JP2023083715A - Image forming apparatus - Google Patents

Abstract

To perform printing with stable image magnification through the period of use of an image forming apparatus.SOLUTION: An image forming apparatus comprises: an intermediate transfer belt 8 to which a toner image formed on a photoconductor drum 1 of an image forming unit S is transferred; a secondary transfer roller 15 that forms a secondary transfer nip part N2 and transfers the toner image on the intermediate transfer belt 8 to a transfer material P; a registration roller 14 that is arranged upstream of the secondary transfer roller 15 in a transfer material conveyance direction and conveys the transfer material P to the secondary transfer nip part N2; an intermediate transfer motor M1 that drives a drive roller 9 rotating the intermediate transfer belt 8; a feeding motor M2 that drives the registration roller 14; and a control unit 70 that controls the rotation speed of the intermediate transfer motor M1 and the feeding motor M2. The control unit 70 adjusts the rotation speed of the feeding motor M2 based on the frictional force between the intermediate transfer belt 8 and the transfer material P at the secondary transfer nip part N2 and the relationship between the frictional force and the image magnification of an image transferred to the transfer material P at the secondary transfer nip part N2.SELECTED DRAWING: Figure 1

Description

The present invention relates to image forming apparatuses such as laser printers, copiers, and facsimiles.

2. Description of the Related Art Conventionally, as an image forming apparatus using an electrophotographic method, there is an intermediate transfer type image forming apparatus using an intermediate transfer member. In an intermediate transfer type image forming apparatus, a toner image formed on a photoreceptor is transferred to an intermediate transfer body, and then the toner image on the intermediate transfer body is transferred onto a transfer material. An intermediate transfer belt formed of an endless belt is widely used as the intermediate transfer member.

At the secondary transfer portion where the toner image on the intermediate transfer member is transferred to the transfer member, the transfer material is nipped and conveyed between the intermediate transfer member and the secondary transfer roller. As one of such mechanisms, the secondary transfer roller is driven by a gear, and the transfer material obtains a conveying force from the frictional force between the intermediate transfer member and the secondary transfer roller (hereinafter referred to as a "secondary transfer drive configuration"). )It has been known. On the other hand, from the viewpoint of cost reduction, for example, Japanese Patent Application Laid-Open No. 2002-200002 proposes a configuration in which the secondary transfer roller is driven by the rotation of the intermediate transfer body through the transfer material (hereinafter referred to as "secondary transfer driven configuration"). . Further, a registration roller (hereinafter referred to as a registration roller) that performs registration of the transfer material is arranged upstream of the secondary transfer portion in the direction in which the transfer material is conveyed. For example, in Patent Document 2, the transfer material is loosened between the registration roller and the secondary transfer portion, and the conveying speed of the transfer material is set by the registration roller so that the transfer material conforms to the intermediate transfer body. A configuration for suppressing image defects that occur in the transfer section is disclosed.

In the secondary transfer driven configuration described above, the transfer material does not receive a conveying force from the secondary transfer roller, so the conveying force received by the transfer material at the secondary transfer portion depends on the frictional force between the intermediate transfer member and the transfer material. become. Therefore, the surface properties of the transfer material and the presence or absence of the toner image also affect the conveying force. If sufficient transfer material conveying force cannot be obtained from the secondary transfer portion alone, the rigidity of the transfer material is used to assist the transfer material conveying force at the secondary transfer portion with the conveying force of the registration roller. There is also disclosed a technique for keeping the conveying speed of the transfer material constant in the next transfer portion.

JP 2016-194593 A JP 2006-267656 A

Recently, image forming apparatuses are required to have a longer life. Therefore, as the image forming apparatus is used for a longer period of time, the surface condition of the intermediate transfer member changes more, and the conveying force for conveying the transfer material also changes more. As a result, it becomes difficult to maintain a constant conveying speed of the secondary transfer unit throughout the period of use of the image forming apparatus, and the elongation of the image formed on the transfer material (image magnification) may change. A problem arises.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to perform printing with a stable image magnification throughout the period of use of an image forming apparatus.

In order to solve the above problems, the present invention has the following configuration.

(1) a plurality of image forming units having photosensitive drums for forming toner images on the photosensitive drums; an intermediate transfer belt onto which the toner images formed on the photosensitive drums of the image forming units are transferred; a transfer material disposed opposite to a roller around which the intermediate transfer belt is stretched through the transfer belt, forming a nip portion with the roller, and conveying the toner image on the intermediate transfer belt to the nip portion; a transfer roller that transfers the transfer material to the transfer roller, a transport roller that is arranged upstream of the transfer roller in the transport direction of the transfer material and transports the transfer material to the nip portion, and a roller that is opposed to the transfer roller and is different from the roller. A first motor for driving a drive roller that rotates the intermediate transfer belt, a second motor for driving the conveying roller, and a controller for controlling rotational speeds of the first motor and the second motor. and the control means controls the friction force between the intermediate transfer belt and the transfer material at the nip portion corresponding to the number of transfer materials conveyed to the nip portion, and the friction force at the nip portion. and an image magnification of the image transferred from the intermediate transfer belt to the transfer material, and adjusting the rotational speed of the second motor.

According to the present invention, it is possible to perform printing with a stable image magnification throughout the period of use of the image forming apparatus.

Schematic cross-sectional view showing a schematic configuration of an image forming apparatus of Examples 1 and 2. Schematic diagram for explaining the dynamic friction coefficient measuring device of Example 1 A diagram showing the relationship between the number of sheets passed and the coefficient of dynamic friction in Example 1. 4 is a diagram showing the relationship between the coefficient of dynamic friction and the image magnification in Example 1. FIG. A diagram showing the relationship between the number of sheets passed, the speed setting of each motor, and the peripheral speed of the registration roller in the first embodiment. FIG. 5 is a diagram for explaining the effects of control in the first embodiment; A diagram showing the relationship between the number of sheets passed, the speed setting of each motor, and the peripheral speed of the registration roller in the second embodiment. FIG. 10 is a flow chart showing a control sequence for motor speed setting according to the second embodiment; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described in detail with reference to the drawings.

<Image forming apparatus>
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus 100 of Example 1. As shown in FIG. The image forming apparatus 100 of the present embodiment employs an intermediate transfer method in which image forming units corresponding to a plurality of toner colors are arranged along an intermediate transfer belt, and are capable of forming a full-color image using an electrophotographic method. It is a tandem type laser beam printer. Note that FIG. 1 omits a paper feeding device for feeding a transfer material on which the image forming section forms an image.

The image forming apparatus 100 has four image forming units S, SY, SM, SC, and SK, arranged in a row. The image forming units SY, SM, SC, and SK respectively form yellow (Y), magenta (M), cyan (C), and black (K) images. In this embodiment, the image forming units SY, SM, SC, and SK have the same configuration and image forming operation, except that they use different colors of toner. Therefore, hereinafter, Y, M, C, and K indicating the toner color at the end of the reference numerals will be omitted except when indicating an image forming unit using a specific toner color.

