Image bearing apparatus that collects image bearing bodies at a common place

ABSTRACT

A photosensitive belt cleaning roller is constructed to discharge residual toner, removed from a photosensitive belt onto an intermediate transferring belt. Accordingly, the residual toner on the photosensitive belt is first removed by the photosensitive belt cleaning roller, is discharged from the photosensitive belt cleaning roller onto the intermediate transferring belt, and is then finally removed from the intermediate transferring belt by the intermediate transferring belt cleaning unit. Accordingly, it is possible to efficiently collect residual toner remaining on the first and second image bearing bodies into a single, common place.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An image forming apparatus according to a preferred embodiment of the present invention will be described while referring to the accompanying drawings wherein like parts and components are designated by the same reference numerals to avoid duplicating description.

FIG. 1 schematically shows the mechanical construction of a color laser printer (image forming apparatus) according to the embodiment of the present invention.

As shown in FIG. 1, the color laser printer has a main casing . Within the main casing , a sheet feeding portion and an image forming portion are provided.

The sheet feeding portion is for feeding a sheet of paper (image recording medium). The sheet feeding portion includes: a feed tray , a feed roller , transport rollers , and registration rollers . The feed tray holds a stack of sheets . Rotation of the feed roller pulls one sheet at a time from the top of the stack. The sheet is then transported to the image forming portion by the transport rollers and the registration rollers .

The image forming portion is for forming a desired image on the sheet of paper . The image forming portion includes: a scanner unit , a process portion , an intermediate transferring belt mechanism portion , a transferring roller , and a fixing portion . The process unit includes: four developing cartridges (Y, M, C, and K), a photosensitive belt mechanism portion , and a scorotron type charger .

The scanner unit is for forming a latent image on a photosensitive belt (described later), which is provided in the photosensitive belt mechanism portion . The scanner unit is provided in the center portion of the main casing . The scanner unit includes: a laser light-emitting portion, a polygon mirror, a plurality of lenses, and a plurality of reflection mirrors (not shown in the drawings) In the scanner unit , the laser light-emitting portion emits a laser beam modulated based on image data. The laser beam passes through the lenses, is reflected by the polygon mirror, and is reflected by the reflection mirrors, thereby performing high-speed scanning of the surface of the photosensitive belt .

The four developing cartridges are provided on the rear side of the main casing . The four developing cartridges are: a yellow developing cartridge Y for supplying toner in yellow, a magenta developing cartridge M for supplying toner in magenta, a cyan developing cartridge C for supplying toner in cyan, and a black developing cartridge K for supplying toner in black. These developing cartridges are aligned vertically and separated at predetermined distances from one another.

Each developing cartridge includes a developing roller , and although not shown in the drawings, a layer thickness regulating blade, a supply roller, and a toner holding portion. A developing cartridge drive portion (shown in FIG. 2) moves the developing cartridges Y, M, C, and K horizontally to selectively bring the developing rollers of the developing cartridges Y, M, C, and K into and out of contact with the surface of the photosensitive belt .

As shown in FIG. 2, the developing cartridge drive portion operates in accordance with a control signal supplied from a CPU . The developing cartridge drive portion includes a motor and a clutch mechanism (not shown in the drawing). The yellow developing cartridge Y, the magenta developing cartridge M, the cyan developing cartridge C, and the black developing cartridge K are coupled to the developing cartridge drive portion . With the motor and clutch mechanism, each developing cartridge (Y, M, C, or K) is switchably moved between a developing position and a standby position. At the developing position, the developing cartridge is in contact with or is set close to the photosensitive belt and performs development using the toner held in the developing cartridge . At the standby position, the developing cartridge is spaced from the photosensitive belt and is in a standby state.

Each of the developing cartridges Y, M, C, and K operates in substantially the same manner. That is, the toner holding portion holds non-magnetic one-component polymerized toner (developing agent) in one of colors of yellow, magenta, cyan, and black. The toner has an electrically positive charging property. Rotation of the supply roller supplies the toner housed in the toner holding portion to the developing roller , and the layer thickness regulating blade regulates the thickness of the toner on the developing roller. Simultaneously, the toner is positively charged to friction between the toner and the developing roller and the layer thickness regulating blade. Accordingly, a thin layer of toner having a predetermined thickness is borne on the developing roller through an electrostatic force.

The photosensitive belt mechanism portion is disposed in front of the four developing cartridges in confrontation with the four developing cartridges . The photosensitive belt mechanism portion includes: a first photosensitive belt roller , a second photosensitive belt roller , a third photosensitive belt roller , and the photosensitive belt .

The first photosensitive belt roller is disposed in substantial confrontation with the black developing cartridge K, which is at the lowest position in the stack of developing cartridges. The second photosensitive belt roller is disposed vertically above the first photosensitive belt roller in substantial confrontation with the yellow developing cartridge Y, which is at the highest position in the stack of developing cartridges. The third photosensitive belt roller is disposed diagonally above the first photosensitive belt roller and diagonally below the second photosensitive belt roller . In this way, the photosensitive belt rollers to are disposed in a triangular arrangement.

The photosensitive belt (first image bearing body) is an endless belt. The endless belt is made of a resin, such as polyethylene terephthalate, (PET), with its outer side surface being vapor deposited with aluminum. An organic photosensitive layer is provided on the outer surface of the aluminum deposition layer.

The photosensitive belt is wound around the photosensitive belt rollers , , to . That is, the photosensitive belt is mounted so that the inner side surface of endless belt is in contact with the outer peripheral surfaces of the photosensitive belt rollers to .

As shown in FIG. 2, a main drive portion operates in accordance with a control signal supplied from the CPU . The main drive portion is provided with a main motor (not shown). The second photosensitive belt roller is coupled to the main motor through a train of gears (not shown). The rollers and are coupled to the roller by the endless belt . Accordingly, when the main drive portion drives the main motor to rotate the second photosensitive belt roller in the counterclockwise direction in FIG. 1, the first photosensitive belt roller and the third photosensitive belt roller rotate in the counterclockwise direction by following the rotational driving, with the photosensitive belt rotating around the photo effective belt rollers to in the counter clockwise directions.

It is noted that other several portions are coupled to the main motor. Representative examples of the several portions include: a first intermediate transferring belt roller (to be described later) in the intermediate transferring belt mechanism portion ; a drive portion (not shown) for driving the feed roller , a drive portion (not shown) for driving the transferring roller , a drive portion (not shown) for driving an intermediate transferring belt cleaning unit (to be described later).

Although not shown in the drawing, the photosensitive belt is formed with a sensing opening at one end in the widthwise direction of the belt . The sensing opening has an approximately rectangular shape, and is formed through the photosensitive belt in its thickness direction to be opened on both of the inner and outer side surfaces. The sensing opening is detected by an origin sensor (FIG. ).

Although not shown in FIG. 1, the origin sensor is disposed in confrontation with the photosensitive belt at a location between the second photosensitive belt roller and the third photosensitive belt roller . The origin sensor includes a light-emitting portion and a light-receiving portion that are disposed in confrontation with each other with the photosensitive belt being located therebetween. The origin sensor sends a detection signal to the CPU when the sensing opening opposes the origin sensor as a result of movement of the photosensitive belt and the light-receiving portion receives light from the light-emitting portion. With reference to the timing when the origin sensor detects the sensing opening, an image forming area and a non-image forming area are defined on the outer side surface of the photosensitive belt as shown in FIG. . On the image forming area, the scanner unit will form an electrostatic latent image for one color component, which will then be developed into a toner image by toner supplied from a corresponding developing cartridge . On the non-image forming area, no electrostatic latent image will be formed or no toner image will be developed.

The scorotoron type charger includes a charge wire, made from tungsten for example, that generates a corona discharge to charge the surface of the photosensitive belt to a uniform positive charge. The scorotoron type charger is disposed below the photosensitive belt mechanism portion at a position between the third photosensitive belt roller and the first photosensitive belt roller and separated from the photosensitive belt by a predetermined distance.

It is noted that the scorotron type charger charges the surface of the photosensitive belt as a preprocess of the exposure process operations by the scanner unit .

The intermediate transferring belt mechanism portion is disposed to the front of the photosensitive belt mechanism portion , and includes a first intermediate transferring belt roller , a second intermediate transferring belt roller , a third intermediate transferring belt roller , and an intermediate transferring belt .

The first intermediate transferring belt roller is disposed in substantial confrontation with the second photosensitive belt roller via the photosensitive belt and the intermediate transferring belt . The second intermediate transferring belt roller is disposed to the front of and below the first intermediate transferring belt roller . The third intermediate transferring belt roller is disposed above the second intermediate transferring belt roller and below and to the front of the first intermediate transferring belt roller .

The intermediate transferring belt (second image bearing body) is an endless belt made from an electrically-conductive resin, such as polyamide or polycarbonate dispersed with conductive particles such as carbon. The intermediate transferring belt is wound around the intermediate transferring belt rollers to .

As described already, the first intermediate transferring belt roller is coupled to the main motor. (not shown)in the main drive portion through another train of gears (not shown) The rollers and are coupled to the roller by the endless belt Accordingly, when the main drive portion (FIG. 2) drives the main motor to rotate the first intermediate transferring belt roller in the clockwise direction in FIG. 1, the second intermediate transferring belt roller and the third intermediate transferring belt roller rotate in the clockwise direction by following the rotational driving, with the belt rotating around the rollers to in the clockwise direction.

It is noted that the main drive portion (FIG. 2) drives the main motor to rotate the second photosensitive belt roller and the first intermediate transferring belt roller to rotate at the same outer peripheral speed so that the photosensitive belt and the intermediate transferring belt move at the same speed.

The outer side surface of the intermediate transferring belt and the outer side surface of the photosensitive belt contact each other at a primary transferring position A, as shown in FIG. 1, and move at the same speed in this contact portion. Accordingly, as shown in FIG. 3, an image forming area and a non-image forming area are defined on the outer side surface of the intermediate transferring belt in correspondence with the image forming area and the non-image forming area defined on the outer side surface of the photosensitive belt . A toner image will be transferred from the image forming area of the belt onto the image forming area of the intermediate transferring belt . No toner image will be formed on the non-image forming area.

The transferring roller is for performing a transferring operation to transfer the toner image on the image forming area of the intermediate transferring belt onto a sheet of paper . The transferring roller confronts against the second intermediate transferring belt roller with the intermediate transferring belt being located therebetween. The transferring roller is moved between a secondary transferring position D and a standby position. At the transferring position D, the transferring roller is in contact with the outer side surface of the belt . At the standby position, the transferring roller is spaced from the belt . In order to transfer a toner image from the belt onto a sheet of paper , the transferring roller is moved from the standby position to the transfer position D. As a result, the transferring roller is brought into contact with the intermediate transferring belt . When the sheet of paper teaches the position between the transferring roller and the intermediate transferring belt , the transferring roller is applied with a predetermined secondary transferring bias voltage, so that a predetermined electric potential difference is established between the transferring roller and the intermediate transferring belt . As a result, the toner image formed on the intermediate transferring belt is transferred onto the sheet that is passing between the intermediate transferring belt and the transferring roller .

It is noted that various methods other than the roller can be employed to transfer the color image from the belt to the sheet of paper .

With the above-described configuration, the color laser printer performs image forming operation as described below.

The surface of the photosensitive belt is evenly and positively charged by the scorotron type charger , before being exposed through high-speed scanning by a laser beam that is emitted from the scanner unit and that is modulated according to image data for one color. In this manner, an electrostatic latent image is formed in the image forming area based on the image data. One developing cartridge holding toner of a corresponding color is moved to the developing position, while the remaining three developing cartridges are still in the standby position. The image forming area of the photosensitive belt , which is now formed with the electrostatic latent image, is brought into contact with the developing roller in the corresponding developing cartridge . Accordingly, toner of the corresponding color is transferred from the developing cartridge to the image forming area of the photosensitive belt . In this way, the electrostatic latent image is developed into a visible toner image of the corresponding color.

When the image forming area of the belt , on which the toner image is formed, reaches the primary transferring position A, the image forming area of the belt also reaches the transferring position A. Accordingly, the image forming area of the belt is brought into contact with the image forming area of the belt . A predetermined primary transferring bias voltage is applied to the intermediate transferring belt at a timing when the image forming areas of the belts and reach the primary transferring position A. More specifically, although not shown in the drawing, a brushtype or a roller-type electrode is provided at a location near to the roller for applying the primary transferring bias voltage to the belt . The primary transferring bias voltage establishes an electric potential difference between the belts and so that the positively-charged toner image will be transferred from the photosensitive belt to the intermediate transferring belt . This transfer operation will be referred to a “primary transfer” hereinafter. In this way, the visible image in the single color is transferred onto the image forming area of the intermediate transferring belt . It is noted that a primary transferring voltage may be applied to the roller instead of to the belt .

The photosensitive belt is further rotated and is subjected to cleaning by a photosensitive belt cleaning roller to be described later. After being electrically discharged by a well-known electrical discharger (not shown), the photosensitive belt is charged again by the charger . Following this, an electrostatic latent image for the next color component is formed and developed by the next developing device . The visible image is then transferred to the image forming area of the belt at the transfer position A. As a result, this visible image is superimposed on the visible image previously transferred onto the intermediated transferring belt . By repeating this processing for the four colors, a final, multicolor image is formed on the intermediate transferring belt . It is noted that the electric potential of the photosensitive belt changes at its positions where the photosensitive belt is subjected to the charging process, to the development process, and to the primary transferring process.

Until the multicolor image is finally formed on the belt , the transferring roller is continuously in the standby state even when the image forming area of the belt passes between the rollers and . After the final, multicolor image is formed in the image forming area of the belt , the roller is moved to the secondary transferring position D. When the image forming area of the belt and the sheet of paper passes between the rollers and , the roller is applied with the predetermined secondary transfer bias voltage. As a result, the multicolor image is transferred onto the sheet of paper . It is noted that the electric potential of the belt changes at its positions where the belt is subjected to the primary transferring process, the secondary transferring process, and the cleaning process (to be described later) executed by the intermediate transferring belt cleaning unit ).

