JP3550650B2 - Image forming method and image forming apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, after sequentially forming a patch image for each color with n different (n ≧ 2) toners in a predetermined toner color order, the density of each patch image is detected collectively, and the The present invention relates to an image forming method and an image forming apparatus that execute an optimum value calculation process for obtaining an optimum value of a density control factor that affects the image density of a toner image for each color based on the image density.
[0002]
[Prior art]
In an image forming apparatus that forms an image using toners of a plurality of colors, it is difficult to maintain a constant toner density due to fatigue of a photoreceptor, fluctuations in toner properties and phenomenon bias-density properties. Therefore, conventionally, at power-on or periodically, the toner density is automatically adjusted by adjusting a density control factor that affects the image density of the toner image, such as a developing bias, a charging bias, and an exposure amount. I have.
[0003]
FIG. 8 is a timing chart showing a conventional image forming method. In this prior art, while an intermediate transfer medium such as an intermediate transfer belt, an intermediate transfer drum, and transfer paper makes one rotation (one cycle of an intermediate medium synchronization signal), first, yellow (Y) toner and four different kinds of toner are used. After the patch image is formed on the intermediate transfer medium with the developing bias, the patch images are sequentially formed on the intermediate transfer medium for each of the toner colors of cyan (C), magenta (M), and black (K) in the same manner as for yellow. Form. Then, a patch image of the final toner color (black in FIG. 1) is formed, and the density of all patch images is detected collectively by the patch sensor. Thereafter, based on the detected data, a developing bias for obtaining the maximum density for each color is calculated, and these are set as optimum values of the density control factors.
[0004]
In this specification, a patch image is formed while changing density control factors such as a developing bias as described above, and after detecting the densities of those patch images, the optimum density control factor is determined based on the image densities. A series of processing for calculating the value is referred to as “optimal value calculation processing”.
[0005]
[Problems to be solved by the invention]
Incidentally, it is not always possible to always accurately determine the optimum developing bias (optimum value) by executing the optimum value calculating process once. For example, if the setting condition of the developing bias at the time of creating a patch image is not appropriate, a plurality of For a specific toner color among the color toners, the optimum value (optimal developing bias) may not be obtained from the detection data. In such a case, it is necessary to execute the optimum value calculation process again.
[0006]
However, in the conventional apparatus, the patch image of the final toner color is formed, and at the same time, the image density is detected and the optimum value of the developing bias is calculated for all the toner colors. Therefore, at the time T0 when the optimum value calculation process is completed, the next image drawing timing has already passed, and the drawing of the yellow patch image is executed unless the intermediate transfer medium has been idle for at least one rotation. I can't.
[0007]
As described above, in the related art, after the optimum value calculation process has failed, performing the same process continuously includes at least one or more rounds of idling operation, which is one of the causes of a decrease in throughput.
[0008]
The present invention has been made in view of the above problems, and has as its object to provide an image forming method and an image forming apparatus capable of calculating an optimum value of a density control factor affecting the image density of a toner image in a short time. And
[0009]
[Means for Solving the Problems]
According to the image forming method of the present invention, a patch image for each color is sequentially formed with n different colors (n ≧ 2) of toner in a predetermined toner color order, and then the density of each patch image is collectively determined. An image forming method for performing an optimum value calculation process for detecting, for each color, an optimum value of a density control factor that affects the image density of a toner image based on the detected image density. Before forming a patch image with the last toner color in the toner color order at the latest, the density of each patch image is detected for a toner color for which a patch image has already been formed, and for each color based on those image densities. A first step of obtaining an optimum value of the density control factor in advance; and, if there is a toner color for which the optimum value could not be obtained in the first step, the optimum value calculating process is immediately performed. And a second step of executing again.
[0010]
Further, the image forming apparatus according to the present invention forms a patch image for each color by image forming means using n different (n ≧ 2) toners in a predetermined toner color order, and then forms the patch image of each patch image. An image forming apparatus which collectively detects a density by a density detection unit, and wherein a control unit calculates an optimum value of a density control factor affecting an image density of a toner image for each color based on the image density, In order to achieve the above object, before forming a patch image with the last toner color in the toner color order at the latest by the control means, each patch image detected by the density detecting means for the toner color on which the patch image has already been formed. If the optimum value of the density control factor is obtained in advance for each color based on the density of Promptly for all toner colors to create a patch image again, and configured to determine the optimum value.
