JP2017138399A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine the most desirable gradation of a test pattern used in maximum density state detection control.SOLUTION: There is provided an image forming apparatus comprising: image forming means that forms a toner image on an image carrier; detection means that optically detects the density of the toner image formed on the image carrier; and control means that controls the operation of the image forming means. The control means executes state detection control of forming, with toner, a control pattern consisting of a plurality of density standards on the image carrier (step S11), estimating a variation in maximum density according to the limit of density detection performed by the detection means with the control pattern, and determining the gradation of the test pattern (step S15). The control means further forms the test pattern on the image carrier with the determined gradation, and executes maximum density state detection control according to a result of density detection performed by the detection means with the test pattern.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus, and more particularly to an electrophotographic image forming apparatus that performs image stabilization control.

  In general, in an electrophotographic image forming apparatus such as a copying machine or a printer, there is a problem that the density of an output image is not stable due to a change in photosensitive characteristics of a photosensitive member or a charge amount of a developer. In order to prevent such deterioration of image quality, each image forming apparatus forms a test pattern with toner on the image carrier under a predetermined image forming condition before or during the printing operation. The density of the test pattern is optically detected, and the result is fed back to image forming conditions such as charging voltage, developing bias voltage, exposure light quantity, and input / output image data characteristics (gamma correction data). 1). This type of feedback control is called image stabilization control, and mainly maintains maximum density, halftone density, and line width (dot diameter).

  When executing image stabilization control, to avoid printing productivity degradation due to interruption of printing operation as much as possible, before printing operation or during continuous printing operation, when paper is not sent to the image forming unit In addition, state detection control for detecting the state of image density is executed. In the state detection control, a test pattern shorter than the test pattern formed at the time of image stabilization control (hereinafter referred to as a control pattern for distinguishing from the test pattern for image stabilization control) is formed on the image carrier, and the optical sensor is used. There is known control for determining whether or not the image density to be printed is within a predetermined range based on the density detection result and determining whether or not the image stabilization control can be executed. In the state detection control, control patterns suitable for each quality are formed in order to confirm the quality such as maximum density, halftone density, and line reproducibility.

JP 2009-217163 A

  Incidentally, the means (optical sensor) for detecting the density of the toner image has a problem that it cannot be detected in a high density region. The density detection by the optical sensor uses the phenomenon that light is almost totally reflected in the area where the toner is not attached, and part of the light is absorbed by the toner and the reflected light is reduced in the area where the toner is attached. ing. As shown in FIG. 8, in the toner adhesion amount detection characteristic by the optical sensor, the sensor output value decreases as the adhesion amount increases. In other words, the optical sensor does not measure the color of the test pattern or the absolute value of the adhesion amount, but detects a change in the concealment ratio that changes as the adhesion amount of the toner increases as a substitute characteristic of the adhesion amount. . Therefore, the detection sensitivity decreases in the high concentration region X shown in FIG. 8, and the concentration cannot be accurately detected.

  In the maximum density control in the image stabilization control, as shown in FIG. 9, the optical sensor controls the maximum density that is not directly detected by using the characteristic that the toner adhesion amount changes linearly with respect to the developing bias voltage. .

  In the maximum density state detection control, the simplest and easiest method is to form a test pattern with the maximum density and detect the maximum density state. However, since the detection sensitivity of the optical sensor is low and the maximum density cannot be detected, it is necessary to form a pattern with gradations having a density lower than the maximum density and predict the state of the maximum density. In order to predict the state of maximum density, from the viewpoint of control accuracy, it is necessary to form a test pattern with as high a density as possible within a range that can be detected by the optical sensor and detect the density. That is, as shown in FIG. 10, the change in the halftone density accompanying the change in the maximum density is larger in the high density portion (high gradation). It is desirable to set the gradation so that a change in density can be detected.

  However, the detectable range of the optical sensor varies depending on individual differences in the sensor itself, variations in mounting accuracy, and the like, and also changes over time due to contamination with toner dust and paper dust. For this reason, even when a test pattern is formed with a high density as much as possible and the density is detected, there remains a problem that the state of the maximum density cannot be accurately detected due to variations among image forming apparatuses and changes with time. That is, as shown in FIG. 11, the maximum density variation cannot be detected in the region Y with the maximum density variation.

  An object of the present invention is to provide an image forming apparatus capable of accurately determining the most preferable gradation of a test pattern used in maximum density state detection control.

An image forming apparatus according to an aspect of the present invention is
Image forming means for forming a toner image on the image carrier;
Detection means for optically detecting the density of the toner image formed on the image carrier;
Control means for controlling the operation of the image forming means;
With
The control means forms a control pattern having a plurality of density levels by toner on the image carrier, estimates a variation in maximum density according to a density detection limit of the control pattern by the detection means, and Execute state detection control to determine the gradation of
The control unit forms a test pattern on the image carrier with the determined gradation, and executes maximum density state detection control according to a density detection result of the test pattern by the detection unit;
It is characterized by.

