HK1058555B - Image forming apparatus - Google Patents

Description

Image forming apparatus

Technical Field

The present invention relates to an image forming apparatus including a plurality of image carriers.

Background

As an example of such an image forming apparatus, there is conventionally known an image forming apparatus including: a photosensitive member, a plurality of developing devices, and an intermediate transfer member. The plurality of developing devices respectively accommodate toners of a plurality of colors. Each developing device includes a developing roller. The photosensitive member (image bearing body) bears a plurality of visible images having respective colors, which are visualized by toner supplied from a plurality of developing rollers. A plurality of visible images having respective colors are transferred to an intermediate transfer member (another image carrier), and are superimposed on one another on the intermediate transfer member. In this manner, the intermediate transfer member carries a composite multicolor image. The multicolor image is then transferred from the intermediate transfer member to the paper. Typical examples of the photosensitive member include a photosensitive drum and a photosensitive belt.

A cleaning device is generally provided in such a color laser printer. After the plurality of visible images are transferred from the photosensitive member onto the intermediate transfer member, the cleaning device removes residual toner remaining on the photosensitive member from the photosensitive member. An auxiliary cleaning device is provided for removing residual toner remaining on an intermediate transfer member from the intermediate transfer member after a color image is transferred from the intermediate transfer member to a sheet.

In one example, a photosensitive member cleaning roller is provided to contact the surface of the photosensitive member. The waste toner captured by the surface of the photosensitive-member cleaning roller is accumulated in a waste-toner storage portion disposed in the vicinity of the photosensitive-member cleaning roller. An intermediate transfer member cleaning roller is additionally provided to contact the surface of the intermediate transfer member. The waste toner captured by the surface of the intermediate transfer member cleaning roller is accumulated in another waste toner storage portion provided in the vicinity of the intermediate transfer member cleaning roller.

In this way, two waste toner cartridges are set in the color laser printer. In this case, however, it is difficult to reduce the size of the entire apparatus. Troublesome maintenance work such as discharging toner accumulated in two different waste toner cartridges needs to be performed.

In view of these problems, a method for first returning toner captured by the surface of the photosensitive member cleaning roller to the photosensitive member at a time other than during the photosensitive member performing the image forming operation has been proposed. Then, the waste toner is transferred from the photosensitive member to the intermediate transfer member. Subsequently, the waste toner present on the intermediate transfer member is captured by the intermediate transfer member cleaning roller and collected in a waste toner storage portion disposed in the vicinity of the intermediate transfer member cleaning roller. With this method, the waste toner can be collected at one place. It becomes relatively easy to reduce the size of the apparatus. The maintenance work becomes simpler.

Disclosure of Invention

With the above-described conventional method, the toner captured by the photosensitive-member cleaning roller is conveyed to the waste-toner storing portion by the photosensitive member and the intermediate transfer member. Therefore, the photosensitive member may be contaminated by the waste toner.

In addition, the ratio of toner transfer from the photosensitive member to the intermediate transfer member is not always 100%. In other words, the entire amount of toner on the photosensitive member cannot be completely transferred from the photosensitive member to the intermediate transfer member. Therefore, the waste toner cannot be collected with high recovery efficiency.

In view of the above-described drawbacks, it is an object of the present invention to provide an improved image forming apparatus which includes a plurality of image bearing bodies and can efficiently collect residual toner remaining on the plurality of image bearing bodies in a single common area.

To achieve the above and other objects, the present invention provides an image forming apparatus comprising: a first image bearing member capable of bearing a toner image on a surface thereof, the first image bearing member being moved to convey the toner image from a developing portion to a first transfer portion; a second image bearing member capable of bearing the toner image on a surface thereof, the second image bearing member receiving the toner image transferred from the first image bearing member at a first transfer position and moving to convey the toner image to a second transfer position; a transfer unit that transfers the toner image from the second image bearing member to an image recording medium at a second transfer position; a first cleaning unit that removes residual toner remaining on the first image bearing member from the first image bearing member after the toner image is transferred to the second image bearing member, the first cleaning unit releasing the removed toner onto the second image bearing member; and a second cleaning unit that removes residual toner remaining on the second image bearing member from 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 the toner discharged from the first cleaning unit from the second image bearing member.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments when taken in conjunction with the accompanying drawings, in which:

fig. 1 schematically shows a mechanical configuration of a color laser printer of one embodiment of the present invention;

fig. 2 schematically shows an electrical configuration of the color laser printer of fig. 1;

FIG. 3 illustrates image forming areas and non-image forming areas formed on a photoreceptor belt and an intermediate transfer belt;

fig. 4A illustrates a state in which the photosensitive belt cleaning roller contacts the photosensitive belt;

fig. 4B illustrates a state in which the photosensitive-belt cleaning roller contacts the intermediate transfer belt;

fig. 5 is a timing chart showing an operation in a case where toner is discharged from the photosensitive belt cleaning roller to the intermediate transfer belt when a printing operation is performed;

fig. 6 is a timing chart showing an operation in a case where toner is discharged from the photosensitive belt cleaning roller to the intermediate transfer belt when the printing operation is stopped;

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

fig. 8 schematically shows a mechanical configuration of a modified color laser printer.

Detailed Description

An image forming apparatus according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings, in which like reference numerals refer to like parts and components to avoid redundancy.

Fig. 1 schematically shows a mechanical configuration of a color laser printer 1 (image forming apparatus) of an embodiment of the present invention.

As shown in fig. 1, the color laser printer 1 has a main casing 2. In the main casing 2, a sheet supply section 4 and an image forming section 5 are provided.

The paper feed section 4 is for feeding a sheet of paper 3 (image recording medium). The sheet feeding section 4 includes: a sheet feed tray 6, a feed roller 7, delivery rollers 8, and registration rollers 9. The sheet feed tray 6 holds a stack of sheets 3. The rotating feed roller 7 can pull one sheet 3 at a time from the top of the stack. The sheet is then conveyed to the image forming section 5 by the conveying roller 8 and the registration roller 9.

The image forming section 5 is used to form a desired image on the sheet 3. The image forming section 5 includes: a scanner unit 10, a processing section 11, an intermediate transfer belt mechanism section 12, a transfer roller 13, and a fixing section 14. The processing unit 11 includes: four developing cartridges 15(15Y, 15M, 15C, and 15K), a photoreceptor belt mechanism section 16, and a scorotron 17.

The scanner unit 10 is used to form a latent image on a photosensitive belt 22 (described later) provided in the photosensitive-belt mechanism section 16. The scanner unit 10 is disposed in a central portion of the main casing 2. The scanner unit 10 includes: a laser emitting part, a polygonal prism, a plurality of lenses, and a plurality of reflecting mirrors (not shown). In the scanner unit 10, a laser emitting portion emits a modulated laser beam based on image data. The laser beam passes through the lens, is reflected by the polygon prism, and is reflected by the mirror, whereby high-speed scanning of the surface of the photosensitive belt 22 is performed.

Four developing cartridges 15 are provided at the rear side of the main casing 2. The four developing cartridges 15 are: a yellow developing cartridge 15Y for supplying yellow toner, a magenta developing cartridge 15M for supplying magenta toner, a cyan developing cartridge 15C for supplying cyan toner, and a black developing cartridge 15K for supplying black toner. These developing cartridges 15 are vertically aligned and spaced apart from each other by a predetermined distance.

Each of the developing cartridges 15 includes a developing roller 18 (although not shown), a layer thickness regulating blade, a sheet supply roller, and a toner holding portion. A developing cartridge driving section 57 (shown in fig. 2) moves the developing cartridges 15Y, 15M, 15C, and 15K horizontally to selectively bring the developing rollers 18 of the developing cartridges 15Y, 15M, 15C, and 15K into and out of contact with the surface of the photosensitive belt 22.

As shown in fig. 2, the developing cartridge driving section 57 operates according to a control signal supplied from the CPU 51. The developing cartridge driving section 57 includes a motor and a clutch mechanism (not shown in the drawings). The yellow developing cartridge 15Y, the magenta developing cartridge 15M, the cyan developing cartridge 15C, and the black developing cartridge 15K are connected to the developing cartridge driving portion 57. Each of the developing cartridges 15(15Y, 15M, 15C, and 15K) is switchably moved between a developing position and a standby position by a motor and clutch mechanism. At the developing position, the developing cartridge 15 contacts or approaches the photosensitive belt 22, and development is performed using the toner held in the developing cartridge 15. At the standby position, the developing cartridge 15 is spaced from the photosensitive belt 22 and is in a standby state.

Each of the developing cartridges 15Y, 15M, 15C, and 15K operates in substantially the same manner. That is, the toner holding portion holds nonmagnetic toner (developer) polymerized from a single component, which has one color of yellow, magenta, cyan, and black. The toner has a positive charge characteristic. The rotary feed roller supplies the toner contained in the toner holding portion to the developing roller 18, and the layer thickness regulating blade regulates the thickness of the toner on the developing roller. At the same time, the toner is positively charged due to friction between the toner and the developing roller 18 and the layer thickness regulating blade. Thus, a thin layer of toner having a predetermined thickness is borne on the developing roller 18 by electrostatic force.

The photosensitive belt mechanism portion 16 is located in front of the four developing cartridges 15, facing the four developing cartridges 15. The photosensitive belt mechanism portion 16 includes: a first photosensitive belt roller 19, a second photosensitive belt roller 20, a third photosensitive belt roller 21, and a photosensitive belt 22.

The first photosensitive belt roller 19 is disposed to substantially face the black developing cartridge 15K at the lowest position of the developing cartridge stack. The second photosensitive belt roller 20 is disposed vertically above the first photosensitive belt roller 19, substantially facing the yellow developing cartridge 15Y at the uppermost position of the developing cartridge stack. The third photosensitive belt roller 21 is located obliquely above the first photosensitive belt roller 19 and obliquely below the second photosensitive belt roller 20. In this way, the photosensitive belt rollers 19 to 21 are arranged in a triangular arrangement.

The photosensitive belt 22 (first image carrier) is an endless belt. The endless belt 22 is made of resin, such as polyethylene terephthalate (PET), and has vapor-deposited aluminum on its outer surface. An organic photosensitive layer is arranged on the outer surface of the aluminum deposition layer.

The photosensitive belt 22 is wound around the photosensitive belt rollers 19, 20 to 21. That is, the photosensitive belt 22 is mounted such that the inner side surface of the endless belt 22 contacts the outer peripheral surfaces of the photosensitive belt rollers 19 to 21.

As shown in fig. 2, a main driving portion 55 is operated according to a control signal supplied from the CPU 51. The main drive portion 55 is provided with a main motor (not shown). The second photosensitive belt roller 20 is connected to the main motor through a series of gears (not shown in the figure). The rollers 19 and 21 are connected to the roller 20 by an endless belt 22. Therefore, when the main driving portion 55 drives the main motor to rotate the second photosensitive belt roller 20 in the counterclockwise direction in fig. 1, the first photosensitive belt roller 19 and the third photosensitive belt roller 21 rotate in the counterclockwise direction following the rotational driving, and the photosensitive belt 22 rotates in the counterclockwise direction around the photosensitive belt rollers 19 to 21.

It should be noted that several other parts are connected to the main motor. Typical examples of several parts include: a first intermediate transfer belt roller 23 (described later) in the intermediate transfer belt mechanism portion 12; a driving portion (not shown) for driving the sheet feeding roller 7; a driving portion for driving the transfer roller 13; a driving section (not shown) for driving an intermediate transfer belt cleaning unit 36 (described later).

Although not shown in the drawings, the photosensitive belt 22 is formed with a sensing opening at one end in the lateral direction of the belt 22. The sensor opening has a substantially rectangular shape, and is formed by the photosensitive belt 22 in the thickness direction thereof so as to be open on the inner and outer side surfaces. The sensing opening is detected by a home sensor 39 (fig. 2).

Although not shown in fig. 1, the origin sensor 39 is disposed to face the photosensitive belt 22 at a position between the second photosensitive belt roller 20 and the third photosensitive belt roller 21. The origin sensor 39 includes a light emitting portion and a light receiving portion which are disposed to face each other with the photosensitive belt 22 therebetween. When the sensing opening is opposed to the origin sensor 39 due to the movement of the photosensitive belt 22, the origin sensor 39 sends a detection signal to the CPU51, and the light receiving portion receives light from the light emitting portion. As for the timing when the origin sensor 39 detects the sensing opening, as shown in fig. 3, an image forming region and a non-image forming region are formed on the outer side surface of the photosensitive belt 22. On the image forming area, the scanner unit 10 will form an electrostatic latent image for one color component, which will then be visualized as a toner image by the toner supplied from the corresponding developing cartridge 15. On the non-image forming area, an electrostatic latent image is not formed or a toner image is not visualized.

The scorotron 17 includes a charging wire, for example made of tungsten, which generates a corona discharge to charge the surface of the photoreceptor belt 22 with a uniform positive charge. The scorotron 17 is located below the photosensitive belt mechanism portion 16 at a position between the third photosensitive belt roller 21 and the first photosensitive belt roller 19, and is separated from the photosensitive belt 22 by a predetermined distance.

It should be noted that the scorotron 17 charges the surface of the photoreceptor belt 22 as a pre-treatment to the exposure process operation of the scanner unit 10.

The intermediate transfer belt mechanism portion 12 is located in front of the photosensitive belt mechanism portion 16, and includes a first intermediate transfer belt roller 23, a second intermediate transfer belt roller 24, a third intermediate transfer belt roller 25, and an intermediate transfer belt 26.

The first intermediate transfer belt roller 23 is disposed to substantially face the second photosensitive belt roller 20 via the photosensitive belt 22 and the intermediate transfer belt 26. The second intermediate transfer belt roller 24 is located in front of and below the first intermediate transfer belt roller 23. The third intermediate transfer belt roller 25 is located above the second intermediate transfer belt roller 24 and below and in front of the first intermediate transfer belt roller 23.

The intermediate transfer belt 26 (second image carrier) is an endless belt made of a conductive resin, such as polyamide or polycarbonate, in which conductive particles such as carbon are dispersed. The intermediate transfer belt 26 is wound around the transfer belt rollers 23 to 25.

As has been described, the first intermediate transfer belt roller 23 is connected to a main motor (not shown in the figure) in the main driving portion 55 through another series of gears (not shown in the figure). The rollers 24 and 25 are connected to the roller 23 by an endless belt 26. Therefore, when the main driving portion 55 (fig. 2) drives the main motor to rotate the first intermediate transfer belt roller 23 in the clockwise direction of fig. 1, the second intermediate transfer belt roller 24 and the third intermediate transfer belt roller 25 rotate in the clockwise direction following the rotational driving, and the belt 26 rotates in the clockwise direction around the rollers 23 to 25.

It should be noted that the main driving portion 55 (fig. 2) drives the main motor to rotate the second photosensitive belt roller 20 and rotate the first intermediate transfer belt roller 23 at the same peripheral speed, so that the photosensitive belt 22 and the intermediate transfer belt 26 move at the same speed.

The outer side surface of the intermediate transfer belt 26 and the outer side surface of the photosensitive belt 22 contact each other at a primary transfer position a as shown in fig. 1, and move at the same speed at the contact portion. Thus, as shown in fig. 3, an image forming area and a non-image forming area are formed on the outer surface of the intermediate transfer belt 26 corresponding to the image forming area and the non-image forming area formed on the outer surface of the photosensitive belt 22. The toner image is transferred from the image forming area of the belt 22 onto the image forming area of the transfer belt 26. No toner image is formed on the non-image forming area.

The transfer roller 13 is for performing a transfer operation to transfer the toner image on the image forming area of the intermediate transfer belt 26 onto the sheet 3. The transfer roller 13 faces the second intermediate transfer belt roller 24 with the intermediate transfer belt 26 therebetween. The transfer roller 13 moves between a primary transfer position D and a standby position. At the transfer position D, the transfer roller 13 is in contact with the outer side surface of the belt 26. In the standby position, the transfer roller 13 is spaced from the belt 26. To transfer the toner image from the belt 26 onto the sheet 3, the transfer roller 13 is moved from the standby position to the transfer position D. Thus, the transfer roller 13 contacts the intermediate transfer belt 26. When the sheet 3 reaches the position between the transfer roller 13 and the intermediate transfer belt 26, the transfer roller 13 is applied with a predetermined secondary transfer bias so as to establish a predetermined potential difference between the transfer roller 13 and the intermediate transfer belt 26. Thus, the toner image formed on the intermediate transfer belt 26 is transferred onto the sheet 3 passing between the intermediate transfer belt 26 and the transfer roller 13.

It should be noted that the color image may be transferred from the belt 26 to the sheet 3 by various methods other than the roller 13.

With the above configuration, the color laser printer 1 performs an image forming operation as described below.

The surface of the photosensitive belt 22 is uniformly charged with positive charges by the scorotron 17 before exposure by high-speed scanning of a laser beam emitted from the scanner unit 10 and modulated according to image data for monochrome. In this way, an electrostatic latent image is formed in the image forming region based on the image data. One developing cartridge 15 holding the toner of the corresponding color is moved to the developing position while the remaining three developing cartridges 15 are still in the standby position. The image forming area of the photosensitive belt 22, on which the electrostatic latent image is currently formed, contacts the developing roller 18 in the corresponding developing cartridge 15. Accordingly, the toner of the corresponding color is transferred from the developing cartridge 15 to the image forming area of the photosensitive belt 22. In this way, the electrostatic latent images are visualized as visible toner images of the respective colors.

When the image-forming area of the belt 22 on which the toner image is formed reaches the primary transfer position a, the image-forming area of the belt 26 also reaches the transfer position a. Thus, the image forming area of the belt 26 contacts the image forming area of the belt 22. When the image forming areas of the belts 22 and 26 reach the primary transfer position a, a predetermined primary transfer bias is applied to the intermediate transfer belt 26. More specifically, although not shown in the drawings, a brush-type or roller-type electrode is provided at a position near the roller 23 for applying a primary transfer bias to the belt 26. The primary transfer bias establishes a potential difference between the belts 22 and 26 to cause the positively charged toner image to be transferred from the photoreceptor belt 22 to the intermediate transfer belt 26. Such a transfer operation is hereinafter referred to as "primary transfer". In this way, the visible image of the single color is transferred to the image forming area of the intermediate transfer belt 26. It should be noted that the primary transfer voltage may be applied to the roller 23 instead of the belt 26.

The photosensitive belt 22 is further rotated and cleaned by a photosensitive belt cleaning roller 35 to be described later. After being discharged by a known discharger (not shown), the photoreceptor belt 22 is charged again by the charger 17. Subsequently, an electrostatic latent image for the next color component is formed and visualized by the next developing device 15. The visible image is then transferred to the image forming area of the belt 26 at position a. Thereby, the visible image is superimposed on the visible image previously transferred onto the intermediate transfer belt 26. By repeating this process for four colors, a final multicolor image is formed on the intermediate transfer belt 26. It should be noted that the potential of the photosensitive belt 22 varies at positions where the photosensitive belt 22 is subjected to the charging process, the developing process, and the primary transfer process.

Even as the image forming area of the belt 26 passes between the rollers 13 and 24, the transfer roller 13 continues to be on standby until the multicolor image is finally formed on the belt 26. After the final multicolor image is formed in the image forming area of the belt 26, the roller 13 is moved to the secondary transfer position D. When the image forming area of the belt 26 and the paper pass between the rollers 13 and 24, the roller 13 is applied with a predetermined secondary transfer bias. Thereby, a multicolor image is transferred onto the sheet 3. It should be noted that the potential of the belt 26 varies at positions where the belt 26 is subjected to a primary transfer process, a secondary transfer process, and a cleaning process (to be described later) by the intermediate transfer belt cleaning unit 36.

The fixing section 14 is located in front of the intermediate transfer belt mechanism section 12 and at a position downstream of the secondary transfer position D in the sheet conveying direction. The fixing section 15 includes a heat roll 27, a pressure roll 28, and a pair of conveying rolls 29. The hot roller 27 has an inner metal layer and an outer silicone rubber layer. Although not shown in the drawing, a halogen lamp is installed in the heat roller 27. Halogen lamps are used to heat the metal and silicone rubber layers. The pressure roller 28 presses against the heat roller 27. A pair of conveying rollers 29 is located downstream of the heat roller 27 and the pressure roller 28 in the conveying direction of the sheet 3.

When the transfer roller 13 transfers the multicolor image onto the sheet 3, the sheet 3 passes between the heat roller 27 and the pressure roller 28 so that the multicolor image is thermally fixed on the sheet 3.

The sheet 3 having the multicolor image thermally fixed is then conveyed toward a pair of sheet discharging rollers 30 by the conveying rollers 29, and further conveyed onto a sheet discharging tray 31 formed in the upper portion of the main casing 2 by the sheet discharging rollers 30.

According to the present embodiment, the photoreceptor belt cleaning roller 35 is provided to collect residual toner remaining on the surface of the photoreceptor belt 22 after the toner image is transferred from the photoreceptor belt 22 onto the intermediate transfer belt 26.

The photosensitive belt cleaning roller 35 is used to perform a cleaning operation of the surface of the photosensitive belt 22. The photosensitive-belt cleaning roller 35 is disposed on the side opposite to the developing cartridge 15 with respect to the photosensitive-belt mechanism section 16. The photosensitive belt cleaning roller 35 is located at a position between the second and third photosensitive belt rollers 20 and 21 and is adjacent to the third photosensitive belt roller 21.

The photosensitive-belt cleaning roller 35 is a rotary member having a roller shaft and an outer peripheral portion disposed around the roller shaft. The outer peripheral portion is made of an elastic material that can capture toner, such as silicone rubber.

The photosensitive belt cleaning roller 35 is rotatably supported in the main casing 2. The photoreceptor belt cleaning roller 35 is movable to contact and separate from the photoreceptor belt 22 and the intermediate transfer belt 26. More specifically, the photosensitive belt cleaning roller 35 is movable between a first position shown in fig. 4A and a second position shown in fig. 4B. When roller 35 is in the first position, the outer peripheral portion of roller 35 contacts photoreceptor belt 22 at a contact position B. When the roller 35 is located at the second position, the outer peripheral portion of the roller 35 contacts the intermediate transfer belt 26 at a contact position C. In this manner, the roller 35 contacts a selected one of the belts 22 and 35.

The photosensitive-belt cleaning-roller driving section 56 is provided as shown in fig. 2 to drive the photosensitive-belt cleaning roller 35 to rotate and move the photosensitive-belt cleaning roller 35 between the first position of fig. 4A and the second position of fig. 4B. The photosensitive-belt cleaning-roller driving section 56 is operated in accordance with a control signal supplied from the CPU 51. Although not shown in the drawings, the photosensitive belt cleaning roller driving portion 56 includes a cam mechanism and a cleaning roller driving motor. The cam mechanism is used to move the photosensitive belt cleaning roller 35 in any one of the first and second positions of fig. 4A and 4B. The cleaning roller drive motor is used to apply a driving force to the roller shaft of the roller 35 and the cam mechanism.

In the present embodiment, as shown in fig. 1, a conversion member 351 is provided in the main casing 2 so as to be rockable by a cam mechanism. The cleaning roller driving motor is fixed to a free end portion of the conversion member 351. The cleaning roller 35 is connected to an output shaft of the cleaning roller driving motor while being electrically insulated therefrom. In this way, the roller 35 is mounted on the free end portion of the conversion member 351 together with the cleaning roller driving motor. The rocking of the switching member 351 can move the cleaning roller 35 between the first and second positions shown in fig. 4A and 4B. Thus, the cleaning roller 35 contacts a selected one of the belts 22 and 26 while being separated from the unselected belt.

It should be noted that, according to the present embodiment, the contact/separation mechanism for bringing the roller 35 into and out of contact with the tapes 22 and 26 employs the conversion member 351. However, other various configurations may be adopted as the contact/separation mechanism.

As shown in fig. 2, a cleaning bias applying circuit 53 is provided to apply first and second cleaning biases to the cleaning roller 35. When the cleaning roller 35 contacts the photosensitive belt 22, the cleaning bias applying circuit 53 applies a first cleaning bias to the roller 35, the first cleaning bias being lower than the potential of the belt 22 at the contact position B by a first potential difference. Accordingly, a first potential difference is established between the cleaning roller 35 and the belt 22 to cause the positively charged toner to be attracted from the photosensitive belt 22 to the roller 35 in one direction by the electrostatic force.

As shown in fig. 4A, when the cleaning roller 35 contacts the photosensitive belt 22, the cleaning roller driving section 56 drives the cleaning roller 35 to rotate in the clockwise direction in fig. 4A, and the cleaning bias applying circuit 53 applies a first cleaning bias to the roller 35 to transfer residual toner remaining on the photosensitive belt 22 onto the cleaning roller 35. Since the roller 35 rotates in the clockwise direction, the portion of the cleaning roller 35 contacting the tape 22 moves in the same direction as the portion of the tape 22 contacting the cleaning roller 35.

