Patent Publication Number: US-2023163494-A1

Title: Strain relief plug for lead wires on a printed circuit board

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 63/281,276 dated Nov. 19, 2021, the contents of which are incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     The subject disclosure relates to strain relief for connector wires, and more particularly to a strain relief that may be readily inserted into a printed circuit board to relieve pulling forces imparted on connector wires secured to a connector device. 
     BACKGROUND 
     Lead wires may be secured to a connector by soldering or bonding procedures to attain an electrical connection, but these securing options are relatively weak and are subject to failure upon mechanical pulling forces imparted on the wires. When soldering lead wires to a printed circuit board, the solder joint may be subject to stress that requires strain relief. If the cable wire flexes, the quality of the electrical conductivity will degrade and the wire may break off of the printed circuit board, resulting in device failure. During assembly, testing, use, and maintenance of printed circuit boards having such connections, the lead wires are frequently pulled from the modules and boards. In order to protect the soldered joints, strain relief devices have been developed. 
     Existing products in the marketplace to fulfill the necessity for strain relief of wires on a printed circuit board demonstrate opportunities for improvement. Strain relief of wires adhered to printed circuit boards has been accomplished by various means. In many instances, electrical connections are made within a connector housing that is then affixed to the printed circuit board. In these devices, the apparatus contains and protects bare wire contacts, pin-socket, or soldered connections. In such instances, all of the electrical connections are made in an array at one location. This requirement constrains the configuration of the electrical and may not be suitable for all applications. 
     Strain relief devices also exist that o not function as connectors. The mechanism by which the strain relief device is attached to the printed circuit board or wire rack is one feature that characterizes them. These include press-fitting posts, stand-offs, through-hole technology, screws, adhesives, and side clamping mechanisms. Complex multi-part assemblies may require tools and installation time that are unsuitable for high volume production. Simple designs may employ snaps, clips, or ties to secure wires in places, but these may exhibit weak structural integrity unsuitable for applications requiring high reliability. These and others frequently exhibit excessive vertical profiles that extend the height of the assembly significantly above the height of the printed circuit board. This precludes their use in low profile applications, such as those of an electric motor. As always, planform area is an important consideration in the design of circuit board layouts. Reliability and ease of use are often in conflict while both remain important considerations in the design of electronics. An efficient solution is required to advance the state of the art. 
     The subject disclosure is contemplated for use in an electric motor of the type such as a permanent magnet brushless motor that is disclosed by U.S. Pat. No. 7,105,973 BS, issued Sep. 12, 2006, the entirety of which is corporate by reference herein. The subject disclosure may also be implemented by those skilled in the art to other electric motor types and topologies including, but not limited to linear motors, outside rotating motors, hybrid steppers, permanent magnet steppers, variable reluctance motors, switched reluctance motors, or other polyphase electric motors. 
     An electric motor using a printed circuit board with a strain relief plug includes a rotor (not pictured) and a stator having a plurality of coils wrapped thereon. the coils comprising field windings. Electric motors may have single or multi-phase windings, and it is common for multiphase stators to be connected in either a star-wye connection pattern or a delta connection pattern with each motor phase having one or more stator field windings coils. 
     The flow of current into the field windings can be controlled and adjusted by motor control electronics via lead wires to produce a desired magnetic field and corresponding motor performance. Lead wires of individual motor phases, which are connected to the motor control electronics, may be soldered to the printed circuit board, and require strain relief using the technology of the subject disclosure. 
     The printed circuit board may also contain sensor devices used by the motor control electronics, such as position sensors or thermal devices. The lead wires of the individual sensor devices may be soldered to the printed circuit board and require strain relief using the technology of the subject disclosure. 
