JP2007010957A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which desired image quality can be obtained appropriately by selecting a fixing device with a fixing roller different in separation characteristics, in accordance with information of a recording paper and image information of an image formed on the recording paper. <P>SOLUTION: The image forming apparatus has a plurality of fixing devices composed of a pair of a fixing roller and a pressure roller and selects one of the plurality of fixing devices, from the information of the recording paper and the image information of the image formed on the recording paper. In the image forming apparatus, the plurality of fixing devices are different from each other in the separation characteristics of the recording paper. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a printer, and more particularly to a multifunctional image forming apparatus having a plurality of fixing devices.

  Conventionally, a method of transferring a toner image on an image carrier formed by an image forming unit onto a recording paper and fixing the toner image on the recording paper with a fixing device having a heated fixing roller has been adopted. .

  The fixing roller covers the outer periphery of a tube made of aluminum or the like with an elastic layer, and further has a releasing effect by covering it with a fluorine resin (for example, PFA) layer. However, when the printing rate of the toner image on the recording paper is large If the image position occupies the leading edge of the recording paper or if the curvature of the fixing roller is small, the recording paper cannot be completely separated from the fixing roller, causing a problem of winding and jamming. This tendency is stronger as the bending rigidity of the recording paper is smaller.

In order to avoid this problem, a plurality of fixing devices are provided, the bending rigidity of the recording paper is detected, and an appropriate fixing device is selected according to the characteristics. For example, since a recording paper with high bending rigidity is a thick paper, a method of reducing the conveyance speed, increasing the pressure applied to the fixing roller, or increasing the heating energy (for example, see Patent Document 1) Provide multiple fixing devices with different fixing conditions, detect recording paper information and image information, and select a fixing device that can obtain the desired image quality according to the type of recording paper and the type of image without reducing the image forming efficiency A method (for example, see Patent Document 2) has been proposed.
Japanese Patent Laid-Open No. 9-258597 JP 2002-123108 A

  However, as the printing speed (sheets / minute) becomes faster, it is necessary to increase the diameter of the roller (decrease the curvature) in order to ensure the heating time at the nip portion involved in the fixing process of the fixing roller. . This reduces the separation performance of the recording paper from the fixing roller.

  The present invention selects a fixing device in which fixing rollers having different separation characteristics are arranged according to information on recording paper such as the amount of recording paper, the type of paper, and the image information of an image formed on the recording paper. An object of the present invention is to provide an image forming apparatus capable of accurately obtaining a desired image quality.

  A plurality of fixing devices each composed of a pair of a fixing roller and a pressure roller, and one of the plurality of fixing devices based on information on the recording paper and image information of an image formed on the recording paper. In the image forming apparatus for selecting the image forming apparatus, the plurality of fixing devices have different recording sheet separation characteristics.

  Since the recording paper can be easily separated from the fixing roller without being affected by the type of recording paper (the amount of paper, the type of paper) and the type of image (printing rate, image position), jamming during the fixing process can be avoided.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described.

  FIG. 1 is an explanatory diagram showing the overall configuration of the image forming apparatus.

  In FIG. 1, the image forming apparatus includes a double-sided document automatic feeder RADF and an image forming apparatus main body A.

  The double-sided document automatic feeder RADF is located at the upper part of the image forming apparatus main body A and can be opened and closed. The document on the document feed tray a is transported to a paper feed roller b, a separation roller c, a registration roller d, and a transport drum e, and the document is transported.

  Next, the image forming apparatus main body A includes an image reading apparatus 1, a control unit 2 serving as control means, an image writing apparatus 3, an image forming means 4, a cassette paper feeding means 5, a conveying means 6, and fixing devices 70 and 71 (72). ), Paper discharge means 8, re-conveyance means 9 and the like. Details of the fixing device will be described later.

  The optical system of the image reading apparatus 1 includes an exposure unit 14 including a light source and a first mirror, a V mirror unit 15 including a second mirror and a third mirror, a lens 16, and a CCD image sensor 17. Document reading by the double-sided document automatic feeder RADF is performed at a position where the exposure unit 14 is stopped at the initial position below the slit exposure glass 13. Reading a document on the platen glass 11 is performed while moving the exposure unit 14 and the V mirror unit 15.

  Image information of the original image read by the image reading apparatus 1 is subjected to image processing by the control unit 2 including image processing means, converted into a signal as image data, and temporarily stored in a memory. Output light from a semiconductor laser (not shown) included in the image writing means 3 is applied to the photosensitive drum 21 which is an image carrier to form an electrostatic latent image.

  In the image forming means 4, a charge (negative charge in the present embodiment) is added to the photosensitive drum 21, which is an image carrier, by the charger 22, and the electrostatic latent image is irradiated by laser light from the image writing means 3. An image is formed, and the electrostatic latent image is visualized by the developing device 23 to become a toner image (negative charge in the present embodiment). Next, the sheet is conveyed from the cassette sheet feeding means 5 and transferred by the transfer device 29A onto the recording paper P, which is a transfer material synchronized with the toner image on the photosensitive drum by the registration roller 55 via the conveying roller 50. The recording paper P is peeled off by the separator 29B. The sheet P on which the toner image has been transferred is conveyed by the conveying means 6, fixed by the fixing means 70 or 71 (72), and discharged by the paper discharging means 8 to the paper discharge tray 81 outside the apparatus.

  On the other hand, the transfer residual toner is removed by a cleaning device 26 as a cleaning means. In the case of duplex copying, the recording paper P on which the image is formed on the first surface is sent to the re-conveying means 9 by the conveying path switching plate 82 and reversed by the reversing mechanism 9a. After the image is formed, the paper is ejected by the paper ejection means 8 to a paper ejection tray 81 outside the apparatus. In the case of reverse paper discharge, the recording paper P branched from the normal paper discharge path by the transport path switching plate 82 is switched back and upside down in the reverse paper discharge unit 83, and then the paper discharge means 8 removes the recording paper P from the outside of the apparatus. The paper is discharged to the paper discharge tray 81.

  Next, the fixing device according to the present invention will be described.

  As described above, the bending rigidity of the recording paper and the type of image (printing rate, image position, etc.) influence the separation performance of the fixing roller. However, the present invention transfers the information on the recording paper and the recording paper. It is characterized in that an appropriate one is selected from a plurality of fixing devices having different separation performances based on image information of an image.

  That is, the bending rigidity of the recording paper is detected by the paper type detection means S1, and the type of the image is detected by the image detection means S2. The detected information is transmitted to the control unit 2, and the control unit 2 instructs the opening of the conveyance valve 6A (indicated by a solid line in FIG. 1) for guiding the recording sheet to an appropriate fixing device, and the recording sheet is selected. Fixing is performed by the fixing device 70.

  FIG. 2 is a diagram for explaining the paper type detection means.

  FIG. 3 is a diagram for explaining the image information detection means.

  In FIG. 2, S <b> 1 is an optical sensor that detects the amount of deflection of the leading edge of the recording paper, and is provided at a position at a predetermined distance f from the registration roller 55.

  The recording paper P is nipped and conveyed by the registration rollers 55, and the leading end is detected at a distance f. If the bending rigidity (amount) of the recording paper P is small, it bends greatly as shown by a solid line, and if the bending rigidity is high, the bending amount becomes small as shown by a dotted line. The bending stiffness of the recording paper P is detected from the change in the amount of light received by the sensor S1 depending on the amount of deflection, and the information is transmitted to the control unit 2, so that the control unit 2 selects a fixing device corresponding to the bending stiffness. Instruct and actuate the transfer valve 6A via a drive unit (not shown). The easiness of winding can be detected by detecting the amount of bending (mass per unit area) and the amount of bending related to the bending stiffness that varies depending on the type of paper.

  In other words, recording paper with high bending rigidity is less frequently wound on the fixing roller, and conversely, recording paper with low bending rigidity is large. Therefore, a fixing device that takes measures corresponding to bending rigidity is selected and winding is avoided. Is done.

  In FIG. 3, S2 is an optical sensor that detects the printing rate (amount) and detects the printing rate and image position (distance from the leading edge of the recording paper to the printing unit) of the toner image transferred onto the recording paper P. The detected information is transmitted to the control unit 2, and the printing rate and the image position are calculated. Further, the control unit 2 instructs to select an appropriate fixing device for the printing rate and the image position, and operates the conveyance valve 6A via a driving unit (not shown).

  In other words, an image with a high printing rate has a large amount of toner, and thus easily adheres to the fixing roller. Even when a toner image is located near the leading edge of the recording paper, the recording paper is difficult to separate from the fixing roller. Therefore, it is possible to avoid the winding by selecting a fixing device having a measure corresponding to the predetermined print rate or image position corresponding to the separation limit as a reference.

  A program for the printing rate and image position and the corresponding fixing device is recorded in the control unit 2.

  Next, a description will be given of a plurality of fixing devices in which a countermeasure against winding is taken.

  FIG. 4 is a diagram showing a pair of a fixing roller and a pressure roller in the present embodiment.

  In FIG. 4, H is a halogen lamp as a fixing heat source. Reference numerals 70A, 71A and 72A denote fixing rollers. The fixing rollers 70A and 70B are formed by covering an aluminum base tube with a silicone rubber (rubber hardness JISA 20 °) as an elastic layer having a thickness of 3 mm, further covering with a PFA layer as a release layer, and having an outer diameter of 60 mm. The fixing roller 72A has an aluminum tube covered with a silicone rubber (rubber hardness JISA 20 °) as an elastic layer having a thickness of 4 mm, and further covered with a PFA layer as a release layer, and has an outer diameter of 40 mm.

  Reference numerals 70B, 71B, 72B denote pressure rollers. The pressure rollers 70B and 71B cover the aluminum base tube with a 1 mm thick elastic layer of silicone rubber (rubber hardness JISA 20 °) and further with a release layer PFA layer, and have an outer diameter of 60 mm. In the fixing roller 72B, the aluminum base tube is covered with silicone rubber (rubber hardness JISA 20 °) which is an elastic layer having a thickness of 1 mm, and further covered with a PFA layer as a release layer, and has an outer diameter of 35 mm.

  In FIG. 4A, 70C is an oil supply device that applies silicone oil having a viscosity of 100 to 10000CS to the fixing roller 70A, and R is an oil application roller of felt material. By applying silicone oil to the fixing roller 70A, the recording paper is easily separated from the roller.

  The fixing roller 72A and the pressure roller 72B in FIG. 4C have a larger roller curvature and a larger elastic layer thickness / outer diameter ratio than those in FIGS. 4A and 4B, and the recording paper is separated. The structure is easy to do. Further, the fixing device having a smaller fixing roller diameter has a smaller hardness of the elastic layer. These are for increasing the nip width and improving the heat conduction effect to the recording paper as much as possible. For recording paper with a printing rate of 50 to 100%, the winding frequency is extremely high, so the type shown in FIG. 4 (a) having the maximum coating amount or the type having the minimum diameter shown in FIG. 4 (c) is selected. preferable.

  Further, when the present invention is applied to a color image forming apparatus, it is preferable to select the fixing device for applying the silicone oil shown in FIG.

As an example, when printing is performed with an image forming apparatus having two fixing devices 70 and 71 shown in FIGS. 4A and 4B, the recording paper is plain paper and coated paper with a weight of 80 g / m ² or less. Since the optical sensor S1 has a predetermined bending rigidity or less (both are easy to wind) on both sheets, the fixing device 70 with good separation is selected. Further, in the case of plain paper and coated paper having a paper weight of 81 g / m ² or more and 127 g / m ² or less, the optical sensor S1 has a fixing device 71 whose separation performance is inferior to that of the fixing device 70 because the plain paper has a predetermined bending rigidity or more. In this case, since the coated paper has a predetermined bending rigidity or less, the fixing device 70 with good separability is selected. Further, in the case of plain paper and coated paper with a paper amount of 128 g / m ² or more, the sensor S1 has a predetermined bending rigidity or more (not easy to wind) for both papers, so there is no need to make the fixing device 70 with good separation. The fixing device 71 is selected.

