JPH02219012A - Laser beam scanning optical system - Google Patents

Abstract

PURPOSE:To easily attain the automation of mass-production by making the light source part of the laser beam scanning system into a unit, and adjusting the position of the light source part unit in the direction of the optical axis corresponding to the housing of the laser beam scanning optical system. CONSTITUTION:The light source part consisting of a semiconductor laser element 2, a condenser lens 3, and a cylindrical lens 4 is unitized. Then a semiconductor laser element 2 is moved on a jig dedicated to adjustment in the direction of the optical axis to execute 1st adjustment for adjusting the relative position between the semiconductor laser element and condenser lens 3, thereby adjusting image formation in a main scanning direction. Then the light source part unit after the 1st adjustment is incorporated in the laser beam scanning optical system main body and the whole light source part unit is moved in the direction of the optical axis to adjust image formation in the subscanning direction. Consequently, the image formation of the light source is adjusted rationally and efficiently from outside the housing of the device to attain automatic adjustments and mass-production.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a laser beam scanning optical system used in laser beam printers, facsimile machines, optical discs, and the like.

BACKGROUND ART AND ITS PROBLEMS Generally, a light source section of a laser beam scanning optical system of a laser beam printer or facsimile machine is composed of a semiconductor laser element, a collimator lens, and a cylindrical lens. The laser beam radiated from the semiconductor laser element has a certain spread, and is collimated by a collimator lens into a parallel beam.The cylindrical lens, which has a refraction effect only in the sub-scanning direction, changes its shape onto the polycon mirror in the main-scanning direction. The spot shape is changed to a substantially linear spot in the longitudinal direction. The modified laser beam is deflected and scanned by a polycon mirror, and an image is formed on a scanning line.

By the way, the imaging position of the laser beam on the scanning line differs from device to device in both the main scanning direction and the sub-scanning direction due to the focal length error of the collimator lens, the cylindrical lens, and the astigmatism error of the semiconductor laser element.

Therefore, it is necessary to perform imaging adjustment for each individual device.

For this reason, to adjust the image formation of a conventional laser beam scanning optical system, a collimator lens fixed to the device housing is placed between them, and a semiconductor laser element and a cylindrical lens are placed on both sides, and their optical axes are aligned. Temporarily place it so that its position can be adjusted in the longitudinal direction of the axis, and first move the semiconductor laser element in the longitudinal direction of the optical axis to adjust the laser beam in the main scanning direction so that it is most focused on the scanning line.
The semiconductor laser element is fixed to the device housing, and then the cylindrical lens is adjusted so that the laser beam in the sub-scanning direction is focused most on the scanning line by moving the cylindrical lens in the optical axis direction. It is known that the device is fixed to the device housing. At this time, the movement of the cylindrical lens in the optical axis direction has no refraction effect in the main scanning direction, so it has the same effect as flat glass, and therefore the imaging position in the main scanning direction does not move.

Alternatively, as shown in Japanese Unexamined Patent Publication No. 59-224816, the semiconductor laser element and the collimator lens are made into an integrated structure, and the optical axes of the integrated structure and the cylindrical lens are aligned so that the position can be adjusted in the optical axis direction. First, the integrated structure of the semiconductor laser element and the collimator lens is moved in the optical axis direction to adjust the imaging of the laser beam in the main scanning direction, and then the integrated structure is placed in the device housing. fixed,
It is known that the cylindrical lens is then moved in the optical axis direction to adjust the imaging of the laser beam in the sub-scanning direction, and then the cylindrical lens is fixed to the device housing.

However, in the case of any of the above laser beam scanning optical systems, the position of the cylindrical lens is adjusted while the cylindrical lens is incorporated inside the device housing, so adjustment work must be done inside the device. First, there was a problem in that automation during mass production was difficult.

Therefore, the laser beam scanning optical system according to the present invention includes (a) (1) a laser beam light source; (2) a first optical element that condenses or converts the laser beam radiated from the light source into parallel light; , (3) a second optical element that condenses the laser beam emitted from the first optical element into a substantially straight line in a direction parallel to the deflection scanning plane; (b) means for adjusting the position of at least either the laser beam light source or the first optical element in the optical axis direction; (c) the light source unit relative to the housing of the laser beam scanning optical system; and a means for adjusting the position in the optical axis direction.