When the cleaning roller 35 contacts the photosensitive belt 22, the photosensitive-belt cleaning-roller driving section 56 drives the roller 35 to rotate at a speed different from that of the belt 22. In this manner, according to the present embodiment, the photosensitive-belt cleaning-roller driving section 56 applies a rotational driving force to the cleaning roller 35 to move the portion of the roller 35 contacting the belt 22 at a different speed from the portion of the belt 22 contacting the roller 35. Thus, a speed difference occurs between the contact portions of the belt 22 and the roller 35. The roller 35 can perform cleaning of the photosensitive belt 22 even without occurrence of a speed difference. However, the formation of the speed difference applies an external force to the residual toner on the photosensitive belt 22. The external force increases the cleaning action of the cleaning bias. It should be noted that the roller 35 may rotate faster than the belt 22. Or conversely, the roller 35 may rotate slower than the belt 22.

A first auxiliary roller 45 is disposed at a position such that the roller 45 faces the photosensitive belt cleaning roller 35 with the photosensitive belt 22 therebetween. When the cleaning roller 35 contacts the tape 22, the tape 22 is sandwiched between the rollers 35 and 45. The first auxiliary roller 45 has a roller shaft covered with a roller portion. The roll shaft is made of metal. The roller portion has a hardness substantially equal to or less than that of the cleaning roller 35. For example, the roller portion is made of foam rubber such as urethane foam rubber. The first auxiliary roller 45 is located at a position where the roller 45 can press the photosensitive belt 22 from the side opposite to the cleaning roller 35 when the cleaning roller 35 contacts the photosensitive belt 22. That is, as shown in fig. 4A, when the cleaning roller 35 contacts the photosensitive belt 22, the cleaning roller 35 presses the belt 22 rightward, and the first auxiliary roller 45 presses the belt 22 leftward.

If the auxiliary roller 45 is not provided, the pressing of the cleaning roller 35 may elongate the tape 22, and the elongate tape 22 may become loose. However, according to the present embodiment, when the roller 35 contacts the tape 22, the tape 22 is sandwiched between the rollers 35 and 45. Thus, the rollers 35 and 45 press the tape 22 in opposite directions. Preventing the strap 22 from becoming longer or loose. Ensuring that the strap remains properly tensioned.

When the cleaning roller 35 contacts the intermediate transfer belt 26, the cleaning bias applying circuit 53 applies a second cleaning bias, which is higher than the potential of the belt 26 at the contact position C by a second potential difference, to the roller 35. Accordingly, a second potential difference is established between the cleaning roller 35 and the belt 26, so that the positively charged toner is attracted from the roller 35 to the belt 26 in one direction by the electrostatic force.

As shown in fig. 4B, when the cleaning roller 35 contacts the intermediate transfer belt 26, the cleaning roller driving section 56 drives the cleaning roller 35 to rotate in the counterclockwise direction in fig. 4B, and the cleaning bias applying circuit 53 applies a second cleaning bias to the roller 35 to transfer residual toner remaining on the cleaning roller 35 onto the belt 26. Since the roller 35 rotates in the counterclockwise direction, the portion of the cleaning roller 35 contacting the tape 26 moves in the same direction as the portion of the tape 26 contacting the cleaning roller 35.

A second auxiliary roller 46 is disposed at a position such that the roller 46 faces the photoreceptor belt cleaning roller 35 with the intermediate transfer belt 26 therebetween. When the cleaning roller 35 contacts the tape 26, the tape 26 is sandwiched between the rollers 35 and 46. The second auxiliary roller 46 has the same configuration as the first auxiliary roller 45. The second auxiliary roller 46 is located at a position where the roller 46 can press the tape 26 from the side opposite to the cleaning roller 35 when the cleaning roller 35 contacts the tape 26. Thus, when roller 35 contacts tape 26, tape 26 is sandwiched between rollers 35 and 46, and rollers 35 and 46 press tape 26 in the opposite direction. In this manner, the strap 26 is prevented from becoming longer or loose in the same manner as the strap 22.

As shown in fig. 4A and 4B, the length of the photosensitive belt 22 from the transfer position a to the contact position B is substantially equal to the length of the intermediate transfer belt 26 from the transfer position a to the contact position C.

As shown in fig. 1, after the multicolor toner image is transferred onto the sheet 3, an intermediate transfer belt cleaning unit 36 is provided to collect residual toner remaining on the surface of the intermediate transfer belt 26.

The intermediate transfer belt cleaning device 36 is used to clean the intermediate transfer belt 26. An intermediate transfer belt cleaning device 36 is located in front of the intermediate transfer mechanism portion 12, and faces the third intermediate transfer belt roller 25 via the intermediate transfer belt 26.

The intermediate transfer belt cleaning unit 36 includes: an intermediate transfer belt cleaning cartridge 37, an intermediate transfer belt cleaning roller 38, a secondary intermediate transfer belt cleaning roller 38a, and an intermediate transfer belt cleaning blade 38 b.

The intermediate transfer belt cleaning cartridge 37 has a box shape formed with an opening on the side facing the intermediate transfer belt 26. The space at the bottom of the intermediate transfer belt cleaning cartridge 61 forms a waste toner accumulating portion for accumulating the toner scraped off by the intermediate transfer belt cleaning blade 38 b.

The intermediate transfer belt cleaning roller 38 includes a metal core covered with an outer peripheral portion made of an elastic material (e.g., silicone rubber). The intermediate transfer belt cleaning roller 38 is rotatably supported at the opening of the intermediate transfer belt cleaning cartridge 27 at a position facing the third intermediate transfer belt roller 25. The intermediate transfer belt cleaning roller 38 is driven by a predetermined driving portion (not shown in the figure) so as to move between a position where the roller 38 contacts the belt 26 and another position where the roller 38 does not contact the belt 26. When the roller 38 contacts the tape 26, the outer peripheral portion of the roller 38 contacts the surface of the tape 26 on the side thereof opposite to the side where the roller 25 contacts the tape 26. The secondary intermediate transfer belt cleaning roller 38a is a metal roller. The intermediate transfer belt cleaning blade 38b is made of an elastic material such as urethane.

The intermediate transfer belt cleaning roller 38 is spaced a predetermined distance from the intermediate transfer belt 26 until a multicolor image (superimposed by four color toner images) is finally formed on the intermediate transfer belt 26. The intermediate transfer belt cleaning roller 38 is in contact with the intermediate transfer belt 26 when the final multicolor image is formed on the intermediate transfer belt 26 and transferred from the belt 26 to the sheet 3. Another cleaning bias is applied to the intermediate transfer belt cleaning roller 38 so as to establish a potential difference between the belt 26 and the roller 38, so that the positively charged residual toner is attracted from the belt 26 to the cleaning roller 38 in one direction by the electrostatic force.

After the multicolor image is transferred onto the sheet 3, the residual toner remaining on the intermediate transfer belt 26 is conveyed according to the rotation of the intermediate transfer belt 26. When the remaining toner reaches the position where the toner faces the cleaning roller 38, the toner is removed by the cleaning roller 38. The removed toner is conveyed to a position where the toner faces the cleaning roller 38a in accordance with the rotation of the intermediate transfer belt cleaning roller 38. The toner is then captured by the cleaning roller 38 a. Thereafter, the toner captured by the cleaning roller 38a is scraped off by the intermediate transfer belt cleaning blade 38b and accumulated in the waste toner accumulation portion.

As shown in fig. 2, the origin sensor 39, the main driving portion 55, the photosensitive-belt cleaning-roller driving portion 56, the cleaning bias applying circuit 53, and the developing-cartridge driving portion 57 are connected to the CPU 51.

The CPU51 includes a RAM 58 and a ROM 59. The CPU51 is used to control the entire portion of the color laser printer 1. The RAM 58 is used to temporarily store image data. The ROM 59 previously stored: a control program for controlling the cleaning bias applying circuit 53, the main control section 55, the developing cartridge driving section 57, and other control programs.

The cleaning bias applying circuit 53 is for generating first and second cleaning biases. The roller shaft of the photosensitive-belt cleaning roller 35 is electrically connected to a cleaning bias applying circuit 53. The cleaning bias applying circuit 53 applies first and second biases to the photosensitive-belt cleaning roller 35 through the roller shaft. The on/off timing of the first and second biases and the values of the first and second biases (on-biases) are controlled by a control signal supplied from the CPU51 to the cleaning bias applying circuit 53.

When the photosensitive-belt cleaning roller 35 contacts the photosensitive belt 22 at the position B shown in fig. 4A, the cleaning bias applying circuit 53 applies a first cleaning bias to the roller 35, the first cleaning bias establishing a first potential difference between the roller 35 and the belt 22, the potential of the roller 35 being lower than the potential of the belt 22. In this manner, a bias is applied between the roller 35 and the belt 22 in a direction in which positively charged toner will be transferred from the belt 22 to the roller 35.

When the photosensitive-belt cleaning roller 35 contacts the intermediate transfer belt 26 at the position C shown in fig. 4B, the cleaning bias applying circuit 53 applies a second cleaning bias to the roller 35, the second cleaning bias establishing a second potential difference between the roller 35 and the belt 26, the potential of the roller 35 being higher than the potential of the belt 26. In this way, a bias is applied between the roller 35 and the belt 26 in one direction, in which the positively charged toner is transferred from the roller 35 to the belt 26.

When the toner image of each color is formed on the photosensitive belt 22, the roller 35 is at the first contact position B. After the toner image of one color formed on the image forming area of the belt 22 is transferred to the belt 26 at the transfer position a, the residual toner remaining on the image forming area is conveyed to the position B of the toner facing roller 35 in accordance with the movement of the belt 22. At position B, the remaining toner is transferred from the belt 22 onto the roller 35.

After all the four color toner images are transferred from the belt 22 to the belt 26 and the remaining toners thereof are captured by the roller 35, the roller 35 is moved from the first position of fig. 4A to the second position of fig. 4B, in which the roller 35 is in contact with the belt 26 at the contact position C. More specifically, after the image-forming area of the belt 22 on which the toner image of the fourth color is formed passes between the rollers 20 and 23, the image-forming area of the belt 22 on which the residual toner remains passes between the rollers 35 and 45. When the image-forming area of the belt 22 passes completely between the rollers 35 and 45 and the leading edge of the non-image-forming area of the belt 22 reaches position B between the rollers 35 and 45, the roller 35 moves from the first position of fig. 4A to the second position of fig. 4B. Thus, the roller 35, which has all the remaining toners of four colors carried thereon at present, comes into contact with the tape 26 at the contact position C. At this time, since the length of the belt 22 between the positions a and B is substantially equal to the length of the belt 26 between the positions a and C, and since the belts 22 and 26 move at the same speed, the leading edge of the non-image forming region of the belt 26 reaches the position C. Therefore, the remaining toners of the four colors presently loaded on the roller 35 are properly transferred to the non-image forming area of the belt 26. Roller 35 dwells at the second position of fig. 4B for a moment and returns to the first position of fig. 4A before the image forming area of belt 26 reaches a position between rollers 35 and 46. In this way, the residual toner of all colors that has been temporarily captured on the roller 35 can be discharged to the non-image forming area of the belt 26.

In the color laser printer 1 having the above-described configuration, a multicolor image is formed on the sheet 3 in the manner shown in fig. 5.

First, an electrostatic latent image for a yellow component is formed on the photosensitive belt 22 by the scanner unit 10. The yellow developing cartridge 15Y is moved forward in the horizontal direction by the developing cartridge driving portion 57, whereby the developing roller 18 of the yellow developing cartridge 15Y is brought into contact with the image forming area of the photosensitive belt 22 on which the electrostatic latent image for yellow is formed. During this operation, the remaining developing cartridges 15 are moved rearward in the horizontal direction by the developing cartridge driving portion 57, whereby the remaining developing rollers 18 are spaced from the photosensitive belt 22. In this way, only the yellow toner contained in the yellow developing cartridge 15Y forms a yellow visible image in the image forming area of the photosensitive belt 22 (t 1).

Then, when the yellow visible image reaches the transfer position a due to the movement of the photosensitive belt 22, the yellow visible image is transferred to the image forming area of the intermediate transfer belt 26 by applying a primary transfer bias between the photosensitive belt 22 and the intermediate transfer belt 26(t 2).

Then, when the electrostatic latent image for magenta is formed again on the photosensitive belt 22, the magenta developing cartridge 15M is moved forward in the horizontal direction by the developing cartridge driving portion 57, whereby a visible image for magenta is formed in the image forming area of the photosensitive belt 22 (t 3).

Then, in the same manner as previously described, when the magenta visible image reaches the transfer position a due to the movement of the photosensitive belt 22, the magenta visible image is transferred to the image forming area of the intermediate transfer belt 26 by applying a primary transfer bias between the photosensitive belt 22 and the intermediate transfer belt 26(t 4). The yellow toner image has been transferred onto the image forming area of the intermediate transfer belt 26 so that the magenta visible image is superimposed on the yellow visible image.

The same procedure as described above is repeated for the cyan toner contained in the cyan developing cartridge 15C and the black toner contained in the black developing cartridge 15K. Thereby, the four color toner images for a single sheet are superimposed on each other in the image forming area of the intermediate transfer belt 26, and a multicolor image is formed (t5 to t 8).

Then, in the primary transfer operation, the multicolor image in the image forming region of the intermediate transfer belt 26 is collectively transferred onto the sheet 3 passing between the intermediate transfer belt 26 and the transfer roller 13 while the transfer roller 13 contacts the intermediate transfer belt 26, and a secondary transfer bias is applied between the rollers 13 and 26(t 9).

During the development of the visible image on the photosensitive belt 22 (t1, t3, t5, and t7) and the primary transfer of the visible image to the intermediate transfer belt 26(t2, t4, t6, and t8), the photosensitive-belt cleaning roller 35 is placed in a state in which: the photosensitive belt cleaning roller 35 contacts the photosensitive belt 22, and the photosensitive belt 22 is sandwiched between the photosensitive belt cleaning roller 35 and the first auxiliary roller 45. Thus, the photosensitive-belt cleaning roller 35 contacts the photosensitive belt 22 for one period, in which toner images for individual sheets (each formed of a yellow toner, a magenta toner, a cyan toner, and a black toner) are successively carried on the photosensitive belt 22.

Thus, when the roller 35 contacts the photosensitive belt 22, the cleaning bias applying circuit 53 applies a first cleaning bias to the roller 35 so as to establish a first potential difference in one direction between the belt 22 and the roller 35, in which toner on the photosensitive belt 22 is transferred from the photosensitive belt 22 to the photosensitive belt cleaning roller 35. Thus, after the toner image of each color is transferred onto the intermediate transfer belt 26, the residual toner remaining on the image forming area of the photosensitive belt 22 is captured by the photosensitive belt cleaning roller 35 when the residual toner reaches a position where the toner opposes the photosensitive belt cleaning roller 35 due to the movement of the photosensitive belt 22.

Each time the period in which the photoreceptor belt 22 is required to produce a toner image for a single sheet and transfer the toner image to the belt 26 ends, the image forming area of the photoreceptor belt 22 passes between the photoreceptor belt cleaning roller 35 and the first auxiliary roller 45 due to the endless movement of the photoreceptor belt 22. At this time, the photosensitive-belt cleaning roller 35 is spaced from the photosensitive belt 22 by the photosensitive-belt cleaning-roller driving portion 56, and is moved to the intermediate transfer belt 26 side (t 10). Thereby, the photosensitive-belt cleaning roller 35 is placed in a state: the photosensitive-belt cleaning roller 35 contacts a non-image-forming area of the intermediate transfer belt 26, and the intermediate transfer belt 26 is sandwiched between the photosensitive-belt cleaning roller 35 and the second auxiliary roller 46.

At the same time, the cleaning bias applying circuit 53 applies a second cleaning bias to the roller 35 to establish a second potential difference in one direction between the roller 35 and the belt 26, in which the toner on the photosensitive belt cleaning roller 35 is transferred onto the intermediate transfer belt 26. Due to this process, the toner captured by the photosensitive belt cleaning roller 35 is efficiently discharged to the non-image forming area of the intermediate transfer belt 26.

Before the image forming area of the intermediate transfer belt 26 reaches the position between the photosensitive belt cleaning roller 35 and the second auxiliary roller 46 in accordance with the movement of the intermediate transfer belt 26, the photosensitive belt cleaning roller 35 is spaced from the intermediate transfer belt 26 and moved back to the photosensitive belt 22 side (t 11). Thereby, the photosensitive-belt cleaning roller 35 is again placed in a state: the roller 35 contacts an image forming area of the photosensitive belt 22, and the photosensitive belt 22 is sandwiched between the roller 35 and the first auxiliary roller 45. Therefore, as shown in fig. 5, the image forming area of the photosensitive belt 22 can be cleaned even in the case where the toner image development (t1 ') and the primary transfer (t 2') for the next page start, and it is not necessary to wait for the photosensitive belt 22 to rotate once, but immediately after the development for a single page is completed (t 7).

