GB2309189A

GB2309189A - Laser beam machines

Info

Publication number: GB2309189A
Application number: GB9703782A
Authority: GB
Inventors: Hisao Tanaka; Takeshi Irino; Akira Ishimori; Akaru Usui; Shigehiro Yoshiyasu
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1995-02-28
Filing date: 1996-02-28
Publication date: 1997-07-23
Anticipated expiration: 2016-02-28
Also published as: GB2309188A; GB9703782D0; GB2309188B; GB2309189B; GB9703780D0

Description

1 LASER BEAK 14ACHINES 2309189 The present invention pertains generally to

laser beam machines and more particularly to their optical f iber wiring and beam output optical assemblies having improved structures.

It is known that a carbon dioxide gas (C02) laser, which features high beam quality (i.e., light-condensing capability), is an excellent light source for use in laser beam cutting of metal plates and sheets. Various types of C02 laser beam machines using mirrors and infrared-transparent optical fibers have thus far been proposed and developed for practical applications. on the other hand, yttrium-aluminum-garnet (YAG) lasers have been used in marking and trimming applications, f or instance, because they have been able to provide good beam quality only in low-power ranges. However, recent technological advances have made it possible to develop YAG lasers which would offer as good beam quality as the C02 lasers even at output power levels exceeding 100 W. As a result, it has become possible for the YAG lasers, which utilize visiblelight-transparent optical fibers featuring a high degree of operability and multi-purpose applicability, to achieve such cutting performance that is comparable to the C02 lasers.

FIG. 4 is a perspective diagram illustrating a lightcondensing head positioning mechanism of a C02 laser beam machine utilizing an in f raredtransparent optical fiber, of Z which example is disclosed in Japanese Patent Application No. 57-124586. In FIG. 4-, there are provided a flexible optical fiber cable 1 containing an infrared- transparent optical fiber measuring 10. 6 gm in wavelength at C02 laser connected to a laser oscillator (not shown) and a beam output optical assembly 2 connected to the end of the optical fiber cable 1. Designated by the numeral 3 is a table on which a workpiece W, e. g., a piece of sheet metal, is fixedly mounted. Designated by the numeral 4 is a positioning mechanism for moving the beam output optical assembly 2 above the workpiece W in a twodimensional processing pattern. The positioning mechanism 4 includes a first carriage member 4-2 which moves along a pair of rails 4-1 and a second carriage member 4-3 which moves at right angles to the rails 4-1 along another pair of rails 4-4. The beam output optical assembly 2 is mounted to the second carriage member 4-3.

Described in the following is how the C02 laser beam machine of the above construction operates when marking a graphic or text pattern on the workpiece W. A marking process is commenced by first positioning the beam output optical assembly 2 just above a specified location of' the workpiece W. A controller (not shown) transmits a control signal produced in accordance with readily entered marking pattern data. This control signal controls opening and closing operations of a shutter provided inside a C02 laser oscillator (not shown) in order to intermittently deliver and interrupt laser light. The 3 laser light of an appropriate energy level transmitted to the beam output optical assembly 2 via the optical f iber cable 1 is switched on and off in this manner. The beam output optical assembly 2 is moved by the first carriage member 4-2 and second carriage member 4-3 of the positioning mechanism 4 above the workpiece W. When exposed to a laser beam radiated f rom the beam output optical assembly 2, resulting heat causes an exposed surf ace zone of the workpiece W to evaporate or melt so that the specified pattern is marked on the workpiece W in accordance with the movement of the beam output optical assembly 2 and the laser light switching on/off sequence.

The above-described C02 laser beam machine employs an optical fiber for laser light transmission. Unlike laser machining systems using mirrors for laser beam transmission, this type of laser beam machine can not be used for cutting a steel plate, for instance, due to a large transmission loss of the 10.6 gm in f rared-transpa rent optical fiber. Development of a low transmission loss optical fiber has therefore been awaited. YAG laser machining systems also have a similar problem. Although transmission loss of optical fibers used for carrying visible light is sufficiently low,output power of a YAG laser that can provide satisfactory beam quality is limited to a few tens of watts.

Generally, it is necessary to eject an assist gas together with a laser beam through a coaxial nozzle to realize a high-quality cutting process. Different assist gases are 4 used for different types of workpiece. As an example, oxygen is most often used for steel plates and stainless steel plates. In this example, it is possible to increase the cutting speed and reduce the amount of dross (i.e., waste product deposits caused in cutting operations) by increasing the gas pressure. Also effective for making efficient use of laser beam energy, increasing the cutting speed and reducing thermal distortion is to converge the laser beam on as small a spot as possible. It is a common practice in laser beam machining to construct beam output optical systems in consideration of the above aspects.

