JPH07181412A - Multibeam scanner - Google Patents

Abstract

PURPOSE:To realize a multibeam scanner which facilitates adjustment of scanning line pitches and has excellent stability of the scanning line pitches with lapse of time. CONSTITUTION:This multibeam scanner is substantially integrally constituted with a light source device and has beam inclining means which are set with a prescribed inter-beam angle thetaB in a direction for setting a prescribed inter- beam angle and inclines the direction of the plane copossessed by n-pieces of synthesized beams at a prescribed angle thetaR of inclination with the direction corresponding to main scanning between the respective light beams of the synthesized beams emitted from this light source. The angles thetaB and thetaR are so set that conditions (I) thetaB. sinthetaR=tan<-1>-thetaRtheta(Ps/¦fS¦) and (II) thetaB>=tan<-1>(PS/¦fS¦) are satisfied with respect to the focal length fS in the direction corresponding to sub-scanning of an imaging optical system and the scanning line pitch PS on the plane to be scanned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a "multi-beam scanning device". The present invention can be used in laser printers, digital copying machines, laser facsimiles and the like.

[0002]

2. Description of the Related Art Light beams from a plurality of semiconductor lasers are collimated to form sub-scanning corresponding directions (on a virtual optical path in which an optical path from a light source to a surface to be scanned is linearly expanded along an optical axis). It refers to a direction parallel to the sub-scanning direction.
A direction corresponding to the main scanning direction in the virtual direction and parallel to the main scanning direction is referred to as a main scanning corresponding direction) and is combined with a minute angle, and is combined onto the surface to be scanned by the imaging optical system via the deflecting means. A "multi-beam scanning device" is known in which an image is formed as a plurality of light spots and a plurality of lines are scanned at one time.

For the sake of concreteness of description, if the number of semiconductor lasers is two, it is possible to scan two lines at a time by the above method. At this time, two light beams are formed in the "direction corresponding to sub-scanning". When the angle is “θ _S ”, the line spacing between the scanning lines formed by the two light spots formed on the surface to be scanned, that is, the scanning line pitch: P _S is the focal length of the imaging optical system in the sub-scanning corresponding direction. as "f _S" a, P _S = | given by _{^{tan ~ 1 θ S (1)}} | f S. Generally, | f _S | is about 50 to 300 mm, and P _S is, for example, “scanning density” of 400 d.
Assuming pi, it is 63.5 μm. Scan line pitch P
_{For S} = 63.5 μm, the above range of | f _S |
Angle: θ _S is 0.7 to 4.4 when calculated based on the equation (1).
It will be a minute. This is an extremely small angle. Moreover,
Even if the angle: θ _S slightly fluctuates “± 10 seconds”, the scanning line pitch fluctuates ± 2.4 to 14.5 μm.

That is, the angle: θ _S must be adjusted with extremely high accuracy in order to realize good multi-beam scanning while keeping the scanning line pitch appropriate. As a method for adjusting the angle between the light beams, the method disclosed in Japanese Utility Model Laid-Open No. 62-109134 and the method disclosed in Japanese Patent Laid-Open No. 60-166916 are known.

However, in the former method, since the angle θ _S is directly and manually adjusted, a high degree of skill is required for accurate adjustment and the ease of adjustment is lacking. In the latter method, the servo mechanism is used for automatic adjustment, but the mechanism is complicated and the cost is high.
It is difficult to control dimensionally stably.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is easy to adjust the scanning line pitch, and the multi-beam scanning device is excellent in the stability of the scanning line pitch over time. For the purpose of providing.

[0007]

A multi-beam scanning device according to a first aspect of the present invention is configured such that "n (≧ 2) semiconductor lasers and n light beams from these semiconductor lasers are substantially parallel to each other. A light source device having n collimating lenses as light fluxes, a beam combining means for combining n light beams converted into parallel light fluxes, and a deflecting means for deflecting a plurality of light beams emitted from the light source device, An imaging optical system for forming a plurality of light beams emitted from the light source device as light spots on a surface to be scanned via the deflecting means, and a multi-beam scanning device characterized by the following features. And

That is, the light source device is "substantially integrally formed", and a predetermined "beam angle: θ _B " is a predetermined "beam interval" between the light beams of the combined beam emitted from the light source device. It has a “beam tilting means” that tilts the direction of the plane shared by the n beams that are combined and set in the “angle setting direction” with respect to the main scanning corresponding direction by a predetermined tilt angle: θ _R. When the focal length of the imaging optical system in the sub-scanning corresponding direction is f _S and the scanning line pitch on the surface to be scanned is P _S , the angles: θ _B and θ _R satisfy the condition (I) θ _B · sin θ _R = tan ~ ¹ (P _S / | f _S
│) (II) θ _B > = tan ~ ¹ (P _S / │f _S │) is set to be satisfied.

Various forms are possible as the "beam tilting means" for tilting the direction of the plane shared by the synthesized n beams with respect to the main scanning corresponding direction by a predetermined tilt angle: θ _R. The light source device itself may be tilted with respect to the main scanning corresponding direction to set the angle: θ _R "(Claim 2), or" the image is rotated between the light source device and the deflecting means. A plane for sharing the chief ray of a plurality of light beams incident on the imaging optical system by providing a beam tilting means including a child,
A predetermined inclination angle: θ _R with respect to the main scanning corresponding direction ”may be set (claim 3).

Further, a plurality of collimating lenses in the light source device are provided on the same substrate in one row with their optical axes parallel to each other, and a plurality of semiconductor lasers are arranged on the substrate via their respective supports. The predetermined inter-beam angle: θ _B can be set by the positional relationship between the position of the light emitting portion of each semiconductor laser and the optical axis of the corresponding collimating lens (claim 4).

The "beam combining means" in the light source device is
It is possible to have a half-wave plate, a polarization beam splitter, and a quarter-wave plate (Claim 5), or, as in the invention according to Claim 6, the beam combining means is "n-1". It is also possible to have a "beam combining prism" in which one beam splitter and one mirror are integrated.

Further, between the light source device and the imaging optical system,
It is possible to "have the beam shaping aperture separately from the light source device" (claim 7).

The invention according to claim 8 is the above-mentioned claims 1 to 7.
In addition to the configuration of the described multi-beam scanning device, "tilt angle:
θ _R can be switched among a plurality of angles set in advance according to a plurality of scanning line pitches. ”The beam tilting means is controlled according to the pixel density, and the tilt angle: θ _R is switched and controlled. It has "control means".

[0014]

As described above, according to the present invention, the focal length in the sub-scanning corresponding direction of the imaging optical system is f _S , the scanning line pitch is P _S on the surface to be scanned, and the angles are θ _B and θ.
By setting _R so as to satisfy the conditions (I) and (II), a desired scan line pitch: P _S is set.

The imaging optical system is an ordinary fθ lens or the like when a plurality of light beams from the light source device are deflected as parallel light beams, and the light beam from the light source is a line image imaging optical system. Therefore, when an image is formed as a "line image" in the vicinity of the starting point of the deflection by the polarization means, the anamorphic anamorphic relationship is formed in which the image formation position of the line image and the surface to be scanned have a geometrical-optical conjugate relationship with respect to the sub-scanning corresponding direction. The fθ lens and the like and the above-mentioned line image forming optical system form an “image forming optical system”. In the latter case, "the focal length of the imaging optical system in the sub-scanning corresponding direction"
Is defined as the "product" of the focal length of the linear image forming optical system: f _cy and the lateral magnification of the anamorphic fθ lens or the like in the sub-scanning corresponding direction: β.

[0016]

EXAMPLES Specific examples will be described below. Figure 1
An embodiment in which the invention described in claims 1, 2, 5, 6, and 7 is applied when the number of semiconductor lasers is two is shown.

Reference numeral 10 indicates a light source device. The light source device 10 includes two semiconductor lasers 11 and 12, two collimating lenses 13 and 14, a half-wave plate 15,
It has a beam combining prism 16 and a quarter-wave plate 17, which are relatively positioned and “substantially integrated” in a casing shown by a broken line.

The light beams emitted from the semiconductor lasers 11 and 12 (both of which are linearly deflected and whose deflection directions are parallel to each other) are converted into "substantially parallel light beams" by the collimating lenses 13 and 14, respectively. The light beam emitted from the semiconductor laser 12 and made into a parallel light flux by the collimator lens 14 is a mirror surface 16 of the beam combining prism 16.
1 and further reflected by the polarization beam splitter surface 162 of the prism 16, and the quarter wavelength plate 17
Is converted into “circularly polarized light” and emitted from the light source device 10.

On the other hand, the light beam emitted from the semiconductor laser 11 and collimated by the collimator lens 13 has its polarization direction rotated by 90 ° by the ½ wavelength plate 15, and the polarization beam splitter of the beam combining prism 16 is rotated. The light passes through the surface 162, is converted into circularly polarized light by the quarter-wave plate 17, and is emitted from the light source device 10. In this way
The light beams from the semiconductor lasers 11 and 12 are collimated, combined, and emitted from the light source device 10. Half-wave plate 15, beam combining prism 16, and quarter-wave plate 17
And constitute a "beam combining means" (claim 5).

The two light beams emitted from the light source device 10 are
The beam is shaped into a predetermined beam shape by the beam shaping aperture 30 and is incident on the cylinder lens 30 which is a line image forming optical system. The cylinder lens 30 has a positive power only in the sub-scanning corresponding direction, converges the two parallel light beams only in the sub-scanning corresponding direction, and performs main scanning in the vicinity of the deflecting / reflecting surface of the rotary polygon mirror 40 as a deflecting means. A long line image is formed in the corresponding direction.

When the two light beams are reflected by the deflecting / reflecting surface of the rotary polygon mirror 40, they enter the fθ lens 32 and fθ
By the action of the lens 32, images are formed on the surface to be scanned 50 as two light spots. That is, the fθ lens 32 is an anamorphic lens in which the position of the deflecting / reflecting surface of the rotary polygon mirror 40 and the position of the surface to be scanned 50 have a “geometrical optical conjugate relationship in the sub-scanning corresponding direction”, and the cylinder lens 30.
Together with this, it constitutes an “imaging optical system”. Therefore, as described above, the focal length of the imaging optical system is the product of the focal length of the cylinder lens 30 in the sub scanning corresponding direction: f _cy and the lateral magnification of the fθ lens 32 in the sub scanning corresponding direction: β. _cy · β ”.

When the rotary polygon mirror 40 rotates at a constant speed, the two light beams are deflected at a constant angular velocity, and the surface to be scanned 50 is scanned at a constant speed for two lines at a time by the two light beams. A photoconductive recording medium is generally arranged at the position of the scanned surface 50.

FIG. 2 shows how the two light beams are imaged. FIG. 2 shows the surface to be scanned 5 from the cylinder lens 30.
2 shows a state in which the optical path reaching 0 is linearly developed, (a) is drawn so that the vertical direction in FIG. 2 corresponds to the main scanning corresponding direction, and (b) is the vertical direction in the drawing corresponding to the sub scanning corresponding direction. It is drawn to correspond to. The light beam B1 shown by the solid line is shown in FIG.
The light beam is emitted from the semiconductor laser 11 shown in FIG. A light beam B2 shown by a broken line is a light beam emitted from the semiconductor laser 12.

Returning to FIG. 1, the “light emitting portion” of the semiconductor laser 11 is located on the optical axis of the collimating lens 13, and the light beam emitted from the semiconductor laser 11 is parallel to the optical axis of the collimating lens 13. It becomes a parallel light flux. The optical axis of the collimator lens 13 coincides with the "imaging optical system (30, 32)" in a state where the optical path from the light source to the surface to be scanned is developed.

On the other hand, the optical axis of the collimator lens 14 is also “optical axis aligned” with the optical axis of the imaging optical system, but the “light emitting portion” of the semiconductor laser 12 is slightly deviated from the optical axis of the collimator lens 14. Due to this "deviation", the parallel light flux emitted from the collimator lens 14 becomes a beam that is inclined with respect to the optical axis of the collimator lens 14, and thus the optical axis of the imaging optical system. Therefore, 2 emitted from the light source device
Of the light beams of the book, the light beam (the above-mentioned light beam B1) which is collimated by the collimator lens 12 is parallel to the optical axis of the imaging optical system, while the collimator lens 14 collimates the parallel light beam. The converted light beam B2 has an inter-beam angle: θ _B with the light beam B1.

Explaining the example shown in FIG. 1, the straight line connecting the light emitting portions of the semiconductor lasers 11 and 12 (inter-beam angle setting direction) is parallel to the direction connecting the centers of the collimating lenses 13 and 14. The light emitting portion of the semiconductor laser 12 has the collimating lens 1 in the beam angle setting direction.
That is, there is a slight deviation from the optical axis of No. 4. Therefore,
Between the two light beams B1 and B2 which are combined and emitted, there is an opening of the inter-beam angle: θ _B in a plane sharing the optical axes of the collimator lenses 13 and 14.

As shown in FIG. 1, the light source device 10 is tilted clockwise from the direction corresponding to the main scanning by the "tilt angle: θ _R " with the optical axis of the collimator lens 13 as the rotation axis. Therefore, the above-mentioned beam angle setting direction is tilted by the tilt angle: θ _{R with} respect to the main scanning corresponding direction. That is,
A light source device holding mechanism (not shown) for fixing the light source device 10 by inclining the light source device 10 with respect to the main scanning direction by an inclination angle of θ _R ,
This constitutes the "light beam tilting means" (claim 2).

As described above, the inter-beam angle: θ _B exists between the light beams B1 and B2 emitted from the light source device 10, and the inter-beam angle setting direction is the inclination angle: θ _{R with} respect to the main scanning corresponding direction. since the tilted by two light spots imaged on the scanned surface 50 in the main scanning direction a distance: P _M, the distance in the sub-scanning direction: will only shift that P _S, the distance: P _S is It will give the scan line pitch. In this example, the beam angle setting direction is set to the semiconductor laser 1
Although the arrangement directions of 1 and 12 are set, the present invention is not limited to this, and the “beam angle setting direction” can be set to an arbitrary direction, for example, a direction orthogonal to the arrangement direction of the collimator lenses 13 and 14.

FIG. 3 shows the relationship between the two light beams B1 and B2 (indicated by the chief rays) emitted from the light source device. Between the light beams B1 and B2, the angle between the beams is:
Since θ _B is set and the inter-beam angle setting direction is inclined with respect to the main scanning corresponding direction by: inclination angle: θ _R , the two light beams B1 and B2 are mutually “ The angles of “θ _M ” are formed, and the angles corresponding to the sub-scanning corresponding directions form the angles of “θ _S ”.

The angles: θ _M and θ _S are the inter-beam angle: θ _B , the tilt angle: θ _R and tan θ _M = tan θ _B · cos θ _R
(2) tan θ _S = tan θ _B · sin θ _R
There is a relationship of (3).

Since θ _M , θ _S , and θ _B are minute angles, these equations (2) and (3) are expressed by θ _M = θ _B · cos θ _R (2 ′) θ _S = θ _B · sin θ _R ( 3 ') can be represented. The focal length of the imaging optical system is f _M for the main scanning corresponding direction and | f _S | (= for the sub scanning corresponding direction.
f _cy · β), P _M and P _{S in} FIGS. 1 and 3 are P _M = f _M · θ _M = f _M · θ _B · cos θ _R (4) P _S = | f _S | · tan θ _S = | F _S | · tan (θ _B · sin θ _R ) (5)

Therefore, in order to realize the desired scanning line pitch: P _S , the angles: θ _B , θ _R should satisfy (5), and for that purpose, “θ _B · sin θ _R = _{^{tan ~ 1 (P S / |}} f S |) "that is, the condition (I) need be satisfied.

Here, a specific numerical example will be given.

In the configuration of the embodiment shown in FIG. 1, the focal length of the imaging optical system is f _M = 200 mm in the main scanning corresponding direction,
It is considered that | f _S | = 75 mm is set in the sub-scanning corresponding direction, the inter-beam angle is set to: θ _B = 20 ′, and the scanning line pitch: P _S is adjusted by the tilt angle: θ _R. Pixel density: 24
When θ _R , θ _S , θ _M , P _S , and P _M are given to 0, 300, 400480, 600, and 800 dpi, the following is obtained.

Pixel density (dpi) 240 300 400 480 600 800 800 _R (unit: degree) 14.03 11.19 8.37 6.95 5.54 4.18 θ _S (unit: min) 4.85 3.88 2.91 2.42 1.94 1.46 θ _M (unit: min) 19.4 19.6 19.8 19.9 19.9 19.9 P _S (unit: μm) 105.8 84.7 63.5 52.9 42.3 31.8 P M ( unit: mm) 1.13 1.14 1.15 1.16 1.16 1.16 Δθ R ( in minutes) 42 34 25 21 17 13 Δθ S ( in seconds) 15 12 8.7 7.3 5.8 4.4.

“Δθ _R ” represents the adjustment accuracy for keeping the scanning line pitch: P _S within the setting error: 5%. "Δ
“θ _S ” represents the adjustment accuracy for making the setting error within 5% only by adjusting θ _S , and is for comparison.

If the inter-beam angle: θ _B is set and the scanning line pitch is adjusted with the tilt angle: θ _{R as} in the present invention, θ _S
The accuracy of the adjustment is remarkably gentle and the scanning line pitch can be easily set, as compared with the case where the adjustment is performed only by the adjustment.

However, if the inter-beam angle: θ _B is set too large, the beam pitch in the deflecting means expands, and it is necessary to enlarge the deflecting / reflecting surface, and the tilt angle:
Since the adjustment accuracy with respect to θ _R also becomes strict, it is preferable to set it to 2 to 3 degrees or less.

If the angle between beams: θ _B is too small,
Since the predetermined scanning line pitch cannot be obtained, the lower limit of the inter-beam angle: θ _B must satisfy the condition (II), that is, “θ _B > = tan ~ ¹ (P _S / | f _S |)”. is necessary.

FIG. 4 schematically shows only an essential part of one embodiment of the invention according to claim 3. In order to avoid complication, the same symbols as those in FIG.

In this embodiment, the light source device 10 is not provided with the tilt angle: θ _R , and therefore the inter-beam angle setting direction is parallel to the main scanning corresponding direction.
The two light beams emitted from 0 are in a plane including the main scanning corresponding direction and the optical axis of the imaging optical system, and the inter-beam angle: θ.
Given _B. Note that one of the two light beams
As in the case of the embodiment of FIG. 1, the book has its chief ray aligned with the optical axis of the imaging optical system.

These two light beams are incident on the image rotator 60 and have a predetermined inclination angle with respect to the main scanning corresponding direction:
θ _R Tilted. The beam tilt means is the image rotator 6.
0 and appropriate means (not shown) in the step of adjusting the rotation of the 60 around the optical axis.

Various forms of the image rotator can be used. The image rotator 60 used in the embodiment shown in FIG. 4 is a trapezoidal Dove prism as shown in FIG. 5A, and is rotatable around the optical axis.

When the Dove prism 60 is rotated around the optical axis, the one of the two light beams incident on the Dove prism 60 which matches the optical axis does not change. The angle of the light beam, which is inclined by θ _B , rotates around the optical axis as the Dove prism 60 rotates and exits from the Dove prism 60. Therefore, by adjusting the rotation angle of the Dove prism 60, the two light beams The beam can be given a tilt angle: θ _R.

After the Dove prism 60, it is exactly the same as the embodiment of FIG. As the “image rotator”, instead of the Dove prism 60 shown in FIG. 5A, a concave prism 61 for reflecting light rays three times inside the prism as shown in FIG. 5B, and FIG. ), A curved flat mirror 62A and a flat mirror 62B are associated and integrated (the function is exactly the same as that of the concave prism of (b)), or, as shown in FIG. 5 (e), The two wedge prisms 63A and 63B arranged in series in the optical axis direction, and those independently rotating and adjusted with respect to the optical axis can be preferably used. The wedge prisms 63A and 63B are prisms having a “wedge” cross-sectional shape, as shown in FIG.

FIG. 6 shows an embodiment of the invention described in claim 4. The invention according to claim 4 is "a structure of a light source device".
It is characterized by. The structure of the light source device shown in this embodiment is the same as the light source device 10 in the embodiment of FIGS.
Available as a configuration.

In order to avoid complication, the same reference numerals as those in FIG. 1 are used in FIG. 6 for those which are not likely to be confused.

The collimator lenses 13 and 14 are provided in a line in the vertical direction of the figure with the optical axis parallel to the same substrate 101, and the semiconductor lasers 11 and 12 are provided via the respective supports 102A and 102B. It is arranged on the substrate 101.
The light emitting portion of the semiconductor laser 11 has a collimating lens 1
The substrate 10 is aligned so as to be located on the optical axis of the substrate 3.
It is fixed at 1. On the other hand, the semiconductor laser 12
Can be finely adjusted in the vertical direction in the figure. By this fine adjustment, the light emitting portion of the semiconductor laser 12 and the collimator lens 14 can be adjusted.
By adjusting the "deviation" with respect to the optical axis of, the "inter-beam angle" is given between the two combined light beams B1 and B2, and the inter-beam angle: θ depending on the magnitude of the "deviation".
The size of _B is determined. That is, the semiconductor lasers 11, 1
2 light emitting part positions and corresponding collimating lenses 13 and 1
The inter-beam angle: θ _B is set according to the positional relationship with the optical axis of No. 4.

On the other hand, a holding body 103 is provided on the right side of the substrate 101 in the figure. The holder 103 includes a beam combining prism 16, a half-wave plate 15, and a quarter-wave plate 1.
7 and 7 are fixedly held as shown in the figure and fixed to the right side of the substrate 101.

Therefore, the light beam B1 emitted from the semiconductor laser 11 is collimated by the collimator lens 13, the polarization direction is rotated 90 degrees by the half-wave plate 15, and the light beam B1 is transmitted through the polarization beam splitter surface 162. Collimated lens 1 converted into circularly polarized light by quarter wave plate 17
It is emitted as a parallel light flux that matches the optical axis of 3.

The light emitted from the semiconductor laser 12 is collimated by the collimator lens 14 and is reflected by the mirror 16.
2 and the polarization beam splitter surface 162 are sequentially reflected,
The light beam B is converted into circularly polarized light by the quarter-wave plate 17
1, the inter-beam angle: θ _B in the drawing becomes a light beam B2 inclined and emitted.

With this structure of the light source device, since the "semiconductor laser and collimator lens pair" are arranged in close proximity to each other on the same substrate, expansion and contraction due to mechanical disturbance such as vibration or temperature change of the substrate. Even if occurs, it is difficult for the relative variation in the emission direction of each light beam to occur, and a stable scanning line pitch can be maintained over time.

The light source device shown in FIG. 6 is also an embodiment of the invention described in claim 5. That is, "beam combining means"
Is a half-wave plate 15 and a polarization beam splitter 162.
And a quarter wavelength plate 17. As is well known, the light beam emitted from the semiconductor laser is a substantially “linearly polarized light beam”. Therefore, by combining this with a combination of a half-wave plate and a polarization beam splitter, the light from each semiconductor laser can be obtained. Can be combined with minimum light loss, the efficiency of light utilization in multi-beam scanning can be improved, and high-speed optical scanning can be realized.

Further, the two combined light beams are converted into "1 /
It is used after being converted into circularly polarized light by a four-wave plate. Figure 7
Shows the well-known relationship between the incident angle and the reflectance for P, S polarized light and circularly polarized light. For example, the incident angle change region in the rotary polygon mirror is set to 3 in correspondence with the effective region of optical scanning.
If the angle is 0 ° ± 20 ° (10 to 50 °), the reflectance variation in this incident angle region is the smallest in the case of “circularly polarized light”, and is accompanied by the “change of the incident angle” on the deflective reflection surface. In addition to effectively suppressing the fluctuation of the reflectance, fθ after the deflecting means
Since the reflectance and the transmittance of the lens and the like are the same for each light beam, the fluctuation of the exposure intensity due to the image height of the light spot can be suppressed to a small level, and the uneven exposure between the light beams does not occur.

The embodiment shown in FIG. 6 is an embodiment of the invention described in claim 6. That is, for the number of semiconductor lasers: n = 2, the number of “beam combining means” is n−1, that is, one beam splitter (polarization beam splitter surface 1).
62) and a beam combining prism 16 in which one mirror (mirror 161) is integrated.

In the embodiment described with reference to FIGS. 1 to 6, the number of semiconductor lasers: n is 2, but in the present invention,
The number of semiconductor lasers: n is not limited to 2, but may be an appropriate number of 3 or more. In this case, generally, n light beams are combined by inclining each other by a predetermined inter-beam angle, and in principle, n-1 beam splitters and one mirror may be used for composition. , N beam splitters and one mirror are “separate” from each other, alignment between these beam splitters and mirrors is troublesome, and even after alignment, mechanical alignment is difficult. Disturbances due to vibrations and the like tend to cause mutual positional deviations, and it is difficult to achieve temporal stability of the scanning line pitch.

In order to solve such a problem, claim 6
As described in the invention, "n-1 beam splitters and 1
It is better to integrate the mirrors as a beam combining prism. In that case, it is needless to say that a polarized beam splitter is preferable as the beam splitter from the viewpoint of light utilization efficiency.

FIG. 8 shows two embodiments in which the invention of claim 6 is applied when n = 4. In (a), the slope portion 16A1 of the beam combining prism 16A is a mirror,
The beam splitter surfaces 16A2, 16A3, 16A4 are
Both are polarization beam splitter surfaces. In (b), the mirror 16B1 is provided inside the beam combining prism 16B.
Is provided, and the beam splitter surfaces 16B2, 16B3
16B4 is a polarization beam splitter surface.

Further, with respect to the beam combining prism, 1 /
The two-wave plate 14 and the quarter-wave plate 17 may be integrated.
FIG. 9 shows two examples of this case. An example of (a) is shown in FIG.
In the example of the light source device shown in FIG. 1, the half wave plate 15 and the quarter wave plate 17 are
This is an example in which the two-wave plate 15 is integrated by sandwiching the polarization beam splitter surface and bonding the two. (B) is an example in which the ½ wavelength plate 15 is opposed to the mirror and the ½ wavelength plate 17 is integrated with the beam combining prism 16 so as to correspond to the polarization beam splitter surface.

In the example shown in FIGS. 9A and 9B, the deflection direction of the light beam emitted from each semiconductor laser is (a).
And (b) are different from each other by 90 degrees.

Beam shaping aperture 2 shown in FIGS.
0 is commonly used for two light beams combined by the light source device. In principle, the beam shaping by the beam shaping prism may be performed for each light beam before the light beams from the respective semiconductor lasers are combined. However, in order to perform beam shaping for each light beam before combining, there is the trouble of separately aligning and assembling beam shaping apertures equal to the number of light beams, and at the position of each beam shaping aperture, When an error occurs due to an assembly error or a change with time, the light beam deviates from the original light beam in the “direction orthogonal to the optical axis”.

For example, FIG. 10 (a) shows a case where the light beam B2, which is originally like a "dashed line", shifts as shown by the solid line. Such shift shifts the light spot position,
This causes problems such as scan line bending.

When the beam shaping aperture is provided as a part of the light source device, the "main axis of the aperture" is
Since it is not always parallel to the main / sub-scanning corresponding direction, the light spot shape on the surface to be scanned may be an “inclined shape” as shown in FIG.

In order to effectively solve such a problem, the "beam shaping aperture" as in the invention of claim 7 is used.
Is separately provided from the light source device between the light source device and the imaging optical system. The embodiment shown in FIGS. 1 and 4 has such a structure.

In this way, since the light beams are combined and then beam-shaped, as shown in FIG. 10C, even if the light beam shifts on the light source device side, the beam-shaped light is There is no shift in the beam and there is no risk of the light spot shape tilting.

FIG. 11 shows an embodiment in which the invention described in claim 8 is applied to the apparatus example shown in FIG. Therefore, as for what seems not to be confused,
The same symbols as in are used.

As shown in FIG. 11A, the signal from the pixel density switching signal generating means 87 is transmitted through the scanning frequency control means 88 on the one hand to the rotary polygon mirror 4 which is a deflecting means.
On the other hand, it controls the scanning line pitch detection means 86, the stepping motor driver 85, the pixel clock control means 84, and the drive current control means 82.

An "image clock" controlled in accordance with the pixel density is issued from the pixel clock control means 84, and this image clock is applied to the AND gate 83, and the AND gate 83 is timed by the applied image clock. Then, the “pixel data” is output to the laser driver 81.

The laser driver 81 passes the "control current controlled by the drive current control means 82 according to the pixel density" to the semiconductor laser in accordance with the pixel data from the AND gate, and causes each semiconductor laser to respond to the pixel data. Make it blink.

As shown in FIG. 11B, the drive gear 85A provided on the stepping motor 850 is integrated with the outer periphery of the holder 601 which holds the Dove prism 60, which is an image rotor, rotatably around the optical axis. The driven gear 602 is meshed.

Further, as shown in FIG. 11A, a position sensor 7 such as a CCD sensor is provided near the surface 50 to be scanned.
0 is provided so that the scanning line pitch can be detected by scanning two light spots.

Tilt angle given by the beam tilting means:
θ _R can be switched between “a plurality of angles preset according to a plurality of scanning line pitches”, and the tilt angle: θ is controlled by controlling the “beam tilting means” by the control means according to the pixel density. _R is switched and controlled. In this example, the beam tilting means includes a Dove prism 60, a holder 601, and a stepping motor 850.

The "control means" is composed of the pixel density switching signal generating means 87, the position sensor 70 and the scanning line pitch detecting means 86.

When converting the pixel density, a "signal" is generated from the pixel density switching signal generating means 87. This signal controls the scanning frequency control circuit 88 to set the rotation speed of the rotary polygon mirror 40 to a rotation speed according to the selected pixel density. On the other hand, the signal is the pixel clock control means 8
4, the pixel clock is adjusted in accordance with the new pixel density, the drive current control means 82 is controlled, and the light emission amount of the semiconductor laser is set to a size suitable for the new pixel density.

Optical scanning is performed at this new light intensity and scanning speed, and the scanning line pitch at that time is detected by the scanning line pitch detecting means 86 via the position sensor 70. The scanning line pitch detecting means 86 sends a signal according to the detected scanning line pitch to the stepping motor driver 85.

The stepping motor driver 85 is controlled by a signal from the pixel density switching signal generating means 87,
Based on the signal from the scanning line pitch detecting means 86, the stepping motor 850 is driven to rotate the dove prism 60 around the optical axis. With this rotation, the scanning line pitch changes in minute steps. Scanning line pitch detecting means 85
However, when the "pitch specified by the signal from the pixel density switching signal generating means 87" is detected, the means 85 controls the stepping motor driver 85 to stop the driving of the stepping motor 850. In this way, the desired pixel density can be realized, and the beam tilting means is switched to a new tilt angle: θ _R. In the above case, the tilt angle:
Switching amount of θ _R : With respect to δθ _R , the rotation amount of the Dove prism 60 around the optical axis is “½ · δθ _R ”.

In the case of the embodiment shown in FIG. 1, the light source device 10 itself can be rotated by a stepping motor so that the inclination angle can be similarly switched to convert the pixel density.

[0078]

As described above, according to the present invention, a novel multi-beam scanning device can be provided. Since the multi-beam scanning device of the present invention is configured as described above, it is easy to adjust the scanning line pitch, the proper scanning line pitch can be set easily and surely, and the scanning line pitch can be changed with time. Excellent stability (claims 1-8).

According to the second aspect of the invention, since the light source device itself is rotated for adjustment, the scanning line pitch can be continuously changed, and the scanning line pitch can be easily adjusted. According to the third aspect of the present invention, since the tilt angle is set by rotating the image rotator, which is smaller than the light source device, the tilt angle setting mechanism can be downsized, and the light source device becomes fixed. Good stability of characteristics.

[0080] In the present invention of claim 4 wherein, even if a disturbance such as vibration, a beam between the angle between the light beams emitted from the light source device: theta _B hardly changes, easy to maintain a stable scanning line pitch . According to the fifth aspect of the invention, the light beams can be combined with good light utilization efficiency, and variations in exposure intensity due to the image height of the light spot, so-called shading, and exposure amount difference between the light beams can be effectively prevented.

According to the sixth aspect of the invention, the combined state of the light beams is unlikely to change with time, and a stable scanning line pitch can be obtained. According to the invention described in claim 7, it is possible to prevent mutual beam shift between the multiple beams and inclination of the light spot shape. According to the invention described in claim 8, the scanning line pitch can be easily and surely switched according to the pixel density.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the invention described in claims 1, 2, 5, 6, and 7.

FIG. 2 is a diagram for explaining the operation of the imaging optical system in the spin example.

FIG. 3 is a diagram for explaining a relationship between an inter-beam angle: θ _B and each inclination: θ _R.

FIG. 4 is a diagram for explaining one embodiment of the invention described in claims 1, 3, 5, 6, and 7.

FIG. 5 is a diagram showing four examples of image rotators.

FIG. 6 is a diagram for explaining the first embodiment of the invention according to claim 4;

FIG. 7 is a diagram for explaining an effect of the invention according to claim 5;

FIG. 8 is a diagram for explaining an embodiment of the invention according to claim 6;

FIG. 9 is a diagram for explaining a modified embodiment of the invention according to claim 6;

FIG. 10 is a diagram for explaining an effect of the invention described in claim 7;

FIG. 11 is a diagram for explaining one embodiment of the invention according to claim 8;

[Explanation of symbols]

 10 Light Source Device 11, 12 Semiconductor Laser 13, 14 Collimating Lens 15 1/2 Wave Plate 16 Beam Combining Prism 17 1/4 Wave Plate 20 Beam Shaping Aperture 30, 32 Imaging Optical System 40 Deflection Means 50 Scanned Surface

Claims (8)

[Claims] 1. An n (≧ 2) number of semiconductor lasers, an n number of collimator lenses for converting n number of light beams from these semiconductor lasers into substantially parallel light fluxes, and n number of parallel light fluxes. A light source device having a beam combining means for combining light beams, a deflection means for deflecting a plurality of light beams emitted from the light source device, and a plurality of light beams emitted from the light source device via the deflection means. In a multi-beam scanning device having an image forming optical system for forming an image as a light spot on a surface to be scanned, the light source device is configured substantially integrally, and
A predetermined inter-beam angle: θ _B is set in a predetermined inter-beam angle setting direction between the light beams of the combined beam emitted from the light source device,
There is a beam tilting means for inclining a predetermined tilt angle: θ _R with respect to the main scanning corresponding direction, and the focal length of the imaging optical system in the sub scanning corresponding direction is f.
_{Where S} is the scanning line pitch on the surface to be scanned, and P _S is the scanning line pitch, the above angles: θ _B and θ _R are given by the condition (I) θ _B · sin θ _R = tan to ¹ (P _S / | f _S
|) (II) A multi-beam scanning device characterized in that θ _B > = tan ~ ¹ (P _S / | f _S |) is set to be satisfied. 2. The multi-beam scanning device according to claim 1, wherein the beam tilting means is configured to set the angle: θ _R by tilting the light source device itself with respect to the main scanning corresponding direction. apparatus. 3. A beam tilting means including an image rotator is provided between the light source device and the deflecting means, and a plane sharing a chief ray of a plurality of light beams incident on the imaging optical system is adapted for main scanning. A multi-beam scanning device having a predetermined tilt angle: θ _R with respect to the direction. 4. A plurality of collimator lenses in a light source device are provided on the same substrate in one row with their optical axes parallel, and a plurality of semiconductor lasers are arranged on the substrate via respective supports. 4. The multi-beam according to claim 1, 2 or 3, wherein the predetermined inter-beam angle: θ _B is set according to the positional relationship between the position of the light emitting portion of each semiconductor laser and the optical axis of the corresponding collimating lens. Scanning device. 5. The multi-beam scanning device according to claim 1, wherein the beam synthesizing means has a half-wave plate, a polarization beam splitter, and a quarter-wave plate. . 6. The multi-beam scanning device according to claim 4, wherein the beam synthesizing means has a beam synthesizing prism in which n-1 beam splitters and one mirror are integrated. 7. A beam shaping aperture is provided between the light source device and the imaging optical system as a separate body from the light source device, according to claim 1, 2, 3 or 4 or 5 or 6. Multi-beam scanning device. 8. An inclination angle: θ _R can be switched between a plurality of angles set in advance according to a plurality of scanning line pitches,
The tilt angle is controlled by controlling the beam tilting means according to the pixel density:
A multi-beam scanning device comprising control means for switching and controlling θ _R.