JPH05103162A - Image forming device - Google Patents

Abstract

PURPOSE:To provide stable and clear dot configuration by making a semiconductor laser emit light with intensity modulation rectangular wave signal modulated by a specified reference signal. CONSTITUTION:An analogue picture element density signal synchronous with a picture element clock DCK which goes through a D/A converter 301 is supplied to a differential amplifier 302's inversion terminal whose normal terminal is provided with a reference signal RS of required duty rectangular wave corresponding to a reference wave generator 304's setting. Then, an intensity modulation rectangular wave signal DAS modulated with signal RS is generated by the amplifier 302, and so the light emission of a semiconductor laser 31 is controlled. Thus beam emitted by the laser 31's enters into a photodetector so as to form the image with stable and clear dot configuration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies a laser beam emitted from a semiconductor laser to an electrophotographic photosensitive member (hereinafter, simply referred to as a photosensitive member) by a modulation signal obtained by modulating an image density signal with a reference wave signal. The present invention relates to an image forming apparatus that forms an image having a dot configuration.

[0002]

2. Description of the Related Art In recent years, in an image forming apparatus that forms an electrostatic latent image on a photoconductor and develops the latent image to obtain a visible image, it is easy to improve the image quality, convert it, edit it, etc. Research and development of a digital image forming apparatus capable of forming an image have been actively conducted. In this image forming apparatus, for example, a laser, an LED array, a light emitting element using a liquid crystal shutter, or the like is driven by a digital image signal from a computer or an original reading device to perform spot exposure on a uniformly charged photosensitive member to form a dot structure. To form an electrostatic latent image of.

As a scanning optical system which is optically modulated by a digital image signal as described above, a scanning optical system which exposes an intensity-modulated laser beam obtained by directly driving a semiconductor laser by a digital image signal, or a digital image signal and a triangular wave shape is used. There is known a device in which a reference signal is converted into a pulse width modulation signal by a comparator and a semiconductor laser is driven by this pulse width modulation signal. A laser beam modulated by such a digital image signal has a rounded or elliptical luminance distribution whose skirt spreads to the left and right and approximates a normal distribution. For example, in the case of a semiconductor laser beam, the luminance is usually 1 to 6 mW. The width in the main scanning direction or the sub scanning direction on the photoconductor is 20 to 100
It gives a round or elliptical spot of μm. Even if the electrostatic latent image formed by such a beam is developed by reversal development to form an image having a dot structure, an image with poor sharpness is often obtained.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional image forming apparatus for writing on a photosensitive member with a semiconductor laser beam as described above, and has a stable sharpness. An object of the present invention is to provide an image forming apparatus capable of forming an image having excellent dot configuration.

[0005]

According to the present invention, a laser beam emitted from a semiconductor laser is incident on an electrophotographic photosensitive member by a modulation signal obtained by modulating an image density signal with a reference wave signal to form an image having a dot structure. In the image forming apparatus, a rectangular wave signal is used as the reference wave signal, and the modulation signal is an intensity-modulated rectangular wave signal. This configuration achieves the above object.

[0006]

That is, since the image forming apparatus of the present invention writes on the photosensitive member by the laser beam emitted from the semiconductor laser with the intensity-modulated rectangular wave signal, the spot sizes are uniform and the sharpness is stable. An image having a dot structure can be formed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view showing the structure of an image forming apparatus to which the present invention is applied.
A drum-shaped photosensitive member 1, a scorotron charger 2 arranged around it, a scanning optical system 3, developing devices 4Y, 4M, 4C loaded with yellow Y, magenta M, cyan C, and black B toners, respectively. 4B, a pre-transfer charger 5, a scorotron transfer device 6, a separator 7, a cleaning device 8, a static eliminator 9, a paper feeding device 10 for feeding the recording paper between the photoconductor 1 and the transfer device 6, and a separator 7. The roller fixing device 11 fixes the toner image on the recording paper separated from the photoconductor 1.

As shown in FIG. 2, the photoconductor 1 is composed of three layers of a conductive support 1A, an intermediate layer 1B and a photosensitive layer 1C.
The conductive support 1A in the above example is made of aluminum, steel, copper or the like having a diameter of 150 mm, but is not limited to this, and paper,
The conductive support 1 is also a belt-shaped one in which a metal layer is laminated or vapor-deposited on a plastic film, or a metal belt such as a nickel belt produced by the electro-etching method.
Used as A.

The intermediate layer 1B is ± 500 of the photosensitive layer 1C.
Withstands high electrification of up to ± 2000 V, for example, when it is positively electrified, it prevents the injection of electrons from the conductive support 1A and obtains excellent light attenuation characteristics by avalanche development. It is desirable to have, for example, Japanese Patent Application No. 61-1
The positively charged charge transport material described in 88975 is 1
It is preferably composed of the following substances added in an amount of 0% by weight or less.

As the material constituting the intermediate layer 1B,
(1) Polyvinyl alcohol (poval), polyvinyl methyl ether, polyvinyl ethyl ether and other vinyl polymers, (2) polyvinyl amine, poly-N-vinyl imidazole, polyvinyl pyridine (quaternary salt), polyvinyl pyrrolidone, vinyl pyrrolidone-acetic acid Nitrogen-containing vinyl polymers such as vinyl copolymers, (3) polyether polymers such as polyethylene oxide, polyethylene glycol, polypropylene glycol, etc. (4) polyacrylic acid and its salts, polyacrylamide, acryl such as poly-β-hydroxyethyl acrylate Acid-based polymers, (5) polymethacrylic acid and salts thereof, methacrylic acid-based polymers such as polymethacrylamide and polyhydroxypropylmethacrylate, (6) methyl cellulose, ethyl cellulose , Carboxymethyl cellulose, hydroxyethyl cellulose, ether cellulosic polymers such as hydroxypropyl methylcellulose,
(7) Polyethyleneimine-based polymers such as polyethyleneimine, (8) Polyalanine, polyserine, poly-L-glutamic acid, poly- (hydroxyethyl) -L-glutamine, poly-δ-carboxymethyl-L-cysteine, polyproline , Lysine-tyrosine copolymer, glutamic acid-lysine-alanine copolymer, polyamino acids such as silk fibroin, casein, (9) starch acetate, hydroxyethyl ethyl starch, starch acetate, hydroxyethyl starch, amine starch, phosphate starch, etc. And derivatives thereof, and (10) polyamides such as soluble nylon and methoxymethyl nylon (8 type nylon), which are soluble in a mixed solvent of water and alcohol.

The photosensitive layer 1C basically comprises a phthalocyanine fine particle having a particle diameter of 0.1 to 1 μm, which is a photoconductive pigment, an antioxidant and a binder resin, without using a charge transporting substance together. It is formed by preparing a coating liquid in which phthalocyanine fine particles are mixed and dispersed by using a solvent, coating the coating liquid on the intermediate layer 1B, drying and optionally heat treating.

When the photoconductive material and the charge transport substance are used in combination, the weight ratio of the photoconductive pigment to the photoconductive pigment is ⅕ or less, preferably 1/1000 to 1/10. A photoconductive material consisting of a small amount of a charge transport substance and an antioxidant are dispersed in a binder resin to form a photosensitive layer.
By using the high γ photoconductor 1 obtained in this way, a sharp latent image can be formed despite the spread of the beam diameter, and recording with high resolution can be effectively performed. The thickness of the photosensitive layer 1C may be one that gives a high γ,
Even if the potential gradient with respect to the normal received light is relatively constant,
5 to 100 μm, preferably 10 to 50 μm.

FIG. 3 is a graph showing the characteristics of the preferable high γ photoconductor 1. In the figure, V ₁ is the charging potential (V), V ₀
Is the initial potential (V) before exposure, L ₁ is the initial potential V ₀ of 4/5
Amount of laser beam irradiation (μJ /
cm ² ) and L ₂ represent the irradiation light amount (μJ / cm ² ) of the laser beam required for the initial potential V ₀ to be attenuated to ⅕. L ₂ /
The preferable range of L ₁ is 1.0 <L ₂ / L ₁ ≦ 1.5. Then, the photosensitivity is set to (E1 / 2) at the position corresponding to the middle stage of exposure when the initial potential V ₀ is attenuated to 1/2, and the initial potential V ₀ is attenuated to 9/10. When the light sensitivity at the position corresponding to the initial stage is (E9 / 10), (E
1/2) / (E9 / 10) ≧ 2, preferably (E1 / 2)
A photoconductive semiconductor that gives the relationship of / (E9 / 10) ≧ 5 is selected. Here, the photosensitivity is defined by the absolute value of the potential decrease amount with respect to the minute exposure amount.

As shown in FIG. 3, the light attenuation curve of the high-γ photoconductor 1 has a small absolute value of the differential coefficient of the potential characteristic, which is the photosensitivity, when the light amount is small, and increases sharply as the light amount increases. That is, specifically, the light attenuation curve shows a nearly flat light attenuation characteristic with a slight period of poor sensitivity characteristic in the early stage of exposure, but it changes from the middle to the latter half of the exposure to become extremely high in sensitivity. It becomes an ultra-high γ characteristic that drops linearly. It is considered that the photoconductor 1 obtains a high γ characteristic by utilizing the avalanche phenomenon under the high charge of +500 to + 2000V. In other words, the carrier generated on the surface of the photoconductive pigment in the early stage of exposure is effectively trapped in the interface layer between the pigment and the coating resin, so that the light attenuation is surely suppressed, and as a result, it is extremely suppressed after the middle stage of exposure. It is understood that a sudden avalanche phenomenon occurs. As an example using such a high γ photoconductor 1, V ₁ = 1000 (V), V ₀ = 950 (V), L ₂ / L ₁ =
1.2, the condition of the potential of the exposed portion is 10V.

In the example of FIG. 1, since the color toner image is superposed on the photosensitive member 1, long-wavelength light such as infrared light which is not shielded by the color toner image is used as the beam light from the scanning optical system 3, A photoreceptor having spectral sensitivity is required. As an example of the photoconductor 1, a drum-shaped conductive support 1A made of aluminum having a diameter of 150 mm is used, and a thickness of ethylene-vinyl acetate copolymer is provided on the support 1A.
A 0.1 μm intermediate layer 1B is formed, and a film thickness is formed on this intermediate layer 1B.
The photosensitive layer 1C having a thickness of 35 μm is provided.

The scanning optical system 3 projects a beam optically modulated on the basis of an image density signal of a predetermined bit onto the peripheral surface of the uniformly charged photoconductor 1 to form an electrostatic latent image.
The scanning optical system 3 in the example of FIG. 1 includes a semiconductor laser 31, a beam diameter adjusting means 32, a polygon mirror 33, an fθ lens 34, a tilt correction lens 35 for correcting the influence of tilt of the polygon mirror 33, a mirror 36, and a scanning end mirror 37. , The index sensor 38.

The index sensor 38 detects the surface position of the polygon mirror 33 which rotates at a predetermined speed, and synchronizes the beam modulated by the image data in the main scanning direction to perform the optical scanning incident on the photoconductor 1. Used.

The semiconductor laser 31 has a wavelength of GaAlAs or the like.
A device that outputs a laser beam of about 800 nm is preferably used. This is because, as mentioned above, since the color toner images are sequentially superposed on the photoconductor 1, it is preferable that the exposure is carried out by the wavelength light which is less absorbed by the colored toner.

The developing devices 4Y, 4M, 4C and 4B have a common structure as shown in FIG. 4 except that the colors of the toners of the developers to be loaded are different. The developing device 40 shown in FIG. 4 as a representative thereof has a sleeve 43 in which a magnet roller 44 having rotating N and S poles is contained in a developing tank formed by a lower casing 42 and an upper casing 41, and an upper casing 41. The scraper 45 is made of an elastic plate and is in pressure contact with the sleeve 43 from the fixing member 46 fixed to the first and second screw-shaped stirring members 47 and 48, and the sleeve cleaning roller 49.
The first stirring member 47 moves toward the front side of the paper, and the second stirring member 48
Is a shape that conveys the developer toward the back side of the paper. The lower casing 42 has a wall between the stirring members 47 and 48, and is shaped so that the developer does not stay therein. Instead of the scraper 45, a thin layer forming means composed of a magnetic plate or a magnetic rod may be provided.

The sleeve cleaning roller 49 rotates in the direction of the arrow and scrapes the developer, which has passed through the developing area and has consumed toner, from the sleeve 43. Therefore, the developer conveyed to the developing area can be replaced, and the developing conditions can be stabilized.

The sleeve 43 is provided with a developing bias circuit 80 for applying a voltage having a DC bias component via a protective resistor (not shown) in order to prevent fogging. The developing bias circuit 80 is for vibrating the toner of the developer conveyed by the sleeve 43 between the sleeve 43 and the photoconductor 1 in the developing region where the toner can be transferred to the photoconductor 1 by receiving an electrostatic force. An AC power supply for supplying an AC bias and a high-voltage DC power supply for supplying a DC bias are provided. For example, DC = 800V, AC = 700V, 3KHz with respect to the potential 900V of the photoconductor 1.
Then, the development bias voltage of the above is applied to the development sleeve 43. When an oscillating electric field is generated between the sleeve 43 and the photoconductor 1 by the developing bias circuit 80, the particles of the developer D vibrate between the developing sleeve 43 and the photoconductor 1, so that the developer D is exposed to light. A toner image can be formed by transferring toner particles to the electrostatic latent image on the photoconductor 1 without contacting the body 1.
The toner image formed in the previous development can be prevented from being destroyed.

As the developer D, a two-component developer in which a toner and a carrier are mixed in a ratio by weight of the toner to the carrier of up to several% is used, and the toner is a silica fine particle treated with a charge control agent or an amine compound. Particles having a particle size of 1 to 20 μm mixed with other additives are preferably used in terms of resolution of image quality and gradation reproducibility, and carriers having a particle size of 5 to 50 μm are also preferably used.

Preferred specific examples of the toner and carrier are shown below.

Toner Polystyrene 45 parts by weight Polymethylmethacrylate 44 parts by weight Charge control agent 0.2 to 1.0 parts by weight Coloring agent 3 to 15 parts by weight Toner having a weight average particle diameter of 3 μm after mixing, kneading, pulverizing and classifying the above composition To get Silica is used as an external additive for this toner. The charge amount of this toner is 20 μc / g.

The following colorants may be used as the colorant having a spectral characteristic for preventing a reduction in the amount of light transmitted from the writing system due to the absorption of light by the toner.

[0027] Benzidinne Yello
w) G (CI21090), Benzine Yellow GR (CI21
100), Permanent Yellow
DHG (Product of Hoechst), Brilliant Carmine 6B (CI15850), Rhodamine 6G Lake (Lake) (CI, 45160) Rhodamine B Lake (CI45170), Phthalocyanine Blue Non Crystal (CI741)
60), Phthalocyanine Green (CI74260), Carbon Black, Fat Yellow 5G, Fat Yellow 3G, Fat Red G, Fat Red HRR, Fat Red 5B, Fat Black HB, Zapon Fast (ZaponFast). ) ・ Black R
E, Zapon First Black B, Zapon First Blue HEL, Zapon First Red B
B, Zapon First Red GE, Zapon First Yellow G, Quinacridone Red (CI46500
0) Carrier (resin-coated carrier) Core: Ferrite Coating resin: Styrene / acrylic (4: 6) Magnetization 70emu / g Weight average particle size 30μm (spherical) Specific gravity 5.2g / cm ³ Specific resistance 10 ¹³ Ω · cm or more Formation of a color image, for example, by the image forming apparatus of FIG. 1 having such a configuration is performed as follows.

The photoconductor 1 rotates in the direction of the arrow, the surface of the photoconductor 1 is cleaned by the cleaning device 8, and the charge eliminator 9 removes the charge. The cleaning device 8 and the static eliminator 9 may be exchanged in position, and cleaning may be performed after the static elimination. The surface of the photoreceptor 1 that has been neutralized and cleaned is charged by the charger 2.
Are uniformly charged. The scanning optical system 3 performs image exposure of the Y image by the laser beam on the charged surface to form an electrostatic latent image having a dot structure. The developing device 4Y develops the electrostatic latent image into a Y toner image by reversal development in which toner is attached to the incident spot of the laser beam.

From the developing device 4M in which the Y toner image forming surface is placed in the inoperative state, the separator 7 and the positions of the cleaning device 8 and the static eliminator 9 which are in the inoperative state are passed,
When it reaches the position of the charger 2 again, the charger 2 charges the Y toner image forming surface in the same manner as before. The scanning optical system 3 performs image exposure of the M image by the laser beam on the charged surface, and the electrostatic latent image formed thereby is developed into the M toner image by the developing device 4M.

As described above, a composite toner image of Y and M is formed on the surface of the photoconductor 1. The composite toner image forming surface is charged as before, image exposure of the C image, development by the developing device 4C,
Alternatively, the charging, the image exposure of the B image, and the development by the developing device 4B are repeated to form a color image formed by superposing toner images of three colors or four colors. The color image is transferred by the transfer device 6 onto the recording paper fed by the paper feeding device 10, and the separator 7 separates the recording paper from the photoconductor 1. The separated recording paper has a color image fixed by the roller fixing device 11 and is ejected to the outside of the apparatus.

The surface of the photoconductor 1 on which the color image has been transferred onto the recording paper is cleaned by the cleaning device 8 and neutralized by the static eliminator 9 to prepare for the next similar color image forming process.

Image exposure by the scanning optical system 3 of the image forming apparatus is performed by a laser beam emitted from the semiconductor laser 31 by the drive circuit shown in FIG.

In the drive circuit of FIG. 5, the pixel clock D
The image density signal DATA, which is color-corrected and gradation-corrected from a computer or a scanner, is synchronized with CK and is a D / A converter.
Input to 301 and input analog density signal ADS to differential amplifier circuit 3
02 Input to one input terminal.

On the other hand, the reference wave generator 30 receives the output signal of the reference wave duty adjuster 303 which receives an external command and outputs a duty designation signal in synchronization with the pixel clock DCK.
Reference numeral 4 inputs the rectangular wave reference signal RS having the designated duty to the + input terminal of the differential amplifier circuit 302. As a result, the differential amplification signal DAS output from the differential amplification circuit 302 is converted into the waveform shaping circuit 305.
Cuts a voltage equal to or less than a certain voltage in accordance with an external command to form an intensity-modulated rectangular wave signal DS, and the semiconductor laser 31 is caused to emit light by the intensity-modulated rectangular wave signal DS, and image exposure is performed by the laser beam.

FIG. 6 shows the waveforms of the main signals in the drive circuit of FIG. 5, in which the semiconductor laser is an intensity-modulated rectangular wave signal DS in which the pulse width is constant and only the intensity changes according to the image density.
Since 31 is emitted, image exposure is performed with a laser beam that has a constant spread and only intensity varies depending on pixel density, forming an electrostatic latent image that can develop an image with excellent sharpness or gradation. It The light quantity distribution of the laser beam is broadened by the pulse width of the intensity-modulated rectangular wave signal DS being influenced by the effect of expanding the beam system of the scanning optical system 3.

By changing the duty of the reference wave signal RS by the reference wave duty adjuster 303 as described above, the pulse width of the intensity modulation rectangular wave signal DS changes, and the exposure intensity can be changed effectively. If there is a variation in the sensitivity of the photoconductor 1 or the light emission performance of the laser, or if it is desired to adjust the image density, it can be easily adjusted by changing the duty according to an external command. However, it is preferable that the duty of the reference wave signal RS is in the range of 20 to 60% in order to obtain the intensity-modulated rectangular wave signal DS that causes the semiconductor laser 31 to emit the laser beam as described above. Duty is
If it is less than 20%, the emission becomes unstable, and if it exceeds 60%, the beam spreads and the sharpness of the image decreases.

Further, the photosensitive member 1 has a high γ photosensitive member as shown in FIG. 3, that is, the decrease in the charging potential due to the exposure amount does not decrease to a certain amount, and the exposure amount rapidly increases when the amount exceeds that. In the case of using a signal that decreases, the slice level of the waveform shaping circuit 305 is changed by an external command, and the intensity modulation rectangular wave signal DS output by the waveform shaping circuit 305 is changed.
If is used to emit light from the semiconductor laser 31, not only an image having excellent sharpness but also an image having excellent gradation can be formed. This exposure amount adjusting method can be used as an image density adjusting method using a general photoconductor.

[0038]

According to the image forming apparatus of the present invention, it is possible to stably form an image having a dot structure excellent in sharpness and gradation.

[Brief description of drawings]

FIG. 1 is a schematic configuration perspective view showing an example of an image forming apparatus according to the present invention.

FIG. 2 is a partial cross-sectional view showing an example of a photoconductor.

FIG. 3 is a characteristic graph of a high γ photoconductor.

FIG. 4 is a partial cross-sectional view showing an example of a developing device.

FIG. 5 is a block circuit diagram showing an example of a semiconductor laser drive circuit.

6 is a waveform diagram of main signals in the drive circuit of FIG.

[Explanation of symbols]

 1 Photoconductor 2 Charging Device 3 Scanning Optical System 4Y, 4M, 4C, 4B Developing Device 31 Semiconductor Laser 301 D / A Converter 302 Differential Amplifying Circuit 303 Reference Wave Duty Adjuster 304 Reference Wave Generator 305 Wave Shaping Circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location // G03G 15/00 303 8004-2H

Claims (2)

[Claims] 1. An image forming apparatus for forming an image of a dot structure by injecting a laser beam emitted from a semiconductor laser by a modulation signal obtained by modulating an image density signal with a reference wave signal to an electrophotographic photosensitive member. An image forming apparatus, wherein a rectangular wave signal is used as a signal, and the modulation signal is an intensity modulation rectangular wave signal. 2. The image forming apparatus according to claim 1, wherein the duty of the rectangular wave signal used as the reference wave signal is variable.