JP2021021853A - Image forming device - Google Patents

Abstract

To provide an image forming device with which it is possible to prevent, by a simple composition, the occurrence of trouble such as image degradation or fouling of sheet material (transfer paper) when conveying a sheet material (paper) while being slackened.SOLUTION: The image forming device comprises: a first conveyance unit for performing an image forming process to form an image on a sheet material while conveying the sheet material; a second conveyance unit for conveying the sheet material and located upstream or downstream of the first conveyance unit; a conveyance speed control unit for controlling the conveyance speed of the sheet material in the first and second conveyance units; and a sheet information determination unit for determining length information along the conveyance direction of the sheet material. The conveyance speed control unit exercises control so that the conveyance speed of the sheet material in the second conveyance unit has a prescribed difference in speed relative to the conveyance speed of the sheet material in the first conveyance unit, with the speed difference changed on the basis of length information along the conveyance direction of the sheet material that is determined by the sheet information determination unit.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus such as a copier and a printer.

The image forming apparatus electrostatically transfers the toner image formed on the photoconductor drum onto the paper (sheet material) at the transfer portion, and then heats and melts the toner image at the fixing portion to fix the toner image on the paper. ..

In the transfer unit, the paper is sandwiched between the transfer nip portions where the photoconductor drum and the transfer roller come into contact with each other, and the photoconductor drum and the transfer roller rotate to transfer the paper and transfer the toner image at the same time. In the fixing part, the paper is sandwiched between the fixing nip parts where the heated fixing roller and the pressure roller come into contact, and the fixing path roller and the pressure roller rotate to convey the paper and fix the toner image to the paper at the same time. Will be done.

Then, since the installation interval between the transfer portion and the fixing portion is usually shorter than the length of the minimum paper to be conveyed from the viewpoint of paper transportability, the paper is placed on the transfer nip portion during the transfer. There is a state in which the paper is sandwiched and conveyed by both the fixing nip portions. At this time, if the paper conveying speed at the fixing nip portion becomes faster than the paper conveying speed at the transfer nip portion for some reason, the paper is pulled toward the fixing portion. There is a risk of image deterioration (deficiency) in which the toner image being transferred is displaced from a predetermined transfer position at the transfer nip portion and transferred.

Therefore, the paper is transported so that there is a slack between the transfer nip portion and the fixing nip so that the influence of the paper transport speed at the fixing nip does not reach the transfer nip, and the transfer nip and the fixing nip are further affected. Patent Document 1 discloses an image forming apparatus including a slack forming portion configured so that the slack of the paper does not disappear even if the speed difference from the portion fluctuates to some extent.

Japanese Unexamined Patent Publication No. 2006-219273

As described above, in the conventional image forming apparatus, the paper is loosened and conveyed between the transfer nip portion and the fixing nip, and even if a speed difference of a predetermined value or more occurs between the transfer nip portion and the fixing nip portion, the slack occurs. Deterioration of the image such as image misalignment is suppressed by providing a forming portion that does not disappear. However, if the amount of slack in the paper becomes too large, when the rear end of the paper separates from the transfer nip portion, the paper is conveyed while rubbing against the transfer roller, and the transfer member becomes dirty on the rear end of the paper. There was a risk of getting dirty.

The present invention has been made in view of the above circumstances, and an object of the present invention is to cause problems such as image deterioration and stains on the sheet material (transfer paper) when the sheet material (paper) is loosened and conveyed. It is to provide an image forming apparatus which can prevent such a thing with a simple structure. In particular, an image forming apparatus capable of stably preventing stains generated on the rear edge of paper is provided.

The image forming apparatus according to one aspect of the present invention performs an image forming process for forming an image on a sheet material and conveys the sheet material to a first conveying portion and an upstream side or a downstream side of the first conveying portion. A second transport unit that is located and transports the sheet material, a transport speed control unit that controls the transport speed of the sheet material in the first transport unit and the second transport unit, and a transport direction of the sheet material. The transfer speed control unit includes a sheet information determination unit for determining the length information, and the transfer speed of the sheet material in the second transfer unit is set with respect to the sheet material transfer speed in the first transfer unit. The speed difference is controlled so as to have a predetermined speed difference, and the speed difference is changed based on the length information along the transport direction of the sheet material determined by the sheet information determination unit.

As a result, when the sheet material is loosened and transported between the first transport section and the second transport section, the speed difference can be changed to a preferable value according to the size of the sheet material, resulting in deterioration of the image and the sheet material. It is possible to prevent problems such as dirt from occurring with a simple configuration.

Further, in the above-mentioned image forming apparatus, the sheet material generated by the speed difference during the time during which the sheet material is maintained in a state of being conveyed by both the first conveying portion and the second conveying portion. The difference in the transport amount may be defined as the slack amount, and the speed difference may be changed based on the length information along the transport direction of the sheet material so that the slack amount is equal to or less than a predetermined value.

As a result, even if the size of the sheet material is changed, the amount of slack in the sheet material becomes almost constant, so that problems such as image deterioration and stains on the sheet material are prevented regardless of the size of the sheet material. be able to.

Further, the image forming apparatus described above includes a storage means for storing the slack amount of the sheet material in advance as a target slack amount, and the slack amount of the sheet material is stored in the storage means. A transport speed determining unit that determines the speed difference may be provided so as to be equal to or less than the amount.

As a result, the sheet material can be conveyed so that the amount of slack is close to the target amount of slack, which is a predetermined preferable amount of slack. Therefore, regardless of the size of the sheet material, there are problems such as deterioration of the image and stains on the sheet material. It can be prevented from occurring.

Further, in the above-mentioned image forming apparatus, a plurality of the target slack amounts are set and stored in the storage unit so as to correspond to the type of the sheet material, and the transport speed determination unit is the sheet information determination unit. The speed difference may be determined using the target slack amount corresponding to the type of sheet material determined by.

As a result, even when the target slack amount stored in advance is not preferable, the target slack amount can be changed, so that the slack amount can be set to be preferable during transportation, regardless of the size of the sheet material. , It is possible to prevent problems such as deterioration of the image and stain of the sheet material.

Further, in the above-mentioned image forming apparatus, the target slack amount stored in the storage means may be changed by the operation unit.

