KR100460969B1 - Tandem type laser scanning unit of image forming device - Google Patents

Abstract

A tandem laser scanning unit of an image forming apparatus is disclosed. In the tandem laser scanning unit of the disclosed image forming apparatus, the first step value between the exit point of the laser beam and the normal of the polygon mirror passing through the center of the polygon mirror is the incident point on the polygon mirror of the laser beam and the polygon. The laser diode is arranged toward the polygon mirror so as to be larger than the second step value between the normals of the polygon mirror passing through the center of the mirror, so that the height of the polygon mirror can be reduced while increasing the pitch between the laser beams. The rotational load of the polygon mirror driving unit can be reduced, so that a high output driving unit is not required, thereby reducing the cost. Furthermore, by adding a configuration in which the bow distortion correction means is applied on the optical path between the polygon mirror and the photosensitive drum, the deterioration in print quality due to bow distortion can be prevented.

Description

Tandem type laser scanning unit of an image forming apparatus {Tandem type laser scanning unit of image forming device}

The present invention relates to a tandem laser scanning unit of an image forming apparatus.

In general, an image forming apparatus using a laser forms a laser beam emitted from a laser diode on a photosensitive drum by a video signal of an input image, and sprays toner onto a latent image formed on the photosensitive drum and transfers the image onto a medium such as paper. It is a device that reproduces an image.

A configuration of a conventional laser scanning unit that emits a plurality of laser beams from such a laser printer and forms an image on a plurality of photosensitive drums will be described with reference to FIG.

1 is a front view schematically showing a conventional tandem laser scanning unit.

As shown in the figure, a conventional tandem laser scanning unit includes a laser diode 1, a collimator lens 2, a cylinder lens 3, a polygon mirror 4, an Fθ lens 5 and a reflection mirror 6 It is provided.

The laser diode 1 emits a laser beam used as a light source. Conventionally, four first to fourth laser diodes 1a to 1d are arranged in a line, and the tilt of the laser diode is adjusted so that the center of the emitted laser beam is parallel to the optical axis R1.

The collimator lens 2 makes the laser beams emitted from each of the first to fourth laser diodes 1a to 1d arranged in a row into parallel beams with respect to the optical axis R1.

The cylinder lens 3 makes each parallel beam passing through the collimator lens 2 into a linear beam in the horizontal direction with respect to the scanning direction. That is, the laser beam passing through the collimator lens 2 is converted into a slit beam.

The polygon mirror unit 4 is comprised of the polygon mirror 4a and the drive part 4b. The polygon mirror 4a is pivotally rotated by the driving unit 4b so that the horizontal linear beam passing through the cylinder lens 3 is scanned while moving at an isotropic speed.

The F [theta] lens 5 focuses and polarizes the laser beam refracted at the isoline velocity in the polygon mirror 4a.

The reflecting mirror 6 reflects the laser beam passing through the Fθ lens 5 to the photosensitive drum 9 so that the laser beam is imaged on the outer peripheral surface of the photosensitive drum 9.

However, the laser scanning unit of the conventional image forming apparatus having the above configuration has the following problems, and improvement is required.

First, when four laser diodes are arranged in a line as shown in FIG. 1, the height of the polygon mirror is increased due to the height of the optical components such as the laser diode and the lens.

Second, the polygon mirror has a limitation in size because it requires the precision of the surface must be high, it is not easy to manufacture a high-height polygon mirror while maintaining the surface.

Third, due to the increase in the weight of the polygon mirror as the height of the polygon mirror increases, the rotational load of the polygon mirror becomes large, and there is a problem that a high output driving unit is required.

The present invention has been made to solve the above problems, and provides a tandem laser scanning unit of an image forming apparatus capable of performing an image forming process while reducing the height of a polygon mirror even when using multiple laser beams by a plurality of laser diodes. Its purpose is to.

1 is a front view schematically showing a tandem laser scanning unit of a conventional image forming apparatus;

2 is a front view schematically showing a tandem laser scanning unit of the image forming apparatus according to an embodiment of the present invention;

3 is an enlarged front view of a portion P in FIG. 2;

4 is a perspective view showing a scanning line of a laser beam scanned on a photosensitive drum outer circumferential surface according to an embodiment of the present invention;

5 is a perspective view illustrating that a laser beam reflected from a reflection mirror is reflected from a cylinder mirror and scanned onto a photosensitive drum outer circumferential surface according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

One; Laser diode 2; Collimator lens

3; Cylinder lens 14; Polygon mirror

5; Fθ lens 6; Reflective mirror

17; Cylinder mirror 9; Photosensitive drum

A tandem laser scanning unit of an image forming apparatus according to the present invention for achieving the above object is to scan a plurality of laser beams emitted from a laser diode in accordance with a video signal of an input image to a plurality of photosensitive drums using a polygon mirror In a tandem laser scanning unit of an image forming apparatus, a first step value between an exit point of the laser beam and a normal line of the polygon mirror passing through a center of the polygon mirror is defined as an incident point on the polygon mirror of the laser beam and the Corrects bow distortion caused by a laser diode disposed toward the polygon mirror and an arrangement structure of the laser diode with respect to the polygon mirror so as to be larger than a second step value between the normals of the polygon mirror passing through the center of the polygon mirror. It comprises a bow distortion correction means for It shall be.

