JPH0225826A - Beam scanning method - Google Patents

Abstract

PURPOSE:To prepare a color image with good quality by dislocating the position of a following beam from the position of the most precedent beam in a prescribed value subscanning direction, and matching both the beams with a recording dot when the following beam attains to the recording dot position of the most precedent beam. CONSTITUTION:When a distance in an (x) direction (main scanning direction) on a photosensitive material 2 between a preceding beam B1 and a following beam B2 is assumed as U (mm), the speed in the main scanning directions of the beams B1 and B2 is assumed as VM (mm/s), the delay of the recording start time of the beam B2 from the recording start time of the beam B1 is assumed as (U/VM) (s) and a moving speed in the subscanning direction of the photosensitive material 2 is assumed as Vs, or when the conditions are realized, a scanning is executed in dislocating the position of the beam B2 from the position of the beam B1 by (U/VM)Vs (mm) in the subscanning direction. Thus, the dot positions recorded on the photosensitive material 2 of the beam B1 and beam B1 are completely matched, and the color image with a better quality can be prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a beam scanning method in a color laser printer or the like.

[Background of the invention]

When recording an image by scanning a photosensitive material with a plurality of scanning laser beams, it is necessary to accurately align the dot positions of each beam on the photosensitive material in both the main scanning direction and the sub-scanning direction. A technique for aligning dot positions in the main scanning direction is provided in Japanese Patent Application No. 61-132174.

The gist of this is that multiple beams are scanned with temporal shifts in the main scanning direction, horizontal synchronization is taken independently for each beam, and the time from this horizontal synchronization signal to the start of recording is set to an appropriate value for each beam. The purpose is to align the positions of the dots formed on the silver salt photosensitive material.

[Problem to be solved by the invention]

However, the problem remains that the photosensitive material moves in the sub-scanning direction until the trailing beam reaches a predetermined position, and the dot positions of the leading and trailing beams in the sub-scanning direction are misaligned. . That is, as shown in FIG. 4, the difference in recording time between the leading beam and the trailing beam immediately after it is determined by the velocity of the beam in the main scanning direction being V, 1 (an/s), and the leading beam B.
1 and the trailing beam B2 is L (++vi), it becomes L/VM (s). Also, the sub-scanning speed (for example, the moving speed of the photosensitive material) is Vs (ms+/s)
, the dots of the leading beam and the trailing beam, which should originally be recorded at the same position, are shifted in the sub-scanning direction by Vs (L/V)l ) (+111) due to the above recording time difference ( (See Figures 4 and 5).

Such a shift is undesirable because it causes dark colors at the edge of the image, a decrease in resolution, and deterioration in image quality.

Particularly in images that contain a mixture of floor images such as landscapes and faces, and line drawing images such as letters, if the dot position shift is more than 6μ steel (0.1 pixel) relative to the 60μ-〇 dot diameter, the text will be removed. The sharpness of the images begins to deteriorate.

The present invention was made in view of the above circumstances, and it is possible to completely match the dot positions of multiple beams on the photosensitive material.
An object of the present invention is to provide a beam scanning method that makes it possible to form high-quality color images.

[Means to solve the problem]

For this purpose, the beam scanning method of the present invention shifts the position of the trailing beam in the sub-scanning direction by a predetermined value from the position of the leading beam, and when the trailing beam reaches the recording dot position of the leading beam, the position of the recording dot is shifted from the position of the leading beam. I made it match.

〔Example〕

A beam scanning method according to an embodiment of the present invention will be described below. The gist of the present invention is to correct the position of the trailing beam in advance in the sub-scanning direction by the amount of the shift in order to prevent a shift between the leading beam and the trailing beam in the sub-scanning direction. .

FIG. 1 is an explanatory diagram of the beam scanning method of the embodiment.

In the cough diagram, reference numeral 1 denotes a polygon (rotating polygon mirror) that reflects a laser beam and scans and irradiates it onto a photosensitive material 2. Each of the three laser beams 81 to B3 incident on the polygon 1 has already been modulated by an image signal and is at a delicate angle with respect to each other.

As a result, each beam focused on the photosensitive material 2 is spatially shifted. Although three beams 81 to B3 are shown in FIG. 1, the relationship between the two beams B1 and B2 will be explained first.

Now, the distance in the X direction (main scanning direction) between the leading beam B1 and the trailing beam B2 on the photosensitive material 2 is U (mm), and the speed in the main scanning direction of the beams B1 and 82 is Vs (ms/s). , the delay of the recording start time of beam B2 from the recording start time of beam B1 is (U/VM) (3), and the moving speed of the photosensitive material 2 in the sub-scanning direction is V, or In this example, the position of the beam B2 is shifted from the position of the beam B1 by (U/VM) Vl (mm) in the sub-scanning direction, and scanning is performed.

By doing this, the positions of the dots recorded on the photosensitive material 2 by the beam B1 and the beam B1 (hereinafter, pixels recorded on the photosensitive material by the beam are referred to as recording dots or simply dots) are perfectly aligned. . That is, the beam Bl always precedes the beam B2 in the main scanning direction by U (mm), and the time lag is (U/VW) (s), while the photosensitive material 2 is (U/VM) VS is the sub-scanning direction. Move in the scanning direction.

Since the amount of movement is the distance by which the beam B2 is shifted in the sub-scanning direction in advance, the dots of the beams B1 and B2 match. Such matching is performed successively for all dots.

Further, the relationship between beam B1 and beam B3 is also the same,
When the distance between beams B1 and 83 is U' (IIIm), the dot position of beam B3 is (U'/VM) V s (
Scanning is performed with a shift of 1 mm) in the sub-scanning direction. As a result, the dots of beams B2 and 83 naturally match, and the dots of all the beams at the synchronous position match at the same position (see FIG. 2).

Next, an actual concrete example of the present invention will be explained.

The resolution of the recorded image is 62.5μm (16dot/m
m), the mutual positional deviation of each dot is ΔD
As mentioned above, it is several μ ugly, that is, ΔD/D=0.1 (10
%) The following is desirable. Therefore, the positions of beams B2 and B3 are respectively (U/VM)Vs±0.
1 D (U'/VM) vs. ±0.1 D is desirable.

In order to align each beam to each scanning line with an accuracy within the above-mentioned several μ, an adjusting device 3 shown in FIG.
is used. The adjustment device 3 incorporates a pair of photodiodes 4.4° as sensors arranged symmetrically in the sub-scanning direction, and adjusts the position of the beam from the differential amplifier 5 by balancing the light receiving sources of both photodiodes at 4.4°. For example, if the beam is at the center of photodiode 4.4', it will output 0 (V), if it shifts upward, it will output a positive output, and if it shifts downward, it will output a negative output. . By calibrating the correspondence between this output voltage and the actual amount of deviation in advance, the position of the beam can be quickly measured. Then, based on the position of the leading beam detected first, the mirrors of the optical system are adjusted so that the output voltage of the trailing beam detected second and third becomes a predetermined value. Adjust the position.

〔Effect of the invention〕

From the above, according to the beam scanning device of the present invention, the photosensitive material "-
The dot positions of multiple laser beams in the main scanning direction and sub-scanning direction can be precisely matched, preventing color coating on the image edges, improving resolution and image quality, and producing higher quality color images. Formation becomes possible.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a beam scanning method according to an embodiment of the present invention;
FIG. 2 is an explanatory diagram showing the state of dots of multiple beams recorded by this scanning method, FIG. 3 is a circuit diagram of a beam adjustment device, FIG. 4 is an explanatory diagram of the conventional beam scanning method, and FIG. The figure is an explanatory diagram showing the state of dots recorded by a plurality of beams by a conventional beam scanning method.

Claims (1)

[Claims] (1) Beam scanning in which multiple beams are scanned with temporal shifts in the main scanning direction, and each of these beams is synchronized in the main scanning direction to scan a photoreceptor moving in the sub-scanning direction. In the method, the position of the trailing beam among the beams is shifted in the sub-scanning direction by a predetermined value from the position of the leading beam, and when the trailing beam reaches the recording dot position of the leading beam, it matches the recording dot. beam scanning method.