JPS6054566A - Copying device - Google Patents

Abstract

PURPOSE:To obtain a picture of excellent in reproducibility of intermediate hue with high sharpness, by controlling the areal ratio between the recorded part and nonrecorded part of an intermediate hue pattern formed on a photosensitive body, and correcting a picture reading signal in accordance with the areal ratio. CONSTITUTION:A laser control circuit 1 modulates a laser beams in accordance with an inputted electric signal and scans a photosensitive drum 4, then, forms an electrostatic latent image on the surface of the photosensitive drum. The latent image is visualized by means of a developing device 9 and transferred on a transfer paper 11 by means of a transfer charger 10. On the other hand, electric potential of the latent image formed on the drum 4 is measured by a probe 14 and supplied to a control circuit 17 through a measuring circuit 15 and an AD converter circuit 16. At the control circuit 17 a control signal is added to a charger 6 through a high voltage controlling circuit 19 and a charging current is controlled so as to converge the measured value into a prescribed target value. This control is made by controlling the areal ratio between the recorded part and nonrecorded part of an intermediate hue pattern.

Description

[Detailed Description of the Invention] Field of the Invention] The present invention relates to a copying device, and particularly to a copying device that reads the image intensity of a document as an electrical signal using an imaging device, and performs binarization processing or multi-value processing using a dither method or the like. Accordingly, the present invention relates to a copying apparatus that expresses a halftone image of a document based on the area ratio of recorded portions and non-recorded portions.

[Prior Art] Conventionally, in a light beam scanning type electrophotographic copying device such as a laser beam printer, ED printer, or LCD printer, in which a document information reading device is provided in a light beam scanning printer, it is generally possible to produce stable and high-quality copies. In order to obtain images, the following surface potential control of the photoreceptor has been performed. That is, a light potential is formed by irradiating (on) a light beam such as a laser beam on the photoconductor, and a light potential is formed by erasing (turning off) the light beam such as a laser beam, and at the same time each The electric potential of the electric field 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, thereby converging to the target bright area electric potential or dark '4B' electric potential. was.

However, in such a conventional potential FblJ control method, when a latent image of original IM + information is formed after potential control, the change in the slope of the latent image characteristic (EV characteristic) of the photoreceptor or the laser beam The light intensity molecule f5 of a light beam such as
This causes a difference in the potential distribution of one dot of the dither matrix of one pixel that constitutes the latent halftone image, and as a result, the halftone (developability, This may result in a decrease in sharpness, and the stability of the image quality in the halftone area may not be achieved.

Furthermore, even if a dot latent image is stably formed using the conventional position control method, there may be changes in the development characteristics due to changes in environmental conditions, variations in the front of the developer, or deterioration of the developer. Due to changes in characteristics, dot 14! The development threshold for the image changes, and as a result, the image quality of the halftone area fluctuates. 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, in view of the above-mentioned points, the present invention provides an image quality with high sharpness and good reproducibility of halftones by performing novel potential control, and furthermore, it is possible to obtain high-sharp image quality with good halftone reproducibility. It is an object of the present invention to provide a copying apparatus that can maintain a constant value.

[Example] Please refer to the same page below jj1. A detailed explanation of the present invention will be given below.

FIG. 1 shows an example of the configuration of the He Guangming Copying System, "ti".

As shown in the figure, a laser beam modulated by the laser control circuit 1 in accordance with an electric signal input to the laser control circuit 1 is scanned in a direction toward the photosensitive drum 4 by a scanner mirror 2 and an f/θ lens 3. do. 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 heated using a pre-exposure lamp 5 to equalize the potential of the surface of the photosensitive drum 4, and after being negatively charged with a band 11 and a device 6, it is exposed to a laser beam. , an electrostatic latent image is formed on the surface of the photoreceptor.This electrostatic latent image 71i is made visible by the developing device 9, and transferred to the transfer paper 1 by the transfer charger 10.
1 and fixed by fixing device] 2'? do. The toner remaining on the photosensitive drum 4 without being transferred is removed by the cleaner 1.
3 will be supplemented.

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 detects a latent image formed on the photosensitive drum 4 during surface potential control.゛111: Perform position measurement. Furthermore, the potential 4111 constant (
17i is supplied to the control circuit 17 through the surface potential measurement circuit 15 and the A/D (analog-digital) conversion circuit 16. According to the control formula 11; 4
Do γ. A signal resulting from this calculation is sent out from the control circuit 17 and supplied to the high voltage control circuit 19 through the D/A (digital-to-analog) conversion circuit 18, and the charging current of the charger 6 is controlled in accordance with No. 411. At the same time, the control circuit 17 also supplies the calculation result to the laser drive circuit 1, and the laser light intensity is controlled in accordance with the signal.

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

A potential control operation is performed in accordance with the copy command prior to exposing the original. Therefore, first, normal potential cleaning is performed by pre-rotating the photosensitive drum 4 (step 5TI). Next, the output of the semiconductor laser is turned off (extinguished), and by using the initial value L'/! A bright latent image is also formed in the area 82 on the photosensitive drum 4 by the initial charging current of 11 (11) and the semiconductor laser drive current, and the latent image potentials vD and vL of each are set to Measure with the measurement probe 14 (steps ST2 and 5T)
3).

Next, Wll+the latent image potential V of the determined dark latent image area S,
The absolute difference between D and the predetermined potential target value VDO is within the predetermined tolerance (i & (C1) and 1.11
The absolute difference between the predetermined latent image potential v of the bright latent image region S2 and the predetermined target ratio vLO of that potential +tf (l
V C VLOl) predetermined tolerance value (C2
) is determined (step 5T4). If the determination is negative in step ST4, the charging current ■1 of the primary charger 6 is controlled to Xl + Δ11 according to the control formula Δ11=αVo (where α is a constant), and 11N dynamic current■2 is controlled by △engineering, -β1
△Vo+β2△vL (Iris, β1 and β2 are constants)
According to the control, control to 1ΔI2 and after (step 5T)
Y), Rehi step ST2 D) X, l Vo -Vo
Until o l≦CI and IVL−VLOI≦C2, that is, step ST4 is 118j constant size', s
! 11 of steps ST2 to ST6 described above.
Repeat cho.

If the determination in step ST4 is affirmative, the above-mentioned loop is skipped and the process proceeds to step ST7. In step ST7, the gray standard reflector 21 provided at the tip of the document table 20 shown in FIG.
4. The image is formed on the CCD 2B through the condensing lens 25, and the halftone image data read out by the C0D 28 is temporarily stored in the data conversion ROM 29 through the amplifier (AMP) 27 and the A/D converter 28. , further processed by the dither method in the dither circuit 30. In No. 1, the semiconductor laser is modulated by the laser control circuit 1 to form a uniform halftone latent image at 83 on the surface of the drum 4 as shown in FIG. The approximately average potential Vo of the halftone pattern (dot N image) thus formed is determined by the probe X4 as W1j.

- Fig. 4(A), Fig. 4(B) and Fig. 4(C) each show an enlarged side of one pixel of the halftone pattern formed in the S3 area of Fig. 3; The intermediate tones of the board 21 are expressed by a binary dither method. For example, 16 dots/mm is used as the dot tone at this time. 46(A) to 4(C) show examples in which the area ratio of the recorded area and the non-recorded area is changed during halftone potential control, and the halftone dot latent image is is controlled, for example, from the standard pattern of FIG. 4(B) to the pattern of FIG. 4(A) or FIG. 4(C).

5(A) to 5(C) are characteristic diagrams illustrating halftone potential detection in this example, and the 51st figure (A) shows the light intensity of the laser beam that scans and exposes the photosensitive drum 4. An example of the distribution is shown, and Fig. 5 (B) shows the light intensity of Fig. 5 (A) &JT
An example of the latent image potential Vs of the latent image pattern on the photosensitive drum 4 when exposure is performed with a laser beam having . Furthermore, FIG. 5(C) shows the detection output Vs' when the latent image pattern shown in FIG. 5(B) is relatively scanned by the probe 14.
shows. As shown in FIG. 5(C), the probe 14 does not individually detect the potentials of the non-penetrating portions of FIG.゛) It is detected as ->i:' 41ei of i uniform tIi or Ilfi smaller than the average value.For example, the potentials of the OFF part and the ON part of the laser output over a wide area are respectively -75QV, -
At 170V C7), the detected average potential vs' obtained from the probe 14 when the dot density is 16 dots/mm in the no-dot pattern shown in Figure 4 (El) is -38
It becomes 0V.

Next, the average potential VH of the halftone pattern measured by the probe 14 in step ST7 of FIG. 2 and the predetermined target value VHO, ! corresponding to that potential. :1
7) Determine whether the absolute value of the difference (l V H - V H O l ) is within a predetermined tolerance value (C3) (step 5T8), and if it is a negative determination, the conversion from the control circuit 17 After changing the reference value K of the output value of data B by only Δ (step 5TY), step ST is performed again.
? Return to and repeat the above operation. Here, conversion data B
means that DH' = O for the quantized image density level DH when the reference image density part is read with C0D28.
R for data conversion to convert HX VHO/V)l
It refers to data sent to the address of OM29. The data conversion RD) 42'; 3 is addressed by the density data D read from the original and the conversion data B output from the control circuit 17, and the S3 area in FIG. The dot area ratio of the dot latent image is changed, for example, as shown in FIGS. 4(A) to 4(C).

IV) The operations in steps ST7 to ST9 described above are repeated until IV country 1≦C3, and if an affirmative determination is made in step ST8, the loop is exited and the potential control operation is ended. Here, l VHVHOl
≦03,! : z-'), for example, '' is set as the output value.

Through the above control operations, the charging type construction 1 of the charger 6, the drive I2 of the semiconductor laser and the conversion data B are performed so that the latent image potentials of Vo +vl- and VH are within a predetermined predetermined value (rl'j). The output value of is set.

Note that the coefficients α, β1, and β2 in the above-mentioned control equations indicate fψ of the function in each relational equation.

FIG. 6 shows an example of latent image characteristics when a gray scale image is written as a striped image on the photoreceptor 4 after performing potential control according to the control procedure shown in FIG. Note that the latent image at this time is obtained by reading the JV manuscript information using the CCI 2+3 in the same manner as described above, and after amplifying the video signal read from the CCI 26 with the amplifier 27, AID converter 28 converts it from A/D. The quantized image signal is dithered through a dither circuit 30, and the dithered signal is supplied to a laser control circuit 1 to control the laser beam L passing through the laser control circuit 1 and turn it on and off. , which was obtained by scanning the photoreceptor 4 with the laser beam to form an image. ■, ■, and ■ in FIG. 6 are obtained when the target potential of the first part of the halftone 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 ■, ■, and ■. In addition, in the potential control of (1), (2), and (2), it is assumed that the values of the dark area potential and the bright area potential are the same.

[Effect] As explained above, in conventional equipment; nf'r
Even if the potential of the halftone part and the bright part are made equal and the potential is controlled, a constant potential of the halftone part cannot be obtained or the desired potential cannot be set.However, according to the present invention, it is possible to directly Since the adjustment potential is controlled, such a conventional problem does not occur.

Furthermore, in the present invention, even if the setting of the target value of the dark potential is changed,
Since the target potential of the halftone portion can be set accordingly, optimal control is possible.

Note that the potential control of the first part of the halftone according to the present invention is performed when the original density is approximately 0.5 to 1. 11i, which corresponds to a range of about Q.

It is preferable to do this at the same location. Also, on the Kinomi flow side,
Although the image data is corrected in the data conversion ROM 29, the image data may be corrected in the riser circuit 30 by switching the number (6).

[Brief explanation of drawings]

1 is a schematic configuration diagram showing an example of the copying apparatus of the present invention, FIG. 2 is a flowchart 1 showing an example of the control operation of the apparatus of the present invention shown in FIG. 1, and FIG. 3 is a schematic diagram showing the apparatus of the present invention shown in FIG. Explanation 14, FIG. 4(A) - showing an example of the latent image pattern forming part when detecting the potential of
FIG. 4(C) is an explanatory diagram showing an enlarged example of the dot arrangement of one pixel of the halftone pattern in the area S3 of 31A, and FIGS. 5(A) to 5(C) are respectively Characteristic diagram illustrating the average value potential flllll constant of the device of the present invention shown in Fig. 6.
The figure is a characteristic diagram showing an example of the relationship between the document density Do and the surface potential Vs after the control operation in the second review. 1...Laser control circuit, 2...Scanner mirror, 3...f・θ Lens, 4... Photosensitive drum, 5... Pre-exposure lamp, 6... Charger, 9... Developing device, 10... Transfer charger, 11... Transfer paper, I2... Fixing device, 13... Cleaner, 14... Electrometer probe, 15... Potential measurement circuit, 16... A/D conversion circuit, 17... Control circuit, 18... D/A Variable circuit, l...High voltage control circuit, 20... Original table, 21... Standard reflector, 22... Halogen lamp, 23. 24... Mirror, 25... Lens, 26. ...COD, 27... Amplifier, 28... A/D converter, 29... ROM for data conversion, 30... Dither circuit. Figure 2 Figure 3 Figure 4 Figure (A) Figure 4 (B) Figure 4 (C) Distance - Figure 6\lC

Claims (1)

[Claims] Jj;
A halftone image of the document is recorded on the photoreceptor by binarization processing or multivalue processing. j expressed by the area ratio of the B portion and the non-recorded portion (in a photocopying device, a halftone pattern is formed on the photoreceptor according to an output signal from the image pickup device ξ that has read an image of a predetermined reference density) an image forming means; a detecting means for detecting the state of the halftone pattern formed on the photoreceptor; and a recording portion of the halftone pattern such that the detection 4rti obtained from the detecting means is within a predetermined range. and a control means for controlling an area ratio between a non-recorded portion and a non-recorded portion, and correcting the document image reading signal based on the controlled area ratio. (hereinafter referred to as margin)