Image forming device with cartridge replacement alert system

An image forming device includes a replaceable cartridge, a light-emitting element, a light-receiving element, and a determining unit. The replaceable cartridge accommodates developer therein and includes an agitator and a developing roller rotatable together with the agitator. The light-emitting element is configured to emit a light toward the replaceable cartridge. The light-receiving element is configured to receive the light emitted by the light-emitting element through the replaceable cartridge to output a signal. The determination value is produced based on the signal. The determining unit is configured to determine whether or not the determination value is greater than a predetermined determination threshold upon the agitator having rotated continuously more than a first prescribed number of times. The determining unit determines that the replaceable cartridge should be replaced with a new one when the determination value is greater than the predetermined determination threshold.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application Nos. 2011-041805 filed Feb. 28, 2011, 2011-041808 filed Feb. 28, 2011, and 2011-041816 filed Feb. 28, 2011. The entire content of each of these priority applications is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an image forming device configured to detect optically the quantity of developer present in a replaceable cartridge.

BACKGROUND

In conventional technology, there are image-forming devices configured to detect the quantity of developer remaining in a replaceable cartridge optically. One such device provides a pair of light-transmissive windows in opposing side walls of the cartridge. The device irradiates light into one of the light-transmissive windows and detects light exiting from the other, then determines the quantity of developer remaining in the cartridge based on a signal acquired as a result of this detection. Thus, the image-forming device can make such determinations as when the cartridge needs to be replaced, for example, based on the quantity of developer detected in the cartridge.

SUMMARY

However, it is well known that the charging performance of developer gradually declines as the developer in the cartridge is repeatedly rubbed between the developing roller, thickness-regulating blade, and the like and as the developer is repeatedly agitated by an agitating member. For this reason, some consideration has been given for reducing the number of rotations of the developing roller and agitating member of an image-forming device during operations. However, it was found that such alterations could lead to inaccurate determinations of the replacement timing for the cartridge, particularly when printing a small number of sheets in single image-forming operations.

The reason for this is as follows: the agitating member scatters developer throughout the cartridge by rotating in the cartridge. However, developer that has accumulated in the bottom of the cartridge cannot be sufficiently scattered during the initial stage of rotation, particularly as the quantity of developer in the cartridge decreases. Consequently, when the agitating member first begins rotating, the irradiated light easily passes through the cartridge, enabling the light-receiving element to receive a large quantity (high intensity) of light. Thus, when the image-forming device makes a determination regarding whether the cartridge needs to be replaced while the agitating member is still in its initial stage of rotation (e.g., when only a few sheets are being printed in a single image-forming operation), the image-forming device may determine inaccurately that the cartridge needs to be replaced when in fact there is sufficient developer remaining.

In view of the foregoing, it is an object of the present invention to provide an image-forming device capable of suppressing a decline in developer charging capacity while being capable of accurately determining when a cartridge needs to be replaced.

In order to attain the above and other objects, the invention provides an image forming device including a replaceable cartridge, a light-emitting element, a light-receiving element, and a determining unit. The replaceable cartridge accommodates developer therein and includes an agitator and a developing roller. The agitator is rotatable and configured to agitate developer accommodated in the replaceable cartridge. The developing roller is configured to carry the developer thereon and rotatable together with the agitator. The light-emitting element is configured to emit a light toward the replaceable cartridge. The light-receiving element is configured to receive the light emitted by the light-emitting element through the replaceable cartridge to output a signal. The determination value is produced based on the signal. The determining unit is configured to determine whether or not the determination value is greater than a predetermined determination threshold upon the agitator having rotated continuously more than a first prescribed number of times. The determining unit determines that the replaceable cartridge should be replaced with a new one when the determination value is greater than the predetermined determination threshold.

According to another aspect, the present invention provides an image forming device including a replaceable cartridge, a light-emitting element, a light-receiving element, and a determining unit. The replaceable cartridge accommodates developer therein and includes an agitator and a developing roller. The agitator is rotatable and configured to agitate developer accommodated in the replaceable cartridge. The developing roller is configured to carry the developer thereon and rotatable together with the agitator. The light-emitting element is configured to emit a light toward the replaceable cartridge. The light-receiving element is configured to receive the light emitted by the light-emitting element through the replaceable cartridge to output a signal. The determination value is produced based on the signal each time when the agitator rotates one time. The determining unit is configured to determine whether or not the determination value is greater than a first predetermined threshold when the agitator has made first one rotation and determine that the replaceable cartridge should be replaced with a new one when the determination value is greater than the first predetermined threshold. The determining unit is further configured to determine whether or not the determination value is greater than a second predetermined threshold when the agitator has rotated a prescribed number of times and determine that the replaceable cartridge should be replaced with a new one when the determination value is greater than the second predetermined threshold.

DETAILED DESCRIPTION

Next, a general structure of a laser printer1according to a first embodiment of the present invention will be described. Then, a detailed description will be given on the structure and operations of the laser printer1relating to features of the present invention. Directions given in the following description will be based on the reference of a user operating the laser printer1. Specifically, the right side of the laser printer1inFIG. 1will be considered the “front,” the left side the “rear,” the near side the “left side,” and the far side the “right side.” Further, the “top” and “bottom” of the laser printer1in the following description will be based on the vertical directions inFIG. 1.

As shown inFIG. 1, the laser printer1includes a main casing2and, within the main casing2, a feeding unit3for supplying sheets S of paper to be printed, an exposure unit4, a process cartridge5for transferring toner images onto the sheets S, and a fixing unit8for fixing the toner images on the sheets S with heat.

The feeding unit3is provided in the bottom of the main casing2and primarily includes a paper tray31accommodating the sheets S, and a paper-feeding mechanism32for feeding sheets S from the paper tray31to be printed. The paper-feeding mechanism32supplies the sheets S from the paper tray31toward the process cartridge5(between a photosensitive drum61and a transfer roller63) while separating the sheets S so that only one sheet is fed at a time.

The exposure unit4is disposed in the top section of the main casing2and includes a laser light-emitting unit (not shown), as well as a polygon mirror, lenses, reflecting mirrors, and other components for which reference numerals have not been assigned. The laser light-emitting unit in the exposure unit4emits a laser beam (indicated by a chain line inFIG. 1) based on image data, scanning the laser beam over the surface of the photosensitive drum61at a high speed to expose the same.

The process cartridge5is disposed below the exposure unit4. A cover21provided on the front side of the main casing2can be opened to reveal an opening2A through which the process cartridge5can be mounted in or removed from the main casing2(i.e., the process cartridge5is replaceable). The process cartridge5is configured of a drum unit6, and a developing cartridge7.

The developing cartridge7is detachably mounted on the drum unit6. While mounted on the drum unit6, the developing cartridge7can be detachably mounted in the main casing2. The developing cartridge7primarily includes a developing roller71, a supply roller72, a thickness-regulating blade73, a toner-accommodating section74for accommodating toner, and an agitator75.

In the developing cartridge7having this construction, first the agitator75agitates toner inside the toner-accommodating section74while conveying (supplying) toner toward the supply roller72. With both the developing roller71and supply roller72rotating, the supply roller72continues to supply the toner to the developing roller71. As the developing roller71continues to rotate, toner supplied to the surface thereof passes under the thickness-regulating blade73, and the thickness-regulating blade73regulates the toner carried on the developing roller71to a uniform thin layer.

