JP2005084055A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method and an image forming apparatus which restrict an amount of toner consumption and stabilize image density relative to a toner concentration change. <P>SOLUTION: The image forming method for developing an electrostatic latent image formed on an image carrier 1 with developer containing toner and carrier includes a resource saving mode, an image quality priority mode, and a return mode as image formation modes. In the resource saving mode, toner concentration is set not higher than a set value assigned to the image quality priority mode and target image density is set low, and when switched from the resource saving mode to the image quality priority mode, the return mode is selected until the toner concentration reaches the set value assigned to the image quality priority mode. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming method and an image forming apparatus.

  Image forming apparatuses equipped with a resource saving mode that saves toner consumption have appeared. As described in Japanese Patent Publication No. 61-60480, this type of apparatus is a technique for reducing the toner consumption by narrowing the dot width of one pixel in image information or Japanese Patent Publication No. 9-30042. As described in Japanese Laid-Open Patent Publication No. 2000-175029, a technique for suppressing toner consumption by thinning out an image area at a predetermined rate is shown. In addition, as disclosed in Japanese Patent Laid-Open No. 6-19257, there is a technique in which a user simply uses a density adjusting unit to easily reduce the toner consumption and the fixing temperature.

  On the other hand, examples of publications that disclose a technique for adjusting the toner density include Japanese Patent Laid-Open Nos. 62-25777, 62-25778, and 2-203369. The technique disclosed in Japanese Patent Application Laid-Open No. 62-25777 adjusts the toner density in accordance with the toner replenishment frequency. Japanese Patent Laid-Open No. 62-25778 discloses a technique for adjusting the toner density in accordance with the driving time of the developing unit in order to prevent a change in toner density after copying a large number of sheets. Furthermore, the technique disclosed in Japanese Patent Laid-Open No. 2-203369 corrects a temporary decrease in toner density at the beginning of the developing process when copying a large number of sheets.

Japanese Patent Publication No. 61-60480 Japanese Patent Publication No. 9-30042 JP 2000-175029 A JP-A-6-19257 Japanese Patent Laid-Open No. Sho 62-25777 Japanese Patent Laid-Open No. Sho 62-25778 JP-A-2-203369

  However, the conventional thinning method with the resource saving mode that saves the amount of toner consumed in the above-described conventional example causes a reduction in image quality, and if a complicated processing method is adopted, the memory area is compressed or output. There was a problem of causing a decrease in speed.

  Further, if the toner density itself is changed according to the mode, a problem arises in the stability of the image. For example, when the resource saving mode is switched, the amount of toner replenishment decreases rapidly in order to lower the toner density. Therefore, the output image density immediately after switching is larger than the output image density after the toner density setting value in the resource saving mode is stabilized. Will be different.

  In addition, if the toner adhesion amount is reduced in the resource saving mode and fixing is performed at the normal fixing temperature, hot offset is likely to occur, and the operability of the user, such as a decrease in print quality and frequent paper jams, may be significantly reduced. Is a problem.

  Also, the main usage of copiers and printers is to review documents and output temporary documents for reading mail. In the case of temporary output, many users do not particularly care about image quality, and often place importance on cost and output speed. Therefore, there is a need for an image forming apparatus that can easily set a temporary output mode that prioritizes cost without prioritizing image quality and that prioritizes cost without imposing a burden on the apparatus.

  SUMMARY An advantage of some aspects of the invention is that it suppresses toner consumption and stabilizes image density against changes in toner density.

  It is another object of the present invention to suppress toner consumption, stabilize image density against changes in toner density, reduce power consumption, and do not hinder user operability.

  It is another object of the present invention to suppress toner consumption, stabilize image density against changes in toner density, and allow a user to select a target image density.

  It is another object of the present invention to suppress toner consumption, stabilize image density against changes in toner density, and set the most economical target image density.

  Another object is to stabilize the image density against changes in toner density.

  Another object of the present invention is to stabilize the image density without incurring costs with respect to changes in toner density.

  It is another object of the present invention to allow the user to select whether or not to output when the mode is switched from cost priority to image quality priority.

  It is another object of the present invention to prevent costs when switching from the cost priority mode to the image quality priority mode.

  It is another object of the present invention to improve the impression of image output when cost is prioritized.

  In order to achieve the above object, an invention according to claim 1 is an image forming operation mode in an image forming method for developing an electrostatic latent image formed on an image carrier using a developer containing toner and a carrier. In the resource saving mode, the toner density is set to a value lower than the set value of the image quality priority mode and the target image density is set low. The most important feature is an image forming method in which the return mode is selected until the toner density reaches the set value of the image quality priority mode when switching to the image quality priority mode.

  According to the second aspect of the present invention, the electrostatic latent image formed on the image carrier is developed using a developer containing toner and a carrier to obtain a toner image, and the toner image transferred onto the transfer material is obtained. In the heat forming image forming method, there are three types of image forming operation modes, ie, a resource saving mode, an image quality priority mode, and a return mode. In the resource saving mode, the toner density is equal to or lower than the set value of the image quality priority mode, and When the target image density is set low and the mode is switched from the resource saving mode to the image quality priority mode, the return mode is selected until the toner density reaches the setting value of the image quality priority mode. The image forming method set lower than the mode is the main feature.

  According to a third aspect of the present invention, the image forming method according to the first or second aspect is characterized in that the user can select a target image density in the resource saving mode.

  According to a fourth aspect of the present invention, in the image forming method according to the first or second aspect, in the resource saving mode, the image density is determined such that the output character density is equal to or higher than the lowest legible character density. Features the method.

  According to a fifth aspect of the present invention, the image forming method according to the first or second aspect is characterized in that, in the resource saving mode, the image forming method reduces the toner replenishment amount until a predetermined density is reached.

  A sixth aspect of the present invention is the image forming method according to the first or second aspect, wherein the developing bias is controlled so that the image density is constant when the image quality priority mode is switched to the resource saving mode. Main features.

  According to a seventh aspect of the present invention, in the image forming method according to the sixth aspect, when the image quality priority mode is switched to the resource saving mode, the developing bias is changed based on a table prepared in advance according to a decrease in toner density. The image forming method is a main feature.

  According to an eighth aspect of the present invention, in the image forming method according to the sixth aspect, when the image quality priority mode is switched to the resource saving mode, the developing bias is changed using an approximate expression in accordance with a decrease in toner density. Features the method.

  According to a ninth aspect of the present invention, in the image forming method according to the sixth aspect, when the image quality priority mode is switched to the resource saving mode, the development bias is changed based on a table prepared in advance according to the number of input pixels. The forming method is the main feature.

  According to a tenth aspect of the present invention, in the image forming method according to the sixth aspect, when the image quality priority mode is switched to the resource saving mode, development is performed using an approximate expression according to a decrease in toner density according to the number of input pixels. The main feature is an image forming method for changing the bias.

  According to an eleventh aspect of the present invention, in the image forming method according to the first or second aspect, in the resource saving mode, the toner supply frequency is changed according to the number of input pixels after the toner density is determined to be a predetermined density. The image forming method is a main feature.

  The invention according to claim 12 is characterized in that, in the image forming method according to claim 1 or 2, the image forming method in which the user can select the presence or absence of print output in the return mode.

  A thirteenth aspect of the present invention is characterized in that, in the image forming method of the first or second aspect, in the return mode, the print forming is not performed and only the developing operation is performed.

  The invention according to claim 14 is characterized in that, in the image forming method according to claim 1 or 2, the image forming method for controlling the developing bias so that the image density is constant in the return mode.

  According to a fifteenth aspect of the present invention, in the image forming method according to the fourteenth aspect, an image in which the developing bias is changed based on a table prepared in advance according to an increase in toner density when the resource saving mode is switched to the return mode. The forming method is the main feature.

  According to a sixteenth aspect of the present invention, in the image forming method according to the fourteenth aspect, when switching from the resource saving mode to the return mode, the developing bias is changed using an approximate expression according to a decrease in toner density. Is the main feature.

  According to a seventeenth aspect of the present invention, in the image forming method according to the fourteenth aspect, the image forming method of changing the developing bias based on a table prepared in advance according to the number of input pixels when the resource saving mode is switched to the return mode. Features the method.

  According to an eighteenth aspect of the present invention, in the image forming method according to the fourteenth aspect of the present invention, when the resource saving mode is switched to the return mode, the developing bias is changed using an approximate expression in accordance with the number of input pixels. Main features.

  The invention according to claim 19 is characterized in that, in the image forming method according to any one of claims 1 to 18, the image forming method for printing out a notification stamp to the user in the resource saving mode. .

  According to a twentieth aspect of the present invention, an image forming apparatus using the image forming method according to any one of the first to nineteenth aspects is the main feature.

  According to the first, fifth, sixth and twentieth aspects of the present invention, the toner consumption can be suppressed, and the image density can be stabilized against the change in the toner density.

  According to the second aspect of the present invention, the toner consumption can be suppressed, the image density is stabilized against the change in the toner density, the power consumption is reduced, and the user operability is not hindered. can do.

  According to the third aspect of the present invention, the toner consumption can be suppressed, the image density can be stabilized against the change of the toner density, and the user can select the target image density.

  According to the fourth aspect of the present invention, the toner consumption can be suppressed, the image density can be stabilized against the change in the toner density, and the most economical target image density can be set.

  According to the present invention, the image density can be stabilized against the change in the toner density.

  According to the ninth, tenth, eleventh, seventeenth and eighteenth aspects of the present invention, it is possible to stabilize the image density without incurring costs with respect to changes in the toner density.

  According to the twelfth aspect of the present invention, the user can select whether or not an output is required when the mode is switched from cost priority to image quality priority.

  According to the thirteenth aspect of the present invention, it is possible to avoid the cost when the mode is switched from the cost priority mode to the image quality priority mode.

  According to the nineteenth aspect of the present invention, it is possible to improve the impression of image output when cost is prioritized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The change in toner density in each mode is shown in FIG. It can be seen that the toner density does not change immediately when each mode is changed, but gradually decreases and increases.

  FIG. 2 shows the image density when the development bias is constant when the image quality priority mode is switched to the resource saving mode. As can be seen from FIG. 2, if the developing bias is set to be the same in each mode, the image density is different when the mode is changed and after the toner density is stabilized.

  In order to solve this problem, it is considered to control the developing bias so that the image density becomes constant when the image quality priority mode is switched to the resource saving mode. Generally, the image density is lowered by lowering the developing bias. Therefore, if the developing bias is set as shown in FIG. 3, an output image having a density almost the same as the target image density in the resource saving mode can be obtained from the first output switched to the resource saving mode, and the image density within the same mode can be obtained. The difference is less.

  There are two main factors that change the image density when the toner density is decreasing: a decrease in the toner replenishment amount and a change in the toner charge amount. If the toner replenishment amount is small, the image saturation is low because the degree of saturation of development is small. As the toner concentration decreases, the charge amount of the toner increases and the development becomes difficult and the image density becomes light.

  Immediately after switching from the image quality priority mode to the resource saving mode, the toner charge amount does not change, so the image density is lowered by lowering the developing bias. Next, since the replenishment amount becomes insufficient, the developing bias is gradually increased to increase the adhesion amount. On the other hand, the toner charge amount gradually increases and becomes more difficult to be developed. Therefore, it is necessary to further increase the developing bias in order to maintain the same image density.

  From the above, in order to keep the image density constant while lowering the toner density, it is necessary not to increase the developing bias linearly but to control it with a table as shown in FIG. 4, for example. The developing bias control profile varies depending on the toner replenishing mechanism of the developing device and the charging characteristics of the toner. The setting bias in the image quality priority mode and the resource saving mode may be different.

  When the development bias is controlled by a table, it is obtained by interpolation or extrapolation from the development bias value corresponding to the density value close to the measured toner density. Therefore, in order to increase the control accuracy of the image density, it is necessary to have many table values, and a memory capacity is required.

  One method of control that does not require a large memory area is to express the development bias as a function of toner density. It has been experimentally clarified that the error is reduced by using a function derived from a cubic expression or logarithmic approximation of the toner density for this function.

  As described above, it is possible to keep the image density constant by controlling the developing bias according to the toner density, but it is also possible to control the developing bias without using the measured value of the toner density. It is. The toner density is usually measured using a sensor in the developing device, but a change in toner density can be estimated from the number of input pixels without using a sensor. The number of input pixels can be grasped by a writing unit that normally writes a latent image on an image carrier.

  That is, it is possible to control the developing bias using a table or function for the number of input pixels without using a sensor, and the image density can be kept constant at low cost. If the toner replenishment frequency after the toner density is stabilized is determined from the number of input pixels without using a sensor, control can be performed at a lower cost.

  Further, since the same thing as described above occurs when the mode is switched from the resource saving mode to the image quality priority mode, it is necessary to control the developing bias in order to keep the image density constant. However, when the user switches from the resource saving mode to the image quality priority mode, since the output of high image quality is often requested, the output may not be required until the normal toner density is reached.

  Therefore, the return mode is set until the toner density reaches the set value of the image quality priority mode. In the return mode, it is possible to save energy by operating only the developing device without output. It is also possible for the user to select whether or not to output.

  By the way, although it is a set value of image density in the resource saving mode, the required level of image quality differs depending on the use situation of the user. If there is no cost, there may be a case where it is only necessary to distinguish characters, and there is a case where a certain level of image quality is required even if the toner consumption is slightly increased. Therefore, it is more desirable that the user can select the target image density in the resource saving mode.

  However, as a property of the output device, it is necessary to be able to distinguish at least characters even when outputting a temporary document. In general, it is said that a line density of 0.28 or more is required to distinguish characters. It is necessary to set the image target density in the resource saving mode within a range in which a higher line density is guaranteed.

  Although the method for reducing the target image density to reduce the toner consumption has been described, lowering the target density means that the toner adhesion amount on the recording medium (mainly paper) is reduced.

  If the fixing set temperature is not lowered when the toner adhesion amount is decreased, the toner will be overmelted, so that a so-called hot offset occurs, which causes contamination of the fixing roller, occurrence of paper jam, and deterioration of output image quality. Therefore, when the target image density is lowered, it is necessary to lower the fixing temperature from the viewpoint of maintaining the quality of the image and the machine, and as a result, the power consumption of the apparatus can be suppressed.

  The normal fixing temperature is set to a temperature at which fixing ability can be secured and hot offset does not occur. However, since the resource saving mode is premised on temporary output, it does not necessarily have to be a set temperature at which fixing ability can be secured.

  Further, there may be a function of stamping a user notification for output in the resource saving mode. This function follows the “This document uses recycled paper” stamp when using recycled paper, but the output with such a sentence has a somewhat low level of user image quality requirements from a psychological perspective. It becomes clear from sensory evaluation that it becomes lower. Moreover, since it is immediately understood that the output is temporary, it is easy for the user to organize documents, which is also an advantage for the user.

  FIG. 5 is a configuration diagram of the image forming apparatus according to the embodiment of the present invention. Reference numeral 1 is an example of an image carrier made of a rotating body, and shows a drum-shaped photoconductor. Around the photosensitive member 1, a charging device 2 including a charging roller, a mirror 3 constituting a part of an exposure unit, a developing device 4 including a developing roller 4 a, and a recording member (in the order of rotation indicated by arrows) A transfer device 5 for transferring the developed image onto the transfer paper (P), a cleaning device 6 provided with a blade 6a slidably contacting the peripheral surface of the photoreceptor 1, and the like are disposed.

  The exposure light Lb is scanned via the mirror 3 on the photosensitive member 1 between the charging device 2 and the developing roller 4a. The irradiation position of the exposure light Lb is called an exposure unit 7. The transfer device 5 faces the lower surface of the photoreceptor 1. This facing part is the transfer part 8.

  A pair of registration rollers 9 is provided at a position further upstream of the transfer portion 8. A recording member P guided by a conveyance guide (not shown) and stored in a paper supply tray (not shown) is sent out by the paper supply roller 10 toward the registration roller 9. A fixing device 11 is disposed at a position further downstream of the transfer unit 8.

  In this image forming apparatus, image formation is performed as follows. The photosensitive member 1 starts rotating, and during this rotation, the photosensitive member 1 is uniformly charged by the charging device 2 in the dark, and the exposure light Lb is irradiated to the exposure unit 7 and scanned to form a latent image corresponding to the image to be created. It is formed. The latent image is moved to the developing device 4 by the rotation of the photosensitive member 1, where it is visualized with toner to form a toner image.

  On the other hand, feeding of the recording member P on the sheet feeding tray is started by the sheet feeding roller 10, and the recording member P temporarily stops at the position of the pair of registration rollers 9 through the conveyance path indicated by the broken line, and on the photosensitive member 1. The timing of delivery is awaited so that the toner image coincides with the transfer portion 8. When such a suitable timing arrives, the recording member P stopped on the registration roller 9 is sent out from the registration roller 9 and conveyed toward the transfer unit 8.

  The toner image on the photosensitive member 1 and the recording member P coincide with each other at the transfer unit 8, and the toner image is transferred onto the recording member P by the electric field generated by the transfer device 5. In this way, the recording member P carrying the toner image in the image forming portion around the photoreceptor 1 is sent out toward the fixing device 11. The toner image on the recording member P is fixed to the recording member P while passing through the fixing device 11 and discharged to a paper discharge unit (not shown).

  On the other hand, the residual toner remaining on the photosensitive member 1 without being transferred by the transfer unit 8 reaches the cleaning device 6 as the photosensitive member 1 rotates, and is cleaned while passing through the cleaning device 6 to prepare for the next image formation. It is done.

Set value development bias in image quality priority mode 600V
Toner concentration 5%
Initial charging potential 730V
Target image density setting value (solid density) 1.4
Fixing roller set temperature 180 ° C

  In the above configuration, various controls in the present embodiment will be described in detail. First, the target image density in the resource saving mode is set. FIG. 6 shows the relationship between the line density of the character “-” parallel to the main operation direction from the charts output in various character sizes and fonts under various development conditions and the unreadable probability. is there.

  In the present embodiment, the target image density is set to a line density of 0.4 at which the unreadable probability is 20% or less. It was experimentally determined that the developing bias is the same value as in the image quality priority mode, and the toner density for reproducing the line density is 2.5%. Incidentally, the solid image density at this time is 0.6.

  When the development bias in the resource saving mode is the following four types (FIG. 7), FIG. 8 shows the density change until the toner density is stabilized after the resource saving mode is selected from the image quality priority mode (all output images are shown). Same 5% chart).

A: No control (same setting as picture quality priority mode)
B: Increase linearly
C: Table control from experimental values (interpolation between data)
D: Controlled by third-order approximation of toner density

  As can be seen from FIG. 8, the image density is more stable in the control of C and D than in A and B.

  FIG. 9 shows the maximum value-minimum value of the image density when the toner replenishment timing after the toner density is stabilized in the resource saving mode is A and B below. The output image is a random output of 10,000 sheets of 5%, 15%, and 30% charts.

A: Defined by the number of rotations of the developing device B: Defined by the number of input pixels

  It can be seen that the image density is more stable in the B control in which the toner supply frequency is defined by the number of input pixels.

  FIG. 10 shows a flowchart when the image quality priority mode is selected from the resource saving mode (return mode). The user needs to select whether or not to output. When output is not necessary, only the developing device is rotated until the toner density in the image quality priority mode is reached.

  When the user selects an output in the return mode, the developing bias is controlled by the following four types. At this time, the density change from the selection of the resource saving mode to the image quality priority mode until the toner density is stabilized is shown in FIG. 11 (all output images are the same 5% chart).

A: No control (same setting value as the image quality priority mode)
B: Linear increase C: Table control from experimental values (interpolation between data)
D: Controlled by third-order approximation of toner density

  As can be seen from FIG. 11, the image density is more stable in the control of C and D than in A and B.

  In two types, when the fixing temperature in the resource saving mode is 140 ° C. and when the fixing temperature is the same as the image quality priority mode (180 ° C.), 10,000 sheets of 5% charts are output and the image quality and power consumption are compared. The results are shown in FIG. As shown in FIG. 12, if the fixing temperature is the same as that in the image quality priority mode, a hot offset occurs and the image becomes dirty. Moreover, it turns out that power consumption can be reduced 30% by setting temperature to 140 degreeC.

It is a figure which shows the change of the toner density in each mode. It is a figure which shows the change of image density when developing bias is made constant. It is a figure which shows the change of the developing bias in each mode. FIG. 4 is a table showing a relationship between toner density and development bias. 1 is a configuration diagram of a developing device according to an embodiment of the present invention. It is a figure which shows the relationship between line density and unreadable probability. It is a figure which shows the change of the developing bias in each mode. FIG. 6 is a diagram illustrating density change until the toner density is stabilized. It is a figure which shows the maximum value and minimum value of image density. It is a flowchart when the image quality priority mode is selected from the resource saving mode. It is a figure which shows the change of the image density in each mode. 6 is a chart showing the relationship between fixing temperature, image quality, and power consumption.

Explanation of symbols

1 Photoconductor (image carrier)
4 Development device

Claims (20)

  In an image forming method for developing an electrostatic latent image formed on an image carrier using a developer containing toner and a carrier, there are three types of image forming operation modes: resource saving mode, image quality priority mode, and return mode. In the resource saving mode, the toner density is set to the image quality priority mode when the toner density is lower than the setting value of the image quality priority mode and the target image density is set low. An image forming method comprising selecting a return mode until a value is reached.   In an image forming method for developing a latent electrostatic image formed on an image carrier using a developer containing toner and a carrier to obtain a toner image, and thermally fixing the toner image transferred onto a transfer material, As the image forming operation mode, there are three types of modes, a resource saving mode, an image quality priority mode, and a return mode. In the resource saving mode, the toner density is set to be lower than the set value of the image quality priority mode and the target image density is set low When switching from the resource saving mode to the image quality priority mode, the restoration mode is selected until the toner density reaches the setting value of the image quality priority mode. In the resource saving mode, the fixing set temperature is set lower than the image quality priority mode. An image forming method.   3. The image forming method according to claim 1, wherein a user can select a target image density in the resource saving mode.   3. The image forming method according to claim 1, wherein the toner density is determined so that the output character density is equal to or higher than the lowest legible character density in the resource saving mode.   3. The image forming method according to claim 1 or 2, wherein, in the resource saving mode, the toner replenishing amount is lowered until a predetermined density is obtained.   3. The image forming method according to claim 1, wherein the developing bias is controlled so that the image density becomes constant when the image quality priority mode is switched to the resource saving mode.   7. The image forming method according to claim 6, wherein when the image quality priority mode is switched to the resource saving mode, the developing bias is changed based on a table prepared in advance according to a decrease in toner density. .   7. The image forming method according to claim 6, wherein when the image quality priority mode is switched to the resource saving mode, the developing bias is changed using an approximate expression in accordance with a decrease in toner density.   7. The image forming method according to claim 6, wherein when the image quality priority mode is switched to the resource saving mode, the developing bias is changed based on a table prepared in advance according to the number of input pixels.   7. The image forming method according to claim 6, wherein when the image quality priority mode is switched to the resource saving mode, the developing bias is changed using an approximate expression according to a decrease in toner density according to the number of input pixels. Image forming method.   3. The image forming method according to claim 1, wherein the toner supply frequency is changed according to the number of input pixels after the toner density is determined to be a predetermined density in the resource saving mode. .   3. The image forming method according to claim 1, wherein the user can select whether or not to output a print in the return mode.   3. The image forming method according to claim 1, wherein, in the return mode, only a developing operation is performed without print output.   3. The image forming method according to claim 1, wherein the developing bias is controlled so that the image density is constant in the return mode.   15. The image forming method according to claim 14, wherein when the resource saving mode is switched to the return mode, the developing bias is changed based on a table prepared in advance according to an increase in toner density.   15. The image forming method according to claim 14, wherein when the resource saving mode is switched to the return mode, the developing bias is changed using an approximate expression in accordance with a decrease in toner density.   15. The image forming method according to claim 14, wherein when the resource saving mode is switched to the return mode, the developing bias is changed based on a table prepared in advance according to the number of input pixels.   15. The image forming method according to claim 14, wherein when the resource saving mode is switched to the return mode, the developing bias is changed using an approximate expression in accordance with the number of input pixels.   19. The image forming method according to claim 1, wherein a notification stamp to the user is printed out in the resource saving mode.   An image forming apparatus using the image forming method according to claim 1.

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