JP2007003587A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing image failure such as image blur or image rub due to pulling or excessive slackening of paper in a transfer-fixing interval caused by a conveyance speed change due to a difference in the proportion of images to be printed. <P>SOLUTION: In the image forming apparatus that separately has a photoreceptor drum drive motor and a fixing drive motor, the speed of the fixing drive motor is varied according to the proportion of images to be printed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using a printer such as a laser printer or an LED printer, an electrophotographic system such as a digital copying machine, or an electrostatic recording system.

  2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic method such as a laser beam printer receives data related to printing, coded characters, and image image information from an external information processing device such as a computer, and receives code information in a formatter or the like. When converting to image information, an image image having density information such as a photograph is binarized and converted into image information by performing known image processing such as dither matrix and error diffusion method.

  Next, the electrophotographic engine part will be described with reference to FIG.

  The electrophotographic engine portion includes a primary charger 202 that charges the photosensitive drum 1 along the rotation direction around the photosensitive drum (photosensitive member) 201, and an exposure unit that exposes the photosensitive drum 201 to form an electrostatic latent image. 203, a developing device 204 that forms a toner image by attaching toner (developer) to the electrostatic latent image, a transfer roller (transfer device) 205 that transfers the toner image on the photosensitive drum 201 to the transfer material P, and residual toner A cleaning device 207 to be removed is provided. The transfer material P as a transfer destination of the toner image is fed and conveyed from a paper cassette (not shown) and fed to the photosensitive drum 1. The transfer material P fed to the photosensitive drum 201 is transferred with a toner image by a transfer roller (transfer device) 205 and then conveyed to a heat fixing device 206, where the transfer material P on which the toner image is fixed is outside the device. To be discharged.

As the heat fixing device 206, a heat roller type or film heating type device is widely used. In particular, a method that suppresses power consumption as much as possible without supplying power to the heat fixing device during standby, and more specifically, a film heating method that fixes a toner image on a recording material through a film between a heater unit and a pressure roller. A heat fixing method is proposed in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and the like.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980

  In recent years, a configuration has been adopted in which the distance between the transfer device and the fixing device is made as small as possible from the viewpoint of miniaturization of the device. However, due to this, the moderate slack of the paper provided to absorb the fluctuations in the paper conveyance speed cannot be sufficiently removed, and various image quality problems have become apparent.

  For example, if the paper transport speed for fixing becomes higher than the paper transport speed for transfer to some extent, paper inquiries occur between transfer and fixing, and image blurring occurs where the image is blurred at the transfer section. Conversely, when the transfer paper conveyance speed is faster than the fixing, the paper is excessively slackened between the transfer and fixing, and image rubbing occurs that rubs the printing surface of the paper inside the image forming apparatus.

  In order to solve these image problems, a method for changing the speed of the fixing drive motor has been attempted by providing a sensor for detecting the amount of slack in the paper between the transfer and fixing. There is a problem of doing. Further, since the sensor and the paper come into contact with an unfixed image on the paper, there is a problem that a sensor trace is generated in which the unfixed image at the sensor contact portion is electrostatically scattered.

  Therefore, without using a sensor, the fluctuation of the paper conveyance speed, for example, the amount of thermal expansion of the outer diameter of the pressure roller is predicted from the energization time of the heater, and the fixing speed is controlled by controlling the rotation speed of the fixing drive motor. Attempts have been made, for example, to make the paper transport speed at approximately constant.

  However, with this method, the paper transport speed for fixing is kept substantially constant, but since it does not support changes in the paper transport speed during transfer, image problems such as image blurring and image rubbing can be completely prevented. There is a problem that can not be.

  Here, the fluctuation of the paper conveyance speed in the transfer in question is mainly due to the difference in the printing rate. Conventionally, the transfer roller is driven to rotate the photosensitive drum about 1% slower than the process speed in order to prevent missing characters and the like, and the transfer roller conveys the paper at about 100%, and the peripheral speed difference between the photosensitive drum and the paper Is attached. At this time, the peripheral speed of the transfer roller is generally set about 2-3% faster than the process speed. Therefore, the coefficient of friction between the photosensitive drum and the paper changes depending on the printing rate, that is, the amount of toner interposed between the photosensitive drum and the paper. There is a tendency that the conveyance speed becomes slow.

