Note: Descriptions are shown in the official language in which they were submitted.
CA 02461489 2004-03-19
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ANTI-VIBRATORY HANDLE FOR PERCUSSIVE
AND OTHER RECIPROCATING TOOLS
FIELD OF THE INVENTION
The present invention relates to an anti-vibratory handle for tools producing
vibrations, in particular but not exclusively percussive and other
reciprocating
tools. In operation, this anti-vibratory handle reduces transmission of
vibrations
from the tool to the hand(s) and upper limb(s) of the operator.
BACKGROUND OF THE INVENTION
Protection of hand
Various studies have been conducted on the effectiveness of anti-
vibratory gloves:
- Miwa, T;"Studies on hand protectors for portable vibrating tools, I.
Measurements of the attenuation effect of porous elastic materials" ;
Industrial Health, 2, 95-105 ; 1964
- Miwa, T;"Studies on hand protectors for portable vibrating tools, II.
Simulation of porous elastic materials and their application to hand
protectors" ; Industrial Health, 2, 106-123 ; 1964
- Miwa, T; Yoneska,Y; et Kanada, K; "Vibration isolators for portable
vibrating tools, Part 4. Vibration isolation gloves"; Industrial Health, 17,
141-
152 ; 1979
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- Saunders, R. L.; "Report on the testing of anti-vibration gloves"; B.C.
Research, 4 pages ; 1978
- Voss, P. ; "On the vibration isolating efficiency of gloves"; United kingdom
Informal Group on Human Response to Vibration, Sept. 16-17, Paper 3.1,
9 pages ; 1982
- Villon, S. J.; "Effect of gloves on the transmission of vibration to the
hand" ;
M. Sc. Dissertation, University of Southampton, 140 pages, 1982.
All of these studies have demonstrated the effectiveness of such gloves
for frequencies above the 100-140 Hz range, depending on the individual
wearer. Below this range, however, anti-vibratory gloves are at best
ineffective
or tend to enhance vibrations transmitted to the hands (at resonance
frequencies
ranging from 30 to 45 Hz, depending on the type of glove and on the morphology
of the palm of the worker).
In the particular context of percussion drills, with a dominant frequency
corresponding to the frequency of impact (about 40 Hz), this type of glove may
increase the exposure of workers to vibrations.
It should be noted nevertheless, that wearing gloves prevents direct
contact of the hands with cold surfaces. This is a very positive factor that
may
limit the appearance of symptoms related to Raynaud's syndrome.
Modification of the handle
Numerous investigations have been conducted for the purpose of
damping or insulating vibrations at the level of the handle or between the
body of
the percussion drill and the handle.
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Among the most significant works, a Russian study in 1964 may be cited,
which deals with the development of anti-vibratory handles [Paran'ko, N.M.;
"Hygienic evaluation of vibration and noise damping devices for hand-operated
pneumatic rock drills"; Pat. Fiziol., 4, 32-38; 1964]. Prototypes of handles
developed in the context of this study showed effectiveness approaching a 50%
reduction of vibrations, but in association with either too great an increase
in
weight or poor mechanical resistance.
A patent was granted to Shotwell in 1976 for an anti-vibratory handle for a
portable pneumatic hammer [Shotwell D.B.; "Pneumatic percussion tool having a
vibration dampened handle". Caterpillar Tractor Co.; US Patent No. 3,968,843
issued on July 13, 19761. The invention described in US Patent No. 3,968,843
consists of a rubber element inserted between the handle and the body of the
pneumatic hammer. According to this patent, an attenuation of vibrations at
the
frequencies of interest of the order of 17 dB may be obtained. However, no
statement is made about the durability or ease of handling of the tool.
Aside from the above 'studies, those of Boileau [Boileau P.E.; "Les
vibrations engendrees par les foreuses a bdquille a Ia division Opemiska de
Minnova"; Rapport IRSST B-027, Decembre 1990] tested and compared two
anti-vibratory handles. One of these handles was, among other things,
homemade and equipped with a resilient member placed between the handle
and the body of a percussion drill. And this handle provided an attenuation of
the
order of 20% of the vibrations transmitted to the worker.
