Abstract:
A method and apparatus for evaluating and/or quantifying damage to wire strands of a wire caused during installation of a crimped wire connector, involves launching an ultrasonic wave having known characteristics into a wire at a location that is either the crimp or is adjacent the crimped wire connector, and detecting changes in the characteristics (e.g., amplitude and/or phase shift) of the wave as it is propagates along a length of the wire.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the use of ultrasonic technology to evaluate the integrity of a wire in the immediate vicinity of a crimp connection. 
     BACKGROUND OF THE INVENTION 
     Electrically conductive stranded wires are frequently terminated with a crimped connection as an alternative to electrical connectors made using soldering, welding, conductive adhesives, and various types of solderless techniques such as insulation displacement, compression, wire clamping and interference fit connections. Crimp connectors are often preferred because they are reliable, inexpensive, easily replaced if damaged, and can provide uniform and reproducible electrical and mechanical characteristics. However, damage to the electrically conductive wires can occur in the immediate vicinity of a crimped connection. This can cause a failure mode that significantly shortens the service life of a crimp connection leading to a failure of a system or vehicle employing the connection. Consequently, it is desirable to reliably and inexpensively evaluate the integrity of a crimped connector. 
     It is conceivable that an electrical resistance test through a crimped connector may be used to validate or evaluate the connection. However, such testing is not normally done in a production environment due to the high cost and impracticality of such testing and the inability to accurately predict failures due to certain latent damages such as small nicks or indentations that could be difficult or nearly impossible to detect by resistance testing, but which can create mechanical weaknesses that can propagate and eventually lead to an electrical failure. 
     Another commonly employed technique for determining the damage caused during fabrication of a crimped connector is visual inspection. Unfortunately, visual inspection is not easily employed for small wire diameters or when the crimp connection is not easily accessible, such as when the crimp connector is under a ferrule apron or at a junction between a wire and its insulation. 
     BRIEF SUMMARY OF THE INVENTION 
     In certain embodiments, an ultrasonic wave is propagated from a source along a length of an electrically conductive wire in the vicinity of a crimp connection. At a predetermined distance from the source, the wave is detected and compared with the propagated ultrasonic wave. Based on comparisons, including wave energy and phase shifts, the existence and extent of damage to the wire in the vicinity of the crimp connection is evaluated. 
     In certain embodiments, a step of comparing the propagated ultrasonic wave to the detected ultrasonic wave involves detecting and measuring energy loss and phase shifts between the propagated ultrasonic wave and the detected ultrasonic wave, and the step of evaluating the existence and extent of damage in the wire in the vicinity of the crimp connection involves correlating the measured energy loss and/or measured phase shift to an associated type and extent of damage. 
     It has been found that when an ultrasonic wave is propagated along a predetermined length of a wire in the immediate vicinity of a crimped connector, the wave energy is altered as it propagates through a damaged section of the wire (e.g., a broken, bent or nicked section). In those cases where the break is incomplete (e.g., a nick or notch), the phase of the wave is shifted. A break in one of the strands causes a substantial decrease in amplitude and energy of the wave. The magnitude of the changes depends on the magnitude of the defect, the number of affected strands in the wire, the strand gauge, and the total number of strands. 
     The parameters affecting measurements of the ultrasonic wave energy and phase shift include the wave frequency, wave mode, and initial amplitude, all of which may be optimized to facilitate detection and quantitative evaluation of defects at a crimped connector, including nicks, breaks and bends. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross sectional view of a section of a wire in the immediate vicinity of a crimp connector. 
         FIG. 2A  is a schematic representation of a break in a wire strand. 
         FIG. 2B  is a schematic representation of a bend in a wire strand. 
         FIG. 2C  is a schematic representation of a nick in a wire strand. 
         FIG. 3  is a schematic representation of an apparatus for detecting wire defects near a crimped connector. 
         FIG. 4  is a schematic representation of a cross sectional view of a terminal block with wires connected. 
         FIG. 5  is a schematic representation of a cross sectional view of an alternate terminal block with wires connected. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown in  FIG. 1  is a schematic representation of a terminal section of an insulated electrical conductor  10  comprising a wire  12  coated with an insulator  14 , and having one or more crimped connectors  16 . The wire may comprise multiple strands of wire. Crimped connectors are well known in the art and are described in the literature, such as in U.S. Pat. No. 7,181,942, which is hereby incorporated by reference in its entirety. 
     During the process of terminating a wire with a crimped connector, it is not unusual that defects are created in the conducting core or individual strands of a wire. The types of pathologies or defects that can be created in the individual strands of a wire during a process for terminating the wire with a crimped connector are represented schematically in  FIGS. 2A ,  2 B, and  2 C, which show a break  21 , bend  22 , and nick  23  in wire strands  17 ,  18  and  19 , respectively. 
