JPH0357453B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-beam scanning device that simultaneously scans a surface to be scanned by deflecting a plurality of modulated beams using a scanning device such as a polygon mirror. , relates to a beam position detection method that detects a symbol (hereinafter referred to as an SOS signal) for determining the printing start position on a scanned surface.

The above-mentioned multi-beam scanning device can reduce the number of rotations of the polygon mirror compared to a single-beam scanning device, so it has great advantages in terms of durability and vibration. However, detecting an SOS signal becomes extremely difficult due to the relationship between each beam.

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

For example, as shown in Fig. 1, a semiconductor laser 1 having light emitting parts at intervals of 100 μm is installed at an angle of θ with respect to the main scanning direction, and a collimator lens 2 with a focal length of 5 mm and a polygon mirror 3 with a focal length of 5 mm as shown in Fig. 2 are used. Considering the case of projecting onto the scanned surface with a 500mm fθ lens 4, even if an error of ±30μm is allowed on the scanned surface for a beam interval of 100μm,
Since the beam is expanded 100 times, the angle θ at which the semiconductor laser 1 is tilted must be accurate to sin ^-1 (1/100±3/1000). In addition, when shifting each light emitting part of the semiconductor laser 1 in steps, ±0.3 μm
must be shifted with an accuracy of It is extremely difficult to arrange or manufacture semiconductor lasers with such high precision.

As a modification of the above method, it is conceivable to adjust the mutual positions of the beams on the scanned surface using mirrors 5, 5, 5 provided for each beam, as shown in FIG. That is, each mirror 5, 5, 5 is rotated around an axis parallel to the main scanning direction to adjust the beam interval, and also rotated around an axis parallel to the sub-scanning direction to adjust the main scanning direction of each beam. Adjust the position of the However, this method also adds a new adjustment element of adjusting the mirrors 5, 5, 5, and the adjustment is very delicate, making it a difficult method in practice.

Therefore, it is possible to detect the beam position separately for each beam, but in normal laser beam printers, the beams are set to overlap on the scanned surface in order to prevent gaps between scanning lines. (Figure 4). for example,
When the beam interval is 100 μm, the beam diameter defined by the center intensity 1/e ² is set to be about 200 μm on the surface to be scanned. However, such overlap 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 though the beams overlap. The purpose is to

The above purpose is to configure a plurality of beams so that the irradiation of the scanned surface by each beam is shifted in the main scanning direction with respect to the adjacent beam, and each time the light receiving unit detects each beam, the detected beam is This is achieved by turning off the light immediately after detection.

FIG. 5 is a diagram showing an embodiment of the present invention, in which a plurality of beams B ₁ , B ₂ , B ₃ , B ₄ , B ₅ are shifted in the main scanning direction on the scanning line, and one light receiving element E is arranged vertically on the scanning line. The light-receiving element E is conveniently arranged 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 B overlapping in the sub-scanning direction are each shifted by a distance D in the main-scanning direction so as not to affect other beams.

Since the beam B is a caustic beam, when it is detected by the light receiving element E, the threshold Th is set in the middle of the peak, so that it is less susceptible to errors. Therefore, the distance D needs to be at least half the beam size. The beam size here refers to the size where the beam intensity is 1/e ² of the center intensity. In reality, due to setting errors, it is better to leave a distance D of about twice the beam size.

FIG. 7 is a time chart showing an example of control in the embodiment shown in FIG. In this case, beams B ₁ to _{B 5} are all turned on initially. Then, the beams are turned off in the order in which they are detected by the light receiving element E, and the light receiving element E
The SOS signal of each beam is output.

The beam blinking control can also be performed as shown in FIG. In the time chart of FIG. 8, each beam is turned on after the previous beam is turned off, and when that beam is detected by the light receiving element E, it is turned off. Therefore, when a certain beam strikes the light receiving element E, the other beams are turned off, so the distance D between the beams in the main scanning direction can be made shorter than in the control system shown in FIG.

Figure 9 shows an example of beam arrangement when there are many beams, and the beams are arranged in two groups (B ₁ , B ₂ , B ₃ , B ₄ ) and (B ₅ , B ₆ , B ₇ , _B8 )
These groups are arranged in two stages in the sub-scanning direction and shifted in the main-scanning direction. Here, the distances in the main scanning direction of each beam are set to be 2D apart, and each group is shifted by a distance D.

As described above, the present invention provides a multi-beam scanning device that simultaneously scans a surface to be scanned with at least two modulatable beams such that the irradiation of each beam overlaps in the sub-scanning direction. It is configured so that the illumination of the scanning surface is shifted in the main scanning direction, and each beam is sequentially detected by a light receiving part large enough to receive at least two beams at the same time, and each beam is detected each time. Since the beams are turned off, 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 drawings]

Figure 1 is a diagram showing a semiconductor laser having multiple light emitting parts, Figures 2 and 3 are diagrams explaining a method proposed and considered by the present inventor as an example of beam position detection in a multi-beam scanning device, and Figure 4. 5 and 9 are diagrams illustrating the relationship between the beams and the light receiving section of each embodiment of the present invention, and FIG. FIGS. 7 and 8 are diagrams for explaining the relationship between the outputs of the light receiving elements, and diagrams for explaining the control of the beam position detection method of the present invention. 1... Semiconductor laser, 2... Collimator lens, 3... Polygon mirror, 4... fθ... Lens, 5... Mirror, 6... Photosensitive drum, B... Beam, E... Light receiving element.

Claims (1)

[Scope of Claims] 1. In a multi-beam scanning device that simultaneously scans a scanned surface with at least two modulated beams such that the irradiation of each beam overlaps in the sub-scanning direction, It is configured so that the illumination of the scanning surface is shifted in the main scanning direction, and each beam is sequentially detected by a light receiving part large enough to receive at least two beams simultaneously, and each beam is detected each time. A beam position detection method that turns off the beam.