Abstract:
A method and system, for component replacement, which use a combination of replaceable component life tracking and error condition occurrence history to identify the need for component replacement.

Description:
FIELD OF THE INVENTION 
   This invention relates to determining the replacement need for replaceable components, and more particularly to determination of replacement need for replaceable components based on a combination of usage and error correlation. 
   BACKGROUND OF THE INVENTION 
   Many systems have multiple components that wear at different rates and are replaced as they wear out in order to keep the whole system operating. In such systems the replacement of some or all worn out components may require specially trained service professionals such as field service engineers. Some systems may be provided with replaceable components that are replaceable by the system operator, thereby eliminating, or at least reducing the frequency of, the need to place a service call. This not only may reduce overall maintenance costs, but also reduces system down time by eliminating response time. In either case, replacement by a service call or by the operator, it is desirable to track the usage of replaceable components so as to accurately anticipate when they will fail. U.S. Pat. No. 6,718,285, issued in the name of Schwartz, et al., issued on Apr. 6, 2004, henceforth referred to as the Schwartz patent, discloses a replaceable component life tracking system and is hereby incorporated in this application by reference. 
   The Schwartz patent discloses a replaceable component life tracking system in which the usage of each replaceable component is tracked using a predetermined parameter. In a preferred embodiment, the system is a printing device and the usage of each replaceable component is tracked using the parameter corresponding to the number of pages printed. The life expectancy of each replaceable component is predetermined, and as the usage of each replaceable component is tracked, it is compared to the predetermined life expectancy, and the result periodically reported to the system operator via an operator interface. If any replaceable component usage reaches the life expectancy of that replaceable component, the operator is notified immediately, and instructed that the replaceable component ought to be replaced. 
   For most systems, for a number of reasons, a life tracking process of the type described above only provides an approximate forecast of the end of useful life of the replaceable components. For example, the wear rate of some or all of the replaceable components may not be constant with respect to the predetermined usage parameter. In the printing device embodiment, for example, all printed pages do not necessarily result in the same wear rate for all replaceable components. Furthermore, if the system is one that stops and starts between jobs, wear of the replaceable components may be occurring, but with no incrementing of the usage parameter. It is well known that in systems of this type the components wear faster when many shorter jobs are being run versus fewer longer jobs. Also, most replaceable components do not fail instantaneously due to wear, but rather tend to degrade gradually. 
   As a result of these observations, the decision of when to replace a component as its usage approaches or exceeds the life expectancy is left to the system operator. Furthermore, the operator may be willing to accept some degradation of system performance and therefore replace components less frequently thereby decreasing operating costs. In the printing device embodiment, image quality on the printed pages may degrade slowly and, if the images being printed are less demanding textual images versus pictorial images for example, or if the customers are less demanding, the operator may choose to continue to use a component well past the life forecasted by the life tracking process. 
   SUMMARY OF THE INVENTION 
   In light of the above, a need exists to augment end of life forecasting methods based on usage. The present invention uses error condition history to augment forecasting end of life of replaceable components based on usage. Each replaceable component is cross-referenced to each known error condition of the system with a probability factor, each probability factor being a previously determined probability that the replaceable component could be the cause of the occurrence of the error condition. The frequency of occurrence of each error condition is tracked and accumulated. For each replaceable component, in addition to usage, an error weighting is tracked, the error weighting being the sum, for all error conditions, of the accumulated occurrence frequency of each error condition multiplied by the replaceable component probability factor for that error condition. For each replaceable component a predetermined combination of usage and error weighting is continually compared with a predetermined threshold, and the result reported to the system operator on a periodic basis. Hence the operator&#39;s process of deciding when a replaceable component needs to be replaced is enhanced, compared to a decision based on usage alone. 
   The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which: 
       FIG. 1  is an illustration of a system including a digital printer, a digital front end, and a user interface that is suitable for use with a preferred embodiment of the invention; 
       FIG. 2  is an illustration of a portion of the digital printer of  FIG. 1  with the cabinetry removed showing a number of operator replaceable components; 
       FIG. 3   a  is a basic high-level block diagram illustrating the pertinent control components of the digital printer, digital front end, and graphical user interface for the system of  FIG. 1 ; 
       FIG. 3   b  is the block diagram of  FIG. 3   a  with arrows showing the information processing flow between control components when an error condition is detected; and 
       FIG. 4  is a basic high-level flow chart of the process of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is an illustration of a system  100  suitable for use with the preferred embodiment of the present invention, and includes a digital printer  103 , a Digital Front End (DFE) controller  104 , and a Graphical User Interface (GUI)  106 . Digital printer  103  is provided with Operator Replaceable Component (ORC) devices that enable a typical operator to perform the majority of maintenance on the system without requiring the services of a field engineer. The ORC devices are devices or combinations of devices which are grouped together as components within systems that become worn after periods of use and must be replaced. Specifically, the ORC devices are those components used within digital printing systems that wear with use and must be replaced. Digital printer  103 , in the preferred embodiment, is a NexPress® 2100; however, the present invention pertains to systems in general, and digital printing systems in particular. 
