Patent Publication Number: US-6209575-B1

Title: Tamper proof set screw

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to locking devices and, more particularly, to an apparatus for preventing unauthorized access to a rotating shaft. 
     2. Discussion of the Prior Art 
     Standard industrial exhaust trunk blast gates are used extensively as a means to control the passage of exhaust air volume. An industrial exhaust trunk blast gate of the prior art is shown in detail in FIG.  1 . The blast gate  1 , illustrated in FIG. 1, is constructed as two components, a stationary member  2  (exhaust gate housing), and a sliding member  3  (exhaust gate), which slides in relation to the stationary member  2 . In a typical application, the stationary member  2  is fixed in an exhaust duct in a path through which the exhaust air volume of interest will pass. The stationary member  2  is fixed in place by connecting rigid ductwork to each side of the aperture  4 . Once in place, the sliding member  3  is then positioned relative to the stationary member  2  to cover some portion of the aperture through which the exhaust air will flow. The extent to which the aperture  4  is covered by the sliding member  3  is continuously adjustable from fully exposed to fully closed. Once the desired position of the sliding member  3  in relation to the stationary member  2  is determined, a standard set screw  7  is employed as a pressure fitting mechanism to fix the position of the sliding member. The set screw  16  is threaded into a mating threaded hole  6  in the stationary member with sufficient engagement so as to impinge the sliding member, thereby holding the sliding member in place at the desired position. 
     Additional securing means are sometimes employed to prevent unauthorized access by locking the sliding member  3  in place relative to the stationary member  2 . Because the set screw is vulnerable to unintended and unauthorized operation the additional locking means is utilized as an adjunct to prevent such occurrences. A pin type lock, described at FIG. 2, is typically employed as a locking means. 
     Referring now to FIG. 2 there is illustrated an exemplary pin type lock, well known in the art, such as one available from the Wilson Bohannan Company pin lock type 220ka2 16343a w/078. The lock is comprised of a locking pin  13 , a lock body  11  having a recess  14  for receiving the locking pin  13 . The lock pin having pin portion  8 , a contoured surface  12 , a shaft portion  9 , and a head portion  10 . The operational aspects of the pin lock will be described below. 
     Referring now to FIGS. 2 and 3, when a locking mechanism is utilized as an adjunct to prevent unauthorized tampering of the exhaust gate assembly  1 , a structural modification to both the stationary  2  and sliding  3  members is required. In FIG. 3 equal diameter holes are shown drilled into the face of both the stationary  2  and sliding  3  members to accommodate insertion of the locking pin through both members. A single hole  7  is all that is required to be drilled in the stationary member  2 . The sliding member  2 , however, typically may require a multiplicity of drilled holes  8 ( a-c ) to accommodate the various desired aperture exposures. That is, the system for which the exhaust gate was designed may be required to have the aperture  4  open or closed to greater or lesser degrees depending upon changing system requirements. In general, any number of holes may be drilled into the sliding member  3  to accommodate the required aperture exposure. 
     The operational aspects of the locking mechanism of the prior art will be discussed with reference to FIGS. 2,  3  and  4 . In FIG. 4, the sliding member  3  would first be aligned with the stationary member  2  such that one of a plurality of pinlock holes  8 ( a-c ) in the sliding member would coincide with the single pinlock hole  7  in the stationary member. The particular hole chosen for alignment on the sliding member  2  fixes the degree of exposure in the exhaust aperture  4 . FIG. 4 illustrates the selection of hole  8   c , by way of example, for alignment with pinlock hole  7  on the stationary member  2 . Selecting hole  8   c  for alignment results in an aperture  4  exposure defined by numeral  15 . Once aligned, the locking pin  13 , illustrated in FIG. 2, would then be inserted through aligned pinlock holes  7  and  8   c , respectively. The pin portion  8  of the locking pin  13  would then be inserted into the pinlock body  11  through an recess  14  in the base end of the pinlock body  11 . The recess  14  is of sufficient diameter to receive the pin side  8  of the locking pin  13 . 
     A disadvantage of having to drill multiple holes (i.e.  8 ( a-c )) into the sliding member  2  is that once a particular hole on the sliding member is chosen for the purpose of aligning and locking the two members in place, some portion of the unaligned holes  8  may be located inside the aperture  4  of the stationary member. FIG. 4 illustrates this situation. Specifically, FIG. 4 illustrates the selection of hole  8   c  for alignment. The selection of hole  8   c  for alignment causes the two remaining unaligned holes,  8   a  and  8   b , to be positioned inside the aperture  4  to varying degrees. It is shown at FIG. 4 that hole  8   a  is fully contained within the aperture  4 , while hole  8   b  is only partially contained within the aperture  4 . It is apparent that the desired aperture exposure  15 , as determined by the selection of aligning hole  8   c , will be compromised to the extent that holes  8   a  and  8   c  result in additional exposed surface area. The additional exposed surface area is undesirable for a number of reasons including; (1.) if the sliding member were positioned to be fully closed, exhaust air would still pass through the aperture  4 ; (2.) There is an associated cost associated with the accumulative lost exhaust air over time, (3.) Maintaining control over a desired flow volume would be difficult, and precise adjustments are difficult to achieve, (4.) The structural integrity of the blast gate is compromised. 
     It would therefore be desirable to be able to secure the sliding member in place relative to the stationary member  2  so as to prevent unauthorized and unintended adjustment of the set screw without requiring mechanical modification to either the sliding or stationary members. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished to eliminate the aforesaid disadvantages and problems. It is therefore an object of the present invention to provide an apparatus to prevent unintended and unauthorized operation of a set screw by encasing a vulnerable portion of the set screw in a standard pin type lock which renders the set screw impervious to unauthorized operation. 
     According to one aspect of the invention there is provided a tamper proof set screw including a threaded end portion, a contoured portion and a pin end portion. In operation, the threaded end is threaded through a threaded hole in a stationary member to fully engage, and thereby prevent movement of a sliding member, that slides in relation to the stationary member. Once engaged the sliding member is held in position relative to the stationary member and the pin portion of the set screw is then inserted into a recess of a pin type lock and locked therein to form a combined assembly. The lock freely turns on the set screw thereby preventing unauthorized disengagement of the threaded end portion of the set screw with the sliding member. 
     According to the present invention there is provided an apparatus for locking a set screw including: a first member, a second member for moving relative to the first member, a set screw threadedly engaging the first member, the set screw for engaging the second member to secure a position of the second member relative to the first member, and a locking device for receiving a portion of the set screw extending from the first member, the locking device being permitted to rotate relative to the set screw such that threaded engagement with the first member is maintained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a prior art illustration of a standard industrial exhaust gate. 
     FIG. 2 is a prior art illustration of an exemplary pin lock. 
     FIG. 3 is a prior art illustration of a modified industrial exhaust gate, modified for use with a pin lock. 
     FIG. 4 is a prior art illustration of the modified exhaust gate of FIG. 3 during operation. 
     FIG. 5 is a illustration of an industrial exhaust gate in accordance with the present invention. 
     FIG. 6 is a illustration of a tamper proof set screw in accordance with the present invention. 
     FIG. 7 is a cross-sectional view of the base end of the pin type lock. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     While certain preferred implementations are described herein, it is to be understood that the teachings of the present invention are susceptible of more general usage. 
     With reference now to the drawings, and in particular FIGS. 5 to  7 , a new and improved tamper proof set screw embodying the principles of the present invention will be described. 
     Referring now to FIGS. 5 and 6, an industrial exhaust gate is shown including a stationary portion  30  and a sliding portion  20 . The stationary portion  30  further includes a hole  26  with inner threads for receiving a set screw  21 . FIG. 6 illustrates a tamper proof set screw  21  having a threaded portion  24 , a pin portion  26 , and an engagement portion  28 . A contour  27  defines the boundary between the engagement portion  28  and the pin portion  26 . The tamper proof set screw  21  of the present invention performs several functions including securing the sliding member  20  relative to the stationary member  30  to prevent unauthorized and unintended movement of the sliding member  20  by frictional coupling. To further secure the sliding member  20  relative to the stationary member  30  additional securing means are contemplated in addition to the frictional coupling. For example, in one embodiment the engagement portion  28  could terminate in a tapered end, sized appropriately for mating with an aligned indentation in the sliding member  20 . In an alternate embodiment, the sliding member may include a plurality of dimples on its mating surface. In yet another embodiment, a bayonet coupling may be substituted for the threaded engagement contemplated by the preferred embodiment. In another embodiment, the engagement portion  28  could terminate in a concave tip end. 
     The pin portion  26  of the set screw  21  is adapted to receive an adjustment tool. The adaptation may be configured to receive a flathead screwdriver, wrench, phillips head screwdriver, allen wrench. Other adaptations, not expressly enumerated, are within the intended scope of the present invention. 
     In accordance with the teachings of the present invention, a vulnerable portion  23  of the set screw  21  is configured and dimensioned to fit in a standard pin type lock  22  to guard against undesired access to the set screw  21 . The pin lock assembly  33  described at FIG. 6 requires a key  29  for proper operation. The pin type lock  33  may be of a type described by FIG. 2, however, other lock assemblies, for example, combination, slider, digit, and rotary locks, are all within the scope of the present invention. 
     Referring now to FIGS. 6 and 7, the pin portion  26  of the set screw  21  is configured to fit into an recess  32  of a base end  22  of the pin type lock  33  for engagement. Turning the key  29  causes a spring loaded engagement member  30  to recede from the recess  35  thereby permitting the passage of the pin portion  26  into the recess  35 . Releasing the key causes the spring loaded engagement member  30  to move partially into the interior of the recess  35  engaging the contoured surface  27  of the set screw and thereby preventing the set screw from disengagement with the recess  35 . 
     When the tamper proof set screw is functioning in the standard industrial trunk blast gate lock assemblage, which is merely representative, it is intended that the set screw may only be turned for engaging it with or disengaging it from the sliding portion  14  by possessing a key  30  to release the pin lock  22  from engagement with the pin side  26  of the set screw  21 . 
     Without access to the key, when the pin side  26  of the standard pin type lock  22  is engaged with the tamper proof set screw  20 , the pin lock and screw freely turn on each other thereby prohibiting access to the set screw. 
     Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention.