Image forming apparatus and movement amount detection device

An image forming apparatus includes: a belt to be transported; an image forming body that forms an image on the belt or a recording medium that is transported by the belt; a moving mechanism that moves the belt in a movement direction extending in a thickness direction of the belt; a rotational member including a rotation shaft extending in the movement direction and a contact portion that is rotatable around the rotation shaft and that is in contact with a side surface of the belt regardless of a position of the belt in the movement direction; an acquirer that acquires a physical amount that changes due to rotation of the contact portion around the rotation shaft when the belt moves in a width direction; and a detector that detects a movement amount of the belt in the width direction based on the physical amount acquired by the acquirer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-137626 filed Aug. 25, 2021.

BACKGROUND

(i) Technical Field

The present disclosure relates to an image forming apparatus and a movement amount detection device.

(ii) Related Art

Japanese Unexamined Patent Application Publication No. 2010-256789 discloses a belt meandering amount measurement device that measures a meandering amount of an endless belt that is wound around multiple rollers and rotated. In this belt meandering amount measurement device, a measurement reference portion extending in a rotating direction of a belt and having a predetermined length, a first measurement unit extending parallel in the rotating direction of the belt while being shifted from the measurement reference portion in a width direction of the belt, and a second measurement unit extending parallel in the rotating direction of the belt while being shifted from the measurement reference portion and the first measurement unit in the width direction of the belt are formed at one side end portion in the width direction of the belt. A sensor that outputs voltages in accordance with positions of the measurement reference portion, the first measurement unit, and the second measurement unit in the width direction of the belt is disposed near the one side end portion in the width direction of the belt. As pre-use data setting of the belt, in a state in which the belt rotates without meandering, voltages at the positions of the measurement reference portion, the first measurement unit, and the second measurement unit are measured with the measurement reference portion serving as a reference position. A conversion expression representing a relationship between the measurement result and distances of the first measurement unit and the second measurement unit from the reference position in the width direction of the belt is obtained. When the belt is used, the sensor measures a voltage at a predetermined interval at any position of the measurement reference portion, the first measurement unit, and the second measurement unit, converts the voltage into a distance from the reference position in the width direction of the belt by the conversion expression, and obtains a difference of the distance from the reference position obtained at the predetermined interval to measure a meandering amount of the belt.

SUMMARY

There is an image forming apparatus in which an image forming body that forms an image on a belt and a moving mechanism that moves the belt in a thickness direction thereof are provided in the vicinity of the transported belt. Further, in this image forming apparatus, a rotational member that is rotatable around a rotation shaft in a transport direction of the belt is brought into contact with a side surface of the belt, and a movement amount of the belt in a width direction is detected based on a physical amount that changes in accordance with a rotation angle of the rotational member.

In this image forming apparatus, when the position of the belt in the thickness direction changes, the rotation angle of the rotational member per unit movement amount in the width direction of the belt changes. Thus, this image forming apparatus is not able to accurately detect the movement amount in the width direction of the belt whose position in the thickness direction changes.

Aspects of non-limiting embodiments of the present disclosure relate to accurately detecting a movement amount in a width direction of a belt whose position in a thickness direction changes, as compared with a case where a movement amount in a width direction of a belt is detected based on a physical amount that changes due to rotation of a rotational member that is rotatable around a rotation shaft in a transport direction of the belt.

According to an aspect of the present disclosure, there is provided an image forming apparatus including: a belt to be transported; an image forming body that forms an image on the belt or a recording medium that is transported by the belt; a moving mechanism that moves the belt in a movement direction extending in a thickness direction of the belt; a rotational member including a rotation shaft extending in the movement direction and a contact portion that is rotatable around the rotation shaft and that is in contact with a side surface of the belt regardless of a position of the belt in the movement direction; an acquirer that acquires a physical amount that changes due to rotation of the contact portion around the rotation shaft when the belt moves in a width direction; and a detector that detects a movement amount of the belt in the width direction based on the physical amount acquired by the acquirer.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment according to the disclosure will be described in detail with reference to the drawings. Hereinafter, an upstream side in a transport direction of recording paper P as an example of a recording medium may be simply referred to as an “upstream side”, and a downstream side in the transport direction may be simply referred to as a “downstream side”. Similarly, an upstream side in a circling direction of a transfer belt (belt) (formation target body)52may be simply referred to as an “upstream side”, and a downstream side in the circling direction (transport direction) may be simply referred to as a “downstream side”. In the following description, a reference position of the “upstream side” and the “downstream side” of the transfer belt is a second transfer position T2(nip region Np) described later. That is, a direction from the second transfer position T2toward a pressing roller49after passing through a driving roller44is the “downstream side” of the transfer belt, and a direction from the second transfer position T2toward a second photoreceptor unit30K after passing through a retract roller47is the “upstream side” of the transfer belt.

As illustrated inFIG.1, an image forming apparatus10according to the present exemplary embodiment is of an electrophotographic system that forms a toner image (an example of an image) on recording paper P. The image forming apparatus10includes an image forming section12, a storage section14, a transport section16, and a fixing device18in an apparatus body (not illustrated). Hereinafter, each component of the image forming apparatus10will be described.

In the following description, a width direction (horizontal direction) of the apparatus body is defined as an X direction, an up-down direction (vertical direction) of the apparatus body is defined as a Y direction, and a front-rear direction (a direction orthogonal to a paper surface) orthogonal to the X direction and the Y direction is defined as a Z direction. InFIG.1, the near side of the paper surface is a front side, and the far side of the paper surface is a rear side.

Image Forming Section

The image forming section12has a function of forming a toner image on recording paper P. The image forming section12includes a first photoreceptor unit20, a second photoreceptor unit30, and a transfer device50.

Photoreceptor Units

As illustrated inFIG.1, two first photoreceptor units20and two second photoreceptor units30are provided. Each first photoreceptor unit20and each second photoreceptor unit30are attachable to and detachable from the apparatus body. The image forming apparatus10includes first photoreceptor units20Y and20M for yellow (Y) and magenta (M) and second photoreceptor units30C and30K for cyan (C) and black (K).

