JP2024013928A - Transfer device and image forming device - Google Patents

Abstract

The present invention provides a transfer device and an image forming device that can obtain good transfer performance. [Solution] A control unit serving as a position detection unit calculates an apparent diameter of a secondary transfer pressure roller serving as a transfer roller (S3), and based on the calculated apparent diameter of the secondary transfer roller, The axial center position of the secondary transfer pressure roller is calculated based on the transfer nip (S4). Then, based on the calculated axial center position of the secondary transfer pressure roller, the amount of change in the axial center position of the secondary transfer pressure roller with respect to the initial setting position is calculated (S5), and based on the calculated amount of change, the biasing force is The secondary transfer pressure is adjusted by adjusting the urging force of the pressure spring, which is the urging means, using the transfer pressure adjustment mechanism, which is the adjustment means (S6). [Selection diagram] Figure 7

Description

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

2. Description of the Related Art Conventionally, a transfer device is known that includes a transfer roller that forms a transfer nip with an image carrier, and a biasing member that presses the transfer roller against the image carrier with a biasing force.

Patent Document 1 discloses that, as the transfer device, a secondary transfer roller, which is a transfer roller, is brought into contact with an intermediate transfer belt, which is an image carrier, by the urging force of a pressure spring, which is an urging member, and a secondary transfer is performed, which is a transfer nip. What forms the nip is described. The pressure spring urges the secondary transfer roller toward the intermediate transfer belt via a bearing member that receives the shaft of the secondary transfer roller.

However, due to a change in the diameter of a transfer roller such as a secondary transfer roller, the transfer pressure at a transfer nip such as a secondary transfer nip deviates from a target value, and there is a possibility that good transfer performance may not be obtained.

In order to solve the above problems, the present invention includes a transfer roller that forms a transfer nip with an image carrier, and a biasing member that presses the transfer roller against the image carrier with a biasing force. In the transfer device, a position detection means detects the position of the axial center of the transfer roller in a pressing direction on the image carrier, and a biasing force adjustment adjusts the biasing force based on a detection result of the position detection means. It is characterized by comprising means.

According to the present invention, good transferability can be obtained.

1 is a schematic configuration diagram showing a printer according to an embodiment. FIG. 3 is a schematic configuration diagram showing a K toner image forming unit in the same printer. FIG. 3 is a configuration diagram showing the configuration around the secondary transfer nip of the same printer. FIG. 6 is a diagram illustrating a change in secondary transfer pressure due to a change in diameter of a secondary transfer pressure roller. 7 is a graph showing the relationship between secondary transfer pressure and the axial center position of the secondary transfer pressure roller. FIG. 3 is a control block diagram of secondary transfer pressure adjustment control. FIG. 3 is a control flow diagram of secondary transfer pressure adjustment control. FIG. 7 is a diagram showing a modification of the secondary transfer unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an electrophotographic color printer (hereinafter simply referred to as a printer) will be described below as an image forming apparatus to which the present invention is applied. Note that the field of application of the present invention is not limited to printers, but can also be applied to copying machines, facsimile machines, multifunction devices having a copying function and a FAX function, and the like.

First, the basic configuration of the printer according to the embodiment will be described. FIG. 1 is a schematic configuration diagram showing a printer according to an embodiment. In the figure, the printer according to the embodiment includes four toner image forming units 1Y, 1M, 1C, Equipped with 1K. It also includes an intermediate transfer unit 30, an optical writing unit 80, a fixing device 90, a feeding cassette 100, a pair of registration rollers 101, and the like.

The four toner image forming units 1Y, 1M, 1C, and 1K, which serve as image forming means, use Y, M, C, and K toners of different colors, but otherwise have the same configuration. be exchanged. Taking a toner image forming unit 1K for forming a K toner image as an example, as shown in FIG. It is equipped with a device 6K, a developing device 8K, etc. These devices are held by a common holder and are integrally attached to and detached from the printer main body, so that they can be replaced at the same time.

The photoreceptor 2K has an organic photosensitive layer formed on the surface of a drum-shaped base, and is rotated clockwise in the figure by a driving means. The charging device 6K charges the surface of the photoreceptor 2K with toner by generating electric discharge between the charging roller 7K and the photoreceptor 2K while bringing the charging roller 7K to which a charging bias is applied into contact with or close to the photoreceptor 2K. It is uniformly charged to the same negative polarity as the normal charging polarity. As the charging bias, a voltage obtained by superimposing an alternating current voltage on a direct current voltage is used. The charging roller 7K has a metal core covered with a conductive elastic layer made of a conductive elastic material. Instead of the method of bringing a charging member such as a charging roller into contact with or close to the photoreceptor 2K, a method using a charging charger may be adopted.

The uniformly charged surface of the photoreceptor 2K is optically scanned by a laser beam emitted from an optical writing unit 80, which will be described later, and bears an electrostatic latent image for K. This electrostatic latent image for K is developed into a K toner image by a developing device 8K using K toner. The image is then primarily transferred onto an intermediate transfer belt 31, which will be described later.

The drum cleaning device 3K removes transfer residual toner adhering to the surface of the photoreceptor 2K after passing through the primary transfer process (primary transfer nip described later). It includes a cleaning brush roller 4K that is rotationally driven, a cleaning blade 5K whose free end is brought into contact with the photoreceptor 2K in a cantilevered state, and the like. The rotating cleaning brush roller 4K scrapes off the transferred residual toner from the surface of the photoreceptor 2K, and the cleaning blade scrapes off the transferred residual toner from the surface of the photoreceptor 2K.

The static eliminator removes residual charges from the photoreceptor 2K after being cleaned by the drum cleaning device 3K. By this static elimination, the surface of the photoreceptor 2K is initialized and prepared for the next image formation.

The developing device 8K includes a developing section 12K that accommodates a developing roll 9K serving as a developer carrier, and a developer transport section 13K that stirs and transports the K developer. The developer transport section 13K has a first transport chamber that accommodates the first screw member 10K and a second transport chamber that accommodates the second screw member 11K. Each of these screw members includes a rotary shaft member whose axial ends are rotatably supported by bearings, and a helical blade that protrudes spirally from the circumferential surface of the rotary shaft member.

The first transfer chamber accommodating the first screw member 10K and the second transfer chamber accommodating the second screw member 11K are separated by a partition wall, and both ends of the partition wall in the screw axis direction A communication port is formed in each portion to communicate the two transfer chambers. The first screw member 10K transports the K developer held in the spiral blade from the back side in the direction perpendicular to the plane of the drawing while stirring it in the rotational direction as it is rotated. do. Since the first screw member 10K and the developing roll 9K, which will be described later, are disposed in parallel facing each other, the direction in which the K developer is conveyed at this time is also the direction along the rotational axis of the developing roll 9K. . The first screw member 10K then supplies the K developer to the surface of the developing roll 9K along its axial direction.

After the K developer is transported to the vicinity of the front end of the first screw member 10K in the figure, it enters the second transport chamber through a communication opening provided near the front end of the partition wall in the figure. , is held within the helical blade of the second screw member 11K. Then, as the second screw member 11K is driven to rotate, it is conveyed from the front side to the back side in the figure while being stirred in the rotational direction.

In the second transport chamber, a toner concentration sensor is provided on the lower wall of the casing to detect the K toner concentration of the K developer in the second transport chamber. As the K toner concentration sensor, a magnetic permeability sensor is used. Since the magnetic permeability of the K developer containing the K toner and the magnetic carrier has a correlation with the K toner concentration, the magnetic permeability sensor detects the K toner concentration.

This printer is equipped with Y, M, C, and K toner replenishment means for individually replenishing the Y, M, C, and K toners into the second storage chamber of the Y, M, C, and K developing device. There is. The control unit 50 of the printer stores Vtref for Y, M, C, and K, which is the target value of the output voltage value from the Y, M, C, and K toner concentration detection sensor, in the RAM. If the difference between the output voltage value from the Y, M, C, K toner concentration detection sensor and the Vtref for Y, M, C, K exceeds a predetermined value, Y, M, C, K for a time corresponding to the difference. Drives the M, C, and K toner replenishing means. As a result, the Y, M, C, and K toners are replenished into the second transport chamber of the Y, M, C, and K developing device, and the K toner concentration of the K developer is maintained within a predetermined range.

The developing roll 9K housed in the developing section 12K faces the first screw member 10K and also faces the photoreceptor 2K through an opening provided in the casing. Further, the developing roll 9K includes a cylindrical developing sleeve made of a non-magnetic pipe that is rotationally driven, and a magnet roller fixed inside the sleeve so as not to rotate together with the sleeve. Then, while the K developer supplied from the first screw member 10K is carried on the sleeve surface by the magnetic force generated by the magnet roller, it is conveyed to the development area facing the photoreceptor 2K as the sleeve rotates.

A developing bias having the same polarity as the toner and having a larger absolute value than the potential of the electrostatic latent image on the photoreceptor 2K and a smaller absolute value than the uniformly charged potential of the photoreceptor 2K is applied to the developing sleeve. ing. As a result, a developing potential acts between the developing sleeve and the electrostatic latent image on the photoreceptor 2K, which electrostatically moves the K toner on the developing sleeve toward the electrostatic latent image. Further, a background potential that moves the K toner on the developing sleeve toward the sleeve surface acts between the developing sleeve and the background portion of the photoreceptor 2K. Due to the effects of the development potential and the background potential, the K toner on the developing sleeve is selectively transferred to the electrostatic latent image on the photoreceptor 2K, and the electrostatic latent image is developed into a K toner image.

In FIG. 1, in the toner image forming units 1Y, M, and C for Y, M, and C, Y, M, and C are formed on the photoreceptors 2Y, 2M, and 2C in the same way as the toner image forming unit 1K for K. A toner image is formed. An optical writing unit 80 serving as a latent image writing means is provided above the toner image forming units 1Y, 1M, 1C, and 1K. The optical writing unit 80 optically scans the photoreceptors 2Y, 2M, 2C, and 2K with a laser beam emitted from a laser diode based on image information sent from an external device such as a personal computer. By this optical scanning, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 2Y, 2M, 2C, and 2K.

The optical writing unit 80 irradiates a photoconductor with a laser beam L emitted from a light source through a plurality of optical lenses and mirrors while polarizing the laser beam L in the main scanning direction using a polygon mirror rotationally driven by a polygon motor. . It is also possible to adopt a device that performs optical writing using LED light emitted from a plurality of LEDs in an LED array.

An intermediate transfer unit 30 is provided below the toner image forming units 1Y, 1M, 1C, and 1K as a transfer device that moves an endless intermediate transfer belt 31 in a counterclockwise direction in the figure while stretching it. ing. In addition to the intermediate transfer belt 31 as an image carrier, the intermediate transfer unit 30 includes a drive roller 32, a secondary transfer back roller 33 as a transfer opposing roller, a cleaning backup roller 34, and four primary transfer rollers 35Y, 35M, 35C, and 35K. etc. It also includes a belt cleaning device 37, a concentration sensor, and the like.

The intermediate transfer belt 31, which is an endless belt, is stretched by a drive roller 32, a secondary transfer back roller 33, a cleaning backup roller 34, and four primary transfer rollers 35Y, 35M, 35C, and 35K, which are arranged inside the loop. has been done. The rotation force of the drive roller 32, which is rotationally driven in the counterclockwise direction in the figure by the drive means, causes endless movement in the same direction. In this way, this printer is equipped with the intermediate transfer belt 31 as an endless belt.

The four primary transfer rollers 35Y, 35M, 35C, and 35K sandwich the endlessly movable intermediate transfer belt 31 between the photoreceptors 2Y, 2M, 2C, and 2K. As a result, a primary transfer nip for Y, M, C, and K is formed in which the front surface of the intermediate transfer belt 31 and the photoreceptors 2Y, 2M, 2C, and 2K are in contact with each other. A primary transfer bias is applied to each of the primary transfer rollers 35Y, 35M, 35C, and 35K by a primary transfer power source. By this application, a transfer electric field is formed between the Y, M, C, and K toner images on the photoreceptors 2Y, 2M, 2C, and 2K and the primary transfer rollers 35Y, 35M, 35C, and 35K.

The Y toner formed on the surface of the Y photoreceptor 2Y enters the Y primary transfer nip as the photoreceptor 2Y rotates. Then, the image is primarily transferred from the photoreceptor 2Y onto the intermediate transfer belt 31 by the action of the transfer electric field and nip pressure. The intermediate transfer belt 31 to which the Y toner image has been primarily transferred in this manner then passes through primary transfer nips for M, C, and K sequentially. Then, the M, C, and K toner images on the photoreceptors 2M, 2C, and 2K are primarily transferred onto the Y toner image in order to be superimposed on the image. Through this overlapping primary transfer, a four-color overlapping toner image is formed on the intermediate transfer belt 31. Note that a transfer charger, a transfer brush, or the like may be used instead of the primary transfer rollers 35Y, 35M, 35C, and 35K.

A secondary transfer unit 40 is provided below the intermediate transfer unit 30, which is a belt unit, and includes a secondary transfer pressure roller 42, which is a transfer roller, a secondary transfer belt 41, and the like. The secondary transfer belt 41, which is an endless belt, is rotated clockwise in the figure while being stretched by a plurality of rollers such as a secondary transfer pressing roller 42 disposed inside its loop. The secondary transfer pressure roller 42 is configured to bring the secondary transfer belt 41 into contact with a region around the secondary transfer back roller 33 out of the entire area of the intermediate transfer belt 31 in the circumferential direction. Form a secondary transfer nip.

The secondary transfer pressure roller 42 disposed within the loop of the secondary transfer belt 41 is grounded, whereas the secondary transfer back roller 33 disposed within the loop of the intermediate transfer belt 31 has a A secondary transfer bias is applied by a secondary transfer power source 39 . As a result, there is a secondary transfer between the secondary transfer back roller 33 and the secondary transfer pressure roller 42 that electrostatically moves the toner of negative polarity from the secondary transfer back roller 33 side toward the secondary transfer pressure roller 42 side. A next transfer electric field is formed. Note that instead of the secondary transfer belt 41, the secondary transfer pressure roller 42 may be brought into direct contact with the intermediate transfer belt 31 to form a secondary transfer nip with the intermediate transfer belt 31.

