TRIGGER MECHANISM

MECANISME DE DECLENCHEMENT

English Abstract

A trigger mechanism for an animal trap is disclosed, comprising a trigger plate moveable in a vertical direction and provided with at least one cam surface on its lower face, a retaining pin for preventing release of the trap until triggered, slidable longitudinally thereby to allow release of the trap, the retaining pin being linked to at least one cam follower, such that downward movement of the trigger plate causes the retaining pin to slide thereby causing release of the trap. The trigger plate and the retaining pin are preferably biassed in an adjustable manner so as to allow a degree of selectivity in the animals which are caught.

French Abstract

Mécanisme de détente d'un piège à animal, comprenant une plaque de déclenchement amovible à la verticale et munie d'au moins une surface de came sur la face inférieure, une tige de retenue qui empêche le déclenchement du piège sans élément déclencheur et qui glisse de manière longitudinale pour permettre le déclenchement du piège, la tige de retenue étant rattachée à au moins un galet de came, de sorte que le mouvement vers le bas de la plaque de déclenchement fait glisser la tige entraînant le déclenchement du piège. La plaque de déclenchement et la tige de retenue sont de préférence biaisées de manière ajustable pour permettre une certaine sélection des animaux piégés.

Claims

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The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A trigger mechanism for an animal trap, the mechanism comprising:
a trigger plate moveable in a vertical direction, provided with at least one
cam
surface on its lower face; and
a retaining pin for preventing release of the trap until triggered,
slidable longitudinally thereby to allow release of the trap;
the retaining pin being linked to at least one cam follower, such that
downward
movement of the trigger plate causes the retaining pin to slide thereby
causing
release of the trap.
2. A trigger mechanism according to claim 1, comprising a plurality of cam
surfaces and cam followers.
3. A trigger mechanism according to claim 2, in which the cam surfaces
comprise a first substantially vertical surface and a second inclined surface,
the
cam followers abutting against the inclined surfaces.
4. A trigger mechanism according to any one of claims 1 to 3, including
means for preventing the trigger plate from rotating about a vertical axis.
5. A trigger mechanism according to claim 4, in which the means for
preventing the trigger plate from rotating comprises a rod abutting the first
substantially vertical surfaces of the cam surfaces.
6. A trigger mechanism according to claim 2, in which the cam followers are
provided on a support frame.
7. A trigger mechanism according to claim 6, including means for preventing
the support frame from rotating about a horizontal axis.

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8. A trigger mechanism according to claim 7, in which the means for
preventing the support frame from rotating comprises a rod adjacent a surface
thereof.
9. A trigger mechanism according to any one of claims 1 to 8, in which the
trigger plate is biassed upwardly.
10. A trigger mechanism according to claim 9, in which the biassing of the
trigger plate is adjustable.
11. A trigger mechanism according to any one of claims 1 to 10, in which the
retaining pin is biassed so as to prevent release of the trap.
12. A trigger mechanism according to claim 11, in which the biassing of the
retaining pin is adjustable.
13. A trigger mechanism according to claim 12, in which the retaining pin is
biassed by a spring bearing against a nut on the retaining pin.
14. A trigger mechanism according to claim 13, in which the spring is a
compressed coil spring.
15. A trigger mechanism according to any one of claims 1 to 14, in which the
length of the retaining pin is adjustable.

Description

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TRIGGER MECHANISM
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a trigger mechanism, in particular to
one which is suitable for use in animal traps.
BACKGROUND ART
Animal traps commonly operate via spring activated foot snares, and
are well known devices that require a trigger mechanism to hold and then
release a tension, trap-activating spring. The main prior art traps include US
3,060,623 (Aldrich), US 4,581,843 (Freemont), US 5,157,863 (Godwin),
CA 1,145,935 (Novak), GB 397,268 (Phelps) and my earlier international
application W097/1 1599. Other traps capture animals by means of closing
cage doors, releasing nets, physically striking the animal, etc. etc.
The trigger mechanisms for these traps invariably comprise a bar or
plate that pivots around a fulcrum so as to release a tensioned activating
spring, cage door, etc., when the bar or plate is depressed. However, it is
necessary to construct the bar or plate as a lever in order to provide an
adequate force to overcome friction generated by the compressed spring,
and this requires the bar or plate to be depressed a considerable distance
before the trap is triggered. This allows some animals to withdraw from the
trap before or during its activation, after feeling the trigger plate give way
beneath them. The animals therefore avoid capture. In addition, the
pressure required to trigger these traps will vary purely on the distance
between the fulcrum and the point of depression of the trigger bar or plate.
This makes the trigger mechanisms inherently non-selective regarding the

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size and therefore species of the animal setting them off. Inevitably, this
lever action also limits the length or diameter of the trigger bar or plate in
that the longer the lever, the greater the depression required to trigger the
trap. All of these factors limit both the efficiency and effectiveness of such
traps.
SUMMARY OF INVENTION
The invention seeks to provide a trigger mechanism that requires
minimal depression by a target animal to activate a trap. It also seeks to
provide a trap that is adjustable to the size of the animal setting it off. An
additional intention is to provide a larger trigger-plate to be used,
activating
the trap when depressed by a significant extent substantially anywhere on
its surface.
The present invention therefore provides a trigger mechanism for an
animal trap, comprising a trigger plate movable in a vertical direction and
provided with at least one cam surface on its lower face, a retaining pin for
preventing release of the trap until triggered, slideable longitudinally
thereby
to allow release of the trap, the retaining pin being linked to at least one
cam
follower such that downward movement of the trigger plate causes the
retaining pin to slide, thereby causing release of the trap.
BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present invention will now be described by way
of example, with reference to the accompanying drawings in which;
Figure 1 shows a perspective view of a housing, trigger plate and
internal assembly, suitable for attachment to a mainspring as disclosed in my
earlier application W097/1 1599;