The drum unit6primarily includes the photosensitive drum61, a charger62, and the transfer roller63. With this drum unit6, the charger62applies a uniform charge to the surface of the photosensitive drum61, and the charged surface is subsequently exposed by a laser beam emitted from the exposure unit4, forming an electrostatic latent image on the surface of the photosensitive drum61.

Next, toner carried on the surface of the developing roller71is supplied to the electrostatic latent image formed on the surface of the photosensitive drum61to produce a toner image thereon. The toner image formed on the surface of the photosensitive drum61is subsequently transferred to a sheet S as the sheet S is conveyed between the photosensitive drum61and transfer roller63.

The fixing unit8is disposed on the rear side of the process cartridge5. The fixing unit8primarily includes a heating roller81, and a pressure roller82disposed in confrontation with the heating roller81and applying pressure to the same. The fixing unit8having this construction fixes a toner image transferred onto the sheet S with heat as the sheet S passes between the heating roller81and pressure roller82. After the toner image is fixed to the sheet S, discharge rollers23discharge the sheet S into a discharge tray22.

Next, a detailed structure of the laser printer1and the operations (control process) performed on the laser printer1as they relate to features of the present invention will be described. First, the developing cartridge7and the structure on the main casing2side related to the present invention will be described, followed by a description of a control process performed in the laser printer1.

As shown inFIGS. 2A and 2B, the developing cartridge7includes a gear mechanism76in addition to the developing roller71, toner-accommodating section74, and agitator75. A pair of opposing transparent light-transmissive parts74A (see alsoFIG. 3) is provided one in each of left and right side walls (not assigned reference numerals) of the toner-accommodating section74so as to confront each other in the left-to-right direction.

The agitator75primarily includes a rotational shaft75A rotatably supported in the left and right side walls of the toner-accommodating section74, a flexible sheet member75B for agitating and conveying a toner T in the toner-accommodating section74when the agitator75rotates, and wipers75C for wiping off toner T that has become deposited on the light-transmissive parts74A while the agitator75rotates.

The gear mechanism76is disposed on the left side surface of the developing cartridge7and functions to transmit a drive force inputted from the laser printer1to the developing roller71, supply roller72, and agitator75. The gear mechanism76primarily includes an input gear76A in which the drive force is inputted; a developing roller gear76B and a supply roller gear76C that are both engaged with the input gear76A; and an agitator gear76E that is engaged with the input gear76A via an intermediate gear76D.

The developing roller gear76B, supply roller gear76C, and agitator gear76E are integrally provided on an end of the rotational shaft for the respective developing roller71, supply roller72, and agitator75and respectively drive the developing roller71, supply roller72, and agitator75to rotate. Thus, the gear mechanism76having this construction can rotate both the developing roller71and agitator75in the developing cartridge7from a drive force inputted into the input gear76A.

As shown inFIG. 3, the laser printer1also includes the following components all accommodated in the main casing2: a motor M serving as a drive source, a light-emitting element91, a light-receiving element92, and a control unit100that controls operations of the laser printer1.

A drive force produced by the motor M is inputted into the gear mechanism76of the developing cartridge7via a drive transmission mechanism (not shown) well known in the art and is transferred to the developing roller71and the agitator75.

The light-emitting element91and light-receiving element92are arranged facing each other on opposing sides of the pair of light-transmissive parts74A provided in the developing cartridge7when the developing cartridge7is mounted in the main casing2. A common photosensor known in the art may be employed as the light-emitting element91and light-receiving element92, for example. Light emitted from the light-emitting element91(indicated by a dashed line) enters the developing cartridge7(toner-accommodating section74) through one light-transmissive parts74A, passes through the toner-accommodating section74, and exits the other light-transmissive parts74A, where the light is received by the light-receiving element92.

The light-receiving element92outputs a light reception signal to the control unit100(a determining unit110described later) in response to received light, as shown in the graph ofFIG. 4. The light reception signal is an output voltage that varies based on the amount of received light (the intensity of received light). The light-receiving element92employed in the first embodiment outputs a smaller output voltage for weaker intensities of received light and a larger output voltage for stronger intensities of received light.

When a large amount of toner T is present in the developing cartridge7, light entering the developing cartridge7is shielded by the toner T, as indicated by the double chain line inFIG. 2A. In this case, the light-receiving element92receives very little light. Hence, a light reception signal, such as that shown inFIGS. 4A and 4B, is not received until the quantity of toner T in the developing cartridge7has dropped to some extent.

The control unit100is configured of a CPU, a RAM, a ROM, an input/output interface, and other components not shown in the drawings and functions to control the components of the laser printer1based on preconfigured programs and the like. As shown inFIG. 3, the control unit100primarily includes, as functional units related to the invention, a determining unit110, a drive control unit120, and a storage unit190.

The determining unit110is configured to determine the replacement timing based on the light reception signal continuously outputted from the light-receiving element92. In the first embodiment, the determining unit110executes the replacement timing determination only after the agitator75has rotated continuously more than a prescribed number of times (two times in the first embodiment). Hence, the determining unit110of the first embodiment executes the determination during the third or a later rotation after the agitator75begins rotating.

Here, the agitator75rotating continuously more than the prescribed number of times (two rotations in this example) indicates that an operation has been executed to rotate the agitator75continuously more than two rotations, and more specifically when the laser printer1receives an inputted print job having a large number of pages to be printed in a single image-forming operation (a print job for forming an image on two or more sheets S in one image-forming operation, in this example; hereinafter referred to as a “continuous print job”) and the laser printer1executes an image-forming operation based on this continuous print job; when the laser printer1executes an operation to continuously rotate the agitator75after a count C exceeds a prescribed threshold ThC, as will be described later (seeFIG. 4A).

The method implemented by the determining unit110for determining whether the developing cartridge7needs to be replaced will be described while referring toFIG. 4A. First, the determining unit110calculates the time during which the output voltage value from the light-receiving element92based on the amount of received light exceeds a preset light reception reference value V1during a third or later rotation of the agitator75after the agitator75begins rotating (the fourth rotation in the first embodiment). Next, the determining unit110calculates the ratio of the time during which this output value exceeds the light reception reference value V1to one period constituting the fourth rotation (hereinafter referred to as the “determination value R”). In other words, the determining unit100determines whether or not the determination value is greater than a predetermined determination threshold upon the agitator having rotated continuously more than a predetermined number of times (three in this embodiment). The predetermined number of rotations is no less than the prescribed number of rotations (two rotations in the first embodiment) sufficient to perform an image formation for a single-page print job described later.

The determination is executed in the third or later rotation (when the agitator75has rotated more than the prescribed number of times) for the following reason. The agitator75scatters toner T throughout the developing cartridge7by rotating therein. However, toner that has accumulated in the bottom of the developing cartridge7cannot be sufficiently scattered during the initial rotation of the agitator75(the first and second rotations inFIG. 4A), particularly as the quantity of toner T decreases, as indicated by the solid line inFIG. 2A. Consequently, when the agitator75first begins rotating, the irradiated light easily passes through the developing cartridge7, and the light-receiving element92outputs a large voltage.

However, since the toner T in the developing cartridge7generally is uniformly scattered in the developing cartridge7of the first embodiment by the third and later rotations of the agitator75after the agitator75begins rotating, output voltages (the light reception signal) from the light-receiving element92become a stable waveform. Hence, “two rotations” in the first embodiment corresponds to the number of times the agitator75must rotate before the output voltage from the light-receiving element92stabilizes.

Based on this information, when the determination is executed during the first or second rotations of the agitator75, there is a chance that the accuracy of the determination regarding whether the developing cartridge7needs replacing will be low (e.g., the determination unit110may determine that the developing cartridge7needs replacing when there is still sufficient toner T remaining). Therefore, the determination unit110in the first embodiment executes the determination for determining whether the developing cartridge7needs replacing during the third or a subsequent rotation of the agitator75while the output voltage from the light-receiving element92is stable.

Next, the laser printer1determines whether or not the determination value R exceeds a prescribed ratio (a determination threshold ThR) (R>ThR) and judges that the developing cartridge7needs to be replaced when the determination value R exceeds the determination threshold ThR. If the determination threshold ThR is set to 10% and the determination value R is 11%, for example, then the determination value R exceeds the determination threshold ThR and the laser printer1determines that it is time to replace the developing cartridge7currently mounted in the laser printer1.

After determining that the developing cartridge7needs to be replaced, the determining unit110notifies the user that it is time to replace the developing cartridge7by displaying a message on a display provided on the laser printer1, by playing a warning sound, and the like.

Here, the determining unit110does not make a determination on the replacement timing of the developing cartridge7if the agitator75is rotated only two times or less (the first or second rotations inFIG. 4) since a determination made during the first couple of rotations might be less accurate. Hence, when an operation to rotate the agitator75two or fewer times is repeatedly executed if the determining unit110does not possess the function described later, then there potentially arises a situation in which the replacement timing of the developing cartridge7is determined for an extended period of time.

In the first embodiment, the determining unit110counts an index value indicating the quantity of toner T used during consecutive operations for rotating the agitator75two or fewer times. When this count (index value) C exceeds a predetermined threshold ThC, i.e., when it is estimated that a fixed amount of toner T in the developing cartridge7has been used, the determining unit110is configured to determine that the developing cartridge7needs to be replaced.

More specifically, the determining unit110first counts the number of single-page print jobs, as an example of the index value, while consecutively receiving print jobs for which the agitator75need only be rotated twice to complete the image-forming operation (hereinafter referred to as “single-page print jobs”). Here, a “single-page print job” is defined as a print job for which the agitator75rotates two times during the image-forming operation since the number of pages being printed during one image forming operation is few (one page in this example). Here, the “single-page print job” denotes a print job for which the agitating member is rotated no more than the prescribed number of times because there are few pages to be printed in one image-forming operation. The “prescribed number of rotations” denotes the number of rotations of the agitating member and serves as a borderline between different determination results for cases in which the number of rotations of the agitating member does and does not exceed the prescribed number of rotations when determining whether a determination value exceeds a determination threshold based on the quantity of light received by the light-receiving element.

Hence, when the number of inputted single-page print jobs (the count C) exceeds the threshold ThC (10, for example), then the determining unit110rotates the agitator75more than two times continuously and determines the replacement timing of the developing cartridge7. That is, when the count C exceeds the threshold ThC (C>ThC), as shown inFIG. 4A, the determining unit110controls the drive control unit120to continuously rotate the agitator75two more times without stopping after completing an image-forming operation based on the last inputted single-page print job (after the agitator75has been rotated twice), calculates the determination value R in the fourth rotation from the beginning of rotation, and determines whether the calculated determination value R is greater than the determination threshold ThR (R>ThR?).

Further, the determining unit110resets the count C when the agitator75has rotated continuously more than two times, and more specifically at one of the following timings: prior to rotating the agitator75more than two times (when establishing that the agitator75will be rotated more than two times), while the agitator75is rotated more than two times, or after the agitator75has been rotated more than two times.

More specifically, the determining unit110resets the count C at any one of the following timings: when a continuous print job is inputted while counting the number of times single-page print jobs are inputted consecutively; during or after executing an image-forming operation based on a continuous print job; during or after rotating the agitator75more than two times continuously due to the count C exceeding the threshold ThC; and the like. The replacement timing for the developing cartridge7is determined in such cases in order to avoid such situations in which the replacement timing is not determined for an extended period of time.

Note that when the count C does not exceed the threshold ThC, as in the example ofFIG. 4B, the determining unit110halts rotation of the agitator75via the drive control unit120by completing the image-forming operation based on the current single-page print job. In this case, the agitator75is halted after two rotations from the beginning of rotation.

The drive control unit120has a function for controlling the drive of the agitator75(rotate/stop) and the number of rotations via the drive transmission mechanism (not shown) provided in the laser printer1, and the gear mechanism76, by controlling the drive of the motor M (switching the motor M on/off, controlling the speed of the motor M, and the like). When rotating the agitator75four times, for example, the drive control unit120drives (turns on) the motor M for exactly the time required to rotate the agitator75four times. To halt the agitator75, the drive control unit120halts (turns off) the motor M.

Next, steps in a control process performed in the laser printer1will be described with reference to the flowchart inFIG. 5. When a print job is inputted into the laser printer1(START), in S10ofFIG. 5the control unit100executes an image-forming operation based on the inputted print job and determines whether the inputted print job is a single-page print job.

If the inputted print job is a single-page print job (S10: YES), in S20the control unit100increments by “1” the count C, which indicates the number of consecutively inputted single-page print jobs, and in S30determines whether the count C exceeds the threshold ThC.

If the count C does not exceed the threshold ThC (S30: NO), the control unit100ends the process at the completion of the image-forming operation (END). However, if the count C exceeds the threshold ThC (S30: YES), in S40the control unit100resets the count C to “0” and in S50, after completion of the image-forming operation, continues to rotate the agitator75while calculating the determination value R, and determines whether the determination value R exceeds the determination threshold ThR, i.e., whether the developing cartridge7needs to be replaced.

On the other hand, if the control unit100determines in S10that the inputted print job is not a single-page print job (S10: NO), then in S40the control unit100resets the count C to “0” and in S50determines whether the developing cartridge7needs to be replaced while executing an image-forming operation based on the continuous print job.

If there is sufficient toner T remaining in the developing cartridge7(i.e., if the developing cartridge7does not need to be replaced), in S50the control unit100will determine that the determination value R does not exceed the determination threshold ThR (S50: NO). Accordingly, the control unit100ends the process (END). Note that the control unit100completes the image-forming operation before ending the process when executing an image-forming operation based on a continuous print job.

However, if very little toner T remains in the developing cartridge7(when it is time to replace the developing cartridge7), in S50the control unit100will determine that the determination value R exceeds the determination threshold ThR (S50: YES) and, hence, in S60notifies the user that the developing cartridge7needs to be replaced. Subsequently, the control unit100ends the process (END).

With the configuration described above, the laser printer1according to the first embodiment obtains the following operational advantages. That is, the determining unit110counts the number of times single-page print jobs have been inputted while receiving such single-page print jobs in succession, and determines that the developing cartridge7needs to be replaced when the count C exceeds the threshold ThC. Hence, the laser printer1according to the first embodiment can reduce the total number of rotations of the agitator75than a printer that determines the replacement timing of a cartridge by rotating the agitator75more than two times following every completion of an image-forming operation based on a single-page print job.

By reducing the total rotations of the agitator75, as well as the developing roller71that is configured to rotate together with the agitator75, the laser printer1according to the preferred embodiment can suppress a decline in the charging performance of the toner T, thereby increasing the life of the developing cartridge7. Since the preferred embodiment can also reduce the initial volume of the toner T accommodated in the developing cartridge7while maintaining a lifespan for the developing cartridge7generally equal to a conventional developer cartridge, the developing cartridge7and the laser printer1can be made more compact.

Further, the determining unit110determines the replacement timing of the developing cartridge7after the light reception signal from the light-receiving element92has stabilized, by first rotating the agitator75continuously more than the prescribed number of rotations in order that the toner T is sufficiently scattered within the developing cartridge7. Accordingly, the replacement timing can be more accurately determined than when the determination is made in the initial rotation of the agitator75(in the first or second rotation inFIG. 4B).

In the first embodiment, the determining unit110also resets the count C when the agitator75has been continuously rotated more than two times, thereby preventing unnecessary repetitions of the replacement timing determination. Thus, the laser printer1according to the first embodiment further reduces the total number of times that the agitator75and developing roller71are rotated, thereby further suppressing a decline in charging capacity of the toner T.

While the first embodiment described above uses the number of times single-page print jobs are inputted consecutively as the index for the quantity of toner T being used, the present invention is not limited to this index. For example, the index may be the number of dots (pixels) of the image transferred onto the sheet S when means are provided for counting the number of dots. Alternatively, the index may be the number of sheets S that are printed when means are provided for counting the number of sheets S.

Next, a second embodiment of the present invention will be described, wherein like parts and components are designated with the same reference numerals to avoid duplicating description.

InFIG. 6(andFIG. 7of the third embodiment) referred to in the following description, the arrows depicted in outline (i.e., unfilled arrows) indicate that the agitator75is rotating. If the text “Single-page print job” or “Continuous print job” is included in an arrow, this indicates that the agitator75is rotating to perform an image-forming operation. Arrows having no text indicate that the agitator75is being rotated to determine the replacement timing of the cartridge.

In the first embodiment described above, when the determining unit110determines that the count C exceeds the threshold ThC, the control unit100first completes the image-forming operation based on the last inputted single-page print job, then continues rotating the agitator75without pause to determine the replacement timing for the developing cartridge7. However, it may be difficult to implement a control process to continue rotating the agitator75seamlessly after an image-forming operation is completed due to improved speeds in image-forming operations and the like (i.e., there may be a delay before the control process can be implemented).

Therefore, when the determining unit110according to the second embodiment determines that the count C exceeds the threshold ThC, the determining unit110waits until the next print job has been inputted before rotating the agitator75continuously more than two times in order to determine the replacement timing for the developing cartridge7.

More specifically, as indicated in (a) and (b) ofFIG. 6, when the determining unit110determines that the count C exceeds the threshold ThC (C>ThC), the determining unit110temporarily halts rotations of the agitator75by completing the image-forming operation based on the current single-page print job (timing t1). When the next print job is inputted, the determining unit110determines the replacement timing for the developing cartridge7(R>ThR?).

Note that, if the next inputted job is a continuous print job as shown in (a) ofFIG. 6, the agitator75will be continuously rotated more than two times anyway. Therefore, the determining unit110determines the replacement timing for the developing cartridge7during the image-forming operation as usual. When the next inputted job is a single-page print job as shown in (b) ofFIG. 6, the determining unit110first completes the image-forming operation based on the single-page print job (timing t2), then without pausing continues rotating the agitator75for a total of four rotations while determining the replacement timing for the developing cartridge7(seeFIG. 4A).

Next, a third embodiment of the present invention will be described. When the determining unit110according to the third embodiment determines that the count C has exceeded the threshold ThC, the determining unit110first completes the image-forming operation based on the current single-page print job, then executes an operation to determine the replacement timing for the developing cartridge7by continuously rotating the agitator75a prescribed number of times (four times in this example).

More specifically, as shown inFIG. 7, when the determining unit110determines that the count C exceeds the threshold ThC (C>ThC), the determining unit110temporarily halts the rotation of the agitator75by completing the image-forming operation based on the current single-page print job. Next, with the agitator75beginning from an idle state, the determining unit110rotates the agitator75continuously four times, for example, and executes an operation to determine the replacement timing for the developing cartridge7(R>ThR?) in the fourth rotation. In other words, if the index value count C exceeds the threshold ThC, the determining unit110and the drive control unit120controls the agitator to halt rotating when the image formation for a last print job is completed and further controls the agitator to begin to rotate when a predetermined duration of time is elapsed since the agitator halts rotating.

The present invention according to the second and third embodiments described above can be applied to a laser printer for accurately determining the replacement timing for the developing cartridge7while suppressing a decline in the charging performance of the toner, even in a laser printer performing faster image-forming operations, for example. Put a different way, employing the configurations of the second and third embodiments can improve the speed of image-forming operations.

Next, a fourth embodiment of the present invention will be described. In the first through third embodiments described above, the determining unit110determines the replacement timing for the developing cartridge7when a prescribed number of single-page print jobs has been inputted consecutively (when the count C reaches a value exceeding the threshold ThC). This process is similar to determining the replacement timing at specific intervals (albeit irregular intervals). In the fourth embodiment, the determining unit110is configured to determine the replacement timing for the developing cartridge7at regular intervals.

In other words, at prescribed intervals, the determining unit110according to the fourth embodiment rotates the agitator75continuously a prescribed number of times (four times, for example) while determining the replacement timing for the developing cartridge7. The prescribed interval in the fourth embodiment is a longer duration than the duration required to rotate the agitator75two times.

Specifically, the determining unit110begins counting a time t (START) in the process shown in the flowchart ofFIG. 8at one of the following timings: (1) when the power to the laser printer1is turned on, (2) when the cover21is closed, (3) when an image-forming operation based on the last print job is completed, (4) when the last determination for the replacement timing was made, or the like. In S11the determining unit110determines whether a prescribed time Tht (six hours, for example) greater than the time required to rotate the agitator75two times has elapsed (t>Tht?).

If the prescribed time Tht has elapsed (S11: YES), in S12the determining unit110resets the time t and in S50the determining unit110rotates the agitator75from its halted state four times continuously and determines the replacement timing for the developing cartridge7(R>ThR?).

If the determining unit110determines that it is not time to replace the developing cartridge7(S50: NO), the determining unit110ends the current process (END) and resumes counting the time t (returns to START). However, if the determining unit110determines that it is time to replace the developing cartridge7(S50: YES), in S60the determining unit110notifies the user that the developing cartridge7must be replaced and ends the current process (END).

According to the fourth embodiment described above, the determining unit110determines the replacement timing for the developing cartridge7at intervals of the prescribed time Tht greater than the time required to rotate the agitator75two times. Accordingly, the total rotations of the agitator75and developing roller71is less than the total rotations when the determining unit110determines the replacement timing by rotating the agitator75more than two times after each completion of an image-forming operation based on a single-page print job, thereby suppressing a decline in the charging performance of the toner T. Further, by determining the replacement timing after first rotating the agitator75more than two times continuously, the determining unit110can accurately determine the replacement timing.

Next, a fifth embodiment of the present invention will be described. In the fifth embodiment, the determination unit110includes a function for determining the replacement timing for the developing cartridge7(main determination), and a function for determining whether to execute the main determination (provisional determination). When the determination unit110determines in the main determination that the developing cartridge7needs to be replaced, the determination unit110notifies the user to replace the developing cartridge7by displaying a message on a display provided on the laser printer1, by playing a warning sound, and the like.

The main determination and provisional determination will be described. The main determination according to the fifth embodiment is executed in the third or later rotation after the agitator75begins rotating, when the agitator75has continuously rotated more than a prescribed number of times, and more specifically when the laser printer1receives the continuous print job and executes an image-forming operation based on this continuous print job; and when the laser printer1executes an operation to continuously rotate the agitator75after a determination value R exceeds a provisional prescribed threshold Th1, as will be described later (seeFIG. 9B).

In the main determination, the determining unit110calculates the determination value R during the third or later rotation of the agitator75after the agitator75begins rotating (the fourth rotation in the fifth embodiment). Then, the determining unit110determines whether the determination value R exceeds a main prescribed ratio (a main determination threshold Th1) (R>Th1) and judges that the developing cartridge7needs to be replaced when the determination value R exceeds the main determination threshold Th1.

Further, the determination unit110executes the provisional determination before the agitator75has completed rotating the prescribed number of times upon receiving an inputted the single-page print job. Hence, when a single-page print job is inputted into the laser printer1, the determination unit110in the fifth embodiment executes the provisional determination during this image-forming operation (i.e., while the agitator75is rotating only twice).

The provisional determination is performed similarly to the main determination. As shown inFIGS. 9A and 9B, the determination unit110first calculates the determination value R during the first rotation (or second rotation) of the agitator75. Next, the determination unit110determines whether the determination value R exceeds a prescribed ratio (a provisional determination threshold Th1) larger than the main determination threshold Th2described above. If the provisional determination threshold Th1is set to 20% and the determination value R is 19%, for example, then the determination unit110determines that the determination value R does not exceed the provisional determination threshold Th1. However, if the determination value R is 21%, the determination unit110determines that the determination value R exceeds the provisional determination threshold Th1.

When the determination value R does not exceed the provisional determination threshold Th1(R≦Th1), as in the example ofFIG. 9A, the determination unit110halts rotation of the agitator75via the drive control unit120by completing the image-forming operation based on the current single-page print job (an operation to form images on one sheet S). In this case, the agitator75is halted after two rotations from the beginning of rotation.

However, if the determination value R exceeds the provisional determination threshold Th1(R>Th1), as in the example ofFIG. 9B, the determination unit110stores a flag indicating this information (provisional determination flag) in the storage unit190(e.g., sets F to “1”) and controls the drive control unit120to continuously rotate the agitator75more than two times while executing the main determination.

That is, when determining that the determination value R calculated in the first rotation of the agitator75exceeds the provisional determination threshold Th1, the determination unit110continues to rotate the agitator75two more times without stopping after completing an image-forming operation based on a single-page print job (after the agitator75has been rotated twice), calculates a new determination value R in the fourth rotation since the rotation was initiated, and determines whether the new determination value R is greater than the determination threshold Th2.

Therefore, the determination unit110performs the main determination to determine the replacement timing for the developing cartridge7after finding that the determination value R exceeds the provisional determination threshold Th1. When determining that the developing cartridge7needs to be replaced, the determination unit110notifies the user that it is time to replace the developing cartridge7.

If the determination unit110determines in the main determination that the developing cartridge7does not yet need to be replaced, thereafter the determination unit110executes the main determination at prescribed intervals (i.e., determines whether the determination value R exceeds the determination threshold Th2).

Specifically, after the determination unit110determines that the determination value R exceeds the provisional determination threshold Th1and sets the provisional determination flag (i.e., when F=1), the determination unit110counts the index value indicating the quantity of toner T used when single-page print jobs are inputted consecutively. When this count C exceeds a prescribed value ThC (10, for example), then the determination unit110rotates the agitator75more than two times continuously and executes the main determination, just as when the determination unit110determines whether the determination value R exceeds the provisional determination threshold Th1in the provisional determination (seeFIG. 9B).

After determining in the main determination that the developing cartridge7needs to be replaced, the determination unit110notifies the user that it is time to replace the developing cartridge7. However, when the determination unit110determines that the developing cartridge7does not yet need to be replaced, the determination unit110resumes counting the number of consecutively inputted single-page print jobs.

It should also be noted that the determination unit110resets the count when the agitator75has rotated continuously more than two times and, more specifically, at one of the following timings: when a continuous print job is inputted while counting the number of times single-page print jobs are inputted consecutively and an image-forming operation is executed based on this continuous print job; when rotating the agitator75more than two times continuously due to the count C exceeding the prescribed value ThC; and the like. The count is reset in such cases because the main determination is executed. The determination unit110also resets the provisional determination flag (i.e., resets F to “0”) when the developing cartridge7is replaced with a new product.

Next, steps in a control process performed on the laser printer1according to fifth embodiment will be described with reference to the flowchart inFIG. 10. When a print job is inputted into the laser printer1(START), in S1ofFIG. 10the control unit100executes an image-forming operation based on the inputted print job and determines whether the inputted print job is a single-page print job.

If the inputted print job is not a single-page print job (i.e., a continuous print job; S1: NO), in S2the control unit100executes the main determination during the image-forming operation (during the fourth rotation of the agitator75in the fifth embodiment). However, if the inputted print job is a single-page print job (S1: YES), then in S3the control unit100determines whether the provisional determination flag has been set (if F=1).

If there is a large amount of toner T in the developing cartridge7, in the main determination of S2the determination unit110will determine that the determination value R does not exceed the main determination threshold Th2(S2: NO). Accordingly, the control unit100ends the process (END) when the image-forming operation is completed.

Further, when the developing cartridge7holds a large amount of toner T and the provisional determination flag has not been set (when F=0; S3: NO), in S4the control unit100executes the provisional determination during the image-forming operation (during the first rotation of the agitator75). If there is sufficient toner T in the developing cartridge7, then the determination unit110will determine in this provisional determination that the determination value R does not exceed the provisional determination threshold Th1(S4: NO). Accordingly, in S5the control unit100halts the rotation of the agitator75at the completion of the image-forming operation and ends the process (END).

When the quantity of toner T in the developing cartridge7decreases to a certain extent, in the provisional determination of S4the determination unit110will determine that the determination value R exceeds the provisional determination threshold Th1(S4: YES). In this case, in S6the control unit100sets the provisional determination flag (sets F to “1”) and in S2, after completion of the image-forming operation, continues to rotate the agitator75while executing the main determination. If the control unit100determines that the determination value R does not exceed the determination threshold Th2(S2: NO), the control unit100halts the rotation of the agitator75and ends the process (END).

When a print job is inputted (START) after the determination unit110has determined in the provisional determination that the determination value R exceeds the provisional determination threshold Th1(when the provisional determination flag has been set), in S1the control unit100executes an image-forming operation based on the inputted print job and determines whether the inputted print job is a single-page print job.

If the inputted print job is a single-page print job (S1: YES), in S3the control unit100determines whether the provisional determination flag has been set (i.e., if F=1). Since the provisional determination flag has been set in this example (S3: YES), in S7the control unit100increments the count C, which indicates the number of consecutively inputted single-page print jobs, and in S8determines whether the count C exceeds the threshold ThC (10, for example).

If the count C does not exceed the threshold ThC (S8: NO), the control unit100ends the process at the completion of the image-forming operation (END). However, if the count C exceeds the threshold ThC (S8: YES), in S9the control unit100resets the count C to “0” and in S2, after completion of the image-forming operation, continues to rotate the agitator75while executing the main determination. Upon determining in the main determination that the determination value R does not exceed the determination threshold Th2(S2: NO), the control unit100halts the rotation of the agitator75and ends the process (END).

On the other hand, if the determination unit110determines in S1that the inputted print job is a continuous print job (S1: NO), then in S9the control unit100resets the count C to “0” and in S2executes the main determination during the image-forming operation.

If there is very little toner T remaining in the developing cartridge7(when it is time to replace the developing cartridge7), in S2the control unit100will determine that the determination value R exceeds the main determination threshold Th2(S2: YES). Accordingly, in S10the control unit100notifies the user that the developing cartridge7needs to be replaced and subsequently ends the process (END).

With the configuration described above, the laser printer1according to the fifth embodiment obtains the following operational advantages. That is, the determination unit110executes the provisional determination first when a single-page print job is received and halts the rotation of the agitator75after completion of the image-forming operation when determining in the provisional determination that the determination value R does not exceed the provisional determination threshold Th1. Hence, the laser printer1according to the fifth embodiment can reduce the number of times the agitator75is rotated more than a printer that determines the replacement timing for a cartridge by rotating the agitator75more than two times following every completion of an image-forming operation based on a single-page print job, for example.

By reducing the total rotations of the agitator75, as well as the developing roller71that is configured to rotate together with the agitator75, the laser printer1according to the preferred embodiment can suppress a decline in the charging performance of the toner T, thereby increasing the life of the developing cartridge7. Since the fifth embodiment can also reduce the initial volume of the toner T accommodated in the developing cartridge7while maintaining a lifespan for the developing cartridge7generally equal to a conventional developer cartridge, the developing cartridge7and the laser printer1can be made more compact.

Further, when the determination value R exceeds the provisional predetermined threshold value Th1, the determining unit110executes the main determination by first rotating the agitator75continuously more than the prescribed number of rotations. Accordingly, the replacement timing can be more accurately determined than when the determination is made in the initial rotation of the agitator75(in the first or second rotation).

After determining that the determination value R exceeds the provisional determination threshold Th1in the fifth embodiment, the determination unit110stores this information (sets a provisional determination flag) and executes the main determination at prescribed intervals thereafter (when the number of consecutively inputted single-page print jobs exceeds a prescribed number). Therefore, the laser printer1according to the fifth embodiment can further decrease the total number of rotations of the agitator75and developing roller71more than a printer that executes the main determination after completing each image-forming operation based on a single-page print job when the determination value R was found to exceed the provisional determination threshold Th1.

The prescribed number of rotations in the fifth embodiment is set to the number of times the agitator75must rotate until the light reception signal from the light-receiving element has stabilized. Accordingly, by executing the main determination after first rotating the agitator75continuously more than the prescribed number of rotations, the replacement timing for the developing cartridge7can be accurately determined.

Once the determination unit110has determined in the provisional determination that the determination value R exceeds the provisional determination threshold Th1in the fifth embodiment, the determination unit110executes the main determination at prescribed intervals (each time the count C exceeds the threshold value ThC) thereafter, but the present invention is not limited to this configuration. For example, the determination unit110may execute the provisional determination each time a single-page print job is received, after the determination value R was found to exceed the provisional determination threshold Th1one time, and may be configured to execute the main determination only after several instances in which the determination value R was found to exceed the provisional determination threshold Th1have accumulated, either in total or in succession.

Further, the prescribed interval at which the main determination is executed in the fifth embodiment after the determination value R is found to exceed the provisional determination threshold Th1is set to the timing at which the number of continuously inputted single-page print jobs exceeds a prescribed number, but the present invention is not limited to this interval. For example, the prescribed interval may be determined as the timing at which the number of dots in an image formed on sheets S after the determination value R was found to exceed the provisional determination threshold Th1reaches a prescribed number, when means are provided for counting the number of dots. Alternatively, the prescribed interval may be set to the timing at which the number of sheets S that are printed after the determination value R is found to exceed the provisional determination threshold Th1reaches a prescribed number, when means are provided for counting the number of sheets S. The prescribed interval may also be set to a prescribed elapsed time after the determination value R was found to exceed the provisional determination threshold Th1.

In the fifth embodiment, the determination unit110resets the count C if a continuous print job is inputted while counting the number of continuously inputted single-page print jobs, but the determination unit110may be configured not to reset the count C in this case.

Next, a sixth embodiment of the present invention will be described. In the fifth embodiment described above, when the determining unit110determines that the determination value R exceeds the provisional determination threshold Th1, the control unit100first completes the image-forming operation based on the last inputted single-page print job, then continues rotating the agitator75without pause to execute the main determination. However, it may be difficult to implement a control process to continue rotating the agitator75seamlessly after an image-forming operation is completed due to improved speeds in image-forming operations and the like (i.e., there may be a delay before the control process can be implemented).

Therefore, when the determining unit110according to the sixth embodiment determines that the determination value R exceeds the provisional determination threshold Th1, the determining unit110waits until the next print job has been inputted before rotating the agitator75continuously more than two times in order to execute the main determination.

More specifically, as indicated in (a) and (b) ofFIG. 11, when the determining unit110determines that the determination value R exceeds the provisional determination threshold Th1(R>Th1?), the determining unit110temporarily halts rotations of the agitator75by completing the image-forming operation based on the current single-page print job (timing t1). When the next print job is inputted, the determining unit110executes the main determination (R>Th2?).

Note that, if the next inputted print job is a continuous print job as shown in (a) ofFIG. 11, the agitator75will be continuously rotated more than two times anyway. Therefore, the determining unit110executes the main determination during the image-forming operation as usual. When the next inputted job is a single-page print job as shown in (b) ofFIG. 11, the determining unit110first completes the image-forming operation based on the single-page print job (timing t2), then without pausing continues rotating the agitator75for a total of four rotations while making the main determination (seeFIG. 9B).

In the sixth embodiment described above, the determination unit110executes the main determination after determining that the determination value R is greater than the provisional determination threshold Th1when the next print job is inputted, but the present invention is not limited to this configuration. For example, the determination unit110may execute the main determination only after several print jobs (five print jobs, for example) are inputted following the determination that the determination value R exceeds the provisional determination threshold Th1.

Next, a seventh embodiment of the present invention will be described. When the determining unit110according to the seventh embodiment determines that the determination value R has exceeded the provisional determination threshold Th1in the provisional determination, the determining unit110first completes the image-forming operation based on the current single-page print job, then executes the main determination by continuously rotating the agitator75a prescribed number of times (four times in this example).

More specifically, as shown inFIG. 12, when the determining unit110determines that the determination value R exceeds the provisional determination threshold Th1(R>Th1), the determining unit110temporarily halts the rotation of the agitator75by completing the image-forming operation based on the current single-page print job. Next, with the agitator75beginning from an idle state, the determining unit110rotates the agitator75continuously four times, for example, and executes an operation to make the main determination (R>Th2?) in the fourth rotation.

Note that the determination unit110in the seventh embodiment may execute the determination at prescribed intervals (each time a prescribed number of print jobs are inputted, for example) after determining that the determination value R has exceeded the provisional determination threshold Th1. This configuration further reduces the total number of times the agitator75and developing roller71are rotated.

The present invention according to the sixth and seventh embodiments described above can be applied to a laser printer for accurately determining the replacement timing for the developing cartridge7while suppressing a decline in the charging performance of the toner, even in a laser printer performing faster image-forming operations, for example. Put a different way, employing the configurations of the sixth and seventh embodiments can improve the speed of image-forming operations.

Next, an eighth embodiment of the present invention will be described. The determination unit110according to the eighth embodiment has a function for determining the replacement timing for the developing cartridge7based on the light reception signal outputted from the light-receiving element92. Specifically, at the beginning of an image-forming operation or the like when the agitator75begins rotating, the determination unit110first calculates the time during which the output voltage value from the light-receiving element92based on the amount of received light exceeds a preset light reception reference value V1for each rotation (period) of the agitator75, as shown in the graph ofFIG. 13A.

Next, the determination unit110calculates the ratio of the time during which this output value exceeds the preset light reception reference value V1to one period (the time for rotating the agitator75one complete rotation) for each rotation (hereinafter referred to as the “determination value”). Next, the determination unit110determines whether the calculated determination value exceeds a prescribed ratio (hereinafter referred to as the determination threshold and judges that the developing cartridge7needs to be replaced when the determination value exceeds the determination threshold.

For example, if the determination threshold for the third rotation of the agitator75is set to 10% and the determination value is 11%, then the determination value exceeds the determination threshold, and the determination unit110judges that it is time to replace the developing cartridge7currently mounted in the laser printer1.

As described above, the agitator75scatters toner T throughout the developing cartridge7by rotating therein. However, toner that has accumulated in the bottom of the developing cartridge7cannot be sufficiently scattered during the initial rotation of the agitator75(the first and second rotations inFIG. 13A), particularly as the quantity of toner T decreases, as indicated by the solid line inFIG. 2A. Consequently, when the agitator75first begins rotating, the irradiated light easily passes through the developing cartridge7, and the light-receiving element92outputs a large voltage.

Hence, if the same determination threshold (10%, for example) were applied to the determination value calculated for each of the first rotation and third rotation, for example, the results for determining the replacement timing for the developing cartridge7may be different (may be the opposite).

Therefore, in the eighth embodiment the determination unit110uses a different determination threshold according to the rotation number of the agitator75, from the first rotation through the third rotation. That is, the determination threshold is set to a large value (50%) for the first rotation in which the output values are larger; a smaller value (20%), smaller than that for the first rotation, for the second rotation in which the output values will be smaller than those in the first rotation; and an even smaller value (10%), smaller than that for the second rotation, for the third rotation in which the output values will be smaller than those in the second rotation.

As shown inFIG. 13A, the voltage outputted from the light-receiving element92(the waveform of the light reception signal) stabilizes beginning from the third rotation. Accordingly, in the eighth embodiment the same determination threshold (10%) is set for the third and subsequent rotations, as shown inFIG. 13B.

Therefore, the laser printer1having the above configuration can accurately determine the replacement timing for the developing cartridge7, regardless of the rotation number of the agitator75.

For example, the determination unit110performing a determination during the third or later rotation of the agitator75may determine that the developing cartridge7does not need to be replaced (that the developing cartridge7holds sufficient toner T) when applying a determination threshold of 10%. However, the determination unit110may calculate a determination value of 40% for the same developing cartridge7when performing the determination in the first rotation of the agitator75. If the determination unit110applies the same determination threshold used for the third and subsequent rotations (10%) in this case, then the determination unit110will mistakenly determine that the developing cartridge7needs to be replaced. However, the determination unit110of the eighth embodiment applies a determination threshold of 50% (greater than the determination threshold used in the second and subsequent rotations) when performing the determination in the first rotation having larger output values and, hence, in the above example would not determine that the developing cartridge7needs to be replaced. Accordingly, the control unit100according to the eighth embodiment can accurately determine the replacement timing for the developing cartridge7.

As another example, if the determination unit110calculates the determination value for the third rotation to be 15%, but applies the determination threshold of 20% used in the eighth embodiment for the second rotation, then the determination unit110will determine that the developing cartridge7does not need to be replaced, even though the determination unit110would determine that the developing cartridge7needs to be replaced (has insufficient toner T remaining) if the determination were performed in the first or second rotations. However, the determination unit110in the preferred embodiment applies a determination threshold of 10%, which is smaller than the determination threshold used in the first and second rotations, for a determination performed in the third rotation (and subsequent rotations) in which output values are smaller and, hence, would determine correctly in the above example that the developing cartridge7needs to be replaced. Accordingly, the laser printer1according to the eighth embodiment can more accurately determine the replacement timing for the developing cartridge7.

By reducing the total rotations of the agitator75, as well as the developing roller71that is configured to rotate together with the agitator75, the laser printer1according to the eighth embodiment can suppress a decline in the charging performance of the toner T.

In the eighth embodiment described above, the determination unit110can execute the replacement timing determination without rotating the agitator75the number of times (more than two times) required to scatter the toner T uniformly throughout the developing cartridge7, even when print jobs with few pages are inputted into the laser printer1. Accordingly, the laser printer1according to the eighth embodiment can reduce the total rotations of the agitator75and developing roller71, thereby suppressing a decline in the charging performance of the toner T.

Suppressing a decline in charging performance of the toner T can increase the life of the developing cartridge7. It is also possible to reduce the initial volume of the toner T accommodated in the developing cartridge7while maintaining a lifespan for the developing cartridge7generally equivalent to a conventional developer cartridge, thereby making the developing cartridge7and the laser printer1more compact.

The prescribed number of rotations (three rotations in the eighth embodiment) indicates the number of times the agitator75must rotate before the waveform of the light reception signal stabilizes. Therefore, the same determination threshold can be used for the third and subsequent rotations, reducing the number of determination thresholds that must be preset (the volume of data that must be stored).

In the eighth embodiment, the determination value is a ratio of the time during which the output value from the light-receiving element92exceeds the light reception reference value V1(seeFIG. 13A), but the present invention is not limited to this definition. A ninth embodiment provides another example of the determination value (and determination threshold).

The determination unit110according to the ninth embodiment is configured to determine that the developing cartridge7needs to be replaced when the output value from the light-receiving element92exceeds light reception reference values V1-V3as shown inFIG. 14. In other words, in the preferred embodiment the determination value is the output value from the light-receiving element92, while the light reception reference values V1-V3correspond to the determination threshold.

