JP2006140794A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the calculation accuracy of an image formation condition that is calculated by image density control. <P>SOLUTION: A patch pattern that is discretely formed in a conventional manner is formed as a continuous pattern over the entire variable range of an image formation condition by making the image formation condition for forming a pattern for image density control continuously variable. As a result of this, control accuracy is improved because target density can be directly compared with detected density data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine or a laser beam printer, and a density control method for the image forming apparatus.

  In an image forming apparatus using a conventional electrophotographic method, in order to maintain a toner image density at a predetermined density, an image is obtained based on a detection result obtained by a toner density detecting apparatus provided in the main body of the image forming apparatus. There is an image forming apparatus that finely adjusts conditions relating to formation (see, for example, Patent Document 1).

  FIG. 11 shows an example of a conventional image forming apparatus. In the figure, an image forming apparatus includes a photosensitive drum 1 formed by applying a photoconductor made of an organic photosensitive member (OPC) or the like to an outer peripheral surface of an aluminum cylinder, and this photosensitive drum 1 is a drive (not shown). It is driven by the means in the direction of the arrow shown in the figure and is uniformly charged to a predetermined potential by the roller charger 2.

  A scanner unit 3 including a laser diode 31, a polygonal mirror 33 that is rotationally driven by a high-speed motor 32, a lens 34, and a folding mirror 35 is disposed above the apparatus main body.

  When an image signal is input to the laser driver 37, the laser driver 37 causes the laser diode 31 to emit light. Then, the light passes through the optical path 36 to irradiate the photosensitive drum 1 with optical information corresponding to the image signal, and a latent image is formed on the photosensitive drum 1. When the photosensitive drum 1 further advances in the direction of the arrow, the latent image is developed by the developing device 4 and becomes a toner visible image. The developed toner visible image is transferred onto the transfer paper P by the transfer roller 6 to which a predetermined bias is applied. The transfer paper P is conveyed to the fixing device 14 by the conveying means, and the toner visible image is melted and fixed by the fixing device 14 to be a permanent image.

  On the other hand, the toner remaining on the photosensitive drum 1 is cleaned by a cleaning device 8 such as a fur brush or blade means.

  By the way, the image density of an image forming apparatus, especially a multicolor image forming apparatus, varies depending on its use frequency and use environment. This is due to a change in physical properties of the photosensitive drum 1 or the developing device 4. The image density means an image formed mainly by the maximum image signal. In order to stabilize these fluctuations, a predetermined density detection toner image (hereinafter referred to as “patch”) is formed on the photosensitive drum 1 under different pattern forming conditions, and the density of the patch is measured by an optical density sensor. 23 or the like.

  The different pattern forming conditions are selected step by step so that the patch density has regularity of monotonously increasing or monotonically decreasing.

  A method for calculating the optimum pattern forming condition will be described with reference to FIGS.

As shown in FIG. 2, patches P _{1 to} P ₅ are formed on the photosensitive drum 1 under the pattern forming conditions C _{1 to} C ₅ . The patch densities D _{1 to} D ₅ of the patches P _{1 to} P ₅ are obtained by the optical density sensor 23. From these results, a target pattern forming condition _CT for forming a target density _DT is calculated. When _DT exists between D ₃ and D ₄ as in the example of FIG. 3, the target pattern formation condition _CT is approximately calculated by performing linear interpolation as described below.

C _T = {(V ₄ −V ₃ ) / (D ₄ −D ₃ )} × (D _T −D ₃ ) + V ₃
By making the size of the patch pattern larger than the optical spot diameter formed by the optical density sensor 23, the density of the patch pattern is accurately calculated.
Japanese Patent Laid-Open No. 08-289108 (page 10, FIG. 13)

However, in the above conventional example, when calculating the target pattern forming condition C _T, because only five stages of the pattern formation conditions not used, if most many seeking C _T from the approximate straight line by the interpolation. For this reason, if there is a difference between the interpolation straight line and the actual density curve, the difference causes instability of density. In addition, if the patch density before and after the target density is not formed correctly, or if there is a problem when detecting the patch density, the interpolated straight line will further deviate from the actual density curve. calculation error of the forming conditions C _T becomes large.

  When the number of patches is increased in order to eliminate such an error, the time for forming the patch pattern increases. Particularly in the case of a multicolor image forming apparatus, a time corresponding to the number of colors is added. In addition, when a pattern is formed on a transfer belt that is generally used in a multicolor image forming apparatus, there is a limitation on the number of patches because of the distance limitation of the belt length.

  Although it is possible to avoid the limitation of distance by reducing the size of the patch pattern, it is necessary to change the optical spot diameter of the optical density sensor, which greatly affects the optical characteristics and detection accuracy.

  There is also a problem from the viewpoint of image characteristics. The image characteristics in question here are development characteristics and the like.

  The development characteristics indicate a monotonic increase or monotonic decrease with respect to development conditions. In the conventional example, the target pattern formation conditions are calculated using the characteristics.

  However, some have the following characteristics.

(A) When a fogged image is generated within the range of the pattern forming condition This is a case where the fog is generated under the pattern forming condition for realizing the target density. In this case, since the pattern formation conditions where fog starts to occur cannot be accurately grasped, even the target pattern formation conditions that satisfy the pattern density cannot be adopted due to the fog.

(B) When the development characteristics have a negative characteristic within the range of the pattern formation conditions The negative characteristic means a phenomenon in which the tendency is reversed in the development characteristics that monotonously increase or decrease monotonously. (A) Similarly, since the pattern formation conditions where negative characteristics start to occur cannot be accurately grasped, the calculated target pattern formation conditions may not be accurate.

  In any of the above (a) and (b), the target pattern formation conditions are calculated in view of the obtained patch density results and development characteristics based on basic studies, so that the calculation error increases. End up.

  An object of the invention according to the present application is to provide an image forming apparatus capable of obtaining accurate target pattern forming conditions in view of the above situation.

To achieve the above objective,
A first invention according to the present application includes: a pattern forming unit that forms an image density control pattern on an image carrier; and a density detection unit that reads the density of the image density control pattern. In the image forming apparatus for calculating the image pattern forming condition based on the output of the image, the image density control pattern is configured as a continuous pattern group by continuously changing the image pattern forming condition. Image forming apparatus.

  A second invention according to the present application is the image forming apparatus according to the first invention, wherein the image pattern forming condition is a charging bias for charging the surface of the image carrier.

  According to a third invention of the present application, the image pattern forming condition is a developing bias for developing a toner image on the surface of the image carrier, and the image forming apparatus according to the first invention of the present application is characterized in that .

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the image carrier is a photosensitive drum.

  A fifth invention according to the present application is the image forming apparatus according to the first invention according to the present application, wherein the image carrier is a transfer belt.

  A sixth invention according to the present application is the image forming apparatus according to the first invention according to the present application, wherein the image carrier is an intermediate transfer belt.

  As described above, according to the present invention, a density is detected in an image forming apparatus that has a device for detecting a pattern density and calculates a target pattern forming condition based on the pattern density detected by the device. By making the pattern formation conditions of the pattern continuously variable, it is possible to accurately calculate the target pattern formation conditions that provide an optimal image, so it is possible to maintain a stable image density at all times, and to achieve high image quality. An image can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Hereinafter, Embodiment 1 of the present invention will be described in detail with reference to FIGS. In addition, the thing which carries out the same structure effect as FIG. 11 attaches the same number, and abbreviate | omits description.

  An optical density sensor 23 measures the density of the patch T formed on the photosensitive drum 1, and includes a light emitting element such as an LED, a light receiving element such as a photodiode and CdS, and a holder.

  A control unit 24 of the image forming apparatus includes a CPU 25, to which a ROM 26, a RAM 27, a test pattern generation unit 28, a high voltage control unit 29, and the like are connected in addition to the laser driver 37 and the optical density sensor 23. Of these, the ROM 26 is a read-only memory in which programs and various data for the CPU 25 to control the image forming apparatus are written. The RAM 27 is a readable / writable memory and serves as a work area for data expansion and image density control in the ROM 26. The test pattern generator 28 generates patch image data for image density control. The high pressure control means 29 generates a predetermined high pressure in response to an instruction from the CPU 25.

First, when the CPU 25 detects appropriate timing such as power-on of the image forming apparatus main body, elapsed time since power-on, number of printed sheets (number of formed images), instruction from the host computer or user, the CPU 25 performs image density control. First, the control target density for various bias settings and development bias control is read from the ROM 26 and written to the RAM 27. When a patch image is formed, an appropriate bias set value is read from this and sent to the high voltage control means 29. Thereafter, the CPU 25 starts an initial operation of the image forming apparatus main body and charges the photosensitive drum 1 with a predetermined charging bias. Next, the CPU 25 sends the patch image data generated from the test pattern generating means 28 to the laser driver 37 to form a patch latent image on the photosensitive drum 1 along the rotation direction. Since the spot diameter on the photosensitive drum 1 of the irradiation light of the optical density sensor 23 used in the present embodiment is about φ5, the size of the patch needs to be larger than that, and here, the pattern with a patch width of 7 mm is used. Is used. The latent image of the patch formed on the photosensitive drum 1 is developed by the developing device 4. The toner image of the patch formed on the photosensitive drum 1 is measured by the optical density sensor 23 at an appropriate timing, and the density measurement value is written in the RAM 27. Based on this result, the optimum developing bias _CT is calculated by the method described in the conventional example with reference to FIGS.

CPU25 writes a calculation result development bias _{C T} in RAM 27, the developing bias _{C T} is used in the halftone control and subsequent image formation is followed.

  Next, image density control by a discrete pattern method which is a conventional method as a comparative example will be described.

  There are five density detection patches, which are discretely formed. The reason why the patterns are formed discretely is that the development bias for forming each pattern is varied in the range of several tens of volts. This is because of consideration.

Patches P _{1 to} P ₅ are developed by the developing device 4, patch P ₁ is V ₁ , patch P ₂ is V ₂ , patch P ₃ is V ₃ , patch P ₄ is V ₄ , and patch P ₅ is V _5. Develop each. Thereafter, the optimum developing bias _CT is calculated by the above-described method.

  The present invention is characterized in that the pattern is formed continuously. That is, it is realized by making the developing bias for forming the pattern continuously variable.

  The operation modes such as image density control and density calculation method are the same as in the conventional method.

FIG. 4 is a schematic diagram of a continuously variable pattern. The development bias output, which is one of the high voltage control means, has a resolution of 8 bits (256 steps) by the CPU 25. That is, the development bias V _n can output from V _{0 to} V ₂₅₅ . In this case, since one step of the developing bias is around 1 V, there is no problem with the followability of the developing bias between the steps, and the pattern can be formed with the developing bias continuously variable. At the time of image density control, the CPU 25 updates the development bias every 5 msec to form a pattern, so that in the case of an image forming apparatus with a process speed of 100 mm / sec, the formation of all patterns is completed at about 130 mm or less. Since the developing bias V _n usually has a margin in the outputable range that is necessary for image formation, the pattern length is further shortened by selecting the variable range according to the characteristics of the image forming apparatus. It is also possible.

In the case of the continuously variable pattern, the pattern length for each developing bias is very small with respect to the optical spot (about 5 (mm)) of the optical density sensor 23. However, since the developing bias V _n is a variable optical density it is continuously follow along with the continuously variable, no problem in terms of calculating the target pattern forming condition C _T.

  FIG. 5 is a diagram showing how the control accuracy is excellent when the pattern is formed continuously and variably as shown in this embodiment, compared to the conventional case where the pattern is discretely formed.

The variable range of the developing bias V _n is C _{1 to} C ₅ (V), and the conventional method (discrete pattern) has five points, that is, V _n = C ₁ , C ₂ , C ₃ , C ₄ , C ₅ (n = 1). A pattern of points 5 to 5) is formed.

The system of the present embodiment (continuous variable pattern) forms 256 points, that is, a pattern of points of V _n = V ₁ , V ₂ , V _{3 to} V ₂₅₄ , V ₂₅₅ , V ₂₅₆ (n = 1 to 256). As in Figure 5, the target density D _T, in the case of the conventional discrete patterns to calculate the C _discrete as target pattern forming condition C _T. However, in the case of a continuous variable pattern can be calculated for C _continuous as target pattern forming condition C _T. Conventional discrete patterns result C _discrete and continuous variable results C _Continuous difference [Delta] C = C _Continuous -C _discrete appears as an error which can not be ignored in terms of aim density stabilization. On the other hand, in the case of the continuously variable pattern exemplified in the present embodiment, it is possible to calculate the target pattern forming condition with higher accuracy than in the past, so that it is possible to further increase the maintenance and stabilization of the image density. . In addition, since the control pattern can be executed without increasing the shape of the control pattern, the time required for control is not increased.

  As described above, it is possible to calculate the most preferable pattern forming condition of the image forming apparatus by correcting the density over the entire development bias region. The calculation result is written in the RAM 27. The result written in the RAM 27 is used as a pattern formation condition for a while. Note that it is possible to form a pattern in which only the region of interest is continuously variable without using a continuously variable pattern for all the regions where the development bias is variable, thereby further increasing calculation accuracy.

  The second embodiment of the present invention will be described below in detail with reference to FIGS. In addition, the thing which carries out the same structure effect as FIG. 1 attaches the same number, and abbreviate | omits description.

  In this embodiment, one of the features is that the pattern to be detected is plain, that is, the image data is 00h, and this is a proposal of a method for detecting fog caused by variable pattern forming conditions and further improving the calculation accuracy of control. .

Here, qualitative explanation about fogging will be described with reference to FIG. When charging bias V _C is constant, the toner adheres and even Tsu thin the white portion of the image when larger than there is contrast potential Vg formed by the developing bias V _D value, or smaller than a certain value, " The phenomenon “fog” occurs.

If the value is larger than a contrast potential Vg, among the toner in the developing device, the electric field in which the toner partially polarity is reversed is formed by the contrast potential Vg will be developed in the charge potential V _C of the photosensitive drum 1, This is the so-called “inverted fog”.

If less than a certain value contrast potential Vg, among the toner in the developing device, the toner in the insufficient charged state will be developed in the charge potential V _C of the photosensitive drum 1, so-called "fogging".

  FIG. 7 is a diagram specifically showing density characteristics with respect to the developing bias. Due to the fogging, image density appears in the “inverted fog” and “ground fog” areas shown in FIG. Further, there is a phenomenon in which the image density due to fog increases as the area deviates from the “OK area”.

  Therefore, even if an optimum pattern forming condition that satisfies the image density is obtained, and the condition is an area where fog occurs, the pattern forming condition needs to be corrected.

  In addition, since the fog generation area described above changes depending on the environment in which the image forming apparatus is used and its use situation, it is necessary to prepare a high voltage output so as to cover all the fluctuations.

  However, as described in the present embodiment, by detecting the fog generation area in advance, it is possible to obtain an optimum pattern forming condition that satisfies the image density in the area where fog does not occur.

  That is, the fog region detection control is performed before the execution of the image density control exemplified in the first embodiment.

FIG. 8 shows a flow of a series of image density control.
Step 1: The CPU 25 recognizes that it is the image density control timing, and starts control.
Step 2: In the variable range of the development bias V _{0 to} V ₂₅₅ , the development bias continuous variable control by “white background pattern” (image data 00h) is executed.
Step 3: Based on the density measurement result of the pattern formed in Step 2, the development bias lower limit value V _min and the development bias upper limit value V _mAx that are areas of “image density at which fog does not occur = 0” are calculated and calculated in the RAM 27. Write the result.
Step 4: The CPU 25 starts the next image density control (image density control exemplified in the first embodiment).
Step5: variable range of the development bias is determined by reading the _{V min} and _{V max} from RAM 27.
Step6: calculating an optimal target pattern forming conditions _{C T} (details same manner as in Example 1).

  By going through these steps, it is possible to accurately detect the area where fog occurs and perform image density control within a more selected range, so that target pattern formation conditions that achieve optimal image density can be calculated. Is possible.

  In this embodiment, the development bias is exemplified. However, the variation parameter related to the pattern formation condition is not limited to the development bias, and the charging bias and the transfer bias can be controlled by the same method.

  The third embodiment of the present invention will be described below in detail with reference to FIGS. In addition, the thing which carries out the same structure effect as FIG. 1 attaches | subjects the same number, and abbreviate | omits description.

  In the present embodiment, it is described that the density of the pattern to be detected is effective even when an unexpected density fluctuation is caused by the variable pattern forming condition.

  The unexpected density fluctuation here refers to a case where the image density does not monotonously increase or monotonously decrease in accordance with a change in the pattern forming conditions.

  In general, the image density monotonously increases or monotonously decreases as the development bias, which is a pattern forming condition, changes. However, depending on the development method, such a tendency may not be exhibited.

FIG. 9 is a diagram showing the state (example when negative characteristics appear). When the developing bias V _n is continuously changed from V _{1 to} V ₂₅₆ , the density increases monotonously, but the density increase is not recognized from a certain bias and may start to decrease. This is called “negative characteristics” of development. In particular, this phenomenon is observed in a developing system in which an alternating electric field is applied to the developing bias. Further, in this negative characteristic region, the behavior is unstable and it is very difficult to control.

  In the case of conventional image density control by the discrete pattern method, it is not possible to accurately detect a change point that generates this negative characteristic.

However, when the image density control by the continuous variable pattern scheme according to the present invention, since it is possible to detect the accurately the change point for generating this negative characteristic, the target pattern forming condition C _T is the calculation accuracy more It is obvious that it is expensive.

  The effect will be described with reference to FIG. The broken line consisting of the five-point plot is the result of density control by the discrete pattern of the conventional method. On the other hand, the solid line is the density control result by the continuously variable pattern.

Each calculation result of the optimum pattern formation condition C _T against the target density D _T becomes C _discrete and C _{continuously.} In the case of C _discrete , the condition of the area where the negative characteristic occurs, that is, the area where the development bias is excessively high, the image density may be satisfied, but unlike the proper development bias, The value is in a very unstable region. The term “unstable” as used herein means, for example, that the image density fluctuates or ground fog is likely to occur.

In the present invention, since the density transition of the entire development bias can be detected, it is possible to easily calculate the optimum pattern formation condition C _continuity before the negative characteristic occurs. Therefore, it is possible to stabilize the overall image quality including the image density.

1 is a diagram illustrating an image forming apparatus according to a first embodiment of the present invention. The figure explaining the discrete pattern concerning this invention The figure explaining the optimal pattern formation condition calculation of the image density control concerning this invention The figure explaining the continuously variable pattern concerning this invention The figure explaining the density | concentration calculation method in the continuously variable pattern concerning this invention The figure explaining fog generation | occurrence | production concerning 2nd Example of this invention. FIG. 6 is a relationship diagram between the developing bias and the fog density according to the second embodiment of the present invention. Flowchart according to the second embodiment of the present invention. The figure explaining the negative characteristic concerning 3rd Example of this invention The figure explaining the effect concerning 3rd Example to this invention A diagram for explaining a conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Exposure apparatus 6 Transfer roller 7 Process cartridge 8 Cleaning apparatus 12 Transfer belt 16 Adsorption roller 14 Fixing apparatus 22 Transfer belt cleaning apparatus 23 Optical density sensor

Claims (6)

Pattern forming means for forming an image density control pattern on the image carrier, and density detecting means for reading the density of the image density control pattern, and image pattern forming conditions are determined based on the output of the density detecting means. In the image forming apparatus to calculate,
2. The image forming apparatus according to claim 1, wherein the image density control pattern is configured as a continuous pattern group by continuously changing an image pattern forming condition.   The image forming apparatus according to claim 1, wherein the image pattern forming condition is a charging bias for charging the surface of the image carrier.   2. The image forming apparatus according to claim 1, wherein the image pattern forming condition is a developing bias for developing a toner image on the surface of the image carrier.   The image forming apparatus according to claim 1, wherein the image carrier is a photosensitive drum.   The image forming apparatus according to claim 1, wherein the image carrier is a transfer belt.   The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer belt.