Image forming apparatus implemented by a distributed control system

There are provided an image forming apparatus which implements divisional control using a plurality of control units without an increase in cost and a control method for the apparatus. To accomplish this, this image forming apparatus includes a master control unit that controls the overall image forming apparatus, a plurality of sub-master control units that control a plurality of functions for performing image formation, and a plurality of salve control units that control loads for implementing a plurality of functions. The master control unit is connected to the plurality of sub-master control units via first signal lines. The plurality of sub-master control units are connected to the plurality of slave control units via second signal lines higher in data transfer timing accuracy than the first signal lines.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus implemented by a distributed control system including a plurality of CPU groups having a hierarchical structure.

2. Description of the Related Art

Centralized control using one CPU is performed for printer device control of an image forming apparatus using an electrophotographic system. With an increase in CPU load due to control centered on one CPU, a higher performance CPU is required. In addition, with an increase in printer device load, it is necessary to lay in communication cables (a bundle of communication lines) from a CPU board to distant load driver units. This requires many long communication cables. In order to solve this problem, much attention has been paid to a control form of assigning the respective control modules constituting an electrophotographic system to sub-CPUs.

Examples of constructing control systems by distributing the respective partial module control functions using a plurality of CPUs have been proposed in several control equipment product fields other than copying machines. For example, Japanese Patent Laid-Open No. 2000-071819 has proposed a technique of hierarchically locating functional modules in a vehicle and performing distributed control. Japanese Patent Laid-Open No. 2006-171960 has proposed a technique of applying a similar hierarchical control structure to robot/automation equipment. These sub-CPUs require a communication unit to make them operate as a system as a whole. Japanese Patent Laid-Open No. 2006-171960 has proposed a technique of constructing different communication networks for the respective hierarchical layers for a control network for performing communication among functional modules, thereby constructing a stable control network by load distribution.

However, the above prior arts have the following problems. For example, in a vehicle or the like, based on the premise that a plurality of control modules which are physically distant from each other implement large-capacity data communication and ganged control requiring fast responsiveness, the respective modules are connected to each other via a large-sized, high-speed network. Large-capacity data communication in this case is, for example, communication between a car navigation system and an instrument panel control system. In addition, ganged control is, for example, anti-lock brake control implemented by ganging a steering angle (steering wheel) control module with a brake control module.

When such a system arrangement is directly applied to distributed control of an image forming apparatus, since control of each unit of the image forming apparatus requires precise timing control, the respective modules at higher hierarchical layers are connected to each other via a high-speed network. Since a high-speed network communication unit itself is expensive, the cost of the apparatus increases. As described above, when divisional control is to be applied to an image forming apparatus, an increase in cost due to connection via a high-speed network poses a problem.

SUMMARY OF THE INVENTION

The present invention enables realization of an image forming apparatus which implements distributed control using a plurality of control units without causing any increase in cost.

One aspect of the present invention provides an image forming apparatus comprising: an upper layer control unit that controls the image forming apparatus which forms an image on a printing material; and first and second lower layer control units that are controlled by the upper layer control unit and respectively control first and second processing units for performing image formation, wherein the upper layer control unit is connected to the first and second lower layer control units by a first signal line with a predetermined communication speed, and the first lower layer control unit is connected to the first processing unit by a second signal line having a communication speed higher than the first signal line, and the second lower layer control unit is connected to the second processing unit by a third signal line having a communication speed higher than the first signal line.

Another aspect of the present invention provides an image forming apparatus comprising: an upper layer control unit that controls the image forming apparatus which forms an image on a printing material; and first and second lower layer control units that are controlled by the upper layer control unit and respectively control first and second processing units for performing image formation, wherein the first lower layer control unit controls a feed function of feeding a printing material and the second lower layer control unit controls an image formation function of forming an image on a printing material, and the first lower layer control unit performs control to feed a printing material to a registration roller, and the second lower layer control unit performs control to convey the printing material fed to the registration roller and form an image on the printing material.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

Arrangement of Image Forming Apparatus

The first embodiment will be described below with reference toFIGS. 1 to 13.FIG. 1shows an overview of an image forming apparatus1000according to the first embodiment.

The image forming apparatus1000includes an automatic document feeder100, an image reading unit200, an image forming unit300, and an operation unit10. As shown inFIG. 1, the image reading unit200is mounted on the image forming unit300. The automatic document feeder (DF)100is mounted on the image reading unit200. The image forming apparatus1000implements distributed control by using a plurality of control units (CPUs). The arrangement of each CPU will be described later with reference toFIG. 6.

The automatic document feeder100automatically conveys a document onto a document glass. The image reading unit200outputs image data by reading the document conveyed from the automatic document feeder100. The image forming unit300forms an image on a printing material (printing sheet) based on the image data output from the automatic document feeder100or the image data input from an external apparatus connected via a network. The operation unit10includes a GUI (Graphical User Interface) with which the user performs various types of operations. The operation unit10includes a display unit such as a touch panel and can present information to the user.

<Arrangement of Automatic Document Feeder and Image Reading Unit>

The automatic document feeder100and the image reading unit200will be described in detail next with reference toFIG. 2.FIG. 2is a sectional view showing an example of the arrangement of the automatic document feeder100and image reading unit200according to the first embodiment.

A document set S including at least one sheet is placed on a document tray130. A DF feed roller101, a separation roller102, and a separation pad121separate and convey the sheets of the document set S one by one into the automatic document feeder100. Before a document is conveyed, a document sensor114determines whether any document is placed on the document tray130.

If the document sensor114determines that a document is placed, the DF feed roller101drops on the document surface of the document set S placed on the document tray130and rotates. This operation feeds the uppermost document of the document set. The separation roller102and the separation pad121act to separate the documents fed by the DF feed roller101one by one. A known retard separation technique implements this separation.

