Patent Publication Number: US-10315419-B2

Title: Method for assigning communication addresses

Description:
FIELD OF THE INVENTION 
     This invention pertains to the field of inkjet printing and more particularly to a method for allocating communication addresses in a modular printhead assembly including a plurality of removable jetting modules. 
     BACKGROUND OF THE INVENTION 
     In the field of high speed inkjet printing, it is desirable to be able to print across the width of the print media in a single pass of the print media past a print station. However, for many applications the desired print width exceeds the width of the available printheads. It is therefore necessary to arrange an array of printheads such that each printhead in the array prints a print swath, and the set of print swaths cover the desired print width. Such arrays of printheads are commonly configured in lineheads that include alignment hardware to maintain the desired relative alignment of the printheads, as well as fluid and electronic hardware to support the printheads within the linehead. As new applications are being developed for the use of high speed inkjet printing technology, such as the printing of labels, books, magazines, packaging materials, and décor (such as wallpaper, and laminate material for flooring and countertops), there is a need to develop an increasing number of lineheads to accommodate the increasing number of desired print widths. 
     To simplify the development of the various lineheads, it is desirable to employ a modular design approach for printhead alignment hardware and the supporting fluid and electronic hardware. In an exemplary configuration, each of the modules includes three printheads together with their supporting fluid and electrical hardware. By combining different numbers of modules together, lineheads of different sizes can be created. 
     Even though the printheads are assembled into modules within the lineheads, it is still desirable to be able to separately control and communicate each of the individual printheads within the linehead. There is also a need to be able to remove and replace individual printheads within the lineheads without shutting down the other printheads in the linehead. To achieve these goals, there is a need to automatically and adaptively assign communication addresses to facilitate communication of control signals and data with the various system components. 
     SUMMARY OF THE INVENTION 
     The present invention represents a method for assigning communication addresses to devices within a production system, includes: 
     providing a system controller for controlling the production system, the system controller including a communication port; 
     providing a plurality of communication distribution devices, each of the communication distribution devices including:
         first and second primary communication ports through which the communication distribution device can be connected to another communication distribution device or to the system controller;   a plurality of secondary communication ports, the plurality of secondary communication ports being arranged in a defined sequence; and   means to detect whether the communication distribution device is connected by means of the first primary communication port or the second primary communication port to another one of the plurality of communication distribution devices or to the system controller;       

     connecting the plurality of communication distribution devices together using the first and second primary communication ports in a daisy chain arrangement to form a connected sequence of communication distribution devices, wherein a first communication distribution device in the sequence of communication distribution devices is connected to the system controller via one of its first and second primary communication ports such that each communication distribution device is enabled to communicate with the system controller; 
     providing a plurality of secondary devices; 
     connecting each of the secondary devices to one of the secondary communication ports of one of the communications distribution boards; 
     specifying a first set of communication addresses from which communication addresses can be assigned to each of the communication distribution devices, the communication addresses of the first set of communication addresses having a prescribed sequence; 
     specifying a second set of communication addresses distinct from the first set of communication addresses, from which communication addresses can be assigned to each of the secondary devices, the communication addresses of the second set of communication addresses having a prescribed sequence; 
     wherein the system controller provides a signal to a first communication distribution device in the connected sequence of communication distribution devices via one of its first and the second primary communication ports; 
     upon detecting the signal from the system controller by the first communication distribution device, the first communication distribution board:
         assigns itself a first communication address in the prescribed sequence of the first set of communication addresses;   sequentially assigns communication addresses from the prescribed sequence of the second set of communication addresses to the secondary devices connected to its secondary communication ports; and   communicates information to the next communication distribution device in the connected sequence of communication distribution devices via one of its first and second primary communication ports, the information specifying that the next communication distribution device should assign itself a next communication address in the prescribed sequence of the first set of communication addresses and specifying the next available communication address in the prescribed sequence of the second set of communication addresses that is available to be assigned to the secondary devices connected to the next communication distribution device;       

     upon receiving the communicated information from the previous communication distribution device in the connected sequence of communication distribution devices each subsequent communication distribution device in the connected sequence of communication distribution devices:
         assigns itself the received communication address in the prescribed sequence of the first set of communication addresses;   sequentially assigns communication addresses from the prescribed sequence of the second set of communication addresses to the secondary devices connected to its secondary communication ports starting with the received next available communication address; and   unless it is the last communication distribution device in the connected sequence of communication distribution devices, communicates information to the next communication distribution device in the connected sequence of communication distribution devices via one of its first and second primary communication ports, the information specifying that the next communication distribution device should assign itself a next communication address in the prescribed sequence of the first set of communication addresses and specifying the next available communication address in the prescribed sequence of the second set of communication addresses that is available to be assigned to the secondary devices connected to the next communication distribution device; and       

     transmitting information from each communication distribution device in the connected sequence of communication distribution devices communicate to the system controller, the information specifying the communication addresses assigned to each communication distribution device and the communication addresses assigned to each of the secondary devices connected to each communication distribution device. 
     This invention has the advantage that it enables a plurality of secondary devices to be connected through communication distribution devices to a system controller and automatically assigned communication addresses in a manner that provides the system controller with unambiguous location information for the individual secondary devices. 
     It has the additional advantage that it provides a means for detecting when individual secondary devices or communication distribution devices are either connected to or disconnected from the communication network. Furthermore, the method enables communication addresses to be assigned or unassigned to the newly connected or disconnected devices, while not interfering with communication to other devices that are connected to the communication network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified block schematic diagram of an exemplary continuous inkjet system; 
         FIG. 2  shows an image of a liquid jet being ejected from a drop generator and its subsequent break off into drops with a regular period; 
         FIG. 3  shows a cross sectional of an inkjet printhead of the continuous liquid ejection system in accordance with the present invention; 
         FIG. 4  shows an exemplary timing diagram illustrating drop formation pulses, the charging-electrode waveform, and the break-off of drops; 
         FIG. 5  shows a top view of an exemplary printhead assembly including a staggered array of jetting modules; 
         FIG. 6  shows an exemplary modular printhead assembly including a plurality of printhead modules mounted onto a central rail assembly in accordance with an exemplary embodiment; 
         FIG. 7  shows an exemplary linehead including a single modular printhead assembly positioned over a web of print media; 
         FIG. 8  shows an exemplary linehead including two modular printhead assemblies positioned over a web of print media; 
         FIG. 9  shows an exemplary linehead including four modular printhead assemblies positioned over a web of print media, with one of the modular printhead assemblies not being completely populated with printhead modules; 
         FIG. 10  shows an exemplary linehead including four modular printhead assemblies positioned over a web of print media, with an increased spacing between the center two modular printhead assemblies; 
         FIG. 11  shows an exemplary linehead including a single modular printhead assembly positioned over a web of print media, the modular printhead assembly having two printhead modules aligned to print on the same print swath; 
         FIG. 12  shows a block diagram of exemplary linehead electronics with a plurality of communication distribution devices and attached secondary devices, a system controller being connected to the rightmost communication distribution device; 
         FIG. 13  shows a block diagram of the exemplary linehead electronics with a plurality of communication distribution devices and attached secondary devices, a system controller being connected to the leftmost communication distribution device; 
         FIG. 14  shows additional details for the linehead electronics of  FIG. 13 ; and 
         FIG. 15  shows a block diagram of the linehead electronics with a plurality of communication distribution devices and attached secondary devices, the communication distribution device having an alternate configuration of secondary communication ports. 
     
    
    
     It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale. Identical reference numerals have been used, where possible, to designate identical features that are common to the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. References to “a particular embodiment” and the like refer to features that are present in at least one embodiment of the invention. Separate references to “an embodiment” or “particular embodiments” or the like do not necessarily refer to the same embodiment or embodiments; however, such embodiments are not mutually exclusive, unless so indicated or as are readily apparent to one of skill in the art. The use of singular or plural in referring to the “method” or “methods” and the like is not limiting. It should be noted that, unless otherwise explicitly noted or required by context, the word “or” is used in this disclosure in a non-exclusive sense. 
