JP2009210864A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always print an image on a recording medium with desired image quality regardless of thickness of the recording medium. <P>SOLUTION: An image forming apparatus includes a driving means 18 driving and rotating a transfer roller 16, a guide means 21 capable of guiding the recording medium 17 before reaching a transfer part by changing a guide state, and a control means 5 switching drive between submissive drive that the transfer roller 16 is driven by rotation of a support roller 11 and forcible drive that it is forcibly rotated by drive by the driving means, and allows the guide means 21 to guide the recording medium 17 so as to come into contact with a transfer belt 12 laid on a support roller 11b before the recording medium 17 reaches the transfer part 14 in the forcible drive. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus in which a toner image is transferred to a recording medium by a copying machine, a laser beam printer, a facsimile, or a complex machine thereof.

  Conventionally, as an image forming apparatus, in a transfer unit that transfers a toner image to a recording medium, a driving force from a driving source is transmitted to a photosensitive drum, and an electromagnetic clutch is turned on and transmitted to a transfer roller, A known transfer roller is driven by forcibly driving the transfer roller and turning off the electromagnetic clutch (see, for example, Patent Document 1).

JP-A-9-325620

  However, in the conventional image forming apparatus, since the photosensitive drum and the transfer roller are rotated so as to be synchronized with each other through a gear, printing with a desired image quality cannot be performed due to a difference in the thickness of the recording medium passing therethrough. There is.

  For example, when an image is formed on a material having a thickness larger than that of a normally used recording medium, the photosensitive drum is hard, so that only the transfer roller is deformed and the conveyance center is shifted to the transfer roller side. For this reason, the moving speed of the recording medium becomes faster than the moving speed of the normal recording medium, and the print image magnification increases.

  Further, although a transfer voltage is applied to the transfer roller, if the recording medium comes into contact with the transfer roller before passing between the photosensitive drum and the transfer roller, a sudden discharge occurs before the transfer. . As a result, there is a problem that the toner is scattered to an unnecessary portion, and the transfer performance is deteriorated.

  Therefore, an object of the present invention is to provide an image forming apparatus that can always print on a recording medium with a desired image quality regardless of the thickness of the recording medium.

As a means for solving the above problems, the present invention provides:
A toner image is formed based on the electrostatic latent image formed by exposure writing on the photosensitive drum, the toner image is primarily transferred to a transfer belt, and the transfer belt is further transferred to the primary transferred toner image. An image forming apparatus configured to perform secondary transfer onto a recording medium that passes through a transfer portion between a support roller that is hung and a transfer roller that is disposed to face the support roller.
Drive means for rotationally driving the transfer roller;
Guide means capable of guiding the recording medium before reaching the transfer portion by changing the guide state;
Switching between a driven drive in which the transfer roller is driven by the rotation of the support roller and a forced drive in which the transfer roller is forcibly rotated by the drive of the drive means. In the forced drive, before the recording medium reaches the transfer portion by the guide means, A control unit that guides the transfer belt placed on the support roller so as to contact the transfer belt;
It is equipped with.

A magnification priority selection means for selecting a magnification priority mode for changing a transfer magnification when the toner image formed on the transfer belt is transferred to a recording medium;
It is preferable that the control unit drives the transfer roller to be driven by operating the magnification priority selection unit.

Image quality priority selection means for selecting an image quality priority mode that prioritizes the image quality when the toner image formed on the transfer belt is transferred to a recording medium;
Preferably, the control unit forces the transfer roller to be driven by operating the image quality priority selection unit.

  With the above configuration, it is possible to select driven driving or forced driving according to the difference in printing conditions. For example, when the recording medium is thin or when it is desired to print with priority on the printing magnification, the transfer roller is driven. Accordingly, the transfer roller follows the recording medium passing through the transfer portion, and the toner image formed on the transfer belt can be transferred to the recording medium at a desired magnification. On the other hand, when the recording medium is thick or when it is desired to print with priority on image quality, the transfer roller is forcibly driven, and the recording medium comes into contact with the transfer belt before reaching the transfer portion by the guide means. For this reason, it is possible to prevent discharge from the transfer roller to the recording medium before reaching the transfer portion.

The guide means includes
A first guide plate that guides a surface on the support roller side of a recording medium to be conveyed in a conveyance path from a pair of conveyance rollers to the transfer unit;
A second guide plate rotatable between a forced guide position for forcibly guiding the surface on the support roller side and an auxiliary guide position positioned in a separating direction from the forced guide position toward the transfer roller;
May be provided.

  When the controller forcibly drives the transfer roller, it is preferable to determine the angular velocity ω1 of the transfer roller so that the following equation is satisfied.

  With the above-described configuration, even if the recording medium is thick, the transport speed by the support roller and the transport speed by the transfer roller can be substantially matched at the center in the thickness direction of the recording medium in consideration of the thickness. Therefore, it is possible to perform printing with a desired image quality by preventing the recording medium from being displaced at the transfer portion.

  It is preferable that the control means increases the reference system speed during driven driving compared to the reference system speed during forced driving.

  Here, the reference system speed is an image forming speed on the recording medium, and the conveyance speed of the recording medium is adjusted so that the reference system speed is constant.

  The control means may determine the reference system speed Sv ′ at the time of driven driving so as to satisfy the following expression with respect to the reference system speed Sv at the time of forced driving.

  With the above configuration, the reference system speed during forced driving can be determined in consideration of the thickness t of the recording medium, so that image formation can be performed in a good state and a high-quality image can be obtained.

Monochrome determination means for determining whether printing is in monochrome mode or not,
The control unit preferably drives the transfer roller to be driven when the monochrome determination unit determines that the mode is the monochrome mode.

  According to the present invention, in addition to the normal driven drive printing, the transfer roller is forcibly driven by forcible drive, and the recording medium is brought into contact with the transfer belt before reaching the transfer portion by the guide means. It becomes possible to print with high image quality regardless of the thickness of the image.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a tandem color image forming apparatus to which an electrophotographic technique is applied according to this embodiment. The image forming apparatus generally includes an image forming unit 1, a transfer unit 2, an exposure unit 3, a recording medium supply unit 4, a control unit 5 (see FIG. 3), and the like.

  The image forming unit 1 includes a charging charger 8, a developing roller 9, a cleaning blade 10, and the like around the photosensitive drum 7 in the casing 6. The image forming units 1 are arranged at four locations along the intermediate transfer belt 12 of the transfer unit 2, and image formation of yellow (Y), magenta (M), cyan (C), and black (Bk) is performed from the left side, respectively. As a result, a color image is formed on the surface of the intermediate transfer belt 12.

  The transfer unit 2 spans the intermediate transfer belt 12 between a pair of support rollers 11a and 11b, drives the support roller 11b by a driving means (not shown), and circulates the intermediate transfer belt 12 in the direction of the arrow. A primary transfer unit 13 and a secondary transfer unit 14 are provided.

  The primary transfer unit 13 includes a primary transfer roller 15 that faces the photosensitive drum 7 of each of the image forming units 1 with the intermediate transfer belt 12 sandwiched therebetween. The primary transfer roller 15 applies a positive voltage to the back surface of the intermediate transfer belt 12.

  The secondary transfer unit 14 includes a secondary transfer roller 16 (transfer roller) opposed to one support roller 11b (a roller located on the right side in FIG. 1) with the intermediate transfer belt 12 interposed therebetween. The transferred toner image is transferred to the recording medium 17 (for example, paper).

  As shown in FIG. 2C, the driving force of the motor 18 is transmitted to the secondary transfer roller 16 through the rotating shaft 18a. The rotating shaft 18a is provided with an electromagnetic clutch 19, and when the electromagnetic clutch 19 is turned on, the driving force of the motor 18 is transmitted to the rotating shaft 18a, and is turned off when turned off.

  As shown in FIG. 2A, a guide means including a first guide plate 20 and a second guide plate 21 is provided at the entrance portion of the secondary transfer portion 14. Both guide plates 20 and 21 form a transport path from the pair of transport rollers 24 to the secondary transfer unit 14 through which the recording medium 17 passes. The front end portion of the first guide plate 20 is formed in a twisted shape and extends in the vicinity of the support roller 11b.

  The second guide plate 21 is obtained by bending a plate-like body into a substantially C-shaped cross section, constitutes a part of the transport path, and mainly includes two bent portions (first bent portion 21a and second bent portion). 21b) is guided in sliding contact with the recording medium 17 passing therethrough. The second guide plate 21 is provided so as to be rotatable about the support shaft 21c, and one end (the end opposite to the first bent portion 21a) is attached by an urging member (here, a compression coil spring 21d). It is energized.

  The eccentric guide 22 abuts on the linear portion 21e in the vicinity of the second bent portion 23, and the second guide plate 21 rotates when the eccentric cam 22 rotates. As a result, the second guide plate 21 is positioned at the forced guide position shown in FIG. 2A and the auxiliary guide position shown in FIG.

  The second guide plate 21 is positioned at the forced guide position when the secondary transfer roller 16 is forcibly driven. The second guide plate 21 at the forcible guide position is brought into sliding contact with the recording medium 17 passing through both the bent portions 21a and 21b, and the recording medium 17 is contacted with the support roller 11a via the intermediate transfer belt 12 by the secondary transfer portion 14. Force contact in front of. As a result, the recording medium 17 abuts against the intermediate transfer belt 12 in the region where the support roller 11 is located before reaching the secondary transfer portion 14, and a dimension that allows the recording medium 17 and the intermediate transfer belt 12 to contact is secured to 3 mm or more. It becomes possible to do.

  The second guide plate 21 is positioned at the auxiliary guide position shown in FIG. 2B when the secondary transfer roller 16 is driven. In this case, the second guide plate 21 only prevents the recording medium 17 conveyed by the pair of conveying rollers 24 from being conveyed to other than the secondary transfer unit 14.

  The exposure unit 3 irradiates the photosensitive drum 7 with laser light to form an electrostatic latent image corresponding to image data read by a scanner (not shown).

  The recording medium supply unit 4 sequentially conveys the recording medium 17 accommodated in the cassette 23 to the secondary transfer unit 14 via the conveyance roller 24. The toner image is transferred to the recording medium 17 conveyed to the secondary transfer unit 14, and the toner image transferred by the fixing unit 25 is fixed, and then is carried out to the discharge tray 26.

  As shown in FIG. 3, the control unit 5 drives and controls the units 1 to 4 based on an input signal from the operation panel 27. The operation panel 27 is provided with buttons for selecting various modes.

  For example, buttons 27a to 27d for selecting an image quality priority mode, a magnification priority mode, a monochrome mode, and a color mode are provided. Here, the image quality priority mode is a mode in which optical reading is performed at a resolution higher than the output resolution, and this is subjected to digital scaling to form an image. The magnification priority mode is a mode in which images are repeatedly formed while maintaining the magnification desired by the user. The monochrome mode is a mode in which a monochrome image is formed using a single color toner such as black. The color mode is a mode for forming a color image using four colors of toner.

  Next, the operation of the image forming apparatus having the above configuration, particularly the operation in the transfer unit 2 will be described.

  At the time of image formation, color print data obtained by reading an image by an image reading unit (not shown) or image data output from a personal computer or the like is subjected to predetermined signal processing by the control unit 5 and then yellow (Y ), Magenta (M), cyan (C), and black (Bk) are supplied to the image forming units 1 as image signals of respective colors. Each image forming unit 1 is projected with a laser beam modulated with an image signal on each photosensitive drum 7 to form an image latent image. A yellow, magenta, cyan, and black toner image is formed on each photosensitive drum 7. The formed yellow, magenta, cyan, and black toner images are primarily transferred onto the moving intermediate transfer belt 12 by being sequentially superimposed by the action of the primary transfer roller 15. The toner image formed on the intermediate transfer belt 12 in this way moves to the secondary transfer unit 14 as the intermediate transfer belt 12 moves.

  The secondary transfer unit 14 is driven and controlled as follows according to the mode selected on the operation panel 27.

  That is, when the image quality priority mode is selected, the driving force of the motor 18 is transmitted to the secondary transfer roller 16 via the rotating shaft 18a by turning on the electromagnetic clutch 19. In this case, the rotational speed of the secondary transfer roller 16 is adjusted so that the feed speed of the secondary transfer roller 16 becomes equal to the feed speed of the support roller 11. Specifically, the angular velocity ω1 of the secondary transfer roller 16 is determined so that the following equation is established. In this case, the motor 18 is driven by PLL (Phase Locked Loop) control.

