Power tool with vibration isolated handle

The invention provides a power tool including a tool body and a handle mounted on the tool body at an upper vibration isolation joint and a lower pivot joint. The lower joint permits pivotal movement of the handle relative to the tool body while giving an operator lateral stability and torsional control over the tool. The upper joint serves as a primary vibration isolation joint and includes a spring which is precompressed to a minor fractional portion of its unloaded length and which is positioned between the tool body and the handle to bias the tool body and the handle apart. The spring is compressible from its precompressed state responsive to operator applied pressure, and when operator applied pressure on the handle is maintained within predetermined levels the spring is operable to reduce transmission of vibration from the tool body to the handle during tool operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to vibratory power tools, and more 
particularly to vibratory power tools including systems intended to reduce 
the transmission of vibration from the tool to the tool operator. 
2. Reference to Prior Art 
Various hand-held power tools such as rotary hammers or hammer drills, 
grinders and chain saws, for example, produce vibrations when in operation 
which are transmitted to the tool operator. Those vibrations can cause 
operator discomfort, and prolonged tool use and exposure to vibrations can 
result in operator fatigue, particularly in the hand and arm in which the 
tool is primarily held. 
In an attempt to reduce vibration transmission from the tool to the tool 
operator, hand-held power tools have been provided with vibration damping 
or isolating systems positioned between the portion of the tool that 
generates the vibrations and the handle. Some of those tools employ 
elastomeric members which are compressed responsive to operator applied 
pressure on the tool handle and which are intended to absorb vibrations. 
For example, U.S. Pat. No. 4,749,049 illustrates a hammer drill having a 
handle that is mounted at two locations on the drill housing by a lower 
pivot spring-mounting and an upper spring-mounting, both including 
elastomeric vibration damping elements. Other hand-held power tools 
employing elastomeric damping elements positioned between the tool body 
and a handle are illustrated in U.S. Pat. Nos. 5,213,167, 5,052,500, 
5,046,566, 4,401,167, 4,138,812 and 3,849,883. 
It is also known to employ coil or other spring members at the tool 
body/handle interface in a vibratory power tool for the purpose of 
vibration absorption. Examples of such constructions are provided in U.S. 
Pat. No. 4,478,293 and the Makita Model HR3851 rotary hammer in which the 
handle is mounted on the tool via a leaf spring on one end and a pivot 
joint on the other end. 
It is well accepted in the art that the various spring members used in 
vibration damping systems for hand-held power tools should be designed 
with high spring rates (or spring constants), i.e., considerable force is 
required to deflect the springs even a short distance. Softer spring 
members have been disfavored due to the large spring deflection required 
to provide adequate damping and the relative ease with which the spring, 
and therefore the tool handle, can be "bottomed out" when an operator 
applies excessive force on the handle. In the "bottomed out" condition, 
tool vibrations can be transferred directly to the operator as if no 
vibration damping element were employed at all. While the use of stiffer 
spring members reduces the chances that the tool will "bottom out" under 
operator applied loads, the use of those spring members also results in a 
higher transmissibility of tool vibration to the tool operator. 
SUMMARY OF THE INVENTION 
The invention provides a power tool, such as a hand-held rotary percussive 
tool, including an improved system for isolating a tool operator from 
vibrations generated during tool operation. The improved vibration 
isolation system is believed more capable of reducing the transmission of 
vibrations from the tool to the tool operator than are prior art vibration 
isolating arrangements, and the improved system is expected to provide 
vibration damping or isolation qualities that meet or exceed anticipated 
governmental standards relating to hand and arm vibration exposure. This 
is accomplished by incorporating a soft spring (i.e., a spring having a 
low spring rate) into the vibration isolation system, contrary to the 
teachings of the prior art. 
In particular, the force, F, felt by a tool operator as a result of tool 
vibration is mathematically described as follows: 
EQU F=k.times.d 
where 
k=spring rate for the particular spring; and 
d=spring deflection resulting from vibration. 
The use of a hard spring (i.e., a spring with a high spring rate, k) as 
taught by the prior art results in increased vibration transmission to the 
tool operator or increased tool mass to offset that transmission. Instead, 
Applicants have reduced k by employing a softer spring, thereby reducing 
the resulting force, F, felt by a tool operator, and have backed up the 
soft spring with a harder spring to prevent the tool from bottoming out. 
In a preferred embodiment, the improved vibration isolation system includes 
a soft spring which is supported against buckling in a precompressed 
condition between the tool handle and the source of vibration. To prevent 
the handle from bottoming out, the soft spring is backed up by a harder 
spring which is engaged when the operator applied force on the handle 
exceeds a recommended level for normal power tool operation. The soft 
spring and the hard spring are assembled into a module which is 
self-contained and which is discardable at the end of its service life and 
easily replaceable with another module. 
The invention also provides a power tool including a unique mechanism for 
indicating to a tool operator whether the level of operator applied 
pressure on the tool handle, and ultimately on the work medium, is within 
recommended levels. In particular, many manufacturers recommend that 
operator applied force be maintained within a prescribed range for optimum 
tool performance and efficiency. However, estimation of operator applied 
pressure is left to the subjective judgment of each operator. The present 
invention addresses that problem by providing a reliable control mechanism 
for objectively indicating to an operator the level of operator applied 
pressure exerted on the tool. 
In a preferred embodiment of the invention the improved vibration isolation 
system incorporates the mechanism for indicating operator applied pressure 
levels, and that mechanism incorporates the precompressed soft spring. In 
particular, the soft spring is set so that the pressure needed to 
initially compress it beyond its precompressed condition is approximately 
the minimum recommended operator applied pressure level. Thus, the 
operator has a tactile indication that the minimum recommended operator 
applied pressure level is achieved when the soft spring is initially 
deflected from its precompressed condition. Additionally, the hard spring 
which backs up the soft spring is engaged when the soft spring reaches a 
compressed condition corresponding to a maximum preferred operator applied 
pressure level. Thus, the operator feels a substantially increased spring 
rate when operator applied pressure exceeds the recommended maximum level. 
More particularly, in one embodiment the invention provides a power tool, 
such as a hand-held rotary percussive power tool, for example, including a 
tool body and a handle mounted on the tool body at an upper vibration 
isolation joint and a lower pivot joint. The lower joint permits pivotal 
movement of the handle relative to the tool body while providing lateral 
stability between the handle and the tool body so that an operator can 
exercise lateral and torsional control over the tool. The upper joint 
serves as a primary vibration isolation interface and includes a spring 
which is precompressed to a minor fractional portion of its unloaded 
length and which is positioned between the tool body and the handle to 
bias the tool body and the handle apart. The spring is compressible from 
its precompressed state responsive to operator applied pressure, and when 
operator applied pressure on the handle is maintained at a predetermined 
level (or within a range of levels) the spring is operable to reduce 
transmission of vibration from the tool body to the handle. 
The invention also provides a vibratory tool including a tool body, a 
handle mounted on the tool body, and means for tactiley indicating to a 
tool operator when operator applied pressure on the handle is within a 
preferred range of operator applied pressure levels. The means for 
tactiley indicating to a tool operator when operator applied pressure on 
the handle is within the preferred range of operator applied pressure 
levels includes a spring positioned between the tool body and the handle. 
That means also preferably includes a stop member positioned in parallel 
with the spring. Deflection of the spring from its initial condition is 
felt by an operator to indicate when operator applied pressure has reached 
its minimum recommended level. When the operator applied pressure level 
reaches the maximum recommended pressure the stop member is engaged and 
this engagement is also felt by an operator.

Before embodiments of the invention are explained in detail, it is to be 
understood that the invention is not limited in its application to the 
details of construction and the arrangements of components set forth in 
the following description or illustrated in the drawings. The invention is 
capable of other embodiments and of being practiced or being carried out 
in various ways. Also, it is to be understood that the phraseology and 
terminology used herein is for the purpose of description and should not 
be regarded as limiting. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
Illustrated in FIG. 1 is a hand-held power tool 10 embodying features of 
the invention. In the particular arrangement shown in the drawings the 
power tool 10 is a rotary hammer used to drill holes in concrete, masonry, 
and the like. The rotary hammer 10 includes a tool body 12 adapted to 
support a tool 14, such as a drill bit, for drilling operations and for 
combined drilling and hammering operations. The tool body 12 has a 
longitudinal axis 16 which in the illustrated arrangement is also the tool 
axis. 
As shown in FIG. 1, the tool body 12 includes an outer tool housing 18 
which is preferably molded from plastic material. The outer tool housing 
18 includes (FIG. 2) a pair of laterally spaced apart ears or rings 20 
extending rearwardly from the lower part thereof. The tool body 12 also 
includes (FIG. 3) an inner tool housing 21 which is substantially encased 
within the outer tool housing 18 and which is preferably made of a metal 
alloy material. As shown in FIG. 3, the inner tool housing 21 includes a 
rear surface 22 having a circular raised portion 24, and a pair of tapped 
holes 26 on laterally opposite sides of the raised portion 24 extend 
forwardly from the rear surface 22. 
The rotary hammer 10 also includes a main handle 28 which is mounted on the 
rear end of the tool body 12 at an upper joint 30 and a lower joint 32. 
While not shown in the illustrated arrangement, the rotary hammer 10 can 
also be provided with a secondary handle which in one embodiment extends 
laterally from the tool body 12. The secondary handle provides the tool 
operator with additional control over the rotary hammer 10 and is a 
feature known in the art. 
The handle 28 includes (FIG. 3) opposite halves 34 and 36 that are secured 
together with fasteners 37 (only one of which is shown) or other suitable 
means, and as shown in FIG. 1, the handle 28 is provided with a trigger 38 
to control tool operation. In the illustrated arrangement the position of 
the trigger 38 and the contour of the handle 28 encourage an operator to 
grip the handle 28 at its upper end so that operator applied pressure is 
approximately in line with the axis 16. The handle 28 also includes a hand 
grip portion 40 which, if desired, can be provided with a cushioned 
gripping sleeve or surface (not shown). The cushioned gripping surface 
increases operator comfort and to some extent isolates the tool operator 
from tool vibrations and especially high frequency vibrations such as 
those caused by the drilling operation of the rotary hammer 10. 
As shown in FIG. 2, the handle 28 includes at its lower end a pair of 
hollow cylindrical members 42 and 44 which extend laterally inwardly from 
the opposite handle halves 34 and 36 and which have complementary end 
portions 46 and 48. To form a pivot interface at the lower joint 32, the 
handle halves 34 and 36 are assembled with the cylindrical members 42 and 
44 extending through the rings 20 so that the end portions 46 and 48 
engage and the members 42 and 44 form a bore 50. A bolt and nut 
combination 52 is inserted through the bore 50 and tightened to hold the 
lower joint 32 together while permitting pivotal movement of the handle 28 
relative to the tool body 12 about an axis 54 perpendicular to axis 16. 
To insulate the lower part of the handle 28 to at least a limited degree 
from vibrations and torque reactions, such as can occur when the tool 14 
becomes temporarily lodged in a work medium, the lower joint 32 is 
provided with a pair of elastomeric sleeves 56. As shown in FIG. 2, the 
sleeves 56 are fitted between the cylindrical members 42 and 44 and the 
rings 20 and are provided with flanges 58 to prevent lateral contact 
between the rings 20 and the handle 28. Thus, under all conditions, the 
sleeves 56 prevent a rigid connection between the handle 28 and the tool 
body 12 at the lower joint 32. 
As shown in FIG. 3, the handle 28 includes at its upper end a second pair 
of hollow cylindrical members 59 and 60 which extend laterally inwardly 
from the opposite handle halves 34 and 36 and which are joined by the 
fastener 37. The upper end of the handle 28 also includes a module support 
62 that is fitted between the handle halves 34 and 36 and that forms part 
of the upper joint 30. The support 62 is preferably made of metallic 
material and includes a ring member 63 through which the members 59 and 60 
extend to hold the support 62 against movement relative to the handle 28 
in a direction parallel to axis 16. The support 62 also includes a 
receptacle portion 64 having a base 65 that is provided with a truncated 
convex surface portion 66 for reasons more fully explained below. The 
support 62 is also provided with a pair of slots 66 which are vertically 
elongated as shown in FIG. 4. 
The rotary hammer 10 also includes a primary means for reducing 
transmission of vibration from the tool body 12 to the handle 28. In the 
embodiment illustrated in FIGS. 1-9, the primary means for reducing 
transmission of vibration from the tool body 12 to the handle 28 includes 
(see FIG. 3) a vibration isolation module 68. As is further explained 
below, the module 68 is positioned to reduce force transfer from the tool 
body 12 to the handle 28 in the direction of the axis 16 when operator 
applied pressure is exerted in a pushing direction (indicated by reference 
numeral 70). 
While the vibration isolation module 68 can have other constructions, in a 
first embodiment (see FIGS. 5 and 6) the vibration isolation module 68 
includes a guide member 72 which is preferably molded of plastic material. 
The guide member 72 includes a generally cylindrical base 74 that is 
provided with a channel 76 that is shaped to correspond to the surface 
portion 66 on the base 65. The guide member 72 also includes a cylindrical 
guide surface 78 extending from the base 74, a spring seat surface 80, a 
stop seat surface 82, and a forwardly projecting member 84 having a hole 
86. 
The vibration isolation module 68 also includes an annular spring housing 
88 that is slidable along the guide surface 78 and that includes a spring 
retainer portion 90. The spring retainer portion 90 has a radially 
inwardly directed flange 92 which encircles the forwardly projecting 
member 84. The flange 92 is engageable with the head of a self threading 
fastener 94 installed in the hole 86 to retain the spring housing 88 on 
the guide member 72. 
The vibration isolation module 68 also includes a spring 96 supported on 
the spring seat surface 80 and housed in the spring retainer portion 90 of 
the spring housing 88. As shown in FIG. 6, the spring 96 has an unloaded 
length and is precompressed (i.e., compressed prior to use as a vibration 
absorber) to a length which in the illustrated arrangement (see FIG. 5) is 
a minor fractional portion of its unloaded length. The spring 96, when 
installed in the vibration isolation module 68, biases the guide member 72 
and the spring housing 88 apart. 
The aforementioned means for reducing transmission of vibration from the 
tool body 12 to the handle 28 also includes means for indicating to a tool 
operator when operator applied pressure on the handle 28 is at a 
predetermined preferred or recommended level or within a range of 
recommended levels for optimum tool performance. In the illustrated 
arrangement, such means is incorporated into the vibration isolation 
module 68 and tactiley indicates to an operator the level of operator 
applied pressure, and such means includes an annular snubber or stop 
member 98. The stop member 98 is seated on the stop seat surface 82 of the 
guide member 72 in parallel with the spring 96 and encircles the member 
84. The stop member 98 acts as a back-up spring to spring 96 and is 
preferably made of an elastomeric material having a spring rate that is 
substantially greater than the spring rate of the spring 96 for reasons 
more fully explained below. 
The vibration isolation module 68 is installed in the upper joint 30 and is 
covered by (FIG. 1) an elastomeric bellows 100. As shown in FIG. 3, the 
module 68 is positioned so that the spring retainer portion 90 encircles 
the raised portion 24 and the guide member 72 is received in the 
receptacle portion 64 of the support 62 with the concave surface portion 
76 seated on the convex surface portion 66 of the base 65. That 
arrangement orients the vibration isolation module 68 in generally 
parallel relation to axis 16 and allows the module 68 limited pivotal 
movement about an axis parallel to axis 54. This allows the vibration 
isolation module 68 to adjust to slight misalignments between the handle 
28 and the tool body 12 during tool operation. That arrangement also 
limits displacement of the module 68 relative to either the handle 28 or 
the tool body 12 in a direction transverse to axis 16. 
In the illustrated arrangement, the vibration isolation module 68 does not 
resist forces tending to displace the handle 28 relative to the tool body 
12 in a pulling direction (indicated by reference numeral 102). Such 
forces occur, for example, when an operator withdraws the rotary hammer 10 
from a work medium. Accordingly, the upper joint 30 is provided with means 
for limiting relative movement of the handle 28 away from the tool body 
12. In the illustrated arrangement, such means includes a pair of 
fasteners 104 extending through the slots 67 in the handle 28 and threaded 
into the tapped holes 26 in the inner tool housing 21. The elongated slots 
67 permit a limited range of pivotal movement of the handle 28 about the 
axis 54 of the lower joint 32, and engagement of the fasteners 104 with 
the handle 28 provides some lateral stability at the upper joint 30. 
Elastomeric washers 106 are provided on the bolts 104 to soften any impact 
felt by an operator when the rotary hammer 10 is jerked or otherwise 
withdrawn from a work medium. 
When the vibration isolation module 68 is installed in the upper joint 30 
and the bolts 104 are tightened to the desired setting, the spring 96 is 
further precompressed (see FIG. 3) from its initially precompressed 
condition shown in FIG. 5. By further precompressing the spring 96, the 
guide member 72 and the spring housing 88 are held in firm engagement with 
the handle 28 and the tool body 12, respectively, and effectively form 
parts thereof. Thus, relative movement between the tool body 12 and the 
handle 28 in the direction of axis 16 results in the same relative 
movement between the housing 88 and the guide member 72, and relative 
movement of the tool body 12 and the handle 28 toward one another is 
resisted by the spring 96. The precompressed spring 96 also biases the 
tool body 12 and the handle 28 apart to prevent looseness or rattling 
between the handle 28 and the tool body 12. 
In a preferred embodiment, the recommended operator applied pressure to be 
exerted on the handle 28 for optimum tool performance is represented by a 
range of pressures including a preferred minimum operator applied pressure 
level and a preferred maximum operator applied pressure level. The spring 
96 is chosen so that the preferred minimum operator applied pressure level 
is equal to the pressure required to initially deflect the spring 96 from 
its precompressed condition (FIG. 3) to a further compressed condition 
(such as shown in FIG. 7). A tool operator can feel this spring deflection 
when placing pressure on the handle 28 and is thereby given an objective 
indication that the preferred minimum operator applied pressure is reached 
or exceeded. The preferred maximum operator applied pressure level is 
preferably that pressure required to compress the spring 96 to the 
position shown in FIG. 8 wherein the flange 92 of the spring housing 88 
engages the stop member 98. Any further compression of the spring 96 will 
cause the operator to feel the higher spring rate presented by a 
combination of the spring 96 and the stop member 98. Within the range of 
recommended operator applied pressures indicated by the gap 108 in FIG. 3, 
the spring 96 is capable of absorbing vibrations such as the low frequency 
vibrations generated by the percussive action of the rotary hammer 10 by 
compressing and expanding within that range. Thus, the vibration isolation 
system is designed to provide maximum vibration isolation when the 
operator exerts a recommended operator applied pressure on the handle 28 
because it is at this pressure that tool operation and exposure to 
vibrations is expected to be prolonged. At higher operator applied 
pressures, such as when an operator really leans into the rotary hammer 10 
to deflect the stop member 98 (FIG. 9), tool operation is expected to be 
for only brief periods and therefore vibration isolation is not as 
critical under those conditions. 
For example, in one embodiment the rotary hammer 10 has a recommended 
operator applied pressure on the handle 28 of about 20 lbs.sub.f, and the 
spring 96 is chosen to have a spring rate of about 2 lbs.sub.f /inch of 
spring deflection and an unloaded length of about 12 inches. When 
installed in a power tool, the spring 96 is precompressed to a length of 
about 2 inches. To overcome the force exerted by the precompressed spring 
96 to initially further compress the spring 96 an operator must apply a 
force of slightly greater than about 20 lbs.sub.f. That further spring 
deflection provides the operator with a tactile indication that the 
recommended operator applied pressure has been achieved. Under this 
condition, oscillation of the spring 96 to absorb vibration is readily 
permitted until the recommended operator applied pressure is exceeded and 
the flange 92 of the spring housing 88 bottoms out on the stop member 98. 
Thus, it is expected that an operator will naturally seek to operate the 
rotary hammer 10 at the recommended operator applied pressure level on the 
handle 28 for maximum comfort, especially when tool use is prolonged. In 
this example, the gap 108 is only about one quarter of an inch and the 
operator applied pressure on the handle 28 needed to engage the stop 
member 98 is only about 20.5 lbs.sub.f. 
Illustrated in FIG. 10 is a portion of a power tool including a modified 
handle 110 and a modified tool body 112. As shown in FIG. 11, the handle 
110 and the tool body 112 are designed to receive a vibration isolation 
system in accordance with a second embodiment of the invention. In that 
embodiment the vibration isolation module 68 is replaced with an 
alternative module 114. Module 114 has a modified guide member 116 which 
is supported on the tool body 12, instead of the handle 28 as in FIGS. 
1-9, and the spring housing 88 is supported against the handle 28. 
Otherwise, module 114 operates in the same manner as module 68. 
While in the illustrated arrangement the vibration isolation system and the 
mechanism for indicating to a tool operator whether operator applied 
pressure on the tool handle is within recommended levels form part of a 
rotary hammer, those features, either alone or in combination, could also 
be incorporated into other vibratory tools. This will be understood by 
those skilled in the art after study of the foregoing. 
Various features of the invention are set forth in the following claims.