JP2000330362A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain interference with various frequencies generated in a device to say nothing of spatial frequency by setting the frequency of the AC component of voltage applied to an image carrier so that the interference with the representative spatial frequency of each image formed at every processing speed which can be set may be restrained. SOLUTION: This device acts by selecting two kinds of processing speed. As for electrifying frequency and a moire pitch occurring state at the time of forming an image at the 1st processing speed, an area where the moire pitch is restrained to <=1 mm is 0 to 450 Hz, 840 to 960 Hz and 1080 to 1400 Hz. Meanwhile, there exist plural other areas where the moire pitch is restrained to <=1 mm as for the 2nd processing speed. Then, an electrifying frequency setting means sets the frequency restraining all the interference with the representative spatial frequency of each image formed at every processing speed which can be set, and electrifies by the AC voltage of the electrifying frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a charging means for selectively changing a plurality of process speeds and for charging a photosensitive member by applying a voltage having an AC component to an image carrier. The present invention relates to an image forming apparatus that forms an electrostatic latent image on the image carrier using a light beam.

[0002]

2. Description of the Related Art
In the case of an image forming apparatus, particularly a laser printer, a photosensitive drum as an image carrier is charged by using a discharge wire called a charge corotron. In this case, by using a DC power supply and applying a high voltage to the discharge wire,
By discharging the photoconductor drum, the surface of the photoconductor is uniformly charged.

[0003] However, such charging using a discharge wire is not preferable because, in particular, a large amount of undesired substances is generated due to generation of ozone and generation of knock.

Therefore, it has become mainstream to charge the surface of the photoconductor in a state in which it is in direct contact with the photoconductor drum called a charging roller instead of a discharge wire.

According to this charging roller, since there is almost no electric discharge, the generation of the undesirable gas can be suppressed. However, it is very difficult to uniformly charge the photosensitive drum surface with only a DC applied voltage.
It has been considered that charging is performed by writing a bias that combines AC and DC.

According to this, a uniform charging can be performed on the surface of the photosensitive drum more easily than with a DC-only power supply.

[0007] By the way, as long as the aforementioned alternating current is applied,
In terms of uniform charging, when viewed microscopically, unevenness is generated based on the AC voltage, and the strongly charged portion and the weakly charged portion are repeated at a predetermined pitch.

On the other hand, for example, when an image in which n-dot recording and n-dot non-recording are repeated is formed, the image has a spatial frequency, and when this spatial frequency and the charging frequency are approximated, interference occurs. Interference fringes (moire) may occur in an image.

Therefore, in order to prevent the occurrence of such moiré, it is necessary to determine the charging frequency so as not to approximate the spatial frequency.

Conventionally, when the charging frequency is determined, since the processing speed (process speed) of the printer is fixed (one type is fixed), the charging frequency far from the spatial frequency at this process speed can be uniquely determined. Was.

By the way, with the recent high performance of PCs,
Demands for high speed and high resolution printers have been increasing. Higher speeds have been addressed by increasing the process speed, but this has led to video rates without printers approaching the upper limit of current technology, and in this state the resolution has been doubled (the video rate has been quadrupled). ) Raising hair has become difficult. In order to solve this problem, the video rate has been reduced to twice, and the resolution has been doubled by halving the process speed instead. It is appearing in.

For this reason, it has two kinds of process speeds. The fact that there are two types of process speeds requires that the spatial frequency and the charging frequency at each process speed do not interfere with each other.

That is, two kinds of charging frequency voltages are prepared in advance, and a mechanism or the like for switching based on the determination of the process speed according to the request is required (for example, Japanese Patent Laid-Open No. 6-19278). reference). This leads to an increase in the number of parts and an increase in the size of the device.

In the above description, the spatial frequency is taken as an example. However, there are portions in the apparatus which interfere with the charging frequency, such as the frequency of the developing bias and the natural frequency of the driving system, and adversely affect the image. .

[0015] Therefore, when there are two kinds of charging frequency voltages, the allowable range is very narrow and cannot be easily set.

In consideration of the above facts, the present invention sets a single charging frequency that does not interfere with at least spatial frequencies at a plurality of process speeds, and suppresses interference with not only spatial frequencies but also various frequencies generated in the apparatus. It is an object of the present invention to obtain an image forming apparatus that can perform the above-described operations.

[0017]

According to a first aspect of the present invention, there is provided a light source for irradiating a light beam based on an image signal, an image carrier on which an electrostatic latent image is formed by the light source, and the image carrier. Charging means for substantially uniformly charging the surface of the body with a voltage having an AC component; transfer means for transferring an electrostatic latent image formed on the image carrier to a predetermined recording paper for development; and a process for the image carrier. Speed setting means capable of setting at least two or more types of speeds, and the interference is suppressed with respect to a representative spatial frequency of each image formed at all process speeds that can be set by the speed setting means. Charging frequency setting means for setting a frequency of an AC component of a voltage applied to the image carrier by the charging means.

According to the first aspect of the present invention, for example,
If processing can be performed at a plurality of process speeds, such as 1/2, based on the maximum process speed as an apparatus, the processing speed is increased according to a request, that is,
The process speed is determined by increasing the resolution. Thereby, it is possible to respond to the request.

By the way, if there are a plurality of process speeds, a spatial frequency exists according to the number. If this spatial frequency approximates the charging frequency, it causes moiré. Therefore, the charging frequency setting unit sets a frequency at which interference is suppressed in all of the representative spatial frequencies of the images formed at all the process speeds that can be set by the speed setting unit, and sets the charging frequency. It is charged by AC voltage. As a result, moire does not occur, and a decrease in image quality can be suppressed.

According to a second aspect of the present invention, a voltage which can be selectively changed to one of a first process speed and a second process speed and has an AC component is applied to the image carrier. An image forming apparatus for forming an electrostatic latent image on the image carrier by scanning of a light beam by a scanning unit, wherein the first process speed is set to PS1 ( mm / sec) and the first resolution corresponding to the first process speed PS1 (mm / sec) is R
ES1 (dpi), the second process speed is PS2 (mm
/ sec), the second resolution corresponding to the second process speed PS2 (mm / sec) is RES2 (dpi), n (n is a pitch of a light beam on / off repetitive image, a positive integer)
Assuming that the allowable limit of moire of the dot pitch image is Mn and the spatial frequency SFf2 (Hz) of the n dot pitch image is a frequency (Hz) at which all of the following equations (1) to (6) hold.
Is set to the voltage frequency CRf (Hz) of the AC component of the charging means.

CRf> PS1 / Mn + SFfn1 (1) CRf <-PS1 / Mn + SFfn1 (2) CRf> PS2 / Mn + SFfn2 (3) CRf <-PS2 / Mn + SFfn2 (4) ) CRf> RES1 × PS1 / (25.4 × k) (5) CRf> RES2 × PS2 / (25.4 × k) (6) where K: constant SFn1 = PS1 × RES1 / (25.4) × n)... (7) SFn2 = PS2 × RES2 / (25.4 × n).

According to the invention described in claim 2, generally,
If speed or resolution is required,
The maximum process speed of the device, for example 1 /
If two types of process speeds, ie, two process speeds, are prepared, the resolution can be doubled by the half process speed, and each requirement can be met.

In this case, the voltage frequency C of the AC component of the charging means such that all of the above equations (1) to (6) hold.
By setting Rf (Hz), it does not approximate any of the two representative spatial frequencies, thus suppressing interference,
Moire can be prevented from occurring.

In the second aspect, the equations for setting the charging frequency at two kinds of process speeds are shown. However, the above equations (1), (2) and (5) correspond to the first process speed. Equations (3), (4), and (6) correspond to the second process speed, and if a third or higher process speed is added, an equation corresponding to the third or higher process speed is added. do it. That is, claim 2
Is a basic formula showing that the charging frequency can be set at three process speeds.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Configuration of Optical Scanning Apparatus) FIG. 1 is a schematic diagram of an optical system of the optical scanning apparatus according to the present embodiment. The optical scanning device (FIG. 1) according to the present embodiment is used for a laser printer, a digital copying machine, and the like.

