Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Grapple System for Loq Skiclder
I'echnical Field
This invention relates to a load skidding
vehicle of the type having a load enyaging grapple, and
more particularly to a mechanism for controllably
positioning and releasably locking the grapple with
respect to the vehicle in a number of operating
positions.
Background Art
In certain classes of hauling operations, such
as moving harvested trees from their felling point to a
collection point, there is often no feasible means of
transpor~ing a load other than by dragging it behind a
vehicle. This is generally accomplished either by
attaching the load to ~ load skidding vehicle with a
cable or by grasping the load with a grapple suspended
from an elevated support boom borne by the vehicle.
Basic examples of grapple assemblies for use in load
skidding applications are set forth in U.S. Patent
3,620,394 which issued to Symons et al. on November 16r
25 1971 and U.S. Patent 3,513,998 which issued to Stone et
al. on May 26, 1970.
I~he prime disadvantage of existing grapple
skidders as opposed to cable skidders is that design
strictures of the former necessitate that the grapple
be pivotally connected to its support boom at a pivot
point substantially above and behind the rear axle of
the skidder. This results in the load being borne by
the vehicle at this pivot point, this being the first
point through which the load passes which is also
rigidly connected to the skidding vehicle. This
loading imposed upon the skiddiny vehicle may be
described by a load vector having essentially two
components both of which pass through the support
boom-grapple pivot point. The first, rearwardly
directed from and parallel to the longitudinal axis oE
the skiddiny vehicle, is the force required to overcome
friction between the load and the ground across which
it is skidded. The second, vertical and downwardly
directed, is that portion of the weight of the load
borne by the grapple.
As this load vector passes through a
rearwardly extended elevated position, a substantial
overturning moment exists about the rearmost ground
contacting point of a loaded skidding vehicle.
Conse~uently, current grapple skidders lose
maneuverability when skidding a load. For those
grapple skidders including a plurality of axles, the
rearmost axle will suffer disproportionately great
loading. Moreover, aside from the reduction in
maneuverability there is a relatively low limit on the
size of the load that can be carried with a grapple
skidder. In some instances a load easily handled by a
cable skidder will, if attempted with a grapple skidder
of equivalent power, lift the front of the grapple
skidder from the ground.
Efforts have previously been made toward the
solution of these problems. One scheme involves the
use of a force applying arm attached to the vehicle for
applying a downward force on the loacl at a point
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rearwardly located from the yrapple. Activating the
arm provides a reactive force tending to equalize the
weight distribution on the axles of the vehicle. This
development is disclosed in U.S. Patent 4,140,233 which
issued to Muntjanoff et al. on February 20, 1979.
Another manner of mitigating the problems
detaile~ above involves fastening a cable from the boom
supported grapple to the vehicle such that the cable
may be placed in tension under load con~itions and made
slack under no load conditions. This results in the
load being primarily carried by the cable thereby
lowering the load vector and consequently decreasing
the distance or moment arm from the rearmost point of
skidder-ground contact to the load vector. Decreasing
the moment arm decreases -the overturning momen-t
resulting in increased stability. This scheme is
described in U.S. Patent 3,746,193 which issued to
Eaves on July 17, 1973. Among the disadvantages of
this advance are the need to include a winch on the
skidding vehicle and the difficulties presented in
achieving free rotation of the grapple about its
vertical axis owing to the at-tached cable.
~ nother problem that is common in conventional
grapple type load skidding vehicles is that they permit
free swinging movement of the grapple when the vehicle
is travelling without a load. This movement of the
grapple about its pivot point is often severe enough
that the grapple comes in contact with some portion of
the vehicle, occasionally resulting in damage. A means
of preventing -this involves snubbing the grapple to the
back of the skidding vehicle by means of a cab]e and
winch assembly. Such a scheme is set forth in U.S.
Patent 3,907,137 issued to Korbel et al. on September
23, 1975. The significant disadvantages of this
development are the necessity for a winch and a
potentially obstructing cable.
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The present invention is directed to
overcoming one or more of the problems as set forth
above.
Disclosure of the Invention
In one aspect of -the present invention a load
skidding vehicle is provided with a boom pivotally
mounted thereon and a load yrasping device rotatably
and pivotally connected to the boom. There is also
provided a mechanism for releasably locking and
controllably positioning the grasping device with
respect to the boom such that the grasping device may
be controllably rotated or locked against movement in a
direction aligned with the longitudinal axis of the
vehicle.
Brief Description of the Drawings
Fig. l is a side view of a load skidding
vehicle showing a load control mechanism embodying the
present invention mounted on a parallelogram type
grapple support assembly;
Fig. 2 is a partial top view of the load
skidding vehicle and load control mechanism
corresponding to Fig. l;
Fig. 3 is a partial side view of a load
skidding vehicle with a load control mechanism showing
forward rotation of a grapple owing to extension of the
control cylinder;
Fig. 4 is a partial side view of a load
skidding vehicle with a load control mechanism showing
rearward rotation of the grapple owing to retraction of
the control cylinder;
Fig. 5 is a partial side view of the load
skidding vehicle of Fig. 4 showing downward movement of
the grapple due to the extension of boom cylinder 46;
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Fig. 6 is a partial side view of the load
skidding vehicle of Fig. 5 showing rearward movement of
the grapple due to the extension of arch cylinder 30;
and
Fig. 7 is a side view of a load skidding
vehicle having a load control mechanism embodying the
present invention mounted on an A-frame type grapple
support assembly.
Fig. 8 is a side ~iew of an additional
embodiment of the present in~ention shown mounted on an
A-frame type ~rapple support assembly.
Best Mode for Carrying ~ut the Invention
Referring to Fig. 7, a load control mechanism
is generally indicated by the reference numeral 1 and is
mounted on a load skidding vehicle 2 commonly known as
a "log skidder". The skidder 2 is articulated, having
a ~ront end 4 and a rear end 6 joined by a multiple
a~is pivotal connection 8. The front end 4 has a
chassis 10 and mounted thereon are a wheel assembly 12
power providing means (not shown) and an operator's
station 14 containing controls (not shown) for
operating the skidding vehicle 2.
The rear end 6 has a ~hassis 16 on which are
mounted a wheel assembly 18 and a mounting frame 20.
~ounted on the mounting frame 20 is a support assembly
such as grapple support assembly 29 which is preferably
of the "A-rame" type as shown in Flg. 7.
Alternatively, as shown in Figs. 1-6, a "parallelogram"
type grapple support assembly 29 may be used. These
differ from one another in a manner well known by those
skilled in the art. Vehicles 2 incorporating each of
these typ~s of yrapple support 21 will be discussed
concurrently, as they are very similar. Where there
are differences, these differences will be noted.
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The grapple support assembly 29 is attached by
twin pivotal connections 22 to the rear of mounting
frame 20. This support assembly 29 includes a U-shaped
arch 24 having two arch legs 26 and a crossmember 28
(not shown on Fig. 7) connecting these legs 26. ~rhe
arch 24 is the main support for a boom assembly 84.
Each arch leg 26 ends at its respective pivotal
connection 22. An arch cylinder 30 is pivotally
attached at a first end 32 to an intermediate point 34
of each arch leg 26. A second end 36 of each arch
cylinder 30 is pivotally connected to one of two
forward points 38 on the mounting frame 20, so located
that the arch cylinders 30 are substantially parallel.
The extension of the arch cylinders 30 may be
controllably increased or decreased by means well known
in the art so as to cause the arch 24 to pivot about
its twin pivotal connections 22.
In the "parallelogram"-type grapple support
21, a boom 40 is pivotally connected along a pivotal
axis 41 to the crossmember 28 of the arch 24. In the
"A-frame" type grapple support 21, the boom 40 is
rigidly attached to the crossmember 28. The boom 40
extends rearwardly from the arch 24 for supporting a
grasping device such as grapple assembly 42 and
includes two boom arms 44 which extend rearwardly from
the arch 2~.
In the parallelogram type grapple support ~1,
a pair of boom cylinders 46, each having a first end 48
and a second end 50, are pivotally connected by their
first ends 48 to the boom 40 and by their second ends
50 to the mounting frame 20 such that the two boom
cylinders 46 are substantially parallel. The length of:
the boom cylinders 46 may be controllably increased or
decreased by means well known in the art so as to cause
the boom ~0 to pivot about its connection on the
crossmember 28.
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Pivotally attached a-t a rear pivot point 52 on
-the aftmost portion of the boom 40 is the grapple
assembly 42. The grapple assembly 42 includes a
rotator 54 Lor rotatably positioning the grapple
assembly ~2, grapple arms 56 dependiny from the rotator
54 for grasping loads, a vertical extender 58 attached
to the rotator 54, and means (not shown) for
controllably opening and closing the grapple arms 56.
rrhe rear pivot point 52 passes through the vertical
extender 58.
The vertical extender 58 is pivotally attached
to the uppermost portion of the grapple assembly 42 so
as to allow the grapple assembly 42 to rotate with
respect to the vertical extender 58 along an axis
parallel to the longitudinal axis of the load skidding
vehicle 2. A pivot point 60 for a connecting member 62
is located on the vertical extender 58 a distance above
the rear pivot point 52. This distance must be
sufficiently great as to allow the force appliecl
through the connecting member 62 to create a moment
about the rear pivot point 52 sufficient to counter the
opposite moment induced by a skidded load without
allowing appreciable pivotal movement of the grapple 42
about the rear pivot point 52.
The connecting member 62 is connected at a
first end 64 to pivot point 60 and at a second end 66
to a pivot point 68. Connecting member 62 must be of
sufficient rigidity to withstand the compressive
loading necessary to counter the moment of the load
vector. It is additionally beneficial to orient pivot
points 60 and 68 with respect to the rear pivot point
52 and the arch 24-boom 40 connection such that these
four points approximately define the corners of a
parallelogram.
.
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At pivot point 68 the connecting me:mber 62 is
attached to an upper aft portion of an equalizing link
70. The equalizing link 70 has a lower central point
73 at which it is connected to an upper central point
72 of the crossmember 28. A hydraulic control cylinder
74, having a first end 76 and a second end 78, is
pivotally connected by its first end 76 to a central
forward point 80 on the equalizing link 70. The
equalizing link 70 has the function of rigidly
lQ maintaining the distances bet~een the pivots at 68,72
and 80 such tha,t wikh the arch 24 locked in position
(and consequently point 72 is locked since point 72 is
fixedly attached to arch 24) a force may be transmitted
from the control cylinder 74 to the connecting member
62.
The control cylinder 74 is pivotally attached
at its second end 78 to the mounting frame 20 so that
it lies in a ~ertical plane passing through the
longitudinal axis of the load skidding vehicle 2.
Means (not shown) well known in the art is provided for
operating the control cylinder 74 such that the
distance from the first end 76 of the control cylinder
74 to the second end 78 may be increased, decreased,
maintained at a set length or permitted -to float (that
is, to vary with~minimal resistance). Like means is
included for controlling the boom cylinders 46 and the
arch cylinders 30.
It is apparent from the above described
embodiments that a fluid jack 86 could be connected
immediately intermediate the vertical extender 56 and
the grapple support 21. Such an embodiment is shown in
Fig. 8~ The ~luid jack 82 has first and second ends 88j90,
and is connected by the first end 88 to the vertical
extender 56 and by the second end 90 to the upper central
point 72 of the crossmember 28.
g
Industrial Applicability
The present invention provides a solution to
the difficulties inherent to load skidding vehicles
with freely pivotable load engaging means. The present
embodiment provides means for permitting the grasping
device-boom 40 combination, for the purposes of
skidding operations r to be made e~uivalent to a single
rigid member. The load vector will then pass through a
point lower khan the rear pivot point 52 resulting in a
smaller moment about the rear wheel assembly 18
consequently yielding a more even distribution of the
load between the axles of the load skidding ~ehicle 2.
In the preferred embodiment of this invention
selective immobilization of the grapple 42 with respect
to the boom 40 is achieved by fixing in relation to the
work vehicle 2 two separated points 52,60 on the
grapple assembly 42. While fixing the location of but
a single pivot will not prevent rotation about that
pivot, fixing the locations of two non-colinear pivots
will prevent rotation about either pivot.
The means 62,70,74 for immobilizing the
grapple assembly 42 can assume embodiments other than
that considered the best mode. For example, the
grapple-boom connection 52 could be a pin-type pivot
(as shown in Figs. 1 and 2) wi~h means added for
selectively increasing the friction between the pin and
the two members connected to it to the point where no
rotation is possible under the loadings anticipated.
Operation o~ the load control mechanism 1 that
constitutes the advance of this load skidding vehicle 2
over existin~ designs is achieved through operation of
the control cylinder 74. Contxollable rotation of the
grapple assembly 42 about its rear pivot point 52 is
obtained by increasing or decreasing the length of the
control cylinder 74. This causes the central forward
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pivot point 80, direc-tly attached to the control
cylinder 74, to move, respectively, away from or toward
the mounting frame 20. This serves to rotate the
equalizing link 70 about the pivot point 68
respectively toward or away from the grapple assembly
42. This forces the connecting member 62 to move
rearwardly or forwardly, respectively, resulting in
rotation of the grapple assembly 42 about the rear
pivot 52 toward or away from t~e skidder 2,
respecti~ely. Fig. 3 illustrates the grapple assembly
42 in a forwardly rotated position resulting from
extendi~ the control cylinder 74. ~lg. 4 illustrates
the grapple 42 in a rearwardly rotated position
resulting from retracting the control cylinder 74.
Once the grapple assembly 42 has been rotated
to the desixed angle it may be locked in position.
With the boom assembly 26 locked (achieved by locking
the arch cylinders 30 and also, for the
parallelogram-type grapple support 21, the boom cylinders
46), locking the control cylinder 74 results in
fixing the position of the equalizing link 70 with
respect to the load skidding vehicle 2~ This
immobllizes the position of the pivot point 68 thereby
locking the position of the connecting member 62. Once
this is done, ~he locations with reference to the load
skidding vehicle 2 of the pivot points 60 and 52 are
fixed and consequently the ~rapple assembly 42 is not
free to rotate.
The broad positional flexibility of the
grapple assembly 42 is a major feature o~ the present
embodiment. This is achieved through the combination of
the controllable rotation of the grapple assembly 42
about the rear pi~ot point 52, detailed above, with the
up and down fore and aft positioning capabilities of
the parallelogram-type grapple support assembly 29, the
lat-ter being well known in the art. Fore and aft
movement o~ the grapple assembly 42 is achieved through
control of the arch cylinders 30; extending the arch
cylinders 30 causes movernent of the grapple assembly
away from the vehicle 2, while retracting the arch
cylinder 30 will result in movement toward the vehicle
2. ~n the parallelogram-type grapple support assembly
29, the elevation oE the grapple assembly 42 is altered
through control of the boom cylinders 46. Retraction
of the boom cylinders 46 will raise the grapple
assembly 42 while extension of the boom cylinders 46
will lower it.
A description of the use of the grapple
assembly 42 and grapple support assembly 29 to free the
vehicle 2 when mired in mud will serve to illustrate
the positional capabilities of the present invention.
The following description is applicable to the
parallelogram-type grapple support assembly 29.
Consider the initial grapple assembly 42-work vehicle 2
orientation shown in Fig. 3, a forwardly rotated upper
forward position. This is achieved by retracting both
the arch cylinder 30 and the boom cylinders 46 while
extending the control cylinder 74. From this position,
the grapple assembly 42 is rotated away from the
vehicle 2 by retracting the control cylinder 74 as
illustrated in Fig. 4. Next, the boom cylinders 46 are
extended until the grapple assembly 42 is pressed
firmly into the mud as shown in Fig. 5. Lastly, using
the locked grapple assembly 42 as an anchored point the
arch cylinders 30 are extended forcing the grapple
assembly 42 to move rearwards with respect to the worlc
vehicle 2, or, as is reality, the work vehicle 2 to
move forward in relation to the anchored grapple
assembly 42. The result is shown in E'ig. 60
A prime advantage is the improvement imparted
to the load handling characteristics of a load skiddiny
vehicle. This improvement is achieved by grasping
the load with the grapple assembly 42, positioning it
as near the rear of the vehicle as possible, and locking
the grapple assembly 42 in this position. This
positioning may be achieved in one of two ways: if the
load is suf~iciently light the control cylinder 74
and connecting member assembly 62,58,70 may be used to
rotate the grapple and its load toward the rear of the
vehicle; or, with heavier loads, the load control
mechanism 1 may be placed in float and the vehicle 2
then backed toward the load until the position of the
grapple assembly 42 is as desired at which point the
grapple assembly 42 is locked.
A summary of the advantages detailed in this
application over conventional skidders are as follows-
1) For gi~en loading there is improved
maneuverability.
2) The skidder is capa]ble o handling a
greater total load.
3) When travelling in a no load situation the
grapple can be locked to prevent it from swinging along
the direction of the longitudinal axis of the skidder.
4) When the skidder becomes stuck in swampy
or muddy areas the grapple assembly can be locked,
lowered to the ~round and used to push the vehicle
forward.
5) In the preferred embodiment o this
invention the vertical axis of the grapple can be
controllably rotated about the grapple~boom pivot point
in the vertical plane passing through the longitudinal
axis of the vehicle thereby providing for greater
positional 1exibility.
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6) The load control rnechanism 1 when embodied
as the parallelogram linkage described previously
maintains an essentially constant grapple orientation
so long as the control cylinder 74 is of constant
extension.
The invention herein described is not limited
to use with parallelogram type and A-frame type boom
assemblies such as those illustrated, but is equally
applicable to other types of boom assemblies.
It should be understood that the load skidding
vehicle can assume many other configurations without
departing from the claims. Other aspects, objects and
advantages of this invention can be obtained from a
study of the drawings, the disclosure and the appended
claims.