In the ninth embodiment, the light reception reference value (determination threshold) takes on different values according to the rotation number of the agitator75, from the first rotation through the third rotation (and subsequent rotations). That is, the light reception reference value is set to a large value V3for the first rotation during which the output values are larger; a value V2, smaller than the value V3, for the second rotation during which the output values are smaller than during the first rotation; and a value V1, smaller than the value V2, for the third rotation during which the output values are smaller than during the second rotation (V3>V2>V1).

According to the ninth embodiment described above, the determination unit110can determine the replacement timing for the developing cartridge7with relative accuracy, irrespective of the rotation number of the agitator75and can reduce the total rotations of the agitator75and developing roller71, thereby suppressing a decline in the charging performance of the toner T.

Next, a tenth embodiment of the present invention will be described. The determination unit110according to the ninth embodiment is configured to determine that it is time to replace the developing cartridge7when the output value of the light-receiving element92exceeds the light reception reference values V1-V3. In the tenth embodiment, the determination unit110is configured to determine the replacement timing according to the same method described in the eighth embodiment, while setting the light reception reference value (a “light reception threshold” in the tenth embodiment) to different values, as in the ninth embodiment described above.

As described in the eighth embodiment, when the output value of the light-receiving element92exceeds the light reception thresholds V1-V3as shown inFIG. 13, the determination unit110according to the tenth embodiment calculates the time during which the output values exceed the light reception thresholds V1-V3.

Next, the determination unit110calculates the ratio of the time during which the output values exceed the light reception thresholds V1-V3to the period of the agitator75corresponding to the current rotation. For the first rotation, for example, the determination unit110calculates the ratio of time during which the output values exceed the first threshold V3to the current period. For the fourth rotation, the determination unit110calculates the ratio of time during which output values exceed the light reception threshold V1to the current period.

Next, the determination unit110determines whether the calculated ratio exceeds a prescribed ratio that has been preset (hereinafter referred to as the “threshold ratio”; a single value used commonly for each rotation in the tenth embodiment) and determines that the developing cartridge7should be replaced when the calculated ratio exceeds the threshold ratio. If the threshold ratio is set to 10% irrespective of the rotation number of the agitator75and the calculated ratio is 11%, for example, then the calculated ratio exceeds the threshold ratio, and the determination unit110determines that the developing cartridge7should be replaced.

The determination unit110according to the tenth embodiment described above can determine the replacement timing for the developing cartridge7with greater accuracy than the determination unit110described in the ninth embodiment. Further, as in the eighth and seventh embodiments, the tenth embodiment reduces the total rotations of the agitator75and developing roller71, thereby suppressing a decline in the charging performance of the toner T.

In the tenth embodiment, only the light reception threshold is set to varying values depending on the rotation number of the agitator75, from the first rotation through the third rotation (and subsequent rotations), but the present invention is not limited to these values. In other words, both the light reception thresholds and threshold ratios may be set to varying values based on the rotation number of the agitator75, from the first rotation through a prescribed rotation. Incidentally, setting only the second threshold to varying values according to the rotation number of the agitator75is identical to the eighth embodiment described above.

Specific values given for the prescribed number of rotations of the agitator75, the threshold value for the number of consecutively inputted print jobs, and the like in the first through tenth embodiments are merely examples, and the present invention is not limited to the examples given in the embodiments. For example, the prescribed number of rotations of the agitator75is set to the number of times the agitator75must rotate before the output value of the light-receiving element is stabilized, and varies according to the capacity of the cartridge (quantity of developer that the cartridge can accommodate), the rotational speed of the agitator75, and the like.

In the first through tenth embodiments, the determining unit110calculates the determination value during the fourth rotation of the agitator75after the agitator75begins rotating and determines that the developing cartridge7needs to be replaced when the determination value exceeds the determination threshold, but the present invention is not limited to this method of determination. For example, the determining unit110may calculate the determination value during the third rotation of the agitator75, or during the third rotation and during each subsequent rotation. Further, the determination value may be calculated as the ratio of time during which the output value from the light-receiving element exceeds the light reception reference value V1(seeFIG. 4A) to a fixed time that includes a plurality of rotating periods. The determining unit110may also determine that the developing cartridge7needs to be replaced when the output value of the light-receiving element exceeds the light reception reference value V1(in this case, the light reception reference value V1corresponds to the determination threshold).

The agitator75described in the first through tenth embodiments is merely one example of an agitating member. The agitating member of the present invention may include a plurality of flexible sheet members disposed at intervals in the rotating direction, for example, or may be provided with a light-shielding member disclosed in U.S. Pat. No. 6,337,956.

In the first through tenth embodiments, the light-receiving element92outputs a smaller voltage for weaker intensities of received light and a larger voltage for stronger intensities of received light. However, the laser printer may employ a light-receiving element that outputs a larger voltage for weaker intensities of received light and a smaller voltage for stronger intensities of received light, for example.

The developing cartridge7according to the first through tenth embodiments has a replaceable configuration that allows it to be mounted in or removed from the main casing2while attached to the drum unit6. However, the cartridge may be configured to be directly mounted in or removed from the main casing instead, for example.

While the developing cartridge7is used as an example of the cartridge according to the present invention in the first through tenth embodiments, the present invention is not limited to this cartridge type. For example, the cartridge of the present invention may be a process cartridge integrally (non-detachably) configured of the drum unit6and developing cartridge7of the preferred embodiments.

The laser printer1is given as an example of the image-forming device according to the present invention in the first through tenth embodiments. However, the image-forming device of the present invention may be an LED printer or the like that exposes a photosensitive member with an array of LEDs, for example. Further, the image-forming device is not limited to a printer, but may be a photocopier, multifunction peripheral, or the like provided with an original document reading device, such as a flatbed scanner.

In the fifth through seventh embodiments described above, the determination unit110is configured to execute the main determination (i.e., to determine whether the determination value R exceeds the determination threshold Th2based on the quantity of light received by the light-receiving element92) after first rotating the agitator75continuously more than the prescribed number of times (two times in the preferred embodiments), but the present invention is not limited to this configuration. For example, the determination unit110may be configured to execute both the provisional determination and the main determination while the agitator75has not yet rotated the prescribed number of times (the first through second rotations in the fifth through seventh embodiments). Put another way, the determination unit110may be configured to execute the main determination irrespective of the number of rotations of the agitator75. With this configuration, the determination unit110of the present invention executes the control process described above based on the results of the provisional determination, without notifying the user of the results of the main determination obtained before the agitator75has rotated the prescribed number of times.

In the eight through tenth embodiments described above, the same determination threshold is set for third and subsequent rotations, but the present invention is not limited to this configuration. The determination threshold may be set to varying values based on the rotation number for the prescribed rotation and subsequent rotations, for example. This configuration can further enhance the accuracy for determining the replacement timing for the developing cartridge7executed during each rotation.

In the eight through tenth embodiments described above, the determination threshold is set to different values for each of the first through third rotations of the agitator75, but the present invention is not limited to this configuration. For example, the determination threshold may be set to a first determination threshold for the first rotation, a second determination threshold for the second and third rotations, and a third determination threshold for the fourth rotation, where the first through third determination thresholds are all different values. More specifically, the determination threshold of the present invention should at least include a value set for the first rotation of the agitator75and a different value set for the prescribed rotation of the agitator75.