Transport device and image forming apparatus that can align a transfer belt

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2014-068871 filed Mar. 28, 2014.

The present invention relates to a transport device and an image forming apparatus.

According to an aspect of the invention, there is provided a transport device including a driving roller that drives an endless belt so that the belt rotates, a transfer roller that presses the belt from an inner side of the belt toward an image carrier, which carries a toner image, and transfers the toner image onto the belt, a first stretching roller that stretches the belt, a second stretching roller that stretches the belt the driving roller and the first stretching roller and on a side on which the transfer roller is in contact with the belt, and an adjusting mechanism that adjusts a direction of a rotary shaft of the second stretching roller.

Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a diagram illustrating a schematic internal configuration of an image forming apparatus;

FIG. 2 is a diagram illustrating a schematic internal configuration of a transfer device;

FIG. 3 is a general view of the transfer device as seen from the side on which photoconductor drums are disposed;

FIGS. 4A and 4B are diagrams illustrating a positional relationship between one of first transfer rollers and one of the photoconductor drums;

FIG. 5 is a diagram illustrating the internal configuration of the transfer device;

FIGS. 6A and 6B are diagrams illustrating a mechanism that changes the direction of a rotary shaft of a stretching roller; and

FIGS. 7A and 7B are schematic diagrams of a measuring unit.

FIG. 1 is a diagram illustrating a schematic internal configuration of an image forming apparatus 100 according to an exemplary embodiment of the present invention. The image forming apparatus 100 employs an electrophotographic system and forms an image on a recording medium. The image forming apparatus 100 includes a controller 1 , an image processing unit 2 , a sheet feed unit 3 , and an image forming unit 4 .

The controller 1 includes a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). The controller 1 controls each of the units of the image forming apparatus 100 by causing the CPU to execute a program that is stored in the ROM by loading the program into the RAM. The image processing unit 2 performs various image processing on image data that has been input to the image processing unit 2 and then outputs the image data. Recording media are accommodated in the sheet feed unit 3 . The sheet feed unit 3 sends out the recording media, which are accommodated in the sheet feed unit 3 , one by one. The recording media, which have been sent out from the sheet feed unit 3 , are transported to the image forming unit 4 .

The image forming unit 4 includes photoconductor drums 5 ( 5 Y, 5 M, 5 C, and 5 K), charging devices 6 ( 6 Y, 6 M, 6 C, and 6 K), exposure devices 7 ( 7 Y, 7 M, 7 C, and 7 K), developing devices 8 ( 8 Y, 8 M, 8 C, and 8 K), a transfer device 9 (an example of a transport device), and a fixing device 10 .

Photosensitive layers are formed on surfaces of the photoconductor drums 5 . Each of the photoconductor drums 5 is driven by a driving unit (not illustrated) and rotates about an axis thereof. The charging devices 6 Y, 6 M, 6 C, and 6 K charge the surfaces of the corresponding photoconductor drums 5 Y, 5 M, 5 C, and 5 K to a predetermined potential. The exposure devices 7 Y, 7 M, 7 C, and 7 K expose the surfaces of the corresponding photoconductor drums 5 Y, 5 M, 5 C, and 5 K, which have been charged, to light on the basis of image data that is output from the image processing unit 2 in such a manner as to form electrostatic latent images. The developing devices 8 Y, 8 M, 8 C, and 8 K develop the corresponding electrostatic latent images, which have been formed on the photoconductor drums 5 Y, 5 M, 5 C, and 5 K, by using toners of yellow, magenta, cyan, and black in such a manner as to form toner images. Each of the photoconductor drums 5 is an example of an image carrier that holds a toner image. The charging devices 6 , the exposure devices 7 , and the developing devices 8 are examples of image forming units.

The transfer device 9 transfers the toner images, which have been formed on the photoconductor drums 5 , onto one of the recording media that is transported from the sheet feed unit 3 . Details of the transfer device 9 will be described later. The fixing device 10 includes a fixing roller 101 and a pressure roller 102 . In the fixing device 10 , the fixing roller 101 and the pressure roller 102 apply heat and pressure to the toner images on the recording medium, so that the toner images are fixed onto the recording medium.

In the following description, a three-dimensional rectangular coordinate system is defined for the sake of explanation. In this coordinate system, an x axis represents an axial direction of the photoconductor drums 5 (a direction perpendicular to FIG. 1 ), a y axis represents a direction from the photoconductor drum 5 Y toward the photoconductor drum 5 K, and a z axis represents a height direction of the image forming apparatus 100 . Note that a positive y-axis direction will be hereinafter referred to as a reference direction.

FIG. 2 is a diagram illustrating a schematic internal configuration of the transfer device 9 . The transfer device 9 includes an intermediate transfer belt 90 , a drive roller 91 , first transfer rollers 92 ( 92 Y, 92 M, 92 C, and 92 K), a support roller 93 , a steering roller 94 , stretching rollers 95 A and 95 B, a backup roller 96 , and a second transfer roller 97 . Rotary shafts of the various rollers, which are included in the transfer device 9 , are supported by frames 9 A and 9 B of the transfer device 9 (see FIG. 3 ).

The intermediate transfer belt 90 is a member having the form of an endless belt. The drive roller 91 is a member that drives the intermediate transfer belt 90 so that the intermediate transfer belt 90 rotates. The drive roller 91 drives the intermediate transfer belt 90 so that the intermediate transfer belt 90 rotates in the direction of arrow A 1 in FIG. 2 . The first transfer rollers 92 Y, 92 M, 92 C, and 92 K are members that transfer (transfer in a first transfer process) toner images that have been formed on the photoconductor drums 5 Y, 5 M, 5 C, and 5 K onto the intermediate transfer belt 90 . A transfer bias is applied to the first transfer rollers 92 Y, 92 M, 92 C, and 92 K by a power source (not illustrated), and potential differences are generated between the first transfer rollers 92 Y, 92 M, 92 C, and 92 K and the corresponding photoconductor drums 5 Y, 5 M, 5 C, and 5 K. The first transfer rollers 92 Y, 92 M, 92 C, and 92 K press the intermediate transfer belt 90 from the inner side of the intermediate transfer belt 90 toward the photoconductor drums 5 Y, 5 M, 5 C, and 5 K in a state where the potential differences have been generated, so that the toner images are transferred onto the intermediate transfer belt 90 . In FIG. 2 , the first transfer rollers 92 Y, 92 M, 92 C, and 92 K transfer the toner images onto the intermediate transfer belt 90 at positions further downstream than the drive roller 91 and further upstream than the steering roller 94 in a direction in which the intermediate transfer belt 90 moves (hereinafter referred to as a movement direction). The toner images that have been transferred to the intermediate transfer belt 90 are transported to the second transfer roller 97 . The support roller 93 is a member that supports the intermediate transfer belt 90 . The support roller 93 supports the intermediate transfer belt 90 at a position between the first transfer rollers 92 C and the first transfer rollers 92 K.

The steering roller 94 (an example of a first stretching roller) is a member that stretches the intermediate transfer belt 90 and adjusts the position of the intermediate transfer belt 90 . The steering roller 94 is controlled by a control mechanism (not illustrated) in such a manner that one side of the rotary shaft of the steering roller 94 is displaceable, and the steering roller 94 adjusts the position of the intermediate transfer belt 90 in the x-axis direction. The stretching roller 95 A (an example of a second stretching roller) and the stretching roller 95 B are members that stretch the intermediate transfer belt 90 at positions between the drive roller 91 and the steering roller 94 and on the side on which the first transfer rollers 92 are in contact with the intermediate transfer belt 90 . In FIG. 2 , the stretching roller 95 A stretches the intermediate transfer belt 90 at a position further downstream than the drive roller 91 and further upstream than the first transfer rollers 92 Y in the movement direction of the intermediate transfer belt 90 . The stretching roller 95 B stretches the intermediate transfer belt 90 at a position further downstream than the first transfer rollers 92 K and further upstream than the steering roller 94 in the movement direction of the intermediate transfer belt 90 .

The backup roller 96 is a member that stretches the intermediate transfer belt 90 . The backup roller 96 opposes the second transfer roller 97 with the intermediate transfer belt 90 interposed therebetween. The second transfer roller 97 transfers (transfers in a second transfer process) the toner images, which have been transferred to the intermediate transfer belt 90 , onto one of the recording media that has been transported from the sheet feed unit 3 . A transfer bias is applied to the second transfer roller 97 by a power source (not illustrated), and a potential difference is generated between the second transfer roller 97 and the backup roller 96 . The second transfer roller 97 transfers toner images onto the recording medium by pressing the recording medium toward the intermediate transfer belt 90 in a state where the potential difference has been generated.

