Patent Description:
<CIT> discloses an image forming apparatus having a belt-shaped image carrier, and a transfer roller in a shape with part of the cylindrical circumferential surface cutoff. In the image forming apparatus, a speed variation of an intermediate transfer belt, which occurs at a second transfer position due to rotation of a second transfer roller, is absorbed by two tension rollers, and an influence on image formation is reduced.

<CIT> discloses an image forming apparatus of the type forming a toner image on a photoconductive drum or similar image carrier, transferring it to a paper or similar transfer medium via an belt, and fixing it on the medium by a fixing device. The peripheral speed of the belt is switched to a comparatively low speed matching a fixing and paper transport speed. At this instant, the belt is moved away from the drum. The length of the transfer medium and the distance between a paper transfer position and a fixing position is compared.

<CIT> discloses an image forming apparatus in which rotation of at least one of a transfer-sheet conveying belt and an intermediate transfer belt is controlled so as to match the phases of fluctuation of the surface speed of the intermediate transfer belt and fluctuation of the surface speed of the transfer-sheet conveying belt.

<CIT> discloses an image forming apparatus including an image bearing belt that bears an image; an image creation unit that transfers the image on the image bearing belt; a first driving source; a driving roller that is rotationally driven by the first driving source and causes the image bearing belt to move.

In an image forming apparatus, a load generated between a transfer belt and a transfer roller may differ between two states: one state in which a recording medium transported to a transfer roller passes through a transfer area where an image is transferred to the recording medium, and the other state in which the recording medium is not passing through the transfer area. In relation to this, an image transferred to the recording medium may be distorted due to the presence or absence of a recording medium in the transfer area.

It is an object of the present disclosure to provide an image forming apparatus that prevents distortion of an image transferred to a recording medium, as compared with when a transfer roller is controlled in drive without considering whether a transfer roller transports a recording medium.

The present invention is provided by appended claim <NUM>. The following disclosure serves a better understanding of the present invention. According to a first aspect of the present disclosure, there is provided , among other aspects, an image forming apparatus including: an annular transfer belt having an outer circumferential surface to which an image is transferred; a drive roller on which the transfer belt is wound to cause the transfer belt to move; a transfer roller that transfers an image to a recording medium when the recording medium passes through a transfer area which is formed between the transfer roller and the transfer belt; a drive mechanism that causes the transfer roller to rotate; and a speed adjustment mechanism that adjusts a rotational speed of the transfer roller achieved by the drive mechanism in units of a cycle of the transfer roller, and switches between a first adjustment pattern and a second adjustment pattern to execute switched adjustment pattern in a cycle including a state in which the transfer roller transports the recording medium, the first adjustment pattern for adjusting the rotational speed of the transfer roller, the second adjustment pattern for adjusting the rotational speed of the transfer roller with a pattern different from the first adjustment pattern.

An image forming apparatus according to a second aspect of the present disclosure is the image forming apparatus according to the first aspect of the present disclosure, further including a holding member that holds the recording medium, and causes the recording medium to pass through the transfer area, the transfer roller includes a recess on a circumferential surface, the recess being configured to store the holding member, and when an average value of the rotational speed of the transfer roller at a time of passage of a portion other than the recess of the transfer roller through the transfer area is lower than a specific value, the speed adjustment mechanism adjusts the rotational speed of the transfer roller to be higher than the average value in units of a cycle when the recess passes through the transfer area, and when the average value of the rotational speed of the transfer roller at a time of passage of the portion other than the recess of the transfer roller through the transfer area is higher than the specific value, the speed adjustment mechanism adjusts the rotational speed of the transfer roller to be lower than the average value in units of a cycle when the recess passes through the transfer area.

An image forming apparatus according to a third aspect of the present disclosure is the image forming apparatus according to the second aspect of the present disclosure, in which the first adjustment pattern and the second adjustment pattern adjust the average value of the rotational speed of the transfer roller in units of a cycle, and the speed adjustment mechanism adjusts the rotational speed of the transfer roller so that the average value of the rotational speed of the transfer roller in one cycle in the first adjustment pattern matches the average value of the rotational speed of the transfer roller in one cycle in the second adjustment pattern.

An image forming apparatus according to a fourth aspect of the present disclosure is the image forming apparatus according to any one of the first to third aspects of the present disclosure, further including a torque detector that detects a torque variation of the drive roller. The rotational speed of the transfer roller in the first adjustment pattern and the second adjustment pattern is set based on a result of detection by the torque detector.

An image forming apparatus according to a fifth aspect of the present disclosure is the image forming apparatus according to any one of the first to third aspects of the present disclosure, further including: a drive source that causes the drive roller to rotate; and a current value detector that detects a current value to be supplied to the drive source. The rotational speed of the transfer roller in the first adjustment pattern and the second adjustment pattern is set based on a result of detection by the current value detector.

An image forming apparatus according to a sixth aspect of the present disclosure is the image forming apparatus according to any one of the first to fifth aspects of the present disclosure, further including a belt speed measurer that measures a movement speed of the transfer belt. The rotational speed of the transfer roller in the first adjustment pattern and the second adjustment pattern is set based on a result of measurement by the belt speed measurer.

An image forming apparatus according to a seventh aspect of the present disclosure is the image forming apparatus according to any one of the first to sixth aspects of the present disclosure, in which the speed adjustment mechanism continuously changes information included in the first adjustment pattern and the second adjustment pattern to be executed based on at least one of a torque variation of the drive roller, a current value to be supplied to a drive source for causing the drive roller to rotate and a movement speed of the transfer belt.

An image forming apparatus according to an eighth aspect of the present disclosure is the image forming apparatus according to any one of the first to seventh aspects of the present disclosure, further including a plurality of storage sections configured to store different recording media. Each of the first and second adjustment patterns includes a plurality of adjustment patterns corresponding to the plurality of storage sections, and the speed adjustment mechanism executes one of the plurality of adjustment patterns as the first and second adjustment pattern, the one corresponding to one of the plurality of storage sections, which stores the recording medium transported to the transfer area.

In the image forming apparatus according to the first aspect of the present disclosure, distortion of an image transferred to the recording medium can be prevented, as compared with when the transfer roller is controlled in drive without considering whether the transfer roller transports the recording medium.

In the image forming apparatus according to the second aspect of the present disclosure, it is possible to reduce the propagation of a torque variation due to change in the speed of the transfer roller to the transfer belt and the drive roller, as compared with the case where the rotational speed of the transfer roller is changed at the timing when the portion other than the recess passes through the transfer area.

In the image forming apparatus according to the third aspect of the present disclosure, the rotational speed of the transfer roller at the time of passage of the recess through transfer area can be utilized to adjust the average value of the rotational speed in one cycle of the transfer roller.