  The present invention has been made in view of the above circumstances, and its purpose is to prevent image quality problems such as image elongation, blurring, and image rubbing due to fluctuations in the conveyance speed of the transfer roller portion depending on the printing rate, and to achieve high quality. It is to provide an image forming apparatus capable of obtaining an image at low cost.

  In order to achieve the above object, according to a first invention of the present application, a uniformly charged photoconductor is exposed to form an electrostatic latent image, and the electrostatic latent image is developed with a developer and developed. The transferred image is transferred onto the transfer material by a transfer nip formed by the photosensitive member and the transfer material, and a fixing nip is formed between a pair of fixing members that can rotate at least one of the transfer material image. In an electrophotographic image forming apparatus that is heated and fixed by being inserted to output, the image forming apparatus has a photosensitive member driving motor and a fixing device driving motor separately, and the fixing device according to the printing rate of the output image The speed of the drive motor is changed.

  According to a second aspect of the present application, the image forming apparatus includes an automatic image double-side device that automatically forms an image on both sides of the transfer material, and when the first side image is formed and the second side image is formed on the transfer material. And changing the speed change amount of the fixing drive motor according to the printing rate.

  According to a third aspect of the present application, the image forming apparatus includes means for detecting the thickness of the transfer material, and changes the speed change amount of the fixing drive motor according to the printing rate according to the thickness of the transfer material. Features.

  As described above, according to the first invention of the present application, it is possible to prevent the paper from being attracted and excessively loosened between the transfer and fixing caused by the difference in the printing rate, and image blurring, image rubbing, etc. The occurrence of image defects can be prevented.

  In addition, according to the second invention of the present application, not only the paper attracting and excessive slacking between the transfer and fixing due to the difference in the printing rate but also the curling of the first side and the second side at the time of double-sided printing. It is possible to prevent the paper from being attracted and excessively slackened between the transfer and fixing caused by the difference, and it is possible to prevent image defects such as image blurring and image rubbing.

  Further, according to the third invention of the present application, not only is the paper attracting and excessive slackening between the transfer and fixing due to the difference in the printing rate, but also between the transfer and fixing caused by the difference in the thickness of the paper. Inquiry and excessive slack of the paper can be prevented, and image defects such as image blurring and image rubbing can be prevented.

  Embodiments of the present invention will be described below.

(First embodiment)
FIG. 1 shows an image forming apparatus according to the present invention, that is, an image forming apparatus provided with a fixing device according to the present invention. 1 is a longitudinal sectional view showing a schematic configuration of a laser printer as an example of an image forming apparatus according to the present invention.

  First, the configuration of a laser printer (hereinafter referred to as “image forming apparatus”) will be described with reference to FIG.

  The laser printer shown in FIG. 1 includes a drum-type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined process speed in the direction of the arrow R1 by a driving unit (not shown).

  Around the photosensitive drum 1, a charging roller (charging device) 2, an exposure unit 3, a developing device 4, a transfer roller (transfer device) 5, and a cleaning device 7 are arranged in this order along the rotation direction.

  A paper feed cassette C that stores a transfer material P such as paper is disposed below the apparatus main body M. The paper feed roller 11, the transport roller 8, and the like are sequentially arranged along the transport path of the transfer material P. A top sensor 9, a conveyance guide 10, a fixing device 6 according to the present invention, a conveyance roller 12, a paper discharge roller 13, and a paper discharge tray 14 are arranged.

  Next, the operation of the image forming apparatus having the above configuration will be described.

  The photosensitive drum 1 that is rotationally driven in the direction of arrow R1 by a photosensitive drum driving means (not shown) is uniformly charged to a predetermined polarity and a predetermined potential by a charging roller 2. The surface of the charged photosensitive drum 1 is subjected to image exposure E based on the image information by the exposure means 3 such as a laser optical system on the surface, and the electrostatic charge image is formed by removing the charge in the exposed portion. The electrostatic latent image is developed by the developing device 4. The developing device 4 includes a developing roller 41, and a developing bias is applied to the developing roller 41 so that toner is attached to the electrostatic latent image on the photosensitive drum 1 and developed (visualized) as a toner image.

  The toner image is transferred to a transfer material P such as paper by the transfer roller 5. The transfer material P is stored in the paper feed cassette C, fed by the paper feed roller 11, transported by the transport roller 8, and transferred between the photosensitive drum 1 and the transfer roller 5 via the top sensor 9. It is conveyed to the nip part. At this time, the leading edge of the transfer material P is detected by the top sensor 9 and is synchronized with the toner image on the photosensitive drum 1. A transfer bias is applied to the transfer roller 5, whereby the toner image on the photosensitive drum 1 is transferred to a predetermined position on the transfer material P.

  The transfer material P carrying the unfixed toner image on the surface by transfer is transported to the fixing device 6 along the transport guide 10, where the unfixed toner image is heated and pressurized and fixed on the surface of the transfer material P. . The fixing device 6 will be described in detail later.

  After the toner image is fixed, the transfer material P is transported by the transport roller 12 and discharged by the paper discharge roller 13 onto the paper discharge tray 14 on the upper surface of the apparatus main body.

  On the other hand, after the toner image is transferred, the toner (transfer residual toner) that has not been transferred to the transfer material P and remains on the surface is removed by the cleaning blade 71 of the cleaning device 7 and used for the next image formation.

  By repeating the above operation, image formation can be performed one after another. The image forming apparatus according to the present exemplary embodiment can perform printing at a printing speed of 600 dpi and 35 sheets / min (process speed of about 201 mm / sec).

  Next, an example of the fixing device 6 according to the present invention will be described in detail with reference to FIG. This figure is a longitudinal sectional view along the transfer material P conveyance direction (arrow K direction).

  The fixing device 6 shown in FIG. 1 heats the toner through a fixing film 25 as a film-like fixing rotating body, a pressure roller 26 as a fixing rotating body in contact with the fixing film 25, and the fixing film 25. The main constituent members are a ceramic heater (heater) 20, a temperature control means 27 for controlling the temperature of the ceramic heater 20, and a fixing device rotation control means 28 for controlling the conveyance of the transfer material P.

  The ceramic heater 20 is a resistance heating element, and is formed by forming a resistor pattern 22 on a heat-resistant base material 21 such as alumina by printing, for example, and covering the surface with a glass layer 23. It is long in the left-right direction (that is, the direction perpendicular to the paper surface) in the transport direction (arrow K direction), that is, longer than the width of the transfer material P. The ceramic heater 20 is supported by a heater holder 29 attached to the apparatus main body M. The heater holder 29 is a member formed in a semicircular shape with a heat resistant resin, and also acts as a guide member for guiding the rotation of the next fixing film 25.

  The fixing film 25 has a heat capacity smaller than that of the pressure roller 26. The fixing film 25 is formed by forming a heat-resistant resin such as polyimide into a cylindrical shape, and a release layer such as a fluororesin is provided on the surface. The fixing film 25 has a total thickness of 100 μm or less, and is loosely fitted to the ceramic heater 20 and the heater holder 29 described above. The fixing film 25 is pressed against the ceramic heater 20 by a later-described pressure roller 26, so that the back surface of the fixing film 25 is brought into contact with the lower surface of the ceramic heater 20. The fixing film 25 is configured to rotate in the arrow R25 direction as the transfer material P is conveyed in the arrow K direction by the rotation of the pressure roller 26 in the arrow R26 direction. The left and right end portions of the fixing film 25 are regulated by guide portions (not shown) of the heater holder 29 so as not to be displaced in the longitudinal direction of the ceramic heater 20. Further, grease is applied to the inner surface of the fixing film 25 in order to reduce sliding resistance between the ceramic heater 20 and the heater holder 29.

