Patent Publication Number: US-6712451-B2

Title: Printhead assembly with shift register stages facilitating cleaning of printhead nozzles

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is related to application Ser. No. 09/960,109, filed Sep. 21, 2001, entitled “Printhead Assembly With Minimized Interconnections to an Inkjet Printhead,” the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates in general to a recording apparatus such as, in a preferred example, a printhead and, more specifically, to a printhead assembly that facilitates cleaning of the printhead. More particularly, the invention relates to a printhead assembly having a printhead with a plurality of shift register stages supporting a plurality of actuators, the shift registers stages being located on one side of the recording elements of the printhead, such as inkjet nozzles, to facilitate cleaning of the printhead&#39;s nozzles. 
     BACKGROUND OF THE INVENTION 
     Without limiting the scope of the invention, its background is described in connection with thermal inkjet printers, as an example. Modern printing relies heavily on inkjet printing techniques. The term “inkjet” as utilized herein is intended to include all drop-on-demand or continuous inkjet printer systems including, but not limited to, thermal inkjet, piezoelectric, and continuous, all of which are well known in the printing industry. Essentially, an inkjet printer produces images on a receiver medium, such as paper, by ejecting ink droplets onto the receiver medium in an image-wise fashion. The advantages of non-impact, low-noise, low-energy use, and low cost operation, in addition to the capability of the printer to print on plain paper, are largely responsible for the wide acceptance of inkjet printers in the marketplace. 
     The printhead is the device that is most commonly used to direct the ink droplets onto the receiver medium. A printhead typically includes an ink reservoir and channels which carry the ink from the reservoir to one or more nozzles. Typically, sophisticated printhead systems utilize multiple nozzles for applications such as high-speed continuous inkjet printer systems, as an example. Continuous inkjet printhead device types include electrostatically controlled printheads and thermally steered printheads. Both printhead types are named according to the means used to steer ink droplets ejected from nozzle openings. 
     It is well known in the art of inkjet printing that multiple actuators or heating elements per inkjet nozzle can be used. For example, U.S. Pat. No. 4,751,531 describes the use of a two heater printing nozzle while U.S. Pat. No. 4,695,853 describes the use of a vertical array of 9 heating elements per nozzle. In order to optimize drop formation conditions, it is preferred to utilize independent control circuits for such multi-actuator print nozzle configurations. 
     Inks for high speed ink jet printers, whether of the continuous or drop-on-demand type, must have a number of special characteristics. For example, the ink should incorporate a nondrying characteristic, so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by occasional spitting of ink droplets, the cavities and corresponding nozzles are kept open. The addition of glycol facilitates free flow of ink through the inkjet chamber. Of course, the inkjet printhead is exposed to the environment where the inkjet printing occurs. Thus, the previously mentioned nozzles are exposed to many kinds of air born particulates. Particulate debris may accumulate on surfaces formed around the nozzles and may accumulate in the nozzles and chambers themselves. That is, the ink may combine with such particulate debris to form an interference burr that blocks the nozzle or that alters surface wetting to inhibit proper formation of the ink droplet. The particulate debris should be cleaned from the surface and nozzle to restore proper droplet formation. In the prior art, the cleaning mechanism may consist of a brush, wiper, sprayer, vacuum suction device, and/or spitting of ink through the nozzle. 
     At the same time, there are practical space limitations with respect to the number of layers necessary to implement the control circuits as well as limitations in the number of interconnections that are practical in order to make the design useful and operable. These type of design constraints require the use of serial shift registers to bring the print data to the printhead during printing. Between the stated design constraints lies an optimum solution for maintaining of clean multi-actuated printheads. 
     Thus, inkjet printers can be said to have the following problems: the inks tend to dry-out in and around the nozzles resulting in clogging of the nozzles; cleaning nozzles that have limited accessibility due to the placement of the control electronics poses extra demands on the design of printhead assembly as well as the cleaning members used. 
     Accordingly, what is needed is a way of organizing the printhead assembly such that minimal interference with cleaning is facilitated. A printhead assembly that arranges the shift register stages and actuators to facilitate cleaning of the nozzles would provide numerous advantages. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solution to dealing with the task of cleaning a multi-actuated configuration printhead that has limited space due to the control electronics. The invention provides a printhead assembly with the control circuitry advantageously placed to facilitate cleaning of the printhead assembly. 
