U.S. patent application number 10/364828 was filed with the patent office on 2003-09-18 for floating captive screw.
Invention is credited to Aukzemas, Thomas V., Caulfield, Joseph N., Frattarola, Albert J., Standish, James F. III, Wolf, Boyd.
Application Number | 20030175091 10/364828 |
Document ID | / |
Family ID | 33096652 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030175091 |
Kind Code |
A1 |
Aukzemas, Thomas V. ; et
al. |
September 18, 2003 |
Floating captive screw
Abstract
A captive screw for securing together two panels has a screw and
a spring extending between the screw head and a ferrule. A collar
is formed on the screw shank under the ferrule to limit penetration
of the screw threads in a bottom panel so that the upper panel
floats on the spring.
Inventors: |
Aukzemas, Thomas V.;
(Wilmington, DE) ; Frattarola, Albert J.;
(Swarthmore, PA) ; Wolf, Boyd; (Chadds Ford,
PA) ; Standish, James F. III; (Kennett Square,
PA) ; Caulfield, Joseph N.; (Aston, PA) |
Correspondence
Address: |
Paul & Paul
2900 Two Thousand Market St.
Philadelphia
PA
19103
US
|
Family ID: |
33096652 |
Appl. No.: |
10/364828 |
Filed: |
February 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10364828 |
Feb 10, 2003 |
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09803221 |
Mar 9, 2001 |
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60188406 |
Mar 10, 2000 |
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Current U.S.
Class: |
411/107 |
Current CPC
Class: |
F16B 35/041 20130101;
Y10S 411/999 20130101; F16B 31/04 20130101; F16B 41/002 20130101;
F16B 5/0266 20130101 |
Class at
Publication: |
411/107 |
International
Class: |
F16B 039/00 |
Claims
We claim:
1. A captive screw comprising: a ferrule having an inner annular
ring on an interior surface of the ferrule; a screw having a head,
a shank adapted to pass through the ferrule, a threaded portion at
the end of the shank opposite the head, and a collar formed on the
shank proximate the threaded portion; and a spring extending on the
shank of the screw between the head and the ferrule; wherein the
screw is captivated on the ferrule between the head and the collar,
and the inner ring is dimensioned such that the collar does not
permit movement of the collar past the inner annular ring but
permits the passing through of the threads of the screw through the
collar.
2. The captive screw according to claim 1 wherein the ferrule has a
generally cylindrical exterior surface having a plurality of knurls
for securing the captive screw in a preformed aperture in a first
structure.
3. The captive screw according to claim 1 wherein the inner annular
ring forms a generally circular opening in the ferrule.
4. The captive screw according to claim 2 wherein the ferrule has
an annular lip formed on the exterior cylindrical surface proximate
the top of the ferrule for limiting the penetration of the ferrule
in the preformed aperture in the first structure.
5. The captive screw according to claim 2 wherein the ferrule has
an annular circumferential groove formed in the exterior
cylindrical surface of the ferrule immediately adjacent and below
the annular lip for receiving the plastic flow of material when the
ferrule is pressed into the preformed aperture.
6. A captive screw comprising: a ferrule having a first and a
second opposed ends and an inner annular ring on an interior
surface of the ferrule, said ferrule having an annular lip at one
of said first and second opposed ends and an annular
circumferential exterior groove adjacent said annular a screw
having a head, a shank adapted to pass through the ferrule, a
threaded portion at one end of the shank opposite the head, and a
collar formed on the shank proximate the threaded portion; and a
spring extending on the shank of the screw between the head and the
ferrule; wherein the screw is captivated on the ferrule between the
head and the collar, and the inner annular ring is dimensioned such
that the collar does not permit movement of the collar past the
inner annular ring but permits the passing through of the threads
of the screw through the collar.
7. The captive screw according to claim 6 wherein the annular lip
and the circumferential exterior groove are dimensioned and
configured for pressing the ferrule into a panel and securing the
captive screw in a preformed aperture in a first structure.
8. The captive screw according to claim 6 wherein the end of the
ferrule at which the annular lip is located faces the screw
head.
9. The captive screw according to claim 6 wherein the end of the
ferrule at which the annular lip is located faces the threaded
portion of the screw.
10. The captive screw according to claim 6 wherein the inner
annular ring forms a generally circular opening.
11. The captive screw according to claim 6 wherein the inner ring
is formed by plastic flow of the ferrule during assembly of the
captive screw.
12. A captive screw comprising: a ferrule having a first and a
second opposed ends, said ferrule having: a first annular lip at
one of said first and second opposed ends; an annular
circumferential exterior groove adjacent said first annular lip;
and a second annular lip adjacent to the annular circumferential
exterior groove and located across the annular circumferential
exterior groove with respect to the first annular lip; a screw
having a head, a shank adapted to pass through the ferrule, a
threaded portion at one end of the shank opposite the head, and a
collar formed on the shank proximate the threaded portion; and a
spring extending on the shank of the screw between the head and the
ferrule; wherein the screw is captivated on the ferrule between the
head and the collar, and the ferrule is dimensioned such that the
collar does not permit movement of the collar past the ferrule but
permits the passing through of the threads of the screw through the
collar.
13. The captive screw according to claim 12 wherein the ferrule has
a generally circular interior surface.
14. The captive screw according to claim 12 wherein the annular lip
and the circumferential exterior groove are dimensioned and
configured for pressing the ferrule into a panel and securing the
captive screw in a preformed aperture in a first structure.
15. The captive screw according to claim 12 wherein the first
annular lip extends outwardly away from the ferrule farther than
the second annular lip.
16. The captive screw of claim 12 in combination with a heat
sink.
17. A captive screw comprising: a screw having a head, a shank
adapted to pass through the ferrule, a threaded portion at one end
of the shank opposite the head, and a collar having a plurality of
outwardly extending legs formed on the shank proximate the threaded
portion; and a spring extending on the shank of the screw between
the head and the legs of the collar; wherein said collar is
dimensioned and configured so as not to permit the passing of the
spring past the collar thereby captivating the screw.
18. The captive screw of claim 17 wherein the outwardly extending
legs are substantially flexible thereby permitting the legs to fit
through an aperture in a structure which has a cross section larger
than a cross section of the collar defined by the ends of the legs
when the legs of the collar are in an unflexed state.
19. The captive screw of claim 17 wherein the collar is in the
shape of a crown.
20. The captive screw of claim 16 in combination with a heat sink.
Description
[0001] This application claims the benefit of U.S. patent
application Ser. No. 09/803,221 filed Mar. 9, 2001, entitled
floating captive screw which is based on U.S. Provisional
Application No. 60/188,406 filed Mar. 10, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to captive
screws.
[0004] 2. Brief Description of the Prior Art
[0005] Captive screws are screws that are "captivated" or held
within a collar or ferrule. The ferrule is mounted in a first panel
or like object. The screw portion is captivated so that it can be
moved perpendicular to the first panel and the screw's threads can
engage a corresponding aperture in a second panel, so that the
first and second panels can be secured together. However, when the
panels are unscrewed and disengage, the screw is retained in the
first panel. Captive screws are useful in applications where it is
important to avoid dropping or losing screws during assembly or
repair, such as electronic devices, where a lost screw can cause
catastrophic electrical shorts damaging equipment.
[0006] One particular application for captive screws is to hold
down a heat sink which is mounted on top of a microchip and is
intended to dissipate the heat of the microchip. The microchip, in
turn, is fastened to a circuit board. Oftentimes, between the heat
sink and the microchip a compressible or elastic material in the
form of the sheet is placed. If one were to put the heat sink
directly on top of the microchip, there would be tiny gaps between
the two. Since air conducts heat poorly, these gaps have a
detrimental effect on heat transfer. This interface material in the
form of a sheet is needed and the sheet has a high thermal
conductivity. Recently, microchips during operation have been
getting warmer and warmer as space has been getting more and more
limited on circuit boards. Accordingly, heat sinks have been
getting larger and larger as the requirements for withstanding
vibrations has been getting more stringent. Standoffs have been
used which rise from the board to which the heat sinks are screwed
down. Difficulties encountered with standoffs have been that the
standoffs do not compensate for chip height variation and they do
not provide consistent compression of the interface material
between the chip and the heat sink.
[0007] In the past, various clamps, latches, pins, etc have been
used to hold heat sinks down. Plastic clips have been used,
however, this requires that the use of a screwdriver to screw in
the clip directly onto the circuit board which makes the board
susceptible to damage. Plastic clips, although they are not
clostly, are limited by the weight of the heat sink and the clips
have proven to be unreliable in vibration and drop shock testing.
Some varieties of clips are clipped onto the heat sink at the ends
of fins in the middle of the heat sink. Unfortunately, the middle
fins are the most important fins in a heat sink as they carry most
of the heat load. Therefore, when such clips are used the need for
a larger heat sink results.
[0008] Accordingly, a need exists for a captive screw which is
captive or fixed to a first panel such as a heat sink whereby a
collar on the screw bottoms out at a fixed distance on a lower
panel when the screw is screwed into the lower panel thereby
allowing the captive screw to provide a constant pressure on the
top panel. In addition, the captive screw should be able to pass
stringent vibration testing and be able to allow for thermal
expansion.
[0009] The present invention has been developed in view of the
foregoing and to overcome the deficiencies of the prior art.
SUMMARY OF THE INVENTION
[0010] The present invention solves the problem of providing for
secure fastening of a lower panel to an upper panel while providing
a constant pressure on an upper panel to which the captive screw is
captive.
[0011] In one embodiment of the present invention, a captive screw
is disclosed which includes a ferrule, a screw, and a spring. The
screw has a head, a shank adapted to pass through the ferrule, a
threaded portion at the end of the shank opposite the head, and a
collar formed on the shank proximate the threaded portion. The
screw is captivated on the ferrule between the head and the collar.
The spring extends on the shank of the screw between the head and
the ferrule. Preferably, the ferrule has a generally cylindrical
exterior surface having a plurality of knurls for securing the
captive screw in a preformed aperture in a first structure, such as
a lever. Is also preferred that the ferrule be formed with an inner
ring formed on the interior surface of the ferrule having a
generally circular opening large enough to permit the threads
collar the screw to pass through but not large enough to permit the
spring to pass through.
[0012] In a second embodiment of this invention, the ferrule has an
annular lip and an exterior circumferential exterior groove.
Preferably, the annular lip and exterior groove permit the captive
screw to be press fit in a structure.
[0013] In a third embodiment of the present invention, the ferrule
of the captive screw has a first and a second annular lip which
provide for the captive screw to be pressed into a structure.
[0014] In a fourth embodiment of the present invention, a captive
screw is provided which has a collar connected to the shank of the
screw in the proximity of the threaded portion of the screw. The
collar has outwardly extending legs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a side elevational view of a first embodiment of a
captive screw according to the present invention, partially in
section in a heat sink and a circuit board.
[0016] FIG. 2 is an exploded perspective view of a first embodiment
of the screw of the captive screw of FIG. 1.
[0017] FIG. 3 is a side elevational cross-sectional view of the
captive screw of FIG. 1 in an unfastened position.
[0018] FIG. 4 is a side elevational cross-sectional view of the
captive screw of FIG. 1 in a fastened position.
[0019] FIG. 5 is a side view of the captive screw of FIG. 1 in a
fastened position.
[0020] FIG. 6 is an isometric view of the captive screw of FIG. 1
in a fastened position.
[0021] FIG. 7 is a side view of the captive screw of FIG. 1 in an
unfastened position.
[0022] FIG. 8 is a perspective view of the captive screw of FIG. 1
in an unfastened position.
[0023] FIG. 9 is a top plan view of the captive screw of FIG.
1.
[0024] FIG. 10 is a side view of the screw in the captive screw of
FIG. 1.
[0025] FIG. 11 is a perspective view of the screw in the captive
screw of FIG. 1.
[0026] FIG. 12 is a perspective view of the spring in the captive
screw of FIG. 1.
[0027] FIG. 13 is a top view of the ferrule in the captive screw of
FIG. 1.
[0028] FIG. 14 is a side view of the ferrule in the captive screw
of FIG. 1.
[0029] FIG. 15 is a perspective view of the ferrule in the captive
screw of FIG. 1.
[0030] FIG. 16 is a side elevational view of a second embodiment of
the captive screw of the present invention partially in
section.
[0031] FIG. 17 is a side view of a third embodiment of the captive
screw of the present invention.
[0032] FIG. 18 is a side elevational view of the captive screw of
FIG. 17 partially in section in a structure.
[0033] FIG. 19 is a side elevational view of a fourth embodiment of
a captive screw according to the present invention, partially in
section in a heat sink and a circuit board.
[0034] FIG. 20 is a side elevational view of the captive screw of
FIG. 19 partially in section in a structure.
[0035] FIG. 21 is a perspective view of the captive screw of FIG.
19.
[0036] FIG. 22 is a side elevational view of the captive screw of
FIG. 19.
[0037] FIG. 23 is a bottom view of the captive screw of FIG.
19.
[0038] FIG. 24 is a perspective view of the collar of the captive
screw of FIG. 19.
[0039] FIG. 25 is a perspective view of the collar of the captive
screw of FIG. 19.
DETAILED DESCRIPTION
[0040] The present invention provides a captive screw for securing
a first structure such as a first panel or heat sink to a second
structure such as a circuit board.
[0041] Referring now to the drawings in detail, wherein like
reference numerals indicate like elements throughout the several
views, there is shown in FIG. 1 a captive screw 10 according to the
present invention. The captive screw 10 includes a ferrule 20, a
screw 40 and a spring 50. The screw 40 (FIG. 2) includes a head 42
adapted to receive a driver (FIG. 3), a shank 44 adapted to pass
through the ferrule 20, and a threaded portion 46 at the end of the
shank 44 opposite the head 42. The 40 screw also includes a collar
48 formed on the shank 44 proximate the threaded portion 46.
[0042] The generally cylindrical ferrule 20 can have a plurality of
knurls formed on its exterior cylindrical surface for securing the
captive screw 10 in a preformed aperture 102 in a first structure
100 such as a heat sink by a press fit. The threaded portion 46 of
the screw 40 is intended for securing the captive screw 10 in a
preformed, threaded aperture 112 formed in second structure 110
such as a circuit board shown in FIG. 1 having a chip 5. The chip
is shown on a sheet 6 of flexible material which absorbs
vibrations. The captive screw 10 is positioned precisely relative
to the second structure by virtue of the collar 48 formed on the
shank 44 of the screw 40. The collar 48 limits the depth of
penetration of the screw 40 into a threaded insert 7 which has been
inserted from the bottom of the circuited board 112. Alternatively,
the threaded portion of the captive screw can be screwed directly
into a preformed, threaded aperture in a second structure. By
coming into contact with the threads of threaded insert 7, the
screw 40 is being rotationally driven into the second
structure.
[0043] As can be seen in the FIGS. 1, 3 and 4, the ferrule 20 is
formed with an annular ring section 24. The captive screw 10 is
assembled by placing the spring 50 on the screw 40 and then passing
the screw 40 through the ferrule 20. The annular ring 24 on the
interior surface of the ferrule is large enough to permit the
threads 46 of the screw 40 to pass through but not large enough to
permit the spring 50 to pass through. When the ferrule 20 is formed
during assembly, pressure can be applied uniformly on the generally
cylindrical portion of the ferrule and plastic deformation can form
the annular ring 24. Prior to the pressure being applied to the
ferrule the ferrule can have an annular circumferential groove
which allows for the formation of the ring section. The annular
ring section 24 reduces the size of the opening in the ferrule so
that the resultant opening is slightly larger than the diameter of
the screw shaft 44 but smaller than both the screw head diameter
and the diameter of the collar, thus captivating the screw 40 on
the ferrule 20 in between the screw head 42 and the collar 48. The
collar can be rolled onto the screw after the screw has been
inserted into the ferrule. After installation of the ferrule into
the first structure 100 the end of the ferrule can be flared.
[0044] The ferrule 20 also has an annular lip 28 or stop formed on
the exterior cylindrical surface proximate the top of the ferrule
20 for limiting the penetration of the ferrule 20 in the preformed
aperture 102 in the first structure 100. When the captive screw of
10 the present invention is installed, the collar 48 precisely
limits the vertical position of the screw 40 above the second
structure 110, while the first structure 100 floats above the
second structure 110, while being urged towards the second
structure 110 by the spring 50 of the captive screw 10. For
example, FIG. 6 is a perspective view of the captive screw of the
first embodiment of the invention showing the position of the screw
when the screw is in a fastened position. FIG. 8 is a perspective
view of the captive screw of the first embodiment of the invention
showing the position of the screw when the screw is in a fastened
position.
[0045] In the second embodiment of the invention as shown in FIG.
16, the ferrule 120 also has an annular lip 38 or stop formed on
the exterior cylindrical surface proximate the top of the ferrule
120 for limiting the penetration of the ferrule 120 in the
preformed aperture 102 in the first structure, as well as an
annular circumferential groove 30 formed in the exterior
cylindrical surface of the ferrule immediately adjacent and below
the annular lip 38, for receiving the plastic flow of material 104
when the ferrule 120 is pressed into the preformed aperture. When
the captive screw of 310 the present invention is installed, the
collar 48 precisely limits the vertical position of the screw 40
above the second structure (not shown), while the first structure
100 floats above the second structure, while being urged towards
the second structure by the spring 50 of the captive screw 310. The
captive screw shown in FIG. 1 can be pressed into the underside of
the first structure from the bottom. Alternately, the captive screw
shown could be installed from the top when groove 30 is placed near
the bottom of the first structure 30. Also, the collar of the
second embodiment can be shaped as part of the screw after the
screw has been inserted in the ferrule.
[0046] In the third embodiment of the invention as shown in FIGS.
17 and 18, the ferrule 220 also has a first annular lip 58 or stop
formed on the exterior cylindrical surface proximate the top of the
ferrule 220 for limiting the penetration of the ferrule 220 in the
preformed aperture 102 in the first structure, as well as an
annular circumferential groove 130 formed in the exterior
cylindrical surface of the ferrule immediately adjacent and below
the first annular lip 58, for receiving the plastic flow of
material 104 when the ferrule 220 is pressed into the preformed
aperture. A second annular lip 68 is shown at the opposite end of
the ferrule. When the captive screw of 210 the present invention is
installed, the collar 48 precisely limits the vertical position of
the screw 40 above the second structure (not shown), while the
first structure 100 floats above the second structure, while being
urged towards the second structure by the spring 50 of the captive
screw 210. In this embodiment of the present invention the collar
can be pressed on.
[0047] In the fourth embodiment, FIGS. 19, 20, 21 and 22 show a
captive screw in first structure 100 having a collar 148 which has
outwardly extending legs and a base portion. The collar has
outwardly extending legs 248 and the base portion 348. The ends 448
of the legs 248 extend outwardly and define a collar cross section.
Since the legs are flexible, the ends of the legs deform
elastically and permit the collar to pass through a first structure
when being passed through an aperture in a structure and the
aperture has a smaller cross section than that defined by the ends
of the legs. The arrangement shown in FIG. 19 is one way in which
to install the collar 48 into a second structure 110. The base
portion 348 of the collar limits the penetration of the screw into
the second structure. In the embodiment shown in FIG. 20 the ends
448 of the legs contact the underside of the first structure. The
collar can be in the shape of a crown and the collar can be
threaded on, crimped on or pressed on, etc. The legs are also
dimensioned and configured to not allow the spring to pass over the
legs.
[0048] The collar shown and described in the first three
embodiments can be rolled on pressed on or screwed on.
[0049] The screw in the above embodiments includes a generally
cylindrical head 42 having a central recess 34 formed therein and
adapted to receive a driver. While a Phillip-type driver recess is
illustrated, other types of driver recesses, such as slotted,
Torx.RTM., hexagonal, and the like, and combinations thereof (e.g.
slot-Torx), can also be used. A generally cylindrical upper section
extends coaxially downward from the head 42.
[0050] Preferably, the screw, and ferrule are formed from a
suitable metallic material such as aluminum.
[0051] While the ferrule of the present invention is adapted to be
press fit into the first structure, other means of mounting the
captive screw on the structure can be employed, including
conventional installation methods known as "flare-in," "floating,"
"p.c. board," and "snap-in" installation methods.
[0052] Various other modifications can be made in the details of
the various embodiments of the apparatus of the present invention,
all within the scope and spirit of the invention and defined by the
appended claims.
* * * * *