Patent Publication Number: US-8534662-B2

Title: Image forming apparatus, control method therefor, and computer-readable medium

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus, a control method therefor, and a computer-readable medium and, more particularly, to an image forming apparatus including a function of automatically ordering an exchange part. 
     2. Description of the Related Art 
     Various consumables and exchange parts used in an image forming apparatus such as a printer or copying machine are conventionally exchanged as part of maintenance when a serviceman or the like visits the user regularly or upon receiving a report from him/her. Note that the various consumables indicate a toner bottle, a toner cartridge, and the like, and the exchange parts indicate a dram unit, a feed roller, and the like. 
     To further reduce the down time of the image forming apparatus in the future, however, it is desirable that the user can readily perform maintenance operations without depending on operations by the serviceman. 
     To meet the needs, an image forming system has been considered in which an image forming apparatus determines, if the remaining amount of a consumable is small or an exchange part consumed level is high, that it will be necessary to exchange the consumable or part soon, and automatically orders it. The system is characterized in that an order is sent before a conventional life-time warning in consideration of the number of dates necessary for delivery and the like. 
     On the other hand, in the image forming apparatus, a rubber part of the feed roller, which contacts a paper sheet, wears due to the use of it over a long period, and thus a feed failure occurs, thereby causing a paper jam. To solve this problem, for example, a technique described in Japanese Patent Laid-Open No. 2011-32081 been proposed. In this conventional technique, a feed speed when a paper sheet is sent out from a feed cassette is detected. If the detected speed becomes lower than a preset value, the priority level of the feed cassette for being selected as a feed source is changed. 
     In the above-described automatic order system, ordering the feed roller indicates that deterioration of the feed roller has occurred at this time. If a paper sheet is repeatedly fed in this state, a device malfunction such as a paper jam due to a feed failure may often occur. 
     To avoid this problem, the technique described in Japanese Patent Laid-Open No. 2011-32081 is applicable. In this technique, however, the consumed level of the feed roller is determined by successively detecting a feed speed, a protection operation of changing the priority level works in a next feed operation. 
     The present invention has been made in consideration of the above technical background, and provides an image forming apparatus for automatically ordering a feed roller to avoid, at an early timing as compared with the conventional technique, a situation in which a deteriorating feed roller is frequently used to cause a device malfunction such as a paper jam to often occur. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided an image forming apparatus which includes a plurality of feeding units each formed by an exchangeable part, and selects one of the plurality of feeding units based on priority levels of the plurality of feeding units in a feed operation, comprising: a monitoring unit configured to monitor a consumed level of the part forming the feeding unit; a notification unit configured to send a notification to a user in a case where the monitoring unit detects that a life-time of the part has been reached; an ordering unit configured to order the part before the monitoring unit detects that the life-time of the part has been reached; and a changing unit configured to change the priority level of the feeding unit formed by the part being ordered to be lower than the priority levels of other feeding units. 
     According to another aspect of the present invention, there is provided a control method for an image forming apparatus which includes a plurality of feeding units each formed by an exchangeable part, and selects one of the plurality of feeding units based on priority levels of the plurality of feeding units in a feed operation, the method comprising: monitoring a consumed level of the part forming the feeding unit; sending a notification to a user in a case where it is detected in the monitoring step that a life-time of the part has been reached; ordering the part before it is detected in the monitoring step that the life-time of the part has been reached; and changing the priority level of the feeding unit formed by the part being ordered to be lower than the priority levels of other feeding units. 
     According to the present invention, it is possible to reduce the frequency of occurrence of a malfunction in an image forming apparatus as compared with the conventional technique, thereby enabling to continue a stable feed operation. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing an example of the overall configuration of an image forming system; 
         FIG. 2  is a sectional view showing an example of the reader unit and printer unit of an image forming apparatus  102 ; 
         FIG. 3  is a block diagram showing an example of the arrangement of the image forming apparatus  102 ; 
         FIG. 4  is a block diagram showing an example of the configuration of a control program executed by the image forming apparatus  102 ; 
         FIG. 5  is a table showing an example of the registered data of a part management table; 
         FIG. 6  is a sequence chart showing an example of a feed roller automatic order procedure; 
         FIG. 7  is a flowchart illustrating an example of the operation of a feed stage selection processing unit  455 ; 
         FIG. 8  is a flowchart illustrating feed stage candidate list initial value generation processing according to the first embodiment; 
         FIG. 9  is a flowchart illustrating feed stage candidate list initial value generation processing according to the second embodiment; and 
         FIG. 10  is a view showing an example of the detailed arrangement of a cassette  311 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Embodiments for carrying out the present invention will be described below with reference to the accompanying drawings. 
     First Embodiment 
     System Configuration 
       FIG. 1  is a view for explaining the configuration of an image forming system according to the embodiment.  FIG. 1  shows an example of the image forming system in which an image forming apparatus  102  and a management server  106  are connected to each other via the Internet. Note that the image forming apparatus  102  includes a printer or an MFP (MultiFunction Peripheral). 
     Referring to  FIG. 1 , a LAN (Local Area Network)  101  communicably connects the image forming apparatus  102  to be managed by the management server  106  with information processing apparatuses  104  and  105 . An information processing apparatus  103  serves as a proxy server. Furthermore, the information processing apparatus  104  serves as a firewall arranged for increasing the security of communication with the Internet  108 . 
     The personal computers (PCs)  105  are used by general users for business operations, and are interconnected via the LAN  101 . The management server  106  collectively manages the operation states of a plurality of image forming apparatuses  102  arranged within the firewall (in an intranet environment  107 ). Note that the management server  106  receives the operation mode setting of the image forming apparatus  102 , operation information such as a counter value and operation log, failure information indicating a hardware failure or frequent paper jams, a notification about a part automatic order, and the like. Note that in the actual image forming system, a plurality of intranet environments  107  and the management server  106  are interconnected via the Internet  108 . 
     The image forming apparatus  102  performs communication via the LAN  101  according to its own communication schedule. At this time, the image forming apparatus  102  processes its own operation mode setting, operation information such as a counter value and operation log, failure information indicating a hardware failure or frequent paper jams, a notification about a part automatic order, and the like to obtain communication data, and then transmits them to the management server  106  via the Internet  108 . 
     Furthermore, the management server  106  sends, to the image forming apparatus  102 , a command instruction to update setting information or to restart the apparatus. As a communication method for this operation, MIB (Management Information Base) is exchanged according to SNMP (Simple Network Management Protocol). 
     Although protocols such as HTTP and HTTPS are assumed to be the communication protocol, the present invention is not particularly limited to them. For example, in the example of the image forming system shown in  FIG. 1 , the image forming apparatus  102  uses HTTPS to transmit data to the management server  106  via the proxy server (information processing apparatus  103 ) and the firewall (information processing apparatus  104 ). 
     The management server  106  issues a command for the image forming apparatus  102  to control it. The image forming apparatus  102  acquires a command from the management server  106  at regular intervals (or in response to an instruction from the management server  106 ) (to be referred to as a command request hereinafter). The command issued by the management server  106  is, therefore, saved within the management server  106  until it is acquired by the image forming apparatus  102 . 
     As a command acquisition method, for example, the image forming apparatus  102  uses an SSL certificate saved within itself to perform HTTPS communication with the management server  106 . At this time, when the image forming apparatus  102  starts communication using a specific SSL certificate, the management server  106  recognizes that the communication partner is an image forming apparatus as a management target. 
     A monitoring apparatus (not shown) for executing the following communication processing is arranged within, for example, the image forming apparatus  102 . The monitoring apparatus is assigned with an ID for uniquely identifying the apparatus. After HTTPS communication is established, the monitoring apparatus uses a protocol such as SOAP to transmit the ID to the management server  106 . This allows the management server  106  to specify the image forming apparatus  102  which has performed communication. 
     The management server  106  enables to control the specific image forming apparatus  102  via the Internet  108  by adding a command to a response to the ID. 
     [Image Forming Apparatus] 
       FIG. 2  is a sectional view showing the hardware arrangement of the image forming apparatus  102  shown in  FIG. 1 . 
     The document feeding unit of a reader unit  200  feeds documents one by one from the top onto a platen glass  211 . After the end of a document reading operation, the document feeding unit discharges the document on the platen glass  211  to a discharge tray  219 . When a document is conveyed onto the platen glass  211 , a lamp  212  is turned on, and an optical unit  213  starts moving to expose and scan the document. Light reflected by the document at this time is guided to a CCD image sensor (to be referred to as a CCD hereinafter)  218  by mirrors  214  to  216  and a lens  217 . The CCD  218  reads the scanned document image. Image data output from the CCD  218  undergoes predetermined processing and is then transferred to the controller unit  400 . The reader unit  200  includes a document detection sensor  250  which detects the presence/absence of a document. The document detection sensor  250  is formed by a lever sensor or optical sensor. 
     A laser driver  321  of a printer unit  300  drives a laser emitting unit  322  to emit a laser beam corresponding to the image data output from the controller unit  400 . The laser beam irradiates a photosensitive drum  323 , on which a latent image corresponding to the laser beam is formed. A developing unit  324  applies a developer to the latent image portion on the photosensitive drum  323 . 
     The printer unit  300  includes, as paper storage units (feeding units), drawer-shaped cassettes  311  to  314  and a manual feed stage  315  on a tray exposed outside of the apparatus. They will be collectively called “feed stages” hereinafter. Except for the manual feed stage  315 , paper sheets are conventionally supplied by drawing a cassette, adding paper sheets as printing media in it, and closing it. 
     Each feed stage includes a feed sensor. Sensors  351 ,  352 ,  353 , and  354  are provided in the cassettes  311 ,  312 ,  313 , and  314 , respectively. A sensor  355  is provided in the manual feed stage  315 . 
     In synchronism with the start of emission of a laser beam, a paper sheet is fed from one of the cassettes  311  to  314  and the manual feed stage  315 , and is conveyed to a transfer unit  325  through a conveyance path  331  to transfer, to the paper sheet, the developer attached to the photosensitive drum  323 . A conveyance belt  326  conveys the developer-attached paper sheet to a fixing unit  327 , and the developer is fixed onto the paper sheet by the heat and pressure of the fixing unit  327 . The paper sheet having passed through the fixing unit  327  is discharged through conveyance paths  335  and  334 . Alternatively, to reverse the printed surface and then discharge the paper sheet, the paper sheet is guided to a conveyance path  338  through a conveyance path  336 , and conveyed from there in an opposite direction to pass through conveyance paths  337  and  334 . 
     When double-sided printing is set, the paper sheet is guided from the conveyance path  336  to a conveyance path  333  by a flapper  329  after passing through the fixing unit  327 . The paper sheet is then conveyed in an opposite direction, and guided to a re-feed conveyance path  332  through the conveyance path  338  by the flapper  329 . The paper sheet guided to the re-feed conveyance path  332  is fed again to the transfer unit  325  through the conveyance path  331  at the above-described timing. The paper sheet discharged through the conveyance path  334  is conveyed to a discharge bin  328  and stacked. 
     [Cassette] 
       FIG. 10  shows the arrangement of the cassette  311  of the feed stages of the printer unit  300 . The cassette  311  includes a cassette opening/closing sensor  361 , a feed roller  362 , a separation roller  363 , a conveyance roller  364 , a lifter  365 , a lift position detection sensor  366 , a paper detection sensor  367 , and a feed sensor  368 . The cassette opening/closing sensor  361  detects opening/closing of the cassette. The feed roller  362  feeds a supplied paper sheet. The separation roller  363  separates the stacked paper sheets not to feed a plurality of paper sheets. The conveyance roller  364  conveys a separate paper sheet to a conveyance path. The lifter  365  lifts up the supplied paper sheet to contact the feed roller. The lift position detection sensor  366  detects the lift-up position of the paper sheet by the lifter  365 . The paper detection sensor  367  detects whether there is a paper sheet within the cassette. The feed sensor  368  detects whether a paper sheet has been successfully fed. Paper sheets  370  shown in  FIG. 10  indicate paper sheets supplied in the cassette  311 . 
     [Controller Unit] 
     The arrangement of the controller unit  400  within the image forming apparatus  102  will be described based on a block diagram shown in  FIG. 3 . Each component of the controller unit  400  is connected with a system bus  409 . 
     A ROM  403  stores a control program for the image forming apparatus  102 . A CPU  401  executes the control program. The control program includes a program in which instructions associated with processing in  FIG. 4  (to be described later) are described. A RAM  402  is used as, for example, a work memory area for executing a program, and an image memory area for temporarily storing image data. 