FIG. 5 is a cross-sectional view showing the structure of a conventional beam output optical assembly 2 used in YAG laser beam machines which employ optical fibers transparent to visible light. In FIG. 5, designated by the numeral 1 is an optical fiber cable containing an vi s ible- light -transparent optical fiber in a flexible protective jacket. The beam output optical assembly 2 comprises a nozzle centering mechanism 12, a beam output optical assembly housing 2-1 provided with an assist gas inlet 15, a collimator lens 14 and a condenser lens 13. Designated by the numeral 11 is an optical fiber joint which connects the optical fiber cable 1 to the beam output optical assembly 2. The optical fiber joint 11 comprises an optical connector 11- 1 including a plug 11-1a and a receptacle 11-1b. The receptacle 11-1b is screwed to one end of the beam output optical assembly housing 2-1. Mounted to the beam output optical assembly housing 2-1 at the opposite end to the optical fiber joint 11, the nozzle centering mechanism 12 includes a nozzle 12-1, a first nozzle holder 12-2, nozzle adjusting screws 12-3 mounted on the first nozzle holder 12-2 and a second nozzle holder 12-4.

Operation of the beam output optical assembly 2 of FIG.

is now described. The laser light transmitted through the optical fiber cable 1 is emitted from the end of the optical fiber at the optical connector 11-1 of the optical fiber joint 11. The laser light propagates through the air in a diverging pattern until it reaches the collimator lens 14, which brings the laser light into a parallel beam. The condenser lens 13 causes the parallel beam to converge so that the laser beam outgoing through the nozzle 12-1 is focused on the surface of a workpiece W. Before starting a cutting operation, a machine operator carries out an adjustment for aligning the laser beam with the center of the nozzle 12-1 by turning the nozzle adjusting screws 12-3. With this adjustment, an assist gas injected from the assist gas inlet 15 is uniformly blown onto a currently processed spot to accomplish a successful cutting operation.

Since the assist gas is injected under about 10 kg /CM2 the atmospheric pressure at maximum into a space confined by the nozzle 12-1 having a small orifice typically measuring about 2 mm in diameter, a thick single lens is used as the condenser lens 13 to avoid its physical damages. This poses another problem that it is necessary to use an expensive aspherical lens in order to prevent spherical aberration that can lead to degradation of laser light converging performance.

6 Documentk 118208 The present invention provides laser beam machines as set forth in claims 1 and 2.

In one embodiment the laser beam machine comprises a beam output optical dexlice including a collimator lens for converting incident laser light into parallel rays of light, a condenser lens for converging the parallel rays of light, and a housing for holding the collimator lens and condenser lens, the housing having a gas inlet for injecting an assist gas, wherein the collimator lens and condenser lens are compound lenses, each including a -7 plurality of lenses, and the laser light converged by the condenser lens is emitted together with the assist gas; a transmitting medium fixing device for fixing a laser light transmitting medium to the housing; a condenser lens holder for holding the condenser lens, the condenser lens holder having a first group of through holes in its wall just between constituent lenses of the condenser lens; a condenser lens support for fixing the condenser lens holder to the housing, maintaining a gap therebetween, the condenser lens support having a second group of through holes extending in parallel with the laser light path; and a pressureproof optical glass plate provided between the collimator lens and condenser lens for shutting out the assist gas.

The first and second groups of through holes provided respectively in the condenser lens holder and condenser lens support reduce pressure differentials between both sides of each individual lens. This arrangement, associated with the pressure-proof optical glass plate, helps reduce spherical aberration, converge the laser light more sharply, improve machining performance, and eliminate adverse effects of the assist gas pressure on the individual lenses The above laser beam machine may comprise, instead of the pressure-proof optical glass plate, a sealing mechanism provided between the transmitting medium fixing device and the housing for shutting out the assist gas; a collimator lens holder for holding the collimator lens, the collimator lens a holder having a third group of through holes in its wall just between constituent lenses of the collimator lens; and a collimator lens support for fixing the collimator lens holder to the housing, maintaining a gap therebetween, the collimator lens support having a fourth group of through holes extending in parallel with the laser light path.

The first to fourth groups of through holes provided respectively in the condenser lens holder, condenser lens support, collimator lens holder and collimator lens support reduce pressure differentials between both sides of each individual lens. This arrangement, associated with the sealing mechanism provided between the transmitting medium fixing device and the housing, helps reduce spherical aberration, converge the laser light more sharply, improve machining performance, and eliminate adverse effects of the assist gas pressure on the individual lenses is 9 The invention will be described further, with reference to the accompanying drawings, in which:

FIG, 1 is a cross-sectional view of a beam output optical assembly used in a laser beam machine according to a first embodiment of the invention; FIG. 2 is a cross-sectional view of a beam output optical assembly used in a laser beam machine according to a second embodiment of the invention; FIG. 3 is a fragmentary cross-sectional view showing a cable connecting structure of the beam output optical assembly according to the second embodiment of the invention; FIG. 4 is a perspective diagram illustrating a positioning mechanism of a conventionalC02 laser beam machine; and FIG. 5 is a cross-sectional view of a beam output optical assembly used in a conventional YAG laser beam machine.

FIG. 1 is a cross-sectional view of a beam output optical assembly 2 used in a laser beam machine according to a first embodiment of the invention. In FIG. 1, elements designated by the numerals 1, 2 - 1, 11, 11- 1, 11la, 11- lb, 12-1 and 15 are identical or equivalent to those used in the e arher- described conventional laser beam machine. Their detailed description is therefore omitted here.

Referring to FIG 1, designated by the numeral 41 is a collimator lens comprising a plurality of lenses which are combined by a lens holder 41-1, and designated by the numeral 42 is a condenser lens comprising a plurality of lenses which are combined by a lens holder 42-1. Designated by the numerals 41-2 and 42-2 are lens supports by which the collimator lens 41 and condenser lens 42 are fixed to the beam output optical assembly housing 2-1, respectively. Designated by the numeral 44-1 are a first group of eight through holes provided around the lens holder 42-1 at 451 angular intervals just between constituent lenses of the condenser lens 42, and designated by the numeral 44-2 are a second group of eight through holes provided around the lens support 42-2 at 45 angular intervals. Designated by the numeral 43 is a pressure-proof optical glass plate provided between the collimator lens 41 and condenser lens 42.

Discussed in the following is how the construction of the first embodiment works. The laser light emitted from the optical fiber cable 1 is brought into a parallel beam by the collimator lens 41. This parallel beam passes through the pressure-proof optical glass plate 43 and is converged by the condenser lens 42 in such a way that the laser light outgoing through the nozzle 12-1 focuses on the surface of a workpiece W. Both the collimator lens 41 and condenser lens 42 are compound lenses which can better compensate for spherical aberration than single spherical lenses. This serves to reduce the diameter of the focused beam spot on the workpiece W, increase incident energy density and thus improve machining 11 is performance. A high-pressure assist gas is injected through the assist gas inlet 15 and blown onto the workpiece W through the nozzle 12-1. Since the assist gas is shut out by the pressure-proof optical glass plate 43, the collimator lens 41 is protected from undesirable effects of the gas pressure. Although the individual lenses of the condenser lens 42 are subjected to the pressure of the assist gas, there occurs no pressure differential between both sides of each individual lens. This is because there are provided the through holes 441 in the lens holder 42-1 which holds the individual lenses and the through holes in the lens support 422 to which the condenser lens 42 is screwed.

As seen above, both the collimator lens 41 and condenser lens 42 are configured as compound lenses. This arrangement helps reduce spherical aberration, focus the laser light more sharply and improve machining performance. In addition, provision of the pressure-proof optical glass plate 43 between the collimator lens 41 and condenser lens 42, associated with the through holes 44-1 and 44-2 provided in the lens holder 42-1 just between individual lenses and in the lens support 42-2, eliminates adverse effects of the assist gas pressure on the individual lenses and prevents their distortion and fracture.

121 FIG. 2 is a cross-sectional view of a beam output optical assembly 2 used in a laser beam machine according to the second embodiment of the invention, and FIG. 3 is its enlarged fragmentary cross-sectional view. In these drawings, elements designated by the numerals 1, 2-1, 11, 11-1, 11-1a, 11-1b, 12-1 and 15 are identical or equivalent to those used in the earl ier-described conventional laser beam machine while elements designated by the numerals 42, 42-1, 42-2, 44-1 and 44-2 are identical to those described with reference to the f irst embodiment. Their detailed description is therefore omitted here.

Referring to FIG. 2, designated by the numeral 51 is a collimator lens comprising a plurality of lenses which are combined by a lens holder 51-1, and designated by the numeral 52-2 is a lens support by which the lens holder 51-1 is fixed to the beam output optical assembly housing 2-1. Designated by the numeral 52-1 are a third group of eight through holes provided around the lens holder 51-1 at 45' angular intervals at locations just between constituent lenses of the collimator lens 51, and designated by the numeral 52-2 are a fourth group of eight through holes provided around the lens support 51-2 at 45 angular intervals.

