JPH0432871A - Image forming device - Google Patents

Abstract

PURPOSE:To easily and stably carry out image control by varying a reference wave signal by means of this image forming device carrying out an image formation with a modulating signal that an image density signal is modulated with the reference wave signal. CONSTITUTION:This image forming device 100 is composed of a drum-like photosensitive body 1 turning it in the direction of an arrow, a scorotron electrifier 2 giving an uniform charge on the photosensitive body 1, a scanning optical system 3, developing units 4A - 4D in which yellow, magenta, cyan, and black toner are charged, a pretransfer electrifier 61, a scorotron transfer unit 62, a separating unit 63, a fixing roller 64, a cleaning device 70, and a destaticizer 74. Then, the photosensitive body 1 has light attenuating characteristics so that the potential of the photosensitive body is not attenuated in an exposing initial stage, but it is rapidely attenuated in an exposing middle stage, and the image formation is carried out by oscillating a semiconductor laser with the modulating signal that the image density signal is modulated with the reference wave signal. At this time, the reference wave signal is varied, so that the image control is carried out. Thus, response with respect to a driving signal is improved, a beam intensity change fluctuated by the environmental factor of heat, etc., is reduced, and a latent image formation can be stably carried out.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an image forming apparatus using electrophotography, and particularly to an image forming apparatus that forms an electrostatic latent image on a photoreceptor using exposure light that is beam-modulated using digital image data from a computer or the like.

[Background technology]

In recent years, in fields such as electrophotography, where an electrostatic latent image is formed on a photoreceptor and this latent image is developed to produce a visible image, it is possible to easily improve image quality, convert, edit, etc., and form high-quality images. Research and development of image quality forming methods using digital methods is being actively conducted. This image forming method uses a light emitting element such as a laser, an LED array, or a liquid crystal shutter to spot-expose a digital image signal from a computer or a copy document onto a negatively charged photoreceptor to form a dot-shaped image. do. As a scanning optical link that modulates light using a digital image signal, a device that uses a semiconductor laser and directly modulates the pulse width of the laser has been proposed (Jikokai No. 62-39976). A beam modulated by a digital image signal has a round or elliptical brightness distribution approximating a normal distribution with the tails expanding left and right. For example, in the case of a semiconductor laser beam, usually
At a brightness of 1 to 6 mW, the pulse width is extremely narrow, round or elliptical, with a pulse width of 20 to 100 μm in either the main scanning direction or the sub-scanning direction, or both, on the photoreceptor. However, even if an electrostatic latent image formed by such a beam is developed, preferably by reversal development, to form an image, the image often has poor sharpness. In devices that perform multilevel modulation of the beam by direct intensity modulation or pulse width modulation, the beam intensity changes little with respect to the initial drive current of the laser semiconductor, and is easily fluctuated by environmental factors such as heat. The linearity with respect to the current l is poor, and there is a problem with the response to the drive signal, so it is necessary to compensate with a circuit. For this reason, it has been difficult to increase the speed of intensity modulation and pulse width modulation as multilevel modulation methods. In particular, the poor linearity of intensity modulation has hindered its practical application. These photoreceptors generally have high sensitivity at the initial stage of exposure,
This is due to the fact that fluctuations in the photoreceptor are easily picked up and a sharp dot-shaped latent image is not formed.

[White eyes]

In view of the above-mentioned problems, an object of the present invention is to provide an image forming apparatus that can stably form a latent image by improving response to drive signals and reducing changes in beam intensity that vary due to environmental factors such as heat. Our goal is to provide the following.

[Means to solve the problem]

The present invention achieves the above object by using a modulation signal obtained by modulating an image density signal with a reference wave signal for a photoconductor having a light attenuation characteristic in which the photoconductor potential does not attenuate in the early stage of exposure but rapidly attenuates in the middle of exposure. This is an image forming apparatus that forms an image by oscillating a semiconductor laser, and is characterized by performing image control by making a reference wave signal variable. Furthermore, the present invention can be more effective if the reference wave signal is characterized in that a preferable output can be obtained by selectively using it depending on whether the image has soft or high contrast. Further, the image density signal is intensity-modulated with a reference wave signal. Further, the present invention is characterized in that a modulation signal obtained by amplitude modulating a high frequency signal using a modulation signal obtained by modulating the image density signal with a reference wave signal is used. Furthermore, the image density signal is Norse-radially modulated using a reference wave signal.

【Example】

Next, embodiments of the present invention will be described based on the accompanying drawings. First, the configuration of the image forming apparatus 100 of this embodiment will be described. FIG. 1 is a perspective view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention, FIG. 3 is a sectional view showing a specific example of the configuration of a high γ photoreceptor, and The figure is a sectional view showing a developing device applied to the image forming apparatus of this embodiment. The image forming apparatus 100 of this embodiment uniformly charges a photoreceptor and then performs processing such as aging correction, gradation correction, and masking correction on an image density signal that is A/D converted from a computer or a scanner. Based on the modulation signal obtained by comparing the analog image density signal obtained by D/A converting the processed digital image density signal with the reference wave signal (intensity modulation or pulse width modulation)・A dot-shaped electrostatic latent image is formed from the exposure, and this is reversely developed with toner to form a dot-shaped toner image.The above exposure and development steps are repeated to form a color toner image on the photoreceptor l. The image forming apparatus 100 includes a drum-shaped photoreceptor (hereinafter simply referred to as photoreceptor) 1 that rotates in the direction of an arrow. The photoreceptor 1
A scorotron charger 2 that applies a negative charge to the top, a scanning optical system 3, and developing devices 4A, 4B, and 4C loaded with yellow, magenta, green, and black toners. 4D, a pre-transfer charger 61, a scorotron transfer device 62, a separator 63, a fixing roller 64, a cleaning device 70, and a static eliminator 74. The main configuration of this embodiment will be explained below. As shown in FIG. 3, the photoreceptor 1 consists of a conductive support IA, an intermediate layer IB, and a photosensitive layer 1c, and the thickness of the photosensitive layer IC is:
Approximately 5 to 100 μm, preferably 10 to 50 μm
A drum-shaped conductive support IA made of aluminum with a diameter of 150 mm is used, and ethylene-
Intermediate layer I with a thickness of 0.1 μm made of vinyl acetate copolymer
A photosensitive layer IC having a thickness of 35 μm is provided on the intermediate layer IB. As the conductive support IA, aluminum, steel,
A drum with a diameter of 150 mm made of copper or the like is used, but other metal belts such as a belt made by laminating or vapor depositing a metal layer on paper or plastic film, or a nickel belt made by the electroplating method are also used. Good too. In addition, the intermediate layer 1B has a range of ±500 to
It is desirable to have hole mobility so that it can withstand high charging of ±2000 V, for example, in the case of positive charging, prevents injection of electrons from the conductive support IC and obtains excellent light attenuation characteristics due to the avalanche phenomenon. Therefore, for the intermediate layer IB, for example, the applicant's patent application No. 18897, which was proposed earlier by the present applicant,
10 of the positively charged charge transport substance described in the specification of No. 5.
It is preferable to attach weight x or less. As the intermediate layer IB, the following resins, which are usually used in photosensitive layers for electrophotography, can be used. (1) Vinyl polymers such as polyvinyl alcohol (Poval), polyvinyl methyl ether, polyvinylethyl ether, etc. (2) Polyvinylamine, poly-N-vinylimidazole, polyvinylpyridine (quaternary salt), polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate Nitrogen-containing vinyl polymers such as copolymers (3) Polyether polymers such as polyethylene oxide, polyethylene glycol, and polypropylene glycol (4) Acrylic acids such as polyacrylic acid and its salts, polyacrylamide, and poly-β-hydroxyethyl acrylate (5) Methacrylic acid-based polymers such as polymethacrylic acid and its salts, polymethacrylamide, and polyhydroxypropyl methacrylate (6) Ether fibers such as methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and hydroquinpropylmethylcellulose (7) Polyethyleneimine polymers such as polyethyleneimine (8) Polyalanine, polyserine, poly-L-glutamic acid, poly(hydroquinethyl)-L-glutamine,
Poly-δ-carboxymethyl-L-cysteine, polyproline, lysine-tyrosine copolymer glutamic acid-
Polyamino acids such as lysine-alanine copolymer, silk fibroin, and casein (9) Starch acetate, hydroxyl ethyl starch, starch acetate, hydroxyethyl starch,
Starch and its derivatives (10) such as amine starch and 7-osphate starch (10) Polyamides such as soluble nylon and methoxymethyl nylon (type 8 nylon) are polymers that are soluble in a mixed solvent of water and alcohol. ICs are basically photosensitive layers. Specifically, 7-talonoanine fine particles with a diameter of 0.1 to 1 μm made of a photoconductive pigment, an antioxidant, a binder resin, and a solvent for the binder resin are used without using a charge transport substance. A coating solution is prepared by mixing and dispersing phthalocyanine particles with a diameter of 1 μm, and this coating solution is applied to the intermediate layer, dried, and heat-treated if necessary. In addition, when a photoconductive material and a charge transport substance are used together, a small amount of charge of 115 or less, preferably 1/1000 to 1/10 (weight ratio) of the photoconductive pigment and the photoconductive pigment may be used together. A photosensitive layer is constructed by dispersing a photoconductive material consisting of a transport substance, an antioxidant, and a binder resin. In this embodiment, since the color toner image is superimposed on the photoreceptor, a photoreceptor having spectral sensitivity on the long wavelength side is required so that the beam from the scanning optical system 3 does not block the color toner image. The scanning optical system 3 projects a beam that is optically modulated based on an image density signal of a predetermined bit onto the uniformly charged peripheral surface of the photoreceptor 1 to form an electrostatic latent image. The scanning optical system 3 includes a semiconductor laser 31 as shown in FIG.
, mirrors 32a to 32C1, a polygon mirror 36, an fθ lens 38, a tilt correction lens 37a for correcting tilt caused by the polygon mirror 36, and an index sensor 39. The index sensor 39 detects the surface position of the polygon mirror 36 rotating at a predetermined speed, and is used to perform optical scanning using modulated image data, which will be described later, by synchronizing the main scanning direction. The semiconductor laser 31 is made of GaAlAs or the like, and since the color toner images are sequentially superimposed on the photoreceptor 1, exposure with light of a wavelength that is less absorbed by the colored toner is preferable.
The wavelength of the beam in this case is 800 nm.Q FIG. 2 is a schematic diagram showing the characteristics of a high γ photoreceptor. In the figure, vl is the charged potential (V), VO is the initial potential before exposure (V), and Ll is the amount of laser beam irradiation required for the initial potential V0 to attenuate to 415 (/l J/am)
), L! represents the amount of laser beam irradiation (μJ/c+a'') required for the initial potential V to attenuate to 115. The preferable range of L+/Lx is 1.0≦L r /L 2 ≦1.5. In this example, v, -1000 (V), Vo-9
50(v), t, /L, -L2. Further, the potential of the photoreceptor in the exposed area is 10V. The photosensitivity at the position corresponding to the middle of exposure when the light attenuation curve attenuates the initial potential (Va) to 1/2 is expressed as El/□,
When the photosensitivity at a position corresponding to the initial stage of exposure when the initial potential (Vo) is attenuated to 9/10 is E, (E l/2)/(E I/l.)≧2 is preferable. A photoconductive semiconductor is selected that provides the relationship (E I / (E I,, 0) ≧ 5. Here, photosensitivity is defined as the absolute value of the amount of potential decrease with respect to a small amount of exposure. In the light attenuation curve of the photoreceptor 1, as shown in Fig. 2, the absolute value of the differential coefficient of the potential characteristic, which is photosensitivity, is small when the amount of light is low, and attenuates steeply as the amount of light increases.Specifically. As shown in Figure 2, the light attenuation curve shows that at the beginning of exposure, the L11 sensitivity characteristics are poor for a certain period and the light attenuation characteristics are almost flat, but from the middle of exposure to L2, there is a negative change. It becomes an ultra-high sensitivity and has an ultra-high gamma characteristic that decreases almost linearly.The photoreceptor l is specifically +500 to +2000.
It is thought that high gamma characteristics are obtained by utilizing the avalanche phenomenon under high charging of v. In other words, carriers generated on the surface of the photoconductive pigment in the early stage of exposure are effectively trapped in the interface layer between the pigment and the coating resin, and light attenuation is reliably suppressed, resulting in an extremely rapid avalanche in the middle stage of exposure. It is understood that a phenomenon occurs. The developing units 4A, 4B, 4C, and 4D have a common configuration as shown in FIG. 4, except for the color of developer loaded therein.The configuration of the developing device 40 will be described below as a representative. The developing device 40 includes a sleeve 43 containing a magnet roller 44 having N and S poles that rotates in a developing tank formed by a lower casing 42 and an upper casing 41, a fixing member 46 fixed to the upper casing 41, and a sleeve 43. It is provided with a scraper 45 made of an elastic plate pressed against the wafer, first and second screw-shaped stirring members 47.4B, and a sleeve cleaning roller 49. The first stirring member 47 moves toward the front of the paper! The second stirring member 48 is shaped to be conveyed toward the back of the page. A wall is provided between the stirring members 47 and 48 so that the developer does not stagnate. In addition, scraper 4
5 may be replaced with a thin layer forming means made of a magnetic plate or a magnetic bar. The sleeve tally roller 49 rotates in the direction of the arrow and transfers the developer that has passed through the development area and consumed toner to the sleeve 4.
Scrape from 3. Therefore, the developer conveyed to the development area can be replaced, and the development conditions are stabilized. The sleeve 43 is provided with a developing bias circuit 80 that applies a voltage having a DC bias component via a protective resistor (not shown) to prevent fogging. The developer used here is a two-component developer, and the toner has a particle size of 1 to 20 μm, and is a mixture of silica fine particles treated with a charge control agent or an amine compound and other additives. . Like the toner, it is advantageous for the carrier constituting the developer to have a small particle size from the viewpoint of image resolution and gradation reproducibility. For example, when the carrier in the developer layer has a small particle size of 5 to 50 μm, a magnetic brush of uniform height can be formed. The development bias circuit 80 supplies an alternating current bias to cause the toner to vibrate between the sleeve 43 and the photoreceptor 1 in the development area where the toner conveyed by the sleeve can transfer to the photoreceptor 1 under electrostatic force. It is equipped with an AC power supply and a high-voltage DC power supply that supplies DC bias. This example Teha V D
C=800V, VAC=700V. It is 3KHz. In this way, the developing bias circuit 80
generates an oscillating electric field between the sleeve 43 and the photoreceptor l, so the developer particles vibrate between the sleeve 43 and the photoreceptor l, preventing the developer from coming into contact with the photoreceptor l. Since a toner image is formed by toner particles on the photoreceptor l even if the toner image is removed, the previous toner image is not destroyed. A one-component developer can also be used as the developer. ■In non-contact development using component or two-component developers, it is difficult to develop fine latent images because the developer does not come into contact with the latent image. By forming an image, the developability of fine parts can be improved by improving latent image formation. From this, the present invention using a high γ type photoreceptor is more effective not only in contact development but especially in non-contact development. Next, the structure of the developer used in this example will be described. (Developer formulation) Toner polystyrene 45 parts by weight Polymethyl methacrylate 44 parts by weight Charge control agent
0, -2 to 1.0 parts by weight colorant
3 to 15 parts by weight The above composition is mixed, kneaded, crushed, and then classified to obtain a toner having a weight average particle size of 3 μm. Silica was used as an external additive for the toner. Further, the amount of charge of the toner is 20 μc/g. The following may be used to provide spectral characteristics that prevent the amount of transmitted light from the writing system from decreasing due to light absorption by toner. Benzidine Yellow
ow) G (C, 1゜21090), Henjin IIC+
-GR(C,l-21100), Permanent YeO
-(Permanent Yellow) DHG (Hoechst product), Brilliant Carmine (Br1
1 ant Carmine) 6 B (C, 1,158
50), Rhodamine 6G Lake (C,1
45160) Rhodamine B Lake (C, 1, 45170
), Phthalocyanine Blue Non-Crystal (Ph
thalocyanine Blue non Cry
stal) (C, 1,74160), phthalocyanine.
