A method of maintaining a liquid ink printhead

Abstract

 A liquid ink printer (10) and a method of operation therefore having a maintenance device (30) in communication with a liquid ink printhead (20) to direct the liquid ink printhead to eject purge ink drops from the ink ejecting orifices as a function of image data. The maintenance device (30) includes a maintenance circuit having an image data input for receiving the image data and a maintenance circuit output transmitting a maintenance signal to the liquid ink printhead (20) to cause the ink ejecting orifices thereof to eject purge ink as a function of the received image data. A timer is used to determine the time period between the ejection of ink drops from an individual nozzle to thereby determine if a sufficient number of ink drops are fired to prevent viscous plugs from forming in the nozzles. If the ink nozzles are not ejecting a required number of drops to prevent viscous plugs from forming, a purge operation is performed to project purge ink or purge drops from the respective nozzles to thereby maintain proper operation thereof.

Description

[0001] This invention relates generally to maintaining the operation of a liquid ink printhead in a liquid ink printer

[0002] Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax based, or thermal, have at least one printhead from which droplets of ink are directed to a recording medium. Within the printhead, the ink may be contained in a plurality of channels where power pulses are used to cause the droplets of ink to be expelled, as required, from orifices or nozzles at the ends of the channels.

[0003] In a thermal ink jet printer, the power pulses that result in a rapidly expanding gas bubble to eject the ink from the nozzle are usually produced by resistors, also known as heaters, each located in a respective one of the channels, which are individually addressable by voltage pulses to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in that particular channel and ink bulges from the channel orifice. At that stage, the bubble begins to collapse. The ink within the channel retracts and separates from the bulging ink which forms a droplet moving in a direction away from the channel orifice and towards the recording medium. The channel is then re-filled by capillary action, which in turn draws ink from a supply container. Operation of a thermal ink jet printer is described in, for example, US-A-4,849,774

[0004] One particular form of thermal ink jet printer is described in US-A-4,638,337. That printer is of the carriage type and has a plurality of printheads, each with its own ink supply cartridge, mounted on a reciprocating carriage. The nozzles in each printhead are aligned perpendicularly to the line of movement of the carriage and a swath of information is printed on the stationary recording medium as the carriage is moved in one direction. The recording medium is then stepped, perpendicularly to the line of carriage movement, by a distance equal to the width of the printed swath The carriage is then moved in the reverse direction to print another swath of information.

[0005] A pagewidth ink jet printer is described in US-A-5,192,959. The pagewidth printer includes a full width printhead or printbar which is stationary during printing operations. A sheet of paper is stepped past the printhead and ink is ejected along the entire width of the recording medium for recording images.

[0006] It has been recognized that there is a need to maintain the ink ejecting nozzles and channels of an ink jet printhead, for example, by periodically by capping the printhead when the printer is idle for extended periods of time. Capping of the printhead is intended to prevent the ink in the printhead from drying out thereby preventing ink from being properly ejected from a nozzle There is also a need to prime a printhead before use, to ensure that the printhead channels are completely filled with ink and contain no contaminants or air bubbles, and to also periodically eject ink from the nozzles to maintain proper functioning of the nozzles and channels. By ejecting ink from the nozzles, also known as ink purging, the nozzles are maintained in an operating condition and do not become clogged with dried ink if the nozzles are exposed to air for extended periods of time This is especially critical in pagewidth type printers where the nozzles at the end of an array typically do not eject ink often enough to insure the continued proper operation of the nozzles. Maintenance and/or priming stations for the printheads of various types of ink jet printers are described in, for example, US-A-4,855,764; 4,853,717 and 4,746,938 while the removal of gas from the ink reservoir of a printhead during printing is described in US-A-4,679.059.

[0007] US-A-5,248,999 to Mochizuki, describes an ink jet type recording device having an ink purging feature. A memory circuit is provided for storing data representing the quantity of waste ink sucked out by a suction pump. A control circuit is provided for nullifying an ink purging instruction when the sum of the quantities of waste ink exceeds a predetermined value. When it is detected through the memory circuit that the sum of the quantities of waste ink thus sucked out is beyond the capacity of the waste ink tank, the ink purging operation is suspended irrespective of a forcible ink purging instruction from the switch.

[0008] US-A-5,266,975 to Mochizuki et al., describes an ink jet printing apparatus having means for preventing excessive ink purging and is a continuation of the previously described US-A-5,248,999.

