Patent Publication Number: US-8985756-B2

Title: Dynamic dryer control in printing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to and thus the benefit of an earlier filing date from U.S. Provisional Patent Application No. 61/485,041 (filed May 11, 2011), the entire contents of which are incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the field of print dryers and, in particular, to variable heat control of these dryers during printing. 
     BACKGROUND 
     In color printing, a printer prints input data onto a print medium, such as paper. A CMYK printer, for example, represents bitmap data with various levels of cyan (C), magenta (M), yellow (Y), and black (K) ink. Each of these inks has a unique chemical makeup and fluid content (e.g., carrier fluids including water) that result in differing drying characteristics. In other words, some ink combinations contain more fluid than other ink combinations and therefore require additional drying to attach the ink particles to the print medium. 
     Printer systems are typically configured with heaters or dryers that are used to evaporate the fluid content of the ink such that the ink attaches to the print medium. In production printing systems, these dryers have multiple elements that radiate heat to a continuous form print medium, or “web”, so as to dry the ink onto the print medium after the print engine applies the ink to the print medium. To accommodate the different drying characteristics of inks, the heating elements are generally configured to radiate a uniform heat that is established based on the area of the substrate that contains the highest concentration of ink. Thus, by ensuring that the highest concentration of ink is dried on the print medium, all inks are virtually assured of being attached to the print medium. Generally, a portion of the radiant heat energy from the print dryer is absorbed into the dryer&#39;s structural members and shields. Certain print dryers, such as infrared dryers, also use an exhaust system to remove the evaporated carrier fluid as well as the absorbed heat from the immediate environment. 
     In any case, the uniform application of heat to the print medium results in the unnecessary consumption of energy since not all applications of ink require the same amount of heat for evaporation of the carrier fluids. This results in more expensive printing operations, particularly in the case of high-speed production printing systems. Moreover, the excessive application of heat to certain parts of the print medium results in a potential fire hazard. For example, areas of the print medium with lower concentrations of ink sometimes dry faster, causing the print medium to be overheated. And, in some instances, paper dust from the print medium propagates through the dryer and catches fire. 
     SUMMARY 
     Embodiments described herein provide dynamic dryer control for a printer. In one embodiment, a dryer system includes a dryer operable to dry ink applied to a print medium. The system also includes a controller communicatively coupled to the dryer and operable to filter a bitmap to provide variable heat control of the dryer and vary the heat from the dryer to the applied ink according to the bitmap to attach the ink to the print medium. For example, the controller may filter a bitmap to identify image regions in the bitmap, determine a level of heat control for each of the identified image regions in the bitmap, locate the image regions represented on the print medium with ink applied to the print medium, and independently apply heat to each of the image regions of applied ink based on the determined levels of heat control. 
     The print medium may be a continuous form print medium. In this regard, the controller (e.g., a feed-forward controller) is further operable to determine a speed at which the continuous form print medium is moving, to generate a heat control signal operable to provide the variable heat control of the dryer, and to delay transmission of the heat control signal based on the determined speed of the continuous form print medium until the ink applied to the continuous form print medium is within range of the dryer. 
     Generally, the dryer is a radiant heat dryer, such as an infrared dryer that includes a plurality of heating elements. In this regard, the controller is further operable to filter the bitmap to identify average image regions in the bitmap, and to generate heat control signals based on the identified average image regions for application to the heating elements to provide the variable heat. For example, the controller may process the bitmap through a probability distribution function to generate time varying heat control signals for the heating elements across the web, thereby providing time/spatial varying heat control of the dryer. 
     The controller may be further operable to determine a color density for a portion of the print medium based on the identified average image regions, and to generate a heat control signal for each heating element that corresponds to the color density for the portion of the print medium. The controller may be further operable to generate the heat control signal for each heating element based on a lookup table that maps color density values to drying temperature. The controller may be further operable to filter the identified average image regions via an inverse response of the dryer to provide heating from the dryer that is independent of ink volume changes. The controller may be further operable to serialize image data of the bitmap to expedite generation of heat control signals used to vary the heat from the dryer. The controller may be further operable to filter another bitmap to generate a heat control signal for use by the dryer to dry the applied ink according to the other bitmap. The controller may be also operable to provide the variable heat control of the dryer based on a color of the ink applied to the print medium and/or based on absorption of the print medium. 
     The various embodiments disclosed herein may be implemented in a variety of ways as a matter of design choice. For example, the embodiments may take the form of physical machines, computer hardware, software, firmware, or combinations thereof. In another embodiment, a computer readable medium is operable to store software instructions for converting the input data to the color space of the printer. These software instructions are configured so as to direct the processor or some other processing system to operate in the manner described above. Other exemplary embodiments may be described below. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present invention are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
         FIG. 1  is a block diagram of a dryer system in an exemplary embodiment. 
         FIG. 2  is a flowchart of a process for drying ink applied to a tangible medium in an exemplary embodiment. 
         FIG. 3  is a block diagram of a printer system using the dryer system of  FIG. 1  in an exemplary embodiment. 
         FIG. 4  is a detailed block diagram of a dryer system in an exemplary embodiment. 
         FIG. 5  is a filter output used in generating a heat control signal in an exemplary embodiment. 
         FIG. 6  is an exemplary filter process operable to find a maximum value of color values within a particular image region. 
         FIG. 7  is a block diagram of a computer system operable to execute computer readable medium embodying programmed instructions to perform desired functions in an exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The figures and the following description illustrate specific exemplary embodiments of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within the scope of the invention. Furthermore, any examples described herein are intended to aid in understanding the principles of the invention, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the invention is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
       FIG. 1  is a block diagram of a dryer system  100  in an exemplary embodiment. The dryer system  100  includes a controller  115  and a dryer  120 . The dryer system  100  is operable to provide variable heat so as to dry ink that is applied to a print medium  125 . The dryer system  100  processes a bitmap  110  to determine different levels of heat to apply to the print medium  125  so as to correspondingly evaporate inks on the print medium  125  having different concentrations of ink. The controller  115  may be configured in a variety of ways as a matter of design choice. For example, the controller  115  may be configured as a general-purpose computer processor that executes software instructions to process the bitmap  110  and generate heat control signals that are operable to control the dryer  120 . Alternatively, the controller  115  may be implemented as an analog system with a feedback control. 
     Printing system dryers, such as the dryer  120 , exist in many forms. Some high-speed production printing systems use ultraviolet dryers that radiate ultraviolet light to attach special ultraviolet sensitive inks applied to the print medium. Others may use an infrared heater or other radiant heater that includes a plurality of heating elements, each of which radiates heat to the print medium  125  to evaporate the carrier fluids and/or other liquids in the ink applied. In any case, the dryer  120  is communicatively coupled to the controller  115  such that the controller  115  may independently control the heating elements of the dryer  120  to provide a variable heat control to the print medium  125  based on the bitmap  110 . 
     The dryer system  100  is operable with a variety of printers. For example, the dryer system  100  may be configured with a high-speed production printing system that is operable to print large volumes of information, such as newspapers, enterprise payrolls, etc. In this regard, the print medium  125  may be a continuous form print medium, or “web”. The bitmap  110  is generally a grid of pixels, or “pels”, of varying color values used to form an image. When used in printing, the bitmap  110  directs the print engine to mark the print medium  125  with ink or toner to physically display the image of the bitmap  110  on the print medium  125 . Thus, the ink applied to the print medium  125  is a physical representation of the data contained in the bitmap  110 . 
     The particular operations of the dryer system  100  are now discussed with respect to flow chart  200  of  FIG. 2 . More specifically, the flow chart  200  illustrates a process for dynamically drying ink applied to the print medium  125  in an exemplary embodiment. The dryer system  100  initiates when the controller  115  receives the bitmap  110 , in the process element  202 . Thereafter, the controller  115  initiates processing of the bitmap  110 , in the process element  204 , by filtering the bitmap  110  to identify various regions therein. For example, the bitmap  110  may comprise a variety of colors arranged to convey an image. Each color in the image may represent a different concentration of ink due to a particular ink or combination of inks being applied to the print medium  125 . However, certain regions of ink concentration may be identified by filtering the bitmap  110 . In this regard, the controller  115  may filter the bitmap  110  by averaging the color values therein to identify image regions which, when applied to the print medium  125 , may have higher ink concentrations than other image regions. Based on these identified image regions, the controller  115  may determine various levels of heat control for the identified image regions, in the process element  206 , such that the dryer  120  may dry the identified image regions accordingly. Then, the controller  115  may locate the image regions on the print medium  125  that are represented by the applied ink, in the process element  208 . That is, the controller  115  may use the identified image regions of the bitmap  110  to locate those image regions on the print medium  125  as the print medium  125  passes by the dryer  120  after the ink has been applied to the print medium  125 . The dryer  120  may then apply heat to the print medium  125  to dry the image regions based on the determined levels of heat control for the identified image regions, in the process element  210 . For example, the controller  115  may apply heat control signals to corresponding heating elements to independently heat the identified image regions on the print medium  125 . 