IJ-7 (C, 1,74260), carbon black, Fat Yellow 5G, 7 Fat Yellow 3G1 Fat Red G1 Fat Red H
RR, 7 Atsut Red 5B, 7 Ant Bra Nk HB
, ZaponFasi ・Black B1 Zapon 7 Earth Black B1 Zapon First Blue) IFL, Zapon First Red BB, Zapon First Red GE, Zapon Fasi
First Yellow G1 Quinacridone Red (c,
+, 465000) Carrier (resin coated carrier) Core ferrite coating resin: styrene acrylic (4: 6) Magnetization 70emu/g Weight average particle size 3oμm (spherical) Specific gravity
5-2 g/am' Specific resistance: 1013 Ω・Cl11 or more A mixture of the above compositions is used as a developer f:. The l1IlIR and operation of the first drive circuit of the scanning optical system will be explained below. FIG. 5 is a block diagram showing the first drive circuit of the scanning optical system. As shown in FIG. 5, the drive circuit 300 of the scanning optical system 3 forms an intensity modulation signal based on an image density signal (image density data) from a computer or scanner, and drives the semiconductor laser 31 with the modulation signal. . Note that the laser drive circuit 300 may be provided with means for feeding back a signal corresponding to the amount of beam light from the semiconductor laser 31, and may be driven so that the amount of light is constant. As shown in FIG. 5, the drive circuit 300 includes a reference wave signal generation circuit 310, a buffer circuit 320, and a differential amplifier circuit 340.
．． 350, DC variable power supply 360 and D/A converter 330
It consists of. The reference wave signal generation circuit 310 generates a triangular wave by an integrator including a variable resistor 311 and a capacitor 312. Furthermore, the triangular wave has a capacitor 313 and an i-layer resistor 31.
5 to the base terminal of the transistor 321. The reference wave signal generation circuit 310 has two variable resistors. That is, the variable resistor 311 is for adjusting the amplitude of the triangular wave. The variable resistor 314 is for adjusting the bias or offset of the triangular wave. The triangular wave passes through the buffer circuit 320 and is then sent to the differential amplifier 34.
Input to the positive input terminal of 0. The differential amplifier 340 is connected to the buffer circuit 320 as described above.
Through! D/A converter 330 converts a digital image density signal consisting of a reference wave and predetermined bits, for example 8 bits, into a D/A converter;
The converted analog concentration signal is hyperdynamically amplified. The obtained intensity modulation signal is then output to the input terminal of the differential amplifier 350. The differential amplifier 350 has a negative input terminal connected to the variable DC power supply 3.
By applying the output signal from 60, the intensity modulation signal input to the positive terminal is level-shifted by the DC component and output. This level shift corresponds to the white background in the image. As a result, the differential amplifier 350 outputs an intensity modulated signal synchronized with the pixel clock DCK. This signal becomes a drive signal for driving the semiconductor laser 31 on and off. FIG. 6 is a time chart showing waveforms of various parts of the first drive circuit. In the figure, (a) is a reference pulse SCK, and the pulse SCK is synchronized with the pixel clock DCH. The signal indicated by the broken line in (b) is adjusted to the recording characteristics.
After color correction and gradation correction, the signal is D/A converted and is an analog density signal, and the signal indicated by a solid line is a reference wave signal which is an output signal of the buffer 320. (c) is the differential amplifier 3
This is a modulation signal intensity-modulated by 40. In the figure, the solid line indicates the case of high-tone image reproduction, and the broken line indicates the case of soft-tone image reproduction. By increasing the amplitude, the diameter of recording dots in high density areas becomes smaller, while dots are reliably formed in low density areas. It is preferable to reduce the amplitude for text and line images, while increasing the amplitude for gradation images to give a preferable image reproduction. The density signal corresponding to the recording pixel and the reference signal are synchronized, and an intensity modulation signal corresponding to the image density is generated. (d) is a signal obtained by level-shifting the intensity modulation signal. As described above, this level shift corresponds to the white background in the image. FIG. 7 is an explanatory diagram for explaining the relationship between the level-shifted intensity modulation signal from the drive circuit of the first embodiment and the amount of light emitted from the semiconductor laser. In the figure, the graph shows input/output characteristics showing the relationship between the input current to the semiconductor laser 3j and the amount of light emitted. A
is the region of spontaneous emission, a is the threshold current,
If a current larger than this threshold current σ is inputted, stimulated emission will occur. In other words, it is a region where stimulated emission occurs. (a) shows the semiconductor laser 311: the input current. As described above, a current whose level is shifted by an amount corresponding to the white background in the image is input to the semiconductor laser. This improves the startup performance of the semiconductor laser 31. (b) shows the semiconductor laser 3 according to the input current.
