JP2017021233A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device that can provide stable image quality and reduce a waiting time.SOLUTION: An image formation device determines whether image density varies when power is turned on or a print job is inputted, and performs process control only when it determines that the image density varies. The image formation device switches between a process control 1 to perform adjustment by making an image density adjustment pattern according to the temperature of a fixation device and a process control 2 not making the image density adjustment pattern. The image formation device can provide stable image quality while reducing an unnecessary waiting time when the reloading completion time of the fixation device is short. In addition, if it determines that the variation of the image density is large, it performs process control and can provide a stable image during printing.SELECTED DRAWING: Figure 14

Description

  The present invention relates to a printing type image forming apparatus using electrophotographic technology.

  In an image forming apparatus of a printing method using electrophotographic technology, image density adjustment (process control) is performed at a predetermined timing when the power is turned on or when printing is performed, so that the image density during printing is kept constant. . In addition, in an image forming apparatus mainly used for office use, “waiting time” (in this specification, the time required from power-on to printing and the time required to return from the energy saving mode and enable printing) ) Reduction is required. Therefore, the execution judgment of process control is added according to the use environment, the number of printed sheets, and the leaving time. For this reason, a technique that does not perform unnecessary adjustment is known.

  In addition, it is known that the temperature rise time until the completion of reloading of a heat fixing device including a fixing roller and a pressure roller, for example, for fixing the toner on the recording paper varies depending on the previous use conditions. Furthermore, it is also known that the development time of the controller varies depending on the resolution and type of the input image.

  The conventional process control may be executed even when the fixing device reload completion time is short, for example, even if some modules complete the print preparation until the user waits for the completion of other controls such as process control. Could not be used (increase in "waiting time").

  Patent Document 1 discloses a technique for executing process control when a change in image density is detected for the purpose of reducing “waiting time”. However, even if the completion time of reloading of the fixing device is short, for example, even if some modules complete the print preparation, the user cannot use until waiting for the completion of other controls such as process control. The problem has not been resolved.

  The present invention determines whether or not the image density has changed during printing, and switches the process control method in accordance with the reload completion time and / or controller time of the fixing device, thereby constantly providing stable image quality. An object of the present invention is to provide an image forming apparatus capable of reducing the “waiting time”.

  An image forming apparatus according to the present invention includes an image carrier, a developing device including a developer carrier that develops a toner image on the image carrier, and toner adhesion of the toner image developed on the image carrier. A toner adhesion amount detection means for detecting the amount; a first image density control means and a second image density control means capable of suppressing the fluctuation amount of the image density when it is determined that the image density is fluctuating; First image density control execution determining means for determining whether or not to execute control by the first image density control means or the second image density control means, and the first image density control means includes the image The second image density control means is a means for detecting a toner adhesion amount on the carrier and adjusting an image forming condition based on the result. Is a means of adjusting image forming conditions using A second image density control execution determination unit that predicts a time required to start the output of the forming apparatus and determines execution of the first image density control unit or the second image density control unit; When the control execution determination means determines that either the first image density control means or the second image density control means is necessary, the second image density control execution determination means causes the first image density control means or the Which of the second image density control means is executed is determined.

  According to the present invention, the reloading of the fixing device is performed by switching between the process control 1 for forming and adjusting the image density adjustment pattern according to the temperature of the fixing device and the process control 2 for not forming the image density adjustment pattern. Stable image quality can be provided while reducing unnecessary "waiting time" when the completion time is short.

1 is a schematic cross-sectional view illustrating a configuration of a full-color color printer. It is a flowchart for demonstrating the process control 1 (image density control 1) at the time of non-printing. It is a figure for demonstrating the case where a charging bias is changed in steps at the time of laser full lighting. It is a figure shown about the pattern imaged by each FCR (abbreviation of Front, Center, Rear) when a bias is switched like FIG. It is sectional drawing shown about the structure of an optical sensor. It is a figure explaining the sensor output when the pattern which changed the density in steps is detected. It is a figure for demonstrating the pattern 1 for adjustment (dot pattern). It is a figure for demonstrating the dot structure of the dot pattern for every area ratio. It is a flowchart for demonstrating density control at the time of printing (control at the time of printing). (A) is a figure explaining the temperature rising time of a fixing device. FIG. 10B illustrates the relationship between the fixing roller temperature, the fixing device state, and the reload completion time. It is a figure explaining the conventional image density control flowchart (problem). It is a figure explaining the simple process control 2 (2nd image density control means). It is a figure explaining the correlation of Q / M fluctuation | variation-image density fluctuation | variation, and leaving time, temperature / humidity, and Q / M fluctuation | variation amount. It is a flowchart which shows the 1st example of image density control. It is a flowchart which shows the 2nd example of image density control. It is a figure explaining the image density control flowchart of 5th embodiment. It is a figure explaining the estimated image density fluctuation amount by a temperature change and leaving time.

An embodiment of the present invention will be described.
The present invention has the following characteristics in order to provide stable image quality and reduce “waiting time”. In short, if it is determined that the image density variation is large, a stable image is always provided during printing by executing process control. Also, when the image density fluctuation is large and the temperature of the fixing roller is high with reference to the previous use conditions, it takes almost no time until the temperature rises, so the reload completion time of the fixing device is shortened. At this time, by executing the process control 2 that does not create the image density adjustment pattern, it is possible to avoid the “waiting time” for waiting for the completion of the process control as in the conventional control. Yes.

  That is, it is determined whether the image density has changed when the power is turned on or when a print job is input, and process control is performed only when it is determined that the image density has changed. At this time, the process control 1 for forming and adjusting the image density adjustment pattern according to the temperature of the fixing device and the process control 2 for not forming the image density adjustment pattern are switched. As a result, it is possible to provide stable image quality while reducing unnecessary “waiting time” when the reload completion time of the fixing device is short. If it is determined that the image density fluctuation is large, the process control is executed, so that a stable image can always be provided during printing.

