JPH05112032A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an inexpensive image forming device which forms an image with an improved resolution and a high quality by a method wherein edges of adjacent pixels in all scanning directions are detected, and based on this detected result, a pixel recording position is modulated. CONSTITUTION:An image forming device comprises a photosensitive body 401 serving as a rotating drum-form image forming body; a scorotron charger 402 applying uniform charges on the photosensitive body 401; an optical scanning system 430 ; a plurality of developers 441-444; and a cleaning device 470. In this case, edges of adjacent pixels at least in main- and sub-scanning directions are detected. In accordance with a signal obtained by modulating image density data by a reference wave of a different phase on the basis of the detected edges in all the directions, a laser diode 431 of the optical scanning system 430 is emitted. Furthermore, in a similar manner, a reflecting mirror 452 made of a piezoelectric element 454 is controlled. In this manner, a pixel recording position is modulated, whereby an image is improved in resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for performing dot recording and reproducing characters and halftones by a laser diode oscillated by a modulation signal obtained by modulating density data by a reference wave signal.

[0002]

2. Description of the Related Art In the field of electrophotographic image forming apparatuses, a document image is read by a scanner as an image signal, and the image signal is subjected to gradation correction, A / D conversion, and shading correction to refer to image density data. A digital image obtained by halftone reproduction by modulating with a wave signal is obtained.

An image signal obtained by reading a document image with a scanner has an edge portion of the image read as a halftone density due to an aperture of a solid-state image pickup device incorporated in the scanner. When a latent image is formed on the photoconductor using the image density data obtained from this image signal, the recording pixels corresponding to the edge portion of the latent image are averagely recorded in the recording pixels when the density is intermediate. Therefore, the sharpness of the image is reduced and the image is recorded. Conventionally, it has been known that the image signal is subjected to MTF correction by sharpening with a differential filter, a Laplacian filter or the like. However, this means that only the edges of the image are emphasized, and the uniformity of the halftone image is relatively reduced.

On the other hand, even if an interpolated character or figure is created from CG or font data, there is a similar problem. That is, when the edge portion is smoothly interpolated by the intermediate density with the interpolation data, the recording pixel corresponding to the edge portion is recorded as the average density in the pixel, so that the resolution of the recorded image is reduced.

[0005]

For the above reasons, there has been a problem that the intermediate density processing that effectively works at the image edge portion is necessary.

In view of the above problems, it is an object of the present invention to improve the resolution of an image formed from a scanner, CG, font data, etc., and to provide at low cost an image forming apparatus for performing high-quality image recording. ..

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which forms an electrostatic latent image on an image forming body by oscillating a laser diode with a modulation signal obtained by modulating image density data with a reference wave signal. An omnidirectional edge detection circuit that detects at least the edges of the pixels in the main scanning direction and the subscanning direction, and a modulation signal that is obtained by modulating image density data with reference waves having different phases based on the detection result of the omnidirectional edge detection circuit. It is achieved by an image forming apparatus characterized in that it has a recording position modulating means for modulating a pixel recording position by combining an oscillating laser diode and a reflecting mirror composed of a piezo element controlled based on the detection result.

[0008]

EXAMPLE The configuration of an image forming apparatus according to an example of the present invention will be described. FIG. 1 is a perspective view showing a schematic configuration of the image forming apparatus of this embodiment.

In the image forming apparatus, an analog image density signal and a reference wave signal obtained by D / A converting digital image density data from a computer or a scanner after uniformly charging a photoconductor as an image forming body. A dot-shaped electrostatic latent image is formed by the spot light whose pulse width is modulated based on the modulation signal obtained by differential amplification, and this is inversely developed with toner to form a dot-shaped toner image, and the charging is performed. , A color toner image is formed on a photoconductor by repeating the exposure and development steps, the color toner image is transferred onto a recording paper, separated from the photoconductor, and fixed to obtain a color image. The gradation is expressed by changing the area of dots by modulation. Further, in the image signal created by the computer or read by the scanner as described above, when an edge portion having a high image density touches a read pixel, the signal at the corresponding pixel becomes the same as the intermediate density in the uniform image. .. Further, in the conventional pulse width modulation, the recording dots are formed separately in the central portion of the pixel in both the recording at the edge portion and the recording in the halftone area, so that only a rough resolution can be expressed.

Therefore, in the image forming apparatus of the present invention, the recording position modulation for displacing the electrostatic latent image position of the recording dot in the main scanning direction and the sub scanning direction is performed by one laser beam to form an image with improved resolution. It is possible to obtain at low cost.

The image forming apparatus includes a photoconductor (hereinafter, simply referred to as a photoconductor) 401 that is a drum-shaped image forming body that rotates in the direction of an arrow, and a scorotron that applies a uniform charge to the photoconductor 401. Charging device 402, scanning optical system 430, developing devices 441 to 44 loaded with yellow, magenta, cyan, and black toners
4. Consists of a cleaning device 470 and the like.

The scanning optical system 430 uses laser light emitted from a laser diode 431 made of semiconductor to collimator lens 4
A laser beam is formed as parallel light at 32. This laser beam is slightly bent by a reflecting mirror 452 and then reflected and deflected by a rotating polygon mirror 434 rotating at a constant speed.
By the θ lens 435 and the cylindrical lenses 433 and 436, an image is formed on the circumferential surface of the uniformly charged photoreceptor 401 in the form of a minute spot, and a laser spot is scanned to perform image exposure. Here, the fθ lens 435 is a correction lens for performing optical scanning at a constant speed, and the cylindrical lenses 433 and 436 are lenses that correct the variation of the spot position due to the surface tilt of the rotary polygon mirror 434. The reflecting mirror 452 is a reflecting mirror for recording position modulation in the sub-scanning direction, which is formed of a piezo element such as crystal or barium titanate, and its inclination changes depending on the voltage applied to the piezo electrode 454 of the reflecting mirror 452. The laser spot position is displaced as shown in FIG. 2 by slightly changing the beam reflection direction. Further, the scanning optical system 430 is provided with an index detection circuit (not shown), and the index mirror is used.
The surface position of the rotary polygon mirror 434 which rotates at a predetermined speed is detected by the index signal emitted from the index sensor 439 by the laser beam reflected by the laser beam 438, and a modulated digital image which will be described later in a raster scanning method according to the cycle in the main scanning direction. Optical scanning is performed with a density signal.

The laser diode 431 is, for example, GaAlAs.
It has a maximum output of 5 mW and a light efficiency of 25%. Further, since the color toner images are sequentially superposed on the photoconductor 401, it is preferable to perform exposure with light having a wavelength that is less absorbed by the colored toner.

FIG. 3 is a perspective view showing an example of the reflecting mirror 452. As shown in FIG. 3, the reflecting mirror 452 is formed by forming a piezo element such as crystal or barium titanate so as to have an L-shaped cross section, and the upper surface of the reflecting mirror portion 452a is mirror-finished. Vapor deposition of aluminum, silver, etc. is performed. In addition, electrodes 454a and 454b are provided on both surfaces of the leg 452b by vapor deposition of a conductor such as gold, silver, or copper. electrode
When a voltage is applied to 454a and 454b, the leg 452b contracts or expands according to the direction of the crystal axis, so that the inclination angle of the reflecting mirror 452a can be changed to change the reflection direction of the laser beam. Both the electrode 454a and the electrode 454b are connected to the piezo electrode 454.
I will decide.

By changing the tilt angle of the reflecting mirror 452 in the scanning optical system 430, the position of the laser spot on the photoconductor 401 can be displaced as shown in FIG. For example, the position of the laser spot when no voltage is applied to the electrodes 454a, 454b of the reflecting mirror 452 is 31a (solid line), for example, when a positive voltage is applied to the electrode 454a and a negative voltage is applied to the electrode 454b.
If it is displaced to the position of 31b (dashed line), the electrodes 454a, 45
If the direction of the voltage applied to 4b is reversed, it can be displaced to the position of 31c (dotted line). The applied voltage value of the piezo electrode 454 is determined so that the displacement amount of the center of the laser spot 31b and the laser spot 31c from the center of the laser spot 31a is equal to or less than 1/2 of one pixel.

The applied voltage can change the voltage value applied in the same direction to displace the laser spot position as shown in FIG. 2, or continuously change the applied voltage value to continuously change the laser spot position. It can also be displaced. Further, in the reflecting mirror 452, the reflecting mirror portion 452a and the leg portion 452b may be formed separately, and only the leg portion 452b may be formed of a piezo element.

The photosensitive member 401 used in this embodiment is a photosensitive member having a high γ characteristic, and a specific structural example thereof is shown in FIG.

As shown in FIG. 9, the photosensitive member 401 comprises a conductive support 401A, an intermediate layer 401B and a photosensitive layer 401C. Photosensitive layer 40
The thickness of 1C is about 5 to 100 μm, preferably 10 to 50
μm. The photosensitive member 401 uses a drum-shaped conductive support 401A made of aluminum having a diameter of 150 mm, and the conductive support 40
Thickness of 0.1A consisting of ethylene-vinyl acetate copolymer on 1A
A μm intermediate layer 401B is formed, and a film thickness of 35 μm is formed on the intermediate layer 401B.
It is configured by providing a photosensitive layer 401C of μm.

As the conductive support 401A, a drum of aluminum, steel, copper or the like having a diameter of about 150 mm is used. In addition to this, a belt-shaped one in which a metal layer is laminated or vapor-deposited on paper or a plastic film, or an electric conductor is used. It may be a metal belt such as a nickel belt made by the Chu method. Further, the intermediate layer 401B withstands a high charge of ± 500 to ± 2000 V as a photoconductor, for example, in the case of positive charge, it blocks injection from the conductive support 401A of the electron and obtains excellent light attenuation characteristics due to avalanche phenomenon. As described above, it is preferable that the intermediate layer 401B has hole mobility, so that, for example, Japanese Patent Application No.
It is preferable to add 10% by weight or less of the positively chargeable charge transport material described in the specification of No. 5. As the intermediate layer 401B,
Usually, for example, the following resins used for the photosensitive layer for electrophotography can be used.

(1) Vinyl-based polymers such as polyvinyl alcohol (poval), polyvinyl methyl ether and polyvinyl ethyl ether, (2) polyvinyl amine, poly-N
-Vinylimidazole, polyvinylpyridine (quaternary salt), polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer and other nitrogen-containing vinyl polymers, (3) polyethylene oxide, polyethylene glycol, polypropylene glycol and other polyether polymers, (4)
Acrylic acid-based polymers such as polyacrylic acid and its salts, polyacrylamide and poly-β-hydroxyethyl acrylate, (5) Polymethacrylic acid and its salts, methacrylic acid-based polymers such as polymethacrylamide and polyhydroxypropylmethacrylate , (6) Ether cellulose polymers such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose,
(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 Poly-amino acids such as amino-tyrosine copolymer, glutamic acid-lysine-alanine copolymer, silk fibroin, casein, (9) starch acetate,
Starch and its derivatives such as hydroxyethyl ethyl starch, starch acetate, hydroxyethyl starch, amine starch, and phosphate starch, (10) Mixing water and alcohol such as polyamide soluble nylon and methoxymethyl nylon (8 type nylon) Polymer soluble in solvent.

The photosensitive layer 401C is basically prepared by mixing a phthalocyanine fine particle having a diameter of 0.1 to 1 μm, which is made of a photoconductive pigment, and an antioxidant and a binder resin without using a charge transport material together, using a solvent for the binder resin. It is formed by dispersing the solution to prepare a coating solution, coating the coating solution on the intermediate layer, drying and optionally heat treatment.

When the photoconductive material and the charge transport material are used in combination, the photoconductive pigment and one of the photoconductive pigments are used.
/ 5 or less, preferably 1/1000 to 1/10 (weight ratio) of a small amount of a charge transport substance, and dispersed in a photoconductive material, an antioxidant and a binder resin to form a photosensitive layer. By using such a high-γ photoconductor, a sharp latent image can be formed despite the spread of the beam diameter, and recording with high resolution can be effectively performed.

In this embodiment, the color toner image is transferred to the photosensitive member 401.
Since the laser beams from the scanning optical system 430 are superposed on each other, a photosensitive member having infrared spectral sensitivity and an infrared laser diode are used so that the laser beam from the scanning optical system 430 is not blocked by the color toner image.

Next, the light attenuation characteristics of the high γ photoconductor used in this embodiment will be described.

FIG. 8 is a graph showing the characteristics of the high γ photoconductor. In the figure, V ₁ is a charging potential (V), V ₀ is an initial potential (V) before exposure, and L ₁ is a laser beam irradiation light amount (μJ / cm) required for the initial potential V ₀ to be attenuated to 4/5. 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.

A preferred range of L ₂ / L ₁ is _{1.0 <L 2 / L 1 ≦} 1.5.

In this embodiment, V ₁ = 1000 (V), V ₀ = 950
(V), L ₂ / L ₁ = 1.2. Also, the photoconductor potential in the exposed area is 1
It is 0V.

The photosensitivity at the position corresponding to the mid-exposure period when the light attenuation curve attenuates the initial potential (V ₀ ) to 1/2 is E1 /.
2, and the photosensitivity at the position corresponding to the initial exposure stage when the initial potential (V ₀ ) is attenuated to 9/10 is E9 / 10, (E1 / 2) / (E9 / 10) ≧ 2 is preferable. A photoconductive semiconductor that gives a relationship of (E1 / 2) / (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. 8, in the light attenuation curve of the photoconductor 401, the absolute value of the differential coefficient of the potential characteristic, which is the photosensitivity, is small when the amount of light is small, and increases sharply as the amount of light increases. Specifically, as shown in FIG. 8, the light attenuation curve shows that the sensitivity characteristic is slightly flat in the early stage of exposure and is almost leveled off, but from the middle stage to the latter stage of the exposure, it is remarkably high. The sensitivity becomes an ultra-high γ characteristic that drops almost linearly. Specifically, the photoconductor 401 is considered to obtain a high gamma characteristic by utilizing the avalanche phenomenon under the high charge of +500 to + 2000V. That is, the 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 the light attenuation is surely suppressed. It is understood that an avalanche phenomenon occurs.

FIG. 4 is a block diagram showing an embodiment of the image processing circuit used in the image forming apparatus of the present invention.
FIG. 3 is a block diagram showing a modulation circuit of this embodiment.

The image processing circuit 200 of this embodiment is a circuit for driving a laser diode 431 by a modulation signal obtained by pulse-width-modulating image density data, and corresponds to, for example, a plurality of pixels adjacent in all vertical, horizontal, and diagonal directions. The image density data storage circuit 210, the read circuit 220, and the latch circuit are provided with a function of detecting a density gradient between pixel density data to be formed and displacing a laser spot formed on the photoconductor 401 in the main / sub scanning direction. 230, omnidirectional edge detection circuit 241, select circuit 24
3. Modulation circuits 260A to 260C, a synthesis circuit 270, a reference clock generation circuit 280, a delay circuit group 282, a delay circuit 244, a piezo driver 245, a laser driver 250 and the like.

The image density data storage circuit 210 is a normal page memory (hereinafter simply referred to as the page memory 210), a RAM (random access memory) for storing in page units, and at least one page (for one screen). It has a capacity for storing corresponding multi-valued image density data. Further, if it is an apparatus adopted for a color printer, it will have a page memory for storing image density signals corresponding to a plurality of color components, for example, yellow, magenta, cyan and black color components.

The readout circuit 220 synchronizes with the reference clock DCK ₀ by using the index signal as a trigger, and stores, for example, image density data in the horizontal, vertical and diagonal directions of three adjacent scanning lines in an image density data storage circuit (page memory). The data is read from the omnidirectional edge detection circuit 241 from 210 and the image density data corresponding to the central scanning line to be recorded among the three scanning lines is sent to the latch circuit 230.

The latch circuit 230 includes an omnidirectional edge detection circuit 2
This is a circuit that latches the image density data only while the processing of 41 is being executed.

The reference clock generation circuit 280 is a pulse generation circuit, which generates a pulse signal having the same repetition period as the pixel clock and outputs the pulse signal to the read circuit 220, the delay circuit group 282, and the modulation circuits 260A to 260C. For convenience, this clock is referred to as a reference clock DCK ₀ .

In the delay circuit group 282, a plurality of pixel clocks DC having a phase difference of 1 / n cycle with respect to the reference clock DCK ₀
This is a circuit for generating K ₁ and DCK _2. Here, the pixel clock DCK ₁ whose phase is delayed from the reference clock DCK _{0 by} 1/3 cycle from the terminal φ ₀ to the modulation circuit 260B and the reference clock from the terminal φ 1 The pixel clock DCK ₂ which is delayed by 2/3 cycle with respect to DCK _0, that is, the phase is advanced by 1/3 cycle is output to the modulation circuit 260C.

The omnidirectional edge detection circuit 241 is arranged between the image density data corresponding to a plurality of pixels adjacent to each other in all directions, that is, in the vertical, horizontal and diagonal directions with respect to the image density data in the three running lines input in parallel. The differential value is obtained by sequentially differentiating, the selection signal corresponding to the differential value is read from the built-in memory, and the select circuit 243 and the piezo driver 2
This is a circuit that detects the edges in all directions that are sent to 45 and their directions. That is, the omnidirectional edge detection circuit 241 detects the data corresponding to the edge from the adjacent image density data of three lines, and further detects the direction of the edge. Here, the edge direction is a direction in which there is a change from low density to high density in the image density data, and the output circuit outputs the image density data to the selection circuit 243 according to the detected edge direction. A selection signal for selecting whether or not, and a selection signal for designating an applied voltage value applied to the piezo electrode 454 is sent to the piezo driver 245. In this way, the recording position modulation is performed so that the recording position of the latent image of the edge portion is brought closer to the higher image density.

When the specific value of the differential value is α, the difference value is “+1” when the differential value is α or more, and is “−1” when the differential value is −α or less. If the image data other than the edge, that is, the differential value is between −α and + α,
The difference value is “0”. The difference value thus obtained is (−1,0) in the main scanning direction, (0, −1) in the sub scanning direction, and (0, −1) in the left diagonal direction, If it is (0, 0) in the right diagonal direction, the moving position of the laser spot for this combination of difference values is read from the reference table in the ROM. In this example, the input data of the above combination is (+1, -1). As a result, the omnidirectional edge detection circuit 241 outputs a selection signal of (+1, -1) so that the recording position is shifted by 1/3 cycle in the main scanning direction and downward in the sub scanning direction for recording.

Further, the difference value is (0,
−1), (0,0) in the sub-scanning direction,
If it is (0,0) in the left diagonal direction and (0,0) in the right direction, the selection signal is (-1,0), and the recording position in this case is -1/0 only in the main scanning direction. It becomes a selection signal to displace three cycles.

The select circuit 243 has different output terminals D _{0 to} D ₂ depending on the selection signal from the omnidirectional edge detection circuit 241.
To output image density data. Specifically, if the selection signal is "0", the image density data is sent from the output terminal D _0, and the image density data sent from D ₁ and D ₂ is of the image density on a white background. If the selection signal is "+1", the image density data is sent from the output terminal D ₁ , and D ₀ , D ₂
The image density data sent from the device sends the image density data corresponding to the image density of the white background. If the selection signal is "-1", the image density data is sent from an output terminal D _2, D _0,
The image density data sent from D1 is the image density data corresponding to the image density on a white background.