It shows the amount of light emitted from 1. In the figure, the dashed-dotted line indicates the half-reduced exposure light amount of the high-gamma photoreceptor used in Example 1. In other words, since it is a high γ photoreceptor, the semiconductor laser 3
The exposure amount from 1 is reduced by half, that is, the potential V. I/2
A latent image will not be formed if the exposure light amount is less than that required to form VO. For this reason, even if the level-shifted DC component is higher than the threshold current a, it will correspond to a white background. In other words, in this embodiment, the semiconductor laser 31 is caused to oscillate even in a portion corresponding to a white background. Instead of using the DC component, the amplitude of the reference wave signal may be set to a large value so that the exposure amount of the white background portion is approximately equal to or less than the half-reduced exposure amount. (c) shows the exposure dot distribution recorded on the photoreceptor l. The position of the half-decreased exposure light amount in this exposure dot distribution is shown by a broken line, and the area beyond this point is high γ.
It is formed as a latent image due to the characteristics of the photoreceptor. In other words, a latent image consisting of dots of different sizes according to the density signal is obtained, and a dot-like image density distribution formed by developing the latent image is shown. Furthermore, a sharp and small dot-shaped latent image can be formed. In reality, the exposure dot distribution is wider than the blurring of the scanning optical system 3, so the recorded dot diameter tends to be large in high density areas and small in low density areas. Well, in relation to the amplitude of the reference wave, the line looks like a dotted line when the amplitude is small, whereas the line looks like a broken line when the amplitude is small. That is, the diameter of the recording dot is small in the high illuminance area (corresponding to high density), and the diameter of the recording dot is large in the low illuminance area (corresponding to the low density area). In this way, in the case of amplitude holes, image reproduction has high gradation. The image forming process of the image forming apparatus 100 of this embodiment will be described below. After the photoreceptor is charged by a scorotron charger 2, it is imagewise exposed by a beam of light from a scanning optical system 3, and electrostatic latent images corresponding to each color are formed on the drum-shaped photoreceptor l. Among the electrostatic latent images corresponding to the respective colors, the electrostatic latent image corresponding to yellow is formed by irradiation with laser light that is optically modulated by yellow data (digital density data). The electrostatic latent image corresponding to yellow is transferred to the first developing device 4.
A is developed, and a first dot-shaped toner image (yellow toner image) with extremely high sharpness is formed on the photoreceptor l. This first toner image is not transferred to the recording paper P, but after its surface potential is neutralized to approximately zero by alternating current corona discharge from the static eliminator 74, it is subjected to optical static neutralization using infrared light. Next, the photoreceptor 1 is charged again by the scorotron charger 2. Next, the laser light is optically modulated using magenta data (digital density data), and the modulated laser light is irradiated onto the photoreceptor 1 to form an electrostatic latent image. This electrostatic latent image is developed by the second developing device 4B to form a second toner image (magenta toner image). In the same manner as described above, after static electricity removal and charging laser beam irradiation, the third toner image (cyan toner image) is sequentially developed by the third developing device 4C, and the three-color toner image is sequentially laminated on the photoreceptor 1. is formed. Finally, a fourth toner image (black toner image) is formed, and four-color toner images are sequentially stacked on the photoreceptor l. According to the image forming apparatus +00 of this embodiment, the photoreceptor has excellent high comma characteristics, and this excellent high gamma characteristic is achieved by repeating the charging, exposure and development process many times from above the toner image. Even when the latent images are formed by overlapping them, a latent image is stably formed. In other words, even if a beam is irradiated from above the toner image based on a digital signal, a dot-shaped electrostatic latent image with high sharpness without fringes can be formed, and as a result, a toner image with high sharpness can be obtained. can. These four-color toner images are transferred onto the recording paper P fed from the paper feeder by the action of the transfer device 62 after the photoreceptor L is charged by the charger 61 (this may be omitted). The recording paper P carrying the transferred toner image is separated from the photoreceptor 1 by the separation electrode 63, is conveyed by a guide and a conveyor belt, is carried into the fixing device 64, is heated and fixed, and is discharged onto a paper discharge tray. On the other hand, the toner remaining on the surface of the photoconductor l after the transfer is completed is removed by the blade, fur brush, or magnetic plan of the cleaning device R70, which was released during the toner image formation, and the toner is The electric charge is removed by the electric device 74, so that there is no problem in the formation of the next multicolor image. Note that the lamp and the corona static eliminator 74 may be placed before the cleaning, and the static elimination process of each toner image forming process may be omitted if the DC component of the input current to the semiconductor laser 31 is below the threshold current σ. You can. Other shapes can also be used as the reference wave. When a reference wave having one cycle of two triangular waves of different sizes so as to coincide with twice the synchronization of recording pixels was selected as the reference wave, a clear image with high gradation was obtained. Furthermore, when the same triangular wave was used (one cycle was twice the recording pixel cycle), a clear image with high resolution was obtained. In general, high-gamma photoreceptors tend to reproduce images with high contrast, and having multiple peaks as described above within one cycle of the reference wave is effective for improving gradation. When the same triangular wave was used as the reference wave (one period was the same as the recording pixel period), a clear image with high resolution was obtained. Further, the period of the reference wave can be set larger than the recording pixel synchronization. For example, similarly preferable results can be obtained even if the period is four times that of the recording pixels. In this example, the semiconductor laser 31 was used and the intensity modulation was described in the example, but the invention is not limited to this, and the intensity modulation can be similarly performed using other light emitting elements such as an LED array. Light modulation can be performed using the concentration signal, and a similar effect can be obtained. FIG. 8 is a block diagram showing a drive circuit of the second embodiment of the scanning optical system 3. The drive circuit 300 intensity-modulates an analog image density signal with a reference wave signal, modulates a carrier wave signal with the intensity-modulated signal, and applies a modulation signal obtained by level diadding this to the semiconductor laser 31. Generation circuit 310
