JPS629309A - Beam expander lens barrel - Google Patents

Abstract

PURPOSE:To prevent a lens interval from varying owing to variation in environmental temperature by using a material which has a <=1X10<-6>/deg coefficient of thermal expansion for a cylinder part which has a lens holding part fitted on both sides. CONSTITUTION:Holding parts 12 and 13 which hold lenses 14 and 15 are fitted on both sides of the cylinder part 11. The holding parts 12 and 13 are made of materials with good workability and the cylinder part 11 is formed of the material having a <=1X10<-6>/deg coefficient of thermal expansion. Therefore, even if the environmental temperature varies, a beam convergence position is made constant because the lens interval is unchanged.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a lens barrel of a beam expander.
The present invention relates to an improvement of a lens barrel for a beam expander that expands the beam diameter of a light beam in a laser scanning device or the like.

(Technical Background and Prior Art of the Invention) In a laser scanning device, the oscillated laser beam is temporarily expanded in order to make the spot of the light beam formed by the imaging lens as small as possible. A beam expander is used.

For example, as shown in FIG. 2, a thin laser beam 21 is made incident on a first convex lens 22 with a short focal length f1, and after being focused on a focal point 23 of the convex lens 22, the laser beam 21 is focused from the focal point 23 to its own focal length f2. A relatively long focal length f
The beam is advanced while expanding its diameter to the second convex lens 24 of No. 2, and the beam 25 with a large diameter is
There are known methods that allow you to obtain the following. Conventionally, in a beam expander having such a structure, the lens 22.
The lens barrel 26 that holds the lens barrel 24 is made of a material that is relatively processable (that is, machinability and moldability), such as aluminum, iron, or plastic, in order to easily process the lens holding part.
It was formed from good materials.

However, in the above-mentioned beam expander that has a lens barrel made of aluminum, iron, plastic, etc., the lens barrel expands and contracts due to environmental temperature fluctuations, changing the focal length, which changes the convergence position of the beam and changes the scanning plane. The beam spot diameter will change. Such a shift in the convergence position is particularly a problem in a device that combines a plurality of laser beams into one beam through a condensing system for scanning. That is, the convergence position of each beam changes and the scanning beam diameter at a fixed focal plane increases, resulting in problems such as a decrease in scanning accuracy.

(Object of the Invention) The present invention has been made in view of the above circumstances, and an object thereof is to provide a lens barrel for a beam expander that can prevent the lens interval from changing due to fluctuations in environmental temperature. That is.

(Structure of the Invention) The beam expander lens barrel of the present invention has an intermediate cylindrical portion that connects two lens holding portions with a 1×10′/de
It is characterized in that it is formed from a material having a coefficient of thermal expansion equal to or less than g, and is constructed by combining this cylindrical part and the lens holding part.

(Embodiments) Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows a beam expander lens barrel according to one embodiment of the present invention. This beam expander lens barrel 10 includes a cylindrical portion 11, a 113th lens holding portion 12.13 fitted to both ends of the cylindrical portion 11, and a second lens holding portion 12.
It consists of These lens holding parts 12 and 13 are formed by cutting a material with relatively good machinability, for example, aluminum with good machinability, and hold the first convex lens 14 and the second convex lens 15, respectively. . Note that each of these convex lenses 14.15 is fixed by a lens presser 16.17 that is combined with the lens holding portion 12.13 by, for example, fitting or screwing.

The lens holding parts 12.13 each have a convex lens 14.15.
In order to hold the lens, it is provided with an annular protrusion or a thread for screwing the lens holder 16, 17, but since it is formed using aluminum with good machinability as mentioned above, it can be easily cut. Processed vine. In addition to the above-mentioned aluminum, these lens holding parts 12 and 13 may be made of iron, which has good machinability, or plastic, which has good moldability.

The cylindrical portion 11 connecting the lens holding portions 12 and 13 is formed into a simple cylindrical shape as shown in the figure.
It is made of a material with a thermal expansion coefficient of 1×104/(jeQ or less, such as Invar, Super Invar, or Neoceram.The thermal expansion coefficient of aluminum mentioned above is 2.
．． The coefficient of thermal expansion of the above material is about 3×10'/deg, and compared to this, the coefficient of thermal expansion of the above material is 1/20th of a g. By forming the cylindrical portion 11 using such a material, it is extremely difficult to expand or contract even if the environmental temperature fluctuates, and therefore the distance between the convex lenses 14 and 15 is difficult to change. Note that the above-mentioned Invar, Super Invar, Neoceram, etc. are extremely difficult to cut, but the cylindrical part 1
1 only needs to be formed into a simple cylindrical shape and does not require any particularly complicated cutting work (it is sufficient to simply cut a pipe-shaped object), so it can be easily manufactured.

(Effects of the Invention) As explained in detail above, the beam expander lens barrel of the present invention is easy to manufacture and can prevent changes in lens spacing due to environmental temperature fluctuations as much as possible. Accordingly, in the laser scanning device described above, it is possible to prevent the beam convergence position from changing greatly depending on the environmental temperature and the diameter of the scanning beam spot from changing.

[Brief Description of the Drawings] Fig. 1 is a side sectional view showing an embodiment of the beam expander lens barrel of the present invention, and Fig. 2 is a side sectional view showing an example of a conventional beam expander lens barrel. be. 10...Beam expander lens barrel 11...Cylinder part 12.13...Lens holding part 14.
15...Lens Fig. 1 Fig. 2

Claims (2)

[Claims] (1) In a beam expander lens barrel having lens holders at both ends of the cylindrical part, the cylindrical part is 1×10^-^
Formed from a material having a coefficient of thermal expansion of 6/deg or less,
A beam expander lens barrel characterized by a combination of these two parts. (2) The beam expander lens barrel according to claim 1, wherein the cylindrical portion is made of Invar, Super Invar, or Neoceram.