JP3049559B2 - Electrophotographic equipment - Google Patents

Description

The present invention relates to an electrophotographic apparatus such as a laser printer,
In particular, the present invention relates to an electrophotographic apparatus provided with a laser scanning device that independently controls modulation of a laser light source including a plurality of laser diodes.

[Conventional technology]

2. Description of the Related Art Conventionally, there has been known an electrophotographic apparatus including a so-called multi-beam scanning device for simultaneously scanning a plurality of lines on a photoreceptor using a plurality of laser beams that are independently modulated to increase the scanning speed. . In such an electrophotographic apparatus, one pixel is constituted by a plurality of predetermined spots of laser light, and a predetermined selected spot selected according to the number of gradations is selected from the total number of spots constituting the one pixel. The gradation display is performed by irradiating a laser beam and coloring an area corresponding to the ratio of the number of selected spots to the total number of spots constituting one pixel.

FIG. 5 is a schematic diagram for explaining the outline of a beam scanning device in this type of electrophotographic apparatus, wherein (a) is a plan view,
(B) is a side view.

As shown in FIG.
A lens system between a laser array (laser diode array) 10 as a laser beam generating means having laser oscillation regions 10a and 10b and a photosensitive drum 20 as a photosensitive member.
30 (including a collimating lens), a reflecting mirror 40, a rotary polygon mirror 50 as a beam deflecting means, and an fθ lens 60 are arranged in this order. A reflecting mirror 70 and a sensor are provided near one end of the photosensitive drum 20. A main scanning synchronization signal generator 90 is provided in which the sensor 80 receives the laser beam before scanning of the photosensitive drum 20 and generates a main scanning synchronization signal based on the received light signal. .

According to the above configuration, two laser beams L ₁ and L ₂ modulated independently from the laser oscillation regions 10 a and 10 b of the laser array 10 in synchronization with the synchronization signal generated by the main scanning synchronization signal generator 90. Fired at the same time, lens system 30, reflector 40
Via a rotating polygon mirror 50. The two laser beams reflected by the rotating polygon mirror 50 rotating in the direction of arrow A at a predetermined speed reach the photosensitive drum 20 rotating in the direction of arrow B through the fθ lens 60, and the two different laser beams on the scanning surface thereof Are simultaneously scanned in the direction of arrow C. That is, by arranging the spots of the two laser beams on the photoreceptor so as to intersect with the scanning direction of the laser beams, two lines are scanned simultaneously as described above. In this way,
Scanning of two lines is performed by one reflecting surface of the rotary polygon mirror 50, and scanning of two lines is performed by the following reflecting surface so that a predetermined electrostatic latent image is formed on the photosensitive drum. It has become.

In an electrophotographic apparatus equipped with the laser beam light scanning device as described above, Japanese Patent Application Laid-Open
As disclosed in JP-A-62-49781 and JP-B-62-15871, there is a method of increasing the number of input gradations by modulating a laser beam with multi-level modulation.

The technique disclosed in Japanese Patent Application Laid-Open No. 62-49781 is to perform pulse width modulation on a drive signal of a laser diode.
The characteristic is that the modulation speed increases as the number of gradations increases. Further, the technique disclosed in Japanese Patent Publication No. 62-15871 is to apply a periodic power modulation to an input image signal to obtain a pseudo halftone dot pattern effect. Since the set intensity of the diode is changed, the characteristics of the photoconductor fluctuate and there is a problem in stability. However, according to these methods, a desired gradation expression can be obtained by selecting an appropriate halftone dot forming algorithm.

[Problems to be solved by the invention]

FIG. 6 is a block diagram for explaining the configuration of an electrophotographic apparatus according to the prior art, wherein 1 is an image input means (image input terminal) such as an image scanner, and 2 is the definition or density of an image. Image processing means (image processing system) for performing processing such as color correction,
Reference numeral 3 denotes a tone correction means having a look-up table or the like (tone reproduction correction circuit); 4 a binarization circuit (screen generator) comprising a font rom table or a threshold table; 51 and 52 laser drivers; A deflector (laser scanning device) 7 is an image output means (image output terminal).

In the configuration shown in the figure, density data (analog signal), which is image data output from the image input means 1, is subjected to definition, density, unnecessary frequency component removal, color distribution adjustment for a color image, and the like in an image processing circuit 2. Is performed, and the gradation reproducibility is corrected by the gradation correction circuit 3. When the density data (for example, 8-bit data of 0 to 255) input by photoelectric conversion is output by the image output device, the gradation correction circuit 3 changes the highlight from the highlight so that the print image has a predetermined gradation. Is corrected by data conversion with reference to a look-up table.

However, in this configuration, a signal that has been subjected to common gradation correction by the gradation correction circuit 3 is supplied to the drive circuits (laser drivers) 51 and 52 of the two laser diodes. Part and shadow part, or halftone gradation part cannot be corrected independently,
For example, if the power of the laser beam is increased to emphasize the highlight part, the amount of adjustment also extends to the shadow part,
There is a disadvantage that desired gradation characteristics cannot be determined.

As described above, in the related art, since the gradation correction circuit 3 covers only the highlight to the shadow of the image independently, when the gradation reproducibility changes, or when a desired gradation setting is performed. Also, gradation correction from highlight, which is a high luminance part, to shadow, which is a low luminance part, of an image signal is performed at the same time. For example, there is a problem in that only the reproducibility of the highlight portion is improved because only the highlight expression is reduced, and the correction control for keeping the shadow portion as it is cannot be performed.

Also, when it is desired to express a tone with emphasis on highlights for an original containing many highlights, the highlight / shadow separation cannot be controlled as described above, so that tone control cannot be performed independently for only highlights. Further, there is a disadvantage that it is impossible to control only a specific gradation portion.

Of course, it is conceivable to rewrite the correction value of the gradation correction circuit 3 each time. However, rewriting the numerical values set in the look-up table in real time complicates the configuration, increases the cost, and is realistic. is not.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multi-beam type electrophotographic apparatus in which highlight / shadow of an image signal or a specific gradation portion can be independently controlled to improve gradation characteristics by solving the above-mentioned problems of the prior art. To provide.

[Means for solving the problem]

In order to achieve the above object, the electrophotographic apparatus of the present invention comprises:
Image input means for inputting image data, image processing means, gradation correction means, binarization means, a plurality of laser diode driving means, and each driven by a drive signal output of the plurality of laser diode driving means. A laser light source comprising a plurality of laser diodes and arranged so that the spot of each laser light intersects the scanning direction, and a light beam scanning means having a deflector for deflecting and scanning the light beam emitted from the laser light source, and An image output means of an electrophotographic system, and irradiating the laser beam to a predetermined selected spot selected from the total number of spots constituting one pixel according to the number of gradations, thereby constituting the one pixel An electrophotographic apparatus for performing gradation display by coloring an area corresponding to a ratio of the number of selected spots to the number of all spots, wherein the plurality of laser diodes The laser light output control means is provided independently for each drive means, and the gradation reproducibility is improved by making the outputs of the plurality of laser diodes different for each scanning line.

[Action]

By controlling at least one output power of the plurality of laser diodes independently of the other laser diodes, the reproducibility of a halftone dot formed by turning on / off the plurality of laser diodes is controlled to be different depending on the scanning line. As a result, an output image having desired gradation reproduction and gradation control can be obtained.

For example, when performing gradation display of a highlight portion (or a shadow portion), gradation is increased or decreased by increasing or decreasing the number of laser light spots of a laser diode having a small output power or a laser diode having a large output power according to the output characteristics of the laser diode. Is changed, it is possible to perform more appropriate gradation display.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings for an electrophotographic apparatus having a laser scanning device provided with two laser diodes.

1A and 1B are explanatory diagrams of an embodiment of an electrophotographic apparatus according to the present invention, in which FIG. 1A is a block diagram, FIG. 1B is an explanatory diagram of image scanning in an image output device, and FIGS. FIG. 3 is a characteristic diagram of a tone correction unit in FIG.

In FIG. 1 (a), 1 is an image input means (image input terminal) such as an image scanner, and 2 is an image processing means (image processing) for performing processing such as definition and density of an image and color correction in the case of a color image. System), 3 is a tone correction means having a look-up table or the like (tone reproduction circuit), 4 is a binarization circuit (screen generator) having a font rom table or a threshold table, and 51 and 52 are laser drivers Reference numerals 511 and 521 denote laser output adjusting means (LDC-1 and LDC-2) for adjusting the laser output power based on the drive pulse width and current value of the laser diode, 6 denotes a laser deflector (laser scanning device), and 7 denotes an image output means ( The same reference numerals as those in FIG. 3 correspond to the same parts.

In FIG. 1, an analog image signal (density data) input by photoelectric conversion by an image input unit 1 is subjected to A / D conversion, and then subjected to spatial frequency processing, density correction in an image processing circuit 2 and color distribution in the case of a color image. After processing such as
The signal is applied to the gradation correction circuit 3.

The gradation correction circuit 3 has, for example, a look-up table storing density gradation curve data for combining the photoelectric conversion characteristics of the image input device 1 and the dot print characteristics of the image output device 7. The image exposed and developed / fixed by the laser diode driven by the printer is changed to a print output image having a desired gradation characteristic. The image data after the gradation correction is converted into a modulation signal (drive signal) of a laser diode by a binarization circuit 4 of a font rom table or a threshold table system as in the prior art, and supplied to laser drivers 51 and 52. The outputs of the laser drivers 51 and 52 are applied to a laser deflector 6, and an image is reproduced by an image output unit 7 including a photoconductor through exposure, development, and fixing processes.

Note that the output of the image processing circuit 2 is provided at a stage prior to the gradation correction circuit.
The data is subjected to A / D conversion, and is applied as an address signal to a gradation correction look-up table provided in the gradation correction circuit 3 as 256-bit density data of, for example, 8 bits (0 to 255). The look-up table outputs correction data corresponding to the input density data to the binarization circuit 4 as a value corresponding to the set characteristic curve.

In the binarization circuit 4, a dot matrix (for example, 4 ×) is formed according to the corrected density data inputted with reference to the font ROM table or the threshold value table.
A binary signal corresponding to each dot of 4) is created and supplied to the laser drivers 51 and 52 after D / A conversion.

As shown in FIG. 1B, for example, a pixel composed of 4 × 4 fine pixels is converted into an odd line by two laser beams.
When scanning is performed with lo and even lines le, the laser output such as the laser power and beam diameter of both are set to normal as described above. The result is a composite.

The details of the above-described binarization circuit are disclosed in Japanese Patent Application Laid-Open Nos. 1-185069 and 1-216841.

FIG. 2 is a characteristic diagram of the gradation correction output C _out a shows the Hare tone correction circuit for gradation input C _in the image signal.

In an electrophotographic apparatus using two laser beams, as described above, the power, beam diameter, and gradation correction circuits 31 and 32 of the odd-numbered and even-numbered scanning lines must be equal. Accordingly, the speed can be increased as compared with the case of using one laser beam.

Now, for the two laser beams, the tone reproducibility is set by setting the power, beam diameter, and tone correction circuit of the laser diode as shown by the characteristic curve E in FIG. 2B. Suppose you did. At this time, when an image is formed by only one laser beam, half of the number of dots forming the halftone dot of the image (the fine pixel indicated by the diagonal right or the fine pixel indicated by the diagonal left in FIG. 1B) 2), the gradation reproducibility has the characteristic shown in FIG. 2A. Therefore, if irradiation is performed with two light beams, an ideal gradation reproduction characteristic can be obtained as shown in FIG.

If the output (power) of one of the laser beams is made smaller than normal, the gradation reproducibility has a downwardly convex characteristic as shown in FIG. As shown in (a) of FIG. Therefore, by setting one output of the two laser diodes to be large and the other output to be small, the former can control the shadow part and the latter can control the highlight part independently.

In order to perform the above control, as shown in FIG. 1 (a), a laser driver (LD-1) 51 and a laser driver (LD-2) 52 for controlling each of two laser beams are used. Output adjusting means 511 and 521 are provided, and the output adjusting means can adjust the output of the two laser diodes provided in the laser scanning device 6. The output adjusting means 511 and 521 are constituted by means for changing the laser driving current value and the width of the driving pulse. The control of the laser output is not limited to the above-mentioned means, but can be executed by changing the spot width of the laser beam on the photoconductor by changing the slit width / opening provided in the laser deflection system of the laser scanning device 6, for example. Further, the present invention can also be implemented by using a laser light source having three or more laser light emitting regions which emit laser beams having different outputs as laser diode arrays, and switching the laser regions.

For example, if you want to output a highlight-enhanced image,
Operating the adjusting means 521 of the laser driver 52 on the emphasis side,
And adjusting means for the first laser driver 51 if necessary.
It is sufficient to operate 511 on the weak side. The adjusting means 51
1,521 can be constituted by a manual operator similar to the conventional high key / low key operation means.

As described above, it is possible to perform the gradation control in a closed state between the maximum value and the minimum value of the density data of the image input as the image output device, and the control of the process is facilitated. In the case of a laser beam printer using two laser beams,
Even if the outputs of the two lasers are changed to 0.7 times and 1.3 times in a state where a tone reproduction close to the ideal is obtained as shown by (c) and (c) in FIG. The gradation is a +
As shown in (b), the gradation characteristics of the ideal curve are almost the same as those of (c). At this time, if the output of the laser beam corresponding to (b) is further reduced, the highlight portion will be reproduced finely, and tone reproduction with emphasis on highlight will be performed. Conversely,
If the output of the laser beam corresponding to (a) is further increased, the shadow portion will be reproduced finely, and tone reproduction will be performed with emphasis on shadow.

In many cases, in an electrophotographic laser printer or the like, the gradation reproducibility due to environmental changes, aging changes, noise, etc. is high-key (high contrast) as shown in the characteristic curve of FIG. ) It will change closer. At this time, in order to eliminate the collapse of the shadow portion and the skip of highlights, conventionally, a troublesome method such as rewriting the gradation correction circuit 3 has been adopted. By changing hardware parameters such as conditions, spot shape of laser diode, switching of laser diode itself, etc., it is possible to correct the reproduction gradation, simplify the gradation correction algorithm, and improve the control system. , And cost can be reduced.

Although the above description has been made on the assumption that two laser beams are used, the present invention is also applicable to an electrophotographic apparatus using one laser beam.

FIG. 3 is a block diagram of an electrophotographic apparatus for explaining another embodiment of the present invention, wherein the same reference numerals as those in FIG. 1 correspond to the same parts, 5 is a laser driver, 510 is an output control means of the laser driver. It is.

In this figure, this embodiment differs from the configuration of FIG. 1 in that the number of laser drivers 5 is one, and therefore the number of laser diodes of the laser light source is also one. In synchronism with the scanning, the output control means 510 changes the drive current value or drive pulse width of the laser diode for each odd / even line or for each scan line, and obtains the same effect as that described in FIG. It is like that.

Note that the present invention is not limited to the one in which the power of the laser beam is changed between the odd line and the even line as in the above embodiment. For example, as shown in FIG. 4, a multi-beam laser diode (laser element) The cavity width is made different for each laser beam, one is larger than the normal size, and the other is made smaller, so that the one with the larger cavity has the characteristics shown in FIG. The characteristics shown in FIG.
The same gradation control effect as in the above embodiment can be obtained by the difference in laser power due to the difference in cavity.

When scanning the photosensitive member with a plurality of laser beams, the same effect can be obtained by changing the scanning time of the laser diode (the rising or falling time of the laser). That is, when the scanning time is long, the gradation reproducibility is as shown in FIG. 2A, and when the scanning time is short, it is as shown in FIG. By utilizing this, the reproduction gradation of the highlight / shadow part or the intermediate gradation part can be controlled.

Although not described as an example, the present invention
It is also possible to further increase the degree of freedom of correction by using more than one laser beam.

〔The invention's effect〕

As described above, according to the present invention, in an electrophotographic apparatus capable of high-speed writing using a plurality of laser beams, the power of the plurality of laser beams is changed for each scanning line to obtain a desired gradation. An electrophotographic apparatus having excellent functions that can easily obtain an output image with high image quality can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of an electrophotographic apparatus according to the present invention, FIG. 2 is a characteristic diagram of a gradation correcting means, FIGS. 3 and 4 are explanatory diagrams of another embodiment of the present invention, FIG. 5 is a block diagram illustrating the outline of a laser scanning device in the scanning device of the electrophotographic apparatus, and FIG. 6 is a block diagram illustrating the configuration of a conventional electrophotographic apparatus. DESCRIPTION OF SYMBOLS 1 ... Image input means, 2 ... Image processing means, 3 ... Gradation correction means, 4 ... Binarization circuits, 51 and 52 are laser drivers, 511 and 521 ... Light amount adjustment means, 6 ... Laser scanning device , 7 ... Image output means.

────────────────────────────────────────────────── ─── front page continued (51) Int.Cl. ⁷ identifications FI H04N 1/29 (56) references Patent Sho 63-173074 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ , DB name) H04N 1/04-1/207

Claims (1)

(57) [Claims] 1. An image input unit for inputting image data, an image processing unit, a gradation correction unit, a binarization unit, a plurality of laser diode driving units, and a driving signal of the plurality of laser diode driving units. A laser light source comprising a plurality of laser diodes each driven by an output and having a laser light source arranged so that a spot of each laser light intersects the scanning direction, and a light having a deflector for deflecting and scanning the light beam emitted from the laser light source. Beam scanning means, and an electrophotographic image output means, and irradiates the laser light to a predetermined selected spot selected according to the number of gradations from the total number of spots constituting one pixel, In the electrophotographic apparatus for performing gradation display by coloring an area corresponding to a ratio of the number of selected spots to the number of all spots forming one pixel, An electrophotographic apparatus wherein the laser light output control means is independently provided for each of the diode driving means, and the output of the plurality of laser diodes is made different for each scanning line, thereby improving gradation reproducibility. .