More recently, a study conducted in 1998 by the firm Boart Longyear Inc.
led to the development of a new handle [Prajapati K., Hes P.; "Reduction of
hand-arm transmitted Vibration on Pneumatic Jackleg Rock Drills", Congrds
CIM, Sudbury]. Tests showed an approximately 50% attenuation of non-
weighted vibration levels. This attenuation is due primarily to a decrease of
high
frequency (> 640 Hz) vibrations. The presented spectra fail to show any
attenuation at the frequency of impact defined by Boileau [Boileau P.E.; "Les
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vibrations engendrdes par les foreuses & bdquille ~ la division Opemiska de
Minnova"; Rapport IRSST B-027, Decembre 1990], among others, as the
principal component of the weighted spectrum. The impact of the use of such a
handle on the exposure of workers to vibrations thus remains minimal.
Prior works applied to other tools
Numerous studies have been conducted with the aim of reducing
vibrations transmitted from chainsaws to the hands of the operator. The
concept
most generally used is uncoupling the chain guard and the saw handle from the
moving mechanical parts (internal combustion engine and chain drive system)
[Bierstecker, M.; "Vibration mount on a chainsaw"; US Patent No. 4,670,985
issued June 9, 1987] [Gassen J.R.; Suchdev L. S.; "Vibration Reducing
Chainsaw Handle", US Patent No. 5,016,355 issued May 21, 1991]. Recent
machines equipped with this type of suspension have greatly reduced the
exposure of forestry workers to vibrations.
Various other studies have been conducted on concrete breakers.
Although the source of the vibrations in concrete breakers is very similar to
that
observed in air-leg percussion drills, the modes of operation of the two tools
are
quite different. The operator must hold continuously the concrete breaker
using
both hands and the direction of the work is generally vertical. Also, gripping
of
the concrete breaker differs greatly from gripping of the air-leg percussion
drill,
which is used essentially for making horizontal holes. In air-leg percussion
drills,
the drive force is produced essentially by the air-leg and the miner
intervenes
mainly to make the pilot hole necessary to keep the machine on the desired
axis.
The solutions developed within the context of these studies are therefore not
directly applicable to percussion drills. One type of solution that may be
cited is
the development of flexible hoop-type handles or the installation of dynamic
absorbers [IRGO-Pic, Ingersoll-Rand trade mark].
CA 02461489 2008-08-19
SUMMARY OF THE INVENTION
The present invention relates to an anti-vibratory handle for installation on
a percussion drill supplied with a pressurized fluid and producing vibrations
in the
direction of an axis of reciprocation of the percussion drill. The anti-
vibratory handle
comprises: a stationary portion for being mounted to a body of the percussion
drill and
comprising a distal end; a mobile portion comprising a hand-grip member and a
proximal end; a control of the operation of the percussion drill mounted on
the hand-
grip member; and an articulation between the stationary and mobile portions.
The
articulation comprises: a pivot means defining a pivot axis and
interconnecting the
distal end of the stationary portion and the proximal end of the mobile
portion whereby
the distal end of the stationary portion and the proximal end of the mobile
portion
rotate with respect to each other about the pivot axis; and a resilient
vibration-damping
assembly interposed between the distal end of the stationary portion and the
proximal
end of the mobile portion to avoid transmission of vibrations through the
articulation.
The anti-vibratory handle also comprises at least one conduit for transmitting
pressurized fluid between the percussion drill and the percussion drill
operation control
to allow the percussion drill to be operated through the percussion drill
operation
control, the at least one conduit extending through the stationary portion,
the distal end
of the stationary portion, the proximal end of the mobile portion and the
mobile portion
and including a deformable conduit portion between the distal end of the
stationary
portion and the proximal end of the mobile portion that extends through the
articulation
past the pivot means and the resilient vibration-damping assembly and deforms
with
rotation of the distal end of the stationary portion and the proximal end of
the mobile
portion with respect to each other about the pivot axis.
The foregoing and other objects, advantages and features of the present
invention will become more apparent upon reading of the following non-
restrictive
description of illustrative embodiments thereof, given by way of example only
with
reference to the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
Figure 1 is a schematic illustration of the basic concept of the non-
restrictive illustrative embodiment of the anti-vibratory handle according to
the
present invention;
Figure 2 is an exploded view of an anti-vibratory handle according to the
non-restrictive illustrative embodiment according to the present invention,
adapted for a JOYTM percussion drill;
Figure 3 is a side elevational view of a JOYTM percussion drill on which
an anti-vibratory handle as illustrated in Figure 2 has been installed;
Figure 4 is a graph of the weighted global acceleration "versus" the
frequency of vibration showing a typical spectrum obtained during laboratory
tests, with a triaxial accelerometer mounted on the handle at the level of the
hang-grip member and two 0.635 mm thick and 12.7 mm wide resilient members
made of neoprene duro 40, with strong gripping of the hand-grip member by the
worker;
Figures 5a is a side elevational view of a resilient member for use in the
illustrative embodiment of anti-vibratory handle of Figure 2;
Figures 5b is a front elevational view of the resilient member of Figure 5a;
Figure 6 is a graph of the acceleration "versus" the frequency of vibration
showing a typical spectrum obtained during in-situ tests, with a triaxial
accelerometer mounted on the handle at the level of the hand-grip member;
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Figure 7a is a schematic diagram illustrating the direction of movement of
the anti-vibratory handle of Figure 2 for a JOYTM percussion drill;
Figure 7b is a schematic diagram showing an angle for an arm
member of a mobile portion of the anti-vibratory handle according to the
illustrative embodiment of the present invention, optimized for the JOYTM
percussion drill;
Figure 8a is a cross sectional, side elevational view of the anti-vibratory
handle according to the non-restrictive illustrative embodiment of the present
invention, optimized for the JOYTM percussion drill;
Figure 8b is a cross sectional, top plan view of the anti-vibratory handle
according to the non-restrictive illustrative embodiment of the present
invention, optimized for the JOYTM percussion drill;
Figure 9 is an exploded, three-dimensional perspective view of the anti-
vibratory handle of Figures 8a and 8b; and
Figure 10 is an exploded, three-dimensional perspective view of an anti-
vibratory handle according to the non-restrictive illustrative embodiment of
the present invention, optimized for a SECANTM percussion drill.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
The development of an anti-vibratory handle for tools producing
vibrations, such as percussive and other reciprocating tools, may be expressed
in terms of three challenges:
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- To develop an anti-vibratory handle effective at low frequencies (=_ 30
Hz), therefore involving large reciprocating movements.
- To ensure the passage of the tool control (electrical, pneumatic or
hydraulic control) through a suspension.
- To design a system both simple and robust for use under extremely
severe operating conditions, for example in underground mines.
Figure 1 illustrates the basic concept of the illustrative embodiment of the
anti-vibratory handle according to the present invention, consisting of
installing a
pivot spaced apart from but parallel to the point of gripping of the handle.
More specifically, Figure 1 illustrates the body 11 of a percussion drill 12.
This percussion drill 12 is provided with an anti-vibratory handle 14
according to
the illustrative embodiment of the present invention.
Although the preferred embodiment of the present invention will be
described in relation to a percussion drill, is should be kept in mind that
the
present invention can be applied to other types of tools producing vibrations,
in
particular but not exclusively percussive and other reciprocating tools.
In accordance with the non-restrictive illustrative embodiment, the anti-
vibratory handle 14 comprises at least one arm member 15 having a proximal
end connected to the body 11. The anti-vibratory handle 14 also comprises a
hand-grip member 16 connected to the distal end of the arm member 15 through
at least one arm member 17 and an articulation 18 comprising a pivot (not
shown).
Still referring to Figure 1, the double arrows 19, 20, 21, 22 and 23
represent the nature, direction and amplitude of the main vibrations to which
a
percussion drill is subjected.
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The double arrows 19 and 20 illustrate the vibrations of the body 11 of the
drill 12 along the axis of percussion. As can be seen in Figure 1, the hand-
grip
member 16 and the pivot of the articulation 18 are parallel to each other but
perpendicular to the axis of percussion (see double arrows 19 and 20).
According to the non-restrictive illustrative embodiment, the arm member 17,
when non operating, defines with the arm member 15 an angle slightly lower
than 900 about the articulation 18, of the order of, for example, 75 .
Under the influence of the back-and-forth movement (see double arrow
19 and 20 of Figure 1) of the drill 12 along the axis of percussion, the
handle 14
pivots about the articulation 18 (see double arrow 22) whereby the hand-grip
member 16 moves along an arc of a circle (see double arrow 21) having a radius
equivalent to the distance separating the axis of the pivot of the
articulation 18
and the axis or center of inertia of the hand-grip member 16 bearing the
hand(s)
of the worker.
Although the attenuation of the vibrations along the axis of percussion
(see double arrows 19 and 20) will produce a slight increase in vibratory
movement along the longitudinal axis of the arm member 17 (see double arrow
23), the rotary concept of the anti-vibratory handle 14 affords major
advantages
in terms of design simplicity. In fact, it is relatively easy to obtain pure
rotation.
This type of movement can be achieved by means of a simple pivot supported
by self-lubricating bearings. There are numerous low-cost, commercially
available products for producing pure rotation.
Vibratory insulation is obtained by means of resilient members (not
shown in Figure 1) inserted within the articulation 18. These resilient
members
can comprise torsion insulators or pieces of resilient material inserted
between
jaws formed between mobile and stationary parts of the articulation 18.
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For pneumatic percussion drills, the angular movement of the hand-grip
member 16 about the articulation (see double arrows 21 and 22) will remain
small; for example, an angular movement of t5 (see double arrows 21 and 22)
can be used for an axial displacement (see double arrow 20) of the anti-
5 vibratory handle 14 handle of about 2 cm. With such a smail angular
movement,
pneumatic connections under the form of flexible plastic tubes could be used
without onset of material fatigue, even after a large number of bending
cycles. In
this manner, no complex air-tight connections are required and the structure
of
the articulation is thus greatly simplified to substantially reduce the costs.
Figure 2 is an exploded view of an anti-vibratory handle according to the
illustrative embodiment according to the invention, adapted for a JOYTM
percussion drill. The anti-vibratory handle of Figure 2 is generally
identified by
the reference 24.
The anti-vibratory handle 24 first comprises a stationary portion 25
integrated to the percussion drill (not shown) via a fixation cone 26 of the
same
type as those used for mounting conventional handles. Fixedly connected
perpendicular to the fixation cone 26 is an arm member 27 extending in the
direction of the axis of percussion. The arm member 27 comprises a pairs of
opposite, longitudinal top and bottom flat faces 50 and 51. The distal end 28
of
the arm member 27 forms part of the articulation 18 (Figure 1).
The anti-vibratory handle 24 also comprises a mobile portion 29
comprising an arm member 30. The distal end of the arm member 30 is formed
with a conical attachment device 31 of the type providing for direct
attachment of
a conventional hand-grip member (not shown) including controls for the
operation of the percussion drill. This conventional hand-grip member may be
identical in all respects to the existing JOYTM handle. The proximal end 32 of
the
arm member 30 also forms part of articulation 18 (Figure 1). When non
operating, the arm member 30 is inclined towards the stationary portion 25 to
define with the axis of percussion an angle slightly lower than 90 about the
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articulation of the anti-vibratory handle 24, this angle being of the order
of, for
example, 75 .
The distal end 28 of the arm member 27 is formed with two parallel side
ears 33 and 34 with respective, coaxial threaded holes 35 and 36. The distal
end
28 further comprises, between the ears 33 and 34, a flat face 37 perpendicular
to the longitudinal axis of the arm member 27. A series of three axial holes
such
as 38 are drilled through the flat face 37 between the two ears 33 and 34.
These
axial holes 38 are in communication with pressurized air transmitting conduits
formed through the arm member 27.
. The proximal end 32 of the arm member 30 has the general configuration
of a hollow rectangular box-like structure with a face open toward the distal
end
28 of the arm member 27. The rectangular box-like structure comprises:
- a pair of opposite side walls 39 and 40 formed with respective coaxial
holes 41 and 42;
- a second pair of opposite top and bottom walls 43 and 44; and
- an internal bottom wall 53 formed with a series of three holes 52 opposite
to but corresponding to the series of three holes 38.
Again, these holes 52 are in communication with pressurized air transmitting
conduits formed through the arm member 30.
The articulation 18 between the arm members 27 and 30 finally
comprises three flexible tubes such as 45 of equal length and two generally
flat
resilient members 46 and 47 L-shaped in cross section to define respective
shoulders 48 and 49. For example, the tubes 45 can be made of plastic material
and the resilient members made of elastomeric material.
During installation, the following operations are performed:
- The three flexible tubes 45 comprise respective first ends respectively
inserted into the three holes 38.
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- The resilient member 46 is applied to the top flat face 50 of the arm member
27 with the shoulder 48 applied to the end flat face 37.
- The resilient member 47 is applied to the bottom flat face 51 of the arm
member 27 with the shoulder 49 applied to the end flat face 37.
- The rectangular box-like structure of the proximal end of the arm member 30
is positioned over the distal end 28 of the arm member 27, more specifically
over the ears 33 and 34 and the resilient members 46 and 47. The resilient
members are bevelled at 54 and 55 to facilitate this operation. The three
flexible tubes 45 comprise respective second ends respectively inserted,
during this operation, into the three holes 52.
- To complete the assembly, a bushing 56 made of any suitable attrition-
resistant material such as bronze is inserted in hole 41, and a shoulder screw
57 is driven into the threaded hole 35 through the bushing 56. In the same
manner, a bushing 58 made of any suitable attrition-resistant material such
as bronze is inserted in hole 42, and a shoulder screw 59 is driven into the
threaded hole 36 through the bushing 55. Therefore, the shoulder screws 57
and 59 tightened into the respective threaded holes 35 and 36 form with the
bushings 56 and 58 and the holes 41 and 42 the pivot of the articulation 18
(Figure 1).
In operation, the three tubes 45 will ensure transmission of pressurized
air between the percussion drill and the control on the hand-grip member to
enable control of the operation of the percussion drill by the worker. Sealing
between the tubes 45 and the holes 38 and 52 is ensured by inflation of the
tubes 45 when the air-leg of the percussion drill is supplied with pressurized
air.
As indicated in the foregoing description, with the small angular movement of,
for
example, t5 between the arm members 27 and 30, the flexible plastic tubes 45
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will bend without onset of material fatigue, even after a large number of
bending
cycles.
Also in operation, the resilient member 46 is compressed between the top
flat face 50 of the arm member 27 and the inner face of the top wall 43, while
the
resilient member 47 is compressed between the bottom flat face 51 of the arm
member 27 and the inner face of the top bottom wall 44. During small angular
movements of the arm member 30 about the arm member 27, the stiffness of the
resilient, for example elastomeric members 46 and 47 is linear. If the
amplitude
of the angular movements increases, the greater compression of the members
46 and 47 considerably increases their stiffness. Thanks to their non linear
behaviour, the resilient members 46 and 47 thus act both as vibration-damping
insulators and flexible cushions intended to limit the angular movements of
the
arm member 30 about the arm member 27 for example to the above mentioned
angular value of 50.
The shoulders 48 and 49 of the resilient members 46 and 47, located
between the end flat face 37 and the internal bottom wall 53, retain the
resilient
members 46 and 47 in position between the top flat face 50 of the arm member
27 and the inner face of the top wall 43 and between the bottom flat face 51
of
the arm member 27 and the inner face of the top bottom wall 44, respectively.
This anti-vibratory handle 24 of Figure 2 provides an effective and
relatively simple suspension. This suspension may be very readily adapted to
existing percussion drill, since the attachment cones on the arm members 27
and 30 can be identical to those of conventional handle models.
Figure 3 illustrates the anti-vibratory handle 24 of Figure 2 installed on a
JOYTM percussion drill. The hand-grip portion of the handle remains at exactly
the same height as on a conventional model, thus allowing access for the
replacement of water tubes. Likewise, the worker finds the controls at exactly
the
same location as on the conventional handles.
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Laboratory tests were conducted to demonstrate the efficiency of the anti-
vibratory handle according to the illustrative embodiment of the present
invention. For that purpose, a prototype of the anti-vibratory handle was
built,
and installed and tested on a vibrating table. All the measurements were made
through a triaxial accelerometer mounted at the level of the hand-grip member
of
the anti-vibratory handle. Of course the accelerometer was connected to a
measurement system.
A typical spectrum as obtained during the laboratory tests, with a triaxial
accelerometer mounted on the handle at the level of the hand-grip member is
illustrated in Figure 4. The graph of Figure 4 shows that an overall measured
attenuation greater than 50% was obtained with two 0.635 mm thick and 12.7
mm wide resilient members made of neoprene duro 40, with strong gripping by
the worker.
Various laboratory tests were conducted on a series of resilient members
in order to validate the influence of parameters such as shape, applied
gripping
force and attachment of the resilient members. Resilient members made of
various materials were tested, even though the constraints of resistance to
lubricants and other external chemical agents required by trade specifications
limit the choice of resilient members to polyurethane.
Effect of gripping force:
An initial series of laboratory tests examined the effect of the hand on the
anti-vibratory insulation provided by the handle. As expected, insulation
increased directly with gripping force. Thus for rubber insulators 12.7 mm
wide,
attenuation in weighted values passed from 45% to 68% by increasing gripping
force. Similarly, a polyurethane insulator 25 mm wide brought an increase of
nearly 10% in free vibrations while an insulation of about 25% was obtained by
applying a gripping force.
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Effect of the type of elastomer attachment:
Series of tests were carried out in which resilient members were glued to
5 the stationary and mobile parts of the anti-vibratory handle according to
the
illustrative embodiment of the present invention. The purpose of these tests
was
to simulate the use of resilient members vulcanized to the handle. The results
revealed that gluing strongly decreases the anti-vibratory efficiency of the
handle. The overall levels measured for the same resilient members either
glued
10 or simply inserted may vary up to two-fold. This is due mainly to the glued
resilient members working as much in the compression as in the stretching
mode whereas the non-glued resilient members work only in the compression
mode. The choice naturally turned towards freely inserted resilient members;
in
this manner, the problems of gluing the resilient members was avoided and a
15 more resilient and efficient suspension was obtained.
Effect of the shape of the resilient members:
The stiffness of the resilient members is determined in part by the type of
material and also by its shape. When, for example, an elastomer is compressed
in a single direction, it tends to expand in the other directions (Poisson
effect). If
this expansion movement is restricted, the resilient member stiffens
considerably. A.resilient member confined laterally by rigid walls will thus
stiffen
upon compression. Similarly, for a given contact surface, a resilient member
made of two sections will be more resilient than a resilient member made of a
single piece.
Figures 5a and 5b illustrates a resilient member 60 for use as resilient
members 46 and 47 of Figure 2. The resilient member 60 is L-shaped in cross
section, defines two legs 61 and 62 and a shoulders 63, and is bevelled at 64.
The shoulder 63 will, as explained in the foregoing description, keep the
resilient
member in place. The two legs 61 and 62 terminate in respective, thicker
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cushions 65 and 66. These cushions 65 and 66 keep the resilient member 60
compressed in the equilibrium position of the anti-vibratory handle 24 of
Figure
2. If the worker applies a significant pulling or pushing force on the anti-
vibratory
handle 24, the entire legs 61 and 62 are compressed between the box-like
structure of the mobile portion 29 and the arm member 27 of the drill-mounted
stationary portion 25. Under this condition, the suspension firms up and acts
as
a resilient bumper, limiting the pivoting movement of the anti-vibratory
handle
24 about the shoulder screws 57 and 59. This concept provides at the same
time good vibration insulation within the normal range of pulling and pushing
forces applied to the anti-vibratory handle 24 and a still resilient bumper
when
an important pushing or pulling force is applied. It should be noted here that
elastomers can withstand very heavy compression loads before showing
permanent deformation.
It should be mentioned here that resilient members of other forms or
nature can be used. For example, a torsion member can be used. This torsion
member will be made of resilient material and interposed between the arm
members 27 and 30. It is believed to be within the knowledge of those of
ordinary skill in the art to design a torsional resilient member or other type
of
resilient member having the same function as the resilient members 46, 47 and
60.
In-situ tests were also conducted to evaluate the behaviour of the anti-
vibratory handle according to the illustrative embodiment of the present
invention, during use under normal conditions of drilling.
In addition to the anti-vibratory efficiency of the handle, the robustness of
the concept and its impact on the overall ergonomic quality of the percussion
drill
were also evaluated.
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AII measurements were conducted on a JOYTM percussion drill under
normal conditions at the 130 meter level of a laboratory mine. The results
given
hereinafter were obtained during actual drilling sessions.
A triaxial accelerometer connected to a data acquisition and processing
system was used to measure and analyse the vibrations. The triaxial
accelerometer was attached to the end of the hand-grip member with the base of
the accelerometer located on a vertical axis on top of the handle, hence at
the
same level as the operator's hands in the normal working position.
Table 1 summarizes the acceleration values measured by the triaxial
accelerometer on the hand-grip member to show the effect of the tested anti-
vibratory handle (see Figures 2 and 3) on the vibrations produced at the level
of
the worker's hands. More specifically, Table 1 shows the attenuations obtained
with the anti-vibratory handle along the x-axis, the y-axis and the z-axis.
For
example, in the axis of percussion (x-axis), the attenuation is greater than
50%.
In the axes perpendicular to the axis of percussion (y-axis and z-axis), a
slight
increase of the vibrations is observed, due to rotation of the handle about
the
articulation. This results in a global reduction in vibrations of the order of
30 %.
x-axis y-axis z-axis OVERALL
Conventional 17.5 7.9 9.1 21.2
handle
Anti-vibratory 8.1 8.2 10 15.3
handle
% attenuation 53% -4% -11 % 28%
Table 1
Moreover, the spectrum illustrated in Figure 6 clearly shows the vibration-
attenuating effect of the anti-vibratory handle in the axis of percussion of
the
drill.
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The anti-vibratory handle was used to drill more than 30 meters
without showing any sign of weakness, thus demonstrating at the same time
both the robustness and the reliability of the concept.
Analysis of high-speed filming showed that the movement of the handle
attachment point is not parallel to the axis of percussion of the JOYTM drill
but
40 apart from this axis of percussion as shown in Figures 7a and 7b. This is
due
to the center of gravity of the percussion drill not being situated in the
axis of
percussion, which brings about a slight rotational movement of the percussion
drill about its point of attachment to the air-leg. Figures 7a and 7b show, in
an
amplified manner, the rotational movement of the percussion drill and the anti-
vibratory handle.
Figure 7a illustrates the situation for the case of the anti-vibratory handle
24 of Figures 2 and 3. This design has been optimized for a percussion drill
in
which the movement of the articulation 18 (Figure 1) is parallel to the axis
of
percussion. Although this design is effective for a displacement of the
articulation
of the anti-vibratory handle parallel to the axis of percussion, it brings
about a
slight increase of the vibrations perpendicular to the axis of percussion. In
order
to address this problem, the solution illustrated in Figure 7b was developed.
By
inclining the neutral position of the arm member 30 (Figure 2) to an angle
generally 90 apart from the direction of movement of the articularion 18, it
is
possible to compensate for the vibrations perpendicular to the axis of
percussion.
Figures 8a and 8b are cross sectional, side elevational and top plan
views of the anti-vibratory handle 24 optimized for the JOYTM percussion
drill,
while Figure 9 is an exploded, three-dimensional perspective view of this
handle.
The differences between the anti-vibratory handle of Figures 8 and 9
with respect to the anti-vibratory handle of Figure 2 are the following:
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- The neutral angle of the arm member 30 has been adjusted to absorb
vertical as well as horizontal vibrations produced by a JOYTM percussion drill
(see Figure 7b).
- The arm member 27 of the stationary portion 25 of the handle 24 is not only
wider but has been shortened in order to position the hand-grip member of
the anti-vibratory handle 24 at the same position as the hand-grip member
of the original handle of the JOYTM percussion drill. The dimensions of the
box-like structure of the mobile portion 29 of the anti-vibratory handle 24
has been modified to receive the modified arm member 27.
- The anti-vibratory handle 24 of Figures 8 and 9 uses the resilient member
of Figures 5a and 5b as resilient members 46 and 47 (Figure 2).
- Hole 41 is wider to receive a bushing 90 from the inside of the box-like
structure of the mobile portion 29. An embedded screw 91 is driven into the
threaded hole 35 through the bushing 90 to form a more robust pivot. Screw
91 is confined in hole 41 and does not protrude from wall 39 of the box-like
structure of the mobile portion 29.
- Hole 42 (Figure 2) is wider to receive a bushing 92 from the inside of the
box-
like structure of the mobile portion 29. An embedded screw 93 is driven into
the threaded hole 36 through the bushing 92 to form a more robust pivot.
Screw 93 is confined in hole 42 and does not protrude from wall 40 (Figure 9)
of the box-like structure of the mobile portion 29.
- The suspended mass of the mobile portion 29 has been increased by 720
grams (2930 g compared to 2210 g for the anti-vibratory handle 24 of Figure
2), allowing for further reduction of the vibration levels;
- Air ducts of wider diameter, allowing faster response of the air-leg.
CA 02461489 2004-03-19
The resulting anti-vibratory handle 24 of Figures 8 and 9 is easier to
machine and possesses a greater robustness.
5 The attenuation of the vibrations perpendicular to the axis of percussion
by anti-vibratory handle 24 of Figures 8 and 9 optimized for the JOYTM drill
is
estimated to about 50%. Maintaining the same performances along the two other
axes would give an overall attenuation of 40%.
10 Increasing the suspended mass and machining precision for mass
production would further increase the performances of the anti-vibratory
handle
24, up to 50% attenuation overall along the three axes.
Figure 10 illustrates an anti-vibratory handle 24 optimized for a
15 SECANTM percussion drill.
The main difference between the original handles of SECANTM and
JOYTM percussion drills is the presence of a push-button valve on the hand-
grip
member.
As it was the case for the JOYTM percussion drill, the angle of movement
of the hand-grip member was examined using a high-speed camera in order to
optimize the design by maximizing the absorption of vibrations perpendicular
to
the axis of percussion. In the case of the SECANTM percussion drill, the angle
of
movement is smaller than for JOYTM percussion drills, having a value of about
150.
The anti-vibratory handle of Figure 10, optimized for SECANTM
percussion drills, presents the following differences with the anti-vibratory
handle of Figures 8 and 9, optimized for JOYTM percussion drills:
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- The hand-grip portion of the air-leg quick retraction valve (it should be
noted
that the valve used is the same as for the original rigid handle).
- The neutral angle of the arm member 30 is perpendicular to the 150 angle of
movement of the SECANTM percussion drill;
- The suspended mass of the mobile portion 29 is the same as that of the anti-
vibratory handle 24 of Figures 9 and 10.
- The total added mass is 630 g.
The above described concept of anti-vibratory handle for percussion drills
presents, amongst others, the following advantages:
- Attenuation of the vibrations is nearly 50% in the axis of percussion and
30%
overall.
- No sign of apparent wearing of the anti-vibratory handle was detected after
more than 30 m of drilling.
- The impact of the suspension of the anti-vibratory handle on tool handling
seems negligible. Comments from experienced workers indicate that the
impact of the suspension on tool handling is negligible.
- The new suspension can be directly installed on existing machines. The
illustrative embodiment of anti-vibratory handle optimized for JOYTM drills
adapts directly to the drill and involves the same control elements as those
used on the original handle. The illustrative embodiment of anti-vibratory
handle optimized for the SECANTM drill allows this same ease of
replacement. The work time necessary for a mechanic to install the anti-
vibratory handle on an existing percussion drill is estimated at a few
minutes.
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Although the present invention has been described hereinabove by way
of a non-restrictive illustrative embodiment thereof, this embodiment can be
modified at will, within the scope of the appended claims, without departing
from
the nature and spirit of the subject invention. For example, it should be
understood that the anti-vibratory handle according to the non-restrictive
illustrative embodiment of the present invention can be optimized for every
type of percussion drill or other tool producing vibrations.