Thereafter, a DF convey roller pair103conveys the document separated by the separation roller102and the separation pad121to a DF registration roller104. The document then comes into contact with the DF registration roller104. This makes the document bend in the form of a loop and eliminates any skew in conveyance.

A feed path to convey the document passing through the DF registration roller104in the direction of a scanning glass201of the image reading unit200is located downstream of the DF registration roller104. A read timing sensor112is located downstream of the DF registration roller104. When a predetermined period of time has elapsed after the read timing sensor112has detected the document, the image reading unit200starts reading the document.

More specifically, a large roller107and a DF convey roller105convey the document fed to the feed path onto the platen. In this case, the large roller107comes into contact with the scanning glass201. The document fed by the large roller107passes through a DF convey roller106and moves between a roller116and a moving glass118. The document is then delivered onto a document delivery tray131through a DF delivery flapper120and DF delivery rollers108. At this time, a reverse surface image reading unit117reads the reverse surface image of the document. A delivery sensor113is a sensor for detecting whether a document has been properly delivered onto the delivery tray.

The document tray130includes a guide regulating plate which can slide in the sub-scanning direction of a placed document set, and a document width sensor to detect a document width in cooperation with the guide regulating plate. A combination of the document width sensor and a DF pre-registration sensor111makes it possible to discriminate the document size of the document set placed on the document tray130. In addition, a document length sensor provided in the convey path can detect the length of a document from the distance that the document is conveyed from the instant the leading end of the conveyed document is detected to the instant the trailing end of the document is detected. A combination of a detected document length and a document width sensor also makes it possible to discriminate the document size.

The image reading unit200optically reads the image information printed on a document and photoelectrically converts the information to output the result as image data. For this purpose, the image reading unit200includes the scanning glass201, a platen glass202, a scanner unit209having a lamp427and a mirror204, mirrors205and206, a lens207, and a CCD sensor428. A white board210is configured to generate white-level reference data based on shading.

The control arrangement of the image forming apparatus1000will be described next with reference toFIG. 3.FIG. 3is a block diagram showing the control arrangement for each device of the image forming apparatus1000according to the first embodiment.

The automatic document feeder100includes a CPU400, a ROM401, a RAM402, a motor403, a sensor404, a lamp405, a solenoid406, a clutch407, a CIS408, and an image processing unit409. The CPU400is a central processing unit, which controls each block of the automatic document feeder100. The ROM401is a read only memory, which stores control programs to be read and performed by the CPU400. The RAM402is a random access memory, which includes output and input ports and stores input data and data for operation. The motor403to drive various types of convey rollers, the solenoid406, and the clutch407are connected to the output ports. Various types of sensors404are connected to the input ports.

The CPU400controls sheet conveyance in accordance with a control program stored in the ROM401connected to the CPU400via a bus. The CPU400performs serial communication with a CPU421of the image reading unit200via a line451to exchange control data with the image reading unit200. The CPU400notifies, via the line451, the image reading unit200of an image start signal as a reference for the leading end of document image data.

The reverse surface image reading unit117inFIG. 2includes the lamp405and the contact image sensor (CIS)408, and transfers a read image to the image processing unit409. The image processing unit409processes the read image and outputs the result via a line454to make an image memory429hold it.

The image reading unit200includes the CPU421, a ROM422, a RAM423, an inter-sheet correction unit424, an image processing unit425, a motor426, a lamp427, a CCD sensor428, and the image memory429. The CPU421comprehensively controls the respective blocks of the image reading unit200. The ROM422, which stores control programs, and the RAM423, which is a work RAM, are connected to the CPU421. The motor426is a driver circuit for driving an optical driving motor. The CCD sensor428is an obverse surface image reading unit, which reads the obverse surface image of a document.

The inter-sheet correction unit424performs various inter-sheet corrections to be performed between conveyed documents, e.g., read light amount correction for light amount variations with time and dust detection processing. The image signal imaged on the CCD sensor428by the lens207is converted into digital image data. The image processing unit425then writes the data in the image memory429after performing various types of image processing.

The data written in the image memory429are sequentially transmitted to a controller460via a controller IF453. The CPU421notifies, via a controller IF452, the controller460of an image start signal as a reference for the leading end of document image data at a proper timing. Likewise, the CPU421of the image reading unit200notifies, via the controller IF453, the controller460of the image start signal notified from the DF via a communication line at a proper timing.

The controller460includes a CPU461, an amplification circuit462, a correction circuit463, an image memory464, an external I/F465, an operation unit I/F466, and a printer control I/F215. The operation unit10connected to this apparatus via the operation I/F unit466includes a liquid crystal display with a touch panel with which the operator inputs the contents of processing to be performed and which notifies the operator of information associated with processing, warnings, and the like.

The CCD sensor428and the CIS408output an analog image signal for each read line and sends it to the controller460via the image processing units425and409in the process of scanning a document image. The amplification circuit462amplifies these signals and transmits the resultant signals to the correction circuit463. The correction circuit463performs correction processing for an image signal and writes the result in the image memory464. This apparatus performs the above processing for a document image area to form a read image of the document.

The external I/F465is an interface for exchanging image information, code information, and the like with an apparatus outside the image forming apparatus1000. More specifically, as shown inFIG. 5, a facsimile apparatus501and a LAN interface apparatus502can be connected to the external I/F465.FIG. 5is a block diagram showing the external apparatuses connected to the image forming apparatus1000according to the first embodiment. Note that mutual communication among the facsimile apparatus501, the LAN interface apparatus502, and the CPU461implements procedure control for the exchange of image information and code information with the facsimile apparatus501and the LAN interface apparatus502.

