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CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an add-on type of tamper-resistant lock structure for a cover and to a method of establishing a tamper-resistant locking connection between a cover and a device on which it is mounted. 
     By way of background, there are numerous boxes and other devices in existence which have covers which are movable relative to the remainder of the device. In the past various types of locking devices were used in conjunction with such devices. 
     BRIEF SUMMARY OF THE INVENTION 
     It is one object of the present invention to provide a tamper-resistant lock structure which can be added onto a device which is modified in a simple and expedient manner. 
     Another object of the present invention is to provide a method of establishing a tamper-resistant locking connection between a cover and another part of the device. Other objects and attendant advantages of the present invention will readily be perceived hereafter. 
     The present invention relates to a tamper-resistant lock structure comprising a shroud, a cavity in said shroud, an end wall in said shroud, a bore in said end wall, a bolt, a shank on said bolt extending through said bore, a head on said bolt located in said cavity, a liner in said cavity between said head and said shroud, and a key-receiving configuration on said head. 
     The present invention also relates to a tamper-resistant lock structure comprising a nut for affixation to a device, a shroud, an end wall on said shroud, a bore in said end wall, a bolt, a shank on said bolt extending through said bore and received in said nut, a cavity in said shroud, a liner in said cavity located between said head and said shroud, a head on said bolt located in said liner, and a key-receiving configuration on said head. 
     The present invention also relates to an improvement to a device having a part and a cover which moves relative to said part, the improvement of a tamper-resistant lock structure addition to said device comprising a nut attached to said part, an aperture in said cover, a shroud mounted on said cover in alignment with said nut, an end wall on said shroud, a bore in said end wall, a cavity in said shroud, an inner surface of said shroud defining said cavity, a bolt, a shank on said bolt extending through said bore in said end wall and said aperture in said shroud, a head on said bolt in said cavity, and a key-receiving configuration on said head. 
     The present invention also relates to a method of establishing a tamper-resistant locking connection between a cover and a flange on a device comprising the steps of forming a first aperture in said cover, forming a second aperture in said flange, placing a nut in alignment with said second aperture, providing a shroud with a cavity and an end wall and a bore in said end wall, providing a bolt having a head and a shank, inserting said shank through said bore in said end wall and through said first aperture and into said nut with said head of said nut contained in said cavity. 
     The various aspects of the present invention will be more fully understood when the following portions of the specification are read in conjunction with the accompanying drawings wherein: 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a perspective view of an electric meter box mounting the tamper-resistant lock structure of the present invention; 
     FIG. 2 is an enlarged fragmentary side elevational view partially in cross section taken substantially along line  2 — 2  of FIG. 1 of the lock structure mounted on the meter box of FIG. 1; 
     FIG. 3 is a fragmentary exploded view of the parts of FIG. 2; 
     FIG. 4 is an enlarged fragmentary cross sectional view taken substantially along line  4 — 4  of FIG.  1  and showing only certain of the parts shown in FIG. 2; 
     FIG. 5 is a view of the U-nut taken substantially in the direction of arrows  5 — 5  of FIG. 3; 
     FIG. 6 is a cross sectional view of the bolt taken substantially along line  6 — 6  of FIG. 3; 
     FIG. 7 is an end view of the bolt head taken substantially in the direction of arrows  7 — 7  of FIG. 6; 
     FIG. 8 is an end elevational view of the liner taken substantially in the direction of arrows  8 — 8  of FIG. 3; 
     FIG. 9 is a cross sectional view of the liner taken substantially along line  9 — 9  of FIG. 8; 
     FIG. 10 is a cross sectional view of the shroud taken substantially along line  10 — 10  of FIG. 3; 
     FIG. 11 is an end elevational view of the shroud taken substantially in the direction of arrows  11 — 11  of FIG. 10; 
     FIG. 12 is an end elevational view of the shroud taken substantially in the direction of arrows  12 — 12  of FIG. 10; 
     FIG. 13 is a fragmentary cross sectional view of another shroud embodiment of the present invention; 
     FIG. 14 is a fragmentary cross sectional view taken substantially along line  14 — 14  of FIG. 13; 
     FIG. 15 is a fragmentary cross sectional view taken substantially along line  15 — 15  of FIG. 13; 
     FIG. 16 is a fragmentary side elevational view of another embodiment of the present invention having a different type of liner, without the protective cap which is used with this embodiment; 
     FIG. 17 is an end elevational view taken substantially in the direction of arrows  17 — 17  of FIG. 16 without the tie for the seal; 
     FIG. 18 is a fragmentary side elevational view, partially in cross section of the liner of FIG. 16; 
     FIG. 19 is an end elevational view taken substantially in the direction of arrows  19 — 19  of FIG. 18; 
     FIG. 20 is an end elevational view taken substantially in the direction of arrows  20 — 20  of FIG. 18; 
     FIG. 21 is a cross sectional view taken substantially along line  21 — 21  of FIG.  22  and showing the embodiment of FIG. 16 in position on the cover of the container, with certain parts omitted in the interest of clarity; 
     FIG. 22 is an end elevational view taken substantially in the direction of arrows  22 — 22  of FIG. 21; 
     FIG. 23 is an end elevational view taken substantially in the direction of arrows  23 — 23  of FIG. 21 but showing only the protective cover; 
     FIG. 24 is an exploded side elevational view partially in cross section, of another embodiment of the present invention; 
     FIG. 25 is a fragmentary side elevational view, partially in cross section, of still another embodiment of the present invention; and 
     FIG. 26 is a fragmentary side elevational view, partially in cross section, of still another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1 an electric meter box  10  is shown mounting two tamper-resistant lock structures  11  of the present invention. The lock structures  11  are add-on devices which lock box cover  12  against being swung to an open position about a hinge (not shown) located in area  13 . The lock structure  11  secures cover  12  having flange  14  thereon to flange  15  (FIG. 2) which is bent upwardly from end wall  17 . It will be appreciated that one or more lock structures  11  can be used with any type of device which has a cover. 