In the configuration described above, first, the laser beam light source or the first
By adjusting the position of at least one of the optical elements in the optical axis direction, the first image plane adjustment in the main scanning direction and the sub-scanning direction is performed as shown in FIG. However, here, normally, the image plane adjustment of the light source unit alone is performed exclusively in the main scanning direction of the laser beam.

Next, by adjusting the position of the light source unit in the optical axis direction with respect to the housing of the laser beam scanning optical system, the image plane is adjusted only in the sub-scanning direction as shown in FIG. At this time,
The image plane position in the main scanning direction does not change.

EXAMPLE Hereinafter, an example of a laser beam scanning optical system according to the present invention will be described with reference to the accompanying drawings.

In FIG. 1, the laser beam scanning optical system (1) includes a semiconductor laser element (2), a condenser lens (3), a dinontrical lens (4), a voricon mirror (5), a toroidal lens (6), and a beam splitter. (7), a spherical mirror (8>), a photosensitive drum (9), an imaging start position detection sensor (hereinafter referred to as an SOS sensor) (10), and its dedicated mirror (11).

A laser beam radiated from a semiconductor laser element (2), such as a double heterojunction type semiconductor laser element, is focused at a finite rear position by a condensing lens (3), and then passed through a cylindrical lens ( 4), the spot shape is changed to a substantially linear spot shape with the main scanning direction being the longitudinal direction, and reaches the polygon mirror (5). The polygon mirror (5) is driven to rotate at a constant speed in the direction of arrow (a), and the laser beam is scanned in a direction perpendicular to this rotation axis and guided to the toroidal lens (6). The toroidal lens (6) has an entrance surface and an exit surface that are concentric within the scanning plane, has constant power in a direction perpendicular to the scanning plane, and corrects the tilt of the polygon mirror (5). The beam that has passed through the toroidal lens (6) passes through the beam brick (7), is reflected by the spherical mirror (8), and returns to the beam splitter (7).
The light returns to the point where it is reflected and reaches the photoreceptor drum (9) via a folding mirror system (not shown in the figure). Here, the spherical mirror (8) is used to correct field curvature on the photoreceptor drum (9>).

On the other hand, the SoS sensor (10) has a function of correcting the image formation position error for each scan due to the error in mirror surface division of the polygon mirror (5), and detects the image formation start position in the main scanning direction. It is installed at a position equivalent to the scanning surface of the photoreceptor drum (9) via a dedicated SOS sensor mirror (11).

Furthermore, the state of refraction of the laser beam will be explained in detail by dividing it into the main scanning direction and the sub-scanning direction. FIG. 2a shows the state of refraction of the laser beam in the main scanning direction.

The laser beam radiated from the semiconductor laser element (2) becomes a beam condensed at a finite rear position by the condensing lens (3). This beam passes through a cylindrical lens (4) that has no refraction effect in the main scanning direction and reaches a polygon mirror (5).

The beam is deflected and scanned by a polygon mirror (5) and guided to a toroidal lens (6). Toroidal lens (
6) has a slight diffusion effect on the incident light flux. The beam transmitted through the toroidal lens (6) forms a point image near the photosensitive drum (9) by a spherical mirror (8).

On the other hand, Fig. 2b shows the state of refraction of the laser beam in the sub-scanning direction, and the laser beam radiated from the semiconductor laser element (2) is focused at a finite rear position by the condensing lens (3). . This beam is refracted by a cylindrical lens (4) having a refraction effect in the sub-scanning direction on the deflection surface of the polygon mirror (5) so as to form a substantially linear image with the main-scanning direction being the longitudinal direction. The beam is deflected and scanned by a polygon mirror (5) and guided to a toroidal lens (6). The toroidal lens <6) works to condense the incident light beam, and the toroidal lens (6)
) The beam transmitted through the spherical mirror (8) forms a point image near the photoreceptor drum (9).

By the way, the astigmatism of the semiconductor laser element (2) (aberration that occurs because the apparent light emitting position is different when vertical and horizontal to the cemented surface) and the focal length of the condensing lens (3) and dinontrical lens (4) Due to the error, the imaging position of the laser beam on the photosensitive drum (9) differs for each device in both the main scanning direction and the sub-scanning direction. Therefore, it is necessary to perform imaging adjustment for each individual device. Among these, the error in focal length between the condenser lens (3) and the cylindrical lens (4) can be kept very small by using a molded resin lens or the like. Therefore, it is important to adjust the astigmatism error of the semiconductor laser. This can be corrected by adjusting the relative positions of the semiconductor laser element (2) and the condenser lens (3).

The laser beam scanning optical system according to the present invention includes a semiconductor laser element (2), a condensing lens (3), and a cylindrical lens (3).
4) is made into a unit, and by moving the semiconductor laser element (2) in the optical axis direction on an adjustment jig in advance, the relative relationship between the semiconductor laser element (2) and the condensing lens (3) can be adjusted. Perform a first adjustment to adjust the position, perform image formation adjustment in the main scanning direction, and then incorporate the light source unit that has undergone the first adjustment into the main body of the laser beam scanning optical system, and then remove the entire light source unit. Image formation adjustment in the sub-scanning direction is carried out by moving in the optical axis direction.

The purpose of the first adjustment is to correct astigmatism errors due to individual differences in the semiconductor laser element (2). The second adjustment is performed using a condensing lens (3) that has a refraction effect in the sub-scanning direction.
, the purpose is to correct the focal length error of the cylindrical lens (4).

The above embodiment will be explained using a more specific device. Figures 3 to 5
The figure shows a device actually incorporating a laser beam scanning optical system.

The laser beam scanning optical device (12) includes a light source unit (
13), polygon mirror (5), toroidal lens (6)
〉, beam splitter (7), spherical mirror (8), SO
It consists of an S sensor (10), its dedicated mirror (11), return mirrors (14a) and (14b), and a housing (15).

As shown in FIG. 6, the light source unit (13) includes a semiconductor laser element (2) fitted into a square cylindrical member (16a).
), a condenser lens (3) fitted into the hollow center of a cylindrical member (16b), and a cylindrical lens (4) fitted into the member (16c). Semiconductor laser element (2), condensing lens (3), cylindrical lens (
4), each optical axis is made to coincide with each other, and the semiconductor laser element (2) is movable in the optical axis direction together with its holding member (16a).

Now, although the light source unit (13) is not shown, the member (16b) is placed against the member (16b) on a special jig for adjustment.
6a) back and forth in the optical axis direction, the first adjustment is performed so that the laser light emitted from the semiconductor laser element (2) is focused at the designed focusing position. After adjustment, the parts (
16a) to the member (16b) using the fixing screw (17).
Fix using a). In this way, image formation adjustment in the main scanning direction is performed in advance.

Next, the member (1) holding the cylindrical lens (4) is
6c) to the member (16b), and the thus assembled light source unit (13) is attached to the housing (15) of the laser beam scanning optical device (12) in the optical axis direction as shown in FIG. Can be temporarily installed so that it can be moved.

The laser light radiated from the temporarily installed light source unit (13) is transmitted through a polygon mirror (5), a toroidal lens (
6), beam splitter (7), spherical mirror (8), folding mirrors (14a), (14b) and reach a photosensitive drum (not shown).

Here, the light source unit (13) temporarily installed in the laser beam scanning optical device (12) is moved in the optical axis direction and subjected to a second adjustment so that the laser beam focuses a point image near the photoreceptor drum. Ru. After adjustment, the light source unit (13>) is fixed to the housing (15) of the laser beam scanning optical device (12) using the fixing screw (17b).

This performs imaging adjustment in the sub-scanning direction.

FIGS. 8 and 9 show graphs of changes in the image plane when the first adjustment and the second adjustment are performed in the laser beam scanning optical device (12).

FIG. 8 shows an example of changes in the image plane during the first adjustment. The vertical axis represents the curvature of field based on the designed focal position of the adjustment jig, and the horizontal axis represents the image height. In the figure, the curve (AI).

(B1) shows image planes in the main scanning direction and the sub-scanning direction before adjustment, respectively. Next, when the semiconductor laser element (2) is moved 0.01 mm in the optical axis direction away from the deflection point of the polygon mirror (5), the field curve (AI)
(Bl) changes to the field curves (A2) and (B2), respectively, and is adjusted so that the laser beam radiated from the semiconductor laser element (2) is focused at the designed focusing position.

Next, FIG. 9 shows an example of the change in the image plane during the second adjustment. The surface curvature is taken, and the horizontal axis is the image height. In the figure, image plane curves (A3) and (B3) indicate image planes in the main scanning direction and the sub-scanning direction before the second adjustment. At this time, the first
By adjusting the field curve in the main scanning direction (A3>, -
The laser beam is adjusted so as to be focused on the imaging surface of the photoreceptor drum of the laser beam scanning optical device (12). Then, when the light source unit (13) is moved 1 mm away from the deflection point of the polygon mirror (5), it moves toward the image plane! (
A3) and (B3) are the field curves (A4) and (B4), respectively.
). At this time, the field curve (A3) hardly changes, and the amount of change is about 0.1 mm over the entire area. Therefore, depending on the second adjustment, only the image plane in the sub-scanning direction changes,
The image plane adjustment in the main scanning direction set in the first adjustment is not disrupted, and each can be operated independently.

Further, the cylindrical lens (4) and the toroidal lens (6) have different refractive effects in the main scanning direction and the sub-scanning direction, as do the pixel elements. Therefore, there is a possibility that the generating line may be twisted before and after the deflection of the polygon mirror (5), which is the deflection means, and in that case, a point image will not be formed on the photoreceptor drum. Therefore, if necessary, by rotating the light source unit l-(13) around the optical axis, the N line of the cylindrical lens (4) can be connected to the Troigle lens (13) fixed inside the housing (15). It must be aligned with the bus line of 6). For this reason, the light source unit (13
) into a cylindrical shape that is easy to rotate. However, making the light source unit (13) cylindrical is not essential to the present invention.

Note that the laser beam scanning optical system according to the present invention is not limited to the above-mentioned embodiments, and can be variously modified within the scope of the invention.

The laser light source is not limited to the semiconductor laser element (2), but may be a solid laser or a gas laser. Further, the same effect can be obtained by using a collimator lens instead of the condensing lens (3). However, when the condensing lens (3) is used, it has the advantage that the position of the image formation is easier to confirm than the collimator lens, so that the adjustment work is easier.

Further, in the above embodiment, the optical R section unit (13) fixed the condensing lens (3) and moved the semiconductor laser element (2) in the optical axis direction to perform the first image formation adjustment. There is no need to limit it to this, and the adjustment may be made by fixing the semiconductor laser element (2) and moving the condensing lens (3) in the optical axis direction.

Effects of the Invention As described above, according to the present invention, since the light source section of the laser beam scanning optical system is made into a unit, the image formation adjustment of the light source section can be performed easily.
It can be performed rationally and efficiently from outside the device housing, and automatic adjustment can be easily performed.

Furthermore, the light source unit can be assembled independently from the main unit, and the relative positions of each light source and optical element within the light source unit can be adjusted in advance using a dedicated jig before being stocked. It is not necessary to start the image formation adjustment after the main body device is assembled, and the image formation adjustment can be carried out in a short time after the light source unit is installed in the main body device, and mass production becomes possible. Furthermore, since the structure for holding the light source unit in the housing is simple, the number of parts is small, and the device is miniaturized.

[Brief explanation of the drawing]

The drawings show an embodiment of the laser beam scanning optical system according to the present invention, FIG. 1 is a perspective view showing the basic configuration of the laser beam scanning optical system, FIGS. 2a and 2b are explanatory diagrams of laser beam refraction, Fig. 3 is a plan view of the inside of the laser beam scanning optical device, Fig. 4 is a central sectional view of the device shown in Fig. 3, Fig. 5 is an external front view of the device shown in Fig. 3, and Fig. 6 is a A sectional view of the light source unit, Fig. 7 is an explanatory diagram of the installation of the light source unit, Fig. 8 is a graph showing the image plane change during the first adjustment, and Fig. 9 is an image plane change during the second adjustment. This is a graph showing. (1)...Laser beam scanning optical system, (2)...Semiconductor laser element, (3)...Condensing lens, (4)...
-Cylindrical lens, (13)...Light source unit, (15)...Casing, (16a), (16b)--
・Holding members, (17a), (17b) ”・Screws.

Claims (1)

[Claims] 1. A laser beam scanning optical system that deflects and scans a beam emitted from a laser beam source and forms an image on a scanning line, which comprises a laser beam source and a laser beam emitted from the light source. A first optical element that converts into light or parallel light, and a second optical element that focuses a laser beam emitted from the first optical element into a substantially straight line in a direction parallel to the deflection scanning plane. a light source unit integrated with optical axes aligned; means for adjusting the position of at least either the laser beam light source or the first optical element in the optical axis direction; A laser beam scanning optical system comprising: means for adjusting the position in the optical axis direction with respect to the housing.