METHOD OF HANDLING HARVESTED TREES

METHODE DE MANUTENTION DES ARBRES ABATTUS

English Abstract

ABSTRACT OF THE DISCLOSURE
A method of handling tree trunks is provided.
The tree trunks are loaded on a bunk pivoted on a
transport vehicle with the tree butts in alignment
and projecting to the rear. The tree butts extend far
enough to the rear and the bunk is sufficiently close
to the ground that, upon pivoting of the bunk to bring
the butt ends of the trees to the ground, contact between
the butt ends and the ground occurs before the trees
begin to slip off the bunk. The pivoting of the bunk
is then halted, and the vehicle moves forwardly to
allow the trees to be dragged off the bunk by the fric-
tion with the ground. In this manner, the trees are
deposited on the ground with their ends in alignment.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of handling a plurality of delimbed
tree trunks, which comprises the steps:
a) loading the tree trunks on a bunk
pivotally mounted on a transport vehicle with the
butt ends of the tree trunks in substantial
alignment and projecting to the rear of the bunk, the bunk
being spaced above the ground and being pivotal about an
axis transverse to the direction of motion of the vehicle,
the butt ends being sufficiently far to the rear and the
bunk being sufficiently close to the ground that, upon pivotal
motion of the bunk to rock the butt ends of the tree trunks
down to the ground, contact between the butt ends and the
ground takes place before any of the tree trunks assumes an
angle to the horizontal whose tangent is either the coefficient
of static friction between tree trunks, or the coefficient
of static friction between a tree trunk and the bunk, which
ever is the lesser;
b) transporting the tree trunks to a desired
unloading location,
c) pivoting the bunk to rock the butt ends of the
tree trunks down to contact the ground without any sliding
of tree trunks with respect to each other or with respect
to the bunk,
d) halting the pivoting upon contact between the
butt ends and the ground, and
e) moving the vehicle forwardly while maintaining
the bunk in the position at which it stopped pivoting, to
allow the tree trunks to be dragged fully off the bunk
due to the contact with the ground, while the tree trunks
remain in alignment.
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2. In a method of handling a plurality of delimbed
tree trunks, the steps of:
a) providing a transport vehicle having a loading
bunk with a substantially flat tree trunk supporting
surface, the bunk being pivotally mounted to the vehicle
about a horizontal axis transverse to the direction of travel
of the vehicle, the axis being at a distance
x from the ground, the flat tree trunk supporting surface
being a distance z from the axis as measured along a line
perpendicular to the surface,
loading the tree trunks on the bunk with their butt
ends substantially in alignment and projecting to the rear
of the bunk sufficiently far that the distance y from the
said axis to the butt ends of the bottom tree trunks satis-
fies the equation:
<IMG>
where .delta. is the lesser of:
1) the angle whose tangent is the coefficient of
static friction between tree trunks,
2) the angle whose tangent is the coefficient of
static friction between a tree trunk and
said tree trunk supporting surface;
b) transporting the tree trunks to a desired
unloading location,
c) pivoting the bunk to rock the butt ends of the
tree trunks down to contact the ground without any sliding
of tree trunks with respect to each other or with respect
to the bunk,
d) halting the pivoting upon contact between the
butt ends and the ground, and
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e) moving the vehicle forwardly while maintaining
the bunk in the position at which it stopped pivoting, to
allow the tree trunks to be dragged fully off the bunk
due to the contact with the ground, while the tree trunks
remain in alignment.
13

Description

~08;~537
This invention relates generally to the tree-
harvesting industry, and has to do particularly with a
method for handling delimbed tree trunks in such a manner
that the tree t~unks can be deposited at an unloading location
with their butt ends substantially aligned.
BAC GROUND OF THIS INVENTION
Several of the large types of machines designed
to fell, delimb and handle trees include storage locations
on the vehicle in the form of ~ivoting box arrangements,
known in the industry as bunks. Machines known as feller-
forwarders and loader-forwarders are in this category.
One prior art device capable of felling trees and of trans-
porting the trees in a box-like bunk is disclosed in United
States Patent No. 3,797,541, Kurelek et al issued ~arch 19,
1974 and entitled "Machine for Harvesting and Accumulating
Trees".
While the machine disclosed in United States Patent
~o. 3,797,541 utilizes a tilted bunk with a closed rear end,
there are several machines conventionally utilized in which
the bunk has side walls only, or includes side-retaining
means in the form of upstanding braces or posts along the
side edges. In the latter kind of bunk, there are no retain-
ing means at the forward and rearward end, and the bunk is
capable of assuming a level or substantially horizontal
position for the transportation of the trees, thereby minimiz-
ing longitudinal shifting during the travel of the vehicle.
When the vehicle reaches an unloading location, the
bunk is tilted to the rear, in order to bring the rearward
end of the tree trunks (normally the butt ends) down toward
the ground. However, due to the fact that conventional bunks
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.
are normally located rather high up on the vehicle, the angle
assumed by the tree trunks before contact with the ground
takes place is such that the static friction between
tree trunks or between the tree trunks and the bunk is over-
come, and some or all of the tree trunks begin to slide
relative to each other and relative to the bunk. When the
vehicle pulls forward to leave the tree trunks behind, the
tree trunks are left on the ground without any particular
alignment of the butt ends. The irregular and somewhat
confused pile of tree trunks which results presents certain
difficulties in regard to subsequent forrestry operations,
for example in tallying, assessing species, and so forth.
These subsequent operations would be very much facilitated
if the pile of tree trunks in the bunk could be deposited on
the ground with the butt ends remaining in alignment. The
butt ends would then all be visible simultaneously from a
single position, and the various forms of assessment could
be readily made without having to move trees, uncover buried
butt ends, and so forth. ~-
GENERAL DESCRIPTION OF THIS INVENTION
. ..
In view of the foregoing, it is an aspect of this
invention to provide a method for handling delimbed tree
trunks, which makes it possible to unload a pile of tree
trunks from a bunk with the trees in the same rerative
position as they occupied while sitting on the bunk.
Accordingly, this invention provides a method of
handling a plurality of delimbed tree trunks, which
comprises the steps:
a) loading the tree trunks on a bunk
pivotally mounted on a transport vehicle,
,
. . ~ . . ! ~ , .

with the butt ends of ~iQ~eSe3trunks in ~;ubstantial
alignment and projecting to the rear of the bunk, the bunk
being spaced above the ground and being pivotal about an
axis transverse to the direction of motion of the vehicle,
the butt ends being sufficiently far to the xear and the
bunk being sufficiently close to the ground that, upon pivotal
motion of the bunk to rock the butt ends of the tree trunks
down to the ground, contact between the butt ends and the
ground takes place before any of the tree trunks assumes an
angle to the horizontal whose tangent is either the coefficient
of static friction between tree trunks, or the coefficient
of static friction between a tree trunk and the bunk, which
èver is the lesser;
b) transporting the tree trunks to a desired
unloading location,
` c) pivoting the bunk to rock the butt ends of the
tree trunks down to contact the ground without any sliding
of tree trunks with respect to each other or with respect
to the bunk,
d) halting the pivoting upon contact between the . .
butt ends and the ground, and
e) moving the vehicle forwardly while maintaining ~ :
the ~unk in the position at which it stopped pivoting, to
allow the tree trunks to be dragged fully off the bunk
due to the contact with the ground, whiIe the tree trunks
remain in alignmen~.
GENERAL DESCRIPTION OF THE DRi~WINGS
.
One embodiment of an apparatus adapted to carry
out the method of this invention is illustrated in the
accompanying drawings, in which like numerals denote like
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1083S~7
parts throughout the several views, and in which:
Figure 1 is a perspective view of a simplified
loader-forwarder ~dapted toicarry out the method of this
invention;
Figures 2, 3 and 4 are sequential views showing
sequential steps in the method of this invention; and
Figures 5 and 6 are schematic diagrams showing
the geometric considerations which enter into the method
of this invention.
PARTICULAR DESCRIPTION OF THE DRAWINGS
In Figure 1 is shown a vehicle 10 which includes
a front portion 12 and a rear portion 14 articulated together
as is well known in large, all-terrain vehicles. The
forward portion 12 contains the drive mechanism and controls,
whereas the rearward portion 14 supports a bunk 16 which is
pivotally mounted at an axis 18 with respect to the rearward
portion 14 of the vehicle 10. The vehicle would normally
also include either an articulated loading arm or an articu-
lated felling and loading arm. These additional mechanisms
do not relate in any way to this invention, and have been -
omitted for the sake of simplifying the drawing.
As can be seen in Figure 2, a hydraulic cylinder
20 has its lower end 22 pivotally mounted to the rearward
portion 14 of the vehicle 10, and has its upper end 23, which is
secured to the hydraulic piston, pivoted to the bunk 16
at a location forwardly displaced from the location of the
pivotal axis 18.
The bunk includes a substantially flat tree-
supporting surface (not visible in Figure 1 as it is
covered with tree trunks), from the side edges of which short
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:~t33537
side walls 25 are upstanding. Extending upwardly and out-
wardly at an angle from each side wall 25 are three posts
~7. As is obvious, the function of the posts is to retain
a substantial number of tree trunks on the bunk.
Finally, the vehicle 10 includes an operator's
cab 30, and the usual deep-tread tires 32.
As can be seen in Figure 2, a plurality of
tree trunks 34 are contained upon the bunk 16 with the
butt ends 36 in substantial vertical alignment and project-
ing to the rear of the bunk 16. It is also clear that the
bunk is spaced above the ground level 38 and it will be
understood that in the operation of pivoting the bunk in
the clockwise direction as seen in Figure 2 by extending
the hydraulic cylinder 20, the butt ends of the lowexmost
tree trunks will follow the tra~ectory shown by the
broken-line arrow identified by the numeral 40 in Figure 2.
The essence of the method of this invention is
to ensure that the butt ends 36 of the trees 34 are sufficiently
far to the rear with respect to the pivotal axis 18, having .
regard to the closeness of the bunk to the ground, that, :
upon pivotal motion of the bunk 16 to rock the butt ends
of the tree trunks down to the ground, the butt ends will
contact the ground before any of the tree trunks begin to
slide, either with respect to each other, or with respect to
the bunk.
In more technical language, these conditions are
met by ensuring that the butt ends of the trees are
sufficiently far to the rear with respect to the pivotal
axis 18 that, as the bun~ rocks clockwise (as seen in Figure
2) to bring the tree trunks down to the yround, contact
,
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~8~537
between the butt ends and the ground takes place before
any of the tree trunks assumes an angle to the horizontal
whose tangent is either the coef~icient of static Exiction
between tree trunks, or the coefficient of static friction
between a tree trunk and the bunk, which ever is the lesser.
This will ensure that the tree trunks will
contact the ground at their butt ends in the configuration
shown in Figure 3, with none of the tree trunks sliding
either with respect to each other or with respect to the
bunk 16. Upon achieving the position of Figure 3, the
operator then slowly drives the vehicle forwardly, so that
the contact between the butt ends of the trees and the
ground will exert a drag or restraint on the trees, whereby
the bunk can, in effect, be withdrawn out from under the
trees. Figure 4 shows the vehicle 10 after a certain . ..
degree of travel, almost to the point where the top ends :
` of the tree trunks will clear the bunk 16.
Thus, the method of this invention involves firstly ~.
loading the tree trunks onto the bunk in accordance with the
criteria set out earlier and described with reerence to
Figure 2, then transporting the tree trunks to a desired
unloading location, then pivoting the bunk to rock the
: butt ends of the tree trunks.down to contact the ground with-
out any sliding of the tree trunks with respect to each
: other or with respect to the bunk, then halting the pivoting
upon contact between the butt ends and the ground, and
. ~inally moving the vehicle forwardly while maintaining the
bunk in the position at which it stopped pivoting, to allow
the tree trunks to be dragged fully off the bunk due to the
contact with the ground, while thc tree tranks remain in
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~Lo~335~7
alignment.
The geometry of the criter a which technically
define the method herein described is iliustrated in
Figures 5 and 6, to which attention is now directed.
In Figure 5, a rear wheel 32 is illustrated and
the line 38 is again the ground level. The point P in
Figure 5 represents the pivotal axis which is shown at
18 in Figure 2. The distance x between the points P
and M represents the height of the pivotal point P above
the ground. The height x is also illustrated in Figure 2.
The distance z between the points P and N represents the
perpendicular distance from the pivot point P to the sur-
face of the bunk which contacts the lowermost tree trunks.
The surface is identified in Figure 5 by the numeral 42.
A portion o~ one of the lowermost tree trunks is sho,wn in
Figure 5 at the numeral 43, this being the rearward or butt-
end portion. The line y extending between the points P
and O is the distance between the pivot axis and the
reaxmost end point of the lower tree trunks. The broken
line 40 in Figure S again represents the trajectory of the
butt ends of the lowermost tree trunks as the bunk pivots
about the axis 18 (point P in Figure 5). Thus, the line 40
is merely a circular arc whose centre is at the point P.
The point T is the intersection of the arc 40 with the
ground level 38, and it thus follows that the di~tance
between P and T must be the same as the distance between
P and O. Thus, both PO and PT represent the distance ~.
The angle c~ represents ~ PTM, while the ~ngle
represents G PON.
When ehe bunk has p~voted to as.sume the position ~
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~8~5~7
shown in Figure 3, with the butt ends of the lowermost tree
trunks resting against the ground level 38, the angles o~
and ~ have come together to define theirsum, which is
identified in Figure 6 as the angle ~r In effect, the
points O and T are now superimposed in Figure 6.
Having defined the various lengths involved with
the method herein described, the condition under which the
sliding of the trees is avoided will be satified if the
following condition i5 met:
sin~l z + sin~l x
Y Y
, where ~ i5 the lesser of:
1) the angle whose tangent is the coefficient of
static friction between tree trunks, ~`
2) the angle whose tangent is the coefficient of
static friction between a tree trunk and
the trunk-contacting surface of the bunk.
(The above formula utilizes the standard trigono-
metric designation of sin 1 to indicate "the angle whose
sine is").
As an example of typical coefficients of static
friction which are encountered in the field to which this
invention relates, reference may be had to Marks' Mechanical
Engineer's Handbook, 6th edition, 1958, McGraw-Hill Book
Company Inc., page 3-40, where coefficients of static
and sliding friction are given for various materials.
- The coefficient of static friction for oak on oak is given -
as .62 where the force promoting slidiny is parallel to the
grain, and .54 where the force promoting sliding is perpendicu-
lar to the grain.
The same table gives the coefficient of .sliding
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1~835~7
friction for cast iron on oak is . 49, and since the coef~ic-
ient of sliding friction is always less than the coefficient
of static friction, it is reasonable to assume a coefficient
of static friction for cast iron on oak in the region of
about .6.
In order to initiate the sliding of a given item
over a surface under its own weight as the surface gradually
tilts away from the horizontal, the angle made by the
surface with the horizontal must reach a point where its
tangent is the same as the coefficient of static friction
between the materials of the surface and of the article.
Taking an approximate coefficient of static friction for
the tree trunks with respect to each other and with respect
to the bunk in the area of .6, it is a simple matter to deter-
mine that sliding of some form is likely to be initiated
at around an angle of 30 to the horizontal.
The angle shown in Figure 3, at which contact
takes place between the butt ends of the trees and the ground,
is in the area of 25, this being considered a "safe" maximum
angle with respect to the horizontal. It will be understood,
however, that it is not feasible to establish a definite
maximum angle to the horizontal, for the simple reason that
t~e coefficients of friction between different tree materials
and tree conditlons will vary to some extent.
: .
7,'
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