JP5691484B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that forms a color image using both a direct transfer system and an indirect transfer system, and an image forming method that is performed by the image forming apparatus.

  In a color electrophotographic image forming apparatus having a plurality of drums, a reference toner is used in a full color image forming apparatus in which K (black) is transferred by a direct transfer method and YMC (yellow, magenta, cyan) is transferred by an indirect transfer method. A technique is known in which the density of a pattern is detected by an optical toner density detection unit on a direct transfer belt and an indirect transfer belt, and the image density is corrected based on the detected density (for example, Patent Documents). 1: Refer to Japanese Patent Application Laid-Open No. 2002-323801).

  In the present invention, in order to be able to adjust transfer conditions according to usage conditions of individual users, a visible image density before transfer and a visible image density of transfer residual are detected by a sensor that detects a visible image on the photoreceptor. , And a transfer rate is measured based on the detected concentrations of both, and control is performed so that an appropriate transfer condition is selected and determined based on the measured transfer rate.

  However, since the toner density detection in the prior art detects the toner density at the two toner density detection units on the direct transfer belt and the indirect transfer belt, the difference in toner density detection between the respective detection units is unknown. For this reason, the toner density detection unit on the direct transfer belt detects the reference toner pattern in which the K color is transferred by the direct transfer method, and the toner density detection unit on the indirect transfer belt detects the reference toner pattern in which the YMC color is transferred by the indirect transfer method. In the case of detection by the color difference, there is a difference between the K toner density detection and the YCM toner density detection. there were.

  Therefore, the problem to be solved by the present invention is to prevent a density difference from occurring between the image density on the direct transfer medium and the image density on the indirect transfer medium.

In order to solve the above-described problems, the present invention is an image forming apparatus that forms a color image by using both a direct transfer method and an indirect transfer method, and is primarily transferred to an indirect transfer medium that forms an image by the indirect transfer method. A first density detecting means for detecting the density of the transferred image, and a density of the image secondarily transferred to the direct transfer medium for forming the image transferred by the direct transfer method on the image transferred to the indirect transfer medium. to a second density sensing means, before SL when the density of the image is the same formed density of an image and formed on the indirect transfer medium onto the direct transfer medium, said first and second density detection Correction means for setting a correction value for the detection outputs of the first and second density detection means so that the detection outputs of the image density detected by the means can be regarded as the same output . And

  In the embodiments described later, the indirect transfer medium is on the indirect transfer belt 6, the first density detection means is on the first density detection sensor 12, the direct transfer medium is on the direct transfer belt 9, and the second density detection means. Corresponds to the second density detection sensor 15, the third density detection means corresponds to the first density detection sensor 12, the correction means corresponds to the image density sensor correction control unit 22, and the image pattern corresponds to the reference pattern 10.

  According to the present invention, it is possible to prevent a density difference from occurring between the image density on the direct transfer medium and the image density on the indirect transfer medium.

1 is a schematic configuration diagram showing a configuration around a transfer portion of a full-color image forming apparatus using both a direct transfer system and an indirect transfer system. FIG. 5 is an explanatory diagram illustrating an example of Y, M, and C reference pattern images formed on an intermediate transfer belt. It is explanatory drawing which shows the attachment position of the density | concentration detection sensor for pattern detection, and the state of ON / OFF of the cleaning operation in a cleaning part. FIG. 4 is a functional block diagram illustrating a control configuration of toner density detection correction control in the image forming apparatus according to the present embodiment. 6 is a flowchart showing a control procedure of toner density detection correction control performed with the control configuration of FIG. 4.

  In the present invention, when correcting the difference in image density detection output of the density detection means for detecting the density of the image on the direct transfer medium and the indirect transfer medium, the image density on the indirect transfer medium and the direct transfer from the indirect transfer medium are directly transferred. The density of the residual image after transfer to the medium is detected by the density detector on the indirect transfer medium, and the transfer rate is calculated from the difference between before and after transfer, or the image density transferred directly to the transfer medium is directly determined. Both densities are detected by comparing the density of the image detected by the density detector on the transfer medium and obtained by the density detector on the indirect transfer medium with the density of the image detected by the image detector on the direct transfer medium. The difference in output in the density detection of the means is obtained and corrected.

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

  FIG. 1 is a schematic configuration diagram showing a configuration around a transfer portion of a full-color image forming apparatus using both a direct transfer system and an indirect transfer system. In the figure, a K-color toner image is formed on the photosensitive member 1 and transferred to a sheet conveyed from below in the drawing by a transfer bias of a transfer roller 2 by a direct transfer method. The toner images of Y, M, and C are formed on the photoreceptors 3, 4, and 5, overlapped by the intermediate transfer belt 6, and the roller 8 in the transfer portion of the roller group in which the intermediate transfer belt 6 is stretched. At the nip portion of the secondary transfer roller 7, it is further transferred onto the paper on which the K color is transferred by the transfer bias by the secondary transfer roller 7, and a full color image in which the four colors are superimposed is obtained. In the present embodiment, the secondary transfer roller 7 also serves as one of a pair of rollers on which a direct transfer belt 9 is stretched.

