Abstract:
An electrical conductor strain relief for connecting electrical conductors to a printed circuit board. The strain relief includes a first member having a first array of first conductor receiving holes and a second member having a second array of second conductor receiving holes. The second member is connectable to the first member at a predetermined fixed location such that the second holes are at least partially aligned with respective ones of the first holes as pairs of holes. The first and second holes of each pair of holes have center axes which are offset relative to each other.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a strain relief for electrical conductors and, more particularly, to a multi-piece strain relief with offset conductor receiving holes. 
     2. Earlier Developments 
     U.S. Pat. Nos. 4,886,942 and 5,462,451 disclose unitary strain reliefs for connecting electrical conducts to printed circuit boards. U.S. Pat. No. 3,865,461 discloses a two-piece strain relief each with a hole to receive the cable, but become offset by rotation of the pieces to clamp the cable. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention an electrical conductor strain relief for connecting electrical conductors to a printed circuit board is provided. The strain relief comprises a first member and a second member. The first member has a first array of first conductor receiving holes. The second member has a second array of second conductor receiving holes. The second member is connectable to the first member at a predetermined fixed location such that the second holes are partially aligned with respective ones of the first holes as pairs of holes. The first and second holes of each pair of holes have center axes which are offset relative to each other. 
     In accordance with one method of the present invention a method of providing a strain relief for conductors attached to a printed circuit board is provided comprising steps of inserting the conductors through separate first holes in a first strain relief member; inserting the conductors through separate second holes in a second strain relief member; attaching the first strain relief member to the printed circuit board and attaching the second strain relief member to the first strain relief member. The first and second holes are respectively aligned with each other at an offset such that each of the conductors pass through a respective pair of the first and second holes with a bend at a junction between the first and second strain relief members. 
     In accordance with another embodiment of the present invention a printed circuit board and electrical conductor assembly is provided comprising a printed circuit board; electrical conductors soldered to the printed circuit board; and a strain relief connected to the printed circuit board and having the electrical conductors pass therethrough. The strain relief comprises two members with first and second arrays of holes respectively therethrough. A first one of the members is attached to the printed circuit board and a second one of the members is attached to the first member with holes of the first and second arrays being aligned with each other at an offset such that the electrical conductors pass through the holes and are bent at a junction between the two members. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of an assembly incorporating features of the present invention; 
     FIG. 2 is a partial cut-away front elevational view of the assembly shown in FIG. 1; 
     FIG. 3 is an exploded perspective view of the strain relief shown in FIGS. 1 and 2; 
     FIG. 4 is a perspective view of the bottom of the lower strain relief member shown in FIG. 3; and 
     FIG. 5 is an enlarged partial view showing the upper and lower strain relief members being connected to each other. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown a perspective view of an assembly  10  incorporating features of the present invention. Although the present invention will be described with reference to the single embodiment shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used. 
     The assembly  10  generally comprises a printed circuit board  12 , electrical conductors  14 , and a strain relief  16 . The printed circuit board  12  can be any type of circuit substrate or, alternatively, any suitable type of electronic component. Referring also to FIG. 2, the electrical conductors  14  are separate wires which each have an electrically conductive core  18  and a dielectric insulative cover  20 . However, in alternate embodiments other types of electrical conductors could be provided, such as multi-conductor cables. The conductors  14  pass through the strain relief  16 . Exposed ends  22  of the conductive cores  18  pass through holes in the printed circuit board  12  and are soldered to the printed circuit board. 
     The strain relief  16  is provided to protect the integrity of the electrical connection of the conductors  14  to the printed circuit board  12  by preventing the conductors  14  being pulled away from the board  12  at the soldered connection. In this embodiment the strain relief  16  is comprised of two members; a lower or bottom member  24  and an upper or top member  26 . In an alternate embodiment the strain relief may be comprised of more than two members. In a preferred embodiment the members  24 ,  26  are both one-piece members comprised of molded dielectric material, such as polycarbonate. However, any suitable materials or combination of materials could be used. 
     Referring also to FIGS. 3 and 4, the bottom member  24  generally comprises a plurality of conductor receiving holes  28 , two snap-lock mounting holes  30 , and two PCB mounting posts  32 . The holes  28  are sized to allow passage of the conductors  14  therethrough with a very small or virtually no spacing therebetween. The holes  28  can be arranged as two rows with an equal spacing A between adjacent holes in each row. The holes  28  nearest the center  34  of the bottom member  24  are spaced a distance B from the center. In this embodiment B is A/2 such that all the holes in each row are equally spaced from each other in a uniform pattern. However, in alternate embodiments any suitable spacing or pattern of the holes  28  could be provided so long as the spacing or pattern cooperates with the spacing and pattern of conductor receiving holes in the upper member  26  as further understood below. The mounting posts  32  extend from the bottom side of the bottom member  24  and are inserted into holes  36  in the printed circuit board  12  to stationarily and fixedly mount the bottom member  24  to the printed circuit board  12 . However, any suitable means could be used to stationarily mount the bottom member  24  to the printed circuit board  12 . 
     The top member  26  generally comprises a plurality of conductor receiving holes  38  and two snap-lock latches  40 . The holes  38  are preferably the same size as the holes  28  and are the same in number. The holes  38  have tapered entrances  42  for easier insertion of the conductors  14  into the holes  38 . The holes  38  are arranged in two rows, but as two sub-arrays  44 ,  45 ; one on each side of the center  46  of the top member  26 . The center-to-center spacing C between holes  38  in each sub-array is preferably the same as spacing A; such as about 0.165 inch. However, any suitable dimension could be provided. However, the center-to-center spacing D of the holes  38  closest to the center  46  is preferably larger than the spacing C, such as by a difference of about 0.010-0.015 inch. However, in an alternate embodiment D could be smaller than C. The holes  38  closest to the center  46  are spaced from the center  46  by distances E and F. The distances E and F could be the same, but in a preferred embodiment they are different such as 0.083 inch and 0.0825 inch. However, any suitable distances or dimensions could be provided. The snap-lock latches  40  are located at opposite ends of the top member  26 . Each latch  40  extends from the body of the top member  26  in a general cantilever fashion. Each latch  40  is resiliently deflectable with a tapered leading edge  48  and a latching surface  50 . 
     As seen best in FIG. 2, the top member  26  is mounted on top of the bottom member  24 . The snap-lock latches  40  are snap-lock latched into the holes  30  to stationarily and fixedly mount the top member  26  to the bottom member  24  at a predetermined position. The holes  38  of the top member  26  are aligned with the holes  28  of the bottom member  24  as pairs of holes which the respective individual conductors  14  pass through. Although the holes  28 ,  38  are partially aligned, the center axes  28   ca  and  38   ca  of the holes  28 ,  38  are slightly offset from each other by an offset G. In a preferred embodiment the offset G is about 0.015 inch. However, in alternate embodiments any suitable size of offset could be provided. The centers  34 ,  46  of the members  24 ,  26  are aligned when the two members  24 ,  26  are connected to each other. Because of the different spacings of the sub-arrays  44 ,  45  from the center  46  and the different uniform spacing of the holes  28  from the center  34 , the offset G of the top holes  38  relative to the bottom holes  28  on opposite sides of the centers  34 ,  46  are in opposite directions. This helps to balance or counteract the forces exerted by the deformation of the conductors  14  that occurs when the two members  24 ,  26  are connected. 
     When the two members  24 ,  26  are connected to each other, because of the offset G and the tight fit of the conductors  14  in the holes  28 ,  38 , the conductors  14  are bent at the junction  52  between the two members  24 ,  26 . The bend in wire  14 , along with the size of the holes  28 ,  38 , causes a gripping or clamping action by the strain relief  16  on the conductors  14 . Because the strain relief  16  is fixedly and stationarily mounted on the printed circuit board  12 , the strain relief  16  prevents any force on the conductors  14  past the top side of the top member  26  being exerted on the connection of the ends  22  to the printed circuit board  12 . The two members  24 ,  26  are preferably attached to each other after the posts  32  are positioned in the holes of the printed circuit board and after the conductors  14  are passed through the holes  28 ,  29 . Preferably the bottom member  24  is attached to the board  12  before the top member  26  is attached to the bottom member  26 . However, any suitable assembly procedure could be used. 
     As seen in FIG. 5, the center axes  28   ca ,  38   ca  of the holes  28 ,  38  are offset even during the initial engagement of latch  40  with hole  30 . In other words, the center axes  28   ca ,  38   ca  preferably remain offset between the initial engagement position shown in FIG. 5 to the final engagement position shown in FIG.  4 . 
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.