As described above, this embodiment uses the CIS408as the reverse surface image reading unit of the automatic document feeder100, and the CCD sensor428as the obverse surface image reading unit of the image reading unit200. However, it is possible to use any sensor which can read images.

The image forming unit300will be described in detail next with reference toFIG. 4.FIG. 4is a sectional view showing an example of the arrangement of the image forming unit300according to the first embodiment. Note that the image forming unit300according to this embodiment uses an electrophotographic system. Note that the letters Y, M, C, and K as the suffices of reference numerals inFIG. 4indicate the respective engines corresponding to yellow, magenta, cyan, and black toners. In the following description, an engine corresponding to all types of toner will be denoted by a reference numeral without any of the letters Y, M, C, and K as suffixes, and an engine corresponding to each type of toner will be denoted by a reference numeral having a corresponding one of the letters Y, M, C, and K as a suffix.

A photosensitive drum (to be simply referred to as a “photosensitive member” hereinafter)225serving as an image carrier for forming a full-color electrostatic image is provided to be rotated by a motor in the direction indicated by arrow A. A primary charger221, an exposure device218, a developing device223, a transfer device220, a cleaner device222, and a charge remover271are arranged around the photosensitive member225.

A developing device223K is a developing device for monochromatic developing, and develops a latent image on a photosensitive member225K with a toner of K. Developing devices223Y,223M, and223C are developing devices for full-color developing, and respectively develop latent images on photosensitive members225Y,225M, and225C with toners of Y, M, and C. The transfer device220multilayer-transfers the toner image of each color developed on the photosensitive member225onto a transfer belt226as an intermediate transfer member altogether. As a result, the toner images of the four colors are superimposed.

The transfer belt226is spanned around rollers227,228, and229. The roller227functions as a driving roller which is coupled to a driving source to drive the transfer belt226. The roller228functions as a tension roller to adjust the tension of the transfer belt226. The roller229functions as a backup roller of a transfer roller as a secondary transfer device231. A transfer roller drive unit250is a driving unit for making the secondary transfer device231come into contact with or withdraw from the transfer belt226. A cleaner blade232is provided below the transfer belt226after the position where the belt passes through the secondary transfer device231. The blade scrapes off the residual toner on the transfer belt226.

A registration roller255, a feed roller pair235, and vertical path roller pairs236and237feed printing materials (printing sheets) stored in cassettes240and241and a manual paper feed unit253to the nip portion, i.e., the contact portion between the secondary transfer device231and the transfer belt226. Note that at this time, the transfer roller drive unit250makes the secondary transfer device231be in contact with the transfer belt226. The toner image formed on the transfer belt226is transferred onto a printing material at this nip portion. Thereafter, the fixing device234thermally fixes the toner image transferred on the printing material. The printing material is then delivered outside the apparatus.

The cassettes240and241and the manual paper feed unit253respectively include sheet absence sensors243,244, and245each for detecting the presence/absence of a printing material. In addition, the cassettes240and241and the manual paper feed unit253respectively include feed sensors247,248, and249each for detecting a failure to pick up a printing material.

Image forming operation by the image forming unit300will be described below. When image formation starts, pickup rollers238,239, and254convey printing materials stored in the cassettes240and241and the manual paper feed unit253one by one to the feed roller pair235. When the feed roller pair235conveys the printing material to the registration roller255, a registration sensor256located immediately before the registration roller255detects the passage of the printing material.

When the registration sensor256detects the passage of a printing material, the apparatus according to this embodiment temporarily interrupts convey operation after the lapse of a predetermined period of time. As a result, the printing material comes into contact with the registration roller255at rest, and convey operation stops. At this time, a convey position is so fixed as to make the end portion of the printing material in the traveling direction perpendicular to the convey path, thereby correcting any skew of the printing material, i.e., the state in which the conveying direction of the printing material is shifted from the convey path. This processing will be referred to as position correction hereinafter. Position correction is required to minimize any subsequent ramp of the image forming direction relative to the printing material. After position correction, the registration roller255is started to supply the printing material to the secondary transfer device231. Note that the registration roller255is coupled to a driving source to be rotated/driven by transmission of drive through a clutch.

The surface of the photosensitive member225is then negatively charged uniformly to a predetermined charge potential by applying a voltage to the primary charger221. Subsequently, the exposure device218including a laser scanner unit performs exposure so as to set an image portion on the charged photosensitive member225at a predetermined exposure potential, thereby forming a latent image. The exposure device218turns on and off laser light based on the image data sent from the controller460via the printer control I/F215, thereby forming a latent image corresponding to the image data.

In addition, a developing bias set in advance for each color is applied to the developing roller of the developing device223, and the above latent image is developed with toner and visualized as a toner image when passing through the position of the developing roller. The transfer device220transfers the toner image onto the transfer belt226. The secondary transfer device231then transfers the image onto the printing material conveyed by the feed unit. Thereafter, the printing material passes through a post-registration convey path268, and is conveyed to a fixing device234through a fixing convey belt230.

In the fixing device234, first of all, pre-fixing chargers251and252charge the printing material to prevent image disturbance by compensating for the attraction power of toner, and fixing rollers233thermally fix the toner image. Thereafter, a delivery flapper257switches the convey path to a delivery path258to make delivery rollers270deliver the printing material onto a delivery tray242.

The cleaner device222removes and recovers the residual toner on the photosensitive member225. Lastly, the charge remover271uniformly removes the charges on the photosensitive member225to near 0 volts to prepare for the next image formation cycle.

The color image formation start timing of the image forming apparatus1000allows to form an image at an arbitrary position on the transfer belt226because of simultaneous transfer of toner images of Y, M, C, and K. However, it is necessary to determine an image formation start timing while considering the shifts in the transfer positions of toner images on the photosensitive members225Y,225M, and225C.