The features of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a conceptual cross-sectional view for explaining a full-color color printer configuration. Four drum-shaped photoconductors 3Y, 3M, 3C, and 3BK as image carriers are disposed in parallel at equal intervals in the horizontal direction at the center of the apparatus main body 2 of the color printer 1. The subscripts Y, M, C, and BK of the code indicate yellow, magenta, cyan, and black colors, respectively. Hereinafter, these subscripts are omitted as appropriate.

The photoreceptor 3Y for yellow image will be described.
The photoreceptor 3Y has a structure in which an organic semiconductor layer, which is a photoconductive substance, is provided on the surface of an aluminum cylinder having a diameter of about 30 to 100 mm, for example, and is driven to rotate clockwise in the drawing. A developing device 6Y having a charging roller 4Y and a developing roller (hereinafter also referred to as “developing sleeve”) 5Y as a developer carrying member, a cleaning device 7Y, and the like are provided around the lower side of the photosensitive member 3Y in accordance with an electrophotographic process. The image forming means are arranged in order. These are integrally accommodated in one housing to form a process cartridge, and the process cartridge is detachable from the apparatus main body 2. The same applies to the photoconductors 3M, 3C, and 3BK for magenta, cyan, and black images, except that the color of the toner to be used is different.

  An exposure device 8 for forming an electrostatic latent image is provided below each process cartridge. The exposure device 8 performs scanning while irradiating the photoconductors 3Y, 3M, 3C, and 3BK uniformly charged by the charging roller with laser light corresponding to the image data of each color. An elongated space (slit) is secured between each charging roller 4 and each developing roller 5 so that the laser light emitted from the exposure device 8 enters the photoreceptors 3Y, 3M, 3C, and 3BK. Yes. As the exposure apparatus 8, a laser scanning system using a laser light source, a polygon mirror or the like is shown, but an exposure apparatus of a system combining an LED array and an imaging means can also be used.

  Above the photoreceptors 3Y, 3M, 3C, and 3BK, an intermediate transfer belt 12 is provided as a toner pattern carrier that is supported by a plurality of rollers 9, 10, and 11 and is driven to rotate counterclockwise in the drawing. It has been. Here, the intermediate transfer belt 12 is a toner pattern carrier. However, when the toner pattern on the photoconductor 3 is directly detected, the photoconductor is a toner pattern carrier. In addition, when a toner image on the photosensitive member 3 is directly transferred to a recording medium while conveying a recording medium such as paper, and a toner pattern is formed on the recording medium, the recording medium serves as a toner pattern carrier. The intermediate transfer belt 12 is common to the photoreceptors 3Y, 3M, 3C, and 3BK, and is in a substantially horizontal state so that a part of each photoreceptor 3Y, 3M, 3C, and 3BK after the developing process comes into contact. It is arranged flat.

  Transfer rollers 13Y, 13M, 13C, and 13BK are provided on the inner peripheral portion of the intermediate transfer belt 12 so as to face the photoreceptors 3Y, 3M, 3C, and 3BK. In the outer peripheral portion of the intermediate transfer belt 12, for example, a cleaning device 14 is provided at a position facing the roller 11. The cleaning device 14 is configured to remove unnecessary toner remaining on the surface of the intermediate transfer belt 12. The intermediate transfer belt 12 is, for example, a belt based on a resin film or rubber having a base thickness of 50 to 600 μm, and has a resistance value capable of transferring toner images from the photoreceptors 3Y, 3M, 3C, and 3BK. Have

  A toner image is formed on each photoconductor 3 by a toner image forming unit including the photoconductor 3, the charging roller 4, the developing device 6, the cleaning device 7, and the exposure device 8, and these toner images are transferred to the intermediate transfer belt by the transfer roller 13. 12 is transferred so as to be overlaid on top.

  In the apparatus main body 2, a plurality of stages, in this example, two stages of paper feed cassettes 23 and 24 are arranged below the exposure apparatus 8 so as to be freely drawn out. The paper S as a recording medium stored in these paper feed cassettes 23 and 24 is selectively fed by corresponding paper feed rollers 25 and 26. The fed paper S is transported substantially vertically along the transport path 27 toward the secondary transfer position.

  An endless transport belt 35 is disposed on the side of the intermediate transfer belt 12. In the loop of the conveyance belt 35, the secondary transfer roller 18 as a secondary transfer unit is provided so as to face the roller 9 that is one of the support rollers of the intermediate transfer belt 12. The roller 9 and the secondary transfer roller 18 are pressed against each other with the intermediate transfer belt 12 and the conveyance belt 35 interposed therebetween to form a predetermined transfer nip.

  In the transport path 27 immediately before the secondary transfer position, a registration roller pair 28 is provided that takes a paper feed timing to the secondary transfer position. Above the secondary transfer position, a transport discharge path 30 that is continuous with the transport path 27 and is connected to the discharge stack portion 29 at the top of the apparatus main body 2 is formed. A fixing device 31 having a fixing roller and a pressure roller, a paper discharge roller pair 32, and the like are disposed in the transport paper discharge path 30.

  In the apparatus main body 2, toner of each color used in each of the photoconductors 3Y, 3M, 3C, and 3BK is stored in a space below the paper discharge stack unit 29, and the toner is conveyed to the corresponding developing device 6 by a pump or the like. A toner container storage portion 33 that can be supplied is provided.

An operation of forming an image on the paper S in the color printer 1 having the above configuration will be described.
First, an image signal corresponding to an output image is transmitted to the controller 50 from a personal computer (hereinafter referred to as “PC”), a scanner, a facsimile, or the like. The controller 50 converts this image signal into an appropriate output image signal determined by a control operation to be described later, and transmits it to the exposure device 8.

  In the exposure device 8, a laser beam corresponding to image data for yellow emitted from a semiconductor laser is irradiated onto the surface of the photoreceptor 3Y uniformly charged by the charging roller 4Y, whereby an electrostatic latent image is formed on the photoreceptor 3Y. It is formed. This electrostatic latent image is developed with yellow toner after being developed by the developing device 6Y, becomes a visible image, and is subjected to a transfer action by the transfer roller 13Y on the intermediate transfer belt 12 that moves in synchronization with the photoreceptor 3Y. Transcribed.

  Such latent image formation, development, and transfer operations are sequentially performed in the same manner on the photosensitive members 3M, 3C, and 3BK. As a result, yellow Y, magenta M, cyan C, and black BK toner images are carried on the intermediate transfer belt 12 as a full color toner image that is sequentially overlapped and conveyed.

  On the other hand, the sheet S is fed from one of the sheet feeding cassettes 23 and 24 and is conveyed to the registration roller pair 28 through the conveyance path 27. The sheet S is sent out from the registration roller pair 28 in time with the full color toner image on the intermediate transfer belt 12, and the full color toner image on the intermediate transfer belt 12 is transferred onto the sheet S by the action of the secondary transfer roller 18. . The sheet S on which the full-color toner image has been transferred is conveyed to the fixing device 31 by the conveying belt 35, and is discharged onto the discharge stack portion 29 by the discharge roller pair 32 after the fixing process by the fixing device 31.

In the case of duplex printing, the fixed sheet S is guided to the reversing path 36 by switching the switching claw 38, and the reversed sheet S is switched from the refeed path 37 to the registration roller pair 28 by switching the switching claw 39. Refeed the paper and turn the paper over. At this time, a toner image to be a back image is formed and carried on the intermediate transfer belt 12, and the toner image is transferred to the back surface (second surface) of the paper S and discharged after a fixing process by the fixing device 31. Paper is discharged onto the paper discharge stack unit 29 by the paper roller pair 32.
Although the case of full-color printing has been described here, even in the case of monochrome printing with a specific color or black, the operation is the same except that there are photosensitive members that are not used.

  The non-printing time means a non-image forming time when the image forming apparatus (color printer 1) is not outputting an image, such as a start-up operation after power-on or when the photosensitive member 3 is idle before and after image output. . Non-printing control is executed in the adjustment mode. In general, in an image forming apparatus, even if an image density is detected and density correction is performed once, the density shifts with time. In particular, when the temperature / humidity inside the image forming apparatus changes or when there is a long standing time, the density tends to deviate. In addition, the density deviates as the number of output sheets increases. Therefore, after printing a predetermined number of output determined experimentally, or when the temperature and humidity detection sensor installed inside the image forming apparatus detects a change beyond the experimentally determined threshold, the And is stored in a memory inside the controller 50. The same applies when the image forming apparatus is not used beyond the experimentally determined standing time.

  The controller 50 determines whether or not the adjustment timing is as described above according to the program stored therein (FIG. 2, step S1). If it is determined that the adjustment timing is reached, as shown in FIG. 3, the charging bias and the developing bias of the developing device 6 are switched, and the gradation device pattern shown in FIG. The body 3 is exposed with full laser light.

  In general, the toner pattern may mean the entire gradation pattern, or it may mean individual toner patterns constituting the gradation pattern. An adjustment toner pattern 1 described later means the entire gradation pattern. Full lighting means that an area corresponding to the toner pattern in FIG. 4 is continuously exposed without making dots with laser light. When exposed in this way, the photosensitive member potential of the toner pattern after exposure becomes substantially the same value as shown in FIG.

  With respect to this toner pattern, when the development bias is switched stepwise as shown in FIG. 3, development is performed so that the toner increases in proportion to the difference between the toner pattern potential and the development bias. As a result, as shown in FIG. 4, ten toner patterns (adjustment toner patterns 1) having different densities are formed on the photoreceptors of the respective colors (FIG. 2, step S2). The toner pattern has three positions (F), rear (R), and center (C) before the laser scanning direction (hereinafter referred to as “main scanning direction”) on the photosensitive member 3, that is, the moving direction of the intermediate transfer belt 12. Made in the end region and the central region in the orthogonal direction. In FIG. 4, black, cyan, magenta, and yellow toner patterns are formed from the top.

  The smaller the size of the toner pattern, the smaller the toner consumption. The toner pattern of the present embodiment has a rectangular shape, the length in the main scanning direction is 5 mm, and the length in the sub-scanning direction that is the moving direction of the intermediate transfer belt 12 and orthogonal to the main scanning direction is 7 mm. The reason why the charging bias is switched in synchronism with the developing bias is that, if the difference between the developing bias and the charging bias is too large, the two-component developing device has problems such as carrier adhering to the photoreceptor 3. The interval between the toner patterns in the sub-scanning direction is 4 mm.

  In FIG. 4, the total length L of the gradation pattern is 434 mm, and the pitch L1 between the photosensitive drums is 110 mm. The toner pattern formed on the photoreceptor 3 is transferred onto the intermediate transfer belt 12 by the transfer roller 13. As a result, as shown in FIG. 4, ten toner patterns of each color are formed on the intermediate transfer belt 12 at three positions, the front (F), the rear (R), and the center (C). Next, the reflection density of the toner pattern is detected by the reflective optical sensors 40F, C, and R as toner pattern detection means (FIG. 2, step S3). As shown in FIG. 4, the optical sensor 40C is located at the center of the image light, and the distance L2 between the optical sensor 40C and the optical sensors 40F and 40R is 160 mm. Moreover, in FIG. 4, the code | symbol K has shown the reference | standard point.

  For example, as shown in FIG. 5, the optical sensor 40 includes a light emitting element 40B-1, a regular reflection light receiving element 40B-2, and a diffuse reflection light receiving element 40B-3. Hereinafter, the optical sensor is also simply referred to as a sensor. The irradiation light of the light emitting element 40B-1 is reflected on the intermediate transfer belt 12. The regular reflection light is detected by the regular reflection light receiving element 40B-2, and the diffuse reflection light is detected by the diffuse reflection light receiving element 40B-3.

  The output of the regular reflection light receiving element 40B-2 with respect to the density of the black toner pattern is such that the regular reflection light decreases as the amount of toner increases. Therefore, the density control is performed using the regular reflection light receiving element 40B-2. On the other hand, the output of the diffuse reflected light receiving element 40B-3 with respect to the density of the color toner pattern is controlled by using the diffuse reflected light receiving element 40B-3 because the diffuse reflected light increases as the toner amount increases. The sensor output of a plurality (for example, 10) of toner patterns is as shown in FIG. 6 for a black toner pattern, for example.

  When the toner pattern passes just below the sensor as the intermediate transfer belt 12 moves, the sensor output changes with time in accordance with the density of the black toner pattern. For this sensor output, a threshold value that can be distinguished from the background portion having no toner pattern is set, and a sensor output corresponding to the toner pattern position or toner pattern density is specified by using a trigger when the sensor output has decreased from the threshold value.

  Then, in any of the four photoconductors 3Y, 3M, 3C, and 3BK, the timing at which the toner pattern is first written is used as a trigger to determine the timing at which the toner pattern comes immediately below the sensor from the layout of each component and the process linear velocity. Can be predicted. Therefore, the toner pattern may be read at that timing, but it is necessary to increase the toner pattern in consideration of errors. On the other hand, the light emitting element 40B-1 starts to emit light a certain time earlier from the timing when the toner pattern comes directly under the sensor, performs data sampling continuously, and specifies the toner pattern using the above-described threshold value. You can also. According to this, the size of the toner pattern can be made smaller than the method of determining the exposure / reading timing of the toner pattern from the timing on the layout. When the size of the toner pattern is reduced, the toner consumption can be reduced accordingly. It is also desirable to reduce the detection area of the optical sensor 40 in order to reduce the size of the toner pattern. Due to the downsizing of the light emitting element and the light receiving element or the installation of a slit or the like, the sensor detection region of this embodiment has a circular shape with a diameter of 1 mm.

  The sensor detection area is desirably 2 mm or less. In this embodiment, as shown in FIG. 4, the length of the toner pattern in the sub-scanning direction is 7 mm. However, in consideration of the number of data samples, pattern edge detection accuracy, and the like, it may be about 5 mm. The length of the toner pattern in the sub-scanning direction is preferably in the range of 5 to 7 mm. The reflection density of each toner pattern is known from the sensor output of the toner pattern (step S3 in FIG. 2). Ten data of the reflection density with respect to the development bias are plotted on a graph with the development axis on the horizontal axis and the reflection density on the vertical axis, and the slope γ of the straight line when these data are approximated by a straight line is obtained (FIG. 2, Step S4). This inclination γ represents the developing ability of each toner developing device. The slope γ can be controlled by changing the toner density of the developer. When the slope γ is larger than the target value, the toner density is lowered, and when the slope γ is lower, the slope γ can be made closer to the target value by increasing the toner density. Even if the slope γ is not changed, the maximum density can be adjusted by changing the developing bias.

  If the absolute value of the developing bias is increased, the amount of toner to be developed increases, and the reflection density of the maximum density toner pattern increases. Conversely, if the absolute value of the developing bias decreases, the reflection density decreases. When changing the developing bias, it is necessary to change the charging bias in conjunction with it and keep the difference between the photosensitive member charging potential and the developing bias in a region where the toner is not developed constant. In this embodiment, when the value of the slope γ is within a predetermined range, the development bias and the charging bias are changed so that the target maximum reflection density is obtained, and when the slope γ is out of the predetermined range, the toner density is changed. The control target value is changed so that the slope γ falls within a predetermined range.

  The change amount of the developing bias and the charging bias can be easily obtained from the experimentally determined value and the detection result of the sensor (FIG. 2, step S5). The relationship between the slope γ and the toner density can also be experimentally obtained in advance, and the toner density amount to be changed can be obtained from the data and the detected slope γ (FIG. 2, step S5).

Generally, the toner density in the developing device can be detected using a toner density sensor, and toner is replenished based on the sensor output so that the target toner density is obtained. When the toner density to be changed is determined, the control target value of the toner density sensor is changed and the toner density is set (FIG. 2, step S6). Further, a developing bias and a charging bias are set (FIG. 2, step S6).
With the above control, the temporal and environmental density fluctuations of the developing device 6 can be corrected.

  Next, as shown in FIG. 7, a dot pattern (adjustment toner pattern 1) is formed. This dot pattern is composed of dots as shown in FIG. 8 and has a different area ratio. In other words, it is an area gradation pattern. In the example of FIG. 7, dot patterns of black, cyan, magenta, and yellow are formed in order from the top.

  In the digital image forming apparatus, the intermediate density is expressed by a ratio of dots occupying per unit area, that is, an area ratio. By changing the area ratio, low density, intermediate density, and high density can be realized. Due to the sensitivity fluctuation of the photosensitive member 3 and the like, even if the exposure by full lighting is performed, fluctuation may occur in the intermediate density composed of dots. In order to correct this variation, a plurality of toner patterns composed of dot patterns with different area ratios are created on the intermediate transfer belt 12 under the same charging output, developing bias, and exposure conditions as in normal image output. Detected by the sensor 40 (FIG. 2, step S7).

  The left vertical line of dot patterns shown in FIG. 8A is an example of cyan, and the right vertical line of dots shown in FIG. 8B is an example of black. The dots increase from the upper side to the lower side in the figure. The area ratio of the cyan dot pattern is 12.5%, 25.0%, 37.5%, 50.0%, 62.5%, and 100% in order from the top. The area ratio of the black dot pattern is 12.5%, 25.0%, 37.5%, 50.0%, 62.5%, and 50% in order from the top. Dot patterns with different area ratios correspond to output image signals.

  The reflection density of the dot pattern is obtained from the sensor output, and an approximate function in a graph with the horizontal axis representing the output image signal and the vertical axis representing the dot pattern reflection density is calculated (FIG. 2, step S8). At the same time, the pattern density with an area ratio of 50% for black and the pattern density with an area ratio of 100% for yellow, magenta, and cyan are stored in the controller 50 (FIG. 2, step S8). From the calculated approximate function, an output image signal (dot area ratio) required to output the reflection density required by an input signal from a PC or the like can be obtained (FIG. 2, step S9). Therefore, it is possible to determine the output image signal necessary for obtaining the density required by the input signal from the input image signal (step S9 in FIG. 2). Finally, the controller 50 determines a density target value for control during printing performed during the image forming operation (step S10 in FIG. 2).

