JP3271817B2 - Optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly to an optical scanning device capable of optically scanning a plurality of lines at a time using a semiconductor laser array as a light source.

[0002]

2. Description of the Related Art A "semiconductor laser array" is known as a monolithic light source element in which a plurality of minute laser light sources are arranged at equal intervals in a row direction. Since each laser beam emitted from a plurality of laser light sources in a semiconductor laser array can be intensity-modulated independently of each other, a method of "optical scanning a plurality of lines at once" by using this as a light source. An optical scanning device has been proposed (JP-B-60-33019).

Since the distance between laser light sources in a semiconductor laser array is small, light beams from a plurality of laser light sources can be deflected by a common optical deflector and imaged by a common imaging optical system. Therefore, at least one of the laser light sources is assumed to have a linear virtual optical path developed along the optical axis from an optical path extending from the light source to the surface to be scanned along the sub-scanning direction. Means a direction parallel to the sub-scanning direction. A direction parallel to the main scanning direction on the optical path is called a main scanning corresponding direction). In this manner, the trajectory of the light spot on the surface to be scanned by the laser beam from the laser light source shifted from the optical axis of the imaging optical system, that is, the `` scanning line '' is not a straight line. Draw a curve, so-called The bending of the scanning line "occurs.

In general, when a scanning line is bent, the distance between adjacent scanning lines changes with the image height of a light spot. In such a situation, when optical writing by optical scanning is performed, writing and recording are performed. "Density unevenness" appears in the image.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and provides a novel optical scanning device capable of effectively reducing the insufficiency of optical scanning caused by the above-described bending of the scanning line. Aim.

[0006]

According to an optical scanning apparatus of the present invention, "n (> 1) light beams from a semiconductor laser array are deflected by a common light deflecting means and scanned by a common imaging optical system. Optical scanning of n lines at a time by condensing as n light spots on a surface "
The features are as follows.

In other words, the semiconductor laser array is arranged such that the direction of arrangement of the light emitting sections is inclined at an inclination angle θ with respect to the sub-scanning corresponding direction. The inclination angle: theta is "when the trajectories of n optical spot on the scanned plane l _{i (i} = 1~n), adjacent loci: l _i, the spacing between the l i _{+ 1:} P _si
Average in the effective main scanning area of (i = 1 to n-1): P
_sia is a predetermined value that is equal to each other for i = 1 to n−1 ”.

[0008] Here, the average: P _sia is strictly, when the image height position in the main scanning direction of the light spot z, the length of the effective main scanning region and _{Z 0, P sia = {∫P} si (z) Defined by dz ₀ / Z ₀ , but as in the embodiment described later, the interval: P _si (Zj) at a plurality of appropriately selected image height positions: Zj (j = 1 to m) An average, that is, {ΣP _si (Zj)} / m (the sum takes a subscript: j and takes 1 to m) may be used.

The trajectories of n light spots on the surface to be scanned: l _i (i = 1 to n) are desirably set to be symmetrical with respect to the reference scanning line in the sub-scanning direction ( Claim 2). The “reference scanning line” is a scanning line that is a straight line when the scanned surface is ideally scanned by a virtual light beam whose principal ray coincides with the optical axis of the imaging optical system.

According to the optical scanning device of the present invention, the synchronous light detecting section for detecting the deflection light beam heading to the optical scanning area and synchronizing the optical scanning is composed of "n deflection light beams separated in the sub-scanning corresponding direction". (A third aspect of the present invention).

[0011]

FIG. 2 schematically shows only an essential part of an example of an optical scanning apparatus to which the present invention is applied. Reference numeral 1 indicates a light source. Light source 1
Uses a semiconductor laser array as a light source element. The semiconductor laser array used for the light source element is
As shown by reference numeral 10 in FIG. 1B, a plurality of minute laser light sources 20 are monolithically arranged at regular intervals in one direction (the y direction in the figure), and are emitted from each laser light source 20. The intensity of the divergent laser beam can be intensity-modulated independently for each laser light source. The far field pattern of each emitted laser beam has an elliptical shape with the minor axis direction being the arrangement direction (y direction) of the laser light sources 20 as illustrated.

Returning to FIG. 2, a plurality of laser beams from the light source 1 are converted into parallel beams by the collimator lens 2, and the beam diameter is regulated by the aperture 9 before being incident on the cylinder lens 3. The cylinder lens 3 has a positive power only in the sub-scanning corresponding direction, and converges the plurality of laser beams only in the sub-scanning corresponding direction to form a line image long in the main scanning corresponding direction.

The light deflecting means 4 which is a rotary polygon mirror having a deflecting / reflecting surface 4A near the image forming positions of these line images is
The plurality of laser beams are simultaneously reflected and deflected. The plurality of laser beams by the light deflecting unit 4 are transmitted through the optical scanning lens 5 and the correction lens 6, the optical path is bent by the optical path bending mirror 8, and condensed on the photoconductive photoreceptor 7 as a plurality of light spots. I do. The surface of the photoconductor 7 matches the surface to be scanned.

When a plurality of light beams are simultaneously deflected by the light deflecting means 4, a plurality of lines are scanned at once by the plurality of light spots. In other words, a plurality of light beams from the semiconductor laser array are deflected by the common light deflecting means 4 and are constituted by a common imaging optical system (a collimating lens 2, a cylinder lens 3, an optical scanning lens 5, and a correction lens 6). ) Collects light spots on the surface to be scanned as a plurality of light spots, and optically scans a plurality of lines at once.

Since the above-mentioned imaging optical system generally has an enlargement magnification in the direction corresponding to the sub-scanning, the semiconductor laser array 10
If the arrangement direction of the laser light sources 20 in FIG. 1B corresponds to the sub-scanning corresponding direction,
Arrangement pitch of: the P _0, which was enlarged by the magnification becomes the scanning line pitch of the optical scanning, the scanning line pitch in this case is that generally too large to.

Therefore, usually, as shown in FIG.
The arrangement direction of the laser light sources 20 of the semiconductor laser array 10 is inclined with respect to the sub-scanning corresponding direction: X by an inclination angle: θ. In this way, the arrangement pitch of the laser light sources 20 in the sub-scanning corresponding direction is P ₀ · sin θ, and a desired scanning line pitch can be obtained by adjusting the inclination angle: θ.

As described above, when the semiconductor laser array 10 is inclined with respect to the sub-scanning corresponding direction, FIG.
(D), the plurality of light spots SP in the main scanning direction is formed on the surface to be scanned: offset from each other to X _0. Therefore, when performing optical writing by optical scanning, the timing of starting optical scanning is shifted for each optical spot so that optical scanning by each optical spot optically scans the same optical scanning area.

[0018] As described above, the sub-scanning corresponding direction as in FIG. 1 (c), the tilt angle: the semiconductor laser array 10 is inclined at theta, the arrangement pitch of the laser light source in the sub-scanning direction: P _LS is Although P is a ₀ · sin [theta, scan line pitch in this case the surface to be scanned on: P _S is the focal length of the collimator lens 2 in FIG. 2: f _C, the focal length in the sub-scanning direction of the cylindrical lens 3: f _CY ,
Sub-scanning direction lateral magnification at the combined system of the optical scanning lens 5 and the correcting lens 6: using a beta, the _{/ P LS = f C · P} S (f CY · β) (1).

However, the trajectory of each light spot that scans the surface to be scanned due to the above-mentioned "bending of the scanning line" is shown in FIG.
As shown in (a), the curve becomes a curve, and the designed scanning line pitch: P _LS is achieved only at a “specific image height”, and the interval between the trajectories of adjacent light spots increases with the image height of the light spot. Will change.

By adjusting the inclination angle θ of the arrangement direction of the laser light sources in the semiconductor laser array with respect to the sub-scanning direction by the research of the inventor, the adjacent trajectories of a plurality of light spots on the surface to be scanned: l _i , l _{i + 1}
, The average of P _si (i = 1 to n−1) in the effective main scanning area: P _sia (using P _si (Zj) in FIG.
P _si (Zj)} / m) is found to be a predetermined value: P _S equal to each other for i = 1 to n−1.

[0021] Thus, the above average: P _sia predetermined value: if set to be equal to P _S, variation average value of interval between the scanning lines comrades by each light spot: uniformly generate about the P _S Therefore, it is possible to realize a state where the pitch of the scanning line by each light spot is closest to the designed value: P _S.

Each scanning line on the surface to be scanned is shown in FIG.
As shown in (a), it is preferable that the image is symmetric with respect to the reference scanning line. In the illustrated example, the number of scanning lines is four and the number of scanning lines is even, and these are symmetrically set to two on both sides of the reference scanning line in the sub-scanning direction. When the number of scanning lines is an odd number, it is sufficient that one central line is matched with the reference scanning line, and the other is symmetrically allocated to both sides of the reference scanning line. In this way, the deviation of the laser light source corresponding to each scanning line from the optical axis of the imaging optical system can be minimized, so that the influence of the scanning line bending can be minimized.

[0023]

EXAMPLES Specific examples will be described below. In the optical scanning device having the configuration as shown in FIG.
A semiconductor laser array 10 in which four laser light emitting units 20 as shown in FIG.
(B)). The arrangement pitch P ₀ of the laser light sources 20 is 100 μm.

Regarding the optical scanning lens 5 and the correction lens 6, counting from the light source side, the radius of curvature of the i-th lens surface is Rpi in the main scanning corresponding direction and Rsi (i = 1 to 8) in the sub-scanning direction. ), The distance between the i-th and (i + 1) -th lens surfaces on the optical axis is represented by Di (i = 1 to 7), and the refractive index of the material of the j-th lens is represented by Nj counted from the light source side. Distance on the optical axis from the starting point of deflection in the light deflecting means to the lens surface on the deflection reflecting surface side of the optical scanning lens 5: d ₀
Is given as d ₀ with the focal length of the optical scanning lens 5 as 100.
= 16.108.

I Rpi Rsi Dij Nj 1 -18.156 -18.156 0.709 1 1.58205 2 -119.288 -119.288 0.661 3 -76.551 -76.551 5.341 2 1.59670 4 -22.922 -22.922 3.106 5 1109.007 1109.007 6.847 3 1.59690 6 -48.483 -48.483 7-537.779 17.079 1.200 4 1.57219 8 ∞ ∞ focal length of the collimating lens 2: f _c = 10.800,
Focal length of cylinder lens 3 in the direction corresponding to sub-scanning: f _CY
= 402.449. Further, the lateral magnification of the optical scanning lens 5 and the correction lens 6 in the sub-scanning corresponding direction: β = −
0.500, and the effective deflection angle by the light deflection means 4 is 2
ω = 75.2 degrees. Of course, as shown in FIG. 1 (a), the four scanning lines by the four laser light sources are symmetrical to each other on both sides of the reference scanning line by two, so that the semiconductor laser array and the scanning optical system optical axis are aligned. The positional relationship was determined.

The light scanning density in the sub-scanning direction is 800d
When set to pi, the pitch of the scanning lines on the surface to be scanned is 31.75 μm. According to the above equation (1), the arrangement pitch of the laser light sources in the sub-scanning corresponding direction at this time:
When P _LS is obtained, P _LS = 1.704 μm, which is a matter of design, and does not take into account the bending of the scanning line. the average spacing between: P _sia is not a 31.75μm.

The inclination angle of the semiconductor laser array 10: Adjust theta, when the P _LS is the 1.671Myuemu,
Average spacing between adjacent scan lines: P _sia becomes 31.75Myuemu. When a plurality of image heights are indicated by deflection angles, the distance between adjacent scanning lines at each image height: P _si (Zj) (unit: μm) is shown below.

Image height (deflection angle: unit: degree) P _S1 (Zj) P _S2 (Zj) P _S3 (Zj) 37.6 32.6 32.6 32.6 36.6 32.58 32.58 32 .58 32.0 32.4 32.4 32.4 27.0 32.13 32.12 32.13 23.0 31.89 31.88 31.89 18.4 31.63 31.62 31.63 13.8 31.39 31.38 31.39 9.2 31.19 31.18 31.19 4.6 31.04 31.04 31.04 0.0 30.96 30.96 30.96 -4 6.6 30.95 30.94 30.95 -9.2 31.01 31.00 31.01-13.8 31.14 31.14 31.14 -18.4 31.34 31.34 31.34 −23.0 31.61 31.60 31.61 −27 0 31.92 31.92 31.92 -32.0 32.26 32.26 32.26-36.6 32.59 32.60 32.59-37.9 32.65 32.66 32.65 { {P _si (Zj)} / m (P _sia ) 31.75 31.75 31.75.

The following method was used to adjust the inclination angle θ of the semiconductor laser array. That is, as shown in FIG. 2, four laser beams deflected by the optical deflector 4 and directed to the optical scanning unit are turned back by the mirror 100, and transmitted through the cylinder lens 100 equivalent to the correction lens 6.
Each laser beam forms a light spot on the D-line sensor 103 in a state equivalent to that on the surface to be scanned.

In the state where the optical arrangement of the optical scanning device is fixed, when the inclination angle of the semiconductor laser is determined, the state of the scanning line by each laser beam is uniquely determined.
_In a state where the tilt angle is determined so that _sia becomes 31.75, P _{si at} the position of the CCD line sensor 103 is determined.
(Zj) is also uniquely determined.

Therefore, utilizing this fact, the inclination angle θ of the semiconductor laser array was adjusted. That is, CCD
When the output of the line sensor 103 is processed by a differentiating circuit and converted into a light distribution signal, and displayed on an oscilloscope, peaks corresponding to each light spot as shown in FIG. 3 are obtained. : D is adjusted so as to have a predetermined size.

The mirror 100 and the cylinder lens 1
00, the CCD line sensor 103 is used as a synchronous light detecting unit 100 for synchronizing optical scanning during optical scanning.

[0033]

As described above, according to the present invention, a novel optical scanning device can be provided. Since this optical scanning device is configured as described above, the fluctuation of the interval between the scanning lines due to the plurality of light spots is extremely small, so that good optical scanning can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a characteristic portion of the present invention.

FIG. 2 is a diagram showing an optical arrangement of an optical scanning device to which the present invention is applied.

FIG. 3 is a diagram for explaining only the characteristic portion of the embodiment of the invention described in claim 3;

[Explanation of symbols]

10 semiconductor laser array 20 laser light source SP beam spot θ tilt angle _{l 1, l 2, l 3} , distance l ₄ light spot locus (scanning line) P _si (Zj) adjacent scan lines

Claims (3)

(57) [Claims] 1. A method in which n (> 1) light beams from a semiconductor laser array are deflected by a common light deflecting means and condensed as n light spots on a surface to be scanned by a common imaging optical system. An optical scanning device for performing n-line optical scanning at a time, wherein an arrangement direction of light-emitting units in a semiconductor laser array is arranged at an inclination angle of θ with respect to a sub-scanning corresponding direction, and n on a surface to be scanned. L _i (i
= 1 to n), the average P _sia in the effective main scanning area of the interval between adjacent trajectories: l _i , l _{i + 1} : P _si (i = 1 to n−1) is i = 1 An optical scanning device characterized in that the inclination angle: θ is set so as to have predetermined values equal to each other with respect to .about.n-1. 2. The optical scanning device according to claim 1, wherein a locus of n light spots on the surface to be scanned: l _i (i
= 1 to n) are set symmetrically with respect to the reference scanning line in the sub-scanning direction. 3. The optical scanning device according to claim 1, wherein a synchronous light detecting section for detecting a deflecting light beam directed to the optical scanning area and synchronizing the optical scanning is separated in the sub-scanning corresponding direction. An optical scanning device comprising an optical sensor capable of receiving the n deflected light beams.