Image forming apparatus with cartridge-replacement indicator

An image forming apparatus includes: a first cartridge configured to contain developer of a first color; a second cartridge configured to contain developer of a second color; a processor; and memory storing computer readable instructions that, when executed by the processor, causing the image forming apparatus to: indicate the necessity to replace the first cartridge by using at least information based on a first use amount and information based on a number of printed sheets; and indicate the necessity to replace the second cartridge by using at least information based on a second use amount without using the information based on the number of printed sheets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No. 2012-201864 filed on Sep. 13, 2012, the entire subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

Illustrative aspects of the present invention relate to an image forming apparatus having a control device configured to indicate a necessity to replace a developer container.

BACKGROUND

For an image forming apparatus, there has been proposed a control device which indicates a necessity to replace a cartridge in a case where a remaining amount of toner in the cartridge detected by an optical sensor is less than a defined value, or in a case where a number of revolutions of a developing roller detected by a revolution counter exceeds a defined value.

SUMMARY

Illustrative aspects of the present invention appropriately determine a timing for replacement of each cartridge in an image forming apparatus having a plurality of cartridges.

According to one illustrative aspect of the present invention, there is provided an image forming apparatus comprising: a first cartridge configured to contain developer of a first color; a second cartridge configured to contain developer of a second color; a processor; and memory. The memory store computer readable instructions that, when executed by the processor, causing the image forming apparatus to indicate a necessity to replace the first cartridge and the second cartridge. The processor is configured to cause the image forming apparatus to: indicate the necessity to replace the first cartridge by using at least information based on a first use amount, which corresponds to an amount of use of the developer of the first color contained in the first cartridge, and information based on a number of printed sheets; and indicate the necessity to replace the second cartridge by using at least information based on a second use amount, which corresponds to an amount of use of the developer of the second color contained in the second cartridge, without using the information based on the number of printed sheets.

DETAILED DESCRIPTION

In the above-described related-art method, since an influence of paper dust coming into a cartridge during printing control is not considered, a printing defect may result from the influence of paper dust before the remaining amount of toner or the number of revolutions of a developing roller satisfies the above-described condition. In order to solve this problem, for example, it may be considered to add a condition for the number of printed sheets as a condition for determining replacement of a cartridge. However, in a color printer having a plurality of cartridges, there exist a cartridge which is easy for the paper dust to enter, and a cartridge which is difficult for the paper dust to enter due to layout of the cartridges. Thus, it may be difficult to perform appropriate control even if a condition for the number of printed sheets is simply added.

Therefore, illustrative aspects of the present invention appropriately determine a timing for replacement of each cartridge in an image forming apparatus having a plurality of cartridges.

According to a first illustrative aspect of the present invention, there is provided an image forming apparatus comprising: a first cartridge configured to contain developer of a first color; a second cartridge configured to contain developer of a second color; a processor; and memory. The memory store computer readable instructions that, when executed by the processor, causing the image forming apparatus to indicate a necessity to replace the first cartridge and the second cartridge. The processor is configured to cause the image forming apparatus to: indicate the necessity to replace the first cartridge by using at least information based on a first use amount, which corresponds to an amount of use of the developer of the first color contained in the first cartridge, and information based on a number of printed sheets; and indicate the necessity to replace the second cartridge by using at least information based on a second use amount, which corresponds to an amount of use of the developer of the second color contained in the second cartridge, without using the information based on the number of printed sheets.

According to this configuration, for example, in a case where the first cartridge is configured to be easier for powder generated from sheets to enter, compared to the second cartridge, it is possible to appropriately determine a timing for replacement of each cartridge.

Consequently, information based on the number of printed sheets (information corresponding to an amount of sheet powder) is used to indicate the necessity to replace the first cartridge. Thus, for example, even before the condition for the amount of use is satisfied, when the condition for the number of printed sheets is satisfied, the necessity to replace the first cartridge is indicated. Therefore, before the first cartridge is influenced by sheet powder entering the first cartridge, it is possible to replace the first cartridge, and to improve image quality.

Further, the information based on the number of printed sheets is not used to determine the timing for replacement of the second cartridge. Therefore, it is possible to appropriately determine the timing for replacement of the second cartridge unlikely to be influenced by sheet powder, according to the amount of use of the developer.

According to a second illustrative aspect of the present invention, the processor is configured to cause the image forming apparatus to: in a case where any one condition of a plurality of conditions including at least a first condition that the first use amount exceeds a first threshold value and a second condition that the number of printed sheets exceeds a third threshold value is satisfied, indicate the necessity to replace the first cartridge; and in a case where the second use amount exceeds a second threshold value, indicate the necessity to replace the second cartridge.

