Electric heating – Metal heating – By arc
Reexamination Certificate
1998-06-02
2002-08-20
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121680, C219S121690, C219S121850
Reexamination Certificate
active
06437285
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system for treating surface material overlying a cylindrical interior work surface, and more particularly, to a system for ablating contaminates and other unwanted material from a cylindrical interior worksite using a laser.
BACKGROUND OF THE INVENTION
Using industrial lasers to treat surface material is known in the prior art. These treatments include glazing, sealing, marking, and drilling. Of particular relevance to this invention are a number of proposals to remove, by laser ablation, material from an underlying substrate. For example, United States patents have issued for removing paint, grease, dirt, rubber, ceramic, mineral scale, dielectric, and electrical conductor surface material by means of laser ablation. See:
U.S. Pat. No. Re. 33,777 issued to Woodroffe [paint, grease, and ceramics]
U.S. Pat. No. 5,592,879 issued to Waizmann [dirt]
U.S. Pat. No. 5,637,245 issued to Shelton et al. [rubber]
U.S. Pat. No. 5,113,802 issued to Le Blanc (mineral scale]
U.S. Pat. No. 4,671,848 issued to Miller et al. [dielectric coating]
U.S. Pat. No. 3,941,973 issued to Luck et al. [electric conductor]
Previously, removing surface material frequently required physical or chemical methods. These methods included physical abrasion, blasting surfaces with media such as sand, and using chemical solvents. Not only did these methods often damage the substrate, but the removal of surface material created a new problem; disposing of a waste stream bloated with contaminated cleaning material.
The potential commercial advantages of using laser ablation are significant. Not only is the waste stream to be treated and disposed of much reduced but also there is potentially less recontamination of the surface itself For example, chemicals used in the prior art to strip surface contaminates themselves could recontaminate the surface. Another advantage is t hat a beam of electromagnetic radiation may be fine-tuned to ablate surface material ranging from micro fine contaminants to visible discrete particles. And, of course, the beam can navigate exceedingly narrow passageways as well as ablate material from microscopic pores. However the problems inherent in creating a workable system have limited laser ablation technology to a few niche applications. These problems include high cost, non transportable equipment, contamination of optics by ablated material, laser damage to internal optics, deficient feedback and control, inadequate safety systems, lack of ablation waste collection and containment, the need to isolate sensitive equipment from soiled worksites, interference of ablation detritus with the beam at the work surface, and the difficulty of delivering a quality beam of electromagnetic radiation over a distance.
Removing contaminates from the inside of tubes and pipes is particularly difficult; first because of the difficulty of accessing the contaminated area, i.e., a long tube requires a long tool which may be difficult or impossible to manipulate; second the hazard of leaving contaminates behind; thirdly, in using chemicals to remove contaminates from tubes there is the additional difficulty in removing solvent residue, leading to recontamination later on.
Aircraft oxygen systems include many pipes of small diameter, which must be cleaned thoroughly without leaving any chemical residue, which could adversely affect passengers or crew. Gaseous diffusion plants have miles of piping, which are contaminated with highly toxic materials that must be removed safely and completely. The is a great need and ready market for a system and process for readily cleaning the inside of tubes and pipes that eliminates the use of solvents and can safely remove the reaction products of cleaning.
SUMMARY OF THE INVENTION
The present invention has as its object to provide a method and apparatus by which surface material may be ablated effectively and safely with minimal collateral damage to the worksite. The primary components of the apparatus are a back end system (kept distant from the worksite), a work head, and an umbilical tube connecting the back end and the work head.
A design philosophy of this invention is to isolate bulky equipment in the back end, which may be housed inside a small truck or trailer, to make the work head lightweight and durable enough to be handheld or incorporated in a robotic arm, and to link the back end and work head with the umbilical tube.
The laser in the back end generates a pulsed input beam of electromagnetic radiation, preferably a CO2 or a Q-switched Nd: YAG laser emitting coherent infrared light. The beam is collimated and focused onto a collector face of a fiber optic strand. The fiber is tapered from the collector face to the strand body. Then the pulsed beam travels along the strand body, enclosed in the umbilical tube, until it reaches the work head and emerges from an exit face. After lenses within the work head recollimate and refocus the beam, an angled rotating mirror spinning on the body axis of the work head receives the beam and directs the series of pulses outward from the work head axis, in a circular or spiral path to the work surface on the inside of the tube. In addition to incorporating the fiber exit face, lenses, and rotating mirror, an embodiment of the work head includes a propeller mounted on a rotatable body section containing the mirror with the propeller driven by an air stream flowing in the tube past the work head body. The air stream also provides the benefit of cooling the work head and associated mirror and lenses while additionally carrying away the reaction products of the decomposed surface material.
The work head is aligned with the central axis of the workpiece tube (i.e., a pipe or tube of larger diameter) and inserted therein up to a depth as much as the length of a connected umbilical tube. A preferred embodiment of the intention has resilient fingers mounted on the front and rear of the work head to support it inside the tubular workpiece while the umbilical tube draws the work head distally through the tube. An operator activates the ablation process after setting controls to establish the rotation speed of the mirror (the air flow), and the withdrawal rate of the work head by pinch rollers frictionally engaged on the distal part of the umbilical tube between the work head and the back end. A safety interlock system, serves as a safety measure; if the work head is not installed in the workpiece tube with proper covers at the ends, the interlock deactivates the laser.
Exterior to the work head are an exhaust outlet receiving the contaminated air stream connected to a hose and a blower to evacuate ablated detritus. The air stream is drawn in through a laser light baffle from ambient air at the front of the workpiece tube, and flows along the body of the work head between the body and the interior work surface of the surrounding tube. The air stream drives angled fan vanes of a propeller connected to the outside of a free spinning tubular mirror assembly containing the work head mirror. At either end of the mirror assembly there are mounted circumferentially rotating ball bearing races mounted to the associated front and back portions of the work head. Optionally, another sub-system connected to the workpiece forces a substantially inert gas (an “air knife”) in place of the ambient air, across the surface being ablated to sweep detritus away from the beam and into the evacuation system.
Ablated material and debris are kept out of contact with the exit face of the laser fiber by a clear window between the mirror and the exit face. The natural divergence of the beam exiting the exit face and the spacing of the window prevents the laser power from damaging the window.
Other subsystems in the back end include a power supply and distribution system (to provide electricity to subsystems in both the back end and the work head), systems to provide pressurized gas to the work piece, a system to circulate coolant through the subsystems,
Fuchser Terry
Thomas James W.
Evans Geoffrey S.
General Lasertronics Corporation
Steres George M.
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