[0009] In accordance with one aspect of the present invention, there is provided a liquid ink printer of the type in which liquid ink is deposited on a recording medium in response to image data received thereby. The printer includes a liquid ink printhead, including an ink carrying conduit terminated by an ink ejecting orifice ejecting ink drops in response to the image data and a maintenance device, in communication with the liquid ink printhead, directing the liquid ink printhead to eject purge ink drops from the ink ejecting orifice as a function of the image data.

[0010] Pursuant to another aspect of the invention, there is provided a method of maintaining the proper operation of a liquid ink printhead printing an image on a recording medium by depositing ink drops from an ink ejecting orifice in response to image data. The method includes the steps of determining the necessity of ejecting a purge ink drop as a function of the image data and ejecting the purge ink drop from the ink ejecting orifice to maintain the proper operation of the ink ejecting orifice based on the determining step.

[0011] The present invention will be described further, in connection with a preferred embodiment. with reference to the accompanying drawings wherein:

FIG. 1 illustrates a partial, schematic, perspective view of an ink jet printer including a maintenance station and carriage driven printhead;

FIG. 2 illustrates a block diagram of an electronic circuit for an ink jet printer incorporating aspects of the present invention;

FIG. 3 is a flow diagram illustrating a maintenance operation for selectively ejecting purge drops from the nozzles of a printhead;

FIG. 4 illustrates a circuit diagram for a drop count/purge circuit according to an embodiment of the present invention and

FIG. 5 is a flow diagram illustrating another maintenance operation for selectively ejecting purge drops from the nozzles of a printhead.

[0012] FIG. 1 illustrates a partial, schematic, perspective view of an ink jet printer 10 having an ink jet printhead cartridge 12 mounted on a carriage 14 supported by carriage rails 16. The printhead cartridge 12 includes a housing 18 containing ink for supply to a thermal ink jet printhead 20 which expels drops of ink under control of electrical signals received from a controller or central processing unit of the printer 10 through an electrical cable 22. The printhead 20 contains a plurality of ink channels (not shown) which carry ink from the housing 18 to respective ink ejecting orifices or nozzles (also not shown). When printing, the carriage 14 reciprocates or scans back and forth along the carriage rails 16 in the direction of an arrow 24. As the printhead cartridge 12 reciprocates back and forth across a recording medium 26, such as a sheet of paper or a transparency, drops of ink are expelled from selected ones of the printhead nozzles towards the sheet of paper 26 to form an image. The ink ejecting orifices or nozzles are typically arranged in a linear array perpendicular to the scanning direction 24. During each pass of the carriage 14, the recording medium 26 is held in a stationary position. At the end of each pass, however, the recording medium is stepped in the direction of an arrow 28. For a more detailed explanation of the printhead and printing thereby refer to U.S-A-4,571,599 and U.S. Patent No. Reissue 32,572

[0013] At one side of the printer 10, outside a printing zone, which encompasses the width of the recording medium 26, is a maintenance station 30, a portion thereof which is illustrated At the end of a printing operation, or at other times when necessary, the printhead carriage 14 is moved to a maintenance position confronting the maintenance station 30 which includes a chamber 32 to which a section device is connected and through which a vacuum is applied through a vacuum line 34. The chamber 32 includes an opening having attached thereto a maintenance/priming element 36 which contacts the printhead 20 when the carriage is located at the maintenance station position. During a priming operation, a vacuum pump (not shown) applies a vacuum to the vacuum line 34 through a waste tank (not shown) for removing ink or debris to insure proper operation of the ink jet nozzles of the printhead 20. The maintenance/priming element 36, when in contact with the printhead 20. maintains an airtight seal around the printhead nozzles. U.S.-A-5,210,550 describes a maintenance station for ink jet printers in more detail.

[0014] The carriage 14 is moved back and forth in the scanning direction 24 by a belt 38 attached thereto. The belt 38 is driven by a first rotatable pulley 40 and a second rotatable pulley 42. The first rotatable pulley 40 is, in turn, driven by a reversible motor 44 under control of the controller of the ink jet printer. In addition to the toothed-belt/pulley system for causing the carriage to move, it is also possible to control the motion of the carriage by using a cable/capstan, lead screw, or other mechanism as known by those skilled in the art. To control the movement and/or position of the carriage 14 along the carriage rail 16, includes an encoder having a linear strip 44 including photographically or mechanically reproduced fiducial marks 46. The pattern 46 is sensed by a sensor 48, such as a photodiode, attached to the printhead carriage 14. The linear strip 44 extends into an area outside the width of the recording medium 26 such that carriage control to a position in front of the maintenance station 30 can be accomplished when necessary. Other positioning devices such as rotary encoders or other known techniques are also possible.

[0015] At the completion of a printing operation or when necessary, the printhead cartridge 12 is moved to a position outside the printing zone to engage the maintenance station 30 When the printhead 20 is aligned therewith, the maintenance station 30 is moved towards the printhead 20 until the priming element 36 contacts the printhead. In known priming operations, the printhead 20, typically ejects ink from all of the nozzles of the printhead to thereby purge the printhead nozzles and to force any ink from the nozzles which may have dried sufficiently to impede the proper ejection of ink therefrom. Typically, ink is ejected from every nozzle after a fixed printing interval into the maintenance station. These purging drops remove the viscous plug that forms at the ink jet nozzle to air interface due to the evaporation of the volatile components of the ink.

[0016] In one known printer, it has been found that for every 45 seconds of the ink jet nozzles being exposed to air, 25 drops of ink per nozzle are required to be ejected to protect from soft printing failure/defects such as clogged nozzles which cause missing lines of text. While this ink purging only wastes an amount of ink approximately equal to an amount deposited four pages of simple text printing, it does require the movement of the printhead cartridge to the maintenance station located off the printed page, therefore resulting in a decrease in print speed or throughput reduction. In addition, depending on the ink formulation and the ejector or nozzle design, the requirements for purging differ. For a full width array printer, purging drops for each nozzle are fired in the interdocument region between printed pages based on the assumption that some nozzles on the array were not fired, particularly those in the margins. Due to the large number of nozzles contained within a full width array printbar and the purge frequency required for some ink formulations, the amount of wasted ink can be considerable. Such ink purging without taking into account whether or not a nozzle has ejected ink results in inefficient maintenance of the printhead nozzles.

[0017] In view of these problems, the present invention includes an apparatus and a method for determining which of the nozzles within a printhead require maintenance and then selectively purging ink from only those nozzles instead of purging ink from the entire array of nozzles. Such intelligent maintenance not only increases the throughput in scanning type ink jet printers, but also reduces the amount of wasted ink in full width array printers. In fact, in the case of scanning type printhead carriages having partial width array printheads, the increase in throughput can be significant since typically all of the nozzles in a partial width array printhead eject ink sufficiently often to make many maintenance operations unnecessary.

[0018] FIG. 2 illustrates a block diagram of an electronic circuit for an ink jet printer incorporating an embodiment of the present invention. The ink jet printer 10 includes a controller or central processing unit (CPU) 50 which controls the operation of the printer including various circuitry not illustrated such as, paper feed driver circuits, carriage motor control circuits, and user interface circuitry. The CPU 50 typically communicates over a bus with the various printer circuits and a memory 52 which includes read only memory (ROM) and/or random access memory (RAM) The read only memory can include an operating program for the CPU 50 for controlling the printer and the random access memory can include accessible memory including print buffers for the manipulation of data and for the storage of printing information in the form of bitmaps received from an input device such as a video engine 54. The video engine 54 can be found in any number of devices generating print data including a personal computer or a scanner such as that found in a facsimile machine. In addition, the CPU 50 under control of a clock 56 which is used to control various timing operations throughout the printer as is known by those skilled in the art.

[0019] The CPU 50 also controls the ejection of ink from the nozzles each of which is associated with a respective heater 58 through operation of a drop ejector controller 60. In one particular embodiment, a thermal ink jet printhead includes an integrated circuit having 192 of the thermal ink jet heaters 58 which are powered by a burn voltage 62 which is typically around 40 volts. Each of the heaters 58 is additionally coupled to a power MOS FET driver 64 coupled to a ground 66. The drivers 64 energize the heaters 58 for expelling ink drops from the nozzles. While, the present invention is applicable to any number of ink jet heaters 58, however, six heaters 58 are shown in FIG. 2 for illustrative purposes. Selective control of each of the drivers 64 is accomplished by an AND gate 68 having the output thereof coupled to the gate of the driver 64. The AND gates allow for the sequential firing of banks or segments of the nozzle array wherein each bank includes two or more nozzles. The drop ejector controller 60 receives control information from the CPU to simultaneously energize each heater within a bank and to sequentially fire each bank of heaters 58 as described in U.S.-A-5,300,968. As illustrated therein, a bi-directional shift register controls a 192 nozzle ink jet printhead where eight heaters are energized simultaneously and the banks of eight heaters are controlled sequentially.

