FIELD OF THE INVENTION
The present invention relates to an improved counterweight hook latch device for
crane applications.
BACKGROUND OF THE INVENTION
According to the prior art, spring loaded hook latches are employed for cranes
under industrial application to prevent the lifting tackles such as chain, rope sling
from slipping out of the crane hook. The basic arrangement consists of a metal
plate bent at sides and long enough to close the hook opening with a spring to
always maintain the hook latch in closed condition.
In the existing practice, there remains a risk for frequent damage of the spring
after a continuous usage. Also, it is relatively difficult for a single person to
remove the lifting tackle from the crane hook. This is because, while removing
the lifting tackle from the hook, the person has to simultaneously hold the spring
loaded hook latch back. There is also a risk of sideways movement of the hook
latch which can cause the slipping of the lifting taickle from the crane hook.
. Patent No. JP2005022806A - entitled "Crane Hook Provided with locking device",
discloses a locking device composed of a bracket fixed to a neck part of a hook
body , a frame that is rotatable within a vertical plane parallel to a curvature
direction of a hook part of the hook body , and a locking piece installed on the
frame to be rotatable in a perpendicular plane to the curvature direction of the
hook part. For setting the suspension ring , the hook body is moved in parallel
to rotate the locking piece at an upper end part of the suspension ring toward
the depth of the hook part to release locking. In removing the suspension ring,

the hook body is slightly lowered and turned to rotate the locking piece in a
perpendicular direction to the curvature direction of the hook part at the upper
end part of the suspension ring to release locking.
US5480202A entitled - " Anti-snag plate for crane hooks" describes an anti-
snag plate for crane hooks, comprising a crane hook having a shank with an
upper end and a lower end. The shank is curved and bent in a J-shaped
configuration to design an upwardly extending point. The shank has an aperture
adjacent to the main aperture. A safety plate is formed of an elongated
configuration having an upper end with downwardly extending plates with
apertures therethrough positionable in alignment with the minor aperture of the
shank. The lower end of the safety plate is formed with a concave recess
positionable in contact with the interior surface of the upstanding projection and
movable downwardly with respect thereto. An anti-snag plate is formed in a
rectangular configuration with an upper end and a lower end. The upper end is
formed with downwardly extending plates and apertures there through
positionable in alignment with the apertures of the safety plate and the minor
apertures of the shank. The lower end is positionable upon the upper free end of
the projection. A pivot pin is positioned through the minor aperture as well as
the apertures of the anti-snag plate and the safety plate and a resilient member
positioned upon the upper surface of the anti-snag plate and the lower surface of
the safety plate to move such plates together toward the tip of the of projection.
US5020843A entitled- "Crane Hook Latch with sliding locking bar". According to
this invention, a gate latch is mounted on a hook shank and spanning the mouth
of the hook from its shank to its tip, and comprises a sliding lock bar which can
be selectively linearly positioned in closed condition retention slots to prevent

opening of the gate latch or in open condition retention slots to permit rotation
of the gate latch from a closed to an open condition.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved counterweight
hook latch device for crane applications, which eliminates the prior art
disadvantages.
Another object of the invention is to propose an improved counterweight hook
latch device for crane applications, which reduces the time and efforts of the
operator to engage and disengage lifting tackles on the crane hook.
SUMMARY OF THE INVENTION
In order to overcome the drawbacks of the spring prior art loaded hook latch
system and to simplify the system, the present invention provides an improved
hook latch device operable under counterweight principle. The device consists of
at least two side plates, which are shaped metal plates and joined by a
counterweight rod on one end and a connecting rod on the other end. In this
device, when an operator engages the lifting tackle in the hook by pushing the
latch, the latch gets locked with the hook due to counterweight action upon
placing the lifting tackle. Here, the counterweight performs the function of a
spring in a spring loaded hook latch. But for removing the lifting tackle from the
hook, the

operator has to exert more effort in a prior art spring loaded hook latch, in
which, the operator has to simultaneously hold the lifting tackle by one hand and
has to remove the lifting tackle with the other hand. This extra effort needed in
prior art, reduced by a great extent in the improved system by employing the
counterweight principle.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The proposed invention shall be better understood by the following description of
the accompanied drawings.
Figure 1 - shows an assembly drawing of a counterweight hook latch device
fitted on a crane hook according to the invention.
Figure 2 - shows a detailed view of the counterweight hook latch unit device
according to the invention in disassembled condition.
DETAILED DESCRIPTION OF THE INVENTION
In the improved counter-weight hook latch device, the principle of
counterweight is employed. Figure 1 shows the inventive device (1) fitted on a
Crane Hook (2). As shown in figure 2 , device consists of at least two metal
plates, i.e. Side plates (3), cut in a specific shape; a connecting rod (4); a
counterweight rod (5), to join the side plates (3); and a split pin (6) for the
connecting rod (4).

In this device, it is relatively easy to remove the lifting tackle (2) from the crane
hook (1) in a single operation, due to absence of a spring system. Due to the
counterweight arrangement the hook latch (2) remains always in closed position.
Also, since both the metal plates (3) are fitted closely around the hook (2), the
lateral movement of the hook latch (2) is also restricted.

WE CLAIM :
1. An improved counterweight hook latch device for crane applications,
comprising :
- at least two side plates (3) shaped corresponding to that of the crane
hook (2), the side plates (3) being detachably attached substantially
closely around a crane hook (1);
- a connecting rod (4) joining a first end of the side plates (3) via a split pin
(6); and
- a counter-weight rod (5) attaching a second end of the side plates (3)
such that the device (2) can be disposed and removed from the crane
hook (j) according to the counter-weight principle.
2. The device as claimed in claim 1, wherein the side plates (3) are formed
of metal.

ABSTRACT

The invention relates to an improved counterweight hook latch device for
crane applications, comprising : at least two side plates (3) shaped
corresponding to that of the crane hook (2), the side plates (3) being
detachably attached substantially closely around a crane hook (1); a
connecting rod (4) joining a first end of the side plates (3) via a split pin (6);
and a counter-weight rod (5) attaching a second end of the side plates (3)
such that the device (2) can be disposed and removed from the crane hook
(j) according to the counter-weight principle.