JPH02146573A - Image forming device - Google Patents

Abstract

PURPOSE:To constantly form an appropriate image by interlocking a means varying the bias potential of the substrate of an image carrier together with a developing bias potential varying means in the same polar direction. CONSTITUTION:The VS variable means for varying the bias potential VS of the image carrier is interlocked with the VB variable means varying the developing bias voltage VB in the same polar direction. Namely, plural interlocking means share a shaft 22, and its rotation varies the resistance values of interlocking variable resistances 23 and 24. The former resistance 23 is to adjust an output voltage from a developing power source 17, and an output terminal DB is connected to a developing sleeve 9. The later variable resistance 24 is to adjust an output from a photosensitive substrate bias power source 18, and an output terminal SB is connected to the substrate 3 of the photosensitive body. Thus, the gradation of the image is varied without developing fogging and image quality is adjusted appropriately.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is an image forming apparatus using an electrophotographic method, and is capable of adjusting the image quality of an output image to an optimum level.
The present invention relates to an image forming apparatus having a trJ mechanism.

(Prior Art) Image forming apparatuses using electrophotography include electrophotographic copying machines, facsimile receivers, laser beam printers, and the like. As an example, FIG. 2 shows a process layout diagram of the main parts of a laser beam printer.

In the figure, a photosensitive drum 1 consisting of a photosensitive layer 2 and a substrate 3, which is an image carrier, is uniformly charged by a charger 4, which forms an image while rotating in the direction of the arrow. The photosensitive drum 1 is exposed to a laser beam 5 modulated in accordance with an image signal, and an electrostatic latent image is formed on the photosensitive drum 1. Subsequently, the drum 1 undergoes a developing process by a developing device 6, and the latent image is visualized. Thereafter, the developed image is transferred by a transfer charger 12 onto a transfer paper (omitted in this figure) that has been guided by a transfer guide 11. The transferred toner image is fixed on a transfer paper by a fixing device (not shown), and is discharged outside the machine to obtain a hard copy. On the other hand, after the untransferred developed toner remaining on the drum 1 is cleaned by the cleaning device 13 and the residual charge is short-circuited and extinguished by the irradiation of the pre-exposure light source 10, the drum 1 is transferred to the first step, which is the primary charging process. sent to and used repeatedly.

An example of the developed image 21 formed on the photosensitive drum 1 is shown in FIG. This developed image 21 is transferred onto the transfer paper 20. In the process in which the laser beam 5, which is image exposure light, is irradiated onto the photosensitive drum l, the laser beam is irradiated not on the part corresponding to the developed image 21 (the black part in the figure) but on the background part (the white part in the figure). A background scanning method is used.

FIG. 4 shows the behavior of the surface potential of the photosensitive drum 1 during formation of a latent image, and shows an example in which a phthalocyanine-based organic semiconductor is used as the photosensitive layer 2 of the photosensitive drum 1, and the -order charging is performed with negative polarity. Indicated.

The surface potential obtained by the primary charger 4 is converted into a latent image potential with a difference of IVd-V or 1 between dark decay and bright decay due to laser irradiation, that is, a contrast of about 550V. In this developing step, as shown in FIG. 2, a magnetic component developer is used as the developing toner T. The toner T in the developing device 6 is mutually J! l Rubbing, developing sleeve 9 and doctor blade 7'
:? Which contact friction causes a charge. Then, it is placed on the sleeve 9 with a uniform thickness by the doctor blade 7 and is conveyed as the sleeve 9 rotates. An AC power source 15 and a DC power source 16 are connected in series to the sleeve 9, which is a developing means, and a biased AC bias voltage is applied thereto. When the sleeve 9 rotates and comes closest to the drum 1, the toner T jumps to the latent image area to be developed due to the electric attraction force due to the electric field between the potential of the sleeve 9 and the potential of the electrostatic latent image. , development is performed. At this time, a portion of the latent image shown in FIG. 4 corresponding to the dark potential Vd is developed. In other words, the toner T has a polarity opposite to that of the charging electrode (
In this case, it is positively charged. The development in which the toner T jumps and adheres to the dark areas in this way is called normal development.

