JPH0833534B2 - Image forming device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image forming apparatus using a ferroelectric liquid crystal.

[Prior Art] Clarke and Lager Wall, JP-A-56-107216
A ferroelectric liquid crystal device exhibiting a high-speed response and a memory property has been proposed in U.S. Pat.

This ferroelectric liquid crystal is disclosed, for example, by Kaneko in JP-A-59-129.
No. 837 or No. 59-193426 by Kannabe et al.,
Line-sequential writing can be performed by the driving method disclosed in Japanese Patent Laid-Open Nos. 59-193427 and 60-31121.

Moreover, in applying the multiplexing drive to the ferroelectric liquid crystal element in Japanese Patent Laid-Open No. 60-33535, Kamibe et al. Apply an AC voltage equal to or lower than a threshold voltage to a pixel (shutter opening) on a non-selected scanning line. It proposes an improved driving method for eliminating the DC component applied to the pixels on the non-selected scan lines by applying the voltage. According to this driving method, for example, even when a black signal is continuously applied from the data line to the pixels written in white on the non-selected scanning line, the white written state can be maintained. Improvements have been made in points.

[Problems to be solved by the invention]

By the way, when the present inventors used a ferroelectric liquid crystal element driven by a multiplexing method in a printer head of an electrophotographic copying machine, the transmittance of the liquid crystal micro-shutter portion under a bright state (shutter opening) was reduced. Has been found to vary depending on the pulse applied during non-selective scanning, making it impossible to obtain a print image expressing the desired gradation. As shown in FIG. 9, a method for obtaining a print image expressing gradation by using an electrophotographic printer using a liquid crystal micro-shutter array is shown in FIG. There is known a method of obtaining a gradation print image by controlling the transmittance in the liquid crystal micro-shutter unit because discharge is generated.

Therefore, in producing a gradation print image with an electrophotographic printer using a liquid crystal micro-shutter array, fluctuations in transmittance at the liquid crystal micro-shutter portion are not desirable. In particular, according to the experiments conducted by the present inventors, the variation in the transmittance of the liquid crystal micro shutter in the dark state (shutter blocking) has almost no effect on the production of a gradation print image. However, it was found that the transmittance variation at the opening of the shutter had a fatal effect on the gradation expression.

The phenomenon described above is caused by the ferroelectric liquid crystal micro-shutter part on the non-selected scanning line (hereinafter referred to as the FLC micro-shutter part).
If an AC pulse is applied even if the voltage is below the threshold voltage,
It was found that the liquid crystal molecules fluctuate depending on the polarity of the AC pulse, and therefore the transmittance of the FLC micro shutter on the non-selected scan line fluctuates according to the polarity of the AC pulse.

According to the optical response curve 11 shown in FIG. 1 (a), when a V ₀ pulse below the threshold voltage is applied to the ferroelectric liquid crystal aligned to the bright level, the liquid crystal molecules are once aligned to the dark level side, It turns out that it will return to the original bright level again. Further, according to the optical response curve 13 shown in FIG. 1 (b), when a V ₀ pulse below the threshold voltage is applied to the ferroelectric liquid crystal aligned in the dark level, the liquid crystal molecules are once aligned in the bright level side. Then, it turns out that it will return to the original dark level again. Therefore, since the V ₀ pulse and the V ₀ pulse are alternately applied from the data line to the FLC micro shutter section on the non-selected scanning line, the FLC
In the micro shutter section, the transmittance changes according to the V ₀ pulse and the V ₀ pulse.

[Means for Solving Problems] and [Operation] Therefore, an object of the present invention is to provide an image forming apparatus which solves the above problems.

The present invention relates to an electrophotographic image forming apparatus including a light source, a photoconductor, and a liquid crystal shutter array arranged in an optical path between the light source and the photoconductor, wherein the liquid crystal shutter array is a scanning device. A plurality of shutter parts formed by arranging chiral smectic liquid crystal at the intersections of the line groups and the data line groups, and the shutter parts on the selected scanning line are set to the bright state or the dark state, and on the unselected scanning lines. A means for applying a scanning signal to the scanning line and a data signal to the data line so that the alternating waveform voltage is applied to the shutter portion, and the polarity of the alternating waveform voltage at the time average value is selected. It is characterized in that it has the same polarity as the polarity of the voltage that brings the shutter portion on the scanning line into the bright state.

According to the present invention, variation in the transmittance of the non-selected shutter portion in the bright state due to the alternating waveform voltage is suppressed, and a good electrostatic latent image is formed on the photoconductor. In this way, high quality image formation by the electrophotographic method becomes possible.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to the drawings as necessary.

As the liquid crystal material used in the present invention, those particularly suitable are
A chiral smectic liquid crystal having ferroelectricity. Specifically, the chiral smectic C phase (Sm
C ^* ), chiral smectic G phase (SmG ^* ), chiral smectic F phase (SmF ^* ), chiral smectic I phase (SmI ^* ) or chiral smectic H phase (SmH ^* ) liquid crystal Can be used.

 For more information on ferroelectric liquid crystals, see, for example, “Le Jouille”.
"Lunard de Fujique Lettle" ("LEJOURNAL
DE PHY SIQUE LETTRE ")36(L-69) 1975 "Fuerlo Ele
Kritsk Liquid Crystal "(Ferroelectric
Liquid Crystals; “Applied Fujitsukusu Letter
("Applied Physics Letters")36(11) 1980
"Sub-micro second bistable electro
Optics, Switching, In, Liquid, Chris
Tars "(" Submicro Second Bistable Electrooptic
Switching in Liquid Crystals ");" Solid physics "16
(141) 1981 “Liquid crystal” and the like. Ferroelectricity
Specific examples of the liquid crystal compound include p-decyloxybenzili.
Den-p'-amino-2-methylbutyl cinnamate
(DOBAMBC), p-hexyloxybenzylidene-p'-
Amino-2-chloropropyl cinnamate (HOBACP
C), p-decyloxybenzylidene-p'-amino-2
-Methylbutyl-α-cyanocinnamate (DOBAMBC
C), p-tetradecyloxybenzylidene-p'-ami
No-2-methylbutyl-α-cyanocinnamate (TDOB
AMBCC), p-octyloxybenzylidene-p'-a
Mino-2-methylbutyl-α-chlorocinnamate (OO
BAMBCC), p-octyloxybenzylidene-p'-a
Mino-2-methylbutyl-α-methylcinnamate, 4,
4′-Asoxycin
Butyl ester 4-0- (2-methyl) -butyl ester
Zolsilidene-4'-octylaniline (MBRA 8), 4
-(2'-methylbutyl) phenyl-4'-octylio
Xybiphenyl-4-carboxylate, 4-hexyl
Oxyphenyl-4- (2 ″ -methylbutyl) biphenyl
Le-4'-carboxylate, 4-octyloxyphene
Nyl-4- (2 "methylbutyl) biphenyl-4'-carb
Ruboxylate, 4-heptylphenyl-4- (4 "-
Methylhexyl) biphenyl-4'-carboxyl
4- (2 "-methylbutyl) phenyl-4- (4"
-Methylhexyl) biphenyl-4'-carboxyl
Can be used.

In particular, as the preferable ferroelectric liquid crystal, a liquid crystal exhibiting a cholesteric phase on the high temperature side can be used, and for example, a phenyl ester liquid crystal having a phase transition temperature described in the examples below can be used. .

When an element is formed using these materials, the element can be supported by a copper block or the like in which a heater is embedded, if necessary, because the temperature is maintained such that the liquid crystal compound is in a desired phase.

FIG. 2 is a schematic drawing of an example of a cell for explaining the operation of the ferroelectric liquid crystal. Hereinafter, as a desired phase
Take SmC ^* as an example.

21a and 21b are In ₂ O ₃ or ITO (Indium-Tin Oxide)
Is a substrate (glass plate) covered with a transparent electrode composed of a thin film such as SmC ^* phase, in which the liquid crystal molecular layer 22 is oriented so as to be perpendicular to the glass surface. A thick line 23 represents a liquid crystal molecule, and the liquid crystal molecule 23 continuously forms a spiral structure in the plane direction of the substrate. The angle between the central axis 25 of this helical structure and the axial direction of the liquid crystal molecules 23 is expressed as. The liquid crystal molecule 23 has a dipole moment (P⊥) 24 in a direction orthogonal to the molecule. When a voltage of a certain threshold value or more is applied between the electrodes on the substrates 21a and 21b, the helical structure of the liquid crystal molecules 23 is unraveled,
The orientation of the liquid crystal molecules 23 can be changed so that all the dipole moments (P⊥) 24 are oriented in the electric field direction. The liquid crystal molecules 23 have an elongated shape and exhibit refractive index anisotropy in the major axis direction and the minor axis direction thereof. It is easily understood that the liquid crystal optical element has optical characteristics that change depending on the polarity.