The fixing portion is disposed to the front of the intermediate transfer belt mechanism portion and at a position downstream in the sheet transport direction from the secondary transferring position D. The fixing portion includes a thermal roller , a pressing roller , and a pair of transporting rollers . The thermal roller has an internal metal layer and an external silicone rubber layer. Although not shown in the drawing, a halogen lamp is installed within the thermal roller . The halogen lamp is for heating up the metal and silicone rubber layers. The pressing roller presses against the thermal roller . The pair of transporting rollers are positioned downstream from the thermal roller and the pressing roller in the transport direction of the sheet .

After the transferring roller transfers the multicolor image onto a sheet , the sheet passes between the thermal roller and the pressing roller so that the multicolor image is thermally fixed onto the sheet .

The sheet with the thermally-fixed multicolor image is then transported toward a pair of sheet discharging rollers by the transporting rollers , and is further delivered by the sheet discharging rollers onto a sheet discharging tray , which is formed in an upper portion of the main casing .

According to the present embodiment, the photosensitive belt cleaning roller is provided for collecting residual toner that remains on the surface of the photosensitive belt after the toner image is transferred from the photosensitive belt onto the intermediate transferring belt .

The photosensitive belt cleaning roller is for performing cleaning operation of the surface of the photosensitive belt . The photosensitive belt cleaning roller is disposed on one side opposite to the developing cartridges with respect to the photosensitive belt mechanism portion . The photosensitive belt cleaning roller is disposed at a location between the second and third photosensitive belt rollers and and close to the third photosensitive belt roller .

The photosensitive belt cleaning roller is a rotary member which has a roller axis and an outer peripheral portion, which is provided around the roller axis. The outer peripheral portion is made of a resilient material, such as silicone rubber, that is capable of capturing toner.

The photosensitive belt cleaning roller is rotatably supported in the main casing . The photosensitive belt cleaning roller is movable so as to be brought into contact with and separated from the photosensitive belt and the intermediate transferring belt . More specifically, the photosensitive belt cleaning roller is movable between a first position shown in FIG. 4A and a second position shown in FIG. B. When the roller is located at the first position, the outer peripheral portion of the roller is in contact with the photosensitive belt at a contact position B. When the roller is located at the second position, the outer peripheral portion of the roller is in contact with the intermediate transferring belt at a contact position C. In this way, the roller is in contact with a selected one of the belts and .

A photosensitive belt cleaning roller drive portion is provided as shown in FIG. 2 to drive the photosensitive belt cleaning roller to rotate and to move the photosensitive belt cleaning roller between the first position of FIG. A and the second position of FIG. B. The photosensitive belt cleaning roller drive portion operates in accordance with a control signal supplied from the CPU . Although not shown in the drawings, the photosensitive belt cleaning roller drive portion includes a cam mechanism and a cleaning roller drive motor. The cam mechanism is for moving the photosensitive belt cleaning roller in either one of the first and second positions of FIGS. 4A and 4B. The cleaning roller drive motor is for applying a driving force to the roller axis of the roller and to the cam mechanism.

In the present embodiment, as shown in FIG. 1, a switching member is provided in the main casing so as to be capable of being rocked by the cam mechanism. The cleaning roller drive motor is fixed to a free end portion of the switching member , The cleaning roller is connected to an output axis of the cleaning roller drive motor, while being electrically insulated therefrom. In this way, the roller is mounted on the free end portion of the switching member together with the cleaning roller drive motor. Rocking of the switching member moves the cleaning roller between the first and second positions shown in FIGS. 4A and 4B. Accordingly, the cleaning roller is brought into contact with a selected one of the belts and , while being separated from the non-selected one.

It is noted that according to the present embodiment, the contact/separation mechanism for bringing the roller into contact with and out of contact with the belts and employs the switching member . However, other various configurations can be employed as the contact/separation mechanism.

As shown in FIG. 2, a cleaning bias applying circuit is provided to apply the cleaning roller with first and second cleaning bias voltages While the cleaning roller is in contact with the photosensitive belt , the cleaning bias applying circuit applies the roller with the first cleaning bias voltage, which is lower than the electric potential of the belt at the contact position B by a first electric potential difference. Accordingly, the first electric potential difference is established between the cleaning roller and the belt so that the positively-charged toner will be electrostatically attracted in a direction from the photosensitive belt to the roller .

As shown in FIG. 4A, while the cleaning roller is in contact with the photosensitive belt , the cleaning roller drive portion drives the cleaning roller to rotate in a clockwise direction of FIG. 4A, while the cleaning bias applying circuit applies the first cleaning bias voltage to the roller to transfer residual toner remaining on the photosensitive belt onto the cleaning roller . Because the roller rotates in the clockwise direction, a portion of the cleaning roller that is contact with the belt moves in the same direction with a portion of the belt that is contact with the cleaning roller .

While the cleaning roller is in contact with the photosensitive belt , the photosensitive belt cleaning roller drive portion drives the roller to rotate in a speed different from the belt . In this way, according to the present embodiment, the photosensitive belt cleaning roller drive portion applies the cleaning roller with a rotational driving force so that the portion of the roller that contacts with the belt moves in a speed different from the portion of the belt that contacts with the roller . Thus, a speed difference occurs between the contact portions of the belt and the roller . Even in the case where no speed difference occurs, the roller can perform cleaning of the photosensitive belt . However, generating the speed difference applies an external force to the residual toner on the photosensitive belt . The external force increases the effect of cleaning by the cleaning bias voltage. It is noted that the roller may rotate faster than the belt . Or otherwise, the roller may rotate slower than the belt .

A first auxiliary roller is provided at a position so that the roller confronts the photosensitive belt cleaning roller with the photosensitive belt being located therebetween. When the cleaning roller is in contact with the belt , the belt is sandwiched between the rollers and . The first auxiliary roller has a roller axis covered with a roller portion. The roller axis is made of metal. The roller portion has a hardness that is approximately equal to or less than that of the cleaning roller . For example, the roller portion is made of a foam member such as urethane foam. The first auxiliary roller is disposed at such a position that the roller can press the photosensitive belt from a side opposite to the cleaning roller when the cleaning roller contacts the photosensitive belt . That is, as shown in FIG. 4A, when the cleaning roller contacts the photosensitive belt , the cleaning roller presses the belt rightwardly, while the first auxiliary roller presses the belt leftwardly.

If no auxiliary roller were provided; pressing of the cleaning roller will possibly elongate the belt , and the elongated belt will be loosened. According to the present embodiment, however, the belt is sandwiched between the rollers and when the roller is in contact with the belt . Accordingly, the belt is pressed by the rollers and in opposite directions. The belt is prevented from being elongated or loosened. It is ensured that the belt is maintained as being properly taut.

While the cleaning roller is in contact with the intermediate transferring belt , the cleaning bias applying circuit applies the roller with the second cleaning bias voltage, which is higher than the electric potential of the belt at the contact position C by a second electric potential difference. Accordingly, the second electric potential difference is established between the cleaning roller and the belt so that the positively-charged toner will be electrostatically attracted in a direction from the roller to the belt .

As shown in FIG. 4B, while the cleaning roller is in contact with the intermediate transferring belt , the cleaning roller drive portion drives the cleaning roller to rotate in a counterclockwise direction of FIG. 4B, while the cleaning bias applying circuit applies the second cleaning bias voltage to the roller to transfer residual toner remaining on the cleaning roller onto the belt Because the roller rotates in the counterclockwise direction, a portion of the cleaning roller that is contact with the belt moves in the same direction with a portion of the belt that is contact with the cleaning roller .

A second auxiliary roller is provided at a position so that the roller confronts the photosensitive belt cleaning roller with the intermediate transferring belt being located therebetween. When the cleaning roller is in contact with the belt , the belt is sandwiched between the rollers and . The second auxiliary roller has the same configuration with the first auxiliary roller . The second auxiliary roller is disposed at such a position that the roller can press the belt from a side opposite to the cleaning roller when the cleaning roller contacts the belt . Accordingly, when the roller is in contact with the belt , the belt is sandwiched between the rollers and and the belt is pressed by the rollers and in opposite directions. In this way, the belt is prevented from being elongated or loosened in the same manner as the belt .

As shown in FIGS. 4A and 4B, a length on the photosensitive belt from the transferring position A to the contact position B is approximately equal to a length on the intermediate transferring belt from the transferring position A to the contact position C.

As shown in FIG. 1, the intermediate transferring belt cleaning unit is provided for collecting residual toner that remains on the surface of the intermediate transferring belt after the multicolor toner image is transferred onto the sheet .

The intermediate transfer belt cleaning apparatus is for cleaning the intermediate transfer belt . The intermediate transfer belt cleaning apparatus is disposed in front of the intermediate transferring mechanism portion , and in confrontation with the third intermediate transferring belt roller though the intermediate transferring belt .

The intermediate transferring belt cleaning unit includes: an intermediate transferring belt cleaning box , an intermediate transferring belt cleaning roller , a secondary intermediate transferring belt cleaning roller , and an intermediate transferring belt cleaning blade

The intermediate transferring belt cleaning box has a box shape formed with an opening at the side in confrontation with the intermediate transferring belt . The space at the bottom of the intermediate transferring belt cleaning box forms a waste toner accumulation portion for accumulating toner that is scraped off by the intermediate transferring belt cleaning blade

The intermediate transferring belt cleaning roller includes a metal core covered with an outer peripheral portion made of a resilient material such as a silicone rubber. The intermediate transferring belt cleaning roller is rotatably supported at the opening of the intermediate transferring belt cleaning box at a position in confrontation with the third intermediate transferring belt roller . The intermediate transferring belt cleaning roller is driven by a predetermined drive portion (not shown) to move between a position at which the roller is in contact with the belt and another position at which the roller is out of contact with the belt . When the roller is in contact with the belt , the outer peripheral portion of the roller contacts the surface of the belt at its side that is opposite to the side where the roller contacts the belt . The secondary intermediate transferring belt cleaning roller is a metal roller. The intermediate transferring belt cleaning blade is made of a resilient material such as urethane.

The intermediate transferring belt cleaning roller is being out of contact with the intermediate transferring belt by a predetermined distance until the multicolor image (superimposed four-color toner images) is finally formed on the intermediate transferring belt when the final, multicolor image is formed on the intermediate transferring belt and transferred from the belt onto the sheet , the intermediate transferring belt cleaning roller is brought into contact with the intermediate transferring belt . Another cleaning bias voltage is applied to the intermediate transferring belt cleaning roller to establish an electric potential difference between the belt and the roller so that the positively-charged residual toner will be electrostatically attracted in a direction from the belt to the cleaning roller .

After the multicolor image is transferred onto the sheet , the residual toner remaining on the intermediate transferring belt is conveyed according to the rotation of the intermediate transferring belt . When the residual toner reaches the position where the toner confronts the cleaning roller , the toner is removed by the cleaning roller . According to rotation of the intermediate transferring belt cleaning roller , the removed toner is conveyed to the position where the toner confronts the cleaning roller The toner is then captured by the cleaning roller . After that, the toner captured by the cleaning roller is scraped off by the intermediate transferring belt cleaning blade and is accumulated in the waste toner accumulating portion.

As shown in FIG. 2, the origin sensor , the main drive portion , the photosensitive belt cleaning roller drive portion , the cleaning bias applying circuit , and the developing cartridge drive portion are connected to the CPU .

The CPU includes a RAM and a ROM . The CPU is for controlling the entire portions of the color laser printer . The RAM is for temporarily storing image data. The ROM previously stores: a control program for controlling the cleaning bias applying circuit , the main drive portion , the developing cartridge drive portion , and other control programs.

The cleaning bias applying circuit is for generating the first and second cleaning bias voltages. The roller axis of the photosensitive belt cleaning roller is electrically connected to the cleaning bias applying circuit . The cleaning bias applying circuit applies the first and second bias voltages to the photosensitive belt cleaning roller through the roller axis. The ON/OFF timings of the first and second bias voltages and the values of the first and second bias voltages (ON-bias voltages) are controlled by control signals supplied from the CPU to the cleaning bias applying circuit .

When the photosensitive belt cleaning roller is in contact with the photosensitive belt at position B as shown in FIG. 4A, the cleaning bias applying circuit applies the roller with the first cleaning bias voltage that establishes the first electric potential difference between the roller and the belt , with the potential of the roller being lower than that of the belt . In this way, the bias is applied between the roller and the belt in a direction in which the positively-charge toner will be transferred from the belt to the roller .

When the photosensitive belt cleaning roller is in contact with the intermediate transferring belt at position C as shown in FIG. 4B, the cleaning bias applying circuit applies the roller with the second cleaning bias voltage that establishes the second electric potential difference between the roller and the belt , with the potential of the roller being higher than that of the belt . In this way, the bias is applied between the roller and the belt in a direction in which the positively-charged toner will be transferred from the roller to the belt .

While the toner image of each color is being formed on the photosensitive belt , the roller is in the first contact position B. After the toner image of one color formed on the image forming area of the belt is transferred to the belt at the transfer position A, according to the movement of the belt , the residual toner remaining on the image forming area is conveyed to the position B where the toner confronts the roller . At the position B, the residual toner is transferred from the belt onto the roller .

After toner images of all the four colors are transferred from the belt to the belt and their residual toners are captured by the roller , the roller is moved from the first position of FIG. 4A to the second position of FIG. 4B, wherein the roller is brought into contact with the belt at the contact position C. More specifically, after the image forming area of the belt formed with the toner image of the fourth color passes between the rollers and , the image forming area of the belt with the residual toner remaining thereon passes between the rollers and . When the image forming area of the belt completely passes between the rollers and and the leading edge of the non-image forming area of the belt reaches the position B between the rollers and , the roller is moved from the first position of FIG. 4A to the second position of FIG. B. As a result, the roller , which is now bearing thereon residual toner of all the four colors, is brought into contact with the belt at the contact position C At this time, the leading edge of the non-image forming area of the belt reaches the position C because the length of the belt between the positions A and B is substantially equal to the length of the belt between the positions A and C and because the belts and move with the same speeds. Accordingly, the residual toner of four colors now loaded on the roller is properly transferred to the non-image forming area of the belt . The roller is in the second position of FIG. 4B for a while, and moves back to the first position of FIG. 4A before the image forming area of the belt reaches the position between the rollers and . In this way, it is possible to discharge, onto the non-image forming area of the belt , residual toner of all the colors which has been temporarily captured on the roller .

In the color laser printer with the above-described configuration, a multicolor image is formed on the sheet in a manner shown in FIG. .

First, an electrostatic latent image for yellow color component is formed on the photosensitive belt by the scanner unit , The yellow developing cartridge Y is moved frontward in the horizontal direction by the developing cartridge drive portion , thereby letting the developing roller of the yellow developing cartridge Y contact the image forming area of the photosensitive belt , on which the electrostatic latent image for yellow color has been formed. During this operation, the remaining developing cartridges are moved backward in the horizontal direction by the developing cartridge drive portion , thereby spacing the remaining developing rollers from the photosensitive belt . In this way, a visible image in yellow is formed in the image forming area of the photosensitive belt only by the yellow toner contained in the yellow developing cartridge Y (t).

Then, by applying a primary transferring bias between the photosensitive belt and the intermediate transferring belt , the yellow visible image is transferred onto the image forming area of the intermediate transferring belt when the yellow visible image reaches the transferring position A as a result of movement of the photosensitive belt (t).

Next, when an electrostatic latent image for magenta color is formed again on the photosensitive belt , the magenta developing cartridge M is moved frontward in the horizontal direction by the developing cartridge drive portion , thereby forming a visible image in magenta in the image forming area of the photosensitive belt (t).

Then, in the same manner as described above, by applying a primary transferring bias between the photosensitive belt and the intermediate transferring belt , the magenta visible image is transferred onto the image forming area of the intermediate transferring belt when the magenta visible image reaches the transferring position A as a result of movement of the photosensitive belt (t). The yellow toner image has already been transferred onto the image forming area of the intermediate transferring belt , so that the magenta visible image is superimposed on the yellow visible image.

The same processing as described above is repeated with the cyan toner held in the cyan developing cartridge C and the black toner held in the black developing cartridge K. As a result, four-color toner images for one page are superimposed one on another in the image forming area of the intermediate transferring belt , and a multicolor image is formed (t to t).

Then, the multicolor image in the image forming area of the intermediate transferring belt is collectively transferred, in a secondary transfer operation, onto the sheet passing between the intermediate transferring belt and the transferring roller while the transferring roller is contacting the intermediate transferring belt and the secondary transferring bias is being applied between the rollers and (t).

During the development of the visible images on the photosensitive belt (t, t, t, and t) and the primary transferring of the visible images onto the intermediate transferring belt (t, t, t, and t), the photosensitive belt cleaning roller is placed by the photosensitive belt cleaning roller drive portion in a state where the photosensitive belt cleaning roller contacts the photosensitive belt and the photosensitive belt is sandwiched between the photosensitive belt cleaning roller and the first auxiliary roller . Thus, the photosensitive belt cleaning roller contacts the photosensitive belt during a period, in which the toner images for one page (respective toner images separately formed with the yellow toner, the magenta toner, the cyan toner, and the black toner) are successively borne on the photosensitive belt .

While the roller is thus being in contact with the photosensitive belt , the cleaning bias applying circuit applies the first cleaning bias to the roller to establish the first potential difference between the belt and the roller in a direction in which the toner on the photosensitive belt is transferred from the photosensitive belt onto the photosensitive belt cleaning roller . Thus, residual toner, which remains on the image forming area of the photosensitive belt after the toner image of each color is transferred onto the intermediate transferring belt , is captured by the photosensitive belt cleaning roller when the residual toner reaches the position where the toner opposes the photosensitive belt cleaning roller as a result of improvement of the photosensitive belt .

Each time a period, required by the photosensitive belt to produce the toner images for one page and to transfer the toner images onto the belt , is ended, the image forming area of the photosensitive belt passes between the photosensitive belt cleaning roller and the first auxiliary roller as a result of the circular movement of the photosensitive belt . At this timing, the photosensitive belt cleaning roller is spaced from the photosensitive belt by the photosensitive belt cleaning roller drive portion and is moved to the intermediate transferring belt side (t). As a result, the photosensitive belt cleaning roller is placed in a state where the photosensitive belt cleaning roller contacts the non-image forming area of the intermediate transferring belt , with the intermediate transferring belt being sandwiched between the photosensitive belt cleaning roller and the second auxiliary roller .

Simultaneously, the cleaning bias applying circuit applies the second cleaning bias to the roller to establish the second potential difference between the roller and the belt in a direction in which the toner on the photosensitive belt cleaning roller is transferred onto the intermediate transferring belt . As a result of this processing the toner captured by the photosensitive belt cleaning roller is discharged to the non-image forming area of the intermediate transferring belt with efficiency.

The photosensitive belt cleaning roller is spaced from the intermediate transferring belt and is moved back to the photosensitive belt side (t) before the image forming area of the intermediate transferring belt reaches the position between the photosensitive belt cleaning roller and the second auxiliary roller according to the movement of the intermediate transferring belt . As a result, the photosensitive belt cleaning roller is placed again in a state where the roller contacts the image forming area of the photosensitive belt , with the photosensitive belt being sandwiched between the roller and the first auxiliary roller . Accordingly, as shown in FIG. 5, it is possible to perform the cleaning of the image forming area of the photosensitive belt even in the case where toner image development (t′) and primary transferring (t′) for the next page are started without waiting for the photosensitive belt to make one rotation but immediately after development for one page (t) is finished.

After the secondary transferring is started (t), the intermediate transferring belt cleaning roller is placed in a state here the roller contacts the intermediate transferring belt and the cleaning bias is applied to the roller to establish the electric potential difference between the roller and the intermediate transferring belt (t). Thus, residual toner, which remains on the image forming area of the intermediate transferring belt after the multicolor image is transferred onto the sheet , is captured by the intermediate transferring belt cleaning roller when the residual toner reaches the position where the toner opposes the intermediate transferring belt cleaning roller as a result of rotation of the intermediate transferring belt .

Toner discharged from the photosensitive belt cleaning roller onto the non-image forming area of the intermediate transferring belt is also captured by the intermediate transferring belt cleaning roller when the toner reaches the position where the toner opposes the intermediate transferring belt cleaning roller as a result of rotation of the intermediate transferring belt . Thus, residual toner remaining on the photosensitive belt is also collected in the intermediate transferring belt cleaning box of the intermediate transferring belt cleaning unit .

As described above, in the color laser printer of the present embodiment, the photosensitive belt bears thereon a toner image and conveys the toner image to the primary transferring position A. At the primary transferring position A, the toner image is transferred from the photosensitive belt to the intermediate transferring belt . The intermediate transferring belt conveys the toner image to the secondary transferring position D. At the secondary transferring position D, the toner image is transferred to the image recording medium . The photosensitive belt cleaning roller is provided to remove residual toner that remains on the photosensitive belt after the toner image is transferred to the intermediate transferring belt at the primary transferring position A. The intermediate transferring belt cleaning unit is provided to remove residual toner that is remained on the intermediate transferring belt after the toner image is transferred to the image recording medium at the secondary transferring position D. The photosensitive belt cleaning roller is constructed to discharge the removed residual toner onto the intermediate transferring belt . Accordingly, the residual toner on the photosensitive belt is first removed by the photosensitive belt cleaning roller , is discharged from the photosensitive belt cleaning roller onto the intermediate transferring belt , and is then finally removed from the intermediate transferring belt by the intermediate transferring belt cleaning unit . Accordingly, it is possible to efficiently collect residual toner remaining on the first and second image bearing bodies and into the single, common place .