According to a third illustrative aspect of the present invention, the plurality of conditions includes a third condition that a driving amount of a rotator for performing conveyance of the developer exceeds a fourth threshold value. According to a fourth illustrative aspect of the present invention, the third condition is that a driving amount of a rotator of the first cartridge for performing conveyance of the developer of the first color exceeds the fourth threshold value.

According to this configuration, the condition for the driving amount of the rotator is also used to determine the timing for replacement of each cartridge. Therefore, even in a case where the driving amount of the rotator increases and the developer is deteriorated, it is possible to urge replacement of the corresponding cartridge.

According to a fifth illustrative aspect of the present invention, the processor is configured to cause the image forming apparatus to: in a case where the first use amount exceeds a first threshold value, indicate the necessity to replace the first cartridge; in a case where the second use amount exceeds a second threshold value, indicate the necessity to replace the second cartridge; and in a case where the number of printed sheets exceeds a third threshold value, change the first threshold value to a sixth threshold value that is smaller than the first threshold value.

According to a sixth illustrative aspect of the present invention, the processor is configured to cause the image forming apparatus to: in a case where the first use amount exceeds a first threshold value, indicate the necessity to replace the first cartridge; in a case where the second use amount exceeds a second threshold value, indicate the necessity to replace the second cartridge; and in a case where the number of printed sheets exceeds a third threshold value, perform correction on the first use amount such that the corresponding amount of use increases than normal.

According to a seventh illustrative aspect of the present invention, the image forming apparatus further comprises an optical sensor configured to measure the first use amount and the second use amount.

According to an eighth illustrative aspect of the present invention, the number of printed sheets is counted by a page counter.

According to a ninth illustrative aspect of the present invention, the image forming apparatus further comprises a sheet sensor configured to detect passage of a sheet, wherein the page counter is configured to count the number of printed sheets on a basis of an output value from the sheet sensor.

According to this configuration, the timing for replacement of the first cartridge is determined on the basis of the number of sheets actually printed. Therefore, it is possible to efficiently suppress the influence of sheet powder.

According to a tenth illustrative aspect of the present invention, the rotator is a developing roller, and the driving amount is the number of revolutions of the developing roller.

According to the present invention, in an image forming apparatus having a plurality of cartridges, it is possible to appropriately determine a timing for replacement of each cartridge.

Subsequently, a first exemplary embodiment of the present invention will be described. In the following description, first, the overall configuration of a color printer which is an example of an image forming apparatus will be described, and then the characterizing portions of the present invention will be described in detail.

In the following description, directions of a color printer refer to the directions as seen from a user facing to the color printer during its use. To be more specific, referring toFIG. 1, a left-side direction and a right-side direction of the drawing sheet are referred to as a “front side” and a “rear side” of the color printer, respectively. Also, a direction away from a viewer ofFIG. 1is referred to as a “left side”, and a direction toward the viewer ofFIG. 1as a “right side”. An upward and downward direction inFIG. 1is referred to as a “vertical direction” or an “upward and downward direction” as it is.

As shown inFIG. 1, a color printer1includes a sheet feeding unit20configured to feed a sheet P, an image forming unit30configured to form an image on the fed sheet P, and a sheet discharging unit90configured to discharge the sheet P, on which the image has been formed, inside a main apparatus body10.

The sheet feeding unit20includes a sheet feeding tray21and a sheet conveying device22. The sheet feeding tray21is configured to accommodate the sheet P. The sheet conveying device22is configured to convey the sheet P from the sheet feeding tray21to the image forming unit30.

The image forming unit30includes a scanner unit40, a process unit50, a transfer unit70and a fixing unit80.

The scanner unit40is provided at an upper portion of the inside of the main apparatus body10. The scanner unit40includes a laser beam emitting unit, a polygonal mirror, lenses, a reflective mirror, etc. (not shown). Further, in the scanner unit40, laser beams are irradiated onto the surfaces of photosensitive drums51which are examples of photosensitive elements (which will be described later), through paths shown by alternate long and two short dashes lines inFIG. 1, during high-speed scanning.

The process unit50is configured to be installable in and removable from the main apparatus body10through an opening10A which is formed by opening a front cover disposed on a front surface of the main apparatus body10. The process unit50includes a drawer60, four photosensitive drums51that are rotatably supported by the drawer60, four developing cartridges52that are removably installed as examples of cartridges in the drawer60such that the developing cartridges correspond to the photosensitive drums51, respectively.

