JP2007193165A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of shortening useless waiting time until image forming operation is started by setting appropriate idling time so that paper wrinkles and unevenness of fixing property can be prevented from occurring because heat is accumulated without being consumed in a paper non-passing area as shown when a toner image is fixed on large-size paper after consecutively fixing a toner image on small-size paper by a fixing means. <P>SOLUTION: The image forming apparatus is equipped with: an idling performing means for performing the idling of a rotating member when the toner image is consecutively fixed on paper whose size is smaller than maximum size by the fixing means and then an unfixed toner image is fixed on paper whose size is larger than the size of the paper on which the toner image is consecutively fixed; and an idling time control means for controlling an idling time when the idling performing means performs the idling in accordance with image information of the paper to which fixing processing is performed next. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having these functions, which employs an electrophotographic method, and in particular, a toner image is continuously applied to a small size paper by a fixing unit. After fixing, a technical problem associated with storing heat without being consumed in the non-sheet passing area, such as when fixing a toner image on a large size paper, requires a long non-sheet passing blank time. The present invention relates to an image forming apparatus that can be solved without any problems.

JP 04-322284 A Japanese Patent Laid-Open No. 11-73055 JP 2002-72763 A JP-A-11-52788

  Conventionally, in an image forming apparatus such as a copying machine or a printer that employs this type of electrophotographic method, a toner image is formed on a photosensitive drum according to image information, and the toner image formed on the photosensitive drum Or a plurality of toner images of different colors such as yellow, magenta, cyan and black, which are sequentially formed on the same or a plurality of photosensitive drums, are temporarily transferred onto the intermediate transfer member. After being transferred in a superposed state, the image is transferred from the intermediate transfer body onto the paper at once, and then the toner image is fixed on the paper by a fixing device, thereby forming a monochrome or full-color image. ing.

  By the way, in such an image forming apparatus, when fixing the toner image onto the paper by the fixing device, when fixing processing is performed by continuously passing a small size paper, a heating member such as a heating roll of the fixing device. Is heated so that the maximum size paper can be fixed, and in the non-sheet passing area corresponding to the size difference between the maximum size paper and the small size paper, heat is not consumed in the fixing nip portion, and heat is stored. Will be.

  As a result, in the image forming apparatus, the temperature of the non-sheet passing area of the heating roll of the fixing device is raised to a temperature higher than a predetermined fixing temperature, and the portion of the non-sheet passing area of the heating roll is excessively large. There is a problem that the sheet expands due to heat and wrinkles are generated on the sheet or a difference in fixing property occurs between the sheet passing area.

  In view of this, a technique disclosed in Japanese Patent Laid-Open No. 04-322284 has already been proposed as a technique that can solve the problems associated with the temperature rise of the non-sheet passing portion of the fixing device.

  An image forming apparatus according to Japanese Patent Application Laid-Open No. 04-322284 includes a fixing roller and a pressure roller pressed against the fixing roller, and heats and fixes the unfixed toner image on the transfer paper by heating at least the fixing roller. A fixing device that detects the temperature of a plurality of regions that are provided in the fixing device and differ in the axial direction of the fixing roller, and a means that detects that the transfer paper has been discharged. In an image forming apparatus capable of obtaining a plurality of recording images of different paper sizes, a plurality of recording images having a paper size other than the maximum size are formed, and the last transfer paper is detected by the signal detected by the discharge detection unit. The roller is configured to idle for a predetermined time.

  However, in the case of the image forming apparatus according to Japanese Patent Laid-Open No. 04-322284, the last transfer sheet is configured to idle for a predetermined time by a signal detected by the discharge detection means. When the fixing roller is idled for a predetermined time until the temperature distribution of the fixing roller is sufficiently uniform between the previous job and the next job, a long blank time is required for the idle rotation time. The substantial operation of the image forming apparatus is shortened, and there is a problem that the image forming apparatus cannot be applied to an image forming apparatus that requires high productivity in recent years.

  Therefore, as techniques that can solve the above-mentioned problems, those disclosed in JP-A-11-73055, JP-A-2002-72763, JP-A-11-52788, and the like have already been proposed. .

  A method for controlling an image forming apparatus according to the above Japanese Patent Application Laid-Open No. 11-73055 includes a rotatable fixing member having a rotating body having an outer peripheral surface for heat conduction to a sheet-like transfer material carrying an unfixed image. A rotary pressure member that is pressed against the fixing member through the transfer material, a heating unit that heats at least the fixing member, and a drive mechanism that rotates the pressure member. A method for controlling an image forming apparatus including a heat fixing device, wherein a driving mechanism rotates a pressure body a plurality of times in one direction for a first specified time after continuous fixing processing to a plurality of transfer materials. In the control method of the image forming apparatus provided with the heating and fixing device, after a continuous fixing process over a plurality of sheets to a small size paper which is a transfer material having a smaller size than the transfer material of B5 size, it is longer than the first specified time. Over the second specified time Drive mechanism is configured to allowed to multiple rotating pressing body in one direction.

  Also, the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 2002-72763 (A01) is a heating that fixes an unfixed toner image on a recording sheet that rotates while being pressed against each other and passes through a fixing area formed by the pressing area. Rotating member for fixing and rotating member for pressure fixing, (A02) Large-sized sheet used for fixing a large-sized sheet disposed inside the rotating member for heating and fixing and extending in the width direction of the recording sheet A heating fixing member having a heater and a small size use heater used for fixing a small size sheet as compared to the large size sheet, and the heating fixing rotating member; (A03) sheet size and image used in the previous job; Previous job information storage means for storing the number of recordings, (A04) Measure the elapsed time from the end of the previous job to the input of the next job command signal Overtime detection means, (A05) Sheet size storage means for detecting and storing the sheet size used in the next job, (A06) The sheet used in the previous job is a small size sheet and the sheet used in the next job is large In the case of a size sheet, there is provided idle rotation execution means for performing only idle rotation of the heating and fixing rotation member and the pressure fixing rotation member by turning on only the small size use heater according to the elapsed time. It is configured.