  Although not shown, an electrophotographic imaging element, that is, a charging unit, an optical writing unit, a developing unit, a cleaning unit, and a static eliminating unit are arranged on the outer periphery of the photoreceptors 1, 3, 4, and 5, The former is directly transferred to the sheet and the latter is transferred to the intermediate transfer belt 6 by a transfer section (not shown) that performs primary transfer to the transfer roller 2 and the intermediate transfer belt 6. The optical writing unit is set between the charging unit and the developing unit, and a primary transfer unit is provided between the developing unit and the cleaning unit.

  In the optical writing unit, for example, optical writing using a polygon mirror or optical writing using a laser diode array is performed.

  FIG. 2 is an explanatory diagram showing an example of Y, M, C reference pattern images formed on the intermediate transfer belt, and FIG. 3 is an installation position of the density detection sensor for pattern detection, and ON / OFF of the cleaning operation in the cleaning unit. It is explanatory drawing which shows the state of OFF.

  As shown in FIG. 2, the toner images of the Y, M, and C reference patterns are formed on the photoreceptors 3, 4, and 5, transferred to the intermediate transfer belt 6, and visualized as the Y, M, and C reference patterns 10. It becomes. In the present embodiment, the reference pattern 10 has a plurality of density patterns formed in a row along the transport direction for Y, M, and C. The density of the reference pattern 10 on the intermediate belt 6 is measured by the first density detection sensor 12.

  The density of the pattern directly transferred from the intermediate transfer belt 6 to the transfer belt 9 is measured by the second density detection sensor 15. The residual transfer image remaining without being transferred on the intermediate transfer belt 6 is turned off by turning off the belt cleaning 16, goes around the intermediate transfer belt 6, and again measures the density with the sensor 12. When the density measurement of the transfer residual image is completed, the belt cleaning 16 is turned on. Otherwise, during normal image generation, the intermediate transfer image and the untransferred image overlap, and a defective image is generated. The first and second density detection sensors 12 and 15 are reflection type optical sensors that detect reflected light from the density pattern with a photodiode and output a voltage corresponding to the density.

  FIG. 4 is a functional block diagram showing a control configuration of toner density detection correction control in the image forming apparatus according to the present embodiment. The control configuration according to the present embodiment is such that an image density sensor correction control unit 22, an indirect transfer control unit 23, and a direct transfer control unit 24 are connected around a print control unit 21, and the indirect transfer control unit 23 includes: The Y image forming unit 3A, the M image forming unit 4A, the C image forming unit 5A, and the first image density sensor 12 are controlled, and the direct transfer control unit 24 controls the K image forming unit 1A and the second image density sensor 15. Is configured to do.

  The print control unit 21 controls the entire system in order to execute full color printing or monochrome printing. The density sensor correction control unit 22 corrects an output difference between the first image density sensor 12 of the indirect transfer control unit 23 and the second image density sensor 15 of the direct transfer control unit 24.

  The indirect transfer control unit 23 controls the Y, C, and M image forming units 3A, 4A, and 5A, the intermediate transfer belt 6 and the secondary transfer roller 7, and images for transfer onto the sheet, and Y, C, and An M reference pattern 10 is formed, and an image or the reference pattern 10 is transferred onto a sheet or a direct transfer belt 9.

  The direct transfer control unit 24 controls the K image forming unit A1 and the transfer roller 2 to form an image for transfer onto a sheet. The K image forming unit 1A includes the image forming elements around the photoconductor 1, and controls the photoconductor 1 and the image forming elements to form a toner image.

  FIG. 5 is a flowchart showing a control procedure of toner density detection correction control performed in the control configuration of FIG. This process is executed by the image density sensor correction control unit 22.

  In this process, first, each reference pattern 10 for each color of YMC is formed on the photoreceptors 3, 4, 5 of the image forming units 3A, 4A, 5A (step S1). Next, the patterns on the photoconductors 3, 4, and 5 are transferred onto the intermediate transfer belt 6, 10 rows of reference patterns are formed on the intermediate transfer belt 6, and the density of each reference pattern 10 is detected by the first density detection sensor 12. Is detected (step S2). Let X be the density detected at this time. The density is electrically obtained as a detection output of the density detection sensor.