   DFE controller  104  in the preferred embodiment is operatively associated with the digital printer  103 , and includes a computational element  105  for controlling the digital printer. Computational element  105  contains a substantial number of processing components that perform a number of functions including raster image processing, database management, workflow management, job processing, ORC service management including tracking of ORC usage, etc. Graphical User Interface (GUI)  106  communicates with computational element  105  and with the operator. Tracking of ORC usage in this preferred embodiment is disclosed in the above referenced Schwartz patent. In the preferred embodiment, GUI  106  provides the operator with the ability to view the current status of ORC devices in the digital printer  103 , and to thus perform maintenance in response to maintenance information provided on the graphical display of GUI  106 , as well as to alerts that are provided from the DFE controller  104 . It should be understood that while the preferred embodiment details a system  100  with a digital printer  103  having at least one computational element and another computational element associated with DFE controller  104 , similar systems can be provided with more computational elements or fewer computational elements, and that these variations will be obvious to those skilled in the art. In general, virtually any interactive device can function as DFE controller  104 , and specifically any Graphics User Interface (GUI)  106  can function in association with DFE controller  104  as employed by the present invention. 
   Referring now to  FIG. 2  of the accompanying drawings, a portion of the inside of the digital printer  103  is schematically illustrated, showing the image forming reproduction apparatus, designated generally by the numeral  200 . The reproduction apparatus  200  is in the form of an electrophotographic reproduction apparatus, and more particularly a color reproduction apparatus, wherein color separation images are formed in each of four color print modules, and transferred in register to a receiver member as a receiver member is moved through the apparatus while supported on a paper transport web (PTW)  216 . The apparatus  200  illustrates the image forming areas for a digital printer  103  having four color print modules, although the present invention is applicable to printers of all types, including printers that print with more or less than four colors. 
   The elements in  FIG. 2  that are similar from print module to print module have similar reference numerals with a suffix of B, C, M and Y referring to the color print module for which it is associated; black, cyan, magenta and yellow, respectively. Each print module ( 291 B,  291 C,  291 M,  291 Y) is of similar construction. PTW  216 , which may be in the form of an endless belt, operates with all the print modules  291 B,  291 C,  291 M,  291 Y and the receiver member is transported by PTW  216  from module to module. Four receiver members, or sheets,  212   a, b, c  and  d  are shown simultaneously receiving images from the different print modules, it being understood that each receiver member may receive one color image from each module and that in this example up to four color images can be received by each receiver member. The movement of the receiver member with the PTW  216  is such that each color image transferred to the receiver member at the transfer nip of each print module is a transfer that is registered with the previous color transfer so that a four-color image formed on the receiver member has the colors in registered superposed relationship on the receiver member. The receiver members are then serially detacked from the PTW  216  and sent to a fusing station (not shown) to fuse or fix the toner images to the receiver member. The PTW  216  is reconditioned for reuse by providing charge to both surfaces using, for example, opposed corona chargers  222 ,  223  which neutralize the charge on the two surfaces of the PTW  216 . These chargers  222 ,  223  are operator replaceable components within the preferred embodiment and have an expected life span after which chargers  222 ,  223  will require replacement. 