Note that in the image forming unit300, it is possible to continuously feed printing materials from the cassettes240and241and the manual paper feed unit253. In this case, in consideration of the sheet length of a preceding printing material, sheets are fed from the cassettes240and241and the manual paper feed unit253at the shortest intervals at which no printing materials overlap each other. As described above, after position correction, the printing material is supplied to the secondary transfer device231by starting the registration roller255. When the printing material reaches the secondary transfer device231, the registration roller255is temporarily stopped again. The purpose of this is to correct the position of a succeeding printing material in the same manner as the preceding printing material.

The operation to form an image on the reverse surface of a printing material will be described in detail next. When forming an image on the reverse surface of a printing material, this apparatus forms an image on the obverse surface of the printing material first. When an image is to be formed on only the obverse surface, the fixing device234thermally fixes a toner image on the printing material first, and then directly delivers the printing material onto the delivery tray242. Assume that the apparatus is to successively form an image on the reverse surface. In this case, when a sensor269detects the printing material, the delivery flapper257switches the convey path to a reverse surface path259. Accordingly, reverse rollers260rotate to convey the printing material to an obverse/reverse surface inversion path261. After the printing material is conveyed on the obverse/reverse surface inversion path261by a distance corresponding to the width in the feed direction, the reverse rollers260rotate in the reverse direction to switch the traveling direction of the printing material. Obverse/reverse surface path convey rollers262are driven to convey the printing material to an obverse/reverse surface path263with the obverse surface, on which the image is formed, facing down.

When the printing material is conveyed to re-feed rollers264along the obverse/reverse surface path263, a re-feed sensor265located immediately before the re-feed rollers264detects the passage of the printing material. When the re-feed sensor265detects the passage of the printing material, the apparatus according to this embodiment temporarily interrupts the convey operation after the lapse of a predetermined period of time. As a result, the printing material comes into contact with the re-feed rollers264at rest, and the convey operation temporarily stops. At this time, the position of the printing material is so fixed as to make the end portion of the printing material in the traveling direction perpendicular to the convey path, thereby correcting any skew of the printing material, i.e., the state in which the conveying direction of the printing material is shifted from the convey path in the re-feed path. This processing will be referred to as position recorrection hereinafter.

Position recorrection is required to minimize any subsequent ramp of the image forming direction relative to the reverse surface of the printing material. After position recorrection, the re-feed rollers264are started to convey the printing material onto a feed path266with the obverse and reverse surfaces being inverted. Subsequent image forming operation is the same as the above image forming operation for the obverse surface, and hence a description of the operation will be omitted. The printing material with images being formed on its obverse and reverse surfaces is delivered onto the delivery tray242by switching the convey path to the delivery path258using the delivery flapper257.

Note that the image forming unit300can continuously feed printing materials in the two-sided printing mode as well. However, since this apparatus includes only one system for operation including forming an image on a printing material and fixing formed toner images, it is not possible to simultaneously print images on the obverse and reverse surfaces. In the two-sided printing mode, therefore, the image forming unit300alternately forms images on printing materials fed from the cassettes240and241and the manual paper feed unit253and printing materials which are inverted for reverse-surface printing and re-fed to the image forming unit.

In the image forming unit300, the respective loads shown inFIG. 4are grouped into four control blocks to be described later, namely a convey module A280, a convey module B281, an image forming module282, and a fixing module283, and each block is autonomously controlled. The image forming unit300also includes a master module284for comprehensively controlling the four control blocks to make them function as an image forming apparatus. A control arrangement for each module will be described below with reference toFIG. 6.

FIG. 6is a block diagram schematically showing the connection between a master CPU, sub-master CPUs, and slave CPUs according to the first embodiment. In this embodiment, a master CPU (master control unit/upper layer control unit)1001provided in the master module284controls the overall image forming apparatus1000based on instructions and image data sent from the controller460via the printer control I/F215. The convey module A280, convey module B281, image forming module282, and fixing module283for performing image formation respectively include sub-master CPUs (sub-master control units/lower layer control units)601,901,701, and801for controlling the respective functions. The master CPU1001controls the sub-master CPUs601,901,701, and801. The respective functional modules include slave CPUs (slave control units/processing units)602,603,604,605,902,903,702,703,704,705,706,802, and803for making the loads for performing the respective functions operate. The sub-master CPU601controls the slave CPUs602,603,604, and605. The sub-master CPU901controls the slave CPUs902and903. The sub-master CPU701controls the slave CPUs702,703,704,705, and706. The sub-master CPU801controls the slave CPUs802and803.

As shown inFIG. 6, the master CPU1001and the plurality of sub-master CPUs601,701,801, and901are connected to each other via a common network type communication bus (first signal line)1002. The sub-master CPUs601,701,801, and901are also connected to each other via a network type communication bus (first signal line)1002. Note that the master CPU1001and the plurality of sub-master CPUs601,701,801, and901may be ring-connected to each other. The sub-master CPU601is further connected one-to-one to the plurality of slave CPUs602,603,604, and605(peer-to-peer connection) via high-speed serial communication buses (second signal lines)612,613,614, and615. Likewise, the sub-master CPU701is connected to each of the slave CPUs702,703,704,705, and706via a corresponding one of high-speed serial communication buses (second signal lines)711,712,713,714, and715. The sub-master CPU801is connected to each of the slave CPUs802and803via a corresponding one of high-speed serial communication buses (second signal lines)808and809. The sub-master CPU901is connected to each of the slave CPUs902and903via a corresponding one of high-speed serial communication buses (second signal lines)909and910. In this case, each high-speed serial communication bus is used for short-distance, high-speed communication.

In the image forming apparatus1000according to this embodiment, functional division is performed to implement control requiring timing-dependent responsiveness within the functional modules comprehensively controlled by the respective sub-master CPUs. For this reason, high-speed serial communication buses with high responsiveness are used for communication between the respective slave CPUs for driving the end loads and the respective sub-master CPUs. That is, as the second signal lines, signal lines with higher timing accuracy for data transfer than the first signal lines are used.

On the other hand, the sub-master CPUs601,701,801, and901and the master CPU1001mutually perform only the operation of comprehensively controlling a rough processing procedure for image forming operation without requiring any precise control timings. For example, the master CPU1001issues instructions to start a pre-image formation process, a pre-feed process, and a post-image formation process to the sub-master CPUs. The master CPU1001also issues, to the sub-master CPUs, instructions based on the modes designated by the controller460(e.g., the monochrome mode and the two-sided image formation mode) before the start of image formation. The sub-master CPUs601,701,801, and901mutually perform only operation requiring no precise timing control. That is, the control of the image forming apparatus is divided into control units which do not mutually require precise timing control, and the respective sub-master CPUs control the respective control units at precise timings. This makes it possible for the image forming apparatus1000to minimize the communication traffic and perform connection with the inexpensive, low-speed network type communication bus1002. Note that it is always necessary to mount the master CPU, sub-master CPUs, and slave CPUs on uniform control boards. It is possible to variably locate them on control boards in accordance with situations concerning apparatus implementation.

The specific locations of the master CPU, sub-master CPUs, and slave CPUs in this embodiment will be described with reference toFIG. 7in terms of board arrangement.FIG. 7is a view showing an example of the control boards of the image forming apparatus1000according to the first embodiment.

This embodiment can use various control board arrangements, as shown inFIG. 7. For example, the sub-master CPU601and the slave CPUs602,603,604, and605are mounted on the same board. In addition, it is possible to mount a sub-master CPU and slave CPUs on independent boards, respectively, like the sub-master CPU701and the slave CPUs702,703, and704or the sub-master CPU801and the slave CPUs802and803. Furthermore, it is possible to mount some slave CPUs on the same board, like the slave CPUs705and706. Moreover, it is possible to mount only some of the sub-master CPUs and the slave CPUs on the same board, like the sub-master CPU901and the slave CPU902.

<Arrangement of Each Control Module>

The function and arrangement of each control module will be described in detail with reference toFIGS. 8 to 11.FIG. 8is a view showing an example of the arrangement of the convey module A280according to the first embodiment.

The convey module A280takes charge of feed control (feed function) until each of printing materials stored in the cassettes240and241and the manual paper feed unit253comes into contact with the nip portion of the registration roller255at rest. The convey module A280includes the sub-master CPU601to comprehensively control feed control and the slave CPUs602,603,604, and605to drive the respective loads. In addition, load groups to be directly controlled are connected to the respective slave CPUs.

The slave CPU602has, as loads, a driving source motor606for driving the pickup roller238associated with the cassette240, the sheet absence sensor243, and the feed sensor247, and performs control until a printing material is transferred to the feed path266. The slave CPU603has, as loads, a driving source motor607for driving the pickup roller239associated with the cassette241, the sheet absence sensor244, and the feed sensor248, and performs control until a printing material is transferred to the feed path266. The slave CPU604has, as loads, a driving source motor608for driving the pickup roller254associated with the manual paper feed unit253, the sheet absence sensor245, and the feed sensor249, and performs control until a printing material is transferred to the feed path266. The slave CPU605has, as loads, driving source motors609,610, and611for driving the feed roller pairs235,236, and237and the registration sensor256. The slave CPU605controls these loads to perform control until each of printing materials transferred from the cassettes240and241and the manual paper feed unit253is conveyed to come into contact with the nip portion of the registration roller255, and is temporarily stopped. In this embodiment, the sub-master CPU601is connected one-to-one to the slave CPUs602,603,604, and605via the independent high-speed serial communication buses612,613,614, and615.

FIG. 9is a view showing an example of the arrangement of the image forming module282according to the first embodiment. The image forming module282takes charge of image formation control (image formation function) until the full-color toner image formed by an electrophotographic process is transferred onto the transfer belt226and is re-transferred onto the printing material transferred by the convey module A280. The image forming module282includes the sub-master CPU701to comprehensively perform image formation control and the slave CPUs702,703,704,705, and706to drive the respective loads. Load groups to be directly controlled are connected to the respective slave CPUs.

The slave CPU702has, as loads, an exposure device218K, the developing device223K, a primary charger221K, a transfer device220K, a cleaner device222K, and a charge remover271K, and performs control until a black toner image is transferred onto the transfer belt226. The slave CPU703has, as loads, an exposure device218M, the developing device223M, a primary charger221M, a transfer device220M, a cleaner device222M, and a charge remover271M, and performs control until a magenta toner image is transferred onto the transfer belt226. The slave CPU704has, as loads, an exposure device218C, the developing device223C, a primary charger221C, a transfer device220C, a cleaner device222C, and a charge remover271C, and performs control until a cyan toner image is transferred onto the transfer belt226. The slave CPU705has, as loads, an exposure device218Y, the developing device223Y, a primary charger221Y, a transfer device220Y, a cleaner device222Y, and a charge remover271Y, and performs control until a yellow toner image is transferred onto the transfer belt226.

The slave CPU706has, as loads, a motor708for the roller227to rotate/drive the transfer belt226, a high-voltage signal output device to drive the secondary transfer device231, and driving source motors709and710to drive the transfer roller drive unit250and the registration roller, respectively. The slave CPU706controls these loads to perform control until the toner images of the four colors multilayer-transferred on the transfer belt226are re-transferred onto a printing material by using the secondary transfer device231. Note that in this embodiment, the sub-master CPU701is connected one-to-one to the slave CPUs702,703,704,705, and706via the independent high-speed serial communication buses711,712,713,714, and715.

