U.S. patent application number 10/971272 was filed with the patent office on 2005-12-08 for zero center of mass archery cam.
Invention is credited to Gallops, Henry M. JR..
Application Number | 20050268892 10/971272 |
Document ID | / |
Family ID | 46205383 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050268892 |
Kind Code |
A1 |
Gallops, Henry M. JR. |
December 8, 2005 |
ZERO CENTER OF MASS ARCHERY CAM
Abstract
One preferred embodiment of the present invention provides a cam
having an axle location for mounting the cam to an archery bow,
where the center of mass of the cam is substantially coaxial with
the axle location. Preferable the cam has an eccentric geometric
rotation profile with regard to a rotation axis, typically an
irregular geometry with a non-centered axle location, or a circular
profile with an axle location offset from the center of the
circular profile. The mass of the cam is balanced to have an
effectively equal mass distribution around the axle location. In an
alternate preferred embodiment, the cam has a balanced center of
mass aligned with the axle location in an X-Y orientation, and may
also have a balanced center of mass through the thickness of the
cam in an X-Z or Y-Z orientation.
Inventors: |
Gallops, Henry M. JR.;
(Gainesville, FL) |
Correspondence
Address: |
WOODARD, EMHARDT, MORIARTY, MCNETT & HENRY LLP
BANK ONE CENTER/TOWER
111 MONUMENT CIRCLE, SUITE 3700
INDIANAPOLIS
IN
46204-5137
US
|
Family ID: |
46205383 |
Appl. No.: |
10/971272 |
Filed: |
October 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60576664 |
Jun 3, 2004 |
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60585764 |
Jul 6, 2004 |
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Current U.S.
Class: |
124/25.6 |
Current CPC
Class: |
Y10S 124/90 20130101;
F41B 5/105 20130101; F41B 5/10 20130101 |
Class at
Publication: |
124/025.6 |
International
Class: |
F41B 005/10 |
Claims
What is claimed is:
1. An archery bow, comprising: an archery bow riser; a pair of bow
limbs, each bow limb having a proximal end and a distal end, with
said proximal ends secured to said riser; at least one axle mounted
adjacent the distal end of one bow limb; a cam eccentrically
rotatably mounted on said axle; and, a bowstring extending between
the distal ends of said limbs and configured to be fed outward from
said cam when the archery bow is drawn; wherein said cam has a
center of mass aligned coaxially with said axle.
2. The archery bow of claim 1, wherein said cam includes at least
one weight mounted to a cam body.
3. The archery bow of claim 2, wherein said weight is made from a
material with a specific gravity different from the material of
said cam body.
4. The archery bow of claim 3, wherein said cam body is formed from
aluminum.
5. The archery bow of claim 4, wherein said weight is formed from
brass.
6. The archery bow of claim 2, wherein said cam defines at least
one lightening hole.
7. The archery bow of claim 1, wherein said cam has a geometrically
irregular rotation profile.
8. The archery bow of claim 1, wherein said cam is mounted to said
axle in a location offset from the center of the cam's rotation
profile.
9. The archery bow of claim 1, comprising at least one module
mountable to form a part of said cam to partially define a draw
length of the bow, wherein said cam has a center of mass aligned
coaxially with said axle when said module is mounted.
10. The archery bow of claim 9, comprising at least a second module
mountable to form a part of said cam to partially define a second
draw length of the bow, wherein said cam has a center of mass
aligned coaxially with said axle when said second module is
mounted.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to archery bows, and in
preferred embodiments provides a cam for a compound archery bow, a
compound bow and cam, and a method of making and arranging a
cam.
BACKGROUND OF THE INVENTION
[0002] The present invention deals primarily with compound archery
bows, generally including a bow frame and a cable system on the
frame mounted to at least two rotational elements such as wheels.
Early compound bow wheels or cams were basically a round wheel with
the axle hole located off center to produce let-off as the bow is
pulled to full draw. These eccentrically mounted wheels have a mass
center off-set from the axle hole. When rotated about an axle, the
inertia of the off-center mass produces a kick which causes the
rest of the system to gyrate. This causes a kick or vibration/shock
movement which is imparted to the bow and archer when the bow is
shot. This kick can disrupt the archer's aim or the archer absorbs
this energy as opposed to the energy being transferred to the arrow
or the arrow's flight.
[0003] As bow efficiencies increased and the need for higher
performance and velocities were required, the off-center mass kick
of eccentric mass cams was amplified. One response to this
vibration/shock was to use a sacrificial dampening device. One of
the first devices designed was a forward stabilizer, which mounted
on the front portion of the riser. When the bow was shot, a portion
of the excess vibration was absorbed by the stabilizer. As time
evolved, other types of dampening systems were designed including
devices that were mounted in the riser for the purpose of absorbing
vibration. These dampening systems do not absorb all of the
vibration.