  In the image forming apparatus, the control unit forms a control pattern having a plurality of density levels with toner on the image carrier, and the gradation at which the density detection result of the control pattern by the optical detection unit becomes the maximum density is obtained. State detection control for determining the gradation of the test pattern in the maximum density state detection control is executed. As a result, the most preferable gradation of the test pattern used in the maximum density state detection control, which is the premise of the image stabilization control, is accurately determined regardless of the individual difference of the apparatus and the change over time.

  According to the present invention, the most preferable gradation of the test pattern formed on the image carrier for maximum density state detection control can be accurately determined.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. It is a flowchart figure which shows image stabilization control. It is a schematic diagram which shows a gamma correction control pattern. It is a flowchart figure which shows state detection control. It is a chart figure which shows the detection density of a gamma correction control pattern. It is a chart figure which shows the setting density | concentration of a test pattern. It is a flowchart figure which shows maximum density | concentration state detection control. It is a graph which shows the toner adhesion amount detection characteristic by an optical sensor. 6 is a graph showing a toner adhesion amount with respect to a developing bias voltage. It is a graph which shows the fluctuation | variation of the halftone density accompanying the fluctuation | variation of the maximum density. It is a graph which shows the area | region which cannot detect the fluctuation | variation of the maximum density | concentration.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same member and part in each figure, and the overlapping description is abbreviate | omitted.

  An image forming apparatus 1 according to an embodiment forms a color image by a tandem method as shown in FIG. That is, four process units 10 (a unit for yellow image 10y, a unit for magenta image 10m, a unit for cyan image 10c, and a unit for black image 10k) are juxtaposed and formed on each photoconductor 11. The toner images of the respective colors are transferred / combined (primary transfer) onto the intermediate transfer belt 31 that is rotationally driven in the direction of arrow A by an electric field applied from each transfer roller 32. Thereafter, the composite toner image is secondarily transferred onto a recording medium (paper) by an electric field applied from the transfer roller 35.

  Around each photoconductor 11, a charging roller 12, a developing device 13, a residual toner cleaning blade 14, and the like are arranged, and a laser scanning optical unit 20 that forms an electrostatic latent image on the photoconductor 11. Has been placed. A process in which a toner image is formed on the photoconductor 11 by an electrophotographic method using this type of process unit 10, the toner image is primarily transferred onto the intermediate transfer belt 31, and then secondarily transferred onto a recording medium is well known. is there.

  The recording medium (paper) is stacked and accommodated in the paper feed cassette 50 and is fed one by one by the paper feed roller 51. The fed paper is conveyed to the secondary transfer section via the registration roller pair 52, and the toner image is secondarily transferred from the intermediate transfer belt 31. Thereafter, the toner is heated and fixed by the fixing unit 55, and is discharged from the discharge roller pair 56 to the discharge unit 57.

  In the image forming apparatus 1, first, a pattern is formed with a toner on the photosensitive member 11 with image forming conditions such as a charge amount, an exposure light amount, and a developing bias voltage as predetermined values, and transferred onto the intermediate transfer belt 31. Then, the density of the toner pattern transferred onto the intermediate transfer belt 31 is optically detected by the sensor SE1, and based on this detected value, image stabilization control, state detection control, and maximum density state detection described below are performed. Take control. These controls are executed by the CPU constituting the control unit 60 together with the overall control of the image forming apparatus 1.

  As shown in FIG. 2, the image stabilization control is calibrated so that the output voltage of the optical sensor SE1 is appropriate (step S1), and the toner adhesion amount (development efficiency) becomes the maximum density. Thus, the developing bias voltage is controlled (step S2), the LD light amount (exposure light amount) of the optical unit 20 is appropriately controlled (step S3), and gamma correction control is executed (step S4).

  FIG. 3 shows control patterns 36Y (yellow), 36M (magenta), 36C (cyan), and 36K (black) used for gamma correction control. The control patterns 36Y, 36M, 36C, and 36K are shown in a state where they are formed on the respective photoreceptors 11 and transferred onto the intermediate transfer belt 31 in FIG. 3, and a plurality of control patterns 36 from low density to maximum density are shown. It is formed with gradation. The gamma correction is a well-known control performed using this control pattern, and this control pattern is also used in the state detection control in this embodiment.

  FIG. 4 shows a procedure for calculating the detection range of the optical sensor SE1 using the control patterns 36Y, 36M, 36C, and 36K used for gamma correction control and determining the gradation of the test pattern used in the maximum density state detection control. Indicates. Specifically, the control pattern for gamma correction is formed on the intermediate transfer belt 31 (step S11), the density is detected by the optical sensor SE1 (step S12), and the detected value is converted into the density (step S11). S13). The density with respect to the detection value of the optical sensor SE1 is measured in advance and is stored in the CPU 60 in a lookup table or the like.