   Each color print module includes a primary image-forming member (PIFM), for example a rotating drum  203 B, C, M and Y, respectively. The drums rotate in the directions shown by the arrows and about their respective axes. Each PIFM  203 B, C, M and Y has a photoconductive surface, upon which a pigmented marking particle image is formed. The PIFM  203 B, C, M and Y have predictable lifetimes and constitute ORC devices. The photoconductive surface for each PIFM  203 B, C, M and Y within the preferred embodiment is actually formed on outer sleeves  265 B, C, M and Y, upon which the pigmented marking particle image is formed. These outer sleeves  265 B, C, M and Y, have lifetimes that are predictable and therefore, are ORC devices. In order to form images, the outer surface of the PIFM is uniformly charged by a primary charger such as corona charging devices  205 B, C, M and Y, respectively or other suitable charger such as roller chargers, brush chargers, etc. The corona charging devices  205 B, C, M and Y each have a predictable lifetime and are ORC devices. The uniformly charged surface is exposed by suitable exposure mechanisms, such as, for example, a laser  206 B, C, M and Y, or more preferably an LED or other electro-optical exposure device, or even an optical exposure device, to selectively alter the charge on the surface of the outer sleeves  265 B, C, M and Y, of the PIFM  203 B, C, M and Y to create an electrostatic latent image corresponding to an image to be reproduced. The electrostatic latent image is developed by application of charged pigmented marking particles to the latent image bearing photoconductive drum by a development station  281 B, C, M and Y, respectively. The development station has a particular color of pigmented marking particles associated respectively therewith. Thus, each print module creates a series of different color marking particle images on the respective photoconductive drum. The development stations  281 B, C, M and Y, have predictable lifetimes before they require replacement and are ORC devices. In lieu of a photoconductive drum, which is preferred, a photoconductive belt can be used. 
   Each marking particle image formed on a respective PIFM is transferred electrostatically to an intermediate transfer module (ITM)  208 B, C, M and Y, respectively. The ITM  208 B, C, M and Y have an expected lifetime and are, therefore, considered to be ORC devices. In the preferred embodiment, each ITM  208 B, C, M and Y, has an outer sleeve  243 B, C, M and Y that contains the surface to which the image is transferred from PIFM  203 B, C, M and Y. These outer sleeves  243 B, C, M and Y are considered ORC devices with predictable lifetimes. The PIFMs  203 B, C, M and Y are each caused to rotate about their respective axes by frictional engagement with their respective ITM  208 B, C, M and Y. The arrows in the ITMs  208 B, C, M and Y indicate the direction of their rotation. After transfer, the marking particle image is cleaned from the surface of the photoconductive drum by a suitable cleaning device  204 B, C, M and Y, respectively to prepare the surface for reuse for forming subsequent toner images. Cleaning devices  204 B, C, M and Y are considered ORC devices for the present invention. 
   Marking particle images are respectively formed on the surfaces  242 B, C, M and Y for each of the outer sleeve  243 B, C, M and Y for ITMs  208 B, C, M and Y, and transferred to a receiving surface of a receiver member, which is fed into a nip between the intermediate image transfer member drum and a transfer backing roller (TBR)  221 B, C, M and Y, respectively. The TBRs  221 B, C, M and Y have predictable lifetimes and are considered to be ORC devices for the invention. Each TBR  221 B, C, M and Y, is suitably electrically biased by a constant current power supply  252  to induce the charged toner particle image to electrostatically transfer to a receiver member. Although a resistive blanket is preferred for TBR  2211 B, C, M and Y, the TBR  221 B, C, M and Y can also be formed from a conductive roller made of aluminum or other metal. The receiver member is fed from a suitable receiver member supply (not shown) and is suitably “tacked” to the PTW  216  and moves serially into each of the nips  210 B, C, M and Y where it receives the respective marking particle image in a suitable registered relationship to form a composite multicolor image. As is well known, the colored pigments can overlie one another to form areas of colors different from that of the pigments. 
   The receiver member exits the last nip and is transported by a suitable transport mechanism (not shown) to a fuser where the marking particle image is fixed to the receiver member by application of heat and/or pressure. A detack charger  224  may be provided to deposit a neutralizing charge on the receiver member to facilitate separation of the receiver member from the PTW  216 . The detack charger  224  is another component that is considered to be an ORC device for the invention. The receiver member with the fixed marking particle image is then transported to a remote location for operator retrieval. The respective ITMs  208 B, C, M and Y are each cleaned by a respective cleaning device  211 B, C, M and Y to prepare it for reuse. Cleaning devices  211 B, C, M and Y are considered by the invention to be ORC devices having lifetimes that can be predicted. 
   In feeding a receiver member onto PTW  216 , charge may be provided on the receiver member by charger  226  to electrostatically attract the receiver member and “tack” it to the PTW  216 . A blade  227  associated with the charger  226  may be provided to press the receiver member onto the belt and remove any air entrained between the receiver member and the PTW. The PTW  216 , the charger  226  and the blade  227  are considered ORC devices. 
   The endless transport web (PTW)  216  is entrained about a plurality of support members. For example, as shown in  FIG. 2 , the plurality of support members are rollers  213 ,  214 , with preferably roller  213  being driven as shown by motor  292  to drive the PTW. Support structures  275   a, b, c, d  and  e  are provided before entrance and after exit locations of each transfer nip to engage the belt on the backside and alter the straight line path of the belt to provide for wrap of the belt about each respective ITM. This wrap allows for a reduced pre-nip ionization and for a post-nip ionization which is controlled by the post-nip wrap. The nip is where the pressure roller contacts the backside of the PTW or where no pressure roller is used, where the electrical field is substantially applied. However, the image transfer region of the nip is a smaller region than the total wrap. Pressure applied by the transfer backing rollers (TBRs)  221 B, C, M and Y is upon the backside of the belt  216  and forces the surface of the compliant ITM to conform to the contour of the receiver member during transfer. The TBRs  221 B, C, M and Y may be replaced by corona chargers, biased blades or biased brushes, each of which would be considered by the invention to be an ORC device. Substantial pressure is provided in the transfer nip to realize the benefits of the compliant intermediate transfer member which are a conformation of the toned image to the receiver member and image content on both a microscopic and macroscopic scale. The pressure may be supplied solely by the transfer biasing mechanism or additional pressure applied by another member such as a roller, shoe, blade or brush, all of which are ORC devices for the present invention. 
   The receiver members utilized with the reproduction apparatus  200  can vary substantially. For example, they can be thin or thick paper stock (coated or uncoated) or transparency stock. As the thickness and/or resistivity of the receiver member stock varies, the resulting change in impedance affects the electric field used in the nips  210 B, C, M, Y to urge transfer of the marking particles to the receiver members. Moreover, a variation in relative humidity will vary the conductivity of a paper receiver member, which also affects the impedance and hence changes the transfer field. Such humidity variations can affect the expected lifetime of ORC devices. 
   Appropriate sensors (not shown) of any well known type, such as mechanical, electrical, or optical sensors for example, are utilized in the reproduction apparatus  200  to provide control signals for the apparatus. Such sensors are located along the receiver member travel path between the receiver member supply, through the various nips, to the fuser. Further sensors are associated with the primary image forming member photoconductive drums  203 , the intermediate image transfer member drums  208 , the transfer backing members  221 , and the various image processing stations. As such, the sensors detect the location of a receiver member in its travel path, the position of the primary image forming member photoconductive drums  203  in relation to the image forming processing stations, and respectively produce appropriate signals indicative thereof. 
   Sensors on the primary image forming member photoconductive drums  203  measure the initial surface voltage, V zero , produced by the primary corona charging devices  205 , and the surface voltage, E zero , after exposure by the exposure mechanisms  206 . Additional sensors located along the receiver member travel path measure the density of marking particle process control patches developed on the primary image forming member photoconductive drums  203  by development stations  281 , and transferred via the intermediate image transfer member drums  208 , directly to the paper transport web  216 . 
   All sensor signals are fed as input information to Main Machine Control (MMC) unit  290 , which contains a computational element, and communicates with DFE controller  104 . Based on such sensor signals, the MMC unit  290  produces signals to control the timing of the various electrostatographic process stations for carrying out the reproduction process and to control drive by motor  292  of the various drums and belts. The MMC unit  290  also maintains image quality within specification using feedback process control based on the density of marking particle process control patches described above. The production of control programs for a number of commercially available microprocessors, which are suitable for use with the MMC, is a conventional skill well understood in the art. 
   All operating parameters monitored by the above described sensors are expected to remain within certain limits for normal operation of digital printer  103 . Any operating parameter value being outside normal operating limits constitutes an error condition. All possible error conditions are predetermined, assigned an error code, and stored in memory in MMC unit  290 . If MMC unit  290  detects, from any sensor input signals, an error condition, it records the error code and sends the error code to the DFE controller  104 . Each ORC device in digital printer  103  is known to relate to specific error conditions, and is cross-referenced to each error condition with a probability factor, which is a predetermined probability that the ORC device could cause the error condition. The probability factor is based on empirical knowledge of each ORC device, and can range from zero for an ORC/error condition where the ORC has no relationship to the error condition, to close to 100% for an ORC/error condition where a strong relationship exists between the ORC and the error condition. A cross-reference data table of ORC/error condition probability factors is stored in the DFE controller  104 . 
