Abstract:
An ink drop detector includes a sensing target which is imparted with an electrical stimulus when struck by at least one ink drop burst which has been ejected from an ink drop generator. The detector also includes electronics coupled to the sensing target which characterize the electrical stimulus in terms of a mathematical phase. Methods for analyzing ink ejected from an ink drop generator, and a method for optimizing ink drop generator firing frequency are also provided.

Description:
[0001]    Printing mechanisms, such as inkjet printers or plotters, 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. The printzone is defined by a 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. Conventional methods for expelling ink from the printhead orifices, or nozzles, include piezo-electric and thermal techniques which are well-known to those skilled in the art. 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.  
           [0002]    In a thermal inkjet system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains columnar arrays of heater elements, such as resistors, which are individually addressable and energized to heat ink within the vaporization chambers. The energy which is applied to a given resistor to heat the ink to the point of drop ejection is referred to as the turn-on energy. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor.  
           [0003]    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. For example, a typical inkjet printing system may have a single printhead with only black ink; or the system may have four printheads, one each with black, cyan, magenta, and yellow inks; or the system may have three printheads, one each with cyan, magenta, and yellow inks. Of course, there are many more combinations and quantities of possible printheads in inkjet printing systems, including seven and eight ink/printhead systems.  
           [0004]    Each process color ink is ejected onto the print media in such a way that the drop size, relative position of the ink drops, and color of a small, discreet number of process inks are integrated by the naturally occurring visual response of the human eye to produce the effect of a large colorspace with millions of discernable colors and the effect of a nearly continuous tone. In fact, when these imaging techniques are performed properly by those skilled in the art, near-photographic quality images can be obtained on a variety of print media using only three to eight colors of ink.  
           [0005]    This high level of image quality depends on many factors, several of which include: consistent and small ink drop size, consistent ink drop trajectory from the printhead nozzle to the print media, and extremely reliable inkjet printhead nozzles which do not clog. Ink drop detectors may be employed in a printing mechanism to monitor nozzles for clogging, but it would be useful to also monitor drop size and trajectory. More specifically, it would be beneficial to be able to measure the numerous factors which affect ink drop size and trajectory.  
           [0006]    Therefore, it is desirable to have a method and mechanism for effectively, efficiently, and economically measuring ink system characteristics which affect ink drop size and trajectory, such as viscosity, electrical conductivity, dye load, surface tension, drop firing turn-on energy, drop velocity, and ink age. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a schematic diagram illustrating one embodiment of a printing mechanism which may employ embodiments of a drop detection system to identify ink system characteristics.  
         [0008]    [0008]FIG. 2 is a graph illustrating a possible voltage signal which may result from bursts of ink droplets as detected by a drop detection system.  
         [0009]    [0009]FIG. 3 is a graph illustrating a subset of the voltage signal in FIG. 2, corresponding to a single burst of ink drops.  
         [0010]    [0010]FIGS. 4A and 4B illustrate possible graphs of ink system characteristics such as conductivity and drop size, respectively, versus a determined electrostatic drop detection score.  
         [0011]    [0011]FIGS. 5A and 5B illustrate possible graphs of ink system characteristics such as velocity and turn-on-energy, respectively, versus a determined electrostatic drop detection phase.  
         [0012]    [0012]FIG. 6 illustrates possible graphs of ink system characteristics such as break-off-point versus a determined electrostatic drop detection score and versus a determined electrostatic drop detection phase.  
         [0013]    [0013]FIG. 7 illustrates an embodiment by which a determined electrostatic drop detection score and phase may be used to optimize image quality for use with various types of ink.  
         [0014]    [0014]FIG. 8 illustrates a possible graph of ink drop generator firing frequency versus resultant ink drop weight.  
         [0015]    [0015]FIG. 9 illustrates an embodiment by which an optimized firing frequency may be determined for an ink drop generator. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    [0016]FIG. 1 schematically illustrates an embodiment of a printing mechanism, here shown as an inkjet printer  20 , constructed in accordance with the present invention, 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, cameras, video printers, and facsimile machines, to name a few. For convenience the concepts introduced herein are described in the environment of an inkjet printer  20 .  
         [0017]    While it is apparent that the printer components may vary from model to model, the typical inkj et printer  20  includes printer control electronics, illustrated schematically as a controller  22  that receives instructions from a host device, such as a computer or personal digital assistant (PDA) (not shown). Printer host devices, such as computers and PDA&#39;s are well known to those skilled in the art.  
         [0018]    The typical inkjet printer  20  will include an ink drop generator  24  which is capable of ejecting drops of ink onto a print media. Ink drop generator  24  may be configured to work with pigment based inks or dye based inks. The dye and pigment based inks may be of different colors, such as, for example, black, cyan, magenta, or yellow. The printing mechanism  20  may contain a single drop generator  24  for use with a single color of ink; multiple ink drop generators  24 , each for use with a single color of ink; a single drop generator  24  for use with multiple colors of ink; multiple drop generators  24 , each for use with multiple colors of ink; or a combination of drop generators  24  where at least one is for use with a single color of ink and at least one is for use with multiple colors of ink. It is apparent that other types of inks may also be used in the ink drop generators  24 , such as paraffin-based inks, as well as hybrid or composite inks having both dye and pigment characteristics. A printing mechanism  20  may have replaceable ink drop generators  24  where each drop generator  24  has a reservoir that carries the entire ink supply as the drop generator  24  reciprocates over the print media. As used herein, the term “ink drop generator” may also refer to an “off-axis” ink delivery system, having main stationary reservoirs (not shown) for each ink (black, cyan, magenta, yellow, or other colors depending on the number of inks in the system) located in an ink supply region. In an off-axis system, the ink drop generators  24  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 ink drop generator  24  travel, so only a small ink supply is propelled while printing. Other ink delivery or fluid delivery systems may also employ the systems described herein, such as replaceable ink supplies which attach onto ink drop generators having permanent or semi-permanent print heads.  
         [0019]    Each ink drop generator  24  has an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. The nozzles of each ink drop generator  24  are typically formed in at least one, but typically two columnar arrays along the orifice plate. Thus, the term “columnar” as used herein may be interpreted as “nearly columnar” or substantially columnar, and may include nozzle arrangements slightly offset from one another, for example, in a zigzag arrangement. The ink drop generator  24  is illustrated as having a thermal inkjet printhead  26 , although other types of printheads, or ink drop generators may be used, such as piezoelectric printheads. The thermal printhead  26  typically includes a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed which ejects a droplet  30  of ink from the nozzle. The printhead  26  resistors are selectively energized in response to firing command control signals  28  delivered from the controller  22  to the ink drop generator  24 .  
         [0020]    [0020]FIG. 1 also schematically illustrates an ink drop detector  32 . The ink drop detector  32  includes a conductive target  34  which is electrically coupled to electronics  36 . Electronics  36  provide a bias voltage to the conductive target  34 . Alternatively, a biasing plate  38  may be used in addition to target  34 , with the electronics  36  providing the biasing voltage to the biasing plate  38 . An electric field is created by the bias voltage, causing a charge to build up on ink droplets  30  as they leave the printhead  26 . In order to make a drop detection measurement, the printhead  26  is positioned over the target  34 , and thereafter the ink droplets  30  may be ejected, charged, and detected according to the apparatus and method described in U.S. Pat. No. 6,086,190, assigned to the Hewlett-Packard Company, the present assignee.  
         [0021]    The target  34  may also be coupled to filtering electronics and an amplifier which are part of electronics  36 . The charged ink droplets  30  induce an electrical stimulus, such as a current spike, when they contact the target  34 , and this current spike may be sensed and amplified by the electronics  36 . For efficiency, a grouping of printhead  26  nozzles are typically fired together in one ink burst  40  over the target  34 . Although ink burst  40  is illustrated as a group of three ink droplets  30  in FIG. 1, any number of ink droplets may be included in an ink drop burst  40 .  
         [0022]    As illustrated in FIG. 2, when a series of ink drop bursts  40  are fired onto the target  34 , a signal voltage  42  proportional to the current spikes from the charged ink bursts  40  will be generated by the electronics  36 . Signal voltage  42 , as illustrated in FIG. 2, may be subdivided into separate ink drop burst  40  sections: Ink burst  40 A, ink burst  40 B, ink burst  40 C, and ink burst  40 D. Of course, controller  22  may instruct the ink drop generator  24  to fire any number of ink bursts  40  onto the target  34 , and the fact that there are four ink drop bursts  40  illustrated in FIG. 2 is merely for sake of example. Based on the timing between the initiation of consecutive ink bursts  40 , the controller  22 , which is coupled to electronics  36 , will be able to sample the signal voltage  42  and separately examine each ink drop burst  40 . Alternatively, an average of separate ink drop bursts  40  may be taken before sampling the voltage signal to increase accuracy. For simplicity, however, the description of this embodiment only discusses sampling a single ink drop burst, although average signals of multiple ink drop bursts are meant to be included as well.  
         [0023]    [0023]FIG. 3 shows the signal voltage  44  corresponding to ink burst  40 B from FIG. 2. Controller  22  may analyze each ink burst  40  separately or the controller may analyze an average of multiple ink bursts  40 . An analog-to-digital converter which is part of electronics  36  or controller  22  will sample signal voltage  44  at a predetermined frequency or frequencies which are chosen to avoid aliasing with the burst frequency and to provide an accurate picture of the ink burst  40  signal curve  44 . In the example of FIG. 3 and for the sake of illustration, ten sampled data points, X 1  through X 10 , were taken from the signal voltage  44  which corresponds to ink burst  40 B. The appropriate number of sample points may be determined based on the needs of a given system, but for simplicity, ten sampled data points X 1  through X 10  are illustrated in FIG. 3. By taking the sample points X 1 -X 10  at substantially equal intervals, we can apply a digital signal processing technique, such as a Fourier Transform, to the sample points X 1 -X 10  to calculate an Electrostatic Drop Detect (EDD) Score  46  (illustrated and discussed later with regard to FIGS. 4A, 4B,  6  and  7 ) which corresponds to a vector and we may also calculate an EDD Phase  48  (illustrated and discussed later with regard to FIGS. 5A, 5B,  6 , and  7 ), based on the signal position within the ink burst signal curve  44 . Although the sample points X 1  through X 10  are illustrated in FIG. 3 as being equally spaced, a Fourier Transform could be applied effectively in some applications when the sample points are not equally spaced. The EDD Score  46  and the EDD Phase  48  may be calculated, for example, with the following formulae: 
           EDD  Score={square root}{square root over (α 2 +β 2 )}         EDD                 Score     =         α   2     +     β   2                   EDD                 Phase     =       tan     -   1            [     β   α     ]                   where                   α     =       ∑     n   =   1     M          (       X   n     ·     cos        (   n   )         )                   where                   β     =       ∑     n   =   1     M          (       X   n     ·     sin        (   n   )         )                               
         [0024]    and where M equals the number of sample data points taken in the burst. In the example illustrated in FIG. 3, there are ten sample data points X 1 -X 10 . Also note that EDD Phase  48  (a mathematical phase) may be represented by using the phase ratio of [β/α], depending on the application, rather than taking the arc tan of [β/α].  
         [0025]    The EDD Score  46  and the EDD Phase  48  associated with a particular ink drop burst  40  can be correlated with particular characteristics of an ink system. As FIGS. 4A and 4B illustrate, characteristics such as ink electrical conductivity  54 , and ink drop size  56  have a relationship with the EDD Score  46 . As each ink droplet  30  in an ink drop burst  40  is being ejected over the conductive target  34 , the ink droplets  30  will tend to accumulate a charge on their surface as the presence of the electric field from the biasing voltage effects a shift of electrons. When the ink droplets  30  break off, the charge which has accumulated thereon is held on the droplets  30 . The higher the total charge on the ink droplets  30  in an ink drop burst  40 , the higher the corresponding EDD Score  46  will be for a given ink drop burst  40 . The more conductive an ink formulation is, the easier it will be for charge to build up on the surface of an ink droplet  30  of that formulation. Therefore, as FIG. 4A illustrates, EDD Score  46  will have a direct relationship with ink conductivity  54 . As ink conductivity  54  increases above some known point K 1 , the corresponding EDD Score  46  will also increase. If the conductivity  54  were to decrease below known point K 1 , then the corresponding EDD Score  46  would also decrease. Similarly, the larger an ink droplet  30  is, the more charge it can hold. Therefore, as FIG. 4B illustrates, EDD Score  46  will have a direct relationship with ink drop size  56 . As ink drop size  56  increases above some known point K 2 , the corresponding EDD Score  46  will also increase. If the drop size  56  were to decrease below known point K 2 , then the corresponding EDD Score  46  would also decrease. Additionally, if the density of the ink is known, then drop weight may also be calculated from a known drop size  56 .  
         [0026]    As FIGS. 5A and 5B illustrate, ink system characteristics, such as ink turn-on-energy (TOE)  58  and drop velocity  60 , have a relationship with the EDD Phase  48 . Turn-on-energy (TOE)  58  refers to the amount of power which is applied to a resistor in a printhead  26  to vaporize part of the ink in the printhead, thereby creating a bubble of gas in the printhead  26 . The gas expands, forcing an ink droplet  30  out of the printhead  26 . If the energy placed into the resistor is not sufficient to vaporize the ink, no gas bubble will form and no ink will be ejected. The minimum turn-on-energy is defined as the minimum amount of energy necessary to cause a droplet  30  of ink to eject from a printhead  26 . As FIG. 5A illustrates, at a low TOE, there will be no ejection of ink, therefore no EDD Phase  48  is calculable. Once a minimum TOE level  62  is reached, ink droplets  30  will be formed and ejected from the printhead  26 . An EDD Phase  48  may be calculated as indicated above and plotted versus TOE  58 . TOE  58  levels may be increased above the minimum TOE level  62 , and as FIG. 5A illustrates, the EDD Phase  48  will increase with increases in TOE  58 . As TOE  58  increases, ink droplets  30  will be ejected from the printhead  26  with more velocity  60 . As FIG. 5B illustrates, droplets  30  with higher velocities will result in an increase in EDD Phase  48 . Since velocity  60  tracks with TOE  58 , the EDD Phase  48  will also increase with increasing TOE  58 , provided the minimum TOE level  62  has been reached.  
         [0027]    [0027]FIG. 6 illustrates an ink system characteristic, break-off-point (BOP)  64  which can be measured by both changes in EDD Phase  48  and EDD Score  46 . Break-off-point (BOP)  64  takes into account ink properties such as viscosity, surface tension, dye load, and age of the ink. A small or short BOP  64  indicates that an ink droplet has broken free of the printhead  26  more quickly than the a droplet  30  with a high or long BOP  64 . A droplet  30  which breaks free of the printhead  26  in a shorter time, will tend to have an apparently higher velocity traveling from the printhead  26  to the conductive target  34 . A droplet  30  which takes longer to break free of the printhead  26  will have an apparently lower velocity. Thus, the EDD Phase  48  versus BOP  64  curve  66  in FIG. 6 has an inverted relationship to the EDD Phase  48  versus velocity  60  graph in FIG. 5B. BOP  64  also has a relationship with EDD Score  46 . A droplet  30  which takes a long time to break-off will be in contact with the printhead  26  longer, and therefore will build up a larger charge than a droplet  30  which breaks off sooner. Since a higher charge on the ink droplets  30  corresponds to a higher EDD Score  46 , FIG. 6 illustrates that EDD Score  46  will increase  68  with longer BOP  64 . Thus, a three-dimensional model  70  may be arrived at with variables of BOP  64 , EDD Score  46 , and EDD Phase  48 . A possible three dimensional shape for this BOP  64  relationship is illustrated in FIG. 6, although the exact nature of the three-dimensional relationship may vary with ink formulations and printing systems, and may need to be determined empirically or with adequate modeling of known ink compositions.  
         [0028]    EDD Score  46  and an EDD Phase  48  may be calculated as indicated above for an ink droplet  30  or an ink burst  40  containing multiple droplets  30 . EDD Score  46  has a quantifiable relationship with ink conductivity  54  and ink drop size  56 . EDD Phase  48  has a quantifiable relationship with turn-on-energy (TOE)  58  and ink drop velocity  60 . Ink system characteristics such as break-off point (BOP)  64 , as well as ink viscosity, surface tension, dye load, and ink age, have a quantifiable relationship with both EDD Score  46  and EDD Phase  48 . Given these various relationships which exist between the ink system characteristics, and which may be predetermined, a printing mechanism  20  may be configured to detect and determine changes in the ink properties or changes in the ink system characteristics and make adjustments to ink drop generator  24  firing voltages, printing speeds (determined among other things by printhead  26  firing frequencies and ink drop generator  24  velocity in a reciprocating ink drop generator  24  system), ink drop size, ink drop placement, and other image quality attributes within the controller&#39;s  22  control to optimize print quality for the type of ink being used.  
         [0029]    [0029]FIG. 7 illustrates a process by which EDD Score  46  and EDD Phase  48  may be used in a printer  20  to optimize image quality for use with any inks. The printhead  26  may be aligned  72  with the conductive target  34 . An ink droplet  30  or an ink drop burst  40  may be fired  74  from the printhead  26 . An EDD Score  46  and an EDD Phase  48  may each or both be calculated  76 , depending on what ink system characteristics are of interest. If it is desired  78  to examine an ink system characteristic which tracks with EDD Score  46 , such as ink conductivity  54  or drop size  56 , then these characteristics may be determined  80  by reference  82  with a database  84  containing values for known ink system characteristics versus EDD Score  46 . If it is desired  86  to examine an ink system characteristic which tracks with EDD Phase  48 , such as turn-on-energy (TOE)  58  or ink velocity  60 , then these characteristics may be determined  88  by reference  90  with a database  84  containing values for known ink system characteristics versus EDD Phase  48 . If it is desired  92  to examine an ink system characteristic which tracks with respect to both EDD Score  46  and EDD Phase  48 , such as break-off-point (BOP)  64 , then such a characteristic may be determined  94  by reference  96  with a database  84  containing values for known ink system characteristics versus both EDD Score  46  and EDD Phase  48 . The determined ink system characteristics can be compared  98  to known ink system characteristics, and then parameters such as printhead firing voltages, printing speeds, and ink droplet firing rates may be adjusted  100  by the controller  22  to optimize image quality for aging, changing, or non-manufacturer inks. Such optimization will tend to minimize the variability of ink drop size and ink drop placement, as well as allow a particular drop size to be selected at a maximized drop firing rate.  
         [0030]    [0030]FIG. 8 illustrates a typical graph of ink drop weight  102  versus printhead firing frequency  104 . This type of graph is typically generated manually during the development stage of a printing system by varying the printhead firing frequency  104  and weighing drop samples. This process is not practical or economical to perform in a printing mechanism.  
         [0031]    As the graph in FIG. 8 illustrates, the drop weight  102  typically stays relatively constant as firing frequency  104  is increased until a pivotal firing frequency  106  is reached. Beyond this pivotal firing frequency  106 , as firing frequency  104  increases, the drop weight  102  will start to significantly decrease. This occurs due to the fact that the ink chambers in the printhead  26  are no longer able to refill completely before a new firing signal is received at the higher firing frequencies  104 . Although it would be ideal to operate at the pivotal firing frequency  106 , a nominal firing frequency  108 , considerably less that the pivotal firing frequency  106 , is typically chosen to ensure consistency of ink drop size and weight despite ink characteristics which may change over time. Having a predictable ink drop size and weight enables high image quality. Operating at the nominal firing frequency  108 , which is slower than the pivotal firing frequency  106 , may result in slower throughput (printed pages per minute) than if the pivotal firing frequency  106  was used. This has been an acceptable tradeoff in the interest of consistent image quality despite the likelihood that ink characteristics may change.  
         [0032]    However, using the embodiments described herein, and their equivalents, firing frequency  104  may now be varied and drop size  56  and drop weight  102  calculated automatically at several frequencies. FIG. 9 illustrates an embodiment of a process by which this may be accomplished. A series of ink droplets  30  or a series of ink drop bursts may be fired  110  onto an electrostatic drop detector target at a known firing frequency to generate a series of electrical stimuli. An EDD Phase  48  and an EDD Score  46  may be calculated  112  for each electrical stimulus in the series. A drop weight may be determined  114  for each ink droplet based on the EDD Scores  46  and EDD Phases  48 . A statistical drop weight may be determined  116  for the known firing frequency. The statistical drop weight may be an average of drop weight values in the series, a windowed average, a mean drop weight, or other appropriate statistical measurement which is well within the means of a person of ordinary skilled in the art to determine. The statistical drop weight may be stored  118  with a corresponding known firing frequency in a dataset for further examination. The firing frequency may then be changed  120  and the previous steps  110 ,  112 ,  114 ,  116 , and  118  may be repeated  122  until a desired range of firing frequency  104  is covered. When the desired range of firing frequency is covered  124 , the highest firing frequency before which drop weight significantly falls may be determined  126  by looking at the stored dataset of drop weight values and firing frequencies. The highest frequency before which drop weight significantly falls is the pivotal firing frequency  106 . The printer may be set  128  to operate at this pivotal firing frequency  106  to obtain the highest possible throughput (printed pages per minute) given the inks currently installed in the product. The printer controller may automatically and periodically re-determine the pivotal firing frequency  106 , using a process like the embodiment of FIG. 9, to ensure that the highest image quality at the highest throughput is being realized. This allows the printer to adjust to aging or changing inks and printheads, as well as allowing the printer to work well with inks from other manufacturers or new inks from the printer manufacturer which were unavailable at the time the printer  20  was built.  
         [0033]    Ink usage measurements can also benefit from the ability of a printer  20  to accurately calculate ink drop size  56 . Previous attempts to track ink usage from a given ink drop generator  24  have been based on drop counting techniques. At first, these drop counting techniques were simply keyed off of the controller&#39;s  22  firing command signals  28 . Each time a nozzle was told to fire, a counter was incremented inside of the controller  22 . Based on a knowledge of an ink drop generator&#39;s  24  starting ink volume, an assumption regarding the average drop size, and an assumption that when a nozzle was told to fire that it actually did fire, an estimate of ink usage could be arrived at. Unfortunately, nozzles do not always fire due to resistor failure or clogging, and drop size may significantly vary from one ink formulation to another, from one ink drop generator  24  to another, and by ink manufacturer. This results in an inaccurate ink usage measurement.  
         [0034]    An different ink usage measurement system relied on a periodic check to determine if in fact the printhead  26  nozzles were firing. This was accomplished through the use of a low cost ink drop detector, such as the one employed in U.S. Pat. No. 6,086,190. A sequence of firing command control signals  28  were sent from the controller  22  to the ink drop generator  24  to cause the printhead  26  nozzles to fire ink droplets. The controller  22  was able to track if an ink droplet was ejected from each printhead  26  nozzle as requested by looking for corresponding signals from the ink drop detector. As a result, the ink usage measurement is more accurate in this type of system because non-firing nozzles were not counted. Unfortunately, this type of measurement still takes into account an assumption of ink drop size. Ink drop size, however, may vary and the result is a less than accurate ink usage measurement.  
         [0035]    Using the embodiments and their equivalents disclosed herein, it is possible to not only know whether a printhead  26  nozzle is functioning, but also to know what ink drop size is being ejected from each nozzle on the printhead. By periodically updating this information, a highly accurate ink usage measurement may be made tracking the actual volume of ink which is ejected from an ink drop generator  24 . Operators of a printer  20  may then either track their ink usage or receive accurate warning that they will soon need to replace the ink supplies in the printer  20 .  
         [0036]    An ink drop detector  32  may be used to determine ink system characteristics, enabling a printing mechanism to reliably use ink drop detection readings to provide users with consistent, high-quality, and economical inkjet output despite printheads  26  which may clog over time and despite ink formulations which may change, age, or are supplied from another manufacturer. In discussing various embodiments of ink system characteristic identification, various benefits have been noted above.  
         [0037]    Although the ink system characteristics described herein include ink conductivity, ink drop size, ink drop weight, ink drop velocity, turn-on-energy, break-off-point, viscosity, dye-load, surface tension, and age of the ink, it is apparent that other ink system characteristics may be determined with relation to EDD Score, EDD Phase, or EDD Score in conjunction with EDD Phase. Such ink system characteristics are deemed to be within the scope of the claims below. Additionally, it is apparent that a variety of other structurally and functionally equivalent modifications and substitutions may be made to determine ink system characteristics according to the concepts covered herein depending upon the particular implementation, while still falling within the scope of the claims below.