JP2000147396A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To individually detect two laser beams by two mirrors reflecting two laser beams and one laser beam detection sensor used in the conventional method in an image forming device using two laser beams. SOLUTION: A reflection mirror 8 for a laser 1, a reflection mirror 9 for a laser 2 and the laser beam detection sensor 7 are disposed so that an optical distance between the mirror 8 and the sensor 7 may be equal to an optical distance between the mirror 9 and the sensor 7. Thus, two laser beams having a time difference in scanning a position in the same scanning direction being several 100 ns are surely detected by one laser beam detection sensor whose conventional response speed is several μs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus equipped with a two-beam laser.

[0002]

2. Description of the Related Art FIG. 7 is a diagram for explaining a conventional technique.
The laser beam radiated radially by the one-beam laser diode 16 is converted into parallel light by the collimator lens 2, and focused only on the polygon mirror 4 provided for scanning the laser beam by the cylindrical lens 3 in the vertical direction. . The laser beam scanned by the polygon mirror 4 is converted again by the toric lens 5 into parallel light. With the cylindrical lens 3 and the toric lens 5, a change in the optical path due to an error in the tilt angle of the polygon mirror 4 can be corrected. The laser beam that has passed through the toric lens 5 keeps the laser beam scanning speed on the photosensitive drum 11 constant by the fθ lens 6,
In addition, the laser beam is focused on the surface of the photosensitive drum 11 and the laser beam spot diameter on the photosensitive drum 11 is corrected to be constant. The laser beam passing through the fθ lens 6 is irradiated on the surface of the photosensitive drum 11 by the reflection mirror 10.

The conventional one-beam laser detection system will be described below. The laser beam is reflected by the mirror 13 provided in the non-image area, and the laser beam is emitted to the laser beam detection sensor 7. The laser beam detection sensor 7 detects the laser beam and uses it as a signal for determining an image writing position in the main scanning direction.

Conventionally, the above-mentioned means has detected the writing start position of the one-beam laser in the main scanning direction by one laser beam detection sensor.

[0005] By analogy with the above configuration, by providing another laser beam reflecting mirror 13 and another laser beam detection sensor 7, it is possible to detect two laser beams by the conventional technique.

[0006]

However, when two laser beams are detected by two laser beam detecting sensors, a reflecting mirror for reflecting the laser beam and a laser beam detecting method are used as compared with a configuration in which one laser beam is detected. Since it is necessary to provide one sensor at a time, it is inevitable that the cost is increased as compared with a device that detects one laser beam. In addition, the wiring and circuit components associated with the newly provided laser beam detection sensor cause cost increase and complicated configuration.

When two laser beams are detected by the laser beam detection sensor used in the conventional example, the response speed of the laser beam detection sensor is about several μs, and each laser beam is irradiated to the laser beam detection sensor. Since the time difference is at most several hundred ns, the two laser beam detections cannot be reliably separated.

Further, when two laser beams are detected by the laser beam detection sensor used in the conventional example, since the angles of the laser beams applied to the laser beam detection sensors are different from each other, the error of each laser beam detection becomes large. There was a problem.

A first object of the present invention is to provide an image forming apparatus using two laser beams, two mirrors for reflecting two laser beams, and one mirror conventionally used.
Two laser beams are individually detected by one laser beam detection sensor.

A second object of the present invention is to reduce a laser beam detection error when two laser beams are irradiated on a laser beam detection sensor at different angles in an image forming apparatus using two laser beams. It seeks to provide a means.

[0011]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a conventional laser beam detecting sensor having a response speed of several μs; The two laser beams are surely detected. A laser beam reflecting mirror is provided in each of the non-image area at the start of writing in the main scanning direction and the non-image area at the end of writing in the main scanning direction. It is intended to provide a method for surely detecting a beam. With this configuration, the cycle of each laser beam applied to the laser beam detection sensor can be made sufficiently longer than the response speed of the conventional laser beam detection sensor. By arranging the laser beams on the laser beam detection sensor at the positions of L1 = L2 so that the spot diameters of the laser beams are the same, the laser beam detection error can be reduced.

In order to achieve the first object, an image forming apparatus according to a second aspect of the present invention comprises a conventional laser beam detection sensor having a response speed of several μs and a time difference of 100 n.
s is surely detected. A laser beam reflecting mirror is provided in each of the non-image area at the start of writing in the main scanning direction and the non-image area at the end of writing in the main scanning direction. It is intended to provide a method for surely detecting a beam. With this configuration, the cycle of each laser beam applied to the laser beam detection sensor can be made sufficiently longer than the response speed of the conventional laser beam detection sensor. A laser beam detection error can be reduced by arranging the laser beams on the laser beam sensor at the positions of L3-L1 = L2-L3 so that the spot diameters of the laser beams are the same.

[0013] In order to achieve the third object, the two laser beams are irradiated to the laser beam detection sensor at different incident angles from each other. It is characterized in that two laser beam spot diameters on the light receiving element surface of the sensor are made the same, and a laser beam detection error is reduced.

[0014]

(Embodiment 1) FIG. 1 is a diagram illustrating a main-scanning-direction image writing position detecting means using a two-beam laser according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 1 denotes a laser diode that emits a two-beam laser. The laser beam radiated radially by the two-beam laser diode 1 is converted into parallel light by the collimator lens 2 and is focused only on the polygon mirror 4 provided for scanning the laser beam by the cylindrical lens 3 only in the vertical direction. . The laser beam scanned by the polygon mirror 4 is converted again by the toric lens 5 into parallel light. With the cylindrical lens 3 and the toric lens 5, it is possible to correct an optical path change due to an error in the surface tilt angle of the polygon mirror 4. The laser beam that has passed through the toric lens 5 keeps the laser beam scanning speed on the photosensitive drum 11 constant by the fθ lens 6, and focuses the laser beam on the surface of the photosensitive drum 11 to reduce the laser beam spot diameter on the photosensitive drum 11. Correct to a constant. fθ lens 6
Is irradiated on the surface of the photosensitive drum 11 by the reflection mirror 10.

The laser beam detection system in the first embodiment will be described below. In the first embodiment, two laser beams are used, so that two laser beams are respectively detected. Here, as shown in the two-beam laser circuit diagram of FIG. First, the reflection mirror 8 provided in the non-image area on the side of the image writing start position in the main scanning direction reflects only the laser 1 to the laser beam detection sensor 7. The reflection mirror 9 provided in the non-image area on the image writing end position side in the main scanning direction reflects only the laser 2 to the laser beam detection sensor 7.

As shown by the optical distance in FIG. 2, the laser beam sensor 7 is positioned such that L1 = L2 so that the spot diameters of the laser beams of the laser 1 and the laser 2 coincide on the laser beam sensor 7. To be provided. This is because if the optical distances are the same, the spot diameters become the same, and if the spot diameters of the two laser beams on the laser beam detection sensor 7 are the same, the laser beam detection error can be reduced. .

The laser beam detection sensor 7 detects a laser beam, and the detection signal is used as a signal for determining an image writing position. The laser beam detection sensor 7 is provided on a laser beam scanning surface, that is, on a non-image area above or below an image area.

FIG. 5 is a time chart for explaining the light emission timing of the laser 1 and the laser 2. Reflection mirror 8
In the vicinity, only the laser 1 emits light, and in the vicinity of the reflection mirror 9, only the laser 2 emits light. The scanning cycle of the laser beam from the reflecting mirror 8 to the reflecting mirror 9 is several 100 μs. By providing a mirror so that a non-image area on the image writing start position side and a non-image area on the image writing end position side, that is, a cycle sufficiently longer than the response cycle (several μs) of the laser beam detection sensor 7 can be obtained. Even with a conventional laser beam detection sensor having a response speed of several μs, the time difference for scanning the same scanning direction position is several hundreds.
ns can be reliably detected.

FIG. 6 shows a reflection mirror 8 and a reflection mirror 9.
The laser beam reflected by the laser beam detection sensor 7
FIG. 4 is a side view of a laser beam detection sensor in which the incident angle is different but the laser beam spot diameter is the same on the light receiving element surface 15. Regardless of the angle of the laser beam incident on the upper surface of the light receiving element 15 by the condenser lens 14, the spot diameter of the laser beam on the light receiving element 15 is corrected to be the same.

(Embodiment 2) FIG. 3 shows Embodiment 2 of the present invention.
FIG. 4 is a diagram illustrating a main-scanning-direction image writing position detecting unit using a two-beam laser, which shows the following.