[0004] Another method of dissipating the overall bow kick was the
use of a perimeter weight in the cam to offset limb kick. Since the
limbs travel in a forward direction when shot, there was a forward
movement and inertia imparted to the bow, away from the archer. By
mounting a weight on the outside perimeter of the cam, in a fashion
that moved in the opposite direction of the limb as the bow was
shot, the effects of the limb movement were partially counteracted
or cancelled.
[0005] Another effort to cancel the bow's kick or forward movement
was found in the geometry of the bow. By orienting the limbs in
such a way that the limb tip movement was closer to vertical
movement, it was discovered that some of the forward limb kick was
eliminated. When the bow is pulled to full draw, the limbs were
pulled towards each other as opposed to moving towards the archer.
When the bowstring was released, the limb tips would move in a near
vertical direction. By creating this opposing movement, the limbs
and cams somewhat cancelled each other, creating a more pleasurable
shooting bow. Nevertheless, even when the perimeter weighted cam
and vertical limb technology were used together, the bow still
typically had a kick.
[0006] An improved bow and cam are desired.
SUMMARY OF THE INVENTION
[0007] One preferred embodiment of the present invention provides a
cam having an axle location for mounting the cam to an archery bow,
where the center of mass of the cam is substantially coaxial with
the axle location. Preferable the cam has an eccentric geometric
rotation profile with regard to a rotation axis, typically an
irregular geometry with a non-centered axle location, or a circular
profile with an axle location offset from the center of the
circular profile. The mass of the cam is balanced to have an
effectively equal mass distribution around the axle location. In an
alternate preferred embodiment, the cam has a balanced center of
mass aligned with the axle location in an X-Y orientation, and may
also have a balanced center of mass through the thickness of the
cam in an X-Z or Y-Z orientation.
[0008] In certain embodiments of the present invention, by
arranging, placing or reducing the weight/mass at one or more
locations on the cam (FIG. 2), the effective center of mass can be
zeroed to the centerline of the axle to reduce or eliminate this
gyration or kick. In a preferred embodiment, a "zeroed" cam with a
center of mass co-axial with the axle location will spin freely as
a concentric wheel does on a central axis. The even distribution of
mass around the axle eliminates the traditional kick or gyration
upon bowstring release typically created by an eccentrically
located axle hole.
[0009] In a preferred embodiment of the present invention, an
archery bow encompasses an archery bow riser and a pair of bow
limbs. Each bow limb has a proximal end and a distal end, with the
proximal ends secured to the riser. At least one axle is mounted
adjacent the distal end of one bow limb and a cam is eccentrically
rotatably mounted on the axle. Additionally, a bowstring is
extended between the distal ends of the limbs and configured to be
fed outward from the cam when the archery bow is drawn wherein the
cam has a center of mass aligned coaxially with the axle.
[0010] In another preferred embodiment of the present invention, a
cam for an archery bow comprises a rotatable cam body for an
archery bow. The cam body defines a profile and an axle location is
defined through the cam body such that the cam body profile is
eccentrically rotatable around the axle location. The center of
mass of the cam body is substantially coaxial with the axle
location.
[0011] In yet another preferred embodiment of the present
invention, a dual-feed single-cam compound bow has a pair of
flexible resilient bow limbs forming first and second distal bow
limb ends with a riser connecting the proximal bow limb ends
thereof and a drop-off cam journaled on an axle pin at the first
distal bow limb end. The cam has eccentric peripheral groove
portions wherein each groove portion is journaled on the axle pin.
The cam has a side profile with a center of mass axis coaxial with
the axle pin.
[0012] Additionally, the dual-feed single-cam compound bow includes
of a pulley concentrically journaled at the second distal bow limb
end and has a peripheral groove. An elongated cable has an
intermediate portion trained around the concentric pulley to form
two cable sections which extend between the pulley and the cam. One
section forms a bowstring which has feed-out end portions at both
ends thereof, and the other section forms a take-up portion at the
pulley end thereof and a feed-out portion at the cam end thereof.
The sections are both received in eccentric groove portions
peripheral to the cam in a manner to provide a pair of feed-out
sections extending from the cam toward the pulley. An anchor cable
extends between the two limbs, with one end thereof fixed to the
second bow limb end and the other anchor cable end fixed to the cam
and trained in a take-up groove portion of the cam to produce
controlled flexing of the bow limbs during the drawing of the
bowstring.
[0013] In yet another preferred embodiment of the present
invention, a cam for an archery bow includes a cam body for an
archery bow wherein the cam body has a thickness and defines at
least one cable path with the path defining a cam plane. An axle
passage is defined through the cam body perpendicular to the cam
plane, wherein at least one cable path is eccentric to the axle
passage. In addition, the cam body has a geometrically unequal
distribution of mass through the thickness of the cam body with
respect to the axle passage and the center of mass of the cam body
along the axis of the axle passage is located substantially at the
midpoint of the axle passage.
[0014] In still yet another preferred embodiment of the present
invention, a method of balancing a cam for an archery bow involves
forming a cam body mountable on an archery bow defining an X-Y
plane and defining at least one cable path. An axle location is
defined on the body perpendicular to the X-Y plane such that the at
least one cable path is eccentrically rotatable around the axle
location, and the center of mass of the body is offset from the
axle location. The center of mass of the body is adjusted in the
X-Y plane so that the center of mass is coaxial with the axle
location.
[0015] It is an object of certain preferred embodiments of the
present inventions to provide an improved archery bow, cam and
method.
[0016] Other objects of the embodiments of the present invention
will be clear from the description, figures and claims herein.
DESCRIPTION OF THE FIGURES
[0017] FIG. 1 is a profile of a cam according to the prior art.
[0018] FIG. 2 is a profile of a cam illustrating one preferred
embodiment of the present invention.
[0019] FIG. 3 illustrates a bow according to a preferred embodiment
of the present invention.
[0020] FIGS. 4A and 4B are profiles of a cam illustrating an
alternate preferred embodiment of the present invention.
[0021] FIGS. 5A-D are profiles of a cam illustrating a further
preferred embodiment of the present invention.
[0022] FIG. 6 illustrates a bow according to a preferred embodiment
of the present invention with the cam of FIGS. 5A-D.
[0023] FIGS. 7A and 7B are profiles of the cam and cable system
used in FIG. 6.
[0024] FIG. 8 is a profile of the cam and cable system of FIGS. 7A
and 7B in a drawn position.
[0025] FIGS. 9A-E illustrate embodiments of cam modules usable with
the cam of FIGS. 5A-D.
[0026] FIG. 10A illustrates a weight usable in certain preferred
embodiments of the present invention.
[0027] FIG. 10B illustrates a module mounting screw usable in
certain preferred embodiments of the present invention.
[0028] FIG. 11A is an X-Z profile of a cam illustrating an
alternate preferred embodiment of the present invention.
[0029] FIG. 11B is an X-Y profile of the cam of FIG. 1I A.
[0030] FIG. 12 illustrates a bow according to an alternate
preferred embodiment of the present invention.
[0031] FIG. 13 illustrates a bow according to a further preferred
embodiment of the present invention.
[0032] FIG. 14 is a graph illustrating test data from a prior art
bow and a bow according to a preferred embodiment of the present
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0033] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated and specific language will be used to
describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended, such
alterations, modifications, and further applications of the
principles of the invention being contemplated as would normally
occur to one skilled in the art to which the invention relates.
[0034] One preferred embodiment of the present invention provides a
cam having an axle location for mounting the cam to an archery bow,
where the center of mass of the cam is substantially coaxial with
the axle location. Preferable the cam has an eccentric geometric
rotation profile with regard to a rotation axis, typically an
irregular geometry with a non-centered axle location, or a circular
profile with an axle location offset from the center of the
circular profile. The mass of the cam is balanced to have an
effectively equal mass distribution around the axle location. In an
alternate preferred embodiment, the cam has a balanced center of
mass aligned with the axle location in an X-Y orientation, and may
also have a balanced center of mass through the thickness of the
cam in an X-Z or Y-Z orientation.
[0035] Typically a compound bow 200 (FIG. 3) includes a riser or
handle 205, two limbs 207 extending from the riser with proximal
ends 208 secured to the riser, rotational elements such as wheels,
pulleys or cams mounted on axles 230 adjacent the distal ends 209
of the limbs, and a cable system 210 with a bowstring portion 212
arranged between the rotational elements on limb tips 209 opposite
the riser. As the bowstring portion 212 of the cable system 210 is
drawn and "let-out" by the rotational elements, the limb tips 209
resiliently and flexibly travel towards each other, storing energy
in the limbs and are controlled and held by the cable system. When
the bowstring is released, the limb tips spring back into place,
taking up the cable system and imparting energy to an arrow nocked
to the bowstring portion 212. The rotational elements generally
rotate in one direction to let-out portions of the cable system,
such as the bowstring when the bow is moved to a drawn position,
and generally rotate in the opposite direction to take-up portions
of the cable system and bowstring when the bowstring is
released.
[0036] A compound bow typically has at least one cam defining an
eccentric path within the cable system so that the force to draw
the bowstring drops or is "let-off" as the bowstring is drawn. This
drop-off effect preferably assists an archer to draw and hold the
bow at a drawn position for a longer period of time, for example
while aiming.
[0037] Generally a rotational element such as a cam defines a
substantially planar X-Y direction, generally in longitudinal
alignment with a bow and bowstring and generally encompassing the
movement path of the bowstring as the bow is drawn and released.
Although a cam may have a greater or lesser thickness, depending on
the design and integral or mounted components, for example due to
multiple grooves or modules, the axle location and X-Y center of
mass lines referred to herein are generally substantially
perpendicular to the X-Y plane of the cam and/or the length of the
bow.
[0038] When considering a mass body, the body is defined as a
matter of physics to have a "center of mass". The center of mass in
three dimensions is defined at a point representing the mean
position of the matter in the body. In another way of stating it,
the center of mass of a body is the point that moves as though all
of the mass were concentrated there and all external forces were
applied there. The center of mass does not need to be a physically
defined structure, and can be a virtual point calculated from the
weighted mean of the mass portions of the body. The weighted mean
accounts for the amount and specific gravity of each material used
and its relative position. The center of mass is sometimes called
the center of inertia.
[0039] From the perspective of a two-dimensional analysis, i.e. a
defined plane, the center of mass is defined as a point
representing the mean position of the weighted matter in the body
with respect to that plane. A center of mass axis is perpendicular
to the defined plane and passes through the center of mass point on
the plane. References to the "center of mass" herein, when
discussed in the context of a plane, are used interchangeably with
the center of mass axis, unless specified otherwise or made clear
in context.
[0040] Directions referred to herein, such as forwardly,
rearwardly, vertically and horizontally are intended to be from the
perspective of an archer holding an archery bow and are not
intended to be absolute. The bow is considered to be held in a
substantially vertical position for use, with the bowstring and
riser generally considered vertical. Forwardly refers to the
direction from the bowstring towards the riser in which direction
the arrow is intended to leave the bow. Rearwardly refers to the
direction extending from the riser towards the bowstring and the
archer. Other directional references are intended to apply from
this perspective.
[0041] In one preferred embodiment of the present invention, the
mass of the cam is designed so that the X-Y center of mass is
co-axial with the cam's axle. In certain specific embodiments, one
or more masses are located, arranged or removed on the cam to
"weight" or "zero" the cam in order to move the X-Y center of mass
axis so it is effectively co-axial with the centerline of the cam's
axle location.
[0042] In one prior art example (FIG. 1), an irregular or eccentric
mass cam typically will have an irregular mass distribution offset
with respect to the axle, causing the cam to change moments or
gyrate as it rotates while the bowstring is being pulled to a full
draw position to be released. This gyration causes a kick upon
release of the bow string. Among other effects, the change in
moment and angular force causes the cam's axis to attempt to
precess and nutate around the desired cam rotation axis.
[0043] As an example, FIG. 1 shows a typical eccentric mass cam of
the prior art. Cam 10 includes an irregular cam body 20, with an
eccentrically located axle location such as axle hole 30. In this
example, a perimeter weighted cam is used, meaning that a weight 26
is placed on the cam tip at the outside perimeter of the cam 10,
such as described in U.S. Pat. No. 5,809,982 with the named
inventor Mathew A. McPherson. In cam 10, the axis of the center of
mass 50 is offset in relation to the axle hole 30. Typically, the
center of mass 50 is offset a considerable distance F from the axle
hole 30. The typical center of mass on this type of cam/wheel is
located anywhere from 3/8" to 5/8" from the axle hole, depending on
the diameter of the eccentric cam. When used in a bow, cam 10
creates an eccentric or offset gyrating kick. This kick can
interfere with the user's aim and typically is only partially
absorbed by any dampeners and counter-weights, with the remaining
kick transmitted to and absorbed by the user.
[0044] In certain embodiments of the present invention, by
arranging, placing or reducing the weight/mass at one or more
locations on the cam (FIG. 2), the effective center of mass can be
zeroed to the centerline of the axle to reduce or eliminate this
gyration or kick. In a preferred embodiment, a "zeroed" cam with a
center of mass co-axial with the axle location will spin freely as
a concentric wheel does on a central axis. The even distribution of
mass around the axle eliminates the traditional kick or gyration
upon bowstring release created by an eccentrically located axle
hole.
[0045] The weight/mass added to a cam can be made from the same
material, or made from a material of a higher or lower specific
gravity. In an alternate embodiment, mass is removed from portions
of the cam profile, either alone or in combination with adding mass
to portions of the cam in order to balance the center of mass with
the axle location. Optionally, the mass can be integrated into the
material of the cam body or can be mounted to the cam as a
component.
[0046] In further preferred embodiments of the present invention,
cams having a center of mass coaxial with the axis can be used with
"one cam," "two cam" or "Cam&1/2.RTM." style bows, where the
mass centered cams are located at least at one limb tip 209, and
optionally at the tips of both limbs. Each cam is preferably
mounted with an axle pin 230 extending between the cam and the limb
tip, for example within fork, split or quad limb designs. An axle
or axle pin is typically a metal bar or tube extending through the
cam body.
[0047] A one cam bow (shown in FIG. 3) typically has one eccentric
cam at one limb tip, and a circular idler wheel at the opposing
limb tip. The idler is typically mounted to the upper limb and the
cam mounted to the lower limb; however, this can be reversed if
desired. A centrally mounted circular idler wheel, with equal
weight distribution, typically will not exhibit a moment or kick
around the idler wheel axis. The present invention allows both the
idler wheel and opposing cam to rotate without eccentric gyration.
One example of a one cam style bow is taught in U.S. Pat. No.
5,368,006, incorporated herein by reference.
[0048] A two cam system uses mirror imaged cams that must be kept
in perfect time or synchronization in order to function properly. A
"Cam&1/2.RTM." or "one & one half cam" hybrid style system,
does not use a circular idler wheel, and instead uses two hybrid
cams. Like a two cam system, a Cam&1/2 style system needs to be
timed in order to shoot properly. Unlike a two cam system, a
Cam&1/2 style system uses cams that are not a mirror image of
one another. Two "zeroed" or mass centered cams of the present
invention can be used in either a two cam or Cam&1/2 style
system to allow both cams to rotate without eccentric gyration.
[0049] In some preferred embodiments, mass zeroed cams are used
with bows where the bow limbs and riser emphasize vertical limb
movement. In these embodiments the limb tips are designed to travel
primarily vertically as the bow's bowstring is released. This can
be done, for example, by pre-curving the limbs or by changing the
limb pocket or connection angle on the riser to a more horizontal
angle. The vertical limb movement combined with zeroed cams further
substantially reduces the kick and vibration of the bow upon
release. This preferably assists a user's aim and provides more
efficient energy transfer. This vertical limb movement plus mass
zeroed cams can be used on the three types of cam systems now used
in the archery industry. Examples of bows with pre-curved limbs are
taught in U.S. Pat. Nos. 5,749,351; 5,901,692 and 5,921,227,
incorporated herein by reference.
[0050] The following illustrations primarily show the center of
mass on a "one cam system;" however, use of the present invention
is not limited to a one cam system. Adaptation and use with other
style systems will be understood by those of skill in the art.
[0051] FIG. 2 shows a "zero center of mass cam" 100 according to a
preferred embodiment of the present invention. Cam 100 includes a
non-circular cam body 120, with an eccentrically located axle
location such as axle hole 130. The axis of the effective center of
mass 150 is co-axial in relation to the axle hole 130.
[0052] One option for centering the center of mass over the axle
hole is by locating one or more weights 140, such as a brass
weight, on cam body 120 in one or more proper locations to move the
effective center of mass 150. The weight may be a continuous piece
or multiple pieces spaced as desired to effectively move and
balance the center of mass as desired.
[0053] The center of mass location 150 can be separately adjusted
by machining lightening holes 146 to remove material in one or more
locations on a weight or cam body 120. The lightening holes may
extend all or partially through portions of the weight or cam body.
Preferably, by balancing the design of the cam body 120, one or
more weights 140 and one or more holes 146, the X-Y center of mass
150 can be located at the exact centerline of the axle location
130. This creates a cam which spins with a substantially reduced
and minimal kick or gyration. Examples of preferred weighting
materials include aluminum, brass, copper, zinc, lead, tungsten,
stainless steel, rubber, plastic and polymer based materials.
[0054] FIG. 3 shows a one-cam style bow 200 with a cam 100 and a
circular idler wheel 220 according to one preferred embodiment of
the present invention. In this embodiment, cam 100 includes two
feed out tracks for bowstring 212 and cable portion 214, and a
take-up track for an anchor cable 216 as the bow 200 is drawn. In
this embodiment, the center of mass 150 is coaxial with an axle 230
through limb tip 209.
[0055] The weights and lightening holes can be separate or combined
with components integral with or mountable on the cam. For example,
some cams, such as one cam systems, have two feed-out cable tracks
and one anchor cable take-up track. The tracks are defined by
independent sub-cam profiles on the cam. The cam profiles may be
defined, for example, using continuous grooves or non-continuous
grooves such as posts with or without groove portions. Weights or
holes to adjust the center of mass can be separate or combined with
these cam profiles.
[0056] FIGS. 4A and 4B show side views of an alternate embodiment
of a "zero center of mass cam" 100' according to a preferred
embodiment of the present invention. Cam 100' includes a
non-circular cam body 120', with an eccentrically located axle
location such as axle hole 130'. The axis of the effective center
of mass 150' is co-axial in relation to the axle hole 130'. A
weight 140' is mounted to cam body 120'. Lightening holes 146' are
defined in cam body 120' and weight 140'. Cam body 120' defines a
bowstring cam 112', a return cable cam 114' and an anchor cable cam
116'. In this embodiment, cam body 120' is machined from one piece
of material, such as 6061T6 aluminum.
[0057] FIGS. 5A-D show views of a further embodiment of a "zero
center of mass cam" 300 according to a preferred embodiment of the
present invention. Cam 300 includes a non-circular cam body 320,
with an eccentrically located axle location such as axle hole 330.
A weight 340 is mounted to cam body 320. One or more lightening
holes 346 are defined in cam body 320 and weight 340. Cam body 320
preferably defines a bowstring cam 312, a return cable cam 314 and
an anchor cable cam 316. The effective center of mass axis 350 is
co-axial in relation to the central axis A-A of axle hole 330.
[0058] In certain embodiments, modules such as module 324 are
mounted to cam body 320 to partially define one of the cams or
tracks, for example anchor cable cam 316. Module 324 is mounted to
cam body 320 with two screws 328. In a preferred embodiment, a
module is selected from various modules, such as shown in FIGS.
9A-E, and each module can be substituted on the cam body to change
the profile of the anchor cable cam and the bow's effective draw
length.
[0059] FIG. 6 shows a one-cam style bow 200 with a circular idler
wheel 220 and cam 300. Cable system 210 with respect to cam 300 is
illustrated in detail in FIGS. 7A and 7B. As illustrated, bowstring
portion 212 is received in a bowstring path 312' defined by
bowstring cam 312. An end of bowstring 212 is anchored to an anchor
peg 313. Return cable 214 is received in a return cable path 314'
defined by return cam 314. One end of return cable 214 is anchored
to an anchor peg 315. Anchor cable 216 is received in a anchor
cable path 316' defined by an anchor cam 316. One end of anchor
cable 216 is anchored to an anchor peg 317. The anchor pegs may be
fixed, or in some embodiments are adjustable in position. In a
preferred embodiment, the bowstring cam, return cam and anchor cam
are each journaled around the axle location.
[0060] In a one-cam style system, bowstring 212 and return cable
214 are portions of one cable with an intermediate portion received
around an idler wheel on the distal limb. Anchor cable 216 may
extend from cam 300, to the opposing limb tip, and may be anchored
to the limb tip, for example with a split-Y yoke mounted to the
idler wheel axle. In a brace or undrawn configuration, bowstring
212 defines a substantially straight or vertical line between and
with respect to the outer or rearward edges of the cam and idler
wheel.
[0061] Cam 300 and portions of cable system 210 are illustrated in
FIG. 8 in detail with the bow in the drawn configuration. When
bowstring 212 is drawn, cam 300 on the lower bow limb rotates, in a
clockwise direction from the perspective of FIG. 7B to FIG. 8.
Bowstring 212 is let-off from bowstring cam 312 and extends
rearwardly at an increasing angle as the bow is drawn. Return cable
214 is let-off from return cam 314 towards idler wheel 220. Anchor
cable 216 is taken up by anchor cam 316. The configuration of
anchor cam 316 preferably defines a stop mechanism or bumper for
the anchor cable, inhibiting further rotation and indicating that
the bow has reached a fully drawn position. In the fully drawn
position, anchor cable 216 is preferably substantially straight and
vertical between the cam 300 and the opposing limb tip mounting
point, such as axle 230. Typically, the anchor cam stop position
stops the anchor cable in a vertical position substantially
adjacent the cam axle. The overall cam rotation is approximately
180 degrees.
[0062] Some bows allow interchangeable modules to be mounted on one
or two cams to change the bow draw length. In a still further
embodiment, a cam can be matched with one module or a set of
different profile modules designed to zero the center of mass when
the cam is used with any one of the modules. FIGS. 9A-E illustrate
one set of such modules, including modules 324, 324', 324", 324'"
and 324"". Each module is preferably designed to be mounted on cam
body 320 to form a portion of anchor cam 316, with each module
assisting to define a different geometry anchor cable path 316'.
The modules each have a defined mass and solid portions plus
weights and/or lightening holes.
[0063] Various fasteners can be used to attach a module to the cam
body. Typically a module is mounted to cam body 320 using two
module fasteners, such as flat head cap screws 328 as illustrated
in FIG. 10B. Preferably the module fasteners extend at least
partially through the module and the cam body. Preferably at least
one fastener is used and two or more is preferred.
[0064] Preferably each module is designed and arranged with a
geometry and mass such that any one of the modules can be mounted
on cam body 320 with the result that the center of mass 350 of cam
300 is maintained as coaxial with the axis of axle 330. Additional
mass or lightening holes can be added or defined in each module to
obtain the desired configuration. The overall balancing arrangement
of the module and cam also factors in the mass, location and
specific gravity of the module fasteners and fastener holes.
[0065] An example profile of a weight 340 is illustrated in FIG.
10A. An example profile of a module screw 328 is shown in FIG. 10B.
Preferably the materials used for the cam, cam module, weight and
any fasteners are chosen for their strength and specific gravity
and considered in the overall analysis to balance or zero the cam.
For illustration purposes, as an example only, the cam body 320 and
cam module 324 or modules are formed from an aluminum material or
alloy with a specific gravity of 0.097 lbs/in.sup.3. In this
example, weight 340 is formed from a brass alloy with a specific
gravity of 0.305 lbs/in.sup.3, and the module screws are formed
from a steel alloy with a specific gravity of 0.25
lbs/in.sup.3.
[0066] FIGS. 11A and 11B illustrate a version of "zero center of
mass cam" 300. Cam 300 is balanced in at least two and preferably
three dimensions with regard to the center of mass in the X-Y, Y-Z
and X-Z planes. Cam 300 includes a non-circular cam body 320, with
an eccentrically located axle location such as axle hole 330. As
discussed above, the axis of the X-Y effective center of mass 350
is preferably co-axial in relation to the axle hole 330. One option
for centering the X-Y center of mass over the axle hole is by
locating one or more weights 340, such as a brass weight, and
lightening holes 346 arranged with mass or openings in one or more
proper locations to move the effective X-Y center of mass 350.
[0067] As an additional option, the Y-Z center of mass 360 of cam
300 is preferably centrally balanced in a Y-Z orientation on cam
body 320. The cam profiles may be formed with portions having
different sizes and corresponding masses, as shown most clearly in
FIG. 11A, tending to offset the effective Y-Z center of mass 360
from the Y-Z center 365 of cam 300. For clarity, FIG. 11A
illustrates the Y-Z center of mass 360 before balancing, shown as
slightly offset in the Z-direction with respect to the center or
midpoint 365 of passageway 330 for the cam axle.
[0068] As a preferred feature, preferably the Y-Z center of mass
360 is balanced or "zeroed" to align the Y-Z center of mass 360
with the center 365 of cam 300. This reduces and preferably
eliminates any side-to-side wobble or kick of the cam as the
bowstring is released and the cam rotates around its axle. The Y-Z
center of mass 360 can be moved to one side or the other by adding
mass and weight of the same or a different material at one or more
points and/or by creating holes or voids to lighten one or more of
the cam profiles. Preferably the center or midpoint 365 of the
passageway and axle also corresponds to the centerpoint of the
corresponding limb tip when the cam is mounted.
[0069] One example of adding mass is by adding an annular element,
such as a washer 348 mounted to one side of cam 300. Preferably any
added or removed mass for Y-Z balancing is aligned with the axle
location 330 or distributed around the axle location with the X-Y
center of mass of the added or removed weight or hole aligned with
the axle location to maintain the cam's X-Y balanced center of
mass. Similarly, mass or lightening holes can be arranged and added
or removed to balance the cam in the X-Z perspective while
maintaining the cam's X-Y center of mass. In one preferred
embodiment, the cam is balanced in the X-Y, the X-Z and the Y-Z
dimensions.
[0070] Cams having Y-Z and X-Z balanced centers of mass can be used
with "one cam," "two cam" or "Cam&1/2.RTM." style bows, where
the mass centered cams are located at least at one limb tip, and
optionally at the tips of both limbs. Preferably the cams are
optimized to be balanced in the X-Y, Y-Z and X-Z planes to minimize
wobble or kick in three dimensions.
[0071] In some alternate preferred embodiments, mass zeroed cams
are used with bows where the bow limbs and riser emphasize vertical
limb movement. In these embodiments the limb tips are designed to
travel primarily vertically as the bow's bowstring is released. In
certain examples, the bow limbs are mounted with the distal limb
ends tangent with a line at an interior angle from a vertical axis
line defined by the riser. The interior angle is preferably in a
pre-drawn range of approximately 70-90.degree. and preferably is at
least 75.degree..
[0072] A vertical style bow 400 with pre-curved limbs emphasizing
vertical movement of the limb tips is illustrated in FIG. 12. Bow
400 is illustrated in a two-cam style configuration, with mirror
image eccentric cams mounted at the upper limb tip and the lower
limb tip.
[0073] A bow 500 with more horizontally arranged limbs and angled
limb pockets is illustrated in FIG. 13. In bow 500, angled limb
pockets preferably form an angle from the vertical axis of the
riser. Preferably the pocket angle is greater than 15.degree. and
preferably is greater than approximately 45.degree.. Typically, the
pocket angle and limb curve combine for a total interior angle of
approximately 70.degree.-90.degree. and preferably at least
75.degree.. This limb arrangement is sometimes referred to as
parallel limbs. Bow 500 is shown with cam 300 mounted on the lower
limb tip. A parallel limb style bow typically has a shorter
bowstring length and draw than a bow with more vertically angled
limbs.
[0074] The vertical limb movement combined with zeroed cams further
substantially reduces the kick and vibration of the bow upon
release. This preferably assists a user's aim and provides more
efficient energy transfer. This vertical limb movement plus mass
zeroed cams can be used on the three types of cam systems now used
in the archery industry.
EXAMPLE
[0075] To test and illustrate the kick or vibration/shock reduction
of an embodiment of the present invention, a bow mounted with a cam
according to the present invention was tested against a bow mounted
with a perimeter weighted cam (PWC). The test bow used was a
Jennings model CK3.5 bow equipped with a perimeter weighted cam and
then equipped with a "zero center of mass" cam according to a
preferred embodiment of the present invention. The test data is
shown in graphical form in FIG. 14.
[0076] The specifications for the Jennings model CK3.5 bow with a
perimeter weighted cam were as follows:
1 Test Results Friction (ft-lbs) 6.86 Fwd Curve (ft-lbs) 75.99 Rev
curve (ft-lbs) 69.13 % Let-Off (effective) 83.47 Min Force (lbs)
11.00 True Draw (in) 27.11 A-A (in) 35.25 Brace (in) 8.20 Power
Stroke (in) 18.91 Peak Force (lbs) 66.59 AMO Draw Length (in) 28.86
Holding Wt (lbs) 11.00
[0077] The specifications for the Jennings model CK3.5 bow with a
zero center of mass cam were as follows:
2 Test Results Friction (ft-lbs) 5.77 Fwd Curve (ft-lbs) 77.01 Rev
curve (ft-lbs) 71.24 % Let-Off (effective) 73.97 Min Force (lbs)
17.14 True Draw (in) 27.12 A-A (in) 35.00 Brace (in) 8.45 Power
Stroke (in) 18.67 Peak Force (lbs) 65.84 AMO Draw Length (in) 28.87
Holding Wt (lbs) 17.14
[0078] Data for each bow configuration was collected over ten
tests. The arrow used for all tests weighed 398.8 grains
[0079] An accelerometer from PCB was mounted at the bow handle
portion to simulate an archer's grip points, and was used (#352A10
SN 24060) in conjunction with National Instruments software
"VirtualBench" version 2.6 to collect data indicating the gravities
(g) applied to the bow upon release of the bow. The root mean
square "RMS" method was used to process the data. The RMS method is
frequently used in statistics to calculate magnitudes with respect
to a varying function. The RMS method allows a calculation of the
overall magnitude, in this case vibration or shock, delivered to
the system.
[0080] In the present measurements, the accelerometer had a
sensitivity of 10.30 mV/g as provided in the manufacturer's
calibration card. Data was measured in increments of 0.000391
seconds. Raw data was measured and used for a time period from 0
seconds to 0.4 seconds, after which time the system vibration has
diminished to substantially equilibrium. The raw data, measured in
volts, was divided by 0.0103 to convert to gravities "g's" as
"modified data." Under the RMS method, the modified data was
squared and the mean was calculated. The square root of the mean
was taken to result in a RMS vibration/shock value. The ratio of
the PWC RMS value to the zero center of mass cam RMS value provides
the percentage reduction in vibration/shock between the tests.
[0081] The data results were as follows:
3 CK3.5 PWC Square root Test Mean g's.sup.2 (RMS) (g's) 35-1
957.5582 30.94444 35-2 998.0024 31.59118 35-3 949.0807 30.80715
35-4 1030.352 32.0991 35-5 1068.251 32.68411 35-6 1072.245 32.74515
35-7 1028.961 32.07743 35-8 1009.942 31.77958 35-9 1026.007
32.03134 35-10 1025.65 32.02577
[0082]
4 CK3.5 Zero Center Of Mass Cam Square root Test Mean g's.sup.2
(RMS) (g's) 35-1 780.9944 27.94628 35-2 880.0692 29.66596 35-3
870.8732 29.51056 35-4 894.4499 29.90736 35-5 865.0753 29.41216
35-6 896.1159 29.93519 35-7 918.9028 30.31341 35-8 870.4562
29.50349 35-9 904.9971 30.08317 35-10 882.9703 29.71482
[0083] The mean RMS for the CK3.5 with the PWC was 31.8785 g's. The
mean RMS for the CK3.5 with the zero center of mass cam was 29.5992
g's. This illustrates a 7.15% mean drop in the magnitude of the
vibration or kick transmitted to the bow equipped with the zero
center of mass cam in comparison to the bow equipped with the
perimeter weighted cam.
[0084] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiment has been shown
and described and that all changes and modifications that come
within the spirit of the invention are desired to be protected.
* * * * *