U.S. patent application number 12/387895 was filed with the patent office on 2010-11-11 for method and apparatus for optimal nock travel for a compound archery bow.
Invention is credited to Joseph H. Marzullo.
Application Number | 20100282226 12/387895 |
Document ID | / |
Family ID | 43061615 |
Filed Date | 2010-11-11 |
United States Patent
Application |
20100282226 |
Kind Code |
A1 |
Marzullo; Joseph H. |
November 11, 2010 |
Method and apparatus for optimal nock travel for a compound archery
bow
Abstract
The invention is a method and apparatus for correcting the
natural nock travel of a compound bow. The bow has a cable guard
rod attached to a riser supporting a cable slide at an angle to the
nock travel path. The rod has a distal portion attached to the
riser, a central portion angled upward relative to the distal
portion, and, a proximal portion angled downward so as to form an
exterior angle falling within the range of 25-40.degree. between
the proximal and distal portions of the cable guard rod. The bow
has a cam mounted on an upper limb, a cam mounted on a lower limb,
and two cables which are connected to the first cam, pass through
the cable slide, and are connected to the second cam. There is also
a bow string connected between the cams which can be drawn rearward
then released to provide energy.
Inventors: |
Marzullo; Joseph H.;
(Harwinton, CT) |
Correspondence
Address: |
Paul A. Levitsky
107 Grist Mill Road
Monroe
CT
06468
US
|
Family ID: |
43061615 |
Appl. No.: |
12/387895 |
Filed: |
May 8, 2009 |
Current U.S.
Class: |
124/25.6 ; 124/1;
124/88 |
Current CPC
Class: |
F41B 5/14 20130101; F41B
5/10 20130101 |
Class at
Publication: |
124/25.6 ;
124/88; 124/1 |
International
Class: |
F41B 5/10 20060101
F41B005/10; F41B 5/14 20060101 F41B005/14 |
Claims
1. A compound bow having a handle and a riser, said compound bow
further comprising: (a) a plurality of limbs; (b) a cable guard rod
attached to said riser and wherein said cable guard rod is
fashioned so as to support a cable slide at an angle to the nock
travel path of said compound bow; and, wherein further said cable
slide is slidably mounted on said cable guard rod so as to reduce
the cantilever load on a set of one or more cams or wheels; (c) a
first cam or first wheel comprising said set of one or more cams or
wheels, having a first axle, mounted on an upper one of said
plurality of limbs; (d) a second cam or second wheel comprising
said set of one or more cams or wheels, having a second axle,
mounted on a lower one of said plurality of limbs; (e) a first
cable and a second cable, wherein said first and said second cables
are connected to said first cam or said first wheel, pass through
said cable slide, and are connected to said second cam or said
second wheel; and (f) a bow string connected at one end to said
first cam or said first wheel and at another end to said second cam
or said second.
2. The compound bow of claim 1, wherein said cable guard rod is
attached to said riser by securably inserting said rod within a
supporting block and mounting said supporting block on said
riser.
3. The compound bow of claim 1, wherein the distal end of said
cable guard rod is attached to said riser and is substantially
perpendicular to said riser.
4. The compound bow of claim 1, wherein the distal end of said
cable guard rod is securably attached to said riser by inserting
said distal end within an opening of said riser.
5. The compound bow of claim 1, wherein said cable guard rod is
made from a material chosen from the group consisting of: (a)
aluminum; (b) a composite capable of maintaining rigidity while
under pressure from a set of forces exerted by said compound bow
during operation; and (c) steel.
6. The compound bow of claim 1, wherein the angle of said cable
guard rod is determined by the displacement of said first and
second cables to result in a lateral displacement of said cable
slide so as to provide clearance for fletching of an arrow to be
shot by said compound bow.
7. The compound bow of claim 1, wherein said cable guard rod is
manufactured as a single piece.
8. The compound bow of claim 1, wherein said cable guard rod is
manufactured as a plurality of pieces and wherein said pieces are
joined by joining means so as to maintain performance of said cable
guard rod.
