High removal rate laser-based coating removal system

• US 5,986,234 A
• Filed: 03/28/1997
• Issued: 11/16/1999
• Est. Priority Date: 03/28/1997
• Status: Expired due to Fees

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Mrowka, Stanley, Hackel, Lloyd, Dane, C. Brent, Matthews, Dennis L., Da Silva, Luiz B., Celliers, Peter M.
• Primary Examiner(s): Evans, Geoffrey S.
• Application Number:
  US08/829,519
• Time in Patent Office: 963 Days
• Field of Search: 219/121.68, 219/121.69, 219/121.78, 219/121.74, 219/121.62, 359/334, 359/347, 359/348, 359/569, 372/94, 372/106, 134/1
• US Class Current: 219/121.68
• CPC Class Codes: B08B 7/0042 by laser
• CPC Class Codes: B23K 26/032 using optical means
• CPC Class Codes: B23K 26/066 by using masks
• CPC Class Codes: B23K 26/0884 in at least in three axial directions, e.g. manipulators, robots
• CPC Class Codes: B23K 26/142 for the removal of by-products
• CPC Class Codes: B23K 26/1476 Features inside the nozzle for feeding the fluid stream through the nozzle

Abstract

A compact laser system that removes surface coatings (such as paint, dirt, etc.) at a removal rate as high as 1000 ft² /hr or more without damaging the surface. A high repetition rate laser with multiple amplification passes propagating through at least one optical amplifier is used, along with a delivery system consisting of a telescoping and articulating tube which also contains an evacuation system for simultaneously sweeping up the debris produced in the process. The amplified beam can be converted to an output beam by passively switching the polarization of at least one amplified beam. The system also has a personal safety system which protects against accidental exposures.

Claims

1. A coating removal system, comprising:

a laser to provide a laser beam, wherein said laser comprises;

at least one optical amplifier;

means for producing a polarized low power laser beam with an exponentially rising leading edge having a time constant τ

determined from the formula

τ

=1/(dG(t)/dt)˜

P_o n/E_sat A), where G(t) is the time varying gain, P_o is the output power, n is the number of amplifier pulses, E_sat is the saturation fluence of the gain media and A is the cross sectional area of the amplifier;

at least one optical amplifier;

means for providing multiple amplification passes of said polarized low power laser beam, said multiple amplification passes propagating through said at least one optical amplifier to produce at least one amplified beam with nearly constant output power determined by said time constant of said exponentially rising leading edge of said polarized low power laser beam;

means for reversing the phase of said polarized low power laser beam and its propagation direction after half of said multiple amplification passes through said at least one optical amplifier, said reversing means including stimulated-Brillouin-scattering (SBS), wherein said amplified beam retraces its path and relative polarization through said at least one optical amplifier; and

means for converting said at least one amplified beam into at least one output beam by passively switching the polarization of said at least one amplified beam;

wherein said coating removal system further comprises;

a workhead comprising means for delivering said laser beam to a work surface;

means for delivering said laser beam from said laser to said workhead; and

means for collecting debris produced by the interaction of said laser beam with a coating located on said work surface.

2. The coating removal system of claim 1, wherein said means for delivering said laser beam to a work surface comprises a diffractive optic.

3. The coating removal system of claim 2, wherein said diffractive optic is selected from a group consisting of a kinoform phase plate and a random phase zone plate, wherein said diffractive optic reduces the spatial coherence of said laser beam and produces a very uniform beam intensity distribution at said work surface.

4. The coating removal system of claim 2, further comprising a focusing lens.

5. The coating removal system of claim 4, further comprising an enclosure and debris shield surrounding said focusing lens and said diffractive optic.

6. The coating removal system of claim 1, wherein said means for delivering said laser beam from said laser to said workhead comprises a telescoping and articulating arm.

7. The coating removal system of claim 6, wherein said telescoping and articulating arm comprises a counterweight.

8. The coating removal system of claim 1, wherein said means for delivering said laser beam to a work surface comprises a system for high speed, galvanometer driven spatial rastering of said laser beam, wherein said system moves said laser beam over said work surface.

9. The coating removal system of claim 8, further comprising a feedback system which may be used in conjunction with said system for high speed, galvanometer driven spatial mastering of said laser beam, wherein said feedback system comprises at least one photosensor, wherein said feedback system controls the amount of energy delivered to any given region of said work surface by monitoring laser energy levels at said photosensor, and wherein said feedback system terminates the cleaning operation when the appropriate layers have been removed.

10. The coating removal system of claim 1, wherein said means for delivering said laser beam to a work surface comprises an interlock system, further comprising at least one proximity sensor, wherein said interlock system shuts off or blocks said laser beam when said workhead is not within a prescribed distance from said work surface.