WO2008084216A1

WO2008084216A1 - Laser wire strippers

Info

Publication number: WO2008084216A1
Application number: PCT/GB2008/000051
Authority: WO
Inventors: Peter Dickinson; Paul Taylor; Jon Davies; Robert Herron; Christopher Leyson; Tyge Eldridge
Original assignee: Spectrum Technologies PLC
Current assignee: Spectrum Technologies PLC
Priority date: 2007-01-08
Filing date: 2008-01-08
Publication date: 2008-07-17
Anticipated expiration: 2009-07-08
Also published as: GB0700272D0

Abstract

A laser wire stripper comprises a stripper head connected to a remote base unit by means of a flexible tube containing a waveguide. The base unit contains a laser emitting laser radiation at a power and wavelength effective for removal of plastic insulation from a wire, the radiation being passed from the base unit to the stripper head through the waveguide. The stripper head includes optics for causing the laser to cut through the insulation circumferentially without damage to the underlying conductor. Exhaust gas from the laser cutting process is confined within an enclosed space surrounding the laser stripping zone and ducted back to the base unit through the duct and exhausted by means of an extractor fan in the base unit. Various optics schemes are described.

Description

Laser Wire Strippers

This invention relates to laser wire strippers, and in particular to portable laser wire strippers. The invention also extends to optics schemes for use in all types of laser wire strippers. In this specification the term 'wire stripper¹ is used to mean a device which facilitates the removal of an outer, insulating, layer from a single or multi- core cable. Although we do not exclude arrangements in which the wire stripper removes the insulation completely from the wire, the invention is primarily concerned with a process in which the insulation is cut, e.g. circumferentially, to allow a portion to be slid off the free end of the wire.

Although portable wire strippers may be used in many different applications, the aircraft industry is of particular interest. Modern aircraft contain several hundred kilometres of wires for control communication and actuation, and most of the cables need to be stripped of insulation at the opposite ends to allow connection to a suitable terminal. During routine maintenance and repair a service engineer may need to replace a wire in the wiring harness and this will require the wire to be stripped at opposite ends. This is often done in situ, in a confined space on the aircraft and so conventionally a hand-operated mechanical stripper is used. The use of portable laser wire strippers is also of relevance to the initial manufacture, particularly where wiring is stripped on the wire harness form board or in situ after locating in the aircraft.

Mechanical wire strippers typically comprise two opposing blades with V notches in them designed to sever the insulating coating. Because the wires in use vary considerably in diameter, typically from single strand 0.1mm to multi- strand 10mm or more, the engineer is typically provided with a set of mechanical wire strippers for different sized wires. This is because it is important to ensure that the conducting core is not nicked or otherwise damaged by the blades of the stripper. This is because a nick will compromise the mechanical strength of the core and lead to possible premature failure and it also reduces the conducting cross-section which leads to potential hotspots in the harness which is potentially dangerous, as well as increasing the resistance of the conductor. However, although the service engineer is provided with a set of wire strippers for different wires, or possibly a mechanical stripper with an adjustable blade separation, the wrong sized stripper may be used with the consequences of damages to the conductor as previously discussed. Equipment may also be out of calibration or may require maintenances and replacement blades, resulting in incorrect operation and damage to the conductor. Also, in some instances it has been known for the insulation to be stripped off using a scalpel blade or a razor blade which has a high risk of damaging the underlying conductor.

Accordingly, there is a need for a portable hand held wire stripper that can be used in confined spaces to remove insulation from a wide range of diameters of wire without significant damage to the underlying conductor core. Elsewhere, it is known to use a laser to effect wire stripping without damage to the underlying conducting core, and such laser wire strippers are used in the aircraft industry; example of such a device is described in US patent 4,970,367. However, although such a device is extremely effective, it is large in size, partly due to the need to house a CO₂ laser or a similar laser capable to delivering sufficient power at the appropriate wavelength (typically in the infrared/far infrared wavebands) to vaporise or ablate the insulation. This means that the device is only suitable for bench use. Whilst described as being portable, in the context of the earlier patent this is in the sense of being moveable from one location to another in an assembly plant. There is no suggestion that the device could be carried into the confined spaces onboard an aircraft to effect in situ wire stripping.

Accordingly, in one aspect, this invention provides a laser wire stripper comprising: a base unit including a laser for emitting laser radiation; an elongate flexible waveguide means for receiving and passing laser radiation emitted by said laser, and a hand held stripper head for receiving laser radiation passed down said flexible waveguide means, said stripper head including: wire location means for locating in a stripping zone a wire carrying insulation to be stripped, and optics means for receiving said laser radiation delivered to said stripper head and for directing it onto a wire in said stripping zone to move along and/or across and/or around a laser cutting path selectively to remove the wire insulation from said path. In the above arrangement, the hand held stripper head allows the device to be used in situ in confined spaces e.g. onboard an aircraft, in a communications console, a telephone exchange, a motor vehicle etc., without requiring the wire to be removed to a bench for wire stripping. Locating the laser in a separate base unit reduces the size of the stripper head and makes it lighter.

Preferably, the optics means is operable to cause the laser to follow a path which circumscribes the wire to be stripped so as to make a circumferential cut. The flexible waveguide may comprise a hollow waveguide made of a flexible tube of e.g. glass, metal or plastic that has a highly reflective coating on the inner surface. Such a waveguide is designed to deliver the laser powers required for laser stripping, typically 10 to 20 watts, with low loss, although they are capable of transmitting much higher power. The waveguide may be a follow or solid optical fibre or the like. Suitable optical fibres include a polycrystalline

Infra red fibre (PIR fibre) manufactured in a core/clad structure of superior quality from pure AgCI: AgBr solid solution crystals. Such a fibre is also designed to deliver the laser powers required (typically 10-20W).

The laser may typically emit radiation at a wavelength of the order of microns, but any suitable laser may be used that can generate a beam capable of removing insulation without damage to the underlying conductor.

Preferably, the wire location means is adjustable so that the distance from the end of the wire to the laser cutting path may be preset to allow a corresponding length of the portion of the insulation to be stripped. Preferably, the optics includes a focusing lens means for focusing the laser on to said cutting path, with the focusing lens means being adjustable to focus the radiation beam onto the insulation of wires of different diameter. The focusing lens may be adjustable between 2 or more discrete positions such as 'large diameter', 'small diameter' wires. In one arrangement, said optics includes a drive motor for rotating at least part of the optics means to cause the laser radiation to move around a circumferential cutting path, with there being control means for controlling the rotational speed of the rotating optic element or elements. Preferably also the wire stripper includes means for adjusting the output power of the laser. In general, for cutting of an insulation of given material and thickness, the rotational speed of the optics (which determine the linear cutting speed) and the laser power required are dependent variables; an increase in cutting speed requires greater laser output. The optics means conveniently comprises a plurality of deflecting means for guiding the laser beam towards the wire, such as e.g. mirrors, for deflecting the laser beam from entry into the stripper head to arrive at the cutting path and the stripper head may include means for directing a cleaning jet of gas on the final deflecting means to clear it of debris acquired whilst stripping, and to assist the stripping process - for example it may be oxygen-enriched. In one embodiment, the optics means includes a plurality of mirrors, with a focusing lens means disposed between the last mirror and the penultimate mirror, with the focusing lens means serving to isolate the penultimate mirror means and the optics upstream thereof from the space in which the wire is stripped, thereby to prevent the atmosphere from the stripping zone reaching the upstream optics.

Preferably, the stripper head defines a stripping zone which is a generally enclosed space having a gas outlet which is connected to a flow passage associated with said flexible waveguide means to communicate with an extractor fan or the like disposed in the base unit. This is important where the stripper is used in an environment where there may be a potential explosion hazard due to presence of fuel vapour. Preferably, the flow passage comprises a hollow flexible tube through which said waveguide means passes generally concentrically. In this fashion the tube serves the dual function of not only conveying the atmosphere from the stripping zone for exhaust well away from the stripping zone, but also serves mechanically to protect the waveguide. Furthermore, the tube may serve to mechanically limit the bending radius of the waveguide means to prevent the bending radius beyond a preset lower design limit. The waveguide means could instead pass along the outside of the hollow flexible tube.

Power and control signals may be delivered between the stripper head and the base unit by means of conductors passing down the inside of the tube.

Whilst the stripper may be powered via a power cord connected to the base unit, it is preferred for the base unit to contain a rechargeable battery so that the stripper can be self-powered when required.

Various options are available for the optics. The optics may conveniently include three reflecting means mounted on a cradle, mounted for rotation.

In another arrangement said optics comprises a beam splitter to generate two laser beams, and respective reflecting means for directing said laser beams onto opposite sides of said wire in use, and means for causing said optics to move the laser beams generally transversely of the wire to create cuts.

Preferably said beam splitting means and said respective reflecting means are fixed, and

Said beam focusing means is provided upstream of the beam splitting means, and drive means is provided to impart movement to said focusing means to effect beam movement.

Alternatively, a fixed focusing means may be provided upstream of said beam splitting means, with beam deflecting means being operable to shift the axis of incidence of the laser beam on said beam splitter. Said beam deflecting means may comprise a reflecting means, and a drive means for imparting movement to said reflecting means. This could be a linear or angular movement. Said beam deflection means may be disposed upstream or downstream of said fixed focusing means. In another arrangement said optics may comprise respective fixed reflecting means for directing said laser beam onto opposite sides of said wire in use, and a beam directing means operable alternately to pass the beam to said fixed reflecting means, and further operable to deflect the beam when incident on said fixed reflecting means to cause said beam to move generally transversely relative to said wire.

The beam directing means conveniently comprises an angularly moveable reflecting means. in another aspect, this invention provides a laser wire stripper including a source of laser radiation operable to emit a beam of laser radiation, wire location means for locating in a stripping zone a wire carrying insulation to be stripped, respective fixed reflecting means for directing said laser beam onto opposite sides of said wire in use, a beam splitter for generating two beams, one to be incident on a respective fixed reflecting means, and means for shifting the axis of the laser beam upstream of said beam splitter to move the laser beams generally transversely of the wire to create cuts.

In yet another aspect, this invention provides a laser wire stripper including a source of laser radiation operable to emit a beam of laser radiation, wire location means for locating in a stripping zone a wire carrying insulation to be stripped, respective fixed reflecting means for directing said laser beam onto opposite sides of said wire in use, and beam directing means deflectable alternately to pass the beam to the two fixed reflecting means, and further operable to deflect the beam incident on said fixed reflecting means to cause said beam to move generally transversely relative to said wire. Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description.

By way of example only, a specific embodiment of this invention will now be described, reference being made to the accompanying drawings in which: Figure 1 is a schematic view of a portable hand held laser wire stripper in accordance with this invention;

Figure 2 is a diagram showing the optical components making up the rotating cradle in the embodiment of Figure 1;

Figure .3 is an alternative optics scheme for directing the laser beam to strip a wire by applying linear motion to an assembly comprising four mirrors and two lenses to translate the assembly relative to a wire, and

Figures 4(a), (b) and (c) are views of optics schemes in which a single optical element is moved to direct the laser beam.

Referring to the drawings, the illustrated embodiment of a hand held laser wire stripper is designed to be used in confined spaces so that an engineer may use it in situ to strip wires of different size. The stripper comprises a hand held stripper unit 10 connected to a base unit 12 by means of a flexible umbilical 14 made up of an outer flexible extractor tube 16 with a hollow waveguide 18 running through it.

The base unit 12 houses a CO₂ laser 20 which emits laser radiation at a wavelength of about 10 microns and which directs its output beam into the inlet end of the hollow waveguide 18. The laser emits power in a range of from 0.5 to 50 watts so as to provide sufficient beam energy to cut through wire insulation. The base unit also includes an extractor fan 22 connected to the inlet end of the flexible extractor tube 16 by a manifold 24. Also provided in the base unit is cooling 26 for the laser, together with a power supply 28, a battery 30 and a controller 32 for controlling both the laser 20 and various components of the stripper head 10. Control signals and power to the head are supplied by means of conductors (not shown) which also pass down the inside of the flexible extractor tube 16.

The stripper head 10 comprises a housing 34 defining a generally enclosed space 36 which has an outlet port 38 connected to the flexible extractor tube 16. The flexible waveguide 18 is fixed to a suitable connector 40 which passes light to a collimator 42 that can be aligned in the X and Y directions and focused. Laser radiation passing through the hollow waveguide 16 and the collimator 42 passes to a rotating cradle 44 which houses three mirrors 46, 48, 50 and a further focusing lens 52 arranged upstream of the last mirror 50. This optics arrangement focuses the laser beam on a wire 54 to be stripped. The cradle is mounted to rotate about an axis concentric with the axis of the wire 54 to cause the focused laser beam to scribe around the insulation coating and to remove the insulation without damaging the underlying conductor. The cradle 44 is rotated by means of a DC motor 56 and two bevel gears 58 and 60 respectively.

During operation, the laser beam will generate fumes as it vaporises the insulating coating and a gas cylinder 62 is provided in the stripper head for periodically blasting via a hose 64 a jet of gas at the final, exposed mirror 50 to clear it of debris. Upstream of the focusing lens 52 the optical pathway is sealed against the ingress of fumes etc. from the laser cutting process. The jet of gas may also be used to help the stripping process.

