JPH0432870A - Image forming device - Google Patents

Abstract

PURPOSE:To improve gradation in recording characteristics and to stably carry out a latent image formation by setting the maximum and minimum values of an image density signal inside a reference wave signal. CONSTITUTION:This image forming device 100 is composed of a drum-like photosensitive body 1 turning in the direction of an arrow, a scorotron electrifier 2 imparting 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 damped in an exposing initial stage, but it is rapidely attenuated in an exposing middle stage, and an image formation is carried out with a modulating signal that the image density signal is modulated with the reference wave signal. At this time, the maximum and minimum values of the image density signal are set inside the reference wave signal. Thus, the response with respect to a driving signal is improved, a beam intensity change fluctuated by the environmental factor of heat, etc., is reduced, and the latent image formation can be stabley 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 forms a dot-shaped image by spot-exposing a digital image signal from a computer or a copy document onto a charged photoconductor using a light-emitting element such as a laser, LED array, or liquid crystal/Yatta. do. As a scanning optical yarn feeding system that optically modulates light using a digital image signal, an apparatus has been proposed that uses a semiconductor laser and directly modulates the pulse width of the laser (Jikou No. 6239976). The beam modulated by the digital image signal has a round or elliptical brightness distribution with tails that spread to the left and right and approximates a normal distribution. The pulse width in either the main scanning direction or the sub-scanning direction or both has an extremely narrow round or elliptical shape of 20 to 100 μm. However, even if an electrostatic latent image formed by such a beam is developed preferably by reversal development to form a dot 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 in terms of circuitry. 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.

【the purpose】

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. The image forming apparatus performs image formation, and is characterized in that the maximum and minimum values of the image density signal are located inside the reference wave signal. In addition, the exposure intensity corresponding to a white background is reduced to half and the exposure light amount is approximately concave.
Further effects can be exhibited if the method is characterized by the following. 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 pulse width 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, 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 shading correction, gradation correction, and masking correction on an image density signal that is A/D converted from a computer or a scanner. This processed digital image density signal is obtained by D/A conversion; the spot exposure number is intensity-modulated or pulse-width-modulated based on the modulation signal obtained by comparing the analog image density signal and the reference wave signal. ; forming a more dot-shaped electrostatic latent image, reversing this with toner to form a dot-shaped toner image, and repeating the exposure and development steps to form a color toner image on the photoreceptor 1; The color toner image is transferred, separated and fixed to obtain a color image. 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;
A scorotron charger 2 that applies a uniform charge thereon, a scanning optical system 3, and developing devices 4A, 4B, and 4C loaded with yellow, magenta, cyan, 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 1c is as follows.
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-
It is constructed by forming an intermediate layer IB made of vinyl acetate copolymer and having a thickness of O.lpm, and providing a photosensitive layer IC having a thickness of 35 μm on this 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 of paper or plastic film laminated or vapor-deposited with a metal layer, or a nickel belt made by an 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 add less than % by weight. 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) polyhinylamine, poly-N-vinylimidazole, polyhinylpyridine (quaternary salt), polyhinylpyrrolidone, vinylpyrrolidone - Nitrogen-containing vinyl polymers such as vinyl acetate copolymers (3) Polyether polymers such as polyethylene oxide, polyethylene glycol, polypropylene glycol, etc. (4) Polyacrylic acid and its salts, polyacrylamide, poly-β-hydroxyethyl acrylate, etc. Acrylic acid polymers (5) Methacrylic acid polymers such as polymethacrylic acid and its salts, polymethacrylamide, and polyhydroxypropyl methacrylate (6) Ethers such as methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose Cellulose polymer (7) Polyethyleneimine polymer such as polyethyleneimine (8) Polyalanine, polyserine, poly-L-glutamic acid, poly-(hydroxyethyl)-L-glutamine,
Poly-δ-carboxymethyl-7 stain, polyproline, lysine-tyrosine copolymer glutamic acid-
Polyamino acids such as lysine-alanine copolymers, silk fibroin, and casein (9) Starches and their derivatives such as starch acetate, hydroxyethyl starch, starch acetate, hydroxyethyl starch, amine starch, and phosphate starch (10) Soluble polyamides The photosensitive layer IC is basically a polymer such as nylon, methoxy/methyl nylon (type 8 nylon), etc., which is soluble in a mixed solvent of water and alcohol. A coating solution is prepared by mixing and dispersing 7-lycyanine fine particles with a diameter of ~1 μm, an antioxidant, and a binder resin into 7-talo/anine fine particles with a diameter of 0.1 to 1 μm using a binder resin solvent, This coating liquid 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, l
A photoconductive pigment and 115 or less of the photoconductive pigment,
Preferably, the photosensitive layer is composed of a small amount of a charge transporting material of 1/1000 to 1/10 (weight ratio), and is dispersed in a photoconductive material, an antioxidant, or an interresin. 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 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.
