JP2006023655A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means controlling perturbation in loop control due to production of a reverse loop, evading enlargement of the apparatus and achieving improvement in stability of the loop control at low cost in an image forming apparatus carrying out loop control of a transfer material by controlling the difference in transporting speed in a transfer means and a fixing means and to provide the image forming apparatus realizing stability in image quality. <P>SOLUTION: Transportation is carried out while maintaining the amount of loop in the transfer material P between a transfer part and a fixing part to be within a given range by changing transporting speed of the transfer material P according to the detected result of a loop amount detection means 80 detecting the loop amount of the transfer material P transported from the transfer part to the fixing part; a transfer material drawing means 90 drawing the transfer material P in the direction of the detected loop by the loop detection means 80 is provided between the transfer part and the fixing part; and the size of the drawing force for the transfer material P by the transfer material drawing means 90 is set within a range in which the loop in the transfer material P can be canceled by the difference in the transporting speed of the transfer means 5 and the fixing means 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or the like that forms an image by an electrophotographic system, an electrostatic recording system, a magnetic recording system, or the like.

  2. Description of the Related Art Conventionally, in an image forming apparatus, for example, an electrophotographic image forming apparatus as an example has a rotatable drum-shaped photosensitive member, that is, a photosensitive drum, as an image carrier. In a general image forming process, the surface of the photosensitive drum is uniformly charged by a charging device, and then image information is obtained by a latent image forming unit, or in an electrophotographic system by an exposure device such as an LED or a laser scanner. And an electrostatic latent image is formed. Thereafter, the electrostatic latent image is developed as a developer image (toner image) by electrostatically attaching toner as a developer by a developing device. The toner image on the surface of the photosensitive drum is electrostatically transferred by a transfer unit onto a transfer material such as paper that has been transferred to a transfer unit facing the photosensitive drum by a transfer material transfer unit included in the transfer unit. Then, the transfer material is conveyed from the transfer unit to the fixing unit provided with the fixing unit, and the toner image on the transfer material is heated while being nipped and conveyed between the fixing roller and the pressure roller, for example, as the fixing unit. And fixed.

  Here, generally, the conveyance speed of the transfer material in the transfer unit and the fixing unit is set to substantially the same speed. However, since the conveyance speed by the fixing unit changes due to a change in the outer diameter due to thermal expansion or the like of the fixing roller or the pressure roller, a difference in conveyance speed may occur between the transfer unit and the transfer unit.

  At this time, if the conveying speed of the fixing unit exceeds that of the transfer unit, tension is generated in the transfer material straddling the transfer unit and the fixing unit. This tension causes slippage between the transfer material and the photosensitive drum at the transfer portion, and the image is stretched and transferred, or a color image forming apparatus for transferring a plurality of color toner images in a superimposed manner. However, there is a problem that “color shift” occurs in which the transfer positions of the toner images of the respective colors are shifted and the image quality is deteriorated.

  As a means for avoiding this problem, the transfer material or the fixing means is transported at a conveyance speed so that a slack (hereinafter referred to as “loop”) is formed on the transfer material before the entrance of the fixing portion, and the loop amount is constant. There is a method of controlling (hereinafter referred to as “loop control”). By this loop control, the transfer material can be transported without generating tension.

  Hereinafter, an example of conventional loop control will be described with reference to FIGS. 9, 10, and 11. 9 and 10 are provided with a fixing device 20 including a fixing unit including a fixing roller 23 and a pressure roller 24 from a transfer unit which is a nip portion between the photosensitive drum 1 and the transfer unit 12 in the image forming apparatus. FIG. 9 is an enlarged cross-sectional view showing a schematic configuration up to the fixing unit. FIG. 9 shows a state in which the loop amount of the transfer material P during loop control is the largest, and FIG. 10 shows a transfer material P during loop control. This shows a state in which the loop amount is the smallest. Here, a case where the transfer material P is conveyed from the bottom to the top from the transfer portion to the fixing portion in a so-called vertical arrangement configuration will be described as an example.

  9 and 10, the transfer material P is indicated by a broken line P in FIG. 9 and FIG. 10, and is a conveyance path in the arrow direction A from the lower side to the upper side in the drawing, that is, a transfer portion that is a nip portion between the photosensitive drum 1 and the transfer unit 12. From the two rotating bodies 23 and 24 that are fixing means constituting the fixing device 20 and the fixing portion that is a nip portion, the toner is conveyed. In the figure, the fixing device 20 is provided on the upper left side from the transfer unit, and the conveyance path of the transfer material P is bent in a curve shape in the direction toward the upper left.

  The transfer material P includes two pairs of rotating bodies from the transfer unit to the fixing unit, the photosensitive drum 1 and the transfer roller 12 as the transfer unit in the transfer unit, and the pressure roller 24 and the fixing unit as the fixing unit in the fixing unit. It is carried by the roller 23 and is nipped and conveyed between them. Therefore, loop control is performed by these rotational speeds.

  In the transfer unit, the photosensitive drum 1 is driven from a drive source (not shown) via a gear train or the like. As the transfer means, a transfer roller 12 is used, and the photosensitive drum 1 is driven to rotate. Therefore, the transfer speed of the transfer material P in the transfer portion is determined by the driving speed of the photosensitive drum 1. Here, the driving speed of the photosensitive drum 1 is constant.

  On the other hand, the fixing device 20 is configured such that the fixing roller 23 is driven to rotate by driving the pressure roller 24 from a drive source (not shown) via a gear train or the like. Therefore, the conveyance speed of the transfer material P in the fixing device 20 is determined by the driving speed of the pressure roller 24. The driving speed of the pressure roller 24 can be changed.

