JPH0574263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a recording apparatus that corrects the gradation characteristics of an input image signal and records the image signal.

[Prior Art] Conventionally, in a light beam scanning type electrophotographic copying apparatus in which a light beam scanning type printer such as a laser beam printer, an LED printer, or an LCD printer is equipped with a document information reading device, it is generally possible to produce stable and high quality copied images. In order to obtain this, the following surface potential control of the photoreceptor has been carried out. That is, a bright area potential is formed by irradiating (turning on) a light beam such as a laser beam on the photoconductor, and a dark area potential is formed by erasing (turning off) the light beam such as a laser beam, and at the same time, each potential is It is detected by a predetermined sensor, and the beam output of a laser beam or the like or the high voltage output of a charger is controlled according to the detected value.
As a result, the target bright area potential or dark area potential was converged.

However, in such a conventional potential control method, when a latent image of document information is formed after performing potential control, there is a change in the slope of the latent image characteristic (EV characteristic) of the photoreceptor, or a change in the slope of the latent image characteristic (EV characteristic) of the photoconductor, or Due to changes in the light intensity distribution of the light beam, etc., a difference occurs in the potential distribution of one dot of the dither matrix of one pixel that makes up the halftone latent image, and as a result, the reproducibility of the halftone of the image after development changes. Otherwise, the sharpness may be lowered, and the stability of the image quality in the halftone part cannot be obtained.

Furthermore, with conventional potential control methods, even if a dot latent image is stably formed, changes in development characteristics due to changes in environmental conditions, variations in developer lots, or changes in development characteristics due to developer deterioration may occur. In some cases, the development threshold for the dot latent image changes, resulting in a change in the image quality of the halftone area. Such variations in image quality in halftone areas have been a particular problem in color copying apparatuses that create full-color images because they appear as poor color balance.

[Purpose] Therefore, the present invention detects the potential of an intermediate-level latent image formed on an image carrier and controls the tone correction characteristics of an input image, thereby achieving good reproduction with a relatively simple configuration. An object of the present invention is to provide a recording device that can obtain images.

In order to achieve this object, the recording apparatus of the present invention forms a latent image on an image carrier according to a given image signal, and develops the latent image to perform recording. Input means for inputting an image signal (corresponding to the CCD 26 and A/D converter 28 in the embodiment), gradation correction means for correcting the gradation characteristics of the digital image signal (also the data conversion ROM 29), A halftone processing means (also a dither circuit 30) that performs halftone processing on the digital image signal corrected by the halftone correction means, and a light beam modulated by the digital image signal halftone processed by the halftone processing means. An irradiation means (also the laser control circuit 1) that irradiates, and an image carrier (also the drum 4) that holds the image formed by the light beam irradiated by the irradiation means as a latent image.
and a detection means (also the probe 14) for detecting the potential of the latent image formed on the image carrier, and according to the potential of the latent image detected by the detection means,
control means (also a control circuit 17) for controlling correction characteristics by the gradation correction means, and the irradiation means produces at least a dark latent image on the image carrier;
forming a bright area latent image and a latent image at an intermediate level therebetween; The method is characterized in that the formation conditions of the latent image formed in the gradation correction means are controlled, and then the correction characteristics by the tone correction means are controlled in accordance with the potential of the latent image at the intermediate level detected by the detection means. .

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of a copying apparatus according to an embodiment of the present invention. As shown in the figure, a laser beam modulated by the laser control circuit 1 according to an electric signal input to the laser control circuit 1 is connected to a scanner mirror 2 and an f.
The photosensitive drum 4 is scanned in the longitudinal direction by the θ lens 3. Further, the photosensitive drum 4 is rotated in the direction of the arrow in the figure to enable two-dimensional scanning of the laser beam. The photosensitive drum 4 is made of an organic photoconductor, and a pre-exposure lamp 5 is used to equalize the potential on the surface of the photosensitive drum 4. A charger 6 is used to negatively charge the photosensitive drum 4, and then a laser beam is exposed to the surface of the photosensitive drum. forming an electrostatic latent image thereon. This electrostatic latent image is visualized by a developing device 9, and a transfer charger 10
The image is transferred onto the transfer paper 11 by the image forming apparatus 1 and fixed by the fixing device 12. Toner remaining on the photosensitive drum 4 without being transferred is collected by a cleaner 13.

On the other hand, a probe 14 of a surface electrometer is disposed close to the surface of the photosensitive drum 4 at a position after laser beam exposure, and the probe 14 measures the potential of a latent image formed on the photosensitive drum 4 during surface potential control. I do. Furthermore, the potential measurement value measured by the probe 14 is sent to the surface potential measurement circuit 15 and the A/D.
The voltage is supplied to the control circuit 17 through the (analog-digital) conversion circuit 16, and the control circuit 17 performs calculations according to a predetermined control formula so that the measured potential value converges to a predetermined target value. The signal of this calculation result is sent from the control circuit 17 and D/A (digital)
high voltage control circuit 1 through analog) conversion circuit 18
9, and the charging current is controlled according to the signal. At the same time, the signal of the calculation result is sent to the control circuit 17.
The signal is also supplied to the laser drive circuit 1, and the laser light intensity is controlled according to the signal.

Next, an example of the potential control operation of the apparatus of the present invention shown in FIG. 1 will be described in further detail with reference to the flowchart shown in FIG.

In accordance with the copy command, a potential control operation is performed prior to exposing the original. Therefore, first, normal potential cleaning is performed by pre-rotating the photosensitive drum 4 (step ST1). Next, the output of the semiconductor laser is turned off (disappeared), and a dark latent image is formed in the area _S1 on the photosensitive drum 4 as shown in FIG. 3 using the primary charging current of the initial value. A bright latent image is also formed in the area S ₂ on the photosensitive drum 4 using the primary charging current and the semiconductor laser driving current, and the respective latent image potentials V _D and V _L are measured by the potential measurement probe 1.
4 (steps ST2 and ST3). next,
The absolute value of the difference between the measured latent image potential V _D of the dark latent image area S ₁ and the predetermined target value V _DO of that potential (|V _D −V _DO | is the predetermined tolerance (C ₁ ) and the measured bright latent image area S ₂
Determine whether the absolute value (|V _L − V _LO |) of the latent image potential V _L of the potential V L and the predetermined target ratio V _LO of that potential is within the predetermined tolerance value (C ₂ ) ( Step ST4). If step ST4 is negative, the charging current I ₁ of the primary charger 6 is controlled by the control formula ΔI ₁ =
I ₁ + ΔI ₁ according to αV _D (where α is a constant) (step ST5), or the drive current of the semiconductor laser
After controlling I ₂ to I 2 +ΔI ₂ according to the control formula ΔI ₂ = _{β 1} ΔV _D + β ₂ ΔV _L (where β ₁ and β ₂ are constants) (step ST6), the process returns to step ST2 and | V _D −V _{D O}
The processes of steps ST2 to ST6 described above are repeated until |≦C ₁ and |V _L −V _LO |≦C ₂ , that is, until step ST4 becomes an affirmative determination.

If the determination in step ST4 is affirmative, the process exits from the above-mentioned loop and proceeds to step ST7. Step ST7
In this step, a gray standard reflector 21 provided at the tip of the document table 20 shown in FIG. lens 25
The image is formed on the CCD 26 through the amplifier (AMP), and the halftone image data read out by the CCD 26 is
27, for data conversion through A/D converter 28
The semiconductor laser is modulated by the laser control circuit 1 using the signal stored in the ROM 29 and further processed by the dither method by the dither circuit 30, so that a uniform halftone latent image is formed on the surface of the drum 4 as shown in FIG. S ₃
Formed in the area of The approximate average potential V _H of the halftone pattern (dot latent image) thus formed is measured using the probe 14 .

4A, 4B, and 4C are one halftone pattern formed in the S3 area of FIG. ₃ , respectively.
The enlarged side of the pixel is shown, and the standard reflector 21 is shown in this way.
The intermediate tones of are expressed by the binary dither method.
The dot density at this time is, for example, 16 dots/
Adopt mm. Furthermore, FIGS. 4A to 4C show examples in which the area ratio of the recorded area and the non-recorded area is changed during halftone potential control. The pattern shown in FIG. 4B is changed to the pattern shown in FIG. 4A or FIG. 4C.

5A to 5C are characteristic diagrams for explaining halftone potential detection in this example, and FIG. 5A shows an example of the light intensity distribution of the laser light that scans and exposes the photosensitive drum 4, FIG. 5B shows an example of the latent image potential V _S of the latent image pattern on the photosensitive drum 4 when exposure is performed with a laser beam having the light intensity distribution shown in FIG. 5A.
Furthermore, FIG. 5C shows the detection output V _S ' when the latent image pattern shown in FIG. 5B is relatively scanned by the probe 14. As shown in FIG. 5C, the probe 14 does not individually detect the potentials of the non-exposed areas shown in FIG. 5B, but detects the potentials of the non-exposed areas as an average value or a constant value smaller than the average value. . For example, when the potentials of the OFF part and the ON part of the laser output over a wide area are -750V and -170V, respectively, the dot density is determined using the dot pattern shown in Figure 4B.
The detected average potential V _S ' obtained from the probe 14 at 16 dots/mm is -380V.

Next, the average potential of the halftone pattern measured by the probe 14 in step ST7 of FIG.
Determine whether the absolute value of the difference between V _H and the predetermined target value V _HO corresponding to that potential (|V _H − V _H0 |) is within the predetermined tolerance value (C ₃ ). (Step ST8), if it is a negative determination, after changing the reference value K of the output value of the conversion data B from the control circuit 17 by ±ΔK (step ST8),
ST9), return to step ST7 again and repeat the above operation. Here, the conversion data B is such that the quantized image density level D _H when the reference image density part is read by the CCD 26 is converted as D _H ′=D _H ×V _HO /V _H. This refers to the data sent to the address of the data conversion ROM 29. The data conversion ROM 29 is addressed by the density data D read from the original and the conversion data B output from the control circuit 17, and converts the dot latent image in the S3 area in FIG _{. 3} according to the output value of the data B. ,
For example, the dot area ratio is changed as shown in FIGS. 4A to 4C.

Repeat the above steps until ｜V _H −V _H0 ｜≦C ₃ .
The operations in ST7 to ST9 are repeated, and when an affirmative determination is made in step ST8, the loop is exited and the potential control operation is ended. Here, |V _H
For example, the output value when −V _H0 ｜≦C ₃ is
K′ is set.

Through the above control operations, the charging current I ₁ of the charger 6 and the driving current of the semiconductor laser are adjusted so that the latent image potentials of V _D , V _L and V _H are within predetermined values.
The output values of I ₂ and conversion data B are set.

Note that the coefficients α, β ₁ and β ₂ in the above-mentioned control equation indicate the slope of the function in each relational equation.

FIG. 6 shows an example of latent image characteristics when a gray scale image is written on the photoreceptor 4 as an original image after potential control is performed according to the control procedure shown in FIG.
Note that the latent image at this time is created by reading the document information with the CCD 26 as described above, and after amplifying the video signal read out from the CCD 26 with the amplifier 27, the A/
The D converter 28 performs A/D conversion and quantization, the quantized image signal is dithered through the dither circuit 30, and the dithered signal is supplied to the laser control circuit 1 and passes through the laser control circuit 1. The image is obtained by controlling the laser beam on and off and scanning the photoreceptor 4 with the laser beam to form an image. 6 and 6 are obtained when the target potential of the halftone portion is set in three ways in the potential control of this example shown in FIG. The gradient γ (gamma) of the latent image characteristic at this time increases in the order of <<. In addition,,
, it is assumed that the values of the dark area potential and the bright area potential are the same.

As explained above, in conventional devices, even if the potential is controlled by aligning the dark potential and the bright potential, a constant potential in the halftone region cannot be obtained, or the potential cannot be set to the desired potential. However, according to this embodiment, since the halftone potential is directly controlled, such a conventional problem does not occur.

Further, in this embodiment, even if the setting of the target value of the dark part potential is changed, the target potential of the halftone part can be set accordingly, so that optimal control is possible.

Note that it is preferable that the potential control of the halftone portion in this embodiment is performed at a potential corresponding to a range of approximately 0.5 to 1.0 in document density. Further, in this embodiment, the image data is corrected in the data conversion POM 29, but the image data may be corrected by switching the threshold value in the riser circuit 30.

[Effects] As described above, according to the present invention, a relatively simple configuration can be achieved by detecting the potential of an intermediate level latent image formed on an image carrier and controlling the tone correction characteristics of an input image. Good reproduced images can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a copying apparatus according to an embodiment of the present invention, FIG. 2 is a flowchart showing an example of the control operation of the apparatus of the present invention shown in FIG. 1, and FIG. FIGS. 4A to 4C are explanatory diagrams showing an example of the latent image pattern forming part when detecting the potential of the device of the present invention, each showing one pixel dot of the halftone pattern in the area S3 of FIG _{. 3} . FIGS. 5A to 5C are explanatory diagrams showing an enlarged arrangement example, and FIGS.
The figure is a characteristic diagram showing an example of the relationship between the document density D ₀ and the surface potential V _S after the control operation shown in FIG. 2. 1... Laser control circuit, 2... Scanner mirror, 3... f/θ lens, 4... Photosensitive drum, 5
... Pre-exposure lamp, 6 ... Charger, 9 ... Development device, 10 ... Transfer charger, 11 ... Transfer paper, 12
... Fixing device, 13 ... Cleaner, 14 ... Electrometer probe, 15 ... Potential measurement circuit, 16 ...
A/D conversion circuit, 17... Control circuit, 18...
D/A conversion circuit, 19... High voltage control circuit, 20...
...Original table, 21...Standard reflector, 22...Halogen lamp, 23, 24...Mirror, 25...Lens, 26...CCD, 27...Amplifier, 28...
A/D converter, 29...ROM for data conversion, 3
0...Dither circuit.

Claims (1)

[Scope of Claims] 1. In a recording device that forms a latent image on an image carrier according to a given image signal, develops the latent image, and records the image, the input means inputs a multi-tone digital image signal. and gradation correction means for correcting gradation characteristics of the digital image signal; halftone processing means for performing halftone processing on the digital image signal corrected by the gradation correction means; and halftone processing means for performing halftone processing on the digital image signal corrected by the gradation correction means; an irradiation unit that irradiates a light beam modulated by a processed digital image signal; an image carrier that holds an image formed by the light beam irradiated by the irradiation unit as a latent image; a detection means for detecting the potential of the latent image formed; and a control means for controlling correction characteristics by the gradation correction means according to the potential of the latent image detected by the detection means, the irradiation means The control means forms at least a dark latent image, a bright latent image, and an intermediate level latent image on the image carrier; The formation conditions of the latent image formed on the image carrier are controlled according to the potential of the latent image, and then the gradation is controlled according to the potential of the latent image at the intermediate level detected by the detection means. A recording device characterized in that a correction characteristic by a correction means is controlled.