JP2006337816A - Color image forming apparatus and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus which has a simple configuration and is capable of producing a proper transfer current as much as possible, even if environmental conditions are changed or variation in primary transfer set conditions exists, and to provide the control method of the color image forming apparatus. <P>SOLUTION: A color printer successively primarily transfers toner images formed in respective colors on photoreceptor drums 31Y, 31M, 31C and 31K onto an intermediate transfer belt 10 rotated in the direction of an arrow A. Resistance elements 16Y, 16M, 16C and 16K whose resistance values have environmental dependency and changeover switches 17Y, 17M, 17C and 17K are provided between primary transfer rollers 11Y, 11M, 11C and 11K arranged in respective primary transfer sections and a single high voltage power supply 15. Then, the resistance elements 16 are operated with respect to required primary transfer rollers 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a color image forming apparatus, and more particularly, to a tandem color image forming apparatus using an electrophotographic method and a control method thereof.

  In general, as a color image forming apparatus using an electrophotographic method, four color toner images of YMCK are formed on four photosensitive members, respectively, and the toner images are sequentially primary on an intermediate transfer belt that is driven to rotate in one direction. A tandem type for transcription is provided.

  By the way, in this type of tandem color image forming apparatus, the primary transfer property varies due to variations in the setting conditions of the primary transfer portion, and in some colors, the photoreceptor is caused by excessive primary transfer current. In other colors, there is a problem that white spots occur due to insufficient primary transfer current in other colors. In addition, the difference in primary transfer voltage caused by variations in the setting conditions of the primary transfer portion differs depending on environmental conditions, and the difference is small in a high-temperature and high-humidity environment and large in a low-temperature and low-humidity environment. Here, the variation in the setting conditions of the primary transfer portion means the variation in the pressing force of the primary transfer roller of each YMCK, the variation in the nip width between the primary transfer roller and the intermediate transfer belt, and the like.

  Conventionally, as disclosed in Patent Documents 1 and 2, in order to adjust the transfer current, a variable connected to the transfer member according to the humidity detected by the humidity sensor or the current value flowing into the transfer member. The resistance value of the resistor was controlled.

However, in this type of control technology, it is possible to optimize the transfer current due to a change in humidity. However, as described above, the setting of the appropriate transfer current based on the variation of the primary transfer setting conditions is not considered. It was. Further, controlling the resistance value of the variable resistor has led to a complicated control mechanism.
JP-A-6-202502 JP 2003-57917 A

  Accordingly, an object of the present invention is to provide a color image forming apparatus capable of generating an appropriate transfer current as much as possible even when environmental conditions change or there are variations in primary transfer setting conditions with a simple configuration. It is in providing the control method.

  In order to achieve the above object, an image forming apparatus according to the present invention is a tandem type that sequentially transfers toner images formed in different colors on a plurality of photoconductors onto an intermediate transfer body that moves in one direction sequentially. In the color image forming apparatus, a single power source that applies a transfer voltage to a primary transfer electrode member that generates an electric field for transferring a toner image of each color to an intermediate transfer member, and the power source and at least one primary transfer And a resistance element having an environment dependency interposed between the electrode member and the electrode member.

  In the image forming apparatus according to the present invention, a single power source is provided for the primary transfer electrode member of each color, and a resistance element is interposed between the power source and at least one primary transfer electrode member. It consists of a simple structure, and it is possible to correct variations in the setting conditions of the primary transfer portion of each color by using a resistance element. Moreover, this resistance element has an environmental dependency (a resistance value changes depending on the environmental condition). Therefore, even if the environmental conditions change, the primary transfer voltage can be automatically controlled to obtain an appropriate transfer current as much as possible. Therefore, problems such as the occurrence of negative memory on the photoreceptor and white spots on the image are prevented.

  In the image forming apparatus according to the present invention, it is preferable that the resistance element is interposed between a single power source and a plurality of primary transfer electrode members, and a changeover switch for bypassing the resistance element is provided. . Since the primary transfer current varies depending on each color, it is possible to selectively interpose a resistance element only to the primary transfer electrode member that needs to be corrected by turning on / off the changeover switch.

  The resistance element may be interposed between a primary transfer electrode member located on the most downstream side in the moving direction of the intermediate transfer member and a single power source. Of the primary transfer electrode members provided in a plurality along the movement direction of the intermediate transfer body, the primary transfer electrode member positioned on the most downstream side in the movement direction of the intermediate transfer body is driven by the intermediate transfer body at the primary transfer portion. Since the roller is inevitably pulled by the roller, the pressure contact force is set large, so that the nip width is large and the primary transfer efficiency is high. By interposing a resistance element with respect to such a primary transfer electrode member, the primary transfer current is optimized.

  It is preferable to use an element having ion conductivity as the resistance element. Resistive elements having ionic conductivity can be suitably used in the present invention because they have small variations in resistance values between production lots and large environmental dependency of changes in resistance values.

  Furthermore, a detecting means for detecting the density of the toner image primarily transferred onto the intermediate transfer member may be provided. By detecting the density of the toner image primarily transferred onto the intermediate transfer body, the primary transfer voltage can be corrected to an appropriate value, and a primary transfer electrode that requires the resistance element to intervene. The member can be detected.

According to the present invention, there is provided a color image forming apparatus control method comprising: a color image forming apparatus provided with the toner image density detecting means;
After the solid pattern formed with toner on the photosensitive member is primarily transferred to the intermediate transfer member, a halftone pattern having a larger area than the solid pattern is formed with the toner on the photosensitive member at a position corresponding to the solid pattern. A step of primary transfer to an intermediate transfer member;
Detecting the density of the halftone pattern primarily transferred onto the intermediate transfer member by the detecting means, and detecting density unevenness of the halftone pattern;
An adjustment step of lowering or increasing the primary transfer voltage when the detected density unevenness is equal to or higher than a predetermined level;
Repeating the adjustment step until the detected density unevenness is equal to or lower than a predetermined level, and storing the primary transfer voltage immediately before the density unevenness is equal to or lower than the predetermined level;
It is provided with.

  Through the above steps, primary transfer characteristics can be detected for each color, and an appropriate primary transfer voltage can be obtained.

  Further, among the primary transfer voltages of the respective photosensitive members stored in the storing step, the highest voltage is set as the primary transfer voltage for image formation, and the primary transfer voltage lower than the primary transfer voltage for image formation. As for the photoconductor stored as, the resistance element may be interposed between the power source and the primary transfer electrode member by opening the changeover switch. Thus, the resistance element can be interposed in the necessary primary transfer electrode member.

  Embodiments of a color image forming apparatus and its control method according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus, see FIG. 1)
The image forming apparatus shown in FIG. 1 is an electrophotographic color printer, which includes a printer main body 1 configured to synthesize four-color images in a so-called tandem method, an image reading device 2, and a control unit 3. It is configured.

  The image reading device 2 is a well-known device that reads an image of an original placed on an original platen glass (not shown) by an image sensor such as a CCD element. The original image is RGB (red, green, blue) by the image sensor. They are separated into the three primary colors and converted into electrical signals. The image data is subjected to various types of data processing in the control unit 3 and further converted into YMCK (yellow, magenta, cyan, black) reproduction colors. The YMCK image data is stored in the memory 4 of the control unit 3 and subjected to necessary correction such as misalignment correction.

  The printer main body 1 includes a print head 30 (30Y, 30M, 30C, 30K) that forms a YMCK image including a photosensitive drum 31, a laser scanning optical device 32, a developing device 33, a charging device (not shown), and a residual toner cleaning device. ) Are juxtaposed directly below the intermediate transfer belt 10. In each print head 30, the laser scanning optical device 32 receives the transfer of the YMCK image data, forms a latent image on the photosensitive drum 31, and forms a toner image by the developing device 33. Such an electrophotographic process is well known and will not be described.