  In this embodiment, the image forming apparatus provided with two fixing devices has been described. However, three or more fixing devices having different separation performances may be provided. For example, several fixing devices having different silicone oil application amounts and several fixing devices having different fixing roller curvatures may be provided.

  Further, as shown in FIG. 5, the fixing rollers are arranged in series, and the fixing roller and the pressure roller are predetermined during the fixing process except for the fixing device selected by the control unit 2 based on the information of the optical sensors S1 and S2. It is also possible to adopt a structure that is separated by the length of.

  FIG. 5 is a diagram illustrating a plurality of fixing devices arranged in series.

  Next, fixing device selection will be described with reference to a flowchart from the start of image formation.

  FIG. 6 is a flowchart of an image forming process related to fixing device selection.

  In FIG. 1 and FIG. 6, when copying or printing is started (image formation start) in step T <b> 1, a toner image is formed on the photosensitive drum 21 by the image forming unit 4. After being synchronized with the toner image, the recording paper P is nipped and conveyed by the registration rollers 55, and in step T2, the bending rigidity as information of the recording paper P is detected by the optical sensor S1, and the toner image is further transferred. The recording paper P transferred by the device 29A is separated from the photosensitive drum 21 by the separator 29B. In step T3, image information (printing rate, image position, etc.) of the transferred toner image is detected. In step T4, one of the plurality of fixing devices is selected based on the recording paper / image information, and the transport valve 6A leading to it is operated. In step T5, the fixing process is performed. In step T6, image formation as a copy or print is completed. In the case of continuous printing, the process proceeds to N and the next image formation is started. In the case of single-sheet printing, the process proceeds to Y and printing is finished.

1 is an explanatory diagram illustrating an overall configuration of an image forming apparatus. It is a figure for demonstrating a paper type detection means. It is a figure for demonstrating an image position detection means. It is a figure which shows the pair of the fixing roller and heating roller in this Embodiment. It is a figure which shows the several fixing device arrange | positioned in series. FIG. 6 is a flowchart of an image forming process related to fixing device selection.

Explanation of symbols

2 Controller 21 Photosensitive drum 55 Registration roller 6A Conveyance valve 70, 71, 72 Fixing device 70A Fixing roller 70B Pressure roller 70C Oil supply device H Halogen lamp S1, S2 Optical sensor

Claims (11)

A plurality of fixing devices each composed of a pair of a fixing roller and a pressure roller, and one of the plurality of fixing devices based on information on the recording paper and image information of an image formed on the recording paper. In the image forming apparatus for selecting the image forming apparatus, the plurality of fixing devices have different recording sheet separation characteristics. The image forming apparatus according to claim 1, wherein an application amount of the release agent applied to the plurality of fixing devices is different. The image forming apparatus according to claim 2, wherein the release agent is a silicone oil having a viscosity of 100 to 10000 CS. The image forming apparatus according to claim 1, wherein the fixing rollers of the plurality of fixing devices have different curvatures. The fixing roller and the pressure roller are each composed of a metal core, an elastic layer, and a release layer, and the fixing device having a smaller diameter of the fixing roller has a larger elastic layer thickness / outer diameter ratio. The image forming apparatus according to claim 4. The fixing roller and the pressure roller are each composed of a metal core, an elastic layer, and a release layer, and the fixing device having a smaller diameter of the fixing roller has a smaller hardness of the elastic layer. Item 5. The image forming apparatus according to Item 4. The image forming apparatus according to claim 1, wherein the information on the recording paper is set according to a paper amount and a paper type. 8. The image forming apparatus according to claim 7, wherein when a fixing device having excellent separation characteristics is selected based on information on the recording paper, the coated paper is smaller in amount than the plain paper. The image forming apparatus according to claim 1, wherein the image information is a printing rate, an image position, and color information. In the case where the fixing device is selected based on image information having a recording sheet printing rate of 50 to 100%, the fixing device having the largest application amount of the release agent or the smallest diameter of the fixing roller is selected. The image forming apparatus according to any one of claims 1 to 6. The image forming apparatus according to claim 9, wherein when the fixing device is selected according to color information of a color image, the fixing device with the largest application amount of the release agent is selected.

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