  Then, by changing the driving speed of the pressure roller 24 in the fixing unit in accordance with the detection result of the loop amount detection means 80 of the transfer material P described later, the loop amount of the transfer material P is kept within a certain range. I have control. Here, the conveyance speed in the fixing device 20 can be switched between two modes, a Hi mode and a slow Lo mode, which are faster than the conveyance speed of the transfer material P in the transfer portion by the transfer roller 12.

  In the transfer process of the transfer roller 12 from the transfer unit to the fixing unit, the transfer material P sandwiched between both the photosensitive drum 1 and the transfer roller 12 and the fixing device 20 is the toner of the transfer material P. When a surface onto which an image is transferred is defined as an image surface and the back side thereof is defined as a conveyance surface, a loop having a convex surface on the conveyance surface is formed. Since the conveying surface side is convex, that is, the image surface is concave, it is possible to prevent image quality deterioration such that the toner image on the transfer material P is rubbed before fixing and the image is disturbed.

  Between the transfer portion and the fixing portion, a fixing entrance guide 70 as a conveyance guide member for the transfer material P is provided. The fixing entrance guide 70 guides the transfer material P conveyed from the transfer portion to the fixing device 20, and is provided on the conveyance path so that the transfer material P is smoothly conveyed from the transfer portion to the fixing device 20 by the transfer roller 12. The shape is along.

  The fixing entrance guide 70 is provided with a loop amount detecting means 80 for detecting the loop amount of the transfer material P from the transfer portion to the fixing portion.

  When the transfer material P is conveyed, the loop amount detection means 80 rotates so that the tip of the lever member 80a abuts on the transfer material P and the tip of the lever member 80a abutting on the transfer material P draws an arc around the shaft 80b. It is configured to be possible. At the rotation part of the lever member 80a, a flag 80c having a sectoral cross section with the shaft 80b as the center is provided on the side opposite to the transfer material P contact side. The displacement amount of the flag 80c is detected by a photo interrupter 80d as a displacement amount detecting means for detecting the position of the arc portion of the flag 80c.

  The photo interrupter 80d is a member in which a light emitting element and a light receiving element are arranged so as to face each other across a space. This photo interrupter 80d is provided in the vicinity of the rotation shaft 80b of the lever member 80a, and whether or not the photo interrupter 80d is shielded by the flag 80c provided on the opposite side of the lever 80a entering the space by the rotation. Thus, it is possible to detect whether or not the loop amount of the transfer material P has reached a predetermined value or more. The predetermined value is set according to the shape of the flag 80c, but is determined here by the length of the sectoral arc.

  Here, when the loop of the transfer material P is larger than a predetermined amount, the photo interrupter 80d has the lever 80a close to an angle parallel to the transfer material P as shown in FIG. FIG. 10 shows a case where the flag 80c on the rotating shaft shields the photo interrupter 80d, the detection signal of the photon interrupter 80d is turned off, and the loop of the transfer material P is smaller than a predetermined amount. As shown, the lever 80a is inclined at an angle close to the perpendicular direction with respect to the transfer material P, the tip of the lever 80a pushes out the transfer material P, the transfer material P is pushed out to the transfer surface side, The convexity becomes small, the flag 80c of the rotation axis does not shield the photointerrupter 80d, and the detection signal of the photointerrupter 80d is turned on. It is provided to the location.

  FIG. 11 is a timing chart showing the state change of the detection signal of the photo interrupter 80d during the loop control and the state change of the driving speed of the pressure roller 24 of the fixing device 20 in time series in the conventional example.

  When the detection signal of the photo interrupter 80d is in an OFF state, that is, when the loop amount is large, the loop amount of the transfer material P can be reduced by switching the conveyance speed in the fixing device 20 to the Hi mode. Conversely, when the detection signal of the photo interrupter 80d is in an ON state, that is, when the loop amount is small, the loop amount of the transfer material P can be increased by switching the conveyance speed in the fixing device 20 to the Lo mode.

  That is, the transfer material P is conveyed from the transfer unit to the fixing unit while maintaining the loop amount within a certain range while the conveyance speed in the fixing device 20 is adjusted by the time ratio between the Hi mode and the Lo mode by loop control.

  As a conventional example in which loop control as described above is performed, for example, there are image forming apparatuses proposed in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5.

  However, in an image forming apparatus that performs conventional loop control, the loop formed on the transfer material P between the transfer unit and the fixing unit is a one-way loop in which the conveyance surface side of the transfer material P is convex. The shape is assumed.

  However, for example, when the loop amount is increased from a state where there is almost no loop of the transfer material P, the loop shape (hereinafter referred to as “reverse loop”) in which the conveyance surface side of the transfer material P is not convex but the image surface side is convex. May occur suddenly.

  The state of the transfer material P when the reverse loop occurs is shown in FIG. When a reverse loop occurs, as in the case where the loop amount shown in FIG. 10 is small, the flag 80c does not shield the photointerrupter 80d, so the loop amount detection means 80 erroneously states that the loop amount of the transfer material P is small. It will be detected. Therefore, in the loop control in which the erroneous detection is caused, the conveyance speed of the fixing device 20 is kept in the Lo mode in order to further increase the loop amount. Then, the loop control has an instability of control such as falling into an infinite loop in the direction of increasing the reverse loop amount and causing the control itself to fail.