The stripper unit has a wire inlet port 66 through which a wire to be stripped is introduced into the head and held in the required position whilst the laser stripping is effected. A sealing collet 68 is aligned with the inlet port 66 and holds the wire on the rotation axis. The sealing collet 68 has a rubber type seal that isolates the inner space 36 in which the laser cutting is done from the external environment. The longitudinal position of the laser cut, and thus the length of insulation removed, is set by the axial position of the abutment surface 69 which limits input movement of the wire. This may be adjusted by a suitable mechanical adjustment (not shown) to allow the stripped dimension to be varied.

In addition, the stripper head 10 may include suitable controls (not shown) to allow the speed of the motor to be adjusted, and to allow the power of the laser to be adjusted. If required, the power of the laser beam delivered to the optics may be detected in the stripper head by a suitable sensor and this power measurement used to control the output power of the base unit to ensure a uniform delivery of power to the wire.

The waveguide may be any suitable form of flexible guide. Specific mention is made of hollow size waveguides but we do not exclude using other waveguide fibres or waveguides of other forms.

Where a hollow waveguide is used, it may be any suitable IR transmitting hollow waveguide made for example of metal, plastics, glass tubes with a highly reflective coating. A suitable source of hollow silica waveguide is available from Polymicro Technologies LLC. Where a PIR fibre is used, it may be any suitable IR transmitting optical fibre. A suitable source of PIR fibre is available from A. R. T. Photonics GmbH.

The stripping cut made by the laser may, be of any suitable shape; it may be circumferential or lateral, straight or curved, continuous or discontinuous although circumferential is preferred. Although in the embodiment the movement of the laser beam is achieved by means of a motor, in other embodiments it could be moved manually.

Figure 2 shows the optics scheme used in the embodiment of Figure 1. The mirrors 46, 48, 50 and the focusing lens 52 are mounted on a rotating cradle which directs the laser to circumscribe the wire to be stripped as the cradle rotates.

In Figure 3 four mirrors 70, 72, 74, 76 (one_; 70, also acting as a beam splitter) and two lenses 78, 80 are provided to create two beams that are incident on opposite sides of the wire 54. The optics assembly is translated in the direction of the arrow to cause the beams to traverse the wire to make coterminous cuts on opposite sides.

Alternative optical geometries are also possible. Due to the fact that only a small strip length is required, it is possible to use simple linear stripping optical arrangements using the minimum number of components.

Referring now to Figures 4(a) to 4(c), in these proposals a single optical component (lens or mirror) is moved to achieve the strip. Figure 4(a) below shows an example of a lens 80 creating the motion. The laser beam passes through the lens 80 and a beam splitter 70. The beam splitter creates two equally powered beams which are reflected onto the wire by two fixed mirrors

72, 74. The motion of the focal point is achieved by moving the lens off axis. This approach is not usually recommended in design of laser optics, as misalignment of the lens 80 compared to the axis will result in optical aberrations to the beam which for most applications would be unacceptable. However, in this application the laser needs to cut only a small strip length is required, typically a few millimetres. Over this range the aberrations are sufficiently small to be negligible.

Another alternative is shown in Figure 4(b). Here the lens 80 is fixed and a single rotating beam-splitting mirror 70 creates two. beams which are reflected by two fixed mirrors 72, 74 as before. Again this translates the beam but causes aberrations. In addition the focal plane is no longer straight, but curved due to the effect of tilting the beam. Normally a special f-theta lens would need to be used to counteract this. Whilst we do not exclude that possibility, this is not absolutely necessary in this application because the amount of travel is low, and the change in focus can be used to enhance the strip quality by ensuring the focal plane coincides with the edges of the wire which are difficult to strip. In this case the lens 80 can go before or after the tilting mirror 82.

Figure 4(c) shows a further arrangement that dispenses with the beam splitter 70, giving the simplest geometry. An angularly adjustable mirror 82 is provided which is set to a first position, to direct the beam onto the first fixed mirror 72, and the angle oscillated slightly to give the lateral motion at the wire. The mirror then rotates to the second position, to direct the beam onto the second fixed mirror 74, and the oscillation repeated. All of these geometries have the advantage of being cheaper, more compact and easier to realize than the more traditional approaches.

Claims

1. A laser wire stripper comprising: a base unit including a laser for emitting laser radiation; an elongate flexible waveguide means for receiving and passing laser radiation emitted by said laser, and a stripper head for receiving laser radiation passed down said flexible waveguide means, said stripper head including: wire location means for locating in a stripping zone a wire carrying insulation to be stripped, and optics means for receiving said laser radiation and directing it on to a wire in said stripping zone to move along, and/or across and/or around a laser cutting path selectively to remove the wire insulation from said path.

2. A laser wire stripper according to Claim 1 , wherein the optics means is operable to cause the laser radiation to follow a path that circumscribes the wire to be stripped.

3. A laser wire stripper according to Claim 1 or Claim 2, wherein the flexible waveguide means comprises a hollow waveguide.

4. A laser wire stripper according to Claim 1 or Claim 2, wherein the flexible waveguide means comprises an optical fibre.

5. A laser wire stripper according to any of the preceding Claims, wherein said wire location means is adjustable to allow the distance of the cutting path from the end of the wire to be adjusted to allow the length of the portion of the wire to be stripped to be pre-selected.

6. A laser wire stripper according . to any of the preceding Claims, wherein the optics includes a focusing lens for focusing the laser radiation on to said cutting path.

7. A laser wire stripper according to Claim 6, wherein the focusing means is adjustable to focus the radiation beam on to wires of different diameter.

8. A laser wire stripper according to any of the preceding Claims, wherein said optics includes a drive motor for rotating at least part of said optics to cause the laser radiation to pass along a circumferential cutting path, and said stripper further includes control means for controlling the rotational speed of said drive motor and thereby the laser cutting speed.

9. A laser wire stripper according to any of the preceding Claims, wherein the optics includes a series of deflecting means for causing said radiation beam to arrive at said cutting path, the stripper further including means for directing a gas jet at the final deflecting means to clear it of debris acquired during operation of the laser.

10. A laser wire stripper according to any of the preceding Claims, wherein the laser stripping zone is a generally enclosed space having a gas outlet which is connected to one end of the flow passage which is associated with said waveguide means and which communicates at its other end with gas extraction means disposed in the base unit.

11. A laser wire stripper according to Claim 10, wherein the flow passage is defined by a flexible tube connecting the stripper head to the base unit and through which the waveguide means passes.

12. A laser wire stripped according to Claim 10, in which said optics includes three reflecting means mounted on a cradle, mounted for rotation.

13. A laser wire stripper according to Claim 1 , wherein said optics comprises a beam splitter to generate two laser beams, and respective reflecting means for directing said laser beams onto opposite sides of said wire in use, and means for causing said optics to move the laser beams generally transversely of the wire to create cuts.

14. A laser wire stripper according to Claim 13 wherein said beam splitting means and said respective reflecting means are fixed.

15. A laser wire stripper according to Claim 14, wherein said beam focusing means is provided upstream of the beam splitting means, and drive means is provided to impart movement to said focusing means to effect beam movement.

16. A laser wire stripper according to Claim 14, wherein a fixed focusing means is provided upstream of said beam splitting means, and beam deflecting means is operable to shift the axis of incidence of the laser beam on said beam splitter.

17. A laser wire stripper according to Claim 16, wherein said beam deflecting means comprises a reflecting means, and a drive means for imparting movement to said reflecting means.

18. A laser wire stripper according to Claim 17, wherein said drive means imparts angular movement to said reflecting means.

19. A laser wire stripper according to any of Claims 16 to 18, wherein said beam deflection means is disposed upstream of said fixed focusing means.

20. A laser wire stripper according to Claim 1 , wherein said optics comprises respective fixed reflecting means for directing said laser beam onto opposite sides of said wire in use, and a beam directing means operable alternately to pass the beam to said fixed reflecting means, and further operable to deflect the beam when incident on said fixed reflecting means to cause said beam to move generally transversely relative to said wire.

21. A laser wire stripper according to Claim 20, wherein said beam directing means comprises an angularly moveable reflecting means.

22. A laser wire stripper including a source of laser radiation operable to emit a beam of laser radiation, wire location means for locating in a stripping zone a wire carrying insulation to be stripped, respective fixed reflecting means for directing said laser beam onto opposite sides of said wire in use, a beam splitter for generating two beams, one to be incident on a respective fixed reflecting means, and means for shifting the axis of the laser beam upstream of said beam splitter to move the laser beams generally transversely of the wire to create cuts.

23. A laser wire stripper including a source of laser radiation operable to emit a beam of laser radiation, wire location means for locating in a stripping zone a wire carrying insulation to be stripped, respective fixed reflecting means for directing said laser beam onto opposite sides of said wire in use, and beam directing means deflectable alternately to pass the beam to the two fixed reflecting means, and further operable to deflect the beam incident on said fixed reflecting means to cause said beam to move generally transversely relative to said wire.

24. A laser wire stripper substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.