JP7562986B2 - Image forming apparatus, image forming condition determining method and program - Google Patents

Description

This invention relates to image forming devices such as copiers, printers, and facsimiles, and to methods and programs for determining image creation conditions for such devices.

Conventionally, various types of image forming devices as described above are known, which uniformly charge an image carrier having a photoconductive material with a charging means, expose the surface of the carrier with an exposure means to form an electrostatic latent image with the resulting potential difference, develop the electrostatic latent image into a toner image with a developing device, transfer the image to a transfer material such as paper, and then fix the image on the transfer material using heat, pressure, etc.

Charging and de-electrification of the image carrier is performed by applying a high voltage of about 4500 to 6500 V in DC or AC to a corona charger or charging roller. This type of image forming device is configured to scrape off the residual toner on the image carrier surface by contacting a cleaning blade, cleaning brush, cleaning roller, etc. as a cleaning means to clean the residual toner that has not been transferred to the transfer material and remains on the image carrier.

The waste toner scraped off by the cleaning means is transported by a waste toner transport member provided adjacent to the cleaning member and is stored in a waste toner box provided outside the image forming device.

In these configurations, means for eliminating density defects caused by reduced development characteristics in high-density regions have been proposed in the past. For example, Patent Document 1 proposes changing the toner density control in the developer depending on the slope of the patch during stabilization. Patent Document 2 proposes that in detecting patch density during stabilization, low-density regions are detected by an optical sensor and high-density regions by a potential sensor. Furthermore, Patent Document 3 specifically mentions a method using linear approximation, and states that polynomial approximation can also be used depending on the development characteristics.

JP 2009-080276 A Japanese Patent Application Publication No. 10-063046 JP 2008-116655 A

However, in the case of Patent Document 1, the TC ratio, which is the compounding ratio of the toner and carrier in the developer, is changed, which has a major drawback, such as affecting image quality other than image density. In addition, since the developer in the developing device is changed, it takes time to achieve the effect.

In addition, Patent Document 2 requires an IDC sensor and a potential sensor, which is expensive. Furthermore, Patent Document 3 does not describe detailed conditions or specific content for the linear approximation or polynomial approximation methods.

This invention was made in consideration of this technical background, and aims to provide an image forming device that is small, low-cost, and can efficiently obtain a target image density in a short time without changing the developer, and that can prevent poor density caused by reduced development characteristics in high-density areas, as well as a method and program for determining image creation conditions for the device.

The above object can be achieved by the following means:
(1) a patch creating means for creating two or more patches with different densities;
a density measuring means for measuring the density of the patch created by the patch creating means;
a determining means for determining a developing bias voltage for obtaining a target density from the density measured by the density measuring means;
a determining means for determining whether or not a slope of an approximate straight line in a low density region when the relationship between the density of the patch and the developing bias voltage is expressed by an approximate straight line is smaller than a threshold value;
Equipped with
the determining means, when it is determined by the judging means that the slope is not smaller than a threshold value, determines a developing bias voltage for obtaining a target density from the approximation straight line, and, when it is determined that the slope is smaller than the threshold value, determines a developing bias voltage for obtaining a target density by another determination method.
(2) The image forming apparatus according to paragraph 1, wherein the other determination method is a method of approximating the relationship between the densities of multiple patches and the developing bias voltage to a curve using a polynomial, and determining the developing bias voltage for obtaining the target density from the approximate curve.
(3) The image forming apparatus according to the preceding paragraph 1, wherein the other determination method is a method for determining the developing bias voltage for obtaining the target density determined from the approximation straight line by offsetting the developing bias voltage in a direction that increases the target density.
(4) The image forming apparatus according to the above item 3, wherein the amount of offset of the developing bias voltage is corrected based on at least one of the TC ratio, which is the blending ratio of the toner and the carrier, the humidity, the black-white ratio, and the number of printed sheets.
(5) An image forming apparatus as described in any one of paragraphs 1 to 4 above, wherein when the slope is judged to be smaller than a threshold value, and when at least one of the following conditions is met: a TC ratio, which is a blending ratio of toner and carrier, is smaller than a threshold value, the humidity is lower than a threshold value, the black-white ratio is smaller than a threshold value, or the durability number of pages is greater than a threshold value, the determination means switches the determination method of the developing bias voltage to the other determination method.
(6) The image forming apparatus according to any one of the above items 1 to 5, wherein the frequency with which the developing bias voltage is determined by the determining means is set to be high in accordance with an increase in the number of sheets that can be used in the durability test.
(7) The image forming apparatus according to any one of (1) to (6), wherein the patch creating means creates the patch at the same timing as image stabilization processing is executed.
(8) a patch creation step of creating two or more patches with different densities;
a density measuring step for measuring the density of the patch created by the patch creating step;
a determining step of determining a developing bias voltage for obtaining a target density from the density measured by the density measuring step;
a determination step of determining whether or not a slope of an approximate straight line in a low density region when the relationship between the density of the patch and the developing bias voltage is expressed by an approximate straight line is smaller than a threshold value;
The image forming apparatus executes the above.
a developing bias voltage determining step of determining a developing bias voltage for obtaining a target density from the approximation straight line when the inclination is determined to be not smaller than a threshold value by the judgment step, and a developing bias voltage for obtaining a target density by another determination method when the inclination is determined to be smaller than a threshold value by the judgment step.
(9) a patch creating means for creating two or more patches with different densities;
a density measuring means for measuring the density of the patch created by the patch creating means;
A computer of an image forming apparatus comprising:
a determining step of determining a developing bias voltage for obtaining a target density from the density measured by the density measuring means ;
a determination step of determining whether or not a slope of an approximate straight line in a low density region when the relationship between the density of the patch and the developing bias voltage is expressed by an approximate straight line is smaller than a threshold value;
Run the command,
The program causes the computer to execute a process in which, in the determination step, if it is determined in the judgment step that the slope is not smaller than a threshold value, a developing bias voltage for obtaining a target density from the approximation straight line is determined, and if it is determined that the slope is smaller than the threshold value, a developing bias voltage for obtaining a target density using another determination method.

According to the invention described in the preceding paragraphs (1) and ( 8 ), when the relationship between the density of two or more patches whose density has been changed and the developing bias voltage is expressed by an approximate straight line, it is judged whether the slope of the approximate straight line in the low density region is smaller than a threshold value , and if it is judged that the slope is not smaller than the threshold value , the developing bias voltage for obtaining the target density from the approximate straight line is determined. If it is judged that the slope is smaller than the threshold value , the developing bias voltage for obtaining the target density is determined by another determination method .

Therefore, when the development characteristics change over time and the gradient of the approximation line becomes smaller than the threshold value , the development bias voltage image forming conditions are determined by another determination method, so that it is possible to obtain a target density with higher accuracy than when the image forming conditions are determined by the same determination method as before the change. Moreover, since the determination method of the development bias voltage is switched by judging the gradient of the approximation line and the magnitude of the threshold value , it is not necessary to change the developer, such as by changing the TC ratio, which is the blending ratio of the toner and carrier in the developer, and it is not necessary to use both an IDC sensor and a potential sensor, so that it is possible to obtain the target image density efficiently and in a short time with a small and low-cost device, and it is possible to minimize the decrease in productivity due to the increase in the amount of information and the long calculation time, and the load on the monitoring means, and it is possible to provide a stable high-quality image.

According to the invention described in the preceding paragraph ( 2 ), the other determination method is a method in which the relationship between the densities of multiple patches and the developing bias voltage is approximated to a curve using a polynomial, and the developing bias voltage for obtaining the target density is determined from the approximated curve. Therefore, even in a state in which the development characteristics have deteriorated and have plateaued in the high density region, the developing bias voltage for obtaining the target density can be determined more accurately.

According to the invention described in the preceding paragraph ( 3 ), the other determination method is a method in which the developing bias voltage for obtaining the target density determined from the approximation straight line is determined by offsetting the developing bias voltage in the direction of increasing the target density. Therefore, even in a state in which the developing characteristics have deteriorated and plateaued in the high density region, the developing bias voltage for obtaining the target density can be accurately and simply determined.

According to the invention described in the preceding paragraph ( 4 ), the amount by which the developing bias voltage is offset is corrected based on at least one of the factors that cause deterioration of the development characteristics, namely, the TC ratio, which is the blending ratio of toner and carrier, the humidity, the black-white ratio, and the number of printed pages, so that the accuracy of determining the developing bias voltage can be improved.

According to the invention described in the preceding paragraph ( 5 ), when it is determined that the slope is smaller than the threshold value, and when at least one of the following applies: the TC ratio, which is the blending ratio of toner and carrier, is smaller than the threshold value, the humidity is lower than the threshold value, the black-white ratio is smaller than the threshold value, or the endurance number of sheets is greater than the threshold value , the method for determining the developing bias voltage is switched to another determination method. Therefore, the method for determining the developing bias voltage is switched to another determination method only when there is a high possibility of a deterioration in development characteristics in high density areas, and an increase in the processing load associated with determining the developing bias voltage using another determination method can be suppressed.

According to the invention described in the preceding paragraph ( 6 ), since the frequency of determining the developing bias voltage is set high in accordance with the increase in the number of sheets used, when the possibility of the deterioration of the developing characteristics in the high density region becomes greater, the determining method of the developing bias voltage can be efficiently switched to another determining method. This makes it possible to prevent the deterioration of the developing characteristics at the end of the life when the number of sheets used increases, thereby extending the life of the developing device and providing high quality images for a long period of time.

According to the invention described in the preceding paragraph ( 7 ), the patch creation means creates a patch at the timing when the image stabilization process is executed. Therefore, at the appropriate timing of the image stabilization process, it is possible to determine whether the slope of the approximation line has become smaller or whether the developing bias voltage should be switched to another determination method.

According to the invention described in the preceding paragraph ( 9 ), when it is determined that the slope of the approximation line is not smaller than the threshold value , the computer can be caused to execute a process of determining a development bias voltage for obtaining a target density from the approximation line , and when it is determined that the slope is smaller than the threshold value , determining a development bias voltage for obtaining a target density by another determination method .

1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention; 2 is a schematic enlarged cross-sectional view of the imaging cartridge. FIG. FIG. 13 is a diagram showing a state in which a patch pattern made up of a plurality of patches is formed on a primary transfer belt. 13A is a graph for explaining that the output of the IDC sensor is saturated in a high-concentration region, and FIG. 13B is a graph for explaining the calculation of the condition for achieving the target maximum concentration by linear approximation. 1A is a graph showing the relationship between the developing bias and the amount of toner adhesion when the development characteristics are normal, and FIG. 1B is a graph showing the relationship between the developing bias and the amount of toner adhesion when the developer has deteriorated. 11 is a graph for explaining a process of determining a developing bias for obtaining a target density. 6 is a flowchart for explaining a process for determining a development bias for obtaining a target density, which is performed in the image forming apparatus according to the present embodiment. 11 is a graph for explaining a second determination method. 10 is a flowchart for explaining another example of the process for determining the developing bias for obtaining a target density. FIG. 13 is a diagram for explaining another example of the second determination method. 11 is a flowchart showing a process of determining a developing bias using the second determination method described in FIG. 10 . Graphs (A) to (D) show the relationship between each condition under which development characteristics deteriorate and the offset amount Voff. 11 is a table showing an example of a frequency of determining a development bias.

The following describes an embodiment of the invention with reference to the drawings.

Figure 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention, and Figure 2 is a schematic enlarged cross-sectional view of an imaging cartridge 1. Here, the general process layout is explained.

In FIG. 1, a primary transfer belt 2 equipped with a cleaning device 6 is disposed in the center of the main body of the image forming device, and a waste toner box 7 is disposed below the cleaning device 6. Residual toner collected by the cleaning device 6 of the primary transfer belt 2 is further collected and stored in the waste toner box 7.

A secondary transfer roller 3 is disposed to the right of the primary transfer belt 2. A fixing unit 4 is disposed in the upper right corner of the main body. Below the primary transfer belt 2, imaging cartridges 1, which are integrated development units 20 that develop toner images and image carrier drum units 21, are disposed in the order of black (BK), cyan (C), magenta (M), and yellow (Y) from the right, forming a color tandem type image forming device. The image carrier drum unit 21 includes an image carrier (photosensitive drum) 10 on which a latent image is formed, a charging device 9, and a cleaning device that cleans residual toner on the image carrier 10 after transfer.

Above the primary transfer belt 2, supply developer cartridges 5 for each color containing supply developer are arranged in the same order as the imaging cartridge 1. Below the imaging cartridge 1, an exposure device 8 is arranged to expose the surface potential on the image carrier 10 and form a latent image.

When an image is formed, a predetermined surface potential is formed on the image carrier 10 by the charging device 9, and exposure by the exposure device 8 is started with an image pattern to form a latent image. A predetermined development bias voltage is applied to the development roller 12 (shown in FIG. 2) provided in the development device 20, causing the toner to fly and visualize the latent image. The toner on the image carrier 10 is transferred onto the primary transfer belt 2 by the primary transfer roller 23 inside the primary transfer belt 2, and is further transferred onto the recording material by the secondary transfer roller 3. The recording material then passes through the fixing unit 4, where the unfixed toner is fixed, and is discharged.

Meanwhile, residual toner that remains on the image carrier 10 without being transferred to the primary transfer belt 2 during the primary transfer is scraped off by the cleaning device 6 and collected in the waste toner box 7 by the transport means.

In addition, an IDC sensor 30, which is a density sensor, is disposed along the belt running direction of the primary transfer belt 2, downstream of the image cartridge 1 in the belt running direction and upstream of the secondary transfer position by the secondary transfer roller 3, so as to face the surface of the primary transfer belt 2. The IDC sensor 30 is a reflective optical sensor that incorporates a light-emitting element such as a light-emitting diode and a light-receiving element such as a photodiode, and detects the density of a patch pattern 31 (shown in FIG. 4, described later) consisting of multiple patches 31a formed on the surface of the primary transfer belt 2.

The image forming apparatus includes a control unit 100. The control unit 100 controls the entire image forming apparatus, including the image forming operation. The control unit 100 includes a CPU, which is a calculation device, a ROM in which the CPU's operating programs and the like are stored, and a RAM, which serves as the CPU's working area (none of which are shown).

As described above, the imaging unit 1 shown in FIG. 2 includes a developing unit 20 and an image carrier drum unit 21.

Of these, the development unit 20 is equipped with two transport members 15, 16 that are rotatably installed within the development unit, and the two-component developer, which is composed of toner and carrier contained in the development unit 20, is circulated and stirred within the development device by the two transport members 15, 16. Approximately above the transport member 15, a development roller 12 is arranged, which has multiple magnetic poles arranged inside to transport the developer and is composed of a cylindrical member that is further rotatably installed. The development roller 12 receives the developer from the transport member 15, transports the developer regulated to a target amount by the regulating portion 13 to the development nip portion N, and visualizes the electrostatic latent image formed on the image carrier 10 with toner.

At this time, in the development nip N, in order to make the toner fly onto the image carrier 10, a high voltage consisting of a DC component of -200V to -900V and an AC component of a square wave or sine wave with a frequency of 3 to 7 kHz and Vpp of 1 to 3 kV is applied between the development roller 12 and the image carrier 10 as a development bias voltage (hereinafter simply referred to as development bias) Vdc.

In FIG. 2, reference numerals 17, 18, and 19 respectively denote a cleaning device, a waste toner transport member, and a cleaning roller provided in the image carrier drum unit 21. In addition, the configuration and arrangement of the imaging cartridge 1 are not limited to those shown in FIGS. 1 and 2.

Next, the control during image stabilization processing of the image forming apparatus shown in Figures 1 and 2 (image stabilization control) will be described. Image stabilization processing is a process that adjusts the print image quality to keep color reproduction constant, and is performed based on instructions from the control unit 100, for example, when a large number of prints are being printed or when the temperature or humidity inside the image forming apparatus changes.

Normally, when attempting to form an original image with the highest density (maximum density) among the gradation values, the optimum value of the developing bias voltage is set so that the density of the image actually formed corresponds to that maximum density. It would be ideal if the developing bias voltage value could be used without being changed once it has been set, but in reality, the image density also changes because of changes in development and transfer performance due to deterioration of the toner and components such as the photoconductor drum 10 and intermediate transfer belt 2 over time.

As an example of image stabilization control, a development bias optimization process is performed as appropriate to calculate the optimal value of the development bias voltage, and the development bias voltage value is updated according to the device's current status. In other words, the development characteristics are monitored during image stabilization control.

A patch pattern created with multiple different densities is used during development bias optimization processing. Figure 3 shows a patch pattern 31 consisting of multiple patches 31a formed on the primary transfer belt 2. The patch pattern 31 is created in a position facing the IDC sensor 30, and by linearly approximating the densities of each patch 31a read by the IDC sensor 30, it is possible to calculate the conditions required to obtain the target density.

At this time, it would be better if the IDC sensor 30 could read an image with the same density as the target maximum density, but since the IDC sensor 30 measures reflected light, the output of the IDC sensor 30 saturates in the high density region and the measured value becomes unstable, as shown by the white circles in Figure 4(A), which is a graph with the amount of toner adhesion (synonymous with toner density) on the horizontal axis and the output of the IDC sensor 30 on the vertical axis. Therefore, in practice, a patch pattern 31 is created with multiple patches 31a of different densities in the low density region, and the values read by the IDC sensor 30 for the density of each patch 31a of that patch pattern 31 are linearly approximated as shown in Figure 4(B) to calculate the conditions for the target maximum density.

Normally, the slope of the development characteristics is a stable value from low density to high density, so as shown in FIG. 5(A), the development potential difference ΔV is calculated by approximating the density measurement value of each patch 31a by the IDC sensor 30 to a linear line (linear approximation), and the target density (target density) can be obtained by selecting the development bias Vdc that corresponds to the calculated development potential difference ΔV.

Here, in this embodiment, the development potential difference ΔV refers to the difference between the surface potential of the image carrier (photosensitive drum) 10 and the surface potential (development bias) of the development roller 12.

However, as the number of printed pages increases, the developer deteriorates, causing the fluidity of the developer to decrease, making it difficult for the developer to fly onto the image carrier 10 at the development nip N. This phenomenon has little effect in low-density areas, so the slope of the development characteristics becomes smaller, but the linearity does not change. It has a greater effect in high-density areas, so the increase in the amount of toner adhesion relative to an increase in the development potential difference ΔV becomes smaller, and the development characteristics plateau (see Figure 5B). In this state, even if the development potential difference ΔV obtained from the linear approximation of the low-density area is used, the value will be less than the amount of adhesion that would result in the target density, resulting in an image with a low density.

This phenomenon is becoming more likely to occur due to the recent trend towards more compact machines, which reduces the amount of developer in the developing unit, the shorter time the developer stays in the development nip area due to faster speeds, and the greater degree of developer deterioration due to longer developer life.

To solve these problems, this embodiment employs the following method for determining the development bias, which is an image creation condition for obtaining the target density.

Figure 6 is a graph that explains the process of determining the development bias to obtain the target density.

As shown in Figure 6, when the horizontal axis (x-axis) represents the development potential difference ΔV (development bias) and the vertical axis (y-axis) represents the toner concentration or toner adhesion amount output from the IDC sensor 30, if there is no deterioration of the developer, the slope of the straight line will be large, as shown in the equation y = a1x + b1 obtained by approximating the output value (density of each patch 31a) in the low density region by the IDC sensor 30 shown by the black circles. On the other hand, if the developer has deteriorated, the slope of the straight line will be small, as shown in the equation y = a2x + b2.

Therefore, as shown by the dotted line in Figure 6, the slope a0 is set as a threshold value in advance, and when the slope of the straight line obtained by approximating the output value of the IDC sensor 30 becomes smaller than the threshold slope a0, it is determined that the developer has deteriorated, and the method of determining the development bias, which is the imaging condition for obtaining the target density, is switched from the method used when the slope of the straight line is not smaller than the threshold slope a0, and the development bias is determined.

Figure 7 is a flowchart for explaining the process of determining the development bias for obtaining the target density, which is performed in the image forming apparatus according to this embodiment. The process shown in the flowchart of Figure 7 and the flowcharts following Figure 7 is executed by the CPU of the control unit 100 operating in accordance with an operating program stored in a ROM or the like.

In step S00, the slope of the approximation line in the low density region obtained from the graph showing the relationship between the density of patch 31a and the development characteristics, that is, the slope of the development characteristics, is set to a, and the preset threshold value of the slope of the development characteristics is set to a0. In step S01, it is determined whether a>a0. When the development characteristics are in a normal state, that is, when there is no deterioration of the developer, a>a0 (YES in step S01), so the first determination method is selected in step S02, and then the development bias Vdc, which is an image creation condition, is determined using the first determination method in step S04.

In step S01, if a>a0 is not satisfied (NO in step S01), developer deterioration has occurred, so the second determination method is selected in step S03, and then the development bias Vdc, which is an image creation condition, is determined using the second determination method in step S04.

Here, the first and second determination methods will be described. The first determination method is a method in which the output value of the IDC sensor 30 (the density of each patch 31a) is approximated by a straight line, as shown in the equation y = a1x + b1 in Figure 6, and the intersection point between the line (hereinafter also referred to as the approximation line) and the target density is found, the development potential difference ΔV corresponding to the intersection point is found, and the development bias Vdc corresponding to the development potential difference ΔV is further calculated to determine the target density.

On the other hand, if the slope of the approximation line becomes smaller than the threshold slope a0, as mentioned above, the fluidity of the developer decreases due to deterioration of the developer, causing the development characteristics to plateau, and if the development potential difference ΔV is calculated from the intersection of the approximation line and the target density, the value will be smaller than the amount of adhesion that results in the target density, resulting in an image with a low density.

Therefore, as a second determination method, a polynomial curve approximation is used instead of a linear approximation. Specifically, the output value of the IDC sensor 30 in the low density area of the patch 31a is approximated by a polynomial curve as shown in FIG. 8. Then, the intersection point between the approximated polynomial curve and the target density is found, the development potential difference ΔV corresponding to the intersection point is found, and the development bias Vdc corresponding to the development potential difference ΔV is calculated and determined. As can be seen from FIG. 8, the development potential difference ΔV at the intersection point with the target density shifts in the larger direction compared to the linear approximation. This makes it possible to obtain a highly accurate development bias Vdc according to the degree of deterioration of the developer.

Figure 9 is a flowchart showing another example of the process for determining the development bias to obtain the target density. In this example, when the slope of the approximation line is not a>a0, the development bias is not immediately determined using the second determination method, but the development bias Vdc is determined by switching from the first determination method to the second determination method only when there is a high possibility of a decrease in development characteristics in high density areas.

Specifically, in step S10, the slope of the approximation line in the low density region obtained from the graph showing the relationship between the patch density and the development characteristics, that is, the slope of the development characteristics, is set to a, and the preset threshold value of the slope of the development characteristics is set to a0. In step S11, it is determined whether a>a0. When the development characteristics are in a normal state, that is, when there is no deterioration of the developer, a>a0 (YES in step S11), so in step S12, the linear approximation method, which is the first determination method, is selected, and then in step S04, the development bias Vdc, which is the image creation condition, is determined using the first determination method.

In step S11, if a>a0 is not satisfied (NO in step S11), then in step S13, if other conditions are present that adversely affect the development characteristics, that is, if TC (weight percentage of toner in the developer), which is the toner and carrier blend ratio in the developer in the developer, is less than threshold value TC0, or if humidity Hu in the vicinity of the developer is less than threshold value HU0, or if CW ratio (percentage of print adhesion to total solid adhesion per sheet of paper), which is the cumulative black-white ratio within a certain period of time, is less than threshold value CW0, or if the number of sheets worn is greater than threshold value CO0, then it is determined whether or not at least one of the following conditions is satisfied simultaneously. If not satisfied (NO in step S13), it is considered that the deterioration of the developer has not actually progressed very much, so proceed to step S12 and select the first determination method, the linear approximation method.

If at least one of the conditions is met simultaneously in step S13 (YES in step S13), the second determination method is selected in step S14, and then the development bias Vdc, which is an image forming condition, is determined by the second determination method in step S14. The second determination method may be the polynomial curve approximation (polynomial approximation) described above.

In this way, when the slope of the approximation line becomes smaller than the threshold value, and at least one of the following conditions is met: the TC ratio, which is the blending ratio of toner and carrier, is smaller than the threshold value, the humidity is lower than the threshold value, the black-white ratio is smaller than the threshold value, and the durability number is greater than the threshold value, the method for determining the developing bias is switched from the first method to the second method. Therefore, the method for determining the developing bias is switched only when there is a high possibility of a decrease in the development characteristics in the high density region, and an increase in the processing load associated with determining the developing bias Vdc using the second method can be suppressed.

Figure 10 is a diagram for explaining another example of the second determination method. When the development characteristics are deteriorating, the development potential difference ΔV2 (shown by the dotted line in Figure 10) calculated by the normal linear approximation becomes a value lower than the target density.

The development potential difference ΔV (shown by the solid line) obtained by adding a preset offset value ΔVoff to the development potential difference ΔV2 becomes a large value corresponding to the deterioration of the development characteristics, so a development bias can be determined that can obtain the desired density.

Figure 11 is a flowchart showing the process of determining the development bias using the second determination method described in Figure 10.

In step S30, the slope of the approximation line in the low density region obtained from the graph showing the relationship between the patch density and the development characteristics, that is, the slope of the development characteristics, is set to a, and the preset threshold value of the slope of the development characteristics is set to a0. In step S31, it is determined whether a>a0. When the development characteristics are in a normal state, that is, when there is no deterioration of the developer, a>a0 (YES in step S31), so in step S32, it is selected to set the development potential difference ΔV1 obtained by the linear approximation, which is the first determination method, as ΔV, and then in step S34, the development bias Vdc, which is the image creation condition, is determined by the first determination method.

If a>a0 is not satisfied in step S31 (NO in step S31), then in step S33, the second determination method is selected, which is to add the offset amount ΔVoff to the development potential difference ΔV2 obtained by linear approximation, and then in step S34, the development bias Vdc, which is an image creation condition, is determined by the second determination method.

In this way, in this embodiment, the development bias Vdc for obtaining the target density calculated by linear approximation is determined by offsetting it in the direction that increases the target density, so that even when the development characteristics have deteriorated and plateaued in the high density region, the development bias Vdc for obtaining the target density can be accurately and simply determined.

In the above, the offset amount ΔVoff added to the development potential difference ΔV2 obtained by linear approximation is preferably corrected based on at least one of other conditions that cause deterioration of development characteristics, such as the TC ratio of the developer in the developer (weight percentage of toner in the developer), the humidity HU in the vicinity of the developer, the cumulative CW ratio within a recent period (percentage of the amount of print adhesion to the amount of solid adhesion on the entire surface per sheet of paper), and the number of sheets that can be printed (number of sheets printed).

Figures 12(A) to (D) are graphs showing the relationship between each condition and the offset amount ΔVoff. As shown in Figure 12(A), as the TC ratio, which is the blending ratio of toner and carrier, increases, as shown in Figure 12(B), as the humidity HU near the developer increases, or as shown in Figure 12(D), as the cumulative CW ratio increases, it is better to correct the offset amount ΔVoff in the decreasing direction. On the other hand, as shown in Figure 12(C), as the durability number (number of printed sheets) increases, it is better to correct the offset amount ΔVoff in the increasing direction. Such corrections make it possible to more accurately determine the development potential difference ΔV and therefore the development bias Vdc to obtain the target density.

By the way, it is desirable to increase the frequency of monitoring the development characteristics, in other words the frequency of executing the image stabilization process, as the number of sheets used increases. The reason for this is that as the number of sheets used increases, the developer deteriorates and the development characteristics deteriorate, so this can be more effective against this.

Figure 13 shows an example of the frequency of determining the development bias Vdc. In the example of Figure 13, when the endurance number is less than 10,000 sheets, the execution frequency of the image stabilization process (denoted as stabilization frequency in Figure 13) is set to be every 500 sheets, when the endurance number is between 10,000 and 50,000 sheets, every 300 sheets, when the endurance number is between 50,000 and 100,000 sheets, every 200 sheets, and when the endurance number is between 100,000 and 200,000 sheets, every 100 sheets.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, a case has been described in which the image forming condition determined based on the development characteristics is the development bias Vdc, but it may also be the amount of exposure to the image carrier 10 by the exposure device 8, the number of rotations of the development roller 12, the distance at the nip portion N between the development roller 12 and the image carrier 10, etc.

The image forming device can be any type of device, such as a monochrome/color copier, printer, fax machine, or combination of these.

REFERENCE SIGNS LIST 1 imaging cartridge 2 primary transfer belt 3 secondary transfer roller 5 supply developer cartridge 6 cleaning device 7 waste toner box 8 exposure device 9 charging device 10 image carrier 12 developing roller 13 regulating member 15, 16 transport member 20 developing unit 21 image carrier drum unit 23 primary transfer roller 30 IDC sensor 31 patch pattern 31a patch 100 control unit

Claims (9)

A patch creating means for creating two or more patches with different densities;
a density measuring means for measuring the density of the patch created by the patch creating means;
a determining means for determining a developing bias voltage for obtaining a target density from the density measured by the density measuring means;
a determining means for determining whether or not a slope of an approximate straight line in a low density region when the relationship between the density of the patch and the developing bias voltage is expressed by an approximate straight line is smaller than a threshold value;
Equipped with
the determining means, when it is determined by the judging means that the slope is not smaller than a threshold value, determines a developing bias voltage for obtaining a target density from the approximation straight line, and, when it is determined that the slope is smaller than the threshold value, determines a developing bias voltage for obtaining a target density by another determination method. The image forming apparatus according to claim 1, wherein the other determination method is a method in which the relationship between the density of multiple patches and the developing bias voltage is approximated to a curve using a polynomial, and the developing bias voltage for obtaining the target density is determined from the approximate curve. The image forming apparatus according to claim 1, wherein the other determination method is a method in which the development bias voltage for obtaining the target density determined from the approximation line is determined by offsetting the development bias voltage in a direction that increases the target density. The image forming apparatus according to claim 3, wherein the amount of offset of the developing bias voltage is corrected based on at least one of the TC ratio, which is the mixture ratio of toner and carrier, humidity, black-white ratio, and number of printed sheets. The image forming apparatus according to any one of claims 1 to 4, wherein when the gradient is judged to be smaller than the threshold value, and when at least one of the following conditions is met: the TC ratio, which is the blending ratio of toner and carrier, is smaller than the threshold value, the humidity is lower than the threshold value, the black-white ratio is smaller than the threshold value, or the endurance number of sheets is greater than the threshold value, the determination means switches the determination method of the developing bias voltage to the other determination method. An image forming apparatus according to any one of claims 1 to 5, wherein the frequency with which the developing bias voltage is determined by the determination means is set higher in accordance with an increase in the number of sheets that can be used. The image forming device according to any one of claims 1 to 6, wherein the patch creation means creates a patch at the same time as image stabilization processing is performed. A patch creation step of creating two or more patches with different densities;
a density measuring step for measuring the density of the patch created by the patch creating step;
a determining step of determining a developing bias voltage for obtaining a target density from the density measured by the density measuring step;
a determination step of determining whether or not a slope of an approximate straight line in a low density region when the relationship between the density of the patch and the developing bias voltage is expressed by an approximate straight line is smaller than a threshold value;
The image forming apparatus executes the above.
a developing bias voltage determining step of determining a developing bias voltage for obtaining a target density from the approximation straight line when the inclination is determined to be not smaller than a threshold value by the judgment step, and a developing bias voltage for obtaining a target density by another determination method when the inclination is determined to be smaller than a threshold value by the judgment step. A patch creating means for creating two or more patches with different densities;
a density measuring means for measuring the density of the patch created by the patch creating means;
A computer of an image forming apparatus comprising:
a determining step of determining a developing bias voltage for obtaining a target density from the density measured by the density measuring means ;
a determination step of determining whether or not a slope of an approximate straight line in a low density region when the relationship between the density of the patch and the developing bias voltage is expressed by an approximate straight line is smaller than a threshold value;
Run the command,
The program causes the computer to execute a process in which, in the determination step, if it is determined in the judgment step that the slope is not smaller than a threshold value, a developing bias voltage for obtaining a target density from the approximation straight line is determined, and if it is determined that the slope is smaller than the threshold value, a developing bias voltage for obtaining a target density using another determination method.

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