, buffer circuit 320, differential amplifier 340, D/A converter 330, variable resistor 3711 variable gain amplifier 370,
High band power amplifier 380, carrier signal generation circuit 380
It consists of. The reference wave generation circuit 310 generates a triangular wave by an integrator including a variable resistor 311 and a capacitor 312. Further, the triangular wave is input to the base terminal of the transistor 321 via the capacitor 313 and the protective resistor 315. Reference wave generation circuit 310 has two variable resistors. That is, the variable resistor 311 is for adjusting the amplitude of the triangular wave. The variable resistor 314 is for adjusting the bias or offset of the triangular wave. The triangular wave (shown by a solid line in FIG. 9(b), which will be described later) passes through the buffer circuit 320 and is output to the positive input terminal of the differential amplifier circuit 340. On the other hand, the digital image density signal consisting of 8 bits is D/A
The analog image density signal D/A converted by the converter 330 is outputted to the negative input terminal of the differential amplifier 340 mentioned above. As a result, the differential amplifier 340 intensity-modulates the analog image density signal with the reference wave signal, and inputs the modulated signal to the variable gain amplifier 370 via the variable resistance element 371. This signal is generated by amplitude modulating a carrier wave with a frequency of 600 MHz or higher using a variable gain amplifier 370, and amplifying the signal using a high band power amplifier 380;
applied to the electrode. Note that the high-band amplifier 380 also has a function of level-shifting the modulated signal using a DC component. FIGS. 9(a) to 9(d) are time charts showing waveforms of various parts in the drive circuit of this embodiment. In the figure, (a) is a reference pulse SCK, and the pulse SCK is synchronized with the pixel clock DCK. The signal shown by the broken line in (b) is an analog density signal that has been D/A converted after color correction and gradation correction according to the recording characteristics, and the signal shown by the solid line is the output signal of Buff 7A320. It is a wave signal. (c) is a differential amplifier 340
This is an intensity-modulated signal that is intensity-modulated. In the figure, the solid line indicates the case of high-tone image reproduction, and the broken line indicates the case of soft-tone image reproduction. By increasing the amplitude, the diameter of recording dots in high density areas becomes smaller, while dots are reliably formed in low density areas. It is preferable to reduce the amplitude for text and line images, while increasing the amplitude for gradation images to give a preferable image reproduction. The density signal corresponding to the recording pixel and the reference signal are synchronized, and an intensity modulation signal corresponding to the image density is generated. (d) shows the amplitude modulation of the carrier signal using the intensity modulation signal, l: modulation signal, which shows that the level has been further shifted by the high band power amplifier. FIG. 1O is an explanatory diagram for explaining the relationship between the amount of light emitted from the semiconductor laser by the level-shifted intensity modulation signal from the drive circuit of the second embodiment. A is a region where spontaneous emission occurs, σ is a threshold current, and if a current larger than this threshold current σ is input, stimulated emission occurs. In other words, it is a region where stimulated emission occurs. (a)
indicates the current input to the semiconductor laser 31. As described above, a current whose level is shifted by an amount corresponding to the white background in the image is input to the semiconductor laser. This improves the startup performance of the semiconductor laser 31. (b) shows the amount of light emitted from the semiconductor laser 31 according to the conducting current. In the figure, the dashed-dotted line indicates the half-decreased exposure light amount of the high γ photoreceptor used in this example. In other words, since it is a high-gamma photoreceptor, no latent image is formed if the amount of exposure from the semiconductor laser 31 is the amount of light required to reduce the exposure potential by half to 1/2V6. For this reason, even if the level-softened DC component is higher than the threshold current a, it will correspond to a white background. In other words, in this embodiment, the semiconductor laser 31 is caused to oscillate even in a portion corresponding to a white background. Instead of using the DC component, the amplitude of the reference wave signal may be set to a large value so that the exposure amount of the white background portion is approximately equal to or less than the half-reduced exposure amount. Instead of using the DC component, the amplitude of the reference wave signal may be set to a large value so that the exposure amount of the white background portion is approximately equal to or less than the half-reduced exposure amount. (c) shows the exposure dot distribution recorded on the photoreceptor l. The position of the half-decreased exposure light amount in this exposure dot distribution is indicated by a broken line, and the portion beyond this point is formed as a latent image due to the high 1 photoreceptor characteristics. In other words, a latent image consisting of dots of different sizes according to the density signal is obtained, and a dot-like image density distribution formed by developing the latent image is shown. Furthermore, a sharp and small dot-shaped latent image can be formed. In reality, the exposed dot diameter is widened due to the blurring of the scanning optical system, so the recorded dot diameter tends to be large in high-density areas and small in low-density areas. Furthermore, in relation to the amplitude of the reference wave, a solid line appears when the amplitude is small, whereas a broken line appears when the amplitude is large. In other words, the diameter of the recording dot is smaller in the high illumination area (corresponding to high density) and the diameter of the recording dot is smaller in the low illumination area (corresponding to high density).
(corresponding to low density areas), the recording dot diameter becomes large. In this way, when the amplitude is large, the image reproduction has high gradation. Next, a third example will be shown. As shown in FIG. 11, the drive circuit 300 includes a reference wave signal generation circuit 310, a buffer circuit 320, and a differential amplifier circuit 34.
0.350, DC variable power supply 360 and D/A converter 33
Consists of 0. The reference wave signal generation circuit 310 generates a triangular wave by an integrator including a variable resistor 311 and a capacitor 312. Furthermore, the triangular wave has a capacitor 313 and a protective resistor 31.
5 to the base terminal of the transistor 321. The reference wave signal generation circuit 310 has two variable resistors. That is, the variable resistor 311 is used to adjust the amplitude of the triangular wave. The variable resistor 314 is for adjusting the bias or offset of the triangular wave. The triangular wave passes through the buffer circuit 320 and is sent to the comparator 3.
Input to the positive input terminal of 41. The comparator 341 is connected to the buffer circuit 32 as described above.
A digital image density signal consisting of a reference wave passed through 0 and predetermined bits, for example 8 bits, is D/A converted by a D/A converter 330.
Compare with the converted analog concentration signal. The obtained pulse width modulation signal is then output to the input terminal of the differential amplifier 350. The differential amplifier 350 has a negative input terminal connected to the variable DC power supply 3.
By applying the output signal from 60, the intensity modulation signal input to the positive terminal is level-shifted by the DC component and output. This level shift corresponds to the white background in the image. As a result, the differential amplifier 350 outputs a pulse width modulated signal having a DC component synchronized with the pixel clock D (J). This signal becomes a drive signal for turning on and off the semiconductor laser 31. It is a time chart showing waveforms of various parts of the third drive circuit.
K, and the pulse SCK is synchronized with the pixel clock DCK. The signal shown by the broken line in (b) is an analog density signal that has been D/^ converted after color correction and gradation correction according to the recording characteristics, and the signal shown by the solid line is a reference wave signal that is the output signal from the buffer 320. It is. (C) is a modulation signal subjected to pulse width modulation by the comparator 341. In the figure, the solid line indicates the case of high-tone image reproduction, and the broken line indicates the case of soft-tone image reproduction. By increasing the amplitude, the diameter of recording dots in high density areas becomes smaller, while dots are reliably formed in low density areas. It is preferable to reduce the amplitude for characters and line images and to increase the amplitude for gradation images to give a preferable image reproduction. The density signal corresponding to the recording pixel and the reference signal are synchronized, and a pulse width modulation signal corresponding to the image density is generated. (d) is a signal obtained by level shifting the pulse width modulation signal. As described above, this level shift corresponds to the white background in the image. FIG. 13 is an explanatory diagram for explaining the relationship between the level/attenuated pulse width modulation signal from the drive circuit of the third embodiment and the amount of light emitted from the semiconductor laser. In the figure, the graph shows input/output characteristics showing the relationship between the input current to the semiconductor laser 31 and the amount of light emitted. A
is the region of spontaneous emission, σ is the threshold current,
If a current larger than this threshold current a is inputted, stimulated emission will occur. In other words, it is a region where stimulated emission occurs. (a) shows the current input to the semiconductor laser 3I. As mentioned above, shift the level by the amount corresponding to the white background in the image.
; Current will be input to the semiconductor laser. This improves the startup performance of the semiconductor laser 31. (b) shows the amount of light emitted from the semiconductor laser 31 according to the input current. In the figure, the dashed-dotted line indicates the half-decreased exposure light amount of the high γ photoreceptor used in this example. In other words, since it is a high γ photoreceptor, the semiconductor laser 31
The exposure amount from V is reduced by half, that is, the potential V. l/2V
If the amount of exposure light is less than the amount of exposure light required to achieve , no latent image will be formed. For this reason, even if the level-off DC component is higher than the threshold G1 value current α, it will correspond to a white background. In other words, in this embodiment, the semiconductor laser 31 is caused to oscillate even in a portion corresponding to a white background. Instead of the DC component, the amplitude of the reference wave signal may be set large, and the exposure amount of the white background portion may be set to be approximately equal to or less than the half-reduced exposure amount. (C) shows the exposure dot distribution recorded on the photoreceptor j. The position of the half-decreased exposure light amount in this exposure dot distribution is indicated by a broken line, and a portion beyond this point is formed as a latent image due to the high γ photoreceptor characteristics. In other words, although the exposure dot distribution is an elliptical beam, it has become wider due to the blurring of the scanning optical system, but the position of the half-reduced exposure light amount in this exposure dot distribution is shown by a broken line.
A portion beyond this is formed as a latent image due to the high γ photoreceptor characteristics. In other words, a latent image consisting of dots of different sizes according to the density signal is obtained, and a dot-like image density distribution formed by developing the latent image is shown. Furthermore, it is possible to form a small dot-like latent image with the dye. In actuality, since the exposure dot distribution is wider than the blur of the scanning optical system 3, the recorded dot diameter tends to be large in high density areas, and the recorded dot diameter tends to be small in low density areas. Furthermore, in relation to the amplitude of the reference wave, a solid line appears when the amplitude is small, whereas a broken line appears when the amplitude is large. In other words, the recording dot diameter is smaller in high illumination areas (corresponding to high density) and smaller in low illumination areas (corresponding to high density).
(corresponding to low density areas), the recording dot diameter becomes large. In this way, when the amplitude is large, the image reproduction has high gradation. In this embodiment described above, the gradation can be controlled depending on the image to be output. The amplitude of the reference wave signal can also be changed automatically according to the result of image discrimination. Furthermore, by making it possible to independently control the amplitude of the reference wave signal for each color, it is possible to control the gradation and color balance. Furthermore, in this embodiment described above, the print density and color balance can be changed according to the output content. In this case, let the DC components of each reference wave simultaneously or independently
You can change the density and color balance by lifting the image. Although the case where the DC component is larger than the threshold current a is shown, it can also be set smaller than this. Further, it is not necessary to have a direct current component. In this embodiment, the noise is stable against temperature changes and changes in the amount of optical return, and no spike-like noise occurs. Further, in the present invention, other exposure means such as LED or LC3 can be used instead of exposure using a laser beam.

【Effect of the invention】

The present invention forms an image using a modulation signal obtained by modulating an image density signal with a reference wave signal on a photoconductor having a light attenuation characteristic in which the photoconductor potential does not attenuate in the early stages of exposure but rapidly attenuates in the middle of exposure. By making the reference wave signal variable in the forming apparatus, it was possible to provide an image forming apparatus that can easily and stably perform image control. In addition, by providing a modulation signal with a DC component, it was possible to provide an image forming apparatus that can form a small latent image in contrast. Furthermore, by using the reference wave as a modulation signal having a DC component as the image density signal, it is stable against noise, temperature changes, and changes in the amount of light return, and no spike-like noise is generated, so that latent images can be It was possible to provide an image forming apparatus that can perform image formation stably. Furthermore, by using a modulation signal in which a high-frequency signal is amplitude-modulated with a modulation signal in which an image density signal is modulated with the reference wave signal, the noise becomes stable against temperature changes and changes in the amount of optical return, as described above, and Since no spike-like noise is generated, an image forming apparatus capable of stably forming a latent image can be provided. By pulse width modulating the image density signal with the reference wave signal, it was possible to provide an image forming apparatus that can form a sharp and small latent image.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing the characteristics of a high γ photoreceptor, and FIG. 3 is a perspective view showing the characteristics of a high γ photoreceptor. 4 is a sectional view showing a specific configuration example, FIG. 4 is a sectional view showing a developing device applied to the image forming apparatus of this embodiment, FIG. 5 is a block diagram showing the first drive circuit of the scanning optical system, and FIG. FIG. 6 is a time chart showing the waveforms of various parts of the first drive circuit, and FIG. 7 is a time chart for explaining the relationship between the amount of light emitted from the semiconductor laser due to the level-shifted intensity modulation signal from the drive circuit of the first embodiment. 8 is a block diagram showing a drive circuit of the second embodiment of the scanning optical system 3, and FIGS. 9(a) to 9(d) are time charts showing waveforms of various parts in the drive circuit of this embodiment. , 1st
Figure 0 is an explanatory diagram for explaining the relationship between the amount of light emitted from the semiconductor laser depending on the level/attenuated intensity modulation signal from the drive circuit of the second embodiment, and Figure 11 is the third drive circuit of the scanning optical system. FIG. 12 is a time chart showing the waveforms of each part of the third drive circuit, and FIG. 13 is the amount of light emitted from the semiconductor laser by the level-shifted pulse width modulation signal from the drive circuit of the third embodiment. It is an explanatory diagram for explaining the relationship. 1... Photoreceptor 3... Scanning optical system 31...
・Semiconductor laser 100...Image forming device Fig. 1

Claims (5)

[Claims] (1) For a photoreceptor with a light attenuation characteristic in which the photoreceptor potential does not attenuate in the early stages of exposure but rapidly attenuates in the middle of exposure,
An image forming apparatus that performs image formation using a modulation signal obtained by modulating an image density signal with a reference wave signal, wherein the image forming apparatus performs image control by making the reference wave signal variable. (2) The image forming apparatus according to claim 1, wherein the amplitude of the reference wave signal is large for a soft-tone image and small for a high-tone image. (3) The image forming apparatus according to claim 1 or 2, wherein the image density signal is intensity-modulated with a reference wave signal. (4) The image forming apparatus according to claim 3, characterized in that a modulation signal obtained by modulating the amplitude of a high frequency signal using a modulation signal obtained by modulating the image density signal with a reference wave signal is used. (5) The image forming apparatus according to claim 1 or 2, wherein the image density signal is pulse width modulated using a reference wave signal.