FIELD OF THE INVENTION 
     This invention relates to electrophotographic marking machines, and more specifically to an apparatus and method for monitoring operating parameters of the marking machine. 
     BACKGROUND OF THE INVENTION 
     In servicing and repairing electrophotographic (EP) marking machines, it has long been observed that the accurate analysis of the root cause of a functional failure or malfunction is critical in the successful implementation of the proper repair. Accurate and quick error analysis reduces the costs for troubleshooting itself as well as the costs for replacement parts. Any tools suited to the effective and accurate troubleshooting of malfunctions will ultimately yield higher customer satisfaction. 
     In addition, most consumables and components are replaced in accordance with manufacturer&#39;s recommendation which is based on copy or page-count. The end-of-life for the component or consumable is thus inferred rather than measured. As the copy count does not accurately reflect power-up and power-downs of the machine as well as ambient operating conditions, maintenance based on copy or page counts is inherently unreliable. 
     Therefore, the need exists for monitoring the operating conditions of an electrophotographic marking machine, wherein the operating parameters correspond to actual usage of the machine. The need also exists for permitting error analysis and trend analysis. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system for retaining image generation parameters and operating set points in an electrophotographic marking machine. These stored parameters can be compared to EP setpoints together with other key operating parameters as function of copy-count to allow for the evaluation of the component or consumable health. Furthermore, the measured data allow the prediction of the end-of-life point based on customer specific operating conditions such as jobstream, toner throughput, environmental conditions and others which have been known to affect the useful life of consumables and components. 
     With measured data available as consumables or components age with printing (e.g. developer, photoconductor), the prediction of end-of-life allows the pro-active exchange of identified consumables and components and, thus, avoids a service call before the component or consumable fails. A service call placed by the customer due to end-of-life of consumables and/or components is likely avoided, thus increasing the customer perceived reliability and customer satisfaction. 
     In the present invention, a logic and control unit (LCU), or a marking engine controller (MEC) cooperates with the storage of short term and long term data corresponding to different aspects of the electrophotographic process. One aspect of the invention is incorporated into embedded software to allow one to separate the trouble shooting of marking engine failures or malfunctions from the assessment of long term drifts in machine performance, both of which are important in monitoring marking engine performance. 
     The software is integrated with the LCU and provides for on an on-line data recording of predetermined parameters. The predetermined EP-parameters are recorded and stored for later retrieval. Two segments of memory are reserved for selected machine parameters recorded in response to electrophotographic marking for, first, short-term error analysis (for EP-history recording) and, secondly, for machine set points in response to autosetups to allow long-term trend analysis (for EP-trend recording). 
     The invention provides for the measurement and storage of two data sets. For short-term analysis, data corresponding to machine conditions during or associated with electrophotographic marking are gathered. In a first configuration, the data associated with the electrophotographic marking are collected at a high frequency, typically each time an electrophotographic marking is made. For long-term trend analysis, data corresponding to machine set points are gathered less frequently, typically each time an autosetup is performed. Typically, autosetup occurs each time the marking engine is powered up, and additionally at preset intervals, such as six-hour intervals, during periods of continuous operation. The autosetup can also be executed by a field engineer during a service call. While long-term data would be accessible from high-frequency measurements performed over a sufficiently long time, they would have to be extracted from a large excess of data points. With this invention, long-term trends would be observable from a manageable number of data points, while short-term errors could still be conveniently observed from high-frequency measurements. Also, since all but the most recent data are redundant, the older data can be discarded on a first-in, first-out (FIFO) basis. In practice, the last 1000 high-frequency and the last 500 low-frequency data are retained. Therefore, the high frequency data provide a record of the last 1000 frames, while the low-frequency data would typically provide a record of about the last 200 workdays. Discarding older data than necessary minimizes the demands on software and memory. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a diagnositic system for an electrophotographic marking machine. 
     FIG. 2 is a schematic representation of an alternative configuration of a diagnositic system for an electrophotographic marking machine. 
     FIG. 3 is a schematic representation of a further configuration of a diagnositic system for an electrophotographic marking machine. 
     FIG. 4 is a graph of representative data. 
     FIG. 5 is a graph of alternative representative data. 
     FIG. 6 is a graph of further representative data. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the present invention includes a diagnostic system  20  for assessing operability of a machine  22 . 
     The diagnostic system  20  includes a plurality of high-frequency inputs  24  and a plurality of low-frequency inputs  26  from the machine  22 , and a process recorder connected to the inputs  24  and  26 . The inputs or signals corresponding to the inputs are retained in electronic files  32  and  34 , containing respectively data sets of high-frequency data  36  and low-frequency data  38 . Each of the data sets  36  and  38  contains a respective plurality of subsets  40  and  42 , and each subset has a series of consecutive data points from a different input. FIG. 1 shows, by way of example, two each of the high-and low-frequency inputs  24  and  26 , and also one shared input  28  which provides data for both the high-frequency and low-frequency data sets  36  and  38 . In practice, the total number of inputs may typically be ten or more, and several may be shared inputs such as  28 . However, it is not precluded that each and every input will provide data for only one of the data sets  36  or  38 . 
     The recorder  30  is a storage device for retaining the data sets  36  and  38 . Preferably, the recorder  30  is a non-volatile memory in that it retains the data sets independent to the powered status of the machine  22 . The recorder  30  is selectively or permanently connected with a computer  44  having a keyboard  46  and a display  48 . On provision of an appropriate command from the keyboard  46 , the files  32  and  34  can be downloaded into the computer  44 , and selected data retrieved therefrom. The selected data can be displayed as a graphic image  50  on the screen  48 . Optionally, the computer  44  can be connected with a printer  52 , and the image  50  can be printed out as a hard copy  54 . 
     In a preferred embodiment of the invention, shown schematically in FIG. 2, the machine  22  is an electrophotographic (EP) marking machine or engine  60 , such as a copier or printer. The EP machine includes the recorder  30 . The EP machine  60  has a keypad  62  for entering commands, a screen  64  for prompting and displaying commands, a platen  66  for receiving an original document to be copied, and a tray  68  which can receive frames  70  printed by the copier  60 . Neither an original for copying, which is placed on the platen  66 , nor a platen cover are represented in the drawings. Also omitted from the drawings is any representation of an automatic feeder with which EP machines are commonly equipped. The computer  44  is any of a variety of computing devices including, but not limited to dedicated servicing devices as well as laptop computers. The computer  44  and the EP machine  60  are configured to provide operable interconnection during a service call, so that the computer operably connects to the recorder  30 . The operator can download the files  32  and  34  into the computer  44  and display selected data on the screen  48  as a graphic image  50 . Optionally, the computer  44  is connected to a printer  52  to generate a hard copy  54  of the data. It is understood the graphical display and hard copy generation can be done during the service call or at a later time. 
     In another embodiment of the invention, shown schematically in FIG. 3, the EP machine  60  would host the recorder  30 , while the keypad  62  and the screen  64  would not only serve to provide for the day-to-day operation of the EP machine, but would also be interactively connected with the recorder  30 . The relationship between screen  62 , the keypad  64  and the recorder  30  would be identical to that between the computer keyboard  46 , the computer screen  48  and the recorder  30  in the preferred embodiment. This embodiment would be particularly convenient for a trained operator who would normally be stationed at the copier site. 
     The term EP History corresponds to the high frequency data set  36  and the term EP Trend corresponds to the low-frequency data set  38 . A record of EP-History is useful for diagnosing the causes of actual malfunctions. For every printed frame, key EP-parameters are recorded characterizing the operation of all image-forming subsystems. The high-frequency data set  36  includes all selected data for 1000 frames, i.e, the data recording is structured such that all selected data of the last 1000 frames are always available upon request. Should the printer stop with e.g. a fatal error, the service engineer is able to access the last 1000 prints. Typical EP history includes values corresponding to print counter, primary charger voltage, film voltage before exposure, film voltage after exposure, toner concentration, replenisher rate and fuse temperature. 
     The EP Trend data provides a tool for analyzing the long-term drift of the operating conditions of the machine  22 . The paramters of the low frequency (EP trend) data set may include values corresponding to print counter, date and time, film voltage before exposure, film voltage after exposure, toner concentration, toner concentration setpoint, developer life counter. 
     Typically, the machine  22  includes software for setup or power up of the machine. The setup software applies each time the machine  22  is powered up. In addition, as many machines will run continuously (but for maintance) the software includes an automatic, timed, execution. The powered up setup and the automatic initiated setup are termed “autosetups.” With every completed autosetup, the achieved operating conditions are recorded in the low frequency data set as the EP trend data. Each occurance of the autosetup results in the recording of key EP-parameters. The EP parameters include the operating setpoints of the image-forming subsystems. Although the long term, EP trend data, (low-frequency data set  38 ) includes all selected data for 500 autosetups, it is understood the long term data set may include fewer or greater points. The particular number of autosetups recorded is at least partially determined by the specific machine, the operating conditions as well as desired performance parameters. Thus, in the present example, the data recording is structured such that the selected operating conditions of the last 500 autosetups are maintained at the machine. Since the autosetup is initiated each time the machine is powered up, and typically every 6 hours (of continuous operation)., approximately 200 workdays of trend data are normally included in the low frequency data set. 
     The following examples will provide a better understanding of the diagnostic system  20 . However, assistance in trouble shooting the machine  22  accurately and effectively is not limited to the examples shown. 
     EXAMPLE 1 
     Error Analysis using Data of the Short-Term Recorder 
     In an example depicted in FIGS. 4 and 5, the operator and the service technician of the printer observed the loss of developer at apparently random intervals. No cause or machine malfunction could be identified at the time of trouble shooting. Repeatedly, the developer was replaced. FIG. 4 shows a plot in which the x-axis  80  represents the number of frames printed since the last power-up, and the y-axis  82  represents any of a plurality of EP process voltages and also transfer current, which are parameters known in the art. In FIG. 5, the y-axis  82  represents EP controls over the same sequence of prints as those of FIG.  4 . In particular, the recorded controls were charging efficiency, densitometer efficiency and bias offset, which again are terms known in the art. Analysis of the data revealed that the charger efficiency suddenly dropped causing the offset voltage V o −V bias  to drop from the desired 110 V to only 40V. The incident is marked by arrows  84  in FIG. 4 (V o  and V o  average) and FIG. 5 (bias offset average). Similarly, the efficiency of the charger suddenly increased, causing an increase in the offset voltage from the desired 110V to about 170V. A material defect in the high-voltage plastic components of the charger was identified as the root-cause providing a low impedance electrical path to ground triggered by environmental conditions. The charger was replaced and the problems were resolved. 
     EXAMPLE 2 
     Trend Analysis using Date of the Long-Term Recorder 
     As components and consumables age, the image-forming subsystems degrade in their performance. Beyond certain limits, the image quality will suffer. With the long-term recorder incorporated into the MEC, trends in operating setpoints of the image-forming subsystems can be analyzed and projections for end-of-life of consumables and/or components are based on data. In FIG. 6, the x-axis  80  is marked by dates covering about six weeks. Since each autosetup event is recorded in real time, the successive events can be plotted with reference to the x-axis  80 , and trends observed. The example of FIG. 6 shows setpoint data for the primary charging system, the bias voltage, the voltage after exposure and the transfer current, which are represented by the y-axis  82 . All setpoints are increasing as it is expected for new developer and a new photoconductor. With a very low monthly volume of about 55K, the peak in operating points is not yet achieved. Towards the end-of-life of the developer the charge-to-mass ratio of the developer will decrease and with it the setpoints. At the manufacturer&#39;s recommended values for the setpoints, the developer in terms of charge-to-mass ratio is very likely the limiting factor in achieving the desired image quality. The developer should then be changed. 
     Over time, the field engineer based on his own experience and knowledge of the customer job stream will be able to access whether e.g. developer replacement should be performed while he is at the site or deferred until his next visit. In addition, since many EP-process issues are charge-to-mass (Q/m) related, the field engineer with his knowledge of the customer&#39;s jobstream can select a particular customer target indicating a Q/m-related artifact. As part of the field engineer&#39;s adaptive learning, the selected target printed at regular intervals (e.g. every service call) in conjunction with the recorded trend data will yield a customer specific profile for end-of-life of consumables and components. A customer specific profile for usage of consumables or components can further be augmented and refined by employing the use of fuzzy logic predictions rather than deterministic predictions of conventional programming tools. The combination of data recorded by the marking engine itself together with input by customer or field engineer into the maintenance database stored on the machine will after a learning period yield the customer profile. 
     The compositions of the high-frequency and low frequency data data sets,  36  and  38  respectively, are selected based on their role in either short-term or long-term analysis. Each sample data set  36  and  38  is recorded at a different predetermined frequency. Some data are recorded in common for both long-term and short-term analysis, albeit at the different frequencies. 
     It is theoretically possible that the electrophotographic marking machine may be operable for extended periods with only minimal operation. Such an extreme but most unlikely circumstance could reverse the magnitudes of the frequencies or data-gathering periods from those which would normally expected. It will therefore be understood that in the foregoing specification, the usages “short-term”, “long-term”, “high frequency” and “low-frequency”are chosen because they overwhelmingly represent the normal manner of using the machine. 
     While the present invention has been described in terms of an electrophotographic marking machine, it is understood, the invention can be employed with process lines and manufacturing. In particular coating processes, production or creation of products. 
     The present invention has been described in connection with certain embodiments, but it is not intended to limit the scope of the invention to the particular form set forth; on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
A system for assessing the performance of an electrophotographic marking machine is provided, wherein data from several different inputs are gathered in two distinct sets having different frequencies. A high-frequency data set includes parameters typically recorded with each print made, and provide an electrophotographic history which is used in deducing the cause of malfunctions. The lower-frequency data are typically recorded at the time of each autosetup, and provide electrophotographic trend information which is used as a predictor of component and consumable lifetimes. In each data set, only data over an appropriately selected period maintained on a first-in, first-out basis. This system has the advantage of simultaneously providing an intensive recent history for tracing faults, and enabling long-term trends to be discerned without being buried in a redundant excess of data.