Abstract:
Electro-chemical polishing of fine wire contacts is facilitated by welding the wire contacts to a mounting element on a continuous, flexible, metal strip. The assembled contact strip is wound on a spool and transported to the electro-chemical polishing site where the contact strip is drawn into the polishing site at a constant rate under the control of a microprocessor. The progress of the assembled contact strip is monitored by metering rollers and pulse generators that inform the microprocessor of the drive speed of the assembled contact strip. The controller then provides signals to control the take-up and supply spools to ensure that a proper tip polishing operation is carried out.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a system for making electrical contacts available for an electrochemical polishing operation and, more particularly, to providing contacts arranged on a metal strip for provision to the electro-chemical polishing operation. 
     2. Description of Background 
     The use of very fine wires as electrical contacts in positional encoders, in slip-ring assemblies, precision potentiometers, sensors, or the like is known. It is further known that the contact end of each of such fine wires must be polished in order to eliminate any burrs or the like that would decrease the contact area between the contact and its contact surface. Such polishing is also required to cut down on the extent that the wire contact abrades the mating electrical contact surface. 
     One known approach to smoothing or rounding off of the ends of very small diameter wires or springs is disclosed in U.S. Pat. No. 5,189,278 in which a laser beam is used to irradiate the ends of the wire or spring so that the end is melted somewhat. While some advantageous results are had by this approach, the melting of the end of the wire or spring results in a loss of temper of the metal. Moreover, in order to properly irradiate the end of the wire with the laser beam, the wire must be separated by more than a nominal distance from its adjacent wire or spring, so that embodiments in which multiple springs are arranged side-by-side in contact with each other are not available for use with the laser technique described in the above-mentioned U.S. patent. 
     Another approach to smoothing metal objects is known as electro-chemical smoothing, whereby a surface of a conductive metal part can have the burrs removed. One technique for performing such a function is described in U.S. Pat. No. 4,752,376. Nevertheless, application of the electro-chemical smoothing process to extremely fine wire contacts poses difficulties in the implementation because the fine wire assemblies are difficult to handle. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a system whereby the end surfaces of very fine gauge wires forming metal spring contacts can be polished and that can eliminate the above-noted defects inherent in the prior art. 
     Another object of the present invention is to provide a system for continuous polishing or smoothing of the tips of fine gauge wire electrical contacts mounted on a thin, flexible metal strip for ease of transport and polishing in an electro-chemical polishing operation. 
     In accordance with an aspect of the present invention, small diameter wire contacts are fixed onto a flexible metal strip that is wound on a spool and transported to an appropriate location whereat an electro-chemical polishing operation is performed on the tips of the wire contacts in a continuous fashion. The contacts and wire strip are then wound up again on a spool for transport to the ultimate manufacturing location. A metering operation takes place to control the supply and take-up spools under control of a microprocessor that permits various inputs by the user of the system. 
     In accordance with another aspect of the present invention, small diameter wire contacts are fixed onto a flexible metal strip and transported to an appropriate location whereat short lengths of the flexible metal strip are fed to where an electro-chemical polishing operation is performed. The strips with the polished wire contacts are then collected for subsequent use. 
     The above and other objects, features, advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof to be read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front elevational view of a portion of a flexible metal strip having small diameter contact wires attached thereto; 
     FIG. 2 is a view of the tip portion of one of the contact wires shown in FIG. 1 that is bent at a predetermined angle; 
     FIG. 3 is an enlarged cross-sectional view through the contact wire of FIG. 2 prior to polishing; 
     FIG. 4 is a cross-sectional view of the contact wire of FIG. 3 after having undergone an electrochemical polishing operation; 
     FIG. 5 is an enlarged cross-section view of a contact wire that is straight after having undergone an electro-chemical polishing operation; 
     FIG. 6 is a schematic representation of the electro-chemical polishing operation according to an embodiment of the present invention; and 
     FIG. 7 is a schematic representation of the electro-chemical polishing operation according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a portion of a strip of electrical contacts having been previously assembled. More particularly, the assembled contact strip  10  includes a group of fine diameter contact wires shown generally at  12 . In this case the wires are of a diameter of approximately 0.003 inches and are formed of palladium/silver alloy. In each of the groups  12 , there are twenty-two wires arranged side-by-side so that they are in contact with each other. Each group of wires is welded to a metal holder portion forming a mounting element  14  that is a thin gauge metal spring formed of a tempered copper or nickel based alloy. In addition, various other metal alloys can be used. While in this case it is palladium/silver alloy on a copper base strip the wires could be tungsten or stainless steel or the like on a base strip formed of various other metals. 
