JP2017040728A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that, when detecting a covering ratio of a photoreceptor by a patch by using an optical sensor and calculating the amount of toner adhered to the patch on the basis of a detected value, can accurately calculate the amount of toner adhered to the patch.SOLUTION: An image forming apparatus comprises: an image carrier 10; a developing part 20 that forms a toner image on the image carrier 10; an optical sensor 14 that detects a covering ratio of the image carrier 10 by the toner image; a control part that calculates the amount of toner of the toner image adhered to the image carrier 10 on the basis of a detection value from the optical sensor 14; and covering ratio control means 13A that controls the covering ratio so that the amount of toner adhered to the image carrier with respect to the covering ratio is uniquely determined. The control part controls the covering ratio by the formed toner image with the covering ratio control means 13A and subsequently causes the optical sensor 14 to detect the covering ratio.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In an electrophotographic image forming apparatus, a uniformly charged photosensitive member is irradiated with laser light based on image information, thereby forming a latent image on the surface of the photosensitive member. Then, toner is supplied to the photosensitive member on which the latent image is formed by the developing unit, so that the latent image is visualized and a toner image is formed. This toner image is transferred to a sheet conveyed by pressure contact of the transfer unit, and is fixed by a fixing unit, whereby an image is formed on the sheet.

  In such an image forming apparatus, the density of the image, that is, the toner adhesion amount varies depending on the number of images formed and the surrounding environment.

  As a technique for keeping the toner adhesion amount constant, a patch, which is a toner image for detecting the toner adhesion amount, is formed on the photoreceptor, and the concealment rate of the photoreceptor by the patch using an optical sensor (the patch covers the photoreceptor). The ratio of hiding (hereinafter simply referred to as hiding ratio) is detected, the toner adhesion amount of the patch is calculated based on the detected value, and the rotation speed ratio (hereinafter referred to as development θ) of the developing sleeve in the developing unit with respect to the photoreceptor is calculated based on the toner adhesion amount. Patent Document 1 discloses an image forming apparatus that controls a toner adhesion amount to a control target value by determining ().

Here, the development θ is a rotation speed ratio of the developing sleeve in the developing unit with respect to the photosensitive member. That is,
Development θ = rotational speed of developing sleeve / rotational speed of photoconductor. Here, the rotation speed is a peripheral speed. The positive direction of the rotation speed of the photosensitive member is the rotation direction during normal image formation, and the positive direction of the rotation speed of the developing sleeve is the same as the rotation direction of the photosensitive member. Since the rotation direction of the developing sleeve is usually the same as the rotation direction of the photosensitive member, the development θ is positive.

  That is, as a result of calculating the toner adhesion amount by forming the patch by the control unit, if the toner adhesion amount is less than the control target value, the development θ is increased to increase the toner adhesion amount, and the toner adhesion amount is larger than the control target value. If more, feedback control is performed to reduce the development θ and reduce the toner adhesion amount.

  Further, when detecting the concealment rate by the optical sensor, the optical sensor irradiates light on the patch formed on the surface of the photoconductor, and receives light (reflected light) reflected by the surface of the photoconductor through the gap between the patches. . It can be seen that if there is a lot of reflected light, the gap between the patches is large and the concealment rate is low, and if there is little reflected light, the gap between the patches is small and the concealment rate is high. The optical sensor outputs a detection value corresponding to the reflected light to the control unit. The control unit calculates the toner adhesion amount from the detection value of the optical sensor.

JP-A-8-314262

  In Patent Document 1, in the toner adhesion amount control, the toner adhesion amount is calculated from the detection value of the optical sensor corresponding to the reflected light. Thus, when calculating the toner adhesion amount by detecting the concealment rate, even when the same detection value of the concealment rate is obtained, the actual toner adhesion amount differs depending on, for example, development θ at the time of patch formation. From the experiment, it became clear as follows.

  FIG. 15 is a view of the toner formed on the photosensitive member after the patch is formed, as viewed from the upper surface of the patch. FIG. 15A shows a small development θ at the time of patch formation, and the toner shown in FIG. Indicates a case where development θ during patch formation is large. Further, the case where the toner in FIG. 15A and the toner in FIG. 15B become the same amount (toner adhesion amount) is shown.

  Even with the same toner adhesion amount, the smaller the development θ as shown in FIG. 15A, the smaller the toner density (the number of toners per unit volume) and the larger the gap between the toners, and the toner covers the photoreceptor in that part. The concealment rate is low. Conversely, as shown in FIG. 15B, the larger the development θ, the higher the toner density, the smaller the gap between the toners, and the higher the concealment rate. Note that the toner density is saturated as the development θ increases, and FIG. 15B shows a state where the toner density is the highest.

  Thus, since the toner density varies depending on the development θ even with the same toner adhesion amount, the detection value (hiding ratio) of the optical sensor differs under the influence of the toner density. In other words, even when the same concealment rate detection value is obtained, the actual toner adhesion amount varies depending on the development θ at the time of patch formation. As described above, since the toner adhesion amount and the detection value (concealment rate) of the optical sensor do not correspond one-to-one, the toner adhesion amount cannot be accurately calculated from the detection value of the concealment rate. Therefore, in the case of an image forming apparatus that controls the toner adhesion amount by adjusting the development θ, the toner adhesion amount control cannot be accurately performed.

