Abstract:
An alligator clip ( 10 ) whose rear end was originally manufactured to receive a 4 mm plug ( 50 ), is altered to received a 2 mm plug ( 60 ), in a construction that provides a long lifetime of low force insertion and removal and low electrical resistance contact. The sheet metal rear portion with adjacent edges ( 40, 42 ) at the top, is deformed so a bottom part forms an approximately 360° loop ( 130 ), a pair of vertical bottom beams ( 131, 132 ) extending upward from the loop, and a pair of part-cylinders ( 140, 142 ). The part-cylinders create a cylinder contacting region ( 150 ) at the top of the beams to grip the cylindrical 2 mm plug. Upper beams ( 152, 154 ) extend generally upwardly from the upper ends of the part-cylinders.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    One type of alligator test clip has a pair of jaws at its front end that are spring biased together, and that has a socket or pin jack at its rear end that is designed to receive a 4 mm diameter plug. The plug may be used alone for insertion into jacks of equipment to be tested, but may be inserted into the pin jack at the rear of the alligator clip to clamp to a wire. Although the 4 mm plug is the most common in present use, there are significant numbers of 2 mm diameter plugs, and there is a need for alligator clips whose rear ends can receive such 2 mm plugs.  
           [0002]    The alligator clip includes two pieces of sheet metal and a spring, with a first of the pieces having a rear portion bent into a cylinder to form the 4 mm pin jack. The opposite edges of the first piece of sheet metal lie at the top of the cylinder, where the edges are parallel and adjacent. Applicant has previously changed the 4 mm pin jack by compressing opposite sides of the cylinder, to the configuration shown in FIG. 8. While this approach results in a useful 2 mm pin jack, it has serious problems. One problem is that it requires a large force such as twenty pounds to insert and retract the 2 mm plug from the prior pin jack shown in FIG. 8. Also, the electrical resistance was initially significantly higher (about 13 miliohms) then for the 4 mm jack (about 6 miliohms). Also, after perhaps ten or twenty insertions and removals of the 2 mm plug from the prior 2 mm jack, electrical contact was sometimes lost between the jack and plug.  
           [0003]    It is possible to adapt the 4 mm jack to a 2 mm jack by inserting a device with a sleeve and tiny beams, but such contactor adds significantly to the cost. An adaption of the prior 4 mm simple cylindrical jack to a 2 mm jack by merely deforming the jack part of an alligator clip, where the adaption resulted in a 2 mm jack with low insertion and removal force and low electrical contact resistance, with the low insertion and removal forces and low contact resistance continuing over a long cycle of use (numerous insertions and pullouts of the plug) would be of value.  
         SUMMARY OF THE INVENTION  
         [0004]    In accordance with one embodiment of the present invention, an alligator clip is provided with a pin jack at the rear, where the pin jack has been adapted from a cylindrical large diameter jack to a smaller diameter jack, where the small diameter jack provides for small insertion and removal forces and a low electrical resistance connection to a small plug, over a large number of duty cycles. The clip includes a first piece of sheet metal with a rear portion having a pair of parallel edges at its top. The rear portion has a gripping section extending along an axis, where the gripping section has a bottom part that form an approximately 360° bottom loop and a pair of primarily parallel bottom beams that extend upwardly from opposite sides of the bottom loop. The gripping section also has opposite sides each formed into a continuous part cylinder and that together form a cylinder contacting region that grips the small diameter cylindrical plug. Beams extend at least partially upward from the tops of the part cylinders. The edges of the sheet metal lie at the top of the gripping section and extend parallel to each other.  
           [0005]    The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a rear and top isometric view of a prior art alligator clip for receiving a large diameter jack, and showing a portion of the jack, with the clip of this figure being an item that is deformed to form the clip of the invention.  
         [0007]    [0007]FIG. 2 is a top and rear isometric view of a portion of a clip of the present invention for engaging a small diameter plug, and which has been formed from the clip of FIG. 1.  
         [0008]    [0008]FIG. 3 is a side elevation view of the clip of FIG. 2.  
         [0009]    [0009]FIG. 4 is a bottom view of the clip of FIG. 3.  
         [0010]    [0010]FIG. 5 is a rear elevation view of the clip of FIG. 3, taken on line  5 - 5  thereof.  
         [0011]    [0011]FIG. 6 is a sectional view taken perpendicular to the jack horizontal axis and on line  6 - 6  of FIG. 3.  
         [0012]    [0012]FIG. 7 is an enlarged view of the gripping section shown in FIG. 6, and is also taken on line  6 - 6  of FIG. 3.  
         [0013]    [0013]FIG. 8 is a sectional view of a gripping section of a prior art converted clip for engaging a small diameter plug.  
         [0014]    [0014]FIG. 9 is an exploded view showing the manner in which the rear portion of the clip of FIG. 1 is deformed into the gripping section of the clip of FIG. 2.  
         [0015]    [0015]FIG. 10 is a sectional view of the gripping section of a clip of another embodiment of the invention.  
         [0016]    [0016]FIG. 11 is a sectional view of the gripping section of a clip of another embodiment of the invention.  
         [0017]    [0017]FIG. 12 is a sectional view of the gripping section of a clip of another embodiment of the invention.  
         [0018]    [0018]FIG. 13 is a side elevation view of an alligator clip of another embodiment of the invention.  
         [0019]    [0019]FIG. 14 is a view taken on line  14 - 14  of FIG. 13.  
         [0020]    [0020]FIG. 15 is a partial sectional view of the clip of FIG. 13 with a rubber boot.  
         [0021]    [0021]FIG. 16 is a view taken on line  16 - 16  of FIG. 15.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    [0022]FIG. 1 illustrates an alligator clip  10  from which the clip of the present invention is made. The alligator clip includes a body  12  that has first and second body parts  14 ,  16  that are each formed of bent sheet metal, the sheet metal usually being carbon steel which is plated. The two body parts are pivotally connected at a pivot joint  20  to allow front ends  22 ,  24  of the body parts to move together and grip a wire or other element between them to make electrical connection with the element. A coil spring  26  urges the front ends  22 ,  24  together. The first part or piece of sheet metal  14  has a rear portion  30  forming a pin jack  32 . The pin jack is formed by the rear portion of the first piece  14  of sheet metal, by the sheet metal having been bent into an original cylinder  34  with first and second edges  40 ,  42  at the upper, in direction U, end or top of the cylinder. The cylinder extends in a continuous circle from edge  40  around the laterally L opposite sides  44 ,  46  and around the downward D or bottom end  48 . In the particular example shown, the large plug  50  that can be received in the pin jack  32 , has a front end  52  and shaft  54  that are each of 4 mm diameter.  
         [0023]    Although the alligator clip  10  of FIG. 1 is in wide use, there is a substantial demand for alligator clips that can receive small diameter plugs  60  having tips  62  and shafts  64  that are each of 2 mm diameter. One way to convert the clip  10  to receive and make electrical connection with the small diameter plug  60  is to insert a contacting element in the pin jack  32 , where such element has inwardly bowed fingers that engage the small plug  60 . However, such insert adds substantial cost to the clip. Another approach is to deform the pin jack  32  so a section of it has the gripping section cross section shown in FIG. 8 at  70 . In such clip, the first and second laterally spaced edges  40 ,  42  of the sheet metal remain at the top, but the laterally opposite sides of the original cylinder are deformed at  44 A,  46 A into a pair of 360° side loops  80 ,  82  with horizontally-extending side beams  84 ,  86 , and  90 ,  92 . Also, upper and lower portions  100 ,  102  of the original cylinder are deformed into approximately half cylinders that form a tubular, or cylinder section  104  having an inside diameter  106  slightly less than 2 mm. The gap  108  between the edges  40 ,  42  lies in the upper part cylinder portion  100  that grips the plug.  
         [0024]    Although the gripping section  70  of FIG. 8 can receive and connect to a small diameter 2 mm plug, it has disadvantages. Applicant found that, with the carbon steel metal of thickness A of 19 mils (1 mil equals 1 thousandth inch), that the clip required a plug insertion and pullout force for the 2 mm plug, of about twenty pounds. This is a large force for a person to apply to a small jack. While the electrical contact resistance between the large plug  50  of FIG. 1 and the large pin jack  32  was about 5 miliohms, the contact resistance for the 2 mm plug was initially about 13 miliohms. Furthermore, after about ten to twenty insertions and pullouts of the small pin contact from the section  70  of FIG. 8, a plug sometimes lost electrical contact with the gripping section  70  of the jack.  
         [0025]    In accordance with the present invention, applicant deforms the rear portion  30  of FIG. 1 into the configuration shown at  30 B in FIG. 2. The alligator clip  120  of the invention shown in FIG. 2, has a tapered leadin  122  at its rear end and a gripping section  124  extending forward F of the leadin. FIG. 3 is a side view of the clip  120  of the invention, showing the manner in which the rear portion  30 B of the first piece  14 A of sheet metal has been deformed.  