Incidentally, in this specification and the drawings, in a case of specifying the photosensitive drums51, the developing cartridges52and the like corresponding to colors of toner (e.g., developer), symbols of K, Y, M and C corresponding to black, yellow, magenta and cyan are added to their reference symbols. Further, in a case of describing the photosensitive drums51and so on, regardless of the colors of toner, the above-described symbols of K, Y, M and C are omitted.

The photosensitive drums51are arranged along a front-rear direction (e.g., a predetermined direction) in a state where the process unit50is installed in the main apparatus body10. In the drawer60, other components such as four chargers55configured to expose the photosensitive drums51are appropriately provided. Further, each of the developing cartridges52includes a developing roller53configured to feed toner to a corresponding photosensitive drum51, a toner container54configured to accommodate the toner, and other components such as a known layer-thickness regulating blade and a feeding roller.

Inside each developing cartridge52, as shown inFIG. 2, an agitator300configured to stir toner T contained in the corresponding developing cartridge is provided. The agitator300includes a rotating spindle310, a sheet attachment portion320and a sheet member330.

The rotating spindle310is a shaft extending along the axial direction of a corresponding developing roller53(e.g., a left-right direction), and both ends of the rotating spindle310are rotatably supported on left and right side walls521of the corresponding developing cartridge52. The sheet attachment portion320is formed to extend radially outward from the rotating spindle310, and on the fore end of the sheet attachment portion320, the sheet member330is fixed by adhering or the like.

The sheet member330is configured to stir the toner T while its fore end is in sliding contact with the wall of the toner container54, according to the rotation of the agitator300.

Further, at the left and right side walls521of each developing cartridge52, a pair of transmission windows522configured to transmit light of a toner sensor130(which will be described later) is provided.

Referring toFIG. 1again, the transfer unit70is provided between the sheet feeding unit20and the process unit50. The transfer unit70includes a driving roller71, a driven roller72, a conveyance belt73and transfer rollers74which are examples of transfer members.

The driving roller71and the driven roller72are disposed in parallel with an interval in the front-rear direction. The conveyance belt73, which is composed of an endless belt, is stretched between the driving roller71and the driven roller72. The outer surface of the conveyance belt73comes into contact with the photosensitive drums51. Further, inside the conveyance belt73, four transfer unit70are provided to face the photosensitive drums51with the conveyance belt73interposed therebetween. During transferring, a transfer bias is applied to each transfer roller74by constant current control.

The fixing unit80is disposed behind the process unit50and the transfer unit70. The fixing unit80includes a heating roller81and a pressing roller82. The pressing roller82is disposed to face the heating roller81and is configured to press the heating roller81.

In the image forming unit30having the above-described configuration, first, the surfaces of the photosensitive drums51are uniformly charged by the chargers55, and then are exposed by the scanner unit40. As a result, the potentials of exposed portions decrease, whereby electrostatic latent images based on image data are formed on the photosensitive drums51. Subsequently, the toner contained in the developing cartridges52is fed to the electrostatic latent images formed on the photosensitive drums51by the developing rollers53, whereby toner images are carried on the photosensitive drums51.

Next, a sheet P fed on the conveyance belt73passes between the photosensitive drums51and the transfer rollers74, whereby the toner images formed on the photosensitive drums51are transferred onto the sheet P. Then, the sheet P passes between the heating roller81and the pressing roller82, whereby the toner image transferred on the sheet P is thermally fixed.

The sheet discharging unit90includes a plurality of conveying rollers91configured to convey the sheet P. The sheet P with the toner image transferred and thermally fixed thereon is conveyed by the conveying rollers91, and is discharged to the outside of the main apparatus body10.

A control device200is provided inside the main apparatus body10. The control device200is configured to control the color printer1having the above-described configuration.

Four image forming sections30K,30Y,30M and30C are sequentially arranged in order of black, yellow, magenta and cyan from an upstream side to a downstream side of a conveyance direction of a sheet P. In other words, in the present exemplary embodiment, among a plurality of image forming sections30, an image forming section30K for black (a first color) which is disposed on the most upstream side corresponds to a first image forming section, and an image forming section30Y,30M and/or30C for a color other than black (a second color) such as yellow, magenta and cyan corresponds to a second image forming section. Incidentally, in the following description, if necessary, the term “first” is added to the heads of names of members and the like corresponding to black, and the term “second” is added to the heads of names of members and the like corresponding to yellow, magenta and cyan.