FIG. 10is a view showing an example of the arrangement of the fixing module283according to the first embodiment. The fixing module283takes charge of fixing control (fixing function) until a printing material on which a toner image is transferred by the image forming module282is fed to the fixing device234, and the toner image is thermally fixed on the printing material. The fixing module283includes the sub-master CPU801to comprehensively perform fixing control and the slave CPUs802and803to drive the respective loads. Load groups to be directly controlled are connected to the respective slave CPUs.

The slave CPU802has, as loads, a driving source motor804for rotating the fixing convey belt230and a driving source motor805for rotating the fixing rollers233, and performs control until a printing material is transferred from the secondary transfer device231onto the convey path after fixing. The slave CPU803has, as loads, a heater806in the fixing device234, a temperature detection thermistor807, and the pre-fixing chargers251and252. The slave CPU803controls these loads to perform fixing temperature control of the fixing device234by optimally generating heat from the heater while charging the fixing rollers233by using the pre-fixing chargers251and252and feeding back the detection result obtained by the temperature detection thermistor807. Note that in this embodiment, the sub-master CPU801is connected one-to-one to the slave CPUs802and803via the independent high-speed serial communication buses808and809.

FIG. 11is a view showing an example of the arrangement of the convey module B281according to the first embodiment. The convey module B281takes charge of delivery control (delivery function) until a printing material on which an image is fixed by the fixing module283is received, and is delivered outside the image forming unit300or reverse surface inversion control (inversion function) until the obverse and reverse surfaces of a printing material are reversed for reverse surface printing and is transferred to the convey module A280. The convey module B281includes the sub-master CPU901to comprehensively perform delivery control and reverse surface inversion control and the slave CPUs902and903to drive the respective loads. Load groups to be directly controlled are connected to the respective slave CPUs.

The slave CPU902has, as loads, a solenoid904for switching the delivery flapper257, a driving source motor905for driving the delivery rollers270, a driving source motor906for driving the reverse rollers260, and the sensor269. The slave CPU902controls these loads to perform control until a printing material is delivered from the convey path to outside the apparatus after fixing or transferred to the obverse/reverse surface inversion path261. The slave CPU903has, as loads, a driving source motor907for driving the obverse/reverse surface path convey rollers262, a driving source motor908for driving the re-feed rollers264, and the re-feed sensor265. The slave CPU903controls these loads to perform control until a printing material transferred from the inversion path is transferred to the feed path266again. Note that in this embodiment, the sub-master CPU901is connected one-to-one to the slave CPUs902and903via the independent high-speed serial communication buses909and910.

This embodiment implements image formation control for a printing material by combining the autonomous operations of the above four sub-modules. Practical image forming operation is divided into several patterns in accordance with a combination of selection of a feed tray/paper size, designation of one-sided/two-sided printing, designation of monochrome printing/color printing, and the like. When the operator makes settings in advance via the operation unit10and the external I/F465, specific instructions are input. In order to implement operation desired by the operator based on the instructions, it is necessary to perform overall control to make the respective modules systematically operate. In this embodiment, the master CPU1001in the master module284comprehensively controls the sub-master CPUs601,701,801, and901. In this case, a rough procedure for overall control by the master CPU1001is implemented by the exchange of commands by communication between the master CPU1001and the sub-master CPUs601,701,801, and901via the low-speed network type communication bus1002. In addition, this procedure is implemented by the exchange of commands by one-to-one communication between the sub-master CPUs601,701,801, and901and the slave CPUs602,603,604,605,702,703,704,705,706,802,803,902, and903via high-speed serial communication buses.

A control procedure in the image forming apparatus1000according to this embodiment will be described next with reference toFIG. 12.FIG. 12is a sequence chart showing a control procedure in the image forming apparatus1000according to the first embodiment. Note that the sequence chart shown inFIG. 12is based on the assumption that image formation is performed for one printing material.

First of all, in step S1201, the master CPU1001issues instructions to start pre-image formation processes to the sub-master CPUs601,701,801, and901before the start of image formation. Subsequently, in steps S1202, S1203, S1204, and S1205, the sub-master CPUs601,701,801, and901perform pre-processes for image formation. More specifically, the sub-master CPU601performs a pre-feed process. The sub-master CPU701performs a pre-image formation process. The sub-master CPU801performs a pre-fixing process. The sub-master CPU901performs a pre-convey process.

In step S1206a, the master CPU1001instructs the sub-master CPU601to start feeding the first printing material in accordance with an instruction from the operator via the operation unit10or the external I/F465.

Upon receiving an instruction to start feeding a printing material, the sub-master CPU601starts a sheet feed process in step S1207a. In the sheet feed process, a printing material placed on one of the cassettes240and241and the manual paper feed unit253is conveyed to the position of the registration roller255and temporarily stopped. Thereafter, in step S1208a, the sub-master CPU601issues an instruction to start image formation to the sub-master CPU701after the lapse of a predetermined period of time.

Upon receiving an instruction to start image formation, the sub-master CPU701starts conveying a printing material by rotating the registration roller255at rest and performs an image formation process for the photosensitive member225and a transfer process for the transfer belt226and the printing material in step S1209a. Controlling a convey process and an image formation/transfer process for a printing material from the registration roller255using one sub-master CPU makes it possible to perform positioning between the printing material and the image, which requires precise timing control. In addition, even if different sub-master CPUs control a feed process for a printing material to the registration roller255and a convey process for the printing material from the registration roller255, a communication delay between the sub-master CPUs is absorbed by the stop period of a printing material at the registration roller255. Subsequently, in step S1210a, upon confirming that a predetermined period of time has elapsed and the printing material on which an image is formed is conveyed toward the fixing device234, the sub-master CPU701instructs the sub-master CPU801to start fixing.

Upon receiving the instruction to start fixing, the sub-master CPU801performs a thermal fixing process for the printing material in step S1211a. Since no precise timing is required for the start of driving the fixing module283, even if different sub-master CPUs control an image formation/transfer process and a thermal fixing process, any communication delay between the sub-master CPUs poses no problem. Subsequently, in step S1212a, upon confirming that a predetermined period of time has elapsed and the printing material on which the image is fixed is conveyed toward the delivery rollers270, the sub-master CPU801instructs the sub-master CPU901to start paper delivery.

Upon receiving the instruction to start paper delivery, the sub-master CPU901performs a delivery process for the printing material in step S1213a. Since no precise timing is required for the start of driving the convey module B281, even if different sub-master CPUs control a thermal fixing process and a delivery process, any communication delay between the sub-master CPUs poses no problem. Thereafter, in step S1214a, when the delivery process is complete, the sub-master CPU901notifies the master CPU1001of the corresponding information.

Upon receiving the notification of the completion of the delivery process, the master CPU1001instructs the sub-master CPUs601,701,801, and901to start post-image formation processes in step S1215. Thereafter, in steps S1216, S1217, S1218, and S1219, the sub-master CPUs601,701,801, and901perform post-processes for completing image formation. More specifically, the sub-master CPU601performs a post-feed process. The sub-master CPU701performs a post-image formation process. The sub-master CPU801performs a post-fixing process. The sub-master CPU901performs a post-convey process.

The above sequence has exemplified the series of image formation processing from feeding to delivery of one printing material. Assume that this apparatus continuously performs image formation for a plurality of printing materials. In this case, for example, as indicated by steps S1206bto S1214binFIG. 12, when a predetermined period of time has elapsed after the start of image formation on the first printing material, the apparatus can continuously perform image formation. In this case, the apparatus repeatedly performs the processing in steps S1206bto S1214bin accordance with the number of printing materials.

In this case, the intervals at which instructions to start feeding are issued are expected to be shorter than the intervals at which actual printing materials are fed. However, since a precise feed timing of printing materials is defined in the convey module A comprehensively controlled by the sub-master CPU601, it is not necessary for the master CPU1001to strictly guarantee a timing.

Likewise, in order to achieve a predetermined image formation intervals (i.e., productivity), the intervals at which instructions to start image formation for printing materials to be continuously fed are issued are expected to be shorter than the intervals at which image formation is actually performed for printing materials. However, since a precise image formation timing for each printing material is defined in the execution of image formation control in the image forming module comprehensively controlled by the sub-master CPU701, it is not necessary for the sub-master CPU601to strictly guarantee a timing. The exchange of commands at the time of execution of image formation control will be described later in detail.

The exchange of trigger commands for processing, other than the start of paper feeding and image formation described above, between the master CPU1001and the sub-master CPUs601,701,801, and901is defined to only roughly notify the start of processing. That is, since a precise processing procedure for control is not defined, the frequency of issuing commands per unit time is not very high, and it is not necessary to strictly guarantee each command transmission timing.

Therefore, as the network type communication bus1002which connects the master CPU1001to the sub-master CPUs601,701,801, and901, an inexpensive communication bus with a relatively low communication speed corresponding to a communication period of about 10 msec can be used. Such communication buses include, for example, a LIN communication bus (Local Interconnect Network communication bus) and an I2C communication bus (Inter-Integrated Circuit communication bus).

It is also possible, in consideration of reliability, to use a network communication bus such as a CAN communication bus (Control Area Network communication bus). In this case as well, however, since the amount of communication data per unit time can be relatively small, the communication rate can be set low. This can further improve the reliability of communication. In this embodiment, in particular, the control CPU boards on which the master CPU1001and the sub-master CPUs601,701,801, and901are mounted are physically spaced away from each other, and hence the communication network cable for the respective CPUs becomes very long. As the communication network cable length and the network communication rate increase, the apparatus becomes susceptible to the influence of external noise. For this reason, considering robustness against external noise as well, it is useful to set the network communication rate low.

The processing performed by a sub-master CPU and slave CPUs in this embodiment will be described next with reference toFIG. 13.FIG. 13is a sequence chart showing the processing (corresponding to one sheet) to be performed when the image forming module282according to the first embodiment receives an instruction to start image formation. As an example of the processing performed by a sub-master CPU and slave CPUs, the processing performed by the sub-master CPU701and slave CPUs702,703,704, and705of the image forming module282will be described.

First of all, in steps S1301K, S1301M, S1301C, and S1301Y, upon receiving an instruction to start image formation from the sub-master CPU601, the sub-master CPU701issues instructions to rotate/drive the developing rollers to the slave CPUs702,703,704, and705. In steps S1302K, S1302M, S1302C, and S1302Y, the sub-master CPU701issues instructions to set developing biases to predetermined high voltage values at the time of image formation. Because developing bias settings do not depend on the timings among the stations of K, M, C, and Y, the sub-master CPU simultaneously turns on all the four stations at the same time when receiving a command. At the same time, the sub-master CPU issues a trigger command1303to start driving the transfer roller to the slave CPU706.

Subsequently, in steps1304K,1304M,1304C, and1304Y, steps1305K,1305M,1305C, and1305Y, steps1306K,1306M,1306C, and1306Y, and steps1307K,1307M,1307C, and1307Y, the sub-master CPU701notifies the respective stations of instructions to perform a series of processing required for image formation. More specifically, the sub-master CPU701issues, to the respective slave CPUs, trigger commands to start primary charging, exposure, primary transfer, and charge removal. In this case, in order to perform accurate image formation, it is necessary to accurately generate these trigger commands at a predetermined period. In this embodiment, as shown inFIG. 13, the period from the start of primary charging to the start of exposure is set to Tp-e, the period from the start of exposure to the start of primary transfer is set to Tp-t1, and the period from the start of primary transfer to the start of charge removal is set to Tt1-r. Each period T is set in advance in consideration of image quality and productivity.

