JP2772555B2 - Scanning optical device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device that forms a pattern on an image surface by scanning a laser beam on the image surface, and particularly relates to a laser. The present invention relates to an apparatus such as a plate making machine that requires a high density of a pattern to be formed.

[Prior Art] In order to perform drawing with high accuracy, spots must be narrowed down. In order to reduce the spot diameter, it is necessary to brighten the F number of the optical system, and the depth of focus necessarily becomes shallow. Therefore, in order to keep the spot diameter on the scanning surface almost constant, the curvature of field must be kept small.

However, if the optical axis of the scanning lens does not coincide with the optical axis of the light beam incident on the polygon mirror in the plane on which the light beam is scanned by the polygon mirror, the deflection point is changed by the rotation of the polygon mirror. Asymmetrically changes between the plus image height and the minus image height with respect to the optical axis of. Therefore, there is a problem that the curvature of field on the image plane becomes asymmetric, and correction cannot be performed when a lens having a symmetric shape with respect to the optical axis is used.

In order to solve such a problem, a configuration in which the laser beam is incident on the polygon mirror through the optical axis of the scanning lens is considered. According to this configuration, the appearance of the curvature of field is symmetrical, so that the correction can be made with a lens that is symmetric with respect to the optical axis, and the value becomes very small.

However, in order to adopt such a configuration, a static deflector that separates a light beam going from the light source to the polygon mirror and a light beam entering the fθ lens from the polygon mirror is arranged in the optical path of the light reflected by the polygon mirror. It is necessary to do.

Incidentally, Japanese Patent Application Laid-Open No. 60-233616 discloses a configuration in which a light beam from a light source is incident on a polygon mirror through the optical axis of a scanning lens by using a polarizing beam splitter and a quarter-wave plate. .

In the configuration of Japanese Patent Application Laid-Open No. 60-233616, a laser beam is reflected by a polygon mirror within a sub-scanning cross section in order to correct the influence of the inclination of the reflection surface of the polygon mirror with respect to the rotation axis, which is called a surface tilt error. An image is formed on the surface once. Therefore, a total reflection mirror cannot be provided as a static deflector, and a polarizing beam splitter or the like must be used.

However, in the case of the configuration described in the above publication,
Since the angle of incidence of the light beam on the polarization beam splitter changes with the rotation of the polygon mirror, the transmittance of the polarization beam splitter gradually changes from the center to the periphery, causing unevenness in the amount of light on the image plane.

In order to solve each of the problems described above, the present applicant has adopted a configuration in which a laser beam is incident on a polygon mirror through the optical axis of a scanning lens, and a configuration in which a total reflection mirror can be used as a static deflector. This is proposed in Japanese Patent Application No. 1-63934.

That is, before the light beam from the laser light source is incident on the scanning deflector, an image is formed once in the sub-scanning section, and a static deflector is arranged at this image forming position to guide the light beam from the light source to the scanning deflector. The static deflector has a slit mirror that reflects a light beam or a slit mirror that transmits a light beam at an image forming position.

According to such a configuration, most of the light reflected by the scanning deflector passes through the periphery of the slit mirror, or is reflected by the outside of the slit of the slit mirror, and forms a spot on the image plane via the scanning lens. tie.

However, when implementing the above-mentioned proposed technique, it is desirable to reduce the deviation of the luminous flux from the polygon mirror to the scanning lens in order to secure the amount of light on the image plane. It is preferable to make the area of the slit of the entering mirror as small as possible.

However, if the area of the slit mirror or the like is reduced, the accuracy for condensing the light beam on this portion is strictly required.

[Object of the Invention] The present invention has been made in view of the above problems, and it is possible to prevent waveform aberration from deteriorating on an image plane with a relatively simple configuration and perform drawing with high accuracy. Scanning optical device capable of accurately guiding a condensed light beam onto a slit mirror or the like even when the area of the slit mirror or the like is reduced. The purpose is to provide.

Means for Solving the Problems In order to achieve the above object, a scanning optical device according to the present invention employs a configuration in which a laser beam is incident on a scanning deflector from the optical path of a deflected beam by a scanning deflector. ,
An optical element from a laser light source to a static deflector is provided with a holding mechanism for integrally holding the optical element separately from other optical elements.

[Example] Hereinafter, the present invention will be described with reference to the drawings. Fig. 1 ~
FIG. 4 shows an embodiment of the scanning optical device according to the present invention.

First, the arrangement of the optical elements of this device will be described with reference to FIG.

The illustrated optical system includes a laser diode 10 as a light source, a collimating lens 11 that converts divergent light emitted from the laser diode 10 into a parallel light beam, a folding mirror 12 that reflects the collimated light beam, and a line image formed by the light beam. A prism block having a cylindrical lens 13 as a condensing lens to be formed, and a slit mirror 21 as a static deflector provided so as to coincide with the line image position of the light flux
20, a polygon mirror 30 as a scanning deflector for reflecting and polarizing the light beam reflected by the slit mirror 21, and an fθ lens as a scanning lens for condensing the light beam reflected by the polygon mirror 30 and forming a spot on a scanning surface 40 and is equipped.

Here, a surface on which the light beam is scanned by the polygon mirror 30 is defined as a main scanning section, and a surface perpendicular to the main scanning section and including the rotation axis 31 of the polygon mirror is defined as a sub-scanning section.

The prism block 20 has a rectangular parallelepiped shape in which a triangular prism 22 and a trapezoidal prism 23 are bonded, and a slit mirror 21 which is a total reflection mirror is deposited on a bonding surface. The angle of the slit mirror 21 with respect to the main scanning section is approximately 45 °.

The divergent light emitted from the laser diode 10 is collimated and then condensed on a slit mirror 21 by a cylindrical lens 13, and the entire amount of light is reflected by the slit mirror 21 and passes through the optical axis of an fθ lens 40 to form a polygon mirror 30. Head to.

The light beam reflected and polarized by the polygon mirror 30 reaches the prism block 20 again with a predetermined spread. Here, most of the light flux passes through a portion around the slit mirror 21 and enters the fθ lens 40. The light beam emitted from the fθ lens 40 is deflected to the lower side of the base by the mirror 51 provided at the left end of the base 90, and guided by the mirrors 52 and 53 to be conveyed by the feed roller 60 as shown in FIG. A spot to be scanned at a constant speed is formed on a panel 61 to be scanned.

Slit mirror 21 provided to separate the optical path
Since there is no change in the transmittance due to the change in the rotation angle of the polygon mirror 30, there is no change in the spot intensity due to the image height on the scanning plane as in the case where a deflection beam splitter is used.

Next, the specific assembling configuration of each optical element is shown in FIGS.
The description will be made based on FIG. 3, and at the same time, the adjustment direction of each optical element will be described with reference to FIG.

The coordinates in the figure are determined based on the traveling direction of the light beam, the x-axis represents the direction in which the light beam is emitted from the laser diode 10 and the optical axis direction of the fθ lens 40, and the z axis represents the direction of the rotation axis 31 of the polygon mirror 30. Axis, the direction perpendicular to both x and z axes is y
Defined as an axis.

Each optical element is unitized and attached to a flat base 90.

The polygon unit 30 in which the polygon mirror 30 and the motor for driving the polygon mirror 30 are incorporated is immovably fixed to the base 90.

The light source unit 200 provided from the laser diode 10 to the prism block 20 has a lower substrate 201 slidable in the x-axis direction with respect to the base 90, and a lower substrate 201 with respect to the lower substrate 201.
and an upper substrate 202 provided to be rotatable about the x and y axes.

The lower substrate 201 has its position in the y-axis direction determined by two contact pins 203 fixed to the base 90 as shown in FIG. 2, and is screwed to the base 90 through the lower substrate. It is fixed to the base 90 by fixing bolts 204 at the four corners. Since the through holes of the lower substrate 201 into which the respective fixing bolts 204 are inserted are formed larger than the bolt diameters, by loosening these fixing bolts 204, the lower substrate 201 is applied to the fixing pins along the x-axis along the 203. Can be slid in any direction.

The slide adjustment of the light source unit 200 in the x-axis direction has an operation for correcting a focus shift in the sub-scanning direction on the scanning surface due to an error such as a curvature of a lens system and a distance between surfaces.

The upper substrate 202 is positioned in the x and y directions by applying pins 205 fixed to three places of the lower substrate 201. The upper substrate 202 has screw holes formed at four corners thereof screwed with adjustment bolts 206 having tips contacting the lower substrate 201 as shown in FIG. It is fixed to the lower substrate 201 by fixing bolts 207 provided.

Therefore, by loosening the fixing bolt 207 and operating the adjustment bolt 206, the upper substrate 202 can be adjusted around the x and y axes with respect to the lower substrate 201.

The rotation adjustment about the x-axis of the light source unit 200 including the prism block is for correcting the collapse of the spot shape on the scanning surface and the deterioration of the image quality. After the adjustment is completed, it is used to improve the performance of the entire apparatus.

The prism block 20 fixed to the center of the upper substrate is slidable in the y-axis direction with respect to the upper substrate 202. In consideration of the shift of the light beam transmitted from the polygon mirror 30 to the fθ lens 40 side, it is desirable that the area of the slit mirror 21 is as small as possible. The slide adjustment of the prism block in the y-axis direction is necessary to match the positional relationship between the slit mirror and the linear image formed by the cylinder lens 13 when the size of the slit mirror is approximately the same.

As shown in FIG. 1, two legs 210 are fixed to the upper substrate 202 on both sides of the prism block by fixing screws 210a screwed from below. A horizontal plate 211 is provided between the upper ends of the legs 210, and a vertical plate 212 is provided between the legs 210 below the horizontal plate 211.

On a horizontal plate 211, a cylindrical lens barrel 220 in which a laser diode 10 and a collimator lens 11 composed of four lenses of a first lens 11a to a fourth lens 11d are incorporated, and a mirror support for supporting the folding mirror 12 The part 230 is fixed.

The laser diode 10 has a variation in a position where light is emitted for each product. Therefore, the laser diode 10 is configured to be slide-adjustable in the yz direction so that the oscillation light beam can be aligned with the designed optical axis.

The collimator lens 11 is slidable in the y-axis direction in order to adjust the relative relationship with the laser diode 10. This is an adjustment for correcting a focus shift mainly in the main scanning direction on the scanning surface due to an error such as a curvature of the lens system and an inter-surface distance.

The turning mirror 12 is configured to be rotatable about two axes x and y.

In addition, the vertical plate 212 holds the cylinder lens 13 composed of a combination of the positive lens 13a and the negative lens 13b in the holder 24.
Mounted via 0.

Since there is a possibility that the cylinder lens 13 may include variations among products due to processing errors, slide adjustment in the optical axis (x-axis) direction and rotation adjustment around the optical axis are possible. The former adjustment is to adjust the movement of the line image along the optical axis direction to match the focus to the slit mirror,
The latter adjustment is for adjusting the rotation direction of the line image forming direction to match the direction of the slit mirror 21.

In addition, the laser diode 10 and the prism block 20
The above components are integrated as a single unit independent of the other components, increasing the accuracy of assembly, the line image forming position by the cylinder lens 13 and the slit mirror 21
Misalignment can be prevented.

The lens unit 300 has three anamorphic lenses 4
It has an fθ lens 40 composed of 1, 42, and 43, and a lens substrate 301 on which these lenses are arranged. The lens substrate 301 is applied to fixing pins 302 fixed to two places of the base 90 between the light source unit 200 and the position in the x-axis direction is determined, and is fixed to the base 90 by fixing bolts 303 at four corners. Fixed.

Therefore, the lens substrate 301 can be slid in the y-axis direction using the contact pin 302 as a guide by loosening the fixing bolt 303.

The three anamorphic lenses are fixed in the z-axis direction to the lens substrate 301 via a pressing spring plate 311 by a pressing plate 310 provided so as to cover the central lens, and the central lens 42 is It is assembled so as to be freely rotatable around the x and y axes.

The adjustment of the fθ lens 40 is for correcting the inclination of the image plane and the deterioration of the image quality due to the eccentricity error.

As shown in FIG. 3, a support member 312 slightly longer than the height of the lens is screwed to the lens substrate 301 at a portion corresponding to the four corners of the press plate 310, and the press plate 310 is attached to the support member 312. It is fixed using fixing bolts 313.

In addition, each lens has three pins,
., And L-shaped fixing plates 321, 32 fixed to the lens substrate 301 with two fixing bolts from the direction opposite to these contact pins, respectively.
Are fixed to the lens substrate 301 in the x and y directions.

The above-mentioned contact pin 203 for determining the position of the light source unit 200 and the contact pin 3 for determining the position of the lens unit
02 is a position determined based on the rotation center of the polygon mirror 30.

2, a monitor light source unit 400 that irradiates a monitor light beam to a surface different from the surface of the polygon mirror 30 that reflects the drawing light beam as means for detecting the rotational position of the polygon mirror 30 is provided. And a monitor light receiving unit 500 for receiving the monitor light beam reflected by the polygon mirror 30. Since these units are not directly related to the present invention, detailed description will be omitted.

[Effects] As described above, according to the scanning optical device of the present invention, the optical elements from the light source, which requires high assembling accuracy, to the static deflector can be integrally and independently assembled. The positional relationship between the elements, for example, the positional relationship between the line image formed by the condensing lens and the static deflector can be accurately realized without performing adjustment again when assembling to the main body.

[Brief description of the drawings]

1 to 4 show an embodiment of a scanning optical device according to the present invention. FIG. 1 is a side view of a light source unit taken along line II of FIG. FIG. 2 is a plan view of the entire apparatus, FIG. 3 is a view taken on line III-III of FIG.
The figure is a perspective view showing the arrangement of the optical elements. 10 Laser diode 13 Cylinder lens 20 Prism block 21 Slit mirror 30 Polygon mirror 40 fθ lens

Claims (5)

(57) [Claims] 1. A laser light source; a scanning deflector for reflecting and deflecting a light beam from the laser light source to scan in a main scanning section; and a scanning device for condensing the laser light beam reflected by the scanning deflector on an image plane. A lens, a condensing lens for temporarily forming an image in a sub-scanning section perpendicular to the main scanning section before the light beam from the laser light source is incident on the scanning deflector, and a condensing lens in an optical path of light reflected by the scanning deflector. A static deflector that is provided at an image forming position of a light beam by a lens and guides a light beam from a laser light source to a scanning deflector, and that causes reflected light from the scanning deflector to enter a scanning lens; A scanning optical device, comprising: a holding mechanism that holds an optical element up to a container separately from other optical elements and integrally holds the optical element. 2. The scanning optical device according to claim 1, wherein said scanning deflector is a polygon mirror. 3. The scanning optical device according to claim 1, wherein said condenser lens is a cylindrical lens. 4. The static deflector is disposed so as to coincide with an image forming position of a laser beam by the condenser lens, and is a slit elongated in a main scanning direction for reflecting the laser beam from the light source toward a scanning deflector. The scanning optical device according to claim 1, further comprising a mirror. 5. The scanning optical device according to claim 1, wherein the light beam entering from the static deflector to the scanning deflector enters along the optical axis of the scanning lens.