   The following is an example of an error condition related to development stations  281 . Development stations  281  contain developer having a mixture of pigmented marking particles and magnetic carrier particles. The pigmented marking particles become electrostatically charged by tribo-electric interaction with the carrier particles. The charged marking particles are attracted to the electrostatic latent image that was formed on the photoconductive surface of sleeves  265  of the primary image-forming members  203 , thereby developing the latent image into a visible image. As the developer ages due to printing, its ability to develop marking particles onto the photoconductive surface of sleeves  265  of the primary image-forming members  203  decreases. In order to maintain consistent marking particle density levels, the MMC  290  unit must increase various process control parameters and power supply voltages to compensate and to promote increased development of marking particles to the sleeves  265  of the primary image-forming members  203 . As the developer continues to age and process parameters and voltages continue to elevate, they will eventually hit their maximum levels and an error condition will be occur. As the condition worsens, multiple voltages will hit there limits, which will cause a more severe error condition, which could then lead to the stopping of the digital printer  103 . 
   The following is an example of an error condition related to the PIFM&#39;s  203 . Periodically, the MMC unit  290  will execute a calibration routine known as Auto-Process Setup, which is responsible for determining the characteristics of the PIFM&#39;s  203 , calculating process control starting points, and adjusting the process densities to their correct density aim values. During the first phase of this calibration cycle, exposure readings are taken to determine the speed and toe of the PIFM&#39;s  203 . These imaging member parameters are then used to calculate the process control starting points, which are then checked against various minimum and maximum limits. If these limits are exceeded, the MMC unit  290  will flag an error condition. 
   The DFE controller  104  tracks the frequency of occurrence of each error condition, checks the cross-reference data table of ORC/error condition probability factors, and, for each ORC device, computes an error weighting, which is the result of multiplying each probability factor for each error condition times the frequency of occurrence of each error condition. For each ORC device, the DFE controller  104  tracks the error weighting described above and the accumulated life as described in the above referenced Schwartz patent, compares a predetermined combination of ORC error weighting and ORC accumulated life to a predetermined threshold, and periodically reports the results to the operator via the GUI  106 . Any time the threshold is met for any ORC device, DFE controller  104  immediately alerts the operator via GUI  106  and suggests that the ORC device be replaced. 
     FIG. 3   a  is a block diagram illustrating the relationship between the MMC  290 , the DFE controller  104 , and the GUI  106 . The MMC  290 , DFE  104 , and GUI  106  are each composed of a substantial number of signal processing components, but only those pertinent to the preferred embodiment of the present invention are illustrated. In the MMC  290  the EP component  12  represents the collection of sensors in the electrophotographic reproduction apparatus  200  described above, and the ORC Manager  10  is the component responsible for maintaining ORC data, tracking ORC life, and detecting and sending error conditions to the DFE controller  104 . In the DFE controller  104 , the Engine component  16  is responsible for communicating with the EP component  12  and routing the communications to the ORC Service component  18 , which is responsible for all ORC service functions. In the GUI  106 , the Client ORC  22  component is responsible for displaying ORC database tables, and the Client Message Reporting  24  component reports messages to the operator. 
     FIG. 3   b  illustrates, with a series of arrows, the signal processing flow between components when an error condition is detected by the MMC  290 . The first step, arrow  30 , is sending of the error condition to the DFE Engine component  16 . The DFE Engine component  16  forwards the error condition to the ORC Service component  18 , arrow  32 , and to the Client Message Reporting component  24 , arrow  34 . The ORC Service component  18  checks the error threshold database table for applicable ORCs and sends any expired ORCs (based on exceeding threshold) to the ORC Client component  22 , arrow  36 , and to the Client Message Reporting component  24 , arrow  38 . 
     FIG. 4  is a flow chart of the signal processing described above. In the embodiment of  FIG. 4 , the MMC  290  detects an error and asserts the error to the DFE control  104  (step  128 ). The DFE controller  104  passes the appropriate error code to the ORC Service Component  18  (step  130 ). Where it is mapped (step  132 ) with the predetermined combination of ORC error weighting and ORC accumulated life is embodied in the two decision points  134  and  136 . The ORC error weighting is first compared to an error weighting threshold. If the error weighting threshold is met or exceeded, the operator is alerted (step  140 ), and it is suggested to replace the ORC. If the error weighting threshold is not met, the sum of ORC error weighting plus the accumulated life as a % of the life expectancy is compared to a combined threshold. If the combined threshold is met or exceeded, the operator is alerted (step  140 ) and it is suggested to replace the ORC. If the combined threshold is not met, normal processing is continued (step  138 ). The values of the ORC weighting threshold and the combined threshold in  FIG. 3  are adjustable for different types of customer environments and job flows. 
   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.