In FIG. 3, reference numeral 1 denotes a laser diode that emits a two-beam laser. The laser beam radiated radially by the two-beam laser diode 1 is converted into parallel light by the collimator lens 2 and is focused only on the polygon mirror 4 provided for scanning the laser beam by the cylindrical lens 3 only in the vertical direction. . The laser beam scanned by the polygon mirror 4 is converted again by the toric lens 5 into parallel light. Polygon mirror 4 with cylindrical lens 3 and toric lens 5
Can be corrected for the optical path change due to the error of the surface tilt angle in the above. The laser beam that has passed through the toric lens 5 keeps the laser beam scanning speed on the photosensitive drum 11 constant by the fθ lens 6, and focuses the laser beam on the surface of the photosensitive drum 11 to reduce the laser beam spot diameter on the photosensitive drum 11. Correct to a constant. The laser beam passing through the fθ lens 6 is irradiated on the surface of the photosensitive drum 11 by the reflection mirror 10.

The laser beam detection system according to the second embodiment will be described below. In the second embodiment, two laser beams are used, so that two laser beams are respectively detected. Here, as shown in the two-beam laser circuit diagram of FIG. 3, the two laser beams are referred to as laser 1 and laser 2, respectively. First, the reflection mirror 8 provided in the non-image area on the side of the image writing start position in the main scanning direction reflects only the laser 1 to the laser beam detection sensor 7. The reflection mirror 9 provided in the non-image area on the image writing end position side in the main scanning direction reflects only the laser 2 to the laser beam detection sensor 7.

As shown by the optical distance in FIG. 4, the laser beam 2 reflected by the reflection mirror 9 is focused once, diverges again, and is irradiated on the laser beam detection sensor 7. The laser beam detection sensor 7 is provided at a position where L3−L1 = L2−L3 so that the spot diameters of the laser beams of the laser 1 and the laser 2 match on the laser beam detection sensor 7. Here, L1 is the optical distance from the reflection mirror 8 to the laser beam detection sensor 7, L2 is the optical distance from the reflection mirror 9 to the laser beam detection sensor 7, and L3 is the distance from the reflection mirror 9 to the focal point of the laser 2. is there. This is because the laser beam detection error can be reduced if the spot diameters of the two laser beams on the laser beam detection sensor 7 are the same.

The laser beam detecting sensor 7 detects the laser beam and uses it as a signal for determining an image writing position in the main scanning direction. The laser beam detection sensor 7 is provided in a non-image area.

FIG. 5 is a time chart for explaining the light emission timing of the laser 1 and the laser 2. Reflection mirror 8
In the vicinity, only the laser 1 emits light, and in the vicinity of the reflection mirror 9, only the laser 2 emits light. The scanning cycle of the laser beam from the reflecting mirror 8 to the reflecting mirror 9 is several 100 μs. By providing a mirror so that a non-image area on the image writing start position side and a non-image area on the image writing end position side, that is, a cycle sufficiently longer than the response cycle (several μs) of the laser beam detection sensor 7 can be obtained. Even with a conventional laser beam detection sensor having a response speed of several μs, the time difference for scanning the same scanning direction position is several hundreds.
ns can be reliably detected.

FIG. 6 shows a reflection mirror 8 and a reflection mirror 9.
The laser beam reflected by the laser beam detection sensor 7
FIG. 4 is a side view of a laser beam detection sensor in which the incident angle is different but the laser beam spot diameter is the same on the light receiving element surface 15. Regardless of the angle of the laser beam incident on the upper surface of the light receiving element 15 by the condenser lens 14, the spot diameter of the laser beam on the light receiving element 15 is corrected to be the same.

[0028]

As described above, according to the present invention,
Conventional laser beam detection sensors having a response speed of several μs can reliably detect two laser beams having a time difference of several hundred ns for scanning the same scanning direction position.
Further, by performing two laser beam detections performed by the two laser beam detection sensors with one laser beam detection sensor, the cost can be reliably reduced.

Further, according to the present invention, the two laser beam spot diameters on the light receiving element surface of the laser beam detection sensor can be made the same, and the laser beam detection error can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view of an image forming apparatus for explaining a laser beam detection method according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an optical distance according to the first embodiment of the present invention.

