Note: Descriptions are shown in the official language in which they were submitted.
CA 02464819 2004-04-22
APPARATUS AND METHOD FOR MEASURING AND
CONTROLLING PENDULUM MOTION
IN A C BANE
FIELD OF THE INVENTION
This invention relates to apparatus and methods for measuring and responding
to
pendulum motion. In particular, it relates to a magnetically damped
inclinometer.
BACKGROUND OF THE IIWENTION
Gantry-type cranes are often outfitted to serve as container cranes for
loading standard
freight containers into container ships, and also for unloading the containers
from the ships.
Typically, a container ship has a large number of cells or compartments in
which standard freight
containers can be received with only a minimum of clearance, and can be
stacked vertically until
the cells are full. In order to lower a freight container into a cell, the
container must be positioned
with a high degree of accuracy over the cell so that the container can be
lowered directly into the
cell without bumping the deck of the ship or the walls of the cell to any
objectionable extent. A
gantry-type container crane comprises a substantially horizontal supporting
structure or boom
with rails thereon along which a trolley is moveable in either direction by an
electrically
controlled power drive. A hoisting means or system is suspended from the
trolley and is
moveable horizontally therewith. The hoisting system comprises a system of
wire ropes hanging
downwardly from the trolley and connected to a load carrying device,
preferably a spreader bar
grasping device for selectively grasping and releasing a freight container.
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CA 02464819 2004-04-22
A container crane is well adapted for unloading containers from railroad cars
or semi-
trailer trucks and for loading the containers into the cells of a container
ship. In a typical
sequence of operations, the trolley is moved horizontally along the boom and
is stopped directly
over a container on a waiting semi-trailer truck. The spreader bar is lowered
by the hoisting
system into engagement with the container and is actuated so as to grasp the
container, which is
then hoisted to a safe elevation so that the container will clear any
obstacles on the dock or the
container ship. The trolley is then moved outwardly along the boom and over
the container ship
until the trolley is over the cell into which the container is to be loaded.
The object of this
maneuvering is to enable the container to be lowered by the hoisting system
directly into the cell.
However, considerable difficulty has been experienced by crane operators in
aligning the
container with the cell with sufficient accuracy to enable the container to be
lowered into the cell
without any objectionable bumping of the container against the deck of the
ship or the walls of
the cell. This difficulty arises from the fact that the container starts to
swing like the bob of a
pendulum when the trolley is stopped. The container may swing through several
pendulum cycles
before the swinging movement is dissipated sufficiently to enable the crane
operator to lower the
container into the cell. The trolley constitutes the pivotal support for the
pendulum. The
suspension means are formed by the hoisting rope system, and the bob is formed
by the container
and the spreader bar. The problem arising from the pendulum swinging of the
container has been
widely recognized, but no satisfactory solution has heretofore been devised.
United States patents 5,713,477 and 5,909,817 granted to Walter J. Wallace,
Jr. and Mark
A. Wallace, which are hereby incorporated by reference, describe a method and
apparatus for
controlling and operating a container crane or other similar cranes. The
patents disclose a crane
having a horizontal boom or other support structure having at least one rail
thereon, a trolley
along the rail, a rope hoist, and a load carrying device. A control system
causes the driven trolley
to be stopped momentarily at a first position. The control system then
restarts the trolley and
stops it at a second position directly over a transfer position. The control
system includes an
encoder for determining the total length of the pendulum of the crane and the
load: The stopping
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CA 02464819 2004-04-22
of the trolley at the first position causes the load to swing forwardly into
the first quarter of a
pendulum cycle. The control system includes means for adjusting the distance
between the first
and second positions to correspond with the horizontal component traveled by
the load during the
first quarter of the pendulum cycle in order to minimize any residual swinging
movements when
the load is stopped.
While these patents represent a significant step forward in terms of speed and
accuracy in
operating a container crane or the like by minimizing the residual swinging
movements of the
load, the control system disclosed has a number of limitations. In particular,
the control system
has the limitation that it is a predictive, open loop control system where the
magnitude of the
expected pendulum swing is estimated based on the measured length of the
pendulum and the
estimated weight of the load, the speed of the trolley, and other parameters.
When operating
within a narrow range of operating parameters, this open loop control system
may be sufficient to
avoid excessive swinging of the load.
Furthermore, these systems assume a rigid pendulum model; however, the wire
rope,
rollers and other portion of the crane do not combine to form a device that
acts as a rigid
pendulum. Instead, these prior art systems act as more a flexible pendulum.
In order to truly eliminate any residual swinging movements when the load is
stopped and
to allow the container crane and the control system to operate effectively
over a broader range of
operating parameters, it would be desirable to measure the actual pendulum
motion of the load
and to operate the control system with closed loop feedback control. It would
be further desirable
to accurately measure and cancel the swing of the load in a single step prior
to the load swinging
back and forth, thereby preventing the load from creating the swinging pattern
typically
addressed by the prior art systems.