As a result, even if the preferable amount of slack changes due to conditions other than the size of the sheet material, it is possible to prevent problems such as deterioration of the image and stains on the sheet material.

Further, in the above-mentioned image forming apparatus, the first transfer unit is a transfer unit, and the transfer speed determination unit sets the target slack amount to S, the length along the transfer direction of the sheet material to L, and the transfer rate. When the transport speed in the section is Vp and the distance between the transfer section and the second transport section is D, the speed difference is S × Vp / (LD).
It may be decided to be.

Thereby, it is possible to determine a preferable amount of slack, and it is possible to prevent problems such as image deterioration and stains on the sheet material from occurring regardless of the size of the sheet material.

Further, in the above-mentioned image forming apparatus, the second transfer unit is a fixing unit installed on the downstream side of the transfer unit, and the transfer speed determining unit has a sheet transfer speed of the fixing unit as the transfer unit. S × Vp / (LD) than the sheet transfer speed of
You may decide to be slower.

As a result, when the sheet material is conveyed between the transfer portion and the fixing portion, it can be conveyed with a preferable amount of slack, so that problems such as image deterioration and stains on the sheet material are prevented regardless of the size of the sheet material. can do.

Further, in the above-mentioned image forming apparatus, the second transfer unit is a resist unit installed on the upstream side of the transfer unit, and the transfer speed determination unit has a sheet transfer speed of the resist unit as the transfer unit. S × Vp / (LD) than the sheet transfer speed of
You may decide to be as fast as possible.

As a result, when the sheet material is conveyed between the resist portion and the transfer portion, it can be conveyed with a preferable amount of slack, so that problems such as image deterioration and stains on the sheet material are prevented regardless of the size of the sheet material. can do.

Further, in the above-mentioned image forming apparatus, the image forming apparatus has at least one sheet storage unit for storing the sheet material, and the storage unit has size information including the size and storage direction of the sheet material set in the sheet storage unit. And the type information including the thickness and type of the sheet material are stored corresponding to the sheet storage unit, and the transport speed determination unit stores the size information, the type information, and the type, respectively, stored in the storage unit. The speed difference may be determined based on the information and the corresponding target slack amount.

As a result, the size of the sheet material can be reliably detected, so that the transfer speed determining unit can determine a preferable transfer speed, and regardless of the size of the sheet material, deterioration of the image, stains on the sheet material, etc. It is possible to prevent problems from occurring.

According to the present invention, there is provided an image forming apparatus capable of preventing problems such as image deterioration and stains on the sheet material (transfer paper) when the sheet material (paper) is loosened and conveyed with a simple configuration. be able to.

It is a schematic side sectional view which shows the structure of the image forming apparatus which concerns on 1st Embodiment of this invention. It is an enlarged sectional view which shows the structure around the transfer part of the image forming apparatus which concerns on 1st Embodiment of this invention. It is an enlarged cross-sectional view explaining the state of the transfer part, the fixing part, and the transport paper in FIG. It is an enlarged cross-sectional view which shows the structure around the photoconductor drum and the transfer roller of the image forming apparatus which concerns on 1st Embodiment of this invention. It is a figure explaining the state which the paper tip reached the fixing nip when the length along the paper transport direction is short. It is a figure explaining the state which the rear end of the paper reached the transfer nip when the length along the paper transport direction is short. It is a figure explaining the state which the paper tip reached the fixing nip when the length along the paper transport direction is long. It is a figure explaining the state which reached the transfer nip at the rear end of the paper in the case where the length along the paper transport direction is long. It is a block diagram which shows the structure of the image forming apparatus which concerns on 1st Embodiment of this invention. It is a table which shows an example of the occurrence situation of the back edge dirt of the paper of the conventional image forming apparatus. It is a table which shows an example of the occurrence state of the back edge dirt of the paper of the image forming apparatus which concerns on 1st Embodiment of this invention. It is sectional drawing which shows the slack of the paper in the image forming apparatus which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the structure of the image forming apparatus which concerns on 2nd Embodiment of this invention. It is a table which shows an example of the image state of the conventional image forming apparatus. It is a table which shows an example of the state of the image of the image forming apparatus which concerns on 2nd Embodiment of this invention. It is a schematic side sectional view which shows the structure of the image forming apparatus which concerns on 3rd Embodiment of this invention. It is a block diagram which shows the structure of the image forming apparatus which concerns on 3rd Embodiment of this invention.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of them will not be repeated. It should be noted that each figure is a simplified drawing for understanding the present invention.

(First Embodiment)
Hereinafter, the image forming apparatus 100 according to the first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic side sectional view showing a configuration of an image forming apparatus 100 according to a first embodiment of the present invention. FIG. 2A is an enlarged cross-sectional view showing a configuration around a transfer portion of the image forming apparatus 100 according to the first embodiment of the present invention. FIG. 2B is an enlarged cross-sectional view illustrating the state of the transfer portion, the fixing portion, and the transport paper in FIG. 2A. FIG. 3 is an enlarged cross-sectional view showing the configuration around the photoconductor drum 31b and the transfer roller 31d of the image forming apparatus 100 according to the first embodiment of the present invention.

As shown in FIG. 1, the image forming apparatus 100 according to the first embodiment of the present invention includes an image reading unit 2, an image forming unit 3, and a document conveying unit 4.

The document transport unit 4 is supported so as to be openable and closable with respect to the image reading unit 2. When the document transport section 4 is opened, the document mounting table 21 provided on the upper surface of the image reading section 2 is opened. The operator can manually place the document directly on the document placing table 21. Further, the image reading unit 2 is provided with a document passing section 22 on the upper surface separately from the document placing table 21, and the document transporting section 4 automatically passes the document so as to pass over the document passing section 22. To transport. The image reading unit 2 reads a document placed on the document placing table 21 or a document conveyed from the document conveying unit 4 and passing over the document passing section 22 to generate image data.

The image forming unit 3 includes a transfer unit 31, a fixing unit 32, a resist unit 36, a paper feed cassette 33a and 33b, and a paper output tray 34.

The transfer unit 31 includes a photoconductor drum 31b, which is a drum-type image carrier. Further, the transfer unit 31 is provided with an optical scanning device 31a, a developing device 31c, a transfer roller 31d, a drum cleaning device 31e, a charger 31f, and a static eliminator (not shown) around the outer periphery of the photoconductor drum 31b. There is. The drum cleaning device 31e removes and recovers residual toner on the surface of the photoconductor drum 31b. The static eliminator removes residual charges on the surface of the photoconductor drum 31b. The charger 31f uniformly charges the surface of the photoconductor drum 31b to a predetermined potential. The optical scanning device 31a exposes the surface of the photoconductor drum 31b to form an electrostatic latent image. The developing device 31c develops an electrostatic latent image on the surface of the photoconductor drum 31b to form a toner image on the surface of the photoconductor drum 31b. The transfer roller 31d is arranged to face the photoconductor drum 31b, and a transfer nip portion 31g is formed between the transfer roller 31d and the photoconductor drum 31b. The transfer roller 31d has a semi-conductive elastic layer on its surface, and the paper P (sheet material) conveyed from the resist portion 36 is sandwiched between the transfer nip portions 31 g and conveyed. When the paper P passes through the transfer nip portion 31g, the toner image on the surface of the photoconductor drum 31b is transferred and conveyed to the fixing portion 32.

The fixing portion 32 is provided on the downstream side of the transfer portion 31, and has a heating roller 32d having a heat source inside, a fixing roller 32a having a heat-resistant elastic layer on the surface, and a fixing belt 32e suspended by the heating roller 32d and the fixing roller 32a. A pressure roller 32b for sandwiching the fixing belt 32e with the fixing roller 32a is provided. The pressure roller 32b conveys the paper P by rotating the paper P with the paper P sandwiched between the pressure roller 32b and the fixing belt 32a. A fixing nip portion 32c is formed between the fixing belt 32e and the pressure roller 32b. The toner image on the paper P is melted and fixed to the paper P by coming into contact with the fixing belt 32e heated to a high temperature by the heating roller 32d at the fixing nip portion 32c.

The paper transport path transports the paper P stored in the paper feed cassette (sheet storage unit) 33 one by one to form an image, and discharges the image-formed paper P to the output tray 34. is there. The output tray 34 is provided above the paper feed cassette 33 and below the image reading unit 2.

The resist unit 36 is provided on the upstream side of the transfer unit 31 and has a resist roller 36a. The resist roller 36a temporarily holds the paper P conveyed from the paper feed cassettes 33a and 33b. A resist nip portion 36b is formed in which the resist roller 36a sandwiches the paper P. Then, the resist roller 36a resumes rotation at the timing when the tip of the toner image on the photoconductor drum 31b coincides with the tip of the paper P, and conveys the paper P to the transfer nip portion 32g.

The paper feed cassettes 33a and 33b store the paper P, and a plurality of sheets of paper P can be placed on the paper cassettes 33a and 33b.

Paper P having different sizes is stored in the paper feed cassette 33a and the paper feed cassette 33b. For example, A4 size paper Pa is stored in the paper feed cassette 33a, and A3 size paper Pb is stored in the paper feed cassette 33b. Further, the direction of the paper P to be conveyed may be different, and the so-called vertical feed in which the paper P is conveyed in the longitudinal direction of the paper P and the so-called horizontal feed in which the paper P is conveyed in the lateral direction of the paper P are respectively. The stored paper cassette may differ depending on the situation. For example, the paper feed cassette 33a stores A4 size paper Pa for vertical feeding, and the paper feed cassette 33b stores A4 size paper Pa for horizontal feeding.

The pickup units 37a and 37b pick up the paper P from the paper feed cassettes 33a and 33b, respectively, and intermittently feed the paper P one by one to the resist unit 36.

The paper ejection tray 34 is a place where the paper P to which the toner is fixed is discharged in the fixing portion 32, and the paper P conveyed from the fixing portion 32 is discharged to the paper ejection tray 34 by the paper ejection roller 34a.

As described above, the paper P is conveyed from the paper feed cassette 33a or the paper feed cassette 33b in the order of the resist unit 36, the transfer unit 31, the fixing unit 32, and the paper output tray 34. Of these, the paper transfer from the transfer unit 31 to the fixing unit 32 will be described with reference to FIG. 2B.

First, the arrangement relationship between the transfer unit 31 and the fixing unit 32 will be described. The transfer unit 31 and the fixing unit 32 have a straight line Ct connecting the center of the photoconductor drum 31b and the center of the transfer roller 31d in the transfer unit 31, and the center of the fixing roller 32a and the center of the pressure roller 32b in the fixing unit 32. The intersection X with the connecting Cf is arranged so as to be on the photoconductor drum 31b side with respect to the straight line L connecting the transfer nip portion 31g and the fixing nip portion 32c. That is, the transfer portion 31 and the fixing portion 32 are arranged so that the transfer paper discharge direction a from the transfer nip portion 31g and the fixing paper discharge direction b from the fixing nip portion 32c intersect each other. A pre-fixing guide 32f is arranged on the upstream side of the fixing nip portion 32c in the paper transport direction, and the paper P discharged from the transfer nip portion 32g has a fixing nip portion in the transport direction by the pre-fixing guide 32f. It is changed to go to 32c. That is, the paper P that has passed through the transfer nip portion 31g and is ejected in the transfer paper discharge direction a is changed in the transport direction to the fixing nip portion 32c side, that is, in the direction of the arrow c by the pre-fixing guide 32f, and the fixing nip portion is directly changed. You will be guided to 32c.

Since the paper P that has passed through the transfer nip portion 31g in this way is curved and conveyed by the pre-fixing guide 32f, when the tip of the paper P (paper tip Tp) reaches the fixing nip portion 32c, the paper P A deflection is formed between the transfer nip portion 31g and the fixing nip portion 32c.

The amount of bending of the paper P generated at this time is expressed by the distance d from the straight line L connecting the transfer nip portion 31g and the fixing nip portion 32c.

Next, the paper P that has reached the fixing nip portion 32c continues to be conveyed by the transfer nip portion 31g and the fixing nip portion 32c until the rear end (paper rear end Ep) passes through the transfer nip portion 31g. ..

At this time, if the paper transport speed of the fixing nip portion 32c becomes faster than the transfer nip portion 31g for some reason, the amount of deflection d formed when the paper tip Tp reaches the fixing nip portion 32c increases with the passage of time. Start to decrease. When the bending amount d of the paper P becomes 0, the paper P is in a taut state, and the paper transport speed of the fixing nip portion 32c is transmitted directly to the transfer nip portion 31g through the paper P. That is, the transfer speed of the paper P at the transfer nip portion 31g is directly affected by the speed of the fixing nip portion 32c and increases with the impact, so that the toner image is displaced from the transfer deviation, that is, the so-called predetermined transfer position. It is transferred and image loss occurs.

Therefore, in order to suppress the occurrence of such transfer deviation, it is generally practiced to set the paper transfer speed of the fixing nip portion 32c to be slightly slower than the paper transfer speed of the transfer nip portion 31g. However, when the control for providing a constant speed difference is performed in this way, the amount of deflection d of the paper P formed by the pre-fixing guide when the paper front end Tp reaches the fixing nip portion 32c is such that the paper rear end Ep is the transfer nip. It will continue to increase until the portion 31 g is removed.

That is, the longer the length of the paper P along the transport direction, the larger the amount of deflection d immediately before the rear end Ep of the paper passes through the transfer nip portion 31g. This state is shown in FIG. P1 shown in FIG. 3 shows a state immediately before the paper rear end Ep of the paper Pa having a short length along the transport direction of the paper P passes through the transfer nip portion 31 g. P2 shown in FIG. 3 shows a state immediately before the paper rear end Ep of the paper Pb having a long length along the transport direction of the paper P passes through the transfer nip portion 31g.

Then, when the bending of the paper P becomes large as shown in P2 in FIG. 3, the rear end Ep of the paper that has passed through the transfer nip portion 31g is conveyed while rubbing against the transfer roller 31d, and the dirt on the transfer roller 31d is removed. There is a problem that the rear edge of the paper is rubbed against the rear edge of the paper and the rear edge of the paper is soiled. This is an adverse effect that the direction away from the transfer nip portion 31g of the rear end Ep of the paper is on the fixing roller 32a side.

The phenomenon in which the amount of deflection of the paper P described above increases as the length of the paper P along the transport direction increases will be described in detail with reference to FIGS. 4A, 4B, 5A, and 5B. 4A and 4B are views for explaining the amount of bending of the paper P generated between the transfer nip portion 31g and the fixing nip portion 32c when the length of the paper P along the transport direction is short. FIG. 5B is a diagram illustrating the amount of bending of the paper P generated between the transfer nip portion 31g and the fixing nip portion 32c when the length of the paper P along the transport direction is long. In both figures, for the sake of clarity, there is no pre-fixing guide 32f, and the paper P is conveyed straight from the transfer nip portion 31g to the fixing nip portion 32c.

4A and 5A are diagrams illustrating a state in which the paper tip Tp reaches the fixing nip portion 32c, and Vp in the figure is the paper transfer speed (= process speed = transfer roller speed, hereinafter) at the transfer nip portion 31g. (Sometimes referred to as process speed or transfer peripheral speed), and Vf is the paper transport speed at the fixing nip portion 32c (= fixing roller speed = pressurizing roller speed, hereinafter may be referred to as fixing peripheral speed). L is the length along the transport direction of the paper P to be transported, A is the shortest distance between the transfer nip portion 31 g and the fixing nip portion 32c, and B is the length L along the transport direction of the paper P. It is a value obtained by subtracting the shortest distance A between the transfer nip portion 31g and the fixing nip portion 32c, and S is a section between the transfer nip portion 31g and the fixing nip portion 32c. Since the transfer nip portion 31g and the fixing nip portion 32c are arranged in a straight line, the amount of bending d of the paper P when the paper tip Tp reaches the fixing nip portion 32c becomes 0 (FIGS. 4A and 5A). ..

The paper material transport speed (fixing peripheral speed) Vf in the fixing nip portion 32c is set to have a predetermined speed difference ΔV from the paper transport speed (process speed Vp) in the transfer nip portion 31g. Here, the speed difference ΔV is represented by the ratio of the peripheral speeds. Therefore, the paper transport speed (fixing peripheral speed Vf) in the fixing nip portion 32c is represented by (1-ΔV) Vp. For example, if ΔV = 0.002, then (1-ΔV) Vp = (1-0.002) Vp = 0.998Vp, which is 99.8% of Vp, which is 0.2% faster than Vp. It means slow.

Next, the bending generated in the paper P during transportation will be described. The paper P that has reached the fixing nip portion 32c is conveyed at a paper conveying speed that is ΔV slower than the paper conveying speed (process speed Vp) of the transfer nip portion 31g. Therefore, in the section Sa, the amount of paper fed from the fixing nip portion 32c is smaller than the amount of paper fed from the transfer nip portion 31g, so that the paper is accumulated in excess. The accumulated amount of the paper P causes the paper P to bend.

The retention of the paper P continues to increase until the rear edge Ep of the paper passes through the transfer nip portion 31 g, and the amount of bending of the paper continues to increase accordingly. Therefore, as described above, the longer the length of the paper P, the larger the amount of bending d. For example, FIGS. 5A and 5B show a state in which the paper P has a length L twice that of FIGS. 4A and 4B, and the time until the rear end Ep of the paper passes through the transfer nip portion 31g. Is more than twice as long as in FIG. 4, so that the value of the amount of deflection d2 generated on the paper P is considerably larger than that in d1 in FIGS. 4A and 4B.

In this way, the amount of deflection d of the paper P is such that when a predetermined speed difference ΔV is provided between the transfer speeds of the transfer nip portion 31 g and the fixing nip portion 32c, the paper P is conveyed by both the transfer nip portion 31 g and the fixing nip portion 32c. It increases as the time spent is longer. It also changes depending on the paper type depending on the type and thickness of the paper P. Therefore, there is a problem that accurate measurement is difficult. In particular, in an actual image forming apparatus, the paper P is already bent when the paper tip Tp reaches the fixing nip portion 32c at the pre-fixing guide 32f, so that accurate measurement becomes more difficult. Therefore, it is very difficult to adjust the speed difference ΔV based on the amount of bending d of the paper P.

Therefore, in the present embodiment, attention is paid to the time during which the paper P is conveyed by both the transfer nip portion 31g and the fixing nip portion 32c, and the retention length of the paper P generated in the section Sa during this time is set to the slack amount S. It was decided to use it as an index instead of the amount of bending d of the paper P. In other words, the difference in the amount of paper P transported (conveyed length) generated by the speed difference ΔV during the time during which the paper P is maintained in a state of being transported by both the transfer nip portion 31 g and the fixing nip portion 32c. Was defined as the amount of slack, and was used as an index in place of the amount of deflection d.

As will be described in detail later, with this definition, it is possible to grasp the bending state of the paper immediately before the rear end Ep of the paper passes through the transfer nip portion 31g without directly measuring the bending amount of the paper P. This is because there is a correlation between the amount of deflection d and the amount of slack S.

From here, a method of preventing stains on the rear edge of the paper by using the amount of slack S will be specifically described. FIG. 6 is a block diagram showing the configuration of the image forming apparatus 100 according to the first embodiment of the present invention.

As shown in FIG. 6, the image forming apparatus 100 includes a transfer speed determination unit 11, a transfer speed control unit 12, a storage unit 13, a transfer drive unit 14a, a fixing drive unit 14b, and a paper feed cassette determination unit 15.

The transfer speed determination unit 11, the transfer speed control unit 12, and the paper feed cassette determination unit 15 are composed of, for example, a microcomputer such as a CPU (Central Processing Unit). The storage unit 13 is, for example, a non-volatile memory such as a ROM (Read Only Memory) or a volatile memory such as a RAM (Random Access Memory). The transfer drive unit 14a is a motor that drives the transfer roller 31d. The fixing drive unit 14b is a motor that drives the fixing roller 32a and the pressurizing roller 32b.

The size and orientation information of the paper P housed in the paper feed cassette 33a and the paper feed cassette 33b is stored in the storage unit 13 in advance by an input operation unit or the like (not shown). For example, the size of the paper P stored in the paper feed cassette 33a is A4, the storage direction is the horizontal feed direction, and the size of the paper P stored in the paper feed cassette 33b is A3, and the storage direction is A3. It is stored in the storage unit 13 that the paper is fed vertically. Information on the paper size and the accommodating direction may be stored in the storage unit 13 by reading the positions of the paper guides (not shown) included in the paper feed cassette 33a and the paper feed cassette 33b.

Further, the above-mentioned slack amount S is stored in advance in the storage unit 13 as the target slack amount S. The value of the target slack amount S may be stored in the storage unit 13 as an initial value in advance, or may be changed and overwritten by an input operation unit (not shown). Further, it may be collectively read from a memory device such as USB and stored. The storage unit 13 also stores basic data such as the process speed Vp, the fixing peripheral speed Vf, and the distance between the transfer nip portion 31g and the fixing nip portion 32c.

The paper feed cassette determination unit 15 determines whether the paper P is picked up from the paper feed cassette 33a or the paper feed cassette 33b when the image forming apparatus 100 operates, and follows the transport direction of the conveyed paper P. The length information of the paper is sent to the transport speed determination unit 11. For example, when the paper size is A4 and the paper P is conveyed from the paper cassette set for vertical feed, the paper length information 279 mm along the transfer direction is sent to the transfer speed determination unit 11. .. The paper feed cassette determination unit 15 may be provided as a part of the function of the transfer speed determination unit 11 described below.

The transport speed determination unit 11 has the fixing roller 32a and the fixing roller 32a for the transfer roller 31d based on the paper length information, the basic information, and the target slack amount S stored in advance in the storage unit 13 determined by the paper feed cassette determination unit 15. The speed difference ΔV of the pressure roller 32b is determined.

The transfer speed control unit 12 controls the transfer drive unit 14a and the fixing drive unit 14b so that the speed difference ΔV determined by the transfer speed determination unit 11 is obtained.

The transport speed determination unit 11 reads from the storage unit 13 the length L of the paper P sent from the paper feed cassette determination unit 15 along the transport direction, the target slack amount S read from the storage unit 13. Using the process speed Vp, which is the peripheral speed of the photoconductor drum 31b, and the distance D between the transfer nip portion 31g and the fixing nip portion 32c read from the storage unit 13, at the peripheral speed of the fixing roller 32a and the pressurizing roller 32b. The speed difference ΔV between a certain fixing peripheral speed Vf and the process speed Vp,
S × Vp / (LD)
To determine as.

That is, the fixing peripheral speed Vf is S × Vp / (LD) rather than the process speed Vp.
Decide to be slower.

Here, the process speed Vp, which is the peripheral speed of the photoconductor drum 31b, and the transfer peripheral speed Vt of the transfer roller 31d are the same value, which means the paper transport speed in the transfer nip portion 31g. Similarly, the fixing peripheral speed Vf means the paper conveying speed in the fixing nip portion 32c.

The transport speed determination unit 11 calculates the speed difference ΔV from the above equation using the target slack amount S, but the speed difference ΔV may be calculated using a value smaller than the target slack amount S.

The speed difference ΔV calculated as described above is sent to the transport speed control unit 12 together with other roller rotation speed information, and the transport speed control unit 12 individually controls the rotation drive speed of each roller.

Regarding the target slack amount S, a preferable value may change depending on the type of the paper P, for example, the thickness (basis weight g / m ² ) and the presence or absence of the surface coating. Therefore, the storage unit 13 is set to the type of the paper P. A plurality of target slack amounts S are stored in the storage unit 13 accordingly, and the speed difference ΔV of the fixing peripheral speed Vf from the transfer peripheral speed Vt is determined using the target slack amount S according to the type of the paper P. May be good.

As described above, according to the image forming apparatus 100, the paper P is conveyed from the transfer unit 31 to the fixing unit 32 so that the amount of slack S is preferable. As a result, even when an image is formed on a paper having a different size of the paper P, particularly a paper having a different length along the transport direction, image deterioration such as image deviation (transfer deviation) and stains on the rear edge of the paper P are eliminated. Can be prevented.

(Example 1)
An embodiment of the image forming apparatus 100 according to the first embodiment will be described below.

FIG. 7 is a table showing an example of the occurrence of stains on the rear edge of the paper of the conventional image forming apparatus. FIG. 8 is a table showing an example of a state in which stains on the rear edge of the paper of the image forming apparatus according to the first embodiment of the present invention are generated.

FIG. 7 shows the transport direction of the paper P under the condition that the speed difference ΔV between the transfer peripheral speed Vt and the fixing peripheral speed Vf is constant (0.2%), that is, the fixing peripheral speed Vf is 0.2% slower than the transfer peripheral speed Vt. The result of confirming whether or not the rear edge of the paper is contaminated when the image is formed on the papers having different lengths according to the above is displayed together with the amount of slack under each paper condition.

The paper P used for image formation is so-called standard plain paper with a basis weight of 64 g / m ² , and there are three types: A4 horizontal feed (210 mm), A4 vertical feed (297 mm), and A3 vertical feed (420 mm). An image was formed on the image. Although the speed difference ΔV is constant at 0.2%, the amount of slack S generated when an image is formed on each paper P is A4 horizontal feed, A4 vertical feed, and A3 vertical feed according to the above-mentioned calculation formula. In this order, the values are 0.23 mm, 0.40 mm, and 0.65 mm.

From FIG. 7, when the speed difference ΔV is controlled to be constant, the slack amount S increases as the length of the paper P forming the image along the transport direction increases, and the A3 length having the longest length along the transport direction increases. It can be seen that the rear edge of the paper is contaminated under the feed conditions.

The transfer peripheral speed Vt at this time is 175 mm / s, the fixing peripheral speed is 174.65 mm / s, and the process speed Vp is the same value as the transfer peripheral speed Vt. The distance between the transfer nip portion 31g and the fixing nip portion 32c is 95.5 mm.

In FIG. 8, when the speed difference ΔV between the transfer peripheral speed Vt and the fixing peripheral speed Vf is changed according to the length along the transport direction of the paper P forming the image, stains occur on the rear edge of the paper. It is a figure which showed the result of having confirmed. The distance between the transfer nip portion 31g and the fixing nip portion 32c is 95.5 mm, which is the same as the condition shown in FIG.

Similar to FIG. 7, there are three types of paper used for image formation: A4 horizontal feed (210 mm), A4 vertical feed (297 mm), and A3 vertical feed (420 mm), and the speed difference when forming an image on each paper. ΔV was 0.2%, 0.1%, and 0.1%, respectively. The corresponding fixing peripheral speeds are 174.65 mm / s, 174.83 mm / s, and 174.83 mm / s, respectively. The amount of slack generated under each paper condition is 0.23 mm, 0.20 mm, and 0.32 mm, respectively.

From FIG. 8, it can be seen that the rear edge of the paper is not contaminated under any of the conditions.

Summarizing the above, it is possible to prevent the rear edge of the paper from being contaminated by controlling the speed difference ΔV to be changed based on the length information along the transport direction of the paper P. Further, from the result of FIG. 8, a plurality of target slack amounts S are set so as to correspond to the length of the paper P along the transport direction, and the speed difference ΔV is set according to the length of the paper to be transported along the transport direction. It can be seen that the same result can be obtained even if it is set. Further, in FIG. 8, since the rear edge of the paper is not contaminated under any of the conditions, the target slack amount S is set to, for example, 0.2 mm regardless of the length in the paper transport direction, and is along the transport direction of the paper P. It can be seen that the velocity difference ΔV may be determined based on the length. Further, as a result of FIG. 7, even if the slack amount S of the A4 vertical feed is 0.4 mm, the rear end stain is not generated, so that the target slack amount S may be set to 0.4 mm.

As described above, the paper transport speed (fixing peripheral speed Vf) in the fixing nip portion 32c is controlled to have a predetermined speed difference ΔV with respect to the paper transport speed (process speed Vp) in the transfer portion, and the speed is controlled. By changing the difference ΔV based on the length information along the conveying direction of the paper P, it becomes possible to effectively prevent the rear edge of the paper from becoming dirty.

Further, by determining the speed difference ΔV using the target slack amount S and the length along the transport direction of the paper P, it becomes possible to effectively prevent the rear edge of the paper from being soiled.

(Second Embodiment)
Hereinafter, the image forming apparatus 100a according to the second embodiment of the present invention will be described with reference to the drawings.

FIG. 9 is a cross-sectional view showing the slack of the paper P in the image forming apparatus 100a according to the second embodiment of the present invention. FIG. 10 is a block diagram showing a configuration of an image forming apparatus 100a according to a second embodiment of the present invention.

The image forming apparatus 100a according to the second embodiment is different in that the control performed on the fixing unit 32 in the first embodiment is performed on the resist unit 36, and the other configurations are the same. Therefore, different points will be described, and the same points will be omitted.

As shown in FIG. 9, the paper P3 is loosely conveyed between the resist section 36 and the transfer section 31 by the pre-transfer guides 31h and 31h. Therefore, by controlling the transfer speed of the resist unit 36 to be faster than the transfer speed of the transfer unit 31, it is possible to suppress the occurrence of image deterioration such as image misalignment on the paper P3 (same as the first embodiment). The reason) is that in the case of paper having a long length along the conveying direction of the paper P, the slack becomes too large, and when the rear end Ep of the paper passes through the resist nip portion 36b, it rubs against the resist roller 36a and becomes dirty. Or (the same phenomenon as in the first embodiment), the paper may come too close to the transfer nip portion 31g, and abnormal discharge (discharge marks / scattering) may occur.

From here, as in the first embodiment, a method of preventing the occurrence of image defects by using the amount of slack S will be specifically described.

Further, as shown in FIG. 10, the image forming apparatus 100a has a resist driving unit 14c which is a motor, and the resist driving unit 14c drives the resist roller 36a.

The transfer speed determination unit 11 determines the transfer roller 31d, the fixing roller 32a, and the pressurizing roller based on the length of the paper P determined by the paper feed cassette determination unit 15 and the target slack amount S stored in advance in the storage unit 13. Determine the peripheral speed of 32b. The target slack amount S may be the same as or different from the target slack amount between the transfer unit 31 and the fixing unit 32. The target slack amount S is a preferable slack amount on the paper P, and may be a slack amount that does not cause image deterioration.

The transfer speed control unit 12 controls the transfer drive unit 14a and the resist drive unit 14c so that the peripheral speed is determined by the transfer speed determination unit 11, and drives the transfer roller 31d and the resist roller 36a.

In the transport speed determination unit 11, the target slack amount is S, the length of the paper P along the transport direction is L, the process speed which is the peripheral speed of the photoconductor drum 31b is Vp, and the resist nip unit 36b and When the distance between the transfer nip portions 31g is D, the peripheral speed difference between the peripheral speed of the transfer roller 31d and the peripheral speed of the resist roller 36a is S × Vp / (LD).
To determine as.

Then, the peripheral speed of the resist roller 36a is S × Vp / (LD) higher than the peripheral speed of the transfer roller 31d.
The peripheral speed of the resist roller 36a and the peripheral speed of the transfer roller 31d are determined so as to be as fast as possible.

(Example 2)
An example of the image forming apparatus 100a according to the second embodiment will be described below.

FIG. 11 is a table showing an example of the image state of the conventional image forming apparatus. FIG. 12 is a table showing an example of an image state of the image forming apparatus according to the second embodiment of the present invention.

As shown in FIG. 11, in any of A4 horizontal feed, A4 vertical feed, and A3 vertical feed, the resist peripheral speed Vr, which is the peripheral speed of the resist roller 36a, and the transfer peripheral speed Vt, which is the peripheral speed of the transfer roller, are set. When the speed difference ΔV was fixed at 0.3%, banding occurred for the A4 horizontal feed, but no discharge marks or scattering occurred. With regard to A4 vertical feed, neither banding nor discharge marks / scattering occurred. Banding did not occur with regard to A3 vertical feed, but discharge marks and scattering occurred. Here, banding means that the paper P does not bend between the resist portion 36 and the transfer portion 31, and the paper P abuts and rubs against the pre-transfer guides 31h and 31h between the transfer nip portion 31g and the resist nip portion 36b. It happens because of that. That is, banding is an image defect due to so-called transfer deviation caused by a decrease in the paper transport speed, that is, the transfer peripheral speed Vt in the transfer unit 31. Discharge marks and scattering are phenomena that occur when the paper P bends more than necessary between the transfer nip portion 31g and the resist nip portion 36b, causing the paper P to approach the photoconductor drum 31b at the transfer nip portion 31g. is there. That is, the image defect is caused by abnormal discharge or rubbing caused by the paper P approaching or coming into contact with the photoconductor drum 31b on the inlet side of the transfer nip portion 31g. The process speed is the same as the transfer peripheral speed Vt and is 175 mm / s. The slack amounts in each of the A4 horizontal feed, the A4 vertical feed, and the A3 vertical feed are 0.49 mm, 0.75 mm, and 1.12 mm.

On the other hand, FIG. 12 shows the occurrence of image defects in the image forming apparatus 100a according to the second embodiment. FIG. 12 shows the result of controlling the speed difference ΔV of the resist peripheral speed Vr from the transfer peripheral speed Vt to be changed according to the length along the conveying direction of the paper P, which is not constant. Specifically, the speed difference ΔV is 0.5%, 0.3%, 0.2% in the order of A4 horizontal feed, A4 vertical feed, and A3 vertical feed, and the length along the transport direction of the paper P. It is changed by. The resist peripheral speed Vr at this time is 175.88 mm / s, 175.53 mm / s, and 175.35 mm / s in the order of A4 horizontal feed, A4 vertical feed, and A3 vertical feed.

The amount of slack is 0.82 mm, 0.76 mm, and 0.75 mm in the order of A4 horizontal feed, A4 vertical feed, and A3 vertical feed. The process speed Vp is the same as the transfer peripheral speed Vt and is 175 mm / s. The process speed Vp is the paper transfer speed at the transfer nip portion 31 g, and the resist peripheral speed Vr is the same as the paper transfer speed at the resist nip portion 36b. The distance between the resist nip portion 36b and the transfer nip portion 31g is 45.1 mm.

From FIG. 8, it can be seen that when the speed difference ΔV is not constant and is controlled to be changed according to the length along the conveying direction of the paper P, neither banding nor discharge marks / scattering occur under any condition.

From the above results, it can be seen that under the conditions of this embodiment, the speed difference ΔV may be set so that the amount of slack is 0.7 mm to 0.8 mm. Regarding banding, if the pre-transfer guides 31h and 31h are movable, it can be prevented even if the slack amount S is 0.7 mm or less. Therefore, even if the target slack amount S is smaller than 0.7 mm, it can be prevented. Good.

(Third Embodiment)
Hereinafter, the image forming apparatus 100b according to the third embodiment of the present invention will be described with reference to the drawings.

FIG. 13 is a schematic side sectional view showing the configuration of the image forming apparatus 100a according to the third embodiment of the present invention. FIG. 14 is a block diagram showing a configuration of an image forming apparatus 100a according to a third embodiment of the present invention.

The image forming apparatus 100b according to the third embodiment is different from the image forming apparatus 100 according to the first embodiment in that it includes a paper size detecting sensor 16 for detecting the size of the paper P, and has other configurations. Are the same. Therefore, different points will be described, and the same points will be omitted.

As shown in FIG. 13, in the image forming apparatus 100b, the paper size detection sensor 16 is installed in the transport path upstream of the resist unit 36. The paper size detection sensor 16 detects the size of the conveyed paper P. The paper size detection sensor 16 measures, for example, the time from the passage of the front end of the paper P to the passage of the rear end at the reference point of the transport path of the paper P, and transports the paper P based on the measured time and the transport speed. The length of the paper P along the direction may be detected.

As shown in FIG. 14, the length of the paper P along the transport direction detected by the paper size detection sensor 16 is sent to the transport speed determination unit 11.

For example, since the size of the paper P placed on the output tray 34 is not fixed, when the paper P placed on the output tray 34 is conveyed, the paper detected by the paper size detection sensor 16 The length of P is used to determine the peripheral speeds of the transfer roller 31d, the fixing roller 32a, and the pressure roller 32b.

Further, although the size of the paper P stored in the paper feed cassettes 33a and 33b is fixed, even if the operator mistakenly stores the paper P of a different size, the paper size detection sensor 16 detects the paper along the transport direction. Since the length of P can be detected correctly, the paper P can be conveyed so as to have a preferable amount of slack.

(Other embodiments)
In the first to third embodiments, the transfer speed determination unit 11 calculates the transfer speed of the transfer unit 31, the transfer speed of the fixing unit 32, and the transfer speed of the resist unit 36. For example, the paper along the transfer direction. For each length of P, the preferable transfer speed of the transfer unit 31, the transfer speed of the fixing unit 32, and the transfer speed of the resist unit 36 are stored in the storage unit 13 in advance, and the paper feed cassette determination unit 15 or the paper size detection sensor The length P of the paper along the conveying direction may be detected by 16 and the conveying speed corresponding to the length may be selected from those stored in the storage unit 13.

In the first to third embodiments, the image forming apparatus 100, 100a, 100b is a monochrome image forming apparatus, but may be, for example, an intermediate transfer type color multifunction device capable of forming a full-color image. Specifically, it may be a so-called tandem type color image forming apparatus in which a plurality of electrostatic latent image carriers (specifically, photoconductors) on which toner images are formed are arranged side by side in a predetermined direction.

The present invention is not limited to the embodiments described above, and can be implemented in various other forms. Therefore, such embodiments are merely exemplary in all respects and should not be construed in a limited way. The scope of the present invention is shown by the claims and is not bound by the text of the specification. Furthermore, all modifications and modifications that fall within the equivalent scope of the claims are within the scope of the present invention.

2 Image reading unit 3 Image forming unit 4 Document transport unit 11 Transport speed determination unit 12 Transport speed control unit 13 Storage unit 14a Transfer drive unit 14b Fixing drive unit 14c Resist drive unit 15 Paper feed cassette discrimination unit (sheet information discrimination unit)
16 Paper size detection sensor (sheet information discriminator)
21 Document mounting table 22 Document passing section 31 Transfer section (first transport section)
31a Optical scanning device 31b Photoreceptor drum 31c Developing device 31d Transfer roller (roller of first transport unit)
31e Drum cleaning device 31f Charger 31g Transfer nip section 31h Pre-transfer guide 32 Fixing section (second transport section)
32a Fixing roller (roller of the second conveyor)
32b Pressurized roller (roller of the second conveyor)
32c Fixing nip 32d Heating roller 32e Fixing belt 32f Pre-fixing guides 33a, 33b Paper feed cassette 34 Paper output tray 36 Resist part (second transport part)
36a Resist roller (roller of the second conveyor)
36b Resist nip part 37a, 37b, 37c Pickup part 100 Image forming device P, Pa, Pb, P1, P2, P3 Paper (sheet material)
L Line connecting the transfer nip and the fixing nip Vp process speed (sheet material transfer speed, paper transfer speed)
Vt transfer peripheral speed (sheet material transfer speed, paper transfer speed)
Vf fixing peripheral speed (sheet material transfer speed, paper transfer speed)

Claims (9)

A first transport unit that performs image forming processing to form an image on the sheet material and transports the sheet material,
A second transport unit located on the upstream side or the downstream side of the first transport unit and transporting the sheet material,
A transport speed control unit that controls the transport speed of the sheet material in the first transport unit and the second transport unit, and
The sheet information determination unit for determining the length information along the transport direction of the sheet material is provided.
The transport speed control unit controls the transport speed of the sheet material in the second transport unit so as to have a predetermined speed difference with respect to the sheet material transport speed in the first transport unit, and the speed difference is An image forming apparatus that is changed based on the length information along the transport direction of the sheet material determined by the sheet information determination unit. The image forming apparatus according to claim 1.
During the time during which the sheet material is maintained in a state of being transported by both the first transport unit and the second transport unit, the difference in the transport amount of the sheet material generated by the speed difference is defined as the slack amount.
An image forming apparatus that changes the speed difference based on length information along a conveying direction of the sheet material so that the amount of slack is equal to or less than a predetermined value. The image forming apparatus according to claim 2.
A storage means for storing the slack amount of the sheet material in advance as a target slack amount is provided.
An image forming apparatus including a transport speed determining unit that determines the speed difference so that the amount of slack of the sheet material is equal to or less than the target amount of slack stored in the storage means. The image forming apparatus according to claim 3.
A plurality of the target slack amounts are set so as to correspond to the type of the sheet material and are stored in the storage unit.
The transport speed determination unit is an image forming apparatus that determines the speed difference using a target slack amount corresponding to a type of sheet material determined by the sheet information determination unit. The image forming apparatus according to claim 3 or 4.
The target slack amount stored in the storage means is an image forming apparatus that can be changed by an operation unit. The image forming apparatus according to any one of claims 3 to 5.
The first transport unit is a transfer unit and
The transfer speed determining unit sets the target slack amount to S, the length of the sheet material along the transfer direction to L, the transfer speed at the transfer unit to Vp, and the distance between the transfer unit and the second transfer unit. When D is set, the speed difference is S × Vp / (LD).
An image forming apparatus that determines to be. The image forming apparatus according to claim 6.
The second transport unit is a fixing unit installed on the downstream side of the transfer unit.
In the transfer speed determining unit, the sheet transfer speed of the fixing unit is S × Vp / (LD) higher than the sheet transfer speed of the transfer unit.
An image forming apparatus that determines to be slow only. The image forming apparatus according to claim 6.
The second transport unit is a resist unit installed on the upstream side of the transfer unit.
In the transfer speed determining unit, the sheet transfer speed of the resist unit is S × Vp / (LD) higher than the sheet transfer speed of the transfer unit.
An image forming device that determines to be as fast as possible. The image forming apparatus according to any one of claims 3 to 8.
It has at least one sheet storage unit for storing the sheet material, and has at least one sheet storage unit.
The storage unit stores size information including the size and storage direction of the sheet material set in the sheet storage unit and type information including the thickness and type of the sheet material corresponding to the sheet storage unit.
The transport speed determining unit is an image forming apparatus that determines the speed difference based on the size information, the type information, and the target slack amount corresponding to the type information stored in the storage unit, respectively.

Images