According to a preferred embodiment of the present invention, the bow distortion correction means is located on the optical path between the polygon mirror and the photosensitive drum.

Here, the bow distortion correction means is characterized in that it comprises a cylinder mirror.

The plurality of laser diodes may be arranged symmetrically with respect to the normal of the polygon mirror passing through the center of the polygon mirror.

A tandem laser scanning unit of an image forming apparatus according to the present invention for achieving the above object is to scan a plurality of laser beams emitted from a laser diode in accordance with a video signal of an input image to a plurality of photosensitive drums using a polygon mirror In a tandem laser scanning unit of an image forming apparatus, a first step value between an exit point of the laser beam and a normal line of the polygon mirror passing through a center of the polygon mirror is defined as an incident point on the polygon mirror of the laser beam and the Two pairs of laser diodes disposed toward the polygon mirror such that they are greater than a second step value between the normals of the polygon mirrors passing through the center of the polygon mirror, and symmetrically up-down with respect to the normals of the polygon mirrors passing through the center of the polygon mirror Characterized in that it comprises a.

According to a preferred embodiment of the present invention, each laser beam direction emitted from the two pairs of laser diodes and the normal line of the polygon mirror are each characterized by having the same angle θ.

Here, the laser beam emitted from one laser diode selected from any one of the two pairs of laser diodes, and the normal of the polygon mirror passing through the center of the polygon mirror among the other pair of the two pairs of laser diodes The laser beam emitted from the laser diode positioned in the region opposite to the region where the selected laser diode is located has the same incidence point.

And bow distortion correction means for correcting bow distortion caused by the arrangement structure of the laser diode with respect to the polygon mirror.

The bow distortion correction means is located on an optical path between the polygon mirror and the photosensitive drum.

In addition, the bow distortion correction means is characterized in that it comprises a cylinder mirror.

The above objects and other features of the present invention will become more apparent by describing the preferred embodiments of the present invention in detail with reference to the accompanying drawings. For reference, in describing the embodiments of the present invention, the same reference numerals refer to the same parts and members as those in the related art.

2 is a front view schematically showing a tandem laser scanning unit of an image forming apparatus according to an embodiment of the present invention.

Referring to the drawings, the tandem laser scanning unit of the image forming apparatus according to the present invention includes a laser diode 11, a collimator lens 2, a cylinder lens 3, a polygon mirror unit 14, an Fθ lens 5, A reflective mirror 6 and a cylinder mirror 17.

Here, the reference axis R2 is the normal of the polygon mirror 14a passing through the center of the polygon mirror 14a of the polygon mirror unit 14.

The laser diode 11 emits a laser beam used as a light source. The laser diode 11 includes four first to fourth laser diodes 11a to 11d.

The first to fourth laser diodes 11a to 11d may have a first step value between the emission point of the laser beam and the reference axis R2 and the incident point on the polygon mirror of the laser beam and the reference axis R2. Is disposed toward the polygon mirror so as to be larger than the second step value between).

That is, the first to fourth laser diodes 11a to 11d are respectively tilted so that the center direction of the emitted light has a predetermined angle θ with respect to the reference axis R2.

The first laser diode 11a and the fourth laser diode 11d are vertically symmetric about the reference axis R2, and the second laser diode 11b and the third laser diode 11c are also the reference axes R2. It is symmetrically up and down about.

A laser beam emitted from one laser diode selected from any one of the first and fourth laser diodes 11a and 11d and the second and third laser diodes 11b and 11c is incident on the polygon mirror. The first incident point is based on the reference axis R2 among the remaining pairs of the first and fourth laser diodes 11a and 11d and the second and third laser diodes 11b and 11c. The laser beam emitted from the laser diode located in an area opposite to the area where the laser diode incident to the first incident point is located includes a second incident point of entering the polygon mirror. This will be described with reference to the drawings.

3 is an enlarged front view of a portion P in FIG. 2. Referring to the drawings, the first point E1 at which the laser beam by the first laser diode 11a and the third laser diode 11c is incident on the polygon mirror 14a is shown, and the second laser diode 11b is shown. And a second point E2 at which the laser beam by the fourth laser diode 11d is incident on the polygon mirror 14a. The first optical path line La and the second optical path line Ld when the center of the emission light of each of the first laser diode 11a and the fourth laser diode 11d are parallel to the reference axis R2 are dotted lines. Shown.

In the case of having the arrangement structure of the laser diode 11 with respect to the polygon mirror 14a as in the present embodiment, the output point of the laser diode 1 and the first and second points E1 and E2 are predetermined. If the distance L, the step between the first optical path line La and the first point E1 has a value of L · tanθ. Similarly, the level difference between the second optical path line Ld and the second point E2 also has a value of L · tanθ.

By having such a structure as described above, the polygon mirror 14a which is lower by 2 · L · tanθ than the center of the emission light of the first to fourth laser diodes 11a to 11d is parallel to the reference axis R2. Even with the height of the laser beam can be scanned.

The collimator lens 2 makes the laser beam emitted from each of the first to fourth laser diodes 11a to 11d into a parallel beam with respect to the emission direction.

The cylinder lens 3 makes each parallel beam passing through the collimator lens 2 into a linear beam horizontal in the scanning direction. That is, the laser beam passing through the collimator lens 2 is converted into a slit beam.

The polygon mirror unit 14 is comprised of the polygon mirror 14a and the drive part 14b. The polygon mirror 4a is pivotally rotated by the driving unit 4b so that the horizontal linear beam passing through the cylinder lens 3 is scanned while moving at an isotropic speed.

The polygon mirror 14a according to the present invention can be significantly reduced in height while keeping the same spacing between laser beams as compared with the prior art.

The F [theta] lens 5 focuses and polarizes the laser beam refracted at the isoline velocity in the polygon mirror 4a. In addition, the Fθ lens 5 is reflected by the polygon mirror 14a to correct the focus position and scanning width of the laser beam whose optical path is changed.

The reflection mirror 6 reflects the laser beam passing through the F? Lens 5 at a predetermined angle.

Meanwhile, the present invention is characterized in that the light emitted from the laser diodes 11a to 11d is incident on the polygon mirror 14a while having a predetermined angle θ with respect to the normal of the polygon mirror 14a. With the same configuration, so-called bow distortion appears in which the scanning line for scanning the laser beam reflected by the reflecting mirror 9 does not become a straight line but a curved scanning line appears like a bow.

4 is a perspective view illustrating a scanning line of a laser beam scanned on an outer circumferential surface of the photosensitive drum.

4, the scanning line in which the laser beam reflected from the reflection mirror 6 is scanned should be a line segment SL1 indicated by a dotted line. However, the reflection mirror when the light emitted from the first to fourth laser diodes 11a to 11d is incident on the polygon mirror 14a with a predetermined angle θ with respect to the normal of the polygon mirror 14a. The scanning line in which the laser beam reflected by (6) is scanned becomes a curve SL2. That is, bow distortion appears.

Due to this bow distortion, when the laser beam is imaged on the photosensitive drum 9 and a predetermined image is printed on the paper, the thermal printing of the paper 30 appears in a curved manner, thereby degrading the image quality of the printing.

According to this embodiment, the cylinder mirror 17 is formed on the optical path between the reflection mirror 6 and the photosensitive drum 9 in order to prevent the bow distortion as described above. Bow distortion is generated because the laser beam emitted from the laser diode 11 is incident on the polygon mirror 14a while having a predetermined angle θ with respect to the normal of the polygon mirror 14a. 17 may be located on an optical path between the polygon mirror 14a and the photosensitive drum 9.

FIG. 5 is a perspective view showing that the laser beam reflected by the reflection mirror is reflected by the cylinder mirror 17 and scanned on the photosensitive drum outer circumferential surface. A description with reference to FIG. 5 is as follows.

The cylinder mirror 17, also called a curved mirror, reflects the laser beam reflected by the reflection mirror (6 in Fig. 2) to the photosensitive drum 9. As shown in FIG. 5, the cylinder mirror 17 is curved in the x-axis and y-axis directions.

Accordingly, the laser beam scanning of the laser diode 11 by bow distortion is caused by the incident and reflected light of the laser diode 11 to the polygon mirror 14a while having a predetermined angle θ with respect to the normal of the polygon mirror 14a. As the scanning line is incident on the curved reflective surface of the cylinder mirror 17, it is represented by the line segment SL3. If the cylinder mirror is a planar reflecting surface with no curved surface, a scan line like curved surface SL5 will appear.

The laser beam reflected by the cylinder mirror 17 is scanned on the outer circumferential surface of the photosensitive drum 9 so that a scanning line such as line segment SL4 appears.

By employing the cylinder mirror 17 as described above, the bow distortion appearing when the laser beam is scanned is corrected, thereby providing a good print quality.

As described above, the laser beam emitted by the four light sources is arranged on the polygon mirror 14a as the arrangement structure of the first to fourth laser diodes 11a to 11d with respect to the polygon mirror 14a as described above. First and second points E1 and E2 are formed. Therefore, according to the structure as described above, the laser diodes are arranged so that N / 2 incident points are formed on the polygon mirror 14a.

While the invention has been shown and described with respect to preferred embodiments for illustrating the principles of the invention, the invention is not limited to the construction and operation as shown and described. Rather, those skilled in the art will appreciate that various changes and modifications can be made to the present invention without departing from the spirit and scope of the appended claims. Accordingly, all such suitable changes and modifications and equivalents should be considered to be within the scope of the present invention.

In the tandem laser scanning unit of the image forming apparatus according to the present invention as described above, the first step value between the emission point of the laser beam and the reference axis is the second between the incident point on the polygon mirror of the laser beam and the reference axis. With the configuration of the laser diodes arranged toward the polygon mirror so as to be larger than the step value, it is possible to reduce the height of the polygon mirror while increasing the pitch between the laser beams, thereby reducing the rotational load of the polygon mirror driving unit, thereby providing high output. There is an advantage of cost savings because the drive is not required.

Further, by adding a configuration in which the bow distortion correction means is applied on the optical path between the polygon mirror and the photosensitive drum, the deterioration in print quality due to bow distortion can be prevented.

Claims (10)

In a tandem laser scanning unit of an image forming apparatus, which scans a plurality of laser beams emitted from a laser diode in accordance with a video signal of an input image to a plurality of photosensitive drums using a polygon mirror, A first step value between the exit point of the laser beam and the normal of the polygon mirror passing through the center of the polygon mirror is between the point of incidence on the polygon mirror of the laser beam and the normal of the polygon mirror passing through the center of the polygon mirror. A laser diode disposed toward the polygon mirror so as to be larger than a second step value of the laser diode; And And bow distortion correction means for correcting bow distortion caused by the arrangement structure of the laser diode with respect to the polygon mirror. The bow distortion correction means according to claim 1, And a tandem laser scanning unit of the image forming apparatus, wherein the tandem laser scanning unit is positioned on an optical path between the polygon mirror and the photosensitive drum. The method of claim 2, wherein the bow distortion correction means, A tandem laser scanning unit of an image forming apparatus, comprising a cylinder mirror. The method according to any one of claims 1 to 3, wherein the plurality of laser diodes, And a tandem laser scanning unit of the image forming apparatus, wherein the tandem laser scanning unit is disposed symmetrically with respect to the normal of the polygon mirror passing through the center of the polygon mirror. In a tandem laser scanning unit of an image forming apparatus, which scans a plurality of laser beams emitted from a laser diode in accordance with a video signal of an input image to a plurality of photosensitive drums using a polygon mirror, A first step value between the exit point of the laser beam and the normal of the polygon mirror passing through the center of the polygon mirror is between the point of incidence on the polygon mirror of the laser beam and the normal of the polygon mirror passing through the center of the polygon mirror. A tandem of the image forming apparatus, wherein the pair of laser diodes is disposed toward the polygon mirror so as to be larger than the second step value of the beam and is vertically symmetrical with respect to the normal of the polygon mirror passing through the center of the polygon mirror. Laser scanning unit. The method of claim 5, wherein The tandem laser scanning unit of the image forming apparatus, wherein each of the laser beam directions emitted from the two pairs of laser diodes and the normal of the polygon mirror have the same angle? The method of claim 6, The laser beam emitted from one laser diode selected from one of the two pairs of laser diodes, and the normal of the polygon mirror passing through the center of the polygon mirror among the other pairs of the two pairs of laser diodes A tandem laser scanning unit of an image forming apparatus, wherein a laser beam emitted from a laser diode located in an area opposite to a region where a selected laser diode is located has the same incident point. The method according to any one of claims 5 to 7, And bow distortion correction means for correcting bow distortion caused by the arrangement structure of the laser diode with respect to the polygon mirror. The method according to claim 8, wherein the bow distortion correction means, And a tandem laser scanning unit of the image forming apparatus, wherein the tandem laser scanning unit is positioned on an optical path between the polygon mirror and the photosensitive drum. The method according to claim 9, wherein the bow distortion correction means, A tandem laser scanning unit of an image forming apparatus, comprising a cylinder mirror.