SUMMARY OF THE INVENTION
In keeping with the foregoing discussion, the present invention provides
apparatus and
methods for measuring and controlling pendulum motion of a load when operating
a container
3
_.. .______..__._....__.._.__._.~ 02464819 2004-04-22 ________ .__..... . .___
_
crane or the like. Several embodiments of damped inclinometers are used to
determine and
provide information to respond to the initial sway of the load prior to
bringing the load to a stop.
The inclinometer has a shaft with attached pendulum that rotates. In some
embodiments, the
rotation causes an index member to rotate past one or a set of magnets or
electromagnets that are
connected to the load or spreader bar. The magnet or electromagnet rnay be
mounted directly the
spreader bar or it may be in the form of an off center ring. The index member
may be a
ferromagnetic material, a magnet, a ferrous member or an electromagnet.
Another embodiment
uses a spring to bias two magnets apart. A cam is attached to the shaft such
that, as the pendulum
and shaft rotate, a roller connected with the load or spreader bar allows the
spring to push the
magnets farther apart.
The apparatus for measuring and controlling pendulum motion of the present
invention is
adapted for use with a gantry-type container crane or the like for loading and
unloading standard
freight containers from container ships. A pendulum swing measuring apparatus
directly
measures the pendulum swing of the container as it is transported by the crane
and sends a
feedback signal indicative of the position or the angle of inclination of the
container to the
motion control system of the container crane. The feedback signal is used in
performing the
method for measuring and controlling pendulum motion in a container crane
according to the
present invention. A pendulum motion cancellation protocol is used to bring
the container to a
stop precisely over the intended position with little or no residual pendulum
motion.
The pendulum swing measuring apparatus may take any one of several possible
forms. A
first embodiment of the apparatus utilizes a pendulum-type inclinometer
mounted on the spreader
bar of the container crane for directly measuring the load sway of the
container. A second
embodiment of the apparatus utilizes an emitter on the spreader bar and a
sensor array on the
carriage to measure load sway of the container. A third embodiment of the
apparatus utilizes
optical scanning technology to measure load sway of the container. The
feedback signal from the
pendulum swing measuring apparatus is used to determine the parameters of the
pendulum
motion cancellation protocol. By directly measuring the pendulum motion of the
load and using
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closed loop feedback control, the apparatus and methods of the present
invention can be used to
optimize the effectiveness of the pendulum motion cancellation protocol.
Additional features of the invention include spreader bar scanners and
carriage scanners
for identifying and/or detecting the position of containers in the load. A
modified container crane
utilizing a carriage within a carriage can be used in conjunction with the
apparatus and methods
described.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG 1 illustrates a first embodiment of an apparatus for measuring and
controlling
pendulum motion in a container crane built in accordance with the present
invention. A
pendulum-type inclinometer mounted on the spreader bar measures load sway of
the container.
FIG 2 illustrates a second embodiment of an apparatus for measuring and
controlling
pendulum motion in a container crane built in accordance with. the present
invention. An emitter
on the spreader bar and a sensor array on the carriage measure load sway of
the container.
FIGS 3 and 4 illustrate a third embodiment of an apparatus for measuring and
controlling
pendulum motion in a container crane built in accordance with the present
invention. Optical
scanning technology is used to measure load sway of the container.
FIG 5 illustrates a spreader bar and a carriage equipped with scanners for use
with the
apparatus of FIGS l, 2 and 3 for identifying and/or detecting the position of
containers in the
load.
FIGS 6-12 illustrate the operation of the apparatus of FIGS l, 2 and 3
performing the
method for measuring and controlling pendulum motion in a container crane
according to the
present invention in use for loading containers onto a cargo ship.
FIGS 13-18 illustrate the operation of the apparatus of FIGS l, 2 and 3
performing the
method for measuring and controlling pendulum motion in a container crane
according to the
present invention in use for unloading containers from a cargo ship.
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FIG 19 illustrates an apparatus for controlling pendulum motion in a container
crane
according to the present invention utilizing a carriage within a carriage.
FIGS 20-26 illustrate the operation of the apparatus of FIG 19 performing the
method fox
controlling pendulum motion in a container crane according to the present
invention in use for
loading containers onto a cargo ship.
FIGS 27-31 illustrate the operation of the apparatus of FIG 19 performing the
method for
controlling pendulum motion in a container crane according to the present
invention in use for
unloading containers from a cargo ship.
FIG 32 is a perspective view of a magnetically damped inclinometer using an
electromagnet.
FIG 33 is a perspective view of the magnetically damped inclinometer of FIG 32
having a
proximity sensor.
FIG 34 is a perspective view of a magnetically damped inclinometer 60 using a
plurality
of permanent magnets.
I~IG 35 is a detail view of an alternate configuration of the magnets in the
inclinometer of
FIG 34.
FIG 36 is a perspective view of a magnetically damped inclinometer having a
spring-
loaded cam.
FIG 37 shows a detail view of an inclinometer having an actuator to change the
air gap
between the magnetic elements.