In the image forming apparatus according to the fourth aspect of the present disclosure, each adjustment pattern can be set based on the result of torque detection by the drive roller.

In the image forming apparatus according to the fifth aspect of the present disclosure, each adjustment pattern can be set based on the current value supplied to the drive source that drives the drive roller.

In the image forming apparatus according to the sixth aspect of the present disclosure, each adjustment pattern can be set based on the result of measurement by the belt speed measurer.

In the image forming apparatus according to the seventh aspect of the present disclosure, the information included in the adjustment pattern is continuously changed during the operation of the image forming apparatus.

In the image forming apparatus according to the eighth aspect of the present disclosure, a different control pattern is executed for each of the recording media.

Exemplary embodiment of the present disclosure will be described in detail based on the following figures, wherein:.

Hereinafter, an exemplary embodiment for implementing the present disclosure will be described with reference to the drawings. Note that in the following, the range necessary for description for achieving the object of the present disclosure is schematically shown. The range necessary for description of the relevant part of the present disclosure will be principally described, and part for which description is omitted is implemented by a publicly known technique.

<FIG> is a schematic explanatory diagram illustrating an example of an image forming apparatus according to a first exemplary embodiment of the present disclosure. As illustrated in <FIG>, an image forming apparatus <NUM> according to the exemplary embodiment may be a so-called electrophotographic image forming apparatus that transfers a desired image (toner image) to a recording medium P made of paper, for example. The image forming apparatus <NUM> may include an image former <NUM>, a transport unit <NUM> and a control device <NUM>. <FIG> is a view of the principal component of the image forming apparatus <NUM> as seen from the front, and the following description is given assuming that the width direction is X direction, the depth direction is Y direction, and the height direction is Z direction. In addition, various components included in <FIG> are illustrated with their structure simplified.

The image former <NUM> may be a unit for forming a toner image (an example of an image) on a recording medium P. In order to form a toner image on the recording medium P, the image former <NUM> may have a toner image former <NUM>, and a transfer device <NUM>.

In order to form a toner image for each color on the outer circumferential surface of the later-described intermediate transfer belt <NUM> included in the transfer device <NUM>, multiple toner image formers <NUM> may be provided along the intermediate transfer belt <NUM> in the transport direction (also referred to as the circumferential direction) RD1. In the present exemplary embodiment, as an example, the toner image formers <NUM> for a total of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are successively provided from the upstream side in the transport direction of the intermediate transfer belt <NUM>. Note that (Y), (M), (C), (K) illustrated in <FIG> indicate components corresponding to the above-mentioned colors. In the following description, when yellow (Y), magenta (M), cyan (C), black (K) need to be distinguished, the symbol of each member is suffixed with (Y), (M), (C), or (K), and when the colors do not need to be distinguished, (Y), (M), (C), and (K) may be omitted. Furthermore, the toner image former <NUM> of each color can have a similar configuration except for the type of toner, thus only the configuration of the toner image former <NUM> (Y) representing the toner image former <NUM> of all the colors will described below. In addition, only the components of the toner image former <NUM> (Y) are labeled with a symbol in <FIG>, and symbols for the components of other toner image formers <NUM> are omitted. Incidentally, of the toner image formers <NUM>, the toner image formers <NUM> (Y), <NUM> (M), and the toner image formers <NUM> (C), <NUM> (K) have different relative positions with respect to the intermediate transfer belt <NUM>, thus the layouts of the components are slightly different, but the components are common.

As illustrated in <FIG>, the toner image former <NUM> (Y) may include a photoconductor drum <NUM> which rotates in one direction (the counterclockwise in <FIG>). In addition, a charger <NUM>, an exposure device <NUM>, a developing device <NUM>, and a removal device <NUM> are successively disposed around the photoconductor drum <NUM>.

The following example may be given as an example of a process of first transfer to the intermediate transfer belt <NUM> using the photoconductor drum <NUM>. Specifically, first, the photoconductor drum <NUM> is charged by the charger <NUM>. Subsequently, the photoconductor drum <NUM> charged by the charger <NUM> is exposed to light using the exposure device <NUM> to form an electrostatic latent image on the photoconductor drum <NUM>. When an electrostatic latent image is formed, it is then developed using the developing device <NUM> to form a toner image. The toner image formed on the photoconductor drum <NUM> is transferred (first transferred) to the intermediate transfer belt <NUM> as a yellow image. Finally, the toner remaining on the photoconductor drum <NUM> surface after the transfer to the intermediate transfer belt <NUM> is removed by the removal device <NUM>. The toner image former <NUM> (Y) performs the above-described process at a specific timing, thereby making it possible to transfer the yellow toner image on the intermediate transfer belt <NUM>.

The transfer device <NUM> may be a device for transferring toner images formed by multiple toner image formers <NUM> to the recording medium P. Specifically, the transfer device <NUM> may include an annular intermediate transfer belt (an example of a transfer belt) <NUM>; a drive roller <NUM> on which the intermediate transfer belt <NUM> is wound, and which causes the intermediate transfer belt <NUM> to rotate in a circumferential direction (the clockwise direction in <FIG>) RD1; multiple support rollers <NUM> on which the intermediate transfer belt <NUM> is wound, and which are to support the intermediate transfer belt <NUM> in a profile (posture) along a desired path; a steering roller <NUM> that prevents meandering movement and deviation movement of the intermediate transfer belt <NUM>; one to multiple tension rollers <NUM> that apply tension to the intermediate transfer belt <NUM>; first transfer rollers <NUM> that bring the intermediate transfer belt <NUM> into contact with the photoconductor drum <NUM> of each color to first transfer an image; and a second transfer roller <NUM> that second transfers an image formed on the intermediate transfer belt <NUM> to the recording medium P passing through a transfer area TA of the intermediate transfer belt <NUM>, the transfer area TA being formed between the later-described transfer cylinder <NUM> and the second transfer roller <NUM>. A publicly known configuration may be used as the specific configuration of the above-described several types of rollers. For example, the axial length of each roller may be slightly longer than the width of the intermediate transfer belt <NUM>, and the diameter of the roller may be adjusted as appropriate according to the application. In addition, the above-described several types of rollers may be provided so that their axial directions extend in the depth direction (Y direction) of the image forming apparatus <NUM>. Furthermore, of the above-described multiple rollers, the rollers other than the drive roller <NUM> may each be comprised of a driven roller not connected to a drive source such as a motor.

