JPH07271139A - Image forming device - Google Patents

Abstract

PURPOSE:To control a developing current to be always constant by variably controlling the value of a bias voltage impressed on a developing sleeve in accordance with the variation of distance between a photoreceptor and the developing sleeve. CONSTITUTION:The developing current flows between the photoreceptor 1 and the developing sleeve 21 in the case of developing, and a voltage is generated in a resistance R. The generated voltage is inputted to a developing current detecting means 80, and is outputted from the means 80 as a smooth developing current. The developing current is inputted to a control part 90. The part 90 compares the developing current with a previously set value, and variably controls the voltage of an AC power source 75 or a DC power source 76 in order to make the value of the developing current equal to the set value. That is, the part 90 controls so that the bias voltage is dropped since the distance between the photoreceptor 1 and the developing sleeve 21 is short and developing property is enhanced, and the bias voltage is boosted since the distance between the photoreceptor 1 and the developing sleeve 21 is long and the developing property is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to improvement of a developing portion of a multicolor image batch transfer type color image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, color image forming apparatuses have been known, and various methods are used for forming color images. For example, a method in which the toner image transfer process is repeated for each color, a photosensitive drum is prepared for each color type, and each color is transferred to the recording paper while the recording paper passes through each photosensitive drum, a color image is obtained. There is known a method for forming a toner image, a method for forming a toner image for each color type on a single photosensitive drum in a laminated manner, and a batch transfer of these multicolor images on a recording paper. The method used in the present invention relates to the above-described multicolor image batch transfer type color image forming apparatus.
The operation of the multi-color image batch transfer type color image forming apparatus will be described below.

FIG. 6 is a diagram showing a structural example of a multi-color image batch transfer type color image forming apparatus. In the figure, reference numeral 1 denotes a photosensitive drum which is an image bearing member, and is an OPC photosensitive member coated on the drum, which is electrically grounded and driven and rotated clockwise. Reference numeral 2 denotes a scorotron charger, which uniformly charges the peripheral surface of the photosensitive drum 1 at the potential VH to the potential VG.
Given by corona discharge by a grid and corona discharge wire held on. Prior to the charging by the scorotron charger 2, an exposure device using a light emitting diode or the like (for example, P
CL) 3 is used to remove the charge from the peripheral surface of the photoconductor.

After uniformly charging the photoreceptor, the image exposing means 10
Thus, image exposure is performed based on the image signal. The image exposure means 10 uses a laser diode (not shown) as a light emitting source, performs scanning while the optical path is bent by a reflecting mirror 12 via a rotating polygon mirror 11, fθ lens, etc., and rotation of the photosensitive drum 1 (sub scanning). Form an electrostatic latent image. Here, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential VL.

At the periphery of the photoconductor drum 1, there is provided a developing device 20 in which a developer containing toner such as yellow (Y), magenta (M), cyan (C), black (K) and a carrier is incorporated. First, the development of the first color is performed by the developing sleeve 21 which has a magnet built therein and holds the developer and rotates. The developer is composed of a carrier in which ferrite is used as a core and an insulating resin is coated around the core, and a toner in which a pigment as a main material and a charge control agent, silica, titanium oxide and the like are added, The developer is regulated to a layer thickness (developer) of 100 μm to 600 μm on the developing sleeve 21 by the layer forming means and is conveyed to the developing area.

The gap between the developing sleeve 21 and the photosensitive drum 1 in the developing area is larger than the layer thickness (developer) of 0.2.
The thickness is set to mm to 1.0 mm, and the AC bias having the voltage value VAC and the DC bias having the voltage value VDC are superimposed and applied during this period. Since VDC and VH and toner charge have the same polarity,
The toner that has been given the opportunity to leave the carrier by VAC does not adhere to the VH portion, which has a higher potential than VDC,
It adheres to the VL portion having a lower potential than VDC and is visualized (reversal development).

After the visualization of the first color is completed, the image forming process of the second color is started, the uniform charging is performed again by the scorotron charger 2, and the electrostatic latent image based on the image data of the second color is exposed by the image exposing means. Formed by 10. At this time, the charge removal by the exposure device 3 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Again, an electrostatic latent image similar to that of the first color is formed on a portion of the photoconductor having a potential of VH all over the peripheral surface of the photoconductor drum without the image of the first color and developed. However, in the portion where the image with the first color image is developed again, the toner adhering to the first color shields light and an electrostatic latent image of potential VM is formed by the electric charge of the toner itself, so that VDC Development is performed according to the potential difference of VM. In the part where the images of the first and second colors overlap,
When the development of the first color is performed by forming an electrostatic latent image of VL, the balance between the first color and the second color is lost, so the exposure amount of the first color may be reduced to an intermediate potential of VH>VM> VL. is there.

An image forming process similar to that of the second color is performed for the third and fourth colors, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 1. On the other hand, the recording paper P carried out from the paper feeding cassette 15 via the half-moon roller 16 is temporarily stopped, and when the transfer timing is adjusted, the paper feeding roller 17
The paper is fed to the transfer area by the rotation operation of.

In the transfer area, a transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 1 in synchronism with the transfer timing, and the supplied recording paper P is nipped and a multicolor image is transferred at once. To be done.

Next, the recording paper P is de-charged by the separating brush 19 which is brought into pressure contact with each other almost at the same time, separated by the peripheral surface of the photosensitive drum 1 and conveyed to the fixing device 30, where the heat roller 31 and the pressure roller 32 are heated. After the toner is fused by applying pressure, the toner is ejected to the outside of the apparatus through the paper ejection roller 41. Incidentally, the transfer roller 18 and the separation brush 1 described above.
After the recording paper P has passed through, 9 is retracted from the peripheral surface of the photosensitive drum 1 to prepare for the formation of the next toner image.

On the other hand, the photosensitive drum 1 from which the recording paper P is separated
Removes and cleans the residual toner by pressing the blade 51 of the cleaning device 50, and again receives the charge removal by the exposure device 3 and the charge by the scorotron charger 2 to start the next image forming process. The blade 51 moves immediately after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 1.

Note that the image forming apparatus shown in the figure can also be manually fed in addition to being fed by an automatic sheet feeding mechanism. The recording paper P manually fed by the manual feed tray 60 is conveyed by the rotation of the pickup roller 61,
The sheet is fed to the transfer area through the same process as the sheet feeding from the sheet feeding cassette 15 described above.

In this type of apparatus, the accuracy of the distance between the photosensitive drum 1 and the developing sleeve 21 has a great influence on the image quality. Therefore, various methods have been conventionally used to keep the distance between the photosensitive drum 1 and the developing sleeve 21 constant.

FIG. 7 is a diagram showing an example of the structure of the developing portion.
The same parts as those in FIG. 6 are designated by the same reference numerals. The figure shows the photosensitive drum 1 and the developing sleeve (developing roll) 21 as viewed in the axial direction of the cylinder. In order to keep the distance D between the photosensitive drum 1 and the developing sleeve 21 (hereinafter, abbreviated as developing distance) D constant, the abutting rollers 65 are applied to both ends of the developing sleeve 21.
Is provided to regulate the distance between the photosensitive drum 1 and the developing sleeve 21. The abutting roller 65 is mounted coaxially with the rotation axis of the developing sleeve 21 via a bearing (not shown). When the developing sleeve 21 rotates, the developing sleeve 21 rotates accordingly, and during this time, the photosensitive drum 1
Of the photoconductor drum 1 which contacts the end portion 1a of the photoconductor drum 1 and rotates in the same manner.

[0016]

The above-mentioned conventional method for keeping the developing distance constant has the following problems. According to this method, the distance between the end portion 1a of the photosensitive drum 1 and the abutting roller 65 is accurately regulated. However, since an error in the outer shape of the developing sleeve 21 cannot be compensated, rollers having different diameters are combined depending on the roll diameter. In addition, even if an average developing distance is secured, if the roll is shaken, the developing distance will change according to the rotation of the roll during development.

On the other hand, the bias voltage as described above is applied to the developing sleeve 21, but since the conventional bias power source is a constant voltage source, when the developing distance changes,
The developing electric field fluctuates, and the developability changes. As a result, the image density changes.

FIG. 8 is a diagram showing the characteristics of the conventional device. Conventionally, the AC bias power supply is a constant voltage source, so the power supply voltage VAC is always constant as shown in (a). On the other hand, since the developing distance D changes in VAC / D, it changes as shown in (b) and the image density changes. In order to always keep the image density constant, this VAC / D may be kept constant. This means that the developing current flowing through the bias power supply should be kept constant.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of controlling the developing current so that it is always constant.

[0020]

SUMMARY OF THE INVENTION The present invention for solving the above-mentioned problems is an image forming apparatus configured to transfer a visible image formed by adhering a developer to a photoconductor by a developing device, to a recording paper. A developing current detecting means for detecting a change in the developing bias current applied to the developing device is provided, and the value of the bias voltage applied to the developing sleeve so that the developing current detected by the developing current detecting means becomes a predetermined value. The feature is that it is made variable.

[0021]

The change in the distance between the photosensitive drum and the developing sleeve (developing distance) means the change in the capacitor capacity. When the capacitor capacity changes, the current (development current) flowing through this capacitor also changes. Therefore, if the developing current is always set to a predetermined value, the developing property will not be deteriorated. Therefore, a developing current detecting means for detecting a change in the developing bias current applied to the developing device for each color is provided and applied to the developing sleeve so that the developing current detected by the developing current detecting means becomes a predetermined value. The value of the bias voltage was made variable. This makes it possible to control the developing current so that it is always constant, and the developing property is also improved.

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing a main part of an embodiment of the present invention. The same parts as those in FIG. 7 are designated by the same reference numerals. In the figure, 1 is a photosensitive drum, and 20 is a developing device for adhering toner onto the photosensitive drum 1 according to an electrostatic latent image. In the case of a color image forming apparatus, the developing devices 20 are provided by the number corresponding to the color types Y (yellow), M (magenta), C (cyan), and K (black).

In the developing device 20, 21 is a developing sleeve for attaching toner to the surface of the photosensitive drum 1, and 7
Reference numeral 1 is a developer, 70 is a container for containing the developer 71, 72 is a blade for regulating the layer thickness of the developer 71, and 73 and 74 are stirring screws for stirring the developer 71.

Reference numeral 75 is an AC power source for applying an AC electric field to the developing sleeve 21, and 76 is a DC power source for applying a DC electric field to the developing sleeve 21. The AC power supply 75 and the DC power supply 76 are connected in series. R is a resistance for developing current detection, one end of which is connected to the DC power supply 76 and the other end is connected to the ground potential.

Reference numeral 80 is a developing current detecting means for detecting a developing current by inputting a voltage corresponding to the developing current taken out from one end of the resistor R. 90 is the developing current detecting means 80
Is a control unit that controls the voltage of the AC power supply 75 and / or the value of the DC power supply 76 so that the developing current reaches a predetermined value (constant value). In the case of the color image forming apparatus, the AC power supply 75, the DC power supply 76, the developing current detecting means 80, and the control unit 90 shown in the figure are also provided by the number of colors. The operation of the apparatus configured as described above will be described below.

An electrostatic latent image corresponding to an image is formed on the surface of the photosensitive drum 1 while the photosensitive drum 1 is rotating in the direction of the arrow in the figure. Moreover, the surface thereof has the potentials of VH and VL according to the image. On the other hand, the developing device 20
Then, the developer 71 whose layer thickness is regulated by the blade 72
Adheres to the developing sleeve 21 and approaches the surface of the photoconductor, and the toner of the developing sleeve 21 flies to the surface of the photoconductor in accordance with the potential difference between the surface potential of the developing sleeve 21 and the surface potential of the photoconductor drum 1. A visible image is formed on the surface of the photoconductor.

FIG. 2 is a diagram showing an example of operation waveforms of each section.
(A) is an example of a voltage waveform applied to the developing sleeve 21,
(B) shows the voltage waveform at one end A of the resistor R, and (c) shows the output waveform of the developing current detecting means 80.
In (a), a DC potential VDC is applied to the developing sleeve 21, and an AC voltage VAC is superposed on this DC potential VDC. As a result, the AC voltage VAC fluctuates up and down around VDC as shown in the figure. Here, a rectangular wave is used as the AC waveform, but a sine wave may be used. However, a square wave is more preferable.

At the time of development, a developing current flows between the photosensitive drum 1 and the developing sleeve 21. This developing current is the resistance R
And a voltage as shown in (b) is generated in the resistor R. This voltage waveform is a development current waveform. This generated voltage is input to the developing current detecting means 80, and is output as a smooth developing current as shown in FIG. 2C from the developing current detecting means 80.

This developing current is input to the controller 90. The controller 90 compares the developing current with a preset value, and variably controls the voltage of the AC power supply 75 and / or the DC power supply 76 so that the developing current becomes equal to the preset value. That is, if the distance between the photoconductor drum 1 and the developing sleeve 21 is short, the developing property is high, so that the bias voltage is lowered, and if the distance between the photoconductor drum 1 and the developing sleeve 21 is long, the developing property is low, so that the bias voltage is Controls such as raising are performed. In addition, the voltage variable control here is
The voltage of one or both of the AC power supply 75 and the DC power supply 76 may be changed, but when changing the power supply voltage of one, it is more effective to change the voltage of the AC power supply 75.

As a result, the developing current flowing between the photosensitive drum 1 and the developing sleeve 21 converges to a predetermined value. As a result of the constant developing current, even if the developing distance changes, the developability is not affected, the density becomes constant, and a high-quality image can be obtained.

FIG. 3 is a diagram showing a characteristic example of the present invention. Although the AC bias voltage VAC fluctuates as shown in (a),
A value VAC / D obtained by dividing the AC voltage VAC by the developing distance D becomes constant as shown in (b). The constant VAC / D means that the constant developability is always maintained. It can be seen that the developing characteristics of the present invention are improved as compared with the characteristics of the conventional example of FIG.

FIG. 4 is a block diagram showing a concrete example of the structure of the developing current detecting means 80. The detection signal extracted from the resistor R enters the amplifier 81 and is amplified, and then the rectifier 82.
It enters and is rectified and becomes a DC voltage. This DC voltage is
The peak detector 83 is then entered and peak-held.
The output of the peak detector 83 enters the subsequent filter 84 to remove unnecessary frequency components, and is then taken out as an output signal.

FIG. 5 is a diagram showing a characteristic example of the filter 84. The characteristics shown in (a) are the DC component and the developing sleeve 21.
The signal in the frequency domain in which the uneven rotation occurs is passed. f _D is the rotation frequency of the developing sleeve 21. The characteristic shown in (b) is a low-pass filter that passes only components up to the rotation frequency f _D of the sleeve 21.

In the above-mentioned embodiment, the resistor is used to detect the developing current, but the present invention is not limited to this.
Any structure may be used as long as it can detect a current. For example, CT (current transformer) or the like can be used.

According to the present invention, it is possible to control so that a constant developing current flows even if the distance between the photosensitive drum and the developing sleeve varies, but in reality, the developing layer including the developer layer is also developed. Control is performed regarding the variation in the distance between the sleeve and the photosensitive drum. Then, the bias voltage control is performed so that the developing current becomes constant even if the developer layer changes.

[0036]

As described above in detail, according to the present invention, the distance between the photosensitive drum and the developing sleeve (developing distance).
It is possible to provide a developing device capable of controlling the developing current to be constant by variably controlling the bias voltage value applied to the developing sleeve according to the fluctuation of Therefore, according to the present invention, a high-quality image having a constant density can be obtained. Particularly, it is suitable for use in a color image forming apparatus of a multicolor image batch transfer system.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of operation waveforms of each unit.

FIG. 3 is a diagram showing a characteristic example of the present invention.

FIG. 4 is a block diagram showing a specific configuration example of a developing current detection unit.

FIG. 5 is a diagram showing a characteristic of a filter.

FIG. 6 is a diagram showing a configuration example of a multi-color image batch transfer type color image forming apparatus.

FIG. 7 is a diagram showing a conventional configuration example of a developing portion.

FIG. 8 is a diagram showing characteristics of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 20 Development device 21 Development sleeve 70 Container 71 Developer 72 Blades 73, 74 Stirring screw 75 AC power supply 76 DC power supply 80 Development current detection means 90 Control unit R Current detection resistance

Claims (2)

[Claims] 1. An image forming apparatus configured to transfer a visible image formed by adhering a developer to a photoconductor by a developing device, to detect a change in a developing bias current applied to the developing device. A developing device comprising: a developing current detecting means, wherein the value of the bias voltage applied to the developing sleeve is varied so that the developing current detected by the developing current detecting means has a predetermined value. 2. A multicolor image is formed on a recording paper by repeating a step of applying a developer of one color onto a photoconductor by a developing device a plurality of times to form a visible image of a plurality of colors on the photoconductor. In an image forming apparatus configured to collectively transfer the developing current, a developing current detecting unit for detecting a change in the developing bias current applied to the developing device for developing each color is provided, and the developing current detected by the developing current detecting unit is A developing device, wherein the value of the bias voltage applied to the developing sleeve is changed so as to be a predetermined value.