JPH0357452B2 - - 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 signal (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 mutual position of the beam generators, detect only one beam position of each beam, and correct the position of the other beams to generate an SOS signal. There is a way to do this.

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, a polygon mirror 3 and a focal point as shown in FIG. Considering the case of projecting onto the scanned surface with fθ lens 4 at a distance of 500 mm, even if an error of ±30 μm is allowed on the scanned surface for a beam interval of 100 μm, the beam will be expanded 100 times. The angle θ at which the semiconductor laser 1 is tilted must have an accuracy of sin ^-1 (1/100±3/1000). In addition, when shifting each light emitting part of the semiconductor laser 1 in steps, ±0.3μ
It must be shifted with an accuracy of m. 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, if the beam spacing is 100 μm, the beam diameter defined as 1/e ² of the center intensity is 200 μm on the scanned surface.
The settings are set so that the 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 purpose of the above is to arrange multiple light receiving sections to detect the position of each beam by shifting them in the main scanning direction on the scanning line of each beam, and to turn on the beam, detect the beam by the corresponding light receiving section, and turn on the beam. This is achieved by performing the steps in the order of the detected beams starting from the scanning start side. That is, the beam is turned on before it hits the light receiving part, and when this beam is detected, it is turned off and the next beam is turned on at a predetermined timing, and then each beam is turned on and off in turn. It detects and turns off the light.

By controlling in this way, the position of each beam can be detected accurately.

Embodiments of the present invention will be described below with reference to the drawings.

_{The embodiment of FIG .}
E ₁ , E ₂ , E ₃ , E ₄ , and E ₅ are arranged on the scanning line of each beam so as to be shifted from each other in the main scanning direction.
As shown in FIG.
placed on the side of the

The spacing between each light receiving section in the main scanning direction must be such that when the beam is turned on, it will not affect the light receiving section for the previous beam due to the size of the light receiving section in the main scanning direction, the size of the beam, the position error in the scanning direction, etc. be. In addition, it is desirable that the size of the light receiving section is large enough to cover the beam size in order to obtain as much incident light as possible in the sub-scanning direction, and in the main scanning direction as shown in Figure 6. Although the beam is a Gaussian beam and the threshold Th is set in the middle of the peak, it is less susceptible to errors, so it is necessary to have at least half the beam size.

In the embodiment shown in FIG. 5, each beam is turned off at the seventh
This is done as shown in the figure. That is, the first beam B ₁ is lit first, and this beam B ₁ is the light receiving element.
When detected by E ₁ , beam B ₁ is turned off, then beam B ₂ is turned on at a predetermined timing, and when this beam B ₂ is detected by light receiving element E ₂ , beam B ₂ is turned off. Continue sequentially until beam B ₅ .

As a result, detection signals S ₁ , S ₂ , S ₃ , S ₄ , and S ₅ are outputted from each of the light receiving elements E ₁ to E ₅ corresponding to each beam position. Then, beam B ₁ is transmitted after a time T ₁ from the detection signal S ₁ , and beam B ₂ is transmitted after a time T ₂ from the detection signal S _2.
After a certain time delay for each beam, the printing start position is aligned and printing is performed.

The embodiment shown in FIG. 8 uses one light receiving element Eo,
The aperture of this light receiving element Eo is shifted in the main scanning direction.
Screen with A ₁ , A ₂ , A ₃ , A ₄ , A ₅ , A ₆ opened
It is covered with SP. In this case as well, the control is
Proceed as shown. However, the detection signal S ₁ ~
_S6 is output from one light receiving element Eo. In the present invention, the beams B ₁ to _{B 6} may be slightly shifted in the main scanning direction as shown in FIG.

As can be seen from the overlapping state of the beams in FIG. 5, adjacent beams overlap, but distant beams do not overlap.

Therefore, it is possible to divide the beam into groups and arrange the light receiving elements in multiple stages.

FIG. 9 shows an embodiment based on the above consideration, in which light receiving elements E ₁ , E ₂ , _{E 3} for beams B ₁ , B ₂ , B ₃ and light receiving elements E ₄ , E ₄ for beams B 4 , B ₅ , B ₆ , It is divided into E ₅ and E ₆ and arranged in two stages in the sub-scanning direction.

Figure 10 further develops this, beams B ₁ ,
One light receiving element E _A is used for beams B ₄ , B ₂ and B ₃ .
Another light receiving element E _B is provided with respect to B ₅ and B ₆ at an angle with respect to the main scanning direction, and these light receiving elements E _A ,
E _B is covered with a screen SP having apertures A ₁ to _{A 6} for each beam. At this time, the screen SP may be provided for each light receiving element.

The embodiment shown in FIG. 11 uses one light receiving element Eo,
Openings A ₁ lined up in two stages on the screen SP that covers this,
A ₂ , A ₃ , A ₄ and A ₅ , A ₆ , A ₇ , A ₈ are provided. In this case, the apertures in each stage are arranged so as not to overlap each other when viewed from the sub-scanning direction, and a light receiving element with good responsiveness is used.

As described above, the present invention is capable of simultaneously scanning a surface to be scanned with at least the first and second modulated beams, in which the irradiation of each beam is substantially aligned in the sub-scanning direction, and the irradiation of adjacent beams overlaps with each other. In a multi-beam scanning device that scans in a state where each beam is The first beam is arranged so as to lead in the main scanning direction with respect to the second light receiving part corresponding to the second beam, and the first beam is turned on before reaching the first light receiving part. After one beam is detected by the first light receiving section, the adjacent second beam is turned on, and the first beam is detected by the second beam.
Since the light is turned off before reaching the light-receiving section of the beam, the position of each beam can be accurately detected even though the beam irradiation overlaps on the surface to be scanned.

Furthermore, the number of light receiving elements can be reduced by covering the common light receiving elements with a screen having openings that are shifted in the main scanning direction on the scanning line of each beam.

Furthermore, by dividing each beam into groups and arranging the light receiving sections for each group in multiple stages in the sub-scanning direction, the detection device can be configured compactly even when many beams are used.

[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. 1 is a diagram illustrating the relationship between a plurality of beams on a light emitting part and a surface to be scanned; FIGS. , FIG. 6 is a diagram for explaining the relationship between the beam and the output of the light receiving element, and FIG. 7 is a diagram for explaining the control of the beam position detection method of the present invention. 1... Semiconductor laser, B... Beam, 2...
Collimator lens, E... Light receiving element, 3... Polygon mirror, A... Aperture, 4... fθ lens, M
...Detection device, 5...Mirror, S...Detection signal,
6...Photosensitive drum, SP...screen.

Claims (1)

[Scope of Claims] 1. At least the first and second modulated beams simultaneously scan the surface to be scanned, and the irradiation of each beam is substantially aligned in the sub-scanning direction, and the irradiation of adjacent beams overlaps each other. In a multi-beam scanning device that scans in a state where each beam is part is second
The second light receiving section corresponding to the beam is shifted in advance in the main scanning direction, and the first beam is turned on before reaching the first light receiving section, so that the first beam is Beam position detection in which the adjacent second beam is turned on after being detected by the first light receiving section, and the first beam is turned off before the first beam reaches the second light receiving section. Method.