Abstract:
In accordance with the present invention, there is provided a method of automatically verifying the acceptable insertion of at least one Z-pin into a composite laminate. The method comprises the initial step of positioning at least one Z-pin upon the composite laminate. Thereafter, an insertion force is applied to the Z-pin at a first level which is sufficient to commence an insertion process wherein the Z-pin is driven into the composite laminate at a first insertion speed. The insertion force applied to the Z-pin is continuously monitored, with the first insertion speed being reduced to a second insertion speed in response to a monitored increase in the insertion force from a first level to a second level. The application of the insertion force to the Z-pin is discontinued and the insertion process terminated in response to a monitored increase in the insertion force from the second level to a third level. To confirm an acceptable insertion, the reduction from the first insertion speed to the second insertion speed is verified, as is the increase of the insertion force to the third level.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation-in-part of U.S. application Ser. No. 11/158,400 entitled AUTOMATED Z-PIN INSERTION TECHNIQUE USING UNIVERSAL INSERTION PARAMETERS filed Jun. 22, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT  
       [0002]     The invention disclosed in the present application was developed under a contract research and development (CRAD) program funded by the Office of Naval Research (ONR).  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates generally to reinforced composites, and more particularly, to a two-speed insertion process for Z-pinning/joining uncured composite laminates to each other.  
         [0004]     The use of composites as primary structures in aerospace applications is becoming increasingly widespread in the aerospace industry. Traditional composite materials are made up of a resin matrix material and a quantity of two-dimensional fibers, continuous in the X-Y axis direction, but laminated in layers to produce a material thickness. Composite material construction, wherein a fiber material such as a glass fiber, carbon fiber, or aramid fiber is combined with a matrix material, such as thermoplastic or thermoset resins, is an example of a traditional two-dimensional structure.  
         [0005]     Many structural composites, such as structural composite air frames, usually include multiple stiffeners. The stiffeners supply rigidity and stiffness that is required under certain flight load conditions. One typical stiffener is referred to as a hat stiffener. Hat stiffeners, named for their shape, are typically applied to aerospace structural composite components via their skin.  
         [0006]     Historically, composite hat stiffeners were attached to composite skins with conventional mechanical fasteners. In another attachment process sometimes employed, the hat stiffeners were co-cured to the skin of the structural composite material concurrently with the curing with the structural composite material itself. However, in both this process and that wherein the hat stiffeners were mechanically bolted and/or adhesively bonded to the skin, the failure mode typically occurred at the inner hat stiffener to skin surface.  
         [0007]     In order to resolve the occurrences of failure using the aforementioned attachment processes, Z-pinning is now frequently used in the aerospace industry to facilitate the attachment of one or more stiffeners to a composite skin. In this regard, with the development of Z-pins, methods for supporting the Z-pins in a carrier, and methods for inserting the Z-pins into uncured composite materials, the hat stiffeners and skin are able to be joined to each other prior to being cured. Joining composite parts together with Z-pins offers several advantages over conventional mechanical fasteners, such as lighter weight, more even distribution of the load, lowers costs, and co-curing of the two parts. In one currently employed Z-pinning process used in conjunction with hat stiffeners, a Z-pin carrier pre-form is disposed on that surface of the hat stiffener which is to be secured to the skin of the underlying structural composite material or laminate. The pre-form typically comprises contiguous layers of low and high density foam having a multiplicity of Z-pins embedded therein. The Z-pins are forced from the carrier pre-form through the hat stiffener and into the underlying laminate using a device such as a hydraulic press or an ultrasonic device (e.g., an ultrasonically excited horn) which uses high frequency energy to vibrate the Z-pins within the carrier pre-form to force them through the stiffener and into the underlying laminate.  