  The pressure roller 26 is provided with a heat-resistant release layer 262 having elasticity such as silicone rubber on the outer peripheral surface of a metal core 261, and a fixing film from below by the outer peripheral surface of the release layer 262. 25 is pressed against the ceramic heater 20 to form a fixing nip portion N (hereinafter simply referred to as “nip N”) with the fixing film 25.

  The temperature control means 27 controls the thermistor 24, which is a temperature detection means attached to the back surface of the ceramic heater 20, and the triac 272 based on the temperature of the ceramic heater 20 detected by the thermistor 24, thereby controlling the energization of the ceramic heater 20. CPU 271 to be used.

  The fixing device rotation control unit 28 includes a motor 281 that rotates the pressure roller 26 and a CPU 282 that controls the rotation of the motor 281. As the motor 281, for example, a stepping motor or a DC motor can be used, and the pressure roller 26 can be continuously rotated in the direction of the arrow R <b> 26.

  A motor 281 that predicts the warming condition of the pressure roller 26 from the energization time and non-energization time of the heater 20 and rotates the pressure roller 26 according to the thermal expansion amount of the outer diameter of the pressure roller 26. Is adjusted as appropriate so that the paper transport speed of the fixing device 6 is substantially constant.

  As described above, the paper conveyance speed of the fixing device 6 is controlled to be substantially constant, but the paper conveyance speed at the portion of the transfer roller 5 varies depending on the output image printing rate. FIG. 3 shows an example of the relationship between the printing rate of the output image and the paper conveyance speed (sub-scanning magnification) of the 5 parts of the transfer roller. As can be seen from FIG. 3, as the printing rate increases, the paper feeding speed increases, and when the printing rate exceeds about 30%, the paper feeding speed increases to 100.4%. Note that the paper conveyance speed (sub-scanning magnification) is calculated from the amount of deviation in the paper conveyance direction K of the interval of the lattice image actually output when the lattice pattern image data at intervals of 10 mm is printed. Accordingly, when the paper conveyance speed is faster than the process speed, the lattice spacing is larger than 10 mm, and is larger than 100%. When the paper conveyance speed is slower than the process speed, it is smaller than 10 mm and smaller than 100%. The relationship between the printing rate and the paper conveyance speed (sub-scanning magnification) is obtained by printing a composite image in which images having different printing rates are superimposed on a lattice pattern image.

  As described above, since the paper conveyance speed of the transfer roller 5 is changed depending on the printing rate, the paper is attracted between the transfer and fixing, and the image is blurred or excessively loosened. May cause image defects such as image rubbing.

  Therefore, in this embodiment, control is performed to change the rotational speed of the fixing device driving motor 281 in accordance with the printing rate of the output image.

  The fixing device driving motor speed control of this embodiment will be specifically described with reference to the flowchart of FIG.

  First, in the formatter 30 of the image forming apparatus M, encoded character and image image information transmitted from a host computer (not shown) is converted into binarized image data (S101). Next, a printing rate, that is, a ratio of dots in the entire image data is calculated from the binarized image data (S102). The fixing device driving speed is determined according to the calculated printing rate (S104 to S106), and the rotation speed of the fixing device driving motor 281 is switched at a predetermined timing until the paper reaches the fixing device 6 (S107 to S109). .

  The above operation is repeated and printing is performed up to the designated number (S110).

  In this embodiment, the print rate of the output image is calculated from the image data of the formatter. However, it is also possible to calculate from the ratio of the integrated value of the laser emission time and the non-light emission time.

  Table 1 shows whether image blurring and image blurring occur when the rotational speed of the fixing drive motor 281 is changed or not changed according to the printing rate as in this embodiment.

  As can be seen from Table 1, when the fixing drive motor speed control based on the printing rate is not performed, image blurring occurs due to paper inquiries between transfer and fixing at a low printing rate, and excessive paper transfer between fixing and fixing at a high printing rate. The image is rubbed due to the slack. On the other hand, it can be seen that the speed control of this embodiment does not cause image defects such as image blurring and image blurring regardless of the printing rate.

  As described above, by changing the speed of the fixing drive motor 281 depending on the printing rate, it is possible to prevent image defects such as image blurring and image rubbing due to paper drawing between transfer and fixing and excessive slack.

  In this embodiment, in an image forming apparatus having an automatic image double-side device that automatically forms images on both sides of paper, the case where an image is formed on the front side (hereinafter referred to as the first side) and the back side (hereinafter referred to as the second side). The control for changing the speed of the fixing drive motor 281 when an image is formed will be described. The other conditions are the same as in the previous embodiment, and a repetitive description is omitted.

  First, the operation of the image forming apparatus during automatic duplex printing will be described.

  After the image formation on the first side is performed in the same procedure as in the first embodiment, the transfer material P is sent to the paper discharge guide 50 side, and a part (the front end portion) is once discharged outside the printer main body. Thereafter, the paper is switched back by the paper discharge roller 13 and sent to the second surface paper supply roller 51. The transfer material P that has been reversed upside down in this way is sent again to the photosensitive drum 1 by the registration roller pair 8 and printing on the second surface of the transfer material P is performed. By repeating the above operation, images can be automatically formed on both surfaces of the transfer material P.

  Next, the difference in the state of paper transport between transfer and fixing during automatic duplex printing will be described.

  FIGS. 5A and 5B show an example of the difference in the paper conveyance state between the first side and the second side during automatic duplex printing. FIG. 5 shows a case in which the fixing device of this embodiment warps to the opposite side to a general printing surface, where (a) shows the paper conveyance state on the first surface and (b) shows the second surface. As can be seen from FIG. 5, the second surface is transported along the transport guide 10 by the influence of curl rather than the first surface. Accordingly, the second surface is unlikely to attract paper between the transfer and fixing, and the looseness is likely to occur.

  Therefore, in this embodiment, when the image is formed on the second side of automatic double-sided printing, where paper looseness is likely to occur between transfer and fixing, control is performed to set the rotation speed of the fixing drive motor faster than that on the first side.

  The control of this embodiment will be specifically described with reference to the flowchart of FIG.

  First, the coded character and image image information transmitted from the host computer (not shown) in the formatter 30 of the image forming apparatus M is converted into binarized image data (S201), and binarized. From the image data, the printing rate, that is, the ratio of dots in the entire image data is calculated (S202). Next, it is determined whether the first side or the second side of the automatic double-sided printing (S203). In the case of the second side, the rotation speed of the fixing driving motor 281 for the second side is determined according to the calculated printing rate (S204-). S207), the rotation speed is switched at a predetermined timing (S208 to S210). In the case of the first surface, the same control as in the first embodiment is performed (S211).

  The above operation is repeated, and printing is performed up to the designated number (S212).

  Table 2 shows the results of checking for image defects when the fixing drive motor control of this embodiment is performed and not performed on the second surface of automatic duplex printing.

  From Table 2, when printing the second side of the automatic duplex printing, if the fixing drive motor control is not performed, image rubbing occurs due to excessive looseness of the paper between the transfer and fixing, whereas in the control of this embodiment, It can be seen that image rubbing does not occur.

  As described above, by changing the fixing device driving speed control based on the image printing rate on the first and second sides of automatic double-sided printing, image blurring and image rubbing due to paper pulling between transfer and fixing and excessive slack It is possible to prevent image defects such as the above.

  In this embodiment, control for changing the speed change of the fixing drive motor according to the printing rate according to the paper thickness according to the paper thickness will be described. The other conditions are the same as in the previous embodiment, and a repetitive description is omitted.

  Depending on the thickness of the paper, the paper state varies greatly between the transfer and fixing because the paper strain differs. FIG. 7 shows the difference in paper conveyance state when plain paper and thick paper are passed. As can be seen from FIG. 7, plain paper is weak along the conveyance guide 10 because it is weak, whereas thick paper with strong paper stiffness is conveyed along the conveyance guide 10. Accordingly, thick paper tends to attract paper between transfer and fixing, and image blurring tends to occur more easily than plain paper.

  Therefore, in this embodiment, control is performed to set the rotation speed of the fixing drive motor 281 slower when the thick paper is passed than when the sealed paper is passed. In this embodiment, an example in which the rotation speed of the fixing drive motor 281 is changed in conjunction with the user's paper type setting (fixing thick paper mode: a mode for improving the fixing property) will be described. However, the thickness of the paper is detected. The same effect can be obtained by a method of changing in conjunction with the detection result of the sensor.

  The control of this embodiment will be specifically described with reference to the flowchart of FIG.

  First, in the formatter 30 of the image forming apparatus M, encoded characters and image image information transmitted from a host computer (not shown) are converted into binarized image data (S301), and a binarized image is obtained. From the data, the printing rate, that is, the ratio of dots in the entire image data is calculated (S302). Next, it is determined whether or not the fixing cardboard mode is set (S303). If the fixing cardboard mode is set, the fixing device driving speed for cardboard is determined according to the calculated printing rate (S304 to S304). (S307), the rotation speed is switched at a predetermined timing (S308 to S310). If the cardboard mode is not set, the same control as that in the first embodiment is performed (S311).

  The above operation is repeated and printing is performed up to the designated number (S312).

Table 3 shows the results of confirming the occurrence of image blur and image blur when the speed control of the fixing drive motor 281 is performed according to the paper thickness and when it is not performed. Note that Xx4024 (163 g / m ² ) was used for confirmation of image defects.

  As can be seen from Table 3, by changing the speed of the fixing device in accordance with the thickness of the paper, it is possible to prevent image blur that tends to occur during thick paper printing.

  As described above, by changing the rotation speed of the fixing drive motor according to the printing rate depending on the paper thickness, image blurring and image rubbing caused by excessive tension or looseness of the paper between the transfer and fixing, regardless of the thickness of the paper. Image defects can be prevented.

1 is a configuration diagram of an image forming apparatus according to the present invention. Configuration diagram of heat fixing apparatus according to the present invention Diagram showing the relationship between the printing rate and the paper transport speed of the transfer roller The figure showing the flowchart of control of Example 1. (A) The figure showing the paper conveyance state of the 1st page of automatic duplex printing (b) The figure showing the paper conveyance state of the 2nd page of automatic duplex printing The figure showing the flowchart of control of the present Example 2. (A) The figure showing the paper conveyance state of plain paper (b) The figure showing the paper conveyance state of thick paper The figure showing the flowchart of control of the present Example 3. Configuration of conventional image forming apparatus

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging roller (charging means)
3 Laser scanner (exposure means)
4 Developing device 5 Transfer roller 6 Fixing device 7 Cleaning device 71 Cleaning blade 9 Top sensor 10 Transport guide 20 Heating member (heater)
21 Ceramic substrate 22 Heating resistance layer 23 Thin glass protective layer 24 Temperature sensing element 25 Thin film (fixing film)
26 Pressure roller 261 Pressure roller mandrel 27 Fixing device temperature control means 271 Fixing device temperature control CPU
272 Triac 28 Fixing device rotation control means 281 Fixing drive motor 282 Fixing device rotation control CPU
29 Stay holder N Fixing nip P Transfer material

Claims (3)

A uniformly charged photoconductor is exposed to form an electrostatic latent image, the electrostatic latent image is developed with a developer, and the developed image is transferred to a transfer material by a transfer nip formed by the photoconductor and the transfer material. An electrophotographic image forming apparatus that forms a fixing nip between a pair of fixing members, at least one of which can be transferred, and which is heated and fixed by being inserted into the fixing nip and outputting the image on the transfer material. In
The image forming apparatus has a photoreceptor driving motor and a fixing device driving motor separately,
An image forming apparatus, wherein a speed of a fixing device driving motor is changed in accordance with a printing rate of an output image. The image forming apparatus includes an automatic image double-side device that automatically forms an image on both sides of a transfer material,
2. The image forming apparatus according to claim 1, wherein the speed change amount of the fixing drive motor is changed according to the printing rate between the first side image formation and the second side image formation of the transfer material. The image forming apparatus includes a means for detecting the thickness of the transfer material,
The image forming apparatus according to claim 1, wherein the speed change amount of the fixing drive motor according to the printing rate is changed according to the thickness of the transfer material.

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