  In view of this, an object of the present invention is to provide an image forming apparatus capable of calculating the toner adhesion amount with higher accuracy.

  In order to solve the above problems, an aspect of the present invention includes an image carrier, a developing unit that forms a toner image on the image carrier, an optical sensor that detects a concealment rate of the image carrier by the toner image, an optical A control unit that calculates the toner adhesion amount of the toner image on the image carrier based on the detection value of the sensor, and the concealment rate so that the toner adhesion amount relative to the concealment rate is uniquely determined And a concealment rate control unit for controlling the concealment rate, and the control unit controls the concealment rate for the formed toner image by the concealment rate control unit, and then causes the optical sensor to detect the concealment rate. The gist is that it is a forming apparatus.

  According to the present invention, when the concealment rate of the photosensitive member by the patch is detected using the optical sensor and the toner adhesion amount of the patch is calculated based on the detected value, the toner adhesion amount can be calculated with high accuracy.

1 is a cross-sectional view schematically showing a part of an image forming apparatus. It is a block diagram which shows a functional structure. 6 is a flowchart showing a flow of toner adhesion amount control processing. 6 is a graph showing a relationship between a detection value of an optical sensor and a toner adhesion amount. 4 is a graph showing a relationship between toner adhesion amount and development θ. 10 is a flowchart showing a flow of toner adhesion amount control processing according to the second embodiment. It is a figure for determining the rotational speed ratio N of a leveling roller. It is a figure for determining the correction coefficient (alpha). 10 is a flowchart illustrating a flow of toner adhesion amount control processing according to a third embodiment. It is a figure for determining correction coefficient (beta). FIG. 10 is a cross-sectional view schematically illustrating a part of an image forming apparatus according to a fourth embodiment. It is a block diagram which shows the functional structure which concerns on 4th Embodiment. 10 is a flowchart illustrating a flow of toner adhesion amount control processing according to a fourth embodiment. It is a figure for determining the frequency correction coefficient M. It is a figure which shows the relationship between development (theta) and the concealment rate in the same toner adhesion amount.

<First Embodiment>
FIG. 1 is a cross-sectional view schematically showing a part of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus of this embodiment is an electrophotographic monochrome printer having a black developing unit 20. The image forming apparatus according to the present embodiment can acquire image data from an external device and form a monochrome image on a recording material based on the image data.

  Examples of the external device include a document reading device and a personal computer (PC).

  As the recording material, paper, film, cloth or the like can be used.

  The photoreceptor 10 is a cylindrical body and rotates in the direction of the arrow. In this embodiment, the rotational speed of the photoconductor 10 is constant. The photoconductor 10 functions as an image carrier that carries a toner image formed by the developing unit 20.

  Around the photoreceptor 10, a charging unit 11, an exposure unit 12, a developing unit 20, a transfer unit 30, and a cleaning unit 15 are arranged.

  When image data is acquired from an external device and image formation is started, the surface of the photoreceptor 10 is uniformly charged by the charging unit 11. Before charging is performed by the charging unit 11, the potential charged in the previous image formation is neutralized by using a light emitting diode or the like (not shown).

  Based on the acquired image data, the exposure unit 12 irradiates the surface of the photoreceptor 10 with laser light. Thereby, the surface of the photoreceptor 10 is exposed, and a latent image corresponding to the image data is formed.

  The latent image formed on the surface of the photoreceptor 10 is supplied with toner from the developing unit 20 and becomes a toner image. The developing unit 20 is supplied with toner from a toner supply unit (not shown). A reversal developing method is used as a developing method of the developing unit 20, and the toner from the developing unit 20 adheres to the exposed portion of the surface of the photoreceptor 10 to form a toner image.

  The toner image formed on the surface of the photoconductor 10 is transferred by the transfer unit 30 to a recording material conveyed from the right side of FIG. The transfer unit 30 is composed of a plurality of rollers and a belt spanned between the rollers, and the belt rotates in the direction of the arrow as the rollers rotate. The roller facing the photoconductor 10 contacts the photoconductor via a belt, and forms a transfer nip between the photoconductor 10 and the belt. When the conveyed recording material passes through the transfer nip, a toner image is transferred to the recording material.

  The recording material onto which the toner image has been transferred in the transfer unit 30 is conveyed to a fixing unit (not shown), and is heated and pressed by the fixing unit. As a result, the toner on the recording material is melted and fixed on the recording material. Thereafter, the recording material is discharged from the image forming apparatus.

  In this way, the image forming apparatus of the present embodiment can acquire image data from an external device and form a monochrome image on a recording material based on the image data.

  The toner remaining on the photosensitive member 10 without being transferred to the recording material in the transfer unit 30 is collected by the cleaning unit 15.

  Next, the configuration and operation of the developing unit 20 will be described.

  The developing unit 20 stores toner and a carrier in the container. The toner is composed of a resin, a colorant, and other additives. The carrier is composed of metal particles such as iron and has magnetism.

  In the container of the developing unit 20, stirring screws 21 </ b> A, 21 </ b> B, 21 </ b> C and a developing sleeve 23 are arranged so that the rotation axis thereof is parallel to the photoreceptor 10.

  The space in the container of the developing unit 20 is divided into left and right by a partition wall. The stirring screws 21A and 21B are disposed on the right side of the partition wall, and the stirring screw 21C and the developing sleeve 23 are disposed on the left side of the partition wall. The left and right spaces communicate with each other at a communication portion that is an end of the partition wall.

  The stirring screws 21A, 21B, and 21C stir the toner and the carrier by rotation. As a result, friction occurs between the toner and the carrier, and the toner and the carrier are charged with opposite polarities. In this embodiment, the toner is charged with a negative polarity, and the carrier is charged with a positive polarity. The toner charged to a negative polarity adheres to the periphery of the carrier charged to a positive polarity by mutual electrical suction.

  The toner and the carrier are conveyed leftward in the container of the developing unit 20 while being agitated by the agitating screws 21A and 21B, and are moved from the right side to the left side of the partition via the communication unit. The toner and carrier charged by the stirring screws 21A and 21B and conveyed to the left side of the partition wall are conveyed by the stirring screw 21C and attracted to the developing sleeve 23.

  The developing sleeve 23 is made of a resin such as polyester, and a magnet roller made of a conductive metal such as aluminum is fixedly disposed therein. The developing sleeve 23 can rotate at a variable speed in the direction of the arrow. The magnet roller has a plurality of magnetic poles in the circumferential direction, and the developing sleeve 23 can attract and carry the carrier by a magnetic field generated from the magnetic poles of the magnet roller. The developing sleeve 23 rotates in the direction of the arrow while carrying the carrier, and conveys the carrier and the toner attracted to the carrier.

  Above the developing sleeve 23, a regulating member (not shown) is disposed at a predetermined distance from the developing sleeve 23. The regulating member is a plate-like member made of a magnetic material, and the toner and the carrier are raised by a magnetic field formed by the magnet roller and the regulating member to form a magnetic brush. The toner and the carrier are regulated to have a constant layer thickness by the regulating member during conveyance by the developing sleeve 23.

  The toner and the carrier are conveyed to a developing position facing the photoconductor 10 as the developing sleeve 23 rotates.

  Only the DC voltage is applied to the developing sleeve 23 by the power supply unit 80 (see FIG. 2), and only the toner is detached from the developing sleeve 23 by the electric field formed between the developing sleeve 23 and the photosensitive member 10, At the development position, toner is supplied to the latent image formed on the surface of the photoconductor 10 to form a toner image.

  By such an operation, a toner image can be formed on the surface of the photoconductor 10, but at that time, the toner is consumed and the toner in the container of the developing unit 20 is reduced. Therefore, toner is supplied from a toner supply unit (not shown) to the developing unit 20.

  Further, the carrier deteriorates with stirring of the stirring screws 21A, 21B, and 21C. If the carrier deteriorates, the charging performance during stirring deteriorates and causes a problem in image formation. Therefore, the carrier is replaced with a new one together with the developing unit 20.

  Next, toner adhesion amount control will be described. The toner adhesion amount control determines the rotation speed ratio (development θ) of the developing sleeve 23 with respect to the photoreceptor 10 in order to prevent the image density, that is, the toner adhesion amount from changing due to the influence of the number of image formations and the surrounding environment. In this way, the toner adhesion amount is controlled to a constant control target value.

  FIG. 2 is a block diagram showing a functional configuration.

  The control unit 90 includes a CPU 91 and a storage unit 92.

  The CPU 91 controls each part of the image forming apparatus and performs various arithmetic processes according to the program.

  The storage unit 92 is a device that temporarily stores various data received through various sensors or a network, and stores a program for the CPU 91 to control each unit of the image forming apparatus and image data acquired from an external device. is there. The program and data stored in the storage unit 92 are read and processed by the CPU 91.

  The photoconductor 10 carries a patch formed by the developing unit 20.

  When the developing unit 20 receives an instruction from the control unit 90, the developing unit 20 forms a patch on the surface of the photoconductor 10. At this time, the developing unit 20 rotates the developing sleeve 23 according to the development θ determined by the control unit 90. When the rotation speed of the developing sleeve 23 is increased to increase the development θ, the toner adhesion amount when the patch is formed increases. When the rotation speed of the developing sleeve 23 is decreased to reduce the development θ, the toner adhesion amount when the patch is formed decreases.

  As shown in FIG. 1, the leveling roller 13 </ b> A is a roller that is disposed at a position facing the photoconductor 10 so as to be able to contact and separate from the photoconductor 10 and presses a patch formed by the developing unit 20. The leveling roller 13A is formed of a conductive metal such as aluminum. The leveling roller 13A is rotated in the direction of the arrow by a drive source (not shown), and the rotation speed can be controlled by the control unit 90. The leveling roller 13A functions as a concealment rate control unit that controls the concealment rate so that the amount of toner attached to the concealment rate of the photoreceptor 10 by the patch is uniquely determined by pressing the patch.

