JP2009300834A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that can carry out density control by detecting image density after fixation, wherein the apparatus may not carry out density correction if a density sensor is soiled or an abnormality is found in an image. <P>SOLUTION: The image forming apparatus includes: an image forming means for forming, on an image carrier 1, a toner image of a predetermined reference image; the density sensor 11 for reading the toner image of the reference image; a fixing means 8 for thermally fixing the toner image to be transferred on a recording medium; and the density sensor 9 for reading the reference image fixed on the recording medium by the fixing means. The image forming apparatus determines whether the density correction is to be carried out or not based on output values of: the density sensor for reading the toner image; and the density sensor for reading the reference image fixed on the recording medium. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a digital copying machine, a printer, and a facsimile that forms an image using an electrophotographic system.

  In an electrophotographic image forming apparatus, a semiconductor laser is driven in accordance with input image data, and a toner image formed on a photoconductor is transferred to a recording medium in accordance with the image data. The formed toner image is fixed by a fixing device and discharged as an output image.

  In recent years, image forming apparatuses such as copying machines and printers are required to form images with high image quality and high stability. For this reason, the following techniques have been proposed in order to always maintain the density of an image to be formed in an appropriate state.

  That is, after a reference image having a predetermined density is formed, a conversion table is created by comparing a density measurement value obtained by measuring the density of the formed reference image with an ideal density target value. Then, the image density control is performed by converting image data input using the conversion table into a density characteristic of a toner image formed according to the image data.

  As for the density measurement of the reference image necessary for performing such density control, there are many that are measured before the toner image formed as the reference image is transferred to the recording medium and those after the transfer and before the fixing. . However, in these density measurement methods, there is a difference between the density of the actually obtained image and the measured image due to variations in the transfer amount of the toner image from the photoconductor to the recording medium and the degree of fixing on the recording medium. Therefore, it is difficult to perform high-precision concentration control.

  For this reason, there is also a method in which an output image is read by an image reading device such as a reader, and density control is performed based on the reading result. However, since the output image has to be set in the image reading apparatus, the operation is troublesome, and in the case where the image reading apparatus such as a printer is not provided, the density adjustment using the output image can be performed. could not.

Therefore, in the conventional image forming apparatus, a density sensor is provided in the recording medium conveyance path immediately after fixing and the density is adjusted based on the image after fixing (for example, refer to Patent Document 1), or the density is provided in the reverse pass portion after fixing. Some sensors are provided to adjust the density (for example, see Patent Document 2).
JP 2000-1332013 A JP-A-10-268589

  However, the density sensor in the image forming apparatus may become dirty due to the influence of paper dust or toner scattering due to conveyance of the recording medium. Contamination of the density sensor cannot be ignored when performing density correction that is important for guaranteeing image quality.

  The present invention has been made by paying attention to the above points, and in an image forming apparatus capable of adjusting the density by detecting the image density after fixing, the density sensor is dirty or the image is abnormal. In this case, an object of the present invention is to provide an image forming apparatus capable of performing no density correction.

  In order to achieve the above-mentioned object, the present invention comprises the following configurations (1) to (3).

  (1) An image forming unit that forms a toner image of a predetermined reference image on an image carrier, a density sensor that reads the toner image of the reference image, and a fixing unit that heats and fixes the toner image transferred onto a recording medium And a density sensor for reading the reference image on the recording medium fixed by the fixing unit, and a density sensor for reading the reference image on the fixed recording medium. An image forming apparatus that determines whether or not density correction can be performed from an output value.

  (2) In an image forming apparatus further provided with an image reading device and an operation unit, when it is determined from the output value of a density sensor that reads a reference image on the fixed recording medium that the sensor is abnormal, The image forming apparatus according to (1), wherein the fixed reference image is read by the image reading device, and a notification for urging to perform density correction is displayed on the operation unit.

  (3) The density sensor for reading the toner image and the reference image on the fixed recording medium are read from the output value of the density sensor for reading the toner image and the density sensor for reading the reference image on the fixed recording medium. The image forming apparatus according to (1), wherein it is determined whether or not there is an abnormality in the density sensor.

  According to the present invention, in an image forming apparatus capable of detecting the density of an image on a recording medium after fixing and adjusting the density, density correction is not performed when the density sensor is dirty or the image is abnormal. Therefore, unintended image quality degradation can be prevented.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

  FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention.

  In FIG. 1, a photosensitive drum 1 serving as an image carrier is rotatably supported. Around the photosensitive drum 1, a pre-exposure lamp, a corona charger, a laser exposure optical system 2, a potential sensor, an intermediate transfer member 3, and a cleaning are provided. A container 4 and a rotary developer 5 are arranged.

  The rotatable rotary developing member 5 has four color developing devices: a black developing device 5K, a yellow developing device 5Y, a magenta developing device 5M, and a cyan developing device 5C. The rotary developer 5 rotates around a cylindrical rotation shaft provided at the center of the rotary developer in the counterclockwise direction indicated by an arrow a in the drawing, and a developer of a desired color is connected to the photosensitive drum 1 when necessary. It is possible to move to the opposite development position.

  In the laser exposure optical system 2, the image signal from the reader unit is converted into an optical signal by the laser output unit, and the laser beam converted into the optical signal is reflected and scanned by a polygon mirror that rotates at a constant speed. The light is projected onto the surface of the photosensitive drum 1 through the reflection mirror.

  At the time of image formation, the photosensitive drum 1 is rotated, and the photosensitive drum after being neutralized by the pre-exposure lamp is uniformly charged by a charger, and the light image E of the first color is irradiated to form a latent image on the photosensitive drum. . Next, the latent image on the photosensitive drum is developed with a toner based on a resin and a pigment by a developing device to form an image on the photosensitive drum.

  Thereafter, the toner image formed on the photosensitive drum is primarily transferred to the intermediate transfer member 3.

  When the development of the first color is completed, the rotary developer 5 is rotated by 90 ° in the direction of arrow a in the figure, and the developing device for the second color is moved to the development position facing the photosensitive drum 1. After the primary transfer, the photosensitive drum 1 cleaned by the cleaning device 4 repeats the latent image formation, development, and primary transfer with the second, third, and fourth colors as in the first color, and each color on the intermediate transfer body 3 is repeated. The toner images are sequentially superimposed.

  Here, the toner in the developing device is replenished as needed from the toner storage portion at a desired timing so as to keep the toner ratio (or toner amount) in the developing device constant.

  On the other hand, the recording medium is conveyed one by one from the storage units 61, 62, 63, 64 by the respective paper feeding means 71, 72, 73, 74, and the skew is corrected by the registration rollers 75, and at a desired timing. It is conveyed to the secondary transfer unit 76.

  The recording medium onto which the toner image has been transferred by the secondary transfer unit 76 passes through the conveyance unit 77, is fixed with the toner image by the heat roller fixing device 8, and is discharged to the paper discharge tray 65 or the paper post-processing device.

  Further, when images are formed on both sides of the recording medium, the recording medium is once guided to the reversing path 66 by driving the conveyance path switching guide immediately after the recording material passes through the heat roller fixing device 8. Thereafter, by reverse rotation of the reverse roller 78, the rear end at the time of feeding is set at the head, the sheet is withdrawn in the direction opposite to the fed-in direction, and is sent to the duplex conveyance path 67. After that, the paper passes through a double-sided conveyance path 67, temporarily stops for skew correction and timing by the double-sided conveyance roller 79, and is conveyed to the registration roller 75 at a desired timing, and the other surface is again subjected to the image forming process described above. Transfer the image to.

  Here, the operation of the image forming apparatus during image density adjustment, which is a feature of the present invention, will be described in detail.

  2 is a cross-sectional view of the density sensor arrangement in the recording medium conveyance path of the present embodiment, and FIG. 3 is a cross-sectional view of the density sensor and the recording medium of the present embodiment.

  During image density adjustment, the latent image formation, development, and primary transfer are repeated as in the above-described normal double-sided image formation, and the toner image is secondarily transferred to the recording medium conveyed to the secondary transfer unit. The recording medium subjected to the secondary transfer is heated and fixed by the heat roller fixing device 8, and the conveyance path switching guide is driven. Sent.

  The image formed here is a standard image having a predetermined density, and the standard image on the conveyed recording medium is irradiated with reference light from the irradiation means 91 in the density sensor 9 after fixing. The reflected light from the reference light is received by the light receiving means 92, a signal corresponding to the received light quantity is output, and a conversion table is created by comparing the density measurement value obtained from the output value with the density target value. Thus, the density adjustment is performed by converting the density characteristics of the image data using the conversion table.

  FIG. 4 is a diagram showing the relationship between the arrangement of the post-fixing density sensor 9 in the main scanning direction, the density level on the paper surface, and the divided blocks capable of controlling the laser light quantity.

  The density sensor 9b is disposed at the center in the main scanning direction (axial direction of the photosensitive member), and the density sensor 9a is disposed at the end of the image area. By arranging in this way, it is possible to read the output of the density sensor at the center in the main scanning direction and at the end in the main scanning direction. Since the end of the light amount of the laser beam on the photosensitive member falls due to the characteristics of the f-θ lens, the difference between the central portion and the end portion can be easily calculated with this arrangement. The divided blocks are divided into n in the main scanning direction, and the laser light quantity can be set for each block.

  FIG. 5 is a block diagram illustrating a schematic configuration of a control system of the printer unit of the image forming apparatus.

  In this block diagram, 101 is a CPU that controls the printer unit, 102 is a ROM that stores sequences and the like necessary for control, and 103 is a RAM that stores setting values and the like necessary for control. Reference numeral 104 denotes a paper conveyance control unit that controls a motor 120 and a sensor 121 related to paper conveyance, 105 denotes a high voltage control unit that controls high voltage such as development, charging, and transfer, and 106 controls a laser light quantity and a polygon motor. This is a laser driver control unit. Reference numeral 107 denotes a post-fixing density sensor control unit that controls the post-fixing density sensor 9 that reads a fixed image. Reference numeral 108 controls a motor for driving the photosensitive drum and the intermediate transfer member, and the reference of the leading edge of the image An image forming control unit for controlling the sensor. Further, the image forming apparatus includes a pre-fixing density sensor control unit 109 that controls the pre-fixing density sensor 11 that reads an image before fixing.

  FIG. 6 shows a flowchart of the density correction sequence. A density correction sequence is started, a predetermined patch image is formed (S101), and an unfixed toner image on the photosensitive drum 1 is read by the density sensor 11 before fixing (S102). Then, the toner image of the patch is primarily transferred from the photosensitive drum 1 to the intermediate transfer body 3, and then secondary transfer is performed on the recording medium. Then, the fixed patch image on the recording medium (S103) is read by the density sensor 9 after fixing (S104), and the recording medium is discharged (S105).

With reference to the output value of the pre-fixing density sensor 11 and the output value of the post-fixing density sensor 9, it is determined whether or not to perform density correction (S106). If density correction is to be performed, a conversion table is created (S107), and density correction ends. When it is determined in S106 that the density correction is not performed, the operation unit is notified and displayed so that the patch image on the recording medium is read by an image reading apparatus such as a scanner incorporated in the image forming apparatus, and displayed.
FIG. 7 shows a flowchart for determining whether to perform density correction. When it is determined whether or not the density correction shown in FIG. 6 can be performed (S106), it is determined whether or not the density correction can be performed as shown in this flowchart. First, it is determined whether the output value of the pre-fixing density sensor 11 is within a predetermined value (S201). When the threshold value is within the predetermined range, the process proceeds to S202. When the threshold value is outside the predetermined range, the process proceeds to S203.

  In S202, it is determined whether the output value of the density sensor 9 after fixing is within a predetermined range (S202). If it is within the predetermined range, it is determined that both the density sensor 11 before fixing and the density sensor 9 after fixing are free of dirt. In step S206, it is determined that density correction is possible. In S202, when it is out of the predetermined range, it is determined that the density sensor 9 after fixing is dirty (S204), and it is determined that density correction is impossible (S205).

  When the output of the density sensor before fixing is outside the predetermined range in S201, the process proceeds to S203. In S203, it is determined whether the output value of the density sensor 9 after fixing is within a predetermined range. If the output value is within the range, it is determined that the density sensor before fixing is dirty, and it is determined that density correction is possible ( S209). On the other hand, when it is out of the predetermined range, the process proceeds to S210, where it is determined that both the density sensor 11 before fixing and the density sensor 9 after fixing are dirty or there is an image abnormality (S210), and it is determined that density correction is impossible. (S211).

  In the flowchart of FIG. 7, it is assumed that a conversion table is created by referring to the output of the density sensor 9 after fixing in the density correction. However, in the density correction, when both the pre-fixing density sensor 11 and the post-fixing density sensor 9 are used, the density correction can be performed only in the case of S207.

  As described above, the image forming apparatus of the present embodiment has a function of not performing density correction when the density sensor is dirty or the image is abnormal.

  Thus, in an image forming apparatus capable of detecting the density of an image on a recording medium after fixing and adjusting the density, density correction is not performed when the density sensor is contaminated or the image is abnormal. Therefore, unintended image quality degradation can be prevented. In that case, an image reading apparatus such as a scanner of the image forming apparatus displays the patch image on the recording medium on the operation unit, and prompts the user to adjust the density by setting the output image on the image reading apparatus. Thus, it is possible to continue the image forming operation while preventing image quality deterioration.

Sectional drawing of the image forming apparatus of the Example of this invention Sectional drawing of the density sensor arrangement | positioning part in the recording-medium conveyance path of the image forming apparatus of an Example Sectional drawing of density sensor and recording medium of embodiment A diagram showing the relationship between the arrangement of density sensors after fixing in the main scanning direction, the density level on the paper, and the divided blocks that can control the amount of laser light 1 is a block diagram illustrating a schematic configuration of a control system of an image forming apparatus according to an embodiment. Flowchart showing the density correction sequence of the embodiment Flowchart for determining whether density correction is possible in the embodiment

Explanation of symbols

1 Photosensitive drum (corresponding to image carrier)
2 Laser exposure optical system (corresponding to image forming means)
3 Intermediate transfer member 8 Heat roller fixing device (corresponding to fixing means)
9 Density sensor after fixing (corresponding to the density sensor that reads the reference image on the recording medium)
9a, 9b Density sensor 11 Pre-fixing density sensor (corresponding to density sensor for reading toner image)
66 Reverse path 67 Double-sided transport path 76 Secondary transfer unit 77 Transport unit 91 Irradiating unit 92 Light receiving unit

Claims (3)

An image forming means for forming a toner image of a predetermined reference image on the image carrier;
A density sensor for reading the toner image of the reference image;
Fixing means for heating and fixing the toner image transferred onto a recording medium;
In an image forming apparatus including a density sensor that reads a reference image on a recording medium fixed by the fixing unit,
An image forming apparatus that determines whether or not density correction can be performed from an output value of a density sensor that reads the toner image and a density sensor that reads a reference image on the fixed recording medium. In an image forming apparatus further comprising an image reading device and an operation unit,
When it is determined from the output value of the density sensor that reads the reference image on the fixed recording medium that the sensor is abnormal,
The image forming apparatus according to claim 1, wherein the fixed reference image is read by the image reading device, and a notification that prompts the user to perform density correction is displayed on the operation unit. From the output value of the density sensor that reads the toner image and the density sensor that reads the reference image on the fixed recording medium,
The image forming apparatus according to claim 1, wherein the image forming apparatus determines whether there is an abnormality in the density sensor that reads the toner image and the density sensor that reads the reference image on the fixed recording medium.

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