Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02622041 2008-02-21
Rope Tensioner
FIELD OF THE INVENTION
[0001] The present invention relates to a rope tensioner. More particularly,
the invention relates to a
rope tensioner for maintaining rope tension on a mechanical device that is
used to wind up
the rope.
BACKGROUND OF THE INVENTION
[0002] Mechanical lifting devices are widely used for loading and unloading of
freight; for
movement of materials; for assembling of heavy equipment. These mechanical
lifting
devices are generally equipped with a winch, hoisting ropes and sheaves that
can be
used both to lift and lower materials. Mechanical lifting devices commonly
come in the
form of cranes, drill rigs or the like.
[0003] A mechanical lifting device 100 such as a drill rig generally used in
the resource industry
for exploring for minerals, is shown in Figure 1. A sheave 102 is generally
located at a
hard to reach height and much higher than a winch 104. A rope 106 is paid out
from the
winch 104 and pulled back by being rewound on the winch. The rope extends from
the
winch 104 to the other side of the sheave and is connected to a holding means,
for
example, a hoisting plug 108.
[0004] In some drill rigs, the hoisting plug is handled manually. The hoisting
plug is therefore kept
as light as possible. The handler has to move the hoisting plug away from the
drill boom
when he picks up or lays down drill pipe behind the rig or stacks the rod in
the rod rack.
Therefore single lines and hoisting plugs are generally used for easy
handling.
[0005] For heavy duty ropes in the mechanical lifting device 100, the diameter
of the rope 106
could be up to one inch, therefore the rope 106 may be stiff. On the other
hand, the
hoisting plug 108 may not be heavy enough, especially when no load is put on
the
hoisting plug 108, to keep enough rope tension between the winch 104 and the
sheave
102.
[0006] In the absence of sufficient rope tension, when the winch 104 winds up
the rope 106, the
rope 106 may not wind on the winch properly, may snarl at the winch, cross
over the rope
1
CA 02622041 2008-02-21
already wound on the winch, thus causing damage to the rope when the hoisting
plug 108 is
subsequently raised with a load on it. The snarled rope is often extremely
difficult to clear.
[0007] Furthermore, the hoisting plug 108 may need to be pulled down on the
other side if it is not
heavy enough to pull the stiff wire rope over the sheave.
[0008] US Patent 4,113,237 describes a cable pay-out drive on a crane having a
set of three
sheaves, one of which is driven in the lowering direction. The pay-out drive
pulls the rope off
the freely rotatable drum of the crane in the payout direction.
[0009] The cable pay-out drive described in US Patent 4,113,237 is free to
idle in the raising
direction, therefore there is no rope tension in the raising direction
actively provided by the
cable pay-out drive. Furthermore drawing a heavy duty cable through a non-
linear path
defined by three offset sheaves shortens the life of a single heavy duty rope
due to the
reversing bending caused by the offset sheaves. Furthermore, the construction
of three
offset sheaves adds complexity and cost, since the existing idler sheave that
is required at
the top of the boom is not utilized for providing the desired rope tension.
[oolo] Therefore, there is a need to for an improved rope tensioner.
SUMMARY OF THE INVENTION
[0011] It is an object of the invention to provide an improved rope tensioner
and a method for
providing desired rope tension in a mechanical lifting device.
[0012] In accordance with one embodiment of the present invention, there is
provided a rope
tensioner in a mechanical lifting device, the mechanical lifting device
includes a winch, a
holding means, and a rope, the rope tensioner comprises a sheave guiding the
rope from
the winch to the holding means; and a driving means operatively driving the
sheave
resulting in a tension between the sheave and the winch.
[0013] In accordance with one embodiment of the present invention, there is
provided a method
for providing rope tension in a mechanical lifting device, the mechanical
lifting device
includes a winch, a holding means, and a rope, the method comprising the steps
of:
guiding the rope from the winch to the holding means through a sheave; and
providing a
tension between the sheave and the winch through a driving means operatively
driving
the sheave.
2
CA 02622041 2008-02-21
[0014] Preferably, the driving means is a hydraulic motor.
[0015] Preferably, the mechanical lifting device is a drilling rig.
[0016] Preferably, the tension is predefined.
[0017] Preferably, the holding means is a hoisting plug.
[0018] Preferably, the rope tensioner includes a pressure roller pressing the
rope against the
sheave.
[0019] Preferably, the driving means is controlled by a winch release circuit.
[0020] Preferably, the rope tensioner includes a means for changing mechanical
advantage
between the driving means and the sheave.
[0021] Preferably, the means for changing mechanical advantage between the
driving means
and the sheave is a sprocket and chain mechanism.
[0022] Preferably, the rope tensioner includes a hydraulic pump.
[0023] Preferably, the rope tensioner includes a relief valve.
[0024] This summary of the invention does not necessarily describe all
features of the invention.
[0025] BRIEF DESCRIPTION OF THE DRAWINGS
[0026] These and other features of the invention will become more apparent
from the following
description in which reference is made to the appended drawings wherein:
Figure 1 shows a prior art mechanical lifting device;
Figure 2 shows a mechanical lifting device with a rope tensioner in accordance
with one
embodiment of the present invention;
Figure 3 (A) is a perspective view of a rope tensioner in accordance with one
embodiment of the present invention;
Figure 3 (B) is a cut away perspective view of the rope tensioner shown in
Figure 3 (A);
and
3
CA 02622041 2008-02-21
Figure 4 is a schematic of a hydraulic circuit of the rope tensioner in
accordance with one
embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0027] Reference will now be made in detail to some specific embodiments of
the invention
including the best modes contemplated by the inventors for carrying out the
invention.
Examples of these specific embodiments are illustrated in the accompanying
drawings.
While the invention is described in conjunction with these specific
embodiments, it will be
understood that it is not intended to limit the invention to the described
embodiments. On
the contrary, it is intended to cover alternatives, modifications, and
equivalents as may
be included within the spirit and scope of the invention as defined by the
appended
claims. In the following description, numerous specific details are set forth
in order to
provide a thorough understanding of the present invention. The present
invention may be
practiced without some or all of these specific details. In other instances,
well-known
process operations have not been described in detail in order not to
unnecessarily
obscure the present invention.
[0028] In this specification and the appended claims, the singular forms "a,"
"an," and "the"
include plural references unless the context clearly dictates otherwise.
Unless defined
otherwise, all technical and scientific terms used herein have the same
meaning as
commonly understood to one of ordinary skill in the art to which this
invention belongs.
[0029] The term "rope" is intended to describe wires twisted or braided to
improve tensile
strength for pulling. Other terms used in the art may include, but not limited
to, wire rope,
cable, or the like.
[003o] The term "winch" is intended to describe a mechanical device used to
wind up a rope or
the like. A winch generally comprises a winch drum. Winch may be powered by,
but not
limited to, electric, hydraulic, pneumatic or internal combustion drives.
[0031] The term "sheave" is intended to describe a wheel with a groove between
two flanges
around its circumference, whereby the groove generally locates a rope, cable
or belt.
Sheave is generally used to change the direction of an applied force, transmit
rotational
motion, or realize a mechanical advantage in either a linear or rotational
system of
motion.
4
CA 02622041 2008-02-21
[0032] The term "hydraulic motor" is intended to describe a mechanical
actuator that converts
hydraulic pressure and flow into torque and rotation.
[0033] Figure 2 shows a rope tensioner 202 in accordance with one embodiment
of the present
invention, in a mechanical lifting device 200, such as a rig.
[0034] Also referring to Figure 3 (A) and (B), the rope tensioner 202 produces
a tensioning
torque on the sheave 302 so that the rope 106 between the sheave 302 and the
winch
104 is always under a specified tension whether the winch and sheave is
stationary or
lowering the hoisting plug 108. When raising the hoisting plug 108, the
tensioning torque
on the sheave is overcome by the main winch pull.
[0035] In accordance with one embodiment of the present invention, a driving
means, for
example a hydraulic motor 304 is used to supply the tensioning torque to the
sheave
302. The tensioning torque on the sheave can be produced in a number of ways.
The
hydraulic motor 304 may drive the axis 306 of the sheave 302 directly (not
shown), or
through a means for changing mechanical advantage, for example, a sprocket 308
attached to the sheave 302 and then drive the sprocket 308 by a smaller
sprocket 310
mounted on the hydraulic motor 304 as shown in Figure 3 (B). The use of a
means for
changing mechanical advantage may further provide additional freedom and
convenience to place the hydraulic motor at a desired location and connect the
hydraulic
motor to the sheave. The wire rope may have to be pressed against the sheave
so no
sliding occurs between the sheave and the rope. The hydraulic motor 304
displacement
and sprocket ratio is chosen so that the desired tension is put on the winch
104.
[0036] Pressure rollers may be used to keep the rope 106 in the groove of the
sheave 302 and
prevent slipping between the rope and the sheave.
[0037] When the rope 106 has to be pulled off the winch 104, for example when
drilling with the
hoisting plug attached to the drill rod in a drilling rig, then the work ports
of the hydraulic
motor 304 are connected so that the sheave is not tensioned during the
drilling
operation.
[0038] Figure 4 illustrates a exemplary hydraulic circuit to accomplish the
desired tensioning
torque on the winch 104. Also referring to Figures 3 and 4, the hydraulic
motor 304, 402
is pressurized by a constant pressure such as by a pressure compensated pump
404.
CA 02622041 2008-02-21
When the winch is stationary, the hydraulic motor 304, 402 is in a stall
condition and is
putting a constant tensioning on the rope between the winch 104 and the sheave
302 of
the rope tensioner 202. When the holding means, for example the hoisting plug
108 is
lowered, the hydraulic pump 404 puts out enough flow to maintain the desired
constant
tension on the rope between the winch 104 and the sheave 302 of the rope
tensioner
202.
[0039] When the hoisting plug 108 is raised by the winch 104, the hydraulic
motor 304, 402 is
forced by the force of the winch 104 to turn in the reverse direction and acts
a hydraulic
pump. The hydraulic motor 304, 402 working as a pump in the reverse direction
forces
flow over a relief valve 406 since the flow cannot pass over check valve 408.
The set
pressure of the relief valve 408 is set so that the relief valve will close at
a pressure
higher than that produced by hydraulic pump 404. Since the hydraulic motor
304, 402 is
acting as a hydraulic pump, the sheave 302 of the rope tensioner 202 provides
a
resistance so that a rope tension is maintained while the hoisting plug 108 is
being
raised.
[004o] The hydraulic circuit may further include a valve 410 that is shifted
so that the hydraulic
motor 304, 402 work ports are connected when the rope 106 is pulled off the
winch 104,
for example, during the drilling operation. This valve can be opened
automatically by the
same hydraulic signal that releases the parking brake on the winch so the rope
can be
pulled off the drum.
[0041] Optionally, provision can be made so that the line 412 from the
hydraulic tank to the
hydraulic motor 304, 402 will not empty when the hydraulic motor304, 402 is
acting as a
hydraulic pump while the hoisting plug 108 is being raised.
[0042] The present invention has been described with regard to one or more
embodiments.
However, it will be apparent to persons skilled in the art that a number of
variations and
modifications can be made without departing from the scope of the invention as
defined
in the claims.
6
