WO1997013172A1

WO1997013172A1 - Protective window assembly for a laser beam generating apparatus

Info

Publication number: WO1997013172A1
Application number: PCT/US1996/015968
Authority: WO
Inventors: Robert D. Herpst
Original assignee: Herpst Robert D
Priority date: 1995-10-06
Filing date: 1996-10-04
Publication date: 1997-04-10
Also published as: AU7390796A

Abstract

A protective window assembly (2) and its use with a focusing lens in a laser beam generating apparatus to protect the focusing lens against contamination and the like. A protective window assembly (2) includes a housing (4) defining a cavity (6) for receiving the protective window (8). The cavity is defined by opposed walls (10 and 12) of the housing (4) and a flange (14) against which the protective window (8) rests when secured within the cavity (6). The housing (4) has a forward end (16) and a rearward end (18). The forward end (16) is positioned in proximity to the target (e.g. workpiece) which is contacted by the laser beam. Protective gaskets (22) may be provided. Set screws (20) are provided to secure the protective window assembly (2) to the assembly containing the focusing lens.

Description

PROTECTIVE WINDOW ASSEMBLY FOR A LASER BEAM GENERATING APPARATUS

RELATED APPLICATION

This is a continuation-in-part application of pending U.S. Serial No. 08/540,561 filed October 6, 1995.

FIELD OF THE INVENTION

The present invention is directed to a protective window assembly for use in conjunction with or integral with a focusing lens assembly in a laser beam generating apparatus in which a protective window is provided for protecting the focusing lens and especially any lens coating thereon against contamination. The protective window is situated within a single housing containing the focusing lens or in a separate housing which is operatively secured to an assembly containing the focusing lens.

BACKGROUND OF THE INVENTION

Lasers are a common and important mechanism for cutting, marking, welding, and surface modifying substrates such as metals including stainless steel. The term "Laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. The most common stimulating media are carbon dioxide gas and neodymium yttrium aluminum garnite (Nd:YAG).

Maximizing laser productivity depends on output power, laser beam quality, and ease of operation of the device for its intended purpose. One of the more common reasons for poor laser performance is the result of contamination of the laser apparatus, particularly the focusing lens. Sources of laser contamination include impurities in the laser gases or in the nozzle pressurizing gas, vacuum-system leaks, back-streaming of vacuum pump oil into the laser cavity, sputtering of metal atoms from electrodes, fingerprints and vacuum grease, and contaminants present where optics are stored, and the like.

Most laser systems use some type of nozzle in front of the final focusing lens. The nozzle delivers a pressurized gas to the workpiece and is designed to prevent debris from spraying onto the focusing lens. Contamination of the focusing lens is one of the prime reasons for poor laser performance and downtime of laser operations. However, no nozzle system is perfect and some debris, fume or backspatter will occasionally reach the lens.

More recently laser systems have employed a protective window to protect the focusing lens against contamination. The protective window is positioned in front of the focusing lens both of which are contained within a lens assembly. This system is disadvantageous because the protective window, which can alter the focal length of the laser beam, requires modification or disassembly of the lens assembly to replace or renew the protective window. Such a system is frequently impractical because the lens holder is not designed to accomodate a protective window.

The focusing lenses employed in laser systems are typically expensive and great care is taken to ensure that they remain free from contamination. However, to date, there has been no effective system for protecting the focusing lens against contamination in a cost efficient and effective manner. It would therefore be a significant advance in the art of employing lasers, to provide a device for effectively protecting the focusing lens of a laser beam generating apparatus.

SUMMARY OF THE INVENTION

The present invention is directed to a protective window assembly and to its use with or integral with a focusing lens assembly in a laser beam generating apparatus in which the focusing lens is protected by the protective window contained within the protective window assembly. The protective window assembly is either releasably secured to the focusing lens assembly containing the focusing lens or integral therewith. When the focusing lens assembly and the protective window assembly are secured together the focusing lens is effectively protected from contamination in a cost efficient and effective manner. Replacement or renewal of the protective window can be accomplished without altering or disassembling the focusing lens assembly.

In particular, the present invention is directed to a protective window assembly alone which can be releasably secured to or is integral with a focusing lens assembly for use with a laser beam generating apparatus. The protective window assembly comprises:

(a) a housing having a cavity for securing a protective window therein; and (b) securing means for securing the housing to a focusing lens assembly containing a focusing lens.

In one aspect of the invention, the housing for securing the protective window is releasably securable to a focusing lens assembly. In an alternative embodiment of the invention, the protective window assembly is integral with the focusing lens assembly.

In a preferred aspect of the present invention, the protective window assembly housing allows the passage of gas therethrough to equalize pressure about the protective window to thereby prevent rupture or breakage of the protective window.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings in which like reference characters indicate like parts are illustrative of embodiments of the invention and are not intended to limit the invention as encompassed by the claims forming part of the application.

Figure 1 is a partially exploded side view of a window assembly in accordance with the present invention;

Figure 2 is a front view of the embodiment of the window assembly shown in Figure l; Figure 3 is a rear view of the embodiment of the window assembly shown in Figure l;

Figure 4 is an exploded view of a focusing lens assembly including the window assembly shown in Figure 1;

Figure 5 is a cross-sectional side view of the focusing lens assembly shown in Figure 4;

Figure 6 is a cross-sectional side view similar to Figure 5 using threads and grooves to secure the lens mount and protective window assembly together;

Figure 7 is a cross-sectional side view similar to Figure 5 using an O-ring to secure the lens mount and the protective window assembly together;

Figure 8 is a cross-sectional side view of another embodiment of the invention for securing the lens mount and the protective window assembly together;

Figure 9 is a cross-sectional exploded side view of an embodiment of the invention in which the housing for the protective window contains holes for equalizing pressure about the protective window;

Figure 10 is a view similar to Figure 9 showing the protective window secured within the housing; and

Figure 11 is a cross-sectional view of an embodiment of the invention wherein the protective window is secured within the lens assembly. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a protective window assembly and to its use in conjunction with a focusing lens assembly for protecting a focusing lens used in a laser beam generating apparatus. The protective window assembly employed in the present invention protects the focusing lens against contamination and breakage and provides such protection in a cost efficient and effective manner. The protective window assembly may be sold alone or may be combined as either a removable or integral part of a focusing lens assembly which can be inserted into a laser beam generating apparatus.

Referring to Figures 1-3, there is shown a protective window assembly for use in accordance with the present invention. The protective window assembly 2 includes a housing 4 defining a seat or cavity 6 for receiving a protective window 8, typically made of an optical material which is highly transmissive and relatively non-absorbing at a wave- length particular for the laser medium (e.g. 10.6μ for CO₂ lasers). Such optical materials, include potassium chloride, sodium chloride and the like. The cavity 6 is defined by opposed walls 10 and 12 of the housing 4 and a flange 14 against which the protective window 8 rests when secured within the cavity 6. The cavity 6 preferably has a shape complimentary to the shape of the window. In a preferred form of the invention both the protective window and the seat are in the shape of a cylinder.

The housing 4 has a forward end 16 and a rearward end 18. The forward end 16 is positioned in proximity to the target (e.g. workpiece) which is to be contacted by the laser beam. The rearward end 18 of the housing 4 has an opening 19 for receiving the protective window 8. Thus, the protective window 8 lies between the workpiece and the focusing lens as explained in detail hereinafter.

The cavity 6 must be of sufficient size to house the protective window 8. In addition, there must be provided some means of securing the protective window assembly 2 to an assembly containing the focusing lens. The securing means may be in the form of threads and grooves, set screws, O-rings, cap screws and other similar means. As shown specifically in Figures 1-3, set screws 20 are provided to secure the protective window assembly 2 to the assembly containing the focusing lens. The set screws 20 are insertable into the housing 4 so that they may contact the assembly containing the focusing lens as it lies within the seat 6 as discussed in detail hereinafter.

In one embodiment of the invention, at least one and preferably a pair of gaskets 22 are employed to provide a seal around the protective window 8 so as to provide added protection for the protective window against breakage. A protective gasket 22 may be provided within the seat 6 against the flange 14 followed by the protective window 8. In a still further embodiment, a second gasket, as specifically shown in Figure 1 , may be provided on the rearward side of the window 8 within the cavity 6.

In a preferred form of the invention, the protective window assembly mates with a lens assembly containing a lens mount and a focusing lens therein used to focus the laser beam in the direction of the workpiece. The mating of the protective window assembly and lens assembly enables the user to readily employ a protective window in accordance with the invention in a cost efficient manner. The protective window assembly may be prepackaged and when use of the laser is desired, engaged to the lens mount. The protective window assembly can be readily removed and replaced by another assembly or renewed by repolishing or replacing the protective window without significant downtime of the laser operation.

Referring to Figure 4, there is shown a lens assembly 30 comprised of a lens mount 31 including a housing 32 having a forward end 34 and a rearward end 36. The respective ends 34 and 36 define an area 38 for securing a focusing lens 40 as well as other lens mount components therein. Typical lens mount components include seals 42, a compression spring 44 for urging the focusing lens 40 securely within the space 38, and a retaining ring 46 for securing all of the lens mount components within the space 38.

The lens mount 31 is releasably secured to the window assembly 2. In this regard, the lens mount 31 and/or the window assembly 2 are provided with a means for releasably securing the same together during laser operations. The window assembly and lens mount may thereafter be separated when the laser operation is terminated.

Referring to Figure 5, there is shown a fully engaged protective window assembly 2 to a focusing lens assembly 30. The protective window 8, shown positioned between respective gaskets 22 lies between the forward end 16 of the protective window assembly 2 and the focusing lens 40 positioned within the lens mount 31. In this way, debris such as oil, dirt, grease and the like cannot contact the lens because of the position of the protective window 8 within the cavity 6 of the protective window assembly 2.

The lens mount 31 may be releasably secured to the protective window assembly 2 in a variety of ways. As shown specifically in Figure 5, the housing 32 of lens mount 31 is engaged by set screws 20. The set screws 20 can be rotated to contact the housing 32 to secure the lens mount 31 to the protective window assembly 2. In a preferred form of the invention, an integral flange 50 extends from the housing 32. The flange 50 is placed against the protective window directly or through the gasket 22 with sufficient force to maintain the protective window 8 in a fixed location with the protective window assembly 2. The flange is secured in place as is, and the lens mount 31 secured to the protective window assembly 2, by the pressure exerted by the set screws 20 on the housing 32.

As previously indicated, alternate means of securing the lens mount to the protective window assembly can be employed such as through the use of O-rings, threads and grooves and the like.

Referring to Figure 6, there is shown an embodiment of the invention wherein the lens mount can be screwed into operative engagement with the protective window assembly. More specifically, the housing 32 of the lens mount 31 in proximity to the forward end 34 is provided with grooves 60. The housing 4 in proximity of the rearward end 18 of the protective window assembly 2 is provided with corresponding threads 62. In operation, the lens mount 31 is secured to the protective window assembly 2 by rotating the lens assembly until the grooves 60 mate with the corresponding threads 62. The protective window assembly can be disengaged by rotating the same in the opposite direction until the threads 62 are released from the grooves 60. It will be understood that protective window assembly 2 can be provided with grooves and the lens mount with threads to achieve the same mode of operation.

In another embodiment of the invention, the protective window assembly 2 is engaged to the lens mount 31 through an O-ring within the housing. Referring to Figure

7, the housing 4 of the protective window assembly 2 has an annular channel 70 containing an O-ring 72. The O-ring engages under pressure the housing 32 of the lens mount 31 to thereby urge the lens mount 31 within the seat 6 of the protective window assembly 2.

In a further embodiment of the present invention, the lens mount is provided with a tapered flange. There is also provided an adapter having an O-ring thereon. The adaptor is press-fitted on to the lens mount and the same is inserted into the protective window assembly in a manner similar to that described in connection with Figure 7.

Referring to Figure 8 there is shown a typical lens mount 31 having a flange 50 at the forward end 34 thereof as described in connection with Figure 4. The flange 50 frequently has a taper 80 . The taper is typically in the range of from about 10 to 20 degrees. As shown specifically in Figure 8, it is necessary to provide an adaptor 82 having a tapered interior surface 84 thereof which can be secured about the tapered surface 80 of the flange 50 of the lens mount 31 when the lens mount and adaptor 82 are secured together. Placed about the adaptor 82 is an O-ring 86 which secures the lens mount 31 to the protective window assembly 2 as described previously in connection with Figure 1.

When the protective window assembly 2 and the lens mount 31 are secured together as described in the embodiments shown in Figures 5-8, the protective window 8 lies between the focusing lens 40 and the target (e.g. workpiece) (not shown) lying beyond the forward end 16 of the protective window assembly 2. This results in a highly efficient form of protection for the focusing lens during operation of the laser. Gases (e.g. nitrogen) under high pressure are used to assist in the laser operation. The assist gas provides an atmosphere superior to shop air to enhance the cutting action and, as described previously, to also blow away splatter from the focusing lens. Under some circumstances such as in the cutting of stainless steel, the pressure of the gases can be very high (e.g. 150 to 300 psig). High pressure gas can break or rupture the window which is used to protect the lens. In accordance with a preferred embodiment of the present invention there is provided an embodiment wherein the high gas pressures around the protective window are neutralized.

Referring to Figures 9-10, the protective window assembly 100 includes a holder

102 for the protective window 104. The holder 102 is shown with a threaded retaining screw 106 that mates with corresponding grooves 108 within the housing 110 to secure the holder therein. Included as part of the holder 102 is a seat 11 1 for securing the protective window in operative position within the protective window assembly 100.

In accordance with the present invention, the holder 102 is provided with at least one aperture 112 which allows the high pressure gas to pass around the protective window 104. The gas pressure therefore equalizes (i.e. similar or equal pressures are exerted on the front and the back of the protective window). The equalization of pressure about the protective window is desirable because protective windows are made of materials (e.g. potassium chloride) which generally have low apparent elasticity.

In operation, the protective window 104 is inserted into the holder 102 and the adaptor 82 with the O-ring 86 thereon is secured within the holder 102. The combined assembly (i.e. the holder and the adaptor) are reversibly secured to the housing 110. If excess gas pressure is exerted on the protective window 104 during operation of the laser, the gas passes through the apertures 112 until pressure on the front and back side of the window is equalized. The protective windown assembly of the present invention can be utilized for any laser beam generating assembly such as for carbon dioxide lasers and NdrYAG lasers as well as others.

The protective window assembly may be constructed so as to be part of the focusing lens assembly either releasably sealed thereto or integral therewith.

Referring to Figure 11 , there is shown a protective window assembly 120 secured within a lens assembly 122. In particular, the protective window assembly 120 includes a housing 124 which may be releasably secured to the lens assembly 122 through a securing device 126 such as threads and groves or may be integral with the lens assembly (i.e. not removable therefrom).

The protective window assembly is shown between the focusing lens 128 and the focal point 130 of the laser beam. The protective window 132 is maintained in place by a flange 134 and a retaining device 136 such as a retaining screw or a compression spring.

Removal of the protective window 132 can be accomplished by releasing the retaining device 136.

As described in connection with the embodiments of Figures 9 adn 10, the protective window assembly may be provided with means for equalzation gas pressure about the protective window. As shown in Figure 11 , assist gas which enters the lens assembly through one or more inlets 138, can move around the protective window 132 through openings 140 in the housing 124.

It will be understood that the protective window assembly 120 shown in Figure 11 is releasably secured within the lens assembly 122. Alternatively, the protective window assembly 120 may be made integral with the lens assembly 122 by eliminating the securing device 126. The protective window 132 would, in this embodiment, be releasable from the protective window assembly by releasing the retaining device 136.

Claims

WHAT IS CLAIMED IS:

1. A protective window assembly comprising:

(a) a housing having a cavity for securing a protective window; and (b) housing securing means for securing the housing to a lens assembly containing a focusing lens.

2. The protective window assembly of claim 1 further comprising a protective window in said cavity.

3. The protective window assembly of claim 1 further comprising protective window retaining means for retaining the protective window within the cavity.

4. The protective window assembly of claim 3 wherein the protective window retaining means is a retaining screw or compression spring.

5. The protective window assembly of claim 1 comprising gas passing means for allowing the equalization of gas pressure around the protective window.

6. The protective windown assembly of claim 5 wherein the gas passing means comprises at least one aperture in the protective window assembly.

7. The protective window assembly of claim 1 wherein the housing securing means comprises a forward end adapted to mate with a corresponding end of a lens assembly.

8. The protective window assembly of claim 1 comprising an annular channel within the housing and an O-ring positioned therein for securing the protective window assembly to a lens assembly.

9. The protective window assembly of claim 1 further comprising an adaptor having an inner surface for engaging the lens assembly and means for securing the adaptor within the protective window assembly.

10. The protective window assembly of claim 9 wherein the means for securing the adaptor to the protective assembly comprises an O-ring on the outer surface of the adaptor.