       FIG. 3  schematically illustrates an apparatus for detecting wire pathologies or defects near a crimp connector. The apparatus comprises transmitting transducers  20  for launching an ultrasonic wave mode into the wire (e.g., in a direction transverse to the longitudinal direction of the wire), causing a conversion of some of the compressional wave energy into shear wave propagation along the length direction of the wire. The apparatus also includes a receiving transducer  30  that detects the ultrasonic wave and converts it into an electrical output for measurement and analysis. The electrical output from the receiving transducer is compared to either the output from a substantially identical wire and crimped connector that is known to be of good quality or it is compared with the electrical input from the transmitting transducer.  FIG. 3 , as shown, depicts the receiving transducer  30  on the exterior of the insulation of the wire to detect the wave. However, in an alternative embodiment (not shown), the receiving transducer may be in direct electrical communication with the wire in order to permit interrogation of the wire between two crimp connectors. 
     As described in U.S. Pat. No. 7,181,942, the ultrasonic wave transmitted into the wire can be launched at the same time and/or by an ultrasonically equipped device used for crimping the wire to a ferrule. For example, a crimped connector  16  can be installed using a RayChem model AP 1377 (M22520/37/01) crimper equipped with an ultrasonic transducer, which launches a shear wave that passes perpendicularly to the wire and the particle displacement is along the wave axis. This causes a longitudinal wave to be launched down the wire axis (i.e., longitudinally). However, this is not a limitation, as there are other means for launching ultrasonic wave modes into the wire. 
     As an ultrasonic wave mode travels along the wire it encounters energy loss mechanisms and/or phase shifts at defect or pathology locations. As the specific ultrasonic wave mode, which is affected by any existing defects or pathologies, passes through the length of wire, the resulting electrical waveform that is detected can be recorded, digitized and/or stored. The waveform may be compared with a waveform from a high quality crimped connector to determine whether the crimped connector is acceptable. Alternatively, or additionally, the system may be designed to make comparisons based on phase shifts and/or attenuation effects encountered in both absolute measurements and in comparison measurements. 
     A capacitive detector designed to differentiate between longitudinal and shear particle displacements may be installed at a predetermined longitudinal distance from the location at which the compressional wave is launched into the wire. As the shear wave, which is affected by any existing pathologies, passes through the length of wire between the transmitter and the detector (ultrasonic wave receiver), the resulting electrical waveform record can be digitized and stored, such as for analysis by a computer algorithm. 
     It should be understood that the illustrated positions of the ultrasonic transmitter and ultrasonic receiver can be reversed, provided that the ultrasonic wave transmitting transducer is positioned in reasonable proximity to the crimped wire connector (i.e., adjacent the crimped wire connector to facilitate launching of the ultrasonic wave into the crimped wire), and the ultrasonic wave receiving transducer is positioned a predetermined distance from the transmitting transducer such that an ultrasonic wave launched into the wire and propagated along the length direction of the wire will pass through the crimped wire connector before being received at the receiving transducer. 
     Physical embodiments include but are not limited to different transducers, different mountings, and different couplings. 
     In the case of an incomplete break (e.g., a nick) the wave is changed. When a wave propagated through a nicked strand is combined with waves propagated through undamaged strands, the phase is shifted. Upon reception, the electrical output from the receiving transducer is phase-compared with the electrical input to the transmitting transducer in, for example, a pulsed phase-locked loop arrangement. The phase shift is indicative of a bend and/or nick pathology or damage. While a nick or bend in a wire strand will result in phase shift, a break in a wire strand will cause a further decrease in amplitude, and hence a further decrease in wave energy. In all cases, the magnitude of the change (phase shift or energy loss) will depend on the size of the defect, the number of affected strands, the strand gauge, and the total number of strands. 
     In the case of insufficient coupling between the terminal of the wire (pigtail) an insufficient signal will be detected. In all cases the frequency dependence of the detected wave also depends upon the transducer mode. Shape and size of the transducer, and the contact asperity pattern. 
     Comparisons may be made by a person using an oscilloscope or can be done by a computer algorithm operating on the digitized information. 
     In another embodiment, this technology is applied to wires that are spliced through a compression mechanism on a terminal block  40   a ,  40   b  ( FIGS. 4 and 5 ). Transducers  20   a ,  20   b  emit an ultrasonic wave which travels through the connecting mechanism  41   a ,  41   b  of the terminal block. An ultrasonic mode passes along the wire  14  and is detected with transducer  30   a ,  30   b  selected to receive the wave mode in the wire. The amplitude of the wave mode of the received wave depends upon asperity contact density and contact pattern between the terminal block  40   a ,  40   b  and the wire  14 . This embodiment allows for determination of a properly tensioned terminal block so that minimum resistance across the connector is achieved and maintained. The technique can be employed during service life to assure no slippage or oxidation/corrosion at the junction between wire and block. 
     While preferred embodiments and example configurations of the invention have been herein illustrated, shown and described, it is to be appreciated that various changes, rearrangements and modifications may be made therein, without departing from the scope of the invention as defined by the appended claims. It is intended that the specific embodiments and configurations disclosed are illustrative of the preferred and best modes for practicing the invention, and should not be interpreted as limitations on the scope of the invention as defined by the appended claims and it is to be appreciated that various changes, rearrangements and modifications may be made therein, without departing from the scope of the invention as defined by the appended claims.