After the start of the secondary transfer (t9), the intermediate transfer belt cleaning roller 38 is placed in a state: the roller 38 contacts the intermediate transfer belt 26, and a cleaning bias is applied to the roller 38 so that a potential difference is established between the roller 38 and the intermediate transfer belt 26(t 12). Thus, when the residual toner reaches the position where the toner is opposed to the intermediate transfer belt cleaning roller 38 due to the rotation of the intermediate transfer belt 26, the residual toner remaining on the image forming area of the intermediate transfer belt 26 after the multicolor image is transferred onto the sheet 3 is captured by the intermediate transfer belt cleaning roller 38.

When the toner reaches the position where the toner is opposed to the intermediate transfer belt cleaning roller 38 due to the rotation of the intermediate transfer belt 26, the toner discharged from the photosensitive belt cleaning roller 35 onto the non-image forming area of the intermediate transfer belt 26 is also captured by the intermediate transfer belt cleaning roller 38. Thus, the residual toner remaining on the photosensitive belt 22 is also collected in the intermediate transfer belt cleaning cartridge 37 of the intermediate transfer belt cleaning unit 36.

As described above, in the color laser printer 1 of the present embodiment, the photosensitive belt 22 carries the toner image thereon, and conveys the toner image to the primary transfer position a. At the primary transfer position a, the toner image is transferred from the photosensitive belt 22 to the intermediate transfer belt 26. The intermediate transfer belt 26 conveys the toner image to the secondary transfer position D. At the secondary transfer position D, the toner image is transferred to the image recording medium 3. After the toner image is transferred to the intermediate transfer belt 26 at the primary transfer position a, a belt cleaning roller 35 is provided to remove residual toner remaining on the photosensitive belt 22. After the toner image is transferred to the image recording medium 3 at the secondary transfer position D, an intermediate transfer belt cleaning unit 36 is provided to remove residual toner remaining on the intermediate transfer belt 26. The photoreceptor belt cleaning roller 35 is configured to discharge the removed residual toner onto the intermediate transfer belt 26. Therefore, the residual toner on the photosensitive belt 22 is first removed by the photosensitive-belt cleaning roller 35 and discharged from the photosensitive-belt cleaning roller 35 to the intermediate transfer belt 26, and finally the toner is removed from the intermediate transfer belt 26 by the intermediate transfer-belt cleaning unit 36. Therefore, the residual toner remaining on the first and second image bearing bodies 22 and 26 can be efficiently collected into the single common area 36.

In this manner, the photosensitive belt 22 and the intermediate transfer belt 26 are provided so as to be able to carry toner thereon, and are circularly moved to convey the toner image. The photoreceptor belt cleaning roller 35 removes residual toner remaining on the photoreceptor belt 22. The intermediate transfer belt cleaning unit 36 removes residual toner remaining on the intermediate transfer belt 26. The toner is discharged from the photosensitive-belt cleaning roller 35 onto the intermediate transfer belt 26.

Therefore, the toner on the photosensitive belt 22 is removed by the photosensitive-belt cleaning roller 35, then discharged from the photosensitive-belt cleaning roller 35 onto the intermediate transfer belt 26, and further removed from the intermediate transfer belt 26 by the intermediate transfer-belt cleaning unit 36. The residual toner on the photosensitive belt 22 and the intermediate transfer belt 26 can be efficiently collected in a single common area.

The photoreceptor belt cleaning roller 35 contacts the image forming area of the photoreceptor belt 22, thereby capturing residual toner on the photoreceptor belt 22. The photoreceptor belt cleaning roller 35 contacts the non-image forming area of the intermediate transfer belt 26, thereby discharging the residual toner to the non-image forming area.

With this configuration, it is possible to prevent a situation in which the discharge of the residual toner exerts an influence on the toner image borne on the intermediate transfer belt 26. Also, even when the intermediate transfer belt 26 carries a toner image in its image forming area, the residual toner can be discharged from the photosensitive-belt cleaning roller 35 to the intermediate transfer belt 26. The toner removing function of the photosensitive belt cleaning roller 35 can be restored even when the color laser printer 1 performs a printing operation. Cleaning of the photoreceptor belt 22 may be performed in an efficient manner.

A first cleaning bias is applied to the roller 35 to establish a first potential difference between the roller 35 and the belt 22. Toner can be removed from the photoreceptor belt 22 to the roller 35 in an efficient manner. A second cleaning bias is applied to the roller 35 to establish a second potential difference between the roller 35 and the tape 26. Toner can be discharged from the photosensitive-belt cleaning roller 35 to the intermediate transfer belt 26 in an efficient manner.

The photosensitive-belt-cleaning-roller driving portion 56 controls the photosensitive-belt cleaning roller 35 to selectively contact the photosensitive belt 22 and the intermediate transfer belt 26. The length of the photosensitive belt 22 from the transfer position a to the contact position B is set to be substantially equal to the length of the intermediate transfer belt 26 from the transfer position a to the contact position C. The photoreceptor belt cleaning roller 35 may be controlled to contact the image forming area of the photoreceptor belt 22 and to contact the non-image forming area of the intermediate transfer belt 26.

The photoreceptor belt cleaning roller driving section 56 controls the photoreceptor belt cleaning roller 35 to contact the photoreceptor belt 22 for a period of time required for the photoreceptor belt 22 to carry and convey a toner image for a single sheet, and to contact the intermediate transfer belt 26 every time after the period ends. The toner accumulated on the photoreceptor belt cleaning roller 35 may be discharged to the intermediate transfer belt 26 each time after the photoreceptor belt 22 is used to form an image for a single sheet. The toner removing function of the photosensitive belt cleaning roller 35 can be recovered and the cleaning of the photosensitive belt 22 can be efficiently performed.

The photoreceptor belt cleaning roller 35 is a rotatable member, that is, a member capable of capturing toner from the photoreceptor belt 22 while contacting the belt 22 at its outer peripheral portion, and capable of discharging toner to the intermediate transfer belt 26 while contacting the belt 26 at its outer peripheral portion. By rotating the photosensitive belt cleaning roller 35, the toner can be captured using the entire portion of the outer peripheral portion. Toner can be effectively removed from the photosensitive belt 22. By rotating the photosensitive belt cleaning roller 35, the toner can be discharged from the entire portion of the outer peripheral portion. The toner can be efficiently discharged to the belt 26.

In particular, according to the present embodiment, the outer peripheral portion of the photosensitive-belt cleaning roller 35 is made of an elastic material. Therefore, when the photosensitive-belt cleaning roller 35 is pressed against the photosensitive belt 22, the nip portion (contact surface) of the roller 35 can be widened, and the toner can be effectively removed from the photosensitive belt 22. The contact pressure (the pressure applied to the photosensitive belt 22 by the belt cleaning roller 35) required to widen the nip portion can be reduced. Even when the photosensitive-belt cleaning roller 35 contacts and separates from the belt 22, the variation in the moving speed of the belt 22 can be suppressed.

Since the outer peripheral portion of the roller 35 is made of an elastic material, when the roller 35 is pressed against the belt 26, it is possible to widen the nip (contact surface) of the roller 35 and to efficiently discharge the toner to the belt 26. The contact pressure (the pressure applied to the belt 26 by the belt cleaning roller 35) required to widen the nip portion can be reduced. Even when the cleaning roller 35 contacts and separates from the belt 26, the variation in the moving speed of the belt 26 can be suppressed.

Upon contacting the photosensitive belt 22, the photosensitive-belt cleaning roller 35 rotates in one direction so that a portion of the roller 35 contacting the belt 22 moves in the same direction as a portion of the belt 22 contacting the roller 35. Upon contacting the tape 26, the photosensitive-tape cleaning roller 35 rotates in one direction so that the portion of the roller 35 contacting the tape 26 moves in the same direction as the portion of the tape 26 contacting the roller 35. The influence of the moving speed applied to the photosensitive belt 22 and the intermediate transfer belt 26 by the photosensitive-belt cleaning roller 35 can be further reduced.

When the photosensitive-belt cleaning roller 35 contacts the photosensitive belt 22, the photosensitive-belt cleaning-roller driving portion 56 rotationally drives the photosensitive-belt cleaning roller 35 such that a speed difference is generated between a portion of the cleaning roller 35 contacting the belt 22 and a portion of the belt 22 contacting the roller 35. The frictional force applied in the contact portion of the cleaning roller 35 and the belt 22 can be increased, making it possible to more reliably remove the toner from the photosensitive belt 22.

The first auxiliary roller 45 is disposed at a position: the roller 45 opposes the photosensitive belt cleaning roller 35, and the photosensitive belt 22 is sandwiched between the rollers 35 and 45. The photosensitive belt 22 is prevented from becoming loose by pressing the cleaning roller 35 against the photosensitive belt 22. When the cleaning roller 35 contacts and separates from the photosensitive belt 22, the influence of the circulating moving speed applied to the photosensitive belt 22 can be suppressed.

The second auxiliary roller 46 is disposed at a position: the roller 46 is opposed to the photosensitive-belt cleaning roller 35, and the belt 26 is sandwiched between the rollers 35 and 46. The belt 26 is prevented from becoming loose by pressing the cleaning roller 35 against the belt 26. When the cleaning roller 35 contacts and separates from the belt 26, the influence of the circulating moving speed applied to the belt 26 can be suppressed.

While the invention has been particularly described, in conjunction with specific embodiments thereof, it will 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 above-described embodiment, each time the period in which the photosensitive belt 22 is used to carry a toner image for a single sheet is ended, the remaining toner is discharged from the photosensitive belt cleaning roller 35 to the intermediate transfer belt 26. However, the remaining toner may be discharged from the roller 35 to the belt 26 in other various manners. For example, the photoreceptor belt cleaning roller drive section 56 may control the photoreceptor belt cleaning roller 35 to contact the photoreceptor belt 22 for a period of time during which the photoreceptor belt 22 is available to carry toner images for a plurality of pages, and control the photoreceptor belt cleaning roller 35 to contact the intermediate transfer belt 26 each time after the period ends.

In this modification, the frequency at which the photosensitive-belt cleaning roller 35 contacts and separates from the photosensitive belt 22 can be reduced. This can suppress the occurrence of noise and reduce power consumption. It is ensured that the moving speed of the photosensitive belt 22 does not fluctuate. The occurrence of color shift can be suppressed. More specifically, the mutual shift of the positions of the respective color images can be suppressed in the final multicolor image.

In the above-described embodiment, when the photosensitive-belt cleaning roller 35 contacts the photosensitive belt 22, the photosensitive-belt cleaning roller 35 is rotationally driven so that a speed difference is generated between a portion of the photosensitive-belt cleaning roller 35 contacting the photosensitive belt 22 and a portion of the belt 22 contacting the roller 35. However, the photosensitive-belt cleaning roller 35 may be rotationally driven so that the portion of the photosensitive-belt cleaning roller 35 contacting the photosensitive belt 22 moves at the same speed together with the portion of the belt 22 contacting the roller 35.

For example, the photoreceptor belt cleaning roller 35 may be rotated by moving it to follow the photoreceptor belt 22 while contacting the photoreceptor belt 22. That is, the roller 35 may be rotated by friction generated due to contact between the surface of the roller 35 and the surface of the belt 22. Similarly, the photosensitive belt cleaning roller 35 may rotate by following the movement of the intermediate transfer belt 26 while contacting the belt 26. That is, the roller 35 may be rotated by friction generated due to contact between the surface of the roller 35 and the surface of the belt 26.

The mechanism for rotating the cleaning roller 35 can be simplified. The load fluctuation on the belt 22 can be further reduced when the cleaning roller 35 contacts and leaves the belt 22. The load fluctuation on the belt 26 can be further reduced when the cleaning roller 35 contacts and leaves the belt 26. The fluctuation in the moving speed of the tape 26 can be further reduced.

In the above-described embodiment, when the printing (output) operation is performed in the color laser printer 1, the remaining toner is discharged from the photoreceptor belt cleaning roller 35 to the intermediate transfer belt 26. However, the toner discharge time may be changed. For example, as shown in fig. 6, after all of the four color images for a single page are transferred from the tape 22 to the tape 26, the printing operation may be temporarily stopped. When the printing operation is stopped, the remaining toner is discharged from the photosensitive-belt cleaning roller 35 to the intermediate transfer belt 26. In this modification, the residual toner may be discharged not only onto the non-image forming area of the intermediate transfer belt 26 but also onto the image forming area. In the case where the remaining toner is discharged onto the image forming area, the transfer roller 13 must be spaced from the intermediate transfer belt 26 when the image forming area of the belt 26 passes between the rollers 13 and 24. It is possible to prevent the residual toner from being transferred from the intermediate transfer belt 26 to the transfer roller 13.

In the above-described embodiment, the control signal from the CPU51 is supplied to the cleaning bias applying circuit 53. Therefore, the on/off timings of the first and second cleaning biases and the values of the first and second cleaning biases (on biases) are controlled by the CPU 51. However, the cleaning bias applying circuit 53 may be changed in various ways.

For example, the cleaning bias applying circuit 53 may have a simple configuration as shown in fig. 7. In this case, the circuit 53 includes a power source B1, a power source B2, a contact terminal T1, and a contact terminal T2. Contact terminal T1 is connected to power source B1 and is located at a position such that contact terminal T1 contacts roller 35 when roller 35 contacts tape 22. The power source B1 is used to apply a first cleaning bias that is lower than the potential of the tape 22 by a first potential difference. Thus, when roller 35 contacts tape 22, power supply B1 applies a first cleaning bias to roller 35 to establish a first potential difference between roller 35 and tape 22 to transfer toner from tape 22 to roller 35.

The contact terminal T2 is connected to the power source B2 and is located at another position where the contact terminal T2 can be brought into contact with the roller 35 when the roller 35 contacts the tape 26. The power source B2 is used to apply a second cleaning bias that is a second potential difference higher than the potential of the tape 26. Thus, when roller 35 contacts tape 26, power supply B2 applies a second cleaning bias to roller 35 to establish a second potential difference between roller 35 and tape 26 to transfer toner from roller 35 to tape 26.

As shown in fig. 8, the photosensitive belt 22 may be replaced with a photosensitive drum 122. The photosensitive drum 122 has a photosensitive material layer on the outer peripheral surface thereof, on which an electrostatic latent image is formed by the scanner unit 10, and is visualized as a toner image by the corresponding developing cartridge 15. The photosensitive drum 122 thus carries thereon a toner image, rotating about its rotational axis, to transport the toner image to the primary transfer position A, where the toner image is transferred to the belt 26. In this case, the first auxiliary roller 45 becomes redundant.

Similarly, although not shown in the drawings, the transfer belt 26 may be replaced with an intermediate transfer drum, the peripheral portion of which may receive the toner image from the photosensitive belt 22 or the photosensitive drum 122. The intermediate transfer drum can convey the toner image to the secondary transfer position D according to its rotation about the rotation axis. In this case, the second auxiliary roller 46 becomes redundant.

The above embodiment relates to the color laser printer 1. However, the present invention is not limited to the color laser printer, but may be applied to any other type of image forming apparatus as long as the image forming apparatus has a plurality of image carriers.

In the above embodiments, the toner is positively charged. Therefore, the first cleaning bias applied to the cleaning roller 35 when the roller 35 contacts the tape 22 is lower than the potential of the tape 22. Since the polarity of the roller 35 is negative with respect to the tape 22, the positively charged toner can be efficiently transferred from the tape 22 to the roller 35. The second cleaning bias applied to the roller 35 when the roller 35 contacts the belt 26 is higher than the potential of the belt 26. Since the polarity of the tape 26 is negative with respect to the roller 35, the positively charged toner can be efficiently transferred from the roller 35 to the tape 26. However, the toner may be made of a material having a negative charge. In this case, the first cleaning bias must be set to a potential higher than that of the tape 22. Since the polarity of the roller 35 is positive with respect to the tape 22, the negatively charged toner can be efficiently transferred from the tape 22 to the roller 35. The second cleaning bias must be set to a potential lower than that of the tape 26. Since the polarity of the tape 26 is positive with respect to the roller 35, the negatively charged toner can be efficiently transferred from the roller 35 to the tape 26.

Claims (19)

1. An electrophotographic imaging apparatus comprising:

a photosensitive member (22) capable of bearing a toner image on a surface thereof, the photosensitive member being moved to convey the toner image from a developing portion to a primary transfer position (a);

an intermediate transfer belt (26) capable of bearing a toner image on a surface thereof, the intermediate transfer belt receiving the toner image transferred from the photosensitive member at a primary transfer position and moving to convey the toner image to a secondary transfer position (D);

a transfer unit that transfers the toner image from the intermediate transfer belt to an image recording medium at a secondary transfer position (D);

a photoreceptor belt cleaning roller (35) that removes residual toner remaining on the photoreceptor member from the photoreceptor member after the toner image is transferred to the intermediate transfer belt, the photoreceptor belt cleaning roller releasing the removed toner onto the intermediate transfer belt; and

an intermediate transfer belt cleaning unit (36) that removes residual toner remaining on the intermediate transfer belt from the intermediate transfer belt after a toner image is transferred from the intermediate transfer belt to an image recording medium, the intermediate transfer belt cleaning unit removing toner discharged from the photoreceptor belt cleaning roller from the intermediate transfer belt.

2. The electrostatographic imaging apparatus of claim 1,

characterized in that the intermediate transfer belt has on its surface an image forming area of the intermediate transfer belt which receives the toner image from the photosensitive member on its image forming area and a non-image forming area of the intermediate transfer belt which discharges the removed toner onto the non-image forming area of the intermediate transfer belt.

3. The electrostatographic imaging apparatus of claim 1,

characterized in that the residual toner is charged, an

Wherein the photosensitive belt cleaning roller includes:

a cleaning member that receives the residual toner from the photosensitive member;

a contact/separation mechanism that causes the cleaning member to contact the surface of the photosensitive member when away from the intermediate transfer belt, and causes the cleaning member to contact the surface of the intermediate transfer belt when away from the photosensitive member; and

a bias applying unit that establishes a first potential difference between the photosensitive member and the cleaning member when the cleaning member contacts the photosensitive member to transfer the charged residual toner from the photosensitive member to the cleaning member in one direction, and establishes a second potential difference between the cleaning member and the intermediate transfer belt when the cleaning member contacts the intermediate transfer belt to transfer the charged residual toner from the cleaning member to the intermediate transfer belt in one direction.

4. The electrostatographic imaging apparatus of claim 3,

characterized in that the photosensitive member has on its surface an image forming area of a photosensitive belt and a non-image forming area of a photosensitive belt, the intermediate transfer belt has on its surface an image forming area of an intermediate transfer belt and a non-image forming area of an intermediate transfer belt, the intermediate transfer belt receives a toner image from the image forming area of the photosensitive belt of the photosensitive member in the forming area of the intermediate transfer belt at a primary transfer position, and

wherein the contact/separation mechanism causes the cleaning member to contact an image forming area of the photosensitive belt of the photosensitive member, thereby causing the cleaning member to receive residual toner remaining on the image forming area of the photosensitive belt, and the contact/separation mechanism causes the cleaning member to contact a non-image forming area of the intermediate transfer belt, thereby causing the cleaning member to discharge the received toner onto the non-image forming area of the intermediate transfer belt.

5. The electrostatographic imaging apparatus of claim 4,

characterized in that a surface of the photosensitive member contacts a surface of the intermediate transfer belt at a primary transfer position to transfer the toner image from the photosensitive member to the intermediate transfer belt,

wherein the contact/separation mechanism causes the cleaning member to contact the surface of the photosensitive member at a toner removing position on the photosensitive member and to contact the intermediate transfer belt at a toner discharging position on the intermediate transfer belt, and

wherein a length of the photosensitive member from the primary transfer position to the toner removing position is substantially equal to a length on the intermediate transfer belt from the primary transfer position to the toner discharging position.

6. The electrostatographic imaging apparatus of claim 5,

characterized in that the contact/separation mechanism contacts the cleaning member to the photosensitive member for a predetermined period of time required for the photosensitive member to carry thereon a toner image for a predetermined number of pages, the contact/separation mechanism contacting the cleaning member to the intermediate transfer belt every time the predetermined period of time ends.

7. The electrostatographic imaging apparatus of claim 6,

characterized in that the predetermined number is equal to 1.

8. The electrostatographic imaging apparatus of claim 6,

characterized in that the predetermined number is greater than 1.

9. The electrostatographic imaging apparatus of claim 3,

characterized in that the cleaning member is a rotary member having a central axis and an outer peripheral portion around the central axis and capable of rotating around the central axis, and

wherein the contact/separation mechanism causes an outer peripheral portion of the rotary member to selectively contact the photosensitive member and the intermediate transfer belt.

10. The electrostatographic imaging apparatus of claim 9,

characterized in that the outer peripheral portion of the rotary member is made of an elastic material.

11. The electrostatographic imaging apparatus of claim 9,

characterized in that when the contact/separation mechanism causes a rotary member to contact the photosensitive member, the rotary member is rotated in one direction to move a peripheral portion of the rotary member and a mutually contacting portion of the surface of the photosensitive member in the same direction,

wherein, when the contact/separation mechanism causes the rotary member to contact the intermediate transfer belt, the rotary member is rotated in the other direction, causing the outer peripheral portion of the rotary member and the mutually contacting portion of the surface of the intermediate transfer belt to move in the same direction.

12. The electrostatographic imaging apparatus of claim 11,

characterized in that it further comprises an image bearing member driving unit which drives the photosensitive member and the intermediate transfer belt to move;

wherein, when the contact/separation mechanism causes the rotary member to contact the photosensitive member, the rotary member rotates following the movement of the photosensitive member due to friction generated by the contact between the outer peripheral portion of the rotary member and the surface of the photosensitive member, and

wherein, when the contact/separation mechanism causes the rotating member to contact the intermediate transfer belt, the rotating member rotates following the movement of the intermediate transfer belt due to friction generated by the contact between the outer peripheral portion of the rotating member and the surface of the intermediate transfer belt.

13. The electrostatographic imaging apparatus of claim 11,

characterized in that it further comprises a rotary member driving unit which drives the rotary member to rotate at a rotational speed when the cleaning member contacts the photosensitive member: the rotation speed causes the outer peripheral portion of the rotating member and the mutually contacting portion of the surface of the photosensitive member to move in the same direction but at different speeds from each other.

14. The electrostatographic imaging apparatus of claim 3,

characterized in that the photosensitive member includes a photosensitive belt (22) wound around a plurality of photosensitive belt rollers (19-21) and rotatable around the peripheries of the photosensitive belt rollers, and

it also comprises a first auxiliary roller (45) arranged in such a position that: when the contact/separation mechanism causes the cleaning member to contact the photosensitive belt, the photosensitive belt is sandwiched between the first auxiliary roller and the cleaning member.

15. The electrostatographic imaging apparatus of claim 3,

characterized in that the intermediate transfer belt is wound around a plurality of intermediate transfer belt rollers (23-25) and is rotatable around the periphery of the plurality of intermediate transfer belt rollers, an

It also comprises a second auxiliary roller (46) arranged in such a position that: when the contact/separation mechanism causes the cleaning member to contact the intermediate transfer belt, the intermediate transfer belt is sandwiched between the second auxiliary roller and the cleaning member.

16. The electrostatographic imaging apparatus of claim 1,

wherein the photosensitive member includes a photosensitive material on a surface thereof;

it still includes:

a latent image forming unit capable of forming a plurality of latent images of a plurality of different colors on the surface of the photosensitive member; and

a plurality of developing units that store toners of a plurality of different colors and develop the plurality of latent images into a plurality of toner images of a plurality of colors by using the toners,

wherein the intermediate transfer belt receives a plurality of toner images at the same position on the surface thereof, the plurality of toner images being superimposed on each other on the surface of the intermediate transfer belt, thereby forming a final multicolor toner image, and

wherein the transfer unit transfers the final multicolor toner image onto an image recording medium.

17. The electrostatographic imaging apparatus of claim 16,

wherein the intermediate transfer belt is wound around a plurality of intermediate transfer belt rollers and is rotatable around the peripheries of the plurality of intermediate transfer belt rollers.

18. The electrostatographic imaging apparatus of claim 16,

wherein the photosensitive member includes a photosensitive endless belt wound around a plurality of photosensitive belt rollers, having a photosensitive layer on an outer surface thereof, and being rotatable around peripheries of the plurality of photosensitive belt rollers.

19. The electrostatographic imaging apparatus of claim 16,

characterized in that the photosensitive member includes a photosensitive drum which is rotatable about a rotation axis thereof and has a photosensitive layer on an outer peripheral surface thereof.