[0001] The invention relates to a vibration dampened machine handle by which a machine tool
such as a hydraulic hammer may be pressed in a direction towards a work place.
[0002] Machine tools such as hydraulically or pneumatically operated drilling hammers,
pneumatic drills, screw tools and angle sander-grinders transmit strong vibrations
to the handle by which the operator presses them against the work place. The action
of these vibrations on the operator's hands may in the course of time result in permanent
occupational injuries, a phenomemon known under the name "white fingers". Efforts
are therefore made to develop machine handle devices with improved vibrational dampening.
[0003] For two-hand operated machine tools such as hydraulic hammers a design is known
wherein the grips are connected to the machine tool via an elastic, shock absorbing
rubber body. The grips extend transversely to the longitudinal axis of the machine
tool and are connected to these rubber bodies at one end and are furthermore covered
by foam rubber or another shock absorbing material. The amplitude of the machine tool
vibrations is largest in the direction of its longitudinal axis and due to the elastic
intermediate piece and the reduction by lever action these vibrations are only transmitted
to the grips with attenuated intensity.
[0004] In this design the effectiveness of the vibrational dampening depends substantially
on the elasticity properties of the rubber bodies. The vibrational dampening will
be the better the softer the rubber bodies are.
[0005] However, the rubber bodies may not be made too soft since the grips are to be used
for pressing the machine tool against the work place and therefore may not be too
yiel ding. The described design moreover has the drawback that the grips make a swinging
movement about the ends where they are connected to the machine tool, in such a manner
that their mutual angular position is changed when the operator presses against the
machine tool or lifts it by grasping the grips. Particularly the latter has proved
to be of comparatively great inconvenience in the use of hydraulic hammers since
the operator gets the impression that the tool will not properly follow the movements
when lifted from or pressed against the work place.
[0006] European published specification no. 0 156 387 describes a vibration dampened machine
handle of the kind mentioned above and which as described in the introduction to claim
1 comprises a grip which is connected to an intermediate member via a first body
made of rubber or similar material, said intermedate member being connected to the
machine tool via a second body made of rubber or similar material. The machine handle
device according to the published specification is furthermore provided with an "impact
body" arranged loosely within the grip, said "impact body" serving to counteract
the vibrations of the grip by striking the inner walls thereof. The design and the
arrangement of the individual units in the machine handle according to the mentioned
specification must moreover be chosen and dimensioned such that there occurs a nodal
point in the area of the grip where the operator will most probably take hold.
[0007] However, by the examples shown in the mentioned specification of grips having a
free end, the grip just as is the case of the previously mentioned prior art will
produce a swinging movement about the end by which it is connected to the machine
tool when lifting the machine tool or pressing same against the work place.
[0008] Relative to the prior art it is the task of the invention to provide a vibration
dampened machine handle wherein the vibration dampening units cooperate in such a
manner that it is possible to use a grip with a free end, without the angle between
the longitudinal axis of said grip and the other parts of the machine tool changing
when the machine tool is pressed against the work place or is lifted by lifting it
at the grip.
[0009] According to the invention this task is accomplished by designing the machine handle
device described in the introduction to claim 1 with the structural characteristics
disclosed in the patent claim.
[0010] The rubber bodies used to provide resiliency are according to the invention axially
symmetrical and mounted in such a manner that their axes extend parallelly to each
other in a plane which is transverse to the direction in which the machine tool is
pressed towards the work place. The grip and the intermediate member are connected
to the first rubber body in such a manner that they are turned relatively to each
other about the axis of the first rubber body under torsional stress thereof when
the machine tool is pressed towards the work place. The intermediate member and the
machine tool are connected to the second rubber body in such a manner that they are
turned relatively to each other about the axis of the second rubber body under torsional
stress thereof when the machine tool is pressed towards the work place. Furthermore
the grip comprises a substantially axially symmetrical hand part extending in parallel
to the axes of the rubber bodies, said hand part being connected to the first rubber
body via at least one transverse part, and the hand part is arranged in such a manner
relative to the rubber bodies that a line extending from the axis of the hand part
in the direction towards the work place intersects the plane, wherein the axes of
the rubber bodies are situated, between said axes.
[0011] By this design of the machine handle device the hand part of the grip will generally
extend transversely to the direction towards the work place, and it will not swing
relative to the machine tool but be displaced parallelly thereto by its swinging
about the axes of the two rubber bodies due to the machine tool vibrations or due
to a pressing or pulling action on the hand part, which displacement is moreover combined
with a quite negligible rotation of the hand part about its own longitudinal axis.
The rotation, however, is far less inconvenient than the pivoting movement of the
hitherto known grips with a free end about the rubber body by which they are connected
to the machine tool.
[0012] The design of the machine handle device disclosed in the claim furthermore implies
that there is a comparatively long lever arm between the vibration source and the
hand part of the handle device, as said path is folded twice about the pivotal joints
formed by the rubber bodies. The improvement of the purely kinematic characteristic
of motion of the machine handle device is thus accompanied by improvements in the
dampening properties. Practical experience moreover shows that in torsion rubber
shows dampening and resiliency properties which are highly adapted to the present
purpose.
