Note: Descriptions are shown in the official language in which they were submitted.
CA 02282004 1999-09-09
METHOD AND DEVICE FOR COMPENSATING CRANE BOOM
DEFORMATION IN LOAD LIFTING AND PLACING
The invention relates to a method and device for compensating for
crane boom deformation during load lifting and placing.
It is known that a crane boom deforms relative to its unloaded
condition when lifting a load, this deformation being proportional to the
load. Optimizing the capacity of a crane boom requires that these
deformations be taken into account.
Problems may result especially in lifting and placing a load. Fig. 3
depicts a crane boom 1 of a crane in the unloaded condition, a load 2 to
be lifted being secured to the crane hook. To achieve lifting, the lifting
1 o force F~, which counteracts the force resulting from the weight of the
load, FL, is gradually increased. Only when the force Fl;rc exceeds the force
FL is the load lifted from the ground. When the lifting force Flirt is still
somewhat less than the force FL incurred by the weight of the load,
considerable forces act on the crane boom 1 even though the load 2 to be
lifted is still fully on the ground. This results in deformation of the crane
boom 1 as is illustrated in Fig. 4a. The deformation of the crane boom 1
caused by the lifting force results in an increase in the horizontal distance
of the boom jib away from the fulcrum point~of the upper structure, this
distance generally being termed radius or length of jib.
2 o Fig. 4b depicts vectorially the forces acting on the load 2 when the
boom is deformed in such manner. Due to the increased radius of the
crane boom 1, the force F'urc which acts on the load is composed of a
vertical component F~;rc, for overcoming the weight force FL incurred by the
load, and a horizontal component Fp. When lifting force Fl;n is sufficient to
2 5 overcome the force incurred by the weight of the load, the force Fp acting
in the horizontal direction results in the load swinging upon being lifted.
This may result in hazardous situations when e.g. unloading concrete
wall elements from a truck since the lifted load has uncontrolled
movement and, thus, becomes a hazard to man and equipment in the
3 o vicinity. Also, such a situation requires a greater force F'i;rc to be
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generated by the hoisting mechanism in order to lift the load. This is
greater than the lesser force F~,c which would be required if the lifting
force is applied in a purely vertical direction by a boom which is not
shifted laterally by such deformation as illustrated in Figure 4a.
Similar undesirable effects occur when placing the load. As
illustrated in Fig. 5, the crane boom 1, supporting a lifted load, is
deformed as it is just about to place the load. This is shown at A in Fig. 5.
When load is placed and the force acting on the load 2 from the crane
boom 1 is then slowly reduced, this results in the crane boom 1
1 o translating into its non-deformed unloaded condition, as identified by B
in
Fig. 5. To unhook or release the load, the jib of the boom 1 needs to be
repositioned directly above the load 2 since, otherwise, the crane hook on
release would tend to swing once released. However, the situations in
placing the load are generally not as critical or dangerous as in lifting the
load since the friction force of the load at the moment of placement
prevents the load itself from swinging.
To compensate for the deformation of the boom during lifting and
placing of a load, the crane operator must change the angle of the boom 1
by actuating the elevating mechanism 3 in order to compensate for the
2 o increase or decrease in radius resulting from deformation. Thus, the
operator would compensate by elevating the boom during lifting and
compensate the reduced deformation of the boom when placing the load
by lowering the boom. Since operation of the crane boom must always be
as near optimum as possible, and the deformation of the crane boom may
be considerable as a result of the high forces involved, proper
compensation is important for lifting and placing a load.
In these compensating actions, i.e. elevating and lowering the boom,
the crane operator acts as the controller. The flow of information in such
a compensating action is illustrated in Fig. 6. The crane operator observes
the working area and takes note, e.g. when lifting a load, of the
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momentary radius of the crane boom in the unloaded condition. This
serves as the target value for him for the radius of the boom in the
complete elevating procedure. A device for limiting the loading moment
(LML) shows him the information obtained via sensors as to the actual
condition of the boom, it being particularly the information regarding the
radius that is of importance to him, this serving as the actual value for
his controlling response. In addition, other values as regards the actual
condition of the crane could also be displayed to be likewise taken into
account in compensating the situation. For this purpose the crane
l0 operator needs to always keep an eye on the working area, in addition to
noting the displayed actual values, to keep a check on the effect of his
actions.
In such a compensating procedure it is necessary that the crane
operator has sufficient experience. Otherwise, uncontrolled and, thus,
hazardous operating conditions may easily arise in lifting the load. The
crane operator needs to observe several displays at the same time whilst
operating various control levers to suitably control the hoisting or lifting
mechanism for lifting the load, and suitably track the elevating
mechanism to compensate for deformation of the crane boom. This puts a
2 0 considerable strain on the crane operator, who is required to
simultaneously observe various displays and operate the various control
levers, so that he may no longer be able to fully concentrate at all times
on the working area. This increases the chances that hazardous operating
conditions may arise. This may result in danger for man and machines in
2 5 the vicinity when a load is lifted.
An object of the present invention is to provide a method and device
for compensating the deformation of a crane boom upon lifting and
placing of a load by which safety in crane operation may be enhanced.
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In accordance with the invention, a controller device is provided
which receives data pertaining to the sensed deformation of the crane
boom, as well as a target value for the position of the crane boom. From
these two input variables, i.e..the target value for the position of the crane
boom and the actual value of crane boom deformation as measured or
established from measured variables, suitable control signals are
established by a controller device which signal or control at least one
positioner for the crane boom. The crane boom is, thus, maintained in a
suitable position during lifting or placement of a load, substantially in its
l0 target position.
For example, for an ever-increasing lifting force and a
corresponding increasing deformation of the crane boom, resulting in an
increased radius, the position of the crane boom is modified so that the
target position of the crane boom, more particularly of the crane boom jib,
remains substantially unchanged. The jib of the crane boom is thereby
maintained plumb above the load to be lifted without any horizontal
displacement, irrespective of the magnitude of the momentary lifting force.
More particularly, the angle of elevation of the crane boom may be
adjusted by the boom elevating mechanism so that the crane boom jib
2 o remains plumb above the load to be lifted even with increasing curvature
of the crane boom.
It is also possible to maintain the angle of elevation of the crane
boom constant and to alter, e.g., the length of the crane boom or the
position of the crane carnage. The controlling action may also be achieved
2 5 by modifying concurrently several manipulated variables such as, e.g., the
length of the crane boom and the angle of elevation, as long as it is
achieved during lifting or placement of a load that the jib of the boom
always remains substantially directly above the load which is standing on
the ground despite changes in boom condition resulting from the lifting
3 0 forces.
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In detecting the deformation of the crane boom, the measured
values of various sensors may be employed. In this respect it is of
particular advantage to employ the following sensors: a position
transducer arranged at the jib of the crane boom for measuring at the
lower end the momentary angle of elevation of the crane boom jib; a
position transducer disposed on the crane boom jib and measuring the
momentary angle of elevation of the crane boom jib; a linear transducer
for measuring the overall length of the crane boom; a pressure transducer
on the elevating mechanism, especially on the elevating cylinder; a
1 o transducer for measuring the load or change fn load of a single section
(i.e., a telescoping section of the boom), such as one or more strain gauges
or a load sensing roller arranged at the upper end of the crane boom and
located on the upper end of the elevating jib for measuring the force
acting momentarily on the jib of crane boom. It is possible thereby to
make use of the data provided by all of the above sensors in detecting the
deformation or radius of the crane boom. In addition, of course, use may
be made of further data sensed by further sensors of the crane or crane
boom to support the controlling action.
It is also possible to detect the deformation of the crane boom with
2 0 but one of the aforementioned sensors or with any combination thereof.
Thus, the deformation of the crane boom may be detected e.g. by making
use only of the data of a position transducer on the underside or in the
lower region of the boom, a position transducer on the upper side or in
the upper region of the crane boom and a linear transducer which senses
2 5 the overall length of the crane boom. As an alternative it is also
possible
to use the data of other sensors for the controlling action from which the
actual deformation of the crane boom may be detected. This may also be
done e.g. by means of the data of a pressure transducer on the elevating
cylinder or a linear transducer for detecting the length of the crane boom
3 o as a whole. In addition, for this purpose use may be made of the data
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furnished by a position transducer in the upper or lower region of the
crane boom, it also being possible to detect the data relevant to
controlling the deformation of the crane boom by making use of a
combination of the aforementioned sensors.
To enhance the quality of the controlling action it may be of
advantage to obtain the deformation values of the crane boom on the
basis e.g. of families of characteristics detected by testing prior to actual
use of the crane.
The aforementioned combinations of the individual sensors are
cited merely as exemplary embodiments, it being possible to make use of
other sensors for measuring specific variables, whereby then the total
deformation of the crane boom may be sensed from the combination of
the variables detected by these sensors.
In one embodiment of the invention the deformation of the crane
boom may be detected by the actual value of the radius of the crane boom
being sensed by one or more suitable sensors. It is also possible as
described above, to detect the magnitude of the momentary deformation
or radius of the crane boom from individual or several measured variables
of the crane, such as the actual boom length or actual boom elevation, in
2 o conjunction with the momentary lifting force. In general, each and every
individual measured variable or combination of measured values may be
used to determine the deformation of the crane boom from which it may
be detected how the deformation or radius of the crane boom has
changed. This then provides a measure of the horizontal spacing between
the standing load and boom jib.
In addition to the measured values serving to detect the
deformation of the crane boom, the controller device may also be
furnished advantageously with even further values, such as the desired
rate and direction of movement of the hoisting or lifting mechanism. This
3 o manipulated variable may be entered by the crane operator via a control
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lever. From the desired rate of the hoisting mechanism the controller is
able to detect the deformation time profile that the crane boom will
probably have and, thus, suitably control the positioner of the crane boom
to maintain the latter in its target position.
For the target value for the position of the crane boom it is preferred
to use the radius of the boom immediately prior to placement of a load or
immediately prior to lifting a load, the crane boom jib in each case being
located plumb above the load without any lateral displacement. When the
controlling action is in accordance with this target value, the conditions of
1 o the crane boom in lifting or placing a load as shown in Figs. 4 and 5 may
be avoided. It is also possible, however, to take the position of the crane
boom on activation of the controller device as the target value. It would
then be the task of the crane operator to make sure that the controller
device is activated at a suitable moment in time, i.e. when the boom jib is
precisely above the load.
The signals output by the controller device are preferably those with
which the positioner of the crane boom, such as the elevating mechanism
of the crane may be controlled, so that the rate of change in the angle of
elevation of the crane boom, and also the direction of the change in the
2 o angle of elevation, may be controlled via the rate and direction of
movement of the elevating mechanism. As a result, the horizontal
departure of the crane boom jib from the target position, the position
plumb above the load, may be controlled. For example, in the operating
condition as shown in Fig. 4a, in which the crane boom jib is no longer
2 5 located plumb above the load to be lifted, the elevating mechanism can be
controlled so that the angle of elevation of the crane boom is increased,
thereby returning the jib of the crane boom to a position which is plumb
above the load to be lifted.
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It is further of advantage to control the hoisting mechanism as the
crane boom positioner, i.e. by controlling the hoisting mechanism so that
the rate and/or direction of movement of the hoisting mechanism is
controlled. In this arrangement the controlling action may be done, for
example, in conjunction with the control of the elevating mechanism, as
described above, so that the complete lifting or placement action of a load
is controlled so that no jerking movements or undesirable side swinging
movements of the load occur.
It is also possible to control automatically only one variable, or only
1 o certain variables of a positioner as noted above, whereby other control
variables may be defined directly by the crane operator, such as detecting
whether the hoisting mechanism is to implement a lifting or lowering
movement. The controller device needs only to receive suitable input
variables from which the deformation or actual departure of the crane
boom from a target condition may be sensed in order to determine
therefrom suitable control signals which are then output to bring the
crane boom, more particularly the crane boom jib, to the desired position.
Since embodiments are possible in which a plurality of input
variables are applied to the controller device, such as the actual value of
2 o the angle of the boom, the actual value of the length of the boom, the
measured lifting force and the like, and furthermore, a plurality of output
variables need to be output from the controller device, such as the
direction and rate of movement of the hoisting mechanism and the
direction and rate of change of the actual position of the elevating
mechanism, it is of advantage to use a fuzzy controller. This kind of
control may be appreciated as a kind of fuzzy expert system, the control
response of which may be defined in a quasi-natural language on the
basis of linguistic expressions, one exemplary definition of the controlling
action being e.g.:
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WHEN radius of the jib position is rather large AND lifting is rapid
THEN raise the boom angle quickly AND lift the load slowly
By way of explanation, the preceding logical statement relates to a
situation wherein a large control deviation, such as a long radius, occurs,
and the crane operator further dictates that lifting is to be achieved at a
relatively high rate. In this situation, the fuzzy controller device would
output control signals which prompt a fast change in the radius to the
target position, such as a fast increase in the angle of elevation of the
crane boom relative to the horizontal, and at the same time the hoisting
mechanism is controlled so that the rate at which the load is to be lifted is
made to be relatively slow, i.e. slower than defined by the crane operator.
In a situation as set forth, it may even be necessary that the load is
lowered at moments, rather than raised, in order to control deformation of
the boom.
In general, a fuzzy control action is composed of a plurality of such
linguistic conditions for describing the various possible control actions.
Collectively, such control actions comprise the control algorithm. For
implementing such a controlling action, recourse may be made to the
experience of the crane operator who, as already mentioned, needs to
2 o implement boom elevating and lowering actions manually in the usual
manner.
An apparatus in accordance with the invention for compensating for
the deformation of a crane boom in lifting or placing a load comprises a
positioner for positioning the crane boom so that it may be maintained
substantially in a target position, i.e., so that the crane boom jib exhibits
substantially no horizontal displacement from a target position. Further, a
measuring device, or a combination of several measuring devices, is
provided in a controller device for detecting the deformation of the crane
boom for defining a target value for the crane boom position. The
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positioner for the crane boom is coupled to the controller device so that
the target position of the crane boom may be set by the controller device
from the defined target and actual values.
Preferably the device for measuring or detecting the deformation of
the crane boom is a sensor, or a combination of several sensors, capable
of measuring or detecting the radius and/or curvature of the crane boom,
as indicated above.
Sensors may be provided which measure, e.g., the boom length, the
angle of elevation of the boom, or the actual lifting force acting on the
1 o crane boom. It is not necessary, of course, as already mentioned above,
that all of the aforementioned sensors are used. It is possible that only
one or more sensors are used in combination for measuring or detecting
the deformation of the crane boom.
In a preferred embodiment, the elevating mechanism of the crane is
used as the positioner for controlling the position of the crane boom and
maintaining the boom at a target position. In such an embodiment the
rate and/or direction of the change in the angle of elevation of the crane
boom may be adjusted in order to maintain the target position. It is
likewise possible to use the hoisting mechanism of the crane for the
2 o controlling action. It is also possible to make use of the elevating
mechanism and hoisting mechanism in combination for suitably
maintaining the target position of the crane boom, such as by adapting
the lifting force produced by the hoisting mechanism in lifting a load to
the momentary position of the elevating mechanism so that no excessive
or jerking deformation of the crane boom may occur.
Preferred embodiments of a method and apparatus in accordance
with the invention will now be discussed with reference to the
accompanying drawings in which:
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Fig. 1 is a block diagram representing the control loop in
accordance with the invention;
Fig. 2 is a flow diagram of the information in accordance with the
invention for controlling the deformation of the crane boom;
Fig. 3 is an illustration of an unloaded crane boom to which a load
is secured,
Fig. 4a is an illustration of a loaded crane boom applying a lifting
force to a load, wherein the lifting force has not increased to a magnitude
sufficient to actually lift the load;
l0 Fig. 4b is a force diagram representing the forces occurring at the
load as shown in Fig. 4a;
Fig. S is an illustration of a loaded crane boom directly after having
placed a load as well as of an unloaded crane boom; and
Fig. 6 is a flow diagram of the information for conventionally
elevating or lowering the crane boom by the crane operator.
Referring now to Fig. 1 there is illustrated an embodiment of a
control loop in accordance with the invention whereby the crane operator
is able to switch the controller in and out of circuit and to define merely
manipulated variables or target variables for the direction and/or rate of
2 0 movement of the hoisting mechanism for the controller. The crane
operator is thus able, e.g., via a single control lever for the hoisting
mechanism, to affect lifting and placing of a load with the controller
device controlling the boom so that the crane boom jib is always
maintained above the load (at the target position) and no horizontal
shifting of the jib occurs which, as described above, may result in
hazardous swinging when lifting a load.
The controller 10 as shown in Fig. 1 receives input of data
representing actual values of variables as measured by sensors 12 which
define the actual condition of the boom. Useful data may be provided by
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sensors which measure the curvature or radius of the boom; the angle of
elevation of the boom, more particularly the angle of elevation at the
upper and lower ends of the boom, respectively; the boom length; the
forces acting on the boom; or the pressure existing at the elevating
cylinder. The actual value of the angle of elevation of the boom and the
actual value of the length of the boom are particularly useful values.
In this arrangement the values measured by the sensors are first
transferred to a boom monitor 14 which may also handle additional
functions, such as load moment limiting (LML). Boom monitor 14 then
1 o applies the values as measured by the sensors and, where necessary,
further processed, to the controller 10. At this stage certain features may
already be extracted from the measured values, for example, in making
use of characteristics or suitable computations.
The boom monitor 14 may further record the actual values of the
boom characteristics measured by the sensors upon activation of the
controlling action, such as the sensed radius, as the target values to
which the subsequent controlling action is to respond. It is likewise
possible, as evident from Fig. 1, to record the target value in a separate
memory MEM 16. In this arrangement the target value may be recorded,
2 0 e.g., upon activating the controller. It is also possible, however, to
store
the target value automatically upon sensing the load or upon lifting the
load. This may be done, e.g., as soon as a freely selectable tensile force
(e.g. 50 KG) is exceeded. It is the difference between this stored target
value and the measured actual value of the radius - the error - that is
2 5 applied to the controller.
Input from the operator is provided manually by levers and
switches or the like, identified collectively at 18 in Figure 1. Signals for
operator input of movement direction, rate of movement, etc., and
activation or de-activation of the controller may be thus input. From the
3 0 input variables the controller detects, by means of the fuzzy control
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algorithm specified by linguistic expressions, the output variables for
controlling the hoisting mechanism and/or the elevating mechanism
and/or the telescoping mechanism. Signals controlling the direction
and/or rate of change are output, as shown at l0a and lOb to the
hoisting mechanism, and/or at lOc and lOd to the elevating mechanism.
Such control may also be applied by the controller to a telescoping
mechanism (not shown). The hoisting mechanism influences the
deformation of the boom via the lifting force applied to the lifting cable
supported by the boom. The elevating mechanism sets or adjusts the
angle of elevation of the boom. In this arrangement the length of the boom
or the angle of elevation must always be adjusted or controlled so that the
momentary deformation of the crane boom resulting from the changing
load is compensated in each case so that the jib of the crane boom has
substantially no horizontal departure from its target position.
Referring now to Fig. 2 there is illustrated a flow diagram of the
information in an operation for compensating for boom deformation in
accordance with the invention. The working area is firstly observed by the
crane operator. When the crane operator sees that, e.g., a load is to be
lifted, he activates the controlling action and defines a manipulated value
2 0 for the hoisting mechanism via a control lever. The controlling action
receives as additional input data representing the actual values detected
by the sensors for the deformation of the boom, which are transferred
from the boom monitor by, for example, a CAN bus, to the controlling
action.
2 5 From these input variables control signals for the movement of the
winch of the hoisting mechanism and/or for the elevating mechanism are
output, both of which influence the position and shape of the boom.
Accordingly, the crane operator simply defines a manipulated value, e.g.,
rate of lift for desired lifting of a load. The controlling action controlling
3 0 the crane boom, such as the 'elevating mechanism and hoisting
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mechanism, take into account the defined manipulated value so that
substantially no variation of the radius of the crane boom occurs. The
boom monitor, which may also serve to define or limit the loading
moment, as described above, indicates the measured actual value of the
crane boom to the crane operator.
Accordingly, the controlling action in accordance with the invention
relieves the crane operator from some of the monitoring tasks typically
required of him hitherto in lifting and placing a load so that he is now
able to more fully concentrate on the working area.
