JP2003195607A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus capable of preventing the electrification rise of developer on each developer carrier 5a to 5d while timely performing a refreshing process, and capable of preventing the occurrence of a defective image such as an image of reduced image density and a fogged image. <P>SOLUTION: The refreshing processes for several developer carriers 5a to 5d are simultaneously performed, and the apparatus is controlled so that the refreshing process may be performed for such the developer carriers 5a to 5d that the average printing density on the image corresponding to the developer carriers 5a to 5d becomes below a prescribed value. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly, to a refreshing step of carrying toner on a developer carrier to the electrostatic latent image carrier side to refresh the developer on the developer carrier. The present invention relates to a color image forming apparatus to be implemented.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, when an image is repeatedly formed, particularly when an original document printing rate on the image is low, the image forming apparatus jumps from a developer carrying member to an electrostatic latent image portion (photosensitive drum). Since the amount of toner is small, the toner particles in the developing device are less likely to be replaced, and the developer is excessively charged, resulting in a decrease in image density and fog.

Conventionally, the surface shape, materials, or external additives of the toner have been optimized so as to stabilize the charge controllability of the toner. Such a phenomenon was likely to occur.

Therefore, as disclosed in Japanese Unexamined Patent Publication No. 2000-310909, when the printing rate is low, that is, when the number of printing dots is small in one image, the toner in the developer carrying portion is removed after the image formation. It has been proposed to provide a refreshing step of refreshing the developer on the surface of the developer carrying portion by applying an electric field to the developer carrying portion so as to consume it, thereby preventing image deterioration.

[0005]

However, the conventional image forming apparatus is only related to the refresh process for the monochrome (one color) image forming apparatus, and not to the color image forming apparatus having a plurality of developing devices. There wasn't.

An apparatus having a plurality of developing devices, such as a color image forming apparatus, needs to be considered from a case of a high printing rate such as a photograph or a graphic image to a case of a low printing rate such as only a logo mark. Yes (for example, the case where only the company logo mark is inserted into a conventional monochrome image), and there are many variations in the printing rate among the developing devices.
Therefore, in the color image forming apparatus, the level and frequency of the refreshing process vary for each developing device, but unless the processes are unified and controlled, the time other than printing becomes long and the productivity decreases. There is a problem that it will end up.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is directed to a developer carrying member that conveys a developer containing toner to a developing area while facing the electrostatic latent image carrying member. In a color image forming apparatus, wherein a plurality of color image forming apparatuses are provided, the toner on the developer carrying member is conveyed to the electrostatic latent image carrying member side to refresh the surface of the developer carrying member during non-image formation. The refreshing process is controlled so that the refreshing step is performed on the developer carrying body whose average print density on the image corresponding to the developer carrying body is lower than a predetermined value, and the refreshing process for the two or more developer carrying bodies is performed. This is a color image forming apparatus that is controlled so as to perform the operations simultaneously.

In addition, the refresh process of the present invention is colored.
A description will be given of a two-component developing device suitably used in an image forming apparatus. A step of forcibly causing the toner in the developer carried on the surface of the developer carrying body to fly to the electrostatic latent image carrying body during non-image formation. Is. When a developing device of the type in which the developer on the developer carrier is collected in the developing tank during non-image formation, the developer must be transported on the developer carrier. By this refreshing step, the toner in the developer is consumed by a predetermined amount and a new toner is replenished, the average charge amount of the toner in the developer is lowered, and the toner is jetted to the surface of the electrostatic latent image bearing member. The toner can be cleaned by a cleaning means provided around the electrostatic latent image carrier, and if a refreshing process is appropriately performed, the charging property of the developer does not change even after long-term use, and the image density is reduced. Image defects such as fogging can be solved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining the outline of the color image forming apparatus of the present invention. Reference numeral 1 is a color image forming apparatus. 2 is a photoconductor drum, which is OPC or a-Si
A photoconductor is used. A charging roller 3 is configured so that a predetermined bias voltage can be applied to the surface of the photosensitive drum 2 from a power source (not shown). An exposure unit 4 forms a latent image by irradiating image information from an external terminal on the charged surface of the photosensitive drum 2 with a laser beam. In this case, L
ED light may be used.

A developing device 5 develops color toner on the formed latent image. The developing device 5a develops yellow from the upstream side in the rotation direction of the photoconductor 2, the developing device 5b develops magenta, and the cyan develops. A developing device 5c and a developing device 5d for developing black are arranged. In each developing device 5, a toner container 50a containing yellow toner and a developing container 51a for developing the toner replenished by a replenishing roller 52a.
However, a toner container 50 containing magenta toner is also provided.
b, a developing container 51b for developing the toner replenished by the replenishing roller 52b, a toner container 50c containing cyan toner and a developing container 51c for developing the toner replenishing by the replenishing roller 52c, further containing black toner. A toner container 50d and a developing container 51d for developing the toner replenished by the replenishing roller 52d are disposed above the color image forming apparatus. A magnetic toner is used as the black toner of the present invention, and a non-magnetic toner is used as the other color toners. Reference numeral 31 is a cleaning unit, which removes untransferred toner from the photosensitive drum 2 which will be described below.

Reference numeral 6 denotes an intermediate transfer drum, which repeats the operation of temporarily transferring the toner developed on the photosensitive drum 2 by applying a predetermined bias for each toner, thereby performing color superposition. 6a is a secondary transfer roller, 6b
Is a cleaning roller. Although not shown, the secondary transfer roller 6a and the cleaning roller 6b are provided with a retracting mechanism that retracts the intermediate transfer drum 6 until the colors are completely overlapped.

A paper feeding unit 7 is arranged below the color image forming apparatus 1 and is loaded with a large amount of paper. The paper feeding unit 70 conveys the uppermost paper by a paper feeding roller 70.
a, and a manual feed section b for transporting sheets one by one.
The sheet fed from the sheet feeding means 7 is a registration roller 60.
The toner is conveyed to the secondary transfer roller 6a at the timing of the color-superposed toners on the intermediate transfer drum 6 after the front ends are aligned and timed. After the transfer, the sheet is conveyed by the conveying belt 8 toward the exit side. A fixing unit 9 is arranged near the exit side and fixes the secondarily transferred toner on the sheet by heat and pressure.

Numeral 10 is a paper discharge means, which is a face-up tray 10a for discharging the heat-fixed paper by the fixing means 9 with the print side up and a face-down tray 10b for discharging the print side down. Are arranged.

The specific operation of the color image forming apparatus shown in FIG. 1 will be described. The photosensitive surface of the photosensitive drum 2 is charged by the charging roller 3 and the charged photosensitive drum 2 is charged.
On the photosensitive surface of, the surface charge is exposed by the exposure means 4 based on image information to form an electrostatic latent image.

The electrostatic latent image on the photosensitive drum 2 is, for example, magenta (red), yellow (yellow), cyan (blue) color toner, and black (black) toner by four developing devices 5a to 5d. Are sequentially developed using. Then, every time this development is performed, the toner image is primary-transferred in order on the surface of the intermediate transfer drum 6 which rotates in contact with the photosensitive drum 2,
Finally, the color toner images of four colors are multi-transferred onto the intermediate transfer drum 6.

An intermediate transfer drum 6 onto which a color toner image has been multi-transferred from the photosensitive drum 2, and a secondary transfer roller 6a.
The sheet that is sandwiched between the sheet and the sheet is fed by the secondary transfer roller 6a, which causes the sheet to be charged.
The multiple color toner images are secondarily transferred.

The sheet on which the color toner image has been secondarily transferred passes between the secondary transfer roller 6a and the intermediate transfer drum 6, and is then conveyed leftward in the figure by the conveyor belt 8.
It is fixed as a full-color image by the fixing means 9.

Next, the refreshing process using the developing device 5a will be described. At the time of image formation, the charging roller 3 uniformly charges the photosensitive drum 2 to about +400 [V], and the exposing unit 4 forms an electrostatic latent image on the photosensitive drum 2. At this time, the surface potential of the photoconductor after exposure is about +
It is 10 [V]. Photoconductor drum 2 and developing device sleeve 5
An alternating electric field (Vdc = 160 [V], Vp
p = 1.0 [kV] and f = 3.6 [kHz]) to develop a toner image on the exposed portion of the photosensitive drum 2. The developed toner image on the photosensitive drum 2 is transferred to the intermediate transfer drum 6 with a potential difference of about −100 to −800 [V], and transferred onto the paper by the secondary transfer roller 6a. At this time, a negative high-voltage bias is applied to the secondary transfer roller 6a, although it depends on the environment, the type of recording medium, the resistance, and the like. The toner in the developer is positively charged toner, and the average particle size of the toner is 5.0 to 8.0 [μm].
And Further, the developer can have a two-component constitution,
The average particle size of the carrier used here is 30 to 90 [μ
m]. Here, after the image from the developing device 5a is transferred to the intermediate transfer member 6, the image from the developing device 5b is transferred to the intermediate transfer drum 6, and similarly, after being repeatedly transferred to the intermediate transfer drum 6 with the developing devices 5c and 5d. It is also possible to form a four-color image by transferring it onto a sheet.

In such a color image forming apparatus,
The image data is measured as the number of dots by a CPU (not shown) in the main body, the print density an on the image is measured, and the print densities a1, a2, a for each surface of the measured paper are measured.
3 ,. ． ． , An average print density A of less than 3 [%], the image formation is stopped, the non-image forming state is set, and the toner in the developer on the developing sleeve 53a is developed on the photosensitive drum 2 side. Developing sleeve 53 so that
An electric field is applied to a. In this embodiment, the case where the image formation is immediately stopped has been described. However, when the continuous printing is in progress, the image forming may be performed after the continuous printing is completed. The print rate is A4 for paper of A4 size or smaller.
If the size of the paper is larger than A4 size, the size is converted into the maximum size of paper that can be printed by the image forming apparatus. This is because it is converted into a time obtained by multiplying the length of the developer carrying area on the developing sleeve 53a perpendicular to the sheet conveying direction by the time required for image formation. It may be calculated for each paper size for the sake of accuracy, but since the process becomes complicated, the development time is the development time required to print the A4 size or the maximum paper size. Further, since the developing device 5 of the color image forming apparatus of this embodiment is configured to collect the developer on the developing sleeve 53a into the developing tank during non-image formation, the developer on the developing sleeve 53a during the refreshing process. Needs to be supplied.

The electric field applied to the developing sleeve 53a is a DC voltage on which AC components of a rectangular wave, a triangular wave, and a sine wave are superimposed. The image print density is calculated for each print, the average print ratio of a certain fixed number (for example, 1 to 500) is calculated, and when the image is not formed on the photosensitive drum 2 according to the print density (non-image). Developing sleeve 5)
The toner in the developer is developed from 3a to consume the toner. The toner adhering to the photosensitive drum 2 in the refreshing step is cooled (cleaned) by the cleaning means 31 as the photosensitive drum 2 rotates.
At this time, since the DC bias voltage having the same polarity as the toner is applied to the intermediate transfer drum 6, the toner does not adhere to the intermediate transfer drum 6. When this voltage is not applied, the toner is transferred to the intermediate transfer drum 6, but after the DC bias voltage having the same polarity as the toner is applied to the secondary transfer roller 6a or retracted, the toner of the intermediate transfer drum 6 is removed. The toner does not remain attached by being cleaned by the cleaning roller 6b.

As described above, in the refreshing step, after the average printing rate is calculated, the toner consumption is performed when the photosensitive drum 1 which is the electrostatic latent image carrier and the developing sleeve 53a which is the developer carrier are in the driving state. The alternating bias is controlled so that It has been experimentally confirmed that the toner charge-up easily occurs when the average printing rate is 3% or less. Further, when the average printing rate becomes low, the amount of toner with an excessive amount of charge increases, and the bias application time for returning the charge of the toner with an excessive amount of charge to normal is lengthened and toner is transferred to the photosensitive drum. It is necessary to increase the amount of development. Therefore, the toner consumption amount in the non-image part is set to correspond to the minimum 3% document printing, but by setting several refresh modes, the setting is made so that the situation (usage environment, etc.) can be dealt with. Is desirable. Further, in the refreshing process, the refreshing electric field is increased by increasing the effective value from the electric field at the time of image formation,
The toner can be easily consumed. Next, the operation of the present embodiment will be described using the flowchart shown in FIG. At the first stage when the user uses the color image forming apparatus 1, the page counting means of the recording medium of the control device (not shown) is reset (step 1), and the dot number of one page and the printing rate of the image pattern are changed every image formation. The average printing rate is calculated and stored together with the accumulation (step 2).

Even when the predetermined number of pages (64) is reached (step 3), the process returns to step 50 until the average print ratio A becomes A <3% (step 4), and the page number is reset.
The printing rate and the average printing rate in step 2 are continuously updated. Again, page counts 64 (step 3)
Then, when the average printing rate A becomes A <3% (step 4),
The breakdown of the average printing rate is A <0.5% (step 5), A <1% (step 7), A <2% (step 9), or A <3% ( It is determined whether or not step 11), and if A <0.5%, the bias is applied for 3.6 sec (step 6), and if A <1%, the bias is 1.8 sec. Applied for 8 seconds (step 8) and the bias is 1.2 when A <2%.
The voltage is applied for sec (step 10), and when A <3%, the bias is applied for 0.6 sec (step 12).

Next, the operation of this embodiment will be described with reference to the flowchart shown in FIG. At the first stage when the user uses the color image forming apparatus 1, the page counting means of the recording medium of the control device (not shown) is reset (step 21), and the dot number of one page and the printing rate of the image pattern are changed every image formation. The average printing rate is calculated and stored together with the accumulation (step 22).

Even if the predetermined number of pages (64) is reached (step 23), the process returns to step 50 (step 24) until the average print ratio A becomes A <3%, and the number of pages is reset. The printing rate and the average printing rate in step 12 are continuously updated. Again, when the page counts 64 (step 23) and the average printing rate A becomes A <3% (step 24), the breakdown of the average printing rate is A <0.5% (step 25), Whether A <1% (step 27),
It is determined whether A <2% (step 29) or A <3% (step 31). If A <0.5%, a bias of 200 V (DC component V _DC is 200 V) is applied. It is applied for 2 seconds (step 26), when A <1%, a bias of 150 V is applied for 2 seconds (step 28), and when A <2%, a bias of 100 V is applied for 2 seconds. (Step 30), A
When <3%, a bias of 50 V is applied for 2 seconds (step 32).

Although the above steps have been described for one developing device 5a, the same work is performed for the other developing devices 5b-5d. Here, the refreshing process is sequentially performed on the plurality of developing devices 5a to 5d at the same time.
The determination of this timing may be performed by moving up the average printing rate of another developing device when a certain number of developing devices 5a to 5d reaches a predetermined number, or vice versa, but when mixing color printing with monochrome printing For the above, the former calculation method is desirable.

The present invention is provided with a developing sleeve 53a which faces the photoconductor drum 2 and conveys the developer to the developing area, so that the toner image on the photoconductor drum 2 is transferred onto the paper when it is not transferred. It is characterized in that the toner on the developing sleeve 53a is refreshed after finishing, immediately before the next printing, or when the power is turned on.

Then, when the average print density on the image corresponding to the developing sleeve of each of the developing devices 5a to 5d is lower than a predetermined value, the refreshing process is performed only in the corresponding developing device.

Even when the print density on the image is smaller than the predetermined value, the print density is averaged by continuing the printing. It is desirable to take the AND of, that is, refer to the average print density. Therefore, an average print density processing means for counting the print density corresponding to the image pattern on the image and calculating the average value is provided, and the refreshing process is performed when the average print density is below a predetermined value. Further, when the average print density is lower than a predetermined value, the refresh process time is controlled to be variable as shown in FIG. 2 or the developing bias is varied as shown in FIG. 3 according to the average print density. It is preferable to control as follows.

Then, the refreshing step is carried out after the image formation on one recording medium is completed, or
After the set number of images have been formed, a predetermined number (for example,
It is possible to do this every 64 sheets, 100 sheets, etc.,
In the color image forming apparatus 1 having many structures such as the plurality of developing devices 5a to 5d or the intermediate transfer drum 6, the number of steps is long, and the operation time of the apparatus is too long, resulting in poor usability. Because it becomes too much
The frequency may be reduced for each predetermined number of sheets.

Further, the refreshing process of each of the plurality of developing devices 5a to 5d is performed at the same time.
This is because the usability becomes too poor and the refreshing process time frequently occurs. For this purpose, it is advisable to arrange a predetermined number of sheets for each of the developing devices 5a to 5d, or to arrange the refreshing process of another developing device with respect to one developing device as a reference. The timing for performing the refreshing process is
It does not matter just before printing, immediately after printing, or immediately after turning on the power.

Further, a sensor device for measuring temperature and humidity is provided in the developing device, and when the temperature and humidity are below a predetermined value, or the average print density is below a predetermined value and the temperature and humidity are below a predetermined value. The refreshing step may be performed when the temperature is below the range. This is because excessive charging tends to occur especially at low humidity.

In addition, depending on the situation, the refresh process
It may be manually performed by using a command from the front panel or a computer, or the bias application time and the bias value during the refreshing process of the developing devices 5a to 5d may be variable. Further, the developing devices 5a to 5d
It is also an effective means to change the reference average print density for each time and to set the presence or absence of control.

The predetermined value of the average print density is preferably 3%. This is because, as shown in FIG. 4, the image density after printing endurance evaluation is low when the printing rate is lower than 3%.

Further, during the refreshing step, it is effective to turn off the potential of the photosensitive drum 1 and simplify the exposure without exposing it, for the sake of simplicity. This is because when a plurality of developing devices 5a to 5d are provided, the potentials and the exposure settings are often different depending on each developing device, and it is effective to omit this process and perform the refreshing process only with the developing bias. This is because.

The page count of zero in the present embodiment may be considered in the unit of operation time of the developing device. In the case of A4 size, it is converted to 1 page as it is, and when it is smaller than A4 size, it is converted to 1 page of A4 size as it is. , If the size is larger than the A4 size, the A4 size may be counted as two pages. Further, in this embodiment, the one-component developer has been described, but the same effect can be obtained even with a two-component developer. Then, in the case of a color image forming apparatus using the two-component developer and having the configuration as in the present invention, the developing sleeve comes out from the developing sleeve to the photosensitive drum (the toner is attached to the carrier), and the image forming process is not performed. The developer on the developing sleeve of the developing device is to be collected in the developing device, and in the case of the tandem type color image forming apparatus, it is in a state that it is always exposed. Further, the refreshing step using a two-component developer means refreshing the developer.

[0036]

Embodiment (First Embodiment) First, an embodiment will be described with respect to one developing device 5a.

In this example, the average print density (print ratio) A was calculated for every 64 sheets. Based on this printing rate, a refreshing step was performed after the 64th sheet was output. In order to consume the toner by developing the toner from the developing sleeve 53a in a state where the image is not formed on the photoconductor drum 2 (at the time of non-image formation), it is assumed that the photoconductor drum 2 is not charged and the printing rate is changed. A bias was applied so that the toner amount could be consumed. The bias condition is “Vdc = 160 [V],
Vpp = 1.0 [kV] and f = 3.6 [kHz] ”, and in order to prevent toner from adhering to the secondary transfer roller 6a when a bias is applied, the secondary transfer roller 6a has a high positive voltage. Apply a bias. The linear velocity of the photosensitive drum 1 in this embodiment was set to 134 [mm / sec]. The alternating bias application time corresponding to each printing rate was set so that the thin printing on the photosensitive drum 1 did not occur. FIG. 5 shows set values in this embodiment. In the figure, the toner consumption amount and the alternating bias application time during the refreshing process for each printing rate are shown.

Data experimentally conducted under the above conditions were plotted with the image density ID as the vertical axis and the number of prints as the horizontal axis.
FIG. 6 shows the transition of the image density at each print rate density. When the black standard is set to Macbeth density of 1.4, according to FIG. 4, it can be confirmed that the image density after printing endurance is low when the printing rate is lower than 3%. According to FIG. 6, since the toner is consumed by applying the bias at the time of non-image formation based on the printing rate, it was confirmed that the good image density is maintained even after the printing endurance. Second Embodiment Next, another embodiment will be described for one developing device 5a.

Based on the first embodiment, the developing bias application value corresponding to each printing rate was set. FIG. 7 shows set values in this embodiment. In the figure, the toner consumption amount and the developing bias application value at the time of the refreshing process for each printing rate are shown. Even in this case, the same results as in FIG. 6 were obtained, and it was confirmed that the good image density was maintained even after printing was completed. (Third Embodiment) The same setting as in the first or second embodiment is applied to a color image forming apparatus having four developing devices. The developing device A had a printing rate of 4%, B was 1.5%, C was 1.0%, and D was 0.5%. This is the printing rate (A is black, B, C, D when it is assumed that a table or text is printed for business use without using graphic images such as photographs.
Is a color developing device).

Also in this case, it was confirmed that the image density of each developing device was maintained by applying the refreshing process set according to the print density to each developing device. In this way, the characteristics of each developing device can be kept constant even if the printing density differs depending on the developing device. It can be said that this is a particularly effective means when a stable image is required while having a complicated structure such as a color machine.

[0041]

As described above, according to the color image forming apparatus of the present invention, the refresh process is performed at the same time for each of a plurality of developer carriers, and the image corresponding to the developer carrier is formed. By controlling so that the refresh process is performed on the developer carrier whose average print density is lower than the specified value, the charge on the developer on each developer carrier is prevented from rising while the refresh process is performed in a timely manner, and the image density is reduced. It is possible to provide a color image forming apparatus that solves image defects such as fogging and fog.

[Brief description of drawings]

FIG. 1 is a diagram showing a color image forming apparatus of the present invention.

FIG. 2 is a flowchart showing a refresh process of the present invention.

FIG. 3 is a flowchart showing another refresh process of the present invention.

FIG. 4 is a diagram showing a relationship between print density and image density.

FIG. 5 is a table showing the first condition of the refresh process of the present invention.

FIG. 6 is a diagram showing a relationship between print density and image density performed under the first condition.

FIG. 7 is a table showing a second condition of the refresh process of the present invention.

[Explanation of symbols]

1: Color image forming apparatus 2: Photoconductor drum 3: With charging roller 4: exposure means 5, 5a to 5d: developing device 53a: developing sleeve 6: Intermediate transfer drum 6a: Secondary transfer roller 6b: Cleaning roller 7: Paper feeding means 8: Conveyor belt 9: Fixing means 10: Paper discharging means

Claims (7)

[Claims] 1. A plurality of developer carrying members for carrying a developer containing toner to a developing area are provided facing the electrostatic latent image carrying member.
In a color image forming apparatus, which carries out a refreshing step of refreshing the surface of the developer carrying body by conveying the toner on the developer carrying body to the electrostatic latent image carrying body side during non-image formation, the developer carrying body Is controlled such that the refreshing step is performed on the developer carrying member whose average print density on the image is below a predetermined value, and the refreshing step is performed on two or more developer carrying members at the same time. A color image forming apparatus that is controlled as described above. 2. The front panel or a command from a computer can change or set the predetermined value, which is a reference for the judgment of the refreshing process, for each developer carrier. The color image forming apparatus according to claim 1. 3. The color image forming apparatus according to claim 1, wherein the refreshing step can be appropriately performed for each developer carrier by a command from the front panel or a computer. 4. The color image forming apparatus according to claim 1, wherein the refreshing step is performed without applying a surface potential on the electrostatic latent image carrier. 5. The color image forming apparatus according to claim 1, wherein in the refreshing step, a bias voltage application condition applied to the developer carrying member is changed according to the value of the average print density. 6. A temperature / humidity measuring means for measuring the temperature and humidity in a color image device is provided, and when the temperature / humidity measuring means detects a temperature or humidity lower than a predetermined value, a refreshing process is performed. 6. The color image forming apparatus according to claim 1, wherein a bias voltage application condition applied to the developer carrying member is changed from a default value. 7. The average print density is converted to A4 when the paper size to be printed is A4 or smaller, and to the maximum printable paper size when the paper size is A4 or larger.
The described color image forming apparatus.