DETAILED DESCRIPTION OF THE INVENTION
The apparatus for measuring and controlling pendulum motion of the present
invention is
adapted for use with a gantry-type container crane or the like for loading and
unloading standard
freight containers from container ships. A pendulum swing measuring apparatus
directly
measures the pendulum swing of the container as it is transported by the crane
and sends a
feedback signal indicative of the position or the angle of inclination of the
container to the
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motion control system of the container crane. The feedback signal is used in
performing the
method for measuring and controlling pendulum motion in a container crane
according to the
present invention. A pendulum motion cancellation protocol is used to bring
the container to a
stop precisely over the intended position with little or no residual pendulum
motion. The
pendulum swing measuring apparatus may take any one of several possible forms
as described
below.
FIG 1 illustrates a first embodiment of the apparatus for measuring and
controlling
pendulum motion in a container crane built in accordance with the present
invention. The
container crane includes a carriage I movably mounted on one or more
horizontal rails (not
shown) and a spreader bar 3 suspended by lifting cables 2 from the carriage 1.
Generally, the
carriage I is motorized and rides horizontally along the rails on wheels or
rollers. The spreader
bar 3 will generally have clamps, hooks, straps, cables or other means for
grasping and lifting a
container 4. The construction details of the container crane itself are not
important to the
1f operation of present invention, which is intended to be compatible with any
standard container
crane or the like. An example of a typical container crane can be found in
U.S. patents 5,713,477
and 5,909,817, which have previously been incorporated by reference.
A pendulum-type inclinometer 5 is mounted on the spreader bar 3 to measure the
load
sway or pendulum motion of the container 4. The inclinometer 5 has a pendulum
6 with a plumb
weight 7 and an encoder or potentiometer 9 for measuring the angle of
inclination of the
pendulum 6 with respect to a reference point 8, which indicates a vertical or
neutral position,
shown as Position A in FIG 1. Acceleration of the carriage 1 to the right, as
indicated by arrow R,
will result in a pendulum swing of the spreader bar 3, and the container 4
which is attached to it,
toward the left relative to the carriage 1, as shown in Position F3.
Acceleration of the carriage 1 to
the left, as indicated by arrow L, will result in a pendulum swing of the
spreader bar 3, and the
container 4 which is attached to it, toward the right, as shown in Position C.
The inclinometer 5
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~ 02464819 2004-04-22
sends an analog or digital feedback signal indicative of the angle of
inclination of the container 4
to the motion control system of the container crane.
FIG 2 illustrates a second embodiment of an apparatus for measuring and
controlling
pendulum motion in a container crane built in accordance with the present
invention. An emitter
14 mounted on the spreader bar 3 emits a signal indicating the position of the
spreader bar 3 and
the container 4, and a sensor array 11, 12, 13 mounted on the carriage 1
measures the.load sway
or pendulum motion of the container 4. The lifting cables 2 have been omitted
from the drawing
for clarity.
In one particularly preferred embodiment, the emitter 14 directs a beam of
light 15, such
as a laser beam or a narrow pencil beam of visible, infrared or ultraviolet
light toward the sensor
array 11, 12, 13. The sensor array 1 l, 12, 13 may be made up of a series of
photodiodes,
phototransistors or other photosensitive sensors or it may be constructed from
one or more
position sensitive light detectors. When the emitter 14 and the container 4
axe in a vertical or
neutral position, shown as Position A, the light beam 15 strikes the central
sensor 11. When the
carriage 1 accelerates to the right R, the spreader bar 3 and container 4 will
swing to the left
relative to the carriage 1 (Position B) and the light beam 15 will strike
sensor array 13. When the
carriage 1 accelerates to the left L, the spreader bar 3 and container 4 will
swing to the right
(Position C) and the light beam 15 will strike sensor array 12. 'the sensor
array 11, 12, 13 sends
an analog or digital feedback signal indicative of the angle of inclination of
the container 4 to the
motion control system of the container crane.
In an alternative embodiment, the emitter 14 may emit a broad beam of light 15
and a
pinhole 50 or a lens may be used to create a narrow beam of light 15', which
is directed onto the
sensor array 11, 12, 13. Other alternative embodiments may use an emitter 14
that emits an
acoustic or radiofrequency signal and a sensor array 1 l, 12, 13 that is
sensitive to acoustic or
radiofrequeney signals.
8
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FIG 3 illustrates a third embodiment of an apparatus for measuring and
controlling
pendulum motion in a container crane built in accordance with the present
invention. An optical
scanner 21 is mounted on the carriage 1 and is directed downward toward the
spreader bar 3 and
the container 4. The optical scanner 21 detects the position of the spreader
bar 3 and container 4
with respect to the carriage 1. Optionally, the spreader bar 3 and/or the
container 4 may include
optical indicia 17 for facilitating the position detection by the optical
scanner 21. The lifting
cables 2 have been omitted from the drawing for clarity.