     SUMMARY 
     The subject technology is directed to a strain relief plug to restrict movement of one or more lead wires on a printed circuit board. The strain relief plug includes an elongated stem along a vertical axis of the strain relief plug. The strain relief plug includes an in-board flange defined by the elongated stem, the in-board flange configured to seat in a bore defined by the printed circuit board restricts lateral motion of the strain relief plug. The strain relief plug includes an anchor defined by a first end of the elongated stem configured to prevent the strain relief plug from releasing from the printed circuit board. The strain relief plug includes a bar defined by a second end of the elongated stem and transverse the vertical axis, the bar forming one or more lead wire channels to trap the one or more lead wires. 
     In one implementation, the bar may include turned ends. In another implementation, the anchor may include one or more flexible barbs. In another implementation, the one or more flexible barbs of the anchor may extend outwardly from the elongated stem transverse the vertical axis to form a gap between the anchor and the bar, the gap sized relative to a thickness of the printed circuit board. In another implementation, the strain relief plug may include one or more brackets defined by the elongated stem and extending transverse the vertical axis, the one or more brackets joining the bar, wherein the anchor extends outwardly toward the one or more brackets to form a gap between the anchor and the one or more brackets, the gap sized relative to a thickness of the printed circuit board. 
     In another implementation, the bar may be configured to pin the one or more lead wires against the printed circuit board. 
     In yet another implementation, the one or more lead wire channels is sized relative to a thickness of the printed circuit board and one or more lead wires. 
     In yet another implementation, the in-board flange may include a radial body having a tapered profile on an edge thereof to aid installation into the bore defined by the printed circuit board. The in-board flange restricts lateral motion of the strain relief plug while the anchor feature prevents the plug from releasing from the printed circuit board, but the combination of these two features does not over constrain the azimuthal orientation of the plug. Providing a range of angular positions for the installation of the strain relief plug to align with respect to various positions of wires is a significant advantage of the present invention. 
     In yet another implementation, the bar, defined by a second end of the elongated stem and transverse the vertical axis, may include a reinforcing spine affixed to the bar. 
     The subject technology is directed to a printed circuit board including one or more lead wires soldered to the printed circuit board forming one or more solder joints. The printed circuit board includes a strain relief plug having an elongated stem along a vertical axis of the strain relief plug, an in-board flange defined by the elongated stern, the in-board flange configured to seat in a bore defined by the printed circuit board, an anchor defined by a first end of the elongated stem having one or more flexible barbs configured to prevent the strain relief plug from releasing from the printed circuit board, and a bar defined by a second end of the elongated stem and transverse the vertical axis, the bar having turned ends to form one or more lead wire channels to trap the one or more lead wires. The one or more barbs extend outwardly toward the bar to form a gap between the one or more barbs and the turned ends, the gap sized relative to a thickness of the printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of the present disclosure are discussed herein with reference to the accompanying Figures. It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements can be exaggerated relative to other elements for clarity or several physical components can be included in one functional block or element. Further, where considered appropriate, reference numerals can be repeated among the drawings to indicate corresponding or analogous elements. For purposes of clarity, however, not every component can be labeled in every drawing. The Figures are provided for the purposes of illustration and explanation and are not intended as a definition of the limits of the disclosure. 
         FIG.  1    is an isolated perspective view of a strain relief plug in accordance with the subject disclosure. 
         FIGS.  2   a - 2   b    are cross-sectional perspective views of the strain relief plug of  FIG.  1    installed on a printed circuit board. 
         FIG.  3    is a perspective view of the strain relief plug of  FIG.  1    installed on a printed circuit board, including one or more lead wires. 
         FIGS.  4   a - 4   e    are overhead perspective views of the strain relief plug of 
         FIG.  1    installed on a printed circuit board. 
         FIG.  5    is a side perspective view of the strain relief plug of  FIG.  1    installed on a printed circuit board, showing a wire gap between one or more lead wires and the printed circuit board. 
         FIGS.  6   a - 6   b    are cross-sectional views of another implementation of a strain relief plug in accordance with the subject disclosure. 
         FIG.  7   a    is a top view of an electric motor armature with connections to a printed circuit board, wherein the strain relief plug of  FIG.  1    is installed thereon, acting on sensor lead wires. 
         FIG.  7   b - 7   c    are perspective views of the electric motor armature of  FIG.  7     a.    
         FIG.  7   d    is a side view of the electric motor armature of  FIG.  7   a   , displaying the profile height of the strain relief plug relative to the thickness of the sensor lead wires and printed circuit board thickness. 
     
    
    
     DETAILED DESCRIPTION 
     The subject technology overcomes many of the prior art problems associated with strain relief devices. The advantages, and other features of the technology disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain exemplary embodiments taken in combination with the drawings and wherein like reference numerals identify similar structural elements. It should be noted that directional indications such as vertical, horizontal, upward. downward, right. left and the like. are used with respect to the figures and not meant in a limiting manner. 
     Referring now to  FIG.  1   , a strain relief plug  100  is shown. The strain relief plug  100  may be readily installed to a printed circuit board or other installations to protect solder joints or other fragile secured wire connections from detrimental pulling forces, tension, stress, and the like. There is a great variety of electrical and solid state equipment including printed circuit boards or modules which are interconnected with other printed circuit boards or modules. This interconnection is enabled by securing interconnecting lead wires through the agency of relatively fragile bonds or solder joints on thin metallic solder pads. In all such instances, it is beneficial that these fragile connections be protected from any damaging mechanical forces encountered in assembling, using, maintaining, and servicing the equipment. 
     A coordinate system is used herein to help characterize implementations of the strain relief plug  100 . For example, a vertical axis  104 , a transverse axis  130 , and an axial axis  146  are referenced. The vertical axis  104  defines a vertical direction of the strain relief plug  100 , the transverse axis  130  is disposed at a 90 degree angle relative to the vertical axis  104  and defines a lateral direction of the strain relief plug  100 , and an axial axis  146  is disposed at a 90 degree angle relative to the vertical axis  104  and the transverse axis  130  and defines an axial direction of the strain relief plug  100  and a lead wire direction. 
     Referring briefly to  FIGS.  2   a - 2   b    for context, a cross-sectional view is illustrated of a conventional printed circuit board  202  with the strain relief plug  100  of  FIG.  1    installed therein. The printed circuit board  202  may include one or more typical flat laminated composites made from non-conductive substrate materials with one or more layers of copper circuitry buried internally or on an external surface. The printed circuit board  202  may include a first surface  204  and an opposing second surface  206  with conventional conductors etched on either the first or second surfaces  204 ,  206 . As referenced herein, the printed circuit board  202  includes a thickness t, shown in greater detail with reference to  FIG.  2   a   . The thickness is defined by a height of a connecting surface  208  joining the first surface  204  and the second surface  206 . 
     Referring to  FIGS.  1 ,  2     a , and  2   b  together, the strain relief plug  100  may be molded from a slightly resilient or flexible plastic. Alternatively, the strain relief plug  100  may include copper, silver, aluminum, gold, steel, or brass portions. The strain relief plug  100  is formed in the general configuration of a “T”, which includes an elongated stem  102 . The elongated stem  102  runs parallel to a vertical axis  104  of the strain relief plug  100 . As illustrated in  FIG.  1   , the elongated stem  102  terminates at a first end  106  thereof. 
     The first end  106  includes an anchor  108  defined thereby. The anchor  108  may include one or more flexible barbs  110  configured to prevent the strain relief plug  100  from releasing from the printed circuit board  202 . The bore  210  of the printed circuit board  202  may force an inner surface  112  of the one or more flexible barbs  110  to associate with a peripheral surface  114  of the elongated stem  102  upon insertion. Once the first end  106  of the elongated stem  102  has cleared the bore  210  of the printed circuit board  202 , the one or more barbs  110  may unassociate and broaden from the peripheral surface  114  such as to rivet, clamp, pin, screw, or otherwise fasten to the printed circuit board  202 . 
     In other implementations, the anchor  108  may include an enlargement or a knob-like projection. In this regard, the anchor  108  may be removably coupled to the elongated stern  102 . Upon installation of the strain relief plug  100  into the bore  210  of the printed circuit board  202 , and once the first end  106  of the elongated stern  102  has cleared the bore  210  of the printed circuit board  202 , the anchor  108  may thereafter be coupled to the first end  106  of the elongated stern  102  such as to rivet, clamp, pin, screw, or otherwise fasten to the printed circuit board  202 . 
     Disposed between the first end  106  and a second end  116  of the elongated stern  102  is an in-board flange  118  defined by the elongated stem  102 . The in-board flange  118  may include a radial body. In this regard, the in-board flange  118  may include a curvilinear geometric shape, such as that of a cylinder. The in-board flange  118  may include a first opposing surface  120 , a second opposing surface (not shown) opposite thereto, and a lateral side  123  joining the first opposing surface  120  and the second opposing surface. The lateral side  123  may include a height  124  relative to the vertical axis  104  of the strain relief plug  100 . 
     The height  124  of the lateral side  123  of the in-board flange  118  may resemble the thickness t of the printed circuit board  202 . For example, the height  124  may be the same as the thickness t of the printed circuit board  202 , slightly larger the thickness t of the printed circuit board  202 , or slightly less than the thickness t of the printed circuit board  202 . In the same respect, the in-board flange  118  may include a radius  126 . The radius  126  may resemble a radius of the bore  210  defined by the printed circuit board  202 , shown in greater detail with reference to  FIG.  2   a   . For example, the radius  126  may be the same as the radius of the bore  210 , slightly larger the radius of the bore  210 , or slightly less than the radius of the bore  210 . 
     The in-board flange  118  configured to seat in a bore  210  defined by the printed circuit board  202  restricts transverse  130  motion of the strain relief plug  100 , does not restrict rotation of the plug  100 , and allows for installation at an arbitrary angular position. 
     The in-board flange also does not over constrain an azimuthal orientation of the plug  100 . This provides a range of angular position for the installation of the strain relief plug  100  to align with respect to various position of wires  212 . 
     In  FIGS.  2   a   - 2   b,  the in-board flange  118  fits snug in the bore  210 . Thus, the in-board flange  118  has a smaller radius  126  than the radius of the bore  210 . The difference in radius may be miniscule to enable a close-fit between the two components. 
     The in-board flange  118  may include a beveled edge  122 . The beveled edge  122  may have a tapered profile to aid installation of the strain relief plug  100  into the bore  210  defined by the printed circuit board  202 . The beveled edge  122  may slope inwardly such that the first opposing surface  120  has a greater radius than the second opposing surface. As such, the beveled edge  122  may include a varying radius. 
     The second end  116  of the elongated stem  102  defines a bar  128 . The bar  128  extends along a transverse axis  130  relative to the vertical axis  104  of the strain relief plug  100 . In one implementation, the bar  128  may include a three-dimensional U-shape having a flat mounting surface  132  and one or more subjacent surfaces  134 . In another implementation, the bar  128  may include a portion of a three-dimensional annular shape, torus shape. or ellipsoid shape. In yet another implementation, the bar  128  may include a three-dimensional rectangular shape having a flat mounting surface  132  and one or more flat subjacent surfaces  134 . 
     In one implementation, the bar  128  may include a spine  150  mounted to the mounting surface  132 . The spine  150  may extend along the transverse axis  130  and provide support to the U-shape structure of the bar  128 . 
     The bar  128  may include turned ends  136 . For example, the mounting surface  132  may extend along the transverse axis  130  to a mounting surface curve  138 , and thereafter extend vertically along the vertical axis  104 , parallel to the elongated stem  102 , defining the turned ends  136 . The mounting surface  132  may meet the one or more subjacent surfaces  134  at a turned end periphery  140  to form the three-dimensional U-shape mentioned. 