     The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of the ordinary skills in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention. 
     The present invention is directed at providing an effective means for a controller to communicate with individual devices that are part of a production system. In particular, the invention is directed toward assigning communications addresses in a production system in which some of the devices are communication hubs or communication distribution devices through which the controller can communicate with a plurality of secondary devices. The invention supports configurations in which a particular secondary device in the production system may be deactivated or removed from the production system while other secondary devices in the production system are still active and in communications with the system controller. 
     The invention will be described in terms of an embodiment in which the production system is an inkjet printing system including a plurality of inkjet printheads in communications with a system controller. The invention, however, is not limited to inkjet printing, but can also be used for other types of production devices. Another exemplary embodiment of a production system includes a plurality of robotic devices, in which at least some of the robotic devices are equipped with a plurality of specialty end of arm devices that each can communicate with the system controller via the robotic device. The system controller must be able to communicate both with the robotic device and also with the plurality of end of arm devices. 
     As described herein, exemplary embodiments of the present invention provide a printhead or printhead components typically used in inkjet printing systems. However, many other applications are emerging which use printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. As such, as described herein, the terms “liquid” and “ink” refer to any material that can be ejected by the printhead or printhead components described below. 
     Referring to  FIG. 1 , a continuous printing system  20  includes an image source  22  such as a scanner or computer which provides raster image data, outline image data in the form of a page description language, or other forms of digital image data. This image data is converted to half-toned bitmap image data by an image processing unit (image processor)  24  which also stores the image data in memory. A plurality of drop-forming transducer control circuits  26  reads data from the image memory and apply time-varying electrical pulses to a drop-forming transducers  28  that are associated with one or more nozzles of a printhead  30 . These pulses are applied at an appropriate time, and to the appropriate nozzles, so that drops formed from a continuous inkjet stream will form spots on a print medium  32  in the appropriate position designated by the data in the image memory. 
     Print medium  32  is moved relative to the printhead  30  by a print medium transport system  34 , which is electronically controlled by a media transport controller  36  in response to signals from a speed measurement device  35 . The media transport controller  36  is in turn is controlled by a micro-controller  38 . The print medium transport system  34  shown in  FIG. 1  is a schematic only, and many different mechanical configurations are possible. For example, a transfer roller could be used in the print medium transport system  34  to facilitate transfer of the ink drops to the print medium  32 . Such transfer roller technology is well known in the art. In the case of page width printheads, it is most convenient to move the print medium  32  along a media path past a stationary printhead. However, in the case of scanning print systems, it is often most convenient to move the printhead along one axis (the sub-scanning direction) and the print medium  32  along an orthogonal axis (the main scanning direction) in a relative raster motion. 
     Ink is contained in an ink reservoir  40  under pressure. In the non-printing state, continuous inkjet drop streams are unable to reach print medium  32  due to an ink catcher  72  that blocks the stream of drops, and which may allow a portion of the ink to be recycled by an ink recycling unit  44 . The ink recycling unit  44  reconditions the ink and feeds it back to the ink reservoir  40 . Such ink recycling units are well known in the art. The ink pressure suitable for optimal operation will depend on a number of factors, including geometry and thermal properties of the nozzles and thermal properties of the ink. A constant ink pressure can be achieved by applying pressure to the ink reservoir  40  under the control of an ink pressure regulator  46 . Alternatively, the ink reservoir  40  can be left unpressurized, or even under a reduced pressure (vacuum), and a pump can be employed to deliver ink from the ink reservoir  40  under pressure to the printhead  30 . In such an embodiment, the ink pressure regulator  46  can include an ink pump control system. The ink is distributed to the printhead  30  through an ink channel  47 . The ink preferably flows through slots or holes etched through a silicon substrate of printhead  30  to its front surface, where a plurality of nozzles and drop-forming transducers, for example, heaters, are situated. When printhead  30  is fabricated from silicon, the drop-forming transducer control circuits  26  can be integrated with the printhead  30 . The printhead  30  also includes a deflection mechanism  70  which is described in more detail below with reference to  FIGS. 2 and 3 . 
     Referring to  FIG. 2 , a schematic view of continuous liquid printhead  30  is shown. A jetting module  48  of printhead  30  includes an array of nozzles  50  formed in a nozzle plate  49 . In  FIG. 2 , nozzle plate  49  is affixed to the jetting module  48 . Alternatively, the nozzle plate  49  can be integrally formed with the jetting module  48 . Liquid, for example, ink, is supplied to the nozzles  50  via ink channel  47  at a pressure sufficient to form continuous liquid streams  52  (sometimes referred to as filaments) from each nozzle  50 . In  FIG. 2 , the array of nozzles  50  extends into and out of the figure. 
     Jetting module  48  is operable to cause liquid drops  54  to break off from the liquid stream  52  in response to image data. To accomplish this, jetting module  48  includes a drop stimulation or drop-forming transducer  28  (e.g., a heater, a piezoelectric actuator, or an electrohydrodynamic stimulation electrode), that, when selectively activated, perturbs the liquid stream  52 , to induce portions of each filament to break off and coalesce to form the drops  54 . Depending on the type of transducer used, the transducer can be located in or adjacent to the liquid chamber that supplies the liquid to the nozzles  50  to act on the liquid in the liquid chamber, can be located in or immediately around the nozzles  50  to act on the liquid as it passes through the nozzle, or can be located adjacent to the liquid stream  52  to act on the liquid stream  50  after it has passed through the nozzle  50 . 
     In  FIG. 2 , drop-forming transducer  28  is a heater  51 , for example, an asymmetric heater or a ring heater (either segmented or not segmented), located in the nozzle plate  49  on one or both sides of the nozzle  50 . This type of drop formation is known and has been described in, for example, U.S. Pat. No. 6,457,807 (Hawkins et al.); U.S. Pat. No. 6,491,362 (Jeanmaire); U.S. Pat. No. 6,505,921 (Chwalek et al.); U.S. Pat. No. 6,554,410 (Jeanmaire et al.); U.S. Pat. No. 6,575,566 (Jeanmaire et al.); U.S. Pat. No. 6,588,888 (Jeanmaire et al.); U.S. Pat. No. 6,793,328 (Jeanmaire); U.S. Pat. No. 6,827,429 (Jeanmaire et al.); and U.S. Pat. No. 6,851,796 (Jeanmaire et al.), each of which is incorporated herein by reference. 
     Typically, one drop-forming transducer  28  is associated with each nozzle  50  of the nozzle array. However, in some configurations, a drop-forming transducer  28  can be associated with groups of nozzles  50  or all of the nozzles  50  in the nozzle array. 
     Referring to  FIG. 2  the printing system has associated with it, a printhead  30  that is operable to produce, from an array of nozzles  50 , an array of liquid streams  52 . A drop-forming device is associated with each liquid stream  52 . The drop-formation device includes a drop-forming transducer  28  and a drop-formation waveform source  55  that supplies a drop-formation waveform  60  to the drop-forming transducer  28 . The drop-formation waveform source  55  is a portion of the mechanism control circuits  26 . In some embodiments in which the nozzle plate is fabricated of silicon, the drop-formation waveform source  55  is formed at least partially on the nozzle plate  49 . The drop-formation waveform source  55  supplies a drop-formation waveform  60 , which typically includes a sequence of pulses having a fundamental frequency f o  and a fundamental period of T o =1/f o , to the drop-formation transducer  28 , which produces a modulation in the liquid jet with a wavelength λ. The modulation grows in amplitude to cause portions of the liquid stream  52  to break off into drops  54 . Through the action of the drop-formation device, a sequence of drops  54  is produced. In accordance with the drop-formation waveform  60 , the drops  54  are formed at the fundamental frequency f o  with a fundamental period of T o =1/f o . In  FIG. 2 , liquid stream  52  breaks off into drops with a regular period at breakoff location  59 , which is a distance, called the break off length, BL from the nozzle  50 . The distance between a pair of successive drops  54  is essentially equal to the wavelength λ of the perturbation on the liquid stream  52 . The stream of drops  54  formed from the liquid stream  52  follow an initial trajectory  57 . 