The first developing cartridge52K is disposed on the most upstream side in the conveyance direction of the sheet P, such that the first developing cartridge52K is easier for paper dust generated from the sheet P to enter, as compared to the second developing cartridges52Y,52M and52C disposed on the downstream side. Specifically, paper dust having not been recovered by a belt cleaning roller (not shown) is brought to the positions of the photosensitive drums51by rotation of the conveyance belt73. Then, paper dust attached to the photosensitive drums51is attached to the developing rollers53and enters the developing cartridges52. Since the belt cleaning roller is disposed below the conveyance belt73, a large amount of the paper dust having not been recovered by the belt cleaning roller enters the developing cartridge52K disposed on the most upstream side. Then, the timing for replacement of each developing cartridge52is determined by the control device200.

The control device200includes, for example, a CPU (which is an abbreviation for central processing unit), a RAM (which is an abbreviation for random access memory), a ROM (which is an abbreviation for read only memory) and an input/output circuit. The control device200is configured to perform computing processes on the basis of inputs from various sensors, the contents of a print command, and programs, data and the like stored in the ROM, thereby performing a known warm-up operation, printing control, etc. Here, the warm-up operation means a printing preparation operation, specifically, control to rotate the agitators300, the developing rollers53and the like for a predetermined period before feeding of the sheet P from the sheet feeding tray21starts.

Further, in the present exemplary embodiment, especially, the control device200is configured to perform control to determine a timing for replacement of each developing cartridge52on the basis of inputs from a sheet sensor110, which serves as an example of a sheet sensor, and the toner sensors130(shown inFIGS. 1 and 2), and the numbers of revolutions of the developing rollers53counted by a revolution counter220(which will be described later). Incidentally, the toner sensors130are provided on a one-to-one basis for the developing cartridges52; however, inFIG. 2, for the sake of convenience, only one toner sensor130is representatively shown.

The sheet sensor110is configured to detect passage of a sheet P. The sheet sensor110is disposed on a conveyance path between the sheet conveying device22and the image forming unit30(the conveyance belt73). A detection value detected by the sheet sensor110is output to the control device200.

Incidentally, the sheet sensor110has a known structure. To provide a brief explanation, the sheet sensor110is composed of a detection arm111, which is configured to swing by being in contact with the sheet P, and an optical sensor configured to detect swinging of the detection arm.

The toner sensors130are optical sensors. Each toner sensors130include a light emitting unit131and a light receiving unit132. The light emitting unit131and the light receiving unit132are disposed to face each other such that a pair of transmission windows522provided at the left and right side walls521of a corresponding developing cartridge52is interposed therebetween in the left-right direction.

As shown by a broken line inFIG. 2, light emitted from the light emitting unit131enters the corresponding developing cartridge52through one transmission window522and is received by the light receiving unit132through the other transmission window522. The light receiving unit132is an element whose output voltage value varies according to the intensity of received light. The light receiving unit132is configured to receive light and output a light reception signal (a light reception amount) to the control device200(specifically, a determining unit230). More specifically, the toner T is stirred by the agitators300, and then the light emitting units131emit light. Then, the light receiving units132detect light reception amounts corresponding to the amounts of use of the toner T.

Here, a first light reception amount, which is detected by a toner sensor130for the first developing cartridge52K, corresponds to a first use amount showing the amount of use of toner stored in the first developing cartridge52K. Also, a second light reception amount detected by a toner sensor130for the second developing cartridge (e.g.,52Y,52M and52C) corresponds to a second use amount showing the amount of use of toner stored in the second developing cartridge (52Y,52M and52C).

The control device200is configured to include a page counter210, the revolution counters220and the determining unit230.

The page counter210is configured to count the number of sheets P printed using the first developing cartridge52K. Specifically, the page counter210is configured to count the number of sheets P printed using the first developing cartridge52K (that is, the total number of printed sheets) on the basis of an output value from the sheet sensor110.

More specifically, the page counter210starts to count the total number of printed sheets from when a new first developing cartridge52K is installed in the main apparatus body10, and counts up the total number of printed sheets whenever printing control is performed, until the life of the corresponding first developing cartridge52K comes to an end (that is, replacement timing of the corresponding first developing cartridge comes). Further, when the lifetime of the first developing cartridge52K comes (when performing indication of a necessity to replace, which will be described later), the page counter210resets the total number of printed sheets to zero. The resetting of the total number of printed sheets may be performed when a new developing cartridge is installed.