9. The compound bow of claim 1, wherein said cable guard rod is
fashioned so as to comprise three portions, said three portions
comprising: (a) a distal portion attached either directly, or
indirectly, to said riser and essentially perpendicular to said
riser; (b) a central portion attached to said distal portion and
angled relative to said distal portion; and (c) a proximal portion
attached to said central portion and angled toward the natural
travel path of said bowstring so as to form an exterior angle
within the range of 25-40.degree. between said proximal and said
distal portions of said cable guard rod.
10. The compound bow of claim 1, wherein said cable guard slide is
mounted on said cable guard rod so as to accept said first cable
and said second cable passing therethrough; and, wherein the
forward or rearward motion of said first and said second cables
causes said cable guard slide to slidably move along said cable
guard rod in an angular path along said cable guard rod relative to
the nock travel path.
11. The compound bow of claim 1, characterized in that as said
bowstring is drawn rearward by a bow user during operation thereof,
said plurality of limbs flex rearward, said cams rotate thus
shifting said first and said second cables, and causing said cable
guard slide to move toward the natural travel of the bowstring path
along said proximal portion of said cable guard rod.
12. A cable guard rod for a compound bow, said cable guard rod
characterized in that: (a) said cable guard rod is fashioned so as
to support a cable slide at an angle to the travel path of an arrow
being discharged by said compound bow; and (b) said cable slide is
slidably mounted on said cable guard rod so as to reduce the
cantilever load on a set of one or more cams or wheels.
13. The cable guard rod of claim 12, wherein said cable guard rod
is made from a material selected from the group consisting of: (a)
aluminum; (b) a composite; and (c) steel
14. The cable guard rod of claim 12, wherein said cable guard rod
is affixed to a riser of said compound bow wherein the distal end
of said cable guard rod is securably attached to said riser by
inserting said distal end within an opening of said riser.
15. The cable guard rod of claim 12, wherein said cable guard rod
is attached to a riser of said compound bow by securably inserting
said rod within a supporting block and mounting said supporting
block on said riser.
16. The cable guard rod of claim 12, wherein said cable guard rod
is fashioned so as to comprise three portions, said three portions
comprising: (a) a distal portion attached either directly, or
indirectly, to said riser and essentially perpendicular to said
riser; (b) a central portion attached to said distal portion and
angled relative to said distal portion; and (c) a proximal portion
attached to said central portion and angled so as to form an
exterior angle within the range of 25-40.degree. between said
proximal and said distal portions of said cable guard rod.
17. A method of correcting the angled nock travel of a compound bow
so as to be essentially aligned with the natural nock travel of
said compound bow, said compound bow having a riser, an upper limb,
a lower limb, a first cable, a second cable, and a set of one or
more cams or wheels, said method comprising the steps of: (a)
mounting a cable guard rod on said compound bow, said cable guard
rod having a distal portion attached to said riser, a central
portion, and a proximal portion; (b) mounting a cable slide on said
cable guard rod so as to support said cable slide at an angle to
the travel path of an arrow being discharged by said compound bow,
and wherein said arrow comprises a shaft and a set of fletching,
and wherein said cable slide is slidably mounted on said cable
guard rod so as to reduce the cantilever load on said set of one or
more cams or wheels; (c) drawing a bowstring connected at one end
to said upper limb of said compound bow and at the opposite end to
said lower limb of said compound bow, and causing said upper limb
and said lower limb to flex rearward; (d) rotating said at least
one cam, so as to shift said first and said second cables, and
causing said cable guard slide to move in a downward path along the
proximal portion of said cable guard rod; and (e) releasing said
bowstring to propel said bowstring and said arrow forward and
causing said first and said second cables to move forward and, in
turn, moving said cable slide upward along said cable guard rod to
allow said arrow to move forward without making contact with said
cable slide.
18. The method of claim 17, wherein said cable guard rod is
fashioned so as to comprise three portions, said three portions
comprising: (a) a distal portion attached either directly, or
indirectly, to said riser and essentially perpendicular to said
riser; (b) a central portion attached to said distal portion and
angled upward relative to said distal portion; and (c) a proximal
portion attached to said central portion and angled downward so as
to form an exterior angle within the range of 25-40.degree. between
said proximal and said distal portions of said cable guard rod.
19. The method of claim 17, further comprising the step of
manufacturing said cable guard rod from a material selected from
the group consisting of: (a) aluminum; (b) a composite; and (c)
steel.
20. The method of claim 17, further comprising the step of
correcting the natural nock travel of said compound bow by said
angular movement of said cable slide.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method and apparatus for
a compound archery bow of a type used for hunting, target shooting,
or related activities. More specifically, the present invention
relates to a method and system for stabilizing the nock point
travel of a compound bow so as to optimize the bow's accuracy while
reducing wear on cables caused by cam tilt forces.
[0003] 2. Description of the Related Art
[0004] Compound archery bows, such as that shown in FIG. 1,
generally provide a number of benefits over traditional bows (also
known as long bows). They store a lot more energy due to the
profiles of the cams which flex the limbs while the bow is drawn.
This results in an arrow that is shot with higher velocity and more
energy. They also provide another important benefit over
traditional bows, in that when the bow is drawn to its maximum
point, the cams provide a mechanical advantage to the archer that
reduces the holding weight of the bow by approximately 75-80%.
[0005] A traditional bow has a bow string, a handle and an upper
and a lower limb. One end of a bowstring is attached to the upper
limb of the bow while the other end of the string is attached to
the lower limb. With a typical compound bow, however, as is shown
in FIG. 1, the bow has a bow string 8, a handle 40, two limbs 46a,
46b, plus one or two cables 4, 6 which are fastened to the cam or
cams 30a, 30b or limb(s) 46a, 46b, plus a cable guard rod 10 and
cable slide 2 or, in an alternative, a roller cable guard 18 (as is
shown in FIG. 3).
[0006] The cables 4, 6 are in the path of the arrow 14 (as is shown
in FIG. 4) and its fletching when shot, and must be offset 20 (see
FIG. 4) from the line of arrow travel to prevent collision of the
arrow 14 and its fletching 12 into the cables 4, 6. The cams 30a,
30b should be designed in such a way as to provide an arrow launch
that is as straight as possible, both vertical and
horizontally.
[0007] Turning to FIG. 6, there is shown a top view of the nocking
point travel of the typical compound bow. Accuracy may be degraded
by an arrow launch that is not straight and/or has a vertical path
that deviates from a reference plane that is perpendicular to the
string. Lateral motion is defined by deviation from a plane that is
perpendicular to the limbs 46a, 46b (see FIG. 1) or its "natural
travel path" 28 (see FIG. 12A). Deviation from the natural travel
path degrades accuracy.
[0008] The natural travel path 28 is always negatively affected by
offsetting the cables 4, 6. Virtually all compound bows made today
have a cable guard 10 (see FIG. 1) in one form or another, and they
offset the cables 4, 6 to provide clearance for the arrow and its
fletching. This is required when the arrow is launched/shot.
Typically, the bow's cables are confined within a cable slide 2
that mounts on a cable guard rod 10 which is mounted in the riser
16; or, a roller cable guard 18 (see FIG. 3) which is mounted on
the riser 16.
[0009] Turning to FIG. 3, there is shown an enlargement of the end
view of a prior art compound bow. The cables are held offset 20
through the entire draw cycle.
[0010] Some bows (such as that shown in FIG. 3) use a fixed set of
rollers 18 to confine the cables 4, 6 to achieve the required
fletching clearance 20. The rollers are generally fixed to bracket
22 that is fastened to the bow's riser 16. The cables are held
offset to provide fletching clearance 20 through the entire draw
cycle.
[0011] It is not generally understood what affect a cable guard and
the resulting cable offset has on the flight of the arrow, the
nocking point, bow string travel, and the resulting arrow flight
aberration as is illustrated in FIG. 5. Additionally, the twisting
of the bow handle 40 in the archer's hand 42 also produces flight
aberration that is unique to the archer (see FIG. 7).
[0012] The string travel when measured at the arrow nocking point
26 located on the bow string 8 with absolute minimum cable guard
offset follows a path that is essentially straight and
perpendicular to the bow's limbs as they are flexed--its "natural
travel path".
[0013] Turning next to FIG. 5, there is shown a side view of the
cam tilting forces at play during the typical draw cycle of a
compound bow. The addition of a cable guard 10 and the cable offset
20 imposes a side load 48 on the bow's cam(s) 30a, 30b which causes
a tilt 32 and a change in position of the bow string with respect
to its natural travel path. The tilting 32 increases as the bow is
drawn and reaches its peak draw weight (see FIG. 11A). This effect
imposes much higher loads on the cam axles 34a, 34b; and,
therefore, the cams 30a, 30b by the flexure of the limbs 46 which
increases dramatically as the bow is drawn. During this latter
action, the loads can be as high as 400 lbs. These high loads
imposed off center on the cams create a very large load imbalance
(see FIG. 11A) which causes the cam(s) to tilt. The cam(s) radius
(see FIGS. 11A and 11B) also increases through the draw cycle and
moves the string farther from the cam(s) center line producing a
mechanical advantage for the archer drawing the bow; but, causing
even more cam tilting and lateral displacement of the bow
string.
[0014] The combined effect of the cable guard offset and increasing
cable loads results in a cam tilt that produces an angular lateral
displacement of the bow string during the bow's draw cycle. It
causes the bow to twist in the archer's hand and results in
undesirable "angular nocking point/bow string travel".
[0015] As is shown in FIG. 6, the bow string lateral displacement
causes the arrow to be launched at an angle 50 which may be as high
as 5 degrees with regard to the bow string's natural string travel
28. When the arrow is shot, the bow string and nocking point does
not align to the natural string travel 13. During launch, the arrow
has an acceleration force imposed upon it that is not aligned with
the arrow centerline and its natural string travel, this creates a
side acceleration force 36 on the arrow which is essentially 90
degrees to the arrow's center line. This can result in arrow flight
that slews back and forth, commonly known as "fishtailing".
[0016] Turning to FIG. 7, there is shown a top view of the handle
torque effect of a compound bow. The "angular nocking point/bow
string travel" 24 also results in a rotation or twisting of the bow
in the archer's hand 42. It is commonly referred to as "torque".
Although only a few degrees in bow rotation, torque is undesirable
as it causes the arrow to fly to left for right handed archers, and
to the right for left handed archers. This is detrimental to the
archer achieving accurate and consistent arrow flight. The archer
will have to try and compensate for this cable guard induced error,
"angular nocking point/bow string travel" 50.
[0017] The stock or existing angular nocking point/bow string
travel 50, the natural travel path 28, and the optimized nocking
point/string travel may be accurately verified by plotting their
travel on a lateral nock travel testing fixture. The optimized
nocking point and string travel will closely parallel the natural
travel path.
[0018] What is not appreciated by the prior art are problems
created by the cables being offset to provide fletching clearance,
the unintended consequence of which is cam tilt. Therefore, an
ideal condition would be to provide fletching clearance as the
arrow's fletching approaches the cables, and quickly reduce the
cable offset during the rest of the shot. This will result in a
nocking point travel that closely follows the natural string travel
path 28 by virtually eliminating cam tilt.
[0019] Accordingly, there is a need for an improved method and
apparatus for providing fletching clearance as the arrow's
fletching approaches the cables, and quickly reducing the cable
offset during the rest of the shot. This will result in a nocking
point travel that closely follows the natural string travel path 28
by virtually eliminating cam tilt. The result of an optimized
nocking point/string travel which closely follows the natural
string path 28 also results in almost zero handle rotation and
twisting of the bow in the archer's hand 42. The bow that is
without torque/handle rotation will result in a bow with more
accuracy and repeatability in discharging the arrow and is
considered to be "forgiving".
[0020] Additionally, there is a need for a method and apparatus
that optimizes arrow nocking point/bow string travel by closely
following the natural string path, which is essentially straight
with no side acceleration forces. This condition will impart the
least possible lateral flight aberration.
OBJECTS AND SUMMARY OF TH INVENTION
[0021] An object of the present invention is to provide an improved
method and apparatus for providing fletching clearance as the
arrow's fletching approaches the cables, and quickly reducing the
cable offset during the rest of the shot.
[0022] Another object of the present invention is to provide a
method and apparatus that optimizes arrow nocking point/bow string
travel by closely following the natural string path, which is
essentially straight with no side acceleration forces.
[0023] The present invention relates to a method and apparatus for
correcting the angular nock travel of a compound bow. The bow has a
cable guard rod attached to a riser supporting a cable slide at an
angle to the nock travel path. The rod has a distal portion
attached to the riser, a central portion angled upward relative to
the distal portion, and, a proximal portion angled downward so as
to form an exterior angle falling within the range of 25-40.degree.
between the proximal and distal portions of the cable guard rod.
The bow has a cam mounted on an upper limb, a cam mounted on a
lower limb, and two cables which are connected to the first cam,
pass through the cable slide, and are connected to the second cam.
There is also a bow string connected between the cams which can be
drawn rearward then released to provide energy.
[0024] According to an embodiment of the present invention, there
is provided a method and apparatus for a compound archery bow of a
type used for hunting, target shooting, or similar endeavor. The
compound bow has a handle and a riser, and at least an upper and a
lower limb. A cable guard rod is attached to the riser; and is made
in such a way as to support a cable slide at an angle to the nock
travel path of the compound bow. The cable slide is slidably
mounted on the cable guard rod.
[0025] Additionally, the compound bow has a first cam, having a
first cam axle, mounted on the upper limb; and, a second cam,
having a second cam axle, is mounted on the bow's lower limb. The
bow also has a first cable and a second cable, wherein the first
and second cables are connected to the first cam (or a wheel), pass
through the cable slide, and are connected to the second cam (or a
wheel). There is also a bow string connected at one end to the
first cam and at another end to the second cam.
[0026] In an embodiment of the present invention, the bow's cable
guard rod is attached to the riser by securably inserting the rod
within a supporting block and mounting the supporting block on the
riser. In an alternative embodiment of the present invention, the
distal end of the cable guard rod is attached to directly to the
riser by inserting the distal end within an opening of the riser.
The cable guard rod, at least at the distal end, is substantially
perpendicular to the riser.
[0027] The cable guard rod can be made of any material suitable to
the purpose such as aluminum, steel, or a composite capable of
maintaining rigidity while under pressure from the forces exerted
on the compound bow during operation.
[0028] The cable guard rod can be manufactured as a single piece or
as two or more pieces and wherein the pieces are joined by any
means such as welding, screw and bolt combination, or similar
process so as to maintain performance of the cable guard rod.
[0029] The cable guard rod is fashioned so as to comprise three
portions; these include: a distal portion attached either directly,
or indirectly, to the riser and essentially perpendicular to the
riser; a central portion attached to the distal portion and angled
upward relative to the distal portion; and, a proximal portion
attached to said central portion and angled downward so as to form
an exterior angle falling within the range of 25-40.degree. between
the proximal and distal portions of the cable guard rod.
[0030] The cable guard slide is mounted on the cable guard rod so
as to accept the first cable and the second cable passing
therethrough. The forward or rearward motion of the first and
second cables causes the cable guard slide to slidably move along
the cable guard rod in an angled path relative to the nock travel
path.
[0031] As the bowstring is drawn rearward by a bow user during
operation, the top and bottom limbs of the compound bow flex
rearward causing the cam(s) to rotate, thus shifting the first and
second cables, and causing the cable guard slide to move in a
downward path along the proximal portion of the cable guard
rod.
[0032] In another embodiment of the present invention, there is
included a method of correcting the natural nock travel of a
compound bow. The compound bow has a riser, an upper limb, a lower
limb, a first cable, a second cable, and at least one cam, and
wherein the method comprises the step of mounting a cable guard rod
on the compound bow, the cable guard rod having a distal portion
attached to the riser, a central portion, and a proximal portion.
Additionally, the method includes mounting a cable slide on the
cable guard rod so as to support the cable slide at an angle to the
travel path of an arrow being discharged by the compound bow, and
wherein the cable slide is slidably mounted on the cable guard
rod.
[0033] A further set of steps of the method include: drawing a
bowstring connected at one end to the upper limb of the compound
bow and at the opposite end to the lower limb of the compound bow,
and causing the upper limb and the lower limb to flex rearward;
and, rotating at least one cam, so as to shift the first and second
cables, and causing the cable guard slide to move in a downward
path along the proximal portion of the cable guard rod. From that
point, the method includes releasing the bowstring to propel the
bowstring and the arrow forward and causing the first and second
cables to move forward; and, in turn, moving the cable slide upward
along the cable guard rod to allow the arrow to move forward
without making contact with the cable slide. This insures
correction of the angular nock travel 24 of the compound bow by the
angular movement of the cable slide, thus substantially eliminating
cam tilt.
[0034] The above, and other objects, features and advantages of the
present invention, will become apparent from the following
description read in conjunction with the accompanying drawings, in
which like reference numerals designate the same elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a side elevational view of a typical compound bow
which could be adapted to support the present invention.
[0036] FIG. 2 is an end view of a typical compound bow which could
be adapted to support the present invention.
[0037] FIG. 3 is a section elevational view of a typical compound
bow using a roller cable guard.
[0038] FIG. 4 is an enlargement of the end view of FIG. 2.
[0039] FIG. 5 is a side view of the cam tilting forces at play
during the typical draw cycle of a compound bow.
[0040] FIG. 6 is a top view of the nocking point travel of the
typical compound bow.
[0041] FIG. 7 is a top view of the handle torque effect of a
compound bow.
[0042] FIG. 8 is a top view of an embodiment of the cable guard rod
of the present invention.
[0043] FIG. 9 is a top view of a second embodiment of the cable
guard rod of the present invention.
[0044] FIG. 10 is a top view of a third embodiment of the cable
guard rod of the present invention.
[0045] FIG. 11A is a graph of the loads and movements exerted by
prior art compound bows.
[0046] FIG. 11B is a chart of the loads and movements exerted by
prior art compound bows.
[0047] FIG. 12A is a graph of a nock travel plot of a first
contemporary, commercially available, compound bow; and, the nock
travel plot of the same bow retrofitted with the present
invention.
[0048] FIG. 12B is a graph of a nock travel plot of a second
contemporary, commercially available, compound bow; and, the nock
travel plot of the same bow retrofitted with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] Reference will now be made in detail to several embodiments
of the invention that are illustrated in the accompanying drawings.
Wherever possible, same or similar reference numerals are used in
the drawings and the description to refer to the same or like parts
or steps. The drawings are in simplified form and are not to
precise scale. For purposes of convenience and clarity only,
directional terms, such as top, bottom, up, down, over, above, and
below may be used with respect to the drawings. These and similar
directional terms should not be construed to limit the scope of the
invention in any manner. The words "connect," "couple," and similar
terms with their inflectional morphemes do not necessarily denote
direct and immediate connections, but also include connections
through mediate elements or devices.
[0050] The preferred embodiments of the present invention are
illustrated in FIGS. 8, 9 and 10.
[0051] Turning first to FIG. 8, there is shown a top view of an
embodiment of the cable guard rod 10 assembly of the present
invention. The assembly has a cable slide 2 profiled to provide
fletching 12 and cable clearance 20 when used with an optimized
cable guard angle. The cable slide 2 allows the cables 4, 6 to pass
therethrough.
[0052] The cable guard rod 10/bracket 22 is mounted, either
directly or indirectly, to the bow's riser 16 of the frame. The
cable guard rod 10 is comprised of two parts (an upper half and a
lower half) and its corresponding bracket 22. The cable guard rod
10 and bracket 22 can be made of any material suitable to the
purpose, though a preferred embodiment would be the use of aluminum
or a composite. The bow's cables 4, 6 are located in a cable slide
2 which slides on the cable guard rod 10. The sliding block 2 has a
means of locating and trapping the bow's cables to prevent them
from contacting each other during normal operation. The cable slide
2 must move laterally approximately 0.6'' towards the arrow 14
within the rearward/forward motion determined by the cable's 4, 6
movement to provide clearance 20 for the fletching 12.
[0053] There is created an exterior angle 25 from the upper portion
of the cable guard rod 10 to the lower portion of the cable guard
rod. The lower portion of the cable guard rod 10 being essentially
perpendicular to the riser 16. The actual angle of the cable guard
rod 10 is determined by the rearward and forward displacement of
the cables to result in the lateral displacement of 0.6''. The
angle 25, which is preferably within the range of 25 to 40.degree.,
has been optimized to cause the nocking point/bow string offset to
provide arrow 14 fletching 12 clearance at the end of the shot and
minimum clearance prior to that point, this causes the nocking
point and bowstring travel to closely follow the "natural string
path" 28.
[0054] The cantilever load imposed by the fixed cable guard
displacement on the cam(s) and or wheel, as previously discussed
with reference to the prior art, causes the tilting which results
in nock travel at an angle with respect to the natural travel path.
The substantial reduction in the cantilever load by the angled
cable guard rod creates a nock travel that tracks essentially
straight with respect to the natural travel path of the
string/nocking point.
[0055] Turning next to FIG. 9, there is shown a top view of a
second embodiment of the cable guard rod of the present
invention.
[0056] The cable guard rod 10 is preferably a single piece which is
mounted to the bow's riser 16. The cable guard rod 10 can be made
of any material suitable to the purpose, though a preferred
embodiment would be the use of aluminum or a composite. The bow's
cables 4, 6 are located in a cable slide 2 which slides on the
cable guard rod 10. The cable slide 2 has a means of locating and
trapping the bow's cables to prevent them from contacting each
other during normal operation. The cable slide 2 must move
laterally approximately 0.6'' towards the arrow 14 within the
rearward/forward motion determined by the cable's 4, 6 movement so
as to provide clearance 20 for the fletching 12.
[0057] There is created an exterior angle 25 from the upper portion
of the cable guard rod 10 to the lower portion of the cable guard
rod. The lower portion of the cable guard rod 10 is essentially
perpendicular to the riser 16. The actual angle of the cable guard
rod 10 is determined by the rearward and forward displacement of
the cables to result in the lateral displacement of approximately
0.6''. The angle 25, which is preferably within the range of 25 to
40.degree., has been optimized to cause the nocking point/bow
string offset to provide arrow 14 fletching 12 clearance 20 at the
end of the shot and minimum clearance prior to that point, this
causes the nocking point and bowstring travel to closely follow the
"natural string path" 28.
[0058] As with FIG. 8, the cantilever load imposed by the fixed
cable guard displacement on the cam(s) and or wheel, as previously
discussed with reference to the prior art, causes the tilting which
results in nock travel at an angle with respect to the natural
travel path. The substantial reduction in the cantilever load by
the angled cable guard rod creates a nock travel that tracks
essentially straight with respect to the natural travel path of the
string/nocking point.
[0059] With reference next to FIG. 10, there is shown a top view of
a third embodiment of the cable guard rod of the present
invention.
[0060] The cable guard rod 10/block 44 is mounted, either directly
or indirectly, to the bow's riser 16 of the frame. The cable guard
rod 10 is comprised of two parts (an upper half and a lower half)
and its corresponding block 44. The cable guard rod 10 and bracket
22 can be made of any material suitable to the purpose, though a
preferred embodiment would be the use of aluminum or a composite.
The bow's cables 4, 6 are located in a cable slide 2 which slides
on the cable guard rod 10. The sliding block 2 has a means of
locating and trapping the bow's cables to prevent them from
contacting each other during normal operation. The cable slide 2
must move laterally approximately 0.6'' towards the arrow 14 within
the rearward/forward motion determined by the cable's 4, 6
movement.
[0061] There is created an exterior angle 25 from the upper portion
of the cable guard rod 10 to the lower portion of the cable guard
rod 10. The lower portion of the cable guard rod 10 is essentially
perpendicular to the riser 16. The actual angle of the cable guard
rod 10 is determined by the rearward and forward displacement of
the cables to result in the lateral displacement of 0.6''. The
angle 25, which is preferably within the range of 25 to 40.degree.,
has been optimized to cause the nocking point/bow string offset to
provide arrow 14 fletching 12 clearance 20 at the end of the shot
and minimum clearance prior to that point, this causes the nocking
point and bowstring travel to closely follow the "natural string
path" 28.