The intermediate transfer belt <NUM> may be comprised of an annular belt member having an outer circumferential surface to which an image is transferred, and more specifically, comprised of an endless belt. The intermediate transfer belt <NUM> may be disposed so that its width direction extends in the depth direction (Y direction) of the image forming apparatus <NUM>. The intermediate transfer belt <NUM> may be a belt that comes into contact with the photoconductor drum <NUM> of the toner image former <NUM> of each color by the first transfer roller <NUM>, and a toner image is thereby transferred (first transferred) to the belt successively. In addition, the transferred toner image may be transferred (second transferred) to the surface of the recording medium P passing through the transfer area TA which is formed by the intermediate transfer belt <NUM> coming into contact with the later-described transfer cylinder <NUM> by the second transfer roller <NUM>.

The rotational axis of the drive roller <NUM> is connected to a drive roller motor <NUM> (see <FIG>) as an example of a drive source. The drive roller <NUM> receives a driving force from the drive roller motor <NUM> to rotate, thereby causing the intermediate transfer belt <NUM> winding on the drive roller <NUM> to circumferentially rotate in the circumferential direction RD1. The rotational axis of the drive roller <NUM> may be connected to the drive roller motor <NUM> via a well-known reducer. The drive roller <NUM> according to the present exemplary embodiment is disposed to be in contact with the inner circumferential surface of the intermediate transfer belt <NUM> at a position downstream of the transfer area TA in the transport direction of the intermediate transfer belt <NUM> and upstream of the toner image former <NUM> (Y).

The transport unit <NUM> may perform a series of transports for moving the recording medium P to the transfer position of the image to transfer the image onto the recording medium P, and for discharging the recording medium P with the transferred image to the outside of the image forming apparatus <NUM>. The transport unit <NUM> may include a transport path <NUM> along which the recording medium P is transported; a storage section <NUM> that stores one to multiple recording media P before image formation; a second transfer body <NUM> which transfers an image to the recording medium P, a fixing device <NUM> that subsequent to transfer of an image, fixes the image to the recording medium P; and a recording medium detection sensor <NUM> provided at a position adjacent to the storage section <NUM> on the transport path <NUM> to detect the position of the recording medium P by detecting passage of the recording medium P.

The transport path <NUM> starts at the storage section <NUM>, and allows the recording medium P with an image printed to pass through the transfer area TA, then to pass through between a pair of rollers included in the fixing device <NUM>, and to be discharged to an output tray (not illustrated) provided in the image forming apparatus <NUM>. Multiple rollers (not illustrated) for transport may be disposed along the transport path <NUM>. Although only one tray is illustrated as the storage section <NUM> in <FIG>, multiple storage sections <NUM> may be provided. In the image forming apparatus <NUM> provided with multiple storage sections <NUM>, respective recording media P stored in the storage sections <NUM> may differ in the size and material, and the thickness.

<FIG> is an enlarged perspective view illustrating part of the second transfer body of the image forming apparatus according to the first exemplary embodiment of the present disclosure. As illustrated in <FIG> and <FIG>, the second transfer body <NUM> may be disposed between the storage section <NUM> and the fixing device <NUM> on the transport path <NUM> to transport the recording medium P to the transfer area TA, and transfer an image formed on the intermediate transfer belt <NUM> to the surface of the recording medium P. The second transfer body <NUM> may include a transfer cylinder <NUM> as an example of a transfer roller, a pair of sprockets <NUM>, a pair of chains <NUM>, and a gripper <NUM>.

The transfer cylinder <NUM> is an example of a transfer roller that forms the transfer area TA between the intermediate transfer belt <NUM> and itself, and when the recording medium P passes through the transfer area TA, transfers an image formed on the surface of the intermediate transfer belt <NUM> to the surface of the recording medium P. The transfer area TA formed by the transfer cylinder <NUM> refers to the area (the area is also referred to as a nip area) where the recording medium P is interposed between the surface of the intermediate transfer belt <NUM> with the back surface supported by the second transfer roller <NUM>, and the surface of the transfer cylinder <NUM>. The second transfer roller <NUM>, which supports the intermediate transfer belt <NUM> to bring it into contact with the transfer cylinder <NUM>, may be able to change its position in a direction to be closer to or away from the transfer cylinder <NUM>. When the position of the second transfer roller <NUM> is changed, mostly the length of the transfer area TA in the circumferential direction RD1 may change. Note that although the above-described transfer cylinder <NUM> has been illustrated as a transfer roller in the present exemplary embodiment, the transfer roller is not limited to this, and may be a roller that brings the recording medium P into contact with the intermediate transfer belt <NUM> to perform the second transfer. In relation to this, the image forming apparatus of the present disclosure may not have the below-described other specific components, for example, the gripper <NUM> and a recess 50A of the second transfer body <NUM>.

The transfer cylinder <NUM> is fixed to a rotational axis <NUM>. The rotational axis <NUM> may be connected to a transfer cylinder motor <NUM> (see <FIG>) as an example of a drive mechanism, and may receive a driving force from the transfer cylinder motor <NUM>, and rotate, thereby causing the transfer cylinder <NUM> to rotate in one direction (hereinafter also referred to as a "rotational direction") RD2, and to circumferentially rotate the pair of chains <NUM> via the pair of sprockets <NUM>. When the recording medium P is caught by the gripper <NUM>, the recording medium P is transported to the transfer area TA along with the circumferential rotation of the pair of chains <NUM>. The rotational axis <NUM> of the transfer cylinder <NUM> may be connected to the transfer cylinder motor <NUM> via a well-known reducer. Note that although it is illustrated that the transfer cylinder motor <NUM> is connected to the rotational axis <NUM> in the present exemplary embodiment, the connection position of the transfer cylinder motor <NUM> can be changed in a range capable of maintaining its function. Specifically, for example, the transfer cylinder motor <NUM> may be connected to the pair of sprockets <NUM> which are rotated in conjunction with the transfer cylinder <NUM> by the pair of chains <NUM>.

A pair of transfer cylinder-side sprockets <NUM> may be mounted on axial both ends of the transfer cylinder <NUM>. As illustrated in <FIG>, the pair of transfer cylinder-side sprockets <NUM> may be configured to be disposed so as to interpose the transfer cylinder <NUM> therebetween, and rotate along with the transfer cylinder <NUM> by being fixed to the rotational axis <NUM>. The outer diameter of the pair of transfer cylinder-side sprockets <NUM> may be smaller than the outer diameter of the transfer cylinder <NUM>. The pair of chains <NUM> are wound on the pair of transfer cylinder-side sprockets <NUM>, respectively.

The transfer cylinder <NUM> may be comprised of a base material 50B, and a surface layer 50C replaceably wound on the outer circumference of the base material 50B. A metal material such as a stainless steel may be used for the base material 50B, and a resin material, such as polyurethane rubber, ethylene propylene rubber (EPM), silicone gum, fluorine rubber (FKM), epichlorohydrin/butadiene rubber may be used for the surface layer 50C. The length of the circumference of the transfer cylinder <NUM> usable in the exemplary embodiment may be substantially equal to the length of the maximum paper size along the transport direction of the recording medium P usable in the image forming apparatus <NUM>. However, instead of this, the length of the circumference of the transfer cylinder <NUM> may be shorter than or longer than the length of the recording medium P with the maximum paper size along the transport direction. Furthermore, in the outer circumference of the transfer cylinder <NUM>, the recess 50A is formed which can store the gripper <NUM> and extends in the axial direction of the transfer cylinder <NUM>. Although only one recess is formed as the transfer cylinder <NUM> according to the exemplary embodiment, two or more recesses may be formed at intervals.

As with the pair of transfer cylinder-side sprockets <NUM> connected to the transfer cylinder <NUM>, the pair of chains <NUM> are wound on the pair of sprockets <NUM> which may support the pair of chains <NUM> along with the pair of transfer cylinder-side sprockets <NUM> in a particular posture. The pair of sprockets <NUM> are disposed at a position (- X direction relative to the transfer cylinder <NUM> in <FIG>) nearer to the fixing device <NUM> than the transfer cylinder <NUM>. In addition, the pair of sprockets <NUM> may be rotatably supported integrally on the shaft by the apparatus body (not illustrated) of the image forming apparatus <NUM>.

As illustrated in <FIG>, the pair of chains <NUM> are formed to be annular, and may be wound on the pair of sprockets <NUM> and the pair of transfer cylinder-side sprockets <NUM>. As illustrated in <FIG>, the pair of chains <NUM> may be disposed at intervals in the depth direction (Y direction in <FIG> and <FIG>) of the image forming apparatus <NUM>. A configuration is illustrated in which when the transfer cylinder <NUM> receives a power from the transfer cylinder motor <NUM> to rotate in the one direction RD2, the pair of chains <NUM> similarly circumferentially rotate in the one direction (counterclockwise direction in <FIG>). In order to allow the recording medium P to be easily transported by following the surface of the transfer cylinder <NUM>, the winding angle should be at least <NUM> degrees or more. In addition, as illustrated in <FIG>, a mounting member <NUM> on which the gripper <NUM> is mounted is bridged over the pair of chains <NUM> in the depth direction of the image forming apparatus <NUM>. One to multiple pieces of the mounting member <NUM> are fixed to the pair of chains <NUM> at predetermined intervals in the circumferential direction of the chains <NUM>.

<FIG> is a further enlarged perspective view illustrating a gripper portion of the second transfer body illustrated in <FIG>. As illustrated in <FIG> and <FIG>, multiple grippers <NUM> may be mounted on the mounting member <NUM> at predetermined intervals in the depth direction of the image forming apparatus <NUM>. In other words, each gripper <NUM> may be mounted to the chains <NUM> via the mounting member <NUM>. The gripper <NUM> is an example of a holding member that has a function of holding the front edge of the recording medium P in the transport direction. Specifically, as illustrated in <FIG>, each gripper <NUM> has a nail 53A and a nail stand 53B. The gripper <NUM> can hold the recording medium P by pinching the front edge of the recording medium P between the nail 53A and the nail stand 53B. The gripper <NUM> holds the front edge other than an image area of the recording medium P, where the image area is the area to which a toner image is transferred. The gripper <NUM> can hold the recording medium P by a configuration in which, for example, the nail 53A is pressed against the nail stand 53B by a spring or the like, as well as the nail 53A is opened or closed to the nail stand 53B by an operation of a cam or the like.

By the above-described series of configurations, the transport operation is performed in the transport unit <NUM> as follows. Specifically, the recording medium P is first delivered to the transport path <NUM> from the storage section <NUM> by a transport roller or the like (not illustrated). Subsequently, when the recording medium P reaches a part on the transport path <NUM>, where the second transfer body <NUM> is disposed, the front edge of the recording medium P is held by the gripper <NUM>. The gripper <NUM> holding the front edge of the recording medium P is further moved on the transport path <NUM> along with the circumferential rotation of chains <NUM>, then the gripper <NUM> is stored in the recess 50A of the transfer cylinder <NUM>. The gripper <NUM> stored in the recess 50A further transports the recording medium P along with the rotational movement of the transfer cylinder <NUM>, and the recording medium P passes through the transfer area TA while being held by the gripper <NUM>. After passing through the transfer area TA, the recording medium P is transported to the fixing device <NUM>, and transferred toner images are fixed. The recording medium P with the toner images fixed is discharged to an output tray (not illustrated) provided at an appropriate position of the image forming apparatus <NUM>.

The control device <NUM> may function as a controller that controls a series of operations in the image forming apparatus <NUM>. In addition, the control device <NUM> may be comprised of a well-known computer, for example. Here, a well-known computer may include at least a volatile or nonvolatile memory (for example, a random access memory (RAM) and a hard disk drive (HDD)), and a processor represented by a central processing unit (CPU). In relation to this, various types of operations of the control device <NUM> described below can be provided in the form of a program stored in a memory or in the form of a non-transitory computer-readable medium.

<FIG> is a functional block diagram illustrating an example of the control device illustrated in <FIG>. In <FIG>, of various types of functions of the control device <NUM>, only the functions related to speed control of the image former <NUM> and the transport unit <NUM> are shown, and a description of a configuration to implement other functions is omitted. As illustrated in <FIG>, the control device <NUM> may include a first drive controller <NUM> that operates the drive roller motor <NUM>, a second drive controller <NUM> that operates the transfer cylinder motor <NUM>, and a speed adjustment mechanism <NUM> that adjusts the rotational speed of the transfer cylinder motor <NUM>.

The first drive controller <NUM> may be comprised of a driver that outputs a drive signal to the drive roller motor <NUM> based on a received control pulse signal. It is possible to use a motor, for example, an AC servo motor or a stepping motor as the drive roller motor <NUM> that operates based on the drive signal from the first drive controller <NUM>, the motor being capable of measuring the load torque and controlling the speed with high accuracy. After receiving a drive signal from the first drive controller <NUM>, the drive roller motor <NUM> may operate in a speed control mode in which the drive roller <NUM> is rotated at a specific target rotational speed, and may circumferentially rotate the intermediate transfer belt <NUM> in the circumferential direction RD1.

The second drive controller <NUM> may be comprised of a driver that outputs a drive signal to the transfer cylinder motor <NUM> based on a received control pulse signal. It is possible to use a motor, for example, an AC servo motor or a stepping motor as the transfer cylinder motor <NUM> that operates based on the drive signal from the second drive controller <NUM>, the motor being capable of measuring the load torque and controlling the speed with high accuracy. After receiving a drive signal from the second drive controller <NUM>, the transfer cylinder motor <NUM> rotates the rotational axis <NUM> at a specific rotational speed, and rotates the transfer cylinder <NUM> in the rotational direction RD2. The second drive controller <NUM> and the transfer cylinder motor <NUM> are each an example of a drive mechanism.

As described above, in the image forming apparatus <NUM> according to the present exemplary embodiment, the intermediate transfer belt <NUM> is circumferentially moved in the circumferential direction RD1 by rotating the drive roller <NUM> by the drive roller motor <NUM>, and the transfer cylinder <NUM> is rotated by the transfer cylinder motor <NUM>. The circumferentially moving intermediate transfer belt <NUM> and the rotating transfer cylinder <NUM> come into direct or indirect contact with each other at the transfer area TA, thus the speed of the circumferential movement of the intermediate transfer belt <NUM> may be affected by not only the rotational speed of the drive roller <NUM> but also the rotational speed of the transfer cylinder <NUM>. Specifically, for example, when the rotational speed of the drive roller <NUM> is lower than the rotational speed of the transfer cylinder <NUM>, at least part of the torque of the transfer cylinder <NUM> acts to increase the circumferential movement speed (in other words, act as an accelerator) of the intermediate transfer belt <NUM> through the transfer area TA. Conversely, when the rotational speed of the drive roller <NUM> is higher than the rotational speed of the transfer cylinder <NUM>, at least part of the torque of the transfer cylinder <NUM> acts to decrease the circumferential movement speed (in other words, act as a brake) of the intermediate transfer belt <NUM> through the transfer area TA. In this manner, an action due to the load from the transfer cylinder <NUM> triggered by the speed difference between the circumferential speed of the intermediate transfer belt <NUM> and the rotational speed of the transfer cylinder <NUM> may cause a variation in the circumferential speed of the intermediate transfer belt <NUM> and expansion and contraction of the intermediate transfer belt <NUM> itself. Such an unexpected variation in the circumferential speed of or expansion and contraction of the intermediate transfer belt <NUM> may cause banding (streak of lines extending in a direction crossing the transport direction of the intermediate transfer belt <NUM>, and an image density unevenness) and misalignment of color registration (positioning of the image of each color).

In addition, the value of the torque of the drive roller motor <NUM> necessary for the intermediate transfer belt <NUM> to circumferentially move at a specific speed varies with the operational state of the image forming apparatus <NUM>. Specifically, the torque value required for the drive roller motor <NUM> differs between two states: one state in which the recording medium P is passing through the transfer area TA, and the other state in which the recording medium P is not passing through the transfer area TA. It is presumed that this is caused by at least one of variation in amount of bite, variation in frictional force, and an electrostatic adsorption force, the variation in amount of bite being into at least one of the second transfer roller <NUM> and the transfer cylinder <NUM> and associated with the passage of the recording medium P, the variation in frictional force being due to change of the object in contact with the intermediate transfer belt <NUM> at the transfer area TA from the transfer cylinder <NUM> to the recording medium P (or from the recording medium P to the transfer cylinder <NUM>), the electrostatic adsorption force being generated between the second transfer roller <NUM> and the transfer cylinder <NUM> by a transfer bias current applied to the second transfer roller <NUM> to transfer a toner image to the recording medium P.

In the image forming apparatus <NUM> according to the present exemplary embodiment, in consideration of the above-described points, the speed adjustment mechanism <NUM> is used to eliminate the speed difference between the circumferential speed of the intermediate transfer belt <NUM> and the rotational speed of the transfer cylinder <NUM>.

The speed adjustment mechanism <NUM> adjusts the rotational speed of the transfer cylinder <NUM> by selectively using the below-described two different adjustment patterns based on the transport position of the recording medium P. The rotational speed of the transfer cylinder <NUM> adjusted by the speed adjustment mechanism <NUM> can function to eliminate the speed difference between the circumferential speed of the intermediate transfer belt <NUM> and the rotational speed of the transfer cylinder <NUM>. As illustrated in <FIG>, the speed adjustment mechanism <NUM> may include at least medium position predictor <NUM>, a reference position detector <NUM>, an adjustment pattern selector <NUM>, and a control data storage <NUM>.

The medium position predictor <NUM> may predict the position of the recording medium P transported on the transport path <NUM>. The medium position predictor <NUM> is illustrated which predicts the timing when a state in which the transfer cylinder <NUM> transports the recording medium P is assumed by specifically predicting the timing when the transport of the recording medium P by the transfer cylinder <NUM> is started, and the timing when the transport of the recording medium P by the transfer cylinder <NUM> is completed. The medium position predictor <NUM> may be connected to the recording medium detection sensor <NUM>. The medium position predictor <NUM> can predict the position of the recording medium P transported along the transport path <NUM> with high accuracy by taking the following into consideration: the result of detection by the recording medium detection sensor <NUM>, and in addition, the circumferential speed of the pair of chains <NUM> and the details of operational instructions obtained by the control device <NUM>, specifically, execution or non-execution of duplex printing.

The reference position detector <NUM> may identify the cycle of the transfer cylinder <NUM> by detecting a specific position as a reference in the transfer cylinder <NUM>. As the reference position detector <NUM>, for example, a photo sensor (see <FIG>) may be used which detects passage of an actuator mounted on the rotational axis <NUM>, for example. The above-mentioned specific position as a reference is not particularly limited. However, in the present exemplary embodiment, in order to facilitate the understanding, the position immediately before the recess is provisionally defined as the reference position RP (see <FIG>). According to the claimed invention, one cycle of the transfer cylinder <NUM> is defined as the time since the reference position RP passes through the transfer area TA until the reference position RP reaches the transfer area TA again.

The adjustment pattern selector <NUM> may select an adjustment pattern to be used for control of the transfer cylinder <NUM> based on the position of the recording medium P predicted by the medium position predictor <NUM>, more specifically, based on whether the recording medium P is transported at the predicted position by the transfer cylinder <NUM>. The adjustment pattern may be selected in units of the cycle detected by the reference position detector <NUM>. Here, what is meant by that the adjustment pattern is selected and applied "in units of the cycle" is that the adjustment pattern is selected and applied every cycle of the transfer cylinder <NUM>, or every two or more specific cycles. In addition, the adjustment pattern selector <NUM> generates a control pulse signal based on the selected adjustment pattern, and transmits the generated control pulse signal to the second drive controller <NUM>, and may use a system called an electronic cam in general.

The control data storage <NUM> may be comprised of a recording medium capable of storing various data necessary to make rotational speed adjustment of the transfer cylinder <NUM>. The control data storage <NUM> may store at least control data corresponding to the first adjustment pattern and the second adjustment pattern. Here, the "adjustment pattern" refers to control information for rotating the transfer cylinder <NUM>, and is called "cam data" in the electronic cam.

The first adjustment pattern includes control information (hereinafter also referred to as "adjustment pattern data") for adjusting the rotational speed of the transfer cylinder <NUM> in a cycle including at least a state in which the transfer cylinder <NUM> transports the recording medium P. The control information included in the first adjustment pattern may be identified in advance by an experiment or the like. The rotational speed in the first adjustment pattern may be set for rotation at a constant speed value during a particular cycle, or may be set for changing the speed value at a specific timing during a cycle.

The second adjustment pattern is different from the first adjustment pattern, and includes control information for adjusting the rotational speed of the transfer cylinder <NUM>. The second adjustment pattern may be applied to adjustment of the number of rotations in a cycle not including a state in which the transfer cylinder <NUM> transports the recording medium P. Here, the cycle not including a state in which the transfer cylinder <NUM> transports the recording medium P refers to, for example, the following cycles: a cycle corresponding to a timing when only the first transfer operation is performed by the image former <NUM>, and a cycle corresponding to a timing when image quality adjustment is made while allowing the intermediate transfer belt <NUM> to move.

<FIG> and <FIG> are each an operation explanatory diagram of a transfer area portion of the image forming apparatus illustrated in <FIG>. In <FIG> and <FIG>, a portion corresponding to the transfer area TA is illustrated with a large scale. Hereinafter, a technique of speed adjustment by the speed adjustment mechanism <NUM> including the above-described configuration will be illustrated with reference to <FIG> and <FIG>. In the description shown below, the adjustment pattern selector <NUM> is illustrated which can change the adjustment pattern for the rotational speed of the transfer cylinder <NUM> every cycle, in other words, can change the adjustment pattern every time the reference position RP passes through the transfer area TA. As the recording medium P to which an image is transferred, such a recording medium is illustrated whose length in the transport direction is shorter than the length of the circumference of the transfer cylinder <NUM> (see <FIG>).

First, when the power supply for the image forming apparatus <NUM> is turned on, a transfer operation of an image to the recording medium P is started triggered by, for example, an operation performed by an operator on a user interface (for example, a touch panel or a button) of the image forming apparatus <NUM>, or reception of an operational instruction transmitted via a network from a client computer or the like. Then in the image forming apparatus <NUM>, image formation by the toner image former <NUM> of each color is started, and a first transfer operation on an image of each color to the intermediate transfer belt <NUM> is started. The rotational movement of the transfer cylinder <NUM> may begin concurrently with the start of the above-mentioned first transfer operation, or may begin preceding the start (see <FIG>). The rotational movement of the transfer cylinder <NUM> may be performed in such a manner that the adjustment pattern selector <NUM> selects the second adjustment pattern, and transmits a control pulse signal adjusted based on the second adjustment pattern to the second drive controller <NUM>.

Next, when transport of the recording medium P from the storage section <NUM> is started, and passage of the recording medium P is detected by the recording medium detection sensor <NUM>, after elapse of a specific waiting time, the medium position predictor <NUM> selects the first adjustment pattern, and generates a control pulse signal adjusted based on the first adjustment pattern (or proceeds to control using the first cam data). The control pulse signal generated here is transmitted to the second drive controller <NUM> so that adjustment of the rotational speed of the transfer cylinder <NUM> by the first adjustment pattern is started at the timing right before the transfer cylinder <NUM> starts transfer to the recording medium P, for example, the timing when a cycle of the transfer cylinder <NUM> is reached, the cycle including the timing when the transfer cylinder <NUM> starts transport of the recording medium P (see <FIG>).

The recording medium P is transported to the transfer cylinder <NUM> with the rotational speed adjusted by the first adjustment pattern, and passes through the transfer area TA (see <FIG>), thus an image formed on the intermediate transfer belt <NUM> is transferred to the surface of the recording medium P. In the transfer cylinder <NUM>, even after the recording medium P has passed through the transfer area TA, adjustment of the rotational speed by the first adjustment pattern is continued until the reference position RP passes through the transfer area TA again.

In order to identify the adjustment pattern for the rotational speed of the transfer cylinder <NUM> in a cycle after the reference position RP of the transfer cylinder <NUM> reaches the transfer area TA again, the adjustment pattern selector <NUM> selects an adjustment pattern based on whether transport of a new recording medium P has started by the transfer cylinder <NUM>, based on the output of the medium position predictor <NUM>. Specifically, when the subsequent cycle includes a timing to start transport of a new recording medium P, the adjustment pattern selector <NUM> continues the adjustment of the rotational speed based on the first adjustment pattern, and when the subsequent cycle does not include a timing to start transport of a new recording medium P, the adjustment pattern selector <NUM> generates a control pulse signal in order to change to the adjustment of the rotational speed based on the second adjustment pattern (or proceeds to control using the second cam data).

As described above, in a cycle including a state in which the transfer cylinder <NUM> transports the recording medium P, the speed adjustment mechanism <NUM> according to the claimed invention can cause the transfer cylinder <NUM> to move at the rotational speed adjusted based on the first adjustment pattern, and in other cycles, the speed adjustment mechanism <NUM> can cause the transfer cylinder <NUM> to move at the rotational speed adjusted based on the second adjustment pattern. Thus, the adjustment pattern for the rotational speed of the transfer cylinder <NUM> can be changed depending on whether the recording medium P passes through the transfer area without requiring an operation by an operator. Therefore, it is possible to prepare the first adjustment pattern corresponding to an optimal rotational speed of the transfer cylinder <NUM> at the timing when the recording medium P passes through the transfer area TA. Thus, distortion of an image transferred to the recording medium P can be prevented, as compared with when the transfer cylinder <NUM> is controlled in drive without considering whether the transfer cylinder <NUM> transports the recording medium P.

As an option, in addition to the above-described components, the speed adjustment mechanism <NUM> may include a torque detector <NUM> that detects the torque of the drive roller <NUM>, in other words, the torque of the drive roller motor <NUM>. The torque detector <NUM> may detect the torque value of the drive roller motor <NUM> directly from the drive roller motor <NUM> or via a servo amplifier (not illustrated) provided separately from the drive roller motor <NUM>. The torque value detected by the torque detector <NUM> may be used to generate the above-described first and second adjustment pattern data.

In the present exemplary embodiment, the drive roller motor <NUM> operates in the speed control mode in which the drive roller <NUM> is rotated at a specific target rotational speed. Thus, a strong correlation is observed between the current value supplied to the drive roller motor <NUM> and the torque value of the drive roller motor <NUM>. As another option, in addition to the above-described components, the speed adjustment mechanism <NUM> may use a current value detector (not illustrated) that detects the current value supplied to the drive roller motor <NUM>. As with the torque value detected by the above-described torque detector <NUM>, the current value detected by the current value detector can also be used to generate the above-described first and second adjustment pattern data. The current value detector may be used instead of the torque detector <NUM> or in addition to the torque detector <NUM>.

As another option, in addition to the above-described components, the speed adjustment mechanism <NUM> may further include a belt speed measurer <NUM> that can measure the circumferential speed of the intermediate transfer belt <NUM>. The belt speed measurer <NUM> may be connected to a speed sensor <NUM> provided in a support roller 33A (see <FIG>) disposed downstream in the circumferential direction RD1 of the intermediate transfer belt <NUM> with respect to the position where one of multiple rollers <NUM> that support the intermediate transfer belt <NUM> is disposed, specifically, the toner image former <NUM> (K) for black (K) is disposed, for example. Note that the mounting position of the speed sensor <NUM> is not limited to this, and may be another position as long as the position allows the speed of the intermediate transfer belt <NUM> to be measured. As with the torque value detected by the above-described torque detector <NUM> and the current value detected by the current value detector, the circumferential speed of the intermediate transfer belt <NUM> measured by the belt speed measurer <NUM> can also be used to generate the above-described first and second adjustment pattern data.

In the above-described first exemplary embodiment, the control information included in the first and second adjustment patterns has been illustrated which is formed of any predetermined values; however, the present disclosure is not limited to this. Specifically, the control information included in each adjustment pattern may be continuously changed to an appropriate value by using, for example, at least one of the torque detector <NUM>, the current value detector and the belt speed measurer <NUM> described above, and utilizing these detection results and measurement result (specifically, at least of the torque variation of the drive roller <NUM>, the current value supplied to the drive roller motor <NUM> and movement speed of the intermediate transfer belt <NUM>). In other words, the control information including various types of parameters included in each adjustment pattern may be capable of being updated to appropriate information during the operation of the image forming apparatus <NUM>. Thus, an optimal adjustment result may be obtained continuously by applying each adjustment pattern. In addition, it is also possible to cope with a difference in the optimal adjustment pattern caused by a difference in the individual difference of the surface layer 50C of the transfer cylinder <NUM>, in the operation environment of the image forming apparatus <NUM>, and in the type of the recording medium P used, for example. Furthermore, it is also possible to reduce the frequency of maintenance for change (fine adjustment) of the control information included in the adjustment pattern.

In the above-described exemplary embodiment, the speed adjustment mechanism <NUM> changes the rotational speed of the transfer cylinder <NUM> by switching between two different adjustment patterns, and executing one of them. When the rotational speed of the transfer cylinder <NUM> is changed, even if the amount of change is very small (for example, around <NUM>%), the change can have an effect (as an accelerator or a brake) on the circumferential speed of the intermediate transfer belt <NUM> or the rotational speed of the drive roller <NUM>. Thus, in the first and second adjustment patterns selected by the speed adjustment mechanism <NUM> according to the present exemplary embodiment, the timing to change the rotational speed may be set to the moment when the recess 50A passes through the transfer area TA. At the timing when the recess 50A passes through the transfer area TA, the transfer cylinder <NUM> and the intermediate transfer belt <NUM> are in a non-contact state, thus it is possible to prevent an effect on the speed of intermediate transfer belt <NUM>.

In the above-described exemplary embodiment, the rotational speed of the transfer cylinder <NUM> is adjusted to reduce the speed difference between the circumferential speed of the intermediate transfer belt <NUM> and the rotational speed of the transfer cylinder <NUM>. Specifically, the rotational speed is changed by switching between and executing one of the two different adjustment patterns in units of the cycle. When the rotational speed is changed in units of the cycle, the timing when the recess 50A passes through the transfer area TA, in other words, the timing when the transported recording medium P starts to pass through the transfer area TA is not constant. In order to reduce such a deviation in the timing, when the torque value of the drive roller motor <NUM> at the time of passage of the portion other than the recess 50A of the transfer cylinder <NUM> through the transfer area TA is higher than the torque value at the time of passage of the recess 50A through the transfer area TA, the torque is decreased by increasing the speed of the transfer cylinder <NUM> when passing through the transfer area TA, thus the speed adjustment mechanism <NUM> may adjust the rotational speed of the transfer cylinder <NUM> at the time of passage of the recess 50A through the transfer area TA to be relatively lower. When the torque value of the drive roller motor <NUM> at the time of passage of the portion other than the recess 50A of the transfer cylinder <NUM> through the transfer area TA is lower than the torque value at the time of passage of the recess 50A through the transfer area TA, the torque is increased by decreasing the speed of the transfer cylinder <NUM> when passing through the transfer area TA, thus the speed adjustment mechanism <NUM> may adjust the rotational speed of the transfer cylinder <NUM> at the time of passage of the recess 50A through the transfer area TA to be relatively higher.

In addition, in the image forming apparatus <NUM>, the timing of formation of images on the intermediate transfer belt <NUM>, in other words, the interval (pitch) between images formed on the intermediate transfer belt <NUM> is adjusted to correspond to the timing when the recording medium P passes through the transfer area TA. Thus, when the timing when the recording medium P passes through the transfer area TA is not constant, the operation timing of the toner image former <NUM> of each color needs to be adjusted to correspond to the timing when the current recording medium P passes through the transfer area TA. Thus, in the speed adjustment mechanism <NUM> according to the present exemplary embodiment, in consideration of the above-described points, even when either one of the first and second adjustment patterns is applied, it is desirable to achieve a matched average value of the rotational speed in each cycle of the transfer cylinder <NUM>.

<FIG> are each an example of a result of adjustment made by the speed adjustment mechanism in the image forming apparatus illustrated in <FIG>, <FIG> is a graph illustrating a variation in the torque value of the drive roller before adjustment is made by the speed adjustment mechanism, <FIG> is a graph illustrating a variation in the amount of speed adjustment to the transfer cylinder for which adjustment is made by the speed adjustment mechanism, and <FIG> is a graph illustrating a variation in the torque value of the drive roller after adjustment is made by the speed adjustment mechanism. In <FIG>, the horizontal axis indicates time, and the vertical axis indicates variation in the torque value of the drive roller motor <NUM>. In contrast, in <FIG>, the horizontal axis indicates time, and the vertical axis indicates amount of adjustment to the rotational speed of the transfer cylinder <NUM>. In addition, <FIG> illustrate variation in the rotational speed in two cycles in which change is made from the state in which the second adjustment pattern is applied to the state in which the first adjustment pattern is applied. Here, an adjustment value for the rotational speed of the transfer cylinder <NUM> is set to achieve a specific value of the average speed of the transfer cylinder by measurement in advance so that the torque average value of the drive roller motor <NUM> when the recess 50A passes through the transfer area TA is substantially equal to the torque average value of the drive roller motor <NUM> when the portion other than the recess 50A passes through the transfer area TA. It is assumed that the torque value of the drive roller motor <NUM> when the rotational speed of the transfer cylinder is not adjusted is as illustrated in <FIG>. The speed adjustment mechanism <NUM> adjusts the rotational speed of the transfer cylinder <NUM>, thereby setting an adjustment value for the rotational speed of the transfer cylinder <NUM> to achieve the values as illustrated in <FIG> in which the torque variation of the drive roller motor <NUM> in units of the cycle is approximately uniform. In this case, for example, the torque variation of the drive roller motor <NUM> in units of the cycle should be adjusted using the speed adjustment value as illustrated in <FIG>. In <FIG>, the vertical axis indicates torque value; however, the circumferential speed of the intermediate transfer belt <NUM> may be used instead of the torque value. In other words, the rotational speed of the transfer cylinder <NUM> may be adjusted by the speed adjustment mechanism <NUM> so that the circumferential speed of the intermediate transfer belt <NUM> in units of the cycle is substantially uniform.

In order to achieve the above-mentioned matched average value of the rotational speed in one cycle of the transfer cylinder <NUM>, it is determined whether the average value of the speed at the time of passage of the portion other than the recess 50A of the transfer cylinder <NUM> through the transfer area TA matches a predetermined specific value. When the average value of the speed at the time of passage of the portion other than the recess 50A of the transfer cylinder <NUM> through the transfer area TA is lower than the specific value, the speed at the time of passage of the recess 50A through the transfer area TA is increased, and the control information for an applied adjustment pattern is set so that the average speed value in the one cycle matches the specific value. Conversely, when the average value of the speed at the time of passage of the portion other than the recess 50A of the transfer cylinder <NUM> through the transfer area TA is higher than the specific value, the speed at the time of passage of the recess 50A through the transfer area TA is decreased (see, for example, the variation in the speed adjustment value in one cycle to which the second adjustment pattern is applied in <FIG>), and the control information for an applied adjustment pattern is set so that the average speed value in the one cycle matches the specific value. When the average value of the rotational speed in one cycle of the transfer cylinder <NUM> matches the specific value, the control information for an applied adjustment pattern may be set so that the speed at the time of passage of the recess 50A through the transfer area TA matches the speed at the time of passage of the portion other than the recess 50A through the transfer area TA (see, for example, the speed change in one cycle to which the first adjustment pattern is applied in <FIG>). When the timing of change in the rotational speed of the transfer cylinder <NUM> is the time of passage of the recess 50A through the transfer area TA as illustrated in <FIG>, the speed change of the transfer cylinder <NUM> does not affect the intermediate transfer belt <NUM>.

As described above, when the average value of the rotational speed of the transfer cylinder <NUM> with the first and second adjustment patterns applied is matched with the specific value by changing the speed at the time of passage of the recess 50A through the transfer area TA, the interval between images formed on the intermediate transfer belt <NUM> can be made constant. Consequently, it is not necessary to successively check the timing when the recording medium P passes through the transfer area TA. When an image is formed on the intermediate transfer belt <NUM>, various types of image quality adjustment are easily applied.

<FIG> are each another example of a result of adjustment made by the speed adjustment mechanism in the image forming apparatus illustrated in <FIG>, <FIG> is a graph illustrating a variation in the amount of speed adjustment to the transfer cylinder for which adjustment is made by the speed adjustment mechanism, and <FIG> is a graph illustrating a variation in the torque value of the drive roller after adjustment is made by the speed adjustment mechanism. In <FIG>, the vertical axis and the horizontal axis correspond to those in <FIG> described above. An example has been illustrated in which the rotational speed when the portion other than the recess 50A passes through the transfer area TA is made constant by the control of the rotational speed illustrated in <FIG>; however, the present disclosure is not limited to this. Specifically, as illustrated in <FIG>, the rotational speed at the time of passage of the portion other than the recess 50A through the transfer area TA may be continuously varied. However, even when the rotational speed at the time of passage of the portion other than the recess 50A through the transfer area TA is continuously varied, as with the average speed value in other cycles, the average value of the rotational speed of the transfer cylinder <NUM> in one cycle is controlled to match a specific value. As a specific method, as illustrated in <FIG>, the rotational speed at the time of passage of the recess 50A of the transfer cylinder <NUM> through the transfer area TA may be adjusted so that the total of the areas A1 and A2 surrounded by the line indicating variation in the rotational speed at the time of passage of the portion other than the recess 50A of the transfer cylinder <NUM> through the transfer area TA, and the line indicating the zero value of the speed adjustment amount is equal to the total of the areas Bl and B2 surrounded by the line indicating variation in the rotational speed at the time of passage of the recess 50A of the transfer cylinder <NUM> through the transfer area TA, and the line indicating the zero value of the speed adjustment amount. Thus, even when the rotational speed at the time of passage of the portion other than the recess 50A through the transfer area TA is not constant, the interval between images formed on the intermediate transfer belt <NUM> can be made constant.

Claim 1:
An image forming apparatus (<NUM>) comprising:
an annular transfer belt (<NUM>) having an outer circumferential surface to which an image is transferred;
a drive roller (<NUM>) on which the transfer belt (<NUM>) is wound to cause the transfer belt (<NUM>) to move;
a transfer roller (<NUM>) that transfers an image to a recording medium when the recording medium passes through a transfer area (TA) which is formed between the transfer roller (<NUM>) and the transfer belt (<NUM>);
a drive mechanism (<NUM>) that causes the transfer roller (<NUM>) to rotate; characterised by
a speed adjustment mechanism (<NUM>) that adjusts a rotational speed of the transfer roller (<NUM>) in units of a cycle of the transfer roller (<NUM>), wherein the cycle refers to a time since a reference position (RP) passes through the transfer area (TA) until the reference position (RP) reaches the transfer area (TA) again, and switchably executes one of a first adjustment pattern and a second adjustment pattern in a cycle including a state in which the transfer roller (<NUM>) transports the recording medium, the rotational speed being achieved by the drive mechanism (<NUM>), the first adjustment pattern for adjusting the rotational speed of the transfer roller (<NUM>), the second adjustment pattern for adjusting the rotational speed of the transfer roller (<NUM>) by a pattern different from the first adjustment pattern, wherein
the first or second adjustment pattern for the rotational speed of the transfer roller (<NUM>) are changed depending on whether the recording medium passes through the transfer area (TA).