Image forming apparatus

An image forming apparatus includes a sheet supply unit for supplying a printing medium; and a sheet discharge unit for discharging the printing medium after an image is transferred to the printing medium. Further, the image forming apparatus includes a transport path medium number storage unit for storing a transport path medium number; a discharge number storage unit for storing a discharge number; an upper limit print number storage unit for storing an upper limit print number; an addition unit for calculating an addition sum of the discharge number and the transport path medium number; a number comparison unit for comparing the addition sum with the upper limit print number; and a sheet supply stop unit for stopping the sheet supply unit when the addition sum exceeds the upper limit print number.

BACKGROUND OF THE INVENTION

The present invention relates to an image forming apparatus having a sheet supply unit for supplying a printing medium and a sheet discharge unit for discharging the printing medium after an image is transferred to the printing medium.

A conventional image forming apparatus such as a printer includes a function of administrating the number of printed sheets or print number (refer to Patent Reference). The conventional image forming apparatus is provided with a counter for counting the print number, so that the counter is updated every time a printing medium is discharged. An administrator monitors the counter regularly for managing the print number.Patent Reference: Japanese Patent Publication No. 2000-194239

In the conventional image forming apparatus, when a printing operation is performed continuously, before a precedent printing medium is discharged from the image forming apparatus, a subsequent printing medium is supplied. Accordingly, even though an upper limit is set at a specific print number to stop the printing operation, an actual print number may exceed the upper limit.

In view of the problems described above, an object of the invention is to provide an image forming apparatus, in which, it is possible to stop a printing operation at an upper limit when the upper limit is set at a specific print number.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to a first aspect of the present invention, an image forming apparatus includes a sheet supply unit for supplying a printing medium; and a sheet discharge unit for discharging the printing medium after an image is transferred to the printing medium.

Further, the image forming apparatus includes a transport path medium number storage unit for storing a transport path medium number or a number of printing media in a transport path disposed between the sheet supply unit and the sheet discharge unit when the sheet supply unit supplies the printing medium and the sheet discharge unit discharges the printing medium; a discharge number storage unit for storing a discharge number or a number of the printing media discharged from the sheet discharge unit, and for updating the discharge number by adding one to the discharge number when the sheet discharge unit discharges the printing medium; an upper limit print number storage unit for storing an upper limit print number or a maximum number of the printing media that the sheet discharge unit is capable of discharging; an addition unit for calculating an addition sum of the discharge number stored in the discharge number storage unit and the transport path medium number stored in the transport path medium number storage unit when the sheet discharge unit discharges the printing medium; a number comparison unit for comparing the addition sum calculated by the addition unit with the upper limit print number stored in the upper limit print number storage unit; and a sheet supply stop unit for stopping the sheet supply unit when the number comparison unit compares the addition sum with the upper limit print number, and the addition sum exceeds the upper limit print number.

In the first aspect of the present invention, when the number comparison unit compares the addition sum with the upper limit print number, and the addition sum exceeds the upper limit print number, the sheet supply stop unit stops the sheet supply unit. Accordingly, when the print number reaches the upper limit print number, the sheet supply unit does not supply the printing medium, thereby preventing the printing operation from exceeding the upper limit print number.

According to a second aspect of the present invention, the sheet supply unit may include a plurality of sheet supply sections according to different types of printing media. A printing medium supply detection unit is disposed in each of the sheet supply sections. The transport path medium number storage unit stores the transport path medium number in advance with respect to each of the sheet supply sections. The addition unit calculates the addition sum of the discharge number stored in the discharge number storage unit and the transport path medium number stored in the transport path medium number storage unit every time the sheet discharge unit discharges the printing medium.

In the second aspect of the present invention, the printing medium supply detection unit is disposed in each of the sheet supply sections. Accordingly, it is possible to quickly detect the printing medium upon supplying, thereby increasing a speed of the printing operation.

According to a third aspect of the present invention, an image forming apparatus includes a sheet supply unit for supplying a printing medium; and a sheet discharge unit for discharging the printing medium after an image is transferred to the printing medium.

Further, the image forming apparatus includes a transport path medium number storage unit for storing a transport path medium number or a number of printing media in a transport path disposed between the sheet supply unit and the sheet discharge unit when the sheet supply unit supplies the printing medium and the sheet discharge unit discharges the printing medium, and for updating the transport path medium number by adding one to the transport path medium number when the sheet supply unit supplies the printing medium and by subtracting one from the transport path medium number when the sheet discharge unit discharges the printing medium; a discharge number storage unit for storing a discharge number or a number of the printing media discharged from the sheet discharge unit, and for updating the discharge number by adding one to the discharge number when the sheet discharge unit discharges the printing medium; an upper limit print number storage unit for storing an upper limit print number or a maximum number of the printing media that the sheet discharge unit is capable of discharging; an addition unit for calculating an addition sum of the discharge number stored in the discharge number storage unit and the transport path medium number stored in the transport path medium number storage unit when the sheet discharge unit discharges the printing medium; a number comparison unit for comparing the addition sum calculated by the addition unit with the upper limit print number stored in the upper limit print number storage unit; and a sheet supply stop unit for stopping the sheet supply unit when the number comparison unit compares the addition sum with the upper limit print number, and the addition sum exceeds the upper limit print number.

In the third aspect of the present invention, when the number comparison unit compares the addition sum with the upper limit print number, and the addition sum exceeds the upper limit print number, the sheet supply stop unit stops the sheet supply unit. Accordingly, when the print number reaches the upper limit print number, the sheet supply unit does not supply the printing medium, thereby preventing the printing operation from exceeding the upper limit print number.

According to a fourth aspect of the present invention, the sheet supply unit may include a plurality of sheet supply sections according to different types of printing media. A printing medium supply detection unit is disposed in the sheet supply unit for detecting the printing medium supplied from one of the sheet supply units. A printing medium discharge detection unit is disposed for detecting the printing medium discharged from the sheet discharge unit. The transport path medium number storage unit updates the transport path medium number by adding one to the transport path medium number when the printing medium supply detection unit detects the printing medium supplied from one of the sheet supply sections, and by subtracting one from the transport path medium number when the printing medium discharge detection unit detects the printing medium discharged from the sheet discharge unit.

In the fourth aspect of the present invention, the printing medium supply detection unit is disposed in each of the sheet supply sections. Accordingly, it is possible to quickly detect the printing medium upon supplying, thereby increasing a speed of the printing operation.

As described above, in the present invention, when the print number reaches the upper limit print number set in advance, the sheet supply unit does not supply the printing medium, thereby preventing the printing operation from exceeding the upper limit print number.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereunder, embodiments of the present invention will be explained with reference to the accompanying drawings. In the description below, a color printer is described as an example of an image forming apparatus.

First Embodiment

A first embodiment of the present invention will be explained.FIG. 1is a schematic sectional view showing an image forming apparatus1according to the first embodiment of the present invention. The image forming apparatus1is an apparatus such as a printer for printing image data sent from a host device such as a personal computer.

As shown inFIG. 1, the image forming apparatus1includes a first sheet supply unit11for storing a printing medium25having an A4 size; a second sheet supply unit12for storing the printing medium25having an A3 size; a developing unit13for forming a toner image through an electric-photography process and transferring the toner image to the printing medium25; a fixing unit14for fixing the toner image transferred to the printing medium25; a transfer belt15for transporting the printing medium25upon transferring; and an entrance sensor16disposed on a first transport unit18for detecting the printing medium25supplied from the first sheet supply unit11or the second sheet supply unit12. In the embodiment, the first sheet supply unit11and the second sheet supply unit12constitute a sheet supply unit.

The image forming apparatus1further includes a discharge sensor17disposed between a second transport unit19and a discharge roller20for detecting the printing medium25discharged; the first transport unit18for transporting the printing medium25thus discharged to the transfer belt15; the second transport unit19for transporting the printing medium25from the fixing unit14to the discharge roller20; the discharge roller20for transporting the printing medium25to a discharge sheet tray21; the discharge sheet tray21for placing the printing medium25discharged from the discharge roller20; and a print control system (not shown inFIG. 1) for controlling a printing operation. In the embodiment, the discharge roller20and the discharge sheet tray21constitute a sheet discharge unit.

FIG. 2is a block diagram showing the print control system of the image forming apparatus1according to the first embodiment of the present invention. As shown inFIG. 2, the print control system includes a central processing unit (CPU)31; a memory32; a count control unit33; an operation panel34; an image processing unit35; a system control unit36; a process control unit37; an interface38; a motor39; and a sensor group40.

In the embodiment, a system bus41is connected to the central processing unit (CPU)31; the memory32; the count control unit33; the operation panel34; the image processing unit35; the system control unit36; the process control unit37; and the interface38. The motor39and the sensor group40are connected to the system control unit36.

In the embodiment, according to a print control program stored in the memory32, the CPU31controls the memory32; the count control unit33; the operation panel34; the image processing unit35; the system control unit36; the process control unit37; and the interface38.

In the embodiment, the memory32includes a random-access-memory (RAM), a read-only-memory (ROM), and the likes, and stores a program to be executed with the CPU31and print data input from the interface38. The memory32further stores a print possibility flag indicating whether the printing medium25is supplied. When the print possibility flag is “ON”, the printing medium25is supplied. When the print possibility flag is “OFF”, the printing medium25is stopped.

FIG. 3is a block diagram showing the count control unit33shown inFIG. 2according to the first embodiment of the present invention. In the embodiment, the count control unit33manages a print number or a number of printed sheets, and determines whether the printing operation is performed. As shown inFIG. 3, the count control unit33includes a print number counter331; a print number upper limit storage unit332; an addition unit333; a comparison unit334; and a table335.

In the embodiment, the print number counter331stores a discharge number or a number of the printing media25discharged to the discharge sheet tray21. Every time when the printing medium25is discharged to the discharge sheet tray21, the CPU31send an addition signal to the print number counter331, so that the print number counter331adds one to the discharge number stored in advance. The print number upper limit storage unit332stores an upper limit print number or a maximum number of the printing media25that the sheet discharge unit is capable of discharging to the discharge sheet tray21. An administrator inputs the upper limit print number through the operation panel34.

In the embodiment, the addition unit333calculates an addition sum or an addition number by adding a transport path medium number stored in the table335to the discharge number stored in the print number storage unit331when the sheet discharge unit discharges the printing medium, and then sends the addition sum to the comparison unit334.

In the embodiment, the comparison unit334compares the addition sum input from the print number counter331with the upper limit print number stored in the print number upper limit storage unit332. When the addition sum exceeds the upper limit print number, the comparison unit334sends a print possibility signal to the CPU31through the system bus41, so that the printing operation is not performed. When the addition sum is less than the upper limit print number, the comparison unit334sends the print possibility signal to the CPU31through the system bus41, so that the printing operation is performed.

FIG. 4is a schematic view showing an example of the table335shown inFIG. 3according to the first embodiment of the present invention. As shown inFIG. 4, according to the sizes of the printing media25, the table335stores in advance the transport path medium number or a number of the printing media25in the first transport unit18, the transfer belt15, and the second transport unit19on a downstream side of the entrance sensor16when the printing medium25is supplied to the first sheet supply unit11or the second sheet supply unit12, and the printing medium25is discharged to the discharge sheet tray21.

FIG. 5is a schematic view showing the operation panel34shown inFIG. 2according to the first embodiment of the present invention. The operation panel34receives an input from a user, and displays a status of the image forming apparatus1. As shown inFIG. 5, the operation panel34includes a display unit341for displaying contents of an input from the administrator and the user and a status of the image forming apparatus1; a menu key342for displaying a menu; a selection key343for selecting a function displayed on the display unit341; a cancel key344for canceling a function displayed on the display unit341; a cursor key345for scrolling contents displayed on the display unit341; and a ten key346for inputting numerical information. The cursor key345has an upper arrow key, a lower arrow key, a left arrow key, and a right arrow key.

In the embodiment, the image processing unit35shown inFIG. 2performs various image processing with respect to the print data stored in the memory32. Further, the system control unit36is connected to the sensor group40and the motor39, so that the system control unit36sends a status of the image forming apparatus1detected by the sensor group40to the CPU31and controls rotations of the motor39.

In the embodiment, the process control unit37controls the developing unit13, the fixing unit14, the transfer belt15, and the likes. The interface38has a function of connecting the image forming apparatus1to a host control unit of the host computer directing the printing operation, so that only the print data and a command are input from the host computer, and a status of the image forming apparatus1is output to the host computer.

In the embodiment, the motor39transports the printing medium25, and drives the transfer belt15and rollers of the developing unit13and the fixing unit14. The sensor group40is formed of a plurality of sensors including the entrance sensor16, the discharge sensor17, and the likes for monitoring an operation state of the image forming apparatus1.

An operation of the image forming apparatus1will be explained next. The operation is divided into an operation of setting the print number upper limit and an operation of printing continuously (continuous printing). The operation of setting the print number upper limit will be explained first.FIG. 6is a flow chart No.1showing the operation of the image forming apparatus1according to the first embodiment of the present invention.

In step S1, when the administrator pushes the menu key342of the operation panel34, the operation panel34notifies the CPU31that the menu key342is pushed. In step S2, the CPU31displays a menu screen on the display unit341of the operation panel34. In step S3, the administrator uses the cursor key345to move a cursor to an administrator setting screen display item among menu items displayed on the menu screen, and pushes the selection key343. Accordingly, the operation panel34notifies the CPU31that the administrator setting screen display item is pushed. In step S4, the CPU31displays an administrator setting screen on the display unit341of the operation panel34.

In step S5, the administrator uses the cursor key345to move the cursor to an administrator password input screen display item among items displayed on the administrator setting screen, and pushes the selection key343. Accordingly, the operation panel34notifies the CPU31that the administrator password input screen display item is pushed. In step S6, the CPU31displays an administrator password input screen on the display unit341of the operation panel34.

In step S7, the administrator uses the cursor key345to move the cursor to a password input column displayed on the administrator password input screen. Then, the administrator inputs a password in the password input column, and pushes the selection key343. Accordingly, the operation panel34notifies the CPU31of the password thus input. In step S8, the CPU31refers to a certification list (not shown) stored in the memory32for certifying an administrator authorized to set the print number upper limit. Then, the CPU31determines whether the password notified from the operation panel34is registered in the certification list.

When the CPU31determines that the password is not registered in the certification list, the process is completed without setting the print number upper limit. In step S9, when the CPU31determines that the password is registered in the certification list, the CPU displays a print number upper limit setting screen on the display unit341of the operation panel34.

In step S10, the administrator uses the cursor key345to move the cursor to a select screen display item of valid/invalid of the print number upper limit displayed on the print number upper limit setting screen, and pushes the selection key343. Accordingly, the operation panel34notifies the CPU31that the select screen display item of valid/invalid of the print number upper limit is pushed. In step S11, the CPU31displays a select screen of valid/invalid of the print number upper limit on the display unit341of the operation panel34.

In step S12, the administrator uses the cursor key345to move the cursor to a setting validation item for validating a setting displayed on the select screen of valid/invalid of the print number upper limit, and pushes the selection key343. Accordingly, the operation panel34notifies the CPU31that the setting validation item is pushed. In step S13, the CPU31displays an input screen of the print number upper limit on the display unit341of the operation panel34.

In step S14, the administrator uses the cursor key345to move the cursor to a print number upper limit input column displayed on the input screen of the print number upper limit. Then, the administrator uses the ten key346to input the print number upper limit in the print number upper limit input column, and pushes the selection key343. Accordingly, the operation panel34outputs the print number upper limit thus input to the CPU31through the system bus41.