Figure 5 shows the bright area potential V when laser irradiated! Toner does not adhere to the L (negative potential) portion, and the dark potential Vd (
This figure shows how positively charged toner adheres to the portion where the potential is higher on the negative side than Vi.

Conventionally, in such a developing system, in order to adjust the developed image by c degrees, the DC power supply 16 is turned on between the bright area potential Vl and the dark area potential Vd.
The developing bias potential vB was changed by changing the voltage of . That is, as shown in FIG. 5, when it is desired to increase the image density, the developing bias potential is changed from we to VB+ to make it easier for toner to fly from the developing sleeve 9 to the Vd portion on the drum. Conversely, when it was desired to lower the image density, the developing bias potential was changed from Ve to VB2 to make it difficult for the toner to fly.

(Problems to be Solved by the Invention) However, in such a method, since the difference between the dark potential Vd and the bright potential 7 of the electrostatic latent image is constant, there is a drawback described below.

That is, when (1) the development bias potential is changed from v6 to VB+, the difference from the bright area potential (1) -VS+l becomes smaller. As a result, development occurs in which toner adheres to the white background (bright area) of the image, so-called fogging.

(2) Conversely, when the developing bias potential is changed from vn to V[12, the t potential difference IVI-VB21 increases. Therefore, some toners (in this example, (-), hereinafter referred to as "standard polarity toner"), which are contained in the toner, have a polarity different from the normal polarity toner (in this example, (+), hereinafter referred to as "standard polarity toner"). Reverse polarity toner) adheres to the white background area (bright area potential 7), causing fogging, line thickening, and protrusion. There was such a problem.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and its purpose is to enable the development bias and the substrate bias of the photoreceptor to be adjusted in conjunction with the image quality adjustment of the output image, so that the bias is always properly adjusted. An object of the present invention is to provide an image forming apparatus that can form images of a high quality.

(Means for Solving the Problems) According to the present invention, an electrostatic latent image is formed by performing image exposure on a uniformly charged image carrier, and a developing bias voltage VB is applied to the electrostatic latent image. In an electrophotographic apparatus that forms a visible image by regular development using a developing means, the substrate bias potential VS of the substrate of the image carrier is changed when adjusting the image quality such as the density and line width of the output image. VS variable means,
Appropriate image quality adjustment is achieved by providing a (6) variable means for changing the developing bias voltage VB in the same polarity direction as this VS variable means, and an interlocking means for linking the two variable means. This is what I did.

(Function) When changing the substrate bias potential vS of the image carrier and the development bias potential v in the same polar direction, the bright area potential Vg changes in the same polar direction as the substrate bias potential VS, but the dark area potential Vd hardly changes due to its characteristics, therefore,
IVi-VS I, which is a factor in so-called fog (see column 2) of problems to be solved by the invention, remains constant, and the development contrast 1Vd-Val, which determines the density of an image, can be changed without causing fog.

(Example) A first example of the present invention will be described with reference to FIG. 1 and FIGS. 6 to 8.

FIG. 1 is a process layout diagram of the main parts of the laser beam printer of this embodiment. Let us consider a case where the photoreceptor 1 is an organic photoreceptor sensitized on the long wavelength side, and the negative charge is made negative as in the conventional example (FIG. 4). In this case, the grid bias of the grid 19 of the primary charger 4 is set to a negative voltage.

A substrate bias potential VS is applied to the substrate 3 of the image carrier 1 by a variable bias power supply 18 . The development bias potential V8 for the development sleeve 9 and the bias voltage VS for the photoreceptor substrate 3 can be adjusted by varying the development bias voltage frA17 and the photoreceptor substrate bias power supply 18 using the interlocking means 16.

