Patent Publication Number: US-2013248501-A1

Title: Rotating laser wire stripping system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Provisional Patent Application No. 61/613,565 filed Mar. 21, 2012, and is incorporated herein as set forth in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is directed to a laser wire stripping system, and more particularly, a system which utilizes a rotating laser head to strip wires located across a large area. 
     A rotating laser wire stripping system removes insulation from wires, multi-conductor cables, or shielded cable by using the laser power to melt or ablate the insulation so that it can be pulled or peeled from the wire or cable. As is known in the prior art, a laser system has a single wire channel assembly which provides a pathway for allowing a laser light from a source to travel through the channel assembly to a cylindrical cavity in the channel assembly. A collet is provided as a passageway for insertion of a wire into the cavity. The collet has an opening, which when the wire is properly inserted into the cylindrical cavity, is in alignment with the pathway allowing the laser light to travel to the wire in order to remove insulation from the wire. A housing assembly holds the channel assembly and allows the channel assembly to rotate within the housing assembly about the wire. 
     As is known from U.S. Pat. No. 6,603,094 by way of example, a laser of appropriate wavelength such as a CO 2  laser may be used as the light source for stripping insulation. As the channel assembly rotates about the end of the wire, the laser beam traces a path about the wire and melts lengths of insulation from the wire. Because the laser emits a light beam of about 10640 nm, the metallic core reflects the light and is unaffected by the laser beam as the laser melts the insulation. If the assembly is held stationary, a line may be drawn along the insulation to allow for peeling and stripping in that manner. 
     These prior art laser wire stripper assemblies have been satisfactory for stripping a wire one at a time as it is inserted into the housing assembly. However, the prior art system suffers from several deficiencies. First, the housing assembly is bulky. The housing assembly contains the laser source as well as the rotating channel assembly. 
     A one sized hole is formed in the collet which must be very close to the size of the wire or the wire will droop out of the focus of the laser beam. Furthermore, the hole into which the wire is inserted has to be close to the actual size of the wire to be operated upon and the hole size for each collet is fixed. As a result, the wire will tend to catch on the hole and the collet as the assembly spins around it at a high speed. If the wire is a multiconductor cable with a non-round shape, it is even more prone to this catching. This can tend to twist the wire while it is lasing to cause an uneven or unusable cut on the insulation. Where the collet is interchangeable, a different sized collet must be switched in to accommodate each different sized wire; requiring a “library” of collets and slowing the stripping procedure. 
     The prior art also suffers from the deficiency that there is no method with which to set the depth of the wire and therefore the depth of the stripped length. This is currently done by adjusting the length of the hole in the collet, but this is extremely unwieldy in a practical sense; again requiring a myriad of collets to achieve a reasonable variation of strip lengths. Additionally, there is nothing to hold the wire in place while it is being stripped, forcing the operator to hold the wire until the process is completed. This introduces human error and fatigue into the operation. 
     Furthermore, because of the heat and the burning during the process, debris and smoke are created. The prior art accounts for the smoke and debris by creating an airtight chamber for an air purged ventilation system to protect the objects and a vacuum for removing debris. As a result, the device becomes complicated requiring manufacturing parts to a high tolerance and an extremely difficult assembly. Additionally, because of the rotating assembly structure, it is difficult to mount a sensor to detect that the wire has been inserted and remained inserted during the entire process and therefore, without such a sensor, the system, may not be able to qualify as a Center for Device and Radiological Health (CDRH) Class 1 safe system. 
     Because the assembly contains the laser and the rotating channel assembly, the prior art systems take up work space, which is often scarce, at the wire stripping site. This adds to the expense and inefficiency of the worksite as two or more wire strippers could be placed in the footprint that the current prior art laser wire stripper requires. Secondly, because of the bulkiness of the housing assembly and the arrangement of the laser source, support structure and rotating head within a single housing assembly, the laser wire stripping system is immobile. This requires the wires to be brought to the wire stripper and inserted one at a time. This system is inapplicable to a large manufacturing facility where wire stripping often occurs in situ for wires on a large typical wire harness. And again if the wires in a harness are not uniform, the prior art requires switching out of the collet to accommodate multiple wire gauges within a single harness. 
     By way of example reference is made to  FIG. 1  where a large sophisticated wiring harness  10 , such as those utilized in the aircraft industry is provided. Because of the millions of wires required in sophisticated aircraft and spacecraft, it is practically impossible to wire the craft by hand in the craft itself. To accommodate such sophisticated and complex wiring needs, thousands of wires  12  corresponding to tens of thousands of feet of wiring are provided on a harness  10 . The harness  10  is placed into an aircraft for interconnection with related circuitry including other panels within the aircraft. In order to protect wires  12 , the wires  12  are placed into the harness  10  with full protected insulation thereon. The ends of individual wires  14  are then stripped within harness  10  to provide maximum protection of the wire throughout the assembly process. Because of the high sensitivity of certain applications such as the use of harnessed wires in airplanes, helicopters, spacecraft, missiles and the like, a slight nick to an individual wire  14  can affect operation of the entire system. For this reason, laser stripping is preferred over any mechanical method, but it is impractical because of the wire harness environment which requires mobility of the stripping system to reach each individual wire  14  within harness  10 . 
     Accordingly, a system which overcomes the shortcomings of the prior art is desired. 
     BRIEF SUMMARY OF THE INVENTION 
     A laser stripping system has a laser source for emitting a laser beam. A wire stripping assembly for receiving a wire therein and directing the laser energy towards the wire when the wire is disposed within the wire stripping assembly is optically connected to the laser source by an optical conduit; light tube, or fiber optic. The wire stripping assembly is freely moveable relative to the laser source. 
     In a preferred embodiment, the optical conduit is an optical fiber or light tube. The laser source is disposed away from the wire stripping head, and in a preferred embodiment, the laser source is capable of movement in at least two directions along a plane. Furthermore, the wire stripping head may selectively direct the laser beam along a path which circumnavigates the wire. 
     In yet another preferred embodiment of the invention, the wire stripping assembly includes a fixed collet, an offset assembly includes a lens assembly for receiving the laser light and directing the laser light in a substantially perpendicular direction relative to an insertion axis of the wire. The offset assembly is rotatably mounted relative to the collet to rotate 360 degrees about the axis of insertion of the wire. The wire stripping assembly has an opening, a drive roller and an idler wheel are disposed at the opening to receive the wire. The idler wheel may be biased towards the drive wheel and movable between a first position adjacent the drive wheel and a second position away from the drive wheel to accommodate different gauges of wire. A clamp may be disposed within the assembly for holding the wire during the stripping process. A sensor is disposed within the assembly for detecting the presence of a wire within the assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will be apparent from the written description and the drawings in which: 
         FIG. 1  is a top plan view of a wire assembly disposed within a harness in accordance with the prior art; 
         FIG. 2  is a block diagram of a wire stripping system constructed in accordance with the invention; 
         FIGS. 3 and 4  are views of a wire stripping head constructed in accordance with the invention; 
         FIG. 5  is a schematic diagram of a wire stripping assembly having a rotatable offset optical assembly constructed in accordance with the invention; 
         FIG. 6  is a schematic diagram of a self-centering linkage for a wire stripping assembly constructed in accordance with the invention for enabling the operation on a variety of wire gauges; 
         FIG. 7  is a schematic diagram of an adjustable depth gauge for a wire stripping assembly constructed in accordance with the invention; 
         FIGS. 8   a  and  8   b  are a schematic diagram of a clamp and clamping process within a wire stripping assembly in accordance with the invention; 
         FIGS. 9   a  and  9   b  are schematic diagrams showing a support for a wire to be stripped within a wire stripping assembly, constructed in accordance with the invention; and 
         FIG. 10  is a schematic diagram of a sensor disposed within a wire stripping assembly in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made to  FIG. 2 , in which a system constructed in accordance with the invention and generally indicated as  100  is shown. A laser source  102  includes a laser and the associated electronics as known in the art for creating a laser beam. In a preferred embodiment, laser source  102  is a CO 2  laser source as known in the art, outputting a laser beam of about 10640 nm. A hand held stripping assembly  104  is separate from the housing of laser source  102  and is optically connected to laser source  102  by an optical conduit  106  capable of transmitting the laser beam produced by laser source  102  to hand held wire stripping assembly  104 . Optical conduit  106  may be a light pipe, but in a preferred non limiting embodiment, optical conduit  106  is an optical fiber such as an AgCl:AgBr fiber manufactured by CeramOptec. 