The liquid crystal cell preferably used in the liquid crystal optical element of the present invention can be, for example, 10 μm or less. As shown in FIG. 3, as the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules unwinds and becomes a non-helical structure even when no electric field is applied, and its dipole moment Pa or Pb is upward (34a ) Or downward (34b). An angle that is 1/2 of the angle formed by the molecular axis of the liquid crystal molecular axis 33a and 33b is called a tilt angle (θ). When an electric field Ea or Eb having a polarity equal to or higher than a certain threshold value is applied to such a cell by the voltage applying means 31a and 31b, the dipole moment corresponds to the electric field vector of the electric field Ea or Eb. Then, the direction is changed to the upward direction 34a or the downward direction 34b, and the liquid crystal molecules are aligned in either one of the stable alignment 33a and the other stable alignment 33b accordingly.

As described above, there are two advantages of using such ferroelectricity as a liquid crystal optical element. The first is that the response speed is extremely fast, and the second is that the alignment of the liquid crystal molecules has bistability. The second point is, for example, the third
Explaining further by the figure, when an electric field Ea is applied, the liquid crystal molecules are aligned in one stable alignment 33a, but this state is stable even when the electric field is cut off. When an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented in another stable orientation 33b to change the orientation of the molecules, but they remain in this state even when the electric field is turned off.

It is preferable that the cell thickness is as thin as possible in order to effectively realize such a high response speed and bistability.

The ferroelectric liquid crystal (FLC) micro shutter array 41 shown in FIG. 4 has scanning lines S ₁ , S ₂ , S ₃ , ---- and data lines.
The matrix electrode structure forming the FLC micro-shutter section 42 is wired at the intersections with I ₁ , I ₂ , I ₃ , and ---. The above-mentioned ferroelectric liquid crystal is arranged between the scanning line and the data line.

FIG. 5 shows waveforms of signal pulses applied to the scanning lines and the data lines of the display panel. I ₁ in the figure is the data line I ₁
S ₁ and S ₂ are time-series waveforms of the scanning signals applied to the scanning lines S ₁ and S ₂ , respectively. According to FIG. 5, the scan selection signals alternating at 2V ₀ and 2V ₀ are sequentially applied to the scan lines S ₁ , S ₂ , ----- at the write timings t ₁ , t ₂ , -----. The DC bias voltage Vs is applied to the scanning line when not selected. Alternating data signals are applied to the data lines I ₁ , I ₂ --- in synchronization with the scan selection signals applied at the write timings t ₁ , t ₂ ---. At this time, V ₀ → V ₀
Set the alternating voltage to the shutter shutoff signal and V ₀ → V ₀ to the shutter opening signal.

Further, (I ₁ -S ₂ ) in FIG. 5 represents a time-series waveform of the voltage signal applied to the FLC micro shutter section A shown in FIG.

According to the driving method of the present invention, of the write timing,
At t _0, which is the phase that determines the open / closed state of the FLC micro shutter section 41, a switching pulse of 3V ₀ exceeding the threshold voltage is applied to the FLC micro shutter section A, and the FLC micro shutter section A shifts to the shutter. It is in the open state (bright state). To the FLC micro-shutter section A after the shutter has been opened, the data signal applied to the data line at the write timings t ₂ , t ₃ and ----- and the non-selected scanning of the scanning line are applied. The DC bias voltage Vs is applied. Therefore, an alternating waveform voltage of (V ₀ + Vs) and (−V ₀ + Vs) is applied to the FLC micro-shutter section A during non-selective scanning. In the present embodiment, | Vth |> | (-V ₀ + V
s) |> | (-V ₀ + Vs) | is set so that the voltage value is set so that a pulse of (-V ₀ + Vs) is applied to the FLC micro-shutter under open condition (open in Fig. 5). As shown in the optical response curve 12 shown in FIG. 1, the decrease in the transmittance is suppressed to a small level in the output section as compared with the case where the V ₀ pulse is applied, and (V ₀ + V
In the FLC micro-shutter section under the shutter shut-off state (closed in Fig. 5) to which pulse (s) is applied, the transmittance is higher than that when V ₀ pulse is applied as shown in the optical response curve 14 in Fig. 1. Causing a rise.

