JPH01300275A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce the influence exerted by a memory of a preceding picture element by correcting the exposure quantity of a picture element in a accordance with the exposure quantity of a picture element of a preceding area. CONSTITUTION:An interface controller 1 is provided with a correcting means 50 for correcting the light emission quantity of a laser 3 in accordance with the light emission quantity corresponding to a picture element which precedes by a prescribed distance, and a comparator 19 for comparing an original input signal f1 with a memory signal f2 which has been shifted by a distance l and fetching its AND output is provided on the correcting means 50. In this state, the exposure quantity of a notice picture element is corrected in accordance with the exposure quantity of the picture element which precedes by a prescribed distance by the correcting means 50. In such a way, the influence exerted by a memory of the preceding picture element can be made as small as possible, and a ghost image can be made inconspicuous.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus that forms an image by exposing the surface of an image carrier pixel by pixel by turning on and off a light source such as a laser or an LED. .

(Prior Art) Conventionally, there is an image forming apparatus of this type as shown in FIG. 6, for example. That is, 100 is a laser as a light source, and character and image information converted into electrical signals sent from a host computer (not shown) is signal-processed by an interface controller 101, and the laser 100 is appropriately controlled via a laser drive circuit 102. An image is formed on an image carrier 103 that emits light and rotates at a constant speed by exposing each pixel to light while scanning in a direction perpendicular to the direction of rotation by a scanning means 104.

Image formation is performed by a known electrostatic photographic process, in which an electrostatic latent image is formed on the image carrier 103 by laser light, visualized by the developer 105, and transferred to the transfer paper 107 by the transfer charger 106. The image is transferred on top.

To explain in detail the input signal processing of the laser 100, for example, as shown in FIG. 7 and FIG. It enters the comparator 109 together with the image clock φ sent from the image clock generation circuit 108. Here, an AND output of the input signal f and the image clock φ is obtained and inputted to the laser drive circuit 102. The pulse length of the 0-image clock Φ, which the laser 100 lights up in response to this AND output, is such that the scanning spot on the image carrier 103 moves by one pixel with one pulse of ON signal, so that it reaches one resolution in time. It will be set accordingly.

(Problem 8 to be Solved by the Invention) However, in the case of the above-mentioned prior art, a so-called ghost image, in which the influence of pixels preceding the final image H appears on subsequent pixels, may occur. Figure 9 shows an example of a ghost image, where the influence of the thick alphabet "A" written in the preceding white background is reflected in the solid image in the latter half and the halftone part (formed by thinning and scanning lines). ), the density appears darker or lighter than in the same figure.

The cause of this ghost image is memory development of a previous image formed on the surface of the image carrier 103 or the developing sleeve 105a. That is, when the latent image of the preceding image pattern cannot be sufficiently erased by one rotation of the image carrier 103, or when the characteristics of the developer differ between the consumed part of the developing sleeve 105a and the unconsumed part, etc. To,
Ghost images occur. Therefore, the ghost image is caused by the circumference of the image carrier 103 or the developing sleeve 105.
This occurs at a period of a circumference length.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and its purpose is to:
An object of the present invention is to provide an image forming apparatus capable of erasing a ghost image by correcting the ghost image accordingly.

(Means for Solving the Problem) In order to achieve the above object, the present invention exposes each pixel on an image carrier that moves by turning on and off a light source in response to an image signal. An image forming apparatus for forming an image is characterized by being provided with a correction means for correcting the exposure amount of a pixel of interest in accordance with the exposure amount of a pixel preceding the pixel by a certain distance.

(Function) Thus, the pixel exposure amount is corrected in accordance with the exposure amount of the pixel in the preceding area, thereby reducing the influence of the memory of the preceding pixel.

(Example) The present invention will be explained below based on the illustrated example. 1st
The figure shows an image forming apparatus according to a first embodiment of the present invention, and in this embodiment as well, a case where the image forming apparatus is applied to a laser beam printer will be described as in the conventional example.

In the figure, reference numeral 3 denotes a laser as a light source, which is controlled on/off by an electrical signal from a host computer or the like via an interface controller 1 and a laser drive circuit 2. This interface controller 1 includes a correction means 50 that corrects the amount of light emitted by the laser 3 according to the amount of light emitted by a pixel that precedes by a certain distance.

That is, as shown in FIG. 2, the correction means 50 is provided with a comparator 19 that compares the original input signal f1 with a memory signal f2 shifted by a distance # sentence and extracts the AND output. . This memory signal f2 is formed by the memory 20 and the delay circuit 30.

The laser drive circuit 2 receives an AND signal f3 between the input signal f1 and the image clock φ generated by the image clock generation circuit 31 from the comparator 18, and operates the laser 3.
At this time, the drive current value of the laser 3 is changed in accordance with the signal from the comparator 18 to correct the amount of light emitted by the laser 3.

The beam L emitted from the laser 3 that is driven to turn on in this manner is transmitted through the collimator lens 17 and the polygon mirror 4.
Scanning optical system 40 with fθ lens 5 and reflection mirror 6
Exposure scanning is performed in the direction of the drum axis of the photoreceptor 8 as an image carrier (referred to as the main scanning direction; the same shall apply hereinafter) via the photoreceptor 8, while the photoreceptor 8 is scanned in the direction perpendicular to the main scanning direction ( (hereinafter referred to as the sub-scanning direction. The same shall apply hereinafter) to sequentially expose and scan the surface of the photoreceptor 8.

- On the other hand, the surface of the photoreceptor 8 is uniformly charged by the primary charger 7 and then irradiated with the above-mentioned laser light, and the charge on the part that is hit by the laser light is attenuated, so that the surface is not hit by the laser light. Charges remain in the areas, and an electrostatic latent image is formed depending on whether the laser 3 is turned on or off.

Next, the developing device 9 applies a developer (not shown) on the rotating developing sleeve 9' in accordance with the electrostatic latent image to form a developed image on the surface of the photoreceptor 8.

In the cn+87it, transfer paper P is taken out one by one from a paper cassette 11 via a paper feed roller 10, is brought into contact with a photoreceptor 8 at the same time by a register roller 12, and then transferred by a transfer charger 13. The image is transferred onto paper, and the image on the transfer paper P is fixed by the fixing device 14.

After the transfer process is completed, the surface of the photoreceptor 8 is cleaned of residual developer by a cleaner 15, uniformly exposed to light by an LED array 16, and residual charges are removed, before entering the next image forming process.

In FIG. 3, input signals f1. Image image clock shows the sequence of laser lighting. The input signal f1 is converted into a signal shifted by the periodic sentence of the ghost image by the memory 20 and the delay circuit 30. When compared with the conventional example shown in FIG. 9, al, A2.

A3 is a pulse corresponding to the pixels forming the alphabet rAJ, and bl to b8 are pulses corresponding to the pixels forming the halftone part.

Here, the periodic pattern of the ghost image is, for example, the circumference of the developing sleeve 9', and the diameter of the sleeve 9' is 10 [mm].
], then l = 31.4 [mm]. This is A4 size (210 [mm]
) 300 [dpi] image, on the sequence, 210 X31.4/(24,5/300) 2 = 9
This corresponds to a shift of 88,888 [pixels].

On the other hand, al', a2', and a3' indicate pulses shifted by this amount. The comparator 19 shown in FIG. 2 compares the original input signal f1 and the shifted input signal f2, and outputs the original input signal b4 as an AND signal.

b5. b, is taken out. Then, in the laser drive circuit 2, the pulse b4. b5. Laser lighting pulse d4 for b6 (or image clock C4, C5, Cl5). d5. The drive current of d6 decreases.

As a result, d4. d5. The latent image contrast of the pixel corresponding to da decreases, and the ghost image becomes less noticeable in the image transferred after development.

The above is the case of a positive ghost where the ghost image appears darker than the surrounding image density, but in the case of a negative ghost where the ghost image appears lighter than the surrounding image density, this is shown by the broken line in the laser lighting sequence in Figure 3. As above, the laser lighting pulse d4.

d5. What is necessary is to increase the drive current of d.

FIG. 4 shows a lighting control block diagram of a light source of an image forming apparatus according to a second embodiment of the present invention. In the figure, the same components as in the first embodiment are designated by the same reference numerals and will be explained.
As in the embodiment, the comparator 19 provides an AND output of a signal shifted by the periodic intersection of the original signal and the ghost image. This AND output is sent to the image clock generation circuit 3.
1 to change the pixel clock pulse width for the ghost image.

FIG. 5 shows the control sequence of the second embodiment. Pulse a1. which precedes by the number of pixels corresponding to the ghost image periodic sentence. Original input signal pulse b4 affected by A21A3. b5. b.

The lighting time of the laser 3 driven by the corresponding image clock C4, C5, C(i) is changed to a shorter pulse than the surroundings, so that the lighting time of the laser 3 becomes shorter. As in the embodiment, the ghost image becomes less noticeable.

In the case of a negative ghost, the laser lighting pulse d4. d5
．． The clock pulse width of dI3 may be set to a long pulse.

In this second embodiment, since the lighting drive current value of the laser 3 can be kept constant, the influence of variations in the I (current)-L (light emission amount) characteristics of the laser 3 can be reduced compared to the first embodiment. It has the advantage of not being accepted.

In this embodiment, a laser is used as the light source. However, the light source is not limited to a laser, and an array of many light emitting diodes (LEDs) that controls blinking, or a large number of microscopic liquid crystals ( The present invention can be widely applied to various image forming apparatuses that digitally form images by exposing each pixel, such as those in which LC) cells are arranged in an array and on-off control is controlled according to image signals.

(Effects of the Invention) The present invention has the above configuration and operation, and by correcting the exposure amount of the pixel of interest using the correction means according to the exposure amount of the pixel that precedes by a certain distance, the memory of the preceding pixel is The effect can be obtained that the influence can be minimized and the ghost image can be made less noticeable.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention, FIG. 2 is a control block diagram of a laser in the apparatus shown in FIG. 4 is a control block diagram of the image forming apparatus according to the second embodiment of the present invention. FIG. 5 is a time chart showing the input signal processing sequence of FIG. 6 is a schematic configuration diagram of a conventional image forming apparatus, FIG. 7 is a control block diagram of the apparatus in FIG. 6, FIG. 8 is a time chart showing the input signal processing sequence of FIG. 7, and FIG. 9 is a ghost image It is an explanatory view showing an example. Explanation of symbols 1...Interface controller 2...Laser drive circuit 3...Laser (light source) 8...Photosensitive drum (image carrier) 9'...Developing sleeve 18.19...・Comparator 20...Memory 30ii! Extension circuit 50...
Correction means Fig. 1 Fig. 21 ♂ Fig. 7 Fig. 8 Fig. 9

Claims (1)

[Claims] In an image forming apparatus that performs image formation by scanning exposure for each pixel on an image carrier by turning on and off a light source in accordance with an image signal, the amount of exposure of a pixel of interest is set to that pixel. An image forming apparatus comprising a correction means for correcting the exposure amount of a pixel preceding the pixel by a certain distance.