  As a means for detecting the reverse loop state of the transfer material P, there is a method of adding a photo interrupter 80d for detecting the position of the flag 80c and finely detecting the operation of the flag 80c. However, the control becomes complicated and the cost is high. There was a problem that would become.

Further, even if a loop control method assuming both a loop in which the conveyance surface side is convex and a reverse loop in which the image surface side is convex is constructed by adding a photo interrupter 80d or the like, In order to prevent the toner image from being rubbed against other members or the like, it is necessary to secure a large space near the transfer material P conveyance path, which makes it difficult to reduce the size of the apparatus.
JP-A-7-234604 JP-A-10-97154 JP 2000-344385 A JP 2001-282072 A JP 2003-345150 A

  SUMMARY OF THE INVENTION An object of the present invention is to control the disturbance of loop control due to the occurrence of a reverse loop in an image forming apparatus that controls a transfer material loop by controlling a difference in conveyance speed between a transfer unit and a fixing unit, and avoids an increase in size of the apparatus. It is another object of the present invention to provide a means for improving the stability of loop control at a low cost, and to provide an image forming apparatus that realizes stabilization of image quality.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides an image carrier, image forming means for forming a developer image on the surface of the image carrier according to image information, and the developer image formed on the image carrier. A transfer unit that transfers the transfer material onto the transfer material at the transfer unit; a fixing unit that fixes the developer image transferred onto the transfer material while transferring the transfer material at the fixing unit; and the transfer unit A loop amount detecting means for detecting a loop amount of the transfer material conveyed from the fixing unit to the fixing unit, and a conveyance speed control means for changing the conveyance speed of the transfer material in one or both of the transfer means and the fixing means, The transfer speed control means changes the transfer speed of the transfer material in accordance with the detection result of the loop quantity detection means, thereby setting a predetermined loop amount of the transfer material between the transfer portion and the fixing portion. Images to be transported while keeping within the range In the deposition apparatus,
The transfer material attracting means for attracting the transfer material in the direction of the loop detected by the loop detecting means is provided between the transfer portion and the fixing portion, and the transfer material attracting force of the transfer material attracting means is large. The present invention provides an image forming apparatus characterized in that a transfer material loop is set within a range in which a transfer material loop can be eliminated by a difference in conveyance speed between the transfer unit and the fixing unit.

  The image forming apparatus of the present invention can prevent the reverse loop of the transfer material from the transfer unit to the fixing unit, thereby improving the loop control stability, and as a result, stabilizing the image quality. . This also increases the degree of freedom in designing the transfer material conveyance path and the arrangement of the apparatus in the image forming apparatus.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 shows the overall configuration of the image forming apparatus in this embodiment. This embodiment has four image forming stations (image forming units) each having an image carrier and performing an image forming process until a developer image (toner image) of a different color is formed on the surface thereof. This is an electrophotographic full color laser printer. The image forming unit is detachable from the image forming apparatus as a process cartridge 7 (7a, 7b, 7c, 7d). FIG. 2 is a longitudinal sectional view showing a schematic configuration of the process cartridge 7. The image forming apparatus according to the present invention may be an electrophotographic laser printer, an electrophotographic copying machine, a facsimile, or an electrostatic recording printer, copying machine, facsimile, etc. It may be. First, the overall configuration of the image forming apparatus and its image forming operation will be described.

  The laser printer shown in FIG. 1 includes four pieces as image forming units in the image forming apparatus 100 along the conveyance direction (arrow A) of the transfer material P, here in the vertical direction from bottom to top. Image forming stations Sa, Sb, Sc, and Sd. This is an image forming apparatus having a so-called vertical arrangement configuration. Cyan, yellow, magenta, and black toner images are formed in this order. These image forming stations Sa, Sb, Sc, Sd are provided with process cartridges 7a, 7b, 7c, 7d, respectively. Each process cartridge 7a, 7b, 7c, 7d has a drum as an image carrier. The electrophotographic photosensitive members (photosensitive drums) 1a, 1b, 1c, and 1d are disposed. Hereinafter, when it is not necessary to distinguish colors, a, b, c, and d are omitted, and generic names such as “image forming station S”, “process cartridge 7”, and “photosensitive drum 1” are used. I write. This also applies to other members.

  FIG. 2 is an enlarged vertical sectional view of the cyan process cartridge 7a. The configuration and operation of the other three-color process cartridges 7b, 7c, and 7d are the same as those of the cyan process cartridge 7a, and the description thereof will be omitted as appropriate.

  In each image forming station S, the photosensitive drum 1 is rotationally driven counterclockwise in FIGS. 1 and 2 by a driving unit (not shown). A charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are arranged around the photosensitive drum 1 almost in order along the rotation direction.

  The charging device 2 uniformly charges the surface of the photosensitive drum 1. The exposure device (scanner unit) 3 is a latent image forming unit that forms an electrostatic latent image by irradiating the surface of the charged photosensitive drum 1 with a laser beam based on image information. The developing device 4 develops a toner image by attaching toner as a developer to the electrostatic latent image formed by the exposure device 3. The transfer device 5 transfers the toner image formed on the photosensitive drum 1 to the transfer material P. The cleaning device 6 removes the toner (residual toner) remaining on the surface of the photosensitive drum 1 after the transfer.

  Here, each process cartridge 7 is further divided into a photosensitive drum unit 50a and a developing unit 4a (developing device) as shown in a cyan process cartridge 7a in FIG. 2, for example. The photosensitive drum unit 50a is a unit having a photosensitive drum 1a, a charging device 2a, and a cleaning device 6a.

  Hereinafter, these image forming units in this embodiment will be described in detail in order from the photosensitive drum 1.

  Photosensitive drum 1: The photosensitive drum 1 is configured by coating an organic photosensitive semiconductor layer (OPC photosensitive layer) on an outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, for example. Both ends of the photosensitive drum 1 are rotatably supported by a support member (not shown), and a driving force from a drive motor (not shown) is transmitted to one end so that the photosensitive drum 1 in FIG. It is driven to rotate counterclockwise.

  Charging device 2: The charging device 2 is configured as a charging roller (conductive roller) 2 formed in a roller shape, and has a charging bias application power source (not shown). The charging device 2 brings the charging roller 2 into contact with the surface of the photosensitive drum 1 and applies a charging bias to the charging roller 2 by a charging bias application power source so that the surface of the photosensitive drum 1 has a uniform polarity and potential. (Uniformly) charged. In this embodiment, the surface of the photosensitive drum 1 is uniformly charged negatively by the charging device 2 (charging process).

  Exposure device 3: The exposure device 3 is arranged on the left side of each process cartridge 7 in FIG. 1 for each image forming station S, and image light corresponding to an image signal is sent to a scanner motor by a laser diode (not shown). The polygon mirror 9 is rotated at a high speed by (not shown). The image light reflected by the polygon mirror 9 is configured to selectively expose the surface of the charged photosensitive drum 1 through the imaging lens 10 to form an electrostatic latent image. In the present embodiment, the electrostatic latent image is formed by removing the charge in the portion irradiated with the image light (exposure process).

  Developing device 4: Each of the developing devices 4a, 4b, 4c, and 4d includes a toner container 41 that stores toner of each color of cyan, yellow, magenta, and black. As shown in the cyan toner container 41a in FIG. 2, the developing device 4a feeds the toner in the toner container 41a to the toner supply roller 43a by the feeding mechanism 42a, and rotates clockwise (in the direction of arrow Z) in FIG. The toner supply roller 43a and the developing blade 44a pressed against the outer peripheral surface of the developing roller 40a are applied to the outer peripheral surface of the developing roller 40a that rotates in the arrow Y direction that is the rotation direction of the toner supply roller 43a and the counter direction, In addition, a charge is applied to the applied toner. Then, a developing bias is applied by a developing bias applying power source (not shown) to the developing roller 40a that is opposed to and in contact with the photosensitive drum 1a on which the electrostatic latent image is formed, thereby forming the electrostatic latent image on the photosensitive drum 1a. A negative toner is attached to the toner image and developed as a toner image. The other color developing devices 4b, 4c, and 4d have the same configuration as the cyan developing device 4a described above, and perform the same developing operation (developing step).

Transfer device 5: A transfer device 5 as a transfer means is disposed on the right side of the process cartridge 7 in FIG. The transfer device 5 has a conveyor belt 11 that circulates (rotates) so as to be in contact with the photosensitive drum 1. The conveyor belt 11 is made of a film-like member having a volume resistivity of 10 ⁸ to 10 ¹³ Ω · cm and a thickness of 50 to 300 μm. In the present embodiment, the conveyance belt 11 is made of PVdF (polyvinylidene fluoride). The conveyor belt 11 is stretched over four rollers 13, 14, 15, and 16 that are arranged in parallel to each other. Here, since the conveyor belt 11 has a vertically arranged configuration, it is arranged in the vertical direction as a whole. Yes. The conveyance belt 11 rotates in a state where the transfer material P is electrostatically adsorbed on the outer peripheral surface thereof at a portion located between the roller 13 and the roller 14 in FIG. As a result, the transfer material P is sequentially conveyed to the respective transfer portions corresponding to the photosensitive drums 1a, 1b, 1c, and 1d, and the toner image on the photosensitive drum 1 is described below. 12 are sequentially transferred.

  Inside the transport belt 11, four transfer rollers 12a, 12b, 12c, and 12d are disposed at positions corresponding to the photosensitive drums 1a, 1b, 1c, and 1d, respectively. These transfer rollers 12 are in contact with the back side of the conveyor belt 11 and sandwich the conveyor belt 11 with the photosensitive drum 1. As a result, first, second, third, and fourth transfer portions (transfer nip portions) are formed between the photosensitive drums 1a, 1b, 1c, and 1d and the conveyor belt 11. In the present embodiment, a positive transfer bias is applied to the transfer rollers 12a, 12b, 12c, and 12d by a transfer bias application power source (not shown), whereby a negative polarity on the photosensitive drums 1a, 1b, 1c, and 1d is applied. In the first to fourth transfer portions, the toner images of the respective colors are sequentially transferred onto the transfer material P that is carried and conveyed on the contact surface of the conveyance belt 11 with the photosensitive drum 1. (Transfer process).

  Cleaning device 6: Residual toner remaining on the photosensitive drum 1 without being transferred to the transfer material P when the toner image is transferred is removed by the cleaning device 6. As shown in FIG. 2, the cyan cleaning device 6a has a cleaning blade 60a that contacts and removes residual toner on the surface of the photosensitive drum 1a. Residual toner removed from the surface of the photosensitive drum 1a by the cleaning blade 60a is sequentially sent to a waste toner chamber 53a provided behind the cleaning frame 51a by the toner feeding mechanism 52a.

