JP3141597B2 - Optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used for an image forming apparatus such as a laser printer or a copying machine, and more particularly to an optical scanning device for simultaneously scanning a plurality of lines with a plurality of light beams.

[0002]

2. Description of the Related Art In an image forming apparatus such as a laser printer, a plurality of lines on a surface to be scanned are formed by a plurality of laser beams in order to increase the speed or the resolution while suppressing an increase in the number of rotations of a rotary polygon mirror. Simultaneous scanning methods have been proposed.

In an optical scanning apparatus that simultaneously scans a plurality of lines with a plurality of laser beams using a plurality of laser light sources such as laser diodes as described above, the dot interval in the non-scanning direction (sub-scanning direction) is used. That is, it is necessary to precisely adjust the beam interval between a plurality of laser beams. Conventionally, as means for adjusting the beam interval, JP-A-60-166916 and JP-A-63-5080 have been used.
No. 9 is known.

Here, a first example of a conventional optical scanning device having means for adjusting the beam interval will be described with reference to FIGS. 9 to 11, for example, one disclosed in Japanese Patent Laid-Open No. 60-166916. I do.

FIG. 9 is an explanatory view showing the configuration of a general optical scanning device when two laser diodes are used. In this optical scanning device, the first laser diode 1
The first beam of P-polarized light emitted from 01 is converted into a parallel light beam by the coupling lens 103, reflected by the mirror 105, and transmitted through the polarizing beam splitter 107. On the other hand, the second beam of S-polarized light emitted from the second laser diode 102 is converted into a parallel light beam by the coupling lens 104, reflected by the mirror 106, and incident on the first beam incident surface of the polarizing beam splitter 107. The light is incident on an orthogonal surface, is reflected by the S-polarized light reflecting surface, and travels in the same direction as the first beam at a predetermined distance from the first beam. The first and second beams emitted from the polarization beam splitter 107 are converted into circularly polarized light by a quarter-wave plate 108, deflected by a deflector 109 having a rotating polygon mirror, passed through a scanning lens 110, and passed through a photoconductor 111. The light is irradiated upward, and two adjacent lines on the photoconductor 111 are scanned.

FIG. 10 is an explanatory view showing an example in which a beam interval adjusting means and a beam interval detecting means are added to the optical scanning apparatus shown in FIG. FIG. 10 shows only main components of the configuration shown in FIG. In the example shown in FIG. 10, a half mirror 113 is inserted between the polarizing beam splitter 107 and the deflector 109 for monitoring the beam interval, and the beam reflected by the half mirror 113 passes through a lens 114 to a photodetector 115. To receive light. In this optical scanning device, one of the coupling lenses 103 and 104 or one of the laser diodes 101 and 102 is moved by a two-dimensional actuator for beam interval adjustment. The beam interval is monitored by a photodetector 115, and the output of the photodetector 115 is fed back to a two-dimensional actuator.

FIG. 11 is an explanatory view showing the photodetector 115. The photodetector 115 includes four light receiving units 115a to 115a.
15d, and the light receiving units 115a and 115b and the light receiving units 115c and 115d are respectively arranged at close positions,
Light receiving units 115a and 115b and light receiving units 115c and 115d
Is set to a desired beam interval. And
When the respective outputs of the light receiving units 115 to 115d are A to D,
So that the differential output (AB)-(CD) becomes zero,
Servo is applied to the two-dimensional actuator so as to move the coupling lens or the laser diode.

Next, a second example of a conventional optical scanning device having a means for adjusting the beam interval will be described with reference to FIGS. 12 and 13, for example, one disclosed in Japanese Patent Application Laid-Open No. 63-50809. I do.

