Patent Grant
9058003
This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2013-066038, filed on Mar. 27, 2013, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.
1. Technical Field
Embodiments of this invention generally relate to an electrophotographic image forming apparatus, such as a copier, a printer, a facsimile machine, and a multifunction peripheral (MFP) having at least two of coping, printing, facsimile transmission, plotting, and scanning capabilities.
2. Description of the Background Art
In image forming apparatuses such as printers, facsimile machines, and copiers, fluctuations in image density and color deviation arise due to environmental changes over time. Accordingly, typically, toner patterns for measurement are formed on a transfer belt, and the density and position thereof are detected.
JP-2002-207337-A proposes, at power-on time or when the number of output sheets reaches a predetermined number, forming multiple toner patterns for positional deviation adjustment on the transfer belt and adjusting positions of yellow, magenta, cyan, and black toner images. Density adjustment of respective color toner image forming units can be performed in a similar manner.
Additionally, JP-2006-293240-A proposes forming a toner pattern in a non-image area for density adjustment during formation of output images.
In view of the foregoing, one embodiment of the present invention provides an image forming apparatus that includes an image bearer, a toner image forming unit including a developing device provided with a developing roller, a detector to detect a toner pattern formed on the image bearer, and a controller to cause the toner image forming unit to form the toner pattern on the image bearer, cause the detector to detect the toner pattern, and adjust an image forming condition of the toner image forming unit based on a detection result generated by the detector.
During a non-printing period, the toner image forming unit forms multiple toner patterns and the detector detects densities of the multiple toner patterns, and, during a printing period, the toner image forming unit forms an output image in an image area and a smaller number of toner patterns in a non-image area. The toner patterns formed during the printing period are smaller in number than those formed during the non-printing period and selected from those formed during the non-printing period.
The multiple toner patterns formed during the non-printing period are formed in both of an end portion and a center portion of the image bearer in a direction perpendicular to a direction in which the image bearer moves, and the smaller number of toner patterns formed during the printing period are formed in the end portion of the image bearer. The controller determines a target density X of the smaller number of toner patterns formed during the printing period using a formula:
X=H×J/I
wherein H represents a mean detected density of the multiple toner patterns formed in the end portion during the non-printing period, J represents a predetermined reference value, and I represents a mean detected density of the multiple toner patterns formed in the end portion and the multiple toner patterns formed in the center portion during the non-printing period.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.
In multicolor image forming apparatuses, each time a predetermined number of sheets are output, the following operations are widely performed to correct fluctuations in the density and the position thereof. Image output is prohibited, multiple toner patterns are formed on a transfer belt, and the density and the position of the toner patterns are detected.
In image forming apparatuses in which toner patterns are formed in parallel to image output, periods in which image output is unfeasible due to adjustments are not caused. In this case, however, the number of toner patterns is limited since the toner patterns are formed outside the image area. Accordingly, the accuracy of adjustment is rather rough, and the adjustment accuracy may be insufficient in full-color images in which gradation reliability is important.
Therefore, it is conceivable to combine the method of forming the toner patterns inside and outside the image area for adjusting image density while no images are output and the method of forming the toner patterns in parallel to image output, thereby stabilizing overall image quality.
Additionally, it is possible that image density is not fully adjusted for some reasons in the method of forming the toner patterns inside or outside the image area while no images are output. In that case, the image density is adjusted gradually to a target density using the method of forming the toner patterns outside the image area.
However, the inventors of the present invention have found that, when there are differences in image density between the image area and the outside thereof, it is possible that the image density is not adjusted to the target density in the method of forming the toner patterns outside the image area.
In view of the foregoing, an object of the embodiment described below is to control image density to a target value in the method of forming the toner patterns inside and outside the image area.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views thereof, and particularly to
In a substantially center portion of an apparatus body 2 of the image forming apparatus 1, four drum-shaped photoreceptors 3Y, 3M, 3C, and 3BK are disposed horizontally, arranged at constant intervals in a lateral direction in
It is to be noted that the suffixes Y, M, C, and BK attached to each reference numeral indicate only that components indicated thereby are used for forming yellow, magenta, cyan, and black images, respectively, and hereinafter may be omitted when color discrimination is not necessary. It is to be noted that reference number 100 in
As a representative, the photoreceptor 3Y for yellow is described. The photoreceptor 3Y includes a cylindrical aluminum base having a diameter of within a range from 30 mm to 100 mm and a photosensitive organic semiconductor layer overlying the surface of the aluminum base, for example. In
Beneath the photoreceptors 3, the charging rollers 4, the developing devices 6, and the cleaning units 7, and an exposure device 8 is provided. The exposure device 8 scans uniformly charged surfaces of the photoreceptors 3 with laser beams according to respective color image data, thereby forming electrostatic latent images thereon. A long, narrow clearance (i.e., a slit) is secured between each charging roller 4 and the corresponding developing roller 5 so that the laser beam emitted from the exposure unit 8 can reach the photoreceptor 3. Although the exposure device 8 shown in
Above the photoreceptors 3, an intermediate transfer belt 12 is looped around multiple rollers 9, 10, and 11. The intermediate transfer belt 12 is rotatable counterclockwise in
Multiple sheet trays (two sheet trays 23 and 24 in the configuration shown in
It is to be noted that, inside the apparatus body 2, a toner container mount 33 to accommodate toner containers for containing toner is provided in a space beneath the stack portion 29. Toner can be transported from the toner container mount 33 to the corresponding developing device 6 by a pump or the like.
It is to be noted that, in
Next, operations to form images on the sheets S are described below.
Initially, image signals are transmitted to a controller 50 of the image forming apparatus 1 from a computer, a scanner, a facsimile machine, or the like. The controller 50 then converts the image signals into output image signals determined by control operations described later and transmits the converted signals to the exposure device 8. The exposure device 8 directs the laser beam emitted from the laser light source, which can be a semiconductor laser, according to image data onto the surface of the photoreceptor 3 charged uniformly by the charging roller 4, thus forming an electrostatic latent image on the photoreceptor 3. The electrostatic latent image is developed into a toner image by the developing device 6, after which the primary-transfer roller 13 primarily transfers the toner image onto the surface of the intermediate transfer belt 12 rotating in synchronization with the photoreceptor 3. The above-described latent image formation, image development, and primary image transfer are performed on the respective photoreceptors 3. Consequently, yellow, cyan, magenta, and black toner images are superimposed one on another on the intermediate transfer belt 12, forming a four-color toner image. The intermediate transfer belt 12 transports the four-color image.
Meanwhile, the sheet S is fed from the sheet tray 23 or 24 to the registration rollers 28 through the paper feeding channel 27. The registration rollers 28 send out the sheet S, timed to coincide with the arrival of the toner image formed on the intermediate transfer belt 12, and the secondary-transfer roller 18 transfers the toner image from the intermediate transfer belt 12 onto the sheet S. Then, the fixing device 31 fixes the toner image on the sheet S (i.e., fixing process), and then the discharge rollers 32 discharge the sheet S carrying the image to the stack portion 29.
In double-side printing, after the fixing process, the sheet S is guided to a reversal conveyance path 36 by switching the position of a switching pawl 38. After the sheet S is reversed, the sheet S is transported again to the registration rollers 28 through a feeding path 37 by switching the position of a switching pawl 39. Thus, the sheet S is turned upside down. At that time, another toner image (i.e., a back side image) is formed on the intermediate transfer belt 12. After the toner image is transferred onto a back side (i.e., a second face) of the sheet S and fixed thereon by the fixing device 31, the sheet S is discharged by the discharge rollers 32 to the stack portion 29.
It is to be noted that, although the descriptions above concern full-color image formation, monochrome images, single-color images, bicolor images, and tricolor images can be formed by similar operations except that one or more of the photoreceptors 3 is not used.
Density control (image quality adjustment) during non-printing period is described below with reference to
It is to be noted that the term “non-printing period” means a period, such as start-up time after power is turned on, idle running time of the photoreceptor 3 before and after image output, and the like, during which the image forming apparatus 1 does not output images. In image forming apparatuses typically, even if image density is adjusted once, the image density changes over time. Image density tends to deviate when temperature and humidity change inside the image forming apparatus and the image forming apparatus has been left unused for a long time (hereinafter “unused period”). Additionally, image density deviates as the number of sheets output increases. Therefore, image forming condition adjustment timings are preliminarily stored in a memory inside the controller 50. The image forming condition adjustment timings include after an experimentally determined number of sheets are printed, when a temperature and humidity detector inside the image forming apparatus detects a change greater than an experimentally obtained threshold, when the unused period exceeds an experimentally determined threshold.
Referring to
When the apparatus is at the adjustment timing (Yes at S1), a charging bias and a developing bias of the developing device 6 are switched to different values stepwise as shown in
It is to be noted that, in
Thus, at S2, ten toner patterns different in image density from each other as shown in
In the configuration shown in
The toner pattern formed on the photoreceptor 3 is transferred by the primary-transfer roller 13 onto the intermediate transfer belt 12. Thus, as shown in
The sensors 40 each include a light-emitting element 40B-1, a specular reflection light sensor 40B-2, and a diffuse reflection light sensor 40B-3. The light-emitting element 40B-1 emits light, which is reflected on the intermediate transfer belt 12. Out of the light thus reflected, specular reflection light is detected by the specular reflection light sensor 40B-2, and diffuse reflection light is detected by the diffuse reflection light sensor 40B-3.
In the case of black toner, the density is adjusted using the specular reflection light sensor 40B-2 since the amount of specular reflection light decreases as the amount of toner adhering to the toner pattern (i.e., density) increases as shown in
By contrast, outputs from the diffuse reflection light sensor 40B-3 are as shown in
Then, sensor outputs in the detection of the ten toner patterns are as shown in
When the toner pattern passes a position vertically under the sensor as the intermediate transfer belt 12 rotates, the sensor outputs changes as shown in
Alternatively, a certain period prior to the timing at which the pattern reaches the position vertically under the sensor, the light-emitting element 40B-1 may start glowing, sample data consecutively, and identify the pattern using the above-described threshold. This operation is advantageous in that the size of the pattern can be reduced from that used in the method of determining the timings of pattern exposure and reading using the timing based on the component layout. Reduction in the toner pattern size is advantageous in that toner consumption can be reduced. Additionally, it is desirable to reduce the detection range of the sensor 40 to reduce the pattern size. In the present embodiment, the detection range of the sensor 40 is circular and has a diameter of 1 mm, for example, due to the compactness of the light-emitting element and the light-receiving element and layout of slits. The detection range of the sensor 40 is preferably 2 mm or smaller. Although the length of the toner patterns in the present embodiment is 7 mm in the sub-scanning direction, it may be about 5 mm considering the data sample number, accuracy in detecting pattern edges, and the like. The length of the toner patterns in the sub-scanning direction is preferably from about 5 mm to about 7 mm.