In one particularly preferred embodiment, the optical spanner is in the form
of a digital
camera 21 with position detection and having a field of view 16 that
encompasses the full range
of motion of the spreader bar 3 and container 4. FIG 4 is a top view of the
spreader bar 3 and
container 4 showing the field of view 16 of the digital camera 21 including a
multiplicity of
graticule divisions 19. As the spreader bar 3 and container 4 rr~ove between
positions A, B and C,
the digital camera 21 detects the position of edges 18 and 20 and/or the
optical indicia 17 with
respect to the graticule divisions 19 and sends an analog or digital feedback
signal indicative of
the position or the angle of inclination of the container 4 to the motion
control system of the
container crane.
FIG 5 illustrates additional features of the invention that may be combined
with the
apparatus of FIG 1, 2 or 3. The carriage 1 of the container crane is equipped
with carriage
scanners 22 that are directed downward and to the left and the right of the
spreader bar 3. The
lifting cables 2 have been omitted from the drawing for clarity. The carriage
scanners 22 are for
identifying the position of the carriage 1 with respect to the containers 4',
4" adjacent to the
target container 4. In addition the carriage scanners 22 may be adapted to
identify the adjacent
containers 4', 4" and/or their contents. Tlle carriage scanners :~2 may be
optical scanners, such as
bar code scanners or digital cameras with position detection. Alternatively,
acoustic or
radiofrequency scanners, range finders or other position detectors may be
used. Each of the
9
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containers, may be provided with optical indicia 23, such as a bar code or the
like, for facilitating
the position detection and/or identification by the carriage scanners 22.
In addition, the spreader bar 3 is equipped with spreader bar scanners 26 and
27. One or
more of the spreader bar scanners 26 are directed downwaxd from the spreader
bar 3 to identify
the target container 4 andlor to detect the position of the spreader bar 3
with respect to the target
container 4. Two more spreader bar scanners 27 are directed slightly downward
and to the left
and the right of the spreader bar 3 to identify the adjacent containers 4', 4"
and/or to detect the
position of the spreader bar 3 with respect to the adjacent containers 4', 4".
The spreader bar
scanners 26, 27 may be optical scanners, such as bar code scanners or digital
cameras with
position detection. Alternatively, acoustic or radiofrequency scanners, range
finders or other
position detectors may be used.
FIGS 6-12 illustrate the operation of the method for measuring and controlling
pendulum
motion in a container crane according to the present invention in use for
loading containers onto
a cargo ship 31. The method may be performed utilizing the apparatus of FIG 1,
2 or 3 and,
optionally, may also utilize the apparatus of FIG 5. FIG 6 shows the carriage
1 of the container
crane positioned above a container 4 on a truck bed or railway car 24.
Optionally, the carriage
scanners 22 and/or spreader bar scanners 26, 27 described in connection with
FIG 5 may be used
to identify the container 4 and/or to monitor the position of the spreader bar
3 relative to the
container 4. The spreader bar 3 is lowered onto the container 4 by the lifting
cables 2 and
attached to it by appropriate means. FIG 7 shows the container 4 being lifted
off of the truck bed
or railway car 24 by the spreader bar 3 and lifting cables 2. Then, the
carriage 1 is accelerated
toward the cargo ship, which is to the right R of the truck bed or railway car
24 in FIG 8. Because
the inertia of the spreader bar 3 and the container 4 resist the acceleration,
the spreader bar 3 and
the container 4 swing left relative to the carriage 1, starting one half of a
pendulum swing. The
pendulum swing measuring apparatus 30, which may be the apparatus of FIG 1, 2
or 3, measures
the pendulum swing and sends a feedback signal indicative of the position or
the angle of
CA 02464819 2004-04-22
inclination of the container 4 to the motion control system of the container
crane. Preferably, the
carriage 1 is accelerated steadily to maintain the lead of the carriage 1 over
the spreader bar 3 and
container 4 and to prevent further oscillations of the container 4 as it
traverses toward the cargo
ship 31, as shown in FIG 9. In transit, the container 4 may be raise or
lowered by the spreader bar
3 and lifting cables 2 so that it is at the proper height when it roaches its
destination.
When the carriage 1 is close to its intended position over the deck or the
cargo hold of the
cargo ship 31, the carriage 1 is maneuvered to induce one half of a pendulum
swing toward the
right, as shown in FIG 10. This may be done, for example, by stopping the
carriage 1 at an
intermediate point a short distance before its final position, as described in
U.S. patents
5,713,477 and 5,909,817. The distance between the intermediate stopping point
and final
position are calculated as a function of the actual load sway, as measured by
the pendulum swing
measuring apparatus 30. If desired, an encoder or the like may be used to
measure the length of
the lifting cables 2 for use in the calculations. When the container 4 is
directly over its intended
position, the carriage 1 is quickly accelerated to the right and stopped at
the final position, as
shown in FIG 1 l, to cancel out the one half of a pendulum swing that was
induced by the
intermediate stop. This brings the spreader bar 3 and container 4 to a stop
precisely over the
intended position with little or no residual pendulum motion. The
effectiveness of the pendulum
motion cancellation can be measured with the pendulum swing measuring
apparatus 30 and
optimized using closed loop feedback control.
