JPS63174013A - Beam diameter adjusting device - Google Patents

Abstract

PURPOSE:To make beam diameter adjusting operation easy and accurate by arranging a beam diameter adjusting means which has an opening part in a specific shape in the optical path of laser light and displacing it along the optical axis. CONSTITUTION:The laser light L from a laser diode is mode incident on a collimator at a specific emission angle and becomes parallel luminous flux, which is mode incident on a beam expander 18. Then, the beam diameter D of the incident laser light L is determined by the emission angle of the diode. For the purpose, a displaceable plate body 32 with the opening part 34 is arranged between condenser lenses 28 and 30 which form a beam expander 18. The beam diameter Db of the laser light L emitted from the lens 30 is therefore settable to a specific value according to the position of the plate body 32. Namely, the plate body 32 is displaced along oblong holes 36a and 36b of a casing 26 through bolts 38a and 38b. Consequently, the beam diameter is easily and accurately adjusted by the simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for adjusting the beam diameter of laser light, etc.
More specifically, a beam diameter adjusting means having an aperture of a predetermined shape is disposed in the optical path of a diverging or converging laser beam, etc., and the beam diameter is easily adjusted by displacing the beam diameter adjusting means along the optical axis. The present invention relates to a beam diameter adjustment device that can be adjusted to

2. Description of the Related Art In recording devices using lasers, such as laser printers, laser diodes are used as light sources for recording and writing, which are small, have a long life, and are easy to adjust output. In this case, since the laser light output from the laser diode is a diverging light, for example, after collimating it with a collimator, the beam diameter is adjusted with a beam expander to create a predetermined writing spot diameter on the scanned object. It is irradiated with

Incidentally, there are variations in the radiation angle of laser light output from a laser diode due to manufacturing errors. Therefore, for example, if the beam expander does not have a beam diameter adjustment function, the writing spot diameter on the scanned object will vary depending on the laser diode used, and the quality of the image formed by the laser beam may deteriorate. There is.

Therefore, in order to solve such a problem, it is conceivable to provide a beam expander with a zoom function so as to be able to adjust the writing spot diameter with respect to the object to be scanned. However, in this case, it has been pointed out that the structure is complicated and very expensive. Also, as another method,
Although it is conceivable to arrange an iris diaphragm in the optical path of the laser beam to adjust the beam diameter, this also has the disadvantage that the structure becomes quite complicated, similar to the zoom function described above.

The present invention has been made to overcome the above-mentioned disadvantages, and includes a beam diameter adjusting means having an aperture of a predetermined shape in the optical path of a diverging or converging laser beam, etc. An object of the present invention is to provide a beam diameter adjusting device that can easily and accurately adjust the beam diameter with an extremely simple configuration by displacing the beam along the optical axis.

In order to achieve the above object, the present invention provides a beam diameter adjusting means having an aperture of a predetermined shape in a diverging or converging light beam, and displacing the beam diameter adjusting means along the optical axis of the light beam. It is characterized by being able to be configured.

Next, preferred embodiments of the beam diameter adjusting device according to the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 indicates a laser optical system in a laser printer to which a beam diameter adjustment device according to the present invention is applied, and this laser optical system 10 includes a laser diode 12) that outputs laser light, a collimator 14, and a beam extractor. It basically consists of a panda 18, a galvanometer mirror 20, a scanning lens 22, and a transfer mask drum 24.

The collimator 14 guides laser light as a diverging light output from the laser diode 12 at a radiation angle θ to the beam expander 18 as a parallel light beam. The beam expander 18 is a beam diameter adjusting device (described later) according to the present invention.
It is used to adjust the laser beam to a predetermined beam diameter. By swinging in the direction of the arrow, the galvanometer mirror 20 transfers laser light whose beam diameter has been adjusted by the beam expander 18 to the transfer mask drum 2.
4 in the main scanning direction (direction of arrow A). The scanning lens 22 guides the laser beam deflected by the galvanometer mirror 20 to the transfer mask drum 24 while keeping the scanning speed constant, and is usually composed of an fθ lens. It is rotationally driven in the sub-scanning direction (direction of arrow B) by a drive source (not shown).

Here, the beam expander 18 including the beam diameter adjusting device according to the present invention includes condensing lenses 28 and 30 at both ends of a cylindrical casing 26, as shown in FIG. A disk-shaped plate 32 that constitutes the beam diameter adjusting device according to the present invention is provided in the intermediate portion. In this case, the plate body 32 has an optical axis 33 of the laser beam in the center.
It has an opening 34 centered at , and is configured to be movable in the direction of arrow C along the optical axis 33 . That is, a long hole 3 parallel to the optical axis 33 is formed in the circumferential side of the casing 26.
6a, 36b are bored, and these long holes 36a,
38a and 38b each having one end fixed to the circumferential side of the plate 32 are inserted through 36b.

Note that the casing 2 is attached to these bolts 38a and 38b.
Nuts 40a and 40b are screwed together to hold the circumferential side of the plate 32 in cooperation with the circumferential side of the plate 32.

The laser optical system including the beam diameter adjusting device of this embodiment is basically constructed as described above, and its operation and effects will be explained next.

Laser light output from the laser diode 12 is incident on the collimator 14 at a predetermined radiation angle θ.

In this case, the collimator 14 guides the laser beam to the beam expander 18 as a parallel beam.

Here, the beam diameter of the laser light incident on the beam expander 18 is determined in advance by the radiation angle θ of the laser diode 12. Therefore, if there is no plate 32 between the condensing lenses 28 and 30 of the beam expander 18, the beam radius of the laser light emitted from the beam expander 18 will be determined by the radiation angle θ.

Therefore, a displaceable plate body 32 having an opening 34 between the condenser lenses 28 and 30 constituting the beam expander 18
By arranging this, it becomes possible to set the beam diameter Db of the laser light emitted from the condenser lens 30 to a predetermined value depending on the position of the plate 32. That is, the plate body 32 is inserted into the elongated hole 3 of the casing 26 via the ports 38a and 38b.
6a and 36b in the direction of arrow C, the beam diameter Db of the laser beam emitted from the condenser lens 30 is set to a predetermined size. In this case, after setting the beam diameter to a predetermined size, the plate body 32 is fixed to the casing 26 by screwing the nuts 40a and 40b.

The laser beam set to a beam radial power D in the beam expander 18 is deflected by a galvanometer mirror 20 and transmitted to a transfer mask drum 24 via a scanning lens 22.
irradiated on top. In this case, the galvanometer mirror 20
The laser beam deflected by the oscillating motion of the galvanometer mirror 20 scans the transfer mask drum 24 in the main scanning direction (in the direction of the arrow). On the other hand, the transfer mask drum 24 is rotating in the direction of arrow B, so that its circumferential surface is two-dimensionally scanned. Incidentally, charges corresponding to predetermined image information, character information, etc. are accumulated on the transfer mask drum 24 by laser light, and based on this charge, for example, toner is transferred onto a predetermined recording paper. The character information and the like are recorded as a visible image.

Here, an adjustment method for irradiating laser light with a predetermined writing spot diameter onto the transfer mask drum 24 will be explained based on FIG. 3.

If the scanning lens 22 is an fθ lens, and if its focal length is f and the wavelength of the laser beam is λ, then the diameter of the writing spot on the transfer mask drum 24 is expressed as follows. In this case, the diameter of the Airy disk formed on the transfer mask drum 24 by the scanning lens 22 is the writing spot diameter D.
3, then K=2.44.

On the other hand, the focal length of the condensing lens 30 of the beam expander 8 is f ax, the diameter of the opening 34 formed in the plate 32 is 8, and the distance between the focal point of the condensing lens 30 and the plate 32 is l. In this case, the beam diameter of the laser beam emitted from the beam expander mite 8 is ! It is expressed as Therefore, from equations (1) and (2), the writing spot diameter is expressed as . Therefore, the diameter of the writing spot formed on the transfer mask drum 24 is the distance of the plate 32 from the focal point of the condenser lens 30! can be adjusted based on equation (3).

