JPS59168418A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a stable proper picture by providing a device which has an image forming means with an optical shutter driving means which drives and controls an optical shutter means according to the state of the device. CONSTITUTION:The direction of light in every direction is shown by 204 and this is, for example, natural light. Polarizing plates 201 and 203 are arranged so that their axes of polarization are at right angles, and thin arrows indicate axes of polarization. Light 204 after passing through the polarizing plate 201 is polarized only in a direction shown by an thick arrow 205 and reaches a liquid crystal material (not shown in a figure) through an upper transparent electrode 202. The liquid crystal material is oriented so that liquid crystal molecules are twisted by 90 deg. without any applied voltage between the transparent electrodes 202. Consequently, the light is rotated optically by 90 deg. and directed through the lower transparent electrode 202 as shown by a thin arrow to be transmitted as 207 as it is. The voltage V is controlled to control the exposure amount of a photosensitive body as shown in the figure, obtaining a stable proper picture.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to an image forming apparatus that forms an image using original shutter control.

Prior Art Conventionally, in this type of device, such as a liquid crystal display,
The transmission characteristics of liquid crystal materials are the threshold.

It has the disadvantage that it is not stable due to fluctuations in voltage, changes due to temperature, humidity, etc., and a single mirror image cannot be obtained. Furthermore, although image forming apparatuses such as original printers using the above-mentioned liquid crystal members have been proposed, they cannot be expected to produce stable images due to the above-mentioned reasons.

OBJECTIVES In view of the above points, an object of the present invention is to provide an image forming apparatus capable of obtaining a stable image that eliminates the above-mentioned drawbacks.

Examples (1st example, 2nd example, 6th example) Below,
Five embodiments to which the present invention is applied will be described with reference to the drawings. This embodiment is an original printer that uses a liquid crystal member as a liquid crystal shutter array, controls light transmission, and creates contrast such as black and white of one pixel to form an image. FIG. 1 is a block diagram of the operating system of an optical printer which is an embodiment of the present invention.

1 is a high voltage transformer, 2 is a surface potential measurement circuit, and 6 is an A/D
, D/A converter, I(, A M, etc. surface Wr
, a position control circuit (CPU), and 6 an island voltage charger. The photosensitive drum 5 is charged by the high-voltage charger B. The light is then exposed through the liquid crystal shutter array 16. Note that since the liquid crystal display array is of a transmission type, it is illuminated by a light source 7. 208
is a liquid crystal shutter array drive circuit. 8 is a surface potential sensor, which is input to the surface potential measuring circuit 2. 9
is a developing cylinder υ, where the electrostatic latent image on the photosensitive drum 5 becomes a visible image.

Next, the image is transferred to copy paper by the transfer charger 16, and the leading edge of the copy paper is aligned with the leading edge of the image on the surface of the photosensitive drum 5. The timing is determined by the τ Fuji roller 12.

Also, prior to this, the paper feed row 210 from the paper feed cassette 11
is being shipped by. The copy paper to which the toner has been transferred is fixed by the fixing roller 214, and then transferred to the paper output tray V.
It is discharged to B15. Further, after the transfer is completed, the photosensitive drum 5 is electrostatically cleaned by an eraser 4.
Prepare for the next image creation. Note that 999 is a light guide lens such as Selfoc for condensing light.

FIG. 2 is a structural cross-sectional view of the liquid crystal / / / / / /'' / / / / / / /7/ / / shutter array. 101 is a glass substrate, 102 is a polarizing plate, 106 is a transparent electrode, 104 is a suppressor, 105 is a liquid crystal material.In other words, the product material is sandwiched between two polarizing plates, and a transparent electrode is placed between the liquid crystal material and the polarizing plate, and when an electric field is applied to this electrode, no change occurs. (2) Figure 3-a is a diagram showing the transmission of light by the liquid crystal shutter array 16 when no voltage is applied to the transparent electrode 202.

204 represents the direction of light in all directions, such as natural light. Polarizing plates 201 and 203 are arranged so that their respective polarization axes are perpendicular to each other. Here, h(1 arrow indicates the polarization axis.'''2e After 204 passes through the polarizing plate 201, it passes through the transparent electrode (upper) 202 and polarization only in the direction shown by the thick arrow of 205 among 204, The liquid crystal material reaches the liquid crystal material (not shown).The liquid crystal material is arranged between the transparent and the a 202, and when no voltage is applied, the liquid crystal molecules are twisted q(If''). 'The light rotates and passes through the transparent electrode (bottom) 202 in the direction of the thick arrow 206.Next, since the polarizing plate 206 has its polarization axis in the direction of the thin arrow, the thick arrow 206 becomes 207 and passes through. 208 is a power source for applying voltage to the transparent electrode, and 209 is a switch for turning this on and off.

On the other hand, FIG. 3-b is a diagram showing light blocking by the liquid crystal Shack array 16 when a voltage is applied to the transparent electrode 202. At this time, since the liquid crystal molecules are arranged uniformly in the direction between the substrates, the optical rotation of the light disappears and the direction of the thick arrow 210 is different from that of the thick arrow 206. Therefore, in the direction of the polarization axis of the polarizing plate 2030, the light originally does not pass through and is cut off.

The liquid crystal shutter is driven by the power supply 2 shown in FIG. However, it is generally known that when liquid crystals are driven using direct current, their characteristics deteriorate rapidly.

For this purpose, it is driven by alternating current, and the drive waveform (rectangular wave) at this time is shown in FIG. Note that the frequency period is f, and both openings are T (1/?).

FIG. 5 shows the relationship between drive voltage and transmittance. The transmittance when liquid crystal driving is performed is 100 cm in V-OV.

The transmittance decreases as the value of {circle around (2)} increases, and the device eventually enters a cut-off state. At this time, the driving voltage V at which the transmittance of 70 cm is exhibited is generally called the lighting threshold voltage (vtb). The five-dot line portion will be explained later.

The amount of exposure on the photoreceptor is two times the same as the second one.
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The figure shows changes in the surface potential of the photosensitive drum 5 during the image forming process.

In other words, the surface potential changes as the sensitive drum 5 is charged by the charger 6, undergoes dark decay until it reaches the exposure point, and is exposed by the liquid crystal array 16 and the light source 7. VSLO is the surface potential when the liquid crystal shutter array is fully opened and light is irradiated onto the sensitive drum 5. Note that the target potential VSLO does not necessarily have to be the case where the liquid crystal shutter array is fully opened. It can be seen from FIG. 6 that the column surface potential decreases greatly when the exposure amount is large. Note that VSL will be described later.

FIG. 7 is a general structural diagram of the liquid crystal shutter array. 601 and 602 are common electrodes, 603 and 604
, 605.

606 is an individual electric wire, and 607 and 608 are liquid crystal shutter sections. In other words, the liquid crystal shutter portions 607, 608, etc. are located on the common type %i 601, 602, and the individual electrodes 603, 604, etc. are located above them, forming a sandwich structure.

Common electrode 601.6 of the liquid crystal shutter array in FIG.
02 and the individual electrodes 603, when the signal waveform shown in FIG. 8 is applied to the collectors 607 and 608. A voltage with a waveform as shown in the figure is applied to , .

Therefore, as described above, the phenomenon of light transmission occurs at a point where no voltage is applied, and the original cutoff occurs at a point where a voltage is applied. This can be expressed in a table as shown in Figure 9. However, the remaining line part is in the original cutoff state. However, A.

B and C correspond to FIG.

However, both 607 and 608 cannot be in transparent mode at the same time. However, this is when writing signals, and if the common electrodes 601 and 602 are in the same phase, all pixels are written.

It is easy to create a transmission or blocking mode.

Next, the drive circuit for one electrode of the liquid crystal shirt is set as ';ry i
.

As shown in the figure.

f is the frequency of the AC rectangular wave for driving the liquid crystal shutter. 121 and 122 are comparators, and when f is inputted, the comparator 121 sends an in-phase pulse, and the comparator 122 sends an anti-phase pulse to the common electrodes 601 and 60.
2. Further, the image signal passes through the switching main channel 123, and one of a, b, and c is selected. This is the 8th
This corresponds to the cases of sections A, B, and C shown in FIGS.

As shown in Figure 5, depending on the driving voltage (amplitude),
You can see that the transmittance of the liquid crystal shutter is changing,
By making the knob (2) variable, it is possible to control the amount of fog light on the photoreceptor.

Table 1 shows the relationship between the driving voltage, the transmittance of the liquid crystal shutter, the exposure amount of the photoreceptor, and the image density.

Driving 'tiL pressure Small ←■→DogTransmittance of liquid crystal shutter Large Exposure amount of small photoreceptor Large Planning Image Density Light Condensation White ← Gray → Black 1 Now, the liquid crystal shutter 16 in Figure 1 is connected to the liquid crystal shutter array drive circuit. 208 jc) Initial value drive voltage (amplitude) VO
When the photosensitive drum 5 is irradiated with K, as shown in FIG.
The surface potential of VSLO should be at . However, if for some reason the voltage does not drop to 'VsLo' and SL does not occur, it is considered that the exposure amount is insufficient and the drive power supply amplitude V needs to be lowered. Then, the surface potential is measured again and fed back to the drive voltage amplitude V to obtain the target surface potential value VSLO.
FIG. 11 shows a flowchart of drive voltage amplitude control for obtaining an appropriate image by approaching the distance 208. Step 1
10, the initial values v of the light source 7 and the liquid crystal shutter drive voltage are
The light is transmitted through O and the photosensitive dosm 5 is exposed (.Next, in step 111, the timing of measurement is determined.
This timing corresponds to the angle θ from the exposure point to the surface potential measurement point in FIG. The same thing can be said even after the ■θ) control is performed in step 113. Next, in step 112, when the number of measurements, such as four, has been completed, the control circuit is terminated.

Furthermore, even if the measurement result V'sL matches the target potential, the controlled rotation is ended. Step 116f is a control procedure when the potential has deviated from the target potential.

VSL) If the measured potential is higher than VSLO, it is considered that the amount of light is insufficient, so by lowering the drive voltage (amplitude), the transmittance of the liquid crystal shutter is increased and brought closer to the target potential VSLO. control. On the other hand, when VSL<VSLO, the opposite is true, and by increasing V4r, the target potential VSLO can be approached.

Next, FIG. 12 shows an example of a control circuit for the amplitude V of the liquid crystal shirt stand 208 shown in FIG. 1. Tsumashi, said 10th
Comparator 1 of the drive circuit for one electrode of the LCD shirt shown in the figure
The basic clock frequency f and the amplitude V are input to the inputs of the inverter 702.21. 2 transistors 'Prl' are connected, and 'inverters 702 and 70 are connected to the 122 input of the comparator.
5. A transistor Tr2 is connected. Further, the comparators 121 and 122 receive digital signals dy es f) g + b, t from the bare surface potential control circuit 6.
A DA converter 701 that converts the data into an analog quantity is connected.

In the D-A converter 701, as shown in FIG. 16, the amplitude (initial value vO) is 9, for example, V=i,
Outputs Vμm, -...Vll, etc. As shown in FIG. 1, the surface potential control circuit 3 inputs the signal from the surface potential sensor 82 and the surface potential measuring circuit 2, and outputs, for example, 110,000 as shown in FIG. 16. That signal is the 12th
The amplitude is set to vl by the DA converter 701 shown in the figure, and is input to the converter 121 and comparator 122.

Note that the amplitude values V-2, V-1, . . . 8 have a difference of Δ■ shown in step 113 of FIG. In FIG. 14, when the liquid crystal drive signal is changed, one of a, b, and C is selected through 126. In Fig. 14, the amplitude of the liquid crystal drive signal 11f at point j
i Ka Vo Kara Vz (Vl-Vo -AV) K
As mentioned above, in step 113 of FIG. 11, when VSL > VSLO
This is a case where the amplitude of the liquid crystal drive waveform is changed to fVx (the value obtained by subtracting ΔV from the initial value Va) because the exposure amount is insufficient. Note that the k point is determined by changing the frequency 1 (or period T) of the drive waveform in FIG. 13, etc. by switching the switch 126 in FIG. The lighting threshold voltage (Vih) shown in FIG. This increases the lighting threshold voltage (vth) by changing the period T of the drive waveform.
It also takes advantage of the fact that things change.

In normal cases, the frequency f (1/T) is several 10 to several 100 Hz
However, it is known that vth increases when the frequency becomes high. This is because the liquid crystal molecules do not change in a fixed direction even when a voltage is applied, and is generally said to be 1 KHz or higher. This state is shown by the dotted line in FIG. When f increases, the 9 curve from yth to yth1 shifts to a solid line.

Therefore, when the driving voltage (2) is kept constant, when f increases, the liquid crystal cell shifts from cutoff to transmission. In other words, the color changes from black to gray to white.

FIG. 15 shows a frequency control circuit for a liquid crystal drive signal. 6
01,602 are the above-mentioned FIGS. 7 and 10.

The common electrode shown in FIG. 12, 607 and 608 are liquid crystal shutter parts, 603 is an individual electrode, and 121° and 122 are comparators. 801 is a J-7 lip-flop, and 803 is a frequency dividing circuit. Frequency dividing port 1vr803. J
Since the flip-flop 801 is well known in the prior art, its details will be omitted.

The frequencies are f-1, fo, fl, fz (T-1, To, respectively.

T1. This shows the case of 4 thoracic species (Tt K compatible).

Then, the wave number (
7 shows the liquid crystal drive waveform when changing the period. Note that the point when the period is changed from TO to Ti is the 15th point.
The point m is when the switch 126 in the figure is changed from b to a.

FIG. 17 shows a flowchart for controlling the frequency (period) of the liquid crystal drive signal described above. Note that Fig. 17 shows the 11th
The same numbers are used for steps as they correspond to those in the figure. In step 116, if VSL>VSLO,
Since the amount of exposure is thought to be insufficient, increase the transmittance (at a constant amplitude) of the liquid crystal shutter section. In other words, the driving frequency is increased so as to correspond to the dotted line in FIG.

Sixth Embodiment Next, still another embodiment to which the present invention is applied will be described with reference to the drawings. Now, assuming that the duty ratio is the time ratio of voltage ON for one cycle, in this embodiment, an appropriate image can be obtained by changing the duty ratio of the liquid crystal drive waveform (the transmittance of the liquid crystal shutter section is controlled, and the exposure amount is controlled). It is something to do.

Generally speaking, when driving a liquid crystal using a voltage that changes the globular value, the effective value of the waveform is the lighting start voltage (vth).
Lights up when it matches.

18, the duty ratio is 100 and the pulse dropout width Δt is 0. ■ is a duty ratio of 50chi,
There is a missing width Δt. Therefore, the duty ratio is controlled by controlling this drop width Δ or the voltage on time capture,
The exposure amount and surface potential are controlled to obtain an appropriate image.

FIG. 19 shows a duty ratio control circuit for liquid crystal drive waveforms. The timer 810 includes a drive signal line (frequency f) and seven selection signal lines Ql, Q2, Q from the optical surface potential control circuit 6.
s, the transistor group Trat, and further connected to C2R. Further, the timer 811 is similarly connected to a drive signal (frequency f) via an inverter 812.

Note that the drive signal after passing through the inverter 812 is
shall be. Furthermore, the timer 811 is connected to the surface potential control circuit 6.
selection signals (lines) Ql, Qg, Qs and transistor group Tra2. C.

) is connected to t. Also, the output time constant of the timer is CX
Since it is determined by the value of R, the time constant can be determined by keeping R constant and turning on the desired transistors using the selection signals Qz, Q2, Qa and wasting the number of C. Note that the outputs fX and fY of the timers 810 and 811 are inverted because of the inverter 812.

First, when there is an output fX from the timer 810, the anti-games 813 and 816 are turned on. Antogame-1-81
5 turns on, the transistor Tra.

Tre is turned on, and the output PX (voltage on time 'I'lTI) of the timer 810 is applied to the common electrode 601. When the AND gate 816 is turned on, since the AND gate 816 is turned on, the transistors Tr7.
Trg turns on. However, due to the negative potential on the emitter side of the transistor Tra, the signal PY whose absolute value is equal to and opposite in polarity (sign) to the output PX to the common electrode 601 is subjected to a closing force σ to the co-destructive electric wire 602. It turns out.

When there is a 113 force f\ from the timer 811, AND gates 814 and 815 are turned on. Ant game +-8
When i 5 is turned on, the transistor "f'rO.

Trxo is turned on, and the output of timer 811 (when voltage is ON)
i:'3'I'm) is applied to common 602 as output PY. Further, when the AND gate 814 is turned on, the transistors Tr11. Trlz turns on.

However, due to the negative potential on the emitter side of the transistor Trx2), an output signal PX having the same absolute value and opposite polarity as the output P-f to the common electrode 602 is applied to the common electrode 601. It turns out.

The time chart for the liquid crystal and drive described above is shown in Figure 20 of gX. Note that the fX and fY are signals output from the timers 810 and 811 at the voltage on time Tm determined by the CR time constant at the rising edge of the f and f signals, respectively.For example, the first rising edge of fX is q1. At the point,
fY is 92 points.

Based on the detailed description above, FIG. 21 shows the driving waveform of the liquid crystal shutter section. The signal waveform applied to the common lightning pole 601 in FIG. 21 is the same (
The signal waveform applied to the common electrode 602 is P in FIG.
It corresponds to Y. After the 8th point, the duty ratio control section starts. After point W, switch 126 in FIG.
is connected to the C terminal. Furthermore, after the U point, the switch 126 is connected to the C terminal.

The flowchart of the duty ratio explained in detail above.
is shown in Figure 22 of the cylinder. Figure 22 is Figure 11 and 1714
! 2B=corresponds, so use the same number for the steps
゛ro. In step 116, for example, Vst<Vs
If Lo is ignored, the exposure amount exceeds 7, so it is necessary to increase the voltage on time of LCD driver (1) a little ((increase the missing width Δt), reduce the duty ratio,
It is controlled to reduce the amount of exposure.

Effects As described above in detail, the present invention provides an image forming device that obtains an appropriate image by controlling the same wave number (period), amplitude, duty ratio, etc. of the electric signal of the optical shutter member according to the shape of the device. It became possible to provide.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an image forming system of an optical printer. FIG. 2 is a structural cross-sectional view of the liquid crystal shutter array. FIG. 3-a is a diagram showing transmission of light when no voltage is applied to the transparent electrode 202. FIG. 3-b is a diagram showing light interruption when a voltage is applied to the transparent electrode 202. FIG. 4 is a diagram showing the liquid crystal jamming drive waveform T(>). FIG. 5 is a diagram showing the relationship between drive voltage and transmittance. FIG. 6 is a diagram showing the relationship between the drive voltage and the transmittance. FIG. 7 is a diagram showing a general structure of a liquid crystal shutter array. FIG. 8 is a diagram showing a signal waveform applied to the liquid crystal shutter array. Figure 10 is a diagram showing the relationship between light transmission and cutoff of the electrode. Figure 10 is a diagram showing the drive circuit of the liquid crystal shutter [゛)1
It is. Figure 11 shows the surface potential control circuit (C
This is a flowchart of amplitude control by P U ). FIG. 12 is a diagram showing 14 circuits in a fixed width system. FIG. 13 u is a diagram showing conversion correspondence of the D-A converter 701. FIG. 14 is a diagram showing a signal waveform whose amplitude is controlled. FIG. 15 is a diagram showing a frequency (period) control circuit. FIG. 16 is a diagram showing a signal waveform whose frequency (period) is controlled. FIG. 17 is a frequency (period) control all+ll- chart. FIG. 18 is an explanatory diagram of the duty ratio. FIG. 19 is a diagram showing a duty ratio control circuit. be. FIG. 20 is a diagram showing a signal waveform whose duty ratio is controlled. FIG. 21 is a diagram showing driving waveforms of the liquid crystal shutter. FIG. 22 shows a flowchart of duty ratio control=1. 208 is a liquid crystal shutter array, and the drive circuit 16 is a liquid crystal shutter array 6 is a surface potential control circuit (CPU).
207 Procedural amendment for 18 years (voluntary) 1981 2 B 13 +1 Commissioner of the Japan Patent Office Kazuo Wakasugi 1 Indication of tenancy 1988 Patent application No. 42822 Bow 2 Title of invention Image forming device 3 Person making the amendment'11 Ia 1: , +- relationship Special r, -
Applicant i1jsf! I! 1 Shimomaruko, Old Ward 3-
30-2 Name (100) Canon Co., Ltd. Representative Kaku 1゛1u Third Department 4th Agent l Awesome! ,ii;mi. 5. Drawing to be corrected 6. Correction details Figure 15 of the drawing will be corrected as shown in the attached sheet.

Claims (1)

[Scope of Claims] (1) In an apparatus having a light shutter means for controlling light onto a photosensitive member and an image forming means for forming an image according to the light, the state of the apparatus is Accordingly, the image forming apparatus further includes an optical shutter drive control means for driving and controlling the optical shutter means in order to obtain the appropriate image. (The image forming apparatus according to claim 1, characterized in that the amplitude of the drive signal for driving the optical shutter means is controlled. The image forming apparatus according to claim 1, characterized in that the frequency of the drive signal for driving the Z-yutter means is controlled so as to obtain a large 2. The image forming apparatus according to claim 1, further comprising controlling a voltage-on time in one cycle of a drive signal for driving said optical shutter means to obtain an image.