The target density value X of the toner pattern in the printing control is determined as follows. That is, the toner pattern created by the toner density, the developing bias, and the charging bias set in step S6 in FIG. 2 is used in the printing control shown in FIG. Toner pattern to be included. The average value of the dot pattern detection density in the end area when the toner pattern is not printed is set as a density target value X. The dot pattern detection density in the end area at the time of non-printing is the dot pattern detected by the optical sensors 40F and 40R in FIG. 5, and the black area ratio pattern and color toner stored in step S8 in FIG. This is the detected density of a pattern with an area ratio of 100%.
In addition to obtaining the average value as described above, the density target value X may be determined by approximating the sensor outputs of a plurality of toner patterns having different area ratios with a straight line.

  FIG. 9 is a diagram for explaining density control during printing (printing time control). The time of printing means the time of image formation (during image formation operation) when the color printer 1 is outputting an image. The toner pattern detection at the time of printing may always be performed, but the density rarely changes greatly. I also want to save toner consumption. Therefore, it is preferable to perform density control by creating a toner pattern for each predetermined number of sheets output, for every predetermined operation time of the color printer 1 or for each predetermined travel distance of the photosensitive member 3 or the developing roller 5, which is experimentally determined.

  In the printing control, first, the controller 50 determines whether or not the image forming condition adjustment timing is reached (step S11 in FIG. 9). When it is determined that the image formation condition adjustment timing has come, the controller 50, as shown in FIG. 9B, in addition to writing the output image in the image area, the non-end of the end portion in the main scanning direction on the intermediate transfer belt 12. In the image region, a toner pattern (adjustment toner pattern 2) is created (FIG. 9, step S12). This toner pattern having a smaller number of patterns than in the non-printing control is selected in advance from the toner patterns (adjustment toner pattern 1) created by the non-printing control. That is, it is the same as the toner pattern in which the density target value X is calculated in the non-printing control flowchart in FIG. By using the same toner pattern, it becomes easier to maintain the state of the color printer 1 immediately after adjusting the developing bias in the non-printing control than when using different toner patterns.

  In the toner pattern of FIG. 8A, the lowermost black toner pattern is an intermediate density pattern, particularly a dot pattern having an area ratio of 50%. The reason why the dot pattern having such an area ratio is used is that in a region where the black toner pattern density (reflection density) is high, a change in sensor output with respect to a change in density becomes small and sensitivity is lowered. Therefore, it is desirable to set the toner pattern density for printing control in an area where the change in sensor output with respect to the change in toner pattern density is large, and the area ratio is about 70% or less. Further, since it is important to compensate for the maximum density, it is preferable that the toner pattern density be high. Therefore, the lower limit of the toner pattern density is 30%.

  The formed toner pattern passes under the optical sensors 40F and 40R, and the reflection density is detected (FIG. 9A, step S13). The data sampling method at this time is substantially the same as that at the time of reading the toner pattern created by the above-mentioned laser full lighting. That is, from the pattern writing timing, the time for the toner pattern to come immediately below the sensor can be found from the layout and process linear velocity. Therefore, the light emitting element 40B-1 is turned on slightly earlier than that time, and the sensor output for the toner pattern position or toner pattern density is specified from the point where it falls below a predetermined threshold value. In the present embodiment, as shown in FIG. 9B, the average density of two identical dot patterns is calculated.

  That is, the reflection density found from the sensor output is compared with the density target value X determined in the previous non-printing control to adjust any one of the target toner density, light quantity, and development bias (FIG. 9A), step S14. ). If the reflection density is lower than the density target value X, the toner density control target value may be increased, the light amount may be increased, or the absolute value of the developing bias may be increased. If the reflection density is higher than the density target value X, these may be decreased. The amount of change is determined experimentally according to the individual image forming apparatus. FIG. 9C shows the relationship between the toner density and the toner adhesion amount when the printing control is executed during printing and the toner density control target value is changed. When the predetermined printing control execution determination is satisfied during printing, the toner density control target value is changed and the toner density is adjusted. By appropriately performing this control at a non-printing control execution interval, it is possible to keep the toner adhesion amount constant without stopping printing. In addition, since the amount of writing light can be increased or decreased relatively quickly compared to the toner concentration, a method of adjusting the light amount and maintaining the toner adhesion amount may be used.

  As described above, in the present embodiment, a plurality of toner patterns (adjustment toner pattern 1) are formed at the time of non-printing, image forming conditions are set with high accuracy, and a smaller number of toner patterns (adjustment toners are used at the time of printing. Pattern 2) is formed in parallel with the output image and detected. Since density control is performed while maintaining the same state as during non-printing during printing, the stable state of the image can be maintained longer than when only density control during non-printing is performed. In addition, finer density control can be performed than when only density control during non-printing is performed.

  FIG. 10A is a diagram for explaining the temperature raising time of the fixing device, and FIG. 10B is a diagram for explaining the relationship between the fixing roller temperature, the fixing device state, and the reload completion time. FIG. 10A shows the temperature rise time until the fixing device 31 shown in FIG. 1 is completely reloaded (printable state). The reload completion time depending on the temperature when starting up the fixing device will be described with reference to FIG.

  The fixing device mainly has two startup temperature thresholds, and detects the temperature of the fixing roller based on an output value from a thermistor provided in the fixing device. In this embodiment, the detected temperatures at start-up are less than 60 ° C., 60 ° C. or more and less than 100 ° C., and 100 ° C. or more are called cold, warm, and hot, respectively, and the reload completion time differs in each case. (FIG. 10 (b)) The thick line in the figure represents the transition of the temperature and elapsed time of the fixing roller until the completion of the cold reloading, and it takes about 60 seconds to raise the temperature and stabilize the fixing temperature. The thin line in the figure represents the transition of the temperature of the fixing roller and the elapsed time until the completion of warm reloading, and it takes about 5 seconds to stabilize the fixing temperature. The dotted line in the figure shows the transition of the temperature and elapsed time of the fixing roller until the completion of the reloading in the hot state, and the reloading completion time is 0 second.

  In this embodiment, the temperature change of the fixing roller of office equipment, which is particularly demanding to reduce “waiting time”, is shown, but the fixing temperature is stabilized in office equipment and production printing (industrial use) equipment. There is generally a large difference in time. In production printing equipment, it is often important to stabilize the fixing temperature and maintain high-quality image quality, so changing the temperature of the fixing roller and the diameter of the roller and increasing the heat capacity will change the temperature over time. In many cases, the fixing temperature is stabilized. At this time, the cold reload completion time is about 360 seconds, and a time difference of about 6 times may occur as compared with the office equipment.

  FIG. 11 is a flowchart of conventional image density control shown for comparison. FIG. 12 is a flowchart for explaining simple process control 2 (second image density control means). FIG. 13 is a diagram for explaining the Q / M fluctuation-image density fluctuation correlation and the correlation between the standing time, temperature and humidity, and the Q / M fluctuation amount.

  First, the problem of conventional control will be described with reference to FIG. FIG. 11 is a flowchart for schematically explaining processing settings executed by the CPU based on the control program stored in the storage device. The process setting is started when the power of the image forming apparatus is turned on or when print data (print job) transferred from an external apparatus such as a personal computer is received.

  When it is determined that the power is turned on (step S11), or until it is determined that the print data transferred from an external device such as a personal computer is received (No). If it is determined that the power has been turned on or print data has been received (Yes), the image density variation information is acquired and referenced (step S12). The image density fluctuation information refers to parameters that are considered to contribute to image density fluctuation during printing, and includes the previous job end time, temperature / humidity change, printed sheet counter, cumulative image area ratio, and the like.

  If it is determined from the image density fluctuation information referenced at this time that the image density fluctuation amount is small (No in step S13), printing is immediately started (step S16). On the other hand, if it is determined that the image density fluctuation amount is large (YES in step S13), the process control 1 (first image density control means) shown in FIG. 2 is executed (step S16), but the image formation preparation time is It is determined whether it is sufficient (step S14). Note that the image formation preparation time refers to the above-described reload completion time (FIG. 10) of the fixing device and controller development time. At this time, if the fixing roller temperature of the fixing device is warm, for example, the image formation preparation time is 5 seconds, and the fixing device completes the preparation for printing. However, since the process control 1 is executed after (or at the same time), printing cannot be started until the execution of the process control 1 is completed.

  In the present embodiment, the process control 1 is about 30 seconds in the FC mode (a mode that is performed at two positions (front (F) and center (C) in the main scanning direction)), and printing is interrupted during this time. Further, when printing in the FC mode, the process control 1 is performed at an interval of about 200 sheets. Therefore, when 1000 continuous print jobs are input, a “waiting time” of 150 seconds at maximum occurs.

  In general, in an image forming apparatus, even if the image density is detected once and the image density and gradation are adjusted, the adjustment result deviates from the adjustment result over time according to the use state. In particular, when the temperature and humidity inside the image forming apparatus change or when there is a long standing time, the image density tends to deviate. That is, in order to continue printing with stable image quality immediately after the power is turned on or immediately after returning to the energy saving mode, it is necessary to periodically execute the process control 1 at a predetermined execution interval to maintain the image density. Further, in order to transfer the toner image onto the paper and perform the fixing process with the fixing device, it is necessary to raise the temperature of the fixing device to a predetermined temperature, and the printing start time is sacrificed in order to stabilize the temperature of the fixing device. There was a case. Therefore, in the present embodiment, attention is paid to the start-up time of modules other than the image forming part such as a fixing device and a controller. If these start-up times are shorter than the time until the end of the execution of the process control 1, a simple process control 2 (second image density control means) that replaces the process control 1 is executed. That is, when the print preparation completion time of the fixing device that is dominant in the “waiting time” is short, the extra “waiting time” does not occur by performing the image density control 2. It is possible to provide means for eliminating unnecessary “waiting time” and stabilizing the image density during printing.

  Next, simple process control 2 (second image density control means) will be described with reference to FIG. As described above, the image density variation information includes the previous job end time, temperature / humidity change, number of printed sheets counter, cumulative image area ratio, and the like. That is, in other words, it is possible to estimate the image density fluctuation amount from these pieces of information. The image forming conditions can be adjusted based on the image density change information without forming the density adjustment gradation pattern. This is because the image density variation is caused by the toner charge amount Q / M variation, and it is known that the toner charge amount Q / M decreases due to leaving or temperature and humidity changes. In FIG. 12, the temperature change T1-T2 is calculated (step S21), the leaving time t1-t2 is calculated (step S22), and the bias change amount vb 'is calculated from the temperature change and the leaving time (step S23). Then, the image forming condition is recalculated as Vb = vb + vb ′ (step S24).

  FIG. 13A schematically shows this, and the image density fluctuation increases in proportion to the toner charge amount Q / M fluctuation amount. Further, it is known that the toner charge amount Q / M decreases as time elapses or as the temperature and humidity change (FIGS. 13A and 13B). Therefore, in the simple process control 2 (second image density control means) in the present embodiment, the time change from the end of the acquired print job to the start of the next print job (left time) and the end of the print and the start of the next print job The image density fluctuation amount (Q / M fluctuation amount) is estimated based on the temperature change information at the time, and the image forming condition adjustment is executed without forming the density adjustment gradation pattern. That is, the environmental fluctuation can be calculated from the difference between the temperature and humidity at the start of the next drive and the temperature and humidity at the end of the previous drive, and the image density fluctuation amount can be predicted according to the environmental fluctuation.

In the present embodiment, the amount of change in the image density is estimated using the left time and temperature change from the end of the previous printing to the next printing execution as the image density fluctuation information. However, the image density fluctuation amount may vary depending on the deterioration state of the developer and the printing mode (image area ratio, etc.) at the previous printing. For example, the estimated image shown in FIG. Variations greater than the amount of concentration variation can occur. In other words, it may be difficult for process control 2 (second image density control means) to adjust image forming conditions only to maintain a constant image density during the previous printing and the next printing. This problem is solved by the above-mentioned control at the time of printing. That is, the image density at the previous printing and the next printing is simply adjusted by adjusting the image forming condition by the process control 2, and even when the adjustment is insufficient, the printing control (third image density control means) is used. This can be solved by finely adjusting the image forming conditions during printing. In other words, in the configuration in which the control at the time of printing (third image density control means) is executed, an optimum image during printing is obtained even when adjustment by the process control 2 (second image density control means) is not sufficient. The concentration can be maintained.

FIG. 14 is a flowchart illustrating a first example of image density control. The flow in FIG. 14 is based on the conventional image density control flow shown in FIG. 11, and the control flow differs depending on whether or not there is an image formation preparation time.
That is, the reload completion time (see FIG. 10) of the fixing device is used as the image formation preparation time. As described above, the reload completion time in this example varies depending on the temperature of the fixing roller.
[Reload completion time of fixing device> Execution completion time of process control 1 (about 30 seconds)]
When the above condition is satisfied, it is determined that the image formation preparation time is sufficient (YES in step S14), and the process control 1 (density control means 1) forms a gradation pattern for density adjustment simultaneously with the temperature rise of the fixing device. ) Is executed (step S15a).
on the other hand,
[Reload completion time of fixing device ≦ execution completion time of process control 1 (about 30 seconds)]
When the above condition is satisfied, it is determined that the image formation preparation time is not sufficient (NO in step S14), and the print job is executed immediately after the execution of the simple second image density control means that does not create the gradation pattern ( Step S15b).
As a result, even if the image density fluctuation amount is considered to be large from the image density fluctuation information after the print job is input, printing can always be performed with a stable image density, and an extra “waiting time” is provided. It is possible to provide higher quality image quality (stability).

FIG. 15 is a flowchart illustrating a second example of image density control.
The relationship between the reload completion time of the fixing device and the temperature of the fixing roller in the fixing device is uniquely determined as shown in FIG. Therefore, the image formation preparation time may be replaced with the fixing roller temperature. In the control flow shown in FIG. 15, the determination result of the fixing roller temperature is used instead of the determination of the image formation preparation time shown in FIG. That is,
[Fixing roller temperature ≧ 60 ° C. (warm, hot)]
When the above condition is satisfied, it is determined that the temperature of the fixing roller is sufficient (YES in step S14), and no time is required until the reloading is completed. Therefore, a simple second image density control unit that does not form a gradation pattern is provided. Execute the print job immediately after execution.
On the other hand,
[Fixing roller temperature <60 ° C. (cold)]
When the above condition is satisfied, it is determined that the temperature of the fixing roller is not sufficient (NO in step S14), and it takes time until the reloading is completed. Therefore, a process of forming a gradation pattern for density adjustment simultaneously with the temperature rise of the fixing device Control 1 (first image density control means) is executed. Note that the image density by creating the gradation pattern can be adjusted with high accuracy.

  In the first and second examples, when it is determined that the image formation preparation time is insufficient (the reloading completion time of the fixing device is 0 second (hot) or 5 seconds (warm)), there is an execution request. Even in this case, image density adjustment need not be executed (third example of image density control).

  Further, when it is determined that the image formation preparation time is sufficient (fixing device reload completion time is 60 seconds (cold)), image density adjustment may be executed during the time until fixing device reload completion (image) Fourth example of concentration control). By performing the image density adjustment during the time until the completion of reloading, even if a slight image density fluctuation can occur, this can be suppressed.

FIG. 16 is a flowchart showing a fifth example of image density control.
FIG. 17 is a diagram for explaining the estimated image density fluctuation amount due to the temperature change and the standing time. The estimated fluctuation amount (100 times) of the image density due to the standing time and the temperature change is shown. It can be confirmed from FIG. 17 that the image density fluctuation amount increases as the standing time and temperature change increase. For example, if the standing time Δt = 40 [min] and the temperature change ΔT = 15 [° C.], it can be estimated that the image density fluctuation amount at the next printing is 14 * 0.01 = 0.14. If the image density fluctuation amount estimated from the acquired image density fluctuation information exceeds the experimentally determined threshold value 0.2, sufficient image density stability can be obtained by adjusting the image forming conditions by the second image density control means. May not be available. Therefore, as shown in FIG. 16, when it is estimated that the image density fluctuation amount is particularly large from the acquired image density information, a gradation pattern for density adjustment is formed, and the density detection result of the gradation pattern is obtained. It is desirable to adjust the image forming conditions based on this. Therefore, only in the case described above, the process control 1 (first image density control unit) may be performed regardless of the temperature of the fixing device (or the reload completion time) to give priority to the stability of the image density. That is, according to this example, the leaving time can be calculated from the difference between the next driving start time and the previous driving end time, and the image density fluctuation amount can be predicted according to the leaving time. In the present specification, means for determining whether or not to execute control by the first image density control means or the second image density control means is referred to as first image density control execution determination means, and is accompanied by toner adhesion amount detection. The means for adjusting the image forming condition using predetermined acquisition information determined in advance is referred to as second image density control execution determination means.

In the first to fifth control examples described above, the image density control unit is switched depending on the reload completion time and temperature of the fixing device. However, the temperature information of the pressure roller may be acquired as the temperature detection unit of the fixing device. is there. The pressure roller temperature has a correlation with the fixing roller temperature,
[Pressure roller temperature = α * Fixing roller temperature]
(Α <1). Therefore, not only the fixing roller temperature but also the temperature of the pressure roller may be used as a control element.

  As described above, in the implementation of the present invention, the interruption of printing by the process control 1 executed when a print job is input, the power is turned on, the energy is restored, and the like are prevented. As a result, when 1000 continuous print jobs are input, the “waiting time” of 150 seconds at the maximum can be reduced. Furthermore, a stable image density can be provided by appropriately adjusting the image forming conditions based on the image density fluctuation information.

