JP7599271B2 - Image forming device - Google Patents

Description

This disclosure relates to an image forming device that can accommodate a drum cartridge and a toner cartridge.

Conventionally, there is known an image forming device that can accommodate a drum cartridge and a toner cartridge (see Patent Document 1). In this image forming device, the toner cartridge is assembled to the drum cartridge, and then the device is mounted in the device body.

JP 2009-265401 A

Generally, the lifespan of a drum cartridge is longer than that of a toner cartridge. For this reason, multiple toner cartridges may be used in conjunction with one drum cartridge. However, deterioration of the drum cartridge can change the characteristics of the photosensitive drum, which can result in a difference in print density between printing with the first toner cartridge and printing with the second or subsequent toner cartridges.

Therefore, the purpose of this disclosure is to stabilize the print density of an image forming device.

In order to solve the above-mentioned problems, the image forming apparatus includes a device main body, a drum cartridge, a toner cartridge, and a control device. The drum cartridge has a photosensitive drum, a transfer roller facing the photosensitive drum or a cleaning roller facing the photosensitive drum, and a drum memory that stores the cumulative number of drum rotations of the photosensitive drum, and is detachable from the device main body. The toner cartridge has a housing that can contain toner, a developing roller, and a toner memory that stores the cumulative dot count.
The control device is capable of executing a process of determining, based on the cumulative drum rotation count, an initial transfer current _I1 to be transferred to the transfer roller when an image is formed with the first toner cartridge, or an initial cleaning bias _VC1 to be applied to the cleaning member when an image is formed with the first toner cartridge, when a second toner cartridge different from the first toner cartridge is used for the drum cartridge to form an image, after the initial transfer current _I1 or the initial cleaning bias _VC1 has been determined, a process of determining, based on the cumulative drum rotation count, an initial transfer current I2 different from the initial transfer current _I1 , or an initial cleaning bias _VC2 different from the initial cleaning bias _VC1 , when an image is formed with the drum _cartridge using a second toner cartridge different from the first toner cartridge.

This configuration allows the print density of the image forming device to be stable even when multiple toner cartridges are replaced with one drum cartridge.

In the above-mentioned configuration, the control device may be configured to change the transfer current applied to the transfer roller or the cleaning bias applied to the cleaning roller in response to an increase in the cumulative number of drum rotations and the cumulative dot count.

This allows the transfer current to be changed according to both the deterioration of the photosensitive drum and the deterioration of the toner, making it possible to keep the amount of toner transferred constant.

In the above configuration, the control device may be configured to increase the absolute value of the transfer current or cleaning bias as the cumulative dot count increases.

In the above configuration, the control device may be configured to increase the transfer current or the absolute value of the cleaning bias as the cumulative number of drum rotations increases.

In the above-mentioned configuration, I ₂ >I ₁ or |V _C2 |>|V _C1 | may be satisfied.

This allows the amount of toner transferred when the second toner cartridge is used to be closer to the amount of toner transferred when the first toner cartridge is used. This makes it possible to stabilize the print density of the image forming device.

In the above configuration, the toner cartridge may be configured to be detachable from the drum cartridge.

In the above-described configuration, the drum cartridge may have a transfer roller and a cleaning roller, and the control device may determine an initial transfer current _I1 and an initial cleaning bias _{VC1. After the initial transfer current I1 and the initial cleaning bias VC1 have been} determined, the control device may determine an initial transfer current _I2 different from the initial transfer current _I1 and an initial cleaning bias _VC2 different from the initial cleaning bias _VC1 based on the cumulative drum rotation count when a second toner cartridge different from the first toner cartridge is used in the drum cartridge to form an image.

The image forming device disclosed herein can stabilize print density.

1 is a cross-sectional view of an image forming apparatus according to an embodiment. FIG. 2 is a diagram illustrating a circuit for applying a charging bias, a transfer current, and a cleaning bias. 11 is a graph showing the relationship between the cumulative number of drum rotations and the charging bias. 1A is a graph showing the relationship between the cumulative dot count and the transfer current reference value, and FIG. 1B is a graph showing the relationship between the cumulative dot count and the cleaning bias reference value. Graph (a) shows the relationship between the cumulative number of drum rotations and the amount of transfer current correction, and graph (b) shows the dot count (cumulative number of drum rotations) and transfer current when multiple developing cartridges are replaced and used for one drum cartridge. Graph (a) shows the relationship between the cumulative number of drum rotations and the cleaning bias correction amount, and graph (b) shows the dot count (cumulative number of drum rotations) and the cleaning bias when multiple developing cartridges are replaced and used for one drum cartridge.

Next, an embodiment of the present disclosure will be described in detail with reference to the drawings as appropriate.
1, the image forming apparatus 1 is a monochrome laser printer, and includes a device main body 2, a feeder unit 3, an image forming unit 4, and a control device 100.

The device body 2 is in the shape of a hollow case. The device body 2 has a pair of left and right side walls 21 and a front wall 22 that connects the side walls 21. The front wall 22 has a body opening 22A. The front wall 22 is provided with a front cover 23 that opens and closes the body opening 22A.

The feeder unit 3 includes a supply tray 31 and a supply mechanism 32. The supply tray 31 is removably attached to the bottom of the device body 2. The supply mechanism 32 feeds the supply tray 31 and the sheet S in the supply tray 31 toward the image forming unit 4.

The image forming unit 4 includes a scanner unit 5, a fixing device 7, a drum cartridge 8, and a toner cartridge 9.

The scanner unit 5 is provided at the top of the device body 2 and includes a laser emitter, a polygon mirror, a lens, and a reflector (not shown). The scanner unit 5 irradiates the surface of the photoconductor drum 81 (described later) with a laser beam at high speed.

The control device 100 includes, for example, a CPU, RAM, ROM, and input/output circuits, and performs printing control by performing calculations based on information about the installed cartridge and programs and data stored in the ROM.

The drum cartridge 8 is disposed between the feeder section 3 and the scanner unit 5. The drum cartridge 8 is detachable from the device main body 2. Specifically, the drum cartridge 8 is detachable from the device main body 2 through a main body opening 22A that is opened and closed by a front cover 23 of the device main body 2. The toner cartridge 9 is detachable from the drum cartridge 8. The toner cartridge 9 is detachable from the device main body 2 while assembled in the drum cartridge 8.

The lifespan of the drum cartridge 8 is longer than that of the toner cartridge 9. A long lifespan here means that the total number of pages that can be printed or the total dot count that can be printed is large. For this reason, multiple toner cartridges 9 can be replaced with one drum cartridge 8 for use. For example, three to five toner cartridges 9 can be replaced with one drum cartridge 8 for use.

The drum cartridge 8 has a frame 80, a photosensitive drum 81, a transfer roller 82, a charger 83, a cleaning roller 84, and a drum memory 85. The toner cartridge 9 can be attached to the frame 80. The photosensitive drum 81 is rotatably supported by the frame 80. The transfer roller 82 is positioned opposite the photosensitive drum 81.

The cleaning roller 84 is provided at a different position from the transfer roller 84 and faces the photosensitive drum 81. The cleaning roller 84 cleans residual toner and foreign matter on the photosensitive drum 81.

The toner cartridge 9 has a housing 90, a developing roller 91, a supply roller 92, a blade 93, and a toner memory 95. The housing 90 can accommodate toner inside. The developing roller 91 supplies toner to the photosensitive drum 81. The supply roller 92 supplies the toner in the housing 90 to the developing roller 91. The blade 93 regulates the layer thickness of the toner supplied to the developing roller 91.

In this drum cartridge 8, the surface of the rotating photosensitive drum 81 is uniformly charged by the charger 83, and then exposed to high-speed scanning of a laser beam from the scanner unit 5. This reduces the potential of the exposed area, and an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 81.

Then, the toner in the toner cartridge 9 is supplied to the electrostatic latent image on the photosensitive drum 81 by the rotating developing roller 91, forming a toner image on the surface of the photosensitive drum 81. Thereafter, the sheet S is transported between the photosensitive drum 81 and the transfer roller 82, so that the toner image carried on the surface of the photosensitive drum 81 is transferred onto the sheet S.

The fixing device 7 includes a heating roller 71 and a pressure roller 72. The pressure roller 72 is positioned opposite the heating roller 71. The pressure roller 72 presses the heating roller 71. The fixing device 7 thermally fixes the toner transferred onto the sheet S while the sheet S passes between the heating roller 71 and the pressure roller 72.

The sheet S that has been thermally fixed by the fixing device 7 is transported to the discharge rollers 24 arranged downstream of the fixing device 7, and is sent from the discharge rollers 24 onto the discharge tray 25.