     As seen in FIG. 1, in this particular construction there are two groups of spring wires  12  attached to each mounting element  14 , which is in the form of a U-shaped element. One group of wires  12  is welded to each arm of the mounting element  14  at a location shown generally at  16  in FIG.  1 . 
     The mounting elements  14  are in turn attached to a band of the same spring-like material  18  at attachment elements  20 . The band  16  is provided with sprocket holes, shown typically at  22 , that are precisely located along the length thereof. The mounting elements  14  and the band  18  need not be separate elements, and the mounting elements and band can be integrally formed as one piece. 
     After the manufacturing and polishing operations have been performed on the spring wires  12  and the assembled contact strip  10  conveyed to the final assembly point, the wires  12  and mounting elements  14  may be separated from the band  18  by separating the mounting elements  14  from the attachment elements  20  at a so-called score line  24  by bending or severing. The detachment of the mounting elements  14  from the band  18  may occur at the site of the end-user of the contacts by means of an automated assembly machine. 
     There are various configurations that the spring contact assemblies can assume, and the showing at  10  in FIG. 1 is only one example of the number of wires per mounting element, as well as the configuration of the mounting element itself. 
     FIG. 2 shows a single wire  30  that makes up the group of wire contacts  12  shown in FIG.  1 . This wire  30  is bent at the head end through an angle A, which can typically be approximately 70°. Alternatively, the wire contacts can be supplied straight for subsequent bending after polishing. 
     FIG. 3 is a close-up view in cross-section of the wire  30  of FIG. 2 showing that at the end portion  40  sharp corners such as at  42  and burrs such as at  44  caused by the manufactured process are originally present. It is these sharp corners  42  and burrs  44  that are desired to be eliminated from the finished product. 
     In that regard, FIG. 4 shows the wire  30  of FIG. 3 having an end portion  40  with a smoothly rounded contour  50  in which the sharp corners  42  and burrs  44  have been eliminated. This is made possible by performing the operations known as electrochemical polishing, which have been discussed hereinabove. 
     FIG. 5 shows a close-up view in cross-section of a single wire  52  that is not bent but is straight. A group of these wires would be used to make up the contact group  12  of FIG.  1 . This wire  52  has already been polished and the burrs and sharp corners have been removed and is then ready to be bent through any angle required by the particular application. 
     FIG. 6 is a schematic representation of an embodiment of the present invention in which the assembled contact strip  10  bearing the mounting elements  14  and contact wires  12  attached to the mounting strip  18  is provided to the electro-chemical processing site. 
     The assembled contact strip  10  is wound about a supply spool  60  that has upper and lower flanges  62  and  64 , respectively. The supply spool  60  is mounted on a spindle  66  that is provided with suitable mounting elements to permit the supply spool  60  to be rotatably mounted thereon. The assembled contact strip  10  is then passed over a metering roller  68  that has a sprocket or the like, not shown, that engages with the sprocket holes  22  of the assembled contact strip  10 . Alternatively, the metering roller could be a soft rubber roller that is rotated by friction with the assembled contact strip  10 . The metering roller  68  is attached to a pulse generator  70  that provides output pulses on line  72  fed to the system controller  74 , which may comprise a microprocessor. The assembled contact strip  10  is then passed into an electro-chemical polishing site  76  that performs the electro-chemical polishing on the tips of the contact wires, as described above. 
     Following the polishing operation, the assembled contact strip  10  passes over a second metering roller  78  that has associated therewith a second pulse generator  80  that provides second pulses on line  82  fed to the system controller  74 . After passing over the second metering roller  78 , which would also include a sprocket, not shown, for interacting with the sprocket holes  22 , the assembled contact strip  10  with the polished tips is wound up on a take-up spool  84  that also has upper flange  86  and lower flange  88  for tracking the assembled contact strip  10  as it is wound up. The take-up spool  84  is mounted on a spindle  90  that is driven by a take-up motor  92 . The take-up motor  92  is controlled by a signal on line  94  from the system controller  74 . 
     In order to provide proper tension on the band as it is fed or drawn into the electro-chemical polishing site  76 , a torque motor  96  can be provided on the supply spindle  66  to provide appropriate tension on the assembled contact strip  10 . Torque motor  94  is controlled by a signal on line  98  from the controller  74 . Alternatively, a mechanical tensioning system, such as a brake band, could be provided at the take-up reel  60  to provide the appropriate tension on the assembled contact strip  10 . 
     Various changes in speed as well as stopping and starting are controlled by the controller  74  by way of the user of the system operating a keyboard  100  that is electrically connected to the system controller  74 . 
     Accordingly, by use of the system shown in FIG. 6, it is possible to provide electro-chemical polishing to small diameter wires  12  mounted on a flexible band  18  that can be drawn through an electro-chemical polishing site  76  for polishing the tips of the fine diameter wires forming the contacts  12  with the result as shown in FIG. 4 or FIG. 5, for example. 
     Although the above description was presented in regard to a continuous contact strip, the present invention also contemplates the use of relatively short lengths of the strip. Such an embodiment is shown FIG. 7, in which the contacts are formed as specific strip lengths. More particularly, an assembled contact strip  110  includes a group of fine diameter wires, shown typically at  112 . Each group of wires is welded to a metal holder portion  114 . 
     A few of the mounting elements  14 , in this case three, are attached to a short length or strip of spring-like material  118  at attachment elements  120 . The strip  118  can have sprocket holes  122  formed therein. Although this embodiment shows three mounting elements  114  attached to the strip  118  fewer or more mounting elements could be employed with the strip length changing attordingly. 
     The materials used in the contact strip  110  of FIG. 7 can be the same as those discribed above in relation to FIG.  1 . 
     The assembled contact strip  110  is fed to an electroo-chemical polishing site  124  by a drive roller pair that includes a drive roller  126  and an idler roller  128 . The drive roller  126  is driven by a motor  130  that is controlled by a system controller, not shown, such as controller  24  in the system of FIG.  6 . 
     The contact strip  110  is thus fed into the polishing site  124  where it is handled in a similar fashion as by the input system that is shown and the electro-chemical tip polishing is performed. 
     Following the polishing operation the polished contact strip  110  is fed to the nip of a pair of output rollers that include a drive roller  132  and idler roller  134 . The drive motor  132  is driven by a motor  136  under control of the system controller, not shown. 
     The output rollers  132 ,  134  then transport the contact strip  110  to a collection location, such as a conveyor belt  138  driven by a motor  140  under control of the system controller, not shown. 
     The input rollers and output rollers can transport the contact strips  110  by friction or drive pins, shown typically at  142 , can be provided on the drive rollers  126 ,  132  for interaction with the sprocket holes  122  formed in the metal strip  118 . Nevertheless, because the rate of passage of the contact strips  110  through the polishing site is not absolutely set by the input and output rates, the input and output drive rates can be met using friction drive rollers. 
     It will be understood, of course, that various modifications and alterations can be made to the embodiment described above without departing from the spirit and scope of the present invention, which is to be defined by the appended claims.