  Further, the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 11-52788 has a fixing roller for fixing an image with heat, and performs an operation for performing a preparatory operation for rotating the fixing roller after the power is turned on and before starting a copying operation. In the forming apparatus, when there is an instruction to start copying by the user, a rotation time determining means for determining a rotation time of the fixing roller in the preparation operation according to a copy condition designated by the instruction, and the rotation time determination And a control means for stopping the preparation operation immediately after confirming the passage of the time determined by the means and starting the copy operation.

  However, the conventional technique has the following problems. That is, in the case of the control method of the image forming apparatus according to the above Japanese Patent Application Laid-Open No. 11-73055, after the continuous fixing process over a plurality of sheets on a small size paper which is a transfer material smaller in size than the B5 size transfer material, This is because the drive mechanism is configured to rotate the pressurizing body a plurality of times in one direction over a second specified time longer than the one specified time, resulting in a temperature rise in the non-sheet passing region. In order to solve the problem, the second specified time has to be set to a certain length, and the idling time is shortened as compared with Japanese Patent Laid-Open No. 04-322284 in which the fixing roller is idly rotated for a predetermined time. Even though it was possible, the idle rotation time could not be set appropriately.

  Further, in the case of the image forming apparatus according to Japanese Patent Application Laid-Open No. 2002-72763, when the sheet used in the previous job is a small size sheet and the sheet used in the next job is a large size sheet, according to the elapsed time. It is configured to include idle rotation execution means for performing only idle rotation of the heating fixing rotating member and the pressure fixing rotating member by turning on only the heater used at the small size, but used at the small size. A separate heater is required, resulting in an increase in cost, and even if idling is performed, it is unclear whether the temperature of the rotating member for heating and fixing sufficiently decreases due to a difference in environmental temperature or the like. Has a problem that cannot be set appropriately.

  Further, in the case of the image forming apparatus according to the above-mentioned Japanese Patent Application Laid-Open No. 11-52788, the image forming apparatus has a fixing roller for fixing the image with heat, and after the power is turned on, the preparatory operation for rotating the fixing roller before starting the copying operation This is related to an image forming apparatus that performs the above-described image processing, and has a problem that the effect cannot be obtained for a problem caused by non-uniform temperature of the non-sheet passing area of the fixing roller due to the previous fixing process. Was.

  Accordingly, the present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to fix a large image after a toner image is continuously fixed on a small size paper by a fixing unit. As in the case where the toner image is fixed on the other paper, the generation of paper wrinkles due to the heat being stored in the non-sheet passing area without being consumed, the occurrence of non-uniform fixing properties, etc. An object of the present invention is to provide an image forming apparatus that can be prevented by setting a rotation time and can reduce a useless waiting time until an image forming operation is started.

That is, according to the first aspect of the present invention, the unfixed toner image is transferred onto the sheet by conveying the sheet on which the unfixed toner image is transferred while being sandwiched by a pair of rotating members each having a heating source. In an image forming apparatus provided with fixing means for fixing to
After fixing a sheet of a size smaller than the maximum size continuously by the fixing unit, when fixing an unfixed toner image on a sheet having a size larger than the sheet of the size fixed continuously, the rotation member Idle rotation execution means for executing idle rotation;
An image forming apparatus comprising: an idle rotation time control unit that controls an idle rotation time executed by the idle rotation execution unit in accordance with image information of a sheet on which a fixing process is performed next.

  According to a second aspect of the present invention, the idling time control means includes an average image density of a sheet on which a fixing process is performed next, image information of a specific area, and an intermediate portion and a rear end along the sheet conveyance direction. 2. The image formation according to claim 1, wherein the idling time is controlled in accordance with at least one of image information of a portion and image information of 100 mm or more from the leading edge of the sheet along the conveyance direction. Device.

  Furthermore, the invention described in claim 3 is the image forming apparatus according to claim 1 or 2, wherein the image information is information about an image structure.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the structure information of the image is information about dot processing or error diffusion processing of the image.

  Furthermore, the invention described in claim 5 is characterized in that the idling time control means controls the idling time of the rotating member to be longer when the image density is lower in the image information. An image forming apparatus according to any one of claims 1 to 4.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the second aspect, the image information is image arrangement information along a sheet conveyance direction.

  Further, in the invention described in claim 7, the idling time control means controls the idling time according to the surface temperature of the rotating member having the heating source immediately before passing the sheet to be fixed next. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

  In the invention described in claim 8, the idle rotation time control means controls the idle rotation time in accordance with the number of continuous paper sheets having a size smaller than the maximum size, and the number of continuous paper sheets to be passed. 8. The image forming apparatus according to claim 1, wherein the idle rotation time is controlled to increase as the number of rotations increases.

  Further, in the invention described in claim 9, the idling time control means controls the idling time in accordance with an elapsed time after continuously passing a sheet having a size smaller than the maximum size, and The image forming apparatus according to claim 1, wherein the idle rotation time is controlled to be shorter as the elapsed time is longer.