[0062] As with FIGS. 8 and 9, the cantilever load imposed by the
fixed cable guard displacement on the cam(s) and or wheel, as
previously discussed with reference to the prior art, causes the
tilting which results in nock travel at an angle with respect to
the natural travel path. The substantial reduction in the
cantilever load by the angled cable guard rod creates a nock travel
that tracks essentially straight with respect to the natural travel
path of the string/nocking point.
[0063] FIG. 11A is a graph of the axle load and draw force (in
lbs.) on the x-axis relative to the draw length (in inches) on the
y-axis, and the cable offset and cam radius of the x'-axis. These
plots are used to illustrate the effects on: cam axle load; stock
cable offset; the cable offset of the present invention; draw
forces; and, the cam radius at the string.
[0064] By referring back to FIG. 5, the graph of FIG. 11A, can be
placed in context. The addition of a cable guard 10 and the cable
offset 20 imposes a side load 48 on the bow's cam(s) 30a, 30b which
causes a tilt 32 and a change in position of the bow string with
respect to its natural travel path. The tilting 32 increases as the
bow is drawn and reaches its peak draw weight. This effect imposes
much higher loads on the cam axles 34a, 34b; and, therefore, the
cams 30a, 30b by the flexure of the limbs 46 which increases
dramatically as the bow is drawn. During this latter action, the
loads can be as high as 400 lbs. These high loads imposed off
center on the cams create a very large load imbalance which causes
the cam(s) to tilt. The cam(s) radius also increases through the
draw cycle and moves the string farther from the cam(s) center line
producing a mechanical advantage for the archer drawing the bow;
but, causing even more cam tilting and lateral displacement of the
bow string.
[0065] FIG. 11B is a chart of the values derived from the plot of
FIG. 11A of the axle load and draw force (in lbs.) on the x-axis
relative to the draw length (in inches) on the y-axis, and the
cable offset and cam radius of the x'-axis. These plots are used to
illustrate the effects on: cam axle load; stock cable offset; the
cable offset of the present invention; draw forces; and, the cam
radius at the string.
[0066] Turning to FIG. 12A, there is shown, by way of example, a
graph of: a nock travel plot of a first contemporary, commercially
available, compound bow; and, the nock travel plot of the same bow
retrofitted with the present invention.
[0067] The baseline 28, or natural travel path, of the specific bow
represents the movement of the string if no extraneous forces were
acting upon it. The angular nocking point 24, or actual bow string
travel path, is the accumulation of forces that have caused this
particular bow string to deviate from the baseline 28. In this
case, the deviation 52 is 5.degree.. When the present invention is
retrofitted to this particular bow, the corrected travel path 29
results in a deviation 50 of 0.degree. 30'.
[0068] In reviewing the advantageous result of the present
invention, we turn next to FIG. 12B where there is shown, by way of
example, a graph of a nock travel plot of: a second contemporary,
commercially available, compound bow; and, the nock travel plot of
the same bow retrofitted with the present invention.
[0069] The baseline 28, or natural travel path, of the specific bow
represents the movement of the string if no extraneous forces were
acting upon it. The angular nocking point 24, or actual bow string
travel path, is the accumulation of forces that have caused this
particular bow string to deviate from the baseline 28. In this
case, the deviation 52 is 2.degree. 48' When the present invention
is retrofitted to this particular bow, the corrected travel path 29
results in a deviation 50 of 0.degree. 6'.
[0070] In the claims, means or step-plus-function clauses are
intended to cover the structures described or suggested herein as
performing the recited function and not only structural equivalents
but also equivalent structures. Thus, for example, although a nail,
a screw, and a bolt may not be structural equivalents in that a
nail relies on friction between a wooden part and a cylindrical
surface, a screw's helical surface positively engages the wooden
part, and a bolt's head and nut compress opposite sides of a wooden
part, in the environment of fastening wooden parts, a nail, a
screw, and a bolt may be readily understood by those skilled in the
art as equivalent structures.
[0071] Having described at least one of the preferred embodiments
of the present invention with reference to the accompanying
drawings, it is to be understood that the invention is not limited
to those precise embodiments, and that various changes,
modifications, and adaptations may be effected therein by one
skilled in the art without departing from the scope or spirit of
the invention as defined in the appended claims.
* * * * *