     Hand held stripping assembly  104  is capable of free movement, i.e. movement in at least two directions relative to laser source  102 . Hand held wire stripping assembly  104  may be a rotating stripping assembly. In one exemplary, but non limiting embodiment, optical conduit  106  provides a laser beam input to wire stripping assembly  104 . Wire stripping assembly  104  has an insertion axis A along which a wire may be inserted into wire stripping assembly  104  for stripping. Wire stripping assembly  104  includes at least one mirror which in a one mirror embodiment is disposed at a 45 degree angle to the path of the laser beam as input from fiber conduit  106 . This angled mirror reflects, or directs the laser beam substantially 90 degrees relative to the insertion axis A (corresponding substantially to the orientation of the wire within wire stripping assembly  104 ). The mirror may rotate about insertion axis A keeping laser beam within the wire stripping assembly  104  at a constant substantially 90 degree orientation relative to insertion axis A throughout  360  degrees or more rotation about the wire. 
     As a result, the laser beam circumnavigates a wire disposed along axis A to melt a circular line of insulation to facilitate removal. In another less preferred embodiment, the mirror may be fixed and movement of the wire stripping assembly  104  relative to a wire disposed therein will cause removal of a line of material along the wire as a result of relative movement of the wire and the mirror. In other words, the hand held device could be rotated about the wire manually or moved along the wire to provide a stripped line to allow peeling back of the insulation. Conversely, the wire may be moved in order to effect stripping. 
     Reference is now made to  FIG. 5  in which a schematic diagram of the rotation assembly for facilitating the beam of light traveling about the wire is provided. Wire stripping assembly  104  includes a collet  120  for selectively holding a wire  122  therein allowing the wire to move into and out of wire stripping assembly  104  in the directions of double-headed arrow A. 
     Wire  122  lies along the axis of insertion and moves in the direction of arrow A substantially along the insertion axis. A rotating optical assembly  130  is disposed within assembly  104  and rotates about insertion axis A in the direction of arrow B. Rotating optical assembly  130  includes one or more mirrors for changing the direction of an incoming beam of laser light  137  output from a laser source such as laser source  102  transmitting to the wire stripping assembly  104  as described above. 
     At least one mirror is disposed within rotating optical assembly  130  to change the path and direction of the incoming laser beam  137  as it enters optical assembly  130 ; even as optical assembly  130  is rotating. In this non-limiting embodiment, a first mirror  132  disposed at substantially a 45 degree angle relative to the axis of the incoming beam  137  receives the incoming laser beam  137  as it enters rotating assembly  130 . A second mirror  134  is disposed within rotating optical assembly  130  at an angle substantially  45  degrees relative to the travel path of laser beam  137  as it leaves first mirror  132 . In this non-limiting embodiment, a third mirror  136  is disposed within rotating assembly  130  downstream along the laser beam path from mirror  134  and is at a substantially 45 degree angle and directs the path of the laser beam  137  through an optical opening within rotatable assembly  130  to impinge axis of insertion A at an angle substantially perpendicular to the axis of insertion. 
     In a preferred, non-limiting embodiment, a focusing lens  138  may be disposed along the path traced by laser beam  137 . A three mirror embodiment is shown by way of example, but any number of mirrors which can deflect the laser beam towards the insertion access at an angle sufficient to perform ablation may be used. 
     Collet  120  is fixed relative to insertion axis A and optical assembly  130 . Optical assembly  130  may be supported on a rotating arm spindle or other type of linkage which rotates the optical assembly about axis of insertion A. In this way, wire  122  is held by a stationary collet  120  as the assembly producing the laser light rotates relative to the insertion axis. Furthermore, collet  120  can be better sized to have the right size opening to corresponding to the wire, as collet  120  no longer needs to spin around wire  122  or travel the distance of the laser beam travel. Therefore, collet  120  can be designed for greater tolerances. 
     As wire  122  is stripped by wire stripping assembly  104 , the prior art suffered from the deficiency that the collet could only accommodate a single gauge wire. While maintaining collet  120  stationary has provided more tolerance to different gauges of wire, collet  120  is still incapable of determining the depth to which the wire is currently inserted or even provide a better guide to wires of different gauges. Reference is now made to  FIG. 6  in which an embodiment of wire stripping assembly  104  having a self-centering and depth measuring assembly is shown. 
     A first wheel  140  and a second wheel  142  are provided at an insertion opening  110  of wire stripping assembly  104 . First wheel  140  is fixed in place, while second wheel  142  is moveable between a first position adjacent, or in contact with, wheel  140  and a second position away from wheel  140 . Wheel  142  is biased towards wheel  140 . In this way, as a wire  122  is inserted along insertion axis A, it forces wheel  142  away from wheel  140  as it moves between wheels  140 ,  142 . Because wheel  140  is biased, the wheels center (maintain wire  122  at a predetermined position relative to the opening), as it travels along insertion axis A. Wire  122  is in in effect pinned between the wheels. 
     In a preferred embodiment, a counter  144 , such as an encoder, a motion sensor, or the like determines the amount of rotation of wheel  142 . Knowing the rotation of wheel  142 , counter  144 , or a computer processor associated therewith, can determine in real time the depth to which wire  122  is inserted within housing  104 . This results from the fact that a distance of rotation of wheel  142  corresponds to a length of wire  122  traversed. 
     In yet another embodiment of the invention, a motor  146  may be operatively coupled to drive wheel  140 . In this way, wires may be ablated to a precise predetermined distance as determined by the amount of rotation of wheel  140  or  142  drawing wire  122  into laser assembly housing  104 . Motor  146  is a two directional motor so that rotation in a first direction inserts the wire into wire stripping assembly  104 , and rotation in the opposite direction smoothly extracts wire  122  from wire stripping assembly  104  to control the fed rate for the slitting process. This eliminates differences between individual operators to provide consistency provided in the appropriate beam exposure time along wire  122  during the slitting process. 
     It should be noted, that wheels  140 ,  142  may replace the function of collet  120 , but may also be used in tandem with collet  120  positioned either upstream or downstream of collet  120  and still utilizing collet  120  as an additional support while allowing for the functionality described above of wheels  140 ,  142 . 
     In an embodiment with collet  120 , an alternative depth gauge may be used. Reference is now made to  FIG. 7  in which a mechanical depth gauge  150  having another structure to provide wire depth measuring is provided. An adjustable depth gauge  150  is slideably mounted within wire stripping assembly  140 . In a preferred embodiment, depth gauge  150  may be mounted on optical assembly  130 . Depth gauge  150  is slideably disposed along insertion axis A; capable of moving between a first position proximate collet  120  to a second position away from collet  120  relative to the first position. Depth gauge  150  may be positioned to the desired stripping depth substantially at any position along optical assembly  130 . As shown in  FIG. 7  it is moveable between a first shorter stripping length represented as the solid adjustable gauge  150  to any position up to an including substantially the position shown in phantom as  150 ′ or beyond. A range finding detector, by way of example, a range finding sensor  131  detects the relative distance between range finding sensor  131  and adjustable depth gauge  150 . By way of example, range finding sensor may be an optical sensor, ultrasonic sensor, radio frequency detector or the like. The change In position of depth gauge  150  along the slide path is converted into a wire depth, as known in the art. In this way, the depth of insertion of wire  122 , critical for determining the length of ablation, is determined even in the absence of the wheel assembly discussed above. 
     During operation, the wire is inserted until it contacts adjustable gauge  150 . In this way, because the sensor and the depth gauge have determined the distance between the collet and the depth gauge, the insertion length of wire  122  is known. Furthermore, in a preferred non-limiting embodiment, adjustable gauge  150  has a conically shaped receiving portion  152  for receiving the leading end of wire  122  and acts as a stop. Because of the conical shape of the receiving portion  152 , as adjustable depth gauge rotates with optical assembly  130 , adjustable depth gauge  150  centers wire  122  while maintaining it in position, without causing the wire to twist as a result of the rotation. 
     Movement of wire  122  during ablation and inaccurate positioning in the first instance, is a shortcoming of the prior art. Because collet  120  is stationary, and it is the optical assembly which rotates relative to the rest of the wire stripping assembly, it is possible to clamp wire  122  in place in the present invention. Reference is now made to  FIGS. 8   a ,  8   b , in which a clamp for maintaining wire  122  in place is provided. 
     A clamp  150  is disposed within stripping assembly  104  along insertion axis A. Clamp  150  is preferably mounted within fixed collet  120  and includes an anvil portion  154  having an area sufficient to support a wire  122  thereon. Clamp  150  includes a pinching mechanism  156  capable of moving or extending towards insertion axis A a sufficient distance to press wire  122  against collet  120  is provided at a position within stripping assembly  104  at an opposed position relative to anvil portion  154  within collet  120  and across insertion axis A. In a preferred, but non-limiting embodiment, pinching mechanism  156  includes an extendable rod which moves from a first position away from anvil  156  to a second position towards anvil  154 . It should also be noted, noted, that any mechanical system capable of trapping, pinning, pushing or pressing, wire  122  within collet  120  may be utilized as pinching mechanism  156 . 
     During operation, wire  122  is inserted along insertion axis A a predetermined distance as determined by the depth gauge as discussed above. Once travel has stopped, pinching assembly  154  clamps wire  122  to anvil  156  to maintain wire  122  in position during the ablation process. 
     During ablation, the rotatable optical assembly  130  moves along insertion axis A to ablate the coating from the wire. As rotational optical assembly  130  moves along insertion axis A, it may either rotate around axis B to ablate the entire wire or not rotate to slit the wire. It should be noted, that in other embodiments, where clamping is not required, optical assembly  130  may operate as the wire is inserted along insertion axis A. 
     Many times, a wire to be stripped is not straight because of bending or drooping and therefore, the wire avoids the focal point of the laser beam as the laser beam moves about and along insertion axis A, or when in the slitting mode, traces a straight line; missing any bends in the wire. Reference is now made to  FIGS. 9   a  and  9   b  wherein a structure for ablating the wire while accommodating bends in the wire  122  is provided. Stationary collet  120  supports a wire  122  within assembly  104 . An optical assembly  230  directs a beam to a focal point along an insertion axis of wire  122 . The operation of optical assembly  230  is the same as optical assembly  130 , including the necessary mirrors and optics to direct a beam as taught above. The primary difference being the inclusion of a support  206  mounted to optical assembly  230 . Support  206  includes a channel  208  therein for receiving and supporting a wire  122 . Channel  208  has a radius sufficiently large so as not to twist wire  122  disposed therein while rotating. 
     As can be seen in  FIG. 9   b , during the ablation or slitting process, optical assembly moves in the direction of Arrow A relative to wire  122 . This is done by the movement of optical assembly  230 . Because wire  122  is supported within channel  208 , channel  208  will straighten/remove-droop in wire  122  as support  206  moves in the direction of Arrow A. Support  206  is substantially adjacent the focal point of exiting laser beam  137 . Substantially adjacent means for the purposes of this invention, close enough such that the support provided by support  206  to drooping wires straightens the wire sufficiently to place the wire  122  at the focal point of laser beam  137  as optical assembly  230  moves along insertion axis A as wire  122  moves relative to channel  208 . Furthermore, because support  208  is disposed upstream of the laser path in the direction of Arrow A as wire  122  is straightened prior to be being ablated by laser beam  137 . In this way, even a drooping wire may be slit (optical assembly  230  does not rotate during movement) or ablated (optical assembly  230  rotates during movement in the direction of Arrow A); even a crooked wire  122  is properly stripped. While the diameter of channel  208  is critical in that it must be sufficiently sized to provide support to wire  122 , it is sufficiently large that rotation of support  206  about wire  122  will not twist wire  122  when disposed within channel  208 . 
     Safety, given the presence of smoke, a hot light source and the like is an issue during the ablation process. Laser beam  137  exits optical assembly  130  at an exit point  135 . Exit point  135  may be a transparent portion of assembly  130 , or a physical opening. In an embodiment in which a physical opening is provided, air can be supplied through a spindle at an entry point to optical assembly  130  in the direction of Arrow C. In a preferred embodiment, it is substantially the same path as laser beam  132  through optical assembly  130  to provide a positive air pressure within optical assembly  130 . The pressure is between  1  to  10  psi. As air exits the small hole forming exit  139 , it enhances the processing capabilities with the cutting operation as the opening is dimensioned to be the size of a traditional cutting nozzle. Furthermore, by providing a positive pressure, the smoke and debris is prevented from entering the optical assembly  130 . The optical assembly  130  is a self-contained sealed optical assembly; as a result no sealing of the other elements of the wire strip assembly is required. The optics are protected. 
     Because the prior art collet is spinning with the entire device, a complex sensor network is required to confirm that the wire has been inserted and remained inserted throughout the process. Reference is now made to  FIG. 10  in which a structure for detecting the presence of wire  122  within stripping assembly  104  at the beginning and during the process is provided. Like numbers are utilized to indicate like structures. The primary difference being the use of a sensor at the collet. A collet  220  includes an access point  222  which provides access to wire  122  as it is inserted through the collet. A presence detector sensor  224  is disposed at access point  222  to sense the presence or absence of wire  122  within collet  220 . Because collet  220  is fixed in the present invention, only a single sensor which may be formed as part of the collet or separately, is required. 
     During operation, the focused laser beam energy, melts, ablates or vaporizes the insulation. With the appropriate laser power and the correct number of rotations (as a function of power, laser frequency and insulation type and thickness) removal of a ring of insulation without damaging the wire, shielding or inner material can be accomplished. Additionally, if the wire is slowly separated from the wire stripping mechanism, and the wire stripping mechanism is the rotational wire stripping mechanism, the focused beam may be directed from a starting point to the end of the wire as rotation continues so that the entire insulation may be removed without the need for manual removal of any insulation. If a non-rotation mode or non-rotating wire stripping assembly is utilized, if the wire is slowly separated from the focused beam along the insertion axis A such that the focused beam is directed from a starting point to the end of the wire, then a slit from the starting point to the end of the wire may be cut in the insulation facilitating removal of the stripped insulation. 
     In a further preferred embodiment, laser source  102  is positioned away from the work area either above or below the work area for laser assembly  104 . This frees up work space to accommodate large harnesses having many wires (scores or even hundreds) to be stripped, or several devices working side by side. In a preferred embodiment, to accommodate large work areas such as are necessary for assembly of harness  10 . For example, system  100  includes a slide  108  moveable in the direction of at least arrow X to move along harness  10  to access the wires  14  of wire assembly  12  which require stripping or even mounted to a movable cart. In an even more preferred embodiment to accommodate larger work areas, such as those typically utilized in the aerospace industry, slide  108  is moveable in the X and Y directions so that laser source  102  may traverse along a plane to enable access of the wire stripping assembly  104  to substantially any spot on the work space presented by harness  10 . To prevent fatigue and to prevent wire stripping assembly  104  from inadvertently falling and damaging harness  10 , a so-called zero gravity arm  110  provides support for wire stripping assembly  104  from slide  108  to maintain wire stripping assembly  104  in a position at a distance above the work area, but within easy access to a user. 
     As will be understood that the stripping assembly in a fixed collet and a rotating optical assembly lends itself to both a table mounted embodiment and the hand-held embodiment of system  100 . Furthermore, by holding the rotating optical assembly still and moving the optical assembly along insertion axis A, the wire may be slit utilizing a fixed collet. Conversely, by rotating the optical assembly utilizing the fixed collet, the outer casing of the wire may be ablated while still allowing for a simpler sensor assembly, a simpler construction, and the like. 
     Thus, while there have been shown, described and pointed out fundamental novel features as applied to the preferred embodiment, it is understood that various omissions, substitutions and changes in the form and details of the device illustrated, and in its operation, may be made by those skilled in the art without departing from the spirit and scope of the disclosure in substantial substitution of elements are fully intended and contemplated. It is also to be understood that the drawings that are not necessarily drawn to scale but they are merely conceptual in nature.