JPH10170845A - Image density switching optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image density switching optical scanning device capable of stably maintaining the beam diameter corresponding to image density, and small in size. SOLUTION: Semiconductor laser elements 1 and 2 are able to be turned on independently of each other and emit laser beams L1 and L2 with wavelengths λ1 and λ2 (λ1 <λ2 ). A beam splitter 3 puts the optical paths of the laser beams L1 and L2 one over the other and is arranged between the semiconductor laser elements 1 and 2 and a collimator lens 4 along the optical path. The laser beams L1 and L2 emitted by the beam splitter 3 have mutually different beam diameters and the optical paths are put one over the other so that their optical axes are aligned with each other. To draw a high-density image, only the semiconductor laser element 1 is turned on and the high-density image is formed on a photosensitive drum. To draw a low-density image, on the other hand, only the semiconductor laser element 2 is turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density switching scanning optical device, and more particularly to an image density switching scanning optical device used for a printing head of a laser printer or a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, as an image density switching scanning optical apparatus, an apparatus having two laser light sources and a collimator lens provided for each of the two laser light sources has been known.

[0003]

However, in the conventional image-density-switching scanning optical apparatus, since an optical system for collimating each laser light source is provided, the apparatus is large. When the image density is switched by changing the magnification β in the sub-scanning direction of the scanning optical system for each laser light source, the beam waist shift amount due to a change in environment (temperature) differs between the laser light sources, and a constant beam diameter is obtained. It was difficult to maintain.

SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized image-density switching scanning optical apparatus which stably maintains a beam diameter corresponding to an image density.

[0005]

In order to achieve the above object, an image density switching scanning optical apparatus according to the present invention comprises: (a) a plurality of laser light sources which are individually turned on; (D) optical path superimposing means for superposing optical paths of laser beams emitted from the laser light source; and (c) light beam converting means for converting the laser beam emitted from the optical path superimposing means into a substantially parallel light beam. The optical path superimposing means is arranged along the optical path between the laser light source and the light beam converting means, and the respective laser beams emitted from the laser light source have different beam diameters and the light beam converting means Emitting light.

[0006] With the above configuration, it is not necessary to provide an optical system for collimating each laser light source, and the apparatus becomes compact. Further, it is not necessary to change the magnification β in the sub-scanning direction of the scanning optics for each laser light source.
The beam waist shift amount between the laser light sources due to the change is reduced, and the beam diameter is stabilized. Here, in order to make the diameter of the laser beam emitted from the light beam converting means different,
For example, a semiconductor laser device that emits laser beams having mutually different wavelengths may be used as the laser light source, and a multi-wavelength sensitive photoconductor having a sensitivity peak at the wavelength of the semiconductor laser device may be provided. Alternatively, as the laser light source, a semiconductor laser element that emits laser beams having different diverging angles may be used. Alternatively, as the laser light source, a semiconductor laser device that emits laser beams having mutually different outputs is used, and further, a regulating member for regulating a light flux of the laser beam emitted from the high-power side semiconductor laser device is provided. Good. By arbitrarily combining these methods, the degree of freedom in setting combinations of image densities is expanded.

Further, by illuminating a plurality of laser light sources in synchronization with each other, the laser beams emitted from the laser light sources may be combined to form an even lower-density image on the image plane. Further, the image density switching scanning optical device according to the present invention has two laser light sources, and the optical path superimposing means transmits a laser beam emitted from one of the laser light sources and transmits the other laser light. It has a surface for reflecting a laser beam emitted from a laser light source, and an interference film for preventing loss of light amount is provided on the surface. This interference film has a high transmittance for a laser beam transmitted through the optical path superimposing means and a high reflectance for a laser beam reflected by the optical path superimposing means. Minimizing light loss when the laser beam passes through the means.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image density switching scanning optical apparatus according to the present invention will be described below with reference to the accompanying drawings. In each embodiment, the same components and the same portions are denoted by the same reference numerals. [First Embodiment, FIGS. 1 to 8] As shown in FIG. 1, an image density switching scanning optical apparatus is composed of a light source block 10, a cylindrical lens 5, a polygon mirror 6, and a scanning lens group 7. ing.

The semiconductor laser elements 1 and 2 of the light source block 10
Numerals 2 are modulated (ON, OFF) independently of each other based on print data input to a drive circuit (not shown), and emit a laser beam when ON. The laser beam is converged substantially parallel by the collimator lens 4 of the light source block 10 and is condensed by the cylindrical lens 5 on the deflection surface of the polygon mirror 6 only in the sub-scanning direction.

The polygon mirror 6 is driven to rotate at a constant speed about an axis of rotation 6a in the direction of arrow a. The laser beam is deflected at a constant angular velocity on each deflecting surface based on the rotation of the polygon mirror 6 and enters the scanning lens group 7. The laser beam refracted and reflected by the scanning lens group 7 is condensed on the photosensitive drum 8 and scans the photosensitive drum 8 in the direction of arrow b. The scanning lens group 7 mainly includes a polygon mirror 6
Has a function of correcting the laser beam deflected at a constant angular speed on the surface to be scanned (photosensitive drum 8) at a constant main scanning speed, that is, a function of correcting distortion. The photosensitive drum 8 is driven to rotate at a constant speed in the direction of arrow c, and an image (electrostatic latent image) is formed on the drum 8 by the main scanning in the direction of arrow b by the polygon mirror 6 and the sub-scanning of the drum 8 in the direction of arrow c. Is formed.

The light source block 10 includes two semiconductor laser elements 1 and 2 having different wavelengths, one cube beam splitter 3 and one collimator lens 4. This will be described in more detail with reference to FIGS. 2 is a front view of the light source block 10, FIG. 3 is a plan view, FIG. 4 is a left side view, and FIG. 5 is a right side view. As shown in FIG.
After the semiconductor laser element 2 is fitted into the cylinder of the cylindrical member 12 having a thread groove formed on the inner periphery, a cylindrical member 13 having a threaded outer periphery is formed using the thread groove formed on the inner periphery of the member 12. And screwed into the cylinder of the member 12
At 3, the semiconductor laser element 2 is pressed against the inner wall surface of the member 12 and fixed. The member 12 is mounted on the block 14 having a V-shape so that the semiconductor laser element 2 is movable in the optical axis direction. After the focus adjustment, the member 12 is fixed to the block 14 by the leaf spring 15 and the screw 16 (see FIG. 3). Fixed. The position of the block 14 is adjusted in a plane perpendicular to the optical axis of the laser beam L2 emitted from the semiconductor laser element 2 so that the semiconductor laser element 2 is arranged at a desired position. Is fixed to the left end using a screw 17 (see FIG. 4).

The semiconductor laser device 1 is fixed to a holder 25 using a leaf spring 27 and screws 28 (see FIG. 3).
The holder 25 is mounted on the base block 18 and positioned in a plane perpendicular to the optical axis of the laser beam L1 emitted from the semiconductor laser element 1 so that the semiconductor laser element 1 is arranged at a desired position. After the adjustment, it is fixed to the base block 18 using screws 29. The traveling direction of the laser beam L1 immediately after being emitted from the semiconductor laser element 1 and the traveling direction of the laser beam L2 immediately after being emitted from the semiconductor laser element 2 have a vertical relationship.

The optical distance (the actual physical distance divided by the refractive index of the medium) from the light emitting point of each of the semiconductor laser device 1 and the semiconductor laser device 2 to the reflection / transmission surface of the beam splitter 3 is Are arranged so as to be equal to each other. By arranging in this manner, the laser beams L1 and L2 from the two light sources exhibit the same behavior with respect to a change in the environmental temperature. L
The relative beam diameter on the scan surface 2 does not change. Further, for example, it is easy to add a configuration for correcting the beam waist position shifted due to temperature fluctuation to the optical system after the collimator lens 4. In the semiconductor laser elements 1 and 2, the direction of the vertical divergence angle with a large angle is parallel to the main scanning direction, and the direction of the horizontal divergence angle with a small angle is perpendicular to the sub-scanning direction. Are arranged as follows.

At a position on the left side of the base block 18,
The beam splitter 3 is fixed by the elastic force of the leaf springs 20, 21. The plate springs 20 and 21 have one ends screwed to the base block 18 with screws 22 (see FIG. 3) and 23 (see FIG. 4). However, the fixing method of the beam splitter 3 is not necessarily limited to such a method. For example, the beam splitter 3 may be fixed to the base block 18 with an adhesive.

At the right side of the base block 18,
A V-shaped groove 18a (see FIG. 5) is formed, and the collimator lens 4 is provided on the V-shaped groove 18a via a lens barrel 31.
It is placed so as to be movable in the optical axis direction. After the focus adjustment, the collimator lens 4 is fixed to the base block 18 by the attachment member 32 and the screw 34 fixed to the base block 18 using screws 33. The optical path length from the semiconductor laser element 1 to the collimator lens 4 and the optical path length from the semiconductor laser element 2 to the collimator lens 4 are set to the same size. As a result, the optical systems of the semiconductor laser elements 1 and 2 become optically equal, and the beam waist shift amounts due to temperature changes become substantially equal. As a result, the relative displacement of the laser beam scanning position between image densities is reduced, and temperature compensation can be easily performed.

The semiconductor laser elements 1 and ₂ emit laser beams L1 and L2 having wavelengths of λ ₁ and λ ₂ (λ ₁ <λ ₂ ), respectively. As the photosensitive drum 8, as shown in FIG. 6, the wavelengths λ ₁ ,
dual wavelength sensitive photosensitive drum having a sensitivity peak lambda ₂ is used. The beam splitter 3 overlaps the optical paths of the laser beams L1 and L2 emitted from the semiconductor laser elements 1 and 2. In the case of the first embodiment, the optical paths are overlapped so that the respective optical axes of the laser beams L1 and L2 emitted from the beam splitter 3 coincide. This beam splitter 3 is a combination of two triangular prisms. The triangular prism constituting the beam splitter 3 is made of a glass material (optically transparent material,
After being made of, for example, optical glass, the interference film 9 is coated on the mating surface 3a. As shown in Table 1, the interference film 9 is formed by alternately stacking SiO ₂ thin films and TiO ₂ thin films on a glass material (in the case of the first embodiment, optical glass).

[0017]

[Table 1]

FIG. 7 is a graph showing the reflectance characteristics of the interference film. The beam splitter 3 is disposed between the semiconductor laser elements 1 and 2 and the collimator lens 4 along the optical path, and its mating surface 3a is arranged in the traveling direction of the laser beams L1 and L2 emitted from the semiconductor laser elements 1 and 2. 4
Inclined 5 degrees. In the image density switching scanning optical apparatus having the above-described configuration, assuming that the focal length of the collimator lens 4 is f _co and the spread angle of the semiconductor laser elements 1 and 2 is θ, the luminous flux of the laser beam immediately after being emitted from the collimator lens 4 The width W _co is represented by the following relational expression (1).

W _co = 2f _co · sin (θ × (√ (2 / ln2)) / 2) (1) Here, if a non-achromatic lens is used as the collimator lens 4, the focal length f _{Since co} changes depending on the wavelengths of the semiconductor laser elements 1 and 2, the light beam width W _co changes. That is, since the wavelength λ ₁ of the semiconductor laser device ₁ is smaller than the wavelength λ ₂ of the semiconductor laser device 2, the focal length f _co1 for the wavelength λ ₁ is larger than the focal length f _co2 for the wavelength λ ₂ . Therefore, the light flux width W _co1 laser beam L1 immediately after emitted the relationship equation (1) from the collimator lens 4 is greater than the light flux width W _{of co2} laser beam L2 (see FIG. 8).

On the other hand, the relationship between the beam diameter when the laser beam enters the cylindrical lens 5 and the scanning lens group 7 and the beam waist diameter on the photosensitive drum 8 is represented by the following relational expressions (2) and (3). Is done. _{D m = (4 · λ ·} f o) / (π · W m) ...... (2) D s = (4 · λ · f cy · β) / (π · W s) ...... (3) However, D _m : beam waist diameter in the main scanning direction on the photosensitive drum D _s : beam waist diameter in the sub-scanning direction on the photosensitive drum W _m : beam diameter of the laser beam in the main scanning direction when entering the scanning lens group W _s : beam diameter in the sub-scanning direction of the laser beam when entering the cylindrical lens λ: wavelength of the laser beam f _o : focal length of the scanning lens group f _cy : focal length of the cylindrical lens β: deflection point and image point Here, if a lens having small longitudinal chromatic aberration is used for the scanning lens group 7, the beam waist diameter D _m on the photosensitive drum 8 is inversely proportional to the beam diameter W _m when entering the scanning lens group 7,
The beam waist diameter D _s is inversely proportional to the beam diameter W _s when entering the cylindrical lens 5.

From the relational expression (2), the wavelength λ ₁ of the semiconductor laser device ₁ and the wavelength λ ₂ of the semiconductor laser device 2 satisfy the following relational expression (4). λ ₂ = (D _m2 · W _m2 ) λ ₁ / (D _m1 W _m1 ) (4) λ ₂ = (D _s2 · W _s2 ) λ ₁ / (D _s1 W _s1 ) (5) D _m1 : Beam waist diameter of the laser beam L1 on the photosensitive drum 8 in the main scanning direction D _m2 : Beam waist diameter of the laser beam L2 on the photosensitive drum 8 in the main scanning direction W _m1 : _Light enters the scanning lens group 7 Laser beam L1
The beam diameter W _{m2 in} the main scanning direction: the laser beam L2 when entering the scanning lens group 7
D _s1 : Beam waist diameter of the laser beam L1 on the photosensitive drum 8 in the sub-scanning direction D _s2 : Beam waist diameter of the laser beam L2 on the photosensitive drum 8 in the sub-scanning direction W _s1 : The beam diameter W _s2 of the laser beam L1 in the sub-scanning direction when entering the cylindrical lens 5: the beam diameter in the sub-scanning direction of the laser beam L2 when entering the cylindrical lens 5 Table 2 is based on the above-mentioned relational expression (4). Image density 600d based on
4 specifically illustrates a combination of wavelengths of the semiconductor laser elements 1 and 2 for forming a beam waist diameter in the main scanning direction on the photosensitive drum 8 corresponding to the image resolution of 800 dpi.

[0022]

[Table 2]

Next, the operation and effect of the image density switching scanning optical device will be described with reference to FIG. High density images,
For example, when drawing an image of 800 dpi, only the semiconductor laser element 1 having a short wavelength λ ₁ (= 585 nm) is modulated and controlled based on the print data, and emits a laser beam L1. The laser beam L1 is reflected on the mating surface 3a of the beam splitter 3. At this time, the interference film 9 formed on the mating surface 3a are the approximately 100% reflectance with respect to wavelength lambda ₁ is the laser beam L1 of 585 nm (see FIG. 7), the light amount of the laser beam L1 It can be reflected with little loss. The laser beam L1 emitted from the beam splitter 3 is applied to a collimator lens 4
Is guided to the cylindrical lens 5 through the lens.

The beam width W _co1 laser beam L1 immediately after the collimator lens 4 exit, as is clear from the equation (1), the light flux width W _{of co2} greater than the laser beam L2. Laser beam L emitted from cylindrical lens 5
1 is condensed on a photosensitive drum 8 via a polygon mirror 6 and a scanning lens group 7. At this time, since the beam diameter W _m1 of the laser beam L1 at the time of entering the scanning lens 7 is larger than the beam diameter W _{m @ 2} of the laser beam L2, on the photosensitive drum 8 of the laser beam L1 by the equation (2) The beam waist diameter D _{m1 in} the main scanning direction is smaller than the beam waist diameter D _m2 of the laser beam L2. Thus, a high-density image is formed on the photosensitive drum 8.
Since the photosensitive drum 8 is a dual-wavelength sensitive photosensitive drum having a peak at a wavelength lambda _1, the light amount of the laser beam L1 is utilized efficiently imaging.

On the other hand, when drawing a low-density image, for example, an image of 600 dpi, a long wavelength λ ₂ (= 780 n
Only the semiconductor laser element 2 of m) is modulated and controlled based on the print data, and emits a laser beam L2. The laser beam L2 passes through the mating surface 3a of the beam splitter 3. At this time, since the interference film 9 formed on the mating surface 3a has a reflectance of approximately 0% with respect to the laser beam L2 having the wavelength λ ₂ of 780 nm (see FIG. 7), the light amount of the laser beam L2 is reduced. It can be transmitted with little loss. The laser beam L2 emitted from the beam splitter 3 is guided to a collimator lens 4. Beam width W of the laser beam L2 immediately after the collimator lens 4 exit _co2 is smaller than the light flux width W _co1 the laser beam L1. Therefore,
The beam waist diameter D _m2 of the laser beam L2 in the main scanning direction on the photosensitive drum 8 is smaller than the beam waist diameter D _m1 of the laser beam L1, and an image having a low image density is formed on the photosensitive drum 8. The photosensitive drum 8 has a wavelength λ ₂
Since the photosensitive drum is a two-wavelength-sensitive photosensitive drum having a peak at a peak, the light amount of the laser beam L2 is efficiently used for image formation.

