Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
- 2 -
BACKGROUND OF THE INVENTION
The present invention relates to an excavator which
employs a clamshell bucket as an e~cavating head.
As a relatively small-sized excavator is known an
excavator ~hich has a base structure including a vehicle
structure such as a caterpillar tractor, a boom having a
lower and an upper end and pivotally supported at the lower
end by the base structure around a first axis, an arm having
a root and a tip end and pivotally supported near the root
end by the upper end of the boom around a second axis, a
clamshell bucket which includes a hydraulically operated
shell opening and closing mechanism and which is attached to
the tip end of the arm, a means for turning the boom relative
to the base structure around the first axis, and a means for
turning the arm relative to the boom around the second axis.
Although an excavator of this type has advantages that it is
simple in structure and easy to operate, it has the drawback
that the depth of excavation available by this excavator,
which is determined by the total length of a link mechanism
composed of the boom, the arm, and the clamshell bucket, is
relatively small.
In this case, of course, the depth reached by the
clamshell bucket would be optionally increased if the clamshell
bucket were suspended via a piece of rope or the like from
the tip end of the arm. However, in such a case it will not
be possible directly to load earth or the like excavated by
the clamshell bucket onto a dump truck or other transporting
means, and perhaps the clamshell bucket will not even be
directly lifted up out of the hole. In other words, the
stroke of the bucket is not increased by this suspension.
SUMMARY OF THE INVENTION
It is therefore the object of the present inventlon to
. ,- .
: : , : . . :- ., .
:~ , : . . ,. - : .
, '
. ` ' .
~ 3 -
~2~ 7~i
provide an excavator which is comparable in simplicity of
structure and ease of operation to the aforementioned conventional
excavator having a base structure, a boom, a clamshell
bucket, and means for operating the boom and the arm, and
yet which provides a substantially larger depth of excavation
than the aforementioned conventional excavator.
In accordance with the present invention, the abovementioned
object is accomplished by an excavator comprising: a base
structure; a boom having a lower and upper end and pivotally
supported around a first axis at its lower end by the base
structure and inclining in a certain direction; a means for
turning the boom around the first axis with respect to the
base structure; an arm having a root and a tip end and
pivotally supported around a second axis near its root end
by the upper end of the boom; a means for turning the arm
around the second axis with respect to the boom; a clamshell
bucket having a suspension frame and a rope-operated shell
opening and closing mechanism; a first pulley and rope
system including a first pulley mounted rotatably at the tip
end of the arm, a second pulley mounted rotatably on the
boom at a position substantially distant from the first
axis, and a first rope, which is connected at one of its
ends to the suspension frame of the clamshell bucket, and
which is extended over, in order from this end, the first and
- second pulleys, and which then bears against the base structure
at a base bearing point substantially distant from the first
axis and spaced therefrom in the direction of inclination of
the boom, the force of its tension being supported by the
base structure at this base bearing point, and which is
connected at its other end to either the base structure or
the boom; and a second pulley and rope system including a
third pulley mounted rotatably at the tip end of the arm
substantially coaxially with the first pulley, a cylinder-
piston actuator having a fixed and a movable end and supportedat the fixed end by the arm, a fourth pulley mounted rotatably
~ ~ " ~ ~ .
~L~%~ 7~
at the movable end of the actuator, a fifth pulley supported
by the arm, a sixth pulley supported by the boom substantially
coaxially with -the second pulley, and a second rope, which
is connected at one of its ends to the shell opening and
closing mechanism, and which is extended over, in order from
this end, the third, fourth, fifth, and sixth pulleys, and
which then bears against the base structure at a point
substantially the same as the base bearing pointl and which
is connected at its other end to either the base structure
or the boom.
-
In an excavator of the aforementioned structure, as theboom is inclined from a relatively upright position downwards
towards the horizontal, and further downwards towards a
downwardly inclined position, so as to lower the clamshell
bucket to the bottom of a hole to be excavated, the spans of
the first and second ropes extended between their fixed end
points and the second and sixth pulleys, respectively, are
gradually shortened, so that the spans of the first and
second ropes extended between the first pulley and the
suspension frame of the clamshell bucket and between the
third pulley and the shell opening and closing mechanism of
the clamshell bucket, respectively, are gradually increased,
whereby the maximum depth which can be reached by the clamshell
bucket is correspondingly increased.
In order to magnify the effect of increasing excavating ~-
depth obtained by the excavator of the present invention,
the first and second pulley and rope systems may further
comprise first and second sheave systems respectively,
extended between a point on the base structure substantially
remote from the first axis and a point on the boom substantially
remote from the first axis, so that the first and second
ropes are conducted through the first and second sheave
systems in their parts between the second and sixth pulleys
and their said other ends, xespectively.
; . .
.
.. . .
-~ 5
7~ii
When the said other ends of the first and second ropes
are connected to the base structure, the bearing points of
the ropes on the base structure may be the connecting points
of the ropes to the base structure. On the other hand, when
the said other ends of the first and second ropes are connected
to the boom, the bearing points of the ropes on the base
structure need to comprise pulleys which support the first and
second ropes from the base structure.
When the first and second sheave systems are provided,
the second and sixth pulleys may be integrated in the first
and second sheave systems, respectively. Further, the first
and second sheave systems may be integrally combined.
The second pulley and rope system may further comprise
a third sheave system extended between the tip end of the
arm and the movable end of the cylinder-piston actuator, so
that the second rope is conducted through this third sheave
system in its part between the third and fifth pulleys,
whereby the output force required for the cylinder-piston
actuator is increased, but its piston stroke decreases.
In an excavator of the abovementioned structure, the
deepest possible excavation is performed when the boom is
inclined downwards to its extreme position, and the arm is
extended vertically downwards. In this state of operation,
the first and the second ropes, if they were directly extended
between the first and the second pulleys and between the
fifth and sixth pulleys, respectively, would interfere with
the edge of the hole. In view of this, it is desirable that
the first and second pulley and rope systems should further
comprise seventh and eighth pulleys respectively, rotatably
supported by the arm, so that the first rope is extended
over the seventh pulley in its part between the first and
second pulleys, while the second rope is extended over the
eighth pulley in its part between the fifth and sixth pulleys.
'
~3~2~3~7~
In order to increase the stability of the clamshell
bucket while it is suspended by the first rope, it is desirable
that the first pulley and rope system should be provided in
duplicate.
BRIEF DESCRIPTION OF T~E DRAWINGS
The present invention will become more fully understood
from the detailed description of several embodiments given
hereinbelow, and the accompanying drawings, which are given
by way of illustration only, and thus are not limitative of
the present invention, and wherein:
Fig. 1 is a side view of an embodiment of the excavator
according to the present invention;
Fig. 2 is a front view of the clamshell bucket and some
related portions in the excavator shown in Fig. 1, as viewed
along an arrow II in Fig. l;
Fig. 3 is a somewhat enlarged side view of the arm
portion of the excavator shown in Fig. l;
Fig. 4 is a front view of the arm portion shown in Fig.
3, as viewed along an arrow IV;
-Fig. 5 is a view similar to a part of Fig. 3, showing a
modificatlon of the structure shown in Fig. 3;
30Fig. 6 is a view which shows the entire pulley and rope
system of the excavator shown in Fig. 1, in development;
Fig. 7 is a diagrammatical perspective view showing the
entire pulley and rope system of the excavator shown in Fig.
1;
Fig. 8 is a view similar to Fig. 1, showing another embodiment
.
.. , . . , ~.
,
,
7 --
~ Z~07~i
of the excavator according to the present invention;
Fig. 9 is a somewhat enlarged side view of the arm
portion of the excavator shown in Fig. 8;
Fig. 10 is a front view of the arm portion shown in
Fig. 9, as viewed along an arrow X;
Fig. 11 is a view which shows the entire pulley and
rope system of the excavator shown in Fig. 8, in development;
and
-
J Fig. 12 is a diagrammatical perspective view showing
the entire pulley and rope system of the excavator shown in
15 Fig 8.
DESCRIPTION OF THE PREFERRED E~sODIMENTS
Referring first to Figs. 1 and 2 for the general structure
20 of the excavator according to the present invention, this
excavator comprises a base structure 10, which, in this
embodiment, is a vehicle body equipped with caterpillar
tracks. A boom 11, which in this embodiment has a slightly
bent shape, and which has a lower end lla and an upper end
25 llb, is pivotally supported at the lower end lla by the base
structure 10, via a pivot shaft 10a, around a first axis.
The boom 11 is rotated around the pivot shaft 10a relative
to the base structure 10 by a hydraulic cylinder-piston
actuator 12 mounted between the base structure 10 and the
30 boom 11 by pivot shafts 12a and 12b. At the upper end llb
of the boom 11 is pivotally supported the root end 14a of an
arm 14, via a pivot shaft 13, about a second axis. The arm
14 is rotated around the pivot shaft 13 relative to the boom
11 by a hydraulic cylinder-piston actuator 15, which is
mounted between the boom 11 and the very extremity of the
root end 14a of the arm 14 by pivot shafts 15a and 16. The
arm 14 has a tip end 14b, from which a clamshell bucket 30
.
,
.-
is suspended as explained in detail hereinunder.
Turning now to Figs. 3 and 4, together with Figs. 1 and2, a pulley and rope system incorporated in the arm portion
of the excavator will be explained. 40 designates generally
a means for opening and closing the clamshell bucket 30.
This means includes a hydraulic cylinder-piston actuator 20,
which has a fixed end 20a which is pivotally mounted to the
arm 14 by a pivot means 16a, and a movable end 20b connected
with an oblique block 41 by way of a fitting 49. The oblique
block 41 has a base plate 41a, and opposite side plates 41b,
41b between which are rotatably mounted three obliquely
aligned pulleys 48a, 48b, and 48c properly spaced from each
other by a shaft 47 supported by said side plates at opposite
ends thereof and spacer means not shown in the figure.
On the upper surface of the arm 14 and adjacent to its
tip end 14b is mounted a straight pulley block 51 by its
bottom plate 51a, from which are supported a pair of side
plates 51b, 51b, between which are rotatably mounted three
straight-aligned pulleys 53a, 53b and 53c properly spaced
from each other by a shaft 52 supported by said side plates
at opposite ends thereof and by spacers. The obliquely
aligned pulleys 48a, etc. and the straight-aligned pulleys
53a, etc. form mutually co-operating pulley systems, wherein
these pulleys are so arranged that the peripheral portions
closest to the viewer, as seen in Fig. 4, of the grooves of
the pulleys 48a - 48c are in alignment with the peripheral
portions closest to the viewer, as seen in Fig. 4, of the
grooves of the pulleys 53a - 53c, respectively, while the peripheral
portions furthest from the viewer, as seen in Fig~ 4, of the
grooves of the pulleys 48a and 48b are in alignment with the
peripheral portions furthest from the viewer, as seen in
Fig. 4, of the grooves of the pulleys 53b and 53c, respectively.
From the tip end 14b of the arm 14 are extended a pair of
side plates 54, 54 in parallel to each other, by which are
supported shafts 61 and 62. At the outside and the inside
:
.
~ 9
~2~7~
of the side plates 54, 54 are provided pulleys 63a, 63b,
63c, and 63d rotatably supported by the shaft 61 and properly
spaced from each other by proper spacing means. In tnis
case, the pulley 63b i5 in alignment with the pulley 53a,
while the pulley 63c is in alignment with the peripheral
portion furthest from the viewer, as seen in Fig. 4, of the
groove of the pulley 48c. In alignment with the pulleys
63a, 63b and 63d are provided three pulleys 65a, 65b, and
65c rotatably supported by the shaft 62 and properly spaced
from each other by proper spacing means.
~ A rope guide frame 70 having a pair of side plates 70a,
70a and a trans~erse plate 70b is connected to the shaft 61
so as to be rotatable therearound by the side plates 70a
being pivotally mounted to the shaft 61. The transverse
plate 70b of the rope guide frame has an opening defined by
a bush 71 which is in alignment with the pulley 63b, and two
other openings defined by bushes 72, 72 which are in alignment
with the pulleys 63a and 63d, respectively.
As a modification of these structures, as shown in Fig.
5, a common bracket 68 which supports the shafts 52, 61 and
62 all together may be provided, so that the common bracket
is mounted to the tip end 14b by fittings 18a and l9a.
Returning again to Fig. 3 and further referring to Fig.
6, on the lower face of the arm 14 between the second axis
at 13 and the tip end 14b of tne arm is mounted a frame 74
with its bottom plate 74a, from which a pair of side plates
74b, 74b are extended. A shaft 75 is supported by the side
plates 74b, 74b at its opposite ends, and three pulleys 76a,
76b, and 76c are rotatably mounted on the shaft 75 and are
properly spaced from each other by spacing means~ In this
case, as shown in Fig. 6, the pulleys 76a, 76b, and 76c are
aligned with the pulleys 63a, 63c, and 63d, respectively.
:. ` , -
,~ , , . ,. . . :
' , '. . ,
,
:
,
--- -- 10 --
~L~%~7$
Referring to Figs. 1 and 6, a bucket stroke-magnifying
mechanism generally designated by 80 is a plurality of
sheave systems, and comprises a pair of frames 81 each
supporting a pivot pin 82, a frame 83 includiny a bottom
plate 83a and side plates 83b, a shaft 8~ supported by the
side plates 83b, pulleys 85a, 85b, 85c, 85d, 85e, and 85f
rotatably supported by the shaft 84 and properly spaced from
each other, a pair of frames 86 each supporting a pivot pin
87, a link element 88 pivotally connecting the frame 83 to
the base structure 10 by way of the pivot pins 82 and 87, a
frame 89 having a bottom plate 89a and side plates 89b
extending at right angles from the base plate 89a and mounted
to a middle portion of the boom 11, a shaft 90 supported by
the side plates 89b, pulleys 91a, 91b, 91c, 91d, 91e, and
91f rotatably supported by the shaft 90 and spaced properly
from each other by spacing means, and ropes 98a, 98b, and 99
engaged with these pulleys. In this case, the pulleys 85a -
85f are arranged obliquely, so that the peripheral portion
of the groove furthest from the viewer of the pulley 85a and
the peripheral portion of the groove closest to the viewer
of the pulley 85b, each as seen in Fig. 6 (and similarly
hereinunder), are in alignment with the groove of the pulley
91a, the peripheral portion furthest from the viewer of the
groove of the pulley 85b is in alignment with the groove of
the pulley 91b, the peripheral portion furthest from the
v.iewer of the groove of the pulley 85c and the peripheral
portion closest to the viewer of the groove of the pulley
85d are in alignment with the groove of the pulley 91c, the
peripheral portion furthest from the viewer of 'he groove of
the pulley 85d is in alignment with the groove of the pulley
91d, the peri.pheral portion furthest from the viewer of the
groove of the pulley 85e and the peripheral portion closest
to the viewer of the groove of the pulley 85f are in alignment
with the groove of the pulley 91e, and the peripheral portion
furthest from the viewer of the groove of the pulley 85f is
in alignment with the groove of the pulley 91f. The wire
.,
. :. ~:
.
:
7 E;
98a is connected at its one end to the frame 89 at its wire
holding element 89c and is extended over the pulleys 85a,
91a,- 85b, 91b, 76a, 65a, and 63a, is passed through the bush
72, and is connected at the other end thereof to a wire
holding element 97 of the suspension frame 93 of the clamshell
bucket 30. Similarly, the wire 98b is connected at its one
end to the wire holding element 89c of the frame 89, is
extended over the pulleys 85e, 91e, 85f, 91f, 76c, 65c, and
63d, is passed through the other bush 72, and is connected
at its other end to the wire holding element 97 of the
suspension frame 93 of the clamshell bucket 30. The wire 99
is connected at its one end to the wire holding element 89c
of the frame 89, is extended over the pulleys 85c, 91c, 85d,
91d, 76b, 63c, 48c, 53c, 48b, 53b, 48a, 53a, 65b, and 63b,
is passed through the bush 71, and is connected at its other
end to the shell opening and closing mechanism 95 of the
clamshell bucket 30. In this case, in more detail, the end
portion of the rope 99 is passed through an opening defined
by a bush 94 in the suspension frame 93 of the clamshell
bucket 30, is extended over several pulleys of the shell
opening and closing mechanism 95, and is connected to the
rope holding element 96 of the suspension frame 93. A rope
operated clamshell bucket such as the bucket 30 is itself
well known in the art, and operates in such a manner that,
when the rope 99 is pulled out from the shell opening and
closing mechanism 95, the clamshell is closed, and when the
rope 99 is fed to the shell opening and closing mechanism,
the clamshell opens.
The abovementioned arrangement of the ropes 98a, 98b,
and 99 is shown in ~ig. 7 in a diagrammatical perspective
view. By this arrangement of pulleys and ropes, when the
clamshell bucket 30 is opened by the rope 99 being loosened
by expansion of the hydraulic cylinder piston actuator 20,
the clamshell bucket 30 is suspended substantially by the
pair of ropes 98a and 98b, and, when the clamshell bucket 30
,: ~ ; ~,
~, .. '
.Zi~3~7~i
- 12 -
is closed by the rope 99 being tightened by contraction of the
actuator 20, the clamshell bucket 30 and generally the load
supported by the bucket are suspended by the rope 99, while the
pair of ropes 98a and 98b are maintained in a slightly loosened
condition so that full closing of the bucket is ensured.
In operation, when the boom 11 is gradually more inclined
from a position such as shown in Fig. 1, so as to lower the bucket
30 to the bottom of a hole which is being excavated, the distance
between the pulleys 85a - 85f arld the pulleys 91a - 91f is gradually
shortened, whereby more of the ropes 98a, 98b, and 99 is fed to
the span portions of these ropes which extend between the tip of
the arm 14 and the clamshell bucket 30, thereby increasing the
depth of the hole whose bottom can be reached by the clamshell
bucket, as compared with a conventional excavator having comparable
dimensions with regard to the base structure 10, the boom 11, and
the arm 14, under the condition that the bucket which is excavating
the bottom of the hole must of course be taken out of the hole to
dump the excavated matter onto a proper transportation means such
as a dump truck or the like.
In other words, in the excavator according to the present
invention, if the relative position between the boom 11 and the
axm 14 is maintained constant, when the boom ll is rotated around
the first axis about the pivot shaft lOa by means of the cylinder-
piston actuator 12, the bucket 30 mo~es up and down for more than
the up and down shift traversed by the tip end of the arm 14.
Thus the excavator of the present invention can excavate a deeper
hole than a conventional excavator having a similar structure
composed of a base structure such as 10, a boom such as 11, an arm
such as 14, and a clamsheIl bucket such as 30 which, however, is
suspended from the tip end of the arm by a simple suspension
; means, wherein all these structural members have similar dimensions
to those of the excavator of the present invention. In this case,
it is important that the parts of the first ropes 98a and 98b and
of the second rope 99 which are extended between the clamshell
bucket and the first and third pulleys, respectively, are increased
~,
.
,
, ~ : , ,:: , .
,
.
~.~2~
- 13 -
or reduced substantially in coincidence with each other due to
change of inclination of the boom 11. This is ensured by the
structure that the pulleys 63a, 63b, and 63c are coaxial with each
other, and the ropes 98a, 98b, and 99 are extended through subst-
antially the same paths along the arm and the boom.
Now, the deepest reach of the bucket 30 is obtained when theboom 11 is inclined downwards as much as possible and the arm 14
is positioned perpendicularly with its tip end 14b pointing
downward. In this state of the excavator, the actual depth of
excavation available is determined by adjusting the length of the
ropes 98a, 98b, and 99 so that the length of the parts of these
ropes extending between the transverse plate 70b of the frame 70
rotatable around the axis of the arm tip end pulleys 63a, 63b, and
63d and the suspension frame 93 of the bucket 30, or in more
detail between the bushes 72 and the rope holding means 97 or
between the bush 71 and the bush 94 is as long as desired, provided
that dimensions of the base structure 10, the boom 11 and the arm
14 have already been determined. In this case, however, a limit
is automatically imposed on the length of these parts, or on the
total length of the ropes, from the conditions that the bucket 30,
after having scooped a load, must be taken out of the hole vertically,
and then must be moved generally sidewards and upwards to reach a
transportation means such as a dump truck. In other words, the
length of the parts of the ropes extending between the frame 70
and the bucket 30, or the total length of the ropes, must be short
enough to ensure the bucket being lifted out of the hole, when the
arm 14 is pointing downwards and the boom ll has been raised up as
high as possible by operation of the cylinder-piston actuator 12.
In this connection, however, a further limit is imposed on the
lengths of the ropes from the condition that, since the ropes
extending between the frame 70 and the bucket 30 are further wound
up over the arm tip end pulleys 63a, 63b, and 63d, as the arm 14
is then raised up, in order to move the bucket 30 from the position
35 where it has just been taken out from the hole to the position
where it has been located on a transportation means, at least this
: . .; : :
. , :: ,... ..
:........... :. : -
~ . : , . .:. ..
. .
.
:
..
- 14 -
winding up clearance must be left as the length of the ropes which
extends between the frame 70 and the bucket 30 when the bucket 30
is located at a position where it has just been taken out from the
hole, otherwise the bucket 30 would interfere with the frame 70
during further lifting of the bucket towards the next transportation
means, thereby obstructing said further lifting of the bucket.
The abovementioned further winding up of the ropes in the
process of transferring the bucket from the outlet of the hole to
the transportation means is mostly due to the structure that the
rotary axis of the pulleys 76a, 76b, and 76c supported by the arm
14 is relatively distant from the axis at 13 of the pivoting of
the arm 14 relative to the boom 11, and that the ropes are extended
from the tip end of the arm 14 towards the bucket 30 over the
outside peripheral portions, as seen from the side of the boom 11,
of the pulleys 63a, 63b, and 63d rotatably supported at the tip
end of the arm.
These problems are obviated in the excavator shown in Figs.
8 - 12, which is a second embodiment of the present invention. In
this second embodiment, pulleys 176a, 176b, and 176c, which have
their rotary axes aligned with the second axis at 13 of pivoting
the arm 14 relative to the boom 11, are provided to replace the
pulleys 76a - 76c in the first embodiment shown in Figs. 1 - 7.
In this connection, as will be better understood from Fig. 11, a
pulley 179 is additionally provided to co-operate with the pulley
176b for the convenience of the mechanical structure at the
pivoting portion between the boom 11 and the arm 14. By this
arrangement, the length of the parts of the ropes extended between
the pulleys 91b, 91d, and 91f supported at a middle portion of the
boom 11 and the pulleys 63a, 63~, and 63d supported at the tip end
of the arm 14 is maintained substantially constant regardless
of pivoting action of the arm 14 relative to the boom 11. Further,
in the second embodiment shown in Figs. 8 - 12, the ropes 98a,
98b, and 99 are extended from the tip end of the arm 14 towards
the bucket 30 over the inside peripheral portions, as seen from
,, .
,
37~
- 15 -
the side of the boom 11, of the pulleys 63a, 63b, and 63d, by co-
operation of pulleys 153a, 153b, and 153e, some of which replace
the pulleys 53a - 53c, while the others are newly provided. By
this arrangement, as the arm 14 is raised up in the process of
further lifting the bucket 30 from the outside of the hole towards
the next transportation means like a dump truck, the ropes are
unwound from the pulleys 63a, 63b, and 63d so as to feed the ropes
to their parts extended between the frame 70 and the bucket 30.
Thus, in the second embodiment shown in Figs. 8 - 12, the
minimum length required for the parts of the ropes extended
between the frame 70 and the bucket 30 when the bucket has just
been taken out of the hole is reduced. This means that the height
of the tip end of the arm 14 from the level at the outlet of the
hole at the moment when the bucket 30 is just taken out of the
hole can be correspondingly reduced, and that, therefore, the
length of the arm can be correspondingly increased, whereby the
reach of the tip of the arm can be also correspondingly increased.
In Figs. 8 - 12, which correspond to Figs. 1, 3, 4, 6, and 7,
; respectively, the portions in the second embodiment corresponding
to those in the first embodiment are designated by the same
reference numerals as in the figures showing the first embodiment.
In this connection, particularly referring to Figs. 9 and 11, 178
is a shaft which rotatably supports the pulley 179 and is in turn
supported at its opposite ends by a pair of side plates 177b which
extend at right angles from a base plate 177a mounted to the boom
11 adjacent to its tip end.
With respect to the basic structure and function explained
with reference to the first embodiment shown in Figs. 1 - 7, it
will be obvious that the second embodiment shown in Figs. 8 - 12
has the same basic structure and operates in the same manner as
the first embodiment.
.,,, . - - ~,: : ,
:
`: ~ :'
- 16 -
The embodiments of the presen-t invention shown above have
comprised a pulley sheave system fixed between the boom and the
base structure with both of its mounting points remote from the
first axis, and by this arrangement, when the boom is rotated
relative to the base structure and the distance between these
mounting points changes, the pulley sheave system has amplified
this change of distance, so that the change of distance be-tween
the clamshell bucket and the tip of the arm has been large, and
accordingly the maximum depth of the hole which can be dug has
been increased. However, it should be noted that this effect of
distance amplification is not strictly necessary for the operation
of the present invention, although it is beneficial. It would be
possible to provide the first and second ropes, after they have
passed over the pulleys attached to the boom, as directly connected
to the base structure without being passed over any other pulleys.
In this case there would be no effect of amplification of the
change of distance between this fastening point and the boom-
mounted pulleys, but this change of distance would be directly
applied to the parts of the ropes between the tip of the arm and
the bucket. Also, it would be possible to provide the first and
second ropes, after they have passed over the pulleys attached to
the boom, as passing over pulleys attached to the base structure
at a point remote from the first axis, and then as fixed to a
point on the boom remote from the first axis. In this case there
would be an effect of amplification of the change of distance
between these two points by a factor of two only. All of these
described possibilities, as well as the two embodiments described
in detail above, embody the principle of the present invention:
that change of distance between a point on the base structure and
a point on the boom, as the boom is inclined relative to the base
structure, is applied to the span of ropes betwen the tip of the
arm and the bucket, in order to increase the effective stroke of
the bucket.
Although the invention has been shown and described with
reference to a preferred embodiment thereof, it should be understood
that various changes and omissions of the form and detail thereof
may be made by one skilled in the art, without departing from the
scope of the invention.
:
' ' ' ' " ` ' ' . ~