     The bar  128  and the anchor  108  form a gap g. For example, in one implementation, the turned end periphery  140  and a flexible barb periphery  148  may form the gap g. The one or more flexible barbs  110  and the turned ends  136  may each include a respective height relative to the vertical axis  104  to adjust the length, width, or height dimension of the gap g. In a preferred implementation, the one or more flexible barbs  110  and the turned ends  136  form a gap g having a vertical dimension resembling the thickness t of the printed circuit board  202  and one or more lead wires  212 . For example, the gap g may have a vertical dimension equal to, slightly less than, or slightly larger than the thickness t of the printed circuit board  202 . 
     To install, the strain relief plug  100  may be inserted into the bore  210  defined by the printed circuit board  202 . The one or more flexible barbs  110  are configured to prevent the strain relief plug from releasing from the printed circuit board  202  as a flexible barb periphery  148  makes contact with the second surface  206  of the printed circuit board  202 . 
     Once the strain relief plug  100  is installed in the bore  210  of the printed circuit board  202  as shown in  FIGS.  2   a   - 2   b,  the turned ends  136  and the one or more flexible barbs  110  make contact with opposite sides of the printed circuit board  202 , restricting movement of the printed circuit board  202  relative to the vertical axis  104  of  FIG.  1   . 
     Additionally, the bar  128  forms one or more lead wire channels  142  to trap or restrict the one or more lead wires  212  on the printed circuit board  202 . In one implementation, the turned ends  136  may include an outward ledge  144  to restrict movement of the one or more lead wires  212  along the transverse axis  130 . In another implementation, the subjacent surface  134  of the bar  128  may restrict movement of the one or more lead wires  212  along the vertical axis  104 . In yet another implementation, the subjacent surface  134  of the bar  128  may restrict movement of one or more lead wires  212  along a transverse axis  130  by pinning the one or more lead wires  212  against the printed circuit board  202 . In yet another implementation, the subjacent surface  134  of the bar  128  may restrict movement of the one or more lead wires  212  along an axial axis  146  by pinning the one or more lead wires  212  against the printed circuit board  202 . In yet another implementation, the turned ends  136 , subjacent surface  134  of the bar  128 , and the first opposing surface  120  of the in-board flange  118  form one or more lead wire channels  142  to trap the one or more lead wires  212  on the printed circuit board  202 . 
     In  FIGS.  2   a   - 2   b,  the one or more lead wires are restricted in motion along the transverse axis  130  of  FIG.  1    by the turned ends  136 , while the one or more lead wires are restricted in motion along the vertical axis  104  of  FIG.  1    by subjacent surface  134  of the bar  128  and the first surface  204  of the printed circuit board  202 . 
     Though, the anchor  108  and in-board flange  118  do not constrain the angular orientation of the plug  100  and allow for variability in the directional alignment of the wires  212  on the printed circuit board  202 . 
     Referring now to  FIG.  3    and  FIGS.  4   a   - 4   e,  a perspective view and overhead views of the strain relief plug  100  installed in the bore  210  of the printed circuit board  202  are shown. The strain relief plug  100  restricts motion of the one or more lead wires  212  along the transverse axis  130  and/or vertical axis  104  shown in  FIG.  1   , with respect to solder joints  402 . In turn, detrimental pulling forces, tension, stress, and the like are mitigated on the solder joints  402 . 
       FIG.  5    shows a perspective view of the strain relief plug  100  installed in the bore  210  of the printed circuit board  202 . In the implementation shown, the anchor  108  includes an enlargement or a knob-like projection. In this regard, the anchor  108  is removably coupled to the elongated stem  102 . Upon installation of the strain relief plug  100  into the printed circuit board  202 , the anchor  108  may thereafter be coupled to the first end  106  of the elongated stern  102  such as to rivet, clamp, pin, screw, or otherwise fasten to the printed circuit board  202 . 
       FIG.  5    also shows a wire gap  502  between the one or more lead wires  212  and the circuit board  202 . As such, the one or more lead wires  212  need not make contact with the first surface  204  of the circuit board  202  to restrict movement. Similarly the one or more lead wires  212  need not make contact with the turned ends  136  of the strain relief plug  100 . Rather, in both scenarios, the first surface  204  or the turned ends  136  may provide a motion boundary in which the one or more lead wires can move along the vertical  104  and transverse axis  130 . 
       FIGS.  6   a - 6   b    show another implementation of a strain relief plug  600 , similar to the strain relief plug  100  of  FIG.  1   . The strain relief plug  600  of  FIGS.  6   a - 6   b    is different from the strain relief plug  100  in that strain relief plug  600  includes one or more brackets  602 . The one or more brackets  602  are defined by the elongated stem  102  and extend along the transverse axis  130  of  FIGS.  6   a   - 6   b,  that is, transverse the vertical axis  104 . The one or more brackets  602  join the turned ends  136  to form one or more lead wire channels  142  that are enclosed, encapsulating at least a portion of the one or more lead wires  212 . The one or more brackets  602  may form a bracket angle  604  or may curve in order to join the turned ends  136 . 
     Additionally, the strain relief plug  600  is different from the strain relief plug  100  in that the bar  128  of strain relief plug  600  transitions into the turned ends  136  at a rigid angle as opposed to the strain relief plug  100  of  FIG.  1   . For example, the bar  128  may transition into turned ends  136  at a 90 degree angle. For example, the bar  128  may transition into turned ends  136  at an angle ranging from 1 to 179 degrees. 
       FIGS.  7   a - 7   d    show top, side, and axial views of an electric motor armature  700  with connections to a printed circuit board  202 . The electric motor armature  700  carries alternating current. Armature windings conduct AC even on DC machines, due to commutator action (which periodically reverses current direction) or electronic commutation, as in brushless DC motors. The armature  700  can be on either the rotor (rotating part) or the stator (stationary part) of an electric motor, depending on the type of electric machine. The strain relief plug  100  of  FIG.  1    is installed to the printed circuit board  202  of the electric motor armature  700 . The strain relief plug  100  restricts motion of the one or more lead wires  212  along the transverse axis  130  and/or vertical axis  104  shown in  FIG.  1   , with respect to solder joints  402 . In turn, detrimental pulling forces, tension, stress. and the like are mitigated on the solder joints  402 . 
     Referring specifically to  FIG.  7   d   , the strain relief plug  100  has a relatively low profile height compared to the thickness of the one or more lead wires  212  and printed circuit board  202  thickness. This low profile helps improve the electric motor assembly torque density. 
     As can be seen, the subject disclosure provides many improvements to strain relief devices. For example, without limitation, the use of the strain relief plug  100 ,  600  described herein provides strain relief in a vertical direction, resembling the thickness of one or more lead wires and the thickness of a printed circuit board, amounting to a reliable way to protect soldered joints and lead wires connected thereto. During assembly, testing, use, and maintenance of printed circuit boards having such connection, the lead wires are frequently pulled from modules and boards. Further, the subject technology can be adapted to any kind of solder joint, module, or board. 
     All of the features as described achieve strain relief for solder joints in a considerably low profile topology component compared to commercially available strain reliefs. That is, the strain relief plugs  100 ,  600  hold lead wires in a manner to prevent stress on a solder joint without adding substantial height to a printed circuit board. 
     As a further advantage, the strain relief plugs  100 ,  600  described herein accomplish strain relief of solder joints on electric motor connection printed circuit boards. Electric motor performance is commonly compared on the basis of torque per length or torque per volume. The low profile of strain relief plugs  100 ,  600  facilitates improvements in torque density on the order of 30% compared to existing products in the marketplace when used for strain relief of solder joints on an electric motor connection printed circuit board. 
     It will be appreciated by those of ordinary skill in the pertinent art that the functions of several elements can, in alternative embodiments, be carried out by fewer elements, or a single element. Similarly, in some embodiments, any functional element can perform fewer, or different, operations than those described with respect to the illustrated embodiment. Also, functional elements shown as distinct for purposes of illustration can be incorporated within other functional elements in a particular embodiment. 
     While the subject technology has been described with respect to various embodiments, those skilled in the art will readily appreciate that various changes and/or modifications can be made to the subject technology without departing from the scope of the present disclosure.