Tamper proof set screw

Details Tamper proof set screw Tamper proof set screw

1998-11-10

2001-04-03

Fox, John (Department: 3753)

Fluid handling

With lock or seal

C070S229000

Reexamination Certificate

active

06209575

ABSTRACT:

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.


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