JP2721386B2 - Scanning optical device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device such as a laser beam printer, and more particularly to a configuration for obtaining a horizontal synchronization signal of a scanning surface.

[Prior Art] Conventionally, in a scanning optical device such as a laser beam printer, a beam is generated by a semiconductor laser or the like in order to form a recorded image on a photosensitive member which is a surface to be scanned. The laser beam is emitted to the reflection surface of a rotating polygon mirror provided at the front stage on the reflection side of the semiconductor laser, and the beam at the side end of the beam deflected and scanned toward the photoreceptor is detected for timing. . In order to detect this beam, the side end of the beam is applied to a folding mirror for a horizontal synchronization signal that reflects the beam,
The beam from the horizontal synchronization signal folding mirror is guided to a horizontal synchronization signal detection element to measure the timing.

FIG. 5 is a diagram showing the outline. In FIG.
The rotating polygon mirror 101 rotates in the direction of the arrow in the figure, and 1
The light beam incident on 01 is deflected and scanned each time it hits each reflecting surface. The light beam that has been deflected and scanned is corrected by a fθ lens composed of two lenses 102 and 103 to correct the light condensing function and the scanning linearity, and scans the photosensitive drum, which is the scanning surface of 104, linearly as indicated by an arrow. . Here, in order to align the reference writing start position on the photoconductor 104 with respect to each reflection surface 101, a timing is set using the light beam immediately before scanning on the photoconductor.
The optical path of the light beam is shown by a two-dot chain line in the figure. This light flux is turned once by the reflecting mirror 105, passes through the condensing lens 106, and reaches the timing detection sensor 107.
Here, if the lens 103 and the photosensitive drum 104 are separated from each other in the optical path, the timing detecting optical path also needs an optical path of a certain length. The mirror needs to be set at a considerable distance from the 103 lens. In another case, as shown in FIG.
Even if the turning mirror is fixed in the vicinity of the lens of 103, the optical path after turning becomes similarly long.

In the above-described conventional apparatus, as the distance between the rotating polygon mirror as an optical deflector or the fθ lens as a scanning lens and the photoconductor to be scanned is increased, the optical path for timing detection becomes longer. However, space limitations of the entire apparatus and problems with accuracy have occurred.

SUMMARY OF THE INVENTION According to the present invention, a timing detection (horizontal synchronization signal detection) light beam is turned by a deflecting means a plurality of times, and the final turning position of the deflecting means and the timing detection position are used for timing detection. A mechanism for timing detection is configured so as to be optically conjugate to the condenser lens.

[Embodiment] FIGS. 1 and 2 are views showing an embodiment of the scanning optical apparatus of the present invention. In FIG. 1, reference numeral 1 denotes a semiconductor laser which is a light source for emitting a laser beam, and a light beam emitted from the light source 1 passes through a collimator lens 2 to be made substantially parallel light and passes through a stop 3 , A predetermined beam size. This light beam is incident on the four rotating polygon mirrors. The rotating polygon mirror 4 rotates at high speed in the direction of the arrow in the figure, and the light beam incident on 4 is deflected and scanned at high speed for each surface of the polygon mirror. The reflected light beam from 4 is transmitted through an fθ lens composed of two elements 5 and 6,
The light-collecting action and the scanning linearity are corrected, and the photosensitive drum, which is the scanning surface 7, is linearly scanned in the direction of the arrow in the figure.
Here, the laser beam from the light source is scanned linearly for each surface of the rotating polygon mirror, but the rotation speed error and unevenness of the motor that rotates the rotating polygon mirror, or the division error of each surface of the rotating polygon mirror, is increased. In order to keep the reference position where the signal starts to be written on the photoconductor even if it is, a part of the light beam deflected and scanned before actually being written on the photoconductor is used for horizontal scanning for the photoconductor. The synchronization signal is being taken. The state of this light beam is shown by a two-dot chain line in FIG. Before being written on the photoreceptor, a part of the light beam that has been deflected and scanned by the rotating polygon mirror 4 and passed through the lenses 5 and 6 is reflected by the first folding mirror 8 and proceeds downward in FIG. . Below there are nine second folding mirrors, this time the light beam upward in the figure is reflected. The upwardly directed light beam passes through 10 condenser lenses.
The light beam is incident on the 11 optical fibers. A sensor 12 for detecting an optical signal is attached to the other end of the optical fiber 11, and by detecting a time when the light beam is incident, a horizontal synchronizing signal for a writing start timing on the photoconductor 7 can be obtained. it can. Further, as shown in this figure, the components other than the photoreceptor 7 are housed in one substrate or box so that the relative positional accuracy can be easily obtained. FIG. 2 shows the state from the second folding mirror 9 to the light beam incident surface of the optical fiber 11 and perpendicular to the plane including the optical axis of the condenser lens 10 and being deflected and scanned by the rotary polygon mirror. The state of the luminous flux for a simple cross section is shown.