The image forming section S has a drum-shaped (cylindrical) photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotationally driven in an arrow direction (clockwise direction) indicated by R1 in the figure. Around the photosensitive drum 1, the following devices are arranged in order along the direction of rotation. First, a charging roller 2, which is a roller-shaped charging member, is arranged, followed by an exposure device 3, which is exposure means, and a developing device 4, which is developing means. A drum cleaning device 6 is arranged as a means for cleaning toner remaining on the photosensitive drum 1 without being transferred onto the intermediate transfer belt 8 to be described later. A primary transfer roller 5 , which is primary transfer means for transferring the toner image on the photosensitive drum 1 to the intermediate transfer belt 8 , is arranged at a position facing the photosensitive drum 1 .

The developing device 4 contains a non-magnetic one-component toner as a developer, and has a developing sleeve 41 as a developer carrying member, a developer applying blade 42 as developer regulating means, and the like. In each image forming section S, the photosensitive drum 1, the charging roller 2, the developing device 4, and the drum cleaning device 6, which are process means, are integrated to form a process cartridge 7 that can be attached to and detached from the image forming apparatus 100. . The exposure device 3 is composed of a scanner unit that deflects a laser beam with a polygonal mirror and irradiates and scans the surface of the photosensitive drum 1, and irradiates the photosensitive drum 1 with a laser beam modulated based on an image signal. be done.

Further, an intermediate transfer belt 8, which is an intermediate transfer member constituted by a movable endless belt, is arranged so as to come into contact with the photosensitive drum 1 of each image forming section S. As shown in FIG. The intermediate transfer belt 8 is stretched with a predetermined tension by three rollers, a drive roller 9 , a tension roller 10 and a secondary transfer counter roller 11 . The drive roller 9 is connected to an intermediate transfer motor M1, which is a first motor, and when the intermediate transfer motor M1 is driven by an instruction from a control unit 70 that controls the image forming apparatus 100, the drive roller 9 rotates. driven. When the drive roller 9 is rotationally driven, the intermediate transfer belt 8 moves (rotates) in the arrow direction indicated by R2 in the figure (belt conveying direction).

The primary transfer roller 5 urges the photosensitive drum 1 with a predetermined pressure via the intermediate transfer belt 8, forming a primary transfer portion N1, which is a nip portion where the intermediate transfer belt 8 and the photosensitive drum 1 come into contact. are doing. A secondary transfer roller 15 is arranged at a position facing the secondary transfer counter roller 11 on the outer peripheral surface side of the intermediate transfer belt 8 . The secondary transfer roller 15 urges the secondary transfer opposite roller 11 with a predetermined pressure through the intermediate transfer belt 8, and is a nip portion where the secondary transfer roller 15 and the intermediate transfer belt 8 are in contact. A secondary transfer portion N2 is formed. The secondary transfer roller 15 rotates following the rotation of the intermediate transfer belt 8 directly or via a transfer material P such as recording paper (secondary transfer driven method). A belt cleaning device 12 , which is cleaning means for the intermediate transfer belt 8 , is arranged at a position facing the tension roller 10 on the outer peripheral surface side of the intermediate transfer belt 8 . In this embodiment, the intermediate transfer belt 8 supported by the drive roller 9, the tension roller 10, and the secondary transfer counter roller 11, and the belt cleaning device 12 are integrated as a unit 13, which is detachable from the image forming apparatus 100. is configured to

<Image forming operation>
Next, an image forming operation in image forming apparatus 100 will be described. When receiving a print request including image data from an external device (not shown) such as a host computer, the video controller 71 transmits a print signal instructing the start of image formation to the control unit 70, and converts the received image data into an image. Convert to bitmap data for formation. The control unit 70 instructs each image forming unit S to start the image forming operation based on the print signal. When the image forming operation is started, the photosensitive drum 1 and the intermediate transfer belt 8 of each image forming station S start rotating in the directions indicated by arrows R1 and R2 in the drawing at a predetermined process speed. In this embodiment, the peripheral speed of the intermediate transfer belt 8 is 300 mm/sec, which is the image forming process speed, and the photosensitive drum 1 rotates at a peripheral speed that is 0.5% faster than the image forming process speed. The surface of the photosensitive drum 1 is uniformly charged to a potential of a predetermined polarity (negative polarity in this embodiment) by the charging roller 2 . At this time, a predetermined charging voltage is applied to the charging roller 2 from a charging voltage applying section (not shown). Next, the charged surface of the photosensitive drum 1 is exposed by being irradiated with laser light emitted from the exposure device 3 according to image signals based on bitmap data corresponding to each image forming station S. , an electrostatic latent image is formed on the surface of the photosensitive drum 1 according to the image signal.

The toner in the developing device 4 is negatively charged by the developer applying blade 42 and applied to the developing sleeve 41 . A predetermined developing voltage is applied to the developing sleeve 41 by a developing voltage applying section (not shown). Then, when the electrostatic latent image formed on the photosensitive drum 1 reaches the facing portion (developing portion) between the photosensitive drum 1 and the developing sleeve 41, the electrostatic latent image on the photosensitive drum 1 contains negative toner. A toner image is formed on the photosensitive drum 1 by being visualized by adhering.

Next, the toner image formed on the photosensitive drum 1 is transferred (primary transfer) by the primary transfer roller 5 onto the rotationally driven intermediate transfer belt 8 at the primary transfer portion N1. At this time, a primary transfer voltage having a polarity opposite to the polarity of the toner during development (positive polarity in this embodiment) is applied to the primary transfer roller 5 from a primary transfer power supply E1, which is a primary transfer voltage applying means. For example, when forming a full-color image, an electrostatic latent image is formed on the photosensitive drum 1 of each image forming station S, and the formed electrostatic latent image is developed to form a toner image. Then, the toner images of each color formed on the photosensitive drum 1 of each image forming section S are sequentially superimposed and transferred onto the intermediate transfer belt 8 at each primary transfer section N1 shown in FIG. A four-color full-color toner image is formed on the intermediate transfer belt).

On the other hand, the transfer material P stacked in a storage cassette (not shown) is conveyed to the registration rollers 14, which are conveying rollers, by a feeding roller (not shown) and an intermediate conveying roller (not shown). The feeding roller (not shown), the intermediate conveying roller (not shown), and the registration roller 14 are rotated by driving force transmitted from the second motor, the feeding motor M2, via a drive train (not shown). driven. After the skew of the transfer material P is corrected by the registration roller 14, the transfer material P is synchronized with the toner image on the intermediate transfer belt 8 to form a secondary transfer roller 15, which is a nip portion formed by the intermediate transfer belt 8 and the secondary transfer roller 15. It is conveyed to the transfer section N2. Then, the toner images carried on the intermediate transfer belt 8 are collectively transferred onto the transfer material P by the secondary transfer roller 15 at the secondary transfer portion N2. At this time, a secondary transfer voltage having a polarity opposite to the polarity of the toner during development (positive polarity in this embodiment) is applied to the secondary transfer roller 15 from the secondary transfer power supply E2, which is a means for applying a secondary transfer voltage. applied.

Thereafter, the transfer material P onto which the toner image has been transferred is conveyed to a fixing device 16, which is fixing means. The transfer material P is pressurized and heated in the process of being nipped and conveyed between the fixing roller and pressure roller of the fixing device 16, and the toner image is fixed on the transfer material P. FIG. The transfer material P on which the toner image is fixed is discharged outside the image forming apparatus 100 . Toner remaining on the intermediate transfer belt 8 after the toner image is transferred onto the transfer material P is removed from the intermediate transfer belt 8 by a cleaning blade of the belt cleaning device 12 .

<Intermediate transfer belt>
Next, the intermediate transfer belt 8 of this embodiment will be described. The intermediate transfer belt 8 is an endless belt member having a circumference of 800 mm and having two layers, a base layer and a surface layer. The base layer is, for example, a layer having a thickness of about 70 μm, in which carbon black as an electric resistance adjusting agent is dispersed in, for example, polyethylene naphthalate resin. The surface layer is a layer that carries a toner image transferred from the photosensitive drum 1, and is a layer having a thickness of about 2 μm, in which an electric resistance adjusting agent such as zinc oxide is dispersed in an acrylic resin as a base material.

Materials used for the base layer of the intermediate transfer belt 8 include the following thermoplastic resins, and a mixture of two or more thermoplastic resins can also be used. Examples of thermoplastic resins include polycarbonate, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polystyrene, polyamide, polyarylate polyethylene naphthalate, polybutylene naphthalate, and thermoplastic polyimide.

The material used for the surface layer of the intermediate transfer belt 8 is preferably a resin material (curable resin) among curable materials from the viewpoint of strength such as wear resistance and crack resistance. An acrylic resin obtained by curing a bond-containing acrylic copolymer is preferred. Unsaturated double bond-containing acrylic copolymers are available as acrylic UV-curable hard coat materials (for example, Lucifural (trade name) manufactured by Nippon Paint Co., Ltd.).

In addition, a conductive material (conductive filler, electrical resistance adjuster) can be added to the surface layer of the intermediate transfer belt 8 in order to adjust the electrical resistance. An electronically conductive material or an ionically conductive material can be used as the conductive material. Examples of electronically conductive materials include particulate, fibrous, and flaky carbon-based conductive fillers such as carbon black. The electronically conductive material may also be particulate, fibrous, or flaky metallic conductive fillers such as silver, nickel, copper, zinc, aluminum, stainless steel, and iron. Furthermore, electronically conductive materials include, for example, particulate metal oxide-based conductive fillers such as zinc antimonate and tin oxide. On the other hand, ion conductive materials include, for example, ionic liquids, conductive oligomers and quaternary ammonium salts. One or more conductive materials may be appropriately selected from among the conductive materials described above, and an electronically conductive material and an ionically conductive material may be mixed and used.

Also, a solid lubricant may be added to the surface layer of the intermediate transfer belt 8 . The solid lubricant can be appropriately selected from polytetrafluoroethylene (PTFE) resin powder, vinyl fluoride resin powder, fluorine-containing particles such as graphite fluoride, and copolymers thereof. In this embodiment, 40 parts by weight of PTFE resin powder is added to the surface layer of the intermediate transfer belt 8 . When the frictional resistance between the cleaning blade of the belt cleaning device 12 and the intermediate transfer belt 8 is high, stick-slip of the cleaning blade may cause abnormal noise and poor cleaning. Therefore, a solid lubricant is used to reduce the frictional resistance between the cleaning blade and the intermediate transfer belt 8 . Note that the more the solid lubricant is added, the lower the strength of the surface layer of the intermediate transfer belt 8 and the easier it is to wear. Therefore, the amount of abrasion (hereinafter referred to as abrasion rate) of the intermediate transfer belt 8 per 10,000 sheets of paper in this embodiment is about 0.03 μm. Here, "passage" refers to the transport (passage) of the transfer material P in the secondary transfer portion N2. Further, "the number of sheets passed" refers to the accumulated number of transfer materials P conveyed in the secondary transfer portion N2.

In this embodiment, the contact area is reduced by roughening the surface layer of the intermediate transfer belt 8 in order to further reduce the frictional resistance. In the surface roughening treatment, a lapping film (Lapika #2000 (trade name) manufactured by KOVAX) having abrasive grains of aluminum oxide with a grain size of 9 μm was applied to the surface of the intermediate transfer belt 8 mounted on a cylinder with a surface pressure of 0.98 N. /mm ² and rotated for 40 seconds. As a result, grooves having an average width W of about 1 μm and an average depth D of about 0.8 μm were formed in the surface layer of the intermediate transfer belt 8 .

<Conveyance of transfer material>
As described above, in the image forming apparatus 100 of this embodiment, the peripheral speed of the registration rollers 14 is set higher than the peripheral speed of the intermediate transfer belt 8 . As a result, the transfer material P is conveyed in a slack state between the registration roller 14 and the secondary transfer portion N2, and the transfer material P is conveyed with sufficient force by utilizing the rigidity of the transfer material P itself. The registration roller 14 has an outer diameter Φ of 14 mm and is made of ethylene propylene diene rubber (EPDM). good. The outer diameter of the registration roller 14 of the present embodiment is reduced by about 0.017% per 10,000 sheets of paper due to abrasion caused by conveying the transfer material P (passage). The conveying speed of the transfer material P is reduced by the reduced amount. In this embodiment, in order to keep the peripheral speed of the registration roller 14 constant, the speed of the feeding motor M2 that drives the registration roller 14 is increased by 0.017% each time the registration roller 14 passes 10,000 sheets.

When the intermediate transfer belt 8 starts to be used, that is, when the image forming apparatus 100 starts to be used, the peripheral speed of the registration rollers 14 is 303 mm/sec. is set 1% faster. The image magnification in this case is approximately 99.8%. Here, the method of measuring the image magnification of this embodiment will be described. The image magnification is obtained by obtaining the ratio of the image length of the actually printed image to the image length of the image data to be printed in the image forming process direction. As a method for measuring the image magnification, an image pattern in which horizontal lines with a line width of 0.2 mm are printed at intervals of 10 mm is printed, and the image length of the actually printed image is measured. Hereinafter, this image pattern will be referred to as an image magnification measurement pattern, and no printing will be performed in areas other than the horizontal line portion.

The target value of the variation in image magnification as a product is ±0.7% (±2 mm on A4 paper), that is, the range is 1.4% (= 0.7% + 0.7%), but the image magnification is Subject to various variations. For example, in this embodiment, the influence of the image pattern is about 0.6%, and the variation of other parts and the deterioration of the parts due to the use of the image forming apparatus 100 are about 0.6%. Therefore, in this embodiment, the variation in image magnification due to the durability of the intermediate transfer belt 8 is 0.2% (=1.4%-0.6%-0.6%) (0.6% for A4 paper). 57 mm).

The surface layer of the intermediate transfer belt 8 wears as paper passes, and the frictional force between the transfer material P and the intermediate transfer belt 8 changes due to the reduction in the amount of solid lubricant and the change in shape. As the period becomes longer, the conveying force of the transfer material P changes. When the peripheral speed of the intermediate transfer belt 8 is constant as in the present embodiment and the peripheral speed of the registration roller 14 is controlled to be constant and higher than the peripheral speed of the intermediate transfer belt 8 as described above, , the frictional force between the transfer material P and the intermediate transfer belt 8 is resistance when the transfer material P is conveyed. Therefore, since the print rate is small as in the image magnification measurement pattern, compared to the case where the frictional force between the transfer material P and the intermediate transfer belt 8 at the secondary transfer portion N2 is large, when the print rate is large, the secondary The intervening toner at the transfer portion N2 reduces the frictional force and lengthens the image. As described above, the image magnification of approximately 99.7% in the image magnification measurement pattern is due to the variation in image magnification of various image patterns (approximately 0.6% (=(100%-99.7% )×2) is set to be approximately 100%.

<Measurement of Dynamic Friction Coefficient Between Intermediate Transfer Belt and Transfer Material>
Next, a method of measuring the dynamic friction coefficient, which is an index indicating the frictional force between the transfer material P and the intermediate transfer belt 8, which affects the image magnification, will be described. In this embodiment, glass coated paper (HP Laser Glossy Brochure Paper 200 gsm) having a highly smooth surface is used as the transfer material P, and the coefficient of dynamic friction with the intermediate transfer belt 8 is measured. The smoothness of the gloss coated paper used was 250 to 500 seconds in JIS P 8119 paper pulp test method using a Bekk smoothness tester (manufactured by Kumagai Riki Kogyo Co., Ltd.). Hereinafter, unless otherwise specified, the term "dynamic friction coefficient" refers to the dynamic friction coefficient between the intermediate transfer belt 8 and the gloss coated paper.

The dynamic friction coefficient was calculated using the apparatus shown in FIG. 2 by the method described below. FIG. 2(a) is a cross-sectional view of the device used for measurement, and FIG. 2(b) is a front view of the device used for measurement. In FIG. 2, the roller Rf is a stainless steel roller with a length of 220 mm and an outer diameter Φ of 18 mm. Then, the intermediate transfer belt 8 used in the image forming apparatus 100 is suspended around the roller Rf. The shaft of the roller Rf is fixed so as not to rotate, and the intermediate transfer belt 8 suspended over the roller Rf is also installed so as not to move. On the other hand, the roller Rn is a foamed rubber roller having a length of 212 mm and an outer diameter Φ of 16 mm. The rubber roller Rn is made of stainless steel with a rubber thickness of 4 mm and a core metal with an outer diameter Φ of 8 mm. Both ends of the core metal are rotatably supported by bearings (not shown). The product hardness of the rubber roller Rn is approximately 30° (load: 4.9 N) in terms of Asker-C hardness.

In the apparatus shown in FIG. 2, a rubber roller Rn is pressed against an intermediate transfer belt 8 suspended by a roller Rf with a pressure of 44 N to form a nip portion. sandwich. A force gauge (FGPX-20 manufactured by Nidec-Shimpo) was used to measure the force required to pull the sandwiched gloss-coated paper in a direction perpendicular to the nip portion at a speed of about 100 mm/sec (hereinafter referred to as pull-out force). Measure using. A reinforcing plate (metal bar) longer than the width of the paper is wrapped around the leading edge of the gloss coated paper to reinforce it. The force is applied uniformly in the longitudinal direction. The reinforcing plate to be used may be of any material and shape as long as it is hard to bend. The core metal portion of the rubber roller Rn is held by a bearing, and the effect on the pull-out force is almost zero. is. The rubber roller Rn is not necessarily held by a bearing, and if the influence of the rotational load of the rubber roller on the measurement is grasped in advance and subtracted from the measured value, for example, a resin sliding bearing may be used.

As described above, in this embodiment, in order to calculate the coefficient of dynamic friction, the pulling force was measured when no toner was present between the intermediate transfer belt 8 and the gloss coated paper. From the relationship between the pull-out force F and the applied force N, the dynamic friction coefficient μ between the intermediate transfer belt 8 and the gloss coated paper is calculated by (Equation 1) shown below. The pull-out force F under each condition in this example is the average value obtained by performing three measurements per condition, with the average value of the last 100 mm of the sheet at which the pulling speed is stabilized as the measured value per time. be.
Dynamic friction coefficient μ = withdrawal force F / applied force N (Equation 1)
It should be noted that the pressing force N in this embodiment is 44N as described above.

<Change in Dynamic Friction Coefficient Accompanied by Conveyance of Transfer Material>
Next, the relationship between the cumulative number of transfer materials P conveyed by the image forming apparatus 100 (also the number of sheets passed) and the coefficient of dynamic friction will be described. FIG. 3 is a diagram showing the relationship between the cumulative number of transfer materials P conveyed by the image forming apparatus 100 (hereinafter referred to as the number of passing sheets) and the coefficient of dynamic friction. In FIG. 3, the horizontal axis indicates the number of sheets passed (unit: sheets), and the vertical axis indicates the coefficient of dynamic friction. As shown in FIG. 3, the coefficient of dynamic friction is 0.38 at the beginning of use of the intermediate transfer belt 8, but as the number of transfer materials P increases, the lubrication distribution near the surface layer of the intermediate transfer belt 8 increases. The amount of PTFE, which is an agent, decreases, and the dynamic friction coefficient rises to 0.50. On the other hand, it can be seen that when the number of transfer materials P passed is 50,000 or more, the surface condition of the intermediate transfer belt 8 is stabilized, and the change in dynamic friction coefficient is small.

In the intermediate transfer belt 8 of this embodiment, a large amount of PTFE resin powder is distributed near the surface layer, and the amount of PTFE resin powder decreases as the acrylic resin, which is the surface layer, is worn. When the number of sheets of paper passing reaches 50,000 or more, the amount of PTFE resin powder that disappears due to wear of the acrylic resin is balanced with the amount of PTFE resin powder that newly appears on the surface, and the coefficient of dynamic friction stabilizes. That is, the variation in the coefficient of dynamic friction shown in FIG. Note that even if the surface layer of the intermediate transfer belt 8 is the same, the magnitude of the effect of the number of passing transfer materials P differs depending on the configuration of the secondary transfer portion N2, the circumferential length of the intermediate transfer belt 8, and the like.

<Relationship between dynamic friction coefficient and image magnification>
Next, FIG. 4 shows the results of investigation of the relationship between the dynamic friction coefficient and the image magnification in this embodiment when the peripheral speed of the intermediate transfer belt 8 is fixed at 300 mm/sec and the peripheral speed of the registration roller 14 is fixed at 303 mm/sec. show. In FIG. 4, the horizontal axis indicates the dynamic friction coefficient, and the vertical axis indicates the image magnification (unit: %). As shown in FIG. 4, in this embodiment, when the dynamic friction coefficient increases by 0.1, the image magnification shrinks (decreases) by about 0.2%. Further, as described with reference to FIG. 3, the coefficient of dynamic friction changes according to the number of sheets of the transfer material P passed. , the dynamic friction coefficient rises to about 0.50 when the number of sheets of transfer material P passed is 50,000 or more. As a result, the dynamic friction coefficient changes by 0.12 (=0.50-0.38) and the image magnification is 0.24% (=0 .2% x 0.12/0.1) will shrink. As a result, the amount of change in image magnification exceeds 0.2%, which is the above-described target amount of change in image magnification caused by the intermediate transfer belt 8 .

<Registration roller speed control>
In this embodiment, the registration rollers 14 are adjusted so that the image magnification is within a predetermined range according to the state of wear of the registration rollers 14 and the change in the dynamic friction coefficient between the transfer material P and the intermediate transfer belt 8 . 14 peripheral speed is controlled. As a control specific to this embodiment, the control unit 70 estimates the frictional force between the intermediate transfer belt 8 and the transfer material P, and changes the surface state of the intermediate transfer belt 8 based on the estimated frictional force. , the peripheral speed of the registration roller 14 with respect to the peripheral speed of the intermediate transfer belt 8 is changed. In the image forming apparatus 100 of the present embodiment, when the gloss-coated paper is fed, the image magnification changes approximately according to the peripheral speed change of the registration roller 14 . Therefore, the control unit 70 adjusts the peripheral speed of the registration roller 14 in correspondence with the change in the image magnification due to the change in the dynamic friction resistance shown in FIG. By keeping the relative speed between the intermediate transfer belt 8 and the transfer material P substantially constant in this manner, it is possible to perform printing with a stable image magnification throughout the period in which the intermediate transfer belt 8 is used.

In this embodiment, there is a correlation shown in FIG. , is estimated based on the accumulated number of transfer materials P conveyed by the image forming apparatus 100 (the number of sheets passed). More specific description will be given. In this embodiment, as described above, in order to correct the peripheral speed of the registration roller 14 due to wear of the registration roller 14, the rotation speed of the feeding motor M2 is set to 0.00 every 10,000 sheets of transfer material P passed. Adjusted to increase by 017%. Further, as described above, the coefficient of dynamic friction changes by 0.12 and the image magnification shrinks by 0.24% until the number of sheets of transfer material P passed reaches 50,000. Therefore, in order to correct the image magnification, the controller 70 performs the following features of this embodiment from the start of use of the intermediate transfer belt 8 until the number of transferred transfer materials P reaches 50,000. have some control. That is, the control unit 70 increases the peripheral speed of the registration roller 14 by 0.048% (=0.24%/(50000 sheets/10000 sheets)) every time 10000 sheets of the transfer material P are fed. Adjust the rotation speed of the feed motor M2. As described above, after the number of transfer materials P passed exceeds 50,000, the change in the surface condition of the intermediate transfer belt 8 is small. Therefore, the control unit 70 adjusts the rotation speed of the feeding motor M2 only by the wear of the registration rollers 14 so that the peripheral speed of the registration rollers 14 is constant, thereby correcting the peripheral speed of the registration rollers 14 . It should be noted that the rotation of the feeding motor M2 may vary depending on the individual circumstances of the image forming apparatus, such as when the rate of change of the coefficient of dynamic friction with respect to the number of passing sheets of transfer material P is different, or when the sensitivity of the image magnification is different due to the change in the coefficient of dynamic friction. The frequency of speed adjustment and the amount of adjustment may be determined.

FIG. 5 shows the setting of the rotation speed of the intermediate transfer motor M1 and the feeding motor M2 according to the number of sheets of the transfer material P in this embodiment described above, and the target value (target value) of the peripheral speed of the registration roller 14. It is a diagram showing. In FIG. 5, the intermediate transfer motor M1 is indicated by a dotted line plotted with circles, the feed motor M2 is indicated by a solid line plotted by black squares, and the registration roller 14 is indicated by a white square. It is a graph connecting the plots with a dashed line. In FIG. 5, the horizontal axis represents the number of sheets of transfer material P passed (unit: sheets), and the vertical axis represents the intermediate transfer motor M1, the feed motor M2, and the registration roller 14 when the initial value is 100%. , the rate of change with respect to the number of sheets of transfer material P passed at each speed. The control unit 70 is The number of sheets of transfer material P passed in the image forming apparatus 100 is stored in a storage unit (memory), and the speeds of the feeding motor M2 and the registration roller 14 shown in FIG. 5 are adjusted according to the number of sheets passed.

<Effect of this embodiment>
Using FIG. 6, changes in image magnification measured using the above-described image magnification measurement pattern from the beginning of use of the image forming apparatus 100 are shown in the case where the control of the present embodiment is performed and the change in the image magnification when the control of the present embodiment is performed. The description will be made in comparison with the case of not doing so. Here, in order to focus on the change in the image magnification due to the change in the surface condition of the intermediate transfer belt 8, the effect based on the result of the experiment will be described while excluding other factors as much as possible. FIG. 6 shows changes in image magnification measured using the above-described image magnification measurement pattern when the control of this embodiment is performed and when it is not performed. In FIG. 6, the horizontal axis indicates the number of sheets of transfer material P passed (unit: sheets), and the vertical axis indicates the change in image magnification (unit: %), assuming that the change in image magnification during use of the image forming apparatus 100 is 0. is shown. Further, in FIG. 6, the graph when the control of the present embodiment is performed is indicated by a solid line connecting the plots of black circles, and the graph when the control of the present embodiment is not performed is indicated by the dashed line connecting the plots of white circles. is shown.

