Note: Descriptions are shown in the official language in which they were submitted.
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This application is a division of Canadian
application 258,652 filed 9 August 1976, now Canadian Patent
1,039,058 issued 26 September 1978.
This invention relates to animal traps and more part-
icularly this invention relates to a low impact leghold type
animal trap.
~ eghold traps have been in use for many years in the
fur trapping industry and are wide spread in their application.
Depending on the size of the trap, a great variety of animals
can be caught, usually without damage to the fur. These traps
have recently been widely criticized because of certain aspects
which are considered by some people to be inhumane. One of the
most important of the disadvantages leading to the charges of
inhumanity is the fact that when the jaws clamp shut on the leg
of the animal, they do so with considerable force and inflict
severe pain.
Interestingly, the basic design of the leghold trap
has not changed over the years with new improvements being made
generally in the trigger assembly or other components not affect-
ing the operating principle of the trap. See, for example,U.S. Patents Nos. 833,827, dated October 23, 1906; 1,356,775
dated October 26, 1920; 1,939,190, dated December 12, 1933; and
3,335,517, dated October 15, 1967.
Although there have been improvements to leghold traps
over the years, the basic construction remains the same today
as it was 100 years ago. Specifically, a pair of jaws pivotally
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mounted on a base plate are moved upwardly from the set
position to the sprung position by spring means urging the
jaws together. As already mentioned, it has been found that
the impact force of the jaws coming together is extremely
high and, in fact, unnecessarily high. In order to pxove
this, a technique was developed at the Laboratories of
Arthur D Little, Inc. for measuri`ng the forces involved in
these traps and a measuring apparatus was constructed.
It will be r~cognized that the behaviour of a trap
cannot be expressed as a single numberl As the trap closes,
the geometry varies continuously and the impact force, there-
fore, varies according to the size of the object between the
jaws. Similarly, the clamping force after impact varies with
jaw opening. Plotting the force versus the jaw opening
accurately defines a trap. As will be discussed more fully
hereinbelow, if means could ~e provided to lessen the impact
forces and provide more uniform clamping force at smaller
openings of the trap, the standard leghold trap can be made
more humane.
Accordingly, it is a primary object of the present
invention to provide a leghold type trap which operates in a
more humane manner than the prior art traps
It is another object of the present invention to
provide a leghold type trap whereîn the clamping force of the
jaws is materially reduced at smaller openings.
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It is yet another object of the present invention
to provide a leghold typ~ trap wherein the impact force of
the jaws is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention will be better understood and objects
other than those set forth above will become apparent when
consideration is given to the following detailed description
thereof. Such description makes reference to the annexed
drawings wherein:-
Figure 1 is a perspective view of a trap according
to one embodiment of the present invention;
Figure 2 is an end view of the trap of Figure l;
Figure 3 is a perspective view of another configura-
tion of a trap according to the first embodiment;
Figure 4 is a side elevation, partially fragmented,
of another configuration of a trap according to the first
embodiment;
Figure 5 is a sectional view taken along the line
5-5 of Figure 4;
Figure 6 is a sectional view taken along the line
6-6 of Figure 4, with the trap in the set position;
Figure 7 is similar to Figure 6 but with the trap
partially closed;
Figure 8 is similar to Figures 6 and 7 with the jaws
in the closed position;
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Figure 9 is a perspective view of a spring and
damper means according to a second embodiment of the present
invention;
Figure 10 is a perspective view of a spring and
damper means and part of a trap according to another configur-
ation of the second embodiment of the present invention;
Figure 11 is an end view, partly in section, of a
prior art trap with the jaws half closed;
Figure 12 is an end view, partially in section, of
a trap according to another embodiment of the present
invention;
Figure 13 is a curve showi.n~ calculated forces
against jaw opening of a prior art trap and a trap according
to the third embodiment of the present invention;
Figure 14 is a curve showing the actual forces
plotted against jaw opening of the pr$or art trap and the
trap according to the third embodiment of the present invention;
Figure 15 is a plan view of a trap according to still
another embodiment of the present i`nvention with the trap in
the set position;
Figure 16 is a front view of the trap of Figure 15
with the trap in the set position;
Figure 17 is a perspective. view of the damper means
used in the trap of Figure 15; and
Figure 18 is a front view o~ the trap of Figure 15
in the closed position.