In FIG. 2, the reflection point A of the second folding mirror 9 is shown.
The light beam incident surface (the position corresponding to the horizontal synchronization signal detection) B of the optical fibers of the optical fibers 11 and 11 is a condensing lens in the plane in FIG.
It is arranged in an optically conjugate relationship to 10. Therefore, for example, even if the second folding mirror 9 is tilted with an error in the mounting state as shown by the broken line, the reflected light travels as shown by the broken line and always enters the incident end face B of the optical fiber 11.
This is because the positions of the points A and B are optically conjugate to the condenser lens. Further, when the distance between the second folding mirror 9 and the condenser lens 10 L _1, the distance between the converging lens 10 and the fiber optic 11 has a L _2, it has a L ₂ / L ₁ ≒ 0.1, optical The target magnification relationship is -0.1 times for B with respect to A. Here, if there is an error in mounting the first folding mirror 8, the position where the light beam reflects on the second folding mirror 9 changes, so that the light flux does not enter the center of the optical fiber surface 11. Become. However, if the optical magnification relationship described above is satisfied by A and B, even if the reflection position is shifted by 1 mm upward at the point A in FIG.
Since the optical magnification between them is -0.1 times, the deviation at the optical fiber incident surface of B only shifts downward by 0.1 mm from the reference (when there is no mounting error of the return mirror) in the figure. It will be reduced to no amount. In the case where the light is guided to the optical fiber surface using a plurality of folding mirrors as in the present invention, the error factor is one by the amount of the second folding mirror as compared with the case where the light is guided to the optical fiber surface using one folding mirror. Extra increase. Accordingly, as described above, the geometrical optical magnification m between the reflection point of the final mirror (second folding mirror) and the position corresponding to the detection of the horizontal synchronization signal is -0.5≤m <0.
It is preferable to set it in the range. Since the beam is always running on the surface deflected and scanned by the rotating polygon mirror (the surface parallel to the paper surface in FIG. 1), the optical fiber surface of the eleventh fiber must pass through even if a mounting error occurs in the reflection mirror. Does not require much precision to do so. Here, if the first return mirror 8 is fixed and the second return mirror 9 is rotated as shown in FIG. 1, an electrical delay and a mechanical incident reference position can be shifted. It is possible to adjust the writing start position on the photosensitive member 7 without the need. The function for adjusting the reflection angle only at the final reflection position (second reflection mirror) is provided so as not to increase the size of the second reflection mirror. That is, the first
If a function for adjusting the reflection angle is provided in the folding mirror and the first folding mirror is rotated, the position of the light beam incident on the second folding mirror changes. As a result, the second folding mirror requires a large reflecting surface. Conversely, unless a function for adjusting the reflection angle is provided in the first folding mirror, the position of the light beam incident on the second folding mirror does not change. As a result, the second folding mirror does not require a large reflecting surface.

In the embodiment described above, two folding mirrors are used. However, in order to further shorten the optical path, it is also possible to use three or more mirrors. In addition, as shown in FIG. 3, by making the light beam incident on one folding mirror twice, the light beam for detecting the horizontal synchronizing signal, the last reflection position in the optical path and the horizontal synchronizing signal detecting position are conjugated. It is also possible to adopt a different configuration. In FIG. 3, the point A and the point B are configured to be optically conjugate to the condenser lens 10. In addition, as shown in FIG.
It is also possible to dispose and configure other optical elements such as. Further, if a slit 14 having an opening in a direction perpendicular to the scanning direction is provided in front of the photodetector 15 for detecting the horizontal synchronization signal, it is possible to detect the horizontal synchronization signal with higher accuracy.

[Effects of the Invention] As described above, a plurality of mirrors are used to fold the optical path of the horizontal synchronizing signal detecting light beam, and the last mirror in the optical path of the horizontal synchronizing signal detecting light beam and the horizontal synchronizing signal are used. By setting the detection equivalent position to a certain conjugate relationship, the scanning optical device including the horizontal synchronization detection mechanism can be made compact, so that the entire device can be reduced in size and can be freely arranged, which is effective in reducing costs. The reliability of detection of the horizontal synchronization signal is also improved.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of the scanning optical device of the present invention,
FIG. 2 is an enlarged view for explaining a horizontal synchronizing signal detecting section of the present invention, FIGS. 3 and 4 are views showing another embodiment of the present invention,
5 and 6 are views showing a conventional example. DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Collimator lens 3 ... Aperture 4 ... Rotating polygon mirror 5,6 ... fθ lens 7 ... Photoconductor drum 8 ... First folding mirror 9 ... Second folding mirror 10 ... Focusing lens 11 Optical fiber 12 Horizontal sync signal detection sensor

Claims (1)

(57) [Claims] A laser for emitting a laser beam; an optical scanner for scanning the laser beam from the laser; a deflecting unit for deflecting the laser beam from the optical scanner; In a scanning optical apparatus having a light collecting means for emitting light and a detecting means for receiving a laser beam from the light collecting means and detecting a horizontal synchronization signal, the laser light from the optical scanner is scanned a plurality of times by the deflecting means. The scanning optical device, wherein the light is reflected and reaches the light collecting means, and the final reflection position of the deflecting means and the detecting means are in an optically conjugate relationship with the light collecting means.