  Next, the detection range of the optical sensor SE1 is calculated (step S14), and the gradation of the test pattern is determined (step S15). As shown in FIG. 5, the output voltage is saturated at a concentration not lower than the detection range of the optical sensor SE1, and the concentration converted from the detected value is also saturated. That is, the density beyond the detection range of the optical sensor SE1 is saturated. Thus, the saturated detected density can be calculated as the detection range of the optical sensor SE1. The detected density of 255 gradations may be treated as a saturated density. The gradation (density) of the test pattern for maximum density state detection control is formed at a density lower than the detected saturation density because it cannot be detected when the maximum density changes in the direction of increasing the maximum density when it is formed at the detected saturation density. It is necessary to calculate the maximum density from the allowable fluctuation range.

  Specifically, as shown in FIG. 6, when the allowable variation range of the maximum density is set to ΔM%, the detection upper limit density of the optical sensor SE1 is L, and the density of the state detection control pattern is T, T = L / (1 + M / 100). It is assumed that the high density portion also fluctuates at the same rate as the fluctuation range of the maximum density.

  The maximum density state detection control is executed at a timing such as immediately before the printing operation after the initial operation when the apparatus 1 is turned on when the paper is not sent to the image forming unit during continuous printing operation. To do. As shown in FIG. 7, a test pattern is formed on the intermediate transfer belt 31 with the gradation determined in step S15 (step S21), and its density is detected by the optical sensor SE1 (step S22). The value is converted into a density (step S23). If the density detection result is within the allowable fluctuation range (YES in step S24), the image forming conditions are finely adjusted (step S25). The image forming conditions include a developing bias voltage, an LD light amount (exposure light amount), and the like. On the other hand, if the density detection result fluctuates beyond the allowable range (NO in step S24), the printing operation is interrupted, the image stabilization control is activated, and the maximum density control is executed (step S26).

  If the density varies in the dark direction, the maximum density control test pattern is set to a light density, and if the density varies in the light direction, the maximum density control test pattern is set to a dark density.

  By the above control, the most preferable gradation of the test pattern used in the maximum density state detection control is determined with high accuracy regardless of individual differences of devices and changes with time.

  The image forming apparatus according to the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the gist thereof.

  In the above embodiment, the gamma correction control is used to calculate the detection range of the optical sensor. However, the density of the control pattern is changed by changing the LD light amount and the development bias voltage, and the detection range of the optical sensor is changed. May be calculated. Further, the density T of the state detection control pattern may be set in advance as a lookup table.

  In addition, the basic configuration and detailed configuration of the image forming apparatus are arbitrary, and may be a multifunction machine having a communication function, a facsimile function, and the like in addition to a printer having only a print function.

  As described above, the present invention is useful for an image forming apparatus, and is particularly excellent in that the most preferable gradation of a test pattern used for maximum density state detection control can be accurately determined.

DESCRIPTION OF SYMBOLS 10 ... Process unit 11 ... Photoconductor 13 ... Developing device 31 ... Intermediate transfer belt 36 ... Control pattern 60 ... Control part SE1 ... Optical sensor for density detection

Claims (8)

Image forming means for forming a toner image on the image carrier;
Detection means for optically detecting the density of the toner image formed on the image carrier;
Control means for controlling the operation of the image forming means;
With
The control means forms a control pattern consisting of a plurality of density levels by toner on the image carrier, estimates a variation in maximum density according to the density detection limit of the control pattern by the detection means, and Execute state detection control to determine gradation,
The control unit forms a test pattern on the image carrier with the determined gradation, and executes maximum density state detection control according to a density detection result of the test pattern by the detection unit;
An image forming apparatus.   In the state detection control, the control unit forms a control pattern having a plurality of density levels by changing any one of the exposure light amount, the developing bias voltage, and the density gradation, and detects the density of the control pattern by the detection unit. The image forming apparatus according to claim 1, wherein a density detection limit of the detection unit is calculated from a result.   The image forming apparatus according to claim 1, wherein the control unit sets the gradation of the test pattern to a gradation that has a density lower than a density detection limit of the detection unit.   The image according to any one of claims 1 to 3, wherein the control means determines the gradation of the test pattern from a maximum density fluctuation allowable range and a density detection limit of the detection means. Forming equipment.   The control means performs the maximum density state detection control during a continuous printing operation when the image forming apparatus is not driven for a predetermined time, when a predetermined number of printings are performed, or when the temperature and humidity change outside a predetermined range. The image forming apparatus according to claim 1, wherein the image forming apparatus is executed when the sheet is not sent to the image forming unit.   6. The control unit according to claim 1, wherein when the density detection result of the test pattern by the detection unit is within a predetermined range, either the development bias voltage or the exposure light amount is changed. The image forming apparatus according to any one of the above.   7. The control unit according to claim 1, wherein when the density detection result of the test pattern by the detection unit is outside a predetermined range, the printing operation is interrupted and image stabilization control is executed. The image forming apparatus according to any one of the above.   The image forming apparatus according to claim 1, wherein the state detection control is executed and a gradation of the test pattern is determined in a manufacturing process of the image forming apparatus.