In addition, the timings at which commands are issued to the slave CPUs702,703,704, and705need to be shifted from each other by a delay period Tstin consideration of positional shifts in terms of the locations of the photosensitive members225K,225M,225C, and225Y. A failure to implement this timing shift with high accuracy will cause printed image pattern offsets (so-called color misregistrations) among the respective stations.

The sub-master CPU701then secondarily transfers the toner images formed on the transfer belt onto a printing material. For this purpose, in step S1308, the sub-master CPU701issues, to the slave CPU706, a registration ON command to rotate/drive the driving source motor710for driving the registration roller255at the timing at which the printing material has reached the position of the secondary transfer device231at the start of secondary transfer. In steps S1309and S1310, the sub-master CPU701issues, to the slave CPU706, a secondary transfer device drive (ON) command to bring the secondary transfer device231into contact with the transfer belt226and a secondary transfer start command.

In this case, in order to properly transfer the image on the transfer belt226to a desired position on the printing material, it is necessary to accurately issue a secondary transfer start command and a registration ON command at a predetermined period. In this embodiment, as shown inFIG. 13, the period from the start of discharging to the start of the driving source motor710is set to Tr-reg, and the period from the start of the driving source motor710to the start of secondary transfer is set to Treg-t2.

As described above, it is necessary to frequently exchange issued commands with considerably high accuracy within a given unit time in the processing procedure between each sub-master CPU and each slave CPU as compared with the processing procedure between the master CPU1001and each sub-master CPU. In addition, in order to continuously form images on a plurality of printing materials, it is necessary to repeatedly perform these series of processes at a given predetermined period. A delay or variation in the processing period at this time will affect the productivity of the image forming apparatus. That is, the processing procedure between each sub-master CPU and each slave CPU can be an important factor in guaranteeing the performance of the apparatus.

This embodiment therefore uses the high-speed serial communication buses711to715to independently ensure the performance represented by a communication period of about 10 μsec for communication between the sub-master CPU701and the slave CPUs702to706. That is, when the master CPU1001is connected to the sub-master CPUs601,701,801, and901at a predetermined communication speed, the sub-master CPU701is connected to the slave CPUs702to706at a higher communication speed. In addition, the high-speed serial communication buses711to715are wired to connect the sub-master CPU701one-to-one to the slave CPUs702to706. This makes it possible to reduce the communication delay losses between the sub-master CPU701and the slave CPUs702,703,704,705, and706to as close as zero as possible, suppress timing variations in the exchange of commands, and improve the accuracy of timing control. This image forming apparatus can therefore improve the image quality at the time of image formation and the productivity at the time of continuous printing.

When such high-speed serial communication is applied between the master CPU1001and the sub-master CPUs601,701,801, and901, increases in cost and communication rate can lead to vulnerability to noise and the like. However, the sub-master CPU701and the slave CPUs702,703,704,705, and706are likely to be mounted at relatively close positions in the location arrangement. Therefore, since a long communication bus is not required between the sub-master CPU and the slave CPUs, the distance that a highly conductive, expensive bus cable required for high-speed communication is laid in can be minimized. In addition, since it is possible to locally narrow down the range of occurrence of high frequency noise which needs to be considered when the communication rate is increased, it is possible to take countermeasures against noise at a low cost, thereby suppressing an increase in cost.

In addition, since the function of the sub-master CPU701is limited to control of only a portion associated with a given functional module, the number of slave CPUs702,703,704,705, and706which are subordinate to the sub-master CPU is limited. That is, the arrangement of one-to-one connection using high-speed serial communication has sufficient feasibility.

Although the arrangement of the sub-master CPU701and slave CPUs702,703,704,705, and706, in particular, has been described with reference toFIG. 13, a similar arrangement can be applied to communication between the remaining sub-master CPUs601,801, and901and the slave CPUs.

Second Embodiment

The second embodiment will be described next with reference toFIG. 14.FIG. 14shows an example of the arrangement of a convey module A280according to the second embodiment. The same reference numerals as in the first embodiment described with reference toFIG. 8denote the same constituent elements in the second embodiment, and a description will not be repeated.

In the first embodiment, the feed path266is not configured to simultaneously receive a plurality of printing materials. That is, printing materials stored in one of the cassettes240and241and the manual paper feed unit253are sequentially transferred one by one to the feed path266. In this embodiment, therefore, there is no need to connect high-speed serial buses one-to-one to the slave CPUs602,603, and604associated with the cassettes240and241and the manual paper feed unit253which are feed units. It is possible to cascade the slave CPUs602,603, and604to the sub-master CPU601via one serial bus616. For example, as shown inFIG. 14, it is possible to perform one-to-many connection (bus connection) between the sub-master CPU601and the slave CPUs602,603, and604. Using such an arrangement can further reduce the number of communication bus lines between the sub-master CPU601and the slave CPUs602,603, and604, and can further reduce the bundle of lines. Note that the sub-master CPU601is connected to the slave CPU605via the serial bus615independent of the serial bus616. This is because, since the slave CPU605needs to receive a printing material fed from one of the cassettes240and241and the manual paper feed unit253at a predetermined timing, it is necessary to perform timing control more accurately than between the sub-master CPU601and the slave CPUs602,603, and604.

Other Embodiments

This application claims the benefit of Japanese Patent Application No. 2009-060115 filed on Mar. 12, 2009, which is hereby incorporated by reference herein in its entirety.