FIG. 3 is a general view of the transfer device 9 as seen from the side on which the photoconductor drums 5 are disposed. In the case where the rotary shafts (not illustrated) of the various rollers, which are included in the transfer device 9 , are not aligned with a reference axis, the intermediate transfer belt 90 may sometimes be skewed. Here, the term “skew” refers to a phenomenon in which the angle formed by the movement direction of the intermediate transfer belt 90 and the reference direction (the positive y-axis direction) deviates from a predetermined angle (the difference between the angle and the predetermined angle exceeds a predetermined threshold) as seen from the side on which the photoconductor drums 5 are disposed. Note that although the movement direction of the intermediate transfer belt 90 may sometimes differ depending on a position on the intermediate transfer belt 90 , here, in the case where there is a point that moves in a direction that is displaced from the reference direction on the intermediate transfer belt 90 , it may be said that the intermediate transfer belt 90 is skewed. In FIG. 3 , a point a 0 on the intermediate transfer belt 90 moves in the direction of arrow A 1 that is displaced from the reference direction, and the intermediate transfer belt 90 is skewed. When the intermediate transfer belt 90 is skewed, a gap S is generated between the intermediate transfer belt 90 and the drive roller 91 on one side of the drive roller 91 . When the gap S is generated, a tension that is applied in the movement direction of the intermediate transfer belt 90 (hereinafter simply referred to as a tension applied to the intermediate transfer belt 90 ) is non-uniform in a width direction of the intermediate transfer belt 90 . For example, in the example illustrated in FIG. 3 , since the tension applied to the intermediate transfer belt 90 is non-uniform, wrinkles are generated in a region D 1 in a surface of the intermediate transfer belt 90 .

FIGS. 4A and 4B are diagrams illustrating a positional relationship between the first transfer roller 92 Y and the photoconductor drum 5 Y. FIGS. 4A and 4B are schematic diagrams illustrating cross-sectional views of the first transfer roller 92 Y and the photoconductor drum 5 Y at different positions in the x-axis direction. Note that a state where the first transfer rollers 92 M, 92 C, and 92 K are pressing the intermediate transfer belt 90 against the photoconductor drums 5 M, 5 C, and 5 K is similar to the state that is illustrated in FIGS. 4A and 4B . FIG. 4A is a schematic diagram (a cross-sectional view taken along line IVA-IVA of FIG. 3 ) of a portion in which a tension F 1 that is applied in the movement direction of the intermediate transfer belt 90 is small, and FIG. 4B is a schematic diagram (a cross-sectional view taken along line IVB-IVB of FIG. 3 ) of a portion in which the tension F 1 , which is applied in the movement direction of the intermediate transfer belt 90 , is large.

As illustrated in FIG. 4A , in the portion in which the tension F 1 , which is applied to the intermediate transfer belt 90 , is small, a pressing force that is applied by the first transfer roller 92 Y to the intermediate transfer belt 90 against the photoconductor drum 5 Y is less likely to be reduced, and thus, a pressure F 2 generated by contact between the photoconductor drum 5 Y and the intermediate transfer belt 90 is large. Therefore, a current easily flows between the first transfer roller 92 Y and the photoconductor drum 5 Y, and toner particles that have moved to the surface of the intermediate transfer belt 90 from the surface of the photoconductor drum 5 Y easily move onto the surface of the photoconductor drum 5 Y again. As a result, in the portion in which the tension F 1 , which is applied to the intermediate transfer belt 90 , is small, the density of toner images that are to be transferred in the first transfer process onto the intermediate transfer belt 90 is low.

As illustrated in FIG. 4B , in the portion in which the tension F 1 , which is applied to the intermediate transfer belt 90 , is large, a pressing force that is applied by the first transfer roller 92 Y to the intermediate transfer belt 90 against the photoconductor drum 5 Y is reduced, and thus, the pressure F 2 generated by contact between the photoconductor drum 5 Y and the intermediate transfer belt 90 is small. Therefore, a current is less likely to flow between the first transfer roller 92 Y and the photoconductor drum 5 Y, and toner particles that have moved to the surface of the intermediate transfer belt 90 from the surface of the photoconductor drum 5 Y are less likely to move onto the surface of the photoconductor drum 5 Y again. As a result, in the portion in which the tension F 1 , which is applied to the intermediate transfer belt 90 , is large, the density of toner images that are to be transferred in the first transfer process onto the intermediate transfer belt 90 is high.