  The optical sensor 14 is a sensor that optically detects the concealment rate of the photoreceptor 10 by the patch. The optical sensor 14 irradiates the patch formed on the surface of the photoreceptor 10 with light, receives light (reflected light) reflected from the patch accordingly, and transmits a detection value corresponding to the reflected light to the control unit 90. To do. When the detection value is large, it means that the concealment rate is low because there is a lot of reflected light. Conversely, when the detection value is small, it means that the concealment rate is high because there is little reflected light. When the detection value is transmitted to the control unit 90, the control unit 90 calculates the toner adhesion amount based on the detection value.

  The power supply unit 80 is a device that applies a voltage to the developing unit 20 and the leveling roller 13A. The voltage applied to the leveling roller 13A by the power supply unit 80 is set so that the toner is less likely to transfer from the patch to the leveling roller 13A. For example, it can be a negative DC voltage such as -500V. Thereby, toner transfer from the patch to the leveling roller 13A can be prevented.

  FIG. 3 is a flowchart showing the flow of the toner adhesion amount control process. The toner adhesion amount control is performed by the control unit 90. The timing for starting the toner adhesion amount control is preferably at the start of the day and when image formation is temporarily stopped.

  When the toner adhesion amount control is not performed, the leveling roller 13A is separated from the photoconductor 10. In performing the toner adhesion amount control, the controller 90 brings the leveling roller 13A into contact with the photosensitive member, and rotates the photosensitive member 10 and the leveling roller 13A (step S101).

  The controller 90 causes the developing unit 20 to form a patch (step S102).

  In this embodiment, the patch is formed three times, and the development θ at the time of patch formation is 1.3 for the first time, 1.35 for the second time, and 1.4 for the third time. The number of patch formations and the development θ at the time of patch formation are not limited to this example, and the development θ at the time of patch formation may be the current development θ (before adjustment) during normal image formation or a value around it. For example, for three patch formations, the development θ may be determined as current development θ × 0.9, current development θ × 1.0, and current development θ × 1.1.

  When forming the patch on the developing unit 20, the control unit 90 determines the development θ at the time of patch formation, determines the rotation speed of the developing sleeve 23 relative to the rotation speed of the photoconductor 10 from the determined development θ, and determines the determined rotation. The developing sleeve 23 is rotated at a speed.

  The control unit 90 acquires environmental information and durability information, and stores them in the storage unit 92 together with the development θ at the time of patch formation and the tone of the patch (step S103).

  In this embodiment, humidity is acquired as environmental information. Humidity is acquired using a humidity sensor (not shown). In order to acquire the humidity in the vicinity of the developing unit 20, the humidity sensor is preferably disposed in the vicinity of the developing unit 20.

  The durability information is information regarding the degree of deterioration of the carrier. In the present embodiment, the number of formed images is acquired as the durability information. The number of images formed is counted by the storage unit 92, and the count is increased by the number of sheets supported when the control unit 90 receives an instruction for image formation.

  Since the carrier deteriorates as the sliding distance becomes longer, the carrier sliding distance may be acquired as another example of the durability information. The sliding distance of the carrier is a distance that the surface of the developing sleeve 23 has moved since the image forming apparatus started to be used. For example, the count of the storage unit 92 is increased by a value obtained by multiplying the rotation speed of the developing sleeve 23 by the time for which the developing sleeve 23 rotates.

  The gradation of the patch is a value that affects the toner adhesion amount independently of the development θ, and is indicated by 0 to 100%. When 0%, the toner adhesion amount is the smallest, and when 100% (solid image), the toner adhesion amount is the largest. The gradation of the patch can be changed by adjusting the energy of the laser light irradiated by the exposure unit 12 or the DC voltage applied by the power supply unit 80.

  The control unit 90 irradiates the optical sensor 14 with light, receives reflected light from the patch, and transmits a detection value corresponding to the reflected light to the control unit 90 (step S104).

  When receiving the detection value from the optical sensor 14, the control unit 90 stores the detection value in the storage unit 92 together with the information acquired in step S103.

  The control unit 90 determines whether or not to form the next patch based on the number of patch formations stored in the storage unit 92 (step S105). When forming the next patch (YES in step S105), the processing of steps S102 to S104 is repeated while changing the development θ.

  In step S105, when the control unit 90 determines not to form the next patch (NO in step S105), based on the detection value of the optical sensor 14 stored in the storage unit 92, the toner of the patch for each detection value The adhesion amount is calculated from the graph of FIG. 4 and stored in the storage unit 92 (step S106).

  FIG. 4 is a graph showing the relationship between the detection value of the optical sensor 14 and the toner adhesion amount. The graph of FIG. 4 is obtained in advance by conducting an experiment in which patches are formed a plurality of times while changing the toner adhesion amount, and is stored in the storage unit 92.

  The relationship between the detection value of the optical sensor 14 and the toner adhesion amount is non-linear as shown in FIG. 4. The larger the detection value of the optical sensor 14, the smaller the toner adhesion amount and the smaller the detection value of the optical sensor 14. There is a large amount of toner adhesion.