The exact stopping and starting or deceleration and acceleration of the
carriage 1 for the
pendulum motion cancellation protocol are not critical to the present
invention. By directly
measuring the pendulum motion of the load and using closed loop feedback
control; the
apparatus and methods of the present invention can be used to optimize almost
any pendulum
motion cancellation protocol. For example in an alternative method, the
carriage 1 may be
decelerated without fully stopping to induce one half of a pendulum swing,
then accelerated and
stopped at the final position to cancel out the one half of a pendulum swing.
Other alternative
methods of maneuvering the carriage 1 to control pendulum swing usable with
the present
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invention are described in U.S, patents 3,921,818 and 4,756,432, which are
hereby incorporated
by reference.
Once the spreader bar 3 and container 4 are stopped over the intended
position, their
positions relative to the adjacent containers may be verified using the
carriage scanners 22 and/or
spreader bar scanners 27 described in connection with FIG 5. As the container
4 is lowered into
place, the spreader bar scanners 27 can be used to monitor its vertical, as
well as horizontal,
position relative to the adjacent containers, as shown in FIG 13.
FIGS 13-18 illustrate the operation of the method for measuring and
controlling
pendulum motion in a container crane according to the present invention in use
for unloading
containers from a cargo ship 31. The method may be performed utilizing the
apparatus of FIG 1,
2 or 3 and, optionally, may also utilize the apparatus of FIG 5. The carriage
1 of the container
crane is moved into position above a container 4 on the deck or in the cargo
hold of the cargo
ship 31, as shown in FIG 13. Optionally, the carriage scanners 22 and/or
spreader bar scanners
26, 27 described in connection with FIG 5 may be used to identify the
container 4 and/or to
monitor the position of the spreader bar 3 relative to the container 4, as
well as its vertical and
horizontal position relative to the adjacent containers. The spreader bar 3 is
lowered onto the
container 4 and attached to it by appropriate means, then the container 4 is
lifted by the spreader
bar 3 and lifting cables 2. Once the container 4 is clear of the cargo hold or
any other obstacles,
the carriage 1 is accelerated toward the off loading location, which is to the
right R of the cargo
ship in FIG 14. Due to their inertia resisting the acceleration, the spreader
bar 3 and the container
4 swing left relative to the carriage 1, starting one half of a pendulum
swing. The pendulum
swing measuring apparatus 30, which may be the apparatus of FIG l, 2 or 3,
measures the
pendulum swing and sends a feedback signal indicative of the position or the
angle of inclination
of the container 4 to the motion control system of the container crane.
Preferably, the carriage 1
is accelerated steadily to maintain the lead of the carriage 1 over the
spreader bar 3 and container
4 and to prevent further oscillations of the container 4 as it traverses
toward the off loading
12
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location, as shown in phantom lines in FIG 15. In transit, the container 4 may
be raise or lowered
by the spreader bar 3 and lifting cables 2 so that it is at the proper height
when it reaches its
destination.
When the carriage 1 is close to its intended position over the off loading
location, such as
a dock, truck bed or railway car 24 the carriage 1 is maneuvered to induce one
half of a
pendulum swing toward the right, as shown in FIG 16. For example, the carriage
1 may be
stopped at an intermediate point a short distance before its final position.
The distance between
the intermediate stopping point and final position are calculated as a
function of the actual load
sway, as measured by the pendulum swing measuring apparatus 30. Again, if
desired, an encoder
or the like may be used to measure the length of the lifting cables 2 for use
in the calculations.
When the container 4 is directly over its intended position, the carriage 1 is
quickly accelerated to
the right and stopped at the final position, as shown in FIG 17, to cancel out
the one half of a
pendulum swing that was induced by the intermediate stop. This brings the
spreader bar 3 and
container 4 to a stop precisely over the intended position with little or no
residual pendulum
motion. The effectiveness of the pendulum motion cancellation can be measured
with the
pendulum swing measuring apparatus 30 and optimized using closed loop feedback
control. The
container 4 is then lowered at the off loading location onto a dock, truck bed
or railway car 24 or
the like, as shown in FIG 18.
As mentioned above, the exact stopping and starting or deceleration and
acceleration of
the carriage 1 for the pendulum motion cancellation protocol are not critical
to the present
invention. By directly measuring the pendulum motion of the load and using
closed loop
feedback control, the apparatus and methods of the present invention can be
used to optimize
almost any pendulum motion cancellation protocol.
FIG 19 illustrates an apparatus for controlling pendulum motion in a container
crane
according to the present invention utilizing a secondary carriage 25 within a
primary carnage 1.
The primary carriage 1 rides horizontally on wheels or rollers along the rails
of a container crane
13
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or the like. The secondary carriage 25 is movably mounted on the primary
carriage 1 so that it
can move back and forth along the same axis as the primary carriage 1. The
primary carriage 1
and secondary carriage 25 are shown schematically since the actual
construction of the mounting
can take any one of many possible forms. For example the primary carriage 1
may include one or
more secondary rails and a motor or the like for moving the secondary carriage
25 along the
secondary rails relative to the primary carriage 1. Alternatively, the
secondary carriage 25 may be
moved relative to the primary carriage 1 by a linear actuator, such as a
hydraulic or pneumatic
cylinder, a rodless cylinder, a linear motor or the like. The range of motion
of the secondary
carriage 25 relative to the primary carriage 1 should be enough for carrying
out the chosen
pendulum motion cancellation protocol. Typically, the secondary carriage 25
will have a Lower
inertia than the primary carriage 1, which will facilitate performing the
pendulum motion
cancellation protocol. In addition, the secondary carriage 25 can be used for
making fine
adjustments in position more easily than the primary carriage 1. Preferably,
the apparatus of FIG
19 will utilize a pendulum swing measuring apparatus 30, such as those
described in connection
with FIGS 1, 2 and 3, and, optionally, may also utilize the apparatus of FIG
5.
FIGS 20-26 illustrate the operation ofthe apparatus of FIG 19 performing the
method for
controlling pendulum motion in a container crane according to the present
invention in use for
loading containers onto a cargo ship 31. In FIG 19, the primaxy carriage 1 is
positioned above a
container 4 on a truck bed or railway car 24, shown in this example with the
secondary carriage
in the far left position relative to the primary carriage 1. Optionally, the
carriage scanners 22
and/or spreader bar scanners 26, 27 described in connection with FIG 5 may be
used to identify
the container 4 and/or to monitor the position of the spreader bar 3 relative
to the container 4.
FIG 20 shows the container 4 being lifted off of the truck bed or railway car
24 by the spreader
25 bar 3 and lifting cables. Then, the primary carriage 1 is accelerated
toward the cargo ship, which
is to the right R of the truck bed or railway car 24 in FIG 21. Due to their
inertia resisting the
acceleration, the spreader bar 3 and the container 4 swing left relative to
the primary carriage l,
14
~ 02464819 2004-04-22
starting one half of a pendulum swing. The pendulum swing measuring apparatus
30, measures
the pendulum swing and sends a feedback signal indicative of the position or
the angle of
inclination of the container 4 to the motion control system of the container
crane. Preferably, the
primary carriage 1 is accelerated steadily to maintain the lead of the primary
carriage 1 over the
spreader bar 3 and container 4 and to prevent further oscillations of the
container 4 as it traverses
toward the cargo ship 31, as shown in FIG 22. In transit, the container 4 may
be raise or lowered
by the spreader bar 3 and lifting cables 2 so that it is at the proper height
when it reaches its
destination.
When the primary carriage 1 reaches its intended position above the deck or
the cargo
hold of the cargo ship 31, the primary carriage 1 is brought to a stop with
the secondary carriage
25 positioned to the left of the target position. Stopping the primary
carriage 1 induces the
spreader bar 3 and the container 4 to swing toward the right, as shown in FIG
23. When the
container 4 is directly over its intended position, the secondary carriage 25
is quickly accelerated
to the right R relative to the primary carriage 1 and stopped at the final
position, as shown in FIG
24, to cancel out the one half of a pendulum swing that was induced by
stopping the primary
carriage 1. This brings the spreader bar 3 and container 4 to a stop precisely
over the intended
position with little or no residual pendulum motion, as shown in FIG 25. The
effectiveness of the
pendulum motion cancellation can be measured with the pendulum swing measuring
apparatus
30 and optimized using closed loop feedback control.
Once the spreader bar 3 and container 4 are stopped over the intended
position, their
positions relative to the adjacent containers may be verified using the
carriage scanners 22 and/or
spreader bar scanners 27 described in connection with FIG 5. As the container
4 is lowered into
place, the spreader bar scanners 27 can be used to monitor its vertical, as
well as horizontal,
position relative to the adjacent containers, as shown in FIG 26.
FIGS 27-31 illustrate the operation of the apparatus of FIG 19 performing the
method for
controlling pendulum motion in a container crane according to the present
invention in use for
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unloading containers from a cargo ship 31. The primary carriage 1 of the
container crane, shown
in this example with the secondary carriage 25 in the center of the primary
carriage l, is moved
into position above a container 4 on the deck or in the cargo hold of the
cargo ship 31. The
spreader bar 3 is lowered onto the container 4 and attached to it by
appropriate means; then the
container 4 is lifted by the spreader bar 3 and lifting cables 2, as shown in
FIG 26. Optionally, the
carriage scanners 22 and/or spreader bar scanners 26, 27 described in
connection with FIG 5 may
be used to identify the container 4 and/or to monitor the position of the
spreader bar 3 relative to
the container 4, as well as its vertical and horizontal position relative to
the adjacent containers.
Once the container 4 is clear of the cargo hold or any other obstacles, the
primary carriage 1 is
accelerated toward the off loading location, which is to the right R of the
cargo ship in FIG 27.
Due to their inertia resisting the acceleration, the spreader bar 3 and the
container 4 swing left
relative to the primary carriage l, starting one half of a pendulum swing. The
pendulum swing
measuring apparatus 30 measures the pendulum swing and sends a feedback signal
indicative of
the position or the angle of inclination of the container 4 to the motion
control system of the
container crane. Preferably, the primary carriage 1 is accelerated steadily to
maintain the lead of
the primary carriage 1 over the spreader bar 3 and container 4 and to prevent
further oscillations
of the container 4 as it traverses toward the off loading location, as shown
in phantom lines in
FIG 28. In transit, the container 4 may be raise or lowered by the spreader
bar 3 and lifting cables
2 so that it is at the proper height when it reaches its destination.
Optionally, the position of the
secondary carriage 25 relative to the primary carriage 1 may be adjusted at
the beginning of the
traverse or in transit, as shown by the arrow L in FIG 27, so that it is in
the proper position for
performing the pendulum motion cancellation protocol when it reaches its
destination.
When the primary carriage 1 reaches its intended position over the off loading
location,
such as a dock, truck bed or railway car 24, the primary carriage 1 is brought
to a stop with the
secondary carriage 25 positioned to the left of the target position. Stopping
the primary carriage 1
induces the spreader bar 3 and the container 4 to swing toward the right, as
shown in FIG 29.
When the container 4 is directly over its intended position, the secondary
carriage 25 is quickly
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accelerated to the right R relative to the primary carriage 1 and stopped at
the final position, as
shown in FIG 30, to cancel out the one half of a pendulum swing that was
induced by stopping
the primary carriage 1. This brings the spreader bar 3 and container 4 to a
stop precisely over the
intended position with little or no residual pendulum motion, as shown in FIG
3 l . The
effectiveness of the pendulum motion cancellation can be measured with the
pendulum swing
measuring apparatus 30 and optimized using closed loop feedback control. The
container 4 is
then lowered onto a dock, truck bed or railway car 24 or the like at the off
loading location.
As with the previously described methods, the exact stopping and starting or
deceleration
and acceleration of the apparatus for the pendulum motion cancellation
protocol are not critical
to the present invention. Other pendulum motion cancellation protocols can be
carried out using
the primary carriage 1 and secondary carriage 25 of the apparatus of FIG 19.
By directly
measuring the pendulum motion of the load and using closed loop feedback
control, the
apparatus and methods of the present invention can be used to optimize almost
any pendulum
motion cancellation protocol.
FIGS 32-36 disclose several versions of magnetically damped inclinometers 60.
Damping
the motion of the pendulum 66 increases the accuracy and reliability of the
inclinometer by
damping out oscillations not causes by the primary sway of the object or load.
This stabilizes the
oscillations for calculation purposes, cancels unwanted harmonics, can be used
to reset the
pendulum indicator to plumb, calibration and diagnostics.
These may be used in place of or in combination with the systems discussed
above. FIG
32 is a perspective view of a magnetically damped inclinometer 60 using an
electromagnet 62. A
rotatable shaft 64 extends from the housing of the encoder or potentiometer 9.
In the systems
shown, the inclinometer 60 is connected with the object or load being moved,
for example
connected with one of the spreader bars. However, the inclinometer 60 may be
attached to the
object or load at any convenient location. A pendulum 66 is fixedly attached
to the shaft 64. To
maximize the accuracy of the measurements and the dampening control, a rigid
or generally rigid
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CA 02464819 2004-04-22
material is used to form the pendulum 66. Any motion of the pendulum 66 causes
a
corresponding rotation of the shaft 64, as indicated by the rotational arrows.
Also attached to the
shaft 64 is an index member 68 formed of a ferrous or ferromagnetic material.
The index
member 68 may be located anywhere along the shaft 64 including, as shown, at
or near the end of
the shaft 64. An electromagnet 62 is attached to the object or load and is
located such that when
the pendulum 66 is in its initial, at-rest position, the index member 68 and
the electromagnet 62
are close together. As the object or load is moved, the pendulum 66 will sway,
causing the shaft
to rotate 64 and moving the index member 68 and the electromagnet 62 apart,
thereby increasing
the air gap. As the pendulum 66 swings back, the index member swings past the
electromagnet.
The force of the electromagnet 62 pulls on the index member 68, thereby
decreasing the extent of
the next swing. Since the force from the electromagnet 62 decreases as the air
gap increases, the
extent of the swing is not significantly reduced, but any excess motion is
reduced. This damping
action takes place each time the pendulum 66 passes the index member 68.
FIG 33 is a perspective view of the magnetically damped inclinometer 60 of FIG
32
having a proximity void 70 located in the shaft 64. A proximity sensor 72 is
located above the
void 70. In alternate embodiments, a projection or other object and sensor
could perform the
same function. The proximity sensor 72 is attached to the load or object and
provides information
to the system regarding the orientation of the pendulum 66. The sensor 72 and
void 70
combination may be used for several purposes, including, but not limited to,
calibration or
recalibration of the system, diagnostics for troubleshooting problems with the
system,
measurements for test systems during research on pendulum motion.
