Image forming apparatus including transfer belt

A post-processing apparatus according to one aspect of the present disclosure includes: transfer belt; roller position adjustment mechanism; position information acquiring portion; first opposing portion which causes transfer belt to contact first image carrier; second opposing portion capable of being positioned at either contact position that causes transfer belt to contact second image carrier or separation position that causes transfer belt to be separated from second image carrier; movement mechanism portion which moves second opposing portion to contact position or separation position; first control portion which controls roller position adjustment mechanism so that transfer belt will return to target position, based on position information acquired by position information acquiring portion; and second control portion which, in the case where transfer belt does not return into a correction range and is out of correction range, controls movement mechanism portion so as to change position of second opposing portion.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2012-239088 filed on Oct. 30, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to an image forming apparatus capable of forming a monochrome image in a single color and a color image composed of a plurality of colors.

An image forming apparatus such as a color printer includes, for example, a plurality of photosensitive drums that allow toner images for respective colors of black, yellow, magenta, and cyan to be formed thereon, and an intermediate transfer belt onto which the toner images formed on the plurality of photosensitive drums are to be transferred. The toner images for respective colors formed on the photosensitive drums are primarily transferred onto the intermediate transfer belt, and then collectively secondarily transferred onto a paper sheet from the intermediate transfer belt. Thus, a color image is formed on a paper sheet.

The above-described intermediate transfer belt extends over a drive roller linked with a drive source such as a motor, and a plurality of driven rollers. The intermediate transfer belt is rotated (endlessly moved) along with rotation of the drive roller, whereby toner images are sequentially transferred at positions opposing to the respective photosensitive drums.

The intermediate transfer belt may meander to deviate in the width direction of a roller during rotation. If the intermediate transfer belt meanders during rotation, when toner images are primarily transferred onto the intermediate transfer belt from the respective photosensitive drums, the positions of the toner images are displaced from each other, and this may cause color shift.

Conventionally, an image forming apparatus is known which includes a meandering resolving mode in which the orientation of a driven roller is set to a meandering resolving position so that the meandering intermediate transfer belt will return to a target position (reference position or such a range), and an equilibrium retaining mode in which the orientation of the driven roller is set to an equilibrium position so that the intermediate transfer belt will be retained at the target position. The image forming apparatus can return the meandering intermediate transfer belt to a target position by executing the meandering resolving mode.

The intermediate transfer belt may abnormally meander due to assembly defect of a drive mechanism such as a drive roller, for example. In the case where the intermediate transfer belt abnormally meanders, it may be impossible to return the intermediate transfer belt to a target position even if the image forming apparatus is operated in the above meandering resolving mode. In this case, printing by the image forming apparatus is automatically stopped. Then, until the defect is repaired, the image forming apparatus cannot perform either color printing and monochrome printing.

SUMMARY

An image forming apparatus according to one aspect of the present disclosure includes a first image carrier, a plurality of second image carriers, a transfer belt of endless belt type, a drive roller, a driven roller, a first opposing portion, a plurality of second opposing portions, a movement mechanism portion, position information acquiring portion, a first control portion, and a second control portion. A toner image is to be formed on the first image carrier. Toner images are to be formed on the plurality of second image carriers. The toner images formed on the first image carrier and/or the second image carriers are to be transferred onto the transfer belt of endless belt type. The drive roller supports the transfer belt in a rotatable manner and is capable of rotating the transfer belt. The driven roller supports the transfer belt in a rotatable manner. The first opposing portion is provided opposing to the first image carrier via the transfer belt and causes the transfer belt to contact the first image carrier. The plurality of second opposing portions are provided opposing to the plurality of second image carriers via the transfer belt and are each capable of being positioned at either contact positions that cause the transfer belt to contact the plurality of second image carriers or separation positions that cause the transfer belt to be separated from the plurality of second image carriers. The movement mechanism portion moves the positions of the plurality of second opposing portions to the contact positions or the separation positions. The position information acquiring portion acquires position information with respect to a width direction about the transfer belt. The roller position adjustment mechanism adjusts the orientation of a rotary shaft of the driven roller. The first control portion determines correction information for returning the transfer belt to a predetermined target position, based on the position information about the transfer belt acquired by the position information acquiring portion, and controls the roller position adjustment mechanism based on the correction information. The second control portion, in the case where, during the control for the roller position adjustment mechanism based on the correction information by the first control portion, the transfer belt does not return into a correction range centered on the target position within a predetermined time and is out of the correction range, controls the movement mechanism portion so as to change the positions of the plurality of second opposing portions.

DETAILED DESCRIPTION

Hereinafter, an embodiment in the case where an image forming apparatus according to the present disclosure is applied to a printer capable of four-full-color printing and monochrome printing will be described with respect to the drawings.

With reference toFIGS. 1 and 2, the entire structure of a printer1according to the present embodiment will be described.FIG. 1is a diagram for explaining placements of constituent elements of the printer1according to the present embodiment.FIG. 2is a block diagram showing the functional configuration of the printer1.FIG. 3is a perspective view showing the external appearance of the printer1.

As shown inFIG. 1, the printer1according to the present embodiment includes an apparatus main body M, a belt device20, an image forming portion30, and a sheet feed/discharge portion40. Besides these constituent elements, as shown inFIG. 2, the printer1includes an operation portion70, a storage portion75, a movement mechanism portion90, and a control portion100.

As shown inFIG. 1, the outer shape of the apparatus main body M of the printer1is formed by a case body BD as a housing.

As shown inFIG. 1, the image forming portion30is a portion that forms a toner image on a paper sheet T as a sheet-like transfer subject material based on predetermined image information. The image forming portion30includes photosensitive drums2a,2b,2c, and2d, charging portions10a,10b,10c, and10d, laser scanner units4a,4b,4c, and4d, developing devices16a,16b,16c, and16d, toner cartridges5a,5b,5c, and5d, toner feed portions6a,6b,6c, and6d, drum cleaning portions11a,11b,11c, and11d, electricity removing devices12a,12b,12c, and12d, primary transfer rollers13a,13b,13c, and13d, a transfer portion50, and a fixing portion60. It is noted that the image forming portion30includes a driven roller16and a drive roller17as a mechanism, and these rollers will be described in the description of the belt device20(described later).

In addition, as shown inFIG. 1, the sheet feed/discharge portion40is a portion that feeds a paper sheet T to the image forming portion30and discharges a paper sheet T having a toner image formed thereon. The sheet feed/discharge portion40includes a sheet feed cassette52, a manual sheet feed portion64, a conveyance path L for a paper sheet T, a registration roller pair80, a plurality of rollers or roller pairs (with no reference characters), and a sheet discharge portion61. It is noted that the conveyance path L is composed of a first conveyance path L1, a second conveyance path L2, a third conveyance path L3, a manual conveyance path La, and a return conveyance path Lb as described later.

Next, each component will be described in the order, the image forming portion30, the sheet feed/discharge portion40, and then the belt device20.

First, the image forming portion30will be described. In the image forming portion30, electric charging by the charging portions10a,10b,10c, and10d, light exposure by the laser scanner units4a,4b,4c, and4d, development by the developing devices16a,16b,16c, and16d, primary transfer by an intermediate transfer belt7(hereinafter, may be referred to as a “belt” with no reference character) and the primary transfer rollers13a,13b,13c, and13d, electricity removal by the electricity removing devices12a,12b,12c, and12d, and cleaning by the drum cleaning portions11a,11b,11c, and11d, are performed sequentially from upstream to downstream (left to right inFIG. 1) along the surfaces of the respective photosensitive drums2a,2b,2c, and2d.

In addition, in the image forming portion30, secondary transfer by the intermediate transfer belt7, a secondary transfer roller8, and the drive roller17, and fixing by the fixing portion60, are performed.

The photosensitive drums2a,2b,2c, and2dare image carriers formed by cylindrical members. In the present embodiment, the photosensitive drum2ais a second image carrier on which a toner image for yellow (Y) is to be formed, the photosensitive drum2bis a second image carrier on which a toner image for cyan (C) is to be formed, the photosensitive drum2cis a second image carrier on which a toner image for magenta (M) is to be formed, and the photosensitive drum2dis a first image carrier on which a toner image for black (B) is to be formed.

Upon formation of a color image, toner images for the respective colors are formed on the photosensitive drums2a,2b,2c, and2d. On the other hand, upon formation of a monochrome image, a toner image for black is formed on the photosensitive drum2dwhile toner images are not formed on the other photosensitive drums2a,2b, and2c.

The photosensitive drums2a,2b,2c, and2dare provided so as to be rotatable in directions indicated by arrows around an axis extending in a direction perpendicular to the movement direction of the intermediate transfer belt7. Electrostatic latent images are to be formed on the surfaces of the photosensitive drums2a,2b,2c, and2d.

The charging portions10a,10b,10c, and10dare provided facing to the surfaces of the respective photosensitive drums2a,2b,2c, and2d. The charging portions10a,10b,10c, and10deach uniformly charge the surfaces of the respective photosensitive drums2a,2b,2c, and2dinto negative (minus polarity) or positive (plus polarity).

