JP2013254140A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output images with stable quality even when the linear velocity of printing is changed.SOLUTION: An image forming apparatus comprises: developing-means that supports at least two or more linear velocities of printing; toner density detection means 101 for detecting toner density; print image information acquisition means 102 for acquiring image information used in forming a latent image on an image carrier; density supply amount calculation means 103 for controlling a toner supply amount on the basis of the toner density detection means 101; image supply amount calculation means 104 for controlling a toner supply amount on the basis of the print image information acquisition means 102; and control means for controlling, when changing linear velocity of printing, a toner supply amount for a predetermined time period on the basis of the image supply amount calculation means 104. The control means 100 holds a calculated value of the density supply amount calculation means 103 as holding-information, and, when changing the linear velocity of printing, controls the toner supply amount on the basis of the holding-information that has been held before changing the linear velocity of printing, as well as control of the toner supply amount based on the image supply amount calculation means 104.

Description

  The present invention relates to an image forming apparatus and an image forming method. More specifically, the present invention relates to an electrophotographic image forming apparatus and an image forming method provided with a two-component developing type developing device.

  Conventionally, various image forming apparatuses using an electrophotographic system have been devised as image forming apparatuses such as copying machines and printers, and are well known in the art. In the image forming process, an electrostatic latent image is formed on the surface of a photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner or the like as a developer to be visualized. The process is established by a process in which the developed image is transferred onto recording paper (also referred to as paper or recording medium) by a transfer device to carry the image, and a toner image on the recording paper is fixed by a fixing device using pressure, heat, or the like. .

  In an electrophotographic image forming apparatus, a developing device that develops an electrostatic latent image on the surface of a photosensitive drum with a two-component developer composed of a carrier and a toner is widely used (two-component developing method). In such a two-component development method, unlike the one-component development method, it is very important to improve the stability of development quality to accurately control the weight ratio of toner and carrier (hereinafter referred to as toner concentration). It is said that.

  For example, it is known that if the toner concentration is too high, background stains occur on the image and the detail resolution is reduced. On the other hand, it is known that when the toner density is low, the density of the solid image portion is lowered and carrier adhesion occurs.

  For this reason, it is necessary to control the toner replenishment amount with respect to the developer and adjust the toner concentration of the developer within an appropriate range.

  As a method for controlling the toner replenishment amount, an output value (hereinafter referred to as Vt) of a toner density detecting means for detecting the toner density of the developer is compared with a target value (hereinafter referred to as Vtref) of the toner density. A method of setting the toner replenishment amount based on the result (hereinafter referred to as Vt replenishment amount calculation) is known.

  As a toner concentration detecting means for detecting the toner concentration, a magnetic permeability sensor is generally used. The magnetic permeability sensor detects the current value of the toner density by comparing the magnetic permeability of the developer that changes with the change of the toner density with the output of the reference density.

  It is also known to use an optical sensor as another toner density detecting means. When using an optical sensor, a reference pattern is formed on the image carrier or intermediate transfer belt, the reflection density of the image area and non-image area of this reference pattern is detected by the optical sensor, and the toner density is detected based on the result. To do.

  In addition, an optical sensor is used to create a reference pattern in areas other than the toner image used for printing on the image carrier and the intermediate transfer belt (edges and between the paper) during image formation, and the reflection density is optically measured. There is also known a method in which a reference value of a magnetic permeability sensor is sequentially controlled based on a result detected by a sensor.

  However, the method using an optical sensor for toner density detection has a problem that it is difficult to use frequently because toner consumption is excessive due to the creation of a reference pattern. For this reason, it is important that the toner density control by the magnetic permeability sensor alone is accurately performed during continuous image formation or when the image mode is changed (when the printing linear speed is changed or when the control logic is changed).

  As another method for controlling the toner replenishment amount, the latent image is consumed by developing the latent image from pixel writing information (hereinafter referred to as image information) used when the exposure device forms a latent image on the image carrier. Then, a method of calculating the expected toner consumption amount and determining the replenishment amount from the consumption amount (hereinafter referred to as image replenishment amount calculation) is also known.

  Vt replenishment amount calculation involves replenishing toner after recognizing that the toner concentration has deviated from the target value Vtref by the toner concentration detection means, and therefore there is a problem that a time lag occurs until toner replenishment is completed. Have. On the other hand, the image replenishment amount calculation has an advantage that the toner can be replenished before the toner density deviates from Vtref because the toner replenishment is performed by predicting the amount of toner consumed. However, in the actual control of the developing device of the image forming apparatus, there is a problem that the toner density gradually deviates from the target value due to an error in the toner replenishment amount and the toner consumption amount.

  Therefore, in order to compensate for the problems of both the Vt replenishment amount calculation and the image replenishment amount calculation, a toner replenishment amount control method combining Vt replenishment amount calculation and image replenishment amount replenishment has also been proposed.

  Incidentally, in the electrophotographic process control of the two-component development method, in addition to the toner density control, it is required to keep the image density constant and keep the development γ appropriate. Note that the development γ is a slope of a linear approximation equation obtained by linearly approximating the relationship between the development potential on each patch pattern and the toner adhesion amount.

  For this reason, in addition to controlling the toner replenishment amount, a toner test pattern (hereinafter referred to as a patch) is formed on the image carrier or intermediate transfer belt, and the toner adheres with an optical sensor designed to detect the toner adhesion amount. It is also important to calculate the amount, and based on the result, control to correct the control factor Vtref and the development potential.