[0013] In the preferred embodiment of the invention disclosed in claims 2 and 3 where either
rubber body is a cylindrical ring which surrounds an axle and which is surrounded
by a cover, the connecting area between the rubber bodies and the adjoining parts
is comparatively large which increases the durability of the machine handle. In the
embodiment of the invention disclosed in claim 4 where the axis of the hand part lies
at a small distance from the plane wherein the axes of the rubber bodies are situated,
in a direction away from the machine tool, it is attained that by applying a light
pressure in a direction towards the work place of the machine tool, the hand part
will take a position in the middle between the rubber bodies whereby the transmission
ratios of the vibrations from the machine tool to the hand part due to the configuration
of the various levers will be the most favourable ratios possible.
[0014] The embodiment of the invention disclosed in claim 5 discloses a simple design of
a hand part which may be grasped with both hands.
[0015] The invention will be further explained in the following with reference to the accompanying
drawings wherein
Fig. 1 is a simplified side view of a vibration dampened machine handle,
Fig. 2 is a top view of the same device as in Fig. 1,
Fig. 3 is a front view of the machine handle including control elements for starting
and stopping the machine tool, and
Fig. 4A and
Fig. 4B are simplified views of alternative embodiments of a machine handle according
to the invention where it is the axles of the torsion springs which are interconnected
instead of the covers.
[0016] Figs. 1 and 2 show a vibration dampened machine handle in an end view and a top view,
respectively. In the drawing screws and other components for assembling individual
units have been left out to facilitate the survey.
[0017] The main units of the machine handle are two axially sym metrical rubber springs
1 and 2 the axes of which extend parallelly to each other and with a grip 3 extending
between the rubber springs. The device comprised by the rubber springs and the grip
is secured to two retaining plates 4 which are connected to a machine tool which is
not shown in detail.
[0018] Both rubber springs 1 and 2 consist of a cylinder shaped rubber body 5 which surrounds
an axle 6 and which is surrounded by a cover 7. The rubber body 5 is fixedly connected
to the axle 6 and the cover 7 so that it is torsion loaded when the axle 6 and the
cover 7 are turned relative to each other about the axis of the rubber body. In the
drawing the parts forming the second rubber spring 2 are shown by reference designators
provided with an apostrophe.
[0019] The two rubber springs 1 and 2 are connected via an intermediate member which in
the shown embodiment of the invention consists of two connecting plates 8 and 9 that
are welded to the opposite sides of the covers 7, 7′.
[0020] As will appear from Fig. 2, the axle 6 of the first rubber spring 1 is secured to
the retaining plates 4 of the machine tool which is provided with two inwardly bent
supporting webs 10. The second rubber spring 2 is connected to the grip 3 via two
transverse mounting fittings 11 which extend transversely to the grip 3. In order
to facilitate the mounting of the individual parts relative to each other the axles
6, 6′ in the rubber springs 1 and 2 are formed with rectangular ends.
[0021] The machine handle shown in the drawings is used for pressing the machine tool (not
shown) in a direction towards the work place. This is effected by pressing the grip
3 in the direction shown by an arrow indicated by the reference numeral 12 in Fig.
1. The force action on the grip 3 causes the axle 6′ in the rubber spring 2 to turn
a little in the direction indicated by the arrow 13, and the cover 7 of the rubber
spring 1 turns a little in the direction indicated by the arrow 14. The turning of
the cover 7 in the direction of the arrow 14 causes the centre in the rubber spring
2 to travel a distance on a circular path about the centre in the rubber spring 1.
The rubber spring 2 therefore approaches the machine tool somewhat against the opposite
torsion moment built up thereby in the rubber body. Conversely, the grip 3 describes
a circular path about centre in the rubber spring 2 against the torsional moment thereby
built up in the rubber body 5′, said moment operating opposite the turning as shown
by reference numeral 13.
[0022] The aggregate effect of the described movements is that both the rubber spring 2
and the grip 3 approach the machine tool 4 a little under the effect of the force
indicated by the arrow 12.
[0023] The movement made by the grip 3 is composed by two oppositely directed circular
arc shaped movements in such a manner that the grip will approximately move on a straight
line. It is therefore a parallel displacement of the grip 3 in the direction 12. i.e.
in the direction towards the work place.
[0024] The design of the machine handle shown in Figs. 1 and 2 therefore means that the
angle between the longitudinal axis of the grip 3 and the machine tool is not changed
when pressing the machine tool in a direction towards the work place. This implies
a very pleasant handling of the machine tool since the operator may apply his full
weight in the pressure without thereby having to change the angular position of his
wrists relative to the tool.
[0025] The torsional rigidity in the springs 1 and 2 is substan tially determined by the
properties of the rubber body and may be freely fixed by the production thereof. The
dimensioning should be such that the grip 3 lies approximately halfway between the
two connecting plates 8 and 9 when the machine tool is used. This produces a wide
clearance of movement for the grip 3 in both directions.
[0026] The design of the machine handle shown in Figs. 1 and 2 moreover brings along the
advantage that the grip 3 will strike the upper connecting plate 8 when the machine
tool is lifted in a direction opposite the arrow 12. The operator is thereby given
the impression that the grip is firmly secured and solid and the machine tool may
be handled highly accurately and purposefully. Finally it should be mentioned that
there is a comparativly long way for the vibrations 15 produced by the machine tool
to be transmitted to the grip 3. The grip 3 is arranged on a comparatively long lever
arm which contributes to make the vibrational dampening in the machine handle quite
effective.
[0027] In Fig. 3 the machine handle is shown in a view in the direction indicated by III
in Fig. 2. Some units have been left out in Fig. 3 to facilitate the survey and moreover
various control means for starting and stopping the machine tool have been included.
[0028] As will appear from Fig. 3, the grip 3 is provided with a release pawl 16 which is
pivotable about an axle 17. The pawl 16 engages a release pawl 18 which is pivotably
suspended in a bearing 19 on the retaining plates 4 which are in connection with
the machine tool. The release pawl 18 exerts a pressure on a starting button 20 starting
the machine tool.
[0029] Due to the design of the machine handle the vibrations of the machine tool are practically
exclusively converted into vertically reciprocating parallel displacements of the
grip 3. The pawl 16 thus slides up and down the pawl 18 but at no time is there any
risk that the machine tool will stop because of the fact that the release mechanism
on the grip 3 moves relative to the machine tool during the work. When the machine
tool is to be stopped, the hold on the lever 21 on the pawl 16 is released whereby
the release botton 20 which is spring loaded in the direction shown by the arrow 22
will swing both the pawl 18 and the release handle 16 in a direction towards the disengaged
position.
[0030] The design of the machine handle thus makes it possible to provide a very simple
solution ot the problem of designing the actuator mechanism on a vibration dampened
machine handle.
[0031] Figs. 4A and 4B show two alternative embodiments of vibration dampened machine handles
according to the invention. In these two embodiments it is the axles of the rubber
springs which are interconnected instead of the covers in that the covers then serve
as connecting units to the machine tool and the grip, respectively. The embodiment
shown in Fig. 4B will particularly be advantageous in cases where the grip is designed
to be gripped by one hand only.
[0032] Having read this specification it will be obvious to a person skilled in the art
that the rubber springs 1 and 2 may either be designed with through-going axles or
with an axle journal vulcanised into both ends. The specific design shown in the drawings
of the individual structural components of the machine handle is moreover merely
to be understood as examples in that the individual parts will always have to be
adapted to the constructional limits set by the machine tool in question.
1. Vibration dampened machine handle by which a machine tool such as a hydraulic hammer
may be pressed in a direction towards a work place and which comprises a grip which
is connected to an intermediate member via a first body made of rubber or similar
material, said intermediate member being connected to the machine tool via a second
body made of rubber or similar material,
characterised in that the rubber bodies (5,5′) used to provide resiliency are axially symmetrical
and mounted in such a manner that their axes extend parallelly to each other in a
plane which is transverse to the direction (12) in which the machine tool is pressed
towards the work place, that the grip (3,11) and the intermediate member (8,9) are
connected to the first rubber body (5′) in such a manner that they are turned relatively
to each other about the axis of the first rubber body (5′) under torsional stress
thereof when the machine tool is pressed towards the work place, that the intermediate
member (8,9) and the machine tool are connected to the second rubber body (5′) in
such a manner that they are turned relatively to each other about the axis of the
second rubber body (5′) under torsional stress thereof when the machine tool is pressed
towards the work place, that the grip (3,11) comprises a substantially axially symmetrical
hand part (3) extending in parallel to the axes of the rubber bodies (5,5′), said
hand part (3) being connected to the first rubber body (5′) via at least one transverse
part (11) and that the hand part (3) is arranged in such a manner relative to the
rubber bodies (5,5′) that a line extending from the axis of the hand part (3) in
the direction (12) towards the work place intersects the plane, wherein the axes of
the rubber bodies (5,5′) are situated, between said axes.
2. Machine handle according to claim 1, characterised in that either rubber body (5,5′) is a cylindrical ring which surrounds an axle (6,6′)
and which is surrounded by a cover (7,7′), that the intermediate member (8,9) extends
between the covers (7,7′), and that the grip (3,11) is connected to the axle (6′)
of the first rubber body (5′) and the machine tool is connected to the axle (6) of
the second rubber body (5).
3. Machine handle according to claim 1, characterised in that either rubber body (5,5′) is a cylindrical ring which surrounds an axle (6,6′)
and which is surrounded by a cover (7,7′), that the intermediate member (23) extends
between the axles (6,6′), and that the grip (3,) is connected to the cover (7′) of
the first rubber body (5′) and the machine tool is connected to the cover (7) of the
second rubber body.
4. Machine handle according to one of claims 1-3, characterised in that the axis of the hand part (3) lies at a small distance from the plane wherein
the axes of the rubber bodies (5,5′) are situated, in a direction away from the machine
tool.
5. Machine handle according to one of claims 1-4, characterised in that the hand part (3) is longer than the rubber bodies (5,5′) and has two free
ends covered by rubber or similar material.