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According to one aspect of the present invention
there is provided in an animal trap of the leghold type having
a base, a pair of U-shaped coactingjaws swingably mounted on said
base, spring means biasing said jaws to a closed position,
and trigger means for locking said jaws in an open position
until released, the improvement comprising means for reducing
the impact of said jaws when they close without significantly
reducing the closing speed or holding power, said base being
elongated and having an upstanding ear at each end thereof;
said jaws each comprising a pair of substantially parallel
spaced legs and a cross member, said legs terminating in pintles
journalled through bores in said ears; said spring means including
a leaf spring having an arm portion with an eye at one end
thereof encircling one of said ears and biased in a direction
so that when said jaws are in an open position and said spring
is released the eye thereof rides up on said one ear and said
one leg of each jaw to thereby close said jaws, said impact
reducing means comprising an inertial snubber pivotally mounted
in a bore in said one ear and having a longitudinal portion
overlying at least a portion of said arm portion of said spring
for engagement therewith and movement thereby to absorb excess
spring energy before the jaws close.
The aspects of the present invention particularly
claimed herein are most clearly illustrated with reference
to Figure 10, herein.
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Referring first to Figure 1, there is ~hown a
jump trap generally designated by the numeral 10 which
has a base 12 having elongated first and second ears 14
and 16 at the ends thereof and a pair of jaws 18 and 20.
Jaws 18 and 20 each comprises a pair of substantially
parallel spaced legs 22 and 24 and cross member 26. The
legs 22 and 24 terminate in laterally outwardly
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directed pintles 28 journaled through bores 30 in ears 14 and
16. Affixed to the longitudinal base 12 is a lateral cross-
piece 32. Upstanding from cross-piece 32 is leg 34 having
pintles 36 journaled through bores 38 in the shank 40 which
is integral with the pan 42. Extending upwardly and outwardly
from one end of cross-piece 32 is an extension 44 carrying dog
46.
It will be seen that legs 22 are relatively straight
extending downwardly from cross-member 26 to pintle 28. In the
prior art trap legs 24 would have the same configuration. The
last essential member of the trap is a spring which, in the
embodiment of Figure 1, is shown as a jump spring 48 which is
in the form of a leaf spring affixed to base 12 at the end 50
which is in the approximity of legs 22. Spring 48 is affixed
to base 12 by any suitable means such as rivets or screws 52.
Spring 48 terminates at the other end portion in opening or eye
54 the shape of which will be described more fully hereinbelow.
It will be recognized, however, that in the prior art traps the
eye 54 is generally circular so that when the trap is set with
the spring forced into a position against base 12 and the jaws
are spread apart and held in place by pan and shank assembly 40,
42 and dog 46 (see Figure 6), and the trap is released, the end
portion of spring 48 carrying eye 54 will move rapidly upwardly
and urge legs 24 into the upright and closed position. But, in
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this embodiment of the present invention, it is noted that
legs 24, when together in an upright position and viewed from
the end as in Figure 2, generally conform to an "hour glass"
shape. That is, each of the legs 24 has a pintle 28 and then
curves outwardly for a short distance at 56, inwardly at 58,
outwardly at 60, and inwardly again at 62 to where the sub-
stantially straight portion 64 begins. The eye 54 of spring
48 has a longitudinally extending cross-piece 66 extending
between legs 24 and terminating in an upwardly extending portion
68.
Thus, in use, the trap is set as already explained and
when triggered by an animal, spring 48 moves upwardly with
outer wall 70 of eye 54 riding along portion 56 of legs 24
thereby urging the jaws to a closed position. However, when
eye 54 reaches the portion 58 of legs 24, the direction of
the jaws is suddenly reversed so that they momentarily begin
to open again. But, as eye 54 reaches portion 60 of legs 24,
the jaws are again urged to a closed position. This momentary
opening of the jaws in the middle of their closing travel
absorbs or dissipates considerable energy which is essentially
unusable energy in terms of the necessary clamping force to hold
an animal and diminishes the impact. The loss in closing time
caused by this momentary reverse motion is negligible. The
direction of travel of jaws, therefore, is in essence, controlled
by an escapement.
