Note: Descriptions are shown in the official language in which they were submitted.
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A METHOD OF CONTROLLING TRANSVERSAL RESONANCE IN A
CATENARY, A HOIST DRUM CONTROL SYSTEM AND A MINE
DRUM HOIST SYSTEM
TECHNICAL FIELD
The present disclosure generally relates to mine drum hoist systems. In
particular, it relates to control of a hoist drum of a mine drum hoist system.
BACKGROUND
Hoist drums which coil the rope in more than one layer normally have Lebus
grooves in which the rope is laid. The grooves are parallel except in the
cross-
over sections in which the groove moves the rope in the axial direction of the
drum a distance which is equal to half the rope diameter, to the next parallel
grove. There are two cross-over sections on the circumference of the drum
surface which means that after a full revolution the rope has been moved by
the Lebus groove one rope diameter. Normally the cross-over sections are
diametrical. This arrangement is called symmetric Lebus.
The drum is normally mounted near the ground surface. The rope runs from
the drum to a head sheave in the head frame above the mine shaft. The rope
angle between the drum and the head sheave is normally in the order of 45
degrees. After passing over the head sheave the rope runs vertically in the
mine shaft. The rope end is connected to a conveyance for transport of
personnel, mineral or equipment. The part of the rope that is between the
hoist drum and the head sheave is called catenary.
The cross-over section pushes the rope over in a short time creating a near
rectangular pulse-shaped "kick" on the rope in a direction perpendicular to
the rope axis, also called transversal kick. The pulse wave can be converted
to
a fundamental sine wave with harmonics by means of Fourier
transformation. If the kick is repeated, i.e. excited with a frequency that
corresponds to the natural or resonance frequency of the catenary the
amplitude of the transversal catenary oscillations will build up to large
unacceptable values. High amplitudes will severely affect the rope life.
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Moreover, high amplitudes can provide discomfort to personnel traveling
with the conveyance.
It is known that by reducing the hoisting, i.e. rope speed when the rope pull
is
near a point where catenary resonance would be generated at that maximum
speed, the resonance point will shift to another rope pull since at the
reduced
speed the excitation or kick frequency of the Lebus on the drum will be
reduced.
For hoists which always run at nominal full speed and with constant load in
the up direction and with zero payload in the down direction, which is the
io case for production hoists, it is normally sufficient to have a pre-set
distance
in the mine shaft where the hoisting speed is reduced. However, this is not
sufficient in case the payload and the speed of the conveyance vary.
SUMMARY
An object of the present disclosure is to solve, or at least mitigate, the
problems of the prior art.
Hence, according to a first aspect of the present disclosure there is provided
a
method of controlling transversal resonance in a catenary of a mine drum
hoist system comprising a hoist drum having Lebus grooves, a head sheave, a
rope having a catenary extending between the hoist drum and the head
sheave and a vertical rope portion, and a conveyance attached to the vertical
rope portion, wherein the method comprises: a) determining a current
payload of the conveyance, b) obtaining a rotation speed of the hoist drum,
corresponding to a first speed of the conveyance, c) determining a transversal
resonance position along the vertical rope portion at which transversal
resonance is generated in the catenary when reached by the conveyance with
the current payload and first speed, wherein the transversal resonance
position is determined based on the current payload and on the hoist speed,
and d) reducing the first speed of the conveyance in a speed reduction zone
which includes the transversal resonance position.
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A technical effect obtainable by reducing the first speed of the conveyance in
a speed reduction zone is that the resonance point is moved away from the
transversal resonance point. As a result transversal resonance does not occur
at the determined transversal resonance position. Moreover, since the first
speed is maintained outside the speed reduction zone, a transversal
resonance position that is moved due to speed reduction will never be
realised, because it is moved to the originally determined transversal
resonance position when the conveyance moves outside the speed reduction
zone. Thus, transversal resonance in the catenary may essentially be avoided
for any payload and any first speed of the conveyance. The payload and/or
speed are thus allowed to vary each time the conveyance is hoisted in the
mine shaft.
One embodiment comprises receiving a first force measurement from a first
load cell of the head sheave and a second force measurement from a second
load cell of the head sheave, wherein step a) involves determining a sum of
force value by adding the first force measurement to the second force
measurement, wherein the current payload is determined based on the sum
of force value.
According to one embodiment the current payload is determined by
subtracting the weight of the vertical rope portion, the weight of the
conveyance and the weight of the head sheave from the sum of force value.
According to one embodiment in step c) the determining of the transversal
resonance position is further based on a resonance frequency of the catenary,
a diameter of the hoist drum, a frequency of an impulse in the rope occurring
at cross-overs of the Lebus grooves, a length of the vertical rope portion
from
a centre axis of the head sheave to a mine shaft opening, a weight of the
conveyance, a rope weight per length unit and the length of the catenary.
According to one embodiment in step c) the transversal resonance position is
obtained from a look-up table which contains pre-calculated transversal
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resonance positions for a plurality of different current payloads and first
speed of the conveyance combinations.
According to one embodiment step d) of reducing the first speed of the
conveyance involves reducing the hoist speed.
One embodiment comprises determining the speed reduction zone based on
the hoist speed obtained in step b), wherein the determining of the speed
reduction zone involves retrieving a speed reduction zone that has been
determined for the transversal resonance position and which has been
determined based on catenary side force values which are proportional to a
difference between a first force measurement measured by a first load cell
and a second force measurement measured by a second load cell.
According to a second aspect of the present disclosure there is provided a
computer program product comprising computer-executable components
which when executed by a processing system causes a hoist drum control
system including the processing system to perform the method according to
the first aspect.
According to a third aspect of the present disclosure there is provided a
hoist
drum control system configured to control transversal resonance in a
catenary of a mine drum hoist system, wherein the hoist drum control system
comprises a storage unit, and a processing system, wherein the storage unit
comprises computer-executable components which when executed by the
processing system causes the hoist drum control system to: determine a
current payload of a conveyance, obtain a hoist speed of a hoist drum,
corresponding to a first speed of the conveyance, determine a transversal
resonance position along a vertical rope portion of a rope to which the
conveyance is attached, at which transversal resonance position, at which
transversal resonance position transversal resonance is generated in the
catenary when reached by the conveyance with the current payload and first
speed, wherein the transversal resonance position is determined based on the
current payload and on the hoist speed, and reduce the first speed of the
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conveyance in a speed reduction zone which includes the transversal
resonance position.
According to one embodiment the processing system is configured to receive
a first force measurement from a first load cell of a head sheave and a second
5 force measurement from a second load cell of the head sheave, wherein the
processing system is configured to determine a sum of force value adding the
first force measurement to the second force measurement, and wherein the
processing system is configured to determine the current payload based on
the sum of force value.
According to one embodiment the processing system is configured to
determine the current payload by subtracting the weight of the vertical rope
portion, the weight of the conveyance and the weight of the head sheave from
the sum of force value.
According to one embodiment the processing system is configured to
determine the transversal resonance position based on a resonance frequency
of the catenary, a diameter of the hoist drum, a frequency of an impulse in
the rope occurring at cross-overs of Lebus grooves of a hoist drum, a length
of
the vertical rope portion from a centre axis of the head sheave to a mine
shaft
opening, a weight of the conveyance, a rope weight per length unit and the
length of the catenary.
According to one embodiment the processing system is configured to obtain
the transversal resonance position from a look-up table which contains pre-
calculated transversal resonance positions for a plurality of different
current
payloads and hoist speed combinations.
According to one embodiment the processing system is configured to
determine the speed reduction zone based on the hoist speed, wherein the
processing system is configured to determine the speed reduction zone by
retrieving a speed reduction zone that has been determined for the
transversal resonance position and which has been determined based on
catenary side force values which are proportional to a difference between a
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first force measurement measured by a first load cell and a second force
measurement
measured by a second load cell.
According to a fourth aspect of the present disclosure there is provided a
mine drum hoist
system comprising: a hoist drum having Lebus grooves, a head sheave, a rope
arranged to
extend between the hoist drum and the head sheave to thereby define a catenary
and a
vertical rope portion, a conveyance arranged to be attached to the vertical
rope portion, a
motor arranged to operate the hoist drum, and a hoist drum control system
according to
the third aspect, arranged to control the motor.
Generally, all terms used in the description are to be interpreted according
to their
ordinary meaning in the technical field, unless explicitly defined otherwise
herein. All
references to "a/an/the element, apparatus, component, means, etc. are to be
interpreted
openly as referring to at least one instance of the element, apparatus,
component, means,
etc., unless explicitly stated otherwise.
BRIEF DESCRIPTION OF THE DRAWINGS
The specific embodiments of the inventive concept will now be described, by
way of
example, with reference to the accompanying drawings, in which:
Fig. 1 is a schematic example of a mine drum hoist system and a hoist drum
control
system;
Fig. 2 is a schematic front view of an example of a mine drum hoist system in
Fig. 1;
Fig. 3a is a schematic side view of a detail of a head sheave in the mine drum
hoist
system in Fig. 1;
Fig- 3b is a schematic front view of a detail of the head sheave in Fig. 1;
Fig. 3c is a schematic front view of the hoist drum and the head sheave in
Fig. 1;
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Fig. 4 is a schematic diagram of a method of controlling transversal
resonance in a catenary of the mine drum hoist system in Fig. 1; and
Figs 5a-5c show graphs of catenary side force values.
DETAILED DESCRIPTION
The inventive concept will now be described more fully hereinafter with
reference to the accompanying drawings, in which exemplifying
embodiments are shown. The inventive concept may, however, be embodied
in many different forms and should not be construed as limited to the
embodiments set forth herein; rather, these embodiments are provided by
way of example so that this disclosure will be thorough and complete, and
will fully convey the scope of the inventive concept to those skilled in the
art.
Like numbers refer to like elements throughout the description.
The present disclosure in general details how transversal resonance in a
catenary may be avoided or at least reduced in a mine drum hoist system by
determining a transversal resonance position along the vertical rope portion
of a rope extending from the head sheave to a conveyance connected to the
vertical rope portion, and by reducing the speed of the conveyance in a speed
reduction zone that includes the transversal resonance position. The
transversal resonance position is determined based on the current payload of
the conveyance which is arranged to be hoisted in the mine shaft by means of
a hoist drum, and on the desired speed at which the conveyance is to move in
the mine shaft, in case the speed is pre-programmed, or on the actual current
speed at which the conveyance moves in the mine shaft, in case the
conveyance speed is operated manually.
By reducing the speed only in the speed reduction zone(s), in case there are
several catenary transverse resonance points, the transversal resonance
point(s) is/are moved away from the determined transversal resonance
point(s).
This disclosure furthermore details which positions along the vertical rope
portion should be categorised as transversal resonance positions in the
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control method, as there may be some transversal resonance positions that
provide less significant transversal resonance in the catenary, where it is
not
necessary to reduce the speed of the conveyance. A tuning method in which
the relevant transversal resonance point(s) is/are selected for the control
method is therefore also disclosed herein. The tuning method also discloses
how the speed reduction zone(s) is/are selected and how much the speed of
the conveyance shall be reduced in the speed reduction zone(s).
Fig.i depicts a mine drum hoist system 1 comprising a hoist drum 5, which is
of Lebus type. The hoist drum 5 hence has a plurality of Lebus grooves 5a, as
shown in Fig. 2. The Lebus grooves 5a have two cross-over sections per turn,
as shown by means of the areas 5b and 5c in Fig. 2.Each cross-over section
translates the Lebus grooves 5a for example half a rope diameter in the axial
direction. In one turn each Lebus groove 5a is hence translated a rope
diameter in the axial direction.
The drum hoist 5 may for example be a single drum hoist or a double drum
hoists. Each of them can be equipped with one or two ropes that carry the
conveyance.
The mine drum hoist system 1 further comprises a head sheave 7, a rope 9
and a conveyance ii. The rope 9 is coiled around the hoist drum 5, in one or
more layers, for example three layers. The rope 9 extends from the hoist
drum 5 to the head sheave 7. The rope 9 has a catenary 9a that extends
between the hoist drum 5, about which the rope is coiled in the Lebus grooves
5a, and the head sheave 7. The rope 9 has a vertical rope portion 9b that runs
from the head sheave 7 to the conveyance. The rope 9 is connected to or
attached to the conveyance 11, so that when the hoist drum 5 is rotated and
the rope 9 is coiled or uncoiled, the vertical position of the conveyance 11
is
altered.
The mine drum hoist system 1 comprises a first load cell 7a and a second load
cell 7b. The head sheave 7 is equipped with the first load cell 7a and the
second load cell 7b. The first load cell 7a and the second load cell 7b are
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utilised for determining a current payload of the conveyance 11 and a
catenary side force on the head sheave 7.
A number of vertical distances are depicted in Fig. 1. A first distance di is
defined as the vertical distance from the head sheave axis A to the mine shaft
opening 13 which is the upper landing level for the conveyance 11. This first
distance di is fixed, and is a known parameter. A second distance d2 is
defined as the vertical distance from the mine shaft opening 13 to the top of
the conveyance 11. The second distance d2 is at its maximum value when the
conveyance is at the bottom landing level. A third distance d3 is determined
as the distance from the head sheave axis A to the top of the conveyance 11,
i.e. the sum of the first distance di and the second distance d2. It is
normally
the second distance d2 that determines a transversal resonance position
along the vertical rope portion 9b, which will be described in more detail in
the following. A transversal resonance position is a position along the
vertical
rope portion 9b at which transversal resonance is generated in the catenary
9a when reached by the conveyance 11 with a particular payload and speed.
The mine drum hoist system 1 comprises a hoist drum control system 3
having a processing system 3a and a storage unit 3h. The storage unit 3b
comprises computer-executable components which when run on the
processing system 3a causes the hoist drum control system 3 to perform the
methods disclosed herein. In particular, the hoist drum control system 3 is
configured to determine a current payload of the conveyance 11. The hoist
drum control system 3 may for example determine the current payload based
on a first force measurement and a second force measurement carried out by
the first load cell 7a and the second load cell 7b, respectively.
The hoist drum control system 3 is moreover configured to obtain a hoist
speed of the hoist drum 5 in metres per second, which is the speed of the
conveyance ii, termed the first speed herein. The hoist speed may be a pre-
programmed parameter for operating the conveyance 11, or it may be a real-
time value obtained for example by measuring the number of revolutions per
time unit of the hoist drum 5.
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The hoist drum control system 3 is furthermore configured to determine a
transversal resonance position along the vertical rope portion 9b at which
transversal resonance is generated in the catenary 9a when reached by the
conveyance ii with the current payload and first speed, and to reduce the
first
5 speed of the conveyance ii in a speed reduction zone which includes the
transversal resonance position.
The transversal resonance position is determined by the hoist drum control
system 3 based on the current payload and on the hoist speed. The
transversal resonance position is equivalent to the second distance d2 for
10 certain positions of the conveyance ii. By reducing the first speed of
the
conveyance 11 to a second speed in the speed reduction zone, by operating the
hoist speed, the transversal resonance position is moved from that
determined by the hoist drum control system 3 to a moved transversal
resonance position. With moved transversal resonance position is meant the
transversal resonance position to which the transversal resonance position is
moved due to the reduction of the first speed. Catenary resonance will
however not occur when the conveyance ii reaches the moved transversal
resonance position because the first speed is only reduced in the speed
reduction zone.
The mine drum hoist system 1 may comprise a motor M and a drive unit 15.
The hoist drum control system 3 may be configured to operate the motor M,
e.g. via the drive unit 15 to thereby control the coiling speed and uncoiling
speed of the rope 9, i.e. the hoist speed, from the hoist drum 5. As a result
the
speed of the conveyance ii may be controlled.
Fig. 3a schematically shows a side view of the head sheave 7, one of the load
cells, in this example the first load cell 7a, the catenary 9a and the
vertical
rope portion 9b. The total force, a sum of force value Ftot, measured by the
first load cell 7a and the second load cell 7b is the sum of the force
provided
by the weight of the head sheave 7 and the vector sum of the rope pull force,
i.e. the vertical component FR and the catenary component FR, which seen as
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vector components have different directions, but they both have the same
magnitude, FR.
According to one variation, the hoist drum control system 3 is arranged to
determine the sum of force value by adding the first force measurement FLa to
the second force measurement FLb, shown in Fig. 3b. The hoist drum control
system 3 is according to one variation configured to determine the current
payload based on the sum of force value Ftot, which is the absolute value of
the vector addition of the first force measurement FLa and the second force
measurement FLb. The current payload may be determined by subtracting the
weight of the vertical rope portion 9b, the weight of the conveyance ii, and
the weight of the head sheave 7 from the sum of force value Ft.t. The catenary
resonance frequency fc, in particular the fundamental resonance frequency,
may be expressed as
1 . ,\I FR
(1)
2.Lc mr
where Lc is the length of the catenary 9a and mr is the weight of the rope in
mass/length unit, e.g. kg/m. A transversal resonance in the catenary is
obtained when an integer multiple of the fundamental rope kick frequency
fexe is equal to the catenary resonance frequency fc. The fundamental rope
kick frequency may be expressed as
, V
fexc = L ' ¨
n=D (2)
where v is the hoist speed in metres/second, and D is the diameter of the
hoist drum 5. In case there are several layers of rope coiled onto the hoist
drum 5, these are also taken into account when calculating the fundamental
rope kick frequency fexe.
The rope pull force value may be expressed as FR=(mc-Fmi+d3*mr)*g, where
mc is the weight of the conveyance ii and mi is the current payload, the third
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distance d3=di+d2, and g is the gravitational acceleration. Thus from the
relation fexc=fC it can be deduced that
((4-v=Lc)2.7nr/g-n1C-Inl)
d 2 = 7C'D dl (3)
mr
In view of equation (3), according to one variation the hoist drum control
system 3 may hence be configured to determine the transversal resonance
position, in addition to the payload and the hoist speed, based on the
resonance frequency of the catenary 9a, the diameter D of the hoist drum 5,
the frequency of an impulse in the rope occurring at cross-overs of the Lebus
grooves, i.e. the rope kick frequency f
-exc, the length of the vertical rope
io portion from a centre axis of the head sheave, i.e. head sheave axis A,
to the
mine shaft opening 13, i.e. the first distance di, the length of the catenary,
the
weight of the conveyance mc, and the rope weight per length unit mr.
A method of controlling transversal resonance in the catenary 9a of the mine
drum hoist system i by means of the hoist drum control system 3 will now be
described with reference to Fig. 4.
In a step a) a current payload mi of the conveyance 11 is determined by means
of the processing system 3a of the hoist drum control system 3. The current
payload may thus for example be determined in the manner described
hereabove.
As has been previously mentioned, step a) may include receiving a first force
measurement from the first load cell 7a of the head sheave 7 and a second
force measurement from a second load cell 7b of the head sheave 7. In this
case step a) involves determining a sum of force value by adding the first
force measurement to the second force measurement, wherein the current
payload is determined based on the sum of the force value Ft.t. In particular,
the current payload may be determined by subtracting the weight of the
conveyance 11, the weight of the vertical rope portion 9b and the head sheave
7 from the sum of force value Ft.t.
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In a step b) a hoist speed v of the hoist drum 5 is obtained. The hoist speed
v,
which is proportional to the first speed of the conveyance 11, may be a
proportional to a desired maximum speed of the conveyance, i.e. a pre-
programmed parameter, or it may be determined in real-time.
It should be noted that it is not necessary for steps a) and b) to be
performed
in the above order; their order may be interchanged.
In a step c) a transversal resonance position, which is a certain second
distance d2, along the vertical rope portion 9b is determined. The transversal
resonance position is determined based on the current payload mi and on the
hoist speed v. The transversal resonance position may according to one
variation be determined by means of equation (3). Alternatively the
transversal resonance position may be retrieved from a look-up table in
which a plurality of combinations of hoist speed and current payload are
stored.
According to one variation in step c) the determining of the transversal
resonance position is further based on a resonance frequency fc of the
catenary, a diameter d of the hoist drum 5, the frequency f
-exe of an impulse in
the rope 9 occurring at cross-overs of the Lebus grooves 5b, the length, i.e.
the first distance di, of the vertical rope portion 9b from a centre axis,
i.e.
head sheave axis A, of the head sheave 7 to a mine shaft opening 13, the
weight of the conveyance mc, the length of the catenary 9a and the rope
weight mr per length unit.
In a step d) the first speed of the conveyance 11 is reduced by the hoist drum
control system 3 by reducing the hoist speed in a speed reduction zone which
includes the transversal resonance position. The reduction of the first speed
may thus for example be obtained by the hoist drum control system 3
controlling the drive unit 15, which in turn operates the motor M that drives
the hoist drum 5.
The speed reduction zone may be determined by retrieving a speed reduction
zone that has been determined for the transversal resonance position during
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a tuning/calibration procedure. The speed reduction zone may during the
tuning procedure be determined based on catenary side force values Fc which
are proportional to a difference between a first force measurement FLa
measured by the first load cell 7a and the second force measurement FLb
measured by the second load cell 7b. This procedure will be described in
more detail in the following.
The tuning of the control procedure for the hoist drum control system 3 is of
importance to be able to determine relevant transversal resonance positions,
to thereby obtain efficient equipment, mineral and personnel transportation
by means of the conveyance ii. Thus, prior to commissioning of the mine
drum hoist system 1 and of the hoist drum control system 3, hoist drum
control may be tuned or calibrated. The tuning procedure will be described in
the following.
Turning to Fig. 3e, this illustration schematically shows a front view of the
hoist drum 5, the head sheave 7, the first load cell 7a and the second load
cell
7b. As may be seen in Fig. 3c, a fleet angle a between a vertical central axis
defined by the head sheave and the catenary 9a is shown in two extreme
positions. The fleet angle a depends on how much rope 9 has been uncoiled
from the hoist drum 5, as the catenary moves between left and right along the
axial direction of the hoist drum 5 during coiling operations.
According to one variation the hoist drum control system 3 is configured to
determine a theoretical catenary side force value Fci by determining the
catenary component FR, which is the rope pull, by means of the first force
measurement FLa with the first load cell 7a and the second load measurement
FLb the second load cell 7b, as has been described previously, and by
multiplying the rope pull with sinus a, i.e. Fesin(a), where a is the fleet
angle. The theoretical side force value Fci, as shown for a number of second
distances d2 is shown in the plot in Fig. 5a. The tuning procedure hence
utilises first force measurements of the first load cell 7a and second force
measurements of the second load cell 7b, measured along the entire mine
shaft in which the conveyance ii is to be transported vertically. It can be
seen
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that the theoretical catenary side force value Fci changes as the conveyance
11
moves along the vertical axis in the mine shaft, i.e. as the second distance
d2
changes. In reality, the plot looks more like the example shown in Fig. 5b,
where catenary oscillation forces due to transversal kicks which increase
5 largely at resonance in the catenary 9a are superimposed onto the
catenary
side force value Fci. A plot with catenary side force values Fc is thus
obtained.
Each area with increased catenary oscillations in a plot like then one shown
in Fig. 5b corresponds to a transversal resonance position. Each catenary side
force value Fc is proportional to the difference between the first force
10 measurement FLa from the second force measurement FLb. The catenary side
force values Fc may thus be determined based on the difference between the
first force measurement FL, and the second force measurement FLb at each
measurement point.
The magnitude of these catenary oscillation forces in the plot in Fig. 5b may
15 be utilised by for example a commissioning engineer to determine whether
a
transversal resonance position is large enough to motivate a speed reduction
of the conveyance and thus whether to determine a speed reduction zone
around such a transversal resonance position. The commissioning engineer
may for example calculate the difference between the maximum and
minimum of a number of values over a period of time for this purpose. By
means of studying the area in which a transversal resonance position occurs,
the speed reduction zone may also be determined, i.e. how far before a
transversal resonance position and how far after a transversal resonance
position a speed reduction zone is to be defined. The speed reduction zone
may for example in a first step be determined or obtained by a qualified guess
by the commissioning engineer when studying a plot like then one presented
in Fig. 5b. The conveyance 11 may afterwards be subjected to a test drive
utilising the determined speed reduction zone. The catenary side force values
Fc are then once again determined by means of the proportionality to the
difference between the first force measurement FL, and the second force
measurement FLb at each measurement point. It can then be verified whether
the determined/guessed speed reduction zone is sufficient for reducing or
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eliminating the catenary oscillations at a transversal resonance position, or
whether the speed reduction zone must be modified. This procedure may be
repeated/iterated until a satisfactory result has been obtained. A thus
determined speed reduction zone for a plurality of transversal resonance
positions may then be stored by the hoist drum control system 3. Thus, when
the hoist drum control system 3 at a later time, for the purpose of
controlling
transversal resonance in the catenary 9a, as described above, determines a
transversal resonance position for a certain payload, the hoist drum control
system 3 may be configured to determine the speed reduction zone for that
transversal resonance position by retrieving a suitable speed reduction zone
for that transversal resonance position during tuning/calibration.
Furthermore, the second speed, i.e. the reduced speed may also be
determined by the commissioning engineer. The method of controlling
transversal resonance in a catenary 9a may thus be tuned/calibrated.
Fig. 5c shows a plot in which the values in Fig. 5a have been subtracted from
the measurement values in Fig. 5b, i.e. Fc2=Fc-F1, to obtain an adjusted
catenary side force values Fc2. The adjusted catenary side force values Fc2
provide better supervision of the tuning since the graph extends parallel to
the x-axis. The maximum and minimum limits can in a simpler manner be
defined and supervised. According to one variation, the hoist drum control
system 3 is configured to determine the difference between the maximum
and minimum of a number of values over a period of time of the catenary side
force values Fc or the adjusted catenary side force values Fcs.
The inventive concept has mainly been described above with reference to a
few examples. However, as is readily appreciated by a person skilled in the
art, other embodiments than the ones disclosed above are equally possible
within the scope of the inventive concept, as defined by the appended claims.