Incidentally, determination on whether a developing cartridge52is new may be performed, for example, using a known new-article detecting mechanism which is provided to the corresponding developing cartridge, or using a known contactless memory which is provided to the corresponding developing cartridge.

The total number of printed sheets counted by the page counter210is output to the determining unit230.

Each revolution counter220has a function of counting the total number of revolutions of a corresponding developing roller53, as an example of a driving amount. Specifically, similarly to the page counter210, each revolution counter220counts up the total number of revolutions of a corresponding developing cartridge52from when the corresponding developing cartridge52is new to when the life of the corresponding developing cartridge52comes to an end. Further, each revolution counter220resets the total number of revolutions to zero upon indicating a necessity to replace the corresponding developing cartridge52is performed. The resetting of the total number of revolutions may be performed when a new developing cartridge is installed.

Here, a first total number of revolutions of the first developing cartridge52K counted by a revolution counter220corresponds to a first driving amount. A second total number of revolutions of the second developing roller (e.g.,53Y,53M and53C) counted by the revolution counter220corresponds to second driving amounts. Further, each total number of revolutions counted by the revolution counter220is output to the determining unit230.

The determining unit230is configured to determine a timing for replacement of each developing cartridge52on the basis of the light reception amounts from the toner sensors130, and the total numbers of revolutions from the revolution counters220. In addition, the determining unit230is configured to further use the total number of printed sheets from the page counter210, as a determination condition, to determine a timing of replacement of the first developing cartridge52K. In other words, the determining unit230is configured to: use a total number of printed sheets corresponding to an amount of paper dust intruded, as a condition, to determine a timing for replacement of the first developing cartridge52K disposed at the most upstream position where it is easy for paper dust to enter; and not to use a condition for a total number of printed sheets to determine a timing for replacement of each of the second developing cartridges52Y,52M and52C disposed on the downstream side where it is difficult for paper dust to enter.

Further, in a case where the determining unit230determines that it is a timing for replacement of a developing cartridge52by use of the above-described condition, a notification unit400is configured to indicate a message to a user that it is necessary to replace the corresponding developing cartridge52. As the notification unit400, for example, a liquid crystal display configured to indicate the message by a text, a picture, and so on, a speaker configured to indicate the message by sound, a lamp configured to indicate the message by flicker of light or the like can be used. Further, a notification unit obtained by combining two or more of a liquid crystal display, a speaker, a lamp and so on can be used.

In other words, the control device200is configured to use information based on an amount of use of toner and information based on the number of printed sheets to indicate the necessity to replace the first developing cartridge52K. Further, the control device200is configured to use information based on an amount of use of toner to indicate the necessity to replace each second developing cartridges52Y,52M or52C, without using the information based on the number of printed sheets.

Specifically, the control device200uses a flow chart ofFIG. 3to determine the timing for replacement of the first developing cartridge52K, and uses a flow chart ofFIG. 4to determine the timing for replacement of each second developing cartridge52(for example,52Y). Incidentally, control based on the flow chart shown inFIG. 4is performed separately with respect to each of the three second developing cartridges52Y,52M and52C; however, in the following description, determining of the timing for replacement of the second developing cartridge52Y will be representatively described.

(Control on Determining Timing for Replacement of First Developing Cartridge52K)

As shown inFIG. 3, upon a print command is received (“START”), first, in STEP S1, the control device200performs the above-described known warm-up operation control.

After STEP S1, in STEP S2, the control device200acquires a first light reception amount corresponding to an amount of use of toner stored in the first developing cartridge52K, from a corresponding toner sensor130. After STEP S2, in STEP S3, the control device200acquires a first total number of revolutions of the first developing roller53K from a corresponding revolution counter220. Then, in STEP S4, the control device200acquires the total number of sheets P printed using the first developing cartridge52K from the page counter210.

After STEP S4, in STEP S5, the control device200determines whether the first light reception amount exceeds a first threshold value T1(which means, whether the first light reception amount is larger than the first threshold value T1). In a case where it is determined that the first light reception amount exceeds the first threshold value T1(“Yes”), in STEP S6, the control device200indicates the necessity to replace the first developing cartridge52K. The first threshold value T1and a second threshold value T2(seeFIG. 4), which will be described later, are determined by experiments, simulations and so on, and may be the same as or different from each other.

After STEP S6, the control device200resets the individual counters210and220(the total number of revolutions and the total number of printed sheets corresponding to the first developing cartridge52K) in STEP S7and then terminates the present control (“END”).

In a case where it is determined in STEP S5that the first light reception amount does not exceed the first threshold value T1(which means, the first light reception amount is equal to or less than the first threshold value T1) (“No”), in STEP S8, the control device200determines whether the first total number of revolutions exceeds a fourth threshold value T4. The fourth threshold value T4and a fifth threshold value T5(seeFIG. 4), which will be described later, are determined by experiments, simulations and so on, and may be the same as or different from each other.

If it is determined in STEP S8that the first total number of revolutions exceeds the fourth threshold value T4(“Yes”), the control device200proceeds to the process of STEP S6; otherwise, the control device200proceeds to the process of STEP S9. In STEP S9, the control device200determines whether the total number of printed sheets exceeds a third threshold value T3. The third threshold value T3may be determined by experiments, simulations and so on.

If it is determined in STEP S9that the total number of printed sheets exceeds the third threshold value T3(“Yes”), the control device200proceeds to the process of STEP S6; otherwise (“No”), the control device200proceeds to the process of STEP S10. In STEP S10, the control device200performs printing control corresponding to one page. Consequently, the control device200is configured to indicate the necessity to replace the first cartridge in a case where any one condition of the first condition of STEP S5, the second condition of STEP S9and the third condition of STEP S8is satisfied.

After STEP S10, in STEP S11, the control device200determines whether the printing control has terminated, that is, whether printing of all pages designated by the print command has terminated. If it is determined in STEP S11that the printing control has not terminated (“No”), the control device200returns to the process of STEP S2; otherwise (“Yes”), the control device200terminates the present control (“END”).

(Control on Determining Timing for Replacement of Second Developing Cartridge52Y)

In a control of determine the timing for replacement of the second developing cartridge52Y, the condition for the total number of printed sheets is not considered. Therefore, the flow chart shown inFIG. 4is basically a flow chart obtained by deleting the processes of STEPS S4and S9ofFIG. 3. In the following description, only differences from the flow chart ofFIG. 3will be described, and identical steps to those ofFIG. 3are denoted by the same reference symbols and detailed descriptions thereof will be omitted.

STEPS S102and S103are substantially identical to STEPS S2and S3ofFIG. 3except that data which are acquired are a second light reception amount and a second total number of revolutions corresponding to the second developing cartridge52Y. In STEP S105, the control device200performs a process substantially identical to that of STEP S5ofFIG. 3. Specifically, the control device200determines whether the second light reception amount exceeds the second threshold value T2.

STEP S106is substantially identical to STEP S6ofFIG. 3, except that a target which is notified is the second developing cartridge52Y. In STEP S107, the control device200resets a corresponding revolution counter220(the total number of revolutions corresponding to the second developing cartridge52Y).

In STEP S108, the control device200performs a process substantially identical to that of STEP S8ofFIG. 3. Specifically, the control device200determines whether the second total number of revolutions exceeds the fifth threshold value T5.

According to the above-described configuration, in the present exemplary embodiment, it is possible to obtain the following effects.

Not only the first light reception amount and the first total number of revolutions but also the condition for the total number of printed sheets are used to determine the timing for replacement of the first developing cartridge52K. Therefore, for example, as shown inFIG. 5, before the first light reception amount reaches the first threshold value T1, and even before the first total number of revolutions reaches the fourth threshold value T4, when the total number of printed sheets exceeds the third threshold value T3, the necessity to replace the first developing cartridge52K is indicated. For this reason, it is possible to replace the first developing cartridge52K before the first developing cartridge is influenced by paper dust entering the first developing cartridge52K, and to improve image quality.

Further, the condition for the total number of printed sheets is not used to determine the timing for replacement of each second developing cartridges52Y,52M or52C. Therefore, it is possible to appropriately determine the timings for replacement of each second developing cartridges52Y,52M or52C, which is hard to be influenced by paper dust, according to an amount of use of toner, a deterioration of toner, etc.

Not only the light reception amount but also the total number of revolutions of each developing roller53are used to determine a timing for replacement of a corresponding developing cartridge52. Therefore, even in a case where toner has been deteriorated due to an increase in the total number of revolutions, it is possible to urge replacement of the corresponding developing cartridge52.

The page counter210counts the total number of printed sheets on the basis of the output value from the sheet sensor110. therefore, it is possible to determine the timing for replacement of the first developing cartridge52K on the basis of the number of sheets P actually printed, and to efficiently suppress the influence of sheet powder.

Subsequently, a second exemplary embodiment of the present invention will be described in detail with reference to appropriate drawings. The present exemplary embodiment is obtained by changing a portion of the above-described control of the control device according to the first exemplary embodiment. Therefore, steps substantially identical to those of the first exemplary embodiment are denoted by the same reference symbols and detailed descriptions thereof will be omitted.

In the first exemplary embodiment, in a case where the total number of printed sheets exceeds the third threshold value T3(“Yes” in STEP S9), immediately, the control device proceeds to STEP S6to indicate the necessity to replace the first developing cartridge52K. However, in the second exemplary embodiment, when the total number of printed sheets exceeds the third threshold value T3, the control device changes a threshold value for a light reception amount which is compared with the first light reception amount, from the above-described first threshold value T1to a sixth threshold value T6that is smaller than the first threshold value T1. As a result, in the case where the total number of printed sheets exceeds the third threshold value T3, the control device proceeds to STEP S6to indicate the necessity to replace the first developing cartridge52K. The sixth threshold value T6needs only to be a value (for example, zero) surely resulting in “Yes” in determination of STEP S50, which will be described later, and may be determined by experiments, simulations and so on.

Specifically, the control device is configured to perform control according to flow charts shown inFIGS. 6 and 7. Here, the flow chart shown inFIG. 6is obtained by eliminating STEPS S4and S9from the flow chart shown inFIG. 3, adding a new process of STEP S200between STEPS S3and S5, and replacing STEP S5ofFIG. 3with a process of STEP S50.

In STEP S200, the control device sets a threshold value for a light reception amount. Specifically, as shown inFIG. 7, in STEP S200, first, in STEP S201, the control device acquires the total number of printed sheets from the page counter210.

After STEP S201, in STEP S202, the control device determines whether the total number of printed sheets exceeds the third threshold value T3. If it is determined in STEP S202that the total number of printed sheets does not exceed the third threshold value T3(“No”), the control device sets the threshold value for the light reception amount to the first threshold value T1in STEP S203, and then proceeds to STEP S50ofFIG. 6.

Meanwhile, if it is determined in STEP S202that the total number of printed sheets exceeds the third threshold value T3(“Yes”), the control device changes the threshold value for the light reception amount from the first threshold value T1to the sixth threshold value T6that is smaller than the first threshold value T1in STEP S204, and then proceeds to STEP S50ofFIG. 6. In STEP S50, the control device determines whether the first light reception amount exceeds the threshold value for the light reception amount set in STEP S200.

By configuring the control device as described above, as shown inFIG. 8, before the first light reception amount reaches the first threshold value T1, and even before the first total number of revolutions reaches the fourth threshold value T4, when the total number of printed sheets exceeds the third threshold value T3, the threshold value for the light reception amount is changed to the sixth threshold value T6smaller than the first threshold value T1. Therefore, it is possible to advance the timing for replacement of the first developing cartridge from a normal timing (a timing when the first light reception amount reaches the first threshold value T1). Therefore, even in this case, it is possible to replace the first developing cartridge before the first developing cartridge is influenced by paper dust, and to improve image quality.

Subsequently, a third exemplary embodiment of the present invention will be described in detail with reference to appropriate drawings. The present exemplary embodiment is obtained by changing a portion of the above-described control of the control device according to the first exemplary embodiment. Therefore, steps substantially identical to those of the first exemplary embodiment are denoted by the same reference symbols and detailed descriptions thereof will be omitted.

In the third exemplary embodiment, the control device performs correction to increase the first light reception amount when the total number of printed sheets exceeds the third threshold value T3. Consequently, in a case where the total number of printed sheets exceeds the third threshold value T3, the control device proceeds to STEP S6to indicate the necessity to replace the first developing cartridge52K.

Specifically, the control device is configured to perform control according to flow charts shown inFIGS. 9 and 10. The flow chart shown inFIG. 9is obtained by eliminating STEPS S4and S9from the flow chart shown inFIG. 3and adding a new process of STEP S300between STEPS S3and S5.

In STEP S300, the control device sets the first light reception amount. Specifically, as shown inFIG. 10, in STEP S300, first, the control device performs the same processes as those of STEPS S201and S202of the second exemplary embodiment.

If it is determined in STEP S202that the total number of printed sheets does not exceed the third threshold value T3(“No”), the control device proceeds to STEP S5ofFIG. 9, without correcting the first light reception amount. Meanwhile, if it is determined in STEP S202that the total number of printed sheets exceeds the third threshold value T3(“Yes”), in STEP S303, the control device performs correction to increase the first light reception amount.

