O 97/16286 PC17US96/16964

HAND OPERATED IMPACT IMPLEMENT HAVING TONED VIBRATION ABSORBER

BACKGROUND OF THE INVENTION

J- Field of the Inven jon

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 plasLiu axe αάvauLageuus over wood because of Lheix

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.

Patent 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.

Ano'cliei Lecl iique for controlling vibration i 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. Patent 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. Patent 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. Patent 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

cflective loi the overall hammer head/handle vibration.

Another technique which addresses hammer vibration

control is disclosed in U.S. Patent 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 Lo

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

pxcvide 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

uhctc Luc Luixcd 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 appieciated as the sa e becomes

better understood after reading the subsequent description

taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of a hand operated impact

implement illustrating a first bending resonance after

striking an object.

FIG. 2 is a graph illustrating inertance versus frequency for the implement of FIG. 1 and for a hand operated impact

implement having a tuned vibration absorber according to the

present invention.

FIG. 3A is a graph of acceleration versus time for the

implement of FIG. 1.

FIG. 3B is a view similar to FIG. 3A for a hand operated

impact implement having a tuned vibration absorber according

to the present invention.

FIG. 4A is a fragmentary elevational view of a hand

operated impact implement having a tuned vibration absorber

according to the present invention.

FIG. 4B is fragmentary elevational view of another hand

operated impact implement having a tuned vibration absorber

according to the present invention.

FIG. 4C io a fragmentary elevational view of yet another

hand operated impact implement having a tuned vibration

absorber according to the present invention.

FIG. 5A is a fragmentary elevational view of still

another hand operated impact implement having a tuned

vibration absorber according to the present invention.

FIG. 5B is a fragmentary elevational view of a portion of

another hand operated impact implement having a tuned

vibration absorber according to the present invention.

FIG. 5C is a fragmentary elevational view of a portion of

yet another hand operated impact implement having a tuned

vibration absorber according to the present invention.

FIG. 6 is a fragmentary elevational view of a portion of

still another hand operated impact implement having a tuned

vibration absorber according to the present invention.

FIG. 7 is a fragmentary elevational view of a portion of

another hand operated impact implement having a tuned

vibration absorber according to the present invention.

FIG. 8 is a sectional view taken along line 8-8 of FIG.

7.

FIG. 9 is a fragmentary elevational view of a portion of

yeI anothei hand operated impact implement having a tuned

vibration absorber according to the present invention.

FIG. 10 is a fragmentary elevational view of another hand

operated impact implement having a tuned vibration absorber

according to the present invention.

FIG. 11 is an enlarged fragmentary elevational view of a

portion of the implement of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

Lools such as ci& 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-

direcLioi.) ci 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 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 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 fiisL 0. G2 ec n s 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 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 cf 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 ul the handle 2i<±

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 Lhio 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

ϋ ei tcd 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 che tuned vibxcttion absox ^~ bex 72G 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 encctpsuiaLed Lhe damping element 324.

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 Lhe 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 che combination of these factors which cL i'mi

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:

1 _ k f = T_ n 2π m (1)

Where: k = stiffness of the damping element and m = mas.

The stiffness of the damping element in

tension/compression can be calculated from:

EA _j t l +S f A _j A^ ² ]

K c = (2)

where E = Young's modulus of material

B material constant

= 2.0 for unfilled materials

= 1.5 for filled materials

A ₁ = load carrying (stressed) area

A _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:

GA,

K (3) h [ l + ( h / SR ) ² ]

where G = shear modulus of material

A 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 iL 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 _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 cn 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.

SLe 5 - Geomt-Lrv D tex-mination

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.