JP2010145463A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, for appropriately controlling the surface potential of a photoreceptor drum at the time image formation in conformation to both long-term use and short-time use of the photoreceptor drum. <P>SOLUTION: The image forming apparatus 100 includes: a photoreceptor drum 10 a primary charger 5; an LED array 6; a developing device 7; a transfer device 8; a storage device 30 storing use history information of at least any one of the photoreceptor drum 10, the primary charger 5 and the LED array 6; and a controller 50 which causes the storage device 30 to store the use history information and controls image formation based on the use history information. The use history information is information for the usage of at least any one of the photoreceptor drum 10, the primary charger 5 and the LED array 6, and the elapsed time after use start of the photoreceptor drum 10. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that controls image formation based on usage history information of a photoreceptor.

  Conventionally, a high-priced electrophotographic image forming apparatus includes a potential sensor for measuring the surface potential of a photoreceptor inside the apparatus main body. Then, the primary charging voltage and the development voltage are determined by measuring the surface potential of the photosensitive member with a potential sensor. By doing so, accurate potential control is always possible, and an appropriate concentration can be stably obtained. On the other hand, when the potential sensor is provided inside the apparatus main body, the cost of the image forming apparatus and the size of the apparatus main body are increased, which hinders the cost reduction of the image forming apparatus and the size reduction of the apparatus main body.

  Therefore, recently, in order to reduce the cost of the image forming apparatus and to reduce the size of the apparatus main body, many image forming apparatuses are not equipped with a potential sensor. In such a configuration, the primary charging voltage and the development voltage are generally determined based on data obtained beforehand from experiments and the like. This makes it possible to perform a certain level of potential control without using a potential sensor, thereby realizing cost reduction of the image forming apparatus and size reduction of the apparatus main body. In order to realize accurate control, a temperature / humidity sensor is provided inside the image forming apparatus, and optimal potential control is performed based on the temperature / humidity value of the photosensitive member measured by the temperature / humidity sensor. Further, in order to realize accurate control, there is an image forming apparatus equipped with a density detection sensor for monitoring the toner density on the surface of the photoreceptor and the density of the toner transferred to the sheet, and feeds back to the potential control. As described above, various ideas have been made for stable image control.

  In particular, when the photosensitivity characteristics of the photosensitive member are lowered in accordance with the usage time or the like, the accuracy of potential control of the charger and the developer is lowered, and the output density becomes unstable. As a result, the image quality of the output image is degraded. In order to suppress the deterioration of the image quality of the output image, it is conceivable to measure the output density with a density detection sensor and feed back to the potential control. It takes time to measure the output density and feed back the output density information. Further, the cost of the image forming apparatus is increased by the cost of the density detection sensor.

  In order to reduce the potential control time and reduce the cost of the image forming apparatus, the charging potential and exposure amount are controlled according to the usage history of the photoconductor, charger, exposure device, developer, etc. The inventions disclosed in Patent Document 1 and Patent Document 2 that can realize stabilization of potential are disclosed.

  In the invention described in Patent Document 1, the control unit controls the exposure of the exposure device based on the total rotation time, stop time, number of copies, and temperature and humidity measured using a temperature and humidity sensor. According to such a configuration, even when the activated gas such as nitrogen oxide generated by the charging device is not lost when the image forming apparatus is left for a short period of time, the exposure of the exposure device is corrected by correcting the decrease in sensitivity of the photoreceptor. Is controlled, a uniform image can be obtained. In addition, since the activated gas such as nitrogen oxide generated by the charging device disappears when the image forming apparatus is left for a long time, a uniform image can be obtained.

  In the invention described in Patent Document 2, image formation is controlled based on information such as the number of sheets required for image formation, the number of jobs formed with an image, and the amount of print pixels. According to such a configuration, since image formation is controlled based on the unique information of the photoconductor, accurate potential control can be performed even when the sensitivity changes, and high image quality is realized.

JP 2001-228657 A JP 2002-072581 A

  However, in the inventions described in Patent Document 1 and Patent Document 2, the change in sensitivity of the photoconductor causes the light portion potential of the photoconductor to return to the original light portion potential when the photoconductor is used for a short period of time. In use, the phenomenon that the light portion potential of the photosensitive member does not return to the original light portion potential is not taken into consideration. That is, when the image forming apparatus exists after 30 days from the start of use of the photosensitive member, the apparatus that is used for 30 days is used for 10 days between the case where it is used for 10 days and the case where it is used for 30 days. The light portion potential of the photosensitive member is higher than that of the apparatus used. This is not prevented even if it is left for a long time as described in Patent Document 1.

  11 and 12 are graphs showing the state of sensitivity deterioration of the photosensitive member. With reference to FIGS. 11 and 12, the phenomenon caused by long-term use and short-term use of the photoreceptor will be described below. FIG. 11A is a graph showing a long-term transition of the light portion potential Vl during exposure of the photosensitive member. This graph shows the bright portion of the photosensitive member during exposure according to the increase in the number of images formed when 500 k sheets are continuously passed under the condition that the image exposure amount and the charging potential are kept constant. The potential (hereinafter referred to as “bright portion potential during exposure”) changes. As the number of sheets increases, the bright portion potential increases with a slope α, which causes a decrease in sensitivity of the photoreceptor. In addition, “morning” shown in FIG. 11A indicates the light portion potential at the start-up of the day, and “last” indicates the light portion potential at the end of the sheet passage on that day. It can be seen that the light portion potential returns by a predetermined amount overnight.

  FIG. 11B is a graph showing a short-term transition of the light portion potential during exposure of the photoreceptor. This graph shows the transition of the light potential of the day. The curve described as “100k” indicates the transition of the bright portion potential when 200 sheets are subsequently passed with respect to the photoconductor used for image formation of 100k sheets. A curve described as “500 k” indicates a transition of the bright portion potential when 200 sheets are subsequently passed with respect to the photoreceptor used for image formation of 500 k sheets. In order to stabilize the image density, it is necessary to change the charging potential of the photosensitive member by the charger and the exposure amount to the photosensitive member by the exposure device corresponding to both.

  FIG. 12A is a graph showing the transition of the light portion potential of the photoconductors having different daily usage amounts. As shown in FIG. 12 (a), the light portion potential increases more as the daily usage amount increases, and the light portion potential increases smaller as the daily usage amount decreases. FIG. 12B is a graph showing the transition of the light portion potential of the photosensitive member when the operation is stopped for a long time during the endurance. As shown in FIG. 12 (b), the light portion potential of the photosensitive member decreases after a long pause. As described above, the deterioration level of the photoconductor varies depending on the usage volume of the photoconductor (for example, the daily usage amount) and the leaving time (for example, the number of days of non-use). Therefore, in the conventional control that does not take into account the amount of storage time and usage time, the adjustment of the surface potential of the photoreceptor corresponding to the reduction in sensitivity of the photoreceptor is insufficient.

  The present invention has been made in view of the above circumstances, and it is possible to appropriately control the surface potential of the photoconductor in image formation in response to both long-term use and short-term use of the photoconductor. It is an object to provide an image forming apparatus.

  In order to achieve the above object, an image forming apparatus of the present invention includes a photosensitive member, a charger that uniformly charges the surface of the photosensitive member, and an electrostatic image formed by exposing the surface of the photosensitive member. At least one of an exposure device to be formed, a developing device for developing a toner image on the surface of the photoconductor, a transfer device for transferring the developed toner image to a sheet, the photoconductor, the charger, and the exposure device. In the image forming apparatus, comprising: an information storage unit that stores one usage history information; and a control unit that stores the usage history information in the information storage unit and controls image formation based on the usage history information. The history information is information on a usage amount of at least one of the photoconductor, the charger, and the exposure unit, and information on an elapsed time after the start of use of the photoconductor.

  As described above, according to the present invention, usage history information is determined based on both the usage amount of at least one of the photoconductor, the charger, and the exposure device, and the elapsed time after the start of use of the photoconductor. . Therefore, the surface potential of the photoconductor is controlled based on the sensitivity deterioration state or recovery state of the photoconductor. As a result, it is possible to appropriately control the surface potential of the photoconductor in forming an image corresponding to both long-term use and short-term use of the photoconductor.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

  FIG. 1 is a cross-sectional view showing a configuration of an image forming apparatus 100 according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 100 is a full-color image forming apparatus using a four-drum system.

  The image forming process will be briefly described. First, the surface of the photosensitive drum 10 that is the “photosensitive member” is uniformly charged by the primary charger 5 that is the “charging device”, and the inside of the reader unit 14 by the LED array 6 that is the “exposure unit”. The image is exposed in accordance with an input image signal from the CCD 13 to form an electrostatic image. The electrostatic image is visualized as a toner image by the developing device 7 as developing means, and transferred onto the sheet P carried and conveyed on the conveying belt 12 by the transfer device 8. The toner image transferred onto the sheet P by the fixing device 9 is fixed. The number of reproduced gradations per pixel is binary, but it may be multivalued. The photosensitive drum 10 corresponds to an “electrophotographic photosensitive member” that is a “photosensitive member”.