It should be noted that the present invention is not limited to the specific embodiments and control examples described above, and various modifications may be made within the scope of the present invention described in the claims unless otherwise specified in the above description. Modifications and changes can be made by those having ordinary knowledge in the art within the technical idea of the present invention.
For example, in the present invention, only the reload completion time of the fixing device and the “waiting time” generated in the process control 1 are mentioned, but in the image forming apparatus, the image development time of the controller also differs depending on the image information of the print job. It is known to occur. Therefore, the present invention can be applied based on the controller development time and the “waiting time” generated in the process control 1.
Thus, the effects described in the embodiments of the present invention are merely examples of the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. It is not a thing.

1: Color printer (image forming apparatus)
3: Photoconductor 4: Charging roller 5: Developing roller 6: Developing device 7: Cleaning device 8: Exposure devices 9, 10, 11: Roller 12: Intermediate transfer belt 13: Transfer roller 14: Cleaning device 18: Secondary transfer roller 23: paper feed cassette 24: paper feed cassette 25, 26: paper feed roller 27: transport path 28: registration roller pair 29: paper discharge stack unit 30: transport paper discharge path 31: fixing device 32: paper discharge roller pair 33: Toner container storage section 35: Conveying belt 36: Reversing path 37: Refeed path 38, 39: Switching claw 40: Optical sensors 40C, 40F, 40R: Optical sensor 40B-1: Light emitting element 40B-2: Receiving specularly reflected light Element 40B-3: Diffuse reflected light receiving element 50: Controller S: Paper

JP 2004-157222 A

Claims (11)

An image carrier;
A developing device including a developer carrier for developing a toner image on the image carrier;
A toner adhesion amount detection means for detecting a toner adhesion amount of a toner image developed on the image carrier;
A first image density control means and a second image density control means capable of suppressing the fluctuation amount of the image density when it is determined that the image density is fluctuated;
First image density control execution determining means for determining whether to execute control by the first image density control means or the second image density control means;
The first image density control means is means for detecting the amount of toner adhering to the image carrier and adjusting image forming conditions based on the detection result.
The second image density control means is means for adjusting image forming conditions using predetermined acquisition information that is determined in advance without detecting the toner adhesion amount,
A second image density control execution determination unit that predicts a time required to start output of the image forming apparatus and determines execution of the first image density control unit or the second image density control unit;
When the first image density control execution determination means determines that either the first image density control means or the second image density control means is necessary, the second image density control execution determination means determines the first image. Deciding whether to execute density control means or the second image density control means;
An image forming apparatus. The image forming apparatus according to claim 1.
The predetermined acquisition information determined in advance is the previous drive end time and the next drive start time of the image forming apparatus,
An image forming apparatus. The image forming apparatus according to claim 1, wherein
2. The image forming apparatus according to claim 1, wherein the predetermined acquired information includes temperature and humidity at the end of previous driving of the image forming apparatus and temperature and humidity at the start of next driving. The image forming apparatus according to any one of claims 1 to 3,
The second image density control execution determination means sets the print preparation completion time of the fixing device as a time required for the output of the image forming device;
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The second image density control execution determination means is
When the execution time of the first image density control means> the time required for the output of the image forming apparatus, the execution of the second image density control means is determined.
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The second image density control execution determination means is
When the execution time of the first image density control means ≦ the time required for the output of the image forming apparatus, the execution of the first image density control means is determined.
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The second image density control execution determination means is
The image forming apparatus, wherein the first image density control means is not executed when the execution time of the first image density control means is greater than the time required for the output of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The second image density control execution determination means is
When execution time of the first image density control means ≦ time required for output of the image forming apparatus, execution of the first image density control means is determined regardless of the determination result of the image density variation amount.
An image forming apparatus. An image carrier;
A developing device including a developer carrier for developing a toner image on the image carrier;
A toner adhesion amount detection means for detecting a toner adhesion amount of a toner image developed on the image carrier;
When it is determined that the image density is fluctuating, the first image density control means and the second image density control means and the first image density control means or the second image density control means that can suppress the fluctuation amount of the image density. First image density control execution determination means for determining whether to execute the image density control means,
The first image density control means is means for detecting the amount of toner adhering to the image carrier and adjusting image forming conditions based on the detection result.
The second image density control means is means for adjusting image forming conditions using predetermined acquisition information that is determined in advance without detecting the toner adhesion amount,
A second image density control execution determination unit that predicts a time required to start output of the image forming apparatus and determines execution of the first image density control unit or the second image density control unit;
When the first image density control execution determination unit determines that the first image density control unit is necessary, the execution of the first image density control unit is determined regardless of the result of the second image density control execution determination unit. To
An image forming apparatus. An image carrier;
A developing device including a developer carrier for developing a toner image on the image carrier;
A toner adhesion amount detection means for detecting a toner adhesion amount of a toner image developed on the image carrier;
First image density control means and second image density control means capable of suppressing the fluctuation amount of the image density when it is determined that the image density is fluctuating;
A third image density control means capable of suppressing the variation amount of the image density at the time of printing,
A first image density control execution determination unit for determining whether to execute the first image density control unit or the second image density control unit;
The first image density control means is means for detecting the amount of toner adhering to the image carrier and adjusting image forming conditions based on the detection result.
The second image density control means is means for adjusting image forming conditions using predetermined acquisition information that is determined in advance without detecting the toner adhesion amount,
The third image density control unit is a unit that detects a toner adhesion amount formed outside an image area on the image carrier during printing, and adjusts an image forming condition based on the result.
A second image density control execution determination unit that predicts a time required to start output of the image forming apparatus and determines execution of the first image density control unit or the second image density control unit;
When the first image density control execution determination means determines that either the first image density control means or the second image density control means is necessary, the second image density control execution determination means determines the first image. Deciding whether to execute density control means or the second image density control means;
An image forming apparatus. The image forming apparatus according to any one of claims 1 to 10,
The image density adjustment pattern that is formed when the first image density control means is executed is a plurality of gradation patterns having different densities.
An image forming apparatus.