JPH01114876A - Image forming device - Google Patents

Abstract

PURPOSE:To achieve the adjustment of line width without positive fog nor inverted fog by synchronizing a development bias potential VB and the umbra potential Vd of a photosensitive body, changing them and making the change width of the potential VB wider than the change width of the potential Vd. CONSTITUTION:A grid 17 is fitted in a primary electrifying device 4. When primary charge is made negative charge, a grid bias is made a negative voltage. A bias voltage with respect to a developing sleeve 9 and a bias voltage with respect to the grid 17 and adjustable by means of an interlocking means 18 and by freely changing development bias electric power source 25 and a grid bias electric power source 26. In the device of the above constitution, when the negative voltage of the grid bias is boosted, a primary charge voltage rises in the negative direction, and the potential ¦Vd¦ rises. Hereby, at the time of the adjustment of the line width of an outputted image, the potential VB and the potential Vd are synchronized and changed by the means 18. The change width of the variation of the potential VB is also changed in the way that it is wider than the change width of the variation of the potential Vd. Thus, the line width can be adjusted without causing such damages as fogging, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus using an electrophotographic method and capable of adjusting the line width of an output image to an optimum value.

[Conventional technology]

Devices that utilize electrophotography include electrophotographic copying machines, facsimile receivers, and laser beam printers. As an example, FIG. 2 shows a process layout diagram of the main parts of a laser beam printer.

In the figure, a photosensitive layer 102, which is an image carrier, and a substrate 10 are shown.
The photosensitive drum 101 consisting of 3 forms an image while rotating in the direction of the arrow. - The photosensitive drum 101 uniformly charged by the charger 104 is exposed to a laser beam 105 modulated in accordance with an image signal, and an electrostatic latent image is formed on the drum 1.
01. Subsequently, the drum 101 is connected to the developing device 1.
The latent image is visualized through the development step of 06.

Thereafter, the developed image is transferred by a transfer charger 112 onto a transfer paper (omitted in this figure) that has been guided by a transfer guide 111. 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 101 is cleaned by a cleaning device 113 and the residual charge is short-circuited and extinguished by irradiation with the pre-exposure light source 110, the drum 101 undergoes the first step of primary charging. sent to and used repeatedly.

An example of the formed image is shown in FIG. A developed image 118 is transferred onto a transfer paper 117. In the process of irradiating the laser beam 105, which is image exposure light, an image scanning method is adopted in which the laser beam 105 is irradiated onto the portion of the photosensitive drum corresponding to the developed image 118, and the background portion is not irradiated with the laser beam. This method irradiates the background with a laser and
This is because, compared to a background scanning method in which only the portion corresponding to 18 is not irradiated with a laser, there is no scanning trace in the background image and the reproducibility of the image is superior.

FIG. 4 shows the behavior of the surface potential of the drum 101 during latent image formation. In this example, a phthalocyanine-based organic semiconductor is used as the photosensitive layer 102 of the photosensitive drum 101, and -order charging is performed with negative polarity.

- The surface potential obtained by the charger 104 is converted into a latent image potential with a difference IVd-v11 between dark attenuation and bright attenuation due to laser irradiation, that is, a contrast of about 550V.

In the developing process, a polar component developer is used as the developing toner T. The toner T in the developing device 106 is charged by mutual friction and contact friction with the developing sleeve 109, doctor blade 107, and the like. Then, it is placed on the sleeve 109 with a uniform thickness by the doctor blade 107, and is conveyed as the magnet roller 108 rotates. An AC power source 115 and a DC power source 116 are connected in series to the sleeve 109, which is a developing means, and a biased AC bias voltage is applied thereto. When the sleeve 109 rotates and comes closest to the drum 101, 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 109 and the electrostatic latent image potential. .

A portion of the latent image shown in FIG. 4 corresponding to the bright area potential Vt is developed, so-called reversal development. The toner is charged by a charging electrode (negative in this case) that develops a relatively high potential Vl in the positive direction. FIG. 5 schematically shows how toner does not adhere to the negative potential portion of the dark area potential Vd, which is the background, and negatively charged toner adheres to the laser irradiation portion Vz near the ground potential.

Conventionally, in such a developing system, in order to adjust the line width of a developed image, the power supply 116 is turned on between the bright area potential vi and the dark area potential Vd.
The developing bias potential v8 was changed by changing the voltage of . As shown in FIG. 5, when it is desired to increase the image density, the developing bias potential is changed from vBφ to v81 to make it easier for toner to fly from the developing sleeve 109 to the VZ portion on the drum. Conversely, when it is desired to lower the image density, the developing bias potential is changed from vBφ to VB□ to make it difficult for toner to fly.

[Problem that the invention is trying to solve] However,
In such a method, the difference between the dark potential Vd and the bright potential VZ of the electrostatic latent image is constant, and therefore there is a drawback described below. When the developing bias potential is changed from vBφ to VBI, the difference 1VaVe+l from the dark area potential Vd becomes smaller. As a result, toner adheres to the white background (dark area) of the image,
So-called fogging occurs. Conversely, when the developing bias potential is changed from vBφ to v8□, the potential difference is 1v,
-v8°l becomes larger. Therefore, some toner (in this example, + in this example, hereinafter referred to as "reverse polarity toner") whose charging electrode is different from the normal polarity toner (in this example, 11 or less, referred to as "standard polarity toner") is contained in the toner. It adheres to the white background area (dark area potential V a ), causing fogging, thick lines, and protrusion.

In order to avoid the above problem, it is also possible to adjust the line width of the image by changing the bright area potential Vl. With this method, it is easy to increase the bright area potential 1Vll and narrow the line width. However, due to the sensitivity limit of the photoreceptor and the output limit of an image exposure light source such as a laser, it is not necessarily easy to increase the difference lVz Vsl between the bright area and the developing bias potential in order to increase the line width. In particular, increasing the amount of light for image exposure in order to lower Vl increases the memory of the photoreceptor (charges remain trapped in the photoreceptor) and accelerates the deterioration of the photoreceptor. At the same time, it has the disadvantage of shortening the life of the light source.

[Means for Solving the Problems (and Effects)] The present invention aims to eliminate the drawbacks of such conventional methods and provide an electrophotographic apparatus that can adjust the line width to an appropriate line width. be.

A first invention for achieving this object is to form an electrostatic latent image by exposing a charged image carrier, and to develop the electrostatic latent image in reverse using a developing means to which a bias voltage is applied. When adjusting the line width of an output image in an electrophotographic apparatus that forms an image, a variable means for changing the dark potential Vd formed by the charging, and a variable means for changing the dark potential Vd in the same polarity direction as the variable means,
', and the width of the change is wider than the width of the change in the dark potential Vd. .

Further, a second invention for achieving this object relates to a specific configuration of the first invention, in which a grid is provided in the opening as a means for changing the dark potential v4 formed by the charging. A charger in which all or part of the grid and the shield are short-circuited, and a potential variable means consisting of a constant voltage element and a variable resistor arranged in series between the grid and the ground are used. Appropriate line width adjustment is carried out by means of an adjusting means having a simple structure in which the variable means is connected and operated so that the amount of change in the developing bias VB is larger than the amount of change in the grid potential.

〔Example〕

FIG. 1 is a diagram for explaining the present invention in detail, and shows the grid 17 being attached to the blower 4. As shown in FIG.

Further, as a photoreceptor, an OPC organic photoreceptor sensitized on the long wavelength side was used. - When the blowing charge is made negative as in the conventional example, the grid bias is made a negative voltage. The bias voltage for the developing sleeve 9 and the bias voltage for the grid 17 are controlled by the developing bias power source 2 using the interlocking means 18.
5 and the grid bias power supply 26.

As shown in FIG. 7, in this embodiment, the axis 2 is used as the continuous image means.
3, and by rotating the shaft 23, the interlocking variable resistance 21 and
22 whose resistance value could be changed was used. The variable resistor 21 is used to adjust the output voltage of the developing bias power supply 25. A voltage output terminal DB of the power source 25 is connected to the developing sleeve 9. The variable resistor 22 is used to adjust the output voltage of the grid bias power supply 26. A voltage output terminal GB of power supply 26 is connected to grid 17 . The rest of the configuration is the same as the configuration shown in FIG. 2, so repeated explanation will be omitted. .

In an apparatus with this configuration, when increasing the image density, the shaft 23 is rotated clockwise. Then, the negative output voltage from the developing bias power supply 25 and the negative output voltage from the grid bias power supply 26 increase. If the negative voltage of the grid bias increases, the negative current voltage becomes negative. Therefore, the dark potential lVd1 becomes high.

Now, the relationship between the dark area potential Vd1, the bright area potential Vj, the developing bias VB, and image quality will be explained using FIGS. 8 to 10.

In FIG. 8, A corresponds to the difference between the bright area potential v1 and the developing bias VB, that is, the development contrast, and is a factor related to the difference between the dark area potential Vd of B and the developing bias VB, that is, the fog in the white background area. In other words, the larger A is, the higher the concentration is.
If B is too small, positive fog will occur, and if B is too large, reverse fog will occur.

FIG. 9 is a diagram showing the relationship when the dark potentials v and l are varied variously. Here, in FIGS. 9(I) to (III), the reason why the change in Vj is smaller than the change in Vd is because
This is because the Vt potential is close to the residual potential level.

In other words, in the OPC organic photoreceptor used in this example, a residual potential of about -50V is generated when the intensity of the laser scanning light is increased, so the VZ potential is lowered to 11 as shown in FIG.
If it is set near 00v, the width of change in Vt becomes smaller with respect to change in Vd.

Next, FIGS. 10(a) to 10(d) show cases in which the dark area potential Vd and the developing bias potential v8 are variously changed. 1st
FIG. 0(a) shows a conventional method in which only the developing bias potential VB is changed. According to this method, as explained in FIG. 8, the fog margin B changes as well as the development contrast A, resulting in problems such as reverse fog. On the other hand, Fig. 1O (b) shows the case where the dark area potential Vd and the developing bias potential V are changed by the same amount, and (n) in (b) is changed to (a) (
Compared with II), the development contrast A is almost unchanged, so the density is about the same as in Figure 10 (a), but the line width is higher than in Figure IO (a) (TI) (b) (T
I) is significantly thicker. This is fog margin B
This is because the so-called root part of the latent image is developed (b
) (rI) has a thicker line width. This means that in the system of FIG. 10(b), the line width does not change much. This will be explained using FIG. 11. Figure 11 shows that the laser spot diameter when stationary is 1/e” of the peak, and is 100 μm in both the main scanning and sub-scanning directions.
This figure shows the potential distribution in the main scanning direction on the photoreceptor when only one dot is lit when scanning with a circular spot laser beam at a scanning density of 400 dots/inch. Note that the dynamic spot diameter during scanning is a so-called horizontal ellipse that is long in the main scanning direction when set as in this example. This means that the light intensity distribution of a stationary spot is G.
This is because the spot diameter during scanning has a shape obtained by integrating this in the main scanning direction, whereas the spot diameter has an auss distribution. Note that the light amount distribution was converted into potential using the light amount potential characteristics of the OPC photoreceptor used in this study.

In Figure 11, a has a Vd of approximately -700VSb has a Vd of approximately -6
In the potential distribution in the case of 00V, Vi 1 and Vz 2 are the potentials in the laser continuously ON state in each case. Furthermore, the laser output is the same in Figures 11a and 11b. At this time, if the developing bias potential VI + v2 is set so that the developing contrast is equal to Vzl and Vi2, that is, Vt, -V 1 = V12 - V 2 , then from FIG. As is clear, Ll<L2.

This also applies to the dot width in the sub-scanning direction and the vertical and horizontal line widths.

On the other hand, FIG. 10(C) shows the change in the developing bias potential v8 greater than the dark area potential Vd, and FIG. 10(b)
It is possible to make the line width thinner. In other words, the first
As shown in Figure 0 (C), the line width can be adjusted within a range that does not cause problems such as reverse fog while suppressing changes in the fog margin B. On the other hand, FIG. 10(d) shows that the change in the developing bias potential v8 is smaller than the dark area potential Vd (
According to this, the development contrast A
Even if the line width changes, the line width remains almost unchanged.

Next, a simple method for synchronously changing the dark potential Vd and the developing bias v8 will be explained using FIG. 12. In FIG. 12, reference numeral 17 is a grid made by the etching method, and the grid 17 and the shield 20 are kept at the same potential in order to stabilize the corona current in the direction of the grid. Then, the grid 17 and the shield 20
are a constant voltage element 27, a variable resistor 28. It is grounded via a correction resistor 29. By applying this variable resistor 28 to the portion shown in FIG. 7 22, the grid bias power supply 26
It is possible to apply a bias potential to the grid without using Note that by setting the grid 17 and the shield 20 at the same potential, it becomes possible to flow sufficient current from the corona wire 32 to the variable resistor 28, but in consideration of environmental fluctuations, it is necessary to connect the constant voltage element 27 in series. It is desirable that most of the grid bias potential be generated by the constant voltage element 27. Furthermore, it goes without saying that the grid bias potential may be changed by switching and using a plurality of constant voltage elements instead of the variable resistor 28.

It is preferable that the constant voltage element 27 be provided on the grid side, that is, on the high voltage potential side, and that the variable resistor 28, which is the variable means, be provided on the lower potential side (the side closer to the ground in FIG. 12). This is because the line width adjusting means is directly touched by the user, and it is desirable that the variable resistor 28 connected thereto is also kept at a low potential.

Furthermore, the shield 20 does not necessarily cover its entire surface with the grid 17.
There is no need to short-circuit the corona wire 32 (or, for example, a part of the portion facing the corona wire 32 may be covered with an insulating material. In other words, the corona wire 32 It is sufficient if the current from the

[Other Examples]

Fig. 13 shows the grid bias voltage V. and various examples of how to change the developing bias potential VB. In this example, in order to stabilize the corona current flowing through the primary charging grid and provide sufficient potential controllability, the above-mentioned shield member and the etched grid were made to have the same potential, and a sufficient amount of corona was applied to the grid. It was used by applying a current.

As a result, the dark potential V of the photoreceptor is approximately equal to the grid bias voltage v0.

In FIG. 13, (a) to (C) are of the type already explained, and among these, (b) is related to the present invention. On the other hand, (d) to (h) are examples when the grid bias potential v0 or the developing bias potential VB is set nonlinearly with respect to the displacement amount of the image adjustment dial, and F1 to F9
is an adjustment scale that resembles the aperture value. In this way, for example, in the example shown in FIG. 13(d), the change in image quality from F1 to F5 can be large, and the change from F5 to F9 can be made gradual. In general, the density changes little in the area where the line width becomes thicker, but as the line width changes in the direction of thinner lines, the change tends to become steeper. When changing the line width in the direction of thinning (as in f), line width control is facilitated by gradually decreasing both V8 and Vd, or the rate of change in v8, or gradually increasing the rate of change in Vd. Can be done.

On the other hand, in cases like g) and (h), the line width changes irregularly, which is not very preferable.

The present invention has been described in detail above, but there are also multiple modes that can be set depending on the purpose, such as a mode for density adjustment and a mode for line width adjustment. Grid bias voltage vG and development bias potential V
For example, how to change B is shown in Fig. 13 (b) to (a).
It is also an effective method to switch the mode by changing to .

In addition. Grid bias potential v0 and development bias potential V
Means for nonlinearly changing B can generally be easily realized using a nonlinear amplifier, but for example, the first
As shown in FIG. 4, it is also possible to nonlinearly change the grid bias potential vG with a simple configuration using a constant voltage element 27, a fixed resistor 30, and a variable resistor 31. In addition. 1st
In FIG. 4, a correction resistor 29 is used for fine adjustment to absorb variations in the constant voltage element 27, resistors 30, 31, etc., and a variable resistor 31 is used for image adjustment.

Above, we have described an example of adjusting the line width by changing VG and v8, but by using this together with a slight change in the laser beam intensity, the line width of the output image can be made even more effective. It can be changed to. Of course, it is possible to adjust the line width simply by changing the laser beam intensity, but
As mentioned above, there are restrictions on the upper and lower limits of the laser output value.

However, v. Alternatively, if the laser output value is changed in conjunction with the change in vF3, a sufficient effect can be obtained even with a slight change in the amount of light.

〔Effect of the invention〕

As explained above, the developing bias potential v8 and the dark potential v4 of the photoconductor are changed in synchronization with each other when adjusting the line width of the output image, and the range of change in the amount of change in the developing bias potential VB is the same as the dark potential Vd. By changing the amount of change so that it is wider than the width of change, it is possible to adjust the line width without causing damage such as reverse fog or normal fog.

In addition, in the charging process, a simple configuration can be used in which a charger has a grid in its opening, all or part of the grid and shield are short-circuited, and the grid is grounded via a constant voltage element and a variable resistor. Therefore, the above objective could be achieved easily and at a very low cost.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the present invention. Figure 2 shows a conventional example. 3 to 5 are principle diagrams of image formation. 6 to 11 are explanatory diagrams of the first invention. FIG. 12 is an explanatory diagram of the second invention. FIG. 13 and FIG. 14 show other embodiments. l・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・Photoreceptor 4.104・
・・・・・・・・・・・・・・・・・・・・・・・・
...Primary charger 5.105...
・・・・・・・・・・・・・・・・・・Laser exposure 9
．． 109・・・・・・・・・・・・・・・・・・
......Developing means 12.112...
・・・・・・・・・・・・・・・・・・・・・Transfer charger 13.113・・・・・・・・・・・・・・・・・・
・・・・・・・・・Cleaner 17・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・
...Primary charger grid 25.116...
・・・・・・・・・・・・・・・・・・Development bias power supply 26・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・ Grid bias power supply 18 ・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・Interlocking means 20...
・・・・・・・・・・・・・・・・・・・・・・・・
......Primary charger shield 27...
・・・・・・・・・・・・・・・・・・・・・・・・
...... Constant voltage element 28.29.31...
・・・・・・・・・・・・・・・・・・Variable resistance 30...
・・・・・・・・・・・・・・・・・・・・・・・・
・・・・・・・・・Fixed resistance number? Figure 3 Figure 4 Figure 5 Figure d Figure 6 Figure 7 Ward No. 10 Figure I

Claims (2)

[Claims] (1) An image in which an electrostatic latent image is formed by performing image exposure on a uniformly charged image carrier, and the electrostatic latent image is reversely developed using a developing means to which a bias voltage is applied to form a visible image. In the forming apparatus, at least a variable means for changing the dark potential V_d formed by the charging, a variable means for the developing bias voltage V_B changing in the same polarity direction as the variable means, and an interlocking means for interlocking the two variable means. ΔV_B is the width of the change in the dark potential V_d, and ΔV_B is the width of the change in the developing bias voltage V_B.
An image forming apparatus characterized in that V_d is set to be smaller than ΔV_B. (2) An image in which an electrostatic latent image is formed by performing image exposure on a uniformly charged image carrier, and the electrostatic latent image is reversely developed using a developing means to which a bias voltage is applied to form a visible image. The forming apparatus includes at least a variable means for changing the dark potential V_d formed by the charging, a variable means for changing the developing bias potential V_B in the same polar direction as the variable means, and a grid at the opening, and the grid and the shield member. a charging means in which all or a portion of the above are short-circuited; a potential variable means having at least a constant voltage element and a variable resistance arranged in series between the grid and the ground; and an interlocking means for interlocking the three variable means. and when the width of the change in the dark potential V_d is ΔV_d, the width of the change in the developing bias voltage V_B is ΔV_B, and the width of the change in the grid potential is ΔV_G, ΔV_d is smaller than ΔV_B. , ΔV_G is set to be smaller than ΔV_B.