WO1990015457A1

WO1990015457A1 - Laser fibrescope

Info

Publication number: WO1990015457A1
Application number: PCT/AU1990/000225
Authority: WO
Inventors: John Leonard Hughes
Original assignee: Australian Electro Optics Pty Ltd
Priority date: 1989-05-29
Filing date: 1990-05-29
Publication date: 1990-12-13

Abstract

This invention relates to a phase-locked, scaleable laser fibrescope system providing for the generation, amplification and steering of a divergent, parallel or focussed laser beam (11) onto a workpiece which is viewed via the same optical fibre bundles (9) as are used to transmit and steer said laser beam, said system consisting of a phase-locked laser oscillator array (1) which is optically matched into a flexible and scaleable bundle of single mode laser fibres which amplify said laser beam output of said oscillator and directs a divergent, parallel or focussed output laser beam onto a portion of a workpiece which is viewed via the same optical fibre bundle as it is used to amplify said laser beam. The laser beam generation and steering of the invention is computer controlled (13), in a preferred mode, the computer is a neural network computer capable of providing the parallel processing capacity necessary to generate, amplify and steer the phase-locked laser beam of the invention onto a workpiece being precision cut or marked with the aid of machine vision provided by viewing the said workpiece through the same fibre bundle optical system (9) used to deliver said laser beam (11) to said workpiece said vision capability being provided by a charged coupled device (CCD) camera (12) in a preferred mode of operation.

Description

Laser Fibrescope

Field of the Invention

This invention relates to a phase-locked, scaleable laser fibrescope system providing for the generation, amplification and steering of a divergent, parallel or focussed laser beam onto a workpiece which is viewed via the same optical fibre bundles as are used to transmit and steer said laser beam, said system consisting of a phase-locked laser oscillator array which is optically matched into a flexible and scaleable bundle of single mode laser fibres which amplify said laser beam output of said oscillator and directs a divergent, parallel or focussed output laser beam onto a portion of a workpiece which is viewed via the same optical fibre bundle as it is used to amplify said laser beam. The laser beam generation and steering of the invention is computer controlled, in a preferred mode, the computer is a neural network computer capable of providing the parallel processing capacity necessary to generate, amplify and steer the phase-locked laser beam of the invention onto a workpiece being precision cut or marked with the aid of machine vision provided by viewing the said workpiece through the same fibre bundle optical system used to deliver said laser beam to said workpiece said vision capability being provided by a charged coupled device (CCD) camera in a preferred mode of operation.

The invention has application for the precision laser beam marking and machining of metals, plastics, wood, rods and ceramics in the industrial, medical and defence fields. Summary of the Prior Art

Prior art laser fibre coupled systems have utilized single, multimode optical fibres to convey the laser beam powers necessary for machining purposes from a high power laser beam generator to the workpiece being machined. Such single, multimode fibre coupled prior art systems did not allow for the coherent output of powerful laser beams to be accurately focussed onto a workpiece being precision marked or machined. Furthermore, such prior art, single fibre laser beam delivery systems did not allow the said workpiece to be viewed during the laser machining or marking in real time. Prior art fibrescope systems allowed for the viewing of objects and their optical image recording but could not simultaneously convey a scaleable and steerable laser beam onto said object. Prior art laser fibrescope systems could not be effectively used, with, for example, robotic arms for the precision marking or machining of materials because of their lack of precision control in guiding powerful laser beams in the focussed mode onto a selected area of the workpiece being machined or marked.

The present invention overcomes the defects of the prior art systems by providing a system which can both view the workpiece being marked or machined whilst at the same time providing for the generation, amplification and steering of a scaleable, phase-locked laser beam onto said workpiece at a power level necessary to carry out the machining or marking. The invention can select a given spot on the workpiece visually and steer a focussed laser beam onto said spot in a manner that overcomes the defects of prior art systems. This invention also overcomes the defects of prior art fibrescope systems when used in conjunction with image processing computers in that the laser beam is both generated, amplified and imaged within the fibrescope system in such a manner that it can be directed accurately to any point within the field of view of a divergent, parallel or focussed output beam as required. By the appropriate distortion of generated Fresnel images it is possible to provide for the steering of the focussed output laser beam of the invention so as to precision machine a given workpiece to a desired three dimensional configuration.

Background of the Invention

The inventor has pioneered the field of laser radar since 1963 when early work was undertaken at the Royal Radar Establishment, Malvern, UK. Laser Radar encompasses the technologies of advanced laser based machine vision systems for the precision laser beam marking and machining of workpieces as the laser machining process is viewed continuously. For example, laser radar provides for the steering of a laser beam onto a target which is then optically detected, preferably in a three dimensional format. To accomplish this task, one requires phased array laser radar which is capable of precisely steering the phase-locked laser output beam onto target. Extensive development of Phased Array Laser Radar techniques over the past twenty-seven years has matured the technologies involved to a stage where they can be effectively applied to high precision laser beam machining and marking of a wide range of different workpieces. In any effective laser based precision machining workstation it is essential to convey the laser beam onto the workpiece via a scaleable, flexible beam delivery system which does not involve the prior art articulated arm beam delivery technology. Neural network computers provide the means of controlling phase- locked arrays of laser beam transmitters in a manner that allows for the steering of the laser beam outputs of said laser beam transmitters forming the output apertures of both the oscillator and amplification sections of the invention. This is achieved in the ι o present invention by selectively switching selected transmitters in the oscillator of the invention so as to form an output beam which is structured in the format of Fresnel images for focussed mode aperture and in the format of numbers, letters and patterns for the marking mode.

15 Summary of the Invention

It is an object of the invention to provide a phase-locked array of single mode optical fibres which can be used to both view a workpiece and transmit a powerful laser beam to mark or machine said workpiece in a divergent or focussed beam mode.

20 Another object of the invention is to generate a phase-locked laser beam in a phase-locked laser oscillator array then match this output beam into a phase-locked bundle of single mode optical fibres.

It is an object of the invention to switch the individual laser oscillators of the array of such oscillators so as to generate

25 concentric Fresnel Zone patterns which, when emitted from the output end of said fibre bundle cause the laser beam to be accurately focussed at a distance corresponding to the geometry of said Fresnel Zone Plates.

It is an object of the invention to generate laser emissions patterns on the output face corresponding to numbers, letters and patterns.

Another object of the invention is to view the workpiece through all of the components necessary to generate the said laser beam.

It is an object of the invention to generate the Fresnel Zone Plate intensity distribution on the output face of the invention by selectively exciting the individual fibres to lasing threshold.

Another object of the invention is to provide means of establishing the distance from the output aperture of the bundle of laser fibres to the workpiece by establishing the dimensions of the focussed laser beam at low power as it illuminates said workpiece. It is an object of the invention to adapt a robotic arm for workpiece machining by producing both the machine vision and laser beam generation, amplification and steering in a single unit.

Brief Description of the Drawings

A better understanding of the invention may be obtained from the following considerations taken in conjunction with the drawings which are not meant to restrict the scope of the invention in any way.

Figure 1 shows a layout of the invention with the laser diode oscillator array inserted into the viewing path. The image generated of said laser oscillator array is matched into the compacted optically polished input face of the fibrescope fibre bundle at a wavelength which matches the lasing properties of the laser ions-doped into the coherently packed, optical fibres forming the body of said fibrescope system. The fibres forming said body of said fibrescope system are separated into several channels to allow for ease of excitation via laser diode arrays, said channels then being recombined into a single

5 bundle of said optical fibres such that the fibre ends are packed into a single, optically polished output face through which is emitted the amplified, phase-locked input beam from the phase-locked output beam of the laser diode oscillator array. The CCD camera used to view through the said invention is pixel matched to the said laser ι o diode oscillator array which is in turn, pixel matched to the input end face of the coherently packed fibre bundle body of the fibrescope body of the invention.

Figure 2 shows the effect of generating the letter "Q" by selectively switching the diode laser elements forming the laser

15 diode oscillator array of the invention and propagating said image through said invention so that it is transmitted via the output face at higher intensity. Figure 3 shows the output pattern in the configuration of a Fresnel Zone Plate generated by appropriately switching the laser diode oscillator array of said invention. By

20 adjusting the phases of the laser beam generating array, that is the said laser diode oscillator array, the laser beam output of the invention can be steered in the divergent, parallel and focussed beam mode.

Figure 4 shows the output of the laser diode oscillator array

25 positioned out of the viewing path of the invention and coupled into said invention via an angled reflector placed in the said viewing path. Figure 5 shows the laser diode oscillator array of the invention replaced by a liquid crystal laser beam imaging system as pioneered in prior art by the inventor.

Detailed Description of the Invention In Figure 1 , numeral 1 indicates the laser diode oscillator array connected as indicated by numeral 2 to its switched power supply (not shown) whose phase-locked single beam output indicated by numeral 3 is passed, via the input, optically polished face indicated by numeral 4 into the fibre bundle indicated by numeral 5 which in ι o turn is divided into smaller bundles indicated by numeral 6. Numeral 7 indicates the laser diode arrays used to excite laser ion doped fibre in bundles 6 whilst numeral 8 indicates the electrical interconnections feeding the electrical power into arrays 7.

Numeral 9 indicates the unexcited sections of bundles 6 which

15 are packed together to form the single output aperture of the invention indicated by numeral 10. The phase-locked output from aperture 10 produces the single beam output of the invention indicated by numeral 11. Numeral 12 indicates the CCD viewing camera connected to a computer via leads indicated by numeral 13.

20 In Figure 2, numeral 10 indicates the output aperture of the invention made up of an array of optical fibre ends indicated by numeral 14, fibre ends 14 having a cladding thickness which is small compared to the core diameter of the said fibres, so that the fibre packing density of face 10 can exceed one million fibre ends per

25 square centimeter, providing high definition imaging capabilities. Numeral 15 indicates an image of a letter "Q^H formed on the transmitted laser beam out of the invention, generated by the appropriate switching of the laser diode oscillator array 1.

In Figure 3, numeral 16 indicates a Fresnel Zone Plate image generated on the output face 10 of the invention. Numeral 17 indicates the central region of Fresnel image 16, a region which can contain up to eighty per cent of the total beam energy emitted by the invention. By delaying the time of emission of selected portions of the Fresnel beam image 10 by adjusting the phases of the appropriate transmitters making up the laser diode oscillator array 1 , it is ι o possible to steer the output beam of the invention within the field of view of CCD camera 12 in the divergent, parallel or focussed modes.

In Figure 4 numeral 18 indicates a beam reflector which reflects the output of laser diode oscillator array 1 indicated by numeral 19. Numeral 20 indicates the viewing path of the CCD camera 12 which is

15 not affected by reflector 18.

In Figure 5, numeral 21 indicates a liquid crystal light valve laser beam imaging system which provides real time images which are propagated into the invention via reflector 18.

The invention has applications in surgical laser systems providing the surgeon with a steerable laser beam within the field of view of a CCD camera image processing system, an attractive feature for performing complex operations within the human body. The invention has applications for mounting onto robotic arms in material processing. The invention has applications as a laser radar system.

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Claims

claim,

1. A laser based, machine vision fibrescope industrial workstation for the precision focussed beam machining of a three dimensional workpiece, said system consisting of a computer controlled camera

5 which is optically matched into a flexible, scaleable, coherently packed bundle of single mode, phase-locked laser fibres which provide both the optical viewing channel and the laser beam amplification and beam delivery channel for the laser beam machining of a three dimensional workpiece to a predetermined configuration, the phase- ι o locked array of laser oscillators required to both generate and steer said output laser beam being also optically matched into the said laser beam delivery bundle so as not to impede the viewing path of the said camera.

2. A system as claimed in Claim 1 where the said laser array

15 oscillator is activated to produce a Fresnel Zone Plate distribution of concentric laser beams which cause the focussing of said structured output laser beam onto said workpiece.

3. A system as claimed in Claim 1 where the distance from the laser beam output aperture to a part on the surface of the workpiece

2o being machined is determined by measuring the diameter of said focussed laser beam focus spot at low power levels using the said viewing camera to process the image of said spot.

4. A system as claimed in Claim 1 where the phase-locked array oscillator is selectively switched so as to generate Fresnel Zone

25 Plate patterns corresponding to the output beam configuration necessary for the precision marking of workpieces. 5. A system as claimed in Claim 1 where the phase-locked array oscillator is selectively switched to generate a laser beam image of a number, letter or pattern which is then amplified in said system to a power level at which it can illuminate the surface of a material in a divergent, parallel or focussed beam mode to burn a mark corresponding to said number, letter of pattern on said surface of said material.

6. A system as claimed in Claim 1 where said system is mounted onto a robotic arm and used to guide the arm so as to allow the o precision machining of three dimensional workpieces.

7. A system as claimed in Claim 1 where said system is mounted onto a robotic arm which is then used to guide the output aperture of the invention in such a manner as to allow its imaged output beam in a divergent, parallel or focussed mode to mark objects that have to be 5 identified at a later stage.

8. A system as claimed in Claim 1 where the distance of the cores of the said single mode laser fibres are less than the diameter of the cladding of said fibres.

9. A system as claimed in Claim 1 where the diameter of the cores o of the said single mode laser fibres are comparable to the diameters of their cladding.

10. A laser radar system whose components are those claimed in Claim 1.