Hand operated impact implement having tuned vibration absorber

A hand operated impact implement having a tuned vibration absorber includes a head for impacting an object, a handle connected to the head, and a tuned vibration damper attached to the handle and/or head to damp overall handle/head vibration of the impact implement after impacting an object.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to impact implements and, more 
particularly, to a hand operated impact implement having a tuned vibration 
absorber. 
2. Description of the Related Art 
Contact of a hand operated impact implement with an object being struck 
combined with structural dynamics of the implement initiates a vibration 
in the implement. The vibration is then transmitted along the implement 
and transferred to a user of the implement. The structural dynamics of the 
implement determine how much vibration from the impact is transformed to 
the user. The structural dynamics are defined by the mass, stiffness and 
damping of the hand operated impact implement. The mass, stiffness and 
damping properties combine to produce a series of implement resonances 
which amplify vibration at a grip end from impacts of the implement. The 
amount of vibration felt at the grip end is a function of the impact force 
and the mass, stiffness and damping of the implement. 
An example of such a hand operated impact implement is a hammer. Typically, 
a hammer has a head and a handle attached to the head. In some hammers, 
the head and handle are integrally cast. The handle is commonly formed 
from either wood or a non-wood material such as steel or fiber reinforced 
plastic. Non-wood materials such as steel and fiber reinforced plastic are 
advantageous over wood because of their durability, especially in an 
overstrike condition. 
However, one disadvantage of a non-wood handle is the amount of vibration 
these handles transmit to the hand and arm of the user. The vibration is 
high in non-wood handles since the damping property of these materials can 
be one hundred (100) to one thousand (1000) times less than a comparable 
wood handle. As a result, vibration in the non-wood handles is high, and 
with extensive use may result in fatigue of the arm and hand muscles of 
the user. This can affect the comfort and productivity of the user. In 
extreme cases of implement multiple use, physiological damage can occur in 
the hand/arm/shoulder of the user. 
Several techniques for increasing damping in hand operated impact 
implements are disclosed in the following U.S. Pat. Nos.: 2,603,260 to 
Floren; 3,089,525 to Palmer; 4,660,832 to Shomo; 4,683,784 to Lamont; 
4,721,021 to Kusznir; 4,799,375 to Lally; 5,180,163 to Lanctot et al.; and 
5,280,739 to Liou. These patents have addressed vibration control with the 
means of a compliant handle and flexible grip. However, these implements 
suffer from the disadvantages of complexity of design, high cost of 
manufacturing and durability of the hand operated impact implement. 
Another technique for controlling vibration in hand operated impact 
implements is to reduce the shock of impact before it enters the handle. 
This can be accomplished by an implement head which is shock mounted or 
isolated from its handle. Examples of these types of implements are 
disclosed in U.S. Pat. Nos. 2,928,444 to Ivins and 3,030,989 to Elliott. 
However, these implements suffer from the disadvantage of potential for 
wear, causing poor durability. 
Still another technique for altering the vibration in hand operated impact 
implements is moving the center of percussion by adding a mass to the 
handle. An example of this type of implement is disclosed in U.S. Pat. No. 
4,674,746 to Benoit. However, this implement suffers from the disadvantage 
that it is limited in ability to reduce vibration since it does not 
provide increased vibration damping. 
Another technique for controlling vibration in hand operated impact 
implements is disclosed in U.S. Pat. Nos. 3,208,724 to Vaughn and 
5,289,742 to Vaughn, Jr. These patents address damping relative to the 
head of the hammer. Vaughn and Vaughn Jr. utilize a pocket in the head, 
typically filled with wood and/or elastomer to dissipate vibration in the 
hammer head. However, these hammers have a positive effect on claw 
fracture and head vibration but are not effective for the overall hammer 
head/handle vibration. 
Another technique which addresses hammer vibration control is disclosed in 
U.S. Pat. No. 5,362,046 to Sims. This patent discloses the use of a 
mushroom-shaped vibration damper for controlling impact implement 
vibration. The mushroom-shaped damper is made of a uniform elastomer and 
can be applied internally and externally to an impact implement handle. 
The mushroom-shaped damper functions by having an elastomer stem which 
provides a stiffness and damping element, and elastomer cap which provides 
a mass element. By its design, the cap motion causes bending in the stem 
which decreases the rate of decay of vibration set up in the implement by 
the impact. However, one disadvantage of this damper, when it is placed 
externally on the implement, is poor durability, especially in the 
application to hand operated impact implements. For example, the 
mushroom-shaped damper will easily get knocked off due to the inherent 
rough use of hand operated impact implements. Another disadvantage of this 
damper is that the cap is made of an elastomer instead of a high density 
material. As a result, the damper requires more volume of the elastomer to 
achieve a given mass needed for optimum vibration reduction and will 
require more packaging space. Due to small confines inside most impact 
implement handles, the mushroom-shaped damper will not be able to 
incorporate a large cap (mass), and hence its vibration reduction 
performance, which is a function of the mass, will be limited. Thus, there 
is a need in the art for reducing vibration in hand operated impact 
implements which provides the benefits of small packaging space, low 
manufacturing complexity, low cost, high durability, and high levels of 
vibration damping of the overall handle/head configuration. 
SUMMARY OF THE INVENTION 
It is, therefore, one object of the present invention to provide a hand 
operated impact implement having high vibration damping. 
It is another object of the present invention to provide a hand operated 
impact implement with a tuned vibration absorber for vibration control of 
the implement. 
It is yet another object of the present invention to provide a hand 
operated impact implement with a tuned vibration absorber for vibration 
control of the implement that reduces vibration transmitted to the hand 
and arm of the user of the implement. 
It is a further object of the present invention to provide a hammer with a 
tuned vibration absorber for vibration control of the hammer. 
To achieve the foregoing objects, the present invention is a hand operated 
impact implement including a head for impacting an object, a handle 
connected to the head and a tuned vibration absorber attached to the 
handle to reduce overall handle/head vibration of the implement after 
impacting an object. 
One advantage of the present invention is that a hand operated impact 
implement is provided having high vibration damping. Another advantage of 
the present invention is that the hand operated impact implement has a 
tuned vibration absorber for vibration control of the implement. Yet 
another advantage of the present invention is that the tuned vibration 
absorber reduces vibration transmitted to the user from grasping the grip 
end of the handle of the hand operated impact implement. Still another 
advantage of the present invention is that the tuned vibration absorber is 
provided for a hammer that increases the damping of the overall 
handle/head configuration of the hammer. A further advantage of the 
present invention is that the tuned vibration absorber does not affect the 
impact efficiency or durability of the hammer. 
Still a further advantage of the present invention is that the tuned 
vibration absorber provides a more efficient way to reduce hand operated 
impact implement vibration than other techniques currently in the art. 
Another advantage of the present invention is that the tuned vibration 
absorber, for its size and manufacturing cost, increases the damping to a 
greater level than other devices. For example, the tuned vibration 
absorber utilizes a small mass that is coupled to an elastomer and can 
increase the damping level of the hand operated impact implement by a 
factor up to ten (10) or more. Since the mass is made of a relatively high 
density material moving in shear, tension/compression or bending, the 
space required to package the tuned vibration absorber is very small and 
can be placed inside a hand operated impact implement easily without 
incurring high manufacturing costs and extensive manufacturing process 
changes. Still another advantage of the present invention is that the 
tuned vibration absorber does not change the normal function, the 
performance or the durability of the hand operated impact implement. The 
hand operated impact implement can still impart the same impact forces in 
the case of hammers since the present invention attenuates vibration after 
the impact forces have occurred. 