Therefore, the FLC micro-shutter section A shown in FIG.
When scanning is selected, a switching pulse of 3V ₀ is applied at t ₀ of t ₁ to open the shutter, and when scanning is not selected.
At t ₂ and t ₃ -----, (V ₀ + Vs) below the threshold voltage → (-V ₀
+ Vs) Alternating waveform voltage is applied. When a (-V ₀ + Vs) pulse is applied to the FLC micro-shutter section A, the transmittance is lowered as shown by the optical response curve 12 in FIG.
It is sufficiently small compared to when the V ₀ pulse is applied. In addition, 3V is applied to this FLC micro shutter A
_Since one polarization axis of 90 ° crossed Nicols and the ferroelectric liquid crystal molecular axis are arranged so that the FLC micro-shutter section A is in the brightest state when ₀ pulse is applied, scanning non- Even if a (V ₀ + Vs) pulse is applied to the FLC micro-shutter section A at the time of selection, its transmittance does not change.

Although not shown, the phase t _{0 of} t ₁ when scanning is selected
A switching pulse of 3V ₀ is applied to the FLC micro-shutter part that is shut off (dark state).
The same (V ₀ + Vs) → (-V ₀ + Vs) alternating waveform voltage as described above is applied, but if a (V ₀ + Vs) pulse is applied when scanning is not selected for this FLC micro shutter. , First
As shown by the optical response curve 14 in the figure, the transmittance when the shutter is shut off increases for a moment. Also, when shutting off the shutter,
Since the darkest state is taken with the arrangement of the polarization axis and the molecular axis so as to take the brightest state when the shutter is opened, even if the (-V ₀ + Vs) pulse is applied when scanning is not selected, No change occurs in the transmittance.

By the way, according to the experiments by the present inventors, even if the degree of increase in the transmittance at the time of shutting off the shutter is large, the image quality of the printed image is hardly affected, but the transmission at the time of opening the shutter is If the degree of decrease in the rate is large, the image quality of the print image is adversely affected, and especially when a gradation print image is created by controlling the amount of light irradiated to the photosensitive drum according to the gradation, the Although the problem that gradation cannot be expressed has been found, the present invention sufficiently suppresses the degree of decrease in transmittance at the time of opening the shutter, and creates a print image that expresses the desired gradation. can do.

Therefore, even if the voltage margin for driving the liquid crystal element is slightly reduced (in this case, the margin corresponding to the bias voltage Vs applied to the non-selected scan lines is reduced), the drive with the bias Vs applied is applied. It was found that the flicker on the display screen is eliminated by the method, so the display quality is much better.

Furthermore, although the present invention causes DC imbalance,
The adverse effect that this DC unbalance is applied to the liquid crystal material is
By adopting a method of performing current passivation with an insulating film such as a SiO ₂ film, a polyimide film, or a polyvinyl alcohol film, the above-mentioned adverse effects can be eliminated.
As a method of carrying out the current passivation, for example, a method of providing the above-mentioned insulating film on the transparent electrode functioning as a scanning line or a data line can be adopted. The thickness of the insulating film used at this time is about 100 Å ~ 2 nm,
A range of 500Å to 5000Å is suitable.

Further, in the present invention, in order to align the ferroelectric liquid crystal,
A uniaxial orientation treatment such as a rubbing treatment can be applied to the above-mentioned insulating film, and an orientation control film having a uniaxial orientation treatment axis can be provided on the above-mentioned insulating film. As the orientation control film used at this time, a polyvinyl alcohol film provided on a SiO ₂ film or a film formed by applying a silane coupling agent can be used.

Further, since the ferroelectric liquid crystal used in the driving method of the present invention has a lower ionic conductivity than the nematic phase,
Even if DC imbalance is used, liquid crystal deterioration can be sufficiently suppressed.

In another embodiment of the invention, the bias voltage shown in FIG.
By superimposing Vs on the data signal, it is possible to eliminate the decrease in transmittance when the shutter is opened. The data signal used in this case is shown in FIG. According to the data signal waveform shown in FIG. 6, FLC when Vs having the same polarity as 3V ₀ that gives a shutter opening at the phase t ₀ that determines the open / closed state is not selected
A bias voltage is applied to the micro shutter section.

FIG. 7 shows another driving example of the present invention. Seventh
According to the drive waveform example shown in the figure, an example in which an AC voltage that generates a bias voltage of Vs with a temporal average value is applied to the scanning line when not selected is clarified. In this example, the FLC micro shutter section to which the shutter opening signal of 3V ₀ is applied at the time of scanning selection has the same polarity as the shutter opening signal at the time of non-selection.
An AC voltage superimposed with a Vs bias voltage is applied,
It is possible to sufficiently suppress the degree of decrease in transmittance when the shutter is opened.

Write pulse widths (t ₁ , t ₂ , − used in the driving method of the present invention
---) is several μsec to several 100 msec, preferably 1 μsec
It can be set to ~ 10 msec, and the voltage peak value V _{0 at} this time is 1 V
-20V, preferably 5-10V. Also, the bias voltage Vs
As the voltage peak value V ₀ 1/5 to 1/50, preferably 1/10
Set to a value of ~ 1/20.

Further, in the driving example of the present invention, 3V ₀ and 3V ₀ during writing
However, the present invention is not limited to this voltage value. When the peak value of this switching pulse is Va, | Va |> | Vth |> | V ₀ | The switching pulse voltage can be set to a value having the relationship of (where Vth is the threshold voltage of the ferroelectric liquid crystal in the write pulse width).

FIG. 8 is a sectional view schematically showing a preferred specific example of the ferroelectric liquid crystal element used in the present invention. FIG.
FIG. 8 is a cross-sectional view of the vertical layer 22 formed by a plurality of chiral smectic liquid crystal molecules as seen from the normal direction, and 81 in FIG. 8 is the liquid crystal molecule 33a or 33b shown in FIG. Vertical layer
The reference numeral 82 represents a projection (C-director), and the reference numeral 82 represents the tip of the liquid crystal molecule 33a or 33b on the vertical layer 22 described above. Therefore, according to FIG. 8, the liquid crystal molecules in the vertical layer 22 are oriented substantially parallel to each other, and the tilt angle θ can be brought close to the maximum tilt angle. This state is referred to as a “new-home” orientation state.

In the uniform orientation state shown in FIG. 8, even in the memory state when the applied voltage is cut off, the high transmittance characteristic or the light shielding characteristic when the voltage is applied can be maintained as it is.

In a preferred embodiment of the present invention, the pretreatment for AC application is effective for the ferroelectric liquid crystal to adopt the uniform alignment state shown in FIG. The tilt θ described above can be increased to an angle equal to or about the same as the tilt in the spiral structure by this AC application pretreatment. As the alternating current used at this time, the voltage is 20 to 500 volts, preferably 30 to 150 volts.
A frequency of 10 to 500 Hz, preferably 10 to 200 Hz can be used as the voltage, and the AC application pretreatment can be performed with the application time of about several seconds to 10 minutes. Further, the AC application pretreatment is performed before the writing of the liquid crystal element according to, for example, a video signal or a data signal, and preferably, the liquid crystal element is incorporated in the device and a wait time when operating the device. Then, the above-mentioned AC application pretreatment can be performed, or the AC application pretreatment can be performed even when manufacturing such a liquid crystal element.

The pre-treatment for AC application can be performed by increasing the tilt angle θ before application to the same degree as the tilt in the spiral structure, and even after removing the AC application, the tilt angle θ is increased. The tilt angle can be maintained.

FIG. 10 is a process diagram of an electrophotographic printer using a FLC micro shutter array. In FIG. 10, the light source 101 (light source for generating an optical signal) is constantly lit and constantly illuminates the liquid crystal-optical shutter array element 100. In this shutter array element 100, a liquid crystal drive circuit (not shown) blocks light rays from a light source 101 to generate a light signal by making a selected area into a light-transmitting state, and irradiates the photosensitive drum 102. The rays can be controlled. Further, in order to obtain the converging property of the light beam from the light source 101 and the optical signal from the shutter array element 100, it is desirable to arrange the lenses 103 and 104 in the optical path.

The photoconductor drum 102 rotates in the direction of rotation of arrow 111, and the pre-exposure station is set prior to the irradiation of the optical signal.
After the entire surface is exposed by 112, it is charged positively or negatively by a charging station 105 equipped with a corona discharge device or the like in advance, and at the place where light is irradiated on the photosensitive drum 102, the charged charge disappears and an electrostatic latent image is formed. It At this time, as a light source used in the pre-exposure station 112, a light beam from the light source 101 incorporated in the shutter array element 100 can be used. Further, a halogen lamp, a fluorescent lamp or the like can be used as the light source in this case. The electrostatic latent image formed in this manner is magnetized by applying a phenomenon bias in the presence of a developer composed of toner and a carrier having the opposite polarity to the polarity at the time of charging at the developing unit 106 or the same polarity at the time of reversal development. After developing by a brush developing method or the like, it is transferred to the image holding member 108 (for example, paper) in the transfer unit 107, and then fixed by heat or pressure in the fixing unit 109 to obtain a completely fixed printed matter. To be

The photosensitive drum that has passed through the transfer unit 107 is cleaned by a cleaning unit 113.
Removes the toner remaining on the surface.

The photoconductor that receives the optical signal generated from the shutter array 100 is not limited to the electrophotographic type photoconductor as described above, but is, for example, a silver salt photographic type photoconductor (for example, monochrome paper, color paper, US 3M "Dry Silver", etc. ) May be sufficient.

〔The invention's effect〕

According to the present invention, when the ferroelectric liquid crystal element is applied to an electrophotographic printer, the latent image forming characteristics of the photosensitive drum can be improved, and it is particularly effective in producing a gradation print image.

[Brief description of drawings]

FIGS. 1A and 1B are explanatory diagrams showing optical response characteristics when a pulse is applied to a ferroelectric liquid crystal under bistable condition. 2 and 3 are perspective views schematically showing the ferroelectric liquid crystal element used in the present invention. FIG. 4 is a plan view of the matrix electrode structure used in the present invention. Fifth
FIG. 6, FIG. 6 and FIG. 7 are explanatory views showing examples of drive waveforms used in the drive method of the present invention. FIG. 8 is a sectional view showing a preferred embodiment of the ferroelectric liquid crystal element used in the present invention. FIG. 9 is an explanatory diagram showing the relationship between the surface potential of the photosensitive drum and the amount of exposure light. FIG. 10 is a process diagram of an electrophotographic printer using a ferroelectric liquid crystal element.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location G09G 3/36 H04N 1/036 B 1/23 103 Z (72) Inventor Tsutomu Toyono 3-chome Shimomaruko, Ota-ku, Tokyo No. 30-2 Canon Inc. (72) Inventor Junichiro Kannabe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP 62-28717 (JP, A)

Claims (3)

[Claims] 1. An electrophotographic image forming apparatus comprising: a light source; a photoconductor; and a liquid crystal shutter array arranged in an optical path between the light source and the photoconductor. A plurality of shutter parts formed by arranging chiral smectic liquid crystal at the intersections of the scanning line groups and the data line groups, and the shutter parts on the selected scanning line are set to the bright state or the dark state, and on the unselected scanning lines. Means for applying a scanning signal to the scanning line and a data signal to the data line so that the alternating waveform voltage is applied to the shutter section of the device, and the polarity in the time average value of the alternating waveform voltage is selected. An image forming apparatus having the same polarity as that of a voltage for bringing a shutter portion on the selected scanning line into a bright state. 2. A bias voltage for making the polarity of the time-averaged value of the alternating waveform voltage the same as the polarity of the voltage for bringing the shutter portion on the selected scanning line into the bright state on the data signal. The image forming apparatus according to claim 1, wherein: 3. A non-selected scanning line is provided with a bias voltage for making the polarity of the time-averaged value of the alternating waveform voltage the same as the polarity of the voltage for bringing the shutter portion on the selected scanning line into the bright state. The image forming apparatus according to claim 1, wherein: