Hand implement vibration isolation system |
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申请号 | US12387853 | 申请日 | 2009-05-07 | 公开(公告)号 | US20090280932A1 | 公开(公告)日 | 2009-11-12 |
申请人 | Robert Tinti; | 发明人 | Robert Tinti; | ||||
摘要 | A vibration isolation system for hand implements including sporting equipment and tools to substantially reduce impact forces from being delivered to the user's hands. Isolation elements provide low spring rates enabling the system to isolate bending vibration, recoil, and twist. An outer shell member substantially encircles the grip end of the hand implement and is spaced outwardly thereto allowing the grip end to freely deflect within the outer shell member. | ||||||
权利要求 | What is claimed is: |
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说明书全文 | This application claims priority under 35 U.S.C. §119(e) of U.S. provisional patent application Ser. Nos. 61/126,692 and 61/192,358 filed on May 7, 2008 and Ser. No. 09/18/2008 respectively, and entitled “Baseball/softball bat and tool handle/grip shock/vibration isolator system” and “Baseball/Softball bat and tool handle/grip shock/Vibration isolator system” respectively, the disclosures of both of which are hereby incorporated herein by reference. The invention relates in general to hand implements used to impact objects. More specifically, the invention relates to a vibration isolation system for use on sporting equipment and tools to substantially reduce impact forces from being delivered to the user's hands. Hand implements used to impact objects generate vibrational forces that are transmitted to the user's hand(s). There have been numerous attempts to reduce the transmission of these forces to the user's hand(s). With respect to baseball bats, one approach is to establish a vibration within the bat that is 180 degrees out of phase with natural vibration of the bat. An example of this approach is found in U.S. Pat. No. 5,772,541 to Buiatti, where a vibration dampening member is allowed to vibrate within the knob of the bat to dampen unwanted lower frequency vibration of the bat. Another approach is to provide a two piece bat connected along an interface with a continuous elastomeric union, as is found in U.S. Pat. No. 5,593,158 to Filice, et al., to prevent vibration from the barrel of the bat from being transmitted to the grip end of the bat. It is believed such continuous elastomeric unions establish unnecessarily high spring rates for the system, which are averse to isolating the transmission of vibrational forces. What is needed is to establish a vibration isolation system that has a very low spring rate for the system, and thereby isolate the transmission of vibrational forces to the user's hand(s). The present invention provides its benefits across a broad spectrum of hand implements. While the description which follows hereinafter pertaining to baseball bats and tennis rackets is meant to be representative of such applications, it is not exhaustive. It is intended that this specification and the claims appended hereto be accorded a breadth in keeping with the scope and spirit of the invention being disclosed despite what might appear to be limiting language imposed by the requirements of referring to the specific examples disclosed. It is one aspect of the present invention to provide a vibration isolation system for hand implements that substantially reduces bending vibrational forces induced upon impact with an object from being transmitted to the user's hand(s). It is another aspect of the present invention to provide a vibration isolation system for hand implements that minimizes the transmission of torsional forces induced upon impact with an object at a point offset from the centerline of the hand implement. It is a feature of the present invention that an outer shell member is provided that substantially encircles and is spaced outwardly from the grip end of the hand implement. It is another feature of the present invention that at least one isolation element is positioned between the grip end of the hand implement and the outer shell member. It is still another feature of the present invention that the ratio of the fundamental bending natural frequency (ω) divided by the natural frequency of the vibration isolation system (ωo) is greater than 1.5. It is still yet another feature of the present invention that the ratio of the effective forcing frequency (ωf) divided by the torsional natural frequency of the vibration isolation system (ωt) is greater than 1.5 It is an advantage of the present invention that, by proper selection and location of isolation elements between the outer shell member and grip end, bending forces induced upon impact with an object are isolated from the user's hand. It is another advantage of the present invention that, by proper selection and location of isolation elements between the outer shell member and grip end, torsional forces induced upon impact with an object at a point offset from the centerline of the hand implement are isolated from the users hand. These and other aspects, features, and advantages are achieved/attained in the apparatus of the present invention that comprises a outer shell member having an inner surface substantially encircling and spaced outwardly from the grip end of a hand implement. The outer shell member sufficiently spaced outwardly from the grip end allowing the grip end to freely deflect within the outer shell member when the impact end of the hand implement impacts an object within an intended zone of contact. At least one isolation element is positioned between the grip end and the outer shell member and supporting the outer shell member about the grip end. The isolation element and outer shell member establish a spring rate (k) of the vibration isolation system when the system is affixed to the hand implement. The spring rate (k) and mass (m) of the hand implement define a natural frequency of the vibration isolation system (ωo), wherein the ratio of the fundamental bending natural frequency (ω) divided by the natural frequency of the vibration isolation system (ωo) is greater than 1.5 By selecting materials for the isolation element that are very soft, a low spring rate (k) is achieved, which in turn allows the ratio (ω/ωo) to be greater than 1.5, and assures that bending vibrational forces are substantially isolated from the users hand(s). For hand implements which may strike on object a point offset from the centerline of the implement, torsional forces are also isolated according to the present invention vibration isolation system. First, an effective forcing frequency (ωf) based on the effective duration of impact with an object of the hand implement must be selected. With these values, and with the polar moment of inertia (J) of the hand implement about its centerline, a torsional spring rate (Kt) of the vibration isolation system affixed to the hand implement can be measured. A torsional natural frequency of the vibration isolation system (ωt) can be determined and if the ratio of the effective forcing frequency (ωf) divided by the torsional natural frequency of the vibration isolation system (ωt) is greater than 1.5, the transmission of torsional forces to the users hands are substantially isolated. By the appropriate selection of material and configuration of the isolation element an optimal torsional spring rate (Kt) is achieved, which in turn allows the ratio (ωf/ωt) to be greater than 1.5, and assures that torsional forces are substantially isolated from the user's hand(s). The aspects, features and advantages of the present invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when it is taken in conjunction with the accompanying drawings wherein: To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements or features common to the figures. Referring to In reality there are numerous modes of vibration. For purposes of the present invention, only the first three modes are considered to determine vibrational deflection along the grip end 16 of the implement in a perpendicular direction from the centerline 32 of the implement 12. The vibrational deflection for each of the first three modes are determined at various locations along the grip end 16, and then added together to establish a vibration deflection profile along the grip end 16. The following vibration deflection profile along the grip end 16 of a little league approved bat is shown in Table 1. Table 1 was produced based on a model YBCX13 Prodigy—13 bat, 29 inches long weighing 16 ounces, manufactured by Worth, Inc., of St. Louis, Mo. Referring to The isolation elements 22 have an inner mounting surface 26 and an outer mounting surface 28. The inner mounting surface 26 is affixed to the grip end 16 and the outer mounting surface 28 is affixed to the outer shell member 20. The isolation elements 22 may be adhesively affixed to the grip end 16 and outer shell member 20, or held in place by friction. Alternatively the isolation elements 22 may be bonded on one side and allowed to slide or held by friction on the other. It is critical to the present invention to select a very soft material for the isolation elements 22, so as to establish a low spring rate (k) of the vibration isolation system 10 as it is affixed to the bat. Materials such as elastomers, rubber, foam, plastic, and the like, may be used. Open cell ethylene vinyl acetate rubber 3 mm thick has proven to be a satisfactory material for the isolation elements 22, such as the material sold as Darice® Foamies 3 mm thick by Darice, Inc. of Strongsville Ohio, being affixed to the outer shell member 20 and grip end 16 with double sided tape. In addition, the “footprint” of the isolation elements, the length of contact they have along the outer shell member 20, must be relatively small compared to the length of the inner surface 24 along the outer shell member 20. For the isolation elements 22 in The isolation elements 22 cross-section may vary along its ‘footprint” length and also about the circumference of the element about the grip end. This may be done to optimize the vibration isolation system 10 by taking into account the vibration deflection profile for a given hand implement, and the node locations corresponding to the fundamental bending natural frequency (ω) of the hand implement, such as, for example, a golf club. It is to be appreciated that the cross-section of the isolation elements may vary depending on application, such as, for example, circular for a baseball bat, rectangular or octagonal for a tennis racket, or oval for a hammer. Referring to k=(F÷d)/number of isolation elements in the system. In the embodiment shown, there are two isolation elements having the same “footprint” and the measured force divided by the deflection must be divided by 2. If there are three isolation elements, it would be divided by 3. According to the present invention, it is the spring rate of one isolation element that is to be determined for calculating the natural frequency of the vibration isolation system (ωo). This can be accomplished by cutting the implement apart around one isolation element, and measuring the spring rate as shown in It is to be appreciated that the spring rate of each isolation element 22 may vary depending on the vibration deflection profile and node locations 18 of the hand implement 12. For purposes of the present invention, the isolation element with the lowest spring rate (k) is to be considered in determining the natural frequency of the vibration isolation system (ωo). It is also to be appreciated that the spring rate of each isolation element 22 may vary depending on the direction in which the spring rate is measured on the implement. For purposes of the present invention, the spring rate is to be measured in the direction in which the hand implement is designed to strike an object. With the spring rate (k) determined and the mass (m) of the bat known, a natural frequency of the vibration isolation system (ωo) is determined by: ωo=(k÷m)1/2 With the fundamental bending natural frequency (ω) of the bat known, and with the natural frequency of the vibration isolation system (ωo) determined, the ratio of the fundamental bending natural frequency (ω) divided by the natural frequency of the vibration isolation system (ωo) is determined. According to the present invention, this ratio (ω/ωo) must be greater than 1.5. If this ratio (ω/ωo) is less than about 1.5, too much vibration will be transmitted to the batters hand(s). If the ratio (ω/ωo) is too low, it can be increased by reconfiguring the isolation elements 22 to obtain a lower spring rate (k) of the isolation elements. The isolation elements can be reconfigured by changing to a softer material, and/or by changing their “footprint” to a smaller length. It is preferred to configure the isolation elements 22 in the system 10 to obtain a ratio (ω/ωo) of 2.0 or above, yet a value of 1.5 or above is sufficient. The greater the ratio (ω/ωo), the greater vibration is isolated from the batters hand(s). For the embodiment shown in When the ratio (ω/ωo) (or forcing frequency/undamped natural frequency—as commonly known to those skilled in the art), increases beyond 1.5, absolute transmissibility (TA) of vibration drops. The lower the absolute transmissibility, the less amount of vibration is transmitted through a damped or undamped system. Although the fraction of critical damping (ζ) of the system in conjunction with the ratio (ω/ωo) determines the actual value of absolute transmissibility (TA) of the system, absolute transmissibility (TA) drops at a much greater rate in relation to the increase in the ratio (ω/ωo). Hence, even without knowing the fraction of critical damping (ζ) of the system, when the ratio (ω/ωo) is greater than 1.5, the absolute transmissibility (TA) is sufficiently lowered for purposes of the present invention to minimize the transmission of vibration from a hand implement to the outer shell member 20 of the vibration isolation system 10. Yet an isolation element 22 with a low fraction of critical damping (ζ) is desirable for a lower transmissibility (TA). As can be seen in Table 2, the ratio (ω/ωo) of the 1st fundamental mode of vibration is the lowest of the first three modes, and why, for purposes of the present invention, the fundamental bending natural frequency ratio (ω) of the 1st fundamental mode of vibration is used in determining the ratio (ω/ωo). Referring to Referring to The vibration isolation system 10 of To those skilled in the art, determining the polar moment of inertia (J) of the tennis racket about the centerline 32 of the racket is well known. Values of the polar moment of inertia (J) will vary somewhat depending on the type and make of racket. The vibration isolation system of the present invention may be configured for a specific racket thereby utilizing a specific polar moment of inertia (J) measured for a specific racket, or an average value of the polar moment of inertia (J) for a number of rackets may be used. The same applies to the other parameters that have to be selected/determined according to the present invention. The effective forcing frequency (ωf) of the tennis racket needs to be determined, a parameter related to the impulse (shock and vibration) received by the racket when impacting a tennis ball. For the baseball bat, the fundamental bending natural frequency (ω) was used, between about 200 Hz to 600 Hz. However, tennis racket frames have a first mode of vibration range of between about 90 Hz to 200 Hz, and for most rackets between about 120-130 Hz. Much of the shock is absorbed by the stretch of the rackets strings and the compression of the tennis ball. The total duration of impact (t) of a tennis ball on the strings of a racket is between about 5-6 milliseconds (compared to about 1 millisecond for a baseball and bat), yet the time for the shock wave of impact to reach a player's hands on a tennis racket is about 2.5 to 4 milliseconds. Hence, the shock wave reaches the player's hand before the ball leaves the strings of the racket. It is believed that the effective forcing frequency (ωf) is best determined based on the pulse of the tennis ball impacting the strings of the racket. According to the present invention, the effective forcing frequency (ωf) is determined by assuming the acceleration pulse of the tennis ball and strings of the racket is a versed sine acceleration pulse. The effective forcing frequency (ωf) for a tennis racket was determined as follows: (t) the total duration of pulse (period) t=5 milliseconds, (tr) the effective duration of impulse tr=(1/2) t=2.5 milliseconds, and (ωf) the effective forcing frequency ωf=(2π/tr)=2513 rad/sec Next, the torsional spring rate (Kt) of the vibration isolation system 10 when affixed to the tennis racket is determined. Referring to Kt=T÷⊖ It is important that the torsional spring rate (Kt) be measured under a very small angle of deflection (⊖), preferably no greater than between about 0.25 to 5.0 degrees, otherwise the measured value will be too high and will not be representative of the systems actual torsional spring rate for purposes of the present invention. It is believed that under a small angle of deflection, the spring rate will be generally linear, but at or near maximum deflection the spring rate will increase exponentially. Hence, the torsional spring rate (Kt) of the system 10 should be measured within a desired angular deflection range for the system, which for a tennis racket is believed to be between about 0.25 to about 3.0 degrees. One way of determining if the torsional spring rate (Kt) was measured correctly is to measure (Kt) at a number of different deflection points/angles within the desired angular deflection range for the system. The correct value for (Kt) will be the value where they are substantially similar. With the torsional spring rate (Kt) measured, the torsional natural frequency of the vibration isolation system (ωt) is determined from the following equation: ωt=(Kt÷J)1/2 With the effective forcing frequency (ωf) of the tennis racket, and with the torsional natural frequency of the vibration isolation system (ωt), the ratio of the effective forcing frequency (ωf) divided by the torsional natural frequency of the vibration isolation system (ωt) is determined. This ratio (ωf/ωt) must be greater than 1.5 in order for the system 10 to effectively isolate torsional forces from being transmitted to the player's hand(s). As with the previous embodiments, this ratio (ωf/ωt) can also be adjusted by reconfiguring the isolation elements 22 to obtain a lower torsional spring rate (Kt) of the vibration isolation system. For the embodiment shown in From value for the torsional spring rate (Kt) determined in Table 3, it is believed that, depending on player preferences, that the range of torsional spring rates (Kt) for various tennis rackets will be between about 3,300 and 40,200 in-lbf/rad. For most other hand implements, it is believed that the range of torsional spring rates (Kt) will be between about 1,140 and 70,000 in-lbf/rad. Referring to
The maximum average impact force (F) of the tennis racket when impacting an object varies depending on the strength and skill level of the player. Generally, a player can generate an impact force of between about 60 to 120 lbs when striking a tennis ball during a groundstroke. In this embodiment, a maximum average impact force (F) was selected of 100 lbs. The maximum off-center distance (d) of the tennis racket is the maximum distance away from the centerline 32 of the racket within the intended zone of contact of which the ball hits the strings. This is the furthest point from the centerline 32 on the racket that contact can be made while providing reasonable accuracy in the return of the ball. Referring to The maximum allowable angle of rotation (φ) of the hand implement when impacting an object is defined herein to be an acceptable maximum twist of the hand implement 12 within the vibration isolation system 10 due to maximum torsion forces transmitted to the system. It is necessary to select this angle as a constraint to maintain the accuracy of the tennis racket in directing the tennis ball to the location that the player desires. Because the tennis ball remains in contact with the strings of the racket while the isolation system 10 rotates, accuracy of the racket can be compromised if the allowable angle of rotation (φ) is too great, such as, for example, about 5 degrees or more. Hence, according to the present invention, the allowable angle of rotation (φ) for a tennis racket is selected to be 3 degrees. The maximum torsional spring rate (Ktmax) is calculated as follows: Ktmax=(F·d)÷φ and the calculated (Ktmax) is then compared to an actual measurement of (Ktmax) following the method discussed in measuring (Kt) shown in It is to be appreciated that the measured (Ktmax) may be the same value, or nearly the same, as the measured (Kt) value. This would be the case if the torsional spring rate remains linear throughout the allowable angle of rotation range of the hand implement, as is believed to be the case in the embodiment shown in The embodiments of the vibration isolation system 10 shown in It is to be appreciated that the vibration isolation system 10 of the present invention can be tuned for different hand implements. The system can be tuned to account for bending vibration, as demonstrated with the bat, recoil, as demonstrated with the tennis racket, and twist, as also demonstrated with the tennis racket. Further, the system 10 can be tuned to account for all three; bending vibration, recoil, and twist. What has been described are preferred embodiments of a vibration isolation system. Those skilled in the art will appreciate that numerous modifications are possible without materially departing from the novel teachings and advantages of the subject matter described herein. Other modifications, substitutions, changes, and omissions may be made in the design and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the present invention. |