Image forming apparatus

An image forming apparatus includes an inclining device for inclining the endless belt so as to keep the an endless belt in a normal range in a widthwise direction of the belt; a blade member for pressing against the belt at a pressing portion to clean it; a detecting portion for detecting deviation of the belt from a normal range in a widthwise direction thereof; and an executing portion for executing an operation in a mode in which a lubricant is supplied to the pressing portion, when the detecting portion detects that the belt is deviated from the normal range.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an electrophotographic image forming apparatus such as an electrophotographic copying machine, an electrophotographic printer, etc., which is equipped with an intermediary transfer belt, a recording medium conveyance belt, or the like.

An image forming apparatus which forms a toner image, transfers the toner image onto recording medium, and fixes the toner image to the recording medium by applying heat and pressure with the use of a fixing device is widely in use. Such an image forming apparatus uses an intermediary transfer belt or a recording medium conveyance belt, that is, a member in the form of an endless belt. The intermediary transfer belt is an endless belt onto which a toner image is temporarily transferred before it is transferred onto recording medium. The recording medium conveyance belt is an endless belt for conveying a sheet of recording medium onto which a toner image is transferred. This member in the form of an endless belt tends to shift in the direction perpendicular to its moving direction. Thus, some image forming apparatuses which employ an intermediary transfer belt, a recording medium conveyance belt, or the like are equipped with a mechanism for steering the belt.

The image forming apparatus disclosed in Japanese Laid-open Patent Application 2000-34031 is provided with a belt steering roller and a motor for tilting the belt steering roller. It is structured so that the belt steering roller is rotationally movable about one of its lengthwise ends. If its member in the form of an endless belt laterally shifts, the steering roller is tilted by the belt tilting motor so that the other end of the belt steering roller moves upward or downward in order to create such a force that makes the belt to shift in the opposite direction.

Japanese Laid-open Patent Application 2001-146335 discloses an image forming apparatus which has a belt steering member, which is rotationally movable about its center in terms of the direction parallel to the direction in which the belt shifts. In the case of this image forming apparatus, as the belt laterally shifts, a force for causing the belt to shifts in the opposite direction from the direction in which the belt shifted is generated by tilting the belt steering member by rotationally moving the belt steering roller about its center in terms of the lengthwise direction of the belt steering roller.

There are various countermeasures for the problem that an endless belt tends to laterally shift as it is circularly moved. Proposed in Japanese Laid-open Patent Application 2001-520611 is one of these countermeasures. This countermeasure is significantly smaller in component count, simpler, and lower in cost than the others. It employs also a belt steering roller, and automatically aligns (centers) the belt by utilizing the imbalance between the friction between the belt and one of the lengthwise end portions of the belt steering belt and the belt, and the friction between the belt and the other lengthwise end portions of the belt steering roller (this belt aligning method hereafter may be referred to as “automatic belt alignment”).

More concretely, each of the lengthwise end portions of the belt steering roller is provided with a friction generating portion. Thus, as the belt laterally shifts, the friction between one end of the belt steering roller and the belt becomes greater than that between the other end of the belt steering roller and the belt. Thus, the difference in the amount of friction between one end of the belt steering roller and the other end is utilized to obtain the torque to rotationally moving the belt steering roller about its center in terms of its lengthwise direction.

However, it was discovered that an automatic belt aligning method such as the described above suffers from the following problem. That is, a cleaning blade is placed in contact with the outward surface (in terms of loop which endless belt forms) of the endless belt supported by the belt steering member. Thus, if the belt is not supplied with toner for a substantial length of time, it is possible that the belt will laterally shift as it is circularly moved.

SUMMARY OF THE INVENTION

According to the present invention, it is possible to prevent the problem that the toner shortage on the intermediary transfer belt, recording medium conveyance belt, or the like causes a belt steering roller to unintendedly tilt, which in turns causes the belt to laterally shift in the unintended direction.

According to an aspect of the present invention, there is provided an image forming apparatus comprising a rotatable endless belt; image forming means for forming a toner image on said endless belt; stretching means for stretching said endless belt; an inclining device for inclining said endless belt so as to keep said endless belt in a normal range in a widthwise direction of said endless belt, said inclining device including a rotatable portion rotatable with rotation of said endless belt, a frictional portion, provided at opposite end portions of said rotatable portion with respect to the widthwise direction of said endless belt, to be rubbed by said endless belt, supporting means for supporting said rotatable portion and said frictional portion, a rotational shaft for rotatably supporting said supporting means, wherein said supporting means rotatable by force produced by the rubbing between said endless belt and said frictional portion to move said endless belt in the widthwise direction; a blade member, provided opposed to said rotatable portion of said inclining device through said endless belt, for pressing against said endless belt at a pressing portion to clean said endless belt; a detecting portion for detecting that said endless belt is deviated from the normal range in the widthwise direction; and an executing portion for executing an operation in a mode in which a lubricant is supplied to the pressing portion, when said detecting portion detects that said endless belt is deviated from the normal range in the widthwise direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiments of the present invention are described with reference to the appended drawings. Incidentally, not only is the present invention applicable to the image forming apparatuses in the following embodiments of the present invention, but also, image forming apparatuses which are partially or entirely different in structure from the image forming apparatuses in the following embodiments, as long as they are structured so that lubricant is intermittently supplied to their belt to stabilize in operation, their automatic belt aligning mechanism.

That is, the present invention is applicable to any image forming apparatus, whether the apparatus is of the tandem type or has only a single image bearing member (drum), and also, whether the apparatus is of the intermediary transfer type or direct transfer type, as long as the apparatus employs an automatic belt aligning mechanism for controlling the lateral shift of its endless belt. The belt which an image forming apparatus to which the present invention is applied may be an intermediary transfer belt, a recording medium conveyance belt, or a fixation belt. The lubricant which an image forming apparatus to which the present invention is applied does not need to be limited to toner. In the description of the following embodiments of the present invention, only the portions which are essential to the formation and transfer of a toner image are described. However, the present invention is applicable to various image forming apparatuses other than those in the following embodiments of the present invention. For example, it is applicable to various printer, copying machines, facsimile machines, and also, multifunction apparatuses capable of performing two or more the preceding machines, which are combinations of one of the image forming apparatuses in the following embodiments, additional devices, equipments, frames, etc.

FIG. 1is a drawing for describing the general structure of a typical image forming apparatus to which the present invention is applicable. Referring toFIG. 1, the image forming apparatus100is a full-color printer of the so-called tandem type, and also, of the so-called intermediary transfer type. More concretely, it has an intermediary transfer belt101, and four image forming stations109Y,109M,109C and109Bk. The image forming stations109Y,109M,109C and109Bk form yellow, magenta, cyan and black toner images, respectively, are aligned along the image bearing surface of the intermediary transfer belt101.

In the image forming station109Y, a yellow toner image is formed on a photosensitive drum103, and is transferred onto the intermediary transfer belt101. In the image forming station109M, a magenta toner image is formed through the procedure similar to that used in the image forming station109Y, and is transferred onto the intermediary transfer belt101in such a manner that the magenta toner image is layered on the yellow toner image on the intermediary transfer belt101. In the image forming stations109C and109Bk, a cyan toner image and a black toner image, respectively, are formed through the procedure similar to that used in the image forming station109Y, and are sequentially transferred onto the intermediary transfer belt101in such a manner that the cyan and black toner images are sequentially layered onto the yellow and magenta toner images on the intermediary transfer belt101.

The four toner images, different in color, on the intermediary transfer belt101are conveyed to the secondary transfer station T2, and are transferred together (secondary transfer) onto a sheet P of recording medium in the secondary transfer station T2. After the transfer (secondary transfer) of the four toner image, different in color, onto the sheet P of recording medium, the sheet P is separated from the intermediary transfer belt101, with the utilization of the curvature of the intermediary transfer belt101, and then, is sent into the fixing device112of the image forming apparatus100. The fixing device112fixes (welds) the toner images on the sheet P to the surface of the sheet P by applying heat and pressure to the sheet P and the toner images thereon. Thereafter, the sheet P is discharged from the image forming apparatus.