  The speeding up of the image forming process described above is realized by simultaneously performing four colors. The first station 1 forms yellow, the second station 2 forms magenta, the third station 3 forms cyan, and the fourth station 4 forms black. The primary charger 5 in this embodiment uses a roller charging method.

  Control of potential relations such as primary charging bias and developing bias during image formation will be described. The storage device 30, which is an “information storage unit” inside the image forming apparatus 100, includes a primary charging potential Vd that is a charging potential of the photosensitive drum 10 and a surface potential of a bright portion during exposure of the photosensitive drum 10. The relationship of a certain bright portion potential Vl during exposure is stored (see FIG. 2). This characteristic is stored in seven stages according to the absolute water content. Further, the development contrast characteristic necessary for supplying the ideal development characteristic in the developing device 7 is also stored in seven stages for each absolute water content (see FIG. 7B). The reason why each is stored independently is to enable density adjustment and use history correction of the photosensitive drum 10 described later.

  Further, the storage device 30 stores use history information of at least one of the photosensitive drum 10, the primary charger 5, and the LED array 6. This usage history information is information on the usage amount of at least one of the photosensitive drum 10, the primary charger 5, and the LED array 6, and the elapsed time after the usage start of the photosensitive drum 10. The usage amount of the photosensitive drum 10 refers to, for example, the number of rotations of the photosensitive drum 10, the number of sheets printed by the photosensitive drum 10, and the number of jobs printed by the photosensitive drum 10. The usage amount of the primary charger 5 refers to, for example, the number of rotations of the charging roller and the high voltage application time when a charging roller is used for the primary charger 5. The usage amount of the LED array 6 refers to, for example, the integrated drive time of the LED and the integrated light emission time of the LED. The elapsed time after the start of use of the photosensitive drum 10 is, for example, the elapsed time from when the photosensitive drum 10 is first rotated after being mounted on the image forming apparatus main body 100a to the present time.

  The usage history information will be described in detail later. In particular, it is assumed that 30 days have passed since the image forming apparatus 100 was started up. When the photosensitive drum 10 rotates 1800 times in one hour within one day within this period, “the number of rotations of the photosensitive drum 10” is recorded as 1800 times, and “after the start of use of the photosensitive drum 10” is recorded. “Elapsed time” is recorded as 30 days.

  The controller 50 serving as a “control unit” stores use history information in the storage device 30 and controls image formation based on the use history information. In controlling the image formation, an optimum primary charging bias in image formation can be obtained based on a Vd′-Vl ′ characteristic obtained by correcting the stored basic Vd−Vl characteristic with a durability index K, which will be described later, and a development contrast characteristic. Then, the control value of the developing bias is determined. Here, when the stored absolute water content at the seven levels differs from the absolute water content calculated from the output of the temperature / humidity sensor 40, which is the “temperature / humidity detection unit” measured at the start of image formation, the absolute water content This is handled by linear interpolation with reference to.

  In addition, the controller 50 performs color conversion on the R, G, and B image signals captured from the CCD 13 in the color conversion processing unit 24 via the input correction circuit, the filter, and the LOG conversion unit when controlling the exposure. M, C, K data. Finally, the gamma conversion processing unit (image signal conversion processing unit) performs gamma conversion in accordance with the output density characteristics of the image forming apparatus 100 and performs exposure from the LED array 6.

  FIG. 2 shows an example of the basic Vd-Vl characteristic. The basic Vd-Vl characteristic will be described in detail with reference to FIG. As shown in FIG. 2, the exposure light portion potential Vl generally follows the movement of the primary charging potential Vd in a non-linear manner. Note that the photosensitive drum 10 used in the present embodiment shows a tendency that the absolute value of the bright portion potential Vl during exposure tends to decrease as the absolute moisture amount increases. Further, the rate of change of the Vd-Vl characteristic with respect to the absolute water content becomes steeper as the absolute water content decreases, and shows a large nonlinearity. Therefore, strictly speaking, the interpolation based on the absolute water amount needs to be performed in a non-linear manner. However, in consideration of the error and the calculation amount, the linear interpolation is determined to be sufficient in the present embodiment. However, it goes without saying that non-linear interpolation improves performance.

  FIG. 3 is a cross-sectional view showing the configuration of the layers of the photosensitive drum 10. With reference to FIG. 3, the photosensitivity characteristics of the photosensitive drum 10 will be described. In this embodiment, the photosensitive drum 10 uses a function-separated type organic photosensitive member. As shown in FIG. 3, the layer structure is an Al base 10a, a base layer 10b, a carrier generation layer 10c, a carrier transport layer 10d, and a surface protective layer 10e. Photocarriers are generated according to the amount of light reaching the carrier generation layer 10c, and are combined with charged electrons on the surface layer of the photosensitive drum 10 to lower the potential.

  Here, in general, the amount of photocarrier generated varies depending on various factors such as the coating film thickness and concentration of the carrier generation layer 10c, the light transmittance in the carrier transport layer 10d and the surface protective layer 10e, and the coating film thickness. . These factors gradually change as image formation is repeated. Further, the surface protective layer 10e affects the change in potential because the surface protection layer 10e is rubbed with the sheet, developer, primary charging agent and the like each time image formation is repeated and the film thickness is reduced.

  However, in recent years, there has been a tendency for the lifetime of the photoreceptor to greatly increase by increasing the hardness of the surface layer, and it is not necessary to consider changes in film thickness. This is the accumulation of residual charge by repeating the above. This phenomenon becomes apparent after long-term use due to the extended life of the surface of the photoreceptor. This mechanism is not clear, but photocarriers generated by repeated charging and exposure are difficult to escape from the underlayer 10b to the Al substrate 10a and accumulate. The cause is thought to be going.

  As described above with reference to FIGS. 9 and 10, the sensitivity of the photosensitive drum 10 is deteriorated. In addition, when the sensitivity of the photosensitive drum 10 is deteriorated, if image formation is continued with the same charging potential and LED emission conditions as before the deterioration, the development contrast cannot be obtained in the reversal development method, and the image density is reduced. Will go down. Therefore, a full-color image is inconvenient because the color changes with respect to the same document when a change in potential more than a certain level occurs.

  In order to correct such “decrease in image density” and “change in color”, techniques such as “increase in the amount of LED light” or “increase in the primary charging potential” are taken so as to dig deeper into the latent image. This is because, according to the Vd-Vl characteristic, the higher the primary charging potential Vd, the larger the latent image contrast can be obtained with the same light amount. In addition, there is a method of converting an image signal when halftone correction is necessary. Therefore, in this embodiment, “shift control of the primary charging potential Vd”, “shift control of the LED light quantity condition”, and “conversion of the image signal” are performed according to the deterioration of the sensitivity of the photosensitive drum 10. A specific method is shown below.

  As described above with reference to FIG. 1, the image forming apparatus 100 includes the controller 50. The controller 50 stores use history information in the storage device 30 and controls image formation based on the use history information. The “usage history information” includes “the amount of rotation N of the photosensitive drum 10” that is “the amount of usage of the photosensitive drum 10” and “the elapsed time after the start of use of the photosensitive drum 10”. There is an accumulated number of days T from the start of use of the photosensitive drum 10.

  The controller 50 determines the durability as “usage frequency value” which is “usage history information” based on “the accumulated rotation speed N of the photoconductor drum 10” and “the accumulated number of days T from the start of use of the photoconductor drum 10”. The index K is calculated. Thus, the potential is controlled by estimating the photosensitivity. The accumulated number of days T is obtained by converting time data obtained by a time calculation unit inside the image forming apparatus main body 100a. The accumulated number of days T can be obtained when the photosensitive drum 10 is used by performing scanning that recognizes the replacement from the operation unit when the photosensitive drum 10 is replaced. In this way, the durability index K is derived from the following equation (1).

前述の耐久指数Ｋは、感光体ドラム１０の使用量を感光体ドラム１０の使用開始後の経過時間で除算した値である。例えば、感光体ドラム１０の積算回転数Ｎ＝５０［ｋ回］として、感光体ドラム１０の使用開始時からの積算日数Ｔ＝１０［日］とする。この場合に、耐久指数Ｋは、５［ｋ回／日］ということになる。コントローラ５０は、耐久指数Ｋを導出して耐久指数Ｋに基づいて画像形成を制御する。

The aforementioned durability index K is a value obtained by dividing the usage amount of the photosensitive drum 10 by the elapsed time after the use of the photosensitive drum 10 is started. For example, the cumulative number of rotations N of the photosensitive drum 10 is set to 50 [k times], and the cumulative number of days T from the start of use of the photosensitive drum 10 is set to 10 [days]. In this case, the durability index K is 5 [k times / day]. The controller 50 derives the durability index K and controls image formation based on the durability index K.

  Here, the correction amount of the exposure light portion potential that must be corrected with respect to the exposure light portion potential Vl of the initial photosensitive drum 10 is S (V), and here, the photosensitivity when the durability index is K. Let α (K) be the rising slope of the light portion potential of the body drum 10. The rising slope α (K), which is “characteristic change data” in which the characteristic of the photosensitive drum 10 changes corresponding to the durability index K, is stored in the storage device 30. This rising slope α (K) is data measured in advance. In this way, the correction amount S (V) of the bright portion potential during exposure is derived from the following equation (2).

コントローラ５０は、前述の耐久指数Ｋから記憶装置３０の内部に記憶される『感光体ドラム１０の明部電位の上昇傾きα（Ｋ）』を導き出す。そして、コントローラ５０は、『感光体ドラム１０の明部電位の上昇傾きα（Ｋ）』及び『感光体ドラム１０の積算回転数Ｎ』に基づいて、露光時明部電位の補正量Ｓ（Ｖ）を導出する。例えば、前述のように耐久指数Ｋ＝５ｋ回／日である場合には、図７（ａ）に示されるように明部電位の上昇傾きα（Ｋ）＝０．５３［Ｖ／ｋ回］となる。したがって、露光時明部電位の補正量Ｓ（Ｖ）＝０．５３［Ｖ／ｋ回］×５０［ｋ回］＝２６．５［Ｖ］となる。例えば、図７（ｂ）に示されるように、環境区分で５の状態の場合には、一次帯電電位Ｖｄの補正量ΔＶｄ＝１．９×２６．５［Ｖ］＝５０．３５［Ｖ］となる。なお、図７（ａ）の中で、Ｋの単位は［ｋ回／日］であり、α（Ｋ）の単位は［Ｖ／ｋ回］である。

The controller 50 derives “the rising slope α (K) of the bright portion potential of the photosensitive drum 10” stored in the storage device 30 from the durability index K. Then, the controller 50 corrects the bright portion potential during exposure S (V) on the basis of “the rising slope α (K) of the bright portion potential of the photosensitive drum 10” and “the accumulated rotational speed N of the photosensitive drum 10”. ) Is derived. For example, when the durability index K = 5k times / day as described above, as shown in FIG. 7A, the rising slope α (K) = 0.53 [V / k times] of the bright part potential. It becomes. Therefore, the correction amount S (V) of the bright portion potential during exposure is 0.53 [V / k times] × 50 [k times] = 26.5 [V]. For example, as shown in FIG. 7B, when the environmental classification is 5, the correction amount ΔVd of the primary charging potential Vd = 1.9 × 26.5 [V] = 50.35 [V]. It becomes. In FIG. 7A, the unit of K is [k times / day], and the unit of α (K) is [V / k times].

  FIG. 4 is a diagram showing the difference in the rate of increase in the light portion potential during exposure of the photosensitive drum with respect to the value of the durability index K. It can be seen that the higher the K, that is, the number of rotations of the photosensitive drum 10 averaged per day, the larger the upward inclination α.

FIG. 5 is a graph showing the relationship between the exposure light portion potential Vl and the exposure amount. When the exposure amount is 0.00 μJ / cm ² , the exposure light portion potential is Vl = 500 [V], and when the exposure amount is 0.50 μJ / cm ² , the exposure light portion potential is Vl = 100 [V]. In this case, the range of the bright portion potential Vl at the time of exposure is 500 [V] −100 [V] = 400 [V]. This is shown by curve X. Note that the exposure light portion potential Vl when the exposure amount is 0.00 μJ / cm ² substantially means the primary charging potential Vd.

Here, due to long-term use of the photosensitive drum 10, the bright portion potential at the time of exposure when the exposure amount is 0.50 μJ / cm ² becomes Vl = 100 [V] +26.5 [V] = 16.5 [V]. Become. In this case, the range of the bright portion potential Vl at the time of exposure is reduced to 500 [V] -126.5 [V] = 373.5 [V]. This is shown in curve Y.

In order to compensate for the decrease of 26.5 [V] in the range (corresponding to development contrast) of the bright portion potential Vl during exposure, the correction amount S (V) = 26.5 [V] of the bright portion potential Vl during exposure is In this case, the correction amount ΔVd of the primary charging potential Vd = 50.35 [V] is required. Therefore, the primary charging potential ΔVd is increased by 50.35 [V], and the bright portion potential during exposure is increased by 50.35 [V]. The light portion potential during exposure when the exposure amount is 0.0 μJ / cm ² is Vl = 550.35 [V], and the light portion potential during exposure when the exposure amount is 0.50 μJ / cm ² is Vl = 150.35. In the case of [V], the range of the bright portion potential Vl during exposure is 550.35 [V] −150.35 [V] = 400 [V]. This is shown in curve Z. Note that the exposure light portion potential Vl when the exposure amount is 0.00 μJ / cm ² substantially means the primary charging potential Vd.

  FIG. 6 shows the transition of the bright portion potential Vl at the time of exposure of the photosensitive drum 10 when the pause is entered. With reference to FIG. 6, the rest time until the next use after the photosensitive drum 10 is used will be described. In the figure, “A” indicates a line for decreasing the sensitivity of the photosensitive drum 10 when rotating 10 k per day, and “B” indicates a line for decreasing the sensitivity of the photosensitive drum 10 when rotating 5 k per day. Yes.

  As shown in FIG. 6, until the photosensitive drum 10 rotates 50 k, the photosensitive drum 10 forms an image at a pace of 10 k per day. When the photosensitive drum 10 rotates 50k, the photosensitive drum 10 is left in a state where it is not operated for 5 days. Thereafter, until the photosensitive drum 10 rotates 100 k again, the photosensitive drum 10 forms an image at a pace of 10 k per day.

  Here, it is assumed that it takes 5 days for the photosensitive drum 10 to rotate 50 k. In this case, since the photosensitive drum 10 is left for 5 days at the time of 50 k rotation, the number of rotations of the photosensitive drum 10 remains at 50 k at the final date of the leaving. Therefore, regarding the unknown in the above-described equation (1), the accumulated rotation number N of the photosensitive drum 10 is 50 k times, and the accumulated number of days T from the start of use of the photosensitive drum 10 is T = 10 days. As a result, the durability index K = 50 k times / 10 days = 5 k times / day. That is, the durability index K is halved, which corresponds to the pace at which the photosensitive drum 10 rotates 5k per day. Then, it can be seen that the potential after being left for 5 days has generally recovered to the vicinity of the sensitivity reduction line of the photosensitive drum 10 when the paper is passed at a pace of 5 k rotations in 1 day from the beginning. Further, the correction amount S (V) of the light portion potential Vl at the time of exposure of the photosensitive drum 10 is expressed by the equation (2) with the durability index K as the average drum rotational speed per day and the cumulative rotational speed N of the photosensitive drum 10. It can be derived by putting it in.

  FIG. 7A shows the value of α with respect to the durability index K stored in advance. For example, in the operation of the photosensitive drum 10 described with reference to FIG. 5 described above, since the durability index K = 5 k times / day, the rising gradient α (K) = 0. 53.

  FIG. 7B shows the absolute water content M, the standard primary charging potential Vd of the photosensitive drum 10, and the correction amount ΔVd of the primary charging potential Vd regarding the environment. Here, the primary charging potential Vd is also called development contrast. This is because an arbitrary development contrast can be obtained when the primary charging potential Vd is changed. A calculation formula for the correction amount ΔVd of the primary charging potential Vd is shown with respect to the standard primary charging potential Vd at that time.

  FIG. 8 is a flowchart showing a process of setting the primary charging potential Vd based on the data. From the above data, the primary charging potential Vd is set according to the flow of FIG. As shown in FIG. 8, the controller 50 starts control (S1). The controller 50 detects which environment it is in (S2). The controller 50 sets a standard primary charging potential Vd of the photosensitive drum 10 with respect to the detected environment (S3). The controller 50 reads “integrated rotation speed N of the photosensitive drum 10” and “integrated days T from the start of use of the photosensitive drum 10” (S4). The controller 50 calculates the value of the durability index K from the aforementioned N and T (S5). Based on the durability index K, the controller 50 calculates α (K) as the rising slope of the bright portion potential of the photosensitive drum 10 (S6). The controller 50 calculates the correction amount S (V) of the bright portion potential Vl during exposure from α (K) and the accumulated rotational speed N of the photosensitive drum 10 from the rising slope of the bright portion potential of the photosensitive drum 10 (S7). . The controller 50 calculates the correction amount ΔVd of the primary charging potential Vd (S8). The controller 50 calculates and sets the standard primary charging potential Vd of the photosensitive drum 10 based on the DC bias of the charging roller of the primary charger 5 and the DC bias Vdc of the developing roller (S9).

  The primary charging potential Vd can be set by controlling the DC bias applied to the charging roller. Generally, the primary charging potential Vd tends to be lower than the DC bias value at the development position. This is because the surface potential is attenuated between the charging position and the development position. However, in the contact AC charging method, the attenuation amount tends to be relatively small, and there is a feature that it does not change greatly before and after the specification of the photosensitive drum 10. In the present embodiment, since the charging potential with respect to the applied DC bias has the relationship shown in FIG. 9, the applied voltage value with respect to the target charging potential can be determined. Hereinafter, the charging potential set at this time is referred to as a corrected initial charging potential. Finally, the controller 50 ends the control (S10).

  FIG. 10 is a graph showing the transition of the saturation value of the potential change in one job for each durability index K. As shown in FIG. 10, short-term potential fluctuations within one job relating to the photosensitive drum 10 tend to saturate when a certain number of sheets are reached. The transition of the saturation value increases depending on the specification, but depends on the durability index K. It can be seen that the greater the durability index K, the greater the transition per revolution of the photosensitive drum 10. Therefore, the potential control within one job needs to be calculated based on the durability index. Therefore, the potential in one job is corrected and controlled.

  The saturation value of the potential change within one job can be expressed by the following equations (3) and (4). The durability index K as “usage frequency value” as “usage history information” based on “accumulated rotational speed N of photoreceptor drum 10” and “accumulated days T from start of use of photoreceptor drum 10” is expressed by the following equation. It is derived by (3). When the saturation value of the potential change is W (V), the slope for each durability index K is β (K), and the cumulative number of rotations of the photosensitive drum 10 is N, the saturation value W (V) of the potential change is Is derived by the following equation (4).

そうすると、耐久指数Ｋ，感光体ドラム１０の積算回転数Ｎから１ジョブ内で補正する電位量が算出でき、１ジョブ内の非作像時に適当な間隔でさらに帯電電位を変更してゆくことで、濃度変化の少ない出力画像を得ることができる。

Then, the amount of potential to be corrected within one job can be calculated from the durability index K and the accumulated rotational speed N of the photosensitive drum 10, and the charging potential can be further changed at an appropriate interval during non-image formation within one job. An output image with little change in density can be obtained.

  Further, after the job is completed, the potential tends to recover to the potential before the job started. Since this transition is relatively fast, it can be considered that the corrected charging potential is returned to the original corrected initial charging potential. Depending on the way of transition, it is also effective to correct the initial charging potential according to the time from the end of a job to the start of the next job by a conventional method.

(Other forms of usage)
In the image forming apparatus 100 according to the present embodiment, the “use amount” included in the use history information is the accumulated rotation number N of the photosensitive drum 10. As a series of controls, the controller 50 first predicts the transition of the bright portion potential of the photosensitive drum 10 from the durability index K and the accumulated rotational speed N of the photosensitive drum 10, and the primary charging potential and the development according to the predicted value. The development contrast is kept constant by changing the bias. In addition, when the passage of the sheet is started with respect to the setting after the correction, the potential fluctuates in accordance with the durability index K and the accumulated rotation speed N of the photosensitive drum 10 even in the job, and thus further correction can be performed. Become.

  However, it is not limited to such an embodiment. That is, the “use amount” included in the use history information may be the use amount of the primary charger 5 or the use amount of the LED array 6. Specifically, the “use amount” includes the total charging time for which the primary charger 5 is charged, the total exposure time for which the LED array 6 is exposed, the number of sheets on which images are formed, the number of jobs on which images are formed, and the printing on which images are formed. Any one of the pixel amounts may be used.

  This “usage amount” is the total number of revolutions N of the photosensitive drum 10, the total charging time for which the primary charger 5 is charged, the total exposure time for which the LED array 6 is exposed, the number of sheets on which images have been formed, and image formation. Any two or more of the number of jobs and the amount of print pixels on which an image is formed may be combined. The combined numerical value may be used as the usage history index. For example, the first wear level value of the photosensitive drum 10 is calculated from the total charging time of the primary charger 5. Similarly, the second wear level value of the photosensitive drum 10 is calculated from the total exposure time of the LED array 6. A numerical value obtained by adding a value obtained by weighting the photoreceptor deterioration level to the first consumption level value and the second consumption level value may be used as a “usage history index” in which the primary charger 5 and the LED array 6 are combined.

  Note that the number of jobs refers to the number of jobs each time a plurality of printed materials are continuously printed. For example, when a 10-page document is printed out once, the number of printed sheets is 10, but the number of jobs is one. The print pixel amount is a method generally called video count, and when the image pixel signals are integrated, it means the integrated amount of the pixel signals of the image.

(Other forms of image formation control)
In the image forming apparatus 100 of this embodiment, the controller 50 controls image formation by correcting the voltage applied to the primary charger 5. That is, when the primary charging potential Vd is corrected, changes in the latent image contrast due to potential fluctuations are suppressed.

  However, it is not limited to such an embodiment. That is, the controller 50 may control image formation by correcting the voltage applied to the developing device 7. Alternatively, the controller 50 may control the image formation by correcting the exposure amount exposed from the LED array 6. Further, gradation correction can be performed in combination with this control. Predictive control based on previously measured data is possible, and gamma conversion can be performed by detecting the reflection density of a predetermined patch image, which is conventionally known.

(Other forms related to cartridge)
Furthermore, in the image forming apparatus 100 of the present embodiment, the photosensitive drum 10 and the storage device 30 are not described as being in a cartridge, but the present invention is not limited to this form. That is, at least the photosensitive drum 10 and the storage device 30 may be integrally formed as a cartridge, and the cartridge may be detachable from the image forming apparatus main body 100a.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. An example of a basic Vd-Vl characteristic is shown. It is sectional drawing which shows the structure of the layer of a photoconductive drum. It is a figure which shows the difference of the electric potential rise with respect to the value of the durability index K. It is a graph which shows the relationship between the bright part electric potential Vl at the time of exposure, and exposure amount. It shows the transition of the light portion potential of the drum when there is a pause. (A) has shown the value of (alpha) with respect to the durability index K memorize | stored beforehand. (B) shows the absolute moisture content M, the standard primary charging potential Vd of the photosensitive drum, and the charging potential correction amount ΔVd regarding the environment. It is a flowchart which shows the process which sets a charging potential based on data. It is a graph which shows the relationship of the charging potential with respect to the applied DC bias. 6 is a graph showing a transition of a saturation value of a potential change in one job for each durability index K. It is a graph which shows the mode of the sensitivity deterioration of a photoconductor drum. It is a graph which shows the mode of the sensitivity deterioration of a photoconductor drum.

Explanation of symbols

5 Primary charger (charger)
6 LED array (exposure device)
7 Developing device 8 Transfer device 10 Photosensitive drum (photosensitive material)
30 storage device (information storage device)
100 Image forming apparatus

Claims (11)

A photoconductor, a charger for uniformly charging the surface of the photoconductor, an exposure device for exposing the surface of the photoconductor to form an electrostatic image, and developing a toner image on the surface of the photoconductor A developing device that transfers the developed toner image to a sheet, an information storage unit that stores use history information of at least one of the photoconductor, the charger, and the exposure device, and the information storage unit A storage unit that stores the usage history information, and a control unit that controls image formation based on the usage history information.
The use history information is information on a usage amount of at least one of the photoconductor, the charger, and the exposure device, and information on an elapsed time after the start of use of the photoconductor. .   The usage history information is a usage frequency value obtained by dividing a usage amount of any one of the photoconductor, the charger, and the exposure device by an elapsed time after the start of use of the photoconductor, and the control unit The image forming apparatus according to claim 1, wherein a use frequency value is derived and image formation is controlled based on the use frequency value.   The amount used includes the number of rotations of the photoconductor, the total charging time for charging the charger, the total exposure time for exposure by the exposure unit, the number of sheets on which images have been formed, the number of jobs on which images have been formed, and the number of images formed. The image forming apparatus according to claim 1, wherein the print pixel amount is any one of the print pixel amounts.   The use history information is a use frequency value obtained by dividing a use amount based on a combination of any two or more of the photoconductor, the charger, and the exposure device by an elapsed time after the start of use of the photoconductor, The image forming apparatus according to claim 1, wherein the control unit derives the use frequency value and controls image formation based on the use frequency value.   The amount used includes the number of rotations of the photoconductor, the total charging time for charging the charger, the total exposure time for exposure by the exposure unit, the number of sheets on which images have been formed, the number of jobs on which images have been formed, and the number of images formed. The image forming apparatus according to claim 1, wherein the image forming apparatus is a use history index derived by combining any two or more of the printed pixel amounts.   The information storage unit stores characteristic change data in which characteristics of the photoconductor change corresponding to the usage history information, and the control unit controls image formation based on the characteristic change data and the usage history information. The image forming apparatus according to any one of claims 1 to 5.   7. The image forming apparatus according to claim 1, wherein the controller controls image formation by correcting a voltage applied to at least one of the charger and the developer. The image forming apparatus described.   The image forming apparatus according to claim 1, wherein the control unit controls image formation by correcting an exposure amount exposed from the exposure unit.   9. The image formation according to claim 1, wherein the control unit converts an image signal by an image signal conversion processing unit that converts an image signal exposed from the exposure unit. 10. apparatus.   10. The apparatus according to claim 1, wherein at least the photosensitive member and the information storage unit are integrally formed as a cartridge, and the cartridge is detachable from an image forming apparatus main body. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the photoconductor is an electrophotographic photoconductor.

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