The correcting method may be any method, for example, a method of multiplying the first light reception amount by a predetermined coefficient, or a method of adding a predetermined correction value to the first light reception amount. Also, the value of the corrected light reception amount needs only to be a value (for example, a value larger than the first threshold value T1) surely resulting in “Yes” in the determination of STEP S5, and the above-described coefficient or correction value may be determined by experiments, simulations and so on, such that the value of the corrected light reception amount becomes that value.

By configuring the control device as described above, as shown inFIG. 11, before the first light reception amount (uncorrected) reaches the first threshold value T1, and even before the first total number of revolutions reaches the fourth threshold value T4, when the total number of printed sheets exceeds the third threshold value T3, the first light reception amount is corrected to increase such that the first light reception amount instantaneously reaches the first threshold value T1. Therefore, it is possible to advance the timing for replacement of the first developing cartridge from the normal timing (a timing when the uncorrected first light reception amount reaches the first threshold value T1). Therefore, even in this case, it is possible to replace the first developing cartridge before the first developing cartridge is influenced by paper dust and to improve image quality.

Incidentally, in the second and third exemplary embodiments, the light reception amount or the threshold value to be compared with the corresponding light reception amount is changed to advance the timing for replacement of the first developing cartridge from the normal timing. However, the present invention is not limited thereto. For example, the total number of revolutions of the first developing roller or the threshold value to be compared with the corresponding total number of revolutions is changed to advance the replacement timing.

Specifically, for example, in a case where the total number of printed sheets does not exceed the third threshold value T3, the threshold value for the number of revolutions may be set to the fourth threshold value T3, and in a case where the total number of printed sheets exceeds the third threshold value T3, the threshold value for the number of revolutions may be changed from the fourth threshold value T4to a threshold value smaller than the fourth threshold value T3. Further, for example, in a case where the total number of printed sheets does not exceed the third threshold value T3, the total number of revolutions may not be corrected, and in a case where the total number of printed sheets exceeds the third threshold value T3, correction may be performed on the total number of revolutions such that the total number of revolutions increases.

In the above-described exemplary embodiments, as photosensitive elements, the photosensitive drums51have been exemplified. However, the present invention is not limited thereto. For example, belt-type photosensitive elements may be used.

In the above-described exemplary embodiments, each developing roller53has been provided integrally with a corresponding developing cartridge52serving as a cartridge. However, the present invention is not limited thereto. Each developing roller may be provided to a developing unit which is a component separate from toner cartridges serving as cartridges. Also, a cartridge may be a process cartridge having a photosensitive drum51and a developing cartridge52integrated with each other.

In the above-described exemplary embodiments, the sheet P such as cardboard, postcard and thin paper have been exemplified as the sheet. However, the present invention is not limited thereto. For example, an OHP sheet may be used.

In the above-described exemplary embodiments, the transfer rollers74have been exemplified as the transfer member. However, the present invention is not limited thereto. The transfer member may be any other member such as a conductive brush or a conductive leaf spring configured to transfer bias can be applied.

In the above-described exemplary embodiments, as an amount of use of toner, a light reception amount detected by an optical sensor (a toner sensor130) has been exemplified. However, the present invention is not limited thereto. For example, a value obtained by integrating the numbers of dots of images printed on sheets may be used as an amount of use.

In the above-described exemplary embodiments, the page counter210configured to the total number of printed sheets on the basis of an output value of the sheet sensor110has been exemplified. However, the present invention is not limited thereto. The page counter may be configured to integrate data on the numbers of printed sheets included in print commands, thereby computing the total number of printed sheets.

In the above-described exemplary embodiments, the first developing cartridge52K has been disposed on the most upstream side such that it is easy for paper dust to enter the first developing cartridge. However, the present invention is not limited thereto. For example, a first developer container may be configured to be easy for paper dust to enter due to the features such as color of toner contained therein. That is, since the present invention needs only to be applicable to the first developing cartridge easiest for paper dust to enter, for example, in a case where a first developer container which is easiest for paper dust to enter is specified from among a plurality of developer containers by experiments, simulations and so on, only with respect to a timing for replacement of the specified first developer container, a condition for the total number of printed sheets may be used.

In the above-described exemplary embodiments, as a driving amount of a rotator, the total number of revolutions of each developing roller53has been exemplified. However, the present invention is not limited thereto. For example, the total number of revolutions of a member (such as an agitator) connected to a driving gear of a developing roller through a gear, the total number of revolutions of a photosensitive drum, a driving time of a developing roller, and so on may be used.

In the above-described exemplary embodiments, the present invention has been applied to the color printer1. However, the present invention is not limited thereto. The present invention may be applied to other image forming apparatuses such as a copy machine and a multi-function apparatus.