It consists of mirrors 32a to 32c, 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, it is preferable to use light with a wavelength that is less absorbed by the colored toner.
The wavelength of the beam in this case is 800 nm. FIG. 2 is a schematic diagram showing the characteristics of a high-gamma photoreceptor. In the figure, ■, is the charged potential (V), Vo is the initial potential (V) before exposure, and Ll is the amount of laser beam irradiation required for the initial potential V0 to attenuate to 415 (/j J/cm"
), L2 represents the amount of laser beam irradiation (μJ/cm”) required for the initial potential Vo to attenuate to 115. The preferable range of L+/Lx is 1.0≦L r / L!≦1.5. In this example, V, −1000 (V), vo −
950 (V), LI/t, 2-1-2. 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 optical attenuation curve attenuates the initial potential (Vo) to 172 is expressed as El/□,
Let E be the photosensitivity at the position corresponding to the initial exposure when the initial potential (■.) is attenuated to 9/10, and when t2, (E I/2)/(E!/□.)≧ 2 Preferably (E + y = ) / (E! y + .)
A photoconductive semiconductor is chosen that gives the relationship ≧5. Note that here, the photosensitivity is defined as the absolute value of the amount of potential drop with respect to the minute exposure amount. 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 small, and attenuates steeply as the amount of light increases. Specifically, the light attenuation curve is as shown in Figure 2. In the early stage of exposure, the sensitivity characteristics are poor for a short period of time L1, showing almost flat light attenuation characteristics, but from mid-exposure stage L1 to L2, the sensitivity changes to extremely high sensitivity and decreases almost linearly. It has ultra-high gamma characteristics. Specifically, the photoreceptor l is +500 to +200
It is thought that high gamma characteristics are obtained by utilizing the avalanche phenomenon under high charging of 0 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. It is understood that a sudden avalanche 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 that includes a magnet roller 44 having north and south poles that rotates in a developer tank formed by a lower casing 42 and an upper casing 41, and a sleeve 43 from a fixing member 46 fixed to the upper casing 41. a screw-shaped first scraper 45 made of an elastic plate pressed against the
and second stirring members 47 and 48, and a sleeve cleaning roller 49. The first stirring member 47 is shaped to be conveyed toward the front of the page, and 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, the scraper 45
Instead, a thin layer forming means made of a magnetic plate or a magnetic bar may be provided. 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 transported in the developing area 1 can be replaced, and the developing 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, 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 vibrate the toner between the sleeve 43 and the photoreceptor 1 in the development area where the toner conveyed by the sleeve can be transferred to the photoreceptor 1 by electrostatic force. It is equipped with an AC power supply and a high-voltage DC power supply that supplies DC bias. This example f j;k
VDC=800V, VAC=700V. It is 3KHz. In this way, the developing bias circuit 8
0 generates an oscillating electric field between the sleeve 43 and the photoreceptor 1, so the developer particles vibrate between the sleeve 43 and the photoreceptor 1, so the developer particles and the photoreceptor 1 come into contact. Even without this, a toner image is formed by toner particles on the photoreceptor 1, so the previous toner image is not destroyed. As the developer, a one-component developer can be similarly used. In non-contact development using a l-component or two-component developer, 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 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
0.2-1.0 parts by weight colorant
Mixing 3 to 15 parts by weight of the above composition, kneading,
After pulverization, the toner is 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 in order to provide spectral characteristics that prevent a decrease in the amount of transmitted light of the beam from the writing system due to light absorption by the toner. Benzidine Yellow
ow) G (C, 1° 21090), Benzine Yellow GR (C, 1, 21100), Permanent Yellow DHG (Hoechst product), Brilliant Carmine (Brill)
liant Carmine) 6 B (C, 11585
0), Rhodamine 6G Lake (C, I
, 45160) Rhodamine B Lake (C, 1,451
70), Phthalocyanine Blue Non-Crystal (
Phthalocyanine Blue non C
rystal) (c, +, 74160), phthalonanine green (C, 1, 74260), carbon black, fat (Fa) yellow 5G, fat yellow 3G, 7at reso FG, fan)...
