JP2003076080A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of forming an excellent image where a stripe pattern recognizable by human eyes caused by bias voltage having an AC component is prevented from occurring. SOLUTION: After an electrifying bias voltage having the AC component is applied to a photoreceptor drum 10 by an electrifying roll 12, a latent image is written on the drum 10 by a latent image forming unit 18, and is developed with toner while applying developing bias voltage having the AC component to the drum 10 by a developing sleeve 20. Thus, the frequency of the latent image forming scanning pulse of the unit 18 is set as basis and is frequency- divided or kept as it is to be the frequency of the electrifying bias voltage and the developing bias voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes an electrophotographic method.
To an image forming apparatus. [0002] 2. Description of the Related Art Conventionally, image formation using an electrophotographic method
In the device, the charging bias voltage is applied
The surface of the photosensitive drum, which is the image carrier, is
And then exposed by a latent image forming means.
Changes the surface potential to form an electrostatic latent image,
A magnetic toner was attached to the electrostatic latent image to obtain a visible image.
Later, this visual image is transferred to a sheet such as paper. here
In a developing unit, an insulating magnetic transformer having no electric field dependence is used.
Toner on the outer peripheral surface of the developing sleeve by frictional charging
And apply a developing bias voltage to the developing sleeve.
Magnetic toner is attached to the electrostatic latent image. The charging bias voltage has an AC component.
The developing bias voltage also has an AC component.
You. Also, place the charging roll and the developing device close to each other.
Have been. Therefore, charging by electromagnetic induction
The AC component of the developing bias voltage is
Charge bias to the AC component of the developing bias voltage
The waveforms of each other are disturbed due to interference of the AC components of the voltage.
You. In this case, especially the AC component of the charging bias voltage interferes
Is charged on the surface of the photoreceptor drum in a streak shape in the axial direction.
Intensity occurs, resulting in unevenness in the image formed on the sheet
I do. This unevenness appears as a stripe pattern, but this is a human
If you can see it with your eyes, the image quality will deteriorate
is there. More specifically, the frequency of the charging bias voltage
To f_cAnd the frequency of the developing bias voltage is f_dThen
The waveform of the charging bias voltage is f_d−f_cFrequency components and f_d
+ F _cWith the frequency components of F_d
+ F_cIs a high frequency component and has a very short period
What is the cause of image unevenness that can be seen by humans?
No. On the other hand, f_d−f_cFrequency component is a period
Appears in the waveform as a long swell, which is seen by human eyes.
This can cause uneven image quality. To solve this problem, Japanese Patent Application Laid-Open No. Hei 5-28
No. 9441, the charging bias
The frequency of the AC component of the voltage and the AC component of the developing bias voltage
The frequency of the minute is a relationship of an integral multiple. This
If the AC component of the charging bias voltage is
Even if the AC component interferes, the unevenness of the electrification intensity
To prevent the image from becoming uneven.
You. That is, here, f_d= Nf_cIn a relationship
(N is an arbitrary integer), f_d−f_c= (N-
1) f_cIt becomes. For example, if n = 2, the swell
Wave number f_d−f_cIs f_cAnd the charging bias voltage is
Even if the bias voltage interferes, f _cItself is a minute with human eyes
It is set to a value that does not
Is not recognized. [0007] However, this is not the case.
However, the following problems remain. Ma
No latent image forming means is arranged near the charging roll.
The latent image forming means is provided in the sub-scanning direction (the circumference of the photosensitive drum).
Exposure while scanning at a constant pitch along the
To form a latent image. That is, this scan
It is performed by a pulse of a fixed cycle. Therefore, the latent image form
Between the scanning pulse of the forming means and the AC component of the charging bias voltage.
Interference causes parts of each other to cancel. In this case, in particular, the pulses of the latent image are canceled.
And part of the latent image to be formed is streaked in the axial direction of the photosensitive drum.
Weakens or stops forming on the sheet
Unevenness also occurs in the formed image. This unevenness is shady
It appears as a striped pattern, which is visible to the human eye
There is. Especially when forming a halftone image,
For example, when copying a halftone original with low density
Means that part of the latent image pulse disappears and the latent image is partially formed
No longer visible, white stripes are clearly recognized by human eyes
Often done. This is the frequency of the scanning pulse of the latent image forming means.
Number f_rThen, the scanning pulse of the latent image forming means becomes f_r−f
_cFrequency components and f_r+ F_cWith the frequency components of
, And f_r−f_cFrequency component has a long period
It swells and overlaps with the scanning pulse, which is a human
This is because it causes visible image unevenness. [0010] Japanese Patent Application Laid-Open No. 5-289441 discloses a method.
In the above-mentioned invention, electromagnetic induction itself may be suppressed.
Because there is no AC component of the charging bias voltage and the developing bias
The AC components of the voltage interfere with each other. others
For example, if the AC component of the charging bias voltage is interfered with,
Department is emphasized. This is the potential of the surface of the photosensitive drum.
Because it will be more or less weak,
As if a latent image had been formed
The image is developed, and the image formed on the sheet becomes uneven.
Live. This unevenness is recognized as fog. Ie
Black stripes are formed in parts that should be white. The present invention has been made in view of the above-mentioned problems.
Due to the bias voltage having an AC component
Good image that prevents the occurrence of stripes that can be recognized by human eyes
An image forming apparatus for forming an image is provided.
You. [0012] Means for Solving the Problems To solve the above problems,
Therefore, according to the first aspect of the present invention, there is an AC component.
Charging means for applying a charging bias voltage to the image carrier,
A developing bias voltage having an AC component is applied to the image carrier.
Developing means for developing the image carrier while applying
The charging bias voltage and the charging bias voltage.
Developing means for shielding the developing bias voltage from the charging means;
And the developing means. [0013] According to the first aspect of the present invention, the charging bias
Charging means to shield the voltage and the developing bias voltage
By providing between the step and the developing means,
It is possible to reliably prevent minute interference. Accordingly
The image formed has stripes that are recognized by the human eye.
It is possible to prevent generation. [0014] BRIEF DESCRIPTION OF THE DRAWINGS FIG.
And will be described in detail. (1) First embodimentA. Configuration of the embodiment First, FIG. 1 shows an image forming apparatus according to a first embodiment of the present invention.
FIG. In the drawing, reference numeral 10 denotes a photoconductor
2 shows a drum (image carrier). When the photoconductor drum 10 is
It is designed to rotate in the measuring direction. Photoconductor drum 10
, A charging roll (charging means) 12 and a latent image formation
(Latent image forming means) 18 and developing unit 19
I have. The charging roll 12 has a charging AC power supply 14 and
AC and DC by charging DC power supply 16
Negative bias voltage (charging bias voltage)
Has been added. Thereby, the surface of the photosensitive drum 10 is
Is negatively charged. In this manner, the charged photosensitive drum
Laser light is illuminated on the surface of the
Fired. By irradiating the laser light in this way,
As a result, the surface potential changes and a latent image is formed. Specifically
The part to be visualized is set to a positive potential or
Although the potential is negative, the potential level decreases. The photosensitive drum 10 on which the latent image has been formed is
The image reaches the imager 19. The developing device 19 is a magnetic toner (not shown).
And a rotating developing sleeve (developing means) 20
And In the developing device 19, the electric field dependency is reduced.
Developing toner particles by frictional charging
It is attached to the outer peripheral surface of the probe 20. Also, development three
The developing unit 20 includes a developing AC power supply 22 and a developing DC power supply.
24, a negative bar that overlaps DC and AC
An bias voltage (development bias voltage) is applied. This
As a result, the toner is negatively charged. And feeling
The portion where the latent image of the optical drum 10 is formed, that is,
In the portion where the potential is set or the potential level is reduced, the toner is
It adheres and a visible image is formed. Formed in this way
The visible image is transferred to a sheet 26 such as paper by a transfer unit (not shown).
It is designed to be transcribed. As described above, the charging rolls 12 and
Bias voltage having an AC component
Is applied. Therefore, the rotation of the photosensitive drum 10
With the rotation, extremely minute
At a constant pitch, in the axial direction of the photosensitive drum 10
Uncharged and undeveloped areas along the line
Minutes occur. However, the charging roll 12 and the developing roller
The frequency of the bias voltage applied to the leave 20 is large.
Is set, and even if an image is formed,
So that it does not appear as strong or weak stripes
ing. On the other hand, the latent image forming unit 18
(Peripheral direction of the photosensitive drum 10) at a constant pitch.
An image is formed. That is, the formation of the latent image has a constant frequency.
It is performed by a holding pulse (latent image forming scanning pulse)
You. For example, if the resolution is 400 psi and the process speed is
(Corresponding to the rotational peripheral speed of the photosensitive drum 10) is 136 m
m / s, the frequency of the pulse of the latent image forming unit 18 is
136 ÷ (25.4 / 400) = 2141 Hz.
Accordingly, as the photosensitive drum 10 rotates, the photosensitive drum
A very small but constant pitch in the circumferential direction of the drum 10
A streak-like latent image along the axial direction of the photosensitive drum 10
Some parts are not formed. However, the charging roll
12 and bias voltage applied to developing sleeve 20
Is set to a large frequency, and even if an image is formed
This part appears as a strong and weak stripe pattern recognized by the human eye.
Not to be. However, the above-described latent image forming scan pulse,
Depending on the interference between the electric bias voltage and the developing bias voltage,
Streak-like non-charged along the axial direction of the photoconductor drum 10
Width of part, undeveloped part, part where latent image is not formed
Spread, and the formed image is recognized by human eyes
White streaks may occur. That is, the frequency of the charging bias voltage is f_c
And the frequency of the developing bias voltage is f_dThen,
Frequency f to bias voltage_d−f_cThis swell
Causes unevenness of an image visible to human eyes. Also, submarine
Let the frequency of the image forming scan pulse be f_rThen, the latent image formation run
F_r−f_cThe swell occurs, which is also the human eye
This can cause unevenness in the image that appears. In this embodiment, in order to prevent this, FIG.
The frequency control means shown in FIG. here
Is the basic pulse of the latent image forming scanning pulse of the latent image forming unit 18
Frequency f_r, And divide this fundamental frequency
And the frequency f of the charging bias voltage_cAnd development vias
Voltage frequency f_dHave gained. In FIG. 3, reference numeral 28 denotes a selector.
The selector 28 receives the frequency signal of the latent image forming unit 18.
Is forced. The frequency signal of the latent image forming unit 18 is, for example, a latent image
From a sensor provided on the forming unit 18 or from a latent image
Can be obtained from the motor driving the vessel 18. Also,
The selector 28 receives the clock signal and the selection signal.
It is. Clock signal and selection signal are not shown
Input from CPU. The selection signal is the frequency signal described above.
And a clock signal to be selected. The frequency signal of the latent image forming unit 18 is
The frequency is obtained directly from the start-up state of the
The clock signal is obtained from another oscillation source. Accordingly
Therefore, the clock signal has the same frequency as that of the latent image forming device 18.
It does not always vibrate at the wave number. Here, the image forming apparatus
Immediately after turning on the power of the
Immediately after the barry, the latent image forming unit 18 is in the off state.
Therefore, the normal scanning frequency cannot be obtained, and the CPU
Selector 28 selects the clock signal according to the selection signal of
Then, the signals are transmitted to the frequency dividers 30 and 32. In this unsteady state
Clock output and charging
The frequency of the bias and the developing bias is
It is not necessary to be based on the wave number. And
In the steady state of the image forming apparatus, the selection signal
The device 28 selects the frequency signal of the latent image forming device 18 and divides the frequency signal.
To the devices 30 and 32. The frequency divider 30 is connected to the base selected by the selector 28.
The base frequency is divided and the frequency of the latent image
Base frequency by charging signal, frequency of charging bias voltage
f_cAnd the frequency f of the developing bias voltage_dIs an integer multiple
become. The frequency obtained by the frequency divider 30 is charged
If the roll 12 is on, it is charged through the gate 34
To the AC power supply 14
The frequency obtained at 32 is when the developing sleeve 20 is on.
Then, it is supplied to the developing AC power supply 22 through the gate 36.
It is supposed to be. Therefore, the gates 34 and 36
Are the AC power source 14 for charging or the developing sleeve 2
A signal representing ON / OFF of 0 is input. In addition,
Here, one or both of the frequency dividers 30 and 32 are not provided.
To match any or all of the above three frequencies.
It is also possible. [0025]B. Operation and effects of the embodiment Here, immediately after the image forming apparatus is turned on,
Immediately after recovery after the clogging, the latent image forming device 1
8 is not turned on, so that the periphery of the latent image
The wave number signal is not input to the selector 28. At that time, C
The selector 28 always oscillates according to the selection signal from the PU.
Clock signal is selected and sent to frequency dividers 30 and 32.
I believe. Frequency dividers 30 and 32 divide the frequency of the clock signal.
To the gates 34 and 36. And at this time
The charging roll 12 is on and passes through the gate 34.
The divided frequency is given to the charging AC power supply 14
You. On the other hand, the developing sleeve 20 is off and the gate 36
And the developing AC power supply 22 is given a frequency.
Not. For this reason, the photoconductor drum by the charging roll 12 is used.
Only the surface charging of the system 10 is performed. Thereafter, the image forming apparatus enters a steady state.
The latent image forming unit 18 is turned on, and the selector 28
The frequency signal of the generator 18 is input. At this time, select
The signal causes the selector 28 to transmit the frequency signal of the latent image
The number is selected and transmitted to the frequency dividers 30 and 32. Frequency divider 3
0, 32 divides this frequency signal to form a gate 34,
36. At this time, the charging roll 12
And the developing sleeve 20 are both turned on,
AC power supply 14 for charging and developing
The divided frequency is supplied to the AC power supply 22. This
Thus, the frequency f of the latent image forming scanning pulse of the latent image forming unit 18 is
_r, Charging bias voltage frequency f_cAnd development bias voltage
Pressure frequency f_dBecomes an integral multiple. FIG. 4 shows a latent image obtained by the above configuration.
Scanning pulse for forming latent image in forming unit 18, charging roll 12
Component of the bias voltage applied to the
Each waveform of the AC component of the bias voltage applied to the probe 20
FIG. Here, as described above, the latent image
The frequency f of the scan pulse of the generator 18_rWith 2141 Hz
Then, the frequency is reduced by half to 1070.5
Hz (f_c) To the charging bias voltage,
2 as it is without providing 2141 Hz (f_d) Frequency
The case where the bias is applied to the developing bias voltage is taken as an example. Figure 4
The solid line shows the pulse waveform, and the broken line shows the mutual electromagnetic induction.
5 shows a waveform generated by interfering. Here, the charging bias voltage is applied to the developing bias voltage.
Even if the pressure interferes, the charging bias voltage frequency f_cIs developed
Frequency f of bias voltage_dBig to be half of
No effect. This is because there is one peak of the developing bias voltage.
Even if it disappears every other time, every other peak remains
The width of the undeveloped portion of the surface of the photosensitive drum 10 is
This is because it can be made smaller. Also, charged vias
Charging bias when the developing bias voltage interferes with the
Even if every other peak of the ass voltage disappears,
Every other peak remains on the surface of the photosensitive drum 10
The width of the uncharged portion can be reduced. In other words, here, f_d= 2f_cIn the relationship
Swell (given as a dashed envelope in FIG. 4).
Frequency f)_d−f_c= F_cAnd f_cItself
Because the value is set to a value that is not readily apparent,
They are not recognized as such. Further, the latent image forming scanning pulse and the charging bias
The same applies to the case where the voltage interferes. In this case, for example
Suppose you copy a halftone original with low density
As shown in FIG. 4, the peak of the latent image forming scan pulse is
A width W1 that partially disappears and no latent image is formed occurs.
I do. However, another peak of the latent image forming scan pulse
The image is formed on the sheet by remaining every other
Does not produce stripes large enough to be recognized by the human eye
No. That is, f_r= 2f_cBecause i have a relationship
The swell (given as the dashed envelope in FIG. 4)
Frequency f_r−f_c= F_cAnd f_cCan it be understood by human eyes?
Is set to a value that is not acceptable.
They are not recognized. From FIG. 4 also, the width W1 is f_c
It can be seen that the wavelength is shorter than the wavelength corresponding to. FIG. 5 is a graph showing a comparative example. here
Then, the frequency f of the pulse of the latent image_r160
5.75 Hz, and the charging bias voltage frequency f_c3
It is set to 1070.5 Hz, which is two-half. In this case, latent image formation
When the scanning pulse partially disappears, no latent image is formed.
Not a large width W2 occurs. Moreover, the peak next to it
Has also partially disappeared. This is f_r−f_c= 1.5f_cTona
This is because that. Therefore, the image formed on the sheet
Sometimes large stripes appear and are easily recognized by human eyes
No. On the other hand, in the first embodiment, recognition by human eyes
It is possible to obtain a good image in which
Wear. [0033]C. Modification example In the above embodiment, the latent image forming scanning pulse is used as a basis.
Then, this is divided, but it is not limited to this.
