JP2008139670A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high quality output free from transfer displacement and curls even in special paper, such as cardboard, regardless of the type/characteristic of a recording material. <P>SOLUTION: The image forming apparatus includes: an image forming means for forming a toner image on an image carrier; a transfer means for transferring the toner image formed on the image carrier to a recording material; and a fixing device for fixing the toner image transferred to the surface of the recording material. In the image forming apparatus, the position of a fixing nip in relation to a transfer position can be altered. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to conveyance of a fixing device in an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by electrophotography.

  In recent electrophotographic color image forming apparatuses, a plurality of image forming units for each color are arranged in parallel for speeding up, and a recording material adsorbed by an electrostatic adsorption conveyance belt is conveyed and sequentially transferred. The number of in-line systems that perform formation is increasing.

  In this method, since the main body tends to be large due to the configuration in which a plurality of image forming units are arranged in parallel, the fixing unit and the bending unit are bent so that the conveyance path is bent immediately after the final transfer portion in order to reduce the size of the entire main body. In many cases, a paper discharge unit is arranged.

In this configuration, for example, as shown in Japanese Patent Application Laid-Open No. 2003-345150, a recording medium in the transfer section is pulled or moved by providing a speed difference so that a recording material loop is formed between the transfer section and the fixing device. This prevents the image quality from being impaired.
Japanese Patent Laid-Open No. 2003-345150

  By the way, in recent years, the use of color LBP has increased with the increase in speed and performance, and there is a tendency that the number of types of recording materials to be supported by the product is increased as compared with the prior art. For this reason, it is difficult to obtain sufficient quality only by controlling the loop amount between transfer and fixing as in the prior art.

  For example, with thick recording materials such as thick paper exceeding 200 g of basis weight, a sufficient loop cannot be provided between the transfer and fixing, and the force to push the recording material back to the transfer section is large, resulting in transfer displacement, and polyethylene terephthalate In the case of a resin sheet or the like, there is a problem that curling occurs due to the curvature of the conveyance path due to the arrangement relationship between the fixing unit and the paper discharge unit as shown in FIG.

In order to solve the above problems, the present invention provides a first invention according to the present application, wherein an image forming means for forming a toner image on an image carrier and a toner image formed on the image carrier are transferred to a recording material. A transfer means; a fixing device for fixing the toner image transferred onto the recording material;
In an image forming apparatus having
The fixing nip position with respect to the transfer position can be changed.

In order to solve the above problems, the second invention according to the present application is an image forming means for forming a toner image on an image carrier, and a toner image formed on the image carrier is transferred to a recording material. A transfer means; a fixing device for fixing the toner image transferred onto the recording material;
In an image forming apparatus having
The fixing nip position relative to the transfer position can be changed by a detection signal from a recording material detection sensor installed in the conveyance path.

In order to solve the above problems, the present invention provides a third invention according to the present application, wherein an image forming means for forming a toner image on an image carrier and a toner image formed on the image carrier are transferred to a recording material. A transfer means; a fixing device for fixing the toner image transferred onto the recording material;
In an image forming apparatus having
The position of the fixing nip with respect to the transfer position can be changed, and the discharge conveyance unit downstream of the fixing device moves in conjunction with the change in position.

In order to solve the above problem, the present invention provides a fourth invention according to the present application, wherein an image forming means for forming a toner image on an image carrier and a toner image formed on the image carrier are transferred to a recording material. A transfer means; a fixing device for fixing the toner image transferred onto the recording material;
In an image forming apparatus having
The position of the fixing nip with respect to the transfer position can be changed, and the position of the discharge stacking surface is moved in conjunction with the change in position.

In order to solve the above-mentioned problems, the fifth invention according to the present application is an image forming means for forming a toner image on an image carrier, and a toner image formed on the image carrier is transferred to a recording material. A transfer means; a fixing device for fixing the toner image transferred onto the recording material;
In an image forming apparatus having
It is characterized in that the position of the fixing nip relative to the transfer position can be changed by a detection signal of a recording material detection sensor of a paper thickness detection sensor, an OHT detection sensor, or a gloss detection sensor installed in the conveyance path.

In order to solve the above-described problems, the sixth invention according to the present application is an image forming means for forming a toner image on an image carrier, and a toner image formed on the image carrier is transferred to a recording material. A transfer unit; and a fixing device that fixes the toner image transferred onto the recording material;
In an image forming apparatus having
The fixing nip position relative to the transfer position can be changed by the bending strength of the recording material being conveyed.

In order to solve the above-mentioned problems, the seventh invention according to the present application is an image forming means for forming a toner image on an image carrier, and a toner image formed on the image carrier is transferred to a recording material. A transfer means; a fixing device for fixing the toner image transferred onto the recording material;
In an image forming apparatus having
The bending strength of the recording material being conveyed is detected by a recording material loop amount detecting means provided in the conveyance path, and the fixing nip position relative to the transfer position can be changed.

In order to solve the above problems, the present invention provides an image forming means for forming a toner image on an image carrier, and transferring a toner image formed on the image carrier to a recording material. A transfer means; a fixing device for fixing the toner image transferred onto the recording material;
In an image forming apparatus having
It is characterized in that the position of the fixing nip with respect to the transfer position can be changed during the first side printing and the second side printing when performing duplex printing.

  As described above, according to the first invention of the present application, transfer deviation and curl can be prevented even in special paper such as cardboard by changing the conveyance path in the fixing unit, and high-quality output can be achieved. Obtainable.

  Further, according to the second and fifth inventions of the present application, the recording material characteristic can be automatically detected by the recording material detection sensor, and it is not necessary to manually switch the fixing nip position, and the user makes an incorrect setting. This can be prevented.

  According to the third aspect of the present application, the sheet discharge angle can be changed with respect to the change in the conveyance direction accompanying the change in the fixing nip position, and the occupied space in the image forming apparatus installation space of the user can be reduced. Can do.

  Further, according to the fourth aspect of the present invention, the position of the sheet discharge stacking surface can be moved with respect to the change in the transport direction accompanying the change in the fixing nip position, and the recording material is buckled and caused by the discharge angle. Deformation can be prevented.

  According to the sixth invention of the present application, the bending strength of the recording material can be detected during conveyance, and it is not necessary to manually change the fixing nip position, thereby preventing the user from making an incorrect setting. be able to.

  According to the seventh invention of the present application, it is possible to automatically detect the bending strength of the recording material during conveyance, and it is not necessary to manually change the fixing nip position, and the user makes an incorrect setting. Can be prevented.

  Further, according to the eighth aspect of the present application, the curl of the recording material generated at the time of image formation on the first surface can be corrected by changing the position of the fixing nip at the time of fixing the second surface, and high quality output can be achieved. Can be obtained.

(Example 1)
Embodiments of the present invention will be described below with reference to the drawings.

{Overall configuration of color image forming apparatus}
First, the overall configuration of the color image forming apparatus will be outlined with reference to FIG. FIG. 1 is a longitudinal sectional view showing the overall configuration of a full-color laser beam printer 100 which is an embodiment of a color image forming apparatus.

  A color image forming apparatus 100 shown in the figure includes four photosensitive drums 1a, 1b, 1c, and 1d arranged in parallel in the vertical direction. The photosensitive drum 1 is driven to rotate counterclockwise in the drawing by a driving means (not shown). A charging device 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1 in order according to the rotation direction, and a laser beam is irradiated around the photosensitive drum 1 based on image information. A scanner unit 3 (3a, 3b, 3c, 3d) for forming an electrostatic latent image on the drum 1, and a developing device 4 (4a, 4b, 4c, 4d) for developing the toner image by attaching toner to the electrostatic latent image ), An electrostatic transfer device 5 that transfers the toner image on the photosensitive drum 1 to the recording material S, and a cleaning device 6 (6a, 6b, 6c, which removes transfer residual toner remaining on the surface of the photosensitive drum 1 after transfer). 6d) and the like are provided.

  Here, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6 are integrated into a cartridge to form a process cartridge 7.

  Hereinafter, the photosensitive drum 1 will be described in detail.

  The photoconductor drum 1 is configured by applying an organic photoconductive layer (OPC photoconductor) to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, for example. The photosensitive drum 1 is rotatably supported at both ends by a support member, and is driven to rotate counterclockwise by transmitting a driving force from a drive motor (not shown) to one end. The

  As the charging device 2, a contact charging type can be used. The charging member is a conductive roller formed in a roller shape. The roller is brought into contact with the surface of the photosensitive drum 1 and the surface of the photosensitive drum 1 is made uniform by applying a charging bias voltage to the roller. To be charged.

  The scanner unit 3 is arranged in a substantially horizontal direction of the photosensitive drum 1, and image light corresponding to an image signal is rotated at high speed by a scanner motor (not shown) by a laser diode (not shown), and a polygon mirror 9 (9a, 9b). , 9c, 9d). The image light reflected by the polygon mirror 9 selectively exposes the surface of the charged photosensitive drum 1 through the imaging lens 10 (10a, 10b, 10c, 10d) to form an electrostatic latent image. It is composed.

  Each of the developing devices 4a, 4b, 4c, and 4d is composed of a developing device that stores toner of each color of yellow, magenta, cyan, and black.

An electrostatic transfer belt 11 that circulates and moves so as to face and contact all the photosensitive drums 1a, 1b, 1c, and 1d is disposed. The electrostatic transfer belt 11 is formed of a film-like member having a thickness of about 150 μm and having a volume resistivity of 10 ¹¹ to 10 ¹⁴ Ω · cm. This electrostatic transfer belt 11 is supported by rollers with four axes in the vertical direction, and circulates and moves so that the recording material S is electrostatically attracted to the outer peripheral surface on the left side in the drawing to bring the recording material S into contact with the photosensitive drum 1. To do. As a result, the recording material S is conveyed to the transfer position by the electrostatic transfer belt 11 and the toner image on the photosensitive drum 1 is transferred.

  The transfer roller 12 (12a, 12b, 12c, 12d) is arranged in parallel at a position in contact with the inside of the electrostatic transfer belt 11 and facing the four photosensitive drums 1a, 1b, 1c, 1d. A positive charge is applied from the transfer roller 12 to the recording material S via the electrostatic transfer belt 11, and a negative polarity on the photosensitive drum 1 is applied to a sheet in contact with the photosensitive drum 1 by an electric field generated by the charge. The toner image is transferred.

  The electrostatic transfer belt 11 is a belt having a circumferential length of about 700 mm and a thickness of 150 μm. The belt is stretched by four rollers, that is, a driving roller 13, driven rollers 14 a and 14 b, and a tension roller 15, and rotates in the direction of the arrow in the figure. Thereby, the toner image is transferred while the above-described electrostatic transfer belt 11 circulates and the recording material S is conveyed from the driven roller 14a side to the driving roller 13 side.

  The paper feeding unit 16 feeds and conveys the recording material S to the image forming unit, and a plurality of recording materials S are stored in the paper feeding cassette 17. At the time of image formation, the paper feed roller 18 (half-moon roller) and the registration roller pair 19 are driven and rotated according to the image forming operation to separate and feed the recording material S in the paper feed cassette 17 one by one, and at the front end of the recording material S , Abuts against the registration roller pair 19 and temporarily stops. After forming a loop, the rotation of the electrostatic transfer belt 11 and the image writing position are synchronized, and the sheet is fed to the electrostatic transfer belt 11 by the registration roller pair 19. .

  The recording material S to which the respective color toner images have been sequentially transferred while being conveyed by the electrostatic attraction belt 11 is then fixed by being heated and pressed by the fixing unit 20.

  As an image forming operation, the process cartridges 7a, 7b, 7c, and 7d are sequentially driven in accordance with the print timing, and the photosensitive drums 1a, 1b, 1c, and 1d are rotated counterclockwise in accordance with the drive. Driven. Then, the scanner units 3 corresponding to the respective process cartridges 7 are sequentially driven. By this driving, the charging roller 2 imparts a uniform charge to the circumferential surface of the photosensitive drum 1, and the scanner unit 3 exposes the circumferential surface of the photosensitive drum 1 according to the image signal to perform photosensitive drum 1. An electrostatic latent image is formed on the peripheral surface. The developing roller in the developing device 4 transfers (transfers) the toner to the low potential portion of the electrostatic latent image to form (develop) the toner image on the circumferential surface of the photosensitive drum 1.

  At the timing when the leading edge of the toner image on the circumferential surface of the most upstream photosensitive drum is rotated and conveyed to a point facing the electrostatic transfer belt 11, the printing start position of the recording material S coincides with that point. Then, the registration roller pair 19 starts to rotate and feeds the recording material S to the electrostatic transfer belt 11.

  The recording material S is pressed against the outer periphery of the electrostatic transfer belt 11 so as to be sandwiched between the electrostatic adsorption roller KR and the electrostatic transfer belt 11, and a voltage is applied between the electrostatic transfer belt 11 and the electrostatic adsorption roller KR. When applied, the recording material S that is a dielectric and the dielectric layer of the electrostatic transfer belt 11 are induced, and the recording material is electrostatically attracted to the outer periphery of the electrostatic transfer belt 11. As a result, the recording material S is stably adsorbed to the electrostatic transfer belt 11 and conveyed to the most downstream transfer unit.

  While being conveyed in this manner, the toner image on each photosensitive drum 1 is sequentially transferred to the recording material S by an electric field formed between each photosensitive drum 1 and the transfer roller 12.

  The recording material S to which the four color toner images have been transferred is separated from the electrostatic transfer belt 11 by the curvature separation ability based on the curvature of the belt driving roller 13 and is carried into the fixing unit 20.

  After the toner image is heat-fixed by the fixing unit 20, the recording material S is discharged to the paper discharge unit 24 by the paper discharge roller pair 22 and 23 with the image surface facing down.

  Here, a heat roller type fixing device widely adopted as an example of the fixing unit 20 will be described.

  A non-fixed toner image to be fixed on the fixing nip portion, which is a mutual pressure contact portion of the roller pair, by rotating the roller pair as a basic configuration with a pressure roller pair of a fixing roller (heating roller) 21a and a pressure roller 21b. A recording material on which is formed and supported is introduced and nipped and conveyed, and an unfixed toner image is fixed on the surface of the recording material by heat of the fixing roller and a pressing force of the fixing nip portion.

  In general, the fixing roller has an aluminum hollow metal roller as a base body (core metal), and a halogen lamp as a heat source is inserted and disposed in the inner space thereof. The temperature of the halogen lamp is controlled and controlled so that the temperature is maintained.

  In particular, as a fixing device of an image forming apparatus that performs full-color image formation that requires the ability to sufficiently heat-melt and mix colors of up to four toner image layers, a fixing roller core has a high heat capacity In addition, a rubber elastic layer for wrapping and uniformly melting the toner image around the outer periphery of the metal core is provided, and the toner image is heated through the rubber elastic layer. There is also a configuration in which a heat source is also provided in the pressure roller so that the pressure roller is also heated and temperature-controlled.

  A feature of the present embodiment is to secure a high-quality output free from transfer deviation and curl by adopting a fixing unit posture suitable for the recording material.

  FIG. 2 is a schematic view around the fixing unit 20.

  In this embodiment, the fixing unit 20 and its driving means 29 are installed on a frame 30, and a mechanism that rotates the entire periphery of the fixing unit with a lever 35 coupled to the cam 36 with respect to the frame 30 is used.

  Here, a flag 31 is provided in the frame 30, and the rotation of the frame is detected by a photosensor 32 provided in the main body with respect to this flag.

  With this configuration, in this embodiment, the user operates the switching lever 35 to rotate the fixing unit 20 with the fulcrum 25 as a starting point, thereby changing the position of the fixing nip with respect to the transfer position.

  After rotating in this way, the bending angle of the recording material formed at the transfer position and the fixing nip position is reduced from α to β as shown in FIG. 3, and as a result, the recording material is sandwiched in the fixing nip. The pushing force F of the recording material onto the transfer portion is alleviated and transfer deviation can be prevented.

(Example 2)
Next, FIG. 4 shows a schematic view of an image forming apparatus according to the second embodiment.

  In this embodiment, a recording material detection sensor 26 is installed after the registration roller pair 19 of the paper feed unit, and the fixing nip position is changed by controlling the driving means 27 for changing the fixing nip through the main body control circuit according to the detection signal of this sensor. It was set as the structure to do.

  A schematic diagram of the fixing unit is as shown in FIG. 8. The fixing unit 20 and its driving means 29 are installed on a frame 30 and the frame is moved up and down by a gear train 33 such as a worm gear train or a rack and a gear. As the drive source, the drive means 27 installed in the main body, for example, a gear train such as a DC motor or a stepping motor is conceivable. However, another implementation means may be configured to distribute from the fixing drive means 29.

  As for sensors, one or more sensor signals, such as optical sensors, potential sensors, arm and microswitch combinations, etc., which detect the thickness, gloss, size, electrical resistance, load and temperature / humidity of the recording material. Is used for control.

  In this configuration, it is possible to detect the type of recording material in the main body of the image forming apparatus, and to take the optimum fixing nip position based on the detection result. It is possible to prevent paper from being used.

(Example 3)
Next, FIGS. 5 and 6 are schematic views of an image forming apparatus according to the third embodiment.

  5 is a diagram before the fixing nip position is moved, and FIG. 6 is a diagram after the fixing nip is moved.

  In this embodiment, the fixing unit 20 is rotated by the driving means 27 installed in the main body, and the driving force distributed by the gear train from the driving means 27 is connected to the rotating means of the paper discharge tray 24.

  As shown in FIG. 7, the rotation angle of the fixing unit 20 and the angle adjustment of the paper discharge tray 24 are performed by adjusting the reduction ratios of the individual gear trains G1 and G2, and fixing is performed according to the type of recording material to be discharged. The nip position and the output tray angle were changed.

  In this configuration, the sheet discharge tray angle also follows the change in the fixing nip position, so that when the recording material discharge angle θ is steep, the recording material is shown in a two-dot chain line during the discharge. It is possible to prevent a buckling trace from occurring due to buckling at 23 parts or the like.

1 is a cross-sectional view of an electrophotographic color image forming apparatus showing a first embodiment of the present invention. 1 is a cross-sectional view (fixed part schematic diagram) of an electrophotographic color image forming apparatus showing a first embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a recording material conveyance path before and after a fixing nip change. FIG. 6 is a cross-sectional view of an electrophotographic color image forming apparatus showing a second embodiment of the present invention. FIG. 6 is a cross-sectional view of an electrophotographic color image forming apparatus showing a third embodiment of the present invention. Sectional drawing of the electrophotographic color image forming apparatus showing the third embodiment of the present invention (after changing the fixing nip position). Sectional drawing (fixing part schematic diagram) of the color image forming apparatus of the electrophotographic system which shows 3rd Example of this invention. FIG. 4 is a cross-sectional view (fixed portion schematic diagram) of an electrophotographic color image forming apparatus showing a second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Scanner unit 5 Electrostatic transfer belt unit 7 Process cartridge 20 Fixing part 21a, b Fixing roller pair 23a, b Paper discharge roller pair 24 Paper discharge tray 26 Recording material detection sensor 27 Driving means 100 Color image forming apparatus S Recording Material

Claims (8)

Image forming means for forming a toner image on the image carrier, transfer means for transferring the toner image formed on the image carrier to a recording material, and a fixing device for fixing the toner image transferred on the recording material ,
In an image forming apparatus having
An image forming apparatus capable of changing a position of a fixing nip with respect to a transfer position.   2. The image forming apparatus according to claim 1, wherein the position of the fixing nip relative to the transfer position is changed by a detection signal of a recording material detection sensor installed in the conveyance path.   The image forming apparatus according to claim 1, wherein the discharge conveyance unit downstream of the fixing device moves in conjunction with a change in the fixing nip position with respect to the transfer position.   The image forming apparatus according to claim 1, wherein the position of the sheet stacking surface moves in conjunction with a change in the position of the fixing nip with respect to the transfer position.   3. The image forming apparatus according to claim 2, wherein the recording material detection sensor is one of a paper thickness detection sensor, an OHT detection sensor, and a gloss detection sensor.   2. The image forming apparatus according to claim 1, wherein the fixing nip position relative to the transfer position is changed according to the bending strength of the recording material being conveyed.   2. The image forming apparatus according to claim 1, wherein the bending strength of the recording material being conveyed is detected by a recording material loop amount detecting means provided in the conveyance path so that the position of the fixing nip relative to the transfer position can be changed.   2. The image forming apparatus according to claim 1, wherein when performing duplex printing, the fixing nip position relative to the transfer position is changed during first-side printing and second-side printing.

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