  The image density of the reference pattern 10 transferred and transferred from the intermediate transfer belt 6 to the direct transfer belt 9 by the secondary transfer roller 7 is detected by the second density detection sensor 15 on the direct transfer belt 9 (step S3). . The detected density is Y. Next, the image density of the reference pattern 10 remaining on the intermediate transfer belt 6 without being directly transferred from the intermediate transfer belt 6 to the transfer belt 9 is detected by the first density detection sensor 12 on the intermediate transfer belt 6 (step S4). . The detected density is Z.

  In step S5, a difference in density detection output (sensitivity) between the first and second density detection sensors is obtained based on the image density detected in steps S2 to S4, and the density difference is corrected.

Specifically, it is performed as follows.
That is, the density detected in steps S2 to S4, here, the density X on the intermediate transfer belt 6 immediately after the formation of the reference pattern, the density Y of the reference pattern after transfer onto the direct transfer belt 9, and the direct transfer onto the transfer belt 9 Between the density Z of the reference pattern remaining on the intermediate transfer belt 6,
X−Z = Y (1)
This relationship should hold. However, if there is a difference between the detection outputs (sensitivities) of the respective density detection sensors 12 and 15, this equation does not hold. Therefore, when there is a difference in the detection outputs (sensitivities) of the density detection sensors 12, 15, correction is performed as follows.

(A) In the case of X−Z> Y In this state, the second density detection sensor 15 on the direct transfer belt 9 is compared with the first density detection sensor 12 on the intermediate transfer belt 6 in the above formula (1). It is shown that the density of the reference pattern 10 is detected lighter than in the case indicated by. Therefore, correction is performed so that the conversion from the detection value (detection voltage) of the second density detection sensor 15 on the direct transfer belt 9 to the density becomes deeper. Alternatively, correction is performed so that the conversion from the detection value (detection voltage) of the first density detection sensor 12 on the intermediate transfer belt 6 to the density becomes thin.

(B) In the case of X−Z <Y In this state, the second density detection sensor 15 on the direct transfer belt 9 is compared with the first density detection sensor 12 on the intermediate transfer belt 6 in the above formula (1). This indicates that the density of the reference pattern 10 is detected higher than in the case indicated by. Therefore, correction is made so that the conversion from the detection value (detection output (voltage)) of the second density detection sensor 15 on the direct transfer belt 9 to the density becomes thin. Alternatively, correction is performed so that the conversion from the detection value (detection voltage) of the first density detection sensor 12 on the intermediate transfer belt 6 to the density becomes deeper.

  The corrections in the cases (a) and (b) are repeated until the expression (1) holds or falls within a predetermined range, and the detection values (detection voltages) of the first density sensor 12 and the second density sensor 15 are repeated. Is corrected so that the relationship between the detected values coincides or substantially coincides with each other. That is, a correction value is set for the detection outputs of the first and second density sensors 12 and 15 so that the outputs can be regarded as the same when the density is the same. In this case, if one is used as a reference, only the other needs to be corrected.

On the other hand, in step S5, correction can be performed using the transfer rate. In this case, from the densities X and Z detected in steps S2 and S4, the transfer rate when transferring directly from the intermediate transfer belt 6 to the transfer belt 9 is
Transfer rate = (X−Z) / X (2)
Is required. Using this transfer rate, with respect to the density Y of the reference pattern 10 on the direct transfer belt 9 detected in step S3,
Transfer rate * X = Y (3)
This relationship should hold. Therefore, in a short period in which the fluctuation of the transfer rate is small, the difference between the detection voltages of the first and second density detection sensors 12 and 15 can be measured by detecting X and Y.

  If the transfer rate is expected to change due to a certain amount of time or a change in temperature / humidity environment, the image density Z of the reference pattern remaining on the intermediate transfer belt 6 is measured again, and the above equation (2) Transfer rate is obtained from When the transfer rate is obtained, the relationship between the densities X and Y is obtained from the equation (3), and the relationships between the detected values of the densities of the first and second density sensors 12 and 15 are matched. In the present embodiment, six reference patterns 10 are formed. The density is detected for each of these six patterns, and the first and second density detection sensors 12 and 15 for these six reference patterns are used. The detection outputs of the first and second density detection sensors 12 and 15 are corrected so that the detected image density difference falls within a predetermined range. However, the density correction control may be simply executed with one reference pattern. it can. It is also possible to perform correction with a plurality of image densities by changing a transfer current in the secondary transfer roller 7, setting a plurality of transfer rates, and forming a pattern with a plurality of densities.

  The timing of executing the processing shown in FIG. 5 is desirably executed every time a predetermined number of prints are made by counting the number of prints.

  The control in the image density sensor correction control unit 22 is executed by the CPU based on a preset program. For example, the program is stored in advance in a ROM (not shown), read out from the ROM, expanded into a RAM, and executed while using the RAM as a work area. Alternatively, the program is preliminarily combined with hardware such as an ASIC and processing by the program. It is executed according to the set procedure. Needless to say, the program may be acquired not only from the ROM of the control device of the image forming apparatus but also from an external medium such as a CD-ROM or from the ROM of the external server via a network.

As described above, according to the present embodiment,
1) It is possible to correct a difference in output with respect to the same density of toner density detection of the first and second density detection sensors 12 and 15 disposed on the indirect transfer belt 6 and the direct transfer belt 9, respectively.
2) When correction is performed using the transfer rate, it is not necessary to detect the density of the untransferred image every time, and control and efficiency in image formation can be improved.
3) Since the first and third density detection means are shared by the first density detection sensor, the minimum number of sensors can be used, and the influence of the difference in sensor density detection can be minimized. it can.
4) Various densities can be detected and corrected by using images with different densities or changing the transfer rate to transfer an image.
5) Since correction is repeatedly performed at a predetermined timing, even when the image density detection output is changed due to a change in sensor sensitivity with time and contamination of the sensor, it can be dealt with at an early timing.
6) Since the correction is executed for each predetermined number of prints, the correction can be reliably performed as a parameter for the number of prints.
There are effects such as.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention, and all technical matters included in the technical idea described in the claims are included. The subject of the present invention. The above embodiment shows a preferred embodiment, but those skilled in the art can realize various alternatives, modifications, variations, and improvements from the contents disclosed in this specification. These are included within the scope defined by the appended claims.

6 Indirect Transfer Belt 9 Direct Transfer Belt 10 Reference Pattern 12 First Density Detection Sensor 15 Second Density Detection Sensor 22 Image Density Sensor Correction Control Unit

JP 2002-323801 A

Claims (9)

An image forming apparatus that forms a color image by using both a direct transfer method and an indirect transfer method,
First density detecting means for detecting the density of an image primarily transferred to an indirect transfer medium for forming an image by an indirect transfer method;
A second density detecting means for detecting the density of the image secondarily transferred to the direct transfer medium for forming the image primarily transferred to the indirect transfer medium by the direct transfer method;
Before SL when the density of the image is the same formed density of an image and formed on the indirect transfer medium onto the direct transfer medium, the detection output of the image density detected by the first and second concentration detection means Correction means for setting a correction value for the detection outputs of the first and second density detection means so that the outputs can be regarded as the same ,
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The image forming apparatus characterized in that the correction means compares the image densities detected by the first and second density detection means to obtain a difference in detection output of the image density and corrects the difference. The image forming apparatus according to claim 1,
A third density detecting means for detecting an image density of an afterimage after secondarily transferred from the indirect transfer medium to the direct transfer medium;
The correcting unit transfers the image from the indirect transfer medium to the direct transfer medium based on the density of the remaining image detected by the third density detecting unit and the density of the image detected by the first density detecting unit. An image forming apparatus characterized in that a rate is obtained and the detection outputs of the first and second density detectors are corrected based on the transfer rate. The image forming apparatus according to claim 3 , wherein
The image forming apparatus characterized in that the first density detecting means and the third density detecting means share one density detecting means to detect the image density. The image forming apparatus according to any one of claims 1 to 4, wherein
2. The image forming apparatus according to claim 1, wherein the primary transferred image includes a plurality of image patterns having a plurality of densities. The image forming apparatus according to claim 3, wherein
The image forming apparatus, wherein the correction unit sets a plurality of transfer rates and corrects detection outputs of the first and second density detection units based on a plurality of image patterns having a plurality of densities. The image forming apparatus according to any one of claims 1 to 6,
The image forming apparatus, wherein the correction unit repeatedly executes the detection output correction operation at a predetermined timing. The image forming apparatus according to claim 7, wherein
2. The image forming apparatus according to claim 1, wherein the predetermined timing is every predetermined number of prints. An image forming method for forming a color image using both a direct transfer method and an indirect transfer method,
A first density detection step of detecting a density of an image primarily transferred to an indirect transfer medium on which an image is formed by an indirect transfer method by a first density detection unit;
A second density detection step of detecting, by a second density detection means, a density of an image secondarily transferred to the direct transfer medium for forming an image primarily transferred to the indirect transfer medium by the direct transfer method; ,
Before SL when the density of the image is the same formed density of an image and formed on the indirect transfer medium onto the direct transfer medium, the detection output of the image density detected by the first and second concentration detection means A correction step of setting a correction value for the detection outputs of the first and second density detection means so that the output can be regarded as the same .
An image forming method comprising: