Note: Descriptions are shown in the official language in which they were submitted.
APPARATUS AND METHOD FOR MEASURING THE TENSION
OF CABLES SUPPORTING A SCAFFOLD IN A SHAFT
FIELD OF THE INVENTION
The present invention relates to an apparatus for measuring the tension on
cables in a vertical shaft.
BACKGROUND OF THE INVENTION
At present, the suspension force on a scaffold suspended in a vertical shaft
is measured by means of tension measuring devices located at the joint between
stabilizing cables and the scaffold. However, during installation, first the
stabilizing cables have to be removed, and the tension measuring device has to
be treated for dust protection and water-proofing. Since the scaffold will be
at a
lower position in the shaft as construction proceeds, there will be higher
tension
on the cables. Consequently, the cables will have a high torque, and will
twist
violently when they are being removed, possibly causing injuries to workers
and
twisting of the scaffold because of unbalanced stress. Moreover, the tension
measuring device must be installed between the cables and the scaffold in the
initial stage of shaft construction, it is difficult to transfer signals from
the
underground area to the shaft mouth, and it is difficult to effect real-time
tension
measurement. As well as the tension measuring device approach, a steel cable
tension measuring device can be clamped onto the steel cable, and the
suspension force of the hanging scaffold measured indirectly by measuring the
force acting laterally on the cable, or a measuring device for measuring
longitudinal deformation of the steel cable can be clamped onto the cable to
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measure the suspension force of the hanging scaffold indirectly. However, the
indirect measurement approach by measuring the lateral force with a device
clamped onto the cable is convenient only for thinner steel cables. For
thicker
suspension and stabilizing cables, the lateral force is very high and the
measurement may be inaccurate because of the short distance and high rigidity.
At the same time, the cable may be damaged because it is bent too much. If a
measuring device for measuring the longitudinal deformation of the cable is
clamped onto the cable to measure the tension indirectly, a set of wireless
node
transmission devices must be added in order to improve the measurement of
cable tension in the hoisting system. That brings a challenge to tension
measuring cost control.
SUMMARY OF THE INVENTION
Technical problem: To overcome the drawbacks in prior art systems, the
present invention provides an apparatus and method for measuring suspension
and stabilizing cable tension in a vertical shaft. The apparatus is
structurally
simple, does not require moving the stabilizing cables and is easy to operate.
The
method can measure tension accurately in real time.
Technical scheme: The apparatus for measuring tension of a suspension or
stabilizing cable in a vertical shaft of the present invention comprises an
apparatus
for measuring the tension on a suspension or stabilizing cable in a vertical
shaft
comprising a signal processor (9), a shaft lid (8), a frame (6) mounted on the
shaft
lid (8), a sheave (5) mounted on the frame (6); a winch (10) mounted on the
frame
(6) beneath and spaced apart from the sheave (5); a cable with one end fixed
to
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the winch (10) and a second end running over the sheave (5) in an inclined
manner
and then extending vertically into the shaft and connected to a scaffold (1)
in the
shaft; a tension measuring device (4) mounted on the frame (6) including a
bearing
pedestal (4-1), a pressure measuring device (4-2), and a bevelled support (4-
3)
fixed to the frame (6), the pressure measuring device (4-2) and the bearing
pedestal (4-1) are mounted on the shaft of the sheave (5) and fixed on the
bevelled
support (4-3); and a frequency measuring device (7) clamping the cable mounted
on the shaft lid (8) for transmitting wireless signals to the signal processor
(9),
which processes the signals and carries out tension calculations.
The angle of inclination of the top surface of the bevelled support is one-
half
of the angle between the inclined section of the suspension or stabilizing
cable
running between a winch and a sheave and the vertical section of the cable.
The frequency measuring device comprises two vibration blocks arranged
symmetrically on the opposite sides of a suspension or stabilizing cable, an
accelerometer fixedly mounted at the outer side of one of the vibration
blocks, a
wireless transmitter on the accelerometer, a plurality of wheels between the
vibration blocks tightly clamping the suspension or stabilizing cable, springs
extending between the upper part and lower ends of the vibration blocks, and
movable translational wheels on the bottom of the vibration blocks clamped to
a
tracks on the shaft.
A method of measuring the tension in a suspension or stabilizing cable in a
vertical shaft using the above-described apparatus, wherein the tension T on
the
cable is measured in real time by the pressure measuring device, and the
tension
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T on the cable is measured at regular intervals using the frequency measuring
apparatus, and the tension measured by the frequency measuring device is used
to correct the pressure measuring device, comprising the following steps:
a) measuring the tension on the cable using the pressure measuring device
in
real time when the tension on the cable acts on the bearing pedestal via the
hoisting sheave. The force acting on the device is transferred to the
pressure measuring device that is fixedly connected to the bearing pedestal.
If the angle between the inclined section of the cable and the vertical
section
of the cable is a, the tension of the cable is T, it is seen from the force
composition principle that the pressure acting on the pressure measuring
device perpendicular to the surface of the pressure measuring device, the
pressure F measured by the pressure measuring device is:
a
F =2T = cos ¨)
,2
and thus, the tension T of the suspension cable or stabilizing cable is:
F
T= 2cos(¨a`
2j
b) measuring the tension on the cable using the frequency measuring device
at
regular intervals. Since the translational wheels clamp into the track on the
shaft lid, the frequency measuring device can move only horizontally. The
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clamping wheels are rotatably mounted on the vibration blocks, and the
clamping springs pull the blocks towards each other pressing the wheels
against the cable whereby the steel cable can move only vertically. The
accelerometer is mounted outside of one of the vibration blocks and
transmits lateral vibration acceleration signals of the cable to the signal
processor via the wireless transmitter on the accelerometer. The signal
processor processes the signals to obtain the lateral vibration frequency w
of the suspension cable or stabilizing cable, and then calculates the tension
of T of the steel cable according to the length I of the cable during
measurement and the density p of the steel wire cable using the equation:
T = ___________________________________ w + pg1
Z2
c) comparing the tension measured by the pressure measuring device
with the
tension measured by the frequency measuring device, thus determining
whether the pressure measuring device is inaccurate and has to be adjusted
or replaced if the difference between the two tension values is higher than
20%.
Beneficial effects: with the above-described apparatus and method, the
suspension or stabilizing cable tension measuring device can effectively avoid
measurement errors incurred by the upsetting moment of the bearing pedestal.
In
addition, a frequency measuring device mounted on the shaft lid is used to
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measure the tension of the steel cable on a regular basis to correct the
tension
result of the pressure measuring device. Thus, inaccurate tension measurement
results caused by a faulty pressure measuring device operating in real time
can be
avoided. The apparatus is simple in structure, convenient to operate, capable
of
performing real time measuring, easy and convenient to install without
removing
stabilizing cable, accurate in measurements and convenient for signal
transmission.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic cross section of a vertical shaft;
Fig. 2 is a schematic front view of a pressure measuring device; and;
Fig. 3 is a schematic front view of a frequency measuring device
In the drawings: 1 is a suspended scaffold, 2 is a suspension cable, 3 is a
stabilizing cable, 4 is a tension measuring device, 4-1 is a bearing pedestal,
4-2 is a
pressure measuring device, 4-3 is a bevelled support, 4-4 is a bolt; 5 is a
sheave, 6
is a frame, 7 is a frequency measuring device, 7-1 is a vibration block, 7-2
is an
accelerometer, 7-3 is a clamping spring, 7-4 is a clamping wheel, 7-5 is a
translational wheel, 8 is a shaft lid, 9 is a signal processor and 10 is a
winch.
DETAILED DESCRIPTION OF THE INVENTION
The suspension and stabilizing cable tension measuring device apparatus
for use in a vertical shaft including a signal processor 9, a shaft lid 8, a
frame 6
mounted on the shaft lid 8, a plurality of spaced apart hoisting sheaves 5
mounted
on the frame 6, and a plurality of suspension cables 2 and stabilizing cables
3 with
one of their ends fixed to winches 10 and the other ends running over the
sheaves
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in an inclined manner, i.e., inclined upwardly with respect to the vertical
from the
winches 10 to the sheaves 5, and then extending over the sheaves and
vertically
into the shaft. The cables are connected to a suspended scaffold 1 in the
shaft. A
tension measuring device 4 is mounted on the frame 6 at each sheave 5. The
5 tension measuring device 4 includes a bearing pedestal 4-1, a pressure
measuring
device 4-2, and a bevelled support 4-3, wherein the bevelled support 4-3 is
connected to the frame 6 by bolts 4-4. The pressure measuring device 4-2 and
the
bearing pedestal 4-1 located on the rotating shaft of the sheave 5 are fixed
on the
bevelled support 4-3. The pressure measuring device 4-2 is mounted on the
bevelled support 4-3 by bolts 4-4. The bearing pedestal 4-1 is connected to
the
pressure measuring device 4-2. The angle of inclination of the top surface of
the
bevelled support 4-3 relative to the horizontal is one-half of the angle
between the
inclined section of the cable 2 or 3 and the vertical section of the cable 2
or 3. The
pressure measuring device 4-2 and the bearing pedestal 4-1 on the shaft of the
sheave 5 are fixed on the inclined top surface of the bevelled support 4-3.