In this way, the photosensitive belt and the intermediate transferring belt are provided so as to be capable of bearing toner images thereon and circularly moving to convey the toner images. The photosensitive belt cleaning roller removes residual toner remaining on the photosensitive belt . The intermediate transferring belt cleaning unit removes residual toner remaining on the intermediate transferring belt . Toner is discharged from the photosensitive belt cleaning roller onto the intermediate transferring belt .

Accordingly, toner on the photosensitive belt is removed by the photosensitive belt cleaning roller , is then discharged from the photosensitive belt cleaning roller onto the intermediate transferring belt , and is further removed from the intermediate transferring belt by the intermediate transferring belt cleaning unit . It is possible to efficiently collect residual toner residing both on the photosensitive belt and on the intermediate transferring belt at a single, common place.

The photosensitive belt cleaning roller is brought into contact with the image forming area of the photosensitive belt , thereby capturing residual toner on the photosensitive belt . The photosensitive belt cleaning roller is brought into contact with the non-image forming area of the intermediate transferring belt , thereby discharging residual toner onto the non-image forming area.

With this construction, it becomes possible to prevent a situation wherein the discharging of residual toner exerts an influence on a toner image borne on the intermediate transferring belt . Also, even while the intermediate transferring belt is beating a toner image in its image forming area, it is possible to discharge residual toner from the photosensitive belt cleaning roller onto the intermediate transferring belt . Even while the color laser printer is performing a print operation, it is possible to restore the toner removing function of the photosensitive belt cleaning roller . It is possible to perform cleaning of the photosensitive belt in an efficient manner.

The first cleaning bias voltage is applied to the roller to establish the first potential difference between the roller and the belt . It is possible to perform the removal of toner from the photosensitive belt to the roller in an efficient manner. The second cleaning bias voltage is applied to the roller to establish the second potential difference between the roller and the belt . It is possible to perform the discharging of toner from the photosensitive belt cleaning roller onto the intermediate transferring belt in an efficient manner.

The photosensitive belt cleaning roller drive portion controls the photosensitive belt cleaning roller to selectively contact either of the photosensitive belt and the intermediate transferring belt . The length on the photosensitive belt from the transferring position A to the contact position B is set approximately equal to the length on the intermediate transferring belt from the transferring position A to the contact position C. It is possible to control the photosensitive belt cleaning roller to contact the image forming area of the photosensitive belt and to contact the non-image forming area of the intermediate transferring belt .

The photosensitive belt cleaning roller drive portion controls the photosensitive belt cleaning roller to contact the photosensitive belt for a period of time, required by the photosensitive belt to bear and convey toner images for one page, and to contact the intermediate transferring belt each time after the period is ended. It is possible to discharge toner accumulated on the photosensitive belt cleaning roller to the intermediate transferring belt everytime after the photosensitive belt is used to form an image for one page. It is possible to restore the toner removing function of the photosensitive belt cleaning roller and to efficiently perform cleaning of the photosensitive belt .

The photosensitive belt cleaning roller is a rotary member that is capable of rotating, that is capable of capturing toner from the photosensitive belt while contacting the belt at its outer peripheral portion, and that is capable of discharging toner to the intermediate transferring belt while contacting the belt at its outer peripheral portion. It is possible to capture toner using the entire portion of the outer peripheral portion by rotating the photosensitive belt cleaning roller . It is possible to efficiently perform the removal of toner from the photosensitive belt . It is possible to discharge toner from the entire portion of the outer peripheral portion by rotating the photosensitive belt cleaning roller It is possible to efficiently perform the discharging of toner to the belt .

Especially, according to the present embodiment, the outer peripheral portion of the photosensitive belt cleaning roller is made of a resilient material. Accordingly, when the photosensitive belt cleaning roller is pressed against the photosensitive belt , it is possible to widen the nip portion (contact surface) of the roller and to efficiently perform the removal of toner from the photosensitive belt . A contact pressure (pressing force exerted by the photosensitive belt cleaning roller onto the photosensitive belt ) that is required to widen the nip portion can be reduced. Even when the photosensitive belt cleaning roller is brought into contact with and is separated from the belt , it is possible to suppress the fluctuation of the moving speed of the belt .

Because the outer peripheral portion of the roller is made of a resilient material, when the roller is pressed against the belt , it is possible to widen the nip portion (contact surface) of the roller and to efficiently perform the discharging of toner onto the belt . A contact pressure (pressing force exerted by the photosensitive belt cleaning roller onto the belt ) that is required to widen the nip portion can be reduced. Even when the cleaning roller is brought into contact with and is separated from the belt , it is possible to suppress the fluctuation of the moving speed of the belt .

While in contact with the photosensitive belt , the photosensitive belt cleaning roller rotates in a direction so that the portion of the roller that contacts with the belt moves in the same direction with the portion of the belt that contacts with the roller while in contact with the belt , the photosensitive belt cleaning roller rotates in a direction so that the portion of the roller that contacts with the belt moves in the same direction with the portion of the belt that contacts with the roller . It is possible to further reduce the influence exerted by the photosensitive belt cleaning roller onto the moving speeds of the photosensitive belt and the intermediate transferring belt .

While the photosensitive belt cleaning roller is in contact with the photosensitive belt , the photosensitive belt cleaning roller drive portion rotationally drives the photosensitive belt cleaning roller so that a speed difference occurs in the portion of the cleaning roller contacting the belt and the portion of the belt contacting the roller . It is possible to increase a frictional force exerted in the contact portions of the cleaning roller and the belt , which makes it possible to perform the removal of toner from the photosensitive belt with more reliability.

The first auxiliary roller is provided at a position that the roller opposes the photosensitive belt cleaning roller with the photosensitive belt being sandwiched between the rollers and . It is possible to prevent the photosensitive belt from being loosened by the pressing of the cleaning roller against the photosensitive belt . It is possible to suppress an influence exerted on the circular movement speed of the photosensitive belt when the cleaning roller is brought into contact with and out of contact from the photosensitive belt .

The second auxiliary roller is provided at a position that the roller opposes the roller with the belt being sandwiched between the rollers and it is possible to prevent the belt from being loosened by the pressing of the cleaning roller against the belt . It is possible to suppress an influence exerted on the circular movement speed of the belt when the cleaning roller is brought into contact with and out of contact from the belt .

While the invention has been described in detail with reference to the specific embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.

For example, in the embodiment described above, the discharging of residual toner from the photosensitive belt cleaning roller to the intermediate transferring belt is performed each time after a period, during which the photosensitive belt is used to bear toner images for one page, is ended. However, the discharging of residual toner from the roller to the belt may be executed in other various manners. For instance, the photosensitive belt cleaning roller drive portion may control the photosensitive belt cleaning roller to contact the photosensitive belt for a period of time, during which the photosensitive belt is used to bear toner images for a plurality of pages, and to control the photosensitive belt cleaning roller to contact the intermediate transferring belt every time after the period is ended.

