JP6503701B2 - Image forming device - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In recent years, with the becoming borderless of MFP [Multifunction Peripheral / Printer / Product] machines, the number of MFP machines used as production machines such as catalog printing and flyer printing is also increasing, and the need to continue high coverage images in the same color is increasing. In particular, in the case of secondary colors in which two toner layers are superimposed, image density unevenness tends to be noticeable, and high image quality is strongly required.

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus in which a density detection sensor is disposed downstream of a transfer portion in an intermediate transfer belt in order to stabilize the quality of an image. In such an image forming apparatus, for example, a correction patch formed of toner on an intermediate transfer belt is formed, and the density detection sensor detects the correction patch to correct an image forming condition for forming an image.

JP 2014-92732 A

  However, in the above-mentioned secondary color and the like in which the toner layer is particularly thick, the pressing force applied to the toner layer closest to the photosensitive member is high, and reverse transfer (the toner adheres from the intermediate transfer belt to the photosensitive member) Phenomenon occurs). The amount of reverse transfer easily occurs when the pressing force is high, and is affected by the hardness of the primary transfer roller, the variation in the amount of spring force, and the variation and change in the outer diameter of the primary transfer roller.

  However, under the present circumstances, variations in pressing force are not reflected in image density correction control etc., and accurate density correction etc. can not be performed for secondary colors where the adhesion amount increases due to the influence of reverse transfer. . As a result, a situation has occurred in which density unevenness of secondary colors is noticeable. Or, in order to prevent uneven density, there is a problem that toner density is increased excessively to wastefully consume toner.

  Although the image forming apparatus disclosed in Patent Document 1 can stabilize the amount of patches passing through the secondary transfer, it does not meet the problems described above. SUMMARY OF THE INVENTION In view of the above problems, the present invention aims to provide an image forming apparatus capable of performing image formation more appropriately.

  The image forming apparatus according to the present invention is arranged to align a rotatable intermediate transfer member and an upstream to a downstream of the rotational direction of the intermediate transfer member, and forms a primary transfer nip portion between the intermediate transfer member and the intermediate transfer member. Primary transfer means for transferring the plurality of image carriers arranged as described above, the toner image carried on each of the image carriers to the intermediate transfer member through the primary transfer nip portion, and the primary transfer means A secondary transfer means for transferring the toner image transferred onto the intermediate transfer body to a sheet of paper, and a toner image on the intermediate transfer body disposed between the primary transfer nip portion on the most downstream side and the secondary transfer means And a pressing force detecting means for detecting the pressing force of the primary transfer nip portion, and based on the detection result of the pressing force detecting means, the transfer of the toner image by the primary transferring means Control the amount or correct the pressure A configuration that performs the operation. According to this configuration, it is possible to perform image formation more appropriately.

  More specifically, as the above configuration, the pressing force detection unit may be configured to detect the pressing force of the primary transfer nip portion using the detection result of the density detection unit.

  More specifically, as the above configuration, the pressing force detecting unit causes the toner image of a predetermined amount to be attached to the intermediate transfer member at the first primary transfer nip portion, and from the detection result of the density detecting unit, The reverse transfer amount in the second primary transfer nip portion downstream of the first primary transfer nip portion is determined, and the pressing force of the second primary transfer nip portion is detected based on the determined reverse transfer amount. It may be configured to

  Further, more specifically as the above configuration, the pressing force detection unit causes the toner image of a predetermined amount to be attached to the intermediate transfer member at the most upstream primary transfer nip portion, and the detection result of the density detection unit The operation of obtaining the reverse transfer amount is performed for each primary transfer nip portion except the uppermost stream, and the pressure contact of each primary transfer nip portion except the uppermost stream is performed based on the determined each reverse transfer amount. It may be configured to detect force.

  According to the image forming apparatus of the present invention, it is possible to perform image formation more appropriately.

FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus according to the present embodiment. FIG. 2 is a schematic configuration diagram of an image forming unit according to the present embodiment and the periphery thereof. It is a graph which shows the relationship between the transfer pressure and the amount of reverse transfer. It is a graph regarding development bias and the amount of toner adhesion. It is another graph regarding development bias and the amount of toner adhesion. It is a graph which shows the relationship between the reference | standard property regarding press-contact force, and measurement.

  Embodiments of the present invention will be described below with reference to the drawings. However, the contents of the present invention are not limited at all to the embodiment.

1. First Embodiment First, a first embodiment will be described. FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus 1 according to the present embodiment. As shown in the figure, the image forming apparatus 1 includes an image forming unit 2, a sheet feeding unit 3, a printing unit 4, a control unit 5, and the like. As a basic operation, the image forming apparatus 1 receives an input of image data from the outside (for example, a PC), and executes a printing operation of discharging a sheet printed (printed) to the outside based on the input.

  The image forming unit 2 plays a role of creating a toner image based on image data and supplying it to the printing unit 4 (conveying by the intermediate transfer belt). The image forming unit 2 corresponds to color printing, and can form a toner image for each color of yellow (Y), magenta (M), cyan (C), and black (K).

  The sheet feeding unit 3 includes a sheet tray for storing sheets, and supplies the sheets to the printing unit 4 in accordance with the timing at which the toner image is supplied. The printing unit 4 transfers and fixes the supplied toner image to a sheet. The sheet printed in this manner is discharged to a sheet discharge tray or the like provided in the image forming apparatus 1.

  The control unit 5 is configured of, for example, a microcomputer, and controls each unit so that various operations of the image forming apparatus 1 are appropriately performed.

  Next, the configuration of the imaging unit 2 and the periphery thereof will be described. FIG. 2 is a schematic block diagram of the imaging unit 2 and the periphery thereof. As shown in the figure, the image forming apparatus 1 includes an intermediate transfer belt (one form of an intermediate transfer member) 21 formed as an endless belt and rollers (22a and 22b) for supporting the intermediate transfer belt 21 in tension. The photosensitive drum 23 provided for each toner of color (Y, M, C, K), a reflective IDC sensor 24 (density detection means), and a secondary transfer roller 25 are provided.

  The photosensitive drum 23 forms a toner image by developing means (not shown), and plays a role as an image carrier that carries the toner image. Each photosensitive drum 23 is yellow (hereinafter referred to as “Y”), magenta (hereinafter referred to as “Y”), from the upstream side to the downstream side in the rotational direction of the intermediate transfer belt 21 (in the direction indicated by the dashed arrow in FIG. 2). It is arranged in order of "color", cyan (hereinafter referred to as "C color"), and black (hereinafter referred to as "K color").

  The intermediate transfer belt 21 is disposed so as to form a primary transfer nip portion with each of the photosensitive drums 23, and is rotated by the rotation of each roller (22a, 22b). The image forming apparatus 1 has the above-described configuration, and has a means (primary transfer means) for transferring the toner image carried on each of the photosensitive drums 23 to the intermediate transfer belt 21 through the primary transfer nip portion. doing. The amount of transfer of the toner image (the amount of toner adhesion) from the photosensitive drum 23 to the intermediate belt 21 changes with the developing bias ΔV.

  In the present embodiment, it is possible to control the force (pressure contact force) with which the intermediate transfer belt 21 and the photosensitive drum 23 are in pressure contact. This control is performed by adjusting the compression amount (spring force amount) of a spring that biases the photosensitive drum 23 toward the intermediate transfer belt 21. In addition, the control is performed by, for example, adjusting the electrostatic pressure of the transfer output. Also good.

  Further, the secondary transfer roller 25 is in pressure contact with the roller 22 b via the intermediate transfer belt 21 to form a secondary transfer nip portion (secondary transfer means). In the secondary transfer nip portion, the toner image primarily transferred to the intermediate transfer belt 21 is conveyed, and the toner image is transferred to the sheet supplied from the sheet feeding unit 3.

