JPH04336859A - High density image forming method - Google Patents

Abstract

PURPOSE:To attain the forming of a latent image with high density and high resolution in a simulating way by forming a high density latent image pattern while beam dots are overlapped properly to use an existing low density engine without any modification. CONSTITUTION:When beam dots radiate to a photosensitive body, a potential distribution of nearly regular distribution is formed at the photosensitive body, a toner is deposited at a position where a latent image forming potential level is Ls or over to form a dot picture. Dots Dn are used whose light intensity is set in a way that the dot potential level L is decreased more than an effective potential level Ls and the dots are overlapped to increase the resulting overlapped dot Dg more than the level Ls. Then the dots Dn are properly overlapped, no effective dot G is formed to a center area Dc in which the dots Dn are not overlapped and a dot G is formed to the overlapped part Dg. Thus, the low density engine is used without any modification to form the latent image with high density and high resolution in a simulating way.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to laser printers and LED
It relates to an image forming method that forms a latent image while forming a beam dot pattern generated in accordance with image information on a photoreceptor, like a printer, and in particular, the formation of a high-density latent image using a low-density print engine. The present invention provides a high-density image forming method that enables.

0002

[Prior Art] Conventionally, a laser beam modulated in accordance with image information is optically scanned by a polygon mirror while a beam dot pattern is irradiated onto the generatrix of a photoreceptor drum rotating in the sub-scanning direction. Laser printers capable of forming a corresponding electrostatic latent image are known, and in this type of device, for example, 300 dpi, which has a low density dot pitch interval, is used for reasons such as low cost and compactness.
In recent years, in order to achieve higher image quality and resolution, printers have been proposed in which the pitch interval is made denser, for example, 600 dpi.

0003

[Problem to be solved by the invention] However, 600d
In order to form a Pi printer, for example, in order to narrow down the beam diameter, the lens configuration and the rotation speed of the polygon mirror must be increased, which not only tends to inevitably lead to an increase in the size of the device, but also increases the size of the photoreceptor drum side. The rotation speed also requires precise control, which leads to a complicated device configuration.

In view of the drawbacks of the prior art, the present invention provides a high-density engine that can form a pseudo-high-density (600 dpi) and high-resolution latent image by using the existing low-density (300 dpi) engine as is. The purpose of the present invention is to provide an image forming method. Another object of the present invention is to provide an image forming method that can selectively form both high-density images and low-density images.

[0005]

Means for Solving the Problems The invention set forth in claim 1 will be specifically explained. First, when a beam dot is irradiated onto a photoreceptor, a potential distribution having an approximately normal distribution shape is formed on the photoreceptor side as shown in FIG. Toner adheres to certain areas and a dot image is formed. (Hereinafter, the part to which toner adheres will be referred to as an effective dot G, and the latent image forming potential level will be referred to as an effective potential Ls.)

On the other hand, for example, in a laser printer engine that performs low-density 300 dpi printing, the size of the beam dot imaged on the photoreceptor is not necessarily 1/300 inch. , larger dots are formed to form portions that overlap each other. Since the dot peripheral portion tends to be below the effective potential level, a continuous linear effective level is ensured by overlapping these portions.

[0007] The present invention has a completely opposite idea to the above-mentioned prior art.
As shown in FIG. 1, lowering the potential level L of the dot,
By using beam dots Dn whose light intensity is set to be smaller than the effective potential level Ls and larger than the potential level Ls due to superposition Dg, and by appropriately overlapping the beam dots Dn, as shown in FIG. Dot D on
No effective dots are formed in the center region Dc where n do not overlap, and effective dots G are formed in the overlapped portion Dg.

Therefore, when dots are printed side by side with a 300-dot engine, effective dots G are formed only in the overlapping portion Dg, but the effective dots G are formed on both sides of one beam dot Dn. As a result, it becomes possible to form effective dots G at pitch intervals that are approximately equivalent to 600 dpi. In this case, it is not necessary that both of the superimposed dots have the above-mentioned light intensity, and as shown in Examples described later, a dot having a normal light intensity and a dot having the above-mentioned light intensity may be combined.

In addition, the beam dots having the above-mentioned light intensity can be easily generated by a modulated beam generated based on a drive signal controlled by pulse width modulation or voltage amplitude modulation, as will be shown in detail in the examples below. generated.

[0010] Basically, high density can be achieved by the method described above. For example, in an LED printer, the above means can be implemented as is, but in a laser printer, an image is created while scanning the beam dot pattern in the main scanning direction. Since the formation is performed in the main scanning direction in which the laser scans, and in the sub-scanning direction in which the scanning interval is set, the means for achieving high density are naturally different.

[0011] First, the means for achieving high density in a laser printer will be explained in the main scanning direction. In a laser printer, ON/OFF of the laser is controlled by electrical pulses. For example, in a 300 dpi engine, the driving pulse time of the laser is 1/300
Equal to the time it takes to scan an inch. (See Figure 3, a) Therefore, in this case, by setting the laser drive pulse time shorter than the time the laser takes to scan 1/300 inch, more specifically, by setting the drive pulse time to 1/2 (
(See FIGS. 3, b and c; hereinafter, this signal will be referred to as a main scanning modulation signal R), it is possible to realize a high dot density of 600 dpi in the main scanning direction.

On the other hand, in the sub-scanning direction, as in the invention described in claim 1, while forming beam dots that overlap in the sub-scanning direction at least on the photoreceptor, the beam dots, including the center area of the dots, are not individually hidden. Dot density in the sub-scanning direction can be increased by modulating the driving pulse for laser beam formation so that it is lower than the image forming potential level and becomes higher than the potential level due to dot overlapping.

More specifically, either voltage amplitude modulation is applied to the main scanning modulation signal R shown in FIGS. 3, b and c to lower the signal level (see FIG.
), or by applying pulse width modulation to shorten the drive pulse width (see Figure 3, e, f, g, hereinafter referred to as PW
(referred to as a sub-scanning modulation signal P) and the dot potential to be imaged on the photoreceptor side can be set as shown in FIG. 1(A).

Therefore, as understood from the respective dot figures in FIG. 3, by using a pulse width modulation circuit or by combining a pulse width modulation circuit and an AM modulation circuit, by setting the modulation period arbitrarily. It becomes possible to increase the density in both the main scanning direction and the sub-scanning direction, and by using the voltage amplitude modulation circuit, it becomes possible to increase the density only in the sub-scanning direction. Note that the means for forming dots smaller than the latent image formation level of the photoreceptor by PWM control can be used to set the pulse time, number of pulses, and pulse position arbitrarily as long as the total driving time is shorter than the time for scanning 1/300 inch. It is. It is also possible to combine it with an AM modulation circuit.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative positions of the components described in this example are not intended to limit the scope of this invention, but are merely illustrative examples. Not too much. Figure 4
1 is an embodiment of the present invention showing a control unit of a laser printer that is designed to achieve high density in both the main scanning direction and the sub-scanning direction.To briefly explain its configuration, in the figure, 1 is a high-resolution laser beam printer. In the controller, for example 6
00 dpi video data is serially transmitted to the data converter 2 side.

In the data conversion section 2, the data is parallel-converted by an S/P conversion circuit 21 and stored in a memory 22, and then high-resolution data is read out from the memory 22 in units of multiple scanning lines to a data conversion circuit 23. The data conversion circuit 23 performs arithmetic processing to set a predetermined pulse period based on the pixel of interest and five pieces of data on the upper, lower, left, and right sides adjacent to the pixel of interest, a total of six data, and uses the calculated pulse period setting. PWM control signal
After serially converting the low resolution data generated by the calculation into the control circuit 24 via the P/S conversion circuit 25,
The signal is sent to the PWM control circuit 24.

In the PWM control circuit 24, the low resolution data is subjected to pulse width modulation based on the control signal, and then sent to the laser beam drive circuit 30 on the low resolution engine 3 side, and the drive circuit 30 generates the data. The generated driving pulse is sent to the semiconductor laser 31, and a beam dot corresponding to the driving pulse is sent to the optical system 32 and the polygon mirror 3.
3 to irradiate/image the photoreceptor 34 side.

FIG. 5 is a schematic diagram showing the correspondence between the driving pulse and the effective dot G obtained by imaging the beam dot Dn generated based on the pulse on the photoreceptor 34. To briefly explain the graph, the pulse train of the first scan train consists of five main scan modulation pulses P and four PW sub-scan modulation pulses P, and the pulse train of the second scan train consists of:
The effective dot G, which is composed of five OFF signals and four PW sub-scanning modulation pulses P and is obtained by imaging the beam dots generated based on both pulse trains on the photoreceptor, is as shown in the left column of the figure. Therefore, five effective dots G are generated on the 300 dpi scanning line and four effective dots G are generated on the non-scanning line corresponding to 600 dpi.

Next, the pulse train of the n-1 scan train consists of four P pulses.
Consists of a W sub-scanning modulation pulse P and two OFF signals, and the n-scanning pulse train consists of one PW sub-scanning modulation pulse P.
, four main scanning modulation pulses R, and one PW sub-scanning modulation pulse P, and furthermore, the pulse train of the n+1 scanning row consists of 2
The effective dots G generated based on these pulse trains are above and below the four effective dots G generated at 300 dpi, as shown in the left column of the figure. Four effective dots G are generated on both sides at 600 dpi, which are shifted stepwise in the main scanning direction.

[0020] Therefore, by various combinations of the above controls,
600d even with a low resolution engine of 300dpi
High resolution pixel data equivalent to pi will be formed.

FIG. 6 shows another embodiment of the control section of the laser printer.The differences from the above configuration will be mainly explained.Instead of the PWM control circuit 24 of the above embodiment, a PWM modulation circuit for main scanning modulation is used. AM modulation control circuit 2 with built-in
7 is attached, and the serial data uniformly main-scanning modulated by the PWM modulation circuit 27 is appropriately voltage-modulated based on the control signal from the data conversion circuit.

FIG. 7 shows the AM modulated drive pulse;
The correspondence relationship with the effective dot G based on the pulse is shown. Also in this graph, in the combination of the main scanning modulation pulse R, the AM sub-scanning modulation pulse A, and the OFF signal, the effective dot G generated on 300 dpi as in the above embodiment,
Effective dots G generated at 600 dpi are generated as appropriate. Therefore, in this embodiment as well, 300
Even in an engine with a low resolution of 600 dpi, high resolution pixel data equivalent to 600 dpi is generated.

Note that the engine 3 side drive circuit in both of the above embodiments is configured so that low-density video data can be directly input, so that the conventional low-density print controller 10 can also be selectively applied. It is configured.

[0024]

[Effect] As described above, according to the invention as claimed in claim 1, a pseudo high density (600 dpi) and high resolution latent image can be formed by using the existing low density (for 300 dpi) engine as is. obtain. Furthermore, according to the invention as claimed in claim 3, since high density is achieved by distinguishing between the main scanning direction and the sub-scanning direction, smoothing processing and gradation processing can be easily performed, and its practical value is It is extremely large. Furthermore, in any of the above inventions, both high-density images and low-density images can be selectively formed, and even if the host side uses high-density software for 600 dpi, low-density software for 300 dpi can be used as is. It is extremely versatile. It has various effects such as

[Brief explanation of drawings]

FIG. 1 shows a superimposed state of beam dots showing the basic configuration of the present invention.

FIG. 2 shows a potential distribution diagram on a photoconductor when the photoconductor is irradiated with a beam dot.

FIG. 3 shows types of drive pulses used in the present invention.

FIG. 4 is a block diagram illustrating an embodiment of the present invention, showing a control unit of a laser printer that achieves high density in both the main scanning direction and the sub-scanning direction.

FIG. 5 is a schematic diagram showing drive pulses generated based on FIG. 4 and their latent image pixel formation state.

FIG. 6 is a block diagram showing another embodiment of the present invention showing a control unit of a laser printer.

FIG. 7 is a schematic diagram showing drive pulses generated based on FIG. 4 and their latent image pixel formation state.

[Explanation of symbols] Dn beam dot Ls Effective potential level Dg Overlapping part

Claims (1)

[Scope of Claims] [Claim 1] In an image forming method in which a latent image is formed while beam dots generated in accordance with image information are formed on a photoreceptor, a beam dot is formed on the image forming position on the photoreceptor. A beam that forms beam dots that overlap each other, and sets a light intensity to at least one of the overlapping dots so that it is lower than the latent image forming potential level of the photoreceptor and becomes higher than the potential level due to dot overlapping. A high-density image forming method, characterized in that a high-density latent image pattern is formed by using dots and appropriately overlapping the beam dots.Claim 2: The beam dots are controlled by pulse width modulation or voltage amplitude modulation. A high-density image forming method according to claim 1, wherein the beam is a modulated beam generated based on a drive signal.Claim 3: An image forming method in a laser printer using an engine in which a prescribed dot pitch interval is set to Ndpi. By setting the laser drive pulse time shorter than the time it takes for the laser to scan 1/N inch, high dot density in the main scanning direction is achieved.On the other hand, in the sub-scanning direction, beams that overlap in the sub-scanning direction on the photoreceptor are While forming dots, the dot height in the sub-scanning direction is adjusted while modulating the driving pulse so that at least one of the superimposed dots is smaller than the latent image forming potential level and becomes larger than the potential level due to dot superimposition. High-density image forming method characterized by achieving high density