In this modification, it is possible to reduce a frequency, at which the photosensitive belt cleaning roller is brought into contact with and out of contact with the photosensitive belt . This makes it possible to suppress the occurrence of noise and to decrease the power consumption. It is ensured that no fluctuations will occur in the moving speed of the photosensitive belt . It is possible to suppress the occurrence of color misalignment. More specifically, it is possible to suppress the shifts of positions in the respective color images from one another in the final, multicolor image.

In the embodiment described above, when the photosensitive belt cleaning roller contacts the photosensitive belt , the photosensitive belt cleaning roller is rotationally driven so that a speed difference causing the portion of the photosensitive belt cleaning roller that contacts the photosensitive belt and the portion of the belt that contacts the roller . However, the photosensitive belt cleaning roller may be rotationally driven so that the portion of the photosensitive belt cleaning roller that contacts the photosensitive belt will move at the same speed with the portion of the belt that contacts the roller .

For example, the photosensitive belt cleaning roller may be provided to rotate by following the movement of the photosensitive belt while being in contact with the photosensitive belt . That is, the roller may be provided to rotate due to the friction generated by the contact between the surface of the roller and the surface of the belt . Similarly, the photosensitive belt cleaning roller may rotate by following the movement of the intermediate transferring belt while being in contact with the belt . That is, the roller may rotate due to the friction generated by the contact between the surface of the roller and the surface of the belt .

The mechanism employed to rotate the cleaning roller can be simplified. It is possible to further reduce fluctuations of a load placed on the belt when the cleaning roller is brought into and out of contact with the belt . It is possible to further reduce fluctuations of a load placed on the belt when the cleaning roller is brought into and out of contact with the belt . It is possible to further reduce fluctuations of the moving speed of the belt .

In the embodiment described above, residual toner is discharged from the photosensitive belt cleaning roller to the intermediate transferring belt while a print (output) operation is being executed in the color laser printer . However, the toner discharging timing may be changed. For example, as shown in FIG. 6, the print operation may be temporarily stopped after all the four color images for one page is transferred from the belt to the belt . While the print operation is being stopped, residual toner is discharged from the photosensitive belt cleaning roller to the intermediate transferring belt . In this modification, residual toner may be discharged not only onto the non-image forming area but also onto the image forming area of the intermediate transferring belt . In the case where the residual toner is discharged onto the image forming area, the transferring roller has to be spaced from the intermediate transferring belt when the image forming area of the belt passes between the rollers and It is possible to prevent the residual toner from being transferred from the intermediate transferring belt to the transferring roller .

In the embodiment described above, the cleaning bias applying circuit is supplied with control signals from the CPU Accordingly, the ON/OFF timings of the first and second cleaning bias voltages and the values of the first and second cleaning bias voltages (ON-bias voltages) are controlled by the CPU . However, the cleaning bias applying circuit may be modified in various manners.

For example, the cleaning bias applying circuit may have a simple configuration as shown in FIG. . In this case, the circuit includes a power source B, a power source B, a contact terminal T, and a contact terminal T. The contact terminal T is connected to the power source B and is located at a position so that the contact terminal T is brought into contact with the roller when the roller is in contact with the belt . The power source B is for applying the first cleaning bias voltage that is lower than the potential of the belt by the first potential difference. Accordingly, when the roller is in contact with the belt , the power source B applies the roller with the first cleaning bias voltage to establish the first potential difference between the roller and the belt so as to transfer toner from the belt to the roller .

The contact terminal T is connected to the power source B and is located at another position so that the contact terminal T is brought into contact with the roller when the roller is in contact with the belt . The power source B is for applying the second cleaning bias voltage that is higher than the potential of the belt by the second potential difference. Accordingly, when the roller is in contact with the belt , the power source B applies the roller with the second cleaning bias voltage to establish the second potential difference between the roller and the belt so as to transfer toner from the roller to the belt .

As shown in FIG. 8, the photosensitive belt may be replaced with a photosensitive drum . The photosensitive drum has a photosensitive material layer on its outer peripheral surface, on which an electrostatic latent image is formed by the scanner unit and is developed into a toner image by a corresponding developing cartridge . The photosensitive drum , thus bearing the toner image thereon, rotates around its rotational axis to convey the toner image to the primary transferring position A, at which the toner image is transferred to the belt . In this case, the first auxiliary roller becomes unnecessary.

Similarly, although not shown in the drawings, the intermediate transferring belt may be replaced with an intermediate transferring drum, whose outer peripheral surface can receive toner images from the photosensitive belt or the photosensitive drum . The intermediate transferring drum can convey the toner images to the secondary transferring position D according to its rotation about its rotational axis. In this case, the second auxiliary roller becomes unnecessary.

The embodiment described above relates to the color laser printer . However, the present invention is not limited to the color laser printer, but can be applied to any other types of image forming apparatus so long as the image forming apparatus has a plurality of image bearing bodies.

In the above-described embodiment, the toner is charged positively. Accordingly, the first cleaning bias voltage, applied to the cleaning roller while the roller is in contact with the belt , is lower than the electric potential of the belt . Because the polarity of the roller relative to the belt is negative, the positively-charged toner can be efficiently transferred from the belt to the roller . The second cleaning bias voltage, applied to the roller while the roller is in contact with the belt , is higher than the electric potential of the belt Because the polarity of the belt relative to the roller is negative, the positively-charged toner can be efficiently transferred from the roller to the belt . However, the toner may be formed of material that is charged negatively. In this case, the first cleaning bias voltage should be set higher than the electric potential of the belt . Because the polarity of the roller relative to the belt is positive, the negatively-charged toner can be efficiently transferred from the belt to the roller . The second cleaning bias voltage should be set lower than the electric potential of the belt . Because the polarity of the belt relative to the roller is positive, the negatively-charged toner can be efficiently transferred from the roller to the belt .

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the preferred embodiment taken in connection with the accompanying drawings in which:

FIG. 1 schematically shows the mechanical construction of a color laser printer according to an embodiment of the present invention;

FIG. 2 schematically shows the electric construction of the color laser printer of FIG. 1;

FIG. 3 shows image forming areas and non-image forming areas defined on a photosensitive belt and an intermediate transferring belt;

FIG. 4A shows a state where a photosensitive belt cleaning roller contacts the photosensitive belt;

FIG. 4B shows a state where the photosensitive belt cleaning roller contacts the intermediate transferring belt;

FIG. 5 is a time chart showing an operation in the case where toner is discharged from the photosensitive belt cleaning roller to the intermediate transferring belt while a print operation is being executed;

FIG. 6 is a time chart showing an operation in the case where toner is discharged from the photosensitive belt cleaning roller to the intermediate transferring belt while a print operation is being stopped;

FIG. 7 shows a modification of a cleaning bias applying circuit; and

FIG. 8 schematically shows the mechanical construction of a color laser printer according to a modification.

