US5436644A — Image forming method

Claim 1

Independent Claim 275 words

A method of writing an image on a photoreceptor with a laser beam, comprising: moving the photoreceptor in a given moving direction; generating a laser beam in accordance with an image signal of a pixel; exposing the photoreceptor with the laser beam so as to form a beam spot, wherein a size of the beam spot is changed in accordance with an image density level represented by the image signal; shifting the laser beam in a main scanning direction perpendicular to the moving direction of the photoreceptor so that a line image of pixels is formed in the main scanning direction; shifting a position of the photoreceptor to be exposed to a next line in a sub-scanning direction with the movement of the photoreceptor; shaping a laser beam so that the beam spot is shaped as an oval having a major axis lying in the main scanning direction, wherein each pixel has a recording unit area and the oval beam spot formed in the recording unit area satisfies the following relation: 0.3×(d.sub.2 /nd.sub.1)≦(a/b)≦0.9×(d.sub.2 /nd.sub.1) wherein "d1" is a first length of the unit area as measured in the main scanning direction; "d2" is a second length of the unit area as measured in the sub-scanning direction; "n" is the number of scanning lines in the unit area for values of n≧1; "a" is a length of the minor axis of the oval beam spot, and "b" is a length of the major axis of the oval beam spot, and wherein when n>1, the recording unit area is divided into plural sub-pixels so as to be formed with plural oval beam spots by plural scanning lines.

Claim 2

Independent Claim 275 words

A method of writing an image on a photoreceptor with a laser beam, comprising: moving the photoreceptor in a given moving direction; generating a laser beam in accordance with an image signal of a pixel; exposing the photoreceptor with the laser beam so as to form a beam spot, wherein a size of the beam spot is changed in accordance with an image density level represented by the image signal; shifting the laser beam in a main scanning direction perpendicular to the moving direction of the photoreceptor so that a line image of pixels is formed in the main scanning direction; shifting a position of the photoreceptor to be exposed to a next line in a sub-scanning direction with the movement of the photoreceptor; shaping a laser beam so that the beam spot is shaped as an oval having a major axis lying in the main scanning direction, wherein each pixel has a recording unit area and the oval beam spot formed in the recording unit area satisfies the following relation: 0.3×(d.sub.2 /nd.sub.1)≦(a/b)≦0.9×(d.sub.2 /nd.sub.1) wherein "d1" is a first length of the unit area as measured in the main scanning direction; "d2" is a second length of the unit area as measured in the sub-scanning direction; "n" is the number of scanning lines in the unit area for values of n≧1; "a" is a length of the minor axis of the oval beam spot, and "b" is a length of the major axis of the oval beam spot, and wherein when n>1, the recording unit area is divided into plural sub-pixels so as to be formed with plural oval beam spots by plural scanning lines.

Claim 3

Dependent Claim 25 words

The method of claim 1, wherein the recording unit area and the plurality of oval beam spots satisfy another relationship in which: 0.4×(d.sub.2 /nd.sub.1)≦(a/b)≦0.8×(d.sub.2 /nd.sub.1).

Claim 4

Dependent Claim 28 words

The method of claim 1, wherein the recording unit area and the plurality of oval beam spots satisfy still another relationships in which: 0.3×(d.sub.2 /n)≦a≦1.5×(d.sub.2 /n) and 0.3d1≦b≦1.5d1.

Claim 5

Dependent Claim 88 words

The method of claim 1, wherein the image comprises a plurality of pixels, each of said plurality of pixels has a recording unit area; and each of said plurality of oval beam spots is formed in a recording unit area; and wherein the shaping step comprises: processing image signals of pixels neighboring a target pixel to obtain a density distribution around the target pixel; and then determining a recording position of each oval beam spot on the photoreceptor in accordance with the density distribution around the target pixel.

Claim 6

Dependent Claim 85 words

The method of claim 4, wherein the shaping step further comprises: comparing an image signal with a reference wave signal to generate a modulating image signal; and modulating the laser beam on the basis of the modulating image signal, so that a plurality of types of reference wave signals are provided; and wherein the determining step includes a step of: selecting one of the reference wave signals in accordance with the density distribution to determine the recording position of each of the oval beam spots.

Claim 7

Dependent Claim 45 words

The method of claim 5, wherein the processing step comprises: determining an average density in the main scanning direction on the photoreceptor from the density distribution; and wherein a selecting step selects one of the reference wave signals in accordance with the determined average density.

Claim 8

Dependent Claim 38 words

The method of claim 1, further comprising forming the photoreceptor from a high γ type photoreceptor material which has a high sensitivity for a large amount of exposure and a low sensitivity for a small amount of exposure.

Claim 9

Dependent Claim 30 words

The method of claim 1, wherein the shaping step includes a step of varying an intensity characteristic of the laser beam in accordance with a density data of a pixel.

Claim 10

Dependent Claim 56 words

The method of claim 8, wherein the varying step comprises: discriminating a type of image as being one of a character image and a halftone image; and regulating the laser beam so that a maximum light amount of the laser beam for a character image is larger than a maximum light amount for a halftone image.

Claim 11

Dependent Claim 70 words

The method of claim 8, wherein the varying step comprises: discriminating a type of image as being one of a character image and a halftone image; and regulating a duty ratio of a control pulse to control an emission time period of the laser beam so that the emission time period of the laser beam for a character image is longer than an emission time period for a halftone image.

Claim 12

Dependent Claim 26 words

The method of claim 1, wherein the shaping step includes a step of pulse-width-modulating the laser beam in accordance with a density data of a pixel.

Claim 13

Dependent Claim 59 words

The method of claim 11, wherein the shaping step includes: discriminating a type of image to be one of a character image and a halftone image; and regulating the pulse-width-modulation of the laser beam so that a maximum light amount of the laser beam for a character image is greater than a maximum light amount for a halftone image.

Claim 14

Dependent Claim 63 words

The method of claim 11, wherein the shaping step includes: discriminating a type of image to be one of a character image and a halftone image; and changing a reference clock pulse in accordance with the discriminated type of image so as to provide one of a one pixel width pulse-width-modulation and a two pixel pulse-width-modulation based on the discriminated type of image.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1998-07-24	1999-01-23	1999-07-25	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2002-07-24	2003-01-23	2003-07-25	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2006-07-24	2007-01-23	2007-07-25	$7700.00	Window Closed / Lapsed

Image forming method

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