Abstract:
A wire manipulator includes a body with a jack for moving clamping arms to hold a wire extremity insert the extremity in an alveolus of a connector. The insertion force is sensed by a force sensor in the clamping arms and is compared with a reference force to stop the insertion process to avoid damage to the wire, the connector and the manipulator.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a wire manipulator, a method for inserting an extremity of a conductive wire section in an alveolus on a connector, and an insertion machine incorporating the manipulator.  
           [0002]    The technical sphere of the invention concerns the production of automatic machines for preparing bundles of electric cables. The U.S. Pat. No. 5,615,478 describes various types of pliers for manipulating electrically conductive wire sections and the integration of the latter in a wire bundle preparation machine, as well as a method and a device for inserting wire extremities in connector alveoli or similar electric components.  
           [0003]    The EP 902 509 patent document shows a system for controlling the quality of crimping of a cable eye stiffener at the extremity of an electric wire section which makes use of a force sensor comprising two piezoelectric ceramic disks, the force sensor being mounted on a crimping press between a crimping tool support and a slide driven in an alternative movement of translation by a rotary motor equipped with a cam so that the sensor is sensitive to the crimping force exerted by the press on the cable eye stiffener to be crimped.  
           [0004]    The use of this type of force sensor generally requires calibration so as to be able to compensate any observed defects of precision and linearity, which complicates the practical use of these sensors. This drawback is particularly sensitive in a case where it is desired to measure the force of inserting a wire extremity in an alveolus, given the fact that an insertion manipulator operates on extremely small series of identical successive insertions and frequently an insertion manipulator successively provokes the insertions of extremities provided with different cable eye stiffeners for which different insertion forces need to be controlled. On the other hand, a crimping press generally carries out a large number of identical crimping operations.  
           [0005]    Piezoelectric ceramic sensors, whose sensitivity is about one or several hundreds of pico coulomb/Newtons, if they are adapted to measuring a crimping force—which is generally more than 2000 Newtons—are ill-adapted to measuring an insertion force—which is generally situated inside a range of between 1 and 100 Newtons.  
           [0006]    In addition, the short response time of this type of dynamic force sensor renders it sensitive to the inertia forces resulting from the established accelerations of the mobile elements of the crimping press to which it is linked. Now the search for high operating rates provokes significant accelerations and as a result significant inertia forces which interfere with the measurement to be made.  
           [0007]    The signals delivered by the piezoelectric sensors are in addition frequently disturbed when the elements—such as connectors or conductive wires—for connecting the sensor to an electronic device for processing the signals delivered by the sensor—such as a load amplifier—are subjected to movements. In fact, these movements can generate parasitic electric loads, particularly via a triboelectric effect. This is the reason it is awkward to use these sensors mounted on mobile machine elements and assumes particular importance since the results of the force measurement are used as a criterion for evaluating the quality of the operation (or insertion) concerned.  
         SUMMARY OF THE INVENTION  
         [0008]    The aim of the manipulator and method according to the present invention is to provide these improved clamps, methods and insertion devices.  
           [0009]    One objective of the present invention is to provide a reliable inexpensive system for the systematic control of the quality for inserting a wire in an alveolus of a component when the extremity of the wire has been previously rendered integral—by crimping or other means—with possibly a cable eye stiffener. After a large number of ineffective attempts, it has been surprisingly found that in accordance with the apparatus and method of the present invention it is possible to use this type of sensor to measure the insertion force of a wire extremity in an alveolus of a connector with sufficient measurement reliability so that the results of this measurement are used to control insertion quality.  
           [0010]    According to one characteristic of the present invention, a wire manipulator is provided comprising a body and a wire support element mounted mobile with respect to the body in which the wire support element comprises a sensor sensitive to a force exerted by this element.  
           [0011]    The present invention concerns in particular a clip for inserting an extremity of a conductive wire into the alveolus of a connector which comprises a body and an arm equipped with a clamping jaw for holding the wire and mounted mobile with respect to the body in which the arm comprises a piezoelectric sensor for measuring an insertion force.  
           [0012]    Because the sensor is integrated in the mobile element of the clip (of the manipulator) and is accordingly situated at the closest to the wire section gripping jaws, the sensitivity of the sensor to the force required to insert the extremity in an alveolus is increased, whereas the sensitivity of the sensor to the parasitic forces resulting in particular from the inertia effects and the mechanisms for moving and opening the clip (of the manipulator) is at the same time reduced.  