Referring back to
In the present embodiment, when the inclination γ is within a predetermined range, the developing bias and the charging bias are changed to attain a target highest reflection density. When the inclination γ deviates from the predetermined range, a control target of the concentration of toner is changed so that the inclination γ falls within the predetermined range. At S5, the amount by which each of the developing bias and the charging bias is changed (hereinafter “adjustment amount”) is calculated. The adjustment amount can be calculated easily from an experimentally determined value and the detection result generated by the sensors 40. The relation between the inclination γ and the concentration of toner can be obtained experimentally as well, and, at S5, the adjustment amount of the concentration of toner can be obtained from the experimentally obtained relation and the detected inclination γ. Typically, toner is supplied to adjust the concentration of toner in developer (or density of toner) inside the developing device 6 to a target value according to outputs from a toner concentration sensor (or toner density sensor). When the target value to which the concentration of toner is adjusted is determined, the control target of the toner concentration sensor is changed, and the concentration of toner is adjusted thereto at S6. Further, the developing bias and the charging bias are adjusted to the calculated values. With the above-described control operation, density fluctuations over time and those caused by environmental changes can be corrected.
Subsequently, dot patterns, such as those shown in
Then, the toner patterns are detected by the sensor 40 at S7 (in
The dots increase in size or area ratio downward in
The dot patterns different in dot area ratio correspond to the output image signals. From the sensor outputs, the reflection densities of the dot patterns are obtained, and, on a graph in which the abscissa represents output image signals and the vertical axis represents the reflection density of the dot pattern, a function of approximation is calculated at S8. Simultaneously, at S8, outputs of the sensor detecting predetermined toner patterns are stored in the controller 50. Specifically, the density of the black dot pattern whose dot area ratio is 50% and the densities of the yellow, magenta, and cyan, dot patterns whose dot area ratio is 100% are stored in the controller 50. At S9, using the calculated function of approximation, the output image signal (dot area ratio) required to output the reflection density instructed by the signal input from the computer or the like can be obtained. Therefore, at S9, according to the input image signal, the output image signal required to attain the density instructed by the input image signal can be determined.
At S10, the controller 50 determines the target density for density control performed while images are output (hereinafter “density control during printing”). The target density of the end pattern in the density control during printing can be calculated using formula 1 below. The density control during printing is described later in further detail.
X=H×J/I Formula 1
wherein X represent the target density of the end pattern formed during printing, H represents a mean detected density of the end patterns formed during the non-printing period, J represents a predetermined reference value, and I represents a mean values of detected densities of the center pattern and the end patterns formed during the non-printing period (hereinafter “mean detected density I”).
The detected densities of the dot patterns formed in the end portions during the non-printing period mean the detected densities of the black dot pattern whose dot area ratio is 50% and color dot patterns whose dot area ratio is 100%, detected by the sensors 40F and 40R shown in
When the mean detected density H as is used as the target density X of the end patterns in density control during printing, the target density X may be extremely small or extremely large when there are differences in density between the image area and portions outside thereof. Therefore, in that case, the mean detected density H is corrected using formula 1. Specifically, the mean detected density H is multiplied by J/I, and the value thus obtained is used as the target density X.
The target density X is determined according to formula 1 from the following reasons.
In the density control during printing, detection and adjustment are executed only at the ends of the image area in the main scanning direction. By contrast, during the non-printing period, the density is determined entirely in the three portions including the center portion. In the case in which the density is proper, even if the density in the end portions is lower to a certain degree, it is tolerable. However, when the density in the center portion is too high, inconveniences arise if the target density in the end portions is set to the value detected at that time. That is, it is possible that the entire density is made too low consequently.
In the image quality adjustment (density control) during non-printing period, if the developability is low and the image forming conditions (image portion potential in particular) are set to the upper limits, the desired density is not attained, and toner images become too light. In that case, in the image quality adjustment during printing, it is necessary to detect that the toner image is too light and to attain the desired density by enhancing the developability and lowering the image portion potential.
However, it fails to detect that the toner image is too light if the detected value is always used as the target value during non-printing period. Then, the image density is kept at the lighter density. Accordingly, when the value detected in the image quality adjustment during non-printing period is not proper, it is necessary to adjust the detected value at the time of setting the target density of the end pattern during printing.
For example, it is conceivable that the density is proper at the completion of image quality adjustment during non-printing period in the cases shown in table 1.
In cases A, B, and C shown in table 1, the mean detected density I of toner patterns at the front (F), rear (R), and center (C) positions coincides with the predetermined reference value J, which is the mean target density of toner patterns at the three positions (I=J).
As described above, the predetermined reference value J is 0.4 mg/cm2. In cases A, B, and C shown in table 1, the mean detected density I is 0.4 and identical to the predetermined reference value J. Thus, the density is proper. For example, in case A, the mean detected density H of the two positions is 0.4. Accordingly, the target density X of the end patterns at the two positions is 0.4. Since the mean detected density H equals to the target density X (H=X), the mean detected density H, which is the detected value, is not varied in the adjustment. In other words, the image density in non-printing period is maintained in formation of end patterns in density control during printing. Similarly, when the mean detected density H is 0.3 and 0.5, the target density X is 0.3 and 0.5, respectively.
Additionally, the predetermined reference value J is 0.4 mg/cm2 even when the mean value of detected densities of end patterns during non-printing period is lower and thus the density at the end position is low.
For example, it is conceivable that the density is not proper at the completion of image quality adjustment during non-printing period in the cases shown in table 2.
In cases D through G shown in table 2, the mean detected density I of toner patterns at the three positions, the front (F), rear (R), and center (C) positions, does not coincide with the predetermined reference value J, which is the mean target density of toner patterns at the three positions (I≠J).
For example, in case D, although the predetermined reference value J is 0.4, the mean detected density I of the three positions is 0.3, and the mean detected density H of the two positions is 0.3. Then, according to formula 1, the target density X of the end patterns at the two positions is 0.4. Since the mean detected density H is not equal to the target density X (H≠X), the mean detected density H, which is the detected value, is corrected to 0.4 in the adjustment.
Further, in case G, although the predetermined reference value J is 0.4, the mean detected density I of the three positions is 0.45, and the mean detected density H of the two positions is 0.5. Accordingly, the target density X of the end patterns at the two positions is 0.444. Thus, the mean detected density H is not equal to the target density X (H≠X), and the mean detected density H, which is the detected value, is corrected toward 0.4 in the adjustment.
That is, it can be detected that the image density during non-printing period is low when the mean detected density H is smaller than the target density X (H<X), and it can be detected that the image density during non-printing period is high when the mean detected density H is greater than the target density X (H>X). Therefore, the image density can be adjusted (increased or reduced) in the image quality adjustment during printing.
Next, descriptions are given below of density control during printing with reference to
It is to be noted that the term “during printing” means that the period during which the image forming apparatus 1 outputs images. Although the toner patterns may be detected constantly during printing, significant changes in density are rather rare. Additionally, it is preferred to save toner. Accordingly, it is recommended to set the image forming condition adjustment timing (timing of toner pattern formation and density adjustment) to each time an image formation variable, such as, the number of output sheets, the run time of the image forming apparatus 1, and the travel distance of the photoreceptor 3 or the developing roller 5, reaches a threshold.
Referring to
Determining that the apparatus is at adjustment timing (Yes at S11), at S12, the controller 50 instructs formation of the end patterns outside an image area IR of the intermediate transfer belt 12 as shown in
Additionally, in the end patterns shown in
In
As shown in
Additionally, in
Further, referring to
Referring back to
Subsequently, in the present embodiment, a mean density of two identical dot pattern shown in
In the above-described embodiment, multiple toner patterns are formed and image forming conditions are set with a higher degree of accuracy in non-printing period, whereas, during printing, a smaller number of end patterns are formed and detected in parallel to formation of output images, thus executing density control while keeping the state similar to that of non-printing period. Therefore, images can be kept stable longer than in a case in which the density control is executed only in non-printing period. Additionally, the density adjustment can be finer than that in a case in which only the density control during printing is executed.
It is to be noted that, in
Further, when the density control during printing is executed similarly while images are formed on the largest size sheet in the apparatus according to the present embodiment, the secondary-transfer roller 18 can be designed such that the width of the secondary-transfer roller 18 corresponds to the largest size sheet and the end patterns on the intermediate transfer belt 12 do not contact the secondary-transfer roller 18. This configuration can obviate the need of disengaging the secondary-transfer roller 18 from the intermediate transfer belt 12 since the end patterns do not contact the secondary-transfer roller 18. It is to be noted that the image forming apparatus 1 further includes a shifting unit to disengage the secondary-transfer roller 18 in the density control during non-printing period so that the secondary-transfer roller 18 do not contact the toner patterns.
If users desire to use larger sheets S in an image forming apparatus in which the secondary-transfer roller 18 is shorter in width than the intermediate transfer belt 12 so that the end patterns do not contact the secondary-transfer roller 18 during printing, the secondary-transfer roller 18 may be replaced with a wider secondary-transfer roller to enable use of larger sheet size extending into the range where the end patterns are formed. In this case, formation of toner patterns in the density control during printing is prohibited to protect the secondary-transfer roller from stains.
As shown in
As described above, in the description above, differences in density between toner images in the image area and those in the non-image area are detected, and image forming conditions of the toner image forming unit are adjusted according to the detection result. With this operation, the image density can be adjusted to the target density in the method of forming the toner patterns inside and outside the image area.
It is to be noted that, although the intermediate transfer belt serves as the image bearer in the above-described embodiment, the apparatus to which the aspects of this specification are applicable is not limited to image forming apparatuses employing the intermediate transfer belt. For example, the intermediate transfer member may be an intermediate transfer drum. Alternatively, the aspects of this specification are applicable to image forming apparatuses employing a direct transfer belt on which sheets are transported to transfer toner images thereto from the photoreceptors. Yet alternatively, the above-described control operation may be executed by detecting toner patterns formed on the photoreceptor. In this case, the image bearer is the photoreceptor, and the photoreceptor is excluded from the toner image forming unit. The toner image forming unit is constructed of devices to form toner images on the photoreceptor.
It is to be noted that, the aforementioned density control may be embodied in the form of an apparatus, method, system, computer program and computer program product, including, but not limited to, any of the structure for performing the methodology illustrated in the drawings. The program may be stored on a computer readable media and is adapted to perform any one of the aforementioned methods when run on a computer device (a device including a processor). Thus, the storage medium or computer readable medium, is adapted to store information and is adapted to interact with a data processing facility or computer device to perform any of the above mentioned control procedures.
Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-066038 | Mar 2013 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5177530 | Takano | Jan 1993 | A |
| 6185386 | Noguchi | Feb 2001 | B1 |
| 20020089579 | Yamanaka et al. | Jul 2002 | A1 |
| 20030137577 | Shinohara | Jul 2003 | A1 |
| 20050214005 | Tokuyama et al. | Sep 2005 | A1 |
| 20060002724 | Fujimori et al. | Jan 2006 | A1 |
| 20060233561 | Yamaoka | Oct 2006 | A1 |
| 20070019976 | Watanabe et al. | Jan 2007 | A1 |
| 20070071469 | Ravitz | Mar 2007 | A1 |
| 20070116480 | Takeuchi et al. | May 2007 | A1 |
| 20070122168 | Tanaka et al. | May 2007 | A1 |
| 20080205923 | Takeuchi et al. | Aug 2008 | A1 |
| 20080253793 | Ishibashi et al. | Oct 2008 | A1 |
| 20080317486 | Monma et al. | Dec 2008 | A1 |
| 20090202263 | Yoshida et al. | Aug 2009 | A1 |
| 20110052239 | Tanaka et al. | Mar 2011 | A1 |
| 20130236200 | Tanaka et al. | Sep 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 2002-207337 | Jul 2002 | JP |
| 2006-293240 | Oct 2006 | JP |
| 2010-015110 | Jan 2010 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20140294412 A1 | Oct 2014 | US |