  In the image quality priority mode, the eccentric cam 22 is rotated to rotate the second guide plate 21 to the forced guide position shown in FIG. As a result, the second bent portion 23 contacts the recording medium 17 supplied from the recording medium supply unit 4 before reaching the secondary transfer portion 14 from the conveying roller 24. The recording medium 17 is forcibly pressed against the intermediate transfer belt 12 at the portion where the support roller 11 is located. Here, the length of the recording medium 17 in contact with the intermediate transfer belt 12 can be secured to 3 mm or more.

  As described above, in the image quality priority mode, since the secondary transfer roller 16 is rotationally controlled as described above, the support roller 11b around which the intermediate transfer belt 12 is stretched regardless of the thickness of the recording medium 17 is controlled. The feeding speed of the recording medium 17 can be made equal on the side and the secondary transfer roller 16 side. Therefore, on the secondary transfer roller 16 side, almost no slip occurs with respect to the recording medium 17, and the transfer state by the secondary transfer roller 16 is good regardless of the amount of biting in the secondary transfer roller 16. Therefore, it is possible to obtain a high quality image.

  Further, since the recording medium 17 can be pressed against the support roller 11b via the intermediate transfer belt 12 before reaching the secondary transfer portion 14 by the second guide plate 21, the recording medium 17 is transferred from the secondary transfer roller 16 before transfer. 17 can be prevented from being discharged. Therefore, in combination with the rotational drive control of the secondary transfer roller 16, the transfer state by the secondary transfer roller 16 can be further improved.

  On the other hand, in the magnification priority mode, the electromagnetic clutch 19 is turned off so that the driving force of the motor 18 is not transmitted to the secondary transfer roller 16 (the electromagnetic clutch 19 is eliminated and the motor 18 is stopped). It is good.) As a result, the recording medium 17 passing through the secondary transfer portion 14 moves due to friction with the intermediate transfer belt 12 that moves according to the rotation of the support roller 11, and the secondary transfer roller 16 is driven to rotate due to friction with the recording medium 17. To do. Therefore, when the recording medium 17 is thin or the like and there is almost no slip between the intermediate transfer belt 12 and the recording medium 17 and between the recording medium 17 and the secondary transfer roller 16, the recording medium 17 is displaced. Therefore, it is possible to print at a desired magnification. In addition, even when the recording medium 17 is thick, the guide position is in the state shown in FIG. Further, although the winding around the intermediate transfer belt 12 is reduced, the transfer current can be reduced in the case of monochrome one color (1200 (V) in the case of color, but 800 (V in the case of monochrome). ) Degree), no discharge before transfer occurs.

  The image forming apparatus according to the present invention is not limited to the configuration of the above embodiment, and various modifications can be made.

  For example, the system speed (the copy creation speed per sheet including the scanning speed of the scanner and the return speed, that is, the image forming speed on the recording medium 17) is changed as follows in the magnification priority mode and the image quality priority mode. You may do it.

  That is, in the magnification priority mode in which the secondary transfer roller 16 is driven, it is preferable to correct the reference system speed Sv ′ according to the following equation with respect to the reference system speed Sv in the image quality priority mode that is forcibly driven. .

  In this case (in the magnification priority mode), by increasing the moving speed of the intermediate transfer belt 12, the recording medium 17 is adjusted so that the corrected reference system speed Sv ′ matches the writing speed of the laser on the photosensitive drum 7. What is necessary is just to increase the conveyance speed. The conveyance speed of the recording medium 17 decreases when the system speed is slower than a value that matches the writing speed of the photosensitive drum 7 by the laser, and conversely increases when it is faster.

  The system speed may be changed automatically based on the type of recording medium 17 (paper type, paper thickness, etc.). For example, if the paper type is different, the friction coefficient with the intermediate transfer belt 12 and the secondary transfer roller 16 is different. Therefore, the drive is driven when the friction coefficient is larger than a predetermined predetermined friction coefficient, and the friction coefficient is smaller. What is necessary is just forced driving. Further, if the paper thickness is different, the driven drive is used when the paper thickness is smaller than a predetermined paper thickness, which is a reference, and the forced drive is used when the paper thickness is larger.

  In addition to the change in the system speed, as described above, during the forced driving, the rotational speed of the secondary transfer roller 16 is controlled, or the recording medium 17 is guided at the forced guide position by the second guide plate 21. By doing so, it is preferable in that the appropriate printing on the recording medium 17 can be performed.

  Further, when printing on the recording medium 17 is performed in the monochrome mode, the secondary transfer roller 16 may be forcibly driven. Whether or not the mode is the monochrome mode may be determined based on an operation on the operation panel 27, or may be determined based on the color data of the read image.

1 is a schematic view of an image forming apparatus according to an embodiment. 1A is an enlarged schematic explanatory view showing a state where the second guide plate is moved to the forced guide position in the secondary transfer portion of FIG. 1, and FIG. 1B is a diagram illustrating the second guide plate positioned at the auxiliary guide position. An enlarged schematic explanatory view showing a state, (c) is a schematic view showing a drive mechanism of a secondary transfer roller. 1 is a block diagram of an image forming apparatus according to an embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming unit 2 ... Transfer unit 3 ... Exposure unit 4 ... Recording medium supply unit 5 ... Control unit 6 ... Casing 7 ... Photoconductor drum 8 ... Charger charger 9 ... Developing roller 10 ... Cleaning blade 11a, 11b ... Support roller 12 ... Intermediate transfer belt 13 ... Primary transfer portion 14 ... Secondary transfer portion 15 ... Primary transfer roller 16 ... Secondary transfer roller (transfer roller)
17 ... Recording medium 18 ... Motor (drive means)
18a ... Rotating shaft 19 ... Electromagnetic clutch 20 ... First guide plate 21 ... Second guide plate (guide means)
21a ... first bent portion 21b ... second bent portion 21c ... support shaft 21d ... compression coil spring 21e ... linear portion 22 ... eccentric cam 23 ... cassette 24 ... conveying roller 25 ... fixing unit 26 ... discharge tray 27 ... operation panel 27a ... image quality Priority mode button 27b ... Magnification priority mode button 27c ... Monochrome mode button 27d ... Color mode button

Claims (8)

A toner image is formed based on the electrostatic latent image formed by exposure writing on the photosensitive drum, the toner image is primarily transferred to a transfer belt, and the transfer belt is further transferred to the primary transferred toner image. An image forming apparatus configured to perform secondary transfer onto a recording medium that passes through a transfer portion between a support roller that is hung and a transfer roller that is disposed to face the support roller.
Drive means for rotationally driving the transfer roller;
Guide means capable of guiding the recording medium before reaching the transfer portion by changing the guide state;
Switching between a driven drive in which the transfer roller is driven by the rotation of the support roller and a forced drive in which the transfer roller is forcibly rotated by the drive of the drive means. In the forced drive, before the recording medium reaches the transfer portion by the guide means, A control unit that guides the transfer belt placed on the support roller so as to contact the transfer belt;
An image forming apparatus comprising: A magnification priority selection means for selecting a magnification priority mode for changing a transfer magnification when the toner image formed on the transfer belt is transferred to a recording medium;
The image forming apparatus according to claim 1, wherein the control unit is configured to drive the transfer roller as a driven drive when the magnification priority selection unit is operated. Image quality priority selection means for selecting an image quality priority mode that prioritizes the image quality when the toner image formed on the transfer belt is transferred to a recording medium;
The image forming apparatus according to claim 1, wherein the control unit is configured to force the transfer roller to be driven by operating the image quality priority selection unit. The guide means includes
A first guide plate that guides a surface on the support roller side of a recording medium to be conveyed in a conveyance path from a pair of conveyance rollers to the transfer unit;
A second guide plate rotatable between a forced guide position for forcibly guiding the surface on the support roller side and an auxiliary guide position positioned in a separating direction from the forced guide position toward the transfer roller;
The image forming apparatus according to claim 1, further comprising: 5. The control unit according to claim 1, wherein, when the transfer roller is forcibly driven, the angular velocity ω <b> 1 of the transfer roller is determined so that the following expression is satisfied. 6. Image forming apparatus.

  6. The image forming apparatus according to claim 1, wherein the control unit increases a reference system speed during driven driving as compared to a reference system speed during forced driving. 6. The image forming apparatus according to claim 6, wherein the control unit determines a reference system speed Sv ′ during driven driving so as to satisfy the following expression with respect to a reference system speed Sv during forced driving.

Monochrome determination means for determining whether printing is in monochrome mode or not,
The image forming apparatus according to claim 1, wherein the control unit drives the transfer roller to be driven when the monochrome determination unit determines that the mode is a monochrome mode. .

Images