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Figure 2 shows the trigger mechanism of Figure 1 viewed from below;
Figure 3 shows a side elevation of the trigger mechanism in the set
position, ie. untriggered;
Figure 4 shows a side elevation of the trigger mechanism in the
process of being set off;
Figure 5 shows an enlarged view of a means to adjust the tension of
the trigger assembly;
Figure 6 shows a plan view of a second embodiment of the present
invention;
Figure 7 shows a side elevation of the embodiment of Figure 6.
DETAILED DESCRIPTION OF EMBODIMENT
Referring to the drawings, the trigger mechanism as shown in Figures
1 and 2 comprises a shallow cylindrical housing 10, aligned vertically, with
an inward facing lip 11 formed around its upper circumference. This retains
a trigger plate 12, which has wedge-like cam surfaces 13 depending from
its lower (internal) surface. A trigger pin 14 is fixed to a frame of
crossbars
15, 16, 17, 18, 19, and a rod 20 is fixed across the centre of a housing.
One end 21 of the trigger pin 14 passes slidably through a hole 22 in the
front of the housing 10, to lie over a slot 23 and thereby close the top
outlet
of that slot. This can be employed to retain the upper arm of a mainspring
of, for example, the trap described in my W097/1 1599. The end 21 of the
trigger pin 14 therefore retains the mainspring under tension. The remainder
of the connector 24 can accommodate a lower arm of a mainspring (not
shown). The other end 25 of the trigger pin 14 (see Figures 3, 4 and 5)
passes through a short length of threaded studding 26 and a coil spring 27

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before being housed in a recess 28 formed in the rear of the housing. A nut
29 is threaded onto the studding 26. The transverse rod 20 passes across
the centre of the housing 10 and rests up against the front of the two centre
cam elements 13 and lies across the crossbars 18 and 19. When the trigger
mechanism is "set" as shown in Figure 3, the coil spring 27 pushes against
the nut 29, which in turn forces the studding 26 against the crossbar 15.
Because the crossbars 15, 16 and 17 are all firmly fixed to the trigger pin
14, and also bear directly on the slanting surfaces of the wedges 13, the
tension of the coil spring 27 pushes the front end 21 of the trigger pin 14
through the hole, thereby retaining the mainspring, and also forces the
wedges 13 upwards thus biassing the trigger plate 12 against the lip 11.
The wedges cannot move forward, due to the presence of the rod 20.
This not only seals the trigger plate 12 against the housing 10,
thereby preventing entry of dirt, etc., but also necessitates that the force
be
applied to the trigger plate 12 in order to depress it. Such a force could be
exerted by the foot of a target animal. The force required to depress the
trigger plate 12 can be adjusted by turning the nut 29 so as to move it either
towards or away from the tension of the coil spring 27. This adjustability
allows the trap to be adjusted to prevent triggering by an animal which is
smaller than the target animal.
When an animal which is at least as heavy as the target animal
depresses the trigger plate 12, as shown by the arrow in Figure 4, the
tension of the coil spring 27 is overcome and the cam elements 13 are
forced down onto the crossbars 15, 16, 17. As the cam elements 13
cannot move forwards due to rod 20, the crossbars 15, 16, 17 are forced
rearwardly so pulling the front end 21 off the trigger pin 14 back from the
slot 23. This releases the arm of the mainspring, triggering the trap.
As shown in Figure 5, the rear end 25 of the trigger pin 14 is
accommodated in its rearwards move by the recess 28.

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A channel 30 is formed around the housing 10 at its upper edge, to
accommodate the noose or snare (not shown) of the trap. In the example
of my trap referred to earlier, the noose is lifted vertically up the animal's
leg
and tightened in one action as the mainspring is released.
The transverse rod 20 not only prevents the cam elements 13 from
moving forwards, hence preventing the trigger plate 12 from rotating
horizontally within the housing 10, but by bearing against the crossbars 18
and 19 also prevents the trigger pin/frame assembly 14-19 from being
rotated vertically by the wedges when the trigger plate 12 is depressed off-
centre. This allows each wedge 13 to bear equally on the crossbars 15, 16,
17 and for the trap to be triggered when the trigger plate 12 is depressed by
a uniform distance substantially anywhere on its surface.
A baseplate 31 can be fitted, to prevent the entry of dirt, etc. It
should preferably have holes 32 in order to allow rainwater to drain away.
Figures 6 and 7 show an alternative trigger pin/plate assembly. This
comprises a short trigger pin 33, threaded at one end 34, and screwed into
a rigid plate 35 at a threaded recess 36 thereon. A locking nut 37 secures
the trigger pin 33 in position, allowing the length of the trigger pin 33 to
be
adjusted. A rear pin 38 is similarly attached to the rigid plate 35. The plate
35 has recesses 39 and slots 40 to allow the cam elements 41 to bear upon
it and drive it rearwardly when the trigger plate 42 is depressed. A rod 43
bears against the rear wedges 41 and raised rails 44 on the rigid plate 35,
thereby preventing forward movement of the cam elements 41 and rotational
movements of the trigger plate 42 and trigger pin/plate assembly 33, 35, 38.
An additional spring 45 may be added to assist in raising the trigger plate
42.
The above trigger mechanisms can be used with substantially any
type of trap, for example to release a mainspring as described above, to
release the closing doors of a cage trap, to release a net or other capturing

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means, or to release the killing spring of a "breakback" trap.

Representative Drawing