The image forming stations109Y,109M,109C and109Bk are practically the same in structure, although they are different in the color (yellow, magenta, cyan and black, respectively) of the toner their developing device uses. Therefore, the process for forming a toner image is described with reference to the image forming station109Y, that is, the yellow image forming station. The process for forming toner image in the image forming stations109M,109C and109Bk will not be described for the sake of not repeating the same description.

The image forming station109Y has the photosensitive drum103. It has also a charge roller104, an exposing device105, a developing device106, and a drum cleaning device108, which are in the adjacencies of the peripheral surface of the photosensitive drum103. The photosensitive drum103has a photosensitive surface layer which is negatively chargeable. It is rotated at a preset process speed in the direction indicated by an arrow mark. As an oscillatory voltage, that is, a combination of DC voltage and AC voltage is applied to the charge roller104, the charge roller104negatively charges the peripheral surface of the photosensitive drum103to a preset potential level, which is equivalent to the potential level VD of an unexposed point of a latent image to be formed on the charged area of the peripheral surface of the photosensitive drum103. The exposing device105writes on the peripheral surface of the photosensitive drum103, an electrostatic latent image of the image to be formed, by scanning the charged area of the peripheral surface of the photosensitive drum103with a beam of laser beam with the use of a rotational mirror while modulating (turning on or off) the beam of laser light according to the image formation data obtained by unfolding the data of the yellow color component obtained by separating the image to be formed, into the primary color components of the image to be formed.

The developing device106makes its development sleeve106sbear two-component developer made up of nonmagnetic toner and magnetic carrier, while charging the developer. It conveys the charged developer to the area in which virtually no space is present between the peripheral surface of the development sleeve106sand peripheral surface of the photosensitive drum103. Further, to the development sleeve106s, a preset oscillatory voltage, which is a combination of DC and AC voltages, is applied, whereby the negatively charged nonmagnetic toner is made to transfer onto the exposed points of the peripheral surface of the photosensitive drum103, which are positive in potential relative to the charged toner. Consequently, the electrostatic latent image on the peripheral surface of the photosensitive drum103is reversely developed.

Transfer roller107forms a transfer station between the peripheral surface of the photosensitive drum103and intermediary transfer belt101. To the transfer roller107, a preset positive voltage is applied, whereby the toner image on the peripheral surface of the photosensitive drum103is transferred onto the intermediary transfer belt101. The drum cleaning device108recovers the toner remaining on the peripheral surface of the photosensitive drum103after the toner image transfer, by rubbing (scraping) the peripheral surface of the photosensitive drum103with its cleaning blade.

The secondary transfer roller111contacts the outward surface of the intermediary transfer belt101, between the image forming station109Bk and cleaning blade102bin terms of the moving direction of the intermediary transfer belt101. It forms the second transfer station T2by being placed in contact with the portion of the intermediary transfer belt101, which is supported by a belt backing roller110from the inward side of the belt loop.

The image forming apparatus100has a recording medium cassette120, in which multiple sheets of recording medium are storable. Each sheet P of recording medium in the cassette120is taken out of the cassette120while being separated from the rest by a separation roller122. Then, it is sent to a pair of registration rollers123, which send the sheet P to the secondary transfer station T2with such a timing that the sheet P arrives at the secondary transfer station T2at the same time as the full-color image (made up of layered four monochromatic toner images different in color) on the intermediary transfer belt101. Then, the toner images and sheet P of recording medium are conveyed together (in layers) through the secondary transfer station T2, while positive voltage is applied to the secondary transfer roller111from an electric power source D2. Consequently, the full-color image is transferred (secondary transfer) from the intermediary transfer belt101onto the sheet P.

The intermediary transfer belt101is a member which is in the form of an endless belt. It is circularly moved in the direction indicated by an arrow mark R2. It is suspended and kept stretched by a driving roller110which is a belt driving member, a steering roller1which is a belt steering member, and a pair of plain rollers113and114. The driving roller110doubles as the secondary transfer roller, and is placed in the inward side of the loop which the intermediary transfer belt101forms, at the secondary transfer station T2. The steering roller1doubles as a tension roller which provides the intermediary transfer belt101with a preset amount of tension. However, the number of the rollers by which the intermediary transfer belt101is suspended and kept stretched does not need to be limited to four as shown inFIG. 1. Further, the structural arrangement for keeping the intermediary transfer belt101suspended and stretched does not need to be limited to the one shown inFIG. 1.

The intermediary transfer belt101is desired not to wrinkle while it is being circularly driven. Thus, the material for the intermediary transfer belt101is desired to be highly resilient resin. More concretely, the material for the intermediary transfer belt101is desired to be PVDF (polyfluorovinylidene), polyamide, polyimide, PET (polyethylene-terephthalate), polycarbonate, or the like.

As for the thickness of the intermediary transfer belt101, if it is excessively thin, it may not be able to withstand friction. On the other hand, if it is excessively thick, it may fail to conform to the curvature of the driving roller110, steering roller1, and plain rollers113and114. That is, it may fail to properly bend. Therefore, it may develop indentations, or may buckle. Therefore, the thickness of the intermediary transfer belt101is desired to be in a range of 0.02 mm-0.50 mm. In the following embodiments of the present invention, the intermediary transfer belt101is a resin belt; its substrate is formed of polyimide. It is 18,000 N/cm2in coefficient of linear elasticity, and 0.08 mm in thickness.

The image forming apparatus100is provided with multiple image forming stations, which are different in the color in which they form a toner image. Further, it is structured so that the multiple image forming stations can simultaneously operate. Therefore, it is very high in productivity. The intermediary transfer belt100is an endless belt, onto the outward surface (in terms of loop it forms) of which toner images, different in color, are temporarily transferred in layers, and from which the layered toner images are transferred together onto a sheet P of recording medium. The intermediary transfer belt101is suspended and kept stretched by multiple rollers, for example, the driving roller110, and is circularly movable. As an endless belt, such as the endless intermediary transfer belt of the image forming apparatus100, which is suspended and kept stretched by multiple rollers, is circularly driven, it tends to laterally shift (it tends to shift in the direction perpendicular to its moving direction), due to the nonuniformity in the diameter of the rollers in terms of their lengthwise direction, inaccuracy in the alignment among the rollers, and/or the like issues.

As described above, one of the methods for controlling the lateral movement of an endless belt is to provide each of the lengthwise ends of each of the multiple belt supporting rollers with a rib. This method, however, suffers from the following problems. That is, the rib deforms the corresponding edge of the endless belt, exacerbating the snaking of the belt, and/or increasing the play between the belt and ribs. Consequently, the method fails to precisely position the belt in terms of the direction perpendicular to the moving direction of the belt. It is possible to provide the inward surface of the endless belt with ribs. This method, however, suffers from its own problem. That is, while the belt is circularly moved, the ribs remain continuously pressed by the belt in the direction perpendicular to the moving direction of the belt. Thus, this method does not allow the belt to be circularly driven faster than a certain velocity. It is also problematic in that the control of the process for pasting the ribs to the belt, and the examination of the belt in terms of the level of precision at which the ribs are adhered to the belt, add to the belt cost.

For the reasons given above, it is common practice to use a combination of a belt steering roller and an actuator in order to control the lateral shift of the endless belt. More concretely, the position of the belt in terms of the direction perpendicular to the moving direction of the belt (which hereafter may be referred simply as “belt position”) is continuously detected, and the belt steering roller is continuously tilted in such a direction and an amount that cancel the amount by which the belt has shifted. However, controlling the steering roller with the use of an actuator requires a complicated control algorithm. It requires also electrical components such as sensors and actuators. Therefore, it is problematic in that it increases the intermediary transfer unit in size and cost.

Thus, the image forming apparatus100uses an automatic belt aligning device (steering roller tilting device) which is significantly smaller in component count, simpler in structure, and lower in cost than an automatic belt aligning device which uses an actuator to tilt the steering roller. More specifically, the image forming apparatus100uses an automatic belt aligning device which to unitizes the difference between the amount of friction between one of the lengthwise end portions of the belt steering roller1and the intermediary transfer belt101, and the amount of friction between the other lengthwise end portion of the belt steering roller1and the intermediary transfer belt101, to automatically control the intermediary transfer belt101in lateral shift.

FIG. 2is a drawing for describing the operation of the automatic belt aligning device.FIG. 3is a perspective view of the automatic belt aligning device.FIG. 4is a broken perspective view of the center portion of the automatic belt aligning device, in terms of the lengthwise direction of the device, and shows the structure of the center portion.FIG. 5is a perspective view of one of the lengthwise end portions of the automatic belt aligning device, and shows how the belt steering roller1is held to the belt steering roller holding plate7.FIG. 6is a drawing for describing the relationship between the width of the intermediary transfer belt101and the length of the belt steering roller1, and the width of contact between the intermediary transfer belt101and the belt steering roller1in terms of the lengthwise direction of the belt steering roller1.

Referring toFIG. 2, the belt steering roller1, which is an example of a belt steering component, is held in such a manner that it can be rotationally moved about its center in terms of its lengthwise direction, in parallel to a vertical plane which coincides with the axial line of the belt steering roller1. Thus, as the intermediary transfer belt101laterally shifts, that is, as the intermediary transfer belt101shifts in the direction perpendicular to its moving direction, the amount of the friction between one of the lengthwise end portions of the belt steering roller1and the intermediary transfer belt101becomes different from the amount of the friction between the other lengthwise end portion of the belt steering roller1and the intermediary transfer belt101, causing thereby the belt steering roller1to tilt in the direction to cancel the lateral shifting of the intermediary transfer belt101. This automatic belt aligning device, which is based on mechanical feedback does not require a motor for tilting the belt steering roller1. Therefore, it consumes absolutely no electric power to control the intermediary transfer belt101in lateral shift. Moreover, it requires no sensors for detecting the lateral shift of the intermediary transfer belt101, no controlling means which computes the angle by which the belt steering roller1is to be tilted and activates the belt steering motor, and no driving force transmitting mechanism which converts the rotational angle of the motor into the angle by which the belt steering roller1is to be tilted. Thus, accuracy with which the intermediary transfer belt101is controlled in lateral shift has no relation to the accuracy with which the amount of the lateral shift of the intermediary transfer belt101is detected by sensors. Therefore, even if the sensors happen to fail to correctly detect the amount of the lateral shift of the intermediary transfer belt101, it does not occur that the intermediary transfer belt101is unnecessarily shifted. Therefore, it does not occur that the intermediary transfer belt101is made to snake by sensor errors.

In terms of the lengthwise direction of the belt steering roller1, the belt steering roller1is made up of three sections: a center section and a pair of lengthwise end sections. The center section is rotatable, whereas the lengthwise end sections are not rotatable. Therefore, the amount of load to which the intermediary transfer belt101is subjected by each lengthwise section of the intermediary transfer belt101is far greater than that to which the intermediary transfer belt101is subjected by the center section of the belt steering roller1. Further, the each lengthwise end section of the belt steering roller1is tapered in such a manner that the farther from the lengthwise center of the belt steering roller1, the greater the external diameter. Therefore, the mechanical feed back is less likely to be affected by the change in the amount of friction between the 1 and intermediary transfer belt101than if the lengthwise end sections are uniform in external diameter. In other words, tapering the lengthwise end sections of the belt steering roller1makes the automatic belt aligning device stable in the effect of automatically aligning the intermediary transfer belt101.

Referring toFIG. 2(a), the automatic belt aligning mechanical device10utilizes the imbalance between the lengthwise end portions of the belt steering roller1, in terms of the friction between the belt steering roller and intermediary transfer belt101, in order to make the belt steering roller1automatically control the intermediary transfer belt101in lateral shift. The belt steering roller1is supported by a steering shaft21so that the belt steering roller1is rotationally movable about the axial line of the steering shaft21. In terms of the lengthwise direction of the belt steering roller1, the center section2of the belt steering roller1is rotatable (by intermediary transfer belt101), whereas the lengthwise end sections3of the belt steering roller1are not rotatable (by intermediary transfer belt101), being substantially higher in the amount of friction between themselves and intermediary transfer belt101than that between the center section2and intermediary transfer belt101.

When the left and right edge portions of the intermediary transfer belt101are on the left and right nonrotational sections3(which hereafter may be referred to as friction rings), the left and right end portions of the intermediary transfer belt101are equal in the amount of friction between the belt steering roller1and intermediary transfer belt101, and therefore, the steering roller1does not tilt. As the intermediary transfer belt101is made to laterally shift as shown inFIG. 2(b) or2(c) by external disturbance, the belt steering roller1automatically tilts in the direction to compensate for the lateral shift of the intermediary transfer belt101, by an angle necessary to compensate for the lateral shift of the intermediary transfer belt101. Thus, the intermediary transfer belt101moves back into the state shown inFIG. 2(a).

Referring toFIG. 2(b), if the intermediary transfer belt101shifts leftward relative to its moving direction, it begins to ride on the left friction ring3of the belt steering roller1, increasing thereby the left side of the intermediary transfer belt101greater in the amount of friction between the intermediary transfer belt101and belt steering roller1. As a result, the belt steering roller1tilts in such a direction that its left side becomes lower than its right side, generating thereby such a force that causes the intermediary transfer belt101, which is being moved in such a manner as to wrap around the belt steering roller1, to shift rightward. Thus, the intermediary transfer belt101moves rightward, automatically cancelling the leftward shift to which has just occurred.

Next, referring toFIG. 2(c), if the intermediary transfer belt101shifts rightward relative to its moving direction, it begins to ride on the right friction ring3of the belt steering roller1, increasing thereby the right side of the intermediary transfer belt101greater in the amount of friction between the intermediary transfer belt101and belt steering roller1. As a result, the belt steering roller1tilts in such a direction that its right side becomes lower than its left side, generating thereby such a force that causes the intermediary transfer belt101, which is being moved in such a manner as to wrap around the belt steering roller1, to shift left. Thus, the intermediary transfer belt101moves left, automatically cancelling thereby the rightward shift which has just occurred.

Referring toFIG. 3, the automatic belt aligning mechanical device10is structured so that the belt steering roller1automatically aligns the intermediary transfer belt101; the imbalance in the amount of friction between the left friction ring3and intermediary transfer belt101and that between the right friction ring3and intermediary transfer belt101causes the belt steering roller1to automatically align the intermediary transfer belt101. The center section2of the belt steering roller1, that is, the belt steering roller1minus the left and right lengthwise sections, takes up the major portion of the belt steering roller1, in terms of the direction parallel to the axial line of the belt steering roller1. It is rotatable by the intermediary transfer belt101. In comparison, each of the lengthwise end sections of the belt steering roller1is a friction ring3. While the center section2(rotatable section) is rotated by the circular movement of the intermediary transfer belt101, the friction ring3cannot be rotated by the circular movement of the intermediary transfer belt101. Therefore, as the intermediary transfer belt101is circularly moved, it rubs the friction ring section3of the belt steering roller1, generating friction between itself and the friction rings3.

The automatic belt aligning mechanism has a rotationally movable plate7, which has a pair of plates6for supporting the belt steering roller1. The steering roller supporting plates6are at the lengthwise ends of the rotationally movable plate7, one for one, and are perpendicular to the plate7. The rotational plate7and steering roller supporting plates6make up a holder for supporting the belt steering roller1. The automatic belt aligning mechanical device10has also a pair of sliding bearings4, which are at the lengthwise ends of the mechanism, one for one. The sliding bearings rotatably support the belt steering roller1. Each bearing is fitted in the groove, with which the corresponding steering roller supporting plate6is provided. It is under the pressure from a compression spring5, remaining pressured in the direction indicated by an arrow mark PT. Thus, the steering roller1functions also as a tension roller for providing the intermediary transfer belt101with a preset amount of tension. That is, because each of the lengthwise ends of the belt steering roller1is kept pressed by the compression spring5in the direction indicated by the arrow mark RT, the steering roller presses on the inward surface of the intermediary transfer belt101, providing thereby the intermediary transfer belt101with the preset amount of tension.

The rotational plate7is supported by a frame stay8. More specifically, the rotational plate7is rotatably supported by a steering shaft (21inFIG. 3) so that it can be rotationally moved about the axial line J of the steering shaft21. The frame stay8is between the side plates of the intermediary transfer unit (124inFIG. 1), and extends from one side plates to the other. It is a part of the boxy frame of the unit124. The frame stay8has a pair of sliding rollers9, which are at the lengthwise ends of the stay8. The rollers9play the role of reducing the friction which occurs as the rotational plate7is rotationally moved.

Referring toFIG. 4, the steering shaft21, which is a rotatable shaft, is fitted in the hole with which the center portion of the rotational plate7is provided. It is solidly attached to the rotational plate7with a small screw24. One end21D of the steering shaft21is shaped so that its cross section is in the form of a letter D. Therefore, the steering shaft21can be held nonrotationally by a tool when the intermediary transfer unit124is assembled. More concretely, the steering shaft21is rotatably supported by a bearing23(ball bearing) solidly attached to the frame stay8, by being put through the bearing23. The opposite end of the steering shaft21from where the small screw24has a stopper26for preventing the steering shaft21from disengaging from the frame stay8. The automatic belt aligning mechanical device10is also provided with a rotary dumper20, which is fitted around the steering shaft21. The rotary dumper20is attached to the frame stay8with a pair of small screws25.

The rotary dumper20generates viscous resistance (drag) as the belt steering roller1is rotationally moved in an oscillatory manner. It is at the center of the automatic belt aligning mechanical device10in terms of the lengthwise direction of the mechanism10. It is a device which uses viscous drag of oil or the like to generate resistance to the rotational movement of the belt steering roller1. It increases (proportionally, in theory) resistance in proportion to the shear speed (rotational speed) of the steering shaft21. Thus, as the change, per unit length of time, in the speed with which the steering shaft21rotates in an oscillatory manner, increases, the rotary dumper20increases in the rotational drag which works against the rotation of the steering shaft21. Therefore, the noises in the change in the difference between the lengthwise ends of the belt steering roller1in terms of the friction between the belt steering roller1and intermediary transfer belt101are eliminated. Therefore, the automatic belt aligning mechanical device10stabilizes in the oscillatory movement of the belt steering roller1.

A straight ring, that is, a ring which is uniform in external diameter in terms of direction parallel to its axial line as shown inFIG. 5(a) may be used as each of the friction rings3of the belt steering roller1. In a case where a straight ring is employed as the friction ring3, the coefficient μs of the static friction of the friction ring3is desired to be set to roughly 0.6 (μs≈0.6).

Further, a tapered ring, that is, a ring shaped so that the more outward in terms of the direction parallel to the axial line of the belt steering roller1as shown inFIG. 5(b), the larger the external diameter, may be employed as the friction ring3. In a case where a tapered ring is employed as the friction ring3, it may be less in coefficient μs of static friction than a straight ring. More concretely, if the angle φ of taper of the tapered ring is 8° (φ=8°), the tapered ring is desired to be roughly 0.3 (μs≈0.3) in coefficient μs of static friction.

In either case, it is assumed that the coefficient of friction of the surface of the friction ring3is set to be larger than that of the rotational section2of the belt steering roller1. As the material for the friction ring3, a resinous substance, such as polyacetal (POM), which is slippery, is used. In consideration of the ill effects of the static electricity attributable to the friction between the friction ring3and intermediary transfer belt101, the friction ring3is made electrically conductive.

The rotational section2of the belt steering roller1is made of aluminum. It is made to be roughly 0.1 in the coefficient μSTR of static friction of its surface (μSTR≈0.1). However, as long as it is less than that of the friction ring3, it may be made of a substance other than aluminum. The coefficient of friction of the friction ring3and that of the rotational section2were measured with the use of Coefficient of Friction Testing Method (JIS K7125) for plastic, film, sheet, etc. More concretely, a sheet of polyimide, which is the material for the inward layer (substrate) of the intermediary transfer belt101, was used as the test piece.

One of the lengthwise end portions of the steering roller shaft30is made D-shaped in cross section so that it can be nonrotationally supported by the sliding bearing4. The rotational section2of the belt steering roller1is rotatably supported by the steering roller shaft30, with the presence of bearings which are in the rotational section2. In comparison, the friction rings3, which make up the lengthwise end portions of the belt steering roller1, one for one, are nonrotationally supported by the steering roller shaft30with the use of a pair of parallel pins.

Therefore, when the intermediary transfer belt101, which is suspended and kept stretched by the steering roller1and the other rollers, is circularly moved, the inward surface of the intermediary transfer belt101does not rub the rotational section2of the belt steering roller1, but, it rubs the friction rings3, which make up the lengthwise end portions of the belt steering roller1, one for one, generating thereby a substantial amount of friction between itself and each of the friction rings3.

However, it is not mandatory that the friction rings3are nonrotationally fitted around the steering roller shaft30. That is, the automatic belt aligning mechanical device10may be structured so that the friction rings3are rotatable. However, in a case where the automatic belt aligning mechanical device10is structured so that the friction rings3are rotatable, the amount of torque necessary to rotate the friction rings3in the circular moving direction of the intermediary transfer belt101needs to be greater than the amount of torque necessary to rotate the rotational section2of the belt steering roller1in the moving direction of the intermediary transfer belt101.

The automatic belt aligning mechanical device10is structured as described above. Therefore, as the area of contact between one of the friction ring portions3of the belt steering roller1and the intermediary transfer belt101becomes greater than a certain value (preset value) as shown inFIG. 2(b) or2(c), the lengthwise end of the steering roller1, which became greater in the friction between the belt steering roller1(friction roller3) and intermediary transfer belt101, is pulled downstream in terms of the moving direction of the intermediary transfer belt101by the intermediary transfer belt101. As a result, the belt steering roller1tilts in such a direction that its lengthwise end which is greater in the friction between its friction ring3and the intermediary transfer belt101will be on the downstream side relative to the other lengthwise end of the belt steering roller1. In other words, the belt steering roller1begins to steer the intermediary transfer belt101. The angle by which the belt steering roller1tilts is proportional to the imbalance between the lengthwise ends of the belt steering roller1in terms of the friction between the belt steering roller1and intermediary transfer belt101.

Referring toFIG. 6(a), the width of the intermediary transfer belt101is greater than the length of the rotational section2of the belt steering roller1, and less than the length of the belt steering roller1(rotational section2+frictional ring sections3). When the intermediary transfer belt101is remaining idealistically (perfectly) aligned (centered) relative to the belt steering roller1by the automatic belt aligning mechanical device10, the length (area) of contact, in terms of the widthwise direction of the intermediary transfer belt101, between the intermediary transfer belt101and one of the friction ring sections3and the length (area) of contact between the intermediary transfer belt101and the other friction ring section3are the same, being w (hatched portions inFIG. 6(a)). When the positional and dimensional relationships between the intermediary transfer belt101and belt steering roller1are as shown inFIG. 6(a), even if the intermediary transfer belt101laterally shifts, it is ensured that the intermediary transfer belt101remains wrapped around at least one of the friction ring sections3; there is friction between the intermediary transfer belt101and at least one of the friction ring sections3. That is, even after the intermediary transfer belt101laterally shifted, the intermediary transfer belt101continues to rub at least one (or both) of the friction ring sections3.

Next, referring toFIG. 6(b), in a case where the width of the intermediary transfer belt101is less than the length of the rotational section2of the belt steering roller1, even if the intermediary transfer belt101laterally shifts, the belt steering roller1is not tilted until the intermediary transfer belt101begins to ride onto (and rub) one of the friction ring sections3. Therefore, it is liable that the belt steering roller1is abruptly tilted (controlled) the moment the intermediary transfer belt101begins to ride onto one of the friction ring sections3. In principle, even if the positional and dimensional relationships between the intermediary transfer belt101and belt steering roller1are as shown inFIG. 6(b), it is possible to utilize the imbalance in the amount of friction between the left and right sides of the automatic belt aligning mechanical device10to automatically align the intermediary transfer belt101. However, in a case where the positional and dimensional relationships between the intermediary transfer belt101and belt steering roller1are as shown inFIG. 6(a), the state of balance in terms of the friction between the left and right side of the automatic belt aligning mechanical device10can be always detected, and the steering roller1is unlikely to suddenly change in angle. Therefore, it is possible to incessantly control the intermediary transfer belt101in lateral shift.

Referring toFIG. 1, a cleaning blade102bis an example of a component placed in contact with the intermediary transfer belt101. It is placed in parallel to the belt steering roller1so that it contacts the outward surface of the portion of the intermediary transfer belt101, which is supported by the belt steering roller1.

Next, referring toFIG. 6(a), the transfer residual toner, that is, the toner having failed to be transferred onto a sheet P of recording medium, and therefore, remaining on the intermediary transfer belt101after the secondary transfer, is recovered by the cleaning blade102bof a belt cleaning device102. The cleaning blade102b, which is formed of urethane rubber, is positioned so that it opposes the steering roller1with the presence of the intermediary transfer belt101between itself and belt steering roller1, and also, so that its base portion is on the upstream side of its cleaning edge in terms of the moving direction of the intermediary transfer belt101. If the cleaning blade102bpresses the intermediary transfer belt101upon the friction rings3, the friction between the intermediary transfer belt101and friction rings3will excessively increases. Therefore, the length of contact between the cleaning blade102band intermediary transfer belt101is made to be less than the length of the rotational sections2of the belt steering roller1.

The state of contact (that is, friction) between the cleaning blade102band intermediary transfer belt101has to be uniform across the area of contact between the cleaning blade102band intermediary transfer belt101in terms of the lengthwise direction of the cleaning blade102b. Therefore, the cleaning blade102bis held so that it always remains parallel to the belt steering roller1. That is, the belt cleaning apparatus102comprises the pair of the aforementioned steering roller supporting lateral plates6for supporting the belt steering roller1by the lengthwise ends of the belt steering roller1, and an arm (unshown) solidly attached to the steering roller supporting lateral plates6. The cleaning device102is supported by the arm (unshown) by its lengthwise ends in such a manner that it is rotationally moved with the belt steering roller1in the oscillatory manner. Thus, as the belt steering roller1is tilted, the belt cleaning device102tilts with the belt steering roller1. Therefore, the cleaning edge of the cleaning blade102bis kept pressed against the belt steering roller1with the presence of the intermediary transfer belt101between itself and belt steering roller1, at the same location in terms of the rotational direction of the belt steering roller1(moving direction of intermediary transfer belt101). Therefore, even if the intermediary transfer belt101laterally shifts, and therefore, the steering roller1tilts, the state of contact between the intermediary transfer belt101and cleaning blade102bdoes not change, and therefore, the cleaning blade102bcontinues to satisfactorily recover the transfer residual toner.

In the following embodiments of the present invention, the angle of the cleaning blade102bof the belt cleaning device102is 25°, and the contact pressure between the cleaning blade102band intermediary transfer belt101is 30 N/m (30 gf/cm). The hardness of the cleaning blade (formed of urethane rubber) is 75 degrees in JIS hardness scale A, and the thickness of the cleaning blade102bis 2 mm. However, the following embodiments of the present invention are not intended to limit the present invention in terms of the specifications of the belt cleaning device102.

However, when the transfer residual toner on the intermediary transfer belt101is removed by the cleaning blade102b, the friction between the intermediary transfer belt101and cleaning blade102bacts as external disturbance upon the intermediary transfer belt101. The effect of this phenomenon becomes very conspicuous as the nip between the intermediary transfer belt101and cleaning blade102breduces in the amount of the toner and its external additive, or runs out of the toner and/or external additive, and therefore, the friction between the intermediary transfer belt101and cleaning blade102bincreases. If the effect of this phenomenon becomes excessive, the automatic belt aligning mechanical device10fails to normally operate; it fails to automatically align (center) the intermediary transfer belt101. Therefore, such problems are likely to occur that the image forming apparatus100outputs images suffering from color deviation, that the intermediary transfer belt101laterally shifts beyond recovery, or the like.

The automatic belt aligning mechanical device10utilizes the friction between the intermediary transfer belt101and friction rings3to keep the intermediary transfer belt101aligned (centered). However, if the friction between the intermediary transfer belt101and cleaning blade102bbecomes excessive, the friction is likely to prevent the automatic belt aligning mechanical device10from normally function, allowing thereby the intermediary transfer belt101to laterally shift beyond recovery.

Therefore, in the following embodiments of the present invention, the image forming apparatus100is operated in the lubrication mode to ensure that even when the intermediary transfer belt101is cleaned by the cleaning blade102b, the intermediary transfer belt101is kept automatically aligned (centered) with the utilization of the imbalance in the amount of friction between the left and right sides of the belt steering roller1.

FIG. 7is a block diagram of the control system, in the first embodiment, for operating the image forming apparatus100in the lubrication mode.FIG. 8is a flowchart of the control sequence, in the first embodiment, to be carried out in the lubrication mode.

Referring toFIG. 1, the image forming station109Bk, which is an example of a lubricant supplying section, is capable of supplying the intermediary transfer belt101with lubricant. More concretely, the image forming station109Bk forms a toner image on the photosensitive drum103(which is an example of an image bearing member), and transfers the toner image as lubricant onto the intermediary transfer belt101.

If the amount of the lateral shift of the intermediary transfer belt101exceeds a preset acceptable range, the control section201, which is an example of a controlling means, operates the image forming apparatus100in the lubrication mode. In the lubrication mode, the control section201makes the image forming station109Bk supply the intermediary transfer belt101with lubricant, and makes the intermediary transfer belt101carry the lubricant to the area of contact between the intermediary transfer belt101and cleaning blade102b. Also in the lubrication mode, while the toner image transferred onto the intermediary transfer belt101from the image forming station109Bk is conveyed through the secondary transfer station T2, such voltage that is the same in polarity as the toner charge is applied to the secondary transfer roller111from an electrical power source D2.

Referring toFIG. 6(a), the image forming apparatus100is provided with a belt position sensor115, which detects the position of the intermediary transfer belt101in terms of the widthwise direction of the intermediary transfer belt101. In the first embodiment, the belt position sensor115is an optical sensor (photo-interrupter), and is positioned so that it overlaps with one of the edges of the intermediary transfer belt101. The sensor115(photo-interrupter) is made up of a pair of optical elements (light emitter and light receptor), and detects the position of the intermediary transfer belt101based on the amount of light received by the light receptor. However, the image forming apparatus100may be structured so that an optical sensor of the reflection type is used in stead of the photo-interrupter, or the edge position of the intermediary transfer belt101is mechanically detected.

The belt position, in which the intermediary transfer belt101is when the length of contact between the intermediary transfer belt101and one of the lengthwise end portions of the belt steering roller1in terms of the lengthwise direction of the belt steering roller1(widthwise direction of intermediary transfer belt101) is equal to the length of contact between the intermediary transfer belt101and the other end portion of the belt steering roller1, is the normal position of the intermediary transfer belt101. Thus, the amount of lateral shift of the intermediary transfer belt101is defined as the distance between the current position of the intermediary transfer belt101and the normal position of the intermediary transfer belt101. Referring toFIG. 6(a), a range A is where the positional deviation of the intermediary transfer belt101from the normal position of the intermediary transfer belt101is no more than 2 mm. The definition that the intermediary transfer belt101is within the normal range in terms of the widthwise direction of the intermediary transfer belt101means that one of the two edges of the intermediary transfer belt101is within the range A. That is, if the lateral shift of the intermediary transfer belt101becomes no less than 2 mm, that is, if one of the edges of the intermediary transfer belt101moves out of the range A, the control section201determines that the automatic belt aligning mechanical device10is not working normally. Whether or not one of the edges of the intermediary transfer belt101is out of the range A is determined based on the output of the belt position sensor115. That is, the belt position sensor115functions as the means for detecting whether or not the intermediary transfer belt101is in the normal range in terms of the widthwise direction of the intermediary transfer belt101.

Next, referring toFIG. 1, the control section201puts the image forming apparatus100in the lubrication mode, based on the output of the belt position sensor115. The lubrication mode is for restoring the automatic belt aligning mechanical device10in its capability for preventing the intermediary transfer belt101from snaking. In the lubrication mode, a toner image dedicated to lubrication, that is, a band toner image which is not for forming an image on recording medium, is formed on the photosensitive drum103of one of the image forming stations109, and is transferred onto the intermediary transfer belt101(this process hereafter will be referred to as “lubricatory toner image formation”). The lubricatory toner image is conveyed to the belt cleaning device102by the intermediary transfer belt101, while the lubricatory toner image is conveyed through the secondary transfer station T2, such DC voltage that is opposite in polarity to the DC voltage applied for image formation is applied to the secondary transfer roller111, in order to ensure that the lubricatory toner image reaches the belt cleaning device102virtually in entirety, while preventing the secondary transfer roller111from being soiled by the lubricatory toner image.

There is no restriction regarding the color of the toner of which the lubricatory toner image is formed. In the first embodiment, however, the lubricatory toner image is formed of black toner with the use of the image forming station109Bk. The lubricatory toner image is formed so that its width matches the entire range of the development area of the developing device in terms of the widthwise direction of the intermediary transfer belt101. Thus, in terms of the widthwise direction of the intermediary transfer belt101, the dimension of the lubricatory toner image is roughly the same as that of the cleaning blade102b. The amount of toner per unit area of the lubricatory toner image is 0.5 mg/cm2, and the dimension of the lubricatory toner image in terms of the moving direction of the intermediary transfer belt101is 10 mm. When the lubricatory toner image is conveyed through the secondary transfer station T2, −300 V of DC voltage is applied to the secondary transfer roller111. However, the numerical values given above regarding the formation and conveyance of the lubricatory toner image are not intended to limit the present invention in terms of the specifications of the belt cleaning device101.

The lubricatory toner image formed through the above described process is conveyed by the intermediary transfer belt101to the area of contact between the intermediary transfer belt101and cleaning blade102b, and remains in the area of contact. In the area of contact between the intermediary transfer belt101and cleaning blade102b, the toner and its external additives function as lubricants, reducing the friction between the intermediary transfer belt101and cleaning blade102b. Thus, the automatic belt aligning mechanical device10is restored in its function of automatically aligning (centering) the intermediary transfer belt101with the utilization of the imbalance in friction between the left and right sides of the belt steering roller1.

Next, referring toFIG. 8along withFIG. 7, as the control section201receives a job, it starts an image forming operation (S101). Then, it receives signals from the belt position sensor115, and determines, based on the signals from the sensor115, whether or not the position of the intermediary transfer belt101is laterally offset from the normal position of the intermediary transfer belt101by no less than 2 mm (S102).

If the lateral deviation of the intermediary transfer belt101is no more than 2 mm (no in S102), the control section201does not put the image forming apparatus100in the lubrication mode, and makes the image forming apparatus100do the job. Then, it determines whether or not the job has been finished (S108). If it determines that the job has been completed (yes in S107), it stops the image forming apparatus100, but, if the job has not been completed (no in S107), it makes the image forming apparatus100start the remaining portion of the job (S101).

If the control section201determines that the lateral deviation of the intermediary transfer belt101is no less than 2 mm (yes in S102), it finishes the on-going image forming operation (S103), and makes the image forming station109Bk form a lubricatory toner image, and applies to the secondary transfer roller111, such DC voltage that is opposite in polarity to the DC voltage to be applied to the secondary transfer roller111during the formation of a toner image to be transferred onto recording medium (S104). That is, as it detects that the intermediary transfer belt101is outside the normal range in terms of the widthwise direction of the intermediary transfer belt101, it supplies the intermediary transfer belt101with toner as lubricant.

After the delivery of the lubricatory toner image to the intermediary transfer belt101, the control section201circularly moves the intermediary transfer belt101several full turns (S105), and determines whether or not the lateral deviation of the intermediary transfer belt101has become no more than 2 mm (S106).

If the control section201determines that the lateral deviation of the intermediary transfer belt101is still no less than 2 mm (no in S106), it forms another lubricatory toner image and delivers the lubricatory toner image to the area of contact between the intermediary transfer belt101and cleaning blade102b(S104). Then, it circularly moves the intermediary transfer belt101several full turns (S105). If the lateral deviation of the intermediary transfer belt101is no more than 2 mm (yes in S106), it determines whether or not the on-going image forming operation has been completed (S107). If it determines that the operation has been completed (yes in S107), it starts working on the remaining portion of the job (S101). If it determines that the job has been completed (yes in S107), it stops the image forming apparatus100.

In the first embodiment, as the automatic belt aligning mechanical device10is made to malfunction by the belt cleaning device102, a “lubricatory toner image” is formed based on the value of the output of the belt position sensor115, in order to restore the automatic belt aligning mechanical device10in its function of making the intermediary transfer belt101and belt steering roller1automatically align (center) themselves relative to each other. Further, it is ensured that even when intermediary transfer belt101is cleaned by the belt cleaning device102which uses the cleaning blade102b, the automatic belt aligning control based on the imbalance in friction between the left and right side of the belt steering roller1is continuously and reliably carried out.

FIG. 9is a block diagram of the control sequence carried out in the lubrication mode in the second embodiment of the present invention.FIG. 10is a flowchart of the control sequence carried out in the lubrication mode in the second embodiment. In the lubrication mode in the first embodiment, the lubricatory toner image was formed based on the value of the output of the belt position sensor115, and was sent to the area of contact between the intermediary transfer belt101and cleaning blade102b. However, if the effects of the external disturbance other than the one attributable to the belt cleaning device102becomes extremely large, supplying the lubricatory toner image to the area of contact between the intermediary transfer belt101and cleaning blade102bsometimes fails to make the intermediary transfer belt101return to the normal position. In such a case, the intermediary transfer belt101laterally shift beyond recovery.

In the second embodiment, therefore, the following control is carried out. That is, if the lateral deviation of the intermediary transfer belt101from the normal position is no less than 2 mm and no more than 3 mm, the same formation and delivery of the lubricatory toner image as those in the first embodiment are done. However, if the lateral deviation of the intermediary transfer belt101is no less than 3 mm and no more than 5 mm, the control section301makes the control panel of the image forming apparatus100display a message that recommends replacing the intermediary transfer belt101. Further, if the lateral deviation of the intermediary transfer belt101is no less 5 mm, the control section301stops the image forming apparatus100in order to prevent the intermediary transfer belt101from breaking, and makes the control panel of the image forming apparatus100display a message that demands replacing the intermediary transfer belt101.

Next, referring toFIG. 10along withFIG. 9, as the control section301receives a job, it starts an image forming operation (S201). Then, it receives signals from the belt position sensor115, and determines, based on the signals from the sensor115, whether or not the position of the intermediary transfer belt101is laterally offset from the normal position of the intermediary transfer belt101by no less than 2 mm (S202).

If the lateral deviation of the intermediary transfer belt101is no more than 2 mm (no in S202), the control section301does not put the image forming apparatus100in the lubrication mode, and makes the image forming apparatus100do the job. Then, it determines whether or not the job has been finished (S203). If it determines that the job has been completed (yes in S212), it stops the image forming apparatus100, but, it determines that the job has not been completed (no in S212), it makes the image forming apparatus100start the remaining portion of the job (S201).

If the control section301determines that the lateral deviation of the intermediary transfer belt101is no less than 2 mm (yes in S202), it determines whether or not the lateral deviation of the intermediary transfer belt101is no less than 3 mm. If the lateral deviation of the intermediary transfer belt101is no less than 3 mm (yes in S204), it determines whether or not the lateral deviation of the intermediary transfer belt101is no less than 5 mm (S209).

If the lateral deviation of the intermediary transfer belt101is no less than 2 mm and no more than 3 mm (no in S204), the control section301finishes the on-going image forming operation (S205), and begins to operate the image forming apparatus100in the lubrication mode (S206). After the completion of the operation in the lubrication mode, the control section301circularly moves several full turns (S207), and determines whether or not the lateral deviation of the intermediary transfer belt101became no more than 2 mm (S208). If the control section301determines that the lateral deviation of the intermediary transfer belt101is still no less than 2 mm, it operates the image forming apparatus100in the lubrication mode again (S206and S207). As the lateral deviation of the intermediary transfer belt101becomes no more than 2 mm, the control section301advances to Step S212.

If the lateral deviation of the intermediary transfer belt101is no less than 3 mm and no more than 5 mm (no in S209), the control section301shows on the display302of the control panel of the image forming apparatus100, a message that warns a user of the nearness of the end of the service life of the intermediary transfer belt101(S210). After the completion of the job (S211), the control section301advances to Step S212.

If the lateral deviation of the intermediary transfer belt101is no less than 5 mm (yes in S209), the control section301stops the image forming apparatus100(S213), and shows on the display302of the control panel, a message that prompts a user to replace the intermediary transfer belt101(S214).

Also in the second embodiment, as the automatic belt aligning mechanical device10is made to malfunction by the belt cleaning device102, a “lubricatory toner image” is formed, based on the value of the output of the belt position sensor115, and delivered to the area of contact between the intermediary transfer belt101and cleaning blade102b, in order to restore the automatic belt aligning mechanical device10in its function of making the intermediary transfer belt101and belt steering roller1automatically align (center) themselves relative to each other. In addition, a message that warms a user of an imminent occurrence of damages to the intermediary transfer belt101, a message that prompts a user to replace the intermediary transfer belt101, or the like, is given before it becomes impossible for the intermediary transfer belt101to be automatically aligned (centered).

FIG. 11is a schematic sectional view of the image forming apparatus in the third embodiment of the present invention, and shows the general structure of the apparatus.FIG. 12is a timing chart of the lubrication mode in the third embodiment.FIG. 13is a block diagram of the control system for operating the image forming apparatus100in the lubrication mode in the third embodiment.FIG. 14is a flowchart of the lubrication mode in the third embodiment.

The third embodiment is the same as the first embodiment except that in the third embodiment, the cleaning blade102bof the belt cleaning device102is separated from the intermediary transfer belt101before it is determined whether or not it is necessary to operate the image forming apparatus100in the lubrication mode. Further, the image forming apparatus100in the third embodiment is the same as that in the first embodiment except that the cleaning blade102bof the belt cleaning device102in the third embodiment is separable from the intermediary transfer belt101. Thus, the structural components inFIGS. 11,13and14, which are the same in function as the counterparts in the first embodiment are given the same referential codes as the counterparts in the first embodiment, respectively, and are not going to be described here in order not to repeat the same descriptions.

Referring toFIG. 11, the image forming apparatus100is provided with a separating mechanism116which can separate the cleaning blade102bof the cleaning device102from the intermediary transfer belt101or place the cleaning blade102bin contact with the intermediary transfer belt101.

The control section401determines, based on the value of the output of the belt position sensor115, whether or not the cleaning blade102bof the cleaning device102is to be separated from the intermediary transfer belt101. More concretely, if the lateral deviation of the intermediary transfer belt101from the normal position of the intermediary transfer belt101is no less than 2 mm, the control section401activates the separating mechanism116to separate the cleaning blade102bof the belt cleaning device102from the intermediary transfer belt101. Then, it determines whether or not the intermediary transfer belt101reduces in the lateral deviation. If the intermediary transfer belt101reduces in the lateral deviation, the control section401operates the image forming apparatus100in the lubrication mode.

As the cleaning blade102bof the belt cleaning device102is separated from the intermediary transfer belt101, the intermediary transfer belt101is freed from the external disturbance attributable to the cleaning device102. Thus, it becomes possible for the belt aligning mechanism10to align the intermediary transfer belt101with the use of its belt steering roller1. There is no restriction regarding the timing for placing the cleaning blade102bof the belt cleaning device102in contact with the intermediary transfer belt101. In the third embodiment, however, in consideration of the length of the downtime of the image forming apparatus100, the control section401places the cleaning blade102bin contact with the intermediary transfer belt101as soon as the lateral deviation of the intermediary transfer belt101becomes no more than 1 mm.

Incidentally, when the cleaning blade102bof the belt cleaning device102is separated from the intermediary transfer belt101or placed in contact with the intermediary transfer belt101, the intermediary transfer belt101may be kept circularly moved, or stationary. In the third embodiment, the intermediary transfer belt101is kept circularly moved.

The friction between the intermediary transfer belt101and the cleaning blade102bof the belt cleaning device102is substantial. Therefore, a “lubricatory toner image” is formed and delivered to the nip between the intermediary transfer belt101and cleaning blade102bto supply the nip with a combination of toner and external additives, as lubricant. The timing for the formation and delivery of the lubricatory toner image may be after or prior to the placement of the cleaning blade102bin contact with the intermediary transfer belt101. However, from the standpoint of making as short as possible the length of time the intermediary transfer belt101is circularly moved while the friction between the intermediary transfer belt101and cleaning blade102bis substantial, it is desired to be immediately before the lubricatory toner image reaches the area of contact between the intermediary transfer belt101and cleaning blade102bthat the cleaning blade102bis placed in contact with the intermediary transfer belt101.

The condition under which the lubricatory toner image is formed and delivered in this embodiment is the same as that in the first embodiment. Further, the lubricatory toner image formed in the third embodiment, and the voltage applied to the secondary transfer roller111of the secondary transfer station while the image forming apparatus100is operated in the lubrication mode, are the same as those in the first embodiment.

Next, referring toFIG. 14along withFIG. 13, as the control section401receives a job, it starts an image forming operation (S301). Then, the control section401receives signals from the belt position sensor115, and determines whether or not the lateral deviation of the intermediary transfer belt101is no less than 2 mm (S302).

If the lateral deviation of the intermediary transfer belt101is no more than 2 mm (no in S302), the control section401continues the image forming operation without putting the image forming apparatus100in the lubrication mode (S310). Then, it determines whether or not the job has been completed (S309). If the job has been completed (yes in S309), the control section401stops the image forming apparatus100. If the job has not been completed (no in S309), the control section401starts the image forming apparatus100to finish the remaining portion of the job (S301).

If the lateral deviation of the intermediary transfer belt101is no less than 2 mm (yes in S302), the control section401finishes the on-going image forming operation (S303). Then, it separates the cleaning blade102bof the belt cleaning device102from the intermediary transfer belt101by activating the separating mechanism116(S304), and lets the intermediary transfer belt101idle (S305). Then, it determines whether or not the lateral deviation of the intermediary transfer belt101is no more than 1 mm, while letting the intermediary transfer belt101idle (S306).

If the lateral deviation of the intermediary transfer belt101or the amplitude (lateral deviation) of the snaking of the intermediary transfer belt101is no less than 1 mm after the idling of the intermediary transfer belt101one minute (no in S306), the control section401determines that even if the image forming apparatus100is operated in the lubrication mode, the automatic belt aligning mechanical device cannot be restored in its function of automatically controlling the intermediary transfer belt101in lateral shift. Thus, the control section401shows on the display302of the control panel, a message that informs a user that the intermediary transfer belt101needs to be examined (S311), and stops the image forming apparatus100.

Referring toFIG. 12, if the amplitude (lateral deviation) of the pattern of snaking of the intermediary transfer belt101becomes no more than 1 mm while the intermediary transfer belt101is idled (yes in S306), the control section401begins to operate the image forming apparatus100in the lubrication mode. Then, if the lateral deviation of the intermediary transfer belt101becomes no more than 1 mm, the control section401forms a lubricatory toner image in the image forming station109Bk, and applies to the secondary transfer roller111, such DC voltage that is opposite in polarity to that applied while a toner image is formed to transferred onto recording medium (S307). It places the cleaning blade102bof the belt cleaning device102in contact with the intermediary transfer belt101by activating the separating mechanism116, before the lubricatory toner image reaches the area of contact between the cleaning blade102band intermediary transfer belt101(S308).

After the image forming apparatus100is operated in the lubrication mode, the control section401determines whether or not the job has been completed. If the job has been completed (yes in S309), the control section401stops the image forming apparatus100. If the job has not been completed (no in S309), the control section401starts the image forming apparatus100to finish the remaining portion of the job (S301).

In the lubrication mode in the third embodiment, in order to determine whether or not the image forming apparatus100is to be operated in the lubrication mode, the control section401separates the cleaning blade102bof the belt cleaning device102from the intermediary transfer belt101before it starts operating the image forming apparatus100in the lubrication mode. Therefore, it does not occur that the image forming apparatus100is unnecessarily operated in the lubrication mode when the intermediary transfer belt101is being made to laterally shift by a source other than the belt cleaning device102.

In the first, second and third embodiments of the present invention, the image forming apparatus was structured so that the intermediary transfer belt101is steered by the belt steering roller1. However, the present invention is also applicable to an image forming apparatus structured so that a recording medium conveyance belt201for conveying a sheet of recording medium, onto which a toner image is transferred, is steered by the belt steering roller1(FIG. 17).

Further, the present invention is also applicable to an image forming apparatus structured so that a member other than the cleaning blade is placed in contact with an intermediary transfer belt or a recording medium conveyance belt. That is, the present invention is applicable to an image forming apparatus even if the apparatus is structured so that a polishing roller, a fur brush, a charge brush, a magnetic roller, a cleaning web, or the like, that is, a cleaning means other than the cleaning blade is placed in contact with an intermediary transfer belt or a recording medium conveyance belt. The lubricant may be powdery lubricant other than toner, or liquid lubricant.

<Detailed Description of Automatic Control of Lateral Shift of Intermediary Transfer Belt>

FIG. 15is a perspective view of the automatic belt aligning mechanism. It is for describing the structure of the mechanism.FIG. 16is a drawing for describing the state in which an endless belt wraps around a belt steering roller.FIG. 16(b) is a plan view of the combination of the endless belt and belt steering roller, as seen from the direction indicated by an arrow mark TV inFIG. 16(a).

The qualitative description of the operation of the belt training mechanism is the same as the one given above with reference toFIG. 2. Here, therefore, the automatic aligning (centering) of an endless belt by the belt steering roller of an automatic belt aligning mechanism is quantitatively described.

Referring toFIG. 15, an automatic belt aligning mechanical device10A has a steering roller97made up of a center section90and a pair of lengthwise end sections91. The center section90is rotatable by the circular movement of an endless belt (50inFIG. 16), but, the lengthwise end sections91cannot be rotated by the circular movement of the endless belt. The steering roller97is supported by a steering roller supporting member92, which is rotatable in an oscillatory manner in the direction indicated by an arrow mark S, about the axial line of the steering shaft93attached to the center of the steering roller supporting member in terms of the lengthwise direction of the steering roller supporting member92. The steering roller supporting member92is kept pressured in the direction indicated by an arrow mark PT by a pressure applying member95which is compressed or released by a cam96. Thus, the steering roller97keeps the endless belt (50inFIG. 16) tensioned.

Next, referring toFIG. 16(a), the lengthwise end sections91of the steering roller97are supported in such a manner that they cannot be rotated by the movement of the endless belt50. Therefore, as the belt50is circularly moved, the lengthwise end sections19are continuously subjected to the friction from the inward surface of the endless belt50. It is assumed here that the endless belt50is being circularly moved in the direction indicated by an arrow mark V, and the angle of contact between the endless belt50and each of the lengthwise end sections91is θs. The width of contact (in terms of direction perpendicular toFIG. 16)between the endless belt50and the lengthwise end section91is a preset unit width.

To think of the portion of the endless belt50, which corresponds to an infinitesimal angle dθ of contact between the endless belt50and the lengthwise end section91of the steering roller97, the upstream side of the portion of the endless belt50, which corresponds to the infinitesimal angle dθ, in terms of the moving direction of the endless belt50, is not being pulled by the belt driving roller, and the downstream side of the above described portion of the endless belt50is being pulled by the belt driving roller. Therefore, if the amount of tensile force which acts on the upstream end of the above described portion of the endless belt50, in the direction parallel to the tangential line to the upstream end is T, the amount of tensile force which acts on the downstream end of the above described portion of the endless belt50, in the direction parallel to the tangential line to the downstream end is T+dT. Thus, the amount of force which the endless belt50applies to each of the lengthwise end sections91of the steering roller97, toward the axial line of the lengthwise end section91may be approximated as Tdθ. Thus, if the coefficient of friction of the lengthwise end section91is μS, the amount dF of friction between the lengthwise section91and endless belt50can be expressed in the form of the following mathematical equation:
dF=μsTdθ(1)

The tensile force T is attributable to the unshown belt driving roller. Therefore, if the coefficient of friction of the belt driving roller is μr, the tensile force dT can be expressed in the form of the following mathematical equation:
dT=μrTdθ(2)

The amount of the tensile force T can be obtained from the following equation obtained by integrating Formula (2′) with respect to angle θS of contact:
T=T1e−μrθ(3)

T1is the amount of the tensile force where θ=0. Combining Equations (1) and (3),
dF=μsT1e−μrθdθ(4)

Referring toFIG. 15, when the direction in which the steering roller supporting member92rotationally moves about the steering shaft93is the one indicated by an arrow mark S, there is an angle α between the rotational direction S and the plane which coincides with the point at which the intermediary transfer belt101begins to wrap around the steering roller97, and the axial line of the steering roller97. Therefore, the amount of the downward component of the force calculable with the use of Equation (4) can be calculated with the use of the following equation:
dFs=μsT1e−μrθsin(θ+α)dθ(5)

Further, the amount (per unit width) of downward force, which is parallel to the direction indicated by the arrow mark S, and which each of the lengthwise end sections91receives from the endless belt50, can be obtained by integrating Equation (5) with respect to angle θS of contact.

Referring toFIG. 16(b), it is assumed here that the endless belt50has shifted leftward of theFIG. 16(b) while the endless belt50is circularly moved in the direction indicated by an arrow mark V, and also, that the left edge portion of the endless belt50is in contact with the corresponding lengthwise end section91of the steering roller97, by a width of w, whereas the right edge portion of the endless belt50is not in contact with the corresponding lengthwise end section91of the steering roller97. Thus, the left lengthwise end section91of the steering roller97is under an amount Fsw of force directed downward in terms of the direction indicated by the arrow mark S, whereas the lengthwise right end section91of the steering roller97is under zero amount of force directed downward in terms of the direction indicated by the arrow mark S. Thus, the difference in the amount of friction between the left and right end sections of the steering roller97is the primary source that generates moment FswL, that is, the force which causes the steering roller97to rotationally move about the steering shaft (93inFIG. 15). The moment which acts in the direction to rotationally move the steering roller97about the steering shaft (93inFIG. 15) is called “steering torque”. In the case of the assumption made as described inFIG. 16(b), the direction of the steering toque is such that makes the left side of the steering roller97, that is, the side to which the endless belt50has shifted, moves downward.

The direction in which moment is generated in the steering roller97based on the above described principle coincides with the direction in which the steering roller97is to be rotationally moved to cause the endless belt50to shift in the opposite direction from the direction in which the belt50has just shifted. Therefore, the lateral shift of the endless belt50caused by external disturbance is cancelled. That is, the endless belt50is automatically aligned.

This application claims priority from Japanese Patent Application No. 152830/2011 filed Jul. 11, 2011 which is hereby incorporated by reference.