Electric heating – Metal heating – By arc
Reexamination Certificate
1998-04-24
2001-09-11
Moore, Chris K. (Department: 1744)
Electric heating
Metal heating
By arc
C015S339000, C134S001000
Reexamination Certificate
active
06288362
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system for treating surface material overlying a substrate, and more particularly, to a system for ablating contaminates and other unwanted material from a 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, 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 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 that a beam of electromagnetic radiation may be fine-tuned to ablate surface material ranging from microfine 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 soily worksites, interference of ablation detritus with the beam at the work surface, and the difficulty of delivering a quality beam of electromagnetic radiation over distance.
A known way to deliver electromagnetic radiation is via fiber optics. However, a persistent problem has been the difficulty of inserting a high power laser beam into a fiber optic strand. Particularly, the entrance face of the strand is a barrier. A high power laser beam impinging upon the entrance face is analogous to a tsunami striking a sea wall. It turns out that in a fiber of a given diameter, the amount of energy that the fiber can transmit is about ten times the amount that can be inserted at the entrance face without damage to the face.
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 an umbilical tube. Within the umbilical tube are transportation and communications conduits between back end services and work head functions.
One subsystem in the back end generates a pulsed beam of electromagnetic radiation, preferably involving a CO
2
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, sets of scanning mirrors arrange the series of pulses according to a selected raster and dither pattern, and direct them to a work surface.
In addition to incorporating the fiber exit face, lenses, and scanning mirrors, the work head includes several other component systems. On its exterior, the work head has an operator trigger, surface interlock system, several operator switches, LED indicator lights, and monitor. An operator activates the ablation process by depressing the trigger. The switches permit the operator to select from several options relating to ablation speed and quality. The monitor permits the operator to view how ablation is progressing. The surface interlock system, at the point of contact between the work head and the worksite, serves as a safety measure; if the work head is not pressed against the worksite with sufficient force, the interlock deactivates the laser.
Interior to the work head are two sections separated by a pane of glass. One section, a nozzle in contact with the surface material during the ablation process, includes the surface interlock system, an intake hose to evacuate ablated detritus, and flexible material on the perimeter of the nozzle to seal and prevent gaps between the nozzle and the worksite during laser operation. Optionally, another system within the nozzle forces a substantially inert gas (an “air knife”) across the surface being ablated to sweep detritus away from the beam and into the evacuation system.
The second work head section, on the opposite side of the glass pane, contains the scanning mirrors which create the rastering and dithering pattern from the pulsed beam. This beam pattern is directed at the glass pane, coated to reduce reflection and maximize transmission of laser radiation, and thence to the work surface. A monitoring system, including a camera and a light source, sends feedback information on ablation progress to the monitor for viewing by the operator. In addition to protection provided by the glass pane, ablated material and debris are kept out of the second section by a system which maintains greater internal air pressure than ambient air pressure.
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), one or more systems to provide pressurized gas to the work head, a system to circulate coolant through the subsystems, a blower to provide suction needed for the nozzle evacuation system, and a system to collect, filter, scrub fumes from, absorb, and otherwise contain the waste stream that the evacuation system delivers to the back end.
It is an object of the present invention to provide a method and apparatus of treating a surface with electromagnetic radiation while minimizing degradation and contamination of underlying substrate.
It is a further object of the invention to isolate bulky equipment from soily environments while making the equipment transportable to stationary worksites.
It is yet a further object of the invention to protect work head optics from worksite ablation detritus.
It is yet a further object of the invention to provide an efficient collection method of ablation detritus and to reduce the volume of a worksite waste stream.
It is yet a further object of the invention to transport a quality electromagnetic radiation beam over distance with delivery of an effective beam ab
O'Banion Laura M.
O'Banion Roland
Thomas James W.
Moore Chris K.
O'Banion Laura M.
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