         [0008]     For purposes of achieving greater efficiencies and economies in the Z-pinning process, it is highly desirable to facilitate the insertion of the Z-pins automatically through the use of a robot. However, attempts at automating the Z-pinning process have proven challenging due to the need for special techniques to accommodate the many variables involved with the Z-pinning process. More particularly, the key variables for automated insertion are insertion speed, insertion force, material age, material thickness, amount of laminate hot debulking, amplitude of the excitation of the horn (when an ultrasonic horn is used), the load bearing capability of the Z-pins, and insertion time. Inserting the Z-pins too fast results in excessive force being applied to the pins, thereby crushing them, or causing them not to penetrate completely through the parts being joined. Inserting the Z-pins too slowly takes excessive time thereby not achieving a reasonable return on investment, or causes the pre-form to overheat which creates a potential for a fire hazard. When an ultrasonic horn is used, increasing the amplitude of the horn oscillation allows for faster insertion, but increases the risk for transferring too much energy into the pre-form causing over-insertion of the Z-pins and melting of the pre-form. Moreover, one set of conditions may be fine for a new material and a thin total thickness, but not optimal for an aged material (e.g., a thirty day age material) that is of a maximum thickness. Indeed, since many of the aforementioned variables interact in a non-linear fashion, it is extremely difficult to predict insertion success with any given combination. As an additional restriction, the insertion time is required to be fast enough to generate a good return on investment for the process. Thus, for automated Z-pin insertion in a production environment, there exists a need in the art for a single set of insertion parameters (universal parameters) which accommodate all the variations likely to be encountered within the specifications.  
         [0009]     The need for a single set of insertion parameters for use in an automated Z-pin insertion process is addressed by Applicant&#39;s co-pending U.S. application Ser. No. 11/158,400 entitled AUTOMATED Z-PIN INSERTION TECHNIQUE USING UNIVERSAL INSERTION PARAMETERS filed Jun. 22, 2005, the disclosure of which is incorporated herein by reference. However, with currently known manual insertion processes, follow-up manual inspection steps are still typically required to verify that the Z-pins were inserted to the full, proper depth. More particularly, in manual inspection processes as currently practiced, the height of the Z-pin carrier pre-form is measured upon the completion of the insertion process through the use of a simple gage to determine if the Z-pins were pressed far enough into the composite laminate to reach full depth. The definition of full depth in this case means that the Z-pins have fully penetrated the composite laminate and reached the bond tool surface. Following cure, an additional visual check is performed to verify that the Z-pins did in fact penetrate the composite laminate ply closest to the tool surface. It is contemplated that a similar manual inspection process may be implemented in relation to the automated Z-pin insertion process/system described in Ser. No. 11/158,400 to verify that the Z-pins were inserted to full depth. In this regard, in the automated insertion process/system, new gages may need to be designed and fabricated for inspectors to perform this inspection process. Thus, there exists a need for a technique which may be used in conjunction with an automated Z-pin insertion process/system for automatically performing the required full depth inspection and alerting the robot operator should a non-acceptable insertion occur. The present invention addresses this need in a manner which will be described in more detail below.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     In accordance with the present invention, there is provided a system for facilitating a two speed insertion process for Z-pinning/joining uncured composite laminates to each other. The insertion process of the present invention employs the use of an ultrasonic horn which is used to deliver ultrasonic energy to the Z-pins within a Z-pin carrier pre-form. In the insertion process, the insertion speed is changed to a lower insertion speed based on the force resistance encountered during insertion, providing a tactile feedback system. No operator intervention is needed as the system adapts to the prevailing conditions. By using this two speed process, it is possible to insert Z-pins into a wider variety of composite laminate conditions that would be impossible using single speed insertion techniques.  
         [0011]     The insertion process of the present invention effectively varies one or more of the above-described variables or parameters based on conditions that exist during the Z-pin insertion process. The process of the present invention effectively ignores the initial conditions or parameters of material age and thickness, in favor of monitoring the force applied to drive the Z-pins into the laminate and using this information to vary the insertion speed. In one embodiment of the present invention, the Z-pins are initially inserted at a rate of 0.25 inches per second, with the insertion speed immediately being dropped to 0.050 inches per second when the insertion force reaches forty (40) pounds. When the insertion force reaches fifty (50) pounds, it is assumed that the Z-pins are all the way through the laminate and contacting a hard tool surface (or barrier sheet).  
         [0012]     As part of the insertion process of the present invention, the moment the ultrasonic horn contacts the pre-form is detected, with the readings for the first ten percent of the insertion being ignored to prevent false triggering. Additionally, production system safety conditions are also monitored as a back-up to the possibility that the fifty pound force trigger is not recognized during the insertion process. Other safety features which may be employed into the process of the present invention to terminate the insertion process include the length of time of insertion and the maximum distance traveled by the ultrasonic horn. If the maximum preset time is reached, the insertion is terminated. Similarly, if the maximum preset depth is reached the insertion is also terminated. One additional safety feature may involve remotely monitoring the temperature of the insertion horn. If the horn temperature exceeds a given threshold, the insertion process is stopped following the current insertion, and the horn allowed to cool before proceeding with further insertions.  
         [0013]     Further in accordance with the present invention, there is provided a technique which may be used in conjunction with the automated insertion process described above to automatically perform a required full depth inspection and alert the robot operator should a non-acceptable insertion occur. As indicated above, the automated insertion process of the present invention employs the use of a set of universal insertion parameters, which in turn facilitate the implementation of a two-speed insertion process based on certain insertion force thresholds. The automated inspection technique of the present invention automatically checks to see if the insertion speed has dropped to the requisite lower level, and further whether the requisite final insertion force was achieved during the insertion process. These particular parameters are automatically checked by analyzing data as it is generated during the insertion process. More particularly, the automated inspection technique relies on the principle that an acceptable insertion is always produced when the insertion speed is reduced from the rate of 0.25 inches per second by achieving the forty pound insertion force threshold and the fifty pound insertion force limit threshold is also reached. For unacceptable Z-pin insertions, the first condition may be met, but the two conditions are never met. These, as well as other features of the present invention, will be described in more detail below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein:  
         [0015]      FIG. 1  is a cross-sectional view of an exemplary Z-pin carrier pre-form having a multiplicity of Z-pins embedded therein;  
         [0016]      FIG. 1A  is a top perspective view of the Z-pin carrier pre-form shown in  FIG. 1 ;  
         [0017]      FIG. 2  is a cross-sectional view illustrating the manner in which carrier pre-forms are positioned upon a hat stiffener for securing the hat stiffener to an underlying laminate through the use of the insertion system and process of the present invention;  
         [0018]      FIG. 2A  is an enlargement of the encircled region  2  shown in  FIG. 2 , further illustrating a portion of the ultrasonic horn of the insertion system and its orientation relative to one of the pre-forms during the insertion process;  
         [0019]      FIG. 3  is a schematic depiction of the various components included in the insertion system used to facilitate the insertion process of the present invention;  
         [0020]      FIGS. 4A and 4B  are side and end views, respectively, of the ultrasonic horn of the insertion system used to facilitate the insertion process of the present invention;  
         [0021]      FIG. 5  is a graphical depiction illustrating the interrelationship between insertion force and insertion speed achieved through the use of the insertion process of the present invention; and  
         [0022]      FIGS. 6A-6E  are graphical depictions illustrating the interrelationship between insertion force and insertion speed as it pertains to acceptable and unacceptable Z-pin insertions facilitated through the use of the insertion process of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same,  FIGS. 1 and 1 A provide cross-sectional and top perspective views, respectively, of an exemplary Z-pin carrier pre-form  10  which may be used in the Z-pinning process of the present invention as will be described in more detail below. The carrier pre-form  10  comprises an upper layer  12  of low density foam and a lower layer  14  of high density foam which is contiguous with the upper layer  12 . In this regard, the top surface of the lower layer  14  is abutted against the bottom surface of the upper layer  12 . Covering the top surface of the upper layer  12  is a layer  16  of polyolefin. The layer  16  is in turn covered by a layer  18  which is fabricated from paper. As such, the layer  16  is disposed between the layer  18  and the upper layer  12 .  
         [0024]     In addition to the layers  12 ,  14 ,  16 ,  18 , the carrier pre-form  10  includes a multiplicity of Z-pins  20  which are embedded within the upper and lower layers  12 ,  14 . More particularly, the Z-pins  20  extend generally perpendicularly between the top surface of the upper layer  12  (which is covered by the layer  16 ) and the exposed bottom surface of the lower layer  14 . The Z-pins  20  also preferably extend in spaced, generally parallel relation to each other, and may be embedded within the upper and lower layers  12 ,  14  in any one of a multiplicity of prescribed patterns. Thus, the particular pattern or arrangement of Z-pins  20  as is shown in  FIG. 1  is exemplary only in that the number, spacing and overall arrangement of the Z-pins  20  within the upper and lower layers  12 ,  14  is application specific. One commonly used material for the Z-pins  20  is graphite, with the Z-pins  20  typically being carbon fibers cured in a bismaleimide resin. As is seen in  FIG. 1A , the carrier pre-form  10  has a generally rectangular configuration with a length L of approximately 12 inches, a width W of approximately 1.1 inches, and a height H of approximately 0.5 inches. However, those of ordinary skill in the art will recognize that the configuration of the carrier pre-form  10  as shown in  FIG. 1A  is also exemplary only in that such carrier pre-form  10  may be provided in any one of a multiplicity of different configurations depending on the particular application. An exemplary carrier pre-form  10  is provided under the trademark Z-Fiber™ from Aztex, Inc.  
         [0025]     As indicated above, the Z-pinning system and process of the present invention is suited for use in joining uncured composite laminates to each other. Referring now to  FIGS. 2 and 2 A, a typical application for the insertion system and process of the present invention is the attachment of a composite hat stiffener  22  to an underlying composite laminate  24 . As is shown in  FIG. 2 , the hat stiffener  22  includes an elongate, enlarged central portion  26 , and a pair of flange portions  28  which are integrally connected to and extend along respective sides of the central portion  26 . Each flange portion  28  has a bottom surface which extends along and in contact with the top surface of the laminate  24 . In addition to the bottom surface, each flange portion  28  includes a top surface which extends at a slight angle relative to the top surface of the laminate  24 . The angle of the top surface of each flange portion  28  relative to the top surface of the laminate  24  as shown in  FIGS. 2 and 2 A is approximately twelve degrees. Though the Z-pinning system and process of the present invention will be described below specifically in relation to the attachment of the hat stiffener  22  to the laminate  24 , those of ordinary skill in the art will recognize that such system and process is suited for use in securing any composite laminate structures to each other, and is not limited to use in securing the hat stiffener  22  to the laminate  24 .  
         [0026]     Referring now to  FIG. 3 , there is provided a schematic depiction of the various components included in the insertion system  29  used to facilitate the Z-pinning process of the present invention. In a preferred embodiment, the system  29  includes an ultrasonic horn  30  which is shown with particularity in  FIGS. 4A and 4B . The ultrasonic horn  30  includes a converter  32  which is operatively coupled to a booster  34 . The booster  34  is in turn operatively coupled to an insertion horn  36 , the distal end of which defines a generally planar anvil  38 .  
         [0027]     In addition to the ultrasonic horn  30 , the system  29  includes a load cell  40  which is disposed adjacent to the converter  32  of the ultrasonic horn  30  and is in electrical communication with a programmable logic controller (PLC)  42 . The PLC  42  is also in electrical communication with an ultrasonic power source  44 , which in turn electrically communicates with the converter  32  of the ultrasonic horn  30 . Further, the PLC  42  is outfitted with a HMI interface  46  which in turn communicates with a robot controller  48 . The robot controller  48  electrically communicates with a multi-axis robot  50  which is operatively coupled to the ultrasonic horn  30  in a manner wherein the robot  50  is able to control and regulate the movement of the ultrasonic horn  30  relative to the composite laminates which are to be secured to each other through the use of the insertion/Z-pinning process of the present invention.  
         [0028]     Referring again to  FIGS. 2 and 2 A, in using the system  29  depicted in  FIG. 3  to facilitate the attachment of the hat stiffener  22  to the laminate  24 , it is contemplated that carrier pre-forms  10  will initially be positioned upon the top surfaces of the flange portions  28  of the hat stiffener  22 . Next, the robot  50  maneuvers a robot end effector of the robot  50  to a prescribed location or position relative to one of the carrier pre-forms  10 . Disposed in the end effector are the ultrasonic horn  30 , a single axis servo motor or drive  54 , and drivers for the PLC  42 . More particularly, the anvil  38  of the ultrasonic horn  30  is maneuvered to a first position P 1  (shown in  FIG. 2A ) which is approximately 0.200 inches above one of the carrier pre-forms  10 . After the end effector has reached this initial position, the robot controller  48  then “freezes” the position of the robot  50  and passes control of the insertion process to the PLC  42 . The PLC  42  communicates with the single axis drive  54  of the end effector in a manner causing the drive  54  to move the anvil  38  to a second position P 2  which is approximately 0.100 inches above the adjacent carrier pre-form  10 . The movement of the anvil  38  to the second position P 2  triggers the start of the insertion process of the Z-pins  20  from within the carrier pre-form  10  through the corresponding flange portion  28  of the hat stiffener  22  and into the underlying laminate  24 .  
         [0029]     As the Z-pinning process commences, the ultrasonic horn  30  is moved downwardly along a vertical axis Z (shown in  FIG. 2A ) by the end effector (and in particular the drive  54 ) such that the anvil  38  comes into direct contact with a portion of the carrier pre-form  10 . As the ultrasonic horn  30  is moved toward the carrier pre-form  10 , the moment that the anvil  38  touches the carrier pre-form  10  and approximately a three pound force is measured by the load cell  40 , ultrasonic energy is turned on and the insertion process continues. The downward movement along the axis Z is continued so as to cause the anvil  38  to exert/maintain downward pressure to those Z-pins  20  of the carrier pre-form  10  which are positioned directly below the anvil  38 . As will be recognized, the combination of mechanical motion (i.e., the downward movement of the ultrasonic horn  30  along the axis Z) and ultrasonic energy generated by the ultrasonic horn  30  effectively drives the Z-pins  20  from the carrier pre-form  10  into and through the hat stiffener  22 . In this regard, during the Z-pin insertion process, the force applied to the carrier pre-form  10  by the anvil  38  to drive the Z-pins  20  through the corresponding flange portion  28  of the hat stiffener  22  and into the underlying laminate  24  is monitored by the load cell  40  which, as indicated above, is in electrical communication with the PLC  42 . The data transmitted to the PLC  42  by the load cell  40  is used to vary the insertion speed of the Z-pins  20 . As will be recognized, the insertion speed corresponds to the rate of travel of the ultrasonic horn  30 , and hence the anvil  38 , downwardly along the axis Z, such rate of travel be governed by the drive  54  which is controlled by the PLC  42 .  
         [0030]     In accordance with one embodiment of the Z-pinning/insertion process of the present invention, the ultrasonic horn  30  is actuated downwardly along the axis Z by the drive  54  such that the anvil  38  acts against certain ones of the Z-pins  20  of the adjacent carrier pre-form  10  in a manner causing them to be initially inserted through the corresponding flange portion  28  and into the underlying laminate  24  at a rate of approximately 0.25 inches per second. The insertion rate of the Z-pins  20  at approximately 0.25 inches per second typically takes place over a first distance D 1  which is shown in  FIG. 2A .  
         [0031]     When the data transmitted by the load cell  40  to the PLC  42  indicates that the amount of insertion force being applied by the ultrasonic horn  30  to the Z-pins  20  reaches approximately forty pounds, the downward rate of travel of the ultrasonic horn  30  along the axis Z by the drive  54 , and hence the insertion speed, is immediately dropped to approximately 0.050 inches per second. The insertion rate of the Z-pins  20  at approximately 0.050 inches per second typically takes place over a second distance D 2  which is also shown in  FIG. 2A . At this time, the load cell  40  continues to transmit data to the PLC  42  representative of the level of downward force being applied to the Z-pins  20  within the carrier pre-form  10  by the anvil  38 . When the force reaches a level of approximately fifty pounds, it is assumed that the Z-pins  20  have been downwardly driven from the upper and lower layers  12 ,  14  of the carrier pre-form  10 , through the corresponding flange portion  28  of the hat stiffener  22 , and all the way through the underlying laminate  24  into contact with a hard tool surface or barrier sheet  56 . The interrelationship between the insertion force and insertion speed is graphically depicted in  FIG. 5 .  
         [0032]     The variability in the insertion speed as described above in relation to the Z-pinning/insertion process of the present invention is regulated by servo loop software  52  which is programmed into the PLC  42 . The servo loop software  52  is adapted to regulate the function of the drive  54 , and precisely controls/regulates the movement of the ultrasonic horn  30  and hence the anvil  38  upwardly and downwardly along the axis Z. After completing the insertion, the PLC  42  passes control back to the robot controller  48  for positioning the end effector of the robot  50  for the next insertion. Servo loop feedback  56  transmitted to the servo loop software  52  by the servo motor  54  is, in conjunction with the data transmitted to the PLC  42  and hence the servo loop software  52  by the load cell  40 , used to facilitate the above-described two-speed insertion process and to provide certain safety features which will be discussed in more detail below. The servo loop feedback  56  and data transmitted by the load cell  40  collectively provide a tactile feedback mechanism which effectively regulates the insertion process in the above-described manner.  
         [0033]     Further in accordance with the Z-pinning/insertion process of the present invention, it is contemplated that the Z-pin insertion system  29  shown in  FIG. 3  may be outfitted with components which allow for the detection of the moment when the anvil  38  defined by the insertion horn  36  contacts the pre-form  10 . In this regard, the servo loop software  52  programmed into the PLC  42  may be adapted to ignore the readings (i.e., the data transmitted from the load cell  40  and/or the servo loop feedback  56 ) for approximately the first ten percent of the insertion of the Z-pins  20  to prevent false triggering. It is also contemplated that certain production system safety conditions may be monitored as a back-up in the event the fifty pound force trigger which would otherwise terminate the insertion process is not recognized by the PLC  42 . Other safety features which may be integrated into the system  29  (e.g., programmed into the PLC  42 ) to terminate the insertion process include the length of time of insertion and the maximum distance along the axis Z traveled by the ultrasonic horn  30  and hence the anvil  38 . In this regard, if a maximum preset time is reached, the insertion may be terminated. Similarly, if a maximum preset depth is reached as dictated by the travel distance of the anvil  38  along the axis Z, the insertion may also be terminated.  
         [0034]     Still further, it is also contemplated that the temperature of the insertion horn  36  may be monitored as an additional safety feature. In this regard, if the temperature of the insertion horn  36  exceeds a given threshold, the insertion process for the Z-pins  20  may be stopped following the current insertion, with the insertion horn  36  being allowed to cool before proceeding with further insertions. The insertion graph depicted in  FIG. 5  may also be used as a record that the Z-pins  20  fully penetrated the flange portions  28  of the hat stiffener  22  and the underlying laminate  24 , thereby eliminating any need for manual inspection by an inspector. A software program could also be written and programmed into the PLC  42  to automatically determine whether all the Z-pin insertions were good (i.e., fully penetrated), with a message being sent to the operator that all the insertions were good, or an error message being recorded for later review should any of the insertions not meet the software criteria of the servo loop software  52 . As will be recognized fully completing the process of Z-pinning the hat stiffener  22  to the laminate  24  would entail programming the PLC  42  to actuate the drive  54  of the end effector as needed to cause the anvil  38  of the ultrasonic horn  30  to sequentially act against all of the Z-pins  20  of all of the carrier pre-forms  10  in a manner which ultimately results in all of the Z-pins  20  being advanced through the flange portions  28  of the hat stiffener  22  and into the underlying laminate  24 .  
         [0035]     Further in accordance with the present invention, there is provided a technique which may be used in conjunction with the automated insertion process described above to automatically perform a required full depth inspection and alert the operator of the robot  50  should a non-acceptable Z-pin insertion occur. As explained above, the automated insertion process of the present invention employs the use of a set of universal insertion parameters, which in turn facilitate the implementation of a two-speed insertion process based on certain insertion force thresholds. The automated inspection technique of the present invention automatically checks to see if the insertion speed has dropped from the initial rate of approximately 0.25 inches per second to the requisite lower level of approximately 0.050 inches per second attributable to the insertion force applied by the ultrasonic horn  30  to the Z-pins  20  reaching about forty pounds, and further whether the requisite final insertion force of about fifty pounds was achieved during the insertion process. These particular parameters are automatically checked by analyzing data as it is generated during the insertion process. As explained above, such data is generated by the load cell  40  and transmitted to the PLC  42 .  
         [0036]     As such, the automated inspection technique of the present invention relies on the principle that an acceptable insertion is always produced when 1) the insertion speed is reduced from the initial rate of approximately 0.25 inches per second to the requisite lower level of approximately 0.050 inches per second, and 2) the insertion force limit threshold of approximately fifty pounds is also reached. For unacceptable Z-pin insertions, the first condition (1) may be met, but both conditions (1 and 2) are never met. The interrelationship between insertion force and insertion speed as it pertains to acceptable and unacceptable Z-pin insertions using the automated inspection technique of the present invention in graphically depicted in  FIGS. 6A-6E . In this regard,  FIGS. 6A and 6D  depict interrelationships which are indicative of acceptable insertions, with  FIGS. 6B, 6C  and  6 E depicting interrelationships which are indicative of unacceptable insertions. It is contemplated that the PLC  42  will be programmed to provide a signal which alerts the operator of the robot  50  that an unacceptable insertion has occurred, and/or provide an alert message in the insertion data generated by the insertion system  29  for quality purposes. With the implementation of the automated inspection technique of the present invention, it is contemplated that manual inspections for full depth insertion of the Z-pins  20  may be eliminated from the production process, thus providing substantial cost savings.  
         [0037]     This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.