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Referring to Figure 3, there is seen another
configuration of a trap falling within the definition of the
first embodiment of the present invention already described.
This trap comprises base 12 and jaws 72 and 74. Each of the
jaws has a leg 76 and an opposite leg 78 each journaled by
means of pintles 28 into upstanding ears 80 and 82. Cross-
piece 32 holds the pan and shank assembly and dog (not shown).
It will be seen that legs 76 are substantially straight while
legs 78 form a similar escapement to that shown in Figure 1.
10 Instead of a jump spring as shown in Figure 1, the configura-
tion of Figure 3 shows a long spring 84 which is also a leaf
spring. Leaf spring 84 has a stationary end 86 and a slidable
end 88. End portion 88 has a pair of eyes 90 and 92 separated
by a cross-piece 94. The operation of this trap is the same
as the operation of the trap of Figure 1 with end portion 88
of spring 84 moving upwardly when the trap is released and
urging the jaws together for the first part of their travel,
momentarily apart, and then together again.
Referring now to Figures 4 through 8, there is seen
20 another configuration of a trap according to this first embodi-
ment of the invention. In this trap, base 12 is provided with
upstanding ears 96 and 98 into which pintles 28 of jaws 100
and 102 are journaled. Cross-piece 32 having upstanding ears
34 and 44 carrying pan and shank assembly 42 and 40, and dog
46, respectively, are the same as previously described.
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As shown in Eigure 4, partially fragmented for ease
of illustration, a long spring basically similar to that shown
in Figure 3 is used having upper portion 104 and lower portion
106 which, in turn, are fixed to eyP members 108 and 110,
respectively. Eye member 110 merely contains an elongated
slot to fit over base portion 112 of ear 98. Eye member 108,
however, has a pair of eyes 114 and 116 (Figure 5) to fit over
ear portions 118 and 120, respectively (Figures 5 and 6).
Between eyes 114 and 116 is cross-piece 122.
As can be clearly seen in Figure 8, the configuration
of legs 124 and 126 of jaws 100 and 102, respectively, includes
a lower foot portion 128 having substantially parallel linear
outer surface 130 and inner surface 132. Moving upwardly from
foot portion 128, there is a first intermediate portion 134
projecting inwardly and having a curved outer surface 136 and
rectilinear inner surfaces 138 and 140, which can be more easily
recognized by reference to Figure 6. Again moving upwardly,
there is second intermediate portion 142 defined by substanti-
ally parallel linear outer and inner surfaces 144 and 146,
respectively. Finally, there is upper portion 148 which is
defined at its outer surface by linear edge 150 and at its
inner surface by curved surface 152 which is transformed to
linear surface 154, linear surface 154 bPing substantially
parallel to linear surface 150.
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For ease in understanding the operation of this
trap, attention is directed to Figures 6 through 8, and in
particular to Figure 7. In Figure 6, the trap is shown in
its set position with jaws 100 and 102 fully open and held
in place by the locking mechanism which comprises the pan 42,
shank 40, and dog 46. This, in turn, compresses the spring
which is held in position by surface 130 of legs 124 and 126
of the jaws 100 and 102. Considering Fi.gure 7, when the jaws
are released and the spring begins to move upwardly, member 108
moving upwardly and bearing against surface 130 urges the jaws
up and toward the closed position. As the member 108 moves to
the position shown in phantom in Figure 7, portion 122 becomes
the operative factor and, by bearing against surfaces 138 and
then 140, it reverses the direction of travel of the jaws and
urges them slightly more open to the position shown in phantom
in Figure 7. As member 108 continues to rise, it bears against
surface 144 to close the jaws and hold them in a closed posi-
tion as shown in Figure 8.
