Patent Grant
6871643
1. Field of the Invention
The present invention relates to compound archery bows, and particularly to eccentrics operable with such bows.
2. State of the Art
Compound archery bows employ a pulley system with bow string rigging arranged to provide a mechanical advantage to deflect flexible bow limbs, and to provide a draw force let-off at full draw. The limbs of a typical compound bow are much more stiff than limbs of a typical prior art single action bow, such as a recurve or long bow. Therefore, the limb deflection of a compound bow can be reduced while still storing sufficient energy to provide enhanced arrow speed compared to such prior art bows. The draw force let-off effected by the pulley arrangement permits an archer to hold an arrow at full draw with reduced exertion, likely resulting in more accurate shot placement than with a single action bow.
For purposes of this disclosure, brace, or a brace condition, is defined as the orientation achieved in a fully strung bow having tension applied to the drawstring solely by the bow limbs. That is, brace is defined as a static position of a bow that is ready to nock an arrow.
The term “pulley” encompasses a single wheel or eccentric element, but also includes an assembly of one or more such components. In the latter case, the term “pulley assembly” is sometimes used. The components that make up a pulley, or pulley assembly, are primarily wheels, or eccentrics. In an archery context, a wheel typically defines a groove, or string track, in which to receive a bow string rigging element, that is concentric with an axis of rotation of the wheel. An eccentric defines a groove, or string track, in which to receive a rigging element, that is spaced by a variable radius from the axis of rotation of the eccentric. Sometimes, an eccentric or wheel may be identified as a “cam” substantially in accordance with its ordinary dictionary meaning. However, in certain cases, principally for marketing language, a bow may be referred to in terms of selected characteristics of its pulley members. In marketing lingo, a pulley, or pulley assembly, may sometimes be referred to as a “cam”.
Bow string rigging for a compound archery bow is to be understood to encompass one or more two-force members that can be arranged to cause pulley rotation during a draw motion. One two-force member is adapted to serve as a drawstring. The drawstring may be a central, or intermediate, stretch of a longer string, or cable, that is entrained about one or more pulleys with ends of the cable being anchored to structure. End stretches of string rigging are typically referred to as cables, regardless of their actual construction. Modern practice typically provides drawstrings made from a multistrand, synthetic material, and end stretches made from other material, including aircraft cable, although any workable arrangement, or combination of materials is acceptable for practice of the invention. A stretch of cable having an end anchored to a limb, or other nonrotating structure, is typically classified as a power cable. A stretch of cable anchored between pulleys is sometimes called a control cable, although a drawstring may be similarly anchored. A stretch of cable may be regarded as a rigging element.
Early compound archery bows, such as disclosed in U.S. Pat. No. 3,486,495 to Allen, employed a pair of pulleys located for eccentric rotation disposed at tip ends of opposite bow limbs. Bow string rigging was entrained about the pulleys such that an end of a rigging element was anchored to each opposite bow limb. Such an anchor arrangement effectively provides two cable reference anchors to the bow. Maintaining timing of the two pulleys with respect to each other in such a string rigging arrangement is critical to achieving stable arrow flight. As the pulleys lose rotational synchronization with each other, the nocking point inherently departs from a straight-line path between full draw and a brace condition. Such nonlinear nocking point travel can cause erratic arrow flight, and loss of accuracy. It is common for a bow carrying such rigging to “go out of time”, due to any number of factors, such as cable stretch, or pulley slipping relative to the cable rigging. Archery bows having such rigging may be classified as “dual cam” bows for marketing purposes.
Several approaches have been proposed to overcome the timing problem associated with typical “dual cam” bows. Among more recent such attempts is an improved pulley system, often referred to as a “single cam” arrangement. McPherson, in U.S. Pat. No. 5,368,006 discloses a bow exemplifying such a configuration. The improved pulley arrangement places an eccentric cam element at only one limb end, and a cooperating idler cam element at the opposite limb end. Such an idler cam is concentric about its mounting axle, so the idler cam cannot effect timing of the opposite pulley. A single cable reference anchor is provided at the limb end carrying the idler. Synchronization between the pair of pulleys mounted on the bow is inherent due to the single eccentric element. Bows of this type may be regarded as true “single cam” bows. However, such true “single cam” bows also inherently force a transverse component in nocking point travel between full draw and brace. The eccentric cam element of one pulley unavoidably unwraps drawstring at a variable rate while the idler cam component of the opposite pulley unwraps drawstring at a constant rate. Therefore, the transverse nocking point travel is nonlinear between full draw and a brace condition in such a “single cam” bow. Such behavior is also evident in certain modified forms of the “single cam” assembly, especially if one, or both, pulleys included in the rigging is/are adjustable to change draw length of the bow.
It can be difficult to set up, or tune, a bow to provide consistent, straight arrow flight. As a first step, the timing between pulley assemblies may need to be adjusted to synchronize pulley rotation. Further adjustments may be required to the nocking point location on the drawstring, and to both lateral and vertical position of the arrow rest, to minimize wobble of an arrow in flight. Once a bow is set up, it can be frustrating if the pulley timing changes, as frequently occurs over time in certain known archery bows. Making an adjustment to the bow, such as changing the draw length, often compromises the tune of the bow by changing the timing between the pulley members. In the case of certain “one cam” bows, a change in draw length inherently causes an undesirable change in the nocking point travel path. A major problem with certain prior art bows is simply keeping rotation of the pulleys synchronized, while permitting a simple, easy adjustment in certain bow characteristics, such as draw length. One attempt to address this problem is disclosed by Larson in U.S. Pat. No. 4,774,927. Larson discloses a pulley having a rotatable cam portion, or module, operable to change a draw length of a bow on which the pulley is mounted.