  The IDC sensor 24 is provided between the K-color primary transfer nip (the most downstream primary transfer nip) and the secondary transfer nip. The IDC sensor 24 can detect the density of the toner image on the intermediate transfer belt 21. The image forming apparatus 1 has the above-described configuration, and is formed to convey the toner image transferred to the intermediate transfer belt 21 by the primary transfer unit to the secondary transfer nip portion.

  The control unit 5 also serves as a pressing force detection unit that detects the pressing force of the primary transfer nip using the detection result of the IDC sensor 24. More specifically, the control unit 5 as pressure contact detection means adheres a predetermined amount of toner image to the intermediate transfer belt 21 at the Y-color primary transfer nip (first primary transfer nip). (Transfer) The operation of obtaining the reverse transfer amount from the detection result of the IDC sensor 24 is executed for each of the primary transfer nips (second primary transfer nips) except for the one of Y color.

  Then, the control unit 5 detects the pressing force of each primary transfer nip portion except for the one of Y color based on the determined reverse transfer amount. The flow of such an operation will be described below with reference to a specific example.

As shown in Table 1, the control unit 5 sets the setting conditions (the aim of the pressing force) of the primary transfer pressing force in each color to four of the first to fourth setting conditions. Then, the control unit 5 strikes a toner patch (one form of a toner image) of Y color with an aim of ² g / m ² (adheres to the intermediate transfer belt 21) for each of the first to fourth setting conditions. It is transported to the sensor 24 so that the concentration can be detected.

For the setting conditions shown in Table 1, the pressure contact force of 6 N is a standard value, and the pressure contact force of 15 N is an excessive value. Under the second to fourth setting conditions, in order to reliably generate reverse transfer at each of the M, C, and K positions, an excessive pressure contact force is intentionally set. Further, since the IDC sensor 24 can not appropriately detect the toner amount when the amount of toner is too large, it is considered to hit the toner patch of Y color at a low value of ² g / m ² .

As a result of performing such an operation, data shown in Table 2 can be obtained for each setting condition. The “toner adhesion amount” in Table 2 indicates the detection result of the toner adhesion amount by the IDC sensor 24, and the “reverse transfer amount” is the reverse transfer amount (g / m ² to “toner from the detection result”. “Position” represents the value obtained by subtracting the value of “adhesion amount”, and “position” indicates at which color position the reverse transfer has occurred.

In addition, the “Over pressure contact force measured value” in Table 2 is calculated based on the above “reverse transfer amount” value from the relationship between the press contact force (transfer contact force) and the reverse transfer amount as shown in FIG. Value. The relationship is information which is known in advance for each toner adhesion amount (2 g / m ^{2 in} this case) on the intermediate transfer belt 21 as shown in FIG. 3, and the control unit 5 The above calculation is possible because it is held.

  According to Table 2, for example, with regard to the second setting condition, although the pressing force was aimed at 15 N at the position of M, it is calculated that it was 13 N based on the reverse transfer amount. This calculated value can be viewed as the detection result of the pressure contact force of the primary transfer nip portion by using the detection result of the IDC sensor 24.

  Moreover, the “normally measured pressing force value” in Table 2 is a value obtained by converting the current calculation result (excessive measured pressing force value) in which the aim of the pressing force is 15 N and when the aim of the pressing force is 6 N is there. That is, it is a value obtained by multiplying 6N / 15N (= 0.4) by the value of the “excess welding pressure actual value”. Such a conversion method is applied because the pressing force is variable depending on the amount of compression of the spring and the like and the deviation of the measured value is proportional to the pressing force. This converted value should be regarded as the detection result of the pressing force at the primary transfer nip by using the detection result of the IDC sensor 24 when the aim of the pressing force is 6 N (standard value). Can do.

Further, “the reverse transfer amount at the maximum adhesion amount” in Table 2 corresponds to the reverse transfer amount when the toner patch of Y color is struck by the maximum adhesion amount (10 g / m ² ) which is usually supposed. The relationship is obtained from the relationship between the pressing force and the reverse transfer amount shown in FIG. Since the relationship shown in FIG. 3 changes due to the environment where the toner fluidity changes and the toner deterioration, the relationship may be further corrected using another table regarding the environment and the toner deterioration degree.

From the above, it was found that the normal pressing forces at the M, C, and K positions were 5.2 N, 6.0 N, and 6.8 N, respectively. Next, using the results, the total reverse transfer amount (reverse transfer sum total) of each color is estimated from the reverse transfer amount at each position, and correction taking into consideration the reverse transfer amount with respect to the initial image density setting 5 g / m ² Set the concentration.

Table 3 is a table of each value in the process of determining the correction adhesion amount from the total reverse transfer amount . The table shows, from the left, "initial toner adhesion amount", "reverse transfer amount" at M color position, "toner adhesion amount after passing" at M color position, "reverse transfer amount at C color position "The amount of toner adhesion after passing" at the position of color C, "the amount of reverse transfer" at the position of color K, "the amount of adhesion before secondary transfer", the "total reverse transfer amount", "the amount of toner adhesion after correction Represents ".

  Note that "total reverse transfer amount" is the total sum of reverse transfer amounts at M, C, and K positions, and "after correction toner adhesion amount" is a corrected amount according to the total reverse transfer amount. It is a toner adhesion amount.

Since Y color is the most upstream color, it becomes the lower layer in the case of the secondary color and is not reverse-transferred. The amount of reverse transfer at each color position is as shown in Table 3 from the relationship shown in FIG. 3 with the pressing force at each color position. The total reverse transfer amount is 0.40 (= 0.12 + 0.13 + 0.15) g / m ² , and the corrected toner adhesion amount based on this value (“adhesion amount before secondary transfer” is 5.0 g / m 2 ^The initial toner adhesion amount value corrected to be ² is 5.43 g / m ² . This value is a value obtained by adding the total reverse transfer amount of 0.40 g / m ² to the initial toner adhesion amount of 5 g / m ² (however, the correction value of 0. It corresponds to the addition of 03 g / m ² ).

In addition, it is necessary to consider the secondary color in combination with the Y color toner for M color. Therefore, it is necessary to estimate the toner adhesion amount of 10.43 (= 5.43 + 5.00) g / m ² by combining the Y and M colors, and the toner adhesion amount after correction is 5.78 g / m ² Is calculated.

Similarly, for the C color, select the one of the upstream Y color and the M color with the higher adhesion amount, and the toner adhesion amount of 10.73 (= 5.73 + 5) g / m ² in which the M color and C color are combined. The corrected toner adhesion amount is calculated to be 5.44 g / m ² . As described above, the maximum image density for each color target is determined, and based on this, it is possible to correct the developing bias ΔV as an image forming condition according to the target image, and to form an image. In this way, the transfer amount of the toner image is controlled by the primary transfer means, and more appropriate image formation is realized.

Further, in addition to the operation described above, the control unit 5 may perform an operation for correcting the adhesion amount at the time of high concentration more accurately. This point will be described below. Since the maximum toner adhesion amount can not be directly measured in the image density correction, the adhesion amount at two points is measured with respect to the development bias .DELTA.V to determine the development bias .DELTA.V for obtaining the target density. However, regarding the high adhesion amount among the two points, in FIG. 4, the adhesion amount measured 3.0 g / m ² when the development bias ΔV is 200 V is the adhesion amount after the occurrence of reverse transfer.

Therefore, in order to perform appropriate correction, the toner adhesion before reverse transfer when the developing bias ΔV is 200 V from the relationship between the toner adhesion amount before and after reverse transfer when the pressure level obtained from the reference transfer pressure and the reverse transfer amount is shaken. Determine the amount 3.4 g / m ² . Since the toner adhesion amount and the development bias ΔV are in a proportional relationship before reverse transfer, the toner adhesion amount before reverse transfer when the development bias ΔV is 300 V is 5.8 (= 3.4-1.0 + 3.4) It is calculated as g / m ² .

When the reverse transfer amount is calculated by the reverse method to the above, the toner adhesion amount after reverse transfer when the development bias ΔV is 300 V is obtained as 5.2 g / m ^2, and the reverse transfer correction curve in the figure is obtained. Can do. In order to obtain a toner adhesion amount of, for example, 5.8 g / m ² according to this curve, it is necessary to output 315 V as the development bias ΔV.

  Similarly, for secondary colors (for example, Y color and M color, etc.), as shown in FIG. 5, it is possible to create a correction curve that accurately estimates the reverse transfer amount of M color according to the toner adhesion amount of Y color. It is also possible to set the M toner adhesion amount. In this way, the correction content of the image forming conditions such as the developing bias ΔV is determined for each color.

  The set M toner adhesion amount is assumed to be the case where the Y toner adhesion amount is the maximum, and when the Y toner is actually small, the method of exposing dots etc. The actual toner adhesion amount can be reduced by the γ correction control of the above. Even when the M color is not the lowermost layer, it is possible to reduce the toner amount by the γ correction control as well.

2. Second Embodiment Next, a second embodiment will be described. In the following description, emphasis will be placed on descriptions of parts different from the first embodiment, and descriptions of common parts will be omitted.

  As described above, in the first embodiment, the transfer density of the toner image by the primary transfer unit is controlled based on the detection result of the IDC sensor 24. On the other hand, in the second embodiment, the pressure contact force is corrected based on the detection result of the IDC sensor 24.

  More specifically, in the second embodiment as well as in the first embodiment, the pressing force of the primary transfer nip portion is detected using the detection result of the IDC sensor 24 (see “Table 2”. Normal pressure contact force actual measurement value (see). Further, in the second embodiment, the pressure contact force is corrected by the ratio of the pressure contact force and the reference pressure contact force, so that the occurrence of reverse transfer or the variation in the amount thereof is suppressed.

  This correction is performed, for example, using the reference line and the relationship between the setting of the primary transfer pressure for actual measurement and the actual measurement (see the graph of FIG. 6). In the graph of FIG. 6, the reference line indicates that the setting and measurement of the primary transfer pressure are the same, and the measurement indicates that the setting and measurement of the primary transfer pressure are different.

  As an example of the correction, when the measured value is 6.8 N when the primary transfer pressure (setting value) is 6 N, the measured value is 6 N using the relationship shown in the graph. The set value is corrected to 5.2N. Thus, the pressure contact force is corrected, and more appropriate image formation is realized.

  The pressure contact control may be, for example, control of contact pressure by a spring, or control of electrostatic pressure of the transfer output. In addition, as a method of measuring the pressing force, a method of using a piezoelectric sheet or the like between the intermediate transfer belt 21 and the photosensitive drum 23 and measuring it may be employed.

3. Others As described above, the image forming apparatus 1 is arranged so as to line up the rotatable intermediate belt 21 and the upstream to downstream of the rotational direction of the intermediate belt 21, and the primary transfer nip portion between the intermediate belt 21 and the intermediate belt 21. A plurality of photosensitive drums 23 arranged to be formed, and a primary transfer nip portion for transferring the toner image carried on each of the photosensitive drums 23 to the intermediate belt 21 via the primary transfer nip portion; A secondary transfer nip portion (secondary transfer means) for transferring the toner image transferred onto the intermediate belt 21 by the transfer means to a sheet, and disposed between the most downstream primary transfer nip portion and the secondary transfer means An IDC sensor 24 for detecting the density of the toner image on the intermediate belt 21 and a pressing force detecting means for detecting the pressing force of the primary transfer nip portion are provided.

  Further, based on the detection result of the pressing force detection means, an operation for performing appropriate image formation (image formation in which the toner images of the respective photosensitive drums 23 are formed in an overlapping manner) is performed.

  Therefore, according to the image forming apparatus 1, it is possible to perform image formation more appropriately. As the operation, in the first embodiment, the control of the transfer amount of the toner image by the primary transfer unit is performed, and in the second embodiment, the operation of correcting the pressing force is performed. It has become.

