JPH0452618A - Light beam scanner - Google Patents

Abstract

PURPOSE:To offer the light beam scanning device which is a zigzag multiple reflection type with small laser light loss by providing a dielectric reflecting multi-layered film, which increases in film thickness with the distance from the rotary shaft of a rotary mirror, on the reflecting surface of a fixed mirror or at least one reflecting surfaces of the rotary mirror. CONSTITUTION:The rotary mirror 10 is fixed on its rotary shaft 12 and the dielectric reflecting multi-layered film 11 which increases in film thickness with the distance X from the axis of the rotary shaft 12. The fixed mirror 14 is arranged in parallel to the rotary shaft 12 while a gap D is left, and a dielectric reflecting multi-layered film 11 is formed on the reflecting surface 14a of the fixed mirror 14 which faces the rotary mirror 12 so that the film thickness increases with the distance from an axis 14c parallel to the rotary shaft 12 similarly to the reflecting surface 10a of the rotary mirror 10. Consequently, a high reflection factor is obtained at any position on the reflecting surface and attenuation is small, so when multiple reflection is caused 10 times, the energy of laser light is suppressed to attenuation of about 83% over the entire deflection area.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning device used in a laser beam printer or the like.

"Prior Art" Conventionally, a mirror consists of a fixed mirror, a rotating mirror having a rotating shaft opposite to the fixed mirror, and a driving means for rotating the rotating mirror back and forth around the rotating shaft and controlling the rotation angle. Japanese Patent Application Laid-Open No. 61-215 discloses a light beam scanning device which has a scanning mirror section and has a configuration in which a laser beam incident on the scanning mirror section is multiple reflected in a zigzag pattern between a rotating mirror and a fixed mirror and is deflected.
It is described in No. 516, etc.

[Problems to be Solved by the Invention] However, in the case of 10 multiple reflections, the total number of reflections reaches 19, and if the reflectance of one time is, for example, 96%, the beam is deflected by the beam scanning device and emitted. The energy of the laser beam is attenuated to 46% (0.96''=0.46).

In addition, dielectric reflective multilayer films, which are normally used to increase reflectance, are designed and manufactured to have high reflectance for predetermined incident angles, wavelengths, and polarization directions. If the conditions deviate from the design value by ±5° or more, high reflectance cannot be obtained. On the other hand, since the scanning range required of a light beam scanning device is usually ±30° or more, the commonly used dielectric reflective multilayer film cannot be used.

As described above, the zigzag multiple reflection type beam scanning device has the problem of large loss of laser light.

The present invention has been made to solve the above-mentioned problems, and aims to provide a zigzag multiple reflection type light beam scanning device in which the loss of laser light is small.

[Means for Solving the Problems] In order to achieve this object, the light beam scanning device of the present invention has the following features:
The scanning mirror unit includes a fixed mirror, a rotating mirror having a rotating shaft opposite to the fixed mirror, and a driving means for rotating the rotating mirror back and forth about the rotating shaft and controlling the rotation angle. , a dielectric reflective multilayer film is provided on at least one of the reflective surface of the fixed mirror or the reflective surface of the rotary mirror, the thickness of which increases depending on the distance from the rotation axis of the rotary mirror.

[Function] In the light beam scanning device of the present invention having the above configuration,
A high reflectance can be obtained even at the position of the reflecting surface, and attenuation is small, so when the number of multiple reflections is 10, the energy of the laser beam can be suppressed to about 83% attenuation in the entire deflection range. Here, calculations were made assuming that the reflectance of the dielectric reflective multilayer film is 99% (0.99+1J=Q, 83).

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of a beam scanning device of the present invention.

Reference numeral 10 denotes a rotating mirror, which is fixed to a rotating shaft 12. The reflective surface 10a on the substrate 10b of this rotating mirror 10 has a fifth
As shown in the figure, a dielectric reflective multilayer film 11 is formed whose thickness increases in accordance with the distance X from the axis of the rotating shaft 12. Incidentally, FIG. 5 is a cross-sectional view taken along the line B--B in FIG. 1, and the magnification in the thickness direction has been increased to make it easier to see.

In order to reduce the load of reciprocating rotational movement, the rotating mirror 10
It is formed into a trapezoidal shape with a portion where the laser beam is not reflected removed.

18 and 20 are two laminated piezoelectric actuators arranged below the rotating mirror 10 and in contact with the rotating shaft 12. A line segment connecting the two contact points is in a positional relationship such that it is orthogonal to the rotating shaft 12 and divided into two equal parts. The other ends of the two laminated piezoelectric actuators that are not in contact with the rotating shaft 12 are fixed to a machine frame (not shown). The two laminated piezoelectric actuators expand in length when voltage is applied from the drive system control circuit 16, apply a couple force to the rotating shaft 12, and reciprocate the rotating shaft 12 and the rotating mirror 10 attached thereto in the direction of the arrow. Make a rotational movement.

A fixed mirror 14 is arranged parallel to the rotating shaft 12 with a gap therebetween. On the reflecting surface 14a of the fixed mirror 14 facing the rotating mirror 12, a dielectric reflective multilayer film 11 is formed on the rotating shaft shown in FIG.
The film is formed so that the film thickness becomes thicker depending on the distance from the axis 14C parallel to 2.

The above constitutes the scanning mirror section 38.

The dielectric reflective multilayer film 11 includes two types of dielectric films having different refractive indexes, for example, a dielectric film 11a of titanium oxide with a high refractive index.
It has a structure in which dielectric films 11b made of silicon oxide and having a bottom refractive index are stacked alternately, and the top layer and the layer in contact with the substrate 10b are dielectric films 11a made of titanium oxide. The thickness of each layer is determined by the following formula.

2XnXdXcosχ=λ/4 where n is the refractive index of the dielectric film, d is the thickness of the dielectric film,
χ is the incident angle, and λ is the wavelength of the laser beam incident on the dielectric reflective multilayer film. As can be seen from the above equation, the larger the incident angle χ, the thicker the film must be. The angle of incidence at each point on the reflecting surfaces of the rotating mirror 10 and the fixed mirror 14 is
The gap between the rotating shaft and the fixed mirror 14, and the distance from the rotating shaft
can be determined in advance by ray tracing.

As will be described later, this increases the distance from the rotating shaft 12. Correspondingly, the film thickness is applied thicker than the above formula, so
High reflectance can be obtained at any reflection point on the reflection surfaces 10a, 14a.

Next, the operation of this embodiment will be explained.

A laser beam emitted from a laser light source (not shown) is passed through a lens system (not shown) to become an incident laser beam 22 with the beam diameter, spread angle, etc. adjusted, and is obliquely incident on the rotating mirror 10 from behind the fixed mirror 14. After receiving the first reflection, it is directed toward the fixed mirror 14.

The laser light that is obliquely incident on the fixed mirror 14 and reflected there is directed again to the rotating mirror 10, where it is reflected a second time. After being similarly reflected several times, the incident laser beam 22 is deflected by the number of multiple reflections times the rotation angle of the rotating mirror 10 and is emitted from the rotating mirror 10. Thereafter, the emitted laser beam 24 is passed through a condensing lens system (not shown) and a lens system for correcting arcuate distortion that occurs during multiple reflections, is made into a minute spot on the target scanning surface, and is linearly scanned.

Next, the expansion of the deflection angle due to zigzag multiple reflection will be explained with reference to FIGS. 2, 3, and 4.

FIG. 2 shows a case where the fixed mirror 14 and the rotating mirror 10 face each other in parallel, and as can be seen from the side view of FIG. 2(b), the incident laser beam 22 undergoes multiple reflections in a zigzag pattern. Finally, the light is reflected by the rotating mirror 10 and emitted. This situation is shown in the second
When viewed from the plan view of Figure (a), the laser beam is not deflected. FIGS. 3 and 4 show the case where the rotary mirror 10 is rotated by a small angle left and right by two laminated piezoelectric actuators.

