JPH07325468A - Developing device and image forming device using the same - Google Patents

Abstract

PURPOSE:To simply obtain high image quality by using a two-component developer and further, to reproduce a stable image by making influence by changes in environment and the history of application extremely little. CONSTITUTION:In this developing device provided with a developer carrier 4 to which a developing bias VB on which an alternating current component VAC is superimposed is applied and making a latent image on a latent image carrier 1 visualizable with the two-component developer G carried on the developer carrier 4, a frequency varying means 6 changing the frequency of the alternating current component VAC is provided on developing bias power supply 5. Moreover, an image forming device using the developing device is constituted to provide or combine a frequency input adjusting means 8 adjusting the frequency of the frequency varying means 6 based on input image information IIN by a latent image forming means 2, a frequency environment adjusting means 10 adjusting the frequency of the frequency varying means 6 based on the use environment information IEN of the developing device 3 and a frequency output adjusting means 12 adjusting the frequency of the frequency varying means 6 based on output image information IOUT by the developing device 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing a latent image formed by an electrophotographic method or an electrostatic recording method with a two-component developer carried on a developer carrier, and more particularly to a developing device. The present invention relates to a developing bias type developing device in which a developing bias in which an AC bias is superposed on a developer carrier is applied, and an image forming apparatus using the developing device.

[0002]

2. Description of the Related Art A developing device for developing a latent image by electrophotography or the like has recently become a part of not only a copying device but also a device such as a computer for forming a digitized image. Various types of developing devices are provided for this type of developing device. For example, by using a two-component developer, a developing bias in which an AC voltage is superposed between the developer carrier and the latent image carrier is used. It is disclosed that the applied type can supply more toner to the latent image on the latent image carrier and has the advantage of increasing the image density, as compared with the type to which the developing bias of only the DC voltage is applied. (For example, JP-A-62-28958).

Further, in the developing device disclosed in Japanese Patent Laid-Open No. 5-119592, toner of 7 to 11 μm is used.
It is disclosed that by using a developing bias on which a high-frequency alternating voltage of 000 to 16,000 Hz is superimposed, it is possible to obtain an image that is faithful to the original and has a high image quality and excellent graininess. Regarding the frequency component of the AC voltage of the developing bias, for example, 2,000 to 4,000
A high resolution image can be obtained with an alternating voltage of Hz (Japanese Patent Laid-Open No. 63-
123069), and 1,000 to 5,000H
There is one in which the effect of preventing fog in the non-image area can be obtained by an AC voltage of z (Japanese Patent Laid-Open No. 61-83564).

Further, Japanese Patent Laid-Open No. 63-113568 discloses a multicolor image forming apparatus in which an image processing unit is devised so that the input image density and the output image density can be matched. .

[0005]

By the way, in order to obtain a high quality image faithful to the original and to maintain the high quality for a long period of time, it is stable from the low density part to the high density part of the image. It is necessary to maintain the above gradation.

Under the demand of this kind, in the conventional developing apparatus, it was possible to change the gradation by changing the DC voltage component of the developing bias. However, if this change is made, Since the potential difference between the image portion on the latent image bearing member and the developer bearing member changes, not only the image density of the solid portion (surface image portion) fluctuates, but also the non-image on the latent image bearing member changes. There has been seen a technical problem that when the potential difference between the image portion and the developing carrier becomes large, the carrier adheres to the non-image portion of the latent image carrier, which causes a carryover phenomenon.

In order to solve such a technical problem, the latent image potential on the latent image bearing member may be adjusted so that the image density of the solid portion does not change. There are many parameters that need to be changed to adjust the latent image potential, such as adjustment of the potential on the carrier, change of exposure dose, and change of the direct current component of the development bias. Controlling the image potential becomes troublesome.

Further, in an image forming apparatus for visualizing a digital latent image, since data processing (digitization) is performed by a computer for conversion from multi-tone input data to output data, gradation expression is stepwise. Every step will occur. For this reason, all the gradation data must be stored in order to match the step-by-step shifts between all the input image densities (input gradation data) and the output image densities (output gradation data). As a result, the image processing unit becomes complicated. Further, even if the shift of each gradation data for each step is controlled, an area that cannot be controlled sufficiently will be generated depending on the size of the step. This area is conspicuous in the low-density area, and the output image has a gradation step, resulting in the appearance of contours along the same density (hereinafter referred to as pseudo contours), which is a cause of impairing image quality. Become.

Further, the required gradation may differ depending on the type of image to be output. For example, in the case of character information, it is desirable that the character portion and the background portion have a high resolution and a high contrast. On the other hand, in the case of a natural image (halftone image) such as a photograph, it is necessary to have a smooth gradation so that there is no difference in gradation. In particular, when the image data contains noise, if the noise is amplified, the outline of the character information may be blurred or the character may not be recognized. On the other hand, in the case of a natural image, a gradation step may occur. is there. Therefore, there has been a demand to optimize the gradation according to the type of image to be output.

Further, due to changes in the environment around the developing device, such as changes in external temperature and humidity, and long-term use and standing for a long time, the used developer and latent image carrier are deteriorated. It was also found that there is a technical problem in that not only the image density but also the gradation changes due to the change in the charging state and the charging state of the latent image carrier.

The present invention has been made in order to solve the above technical problems, and by using a two-component developer, it is possible to easily obtain high-quality image quality equal to or higher than that of printing or photography. Further, the present invention provides a developing device capable of realizing stable image reproduction with less influence of environmental changes and usage history, and an image forming apparatus using the developing device.

[0012]

That is, a developing device according to the present invention has a developer carrier 4 to which a developing bias VB superposed with an AC component VAC is applied, as shown in FIG.
In the developing device which visualizes the latent image on the latent image carrier 1 with the two-component developer G carried on the developer carrier 4, the frequency of the AC component VAC changes in the developing bias power source 5. It is characterized in that the frequency changing means 6 is provided.

In such a technical means, the two-component developer G may be brought into sliding contact with the surface of the latent image carrier 1 or the non-contact jean pink development may be carried out. Further, the average particle diameter of the toner of the two-component developer G and the frequency of the AC component VAC of the developing bias CB may be appropriately selected according to various developing parameters and types of the developer, but the appearance is rough. From the viewpoint of obtaining an image with no graininess and good graininess, the toner of the two-component developer G having at least an average particle diameter of 8 μm or less is used, and the frequency changing means 6 uses the developing bias V.
The frequency f of the AC component VAC of B is 6,000 ≦ f ≦ 20,
It is preferable to set it in the range of 000 (Hz). The average particle diameter of the toner here means a volume average particle diameter.
Further, the circumferential waveform of the AC component VAC is effectively a sine wave, a rectangular wave, a sawtooth wave, etc., and is not limited to a special waveform.

Further, the frequency varying means 6 may be a switch or the like which can manually variably set the frequency f of the AC component VAC, or the frequency of the AC component VAC in association with various detection information described later. The variable f may be automatically variably set, or the manual mode or the automatic mode may be appropriately switched.

Further, in the invention relating to the image forming apparatus using the developing device according to the present invention, as shown in FIG. 1, a latent image carrier 1 and an electrostatic latent image are formed on the latent image carrier 1. Latent image forming means 2 and developing bias VB superposed with AC component VAC
A developing device 3 having a developer carrier 4 to which is applied, and a latent image on the latent image carrier 1 is visualized by a two-component developer G carried on the developer carrier 4. In the image forming apparatus including the above, the developing bias power source 5 of the developing device 3 is provided with frequency changing means 6 for changing the frequency of the AC component VAC, and the input image information IIN by the latent image forming means 2 is detected as an input image. In addition to providing the information detecting means 7, a frequency input adjusting means 8 for adjusting the frequency of the frequency changing means 6 based on the detected and input image information IIN is provided.

In the present invention, the input image information IIN
Examples of the information include information about the density level of the input image (for example, the input image density), information indicating the type of the input image (for example, text, photo mode (including the case where there are a plurality of modes), or The corresponding line screen number) is used. As the input image information detecting means 7, for example, a means for detecting the input image density for one page or a means for detecting the state of the selection switch in the character mode or the photo mode is used.

Another image forming apparatus invention using the developing device according to the present invention, as shown in FIG. 1, has the same latent image carrier 1, latent image forming means 2 and developing device 3 as described above.
In the image forming apparatus including the above, the developing bias power source 5 of the developing device 3 is provided with a frequency changing means 6 for changing the frequency of the AC component VAC, and the use environment information IEN of the developing device 3
With the use environment information detecting means 9 for detecting
It is characterized in that a frequency environment adjusting means 10 for adjusting the frequency of the frequency changing means 6 is provided based on the detected use environment information IEN.

In the present invention, as the use environment information IEN, the environment information of the developing device 3 (for example, temperature, humidity, etc.) and the use history information of the developing device 3 (the number of times of development, the toner and the charging of the latent image carrier 1) are used. Characteristics change, etc.) is used. The use environment information detecting means 9 is, for example, a sensor that detects temperature or humidity, or a counter that counts the number of times of development or the number of times of image formation equivalent thereto, or toner or latent toner. A device or the like that detects the charging potential of the image carrier is used.

Still another image forming apparatus invention using the developing device according to the present invention, as shown in FIG. 1, has the same latent image carrier 1, latent image forming means 2 and developing device as described above. In the image forming apparatus provided with 3, the developing bias power source 5 of the developing device 3 is provided with frequency changing means 6 for changing the frequency of the AC component VAC, and the output image information IOUT by the developing device 3 is detected. The detection means 11 is provided, and the frequency output adjusting means 12 for adjusting the frequency of the frequency changing means 6 based on the detected output image information IOUT is provided.

In the present invention, information indicating the density level of the actual output image (for example, output density information) is used as the output image information IOUT, and the output image information detecting means 11 outputs the output image. Sensors that detect the concentration are used.

Further, these device inventions may be combined appropriately. As shown in FIG. 1, the invention of this type of image forming apparatus is an image forming apparatus including a latent image carrier 1, a latent image forming means 2 and a developing device 3 which are similar to those described above. The developing bias power source 5 is provided with frequency changing means 6 for changing the frequency of the AC component VAC, and the frequency input adjusting means 8, for adjusting the frequency of the frequency changing means 6 based on the input image information IIN by the latent image forming means 2, Frequency environment adjusting means 10 for adjusting the frequency of the frequency changing means 6 based on the use environment information IEN of the developing device 3.
And at least two frequency output adjusting means 12 for adjusting the frequency of the frequency changing means 6 based on the output image information IOUT from the developing device 3.

In this case, the degree of frequency variation for each information may be optimized based on an experiment or the like, and weighting is preferably performed in consideration of the degree of influence on each information. .

[0023]

According to the developing device as described above, the frequency changing means 6 changes the frequency of the AC component VAC of the developing bias power source 5. At this time, if the frequency of the AC component VBC is changed as appropriate, the density level (gradation) of the output image changes accordingly. Therefore, the relationship between the frequency of the AC component VAC and the gradation of the output image is changed in advance. If so, the gradation of the output image can be easily controlled by adjusting the frequency of the AC component VAC without particularly storing the gradation data in advance. Therefore, for example, in a situation where a pseudo contour is generated in a low density portion, by appropriately adjusting the frequency of the AC component VAC of the developing bias, it is possible to realize a smooth gradation property that is faithful to the original and does not cause a jump, Therefore, it becomes possible to obtain a good image without pseudo contours.

When the density level of the output image is predicted or detected in advance by various information, the AC component V of the developing bias power source 5 is calculated based on the predicted or detected information.
The AC frequency is adjusted as appropriate to adjust the density level of the output image to the optimum one. In this case, as a means for predicting or detecting the density level of the output image in advance with various information, for example, the frequency input adjusting means 8 predicts the density level of the output image based on the input image information IIN by the latent image forming means 2. Then, the frequency of the frequency changing means 6 is adjusted, or the frequency environment adjusting means 10 predicts the density level of the output image based on the use environment information IEN of the developing device 3 and determines the frequency of the frequency changing means 6. Alternatively, the frequency output adjusting means 12 detects the density level of the output image based on the output image information IOUT from the developing device 3 and adjusts the frequency of the frequency changing means 6.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the accompanying drawings. Note that the dimensions, materials, and other parameters of the constituent elements described in each embodiment do not limit the present invention unless otherwise specified. Example 1 FIG. 2 shows an example of a copying machine as an image forming apparatus to which the present invention is applied. In the figure, reference numeral 21 is a in the figure.
For example, a drum-shaped photoconductor (latent image carrier) that rotates in a direction, 22 is a charger that charges the surface of the photoconductor 21, and 23
Is an image writing unit that writes an electrostatic latent image on the charged latent image carrier 21, and 24 is a development that visualizes the electrostatic latent image formed on the photoconductor 21 with a two-component developer. A device, 25 is a transfer device for transferring the toner image on the photoconductor 21 to the recording sheet 27 supplied from the sheet supply tray 26, 28 is a cleaner of a blade cleaning system for removing the residual toner on the photoconductor 21, Reference numeral 29 is a charge eliminating lamp for removing residual charges on the photoconductor 21, and 30 is a fixing device for fixing the unfixed toner image transferred on the recording sheet 27.

A concrete example of the image writing unit 23 used in this embodiment is shown in FIG. In the figure, the electric signal sent by the light emission time control circuit 236 becomes an optical signal of the laser beam 235 which is turned on and off by the semiconductor laser 231, passes through the collimator lens 232, and is deflected by the deflecting polygon mirror 233 which rotates at a constant speed. After being reflected and passing through the image forming lens 234, the charged photoconductor 21 is exposed to light, and a digital latent image is formed on the photoconductor 21. The number of screen lines of the output image is determined by the electric signal of the light emission time control circuit 236, the rotation speed of the polygon mirror 233, the number of surfaces, and the moving speed of the photoconductor 21 of the exposure unit.

Next, the details of the developing device used in this embodiment are shown in FIG. In the drawing, the developing device 24 includes a developing roller 243 (a non-magnetic conductive developing sleeve 244 in this embodiment, a fixed magnet 24 having, for example, 7 magnetic poles) at a position facing the developing opening 242 of the developing housing 241.
5 is used), a pair of augers 246 for agitating and transporting the developer are provided in the developing housing 241, and a developing roll is provided at a portion facing the developing roll 243. A trimming member 247 for regulating the developer layer thickness on the surface 243 is provided. Incidentally, reference numeral 24
Reference numeral 8 is a dispense roll for toner supply. The developer 249 used in the developing device 24 is a two-component developer, and a non-magnetic polyester toner is used in this embodiment.

The distance between the trimming member 247 and the developing sleeve 244 is set to 0.5 mm, and the photoconductor 2
The separation distance between 1 and the developing sleeve 244 is set to 0.4 mm. The position of the magnetic pole (developing magnetic pole) that contributes to the development among the magnetic poles in the developing sleeve 244 is set within the re-approaching position ± 5 ° with respect to the photoconductor 21,
The magnetic force of the developing magnetic pole is set to about 1000 gauss on the surface of the developing sleeve 244. Further, the developing bias from the developing bias power source 40 is applied to the surface of the developing sleeve 244. In this embodiment, the DC bias 42 superposed with the AC bias 41 is used as the developing bias. Can be variably set in manual mode or automatic mode. Furthermore, in this embodiment, the photoconductor 21 is charged to -650V during charging, and is -200V during overall exposure.
And the DC voltage of the developing bias is, for example, −50.
It is set to about 0V.

FIG. 5 shows a control system of the frequency of the AC bias 41 of the developing bias power source 40 in this embodiment. In the figure, reference numeral 51 is a switch for selecting the screen ruling of the digital latent image by the image writing unit 23. In this embodiment, there are two types of images for output, a character image and a natural image. The number of screen lines of the latent image is K1 = 200, K2 = 400, K3 = 600
There are three types (unit: number of lines / inch), and the direction of the screen line is the same even in the case of a plurality of colors. Also, reference numeral 5
Reference numeral 2 denotes an input image density detection circuit for detecting the image density (input image density) of the digital latent image for one page by the image writing unit 23.

Reference numeral 60 is a frequency controller, which adjusts the frequency of the developing AC bias 41 according to the number of lines selected by the screen line number selection switch 51 and the input image density from the input image density detection circuit 52. , Has predetermined characteristics based on the following experimental results.

Now, various experiments for setting the characteristics of the frequency controller 60 will be described. First, the following experiment was conducted on the relationship between the number of lines of the digital latent image and the frequency of the developing AC bias 41. Now, in the developing sleeve 244 of the developing device 24, the amplitude of the developing AC bias 41 is 1.2 KV and the potential of the developing DC bias 42 is -50.
It is fixed at 0V and only the frequency of developing AC bias 244 is 2
It was changed to ˜30 kHz. Further, a toner having a volume average particle diameter of 5 μm was used, and all other electrophotographic processes were performed under the same conditions.

The output image evaluation method is as follows. For natural images, the presence or absence of contours (hereinafter referred to as pseudo contours) at the same density, the relationship between image density and density, and for character images, 6 points and 8 points. Character resolution and line image resolution were performed. In particular, the character image used was the character "Hibiki" in the Mincho font, and the digital signal was a single black color. In addition, no special signal processing is performed in order to avoid the influence of resolution due to image processing.

Tables 1 and 2 below show the evaluation results regarding the presence / absence of pseudo contours. Here, Table 1 shows the relationship between the number of screen lines and the presence or absence of the pseudo contour, and Table 2 shows the relationship between the frequency of the developing AC bias 41 and the pseudo contour.

[0034]

[Table 1]

[0035]

[Table 2]

From Table 1, it is understood that the higher the number of lines, the more easily the pseudo contour is generated, while the higher the frequency of the developing AC bias 41, the more easily the pseudo contour is generated.

Next, FIG. 5 shows the relationship between the input image density and the output image density with the screen ruling as a parameter, and FIG. 5 shows the relationship between the input image density and the output image density with the frequency of the developing AC bias 41 as a parameter. 6 shows.

According to FIGS. 5 and 6, it was found that the lower the image density, the more gently the density increases, and the lower the frequency of the developing AC bias 41, the more gently the density increases. However, development AC bias 4
It was found that if the frequency of 1 is too low, the density of the solid part (100%) is decreased, and conversely, if the frequency of 1 is too high, the density of the solid part is decreased. Furthermore, it was also found that a natural image requires a gentle increase in density, but it is not suitable for a character image because the outline of the image is blurred.

Next, Table 3 below shows the evaluation results of the relationship between the screen frequency and the resolution of 6-point and 8-point characters.
FIG. 7 shows the relationship between the screen frequency and the resolution of the line image.
8 shows the relationship between the frequency of the developing AC bias and the resolution of the line image, respectively. Incidentally, in Table 3, ◯ indicates that resolution is possible,
X means that resolution is impossible.