  The intermediate transfer belt 10 is stretched endlessly between a driving roller 21 and a driven roller 22 for applying tension, and is rotationally driven in the direction of arrow A by a rotational driving force transmitted from the driving roller 21. A primary transfer roller 11 is disposed on the inner side surface of the intermediate transfer belt 10 at a position facing each photosensitive drum 31.

  A secondary transfer roller 19 is disposed on the intermediate transfer belt 10 at a portion facing the driving roller 21. Further, a cleaning blade 15 for wiping residual toner comes into contact with the intermediate transfer belt 10 at a portion facing the driven roller 22, and the toner wiped by the blade 15 is stored in a waste bottle 16.

  An automatic paper feeding unit 40 that feeds the stacked sheets one by one is installed in the lower part of the printer main body 1. Further, a fixing unit 50 for heating and fixing the toner is disposed immediately above the secondary transfer portion.

  The toner images formed on the respective photosensitive drums 31 are sequentially primary-transferred onto the intermediate transfer belt 10 that is rotationally driven in the direction of arrow A, and four color images are combined. On the other hand, the sheets are fed one by one from the automatic sheet feeder 40, and the composite toner image is secondarily transferred from the intermediate transfer belt 10 in the secondary transfer section. Thereafter, the sheet is conveyed to the fixing unit 50 where the toner image is heated and fixed, and is discharged from the discharge roller 51 onto the tray 52.

  A sensor 18 for detecting environmental conditions such as temperature and humidity in the machine is installed in the printer main body 1.

(Configuration of primary transfer unit, see FIG. 2)
Here, the photosensitive drum 31 (31Y, 31M, 31C, 31K) is arranged on the outer side of the primary transfer unit with the intermediate transfer belt 10 interposed therebetween, and the photosensitive drum 31 is opposed to the inner side. Primary transfer rollers 11 (11Y, 11M, 11C, 11K) are arranged. Each primary transfer roller 11 is in pressure contact with each photosensitive drum 31 at a position about 4 mm away from the center of the drum 31 in the rotation direction A of the intermediate transfer belt 10.

  Each primary transfer roller 11 has a length of 322 mm, and the pressure contact force is applied by a spring member 12 (12Y, 12M, 12C, 12K) with a constant load of about 1 to 10N. The spring members 12Y, 12M, and 12C act via the links 13Y, 13M, and 13C, and the spring member 12K acts directly in the vertical direction.

  Each primary transfer roller 11 is connected to a high-voltage power supply 15 composed of a single transformer, and a primary transfer voltage is applied from the high-voltage power supply 15 to each primary transfer roller 11. This primary transfer voltage detects a voltage value or a current value when a constant current or a constant voltage is applied to the primary transfer roller 11, and a desired primary transfer voltage or a current value is detected according to the detected voltage value or current value. A primary transfer current is set. Such control is known as ATVC.

  Further, a sensor 35 for optically detecting the density of the toner primarily transferred onto the intermediate transfer belt 10 is provided on the downstream side in the belt rotation direction A with respect to the K-color photosensitive drum 31K. The toner concentration detection sensor 35 is used in the control method described below.

  Incidentally, the primary transfer roller 11 is a conductive rubber roller having a resistance value of 1E + 06 to 1E + 08Ω in an environment of a temperature of about 22% and a humidity of about 50%, which is a commonly used material. The resistance value is not constant. Further, the spring force of each spring member 12 is not constant.

  Therefore, when a constant voltage is applied to the primary transfer voltage selected by the ATVC control from the high-voltage power supply 15 constituted by a single transformer, the resistance value of the primary transfer roller 11 itself varies, the spring member 12 Due to the variation in the spring force, some variation occurs in the primary transfer current that flows into the respective photosensitive drums 31 during the primary transfer.

  As an example, a low-temperature and low-humidity environment of 10 ° C./15% (hereinafter referred to as LL environment), a medium / medium / humid environment of 23 ° C./65% (hereinafter referred to as NN environment), and a high-temperature and high-humidity environment of 30 ° C./85%. (Hereinafter referred to as an HH environment), a primary transfer operating window (hereinafter referred to as a primary transfer OW) when an image is formed by varying the primary transfer voltage applied to the primary transfer roller 11. Are shown in Tables 1-3 below. In Tables 1 to 3, ◯ indicates good, Δ indicates inconspicuous, and X indicates poor. The same applies to Tables 4 to 10 shown below.

  In this specification, the primary transfer OW means a range in which no photosensitive negative memory and white spots occur. When the primary transfer voltage is excessive, the transfer current excessively flows into a portion where there is no toner image, and when a halftone image is formed in this portion after the photosensitive drum 31 rotates once, This is a phenomenon in which the density of a toner image is lowered due to the flow of excess current, and is hereinafter referred to as a P / C memory. White spots are toner images around large-diameter particles when particles larger than toner particles (usually about 6 μm) exist due to toner aggregation in a solid pattern image. Is a phenomenon in which an image becomes blank without primary transfer.

  As is clear from Table 1, in the LL environment, the P / C memory for the K color occurs about 200 to 300 V earlier than the Y, M, and C colors. It is 1600-1800V enclosed by.

  As apparent from Table 2, in the NN environment, the P / C memory for the K color is generated about 100 V earlier than the Y, M, and C colors, so the range of the primary transfer OW is surrounded by a thick line in Table 2. 800-900V.

  As apparent from Table 3, in the HH environment, the P / C memory for the K color is generated about 100 V earlier than the Y, M, and C colors, so the range of the primary transfer OW is surrounded by a thick line in Table 1. 600V.

  As shown in Tables 1 to 3, the primary transfer OW differs for each color due to variations in the resistance value of the primary transfer roller 11 and variations in the spring force of the spring member 12. Further, the difference in primary transfer OW tends to be smaller in the HH environment and larger in the LL environment.

  Therefore, in this embodiment, as shown in FIG. 2, a resistance element 16 (16Y, 16M, 16C, 16K) whose resistance value has an environment dependency is interposed between the high-voltage power supply 15 and each primary transfer roller 11. I let you. At the same time, a changeover switch 17 (17Y, 17M, 17C, 17K) is inserted in parallel with each resistance element 16. The resistance element 16 has an ionic conductivity. Resistive elements having ionic conductivity have small variations in resistance values between production lots, and the resistance dependency is highly dependent on the environment. Specifically, the resistance value of the ion conductive resistance element 16 used in this example is 6E + 05-5E + 06Ω, 23 ° C./65% medium temperature and medium humidity in a high temperature and high humidity environment of 30 ° C./85%. It is 1E + 06-9E + 06Ω under the environment and 7E + 06-8E + 07Ω under the low temperature and low humidity environment of 10 ° C./15%. The resistance element having environment dependency is not limited to a resistance element having ion conductivity.

  As described above, in this embodiment, since the generation of the P / C memory is quick in the K color, the switch 17K is turned off to cause the resistance element 16K to act between the K-color primary transfer roller 11K and the high-voltage power supply 15. . For the other Y, M, and C colors, the switches 17Y, 17M, and 17C are turned on to bypass the resistance elements 16Y, 16M, and 16C.

  Tables 4 to 6 below show the primary transfer OW when the image is formed by turning off the switch 17K and causing only the resistance element 16K to act.

  As is apparent from Table 4, in the LL environment, the primary transfer OW of each color becomes substantially equal by interposing the resistance element 16K in the primary transfer roller 11K of K color, and the range of the primary transfer OW is the table. It was possible to secure up to about 1600 to 2000V surrounded by a thick line in FIG.

  As is apparent from Table 5, in the NN environment, the primary transfer OW of each color is substantially equal by interposing the resistance element 16K in the primary transfer roller 11K of K color, and the range of the primary transfer OW is the table. 5 was able to be secured up to about 800 to 1000 V surrounded by a thick line.

  As is apparent from Table 6, in the HH environment, the primary transfer OW of each color becomes substantially equal by interposing the resistance element 16K in the primary transfer roller 11K of K color, and the range of the primary transfer OW is the table. 6 was able to be secured up to about 600 to 700 V surrounded by a thick line.

  As shown in Tables 4 to 6, with respect to the occurrence of P / C memory and early K color, an ion conductive resistance element 16K is interposed between the primary transfer roller 11K and the high voltage power supply 15 to The primary transfer OW can be made substantially equal for each color under environmental conditions.

(Control method, see FIGS. 3 and 4)
Next, a control method for operating the resistance element 16 between each primary transfer roller 11 and the high-voltage power supply 15 in the color printer shown in FIG. 1 will be described. FIG. 3 is a diagram for explaining a detection method of the P / C memory, and FIG. 4 shows a control procedure for selecting the resistance element 16 to be operated.

  First, a primary transfer voltage is set (step S1), a solid pattern T1 of each color is formed on each photosensitive drum 31 with toner (step S2), and primary transfer is performed on the intermediate transfer belt 10 (step S3). ). The primary transfer voltage is a voltage value determined by the ATVC control.

  Next, the photosensitive drum 31 rotates once, and a halftone pattern T2 having a larger area than the solid pattern T1 is formed in each color with toner at a position corresponding to the solid pattern T1 (step S4). Primary transfer (step S5). Then, the toner density sensor 35 detects the density of the halftone pattern T2 that has been primarily transferred onto the intermediate transfer belt 10 (step S6). Based on this density detection result, density unevenness of the halftone pattern T2 is detected. Density unevenness usually occurs as a negative photosensitive memory, and occurs at the center of the halftone pattern T2 (corresponding to the solid pattern T1 formation location).

  If there is a color whose density unevenness of the halftone pattern T2 detected as described above is below a predetermined level (YES in step S7), the primary transfer voltage setting value is made higher than the previous setting value (step S8). The same process as above is repeated. If the density unevenness is already equal to or higher than a predetermined level at the time of the first density unevenness detection, the next primary transfer voltage set value is set lower than the previous set value and the same process is repeated.

  For all colors, the voltage value at the time when the density unevenness exceeds a predetermined level is set as the P / C memory generation voltage, the voltage value just before that is set as the primary transfer voltage (step S9), and finally the density unevenness. The color when the value becomes equal to or higher than a predetermined level is stored. The changeover switch 17 is turned off for the primary transfer rollers 11 other than this color, and the resistance element 16 is operated.

  When the primary transfer voltage is to be lowered, the above process is repeated until the density unevenness of all the colors becomes a predetermined level or less, and the voltage value when the density unevenness of at least one color becomes the predetermined level or less. Is set as the primary transfer voltage.

  The control method is for determining which of the primary transfer rollers 11 respectively installed for forming four-color images is preferably provided with the resistance element 16 interposed therebetween. However, in practice, the black primary transfer portion closest to the drive roller 21 (in other words, the primary transfer portion positioned on the most downstream side in the rotation direction of the intermediate transfer belt 10 or the primary having the highest transfer efficiency). The primary transfer OW tends to shift in the transfer portion.

  The reason for this is that the driving force applied to the intermediate transfer belt 10 by the driving roller 21 affects the pressing force of the primary transfer roller 11K closest to the driving roller 21 against the belt 10, so that the effect can be reduced by 1 This is because the pressing force of the next transfer roller 11K (spring force of the spring member 12K) is set high. Therefore, the resistance element 16 may be interposed only between the primary transfer roller 11K and the high-voltage power supply 15 in advance.

(Dependence of backup roller position and spring load on primary transfer OW)
Incidentally, a backup roller 36 (see FIG. 2) is provided on the inner surface side of the intermediate transfer belt 10 between the drive roller 21 and the primary transfer roller 11K. The backup roller 36 is installed in order to eliminate the influence of the driving force of the driving roller 21 on the primary transfer pressure by the primary transfer roller 11K.

  When the backup roller 36 is thus installed, the position W (see FIG. 5) and the load of the spring member 12K affect the primary transfer OW. Tables 7 and 8 below show color images when the load of the spring member 12K is 2.0 N and the position W of the backup roller 36 is set to -0.1 mm, -0.3 mm, and -0.5 mm, respectively. The primary transfer OW is shown during formation and monochrome image formation. Table 7 shows the HH environment, and Table 8 shows the LL environment.

  Tables 9 and 10 below show color images when the position W of the backup roller 36 is −0.3 mm and the load of the spring member 12K is set to 0.7N, 1.3N, and 2.0N, respectively. The primary transfer OW is shown during formation and monochrome image formation. Table 9 shows the HH environment, and Table 10 shows the LL environment.

(Other examples)
The color image forming apparatus and the control method thereof according to the present invention are not limited to the above-described embodiments, and can be variously changed within the scope of the gist. In particular, the image forming apparatus to which the present invention is applied may be a color copying machine or a color facsimile in addition to the color printer shown in the above embodiment.

1 is a schematic configuration diagram illustrating an example of a color image forming apparatus according to the present invention. FIG. 4 is an explanatory diagram illustrating a primary transfer unit of the color image forming apparatus. It is explanatory drawing which shows the process of forming a toner pattern on a photoreceptor in the control method which concerns on this invention. It is a flowchart figure which shows the procedure of the said control method. It is explanatory drawing which shows the position of a backup roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Printer main body 10 ... Intermediate transfer belt 11 ... Primary transfer roller 15 ... High voltage power supply 16 ... Resistance element 17 ... Changeover switch 18 ... Environment detection sensor 31 ... Photoconductor drum

Claims (7)

In a tandem type color image forming apparatus for sequentially transferring toner images formed in different colors on a plurality of photoconductors sequentially onto an intermediate transfer member moving in one direction,
A single power source for applying a transfer voltage to a primary transfer electrode member that generates an electric field for transferring the toner image of each color to the intermediate transfer member;
A resistance element having an environmental dependency interposed between the power source and at least one of the primary transfer electrode members;
A color image forming apparatus comprising:   2. The color image forming apparatus according to claim 1, further comprising a changeover switch for interposing the resistance element between the power source and the plurality of primary transfer electrode members, and for bypassing the resistance element. .   2. The color image forming apparatus according to claim 1, wherein the resistance element is interposed between a primary transfer electrode member located on the most downstream side in the moving direction of the intermediate transfer member and the power source.   4. The color image forming apparatus according to claim 1, wherein the resistance element has ionic conductivity.   The color image forming apparatus according to claim 2, further comprising a detecting unit configured to detect a density of the toner image primarily transferred onto the intermediate transfer member. The color image forming apparatus according to claim 5.
A primary pattern formed with toner on the photoconductor is primarily transferred to the intermediate transfer body, and then a halftone pattern having a larger area than the solid pattern is formed on the photoconductor at a position corresponding to the solid pattern. A step of primary transfer to the intermediate transfer member;
Detecting the density of the halftone pattern primarily transferred onto the intermediate transfer member by the detecting means, and detecting density unevenness of the halftone pattern;
An adjustment step of lowering or increasing the primary transfer voltage when the detected density unevenness is equal to or higher than a predetermined level;
Repeating the adjustment step until the detected density unevenness is equal to or lower than a predetermined level, and storing the primary transfer voltage immediately before the density unevenness is equal to or lower than the predetermined level;
A method for controlling a color image forming apparatus. Among the primary transfer voltages of the respective photoconductors stored in the storage step, the highest voltage is set as the primary transfer voltage for image formation and stored as a primary transfer voltage lower than the primary transfer voltage for image formation. 7. The method of controlling a color image forming apparatus according to claim 6, wherein the change-over switch is opened and the resistance element is interposed between the power source and the primary transfer electrode member. .

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