JPS6239365Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a transmission device that efficiently transmits laser light.

[Technical background of the invention and its problems]

When energy is transmitted from laser light through optical fiber,
Optical fibers are used in cases where the processing speed must be slowed down due to a decrease in focused power density, or when laser beam irradiation conditions with relatively high focused power density are required, such as drilling or cutting. There were some aspects in which transmission was not suitable. For example, if you try to focus YAG laser light with a condensing lens and transmit energy with a high average output, it will be difficult to transmit energy with a high average output unless the optical fiber has a large diameter.On the other hand, the laser light emitted from the large diameter optical fiber has already Since the power density is reduced within the optical fiber, even if the optical fiber is focused, a sufficiently high focused power density cannot be obtained, resulting in a problem that removal processing such as drilling becomes impossible. Therefore, for the reasons mentioned above, it is not possible to perform various types of processing on optical fibers.

[Purpose of invention]

The object of the present invention is to provide a transmission device that efficiently transmits high-power laser light through an optical fiber and is suitable for multi-purpose processing.

[Summary of the idea]

The optical system for inputting light into the optical fiber is configured to be a short focal length or long focal length condensing lens depending on the degree of average output of the laser beam, and these lenses are individually arranged on the laser optical path.

[Example of idea]

Figure 1 shows an embodiment of the present invention, in which 1 is a solid-state laser oscillator such as YAG, 2 is an optical fiber for transmission with a transmission diameter of DF, and 3 is a laser beam L emitted from the optical fiber 2 to be processed. This is a condensing lens for irradiation that condenses light onto an object 4. Incidentally, an optical system 5 is provided between the laser oscillator 1 and the input end of the optical fiber 2, and is detachable from the laser beam path. The optical system 5 consists of a long focus lens 6 that is inserted into and removed from the optical path near the laser oscillator 1 side, and a short focus lens 7 that is inserted and removed near the input end of the optical fiber 2, both of which are mounted on a movable mount. 8a, 8b so that it can be inserted into and removed from the laser optical path.

The operation of the above configuration will be explained next.

Before going into this explanation, we will explain the minimum spot diameter and the intensity of focused light (power density) in the "Laser Handbook" (published February 20, 1971, published by Asakura Shoten Co., Ltd.).
P691). That is, as shown in Fig. 4, when a light beam with a spread angle θ (rad) is focused by a lens Cl with a focal length f (cm), the spot diameter of the laser beam L at the focal plane F is expressed by the following formula. It has been known.

d=fθ Furthermore, when the laser beam L is focused, the intensity (power density) F at the focal plane can be obtained by dividing the output power P of the laser by the spot area πd ² /4.
That is, the following equation is obtained.

F=4P/πd ² Therefore, when the focal lengths of the long focal length lens 6 and the short focal length lens 7 are f ₁ and f ₂ respectively, the beam divergence angle θ ₁ is such that the laser output is sufficiently small.
In this case, f ₁ is selected to be sufficiently long so that f ₁ θ ₁ = DF, while the YAG rod in the solid-state laser oscillator 1 is subjected to thermal distortion due to optical excitation, and the laser output is increased under high average laser output conditions. If the beam exhibits a larger beam divergence angle θ ₂ then f ₂ θ ₂ =
Select to be DF. In this way, the focal length fi of the optical system 5 is set in multiple stages from when the laser average output level Pi or the beam spread angle θi of the output beam is small to when it becomes large so as to satisfy the condition fiθi=DF. This allows the incident focused beam at the input end of the optical fiber 2 to fill the input fiber end over substantially the entire area. Figure 2 shows the average output of a pulsed YAG laser.
This shows the relationship between Pav and the beam spread angle θ of the output laser beam, and the average output Pav and the beam spread angle θ of the output laser beam also increase proportionally. Therefore, if the laser beam is introduced into the optical fiber using a short focus lens that forms the maximum allowable incident angle of the optical fiber, even if the laser beam L ₁ has a large laser beam spread angle θ, the effective transmission diameter (core) of the optical fiber will decrease. The beam can be focused and transmitted with significantly reduced loss. When a short focal length lens 7 with a focal length _f1 is selected and metal cutting is attempted, the cutting speed S is as shown in Fig. 3.
is plotted as a curve 10 of large power P _B with respect to plate thickness t. In other words, when the average output is large and the power P _B can be transmitted even under conditions where the beam divergence angle θ is large, the depth of focus becomes shallow, so a sufficiently high cutting speed can be obtained when the plate thickness is thin, but when the plate thickness becomes thick, The cutting speed must be kept low. Furthermore, if the plate thickness exceeds a certain level, it may become impossible to cut, self-combustion may occur due to the influence of oxygen gas when used as an assist gas, or even if the plate can be cut, it will be cut over a wide area.
In this case, cutting is impossible even if the average laser output is reduced. However, in the present invention, when the average output condition of the oscillation output P is smaller than the maximum output P _B , it is configured so that the optical fiber input lens having a focal length f ₁ longer than the above-mentioned f ₂ can be used to input the light. In this case, since the output condition of P _S is as shown in FIG. 2, a laser beam L ₂ having a beam divergence angle θ ₁ smaller than the beam divergence angle θ ₂ is obtained. As a result, if f ₁ is selected such that f ₁ θ ₁ ≒ DF and cutting is performed in the same manner as described above under that condition, the cutting characteristics along the curve 11 of P _S , f ₁ in FIG. 3, that is, P _B , f Compared to the characteristics in case of high average output of ₂ , it is possible to cut even when the plate thickness is thick, but when the plate thickness is thin, the cutting speed becomes low approximately in accordance with the laser average output.

[Effect of idea]

As described above, the present invention is based on the focal length f of the condensing lens that makes the laser beam enter the optical fiber with the incident diameter DF.
The converging lens can be selected so that fθ≒DF between It has become possible to expand the limit value of possible plate thickness. In addition to cutting, it is now possible to drill holes at high speed when the depth is shallow, and to increase the depth, making it possible to perform removal operations such as cutting and drilling. Ta.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention;
The figure shows the relationship between the average output of the laser pulse and the beam divergence angle. Figure 3 shows the relationship between the cutting speed and the thickness of the workpiece depending on the combination of the laser output and the condensing lens. Figure 4 shows the relationship between the laser output and the beam divergence angle. FIG. 2 is a diagram illustrating the minimum spot diameter. 1... Laser oscillator, 2... Optical fiber, 3...
...Condenser lens for irradiation, 5...Optical system, 6...Short focus condenser lens, 7...Long focus condenser lens, 8a,
8b...Moveable stand.

Claims (1)

[Scope of utility model registration request] A laser beam transmission device comprising a condensing lens that condenses a laser beam output from a laser oscillator using an optical system, enters an optical fiber, and condenses the laser beam emitted from the optical fiber onto a workpiece, the optical system comprising: The system consists of a plurality of condensing lenses with different focal points, and among these condensing lenses, a short focal length lens is positioned on the laser beam path in an area where the average output of the laser beam is high, and a long focal length lens is positioned in an area where the average output is low. A laser beam transmission device characterized in that it is provided so as to be freely inserted and removed so as to be positioned in the same position.