  The embodiments of the present invention have been described above by way of specific examples, but the present invention is not limited to the contents. The present invention can be implemented in various specific modes without departing from the scope of the invention.

  The present invention is applicable to an image forming apparatus such as a printer.

1 image forming apparatus 2 imaging unit 21 intermediate transfer belt (intermediate transfer member)
22a, 22b roller 23 photosensitive drum (image carrier)
24 IDC Sensor 25 Secondary Transfer Roller 3 Feeding Unit 4 Printing Unit 5 Control Unit

Claims (3)

A rotatable intermediate transfer member,
A plurality of image carriers arranged so as to line up from the upstream side to the downstream side of the rotational direction of the intermediate transfer body, and pressed to form a primary transfer nip portion with the intermediate transfer body;
Primary transfer means for transferring the toner image carried on each of the image carriers to the intermediate transfer body via a primary transfer nip portion;
A secondary transfer unit for transferring the toner image transferred onto the intermediate transfer body by the primary transfer unit to a sheet;
A density detection unit disposed between the downstreammost primary transfer nip and the secondary transfer unit for detecting the density of the toner image on the intermediate transfer member;
And pressure contact detection means for detecting contact pressure of the primary transfer nip portion,
The pressing force detection unit detects the pressing force of the primary transfer nip portion located downstream, using the detection result by the density detecting unit of the density of the toner image by the primary transfer nip portion located upstream. an image forming apparatus characterized by performing an operation for correcting the amount of transcription control, or the pressure contact force of the toner image by primary transfer means. A rotatable intermediate transfer member,
A plurality of image carriers arranged so as to line up from the upstream side to the downstream side of the rotational direction of the intermediate transfer body, and pressed to form a primary transfer nip portion with the intermediate transfer body;
Primary transfer means for transferring the toner image carried on each of the image carriers to the intermediate transfer body via a primary transfer nip portion;
A secondary transfer unit for transferring the toner image transferred onto the intermediate transfer body by the primary transfer unit to a sheet;
A density detection unit disposed between the downstreammost primary transfer nip and the secondary transfer unit for detecting the density of the toner image on the intermediate transfer member;
And pressure contact detection means for detecting contact pressure of the primary transfer nip portion ,
The pressure contact detection means is
A predetermined amount of toner image is attached to the intermediate transfer member at the first primary transfer nip portion, and based on the detection result of the density detecting means, the second primary transfer downstream of the first primary transfer nip portion Find the amount of reverse transfer at the nip,
The pressure contact force of the second primary transfer nip portion is detected based on the determined amount of reverse transfer ,
An image forming apparatus characterized by performing control of a transfer amount of a toner image by a primary transfer unit or correction of the contact pressure based on a detection result of the pressure detection unit . A rotatable intermediate transfer member,
A plurality of image carriers arranged so as to line up from the upstream side to the downstream side of the rotational direction of the intermediate transfer body, and pressed to form a primary transfer nip portion with the intermediate transfer body;
Primary transfer means for transferring the toner image carried on each of the image carriers to the intermediate transfer body via a primary transfer nip portion;
A secondary transfer unit for transferring the toner image transferred onto the intermediate transfer body by the primary transfer unit to a sheet;
A density detection unit disposed between the downstreammost primary transfer nip and the secondary transfer unit for detecting the density of the toner image on the intermediate transfer member;
And pressure contact detection means for detecting contact pressure of the primary transfer nip portion ,
The pressure contact detection means is
The operation of obtaining a reverse transfer amount from the detection result of the density detecting means by causing a toner image of a predetermined amount to adhere to the intermediate transfer member at the most upstream primary transfer nip portion is the primary except for the most upstream one. Run for the transfer nip,
The pressing force of each primary transfer nip portion excluding the most upstream one is detected based on the determined reverse transfer amounts .
An image forming apparatus characterized by performing control of a transfer amount of a toner image by a primary transfer unit or correction of the contact pressure based on a detection result of the pressure detection unit .