JPS5926006A - Detection of beam position in multibeam scanner - Google Patents

Abstract

PURPOSE:To detect exactly the positions of respective beams by constituting a titled device in such a way that the irradiation of the plane to be scanned by the plural beams deviates in the main scanning direction, disposing photodetection parts perpendicularly on the scanning line of the beams, putting out the beams when a photodetection part detects said beams. CONSTITUTION:Plural beams B1-B5 are deviated in the main scanning direction on the scanning lines thereof, and a photodetector E is disposed for the same perpendicularly on the scanning lines. For example, a photodiode having good responsiveness is used for the photodetector E. The plural beams overlapped in the auxiliary scanning direction are deviated respectively by the distance D at which no influences are given to the other beams. The distance D is required to be at least half the size of the beams. The beams B1-B5 are all lighted initially, then the beams are put out in order of detection with detectors. Since the putting-out of light after the detection is accomplished successively for the respective beams, the positions of the beams are exactly detected even if the beams overlap on the plane to be scanned in the auxiliary scanning direction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a plurality of beams that can be modulated. This relates to a beam position detection method for detecting.

The multi-beam scanning device can reduce the number of rotations of the polycon mirror compared to the shingle beam scanning device, so it has great advantages in terms of durability and vibration resistance. However, S.O.
Detection of the S signal becomes very difficult because it depends on the relationship between each beam.

One method is to accurately determine the relative positions of the beam generators, detect only the position of one of the beams, detect the positions of the other beams, and correct the position of the letter beam to generate the SO5 signal. I can think of a way to do it.

For example, as shown in Fig. 1, semiconductor lasers (1) having light emitting parts are placed at 100μ11 intervals and are set θ 1000 in the main scanning direction, and a collimator lens (1) with a focal length of 5 mm as shown in Fig. 2 ( 2) Polycon mirror (3) and focal length 11i [
Considering the case where an fθ lens (4) of t' 50Q*m is projected onto the scanned surface, even if an error of ±30μIl+ is allowed on the scanned surface for a beam spacing of 1oOμn1, the beam will be 1− Since it is magnified 00 times, the angle θ at which the semiconductor laser (1) is tilted must be as accurate as 0.00 times and not distorted. In addition, semiconductor laser (1
) to make each light emitting part step-like: -2Q, 3μI
It has to be even accurate. It is extremely difficult to arrange or manufacture semiconductor lasers with such high precision.

As a modification of the above method, as shown in FIG. 3, a mirror (5
) (5) Adjustment using (5) can be considered.

That is, each mirror (5) (5) (5) is rotated around an axis parallel to the main scanning direction to adjust the beam spacing, and also rotated around an axis parallel to the sub-scanning direction to adjust each beam. The position in the main scanning direction is adjusted. However, this method also adds a new adjustment element, iIMv of the mirror (51(5) (5)), and the adjustment is very delicate, so it is actually (1 difficult method).

Therefore, it is possible to detect the beam position separately for each beam, but in order to prevent gaps between scanning lines in normal laser beam printers, the beam position is detected separately on the surface to be scanned. (Figure 4). For example, the beam spacing is 100μ! 1), the center 7 intensity is defined as O2, and the beam diameter is set to be about 200 μm on the surface to be scanned. However, such a large harp causes the detection device provided for each beam to detect other beams as well, causing malfunctions.

The present invention has been made in view of these points, and provides a beam position detection method that can accurately detect the beam position of each beam in a multi-beam scanning device even when the beams overlap. Aim for the purpose.

The above purpose is to configure a plurality of beams so that the surface to be scanned is irradiated with the beams in the main scanning direction, and to arrange a light receiving section perpendicularly to the scanning line of the plurality of beams.
This is achieved by extinguishing the beam when the recording/receiving section detects the beam, and sequentially extinguishing each beam after detection.

FIG. 5 is a diagram showing an embodiment of the present invention, in which a plurality of beams Bl
,B2. B8. B4. The light receiving element 15 is arranged so as to be able to move along the scanning line in the main scanning direction, and one light receiving element 15 is arranged perpendicularly to the scanning line. This light receiving element E
is conveniently placed on the side of the photosensitive drum 6 as shown in FIG. 3, and uses a photodiode with good responsiveness, for example.

The plurality of beams 13 that overlap in the sub-scanning direction are shifted in the main-scanning direction by a distance Ml that does not affect the other beams.

Since the beam B is a Gaussian beam, when it is detected by the light receiving element E, setting the threshold Th in the middle of the peak is the least susceptible to errors. Therefore, the distance ^
14 L) requires at least half the beam size.

Here, the size of the beam means that the beam intensity is 1/of the center intensity.
Say the size that becomes e2. In reality, it would be better to leave a distance of 141tD, which is about twice the size of the rebeam, due to errors in the setting ink.

FIG. 7 is a time chart showing an example of control mlj in the embodiment shown in FIG. In this case, beams 131-135 are all turned on initially. The beams are then erased in the order in which they are detected by the light receiving element E, and the SO5 signal of each beam is output from the light receiving element E.

The blinking control of the beam can also be performed as shown in FIG. In the time chart of FIG. 8, each beam lights up after the previous beam is extinguished, and disappears when that beam is detected by the light-receiving element. Therefore, when a certain beam approaches the light receiving element 1, the other beams are extinguished, so f? in the main scanning direction between each beam 4? +1 distance I] can be made shorter than in the control system shown in FIG.

Figure 9 shows an example of beam arrangement when the number of beams is large.
B2.13+l, B4) and (J B6. B7.13
The croup is arranged in two stages in the sub-scanning direction and even in the main-scanning direction. Here, the distance l in the main scanning direction of each beam is 21) 1? l]t? +t L) Make sure to take it as long as you can.

As described above, the present invention provides a multi-beam scanning device that simultaneously scans a scanned surface with a plurality of modulated beams, in which the plurality of beams are arranged such that the beams irradiate the scanned surface in the main scanning direction. In addition, the light receiving section is arranged perpendicular to the scanning line of a plurality of beams, and when the Ai + recording light receiving section detects the beam, the beam is extinguished, and the extinction after the detection is performed once for each beam. Therefore, the position of each beam can be accurately detected even though the beams overlap in the sub-scanning direction on the scanned surface.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a semiconductor racer with multiple light emitting parts.
Figures 2 and 3 are diagrams explaining a method proposed and tested by the present inventor as an example of beam position detection in a multi-beam scanning device, and Figure 4 shows the light emitting parts of multiple beams and the scanned ihj.
5 and 9 are diagrams illustrating the relationship between the beam and the light-receiving unit in each embodiment of the present invention; FIG. 6 is a diagram illustrating the relationship between the beam and the output of the light-receiving element; 7,8
The figure is a diagram illustrating control of the beam position detection method of the present invention. ■...Semiconductor racer 2...Collimator lens 3...Polygon mirror 4...Fθ lens 5...
・Mirror 6°° Photosensitive drum B・Beam
1st death... Light receiving element applicant Minolta Camera Co., Ltd. Figure 1 Figure 2! Figure 3 Figure 5 Figure 6 Figure 7 Figure 3

Claims (1)

[Claims] 1 In a multi-beam scanning device that simultaneously scans a scanning surface with a plurality of modulated beams, the plurality of beams are configured so that the beams to be scanned ih+ are irradiated in the main scanning direction, and the light receiving section is A beam position detection method characterized in that the beams are arranged perpendicularly on a scanning line of a plurality of beams, and when the light receiving section detects the beam, the beam is turned off after the detection, and each beam is sequentially turned off.