As described above, the image density switching scanning optical apparatus uses the laser beam L incident on the collimator lens 4.
Since the optical paths 1 and 2 are overlapped by the beam splitter 3, only one collimator lens 4 is required, and the apparatus can be made compact. Further, it is not necessary to make the sub-scanning magnification β different for each of the semiconductor laser elements 1 and 2, and the semiconductor laser elements 1 and 2 due to environmental (temperature) changes.
The beam waist shift amount between can be reduced,
The beam waist diameter on the photosensitive drum 8 can be stabilized.

[Second Embodiment, FIGS. 9 to 11] A second embodiment will be described in which three different image densities can be switched. The image density switching scanning optical device of the second embodiment is substantially the same as the device of the first embodiment except for the position at which the semiconductor laser element 1 is provided. As shown in FIG. 9, the semiconductor laser device 1 uses a holder 25 shown in FIGS. 2 to 4 in a plane perpendicular to the optical axis of a laser beam L1 emitted from the semiconductor laser device 1. The position is adjusted. That is, the semiconductor laser element 1 is
Laser beams L1 and L emitted from beam splitter 3
After the respective optical axes are adjusted to positions slightly different in the sub-scanning direction (see FIG. 9A) and equal in the main scanning direction (see FIG. 9B), the holder 25 is adjusted. Are fixed to the base block 18 using screws 29. The traveling direction of the laser beam L1 immediately after being emitted from the semiconductor laser element 1 and the traveling direction of the laser beam L2 immediately after being emitted from the semiconductor laser element 2 have a vertical relationship. The optical path length from the semiconductor laser element 1 to the collimator lens 4 and the optical path length from the semiconductor laser element 2 to the collimator lens 4 are set to the same size.

As shown in FIG. 10, the semiconductor laser devices 1 and 2 are connected to an image control circuit 38 via driving circuits 36 and 37, respectively. The print data is sent from the image control circuit 38 to the image signals S1 and S2 and the image signals S3 and S4.
Control (on / off) control of the semiconductor laser elements 1 and 2 via the drive circuits 36 and 37. Then, the control signal S5 is sent from the image control circuit 38 to the drive circuits 36 and 37, and the drive circuits 36 and 37 are driven in synchronization, and the semiconductor laser elements 1 and 2 are simultaneously turned on.

When a high-density image, for example, an image of 800 dpi is drawn in the image-density switching scanning optical apparatus having the above configuration, a short wavelength λ ₁ (= 585 nm) is used.
Is modulated based on the image signals S1 and S2 sent from the image control circuit 38,
Emit the laser beam L1. This laser beam L1
Denotes a beam splitter 3, a collimator lens 4, a cylindrical lens 5, a polygon mirror 6, and a scanning lens group 7.
, A high-density image is formed on the photosensitive drum 8. At this time, as shown in FIG. 11, the beam diameter of the laser beam L1 on the photosensitive drum 8 in the sub-scanning direction is 31.
7 μm (solid line 39a).

In the case of drawing a medium density image, for example, an image of 600 dpi, only the semiconductor laser element 2 having a long wavelength λ ₂ (= 780 nm) is based on the image signals S 3 and S 4 sent from the image control circuit 38. The modulation is controlled, and a laser beam L2 is emitted. The laser beam L2 forms a medium density image on the photosensitive drum 8. At this time,
As shown in FIG. 11, the beam diameter of the laser beam L2 on the photosensitive drum 8 in the sub-scanning direction is 41.3 μm (solid line 39b).

Further, a low-density image, for example, 400 dpi
In the case of drawing the image of, the same print data is sent from the image control circuit 38 to the drive circuits 36 and 37 as the image signals S1 and S2 and the image signals S3 and S4, and the control signal S5 is sent. Accordingly, the semiconductor laser elements 1 and 2 are simultaneously turned on and off synchronously and emit laser beams L1 and L2, respectively. The laser beams L1 and L2 are simultaneously irradiated on the photosensitive drum 8 at the same position in the main scanning direction but slightly different positions in the sub-scanning direction. Therefore, as shown in FIG. 11, the laser beams L1, L2
Has a beam diameter in the sub-scanning direction of 63.5 μm (solid line 39 c), and a low-density image is formed on the photoconductor 8.

As described above, by arranging the two semiconductor laser elements 1 and 2 slightly shifted in the sub-scanning direction and combining the lighting of the semiconductor laser elements 1 and 2, an easy and simple structure is realized. A device is obtained which can switch between two different image densities.

[Third Embodiment, FIGS. 12 and 13] Third Embodiment
In the embodiment, an embodiment using semiconductor laser elements having different divergence angles will be described. The image density switching scanning optical apparatus according to the third embodiment is the same as the first embodiment except that the semiconductor laser element is left.
This is similar to the device of the embodiment.

As shown in FIG. 12, the light source block 40
Are two semiconductor laser elements 41 and 42 and one
Beam-type beam splitter 3 and one collimator lens
4 is provided. The semiconductor laser elements 41 and 42 are respectively
Different wavelength λ₁, Λ_TwoWith a large angle of vertical
Spread angle θ_V1, Θ_V2Direction parallel to the sub-scanning direction.
Horizontal spread angle θ with small degree_H1, Θ_H2Main direction
It is arranged to be parallel to the inspection direction (FIG. 10
(See (a) and (b)). And the spread angle θ_H1, Θ_H2,
θ_V1, Θ _V2Satisfies the following conditional expression.

Θ_H1= Θ_H2, Θ_V1> Θ_V2 In the image density switching scanning optical device having the above configuration,
From the relational expression (1), the output from the collimator lens 4 is obtained.
Beam width W of laser beam immediately after irradiation_coIs a semiconductor laser
It changes depending on the spread angle θ of the elements 41 and 42. You
That is, the divergence angle θ of the semiconductor laser element 41_V1Is semiconductor
The spread angle θ of the laser element 42_V2Because it is bigger,
Of the laser beam L1 immediately after being emitted from the data lens 4
Luminous flux width W _co1Is the luminous flux width W of the laser beam L2._co2Greater than
It will be good.

From the above relational expression (1), the semiconductor laser device
41 divergence angle θ_V1And the spread angle of the semiconductor laser element 42
θ_V2Satisfies the following relational expression (6). θ_V2= 2 / √ (2 / ln2) × sin^-1((W_co2/ W_co1) × sin (θ _V1 × √ (2 / ln2) / 2)) (6) Table 3 shows a pixel density of 600d based on the relational expression (6).
from the collimator lens 4 corresponding to 800 dpi
To form the beam width of the laser beam immediately after it is emitted
Combination of divergence angles of semiconductor laser elements 41 and 42
Are specifically exemplified.

[0037]

[Table 3]

The scanning optical apparatus for switching image densities has the same function and effect as the apparatus of the first embodiment. That is, when drawing a high-density image, a large spread angle θ
Only the _V1 semiconductor laser element 41 is modulated and controlled based on the print data, and emits a laser beam L1. The laser beam L1 forms a high-density image on the photosensitive drum 8 via the beam splitter 3, the collimator lens 4, the cylindrical lens 5, the polygon mirror 6, and the scanning lens group 7. On the other hand, when drawing a low-density image, only the semiconductor laser element 42 having a small spread angle θ _V2 is modulated and controlled based on the print data, and the laser beam L2
Radiate. This laser beam L2 is applied to the photosensitive drum 8
A low density image is formed on top.

Further, as in the first embodiment, a combination in which the wavelengths of the semiconductor laser elements 41 and 42 are different and both the wavelengths and the divergence angles of the semiconductor laser elements 41 and 42 are different from each other is used. The degree of freedom can be increased. Actually, various semiconductor laser devices having wavelengths and divergence angles within the ranges shown in Table 4 are commercially available, and a device suitable for the specification may be appropriately selected from these.

[0040]

[Table 4]

[Fourth Embodiment, FIG. 14] In a fourth embodiment, three different image densities can be switched using semiconductor laser elements having different divergence angles. The image density switching scanning optical device of the fourth embodiment is substantially the same as the device of the third embodiment except for the position at which the semiconductor laser element 41 is provided.

As shown in FIG. 14, the semiconductor laser device 4
1 is a laser beam L emitted from the beam splitter 3
The optical axes 1 and L2 are adjusted to be slightly different in the sub-scanning direction and equal in the main scanning direction. The optical path length from the semiconductor laser element 41 to the collimator lens 4 and the semiconductor laser element 4
2 to the optical path length at the collimator lens 4 are set to the same size. The semiconductor laser elements 41 and 42 are modulated (ON, OFF) by a circuit similar to the control block shown in FIG.
Off) controlled.

When a high-density image is drawn in the apparatus having the above configuration, only the semiconductor laser element 41 having a large divergence angle θ _V1 is modulated and controlled based on the print data to emit a laser beam L2. This laser beam L
2 forms a high-density image on the photosensitive drum 8. When drawing a medium density image, only the semiconductor laser element 42 having a small divergence angle θ _V2 is modulated based on the print data and emits a laser beam L2. This laser beam L
2 forms a medium density image on the photosensitive drum 8. Further, when drawing a low-density image, both the semiconductor laser elements 41 and 42 are synchronously modulated based on the same print data and emit laser beams L1 and L2, respectively. The laser beams L1 and L2 are at the same position on the photosensitive drum 8 in the main scanning direction,
In the sub-scanning direction, slightly different positions are irradiated simultaneously. Therefore, the combined beam formed by combining the laser beams L1 and L2 forms a low-density image on the photosensitive drum 8.

As described above, the two semiconductor laser elements 4
By disposing the semiconductor laser devices 1 and 42 slightly shifted in the sub-scanning direction and combining the lighting of the semiconductor laser devices 41 and 42, it is possible to obtain an apparatus that can easily switch three different image densities with a simple structure. .

[Fifth Embodiment, FIG. 15] The image density switching scanning optical apparatus of the fifth embodiment is the same as the apparatus of the first embodiment except for the aperture regulating plate. The fifth
In the case of the embodiment, the semiconductor laser devices having different wavelengths are used, but it is not always necessary to make them different, and semiconductor laser devices having the same wavelength may be used.

As shown in FIG. 15, an aperture regulating plate 60 is disposed between the semiconductor laser element 2 and the beam splitter 3 to regulate the spread angle of the semiconductor laser element 2 for drawing a low-density image. The effective divergence angle of the element 2 is made smaller than the divergence angle of the semiconductor laser element 1 for drawing a high-density image. The laser beam L2 emitted from the semiconductor laser element 2 is applied to an aperture 61 provided in the aperture regulating plate 60.
When passing through, a part thereof is shielded and the beam diameter is reduced. At this time, since the light amount of the laser beam L2 decreases, the output of the semiconductor laser element 2 is increased to compensate for the decrease. The laser beam L2 having the reduced beam diameter is guided to the collimator lens 4 after transmitting through the beam splitter 3. Beam width W of the laser beam L2 immediately after emitted from the collimator lens 4 _{of co2} is smaller than the beam width W _co1 the laser beam L1, a laser beam L2 forms a less dense image on the photosensitive drum 8. On the other hand, the laser beam L1 forms a high density image on the photosensitive drum 8.

[Other Embodiments] The image density switching scanning optical apparatus according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. In the embodiment, in order to reduce the light amount loss,
Although an interference film is provided on the mating surface 3a of the beam splitter 3 or the two-wavelength photosensitive drum 8 is used, it is not always necessary to use these.

Further, the image density is 800 dpi, 60
0 dpi, 400 dpi, for example, 1200 dpi
Needless to say, the image density may be i, 800 dpi, or the like. In particular, an image density of 1200 dpi or 800 dpi is a range that can be obtained by tuning the entire optical system of the embodiment. Further, three or more laser light sources may be provided.

[0049]

As is apparent from the above description, according to the present invention, the light beam converting means converts the laser beam passing through the optical path superimposed by the optical path superimposing means into a substantially parallel light beam. Need not be provided for each laser light source, and the apparatus can be made compact. Further, it is not necessary to make the magnification β in the sub-scanning direction of the scanning optical system different for each laser light source, and the beam waist shift amount between the laser light sources due to a change in environment (temperature) is reduced, and the beam diameter can be stabilized.

Further, the laser beam emitted from the light beam converting means is made different by changing the wavelength and the divergence angle of the semiconductor laser device, or by regulating the light beam of the laser beam emitted from the high-power semiconductor laser device by the regulating member. The diameter of the beam can be made different, thereby increasing the degree of freedom in setting the combination of image densities. In addition, by turning on a plurality of laser light sources in synchronization, the laser beams emitted from the laser light sources can be combined to form a low-density image on the image surface. Further, by providing an interference film for preventing a light quantity loss in the optical path superposing means, an optical system with a small energy loss of the laser beam can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an image density switching scanning optical apparatus according to the present invention.

FIG. 2 is a front view showing a light source block used in the scanning optical device shown in FIG.

FIG. 3 is a plan view of the light source block shown in FIG.

FIG. 4 is a left side view of the light source block shown in FIG. 2;

FIG. 5 is a right side view of the light source block shown in FIG. 2;

FIG. 6 is a graph showing a photoconductor sensitivity characteristic of a photoconductor drum used in the scanning optical device shown in FIG. 1;

FIG. 7 is a graph showing a reflectance characteristic of an interference film used in the scanning optical device shown in FIG. 1;

FIG. 8 is an optical path diagram of the light source block shown in FIG.

9A and 9B show a second embodiment of the image density switching scanning optical apparatus according to the present invention, wherein FIG. 9A is an optical path diagram of a light source block in a sub-scanning direction, and FIG. 9B is an optical path of a light source block in a main scanning direction. FIG.

10 is a control circuit block diagram of the semiconductor laser device shown in FIG.

FIG. 11 is an energy distribution diagram of a laser beam on a photosensitive drum.

FIG. 12 is an optical path diagram of a light source block showing a third embodiment of the image density switching scanning optical apparatus according to the present invention.

13A and 13B are diagrams illustrating a divergence angle of the semiconductor laser device illustrated in FIG. 12, wherein FIG. 13A is a diagram illustrating a semiconductor laser device having a small divergence angle, and FIG. 13B is a diagram illustrating a semiconductor laser device having a large divergence angle. FIG.

FIG. 14 is an optical path diagram of a light source block showing a fourth embodiment of the image density switching scanning optical apparatus according to the present invention.

FIG. 15 is an optical path diagram of a light source block showing a fifth embodiment of the image density switching scanning optical apparatus according to the present invention.

[Explanation of symbols]

 Reference numerals 1, 2, semiconductor laser element 3, beam splitter 3a, overlapping surface 4, collimator lens 5, cylindrical lens 6, polygon mirror 7, scanning lens group 8, dual-wavelength sensitive photosensitive drum 9, interference film 36, 37 drive Circuit 38 ... Image control circuit 41, 42 ... Semiconductor laser device 60 ... Aperture regulating plate L1, L2 ... Laser beam

Claims (6)

[Claims] A plurality of laser light sources that are individually turned on, an optical path overlapping unit that overlaps optical paths of laser beams emitted from the laser light source, and a laser beam emitted from the optical path overlapping unit. Light beam converting means for converting into a parallel light beam, the optical path superimposing means is disposed between the laser light source and the light beam converting means along the optical path, each laser beam emitted from the laser light source, An image density switching scanning optical apparatus, wherein the light flux converting means is emitted with different beam diameters. 2. The image density switching scanning optical device according to claim 1, wherein said plurality of laser light sources can be turned on synchronously. 3. The laser light source according to claim 1, wherein said laser light source is two laser light sources, and said optical path superimposing means transmits a laser beam emitted from one of said laser light sources and emits a laser beam emitted from the other laser light source. 2. The image density switching scanning optical device according to claim 1, further comprising a surface for reflecting the beam, and an interference film provided on the surface for preventing a loss of light amount. 4. The semiconductor laser device according to claim 1, wherein the laser light source is a semiconductor laser device that emits laser beams having different wavelengths from each other, and further includes a multi-wavelength sensitive photoreceptor having a sensitivity peak at a wavelength of the laser beam of the semiconductor laser device. The scanning optical device according to claim 1, wherein 5. An image density switching scanning optical apparatus according to claim 1, wherein said laser light sources are semiconductor laser elements which emit laser beams having different divergent angles. 6. A regulating member for regulating a light beam of a laser beam radiated from the high-power side semiconductor laser element, wherein the laser light source is a semiconductor laser element which emits laser beams having mutually different outputs. 2. The optical scanning apparatus according to claim 1, further comprising: