JPS60225830A - Image forming device and driving method thereof - Google Patents

Abstract

PURPOSE:To increase number of time division without decreasing an image forming speed by disposing microshutter group which sandwiches a liquid crystal between a substrate provided with plural segment electrodes and a substrate provided with a common electrode into the optical path for exposure. CONSTITUTION:An FET formed on the substrate 301 is provided with a gate electrode 302 connected to a gate line, a source electrode 303 connected to a data line and a drain electrode 304 for taking out a data signal. The electrode 304 is connected to the segment electrodes 307 forming a shutter part. The resistance of an a-Si film 305 decreases and the electrodes 303 and 304 are made conducting when a scanning signal is impressed to the electrode 302. The liquid crystal element is formed by sandwiching the N-P type liquid crystal between the substrate 301 and the counter substrate 311 in the orientation state and a transparent common electrode 312, a light shielding film 314 and an orientation control film 315 are provided on the substrate 311. The liquid crystal shutter array consisting of such element is disposed in the optical path for exposure via orthogonal polarizing plates 319, 320, by which the number of time division is increased without decreasing the image forming speed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus equipped with a printer head having a liquid crystal shutter array in which n (rows) by m (columns) micro shutter groups are arranged in a matrix and a light source, and a method for driving the same.

Until now, liquid crystal display elements and liquid crystal shutter arrays are well known, in which n scanning electrodes and m signal electrodes are arranged in a matrix, and a large number of pixels and shutter openings are formed of liquid crystal, which is a capacitive load element. It is being The driving method for this liquid crystal element is time-division driving in which an address signal is selectively and periodically applied to a group of scanning electrodes, and an information signal of raindrops is selectively applied in parallel to a group of signal electrodes in synchronization with the address signal. has been adopted. In this driving method, in equation (1) of F,
As the number of time divisions increases, VON (on signal)/
As VOFF (off reliability) approaches 1, the opening/closing efficiency of the liquid crystal elements constituting the pixels deteriorates. For this reason, especially in the case of a liquid crystal shutter array, it is not possible to provide an optical signal with a sufficient S/N ratio, and when this is used in the image exposure section (printer head) of an electrophotographic copying machine, it is difficult to produce a good image. I like the drawback of not being able to form.

(In the formula, 1/N; duty ratio.

1/a: bias ratio, ■0: applied voltage) In other words, the best driving condition is 1/1 duty-1, or stick driving, but this driving method requires that each pixel be controlled by a driver circuit. It has become. For example, A
In the case of a liquid crystal-shutter array that can generate a light spot with a pixel density of 16 dots/mm and a transversal width of -4 (Japanese Industrial Standards), 3360 drive circuits are required, and 32 drive circuits per IC. If the drive circuit is integrated, 105 ICs will be required. For this reason, the static driving method has the disadvantage that it is not suitable for driving a liquid crystal shutter array having high-density pixels or shutter openings.

That is, the purpose of the present invention is to increase the number of time divisions without slowing down the image forming speed (process speed), and to reduce the number of driving ICs, it is necessary to increase the breakdown voltage of the IC. This eliminates the conventional problem of not being able to reduce costs, and furthermore, the number of time divisions is only 1, whereas in the past, even if the image forming speed was slowed down, the number of time divisions was at most 4.
An object of the present invention is to provide an image forming apparatus equipped with a liquid crystal shutter array that increases the number of time divisions without slowing down the image forming speed and is therefore inexpensive and high performance, and a method for driving the same.

The object of the present invention is to provide a printer head equipped with an exposure light source and a group of microshutters that control the light beam in the exposure optical path of the exposure light source to either a light blocking state or a light transmitting state; In an image forming apparatus configured to irradiate an image holding member with an optical signal, the micro-shutter group is arranged in a matrix along a plurality of rows and columns, and the micro-shutter group is provided with a thin film and a common electrode. It has a structure in which a liquid crystal is sandwiched between the
applying a scanning signal to the gate line of the thin film transistor;
This is achieved by an image forming apparatus equipped with means for applying an electrical signal corresponding to image information to a data line in synchronization with this scanning signal.

The present invention will be explained below with reference to the drawings.

According to the inventors' experimental study, the gate voltage v of DC
When Δvth is the variation in the vIJ value voltage vth when gnc is applied per unit time (hr), the gate voltage Vgl ( When it exceeds about 4OV~60■), Δv
th is increasing exponentially. This indicates that the lifetime is rapidly shortened when the gate voltage vg exceeds Vgl. However, when the electric field strength applied to the gate insulating film is set to 5 x 105 V/cm or less, the gate voltage Vg can be increased without shortening the lifetime of the TPT, and therefore a sufficient S/N ratio can be achieved. , preferably an S/N ratio of 5 or more, preferably an S of 5 or more
Another feature is that it can generate an optical signal with a /N ratio.

TFT has Vg-Vth>Vs (Vg; gate voltage,
It is used in the non-saturation region of Vth: threshold voltage, VS: data transmission voltage), and is used in the non-saturation region.
(Vx (t); output voltage) is before the start of charging (1=0
), it is expressed by the following formula (2).

In the formula, m, τ (TFT charging time constant) and L (liquid crystal residual voltage potential) are expressed by the following formulas (3), (4) and (5), respectively.
It is expressed as

τ = −C・・・・・・・・・・・・(0Vs In the formula, C is the load amount, Vgh is the gate voltage on the positive side, t is the gate on time, or the following formula ( 4) Indicated by '.

ε0: Vacuum conductivity CF/cm) εS: Insulating film specific conductivity μ: Mobility (Cm2/Vsec) dins: Insulating layer thickness (am) L: Channel length [Cm] W: Channel width (cm) Formula According to (2), increasing the output power Vx (t) can be achieved by increasing the data voltage Vs, but from the relational expression V g −V th > V s, it is possible to increase the gate voltage Vg. It becomes necessary.

However, increasing the gate voltage Vg will shorten the lifetime of the TPT, and for this reason, a practical liquid crystal shutter array, especially an output voltage Vx (t) of more than 20 volts, can be achieved without shortening the lifetime of the TPT. A time-division driving method of a TFT matrix that can be obtained is considered.

Therefore, the inventors of the present invention have conducted extensive studies on the above-mentioned points, and have found that high voltage (e.g. 30 volts or more, especially 40 volts to 60
TP to which the gate voltage Vg of Porto) can be applied.
We were able to find a time-division driving method for the T matrix.

The outside strength of the insulating film is 5X105V/cm
The lifetime of TPT can be maintained by setting the gate insulating film thickness as follows. In a preferred embodiment of the present invention, the gate insulating film is made of 6000 silicon nitride (relative dielectric constant 6.6) doped with hydrogen atoms.
), and the semiconductor film was formed using 2000% amorphous silicon (relative dielectric constant 12), no shortening of the TPT lifetime was observed even when the gate voltage Vg was applied at 40 volts to 60 volts. .

FIG. 2 is a cross-sectional view schematically showing a liquid crystal mode that can be used in the present invention. In the figure, polarizing plates 26 and 27 are arranged in a crossed nicol state, and two polarizing plates 21 and 22 are also arranged. The head alignment process is performed by a method such as a rubbing process so that the initial alignment direction of the liquid I5 is oriented at 45 degrees with respect to the polarized light direction of 26 and 27. At this time, a nematic liquid crystal (NP type liquid crystal) having positive dielectric anisotropy is used as the liquid A25. When a voltage is applied to the common electrodes 23 and 24a, the molecular axis of the liquid crystal 25 between these electrodes is oriented toward the outside of the mold, and a dark state (light-blocking state) with respect to the incident light I is formed.

On the other hand, when the voltage between the electrodes 23 and 24 is made lower than the threshold voltage of the liquid crystal 25, the molecular axis of the liquid crystal 25 between the electrodes is aligned in the initial alignment direction, that is, in the rubbing direction. At this time, the incident light I becomes transmitted light T, and a bright state (light transmission state) is formed.

FIG. 3(A) shows a liquid crystal element used in the present invention. T.P.
T has three terminals: a gate electrode 302 connected to a gate line for applying a scanning signal, a source electrode 303 connected to a data line for applying an information signal, and a drain electrode 304 for extracting this data signal as an output signal. are doing.

Further, the drain electrode 304 is connected to a segment electrode 307 forming a micro shutter section. When a scanning signal is applied to the gate electrode 302, the resistance of the amorphous silicon film 305 decreases, and the source electrode 303 and drain electrode 304 become connected.

In the TPT used in the present invention, hydrogen atom-doped silicon 6000 (relative dielectric constant 6.6) is used as the gate insulating layer 306 sandwiched between the gate electrode 302 and the amorphous silicon film 305 (7). Ru. This silicon nitride film is composed of a chromium/aluminum laminated vapor deposited film that will become the gate electrode 302 and an I To (Indium Tin 0w) that will become the segment electrode 307.
1de) is formed over the entire surface of the substrate 301 patterned in a predetermined shape under glow discharge. In addition, the drain electrode 304 and the segment ring fi30
7 is an insulating film 309 formed of a silicon nitride film doped with hydrogen atoms on a substrate 301 having such TPT and electrodes connected through a through hole 308 provided in the silicon nitride film. and orientation-controlled films are used.

The liquid crystal element according to the present invention has a TPT matrix substrate in which the TPT described above is arranged in a matrix, and a counter substrate 311.
A nematic liquid crystal 313 (NP type liquid crystal) is sandwiched between them in the alignment state shown in FIG. An ITO film serving as a common electrode 31.2 is formed on the counter substrate 311, and furthermore, in the case of the liquid crystal shutter array described above, a chromium/aluminum film is used to block light except for the opening to form a micro-shutter section. A light shielding film 314 made of a laminated vapor-deposited film is laminated on the counter electrode 312. An alignment control film 315 is formed of polyimide or the like on the common electrode 312 and the light shielding film 314.

FIG. 3(B) is a cross-sectional view schematically showing a liquid crystal shutter array used in the present invention. In the liquid crystal shutter array of the present invention, the TFT section 316 is connected to the substrate 3 of the liquid crystal element 317.
It is formed on the same substrate 301' as 01 and outside the liquid crystal element 317. In particular, the TPT 316 is disposed outside a sealing member 318 made of epoxy adhesive or the like formed to seal the liquid crystal 313 between the substrate 301 of the liquid crystal element 317 and the counter substrate 311 provided with the common electrode 312. is preferred. Also, the TFT 316 is the liquid crystal element 3.
It can also be provided on an external circuit board (not shown) such as an IC circuit in addition to the No. 17 substrate 301. In the drawings, the same reference numerals as in FIG. 3(A) represent the same members. Also, 319 and 320 in Figure 5 are crossed Nicol polarizers,
312 is TPT316 made of chrome, aluminum, etc.
The figure represents a light shielding film for the semiconductor film 305 of FIG.

FIG. 4(A) shows a circuit of a TFT matrix substrate used in the liquid crystal sensor array of the present invention, and FIG. 4(B) shows a plan view thereof. The TPT matrix consists of 4011 TFTs arranged in an array.

4012.4013,4014,4015,4016.
4017, 4018.・・・・・・(TFT;401
). TF flea T401 is a gate line (4021, 4022, 4023° 4024) group 402 that applies an off-travel signal to the gate electrode.
, a group 403 of data lines (4031, 4032, . . . ) applying information (data) signals to the source electrodes, and drain electrodes (4051, 4052, 4052, 4053゜4
054) and the micro shutter segment electrodes (4041, 4042, 4043°4044.4045
,4046,4047,4048,...) group 4
04 are connected to each other.

In this embodiment, TPT4011.4 is connected to the data line 4031.
012.4013 and 4014 are commonly connected, and TFTs 4015.4016.4017 and 40 are connected to the data line 4032.
18 are commonly connected. On the other hand, TFTs 4011 and 4015 are commonly connected to the gate line 4021. Similarly, other gate lines are commonly connected to TPT as shown. Although the fourth-order time-division driving method is explained in this embodiment, the present invention can be applied to a second-order, third-order, fifth-order, or higher-order multi-order time division drive method.

In such a TPT matrix structure, the gate electrode (and the gate electrode are drawn out to the gate line), so that no unnecessary capacitance CQ is generated due to this eastern portion.

Furthermore, in this embodiment, the segment electrode group 404 of the micro-shutter is arranged in a staggered manner, but this is because information is written in the micro-shutter section sequentially in a time-sharing manner, so that the segment electrodes 404 of the micro-shutter are always arranged in the adjustment operation direction 405. This is because information on a photosensitive drum (not shown), which is a moving image holding member, is stored in a straight line within one frame.

FIG. 4(C) shows a sectional view taken along line AA' in FIG. 4(B). In the figure, an insulating film 407 covers the entire surface of a gate line 4021 formed as a hill on the substrate 409, and intersecting gates are connected by a conductive film 410. .

An insulating film 4 is formed on these intersecting gate lines.
08, and a data line 4031 is arranged above it.

FIG. 5 shows a schematic configuration for applying an optical signal to a photosensitive drum using a liquid crystal shutter array. However, the charger, developer, cleaning, etc. are omitted. 53
51 is a liquid crystal shutter array as described above, and 51 is a photosensitive drum (amorphous silicon photoconductor, organic photoconductive photoconductor).
, 54 is a light source such as a fluorescent light, 52 is a lens array such as a SELFOC lens, and 55 is a light condensing bar. The photosensitive drum 51 rotates in an adjustment direction 56, and responds to the information signal by irradiating the surface of the photosensitive drum 51 with an optical signal generated from a printer head section 57 consisting of a light source 54 and a liquid crystal shutter array 53. An electrostatic charge image can be formed. For this reason, the device can be made smaller compared to electrophotographic copying machines that emit optical signals generated by laser beams, and the mechanical drive unit, such as the polygon scanner used in laser beam emitting methods, can be made smaller. This has the advantage that there is no noise, and the requirements for strict mechanical precision can be reduced.

Next, the shirt shutter openings (Wl,
W2. An example of forming a dot pattern when performing quaternary time-division driving will be described below.

FIG. 6 shows a specific example of a drive signal force time chart applied to the liquid crystal shutter array. Here, G 1
-04 is gate line 4021゜4022.4023 and 40
In the voltage waveform applied to 24, when potential ■2 is applied, T
The FT is turned on, and conduction is established between the source electrode and the drain electrode. On the other hand, when a single potential is applied, the TPT is in an off state, and the gap between the source electrode and the drain electrode is in a cutoff state and electrically disconnected. Therefore, the mark on the gate electrode is maintained.

C is a voltage waveform applied to the common electrode, which is always held at potential 0 in this embodiment. Sl is a voltage waveform applied to the source electrode (data electrode), and the openings wl, w2 .・
. . is set to either ON or OFF, a voltage that changes the potential to O or V is applied.

Next, the operation control of opening and closing the shutter will be explained, focusing on the opening W1.

At time T11, the potential of the gate electrode connected to the gate line 4021 (Gl) of the TPT 4011 connected to the segment electrode 4041 of the micro-shutter section W1 becomes v2, and the TPT 4011 is turned on. Time τ11 and I12 (τ11+τ12 = T 11 )
Since the potential of the data electrode 4031 (Sl) is V, the potential of the segment electrode 4041 of the micro-shutter section W1 is also approximately -. Therefore, at this time, the micro shutter section W1 is in an off state. At the subsequent time τ13, the potential of the gate electrode connected to the gate line 4021 (Gl) becomes -v1, so even if the data electrode 4031 (Sl)
), the segment electrodes of the micro-shutter section Wl can maintain the potential V. τ13
= TI2 + T13 + T14, T12 is connected to the gate line 4022 (G2), and T13 is connected to the gate line 4023 (
In G3), T14 is a period in which a voltage of v2 is applied to each gate line 4024 (G4). Therefore T 11
+ T I2 + T 13 + T 14 is the l frame period. At time T21 of the following frame period, the potential of the gate electrode (Gl) (7) becomes v2 again, and the TFT40
it is turned on. The first half of this time T21 τ
At 21, the potential of the data electrode (Sl) becomes V, and the voltage V is applied to the segment electrode of the micro shutter section W1.
At the subsequent second half time τ22 (when the on-state IE of the TPT is maintained), the potential of the data voltage m (S t) becomes O, so the potential of the segment electrode of the micro-shutter section W1 changes to 0, and the integrated Time τ23 (=T22+T23+
During T24), the potential O is held. Therefore, since the voltage applied to the liquid crystal corresponding to the micro shutter section W1 is 0, the shutter ON state (light transmitting shape 8) is formed in one frame period as explained in FIG. be done.

In IWI-CI in FIG. 6, the voltage waveform applied between the segment electrode and the common electrode of the micro-shutter section W1, that is, the liquid crystal, is clarified in chronological order. According to this, 1Wt-C1l at time τ12+τ13+τzt
t potential difference is v, and 1W1-CI becomes 0 potential difference at time τ22+τ23 in the next frame period.

The change in transmittance of the micro-shutter W1 in time series at this time is shown by Trl in FIG. According to this diagram, during the period of one hour τ12+τ13+τ21, the transmittance of the micro-shutter section W1 is Trd (dark level), and during the period of time τ22+τ23+τ31, the transmittance of the micro-shutter section W1 reaches Tr (bright level). Gradually rises to T31 in the next frame period
When 1W1-CI becomes V, as shown in the figure, Trd
to return to.

In addition, 1W2-CI in the figure indicates the potential difference in time series between the electrode of the micro shutter W2 and the common electrode, and
2 represents the change in transmittance at that time.

FIG. 7 shows the sequence for producing the light spot image drums Ldl and d211. Among the dots, the first row of dots (dl, d2, d3).

11 d4. ...) correspond to the on and off states of the micro-shutter section Wl, and the second row of drivers) (d'',,d''').

2 2 d3. d4. ...) is micro shutter part w2-2
2.Supports on and off. Further, the dots in each row are micro shutter portions Wl and w2, respectively.

w3. w4. It corresponds to... Here, dots d', d', d2. d3. d3. d4 and 43122 Assume that d4 is at the dark level and the other dots are at the bright level. In the figure, 71 represents the main scanning direction, and 72 represents the sub-scanning direction.

In the time-division driving method of the present invention, when the micro-shutter section is operated by the fourth-order time-division drive as described above, the micro-shutter section is in the ON state (light transmitting state) or the OFF state (light blocking state) during one frame period. ) can be retained.

In other words, when forming dark level dots, the dot generation time for one line (τ12+τ13J21)
The transmittance is set to the dark level (Trd) over the period of time, and when forming dots at the bright level, the dot generation time for one line (τ
22+τ23+τ31), the transmittance is adjusted to the bright level (T
r! l) compared to the simple matrix method used in conventional liquid crystal shutter arrays.
/N ratio can be significantly improved.

Further, in this embodiment, as shown in FIG. 6, during the initial period when the gate line is scanned, a voltage V is added to the information signal inputted in synchronization with this scanning signal. This means that when the voltage applied to the liquid crystal of the type shown in FIG. 2 is 0, the transmittance changes in a waveform with time as shown by X in FIG. 8. This phenomenon is generally called a light bouncing phenomenon. Therefore, according to FIG. 8, since one microshaft part is in the on state for 3τ, the transmittance during each writing is different, and therefore the bright III ratio (contrast of the printed image) of each dot varies. There was a problem that caused Therefore, in this embodiment, in order to make the transmittance of the shutter part in the ON state uniform during each writing operation, as described above, an information signal is input in synchronization with the scanning signal during the initial period of writing. A voltage ■ is applied to the liquid crystal, and a voltage V is forcibly applied to the liquid crystal to form a dark state.Next, even if the micro-shutter section continues to be on, the △ dot writing time τ shown in Fig. 8 is maintained again. The transmittance of each dot in the on state can be made uniform.

Therefore, by setting the forced shutter closing time immediately before or after data writing, a stable amount of transmitted light can be obtained at all times in the open state when the shutter shutter is opened during data writing and when the shutter shutter is closed. It becomes possible to always obtain a printed image with stable contrast. Before applying a data signal to the data electrode to form each dot, a signal is applied so that a voltage is applied to the liquid crystal layer, regardless of whether the previous dot formation was at a bright level or a dark level. I can do it. At this time, a voltage is applied to the liquid crystal layer and the time required for the transmittance to become sufficiently low is τ! It is necessary to provide a sufficient time for the potential of the segment electrode 404 to change to the potential of the data electrode 403 via the TFT 401 at time τ12.

According to experiments by the inventors, when applying a voltage of 20 V to an 8 mm liquid crystal, the time τ11 is approximately 0.24 m s.
e c, therefore, it is sufficient if it is 0.2 m5 ec or more, and the time τ12 should be a number + p - 5 ec (shutter part) density is 16 dots) / mm If the image forming speed (process speed) is 50 mm/sec, then The dot formation time for one row (τ11+τ12+τ13) is 1.25 m5ec
No c', time opening τ11 + τ12 is 125m5ec
It has been found that it is possible to realize quaternary time-division driving by setting the time to 174 hours, that is, 0.3125 msec. Furthermore, it was also found that the brightness ratio was improved to 6.5, and the brightness level was more than double that of the conventional simple matrix drive method.

FIG. 9 shows another specific example of the time division driving method of the present invention. The specific example shown in FIG. 9 is a driving method suitable for further increasing the number of time divisions.

6 o'clock 1tlτ11 (described for one frame) plus the minimum gate on time (minimum time required to obtain the data electrode voltage on the drain side) τ12 (τ11+τ
12), since the gate electrode is an on-state f island,
There is a limit to increasing the number of time divisions. That is, the aperture density was 16 dots/mm and the process speed was 50 dots/mm.
When expressed as mm/sec, the number of time divisions is expressed by the following equation (6).

At this time, the time τ12 is the drinking 5eC-number-j-g s e
c is sufficient, and the number of time divisions n is controlled by the time τ11.

Therefore, as shown in FIG. 9, the time required to forcibly close the shirt opening (τ11
= 0.24m5ec, liquid crystal thickness 8gm, drive voltage 40V) and gate line G1 + G 2 + G 3 +
``' A gate-on pulse is applied sequentially to G n (n: the number of time divisions), and a voltage V is applied to the data electrode in synchronization with this. Therefore, the micro-shutter section is sequentially turned off, and the data is turned off in the following frame period. Apply a selection signal (voltage 0 or ■) to the electrode. That is, apply a voltage V (the potential of the common electrode is O) to the liquid crystal corresponding to the micro-shutter section during the first scanning period tl. All of the micro shutter sections are turned off, and this first
The scanning period t1 corresponds to a refresh period. In the subsequent second scanning period t2, a voltage according to the data signal is applied to the data electrode in synchronization with the scanning signal (τ1) of the gate line, thereby setting a predetermined micro-shutter section to an on state or an off state. This second scanning period t2 corresponds to a data aging period.

In the specific example shown in FIG. 9, the refresh period and the data write period described above are provided alternately for driving, and furthermore, in this example, an arbitrary voltage application period t3 is added between the data write period and the refresh period. However, this arbitrary period t3 can also be omitted.

The number of time divisions n when using such a driving method is expressed by equation (7).

When τl) is set to 5 μSeC, the number of time divisions can be up to 48. It also represents the change in transmittance in time series of the shank section switched by the TPT in which the terminals of the gate line G1 and the data electrode S1 are connected to the Tr in FIG. 9 (TrJL: bright level, Trd: dark level). ).

FIG. 10 shows another specific example. In the driving example shown in FIG. 9 described above, a gate-on pulse is always applied to one TPT during time t1, and the gate is turned on, but in the present invention, the number of time divisions n is set to be relatively small. In the example shown in FIG. 10, the number of time divisions n is 4), thereby making it possible to shorten the data pulse application time. That is, the micro shutter portions Wl, w2, W3 and W4 shown in Fig. 1θ (corresponding to the openings in Fig. 4)
As shown in the transmittance waveform in FIG. 1, when the micro-shutter section W1 is driven first and the aperture section W4 is driven last, if the lighting waveform of the light source is set as L in Fig. 1θ,
At that time, the energy of the transmitted light in the on state at each aperture is WIS, W2N.

The areas are indicated by W3S and W4S. In this case, the opening W
l, W3, and W4 are in the shutter-on state, and the energy of the transmitted light from them becomes WIS>W3S>W4S.As for this drive, as mentioned above, since the data pulse application time τ2 is short, this difference is Almost negligible. For example, when performing fourth-order time division driving with an aperture (shutter) density of 16 dots/mm, a professional speed of 50 mm/see, and a minimum gate on time τ1 of 51 LSeC, the data pulse application time τ2 will be 20 g5ec. . On the other hand, the time τ3 is about 1 m5ec. Therefore, the optical energy WIS, W3 due to this degree of time difference
The difference between S and W4S is almost negligible.

In this way, when the light source is first gated and the refresh period pulse (refresh pulse application period τ4) is estimated, W4S/W2N is obtained.

Now, using a light source with an emission center wavelength of about 650 nm, the aperture density is 16 dots/mm, the process speed is 50 mm/sec, and the light source lighting time N is more than 10 times as long. Also, by setting the data pulse application time τ2, the S/N ratio (W4S/W2N) decreases somewhat, but as mentioned above, W
The time τ is set so that the energy difference between IS and W4S becomes small.
By setting 2, the S/N ratio is greatly improved, and stable electrophotographic print images can always be obtained. Note that time τ5 in the figure is an arbitrary period.

FIGS. 11 and 12 show driving examples representing another aspect of the present invention.

It corresponds to the elementary formation time and is calculated using equation (8).

τ=1/Vp 11N - (8) (in the formula.

Vp; process speed mm/5ec NHpe number of sentences) In Fig. 11, when the TPT gate minimum on time is τ1, τa≧τ1 τb>τ1, and τa and τb are alternately separated to separate the time, and the time τa is the time when the liquid crystal is turned on. This is the refresh (erasing) period in which an electric field is always applied, the aperture is turned off, and a potential is applied to the aperture electrode to prevent changes in transmittance, and the time τb is the potential to control the on and off states of the aperture. is defined as the data writing period applied to the segment electrodes of the micro-shutter section.

FIG. 12 shows a TPT matrix 1202 used in 8th time division driving, a gate line 1201 connected to the TFT,
Segment electrodes 1204 connected to data lines 1202 and openings Wl, w2, . . . are shown. A voltage V2 is applied to a selected gate line 1201 only during a refresh period τa and a write period τb within one pixel formation time τ, and a voltage −vl is applied to other unselected gate lines. That is, as shown in FIG. 11, the voltage v2 is applied to the gate line G1 during the first refresh period τa.
is applied, a voltage -vl is applied to the gate line G1 during the following two sets of write period τb and refresh period τa, and voltage v2 is applied to the gate G1 in the next write period τb.
is applied to the gate line G during the remaining one pixel writing time.
1 is set to -v1. The gate lines G3, G4, and G5 of the gate voltage applied to the gate line G1 are applied to the next gate line G2.
, G6, and G7 are formed. Next, the operation at the opening will be explained.

The potential of the gate line G1 becomes +2 at time τ1 to the segment electrode connected to the micro-shutter section W1, and the voltage V is applied to the data electrode connected to the data line S1. During the subsequent write period τb, the potential of the gate line G1 becomes -
v1 and 3 - TFT12021 is force - to-off state 1
Therefore, the potential V is maintained at the segment electrode of the micro-shutter section W1 regardless of the potential of the data line S1. This means that the micro-shutter section W1 is always applied at time τ1, and the micro-shutter section W1 is turned off. In the subsequent writing period τb, the potential of the gate line G1 is set to 10, and the potential of the data S1 is set to 0 to set the bright level (on state 8). The voltage applied to the segment electrode is applied to the gate line G1 from the subsequent refresh period τa to the end of the one-pixel writing period τ, and the potential of the gate line G1 becomes 1-1, and the TPT 12021 enters the cut-off state, so that the voltage corresponding to the brightness level is maintained. That will happen.

FIG. 13 shows an example in which the number of time divisions n is set to the maximum value when this driving method is used. for example.

Opening density: 16 dots/mm (16pe text)
, process speed 50mm/see, time τCki2
When 40g5ec and time τ1 near 8BseC, the number of time divisions n is 240778 in the drive example shown in Fig. 9.
However, in the case of the driving example shown in FIG. 13, eight-order time division is possible.

In the driving method shown in FIGS. 1 and 12, the on-pulses to adjacent gate lines during one row writing time are continuous with a slight time difference as in the driving example shown in FIGS. 9 and 10. Gate minimum on-time τ1 rather than applied
There will be a time difference only. Therefore, the external circuit (interface circuit that distributes input data for time-division driving)
In this case, the data transfer speed to the data electrode can be increased to the driving method 172 shown in FIGS. Become something.

Further, the driving example shown in FIG. 11 is a case where the optimum time division is not performed, and a gate-on pulse is always applied to any one of the gate lines 01 to G8 at time τd. In other words, there is a time period during which the off-voltage is applied to every gate line within the time τd. Therefore, the data transfer speed to the buffer circuit connected to each gate line can be slowed down, which facilitates circuit setting and is effective in reducing costs.

Further, in the present invention, when forming a toner image on a cut print (transfer paper) using an electrophotographic copying machine as shown in FIG. 15 by attaching a liquid crystal shutter array to the optical signal generating section shown in FIG. It is necessary to set a feeding interval for this transfer paper, and the time Ty of this transfer paper feeding interval is
As shown in FIG. 14, by setting the potential of the data electrode to 0 and the potential of the common electrode to +Vd, when forming one pixel (for example, Tx when forming one copy)
A voltage of opposite polarity can be applied to the liquid crystal. (T
z: Next screen formation period) 0 For example, the transfer paper feeding interval in an electrophotographic copying machine is generally 30 mm to 50 mm when viewed in terms of the paper distance. Therefore, for example, if the paper distance is 50 mm, the process speed is 50 mm.
When the speed is set to 0 mm/sec, the paper interval changes in 1 second, so there is virtually no direct current drive, and therefore the life of the liquid crystal shirt hair array can be improved.

/ FIG. 15 shows an example of an electrophotographic copying machine using the above-mentioned liquid crystal shirt T-array, in which a photosensitive drum 1501 is rotated in the direction of an arrow 1502, and a charger 1503 is first driven.
The photosensitive drum 1501 is uniformly charged, the liquid crystal shutter array 1504 is driven, and the light beam from the light source 1505 placed behind is selectively controlled to open and close to generate an optical signal. An electrostatic latent image is formed by irradiating the photosensitive drum 1501.

This electrostatic latent image is developed by the toner of the developing device 1506, and this toner phenomenon is transferred to the copy paper P (transfer paper) 7 that has passed through the transfer guide reed 1507 and is transferred to the charger 150.
8. The copy sheet P on which the image has been transferred is sequentially separated from the photosensitive drum 1501 by a separation belt device 1509, and then the image is fixed by a fixing device 1510, and the copy sheet P is tilted so that the image is fixed thereon. In addition, the transfer detection photosensitive drum 150
The toner remaining on the surface of the cleaning device 151
t, the photosensitive drum 1501 is neutralized by the pre-exposure device 1512, and the next copying cycle is made possible again. Incidentally, the liquid crystal shutter array 1504 shown in FIG. 15 employs the liquid crystal cell shown in FIG. 2 described above. In other words, the light beam from the exposure light source 1505 is transmitted to the liquid crystal shutter array 1504, which includes a liquid crystal cell. When an image is formed on the photoreceptor 1501 via a lens array 1513 such as a self-off lens, a liquid crystal drive circuit 1514 is operated by a digital signal containing image information obtained by a document information reading device (not shown). By turning on and off the liquid crystal shutter array 1504, a light signal having a pattern of image information is transmitted to the photoreceptor 15.
01 is exposed. In this embodiment, the exposure light source 1505 also has the function of heating the liquid crystal cell, and by operating the liquid crystal cooling fan 1517 with the liquid crystal temperature control circuit 1516 connected to the thermal element 1520, overheating of the liquid crystal cell can be prevented. It is possible to prevent this and maintain the liquid crystal cell at a constant temperature. In the figure, 1518 is a reflective shade, and 1519 is a member for attaching the lens array 1513 to the liquid crystal shutter device.

By the way, a conventional liquid crystal shutter array that does not use TPT has an electrode structure shown in FIG. 16, and in this electrode structure, a driving waveform shown in FIG. 17 is applied.

For example, if the thickness of the liquid crystal is about 8 pm and the common electrode is ±
A rectangular wave of IOV is applied, and the same voltage waveform as that of the common electrode is applied to the signal electrode to turn on the shutter section of the selected row, and Ov is applied to the signal electrode to turn the shutter section off. Apply. In FIG. 17, time TI is A
The absolute value of the voltage applied to each of the liquid crystal layers of A1 and A2 at that time is expressed as lVA, 11°1VA21. In this way, among the shutter parts connected to the signal electrodes,
When one of them is turned on, a voltage of 2V, or 20V, is applied to the liquid crystal layer, but when all the shutter parts connected to the signal electrodes are turned off, a voltage of V, or l is applied to the liquid crystal layer.
0VL or no voltage is applied.

Therefore, the transmittance of A1 is Tctl at time T2, while the transmittance of A2 is Ta2 over time Tl, T2.
, and Ta2>Tdt.

In this case, one dot is formed over time T1 and T2. Therefore, the amount of light received by the photosensitive drum is 1201 (12
10a+1'210b), opening, t7(7),! - is proportional to the area 1202 (1202a+1202b).

Therefore, if the voltage V is lowered, the contrast ratio cannot be maintained.

Furthermore, if the number of time divisions is increased, the area 1702b becomes larger compared to the area 1701a, making it impossible to maintain a brightness ratio.

On the other hand, when 16 dots were formed per 1 mm, the image forming speed was 50 mm/5 (the speed at which 6 to 8 A4 size images are formed per minute in vertical feed), and two-sided split driving was performed. , T1 is 0.625 ms. The shape of the change in transmittance of the liquid crystal shutter at which level is approximately 12th.
It is represented in Figure A1. That is, if TI is made longer, the transmittance Te becomes even larger.

In fact, even if Tl is set to 1.25 m5, 2 time-division driving is performed, and the voltage is set to ±20 V, which is twice the voltage as explained above, the brightness ratio will be about 3 times higher if the irradiation light wavelength is set to 550 nm. .

However, in order to control brightness and darkness in the photoreceptor, it is necessary to further increase the applied voltage. Currently, CH%S can be produced at low cost.

The breakdown voltage of an IC, even a high breakdown voltage one, is about 30V. Therefore, even if the number of time divisions is increased and the number of ICs is decreased, in order to increase the contrast ratio, it is necessary to use an IC with a special high voltage resistance, that is, 60V to 80V, or an IC with a slow image forming speed. They were faced with the choice of whether to apply it only as a device with low pixel density.

In addition, in the conventional liquid crystal diagram shown in Fig. 18, 181
182 indicates the transmittance at a wavelength of 489 nm, and 182 indicates the change in transmittance at a wavelength of 655 nm.

As can be seen from this experimental result, the voltage VLC applied to the liquid crystal layer is 20V when long wavelength (step measurement) illumination is used.
Hereinafter, when illumination with a short wavelength (front side) is used and the voltage is set to 30 V or less, the transmittance increases rapidly.

As explained in 1 above, by driving the liquid crystal shutter using thin film transistors, the waveform of the light transmitted through the shutter can be obtained equivalent to direct driving (driving without time division), although the actual driving is performed in time division. I can do it.

In other words, by enabling time-division driving, the number of data electrodes can be reduced (pixel density 16 dots/m+m,
In the case of total length 210a+m, number of data electrodes during direct drive =
3360 electrodes, number of 8 time division data electrodes=420 electrodes) Therefore, (1) The connection (mounting) between the liquid crystal shutter cell and the driving IC becomes easy, and the mounting cost can be reduced.

(2) The number of ICs can be reduced.

There are other effects.

In addition, since the waveform of the light transmitted through the liquid crystal shutter is the same as that of direct drive, it is possible to take a longer time to write one dot, creating a vehicle that increases the optical energy of the transmitted light when the shutter is open. 6th
As shown in the figure, when the shutter of the DAP type liquid crystal (liquid crystal mode in Figure 2) is opened, the light is gradually transmitted.

As shown in FIG. 6, the waveform of the transmitted light has a lower square shape. The light energy of the transmitted light is the area A, and for example, if the time is doubled, the light energy can be reduced to "-".

Therefore, the contrast ratio (bright light energy [area A)
/Dark area light energy (area B)) can also be dramatically increased.

Now, the emission center wavelength of the light source is 540 nm, the pixel density is 16 dat/mm, and the process speed is 50 mm/sec.
c, when 2-time division driving is performed, it is less than 3 times, but when direct driving is performed, it is possible to increase it to about 6.5 times.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the relationship between the gate insulating film and Δvth. FIG. 2 is a sectional view of a liquid crystal element used in the present invention. FIG. 3(A) is a cross-sectional view of a liquid crystal element using TPT of the present invention, and FIG. 3(B) is a cross-sectional view of another liquid crystal element of the present invention. FIG. 4(B) is a plan view of the liquid crystal shutter array of the present invention, and FIG. 4(C) is a cross-sectional view taken along line AA'. Figure 185 t4 is a perspective view of the printer head used in the present invention. FIG. 6 is an explanatory diagram showing a time chart of drive signals applied to the liquid crystal shutter array of the present invention. FIG. 7 is an explanatory diagram showing the sequence of dot creation using the liquid crystal shutter array of the present invention. Figure $8 is an explanatory diagram showing changes in light transmittance in time series during the shutter-on state. FIG. 9, FIG. 1O, and FIG. 11 are explanatory diagrams showing other specific examples of time charts of drive signals. FIGS. 13 and 14 are explanatory diagrams showing other specific examples of time charts of drive signals applied to the liquid crystal shutter array of the present invention. FIG. 15 is an explanatory diagram schematically showing the image forming apparatus of the present invention. FIG. 16 is a plan view showing the electrode structure of a conventional liquid crystal shutter array. FIG. 17 is an explanatory diagram of a time chart representing a driving waveform applied to a conventional liquid crystal shutter array. FIG. 18 is an explanatory diagram showing the relationship between voltage and light transmittance in a conventional liquid crystal shutter array. 302; gate electrode 306; gate insulating film 305; semiconductor film 303; source (data) electrode 304; drain electrode 307; segment electrode 312; common electrode 314; light shielding film 310, 315; alignment control film 313; liquid crystal 401 (4011, 4012,...), TPT 402 (4021, 4022,...); Gate line 403 (4031, 4032,...); Data line 404 (4041, 4042,...); Segment electrode Wl, W2, W3, ...; micro shutter section 405; sub-scanning line 406; contact hole 57: printer head section 53.1504; liquid crystal shutter array 51.1501. Photosensitive drum 54.1505; light source 52.1513. Lens array T Figure 3 (A> Sir Figure 3 (8) Length Moromi + 1 dot 11 Including y! (Complete)

Claims (1)

[Scope of Claims] (1) A printer head equipped with a light source A and a group of microshutters that control the light beam in the exposure optical path of the exposure light source to either a light blocking state or a light transmitting state; In an image forming apparatus configured to irradiate an image holding member with a light signal from a printer head, the micro-shutter group is arranged in a matrix along the rows and columns of the number of sheets, and the micro-shutter group has a thin +19 h run sister. It has a structure in which a liquid crystal is sandwiched between a submerged substrate and a scanning signal is applied to the gate line of the thin film transistor, and in synchronization with this scanning, a data line is sent to the data line according to the image information. An image forming apparatus characterized by comprising means for applying an electric signal. (2) The image forming apparatus according to claim 1, wherein the thin film transistor is disposed outside a stopper member provided for sealing liquid crystal between opposing substrates. (3) The image forming apparatus according to claim 1, wherein segment electrodes connected to the thin film transistor and the drain are formed on the same substrate. (4) The image forming apparatus according to claim 2, wherein the thin film transistor is formed on an external circuit board. (5) 1iij 6tillQ The external strength applied to the gate insulating film in the channel region of the transistor is 5×10'5
A portrait forming apparatus according to claim 1, wherein the image forming apparatus has a voltage of V/cm or less. (6) The image forming apparatus according to claim 1, wherein the thin film transistor includes amorphous silicon as a semiconductor. (7) A printer head equipped with an exposure light source and a group of microshutters that control the light beam in the exposure optical path of the exposure light source to either a light blocking state or a light transmitting state, and a printer head that converts optical signals from the printer head into an image. In a driving method of an image forming apparatus that irradiates a holding material, the micro shutter group is arranged in a matrix along a plurality of rows and columns,
The micro-shutter group has a structure in which a liquid crystal is sandwiched between a segment electrode and a common electrode forming one shutter part connected to the drain of a thin film transistor,
Corresponding to a first period and several rows, a voltage is applied to form a light blocking state to the liquid crystal between the segment electrode group and the common electrode corresponding to this row during the writing period of the selected row among the plurality of rows. 1. A method for driving an image forming apparatus, comprising: a second period in which a voltage is applied to form a light transmitting state to a liquid crystal between a segment electrode selected from a group of segment electrodes and a common electrode. (8) The method for driving an image forming apparatus according to claim 7, wherein the light source is pulse-lit or the amount of light oil is increased immediately before the first period. (9) The method for driving an image forming apparatus according to claim 7sj4, wherein electric signals having a pulse width equal to the sum of the first period and the second period are sequentially applied to gate lines of thin film transistors. (10) The method of driving an image forming apparatus according to claim 7, wherein the electric signal is applied alternately to the gate line of the thin film transistor in the first period and the second period. (a printer head equipped with an mi light source and a group of micro shutters that control the light beam in the exposure optical path of the exposure light source to either a light blocking state or a light transmitting state;
In a driving method of an image forming apparatus in which an optical signal from a semiconductor is irradiated onto an image holding member, the micro shutter group is arranged in a matrix along a plurality of rows and columns, and the micro shutter group is connected to the drain of a thin film transistor. It has a structure in which a liquid crystal is sandwiched between a segment electrode and a common electrode that form one shutter section connected to A first period in which an electric signal forming a cut-off state is applied to the data line; and after the first period, a scanning signal is applied to the gate line of the thin film transistor, and a segment electrode corresponding to the row to which this scanning signal 1) is applied is applied. A method for driving an image forming apparatus, comprising a second period in which an electric signal forming a light transmission pattern fM is applied to a data line connected to a segment electrode selected from a group in synchronization with the scanning signal. . (12) The exposure light source and the light beam in the exposure light source are in a light blocking state and a light transmitting state y! In a method of driving an image forming apparatus, the printer head includes a micro-shutter group that is controlled to a force of one of the following: The micro-shutter group is arranged in a matrix along a plurality of rows and columns, and has a structure in which a liquid crystal is sandwiched between a segment electrode and a common electrode forming one shutter portion connected to the drain of a thin film transistor. By applying a scanning signal to the gate line of the M film transistor and applying an electric signal corresponding to the image information to the data line in synchronization with the scanning signal, a selected one of the plurality of microshutter groups is selected. After irradiating the image holding member with No. 4.1 formed by bringing the microshaft into a light-transmitting state for a predetermined period of time, a voltage with a polarity opposite to that applied to the liquid crystal at the time of forming the optical signal is applied to the liquid crystal. 1. A method for driving an image forming apparatus, comprising a period for applying voltage.