Abstract:
A network connects plural computer systems to plural printers. A program of each computer system generates data supplied to at least one printer. A print spooler of each computer system stores the print data. Each printer comprises a daemon and local memory. A data control module monitors, via the network, data relating to a print job stored on a computer system and job timing information relating to preferred time for processing the print job. The daemon retrieves a copy of the data when the network becomes available to transfer the data, and stores the print data on the local memory. The retrieval and storage operations occur before the time specified in the job timing information. When the network traffic is low each printer locally stores data that are retrieved and stored prior to the time specified in the job timing information.

Description:
FIELD OF THE INVENTION 
     This invention relates to a print device for connection to a computer system. The invention also relates to a method of acquiring print data from a computer system. 
     BACKGROUND OF THE INVENTION 
     Print devices are commonly used in both domestic and commercial environments to convert print data, generated in a computer system, into hard-copy output. A computer system will generally include one or more application programs, such as a word processor program, from which print data is generated for output to a printer. The print data for a particular print ‘job’ usually comprises a page description language (PDL) file describing the physical content of the printable area, and a job description language (JDL) file for describing attributes of the print job, such as the type of paper to be used, the number of copies to be made, the type of finishing to be applied (e.g. stapled/laminated) and so on. Once a print job is generated by the application program, the print data for that job is applied to a print spooler for output to a printer. 
     A typical print device will comprise a raster-image processor (RIP) for converting the PDL into a file representing the graphical output, e.g. the dots to be printed on a page. This processed data is then passed to a print engine (PE) which converts the processed data into the electrical signals required to drive the physical mechanism of the print device, e.g. the drum of a laser printer, or the carriage/ink nozzles of an inkjet printer. 
     It is becoming increasingly common for a plurality of computer systems to be connected to a plurality of different printers by means of a computer network. In environments where a large number of print jobs are being processed over a period of time, timing information is often specified as part of the print job. This timing information will often represent a preferred time at which the print job should be processed, or perhaps the latest time at which the print job should be processed. In some circumstances, the print job may simply be placed in a queue on the spooler for passing to a printer at the earliest available time. The JDL of each print job may also specify that a particular print device on the network is to be used, e.g. because it is a colour printer or it has the required finisher device. 
     At the time at which the print job is to be processed, it is passed by the computer system to a print device. However, the problem often arises, particularly in networked systems, that the print job cannot be processed at the preferred time, since the data channel between the computer system and the print device is congested with data relating to other print jobs. Furthermore, where a particular print device is specified with a new print job, if that print device is already being used to print a different job, the new print job will have to wait until the other print job has been completed. This problem is particularly prevalent in commercial environments where print jobs are placed in a schedule. In such situations, network traffic tends to occur in clustered bursts and bottlenecks occur. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a print device for connection to a computer system, the print device comprising: a data control module; and a local memory, the data control module being configured to monitor, via a data link, print data relating to a print job stored on a computer system, the print data including job timing information relating to the preferred time at which the print job is to be processed, the data control module also being configured to retrieve a copy of the print data as soon as the data link becomes available to transfer the print data, and to store the print data on the local memory, the retrieval and storage operations being performed prior to the time specified in the job timing information. 
     Accordingly, the print device is capable of maintaining a local storage of print data, the print data being retrieved and stored prior to the time specified in the job timing information at a time when the data link between the print device and a computer to which it is connected is capable of allowing the transfer, e.g. in the case of a computer network, when the network traffic is low. It follows that the print job can thereafter be processed as soon as the print device itself is able to do so. Problems arising due to bottlenecks on the computer network are reduced, since the print data will have been pre-fetched to the print device, and will be ready for processing. 
     The data control module may be further configured to compare the job timing information with a further set of timing information stored on the local memory, the further set of timing information relating to print jobs currently stored on the local memory, and to retrieve a copy of the print data only if the print job can be processed prior to, or generally at, the time specified in the job timing information. The data control module may be further configured to: monitor file size information in the print data stored on the computer system, the file size information relating to the storage capacity required to store the print data; and to compare the file size information with the available storage space of the local memory, the print data being retrieved only if the print data can be stored on the available storage space of the local memory. 
     The data control module is preferable configured to retrieve print data from the computer system asynchronously. 
     The print device further may further comprise a RIP for processing retrieved print data prior to it being stored on the local memory. The print device may further comprise a PE for generating printed output from the processed print data stored on the local memory. In this respect, it should be appreciated that the print device may or may not include a PE. Indeed, where the print device includes no such PE, the print device is simply made available on the network for passing the processed data to one or more PE&#39;s via the network. 
     The data control module may be further configured to output an acknowledgement signal in response to print data being outputted to the PE, the acknowledgement signal being made available for sending to the computer system from which the print data was retrieved. 
     The local memory module is preferable a cache memory module. 
     According to a second aspect of the invention, there is provided a computer network comprising: one or more computer systems capable of generating print data; and a plurality of print devices a print device for connection to a computer system, each print device being capable of retrieving print data from the or each computer system via a data link and comprising: a data control module; and a local memory, the data control module being configured to monitor, via a data link, print data relating to a print job stored on a computer system, the print data including job timing information relating to the preferred time at which the print job is to be processed, the data control module also being configured to retrieve a copy of the print data as soon as the data link becomes available to transfer the print data, and to store the print data on the local memory, the retrieval and storage operations being performed prior to the time specified in the job timing information. 
     As a further point, it is possible to locate to data control module external to the or each print device. 
     According to a third aspect of the invention, there is provided a method of acquiring print data from a computer system, the method comprising: monitoring, by means of a data control module of a print device, print data relating to a print job stored on a computer system, the print data including job timing information relating to the preferred time at which the print job is to be processed; retrieving a copy of the print data as soon as a data link between the data control module and the computer system becomes available to transfer the print data, and storing the print data on a local memory of the print device, the retrieval and storage operations being performed prior to the time specified in the job timing information. 
     The method may further comprise: comparing the job timing information with a further set of timing information stored on a local memory of the print device, the further set of timing information relating to print jobs currently stored on the local memory; and retrieving the print data from the computer system via the data link only if the print job can be processed prior to, or generally at, the time specified in the job timing information. The print data may further include file size information relating to the storage capacity required to store the print data, the step of retrieving the print data from the computer system further comprising comparing the file size information with the available storage space of the local memory, the print data being retrieved only if the print data can be stored on the available storage space of the local memory module. 
     The method may further comprise: processing the retrieved print data using a RIP prior to storing it on the local memory. The method may further comprise generating printed output from the processed print data stored on the local memory. 
     An acknowledgement signal can be generated by the data control module in response to printed output being generated from the processed print data, the acknowledgement signal thereafter being sent to the computer system from which the print data was retrieved. The acknowledgement signal can be used to delete a copy of the print data stored in the computer system. Alternatively, the acknowledgement signal can be used to tag the print data to indicate that it has been printed, the tag being used thereafter by the computer system to indicate to further print devices that the print data has already been processed to generate printed output. 
     According to a fourth aspect of the present invention, there is provided a computer program stored on a computer usable medium, the computer program comprising computer readable instructions for causing a computer system to execute the steps of: monitoring, by means of a data control module of a print device, print data relating to a print job stored on a computer system, the print data including job timing information relating to the preferred time at which the print job is to be processed; retrieving a copy of the print data as soon as a data link between the data control module and the computer system becomes available to transfer the print data, and storing the print data on a local memory of the print device, the retrieval and storage operations being performed prior to the time specified in the job timing information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
         FIG. 1  is a block diagram representation of a computer network; and 
         FIG. 2  is a block diagram representation of a print device used in the computer network of  FIG. 1 ; and 
         FIG. 3  is a flow diagram showing the steps in a method of print data acquisition. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 1 , a computer network  1  comprises first, second and third computer systems  3 ,  5 ,  7  connected to first, second and third print devices  9 ,  11 ,  13  by means of a network  15 . Each computer system  3 ,  5 ,  7  comprises at least one application program capable of generating print data for output to one or more of the print devices  9 ,  11 ,  13 . The print data is output from each application program and stored in a print spooler (not shown) forming part of each computer system  3 ,  5 ,  7 . The first and second print devices  9 ,  11  are general-purpose print devices, whilst the third print device  13  includes a special finishing device, namely an automatic stapler (not shown). 
     Referring now to the block diagram of  FIG. 2 , each of the first, second and third print devices  9 ,  11 ,  13  comprises a controller  16 , a RIP module  17 , a local cache memory  19 , and a PE  21 . The controller  16  comprises a daemon  23 , the operation of which is described below. 
     In use, each of the computer systems  3 ,  5 ,  7  will generate print jobs, comprising a set of print data, over a period of time. Each print job includes a set of timing information specifying, for example, the latest time at which the print job is to be processed for printing to meet a customers specified requirement. Each print job also includes, as part of its JDL data, information as to the size of the print data for that print job, in other words, the memory capacity required to store the print data for that print job. The JDL data also specifies attributes of the particular print job, including whether or not a particular finishing operation, such as stapling, is required. 
     The daemon  23  comprises a computer program which is arranged to monitor print data relating to each print job being stored on the print spooler (not shown) of each of the first, second and third computer systems  3 ,  5 ,  7 . The daemon  23  first determines if the print device with which it is associated is suitable for printing the print job currently being monitored (referred to here as the “monitored print job”). So, for example, if the monitored print job is generated from the first computer system  3  and the JDL data for that print job specifies that the output should be stapled, then the daemon  23  of the first and second print devices  9 ,  11  will determine that they are not able to perform the required print operation, and so will proceed to monitor the next print job on the print spooler. 
     In the next step, the daemon  23  determines whether the monitored print job can be performed by that print device before, or generally at, the time specified in the timing information of the print job. This is effected by the daemon  23  performing a comparison of the timing information with a list of further timing information associated with print jobs already stored in the local memory  19  of its respective print device  9 ,  11 ,  13 . This list of further timing information effectively comprises a schedule of print jobs which that print device intends to print in the future. If the daemon  23  determines that, on the basis of the current comparison, it will not be possible to print the current print job at the specified time since its schedule is completely full prior to that time, it will proceed to monitor further print jobs on the relevant print spooler. 
     If the daemon  23  determines that it will be possible for the monitored print job to be processed prior to, or generally at, the time specified in its timing information (on the basis of the state of its current list of stored timing information), a further test is applied whereby it is determined whether the print data can be stored on the available disk space of the local memory  19 . This is performed using the JDL data, as mentioned above. Provided there is sufficient space on the local memory  19 , the daemon  23  commences a retrieval process in which a copy of the print data for the monitored print job is copied from the relevant print spooler to the local memory  19 . This retrieval process is performed as soon as the network connection  15  becomes available for data transfer, e.g. when the network traffic is low or zero. In the case shown in  FIG. 2 , the print data is first processed by the RIP module  17  prior to it being stored in the local memory  19 , although it will be appreciated that such RIP processing could be performed at a later time. The data is retrieved asynchronously. If the print data is not retrieved and stored in the local memory  19  in its entirety, e.g. due to some error or fault on the network connection  15 , then the daemon  23  will invoke a further retrieval attempt, provided the network connection  15  is still free. If not, the daemon  23  will wait until the network connection is free before attempting the further retrieval attempt. 
     It will be appreciated that, since each of the first, second and third print devices  9 ,  11 ,  13  comprises the controller  16  running the daemon  23 , it is possible that, over time, print data relating to some print jobs will be copied to the memory  19  of more than one print device. For example, if the JDL of a print job specified that no particular finishing was required for a given print job, the operation described above may well result in the print data for that print job being retrieved and stored onto the local memory  19  of each of the first, second and third print devices  9 ,  11 ,  13  (assuming they are each able to print the print job in the time specified by the timing information and that they have sufficient memory space available). Clearly, it will be undesirable for three different copies of the same set of print data to be made. Accordingly, once the print data is processed for printing, the daemon  23  is arranged to send an acknowledgement signal back to the computer system  3 ,  5 ,  7  from which the print job was retrieved. This acknowledgement signal can either be used to erase the copy of the print job stored on the relevant print spooler (thus preventing other print devices from acquiring the same print job or informing them that the job has now been processed) or, alternatively, to tag the JDL file for the copy of the print job on the relevant print spooler. This tag can be used to indicate that the print job has been processed, and so it need not be acquired or processed for printing by the daemon  23  of other print devices. The latter method has the advantage that, in the event of a problem in the local memory  19  of the print device which has acquired the print data for the print job, the tag can simply be reversed so that other devices can once again monitor and acquire the print data for that particular print job. 
     Having acquired and stored print data for a print job in the local memory  19  of one of the first, second or third print devices  9 ,  11 ,  13 , the print data is made available to a suitable PE  21  for further processing (i.e. printing) as soon as the print device has completed other print jobs which were scheduled to occur before the ‘current’ print job. This can be done directly from the memory, i.e. by means of the data path  25 , shown in  FIG. 2 , or by means of the controller  16 . It should be understood that the inclusion of a PE  21  in each print device  9 ,  11 ,  13  is not essential, it being possible to provide a print device simply comprising a controller  16 , a RIP module  17  and local memory  19  which can output data to a remote PE  21  somewhere else on the network  15 . 
       FIG. 3  is a flow diagram which illustrates the main steps in the print data acquisition method summarised above. The steps of those which are performed by the daemon  23  of each of the first, second, and third print devices  9 ,  11 ,  13 . The steps of the method described can be embodied in a computer program. For clarity, these main steps once again detailed below. 
     In a first step  30 , the daemon  23  monitors print data relating to a “next” print job which is stored on a print spooler of one of the first, second, and third computer systems  3 ,  5 ,  7 . In monitoring the next print job, in a next step  32 , it is decided whether or not the relevant print device (i.e. that with which the daemon  23  is associated) is capable of performing the monitored print job. As mentioned above, if the JDL data for the monitored print job specifies a particular finishing operation, for example, then in step  32 , it has to be determined whether the relevant print device is capable of performing that particular finishing operation. If not, the next print job is monitored again in step  30 . If it is so capable, in step  34 , it is determined whether the monitored print job can be performed prior to, or generally at, the required time specified in the timing information of the monitored print job. 
     If the monitored print job cannot be performed prior to, or generally at, the required time, the next print job is again monitored in step  30 . If the monitored print job can be performed prior to, or generally at, the required time, then in step  36 , it is determined whether or not the monitored print job can be stored in the local memory  19  of the relevant print device. This decision is based on the available storage space on the local memory  19 . If sufficient memory is not available, the next print job is again monitored in step  30 . If sufficient memory is available, then it is decided in step  38 , whether or not the traffic load on the network connection  15  permits the print data of the monitored print job to be transferred to the local memory  19  of the relevant print device. If so, then the print data is copied from the relevant computer system to the local memory of the relevant print device, i.e. in step  40 . If not, in step  42 , the network traffic continues to be monitored until the print data can be transferred, at which point the print data is copied to the local memory  19  in step  40 . 
     In the next test, i.e. step  44 , it is determined whether the print data has been filly copied to the local memory  19  of the relevant print device. In this sense, it will be appreciated that a failing network connection  15  can interrupt a copying process and so step  40  may not be fully completed. If the print data is not fully copied, step  42  is performed again until the data is filly copied to the local memory  19 . Once the print data is fully copied, in step  46 , the print job is performed prior to, or generally at, the time specified in the print data. Finally, in step  48 , an acknowledgement signal is returned to the relevant computer device from which the monitored print job was taken, for the reasons described above. Step  30  is then repeated for the next print job and the process repeats. 
     For each stage of the method, if it is determined that a print job has been held up for a predetermined time, e.g. due to an error on the network, an error message is flagged so that an operator can intervene. 
     It will be appreciated that the current state of network traffic has no bearing on the processing of the current print job, since it has been acquired previously (when network traffic was low or zero) and stored within one of the first, second or third print devices  9 ,  11 ,  13 . This ‘pre-fetching’ procedure allows efficient usage of existing network printing systems without requiring the installation of more expensive, faster, networks.