           [0013]    The sensor preferably comprises two washers—or thin plate or disk-shaped pieces—made of a polarised ceramic material which are identical, mounted side by side and compression-prestressed between two parallel faces of two pieces forming part of the arm or manipulator. This makes it possible to embody a simple compact sensor in which each washer is sensitive to the compression forces of the washer and the axial extension forces of the washer, this thus making it possible to measure an insertion force (conventionally positive), as well as an opposite direction (and sign) force. This then makes it possible to measure a traction force exerted on the wire after it has been inserted so as to ensure that the insertion is correctly and fully effected, especially in the case of insertion in an alveolus of a cable eye stiffener equipped with locking tongues.  
           [0014]    So as to favor the sensitivity of the sensor to forces exerted along an axis distinct from the median axis of the two sensitive elements, a mounting is preferably provided in opposition to the latter. Thus, the sensitivity of the sensor to forces moved out of centre (by reference to this median axis) is increased, especially to forces exerted close to a longitudinal extremity of the arm or wire support element which result in a torque—or moment—applied to the sensor.  
           [0015]    It is advantageous to carry out this mounting in opposition by having the two sensitive elements head-to-tail and by providing an equipotential conductor on each of the faces of the pieces surrounding the sensitive elements, a first equipotential connecting the positive pole of a first element sensitive to the negative pole of a second sensitive element, and a second equipotential connecting the negative pole of said first sensitive element to the positive pole of said second sensitive element, each equipotential being preferably respectively connected by a coaxial conductor to one input of a charge amplifier which converts the charge variations of the sensor into a voltage or current, this making in particular it possible to reduce the number of electric connections upstream of the amplifier and accordingly to limit disturbances of the measuring signal likely to result from a stray current resulting from these connections.  
           [0016]    Alternatively, in certain cases, it is possible to provide this mounting in opposition for adding the sensitivities of the two sensitive elements without inverting the polarities of the two elements placed side by side. However, in this case, additional electric connections need to be provided.  
           [0017]    Moreover, in the case where the insertion axis was merged with the median axis of the sensitive elements, the mounting in opposition would be replaced by a mere placing in parallel or even a single sensitive element could be used.  
           [0018]    By using sensitive elements pierced with a central orifice (washer-shaped), it is possible to provide an elongated linking element such as a screw, which extends through the orifice, is used to fix all the portions of the arm or support element extending on both sides of the sensor, and which is also used to stress the sensitive element. So as to allow the sensitive element to dilate, for this linking element, it is recommended to select a material and a section so that the stiffness of this link is clearly less than the stiffness of the sensitive element. This can in particular be embodied by a screw or steel rod whose section is smaller than the support surface (and/or the cross section) of the washer, this linking element then forming a return spring during an axial extension of one of the sensitive elements of the sensor resulting from the application of a moved out of center force on the arm (or wire support element).  
           [0019]    When the clamp or manipulator comprises two arms or wire support elements which are generally mounted mobile with respect to the body—it is preferable to equip each of them with a force sensor. Thus, by adding the measuring signals, this makes it possible to increase the sensitivity of the unit and also, via an OR operation replacing summing and applied to the two measuring signals to benefit from a redundancy of the sensors increasing the reliability of the insertion control system. In addition, the use of several sensitive elements, in particular at least three or four sensitive elements, makes it possible by means of differential measurements to determine several components of the force and thus make it possible to determine its direction.  
           [0020]    So as to limit the disturbances of the signal for measuring the insertion force resulting from accelerations of the clamp or manipulator, it is important that that the weight of the portion “suspended from the sensor” of the arm of support element is as light as possible, and in addition to this effect, it is advantageous to bring the centre of gravity of this portion close to the median axis of the sensitive elements until they are made to coincide, if possible.  
           [0021]    So as to limit disturbances of the measuring signal resulting from deformations of the cable connecting the sensor to an amplifier (charge converter/voltage or current), it is preferable to have this amplifier close to the sensor, especially on the body of the clamp or manipulator.  
           [0022]    In addition it is to be noted that, in an insertion method according to the invention, measuring and control is made in real time during the insertion of a cable eye stiffener or wire extremity in an alveolus of a connector, the force transmitted by at least one portion of an arm or support element of the cable eye stiffener, and when it is detected that the measuring result departs by a reference outside a predetermined maximum deviation range, an order is given to stop an element from moving the clamp or the manipulator so as to stop the insertion procedure, which avoids damaging the connector and/or the cable eye stiffener.  
           [0023]    Said piezoelectric ceramic sensor is preferably used whose output is connected to a load amplifier and the input and/or output of the amplifier is reset to zero before each insertion operation so as to eliminate any residual charges likely to result from the preceding insertion operation and/or likely to result from one or several movements for grasping or approaching the cable eye stiffener or wire extremity.  
           [0024]    For a plurality of successive insertion operations, it is preferable to record a plurality of insertion force data measured for each operation in or on a data storage of a computer so as to calculate and/or have available statistical data representative of insertion quality and its time evolution.  
           [0025]    According to another characteristic of the invention, the machine for inserting cable eye stiffeners or wires in connector alveoli comprises:  
           [0026]    a clamp or manipulator according to the invention;  
           [0027]    a connector support(s);  
           [0028]    at least one activator so as to move the clamp (the manipulator) towards a connector fixed on said connector support; and  
           [0029]    means to control the movement of the clamp (of the manipulator) by the activator according to a force measuring signal delivered by the sensor integrated in the clamp (manipulator). 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0030]    The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:  
         [0031]    [0031]FIG. 1 is a schematic perspective view of an insertion machine in accordance with the present invention;  
         [0032]    [0032]FIG. 2 is an enlarged perspective view of the clamp (manipulator) shown in FIG. 1;  
         [0033]    [0033]FIG. 3 is an exploded perspective view of the clamp shown in FIG. 2;  
         [0034]    [0034]FIG. 4 is a front elevation view of the clamp shown in FIGS. 2 and 3 with two arms ended at their lower extremity by clamping jaws or jaws for seizing a wire section;  
         [0035]    [0035]FIG. 5 is a side elevation view of the clamp shown in FIGS.  2  to  4  showing a load amplifier connected to the force sensor by a conductive wire;  
         [0036]    [0036]FIG. 6 is a graph illustrating the variations of the insertion force (on the ordinate) according to the relative position (on the abscissa) measured along an insertion axis of the extremity of a wire section (or cable eye stiffener crimped to this extremity) with respect to an alveolus of a connector;  
         [0037]    [0037]FIG. 7 is a schematic view of a clamp similar to that shown in FIGS.  2  to  5  with the mounting of two washers made of a piezoelectric ceramic material between the portions of an arm of the clamp; and  
         [0038]    [0038]FIG. 8 is a circuit schematic illustrating the main components of the means for measuring a force via the processing of signals delivered by two pairs of piezoelectric elements respectively integrated with the two mobile arms of a clamp, such as the one shown in FIGS.  2  to  7 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0039]    With reference in particular to FIG. 1, an insertion machine  1  has been specially designed so as to insert a cable eye stiffener  2  crimped at an extremity  3  of a wire section  4  (partially shown) in one of the alveoli  5  of a connector  6 .  
         [0040]    To this effect, the machine  1  includes a connector support  7  mounted mobile with respect to a base (not shown) according to a vertical movement of translation direction shown by an arrow  8  and a movement of rotation shown by a double-headed arrow  9  along a spindle axis  10 , the spindle axis  10  being parallel to longitudinal axes of the alveoli  5 . The insertion of the cable eye stiffener  2  in the alveolus  5  is effected via an insertion movement by translation along the longitudinal axis of this alveolus, such as an axis  11 .  
         [0041]    To this effect, the cable eye stiffener  2  and the extremity  3  are kept approximately aligned during this insertion movement with the alveolus axis  11  by a pair of jaws  12  and  13  (FIG. 2) respectively provided at lower extremities of a pair of arms  14  and  15  of a wire manipulator such as an insertion clamp  16  which jaws squeeze the extremity  3 .  
         [0042]    The insertion results from a movement indicated by a double-headed arrow  17  along the axis  11  of the clamp  16  holding the wire. To this effect, the clamp is mounted mobile with respect to a clamp support  18  along this direction  17  and along a direction indicated by a double-headed arrow  19  orthogonal to the directions  8  and  17 .  
         [0043]    So as to ensure that the force for inserting the cable eye stiffener in the alveolus remains within predetermined limits, the movement  17  for bringing closer together the clamp  16  and the connector  6  under the action of a activator (such as a motor M shown in FIG. 8) is carried out under the control of an electronic signal and data processing unit (UC shown in FIG. 8) according to firstly force measuring signals and secondly signals for measuring the position of the clamp along the axis  11  delivered to the unit UC by a position sensor C (FIG. 8).  
         [0044]    To this effect, the unit UC may comprise a memory (or other data support) in which for each type of alveolus/cable eye stiffener pairing a plurality of data is recorded corresponding to force nominal values (reference) or ranges of force nominal values in the form of tables or graphs, such as the one shown in FIG. 6, with which the force measurements are compared during an insertion cycle. These force nominal values can be obtained by the force measurement made by the sensor integrated with the clamp by means of “trial and error” during the preparatory cycles carried out in conditions representative of the actual insertion conditions.  
         [0045]    The wire manipulator or clamp  16  (FIGS.  2  to  5  and  7 ) comprises a body  20  having two portions: a rear portion  21  and a front portion  32 . The rear portion  21  forms a hollow body (cylinder) of a jack used for closing the jaws  12  and  13  of the clamp. To this effect, the portion  21  has formed therein a bore  22  in which a piston  23  is mounted sliding along a longitudinal axis  24  of the body  20  and of the clamp  16 . This axis  24  is parallel to the axis  11  according to which the jaws  12  and  13  squeeze the extremity  3  of the wire  4 . Two couplings  25  connect this jack to a pneumatic compressed air feed circuit (not shown). A longitudinal extremity  26  of the piston  23  is profiled so as to form two cams  27  respectively supported on two blocks  28  and  29  respectively connected with the two mobile arms  14  and  15  of the clamp  16 . A return spring  30  extending along an axis  31  keeps the blocks  28  and  29  spaced from each other when the pneumatic jack  22  and  23  has not been activated. The front portion  32  of the body  20 , which is rigidly fixed to the rear portion  21 , shelters the front portion of the piston  23  and supports a spindle shaft (not shown) coaxial with the axis  31  and orthogonal to the axis  24  on which the blocks  28  and  29  are mounted sliding so as to enable the jaws  12  and  13  to be brought together or moved apart under the action of the jack  22  and  23  and of the spring  30 .  
         [0046]    As shown in particular in FIGS.  2  to  4 , the clamp  16 , and in particular its elements  14 ,  15 ,  28  and  29  move in translation along the spindle axis  31  and are approximately symmetrical with respect to a median longitudinal plane  33 .  
         [0047]    With reference in particular to FIGS. 3 and 7, the clamp  16  has two mobile wire clamping units each including one of the arms  14  and  15 , one of the sliding blocks  28  and  29  respectively, and a force sensor  34  inserted and stretched between the arm and the associated sliding block.  
         [0048]    Each of the sensors  34  comprises two identical ring-shaped elements  35  embodied in a lead titanate and zirconate-based ceramic material. An electrode is formed on each of the two annular flat faces of each element  35  corresponding to the positive pole and negative pole of the polarised element.  
         [0049]    Each sensor  34  also comprises two approximately identical rectangular plates  36  and  37 . Each plate is in support on two coplanar electrodes respectively provided on the annular faces of the two elements  35 . The plates are at least in part embodied in an electrically nonconducting material, and an electrically conductive coating is provided on an internal face  38  and  39  of each plate  36  and  37  respectively so as to form an equipotential connecting the electrodes of the elements on which these equipotentials rest. Each plate  36  and  37  and its equipotential can be embodied in the form of a printed circuit.  
         [0050]    Each equipotential is respectively connected to a connection terminal  40  and  41  of a terminal unit  42  (FIG. 5) of the sensor  34 . A coaxial cable  43  connects these terminals to the inputs of a load amplifier  44  fixed to the rear portion  21  of the body  20  of the clamp  16  (FIG. 5).  
         [0051]    Each sensor  34  further comprises an intermediate plate  50  (FIG. 3) pierced with two orifices through which the washers extend, this plate forming with the plates  36  and  37  a box containing the two sensitive elements. The plates  36  and  37  are each pierced with two orifices  51  whose center distance corresponds to that of the two elements  35  whereas each arm  14  and  15  is pierced with two orifices  52  separated by the same center distance and that each block  28  and  29  includes two tapped holes  53 , also separated by the same center distance.  
         [0052]    This construction allows the respective joining of each arm  14  and  15  to one of the blocks  28  and  29  by two screws  54  each with an axis  55 .  
         [0053]    The head of each screw  54  takes support on the arm  14  or  15 . Each screw  54  extends through one of the orifices  52  in one of the arms  14  and  15 , through one of the orifices  51  in one of the plates  36  and  37 , and through the central orifice of one of the elements  35 . Each screw  54  is threadably engaged in one of the tapped holes  53 . During tightening of the screws  54 , each element  35  is sandwiched between the plates  36  and  37 , tightened between their faces  38  and  39 , and the plates are also gripped tightly between the arm  14  and the block  28  or the arm  15  and the block  29  respectively.  
         [0054]    Each of the load amplifier modules  44 , FIG. 8, includes an amplifier  45  and a capacitor  46  connected between a negative input and an output of the amplifier. The negative input of the amplifier  45  is connected to the negative terminal  41  (FIG. 7) of the sensor  34 , whereas the positive input is connected to the positive terminal  40  of the sensor and to the circuit ground potential. This mounting forms an integrator delivering at the output a voltage proportional to the cumulative total of the load variations of the two sensitive elements  35  placed head-to-tail between, the plates  36  and  37 .  
         [0055]    This output voltage from each of the load amplifiers  44  is summed together at a signal summer  70  and the summed voltage is delivered to the unit UC by a cable  47 .  
         [0056]    A reed switch  48  or an FET transistor is connected to the terminals of the capacitor  46  in parallel therewith. Closing of the switch  48  (normally open) is controlled by a signal delivered by the unit UC before each insertion operation so as to restore to zero the output of the integrator which corresponds to a point  49  on the graph of FIG. 6.  
         [0057]    The functioning of the equipment according to the present invention is as follows: the approach of the cable eye stiffener  2  with respect to an alveolus  5  is carried out by the actuator M. Owing to the cumulated weight of the cable eye stiffener  2 , the wire extremity  3  and the arm  14  or  15  which weight is suspended from each sensor  34 , this results in accelerating an inertia force, indicated by an arrow  57  in FIG. 7, being applied to the center of gravity of the system suspended from the sensor, which is generally close to a center of gravity  56  (FIG. 7) of the arm  15  (or  14 ). Given the fact that this force is applied outside the portion of the plane of FIG. 7 that extends between the two axes  55  of the sensitive elements, the latter are stressed differentially. The first element  35  situated on the left in FIG. 7 is compressed, whereas the second element  35  (situated on the right in FIG. 7) of the same sensor is “relieved”, that is its compression stress (along its axis  55 ) is reduced. This force in the direction  57  results in an intimate movement in rotation of the arm  15  and the plate  36  with respect to the plate  37  and the block  29  by virtue of the elasticity of the screws  54  connecting them together. This minimum rotation of amplitude is effected approximately along an axis  58  orthogonal to the plane of FIG. 7.  
         [0058]    The variations of the compression forces applied to the two elements  35  under the effect of this force  57 , which are applied in an opposite direction, provoke load variations of contrary directions which, by means of the head-to-tail mounting of the polarities of the elements  35 , are added which facilitates the detection and measurement of the force by the force measuring means ( 44 , UC). This force corresponds to a portion of the graph of FIG. 6 that extends between the point  49  and a point  59  which is in a direction indicated by an arrow  60 , the point  59  corresponding approximately to the contact between the cable eye stiffener  2  and the walls of the alveolus  5 .  
         [0059]    The actual insertion of the cable eye stiffener  2  in the alveolus  5  requires in particular a sufficient force be applied so as to overcome the rubbing of the cable eye stiffener against the walls of the alveolus, as well as generally the forces required to warp the cable eye stiffener and/or the walls of the alveolus. This results in a force, indicated by an arrow  61  in FIG. 7, being applied to the clamping jaws of each arm of the clamp approximately along the wire holding axis  11  in the same direction as the inertia force indicated by the arrow  57 . The insertion force  61  provokes in the same way explained earlier for the force  57  a differential stressing of the two elements  35  of each of the sensors  34  which results in a force signal, such as the one corresponding to the portion of the graph of FIG. 6 extending between the point  59  and a point  62 . When the cable eye stiffener  2  is completely inserted, the forward movement of the clamp is stopped and during the backward movement, the insertion force is cancelled. If appropriate, a force of an opposite direction (traction) is effected on the wire so as to test the resistance to tearing of the mechanical link between the inserted cable eye stiffener and the alveolus receiving it, which corresponds to the portion of the graph of FIG. 6 extending between the point  62  and a point  63  where the force is negative. The jaws  12  and  13  of the clamp  16  are then spaced from each other so as to free the wire extremity  3  via the action of the jack  22  and  23  and then the clamp  16  is moved backwards so as to revert to its initial position which corresponds to the portion of the graph of FIG. 6 that extends between the points  63  and  49 .  
         [0060]    In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.