The drum memory 85 is a medium for storing information, such as an IC chip, but is not limited to an IC chip. The drum memory 85 stores the cumulative number of drum rotations of the photosensitive drum 81.

The toner memory 95 is a medium for storing information, such as an IC chip, but is not limited to an IC chip. For example, the cumulative number of rotations of the developing roller 91, the used dot count, and the remaining amount of toner are stored in the toner memory 95. In this embodiment, the toner memory 95 stores the cumulative used dot count.

As shown in FIG. 2, the image forming apparatus 1 further includes a charging bias application circuit 210, a transfer current application circuit 270, and a cleaning bias application circuit 280.

In this embodiment, positively charged toner is used, and the charging bias application circuit 210 applies a positive potential bias _VT in response to the positively charged toner.

The charging bias application circuit 210 is a circuit for applying a charging bias _VT to the charger 83. The charging bias application circuit 210 is controlled by the control device 100. Specifically, as shown in FIG. 3, the control device 100 gradually increases the charging bias _VT as the cumulative number of drum rotations of the photoconductor drum 81 increases. The relationship between the charging bias _VT and the cumulative number of drum rotations (FIG. 3) is determined based on experimental data acquired in advance so that the surface potential of the photoconductor drum 81 is constant. In this way, the charging performance of the photoconductor drum 81, which deteriorates as the cumulative number of drum rotations increases, is compensated for.

Returning to FIG. 2, the transfer current application circuit 270 is a circuit for applying the transfer current I to the transfer roller 82. The control device 100 determines the transfer current I to be applied to the transfer roller 82 in accordance with the cumulative number of drum rotations and the cumulative dot count.

Specifically, the transfer current I is determined by adding a transfer current reference value I _n corresponding to the cumulative dot count and a transfer current correction amount I _N corresponding to the cumulative drum rotation number (I=I _n +I _N ).

As shown in FIG. 4A, the transfer current reference value _In is _I0 when the cumulative dot count is zero (n=0). The transfer current reference _value In gradually increases as the cumulative dot count increases. Here, the transfer current reference value when the cumulative dot count is n is set to _In . The relationship between the transfer current reference value _In and the cumulative dot count (FIG. 4) is determined by experimental data acquired in advance. In this way, the amount of toner transferred is kept constant as the dot count increases, even if the toner deteriorates.

As shown in FIG. 5A, the transfer current correction amount _IN is zero when the cumulative number of drum rotations is zero (N=0). The transfer current correction amount _IN is set to gradually increase as the cumulative number of drum rotations increases. Here, the transfer current correction amount IN when the cumulative number of drum rotations is _N. The relationship between the transfer current correction amount _IN and the cumulative number of drum rotations (FIG. 5A) is determined by experimental data obtained in advance. In this way, the amount of toner transferred is kept constant as the cumulative number of drum rotations increases, even if the photosensitive drum 81 deteriorates.

In this embodiment, the first toner cartridge, which is the first toner cartridge for one drum cartridge, is used to form an image, and then a second toner cartridge different from the first toner cartridge is used to form an image. Furthermore, the third, fourth, and fifth toner cartridges are used in a similar procedure to form images.

5B, the control device 100 can execute a process for determining an initial transfer current I1 when an image is formed using the first toner cartridge, and a process for determining an initial transfer current _I2 when an image is formed using the second toner cartridge. Similarly, the control device ₁₀₀ can execute a process for determining initial transfer currents _I3 , _I4 , and _I5 when an image is formed using the third, fourth, and fifth toner cartridges.

The initial transfer current is determined based on the cumulative number of drum rotations. When the drum cartridge is new, the cumulative number of drum rotations is zero, so the initial transfer current _I1 = _I0 when the first drum cartridge is installed. The initial transfer current _I2 when the second toner cartridge is installed is derived from the transfer current correction amount shown in FIG. 5(a). When the cumulative number of drum rotations is _N1 , the transfer current correction amount is _IN1 . The initial transfer current _I2 when the second toner cartridge is installed is I0 = _I0 + _IN1 .

In other words, the initial transfer current _I2 when the second toner cartridge is installed is a different value from the initial transfer current _I1 when the first toner cartridge is installed. In this embodiment, the initial transfer current _I2 is a larger value than the initial transfer current _I1 ( _I2 > _I1 ).

Similarly, when image formation is performed with the third, fourth, and fifth toner cartridges attached to the first drum cartridge, the control device 100 increases the absolute value of the initial supply bias in accordance with the cumulative number of drum rotations ( _I5 > _I4 > _I3 > _I2 ).

After the initial transfer current is determined, the control device 100 changes the transfer current I applied to the transfer roller 82 as the cumulative drum rotation count and the cumulative dot count increase. Specifically, the control device 100 gradually increases the transfer current I as the cumulative dot count increases, and gradually increases the transfer current I as the cumulative drum rotation count increases.

2, the cleaning bias application circuit 280 is a circuit for applying a cleaning bias V _C to the cleaning roller 84. The control device 100 determines the cleaning bias V _C to be applied to the cleaning roller 84 in accordance with the cumulative number of drum rotations and the cumulative dot count.

Specifically, the cleaning bias V _C is determined by adding a cleaning bias reference value V _Cn corresponding to the cumulative dot count and a cleaning bias correction amount V _CN corresponding to the cumulative drum rotation number (V _C =V _Cn +V _CN ).

As shown in FIG. 4B, the transfer current reference value I _n is V _C0 when the cumulative dot count is zero (n=0). The cleaning bias reference value V _Cn gradually increases as the cumulative dot count increases. Here, the transfer current reference value when the cumulative dot count is n is V _Cn . The relationship between the cleaning bias reference value V _Cn and the cumulative dot count ( FIG. 4B ) is determined by experimental data acquired in advance. In this way, the cleaning amount is kept constant even if the toner deteriorates as the dot count increases.

As shown in FIG. 6A, the cleaning bias correction amount _VCN is zero when the cumulative drum rotation number is zero (N=0). The cleaning bias correction amount _VCN is set to gradually increase as the cumulative drum rotation number increases. Here, the cleaning bias correction amount when the cumulative drum rotation number is N is set to _VCN . The relationship between the cleaning bias correction amount _VCN and the cumulative drum rotation number (FIG. 6A) is determined by experimental data obtained in advance. In this way, the cleaning amount is made constant as the cumulative drum rotation number increases, even if the photoconductor drum 81 deteriorates.

In this embodiment, the first toner cartridge, which is the first toner cartridge for one drum cartridge, is used to form an image, and then a second toner cartridge different from the first toner cartridge is used to form an image. Furthermore, the third, fourth, and fifth toner cartridges are used in a similar procedure to form images.

6B, the control device 100 can execute a process for determining an initial cleaning bias V _C1 when an image is formed with the first toner cartridge, and a process for determining an initial cleaning bias V _C2 when an image is formed with the second toner cartridge. Similarly, the control device 100 can execute a process for determining initial cleaning biases V _C3 , V _C4 , and V _C5 when an image is formed with the third, fourth, and fifth toner cartridges.

The initial cleaning bias is determined based on the cumulative number of drum rotations. When the drum cartridge is new, the cumulative number of drum rotations is zero, so the initial cleaning bias V _C1 =V _C0 when the first drum cartridge is installed. The initial cleaning bias V _C2 when the second toner cartridge is installed is derived from the cleaning bias correction amount shown in FIG. 6(a). When the cumulative number of drum rotations is N ₁ , the cleaning bias correction amount is V _CN1 . The initial cleaning bias V C2 when the second toner cartridge is installed is V _C2 =V _C0 +V _CN1 .

That is, the initial cleaning bias V _C2 when the second toner cartridge is installed is a different value from the initial cleaning bias V _C1 when the first toner cartridge is installed. In this embodiment, the initial cleaning bias V _C2 is a larger value than the initial cleaning bias V _C1 (V _C2 >V _C1 ).

Similarly, when the third, fourth, and fifth toner cartridges are attached to the first drum cartridge to form an image, the control device 100 increases the absolute value of the initial cleaning bias in accordance with the cumulative number of drum rotations (V _C5 >V _C4 >V _C3 >V _C2 ).

After the initial cleaning bias is determined, the control device 100 changes the cleaning bias V _C applied to the cleaning roller 84 in response to an increase in the cumulative drum rotation count and the cumulative dot count. Specifically, the control device 100 gradually increases the cleaning bias V _C in response to an increase in the cumulative dot count, and gradually increases the cleaning bias V _C in response to an increase in the cumulative drum rotation count.

As described above, the image forming device 1 of this embodiment provides the following advantages:

When a second toner cartridge different from the first toner cartridge is used for the drum cartridge to form an image after the initial transfer current _I1 is determined, the control device 100 determines an initial transfer current _I2 different from the initial transfer current _I1 based on the cumulative drum rotation number. Therefore, as the cumulative drum rotation number increases, the amount of toner transferred becomes constant even if the photosensitive drum 81 deteriorates. Similarly, when a second toner cartridge different from the first toner cartridge is used for the drum cartridge to form an image after the initial cleaning bias V _C1 is determined, the control device 100 determines an initial cleaning bias V _C2 different from the initial cleaning bias V _C1 based on the cumulative drum rotation number. Therefore, as the cumulative drum rotation number increases, the amount of cleaning becomes constant even if the photosensitive drum 81 deteriorates. As a result, according to the image forming device 1, the print density of the image forming device 1 can be stabilized even if a single drum cartridge is replaced with a plurality of toner cartridges for use.

Furthermore, the control device 100 changes the transfer current I applied to the transfer roller 82 in response to an increase in the cumulative number of drum rotations and the cumulative dot count, so that the transfer current I can be changed in response to both the deterioration of the photoconductor drum 81 and the deterioration of the toner. This makes it possible to keep the amount of toner transferred constant.
Similarly, the control device 100 changes the cleaning bias V _C applied to the cleaning roller 84 in response to an increase in the cumulative number of drum rotations and the cumulative dot count, so that the cleaning bias V _C can be changed in response to both the deterioration of the photoconductor drum 81 and the deterioration of the toner, thereby making it possible to keep the cleaning amount of toner constant.

Furthermore, the control device 100 increases the transfer current I in response to an increase in the cumulative dot count. This makes it possible to keep the amount of toner transferred constant even if the toner in the toner cartridge 9 deteriorates. This is because, although the chargeability of the toner decreases as the toner deteriorates, the decrease in the amount of transfer can be suppressed by increasing the transfer current I.
Similarly, the control device 100 increases the absolute value of the cleaning bias V _C as the cumulative dot count increases. Therefore, even if the toner in the toner cartridge 9 deteriorates, the cleaning amount of the toner can be kept constant. This is because, although the charging power of the toner decreases as the toner deteriorates, the decrease in the cleaning amount can be suppressed by increasing the absolute value of the cleaning bias V _C.

Furthermore, the control device 100 increases the transfer current I as the cumulative number of drum rotations increases. This makes it possible to keep the amount of toner transferred constant even if the photoconductor drum 81 deteriorates. This is because, when the photoconductor drum 81 deteriorates, the surface of the photoconductor drum 81 becomes rough and the toner adhesion increases, but by increasing the transfer current I, it is possible to prevent a decrease in the amount of transfer.
Similarly, the control device 100 increases the absolute value of the cleaning bias V _C as the cumulative number of drum rotations increases. This makes it possible to keep the amount of toner cleaned constant even if the photoconductor drum 81 deteriorates. This is because, when the photoconductor drum 81 deteriorates, the surface of the photoconductor drum 81 becomes rough and the toner adhesion increases, but by increasing the absolute value of the cleaning bias V _C , it is possible to prevent the amount of cleaning from decreasing.

In addition, the control device 100 sets the initial transfer current _I2 of the second toner cartridge to a value greater than _I1 ( _I2 > _I1 ). Therefore, the amount of toner transferred when the second toner cartridge is used can be made closer to the amount of toner transferred when the first toner cartridge is used. As a result, the print density of the image forming device 1 can be stabilized. This is because, when multiple toner cartridges are used for one drum cartridge, the photosensitive drum 81 has deteriorated when the second or subsequent toner cartridges are installed.
Similarly, the control device 100 sets the absolute value |V _C2 | of the initial cleaning bias for the second toner cartridge to a value greater than |V _C1 | (|V _C2 |>|V _C1 |). Therefore, the amount of toner cleaned when the second toner cartridge is used can be made closer to the amount of toner cleaned when the first toner cartridge is used. As a result, the print density of the image forming device 1 can be stabilized.

This disclosure is not limited to the above-described embodiments, but can be used in various forms, as exemplified below.

In the above-described embodiment, positively charged toner is used, but negatively charged toner may also be used. In this case, a negative potential bias is applied to the charging bias application circuit 210 and the cleaning bias application circuit.

In the above-described embodiment, the control device determines the initial transfer current _I1 and the initial cleaning bias _VC1 , and after the initial transfer current _I1 and the initial cleaning bias _VC1 have been determined, the control device determines an initial transfer current I2 different from the initial transfer current I1 and an initial cleaning bias _{VC2 different from the initial cleaning bias VC1 based} on the cumulative drum rotation count when a second toner cartridge different from the first toner cartridge is used in _the drum _cartridge to form an image.
However, the control device may be configured to determine the initial transfer current _I1 or the initial cleaning bias _VC1 , and after the initial transfer current _I1 or the initial cleaning bias _VC1 has been determined, the control device may determine an initial transfer current I2 different from the initial transfer current _I1 , or an initial cleaning bias _VC2 different from the initial cleaning bias _VC1 , based on the cumulative number of drum rotations when a second toner cartridge different from the first toner cartridge is used in the drum _cartridge to form an image.

In the above-described embodiment, the control device 100 increases the transfer current I as the cumulative dot count of the drum cartridge 8 increases, but the current value may be determined based on the cumulative number of drum rotations or the amount of toner remaining instead of the cumulative dot count.

In the above-described embodiment, a monochrome laser printer is used as an example of an image forming device, but the image forming device may be a color laser printer, a copier, or a multifunction device.

The elements described in the above embodiments and variations can be implemented in any combination.

REFERENCE SIGNS LIST 1 Image forming apparatus 4 Image forming section 8 Drum cartridge 9 Toner cartridge 81 Photosensitive drum 82 Transfer roller 83 Charger 84 Cleaning roller 85 Drum memory 91 Development roller 95 Toner memory 100 Control device 210 Charging bias application circuit 270 Transfer current application circuit 280 Cleaning bias application circuit I Transfer current _I1 Initial transfer current _I2 Initial transfer current _IN Transfer current correction amount

Claims (6)

An image forming apparatus,
A device body,
a drum cartridge having a photosensitive drum, a transfer roller facing the photosensitive drum or a cleaning roller facing the photosensitive drum, and a drum memory for storing the cumulative number of drum rotations of the photosensitive drum, the drum cartridge being detachable from the main body of the apparatus;
a toner cartridge having a housing capable of accommodating toner, a developing roller, and a toner memory for storing a cumulative dot count;
A control device,
The control device includes:
When a first toner cartridge is used for forming an image on the drum cartridge, a process of determining an initial transfer current I1 to be applied to the transfer roller or an initial cleaning bias VC1 to be applied to the cleaning roller based on the cumulative drum rotation number;
a process of determining an initial transfer current I2 different from the initial transfer current I1 or an initial cleaning bias VC2 different from the initial cleaning bias VC1 based on the cumulative drum rotation number when a second toner cartridge different from the first toner cartridge is used for the drum cartridge to form an image after the initial transfer current I1 or the initial cleaning bias VC1 is determined;
An image forming apparatus capable of executing the following :
The image forming apparatus is characterized in that the control device changes the transfer current applied to the transfer roller or the cleaning bias applied to the cleaning roller in response to an increase in the cumulative drum rotation number and the cumulative dot count. 4. The method according to claim 3, wherein the control device increases the transfer current or increases the absolute value of the cleaning bias in response to an increase in the cumulative dot count.
2. The image forming apparatus according to claim 1 . 4. The method according to claim 3, wherein the control device increases the transfer current or increases the absolute value of the cleaning bias as the cumulative number of drum rotations increases.
3. The image forming apparatus according to claim 1 or 2 . Claims 1 to 5 are characterized in that I2>I1 or |VC2|>|VC1|.
4. The image forming apparatus according to claim 3 . 5. The image forming apparatus according to claim 1, wherein the toner cartridge is detachable from the drum cartridge. the drum cartridge has the transfer roller and the cleaning roller,
The control device controls the initial transfer current I1 and the initial cleaning bias VC
Decide on 1,
An image forming apparatus as described in any one of claims 1 to 5, characterized in that after the initial transfer current I1 and the initial cleaning bias VC1 are determined, the control device determines an initial transfer current I2 different from the initial transfer current I1 and an initial cleaning bias VC2 different from the initial cleaning bias VC1 based on the cumulative drum rotation count when a second toner cartridge different from the first toner cartridge is used in the drum cartridge to form an image.

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