Then, the CPU31outputs the print number upper limit thus input from the operation panel34to the print number upper limit storage unit332in the count control unit33through the system bus41. In step S15, the print number upper limit storage unit332stores and sets the print number upper limit input from the CPU31, thereby completing the process.

The continuous printing operation will be explained next.FIG. 7is a flow chart No.2showing the continuous printing operation of the image forming apparatus1according to the first embodiment of the present invention.

In step S21, the CPU31monitors a state of the interface38all the time, and determines whether the interface38receives the print data from the host device. When the CPU31determines that the interface38does not receive the print data from the host device, the CPU31waits until the interface38receives the print data from the host device. When the CPU31determines that the interface38receives the print data from the host device, the CPU31reads the print data thus received at the interface38, and outputs the print data to the memory32.

Afterwards, the CPU31starts the image processing unit35to perform the image processing on the print data stored in the memory32. Under control of the CPU31, the image processing unit35performs the image processing on the print data stored in the memory32to create the image data. The CPU31transmits the image data thus created at the image processing unit35to the memory32, so that the image data are stored in the memory32.

In step S22, the CPU31refers to the print possibility flag, and determines whether the print possibility flag indicates a print enable state. When the CPU31determines that the print possibility flag does not indicate the print enable state, information indicating a print unable state is displayed on the display unit341of the operation panel34, thereby finishing the continuous printing operation (step S29).

In step S23, when the CPU31determines that the print possibility flag indicates the print enable state, the CPU31detects a printing medium size described in the print data stored in the memory32. According to the printing medium size thus detected, the CPU31selects a sheet supply unit retaining the printing medium25to be printed. For example, when the printing medium size described in the print data stored in the memory32is the A4 size, the CPU31selects the first sheet supply unit11.

In step S24, when the CPU31selects one of the first sheet supply unit11and the second sheet supply unit12retaining the printing medium25to be printed, the CPU31reads the transport path medium number describing the printing medium size thus detected from the table335. Then, the CPU31sends the transport path medium number to the addition unit333.

In step S25, the CPU31starts a printing operation for one sheet of the printing medium25(one sheet printing operation). In particular, the CPU31sends a direction signal to the system control unit36to drive the motor39, so that the system control unit36drives the motor39, thereby transporting the printing medium25and driving the rollers of the developing unit13and the fixing unit14. Accordingly, the one sheet printing operation is started for transferring the image data to the printing medium25. The one sheet printing operation will be explained in more detail later.

In step S26, after the one sheet printing operation, the CPU31determines whether the entrance sensor16sends a sheet supply signal indicating that a trailing edge of the printing medium25passes through the entrance sensor16, that is, the printing medium25is completely supplied. When the CPU31determines that the entrance sensor16does not send the sheet supply signal indicating that the trailing edge of the printing medium25passes through the entrance sensor16, the CPU31waits until the entrance sensor16sends the sheet supply signal indicating that the trailing edge of the printing medium25passes through the entrance sensor16.

In step S27, when the CPU31determines that the entrance sensor16sends the sheet supply signal indicating that the trailing edge of the printing medium25passes through the entrance sensor16, the CPU31determines whether the memory32stores the print data not read yet. When the CPU31determines that the memory32does not store the print data not read yet, the CPU31finishes the process.

In step S28, when the CPU31determines that the memory32stores the print data not read yet, the CPU31refers to the print possibility flag in the memory32, and determines whether the print possibility flag indicates the print enable state. When the CPU31determines that the print possibility flag does not indicate the print enable state, step S29is performed, thereby repeating the process described above. On the other hand, when the CPU31determines that the print possibility flag indicates the print enable state, step S25is performed, thereby repeating the process described above.

The one sheet printing operation in step S25will be explained next.FIG. 8is a flow chart No.3showing the one sheet printing operation in step S25shown inFIG. 7according to the first embodiment of the present invention.

In step S251, when the CPU31starts the one sheet printing operation, the printing medium25is supplied from the sheet supply unit thus selected. For example, when the printing medium size described in the print data input from the host device is the A4 size, the printing medium25having the A4 size is supplied from the first sheet supply unit11.

In step S252, the first transport unit18transports the printing medium25to the transfer belt15, so that the transfer belt15transports the printing medium25to the developing unit13. In step S253, the developing unit13develops the toner image on the printing medium25, and transfers the toner image to the printing medium25. Then, the transfer belt15transports the printing medium25to the fixing unit14.

In step S254, the fixing unit14fixes the toner image to the printing medium25thus transported, and then the printing medium25is transported to the second transport unit19. In step S255, the second transport unit19transports the printing medium25to the discharge roller20. In step S256, the discharge roller20discharges the printing medium25to the discharge sheet tray21. In step S257, the CPU31performs a print possibility determination operation (described later), thereby completing the process.

The print possibility determination operation will be explained next.FIG. 9is a flow chart No.4showing the print possibility determination operation in step S257shown inFIG. 8according to the first embodiment of the present invention.

In step S2571, the CPU31determines whether the discharge sensor17sends a sheet discharge signal through the system control unit36indicating that the printing medium25is discharged. When the CPU31determines that the discharge sensor17does not send the sheet discharge signal indicating that the printing medium25is discharged, the CPU31waits until the discharge sensor17sends the sheet discharge signal. When the CPU31determines that the discharge sensor17sends the sheet discharge signal indicating that the printing medium25is discharged, the CPU31sends the addition signal to the print number counter331through the system bus41, so that the print number counter331adds one to the print number stored in the count control unit33.

In step S2572, when the print number counter331receives the addition signal from the CPU31, the print number counter331adds one to the print number. Then, the addition unit333reads the print number from the print number counter331and reads the transport path medium number from the table335. Then, the addition unit333adds the print number to the transport path medium number, and sends the result, i.e., the addition sum, to the comparison unit334.

In step S2573, when the comparison unit334receives the addition sum from the addition unit333, the comparison unit334reads the upper limit print number stored in the print number upper limit storage unit332, and compares the addition sum with the upper limit print number.

In step S2574, when the comparison unit334determines that the addition sum is less than the upper limit print number, the comparison unit334sends the print possibility signal set to “ON” indicating that the printing operation is possible to the CPU31through the system bus41.

In step S2575, when the comparison unit334determines that the addition sum is equal to or exceeds the upper limit print number, the comparison unit334sends the print possibility signal set to “OFF” indicating that the printing operation is impossible to the CPU31through the system bus41.

In step S2576, when the CPU31receives the print possibility signal set to “ON” from the comparison unit334, the CPU31sets the print possibility flag to the print enable state, thereby completing the print possibility determination operation. Accordingly, the image forming apparatus1is in the state that the printing operation is possible.

In step S2577, when the CPU31receives the print possibility signal set to “OFF” from the comparison unit334, the CPU31sets the print possibility flag to the print unable state, thereby completing the print possibility determination operation. Accordingly, the image forming apparatus1is in the state that the printing operation is not possible.

In the embodiment described above, the comparison unit334compares the addition sum added by the addition unit333with the upper limit print number stored in the print number upper limit storage unit332. When the comparison unit334determines that the addition sum exceeds the upper limit print number, the CPU31stops supplying the printing medium25from the sheet supply unit. Accordingly, when the print number reaches the upper limit print number set in advance, the printing medium25is not supplied from the sheet supply unit. As a result, it is possible to prevent the printing medium25from being printed beyond the upper limit print number when the printing operation is stopped.

Second Embodiment

A second embodiment of the invention will be described below. Similar to the first embodiment, in the second embodiment, the image forming apparatus1is an apparatus such as a printer for printing image data sent from a host device such as a personal computer.

Similar to the first embodiment, the image forming apparatus1includes the first sheet supply unit11; the second sheet supply unit12; the developing unit13; the fixing unit14; the transfer belt15; the entrance sensor16; the discharge sensor17; the first transport unit18; the second transport unit19; the discharge roller20; the discharge sheet tray21; and the print control system (not shown inFIG. 1) for controlling the printing operation. Components in the second embodiment similar to those in the first embodiment are designated by the same reference numerals, and explanations thereof are omitted.

Similar to the first embodiment, the print control system includes the central processing unit (CPU)31; the memory32; the count control unit33; the operation panel34; the image processing unit35; the system control unit36; the process control unit37; the interface38; the motor39; and the sensor group40. Further, the system bus41is connected to the central processing unit (CPU)31; the memory32; the count control unit33; the operation panel34; the image processing unit35; the system control unit36; the process control unit37; and the interface38. The motor39and the sensor group40are connected to the system control unit36.

In the second embodiment, except the count control unit33, the central processing unit (CPU)31; the memory32; the operation panel34; the image processing unit35; the system control unit36; the process control unit37; the interface38; the motor39; and the sensor group40have configurations similar to those in the first embodiment, and explanations thereof are omitted.

FIG. 10is a block diagram showing the count control unit33in the print control system of the image forming apparatus1according to the second embodiment of the present invention. As shown inFIG. 10, the count control unit33includes the print number counter331; the print number upper limit storage unit332; the addition unit333; the comparison unit334; and a transport path medium number counter336. The print number counter331; the print number upper limit storage unit332; the addition unit333; and the comparison unit334have configurations similar to those in the first embodiment, and explanations thereof are omitted. Accordingly, the count control unit33does not have the table335in the first embodiment.

In the embodiment, the transport path medium number counter336stores the transport path medium number or the number of the printing media25in the transport path disposed between the first sheet supply unit11, the second sheet supply unit12, and the sheet discharge tray21when one of the first sheet supply unit11and the second sheet supply unit12supplies the printing medium25, and the printing medium25is discharged to the discharge sheet tray21. Further, the transport path medium number counter336updates the transport path medium number by adding one to the transport path medium number when the printing medium25is supplied, and by subtracting one from the transport path medium number when the printing medium25is discharged.

More specifically, when the CPU31sends the addition signal to the transport path medium number counter336indicating that the printing medium25is supplied, the transport path medium number counter336adds one to the transport path medium number. When the CPU31sends a subtraction signal to the transport path medium number counter336indicating that the printing medium25is discharge, the transport path medium number counter336subtracts one from the transport path medium number.

An operation of the image forming apparatus1in the second embodiment will be explained next. A process of setting the print number upper limit is similar to that in the first embodiment, and explanation thereof is omitted.

The continuous printing operation will be explained first.FIG. 11is a flow chart No.1showing the continuous printing operation of the image forming apparatus1according to the second embodiment of the present invention.