     An accumulation memory  404  is a nonvolatile memory, and stores various data which need to be stored even after the image forming apparatus  102  is turned off. The accumulation memory  404  stores, for example, information such as an operation log, error, jam error, and alarm log. An operation unit  406  includes a display unit in addition to various function keys and a ten-key pad. By operating these keys, the user can instruct to start/stop an operation or instruct various settings when using a function provided by the image forming apparatus  102 , such as a copy or scan function. 
     Furthermore, the user can designate, through the operation unit  406 , various settings for the image forming apparatus  102  itself, and the paper size and paper type of paper sheets accommodated in each of the cassettes  311  to  315 . The operation signal of each key is input to the CPU  401 , which then executes processing corresponding to the key. The CPU  401  displays various screens on the display unit (not shown) of the operation unit  406  as needed. 
     A communication unit  405  serves as an interface unit for connecting to the LAN  101  shown in  FIG. 1 . The CPU  401  can execute communication processing with the management server  106  via the communication unit  405 . A reader I/F  408  serves as an interface unit for controlling driving of the reader unit  200 . A printer I/F  407  serves as an interface unit for controlling driving of the printer unit  300 . 
     [Automatic Order Processing] 
     Feed roller automatic order processing in the image forming system shown in  FIG. 1  will be described with reference to  FIGS. 4 ,  5 , and  6 . 
       FIG. 4  shows an example of the configuration of the control program executed by the CPU  401  of the image forming apparatus  102 . A print job receiving unit  450  receives a print job, and calls a print job control unit  451 . The print job control unit  451  controls the received print job, and calls a print processing unit  452 . The print processing unit  452  processes print data. A feed stage selection processing unit  455  is called when it is necessary to feed a printing paper sheet to execute the print processing unit  452  by the print job control unit  451 , and determines, according to the setting of the print job, a feed stage as a feed source to feed a paper sheet. 
     A part consumption detection unit  453  detects the consumed level of each exchangeable part to be automatically ordered. At this time, the part consumption detection unit  453  detects in consideration of the consumption characteristics which vary depending on the type of part. In this embodiment, a part to be automatically ordered is the feed roller of each feed stage, and the characteristics indicate the number of times the feed roller is used to feed a printing paper sheet. A part order management unit  454  manages, as data (to be described later), the consumed level of each part detected by the part consumption detection unit  453 . If the consumed level satisfies a predetermined condition, a delivery request notification is sent to the management server  106 . 
     Note that information about the consumed level of each part and the like are managed as a part management table  500  shown in  FIG. 5 , and are stored in the accumulation memory  404 . In the part management table  500 , a part ID  501 , a current counter value  502 , an order timing value  503 , a life-time warning value  504 , a predetermined life-time value  505 , and an order flag  506  are defined in advance and registered. Note that the structure of the part management table  500  shown in  FIG. 5  is merely an example, and different values may be defined and registered according to the characteristics of each part. 
     The part ID  501  is a number for uniquely specifying each feed roller. For example, “100001” indicates a feed roller used in the cassette  311  of  FIG. 1 . Similarly, a part ID is assigned to each of the feed rollers mounted in the cassettes of the image forming apparatus  102 . The current counter value  502  indicates the number of times a feed roller indicated by the part ID  501  is used to feed a printing paper sheet. Note that if a feed roller is exchanged due to consumption or the like, the current counter value  502  is reset. The order timing value  503  is a threshold for automatically ordering the feed roller. 
     The life-time warning value  504  indicates the number of feed operations to warn that the life-time of the feed roller indicated by the part ID  501  is about to end. The predetermined life-time value  505  indicates the limit of the number of feed operations processible by the feed roller indicated by the part ID  501 . 
     (Processing Procedure) 
       FIG. 6  is a sequence chart showing the procedure of the feed roller automatic order processing. A case in which the feed roller with the part ID  501  of “100001” is ordered will be described. 
     The part order management unit  454  of the image forming apparatus  102  detects that the current counter value  502  of the part ID “100001” has reached the order timing value  503  (S 601 ). This triggers the part order management unit  454  to send an exchange feed roller delivery request notification to the management server  106  (S 602 ). At this time, the part order management unit  454  changes the order flag  506  of the part ID “100001” managed in the part management table  500  from “OFF” to “ON”. Upon receiving the delivery request notification from the image forming apparatus  102 , the management server  106  sends an appropriate delivery request to a delivery company  110  in response to the request (S 603 ). The delivery request sent by the management server  106  may have any form such as email. The delivery company  110  delivers an exchange feed roller to a user  109  as a designated delivery destination according to the delivery request (S 604 ). 
     If the feed roller with the part ID “100001” is continuously used, the current counter value  502  reaches the life-time warning value  504  (S 605 ). In the embodiment, however, the part order management unit  454  does nothing at this timing. If the feed roller with the part ID “100001” is continuously used thereafter, the part order management unit  454  detects that the current counter value  502  has reached the predetermined life-time value  505  (S 606 ). This triggers the part order management unit  454  to display, for the user  109 , a warning message indicating that the feed roller needs to be exchanged (S 607 ). 
     Upon receiving the warning message, the user  109  exchanges the feed roller with the part ID “100001” for a delivered exchange feed roller (S 608 ). Upon completion of the exchange operation, the part order management unit  454  sends a feed roller exchange completion notification to the management server  106  (S 609 ). At the same time, the part order management unit  454  changes the order flag  506  of the part ID “100001” from “ON” to “OFF”. 
     Referring to the above description, the order flag  506  is “ON” from when the delivery request notification is sent (S 602 ) until the exchange completion notification is sent (S 609 ). 
     Note that the consumed level for determining the feed roller order timing is not limited to the current counter value  502  of the feed roller shown in the embodiment. For example, the operation time of the feed roller, the paper jam rate or paper slip rate when the feed roller is used, or a combination thereof may be used. In this case, the part management table  500  manages a corresponding value. 
     Although in this embodiment, a part to be exchanged is a feed roller, it may be another consumable having an influence on the print efficiency. Furthermore, the present invention may be applied to a plurality of parts mounted in one feed stage. 
     Although in this embodiment, a life-time warning is not displayed in S 605 , it may be displayed so that an administrator or the like can check it. Furthermore, if the delivery request notification is sent in S 602 , information indicating it may be displayed. 
     (Processing Procedure) 
     The procedure of feed stage selection processing by the feed stage selection processing unit  455  of the image forming apparatus  102  will be described with reference to a flowchart shown in  FIG. 7 . Note that processing in each step of the flowchart in  FIG. 7  is implemented when the CPU  401  shown in  FIG. 3  loads the control program stored in the ROM  403  into the RAM  402 , and executes it. 
     After the start of the processing, the feed stage selection processing unit  455  determines whether a feed stage has been designated in a print job (step S 701 ). If a specific feed stage has been designated as a feed source (YES in step S 701 ), the process advances to step S 702 , in which the feed stage selection processing unit  455  determines the designated feed stage as a feed source. The processing then ends. If no specific feed stage has been designated (NO in step S 701 ), that is, “feed stage automatic selection setting” has been designated, the process advances to step S 703 . The feed stage automatic selection setting indicates a mode in which the image forming apparatus selects a feed stage to feed a paper sheet from the plurality of feed stages. 
     In step S 703 , the feed stage selection processing unit  455  executes feed stage candidate list initial value generation processing of making a list of feed stages as feed source candidates. Of the listed feed stages, the first feed stage of the feed stage candidate list has a highest priority level, and the last feed stage of the feed stage candidate list has a lowest priority level. Note that the processing in step S 703  will be described in detail later with reference to  FIG. 8 . 
     In step S 704 , the feed stage selection processing unit  455  executes feed stage automatic selection processing. In this processing, the feed stage selection processing unit  455  determines an appropriate print paper size based on the size of an input document and a combination of various settings in an image forming mode such as a printing scale, output format, and image quality. The feed stage selection processing unit  455  makes a paper feed candidate list of feed stages in which printing paper sheets with the determined size have been supplied. In other words, feed stages which do not satisfy the condition are excluded from the feed stage candidate list (initial value) created in step S 703 . 
     In step S 705 , the feed stage selection processing unit  455  determines whether one or more feed stages are in the feed stage candidate list as the result of the feed stage automatic selection processing (step S 704 ). If one or more feed stages are in the list (YES in step S 705 ), the process advances to step S 706 , in which the feed stage selection processing unit  455  determines the first feed stage of the feed stage candidate list as a feed source. The processing procedure then ends. 
     On the other hand, if no feed stage is in the list (NO in step S 705 ), the process advances to step S 707 , in which the feed stage selection processing unit  455  displays an warning message indicating an appropriate paper sheet absence error on the display unit (not shown) of the operation unit  406  of the image forming apparatus  102 . This prompts the user to exchange the printing paper sheets in one of the feed stages for paper sheets appropriate for execution of the print job. The processing procedure then ends. 
     (Initial Value Generation Processing) 
     The above-described feed stage candidate list initial value generation processing (step S 703  of  FIG. 7 ) will be described in detail with reference to a flowchart shown in  FIG. 8 . Note that the feed stage selection processing unit  455  executes the processing procedure, similarly to the processing of  FIG. 7 . 
     In step S 801 , the feed stage selection processing unit  455  makes a list of currently usable feed stages of the image forming apparatus  102 . The priority order of the feed stages at this time is a device-specific order determined in advance based on various conditions such as the performance. Note that the priority order definition conditions used here are not particularly limited. 
     In step S 802 , the feed stage selection processing unit  455  determines, for each of the feed stages of the feed stage candidate list, whether delivery is being requested for the feed roller used to convey a paper sheet from the feed stage. This determination is made depending on whether the order flag  506  of the above-described part management table  500  is “ON”. The feed roller used to convey a paper sheet will be referred to as a “corresponding feed roller” hereinafter. If there is a feed stage for which the order flag  506  of a corresponding feed roller is “ON” (YES in step S 802 ), the process advances to step S 803 . 
     In step S 803 , the feed stage selection processing unit  455  changes the priority level, in the feed stage candidate list, of the feed stage including the corresponding feed roller for which delivery is being requested. More specifically, the feed stage selection processing unit  455  sequentially checks the feed stages of the feed stage candidate list from the top. If the feed stage selection processing unit  455  finds a feed stage including a corresponding feed roller for which delivery is being requested, the feed stage selection processing unit  455  lowers the priority level of the feed stage by moving it to the end of the feed stage candidate list. The processing procedure then ends to return to the processing shown in  FIG. 7 . This sets the priority levels of the feed stages to be selected in the feed stage candidate list. 
     As described above, it is possible to reduce the frequency with which a feed stage including a corresponding feed roller for which delivery is being requested is determined as a feed source when the feed stage automatic selection setting is designated. This results in the stable operation of the image forming apparatus as a whole with a lower probability of failure. 
     Second Embodiment 
     In the first embodiment, a frequency with which a feed stage including a corresponding feed roller for which delivery is being requested is selected is reduced by lowering the priority level of the feed stage in the feed source determination process of the feed stage automatic selection processing. A feed stage may be always selected as a feed source even using the above-described method, for example, when all the feed stages hold paper sheets with different sizes. 
     To solve this problem, the feed stage including the corresponding feed roller for which delivery is being requested may be prevented from being selected in the feed stage automatic selection processing when a predetermined period of time has elapsed after sending a feed roller delivery request notification. That is, even though the delivery request has been sent, the corresponding part has not been exchanged even after the predetermined period of time has elapsed. In this case, for example, “delivery request date/time” is newly added to a part management table  500  shown in  FIG. 5 , and the data/time when a part order management unit  454  sends an order request notification is registered. 
     A system configuration and the like except for initial value generation processing in step S 703  of  FIG. 7  in this embodiment are the same as those in the first embodiment, and a repetitive description thereof will be omitted. The initial value generation processing in step S 703  of  FIG. 7  according to the embodiment will be described in detail with reference to a flowchart shown in  FIG. 9 . Note that in this embodiment, the feed stage selection processing unit  455  executes the processing, similarly to the first embodiment. 
     In step S 901 , the feed stage selection processing unit  455  makes a list of currently usable feed stages of an image forming apparatus  102 . The priority order of the feed stages at this time is a device-specific order determined in advance based on various conditions such as the performance. Note that the priority order definition conditions used here are not particularly limited. 
     In step S 902 , the feed stage selection processing unit  455  determines, for each of the feed stages of the feed stage candidate list, whether the order flag of a corresponding feed roller is “ON”. If there is a feed stage for which the order flag of a corresponding feed roller is “ON” (YES in step S 902 ), the process advances to step S 903 ; otherwise (NO in step S 902 ), the processing procedure ends. 
     In step S 903 , the feed stage selection processing unit  455  determines whether a predetermined period of time has elapsed after the delivery request notification date/time of the feed roller with the order flag “ON”. If the predetermined period of time has elapsed (YES in step S 903 ), the process advances to step S 905 ; otherwise (NO in step S 903 ), the process advances to step S 904 . 
     In step S 904 , the feed stage selection processing unit  455  changes the priority level of the target feed stage of the feed source candidate list. More specifically, the feed stage selection processing unit  455  sequentially checks the feed stages of the feed stage candidate list from the top. If the feed stage selection processing unit  455  finds a feed stage including a corresponding feed roller for which delivery is being requested, the feed stage selection processing unit  455  lowers the priority level of the feed stage by moving it to the end of the feed stage candidate list. 
     In step S 905 , the feed stage selection processing unit  455  excludes the target feed stage from the feed stage candidate list. More specifically, the feed stage selection processing unit  455  sequentially checks the feed stages of the feed stage candidate list from the top. If the feed stage selection processing unit  455  finds a feed stage for which the order flag of a corresponding feed roller is “ON” and the predetermined period of time has elapsed after the delivery request notification date/time of the feed roller, it excludes the feed stage from the feed stage candidate list. 
     After the processing in step S 904  or S 905  ends, the processing procedure ends. 
     This enables to reduce, as compared with the first embodiment, a frequency with which a feed stage is determined as a feed source when a feed stage automatic selection setting is designated, while delivery of a corresponding feed roller is being requested. This results in the stable operation of the image forming apparatus as a whole with a lower probability of failure. 
     Third Embodiment 
     In the first and second embodiments, a frequency with which a feed stage including a corresponding feed roller for which delivery is being requested is selected is reduced in the feed source determination process of the feed stage selection processing. In this case, the consumed level is determined using the current counter value  502  of the part management table  500  shown in  FIG. 5 . The consumed level of a feed roller, however, does not always increase at a uniform speed, and is known to increase with a smaller number of feed operations than usual depending on the type of printing paper sheets to be fed. 
     In addition to the arrangement described in the above embodiments, the apparatus may be configured not to designate a specific paper type for a given feed stage including a corresponding feed roller for which delivery is being requested. That is, a feed stage including a feed roller for which delivery is being requested (a feed roller with a high consumed level) is prevented from feeding a paper sheet which increases the consumed level as compared with a general paper type. 
     A system configuration and the like except for processing in step S 602  of  FIG. 6  in this embodiment are the same as those in the first embodiment, and a repetitive description thereof will be omitted. The processing in step S 602  of  FIG. 6  according to the embodiment will be described in detail. Note that a description will be provided using a feed roller with a part ID “100001”. 
     When a current counter value reaches an order timing value (S 601 ), a part order management unit  454  sends an exchange feed roller delivery request notification to a management server  106  (S 602 ). The part order management unit  454  changes an order flag  506  of the part ID “100001” from “OFF” to “ON”. The part order management unit  454  also limits a paper type to be designated for a feed stage including the feed roller with the part ID “100001” on condition that the order flag  506  is “ON”. 
     More specifically, if the paper type currently set for a feed stage including a feed roller with a high consumed level should be limited, a warning message is displayed on a display unit (not shown) of an operation unit  406  of an image forming apparatus  102 . The image forming apparatus  102  then prompts the user to change the paper type. If a paper type which increases the consumed level is not designated, the user is prevented from operating the operation unit  406  to change the paper type of the corresponding feed stage to a paper type which increases the consumed level. The paper type to be limited, which increases the consumed level, may be paper with a given grammage or more such as thick paper. Assume that an accumulation memory  404  stores, in advance, as device-specific information, information about a paper type to be limited, which increases the consumed level in one conveyance operation as compared with plain paper. 
     The apparatus is controlled to release the limitation when the part with the high consumed level is exchanged. 
     With the above processing, a feed stage does not feed a paper type which may rapidly increase the consumed level of a feed roller while delivery is being requested for a corresponding feed roller. This results in the stable operation of the image forming apparatus as a whole with a lower probability of failure. 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (for example, computer-readable medium). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2012-005666, filed Jan. 13, 2012, which is hereby incorporated by reference herein in its entirety.