7FHRR, Fat Red 5B, Fat Black HB, ZaponFast
・Black RE, Zapon First Black B, Zapon 7 Earth Blue HFL, Zapon First Red BB, Zapon First Reno FGE, f Bon First Yellow G, Quinacridone Red (C
, 1,465000) Carrier (resin coated carrier) F: Ferrite coating Resin: Styrene/acrylic magnetization
7Qemu/g Weight average particle size 30μm (spherical) ratio 11
5, 2 g/cm' resistivity
A developer was prepared by mixing the above composition with a resistance of 1013 Ω·cm or more. The configuration and D 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 composed of a variable resistor 311 and a capacitor ++312. Furthermore, the triangular wave has a capacitor 313 and a protective resistor 3.
15 to the base i terminal of the transistor 321. The reference wave signal generation circuit 310 has two variable resistors. That is, the variable resistor 311 is the first one that adjusts 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.
A reference wave passed through the reference wave and an analog density signal obtained by D/A converting a digital image density signal consisting of predetermined bits, for example 8 bits, by a D/A converter 330 are differentially 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 leveled/outputted using the DC component. 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 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 a reference wave signal that is the output signal from the buffer 320. It is. In the figure, Vmin corresponds to the minimum value of the image density signal (black background area), and Vmax corresponds to the maximum value of the image density signal (white background area). Since the amplitude of the reference wave exceeds Vmax of the image density signal, exposure is performed even in the white background area. Further, since the amplitude of the reference wave is lower than Vmin of the image density signal, light is partially applied even in the black background area. From these facts, it means that the diameter of the toner in the low concentration area is reliably formed, while the diameter of the toner in the high concentration area is made small. In this way, the recording characteristics of the high-gamma photoreceptor are improved. (c) is a modulated signal whose intensity is modulated by the differential amplifier 340. 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 intensity modulation signal which is shifted by seven levels from the drive circuit of the embodiment of [1] and the amount of light emitted from the semiconductor laser. In the figure, the graph shows the input/output characteristics showing the relationship between the input current to the semiconductor laser 31 and the amount of light emitted. 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 mentioned above, the level is increased by 7 points corresponding to the white background in the image, and a current 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 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 amount of exposure from the semiconductor laser 31 is reduced by half, that is, the potential V0 is reduced to 1/2 Vo.
A latent image will not be formed if the amount of exposure light is less than the amount of exposure light required to achieve this. 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. By setting the amplitude of the reference wave signal large instead of the DC component, the exposure amount at Vmax corresponding to the white background can be halved and the exposure amount P
17. It may be approximately the same or less. (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 a portion beyond this point 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 reality, the exposure dot distribution is wider than the blur of the scanning optical system 3, so the diameter of the recording dots tends to be large in high density areas and small in the low density areas. The image forming process of the image forming apparatus 100 of this embodiment will be described below. After the photoreceptor 1 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 1. 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 with extremely high sharpness (-
A first dot-shaped toner image (yellow toner image) is formed. This first toner image is not transferred onto 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 an infrared beam. 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 l 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). After discharging, charging, and laser beam irradiation in the same manner as described above, the third toner image (cyan toner image) is sequentially developed by the third developing device 4C.
are formed, and three-color toner images are formed on the photoreceptor 1, which are sequentially laminated. 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 100 of the present embodiment, the photoreceptor has excellent high gamma 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, the latent images are 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 1 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 a separation electrode 63, conveyed by a guide and a conveyor belt, carried into a fixing device 64, heated and fixed, and discharged onto a paper discharge tray. On the other hand, after the transfer has been completed, the remaining toner on the surface of the photoreceptor 1 is removed by the blade of the cleaning device 70, which was released during the toner image formation, and by the magnetic plane, and removed from the corona static eliminator and the lamp. The static electricity is removed by a static eliminator 74, so that the next multicolor image formation will not be hindered. Note that the lamp and the corona static eliminator 74 may be placed before cleaning. The static elimination step in each toner image forming step may be omitted if the input current to the semiconductor laser 31 is input and the DC component is less than or equal to the threshold current σ. Other shapes can also be used as the reference wave. When the reference wave was selected to have two triangular waves of different sizes as one turbid period so as to coincide with twice the synchronization of the recorded pixels, a clear image with high NII property 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 a plurality of peaks as described above within one cycle of the reference wave is effective for improving gradation. When using the same triangular wave as the reference wave (one period is 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 embodiment, intensity modulation using the semiconductor laser 31 has been described, but the invention is not limited to this, and intensity modulation of concentration using other light emitting elements such as an LED array can be similarly performed. A similar effect can be obtained by optically modulating the signal. In the above table, the ratio is the level vergence of the image density signal (Vma
x-Vrnin)/2 and the amplitude value of the reference wave signal. The Q mark indicates that the image is good, the Δ mark indicates that the image is slightly inferior, and the X mark indicates that the image is poor. In other words, the amplitude level is the image density signal level width (Vm
ax −Vmin)/2 is preferably 1.1-1.5 times. If the amplitude level is smaller than the image density signal level width, incomplete gradation reproduction will occur in low density areas and high density areas, resulting in a high contrast image. On the other hand, if it becomes larger than 1.5 times, fogging occurs in low density areas and density decreases in high density areas. 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 level-shifted modulation signal to the semiconductor laser 31. Signal 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 inputted to the base m of the transistor 321 via the capacitor 313 and the protective resistor 3. 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 used to adjust 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 multiplier 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 a carrier wave having a frequency of 600 MHz or higher, which is amplitude-modulated by a variable gain amplifier 370 , and a high-frequency voltage amplified by a high-band power amplifier 380 is applied to the electrode of the semiconductor laser 31 . 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 a reference wave signal that is the output signal from the buffer 320. It is. In the figure, Vmin corresponds to the minimum value (black background) of the image density signal, and Vmax corresponds to the maximum value (white background) of the image density signal.The amplitude of the reference wave exceeds Vmax of the image density signal. Therefore, exposure is performed even in the white background area.Furthermore, since the amplitude of the reference wave is lower than Vmin of the image density signal, some exposure is performed also in the black background area. This means forming dots reliably and, on the other hand, forming dots with a small diameter in high-density areas.In this way, the recording characteristics of the high-gamma photoreceptor are improved.(c) shows the difference amplifier 340. This is an intensity modulation signal that has been intensity-modulated by.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. (
( ) indicates a modulated signal obtained by amplitude modulating the carrier signal with the intensity modulated signal, and here indicates that the level was further shifted by a high band power amplifier. FIG. 10 is an explanatory diagram for explaining the relationship between the amount of light emitted from the semiconductor laser and the level-shifted intensity modulation signal from the drive circuit of the second embodiment. A is a region where spontaneous emission occurs, α 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, the level is softened by the amount corresponding to the white background in the image; current 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 one-dot chain line is used in this example and indicates the half-reduced exposure light amount of the high γ photoreceptor. 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 to half 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. By setting the amplitude of the reference wave signal large instead of the DC component, the exposure amount of Vmax corresponding to the white background portion may be set to be approximately equal to or less than the half-reduced exposure amount P17□. (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 a portion beyond this point 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, 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. In the above clothes, the ratio is the level width of image density signal (Vmax
-Vmin)/2 and the amplitude value of the reference wave signal. The mark ◯ indicates that the image is good, the mark △ indicates that the image is somewhat poor, and the mark X indicates that the image is poor. In other words, the amplitude level is the image density signal level width (Vm
ax −Vmin)/2 is preferably 1.1-1.5 times. If the amplitude level is smaller than the image density signal level width, incomplete gradation reproduction will occur in low density areas and high density areas, resulting in a high contrast image. On the other hand, if it becomes larger than 1.5 times, fogging occurs in low density areas and density decreases in high density areas. 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 . 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 pace terminal of 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 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. Then, the obtained I; pulse width modulated signal is 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 60 output signals, 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 DCK. This signal becomes a drive signal for driving the semiconductor laser 31 on and off. FIG. 12 is a time chart showing waveforms of various parts of the third drive circuit. 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 a reference wave signal that is the output signal from the buffer 320. It is. In the figure, Vmin corresponds to the minimum value of the image density signal (black background area), and Vmax corresponds to the maximum value of the image density signal (white background area). Since the amplitude of the reference wave is based on the Vmax of the image density signal, exposure is performed even in the white background area. Furthermore, since the amplitude of the reference wave is lower than Vmin of the image density signal, some light is applied even in the black background area. These considerations mean that dots are reliably formed in low concentration areas, while dots are formed with small diameters in high concentration areas. In this way, the recording characteristics of the high-7 photoreceptor are improved. (c) is pulse width modulated by the comparator 341 and j: modulation signal. 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-shifted 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 spontaneous emission region, α 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 current input to the semiconductor laser 31. As mentioned above, it corresponds to the white background in the image! A current whose level is shifted by 2 minutes 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-decreased exposure light amount of the high γ photoreceptor used in this example.
Ru. 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
A latent image will not be formed if the amount of exposure light is less than that required to achieve . In addition, even if the DC level is 77 or 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. By setting the amplitude of the reference wave signal large instead of the DC component, the exposure amount of Vmax corresponding to the white background portion may be set to be approximately equal to or less than the half-reduced exposure amount P17□. (C) is photoreceptor 1
The exposure dot distribution recorded above is shown. 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, the exposure dot distribution is either an elliptical beam or is spread by the brush 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 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, a sharp and small dot-shaped latent image can be formed. In reality, the exposure dot distribution is wider than the blur of the scanning optical system 3, so the diameter of the recording dots tends to be large in high density areas and small in the low density areas. In the above table, the ratio is the level width of image density signal (Vwax
-Vmin)/2 and the amplitude value of the reference wave signal. An O mark indicates that the image is good, a Δ mark indicates that the image is somewhat poor, and an X mark indicates that the image is poor. In other words, the amplitude level is the image density signal level width (Vm
ax-Vmin)/2 is preferably 1.1-1.5 times. If the amplitude level is smaller than the image density signal level width, incomplete gradation reproduction will occur in low density areas and high density areas, resulting in a high contrast image. On the other hand, when it is larger than 1.5 times, fogging occurs in low density areas and density decreases in high density areas. Furthermore, in this embodiment described above, the print density and color balance can be changed according to the output content. In this case, the density and color balance can be changed by shifting the amplitude and DC component of each reference wave simultaneously or independently. Although the case where the DC component is larger than the threshold current α is shown, it can also be set smaller than this. Moreover, it is not necessary to have a direct current component. In this embodiment, the noise is stable against changes in temperature and changes in the amount of optical feedback, and no spike-like noise occurs. Further, in the present invention, other exposure means such as LED or LC5 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. An image forming apparatus capable of stably forming a latent image by setting the maximum and minimum values of the image density signal inside the reference wave signal to improve gradation in recording characteristics. were able to provide. 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. In addition, when the image density signal is modulated by a reference wave and has a DC component, it is stable against noise, temperature changes, and changes in the amount of light feedback, and no spike-like noise occurs, so latent images are formed. It was possible to provide an image forming apparatus that can stably perform the following steps. 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 feedback, as described above. Since no spike-like noise is generated, it is possible to provide an image forming apparatus that can stably form a latent image. 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 small latent image in a negative manner.

[Brief explanation of the drawing]

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 waveforms of various parts of the first driving circuit, and Fig. 7 explains the relationship between the amount of light emitted from the semiconductor laser according to the intensity modulation signal leveled/filtered from the driving circuit of the first embodiment. 8 is a schematic diagram showing the drive circuit of the second embodiment of the scanning optical system 3, and FIGS. 9(a) to 9(d) are waveforms of various parts in the drive circuit of this embodiment. Time chart showing 1st
Figure 0 is an explanatory diagram 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 second embodiment, and Figure 11 is an explanatory diagram showing the third drive circuit of the scanning optical system. 12 is a time chart showing the waveforms of each part of the third drive circuit, and FIG. 13 is the relationship between the amount of light emitted from the semiconductor laser due to the level-shifted pulse width modulation signal from the drive circuit of the wc3 embodiment. It is an explanatory diagram for explaining.

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 forms an image using a modulation signal obtained by modulating an image density signal with a reference wave signal, characterized in that maximum and minimum values of the image density signal are located inside the reference wave signal. (2) The image forming apparatus according to claim 1, wherein the exposure intensity corresponding to a white background is approximately equal to or less than the half-decreased exposure light amount. (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.