     Therefore, according to one embodiment, disclosed is an inkjet printhead comprising a plurality of nozzles arranged in an array for ejecting ink to form an image on a receiver member and a plurality of actuators associated with each respective nozzle, each actuator being separately drivable to affect ejection of ink from the respective nozzle. The printhead further comprises a plurality of shift registers stages, each stage being associated with a respective nozzle actuator and nozzle actuators associated with each nozzle being associated with different shift register stages. A cleaning assembly is provided for cleaning the nozzles. The shift register stages being adapted to shift data from one stage to a next stage to distribute data to the different stages, wherein the shift register stages are arranged to facilitate cleaning of the plurality of nozzles. According to one specific embodiment, the shift register stages are positioned on the same side of the printhead thereby providing sufficient space for the cleaning mechanism and the nozzles to be moved relative to each other. 
     Further disclosed is an inkjet printhead assembly comprising a plurality of nozzles having corresponding nozzle openings for delivering ink onto a specified receiver medium and a plurality of shift registers operably coupled to a plurality of actuators associated with said nozzles and adapted to cause ink to be delivered through said nozzles openings in the direction of said receiver medium. The printhead assembly further comprises print data drivers operably coupled to the plurality of shift registers via a plurality of interconnections, wherein said shift registers are arranged all to one side of the nozzles to facilitate cleaning of the plurality of nozzles. In one specific embodiment, the plurality of actuators comprise heaters. In another specific embodiment, the shift registers and their respective electrical interconnections using a wire-bonding technique are positioned on one side of said plurality of nozzles thereby providing sufficient space for the cleaning mechanism to be moved relative to the nozzles. 
     In accordance with another aspect of the invention, there is provided a method of providing image data in the printer apparatus, the method comprising providing a plurality of recording elements arranged in an array for recording of an image on a receiver medium; providing a plurality of actuators associated with each respective recording element each actuator being separately drivable to affect recording by a respective recording element; providing a cleaning assembly for cleaning the recording elements; providing a plurality of shift register stages, each stage being associated with a respective different actuator, each recording element being associated with plural different shift register stages and shifting data from one stage to a next stage to distribute data to the different stages, the shift register stages and their respective wire-bond interconnects being located all to one side of the array of recording elements; and advancing the cleaning assembly relative to the array of recording elements wherein the shift register stages and their respective wire-bond interconnections are sufficiently positioned away from the recording elements to facilitate cleaning of the recording elements by the cleaning assembly without the cleaning assembly damaging the shift register circuits. 
     A technical advantage of the present invention is a cost effective method of facilitating cleaning of a printhead assembly in a thermal inkjet printhead. 
     Another technical advantage includes optimum compromise between the length of shift registers and number of heaters to be controlled. In one printhead configuration, twenty 128-bit shift registers are able to operate a 1280 nozzle assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, including its features and advantages, reference is made to the following detailed description of the invention, taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a diagram illustrating an inkjet printhead with a plurality of nozzle openings through which ink flows; 
     FIG. 2 illustrates a single printhead nozzle with two heater elements; 
     FIG. 3 is high-level block diagram of a thermal inkjet printhead assembly where data to the printhead is serialized; 
     FIG. 4 is a detailed block diagram of the electrical interface within a printhead assembly using a serial shift register for driving nozzles in the printhead; 
     FIG. 5 is a circuit diagram of the interconnection between the nozzle heaters and the nozzle drivers; 
     FIG. 6 is a block diagram of the interconnection of the printing system to the printhead; 
     FIG. 7 is a block diagram of a serial shift register configuration in a thermally steered inkjet printhead; 
     FIG. 8 is a block diagram of the data serial shift register configuration of a printhead; 
     FIG. 9 is a block diagram of the data serial shift registers in a printhead configured with small devices; 
     FIG. 10 is a block diagram of the data serial shift registers in a printhead configured with small devices which uses the second embodiment of the invention; 
     FIG. 11 is a block diagram of the data serial shift registers in a printhead configured with small devices which uses the third embodiment of the invention; 
     FIG. 12 is a top plan view schematic of printhead  10 ; 
     FIG. 13 shows a printhead assembly in perspective with the components arranged such that optimum cleaning and maintenance of the printhead is promoted; 
     FIG. 13A is a side view in schematic that illustrates the flow of ink droplets with respect to the printhead assembly shown in FIG. 13; 
     FIG. 14 is a schematic illustration in perspective of the printhead assembly of FIG. 12 installed on a printer carriage with a printhead cleaning station implemented as part of the printer; and 
     FIG. 14A is a side view in schematic that illustrates the printhead with an arrangement of electronics and printhead components to promote optimum cleaning when parked at the cleaning station. 
    
    
     Corresponding numerals and symbols in these figures refer to corresponding parts in the detailed description unless otherwise indicated. 
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. For example, the specific embodiments discussed herein are described in the context of nozzles used in an inkjet printhead which act as recording elements for recording images on a receiver medium, such as paper. It should understood, however, that other types of recording elements such as LEDs, thermal recording elements, and lasers, among others may benefit from the advances provided by the invention. The specific examples discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope or application of the invention. 
     Referring to FIG. 1, therein is shown a cross-section of an inkjet printhead  10  of the type commonly employed in thermal inkjet printers. More specifically, inkjet printhead  10  is a device that is commonly used to direct ink droplets or “drops” onto a receiver medium, such as paper, in an inkjet printer (not shown) and comprises one of several types of recording apparatus to which the invention may be applied. With the inkjet printhead  10 , ink drops exit rapidly enough so as to form an ink drop stream. The terms “ink drops”, “ink droplets”, “ink stream”, and “ink” will be used interchangeably throughout. 
     Inkjet printhead  10  includes an ink reservoir  20 , fluid-flow channels  18  and inlet/outlet tubes  16  which carry the ink  34  from the reservoir  20  to one or more recording elements or nozzles  24 . For convenience and conformity to the figures, the term “nozzles” will be used throughout although it should be understood that nozzle comprises but a single type of recording element to which the invention may be applied. Inkjet printhead  10  also comprises a mounting block  12 , a manifold  14 , and a substrate  22  which internally define the tubes  16  and fluid flow channels  18 , providing paths from the ink reservoir  20  to the nozzles  24 . Typically, the number of nozzles  24  is numerous providing an inkjet printhead with as many as 160, 320 or 1,280 nozzles, according to the design resolution and quality of printhead assembly. Typically, the nozzles may be positioned at 300 dots per inch or higher resolution. Those skilled in the art will, appreciate that the figures are not drawn to scale and have been enlarged in order to illustrate the major aspects of the inkjet printhead  10 . 
     Some inkjet printheads are made using thermally steered ink drop technology. As such, thermally steered inkjet printheads utilize thermal means to steer a continuous stream of ink drops ejected from each of a plurality of nozzle openings  26  in the inkjet printhead  10 . Each of the nozzle openings  26  is also referred to as an “orifice” or a “bore” in the art. For thermal steering, inkjet printhead  10  includes a plurality of upper heaters  28   a  and lower heaters  28   b  (also known as actuators), located about the nozzle openings  26  to permit thermal steering. Specifically, each pair of heaters  28   a ,  28   b  are predisposed about a single nozzle opening  26  for directing the flow of ink drops  34  through the nozzle openings  26 . For simplicity, the terms “heater” and “heaters”, “actuator” and “actuators”, will be used interchangeably and to refer to the singular and plural form of the corresponding part. For reference, U.S. Pat. No. 6,079,821 describes the operation of such a thermally steered inkjet printing in detail. Commonly assigned U.S. application Ser. No. 09/607,840, filed in the name of Lee et al, describes the operation of thermally steered drop-on-demand inkjet printing. 
     FIG. 2 is a cross-section view in perspective of a thermally steered inkjet printhead, such as printhead  10 , illustrating the use of heaters  28   a ,  28   b . Substrate  22  is attached to the gasket manifold  14  which, in turn, is bonded to the mounting block  12  in order to form the sub-assembly of inkjet printhead  10 . The mounting block  12  and the gasket manifold  14  together form a delivery system wherein fluid flow channels  18  are defined. Each fluid flow channel  18  provides a route for the ink stream  36  to exit the nozzle  24  through openings  26 . Predisposed about the nozzle opening  26  are heaters  28   a  and  28   b , which are used to direct the flow of ink stream  36  through the nozzle opening  26  via thermal deflection. 
     Typically, heaters  28   a ,  28   b  are arranged in a split-ring fashion about a corresponding nozzle opening  26 . That is, heaters  28   a ,  28   b  comprise an upper heater and a lower heater, respectively, that allow for thermal deflection of the ink stream  36  exiting the nozzle opening  26  onto a receiver medium, such as paper. Therefore, if an ink stream  36  directed to the upper direction is desired, the lower heater  28   b  is heated, causing the ink stream  36  to bend in the upper direction. If, however, an ink stream  36  directed to the lower direction is desired, then the upper heater  28   a  is heated, causing the ink stream  36  to bend to the lower direction. 
     A nozzle  24  comprises a nozzle cavity  32  for facilitating the flow of ink  34  from the reservoir  20 . In operation, ink from the nozzle cavity  32  is ejected through the opening  26  and exits as an ink stream  36 . At a distance removed from the printhead  10 , the ink stream  36  breaks up into ink drops traveling in the same direction as the ink stream  36 . Heat pulses applied to one or more heaters  28  cause the ink stream  36  to be directed in a printing direction or in a non-printing direction. Typically, ink is recycled from the non-printing direction using a gutter assembly (not shown) that directs the ink to a recycling unit (not shown). Thus, ink  34  travels from the ink reservoir  20  through the fluid flow channels  18  to the inlet/outlet tubes  16  in order to exit the nozzle openings  26 . 
     The flow of ink through the nozzle opening  26  is facilitated by a print engine including a print data driver that drives each nozzle  24  in order to cause ink to flow through a nozzle opening  26  in the desired direction. The electronics utilized to achieve this function include data path and control electronics that are responsible for generating the print data and controlling the flow of print data from the print engine to the printhead. In the design of a printhead electrical interface, it is desired to minimize the number of signals and interconnections of the interface. 
     FIG. 3 illustrates the use of data path and control electronics in a printer system  50  utilizing a thermal inkjet type printhead, such as printhead  10 , where data serialization is applied. Printer system  50  includes a printhead  10  which utilizes two heater elements per nozzle (not shown in FIG.  3 ). The printhead  10  applies ink to media  58  mounted on a drum  60 . In other configurations, the media may be mounted on a flatbed, and the printhead  10  positioned by way of a carriage to print onto the media  58 . Ink is supplied to the printhead  10  from an ink supply system  64 . The data path and control electronics  56  provides control signals  61  to the printhead  10  via interface  54 . 
     As shown, interface  54  includes a serial DATA line  62  which carries serialized data to the printhead  10 . The data is ported through a serial data shift register (discussed below) that restores the parallel nature of the data so that accurate printing is achieved. The data is routed so the assigned raster data is delivered to each of the heaters. Essentially, the data path and control electronics  56  ensures that while data for the next line of an image is being serially shifted down the serial shift register, current data for the line has been latched (saved) and is gated with an “enable” pulse to provide the correct amount of ink to be applied to the media being printed. 
     Physically, interface  54  includes a cable installed within the printer system  50  as part of the printhead assembly. The interface  54  also includes the various logic circuits, signal paths and discrete devices, and other similar components. Depending on the design resolution of the printhead  10 , such components can consume considerable real estate on the printhead assembly. Therefore, the present invention provides a printhead assembly that minimizes the number of interconnections between the data path and control electronics  56  and the printhead  10 . 
     With reference now to FIG. 4, therein is shown a first embodiment of the invention, in the form of a block diagram of an interface  80  contained within the printhead  10 . In essence, the interface  80  of the present invention uses serial shift registers to minimize the number of data lines required to drive the printhead  10 . The interface  80  is configured to operate between the data path and control electronics  56  and the printhead  10  of the printhead assembly in which it is used. It should be understood that the interface  80  of FIG. 4 only shows a small number of circuits compared to what would be used in a more typical printhead supporting a larger number of printing nozzles. 
     As shown, each serial shift register  100  is composed of N shift register stages  104  connected in a serial fashion. Likewise, each serial shift register  102  is composed of N shift register stages  106  connected in a serial fashion. In the configuration shown, each serial shift register  100  of N shift register stages  104  supports data transfer to the upper nozzles, while each serial shift registers  102  with N shift register stages  106  supplies data for the lower heaters. Data is clocked through the shift registers  104 ,  106  upon the occurrence of a rising edge on the “CLOCK” line  94  with a separate clock line implemented for upper and lower heaters. When data has been loaded to all the elements in the serial shift register  100 ,  102 , the Q outputs of the shift register stages  104 ,  106  are captured by use of latch registers  91  via LATCH lines  90 . The latched data then serves to validate whether heat is applied to or not applied at a particular nozzle heater  28 . The output  90   a  from the latch register  91  is gated using an AND logic element  86  with a pulse from an ENABLE line  88  and if a particular heater  28  is chosen for actuation, the latch output will be valid. The result of this AND operation is then used to switch on the nozzle heater driver  84  (FIG.  5 ), thus allowing the particular heater element to be biased with the heater power source. 
     In an actual printhead, the length of the N-bit serial shift registers  100 ,  102  is likely to be 32, 64, 128, 256, or 512 bits. The length of the N-bit serial shift register  100 ,  102  has a significant impact on the speed of access to an individual heater  28 . As previously explained, all N bits in the shift registers  100 ,  102  must be loaded before the LATCH lines  90  can be actuated to transfer the contents of the shift registers into the latch registers  91 . The period of time required to load an N-bit serial shift register limits how rapidly an individual heater can be addressed which, in turn, limits how rapidly a heater can be turned ON and then OFF. The minimum time required to address a heater is a function of the frequency of the clock signal on the CLOCK line  94  and the number, N, of shift register stages  104 ,  106  contained within the N-bit serial shift register  100  or  102 . This relationship is governed by Equation 1 as follows: 
     
       
         Minimum Heater Address Time=(1/ freq   clock )* N   Equ. 1  
       
     
     The upper limit in the choice of a clock frequency is often constrained by the speed of the shift register circuitry. To optimize the heater address time, the serial shift register,  100  or  102 , should contain fewer shift register stages  104  or  106 , to minimize the value of N. However, for a fixed number of nozzles in the printhead, if N is small there will be a larger number of serial shift registers  100  and  102 . In a conventional printhead design, each additional serial shift register requires an additional DATA line  92  and a corresponding additional electrical interconnection to the printhead. A large number of N-bit serial shift registers  100  and  102  will require a large number of electrical interconnections to the printhead, which can be costly or physically incompatible with the desire to manufacture small printheads. 
     Thus, a design conflict exists between minimizing heater address time and minimizing the number of interconnects to the printhead. To minimize the number of DATA lines  92  to the printhead, the number of shift register stages, N, in the N-bit serial shift registers  100 ,  102  would be maximized. However, a large value of N significantly increases the time to address an individual heater and may not be compatible with the fluids in use as well as the printing rates desired. Therefore, the present invention provides additional embodiments and methods of reducing the number of interconnects in the printhead assembly that take into account the heater address time. 
     With reference to FIG. 5, therein is shown the details of the nozzle heaters  28 , which will guide in understanding the additional embodiment of the invention. Heaters  28   a ,  28   b  are located at the opposing sides of a printhead nozzle  24 . An ENABLE line  88  and LATCHED_DATA line  90   a  are ANDED together at AND gate  86 . The output  122  of the AND gate  86  provides a signal to a heater driver  84  which applies power to either upper heater  28   a  or lower heater  28   b , as appropriate. In this example, either one of the two heaters  28   a  or  28   b  associated with a nozzle  24 , is capable of actuating the nozzle. Applying power to either the upper heater  28   a  or the lower heater  28   b  will cause the ink droplet stream to deflect away from the energized heater. 
     With reference now to FIG. 6, therein is shown a printhead assembly, denoted generally as  200 , with interconnections between the print data buffer  204  and the printhead  10 . The nozzle controller  206  processes the image path data to be compatible with the printhead  10  and provides the control signals necessary to operate the printhead  10 . The nozzle controller  206  also transfers the data and control signals via the print-data-and-control-signal bus  208  to the print data buffer  204  which provides a buffer function for all of the signals to the printhead  10 . The nozzle heater power supply  210  provides power to the printhead via power line  212 . 
     FIGS. 7,  8 ,  9 ,  10  and  11  are general block diagrams of respective different data shift register structure for a large printhead, such as printhead  10 , incorporating a significant number of heaters. For simplicity, the data output lines to the respective latching registers from each shift register stage, the CLOCK  94 , LATCH  90 , and ENABLE lines  88  have been omitted in each Figure. For the example of FIG. 7, there are 40 upper 32-bit serial shift registers  100  and 40 lower 32-bit serial shift registers  102 . Each 32-bit serial shift register  100  and  102  has a corresponding data input, DATAU0-DATAU39 and DATAL0-DETAL39, respectively. Thus, there are 80 DATA lines  92  to the printhead. 
     FIG. 8 is a block diagram of an interconnection scheme for a large printhead with a significant number of heaters. As in FIG. 7, 80 of the 32-bit serial shift registers are shown, however, the data structure has been reconfigured to decrease the number of DATA lines  92  by a factor of 4. Specifically, FIG. 8 shows 4 of the 32-bit shift registers serially connected to form a larger 128-bit serial shift register. Only 20 DATA lines  92  are required for this configuration, compared to 80 DATA lines  92  for FIG.  7 . To maintain the same heater address time as in FIG. 7, the frequency of the clock would need to be increased by a factor of 4 since the number of shift register stages in the larger serial shift register has increased from N=32 to N=128. However, there may be physical barriers which prevent the implementation of this architecture. Nevertheless, it is well known that large printheads are often constructed of small devices  108  which are used as modular building blocks for large printheads. 
     FIG. 9 is a block diagram of an interconnection scheme for a large printhead constructed with small devices  108 . In this example, each small device  108  contains two 32-bit serial shift registers for the upper serial shift register  100  and two 32-bit serial shift registers for the lower serial shift register  102 . Each small device  108  also contains 64 nozzles  24  and the associated 64 upper heaters  28   a  and 64 lower heaters  28   b . The small devices  108  provide an opportunity to build printheads in a modular fashion, providing flexibility in the size of the printhead. 
     As shown, the inputs (I) and outputs (O) of the serial shift register stages  100  and  102  allow the user to configure the printhead in a manner similar to FIG.  8 . However, because the interconnection of the serial shift registers of different small devices  108  would require additional connections to the printhead, the additional connections to the printhead would reduce the advantage of using long shift registers. The example printhead of FIG. 9 would require 60 DATA lines  92 . Some of these DATA lines  92  are jumpers from one small device  108  to the next small device  108 , which accounts for two DATA lines  92 . For small devices  108  containing more than two 32-bit registers for the upper serial shift register  100  and more than two 32-bit shift registers for the lower serial shift register  102 , the interconnection scheme shown in FIG. 9 would produce a proportionately greater reduction in interconnections to the printhead as to the connection scheme of FIG.  7 . 
     FIG. 10 is a block diagram of an interconnection scheme for a large printhead constructed with modular small devices  108 . Because of the use of the small device  108 , the printhead could be built in a modular fashion. In the embodiment of FIG. 10, the 32-bit shift registers in the lower serial shift register  102  are connected in serial fashion with the 32-bit shift registers in the upper serial shift register  100 . By serially connecting the 4 shift registers within the small device  108 , the length of the shift register is again 128-bits as it was in FIG. 9, however, this embodiment provides a significant reduction in interconnections to the printhead. For this example, 20 DATA lines  92  would be required to interconnect to the printhead. The seemingly simple approach shown in FIG. 10 is not obvious because the shift registers constructed in this manner contain different types of data, some for upper heaters and some for lower heaters. In addition, the information in the serial data for upper heater associated with nozzle  1  is separated by 32-bits from the data associated with the lower heater associated with nozzle  1 . The creation of this serial bit stream requires that the data associated with a given nozzle (upper heater and lower heater) be separated by the number of bits in the small serial shift registers (32-bits in this example). This can be accomplished by buffering and/or providing controlled delays or selection counters. 
     The embodiment shown in FIG. 10 shows that the upper and lower serial shift registers are serially connected to form a single serial shift register which is used to address the upper and lower heaters  28   a  and  28   b , respectively. Since there is only one serial shift register in the configuration of FIG. 10 (as opposed to two serial shift registers as shown in FIG. 4, FIG.  6  and FIG.  7 ), the number of clock lines and latch lines can also be reduced. In FIGS. 4,  6 , and  7 , two clock lines are required, UPPER_CLOCK  94  and LOWER_CLOCK  94 . In the embodiment of FIG. 10, there is a single serial shift register common to both the upper and lower heaters  28   a ,  28   b , such that the serial shift register can be driven with a single CLOCK line  94 . Thus, the present inventions provides an interconnection mechanism that eliminated the requirement of separate LATCH lines for each serial shift register used in the printhead assembly so that a single serial shift register common to upper and lower heaters can be driven with a single LATCH line  90 . In this way, the embodiment of FIG. 10 saves an additional two interconnections to the printhead by eliminating separate clock and latch connections. 
     With reference now to FIG. 11, there is shown a third embodiment interconnection scheme that minimizes interconnections in the printhead assembly according to the invention. Specifically, as shown in FIG. 10, there is required a 32 bit separation of the two data bits (associated with the two heaters  28   a ,  28   b  at a given nozzle  24 ) in the serial data stream. In contrast, FIG. 11 shows an interconnection of the upper serial shift register  100  and the lower serial shift register  102  where adjacent shift register stages  104 ,  106  in the combined shift register represent two heaters  28   a ,  28   b  associated with one nozzle  24 . The output of a lower shift register stage  106  is connected to input of the upper shift register stage  104  while the output of the upper shift register stage  104  is connected to the input of the lower shift register stage  106 , resulting in an alternating interconnection scheme. This alternating interconnection of the upper shift register stages  104  and lower shift register stage  106  allows the data bits associated with the two heaters  28   a ,  28   b  (associated with a particular nozzle  24 ) to be adjacent to each other in the data stream, rather than being separated by 32 bits, as was the case in FIG.  10 . 
     The creation of adjacent data bits in the data stream associated with the two heaters  28   a ,  28   b  for a given nozzle is much easier and simplifies the circuitry utilized to create the data stream. In this example all 4 of the 32-bit serial shift registers would be interleaved in the fashion described above, so the complete length of the shift register would be 128 bits. The 128-bit shift register would have one DATA line  92  input from outside the small device  108 . FIG. 11 shows that the interconnection scheme can be used to connect the shift register stages  104 ,  106  within one small device  108  in a modular printhead. Thus, the embodiment of FIG. 11 also minimizes the number of DATA lines  92  to a total of 20 for the printhead heater configuration originally described in FIG.  9 . 
     The embodiment shown in FIG. 11 shows the upper and lower shift registers as serially connected to form a single serial shift register which is used to address the upper and lower heaters  28   a  and  28   b , respectively, with respective outputs from respective shift register stages. Since there is only one serial shift register in the interconnection scheme of FIG. 11 (compared to two serial shift registers in the interconnection schemes of FIGS. 4,  6  and  7 ), the total number of CLOCK lines and LATCH lines is reduced. In FIGS. 4,  6 , FIG. 7, two clock lines are required, UPPER_CLOCK  94  and LOWER_CLOCK  94 . In the embodiment of FIG. 11, there is a single serial shift register common to the upper  28   a  and lower heaters  28   b  which can be driven with a single CLOCK line. In this way, the embodiment of FIG. 11 further reduces the number of interconnections of the printhead assembly and eliminates unnecessary clock and latch connections. 
     Table 1 shows the number of interconnects required for the various interconnections schemes of the invention (the interconnects required for the ENABLE signals  88  are not included in the table). 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Total number of interconnects for each embodiment of the invention. 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                 TOTAL 
               
               
                 INTERCONNECT 
                   
                   
                   
                   
                 INTERCON- 
               
               
                 OBJECTIVE 
                 FIG. 
                 DATA 
                 CLOCK 
                 LATCH 
                 NECTS 
               
               
                   
               
               
                 Maximum Address 
                 7 
                 80 
                 2 
                 2 
                 84 
               
               
                 Speed 
               
               
                 Continuous Head 
                 8 
                 20 
                 2 
                 2 
                 24 
               
               
                 Reduction 
               
               
                 Modular Head 
                 9 
                 60 
                 2 
                 2 
                 64 
               
               
                 Reduction 
               
               
                 Modular Head 
                 10  
                 20 
                 1 
                 1 
                 22 
               
               
                 Embodiment 2 
               
               
                 Modular Head 
                 11  
                 20 
                 1 
                 1 
                 22 
               
               
                 Embodiment 3 
               
               
                   
               
            
           
         
       
     
     With reference now to FIG. 12, therein is shown a top-down view of the inkjet printhead  10  arranged so that nozzles  24  and shift register stages  228  facilitate cleaning of the printhead  10  according to the invention. The printhead  10  comprises a plurality of nozzles  24  arranged in a straight line across the printing length of the printhead  10 . This forms an array for ejecting ink to form an image on a receiver member crossing nozzles  10 . 
     A plurality of actuators in the form heat drivers  84 , are provided such that each actuator  84  is associated with each respective nozzle  24 . For simplicity, the terms “actuator” and “heat drivers” shall be referred to interchangeably. Preferably, each actuator  84  is separately drivable to affect ejection of ink from the respective nozzle  24 . The plurality of data shift registers stages, denoted here as  228 , are then arranged such that each stage  228  is associated with a respective nozzle actuator  84  and nozzle actuators  84 , in turn, are associated with each nozzle heater element (either upper  28   a  or lower heater element  28   b ) and with different shift register stages  228 . The shift register stages  228  are adapted to shift data from one stage to a next stage to distribute data to the different stages  228 . Cleaning of the printhead  10  is provided by the positioning of the shift register stages  228  and their electrical interconnections using wire-bonding to bond pads  278  which are positioned on the same side of the printhead  10  substrate  22  such that enough room is provided for a cleaning mechanism (not shown) to reach the nozzles  24  and not cause damage to the shift register circuits on the printhead. FIG. 13A illustrates the position of the bond pads and wirebonds ( 278 ). The fact that shift register stages  228  are arranged on the same side as opposed to other areas of the printhead  10 , means that a space is provided for cleaning of the printhead  10  using well known cleaning techniques such as, for example, by using a brush, wiper, sprayer, vacuum suction device, and/or spitting of ink through the plurality of nozzles  24 . FIG. 13 shows an implementation of a printhead assembly  225  utilizing this shift register arrangement to promote printhead cleaning. 
     The assembly  225  shown in FIG. 13 shows that with this shift register arrangement, the external electrical parts are located up and away from the area of exposure to the ink droplet streams  270  and  275  shown in FIG.  13 A. These components include electrical circuits  230  that are part of electrical interface  54  that are external to the printhead. The circuit board  240  upon which the printhead  10 , and external electrical circuits  230  are located is also the site for cable connections  250  to bring in external data and control signals to the printhead assembly  225 . For applications using continuous inkjet actuators, this arrangement of electronics lends itself to the implementation of a gutter  260  to collect ink droplet streams during periods when there is no data to be written to media. Inkjet droplet stream  270  is directed to deposit on recording media for recording an image, while stream  275  is directed to be recycled using gutter  260  to collect the ink droplets. 
     FIG. 14 illustrates a typical printer arrangement  300  utilizing a carriage assembly  310 . The printhead assembly  225  is mounted upon the carriage assembly  310  which includes, for example, rails upon which the printhead assembly  225  is mounted for movement. Alternatively, the cleaning assembly may be moved to position itself in position for cleaning of the printhead. When it is desired to clean the printhead  10 , the printer&#39;s control system will position the printhead assembly  225  to face the cleaning station  280  to proceed with the cleaning of the print head. In this implementation, a vacuum cleaning system is shown. FIG. 14A shows the printhead parked at the cleaning station  280 , such that a rubber or other material shroud provides a vacuum tight enclosure about printhead  10 . Using the force of the vacuum, inkjet droplets that are located in the nozzle or on the outside surface of the nozzle are drawn into a collection vessel  298 . The vacuum is provided by vacuum pump  295 . Other forms of cleaning devices including blades, brushes, etc. may also be used. With the use of blades, it usually is desirable to provide the surface of the printhead with a planar surface. In the embodiment of FIG. 1, a passivation layer may be provided over substrate  22  to cover the heater elements  28   a ,  28   b and provide a planar surface to the printhead with openings for the nozzle openings. Preferably, the placement of the bond pads  278  on the printhead that are electrically connected to the shift registers near the nozzle will be at least 2 to 3 mm spacing from the nozzle openings to provide clearance for movement of the printhead assembly relative to the cleaning station and for positioning of the printhead assembly at the cleaning station. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. For example, the principles of the invention can be applied to other types of recording elements, such as LEDs, thermal recording elements, lasers, and other recording element configurations. As such, various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments. 
     PARTS LIST 
       10  . . . inkjet printhead 
       12  . . . mounting block 
       14  . . . manifold 
       16  . . . inlet/outlet tubes 
       18  . . . fluid flow channels 
       20  . . . ink reservoir 
       22  . . . substrate 
       24  . . . nozzle or nozzles 
       26  . . . nozzle opening 
       28  . . . heater or heaters 
       28   a  . . . upper heater 
       28   b  . . . lower heater 
       32  . . . nozzle cavity 
       34  . . . ink 
       36  . . . ink stream 
       50  . . . printer system 
       54  . . . interface 
       56  . . . data path and control electronics 
       58  . . . media 
       60  . . . drum 
       61  . . . CONTROL line 
       62  . . . DATA line 
       64  . . . ink supply 
       80  . . . interface 
       84  . . . heater drivers 
       86  . . . AND gate logic element 
       88  . . . ENABLE line 
       90  . . . LATCH line 
       90   a  . . . Latched Data 
       92  . . . DATA line 
       94  . . . CLOCK line 
       100  . . . serial shift register 
       102  . . . serial shift register 
       104  . . . shift register stage 
       106  . . . shift register stage 
       108  . . . small device 
       122  . . . output 
       200  . . . print head assembly 
       204  . . . print data buffer 
       206  . . . nozzle controller 
       208  . . . print-data-and-control-signal bus 
       210  . . . nozzle heater power supply 
       212  . . . power line 
       228  . . . shift register stages 
       225  . . . print head assembly 
       230  . . . external electrical circuits 
       240  . . . print head circuit board 
       250  data and control signal connectors 
       260  gutter 
       270  ink droplet stream to media 
       275  ink droplet stream to gutter 
       278  bond pads and wire bonds 
       280  printhead cleaning station 
       295  vacuum pump 
       298  ink collection bottle 
       300  printer system using carriage 
       310  printer carriage