[0020] To prevent nozzles from developing viscous plugs, to increase printing throughput, or to reduce the amount of ink usage resulting from purging, one embodiment of the present invention includes a timer/register system which incorporates a memory device, such as a register or a memory, storing register bit or memory bit indicating an ejection state for each of the nozzles in the printhead. In one embodiment, the memory 52 includes one or more memory locations 70 for nozzles 1 through N. A software timer maintained by the CPU 50, using clock pulses from the clock 56, is set to a nominal latency time period which is the maximum amount of time during which an individual nozzle must eject ink so that a viscous plug does not form.

[0021] As illustrated in the flow chart of FIG. 3, at a step 72, all of the nozzle bits 1 through N are set to zero in the memory location 70, wherein zero indicates that the nozzle has not ejected ink. The software timer is set to the nominal latency time at step 74, which when started at step 76, is decremented second by second until the timer has timed out as determined at step 78. Whenever a nozzle ejects ink, which can be determined from the print data received from the video engine 54, as described later, the memory bit of the corresponding nozzle is set to an ejection state indicator, for instance a 1. Once the timer has timed out and reaches zero, the memory locations 70 are interrogated by the CPU 50 at step 50 to determine whether any of the bits are zero If any zeroes are found, the printhead is moved into engagement with the maintenance station at step 82 and a purge drop is ejected from the nozzles having the bits set to zero to thereby prevent the formation of a viscous plug. Once the selected nozzle or nozzles have ejected purge drops, all of the nozzle bits are set to zero at step 72 and the process continues as previously described.

[0022] While the described implementation of the invention as illustrated in FIG. 3 determines when the nozzle has last ejected ink, it has also been found that to prevent soft failure/defects in a printhead a number of drops must be ejected over a selected period of time. For instance, it may be necessary that for a preselected period of time in which a nozzle is not capped, more than one drop of ink per ink jet nozzle is required to be ejected to protect from soft printing failures and defects. This is particularly true for pagewidth printers where the printhead typically remains stationary during printing and only ejects purge drops between documents. In fact, printer including a scanning printhead and a stationary pagewidth printhead may require both purging schemes. For instance. it has been found that for carbon black inks, approximately 5-10 drops must be ejected from an individual nozzle every 25 seconds. Consequently, not only would such a printer require the memory locations 70 illustrated in FIG. 2, but would also include a drop count/purge circuit 90 receiving print data from the video engine 54 of FIG. 2.

[0023] The drop count/purge circuit 90 generates a signal indicating the state of the nozzles which is then interrogated by the CPU 50 after specified period of time. The CPU 50 examines the signal transmitted over a nozzle state line 89 and determines whether or not a purge operation should be conducted. If so, a purge signal is generated by the CPU 50 which is transmitted to the drop count/purge circuit 90 which generates signals to cause purge drops to be ejected from the nozzles of the ink jet printhead.

[0024] As illustrated in FIG. 4, the drop count/purge circuit receives print data from the video engine 54. A drop counter 92, one associated with each of the ink jet nozzles, receives print data from the video engine 54 to determine how many drops are ejected from a particular nozzle. Since the present invention is described with respect to a printhead firing banks of nozzles sequentially. each of the drop counters 92 receives the print data corresponding to the respective nozzles under control of a nozzle decoder 94 having an output coupled to a first AND gate 96 and a second AND gate 98. both respectively associated with one of the drop counters 92. The nozzle decoder 94 is controlled by a bank counter 100 and a nozzle counter 102 each operating in response to signals received from the CPU 50 (not shown). The bank counter 100 and the nozzle counter 102 sequence the nozzle decoder 94 through each nozzle within a bank and each bank within the printhead such that the appropriate print data from the video engine is directed to the appropriate drop counter 92. A multiplexer 104 selects either the print data from the video engine or a signal known as an inhibit count signal to be described later.

[0025] When printing begins, the state of the purge signal generated by the CPU 50 causes the multiplexer 104 to select the print data from the video engine which then passes through the multiplexer 104 to the input of the drop counter 92. The drop counter 92 is preloaded with a drop count D_O-D_N, selected to prevent viscous plugs from forming in the nozzles. For instance, the drop counter might be set at 10 drops for a carbon black ink. Likewise, inks of different colors being ejected may each require different purging schedules where the number of purge drops varies from color to color over different periods of time. In addition, humidity and temperature may affect the formation of viscous plugs such that a humidity and/or temperature sensor, monitored by the CPU 50, may generate signals which are used to adjust the purge schedule.

[0026] Once the drop count is determined, then each time the print data from the video engine includes a 1, indicating that a nozzle is to eject a drop of ink, the drop counter is decremented by 1. A comparator 106, coupled to the output of the drop counter 92 determines if the drop counter count has been reduced to 0, indicating that the necessary number of drops to prevent the formation of viscous plugs has been ejected. If so, the comparator 106 generates a 1 which is transmitted over a line as an input to an AND gate 108 which also receives the outputs from the remaining comparators 106B to 106N each being associated with a respective drop counter. The output of the AND gate 108 transmits a signal indicating whether or not any nozzle has ejected the required number of drops over the specified time. At the end of the time period, the output of the AND gate 108 is interrogated by the CPU.

[0027] The output of the comparator 106 is also negated by a NAND gate 110 whose output is returned to one of the inputs of the AND gate 96 and is also transmitted as an input to a multiplexer 112. The multiplexer 112 receives the outputs from the remaining NAND gates 110B through 110N and transmits purge signals to eject purge drops. The output signal of the multiplexer 112 is transmitted to a multiplexer 114 which also receives as an input the print data from the video engine. The output of the multiplexer 114 is either the print data or purge signals sent to the printhead depending on the state of the signal transmitted by the PURGE line.

[0028] FIG. 5 is a flow chart illustrating a method of operation for the circuit of FIG. 4 in conjunction with the CPU 50. Before any printing begins, the initial drop count is loaded , at step 120, into each of the drop counters 92 of FIG. 4. The CPU then starts a countdown timer written in software code. During operation of the circuit illustrated in FIG. 4, the print data from the video engine, which is input to each of the multiplexers 104 under control of the nozzle decoder 94, is used to determine the drop count of the drops ejected by the nozzles. Each of the drop counters use the print data to determine drops ejected and are sequenced in the same manner as the individual heaters of the printhead are sequenced so that the drop counter counts the corresponding number of drops ejected by the heater to which it is associated. The drop counters are decremented one by one with each drop ejection until zero is reached some other value is generated at time the countdown timer times out at step 124 of FIG. 5. At this time, the drop count is analyzed by the CPU by interrogating the nozzle state line. If the nozzles state line is a 1. all drop counters are at zero and no maintenance operation is necessary. The CPU then returns to step 120 to load the initial drop count in each of the individual drop counters 92 and the counting procedure begins again. If, however, the drop count is not 0, that is, the nozzle state line transmits a 0, then the printhead is engaged to a maintenance station at step 130 to eject purge drops. In the case of a scanning type carriage printer, the printhead may be moved to the side of the page where the maintenance station is located and the maintenance station is then moved into contact with the printhead. In the case of a pagewidth printer, however, the printhead may move into contact with a maintenance station which is located away from the paper path or may eject purge drops into the interdocument region In either event the purge drops are ejected from the respective nozzles to reduce each of the drop counts maintained by the drop counters to zero as shown at step 132.

[0029] Once a purge operation begins, the CPU generates the purge signal which is input to each of the multiplexers 104 causing the multiplexers to not select print data from the video engine but instead to input the inhibit count signal so that the drop counters which have not been decremented to zero are now decremented by one each time a purge drop is ejected from a nozzle into the maintenance station. For instance, if a counter is set at 5, then 5 drops must be ejected to complete the maintenance purge operation.

[0030] To eject purge drops, the nozzle decoder 94 sequences through each of the drop counters such that the multiplexer 112 selects the appropriate drop counter for causing a single drop to be ejected from the appropriate nozzle over a print data to printhead line 133. In this fashion, each of the drop counters are sequentially addressed such that the remaining number of drops to be ejected from the respective nozzles are then ejected sequentially through each of the nozzles. This sequential firing of heaters prevents the heaters from being overstressed which could occur if a single nozzle ejects all of the required purge drops in a row. During this time, the output of the AND gate 108 is continually monitored by the CPU at step 134 such that when the output of the AND gate is a 1 thereby indicating that all of the necessary purge drops have been ejected. The CPU 50 then determines whether or not printing has been completed at step 136. If printing has not been completed, the CPU returns to step 120 to load the initial drop count into each of the drop counters so that the procedure can begin again. If, however, printing is complete and no more print jobs are in the queue, then the printhead is capped at step 138.

[0031] In recapitulation, there has been described an apparatus and method for maintaining the proper operation of a liquid ink printhead which prints an image on a recording medium by selectively depositing ink drops from ink ejecting orifices in response to image data. A time period between firing of ink drops from selected nozzles of the printhead is determined such that a maintenance operation can be performed to eject additional purge drops from the respective nozzles so that viscous plugs do not form. It has therefore apparent that there has been provided in accordance with the present invention, a liquid ink printer that satisfies the aims and advantages hereinbefore set forth. While this invention has been described in conjunction with a specific embodiment thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. The present invention is therefore not limited to the embodiments described herein but is equally applicable to other apparatus and methods which determine the time periods between the ejection of drops from a nozzle or the amount of time over which a number of drops are ejected from a nozzle. For instance, it is also possible that when a nozzle has ejected a drop, a value from a free running software timer is loaded into a memory location associated with the particular nozzle. Periodically. the CPU would interrogate all of the registers or memory locations and look for values that are too long, that is, values lower than a preselected value. If any nozzles are found to be not fired within this preselected period of time, the CPU causes the printhead to engage the maintenance station and any nozzles that have not ejected ink often enough then eject purge drops to prevent the formation of viscous plugs. This sequence would continue throughout the printing process. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the appended claims.

Claims

1. A method of maintaining the proper operation of a liquid ink printhead (20) ejecting ink drops on a recording medium (26) to print an image in response to image data, characterised by

determining the necessity of ejecting a purge ink drop as a function of the image data; and

ejecting the purge ink drop from an ink ejecting orifice to maintain the proper operation of the ink ejecting orifice based on said determining step.

2. A method as claimed in claim 1, further comprising calculating the number of ink drops ejected from the ink ejecting orifice during printing of the image.

3. A method as claimed in claim 2, wherein said calculating step comprises calculating the number of ink drops ejected from the ink ejecting orifice during printing of the image over a preselected period of time.

4. A method as claimed in claim 3, comprising determining an optimum number of ink drops to be deposited over the predetermined period of time to insure proper operation of the liquid ink printhead and comparing the calculated number of ink drops ejected from the ink ejecting orifice during printing over the preselected period of time to the determined optimum number of ink drops to be deposited over the predetermined period of time to arrive at a number of purge ink drops to be ejected to maintain the operability of the ink ejecting orifice.

5. A liquid ink printer (10) of the type in which liquid ink is deposited on a recording medium (26) in response to image data received thereby, comprising:

a liquid ink printhead (20), including an ink carrying conduit terminated by an ink ejecting orifice, for ejecting ink drops in response to the image data; and

a maintenance device (30), in communication with said liquid ink printhead. characterised in that said maintenance device directs said liquid ink printhead (20) to eject purge ink drops from said ink ejecting orifice as a function of the image data.

6. A liquid ink printer as claimed in claim 5, wherein said maintenance device comprises a maintenance circuit including an image data input for receiving the image data, and a maintenance circuit output transmitting a maintenance signal to said liquid ink printhead to cause said ink ejecting orifice to eject purge ink as a function of the received image data, a controller including a controller input coupled to said maintenance circuit output, and a controller output, with the controller input receiving the maintenance signal and the controller output transmitting a purge control signal in response to the maintenance signal.

7. A liquid ink printer as claimed in claim 6, wherein said maintenance circuit comprises a drop counter including a counter input, coupled to said image data input, and a counter output, outputting a count signal indicating the number of ink drops being ejected from said ink ejecting orifice as a function of the received image data.

8. The liquid ink printer of claim 7, wherein said liquid ink printhead comprises a plurality of ink carrying conduits and a plurality of ink ejecting orifices, each of said ink carrying conduits terminated by said one of said plurality of ink ejecting orifices, said maintenance circuit comprising a plurality of drop counters, one of said plurality of drop counters being associated with one of said plurality of ink ejecting orifices, each of said plurality of drop counters including a counter input coupled to the image data input with each of said plurality of controller inputs receiving image data, and a counter output outputting a signal indicating the number of drops being ejected from the associated one of said plurality of ink ejecting orifices.

9. A liquid ink printer as claimed in claim 8, wherein said maintenance circuit comprises a state determining circuit, including a plurality of state determining circuit inputs, one of said plurality of inputs coupled to one of said plurality of counter outputs, and a determining circuit output transmitting a state signal indicating the states of said plurality of counters.

10. A liquid ink printer as claimed in any of claims 1 to 9, wherein said maintenance device comprises a memory device, storing an ejection state indicator indicating the ejection state of the ink ejecting orifice.

Drawing