The laser scanner units4a,4b,4c, and4dfunction as light exposure units. The laser scanner units4a,4b,4c, and4dare provided being spaced from the surfaces of the respective photosensitive drums2a,2b,2c, and2d. The laser scanner units4a,4b,4c, and4deach include a laser light source, a polygon mirror, a motor for driving the polygon mirror, and the like (with no reference characters) not shown.

The laser scanner units4a,4b,4c, and4dscan and expose, to light, the surfaces of the respective photosensitive drums2a,2b,2c, and2dbased on image information inputted from an external apparatus such as a PC (personal computer). Electric charges on portions of the surfaces of the respective photosensitive drums2a,2b,2c, and2dthat have been scanned and exposed to light are removed. Thus, electrostatic latent images are formed on the surfaces of the respective photosensitive drums2a,2b,2c, and2d.

The developing devices16a,16b,16c, and16dare provided being associated with the respective photosensitive drums2a,2b,2c, and2dand facing to the surfaces of the respective photosensitive drums2a,2b,2c, and2d. The developing devices16a,16b,16c, and16dapply toners for respective colors to electrostatic latent images formed on the surfaces of the respective photosensitive drums2a,2b,2c, and2d, whereby toner images for respective colors are formed on the surfaces of the respective photosensitive drums2a,2b,2c, and2d. The developing devices16a,16b,16c, and16drespectively correspond to four colors of yellow, cyan, magenta, and black. The developing devices16a,16b,16c, and16dinclude development rollers facing to the surfaces of the respective photosensitive drums2a,2b,2c, and2d, stirring rollers for stirring toners, and the like (with no reference characters).

The toner cartridges5a,5b,5c, and5dare provided being associated with the respective developing devices16a,16b,16c, and16d, and contain toners for respective colors to be fed to the respective developing devices16a,16b,16c, and16d. The toner cartridges5a,5b,5c, and5dcontain a toner for yellow, a toner for cyan, a toner for magenta, and a toner for black, respectively.

The toner feed portions6a,6b,6c, and6dare provided being associated with the respective toner cartridges5a,5b,5c, and5dand the respective developing devices16a,16b,16c, and16d. The toner feed portions6a,6b,6c, and6dfeed toners for respective colors contained in the respective toner cartridges5a,5b,5c, and5dto the respective developing devices16a,16b,16c, and16d. The toner feed portions6a,6b,6c, and6dare connected to the respective developing devices16a,16b,16c, and16dvia toner feed paths not shown.

On a side of the intermediate transfer belt7opposite to the photosensitive drums2a,2b,2c, and2d, the primary transfer rollers13a,13b,13c, and13dare provided opposing thereto, respectively. A predetermined portion of the intermediate transfer belt7is sandwiched between the respective primary transfer rollers13a,13b,13c, and13dand the respective photosensitive drums2a,2b,2c, and2d. The sandwiched predetermined portion is pressed to the surfaces of the respective photosensitive drums2a,2b,2c, and2d.

Primary transfer nips N1a, N1b, N1c, and N1dare formed between the photosensitive drums2a,2b,2c, and2dand the primary transfer rollers13a,13b,13c, and13d, respectively. At the primary transfer nips N1a, N1b, N1c, and N1d, toner images for respective colors developed on the photosensitive drums2a,2b,2c, and2dare sequentially primarily transferred onto the intermediate transfer belt7. Thus, a four-full-color toner image is formed on the intermediate transfer belt7.

It is noted that as described later, the primary transfer rollers13a,13b, and13c, the driven roller16, and a tension roller19are provided so as to be movable in the up-down direction inFIG. 1by the movement mechanism portion90(seeFIG. 8) which is not shown inFIG. 1.

In the printer1, upon formation of a four-full-color toner image, the primary transfer rollers13a,13b, and13c, the driven roller16, and the tension roller19are moved downward inFIG. 1by the movement mechanism portion90. Thus, as described above, the primary transfer nips N1a, N1b, N1c, and N1dare formed between the photosensitive drums2a,2b,2c, and2dand the primary transfer rollers13a,13b,13c, and13d, respectively.

In addition, in the printer1, upon formation of a monochrome toner image, the primary transfer rollers13a,13b, and13c, the driven roller16, and the tension roller19are moved upward inFIG. 1by the movement mechanism portion90. Thus, only the primary transfer nip N1dis formed between the photosensitive drum2dand the primary transfer roller13d.

InFIG. 1, the primary transfer rollers13a,13b, and13care provided opposing to the plurality of photosensitive drums (second image carriers)2a,2b, and2cvia the intermediate transfer belt (belt)7, and form a plurality of second opposing portions that can be moved to either contact positions (described later) that cause the intermediate transfer belt7to contact the plurality of photosensitive drums2a,2b, and2cor separation positions (described later) that cause the intermediate transfer belt7to be separated from the plurality of photosensitive drums2a,2b, and2c.

In addition, inFIG. 1, the primary transfer roller13dis provided opposing to the photosensitive drum (first image carrier)2dvia the intermediate transfer belt7, and forms a first opposing portion that causes the intermediate transfer belt7to contact the photosensitive drum2d. It is noted that the configuration of the movement mechanism portion90will be described later.

A primary transfer bias applying portion (not shown) applies, to the primary transfer rollers13a,13b,13c, and13d, primary transfer biases for transferring toner images for respective colors formed on the respective photosensitive drums2a,2b,2c, and2donto the intermediate transfer belt7.

The electricity removing devices12a,12b,12c, and12dare provided facing to the surfaces of the respective photosensitive drums2a,2b,2c, and2d. The electricity removing devices12a,12b,12c, and12dradiate light onto the surfaces of the respective photosensitive drums2a,2b,2c, and2d, thereby removing electricity (removing electric charge) on the surfaces of the respective photosensitive drums2a,2b,2c, and2dafter primary transfer.

The drum cleaning portions11a,11b,11c, and11dare provided facing to the surfaces of the respective photosensitive drums2a,2b,2c, and2d. The drum cleaning portions11a,11b,11c, and11dremove residual toners or adhered substances on the surfaces of the respective photosensitive drums2a,2b,2c, and2d, and convey the removed toner and the like to a predetermined recovery mechanism, thus recovering them.

The transfer portion50transfers a toner image transferred onto the surface of the intermediate transfer belt7, onto a paper sheet T. The transfer portion50includes the secondary transfer roller8and the drive roller17.

The secondary transfer roller8is a roller for secondarily transferring a four-full-color toner image primarily transferred onto the intermediate transfer belt7, onto a paper sheet T. A secondary transfer bias applying portion (not shown) applies, to the secondary transfer roller8, a secondary transfer bias for transferring a four-full-color toner image formed on the intermediate transfer belt7onto a paper sheet T.

The secondary transfer roller8is caused to contact or be separated from the intermediate transfer belt7. Specifically, the secondary transfer roller8is configured to be movable to a contact position that causes the secondary transfer roller8to contact the intermediate transfer belt7or a separation position that causes the secondary transfer roller8to be separated from the intermediate transfer belt7. In detail, the secondary transfer roller8is placed at the contact position when a four-full-color toner image or a monochrome toner image primarily transferred onto the surface of the intermediate transfer belt7is to be secondarily transferred onto a paper sheet T, and placed at the separation position in the other cases.

The drive roller17is provided on a side of the intermediate transfer belt7opposite to the secondary transfer roller8.

A predetermined portion of the intermediate transfer belt7is sandwiched between the secondary transfer roller8and the drive roller17. A secondary transfer nip N2is formed between the intermediate transfer belt7and the secondary transfer roller8. At the secondary transfer nip N2, a paper sheet T is pressed to the outer surface (surface onto which a toner image has been transferred) of the intermediate transfer belt7. At the secondary transfer nip N2, a four-full-color toner image primarily transferred onto the intermediate transfer belt7is secondarily transferred onto a paper sheet T.

The fixing portion60melts and pressurizes toners for respective colors forming a toner image secondarily transferred onto a paper sheet T, thereby fixing the toners on the paper sheet T. The fixing portion60includes a heating rotary body60ato be heated by a heater (not shown), and a pressurizing rotary body60bto be pressed to the heating rotary body60a. The heating rotary body60aand the pressurizing rotary body60bsandwich a paper sheet T having a toner image secondarily transferred thereon, to pressurize the paper sheet T, while conveying the paper sheet T downstream. When the paper sheet T is conveyed being sandwiched between the heating rotary body60aand the pressurizing rotary body60b, the toner transferred thereon is melted and pressurized. Thus, the toner transferred onto the paper sheet T is fixed on the surface of the paper sheet T.

Next, the sheet feed/discharge portion40will be described. As shown inFIG. 1, the sheet feed cassette52for containing a paper sheet T is provided at a lower portion of the apparatus main body M. The sheet feed cassette52is configured to be drawable in the horizontal direction from the housing of the apparatus main body M. A stacking plate54that allows a paper sheet T to be stacked thereon is provided in the sheet feed cassette52. Paper sheets T, being stacked on the stacking plate54, are contained in the sheet feed cassette52. A paper sheet T placed on the stacking plate54is fed to the first conveyance path L1from a cassette sheet feed portion51provided at an end portion of the sheet feed cassette52on a sheet feed side (end portion at the right inFIG. 1). The cassette sheet feed portion51includes a multi-feed preventing mechanism composed of a forward feed roller55for taking out a paper sheet T on the stacking plate54, and a sheet feed roller pair81for feeding a paper sheet T one by one to the conveyance path L.

The manual sheet feed portion64for containing a paper sheet T is provided on a left side surface (at the left inFIG. 1) of the apparatus main body M. The manual sheet feed portion64is provided mainly for the purpose of feeding, to the apparatus main body M, a paper sheet T having a size or a kind different from that of a paper sheet T set in the sheet feed cassette52. The manual sheet feed portion64includes a manual tray65which forms a part of the left side surface of the apparatus main body M in a closed state, and a sheet feed roller66. A lower end of the manual tray65is attached in a rotatable (openable/closable) manner on the vicinity of the sheet feed roller66. The manual tray65in an opened state allows a paper sheet T to be stacked thereon. The sheet feed roller66feeds a paper sheet T placed on the manual tray65in an opened state, to the manual conveyance path La.

The conveyance path L for conveying a paper sheet T includes the first conveyance path L1from the cassette sheet feed portion51to the secondary transfer nip N2, the second conveyance path L2from the secondary transfer nip N2to the fixing portion60, the third conveyance path L3from the fixing portion60to the sheet discharge portion61, the manual conveyance path La which passes a paper sheet fed from the manual sheet feed portion64to merge into the first conveyance path L1, and the return conveyance path Lb which returns a paper sheet conveyed from downstream to upstream on the third conveyance path L3to the first conveyance path L1while inverting the paper sheet.

The first conveyance path L1conveys a paper sheet T contained in the sheet feed cassette52to the image forming portion30. The manual conveyance path La conveys a paper sheet T contained in the manual sheet feed portion64to the registration roller pair80described later.

In addition, a first merging portion P1and a second merging portion P2are provided on the first conveyance path L1, and a first branching portion Q1is provided on the third conveyance path L3.

The first merging portion P1is a merging portion where the manual conveyance path La merges into the first conveyance path L1. The second merging portion P2is a merging portion where the return conveyance path Lb merges into the first conveyance path L1. The first branching portion Q1is a branching portion where the return conveyance path Lb branches from the third conveyance path L3.

On the first conveyance path L1(in detail, between the second merging portion P2and the secondary transfer roller8), a sheet detection sensor (not shown) for detecting a paper sheet T, and a registration roller pair80for correcting skew (oblique sheet feed) of a paper sheet T or adjusting a timing in accordance with formation of a toner image by the image forming portion30, are provided. The sheet detection sensor is provided immediately before (on the upstream side in the conveyance direction) the registration roller pair80in the conveyance direction of a paper sheet T. The registration roller pair80performs the above correction or timing adjustment based on detected signal information from the sheet detection sensor, to convey a paper sheet T.

A first conveying roller pair82is provided between the first merging portion P1and the second merging portion P2on the first conveyance path L1. The first conveying roller pair82is provided on the downstream side of the sheet feed roller pair81, and holds and conveys a paper sheet T conveyed by the sheet feed roller pair81, to the registration roller pair80.

The return conveyance path Lb is a conveyance path provided for, upon both-side printing on a paper sheet T, causing a side (not printed yet) of the paper sheet T opposite to a side on which printing has been already performed, to face to the intermediate transfer belt7. A plurality of second conveying roller pairs83for conveying a paper sheet T to the second merging portion P2are provided at predetermined intervals on the return conveyance path Lb. The return conveyance path Lb can invert a paper sheet T conveyed from the first branching portion Q1to the sheet discharge portion61side, and return the paper sheet T to the first conveyance path L1, thus conveying the paper sheet T to the upstream side of the registration roller pair80provided on the upstream side of the secondary transfer roller8. At the secondary transfer nip N2, a predetermined toner image is transferred onto a side on which printing has not been performed yet, of the paper sheet T inverted by the return conveyance path Lb.

A rectification member58is provided on the first branching portion Q1. The rectification member58rectifies the conveyance direction of a paper sheet T conveyed from the fixing portion60through the third conveyance path L3from upstream to downstream, so as to be directed toward the sheet discharge portion61, and rectifies the conveyance direction of a paper sheet T conveyed from the sheet discharge portion61through the third conveyance path L3from downstream to upstream, so as to be directed toward the return conveyance path Lb.

The sheet discharge portion61is formed at the end of the third conveyance path L3. The sheet discharge portion61is provided on the upper side of the apparatus main body M. The sheet discharge portion61opens toward the left side surface (leftward inFIG. 1) of the apparatus main body M. The sheet discharge portion61discharges a paper sheet T to the outside of the apparatus main body M. The sheet discharge portion61includes a discharge roller pair53. The discharge roller pair53can discharge a paper sheet T conveyed on the third conveyance path L3from upstream to downstream, to the outside of the apparatus main body M, or convey a paper sheet T to the upstream side of the third conveyance path L3after inverting the conveyance direction of the paper sheet T at the sheet discharge portion61.

A discharged sheet accumulation portion M1is formed on the opening side of the sheet discharge portion61. The discharged sheet accumulation portion M1is formed on the upper surface (outer surface) of the apparatus main body M. The discharged sheet accumulation portion M1is a portion of the upper surface of the apparatus main body M, that is recessed downward. The bottom surface of the discharged sheet accumulation portion M1is formed by a top cover member M2which forms a part of the upper surface of the apparatus main body M. Paper sheets T discharged from the sheet discharge portion61after predetermined toner images have been formed thereon are stacked and accumulated on the upper surface of the top cover member M2forming the discharged sheet accumulation portion M1. It is noted that sensors (not shown) for sheet detection are provided at predetermined positions on the conveyance paths.

Next, the belt device20will be described. The belt device20is a device capable of rotating the intermediate transfer belt7and correcting meandering of the belt. The belt device20includes the intermediate transfer belt7, the driven roller16, the drive roller17, the first drive motor18, the tension roller19, a belt sensor21as position information acquiring portion, a roller position adjustment mechanism22, and a support roller23(seeFIG. 8).

The intermediate transfer belt7is an endless belt extending over a plurality of rollers including the driven roller16, the drive roller17, the tension roller19, and the like. Toner images for respective colors are primarily transferred onto the intermediate transfer belt7from the primary transfer rollers13a,13b,13c, and13d. In addition, the toner images for respective colors primarily transferred onto the intermediate transfer belt7are secondarily transferred onto a paper sheet T at the position of the secondary transfer roller8.

The driven roller16is a roller supporting the intermediate transfer belt7in a rotatable manner. The driven roller16is supported by the roller position adjustment mechanism22(described later).

The drive roller17is a roller that supports the intermediate transfer belt7in a rotatable manner and rotates the intermediate transfer belt7. The drive roller17rotates in a predetermined direction by a rotational force given by the first drive motor18.

The first drive motor18is a device that gives a rotational force to the drive roller17. The first drive motor18is electrically connected to the control portion100(described later). The rotation speed of the first drive motor18is controlled by a drive signal outputted from the control portion100.

The tension roller19is a roller that energizes the intermediate transfer belt7from inside to outside. The energizing force by the tension roller19gives a predetermined tension to the intermediate transfer belt7.

The driven roller16and the drive roller17are set such that their respective rotary shafts (with no references) are parallel to each other, and provided at positions opposite to each other in the longitudinal direction of the intermediate transfer belt7. The intermediate transfer belt7rotates around a plurality of rollers including the driven roller16, the drive roller17, the tension roller19, and the like along with rotation of the drive roller17.

Next, a peripheral part including the belt sensor21and the roller position adjustment mechanism22will be described.FIG. 4is a perspective view showing the belt sensor and the driven roller16of the belt device20.FIG. 5is a perspective view showing the configuration of the belt sensor of the belt device20.FIG. 6is a schematic diagram showing a light reception range of a light reception portion25.FIG. 7is a perspective view showing the driven roller16of the belt device20and a peripheral part thereto.

As shown inFIG. 4(orFIG. 1), the belt sensor21is provided in the vicinity of the driven roller16on the circulation track of the intermediate transfer belt7. As shown inFIG. 5, the belt sensor21includes a light emitting portion24, the light reception portion25, and a light shielding plate26. The light emitting portion24radiates light in a predetermined direction (downward inFIGS. 4 and 5). Light receiving elements r1to r20(described later) of the light reception portion25receive light radiated by the light emitting portion24, and respectively output voltage values corresponding to the light reception amounts as light amount detection signals (position information) to the control portion100. The light reception portion25is provided at a position opposite to the light emitting portion24. The light shielding plate26is a member provided so as to be movable between the light emitting portion24and the light reception portion25.

In addition, as shown inFIGS. 4 and 5, the belt sensor21includes a contact plate27and a joint bar28. As shown inFIG. 4, the contact plate27is a member contacting a belt end surface7aof the intermediate transfer belt7. The joint bar28is a member jointing the contact plate27and the light shielding plate26. The joint bar28is supported in a rotatable manner with respect to the light emitting portion24and the light reception portion25. The contact plate27is supported at one end of the joint bar28via a torsion coil spring29. In addition, the light shielding plate26is fixed on substantially the middle portion of the joint bar28so as to be positioned between the light emitting portion24and the light reception portion25.

Here, the light reception range of the light reception portion25will be described. As shown inFIG. 6, the light reception portion25of the belt sensor21is composed of a plurality of light receiving elements r1to r20(some of them and the reference characters thereof are not shown) arranged along the width direction (left-right direction inFIG. 6) of the belt. Of the light receiving elements r1to r20, the light receiving elements r1to r10provided at the right with reference to a center line a detect meandering on the rear side of the belt end surface7a. In addition, the light receiving elements r11to r20provided at the left with reference to the center line a detect meandering on the front side of the belt end surface7a. It is noted that the front side is a range on the near side with reference to the center line a of the apparatus main body M inFIG. 3, and the rear side is a range on the far side with reference to the center line a of the apparatus main body M inFIG. 3.

The center line a shown inFIG. 6corresponds to a target position of the belt end surface7a. The target position of the belt end surface7ais the position of the belt end surface7awhen the center of the intermediate transfer belt7in the width direction coincides with the center of the driven roller16in the width direction. By causing the position of the belt end surface7ato coincide with the target position, the center of the intermediate transfer belt7in the width direction is caused to coincide with the center of the driven roller16in the width direction.

During rotation of the intermediate transfer belt7, the control portion (first control portion)100described later controls the roller position adjustment mechanism22so as to cause the position of the belt end surface7ato coincide with the target position, thereby correcting (hereinafter, may be referred to as “meandering correction”) meandering of the intermediate transfer belt7. By the meandering correction, position shift of a toner image when a plurality of toner images are primarily transferred onto the intermediate transfer belt7from the photosensitive drums2a,2b,2c, and2dis suppressed, whereby a four-full-color image with no color shift can be obtained.

When the light receiving elements r1to r20have received light radiated by the light emitting portion24, the light receiving elements r1to r20output voltage values corresponding to the light reception amounts as the light amount detection signals to the control portion100. When light radiated by the light emitting portion24is shielded by the belt end surface7a, the voltage values outputted from the light receiving elements r1to r20also vary in accordance with the light shielded amount (light shielding position). The control portion100specifies the position of the belt end surface7abased on the voltage values of the light amount detection signals outputted from the respective light receiving elements r1to r20.

Specifically, for example, inFIG. 6, it will be assumed that the voltage values of the light amount detection signals outputted from the light receiving elements r1to r18are smaller than a predetermined threshold voltage and the voltage value of the light amount detection signal outputted from the light receiving element r19is equal to or greater than the predetermined threshold voltage. In this case, the position of the belt end surface7ais specified as being between the light receiving elements r18and r19. In addition, inFIG. 6, it will be assumed that the voltage values of the light amount detection signals outputted from the light receiving elements r1to r10are smaller than the predetermined threshold voltage and the voltage value of the light amount detection signal outputted from the light receiving element r11is equal to or greater than the predetermined threshold voltage. In this case, the position of the belt end surface7ais specified as being between the light receiving elements r10and r11(that is, the target position).

As shown inFIG. 6, a detection range A1(between border lines b1and b2) in which the light receiving elements r3to r10provided on the rear side and the light receiving elements r11to r18provided on the front side receive light is a range (hereinafter, may be referred to as a “correction range” or “within correction range”) for detecting normal meandering occurring on the intermediate transfer belt7. When the belt end surface7ais within the detection range A1, the control portion100executes first correction (meandering correction in a normal case) described later.

In addition, as shown inFIG. 6, detection ranges A2(between border lines b1and c1and between border lines b2and c2) in which the light receiving elements r1and r2provided on the rear side and the light receiving elements r19and r20provided on the front side receive light are ranges (hereinafter, may be referred to as an “allowable range” or “within allowable range”) for detecting abnormal meandering occurring on the intermediate transfer belt7. It is noted that the detection range A2is also a range out of the detection range A1. When the belt end surface7ais within the detection range A2, the control portion100executes second correction (meandering correction in an abnormal case) described later.

Further, as shown inFIG. 6, detection ranges A3(outside from the border lines c1and c2) outside from the light receiving element r1provided on the rear side and outside from the light receiving element r20provided on the front side are ranges (hereinafter, may be referred to as “out of allowable range”) for detecting more abnormal meandering occurring on the intermediate transfer belt7. When the belt end surface7ais within the detection range A3, the control portion100executes processing for emergency.

InFIG. 4, when the intermediate transfer belt7meanders to deviate in the width direction of the belt, the contact plate27contacting the belt end surface7aalso moves in the width direction of the belt. Along with this, the light shielding plate26jointed with the contact plate27moves between the light emitting portion24and the light reception portion25(seeFIG. 5). At this time, the light reception amount of light received by the light reception portion25varies in accordance with the light shielded amount when the light shielding plate26shields light radiated from the light emitting portion24. The light reception portion25is electrically connected to the control portion100. The light reception portion25outputs voltage values corresponding to the light reception amounts on the light receiving elements r1to r20(seeFIG. 6) as the light amount detection signals to the control portion100. The control portion100specifies the position of the belt end surface7abased on the light amount detection signals outputted from the light reception portion25.

The belt sensor21detects the position of the belt end surface7aat predetermined time intervals. The control portion100controls the roller position adjustment mechanism22so that the position of the belt end surface7acomes close to the target position (seeFIG. 6) in the width direction of the belt, based on the light amount detection signals outputted from the belt sensor21(light reception portion25). Thus, meandering of the intermediate transfer belt7is corrected. Here, the configuration of the roller position adjustment mechanism22will be described before the description of the control by the control portion100.

As shown inFIG. 7, the driven roller16is supported such that, based on one end portion (not shown) of a rotary shaft32, the other end portion32aof the rotary shaft32can be inclined in a predetermined forward/reverse direction. By inclining the other end portion32aof the rotary shaft32in the predetermined forward/reverse direction, the intermediate transfer belt7(belt end surface7a) around the driven roller16can be moved in the width direction of the driven roller16.

Therefore, by adjusting the inclination direction (upward/downward) of the rotary shaft32of the driven roller16, the belt end surface7acan be moved toward the front side in the width direction of the belt or toward the rear side opposite thereto.

In addition, by adjusting the inclination angle of the rotary shaft32of the driven roller16, the speed of movement of the belt end surface7atoward the front side in the width direction of the belt or toward the rear side opposite thereto can be changed.

As shown inFIG. 7, the roller position adjustment mechanism22includes, as main parts, a support frame33, a swing support shaft35, a cam36, a gear37, and a second drive motor38. The support frame33is a member having a bearing34supporting the rotary shaft32of the driven roller16in a rotatable manner. The swing support shaft35is a member supporting the support frame33in a swingable manner. The cam36is a member that swings the support frame33based on the swing support shaft35. The gear37is a member formed concentrically and integrally with the cam36. The gear37and the cam36are supported in a rotatable manner by a support shaft (with no reference character).

The second drive motor38is a device that gives a rotational force to the gear37. The second drive motor38is formed by a pulse motor. The second drive motor38is electrically connected to the control portion100(seeFIG. 1). The control portion100outputs a predetermined number of drive pulses (drive signal) to the second drive motor38, thereby driving the second drive motor38. The second drive motor38has an output shaft39engaged with the gear37.

The support frame33is a member provided in the width direction of the driven roller16and extending along the longitudinal direction of the intermediate transfer belt7. The bearing34is provided at one end portion33aof the support frame33. In addition, the other end portion33bof the support frame33is supported by the swing support shaft35. The cam36contacts a contact portion (not shown) provided at the one end portion33aof the support frame33.

The roller position adjustment mechanism22configured as described above moves the belt end surface7aof the intermediate transfer belt7in the width direction of the belt in the following manner. First, the control portion100outputs a predetermined number of drive pulses based on a light amount detection signal outputted from the light reception portion25, thereby generating a drive force on the second drive motor38. The drive force (rotational force) generated on the second drive motor38is transmitted to the gear37via the output shaft39, whereby the gear37is rotated. Along with this, the cam36formed integrally with the gear37swings the one end portion33aof the support frame33based on the swing support shaft35. Thus, the other end portion32aof the rotary shaft32of the driven roller16, supported by the bearing34, is inclined upward or downward based on the one end portion of the rotary shaft32.

For example, if the other end portion32aof the rotary shaft32of the driven roller16is moved downward on the front side, the driven roller16is inclined to descend from the rear side to the front side. Therefore, the intermediate transfer belt7gradually moves to the front side in the lowering direction along with the rotation thereof. On the other hand, if the other end portion32aof the rotary shaft32of the driven roller16is moved upward on the front side, the driven roller16is inclined to ascend from the rear side to the front side. Therefore, the intermediate transfer belt7gradually moves to the rear side in the lowering direction along with the rotation thereof.

The inclination angle of the rotary shaft32of the driven roller16can be adjusted by the number of drive pulses outputted from the control portion100to the second drive motor38. In addition, the rotation direction of the second drive motor38can be switched by the polarity (+/−) of the drive pulses being changed. By switching the rotation direction of the second drive motor38, the inclination direction of the rotary shaft32of the driven roller16can be changed.

The greater the inclination angle of the rotary shaft32of the driven roller16is made, the faster the movement of the intermediate transfer belt7in the width direction becomes. In addition, when the inclination angle is adjusted, the faster the rotation speed of the drive roller17is made, the faster the movement of the intermediate transfer belt7in the width direction becomes. It is noted that control performed when the control portion100corrects meandering of the intermediate transfer belt7will be described later.

Next, the configurations of the operation portion70, the storage portion75, the movement mechanism portion90, and the control portion100(seeFIG. 2) will be described.

The operation portion70has a plurality of keys (not shown). The plurality of keys are operated in such a case of changing the setting or resetting a job of the printer1, for example. When one of the keys has been operated, the operation portion70transmits a signal corresponding to the operated key to the control portion100. In addition, the operation portion70includes a display panel which displays the state of the printer1, a message, or the like, operation buttons such as a power key and a reset key, and the like (these are not shown).

It is noted that in order to display a message or the like on the display panel, the control portion100(described later) controls a display panel drive portion (not shown) to cause the display panel drive portion to supply a drive signal, a timing signal, and the like to the display panel.

The storage portion75is composed of a hard disk, a semiconductor memory, and the like. The storage portion75stores image data or the like supplied from the above-described external apparatus.

Next, the movement mechanism portion90will be described.FIGS. 8A and 8Bare schematic diagrams showing the configuration of the movement mechanism portion90. InFIGS. 8A and 8B, only the configurations of the movement mechanism portion90and the peripheral part are shown, and the other configuration is not shown. In addition, inFIGS. 8A and 8B, the same constituent elements as those inFIGS. 1 and 2are denoted by the same reference characters.

The movement mechanism portion90includes a frame91, an eccentric cam92, and a third drive motor93.

The frame91is a frame member formed substantially in a rectangular U-shape in planar view. The frame91supports the primary transfer rollers13a,13b, and13c, the driven roller16, the drive roller17, and the tension roller19in a rotatable manner, at both ends of each roller in the width direction. The frame91is supported so as to be rotatable around a rotary shaft23aof the support roller23.

In addition, the frame91is energized by a spring14as an energizing member in the clockwise direction around the rotary shaft23aof the support roller23. The support roller23has a function of supporting the frame91via the rotary shaft23a, and a function of retaining the primary transfer nip N1dupon formation of a monochrome toner image.

The eccentric cam92is a member for moving the frame91to a contact position or a separation position (described later), and fixing the frame91at the contact position or the separation position. As shown inFIG. 8, the eccentric cam92is provided in contact with an upper end portion95of the frame91. The eccentric cam92is supported in a rotatable manner by a cam rotary shaft94. In addition, the eccentric cam92rotates clockwise or counterclockwise by a rotational force given by the third drive motor93.

The third drive motor93is a device that gives a rotational force to the eccentric cam92. The third drive motor93is electrically connected to the control portion100(described later). The rotation of the third drive motor93is controlled by a drive signal outputted from the control portion100.

In the case where four-full-color printing is performed in the printer1, a rotational force is given from the third drive motor93to the eccentric cam92, to rotate the eccentric cam92to a first position at which the major axis direction of the eccentric cam92is substantially perpendicular to the intermediate transfer belt7. When the eccentric cam92has rotated to the first position, the frame91pressed by the eccentric cam92rotates counterclockwise around the rotary shaft23aof the support roller23against the energizing force of the spring14.

As a result, as shown inFIG. 8A, the intermediate transfer belt7contacts the photosensitive drums2a,2b, and2c. Hereinafter, a position where the intermediate transfer belt7contacts the photosensitive drums2a,2b, and2cwhen the positions of the primary transfer rollers13a,13b, and13care changed may be referred to as a “contact position”. It is noted that the primary transfer roller13dalways causes the intermediate transfer belt7to contact the photosensitive drum2d. Therefore, when the intermediate transfer belt7is moved to the contact position where the intermediate transfer belt7contacts the photosensitive drums2a,2b, and2c, the intermediate transfer belt7contacts all the photosensitive drums2a,2b,2c, and2d. Therefore, movement of the intermediate transfer belt7to the contact position enables four-full-color printing in the printer1.

On the other hand, in the case where monochrome printing is performed in the printer1, a rotational force is given from the third drive motor93to the eccentric cam92, to rotate the eccentric cam92to a second position at which the minor axis direction of the eccentric cam92is substantially perpendicular to the intermediate transfer belt7. When the eccentric cam92has rotated to the second position, the frame91rotates clockwise around the rotary shaft23aof the support roller23by the energizing force of the spring14.

As a result, as shown inFIG. 8B, the intermediate transfer belt7is separated from the plurality of photosensitive drums2a,2b, and2c. Hereinafter, a position where the intermediate transfer belt7is separated from the photosensitive drums2a,2b, and2cwhen the positions of the primary transfer rollers13a,13b, and13care changed may be referred to as a “separation position”. It is noted that a line A shown inFIG. 8Bindicates the position of the intermediate transfer belt7in the case of contact position. As described above, the primary transfer roller13dalways causes the intermediate transfer belt7to contact the photosensitive drum2d. Therefore, when the intermediate transfer belt7is moved to the separation position where the intermediate transfer belt7are separated from the photosensitive drums2a,2b, and2c, the intermediate transfer belt7contacts only the photosensitive drum2d. Therefore, movement of the intermediate transfer belt7to the separation position enables monochrome printing in the printer1.

Next, the control portion100will be described. The control portion100includes a CPU, a RAM, and a ROM (not shown). The RAM is a storage device having a function of temporarily storing various types of data and a function as a working area upon calculation. The ROM is a storage device having a function as a flash memory for storing various programs. The CPU is a computing device that reads a program from the ROM and executes the program. The CPU, and the RAM and the ROM receive and transmit data with each other via a data bus (not shown). The CPU executes a program read from the ROM and thereby executes processing in accordance with the content of the program. In addition, the control portion100has a timer function (hereinafter, may be referred to as a “timer”) of counting time.

The control portion100controls the belt device20, the image forming portion30, the sheet feed/discharge portion40, and the movement mechanism portion90. In addition, the control portion100has functions as a first control portion and a second control portion described later. Hereinafter, the control portion100when functioning as the first control portion is referred to as a “control portion (first control portion)100”, and the control portion100when functioning as the second control portion is referred to as a “control portion (second control portion)100”.

The control portion (first control portion)100determines an inclination direction and an inclination angle of the rotary shaft of the driven roller16, based on a light amount detection signal (position information about the transfer belt) outputted from the belt sensor21(acquired by the position information acquiring portion), and controls the roller position adjustment mechanism22so that the rotary shaft of the driven roller16will be directed in the inclination direction at the inclination angle.

Specifically, in the case where the position of the intermediate transfer belt7specified based on a light amount detection signal outputted from the belt sensor21is within the correction range (detection range A1: seeFIG. 6), the control portion (first control portion)100controls the roller position adjustment mechanism22so as to return the intermediate transfer belt7to a predetermined target position (corresponding to the center line a: seeFIG. 6). Hereinafter, meandering correction in the case (normal case) where the position of the intermediate transfer belt7is within the correction range may be referred to as “first correction”.

In addition, in the case where the position of the intermediate transfer belt7specified based on a light amount detection signal outputted from the belt sensor21is out of the correction range and within the allowable range (detection range A2: seeFIG. 6), the control portion (first control portion)100controls the roller position adjustment mechanism22so as to return the intermediate transfer belt7to the predetermined target position, and controls the first drive motor18so as to make the rotation speed of the drive roller17faster than in the first correction. Hereinafter, meandering correction in the case (abnormal case) where the position of the intermediate transfer belt7is out of the correction range and within the allowable range may be referred to as “second correction”.

It is noted that the control portion (first control portion)100determines an inclination direction and an inclination angle of the rotary shaft of the driven roller16by referring to a data table (ROM) on which light amount detection signals (voltage values) outputted from the belt sensor21are respectively associated with inclination directions and inclination angles of the rotary shaft of the driven roller16that are required for returning the intermediate transfer belt7to the predetermined target position.

In addition, upon the control for the roller position adjustment mechanism22in order to return the intermediate transfer belt7to the predetermined target position in the second correction, the control portion (first control portion)100controls the roller position adjustment mechanism22so as to make the inclination angle of the rotary shaft of the driven roller16greater than that in the first correction.

In addition, in the emergency case where the position of the intermediate transfer belt7specified based on a light amount detection signal outputted from the belt sensor21is out (detection range A3: seeFIG. 6) of the allowable range, the control portion (first control portion)100controls the first drive motor18so as to stop the rotation of the drive roller17.

Further, in the case where, even though the roller position adjustment mechanism22is controlled by the function of the first control portion, the intermediate transfer belt7does not return into the correction range centered on the target position within a time t1(predetermined time) and is out of the correction range, the control portion (second control portion)100controls the movement mechanism portion90so as to change the positions of the primary transfer rollers13a,13b, and13c(a plurality of second opposing portions).

Specifically, in the state in which the primary transfer rollers13a,13b, and13c(a plurality of second opposing portions) are positioned at the contact positions, in the case where, even though the roller position adjustment mechanism22is controlled in accordance with the inclination direction and the inclination angle (correction information) of the rotary shaft of the driven roller16by the function of the first control portion, the intermediate transfer belt7does not return into the correction range within the time t1(predetermined time) and is out of the correction range, the control portion (second control portion)100controls the movement mechanism portion90so as to move the primary transfer rollers13a,13b, and13cto the separation positions.

In addition, in the state in which the primary transfer rollers13a,13b, and13c(a plurality of second opposing portions) are positioned at the separation positions, in the case where, even though the roller position adjustment mechanism22is controlled in accordance with the inclination direction and the inclination angle (correction information) of the rotary shaft of the driven roller16by the function of the first control portion, the intermediate transfer belt7does not return into the correction range within the time t1(predetermined time) and is out of the correction range, the control portion (second control portion)100controls the movement mechanism portion90so as to move the primary transfer rollers13a,13b, and13cto the contact positions.

In addition, if the intermediate transfer belt7has returned to the correction range by the control for the movement mechanism portion90which has changed the positions of the primary transfer rollers13a,13b, and13c(a plurality of second opposing portions), the control portion (second control portion)100controls the movement mechanism portion90so as to retain the changed positions of the primary transfer rollers13a,13b, and13c.

The functions of the control portion100as the first control portion and the second control portion described above will be described later with reference to the flowchart.

Next, the operation of the printer1configured as described above will be described. First, with reference toFIG. 1, the fundamental operation of the printer1will be described.

(Operation in Case of Performing One-Side Printing on Paper Sheet T)

A paper sheet T contained in the sheet feed cassette52is fed to the first conveyance path L1by the forward feed roller55and the sheet feed roller pair81, and then conveyed to the registration roller pair80through the first merging portion P1and the first conveyance path L1by the first conveying roller pair82.

On the registration roller pair80, skew correction of the paper sheet T and timing adjustment in accordance with formation of a toner image in the image forming portion30are performed.

The paper sheet T discharged from the registration roller pair80is introduced through the first conveyance path L1to a portion (the secondary transfer nip N2) between the intermediate transfer belt7and the secondary transfer roller8. Then, a toner image is transferred onto the paper sheet T between the intermediate transfer belt7and the secondary transfer roller8.

Thereafter, the paper sheet T is discharged from between the intermediate transfer belt7and the secondary transfer roller8, and then introduced through the second conveyance path L2to a fixing nip between the heating rotary body60aand the pressurizing rotary body60bin the fixing portion60. Then, at the fixing nip, a toner is melted and fixed on the paper sheet T.

Next, the paper sheet T is conveyed through the third conveyance path L3to the sheet discharge portion61, and discharged from the sheet discharge portion61to the discharged sheet accumulation portion M1by the discharge roller pair53. Thus, the one-side printing of the paper sheet T contained in the sheet feed cassette52is completed.

On the other hand, in the case of performing one-side printing on a paper sheet T placed on the manual tray65, the paper sheet T placed on the manual tray65is fed through the manual conveyance path La by the sheet feed roller66, and then conveyed through the first merging portion P1and the first conveyance path L1to the registration roller pair80. The operation performed thereafter is the same as the above-described operation of the one-side printing on a paper sheet T contained in the sheet feed cassette52, and therefore the description thereof is omitted.

(Operation in Case of Performing Both-Side Printing on Paper Sheet T)

In the case of one-side printing, as described above, a paper sheet T on which one-side printing has been performed is discharged from the sheet discharge portion61to the discharged sheet accumulation portion M1, and thus the printing operation is completed.

On the other hand, in the case of performing both-side printing, a paper sheet T on which one-side printing has been performed is inverted from the side for the one-side printing and conveyed again to the registration roller pair80through the return conveyance path Lb, whereby both-side printing is to be performed for the paper sheet T.

In detail, the operation until the paper sheet T on which one-side printing has been performed is discharged from the sheet discharge portion61by the discharge roller pair53is the same as the operation for the one-side printing described above. However, in the case of both-side printing, in the state in which the paper sheet T on which one-side printing has been performed is held by the discharge roller pair53, rotation of the discharge roller pair53is stopped and then the discharge roller pair53is caused to rotate in the reverse direction. If the discharge roller pair53is thus rotated in the reverse direction, the paper sheet T held by the discharge roller pair53is conveyed in the reverse direction (direction from the sheet discharge portion61to the first branching portion Q1) through the third conveyance path L3.

As described above, if the paper sheet T is conveyed in the reverse direction through the third conveyance path L3, the paper sheet T is rectified into the return conveyance path Lb by the rectification member58, and then merges into the first conveyance path L1via the second merging portion P2. Here, the paper sheet T has been inverted from the side for the one-side printing.

Further, the paper sheet T is subjected to the correction or the adjustment by the registration roller pair80, and then introduced through the first conveyance path L1into the secondary transfer nip N2. Since a side of the paper sheet T on which printing has not been performed yet faces to the intermediate transfer belt7as a result of passing through the return conveyance path Lb, a toner image is transferred onto the side on which printing has not been performed yet, whereby both-side printing is performed.

Next, the processing procedure in the case where the control portion (first control portion and second control portion)100executes meandering correction for the intermediate transfer belt7will be described.FIGS. 9,10, and11are flowcharts showing the processing procedure in the case where the control portion (first control portion and second control portion)100executes meandering correction for the intermediate transfer belt7. The processing of the flowcharts shown inFIGS. 9 to 11is repeatedly executed at predetermined time intervals during operation of the printer1.

In step ST101shown inFIG. 9, the control portion (first control portion)100acquires a light amount detection signal from the light reception portion25(belt sensor21).

In step ST102, the control portion (first control portion)100specifies the position (hereinafter, may be referred to as a “detected belt position”) of the belt end surface7aof the intermediate transfer belt7based on the acquired light amount detection signal.

In step ST103, the control portion (first control portion)100determines whether or not the detected belt position is within the correction range (detection range A1). In step ST103, if the control portion (first control portion)100has determined that the detected belt position is within the correction range (YES), the control portion (first control portion)100advances the process to step ST104. On the other hand, in step ST103, if the control portion (first control portion)100has determined that the detected belt position is out of the correction range (NO), the control portion (first control portion)100advances the process to step ST105.

In step ST104(determined YES in step ST103), the control portion (first control portion)100executes the first correction (meandering correction in a normal case), whereby the process of the present flowchart is ended. In the first correction, the control portion (first control portion)100determines a drive direction and a drive amount of the second drive motor38in accordance with the detected belt position, and outputs a drive signal with a drive pulse number corresponding to the drive direction and the drive amount, to the second drive motor38. In addition, the control portion (first control portion)100controls the rotation speed of the first drive motor18so that the rotation speed (belt movement speed) of the drive roller17will become a speed for the first correction. Therefore, the intermediate transfer belt7rotates at the movement speed for the first correction.

On the other hand, in step ST105(determined NO in step ST103), the control portion (first control portion)100determines whether or not the detected belt position is out of the correction range (detection range A1) and within the allowable range (detection range A2). In step ST105, if the control portion (first control portion)100has determined that the detected belt position is out of the correction range and within the allowable range (YES), the control portion (first control portion)100advances the process to step ST106. On the other hand, in step ST105, if the control portion (first control portion)100has determined that the detected belt position is out of the correction range and not within the allowable range (NO), the control portion (first control portion)100advances the process to step ST108.

In step ST106(determined YES in step ST105), the control portion (first control portion)100controls the belt device20to stop output of a drive signal to the first drive motor18, whereby the printer1interrupts print processing. At the same time, the control portion (first control portion)100controls the display panel drive portion (not shown) to display, on the display panel (not shown) of the operation portion70, a message for notifying that the print processing is interrupted because meandering correction for the belt is being performed.

In step ST107, the control portion (first control portion)100executes the second correction (meandering correction in an abnormal case). Specifically, the control portion (first control portion)100sets a drive amount of the second drive motor38to the maximum value irrespective of the detected belt position, and outputs a drive signal with a drive pulse number corresponding to the maximum drive amount, to the second drive motor38. As a result, the inclination angle of the rotary shaft32of the driven roller16becomes greater than the inclination angle set for the first correction.

In addition, in step ST107, the control portion (first control portion)100controls the rotation speed of the first drive motor18to the maximum value so that the rotation speed (belt movement speed) of the drive roller17will become faster than that for the first correction. As a result, the rotation speed of the first drive motor18becomes faster than that for the first correction. Therefore, the intermediate transfer belt7rotates at a speed (high speed) faster than the movement speed for the first correction.

On the other hand, in step ST108(determined NO in step ST105), the control portion (first control portion)100executes processing for emergency. Specifically, the control portion (first control portion)100controls the belt device20to stop output of a drive signal to the first drive motor18, whereby the printer1interrupts print processing (emergency stop). At the same time, the control portion (first control portion)100controls the display panel drive portion (not shown) to display, on the display panel (not shown) of the operation portion70, a message for notifying that the print processing is interrupted because of abnormal meandering of the belt. Then, the process of the present flowchart is ended.

It is noted that in step ST108, the control portion (first control portion)100may control the display panel drive portion (not shown) to display, on the display panel of the operation portion70, a message for notifying that inspection by a maintenance staff is needed, together with the message for notifying that the print processing is interrupted.

In step ST109shown inFIG. 10, the control portion (second control portion)100activates a timer (not shown) to start counting the time t1.

In step ST110, the control portion (second control portion)100determines whether or not the time counted by the timer has reached the time t1. In the determination of step ST110, if the control portion (second control portion)100has determined that the time counted by the timer has reached the time t1(YES), the control portion (second control portion)100advances the process to step ST111. It is noted that the count of the timer is reset when the time counted by the timer has reached the time t1.

On the other hand, in the determination of step ST110, if the control portion (second control portion)100has determined that the time counted by the timer has not reached the time t1yet (NO), the control portion (second control portion)100returns the process to step ST110.

In step ST111(determined YES in step ST110), the control portion (second control portion)100acquires a light amount detection signal from the light reception portion25(belt sensor21).

In step ST112, the control portion (second control portion)100specifies the detected belt position of the intermediate transfer belt7based on the acquired light amount detection signal.

In step ST113, the control portion (second control portion)100determines whether or not the detected belt position is within the correction range (detection range A1). In step ST113, if the control portion (second control portion)100has determined that the detected belt position is within the correction range (YES), the control portion (second control portion)100advances the process to step ST104(seeFIG. 9). On the other hand, in step ST113, if the control portion (second control portion)100has determined that the detected belt position is out of the correction range (NO), the control portion (second control portion)100advances the process to step ST114.

In step ST114(determined NO in step ST113), the control portion (second control portion)100determines whether or not the intermediate transfer belt7is positioned at the contact position where the intermediate transfer belt7contacts the photosensitive drums2a,2b, and2c. In step ST114, if the control portion (second control portion)100has determined that the intermediate transfer belt7is positioned at the contact position (YES), the control portion (second control portion)100advances the process to step ST115. On the other hand, in step ST114, if the control portion (second control portion)100has determined that the intermediate transfer belt7is not positioned at the contact position (NO), that is, is positioned at the separation position, the control portion (second control portion)100advances the process to step ST116.

In step ST115(YES in step ST114), the control portion (second control portion)100controls the movement mechanism portion90to change the position of the intermediate transfer belt7from the contact position to the separation position (move the primary transfer rollers13ato13cto the separation positions).

In step ST116(NO in step ST114), the control portion (second control portion)100controls the movement mechanism portion90to change the position of the intermediate transfer belt7from the separation position to the contact position (move the primary transfer rollers13ato13cto the contact positions).

In step ST117shown inFIG. 11, the control portion (second control portion)100activates the timer (not shown) to start counting a time t2.

In step ST118, the control portion (second control portion)100determines whether or not the time counted by the timer has reached the time t2. In the determination of step ST118, if the control portion (second control portion)100has determined that the time counted by the timer has reached the time t2(YES), the control portion (second control portion)100advances the process to step ST119. It is noted that the count of the timer is reset when the time counted by the timer has reached the time t2.

On the other hand, in the determination of step ST118, if the control portion (second control portion)100has determined that the time counted by the timer has not reached the time t2yet (NO), the control portion (second control portion)100returns the process to step ST118.

In step ST119(YES in step ST118), the control portion (second control portion)100acquires a light amount detection signal from the light reception portion25(belt sensor21).

In step ST120, the control portion (second control portion)100specifies the detected belt position of the intermediate transfer belt7based on the acquired light amount detection signal.

In step ST121, the control portion (second control portion)100determines whether or not the detected belt position is out of the correction range (detection range A1). In step ST121, if the control portion (second control portion)100has determined that the detected belt position is out of the correction range (YES), the control portion (second control portion)100advances the process to step ST108(seeFIG. 9). Thus, in the case where, even after the position of the intermediate transfer belt7is changed, the detected belt position of the intermediate transfer belt7does not return into the correction range, the control portion (second control portion)100advances the process to step ST108, to execute processing of emergency stop.

On the other hand, in step ST121, if the control portion (second control portion)100has determined that the detected belt position is within the correction range (NO), the control portion (second control portion)100advances the process to step ST122.

In step ST122(NO in step ST121), the control portion (second control portion)100determines whether or not the intermediate transfer belt7is positioned at the contact position where the intermediate transfer belt7contacts the photosensitive drums2a,2b, and2c. In step ST122, if the control portion (second control portion)100has determined that the intermediate transfer belt7is positioned at the contact position (YES), the control portion (second control portion)100advances the process to step ST123. On the other hand, in step ST122, if the control portion (second control portion)100has determined that the intermediate transfer belt7is not positioned at the contact position (NO), that is, is positioned at the separation position, the control portion (second control portion)100advances the process to step ST125.

In step ST123(YES in step ST122), the control portion (second control portion)100fixes the position of the intermediate transfer belt7at the contact position. Specifically, the control portion (second control portion)100retains the status of a flag set in a predetermined area of the RAM and indicating that the intermediate transfer belt7has moved to the contact position.

In step ST124, the control portion (second control portion)100sets the print mode to four-full-color printing, and controls the belt device20to output a drive signal to the first drive motor18. Thus, in the printer1, the belt device20is driven and four-full-color printing is restarted. At the same time, the control portion (second control portion)100controls the display panel drive portion (not shown) to display, on the display panel (not shown) of the operation portion70, a message for informing that four-full-color printing is able to be performed, whereby the process of the present flowchart is ended.

On the other hand, in step ST125(NO in step ST122), the control portion (second control portion)100fixes the position of the intermediate transfer belt7at the separation position. Specifically, the control portion (second control portion)100retains the status of a flag set in a predetermined area of the RAM and indicating that the intermediate transfer belt7has moved to the separation position.

In step ST126, the control portion (second control portion)100sets the print mode to monochrome printing, and controls the belt device20to output a drive signal to the first drive motor18. Thus, in the printer1, the belt device20is driven and monochrome printing is restarted. At the same time, the control portion (second control portion)100controls the display panel drive portion (not shown) to display, on the display panel (not shown) of the operation portion70, a message for informing that monochrome printing is able to be performed, whereby the process of the present flowchart is ended.

It is noted that in steps ST124and ST126, the control portion (second control portion)100may control the display panel drive portion (not shown) to display, on the display panel of the operation portion70, a message for notifying that inspection by a maintenance staff is needed, together with the message for notifying that four-full-color printing or monochrome printing is able to be performed.

Next, a specific example in which the control portion (first control portion and second control portion)100performs meandering correction for the intermediate transfer belt7based on the process of the flowcharts shown inFIGS. 9 to 11will be described.

First, the case where the intermediate transfer belt7falls within the correction range by the second correction (meandering correction in an abnormal case) will be described.

FIG. 12is a graph showing transition of the belt end surface7ain the case of performing conventional meandering correction with a fixed belt movement speed.FIG. 13is a graph showing transition of the belt end surface7ain the case of performing meandering correction of the present embodiment. InFIGS. 12 and 13, the horizontal axis indicates a time t and the vertical axis indicates a belt position d (position of the belt end surface7a).

It is noted that dotted-dashed lines “a”, “b1” and “b2” shown inFIGS. 12 and 13correspond to the center line a and the border lines b1and b2shown inFIG. 6, respectively. Therefore, downward transition from the center line a in the graph indicates movement of the belt end surface7atoward the rear side, and upward transition from the center line a in the graph indicates movement of the belt end surface7atoward the front side. InFIGS. 12 and 13, in an interval S2, the intermediate transfer belt7meanders to greatly deviate toward the front side (the same holds true forFIGS. 14 and 15described later).

As shown inFIGS. 12 and 13, when the position of the belt end surface7aof the intermediate transfer belt7is within the correction range (detection range A1) (interval S1), the first correction is executed. In this case, in bothFIGS. 12 and 13, the rotation speed (belt movement speed) of the drive roller17becomes the rotation speed for the first correction.

In addition, when the position of the belt end surface7aof the intermediate transfer belt7is out of the correction range (detection range A1) and within the allowable range (detection range A2) (interval S2), the second correction (meandering correction in an abnormal case) is executed. Here, in the conventional meandering correction (seeFIG. 12), the rotation speed (belt movement speed) of the drive roller17remains the rotation speed for the first correction. Therefore, a time T1is required until the meandering correction for the second correction is finished and the meandering correction for the first correction (interval S3) is reached.

On the other hand, in the meandering correction (seeFIG. 13) of the present embodiment, the rotation speed (belt movement speed) of the drive roller17becomes a rotation speed (high speed) faster than the rotation speed for the first correction. Therefore, a time T2(<time T1) is required until the second correction is finished and the meandering correction for the first correction (interval S3) is reached.

Thus, the meandering correction of the present embodiment shown inFIG. 13can swiftly return the meandering intermediate transfer belt7to the target position by the second correction (interval S2). Accordingly, color shift of a toner image is resolved in a short time, and therefore reduction in productivity of printed matters can be suppressed to the minimum. In addition, in the second correction, since the second drive motor38is driven at the maximum drive amount irrespective of the detected position of the belt end surface7a, the meandering intermediate transfer belt7can be further swiftly returned to the target position. Further, in the emergency case where the position of the belt end surface7aof the intermediate transfer belt7detected by the belt sensor21is out of the allowable range, driving of the drive roller17is stopped, whereby a trouble that the intermediate transfer belt7comes off from the driven roller16can be prevented in advance.

Next, the case where the intermediate transfer belt7does not fall within the correction range even after the second correction is performed for a predetermined time will be described.

FIG. 14is a graph showing transition of the belt end surface7ain the case of performing meandering correction upon four-full-color printing.FIG. 15is a graph showing transition of the belt end surface7ain the case of performing meandering correction upon monochrome printing. The print modes inFIGS. 14 and 15, four-full-color printing is referred to as “color printing”.

As shown inFIG. 14, in the case where the print mode is color printing, when the position of the belt end surface7aof the intermediate transfer belt7is out of the correction range (detection range A1) and within the allowable range (detection range A2) (interval S2), the control portion (first control portion)100executes the second correction described inFIG. 13.

Then, if the position of the belt end surface7aof the intermediate transfer belt7does not return into the correction range (detection range A1) even after the second correction is performed for the time t1in the interval S2as shown inFIG. 14, the control portion (second control portion)100changes the position of the intermediate transfer belt7from the contact position to the separation position after the elapse of the time t1. Thereafter, the control portion (second control portion)100further performs the second correction for the time t2in the state in which the intermediate transfer belt7is positioned at the separation position.

Thereafter, as shown inFIG. 14, in the state in which the position of the intermediate transfer belt7has been changed to the separation position, if the position of the belt end surface7aof the intermediate transfer belt7has returned into the correction range (detection range A1) by the second correction being performed for the time t2, the control portion (second control portion)100fixes the position of the intermediate transfer belt7at the separation position. At the same time, at the time when the meandering correction has shifted to the first correction (interval S3), the control portion (second control portion)100sets the print mode to monochrome printing, to restart printing. In this case, in the printer1, four-full-color printing cannot be executed but monochrome printing can be executed.

On the other hand, as shown inFIG. 15, in the case where the print mode is monochrome printing, when the position of the belt end surface7aof the intermediate transfer belt7is out of the correction range (detection range A1) and within the allowable range (detection range A2) (interval S2), the control portion (first control portion)100executes the second correction described inFIG. 13.

Then, if the position of the belt end surface7aof the intermediate transfer belt7does not return into the correction range (detection range A1) even after the second correction is performed for the time t1in the interval S2as shown inFIG. 15, the control portion (second control portion)100changes the position of the intermediate transfer belt7from the separation position to the contact position after the elapse of the time t1. Thereafter, the control portion (second control portion)100further performs the second correction for the time t2in the state in which the intermediate transfer belt7is positioned at the contact position.

Thereafter, as shown inFIG. 15, in the state in which the position of the intermediate transfer belt7has been changed to the contact position, if the position of the belt end surface7aof the intermediate transfer belt7has returned into the correction range (detection range A1) by the second correction being performed for the time t2, the control portion (second control portion)100fixes the position of the intermediate transfer belt7at the contact position. At the same time, at the time when the meandering correction has shifted to the first correction (interval S3), the control portion (second control portion)100sets the print mode to color printing, to restart printing. In this case, in the printer1, monochrome printing cannot be executed but four-full-color printing can be executed.

The tendency of the above-described meandering of the intermediate transfer belt7varies between the cases where the intermediate transfer belt7is positioned at the contact position and the separation position with respect to the photosensitive drums2ato2c. It is considered that this is because, when the intermediate transfer belt7is made contact with or separate from the photosensitive drums2ato2c, a conveyance speed difference due to torsion or change in tension of the intermediate transfer belt7occurs on the front side or the rear side of the intermediate transfer belt7.

Therefore, in the case where the intermediate transfer belt7does not return into the correction range even after the second correction is performed for a predetermined time (time t1), if the positional relationship (contact/separation) between the photosensitive drums2ato2cand the intermediate transfer belt7is changed, the tendency of meandering of the intermediate transfer belt7can be changed. Therefore, in the second correction, in the case where the intermediate transfer belt7does not return into the correction range, if the positional relationship between the photosensitive drums2ato2cand the intermediate transfer belt7is changed, the possibility that the intermediate transfer belt7will return into the correction range increases.

Then, in the case where the intermediate transfer belt7has returned into correction range after the positional relationship between the photosensitive drums2ato2cand the intermediate transfer belt7has been changed, if the positional relationship between the photosensitive drums2ato2cand the intermediate transfer belt7at this time is fixed, the printer1can be driven in either print mode of color printing or monochrome printing.

The printer1according to the above embodiment provides the following effects, for example.

In the printer1according to the present embodiment, in the case where the intermediate transfer belt7does not return into the correction range even though the roller position adjustment mechanism22is controlled by the function of the first control portion so as to correct meandering of the intermediate transfer belt7, the control portion (second control portion)100controls the movement mechanism portion90so as to change the positions of the primary transfer rollers13ato13c(a plurality of second opposing portions).

Thus, in the second correction, if the intermediate transfer belt7does not return into the correction range, the positions of the primary transfer rollers13ato13care changed, whereby the possibility that the intermediate transfer belt7will return into the correction range increases. Then, if the intermediate transfer belt7has returned into the correction range after the positions of the primary transfer rollers13ato13chave been changed, the printer1can be driven in either print mode of color printing or monochrome printing in accordance with the positions of the primary transfer rollers13ato13cat this time. Therefore, when abnormal meandering of the intermediate transfer belt7has occurred, the printer1according to the present embodiment can prevent, as much as possible, occurrence of the state in which neither color printing nor monochrome printing can be performed.

In addition, if the intermediate transfer belt7has returned into the correction range after the movement mechanism portion90has been controlled so as to change the positions of the primary transfer rollers13ato13c, the control portion (second control portion)100retains the changed positions of the primary transfer rollers13ato13c.

Thus, if the intermediate transfer belt7has returned into the correction range after the positions of the primary transfer rollers13ato13chave been changed, the positions of the primary transfer rollers13ato13cat this time are retained, whereby the printer1can be continuously driven by either print mode of color printing or monochrome printing.

In addition, in the case where the intermediate transfer belt7does not return into the correction range even though the roller position adjustment mechanism22has been controlled by the function of the first control portion so as to correct meandering of the intermediate transfer belt7, if the positions of the primary transfer rollers13ato13care the contact positions, the control portion (second control portion)100controls the movement mechanism portion90so that the positions of the primary transfer rollers13ato13cwill become the separation positions.

Thus, in the case where the positions of the primary transfer rollers13ato13care the contact positions (four-full-color printing), if the intermediate transfer belt7does not return into the correction range, the positions of the primary transfer rollers13ato13cbecome the separation positions (monochrome printing). Therefore, the printer1can execute monochrome printing.

In addition, in the case where the intermediate transfer belt7does not return into the correction range even though the roller position adjustment mechanism22has been controlled by the function of the first control portion so as to correct meandering of the intermediate transfer belt7, if the positions of the primary transfer rollers13ato13care the separation positions, the control portion (second control portion)100controls the movement mechanism portion90so that the positions of the primary transfer rollers13ato13cwill become the contact positions.

Thus, in the case where the positions of the primary transfer rollers13ato13care the separation positions (monochrome printing), if the intermediate transfer belt7does not return into the correction range, the positions of the primary transfer rollers13ato13cbecome the contact positions (four-full-color printing). Therefore, the printer1can execute four-full-color printing. In addition, in this case, the printer1can also execute monochrome printing as well as four-full-color printing.

In addition, the control portion (first control portion)100determines an inclination direction and an inclination angle of the rotary shaft of the driven roller16in accordance with the position of the intermediate transfer belt7detected by the belt sensor21, and controls the roller position adjustment mechanism22so that the rotary shaft of the driven roller16will be directed in the inclination direction at the inclination angle.

Therefore, in accordance with the position of the meandering intermediate transfer belt7, the intermediate transfer belt7can be swiftly returned into the correction range.

Although preferred embodiments of the present disclosure have been thus described, the present disclosure is not limited to the above embodiments but may be carried out in various modes.

The movement mechanism portion90of the present embodiment includes the eccentric cam92and the third drive motor93as a mechanism for moving the frame91supporting the primary transfer rollers13ato13cto the contact position or the separation position with respect to the photosensitive drums2ato2c. Instead, the movement mechanism portion90may be formed by a drive motor and a gear mechanism. In this case, the gear mechanism is rotated by a rotational force of the drive motor, whereby the frame91supported by the rotary shaft23aof the support roller23can be moved to the contact position or the separation position.

The movement mechanism portion90may be formed by a rod and an actuator linked with the frame91. In this case, the rod is driven by motive power generated by the actuator, whereby the frame91supported by the rotary shaft23aof the support roller23can be moved to the contact position or the separation position.

The control portion (first control portion)100of the present embodiment determines an inclination direction and an inclination angle of the rotary shaft of the driven roller16by referring to a data table (ROM) on which light amount detection signals (voltage values) outputted from the belt sensor21are respectively associated with inclination directions and inclination angles of the rotary shaft of the driven roller16that are required for returning the intermediate transfer belt7to a predetermined target position. Instead, an inclination direction and an inclination angle of the rotary shaft of the driven roller16may be calculated by a calculation expression using a light amount detection signal (voltage value) as a parameter.

In the present embodiment, an example where the image forming apparatus according to the present disclosure is applied to a printer capable of four-full-color printing and monochrome printing, has been described. Instead, the present disclosure can be applied to general image forming apparatuses configured such that an endless belt can be moved to a contact position and a separation position with respect to a photosensitive drum. For example, the present disclosure can be applied to a copy machine, a facsimile machine, or the like having such a configuration.