The frequency of the charging bias voltage is set higher than
The frequency of the ias voltage may be based. (2) Second embodimentA. Configuration of the embodiment Next, FIG. 2 shows an image forming apparatus according to a second embodiment of the present invention.
FIG. The configuration of the second embodiment is entirely the first embodiment.
In common with the embodiment, common components are shown in FIG.
The same reference numerals are given and the description is omitted. In the second embodiment, the charging roll 12
A shielding plate 40 is provided between the selector 28 and the selector 28. this
The shielding plate 40 has a charging bias voltage and a developing bias voltage.
Is provided to prevent electromagnetic induction between
For example, it is formed of metal. Also a shielding plate
40 is disposed at a position close to the photosensitive drum 10.
And grounded. [0036]B. Operation and effects of the embodiment FIG. 6 shows a latent image forming device 18 obtained according to the second embodiment.
Latent image forming scanning pulse applied to the charging roll 12
The AC component of the bias voltage and the mark on the developing sleeve 20
Graph showing each waveform of the AC component of the applied bias voltage
It is. Here, by providing the shielding plate 40,
Mutual interference occurs between the charging pulse and the developing pulse.
And both the charging pulse and the developing pulse have the desired waveforms.
ing. FIG. 7 shows a configuration in which a shielding plate 40 is not provided.
A comparative example in the case of the above is shown. In this case, the developing bias
The waveform of the charging bias voltage is added to the voltage. Where
When the charging bias voltage interferes with the bias voltage,
Even if every other peak of the ass voltage disappears,
Every other peak remains on the surface of the photosensitive drum 10
The width of the portion that is not developed can be reduced. Only
And, of course, it is desirable that such peaks do not disappear.
New Further, the developing bias voltage is applied to the charging bias voltage.
When the pressure interferes, the rise behavior of the developing bias voltage
However, it rides on the charging bias voltage. This is the charging
Appears as disturbances in the basic waveform of the bias voltage, causing charging bias
Some of the voltage is emphasized. This is the photosensitive drum 10
The potential difference on the surface causes the surface of the photosensitive drum 10
Development as if a latent image had been formed
Is performed, and the image formed on the sheet also becomes uneven.
You. This unevenness becomes striped fog and is recognized by human eyes.
May be perceived. On the other hand, the second embodiment
Now, it is good to prevent the occurrence of stripes that can be recognized by human eyes.
Good images can be obtained. [0039]C. Modification example Note that the second embodiment has all the configurations of the first embodiment.
However, the present invention is not limited to this.
A shielding plate 40 is provided separately from the frequency control which is a feature
Embodiments can also be used. In this case, the charged via
Between the source voltage and the developing bias voltage.
Need to control the frequency as above to prevent it from happening
Because there is no. [0040] As described above, the image according to the present invention is provided.
According to the image forming apparatus, a bias voltage having an AC component
Prevents the occurrence of stripes that can be recognized by the human eye due to
A good image can be formed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a configuration of a first embodiment according to the present invention. FIG. 2 is a schematic diagram showing a configuration of a second embodiment according to the present invention. FIG. 3 is a block diagram showing frequency control means used in the first embodiment. FIG. 4 is a graph showing waveforms of a latent image forming scan pulse, a charging bias, and a developing bias according to the first embodiment. FIG. 5 is a graph showing waveforms of a latent image forming scan pulse, a charging bias, and a developing bias according to a comparative example. FIG. 6 is a graph showing waveforms of a charging bias and a developing bias according to a second embodiment. FIG. 7 is a graph showing waveforms of a charging bias and a developing bias according to a comparative example. DESCRIPTION OF SYMBOLS 10 photoconductor drum (image carrier), 12 charging roll (charging means), 14 charging AC power supply, 16 charging DC power supply, 18 latent image forming device (latent image forming means), 19
Developing device 20 developing sleeve (developing means), 22 developing AC power source, 24 developing DC power source, 26 sheets,
28 selector, 30, 32 divider, 34, 36
Gate, 40 shielding plate (shielding means).

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Claims (1)

Claims: 1. A charging unit for applying a charging bias voltage having an AC component to an image carrier, and a developing bias voltage having an AC component is applied to the image carrier while applying a developing bias voltage to the image carrier. An image forming apparatus comprising: a developing unit that develops a toner image; and a shielding unit that shields the charging bias voltage and the developing bias voltage is provided between the charging unit and the developing unit. .