[0040]

[Table 3]

From Table 3 and FIGS. 7 and 8, it is understood that the higher the screen frequency, the higher the resolution, and the higher the frequency of the developing AC bias, the higher the resolution. .

Further, the effect of the frequency of the developing AC bias was examined when the average particle size of the toner was changed. The exposure unit writes a digital latent image with a fixed screen line of 200 lines / inch, and the developing unit changes only the frequency to 2 to 30 kHz under the same developing conditions as the previous experiment, and the toner particle size is pulverized.
12μm, 9μm, 7μm, 5μ by changing the classification method
Experiments were carried out with five types of toner having an average particle size of m, 3 μm. FIG. 10 shows an examination of the graininess that expresses the smoothness of the copied image.

In the figure, it was confirmed that when the toner particle size exceeds 8 μm, the graininess deteriorates and the effect of the frequency of the developing AC bias cannot be obtained. However, it was confirmed that a toner having a particle size of 8 μm or less can obtain an image having stable and good graininess at a frequency of 6 kHz or more and 20 kHz or less.

Based on the above experimental results, the characteristics of the frequency controller 60 were set as follows. As a characteristic of the frequency controller 60 according to this embodiment, for example, when K1 = 200, the frequency of the developing AC bias 41 is constant (for example, 10 KHz), whereas K2 =
In the case of 400, the frequency of the developing AC bias 41 is 11 kHz and 45% to 5 when the input image density is 0 to 45%.
10KHz up to 5%, 9KH over 55%
When the input image density is 0 to 45%, the frequency of the developing AC bias 41 is 12 KHz, 45% to 55% is 10 KHz, and 5 is adjusted to z.
It is adjusted to 8 KHz in the range exceeding 5%.

FIG. 11 shows a flowchart relating to the processing of the image forming apparatus according to this embodiment. In the figure, when the number of output image lines from the original is determined by the screen line number selection switch 51, the frequency controller 60 sets the frequency of the developing AC bias (displayed as developing frequency in FIG. 11). Then, according to the input image density information from the input image density detection circuit 52, the frequency controller 60 adjusts the developing frequency based on the characteristic. After that, the developing device 24 develops the original image under the developing conditions, the developed image is transferred to the recording sheet 27 by the transfer device 25, and is fixed to the recording sheet 27 by the fixing device 30.

The recorded image obtained through such an image forming process had a good image quality with smooth density change without pseudo contours.

Example 2 The basic configuration of the image forming apparatus according to this example is Example 1
However, unlike the first embodiment, the frequency controller 60 according to the present embodiment, as shown in FIG. 12, outputs the number of lines selected by the screen line number selection switch 51 and the input image density detection circuit 52. In addition to the input image density, the frequency of the developing AC bias 41 is adjusted according to the temperature information from the temperature sensor 53 and the humidity information from the humidity sensor 54, and it has a predetermined characteristic.

Frequency controller 60 according to this embodiment
Indicates that the relationship between the input image density and the frequency is set for each screen frequency K1, K2, K3 in accordance with the environmental parameter. As the environmental parameter, the temperature sensor 53 is used.
For example, the standard environment (A), the high temperature and high humidity environment (B), and the low temperature and low humidity environment (C) are selected based on the temperature information from the humidity sensor 54 and the humidity information from the humidity sensor 54. For example, when the screen ruling is K1 = 200, the standard environment (A)
In the case of, the frequency of the developing AC bias 41 is constant (for example, 10 KHz), whereas in the case of the high temperature and high humidity environment (B), the frequency of the developing AC bias 41 is 0 to 50% in the input image density. Up to 12 KHz, and in the range exceeding 50%, it is adjusted to 11 KHz, and in the case of a low temperature and low humidity environment (C), the frequency of the developing AC bias 41 is
It is adjusted to 9 KHz when the input image density is 0 to 70% and 8 KHz when the input image density exceeds 70%.

An experiment for setting such characteristics will be shown below. Now, the external environment is 22 ° C 55% RH (Relati
Abbreviation of ve Humidity: relative humidity) (standard environment), 28
° C 90% RH (high temperature and high humidity environment), 10 ° C 30% RH
When the relationship between the input image density and the output image density after density adjustment when the temperature is changed to (low temperature and low humidity environment) is examined, FIG.
The results were obtained as shown by the dotted line in (high temperature and high humidity environment) and FIG. 14 (low temperature and low humidity environment). The experimental conditions in this case were such that the toner concentration of the two-component developer was adjusted so that the toner particle size was 5 μm, the potential of the photoconductor was constant, and the concentration of the solid portion was constant. The line number of the digital latent image was 200 lines / inch.

According to this experiment, the high temperature and high humidity environment (see FIG.
In (dotted line), a sharp rise of density is seen in the middle tone,
It was observed that the density disappeared in the low density area. Further, in the low temperature and low humidity environment (dotted line in FIG. 14), there was observed a phenomenon in which the concentration did not change in the high concentration portion.

In consideration of such environmental changes, the frequency controller 60 is provided so that the same image density (output image density with respect to input image density) as in the standard environment can be obtained even in a high temperature and high humidity environment or a low temperature and low humidity environment. Set the characteristics of. The processing flow of the image forming apparatus according to this embodiment is the same as that of the first embodiment except that the third step in FIG. 11 detects the input image density and the environmental information.

By providing such a frequency controller 60, even in a high temperature and high humidity environment (solid line in FIG. 13) and a low temperature and low humidity environment (solid line in FIG. 14), sufficient gradation can be obtained as in the standard environment. confirmed.

Example 3 The basic configuration of the image forming apparatus according to this example is Example 1
However, unlike the first embodiment, the frequency controller 60 according to this embodiment, as shown in FIG. 15, shows the number of lines selected by the screen line number selection switch 51 and the copy number information from the copy counter 55. The frequency of the developing AC bias 41 is adjusted in accordance with the above, and it has a predetermined characteristic. Frequency controller 6 according to this embodiment
As a characteristic of 0, for example, the screen ruling is K1 = 20.
When the number of copies is less than 1000, the frequency of the developing AC bias 41 is, for example, 8 KHz, and when the number of copies is 1,000 or more and less than 3000, the frequency of the developing AC bias 41 is, for example, 10 KHz and the number of copies is more than 3000. The range is adjusted to 12 KHz.

An experiment for setting such characteristics is shown below. First, a toner having an average particle size of 5 μm and an average particle size of 4
3000 copy samples were taken while keeping the image density constant under the same environmental conditions of 0 Km carrier and developing AC bias 41 of, for example, 9 KHz. In this case, if the number of copies is the first, 1000
FIG. 16 shows the relationship between the input image density and the output image density of the 3rd and 3000th sheets, and FIG. 17 shows an enlarged view of the input image densities 0 to 60. According to the figure, it is understood that the gradation is different especially in the region where the input image density is low when the number of copies is the first, the 1000th, and the 3000th. It is assumed that this is because the developer and the photoconductor deteriorate as the number of copies increases.

In consideration of such a change depending on the number of copies, the characteristics of the frequency controller 60 (the number of copies is 1, 1000, 3000) so that a predetermined image density can be obtained even if the number of copies increases. The characteristic of changing the frequency of the developing AC bias 41 to 8, 10, 12 KHz on the first sheet was set. The processing flow of the image forming apparatus according to this embodiment is the same as that of the first embodiment except that the third step in FIG. 11 detects the number of times of development (in this embodiment, the number of copies is substituted).

In the embodiment provided with such a frequency controller 60, the relationship between the input image density and the output image density for the first, 1000th and 3000th copies is shown in FIG. An enlarged view of 0 to 60 is shown in FIG. According to the figure, when the frequency of the developing AC bias is set to 10 KHz on the 1000th sheet, the gradation is equivalent to that of the 1st sheet and the solid portion (input image coverage 100
%), The same copy sample was obtained. Similarly, the frequency of the developing AC bias 41 is set to 1 on the 3,000th sheet.
When the frequency was set to 2 KHz, a copy sample having the same gradation as that of the first sheet and the same image density in the solid portion was obtained.

Therefore, according to this embodiment, even if the developer or the photoconductor deteriorates with the increase in the number of copies (corresponding to the number of developments), the developer or the photoconductor that does not deteriorate is used as in the case of using the developer or the photoconductor. It was confirmed that sufficient gradation could be obtained.

In this embodiment, if it is desired to finely adjust the image quality in accordance with the input image density, the input image density detecting circuit 52, for example, as shown by a virtual line in FIG.
The input image density may be taken into consideration as a characteristic of the frequency controller 60.

Example 4 The basic configuration of the image forming apparatus according to this example is the same as in Example 1.
20. However, unlike the first embodiment, the frequency controller 60 according to this embodiment, as shown in FIG. 20, uses the frequency information selected from the screen frequency selection switch 51 and the density information from the density sensor 56. Depending on development AC bias 4
It adjusts the frequency of 1 and has a predetermined characteristic. The density sensor 56 is arranged at a position where the density of the developed image on the photoconductor 21 can be detected, as indicated by a phantom line in FIG.

In this embodiment, the frequency controller 60 sets the frequency of the developing AC bias 41 in accordance with the selection signal from the screen ruling selection switch 51, and the density detection from the density sensor 56. Output image density detection circuit 602 that detects the output image density based on the density information for the reference image for printing, and the output image density from this output image density detection circuit 602 and the preset setting value are compared, and the difference And a developing frequency correction circuit 604 that adjusts the set frequency from the developing frequency setting circuit 601 based on the difference data from the comparing circuit 603.

Frequency controller 60 according to this embodiment
FIG. 21 shows a processing flow of the image forming apparatus using the. In the figure, when the number of output image lines from the original is determined by the screen line number selection switch 51, the frequency controller 6
0 sets the frequency of the developing AC bias (indicated as developing frequency in FIG. 21). Next, the image forming apparatus develops the reference image for density detection, the frequency controller 60 detects the density of the reference image, compares this with a set value, and then adjusts the set developing frequency according to the difference. . Thereafter, the developing device 24 develops the original image under the developing conditions, and the developed image is transferred to the recording sheet 27 by the transfer device 25.
And is fixed to the recording sheet 27 by the fixing device 30.

The recorded image obtained through such an image forming process has a good image quality with a smooth density change without pseudo contours and the like.

Example 5 The image forming apparatus according to this example is a combination of, for example, Example 1, Example 2 or Example 3 and Example 4, and its processing flow is shown in FIG. According to this embodiment, it is possible to perform finer image quality adjustment than in the above embodiments.

Sixth Embodiment The image forming apparatus according to the sixth embodiment has a simpler configuration than the first to fifth embodiments. For example, a screen is displayed as information input to the frequency controller 60 in FIG. Only the selection signal of the line number selection switch 51 is used, or only the input image density or environment information is used as the information input to the frequency controller 60 in FIG. 12, or the frequency controller 60 is input in FIG. Only the number of developments (for example, the number of copies) is used as the information to be stored, or only the density information from the density sensor 56 is used as the information to be input to the frequency controller 60 in FIG. The processing flow is shown in FIGS.

[0065]

As described above, according to the developing device of the present invention, the frequency of the developing AC bias can be appropriately variably set so that the output image density (gradation) can be finely controlled. , While maintaining the image density of the solid part,
It is possible to realize a smooth gradation faithful to an original having the same density and no gradation difference, and it is possible to obtain a high-quality image with good graininess in all gradations. Also,
According to the image forming apparatus of the present invention, the input image information,
The frequency of the developing AC bias can be variably set based on the operating environment or the output image information, and the output image density (gradation) can be finely and automatically controlled. It is possible to easily realize the optimization of the image quality depending on the type of the image, or to suppress the influence of the change of the external environment and the change of the usage history to a small level.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a developing device according to the present invention and an image forming apparatus using the same.

FIG. 2 is an explanatory diagram illustrating an image forming apparatus according to a first exemplary embodiment.

FIG. 3 is an explanatory diagram showing a specific example of the image writing unit according to the first embodiment.

FIG. 4 is an explanatory diagram illustrating a specific example of the developing device according to the first embodiment.

FIG. 5 is an explanatory diagram showing a frequency control system for a developing AC bias according to the first embodiment.

FIG. 6 is a graph showing the relationship between the input image density and the output image density with the screen ruling as a parameter.

FIG. 7 is a graph showing a relationship between an input image density and an output image density using a frequency of a developing AC bias as a parameter.

FIG. 8 is a graph showing the relationship between the number of screen lines and the line resolution.

FIG. 9 is a graph showing the relationship between the frequency of the developing AC bias and the line resolution.

FIG. 10 is a graph showing the relationship between the frequency of the developing AC bias and the graininess with the toner particle size as a parameter.

FIG. 11 is an explanatory diagram showing a processing flow of the image forming apparatus according to the first embodiment (second and third embodiments).

FIG. 12 is an explanatory diagram showing a frequency control system for a developing AC bias according to the second embodiment.

FIG. 13 is a graph showing a relationship between an input image density and an output image density according to the presence or absence of a frequency controller in a high temperature and high humidity environment according to the second embodiment.

FIG. 14 is a graph showing a relationship between an input image density and an output image density according to the presence or absence of a frequency controller in a low temperature and low humidity environment according to the second embodiment.

FIG. 15 is an explanatory diagram showing a frequency control system for a developing AC bias according to a third embodiment.

FIG. 16 is a graph showing the relationship between the input image density and the output image density with the number of copies as a parameter in the state without the frequency controller according to the third embodiment.

FIG. 17 is an enlarged view thereof.

FIG. 18 is a graph showing the relationship between the input image density and the output image density with the number of copies of the image forming apparatus according to the third embodiment as a parameter.

FIG. 19 is an enlarged view thereof.

FIG. 20 is an explanatory diagram showing a frequency control system for a developing AC bias according to the fourth embodiment.

FIG. 21 is an explanatory diagram showing a processing flow of the image forming apparatus according to the fourth embodiment.

FIG. 22 is an explanatory diagram showing a processing flow of the image forming apparatus according to the fifth embodiment.

FIG. 23 is an explanatory diagram illustrating a processing flow of the image forming apparatus according to the sixth embodiment.

FIG. 24 is an explanatory diagram showing a modified example of the image forming apparatus according to the sixth embodiment.

FIG. 25 is an explanatory diagram showing another modification of the image forming apparatus according to the sixth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Latent image carrier, 2 ... Latent image forming means, 3 ... Developing device, 4
... developer carrier, 5 ... development bias power source, 6 ... frequency changing means, 7 ... input image information detecting means, 8 ... frequency input adjusting means, 9 ... use environment information detecting means, 10 ... frequency environment adjusting means, 11 ... Output image information detecting means, 12 ... Frequency output adjusting means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Taku Fukuhara 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (6)

[Claims] 1. A two-component developer (4) having a developer carrying member (4) to which a developing bias (VB) superposed with an alternating current component (VAC) is applied, and a developer carrying member (4) carried on the developer carrying member (4). G)
In the developing device for visualizing the latent image on the latent image carrier (1) by the developing bias power source (5), an AC component (VA
A developing device comprising a frequency changing means (6) for changing the frequency of C). 2. The toner according to claim 1, wherein the toner of the two-component developer (G) has at least an average particle size of 8 μm or less, and an alternating current of the developing bias (VB) is applied by the frequency changing means (6). The frequency f of the component (VAC) is 6,000 ≦
A developing device, wherein f is set within a range of 20,000 (Hz). 3. A latent image carrier (1) and a latent image forming means (2) for forming an electrostatic latent image on the latent image carrier (1),
It has a developer carrying member (4) to which a developing bias (VB) superposed with an alternating current component (VAC) is applied, and is latent with a two-component developer (G) carried on this developer carrying member (4). In an image forming apparatus equipped with a developing device (3) for visualizing a latent image on an image carrier (1), an AC component (VAC) is applied to a developing bias power source (5) of the developing device (3). The input image information detecting means (7) for detecting the input image information (IIN) by the latent image forming means (2) is provided with the frequency varying means (6) for changing the frequency of the input image information. An image forming apparatus comprising a frequency input adjusting means (8) for adjusting the frequency of the frequency changing means (6) based on (IIN). 4. A latent image carrier (1) and a latent image forming means (2) for forming an electrostatic latent image on the latent image carrier (1),
It has a developer carrying member (4) to which a developing bias (VB) superposed with an alternating current component (VAC) is applied, and is latent with a two-component developer (G) carried on this developer carrying member (4). In an image forming apparatus equipped with a developing device (3) for visualizing a latent image on an image carrier (1), an AC component (VAC) is applied to a developing bias power source (5) of the developing device (3). The frequency changing means (6) for changing the frequency of the developing device (3) is provided, and the use environment information detecting means (9) for detecting the use environment information (IEN) of the developing device (3) is provided.
An image forming apparatus comprising a frequency environment adjusting means (10) for adjusting the frequency of a frequency changing means (6) based on EN). 5. A latent image carrier (1) and a latent image forming means (2) for forming an electrostatic latent image on the latent image carrier (1),
It has a developer carrying member (4) to which a developing bias (VB) superposed with an alternating current component (VAC) is applied, and is latent with a two-component developer (G) carried on this developer carrying member (4). In an image forming apparatus equipped with a developing device (3) for visualizing a latent image on an image carrier (1), an AC component (VAC) is applied to a developing bias power source (5) of the developing device (3). Is provided with frequency changing means (6) for changing the frequency of the output image, and output image information detecting means (11) for detecting the output image information (IOUT) by the developing device (3) is provided. The image forming apparatus is characterized by further comprising frequency output adjusting means (12) for adjusting the frequency of the frequency changing means (6) based on (1). 6. A latent image carrier (1) and a latent image forming means (2) for forming an electrostatic latent image on the latent image carrier (1),
It has a developer carrying member (4) to which a developing bias (VB) superposed with an alternating current component (VAC) is applied, and is latent with a two-component developer (G) carried on this developer carrying member (4). In an image forming apparatus equipped with a developing device (3) for visualizing a latent image on an image carrier (1), an AC component (VAC) is applied to a developing bias power source (5) of the developing device (3). The frequency input adjusting means (8) is provided with the frequency changing means (6) for changing the frequency of the frequency, and the frequency of the frequency changing means (6) is adjusted based on the input image information (IIN) by the latent image forming means (2). , Based on the output image information (IOUT) from the frequency environment adjusting means (10) and the developing device (3) in which the frequency of the frequency changing means (6) is adjusted based on the use environment information (IEN) of the developing device (3). Output adjustment for adjusting the frequency of the frequency changing means (6) An image forming apparatus characterized by providing at least two stages (12).