Frequency measuring devices 7 that clamp the suspension cables 2 and 3 are
mounted on the shaft lid 8. Each frequency measuring device 7 includes a
vibration block 7-1 located on each side of the cable 2 or 3, and an
accelerometer
7-2 mounted outside of one of the vibration blocks 7-1. The accelerometer is
provided with a wireless transmitter. A plurality of wheels 7-4 clamping cable
2 or 3
rotatably mounted on the insides of the vibration blocks 7-1. Clamping springs
7-3
extend between the upper and lower ends of the vibration blocks 7-1. Movable
translational wheels 7-5 clamped into a track on the shaft lid 8 are located
on the
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bottoms of the vibration blocks 7-1. The frequency measuring devices 7
transmit
wireless signals to the signal processor 9, which processes the signals and
carries
out tension calculations.
The tension T on a suspension or stabilizing cable is measured using the
above-described apparatus in real time by the pressure measuring device 4-2,
and
at regular intervals by the frequency measuring device 7. The obtained tension
result from the device 7 is used to correct the measurement of the pressure
measuring device 4-2 by the following steps:
a) the tension of the suspension cable 2 or 3 is measured by the
pressure
measuring device 4-2 in real time: when the tension of the suspension cable
2 or 3 acts on the bearing pedestal 4-1 via the sheave 5, the downward
force is transferred to the pressure measuring device 4-2. If the angle
between the inclined section and the vertical section of the cable 2 or 3 is
a,
the tension of the cable 2 or 3 is T, it is seen from the force composition
principle that the pressure acting on the pressure measuring device 4-2
perpendicular to the surface of the device 4-2 (i.e, the pressure F measured
by the pressure measuring device 4-2) is:
F ¨ 2T = cos( a )
2
and thus, the tension T on the cable 2 or 3 is:
T= _________________________________________
2cos
ic12)
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. .
b) detecting the tension of the cable 2 or 3 using the frequency measuring
device 7 at regular intervals. Since the translational wheels 7-5 clamp into
the track of the shaft lid 8, the frequency measuring device 7 can move only
horizontally. The clamping wheels 7-4 are rotatably mounted on the
vibration blocks 7-1. The clamping springs 7-3 clamp the wheels 7-4
against the two sides of the steel cable, whereby the steel cable can move
in the vertical direction only. The accelerometer 7-2 is mounted outside of
one of the vibration blocks 7-1 and transmits lateral vibration acceleration
signals of the cable 2 or 3 to the signal processor 9 via the wireless
transmitter on the accelerometer. The signal processor 9 processes the
signals to obtain the lateral vibration frequency w of the cable 2 or 3, and
then calculates the tension T of the cable according to the length I of the
suspension cable 2 or stabilizing cable 3 during measurement and the
density p of the cable using the equation:
,42(02
T = Pz2 __________________________________ + pgl
c) the tension measured by the pressure measuring device 4-2 is compared
with the tension measured by the frequency measuring device 7, thus
determining whether the pressure measuring device 4-2 is inaccurate and
needs to be adjusted or replaced if the difference between the two tension
measurements is higher than 20%.
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Fig. 1 is a schematic cross section of a vertical shaft. In Fig. 2, a hoisting
sheave 5 divides the suspension cable 2 or the stabilizing cable 3 into an
inclined
section and a vertical section. The bevelled support 4-3 is such that the
angle a
between the inclined section of the suspension cable 2 or the stabilizing
cable 3
and the vertical section must be ascertained in advance, so that the angle of
inclination of the top surface of the bevelled support 4-3 is a. The support 4-
3 is
mounted on the frame 5 using bolts 4-4 and nuts, and then the bearing pedestal
4-
1 of the sheave 5 is mounted on the inclined top surface of the bevelled
support 4-
3. The angle between the inclined section and the vertical section of the
cable 2 or
3 is bisected by a line perpendicular to the top surface of the support. The
pressure measured by the pressure measuring device 4-2 is the resultant force
of
the vertical section and the inclined section, i.e.;
F =2T = cos 1
and the tension T on the cable 2 or 3 is:
T= _______________________________________
2cos(a
¨2)
As shown in Fig. 3, since the translational wheels 7-5 clamp into the track of
the shaft lid 8, the frequency measuring device 7 can move only horizontally.
The
clamping wheels 7-4 are rotatably mounted on the vibration blocks 7-1, and the
CA 2936463 2018-08-09
clamping springs 7-3 bias the vibration blocks 7-1 toward each other so that
the
wheels 7-4 permit the steel cable to move in the vertical direction only. The
accelerometer 7-2 is mounted outside of one vibration block 7-1 for
transmitting the
lateral vibration acceleration signals of the cable 2 or 3 to the signal
processor 9 via
a wireless transmitter. The program in the signal processor 9 receives the
signals,
processes the signals according to the length I of the cable 2 or 3 and the
density p
of the cable to determine the tension of the cable using the following
equation::
T - P12 6)2
Pg1
Jr
The tension measurement is carried out on a regular basis to ensure the
accuracy
of the tension measured by the pressure measuring device 4.
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