JP2016099536A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of properly performing image formation.SOLUTION: The image forming apparatus includes a freely rotatable intermediate transfer body, a plurality of image carriers which are arranged side by side from an upstream to a downstream in the rotational direction of the intermediate transfer body and arranged so as to form a primary transfer nip part between the plurality of image carriers and the intermediate transfer body, primary transfer means which transfers a toner image carried by each of the image carriers to the intermediate transfer body through the primary transfer nip part, secondary transfer means which transfers the toner image transferred onto the intermediate transfer body by the primary transfer means to a paper sheet, density detection means which is arranged between the primary transfer nip part at the most downstream and the secondary transfer means and detects the density of the toner image on the intermediate transfer body, and press-contact force detection means which detects the press-contact force of the primary transfer nip part. The control of the transfer amount of the toner image by the primary transfer means or operation for correcting the press-contact force is performed on the basis of the detection result of the press-contact force detection means.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In recent years, with the MFPless [Multifunction Peripheral / Printer / Product] machine becoming borderless, the number of MFP machines used as production machines for catalogs, flyer printing, etc. has increased, and the need to continue to produce high coverage images with the same color is increasing. In particular, for secondary colors expressed by superposing two toner layers, image density unevenness tends to be noticeable, and high image quality is strongly demanded.

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus in which a density detection sensor is arranged on the downstream side of a transfer portion in an intermediate transfer belt in order to stabilize image quality. For example, such an image forming apparatus corrects image forming conditions for forming an image by creating a correction patch formed of toner on an intermediate transfer belt and detecting the correction patch with a density detection sensor.

JP 2014-92732 A

  However, in the secondary color or the like where the toner layer becomes thicker as described above, the pressure contact force applied to the toner layer closest to the photoreceptor becomes high, and reverse transfer (the toner adheres from the intermediate transfer belt to the photoreceptor side) at the downstream primary transfer portion. Phenomenon). The reverse transfer amount is likely to occur when the pressure contact force is high, and is affected by variations and changes in the primary transfer roller hardness and spring force amount, and the primary transfer roller outer diameter.

  However, at present, variations in pressure contact force are not reflected in image density correction control and the like, and accurate density correction for a secondary color in which the adhesion amount increases due to the effect of reverse transfer cannot be performed. . As a result, a situation in which the density unevenness of the secondary color is noticeable has occurred. Or, in order to prevent density unevenness, there is a problem that the toner density is excessively increased to waste toner.

  Note that the image forming apparatus disclosed in Patent Document 1 can stabilize the amount of patch passing through the secondary transfer, but does not address the above-described problem. SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can perform image formation more appropriately.

  The image forming apparatus according to the present invention is arranged so that a rotatable intermediate transfer member and the intermediate transfer member are arranged from upstream to downstream in the rotation direction, and a primary transfer nip portion is formed between the intermediate transfer member and the intermediate transfer member. A plurality of image carriers arranged in such a manner, a primary transfer unit that transfers a toner image carried on each of the image carriers to the intermediate transfer member via a primary transfer nip, and a primary transfer unit A toner image on the intermediate transfer member, which is disposed between a secondary transfer unit that transfers the toner image transferred to the intermediate transfer member onto a sheet, and a primary transfer nip portion on the most downstream side and a secondary transfer unit. A density detection means for detecting the density of the toner and a pressure contact force detection means for detecting the pressure contact force of the primary transfer nip, and based on the detection result of the pressure contact force detection means, the toner image is transferred by the primary transfer means. Control the amount or correct the pressure contact force A configuration that performs the operation. According to this configuration, it is possible to perform image formation more appropriately.

  More specifically, the pressure contact force detection unit may detect the pressure contact force of the primary transfer nip portion using the detection result of the density detection unit.

  More specifically, in the above configuration, the pressure contact detection means attaches a predetermined amount of toner image to the intermediate transfer body at the first primary transfer nip portion, and from the detection result of the density detection means, The reverse transfer amount in the second primary transfer nip portion downstream from the first primary transfer nip portion is obtained, and the pressure contact force of the second primary transfer nip portion is detected based on the obtained reverse transfer amount. It is good also as composition to do.

  More specifically, in the above-described configuration, the pressure contact detection means attaches a predetermined amount of toner image to the intermediate transfer body at the most upstream primary transfer nip portion, and from the detection result of the density detection means. The operation for obtaining the reverse transfer amount is executed for each primary transfer nip portion excluding the most upstream one, and the pressure contact of each primary transfer nip portion excluding the most upstream one based on the obtained reverse transfer amounts. It is good also as a structure which detects force.

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

1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to an exemplary embodiment. FIG. 2 is a schematic configuration diagram of an image forming unit and its periphery according to the present embodiment. It is a graph which shows the relationship between transfer pressure contact force and reverse transfer amount. It is a graph regarding a developing bias and a toner adhesion amount. 6 is another graph regarding the developing bias and the toner adhesion amount. It is a graph which shows the relationship between the standardity regarding press-contact force, and measurement.

  Embodiments of the present invention will be described below with reference to the drawings. However, the content of the present invention is not limited to the embodiment.

1. First Embodiment First, a first embodiment will be described. FIG. 1 is a block diagram illustrating 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 paper 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 for discharging the printed (printed) paper to the outside based on this.

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

  The paper feed unit 3 includes a paper tray for storing paper, and supplies the paper to the printing unit 4 at the timing when the toner image is supplied. The printing unit 4 transfers and fixes the supplied toner image onto a sheet. The paper printed in this way is discharged to a paper discharge tray provided in the image forming apparatus 1.

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

  Next, the configuration of the image forming unit 2 and its periphery will be described. FIG. 2 is a schematic configuration diagram of the image forming unit 2 and its periphery. As shown in this figure, the image forming apparatus 1 includes an intermediate transfer belt (one form of intermediate transfer body) 21 formed as an endless belt, and rollers (22a, 22b), 4 for supporting the intermediate transfer belt 21 in a stretched manner. A photosensitive drum 23 provided for each color (Y, M, C, K) toner, a reflective IDC sensor 24 (density detecting means), and a secondary transfer roller 25 are provided.

  The photosensitive drum 23 functions as an image carrier that carries a toner image formed thereon by a developing unit (not shown). The photosensitive drums 23 are arranged in the direction of rotation of the intermediate transfer belt 21 from the upstream side to the downstream side (in the direction indicated by the broken arrow in FIG. 2), yellow (hereinafter referred to as “Y color”), magenta (hereinafter referred to as “M”). 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 between each of the photosensitive drums 23 and is rotated by rotation of each roller (22a, 22b). The image forming apparatus 1 has the above-described configuration, and has a unit (primary transfer unit) that transfers the toner image carried on each of the photosensitive drums 23 to the intermediate transfer belt 21 via the primary transfer nip portion. doing. The toner image transfer amount (toner adhesion amount) from the photosensitive drum 23 to the intermediate belt 21 varies depending on the developing bias ΔV.

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

  The secondary transfer roller 25 is pressed against the roller 22b 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 paper supplied from the paper supply unit 3.

  The IDC sensor 24 is provided between the K 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 so as 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 serving as a pressure contact detection unit attaches a predetermined amount of toner image to the intermediate transfer belt 21 at the Y primary transfer nip (first primary transfer nip). (Transfer), and the operation for obtaining the reverse transfer amount from the detection result of the IDC sensor 24 is executed for each primary transfer nip portion (second primary transfer nip portion) excluding the Y color.

  Then, the control unit 5 detects the pressure contact force of each primary transfer nip portion excluding the Y color based on the obtained reverse transfer amounts. The flow of such operation will be described below with a specific example.

As shown in Table 1, the control unit 5 sets the primary transfer pressure contact force setting conditions (targets of the pressure contact force) for each color in four ways: first to fourth setting conditions. Then, the controller 5 strikes a Y-color toner patch (one form of toner image) with an aim of ² g / m ² for each of the first to fourth setting conditions (attached to the intermediate transfer belt 21), and this is applied to the IDC. It is conveyed to the sensor 24 so that the density is detected.

Regarding the setting conditions shown in Table 1, the pressure contact force of 6N is a standard value, and the pressure contact force of 15N is an excessive value. In the second to fourth setting conditions, the reverse transfer is surely generated at each position of the M color, the C color, and the K color. In addition, since the IDC sensor 24 cannot perform appropriate detection if the toner amount is excessive, consideration is given to hitting a Y-color toner patch at a low value of ² g / m ² .

As a result of such an operation, data shown in Table 2 is obtained for each setting condition. In Table 2, “toner adhesion amount” indicates the detection result of the toner adhesion amount by the IDC sensor 24, and “reverse transfer amount” indicates the reverse transfer amount (g / m ²⁾ determined from this detection result. "Position of adhesion amount" is subtracted), and "Position" indicates at which color position the reverse transfer has occurred.

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

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

  Also, the “ordinary pressure contact actual measurement value” in Table 2 is a value obtained by converting the current calculation result (excess pressure contact force measurement value) where the target of the pressure contact force is 15 N into the case where the target pressure force is 6 N. is there. That is, a value obtained by multiplying the value of “measured value of excessive pressure contact force” by 6N / 15N (= 0.4). Since 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, such a conversion method is applied. This converted value should be regarded as the detection result of the pressure contact force at the primary transfer nip portion by using the detection result of the IDC sensor 24 when the target of the pressure contact force is 6N (standard value). I can do it.

“Reverse transfer amount at maximum adhesion amount” in Table 2 represents the reverse transfer amount when the Y toner patch is hit by the maximum adhesion amount (10 g / m ² ) normally assumed. Is obtained from the relationship between the pressure contact force and the reverse transfer amount. Since the relationship shown in FIG. 3 changes depending on the environment in which the toner fluidity changes and the toner deterioration, the relationship may be further corrected using another table relating to the environment and the degree of toner deterioration.

As a result, the normal pressure contact forces at the positions of M color, C color, and K color were 5.2 N, 6.0 N, and 6.8 N, respectively. Next, using the result, the total reverse transfer amount (reverse transfer total) of each color is estimated from the reverse transfer amount at each position, and the initial image density setting 5 g / m ^{2 is} corrected in consideration of the reverse transfer amount. Set the density.

  Table 3 is a table of values relating to the process of determining the corrected adhesion amount from the reverse transfer sum. In this table, from the left side, “initial toner adhesion amount”, “reverse transfer amount” at the M color position, “toner adhesion amount after passing” at the M color position, and “reverse transfer amount at the C color position” ”,“ Adhering amount of toner after passage ”at the C color position,“ Reverse transfer amount ”at the K color position,“ Amount of adhesion before secondary transfer ”,“ Total amount of reverse transfer ”,“ Toner amount after correction ” ".

  The “reverse transfer amount sum” is the sum of the reverse transfer amounts at the respective positions of the M color, the C color, and the K color, and the “corrected toner adhesion amount” is a value after correction according to the reverse transfer amount sum. This is the toner adhesion amount.

Since the Y color is the most upstream color, in the case of the secondary color, it is a lower layer and is not reversely transferred. The reverse transfer amount at each color position is as shown in Table 3 based on the pressure contact force at each color position and the relationship shown in FIG. The total reverse transfer amount is 0.40 (= 0.12 + 0.13 + 0.15) g / m ² , and the corrected toner adhesion amount (“adhesion amount before secondary transfer” based on this value is 5.0 g / m 2). is corrected to the ^2, the value of the initial toner adhesion amount) is 5.43 g / ^{m 2.} This value is a value obtained by adding the total amount of reverse transfer 0.40 g / m ² to the initial toner adhesion amount 5 g / m ² (however, as a correction value for the amount of increase in initial toner adhesion amount that facilitates reverse transfer, 0. 03 g / m ² is further added).

For the M color, it is necessary to consider the secondary color in combination with the Y color toner. Therefore, it is necessary to assume a toner adhesion amount of 10.43 (= 5.43 + 5.00) g / m ² by adding the Y and M colors, and the corrected toner adhesion amount is 5.78 g / m ^2. Is calculated.

Similarly, for the C color, the one with the higher adhesion amount of the upstream Y color and M color is selected, and the toner adhesion amount of 10.73 (= 5.73 + 5) g / m ^{2 obtained} by combining the M color and the C color. Therefore, the corrected toner adhesion amount is calculated as 5.44 g / m ² . Since the maximum image density for each color target is determined as described above, an image can be formed by correcting the development bias ΔV as an image forming condition corresponding to the target image based on the maximum image density. In this way, the transfer amount of the toner image by the primary transfer unit is controlled, and more appropriate image formation is realized.

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

Therefore, in order to perform appropriate correction, the toner adhesion before reverse transfer when the development bias ΔV is 200 V is determined from the relationship between the toner adhesion amount before and after reverse transfer when the pressure level obtained from the reference transfer pressure contact force and the reverse transfer amount is changed. The amount 3.4 g / m ² is determined. 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 | required with g / m < ² >.

Further, when the reverse transfer amount is calculated by a method reverse to the above, the toner adhesion amount after reverse transfer when the developing bias ΔV is 300 V is obtained as 5.2 g / m ^2, and the reverse transfer correction curve in the figure is obtained. I can do it. For example, when a toner adhesion amount of 5.8 g / m ² is obtained along this curve, it is necessary to output 315 V as the developing bias ΔV.

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

  Note that the set amount of M-color toner is assumed to be the maximum amount of Y-color toner, and in the case where the amount of Y-color toner is actually small, the exposure dot placement method, etc. With this γ correction control, the actual toner adhesion amount can be reduced. Similarly, when the M color is not the lowest layer, the toner amount can be reduced by the γ correction control.

2. Second Embodiment Next, a second embodiment will be described. In the following description, emphasis is placed on the description of parts different from the first embodiment, and description of common parts is 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 case of the first embodiment, the pressure contact force of the primary transfer nip portion is detected using the detection result of the IDC sensor 24 (see “2” in Table 2). Refer to “Measured values of normal pressure contact force”). 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 occurrence of reverse transfer or variation in the amount thereof is suppressed.

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

  As an example of the above 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. In this way, the pressing force is corrected, and more appropriate image formation is realized.

  Note that the pressing force variable control may be, for example, control of a pressing force by a spring, or may be control of an electrostatic pressure of a transfer output. In addition, as a method for measuring the pressure contact force, a method in which a piezoelectric sheet or the like is sandwiched between the intermediate transfer belt 21 and the photosensitive drum 23 and measurement is performed using the piezoelectric sheet may be employed.

3. Others As described above, the image forming apparatus 1 is arranged so that the intermediate belt 21 is rotatable and the intermediate belt 21 is arranged from upstream to downstream in the rotational direction, and the primary transfer nip portion is provided between the intermediate belt 21 and the intermediate transfer belt 21. A plurality of photosensitive drums 23 arranged to form, a primary transfer nip portion for transferring a toner image carried on each of the photosensitive drums 23 to the intermediate belt 21 via the primary transfer nip portion, and a primary transfer nip portion The toner image transferred to the intermediate belt 21 by the transfer means is disposed between the secondary transfer nip portion (secondary transfer means) for transferring the toner image to the paper, and the most downstream primary transfer nip portion and the secondary transfer means. And 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.

  Further, based on the detection result of the pressure contact detection means, an operation for performing appropriate image formation (image formation formed by superimposing the toner images on the photosensitive drums 23) 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 transfer amount of the toner image is controlled by the primary transfer unit, and in the second embodiment, the operation of correcting the pressure contact force is performed. It has become.

  As mentioned above, although the specific example was given and demonstrated about embodiment of this invention, this invention is not limited to the content. The present invention can be implemented in various specific forms without departing from the spirit of the present invention.

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

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming unit 21 Intermediate transfer belt (intermediate transfer body)
22a, 22b Roller 23 Photosensitive drum (image carrier)
24 IDC sensor 25 Secondary transfer roller 3 Paper feed unit 4 Printing unit 5 Control unit

Claims (4)

A rotatable intermediate transfer member,
A plurality of image carriers that are arranged so as to line up from the upstream to the downstream in the rotational direction of the intermediate transfer member, and are in pressure contact with the intermediate transfer member so as to form a primary transfer nip portion;
Primary transfer means for transferring a toner image carried on each of the image carriers to the intermediate transfer member via a primary transfer nip portion;
A secondary transfer means for transferring the toner image transferred to the intermediate transfer member by a primary transfer means onto a sheet;
A density detection means for detecting the density of the toner image on the intermediate transfer member, disposed between the most downstream primary transfer nip and the secondary transfer means;
A pressing force detecting means for detecting the pressing force of the primary transfer nip portion,
An image forming apparatus that performs control of a transfer amount of a toner image by a primary transfer unit, or an operation of correcting the pressing force based on a detection result of the pressing force detecting unit.   The image forming apparatus according to claim 1, wherein the pressing force detecting unit detects a pressing force of a primary transfer nip portion using a detection result of the density detecting unit. The pressure contact detecting means is
A predetermined amount of toner image is attached to the intermediate transfer member at the first primary transfer nip portion, and a second primary transfer downstream from the first primary transfer nip portion is detected from the detection result of the density detection means. Find the reverse transfer amount at the nip,
The image forming apparatus according to claim 2, wherein the pressure contact force of the second primary transfer nip portion is detected based on the obtained reverse transfer amount. The pressure contact detecting means is
An operation for obtaining a reverse transfer amount from the detection result of the density detecting means by attaching a predetermined amount of toner image to the intermediate transfer member at the most upstream primary transfer nip portion, except for the most upstream one. Execute for the transfer nip,
The image forming apparatus according to claim 2, wherein the pressure contact force of each primary transfer nip portion except the most upstream one is detected based on each obtained reverse transfer amount.