JPS6363016A - Light beam scanner - Google Patents

Abstract

PURPOSE:To obtain a deflector having a good linearity of a scan (scarcely having a distortion), and to obtain a scanner having a high practicability, by sing a columnar reflecting mirror for making a bus vertical to a principal scanning plane, and vibrating the reflecting mirror in the principal scanning surface. CONSTITUTION:A light beam which has been emitted from a laser light source 1 is collimated by a coupling lens 2, passes through a cylindrical lens 3 having play only in the main scanning direction as roughly a parallel luminous flux, made incident on a deflector 4 of a columnar reflecting mirror, and the light beam which has been deflected by the columnar reflecting mirror 4 passes through a cylindrical lens 5 having play only in the sub-scanning direction, and scans on a photosensitive drum 6. The columnar reflecting mirror deflector 4 is driven in the direction vertical to a bisector of an angle made by a light beam going to the scanning center and the incident light beam, in the main scanning plane by a driving device 7. In this way, a light beam scanner of a post-objective type, which has reduced a distortion to <=+ or -0.3% which does not become a problem to practical use can be obtained by a small-sized and simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning device that improves the linearity of scanning speed in a post-objective scanning device.

[Conventional technology]

There are two types of light beam scanning devices used as optical systems in laser beam printers and the like: a pre-objective type in which a focusing lens is placed after the light beam has been deflected, and a post-objective type in which a deflection device is placed after the light beam is focused by a focusing lens. There is. The former has a focusing lens system after the deflection, and performance such as scanning linearity can be corrected with the focusing lens, so it is easy to obtain high performance and is currently the mainstream, but the lens system requires a wide angle and is complicated. In this case, a lens with a large aperture must be used.

The above-mentioned scanning device includes, for example, Japanese Patent Application Laid-Open No. 57-358.
There are No. 23, etc.

In contrast to the above example, in the post-objective type, the focusing lens only needs to focus the axial light beam, so the lens system becomes extremely simple and compact, but the uniformity of the scanning speed due to deflection is achieved. There were performance problems such as not being able to An example of the conventional post-objective type is JP-A-60-133414.

[Problem that the invention seeks to solve]

As described above, in the conventional technology, post-objective type scanning devices have a problem of poor scanning linearity in terms of scanning performance, although the lens system is small and simple. For example, when a rotating polyhedron is used as a deflector, even a deflection of ±20° causes a distortion of 4%.

The purpose of the present invention is to solve the above problems and to find a deflector with good scanning linearity (less distortion).
The object of the present invention is to obtain a highly practical post-objective type scanning device.

[Means for solving problems]

The above purpose is to use a cylindrical reflecting mirror with its generatrix perpendicular to the main scanning plane as a deflector of a post-objective light beam scanning device, and to vibrate the reflecting mirror within the main scanning plane so that the incident light beam hits the cylinder. By changing the position, the direction of the normal line of the cylindrical reflector changes, thereby deflecting the light beam, and further, the amplitude of the vibration of the cylindrical reflector is set to 0.4 times or less the radius of the cross-sectional circle of the cylindrical reflector. This is achieved by

[Effect]

The principle operation of the deflector in the present invention will be explained.

FIG. 7 is a conceptual diagram showing the deflection action of the deflector, and the figure shows a cross section in the main scanning plane.

In Figure 7, when the cylindrical reflector is at position 8,
The incident light beam 10 is reflected in a direction 11. Above direction 1
1 is the scanning center of the target 15. At this time, the normal line of the cylindrical reflecting mirror at the reflection point is set to 13.

The cylindrical reflecting mirror when translated by h in the direction perpendicular to the normal line 13 is shown by broken IA9. At this time, the slope of the normal line becomes as shown at 14, so the incident light beam 10 is reflected in the direction 12. By moving the cylindrical reflecting mirror 8 in parallel in the h direction as described above, the light beam can be deflected.

Next, - linearity of scanning by the above deflector will be explained. Scanning linearity means that the position on the target where the light beam hits moves at a constant speed with respect to time, and the amount of deviation from this constant speed is referred to as distortion.

As shown in FIG. 7, the scanning position Q on the target 15 is determined by the deflection angle θ as follows: Q=tanθ
(1) On the other hand, since the cylindrical reflecting mirror is driven using a mechanical resonance point, etc., the displacement of the cylindrical reflecting mirror is normally determined as follows.

h = h, sinωt −・= (2)
Here, ho is the amplitude, t is the time, and ω is the angular frequency of vibration. Also, from Figure 2, what is the slope between h and the normal line? The relationship is h = Rsiny - (3), and furthermore, as can be seen from the law of reflection in Figure 7, the deflection angle θ
is equal to 2.

Summarizing the above, the following two relationships can be obtained.

Ho.

(2) From equations (3), sin tp = −sinωt・
...(4) From (1) n = tan 2y
−・・−(5) Scanning linearity means (
It is sufficient that Ω in equation 5) has a linear relationship with ωt in equation 4.

Therefore, by eliminating ji from equations (4) and (5), ωt and Q
FIG. 8 shows the relationship with /R as a parameter. In the figure, the horizontal axis is ωt, the vertical axis is tanθ=Ω, the solid line is a graph showing the above relationship, and the numerical values attached next to it are the values of parameters h and /R. Moreover, the straight line shown by a broken line is a straight line where each graph touches near the origin, and the closer the solid line is to each straight line, the smaller the distortion is. As can be seen from Figure 8, for example, the deflection angle is at least ±20
'', the parameter b0/R must be selected between 0.3 and 0.4. In particular, when h,/R=0.4, tanθ=0. 9, that is, up to ±40'', the distortion is 0.3% or less.

As mentioned above, the light beam can be deflected by moving the cylindrical reflecting mirror in parallel within the main scanning plane, and the amplitude of the movement varies. By optimally selecting the ratio h0/R between the radius of curvature R and the radius of curvature R of the cylindrical reflecting mirror, desired linearity can be obtained in scanning.

When used at an even smaller deflection angle, h,/R is 0.3
It may be less than %. When h0/R is 0.4% or more.

It can be seen from FIG. 8 that the range in which linearity can be maintained is extremely small. Therefore, h, /R is preferably 0.4% or less. As mentioned above, in order to obtain linearity, it is important to move the cylindrical reflecting mirror in parallel.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a first embodiment of a light beam scanning device according to the present invention, FIG. 2 is a diagram showing distortion aberration characteristics of the above embodiment, and FIG. 3 is a sectional view of a driving device of the above embodiment. , 4th
The figure is a configuration diagram of a drive device in a second embodiment of the present invention, FIG. 5 is a configuration diagram of a drive device in a third embodiment of the present invention,
FIG. 6 is a sectional view showing a driving device in a fourth embodiment of the present invention. A first embodiment shown in FIG. 1 shows an optical system of a laser printer. Light emitted from a laser light source 1 is collimated by a coupling lens 2.

The light passes through a cylindrical lens 3 having burrs only in the main scanning direction as a substantially parallel light beam, and then enters a deflector 4, which is a cylindrical reflecting mirror. 7 is a driving device for the cylindrical reflecting mirror 4. The light deflected by the cylindrical reflector 4 passes through a cylindrical lens 5 having burrs only in the sub-scanning direction, and then passes through a photosensitive drum 6.
Scan above.

That is, the cylindrical lens 3 focuses the light beam only in the main scanning direction, and the deflector 4 of the next cylindrical reflector focuses the light beam in the main scanning direction.
The position and focal length are set so that the light beam is focused on the target photosensitive drum 6 (in the main scanning direction) by compensating for the divergence of the light beam caused by the light beam. The light beam that has passed through the cylindrical lens 3 becomes a long beam in the sub-scanning direction on the cylindrical reflector deflector 4. The cylindrical reflector deflector 4 is moved within the main scanning plane by a driving device 7.
2 of the angle between the light beam going to the center of scanning and the incident light beam
It is driven in the direction perpendicular to the equisector.

The configuration of the drive device 7 is shown in a sectional view in FIG. The driving device shown in FIG. 3 is a so-called voice coil, and by passing an alternating current through the coil 2o in the magnetic field created by the magnet 21, the mount 23 on which the cylindrical reflector deflector 4 is mounted
moves in the direction of the arrow shown in the figure, performing reciprocating motion. The guide 22 is a bearing and holds the mounting base 23 so that it can move in parallel.

The light beam reflected by the cylindrical reflector deflector 4 passes through the cylindrical lens 5, and at this time, it is focused in the sub-scanning direction, so that the beam shape is approximately circular and has a desired size on the surface of the photosensitive drum 6. Narrowed down to.

Next, the shape, dimensions, etc. of this embodiment will be explained. The deflection angle was ±22°. In this case, from the above-mentioned theoretical explanation, the values of parameters h and /H are set to 0 using FIG.
．． If it is set to 3, sufficient linearity can be obtained. The smaller the radius of curvature of the cylindrical reflector deflector 4, the more compact it becomes, but considering the practical size, it was set to 5 mII+.

Therefore, the driving amplitude of the deflector 4 needs to be 1.5 mm.

The scanning width on the photosensitive drum 6 is ±100 mm, and the distance from the cylindrical reflector deflector 4 to the surface of the photosensitive drum 6 is 2.
It is 50mm.

The focal length of the cylindrical reflector deflector 4 as a lens is f =
-2.5mm. From now on, the focal length and arrangement of the cylindrical lens 3 are as follows.

In order to be reflected by a lens with a focal length f = -2,51 am and focused on the photosensitive drum 6 which is 250 mm away, the light beam incident on the cylindrical reflector deflector 4 is.

Suppose that it is necessary to make the light incident on a point that is a distance S away from the deflector 4 so as to be focused. The above value of S is obtained from (a: distance between the object point and the lens, b: distance between the image point and the lens) as follows.

Therefore, the cylindrical lens 3 is set to focus 2.53 mm away from the cylindrical reflector deflector 4.

The cylindrical lens 3 is placed 20 mm closer to the light source than the cylindrical reflector deflector 4, and at this time, the focal length of the cylindrical lens 3 is fc=22.53ml1
shall be.

In the above embodiment, the distortion is ±
It becomes 0.25mm, which is within the tolerance value ±0, 3mm. The tolerance levels are shown in FIG. 2 by two straight lines 18 and 19.

Various methods for driving the cylindrical reflector deflector 4 are possible in addition to the method shown in FIG. 3, and examples of each method will be shown next.

In the second embodiment of the present invention shown in FIG. 4, a motor rotates a disk 24, and a shaft 27 converts this rotation into reciprocating motion of a mounting base 26. Shaft 27 is fulcrum 2
8 is rotatably fixed to the disk 24, and one end is attached to the fulcrum 2.
9, it is rotatably fixed to the mounting base 26. The mount 26 is supported by the guide 25 and reciprocates in parallel in the direction indicated by the arrow.

In a third embodiment of the present invention shown in FIG. 5, the cylindrical reflector deflector 4 is driven using a piezoelectric element. That is, due to the change in the deflection of the piezoelectric element 33, the arm 35 is swung about the point 34 as a fulcrum, and the mounting base 32 of the one-cylindrical reflector deflector 4 is moved in parallel. The mount 32 is held by guides 30.31.

The piezoelectric element side of the arm 36 is pulled by the spring 36 so as to be in constant contact with the piezoelectric element 33.

The fourth embodiment shown in FIG. 6 is an example in which the number of guides 22 in the first embodiment is reduced to two, and they are arranged as shown at 37 and 38 on both sides of the mounting base 23.

〔Effect of the invention〕

As described above, the light beam scanning device according to the present invention includes a light source that generates a light beam, a coupling lens system that converts the light beam from the light source into a substantially parallel beam, and a generating line whose direction is perpendicular to the main scanning direction. a cylindrical reflecting mirror installed so that By including a cylindrical lens that focuses the beam only in the sub-scanning direction to a single point on the target, and a drive device that reciprocates the cylindrical reflector within the main scanning plane, distortion can be practically eliminated. It is possible to obtain a post-objective type light beam scanning device with a small and simple configuration in which the deviation is reduced to ±0.3% or less, which does not cause any problems.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a first embodiment of a light beam scanning device according to the present invention, Fig. 2 is a diagram showing distortion aberration characteristics of the above embodiment, and Fig. 3 is a cross section showing a driving device of the above embodiment. figure,
FIG. 4 is a block diagram of a drive device in a second embodiment of the present invention, FIG. 5 is a block diagram of a drive device in a third embodiment of the present invention, and FIG. 6 is a block diagram of a drive device in a fourth embodiment of the present invention. FIG. 7 is a conceptual diagram showing the principle of the present invention, and FIG. 8 is a diagram showing scanning linearity. 1... Laser light source 2... Coupling lens 3... Cylindrical lens 4... Cylindrical reflector (deflector) 5... Cylindrical lens 6... Target (photosensitive drum) 7... Drive device substitute Junnosuke Nakamura, a private patent attorney Figure 2 Run 11 A left “f Cmm) 3 Figure Ya 4 Figure == Small 4 Figure 1 F

Claims (1)

[Claims] 1. A light source that generates a light beam, a coupling lens system that converts the light beam from the light source into a substantially parallel beam, and is installed so that the direction of the generatrix is perpendicular to the main scanning direction. a cylindrical reflector, a lens system that makes the light beam from the coupling lens enter the cylindrical reflector as a beam that focuses only in the main scanning direction, and a lens system that directs the light beam reflected by the cylindrical reflector in the sub-scanning direction. A light beam scanning device comprising: a cylindrical lens that focuses the light to a single point on a target; and a drive device that causes the cylindrical reflecting mirror to reciprocate within a main scanning plane. 2. The light beam scanning device according to claim 1, wherein the amplitude of the reciprocating motion of the cylindrical reflecting mirror during driving is 0.4 times or less the radius of the cylindrical reflecting mirror.