Note that, as understood from equation (4), the amount of change ΔD in the writing spot diameter with respect to the amount of movement Δl of the plate 32 is
The diameter of the opening 34 in FIG. Therefore, for example, as shown in FIG. 4, a plate 44 having an opening 42 with a relatively small diameter is provided near the focal point of the condenser lens 30, and an aperture 46 is provided near the condenser lens 30. A plate body 48 having a large diameter is arranged, and these plates 44 and 48
By independently displacing them in the direction of arrow C, it becomes possible to finely and coarsely adjust the writing spot diameter on the transfer master drum 24. In this case, the writing spot diameter is roughly adjusted by the displacement of the plate 44, and the writing spot diameter is finely adjusted by the displacement of the plate 48.

Here, the plate body 32) or the plate body 44 according to this embodiment
It will be readily understood that even if the laser diode 12 and 48 are disposed between the laser diode 12 and the collimator 14 shown in FIG. 1, the writing spot diameter can be adjusted in the same way.

Note that the laser light emitted from the laser diode 12 is not necessarily emitted in the same direction at the radiation angle θ, but is normally emitted so as to form an ellipse with respect to the incident surface of the collimator 14. Therefore, as shown in FIG.
A waveform shaper 54 consisting of a pair of cylindrical lenses 50 and 52 may be disposed between the beam expander 18 and the beam expander 18 . In this case, the cylindrical lenses 50 and 52 are
It has a characteristic of condensing light only in the X direction out of the two directions.

Therefore, the width of the laser beam output from the laser diode 12 in the X direction is corrected by the waveform shaper 54.

Therefore, by disposing a plate 58 having a long rectangular opening 56 in the Y direction between these cylindrical lenses 50 and 52, the writing spot diameter of the laser beam can be effectively adjusted along with waveform shaping. I can do it.

That is, by displacing the plate 58 in the direction of arrow C, it is possible to adjust only the writing spot diameter in the X direction.

Note that it is also possible to derive the same effect as the waveform shaper 54 by tilting the plates 32, 44 and 48 shown in FIGS. 3 and 4 with respect to the optical axis 33.

As described above, according to the present invention, a beam diameter adjusting means having an aperture of a predetermined shape is provided in the optical path of the diverging or converging laser beam, etc. It is configured to be movable along the optical axis. Therefore, the same effect as when changing the aperture diameter by changing the position of the beam diameter adjusting means can be obtained, and the beam diameter can be adjusted extremely easily. In this case, since the amount of change in the beam diameter with respect to the amount of displacement of the beam diameter adjusting means differs depending on the diameter of the opening formed in the beam diameter adjusting means,
If a plurality of beam diameter adjusting means having apertures with different diameters are arranged in the optical path of the laser beam, etc., it is extremely easy to finely and coarsely adjust the beam diameter.

Although the present invention has been described above by citing preferred embodiments, the present invention is not limited to these embodiments (
For example, the beam diameter of not only a diverging laser beam but also a converging laser beam can be similarly adjusted by using the beam diameter adjusting device according to the present invention. Of course, improvements and changes in design are possible.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing a laser optical system of a laser printer to which the beam diameter adjusting device according to the present invention is applied, and FIG. 2 is a perspective cross-sectional explanatory diagram of a beam expander including the beam diameter adjusting device according to the present invention. , FIG. 3 is an explanatory side view of the beam expander shown in FIG. 2, FIG. 4 is an explanatory diagram showing another embodiment of the beam expander to which the beam diameter adjustment device according to the present invention is applied, and FIG. 1 is a perspective explanatory diagram of an optical system having a waveform shaper including a beam diameter adjustment device according to the present invention. 10...Laser optical system 12...Laser diode 14...Collimator 18...Beam expander 20...Galvanometer mirror' 22...Scanning lens 24...Transfer mask drum 28.30...・Condensing lens 32...Plate body 34・
...Opening 44.48...Plate FIG, 1 Standing C

Claims (2)

[Claims] (1) A beam diameter adjusting means having an aperture of a predetermined shape is disposed in the diverging or converging light beam, and the beam diameter adjusting means is configured to be movable along the optical axis of the light beam. Beam diameter adjustment device. (2) In the apparatus according to claim 1, the beam diameter adjusting means includes a first plate having a small diameter opening and disposed in a small diameter portion of the diverging or converging light beam; a second plate having an aperture larger in diameter than the aperture of the plate and disposed in a large diameter portion of the light beam;
A beam diameter adjusting device in which the plate is configured to be independently displaceable along the optical axis of the light beam.