force. The time in the tilt process at which the sampling is averaged should give a value over the designated threshold if the print head is tilting properly. This same feedback could be used in other cam designs, to show resistance and profile. Upon activation of drive motor  160 , the cam  130  rotates, which causes the tilting arm  120  to tilt the printhead  110  from the print position to the standby position. During the rotation, spring force resistance acting on the motor  160  is higher. Controller  180  then analyzes the electrical signals to determine whether the printhead  110  is at a desired location.  
         [0033]      FIG. 2  illustrates in greater detail the components of the cam  3 . As shown in  FIG. 2 , the cam  130  includes two dwells T 1 , T 2 . As an exemplary embodiment, T 1  is when the cam  130  is in standby position (i.e., the printhead  110  is tilted away from the drum  140 ), and T 2  is when the cam  130  is in the wipe position (i.e., in a position to receive a wiper on the printhead  110  during a head cleaning operation).  
         [0034]     It should be appreciated that as the printhead tilts to the standby position T 1 , from the home/print position, more spring resistance is applied to the motor  160  as the cam  130  rotates the tilt arm  120 .  
         [0035]     The cam  130  includes gear teeth and a flat area (e.g., missing gear teeth). The flat area is used to lock the printhead  110  in the print position. In this position, the printhead  110  is not able to tilt. As an exemplary embodiment, the printhead  110  is restrained against the cam  130  by a spring. It should be appreciated that other restraints may be used, for example, but not limited to, a pin, screw, etc.  
         [0036]     It should be appreciated that the printhead  110  must be in the standby position prior to moving the wiper in front of the printhead so that the wiper will not run into the bottom of the printhead  110  and cause damage. Accordingly, there is a need to ensure that the printhead  110  has been properly moved to the standby position.  
         [0037]     Various testing was conducted to monitor the electrical motor signals during this printhead movement. It was determined that when the printhead  110  was rotated by the cam  130  properly, the motor operated above a certain threshold. When moved improperly, the motor signals were lower. From this, it was determined that a threshold could be used to determine whether proper movement was achieved, without the need for a separate standalone sensor that directly measured actual position.  
         [0038]     While the printhead  110  moves from the print position to the standby position, a timer is started. At a predetermined time, samples of the electrical motor signals are sequentially taken. As an exemplary embodiment, five readings are averaged out to determine the average electrical motor signal. If the average is over a predetermined threshold, for example, but not limited to, a resistance value of 2.6 generated by the motor  160 , then the printhead  110  is determined to be properly tilted to the standby position. If the average is below the predetermined resistance threshold of 2.6 generated by the motor  160 , then five more readings are averaged to determine if the printhead  110  has been properly tilted to the standby position. It should be appreciated that extra iterations of readings can be implemented. For example, it has been determined that the printhead  110  usually succeeds after the fourth set of readings. However, if the average motor signal read never goes above the threshold within the specified time, then the controller  180  will declare a fault, which indicates an error in the positioning of the printhead.  
         [0039]     In an exemplary embodiment, the readings are taken every 5 milliseconds for 0.4 seconds. However, it should be appreciated that the invention will work at various intervals by comparing the average samples with a predefined threshold.  
         [0040]     It should be appreciated that other resistance thresholds besides 2.6 may be compared, depending on the particular motor, spring force on the cam, and movement of the printhead for a particular application.  
         [0041]      FIG. 3  is a chart of sampled motor signals when the printhead  110  is in proper working condition. The chart shows the current resistance readings of the motor  160  during the sampling while moving from print/home to standby position.  
         [0042]     As an exemplary embodiment, while tilting the printhead  110  from the print position to the standby position, the operation waits 0.1 seconds and then begins reading the motor signals from the motor  160 . The operation averages five readings, one reading taken every 5 milliseconds over a 0.4 second interval. An averaged reading is then calculated from these readings. If it is determined that the averaged reading is above the resistance threshold of 2.6, then the printhead  110  is determined to be properly tilted to the standby position.  
         [0043]     As shown in  FIG. 3 , the electric motor signals during the 0.4 second sampling interval is above the 2.6 resistance threshold, which indicates the proper engagement of the cam and that the printhead rotated to the standby position.  
         [0044]      FIG. 4  is a chart of sampled electrical motor signals when the cam did not properly engage, the printhead  110  didn&#39;t rotate to the standby position, and is thus not in proper working condition. The chart shows the current resistance readings of the motor  160  during the sampling of the motor signals from home/print position to the standby position.  
         [0045]     As an exemplary embodiment, the initial operation of  FIG. 4  is similarly operated as in  FIG. 3  for measuring motor signals during the tilting motion from home/print position to standby position for the motor  160 . The operation also preferably takes five readings of the motor resistance signals over a 0.4 second interval and obtains an averaged reading.  
         [0046]     As shown in  FIG. 4 , the motor signals during the 0.4 second interval are below the 2.6 resistance threshold, which indicates that the printhead  110  did not properly tilt to the standby position when engaging the cam  130 . Because the average is below the current threshold of 2.6 resistance, five more readings may be performed and averaged. It should be appreciated that additional sets of readings can be performed. For example, it has been found that the printhead  110  usually succeeds after the fourth averaged reading. However, if the averaged motor signals during the specified duration of time tilting from print/home position to the standby position never goes above the threshold of 2.6 resistance, the controller  180  will declare a fault. This can prevent the wiper from hitting the bottom of the printhead  110  when the printhead  110  is improperly positioned.  
         [0047]      FIG. 5  is a flowchart outlining an exemplary embodiment of a method for determining the position of the printhead to this invention. As shown in  FIG. 5 , beginning in step S 100 , the operation starts. The operation of the method continues to step S 200 , where it is determined whether the tilt position of the printhead is in the print position and there is a request for the printhead to be tilted to the standby position.  
         [0048]     If it is determined at step S 200  that the printhead is not being tilted from the print position, operation continues to step S 300  which terminates the checking of the position of the printhead. On the other hand, if it is determined at step S 200  that the printhead is at the print position and tilting is requested, operation proceeds to step S 400 .  
         [0049]     In step S 400 , the printhead starts to move from the print position to the standby position. Operation then proceeds to step S 500 .  
         [0050]     At step S 500 , as the printhead is tilting to the standby position, the operation waits a predetermined time interval, such as 0.1 second, and starts a timer to read the motor  160  electronic signals over a set time interval. As an exemplary embodiment, the set time interval is 0.4 sec (400 millisecond). Operation then proceeds to step S 600 .  
         [0051]     In step S 600 , the operation samples the motor signals every 5 milliseconds and calculates an average. While tilting from home to standby the cam rotates the tilt arm and the motor signals should show higher resistance.  
         [0052]     At step S 700 , an average of 5 motor signals are read and compared against the designated threshold (2.6). If the average is over 2.6, then the operation proceeds to step S 800  and the tilting to standby was a success. Otherwise, the operation at step S 900  compares the time to see if the 0.4 time limit has elapsed. If it has not, it continues sampling at step S 1000  every 5 msecs (S 600 ). It then goes back to S 700  to compare another average of 5 motor signals.  
         [0053]     If at step S 900 , 0.4 seconds of time has elapsed, then the rotation to standby was a failure and something went wrong. At step S  1100 , if the time elapses and the sampling of motor signals never averages above the signal resistance threshold of 2.6, the controller  180  declares a fault, indicating that the printhead was not properly rotated to the standby position.  
         [0054]     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.

Technology Classification (CPC): 1