JP2006215403A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of improving image quality by causing a fine powder toner to be consumed. <P>SOLUTION: The image forming apparatus equipped with a developing device 4 for developing an electrostatic latent image formed on an image carrier 1 to a sensible image by a two-component toner is equipped with a control means 11 which creates a force consumption pattern over the entire width of the image carrier during exchanging of a toner bottle due to a toner end and executes the control to perform toner recovery operation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a printer, a copying machine, and a fax machine. Specifically, an electrostatic latent image formed on an image carrier such as a photoconductor is developed with a two-component developer. The present invention relates to an image forming apparatus including a developing device that forms an image.

In a conventional image forming apparatus provided with a developing device that visualizes an electrostatic latent image formed on an image carrier such as a photoconductor with a two-component developer, the toner in the developing device is a toner or a carrier by stirring. The amount of fine powder tends to increase. This fine powder toner has a high charge amount per unit mass (Q / M), and therefore has an increased adhesion to the carrier. As a result, the fine powder toner spends on the carrier and deteriorates the charging ability of the carrier.
When the charging ability of the carrier is reduced, the newly supplied toner cannot be sufficiently charged, and the amount of toner transported by the carrier is reduced, resulting in problems such as a reduction in image density and deterioration in image quality.
In order to solve such a problem, for example, in Patent Document 1, in order to prevent deterioration in image quality due to toner remaining in the developing device and deteriorated, the printing rate is calculated for each image formation, and the printing rate is calculated. In the case where is less than a predetermined printing rate, a technique has been proposed in which a pattern corresponding to the printing rate is created and toner is forcibly consumed before the next image formation.
Japanese Patent No. 3029648

However, in the above prior art, if forced consumption is performed so as to obtain a predetermined printing rate for each sheet passing, there arises a problem that the toner yield decreases. In addition, since toner is consumed from toner having a large particle size during development, if forced consumption is performed so that a predetermined printing rate is obtained for each sheet passing, the amount of toner developed at one time is small, and the particle size is increased each time. It is difficult to consume highly charged fine powder toner having a small particle size adhering to the carrier. For this reason, in order to consume the fine powder adhering to the carrier, it is necessary to develop a large amount of toner at a time without significantly reducing the toner yield.
The present invention has been made in view of such a background, and an object thereof is to provide an image forming apparatus capable of consuming fine powder toner and improving image quality.

In order to achieve the above object, the invention according to claim 1 is an image forming apparatus including a developing device that visualizes an electrostatic latent image formed on an image carrier with a two-component developer. An image forming apparatus including a control unit that creates a forced consumption pattern over the entire width of the image carrier when the toner bottle is replaced and executes a toner recovery operation is the main feature.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, an image forming apparatus using a line pattern or a halftone pattern as a forced consumption pattern is a main feature.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the control means outputs the output value detected by the toner density detecting means for detecting the toner density in the developing device to create the forced consumption pattern. However, the main feature is an image forming apparatus that performs control until a certain value is reached.

According to the present invention, the fine powder toner can be consumed by creating a forced consumption pattern when the toner bottle at the toner end is replaced, so that the image quality can be maintained. In addition, if this operation is performed at the end of a normal job, both the forced consumption pattern creation time and the replenishment time are required. However, when the operation is performed at the toner end, only the forced consumption pattern creation time is required. Therefore, it is efficient in terms of timing.
Further, when the cleaning margin is small, the image quality immediately after recovery can be kept good without causing a cleaning failure due to the forced toner consumption pattern when the toner bottle is replaced.
Furthermore, when a forced consumption pattern is created, an extreme decrease in toner density can be suppressed, so that carrier adhesion and the like can be suppressed, and image quality immediately after recovery can be kept good.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating an image forming unit of an image forming apparatus according to an embodiment of the present invention. As shown in this figure, a photoconductor drum 1 is provided as an image carrier inside the copying machine main body, and an image forming process is performed around the photoconductor drum 1 in the photoconductor drum rotation direction indicated by an arrow. A charging device 2, a developing device 4, a transfer device 5, a separation device 6, a cleaning device 7, and a charge removal device 8 are arranged for execution.
Note that an exposure light 3, which is a laser modulated by image data, is irradiated between the charging device 2 and the developing device 4 from the writing control device 12. The control unit 11 receives signals from the toner end sensor 9 and the toner density sensor 10 and controls the writing control device 12. In addition, the control operation of the present invention is governed.

The image forming operation in this embodiment will be briefly described. This image forming apparatus employs a reversal development method (N / P development method). In a state where the surface of the photosensitive drum 1 is uniformly negatively charged to about −800 V by the charging device 2, the exposure light 3 is irradiated from the writing control device 12 to the photosensitive drum 1 to correspond to an original image of about −50 V. An electrostatic latent image is formed.
The developing sleeve 4a is rotated by a developing motor (not shown), and the developer is conveyed to the site of the doctor blade 4d by the magnet 4f in the developing sleeve 4a, and after being regulated to a predetermined amount, reaches the developing area of the photosensitive drum 1. At this time, the toner in the developing device 4 is stirred with the carrier and sufficiently charged.
Then, the toner in the developer on the developing sleeve 4a uniformly regulated by the doctor blade 4d is electrostatic latent image on the photosensitive drum 1 by a developing bias of about −550 V applied from a developing bias applying device (not shown). The electrostatic latent image is visualized as a result of electrostatic attraction.
The visible image is electrostatically transferred to transfer paper conveyed from a paper supply unit (not shown) by the action of the transfer device 5, and the transfer paper is separated from the photosensitive drum 1 by the separation device 6. The transfer paper separated from the photosensitive drum 1 is sent to a fixing device (not shown), and the toner image is fixed on the transfer paper. After the image transfer is completed, the toner remaining on the surface of the photosensitive drum 1 is removed by the cleaning device 7, and the residual charge is removed by the charge removing device 8 to prepare for the next copy.

The toner density sensor 10 is disposed under the paddle wheel 4b, and converts the toner density of the developer into a unit area of the carrier, which is a magnetic material, and a passing amount per unit time into a voltage value (Vt value). The amount of toner supplied from the toner supply roller 4c is controlled by the detection information of the toner density sensor 10. The toner is gradually replenished from the toner container 4e using the toner replenishing roller 4c. The toner concentration in the developing device 4 is normally controlled to 4.0 (wt%) by the toner concentration sensor 10.
When the developing device 4 is driven for a long time and the toner is agitated with the carrier by the paddle wheel 4b or the doctor blade 4d over time, the toner is pulverized into fine powder as described above, and the fine particles in the developer The amount of powder toner increases. Further, during development, since the toner having a large particle diameter is developed, the fine toner in the developing device tends to accumulate without being consumed.
Further, since the fine toner has a high charge amount, the amount of adhesion with the carrier is strong and adheres to the surface of the carrier, which deteriorates the charging ability of the carrier. For this reason, a sufficiently charged amount cannot be given to the newly replenished toner, so that the amount of toner transported by the carrier is lowered, and the image density is lowered.
In the present invention, since the fine powder toner that has increased in the developing device 4 over time is consumed, a forced consumption pattern is created at the time of toner end toner replacement, and the toner recovery operation is stabilized by entering the toner recovery operation. The image density can be maintained.

FIG. 2 is a characteristic diagram showing changes in toner charge amount and image density over time. In addition, the change in toner charge amount and image density over time due to the difference in image area ratio is also shown. The solid line in the figure is the change over time when a document with an image area ratio of 6%, which is generally used frequently, is used. The high image area ratio is an image area ratio higher than 6%, and the low image area ratio is an image area ratio less than 6%.
According to this figure, the toner charge amount decreases and the image density also decreases at the same time as the number of sheets passed. The toner density at this time is controlled to about 4 (wt%) by the toner density sensor 10. Further, since the amount of toner that is developed at a time increases as the image area ratio increases, the amount of fine powder accumulated in the developing device 4 is reduced.
This slows down the toner charge amount and suppresses a decrease in image density to some extent. However, when the image area ratio is low, the amount of toner that is developed at one time is small, and fine powder toner accumulates. Therefore, the charge amount decreases rapidly, and the image density decreases when the number of sheets that pass is small.
For any image area ratio, the image density was 1.4 or higher when the charge amount was 30 (μC / g) at the start. However, the toner is caused by the stress due to the driving of the developing device 4 depending on the number of sheets to be passed. When the amount of fine particles increases and the charge amount drops to about 20 (μC / g), the image density decreases to 1.2. Usually, an image density of 1.2 or more is required to provide a good image.

The image forming apparatus described in Example 1 will be described. First, the toner end state is detected based on the output from the toner end sensor 9 disposed in the toner container 4e. In general, when the cumulative number of times that the toner end sensor 9 detects the absence of toner reaches a predetermined number, the control unit 11 determines that the toner in the toner storage unit 4e is in an end state.
FIG. 3 is a flowchart of toner end control. In the image forming apparatus of this embodiment, the toner end is reached after 80 times no toner is detected (S1 to S6). After the toner end, the user replaces the toner with new toner and before entering the toner recovery operation, the exposure light 3 is irradiated by a signal from the writing control unit 12 to create a solid forced toner consumption pattern over the entire width of the photosensitive drum 1.
Here, the fine toner adhering to the carrier surface and the fine toner accumulated in the developing device 4 are consumed. Thereafter, a toner recovery operation is performed to replace the toner in the developing device 4, and a normal copy operation is started. In addition, when a document having a low image area ratio of less than 6% shown in FIG. 2 is used, the number of sheets to be passed is about 20000 or more and the charge amount is 20 (μC / g) or less, but the toner ends. The number of sheets passed is about 12,000.
Since the toner amount reaches the toner end before the charge amount decreases and the image density decreases, a forced consumption pattern is created when the toner at the toner end is replaced, and the fine powder in the developing device can be removed by entering a recovery operation. Therefore, the toner charge amount is stabilized over time, and the image density can be maintained.

An image forming apparatus described in Example 2 will be described. When the contact condition between the photosensitive drum 1 and the cleaning blade of the cleaning device 7 is a narrow cleaning range, a cleaning failure may occur when the forced consumption pattern at the time of toner bottle replacement is solidly formed. is there. When a cleaning failure occurs, the residual toner on the photosensitive drum 1 is transferred and the background becomes dirty.
In the present embodiment, the forced consumption pattern is a line image or a halftone to suppress poor cleaning, and a good image can be provided without causing background stain even during normal copying after recovery.

An image forming apparatus described in Example 3 will be described. If the time for creating the forced consumption pattern is lengthened and the toner density is extremely reduced to about 1.0 wt% or less, carrier adhesion or the like may occur on the photosensitive drum 1. If the carrier adheres, the photosensitive drum 1 may be damaged and an abnormal image may be formed.
Therefore, the output value (Vt value) from the toner density sensor 10 in the developing device 4 is detected during the forced consumption pattern creation, and the forced consumption is performed by the signal from the control unit 11 as soon as the detected output value reaches a certain value. Control to end the pattern. Further, since carrier adhesion does not occur at a toner concentration of 2.0 wt%, control is performed based on the toner concentration sensor output value at this time.
FIG. 4 is a characteristic diagram showing the relationship between the toner density of the toner density sensor and the output value. According to FIG. 4, when the toner concentration is 2 wt%, the Vt value is 4.5 V, and the forced consumption pattern is terminated as soon as this V reaches 4.5 V.
A flowchart of this control is shown in FIG. The toner bottle is replaced at the toner end (S1) (S2), and the forced toner consumption operation is turned on (S3). When the Vt value becomes 4.5V or more (S4), the forced consumption pattern is terminated (S5), and the recovery operation is performed (S6).
By controlling in this way, it is possible to reliably prevent carrier adhesion during forced consumption, so that a good image can be provided during normal copying after recovery.

1 is a schematic diagram illustrating an image forming unit of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a characteristic diagram showing a change in toner charge amount and image density with time. 7 is a flowchart of toner end detection control. FIG. 6 is a characteristic diagram illustrating a relationship between a toner density of a toner density sensor and an output value. 6 is a flowchart illustrating an operation from a toner end to a recovery operation.

Explanation of symbols

1 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 2 Charging device 3 Exposure light 4 Developing device 5 Transfer device 6 Separating device 7 Cleaning device 8 Neutralizing device 9 Toner end sensor 10 Toner concentration sensor (toner concentration detecting means)
11 Control unit (control means)
12 Write controller

Claims (3)

  In an image forming apparatus equipped with a developing device that visualizes an electrostatic latent image formed on an image carrier with a two-component developer, a forced consumption pattern is created over the entire width of the image carrier when a toner bottle is replaced by a toner end. And an image forming apparatus comprising control means for executing control for performing a toner recovery operation.   2. The image forming apparatus according to claim 1, wherein a line pattern or a halftone pattern is used as the forced consumption pattern.   2. The image forming apparatus according to claim 1, wherein the control means generates the forced consumption pattern, and an output value detected by a toner density detecting means for detecting a toner density in the developing device becomes a certain value. An image forming apparatus that performs control up to

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