A feeding cassette 100 that accommodates a plurality of recording sheets P in the form of a stack of sheets is disposed below the intermediate transfer unit 30. In this feeding cassette 100, a paper feeding roller 100a is brought into contact with the topmost recording sheet P of a paper stack, and by rotating this at a predetermined timing, the recording sheet P is placed in the feeding path. send it towards.

A pair of registration rollers 101 is disposed near the end of the feeding path. The registration roller pair 101 stops the rotation of both rollers as soon as the recording sheet P sent out from the feeding cassette 100 is sandwiched between the rollers. Then, the rotational drive is restarted at a timing that allows the sandwiched recording sheet P to be synchronized with the four-color superimposed toner image on the intermediate transfer belt 31 within the secondary transfer nip, and the recording sheet P is directed toward the secondary transfer nip. send out.

The four-color superimposed toner image on the intermediate transfer belt 31, which is brought into close contact with the recording sheet P in the secondary transfer nip, is secondary-transferred all at once onto the recording sheet P by the action of the secondary transfer electric field and nip pressure, resulting in full-color toner images. Become a statue. When the recording sheet P on which the full-color toner image is formed on the surface in this manner passes through the secondary transfer nip, it is separated from the intermediate transfer belt 31 by the curvature. Furthermore, the secondary transfer belt 41 is separated from the secondary transfer belt 41 by the curvature of the separation roller 43 around which the secondary transfer belt 41 is wound.

Transfer residual toner that was not transferred to the recording sheet P adheres to the intermediate transfer belt 31 after passing through the secondary transfer nip. This is cleaned from the belt surface by a belt cleaning device 37 that is in contact with the front surface of the intermediate transfer belt 31. A cleaning backup roller 34 disposed inside the loop of the intermediate transfer belt 31 backs up the cleaning of the belt by the belt cleaning device 37 from inside the loop.

The density sensor is arranged outside the loop of the intermediate transfer belt 31. Of the entire area of the intermediate transfer belt 31 in the circumferential direction, the intermediate transfer belt 31 is opposed to a part where it is wrapped around the drive roller 32 with a predetermined gap therebetween. In this state, when the toner image that has been primarily transferred onto the intermediate transfer belt 31 enters a position facing itself, the amount of toner adhesion (image density) per unit area of the toner image is measured.

A fixing device 90 is disposed downstream of the secondary transfer nip in the sheet conveyance direction. This fixing device 90 forms a fixing nip by a fixing roller 91 that includes a heat generating source such as a halogen lamp, and a pressure roller 92 that rotates while contacting the fixing roller 91 with a predetermined pressure.

The recording sheet P fed into the fixing device 90 is held in the fixing nip in such a manner that its unfixed toner image bearing surface is brought into close contact with the fixing roller 91 . Then, the toner in the toner image is softened by the effects of heat and pressure, and a full color image is fixed.

The recording sheet P discharged from the fixing device 90 is discharged outside the machine after passing through a conveyance path after fixing.

When forming a monochrome image, the printer according to the embodiment adjusts the posture of the support plate supporting the primary transfer rollers 35 (Y, M, C) for Y, M, and C in the intermediate transfer unit 30 using a solenoid or the like. It changes by driving. As a result, the primary transfer rollers 35 (Y, M, C) for Y, M, C are moved away from the photoreceptors 2 (Y, M, C), and the front surface of the intermediate transfer belt 31 is moved away from the photoreceptors 2 (Y, M, C). Separate from (Y, M, C). In this way, with the intermediate transfer belt 31 in contact with only the black photoreceptor 2K, one of the four toner image forming units 1 (Y, M, C, K) forms a black toner image. Only the unit 1K is driven to form a K toner image on the black photoreceptor 2K. Note that the present invention is applicable not only to image forming apparatuses that form color images but also to image forming apparatuses that form only monochrome images.

FIG. 3 is a configuration diagram showing the surrounding configuration of the secondary transfer nip. In the figure, the secondary transfer unit 40 includes a secondary transfer belt 41, which is a transfer belt, and four rollers that support the secondary transfer belt 41 inside the belt loop. Specifically, the four rollers are a secondary transfer pressure roller 42, a separation roller 43, a cleaning facing roller 44, and a drive roller 45. The roles of the secondary transfer pressure roller 42 and the separation roller 43 are as already explained.

Further, the secondary transfer unit 40 is provided with a tension roller 46 that presses the secondary transfer belt 41 from the outer peripheral surface. Tension is applied to the transfer belt 41.

Further, the front end of the secondary transfer cleaning blade 47 is in contact with the front surface of the area where the secondary transfer belt 41 is wound around the cleaning opposing roller 44 . This secondary transfer cleaning blade 47 removes toner and other deposits that have adhered to the front surface of the secondary transfer belt 41.

Further, the secondary transfer unit 40 includes a temperature/humidity sensor 83 serving as an environment detection means, and detects the temperature/humidity around the secondary transfer unit 40 . In this embodiment, a transfer pressure adjustment mode, which will be described later, is implemented based on the detection results of the temperature and humidity sensor 83.

Examples of the material for the secondary transfer belt 41 include resin materials such as polyimide (PI), polyamideimide (PAI), and polyvinylidene fluoride (PVDF). The material is not limited to these materials, and an elastic material may also be used.

The secondary transfer pressing roller 42 has a sponge layer 42b made of a sponge material on the surface of a metal shaft 42a serving as a core metal. Similarly to the secondary transfer pressure roller 42, the secondary transfer back roller 33 also has a sponge layer 33b formed on a metal shaft 33a serving as a core metal. By pressing the secondary transfer pressing roller 42 against the intermediate transfer belt 31 by the urging force of the pressing spring 61 serving as the urging member, the sponge layers of the secondary transfer pressing roller 42 and the secondary transfer back roller 33 are crushed, and the second A sufficient nip width of the next transfer nip is ensured.

A frame member 49 of the secondary transfer unit 40 is swingably supported by a support shaft 48 provided in the printer main body. This frame member 49 is biased by a pressure spring 61 as a biasing member. The pressure spring 61 is a compression spring. The biasing force of the pressure spring 61 biases the secondary transfer pressure roller 42 toward the secondary transfer back roller 33 and presses the secondary transfer pressure roller 42 against the intermediate transfer belt 31 . The urging force of the pressure spring 61 applies a secondary transfer pressure to the recording sheet P passing through the secondary transfer nip.

Further, the secondary transfer unit 40 includes a transfer pressure adjustment mechanism 70 as a biasing force adjusting means that adjusts the secondary transfer pressure by adjusting the biasing force of the pressure spring 61. The transfer pressure adjustment mechanism 70 is configured to be movable within a predetermined range in the direction of expansion and contraction of the pressure spring 61, and includes a spring receiver 71 to which one end of the pressure spring 61 is attached, and a spring receiver 71 for moving the spring receiver 71 in the direction of expansion and contraction. cam 72. The transfer pressure adjustment mechanism 70 also includes a cam motor 73 that rotationally drives the cam 72 .

By moving the spring receiver 71 in the expansion/contraction direction by rotation of the cam 72, the amount of expansion/contraction of the pressure spring 61 is changed, and the biasing force of the pressure spring 61 is changed. When increasing the secondary transfer pressure, the cam 72 moves the spring receiver closer to the frame member 49 (upward in the figure). This compresses the pressure spring 61 and increases the biasing force. Thereby, the secondary transfer pressure against the recording sheet P passing through the secondary transfer nip can be increased. On the other hand, when the secondary transfer pressure is to be weakened, the cam 72 moves the spring receiver 71 in a direction away from the frame member 49 (downward in the figure). As a result, the pressure spring 61 is expanded, the biasing force is weakened, and the secondary transfer pressure can be weakened.

In this embodiment, the spring receiver 71 is moved in the direction of expansion and contraction of the pressure spring 61 by the cam 72, but for example, the spring receiver 71 is moved in the direction of expansion and contraction using a known method such as a link mechanism or a rack and pinion mechanism. Just move it.

In this embodiment, various types of recording sheets P are used, such as plain paper, cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and OHP sheet. The optimal secondary transfer pressure differs depending on the type of recording sheet P. Therefore, in this embodiment, the secondary transfer pressure is adjusted by the transfer pressure adjustment mechanism 70 depending on the type of recording sheet. For example, a user operates an operation panel provided on the printer main body to input type information of the recording sheet P set in the feeding cassette 100. The control unit 50 of this printer controls the transfer pressure adjustment mechanism 70 to adjust the biasing force of the pressure spring 61 based on the input type information of the recording sheet P to the type of recording sheet P set in the feeding cassette 100. Adjust so that the secondary transfer pressure corresponds to Thereby, secondary transfer can be performed with an appropriate secondary transfer pressure depending on the type of recording sheet.

Further, the secondary transfer unit 40 includes a first encoder 81 that is a first rotational speed detection means that detects the rotational speed (angular velocity) of the drive roller 45 that rotationally drives the secondary transfer belt 41. Further, the secondary transfer unit 40 includes a second encoder 82 serving as a second rotational speed detection means for detecting the rotational speed (angular velocity) of the secondary transfer pressure roller 42. Normally, based on the detection result of the second encoder 82, that is, the rotational speed of the secondary transfer pressure roller 42, the secondary transfer is performed so that the surface of the secondary transfer belt 41 moves at a constant speed in the secondary transfer nip. A secondary transfer motor 62 that rotationally drives the belt 41 is feedback-controlled.

However, although it is possible to move the surface of the secondary transfer belt 41 at a constant speed in the secondary transfer nip by the feedback control described above, due to the change in the diameter of the secondary transfer pressure roller 42, the secondary transfer belt 41 moves at the target speed (intermediate The moving speed of the transfer belt may deviate from the same speed as that of the transfer belt. Specifically, based on the detection result of the second encoder 82, the secondary transfer pressing roller 42 is controlled to rotate at a target rotational speed (angular speed). Therefore, when the diameter of the secondary transfer pressing roller 42 becomes larger than the initial value, the actual speed (circumferential speed) of the secondary transfer belt 41 at the secondary transfer nip becomes faster than the initial value. On the other hand, when the diameter of the secondary transfer pressing roller 42 becomes smaller than the initial value, the actual speed (circumferential speed) of the secondary transfer belt 41 at the secondary transfer nip becomes slower than the initial value. As a result, the secondary transfer pressure roller 42 deviates from the target speed, and there is a possibility that wrinkles may occur on the recording sheet or image distortion may occur in the secondary transfer nip.

Therefore, in this embodiment, the diameter of the secondary transfer pressure roller 42 is determined based on the detection results of the first encoder 81 and the second encoder 82, and the diameter of the secondary transfer belt is actually determined in the secondary transfer nip. It calculates whether the vehicle is moving at the same speed.

First, based on the detection result of the first encoder 81, the secondary transfer motor 62 is feedback-controlled to rotate the drive roller 45 at a specified rotational speed (angular speed). Then, the second encoder 82 detects the rotational speed (angular velocity) of the secondary transfer pressure roller 42, which is a driven roller, at this time, and calculates the speed ratio between the drive roller 45 and the secondary transfer pressure roller 42. Since this speed ratio is the diameter ratio of the drive roller 45 and the secondary transfer pressure roller 42 which is a driven roller, the secondary transfer pressure The diameter of the roller 42 can be determined. The drive roller 45 is mainly made of metal such as SUS, and its dimensions hardly change due to the environment or use over time. Further, the drive roller 45 is processed with high precision so that there is almost no dimensional variation.

By determining the diameter of the secondary transfer pressure roller 42 in this way, the change in the diameter of the secondary transfer pressure roller 42 can be determined, and based on this diameter change, the feedback control based on the detection result of the second encoder 82 is performed. Correct the target angular velocity. Thereby, the surface of the secondary transfer belt 41 can be moved at a targeted speed in the secondary transfer nip.

Further, due to a change in the diameter of the secondary transfer pressure roller 42, the position of the pressure spring 61 at the axial center of the secondary transfer pressure roller 42 in the biasing direction (vertical direction in the figure) when the intermediate transfer belt 31 is in contact with the intermediate transfer belt 31 changes. . By changing the position of the pressure spring 61 at the center of the axis of the secondary transfer pressure roller 42 in the biasing direction (vertical direction in the figure), the amount of expansion and contraction of the pressure spring 61 changes, and the biasing force of the pressure spring 61 changes. may change, and the secondary transfer pressure may change.

FIG. 4 is a diagram illustrating a change in the secondary transfer pressure due to a change in the diameter of the secondary transfer pressure roller 42. As shown in FIG.
4(a) shows a case where the secondary transfer pressure roller 42 has a standard diameter, and FIG. 4(b) shows a case where the secondary transfer pressure roller 42 has a diameter smaller than the standard diameter. 4(c) shows a case where the secondary transfer pressing roller 42 has a diameter larger than the reference diameter. In FIG. 4, for the sake of simplicity, the pressure spring 61 directly biases the secondary transfer pressure roller 42; The same applies to the configuration shown in FIG. 3 in which the secondary transfer pressure roller 42 is urged by the pressure roller 42.

When the diameter of the secondary transfer pressure roller 42 is smaller than the reference diameter, as shown in FIG. 4(b), when the axial center O1 of the secondary transfer pressure roller 42 is the reference diameter shown in FIG. 4(a). It is on the intermediate transfer belt 31 side compared to . As a result, the pressure spring 61 is expanded compared to when it has the reference diameter. Since the pressure spring 61 is a compression spring, when it expands, the biasing force is reduced compared to when the pressure spring 61 has the reference diameter, and the secondary transfer pressure is reduced.

On the other hand, when the secondary transfer pressure roller 42 has a larger diameter than the reference diameter, as shown in FIG. 4(c), the axial center O1 of the secondary transfer pressure roller 42 It is located on the opposite side to the intermediate transfer belt 31 side compared to the diameter. As a result, the pressure spring 61 is compressed compared to when it has the reference diameter. Since the pressure spring 61 is a compression spring, when it is compressed, the biasing force increases compared to when the pressure spring 61 has the reference diameter, and the secondary transfer pressure increases.

FIG. 5 is a graph showing the relationship between the secondary transfer pressure and the axial center O1 position of the secondary transfer pressure roller 42. As shown in FIG. Note that the origin of the axial center position of the secondary transfer pressing roller 42 in FIG. 5 is the secondary transfer nip.
As shown in FIG. 5, the closer the axial center position of the secondary transfer pressure roller 42 is to the secondary transfer nip, the more the pressure spring 61 expands and the biasing force decreases, and the secondary transfer pressure increases. is decreasing.

Such a change in the axial center position of the secondary transfer press roller 42 is caused by the following reasons, in addition to the change in the diameter of the secondary transfer press roller 42 itself due to the wear of the sponge layer 42b due to use over time, etc. Change. That is, due to changes in the hardness of the sponge layer 42b of the secondary transfer pressure roller due to environmental changes, the amount of deformation of the sponge layer 42b changes, and the axial center position of the secondary transfer pressure roller 42 changes. Specifically, in a low temperature environment, the sponge layer 42b becomes hard, and the amount of deformation of the sponge layer 42b in response to the biasing force of the pressure spring 61 decreases. As a result, the axial center position of the secondary transfer pressing roller 42 is located on the side away from the secondary transfer nip with respect to the initial setting position. As a result, the pressure spring 61 becomes compressed compared to the initial setting position, the biasing force increases, and the secondary transfer pressure increases.

On the other hand, in a high temperature environment, the sponge layer 42b becomes soft and the amount of deformation of the sponge layer 42b in response to the biasing force of the pressure spring 61 increases. As a result, the axial center position of the secondary transfer pressing roller 42 is located on the secondary transfer nip side with respect to the initial setting position. As a result, the pressure spring 61 is expanded compared to the initial setting position, the biasing force is reduced, and the secondary transfer pressure is reduced.

Furthermore, in a high-humidity environment, the sponge layer 42b expands due to water absorption, the diameter of the secondary transfer pressing roller 42 changes depending on the humidity, and the axial center position of the secondary transfer pressing roller 42 also changes depending on the humidity.

In this way, the axial center position of the secondary transfer pressure roller 42 changes and the secondary transfer pressure changes, so that the secondary transfer pressure deviates from the target secondary transfer pressure, and the secondary transfer performance deteriorates. Image quality may deteriorate.

Therefore, the spring constant of the pressure spring 61 is reduced, and the change in the biasing force caused by the expansion and contraction of the pressure spring 61 in accordance with the change in the axial center position of the secondary transfer pressure roller 42 is made gentler, and the change in the secondary transfer pressure is It is conceivable to suppress this and prevent the secondary transfer pressure from deviating from the target secondary transfer pressure. However, in order to accommodate a wide variety of recording sheets P such as plain paper, cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and OHP sheets, the secondary transfer pressure is It is necessary to have a configuration in which the secondary transfer pressure can be switched from the initial setting pressure to a pressure that is four times as high. In a configuration where the spring constant of the pressure spring 61 is small, in order to be able to switch the secondary transfer pressure from the initial setting pressure to a pressure that is four times the initial setting pressure, the length of the pressure spring 61 has to be long, and the transfer pressure has to be increased. The movement range of the spring receiver 71 of the adjustment mechanism 70 also becomes longer. As a result, the device becomes larger.

Therefore, in this embodiment, the secondary transfer pressing roller 42 presses the secondary transfer belt 41 to form a secondary transfer nip with the intermediate transfer belt 31. Understand the center position of the axis. Then, the secondary transfer pressure is adjusted by the transfer pressure adjustment mechanism 70 based on the grasped axial center position of the secondary transfer pressure roller 42. Hereinafter, the characteristic parts of this embodiment will be specifically explained.

FIG. 6 is a control block diagram of secondary transfer pressure adjustment control.
The control unit 50 includes a CPU (Central Processing Unit) as a calculation means, and storage means such as a RAM (Random Access Memory) and a ROM (Read Only Memory). The CPU of the control unit 50 executes various calculations and controls based on a control program stored in the ROM. For example, the control unit 50 uses the rotation information of the drive roller 45 obtained from the output signal from the first encoder 81 and the rotation information of the secondary transfer pressure roller 42 obtained from the output signal from the second encoder 82. Based on this, the diameter of the secondary transfer roller is calculated. Further, the control unit 50 calculates the position of the axial center O1 of the secondary transfer pressing roller 42 from the calculated diameter of the secondary transfer pressing roller 42. That is, in this embodiment, the control section 50 functions as a position detection means. The position of the axial center O1 of the secondary transfer pressure roller 42 calculated by the control unit 50 is stored in a nonvolatile storage unit 51 made of a flash memory or the like. The storage unit 51 stores the initial setting position of the axial center O1 of the secondary transfer pressure roller 42 and the diameter information of the drive roller 45.

The control unit 50 calculates the initial setting position of the axial center O1 of the secondary transfer pressing roller 42 at the time of factory shipment or when replacing the secondary transfer unit. First, with the secondary transfer pressing roller 42 separated from the intermediate transfer belt 31, the diameter of the secondary transfer pressing roller 42 is measured. Specifically, as described above, the speed ratio between the drive roller 45 and the secondary transfer pressing roller 42 is calculated based on the detection result of the first encoder 81 and the detection result of the second encoder 82. Then, the diameter of the secondary transfer pressing roller 42 is calculated from the diameter of the drive roller 45 stored in the storage section 51 and the speed ratio.

Next, based on the calculated diameter of the secondary transfer pressure roller 42, the position of the spring receiver 71 is adjusted by the transfer pressure adjustment mechanism 70 so that the initial setting pressure is achieved. Next, the secondary transfer pressure roller 42 is brought into contact with the intermediate transfer belt 31 via the secondary transfer belt 41, and in the same manner as described above, the secondary transfer pressure roller 42 when pressed against the intermediate transfer belt 31 (hereinafter referred to as the apparent diameter). Then, based on the calculated apparent diameter of the secondary transfer pressing roller 42, the initial setting position of the axial center O1 of the secondary transfer pressing roller 42 based on the secondary transfer nip is calculated, and the calculated initial setting position is It is stored in the storage unit 51.

Further, the control unit 50 controls the cam motor 73 of the transfer pressure adjustment mechanism 70 based on the calculated position of the axis center O1 of the secondary transfer pressure roller 42, adjusts the biasing force of the pressure spring 61, and Adjust the transfer pressure. That is, in this embodiment, the control section 50 and the transfer pressure adjustment mechanism 70 constitute a biasing force adjustment means.

FIG. 7 is a control flow diagram of secondary transfer pressure adjustment control.
The control unit 50 monitors the temperature and humidity around the secondary transfer unit 40 detected by the temperature and humidity sensor 83. If the temperature and humidity around the secondary transfer unit 40 detected by the temperature/humidity sensor 83 has changed by more than a specified value compared to the previous time of adjusting the secondary transfer pressure (Yes in S1), the transfer pressure adjustment mode is set. implement. This is because, as described above, the hardness of the sponge layer 42b of the secondary transfer pressing roller 42 changes depending on the temperature, and when the secondary transfer pressing roller 42 presses the intermediate transfer belt 31 via the secondary transfer belt 41. The amount of deformation of the sponge layer 42b changes. As a result, the apparent diameter of the secondary transfer pressure roller 42 changes, and the axial center O1 position of the secondary transfer pressure roller 42 is different from the previous adjustment. Furthermore, as the secondary transfer pressing roller 42 expands and contracts due to humidity, the diameter of the secondary transfer pressing roller 42 changes, and the axial center position of the secondary transfer pressing roller 42 may be different from the previous adjustment. be. Therefore, if the temperature or humidity around the secondary transfer unit 40 detected by the temperature/humidity sensor 83 has changed by more than a specified value compared to the previous adjustment of the secondary transfer pressure, the axial center of the secondary transfer pressure roller 42 There is a possibility that the position has changed and the secondary transfer pressure has changed. Therefore, the transfer pressure adjustment mode is implemented.

Further, the control unit 50 counts the number of printed sheets, and when the number of printed sheets since the previous secondary transfer pressure adjustment exceeds a predetermined number (No in S1, Yes in S2), the control unit 50 also switches the transfer pressure adjustment mode. implement. This is because the diameter of the secondary transfer pressing roller may be reduced due to wear over time or wear of the sponge layer 42b, and the axial center position of the secondary transfer pressing roller 42 may change. Therefore, even when the number of prints since the previous secondary transfer pressure adjustment exceeds a predetermined number (No in S1, Yes in S2), the transfer pressure adjustment mode is executed.

In the above, the usage status of the secondary transfer pressing roller 42 is determined based on the number of printed sheets, but for example, the usage status of the secondary transfer pressing roller 42 and the drive time of the secondary transfer motor 62 can be used to determine the usage status of the secondary transfer pressing roller 42. The usage status of the next transfer pressing roller 42 may also be grasped.

When the transfer pressure adjustment mode is implemented, first, the apparent diameter of the secondary transfer pressure roller 42 is calculated in the same manner as described above (S3). Specifically, as described above, the secondary transfer motor 62 is feedback-controlled based on the detection result of the first encoder 81, and the drive roller 45 is rotated at a specified rotational speed. Then, the rotation speed of the secondary transfer pressure roller 42 at this time is detected by the second encoder 82, and the speed ratio between the drive roller 45 and the secondary transfer pressure roller 42 is calculated. Next, the apparent diameter (diameter) of the secondary transfer pressing roller 42 is calculated from the diameter of the drive roller 45 stored in the storage section 51 and the speed ratio.

Next, the control unit 50 calculates the position of the axial center O1 of the secondary transfer pressing roller 42 with respect to the secondary transfer nip position based on the calculated apparent diameter of the secondary transfer pressing roller 42 (S4 ). Next, the difference value between the initial setting position stored in the storage unit 51 and the calculated position of the axis center O1 of the secondary transfer pressure roller 42 is calculated, and the amount of change with respect to the initial setting position is determined (S5). Then, based on this amount of change, the transfer pressure adjustment mechanism 70 adjusts the biasing force of the pressure spring to adjust the secondary transfer pressure (S6).

If the position of the shaft center O1 is located closer to the secondary transfer nip than the initial setting position, the biasing force of the pressure spring 61 will be lower than at the initial setting position, and the secondary transfer pressure will decrease. ing. Therefore, in this case, the cam 72 raises the spring receiver 71 by the calculated amount of change, thereby increasing the biasing force of the pressure spring 61. On the other hand, if the position is on the opposite side of the secondary transfer nip from the initial setting position, the biasing force of the pressure spring 61 increases compared to the initial setting position, and the secondary transfer pressure increases. There is. Therefore, in this case, the cam 72 lowers the spring receiver 71 by the calculated amount of change, thereby reducing the biasing force of the pressure spring 61. Thereby, the secondary transfer pressure is adjusted to the target secondary transfer pressure.

Note that the amount of change with respect to the position of the axis center O1 of the secondary transfer pressure roller 42 calculated in the previous transfer pressure adjustment mode is calculated, and if this amount of change is greater than a specified value, the transfer pressure adjustment mechanism 70 adjusts the pressure spring. The urging force of 61 may be adjusted. In this case, the position of the axial center O1 of the secondary transfer pressure roller 42 calculated in the transfer pressure adjustment mode is stored in the storage unit 51. Then, the previous position of the axial center O1 of the secondary transfer pressure roller 42 stored in the storage unit 51 is updated to the position of the axial center O1 of the secondary transfer pressure roller 42 calculated in the current transfer pressure adjustment mode.

In this way, in this embodiment, it is possible to suppress changes in the secondary transfer pressure due to changes in the position of the axial center O1 of the secondary transfer pressure roller 42, maintain good transfer performance over time, and prevent abnormalities. The generation of images can be suppressed.

Further, in this embodiment, the position of the axial center O1 of the secondary transfer pressing roller 42 is grasped from the diameter of the secondary transfer pressing roller 42, but the position of the axial center O1 of the secondary transfer pressing roller 42 is detected. A mechanism may also be provided. For example, a detection mechanism is provided that includes a filler rotatably supported on the shaft of the secondary transfer pressing roller 42, a spring that brings the filler into contact with the intermediate transfer belt 31, and a sensor that detects the rotational position of the filler. Then, the position of the axial center O1 of the secondary transfer pressing roller 42 with respect to the secondary transfer nip may be detected from the rotational position of the filler detected by the sensor of this detection mechanism.

However, by knowing the position of the axial center O1 of the secondary transfer pressing roller 42 from the diameter of the secondary transfer pressing roller 42, it is possible to transfer the secondary The position of the axial center O1 of the transfer pressure roller 42 can be grasped. Thereby, the number of parts can be reduced compared to the case where the above-mentioned detection mechanism is provided, and the cost of the apparatus can be reduced.

Furthermore, as described above, the secondary transfer back roller 33 also has a sponge layer 33b formed on the metal shaft 33a serving as a core metal, similar to the secondary transfer pressure roller 42. Therefore, as with the secondary transfer pressure roller 42, the appearance of the secondary transfer back roller 33 may change due to wear of the sponge layer 33b due to use over time, changes in the hardness of the sponge layer 33b due to the environment, etc. The diameter also varies. By changing the apparent diameter of the secondary transfer back roller 33, the position of the secondary transfer nip changes in the pressing direction of the secondary transfer pressing roller 42. As a result, the position of the axial center O1 of the secondary transfer pressure roller 42 changes due to the change in the apparent diameter of the secondary transfer back roller 33, and the biasing force of the pressure spring 61 changes, causing the secondary transfer pressure to change. There is a risk.

Therefore, it is preferable to adjust the secondary transfer pressure in consideration of the positional fluctuation of the secondary transfer nip due to the change in the diameter of the secondary transfer back roller 33. The diameter of the secondary transfer back roller 33 can be calculated in the same manner as the diameter of the secondary transfer pressure roller 42. That is, the control unit 50 serving as the nip position detection means detects the rotational speed (angular velocity) of the secondary transfer back roller 33 using an encoder serving as the third rotational speed detection means. Further, the rotational speed (angular velocity) of the drive roller 32 (see FIG. 1) is detected by an encoder serving as a fourth rotational speed detection means. Next, the speed ratio between the secondary transfer back roller 33 and the drive roller 32 is determined from the detection results of each encoder. Then, the control unit 50 determines the apparent diameter of the secondary transfer back roller 33 from the diameter of the drive roller 32 stored in advance in the storage unit 51 and the determined speed ratio.

The control unit 50 calculates the position of the secondary transfer nip based on the axial center of the secondary transfer back roller 33 from the diameter of the secondary transfer back roller 33 calculated in this way, and calculates the amount of change from the initial setting position. Calculate. Then, the position of the spring receiver 71 is adjusted by the transfer pressure adjustment mechanism 70 based on the calculated position of the axis center O1 of the secondary transfer pressure roller 42 and the amount of change from the initial setting position of the secondary transfer nip. , adjust the biasing force of the pressure spring 61. Thereby, deviation of the secondary transfer pressure from the target secondary transfer pressure can be further suppressed.

In this way, by determining the secondary transfer nip position from the apparent diameter of the secondary transfer back roller 33, the secondary transfer nip position can be grasped using an encoder for controlling the speed of the intermediate transfer belt 31. Can be done. This makes it possible to reduce the number of parts compared to the case where a mechanism for directly detecting positional fluctuations of the secondary transfer nip is provided.

Further, in the above description, a compression spring is used as the pressure spring 61, but in the configuration shown in FIG. 8, a tension spring may be used as the pressure spring 61. In this case, if the diameter of the secondary transfer pressure roller 42 becomes smaller than the standard, the pressure spring 61 will expand and the biasing force will decrease, and the secondary transfer pressure will decrease as in the case of a compression spring. do. Further, when the diameter of the secondary transfer pressure roller 42 becomes larger than the standard, the pressure spring 61 is compressed and the biasing force increases, and the secondary transfer pressure increases as in the case of the compression spring. .

Furthermore, in the above description, the secondary transfer pressure roller 42 is in contact with the intermediate transfer belt 31 via the secondary transfer belt 41, but the secondary transfer belt 41 is eliminated and the secondary transfer pressure roller 42 is directly connected to the intermediate transfer belt 31 via the secondary transfer belt 41. A configuration in which the transfer belt 31 is brought into contact with the transfer belt 31 may also be used. In this case, a mechanism for directly detecting the position of the axial center of the secondary transfer pressing roller 42 is provided.

What has been described above is just an example, and each of the following aspects has its own unique effects.
(Aspect 1)
A transfer roller such as a secondary transfer pressure roller 42 that forms a transfer nip such as a secondary transfer nip with an image carrier such as the intermediate transfer belt 31, and a pressure that presses the transfer roller against the image carrier by a biasing force. In a transfer device such as a secondary transfer unit 40 equipped with a biasing member such as a spring 61, a position detection means such as a control unit 50 that detects the position of the axial center O1 of the transfer roller in the pressing direction on the image carrier; , biasing force adjusting means such as a transfer pressure adjusting mechanism 70 that adjusts the biasing force based on the detection result of the position detecting means.
The diameter of the transfer roller may change due to changes over time, the environment, etc., and the position of the axial center of the transfer roller in the pressing direction may change. By changing the position of the axial center of the transfer roller in the pressing direction, the amount of expansion and contraction of the urging member changes, and the urging force of the urging member changes. As a result, the transfer pressure in the transfer nip may deviate from the target value, and good transfer performance may not be obtained.
Therefore, in aspect 1, the urging force of the urging member is adjusted by the urging force adjusting means based on the detection result of the position detecting means. Thereby, it is possible to maintain the biasing force of the biasing member constant regardless of a change in the diameter of the transfer roller, and it is possible to suppress the transfer pressure from deviating from a target value. This makes it possible to maintain good transferability.

(Aspect 2)
In aspect 1, the position detection means such as the control unit 50 calculates the diameter of the transfer roller such as the secondary transfer pressure roller 42, and determines the direction of the pressing direction of the axial center O1 of the transfer roller based on the calculated diameter of the transfer roller. Detect location.
According to this, as explained in the embodiment and as explained using FIG. 4, the position of the axial center O1 of the transfer roller in the pressing direction changes depending on the diameter of the transfer roller. By determining , it is possible to grasp the position of the axial center O1 of the transfer roller in the pressing direction. The diameter of the transfer roller such as the secondary transfer pressure roller 42 can be calculated using an encoder provided for controlling the speed of the secondary transfer member such as the secondary transfer belt 41, as described in the embodiment. As a result, the position of the axial center O1 of the transfer roller can be determined without using a mechanism that detects the position of the axial center of the transfer roller, such as a filler or a sensor that detects the filler, thereby reducing the number of parts. This makes it possible to reduce the cost of the device.

(Aspect 3)
In the second aspect, there is provided a transfer belt such as the secondary transfer belt 41 stretched between at least a transfer roller such as the secondary transfer pressure roller 42 and a drive roller 45, and the position detection means such as the control unit 50 45, and a second rotation speed detection means such as a second encoder 82 that detects the rotation speed of the transfer roller. The diameter of the transfer roller is calculated based on the detection result of the detection means and the detection result of the second rotational speed detection means.
According to this, as described in the embodiment, the rotational speed of the drive roller 45 detected by the first rotational speed detection means such as the first encoder 81 and the second rotational speed detection means such as the second encoder 82 are detected. The rotation speed of the transfer roller such as the secondary transfer pressure roller 42 can be determined, and the diameter ratio of the drive roller 45 and the transfer roller can be determined from the speed ratio. The diameter of the drive roller 45 can be determined from the rotation speed of the drive roller 45 detected by the first rotation speed detection means, the rotation speed of the secondary transfer motor 62, and the reduction ratio. Thereby, the diameter of the transfer roller is calculated from the rotational speed of the drive roller 45 detected by the first rotational speed detection means and the rotational speed of the transfer roller detected by the second rotational speed detection means such as the second encoder 82. be able to.

(Aspect 4)
In any one of aspects 1 to 3, the urging force is adjusted based on the detection result of the position detection means by the urging force adjustment means such as the transfer pressure adjustment mechanism 70, based on the usage status of the transfer device.
According to this, as described in the embodiment, the diameter of the transfer roller becomes smaller due to wear of the transfer roller such as the secondary transfer pressure roller 42 due to use over time. Therefore, by adjusting the biasing force of the biasing member such as the pressure spring 61 with the biasing force adjustment means such as the transfer pressure adjustment mechanism 70 based on the usage status of the transfer device such as the secondary transfer unit 40, the biasing force can be adjusted over time. It is possible to prevent the transfer pressure such as the next transfer pressure from deviating from the target transfer pressure.

(Aspect 5)
In any one of aspects 1 to 4, an environment detection means such as a temperature/humidity sensor 83 for detecting at least one of temperature and humidity around the transfer device such as the secondary transfer unit 40 is provided, and the detection result of the temperature/humidity detection means is Based on this, the urging force is adjusted based on the detection result of the position detection means by the urging force adjusting means such as the transfer pressure adjustment mechanism 70.
According to this, as explained in the embodiment, the hardness of the secondary transfer pressing roller 42 changes depending on the ambient temperature, and this hardness change causes the axial center O1 of the transfer roller to change in the pressing direction against the image carrier. The position changes, the urging force of the urging member such as the pressure spring 61 changes, and the transfer pressure such as the secondary transfer pressure changes. Also, the diameter changes due to expansion and contraction depending on the surrounding humidity. Therefore, by adjusting the urging force based on the detection result of the position detection means by the urging force adjustment means based on the detection result of the environment detection means, it is possible to suppress changes in transfer pressure due to changes in the hardness of the transfer roller. can.

(Aspect 6)
In any one of aspects 1 to 5, a nip position detection means such as a control unit 50 that detects a position in the pressing direction of a transfer nip such as a secondary transfer nip is provided, and the urging force adjustment means such as a transfer pressure adjustment mechanism 70 is provided. The urging force is adjusted based on the position of the transfer nip in the pressing direction and the detection result of the position detection means.
According to this, as explained in the embodiment, it is possible to suppress fluctuations in the transfer pressure such as the secondary transfer pressure due to positional fluctuations of the transfer nip such as the secondary transfer nip, and it is possible to further improve the transfer pressure to the target. It is possible to suppress deviation from the transfer pressure.

(Aspect 7)
In aspect 6, the image carrier is an image carrier belt such as the intermediate transfer belt 31 stretched between a plurality of tension rollers, and the nip position detection means such as the control section 50 is configured to detect one of the plurality of tension rollers. The diameter of a transfer opposing roller such as the secondary transfer back roller 33 that faces a transfer roller such as the secondary transfer pressing roller 42 via the image carrier belt is calculated, and based on the calculated diameter of the transfer opposing roller, the secondary transfer roller is The position of a transfer nip such as a transfer nip in the pressing direction is detected.
According to this, as described in the embodiment, by changing the diameter of the transfer opposing roller such as the secondary transfer back roller 33, the position of the transfer nip such as the secondary transfer nip changes. Therefore, the position of a transfer nip such as a secondary transfer nip in the pressing direction can be detected satisfactorily from the diameter of the transfer opposing roller.

(Aspect 8)
In aspect 7, a third rotational speed detection means such as an encoder that detects the rotational speed of the transfer opposing roller such as the secondary transfer back roller 33 and a plurality of tension rollers that tension the image bearing belt such as the intermediate transfer belt 31 are provided. Of these, the nip position detection means such as the control section 50 has a fourth rotation speed detection means such as an encoder that detects the rotation speed of the drive roller 32 that rotationally drives the image bearing belt, and the nip position detection means such as the control section 50 has a third rotation speed detection means. The diameter of the transfer opposing roller is calculated based on the detection result and the detection result of the fourth rotational speed detection means.
According to this, as described in the embodiment, using the third rotational speed detection means and the fourth rotational speed detection means such as an encoder used to control the speed of the image carrier belt such as the intermediate transfer belt, The diameter of the transfer opposing roller can be calculated. This eliminates the need for a mechanism for detecting the diameter of the transfer opposing roller, making it possible to reduce the number of parts and reduce the cost of the apparatus.

(Aspect 9)
In an image forming apparatus including an image carrier such as an intermediate transfer belt 31 and a transfer device such as a secondary transfer unit 40 that transfers an image carried by the image carrier to a transfer target member such as a recording sheet P, the transfer device As such, a transfer device according to any one of Aspects 1 to 8 was used.
According to this, high-quality images can be obtained over time.

1: Toner image forming unit 30: Intermediate transfer unit 31: Intermediate transfer belt 32: Drive roller 33: Secondary transfer back roller 33a: Metal shaft 33b: Sponge layer 39: Secondary transfer power source 40: Secondary transfer unit 41: 2 Next transfer belt 42: Secondary transfer pressure roller 42a: Metal shaft 42b: Sponge layer 43: Separation roller 44: Cleaning opposing roller 45: Drive roller 46: Tension roller 47: Secondary transfer cleaning blade 48: Support shaft 49: Frame member 50: Control unit 51: Storage unit 61: Pressure spring 62: Secondary transfer motor 70: Transfer pressure adjustment mechanism 71: Spring receiver 72: Cam 73: Cam motor 81: First encoder 82: Second encoder 83: Temperature and humidity sensor O1: Axis center of secondary transfer pressure roller P: Recording sheet

Patent No. 3773671

Claims (9)

a transfer roller that forms a transfer nip with the image carrier;
A transfer device comprising: a biasing member that presses the transfer roller against the image carrier with a biasing force,
a position detection means for detecting the position of the axial center of the transfer roller in the pressing direction on the image carrier;
A transfer device comprising: urging force adjusting means for adjusting the urging force based on a detection result of the position detecting means. The transfer device according to claim 1,
The transfer device is characterized in that the position detection means calculates a diameter of the transfer roller, and detects a position of an axial center of the transfer roller in the pressing direction based on the calculated diameter of the transfer roller. The transfer device according to claim 2,
a transfer belt stretched over at least the transfer roller and the drive roller;
The position detection means has a first rotation speed detection means for detecting the rotation speed of the drive roller, and a second rotation speed detection means for detecting the rotation speed of the transfer roller,
A transfer device characterized in that a diameter of the transfer roller is calculated based on a detection result of the first rotational speed detection means and a detection result of the second rotational speed detection means. The transfer device according to claim 1,
A transfer device characterized in that the biasing force is adjusted based on a detection result of the position detecting device by the biasing force adjusting device based on the usage status of the transfer device. The transfer device according to claim 1,
comprising an environment detection means for detecting at least one of temperature and humidity around the transfer device;
A transfer device, wherein the urging force is adjusted by the urging force adjusting means based on the detection result of the position detecting means based on the detection result of the environment detecting means. The transfer device according to claim 1,
comprising a nip position detection means for detecting a position of the transfer nip in the pressing direction,
The transfer device is characterized in that the urging force adjusting means adjusts the urging force based on the position of the transfer nip in the pressing direction and the detection result of the position detecting means. The transfer device according to claim 6,
The image carrier is an image carrier belt stretched over a plurality of tension rollers,
The nip position detection means calculates the diameter of a transfer opposing roller that faces the transfer roller via the image bearing belt among the plurality of tension rollers, and based on the calculated diameter of the transfer opposing roller, A transfer device characterized by detecting a position of a transfer nip in the pressing direction. The transfer device according to claim 7,
third rotational speed detection means for detecting the rotational speed of the transfer opposing roller;
a fourth rotational speed detection means for detecting the rotational speed of a drive roller that rotationally drives the image bearing belt among the plurality of tension rollers that tension the image bearing belt;
The transfer device, wherein the nip position detection means calculates the diameter of the transfer opposing roller based on the detection result of the third rotational speed detection means and the detection result of the fourth rotational speed detection means. . an image carrier;
An image forming apparatus including a transfer device that transfers an image carried by the image carrier to a transfer target member,
An image forming apparatus characterized in that the transfer device according to claim 1 is used as the transfer device.

Images