  Paper feed cassette 17: A detachable paper feed cassette 17 is disposed below the image forming apparatus main body 100. A plurality of transfer materials P (for example, plain paper, envelopes, transparent films) are stored in the paper feed cassette 17 in a stacked state. The transfer material P in the paper feed cassette 17 is separated and fed one by one by the drive rotation of the paper feed roller 18 (half moon roller) during image formation, and is temporarily stopped by abutting the leading end against the registration roller pair 19. To form a loop. Thereafter, the rotation of the conveyance belt 11 and the image writing position on the photosensitive drum 1 are synchronized, and the sheet is supplied to the conveyance belt 11 by the registration roller pair 19. The transfer material P supplied toward the conveyance belt 11 is adsorbed on the surface of the conveyance belt 11 by an adsorption roller 22 as an adsorption member disposed further upstream than the photosensitive drum 1a on the most upstream side.

  Fixing device 20 (fixing unit): a transfer material on which a plurality of color toner images are transferred while passing through the image forming station Sd on the most downstream side while being carried on the transport belt 11 from the paper feed cassette 17 and transported. P is separated from the conveyance belt 11 by the curvature of the driving roller 13 around which the conveyance belt 11 is wound, and a fixing device 20 including a fixing unit is disposed further downstream (upward) in the subsequent conveyance direction. . The fixing device 20 fixes a plurality of color toner images transferred onto the transfer material P. As a fixing unit, a fixing roller 23 that rotates and a pressure roller that is pressed against the transfer roller P and applies heat and pressure to the transfer material P are applied. And a pressure roller 24. The fixing roller 23 and the pressure roller 24 form a fixing nip serving as a fixing unit.

  Also here, the conveyance guide member 70 and the loop amount detection means 80 of the transfer material P are installed between the image station Sd and the fixing device 20, that is, between the transfer unit and the fixing unit. The loop control by these members will be described later.

  The image forming process in the image forming apparatus 100 by the above-described image forming means is as follows.

  The photosensitive drum 1 in the process cartridge 7 is rotationally driven counterclockwise in accordance with the image formation timing, and is uniformly charged by the charging device 2. The charged photosensitive drum 1 is exposed according to an image signal (image information) by the exposure device 3 to form an electrostatic latent image. At this time, a portion that is not exposed becomes a dark portion (high potential portion), and the potential (dark portion potential) is VD. On the other hand, the exposed portion becomes a bright portion (low potential portion), and the potential (bright portion potential) is set to VL. The developing device 4 forms toner images of cyan, yellow, magenta, and black on the photosensitive drums 1a, 1b, 1c, and 1d by attaching toner to the bright portions of the above-described electrostatic latent image.

  On the other hand, the transfer material P supplied from the paper feed cassette 17 to the transport belt 11 by the paper feed roller 18 and the registration roller pair 19 is transported so as to be sandwiched between the suction roller 22 and the transport belt 11 of the transfer device 5. By being pressed against the surface (outer peripheral surface) of the belt 11 and applying a voltage between the conveyance belt 11 and the suction roller 22, electrostatic adsorption is performed on the surface of the conveyance belt 11. In the image forming apparatus of the present embodiment, a positive voltage is applied from the suction roller 22 side, and the roller (suction counter roller) 14 is grounded. As a result, the transfer material P is stably adsorbed to the transport belt 11 and transported to the fourth transfer section in the most downstream image forming station Sd.

  The transfer material P adsorbed on the surface of the conveyance belt 11 in this way is the first of each color by the rotation of the conveyance belt 11 in the forward direction relative to the rotation direction of the photosensitive drum 1 and clockwise in FIG. To the fourth transfer portion sequentially, and an electric field (transfer) formed in the transfer portion which is a nip portion between each photosensitive drum 1a, 1b, 1c, 1d and each transfer roller 12a, 12b, 12c, 12d The toner images on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred by the electric field.

  The transfer material P onto which the four color toner images have been transferred is separated from the conveying belt 11 by the curvature of the roller (belt driving roller) 13 and is carried into the fixing device 20. The transfer material P is heated and pressurized while being nipped and conveyed by the fixing device 23 and the pressure roller 24 by the fixing device 20, and the four color toner images are fixed on the surface. After the toner image is fixed, the transfer material P is discharged by the paper discharge roller pair 25 onto the paper discharge tray 26 formed on the upper surface of the image forming apparatus main body 100 with the image surface facing downward. On the other hand, the residual toner remaining on the surface of the photosensitive drum 1 is removed by the cleaning device 6 and used for the next image formation. Thus, the four-color full-color image formation is completed.

  Here, the configuration of members related to loop control in the conveyance of the transfer material P between the transfer unit and the fixing unit, which is a characteristic part of the present invention, and a control method of loop control will be described.

  3 and 4 show a schematic configuration of the image forming apparatus according to the present exemplary embodiment from the transfer unit to the fixing unit at the position of the transfer roller 12 (12d) that is the most downstream in the moving direction of the conveyance belt 11 in the conventional example. It is the longitudinal cross-sectional view shown expanded like FIG.9 and FIG.10. 3 shows a state in which the loop amount of the transfer material P during the loop control of the present embodiment is the largest, and FIG. 4 shows a state in which the loop amount of the transfer material P during the loop control of the present embodiment is the smallest. Show.

  The transfer material P is indicated by a broken line P in FIGS. 1 and 2, and is a conveyance path in the arrow direction A from the lower side to the upper side in the drawing, that is, a transfer portion that is a nip portion between the photosensitive drum 1 and the transfer roller 12. From the two rotating bodies 23 and 24 constituting the fixing device 20 and the fixing portion which is a nip portion, the toner is conveyed. In the figure, the fixing device 20 is provided on the upper left side from the transfer part, and the transfer material P is bent in a curved shape in the direction toward the upper left.

  In this embodiment, a driving force is transmitted from a driving source (not shown) to the roller 13 which is one of the rollers that stretch the conveying belt 11 included in the transfer device 5 to drive the conveying belt 11. Therefore, the transfer speed of the transfer material P in the transfer device 5 is determined by the driving speed of the transfer belt 11. The driving speed of the conveyor belt 11 during image formation is constant.

  On the other hand, the fixing device 20 is configured such that the fixing roller 23 is driven and rotated by driving the pressure roller 24 from a motor (not shown) via a gear train or the like. Therefore, the conveyance speed of the transfer material P in the fixing device 20 is determined by the driving speed of the pressure roller 24.

  The driving speed of the pressure roller 24 can be changed in at least two stages by a CPU including a motor driver (not shown) as a conveyance speed control means. Control is performed so that the loop amount of the transfer material P falls within a certain range by switching the driving speed of the pressure roller 24 in accordance with a detection result of a loop amount detection unit 80 described later. The conveyance speed in the fixing device 20 can be switched between two types, that is, a Hi mode and a slow Lo mode, which are faster than the conveyance speed in the transfer device 5, that is, the conveyance speed by the conveyance belt 11.

  Here, as in the conventional example, the surface on which the unfixed toner image of the transfer material P is formed on the transfer material P spanned between the transfer device 5 and the fixing device 20 is the image surface, and the back side is the transport surface. Is defined, a loop having a convex surface is formed. By making the conveying surface convex, in other words, by making the image surface concave, it is possible to prevent deterioration in image quality such that the unfixed toner image on the transfer material P is rubbed before fixing and the image is disturbed. .

  A fixing inlet guide 70 as a conveyance guide member for guiding the transfer material P conveyed from the transfer portion to the fixing portion is provided between the transfer portion and the fixing portion in the transfer material P conveyance path. It is shaped so as to be smoothly conveyed from the transfer unit to the fixing unit. The fixing entrance guide 70 in this embodiment has a curved shape along the conveyance path of the transfer material P, but is not limited thereto, and may be a linear shape.

  Also in this case, the fixing entrance guide 70 is provided with a loop amount detecting means 80 for detecting the loop amount of the transfer material P from the transfer portion to the fixing portion, and the lever member 80a contacts the transfer material P as in the conventional example. The amount of displacement of a flag 80c provided on the opposite side of the lever member 80a with respect to the shaft 80b is the same as that of the conventional example as a displacement amount detecting means. Detected. Whether or not the loop amount of the transfer material P has become a predetermined value or more can be detected based on whether or not the photo interrupter 80d is shielded by the flag 80c entering the space between the light emitting element and the light receiving element of the photo interrupter 80d. .

  As described in the conventional example, when the loop of the transfer material P is larger than a predetermined amount, as shown in FIG. 3, the flag 80c shields the photointerrupter 80d, so that the detection signal of the photon interrupter 80d is It becomes OFF state. When the loop of the transfer material P is smaller than a predetermined amount, as shown in FIG. 4, the flag 80c does not shield the photointerrupter 80d, so that the detection signal of the photointerrupter 80d is turned on.

  FIG. 5 is a timing chart showing the state change of the detection signal of the photo interrupter 80d and the state change of the driving speed of the pressure roller 24 of the fixing device 20 in time series in the loop control in this embodiment. When the detection signal of the photo interrupter 80d is in an OFF state, that is, when the loop amount is large, the loop amount of the transfer material P can be reduced by switching the conveyance speed in the fixing device 20 to the Hi mode. Conversely, when the detection signal of the photo interrupter 80d is in an ON state, that is, when the loop amount is small, the loop amount of the transfer material P can be increased by switching the conveyance speed in the fixing device 20 to the Lo mode. That is, the transfer material P is transported from the transfer unit to the fixing unit by controlling the conveyance speed of the fixing device 20 by the time ratio between the Hi mode and the Lo mode by loop control so that the loop amount is within a certain range. The

  Then, in the loop control by the conveyance speed control means, the conveyance speed in the transfer device 5 is fixed and the conveyance speed in the fixing device 20 is variable. However, the conveyance speed in the transfer device 5 is variable, and in the fixing device 20. The conveyance speed may be fixed. Further, the conveyance speed in both the transfer device 5 and the fixing device 20 may be variable.

  As a feature of the present embodiment, as described above, in addition to the control for adjusting the conveyance speed of the transfer material P in the transfer unit and the fixing unit according to the detection result of the loop detection unit 80 having the same configuration as the conventional example, In addition, a transfer material attracting means for attracting the transfer material P to the transport surface side may be provided between the transfer portion and the fixing portion.

  Here, the transfer material attracting means will be described in detail.

  FIG. 6 is a front view of the fixing inlet guide 70 in this embodiment as viewed from the conveyance surface side. In the fixing entrance guide 70 in the present embodiment, conveyance guide ribs 71 which are a plurality of ribs made of an insulating resin are provided in the conveyance direction. Between the conveyance guide ribs 71, a conveyance guide plate 90 made of a sheet metal of a conductive member is integrally formed as an example of a transfer material attracting unit. The conveyance guide plate 90 is electrically grounded by being fixed to a frame (not shown) of the fixing device 20 or a frame (not shown) of the image forming apparatus 100 main body.

  In this embodiment, the conveyance guide rib 71 is formed to be higher than the conveyance guide plate 90 so that the conveyance surface of the transfer material P does not contact the conveyance guide plate 90. In this embodiment, the conveyance guide rib 71 is about 2 mm higher than the conveyance guide plate 90.

  Further, a lever member 80a constituting the loop amount detecting means 80 is provided at the position of the conveyance guide plate 90 in the longitudinal center of the fixing entrance guide 70, and the conveyance guide plate 90 does not interfere when the lever member 80a swings. Thus, an opening 91 is provided.

  The conveyance guide plate 90 electrostatically attracts the conveyance surface side of the transfer material P to the conveyance guide plate 90 between the transfer portion and the fixing portion, so that the image surface side of the transfer material P is convex. Occurrence is prevented, and the loop shape in which the conveying surface side is always convex is maintained, so that the loop control can be stabilized.

  Here, it is necessary to set the attracting force of the transfer material P by the transfer material attracting means 90 within a range in which a loop generated in the transfer material P due to a difference in transport speed between the transfer device 5 and the fixing device 20 can be eliminated.

  When the attracting force by the transfer material attracting means 90 is outside the above range, the attracting force causes a change in the transport speed of the transfer material P in the transfer device 5 or the fixing device 20, and the transport between the transfer device 5 and the fixing device 20. The loop control that keeps the loop amount of the transfer material P constant by adjusting the speed difference becomes unstable. Further, in this case, an excessive tension is generated in the transfer material P passing through the nip between the transfer portion and the fixing portion due to the attracting force by the transfer material attracting means 90, so that “image stretch” and “color misregistration” are generated. This causes image defects such as “

  In this embodiment, the conveyance guide plate 90 as a transfer material attracting unit is grounded. However, the conveyance guide plate 90 applies a bias that electrostatically draws the conveyance surface of the transfer material P toward the fixing inlet guide 70. You may apply to. In this case, since the attractive force of the transfer material P can be changed depending on the bias value to be applied, the bias value may be varied according to the type of the transfer material and the sheet passing mode of the image forming apparatus.

  For example, the stiffness of the transfer material P varies depending on the type of transfer material P such as plain paper, cardboard, OHP film, or even moisture-absorbing paper, so that the optimum attraction force for preventing reverse loops may differ. is there. In addition, when there are a plurality of paper passing modes in which the paper is fed at a half speed, the optimum attraction force may differ depending on the speed of conveyance. Therefore, by changing the bias value applied to the transport guide plate 90 as the transfer material attracting means to an optimum value according to the type of the transfer material P and the transport speed, it is possible to always adjust the optimum attracting force. Therefore, the loop control can be further stabilized.

  In the present invention, the configuration of the image forming apparatus is not limited to that shown in FIG. 1, but the conveyance path of the transfer material P from the transfer unit to the fixing unit is substantially horizontal and the transfer material P In the image forming apparatus designed so that the conveyance surface side is down, the transfer material P is attracted downward by gravity, so that it is easy to produce a loop shape in which the conveyance surface side is convex. can get. This makes loop control relatively stable.

  On the other hand, in the case of an image forming apparatus having a configuration in which the conveyance path of the transfer material P is nearly vertical as in the present embodiment, and further, a conveyance path in which the image surface of the transfer material P is down, the reverse due to gravity. The present invention is particularly effective in an image forming apparatus having such a configuration because a loop suppression effect is hardly obtained and a reverse loop is easily induced by gravity.

  Note that the number of photosensitive drums may be singular or may not be a multi-color image forming apparatus, and the image forming means may not be a process cartridge. Further, even in a configuration using an intermediate transfer member as a transfer device, the present invention can be applied to the same problem between the secondary transfer portion and the fixing portion. In addition, when there is no description in particular about the structure of each image formation means, etc., it can adjust suitably.

Example 2
Embodiment 2 of the image forming apparatus according to the present invention will be described. In the second embodiment, the schematic configuration and loop control of the image forming apparatus are the same as those in the first embodiment except for the fixing inlet guide 70 and the conveyance guide plate 90, and thus the description thereof is omitted.

  FIG. 7 is an enlarged longitudinal sectional view showing a schematic configuration from the transfer unit to the fixing unit of the image forming apparatus according to the present exemplary embodiment.

  Instead of the conveyance guide plate 90 in the first embodiment, the fixing inlet guide 70 in the present embodiment is provided with a fan 92 as a transfer material attracting unit. The fan 92 operates so that an airflow is formed in the direction of arrow B so as to attract the conveyance surface of the transfer material P to the fixing inlet guide 70.

  FIG. 8 is a front view of the fixing entrance guide 70 viewed from the conveyance surface side in this embodiment. The fixing entrance guide 70 in the present embodiment is entirely made of an insulating resin, and further, conveyance guide ribs 71 that are a plurality of ribs are provided in the conveyance direction. A large number of suction ports 93 for sucking air by the fan 92 are provided in the resin portion between the conveyance guide ribs 71.

  Further, a lever member 80a constituting a loop amount detecting means is provided at the longitudinal center portion of the fixing entrance guide 70, and an opening 91 is provided so as not to interfere when the lever member 80a swings.

  By operating the fan 92 while the transfer material P passes through the fixing inlet guide 70, air suction force that attracts the conveyance surface side of the transfer material P to the fixing inlet guide 70 acts, so that the image surface side of the transfer material P is convex. Since the loop shape in which the conveyance surface side is always convex is maintained, the loop control can be stabilized.

  Further, the loop control of the transfer material P can be further stabilized by changing the suction force of the fan 92 as the transfer material attracting means to an optimal setting value in accordance with the type of the transfer material P and the sheet passing mode. .

  In the configuration of the present embodiment, since the suction force of air is used as the transfer material attracting means, the transfer material P can be attracted regardless of the charged state of the transfer material P. Therefore, the transfer material P is difficult to be charged. Even in an image forming apparatus configured to remove charge from the transfer material P in a humidity environment or between the transfer unit and the fixing unit, the loop control can be stabilized.

  Also in this case, it is necessary to set the magnitude of the attracting force of the transfer material P by the fan 92 as the transfer material attracting means within a range in which the loop can be eliminated by the difference in the conveyance speed between the transfer means 5 and the fixing means 20. is there.

  The present embodiment can also be applied to other than the image forming apparatus having the configuration shown in FIG. 1, but the configuration in which the transfer material conveyance path from the transfer unit to the fixing unit is directed upward in the vertical configuration or the transfer material P This is particularly effective in a configuration having a transfer material conveyance path in which the image surface side is downward.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. FIG. 3 is a cross-sectional view showing an example of a process cartridge equipped with an image forming unit according to the present invention. FIG. 3 is a schematic configuration diagram illustrating an example of a transfer material conveyance state from a transfer unit to a fixing unit according to the present invention. FIG. 3 is a schematic configuration diagram illustrating an example of a transfer material conveyance state from a transfer unit to a fixing unit according to the present invention. 6 is a timing chart illustrating an example of timing of loop detection control and transfer material conveyance speed control according to the present invention. It is a front view which shows an example of the conveyance guide member and transfer material drawing means which concern on this invention. It is a schematic block diagram which shows the other example of the mode of conveyance of the transfer material from the transfer part which concerns on this invention to a fixing part. It is a front view which shows the other example of the conveyance guide member which concerns on this invention, and a transfer material drawing means. It is a schematic block diagram which shows an example of the mode of conveyance of the transfer material from the conventional transfer part to a fixing part. It is a schematic block diagram which shows an example of the mode of conveyance of the transfer material from the conventional transfer part to a fixing part. It is a timing chart which shows an example of the timing of the conventional loop detection control and conveyance speed control. FIG. 10 is a schematic configuration diagram illustrating an example of a state in which a reverse loop occurs in a transfer material conveyance from a conventional transfer unit to a fixing unit.

Explanation of symbols

1 Photosensitive drum (image carrier)
5 Transfer device (transfer means)
11 Conveyor belt (transfer means)
12 Transfer roller (transfer means)
20 Fixing device (fixing means)
23 Fixing roller (fixing means)
24 Pressure roller (fixing means)
70 Fixing entrance guide (conveyance guide member)
80 Loop detecting means 90 Conveying guide plate (transfer material attracting means)
92 Fan (Transfer material attracting means)
93 Suction port (transfer material attracting means)
P transfer material

Claims (9)

An image carrier, image forming means for forming a developer image on the surface of the image carrier according to image information, and the developer image formed on the image carrier while transferring a transfer material A transfer unit that transfers the transfer material onto the transfer material, a fixing unit that fixes the developer image transferred onto the transfer material while transporting the transfer material at the fixing unit, and a transfer unit transported from the transfer unit to the fixing unit. A loop amount detecting means for detecting a loop amount of the transfer material to be transferred, and a transport speed control means for changing the transport speed of the transfer material in either one or both of the transfer means and the fixing means. The means changes the transfer material conveyance speed in accordance with the detection result of the loop amount detection means, and conveys the transfer material while keeping the loop amount of the transfer material within a predetermined range between the transfer unit and the fixing unit. In the image forming apparatus,
The transfer material attracting means for attracting the transfer material in the direction of the loop detected by the loop detecting means is provided between the transfer portion and the fixing portion, and the transfer material attracting force of the transfer material attracting means is large. The image forming apparatus is characterized in that it is set within a range in which a loop of the transfer material can be eliminated by a difference in conveyance speed between the transfer unit and the fixing unit.   The direction of the loop detected by the loop detection means is a direction in which the transfer material protrudes behind the surface to which the developer image is transferred between the transfer unit and the fixing unit. The image forming apparatus according to claim 1, wherein the attracting unit attracts the transfer material from the back side of the surface onto which the developer image is transferred.   A conveyance guide member that guides a transfer material from the transfer portion to the fixing portion is provided between the transfer portion and the fixing portion. 3. The image forming apparatus according to claim 1, further comprising an attaching unit.   4. The image forming apparatus according to claim 1, wherein the transfer material attracting unit electrostatically attracts the transfer material charged by the transfer unit.   5. The transfer material attracting means is composed of a conductive member, and the conductive member is electrically grounded or applied with a bias for electrostatically attracting the transfer material. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the transfer material attracting unit attracts the transfer material by using an air suction force.   The image forming apparatus according to claim 6, wherein the transfer material attracting unit includes a fan that sucks air.   The image forming apparatus according to claim 1, wherein an attracting force of the transfer material by the transfer attracting unit is changed according to a type or a conveyance speed of the transfer material.   The loop amount detection means includes a lever member that can swing according to the loop amount of the transfer material, and a displacement amount detection member that detects the displacement amount of the lever member, and the displacement amount of the lever member is predetermined. The image forming apparatus according to claim 1, wherein the conveyance speed of the transfer material is controlled by the conveyance speed control unit so as to be maintained within the range of the above.

Images