[0011]
In the image forming method and the image forming apparatus configured as described above, before forming the patch image with the final toner color in the toner color order at the latest, each of the patch images of the toner colors for which the patch image has already been formed is used. The density is detected, and the optimum value of the density control factor is determined in advance for each color based on the image density. Then, if the optimum value cannot be obtained for at least one or more toner colors, the optimum value calculation process is immediately executed again.
[0012]
Here, “advanced” means the following. That is, the formal optimum value is a patch image formed for the final toner color, the density of the patch image is detected for all the toner colors at once, and is obtained based on these image densities. At the latest, before forming a patch image with the last toner color in the toner color order, a determination is made as to whether or not it is necessary to perform the optimum value calculation process again on the toner color on which the patch image has already been formed). Means that the optimum value is calculated in advance. Further, "swiftly" means that when the optimum value calculation process is performed again, the patch image formation in the next optimum value calculation process is continuously performed from the patch image formation in the previous optimum value calculation process. Things.
[0013]
In the first step, after detecting the density of each patch image at once, the optimum value of the density control factor for each color may be obtained at once based on the image density. For example, before forming a patch image with the final toner color in the toner color order, a patch image for each color is formed sequentially with toner of (n-1) colors excluding the final toner color, and then each patch is collectively formed. The image density may be detected, and the optimum value of the density control factor may be collectively obtained for each (n-1) toner color based on the image density.
[0014]
In the first step, instead of performing the density detection and the calculation of the optimum value collectively as described above, the density detection and the calculation of the optimum value may be performed for each toner color as follows. That is, each time a patch image is formed for a certain toner color, the image density of the patch image with that toner color is detected, and the optimum value of the density control factor for the toner color is determined based on the image density. May be.
[0015]
Further, the n-color patch images may be formed in a predetermined arrangement order, and the density detection of the patch images may be performed in order from the leading position in the arrangement order. If the image is formed in any one of the 1st to (n-1) th arrangement orders counted from the top position, the density of the final toner color patch image must be at least before the density detection of the last patch image. Detection and optimal value calculation can be performed. In particular, when the patch image of the final toner color is formed at the head position in the arrangement order, the time margin before starting the optimal value calculation process again for the density detection and the optimal value calculation of the patch image is maximized.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
A. Overall configuration of image forming apparatus
FIG. 1 is a diagram showing one embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus forms a full-color image by superimposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), or uses only black (K) toner. To form a monochrome image. In this image forming apparatus, when an image signal is provided from an external device such as a host computer to the main controller 11 of the control unit 1, the engine controller 12 functions as an image forming unit in response to a command from the main controller 11. By controlling each part of E, an image corresponding to the image signal is formed on the sheet S.
[0017]
In the engine section E, a toner image can be formed on the photoconductor 21 of the image carrier unit 2. That is, the image carrier unit 2 includes a photosensitive member 21 rotatable in a direction indicated by an arrow in FIG. 1, and further includes a charging roller 22 as a charging unit, a developing unit around the photosensitive member 21 along the rotation direction. Developing units 23Y, 23C, 23M, and 23K, and a cleaning unit 24 are disposed, respectively. The charging roller 22 is applied with a high voltage from the charging bias generation unit 121 and contacts the outer peripheral surface of the photoconductor 21 to uniformly charge the outer peripheral surface.
[0018]
Then, the laser beam L is emitted from the exposure unit 3 toward the outer peripheral surface of the photoconductor 21 charged by the charging roller 22. As shown in FIG. 2, the exposure unit 3 is electrically connected to an image signal switching unit 122, and emits a laser beam L according to an image signal given through the image signal switching unit 122. The upper surface is exposed by scanning to form an electrostatic latent image on the photoconductor 21 corresponding to the image signal. For example, based on a command from the CPU 123 of the engine controller 12, when the image signal switching unit 122 is conducting with the patch creation module 124, the patch image signal output from the patch creation module 124 is given to the exposure unit 3. Thus, a patch latent image is formed. On the other hand, when the image signal switching unit 122 is electrically connected to the CPU 111 of the main controller 11, the laser light L is applied to the photosensitive member 21 in accordance with an image signal provided from an external device such as a host computer via the interface 112. And an electrostatic latent image corresponding to the image signal is formed on the photoreceptor 21.
[0019]
The electrostatic latent image thus formed is developed by the developing unit 23 with toner. That is, in this embodiment, as the developing unit 23, a developing unit 23Y for yellow, a developing unit 23C for cyan, a developing unit 23M for magenta, and a developing unit 23K for black are arranged along the photoconductor 21 in this order. Have been. These developing units 23Y, 23C, 23M, and 23K are configured to be freely movable toward and away from the photoreceptor 21, and in response to a command from the engine controller 12, the four developing units 23Y, 23M, 23C, and 23K. One of the developing units 23B selectively comes into contact with the photoconductor 21, and a high voltage is applied by the developing bias generation unit 125 to apply the toner of the selected color to the surface of the photoconductor 21 so as to apply the toner to the surface of the photoconductor 21. 21 to make the electrostatic latent image visible.
[0020]
The toner image developed by the developing unit 23 is primarily transferred onto the intermediate transfer belt 41 of the transfer unit 4 in a primary transfer region R1 located between the black developing unit 23K and the cleaning unit 24. The structure of the transfer unit 4 will be described later in detail.
[0021]
A cleaning unit 24 is disposed at a position in the circumferential direction (the direction of the arrow in FIG. 1) from the primary transfer region R1, and scrapes the toner remaining on the outer peripheral surface of the photoconductor 21 after the primary transfer. Drop it.
[0022]
Next, the configuration of the transfer unit 4 will be described. In this embodiment, the transfer unit 4 transfers the rollers 42 to 47, the intermediate transfer belt 41 stretched over the rollers 42 to 47, and the intermediate toner image transferred to the intermediate transfer belt 41 to the sheet S. And a secondary transfer roller 48 for performing the next transfer. A primary transfer voltage is applied to the intermediate transfer belt 41 from a transfer bias generator 126. When the color image is to be transferred to the sheet S, the toner image of each color formed on the photoreceptor 21 is superimposed on the intermediate transfer belt 41 to form a color image. The sheet S is taken out from the cassette 61, the manual feed tray 62 or an additional cassette (not shown) by the paper unit 63, and is conveyed to the secondary transfer area R2. Then, a color image is secondarily transferred to the sheet S to obtain a full-color image. When a monochrome image is to be transferred to the sheet S, only a black toner image is formed on the photoreceptor 21 on the intermediate transfer belt 41, and is conveyed to the secondary transfer region R2 in the same manner as in the case of a color image. Is transferred to the sheet S to obtain a monochrome image.
[0023]
After the secondary transfer, the toner remaining on the outer peripheral surface of the intermediate transfer belt 41 is removed by the belt cleaner 49. The belt cleaner 49 is disposed to face the roller 46 with the intermediate transfer belt 41 interposed therebetween. At an appropriate timing, the cleaner blade contacts the intermediate transfer belt 41 and remains on the outer peripheral surface thereof. Scrape off toner.
[0024]
In the vicinity of the roller 43, a patch sensor PS for detecting the density of a patch image formed on the outer peripheral surface of the intermediate transfer belt 41 as described later is provided. Is provided for detecting the synchronization.
[0025]
Returning to FIG. 1, the description of the configuration of the engine unit E will be continued. The sheet S to which the toner image has been transferred by the transfer unit 4 is disposed downstream of the secondary transfer area R2 along a predetermined paper feed path (two-dot chain line) by the paper feed unit 63 of the paper feed / discharge unit 6. The toner image on the sheet S conveyed to the fixing unit 5 and conveyed is fixed on the sheet S. Then, the sheet S is further conveyed to the sheet discharging unit 64 along the sheet feeding path 630.
[0026]
The paper discharge section 64 has two paper discharge paths 641a and 641b. One paper discharge path 641a extends from the fixing unit 5 to the standard paper discharge tray, and the other paper discharge path 641b is a paper discharge path 641a. , And extends between the re-feed section 66 and the multi-bin unit. Three pairs of rollers 642 to 644 are provided along these paper discharge paths 641a and 641b, and discharge the fixed sheet S toward the standard paper discharge tray or the multi-bin unit side, or to the other side. The sheet is also conveyed to the re-feeding unit 66 side to form an image.
[0027]
As shown in FIG. 1, the re-feeding section 66 transfers the sheet S, which has been reversed and conveyed from the sheet discharging section 64 as described above, along the re-feeding path 664 (two-dot chain line). The sheet is conveyed to a pair of gate rollers 637 and includes three pairs of re-feed rollers 661 to 663 arranged along a re-feed path 664. In this way, by returning the sheet S conveyed from the sheet discharging unit 64 to the gate roller pair 637 along the re-feeding path 664, the non-image forming surface of the sheet S in the sheet feeding unit 63 moves the intermediate transfer belt 41. The secondary transfer of the image to the surface is enabled.
[0028]
In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image provided from an external device such as a host computer via the interface 112, and reference numeral 127 denotes a control of the engine unit E. A RAM for temporarily storing control data for performing the calculation, a calculation result in the CPU 123, and the like, and a reference numeral 128 denotes a ROM for storing a calculation program and the like performed by the CPU 123.
[0029]
B. Density adjustment operation in image forming apparatus
Next, an operation of adjusting the density of an image in the image forming apparatus configured as described above will be described.
[0030]
FIG. 3 is a flowchart showing a density adjustment operation in the image forming apparatus of FIG. In this image forming apparatus, as shown in the figure, it is determined whether or not it is necessary to update the developing bias and the charging bias by executing a density adjusting operation in step S1. For example, after the main power supply of the image forming apparatus main body is turned on, when an image can be formed, the bias setting may be started. Alternatively, the continuous use time may be detected by a timer (not shown) provided in the apparatus main body, and the bias setting may be started every several hours.
[0031]
If "YES" is determined in this step S1 and the bias setting is started, steps S2 and S3 are executed to calculate the optimum developing bias and set it as the developing bias (step S4). Subsequently, step S5 is executed to calculate the optimal charging bias, and the calculated bias is set as the charging bias (step S6). Thus, optimization of the developing bias and the charging bias is performed. Hereinafter, the details of the developing bias calculation process (step S3) and the charging bias calculation process (step S5), each of which corresponds to the optimum value calculation process of the present invention, will be described in detail.
[0032]
B-1. Development bias calculation processing
FIG. 4 is a flowchart showing the content of the developing bias calculation process of FIG. FIG. 5 is a timing chart showing the operation timing of the developing bias calculation process. In the developing bias calculation process (step S3), first, a patch image (Y patch) is created using yellow toner (step S301). In other words, four yellow solid images are sequentially formed on the photoreceptor while the charging bias is set to the default value set in advance in step S2 and the developing bias is switched in four steps at predetermined intervals, and further shown in FIG. Thus, the first patch image PI1 is formed by transferring these to the outer peripheral surface of the intermediate transfer belt 41 in a predetermined arrangement order (step S301).
[0033]
Following the creation of the Y patch, similarly to the above, creation of a patch image (C patch) using cyan toner (step S302), creation of a patch image (M patch) using magenta toner (step S303), and black toner (Step S304) are sequentially executed to generate intermediate images in the order of cyan (C), magenta (M), and black (K) as shown in FIGS. 6B to 6D. The first patch image PI1 is further formed on the outer peripheral surface of the transfer belt 41. In this embodiment, the order of forming patch images (the order of toner colors) is
Yellow (Y) -Cyan (C) -Magenta (M) -Black (K)
However, the arrangement order of the patch images on the intermediate transfer belt 41 is as follows.
Black (K) -Yellow (Y) -Cyan (C) -Magenta (M)
And The reason for employing such an arrangement order will be described later in detail.
[0034]
After the patch images PI1 are formed for all the toner colors in this manner, the patch image PI1 of the 16 (= 4 types × 4 colors) patch image PI1 (in this embodiment, the patch image of black (K) in this embodiment) is used. The image density of the patch image PI1 is sequentially detected by the patch sensor PS, and further, a developing bias corresponding to the target density is obtained based on these image densities, and this is obtained as an optimum developing bias (step S305). As described above, in this embodiment, four types of patch images PI1 are created, these image densities are read at once (actual reading), and then the optimum value of the developing bias is obtained based on those image densities. In this regard, this point is the same as the prior art, but is significantly different from the prior art in the following points.
[0035]
That is, in this embodiment, as shown in FIGS. 4 and 5, the last toner color in the toner color order, that is, the toner color (yellow , Cyan, and magenta), the density of each patch image PI1 is detected (preliminary reading), and the optimum developing bias for yellow, cyan, and magenta is determined in advance based on the image densities (step S306). If it is determined in S307 that the optimum developing bias has been obtained for all of yellow, cyan, and magenta, the process proceeds to the next step S311 while the optimum developing bias is obtained for at least one of the three colors. If not, the developing bias calculation process is performed again. The setting of the effect that row (step S308: Setting of creating re-patch).
[0036]
As described above, in this embodiment, when a patch image is formed with the final toner color (black), it is determined whether or not the optimum developing bias can be obtained for the other toner colors, that is, yellow, cyan, and magenta. If the optimum developing bias cannot be obtained for yellow, cyan, or magenta, as shown in FIG. Patch creation (re-patch creation) using toner can be executed quickly, eliminating the need for idling as in the conventional example shown in FIG. 8, and improving the processing efficiency by quickly performing the developing bias calculation process again. .
[0037]
Also, in the present embodiment, as in the case of other toner colors, the present embodiment promptly shifts to the re-patch creation by devising the arrangement order on the intermediate transfer belt 41 as described below. Can be done. That is, in this embodiment, as shown in FIG. 6D, since the black patch image is formed at the head position, the black patch image first reaches the reading position of the patch sensor PS, and the actual reading is performed. In the initial stage P1 (FIG. 5), the image density of the patch image is read, and the optimum developing bias for the black toner can be obtained. Here, if the optimum developing bias cannot be obtained, it is determined to be “NO” in step S309. Then, when it is determined in this way, the setting of re-patch creation is performed in the same manner as in step S308 (step S310). Since a series of processes for such a black toner is performed in the initial stage P1 of the actual reading, sufficient time is required for re-patch creation. Therefore, as in the case of yellow, cyan, and magenta, even when the optimum developing bias cannot be obtained for black, as shown in FIG. The patch creation (re-patch creation) can be executed quickly, eliminating the need for idling as in the conventional example shown in FIG. 8, and increasing the processing efficiency by quickly performing the developing bias calculation process again.
[0038]
This processing flow will be described below with reference to the flowchart of FIG. That is, as described above, the density detection of each patch image PI1 for yellow, cyan, and magenta by the pre-reading and the setting of the re-patch creation based thereon, the density detection of the patch image PI1 for the black by the actual reading, and the re-patch based on the same When the creation setting is completed, it is determined in step S311 whether or not the setting for the re-patch creation has been performed. If the creation of the re-patch has been set in the step S308 or S310, the process returns to the step S301 and repeats the process. The developing bias calculation process is quickly executed.
[0039]
On the other hand, in any of steps S308 and S310, if the re-patch creation is not set, that is, if the optimum developing bias has been obtained for all the toner colors, the process proceeds to step S312, and as described above. The optimum developing bias obtained as described above is stored in the RAM 127, and is read out from the RAM 127 at the time of calculating a charging bias to be described later or in a normal image forming process, and is set as a developing bias.
[0040]
B-2. Charging bias calculation process
FIG. 7 is a flowchart showing the contents of the charging bias calculation process of FIG. In this charging bias calculation process, similarly to the case of the development bias calculation process, the development bias is set to the optimum development bias obtained in step S3, and the description has been given in the section “B-1. The optimum charging bias is calculated in the same procedure. That is, the optimum charging bias is calculated as follows, and if the optimum charging bias cannot be calculated for at least one color, the charging bias calculation process is repeated and executed again.
[0041]
First, four yellow halftone images are sequentially formed on the photoreceptor while the charging bias is switched in four steps at predetermined intervals, and these are half-imaged in a predetermined arrangement order as shown in FIG. The second patch image PI2 is transferred to the outer peripheral surface of the transfer belt 41 (Step S501).
[0042]
Further, following the creation of the Y patch, similarly to the above, creation of a patch image (C patch) using cyan toner (step S502), creation of a patch image (M patch) using magenta toner (step S503), and The creation of a patch image (K patch) using black toner (step S504) is sequentially performed, and the order of cyan (C), magenta (M), and black (K) is determined as shown in FIGS. Then, the second patch image PI2 is further formed on the outer peripheral surface of the intermediate transfer belt 41. The order in which the patch images are formed (the order of the toner colors) and the order in which they are arranged are the same as those in the above-described development bias calculation process. That is, the order of forming patch images is as follows.
Yellow (Y) -Cyan (C) -Magenta (M) -Black (K)
On the other hand, the arrangement order of the patch images on the intermediate transfer belt 41 is
Black (K) -Yellow (Y) -Cyan (C) -Magenta (M)
And
[0043]
After the patch images PI2 are formed for all the toner colors in this manner, the patch image PI2 of the head position (in this embodiment, the black (K) patch image) out of the 16 (= 4 types × 4 colors) patch images PI2 is used. The image density of the patch image PI2 is sequentially detected by the patch sensor PS (actual reading), and based on these image densities, a charging bias corresponding to the target density is obtained, and this is obtained as an optimum charging bias (step S505). ).
[0044]
Further, in this embodiment, each of the last toner colors in the toner color order, that is, the toner colors (yellow, cyan, and magenta) for which the patch image has been formed before the patch image is formed with the black toner, is used. The density of PI2 is detected (advance reading), and the optimal charging bias for yellow, cyan and magenta is determined in advance based on the image densities (step S506), and all of yellow, cyan and magenta are determined in the next step S507. On the other hand, if it is determined that the optimal charging bias has been obtained, the process proceeds to the next step S511, while if the optimal charging bias cannot be obtained for at least one of the three colors, the process is repeated. Is set to execute the charging bias calculation process (step 508: Set of creating re-patch).
[0045]
On the other hand, as for black, as shown in FIG. 6 (d), since the black patch image PI2 is formed at the head position, the black patch image first reaches the reading position of the patch sensor PS, and the actual reading is performed. In the initial stage, the image density of the patch image is read, and the optimal charging bias for the black toner can be obtained. Here, if the optimum charging bias cannot be obtained, it is determined to be “NO” in step S509. Then, when it is determined in this way, the setting for creating a re-patch is performed in the same manner as in step S508 (step S510).
[0046]
As described above, the density detection of each patch image PI2 for yellow, cyan, and magenta and the setting of re-patch creation based on the preliminary reading, and the density detection of the patch image PI2 for black and re-patch creation based on the actual reading are set. Upon completion, it is determined in step S511 whether re-patch creation has been set. If re-patch creation has been set in step S508 or step S510, the process returns to step S501 to repeat the charging bias calculation process. Is executed promptly.
[0047]
On the other hand, in any of steps S508 and S510, if re-patch creation has not been set, that is, if the optimal charging bias has been obtained for all toner colors, the process proceeds to step S512, and as described above. The optimum charging bias obtained in this way is stored in the RAM 127, and is read out from the RAM 127 at the time of calculating the charging bias described later or in a normal image forming process, and is set as the charging bias.
[0048]
As described above, in the charging bias calculation process (step S5), similarly to the development bias calculation process, when a patch image is formed using the final toner color (black), other toner colors, that is, yellow, cyan, and Since it is possible to grasp in advance whether or not the optimum charging bias can be obtained for magenta, if the optimum charging bias cannot be obtained for yellow, cyan or magenta, FIG. As shown in FIG. 8, the patch creation (re-patch creation) using the yellow toner can be promptly executed subsequent to the patch creation using the final toner color, and there is no need to perform the idling as in the conventional example shown in FIG. The charging bias calculation process can be performed quickly.
[0049]
Also, for black, which is the final toner color, a series of processes of detecting the density of the patch image and setting the re-patch creation based on it is performed at the initial stage of the actual reading, so it is sufficient for the re-patch creation to take place. Therefore, even when the optimum developing bias cannot be obtained, the patch creation (re-patch creation) using the yellow toner can be executed immediately after the patch creation using the final toner color. This eliminates the need for idling as in the conventional example shown in FIG. 8, and allows the developing bias calculation process to be performed again quickly.
[0050]
C. Other
The present invention is not limited to the above-described embodiment, and various changes other than those described above can be made without departing from the gist of the present invention. For example, in the above-described embodiment, the pre-reading is executed before forming the black patch image which is the final toner color, but the pre-reading is performed before forming the immediately preceding magenta patch image. May be.
[0051]
Further, in the above embodiment, it is determined whether or not a batch re-creation should be performed by executing pre-reading of the patch images of toner colors other than the final toner (black) collectively by the patch sensor PS (step S306). To S308 and S506 to S508), each time these yellow, cyan, and magenta patch images are formed, pre-reading is performed to determine whether the optimum developing bias or the optimum charging bias for the corresponding toner color has been obtained. May be determined.
[0052]
Further, in the above embodiment, the black patch image as the final toner color is arranged at the head position in the arrangement order. However, a series of processing of detecting the density of the patch image of the final toner color and setting re-patch creation based on the density detection is performed. The arrangement order may be set to 2 or 3 from the top position as long as the final toner condition is satisfied before the re-patch creation.
[0053]
In the above embodiment, the order of forming patch images, that is, the order of toner colors is
Yellow (Y) -Cyan (C) -Magenta (M) -Black (K)
However, this is an example, and the order of the toner colors is arbitrary. The arrangement order of the patch images on the intermediate transfer belt 41 is arbitrary as long as the final toner condition is satisfied as described above. Furthermore, in this embodiment, four color toners are used, but the type of toner color is not limited to four colors, and the present invention is applied to a general color image forming apparatus that forms an image with a plurality of colors. can do.
[0054]
In the above-described embodiment, the toner image on the photoreceptor 21 is transferred to the intermediate transfer belt 41, and the toner image is used as a patch image to detect the image density. The bias is calculated, but the toner image is transferred to a transfer medium other than the intermediate transfer belt (transfer drum, transfer belt, transfer sheet, intermediate transfer drum, intermediate transfer sheet, reflective recording sheet, transparent storage sheet, etc.). The present invention can also be applied to an image forming apparatus that forms a patch image by using the same. Also, instead of forming a patch image on the transfer medium, a patch sensor for detecting the density of the patch image on the photoconductor is provided, and the patch sensor detects the image density of each patch image on the photoconductor, and the detection result The optimum developing bias and the optimum charging bias may be calculated based on the above.
[0055]
The image forming apparatus according to the above-described embodiment is a printer that forms an image given from an external device such as a host computer via the interface 112 on a sheet such as a copy sheet, a transfer sheet, a sheet, and a transparent sheet for an OHP. However, the present invention can be applied to all electrophotographic image forming apparatuses such as copying machines and facsimile machines.
[0056]
Further, in the above-described embodiment, the optimum values of the developing bias and the charging bias are obtained as the density control factors. The present invention can be applied to a case where an optimum value is obtained.
[0057]
【The invention's effect】
As described above, according to the image forming method and the image forming apparatus according to the present invention, before forming a patch image with a final toner color in the toner color order at the latest, for a toner color on which a patch image has already been formed, If the density of each patch image is detected, the optimum value of the density control factor is determined in advance for each color based on the image density, and the optimum value for at least one or more toner colors cannot be determined. Is designed to execute the optimum value calculating process again promptly, so that it is not necessary to perform the idling as in the related art in order to perform the optimum value calculating process again, and a density control factor that affects the image density of the toner image. Can be calculated in a short time.
[0058]
In addition, the patch images of n colors are formed in a predetermined arrangement order, and the density detection of the patch images is performed in order from the top position in the arrangement order. , The density detection and the optimal value calculation for the patch image of the final toner color are performed in comparison with the density detection of the last patch image. Can be done early. If the optimum value cannot be obtained for the final toner color, the optimum value calculation process is immediately executed again. This eliminates the necessity to perform the calculation, and the optimum value of the density control factor that affects the image density of the toner image can be calculated in a short time.
[Brief description of the drawings]
FIG. 1 is a diagram showing one embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus of FIG. 1;
FIG. 3 is a flowchart illustrating a density adjustment operation in the image forming apparatus of FIG. 1;
FIG. 4 is a flowchart illustrating the content of a developing bias calculation process of FIG. 3;
FIG. 5 is a timing chart showing an operation timing of a developing bias calculation process.
FIG. 6 is a diagram illustrating a forming order of patch images.
FIG. 7 is a flowchart showing the contents of a charging bias calculation process in FIG. 3;
FIG. 8 is a timing chart showing a conventional image forming method.
[Explanation of symbols]
1. Control unit (control means)
2. Image carrier unit
3. Exposure unit
4: Transfer unit
5. Fixing unit
12 ... Engine controller (control means)
123 ... CPU (control means)
E: Engine unit (image forming means)
P1 ... initial stage (for actual reading)
PI1, PI2 ... Patch image
PS: Patch sensor (density detecting means)

Claims (10)

After a patch image for each color is sequentially formed with n different (n ≧ 2) toners in a predetermined toner color order, the densities of the patch images are detected collectively, and based on those image densities. An image forming method for executing an optimum value calculation process for obtaining an optimum value of a density control factor affecting the image density of the toner image for each color.
At the latest, before forming a patch image with the final toner color in the toner color order, the density of each patch image is detected for a toner color on which a patch image has already been formed, and for each color based on those image densities. A first step of determining an optimum value of the concentration control factor in advance;
An image forming method comprising the steps of: immediately executing the optimum value calculating process again if there is a toner color for which an optimum value cannot be obtained in the first step; 2. The image forming method according to claim 1, wherein in the first step, density detection of each patch image is performed collectively, and an optimal value of a density control factor is collectively obtained for each color based on the image density. In the first step, before forming a patch image with a final toner color in the toner color order, after forming a patch image for each color sequentially with (n-1) colors of toner excluding the final toner color, 3. The image according to claim 1, wherein the densities of the respective patch images are collectively detected, and the optimum value of the density control factor is collectively obtained for each of the (n-1) toner colors based on the image densities. Forming method. In the first step, the density detection of each patch image is performed each time a patch image of the corresponding toner color is formed, and the optimal value of the density control factor is sequentially determined each time the density detection of each color is performed based on the image density. The image forming method according to claim 1, which is required. In the first step, before forming a patch image with the last toner color in the toner color order, each time a patch image for each color is sequentially formed with (n-1) colors of toner excluding the final toner color 3. The image forming method according to claim 1, wherein the density of the patch image corresponding to the toner color is detected, and the optimum value of the density control factor for the toner color is sequentially obtained based on the image density. The n-color patch images are formed in a predetermined arrangement order, and the density detection of the patch images is performed sequentially from the top position in the arrangement order,
6. The image forming method according to claim 1, wherein the patch image of the final toner color is formed in any one of the 1st to (n-1) th arrangement orders counted from the top position. The image forming method according to claim 1, wherein the patch image of the final toner color is formed at the head position. After a patch image for each color is formed by an image forming unit using n different colors (n ≧ 2) of toners in a predetermined toner color order, the density of each patch image is collectively detected by a density detecting unit. An image forming apparatus in which the control means calculates, for each color, an optimum value of a density control factor that affects the image density of the toner image based on the image densities.
The control unit, based on the density of each patch image detected by the density detection unit with respect to the toner color on which the patch image has been formed before forming the patch image with the final toner color in the toner color order at the latest. The optimal value of the density control factor is determined in advance for each color, and if there is a toner color for which the optimal value could not be determined, patch images are immediately created again for all toner colors, and the optimal An image forming apparatus for determining a value. The density detecting means can detect the image density in order from the leading patch image,
The image forming means forms the n-color patch images in a predetermined arrangement order, and the final toner color patch image is counted from 1 to (n-1) counting from the top position. The image forming apparatus according to claim 8, wherein the image forming apparatus is formed in any one of the order. The image forming apparatus according to claim 8, wherein the image forming unit forms the patch image of the final toner color at the leading position.

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