JPS62183663A - Picture processor - Google Patents

Abstract

PURPOSE:To remove the adhesion of a toner to a photosensitive drum and to reduce a burden to a cleaner by changing over a picture density signal to a signal from a complete white signal generator for an input picture when detecting the part between recording media. CONSTITUTION:When the detecting part 26 between papers detect the part between the papers, a change over switch 10 is changed over from a picture density level signal outputted from a D/A converter 7 to the output signal from the complete black and white signal generator 9 and inputted to the output terminal 11 of a comparator 11. As a result, the toner does not adhere to a reproducing picture to have the completely white picture. Thereby, the part between the papers, namely, the part between latent images contributing to the transfer is detected to remove the addhesion of the toner to the photosensitive drum 17, remove the burden to the cleaner 23 and eliminate the scatter thereof in the device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing apparatus that manually performs image processing on a density level signal and outputs a pulse width modulation signal.

[Prior Art] This type of device converts a digital image signal into an analog signal in order to obtain gradation when forming an image using, for example, a laser beam printer, based on a digital image signal. The applicant has proposed a method of generating a pulse width modulated signal by comparing this converted signal with a periodic pattern signal such as a triangular wave.

However, as shown in Figure 5, if the level widths of complete heat and complete white of the image signal are matched with the amplitude of the triangular wave, and the density variable range of the input image signal density level is maximized, the original image If there are pure white or pure black areas in the image, this will affect images with subtle changes in density, such as skin tones in portraits, resulting in pale tones becoming white or relatively dark areas becoming solid black. A problem occurs.

In order to avoid this, the applicant has actually proposed making the amplitude of the triangular wave much larger than the image level signal width, as shown in Figure 6, so that the laser diode is not completely turned on or 0FFL. . This causes some fogging in the white background part, and prevents the black background part from becoming completely black, giving the image the gradation properties of a half-tone image.

[Problems to be solved by the invention] However, in such a configuration, the laser diode is completely
Since there is no completely 0N10FFL, the laser diode is completely 0N10FFt between the paper that will form the current output image and the paper that will form the next output image.
,,do not have. As a result, for example, in a laser beam printer, excess toner adheres to the photosensitive drum even between sheets of paper where toner does not need to adhere to the photosensitive drum, that is, between the latent images that contribute to transfer, and the photosensitive drum is exposed. This increases the burden on the cleaner to remove toner from the drum. Further, there is a problem that more toner is scattered inside the machine.

The present invention has been proposed in order to improve the above-mentioned points, and an object of the present invention is to provide an image processing device that eliminates adhesion of toner forming an image at least between latent images that contribute to transfer. be.

[Means for Solving the Problem] In order to solve this problem, for example, the image processing apparatus shown in FIG. It is equipped with a complete white signal generator that generates a width modulation signal, and a changeover switch that switches the manual image to a signal from the complete white signal generator when a gap between recording media is detected by a paper gap detection section.

[Function] In the configuration shown in FIG. 1 or 2, toner is prevented from adhering to the photosensitive drum when the gap between the recording media forming the output image is detected, reducing the burden on the cleaner and eliminating scattering within the machine. do.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Further, in this embodiment, a case where the present invention is applied to a laser beam printer will be explained.

FIG. 4 is a block diagram of an example of an image processing device previously proposed by the applicant.

In the figure, 1 is a document to be a human image, 2 is a lens, 3 is a CCD which is an image sensor, 4 is an image signal amplifier for the CCD 3, and 5 is an A/D converter. Further, 6 is an image processing circuit that performs gamma conversion on, for example, a 6-bit digital signal and converts it into a digital signal, and 7 is a D/A converter that converts the digital signal into an analog signal. 8 is a triangular wave oscillator that generates a triangular wave synchronized with the well-known beam detection signal (BD scratch signal). Also, 11 compares the triangular wave generated from the triangular wave oscillator 8 with the image level signal that is the output of the D/A converter. 12 is a laser driver that causes a laser diode 13 to emit light based on the pulse width output from the comparator 11; 13 is a laser diode; 14 is a scanner composed of a polygon mirror and the like for scanning the laser beam; 15; is an optical system composed of a toric lens, an fθ lens, a folding mirror, etc. Hereinafter, 16 is a primary charger, 17 is a photosensitive drum, 18 is a developer, 19 is a registration roller, 20 is paper, and 21 is a transfer charger. 22 is a separation charger, 23 is a cleaner, 24 is a transport unit for the paper 20, 25 is a fixing unit, and 27 is a pre-exposure light emitting element.

With these configurations, the original 1 is projected onto the C0D 3 via the lens 2. The analog image signal output from the CCD 3 is amplified by an amplifier 4, and converted to a 6-bit digital image signal by an A/D converter 5, for example. The image processing circuit 6 performs γ conversion on the 6-bit digital image signal to convert it into a digital image signal. This image signal is D/A
The converter 7 converts it again into an analog image level signal. On the other hand, the triangular wave oscillator 8 generates a triangular wave synchronized with the beam detect signal.

Now, the comparator 11 compares the analog image level signal and the triangular wave signal. That is, if an image level signal that changes stepwise from the black level to the white level is input as shown in FIG. 5, the output signal of the comparator 11 will change only when the triangular wave signal is larger than the image level signal. Becomes HIGH. That is, it can be seen that as the image level goes from "low" (black) to "high" (white), the pulse width of the output signal of the comparator 11 changes smaller.

From the above explanation, it can be seen that when the reproduced image is completely white, the pulse width on the output side of the comparator 11 is approximately 05. When the reproduced image is completely black, the pulse width is equal to or more than the period of the triangular wave. The laser driver 12 is driven in proportion to this pulse width, and the laser diode 13 emits light. The laser beam output from the laser diode 13 is scanned by a scanner 14 and an optical system 15, and the beam spot scans over a photosensitive drum 17 charged by a primary charger 16. This forms an electrostatic latent image. Next, the toner in the developing device 18 adheres to the area irradiated with the laser beam, and a visible image is formed on the surface of the photosensitive drum 17. On the other hand, the paper 20 is sent to the transfer charger 21 via the registration rollers 19. Further, the toner adhering to the surface of the photosensitive drum 17 is transferred to the paper 20, and the paper 20 is electrostatically separated from the photosensitive drum 17 by the separation charger 22. Next, the paper 20 is transported by a transport unit 24, and is fixed in a fixing unit 25.

On the other hand, the toner adhering to the surface of the photosensitive drum 17 is removed by the cleaner 23, and the electric charges on the surface of the photosensitive drum 17 are eliminated by the pre-exposure light emitting element 27. As a result, a series of electrophotographic processes is completed.

In this way, in the electrophotographic process, the photosensitive drum 17
Above, the longer the light emission time of the laser diode 13, the lower the surface potential due to optical attenuation. Furthermore, in the reversal phenomenon, the lower the surface potential, the higher the density of the photographed image.

Therefore, the density of the image to be photographed and the pulse width of the output signal of the comparator 11 are proportional, and a copied image with a gradation system can be obtained.

However, the functions described above are still insufficient from the viewpoint of an image forming apparatus using electrophotographic technology. This is because, if left as is, image processing of a document such as a photograph will result in the drawback that light tones will become blank, or relatively dark areas will become solid black.

For this purpose, as shown in FIG. 6, the amplitude of the triangular wave output from the triangular wave generator 8 is set to be slightly larger. Further, the relationship between the line signal, the vertical synchronization signal (VSYNC-), and the video signal is shown in the timing chart of FIG. By doing this, small pulses will be output even when the image is white, and even when the image is black, it will be prevented from becoming completely black. When processing, sufficient gradation will be provided. However, even after an output image is formed on the paper 20 and the next paper is set, some toner will adhere to the photosensitive drum 17, putting a burden on the cleaner 23 and causing further scattering inside the machine. It will also happen. For this reason, a function is required to detect the gap between sheets, that is, the gap between latent images that contribute to transfer, and prevent toner from adhering to the photosensitive drum.

A block diagram of an image processing apparatus shown in FIG. 1 is provided to add this function, and will be described below with reference to FIG. 1.

In the figure, 9 is a complete white signal generator 9 that generates a complete white level signal. Further, 10 is a changeover switch for switching between the image density signal from the D/A converter 7 and the signal from the complete white signal generator 9, and 26 is a switch for detecting between latent images contributing to transfer. In this example, a paper gap detection section that detects the paper gap is used. Note that another sensor, a timer, or the like may be used to detect the gap between latent images that contribute to transfer.

Note that the functions of the other components are the same as those shown in FIG. 4, so their explanations will be omitted.

With this configuration, when the paper gap detection unit 26 detects that there is a paper gap, the selector switch 10 is switched from the image density level signal output from the D/A converter 7 to the output signal from the complete white signal generator 9. The signal is then input to the input terminal of the comparator 11.

Incidentally, the level of the complete white level signal outputted from the complete white signal generator 9 is the level of °α°° shown in FIG. In this way, the output pulse width from the comparator 11 is completely at 0 level or almost at O level. As a result, no toner adheres to the reproduced image, making it completely white.

As described above, according to this embodiment, in an image forming apparatus that emphasizes halftones, toner is transferred to the photosensitive drum 17 by detecting the gap between sheets, that is, between latent images that contribute to transfer. This makes it possible to eliminate adhesion of particles, reduce the burden on the cleaner 23, and eliminate scattering inside the machine.

Furthermore, in order to generate a complete white level signal in place of the density level signal of the input image signal, the configuration is not limited to that shown in FIG. 1; for example, the block diagram of the configuration shown in FIG. However, the same effect can be obtained. In FIG. 2, the output of the comparator 11 can be forcibly switched to the output of the complete white signal generator 9 using the changeover switch 10 so that the output becomes completely white when the gap between sheets is detected. In this case, the complete white signal generator 9 outputs an O level pulse width modulation signal corresponding to complete white.

Further, in this embodiment, the laser diode 13 emits light, but the light emitting element is not limited to the laser diode, but may also be an LED, or a combination of a shutter array and a halogen lamp. In short, any light source that can be pulse width modulated can be used.

In addition, although this embodiment describes reversal development using the image scan method as an example, it goes without saying that it can also be applied to regular development using the background scan method. This is achieved by setting the level shown by "βpa" in Figure 3.

[Effects of the Invention] As explained above, according to the present invention, the pulse width of the pulse width modulation signal is set to a predetermined width between the latent images contributing to transfer, so that the pulse width of the pulse width modulation signal is set to a predetermined width. It is possible to eliminate toner adhesion, reduce the burden on the cleaner, and prevent toner from scattering inside the machine.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an image processing device of this embodiment, FIG. 2 is a block diagram of an image processing device of another embodiment, FIG. 3 is a diagram showing pulse width modulation of this embodiment, and FIG. 4 is a block diagram of an image processing device of this embodiment. A block diagram of an example of an image processing device previously proposed by the applicant, Figures 5 and 6 are diagrams showing pulse width modulation previously proposed by the applicant, and Figure 7 is a diagram showing line-to-line signals and 5 is a timing chart showing the relationship between a vertical synchronization signal and a video signal. In the figure, 1... Original, 2... Lens, 3... COD
, 4...Amplifier, 5...A/D converter, 6...
- Image processing section, 7... D/A converter, 8... Triangular wave generator, 9... Complete white signal generator, 10... Changeover switch, 11... Comparator, 12...
Laser driver, 13...Laser diode, 14...
...Scanner, 15...Optical system, 16...-Charger, 17...Photosensitive drum, 18...Developer, 19.
... Registration roller, 20 ... Paper, 21 ... Transfer charger, 22 ... Separation charger, 23 ... Cleaner,
24...Transport unit, 25...Fixing unit, 2
6... Paper gap detection section, 27... Pre-exposure light emitting element. Patent applicant: Canon Co., Ltd.

Claims (3)

[Claims] (1) A density level signal generating means for generating a density level signal, a pattern signal generating means for generating a pattern signal of a predetermined period with an amplitude larger than the maximum value of the density level signal of the density level signal generating means, and the pattern an image forming means that compares a pattern signal generated by the signal generating means with the density level signal, forms a latent image using a pulse width modulated signal, and continuously forms an output image on a recording medium;
An image processing apparatus comprising means for adjusting the pulse width of the pulse width modulation signal to a predetermined width between successively formed latent images. (2) The image processing apparatus according to claim 1, wherein the means for setting the predetermined width sets the pulse width of the pulse width modulation signal to a pulse width corresponding to complete white. (3) The image processing apparatus according to claim 1, wherein the pattern signal is a triangular wave signal.