FIG. 12 is an explanatory diagram showing the configuration of an optical scanning device having a beam interval adjusting means. In this optical scanning device, the first beam emitted from the first laser diode 121 passes through the coupling lens 123, the aperture 125, and the half-wave plate 127, and passes through the polarization beam splitter 128. On the other hand, the second laser diode 1
The second beam emitted from 22 is reflected by the polarization beam splitter 128 via the coupling lens 124 and the aperture 126, and has a predetermined interval from the first beam, and is in the same direction as the first beam. move on. The first and second beams emitted from the polarizing beam splitter 128 are:
Passing through a quarter-wave plate 129 and a cylinder lens 130
The light is deflected by a deflector 131 having a rotating polygonal mirror, is irradiated on a photosensitive member 136 via a scanning lens 132 and a mirror 135, and scans two adjacent lines on the photosensitive member 136. A beam outside the scanning area on the scanning start end side is received by the synchronization detector 134 via the cylinder lens 133.

In this optical scanning device, a prism 137 is inserted into at least one of the optical paths of the first laser diode 121 and the second laser diode 122, and the angle of the prism 137 is changed to thereby change the beam interval in the sub-scanning direction. Can be adjusted.

FIG. 13 is a sectional view of the prism 137 in FIG. As shown in FIG.
Is a prism main body 137a and the prism main body 137
a, a prism holding plate 137b rotatable about a fulcrum 137c, and an adjusting screw 141 for adjusting the position of the prism holding plate 137b. By turning the adjusting screw 141, the emission angle of the beam from the prism is obtained. Changes by Δθ.

According to the first and second examples described above, the dot interval on the surface to be scanned can be changed by a predetermined operation, so that high-resolution printing and high-speed printing can be realized.

[0013]

However, in the first example, since the laser diode or the coupling lens near the laser diode is moved by the actuator to adjust the dot interval, the photosensitive member is moved with respect to the amount of movement of the actuator. Since the sensitivity of the above-mentioned fluctuation of the dot interval is extremely high, there is a problem that adjustment is difficult and high-precision adjustment is difficult.

Further, since the adjustment is performed at the light source portion of the laser, the main scanning direction of the photosensitive member is shifted, or the dot diameter is unstable because it is used in a state shifted from the focal position of the coupling lens. There is a problem that becomes.

In the second example, the dot interval is less sensitive to the amount of movement of the prism than in the first example, so that the dot interval can be easily adjusted. However, since the prism is used, the prism is used. Of the scanning lens has an angle in the sub-scanning direction, and the beam does not pass through the optical axis of the scanning lens.
Therefore, there is a problem that the scanning line is bent on the photoconductor.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device for simultaneously scanning a plurality of lines by a plurality of light beams, wherein the beam interval can be adjusted with high accuracy and the occurrence of deflection of the scanning lines can be prevented. It is to provide a scanning device.

[0017]

An optical scanning device according to the present invention comprises a light source section for generating a plurality of light beams having different optical characteristics, and a light beam from the light source section is deflected to form a light beam on a surface to be scanned. A deflector for scanning, a focusing optical system for focusing each light beam deflected by the deflector on the surface to be scanned, and a light beam provided between the focusing optical system and the surface to be scanned. Having a plurality of reflecting surfaces that selectively reflect each light beam based on the optical characteristics of the light beams, each light beam that has passed through the imaging optical system is reflected by a reflecting surface that selectively reflects each light beam. A mirror for adjusting a beam interval that changes the beam interval of a plurality of emitted light beams by changing an angle with respect to each of the incident light beams while reflecting the light beam on the surface to be scanned is provided.

In this optical scanning device, each light beam from the light source unit is deflected by a deflector, and has an image forming optical system and a beam interval adjustment having a plurality of reflecting surfaces for selectively reflecting each light beam. The light is focused on the surface to be scanned via the mirror for scanning and scans the surface to be scanned. Further, since the beam interval of a plurality of light beams emitted changes by changing the angle of the beam interval adjusting mirror, the beam interval can be adjusted by adjusting the angle of the beam interval adjusting mirror.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 8 relate to one embodiment of the present invention.

FIG. 1 is an explanatory diagram showing the entire configuration of the optical scanning device, and FIG. 2 is an explanatory diagram of the optical scanning device of FIG. 1 as viewed from the axial direction of the photosensitive member. As shown in these figures, the optical scanning device of the present embodiment includes a first laser diode 1 for emitting a first beam 41 of P-polarized light and a second beam 4 of S-polarized light.
A second laser diode 2 that emits light 2, coupling lenses 3 and 4 that convert the beams emitted from the laser diodes 1 and 2 into parallel light beams, and coupling lenses 3 and 4.
From each other are respectively incident on orthogonal planes,
Polarizing beam splitter 5 that transmits the first beam 41, reflects the second beam 42, and emits both beams in the same direction.
A deflector 8 for deflecting each beam from the polarization beam splitter 5; a folding mirror 6 for causing each beam from the polarization beam splitter 5 to enter a rotating polygon mirror of the deflector 8; A cylinder lens 7 is provided between the deflectors 8 and constitutes a part of an optical system for correcting a tilt of the rotary polygon mirror of the deflector 8.

The optical scanning device further includes a scanning lens system 9 for imaging each beam deflected by the deflector 8 on the photosensitive member 13, and a scanning unit between the scanning lens system 9 and the photosensitive member 13. A cylinder mirror 10, an interval adjustment mirror 11, and a registration adjustment mirror 12 are provided in this order from the lens system 9 side. The cylinder mirror 10 constitutes a part of an optical system for correcting the tilt of the rotary polygon mirror of the deflector 8. The interval adjusting mirror 11 adjusts the interval between the two beams, and will be described later in detail.
The registration adjustment mirror 12 is for adjusting the beam position on the photoconductor 13.

The optical scanning device further includes a pickup mirror 15 for reflecting a beam deflected by the deflector 8 out of the scanning area on the scanning start end side,
The lens 1 provided on the optical path of the reflected light of the mirror 15
6, a photosensor 17, a pickup mirror 20 that reflects a beam out of the scanning area on the scanning end end side of the beam deflected by the deflector 8, and a triangle provided on the optical path of the light reflected by the mirror 20. Slit 21
And a photo sensor 22. The photo sensor 17 outputs a synchronizing signal for controlling a writing position of an image. The triangular slit 21 and the photo sensor 22 are for detecting the interval between two beams.

In this optical scanning device, the first P-polarized beam 41 emitted from the first laser diode 1 is
The light is converted into a parallel light beam by the coupling lens 3 and passes through the polarization beam splitter 5. On the other hand, the S-polarized second beam 42 emitted from the second laser diode 2 is converted into a parallel light beam by the coupling lens 4, reflected at a right angle by the polarization beam splitter 5, and in the same direction as the first beam 41. Proceed to. Each beam emitted from the polarizing beam splitter 5 passes through a folding mirror 6 and a cylinder lens 7,
The light is reflected and deflected by the deflector 8, and is irradiated onto the photoconductor 13 via the scanning lens system 9, the cylinder mirror 10, the interval adjusting mirror 11, and the registration adjusting mirror 12. Further, by changing the angle of the interval adjusting mirror 11 with respect to each incident beam, the interval between two beams emitted from the interval adjusting mirror 11, that is, the dot interval in the sub-scanning direction is adjusted. Further, in order to align the dots on the photoconductor 13 in the sub-scanning direction, the dot positions are corrected by the registration adjusting mirror 12. When the interval adjusting mirror 11 is disposed near the photoconductor 13, the registration adjusting mirror 12
Becomes unnecessary.

In the image forming apparatus having the optical scanning device, the photosensitive member 13 is uniformly charged in accordance with a normal xerographic process, and the photosensitive member 13 is irradiated with two laser beams modulated according to image data. 13, an electrostatic latent image is formed, toner is attached to the electrostatic latent image by a developing device, and the electrostatic latent image is visualized as a toner image.
The transfer device transfers the toner image to the sheet.

Next, the distance adjusting mirror 11 will be described in detail with reference to FIGS. FIG. 3 is an explanatory view showing the vicinity of the gap adjusting mirror 11, and FIG. 4 is a sectional view of the gap adjusting mirror 11.

As shown in FIG. 3, the distance adjusting mirror 11
Is held by a bracket 25 that is rotatable about a fulcrum 26. The bracket 25 has a torsion spring 27 in contact with one surface, and a feed screw 28 in contact with the other surface. Then, by rotating the feed screw 28, the angles of the bracket 25 and the gap adjusting mirror 11 can be adjusted.

As shown in FIG. 4, the distance adjusting mirror 11
Is a reflective layer 3 that reflects only P-polarized light on the surface of the transparent plate 30.
1 is coated, and the back surface is coated with a reflective layer 32 that reflects only S-polarized light.

As shown in FIG. 3, a first beam 41 of P-polarized light and a second beam 42 of S-polarized light are
Is incident on the first beam 41, the distance adjusting mirror 1
Since the first beam 41 and the second beam 42 are reflected at the first surface and the second beam 42 are reflected at the back surface of the interval adjusting mirror 11, the first beam 41 and the second beam 42 are parallel at a predetermined interval d unless the incident angle is zero. Is emitted from the interval adjusting mirror 11. Then, the interval d between the two beams changes according to the angle of the interval adjusting mirror 11 with respect to the incident beam.

Feed screw 28 for rotating bracket 25
Are rotated by a driving device (not shown). This drive device performs servo control based on the beam interval detected by the photo sensor 22 so that the beam interval d becomes a desired value.

Since the optical path length is different between the front surface reflection and the back surface reflection of the gap adjusting mirror 11, it is necessary to correct the focus of the laser diode and the coupling lens in advance in order to correct the focus position on the photosensitive member 13. is necessary. Further, since the scanning speed on the photoconductor 13 varies depending on the optical path length, it is necessary to correct the beam modulation speed in order to make the dot interval in the main scanning direction equal for the two beams.

When three or more beams are used, the optical characteristics of each beam are made different, and the distance adjusting mirror 11 is used.
By forming a plurality of reflecting surfaces for selectively reflecting each beam based on the optical characteristics of each beam, it is possible to adjust the beam interval as in the case of two beams. FIG. 5 shows an example of the interval adjusting mirror 11 when three beams are used. The distance adjusting mirror 11 shown in FIG.
0 is coated with a reflective surface 31 that reflects only P-polarized light, a back surface is coated with a reflective surface 32 that reflects only S-polarized light, and a transparent plate 33 is laminated below the reflective surface 32. Is coated with a reflective surface 34 that reflects only light of a specific wavelength. The reflecting surfaces 31 and 32 transmit light of a specific wavelength reflected by the reflecting surface 34. When using the interval adjusting mirror 11 shown in FIG. 5, as the three beams, the first beam is a P-polarized beam of a specific wavelength reflected by the reflecting surface 31, the second beam is transmitted through the reflecting surface 31, An S-polarized beam of a specific wavelength reflected by the third beam uses a specific wavelength beam having a wavelength different from the above, which transmits through the reflecting surfaces 31 and 32 and is reflected by the reflecting surface.

Next, the triangular slit 21 and the photo sensor 22 will be described in detail with reference to FIGS.
FIG. 6 is a plan view of the triangular slit 21 and the photo sensor 22, and FIG. 7 is a side view thereof. As shown in these figures, the triangular slit 21 is formed, for example, by etching a 5 × 10 mm right-angled triangular hole in a stainless steel plate having a thickness of 100 μm by etching, and a photo sensor 22 is provided behind the hole. I have. As shown in FIG. 7, a photo sensor drive board 23 that drives the photo sensor 22 is connected to the photo sensor 22. The triangular slit 21 and the photo sensor 22 are arranged so that the beam crosses in the direction indicated by reference numeral 24 in FIG.

The photo sensor 22 outputs a pulse having a width corresponding to the position where the beam passes through the hole of the triangular slit 21. FIGS. 8A and 8B show the first beam and the second beam, respectively.
3 shows an example of an output pulse of the photo sensor 22 when the light passes through the beam. As shown in these figures, if the pulse width at the time of passing the first beam is t ₁ and the pulse width at the time of passing the second beam is t ₂ , the beam interval can be obtained from t ₂ −t ₁ . When measuring the pulse widths t ₁ and t ₂ , only one of the beams is emitted and measured separately.

Next, the sensitivity of the change in the angle of the space adjustment mirror 11 and the change in the dot space will be described.

For example, the distance adjusting mirror 11 shown in FIG.
The thickness of the transparent plate 30 is 4 mm, the angle of incidence of the beam on the gap adjusting mirror 11 is 30 degrees, the distance from the fulcrum 26 of the bracket 25 to the contact point of the feed screw 28 is 30 mm, and the distance from the gap adjusting mirror 11 to the photosensitive member 13 is 30 mm. Assuming that a 50 mm optical system is designed, the distance traveled by the feed screw 28 to rotate the gap adjusting mirror 11 for one minute is 9 μm, and the pitch for pitch adjustment is 2.63 μm. At this time, the amount of movement of the lead register (beam irradiation position on the photoconductor 13) is 29.
Although it is 1 μm, it is natural that the spacing adjustment pitch becomes smaller or larger by changing the above conditions. Although the focus difference between the front surface reflection and the back surface reflection of the gap adjusting mirror 11 is 2.71 mm, it can be sufficiently corrected by focusing the laser diode and the coupling lens.

As described above, according to the present embodiment, 2
Since the adjustment of the interval between the two beams is performed by the interval adjusting mirror 11 provided at the subsequent stage of the scanning lens system 9, the sensitivity of the variation of the dot interval on the photoconductor 13 to the moving amount of the interval adjusting mirror 11 is reduced. The dot spacing can be adjusted with low accuracy. Further, since the configuration behind the cylinder lens 7 is the same for the two beams, the configuration is simple. Further, since both beams pass through the optical axis of the scanning lens system 9, it is possible to prevent the scanning line from being bent.

[0037]

As described above, according to the present invention, the beam interval of a plurality of light beams is adjusted by the beam interval adjusting mirror provided between the imaging optical system and the surface to be scanned. Therefore, when a plurality of lines are simultaneously scanned by a plurality of light beams, the beam interval can be adjusted with high accuracy. Further, since a plurality of light beams can pass through the optical axis of the image forming optical system, there is an effect that bending of a scanning line can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an overall configuration of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the optical scanning device of FIG. 1 as viewed from an axial direction of a photoconductor.

FIG. 3 is an explanatory view showing the vicinity of an interval adjusting mirror in FIG. 1;

FIG. 4 is a cross-sectional view of the interval adjusting mirror in FIG.

FIG. 5 is a sectional view showing another example of the interval adjusting mirror in FIG. 1;

FIG. 6 is a plan view of a triangular slit and a photosensor in FIG. 1;

FIG. 7 is a side view of the triangular slit and the photo sensor of FIG. 6;

8 is a waveform diagram showing an example of an output pulse of the photo sensor of FIG.

FIG. 9 is an explanatory diagram showing a configuration of a conventional optical scanning device.

FIG. 10 is an explanatory diagram showing a configuration of a conventional optical scanning device having a beam interval adjusting unit and a beam interval detecting unit.

FIG. 11 is an explanatory diagram showing the photodetector in FIG.

FIG. 12 is an explanatory diagram showing a configuration of a conventional optical scanning device having a beam interval adjusting unit.

FIG. 13 is a sectional view of the prism in FIG.

[Explanation of symbols]

1, 2 laser diode, 5 polarization beam splitter, 8 deflector, 9 scanning lens system, 11 interval adjusting mirror, 13 photoconductor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 26/10

Claims (1)

(57) [Claims] A light source for generating a plurality of light beams having different optical characteristics; a deflector for deflecting each light beam from the light source to scan a surface to be scanned; An imaging optical system for converging each of the formed light beams on the surface to be scanned; and an optical system provided between the imaging optical system and the surface to be scanned. A plurality of reflecting surfaces that selectively reflect light, each light beam that has passed through the imaging optical system is reflected by a reflecting surface that selectively reflects each light beam, and is guided onto the surface to be scanned. An optical scanning device, comprising: a beam spacing adjusting mirror that changes a beam spacing of a plurality of light beams emitted by changing an angle with respect to each of the light beams.