  This control requires toner consumption by patch formation as in the toner density detection method using an optical sensor, so that the toner utilization efficiency decreases. Therefore, the patch formation interval is lengthened to reduce the formation frequency, and the following controls [1] and [2] are used in combination with a cycle shorter than the patch detection interval.

[1] Control to keep the toner density constant.
In order to keep the toner density constant, it is necessary to maintain a balance between the toner to be used and the toner supplied to the developing device. For this reason, a sensor for detecting the toner density and a control device for controlling the toner replenishment amount using the output value Vt are used in the developing device. In addition, a control device that controls the amount of toner supply based on image information to be printed is used.

[2] Keep development performance and transfer rate constant.
It is known that the developing ability mainly correlates with the charge amount and adhesion force of toner. An apparatus that directly detects the charge amount and adhesion force of toner is not practical due to its high apparatus cost, and therefore the following predictive control is used.

  In the first predictive control, control is performed using characteristics in which the charge amount varies with temperature and humidity. For example, the toner density target value Vtref is lowered when the temperature and humidity become high. In the case of low temperature and low humidity, the reverse control is performed.

  In the second predictive control, the toner adhesion force is changed depending on the toner balance efficiency. Generally, the toner is held by frictional charging with respect to the carrier. However, if the toner balance per hour is large, the frictional power becomes small and the toner tends to be developed. Try to control the value. For example, the control is to change the toner density target value Vtref in accordance with the print image area.

  As for the control of [1], as described above, a method of estimating the toner density from the change in magnetic permeability is used as a sensor for detecting the toner density. However, this method has a problem that if the developer weight (bulk density) per unit volume changes, the toner concentration cannot be estimated correctly.

  Here, it is known that the change in the bulk density mainly occurs when the printing line speed is changed. If control is performed to make Vt coincide with the target value when the bulkiness changes, an error occurs between the actual toner density and the target value, and the output image quality deteriorates. Therefore, it is necessary to correct the sensor output in a time zone where the bulk density is expected to change (that is, when the printing line speed is changed).

  As such a sensor output correction method, for example, in Patent Document 1, when the printing linear velocity is changed, Vt and Vtref before the change and Vt detected after the change are used for the control of [1]. An image forming apparatus that determines toner density information and a target value is disclosed.

  However, in practice, a certain amount of time is required until Vt after the change of the printing line speed is stabilized due to a sudden change in bulk density immediately after the printing line speed is switched. A certain amount of time is also required to determine the toner density information and Vtref. Therefore, in the correction method described in Patent Document 1, control is performed while using the wrong Vt and Vtref until the correction is performed, that is, the correction is erroneous due to a change in the toner density detection value that occurs when the printing linear speed is changed. There is a problem that toner replenishment amount control is performed based on toner density information.

  In order to solve this problem, Patent Document 2 discloses an image forming apparatus in which the control logic is changed for a fixed time from the change of the printing linear speed or during the printing of a predetermined number of sheets.

  However, in the control for changing the control logic for a certain period after the change of the printing linear speed disclosed in Patent Document 2, the image quality cannot be maintained during the change of the control logic or when the control logic is restored. The problem remained.

  Accordingly, an object of the present invention is to provide an image forming apparatus and an image forming method capable of outputting an image with stable quality even when the printing linear speed is changed.

  In order to achieve such an object, an image forming apparatus according to the present invention includes a developing unit corresponding to at least two printing linear speeds, and a toner concentration in a two-component developer provided in the developing unit and including a carrier and a toner. A toner density detecting unit for detecting a toner, a print image information acquiring unit for acquiring image information used when forming a latent image on an image carrier, and a toner replenishment amount based on a detection result by the toner density detecting unit. A density replenishment amount calculating means; an image replenishment amount calculating means for controlling the toner replenishment amount based on the image information by the print image information acquiring means; and the density replenishment amount calculating means for a predetermined period when the printing linear speed is changed. Control means for controlling the toner replenishment amount based on the image replenishment amount calculation means without performing control based on the image replenishment amount, and the control means includes the density replenishment amount calculation means. The calculated value is held as holding information, and when the printing line speed is changed, the toner supply amount is controlled based on the holding information before the change of the printing line speed, along with the control of the toner supply amount based on the image supply amount calculation means. Is.

  According to the present invention, stable quality image output can be performed even when the printing line speed is changed.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus. FIG. 2 is a schematic diagram illustrating a basic configuration of a developing device. 6 is a graph showing (A) toner density and (B) toner density detection value (Vt) when the printing linear speed is changed. It is a graph (1) which shows the toner density fluctuation | variation which arises at the time of Vt replenishment amount calculation stop. It is a graph (2) which shows the toner density fluctuation | variation produced at the time of a Vt replenishment amount calculation stop. It is a graph explaining the incorrect calculation of the correction amount. 5A is a graph (1) showing a relationship between a change in toner density, (B) a charge amount, and an adhesion amount. 1 is a functional block diagram of an image forming apparatus according to an embodiment. 5 is a control flowchart for maintaining the toner density during the stop of the Vt replenishment amount calculation (first embodiment). (A), (B) It is a graph which shows the example of control information by PID control. 6 is a graph illustrating an example of a result of toner density control (first embodiment). 6 is a graph illustrating an example of a result of toner density detection value (first embodiment). 10 is a graph for explaining a case where the toner density cannot be made temporarily constant after restarting the calculation of the Vt supply amount. FIG. 10 is a control flowchart for maintaining the toner density when the Vt replenishment amount calculation is stopped (second embodiment). FIG. 10 is a control flowchart for maintaining the toner density when the Vt replenishment amount calculation is stopped (third embodiment). 6A is a graph (2) showing a relationship between (A) toner density change, (B) charge amount, and adhesion amount. It is a correction value table which shows an example of the relationship between an image density and a supply amount correction value. FIG. 10 is a control flowchart for maintaining the toner density when the Vt replenishment amount calculation is stopped (fourth embodiment). It is a graph which shows the relationship between Vt and the adhesion amount when the adhesion amount is measured after calculating the correction amount. It is a graph which shows the relationship between the measured adhesion amount and the target adhesion amount. 6 is a correction value table showing a relationship between an adhesion amount difference and a correction amount adjustment value.

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

(Image forming device)
FIG. 1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus. As shown in FIG. 1, around each photosensitive drum 1 (yellow, magenta, cyan, black), a corona charger 2, a developing device 4, a cleaning unit (not shown), a charge removal unit, and the like are arranged. ing. Then, an image forming process is performed on each photosensitive drum 1, and an image of each color is formed on each photosensitive drum 1.

  The photosensitive drum 1 is rotationally driven by a drive motor (not shown). Then, the surface of the photosensitive member 1 is uniformly charged at the position of the corona charging unit 2 (charging process).

  Thereafter, the photosensitive drum 1 reaches the irradiation position of the laser beam emitted from the image writing device 3, and an electrostatic latent image corresponding to each color is formed by exposure scanning at this position (exposure process).

  Thereafter, the surface of the photosensitive drum 1 reaches a position facing the developing device 4, and the electrostatic latent image is developed at this position to form a toner image of each color (developing process).

  Thereafter, the surface of the photosensitive drum 1 reaches a position facing the intermediate transfer belt 8 and the primary transfer portion 5, and the toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 8 at this position ( Primary transfer process). In this way, a color image is formed on the intermediate transfer belt 8.

  The untransferred toner remaining on the photosensitive drum 1 is collected by a cleaning unit (not shown) (cleaning process), and reaches a position facing a neutralization unit (not shown), and at this position, the photosensitive drum 1 is reached. Residual potential is removed.

  The intermediate transfer belt 8 on which the toner images of the respective colors are transferred in a superimposed manner reaches the secondary transfer unit 9. At this position, the toner image is transferred from the paper feeding device 7 to the surface of the paper 6 conveyed through the conveyance path 12 (secondary transfer process).

  Thereafter, the sheet 6 on which the toner image has been transferred is fed into the fixing device 20 and passes through a nip portion between the heating roller (fixing roller) 21 and the pressure roller 22 whose surface is covered with an elastic body. As a result, heat and pressure are applied, and the toner image is fixed on the paper 6 and sent to the downstream conveyance path.

  A cooling device 10 is provided on the downstream side of the fixing device 20, and the paper 6 conveyed to the cooling device 10 is cooled to an appropriate temperature and discharged from the paper discharge port 11. It should be noted that the sheet from an additional sheet feeding device (not shown) can be similarly handled through the transport path 13.

(Developer)
FIG. 2 is a schematic diagram showing a basic configuration of the developing device (developing means) 4. In the developing device 4, a developing sleeve 32 as a developer carrying member and conveying screw portions 34 and 35 as conveying members are disposed in parallel with the photosensitive drum 1 in a developing container 31 and have nonmagnetic toner and a magnetic carrier. A two-component developer (developer) is accommodated in the developing container 31.

  The developing sleeve 32 and the transport screw units 34 and 35 are driven and rotated by a driving device (not shown) at a speed corresponding to a predetermined printing line speed, and the rotation speed is changed by changing the printing line speed (control logic change). It changes to the speed corresponding to the printing line speed.

  The developer in the developer container 31 is transported in the axial direction by the transport screw unit 34 and moves toward the transport screw unit 35 at the end, and is transported in the direction opposite to the transport screw unit 34 by the transport screw unit 35. Then, it is circulated by repeatedly moving toward the conveying screw 34 at the end.

  A part of the developer moves from the conveying screw portion 35 in the developing device 4 to the developing sleeve 32 by the pumping magnetic pole in the developing sleeve 32. Thereafter, as the developing sleeve 32 rotates, the developer is transported to the vicinity of the doctor 33 by the magnetic field of the transport pole in the developing sleeve 32 and the frictional force on the surface of the developing sleeve 32.

  The developer conveyed to the vicinity of the doctor 33 once stays in the doctor upstream portion 36, the layer thickness is regulated by the gap between the doctor 33 and the developing sleeve 32, and the development in which the photosensitive drum 1 and the developing sleeve 32 face each other. Conveyed to the area. A developing bias is applied to the developing sleeve 32 from a power supply device (not shown) to form a predetermined developing electric field in the developing area. This developing electric field applies toner to the electrostatic latent image formed on the photosensitive drum 1. It is formed in the direction of force.

  Therefore, the toner moves to and adheres to the electrostatic latent image on the photosensitive drum 1 to develop the electrostatic latent image on the photosensitive drum 1. In addition, the developer on the developing sleeve 32 that has passed through the developing region leaves the developing sleeve 32 at the developer separating pole position on the developing sleeve 32 and returns to the transport screw unit 35.

  Thereafter, the developer moves to the conveying screw unit 34, is mixed with replenished toner replenished from a toner replenishing device (not shown), is adjusted to an appropriate toner density, and is transported again to the developing sleeve 32 as described above. A magnetic permeability sensor 37 (toner concentration detecting means 101, FIG. 8) for detecting the toner concentration of the two-component developer is installed at the bottom of the developing container 31 of the developing device 4. This magnetic permeability sensor 37 detects the toner concentration of the developer in the developing container 31.

(Prerequisite toner supply control)
First, the toner replenishment amount control which is a premise of the toner replenishment amount control method by the image forming apparatus according to the present invention will be described. FIG. 3 is a graph showing the toner density detection value (Vt) when the printing linear speed is switched.

  As described above, the detected value Vt of the toner concentration detecting means (magnetic permeability sensor 37) that detects the toner concentration using the magnetic permeability changes depending on the bulk density of the developer. In an image forming apparatus that supports two or more printing line speeds, the developer state changes depending on the printing line speed, and the bulk density differs. Therefore, even with the same toner concentration as shown in FIG. The detected Vt is different. For example, even if the Vt when the printing linear velocity is 1 at a certain toner density is a in FIG. 3B, the Vt at the linear velocity 2 and the linear velocity 3 is b in FIG. Or c may be detected.

  In addition, as described above, a transitional state of a change in bulk density occurs particularly immediately after the change of the printing line speed. Therefore, a period in which Vt is not stable as indicated by dotted line frames A and B occurs in FIG. Resulting in.

  Under such circumstances, even if toner density control using Vt is performed and Vt is made to coincide with the target value set at the time of the linear velocity 1, the actual toner density may become darker or thinner than the target. Will occur.

  As a method for avoiding the detected value from changing as shown by a, b, and c in FIG. 3B due to the linear velocity, the target value corresponding to the printing linear velocity is set in advance. It is conceivable that the target value Vtref is changed according to the linear velocity.

  However, the amount of change in Vt depending on the printing linear speed is influenced by the environment, the charged state of the toner, the degree of deterioration of the developer, and the like, and is not always constant. For this reason, in the method of setting the target value to a predetermined value, the set toner density target value Vtref may not be an appropriate value.

  In view of this point, in addition to the Vt before the printing line speed change and the target value Vtref, the Vt after the printing line speed switching is used to calculate how much the detected value has changed, and then Vt or Vtref, or It is also conceivable to correct both of them (see Patent Document 1).

  However, in this method, the correction is performed by detecting the Vt after the change of the printing line speed, and therefore the correction value is obtained during the period when the Vt after the change of the printing line speed is not stable as shown by A and B in FIG. It will not be sought correctly. For this reason, the toner replenishment amount is controlled with an incorrect Vt until the correction value is obtained.

  In order to prevent the toner replenishment amount control due to an erroneous Vt during the periods indicated by A and B in FIG. 3B, the control logic may be temporarily changed when the printing linear speed is changed (patent). Reference 2).

  That is, it is detected whether or not the printing line speed has been changed. If the printing line speed has not been changed, nothing is done. If a change in the printing line speed has been detected, the control logic is changed. When a certain period of time elapses after the phenomenon A) and B) of FIG.

Specifically, during a certain period after the change of the printing linear speed, the control based on the erroneous toner density estimation value is stopped by any one of the following controls [1] to [4].
[1] Stop toner supply.
[2] Control using Vt is stopped and only control using image information is performed.
[3] The coefficient used in the control using Vt is changed.
[4] A preset correction is performed on Vt and the target value, and control is performed using the corrected value.

  In the above control, the toner replenishment amount control by the wrong Vt is performed by stopping the toner replenishment or only the replenishment based on the image information during the period shown by A and B in FIG. Do not do it. Alternatively, by changing the coefficient for calculating the Vt replenishment amount to reduce the replenishment amount, the influence of control due to an erroneous Vt is reduced, or the correction value stored in advance is set to Vt, the target value Vtref, or both. In addition, by performing the control, the influence of the control due to an erroneous Vt is reduced.

  However, even with such a toner replenishment amount control method, there is a problem that the output image quality cannot be stabilized while the control logic is being changed or when the control logic is returned.

  4 and 5 are graphs showing changes in toner density that occur when calculation of the Vt replenishment amount is stopped. When the control logic is changed and the replenishment stop of [1] is performed, the toner density behaves as shown in FIG. This is because when the control logic is changed, toner is not replenished although the toner is consumed by printing, and the toner density is reduced.

  Further, when changing the control logic, if only the control using the image information [2] is performed, the toner density behaves as shown in FIG. 4 or FIG.

  As described above, in the image replenishment amount calculation, in actual control of the image forming apparatus, there is a problem that the toner density gradually deviates from the target value due to an error in the toner replenishment amount and the consumption amount. Is used together to compensate for this error so that the toner density can be maintained at the target value.

  For this reason, if the Vt replenishment amount is not calculated when the control logic is changed, the error between the replenishment amount and the consumption amount is not compensated. Therefore, the toner density is darker than the target value (FIG. 4) and lighter ( FIG. 5) It leaves in either direction.

  As a result, the quality of the printed image is deteriorated because the toner density is away from the target value during the control logic change or immediately after the control logic returns.

  Note that the method of changing the coefficient used in the calculation of the Vt replenishment amount in [3] also weakens the ability to compensate for the error while changing the control logic. Similarly, the toner density is as shown in FIG. 4 or FIG. It will behave.

  Further, in the method of performing the correction set in advance to the Vt and the target value in [4] and controlling using the corrected value, the amount of change is the environment, the charged state of the toner, the deterioration degree of the developer, etc. Therefore, when an error occurs between the correction value and the actual change amount, the control is performed with the error included, which is not desirable.

  Here, FIG. 6 is a graph showing that the correction amount cannot be obtained correctly when the toner density changes when the printing linear speed is changed.

  When calculating the correction amount of Vt and / or Vtref from the Vt and the target value Vtref before the change of the printing linear speed and the Vt after the change of the printing linear speed due to the phenomenon shown in FIG. 4 and FIG. May not be calculated correctly.

  At this time, the correction amount is determined by measuring how much Vt changes before and after the change of the printing linear speed. When the phenomenon of FIGS. 4 and 5 occurs, the correction amount to be originally calculated is shown in FIG. In contrast to the correction amount C, the correction amount U and the correction amount L are calculated. As a result, the correction after changing the printing linear speed is not performed correctly, and as a result, it becomes impossible to control the actual toner density as the target value, which affects the output image quality.

  FIG. 7 is a graph for explaining the relationship between the toner density, the charge amount, and the adhesion amount. Even if it is assumed that there is no error in the control by the image information as shown in FIGS. 4 and 5 and the toner density can be made constant only by the control by the image information, there remains a problem.

  That is, the toner is agitated and conveyed in the developing device, and is frictionally charged during that time. However, if the charge amount of the toner is different at this time, the amount of toner adhering to the image carrier when printing is performed. It will change. Specifically, when the charge amount is low, the adhesion amount increases, and when the charge amount is high, the adhesion amount tends to decrease. Therefore, even if the same toner concentration is maintained, the amount of adhesion varies depending on the charge amount as shown in FIG. 7, and as a result, the quality of the printed image may deteriorate.

  Note that when the image density of the printed image is high, the toner enters and exits the developing device, so the toner agitation time decreases and the charge amount tends to decrease. On the other hand, when the image density is low, the charge amount tends to increase.

[First Embodiment]
Therefore, as shown in the control block diagram of the image forming apparatus according to the toner replenishment control in FIG. 8, the image forming apparatus according to the present embodiment is a developing unit (developing apparatus 4, FIG. 2), a toner density detecting means 101 (permeability sensor 37) for detecting a toner density in a two-component developer composed of a carrier and a toner provided in the developing means, and when forming a latent image on the image carrier Print image information acquisition means 102 for acquiring image information used for the image processing, density replenishment amount calculation means 103 for controlling the toner replenishment amount based on the detection result by the toner density detection means 101, and image information by the print image information acquisition means 102. Based on the image replenishment amount calculation means 104 for controlling the toner replenishment amount based on the control, the control based on the density replenishment amount calculation means 103 is performed for a predetermined period when the printing linear speed is changed. And a control unit 100 that controls the toner replenishment amount based on the image replenishment amount calculation unit 104. The control unit 100 retains the calculated value of the density replenishment amount calculation unit 103 as retention information (storage control information). When the printing line speed is changed, the toner replenishment amount is controlled based on the retained information before the change of the printing linear speed as well as the toner replenishment amount control based on the image replenishment amount calculation means 104 (S103 in FIG. 9). , S104).

  The control unit 100 includes a CPU, a read only memory (ROM), a write / read memory (RAM), an I / O board, and the like, and a toner replenishing device drive motor that drives a toner replenishing device (not shown) via the I / O board. A control signal is transmitted to 106.

  FIG. 9 is a control flowchart for maintaining the toner density during the Vt supply amount calculation stop according to the first embodiment.

  That is, in the image forming apparatus having two or more printing line speeds, when the printing line speed is changed (S101: YES), the Vt replenishment amount calculation is stopped (S102), and the Vt replenishment amount calculation at that time is calculated. The control information is saved (S103). Then, the replenishment amount calculation using the stored control information is started (S104).

  Next, the image forming apparatus starts correction of Vt and / or Vtref from Vt and Vtref before and after the change of the linear velocity and Vt after the change of the linear velocity. When this correction is completed (S105: YES), the control based on the storage control information is stopped (S106), and the Vt replenishment amount calculation is restarted (S107).

  As described above, by performing the control for calculating the replenishment amount using the storage control information after the printing linear speed is changed, it is possible to suppress the influence of the error due to the image replenishment as described above.

  Next, the storage control information will be described. 10A and 10B are diagrams for explaining a specific example of the storage control information.

  In the present embodiment, in normal times, the image replenishment amount calculation and the Vt replenishment amount calculation are performed simultaneously. However, immediately after the printing line speed is changed, as described with reference to FIG. 3, Vt becomes an unreliable value, and thus the Vt replenishment amount calculation is temporarily stopped. Then, as described with reference to FIGS. 4 and 5, there arises a problem that the toner density cannot be kept constant. Therefore, in this embodiment, immediately after the printing line speed is changed, in addition to the image replenishment amount calculation, the value obtained by the previous Vt replenishment amount calculation is stored as storage control information, and the replenishment amount of the storage control information is calculated. Calculation is performed.

  As a specific example of the calculation of the Vt supply amount, for example, PID control can be used. In PID control, the replenishment amount is calculated based on a value obtained by multiplying a difference value between Vt and Vtref, an integral value of the difference, and a differential value of the difference by a coefficient.

Here, assuming that the difference is P, the integral value is I, the differential value is D, and the coefficients to be multiplied are Gp, Gi, and Gd, the replenishment amount is expressed by the following equation (1).
Replenishment amount = (Gp × P) + (Gi × I) + (Gd × D) (1)

  The relationship between Vt, the difference value, the integral value, and the differential value is shown in FIGS. 10A and 10B, for example. In the regions A and B in FIG. 10 where Vt matches Vtref, the difference value and the differential value converge to 0. On the other hand, the integral value does not necessarily converge to 0 due to the behavior of the change in Vt so far, and maintains a constant value.

  In this state, the toner density can be maintained constant. In other words, the balance between the toner consumption amount and the replenishment amount does not match only with the replenishment amount calculated by the image replenishment amount. It means that the error is canceled by adding.

  Therefore, when only the image replenishment amount is calculated when the printing linear speed is switched, the replenishment amount from the integral value is lost, and the toner density cannot be kept constant, and the phenomenon shown in FIGS. 4 and 5 occurs. It will occur.

Therefore, in this embodiment, the integral value of PID control is stored as storage control information when the printing linear speed is changed (S103). Then, the replenishment amount calculated from the storage control information is added to the replenishment amount based on the image replenishment amount calculation (S104). For example, the replenishment amount calculation from the storage control information can be performed by a method of using a value obtained by multiplying the stored integral value by a certain coefficient as the replenishment amount, as in the case of PID control. For example, if the replenishment amount obtained by calculating the image replenishment amount is Spick, the replenishment amount can be calculated as in the following equation (2) using the storage control information Is.
Replenishment amount = Spict + Gi × Is (2)

  As a result, the excess or deficiency of the replenishment amount based on the image information can be supplemented with the replenishment amount based on the stored information, and the toner density can be kept constant.

  FIG. 11 is an example of a graph showing a control result according to the present embodiment. By the above-described control, the excess and deficiency of the replenishment amount calculated by the image replenishment amount can be compensated by the replenishment amount calculation by the stored information, and the toner density can be kept constant. For this reason, as shown in FIG. 11, the toner density after changing the printing linear speed can be kept constant.

  FIG. 12 is another example of a graph showing a control result according to this embodiment. As described above, by keeping the toner density after changing the printing linear speed constant, there is no problem that the correction amount calculation value shown in FIG. 6 is not correct, and an accurate correction value C can be calculated.

  As described above, according to the image forming apparatus according to the present embodiment, it is possible to prevent the toner replenishment amount control from being performed using the wrong toner density information when the printing linear speed is changed, and the control logic can be changed. Deterioration of image quality can be prevented.

[Second Embodiment]
Next, another embodiment of the image forming apparatus according to the present invention will be described. In addition, the description about the same point as the said embodiment is abbreviate | omitted.

  By the control described in the first embodiment, it is possible to keep the toner density constant while the Vt replenishment amount calculation is stopped. However, as shown in FIG. 13, there may occur a case where the toner density cannot be made temporarily constant after restarting the calculation of the Vt replenishment amount (when the control logic is restored).

  This is because once the Vt replenishment amount calculation is stopped, the control information up to that point cannot be taken over. Therefore, as shown in FIG. 13, when restarting the Vt replenishment amount calculation, for example, the toner density may deviate from the target value until the integrated value shown in FIG. 10 reaches a constant value.

  Therefore, in the present embodiment, as shown in the control flowchart of FIG. 14, the storage control information stored at the time of changing the printing linear velocity is used not only when the Vt replenishment amount calculation is stopped but also after the return ( S207). Other processing is the same as the processing in FIG.

  By performing such control, the storage control information (for example, the integrated value I of the PID control) before the change of the printing linear speed can be taken over after the return of the Vt supply amount calculation, as shown in FIG. Thus, there is no divergence between the toner concentration and the target value when restarting the Vt replenishment amount calculation, and the toner concentration can be kept constant.

  As described above, according to the image forming apparatus according to the present embodiment, it is possible to prevent the toner replenishment amount control from being performed using the wrong toner density information when the printing linear speed is changed, and the control logic can be changed. In addition to preventing deterioration in image quality, it is possible to prevent deterioration in image quality that occurs when the control logic is returned by using control information before changing the printing line speed when returning the control logic.

  Note that only the control described in the second embodiment (control at the time of returning the printing line speed) is performed without performing the control described in the first embodiment (control when changing the printing line speed). Also good. In this case, it is possible to maintain the image quality when the Vt supply amount calculation is restored (when the control logic is restored).

[Third Embodiment]
According to the second embodiment, the toner concentration can be kept constant even when the Vt replenishment amount calculation is stopped when the printing linear speed is changed, and the toner concentration can be kept constant after the return of the Vt replenishment amount calculation. Can do.

  Here, it is also desirable to ensure the deterioration of the print image quality due to the change in the adhesion amount shown in FIG. Therefore, in the present embodiment, as in the control flowchart shown in FIG. 15, the replenishment amount based on the image replenishment amount calculation while the Vt replenishment amount calculation is stopped is also corrected (S304 to S306). Other processing is the same as the processing in FIG. The correction is preferably performed in conjunction with the control described in the first and second embodiments. However, the Vt replenishment amount calculation is performed without performing the control described in the first and second embodiments. You may correct | amend independently about the replenishment amount by the image replenishment amount calculation in a stop.

  By performing the control in this way, the toner density can be changed in accordance with the toner state even when the Vt replenishment amount calculation is stopped, so that deterioration of the print image quality can be prevented.

  This will be described with reference to FIG. As described with reference to FIG. 7, since the toner adhesion amount is affected by the toner charge amount, the density of the printed image changes even if the same toner density is maintained. Therefore, the quality of the printed image can be stabilized by changing the toner density according to the charge amount of the toner.

  Examples of the index (print information / environment information) for estimating the charge amount of toner include print image information, toner replenishment amount, temperature and humidity, development γ, and drive time.

  In the present embodiment, the replenishment amount based on the image replenishment amount calculation is corrected based on the print image information. For example, when the image density is high, the toner enters and leaves the developing device, and the charge amount of the toner decreases and the adhesion amount increases. Therefore, if it is determined from the print image information that the image density is high, if the toner density is reduced by correcting the replenishment amount by calculating the image replenishment amount, the increase in the adhesion amount due to the decrease in the charge amount is caused by the decrease in the toner concentration. Since it can cancel, the density of the final printed image can be stabilized.

  Conversely, when it is determined from the print image information that the image density is low, the amount of toner in and out of the developing device is small, the toner charge amount is increased, and the adhesion amount is reduced. When the toner density is increased by making a large correction, the decrease in the adhesion amount due to the increase in the charge amount can be offset by the increase in the toner density, so that the density of the final printed image can be stabilized.

  Note that the image density may be based on information for one print image or for a certain period of time, or a cumulative average for a certain number of sheets for a certain period in the past may be used. Further, as the print image information, the image area ratio or the image area of the image to be printed may be held instead of the image density of the image to be printed.

  As for the correction value of the toner replenishment amount, the degree of change in the toner density at which the adhesion amount becomes constant when an image is output at a plurality of print image densities in advance through experiments or the like is calculated in advance. What is necessary is just to increase / decrease the replenishment amount so that a change can be obtained.

  FIG. 17 is a correction value table showing an example of the relationship between the image density and the supply amount correction value. Specifically, a plurality of print image density levels defined by threshold values and a plurality of replenishment amount correction values corresponding to these levels are stored in advance as a correction value table, and correction according to the image density at the time of printing is performed. What is necessary is just to add / subtract the value to the replenishment amount, or multiply / divide the value.

  In the example of FIG. 17, the case of five levels is taken as an example, but the number of levels is not limited to five and may be any number.

  In the present embodiment, the example using the correction value table has been described. However, for example, a value obtained by multiplying the image density by a coefficient is used as the supply amount correction value, and the supply amount obtained by calculating the image supply amount is added, subtracted, or multiplied and divided. Anyway.

  In this embodiment, the example in which the replenishment amount is corrected based on the print image information has been described. However, the toner replenishment amount, temperature and humidity (temperature around the image forming apparatus), which are other indices related to the toner charge amount, are described. Of course, the correction may be performed using other indices such as the development γ of the developing device and the driving time of the developing device.

  As described above, according to the image forming apparatus according to the present embodiment, the replenishment amount is corrected using the print information / environment information during the control logic change in addition to the control information based on the toner density before the linear speed change. Thus, correction can be performed with higher accuracy than in the above embodiment.

[Fourth Embodiment]
When the Vt replenishment amount calculation is stopped, as described with reference to FIGS. 4 and 5, the toner density may not be kept constant due to an error between the replenishment amount based on the image and the actual consumption amount.

  On the other hand, the problem can be solved by the control described in the first embodiment. For example, when a sudden environmental change occurs during image formation, the toner density cannot be kept constant. As shown in FIG. 6, there may be a case where the correction value cannot be calculated correctly.

  Therefore, in the present embodiment, the correction amount is correctly calculated in response to a sudden environmental change or the like during image formation by the control shown in the control flowchart of FIG. Other processing is the same as the processing in FIG.

  In the present embodiment, the adhesion amount is measured after the correction value calculation of Vt and / or Vtref after the change of the printing linear velocity is completed (when the Vt replenishment amount calculation is resumed) (S406). For example, a method of creating a patch on the image carrier and reading the density of the patch with an optical sensor (attachment amount measuring means 105, FIG. 8) or the like can be used for this adhesion amount measurement.

  When creating a patch, it is not necessary to stop the printing operation, and the patch may be created between the toner images used for printing (between paper sheets) or in a portion other than the printing area.

  Then, after measuring the adhesion amount, the amount of linear velocity correction is adjusted using the measurement result (S407).

  The correction amount adjustment in the present embodiment will be described with reference to FIGS. 19 and 20. FIG. 19 shows the relationship between Vt and the adhesion amount when the adhesion amount is measured after calculating the correction amount. As shown in FIG. 19, if the toner concentration is maintained at an appropriate value b, the measured adhesion amount matches the target adhesion amount as shown in FIG.

  On the other hand, when the toner density becomes low and Vt becomes a in FIG. 19, the adhesion amount becomes lower than the target adhesion amount as shown in FIG. 20, and an adhesion amount difference occurs. Conversely, when the toner density becomes high and Vt becomes c in FIG. 19, the adhesion amount becomes higher than the target adhesion amount as shown in FIG. 20, and an adhesion amount difference occurs.

  Thus, since there is a correlation between the toner density and the adhesion amount, the correct correction amount can be calculated by adjusting the correction amounts of Vt and Vtref using this relationship.

  FIG. 21 is a correction value table showing the relationship between the adhesion amount difference and the correction amount adjustment value. As for the adjustment of the correction value, for example, the relationship between the change amount of the toner density and the difference in adhesion amount is obtained in advance by experiments or the like, and the adjustment value is set as shown in FIG. 21 according to the difference in adhesion amount. Just do it. Then, a correction amount adjustment value corresponding to the adhesion amount difference may be added to or subtracted from the correction amount or multiplied or divided.

  In the example of FIG. 21, the case of five levels is taken as an example, but the number is not limited to five and may be any number.

  In this embodiment, an example using the correction value table has been described. However, for example, a value obtained by multiplying the adhesion amount difference by a coefficient may be used as a correction amount adjustment value, and addition / subtraction or multiplication / division may be performed on the correction amount.