The modulation circuits 260A to 260C have the same circuit configuration as shown in FIG. 5, and are composed of a D / A conversion circuit 261, a comparator 262, and a triangular wave generation circuit 263 for generating a triangular wave, and are sent from the select circuit 243. The image density data to be generated is synchronized with the reference clock DCK ₀ by the D / A conversion circuit 261 and then
It is a circuit for A-converting and comparing the triangular wave generated by the triangular wave generating circuit 263 as a reference wave to obtain a pulse width modulation signal. Modulation circuits 260A to 260C are all reference clocks
The image density data is D / A converted by DCK ₀ , and the phase of the clock input to the triangular wave generation circuit 263 is different.
Therefore, in the modulation circuit 260A, the reference triangular wave based on the reference clock DCK _{0 is used for} comparison, and in the modulation circuit 260B, it is 1/3.
The modulation circuit 26
At 0C, a triangular wave advanced by 1/3 cycle is used for comparison.

The synthesis circuit 270 is the above-mentioned modulation circuit 260A-260.
The piezo driver 245 is a circuit for synthesizing the modulation signal from C, and the piezo driver 245 selects the voltage value applied to the piezo electrode 454 and applies it to the piezo electrode 454 by selecting the voltage value corresponding to the selection signal from the omnidirectional edge detection circuit 241. It is a circuit to do.

Next, the operation of the image processing circuit 200 will be described.

FIGS. 6 (a) to 6 (i) are time charts showing signals of respective parts of the image processing circuit of this embodiment.

In FIG. 6, (a) shows that the image density data for one scanning line read from the page memory 210 based on the reference clock DCK ₀ by using the index signal as a trigger is converted into an analog value by the D / A conversion circuit 261. It shows some of the items. The digital image density data for one scan line is sent from the read circuit 220 to the omnidirectional edge detection circuit 241 and the latch circuit 230 at the same time. The image density data shows a lighter density on the higher level side and a darker density on the lower level side.

(B) shows a state of edge detection in the main scanning direction in the omnidirectional edge detection circuit 241 and shows a differential value in the main scanning direction. As described above, when the absolute value of the differential value exceeds the specific value α, it is determined to be the edge portion, and the direction of the edge is determined by the sign of the sign. Edge detection in other directions is performed in the same manner, and the displacement position of the recording position in the main scanning direction and the sub scanning direction is determined from the ROM table. If the output value is "0", it indicates that the image density data of the same level are continuous. The output signal in the main scanning direction is sent to the select circuit 243 based on the reference clock DCK ₀ .

On the other hand, the latch circuit 230 latches for the time required for the processing of the omnidirectional edge detection circuit 241 and sends it to the select circuit 243. The select circuit 243 sends the image density data from different output terminals as described above based on the select signal from the omnidirectional edge detection circuit 241.

The following (c) to (e) show combinations of selected reference waves and image density data.

(C) shows the modulation operation in the modulation circuit 260B. Image density data is input to the modulation circuit 260B only when the output value from the omnidirectional edge detection circuit 241 is a positive value. When the output value from the direction edge detection circuit 241 is another value, the image density data of the white background is input. The reference wave at this time is a triangular wave having the same repeating period generated from the clock DCK ₁ delayed by 1/3 period with respect to the reference clock DCK ₀ . As a result, the output signal from the modulation circuit 260B is
As shown in (f), a modulated signal delayed by 1/3 cycle is obtained as compared with the case where the pulse width is modulated by the triangular wave based on the reference clock DCK ₀ . The modulation signal shown by the dotted line is an output signal when modulated by a triangular wave with no phase delay.

(D) shows the modulation operation in the modulation circuit 260A, and the modulation circuit 260A has an omnidirectional edge detection circuit 241.
The image density data during the period when the selection signal from "1" is "0", the image density data of the white background is input to the other signals, and the reference is modulated by the triangular wave based on the reference clock DCK ₀ as shown in (g). Outputs a phase modulation signal.

(E) shows the modulation operation in the modulation circuit 260C, in which the image density data of one pixel before is processed and input during the period when the selection signal from the omnidirectional edge detection circuit 241 has a negative value. If the selection signal is other than the above, image density data of a white background is input. The reference wave is a triangular wave with the clock DCK ₂ advanced by 1/3 cycle. This allows the comparator
A modulated signal of pulse width modulation advanced by ⅓ cycle shown in (h) is output after being compared by 262.

(I) shows a modulation signal output from the combining circuit 270. As described above, the image processing circuit 200 in the present embodiment performs the position modulation of the edge portion in the main scanning direction by detecting the edge and the direction of the edge from the image density data by the omnidirectional edge detection circuit 241. A modulation signal in units of one scanning line is output to the laser driver 250 via the combining circuit 270 to cause the laser diode 431 to oscillate.

On the other hand, the selection signal in the sub-scanning direction from the omnidirectional edge detection circuit 241 is modulated by the delay circuit 244 in the modulation circuits 260A to 260A.
It is output to the piezo driver 245 after being delayed by the processing time in the 60C and the synthesis circuit 270. The piezo driver 245 selects the voltage value applied to the selected piezo electrode 454 based on the selection signal from the omnidirectional edge detection circuit 241, and selects the reflection mirror 4
By changing the reflection angle of 52, the laser spot position can be displaced in the center or in the selected sub-scanning direction. The recording position modulation in the sub-scanning direction is performed as described above.

FIG. 7 is a schematic diagram when a latent image is formed by the modulation signal from the image processing circuit 200 as described above. As shown in FIG. 7, the points of the edge portion are recorded closer to the edge in all directions including the main / sub scanning direction. By thus forming the recording position-modulated electrostatic latent image, the resolution of the edge portion can be improved. What is indicated by a dotted line in FIG. 7 is recording by a conventional image forming apparatus.

Next, the image forming process of the image forming apparatus shown in FIG. 1 will be described.

First, the photoconductor 401 is uniformly charged by the scorotron charger 402. The electrostatic latent image corresponding to yellow is formed on the drum-shaped photoconductor 401 by the image density data storage circuit 210.
It is formed by irradiating the laser beam modulated with yellow data (8-bit digital density data) from the inside. The electrostatic latent image corresponding to yellow is reversely developed by the first developing device 441, and a dot-shaped first toner image (yellow toner image) having extremely high sharpness is formed on the photoconductor 401. The first toner image is not transferred to the recording paper, passes under the retracted cleaning device 470, and is again on the photoconductor 401 on the scorotron charger 402.
Is charged by.

Then, the laser beam modulated by the magenta data (8-bit digital density data) is irradiated onto the photoconductor 401 to form an electrostatic latent image. This electrostatic latent image is reversely developed by the second developing device 442,
Toner image (magenta toner image) is formed. In the same manner as above, the reverse development is sequentially performed by the third developing device 443,
A third toner image (cyan toner image) is formed, and
A three-color toner image is sequentially formed on 401. Finally, the fourth toner image (black toner image) is formed,
A four-color toner image is sequentially formed on 401.

According to the image forming apparatus of this embodiment, the photosensitive member
The 401 has excellent high gamma characteristics, and this excellent high gamma characteristic produces a latent image even when toner images are repeatedly formed on the toner image by repeating the charging, exposing, and developing processes many times. It is formed stably. That is, even if a laser beam is irradiated from above the toner image based on a digital signal, a dot-shaped electrostatic latent image with high fringes and high sharpness is formed, and as a result, a toner image with high sharpness can be obtained. You can

These four-color toner images are transferred onto the recording paper supplied from the paper feeding device by the action of a transfer device (not shown).

The recording paper carrying the transferred toner image is separated from the photoconductor 401 by a separator (not shown), carried by guides and a carrying belt, carried into a fixing device (not shown), heated and fixed, and discharged to a paper tray. It

Although the above-described image data flow has been described as a laser printer which outputs data once stored in the page memory 210, the present invention is not limited to this, and the input of image density data from a color scanner and image processing can be performed. If a circuit for applying is provided, it can be applied to another image forming apparatus such as a copying machine.

Further, in this embodiment, the phase is set to (0,
Although three reference waves shifted by a period of ± 1/3) are used, reference waves having other phase differences can be used. For example, the phase difference may be (0, ± 1/4) cycle or (0, ± 1/6) cycle. Further, it is preferable to use three or more reference waves and to use them according to the image density and the edge detection result. For example, a reference wave having a phase difference of (0, ± 1/6, ± 2/6) cycle may be used. By doing so, by selecting reference waves having different phases according to the image density data, it is possible to obtain an image having a high sharpness in harmony with the adjacent image density.

[0063]

As described above, the present invention provides an omnidirectional edge in an image forming apparatus that oscillates a laser diode with a modulation signal obtained by modulating image density data with a reference wave signal to form an image on an image forming body. An omnidirectional edge detection circuit for detecting the image density, and based on the detection result, image density data and reference waves having different phases are selectively combined to change the size of the recording dot and the recording position in the main scanning direction according to the image density. By providing a modulating means and a reflecting mirror composed of a piezo element in the optical path of the scanning optical system, the applied voltage value is changed in a plurality of steps to change the reflection angle in a plurality of steps to displace the recording position in the sub-scanning direction. By providing the recording position modulating means, it is possible to provide an image forming apparatus that improves the sharpness of an image created from a scanner, CG, font data, or the like.

In particular, since the recording position modulating means of the present invention is performed by using one laser diode, an expensive laser diode array and a plurality of delay circuits are not required, so that the structure can be made simple and inexpensive.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a laser spot formed on the photoconductor of FIG.

FIG. 3 is a perspective view showing a reflection mirror for modulating in the sub-scanning direction of FIG.

FIG. 4 is a block diagram of an image processing circuit of an embodiment of the image forming apparatus of the present invention.

5 is a block diagram showing an example of a modulation circuit of the image processing circuit of FIG.

FIG. 6 is a time chart showing signals of respective parts of the image processing circuit according to the present embodiment.

FIG. 7 is a schematic diagram when a latent image is formed by the modulation signal of the present invention.

FIG. 8 is a graph showing characteristics of the high γ photoconductor used in this example.

FIG. 9 is a cross-sectional view showing a specific configuration example of a high-γ photoconductor used in this example.

[Explanation of symbols]

 200 Image processing circuit 210 Image density data storage circuit (page memory) 220 Readout circuit 230 Latch circuit 241 Omnidirectional edge detection circuit 243 Select circuit 244 Delay circuit 260A to 260C Modulation circuit 280 Reference clock generation circuit 282 Delay circuit group 430 Scanning optical system 431 Laser diode 452 Reflector 454 Piezo electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Hasebe Konica Co., Ltd. 2970 Ishikawa-cho, Hachioji-shi, Tokyo

Claims (1)

[Claims] 1. An image forming apparatus for forming an electrostatic latent image on an image forming body by oscillating a laser diode with a modulation signal obtained by modulating image density data with a reference wave signal, in at least a main scanning direction of adjacent pixels. An omnidirectional edge detection circuit that detects edges in the sub-scanning direction, a laser diode that oscillates with a modulation signal obtained by modulating image density data with reference waves having different phases based on the detection result of the omnidirectional edge detection circuit; An image forming apparatus comprising recording position modulation means for modulating a pixel recording position in combination with a reflecting mirror composed of a piezo element controlled based on the result.