Abstract:
An ink jet printer includes a supply of ink, a print head, a cap, a waste tank and a control system. The print head is operatively connected to the supply of ink and ejects drops of ink to form an image. The cap is arranged to receive waste ink from the print head during maintenance operations. The waste tank is operatively connected to the cap for storing the waste ink. The control system is operatively connected to the print head for keeping an estimate of a volume of waste ink that has been discharged into the waste tank and adjusting the waste ink estimate to compensate for evaporation of the waste ink.

Description:
FIELD OF THE INVENTION 
     This invention relates to an ink jet printer. More particularly, this invention is directed to an ink jet printer including a waste tank and a technique, embodied in a method and system, for preventing overflow of the waste tank. 
     BACKGROUND OF THE INVENTION 
     Ink jet printers are well known in the art. Generally, an ink jet printer includes an array of nozzles or orifices, a supply of ink, a plurality of ejection elements (typically either expanding vapor bubble elements or piezoelectric transducer elements) corresponding to the array of nozzles and suitable driver and control electronics for controlling the ejection elements. Typically, the array of nozzles and the ejection elements along with their associated components are referred to as a print head. It is the activation of the ejection elements that causes drops of ink to be expelled from the nozzles. The ink ejected in this manner forms drops which travel along a flight path until they reach a print medium such as a sheet of paper, overhead transparency, envelope or the like. Once they reach the print medium, the drops dry and collectively form a print image. Typically, the ejection elements are selectively activated or energized as relative movement is provided between the print head and the print medium so that a predetermined or desired print image is achieved. 
     Generally, the array of nozzles, supply of ink, plurality of ejection elements and driver electronics are packaged into an ink jet cartridge. In turn, the printer includes a carriage assembly for detachably mounting the ink jet cartridge thereto. In this manner, a fresh ink jet cartridge may be installed when the ink supply of the current ink cartridge has been consumed. In other embodiments an “off axis” ink supply. In these types of systems, the print head is typically a permanent or semi-permanent component while detachable replaceable ink supply cartridges are employed. Suitable plumbing connects the permanent print head with the ink supply cartridges. 
     Additionally, the printer typically includes a maintenance module for maintaining the print head in proper working order. The maintenance module includes a cap for sealing the print head off from ambient air while the print head is not in use, a wiper blade for wiping excess ink and moister from the nozzle face of the print head at selected intervals, a pump for supplying vacuum to the print head via the cap and a waste ink storage tank also operatively coupled to the cap. During maintenance operations, such as: flushes, purges, power flushes, power purges and the like, the print head is capped and vacuum may be applied. The maintenance operations expel and/or draw waste ink out of the print head. So as not to spill waste ink out of the printer, the waste ink is contained within a waste ink tank. Typically, the waste ink tank includes a sealed plastic housing, an absorbent material (foam, etc.) located within the housing for keeping the waste ink from splashing during handling of the printer and suitable plumbing for connecting the housing with the cap. 
     Although the waste ink tank is usually sized to accommodate the anticipated use and expected life of the printer, it is difficult to strike an efficient balance between: anticipated usage, expected life and other considerations, such as: space, cost and risk. For example, a lower risk solution (very remote chance of saturating the absorbent material and causing a leak) may result in undesirable space and cost consequences. As another example, a higher risk solution may result in some users experiencing waste ink leakage. 
     To help address this issue, attempts have been made to monitor the amount of waste ink in the waste tank so that a warning can be provided before the waste tank overflows. Various monitoring techniques, both active and passive, have been developed. One approach is to place a sensor, such as a thermister, float or the like, within the waste tank so that the level of the waste ink may be actively discerned. Although this type of approach works generally well, adding sensors along with their associated circuitry adds complexity and cost to the printer. 
     Various passive approaches, such as the one described in U.S. Pat. No. 5,266,975, rely on counting ink drops that have been discharged into the waste tank. By counting the number of drops and using an estimate of the drop volume, an approximate amount of waste ink that has been discharged may be calculated. Although this type of approach works generally well, the waste ink discharge estimate may not be a reliable indicator of an actual amount of capacity of the waste ink tank that has been consumed. 
     Therefore, there is a need for an improved ink jet printer that accurately tracks the amount of ink accumulated in the waste ink without adversely impacting the cost or complexity of the printer. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an improved ink jet printer that more accurately tracks the amount of ink accumulated in the waste tank without adding costly sensors or other active devices to the waste tank. The ink jet printer includes a supply of ink, a print head, a cap, a waste tank and a control system. The print head is operatively connected to the supply of ink and ejects drops of ink to form an image. The cap is arranged to receive waste ink from the print head during maintenance operations. The waste tank is operatively connected to the cap for storing the waste ink. The control system is operatively connected to the print head for keeping an estimate of a volume of waste ink that has been discharged into the waste tank and adjusting the waste ink estimate to compensate for evaporation of the waste ink. 
     In accordance with the present invention, there is also a corresponding method of operating the ink jet printer summarized above and described in detail below. 
     Therefore, it should now be apparent that the present invention substantially overcomes the disadvantages associated with the prior art. Additional advantages of the invention will be set forth in the description, which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts. 
     FIG. 1 is a simplified schematic of a postage printing system employing an ink jet printer of present invention. 
     FIG. 2 is a routine performed by the postage printing system to prevent overflow of a waste tank in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Postage printing systems are well known in the art. Generally, these systems are readily available from manufacturers such as Pint Bowes Inc. of Stamford, Conn. They often include a variety of different modules which automate the processes of producing mailpieces. A typical high end postage printing system includes a variety of different modules or sub-systems where each module performs a different task on the mailpiece, such as: singulating (separating the mailpieces one at a time from a stack of mailpieces), weighing, moistening/sealing (wetting and closing the glued flap of an envelope), applying/printing evidence of postage, accounting for postage used and stacking finished mailpieces. However, the exact configuration of each postage printing system is particular to the needs of the user. Customarily, the high end postage printing system also includes a transport apparatus which feeds the mailpieces in a path of travel through the successive modules of the postage printing system. 
     Referring to FIG. 1, a simplified schematic of a postage printing system  100 , including a postage metering portion  120  and an ink jet printer  180 . Since a detailed discussion of the postage printing system  100 , and more particularly the postage metering portion  120 , is not necessary for an understanding of the present invention, the description of the postage printing system unrelated to the present invention will be limited. Periodically, the postage metering portion  120  of the postage printing system  100  contacts a data center  50  to download postal funds or for remote inspections. Typically, this is accomplished over ordinary telephone lines, local area networks or other suitable communication pathway. 
     The postage metering portion  120  includes a central micro controller  130 , a user interface  135 , a clock  140 , a vault module  150  and a printer controller module  160 . The central micro controller  130  includes a suitable processor  132 , an associated read only memory (ROM)  134  and an associated random access memory (RAM)  136 . The user interface  135  may be of a conventional variety, such as: LCD display (not shown) and keyboard (not shown). The clock  140  is in communication with the processor  132  for providing real time clock data. The vault module  150  accounts for postage used and includes a non-volatile memory (NVM)  152  for storing various accounting and postal information (not shown), such as: an ascending register, a descending register, a control sum register and a postal identification serial number. The vault module  150  is also in communication with the processor  132  for receiving appropriate read and write commands from the processor  132 . The printer controller module  160  is also in communication with the processor  132  and includes a print head controller  162  an associated ROM  164 , an associated RAM  166  and an associated NVM  168 . The print head controller  162  oversees operation of the printer  180  by providing suitable drive signals and other instructions. Alternatively, the printer controller module  160  could be located within the ink jet printer  180 . 
     The printing portion  180  includes conventional components as are known in the art: a print head  182 , a replaceable cartridge  184  containing a supply of ink and optionally including a data carrier  184   a , and a maintenance system  190  having a cap  192 , a wiper blade  194 , a pump  196  and a waste ink tank  199 . In a maintenance position (not shown), the print head  182  is sealed off from ambient air by the cap  192 , while in a print position (not shown), the print head  182  is located proximate to a mailpiece (not shown) so as to print a postal indicia (not shown) or other message. The wiper blade  194  periodically cleans the print head  182  to remove any excess ink or other debris (not shown) that may have accumulated on the print head  182 . The pump  196  is coupled to the cap  192  and selectively energized in response to signals from the print head controller  162  so as to produce a negative pressure at the cap  192 . In this manner, ink can be drawn out of the print head  182  while the print head  182  is in the maintenance position. The cap  192  is operatively connected to the waste ink tank  199  by any conventional plumbing, such as flexible tubing. In this manner, when the maintenance operations (flushes, purges, and the like) are conducted on the print head  182 , the waste ink (not shown) is accumulated in the waste ink tank  199 . Additionally, the print head  182  receives suitable drive signals from the print head controller  162  so as to selectively energize the plurality of ejection elements (not shown). 
     For use in preventing waste tank  199  overflow, a plurality of operational parameters are stored in the print head controller NVM  168 . The parameters are identified in Table 1 and described in greater detail below. The maximum volume of the waste tank V max  is established according to the capacity of the waste tank  199 . Thus, the size of the waste tank  199  is used to establish V max . 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Operational Parameters 
               
             
          
           
               
                   
                 Variable Name 
                 ID 
                 Value 
               
               
                   
                   
               
             
          
           
               
                   
                 Maximum Waste Tank Volume 
                 V max   
                 300 
               
               
                   
                 Threshold #1 
                 T 1   
                 .85 
               
               
                   
                 Threshold #2 
                 T 2   
                 .90 
               
               
                   
                 Evaporable Content of Ink 
                 E ink   
                 .50 
               
               
                   
                 Evaporable Content of Shipping Fluid 
                 E ship   
                 .15 
               
               
                   
                   
               
             
          
         
       
     
     In this instance, V max  is set equal to 300 cubic centimeters. A first threshold value T 1  is established to define a warning point when the waste ink tank  199  is nearing capacity and represents a percentage of the capacity of the waste tank  199 . In this instance, T 1  is set equal to 85 percent. A second threshold value T 2  is established to define a point when the waste ink tank  199  is in danger of overflowing and printing operations will be disabled. Here again, T 2  represents a percentage of the capacity of the waste tank  199  and is selected based on the accuracy of the waste ink estimates and a desired safety margin. In this instance, T 2  is set equal to 90 percent. An evaporable content of ink E ink  is established to define that percentage of the ink that will evaporate over time. In this instance, E ink  is set equal to 50 percent. An evaporable content of shipping fluid E ship  is established to define that percentage of the shipping fluid (not shown) that will evaporate over time. In some ink jet printers, shipping fluid is used in the print head to protect the print head  182  during storage periods. At first installation, the shipping fluid is purged from the print head  182  in conventional manner prior to normal operations beginning. In this instance, E ship  is set equal to 15 percent. 
     With the structure of the invention described as above, the operational characteristics will now be described with reference to FIG. 2 while recalling the detailed structures described above. Referring to FIG. 2 in view of FIG. 1, a waste tank overflow prevention routine  600  run by the print head controller  162  is shown. The routine  600  may be run in response to any predetermined event, such as: system power up, instruction to perform a maintenance operation, and/or any other desired event. At  602 , an estimate of a volume of waste ink V e  in the waste tank  199  is updated. Basically, the estimate of the volume of waste ink V e  is derived from passive techniques such as: (i) counting ink and shipping fluid drops and using an anticipated drop volume to calculate total volume; (ii) counting maintenance operations and using an anticipated operation volume to calculate total volume; or some other suitable technique. Further, the volume of waste ink V e  includes an adjustment that compensates for evaporation. The estimate of the volume of waste ink V e  is maintained according to the following formula: 
     
       
         V e =ΣV ship +ΣV ink   (1) 
       
     
     where ΣV Ship  is the sum of all shipping fluid discharges into the waste tank  199  and ΣV ink  is the sum of all ink discharges into the waste tank  199 . In turn, each shipping fluid discharge V ship is defined according to the following formula: 
     
       
         V ship =V ship −V ship {E ship }{F ship (t)}  (2) 
       
     
     where the expression V ship {E ship }{F ship (t)} represents an evaporation rate of the shipping fluid as a function of time. Generally, any suitable expression may be employed to account for evaporation. In the preferred embodiment, a function F ship (t) is employed that equals zero (0) at time equal to zero (0) and equals one (1) at time equal to anticipated evaporation duration for the shipping fluid. As a result, at time equal to zero (0), the expression V ship {E ship }{F ship (t)} equals zero (0) and as a result V ship equals its original discharge volume. On the other hand, after the anticipated evaporation duration for the shipping fluid, the term F ship (t) equals one (1) and the expression V ship −V ship {E ship } {F ship (t)} reduces to V ship −V ship {E ship } which equals 0.85 V ship  (V ship −0.15 V ship ). Thus, the shipping fluid discharge V ship  in the waste tank  199  becomes 85 percent of what was originally present. An example of the function F ship (t) that may be employed is {1−{1/C t }} where C equals a constant representative of the shipping fluid&#39;s evaporation rate and the variable t equals elapsed time. Those skilled in the art will appreciate that the ink discharge estimate V ink  may be maintained in analogous fashion to V ship , as described above, and therefore, for the sake of brevity, no further details concerning the ink discharge estimate V ink  will be provided. 
     It should now be appreciated that the waste ink estimate V e  in the waste tank  199  is updated according to the amount of discharged shipping fluid and waste ink with an adjustment for evaporation. Once the waste ink estimate V e  has been updated at  602 , next at  604  a determination is made as to whether or not V e  is greater than or equal to a first threshold T 1  times the maximum waste tank volume V max . If the answer is no, then at  606 , normal operations of the printer  180  are continued. On the other hand, if at  604  the answer is yes, then at  608 , a warning is issued to the operator. This warning make take the form of an audible and/or visual message provided to the operator via the user interface  135 . Furthermore, the warning may also instruct the operator to call customer service. Next, at  610  as an option, a flag is set in meter memory  152  indicating that the first threshold has been exceeded. The use of this flag will be described in greater detail below. Next, at  612 , a determination is made as to whether or not V e  is greater than or equal to a second threshold T 2  times the maximum waste tank volume V max . If the answer is no, then at  606 , normal operations of the printer  180  are continued. On the other hand, if at  612  the answer is yes, then at  614 , the printer  180  is disabled from performing further maintenance operations that discharge ink into the waste tank  199 . In this way, overflow of the waste tank  199  is prevented. 
     Those skilled in the art will now appreciate that the present invention provides significant advantages over the prior art. By accounting for evaporation, the waste ink discharge estimate V e  provides an improved indicator of an actual amount of capacity of the waste ink tank  199  that has been consumed. Also, the additional optional feature of including shipping fluid (if used) in the waste calculations and treating it on a different evaporation content and evaporation rate than the ink further improves the accuracy of the system. The improved accuracy allows for a greater percentage utilization of the waste tank  199  before disabling the printer  180 . This benefit leads to improved system performance (more up time) and lower operating costs for both the manufacturer and the operator. 
     The first threshold exceeded flag may be used to facilitate and efficiently schedule service calls to replace the waste ink tank  199 . From time to time, the postage metering portion  120  of the postage printing system  100  enters into communication with the data center  50 . During a communication session, if the data center  50  sees the first threshold exceeded flag in memory  152 , then the data center  50  may initiate a service call to replace the waste tank  199  without the need for the operator to call customer service. 
     Because key operational parameters of the printer  180  are defined as variables in memory  168 , the printer  180  of the present invention exhibits improved operational flexibility. For example, when a saturated waste tank  199  is replaced, it may be replaced with one of larger, smaller or the same capacity (it should be understood that V e  is also reset to zero (0) at this time). Instead of having to reprogram the printer  180 , the customer service representative merely has to update the number for the maximum volume of the waste tank V max  in memory  168 . In this way, the operator may purchase the same size waste tank  199  or a different size waste tank  199  depending upon various factors, such as: usage pattern, anticipated remaining life of the printer  180 . This provides for increased satisfaction among operators. 
     Similarly, the other key operational parameters of the printer  180  being defined as variables also provide for improved operational flexibility. For example, if empirical testing or improved anticipated drop volume estimates or other factors allow for a reduction in the safety margin before the printer  180  is disabled, then the first threshold value T 1  and the second threshold value T 2  may be adjusted by placing new values into memory  168 . For instance, 0.88 and 0.93, respectively. This may be accomplished by dispatching a customer service representative to load in the new values or by having the data center  50  download new values during a communication session. 
     As another example, if changes in the formulation of the shipping fluid or ink occur that influence their evaporation characteristics, then new values for the evaporable contents of the shipping fluid E ship  and ink E ink  may be provided. Here again, this may be accomplished by dispatching a customer service representative to load in the new values or by having the data center  50  download new values during a communication session. As another alternative, the ink cartridge  184  may contain these values on the data carrier  184   a  so that when a new ink cartridge  184  is installed, the values are obtained from the data carrier  184   a , in any conventional manner, and written into memory  168 . The data carrier  184   a  may employ any type of information storage system, such as: bar code, magnetic stripe or smart chip. As yet another example, still other operational parameters (i.e. evaporation rate constant) of the ink may be parameterized and stored on the data carrier  184   a . As still yet another example, the pump  196  need not operate and the cap  192  need not seal off the print head  182  during maintenance operations. However, such actions are desirable in most instances. 
     Many features of the preferred embodiment represent design choices selected to best exploit the inventive concept as implemented in a postage metering system employing an ink jet printer. However, those skilled in the art will recognize that the concepts of the present invention are applicable to any ink jet printer. 
     Moreover, those skilled in the art will recognize that various modifications can be made without departing from the spirit of the present invention. For example, a single control system may be employed for both the postage metering portion  120  and the printer  180 . As another example, the printer  180  may communicate directly with the data center  50  without having the postage metering portion  120  serve as an intermediary. As another example, the ink supply and the print head may be integrated into the same replaceable cartridge or may exist as separate parts. 
     As still yet another example, the present invention may be adapted for use with an ink jet printer employing more than one type of ink. Some ink jet printers, such as those with color capability, have a concurrent need for different inks. In this application, the present invention contemplates separately tracking the waste discharges of each different ink and providing respective operational parameters for each of the different inks. In this way, the accuracy of the estimate of the waste tank capacity that has been consumed is improved by accounting for different evaporation behavioral characteristics. 
     Therefore, the inventive concepts in their broader aspects are not limited to the specific details of the preferred embodiments but are defined by the appended claims and their equivalents.