JP2893806B2 - 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. .

FIG. 3 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, the two laser beams L ₁ and L ₂ independently modulated from the laser oscillation regions 10 a and 10 b of the laser array 10 in synchronization with the yellow signal generated by the main scanning synchronization signal generator 90. Are fired at the same time, the lens system 30, the 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 two laser beams so that the arrangement direction of the spots on the photoreceptor intersects the scanning direction of the laser beams, simultaneous scanning of two lines is performed 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 provided with the above laser beam light scanning device, in order to improve the gradation reproducibility, as disclosed in JP-A-62-49781 and JP-B-62-15871, There is a method of multi-level modulation of a laser beam to increase the number of input gradations.

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 Application Laid-Open No. Sho 62-15871 is to apply a periodic power modulation to an input image signal to obtain a pseudo halftone dot pattern effect, but it depends on the density of the input signal. Exposure characteristics of the photoreceptor fluctuate, causing a problem in stability. However, according to these methods, it is possible to obtain a desired gradation surface by selecting an appropriate halftone dot forming algorithm.

[Problems to be solved by the invention]

FIG. 4 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 collection circuit); 4 a binarization circuit (screen generator) comprising a font rom table or a threshold table; 8 a signal distributor (data separator); Reference numerals 51 and 52 denote laser drivers, 6 denotes a laser deflector (laser scanning device), and 7 denotes 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 subjected to common gradation correction by the gradation correction circuit 3 is supplied to each of 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 set.

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 capable of independently controlling the highlight / shadow of an image signal or a specific gradation portion by solving the above-mentioned problems of the prior art.

[Means for solving the problem]

The above object is achieved by providing at least one drive signal path of a plurality of laser light sources with a tone correction means for performing tone correction independently of other laser light sources.

[Action]

By making at least one gradation characteristic of the plurality of laser diodes different from other laser diodes, the reproducibility of halftone dots formed by turning on / off the plurality of laser diodes is finely controlled for each laser diode, An output image having desired gradation reproduction and gradation control is obtained.

〔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, wherein FIG. 1A is a block diagram, FIG. 1B is an explanatory diagram of scanning of pixels for gradation correction, and FIGS. 4) is a characteristic diagram of the gradation correction means 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 image definition, density, and color correction in the case of a color image. , 31 and 32 are tone correction means (tone reproduction collection circuits) having independent look-up tables different from each other, 31 is a first tone correction circuit, 32
Is a second gradation correction circuit, 41 and 42 are binarization circuits (screen generators) having a font rom table and a threshold table, 41 is a first binarization circuit, and 42 is a second binarization circuit , 51 and 52 are laser drivers, 511 and 521 are laser light amount adjusting means for adjusting the laser light amount by the drive pulse width of the laser diode, and adjusting the laser light amount by the current value of the laser diode, and 6 are laser deflectors. Laser scanning devices) and 7 are image output means (image output terminals), and the same reference numerals as those in FIG. 3 correspond to the same parts.

In the figure, an analog image signal (density data) input by photoelectric conversion by an image input means 1 is subjected to processing such as removal of unnecessary frequency components, density correction, and color distribution for a color image in an image processing circuit 2. After that, they are A / D converted and applied as digital signals to the two tone correction circuits 31, 32 in parallel.

The image input means 1 optically scans, for example, characters and figures on a document and converts the magnitude of reflected light or transmitted light into an electric signal, while the image output means 7 converts an input pixel into a plurality of dot matrices. Are expressed by the area gradation method, and therefore, each gradation characteristic is different. In general, a gradation correcting unit is provided to obtain a print image corresponding to the gradation characteristics of the document in which the difference in the gradation characteristics has been corrected. In the present embodiment, as shown in FIG.
The laser beam light of the book is assigned to the odd line lo and the even line le, and the gradation characteristic of the odd line lo and the gradation characteristic of the even line le are made different as follows. In order to obtain a desired gradation and a print image. That is, in FIG. 1A, the first gradation correction circuit 31 has a look-up table having a characteristic of, for example, enhancing the low-density gradation, and the second gradation correction circuit 32
Has, for example, a look-up table having a characteristic of enhancing the gradation on the high density side, and an image developed and fixed by exposure with a laser diode driven by data corrected by the characteristics of the two is used to obtain a desired gradation characteristic. Is set to be a print output image having. The image data after the gradation correction is converted into a laser diode modulation signal (drive signal) by binarization circuits 41 and 42 of a font rom table or a threshold table method as in the prior art, and
Given to 1,52. 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 lookup table for correction provided in the tone correction circuits 31 and 32, for example, as 8-bit (0 to 255) 256-level density data. The look-up table outputs correction data corresponding to the input density data to the binarization circuits 41 and 42 as values corresponding to the set characteristic curves.

In the binarization circuits 41 and 42, dot matrices (for example, 4 dots) constituting pixels are formed in accordance with the corrected density data inputted with reference to the font ROM table or the threshold 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.
The image is reproduced by the dot formation described above.

For details of the above-described binarization circuit, see Japanese Patent Application Laid-Open No. Hei.
Japanese Patent Application Laid-Open No. 5069, Japanese Unexamined Patent Application Publication No. 1-216841 and the like disclose.

FIG. 2 is a characteristic diagram of the gradation correction circuit according to a gradation correction output C _out for the grayscale input C _in the image signal.

In an electrophotographic apparatus using two laser beams, the power, beam diameter, and gradation correction circuits 31 and 3 of the laser diodes of the odd line lo and the even line le of the scanning line are used.
By making 2 equal, it is possible to increase the speed as compared with a single 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, only half of the number of dots forming the halftone dot of the image is irradiated with the laser light, and the gradation reproducibility is shown in FIG. Characteristics. Therefore, if irradiation is performed with two light beams, an ideal gradation reproduction characteristic can be obtained as shown in FIG.

If the gradation correction circuit (for example, the first gradation correction circuit 31) for one laser beam is high-key as shown in FIG. Circuit (for example, the second gradation correction circuit 3
If 2) is set to low key as shown in the same row, and you want to output a highlight-enhanced image, for example,
The adjustment means 521 of the second laser driver 52 may be operated on the emphasis side, and the adjustment means 511 of the first laser driver 51 may be operated on the weak adjustment side as needed. The adjusting means 511 and 521 can be constituted by manual operators similar to conventional high key / low key operating 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,
As shown by C + C in FIG. 2A, a tone reproduction close to ideal can be obtained even with I + B, and when it is desired to output the highlight more smoothly, that is, when the output is desired to be output to the low key, as described above. By increasing the power of the laser diode B in FIG. 2 (a) and weakening the power of the laser diode A, a lower key image can be obtained. Strengthen,
A high-key output image can be obtained by reducing the power of the laser diode.

In many cases, in an electrophotographic laser printer or the like, gradation reproducibility tends to be higher than that of a high key as shown by the characteristic curve in FIG. 2 (b) due to environmental changes, temporal changes, noise, and the like. Will change. In such a case, conventionally, a troublesome method such as rewriting the gradation correction circuit (3 in FIG. 4) has been adopted. However, according to the present invention, one setting characteristic of the gradation correction circuits 31 and 32 is used. (Characteristic b) is low-key, so low-key gradation reproduction can be easily set by adjusting the power of the beam light of the laser driver 51 relatively to the power of the beam light of the laser driver 52. Therefore, the feedback control circuit can be simplified, control accuracy can be improved, and cost can be reduced.

In the above description, a gradation correction circuit (first gradation correction circuit 31, second gradation correction circuit 32) in which high-key and low-key characteristics are set for the two laser beams is used. However, not only the characteristic curve shown in FIG. 2 but also a characteristic curve of another shape can be set to perform the gradation correction. Further, the gradation can be corrected by using three or more laser beams. It is also possible to add a correction circuit and further increase the degree of freedom of correction.

〔The invention's effect〕

As described above, according to the present invention, in an electrophotographic apparatus capable of performing high-speed writing with a plurality of laser beams, at least one gradation correction characteristic of the plurality of laser beams is compared with another laser beam. Thus, it is possible to provide an electrophotographic apparatus having excellent functions capable of easily obtaining an output image having a desired gradation with high image quality.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment of an electrophotographic apparatus according to the present invention, FIG. 2 is a characteristic view of a gradation correcting means, FIG. 3 is a configuration diagram schematically illustrating a scanning device in the electrophotographic apparatus, FIG. FIG. 1 is a block diagram illustrating the configuration of an electrophotographic apparatus according to the related art. 1 ... image input means, 2 ... image processing means, 31, 32 ...
... Tone correction means, 41, 42... Binarization circuits, 51 and 52 are laser drivers, 511, 521.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (1)

(57) [Claims] An image input means for inputting image data, an image processing means, a gradation correction means, a binarization means, a plurality of laser diode driving means, and a drive signal output of a plurality of laser diode driving means. And a deflector for deflecting and scanning each of the laser beam lights arranged so that a spot of each of the laser beam lights emitted from each of the plurality of laser diodes intersects a scanning direction. An electrophotographic apparatus comprising a multi-beam scanning device having an image forming apparatus and forming an image by an electrophotographic method, wherein the gradation correcting means and the binarizing means are provided independently for each of the plurality of laser diode driving means, The correction characteristic of the gradation correction means for correcting at least one gradation characteristic of the image data for generating the drive signals of the plurality of laser diodes is changed to another level. An electrophotographic apparatus having improved tone reproducibility by making the correction characteristics different from the correction characteristics of a tone correction means for correcting the tone characteristics of image data for generating a driving signal of a laser diode.