  In the graph of FIG. 4, step is a unit of detection value determined according to reflected light. The optical sensor 14 converts an analog signal into a digital signal when outputting reflected light as a detection value. For example, one step when 5V is output in 1024 steps corresponds to one step, and in this example, it is about 0.005V per step.

As an example of the calculation of the toner adhesion amount, the detection values stored in the storage unit 92 in response to three detections by the optical sensor 14 are 340 step (development θ1.3), 280 step (development θ1.35), and 230 step (respectively). In the case of development θ1.4), the corresponding toner adhesion amounts can be calculated as 3.6 g / m ² , 4.1 g / m ² , and 4.6 g / m ^{2 according} to the graph of FIG.

  When obtaining the graph of FIG. 4, if the experiment is performed by changing the development θ in order to change the toner adhesion amount in the experiment, the toner adhesion amount is affected by the number of image formations and the surrounding environment, and a constant result is obtained. Absent. Therefore, when the graph of FIG. 4 is obtained, the DC voltage of the developing sleeve 23 is changed by the power supply unit 80 to change the toner adhesion amount, and the development θ is fixed (for example, 1.8). Here, when the DC voltage is increased, the toner adhesion amount increases, and when the DC voltage is decreased, the toner adhesion amount decreases.

  However, in the toner adhesion amount control, the patch is actually formed by changing the development θ. As described with reference to FIG. 15, even with the same toner adhesion amount, the density of the toner varies depending on the development θ, so that the concealment rate is different. In other words, even when the same concealment rate detection value is obtained in the toner adhesion amount control, the toner adhesion amount differs depending on the development θ. Therefore, when calculating the toner adhesion amount based on the graph of FIG. 4, the toner adhesion amount and the detection value of the concealment rate do not correspond one-to-one, and thus the actual toner adhesion amount cannot be accurately performed. There was a problem.

  On the other hand, in the present embodiment, the leveling roller 13A is disposed downstream of the development position and upstream of the detection position of the optical sensor 14 in the rotation direction of the photoconductor 10. The leveling roller 13A presses the patch to make the toner density of the patch constant. For example, the toner density is changed to the state shown in FIG. 15B for any toner density.

  As a result, the patch concealment rate is determined by the toner adhesion amount, and the toner adhesion amount and the detection value (concealment rate) of the optical sensor 14 have a one-to-one correspondence, and the toner adhesion amount with respect to the concealment rate is uniquely determined. The toner adhesion amount can be accurately calculated from the detection value of the concealment rate. That is, the leveling roller 13A functions as a concealment rate control means for controlling the concealment rate.

  Returning to FIG. 3, the control unit 90 uses the information on the combination of the development θ at the time of patch formation and the calculated toner adhesion amount stored in the storage unit 92 as many as the number of patches formed, to determine a predetermined toner. The development θ with respect to the adhesion target control value is determined (step S107).

  The process of step S107 will be described using the above example.

  FIG. 5 is a graph showing the relationship between the toner adhesion amount and the development θ.

  FIG. 5 shows information on a combination of the development θ at the time of patch formation and the calculated toner adhesion amount as a result of repeating the processes of steps S102 to S104 with development θ 1.3, 1.35, and 1.4. Development θ, toner adhesion amount) = (1.3, 3.6), (1.35, 4.1), (1.4, 4.6) are shown. Since it is known that there is a linear relationship between the toner adhesion amount and the development θ, a straight line is drawn through three points.

For example, when the control target value of the toner adhesion amount is 4.0 g / m ² , the development θ with respect to the control target value can be determined to be 1.34 using the graph of FIG.

  Here, the graph of FIG. 5 varies depending on the number of images formed and the surrounding environment. Therefore, as shown in the graph of FIG. 4, it cannot be obtained in advance by experiments and stored in the storage unit 92. When the toner adhesion amount control is performed, a patch is repeatedly formed each time the toner adhesion amount and the development θ. It is necessary to seek a relationship.

  When the development θ is determined, the controller 90 separates the leveling roller 13A from the photoconductor 10 and stops the rotation of the leveling roller 13A (step S108).

  The toner adhesion amount control is thus completed.

  In the first embodiment, as described above, the toner adhesion amount and the detection value (concealment rate) of the optical sensor 14 have a one-to-one correspondence, and the toner adhesion amount with respect to the concealment rate is uniquely determined. The toner adhesion amount can be calculated with high accuracy from the detected value. Thereby, it is possible to prevent problems in image formation such as a thin image and a rough image, and to maintain the quality of image formation.

  Further, the leveling roller 13A can be brought into contact with and separated from the photoconductor 10. When the toner adhesion amount control is performed, the leveling roller 13A is brought into contact with the photoconductor 10 and the toner adhesion amount control is not performed. In some cases, the leveling roller 13A is separated from the photoreceptor 10.

  In normal image formation, there is no problem with the image formed after fixing even if the toner image is not pressed by the leveling roller 13A. The image may be distorted. Therefore, when the toner adhesion amount control is not performed, the leveling roller 13A is separated from the photoconductor 10 so that the toner image is not affected during normal image formation. It is also possible to prevent the toner from transferring from the toner image to the leveling roller 13A.

  In the above description, the leveling roller 13A is in contact with the photoconductor 10. However, the leveling roller 13A is not in contact with the photoconductor 10, and the toner thickness (for example, several microns) is reduced. Those that are spaced apart from the photosensitive member 10 are included in the contact of the present invention as long as the patch can be pressed. Such a state is preferable because the load on the photoreceptor 10 by the leveling roller 13A can be reduced.

<Second Embodiment>
FIG. 6 is a flowchart illustrating a flow of toner adhesion amount control processing according to the second embodiment.

  Description of steps common to the first embodiment is omitted, and steps S204 and S207 are described.

  In step S204, the control unit 90 determines the rotation speed of the leveling roller 13A based on the development θ and the tone of the patch obtained in step S203 so that the toner adhesion amount with respect to the concealment rate is uniquely determined. Control (step S204).

The rotational speed of the leveling roller 13A is determined by the following equation.
Rotating speed of leveling roller 13A = Rotating speed of photoconductor 10 × N
Here, N is the rotation speed ratio of the leveling roller 13A with respect to the photoreceptor 10, and is determined based on the development θ and the gradation of the patch, as shown in FIG.

  FIG. 7 is a diagram for determining the rotation speed ratio N of the leveling roller 13A.

  As shown in FIG. 7, the smaller the development θ is, the larger the rotational speed ratio N of the leveling roller 13A is. This is due to the following reason.

  As the development θ increases, the density of the toner is saturated, so the influence on the concealment rate is small. On the other hand, when the development θ is small, the density of the toner is particularly small, and the influence on the concealment rate is large (the concealment rate becomes low). Therefore, in order to reduce the influence of the toner density on the concealment rate, it is necessary to increase the leveling effect by the leveling roller 13A when the development θ is small. When the rotation speed of the leveling roller 13A is increased, the relative speed of the leveling roller 13A with respect to the photoconductor 10 increases, so that the relative position between the toner present on the photoconductor 10 side and the toner present on the leveling roller 13A side. It becomes easy to slip. Accordingly, the rotational speed of the leveling roller 13A is increased in order to increase the leveling effect.

  Further, the higher the gradation of the patch, the larger the rotational speed ratio N of the leveling roller 13A. This is because if the patch gradation is high, the toner adhesion amount is large, and in this case, the leveling effect is increased by increasing the rotation speed of the leveling roller 13A.

  In step S204, since the rotation speed of the leveling roller 13A is controlled based on the development θ and the tone of the patch, the concealment rate can be accurately controlled by the leveling roller 13A. The amount of adhesion can be calculated with higher accuracy.

  Next, step S207 will be described.

  The controller 90 applies a voltage to the leveling roller 13A by the power supply unit 80 so as to prevent toner transfer from the patch to the leveling roller 13A. The toner is transferred to.

  Therefore, in step S207, the control unit 90 estimates the toner transfer amount from the patch to the leveling roller 13A, and corrects the detection value of the optical sensor 14 (step S207).

The detected value of the optical sensor 14 after correction is determined by the following equation.
Detection value of optical sensor 14 after correction = detection value of optical sensor 14 before correction × α
Here, α is a correction coefficient, which is information relating to the toner transfer amount. If it is estimated that the toner transfer amount is large, the correction coefficient α increases. As shown in FIG. 8, the correction coefficient α is determined based on the environmental information and the durability information acquired in step S203.

  FIG. 8 is a diagram for determining the correction coefficient α.

  As shown in FIG. 8, humidity is used as environmental information, and the number of images formed is used as durability information. Note that the number of images formed is reset when the developing unit 20 is replaced.

  As the humidity is higher, the toner is more easily transferred from the patch to the leveling roller 13A. Therefore, the higher the humidity is, the larger the correction coefficient α is.

  When the number of image forming sheets is large, the deterioration of the toner progresses, and the toner easily transfers from the patch to the leveling roller 13A.

  When the process of step S207 is completed, the control unit 90 calculates the toner adhesion amount with respect to the detection value of the optical sensor 14 in step S208. At this time, based on the corrected detection value of the optical sensor 14 determined in step S207. To calculate the toner adhesion amount.

  In step S207, since the toner transfer amount from the patch to the leveling roller 13A is estimated and the detection value of the optical sensor 14 is corrected, the toner adhesion amount can be calculated with higher accuracy from the detection value of the concealment rate.

<Third Embodiment>
FIG. 9 is a flowchart illustrating a flow of processing of toner adhesion amount control according to the third embodiment.

  Description of steps common to the second embodiment will be omitted, and step S307 will be described.

  In step S307, the control unit 90 estimates the toner transfer amount from the patch to the leveling roller 13A, and corrects the control target value of the toner adhesion amount (step S307).

  That is, in step S207, the detection value of the optical sensor 14 is corrected in consideration of the effect of toner transfer from the patch to the leveling roller 13A. In step S307, the control target value of the toner adhesion amount is corrected.

The corrected control target value is determined by the following equation.
Control target value after correction = control target value before correction × β
Here, β is a correction coefficient, which is information relating to the toner transfer amount. If it is estimated that the toner transfer amount is large, the correction coefficient β decreases. As shown in FIG. 10, the correction coefficient β is determined based on the environmental information and the durability information acquired in step S303.

  FIG. 10 is a diagram for determining the correction coefficient β.

  After the process of step S307 is completed, in step S309, the control unit 90 determines the development θ for the control target value from the development θ at the time of patch formation and the calculated toner adhesion amount. At this time, the control unit 90 determines in step S307. The development θ for the corrected control target value is determined.

  For example, when the correction coefficient β is determined to be a small value in step S307, that is, when the control unit 90 estimates that the toner transfer amount is large as a result of estimating the toner transfer amount, the control unit 90 is predetermined in step S309. The development θ for the control target value smaller than the control target value before correction is determined. Referring to FIG. 5, in this case, the control unit 90 determines the development θ smaller than that in the case where the control target value is not corrected.

  This prevents the toner adhesion amount from being excessively controlled even when the leveling roller 13A is separated from the photoconductor 10 to prevent toner transfer during normal image formation. Can do. Therefore, the toner adhesion amount can be calculated with higher accuracy from the detection value of the concealment rate.

<Fourth Embodiment>
FIG. 11 is a cross-sectional view schematically showing a part of the image forming apparatus according to the fourth embodiment.

  FIG. 12 is a block diagram illustrating a functional configuration according to the fourth embodiment.

  The fourth embodiment is different in that the voltage application means 13B is arranged instead of the leveling roller 13A, and other configurations are common to the previous embodiments.

  The voltage application unit 13B is an electrode that is disposed downstream of the development position and upstream of the detection position of the optical sensor 14 in the rotation direction of the photoconductor 10, and can form an electric field by applying a voltage. The output of the voltage applying means 13B can be controlled by the control unit 90. The voltage application unit 13B rearranges the patch passing through the position facing the voltage application unit 13B by applying a voltage so that the toner adhesion amount with respect to the concealment rate of the photoreceptor 10 by the patch is uniquely determined. It functions as a concealment rate control means for controlling.

  FIG. 13 is a flowchart showing a flow of processing of toner adhesion amount control according to the fourth embodiment.

  The controller 90 turns on the voltage of the voltage applying unit 13B (step S401).

  The output of the voltage applying means 13B is a voltage whose direction changes with time. Such a voltage forms an electric field that causes a minute reciprocating motion of the toner on the photoconductor 10 between the photoconductor 10 and the voltage applying unit 13B, and the patch is regenerated by the reciprocating motion of the toner on the photoconductor 10. Be placed.

  For example, a rectangular wave having a DC component of −500 V, an AC component of 2 kV, and a fundamental frequency of 6 kHz can be used as the output of the voltage applying unit 13B.

  Further, the output of the voltage applying unit 13B is preferably such that the time during which the electric field for moving the toner toward the photoconductor 10 is generated is longer than the time during which the electric field for moving the toner toward the voltage applying unit 13B is generated. Thereby, the toner can be stabilized toward the photosensitive member 10 side.

  For example, the duty ratio is 30%, that is, the electric field for moving the toner to the photoconductor 10 side and the electric field for moving the toner to the electrode side of the voltage applying unit 13B are formed at a time ratio of 7: 3. Can be.

  Steps S402 and S403 are the same as steps S102 and S103.

  The control unit 90 controls the output of the voltage applying unit 13B based on the development θ and the tone of the patch so that the toner adhesion amount with respect to the concealment rate is uniquely determined (step S404).

The controller 90 controls the output of the voltage application unit 13B by changing the frequency. The frequency of the voltage applying means 13B is determined by the following equation.
Voltage application means 13B frequency = basic frequency of voltage application means 13B × M
Here, M is a frequency correction coefficient, and is determined based on the development θ and the tone of the patch, as shown in FIG.

  FIG. 14 is a diagram for determining the frequency correction coefficient M.

  As shown in FIG. 14, the frequency correction coefficient M is larger as the development θ is smaller. This is because when the development θ is small, the concealment rate is particularly small and the concealment rate changes remarkably. In this case, the frequency of the voltage application means 13B is increased to increase the leveling effect. Note that when the frequency of the voltage application unit 13B is increased, the reciprocation of the toner becomes finer, so that the effect of the patch rearrangement is increased.

  Further, the frequency correction coefficient M is larger as the patch gradation is higher. This is because when the patch gradation is high, the amount of toner is large, and in this case, the frequency of the voltage application unit 13B is increased to enhance the effect of patch rearrangement.

  In step S404, since the output of the voltage application unit 13B is controlled based on the development θ and the gradation of the patch, the concealment rate can be accurately controlled by the voltage application unit 13B, and the toner adhesion is detected from the detected value of the concealment rate. The amount can be calculated with higher accuracy.

  Steps S405 to S408 are the same as steps S104 to S107.

  In step S409, the control unit 90 turns off the voltage of the voltage applying unit 13B (step S409).

  The toner adhesion amount control is thus completed.

  In the fourth embodiment, since the patch is rearranged by the voltage application unit 13B, the toner adhesion amount and the detection value (concealment rate) of the optical sensor 14 correspond to each other, and the toner adhesion amount with respect to the concealment rate is unambiguous. Therefore, the toner adhesion amount can be accurately calculated from the detection value of the concealment rate.

  Conventionally, a technique is known in which an AC voltage is applied to the developing sleeve 23 by the power supply unit 80 in order to improve image quality during image formation. On the other hand, in the present embodiment, in order to control the concealment rate of the photoreceptor 10 by the patch, the output of the voltage applying unit 13B is controlled to a frequency higher than the AC voltage of the conventional technique.

  In addition, the voltage application unit 13B turns on the voltage when the toner adhesion amount control is performed and turns off the voltage when the toner adhesion amount control is not performed, so that the toner image is affected during normal image formation. Never give.

  It is possible to apply a high frequency AC voltage to the developing sleeve 23 to form the voltage applying means 13B of the present invention. However, the configuration in which the AC voltage is applied to the developing sleeve 23 applies only a DC voltage to the developing sleeve 23. Compared to the configuration to be made, the apparatus becomes larger and costs higher. On the other hand, when the voltage applying means 13B is arranged separately from the developing sleeve 23, although new members increase, the overall configuration is more advantageous in terms of space and cost than the configuration in which the AC voltage is applied to the developing sleeve 23.

  Although the embodiment according to the present invention has been described above, the description in the above embodiment is an example of the image forming apparatus according to the present invention, and the present invention is not limited to this, and does not depart from the gist of the present invention. Can be changed.

  For example, the embodiment has been described using a monochrome printer as an example, but a color printer may be used.

  Further, although the embodiment has been described by taking the photoconductor 10 as an example of the image carrier of the present invention, the image carrier may be an intermediate transfer belt.

10 Photoconductor (image carrier)
11 Charging unit 12 Exposure unit 13A Leveling roller (Concealment rate control means)
13B Voltage application means (concealment rate control means)
14 optical sensor 15 cleaning unit 20 developing unit 21A, 21B, 21C stirring screw 23 developing sleeve 30 transfer unit 80 power supply unit 90 control unit 91 CPU
92 Memory unit

Claims (15)

An image carrier;
A developing unit for forming a toner image on the image carrier;
An optical sensor for detecting a concealment rate of the image carrier by the toner image;
A control unit that calculates a toner adhesion amount of the toner image on the image carrier based on a detection value of the optical sensor, and an image forming apparatus comprising:
Further comprising concealment rate control means for controlling the concealment rate so that the toner adhesion amount with respect to the concealment rate is uniquely determined;
The control unit controls the concealment rate of the formed toner image by the concealment rate control unit, and then causes the optical sensor to detect the concealment rate.   2. The concealment rate control unit is disposed downstream of the toner image forming position of the developing unit and upstream of a detection position of the optical sensor in the rotation direction of the image carrier. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein the concealment rate control unit is a leveling roller that presses the toner image.   The image forming apparatus according to claim 3, wherein the control unit controls a rotation speed of the leveling roller.   The image forming apparatus according to claim 4, wherein the control unit controls a rotation speed of the leveling roller based on a rotation speed ratio of the developing sleeve in the developing unit to the image carrier.   The image forming apparatus according to claim 4, wherein the control unit controls a rotation speed of the leveling roller based on a gradation of the toner image. A power supply for applying a voltage to the leveling roller;
The image forming apparatus according to claim 3, wherein the control unit controls the power supply unit so as to prevent toner transfer from the toner image to the leveling roller.   8. The image formation according to claim 3, wherein the control unit corrects a detection value of the optical sensor based on a toner transfer amount from the toner image to the leveling roller. 9. apparatus.   The control unit determines a rotation speed ratio of the developing sleeve in the developing unit with respect to the image carrier to the control target value of the toner adhesion amount based on the calculated toner adhesion amount, and from the toner image to the leveling roller. 9. The image forming apparatus according to claim 3, wherein the control target value is corrected based on a toner transfer amount.   The image forming apparatus according to claim 8, wherein the control unit estimates the toner transfer amount based on at least one of environmental information and durability information regarding the image forming apparatus. The leveling roller is capable of contacting and separating from the image carrier,
The image forming apparatus according to claim 3, wherein the control unit contacts and separates the leveling roller according to detection of the concealment rate.   The image forming apparatus according to claim 1, wherein the concealment ratio control unit is a voltage application unit that rearranges the toner image by applying a voltage whose direction changes with time.   The image forming apparatus according to claim 12, wherein the control unit controls the output of the voltage applying unit based on a rotation speed ratio of the developing sleeve in the developing unit to the image carrier.   The image forming apparatus according to claim 12, wherein the control unit controls an output of the voltage applying unit based on a gradation of the toner image.   15. The image forming apparatus according to claim 12, wherein the control unit does not apply a voltage by the voltage applying unit during normal image formation.

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