As described above, in the case where the intermediate transfer belt 90 is skewed, and where the tension F 1 , which is applied to the intermediate transfer belt 90 , becomes non-uniform in the width direction of the intermediate transfer belt 90 , unevenness in the density of the toner images, which are to be transferred in the first transfer process onto the intermediate transfer belt 90 , in the x-axis direction is generated. The transfer device 9 according to the exemplary embodiment of the present invention prevents the intermediate transfer belt 90 from being skewed by changing the direction of a rotary shaft al of the stretching roller 95 A.

FIG. 5 is a diagram illustrating the internal configuration of the transfer device 9 when the frame 9 B is viewed from the side on which the frame 9 A is disposed. Note that the internal configuration of the transfer device 9 when the frame 9 A is viewed from the side on which the frame 9 B is disposed is similar to that illustrated in FIG. 5 (is obtained by horizontally reversing the internal configuration illustrated in FIG. 5 ). In order to prevent wear of the photoconductor drums 5 , the transfer device 9 brings the intermediate transfer belt 90 into contact with the photoconductor drums 5 when an image is formed and separates the intermediate transfer belt 90 from the photoconductor drums 5 when an image is not formed. The transfer device 9 moves the first transfer rollers 92 in such a manner as to make transition between a state where the intermediate transfer belt 90 is pressed against the photoconductor drums 5 and a state where the intermediate transfer belt 90 is not pressed against the photoconductor drums 5 . The transfer device 9 includes arm members 901 ( 901 Y, 901 M, 901 C, and 901 K) and a sliding mechanism 902 as a moving mechanism that is used for moving the first transfer rollers 92 . The arm members 901 Y, 901 M, and 901 C are members that support the first transfer rollers 92 Y, 92 M, and 92 C on one side of the rotary shafts of the first transfer rollers 92 and rotate in the direction of arrow A 2 while a point C 1 , a point C 2 , and a point C 3 serve as fulcrums. The arm member 901 K is a member that supports the first transfer roller 92 K on one side of the rotary shaft of the first transfer roller 92 K and rotates in the direction of arrow A 3 while a point C 4 serves as a fulcrum.

The sliding mechanism 902 is a mechanism that is used for causing the arm members 901 to rotate. The sliding mechanism 902 includes two members (a slide member 902 A and a slide member 902 B) that extend from the side on which the drive roller 91 is disposed toward the side on which the steering roller 94 is disposed. The slide member 902 A is a member that is disposed on the side on which the drive roller 91 is disposed and has grooves (not illustrated) into which one ends (ends that do not support the first transfer roller 92 Y and the first transfer roller 92 M) of the arm members 901 Y and 901 M are fitted. An end of the slide member 902 A on the side on which the steering roller 94 is disposed makes contact with an end (an end that does not support the first transfer roller 92 C) of the arm member 901 C. The slide member 902 A is driven by a drive mechanism (not illustrated) so as to slide in the direction of arrow A 5 and causes the arm members 901 Y, 901 M, and 901 C to rotate in the direction of arrow A 2 . The slide member 902 B is a member that is disposed on the side on which the steering roller 94 is disposed and has a groove d 1 into which one side portion of the arm member 901 C is fitted and a groove d 2 into which one end (an end that does not support the first transfer roller 92 K) of the arm member 901 K is fitted. The slide member 902 B is driven independently from the slide member 902 A by a drive mechanism (not illustrated) so as to slide in the direction of arrow A 5 and causes the arm member 901 K to rotate in the direction of arrow A 3 .

FIGS. 6A and 6B are diagrams illustrating a mechanism that changes the direction of the rotary shaft al of the stretching roller 95 A. FIG. 6A is an enlarged view of a portion that is defined by a dashed line L 1 in FIG. 5 FIG. 6B is a diagram illustrating the portion illustrated in FIG. 6A as seen from an area outside the transfer device 9 (i.e., the side opposite to the side illustrated in FIG. 6A ). In this example, the transfer device 9 changes the direction of the rotary shaft al of the stretching roller 95 A by adjusting the position of an end of the stretching roller 95 A on the side on which the frame 9 B is disposed. The transfer device 9 includes an adjusting mechanism that is used for changing the direction of the rotary shaft al of the stretching roller 95 A and adjusting the angle formed by the movement direction of the intermediate transfer belt 90 and the reference direction. The adjusting mechanism includes arm members 903 (examples of support members), a locating member 904 , and an adjusting member 905 .

The arm members 903 support the stretching roller 95 A on one side of the rotary shaft al of the stretching roller 95 A and rotates in the direction of arrow A 4 while a point C 5 serves as a fulcrum. The direction in which the arm members 903 rotate contains a component in a direction normal to the intermediate transfer belt 90 in an area in which the stretching roller 95 A stretches the intermediate transfer belt 90 (a component in the z-axis direction in FIGS. 6A and 6B ) and a component in the direction in which the first transfer rollers 92 rotate as seen from the side on which the photoconductor drums 5 are disposed (a component in the y-axis direction in FIGS. 6A and 6B ). When the arm members 903 rotate, the stretching roller 95 A moves in the direction of arrow A 6 . The slide member 902 A has a protruding portion s 1 that makes contact with one end (an end that does not support the stretching roller 95 A) of the arm members 903 . The slide member 902 A slides in the direction of arrow A 5 , so that the arm members 903 rotate in the direction of arrow A 4 . The slide member 902 A causes, synchronously with the arm members 901 Y, 901 M, and 901 C, the arm members 903 to rotate.

The locating member 904 extends from the side on which one of the ends of the stretching roller 95 A is present toward the side on which the other one of the ends of the stretching roller 95 A is present (i.e., from the frame 9 A toward frame 9 B) and is a member that determines the positions of the arm members 903 . The locating member 904 comes into contact with the arm members 903 when the arm members 903 rotate and determines the positions of the arm members 903 . An end of the locating member 904 on the side on which the frame 9 B is disposed is supported by the adjusting member 905 ( FIG. 6B ), and an end (not illustrated) of the locating member 904 on the side on which the frame 9 A is disposed is supported by the frame 9 A so as not to move.

The adjusting member 905 is a member that adjusts the position of the end of the locating member 904 on the side on which the frame 9 B is disposed. Note that the adjusting member 905 is not disposed on the side on which the frame 9 A is disposed. The adjusting member 905 is screwed onto the frame 9 B at a point C 6 and a point C 7 . The adjusting member 905 moves the position of the end of the locating member 904 on the side on which the frame 9 B is disposed in the direction of arrow A 7 by rotating while the point C 6 serves as a fulcrum and adjusts the position of the end of the locating member 904 on the side on which the frame 9 B is disposed. The direction in which the end of the locating member 904 on the side on which the frame 9 B is disposed is moved contains a component in the z-axis direction and a component in the y-axis direction.

For example, an operator who performs adjustment of skewing of the intermediate transfer belt 90 manually causes, while checking a scale m 1 , the adjusting member 905 to rotate. The scale m 1 is formed on the frame 9 B in such a manner as to allow the operator to recognize a rotation of the adjusting member 905 . As described above, the end (not illustrated) of the locating member 904 on the side on which the frame 9 A is disposed is supported by the frame 9 A so as not to move. Therefore, when the end of the locating member 904 on the side on which the frame 9 B is disposed is moved as a result of the adjusting member 905 being rotated, an axial direction of the locating member 904 changes. When the axial direction of the locating member 904 changes, the locating member 904 makes contact with the arm members 903 at a position on the side on which the frame 9 A is disposed and a different position on the side on which the frame 9 B is disposed on a yz plane, and a difference occurs between a rotation amount of one of the arm members 903 (not illustrated) on the side on which the frame 9 A is disposed and a rotation amount of the other one of the arm members 903 on the side on which the frame 9 B is disposed. The difference in rotation amount causes a difference between an amount of movement of the stretching roller 95 A in the direction of arrow A 6 caused by the arm member 903 on the side on which the frame 9 A is disposed and an amount of movement of the stretching roller 95 A in the direction of arrow A 6 caused by the arm member 903 on the side on which the frame 9 B is disposed, and the direction of the rotary shaft al of the stretching roller 95 A changes. In other words, the relative positions of an end of the rotary shaft al of the stretching roller 95 A on the side on which the frame 9 A is disposed and an end of the rotary shaft al of the stretching roller 95 A on the side on which the frame 9 B is disposed change. As a result, a direction in which the intermediate transfer belt 90 is transported by the stretching roller 95 A changes, and the intermediate transfer belt 90 is prevented from being skewed.

An operator measures, for example, the angle formed by the movement direction of the intermediate transfer belt 90 and the reference direction, uniformity of a tension that is applied to the intermediate transfer belt 90 , a degree of unevenness in the density of toner images, which are to be transferred in the first transfer process onto the intermediate transfer belt 90 , that is generated in the x-axis direction, or the like by using a sensor (not illustrated) and causes the adjusting member 905 to rotate by an amount that corresponds to measurement results. As a specific example, in the case where it is measured that the intermediate transfer belt 90 is skewed to the side on which the frame 9 B is disposed, an operator causes the adjusting member 905 to rotate in such a manner that the position at which the arm member 903 on the side on which the frame 9 B is disposed supports the rotary shaft al of the stretching roller 95 A is higher than the position at which the arm member 903 on the side on which the frame 9 A is disposed supports the rotary shaft al of the stretching roller 95 A. Alternatively, in the case where it is measured that the intermediate transfer belt 90 is skewed to the side on which the frame 9 A is disposed, the operator causes the adjusting member 905 to rotate in such a manner that the position at which the arm member 903 on the side on which the frame 9 B is disposed supports the rotary shaft al of the stretching roller 95 A is lower than the position at which the arm member 903 on the side on which the frame 9 A is disposed supports the rotary shaft al of the stretching roller 95 A.

(Modifications)

The present invention is not limited to the above-described embodiment, and various modifications may be made. Some modifications will be described below. Two or more modifications among the following modifications may be combined and employed.

(1) The adjusting member 905 is not limited to being manually made to rotate. The adjusting mechanism of the transfer device 9 may include a drive mechanism that is used for causing the adjusting member 905 to rotate. In this case, the drive mechanism includes, for example, a cam that makes contact with the adjusting member 905 and a motor or an actuator that supplies power to the adjusting member 905 via the cam. In addition, in this case, the adjusting mechanism of the transfer device 9 includes a measuring unit that measures the angle formed by the movement direction of the intermediate transfer belt 90 and the reference direction, and the drive mechanism may cause the adjusting member 905 to rotate in accordance with an angle that is measured by the measuring unit. Alternatively, the uniformity of the tension, which is applied to the intermediate transfer belt 90 , the degree of the unevenness in the density of the toner images, which are to be transferred in the first transfer process onto the intermediate transfer belt 90 , that is generated in the x-axis direction, or the like may be measured by a sensor, and the drive mechanism may cause the adjusting member 905 to rotate by an amount that corresponds to measurement results. Note that the drive mechanism may cause the adjusting member 905 to rotate in accordance with measurement results that are obtained by multiple sensors that measure different physical quantities such as the angle formed by the movement direction of the intermediate transfer belt 90 and the reference direction, the uniformity of the tension, which is applied to the intermediate transfer belt 90 , the degree of the unevenness in the density of the toner images, which are to be transferred in the first transfer process onto the intermediate transfer belt 90 , that is generated in the x-axis direction, and the like.

FIGS. 7A and 7B are schematic diagrams of a measuring unit. In FIGS. 7A and 7B , the measuring unit includes a sensor R 1 (an example of a first sensor) and a sensor R 2 (an example of a second sensor). FIG. 7A illustrates the positions of the sensors R 1 and R 2 when the transfer device 9 is viewed from the side on which the photoconductor drums 5 are disposed. FIG. 7B illustrates the positions of the sensors R 1 and R 2 when the transfer device 9 is viewed from one side in the width direction of the intermediate transfer belt 90 . Each of the sensors R 1 and R 2 is an edge sensor that senses the position of an edge of the intermediate transfer belt 90 on the side on which the frame 9 A is disposed in the width direction of the intermediate transfer belt 90 . The sensor R 1 (an example of the first sensor) senses the position of the edge of the intermediate transfer belt 90 at a position further downstream than the stretching roller 95 A in the movement direction of the intermediate transfer belt 90 . The sensor R 2 (an example of the second sensor) senses the position of the edge of the intermediate transfer belt 90 at a position further upstream than the stretching roller 95 B in the movement direction of the intermediate transfer belt 90 . Note that each of the sensor R 1 and the sensor R 2 may sense the position of an edge of the intermediate transfer belt 90 on the side on which the frame 9 B is disposed in the width direction of the intermediate transfer belt 90 . In FIGS. 7A and 7B , the measuring unit measures the angle formed by the movement direction of the intermediate transfer belt 90 and the reference direction by using a difference between the position of the edge of the intermediate transfer belt 90 that is sensed by the sensor R 1 and the position of the edge of the intermediate transfer belt 90 that is sensed by the sensor R 2 . A drive mechanism 906 causes the adjusting member 905 to rotate in accordance with an angle that is measured by the measuring unit. In FIGS. 7A and 7B , the transfer device 9 prevents the intermediate transfer belt 90 from being skewed by inclining an end of the rotary shaft al (not illustrated) of the stretching roller 95 A on the side on which the frame 9 B is disposed in the direction of arrow A 8 . The intermediate transfer belt 90 that is indicated by a two-dot chain line is the intermediate transfer belt 90 that is prevented from being skewed.