       FIG. 3  is a block diagram of a printing system  200  using the dryer system  100  of  FIG. 1  in an exemplary embodiment. In this embodiment, the printing system  200  is a CMYK inkjet printing system operable to mark the print medium  125  with various concentrations of cyan (C), magenta (M), yellow (Y), and black (K) inks via the printer  260 . A host system  210  is in communication with the printing system  200  to print a print job  120  onto a print medium  125  via the printer  260 . The resulting print medium  125  may be printed in color and/or in any of a number of gray shades, including black and white. The host system  110  may comprise any computing device, such as a personal computer or a server that is operable to prepare the print job  220  for printing via the printer  260 . The print job  220  may be any file or data that describes how the input data prints on the print medium  125 . For example, the print job  120  may include PostScript data, Printer Command Language (“PCL”) data, and/or any other page description language. The printing system  200  may be capable of printing relatively high volumes (e.g., greater than 100 pages per minute). The print medium  125  may be continuous form paper, cut sheet paper, and/or any other medium suitable for printing. The printing system  200 , in one generalized form, includes the printer  260  that presents a bitmap  110  onto the print medium  125  based on the print job  220 . That is, the printing system  200  may rasterize the data of the print job  220  via the rasterizer  270  to generate one or more bitmaps  110 - 1 -N (where N is simply intended to represent an integer greater than 1 and not necessarily equal to other N references herein) for presentation to the printer  260  such that the printer  260  may apply ink onto the print medium  125  that is representative of the bitmaps  110 . Alternatively, the bitmaps  110  may be rasterized by the host system  210  and transferred to the CMYK printing system  200 . 
     As the bitmaps  110 - 1 -N are transferred to the printer  260  for printing onto the print medium  125 , the bitmaps  110 - 1 -N are also transferred to the controller  115  for processing as described above. More specifically, the controller  115  filters each bitmap  110  to provide variable heat control to the dryer  120 . As mentioned, the dryer  120  may include a plurality of heating elements  225 - 1 -N that are used to evaporate the carrier fluids and/or other liquids from the ink such that the colors of the ink attach to the print medium  125 . In this regard, the controller  115  may generate a plurality of heat control signals each of which being configured to independently control the heating elements  225 - 1 -N of the dryer  120 . That is, the controller  115  may generate a control signal for each of the heating elements  225 - 1 -N to independently control heat radiating from the heating elements  225 - 1 -N to the print medium  125 . Accordingly, each of the heating elements  225 - 1 -N is operable to radiate heat to a region of the print medium  125  that differs from that of other heating elements  225  of the dryer  120 . Moreover, the heat control signals themselves may vary over time to change the radiated heat from a particular heating element  225  over time. Thus, a controller  115  is operable to provide temporal and spatial heat control of the dryer  120  based on a particular bitmap  110  that it receives. Although shown and described with respect to a CMYK printer, the invention is not intended to be so limited. For example, the dryer system  100  may be operable with other types of printers, such as monochrome printers, so as to identify image regions within the bitmaps  110  and dry them as described above. 
       FIG. 4  is a detailed block diagram of the dryer system  100  in an exemplary embodiment. In this embodiment, the controller  115  is configured as a feed forward control system operable to generate heat control signals on a bitmap by bitmap basis. A feed-forward control system is operable to provide a control signal based on an external source, such as the bitmaps  110 - 1 -N. In other words, a controller  115  receives a first bitmap  110 - 1  to generate heat control signals for application to the heating elements  225 - 1 -N of the dryer  120 . The heating elements  225 - 1 -N use the heat control signals to dry the ink applied to the print medium  125  that is representative of the bitmap  110 - 1 . That is, the heating elements  225 - 1 -N respond to the heat control signals to apply time variable radiant heat. Afterwards, the controller may receive and process a second bitmap  110 - 2  to generate heat control signals for application to the heating elements  225 - 1 -N to dry the applied ink that is representative of the bitmap  110 - 2 . The controller  115  then processes a third bitmap  110 - 3  in similar fashion, and so on. 
     In this embodiment, the dryer  120  uses infrared energy to dry the print medium  125 . An infrared radiant dryer uses one or more infrared energy sources (e.g., heating elements  225 - 1 -N). The infrared spectrum determines where the infrared energy is absorbed into the print medium  125  and the inks used thereon. Attachment of the ink&#39;s pigment to the print medium  125  occurs when the infrared energy absorbed into the ink evaporates the water and/or other carrier fluids of the ink after the ink is applied to the print medium  125 . 
     The spectrum of the infrared energy can be chosen such that the carrier fluids absorb radiant energy based on the ink absorption spectrum. The substrate properties of the print medium  125  tend to limit the amount of energy absorbed. Some inks may even be configured to increase the energy absorption within the print medium  125 . Thus, from a simplified ink model, the amount of energy to dry the combination of the substrate of the print medium  125  and ink is generally a function of the ink volume applied, spectral characteristics of each primary color (e.g., C, M, Y, and K), and the spectral characteristics of the print medium  125 , including reflectance and transmittance. 
     To achieve optimal control of the dryer  120 , the function defined in the amount of energy is first modeled. Because of the numerous interactions, one approach is to use theoretical models that define a class of functions for the model. The model is then fit to actual empirical data. Orthogonal functions tend to minimize interaction effects of the drying process. These functions mainly fall into categories known as radial basis functions (e.g., Gaussian, Polyharmonic spline, etc.) and continuous cumulative probability functions (e.g., Weibull distribution, love normal distribution, etc.). The continuous cumulative probability function is an appropriate choice because drying becomes a matter of whether the probability that the amount of ink carrier fluid removed when the dryer  120  control inputs are applied is within a certain range. If the probability is within the expected range, the correct dryer inputs are applied. Because the continuous cumulative probability function is a multidimensional function, the relationship between the carrier fluid remaining on the substrate of the print medium  125  versus the amount of ink applied to the substrate of the print medium  125  for various inputs to the dryer  120  may be defined by holding the probability constant. Then, the correct model can be developed based on a set of empirical data describing the performance of the dryer  120 . 
     The dryer  120  is controlled based in part on derived inputs of the printer  260 . For a practical dryer, it is assumed that the infrared source is subdivided from 1 to N effective energy sources, or heating elements  225 . Each of the heating elements  2251 -N is arranged to produce uniform output across the web within the tolerance limits for a constant input. Then, the ink volume applied to the substrate of the print medium  125  prior to drying can be estimated. 
     Because ink from an inkjet head of the printer  260  is generally a constant volume device for each of its output dropped sizes, the bitmap for each color plane halftone image defines which drops size is applied at each addressable location. By replacing the digital representation of the drops by the physical drop size ink volume, a heat control signal at each pel location for the bitmap  110  can be defined. As mentioned, the dryer  120  is subdivided into N energy sources, where each subdivided energy source radiates a fixed area, and the radiated area is uniform across the web at each boundary between the heating elements  225 . Accordingly, the average amount of energy across the web for each subdivided heating element  225  is assumed to be proportional to the total ink volume across the effective length of the subdivided energy source of the dryer  120  for a single pel row of the bitmap  110 . In other words, the process direction of the print medium  125  width is a reciprocal of the process direction resolution. 
     For the static case, the issue of drying is proportional to the total ink volume in the radiated area. In the dynamic case, however, the ink volume changes based on the print job even though the velocity of the print medium  125  is approximately constant. Accordingly, the dryer control  440  may also use control inputs that take into account the dynamic response of the dryer  120  to change the output power level. The input signal driving the dryer  120  is modified by the inverse response to the dryer  120  to ensure that the energy of the dryer  120  output is relatively independent of the dynamic ink volume changes. The response of the dryer  120  can be determined by applying a step function as an input and then measuring the output of the dryer  120 . Generally, this procedure is performed twice, once for increasing energy and once for decreasing energy. 
     With this premise in mind, filters may be used to find the correct energy input signal for drying when the radiated area width of the subdivided energy source of the dryer  120  is wider than the ability to dry based on coverage. The first of these filters is an average filter  405  that initially filters the bitmap  110  to identify image regions in the bitmap  110  which may use more heat energy than other image regions. An example of such is illustrated in  FIG. 5 . The average filter  405  filters the bitmap  110  and identifies a image region  501  of ink which may require more heating by one or more the heating elements  225  than other image regions of ink on the print medium  125  as it approaches the dryer  120 . In this instance, the image region  501  may require heating by the heating elements  225 - 1  and  225 - 2  while leaving the remaining heating elements off or at some predetermined minimum heat level. 
     In this regard, the bitmap  110  may be collimated into rows for each of the heating elements  225  so as to find the maximum value of color values within a particular image region (e.g., CMYK, monochrome, etc.). This process is performed via the max filter  410 , as illustrated in  FIG. 6 . The max filter  410  uses the identified image region  501  to identify color density values that may be used to compute requisite heat control signals for the heating elements  225 - 1 -N. In this embodiment, the max filter  410  filters the image region  501  and forms two image regions having color density values  601  to generate appropriate heat control signals for the heating elements  225 - 1  and  225 - 2  at the time t 1  as these ink representations of the bitmap  110  come within range of the dryer  120 . These heat control signals based on the color density values  601  initiate “ramping up” of the heating elements  225 - 1  and  225 - 2 . The max filter  410  also extracts the maximum color density value  603  from the image region  501  to generate the time/spatial varying heat control signals for the heating elements  225 - 1  and  225 - 2  at the time t 2  (where the color density values  601 ,  602 ,  603  are increasing order of ink concentration). This row by row identification of maximum color values allows the controller  115  to apply heat control signals to each of the heating elements  225  as the print medium  125  with those color values represented in applied ink passes by the dryer  120 . 
     For each of the heating elements  225 , the output for each color plane in the bitmap  110  at each heating element  225  width is combined as a weighted sum via the weighted summer  415 . If the drop sizes for the primary colors (e.g., C, M, Y, and K) are not the same, the weighting factors account for the drop size effect. For example, because the energy response bandwidth of the dryer  120  is finite, the target energy level may be slightly higher than necessary to ensure adequate drying over the expected range of the ink volume applied to the print medium  125 . Additionally, the response of the dryer  120  for each of the primary inks is different. Because the spectral absorbtion response of each primary ink is generally fixed and because the spectral energy response of the dryer  120  is generally fixed, the composite input to the dryer  120  can be treated as a weighted sum of individual ink volumes, assuming superposition applies. Generally, the model of the dryer  120  assumes that the amount of energy absorbed into the substrate of the print medium  125  is small or at least approximately constant compared to the total energy required. If this assumption is false, the energy response to the dryer  120  using various print mediums can be measured and the inverse response calculated. 
     After the weighted sum is computed, the controller  115  passes the weighted sum through a lookup table  420  to convert the weighted sum to the required levels for the energy source inputs to the dryer  120  to produce the desired energy output from the heating elements  225 . In other words, the controller  115  uses the lookup table  420  to identify a heat control signal for each heating element  225  based on a mapping of color density values to drying temperature. This control data is then serialized for each heating element  225  to expedite generation of heat control signals via the serializer  425 . As part of the serialization process, a delay may be implemented if the dwell time of the dryer  120  is not adequate. In other words, if the heat control signal to a particular heating element  225  does not radiate enough heat for a particular amount of time, the duration and/or intensity of the heat control signal may be increased to the heating element  225 . 
     After the heat control signal data is serialized, the controller  115  may digitally filter the serialized data via the digital filter  430  based on inverse characteristics of the energy response of the dryer  120 . The digital filter  430  improves the overall response time of the heat control by removing noise from the serialized heat control data so as to smooth the input to the dryer  120 . In other words, the smoother heat control signal allows the dryer  120  to respond as desired more quickly. 
     Once each heat control signal is filtered, the transfer of each signal may be delayed by some amount of time by a delay  435 . For example, the speed of the print medium  125  passing by the dryer  120  may be determined and used as a control input to the dryer control module  440  as this generally affects when heat control signals are applied to the dryer  120 . If the heat control signals are generated prior to the representation of the bitmap  110  via the ink applied to the print medium  125 , those heat control signals may be buffered until the print medium  125  comes within range of the dryer  120 . 
     Other inputs to the dryer control module  440  may include the actual width of the print medium  125  as well as the physical distances between heating elements  225 . For example, all areas of the print medium should generally be exposed to the radiant heat of the dryer  120  at some minimal level so as to prevent damage to the print medium  125 , such as cockling and/or paper steering (e.g., degraded paper path performance based on shrinkage towards one edge of the print medium  125 ). Accordingly, the dryer control module  440  may use information pertaining to the physical distances between heating elements as well as the width of the print medium  125  to establish a minimal radiant heat exposure to the print medium  125  from the heating elements  225 . Other inputs to the dryer control module  440  may include safety signals that shut off the application of the heat control signals to the dryer  120 . For example, should the print medium  125  jam somewhere within the printing process, heating of the print medium  125  becomes unnecessary and potentially dangerous as it may cause a fire. Accordingly, indication of a paper jam may be transferred to the dryer control module  440  to turn off the dryer  120 . The dryer control module  440  may also be responsible for providing information indicative of the health of the dryer  120 . For example, the dryer  120  may be configured with a sensor that feeds back to the dryer control module  440  that indicates whether the heating elements  225  are responding to the generated heat control signals. If the heating elements  225  are not responding as desired, one or more the heating elements  225  may require replacement. 
     Although shown and described with respect to the controller  115  digitally processing the bitmap  110  throughout the elements  405  through  440 , the invention is not intended to be limited as such. For example, while the bitmap  110  is most likely a digital representation of the image, that digital representation may be converted to analog form at any point within the processing by the controller  115 . Accordingly, if the bitmap  110  is converted to an analog form prior to processing by the controller  115 , the average filter  405  would be implemented as an analog filter. Conversely, if the bitmap  110  is processed throughout the elements  405  through  435  in digital form, the dryer control module  440  may perform a digital to analog conversion of the heat control signals prior to application of the heat control signals to the dryer  120 . The heating elements  225  may even be digitally controlled by the dryer control module  440 . 
     The invention can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In one embodiment, the invention is implemented in software, which includes but is not limited to firmware, resident software, microcode, etc. 
       FIG. 7  is a block diagram depicting a processing system  700  also operable to provide the above features by executing programmed instructions and accessing data stored on a computer readable storage medium  712 . In this regard, embodiments of the invention can take the form of a computer program accessible via the computer-readable medium  712  providing program code for use by a computer or any other instruction execution system. For the purposes of this description, computer readable storage medium  712  can be anything that can contain, store, communicate, or transport the program for use by the computer. 
     The computer readable storage medium  712  can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor device. Examples of computer readable storage medium  712  include a solid state memory, a magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W), and DVD. 
     The processing system  700 , being suitable for storing and/or executing the program code, includes at least one processor  702  coupled to memory elements  704  through a system bus  750 . Memory elements  704  can include local memory employed during actual execution of the program code, bulk storage, and cache memories that provide temporary storage of at least some program code and/or data in order to reduce the number of times the code and/or data are retrieved from bulk storage during execution. 
     Input/output (I/O)  706  (including but not limited to keyboards, displays, pointing devices, etc) can be coupled to the processing system  700  either directly or through intervening I/O controllers. Network adapter interfaces  708  may also be coupled to the system to enable the processing system  700  to become coupled to other processing systems or storage devices through intervening private or public networks. Modems, cable modems, IBM Channel attachments, SCSI, Fibre Channel, and Ethernet cards are just a few of the currently available types of network or host interface adapters. Presentation device interface  710  may be coupled to the system to interface to one or more presentation devices, such as printing systems and displays for presentation of presentation data generated by processor  702 . 
     Although specific embodiments are described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.