Thusl it will be seen that each of the traps shown in
Figures 1 through 8, while having a slightly different configur-
ation, operates in essentially the same way. It will be appre-
ciated, also, that while these traps are shown and described
by reference to particular type of spring, that is, a jump spring
or a long spring, the actual type of spring is immaterial and
they may be interchanged. In fact, a coil spring type trap
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having a lever of the type shown in Figure 15 could be used
in thi 5 embodiment.
Turning to the next embodiment, attention is directed
to Figure 9 which merely shows a prior art type long spring 154
terminating at either end in an eye 156. This spring when used
in the conventional manner is mounted essentially as shown in
Figure 3 but, of course, using the conventionally shaped jaws
which will be appreciated by referring to Figure 11 or to any
of the prior art patents cited above. At this point it is
important to keep in mind the basic principles underlying the
various embodiments of the instant invention. Specifically, it
must be understood that a leghold trap must grip a captured
animal's leg with sufficient force to prevent escape. A spring
strong enough to provide this force, however, liberates consid-
erable energy when the trap is triggered and most of this energy
is absorbed by the animal's leg. Thus, it is important to be
able to dissipate excess energy harmlessly without compromising
the gripping power of the spring. With this in mind, and return-
ing to Figure 9, there is provided a damper or snubber generally
designated by numeral 158 which comprises an inertia arm 160
extending outwardly from a crank 162 rotating in upstanding legs
164. In operation, the trap begins to close in the conventional
manner, the jaws being driven together by a leaf spring, either
of the long spring or the jump spring type. Before the jaws
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contact the ani~al's leg, however, the sp;cing encounters the
crank 162. Tne spring must turn the cran]c, accelera~ing inertia
arm 160 in order to continue its own motion. Since the arm 160
has higher inertia than the jaws, the spring essentially lags
behind -the jaws and softly clamps the same shut after they have
already closed due to their own momentum.
Figure 10 shows another form of inertial damper
or snubber. In this modification, provision is made in ear
16~ which is upstanding from base 12 of the trap for inserting
hook means 168 of inertial snubber 170. As the spring rises,
the inertial snubber 170, which is in con~act with the spring
and is moved thereby, absorbs energy of the spring to reduce
the impact of the jaw on closing of the jaw.
~efore discussing the next embodiment of the instant
invention, it would be helpful to briefly describe certain of
the factors involved in the use of a typical leghold trap.
For this purpose, a standard Victor number 3 long spring trap --
was used. It will be appreciated by one skilled in the art that
the principles involved apply to any size trap of the leghold
type and that this discussion by reference to a number 3 trap is
for illustrative purposes only. Figure 11 shows the geometry of
the trap jaws in the standard trap. The expression F = LR gives
the static clamping force at any opening. The expression f =
Stan ~ describes the relationship between the jaw angle and the
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spring force. In these calculations, friction was ignored,
as was the minor variation in spring force, since neither
factor would have much effect on the basic relationships.
The "standard #3" curve in Figure 13 shows the
results of a series of calculated data points. One sees a
drastic increase in force a-t less than half inch opening.
This would be likely to severely injure small animals, while
allowing larger ones to escape. Redistributing the spring
force in a more reasonable dis-tribution ~i.s shown on the second
curve of Figure 13, marked "Modified Jaw # 3 Trap". This was
arrived at by selecting desired values of F as e varied.
Returning to the formula F = LR, L barely varies, and both f
and R vary with e:
f = Stan e
R = Ksin e
Therefore, varying e will produce any desired value of F.
Following the above formula, jaws were fabricated as
shown in Figure 12. In this case, jaws 172 and 174 each has a
lower portion 176 having a curved outer surface denoted as "C".
It will be appreciated, therefore, that as the eye of the spring
moves upwardly along surface C urging the jaws closed, e con-
stantly changes. In this particular example, using a number 3
trap, curved surface C was arcuate. Measurements were then taken
on an instrument measuring force in millivolts, the instrument
having previously been calibrated so that 1.84 millivolts was
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equal to one pound. Jaw opening was plotted against force
for both the standard trap and the trap with the jaws modified
as in Figure 12. The curves are set forth in Figure 14 it was
not possible to take measurements at extremely small jaw open-
ings because of the size of the sensor. It will be seen, how-
ever, that the curve for the standard trap is essentially as
calculated and shown in Figure 13 and the curve for the modified
jaw trap essentially follows that predicted as in Figure 13 and,
in fact, was somewhat more level. Clearly, therefore, the
impact force of the jaws closing, regardless of the distance
between the jaws at the time of closing on the leg of an animal,
is held relatively constant and at a relatively low level. In
a sense, the jaws can be "programmed" to provide any desired
force curve.
Turning now to Figure 15, there will be seen a leg-
hold trap of the coil spring type. ThiR trap is shown with two
springs but this embodiment could be used with a single coil
spring of the type shown in Montgomery et al Patent No. 3,335,517.
This trap which is generally designated by the numeral 178 com-
prises a base 180 having upstanding ears 182; jaws 184 compris-
ing a pair of substantially parallel spaced legs 186 and 188
terminating in laterally outwardly directed pintles 189 which
are journaled through bores in ears 182; and cross-piece 190
carrying pan and shank assembly 192, with the pan partially
broken away for clarity of illustration, and dog 194. A generally
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U-shaped spring mount 196 is mounted on cross-piece 190 and
base 180 in such a way that the legs 198 and 200 are aligned
transversely of base 180 and equidistant from cross-piece 190.
Levers 202 and 204 are mounted to pivot on legs 198 and 200,
respectively, of mount 196. Levers 202 and 204 are provided
with openings 206 and 208, respectively, which correspond to
the eyes 156, for example, of spring 154 shown in Figure 9.
Also mounted on legs 198 and 200 are coil springs 210 and 212
which are joined at their far ends by member 214. At the ends
of the coil springs 210 and 212 closest to base 180, end portion
216 and 218 is fixed to the underside of lever 202 and 204,
respectively, so that the levers are normally biased in an up-
ward position as shown in Figure 18. As shown in Figure 15, on
the other hand, the trap is in the set position and the levers
are down and the jaws wide open.
To this point, the description of the trap of Figures
15 through 18 has been a description of a conventional coil
spring leghold trap. But, according to the last embodiment of
the present invention, a pair of inertial snubbers or dampers
is provided which relies on the mass of the trap itself to pro-
vide the inertial damping. The inertial snubber is shown in
Figure 17 and is generally designated by the numeral 220. It
comprises a crank portion 222 and an arm portion 224. As will
be seen from Figure 15, snubber 220 is mounted in such a way
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that crank 222 rides on lever 202 or 204 and is mounted to
pivot about the axis provided by members 198 and 200. Arm
224, when the trap is in the set position lays flat on the
ground with the weight of the trap itself on top of the same.
This can be easily seen in Figure 16.
Turning to Figure 18, it will be seen that when the
trap is sprung, levers 202 and 204 are urged upwardly in the
direction shown by arrows A by springs 210 and 212 thereby urg-
ing jaws 184 together. At the same time, however, cranks 222
are contacted by levers 202 and 204 and caused to rotate about
pivots 198 and 200, respectively. As cranks 222 rotate, arms
224 move in the direction shown by the arrows labelled B. Since
the trap 178 is resting on arms 224, when arms 224 are caused to -
move as shown by arrows B, the trap itself is displaced upwardly.
The mass of the trap 178 causes an inertial dampening of levers
202 and 204 which then lag behind the cl~sing of the jaws 184.
Jaws 184 close gently on the animal's leg and then are tightly
clamped by levers 202 and 204. An additional advantage of this
action is that the upward movement of the complete trap will
cause the jaws to close higher up on the animal's leg thereby
creating a more positive grip as well as a less painful grip.
Additionally, if the animal pulls its leg away from the trap
when it is startled, the trap, in essence, follows this action
and still grips the animal's leg.
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While this inventlon has been particularly shown and
described with reference to preferred embodiments thereof, it
will be understood by those skilled in the art that various
changes in form and details may be made therein without
departing from the spirit and scope of the invention.
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