(2) The transfer device 9 may change the direction of the rotary shaft al of the stretching roller 95 A by adjusting the position of the end of the stretching roller 95 A on the side on which the frame 9 A is disposed. In this case, the adjusting member 905 is disposed on the side on which the frame 9 A is disposed, an end of the locating member 904 on the side on which the frame 9 A is disposed is supported by the adjusting member 905 , and the end of the locating member 904 on the side on which the frame 9 B is disposed is supported by the frame 9 B so as not to move.

(3) A mechanism in which the transfer device 9 changes the direction of the rotary shaft al of the stretching roller 95 A is not limited to the above-described mechanism. For example, the transfer device 9 may change the direction of the rotary shaft al of the stretching roller 95 A by adjusting the positions of the ends of the stretching roller 95 A. In this case, the adjusting member 905 is disposed on both the sides on which the frame 9 A and the frame 9 B are disposed, and the ends of the locating member 904 may be supported by the adjusting members 905 .

(4) The second stretching roller is not limited to the stretching roller 95 A. The stretching roller 95 B may be the second stretching roller. In this case, a mechanism that is similar to the above-described adjusting mechanism and that is used for changing the direction of the rotary shaft of the stretching roller 95 B is disposed further downstream than the first transfer roller 92 K in the movement direction of the intermediate transfer belt 90 . In addition, the transfer device 9 may prevent the intermediate transfer belt 90 from being skewed by individually changing the direction of the rotary shaft al of the stretching roller 95 A and the direction of the rotary shaft of the stretching roller 95 B. In this case, the transfer device 9 includes an adjusting mechanism that is used for changing the direction of the rotary shaft al of the stretching roller 95 A and an adjusting mechanism that is used for changing the direction of the rotary shaft of the stretching roller 95 B.

(5) The adjusting mechanism is not limited to the above-described mechanism. The adjusting mechanism may be any mechanism as long as the mechanism prevents the intermediate transfer belt 90 from being skewed by changing the direction of a rotary shaft of the second stretching roller. For example, the adjusting member 905 may adjust the position of the end of the locating member 904 by sliding on the frame 9 B in the y-axis direction or the z-axis direction. The arm members 903 need not rotate. The arm members 903 may be members that move in the y-axis direction or the z-axis direction.

(6) The reference direction is not limited to the positive y-axis direction. The reference direction may be any one of directions on an xy plane.

(7) The image forming apparatus to which the present invention is applied is not limited to an apparatus that performs color printing. The present invention may be applied to an image forming apparatus that performs only monochrome printing.

(8) The internal configuration of the transfer device 9 is not limited to the above-described configuration. For example, the drive roller 91 may be disposed further downstream than the first transfer rollers 92 in the movement direction of the intermediate transfer belt 90 , and the steering roller 94 may be disposed further upstream than the first transfer rollers 92 in the movement direction of the intermediate transfer belt 90 . Alternatively, the first stretching roller is not limited to the steering roller 94 . The first stretching roller may be any roller as long as the roller stretches the intermediate transfer belt 90 .

(9) The configurations of the units of the image forming apparatus 100 are not limited to the above-described configurations. For example, a fixing device that fixes a toner image that is formed on a recording medium onto the recording medium by radiating a laser beam onto the toner image may be used instead of the above-described fixing device 10 .

The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.