As shown in FIG. 1, the optical scanning device according to the present invention includes a light source unit 100 and a polygon mirror (rotational rotation) for receiving a laser beam emitted from the light source unit 100 and deflecting and scanning in the main scanning direction. A polygon mirror) 104 and an imaging optical system 102 for guiding and imaging the laser beam A that has been deflected and scanned on the surface of the photosensitive drum 106. "Light source unit" The light source unit 100 includes a semiconductor laser 108 that emits a laser beam having a substantially Gaussian distribution.

The laser beam A emitted from the light source unit 100 is a beam having a different divergence angle in a direction parallel and a direction perpendicular to the plane of polarization.
Is considered to be a loose divergent light. On the downstream side of the collimator lens 110, a beam shaping slit 112 is provided. Immediately after passing through the collimator lens 110, light only at the center of the divergent light passes through the slit 112 for beam shaping. It is designed to be incident. This light becomes light converging in the sub-scanning direction near the reflection surface of the polygon mirror 104.

The laser beam A that has passed through the cylindrical lens 114 is reflected by a reflection mirror 116,
The light is deflected in the direction of the polygon mirror 104. The incident angle of the laser beam A to the reflection mirror 116 is determined by the arrangement angle of the reflection mirror 116 itself.

The laser beam A is applied to the polygon mirror 104
Is substantially parallel light wider than the reflecting surface of the light emitting element, and has a so-called overfilled configuration. "Imaging optical system" Reflecting mirror 116 and polygon mirror 10
4, a pair of f having power only in the main scanning
The θ lens 118 is provided. Note that the fθ lens 118 is also on the optical path that is reflected by the reflection mirror 116 and reaches the polygon mirror 104.

The laser beam A deflected by the polygon mirror 104 passes through the fθ lens 118 again, is bent (reflected) at a predetermined angle by the bending mirror 120, is reflected by the cylindrical mirror 122, and is reflected by the photosensitive drum 1.
06 is formed.

The spot of the beam formed on the photosensitive drum 124 by the action of the fθ lens 118 is
One main scanning line is divided and scanned at a constant speed in the main scanning direction from the surface of the photosensitive drum 106.

As described above, when scanning of one line is performed, the laser beam A is deflected by the next reflection surface of the polygon mirror 104, and scanning of the next line is performed.

The polygon mirror 104 from the light source unit 100
Laser beam A reaching folding mirror 126 through
Is guided to a reflection mirror 126 disposed at a position different from that of the cylindrical mirror 122 at the start of one main scan of the polygon mirror 104. The laser beam A reflected by the reflection mirror 126 is transmitted via the lens 127 to the SOS (Star) for setting a write start position on the main scanning line where an image is recorded.
SOS sensor 12 for detecting a (t Of Scan) signal
8 is input. This SOS sensor 1
Reference numeral 28 is connected to a control unit (not shown), and the control unit starts modulating the image signal after a lapse of a predetermined time from when the output signal of 128 is detected from the SOS sensor. "Photosensitive drum 106" As shown in FIG. 2, the photosensitive drum 106 rotates at a constant speed in the clockwise direction (direction of arrow A) in FIG. 2, and is directly above the photosensitive drum 106 in FIG. The position is the image forming section 129 where the laser beam A output from the fθ lens 118 forms an image. Further, around the photosensitive drum 106, the developing unit 130 and the transfer unit 13 are sequentially arranged in the clockwise direction from the image forming unit 129.
1. The cleaner section 132 and the charging section 134 are arranged close to each other.

The charging section 134 has a charging roller 136 and is in contact with the peripheral surface of the photosensitive drum 106. Here, the surface of the photoconductor drum 106 can be uniformly (uniformly) charged by applying a predetermined voltage (a bias voltage combining AC and DC) to the charging roller 136. When a bias voltage is applied to the charging roller 136, the charging roller 136 has a charging frequency because of applying an alternating current. This charging frequency will be described later. (Process Speed) In the optical scanning device as described above, in the present embodiment, two types of process speeds can be selected and operated. The first process speed is 130 mm / sec, and when an image is formed at the first process speed, the resolution is 600 dpi. On the other hand, the second process speed is 65 mm / sec, and when an image is formed at the second process speed,
The resolution becomes 1200 dpi.

Therefore, when the processing speed is prioritized, the first process speed is set, and when the resolution is prioritized, the second process speed is set, and the optical scanning device is controlled.

Here, in the present embodiment, the image is formed at the two process speeds of the first process speed and the second process speed, whereas the charging frequency to the charging roller 136 is 1 Type is fixed.

The fixed charging frequency is determined by the above (1)
This is obtained based on equations (6) to (6). That is,
In the above equations (1) to (6), when forming an image at the first process speed, the spatial frequency in a striped image in which the laser beam A is turned on and off at an n-dot pitch cycle, and the second process In image formation at speed,
In consideration of a spatial frequency in a striped image in which the laser beam A is turned on and off at an n dot pitch cycle, generation of moire can be suppressed for image formation at any process speed. Has become.

The operation of this embodiment will be described below. (Moire-occurring charging frequency characteristics) As the characteristics of the image, for example, when the laser beam A is repeatedly turned on and off at a period of 2 to 6 dots, that is, when a stripe image is formed, the image has different spatial frequencies. . FIG. 3 shows the first
FIG. 4 shows the charging frequency when an image having an n dot pitch cycle is formed at the process speed of 1 and the state of occurrence of moiré pitch. The region where the moiré pitch is suppressed to 1 mm or less is approximately 0 to 450 Hz, 840 to 96 Hz.
It can be seen that the frequencies are 0 Hz and 1,080 to 1,400 Hz.

On the other hand, FIG. 4 shows the charging frequency when an image having an n-dot pitch period is formed at the second process speed and the state of occurrence of moiré pitch, and the pitch can be suppressed to 1 mm or less. It can be seen that the region is approximately 0 to 370 Hz and 1150 to 1300 Hz.

Therefore, if the charging frequency is not set within the range of the area common to both, interference occurs with one of the process speeds, which causes moire. However, if the frequencies in all common regions are appropriate frequencies,
In practice, at too low a frequency, uniform charging is not possible.

Therefore, using the above-described equations (1) to (6), the n value of the n dot pitch period is set to 2 to 5, and
When the value is even, the allowable moiré pitch is 0.5 m.
When m is an odd number, the pitch of the moiré is 1 mm, and a charging frequency band that does not interfere with both the first and second process speeds and enables uniform charging is determined. (Setting of Charging Frequency) First, the lowest frequency in the first process speed and the second process speed of the present embodiment is determined by using the expressions (5) and (6).

First, in equation (5), the lowest frequency at the first process speed is determined.

CRf> RES1 × PS1 / (25.4 × k) (5) Assuming that the constant k is 3.5, the resolution RES1 is 600 (dp
i) The first process speed PS1 is 130 (mm /
sec) to obtain the charging frequency CRf, CR
f> 877 (Hz).

Next, in equation (6), the lowest frequency at the second process speed is determined.

CRf> RES2 × PS2 / (25.4 × k) (6) Assuming that the constant k is 3.5, the resolution RES2 is 1200 (dp
i) The first process speed PS1 is 65 (mm / s)
ec) to obtain the charging frequency CRf, CRf
> 877 (Hz).

That is, at any process speed, 877 Hz is the lowest frequency.

Next, based on the equations (1) and (2), at the first process speed, the n value is set to 2 to 5, and the frequency limit value at each n value is obtained. CRf> PS1 / Mn + SFfn1 (1) CRf <-PS1 / Mn + SFfn1 (2) From the equations (1) and (2),

[0048]

[Table 1]

Next, based on the equations (3) and (4), at the second process speed, the n value is set to 2 to 5, and the frequency limit value at each n value is obtained. CRf> PS2 / Mn + SFfn2 (3) CRf <-PS2 / Mn + SFfn2 (4) From the expressions (3) and (4),

[0050]

[Table 2]

Here, in Tables 1 and 2, the values enclosed by squares are more appropriate values. Otherwise, the expressions (5) and (6)
The frequency is lower than the lowest frequency obtained by the formula or exceeds the applicable frequency. □ By rearranging the enclosed proper values, the maximum value of the charging frequency is CRf <1276, and together with the minimum frequency, the following equation (7) can be obtained.

1153 <CRf <1276 (Hz) (7) By setting the charging frequency in the range of the expression (7), the occurrence of moire can be suppressed.

In this embodiment, two types of process speeds and resolutions have been described as examples. However, the present invention is applicable to a printer having three or more types of process speeds and resolutions. That is, the equations corresponding to the process speed and the number of resolutions may be increased. However, as a trend,
As the number of types increases, the band in which the charging frequency can be set becomes narrower.

According to the present embodiment, in a printer having two (or more) process speeds and resolutions, only one charging frequency that does not interfere with a representative spatial frequency due to these process speeds or the like is determined. Therefore, means for switching the charging frequency and the like are not required, and the number of components can be reduced and the size of the apparatus can be reduced. In addition, since the charging frequency is fixed at one, interference with one charging frequency only needs to be suppressed with respect to the frequency of the bias voltage of the developing unit and the natural frequency of the apparatus.
Design is easier and leads to higher quality.

[0055]

As described above, the image forming apparatus according to the present invention sets a single charging frequency that does not interfere with the spatial frequency at least at a plurality of process speeds. It has an excellent effect that interference with frequency can be suppressed.

[Brief description of the drawings]

FIG. 1 is a perspective view of an optical scanning optical system according to an embodiment.

FIG. 2 is a front view of the photosensitive drum viewed from an axial direction.

FIG. 3 is a charging frequency-moire pitch characteristic diagram at a first process speed.

FIG. 4 is a graph showing charging frequency-moire pitch characteristics at a second process speed.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 light source unit 106 photosensitive drum 129 image forming unit 130 developing unit 134 charging unit 136 charging roller

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaru Sakuma 3-7-1, Fuuchi, Iwatsuki-shi, Saitama F-term in the Fuji Xerox Co., Ltd. Iwatsuki Office (Reference) 2H003 BB11 BB16 CC05 EE12 2H027 ED02 ED03 ED06 EE02 EE03 EE04 FA35 FA37 ZA01

Claims (2)

[Claims] A light source that irradiates a light beam based on an image signal; an image carrier on which an electrostatic latent image is formed by the light source; and a surface of the image carrier substantially uniformly by a voltage having an AC component. Charging means for charging; transfer means for transferring an electrostatic latent image formed on the image carrier to a predetermined recording paper for development; and speed setting means capable of setting at least two or more process speeds of the image carrier. An AC voltage applied by the charging unit to the image carrier so that interference is suppressed with respect to a representative spatial frequency of each image formed at all process speeds that can be set by the speed setting unit. An image forming apparatus comprising: a charging frequency setting unit that sets a frequency of a component. 2. The method according to claim 1, wherein the photosensitive member is charged by applying a voltage having an AC component to the image bearing member, which can be selectively changed to one of a first process speed and a second process speed. An image forming apparatus having an electrostatic latent image formed on the image carrier by scanning a light beam with a scanning unit, wherein the first process speed is set to PS1 (mm / sec), The first resolution corresponding to the process speed PS1 (mm / sec) is RES1 (dpi), and the second process speed is P1
S2 (mm / sec), second process speed PS2 (mm / sec)
RES2 (dpi), n (n is a pitch of a repetitive image of the light beam on and off, a positive integer) and Mn is the allowable limit of moire of the dot pitch image, and the spatial frequency of the n dot pitch image is When SFf2 (Hz),
A frequency at which all of the following equations (1) to (6) hold.
(Hz) to the voltage frequency CRf (H
An image forming apparatus, which is set in z). CRf> PS1 / Mn + SFfn1 (1) CRf <-PS1 / Mn + SFfn1 (2) CRf> PS2 / Mn + SFfn2 (3) CRf <-PS2 / Mn + SFfn2 (4) CRf> RES1 × PS1 / (25.4 × k) (5) CRf> RES2 × PS2 / (25.4 × k) (6) where K: constant SFn1 = PS1 × RES1 / (25.4 × n) .. (7) SFn2 = PS2 × RES2 / (25.4 × n) (8)