FIG 34 is a perspective view of a magnetically damped inclinometer 60 using a
plurality
of permanent magnets. Similar to the inclinometer of FIG 32, the inclinometer
60 shown has a
rotating shaft 64 with a pendulum 66 and ferrous index member 68 attached
thereto. In this
embodiment, permanent magnets 80 are mounted in or on a ring 82. The center of
ring 82 is off
center from the axis of the shaft 64, such that as the pendulum 66 rotates the
shaft 64 from its
initial position, the air gap between the index member and a.ny corresponding
magnet 80 on the
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ring 82 increases. Since the force from the magnet 80 decreases as the air gap
increases, the
extent of the swing is not significantly reduced, but any excess motion is
reduced. This damping
action takes place as the pendulum 66 moves along each swing motion.
FIG 35 is a detail view of an alternate configuration of the magnets in the
inclinometer of
FIG 34. In this embodiment, the index member 68 takes the form of a plurality
of permanent
ferrous or non-ferrous magnets 84 attached around the perimeter of the shaft
64.
FIG 36 is a perspective view of a magnetically damped inclinometer 60 having a
spring-
loaded cam. Similar to the inclinometer of FIG 32, the inclinometer 60 shown
has a rotating shaft
64 with a pendulum 66. In this embodiment, near one. end of the shaft 64 a
first magnet or set of
magnets 90 fixedly attached thereto. A second magnet or set of magnets 92 is
slidably attached to
the shaft 64. In the embodiment shown, the second magnet 92 takes the form of
several magnets
attached to a sliding collar 94 located around the shaft 64. A spring 104 is
located between the
magnets 90, 92. Any type of spring 104 may be used to push the second magnets)
92 away from
the first magnets) 90. In the embodiment shown, the spring 104 takes the form
of a coil spring
104 wound around the shaft 64. The end of the shaft 64 forms a spline 108 that
is located within
a keyway 1 I O of the sliding collar 94. The cam 96 has a cam Lobe 98 forming
a high point. A
roller or other rolling member 100 is connected to the object or load. In the
embodiment shown,
the rolling member 100 rotates around a pin held in a housing 102 attached to
the object or load.
In the initial position, the roller is located against the high point of the
cam lobe 98 and holds the
second magnets) 92 toward the first magnets) 90. As the pendulum 66 rotates
the shaft 64, the
cam 96 rotates and the cam lobe 98 turns to allow the roller 100 to engage a
lower point on the
cam 96. As the rotation takes place the spring 104 pushes the second magnets)
92 away from the
first set of magnets) 90. Each swing motion of the pendulum 66 is damped by
the magnet
attraction between the first and second sets of magnets 90, 92.
Optionally, an actuator 112 may be used in any of the inclinometers 60 shown
to increase
and decrease the air gap between the magnets or electromagnets. The actuator
112 could take the
form of a solenoid, linear actuator or other mechanism to move the magnets
closer or farther
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apart. In the system 60 shown in FIG 36, rolling member 100 is connected to
the actuator 112.
The actuator 112 moves the rolling member 100 and correspondingly the range of
motion of the
sliding collar 94. Typically, the gap would be increased to maximize the
sensitivity during the
initial pendulum motion, thereby creating the most accurate measurement. When
the pendulum
swings back, the actuator 112 would decrease the air gap, thereby maximizing
the damping of the
inclinometer. FIG 37 shows an actuator 112, used with an inclinometer 60 using
a set of magnets
80 mounted on a ring, as shown in FIG 35. In this case, the actuator 112,
moves the ring 82 such
that the magnets 80 or ferromagnetic material on the ring 82 are close to the
magnets) 84 or
ferromagnetic material mounted on the shaft 64, as seen in solid lines, or
farther away from the
magnets) 84, electromagnet, or ferromagnetic material mowited on the shaft 64,
as seen in
phantom lines. If an electromagnet were used, the electromagnet could be
turned off during the
initial swing and turned on during the return swing.
These inclinometers 60 may be used to measure the angle of the spreader bar to
enable
the system to use a single stage response to cancel unwanted sway motion
without calculations.
This creates a system that is faster, more accurate and more reliable than
prior art systems.
The apparatus and methods of the present invention are also readily adaptable
to a
container crane of the type having a carriage movable along two or more axes.
The pendulum
swing measuring apparatus may be adapted for measuring Load sway of the
container along both
axes and the method may be modified for cancellation of pendulum swing motion
along one or
the other of the axes or both simultaneously. The apparatus of FIG 19 is
particularly applicable to
the type of container cranes having a carriage movable along two or more axes
because the
moving beams of such cranes have very high inertia, which makes it more
difficult to perform
the pendulum motion cancellation protocol. A secondary carriage of lower
inertia movable in two
axes relative to the primary carriage greatly facilitates the operation of the
pendulum motion
cancellation protocol.
CA 02464819 2004-04-22
While the present invention has been described herein with respect to the
exemplary
embodiments and the best mode for practicing the invention, it will be
apparent to one of
ordinary skill in the art that many modifications, improvements and
subcombinations of the
various embodiments, adaptations and variations can be made to the invention
without departing
from the spirit and scope thereof.
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