When viewed from the plan view of FIG. 3(a), the incident laser beam 22 is deflected by an angle twice the rotation angle of the rotating mirror 10 each time it is reflected by the rotating mirror 10, and finally receives a large deflection angle. The light is emitted from the rotating mirror 10.

As can be seen from FIGS. 2, 3, and 4, the rotating shaft 12
Since the incident angle of the laser beam becomes larger at a position far from the
, 14a, it is necessary to increase the thickness of the dielectric reflective multilayer film 11 formed on the rotating shaft 12 or the distance from the axis 14b.

An example of a method for forming the above-mentioned dielectric reflective multilayer film will be explained with reference to FIG.

Inside the rotating slit drum 150 inside the vacuum container,
A sputtering source for sputtering a dielectric film-forming material is arranged, and a rotating mirror 10 or a fixed mirror 14 is placed above the slit drum.
are arranged, and the dielectric film-forming material that has passed through the slits 154 of the slit drum 150 adheres to the surface of the rotating mirror 10 or the fixed mirror 14. The slit drum 150
In this method, the rotation speed of the reflective surface is controlled, and a dielectric film having a calculated thickness is formed on the reflective surface 10a or 14a.

This method is a technology used in the production of continuously variable attenuation rate plates.

FIG. 7 is a schematic configuration diagram showing an example in which the beam scanning device of the present invention is applied to a laser marker. In the figure, 52 is a high-power pulsed laser light source (YAG, carbon dioxide laser, etc.)
It is. 118 is a dichroic mirror placed in front of the high-power pulse laser light source 52. Reference numeral 120 denotes an assisting visible laser light source (He--Ne laser, visible semiconductor laser, etc.), which is in a positional relationship such that its optical axis is aligned with the high-power pulsed laser light source 52 via a dichroic mirror 118. 54 is a condensing lens, which is arranged in front of the dichroic mirror 118. The above is the light source section 160 housed in the machine frame (not shown).

One end of the large-diameter optical fiber 56 is fixed to the machine frame of the light source section 160 so as to be located at the focal point of the condensing lens 54, and the other end is fixed to the machine frame (not shown) of the marker head section 122.

Reference numerals 84 and 46 denote a collimating lens and a cylindrical lens, which are arranged in front of the laser beam emitted from the large-diameter optical fiber 56. Reference numeral 38 denotes a scanning mirror section shown in FIG. 1, which is arranged in such a direction that the laser beam that has passed through the cylindrical lens 46 becomes the incident laser beam 22 shown in FIG. 1 and enters the scanning mirror section 38. 60 is a cylindrical mirror, and the laser beam 24 emitted from the scanning mirror section 38
is placed at a position where it reflects in the direction of the object to be marked 62. Further, the axis of the cylindrical mirror 60 is perpendicular to the rotation axis 12 of the scanning mirror section 38. The above is the marker head section 122 housed in a machine frame (not shown).

Reference numeral 62 denotes an object to be marked, and the surface to be marked is the cylindrical mirror 6.
The laser beam is placed at a position where the laser beam reflected at zero is focused. The object to be marked 62 is fixed on a moving means (not shown) that is movable in the direction of arrow A in the figure.

Next, the operation of this laser marker will be explained.

The marking laser light emitted from the high-power pulsed laser light source 52 and the monitoring laser light emitted from the assisting visible laser light source 120 have their optical axes aligned by the dichroic mirror 118, and have a core diameter of about 400 μm by the condensing lens 54. The light is input into a large-diameter optical fiber 56 and transmitted to the laser marker head section 122. The marking laser beam and the assisting visible laser beam emitted from the large-diameter optical fiber 56 by the laser marker head section 122 pass through the condenser lens 58.
As a result, the cross-sectional shape of the laser beam once focused on the object to be marked 62 is circular. After that, the marking object 6 shown by the arrow in the figure passes through the cylindrical lens 46.
The beam diameter in the second feeding direction A is adjusted so as to be focused within the scanning mirror section 38, and the beam is incident on the scanning mirror section 38. The marking laser beam and the monitoring laser beam are deflected within the scanning mirror section 38 and are emitted from the scanning mirror section 38 . The emitted marking laser beam and monitoring laser beam are reflected by the cylindrical mirror 60 and condensed onto the marking object 62 to perform marking. The cylindrical mirror 60 also performs the function of correcting arcuate distortion that occurs during multiple reflections so that linear scanning is performed on the marking surface. The marking object 62 is moved in synchronization with the scanning of the laser beam in the direction of an arrow A perpendicular to the scanning direction P of the laser beam, thereby marking characters and the like. Note that the assisting visible laser light is used to visually confirm the laser marking position.

Also in the above laser marker, the rotating mirror 10 and the fixed mirror 1
4 is coated with a dielectric reflective multilayer film that increases in thickness depending on the distance from the axis of the rotation shaft 12 or the axis 14b in the scanning mirror section 38, thereby reducing attenuation of the marking laser beam. , marking is performed efficiently.

Above, an embodiment in which the light beam scanning device of the present invention is applied to a laser marker has been described in detail based on the drawings, but in addition to this,
It can also be suitably applied to laser beam printers, facsimiles, barcode readers, optical card readers, laser microscopes, laser micros, optical switches, optical exchangers, and the like.

Further, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit thereof.

For example, each of the minute angle rotating mirrors shown in FIGS. 1 and 2 may have a simple rectangular shape instead of a trapezoidal shape as long as the drive system has sufficient driving ability. Furthermore, the two laminated piezoelectric actuators 18 and 20 that apply a couple to the rotating shaft 12 shown in FIG.
Even one laminated piezoelectric actuator is possible if a suitable rotation bearing is used. For example, a configuration may be adopted in which the amount of drive required of the laminated piezoelectric actuator is reduced by combining it with an angle enlarging mechanism using a lever mechanism or the like. Furthermore, in addition to laminated piezoelectric actuators, actuators may also be moving magnets, moving coils, piezoelectric elements with electrodes attached to make torsional movements, or Tezoelectric elements.
Giant magnetostrictive alloys such as r feno 1-D, hydraulic pressure, pneumatic pressure, thermal deformation, etc. can be used.

[Effects of the Invention] As is clear from the detailed description above, according to the present invention,
It is possible to provide a zigzag multiple reflection type beam scanning device with low loss of laser light.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention,
Figures 2, 3, and 4 show zigzag-like multiple reflections (5
FIG. 2 is a diagram illustrating how the deflection angle is expanded by multiple reflections.
FIG. 5 is a sectional view taken along the line B-B in FIG. 1, and FIG. 6 is a diagram illustrating an example of a method for forming a dielectric reflective multilayer film.
FIG. 7 is a schematic configuration diagram of an example of application to a laser marker. In the figure, 10 is a rotating mirror, 12 is a rotating shaft, 14 is a fixed mirror, 1
1 is a dielectric reflective multilayer film, and 38 is a scanning mirror section. @Figure 2 (a) Figure 3 (a) Figure 4 (a) (b) Figure 5 @ Figure 6

Claims (1)

[Scope of Claims] Consisting of a fixed mirror, a rotating mirror having a rotating shaft opposite to the fixed mirror, and a driving means for rotating the rotating mirror back and forth around the rotating shaft and controlling the rotation angle. A light beam scanning device including a scanning mirror section, in which a laser beam incident on the scanning mirror section undergoes multiple reflections in a zigzag pattern between the fixed mirror and the rotating mirror and is deflected; A light beam scanning device comprising a dielectric reflective multilayer film, the thickness of which increases in accordance with the distance from the rotation axis of the rotating mirror, on at least one of the reflecting surface or the reflecting surface of the rotating mirror.