If the control of this embodiment is not executed, the intermediate transfer belt 8 wears and the conveying force of the transfer material P decreases. Therefore, as shown in FIG. 6, when the number of transfer materials P passed exceeds 40,000, the image magnification decreases by about 0.2%. If the number of transfer materials P passed further increases, the amount of change in image magnification from the initial stage due to wear of the intermediate transfer belt 8 will exceed the target of 0.2%. As a result, the image magnification is always small, and the risk of failing to meet ±0.7%, which is the target value of variation in image magnification as a product, increases. On the other hand, when the control of this embodiment is carried out, as shown in FIG. 6, there is almost no change in the image magnification, the image magnification does not greatly deviate from the target, and the image magnification is maintained throughout the period of use of the intermediate transfer belt 8. can be stabilized. As described above, in this embodiment, the speed of the feeding motor M2 is adjusted every 10,000 sheets of the transfer material P passed. The frequency of speed adjustment of the feed motor M2 may be changed.

Further, in the present embodiment, the case where the gloss coated paper is used as the transfer material has been described, but the effectiveness of the present embodiment does not change even when other transfer materials are used. However, the degree of influence on the image magnification differs depending on the type of transfer material P used for measurement. This is because the coefficient of dynamic friction with the intermediate transfer belt 8 varies depending on the surface properties (roughness, presence or absence of coating, etc.) of the transfer material P, and the rigidity of the transfer material P affects the peripheral speed of the registration roller 14 at the secondary transfer portion. This is because the sensitivity of the conveying speed at N2 is different.

Further, it is known that the filler added to the transfer material P has a great influence on the change in the surface condition of the intermediate transfer belt 8 as well. For example, it is known that the surface layer of the intermediate transfer belt 8 is easily scraped when the transfer material P using calcium carbonate as a filler is passed. For example, in this embodiment. It has been described that the amount of PTFE present on the surface of the intermediate transfer belt 8 is balanced after 50,000 sheets of the transfer material P are passed. When a transfer material using calcium carbonate as a filler (Canon Red Label Presentation 80 g paper) or the like was used, the surface layer of the intermediate transfer belt 8 was worn at a speed about 1.5 times faster. Therefore, if the control unit 70 can estimate the transfer material P to be used in the image forming apparatus 100 based on information such as the specified paper feeding mode and the input type of the transfer material P, , control may be performed according to the type of transfer material P (sheet type) used.

Further, in the present embodiment, control for adjusting the peripheral speed of the registration roller 14 by estimating a change in the surface state of the intermediate transfer belt 8 accompanying passage of the transfer material P has been described. For example, the peripheral speed of the registration rollers 14 is adjusted based on the surface state of the intermediate transfer belt 8 such as a density sensor (not shown) included in the image forming apparatus 100 or the detection result of a detection unit that detects a change in the surface state. It may be implemented.

Further, in this embodiment, the rotation speed of the intermediate transfer motor M1 that rotates the intermediate transfer belt 8 is kept constant, and the rotation speed of the feed motor M2 is adjusted to correct the peripheral speed of the registration roller 14, thereby performing the secondary transfer. An example of adjusting the conveying speed of the transfer material P in the portion N2 has been described. In this embodiment, it is important to keep the relative speed between the intermediate transfer belt 8 and the transfer material P at the secondary transfer portion N2 within a predetermined range. Feel free to adjust the speed. In this embodiment, the configuration of the secondary transfer driven system has been described. Applicable. Even in the case of the secondary transfer drive system, the effect of the friction between the intermediate transfer belt 8 and the transfer material P is not 0, and the effect of the present embodiment is produced even in the configuration in which the secondary transfer is driven. As described above, according to the configuration of this embodiment, the conveying speed of the transfer material P relative to the circumferential speed of the intermediate transfer belt 8 is kept within a predetermined range throughout the period of use of the image forming apparatus 100, and printing with a stable image magnification is achieved. It can be carried out.

As described above, according to this embodiment, it is possible to perform printing with a stable image magnification throughout the period of use of the image forming apparatus.

In the first embodiment, the peripheral speed of the registration rollers is controlled so that the image magnification is within a predetermined range according to the state of wear of the registration rollers and the change in the coefficient of dynamic friction between the transfer material and the intermediate transfer belt. An embodiment has been described. In the second embodiment, the peripheral speed of the registration rollers is controlled according to the image pattern difference in addition to the state of wear of the registration rollers and the change in the dynamic friction coefficient between the transfer material and the intermediate transfer belt, and the image magnification is set to a predetermined value. An example of controlling within the range will be described. Note that the image forming apparatus of this embodiment is similar to the image forming apparatus 100 shown in FIG. 1 of Embodiment 1, and the same reference numerals are used for the same apparatuses and the same members, and description thereof will be omitted here. .

<Intermediate transfer belt>
In Example 1, by adding a solid lubricant to the surface layer of the intermediate transfer belt 8, the slipperiness of the surface of the intermediate transfer belt 8 was improved. In this embodiment, the wear resistance of the surface layer of the intermediate transfer belt 8 is improved without applying a solid lubricant to the surface layer of the intermediate transfer belt 8, and the wear rate is 0.03 μm in the first embodiment. was 0.005 μm in Example 2. Further, the method of cleaning the intermediate transfer belt 8 in this embodiment is an electrostatic recovery method using a cleaning brush. A cleaning brush (not shown) is formed by bundling conductive resin fibers such as conductive nylon into a brush shape, and applies a voltage opposite in polarity to the toner to collect the toner on the intermediate transfer belt 8. . The cleaning method using a cleaning brush has problems such as an increase in cost and complication of cleaning control. However, even if there is no lubricant on the surface layer of the intermediate transfer belt 8 as in the present embodiment, stick-slip of the cleaning blade due to friction between the cleaning blade and the intermediate transfer body as in the first embodiment produces abnormal noise. do not. Since other device configurations are the same as those of the first embodiment, descriptions thereof are omitted here.

<Change in Dynamic Friction Coefficient Accompanied by Conveyance of Transfer Material, and Relationship Between Dynamic Friction Coefficient and Image Magnification>
The coefficient of dynamic friction between the intermediate transfer belt 8 and the transfer material P in this embodiment is 0.7 when the image forming apparatus 100 is started to be used. As the transfer material P passes, the surface condition of the intermediate transfer belt 8 changes mainly due to friction with the transfer material P, and while about 50,000 transfer materials P pass, the dynamic friction coefficient changes from 0.7 to 0.7. down to 6. Also in this embodiment, as shown in FIG. 4 of the first embodiment, when the coefficient of dynamic friction changes by 0.1, the image magnification changes by about 0.2%. Therefore, in order to keep the image magnification of the image magnification measurement pattern described in the first embodiment within the target value, the control unit 70 sets 0.04% (=0. 2%/(50000 sheets/10000 sheets)), the peripheral speed of the registration roller 14 is changed. However, in this embodiment, unlike the first embodiment, the dynamic friction coefficient decreases from the beginning of the use of the image forming apparatus 100 . Therefore, one of the features of this embodiment is that the peripheral speed of the registration roller 14 is reduced to keep the image magnification constant.

FIG. 7 shows the setting of the rotation speed of the intermediate transfer motor M1 and the feed motor M2 according to the number of sheets of the transfer material P in this embodiment described above, and the target value (target value) of the peripheral speed of the registration roller 14. It is a diagram showing. In FIG. 7, the intermediate transfer motor M1 is represented by a dotted line plotted with circles, the feed motor M2 is represented by a solid line plotted by black squares, and the registration roller 14 is represented by a white square. It is a graph connecting the plots with a dashed line. In FIG. 7, the horizontal axis represents the number of sheets of transfer material P passed (unit: sheets), and the vertical axis represents the intermediate transfer motor M1, the feed motor M2, and the registration speed when the initial value of the speed is 100%. It represents the rate of change of the speed of the roller 14 with respect to the number of sheets of transfer material P passed. In Example 2, unlike Example 1, the dynamic friction coefficient decreases until 50,000 transfer materials P are passed, and after the number of transferred transfer materials exceeds 50,000, the dynamic friction coefficient becomes substantially constant. At the same time, the peripheral speed of the registration rollers 14 is adjusted to adjust the amount of wear of the registration rollers 14 . Therefore, the speed control of the feeding motor M2 by the control unit 70 for realizing the peripheral speed of the registration roller 14 is such that the rotational speed of the feeding motor M2 is reduced until the number of transfer materials P passed is 50,000, and After exceeding the number of sheets, the rotational speed of the feeding motor M2 is increased again. The control unit 70 is The number of sheets of transfer material P passed in the image forming apparatus 100 is stored, and the speed of the registration roller 14 shown in FIG. 7 is adjusted according to the number of sheets passed.

<Toner coverage rate>
On the other hand, in this embodiment, due to the difference in the specification of the surface layer of the intermediate transfer belt 8, the difference in the conveying speed of the transfer material P due to the image pattern is greater than that in the first embodiment. When toner intervenes between the intermediate transfer belt 8 and the transfer material P, the coefficient of dynamic friction decreases, and the toner adhesion area per area of the transfer material P (excluding margins), which is the printing rate (hereinafter referred to as toner coverage rate). roughly proportional to When the toner coverage rate is 100%, the dynamic friction coefficient decreases to 0.16 regardless of the surface condition of the intermediate transfer belt 8 . That is, when the coefficient of dynamic friction is large when the toner coating rate is small, the difference in the conveying speed of the transfer material P due to the image pattern becomes large.

In particular, at the beginning of use of the intermediate transfer belt 8, the coefficient of dynamic friction between the intermediate transfer belt 8 and the transfer material P at the time of start of use is 0.7. The difference in dynamic friction coefficient is about 0.54 (=0.7-0.16). As described in the first embodiment, when the dynamic friction coefficient changes by 0.1, the image magnification changes by about 0.2%. Therefore, in this embodiment, the toner coverage rate of the image pattern is about 1.1% (≈0.54×(0.2%/ 0.1)) will result in a change in image magnification. As described in the first embodiment, the target range of variation in image magnification is 1.4%, of which variation and deterioration of components account for about 0.6% at maximum. Therefore, it is desirable that the total effect on the image magnification due to the image pattern difference and the change in the surface condition of the intermediate transfer belt 8 be within 0.8% (=1.4%-0.6%). In this embodiment, the intermediate transfer belt 8 of this embodiment is used to keep the variation in image magnification within a predetermined range. ), the peripheral speed of the registration roller 14 is adjusted.

As described in the first embodiment, when receiving a print request from an external device (not shown) such as a host computer, the video controller 71 transmits a print signal instructing the start of image formation to the control unit 70, and prints the received image. Converts data to bitmap data for image formation. The control unit 70 controls the exposure device 3 to irradiate the photosensitive drum 1 of each image forming unit S with laser light according to the image signal based on the converted bitmap data. Based on the image data converted into bitmap data in the video controller 71, the control unit 70 of this embodiment calculates the ratio of the area scanned by the laser beam to the total image area of the transfer material P as a "toner coverage rate." calculate.

As described above, if the toner coverage rate is 100%, the difference in surface condition from that of the intermediate transfer belt 8 in Example 1 has almost no effect on the image magnification. The influence of the difference in the surface state of the belt 8 occurs. Therefore, the control unit 70 calculates an adjustment value for the peripheral speed of the registration roller 14 according to the image pattern, for example, using (Equation 2) shown below, and adjusts the rotational speed of the feeding motor M2.
(100−toner coverage rate)/100×0.6 (%) (Formula 2)

In this embodiment, the image magnification difference due to the image pattern, which is about 1.1% as described above, is reduced to 0.6% or less, which is the target value of the first embodiment, and the maximum adjustment value is set as follows. Although it is set to 0.6%, the maximum adjustment value may be set to 1.1%.

<Speed control of feeding motor>
In this embodiment, as described above, when the transfer material P passes through the secondary transfer portion N2, the dynamic friction coefficient between the intermediate transfer belt 8 and the transfer material P decreases. Therefore, until 50,000 sheets of the transfer material P are passed, 0.04% is subtracted from the adjustment value obtained by the above-described (Equation 2) every time 10,000 sheets are passed, Find the final adjustment value for the peripheral speed of

FIG. 8 is a flow chart showing a control sequence for adjusting the speed of the feed motor M2 that controls the circumferential speed of the registration roller 14 in this embodiment. The processing shown in FIG. 8 is activated and executed by the control unit 70 each time the image forming apparatus 100 prints on the transfer material P. FIG. Information on the number of sheets passed through the intermediate transfer belt, which will be described later, is information on the accumulated number of sheets of the transfer material P passed since the image forming apparatus 100 was operated, and the stored content remains unchanged even when the power of the control unit 70 is turned off. is stored in memory that is not erased.

In step (hereinafter referred to as S) 21, the control unit 70 acquires information about the number of sheets passed through the intermediate transfer belt stored in the memory, and adds 1 to the acquired information of the number of sheets passed through the intermediate transfer belt for updating. In S22, the control unit 70 controls the feeding motor M2 to change the peripheral speed of the registration roller 14 by 0.04% every 10,000 sheets, according to the updated intermediate transfer belt sheet number information. Determine the speed adjustment value.

At S<b>23 , the control unit 70 calculates the toner coverage rate based on the image data to be printed on the transfer material P converted into bitmap data in the video controller 71 . In S24, the controller 70 determines the speed adjustment value of the feed motor M2 according to the calculated toner coverage rate based on the above-described (Equation 2).

In S25, the controller 70 controls the speed adjustment value of the feeding motor M2 calculated according to the number of sheets passed through the intermediate transfer belt and the speed adjustment value of the feeding motor M2 calculated based on the toner coating rate. Adjust the speed of the feed motor M2. As described above, in this embodiment, speed adjustment based on information on the number of sheets passed through the intermediate transfer belt is performed every time 10,000 sheets of the transfer material P are passed, speed adjustment according to the image information (toner coating rate). This is performed each time the material P is passed. The series of processes of S21 and S22 and the series of processes of S23 and S24 are executed in parallel, and the process of S25 is executed after the processes of S22 and S24 are finished.

<Effect of this embodiment>
Table 1 shows changes in the surface condition of the intermediate transfer belt 8 due to the passage of the transfer material P, and changes in the dynamic friction coefficient between the intermediate transfer belt 8 and the transfer material P due to the presence of toner (toner coating rate). 4 is a table showing the effect of improving the image magnification by the control of the present embodiment. In Table 1, the toner coverage rate is three cases of 0%, 50%, and 100%. Shown is the image magnification with and without control.

As shown in Table 1, the image magnification when the control of this embodiment is not performed is 99.2% (the toner coverage rate is 0%) to 100.2% when the number of sheets passed is 0. 3% (100% toner coverage) and has an image magnification variation of 1.1%. Similarly, when the number of sheets passed is 50,000 and 100,000, the image magnification is 99.4% (the toner coverage rate is 0%) to 100.3% (the toner coverage rate is 100%), and 0.4% (the toner coverage rate is 0%). It has an image magnification variation of 9%.

On the other hand, as shown in Table 1, when the number of sheets passed is 0, the image magnification is 99.8% (the toner coverage rate is 0%) to 99.8%. It is 100.3% (the toner coverage rate is 100%), and the image magnification variation is 0.5%. Similarly, when the number of sheets passed is 50,000 and 100,000, the image magnification is 100.0% (the toner coverage rate is 0%) to 100.1% (the toner coverage rate is 100%). The variation in image magnification is 1%. Further, when the control of this embodiment is performed, the image magnification at a toner coverage rate of 0% is 99.8% when the number of sheets passed is 0, and when the number of sheets passed is 50,000 and 100,000, 100.0%.

As described above, as an effect of the control of this embodiment, even if the coefficient of dynamic friction decreases with an increase in the number of sheets passed, the image magnification when the toner coverage rate is 0% is more stable as in the first embodiment. I am able to let Furthermore, by controlling the feeding motor M2 according to the image information, the relative speed between the intermediate transfer belt 8 and the transfer material P at the secondary transfer portion N2 can be adjusted even for image patterns with various toner coating rates. , variation in image magnification can be suppressed. According to Table 1, the variation in image magnification when the control of this embodiment is performed is suppressed to within 0.5% at maximum. As described above, it is possible to further stabilize the image magnification by increasing the maximum adjustment amount according to (Equation 2).

In this embodiment, the toner coverage rate is used as the information about the coverage rate, but the information is not limited to this. For example, in the same manner as the toner coverage rate, the number of toner adhering pixels (pixel count) correlated with the total toner amount on one page of the transfer material that can be calculated based on the bitmap data received by the control unit 70 is displayed as the coverage rate information. may be used as

As described above, according to the configuration of this embodiment, the conveying speed of the transfer material P with respect to the circumferential speed of the intermediate transfer belt 8 can be set within a predetermined range regardless of the image pattern (toner coating rate) throughout the period of use of the image forming apparatus 100. It is possible to print images with stable image magnification.

As described above, according to this embodiment, it is possible to perform printing with a stable image magnification throughout the period of use of the image forming apparatus.

1 photosensitive drum 8 intermediate transfer belt 14 registration roller 15 secondary transfer roller 70 control unit M1 intermediate transfer motor M2 feeding motor N2 secondary transfer nip portion

Claims (10)

a plurality of image forming units each having a photosensitive drum and forming a toner image on the photosensitive drum;
an intermediate transfer belt onto which the toner image formed on the photosensitive drum of the image forming unit is transferred;
The intermediate transfer belt is arranged to face a roller stretched across the intermediate transfer belt, forms a nip portion with the roller, and conveys the toner image on the intermediate transfer belt to the nip portion. a transfer roller for transferring onto a transfer material;
a conveying roller disposed upstream of the transfer roller in a conveying direction of the transfer material and conveying the transfer material to the nip portion;
a first motor that drives a drive roller that rotates the intermediate transfer belt, the roller being different from the roller facing the transfer roller;
a second motor that drives the conveying roller;
a control means for controlling the rotational speeds of the first motor and the second motor;
with
The control means controls a frictional force between the intermediate transfer belt and the transfer material at the nip corresponding to the number of transfer materials conveyed to the nip, and the frictional force at the nip and the intermediate transfer belt. and an image magnification of an image to be transferred onto a transfer material from the second motor. The control means keeps the rotation speed of the first motor constant, and adjusts the speed of the conveying roller faster than the peripheral speed of the driving roller in order to convey the transfer material in a slackened state between the conveying roller and the nip portion. 2. The image forming apparatus according to claim 1, wherein the rotation speed of said second motor is adjusted so that the peripheral speed of said second motor increases. 3. The control means increases the rotation speed of the second motor as the frictional force increases, and decreases the rotation speed of the second motor as the frictional force decreases. image forming device. In the nip portion, the image magnification of the image transferred from the intermediate transfer belt to the transfer material decreases as the frictional force increases, and the image transferred from the intermediate transfer belt to the transfer material decreases as the frictional force decreases. 4. The image forming apparatus according to claim 3, wherein the magnification is increased. 5. The image forming apparatus according to claim 4, wherein said control means adjusts the rotational speed of said second motor each time a predetermined number of transfer materials are conveyed to said nip portion. a storage unit that stores information on the frictional force between the intermediate transfer belt and the transfer material in the nip portion corresponding to the type of transfer material;
The control means acquires information on the frictional force corresponding to the paper type of the transfer material on which the image is formed, from the storage unit each time an image is formed on the transfer material. An adjustment value for the rotation speed of the second motor is calculated according to the image magnification of the corresponding image, and the rotation speed of the second motor is adjusted based on the calculated adjustment value. Item 6. The image forming apparatus according to item 5. The control means calculates an adjustment value for the rotational speed of the second motor according to the amount of wear of the conveying roller each time a predetermined number of transfer materials are conveyed to the nip portion, and the calculated adjustment value is calculated. 7. The image forming apparatus according to claim 1, wherein the rotation speed of said second motor is adjusted based on the value. The control means calculates a printing rate on the transfer material each time an image is formed on the transfer material, calculates an adjustment value for the rotation speed of the second motor according to the calculated printing rate, and 8. The image forming apparatus according to claim 7, wherein the rotation speed of said second motor is adjusted based on the calculated adjustment value. 9. The image forming apparatus according to claim 8, wherein the control unit calculates the coverage ratio based on the area of the transfer material excluding the margin and the area to which the toner adheres. 10. The image forming apparatus according to claim 1, wherein the transfer roller rotates following the rotation of the intermediate transfer belt or the transferred transfer material.

Images