In step S41, the CPU31monitors a state of the interface38all the time, and determines whether the interface38receives the print data from the host device. When the CPU31determines that the interface38does not receive the print data from the host device, the CPU31waits until the interface38receives the print data from the host device. When the CPU31determines that the interface38receives the print data from the host device, the CPU31reads the print data thus received at the interface38, and outputs the print data to the memory32.

Afterwards, the CPU31starts the image processing unit35to perform the image processing on the print data stored in the memory32. Under control of the CPU31, the image processing unit35performs the image processing on the print data stored in the memory32to create the image data. The CPU31transmits the image data thus created at the image processing unit35to the memory32, so that the image data are stored in the memory32.

In step S42, the CPU31refers to the print possibility flag in the memory32, and determines whether the print possibility flag indicates the print enable state. When the CPU31determines that the print possibility flag does not indicate the print enable state, the print unable state is displayed on the display unit341of the operation panel34, thereby finishing the continuous printing operation (step S48).

In step S43, when the CPU31determines that the print possibility flag indicates the print enable state, the CPU31detects the printing medium size described in the print data stored in the memory32. According to the printing medium size thus detected, the CPU31selects a sheet supply unit retaining the printing medium25to be printed according to the printing medium size thus detected. For example, when the printing medium size described in the print data stored in the memory32is the A4 size, the CPU31selects the first sheet supply unit11.

In step S44, the CPU31starts the one sheet printing operation (described later). In particular, the CPU31sends the direction signal to the system control unit36to drive the motor39, so that the system control unit36drives the motor39, thereby transporting the printing medium25and driving the rollers of the developing unit13and the fixing unit14. Accordingly, the one sheet printing operation is started for transferring the image data to the printing medium25.

In step S45, after the one sheet printing operation, the CPU31determines whether the entrance sensor16sends the sheet supply signal indicating that the trailing edge of the printing medium25passes through the entrance sensor16, that is, the printing medium25is completely supplied. When the CPU31determines that the entrance sensor16does not send the sheet supply signal indicating that the trailing edge of the printing medium25passes through the entrance sensor16, the CPU31waits until the entrance sensor16sends the sheet supply signal indicating that the trailing edge of the printing medium25passes through the entrance sensor16.

In step S46, when the CPU31determines that the entrance sensor16sends the sheet supply signal indicating that the trailing edge of the printing medium25passes through the entrance sensor16, the CPU31determines whether the memory32stores the print data not read yet. When the CPU31determines that the memory32does not store the print data not read yet, the CPU31finishes the process.

In step S47, when the CPU31determines that the memory32stores the print data not read yet, the CPU31refers to the print possibility flag in the memory32, and determines whether the print possibility flag indicates the print enable state. When the CPU31determines that the print possibility flag does not indicate the print enable state, the process returns to step S48, thereby repeating the process described above. On the other hand, when the CPU31determines that the print possibility flag indicates the print enable state, the process returns to step S44, thereby repeating the process described above.

The one sheet printing operation in step S44will be explained next.FIG. 12is a flow chart No.2showing the one sheet printing operation in step S44shown inFIG. 11according to the second embodiment of the present invention.

In step S441, when the CPU31starts the one sheet printing operation, the CPU31performs a first print possibility determination operation. The first print possibility determination operation will be explained in more detail later.

In step S442, after the first print possibility determination operation, the CPU31sets the print possibility flag to the print enable state, and the printing medium25is supplied from the sheet supply unit thus selected. For example, when the printing medium size described in the print data input from the host device is the A4 size, the printing medium25having the A4 size is supplied from the first sheet supply unit11.

In step S443, the first transport unit18transports the printing medium25to the transfer belt15, so that the transfer belt15transports the printing medium25to the developing unit13. In step S444, the developing unit13develops the toner image on the printing medium25, and transfers the toner image to the printing medium25. Then, the transfer belt15transports the printing medium25to the fixing unit14.

In step S445, the fixing unit14fixes the toner image to the printing medium25thus transported, and then the printing medium25is transported to the second transport unit19. In step S446, the second transport unit19transports the printing medium25to the discharge roller20. In step S447, the discharge roller20discharges the printing medium25to the discharge sheet tray21. In step S448, the CPU31performs a second print possibility determination operation, thereby completing the process. The second print possibility determination operation will be explained in more detail later.

The first print possibility determination operation will be explained next.FIG. 13is a flow chart No.3showing the first print possibility determination operation in step S441shown inFIG. 12according to the second embodiment of the present invention.

In step S4411, the CPU31determines whether the entrance sensor16sends a sheet supply signal through the system control unit36indicating that the printing medium25is supplied. When the CPU31determines that the entrance sensor16does not send the sheet supply signal indicating that the printing medium25is supplied, the CPU31waits until the entrance sensor16sends the sheet supply signal indicating that the printing medium25is supplied.

In step S4412, when the CPU31determines that the entrance sensor16sends the sheet supply signal indicating that the printing medium25is supplied, the CPU31sends a sheet supply start signal to the count control unit33through the system bus41. Accordingly, the transport path medium number counter336adds one to the transport path medium number indicating the number of the printing media25in the transport path. Under the control of the CPU31, the addition unit333reads the transport path medium number from the transport path medium number counter336. Then, the addition unit333adds the print number to the transport path medium number, and sends the result, i.e., the addition sum, to the comparison unit334.

In step S4413, when the comparison unit334receives the addition sum from the addition unit333, the comparison unit334reads the upper limit print number stored in the print number upper limit storage unit332, and compares the addition sum with the upper limit print number.

In step S4414, when the comparison unit334determines that the addition sum is less than the upper limit print number, the comparison unit334sends the print possibility signal set to “ON” indicating that the printing operation is possible to the CPU31through the system bus41.

In step S4415, when the comparison unit334determines that the addition sum is equal to or exceeds the upper limit print number, the comparison unit334sends the print possibility signal set to “OFF” indicating that the printing operation is impossible to the CPU31through the system bus41.

In step S4416, when the CPU31receives the print possibility signal set to “ON” from the comparison unit334, the CPU31sets the print possibility flag to the print enable state, thereby completing the first print possibility determination operation. Accordingly, the image forming apparatus1is in the state that the printing operation is possible.

In step S4417, when the CPU31receives the print possibility signal set to “OFF” from the comparison unit334, the CPU31sets the print possibility flag to the print unable state, thereby completing the first print possibility determination operation. Accordingly, the image forming apparatus1is in the state that the printing operation is not possible.

The second print possibility determination operation will be explained next.FIG. 14is a flow chart No.4showing the second print possibility determination operation in step S448shown inFIG. 12according to the second embodiment of the present invention.

In step S4481, the CPU31determines whether the discharge sensor17sends the sheet discharge signal through the system control unit36indicating that the printing medium25is discharged. When the CPU31determines that the discharge sensor17does not send the sheet discharge signal indicating that the printing medium25is discharged, the CPU31waits until the discharge sensor17sends the sheet discharge signal.

In step S4482, when the CPU31determines that the discharge sensor17sends the sheet discharge signal indicating that the printing medium25is discharged, the CPU31sends a discharge signal to the count control unit33through the system bus41. Accordingly, the count control unit33subtracts one from the transport path medium number stored in the transport path medium number counter336.

In step S4483, the addition unit333reads the print number from the print number counter331and the transport path medium number from the transport path medium number counter336. Then, the addition unit333adds the print number to the transport path medium number, and sends the result, i.e., the addition sum to the comparison unit334.

In step S4484, when the comparison unit334receives the addition sum from the addition unit333, the comparison unit334reads the upper limit print number from the print number upper limit storage unit332, and compares the addition sum with the upper limit print number.

In step S4485, when the comparison unit334determines that the addition sum is less than the upper limit print number, the comparison unit334sends the print possibility signal set to “ON” indicating that the printing operation is possible to the CPU31through the system bus41.

In step S4486, when the comparison unit334determines that the addition sum is equal to or exceeds the upper limit print number, the comparison unit334sends the print possibility signal set to “OFF” indicating that the printing operation is impossible to the CPU31through the system bus41.

In step S4487, when the CPU31receives the print possibility signal set to “ON” from the comparison unit334, the CPU31sets the print possibility flag to the print enable state, thereby completing the second print possibility determination operation. Accordingly, the image forming apparatus1is in the state that the printing operation is possible.

In step S4488, when the CPU31receives the print possibility signal set to “OFF” from the comparison unit334, the CPU31sets the print possibility flag to the print unable state, thereby completing the second print possibility determination operation. Accordingly, the image forming apparatus1is in the state that the printing operation is not possible.

As described above, in the second embodiment, the comparison unit334compares the addition sum calculated at the print number counter331with the upper limit print number stored in the print number upper limit storage unit332. When the addition sum exceeds the upper limit print number, the CPU31stops supplying the printing medium25from the sheet supply unit. Accordingly, when the print number reaches the upper limit print number set in advance, the printing medium25is not supplied from the sheet supply unit. As a result, it is possible to prevent the printing medium25from being printed beyond the upper limit print number when the printing operation is stopped.

Third Embodiment

A third embodiment of the invention will be described below. Similar to the first embodiment, in the third embodiment, the image forming apparatus1is an apparatus such as a printer for printing image data sent from a host device such as a personal computer.

FIG. 15is a schematic sectional view showing the image forming apparatus1according to the third embodiment of the present invention. As shown inFIG. 15, the image forming apparatus1includes the first sheet supply unit11; the second sheet supply unit12; the developing unit13; the fixing unit14; the transfer belt15; the discharge sensor17; the first transport unit18; the second transport unit19; the discharge roller20; the discharge sheet tray21; a first entrance sensor22; a second entrance sensor23; and the print control system (not shown inFIG. 15) for controlling the printing operation.

Components in the third embodiment similar to those in the first and second embodiments are designated by the same reference numerals, and explanations thereof are omitted. In the third embodiment, instead of the entrance sensor16, the image forming apparatus1is provided with the first entrance sensor22and the second entrance sensor23.

In the third embodiment, the first entrance sensor22is disposed near the first sheet supply unit11for detecting the printing medium25supplied from the first sheet supply unit11. Further, the second entrance sensor23is disposed near the second sheet supply unit12for detecting the printing medium25supplied from the second sheet supply unit12.

Similar to the first embodiment, the print control system includes the central processing unit (CPU)31; the memory32; the count control unit33; the operation panel34; the image processing unit35; the system control unit36; the process control unit37; the interface38; the motor39; and the sensor group40. Further, the system bus41is connected to the central processing unit (CPU)31; the memory32; the count control unit33; the operation panel34; the image processing unit35; the system control unit36; the process control unit37; and the interface38. The motor39and the sensor group40are connected to the system control unit36.

In the third embodiment, except the count control unit33, the central processing unit (CPU)31; the memory32; the operation panel34; the image processing unit35; the system control unit36; the process control unit37; the interface38; the motor39; and the sensor group40have configurations similar to those in the first embodiment, and explanations thereof are omitted.

In the third embodiment, the count control unit33includes the print number counter331; the print number upper limit storage unit332; the addition unit333; the comparison unit334; and the table335. The print number counter331; the print number upper limit storage unit332; the addition unit333; and the comparison unit334have configurations similar to those in the first embodiment, and explanations thereof are omitted.

FIG. 16is a schematic view showing an example of the table335in the print control system of the image forming apparatus1according to the third embodiment of the present invention. As shown inFIG. 16, the table335includes the transport path medium number supplied from the first sheet supply unit11and the transport path medium number supplied from the second sheet supply unit12for each size of the printing medium25.

An operation of the image forming apparatus1in the third embodiment will be explained next. A process of setting the print number upper limit is similar to that in the first embodiment, and explanation thereof is omitted.

The continuous printing operation will be explained first with reference toFIG. 7. It is supposed that the printing medium25having the A4 size is placed in the first sheet supply unit11, and the printing medium25having the A3 size is placed in the second sheet supply unit12.

In step S21, the CPU31monitors the state of the interface38all the time, and determines whether the interface38receives the print data from the host device. When the CPU31determines that the interface38does not receive the print data from the host device, the CPU31waits until the interface38receives the print data from the host device. When the CPU31determines that the interface38receives the print data from the host device, the CPU31reads the print data thus received at the interface38, and outputs the print data to the memory32.

Afterwards, the CPU31starts the image processing unit35to perform the image processing on the print data stored in the memory32. Under the control of the CPU31, the image processing unit35performs the image processing on the print data stored in the memory32to create the image data. The CPU31transmits the image data thus created at the image processing unit35to the memory32, so that the image data are stored in the memory32.

In step S22, the CPU31refers to the print possibility flag, and determines whether the print possibility flag indicates the print enable state. When the CPU31determines that the print possibility flag does not indicate the print enable state, the print unable state is displayed on the display unit341of the operation panel34, thereby finishing the continuous printing operation (step S29).

In step S23, when the CPU31determines that the print possibility flag indicates the print enable state, the CPU31detects the printing medium size described in the print data stored in the memory32. According to the printing medium size thus detected, the CPU31selects one of the first sheet supply unit11and the second sheet supply unit12retaining the printing medium25to be printed. For example, when the printing medium size described in the print data stored in the memory32is the A4 size, the CPU31selects the first sheet supply unit11.

In step S24, the CPU31selects one of the first sheet supply unit11and the second sheet supply unit12retaining the printing medium25to be printed, the CPU31reads one of the first sheet supply unit11and the second sheet supply unit12thus selected, and the transport path medium number describing the printing medium size thus detected from the table335. Then, the CPU31sends the transport path medium number to the addition unit333.

In step S25, the CPU31starts the one sheet printing operation. In particular, the CPU31sends the direction signal to the system control unit36to drive the motor39, so that the system control unit36drives the motor39, thereby transporting the printing medium25and driving the rollers of the developing unit13and the fixing unit14. Accordingly, the one sheet printing operation is performed as described above.

In step S26, after starting the one sheet printing operation, the CPU31determines whether the first entrance sensor22or the second entrance sensor23sends the sheet supply signal indicating that the trailing edge of the printing medium25passes through the first entrance sensor22or the second entrance sensor23, that is, the printing medium25is completely supplied. When the CPU31determines that both of the first entrance sensor22and the second entrance sensor23do not send the sheet supply signal indicating that the trailing edge of the printing medium25passes through the first entrance sensor22and the second entrance sensor23, the CPU31waits until the first entrance sensor22or the second entrance sensor23sends the sheet supply signal indicating that the trailing edge of the printing medium25passes through the first entrance sensor22or the second entrance sensor23.

In step S27, when the CPU31determines that the first entrance sensor22or the second entrance sensor23sends the sheet supply signal indicating that the trailing edge of the printing medium25passes through the first entrance sensor22or the second entrance sensor23, the CPU31determines whether the memory32stores the print data not read yet. When the CPU31determines that the memory32does not store the print data not read yet, the CPU31finishes the process.

In step S28, when the CPU31determines that the memory32stores the print data not read yet, the CPU31refers to the print possibility flag in the memory32, and determines whether the print possibility flag indicates the print enable state. When the CPU31determines that the print possibility flag does not indicate the print enable state, the process returns to step S29, thereby repeating the process described above. On the other hand, when the CPU31determines that the print possibility flag indicates the print enable state, the process returns to step S25, thereby repeating the process described above.

As described above, in the third embodiment, the first entrance sensor22is disposed near the first sheet supply unit11for detecting the printing medium25supplied from the first sheet supply unit11. Accordingly, it is possible to quickly detect that the printing medium25is supplied, thereby increasing a speed of the printing operation.

In the embodiments described above, the image forming apparatus is applied to the printer, and may be applicable to a copier, a facsimile, a multi-function device combining a scanner and a printer, and the likes.

The disclosure of Japanese Patent Application No. 2006-262689, filed on Sep. 27, 2006 is incorporated in the application by reference.