  According to the present invention, heat is not consumed in the non-sheet passing area as in the case where the toner image is fixed on a large size paper after the toner image is continuously fixed on the small size paper by the fixing unit. It is possible to prevent the occurrence of paper wrinkles and non-uniform fixing properties by setting an appropriate idle rotation time, and shorten the wasteful waiting time until the image forming operation is started. An image forming apparatus capable of doing so can be provided.

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

Embodiment 1
FIG. 2 is a block diagram showing a digital color copying machine as an image forming apparatus according to Embodiment 1 of the present invention.

  As shown in FIG. 2, this digital color copying machine is provided with an automatic document feeder (ADF) 2 that automatically feeds a document (not shown) separated one by one at the top of the copying machine main body 1. The automatic document feeder 2 also functions as a platen cover that presses the document placed on the platen glass 3. A document automatically conveyed onto the platen glass 3 by the automatic document conveying device 2 or a document placed on the platen glass 3 is read by the document reading device 4 disposed in the upper part of the copying machine main body 1. It is read and once converted into image data. The document reader 4 is reflected by an illumination lamp 5 that illuminates a document (not shown) placed on the platen glass 3, a half-rate mirror 6 that reflects a reflected light image from the document, and the half-rate mirror 6. The full-rate mirrors 7 and 8 that reflect the reflected light image of the original document to the imaging lens 9, and the optical image of the original document reflected by the full-rate mirrors 7 and 8 are reduced and irradiated to the image reading element 10 including a CCD or the like. And an image reading element 10 composed of a CCD or the like that reads an optical image of a document and converts it into an electrical signal.

  In the digital color copying machine, color image information of a color document read by the document reading device 4 is input to the image processing device 11, and the image processing device 11 performs shading correction and position shift correction as necessary. Predetermined image processing such as brightness / color space conversion, gamma correction, frame deletion, color / moving editing, and the like is performed. The digital color copying machine is also configured to function as a printer, and color image information sent from a host computer such as a personal computer (not shown) is also input to the image processing apparatus 11 of the copying machine. It is configured to be.

  The image data subjected to the predetermined image processing by the image processing apparatus 11 as described above is four colors of yellow (Y), magenta (M), cyan (C), and black (BK) (8 bits each). The material tone data is sent to a ROS 12 (Raster Output Scanner), and the ROS 12 sequentially performs image exposure with laser light according to the color material tone data.

  An image forming means 13 capable of forming a plurality of toner images having different colors is disposed inside the digital color copying machine main body 1. The image forming unit 13 mainly includes a photosensitive drum 14 as an image carrier on which an electrostatic latent image is formed, and a scorotron as a charging device that uniformly charges the surface of the photosensitive drum 14 to a predetermined potential. 15, ROS 12 as image exposure means for performing image exposure on the surface of the photosensitive drum 14, and electrostatic latent images formed on the photosensitive drum 14 are successively developed with different color toners, It is composed of a rotary developing device 16 as developing means capable of forming a plurality of toner images having different colors on the photosensitive drum 14.

  As shown in FIG. 2, the ROS 12 modulates a semiconductor laser (not shown) according to the color material gradation data, and emits a laser beam LB from the semiconductor laser according to the gradation data. The laser beam LB emitted from the semiconductor laser is deflected and scanned by the rotary polygon mirror 17 and is scanned and exposed on the photosensitive drum 14 as an image carrier through the f · θ lens 18 and the reflection mirror 19.

  The photosensitive drum 14 on which the laser beam LB is scanned and exposed by the ROS 12 is driven to rotate at a predetermined speed in the direction of the arrow by a driving unit (not shown). The surface of the photosensitive drum 14 is charged in advance with a predetermined polarity (for example, a negative polarity) and a potential by a scorotron 15 as a charging device for primary charging, and then laser light LB according to color material gradation data. Is subjected to scanning exposure to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 14 includes four color developing devices 16Y, 16M, 16C, and 16BK of yellow (Y), magenta (M), cyan (C), and black (BK). The rotary developing device 16 reversely develops, for example, a toner (charged color material) charged to a negative polarity that is the same polarity as the charged polarity of the photosensitive drum 14 to form a toner image of a predetermined color. In each of the developing devices 16Y, 16M, 16C, and 16BK of the rotary type developing device 16, for example, spherical toner having an average particle size of 5.5 μm is used. The toner image formed on the photosensitive drum 14 is charged with a negative polarity by the pre-transfer charger 20 as necessary, and the amount of charge is adjusted.

  In the digital color copying machine, for example, when a full color image is formed, every time the photosensitive drum 14 rotates, yellow (Y), magenta (M), cyan (C), black (BK). Toner images of each color of yellow (Y), magenta (M), cyan (C), and black (BK), which are sequentially exposed and developed on the photosensitive drum 14, are described later. As described above, primary transfer is performed on the intermediate transfer belt 21 while being superimposed on each other.

  The toner images of the respective colors formed on the photosensitive drum 14 are transferred onto a primary transfer roll 22 as a first transfer unit on an intermediate transfer belt 21 as an intermediate transfer member disposed below the photosensitive drum 14. Are transcribed in multiples. The intermediate transfer belt 21 has a peripheral speed of the photosensitive drum 14 by a drive roll 23, a tension roll 24, a backup roll 25 as a counter roll constituting a part of the secondary transfer means, and driven rolls 26a, 26b, and 26c. Is supported so as to be rotatable along the direction of the arrow at the same moving speed.

  On the intermediate transfer belt 21, four colors of yellow (Y), magenta (M), cyan (C), and black (BK) are formed on the photosensitive drum 14 according to the color of the image to be formed. The toner images of all or a part of the colors are transferred in a state of being sequentially superimposed by the primary transfer roll 22. The toner image transferred onto the intermediate transfer belt 21 is recorded on a recording paper 27 as a recording medium conveyed to a secondary transfer position at a predetermined timing, and a backup roll 25 that supports the intermediate transfer belt 21, Transfer is performed by the pressure contact force and electrostatic attraction force of the secondary transfer roll 28 that constitutes a part of the second transfer unit that is in pressure contact with the backup roll 25. As shown in FIG. 2, the recording paper 27 has a predetermined size from a plurality of paper feeding cassettes 29, 30, 31 a, 31 b arranged in the lower part of the digital color copying machine body 1 by a feed roll 32. Paper is fed. The fed recording paper 27 is transported to the secondary transfer position of the intermediate transfer belt 21 by a plurality of transport rolls 33 and registration rolls 34 at a predetermined timing. Then, as described above, the toner image of a predetermined color is collectively collected on the recording paper 27 from the intermediate transfer belt 21 by the backup roll 25 and the secondary transfer roll 28 as secondary transfer means. It is designed to be transcribed.

  The recording paper 27 onto which the toner image of a predetermined color has been transferred from the intermediate transfer belt 21 is separated from the intermediate transfer belt 21 and then conveyed to the fixing device 36 by the conveying belt 35. As a result, the toner image is fixed on the recording paper 27 by heat and pressure, and in the case of single-sided copying, it is discharged as it is onto the discharge tray 38 outside the apparatus by the discharge roll 37 to complete the color image forming process.

  On the other hand, in the case of double-sided copying, the recording paper 27 on which the color image is formed on the first surface (front surface) is not discharged out of the apparatus as it is, but the conveying direction is changed downward by a reversing gate (not shown). By the roll 39 and the reverse roll 40, it is once conveyed to the reverse passage 41. Then, the recording paper 27 is conveyed to the double-sided passage 42 by the reversing roll 40 which is reversed this time, and is temporarily conveyed to the registration roll 34 by the conveying roll 43 provided in the double-sided passage 42 and stopped. The recording paper 27 is started to be conveyed again by the registration roll 34 in synchronization with the toner image on the intermediate transfer belt 21, and the toner image transfer / fixing process with respect to the second surface (back surface) of the recording paper 27. After being carried out, it is discharged outside the machine.

  In FIG. 2, 44 is a cleaning device for removing residual toner, paper dust and the like from the surface of the photosensitive drum 14 after the transfer process is completed, and 45 is a surface of the photosensitive drum 14 before the cleaning process. A pre-cleaning corotron 46 for removing static electricity and a manual feed tray are respectively shown.

  FIG. 3 is a sectional view showing a fixing device as fixing means of the digital color copying machine. The fixing device is configured to fix the unfixed toner image on the sheet by conveying the sheet on which the unfixed toner image is transferred while being sandwiched by a pair of rotating members each having a heating source. ing.

  As shown in FIG. 3, the fixing device 36 includes a heating roll 51 as a heating rotating member and a pressure roll 52 as a pressing rotating member as a pair of rotating members that are pressed against each other to form a nip portion N. It has. The heating roll 51 and the pressure roll 52 are disposed so as to be switchable between a pressure contact state in which they are pressed against each other at a predetermined pressure and a separated state in which they are separated from each other. The heating roll 51 includes a cored bar 53 formed in a cylindrical shape from a metal such as stainless steel or aluminum, and a heat-resistant elastic body layer 54 made of a heat-resistant silicone rubber or the like that is thickly coated on the surface of the cored bar 53. And a release layer 55 made of tetrafluoroethylene, PFA, or the like coated on the surface of the heat-resistant elastic layer 54. In addition, three halogen lamps 56 are disposed inside the heating roll 51 as heating sources. The heating roll 56 is heated by the halogen lamp 56 from the inside, and the surface temperature of the heating roll 51 is increased. Is configured to detect the surface temperature by the temperature detection sensor 57 and to control the energization to the halogen lamp 56 so that the temperature becomes a predetermined temperature.

  As shown in FIG. 3, the heating roll 51 is configured to be rotationally driven at a predetermined rotational speed by a driving motor M via a driving force transmission means (not shown). Even when the recording paper 27 is not passed, it is configured to be driven to rotate for a predetermined idling time.

  Further, on the surface of the heating roll 51, a cleaning oil-impregnated web 58 impregnated with a release agent such as silicon oil is removed in order to remove foreign matters such as toner adhering to the surface of the heating roll 51. Abutted by a roll 59. The cleaning web 58 is supplied from a web supply roll 60 and is wound up at a predetermined timing by a web winding roll 61.

  On the other hand, the pressure roll 52 is composed of a core metal 62 formed in a cylindrical shape with a metal such as stainless steel or aluminum, and a heat resistant silicone rubber or the like having a heat resistance coated on the surface of the core metal 62 relatively thickly. An elastic body layer 63 and a release layer 64 made of tetrafluoroethylene, PFA or the like coated on the surface of the heat resistant elastic body layer 63 are configured. In FIG. 3, reference numeral 65 denotes a housing of the fixing device 36, and 66 denotes a conveyance roll provided at the outlet of the fixing device 36 for discharging the recording paper 27 fixed by the fixing device 36. ing.

  By the way, in the digital color copying machine according to this embodiment, the sheet on which the unfixed toner image is transferred is conveyed while being sandwiched between a pair of rotating members, at least one of which has a heating source, so that the unfixed toner image is transferred. In an image forming apparatus provided with fixing means for fixing on paper, after the paper having a size smaller than the maximum size is continuously fixed by the fixing means, the paper is larger in size than the paper of the size fixed continuously. When the unfixed toner image is fixed to the image, the idle rotation execution means for executing the idle rotation of the rotation member and the idle rotation time executed by the idle rotation execution means are used as image information of the sheet on which the fixing process is performed next. It comprises so that the idling time control means to control according to it may be provided.

  Further, in this embodiment, the idling time control means includes the average image density of the paper to be subjected to the fixing process next, the image information of the specific area, and the image information from the intermediate portion to the rear end portion along the paper conveyance direction. The idling time is controlled in accordance with at least one of the image information of 100 mm and after from the leading edge of the paper in the transport direction.

  That is, as shown in FIG. 4, the digital color copying machine according to this embodiment includes an MCU 100 having functions as an idling rotation execution unit and an idling time control unit. The MCU 100 includes a fixing device 36. After fixing the recording paper 27 having a size smaller than the maximum size continuously, the heating is performed when an unfixed toner image is fixed on the recording paper 27 having a size larger than the recording paper 27 having the continuously fixed size. The idle rotation of the roll 51 and the pressure roll 52 is executed, and the idle rotation time is controlled according to the image information of the recording paper 27 on which the fixing process is performed next.

  As shown in FIG. 5, the digital color copying machine can form an image on a recording sheet 27 having an A3 size as a maximum size and is smaller than the A3 size, which is the maximum size, for example, a B4 size. Images can be formed on papers of various sizes such as A4 size, B5 size, and postcard size, or on different types of paper such as thick paper and coated paper even with the same size.

  As shown in FIG. 4, the size and paper type of the recording paper 27 are designated by the operation panel 101 connected to the MCU 100, and can be continuously copied and printed by the number designated by the operation panel 101. It is configured as follows.

  Further, as shown in FIG. 2, the recording paper 27 is based on the central portion along the axial direction of the photosensitive drum 14 from the plurality of paper feeding cassettes 29, 30, 31a, 31b or the manual feed tray 46 (see FIG. 2). As shown in FIG. 5, the fixing device 36 also feeds paper using the central portion along the axial direction of the heating roll 51 as a reference (center registration), as shown in FIG. 5. The fixing process is executed.

  On the other hand, the halogen lamp 56 as a heating source of the heating roll 51 is disposed over the entire length of the heating roll 56. Therefore, in the fixing device 36, immediately after the recording paper 27 other than the maximum size, for example, the A4 size recording paper 27 is fed by SEF (Sort Edge Feed) and the fixing process is continuously performed, the heating roll 51 is used. It is known that the temperature of the non-sheet-passing area rises as compared with the sheet-passing area because heat is not consumed by the recording paper 27 but is stored.

  When the next job is started in the fixing device 36 continuously or within a predetermined time after the end of the previous fixing process, the halogen lamp 56 is lit on the heating roll 51 until just before the next job starts. , Thermal energy is replenished throughout the axial direction. Therefore, as shown in FIG. 6, the paper passing area of the heating roll 56 rises to a predetermined set temperature, but the non-paper passing area of the heating roll 56 is greatly deviated from the predetermined set temperature and is about a. Will rise to.

  In this state, when a next job, a job for fixing an unfixed toner image on a paper having a size larger than a continuously fixed size paper, for example, a job for fixing to a maximum size (A3 size) recording paper 27 is executed. In addition to causing a defect in image quality according to the temperature unevenness (a) on the surface of the heating roll 51, if the image forming operation is executed while continuing this state, the fixing member such as the heating roll 51 or the pressure roll 52 is used. In addition, defects due to heat occur, and the life of the fixing device 36 is shortened.

  Therefore, in the above embodiment, before the next job, the idle rotation operation of the fixing device 36 is executed for a predetermined idle rotation time so as to eliminate the temperature unevenness of the heating roll 51 as shown in FIG. It is configured. However, in order to make the surface temperature of the heating roll 51 uniform, it is desirable to set the idling time of the heating roll 51 to be long. However, while the heating roll 51 is idling, the image forming operation such as copying or printing that is the next job cannot be started, and the waiting time becomes long, which hinders work efficiency. The idling time should be kept to the minimum possible time.

  By the way, as a result of intensive studies on the mechanism that causes image quality defects due to temperature unevenness (a) on the surface of the heating roll 51, the present inventors have determined that image quality defects due to temperature unevenness (a) on the surface of the heating roll 51 are present. Is considered to occur as follows.

  The remarkable temperature difference (a) in the fixing nip N between the heating roll 51 and the pressure roll 52 partially enlarges the diameter of the rotating member such as the heating roll 51, and the heating roll 51 and the pressure roll 52. The outer diameter of the cylinder causes a large difference between the nip pressure at the central portion and both end portions in the axial direction and the linear velocity in the circumferential direction. As a result, the conveyance speed of the recording paper 27 becomes too fast at both ends of the heating roll 51 and the like, and image quality defects such as image shifts due to the heating roll 51 rubbing the toner image on the surface of the recording paper 27 occur. It will end up.

  In particular, what has become clear as a result of intensive studies by the present inventors is that the image quality defect occurring on the surface of the recording paper 27 depends on the image information to be fixed on the recording paper 27 to be fixed next. That is the fact. For example, when the image density of the next original, which is image information to be fixed on the recording paper 27 on which the fixing process is performed next, is light (the amount of toner on the recording paper 27 is small), the recording paper 27 and the heating roll 51 etc. The difference in the conveyance speed (linear velocity) of the heating roll 51 significantly affects the conveyance of the recording paper 27.

  On the other hand, when the image density of the next original, which is image information to be fixed on the recording paper 27 to be fixed next, is high (the toner amount on the recording paper 27 is large), It has been found that the toner plays the role of a lubricant, slipping occurs between the recording paper 27 and the heating roll 51 and the like, and the conveying force of the recording paper 27 tends to decrease.

  Therefore, in this embodiment, as shown in FIG. 4, in addition to the function of executing the idling rotation execution means, the MCU 100 that also functions as the idling time control means determines the idling time to be executed next as the fixing process. It is configured to control according to the image information of the paper to be performed.

  More specifically, the image quality defect caused by the non-uniform surface temperature of the heating roll 51 is not passed through the paper passing area of the heating roll 51 when the small-size recording paper 27 is continuously fixed. This occurs because there is a difference in how heat is taken away by the recording paper 27 through the paper area. Accordingly, as shown in FIG. 8, the image quality defect is better as the number of continuous sheets of small-size recording paper 27 is smaller (is less likely to appear). The number of continuous sheets of small-size recording paper 27 is smaller. It gets worse as it grows (prone to appear). In the figure, for the sake of convenience, the relationship between the image quality defect and the number of sheets to be passed is represented by a straight line (primary expression), but the relationship between the two is not limited to a straight line (primary expression), but a curve (secondary expression or cubic expression). Of course, it may be expressed by the following.

  In this embodiment, the MCU 100 includes the average image density of the recording paper 27 to be fixed next, the image information of a specific area, the image information from the middle portion to the rear edge along the conveyance direction of the recording paper 27, the recording paper. 27 is configured to control the idling time in accordance with at least one of the image information of 100 mm and after from the tip of 27 along the conveyance direction.

  Specifically, for example, the average image density (the number of pixels per unit area) of the recording paper 27 is used as the image information of the recording paper 27 to be fixed next, and the entire image area of the recording paper 27 is used. A value obtained by dividing the number of pixels of the formed image by the area of the image area of the recording paper 27 is used as the average image density of the recording paper 27. At that time, in the case of a monochrome image such as a monochrome image, the number of pixels may be counted depending on the presence or absence of the image, and in the case of a color image, yellow (Y), magenta (M), cyan (C), black ( The number of pixels of each color of (BK) is counted. For example, when yellow (Y) and magenta (M) images are formed on the same image area, the number of pixels in the image area is two. Further, when reproducing the halftone when forming the image, the number of pixels in the image area is obtained by multiplying the coefficient corresponding to the density (for example, 256 gradations).

  The image information of the recording paper 27 on which the fixing process is performed next may be calculated by the MCU 100. However, when the load on the MCU 100 becomes too large, the image information is calculated by the image processing apparatus 11. Is of course good.

  As the idling time data controlled by the MCU 100, for example, as shown in FIG. 4, data stored as an LUT in the ROM 101 or the like is used, but the LUT stored in the ROM 101 or the like is appropriately rewritten. You may comprise.

  As shown in FIG. 9, the idling time controlled by the MCU 100 is largely determined depending on whether the image density of the recording paper 27 to be fixed next is dark, thin, or medium. Depending on whether the number of small-size recording papers 27 is small, large, or medium, the idling time of the heating roll 51 is determined to be short, long, or medium.

  As shown in FIG. 9, the idling time controlled by the MCU 100 is controlled so that the idling time of the heating roll 51 is short when the image information of the recording paper 27 to be fixed next is dark. In addition, when the image information of the recording paper 27 to be fixed next is medium, the image of the recording paper 27 to be fixed next is set so that the idling time of the heating roll 51 is medium. When the information is thin, the heating roll 51 is controlled so as to increase the idling time.

  On the other hand, as shown in FIG. 9, the idle rotation time controlled by the MCU 100 is controlled so that the idle rotation time of the heating roll 51 is shortened when the number of small-size recording sheets 27 is small. When the number of sheets of small size recording paper 27 is medium, the number of sheets of small size recording paper 27 is large so that the idle rotation time of the heating roll 51 is medium. The idling time of the heating roll 51 is controlled to be longer.

  Further, as shown in FIG. 9, the idling time controlled by the MCU 100 is when the image information of the recording paper 27 to be fixed next is dark but the number of small-size recording papers 27 is large. The idling time of the heating roll 51 becomes medium or long, or the image information of the recording paper 27 to be fixed next is thin, but the number of small-size recording papers 27 is small. When the number is small, the idle rotation time of the heating roll 51 is controlled to be medium or short.

  Specifically, the MCU 100 is configured to control the idling time based on a table as shown in FIG. The table shown in FIG. 1 is an example, and it is needless to say that the table is not limited to this.

  As described above, the MCU 100 determines and controls the idling time according to the average image density of the sheet on which the fixing process is performed next. However, the MCU 100 is not limited to this, and the MCU 100 conveys the image information of the specific area and the conveyance of the sheet. The idling time is controlled according to at least one of the image information from the middle to the rear end along the direction and the image information after 100 mm along the transport direction from the front end of the sheet. Of course it is also possible.

  In this case, the MCU 100 uses the image information of the document read by the document reading device 4 or the image information sent from a personal computer (not shown), for example, image information of a specific area of the document, for example, the middle of the document. As shown in FIG. 10A, the idle rotation time is determined based on the image information located at both ends in the direction orthogonal to the conveyance direction of the recording paper 27 of the document. Is configured to determine and control. At this time, as the image information of the specific area of the original, for example, image information located rearward from the middle part of the original, and images located at both ends of the original in the direction orthogonal to the conveyance direction of the recording paper 27 of the original Focusing on the information, the image defect caused by the temperature non-uniformity along the axial direction of the heating roll 51 as shown in FIG. 6 is image information located rearward from the intermediate portion of the recording paper 27, This is because it tends to occur in images located at both ends in the direction orthogonal to the conveyance direction of the recording paper 27.

  In the digital color copying machine, the direction of the document read by the document reading device 4 and the conveyance direction of the recording paper 27 may not always coincide with each other, but in the present embodiment, the direction of the heating roll 51 is along the axial direction. Since image defects occur due to uneven temperature, it is necessary to pay attention to an area along the conveyance direction of the recording paper 27 when considering image information.

  Further, as shown in FIG. 10B, the MCU 100 includes image information (average image density) from an intermediate portion (for example, based on the center) to the rear end portion in the conveyance direction of the sheet on which fixing processing is performed next. Depending on the above, the idling time may be controlled.

  Further, as shown in FIG. 10C, the MCU 100 is configured to control the idling time in accordance with image information after 100 mm along the transport direction from the leading edge of the sheet to be fixed next. May be.

  Further, the MCU 100 may be configured to use not only the average image density but also information on the structure of the image as the image information of the sheet on which the fixing process is performed next. As the structure information of the image, for example, dot processing of the image, error diffusion processing, or information on the screen angle can be cited.

  As described above, the image defect caused by the nonuniformity of the surface temperature of the heating roll 51 differs in appearance depending on the image information of the sheet to be subjected to the fixing process next. When the average image density, which is image information, is high, the appearance differs depending on the structure of the image of the sheet on which the fixing process is performed next so that the image defect does not appear easily.

  As the structure of the image on the recording paper 27, an image structure by various image processes such as an image dot process and an error diffusion process is known and is actually used.

  In the above digital color copiers, screens with various structures such as line screens and dot screens are used to improve the reproducibility of halftone images such as photographic images, and the number of screen lines is also high. With this, it tends to increase to 1200 lpi, 2400 lpi, and the like.

  Even in the case of the dot screen, error diffusion processing or the like is used for higher image quality, and the pattern of the toner image formed on the recording paper 27 is microscopically viewed depending on the structure of the image. Unlike the case, the tendency of appearance of image defects due to non-uniformity of the surface temperature of the heating roll 51 changes.

  Therefore, the MCU 100 may be configured to use not only the average image density but also information about the structure of the image as the image information of the sheet on which the fixing process is performed next. As the structure information of the image, as described above, dot processing of the image, error diffusion processing, or information about the screen angle can be mentioned.

  For example, as shown in FIG. 12, the image structure subjected to the error diffusion processing is actually compared with the error distribution even if the same high image density is output as compared with the image structure subjected to the dot processing. Since the image density tends to be lower than that subjected to dot processing, it is necessary to perform the idling time slightly longer than in the case where dot processing is performed. On the other hand, when a light image density is output as a target, it is necessary to perform control for slightly shortening the idling time as compared with the case where dot processing is performed.

  In the above configuration, in the digital color copying machine according to the first embodiment, the toner image is continuously fixed on the small size paper by the fixing unit as described below, and then the toner image is applied on the large size paper. As in the case of fixing, setting an appropriate idling time to generate paper wrinkles due to heat being stored without being consumed in the non-sheet passing area, non-uniform fixing property, etc. The useless waiting time until the image forming operation is started can be shortened.

  That is, in the digital color copying machine, as shown in FIG. 2, a document (not shown) is automatically conveyed onto the platen glass 3 by an automatic document feeder (ADF) 2 and the document (not shown) is read. It is configured to be read by the device 4. The image information of the document read by the document reading device 4 is subjected to predetermined image processing by the image processing device 11. Thereafter, the image information that has undergone predetermined image processing by the image processing apparatus 11 is sent to the ROS 12, and the ROS 12 scans and exposes the laser beam LB on the photoconductor drum 14 based on the image data. An electrostatic latent image is formed on the surface 14. The electrostatic latent image formed on the photosensitive drum 14 is developed by a four-color developing device of yellow (Y), magenta (M), cyan (C), and black (BK) of the rotary developing device 16. Of the 16Y, 16M, 16C, and 16BK, the corresponding color developing devices 16Y, 16M, 16C, and 16BK are sequentially developed into toner images. After the toner images of each color such as yellow (Y), magenta (M), cyan (C), black (BK) and the like formed on the photosensitive drum 14 are primary-transferred on the intermediate transfer belt 21 in a multiplex manner. Then, the secondary transfer is collectively performed on the recording paper 27 from the intermediate transfer belt 21, and then conveyed to the fixing device 36, where a full-color or monochrome image is fixed on the recording paper 27, and then on the discharge tray 38. Discharged.

  At that time, in the digital color copying machine, a plurality of images may be continuously formed on the recording paper 27 having a size smaller than the A3 size which is the maximum size such as the A4 size or the B5 size. Subsequently, the image may be fixed on the recording paper 27 such as A3 size or B4 size which is larger than the A4 size or B5 size.

  In this case, as shown in FIG. 11, the surface temperature of the heating roll 51 of the fixing device 36 is such that the entire region is heated to a temperature substantially equal to the predetermined fixing temperature along the axial direction of the heating roll 51. It has become. In this state, if a plurality of sheets are continuously fixed on the A4 size recording paper 27 smaller than the maximum A3 size in the fixing device 36 as described above, the heating roll 51 and the like are not allowed to pass. In the paper area, since the heat of the heating roll 51 is not taken away by the recording paper 27, the temperature of the non-sheet passing area of the heating roll 51 becomes abnormally high by a as shown in FIG.

  Therefore, in this embodiment, the MCU 100 performs a fixing process on a plurality of A4 size recording papers 27 that are smaller than the maximum A3 size, and then performs a fixing process as a next job. When image fixing to a large A3 size recording sheet 27 is designated, the heating roll 51 is idled for a predetermined idling time without immediately starting the next job.

  Further, when the heating roll 51 is idled for a predetermined idling time, the MCU 100 controls the idling time according to the image information of the recording paper 27 on which the fixing process is performed next. In this case, as illustrated in FIG. 1, the MCU 100 determines that the recording sheet 27 on which the fixing process is performed is an A3 size sheet and the image information of the A3 size recording sheet 27 is thin as an average image density. When the number of continuous sheets of A4 size recording paper 27 is 1 to 50 according to the number of continuous sheets of A4 size recording paper 27 preceding that, the idling time is set to 10 (sec. In the case of 51 to 200 sheets, the idling time is set to 20 (sec).

  As a result, the MCU 100 continues the heating roll 51 with the idle rotation time, the image information of the recording paper 27 to be fixed next, and the A4 size recording paper 27 smaller than the A3 size, which is the maximum size prior to that. Since it is configured to control according to both the number of sheets passed, it is possible to prevent the occurrence of image defects as in the case where the heating roll 51 is fixed at a constant idle time, but the heating roll The idling time of 51 becomes long, and it becomes possible to solve the problem that productivity must be reduced.

  In particular, in conventional image forming apparatuses such as digital color copying machines, image quality tends to be prioritized over productivity. The idling time is often set longer.

  On the other hand, in the digital color copying machine according to this embodiment, the MCU 100 causes the heating roll 51 to have the idle rotation time, the image information of the recording paper 27 to be fixed next, and the maximum size prior to that. Since the control is made in accordance with both the number of continuous A4 size recording sheets 27 smaller than the A3 size and the elapsed time, the idling time of the heating roll 51 can be set appropriately. In addition, it is possible to shorten a useless waiting time until the next image forming operation is started while preventing the occurrence of image defects. As a result, the digital color copying machine can achieve both improvement in image quality and improvement in productivity.

FIG. 1 is a chart showing a setting state of idling time in a digital color copying machine as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a digital color copying machine as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a cross-sectional configuration diagram showing a fixing device of a digital color copying machine as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 4 is a block diagram showing a control circuit of the digital color copying machine as the image forming apparatus according to Embodiment 1 of the present invention. FIG. 5 is an explanatory diagram showing the positional relationship between the heating roll and the paper. FIG. 6 is a graph showing the temperature distribution in the axial direction of the heating roll. FIG. 7 is a graph showing the temperature distribution in the axial direction of the heating roll. FIG. 8 is a graph showing the relationship between the image density, the number of sheets to be passed, and the image defect. FIG. 9 is a chart showing a setting state of the idling time in the digital color copying machine as the image forming apparatus according to Embodiment 1 of the present invention. FIG. 10 is an explanatory diagram showing the positional relationship of image information with respect to a sheet. FIG. 11 is a graph showing the temperature distribution in the axial direction of the heating roll. FIG. 12 is a graph showing the relationship between image density and idling time for different image structures.

Explanation of symbols

  27: recording paper, 36: fixing device, 51: heating roll (rotating member for heating), 100: MCU.

Claims (9)

An image forming apparatus including a fixing unit that fixes an unfixed toner image on a sheet by conveying the sheet on which the unfixed toner image is transferred while being sandwiched by a pair of rotating members each having a heating source. ,
After fixing a sheet of a size smaller than the maximum size continuously by the fixing unit, when fixing an unfixed toner image on a sheet having a size larger than the sheet of the size fixed continuously, the rotation member Idle rotation execution means for executing idle rotation;
An image forming apparatus comprising: an idle rotation time control unit that controls an idle rotation time executed by the idle rotation execution unit in accordance with image information of a sheet on which a fixing process is performed next. The idling time control means includes an average image density of a sheet to be subjected to a fixing process next, image information of a specific area, image information from an intermediate portion to a rear end portion along the sheet conveyance direction, and from a sheet leading end to a conveyance direction. The image forming apparatus according to claim 1, wherein the idling time is controlled according to at least one of the image information of 100 mm and after. The image forming apparatus according to claim 1, wherein the image information is information about an image structure. The image forming apparatus according to claim 3, wherein the structure information of the image is information regarding dot processing or error diffusion processing of the image. 5. The idle rotation time control unit according to claim 1, wherein among the image information, the lower the image density, the longer the idle rotation time of the rotating member is controlled. Image forming apparatus. The image forming apparatus according to claim 2, wherein the image information is image arrangement information along a sheet conveyance direction. 7. The idling time control means controls idling time according to a surface temperature of a rotating member having a heating source immediately before passing a sheet to be fixed next. The image forming apparatus according to any one of the above. The idle rotation time control means controls the idle rotation time in accordance with the number of continuous sheets of paper having a size smaller than the maximum size, and the idle rotation time becomes longer as the number of continuous sheets to pass increases. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled as follows. The idling time control means controls the idling time according to the elapsed time after continuously passing a paper having a size smaller than the maximum size, and the idling time becomes shorter as the elapsed time becomes longer. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled to be

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