     Each tamper-resistant lock structure  11  includes a U-nut  19  (FIGS. 2 and 5) which slips over and is thus attached to flange  15 , and it has its internally threaded extension  20  in line with an aperture  21  which has been formed in flange  15 . In this regard, flange  15  did not previously have an aperture  21  for each lock structure  11  before aperture  21  was formed as a part of the present invention. The U-nut  19  is an existing type of prior art device. It will be appreciated that any other suitable nut device which attaches to flange  15  or is otherwise added to an internal portion of box  10  for receiving bolt  32  (FIG. 3) in threaded relationship can be used in accordance with the present invention. 
     Each tamper-resistant lock structure  11  also includes a shroud  22  having an outer frustoconical surface  23  and a cylindrical cavity  24  (FIG. 10) defined by wall  25 . Shroud  22  also has an end wall  27  with a bore  29  therein and a cylindrical boss  30  extending out of the rear of end wall  27 . Boss  30  is received in aperture  31  which is formed in cover  12  (FIGS. 2,  3  and  4 ) so that the shroud will not move laterally on the cover. In this respect, cover  12  does not originally have apertures  31  for receiving bosses  30 ; apertures  31  were formed as part of the present invention. By virtue of the boss  30  being located in aperture  31 , if the shroud  22  is pounded from a lateral direction, the force will be transmitted to the cover rather than to the threads  34  on shank  33 . 
     The apertures  21  in flange  15  and the apertures  31  in cover  12  are formed in a single drilling operation when the cover is in a closed position. Thus proper alignment of apertures  21  and  31  is assured. 
     The lock structure  11  also includes a bolt  32  having a shank  33  which has threads  34  thereon. The bolt  32  also has a frustoconical end  35  which aids in aligning the bolt with threads  37  of U-nut  19  into which shank  33  is threaded. In this respect, the frustoconical end  35  is guided to threads  37  by frustoconical wall  39  (FIG. 3) of U-nut  19 . The frusto-conical end  35  also aids in aligning the nut  19  with shank  33  by causing it to slide to an aligned position with shank  33  in the event that it moved to a misaligned position on flange  15 . Shank  33  also includes a neck  40  which is received in bore  29  of shroud  22  (FIG.  4 ). Bolt  32  also includes a cylindrical head  41  (FIGS. 3 and 4) which is received in shroud cavity  24 . The outer surface  42  of bolt head  41  is below the end  43  of shroud  22 . A curvilinear groove  44  is formed in bolt head  32  for receiving a mating key (not shown) of the type having a mating curvilinear ridge which is received in groove  44  to turn bolt  32 . 
     Further in accordance with the indicated embodiments of the present invention, the tamper-resistant lock structure  11  includes a liner  45  (FIGS. 3,  4 ,  8  and  9 ), fabricated out of plastic, which fits between the side of bolt head  41  (FIG. 4) and the internal surface  25  of shroud  22 . Liner  45  has a rim  47  (FIGS. 4 and 8) which fits between end wall  27  of shroud  22  and the annular undersurface  49  of bolt head  41  to thereby retain liner  45  against axial movement out of shroud cavity  24 . Additionally, shroud  45  has a plurality of elongated triangular protrusions  50  (FIGS. 3 and 8) on its outer surface spaced at 90° intervals, or any other suitable intervals, to provide an interference or frictional fit between liner  45  and internal wall  25  of shroud cavity  24 . Additionally, a plurality of triangular protrusions  51  (FIG. 8) extend inwardly from rim  47  of liner  45 , and they provide an interference or frictional fit between rim  47  and cylindrical portion  52  (FIGS. 3,  4  and  6 ) of bolt head  41 . Also, a plurality of triangular protrusions  56  are formed on the inside surface of liner  45 , and they provide an interference fit between liner  45  and cylindrical portion  32  of bolt head  41 . Triangular protrusions  56  need only be of a length sufficient to frictionally engage all or part of cylindrical portion  52  of bolt head  41 . The interference fit between protrusions  50  and internal shroud wall  25  and the interference fit between cylindrical bolt portion  52  and protrusions  51  and the interference fit between cylindrical bolt portion  32  and protrusion  56  thus maintain the shroud  22 , bolt  32  and liner  45  in assembled relationship while permitting relative rotation therebetween, as may be necessary when bolt  32  is threaded into U-nut  19 . The interference fit between the parts also permits the assembled bolt, liner and shroud to be digitally manipulated as a unit in mounting these parts on the cover  12 . The thickness of cylindrical portion  52  is greater than the thickness of liner rim  47  so that when surface  48  of cylindrical portion  52  is fully seated against surface  53  of shroud end wall  27 , rim  47  is not squeezed between surface  53  of end wall  27  and annular surface  49  of bolt head  32 . 
     Liner  45  has an end portion  54  (FIGS. 2 and 4) which extends outwardly beyond the end  43  of shroud  22 . End portion  54  has a pair of diametrically opposite apertures  55  therein which receive tie  57 , the ends of which are secured to a seal  59 , or any other suitable tamper-indicating device. It can thus be seen from FIG. 8 that since tie  57  extends between apertures  55 , a ridged key cannot pass tie  57  to mate with curvilinear groove  44  in bolt head  41  unless tie  57  is first removed. 
     In FIGS. 13-15 a modified shroud construction is disclosed. The shroud  22 ′ is identical in all respects to shroud  22  previously described except that the boss  30 ′, which is analogous to boss  30  of shroud  22 , is square and it fits into a square opening  31 ′ in cover  12 ′, which is analogous to cover  12  of FIG.  1 . This construction prevents shroud  22 ′ from rotating relative to cover  12 ′. It will be appreciated that any noncircular shape of a boss analogous to boss  30 ′ and its complementary opening can be used to provide a non-rotatable fit. 
     In FIGS. 16-23 a further embodiment of the present invention is disclosed. In this embodiment the shroud  22  and bolt  32  are identical to those described above relative to FIGS. 1-12. Also, if desired, the shroud may be identical to shroud  22 ′ of FIGS. 13-15. The only difference in the lock structure of FIGS. 16-23 is in the configuration of liner  45 ′, which is analogous to liner  45  of FIGS. 1-12. The liner  45 ′ does not have the cylindrical extension  54  (FIG. 4) of shroud  45 . Instead it has two arcuate ears  60  which extend beyond end  43 ′ of liner  45 ′ and end  43  of shroud  22 . These ears each have an aperture  61  therein. The diametrically opposite apertures  61  receive the tie  57  having ends which are secured in seal  59  (FIGS.  1  and  2 ). Aside from the foregoing, the liner  45 ′ has protrusions  50 ′,  51 ′ and  56 ′ which are analogous to protrusions  50 ,  51  and  56 , respectively, of FIGS. 8 and 9. Also, the liner  45 ′ has a rim  47 ′ which is analogous to rim  47  of FIG.  9 . The protrusions  50 ′,  51 ′ and  56 ′ function in the same manner as described above relative to protrusions  50 ,  51  and  56 , respectively. Also, the rim  47 ′ functions in the same manner as rim  47  of FIG.  9 . 
     The embodiment of FIGS. 16-23 includes a protective cap  65  which fits over shroud  22  as shown in FIGS. 21-23. More specifically, protective cap  65  includes a frustoconical wall  67  and an end wall  69 . A pair of arcuate slots  70  are located in end wall  69  and they receive ears  60  as shown. Protective cap  65  is dimensioned so that when inner surface  71  of end wall  69  abuts end  43  of shroud  22 , there will be a slight annular clearance at  72  between the annular end  73  of protective cap  65  and the surface of wall  12 . As noted above, the tie  57  extends through spaced apertures  61  in ears  67 . Thus, when tie  57  is in its position, protective cap  67  prevents access to the surface of bolt head  32 . 
     While every shroud embodiment described above includes a boss, it will be appreciated that the shroud can function to cooperate in providing the tamper-resistant operation without a boss. In this respect, the end wall of the shroud may be pressed against cover  12 , or it may be spaced therefrom so that it can rotate on its associated bolt, as shown in FIGS. 24-26. 
     In FIG. 24 a lock construction  75  is shown wherein shroud  77  is rotatably mounted on bolt  79 . The lock structure  75  includes a U-nut  19  mounted on flange  15  as described in detail above relative to FIGS. 2,  3  and  5 . In addition, the bolt  79  includes a head  80  having a curvilinear groove therein (not shown) which is of the type shown in FIG. 7 for receiving a key. Shroud  77  has a frustoconical outer surface and it includes a cavity  81  therein and a liner  45 , which is identical in all respects to liner  45  of FIGS. 8 and 9. Liner  45  is positioned in cavity  81 , as shown, with its rim  47  located between the annular edge  82  of bolt head  80  and the annular edge  83  of end wall  84  of shroud  77 . 
     In the embodiment of FIG. 24, bolt  79 , when threaded into U-nut  19 , has the annular surface  85  of cylindrical bolt portion  87  pressed against cover  12 . The axial length a of bolt portion  87  is larger than the axial length b of end wall  84  of shroud  77 . Therefore, there will be a clearance  89  between the end  90  of shroud  77  and the surface of end wall  12  which permits shroud  77  to spin or rotate on bolt  79 . This is advantageous, as well known in the prior art, so that if a wrench is applied to the surface of shroud  77 , the latter will merely spin on bolt  79  without transmitting any torque to bolt  79 . The liner  45  functions in all respects in the same manner noted above relative to the other embodiments of the invention. 
     In FIG. 25 another embodiment of the present invention is disclosed wherein shroud  91 , which has a frusto-conical outer surface, is rotatably mounted on bolt  92 . Shroud  91  includes an annular end wall  93  which is located between the annular edge  94  of bolt head  95  and the surface  96  of cover  12 . The annular end wall  93  of shroud  91  is dimensioned so that its axial length c is smaller than the axial length d of cylindrical portion  97  of bolt  92  thereby providing a clearance  99  between surface  100  of shroud  91  and surface  96  of cover  12 . Thus, shroud  91  can rotate or spin on bolt  92 . The only basic difference between the embodiment of FIG.  24  and the embodiment of FIG. 25 is that the latter does not have a liner  45 . The embodiment of FIG. 25 is used with the shown U-nut  19  and as described above relative to FIG.  24 . 
     In FIG. 26 a still further embodiment of the present invention is disclosed wherein the bolt  92  may be identical in all respects to bolt  92  of FIG.  25 . The shroud  101  varies only from shroud  91  of FIG. 25 in that it has a greater axial length so that a pair of diametrically opposed bores  102  can be made therein to receive a tie such as  57  and an associated seal such as  59  described above relative to FIGS. 2 and 4. The embodiment of FIG. 26 is used with the shown U-nut  19  and as described above relative to FIG.  24 . 
     While the above embodiments have shown a U-nut  19  mounted on a specific flange  15 , it will be appreciated that it is within the scope of the present invention to mount a nut on any other flange relative to which the cover moves or on any other portion of a device as a part of a lock assembly wherein a shroud and a bolt of the above types are mounted on a cover. 
     While the interference fit between the bolt and liner and shroud in the various embodiments has been described above as being effected by protrusions on the liner, it will be appreciated that the interference fit can be effected by frictional or interference engagement between the parts without the use of protrusions or can be effected by protrusions of other configurations. Furthermore, if desired, the frictional or interference engagement can be between only one of the bolt and the liner or the liner and the shroud. Also, while the above description has disclosed a frictional or interference fit between the bolt and the liner and/or the shroud and the liner, it will be appreciated that there need be no interference or frictional fit between the foregoing parts when it is desired to use the liner for the sole purpose of mounting a tie and a seal, as described above. 
     While preferred embodiments of the present invention have been disclosed, it will be appreciated that it is not limited thereto but may be otherwise embodied within the scope of the following claims.

Summary:
A device having a cover with an edge portion which is placed in adjacent relationship to a flange when the cover is in a closed position, a lock structure for locking the cover to the flange including a nut mounted on the flange for receiving the threaded shank of a bolt which extends through a bore in the end wall of a shroud having a cavity therein which contains the head of the bolt having a curvilinear groove therein for receiving a key. A method of adding a lock structure to a cover of a device including the steps of forming a first hole in a flange of the device, mounting a nut on the flange, forming a second hole in the shroud which aligns with the first hole, mounting a shroud in the second hole, extending the shank of a bolt through a portion of the shroud mounted in the hole, with the head of the bolt being contained within a cavity in the shroud.