     The break off time of the droplet for a particular printhead can be altered by changing at least one of the amplitude, duty cycle, or number of the stimulation pulses to the respective resistive elements surrounding a respective resistive nozzle orifice. In this way, small variations of either pulse duty cycle or amplitude allow the droplet break off times to be modulated in a predictable fashion within ±one-tenth the droplet generation period. 
     Also, shown in  FIG. 2 , is a charging device  61  comprising charging electrode  62  and charging-electrode waveform source  63 . The charging electrode  62  associated with the liquid jet is positioned adjacent to the break off point  59  of the liquid stream  52 . If a voltage is applied to the charging electrode  62 , electric fields are produced between the charging electrode and the electrically grounded liquid jet, and the capacitive coupling between the two produces a net charge on the end of the electrically conductive liquid stream  52 . (The liquid stream  52  is grounded by means of contact with the liquid chamber of the grounded drop generator.) If the end portion of the liquid jet breaks off to form a drop while there is a net charge on the end of the liquid stream  52 , the charge of that end portion of the liquid stream  52  is trapped on the newly formed drop  54 . 
     The voltage on the charging electrode  62  is controlled by the charging-electrode waveform source  63 , which provides a charging-electrode waveform  64  operating at a charging-electrode waveform  64  period  80  (shown in  FIG. 4 ). The charging-electrode waveform source  63  provides a varying electrical potential between the charging electrode  62  and the liquid stream  52 . The charging-electrode waveform source  63  generates a charging-electrode waveform  64 , which includes a first voltage state and a second voltage state; the first voltage state being distinct from the second voltage state. An example of a charging-electrode waveform is shown in part B of  FIG. 4 . The two voltages are selected such that the drops  54  breaking off during the first voltage state acquire a first charge state and the drops  54  breaking off during the second voltage state acquire a second charge state. The charging-electrode waveform  64  supplied to the charging electrode  62  is independent of, or not responsive to, the image data to be printed. The charging device  61  is synchronized with the drop-formation device using a conventional synchronization device  27 , which is a portion of the control circuits  26 , (see  FIG. 1 ) so that a fixed phase relationship is maintained between the charging-electrode waveform  64  produced by the charging-electrode waveform source  63  and the clock of the drop-formation waveform source  55 . As a result, the phase of the break off of drops  54  from the liquid stream  52 , produced by the drop-formation waveforms  92 - 1 ,  92 - 2 ,  92 - 3 ,  94 - 1 ,  94 - 2 ,  94 - 3 ,  94 - 4  (see  FIG. 4 ), is phase locked to the charging-electrode waveform  64 . As indicated in  FIG. 4 , there can be a phase shift  108 , between the charging-electrode waveform  64  and the drop-formation waveforms  92 - 1 ,  92 - 2 ,  92 - 3 ,  94 - 1 ,  94 - 2 ,  94 - 3 ,  94 - 4 . 
     With reference now to  FIG. 3 , printhead  30  includes a drop-forming transducer  28  which creates a liquid stream  52  that breaks up into ink drops  54 . Selection of drops  54  as printing drops  66  or non-printing drops  68  will depend upon the phase of the droplet break off relative to the charging electrode voltage pulses that are applied to the to the charging electrode  62  that is part of the deflection mechanism  70 , as will be described below. The charging electrode  62  is variably biased by a charging-electrode waveform source  63 . The charging-electrode waveform source  63  provides a charging-electrode waveform  64 , in the form of a sequence of charging pulses. The charging-electrode waveform  64  is periodic, having a charging-electrode waveform period  80  ( FIG. 4 ). 
     An embodiment of a charging-electrode waveform  64  is shown in part B of  FIG. 4 . The charging-electrode waveform  64  comprises a first voltage state  82  and a second voltage state  84 . Drops breaking off during the first voltage state  82  are charged to a first charge state and drops breaking off during the second voltage state  84  are charged to a second charge state. The second voltage state  84  is typically at a high level, biased sufficiently to charge the drops  54  as they break off. The first voltage state  82  is typically at a low level relative to the printhead  30  such that the first charge state is relatively uncharged when compared to the second charge state. An exemplary range of values of the electrical potential difference between the first voltage state  82  and a second voltage state  84  is 50 to 300 volts and more preferably 90 to 150 volts. 
     Returning to a discussion of  FIG. 3 , when a relatively high level voltage or electrical potential is applied to the charging electrode  62  and a drop  54  breaks off from the liquid stream  52  in front of the charging electrode  62 , the drop  54  acquires a charge and is deflected by deflection mechanism  70  towards the ink catcher  72  as non-printing drop  68 . The non-printing drops  68  that strike the catcher face  74  form an ink film  76  on the face of the ink catcher  72 . The ink film  76  flows down the catcher face  74  and enters liquid channel  78  (also called an ink channel), through which it flows to the ink recycling unit  44 . The liquid channel  78  is typically formed between the body of the ink catcher  72  and a lower plate  79 . 
     Deflection occurs when drops  54  break off from the liquid stream  52  while the potential of the charging electrode  62  is provided with an appropriate voltage. The drops  54  will then acquire an induced electrical charge that remains upon the droplet surface. The charge on an individual drop  54  has a polarity opposite that of the charging electrode  62  and a magnitude that is dependent upon the magnitude of the voltage and the coupling capacitance between the charging electrode  62  and the drop  54  at the instant the drop  54  separates from the liquid jet. This coupling capacitance is dependent in part on the spacing between the charging electrode  62  and the drop  54  as it is breaking off. It can also be dependent on the vertical position of the breakoff point  59  relative to the center of the charge electrode  62 . After the charged drops  54  have broken away from the liquid stream  52 , they continue to pass through the electric fields produced by the charge plate. These electric fields provide a force on the charged drops deflecting them toward the charging electrode  62 . The charging electrode  62 , even though it cycled between the first and the second voltage states, thus acts as a deflection electrode to help deflect charged drops away from the initial trajectory  57  and toward the ink catcher  72 . After passing the charging electrode  62 , the drops  54  will travel in close proximity to the catcher face  74  which is typically constructed of a conductor or dielectric. The charges on the surface of the non-printing drops  68  will induce either a surface charge density charge (for a catcher face  74  constructed of a conductor) or a polarization density charge (for a catcher face  74  constructed of a dielectric). The induced charges on the catcher face  74  produce an attractive force on the charged non-printing drops  68 . The attractive force on the non-printing drops  68  is identical to that which would be produced by a fictitious charge (opposite in polarity and equal in magnitude) located inside the ink catcher  72  at a distance from the surface equal to the distance between the ink catcher  72  and the non-printing drops  68 . The fictitious charge is called an image charge. The attractive force exerted on the charged non-printing drops  68  by the catcher face  74  causes the charged non-printing drops  68  to deflect away from their initial trajectory  57  and accelerate along a non-print trajectory  86  toward the catcher face  74  at a rate proportional to the square of the droplet charge and inversely proportional to the droplet mass. In this embodiment, the ink catcher  72 , due to the induced charge distribution, comprises a portion of the deflection mechanism  70 . In other embodiments, the deflection mechanism  70  can include one or more additional electrodes to generate an electric field through which the charged droplets pass so as to deflect the charged droplets. For example, an optional single biased deflection electrode  71  in front of the upper grounded portion of the catcher can be used. In some embodiments, the charging electrode  62  can include a second portion on the second side of the jet array, denoted by the dashed line charging electrode  62 ′, which supplied with the same charging-electrode waveform  64  as the first portion of the charging electrode  62 . 
     In the alternative, when the drop-formation waveform  60  applied to the drop-forming transducer  28  causes a drop  54  to break off from the liquid stream  52  when the electrical potential of the charging electrode  62  is at the first voltage state  82  ( FIG. 4 ) (i.e., at a relatively low potential or at a zero potential), the drop  54  does not acquire a charge. Such uncharged drops are unaffected during their flight by electric fields that deflect the charged drops. The uncharged drops therefore become printing drops  66 , which travel in a generally undeflected path along the trajectory  57  and impact the print medium  32  to form print dots  88  on the print medium  32 , as the recoding medium is moved past the printhead  30  at a speed V m . The charging electrode  62 , deflection electrode  71  and ink catcher  72  serve as a drop selection system  69  for the printhead  30 . 
       FIG. 4  illustrates how selected drops can be printed by the control of the drop-formation waveforms supplied to the drop-forming transducer  28 . Section A of  FIG. 4  shows a drop-formation waveform  60  formed as a sequence that includes three drop-formation waveforms  92 - 1 ,  92 - 2 ,  92 - 3 , and four drop-formation waveforms  94 - 1 ,  94 - 2 ,  94 - 3 ,  94 - 4 . The drop-formation waveforms  94 - 1 ,  94 - 2 ,  94 - 3 ,  94 - 4  each have a period  96  and include a pulse  98 , and each of the drop-formation waveforms  92 - 1 ,  92 - 2 ,  92 - 3  have a longer period  100  and include a longer pulse  102 . In this example, the period  96  of the drop-formation waveforms  94 - 1 ,  94 - 2 ,  94 - 3 ,  94 - 4  is the fundamental period T o , and the period  100  of the drop-formation waveforms  92 - 1 ,  92 - 2 ,  92 - 3  is twice the fundamental period, 2T o . The drop-formation waveforms  94 - 1 ,  94 - 2 ,  94 - 3 ,  94 - 4  each cause individual drops to break off from the liquid stream. The drop-formation waveforms  92 - 1 ,  92 - 2 ,  92 - 3 , due to their longer period, each cause a larger drop to be formed from the liquid stream. The larger drops  54  formed by the drop-formation waveforms  92 - 1 ,  92 - 2 ,  92 - 3  each have a volume that is approximately equal to twice the volume of the drops  54  formed by the drop-formation waveforms  94 - 1 ,  94 - 2 ,  94 - 3 ,  94 - 4 . 
     As previously mentioned, the charge induced on a drop  54  depends on the voltage state of the charging electrode at the instant of drop breakoff. The B section of  FIG. 4  shows the charging-electrode waveform  64  and the times, denoted by the diamonds, at which the drops  54  break off from the liquid stream  52 . The waveforms  92 - 1 ,  92 - 2 ,  92 - 3  cause large drops  104 - 1 ,  104 - 2 ,  104 - 3  to break off from the liquid stream  52  while the charging-electrode waveform  64  is in the second voltage state  84 . Due to the high voltage applied to the charging electrode  62  in the second voltage state  84 , the large drops  104 - 1 ,  104 - 2 ,  104 - 3  are charged to a level that causes them to be deflected as non-printing drops  68  such that they strike the catcher face  74  of the ink catcher  72  in  FIG. 3 . These large drops may be formed as a single drop (denoted by the double diamond for  104 - 1 ), as two drops that break off from the liquid stream  52  at almost the same time that subsequently merge to form a large drop (denoted by two closely spaced diamonds for  104 - 2 ), or as a large drop that breaks off from the liquid stream that breaks apart and then merges back to a large drop (denoted by the double diamond for  104 - 3 ). The waveforms  94 - 1 ,  94 - 2 ,  94 - 3 ,  94 - 4  cause small drops  106 - 1 ,  106 - 2 ,  106 - 2 ,  106 - 3 ,  106 - 4  to form. Small drops  106 - 1  and  106 - 3  break off during the first voltage state  82 , and therefore will be relatively uncharged; they are not deflected into the ink catcher  72 , but rather pass by the ink catcher  72  as printing drops  66  and strike the print media  32  (see  FIG. 3 ). Small drops  106 - 2  and  104 - 4  break off during the second voltage state  84  and are deflected to strike the ink catcher  74  as non-printing drops  68 . The charging-electrode waveform  64  is not controlled by the pixel data to be printed, while the drop-formation waveform  60  is determined by the print data. This type of drop deflection is known and has been described in, for example, U.S. Pat. No. 8,585,189 (Marcus et al.); U.S. Pat. No. 8,651,632 (Marcus); U.S. Pat. No. 8,651,633 (Marcus et al.); U.S. Pat. No. 8,696,094 (Marcus et al.); and U.S. Pat. No. 8,888,256 (Marcus et al.), each of which is incorporated herein by reference. 
       FIG. 5  shows a diagram of an exemplary inkjet printhead assembly  112 . The printhead assembly  112  includes a plurality of jetting modules  200  arranged across a width dimension of the print medium  32  in a staggered array configuration. The width dimension of the print medium  32  is the dimension in cross-track direction  118 , which is perpendicular to in-track direction  116  (i.e., the motion direction of the print medium  32 ). Such printhead assemblies  112  are sometimes referred to as “lineheads.” 
     Each of the jetting modules  200  includes a plurality of inkjet nozzles arranged in nozzle array  202 , and is adapted to print a swath of image data in a corresponding printing region  132 . Commonly, the jetting modules  200  are arranged in a spatially-overlapping arrangement where the printing regions  132  overlap in overlap regions  134 . Each of the overlap regions  134  has a corresponding centerline  136 . In the overlap regions  134 , nozzles from more than one nozzle array  202  can be used to print the image data. 
     Stitching is a process that refers to the alignment of the printed images produced from jetting modules  200  for the purpose of creating the appearance of a single page-width line head. In the exemplary arrangement shown in  FIG. 5 , three printheads  200  are stitched together at overlap regions  134  to form a page-width printhead assembly  112 . The page-width image data is processed and segmented into separate portions that are sent to each jetting module  200  with appropriate time delays to account for the staggered positions of the jetting modules  200 . The image data portions printed by each of the jetting modules  200  is sometimes referred to as “swaths.” Stitching systems and algorithms are used to determine which nozzles of each nozzle array  202  should be used for printing in the overlap region  134 . Preferably, the stitching algorithms create a boundary between the printing regions  132  that is not readily detected by eye. One such stitching algorithm is described in commonly-assigned U.S. Pat. No. 7,871,145 to Enge, which is incorporated herein by reference. 
     The two lines of nozzle arrays  202  in the staggered arrangement are separated by a nozzle array spacing  138 . It has been found that larger nozzle array spacing  138  result in large amplitudes of the stitching variation, even after stitching correction algorithms are applied. Therefore, it is desirable to reduce the nozzle array spacing  138  as much as possible. With prior art arrangements for mounting the nozzle arrays  202 , such as that described in the aforementioned, commonly-assigned U.S. Pat. No. 8,226,215 to Bechler et al. there is a limit to how small the nozzle array spacing  138  can be. These methods also get expensive and cumbersome when it is necessary to use increasing numbers of jetting modules in the line head to accommodate larger and larger print widths. These limitations are addressed with the modular inkjet printhead assembly illustrated in  FIG. 6 . 
       FIG. 6  shows an exemplary modular printhead assembly  190  including a plurality of printhead modules  260  in accordance with the present invention. More details about such modular printhead assemblies can be found in commonly-assigned U.S. Pat. No. 9,527,319 to Brazas et al., U.S. Pat. No. 9,566,798 to Tunmore et al., U.S. Pat. No. 9,623,689 to Piatt et al., and U.S. patent application Ser. No. 15/590,070 to Tunmore et al., each of which is incorporated herein by reference. In the configuration of  FIG. 6 , each printhead module  260  includes a jetting module  200  and a mounting assembly  240 . The printhead modules  260  are mounted onto a central rail assembly  220 , which includes a rod  224  attached onto the print-medium-facing side of a beam  222  that faces the print medium  32 . The print medium  32  moves past the printhead assembly  190  in an in-track direction  116 . The rail assembly  240  extends across the width of a print zone on the print medium  32  in a cross-track direction  118 . The print zone corresponds to the portion of the print medium  32  onto which the printhead assembly  190  is adapted to print. 
     In the illustrated configuration, the printhead assembly  190  includes three printhead modules  260 , with one being mounted on a downstream side  226  of the beam  222 , and two being mounted on an upstream side  228  of the beam  222 . An advantageous feature of this modular printhead assembly  190  design is that wider print media  32  can be supported by simply extending the length of the rail assembly  220  and adding additional printhead modules  260 . By alternating the printhead modules  260  between the downstream side  226  and the upstream side  228  of the beam  222 , the associated nozzle arrays  202  can be stitched together with appropriate overlap regions  134  (see  FIG. 5 ). 
     Fluid system connectors  216  and electrical connectors  217  are provided for each of the printhead modules  260  to make connections with external system components. While not shown in  FIG. 6 , there are fluid system components and control electronics associated with each printhead module  260 , which are ideally located within the linehead close to their associated printhead module  260 . These include ink pressure sensors, ink temperature sensors, fluid control valves, air flow sources and their associated sensors and control electronics, charging-electrode waveform sources and short detection sensors, drop-formation waveform sources, and memory units for storing printhead operating parameters and reliability data. 
     As new applications are being developed for the use of high speed inkjet printing technology, such as the printing of labels, books and magazines, packaging materials, and décor (such as wallpaper, and laminate material for flooring and countertops), there is a need to develop an increasing variety of linehead configurations to accommodate the increasing number of desired print widths. To simplify the development of the various lineheads, it is desirable to employ a modular design architecture for printhead alignment hardware and the supporting fluid and electronic hardware. In an exemplary architecture, each of the modular printhead assemblies  190  is designed to accommodate three printhead modules  260  along with their supporting fluid and electrical hardware. By combining different numbers of modular printhead assemblies  190  together, lineheads having different print widths can be created as illustrated in  FIGS. 7-11 . Depending on the application, the modular printhead assemblies  190  can be depopulated to include only one or two printheads, as is shown in  FIG. 9 . 
       FIGS. 7-11  each show a production printing system  300  having a linehead  348  with one or more modular printhead assemblies  190  positioned over a web of print media  32 . In  FIG. 7 , the linehead  348  includes a single modular printhead assembly  190  with three printhead modules  260 . Each printhead module  260  prints a separate swath of image data in a corresponding printing region  132  on the print medium  32  as the print medium  32  is transported past the linehead  348 . 
     In  FIG. 8 , the linehead  348  includes two modular printhead assemblies  190 ; one with two printhead modules  260  on the downstream side and one on the upstream side, and the other modular printhead assembly  190  having one printhead module  260  on the downstream side and two printhead modules  260  on the upstream side. 
     The linehead  348  of  FIG. 9  includes four modular printhead assemblies  190 , three of the modular printhead assemblies  190  each have three printhead modules  260 , and a fourth modular printhead assembly  190  (the bottommost one in the figure) is populated with only two printhead modules  260  instead of the normal three printhead modules  260 . 
     The linehead  348  of  FIG. 10  has four modular printhead assemblies  190 , in which the cross-track spacing  355  between the center two modular printhead assemblies  190  has been increased to enable the linehead  348  to print on two side-by-side webs of print media  32 . In some embodiments of  FIG. 10 , the side-by-side webs of media can comprise a first pass and a second pass of the same print media  32 , with the media being laterally shifted, and possibly inverted, between the first and the second passes, as is disclosed in commonly-assigned U.S. Pat. No. 6,050,191 to Enderle et al., which is incorporated herein by reference. 
       FIG. 11  shows a linehead  348  having a single modular printhead assembly  190 . In this embodiment, the printing regions  132  of the two printhead modules  260  totally overlap each other. As disclosed in commonly-assigned U.S. application Ser. No. 15/590,070, filed May 9, 2017, which is incorporated herein by reference, such a configuration can be used to double the print speed of a single printhead printing system, double the in-track resolution, or to print with two different ink colors. 
     In each of the configurations in  FIGS. 7-11 , a system controller  354  is connected to a first end of the linehead  348 . Alternatively, the system controller  354  could be connected to the second end of the linehead  354 , as indicated dashed line system controller  354 . 
     In keeping with the modular printhead assembly architecture, the fluid system components associated with each printhead module  260  are preferably configured as fluid component modules, where each fluid component module is positioned in close proximity to the corresponding printhead module  260 . Similarly, the electronic components associated an individual printhead module  260  are preferably located on one or more electronics boards within the modular printhead assembly  190 . Accordingly, in the illustrated embodiment, each modular printhead assembly  190 , which can include up to three printhead modules  260 , includes a fluid component module and printhead electronics boards (PHE)  358  for each printhead module  260 . 
     As a linehead  348  can include from one to eight or more modular printhead assemblies  190 , each with one to three printhead modules  260  and associated printhead electronics boards  358 , an efficient method must be provided to enable the system controller  354  to communicate with the printhead electronics board  358  associated with a particular printhead module  260  for all the possible linehead configurations. To facilitate communicating with the individual printhead electronic boards  358  within the linehead  348  and distribution of power to the printhead modules  260 , each modular printhead assembly  190  includes a power communication distribution board (PCD)  350  through which power and communication are provided to the one or more electronics boards associated with an individual printhead modules  260 , as shown in  FIGS. 7-11 , and more clearly in the schematic block drawing of  FIG. 12 . The power communication distribution board  350  is sometimes referred to as communication distribution device. 
     Each power communication distribution board  350  has two primary communication ports  352  (a first primary communication port  352 A and a second primary communication port  352 B) through which it can be connected to other power communication distribution boards  350 , or to the system controller  354 . In the illustrated configuration, each power communication distribution board  350  also has three secondary communication ports  356  through which communication and power can pass to secondary devices  364  (e.g., the individual printhead electronics boards  358 ). The secondary communication ports  356  are arranged on the PCD  350  in a defined order (i.e., A, B and C starting nearest to the first primary communication port  352 A). The communication via the PCD  350  with each PHE  358  does not include print data. The high data-rate print data are supplied directly to the PHEs  358  by a print data source  366  via optical fibers  368 . 
     The exemplary configuration of  FIG. 12  shows a linehead  348  that includes a plurality of modular printhead assemblies  190  connected to a system controller  354 . Each of the modular printhead assemblies  190  include a power communication distribution board  350  and three printhead electronic boards  358 , each of the printhead electronic boards  358  being associated with a corresponding printhead module  260  ( FIGS. 7-11 ). 
     The system controller  354  is connected by an umbilical cable  370  to the first primary communication port  352 A of a first PCD  350  in the linehead  348 . The second primary communication port  352 B of the first PCD  350  is connected by a primary cable  372  to the first primary port  352 A of a second PCD  350 . Similarly, additional primary cables  372  connect the adjacent primary communication ports  352  of adjacent PCDs  350 . In this manner, the PCDs  350  within the linehead  348  are connected to each other in a daisy chain arrangement to form a connected sequence of PCDs  350 , with a first PCD  350  (i.e., the rightmost PCD  350  in the illustrated configuration) being connected to the system controller  354 . 
     Each PHE  358  (also referred to as secondary device  364 ), which is located in proximity to a corresponding secondary communication port  356  of the associated PCD  350 , is connected to the adjacent secondary port  356  via a secondary cable  374 . 
     Communication between the system controller  354  and the PCDs  350  and the PHE  358  are via serial links included in the umbilical cable  370 , the primary cables  372  and the secondary cables  374 . To facilitate communications using the serial links, each device (i.e., each PCD  350  and each PHE  358 ) must be assigned a distinct communication address. In the printing system environment, it is important that the system controller  354  know, for each of the PHEs  358 , the printhead position or print swath position for the associated printhead module  260 . To facilitate this, the present invention provides a method for assigning communication addresses to the printhead electronics (i.e., the PHEs  358 ) in an order that is clearly linked to the physical position of the printhead modules  260 . It does this independent of whether the system controller  254  is connected to the rightmost PCD  250  in the connected sequence of PCDs as shown in  FIG. 12 , or to the leftmost PCD  250  as shown in  FIG. 13 . This enables the modular architecture to be used in a large variety of linehead configurations. 
     The process for assigning communication addresses is carried out each time the printing system  300  is powered on. At power on, each of the PCDs  350  within the linehead  348  detect whether it is the PCD  350  at an end of the linehead  348  that is directly connected to the system controller  354 , whether it is the PCD  350  at the opposite end of the linehead  348  from the system controller  354  with one of its primary communication ports  352  not connected to anything, or whether it is a PCD  350  somewhere between the two ends. The PCD  350  that is directly connected via the umbilical cable  370  to the system controller  354  also determines whether the system controller  354  is connected to the first primary communication port  352 A or to the second primary communication port  352 B. Each PCD  350  also determines whether secondary devices  364  are attached to any of its secondary communication ports  356 . The process by which a PCD  350  detects attached devices will be described later. 
     The communication addresses that can be assigned to the PCDs  350  and to the secondary devices  364  (e.g., the PHEs  358 ) come from separate pools or sets of addresses. The first set of communication address consists of addresses that can be assigned to the individual communications distribution devices (i.e., the PCDs  350 ). These addresses have a prescribed order, typically a consecutive number order. In an exemplary embodiment, the first set of communication address has address values ranging from # 32  to # 39 . (For clarity in this description, address values will be denoted with a “#” sign prefix to distinguish them from drawing reference numbers.) 
     The second set of communication addresses, which is distinct from the first set of communication addresses, are those that can be assigned to the individual secondary devices  364 . These addresses will also have prescribed order, typically a numeric order. In an exemplary embodiment, the second set of communication addresses includes two subsets of communication addresses: the first subset includes the values ranging from # 1  to # 24 , and the second subset includes the values ranging from # 40  to # 63 . 
     The PCD  350  that is connected to the system controller  354  can be referred to as the first communication distribution device or the first PCD  350 . Upon detecting that it is connected directly to the system controller  354 , the first PCD  350  assigns itself the first address in the first set of communication addresses (i.e., the address # 32 ). This assignment to the first PCD  350  of the first communication address in the first set of communication addresses is independent of whether the system controller is attached to the first primary communication port  352 A or the second primary communication port  352 B. However, the assignment of the communication addresses for the attached secondary devices  364  preferably depends on which primary communication port  352  is connected to the system controller  354 . 
     If the system controller  354  is connected to the first primary communication port  352 A of the first PCD  350 , then first PCD  350  will assign the first (lowest) address in the second set of communication addresses to the secondary device  364  (i.e., the PHE  358 ) attached to the secondary port  356  closest to the first primary communication port  352 A. This lowest communication address of the second set of communication addresses is # 1  in the exemplary embodiment. Continuing along the sequence of secondary communication ports, the first PCD  350  sequentially assigns communication addresses in ascending order (i.e., # 2  and # 3 ) to the other secondary devices  358  (i.e., the PHEs  358 ) attached to the B and C secondary communication ports  356 . 
     On the other hand, if the system controller  354  is connected to the second primary communication port  352 B of the leftmost PCD  350  as shown in  FIG. 13 , then the leftmost PCD  350  will be designated to be the first PCD  350 . As before, the first PCD  350  will assign itself the lowest address in the first set of communication addresses (i.e., address # 32 ). The first PCD  350  will then assign the last (highest) address in the second set of communication addresses to the secondary device  364  (i.e., the PHE  358 ) attached to the secondary port  356  closest to the second primary communication port  352 B that is connected to the system controller  354  (i.e., port C). This highest communication address of the second set of communication addresses is address # 63  in the exemplary embodiment. Continuing along the C-B-A sequence of secondary communication ports  356 , the first PCD  350  sequentially assigns communication addresses in a descending sequence to the secondary devices  364  attached to the B and A secondary communication ports  356 . 
     As the PCD  350  is assigning communication addresses to the secondary devices  364 , the communication addresses are allocated sequentially, either upward or downward, based on the order of the secondary communication ports  356 . If any of the secondary communication ports  356  are open (i.e., it is detected that they don&#39;t have an attached secondary device  364 ), the communication address is held in reserve for allocation to a secondary device  364  that is attached to that secondary communication port  356  at a later time. If a secondary device  364  is subsequently attached to that open secondary communication port  356 , the communication address held in reserve can be assigned to that secondary device  364  without needing to reassign communication addresses to the other attached secondary devices  364 . After assigning communication addresses to itself and to the attached secondary devices  364 , the first PCD  350  creates a table of assigned communication address for subsequent transmission to the system controller  354 . On the other hand, after the communication addresses have been assigned, if one of the secondary devices  364  is disconnected from a secondary communication port  356 , the communication address that had been assigned to the removed secondary device  364  is unassigned by the PCD  350 , but is held in reserve so that it can be reassigned to any secondary device  364  that is later attached to that secondary communication port  356 . 
     After assigning communication addresses to itself and to the attached secondary devices  364 , the first PCD  350  communicates address information to the next PCD  350  in the connected sequence of PCDs  350  via one of its primary communication ports  352 . In an exemplary embodiment, the address information communicated to the next PCD  350  specifies next communication address in the prescribed sequence of the first set of communication addresses (which the next PCD  350  can assign to itself) and also specifies the next available communication address in the prescribed sequence of the second set of communication addresses that the next PCD  350  can assign to the secondary devices  364  connected to it. 
     For example, consider the case where the first PCD  350  is connected to the system controller  354  using the first primary communication port  352 A as in  FIG. 12 . The first PCD  350  would assign itself communication address # 32 , and would notify the next PCD  350  in the connected sequence that next available address in the first set of communication addresses is # 33 . And if the first PCD  350  has three secondary communication ports  356  which were assigned communication addresses # 1 -# 3  from the first subset of the second set of communication addresses, then the first PCD  350  would notify the next PCD  350  that the next available communication address in the first subset of the second set of communication addresses is # 4 . 
     If, on the other hand, the first PCD  350  is connected to the system controller  354  using the second primary communication port  352 B, then it would have assigned the communication address # 63 -# 61  from the second subset of the second set of communication addresses to its attached secondary devices  364 . In this case, the first PCD  350  would notify the next PCD  350  that the next available communication address from the second subset of the second set of communication addresses is address # 60 . 
     Upon being notified as to the next available communication address in both the first and the second sets of communication addresses, the next PCD  350  in the connected sequence would in a similar manner assign the received next available communication address in the first set of communication addresses to itself, and would sequentially assign the next available addresses in the second set of communication addresses to the secondary devices  364  attached to its sequence of secondary communication ports  356 . If the next available communication addresses were received through the first primary communication port  352 A (as in  FIG. 12 ), then the PCD  350  will increment the communication address for each subsequent secondary device  364 . However, if the communication addresses were received through the second primary communication port  352 B (as in  FIG. 13 ), then the PCD  350  will decrement the communication address for each subsequent secondary device  364 . Alternately, the PCD  350  can determine whether to increment or decrement the communication address for each subsequent secondary device based on whether the next available address is in the first or second subsets of the second set of communication addresses. If the next available address is in the first subset of the second set of communication addresses, then the communication addresses are incremented, and if the next available address is in the second subset of the second set of communication addresses, then the communication addresses are decremented. 
     After assigning communication addresses to itself and to its attached secondary devices  364 , the PCD  350  creates a table of assigned communication address for subsequent transmission to the system controller  354  and continues the process of assigning communication addresses by communicating the next available communication addresses to the next PCD  350  in the connected sequence. This process continues until the last PCD  350  in the connected sequence is reached, in which case the process is terminated since communication addresses have been assigned all of the PCDs  350  and their connected secondary devices  364 . 
     As each PCD  350  assigns communication addresses to itself and to its attached secondary devices  364 , it notifies the system controller  354  that it has completed the assignment of communication addresses. The system controller  354  can then send a query to the PCD  354  to have it transmit its address assignment table to the system controller  354 . Upon receipt of the address assignment tables from each of the PCDs  350 , the system controller can begin communicating with any of the devices (the PCDs  350  and PHEs  358 ) for which it has received a communications address. 
     After the communication addresses are assigned to all the connected devices in this manner, each of the PCDs  350  continues to monitor the connection status at each of its communication ports (i.e., primary communication ports  352  and secondary communication ports  356 ). If there is any change in the connection status due to a new device being connected or a device being removed, the PCD will assign the reserved communication address to the new device, or it will un-assign the communication address of the removed device. The PCD  350  will then notify the system controller  354  of the altered communication address table. 
     This method of assigning the communication addresses to the secondary devices ensures that the communication addresses are always incremented in the same direction relative to the linehead independent of which end of the linehead the system controller is attached to. That is, the communication addresses of the secondary devices  364  (i.e., the PHEs  358 ) always increase from right-to-left across the linehead  348 . 
     In an exemplary embodiment of the invention, the second set of communication addresses includes two distinct subsets of communication addresses. The communication address in one of the subsets are used when the successively assigned communication address are incremented upward, while the communication addresses in the second subset are used when the successively assigned communication address are decremented downward. The use of these two distinct subsets of communication addresses can help the PCDs  350  downstream of the first PCD  350  to determine whether they are to increment or decrement the communication addresses from the received next available communication address as they assign the second set of communication addresses to the attached secondary devices  364 . 
     In certain embodiments as indicated in  FIG. 14 , the PHE  358  associated with a printhead module  260  ( FIG. 8 ) is packaged on two electronics boards. One board, the jetting module electronics board (JME)  362 , is integrated into the field replaceable jetting module  200  ( FIG. 6 ). It includes electronics associated with the drop formations waveform sources  55  ( FIG. 1 ), as well as memory units for storing jetting module operating parameters and reliability data. The second board, the print module control board (PMC)  360 , includes electronics for monitoring ink pressure sensors, ink temperature sensors, controlling fluid control valves, monitoring air flow sensors and controlling air flow sources, for providing the charging-electrode waveform and for detecting charge electrode shorting conditions. In some such embodiments, one of the two types of printhead electronics boards (i.e., the PMCs  360 ) are considered to be secondary devices  364  attached to the secondary communication ports  356  of the PCD  350 , while the second type of board (i.e., the JMEs  362 ), are considered to be tertiary devices  390  attached to tertiary communication ports (not shown) of the PCD  350 . To prevent confusion as to which type of device the system controller  354  is communicating with, a third set of communication address distinct from the first and second sets of communication addresses can be used for assignment to the tertiary devices  390 . As with the second set of communication addresses, the third set of communication address can also include two subsets of communication address; one for use when incrementing the communication addresses and the other for use when decrementing the communication addresses. In certain embodiments, the tertiary devices  390  are connected to the secondary devices  364  using tertiary cables  388  as shown in  FIG. 14 , and communication channels for communicating with the tertiary devices  390  pass through the secondary devices  364 . In such embodiments, there is not a need for tertiary communication ports on the PCD  350 . 
     In certain exemplary embodiments of the invention, the communication cables (the umbilical cable  370 , primary cables  372  and secondary cables  374 ) and communication ports (primary communication ports  352  and secondary communication ports  356 ) can include more than one serial link, as shown in  FIG. 14 . In a preferred embodiment, a serial A link  376  is used for communication with the PCDs  350  and with the PMCs  360 , while a serial B link  378  is used for communication with the JMEs  362 . With separate serial links being used for the PMCs  360  and the JMEs  362 , the communication addresses assigned to the two types of printhead electronics boards associated with a given printhead module  260  can have the same value without introducing ambiguity as to which board the system controller  354  is communicating with. 
     The means by which the PCDs  350  detect the presence of other PCDs  350  and secondary devices  364  in an exemplary configuration is best understood by examining the different signals passed through the primary communication ports  352  and secondary communication ports  356 . As shown in  FIG. 14 , the primary communication ports  352  and primary cables  372  include a plurality of different lines. These include power lines  380 . While a single power line  380  is shown for clarity, it must be recognized that the power lines  380  can include a plurality of different conductors to accommodate a plurality of voltage levels. Also included are a serial A link  376  through which the system controller  354  can communicate with the PCDs  350  and PMCs  360 , and a serial B link  378  for communicating with the JMEs  362 . In certain embodiments, the serial links within the primary and secondary cables  374  correspond to twisted wire pairs that are driven with differential signals. A signal ground wire, distinct from the power ground, is associated with each of the serial links. Also, included in the communication ports and cables, are a pair of IDIn  384  and IDOut  386  lines. The IDOut  386  from one device is connected to the IDIn  384  of the connected adjacent device. Finally, the primary communication ports  352  include loopback signal lines  382 , to provide validation that the connections are being properly made. While the figure shows the loopback feedback line  382  as a single wire, it can include multiple lines through which each PCD  350  can transmit a signal to an adjacent PCD  350  or system controller  354  and through which the adjacent PCD  350  or system controller  354  can send that signal back to signal-originating PCD  350 . 
     The secondary communication ports  356  and secondary cables  374  include similar lines, except that the secondary communication ports  356  do not include the loopback signal lines  382 . The secondary communication ports  356  also each include two sets of IDIn and IDOut signal lines instead of the single set in the primary communication ports  352 . One set of IDIn and IDOut lines are used to test for the presence of an attached PMC  360 , while the second set of IDIn and IDOut lines are used to test for the presence of the JME  362  which is connected via the PMC  360  to the secondary communication port  356  of the PCD  350 . The different signal lines at the secondary communication ports  356  aren&#39;t separately labeled for clarity. 
     On power-up, each PCD  350  transmits a square wave on the IDOut  386  lines of its primary communication ports  352 . The PMC  360 , and JME  362  boards also transmit a square wave on each of their IDOut lines. In one exemplary embodiment, the square wave frequency is 125 Hz. Each of the PCD boards monitors the IDIn  384  lines of their communication ports  352 ,  356  to detect whether such a square wave has been transmitted by an attached device. If nothing is attached to one of the communication ports of a PCD  350 , the IDIn  384  line of that communication port  352 ,  356  will float high. Based on detecting a sustained logic-high signal on the IDIn  384  line of a communication port  352 ,  356  at power up, the PCD  350  can determine that there is not a device attached to that communication port  352 ,  356 . Unlike the other devices, the system controller  354  holds its IDOut  386  line at the logic-low level. The PCD  350  attached to the system controller  354 , upon detecting the sustained logic-low signal instead of the square wave or the logic-high signal at one of its two primary communication ports  352 , determines that it is connected to the system controller  354  using that primary communication port  352 . It then sets the logic level at the IDOut  386  lines of its primary and secondary communication ports  352 ,  356  to low. It then proceeds to assign communication addresses to itself and the attached devices as previously described. The downstream PCD  350  and secondary devices  364  attached to the first PCD  350  upon detecting the change to IDOut  386  signal from the first PCD  350  to logic-low, stop transmitting the square wave signals on their IDOut  386  lines, holding their IDOut  386  lines at logic-high. The PCD  350  transmits the communication addresses on the IDOut  386  line of the communication port to the IDIn  384  of the attached device. In one embodiment, the address information is transmitted at a 250 Hz bit rate. The address information is transmitted as a 32-bit message that includes two start bits, each at logic-low, and one stop bit at logic-high. The device receiving the address message uses its IDOut  386  line to echo the address message back to the first PCD  350 . In addition to echoing back the address message, messages over the IDOut  386  and IDIn  384  lines can include other configuration data, such as baud rates for the serial links, whether the serial link data is encrypted or not, the device type, and device serial number information. Following the echoing of the address message back to the first PCD  350 , the attached PMC  360  and JME  362  boards hold their IDOut  386  lines at logic-low. If these devices are disconnected from the PCD  350 , the corresponding IDIn  384  port of the PCD  350  will no longer be held low and it will float high, providing a signal to the PCD  350  that the device has been removed. 
     The use of the IDOut  386  and IDIn  384  lines within the communication ports and cables that are distinct from the serial links within the communication ports enables them to not only transmit communication address information to the attached devices, but also to monitor whether devices are attached. This enables the PCDs  350  to continually monitor their ports to detect newly connected or disconnected devices, even while continuing to relay communications to the attached devices through the serial links within the communication ports. As the PCD  350  detects a newly connected or disconnected device, it assigns or un-assigns a communication address for that device. It then updates its address assignment table and notifies the system controller  354  of the change in the address assignment table. 
     In certain applications in which the integrity of a communication network is important, the ability to continually monitor for newly connected or disconnected devices on the network, provides a level of security against unauthorized removal and installation of devices on the communication network. 
     When the second PCD  350  receives the next available communication address from the first set of communication address and from the second set of communication addresses, it assigns communication addresses to itself and to each of the attached devices and communicates the communication addresses to the attached devices in the same way. 
     In some embodiments, each PCD  350  transmits to the next PCD  350  in the daisy chain the last used communication addresses from the first set and from the second set of communication address rather than the next available communication addresses. The receiving PCD then determines the next available communication addresses based on the received last used communication address. 
     In some embodiments, the secondary communication ports  356  are not aligned in a row on the PCD  350 , but rather the secondary communication ports  356  are alternately placed along two opposite edges of the PCD  350 , typically the upstream and downstream edges, as shown in  FIG. 15 . This configuration reduces the spacing between the secondary communication ports  356  and the printhead electronics to which they are connected by means of a secondary cable  374 . As was noted earlier, adjacent printhead assemblies  190  within a linehead  348  have opposite orientations; with one printhead assembly having two printhead modules  260  on the downstream side of the central mounting rail assembly  220  ( FIG. 6 ) and one printhead module  260  on the upstream side, and adjacent modular printhead assemblies  190  have one printhead module  260  on the downstream side of the central mounting rail assembly  220  and two printhead modules  260  on the upstream side. 
     To facilitate connection of the secondary cables  374  between the secondary communication ports  356  and the associated PHEs  358 , it is desirable to similarly alter the orientation of adjacent PCDs  350  within the linehead. In the exemplary embodiment of  FIG. 15 , the center PCD  350  has been inverted (denoted by the dashed outline of the PCD  350 ) by rotating the PCD  350  about an axis passing through both primary communication ports  352 . By inverting the PCD  350  in this manner, the first primary communication port  352 A remains on the right side of the PCD  350 , similar to the non-inverted PCDs  350 . (The primary and secondary cables  372 ,  374  have sufficient slack to allow these cables to be twisted to enable making the proper connections to the inverted PCDs  350 .) The addressing of the secondary devices  364  attached to the inverted PCD  350  proceeds as described for the previous embodiments. 
     In the exemplary embodiments, the PCDs  350  do not act as gatekeepers for communications passing through the one or more serial links of the communication ports. Instead all communications received via a serial link at one of primary communication port  352  of a PCD  350  are transmitted to the corresponding serial link of each of the secondary communication ports  356  and of the other primary communication port  352 . 
     While the invention has been described with respect to an embodiment in which the PCDs  350  each have three secondary communication ports  356 , the number of secondary communication ports  356  is not limited to three. The PCDs  350  can have any number of secondary communication ports  356  greater than or equal to 1. Furthermore, the different PCDs  350  within a production system can vary in their number of secondary communication ports  356 . 
     While this invention has been described with respect to a printing system, this invention also has applicability to other types of production systems in which a system controller monitors or controls the operation of a plurality of production tools or instruments. In one such embodiment, the production system includes a plurality of manufacturing cells arranged along a production path, with each cell including a number of devices to act on the units being made. In such a system, each manufacturing cell might include a communication distribution device through which the production tools of the manufacturing cell are connected to a system controller. The communication distribution devices associated with each of the manufacturing cells along the production path are connected in a daisy chain fashion. The present invention is particularly useful in such production systems where there is a need to frequently remove and replace individual tools in the various production cells and a need for the system controller to know where along the production path the individual tools are located. 
     Outside of the field of production systems, the invention has applicability in communication networks in environments such as in hospitals where a variety of different types of patient monitoring instruments can be moved from one patient treatment room to another, and in which a system controller, perhaps at a nurse&#39;s station, must unambiguously know the location of each of the connected patient monitoring instruments. In such an environment, each patient treatment room or patient treatment station might include a communication distribution device, each having a plurality of secondary communication ports to which the patient monitoring instruments can be connected as secondary devices. 
     The present invention has been described with respect to methods and system components for assigning communication addresses in an inkjet printing production system. It will be obvious to one skilled in the art that an equivalent solution can be applied to other types of production systems having a chain of communication distribution devices, each having ports for connecting to a plurality of secondary devices. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           20  printing system 
           22  image source 
           24  image processing unit (image processor) 
           26  control circuits 
           27  synchronization device 
           28  drop-forming transducer 
           30  printhead 
           32  print medium 
           34  print medium transport system 
           35  speed measurement device 
           36  media transport controller 
           38  micro-controller 
           40  ink reservoir 
           44  ink recycling unit 
           46  ink pressure regulator 
           47  ink channel 
           48  jetting module 
           49  nozzle plate 
           50  nozzle 
           51  heater 
           52  liquid stream 
           54  drop 
           55  drop formation waveform source 
           57  trajectory 
           59  breakoff location 
           60  drop formation waveform 
           61  charging device 
           62  charging electrode 
           62 ′ charging electrode 
           63  charging-electrode waveform source 
           64  charging-electrode waveform 
           66  printing drop 
           68  non-printing drop 
           69  drop selection system 
           70  deflection mechanism 
           71  deflection electrode 
           72  ink catcher 
           74  catcher face 
           76  ink film 
           78  liquid channel 
           79  lower plate 
           80  charging-electrode waveform period 
           82  first voltage state 
           84  second voltage state 
           86  non-print trajectory 
           88  print dot 
           92 - 1  drop-formation waveform 
           92 - 2  drop-formation waveform 
           92 - 3  drop-formation waveform 
           94 - 1  drop-formation waveform 
           94 - 2  drop-formation waveform 
           94 - 3  drop-formation waveform 
           94 - 4  drop-formation waveform 
           96  period 
           98  pulse 
           100  period 
           102  pulse 
           104 - 1  large drop 
           104 - 2  large drop 
           104 - 3  large drop 
           106 - 1  small drop 
           106 - 2  small drop 
           106 - 3  small drop 
           106 - 4  small drop 
           108  phase shift 
           112  printhead assembly 
           116  in-track direction 
           118  cross-track direction 
           132  printing region 
           134  overlap region 
           136  centerline 
           138  nozzle array spacing 
           190  printhead assembly 
           200  jetting module 
           202  nozzle array 
           216  fluid connections 
           217  electrical connections 
           220  rail assembly 
           222  beam 
           224  rod 
           226  downstream side 
           228  upstream side 
           240  mounting assembly 
           260  printhead module 
           300  printing system 
           348  linehead 
           350  power communication distribution board (PCD) 
           352  primary communication port 
           352 A first primary communication port 
           352 B second primary communication port 
           354  system controller 
           355  spacing 
           356  secondary communication port 
           358  printhead electronics board (PHE) 
           360  print module control board (PMC) 
           362  jetting module electronics board (JME) 
           364  secondary device 
           366  print data source 
           368  optical fiber 
           370  umbilical cable 
           372  primary cable 
           374  secondary cable 
           376  serial A link 
           378  serial B link 
           380  power line 
           382  loopback signal line 
           384  IDIn 
           386  IDOut 
           388  tertiary cable 
           390  tertiary device