In the following description, in a case where it is necessary to distinguish each color of yellow (Y), magenta (M), cyan (C), or black (K), an alphabet of Y, M, C, or K is added after a reference numeral of each member. In a case where it is not necessary to distinguish each color, an alphabet of Y, M, C, or K may be omitted.

The transfer belt52made of an elastic material of the transfer device50described later includes two straight portions that are straight-line shaped when viewed in the Z direction. The two straight portions are an upper portion52A and a lower portion52B. When viewed in the Z direction, the upper portion52A extends in the X direction, and the lower portion52B is inclined with respect to the X direction. That is, when viewed in the Z direction, an angle θB (seeFIG.1) defined by the lower portion52B and the X direction is an acute angle, and the angle θB is larger than an angle θA (not illustrated) defined by the upper portion52A and the X direction. Note that the angle θA is 0° or an acute angle slightly larger than 0°. When viewed in the Z direction, the upper portion52A and the lower portion52B are mutually arranged in the Y direction. The “straight portion” in the present specification and claims is not limited to a completely straight-line-shaped portion. For example, in the upper portion52A located between a retract roller39and a retract roller48described later, portions pressed by the two first photoreceptor drums22and first transfer rollers41are slightly recessed; however, the upper portion52A corresponds to the “straight portion”. Similarly, in the lower portion52B located between a retract roller40and the retract roller47, portions pressed by the two second photoreceptor drums32and first transfer rollers41are slightly recessed; however, the lower portion52B corresponds to the “straight portion”. A width direction of the transfer belt52extends in the Z direction.

The two first photoreceptor units20face an outer peripheral surface (upper surface) of the upper portion52A and are arranged in the X direction along the upper portion52A. Each first photoreceptor unit20includes the first photoreceptor drum22that rotates in one direction (for example, the counterclockwise direction inFIG.1). Each first photoreceptor drum22is rotatable around a rotation axis20X extending in the Z direction. Each first photoreceptor unit20includes a first charging portion24, a first exposure portion25, a first developing portion26, and a first removing portion27in this order from the upstream side in the rotation direction of the first photoreceptor drum22. Each first photoreceptor unit20further includes a pair of support plates28separated from each other in the Z direction. One of the support plates28is not illustrated inFIG.1. The first charging portion24, the first exposure portion25, the first developing portion26, and the first removing portion27are members extending in the Z direction. Both end portions of the first charging portion24, the first exposure portion25, the first developing portion26, and the first removing portion27in the Z direction are supported by the pair of support plates28. Further, relative movement of the pair of support plates28is restricted. As illustrated inFIG.1, the dimension of each first photoreceptor unit20in the X direction is a horizontal dimension20L.

The two second photoreceptor units30face an outer peripheral surface (lower surface) of the lower portion52B and are arranged along the lower portion52B. Each second photoreceptor unit30includes a second photoreceptor drum32that rotates in one direction (for example, the counterclockwise direction inFIG.1). Each second photoreceptor drum32is rotatable around a rotation axis30X extending in the Z direction. Each second photoreceptor unit30includes a second charging portion34, a second exposure portion35, a second developing portion36, and a second removing portion37in this order from the upstream side in the rotation direction of the second photoreceptor drum32. Each second photoreceptor unit30further includes a pair of second support plates38separated from each other in the Z direction. One of the second support plates38is not illustrated inFIG.1. The second charging portion34, the second exposure portion35, the second developing portion36, and the second removing portion37are members extending in the Z direction. Both end portions of the second charging portion34, the second exposure portion35, the second developing portion36, and the second removing portion37in the Z direction are supported by the pair of second support plates38. Further, relative movement of the pair of second support plates38is restricted. As illustrated inFIG.1, the dimension of each second photoreceptor unit30in the X direction is a horizontal dimension30L.

In the present specification and claims, a term “image forming body” refers to a body that causes toner or ink to adhere to a formation target body (for example, the transfer belt52). That is, the first photoreceptor drum22of the first photoreceptor unit20corresponds to the “image forming body”, and the second photoreceptor drum32of the second photoreceptor unit30corresponds to the “image forming body”. That is, the first charging portion24, the first exposure portion25, the first developing portion26, and the first removing portion27do not correspond to the “image forming body”. Similarly, the second charging portion34, the second exposure portion35, the second developing portion36, and the second removing portion37do not correspond to the “image forming body”. As will be described later, when the image forming apparatus10is of an inkjet type, an inkjet head corresponds to the “image forming body”.

A first distance20B is a distance (adjacent distance) between two portions on which images are formed by the two first photoreceptor drums22or two inkjet heads on the outer peripheral surface of the upper portion52A when viewed in the Z direction. When the first photoreceptor drums22correspond to the “image forming bodies”, two line segments connecting the first photoreceptor drums22and the first transfer rollers41respectively corresponding to the first photoreceptor drums22intersect with the outer peripheral surface of the upper portion52A at two intersection portions of the outer peripheral surface. When the first photoreceptor drums22correspond to the “image forming bodies”, the first distance20B is a distance between the two intersection portions when viewed in the Z direction. When the image forming apparatus10is of an inkjet type, the first distance20B is a distance between center portions of inkjet heads (image forming bodies) corresponding to the first photoreceptor units20.

Further, a second distance30B is a distance between two portions of the outer peripheral surface of the lower portion52B on which images are formed by the two second photoreceptor units30or two inkjet heads when viewed in the Z direction. When the second photoreceptor drums32correspond to the “image forming bodies”, two line segments connecting the second photoreceptor drums32and the first transfer rollers41respectively corresponding to the second photoreceptor drums32intersect with the outer peripheral surface of the lower portion52B at two intersection portions of the outer peripheral surface. When the second photoreceptor drums32correspond to the “image forming bodies”, the second distance30B is a distance between the two intersection portions when viewed in the Z direction. When the image forming apparatus10is of an inkjet type, the second distance30B is a distance between center portions of inkjet heads (image forming bodies) corresponding to the second photoreceptor units30.

As illustrated inFIG.1, a developing roller26A, a recovery auger26B, a supply auger26C, and a stirring auger26D are provided inside the first developing portion26. Similarly, a developing roller36A, a recovery auger36B, a supply auger36C, and a stirring auger36D are provided inside the second developing portion36. The supply auger26C and the stirring auger26D are arranged in the X direction. In contrast, the supply auger36C and the stirring auger36D are arranged in the Y direction. Hence, the horizontal dimension of the second developing portion36is shorter than the horizontal dimension of the first developing portion26. Thus, the horizontal dimension30L is shorter than the horizontal dimension20L.

As illustrated inFIG.1, the two first photoreceptor units20are arranged in the X direction when viewed in the Z direction. That is, the two first photoreceptor units20are not arranged in the Y direction. In contrast, when viewed in the Z direction, portions of the two second photoreceptor units30are arranged in the Y direction. A horizontal dimension30V illustrated inFIG.1is an X-direction dimension of the portions of the two second photoreceptor units30. A horizontal dimension30E illustrated inFIG.1is a horizontal dimension of a portion including the two second photoreceptor units30. A horizontal dimension30G illustrated inFIG.1is a horizontal dimension of a portion including the lower portion52B and the two second photoreceptor units30.

The first charging portion24of each first photoreceptor unit20charges an outer peripheral surface of the first photoreceptor drum22. Then, the first exposure portion25exposes the outer peripheral surface of the first photoreceptor drum22charged by the first charging portion24to light to form an electrostatic latent image on the outer peripheral surface of the first photoreceptor drum22. The first developing portion26develops the electrostatic latent image formed on the outer peripheral surface of the first photoreceptor drum22by the first exposure portion25to form a toner image. After the toner image is transferred to the transfer belt52, the first removing portion27removes the toner remaining on the outer peripheral surface of the first photoreceptor drum22.

The second charging portion34of each second photoreceptor unit30charges an outer peripheral surface of the second photoreceptor drum32. Then, the second exposure portion35exposes the outer peripheral surface of the second photoreceptor drum32charged by the second charging portion34to light to form an electrostatic latent image on the outer peripheral surface of the second photoreceptor drum32. The second developing portion36develops the electrostatic latent image formed on the outer peripheral surface of the second photoreceptor drum32by the second exposure portion35to form a toner image. After the toner image is transferred to the transfer belt52, the second removing portion37removes the toner remaining on the outer peripheral surface of the second photoreceptor drum32.

Transfer Device

As illustrated inFIG.1, the transfer device50includes the four first transfer rollers41serving as first transfer bodies, the transfer belt52serving as an intermediate transfer body, and a transfer cylinder85serving as a second transfer body. That is, the transfer device50first transfers the toner images formed on the outer peripheral surfaces of the respective first photoreceptor drums22to the transfer belt52in a superimposed manner, and second transfers the superimposed toner images to recording paper P.

First Transfer Roller

As illustrated inFIG.1, each first transfer roller41facing the upper portion52A transfers the toner image formed on the outer peripheral surface of the corresponding first photoreceptor drum22to the outer peripheral surface of the transfer belt52at a first transfer position T1between the first photoreceptor drum22and the first transfer roller41. Each first transfer roller41facing the lower portion52B transfers the toner image formed on the outer peripheral surface of the corresponding second photoreceptor drum32to the outer peripheral surface of the transfer belt52at a first transfer position T1between the second photoreceptor drum32and the first transfer roller41. In the present exemplary embodiment, a first transfer voltage is applied between the first transfer roller41and the first photoreceptor drum22, and hence the toner image formed on the outer peripheral surface of the first photoreceptor drum22is transferred to the outer peripheral surface of the transfer belt52at the first transfer position T1. Similarly, a first transfer voltage is applied between the first transfer roller41and the second photoreceptor drum32, and hence the toner image formed on the outer peripheral surface of the second photoreceptor drum32is transferred to the outer peripheral surface of the transfer belt52at the first transfer position T1.

Each first transfer roller41is movable in a thickness direction TD (see an arrow inFIG.1) of the transfer belt52. The thickness direction TD of the transfer belt52in this specification refers to a thickness direction of the transfer belt52when each of retract rollers39,40,47, and48described later is located at a pressing position. Further, a rotation shaft of the first transfer roller41is urged by an urging member (not illustrated) in a direction toward an inner peripheral surface of the transfer belt52.

Transfer Belt

The annular transfer belt52illustrated inFIG.1is wound around the four retract rollers39,40,47, and48, the driving roller44, a steering roller45, a backup roller46, and a pressing roller49, and hence the posture is determined.

Each of the retract rollers39,40,47, and48, which are moving mechanisms of the present exemplary embodiment, is rotatably in contact with the inner peripheral surface of the transfer belt52and is movable in a predetermined advance-retract direction RD. Each of the retract rollers39,40,47, and48is movable in the advance-retract direction RD between a pressing position and a retracted position that is a position on the inner peripheral side of the transfer belt52with respect to the pressing position. The retract roller39is located on the downstream side of the first photoreceptor unit20Y and located on the upstream side of the steering roller45. The retract roller40is located on the upstream side of the second photoreceptor unit30C and located on the downstream side of the steering roller45. The retract roller47is located on the downstream side of the second photoreceptor unit30K and located on the upstream side of the backup roller46. The retract roller48is located on the upstream side of the first photoreceptor unit20Y and located on the downstream side of the driving roller44.

The upper portion52A and the lower portion52B of the transfer belt52are movable in a movement direction MD (seeFIG.1) extending in the thickness direction TD. As illustrated inFIG.2, when the transfer belt52moves in the movement direction MD, the first transfer roller41moves in the thickness direction TD following the transfer belt52.

For example, when the retract rollers40and47are located at the pressing positions, the lower portion52B is located at a first transport position PM1indicated by a solid line inFIGS.2and3. At this time, the second photoreceptor unit30C and the second photoreceptor unit30K may transfer the toner images to the transfer belt52. When the retract rollers40and47are located at the retracted positions, the lower portion52B is located at a second transport position PM2indicated by an imaginary line inFIGS.2and3. At this time, the second photoreceptor unit30C and the second photoreceptor unit30K are not able to transfer the toner images to the transfer belt52. Although illustration is omitted, when the retract roller39and the retract roller48are located at the pressing positions, the upper portion52A is located at a first transport position PM1corresponding to the first transport position PM1inFIGS.2and3. At this time, the first photoreceptor unit20Y and the first photoreceptor unit20M may transfer the toner images to the transfer belt52. When the retract roller39and the retract roller48are located at the retracted positions, the upper portion52A is located at a second transport position PM2corresponding to the second transport position PM2inFIGS.2and3. At this time, the first photoreceptor unit20Y and the first photoreceptor unit20M are not able to transfer the toner images to the transfer belt52. By individually controlling the positions of the respective retract rollers39,40,47, and48, only any one to three of the first and second photoreceptor units20and30may be brought into a state in which transfer to the transfer belt52is possible.

The movement direction MD that is a direction extending in the thickness direction TD of the transfer belt52includes a direction completely parallel to the thickness direction TD and a direction slightly inclined with respect to the thickness direction TD. In a case where the movement direction MD is inclined with respect to the thickness direction TD, an inclination angle defined by the movement direction MD and the thickness direction TD when viewed in the Z direction is any angle of 10° or less.

The driving roller44having a circular cross section is configured to be rotationally driven around an axis44X extending in the Z direction by a driver (not illustrated), and causes the transfer belt52to circle at a predetermined speed in a circling direction indicated by arrow A.

The diameter of the steering roller45having a circular cross section is the same as the diameter of the driving roller44within a range of tolerance. In other words, an outer peripheral length45C of the steering roller45and an outer peripheral length44C of the driving roller44are the same within a range of tolerance. The steering roller45is rotatable around a rotation axis45X extending in one direction. The steering roller45is an example of a change roller. Further, the steering roller45is rotatable around a rotation center shaft that is provided at a center portion of the steering roller45in a direction along the rotation axis45X and that intersects with the rotation axis45X. The position of the steering roller45in the rotation direction around the rotation center shaft when the rotation axis45X is parallel to the Z direction is a neutral position of the steering roller45. Further, the transfer device50includes a driving mechanism (not illustrated) that rotates the steering roller45by applying a driving force to the steering roller45. When the driving mechanism applies, to the steering roller45, a driving force corresponding to a movement amount (meandering amount) of the transfer belt52in the width direction detected by movement amount detection devices17A and17B described later, the meandering of the transfer belt52is suppressed by the steering roller45that is rotated.

The first distance20B of the two first photoreceptor drums22and the second distance30B of the two second photoreceptor drums32are set to be integral multiples of the outer peripheral length44C of the driving roller44and the outer peripheral length45C of the steering roller45. The second distance30B is shorter than the first distance20B. For example, the first distance20B of the present exemplary embodiment is set to be four times the outer peripheral length44C and the outer peripheral length45C, and the second distance30B is set to be three times the outer peripheral length44C and the outer peripheral length45C.

A distance along the transfer belt52between the first transfer position T1of the first photoreceptor drum22on the downstream side and the first transfer position T1of the second photoreceptor drum32on the upstream side is different from the first distance20B and the second distance30B. The distance along the transfer belt52between the first transfer position T1of the first photoreceptor drum22on the downstream side and the first transfer position T1of the second photoreceptor drum32on the upstream side is also set to an integral multiple of the outer peripheral length44C of the driving roller44and the outer peripheral length45C of the steering roller45.

The backup roller46faces the transfer cylinder85with the transfer belt52interposed therebetween. A region where the transfer cylinder85and the transfer belt52are in contact with each other is the nip region Np (seeFIG.1). The nip region Np is the second transfer position T2where the toner images are transferred from the transfer belt52to the recording paper P.

Further, the pressing roller49located on the upstream side of the retract roller48and on the downstream side of the driving roller44is rotatably in contact with the outer peripheral surface of the transfer belt52and presses the transfer belt52toward the inner peripheral side.

Movement Amount Detection Device

A base plate50A (not illustrated inFIG.1, seeFIG.4) on which the first transfer rollers41, the retract rollers39,40,47, and48, and the driving roller44are supported is provided with two movement amount detection devices17A and17B. One movement amount detection device17A is disposed in the vicinity of one side surface52G in the width direction of the upper portion52A, and is located on the downstream side of the first photoreceptor unit20Y and on the upstream side of the first photoreceptor unit20M. The other movement amount detection device17B is disposed in the vicinity of one side surface52G in the width direction of the lower portion52B, and is located on the downstream side of the second photoreceptor unit30C and on the upstream side of the second photoreceptor unit30K. As illustrated inFIGS.4and5, the movement amount detection devices17A and17B each include a rotation unit55and a detection unit60.

The rotation unit55includes a support member56, a rotational member57, a rotation shaft58, and a coil spring59. The support member56, which is a metallic press-formed product, includes a first connecting portion56A, a fixed portion56B, and a second connecting portion56C. The first connecting portion56A and the fixed portion56B intersect with each other, and the first connecting portion56A and the second connecting portion56C intersect with each other.

The rotational member57, which is a metallic press-formed product, includes a base portion57A, a coupling portion57B, a rotating portion57C, and a pressing portion57D. The base portion57A includes a vertical wall portion57A1, a lower portion57A2, and an upper portion57A3. The lower portion57A2and the upper portion57A3are respectively connected to both end portions of the vertical wall portion57A1. The lower portion57A2and the upper portion57A3intersect with the vertical wall portion57A1. That is, the cross-sectional shape of the base portion57A is substantially U-shaped.

One end portion of a metallic rotation shaft58extending in a direction intersecting with the Z direction is fixed to the first connecting portion56A. The rotation shaft58penetrates through the lower portion57A2and the upper portion57A3. The base portion57A (rotational member57) is rotatable relative to the support member56around the rotation shaft58.

One end portion of the coupling portion57B having a flat plate shape and extending in one direction is connected to the upper portion57A3. The upper portion57A3and the coupling portion57B are located on the same plane. One end portion of the rotating portion57C extending in a direction intersecting with the coupling portion57B is connected to the other end portion of the coupling portion57B. When viewed along the rotation shaft58, the rotating portion57C is located on the outer peripheral side of the rotation shaft58.

The rotating portion57C includes a first plate-shaped portion57C1, a second plate-shaped portion57C2, and a contact portion57C3. The rotating portion57C (the first plate-shaped portion57C1, the second plate-shaped portion57C2, and the contact portion57C3) extends in a direction along the rotation shaft58. In this case, the expression “extends in a direction along the rotation shaft58” includes that the rotating portion57C extends in a direction completely parallel to the rotation shaft58and that the rotating portion57C extends in a direction slightly inclined with respect to the rotation shaft58. In a case where the rotating portion57C is inclined with respect to the rotation shaft58, an inclination angle defined by the rotating portion57C and the rotation shaft58when viewed in the Z direction is any angle of 10° or less.

As illustrated inFIGS.6to8, the first plate-shaped portion57C1and the second plate-shaped portion57C2intersect with each other when viewed along the rotation shaft58. An intersection angle θC between the first plate-shaped portion57C1and the second plate-shaped portion57C2is an obtuse angle. The first plate-shaped portion57C1includes a wide portion57C1aand a narrow portion57C1b. The wide portion57C1ais one end portion of the first plate-shaped portion57C1in the longitudinal direction. The narrow portion57C1b, which is a portion of the first plate-shaped portion57C1excluding one end portion, is narrower than the wide portion57C1a. The second plate-shaped portion57C2includes a wide portion57C2aand a narrow portion57C2b. The narrow portion57C2bis narrower than the wide portion57C2a. The longitudinal dimension of the wide portion57C2ais larger than the longitudinal dimension of the wide portion57C1a. The contact portion57C3is formed at a portion of one surface of the rotating portion57C. As described later, the one surface of the rotating portion57C faces the one side surface52G of the transfer belt52. The straight-line-shaped contact portion57C3extending in a direction along the rotation shaft58is a connecting portion between the first plate-shaped portion57C1and the second plate-shaped portion57C2. As illustrated inFIGS.6to8, the contact portion57C3is a round surface.

One end portion of the pressing portion57D having a flat plate shape and extending in one direction is connected to the upper portion57A3. That is, the upper portion57A3, the coupling portion57B, and the pressing portion57D are located on the same plane.

As illustrated inFIG.4, both end portions of the coil spring (second urging member)59are respectively fixed to the first connecting portion56A of the support member56and the vertical wall portion57A1of the rotational member57. The coil spring59is normally elastically deformed. Thus, the rotational member57is urged to rotate in the counterclockwise direction inFIG.9by the urging force generated by the coil spring59.

The detection unit60includes a case61, an optical sensor67, an interlocking member72, and a coil spring (first urging member)77.

The case61has a shape obtained by processing a portion of a rectangular parallelepiped. That is, a recessed portion62is formed in one surface (left side surface inFIG.5) of the case61. Both end portions in the Z direction of one end portion62A of the recessed portion62in a direction along the rotation shaft58are closed by a pair of support walls63. Although not illustrated, bearing portions are formed at the pair of support walls63. In contrast, both end portions in the Z direction of a portion of the recessed portion62excluding the one end portion62A are opened. Further, a space64is formed inside the case61. As illustrated inFIG.5, the space64communicates with the portion of the recessed portion62excluding the one end portion62A. The optical sensor67is fixed to an inner surface of the space64. The optical sensor67includes a light emitting element68and a light receiving element69that face each other. Inspection light emitted from the light emitting element68is received by the light receiving element69. The light emitting element68, the light receiving element69, and the above-described driving mechanism are connected to a control device (detector)80illustrated inFIG.5.

The control device80includes a central processing unit (CPU, or processor), a read only memory (ROM), a random access memory (RAM), a storage, a communication interface (I/F), and an input/output I/F. The CPU, the ROM, the RAM, the storage, the communication I/F, and the input/output I/F are communicably connected to one another via a bus. The CPU is a central processing unit and executes various programs and controls each component. That is, the CPU reads a program from the ROM or the storage, and executes the program using the RAM as a work area. The CPU controls the driving mechanism and performs various types of calculation processing in accordance with the program. This calculation processing includes calculation processing of the movement amount in the width direction of the transfer belt52based on the light amount of the inspection light received by the light receiving element69.

An interlocking member72is an integrally molded product including a supported shaft73, a pressed portion74, and a detected portion75. One end portion of the pressed portion74and one end portion of the detected portion75are connected to the supported shaft73extending in the Z direction. As illustrated inFIG.5, the pressed portion74has a substantially V-shaped cross section, and the detected portion75has a substantially L-shaped cross section.

As illustrated inFIG.5, both end portions of the interlocking member72are rotatably supported by the bearing portions of the pair of support walls63. A distal end portion of the detected portion75is located inside the space64. Most of the pressed portion74is located outside the case61.

Further, as illustrated inFIG.5, both end portions of the coil spring77are respectively fixed to an inner surface of the one end portion62A and the supported shaft73. The coil spring77is normally elastically deformed. Thus, the interlocking member72is urged to rotate in the clockwise direction inFIG.5by the urging force generated by the coil spring77. The urging force of the coil spring77is smaller than the urging force of the coil spring59.

As illustrated inFIGS.4and5, the rotation unit55and the detection unit60are connected to each other. To be specific, the first connecting portion56A of the support member56is fixed to one surface (an upper surface inFIG.5) of the case61, and the second connecting portion56C is fixed to another surface (a left side surface inFIG.5) of the case61. When the rotation unit55and the detection unit60are connected to each other, the pressing portion57D of the rotational member57and the pressed portion74of the interlocking member72come into contact with each other. As described above, the urging force of the coil spring77is smaller than the urging force of the coil spring59. Thus, the pressing portion57D (rotational member57) is rotated in the counterclockwise direction inFIG.9by the coil spring59, and the interlocking member72(pressed portion74) in contact with the pressing portion57D is rotated in the counterclockwise direction inFIG.5against the urging force of the coil spring77. When external forces other than those of the coil spring59and the coil spring77are not applied to the rotational member57and the interlocking member72, the rotational member57is located at an initial position57IP indicated by an imaginary line inFIG.9, and the interlocking member72is located at an initial position72IP indicated by an imaginary line inFIG.5. The rotation unit55is provided with a stopper (not illustrated) for restricting counterclockwise rotation of the rotational member57around the rotation shaft58at the initial position57IP. Further, the fixed portion56B of the support member56of each of the movement amount detection device17A and the movement amount detection device17B each constituted by connecting the rotation unit55and the detection unit60is fixed to the base plate50A by bolts or the like.

When the fixed portion56B is fixed to the base plate50A, an extension direction of the rotation shaft58becomes a direction extending in the movement direction MD. In other words, the extension direction of the rotating portion57C and the rotation shaft58intersects with the transport direction of the transfer belt52. In this case, the expression “direction extending in the movement direction MD” includes a direction completely parallel to the movement direction MD and a direction slightly inclined with respect to the movement direction MD. In a case where the rotation shaft58is inclined with respect to the movement direction MD, an inclination angle defined by the movement direction MD and the axis of the rotation shaft58when viewed in the Z direction is any angle of 10° or less.

When the detected portion75is not located between the light emitting element68and the light receiving element69, the light receiving element69receives all inspection light emitted by the light emitting element68. When the detected portion75is located between the light emitting element68and the light receiving element69, the light receiving element69is not able to receive all or part of the inspection light emitted by the light emitting element68. That is, the light amount of the inspection light received by the light receiving element69changes in accordance with the rotation angle of the detected portion75(interlocking member72) around the supported shaft73. In other words, the light amount of the inspection light received by the light receiving element69changes in accordance with the rotation angle of the rotational member57(rotating portion57C) rotating in association with the detected portion75around the rotation shaft58.

As illustrated inFIGS.1and9, the contact portion57C3of the rotating portion57C of the movement amount detection device17A disposed in the vicinity of the upper portion52A is in contact with the side surface52G of the upper portion52A. Similarly, as illustrated inFIGS.2,3, and9, the contact portion57C3of the rotating portion57C of the movement amount detection device17B disposed in the vicinity of the lower portion52B is in contact with the side surface52G of the lower portion52B. Further, even when the retract rollers39,40,47, and48are located at any positions in the movement direction MD, the contact state between the contact portion57C3of the movement amount detection device17A and the side surface52G of the upper portion52A is maintained, and the contact state between the contact portion57C3of the movement amount detection device17B and the side surface52G of the lower portion52B is maintained.

In this case, a position in the width direction of the transfer belt52indicated by a solid line inFIG.9is defined as a reference position52SP. When the transfer belt52is located at the reference position52SP, the rotational member57(rotating portion57C) is located at a reference rotational position57SP indicated by a solid line inFIG.9in a plan view. The reference rotational position57SP is a position rotated by only a predetermined angle in the clockwise direction in plan view from the initial position57IP indicated by an imaginary line inFIG.9. At this time, the interlocking member72is located at a reference rotational position72SP indicated by a solid line inFIG.5.

The transfer belt52is movable in the width direction. That is, the transfer belt52is movable in the up-down direction inFIG.9from the reference position52SP. When the transfer belt52moves to a first position52P1indicated by an imaginary line inFIG.9, the rotating portions57C (contact portions57C3) of the movement amount detection devices17A and17B that is in contact with the side surface52G of the transfer belt52each move from the reference rotational position57SP to a first rotational position57P1indicated by the imaginary line following the transfer belt52. As a result, the interlocking member72moves from the reference rotational position72SP to a first rotational position72P1indicated by an imaginary line inFIG.5. In contrast, when the transfer belt52moves to a second position52P2indicated by an imaginary line in FIG.9, the rotating portion57C (contact portion57C3) of the movement amount detection device17A that is in contact with the side surface52G of the transfer belt52moves from the reference rotational position57SP to a second rotational position57P2indicated by the imaginary line following the transfer belt52. As a result, the interlocking member72moves from the reference rotational position72SP to a second rotational position72P2indicated by an imaginary line inFIG.5. The first position52P1is a position of the transfer belt52when the transfer belt52according to the present exemplary embodiment is maximally moved upward inFIG.9. The second position52P2is a position of the transfer belt52when the transfer belt52according to the present exemplary embodiment is maximally moved downward inFIG.9. In this manner, the urging forces of the coil spring59and the coil spring77are used to maintain the contact state between the contact portion57C3of the rotational member57and the side surface52G of the transfer belt52and the contact state between the pressing portion57D and the interlocking member72(pressed portion74). The rotational member57and the interlocking member72are rotated in association with the movement of the belt52in the width direction.

Transport Section

As illustrated inFIG.1, the transport section16includes a transport device (not illustrated) that transports recording paper P sent out from the storage section14in a direction of arrow B. The recording paper P sent out from the storage section14is transported to the transfer cylinder85by the transport device. The recording paper P on which a toner image has been second-transferred by passing through the transfer cylinder85(second transfer position T2) is transported to the fixing device18by the transport device.

Fixing Device

As illustrated inFIG.1, the fixing device18includes a heating roller42as an example of a heating member and a pressure roller43as an example of a pressure member. The fixing device18fixes the toner image transferred to the recording paper P by the transfer cylinder85to the recording paper P by sandwiching the recording paper P between the heating roller42and the pressure roller43and heating and pressing the recording paper P.

Next, operations and effects of the image forming apparatus10configured as described above will be described in detail.

In the image forming apparatus10according to the present exemplary embodiment, the transfer belt52that is circled in the arrow A direction by the driving force generated by the driving roller44may meander in the width direction. That is, the transfer belt52may move from the reference position52SP toward the first position52P1and toward the second position52P2, and the rotational member57(rotating portion57C) may rotate from the reference rotational position57SP to the first rotational position57P1and the second rotational position57P2. In other words, the interlocking member72may rotate from the reference rotational position72SP to the first rotational position72P1and the second rotational position72P2. Consequently, as illustrated inFIG.5, the position of the detected portion75in the rotation direction changes. Thus, the light amount (physical amount) of the inspection light received by the light receiving element69changes. That is, the light amount of the inspection light received by the light receiving element69changes due to the rotation of the rotating portion57C around the rotation shaft58. That is, the light amount of the inspection light received by the light receiving element69changes due to the movement amount of the transfer belt52in the width direction from the reference position52SP.

Information relating to the light amount of the inspection light received by the light receiving element69is transmitted from the light receiving element69to the control device80. The control device80that has received this information calculates the movement amount of the transfer belt52in the width direction from the reference position52SP based on the information and controls the above-described driving mechanism.

In the image forming apparatus10according to the present exemplary embodiment, the upper portion52A and the lower portion52B of the transfer belt52are movable between the first transport position PM1and the second transport position PM2in the movement direction MD. As described above, even when the retract rollers39,40,47, and48are located at any positions in the movement direction MD, the contact state between the contact portion57C3of the movement amount detection device17A and the side surface52G of the upper portion52A is maintained, and the contact state between the contact portion57C3of the movement amount detection device17B and the side surface52G of the lower portion52B is maintained. Further, the straight-line-shaped contact portion57C3of the rotating portion57C extends in the direction along the rotation shaft58. Thus, even when the position of the transfer belt52in the thickness direction TD changes, the magnitude of the rotation angle of the rotational member57(rotating portion57C) per unit movement amount of the transfer belt52in the width direction is constant. For this reason, the movement amount detection devices17A and17B (optical sensor67) of the present exemplary embodiment may accurately acquire a physical amount (light amount) as compared with a case of acquiring a physical amount (light amount) that changes due to rotation of a rotating portion that is rotatable around a rotation shaft extending in the transport direction of the transfer belt52. Thus, the image forming apparatus10according to the present exemplary embodiment may accurately detect the movement amount in the width direction of the transfer belt52whose position in the thickness direction TD changes, as compared with the case of acquiring the physical amount (light amount) that changes due to the rotation of the rotating portion that is rotatable around the rotation shaft extending in the transport direction of the transfer belt52.

FIG.10illustrates a rotational member90according to a comparative example of the present disclosure. A rotating portion91of the rotational member90is a plate-shaped member having a rectangular cross-sectional shape. That is, an outer peripheral surface of the rotating portion91is constituted by four flat surfaces. A first corner portion93is formed between a first surface92, which is one of the four surfaces, and a second surface95adjacent to the first surface92. Similarly, a second corner portion94is formed between the first surface92and a third surface96adjacent to the first surface92. The rotational member90extends in a direction parallel to a rotation shaft58. As indicated by a solid line inFIG.10, when the transfer belt52is located at a second position52P2, the first corner portion93of the rotating portion91is in contact with a side surface52G of a transfer belt52. Further, when the transfer belt52is located at a first position52P1, the second corner portion94of the rotating portion91is in contact with the side surface52G.

A line segment Dm1illustrated inFIG.10connects the rotation shaft58and the first corner portion93, and a line segment Dm2connects the rotation shaft58and the second corner portion94. The line segment Dm1is longer than the line segment Dm2. That is, the length of the line segment Dm1differs from the length of the line segment Dm2. Hence, the rotation angle of the rotating portion91around the rotation shaft58when the transfer belt52moves from the second position52P2in the width direction by only a unit movement amount differs from the rotation angle of the rotating portion91around the rotation shaft58when the transfer belt52moves from the first position52P1in the width direction by only the unit movement amount. Hence, there is a possibility that the optical sensor67of this comparative example is not able to accurately acquire the amount of received light (physical amount) that changes due to the rotation of the rotational member90. Thus, there is a possibility that the accuracy of the calculation amount (the movement amount of the transfer device50in the width direction) obtained by the control device80based on the amount of received light is lowered.

In contrast, the contact portion57C3of the rotating portion57C of the image forming apparatus10according to the present exemplary embodiment has a straight-line shape (round surface shape) extending in the direction along the rotation shaft58. Hence, even when the rotational position of the rotating portion57C changes, the length of the line segment connecting the rotation shaft58and the contact position between the contact portion57C3and the side surface52G of the transfer belt52does not change. Thus, the image forming apparatus10according to the present exemplary embodiment may more accurately detect the movement amount of the transfer belt52in the width direction than a case where a portion of the flat-surface-shaped first surface92is brought into contact with the side surface52G of the transfer belt52.

The first corner portion93and the second corner portion94inFIG.10are constituted by corner portions of a plate-shaped member. Hence, when the first corner portion93and the second corner portion94come into contact with the side surface52G of the transfer belt52, the transfer belt52is easily damaged. In contrast, the contact portion57C3of the rotating portion57C of the image forming apparatus10according to the present exemplary embodiment has a round surface shape. Thus, the rotating portion57C of the rotational member57according to the present exemplary embodiment is less likely to damage the transfer belt52than a case where the first corner portion93and the second corner portion94constituted by the corner portions of the plate-shaped member are brought into contact with the side surface52G of the transfer belt52.

Further, in the image forming apparatus10according to the present exemplary embodiment, the cross section of the rotating portion57C intersecting with the direction along the rotation shaft58has different areas depending on the position of the rotating portion57C in the direction. That is, in this case, a proximal end portion of the rotating portion57C that is an end portion connected to the coupling portion57B is defined as “one end portion”, and an end portion of the rotating portion57C provided with the narrow portion57C2bis defined as “the other end portion”. In this case, as is clear fromFIGS.6to8, the area of a cross section of a portion of the rotating portion57C excluding the other end portion of the rotating portion57C is larger than the area of a cross section of the other end portion of the rotating portion57C. In other words, the area of the cross section of the portion illustrated inFIGS.7and8is larger than the area of the cross section of the portion illustrated inFIG.6. The mechanical strength of the rotating portion57C having such a configuration is higher than that in a case where the area of the cross section of the entire rotating portion57C intersecting with the direction along the rotation shaft58is the same as the area of the cross section of the other end portion. Further, as compared with a case where the area of the cross section of the entire rotating portion57C intersecting with the direction along the rotation shaft58is the same as the area of the cross section of the other end portion, the rotational operation of the rotating portion57C having such a configuration around the rotation shaft58is stabilized.

Further, the rotating portion57C of the image forming apparatus10according to the present exemplary embodiment has a plate-shaped structure. For this reason, the rotational operation of the rotating portion57C of the image forming apparatus10is smooth as compared with a case where the rotating portion is a block body.

Further, the image forming apparatus10according to the present exemplary embodiment includes the coil spring77that applies a force to the interlocking member72in a direction in which the interlocking member72is brought into contact with the rotational member57. Thus, the structure of the image forming apparatus10according to the present exemplary embodiment is simpler than that in a case where the rotational member57and the interlocking member72are coupled via a link member.

Further, the image forming apparatus10according to the present exemplary embodiment includes the coil spring59that applies a force to the rotational member57in a direction in which the contact portion57C3is brought into contact with the side surface52G of the transfer belt52. Thus, the structure of the image forming apparatus10according to the present exemplary embodiment is simpler than that in a case where the contact portion57C3(rotational member57) and the transfer belt52are connected by a relatively displaceable mechanism.

Further, the rotational member57of the image forming apparatus10according to the present exemplary embodiment includes the pressing portion57D that may come into contact with the pressed portion74of the detection unit60. Accordingly, the image forming apparatus10according to the present exemplary embodiment may detect the movement amount of the transfer belt52in the width direction in which the position in the thickness direction TD changes by using the detection unit60including the interlocking member72and the optical sensor67.

The second distance (adjacent distance)30B, which is the distance between the rotation axes30X of the two second photoreceptor drums32(image forming bodies) located on the downstream side of the steering roller45and on the upstream side of the transfer position to recording paper P, is an integral multiple of the outer peripheral length45C of the steering roller45. Thus, as compared with a case where the second distance30B is different from an integral multiple of the outer peripheral length45C, an increase in displacement amount of registration of toner images formed on the transfer belt (formation target body)52by the two second photoreceptor drums32located on the downstream side of the steering roller45is suppressed.

Further, in the image forming apparatus10, the first distance20B between the two first photoreceptor drums22and the second distance30B between the two second photoreceptor drums32each are set to be an integral multiple of the outer peripheral length44C of the driving roller44. Thus, as compared with a case where the first distance20B and the second distance30B are set to lengths different from integral multiples of the outer peripheral length44C, an increase in displacement amount of registration of toner images formed on the transfer belt (formation target body)52by the two second photoreceptor drums32located on the downstream side of the steering roller45is suppressed.

Further, the second distance30B between the two second photoreceptor drums32located on the downstream side of the first photoreceptor drums22is shorter than the first distance20B. In a comparative example (not illustrated) in which the second distance30B is set to be longer than or equal to the first distance20B, the second distance30B is set to meet the first distance20B. Thus, the distance along the transfer belt52from the driving roller44to the second photoreceptor unit30K is shorter in this exemplary embodiment than that in the comparative example. As the distance increases, the cumulative amounts of the speed fluctuation of the transfer belt52and the error of the adjacent distance increase. Thus, in the comparative example, the displacement amount of the registration of the toner images between the second photoreceptor unit30C and the second photoreceptor unit30K is likely to be larger than the displacement amount of the registration of the toner images between the first photoreceptor unit20Y and the first photoreceptor unit20M. In contrast, in the exemplary embodiment, since the distance (second distance30B) between the second photoreceptor unit30C and the second photoreceptor unit30K is shorter than that in the comparative example, the cumulative amounts of the speed fluctuation and the error of the adjacent distance are smaller than those in the comparative example. Thus, in the present exemplary embodiment, as compared with a case where the second distance30B is set to be a length longer than or equal to the first distance20B, an increase in the displacement amount of the registration of the toner images is suppressed as the position of the photoreceptor drum is located on the downstream side of the transfer belt52.

Although the image forming apparatus10and the movement amount detection devices17A and17B according to the present exemplary embodiment have been described above based on the drawings, the image forming apparatus10and the movement amount detection devices17A and17B according to the present exemplary embodiment are not limited to those illustrated in the drawings, and may be appropriately changed in design without departing from the gist of the present disclosure.

For example, the image forming apparatus10may be configured such that each of the first photoreceptor units20and each of the second photoreceptor units30form toner images on recording paper P (formation target body) transported by a transport belt (not illustrated) provided instead of the transfer belt52.

In the present exemplary embodiment, a toner image is described as an example of an image. In this case, the toner image is formed by a dry electrophotographic system, but the present disclosure is not limited to this. For example, an image of the present disclosure may be a toner image formed by a wet electrophotographic system or an image formed by an inkjet system.

Further, the image forming apparatus10may be configured such that an ink image or a toner image is formed on an elongated non-annular continuous paper (formation target body) that is wound around multiple rotating bodies including the driving roller44and that is transported by the driving roller44and the rotating bodies while having a shape having at least one straight portion when viewed in the Z direction, and such that the steering roller (change roller)45is rotatably in contact with the inner peripheral surface of the continuous paper.

When the transfer belt52is located at the reference position52SP, an angle formed by a straight line (not illustrated) connecting the contact portion57C3and the rotation shaft58in plan view and the transport direction A of the transfer belt52may be as small as possible. That is, when this angle is small, the difference between the rotation amount of the rotating portion57C around the rotation shaft58when the transfer belt52moves from the reference position52SP in the width direction by only the unit movement amount and the rotation amount of the rotating portion57C around the rotation shaft58when the transfer belt52moves from the first position52P1or the second position52P2in the width direction by only the unit movement amount becomes small. That is, as the angle is smaller, a sensor (for example, the optical sensor67) that acquires the physical amount may more accurately acquire the physical amount that changes due to the rotation of the rotating portion57C. Thus, for example, the present disclosure may be implemented in an aspect of a modification illustrated inFIG.11. The flat-surface shape of a coupling portion57B of this modification is a V-shape. In the example illustrated inFIG.11, a portion of the coupling portion57B is located directly below the upper portion52A. In the example illustrated inFIG.11, when the transfer belt52is located at the reference position52SP, an angle formed by a straight line connecting the contact portion57C3and the rotation shaft58in plan view and the transport direction A of the transfer belt52is substantially 0°.

One of the movement amount detection device17A and the movement amount detection device17B may be omitted from the image forming apparatus10.

The image forming apparatus10may be provided with another movement amount detection device in addition to the movement amount detection device17A and the movement amount detection device17B.

The number of colors of images (toner images or ink images) formed on a formation target body (transfer belt52or recording paper P) need not be four. For example, the number of colors of images may be six.

For example, three or more image forming bodies may be arranged along the upper portion52A. Similarly, three or more image forming bodies may be arranged along the lower portion52B.