As shown in FIG. 6, in this embodiment, as the interlocking means,
The shaft 22 is shared, and variable resistance 2 is linked by rotating the shaft 22.
3. Use one that can change the resistance value of 24. One variable resistor 23 adjusts the output voltage of the developing bias power source 17, and the voltage output terminal DB of this power source 17 is connected to the developing sleeve 9. The other variable resistor 24 is for adjusting the output of the photoreceptor substrate bias power supply 18.

A voltage output terminal SB of this power source 18 is connected to the substrate 3 of the photoreceptor.

The rest of the configuration in FIG. 1 is the same as the conventional configuration shown in FIG. 2, and therefore will not be described again.

If you want to increase the density of the image using the device with the above configuration, axis 2
Rotate 2 counterclockwise. Then, the negative output voltage from the development bias power supply 17 and the negative output voltage from the photoreceptor substrate bias power supply 18 decrease. When the negative voltage of the photoreceptor substrate bias power supply 18 decreases, the substrate bias potential VS of the photoreceptor changes from negative to positive. Similarly, the developing bias potential IVe (negative) 1 is also low. On the other hand, the dark potential Vd hardly changes due to the rectifying effect of the grid 19, so as shown in FIG.
) changes to state (b), and the development contrast IVa - Vd l increases, so the density of the image increases. Conversely, when lowering the density, rotate the shaft 22 clockwise to increase the negative output voltage of the developing bias power supply 17 and the negative output voltage of the photoreceptor substrate bias power supply 18, as shown in FIG. ), the photoreceptor substrate potential VS3 becomes negative and the developing bias potential 1VSl increases.
The prices are also getting higher. On the other hand, the dark potential Vd hardly changes. Therefore, the development contrast lVa −Vd
I becomes smaller.

In other words, the substrate bias potential VS is set by the photoreceptor substrate bias voltage a18 to the difference IVd-V from the dark area potential Vd.
For example, if Sl is shifted to become thicker (b),
The bright area potential Vl shifts in the same direction as the substrate bias potential VS, whereas the dark area potential Vd hardly changes due to the rectifying effect of grid 2 19, and the developing bias potential V[ ] shifts in the same direction as the substrate bias potential VS. Since it is linked to the bias potential VS, the 1v cross-V is a factor related to fogging on the white background.
S hardly changes; therefore, it can be changed so as to increase only the development contrast IVd-VBI, which is a factor related to image density. Conversely, the IVd
When the substrate bias potential VS is shifted so that -VSl becomes smaller (C), the above sentence 17 -VS
It is possible to change so that only the above-mentioned 1Vd-Vel becomes smaller while l remains almost unchanged.

According to experiments, in order to eliminate fog caused by standard polarity toner, the difference between the bright area potential and the developing bias potential is
It is necessary that I>200V. In the case of background scanning, pitch unevenness may be noticeable and fog is likely to appear, and in such cases, a larger value is required. In order to eliminate fog due to toner of opposite polarity, it is necessary that the potential difference 1V - VSl>300V. Therefore, dark area potential Vd=-700V, photoreceptor substrate potential VS -+sov~--50v, bright area potential V! 1
=-100V to -200V, development bias potential VS
= -350V-450V (variable) configuration, potential difference 1V
Developing bias V while maintaining the sentence-v,,1=250V
e and the bright area potential V (photoreceptor substrate potential VS) were varied. As a result, neither the fog due to the standard polarity toner nor the fog due to the reverse polarity toner occurred, and the density could be adjusted within a practically sufficient range.

Note that the difference between the bright area potential and the developing bias potential is 1V2-Va
l does not necessarily need to be kept constant as described above, and can be varied to adjust the density within a range where neither the fog caused by the standard polarity toner nor the fog caused by the reverse polarity toner occurs. Especially when you want to change the image quality such as line width, 1
It is preferable that the sentence -Ve is not constant. The reason for this is the difference between the dark area potential and the development bias potential (development contrast)
However, when Vd - VS I is changed, not only the concentration but also the line width changes slightly.

In addition to 1Vd-Val, IV! This is because Q-Va I affects the line width. That is, when the development contrast 1Vd-Vel is constant, the line width of the image tends to become thinner as 1Vd-Vel increases. Therefore 1
(2) By changing both the values of Sentence-Val and 1VdVel at appropriate rates, the line width can be effectively adjusted.

An example of this is shown in FIG. As shown by the straight line in the figure, when the bright area potential V and the developing bias potential VB are changed, the slope of change in Vl and Va is the same, so the value of 1v - VBl is also constant, and the line width does not change much. . On the other hand,
When the slopes of change in Vl and VB are different as shown by the dotted line in the figure, the values of IV and 1-VB + also change, and the line width can be adjusted. Further, the changes in VJI and Vll do not necessarily have to be linear, and thus this embodiment is very effective for effectively changing the line width while preventing fogging.

(Example 2) The method of the present invention has been described above using the variable bias power supply 18 as a means for applying a bias to the substrate 3 of the photoreceptor. Next, an embodiment of a cheaper and simpler apparatus for carrying out the invention will be described. As shown in FIG. 9, a self-bias can be applied by using a variable resistor 25.

In FIG. 9, the substrate 3 and the primary Wl electrical shield 26 are connected to have the same potential. This is to eliminate the possibility that the self-bias caused by the resistor 25 may not be stabilized because the amount of current flowing through the substrate 3 alone is small and has large fluctuations. That is, since most of the total primary current flows into the primary charger shield 26, a stable self-bias value can be obtained by using this. Also, as shown in Figure 9(a), if the primary 1"f is connected to the shield 27 of the transfer charger instead of the shield 26, it can be used efficiently in a range of different resistance values and flowing currents compared to Figure 9(a). Shifting the substrate bias potential VS is also a rotation.

(Example 3) As shown in FIG. 11, Zener diodes 28 to 31
The self-bias value can be changed by switching with the switch 32. This makes it possible to implement the present invention more easily and at a lower cost than using the variable bias power supply 18.

In addition, the above 2. In the third embodiment, only the VS variable means has been explained, and the 6 variable means and interlocking means are omitted, but various known means can be employed.

Note that the present invention is applicable not only to the laser beam printer shown in the above embodiment but also to any other electrophotographic application apparatus.

(Effects of the Invention) As explained above, by changing the developing bias potential Va and the substrate bias potential VS of the image carrier in conjunction with each other when adjusting the image quality of the output image, the image quality can be improved without causing any adverse effects such as fogging. It becomes possible to adjust.

[Brief explanation of the drawing]

FIG. 1 is a process layout diagram of the main parts of a laser beam printer according to the first embodiment of the image forming bag of the present invention, FIG. 2 is a process layout diagram of the main parts of a laser beam printer according to a conventional example, and FIG. FIG. 4 is a diagram showing the behavior of the surface potential of the photosensitive drum; FIG. 5 is a diagram showing the function of the developing bias potential; FIG. 6 is a diagram showing the interlocking means in FIG. 1;
FIG. 7 is a diagram explaining the operation of the first embodiment, and FIG. 8 is a diagram explaining the operation of the first embodiment.
FIGS. 9 to 11, which are diagrams showing other modifications of the embodiment, are diagrams for explaining the VS variable means of other embodiments. Explanation of symbols 1... Photoreceptor 3... Substrate 4... Primary charger 5... Laser exposure 9...
Developing means 12...Transfer charger 13...Cleaner 16...Interlocking means 17...Developing bias power supply 18...Photoreceptor substrate bias power supply

Claims (1)

[Claims] An image forming apparatus that performs image exposure on a uniformly charged image carrier to form an electrostatic latent image, and develops the electrostatic latent image using a developing means to which a developing bias voltage is applied to form a visible image. V_S variable means for changing the substrate bias potential V_S of the substrate of the image carrier when adjusting the image quality of the output image; and V_B variable means for changing the developing bias potential V_B in the same polar direction as the V_S variable means. and an interlocking means for operating the two variable means in a coupled manner.