  As described above, according to the image forming apparatus of the present embodiment, when the control logic is further returned, the toner adhesion amount is measured, and the values of Vt and Vtref used for toner replenishment amount control based on the toner adhesion amount. By correcting the above, it is possible to perform the correction more accurately than in the above embodiment.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Corona charger 3 Image writing device 4 Developing device 5 Primary transfer part 6 Paper 7 Paper feed device 8 Intermediate transfer belt 9 Secondary transfer part 10 Cooling device 11 Paper discharge port 12, 13 Transport path 20 Fixing Device 21 Heating roller 22 Pressure roller 31 Developing container 32 Developing sleeve 33 Doctor 34, 35 Conveying screw part 36 Doctor upstream part 37 Magnetic permeability sensor 100 Control means 101 Toner density detection means 102 Print image information acquisition means 103 Concentration replenishment amount calculation means 104 Image supply amount calculation means 105 Adhesion amount measurement means 106 Toner supply device drive motor

JP 2010-256690 A Japanese Patent No. 4389434

Claims (10)

Developing means corresponding to at least two printing linear speeds;
A toner density detecting means provided in the developing means for detecting a toner density in a two-component developer comprising a carrier and toner;
Print image information acquisition means for acquiring image information used when forming a latent image on an image carrier;
A concentration replenishment amount calculating means for controlling a toner replenishment amount based on a detection result by the toner concentration detecting means;
Image replenishment amount calculating means for controlling a toner replenishment amount based on the image information by the print image information obtaining means;
Control means for controlling the toner replenishment amount based on the image replenishment amount calculation means without performing control based on the density replenishment amount calculation means for a predetermined period when the printing linear speed is changed,
The control means holds the calculated value of the concentration replenishment amount calculating means as retained information;
An image forming apparatus characterized by controlling a toner replenishment amount based on the held information before the change of the printing linear speed, as well as controlling the toner replenishment amount based on the image replenishment amount calculating means when the printing linear speed is changed. When the control means returns to the control of the toner replenishment amount by the density replenishment amount calculation means and the image replenishment amount calculation means after the elapse of the predetermined period after the change of the printing linear speed,
The image forming apparatus according to claim 1, wherein the held information before changing the printing linear speed is applied to control of a toner replenishment amount based on the density replenishment amount calculation unit. Developing means corresponding to at least two printing linear speeds;
A toner density detecting means provided in the developing means for detecting a toner density in a two-component developer comprising a carrier and toner;
Print image information acquisition means for acquiring image information used when forming a latent image on an image carrier;
A concentration replenishment amount calculating means for controlling a toner replenishment amount based on a detection result by the toner concentration detecting means;
Image replenishment amount calculation means for controlling the toner replenishment amount based on image information by the print image information acquisition means;
Control means for controlling the toner replenishment amount based on the image replenishment amount calculation means without performing control based on the density replenishment amount calculation means for a predetermined period when the printing linear speed is changed,
The control means holds the calculated value of the concentration replenishment amount calculating means as retained information;
When returning to the control of the toner replenishment amount by the density replenishment amount calculation means and the image replenishment amount calculation means after the elapse of the predetermined period after the change of the printing linear speed,
An image forming apparatus, wherein the held information before changing the printing linear speed is applied to control of a toner replenishment amount based on the density replenishment amount calculation means.   4. The control unit according to claim 1, wherein the control unit performs control for correcting a toner replenishment amount based on the image replenishment amount calculation unit based on print information / environment information when the printing linear speed is changed. The image forming apparatus according to any one of the above. An adhesion amount measuring means for measuring the toner adhesion amount;
The control means includes
When returning to the control of the toner replenishment amount by the density replenishment amount calculation means and the image replenishment amount calculation means after the elapse of the predetermined period after the change of the printing linear speed,
5. The image forming apparatus according to claim 1, wherein control of a toner replenishment amount is corrected based on an adhesion amount measurement result obtained by the adhesion amount measuring unit. The control means, at the time of changing the printing line speed,
Based on the output value of the toner density detection means before the change of the printing linear speed, the target value of the toner density and the output value of the toner density detection means after the change of the printing linear speed,
Correcting the output value of the toner density detecting means and / or the target value of the toner density after changing the printing linear speed,
The image forming apparatus according to claim 1, wherein the predetermined period is a time until the correction is completed.   5. The image forming apparatus according to claim 4, wherein the print information / environment information is one of an image area ratio of an image to be printed, an image area of an image to be printed, and a print density of the image to be printed. . A temperature / humidity detecting means for detecting the temperature / humidity around the image forming apparatus;
The image forming apparatus according to claim 4, wherein the print information / environment information is temperature / humidity detected by the temperature / humidity detection unit.   The image forming apparatus according to claim 4, wherein the print information / environment information is a driving time of the developing device or a development γ of the developing device. A toner concentration detection process for detecting a toner concentration in a two-component developer comprising a carrier and toner;
Print image information acquisition processing for acquiring image information used when forming a latent image on the image carrier;
A concentration replenishment amount calculation process for controlling a toner replenishment amount based on a detection result of the toner concentration detection process;
An image replenishment amount calculation process for controlling a toner replenishment amount based on the image information obtained by the print image information acquisition process;
An image forming method for performing a control process for controlling a toner replenishment amount by the image replenishment amount calculation process without performing the density replenishment amount calculation process for a predetermined period when the printing linear speed is changed,
The control process holds the calculated value in the concentration replenishment amount calculation process as holding information,
An image forming method comprising: controlling the toner replenishment amount based on the image replenishment amount calculation process and controlling the toner replenishment amount based on retained information before the change of the printing linear speed when the printing linear speed is changed.

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