Considerable effort has been devoted to developing pulley shapes to preserve a draw weight let-off while maximizing stored energy in a bow's limbs. Pulley shapes encompass the various string and cable grooves-carried on the individual cam elements forming the pulley assemblies. Miller, in U.S. Pat. No. 5,505,185, discloses certain desirable component elements of a pulley assembly, including a power cam element. It would be desirable further to provide an improved profile for pulley elements operable to better harness the stored limb energy for stable transfer of that energy to an arrow to increase certain shooting characteristics of a bow, such as arrow velocity.
End stretches of cables are often anchored to post-type structure carried on a pulley of bow string rigging, or on a component forming such a pulley. Commonly, a relatively short, stubby, post-type anchor is affixed to a cam component for anchoring a cable of an immediately adjacent cam component. In certain cases, an anchor may have a desired foundation location spaced apart, by one or more cam components, from a plane in which the anchored cable acts to apply loads to the anchor. Such circumstances require a tower anchor, which increases the moment arm by which cable loads are amplified with respect to the foundation. Often, cable loads on the anchor structure reach a peak value as an arrow is fired, and the brace cable load, plus an additional impact load, is resisted by the anchor. In some cases, the anchor desirably is arranged to be removable from its foundation, e.g. to replace or to install certain pulley components. In such cases, cable loads may cause failure of the foundation, or of the fastening arrangement used to affix the tower anchor to the foundation.
Prior art bows, in general, often display certain undesirable traits. One such trait is the undesirable “click” produced by rotation of a positive draw stop into interference with a rigging member. Such a click can alert a hunter's quarry to the hunter's presence. One commercially available solution adhesively affixes a dampener pad to a contacting surface of a cam-mounted draw stop surface. Such dampener pad is prone to loss by being scraped from the draw stop surface, or by loss of adhesion between the draw stop surface and the dampener pad.
Excessive vibration subsequent to release of an arrow is another undesirable trait of certain bows. In certain instances, pulleys having press-fit bearing assemblies “walk” or move transversely with respect to their bearing assemblies due to vibration and side load applied from bow string rigging. Sometimes, such pulleys displace or transversely “walk” sufficiently with respect to their mounting bearing that the pulley detrimentally rubs, or scrapes, on spacers or other structure associated with the pulley mounting area. It would be an improvement to provide bow rigging elements operable to address the deficiencies found in prior art archery bows.
The present invention provides an asymmetrical cam system for use in rigging the drawstring and limb-flexing cables for a compound archery bow. Pulley assemblies according to the invention are structured to provide certain beneficial aspects over the prior art “single cam” and “dual cam” systems, while also avoiding certain of their negative aspects. A notable benefit of the asymmetrical cam system of the present invention is their ability to combine the forgiveness and symmetry of a “dual cam” system with the positive draw stop (hard wall), enforced synchronization (or built-in timing) between opposite pulley assemblies, and high let-off associated with “single cam” systems. According to some embodiments, the asymmetrical cam system accommodates a change in draw length of the bow without requiring the use of a bow press. Furthermore, in certain embodiments of pulleys providing adjustable draw length, changing the draw length does not cause a change in either nocking point travel, or the shape of the draw force curve between brace condition and peak draw weight.
A representative bow incorporating the asymmetrical cam system of the present invention typically includes: a handle, or riser, with a top limb and a bottom limb attached to the riser, with the top and bottom limbs extending from the riser to respective top and bottom limb ends. A first pulley is attached for rotation at the end of one limb tip; a second pulley is attached for rotation at the end of the other limb tip. Bow string rigging is entrained about the first and second pulleys, such that the rigging has only a single cable reference anchor to a limb. Also, the first and second pulleys desirably are structured and arranged in harmony with the rigging such that a change in draw length may be accomplished while the bow is strung and at brace condition with a drawstring under full tension from the top and bottom limbs.
Pulleys according to the invention may include rotatable modules configured and arranged to permit a change in draw length without causing a corresponding change in transverse nocking point travel, or otherwise negatively effecting the tune of the bow. Certain pulleys alternatively provide only fixed modules adapted to provide a certain, fixed, draw length. Such nonadjustable pulleys may be employed on a custom basis, to further improve bow performance by reducing pulley mass and rotational inertia. Alternatively, draw length may be adjusted in certain embodiments by replacement of an entire module or cam, or of a portion of a module or cam. Modules, or cams, specifically are not required to rotate with respect to a foundation to accomplish an adjustment in draw length. Other relative motions are within contemplation to effect an adjustment of a module or cam, including shifting, translating, and sliding.
Bow string rigging, of bows according to the invention, typically includes a power cable anchored at a first end to the reference limb anchor, and anchored at a second end to the second pulley for wrapping onto a portion of the second pulley during a draw motion. The rigging further includes a control cable anchored at a first end to an anchor carried on the second pulley and adapted to unwrap from a portion of the second pulley during the draw motion, and anchored at a second end to an anchor carried on the first pulley for wrapping onto a portion of the first pulley during the draw motion. The drawstring is typically anchored at a first end to the first pulley and anchored at a second end to the second pulley, and is arranged to unwrap from each of the first and second pulleys during the draw motion.
It is desirable for pulleys to be configured and arranged to permit a change in draw length without causing a change in the draw force curve in the portion of the curve between brace and up to full bow weight. Certain preferred pulleys resist a change in peak draw weight over the range of draw length adjustment provided by those pulleys. Furthermore, the pulleys typically are configured and arranged to permit making a change in draw length without requiring a change in length of the drawstring or cables of the rigging.
In detail, the first pulley can be classified as a follower pulley and includes a follower string cam. The follower string cam defines a follower string groove operable to wrap and unwrap a first end of the drawstring. In one embodiment, the follower string cam carries a first anchor for the drawstring and a second anchor for an end of a control cable. The follower pulley also includes a follower cam defining a follower control cable groove operable to space the control cable apart from the pulley axle by a variable radius.
The second pulley can be classified as a control pulley and includes a control string cam. The control string cam defines a control string groove operable to wrap and unwrap a second end of the drawstring for the archery bow. In one embodiment, the control string cam carries a first anchor for the drawstring, a second anchor for an end of a power cable, and a third anchor for an end of a control cable. The second pulley also includes a power cam defining a power cable groove operable to space the power cable away from the control pulley axle by a variable radius, and a timing cam. The timing cam defines a timing groove operable to space the control cable apart from the control pulley axle. Certain currently preferred timing cams are concentric about their mounting axis.
One end of the power cable is anchored in some fashion to a bow limb at the cable reference anchor. As previously mentioned, the other end of the power cable can be anchored to the control string cam element of the control pulley. The power cable provides a rotational reference for both of the first and second pulleys with respect to the bow. The single rotational reference prevents timing of the pulleys to vary as a torque is applied to a handle (e.g. by a heavy stabilizer having an extended length) during a draw motion. Rotation of the follower pulley is slaved to the control pulley by the control cable. Therefore, rotation of one pulley may only occur if the other pulley also rotates. Furthermore, the rotation of both pulleys is coordinated with respect to the bow by way of the cable reference anchor.
Certain cam elements forming the respective pulleys are shaped to cooperate with other cam elements. For example, it is generally desired for the operable (working or cable-contacting for wrapping and unwrapping) portion of the timing groove carried by the timing cam to be substantially concentric about the axle of the control pulley. The shape of the follower control cable groove is generally defined to provide an arc length substantially equivalent to an arc length required to wrap onto the follower cam, during a draw motion, a length of control cable equal to the sum of a length of control cable unwrapped from the timing cam during that draw motion, plus a length of power cable wrapped onto the power cam during that draw motion. The wrapped arc length of the follower control cable groove desirably accounts for arc length differences in wrapped and unwrapped power and control cable portions caused by tangency differences between the timing groove and the follower control cable groove relative to the power cable groove. In certain pulley embodiments providing draw length adjustment, portions of the power groove and the control groove may be concentric about a reference structure, such as their respective pivot axles.
Adjustment in draw length for certain embodiments of a bow constructed according to the invention may be accomplished by rotating a control power module with respect to the control string cam, and rotating a follower module with respect to the follower string cam by a corresponding amount. Such an adjustment in draw length can be accomplished without changing the timing of the pulleys with respect to each other, or to the bow. Indicia may be included on one or more pulley components to assist in making equivalent changes to each pulley. The modules preferably are fixed in place, with respect to their corresponding string cams, by one or more removable fasteners arranged as one or more pegs in receiving conduits through the respective module. In certain preferred embodiments of the invention, the draw length can be adjusted while the bow is fully strung and at brace, without requiring use of a bow press.
Once a bow constructed according to principles of the invention is set up, or placed “in tune”, it should remain at least substantially “in tune”, even as its draw length is changed. The arrangement of the rigging and rigging anchors produces a control pulley and a follower pulley that are in static equilibrium at brace. Rotation of the follower pulley is slaved to the control pulley by way of the control cable, which is anchored, or affixed at ends of its span to each pulley. The follower pulley cannot rotate without the control pulley rotating also, and vice versa. Elongation of one or more cable stretches is accommodated by rotation of the two pulleys in approximately equal proportion, thereby resisting a change in pulley timing. Use of a single cable reference anchor, and slaving rotation of the follower pulley to the control pulley, prevents a change in timing between the two pulleys due to either cable stretch or adjustment in draw length. Furthermore, in the event that the two opposed pulleys were mistimed with respect to each other, the operating behavior provided by the instant pulleys generally will produce acceptable nocking point travel and a tunable arrangement. Conversely, an out of time “dual cam” system generally produces erratic nocking point travel.
The invention provides such significant let-off from the arrangement of power and follower cams, and associated power and control cables, that improvements may be made to string cam shapes to additionally improve shooting characteristics of a bow. It is now possible to incorporate a true spiral shape in a significant arc length portion of the perimeter of a string cam. Typically, such spiral shape is located on a portion of a string cam corresponding roughly to the integrated tangent contact points, between a drawstring and the string cam, during at least a part of a let-off portion of the draw and generally terminating at, or near, full draw. In certain embodiments, the spiral structure may occupy an arc about the axis of rotation of the string cam that is up to about 150 degrees, or even more in some cases.
A preferred mounting system for a pulley used in rigging of an archery bow includes a bearing assembly having an outside race providing a stub portion sized for press-fit reception inside a pulley bore. The outside race of the bearing assembly carries a flange, or other structure, disposed to form a structural interference with a pulley surface near a perimeter of the bearing bore. The structural interference between a bearing race flange and structure of a pulley body is operable to prevent undesired displacement of the bearing assembly in an inward direction with respect to the pulley.
Embodiments permitting a draw length adjustment typically include a removable tower anchor for anchoring an end of a control cable. The tower anchor spaces a cable anchor location apart from one cam boundary by a distance greater than the thickness of an interposing cam element. Such an anchor desirably is attached to foundation structure, typically provided by a cam element of the control pulley, by a grade 8 or better fastener. The fastener head forms a reinforcing structure operable to resist a tipping moment applied to the tower anchor by the control cable. Preferred fastener heads include flat head, cap head, and countersink styles, preferably also including a socket head feature to tighten the fastener. A base of the tower anchor desirably provides sufficient size to resist the tipping moment.
Resilient elements may be disposed, in certain embodiments of the invention, for contacting rigging members at certain pulley rotations to attenuate vibration. For example, a resilient element desirably is positioned to contact a power cable, creating an interference and forming a positive draw stop. Such a resilient element operates to reduce cable vibration sounding like a “click” as the draw stop is engaged. Additionally, a resilient element may be disposed at a tail end of one or more string cams to contact the drawstring during pulley over-rotation. Such a tail-mounted resilient element may reduce drawstring vibration subsequent to release of an arrow from a drawn position. Suitable resilient elements display vibration dampening or attenuating characteristics. Certain preferred resilient elements are configured to form an interlocking, self-biased, interference with foundation structure provided by a pulley.
In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention:
As illustrated in
With continued reference to
It is desirable for the nocking point 114 to travel in a substantially straight-line path from release at full draw, passing through brace, and until the arrow separates from the drawstring 116, to resist generation of transverse vibration in, and to promote stability of, the released arrow. Uniformity, or similarity with respect to each other, of the limbs 104 and 106, including their lengths and bending stiffness, has an effect on straightness of the nocking point travel path. Typically, limbs are made as similar as possible in stiffness and in length to minimize variables that complicate bow tuning.
For example, different stiffness between top limb 104 and bottom limb 106 causes different deflections of the limb portions holding pulleys 108 and 110. Those different deflections are difficult to track or predict for purpose of bow tuning. Therefore, it usually is desirable to minimize variability between top and bottom limb deflections, and instead, to arrange the pulley members 108, 110 to unwind portions of drawstring 116 at different rates. That is, the change in drawstring length represented by the quantity (L3−L1) may be different than the quantity (L4−L2). The impact of the different drawstring lengths will be more pronounced on a bow having a tip limb span of 30 inches, compared to a bow with the same amount of nocking point offset, but a 46 inch tip span.
A difference in length of unwrapped drawstring, or cable feed out, will be required between the top and bottom pulleys, assuming similar limb deflections, when L1 is a different length than L2, or else the nocking point 114 unavoidably will depart from a straight-line path. A difference in unwrapped drawstring can be caused by rotating the pulleys at different rates (different pulley timing), or by forming pulleys to have different wrapped arc lengths corresponding to the same pulley angular rotation, or by a combination of both such arrangements.
Certain advantages provided by the instant invention can best be illustrated by comparing characteristics provided by the invention to such characteristics inherent in the prior art archery bows. Referring now to
A common problem with bows of the so-called “dual-cam” type, is that the timing of the pulley members carried on opposite limb ends can shift with respect to each other, resulting in out-of-time cams, and attendant nonlinear nock travel. Nonlinear transverse nocking point travel inherent in an out-of-time, commercially available, “dual-cam” type bow is indicated by data line 120 in FIG. 3. Timing of “dual-cam” bows can be corrupted by uneven cable stretch, by an anchor point shift between one or both pulley members and an associated cable, or even torque applied by an archer's hand—perhaps due to the weight distribution of bow accessories, such as an extended and heavy stabilizer.
The nocking point travel typical in one embodiment of the invention is indicated by experimental data plotted in line 122 in FIG. 3. The transverse component of nocking point travel for the invention may easily be tailored, if desired, to depart from the substantially straight path indicated in FIG. 3. The programmed nocking point path will inherently remain substantially the same, regardless of cable stretch, due to the arrangement of cable and drawstring rigging that is discussed more fully below. As will be discussed in more depth below, timing between pulley elements in the invention is dominated by rotation of a single pulley, so the bow rigging system provided by the invention is much more forgiving than a bow having rigging of the “dual cam” type.
Certain embodiments of the invention are structured to change the draw length of a given bow to fit a particular shooter. Such adjustability permits a store to stock a single bow that is adjustable to fit a variety of sizes of customers. Additionally, a customer may grow in size, and adjust his bow to accommodate such growth. When the draw length is changed, it is desired that such change not detrimentally affect the nocking point travel. Certain embodiments of the invention are operable to permit changing the draw length LD without imposing a deflection in nocking point travel that is transverse to the direction of arrow flight. Preferred embodiments are structured to permit making an adjustment in draw length while the bow, such as bow 100, remains fully strung; with the drawstring under tension.
One characteristic, of certain embodiments of the invention, provides a similar shape to portions of the draw force curve as the draw length is changed. Several plots, 128-138 of draw force vs. draw length corresponding to pulley members according to the invention, adjusted to offer different total draw length, are shown in FIG. 4. Experimentally collected data indicated by plot line 128 are representative of a draw-force plot for a bow having its pulley members adjusted to provide a maximum draw length of about 26½ inches. Data indicated by plot line 138 are representative of the draw-force plot for the same pulley members mounted on the same bow, but adjusted to have an increased maximum draw length of about 29½ inches. The shapes of the initial loading, or force build-up portion, T, and the maximum draw force portions, H128 and H138, remain similar as the draw length is adjusted. However, the length of the maximum draw force portions, Hi of the various data curves does change as draw length changes. As indicated in
The data plotted in
It is currently preferred to form control string cam 150 and timing cam 154 from a contiguous piece of material, such as Aluminum, or certain plastics, to help resist intra-cam deflections. However, it is within contemplation alternatively to form each individual cam as a separate “layer”, and stack three such layers together to form the pulley member 110. In a stacked pulley, the separate layers may be joined through use of fasteners, threaded joints, adhesives, press-fits, or alternative joining mechanisms operable to maintain alignment and proximity of the separate components.
Bore 158 through power cam 152 is defined by an arc subtending greater than 180 degrees and is thereby operable to provide a rotational interface with hub structure 159 operable to space timing cam 154 apart from control string cam 150. This rotational interface assists in locating power cam 152 to make adjustments in draw length. A portion of power cam 152 can first be rotated to the desired orientation with respect to control string cam 150. Then, fastener 160 can be installed through one of a plurality of adjustment locations, generally indicated at 162, for reception in control string cam 150 to secure the rotating portion of power cam 152 in that orientation.
As illustrated in
Alternative adjusting and fastening arrangements operable to fix the orientation of a power cam 152 with respect to a control string cam 150 are also within contemplation. For example, three rows of adjustment locations 162 may be provided in a power cam 152, and three cooperating receiving locations 164 in a control string cam. Additional rows of adjustment locations 162 and additional cooperating receiving locations 164 can also be provided, if desired for a smaller incremental adjustment, or for an additional range in adjustment. Another alternative arrangement may dispense with bore 158 and alternatively provide a plurality of fasteners 160 with a plurality of adjustment locations 162 and receiving locations 164; all arranged to provide a variety of positions for captured retention of power cam 152. However, providing a fixed rotation axis for the rotating module portion of power cam 152 does greatly simplify making an adjustment in draw length over an alternative having more degrees of freedom in which to move the power cam 152.
Continuing to refer to
Still with reference to
After the illustrated power cam 152 is installed in slot 156, a removable tower anchor, generally indicated at 178, can be fastened to control string cam 150. As illustrated, a socket 179 is included in anchor 178 to receive a wrench, such as an Allen wrench to assist in installing tower anchor 178 to its foundation. Anchor 178 generally passes through a void, or aperture, 180 in power cam 152, although other attachment configurations are feasible. Aperture 180 desirably is sized to permit a range of rotation displacement of power cam 152 without interference from anchor 178. It is alternatively within contemplation to provide a wrench flat, or a hexentric cross-section shape, on stem structure 181 of anchor 178 to accommodate a wrench or socket.
One arrangement to fix the anchor 178 to control string cam 150 is embodied in fastener 182. Fastener 182 is received in threaded reception inside anchor 178 to fix anchor 178 relative to a foundation on control string cam 150. Fastener 182 may alternatively be embodied as a socket head cap screw having a head operable as a reinforcing structure to resist a moment applied by control cable 272 to tower anchor 178. An alternative fixing arrangement provides a threaded stub shaft protruding from tower anchor 178. Such a shaft may be formed as an integral part of anchor 178. A protruding threaded stub shaft can be received in threaded reception in control string cam 150, and/or may be received in a separate threaded nut operable as a reinforcing structure to resist a moment applied by control cable 272 to tower anchor 178.
Other fixing arrangements are possible, including press fits, adhesive bonding, and journalled split rings. It is merely desired for the fixing arrangement to resist motion of the anchor 178 relative to the control string cam 150. The fixing arrangement preferably is removable to facilitate installation of, or an exchange of, power cam 152. However, the control cable tower anchor 178 is not required to be removable if the timing cam 154 is removable, or if a passage were cut in the power cam module 183 to allow for installation of the power cam module 183 under the timing cam 154.
Continuing to refer to
Advantages provided by an immobile entry ramp, such as entry ramp 184, include: the power cam module 183 may be kept relatively small; and the drawstring tension can be maintained relatively high at brace, to resist drawstring over-travel when an arrow is fired from a bow. (Drawstring over-travel is defined as deflection of the drawstring from brace condition towards an archer's bow-holding hand.) The fixed entry ramp 184 of power cam 152 can be oriented and arranged to provide a rapid take-up portion on a draw force vs. draw length plot. Correspondingly, the drawstring tension increases as the pulleys over-rotate, effectively reducing drawstring over-travel. Furthermore, the entry ramp 184 can be positioned to prevent a cable stretch, such as a stretch of a power cable, from contacting the module 183, thereby facilitating adjustment of the module 183 at a brace condition.
The control string cam 150, illustrated in
Both of anchor 186 and fixed entry ramp 184 desirably are manufactured integral with control string cam 150 to increase robustness of the pulley 110. However, it is within contemplation for one, both, or other such components, to be affixed to the control string cam 150, or other component, during assembly of a pulley 110 or 108. There are many suitable fastening arrangements, including threaded fasteners, adhesive joints, press fits, and the like, operable to maintain components in position in a pulley 110, or other pulley 108.
Continuing to refer to
It is desirable, in certain embodiments, to include a resilient element 196 arranged first to contact the power cable, whereby to dampen sound produced as structure carried by draw stop 194 contacts the power cable. Resilient element 196 may be formed from any suitable attenuating material, including rubber, viscoelastic materials, urethane, and the like. Illustrated resilient element 196 is installed in interlocking foundation structure 197 provided by power cam 152. Typically, a tension load is applied to resilient element 196, during its installation, to cause a reduction in the cross-section received inside structure 197. Upon release of the tension load, a portion of resilient element 196 forms a self-biased, interference fit with cooperating interlocking structure 197, that is operable to maintain resilient element 196 fixed in place on power cam 152.
Pulley 110 can be carried on axle 198 for mounting for rotation at an archery bow limb tip. Rotation of pulley 110 about axle 198 is typically facilitated by interposing a pair of bearings 200 between the pulley 110 and the axle 198. Workable bearings include flanged roller bearings, as illustrated. It is within contemplation that the bearings 200 may be replaced by ball bearings, sleeve elements (not illustrated), or that the pulley itself may form a sleeve element adapted to fit about axle 198.
With reference to
While follower cam 212 can be provided as an integral part of follower string cam 210, it is currently preferred to arrange follower cam 212 for rotation with respect to cam 210 to provide for making an adjustment in draw length. A follower cam module 214 typically includes a bore structure 240 adapted to interface with hub 236 and facilitate adjustment of module 214 with respect to follower string cam 210. Bore structure 240 illustrated in
Still with reference to
A flat, or somewhat straight portion, generally indicated at 248, may be provided in the edge profile of follower cam 214. Edge portion 248 may operate as a second, or alternative, positive draw stop, functional to resist rotation of pulley 108 beyond full draw by causing a transverse interference between the pulley 108 and the control cable. However, due to the slaved relationship between a pulley 108 and a pulley 110, a hard wall, or positive, stop is achieved by providing a single stop between one of pulleys 108 or 110, and a stretch of a single cable. It is currently preferred to arrange structure carried by the power cam 152 for creating an interference between control pulley 110 and the power cable 270 at full draw.
The rotated position of follower cam module 214 relative to follower string cam 210 can be incrementally fixed by conduits, or adjustment locations, generally indicated at 250. Conduits 250 are illustrated as being arranged in first and second rows in approximately parallel arcs about the axles of associated pulley 108. Individual conduits 250 forming the first and second rows are arranged in a staggered pattern to provide an incremental index between adjacent conduits in one row by an intermediate conduit in the other row. A fastener, or peg, 252 may be inserted through a conduit 252 for reception in one of receiving apertures 254 or 255. Peg 252 therefore can resist rotation between the cams 210 and 214, and also maintain the cams in assembled contact with each other. Typically, peg 252 can be embodied as a threaded fastener received in a threaded bore carried by follower string cam 210. Peg, or fastener, 256 passing through arcuate slot 258 for reception in aperture 260 may be provided, in some embodiments, to assist in maintaining assembly of follower cam module 214 to follower string cam 210.
Similarly to the control pulley 110, follower pulley 108 is carried on an axle 262 for pivoting registration at an end of an archery bow limb tip. As illustrated in
Pulleys 108 and 110 can be mounted for rotation at ends of upper bow limb 264 and lower bow limb 266 in any conventional fashion, one of which is illustrated in FIG. 9. As illustrated, respective pulleys are carried on axles 198, 262 passing transversely through respective limb ends. Also as illustrated, three separate cables are preferably employed in the string rigging of the bow on which pulleys 108 and 110 are mounted. The rigging cables include: a drawstring 268, a power cable 270, and a control cable 272. Of course, it is within contemplation alternatively to reduce the number of cables by combining one or more, and employing a mid-cable anchor arrangement to one or more cam elements. However, use of three separate cables is more simple, robust and permits more easy replacement of cables.
The control pulley 110 anchors a first end 276 of drawstring 268. Anchoring an end of a cable typically involves looping the cable end about an anchor, such as drawstring anchor 174 on control string cam 150. A second end 278 of drawstring 268 is anchored to follower string cam 210 of pulley 108. The actual anchor location for the drawstring 268, and the other cables, is not critical, and can be changed to other workable locations. For example, a workable drawstring anchor location provides for a rotating pulley capable of wrapping and unwrapping the drawstring 268 about the respective string cams 150, 210.
Control pulley 110 also anchors a first end 282 of control cable 272, and first end 284 of power cable 270. A second end 286 of power cable 270 is anchored through a yoke arrangement to opposite sides of axle 262 in upper limb 264. The yoke arrangement forms a “V” shape, with the pulley 108 rotating through the open top part of the “V,” and power cable 270 continuing from the bottom, pointed portion of the yoke towards pulley 110. Such a yoke arrangement distributes load from cable 270 equally to each side of the axle 262 to resist application of a limb twisting force. Of course, other arrangements operable to affix an end stretch of a cable to a limb are within contemplation, including all conventional anchoring arrangements. Certain workable arrangements may replace the above described yoke arrangement with structure such as bracketry rotatably affixed to an axle.
Only one limb is used as a reference for pulley rotation relative to the bow on which the pulleys are mounted. Therefore, the present invention may be characterized as employing a single cable reference anchor. The single cable reference anchor is functional to resist rotation of the pulleys 108 and 110 without also requiring corresponding limb flexing of limbs 104 and 106. A single cable reference anchor and rigging that slaves pulley rotation, as employed by the invention, is operable to form a mathematically determinate, stable, pulley system for consistent, repeatable flexing of limbs of a bow, such as bow 100. A second end 288 of control cable 272 is anchored to follower string cam 210 by looping over illustrated anchor 234.
Because of the illustrated anchoring arrangement for the various cables and drawstring, power cam module 183 and follower module 214 are substantially unaffected by tension in any rigging member. Therefore, power cam module 183 and follower module 214 may be rotated to adjust draw length at brace, when the bow is fully strung, and the drawstring is under tension applied by the bow limbs. Therefore, draw length may be adjusted without placing the bow into a bow vice, or even relaxing the limbs using one or more draw weight adjustment bolts. As illustrated in
With reference to FIG. 9 and especially to
With reference again to
Although the illustrations depict immobile entry ramps 184 and 216 of power cam 152 and follower cam 212 respectively, such fixed entry ramps are not required for the practice of the invention. The fixed entry ramps 184, 216, do provide certain advantages, however. Such fixed entry ramps provide a consistent arc length change versus secant length of unwrapped cable (relative to anchors 186 and 234) to increase drawstring tension as pulleys 108 and 110 rotate past brace subsequent to release of an arrow from a drawn position. Perhaps more importantly, the position and arrangement of fixed entry ramps 184, 216, causes control cable 270 and power cable 272 to move away from axles 198, 262 in a direction toward the riser 102, thereby reducing leverage on the limbs and increasing drawstring tension as pulleys 108 and 110 over-rotate. A change in draw length may be accomplished by rotating modules 183 and 214 without changing the beneficial effect from the fixed entry ramps 184, 216 to reduce drawstring over-travel. Fixed entry ramp 184 also helps to isolate power cam module 183 from transverse contact from power cable 270, permitting more easy rotation of power cam module 183 to adjust draw length. Similarly, fixed entry ramp 216 helps isolate follower cam module 214 from transverse contact from control cable 272 and facilitates rotation of follower module 214.
As shown by comparing
The length and shape of the follower cam groove, or string track (in module 214 plus fixed entry ramp 216, if present), generally is manufactured to provide a wrapped arc length accounting for tangency variations between points of contact of the control cable 272 between the timing cam groove and follower cam groove(s), and similar wrapping contact of the power cable 270 and power cam 152. Such construction can also account for a variable grip below the center of a riser. The timing cam could be eccentric, but then it would be necessary to account for changes in cable wrap with a corresponding change to the follower module to accommodate the change in cable feed out from the additional eccentric. However, in currently preferred embodiments of the invention, an eccentric timing cam inherently causes nocking point departure, between different draw lengths, from a straight-line path.
However, it is within contemplation for an eccentric timing cam to be provided, in certain embodiments, that is fixed to rotate with a power cam 152, or power cam module 183 as draw length is adjusted. Such a timing cam (not illustrated) may be affixed to a power cam, such as power cam 152 at one of a plurality of orientations, if desired to provide additional adjustability. In such an arrangement, a change in draw length may be accomplished without an attendant departure of nocking point travel from a straight-line path.
Furthermore, timing of the pulleys 108, 110 mounted on a rigged bow 100 is significantly more forgiving than if both power cable 270 and control cable 272 approached axles of the respective control pulley 110 and follower pulley 108 by an equal distance. One effect of timing cam 154 is that it establishes a radial spacing between control cable 272 from both of axles 198 and 262. When timing cam 154 is concentric, the minimum spacing of control cable 272 to an axle occurs at axle 198. The spacing of control cable 272 from axle 262 typically also includes an additional component to account for the radial spacing of power cable 270 from axle 198. The inherent radial spacing of the control cable 272 from respective axles 198, 262 provides a lever arm effective to enforce similar rotations between pulleys 108 and 110.
In one currently preferred embodiment of the invention, the minimum radial spacing of a control cable 272 from a centerline of axle 198 is about 0.5 inches, and is a substantially constant value for all rotations of the control pulley 110. In a mating pulley 108, the minimum radial spacing of control cable 272 from a centerline of axle 262 is about 0.675 inches, and occurs at, or near, full draw.
In practical embodiments of archery bows, a minimum radial spacing, or lever arm, of about 0.5 inches between a cable and an axle provides a sufficient lever arm to ensure similar rotation of pulleys 108, 110 (maintain pulley timing). While a smaller radial spacing, or cable offset, is workable, a cable offset that is too small may not sufficiently dominate displacement of the respective pulleys compared to a displacement caused by factors such as cable stretch under cable loading. Since rotation of the control pulley 110 is referenced to a limb by a cable reference anchor, stretch in control cable 272 can permit an undesired, and unequal, rotation of the follower pulley 108 compared to the control pulley 110. A sufficient radial offset of the control cable 272 from rotational axes 198, 262 enforces a pulley synchronizing displacement on the pulley rigging system that typically is orders of magnitude larger than a cable stretch displacement.
The very small radial offset of power cable 270 from the axle 198 provides the large let-off typically associated with a “single cam” arrangement. The power cable 270 illustrated in
Follower pulley 108 also permits control cable 272 to approach the axle 262 on which pulley 108 is mounted to additionally contribute to the let-off in draw weight at full draw. The large let-off in draw weight at full draw obtainable from the cable routing arrangement provided by the invention permits use of string cams 150 and 210 that are shaped to offer improved performance.
It is currently preferred to use control string cams 150 and follower string cams 210 that have substantially the same shape. The respective string cams are typically scaled to account for nocking point offset while holding rotation rate of the string cams equal. That is, given a control string cam 150 of a certain size, the matching follower string cam 210 is generally scaled from the control string cam 150 to unwrap drawstring 116 at a faster or slower rate, but at substantially the same angular rotation, compared to the control string cam 150. A larger string cam will have a higher rate of drawstring feed-out for a given angular rotation of the string cam, and vice-versa. In the case of a nocking point located at the midpoint of a drawstring 116 (nocking point offset is zero), both string cams would typically be the same size. The difference in drawstring feed-out rate between matched string cams typically is set to provide substantially straight-line nocking point travel.
Pulleys 108, 110, or components forming the respective pulleys, may be scaled in size to change draw length in a fixed draw length embodiment of a pulley. When a pulley 108, 110 is scaled for draw length, virtually the entire pulley, including the string cam, and the power cam 152 or follower cam 212, are scaled to achieve the next size. It is sometimes preferable to scale the pulley components because it helps maintain lever arm ratios which in turn preserve the shape of the force draw curve. The timing cam 154 can be scaled independently of the power cam 152. A larger timing cam 154 causes harder wall feel provided by the positive draw stop, and transfers more timing control to the control pulley 110. Of course, the length of the follower groove 224 must reflect any modification to the size/shape of the timing cam 154 carried on the control pulley 110.
In certain cases, such as to match a pair of pulleys 108, 110, to a particular bow 100, the follower cam string profile can include an arcuate portion having an extra expansion or contraction to fine tune nocking point travel. Such a departure from the mating control string cam may occur over roughly 150 degrees of the cam and the quantity of expansion may be varied depending on requirements of the particular bow. Such departure from similar geometry between string cams is not a necessary feature, but can be utilized to improve the shooting characteristics of the pulley set 108 and 110.
As illustrated in
With reference again to
With continued reference to
Modern archery cam elements typically have a thickness, corresponding to a space 308, 312, or 316, of about 0.1875 inches, although thinner cams elements are possible. Therefore, a reasonable minimum length 324 (between a plane 306 and a center of groove 322) for a tower anchor 178 might be about 0.2 inches. In the currently preferred and illustrated embodiment of a tower anchor 178 in
Base 320 of tower anchor 178 desirably has a size and shape operable to resist the tipping moment generated by an anchored control cable 272 (not illustrated). Illustrated base 320 has a diameter of about 0.4 inches. A base having a diameter of about 0.35 inches is also workable. A base having a diameter as small as 0.25 inches can also be operational in certain embodiments of archery bows having sufficiently low cable loads. Other shapes for a base 320, or stem 181, are within contemplation, including square and hexagonal. The latter shapes can also permit purchase for a tool operable to tighten a fastening arrangement for tower 178.
Cable loads on a tower anchor 178 may cause bending loads of considerable magnitude, particularly due to the extended moment arm inherent in the offset length 324. Cable loads may increase dramatically during an accidental dry firing of a bow. Therefore, it is currently preferred to sandwich foundation structure of string cam 150 between base 320 and a surface of a head of fastener 182 to distribute the moment induced loading. Fastener 182 preferably is a fastener of at least grade 8 quality to provide satisfactory durability. Furthermore, it is preferred for fastener 182 to have a flat head socket head, although other head shapes, such as cap head and countersink heads, are workable in certain situations. Sometimes, a counterbore (not illustrated) is provided on the drawstring side of string cam 150 to reduce the length of fastener 182 protruding above plane 304 to permit installation of a pulley 110 between narrow supports at a limb tip 266 (see FIG. 9).
Tower anchor 178 currently is manufactured from a stainless steel, although it is within contemplation alternatively to manufacture anchor 178 from brass, or Aluminum. An alternative mounting arrangement includes providing a shaft protruding from base 320 for threaded reception in a nut operable to provide reinforcing structure on an opposite side of string cam 150. The shaft can be threaded into tower 178, or formed as an integral part of the tower 178. Again, a counterbore may be provided in the drawstring side of string cam 150 to receive the nut. Flats may further be formed in the counterbore to assist in tightening the nut onto the shaft.
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| Number | Date | Country | |
|---|---|---|---|
| 20040074485 A1 | Apr 2004 | US |