CLAIMS

1. An image forming apparatus comprising: a first image bearing member that is capable of bearing a toner image on its surface, the first image bearing member moving to convey the toner image from a developing portion to a first transfer position; a second image bearing member that is capable of bearing a toner image on its surface, the second image bearing member receiving the toner image transferred from the first image bearing member at the first transfer position and moving to convey the toner image to a second transfer position; a transfer unit transferring the toner image from the second image bearing member to an image recording medium at the second transfer position; a first cleaning unit removing, from the first image bearing member, residual toner that remains on the first image bearing member after the toner image is transferred to the second image hearing member, the first cleaning unit discharging the removed toner onto the second image bearing member; and a second cleaning unit removing, from the second image bearing member, residual toner that remains on the second image bearing member after the toner image is transferred from the second image bearing member to the image recording medium, the second cleaning unit removing, from the second image bearing member, the toner discharged from the first cleaning unit.

2. An image forming apparatus according to claim 1, wherein the second image bearing member has an image forming area and a non-image forming area on its surface, the second image bearing member receiving the toner image on the image forming area from the first image bearing member, the first cleaning unit discharging the removed toner onto the non-image forming area of the second image bearing member.

3. An image forming apparatus according to claim 1, wherein the residual toner is electrically charged, and wherein the first cleaning unit includes: a cleaning member receiving the residual toner from the first image bearing member; a contact/separation mechanism causing the cleaning member to contact the surface of the first image bearing member while being separated from the second image bearing member and causing the cleaning member to contact the surface of the second image bearing member while being separated from the first image bearing member; and a bias voltage applying unit establishing, when the cleaning member contacts the first image bearing member, a first electric potential difference between the first image bearing member and the cleaning member to transfer the electrically-charged residual toner in a direction from the first image bearing member to the cleaning member, the bias voltage applying unit establishing, when the cleaning member contacts the second image bearing member, a second electric potential difference between the cleaning member and the second image bearing member to transfer the electrically-charged residual toner in a direction from the cleaning member to the second image bearing member.

4. An image forming apparatus according to claim 3, wherein the first image bearing member has a first image forming area and a first non-image forming area on its surface, the second image bearing member having a second image forming area and a second non-image forming area on its surface, the second image bearing member receiving the toner image at the second image forming area from the first image forming area of the first image bearing member at the first transfer position, and wherein the contact/separation mechanism causes the cleaning member to contact the first image forming area of the first image bearing member to thereby allow the cleaning member to receive the residual toner that remains on the first image forming area, the contact/separation mechanism causing the cleaning member to contact the second non-image forming area of the second image bearing member to thereby allow the cleaning member to discharge the received toner onto the second non-image forming area.

5. An image fanning apparatus according to claim 4, wherein the surface of the first image bearing member contacts the surface of the second image bearing member at the first transfer position to transfer the toner image from the first image bearing member to the second image bearing member, wherein the contact/separation mechanism causes the cleaning member to contact the surface of the first image bearing member at a toner-removing position on the first image bearing member and to contact the second image bearing member at a toner-discharging position on the second image bearing member, and wherein a length defined on the first image bearing member from the first transfer position to the toner-removing position is approximately equal to a length defined on the second image bearing member from the first transfer position to the toner-discharging position.

6. An image forming apparatus according to claim 5, wherein the contact/separation mechanism causes the cleaning member to contact the first image bearing member for a predetermined time period, required by the first image bearing member to bear thereon a toner image for a predetermined number of pages, the contact/separation mechanism causing the cleaning member to contact the second image bearing member every time the predetermined period of time is elapsed.

7. An image forming apparatus according to claim 6, wherein the predetermined number is equal to one.

8. An image forming apparatus according to claim 6, wherein the predetermined number is greater than one.

9. An image forming apparatus according to claim 3, wherein the cleaning member is a rotary member that has a central axis and an outer peripheral portion around the central axis and that is capable of rotating about the central axis, and wherein the contact/separation mechanism causes the outer peripheral portion of the rotary member to selectively contact the first image bearing member and the second image bearing member.

10. An image forming apparatus according to claim 9, wherein the outer peripheral portion of the rotary member is made of a resilient material.

11. An image forming apparatus according to claim 9, wherein the rotary member rotates, while the contact/separation mechanism causes the rotary member to contact the first image bearing member, in a direction that causes a portion of the outer peripheral portion of the rotary member and a portion of the surface of the first image bearing member that contact with each other to move in the same direction with each other, wherein the rotary member rotates, while the contact/separation mechanism causes the rotary member to contact the second image bearing member, in another direction that causes a portion of the outer peripheral portion of the rotary member and a portion of the surface of the second image bearing member that contact with each other to move in the same direction with each other.

12. An image forming apparatus according to claim 11, further comprising an image-bearing-member driving unit driving the first image bearing member and the second image bearing member to move; wherein when the contact/separation mechanism causes the rotary member to contact the first image bearing member, the rotary member rotates following the movement of the first image bearing member due to friction generated by the contact between the outer peripheral portion of the rotary member and the surface of the first image bearing member, and wherein when the contact/separation mechanism causes the rotary member to contact the second image bearing member, the rotary member rotates following the movement of the second image bearing member due to friction generated by the contact between the outer peripheral portion of the rotary member and the surface of the second image bearing member.

13. An image forming apparatus according to claim 11, further comprising a rotary-member drive unit driving, when the cleaning member contacts the first image bearing member, the rotary member to rotate at a rotational speed that causes a portion of the outer peripheral portion of the rotary member and a portion of the surface of the first image bearing member that contact with each other to move in the same direction with each other but at different speeds from each other.

14. An image forming apparatus according to claim 3, wherein the first image bearing member includes a first endless belt that is wound around a plurality of first rotational members and that is capable of rotating around the periphery of the plurality of first rotational members, and further comprising a first auxiliary member that is provided at a position to sandwich the first endless belt between the first auxiliary member and the cleaning member when the contact/separation mechanism causes the cleaning member to contact the first endless belt.

15. An image forming apparatus according to claim 3, wherein the second image bearing member includes an endless belt that is wound around a plurality of rotational members and that is capable of rotating around the periphery of the plurality of rotational members, and further comprising an auxiliary member that is provided at a position to sandwich the endless belt between the auxiliary member and the cleaning member when the contact/separation mechanism causes the cleaning member to contact the endless belt.

16. An image forming apparatus according to claim 1, wherein the first image bearing member includes a photosensitive material on its surface, further comprising: a latent image forming unit that is capable of forming a plurality of latent images for a plurality of different colors on the surface of the first image bearing member; and a plurality of developing units storing toner of the plurality of different colors and developing the plurality of latent images by using the toner into a plurality of toner images of the plurality of colors, wherein the second image bearing member receiving the plurality of toner images at the same position on its surface, the plurality of toner images being superimposed one on another on the surface of the second image bearing member, thereby forming a final multicolor toner image, and wherein the transfer unit transfers the final multicolor toner image onto the image recording medium.

17. An image forming apparatus according to claim 16, wherein the second image bearing member includes an intermediate transfer endless belt that is wound around a plurality of rotational members and that is capable of rotating around the periphery of the plurality of rotational members.

18. An image forming apparatus according to claim 16, wherein the first image bearing member includes a photosensitive endless belt that is wound around a plurality of first rotational members, that has a photosensitive layer on its outer surface, and that is capable of rotating around the periphery of the plurality of first rotational members.

19. An image forming apparatus according to claim 16, wherein the first image bearing member includes a photosensitive drum that is capable of rotating around its rotational axis, and that has a photosensitive layer on its outer peripheral surface.

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