Other objects, features and advantages of the present invention will be 
readily appreciated as the same becomes better understood after reading 
the subsequent description taken in conjunction with the accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
Referring to FIG. 1, one embodiment of an impact implement, such as a hand 
operated impact implement, is generally shown at 10. The implement 10 
typically includes an impact surface or head 12 for contacting or 
impacting an object and a handle 14 connected at one end to the head 12 
for gripping the implement 10. The implement 10 may include a grip cover 
16 at a lower free end of the handle 14, whereby the user grasps the 
implement 10. The head 12 is made of a non-wood material such as steel. 
The handle 14 is made of a non-wood material such as steel or composite 
material. The grip cover 16 is made of an elastomeric material such as 
rubber. It should be appreciated that a hammer is illustrated as an 
example of the hand operated impact implement 10 and includes all types of 
hand operated impact implements and tools such as a claw hammer, ball pein 
hammer, sledge hammer, dead blow hammer, ax, hatchet, pick, drywall hammer 
and masonry hammer. 
Referring to FIG. 1, a first bending resonance or pattern for the hand 
operated impact implement 10 is illustrated. In this particular example, 
the handle 14 is made of a graphite composite. The amount of vibration 
felt at the lower end of the handle 14 is a function of the impact force, 
mass, stiffness and damping characteristics of the hand operated impact 
implement 10. The solid line illustrates the hand operated impact 
implement 10 in an undeformed shape and the phantom line illustrates the 
bending pattern of the handle 14 resulting from the implement 10 striking 
an object and vibrating at a first bending resonance of two hundred ninety 
Hertz (290 Hz) in the direction of a typical impact. The highest amplitude 
for a vibration response tends to occur at the lower end 30 of the handle 
14 and in a middle portion 32 of the handle 14. It should be appreciated 
that the first bending resonance in the direction of a typical impact is 
the most critical for vibration felt at the lower end of the handle 14. It 
should also be appreciated that, if the hand operated impact implement 10 
is impacted laterally (Z-direction), the resonance frequency is the 
lateral (Z-direction) or first bending mode with similar node points and 
maximum deflection points as illustrated in FIG. 1. It should be 
appreciated that the bending pattern shows deflection in the lateral 
(Z-direction). 
Referring to FIG. 2, a graph of inertance versus frequency for the hand 
operated impact implement 10 is illustrated. A driving point frequency 
response 40 is measured at point 30 on the lower end of the handle 14 
(FIG. 1) in the y-direction 34 using a device such as an accelerometer 
(not shown) and an instrument impact hammer (not shown). The x-axis 
represents the frequency 42 measured in Hertz (Hz) for this example. The 
y-axis 44 displays inertance measured in (m/s.sup.2)/N! for this example. 
The measurement peak 47 identifies the first bending resonance in the 
y-direction 34 which is easily excited during use and responsible for the 
vibration that is felt by the user after the hand operated impact 
implement 10 strikes an object. The sharpness of the peak and the 
amplification of inertance at the resonance frequency are indications of 
how damped the handle 14 is. In this example, a baseline or undamped 
response 46 is compared to a damped response 48 for a hand operated impact 
implement 110 having a tuned vibration absorber, according to the present 
invention, to be described. The undamped peak, at point 47, is higher and 
sharper compared to the damped peak, at point 49, providing an indication 
of the effectiveness of the tuned vibration absorber in reducing the 
vibration response of a hand operated impact implement 10 striking an 
object. It should be appreciated that the first bending mode for the hand 
operated impact implement 10 has a loss factor (damping), for example, of 
0.026, and the hand operated impact implement 110 having a tuned vibration 
absorber, according to the present invention to be described, has a loss 
factor, for example, of 0.134. 
Referring to FIG. 3A, a vibration pattern of the hand operated impact 
implement 10 is illustrated. When the hand operated impact implement 10 
strikes an object, the resulting vibration pattern, generally shown at 70, 
of the handle 14 over time can be measured using a device such as an 
accelerometer (not shown) mounted on the handle 14. The location and 
direction for this acceleration response measurement is the same as in 
FIG. 2. The x-axis 72 represents time, which in this example is measured 
in seconds. The y-axis 74 represents acceleration, which in this example 
is measured in (m/s.sup.2). When an object is struck by the hand operated 
impact implement 10, there is an initial impulse amplitude 76 and an 
initial increasing vibration response for the first 0.02 seconds after the 
impulse, which decreases in an exponentially decaying manner 78. It should 
be appreciated that the oscillation frequency over time corresponds to the 
frequency of the first bending resonance. It should also be appreciated 
that the long decay time indicates minimal damping. 
Referring to FIG. 3B, a vibration pattern of a hand operated impact 
implement 110 having a tuned vibration absorber, according to the present 
invention, to be described, is illustrated. The vibration pattern 
generally shown at 80, for the handle over time is measured as previously 
described with regard to FIG. 3A. The x-axis 82 represents time, this 
example is measured in seconds, and the y-axis 84 represents acceleration 
which in this example is measured in (m/s.sup.2). A direct comparison of 
the vibration pattern 80 of FIG. 3B with the vibration pattern 70 of FIG. 
3A illustrates the vibration response decays over a very short time 
period. It should be appreciated that the addition of a tuned vibration 
absorber to a hand operated impact implement, such as a hammer, increases 
the damping level so that when the hammer strikes an object the vibration 
dies out faster, the hand/arm/shoulder vibration transmitted is reduced 
and the hammer has a more solid "feel" at the lower end of the handle. 
Referring to FIG. 4A, one embodiment of a hand operated impact implement 
110 having a tuned vibration absorber, according to the present invention, 
is illustrated. In this example, the impact implement 110 is a hammer of 
the claw type having a head 112 and a handle 114 attached to the head 112. 
The head 112 is made of a metal material such as steel and the handle 114 
is made of a material such as steel, wood or fiber reinforced plastic 
having a urethane sleeve. The implement 110 includes a tuned vibration 
absorber or damper, generally indicated at 120, attached to an end of the 
handle 114. The tuned vibration absorber 120 includes a mass 122 and a 
damping element 124. The tuned vibration absorber 120 is an auxiliary 
vibrating mass which, when attached to a damping element, is tuned to 
vibrate at the bending resonance frequencies in the Y-direction and/or the 
Z-direction. The mass 122 is made of a high density material such as brass 
or steel and the damping element 124 is made of a lower density material 
such as rubber. Using a relatively high density material such as brass or 
steel for the mass 122 allows for better tuned vibration absorber 
performance in a given package space. If the mass 122 is made of a 
relatively low density material, it will require a larger volume of 
material to achieve the same mass as one made from brass or steel. 
The tuned vibration absorber 120 is attached externally to the end of the 
handle 114 by suitable means such as mechanical fasteners, adhesives 
and/or press fit. It should be appreciated that the mass 122 and damping 
element 124 of the tuned vibration absorber 120 can take on any shape. 
However, the optimization of the material, size, and configuration of the 
mass 122 and damping element 124 of the tuned vibration absorber 120 
yields a tuned vibration absorber that functions as a classical tuned 
absorber. For example, a properly tuned absorber can increase the damping 
level of an impact implement up to a factor of ten (10) or more. It should 
be appreciated that the mass 122 has a higher density than the damping 
element 124. It should also be appreciated that the tuned vibration 
absorber 120 can be applied to any wood or non-wood handle and damps the 
overall handle/head system vibration. 
Referring to FIG. 4B, another embodiment of a hand operated impact 
implement 210 having a tuned vibration absorber, according to the present 
invention, is illustrated. Like parts of the impact implement 110 have 
like reference numerals increased by one hundred (100). In this example, 
the impact implement 210 includes the tuned vibration absorber 220 
positioned externally along a middle section of the handle 214 and 
attached to the handle 214 as previously described. It should be 
appreciated that the positioning of the tuned vibration absorber 220 is 
dependent on the size and weight of the handle 214 and can be located at 
any location along the length of the handle 214. 
Referring to FIG. 4C, yet another embodiment of a hand operated impact 
implement 310 having a tuned vibration absorber, according to the present 
invention, is illustrated. Like parts of the impact implement 110 have 
like reference numerals increased by two hundred (200). In this example, 
the impact implement 310 includes the tuned vibration absorber 320 
positioned externally on the head 312 and attached to the head 312 as 
previously described. It should be appreciated that the positioning of the 
tuned vibration absorber 320 is dependent on the size and weight of the 
head 312. It should also be appreciated that the tuned vibration absorber 
320 damps the overall handle/head vibration and not localized head 
vibration. 
Referring to FIG. 5A, still another embodiment of a hand operated impact 
implement 410 having a tuned vibration absorber, according to the present 
invention, is illustrated. Like parts of the impact implement 110 have 
like reference numerals increased by three hundred (300). In this example, 
the impact implement 410 has the handle 414 with a hollow interior chamber 
426, and the tuned vibration absorber 420 is disposed within the hollow 
interior chamber 426 of the handle 414 and attached thereto as previously 
described. It should be appreciated that the mass 422 and damping element 
424 are positioned anywhere along the hollow interior chamber 426 of the 
handle 414 so as to obtain optimum vibration reduction. 
Referring the FIG. 5B, another embodiment of a hand operated impact 
implement 510 having a tuned vibration absorber, according to the present 
invention, is shown. Like parts of the impact implement 110 have like 
reference numerals increased by four hundred (400). In this example, the 
impact implement 510 includes the handle 514 with a hollow recess 527 in 
one end of the handle 514. The tuned vibration absorber 520 is positioned 
within the hollow recess 527. The damping element 524 is attached to a 
wall 528 in the hollow recess 527 in the lower end of the handle 514, and 
the mass 522 is attached to the free side of the damping element 524 as 
previously described. It should be appreciated that there could be a space 
between the mass 522 and the wall 528 of the hollow recess 527. 
Referring to FIG. 5C, another embodiment of a hand operated impact 
implement 610 having a tuned vibration absorber, according to the present 
invention, is illustrated. Like parts of the impact implement 110 have 
like reference numerals increased by five hundred (500). The impact 
implement 610 includes the handle 614 having the tuned vibration absorber 
620 positioned within the hollow recess 627 in the end of the handle 614. 
The tuned vibration absorber 620 includes a mass 622 and, at least one, 
preferably a plurality of damping elements 624 located between the mass 
622 and the wall 628 of the hollow recess 627 in the end of the handle 
614. It should be appreciated that the damping elements 624 may have any 
suitable shape. 
Referring to FIG. 6, another embodiment of a hand operated impact implement 
710 having a tuned vibration absorber, according to the present invention, 
is illustrated. Like parts of the impact implement 110 have like reference 
numerals increased by six hundred (600). The impact implement 710 has the 
tuned vibration absorber 720 positioned within a cap 730 having a cup-like 
shape. The cap 730 is located at the end of the handle 714 of the impact 
implement 710. The damping element 724 can be attached to an interior wall 
732 of the cap 730, and the mass 722 can be attached to the damping 
element 724. It should be appreciated that there may be a space 734 
between the tuned vibration absorber 720 and the free end of the handle 
714. 
Referring to FIGS. 7 and 8, another embodiment of a hand operated impact 
implement 810 having a tuned vibration absorber, according to the present 
invention, is illustrated. Like parts of the impact implement 110 have 
like reference numerals increased by seven hundred (700). The impact 
implement 810 has the tuned vibration absorber 820 positioned within a cap 
830 having a cup-like shape. The cap 830 is located at the end of the 
handle 814 of the impact implement 810. The damping element 824 is 
attached to an interior wall 832 of the cap 830 and a wall 828 of the 
handle 814. The mass 822 is suspended by the damping element 824. 
Referring to FIG. 9, another embodiment of a hand operated impact implement 
910 having a tuned vibration absorber, according to the present invention, 
is illustrated. Like parts of the impact implement 110 have like reference 
numerals increased by eight hundred (800). The impact implement 910 has 
the tuned vibration absorber 920 positioned within a cap 930 having a 
cup-like shape. The cap 930 is located at the end of the handle 914 of the 
impact implement 910. The damping element 924 can be attached to an 
interior wall 932 of the cap 930 and a wall 928 of the handle 914. The 
mass 922 is encapsulated by the damping element 924. 
Referring to FIGS. 10 and 11, another embodiment of a hand operated impact 
implement 1010 having a tuned vibration absorber, according to the present 
invention, is illustrated. Like parts of the impact implement 110 have 
like reference numerals increased by nine hundred (900). In this 
embodiment, the impact implement 1010 includes the handle 1014 with a grip 
cover 1016 surrounding a lower end the handle 1014. The grip cover 1016 
may be fabricated from an elastomeric material such as rubber. The impact 
implement 1010 has the tuned vibration absorber 1020 as including the mass 
1022, previously described, molded inside the grip cover 1016. The grip 
cover 1016 provides the characteristics of the spring and damping element 
of the tuned vibration absorber 1020. It should be appreciated that the 
grip cover 1016 can be formed so that it completely surrounds the mass 
1022. As illustrated in FIG. 11, the grip cover 1016 can be formed such 
that at least one void 1036 exists between the grip cover 1016 and the 
mass 1022, for example, to control the stiffness of the tuned vibration 
absorber 1020 when the modulus of the grip material is too high. It should 
be appreciated that, in conjunction with FIGS. 4A, 4B, 4C, 5A, 5B, 5C, 6, 
7, 8 and 9, the impact implement may include the grip cover surrounding 
the lower end of the handle to provide better ergonomic fit to the hand, 
cover the tuned vibration absorber, and offer some additional vibration 
isolation. 
The tuned vibration absorbers of the present invention are tuned to 
specific frequency(s), have a high damping level, and are of a mass which 
is designed for optimum vibration reduction performance for the impact 
implement it is applied to. The variables which can be changed to optimize 
the performance include: 
Mass Element 
material density 
shape 
Rubber Element Stiffness 
orientation: shear, tensions/compression, bending, torsion, . . . 
material modulus: bulk, Young's, shear 
shape 
Rubber Element Damping 
material damping 
Absorber Tuning 
mass/stiffness ratio 
It is the combination of these factors which determine the level of 
vibration reduction that can be achieved when a tuned vibration absorber 
is applied to an impact implement. It should be appreciated that the key 
element in the absorber is the proper selection of materials for the mass 
and the damping element. 
The tuned vibration absorber includes the mass and the damping element. The 
damping element is a viscoelastic material and the stiffness is controlled 
by the modulus of elasticity and the dimensions of the material. The best 
approach to designing the tuned vibration absorber is to select a mass 
appropriate for the modal mass of the impact implement, and then choose a 
material with the proper modulus of elasticity and damping properties. The 
precise stiffness required to tune the absorber to the proper frequency is 
then controlled by the geometry of the damping element. 
The simplest tuned vibration absorber is one incorporating a mass and a 
simple viscoelastic damping element in tension/compression. The resonance 
frequency of the mass is calculated from: 
##EQU1## 
Where: k=stiffness of the damping element and m=mass. 
The stiffness of the damping element in tension/compression can be 
calculated from: 
##EQU2## 
where E=Young's modulus of material 
B=material constant 
=2.0 for unfilled materials 
=1.5 for filled materials 
A.sub.1 =load carrying (stressed) area 
A.sub.u =non-load carrying (unstressed) area 
h=material thickness 
To obtain a desired resonance frequency, it is essential to know the 
material modulus. Since the modulus of viscoelastic materials vary as a 
function of temperature and frequency, the temperature and frequency of 
the tuned vibration absorber must be known before the damping element can 
be designed. 
If the damping element is designed such that is undergoes shear deformation 
as the mass vibrates, the stiffness can be calculated from: 
##EQU3## 
where G=shear modulus of material 
A.sub.1 =load carrying (stressed) area 
h=material thickness 
R=radius of gyration of shape 
Tuned vibration absorbers designed with more than one damping element 
require the overall stiffness of the series or parallel combination of the 
damping elements for calculating the resonance frequency. 
The general process for designing the tuned vibration absorber for hand 
operated impact implements is described in a step-by-step fashion below. 
It should be appreciated that this is only one design for the tuned 
vibration absorber. 
Step 1--MASS SELECTION 
Based on frequency response testing of the hand operated impact implement 
and finding its overall baseline frequency response 46 as shown in FIG. 2, 
a modal mass can be calculated from the curve. The mass of the tuned 
vibration absorber is then calculated as a value equal to 5-20% of the 
baseline modal mass. Typically, 10% is a good starting value if it can be 
packaged in the available space. 
Step 2--STIFFNESS CALCULATION 
The next step is to determine the stiffness required for tuning. This is 
determined by utilizing the above Equation 1. Generally, this equation is 
solved such that the tuned vibration absorber resonance frequency, 
f.sub.n, is equal to the resonance frequency 47 of the important mode of 
vibration of the hand operated impact implement. Depending on the selected 
mass and amount of tuned vibration absorber loss factor, the tuning may 
require that the frequencies be slightly different. 
Step 3--OPTIMUM DAMPING CALCULATION 
After the mass stiffness has been calculated, the optimum damping is 
calculated based on the desired damping increase. Generally, a material 
loss factor of 0.1-0.3 works best for tuned vibration absorbers which 
utilize a modal mass of 10% of the hand operated impact implement 
resonance modal mass. 
Step 4--MATERIAL SELECTION 
To keep the volume of the tuned vibration absorber mass to a minimum, it is 
most efficient to make the mass from brass or steel. Other high density 
materials could be utilized as well. The volume of material needed to 
achieve the desired mass can then be computed. It's overall dimensions can 
then be computed based on available package space. 
The proper viscoelastic material selection is crucial to the successful 
application of the present invention. The viscoelastic damping material 
selection needs to take many factors into account as previously discussed. 
Generally, it is most important to select a material with modulus and 
damping properties which are linear with temperature if the hand operated 
impact implement will be used over wide ranging temperatures. Usually of 
secondary importance is linearity with respect to dynamic amplitude, 
frequency, and static preload. Many potential material candidates exist 
for hand operated impact implements such as silicone, EPDM, neoprene, 
nitrile and natural rubber. Preferably, moderately damped (0.05 to 0.2 
loss factor) silicone rubber is used due to its linear temperature 
behavior. 
Step 5--GEOMETRY DETERMINATION 
Once the damping material and the motion of the damper (tension, 
compression, shear, or bending) have been selected, the actual geometry 
can then be determined. The geometry of the damping element is calculated 
using the above stiffness equations 2 and 3. The material modulus at the 
temperature, frequency, dynamic amplitude and static preload conditions 
for the hand operated impact implements of the selected damping material 
is used in the equations in conjunction with the needed stiffness value to 
determine the appropriate material thickness and cross-sectional areas. 
The present invention has been described in an illustrative manner. It is 
to be understood that the terminology which has been used is intended to 
be in the nature of words of description rather than of limitation. 
Many modifications and variations of the present invention are possible in 
light of the above teachings. Therefore, within the scope of the appended 
claims, the present invention may be practiced other than as specifically 
described.