         [0026]    [0026]FIG. 7 is a view taken on line  6 - 6  of FIG. 3 showing the cross section of the gripping section  124  of the alligator clip of the invention. The sheet metal has been deformed to form an approximately 360° bend or circle loop  130  at the bottom of the gripping section. A pair of bottom beams  131 ,  132  have lower ends  134  that merge with opposite sides of the circle loop  130 . The bottom beams  130 ,  132  extend primarily upwardly, and preferably directly upwardly and parallel to each other, to their upper ends  136 . At their upper ends  136 , the bottom beams merge with part cylinder portions  140 ,  142  that are each bent into a portion of a cylinder centered on axis  144 . The two part cylinder portions are spaced apart by a distance B which is slightly less than 2 mm, such as 1.95 mm, to grip a plug of nominal 2 mm outside diameter. The two part cylinders  140 ,  142  together form a cylinder region  150  that is similar to a cylinder of the diameter B to receive and engaged a 2 mm diameter plug. The gripping section has a pair of upper beams  152 ,  154  that extend upwardly to the edges  40 ,  42 , with the edges being free and unjoined.  
         [0027]    Applicant has found that the alligator clip  120  of the present invention with the gripping section  124  shown in FIG. 7, provides only a moderate mechanical resistance of about two pound to insertion and retraction of a 2 mm plug, provides a low electrical resistance of about 6 miliohms, and maintains a low electrical resistance (Under 10 miliohms) and the moderate mechanical resistance to insertion and retraction throughout numerous cycles of operation. In fact, applicant found that in some tests the low electrical and mechanical resistances were maintained for ten thousand cycles of insertion and retraction.  
         [0028]    For the particular gripping section  124  in FIG. 7, the overall height C of the section was 277 mils (6.86 mm or 0.277 inch), the radius of curvature G at the loop  130  was 25 mils (0.64 mm) and the separation S between lower beams was 15 mils (0.4 mm). The part cylinders  140 ,  142  each extended by an angle V of about 135° around the axis. 135° is 75% of a half cylinder of 180°. The lengths E and F of the lower and upper beams were 1.9 mm (75 mils). The length E of the lower beams  131 ,  132  are important in determining the insertion and retraction force, and the lengths F of the upper beams are the result of using all of the sheet metal that is initially present. Referring to FIGS. 3 and 4, the overall length of the clip was 1.96 inch and the leadin  122  had an outside diameter J of 0.19 inch. The distance K between the axis  144  and the bottom of the loop  130  was 0.135 inch, with the bottom of the loop lying a distance P of 0.06 inch (1.5 mm) below the bottom  192  of an intermediate wall. The distance P is more than half the diameter B of the cylindrical plug.  
         [0029]    It is not readily apparent why the cross section of the gripping section  124  of FIG. 7 should provide such lower mechanical force in insertion and retraction and such greater reliability in maintaining low electrical contact resistance with the inserted plug. One reason is that the length of the beams  131 ,  132  is greater than that of beams  84 - 92  due to the need for two loops  80 ,  82  in the prior art. Applicant believes that another reason is that in FIG. 7, the part cylinder portions  140 ,  142  need to bend apart only one circle loop  130 , while in the prior art of FIG. 8, the inserted plug must bend apart two circle loops  80 ,  82 . Applicant also believes that the advantage may be due to the fact that there are only two areas of contact in the gripping section  124  of FIG. 7, at the general locations  170 ,  172 . In the gripping section of FIG. 8, there would be three locations that must be spread apart, including locations on the two parts  101 ,  103  of the upper half cylinder, and a part on the lower half cylinder  102 . Also, applicant believes that there are likely to be burrs or other irregularities at the bottom corners  40 E,  42 E of the edges  40 ,  42 , and such burrs may scrape along the plug, impede insertion and retraction of the plug, and give rise to irregularity of mechanical and electrical resistance. In any case, applicants&#39; tests on numerous alligator clips of the type shown in FIGS.  2 - 7  and a comparison with a prior art clip of FIG. 8 shows that applicants&#39; lower and more consistent mechanical and electrical resistance and long lifetime, do in fact, occur.  
         [0030]    In the clip  10  of FIGS. 1 and 2, the first sheet metal part  14  has an intermediate part  190  with a flat bottom  192  that lies in a horizontal plane and with side wall  193 ,  194  that extend upwardly from laterally opposite sides of the bottom wall. The edges  40 ,  42  remain above the level of the bottom wall  192  in the clip  120  of FIG. 2. However, the circle loop  130  in FIG. 2 lies below the level of the bottom  192  after the deformation into the gripping section  124 . This is clearly shown in FIG. 3 where the bottom of the loop  130  is shown lying below the height of the lower surface  192  of the flat bottom.  
         [0031]    [0031]FIG. 9 shows one method for deforming the rear portion  30  of the original clip (for receiving a 4 mm plug) into the gripping section  124  of the clip of the present invention. A pair of dies  180 ,  182  have surfaces  184 ,  186  that are pressed against opposite lateral sides of the initial sheet metal rear portion  30 . Also, a core  190  is inserted into the rear portion. When the dies are pressed together with high force, the rear potion  30  is deformed into the gripping section  124  which has final sides at  140 ,  142 . The deformation can be accomplished in steps by a series of dies. The bottom  193  of the bottom loop  130  lies below the bottom  48  of the original cylinder  34 , which lay slightly (0.03 inch) below the bottom  192  of the intermediate part. The bottom  193  of the bottom loop lies a distance P below the bottom wall, where P is more than twice the thickness of the sheet metal.  
         [0032]    [0032]FIG. 10 illustrates a gripping section  200  of another embodiment of the invention, wherein the bottom beams  202 ,  204  that extend upwardly from an approximately 360° loop  206 , are of greater length, and the upper beams  210 ,  212  are of shorter length. This results in even lower mechanical resistance to insertion and retraction of the plug, but can lead to somewhat greater electrical resistance.  
         [0033]    [0033]FIG. 11 shows another gripping section  220 , where each of the opposite sides  222 ,  224  is half of a square shape (or hexagonal or octagonal), but are basically part cylinder portions because they can engage a cylindrical plug  60  at at least three and preferably at least four locations  211  spaced about the axis  144  of the plug. Two concave cylinder parts such as shown in FIG. 10 at  213 ,  214  engage a cylindrical plug at regions  215 ,  216  (for a smaller diameter plug) or at locations  217 A- 217 D for a larger diameter plug. This holds the plug centered on the axis  144 .  
         [0034]    [0034]FIG. 12 illustrate another gripping section, where the bottom circle loop  272  subtends an angle N of 310°, resulting in each bottom beam  274 ,  276  extending at an incline of 25° from the vertical but still primarily vertical. The part-cylinder portions  280 ,  282  grip a cylindrical plug  284 . The gripping occurs at closely spaced points  290 , at each part-cylinder portion for a small diameter plug, and at widely spaced locations such as  294 ,  296  at each part-cylinder portion for a large diameter plug. Like the other clips, the clip  270  is symmetric about a vertical centerline.  
         [0035]    FIGS.  13 - 16  illustrate another alligator clip  230  that applicant constructed. This clip is similar to the clip of FIGS.  1 - 7 , but with a greater outside radius of curvature G 1  (FIG. 14) of 1 mm and with the lower beams separated a distance S 1  of 1.25 mm. This is five times the separation S in FIG. 7 and the separation S in the prior art of FIG. 8, and is more than 150% of the thickness A of 0.019 inch (0.48 mm) of the sheet metal. This results in much less force required to insert the 2 mm plug. The clip has opposite part cylinder portions  232 ,  234  that each extends by an angle V 1  of only about 75°. The upper beams  250 ,  252  have a height C 1  that is about 60% of the height E 1  of the lower beams  254 ,  256 .  
         [0036]    FIGS.  15 - 16  show a rubber boot  240  that applicant uses to surround the clip. The boot isolates the person holding and applying the clip, from any voltage on the clip. The boot has a section  242  shown in FIG. 15, which closely surrounds the gripping section  244  of the clip and which can add resilience to grip the plug.  
         [0037]    While terms such as “upper”, “bottom”, “horizontal”, etc. have been used to help describe the invention as it is illustrated, it should be understood that the clip can be used in any orientation with respect to the Earth.  
         [0038]    Thus, the invention provides an alligator clip with a jack for a small diameter plug, where the jack has a small mechanical resistance to insertion and retraction of the plug and the jack has a low electrical resistance engagement with the plug, and maintains these characteristics over a long lifetime of use. This is achieved where the jack is formed by deforming an existing larger jack. The clip includes a piece of sheet metal with unjoined edges at the top and two laterally spaced approximately half cylinder portions that can grip a plug between them. The sheet metal has been deformed to form an approximately 360° (at least 300°) bottom circle loop at a bottom end that is opposite the edges, and to form a pair of primarily vertically extending bottom beams that each extends from one side of the loop to the bottom of each half cylinder portion. A pair of upper beams extend primarily upwardly from upper ends of each half cylinder portion. A bottom loop of a large radius of curvature that is at least one and one-half or twice the sheet metal thickness, results is easy pin insertion.  
         [0039]    Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.