FIG. 3 is an outline view of an image forming apparatus for explaining a laser beam detection system according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating an optical distance according to a second embodiment of the present invention.

FIG. 5 is a time chart showing timings at which lasers 1 and 2 emit light according to the first embodiment of the present invention.

FIG. 6 is a side view of a two-beam laser detection sensor according to an embodiment of the present invention.

FIG. 7 is an outline view of an image forming apparatus for explaining a laser beam detection system according to a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 2 beam laser diode 2 collimator lens 3 cylindrical lens 4 polygon mirror 5 toric lens 6 fθ lens 7 laser beam detection sensor 8 reflection mirror for laser 1 9 reflection mirror for laser 2 10 reflection mirror to photosensitive drum 11 photosensitive drum 12 laser beam 13 Reflection mirror for laser beam 14 Condensing lens 15 Light receiving element surface 16 One-beam laser diode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 BA69 BA82 BA87 BA89 BA90 BB30 DA03 DA09 2H045 CA89 2H076 AB05 AB06 AB12 AB18 EA05 EA06 5C072 AA03 BA02 BA04 BA19 DA04 DA21 HA02 HA06 HA08 HA13 HB08

Claims (3)

[Claims] 1. A laser diode for emitting two laser beams, a collimator lens for converting two laser beams radially emitted by the laser diode into parallel light, and a rotation for raster-scanning the parallelized laser beam. A multi-mirror surface, a cylindrical lens that focuses the two laser beams output from the collimator lens only in the vertical direction on the rotating multi-mirror surface, and the two laser beams raster-scanned on the rotating multi-mirror surface again into parallel light. A toric lens for conversion, an fθ lens for converging the two laser beams output from the toric lens on a photosensitive drum surface and scanning at a constant speed, and one laser beam detector for individually receiving the two laser beams A sensor, a first laser beam of the two laser beams First reflecting mirror for reflecting the Zabimu detection sensor, a second of said two laser beams
In the image forming apparatus having a second reflection mirror for reflecting the laser beam to the laser beam detection sensor, the first reflection mirror is provided in the non-image area on the position where writing of the image in the main scanning direction starts, and the second reflection mirror is The optical distance from the first reflection mirror to the laser beam detection sensor is set to L1, the second to the laser beam detection sensor.
When the optical distance from the reflection mirror to the laser beam detection sensor is L2, the first reflection mirror, the second reflection mirror, and the laser beam detection sensor are arranged at positions where L1 = L2. An image forming apparatus. 2. A laser diode for emitting two laser beams, a collimator lens for converting two laser beams radially emitted by the laser diode into parallel light, and a rotation for raster-scanning the parallelized laser beam. A multi-mirror surface, a cylindrical lens that focuses the two laser beams output from the collimator lens only in the vertical direction on the rotating multi-mirror surface, and the two laser beams raster-scanned on the rotating multi-mirror surface again into parallel light. A toric lens for conversion, an fθ lens for converging the two laser beams output from the toric lens on a photosensitive drum surface and scanning at a constant speed, and one laser beam detector for individually receiving the two laser beams A sensor, a first laser beam of the two laser beams First reflecting mirror for reflecting the Zabimu detection sensor, a second of said two laser beams
In the image forming apparatus having a second reflection mirror for reflecting the laser beam to the laser beam detection sensor, the first reflection mirror is provided in the non-image area on the position where writing of the image in the main scanning direction starts, and the second reflection mirror is The optical distance from the first reflection mirror to the laser beam detection sensor is set to L1, the second to the laser beam detection sensor.
L2 is the optical distance from the reflection mirror to the laser beam detection sensor, and the optical distance between the position where the second laser beam reflected from the second reflection mirror is focused and the second reflection mirror is L2. When L3, L3−L1 =
The image forming apparatus according to claim 1, wherein the first reflection mirror, the second reflection mirror, and the laser beam detection sensor are disposed at positions L2 to L3. 3. The image forming apparatus according to claim 1, wherein the first laser beam and the second laser beam are at different angles from the first reflection mirror and the second reflection mirror. Is irradiated, so that the first laser beam and the second laser beam are uniformly collected on a light receiving element surface of the laser beam detection sensor. An image forming apparatus, further comprising: a condenser lens.