FIG. 3 is an enlarged view depicting the structure of the optical fiber joint 11 and its surrounding components shown in FIG. 2. In FIG. 3, designated by the numeral 53 is an 0- 13 ring f itted to the end surf ace of the beam output optical assembly housing 2-1 to which the receptacle 11-1b of the optical fiber joint 11 is fixed, and designated by the numeral 54 is a flat ring gasket seated between the receptacle 11-1b and a ferrule 11-3 which constitutes an integral part of the plug 11-1a. The inside diameter of the flat ring gasket 54 is large enough to allow the laser beam to pass through. Designated by the numeral 11-2 is a retaining nut which accompanies the plug 11-1a for tightening the ferrule 11-3 against the flat ring gasket 54. The optical fiber cable 1 is chemically bonded to the ferrule 11-3 (not shown).

Discussed in the following is how the construction of the seconcl embodiment works. The laser light emitted from the optical fiber cable 1 is brought into a parallel beam by the collimator lens 51. This parallel beam is converged by the condenser lens 42 in such a way that the laser light outgoing through the nozzle 12-1 focuses on the surface of a workpiece W. Both the collimator lens 51 and condenser lens 42 are compound lenses which can better compensate for spherical aberration than single spherical lenses. This serves to reduce the diameter of the focused beam spot on the workpiece W, increase incident energy density and thus improve machining performance. A high-pressure assist gas is injected through the assist gas inlet 15 and blown onto the workpiece W through the nozzle 12-1. Although the individual lenses of the collimator lens 51 and condenser lens 42 are subjected to the 14- is pressure of the assist gas, there occurs no pressure differential between both sides of each individual lens. This is because there are provided the through holes 52-1 and 44-1 in the lens holder 51-1 and lens holder 42-1 which hold the individual lenses and the through holes 52-2 and 44-2 in the lens support 51-2 and lens support 42-2 to which the lens holders 51-1 and 42-1 are screwed, respectively. Furthermore, the optical fiber joint 11 is sealed by means of the 0-ring 53, flat ring gasket 54 and a chemical bond so that leakage of the assist gas is prevented.

As seen above, both the collimator lens 51 and condenser lens 42 are configured as compound lenses. This arrangement helps reduce spherical aberration, focus the laser light more sharply and improve machining performance. In addition, the sealed configuration of the optical fiber joint 11, associated with the through holes 44-1, 44-2, 52-1 and 52-2 provided in the lens holders 42-1 and 52-1 just between individual lenses and in the lens supports 42-2 and 52-2, eliminates adverse effects of the assist gas pressure on the individual lenses and prevents their distortion and fracture.

Claims

Claims:1. A laser beam machine comprising: a collimator lens for

converting incident laser light into parallel rays of light and a condenser lens for converging the parallel rays of light. the collimator lens and the condenser lens being compound lenses, each including a plurality of lenses, and the laser light converged by the condenser lens being emitted together with an assist gas; beam emitting means including a housing for holding the collimator lens and the condenser lens, the housing having a gas inlet for injecting an assist gas; transmitting medium fixing means for fixing a laser light transmitting medium to the housing; condenser lens holding means for holding the condenser lens, the holding means having a first group of through holes in the wall between the lenses of the condenser lens; condenser lens fixing means for fixing the condenser lens holding means to the housing, maintaining a gap therebetween, the condenser lens fixing means having a second group of through holes extending in parallel with the laser light path; and a pressure-proof optical glass plate provided between the collimator lens and the condenser lens for shutting off the collimator lens from the pressure of the assist gas.
2. A laser beam machine comprising: a collimator lens for converting incident laser light into parallel rays of light and a condenser lens for converging the parallel rays of light, the collimator lens and the condenser lens being compound lenses, each c including a plurality of lenses, and the laser light converged by the condenser lens being emitted together with an assist gas:

16 beam emitting means including a housing for holding the collimator lens and the condenser lens, the housing having a gas inlet for injecting an assist gas, transmitting medium fixing means for fixing a laser light transmitting medium to the housing; condenser lens holding means for holding the condenser lens, the holding means having a first group of through holes in the wall between the lenses of the condenser lens; condenser lens fixIing means for fixing the condenser lens holding means to the housing, maintaining a gap therebetween, the condenser lens fixIing means having a second group of through holes extending in parallel with the laser light path; collimator lens holding means for holding the collimator lens, the holding means having a third group of through holes in the wall between the lenses of the collimator lens; collimator lens fixing means for fixing the collimator lens holding means to the housing, maintaining a gap therebetween, the collimator lens fixing means having a fourth group of through holes extending in parallel with the laser light path; and sealing means provided at a mounting portion between the transmitting medium fixing means and the housing.
3. A laser beam machine substantially as described with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings.