U.S. patent application number 13/312860 was filed with the patent office on 2013-06-06 for bolt tension monitoring system.
This patent application is currently assigned to KING ABDULAZIZ CITY FOR SCIENCE AND TECHNOLOGY. The applicant listed for this patent is UTHMAN BAROUDI, ABDELHAFID BOUHRAOUA, SAMIR MEKID. Invention is credited to UTHMAN BAROUDI, ABDELHAFID BOUHRAOUA, SAMIR MEKID.
Application Number | 20130139604 13/312860 |
Document ID | / |
Family ID | 48445231 |
Filed Date | 2013-06-06 |
United States Patent
Application |
20130139604 |
Kind Code |
A1 |
BAROUDI; UTHMAN ; et
al. |
June 6, 2013 |
BOLT TENSION MONITORING SYSTEM
Abstract
The bolt tension monitoring system provides remote monitoring of
the tension of a bolt, thus allowing for remote monitoring of
general structural health and integrity of the fastener. The bolt
tension monitoring system includes a housing adapted for being
retained on a head of a bolt to be monitored. The system further
includes a force transducer positioned between the head of the bolt
and a workpiece surface in which the bolt is fastened and measures
tension between the head of the bolt and the surface. A controller
circuit disposed within the housing calculates a difference between
a currently measured tension between the head of the bolt and the
workpiece surface and an initially measured tension. A wireless
transponder mounted in the housing transmits an alert signal if the
calculated difference exceeds a pre-defined threshold value.
Actuation and power are provided through radio frequency power
harvesting.
Inventors: |
BAROUDI; UTHMAN; (DHAHRAN,
SA) ; MEKID; SAMIR; (DHAHRAN, SA) ; BOUHRAOUA;
ABDELHAFID; (DHAHRAN, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BAROUDI; UTHMAN
MEKID; SAMIR
BOUHRAOUA; ABDELHAFID |
DHAHRAN
DHAHRAN
DHAHRAN |
|
SA
SA
SA |
|
|
Assignee: |
KING ABDULAZIZ CITY FOR SCIENCE AND
TECHNOLOGY
RIYADH
SA
KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS
DHAHRAN
SA
|
Family ID: |
48445231 |
Appl. No.: |
13/312860 |
Filed: |
December 6, 2011 |
Current U.S.
Class: |
73/761 |
Current CPC
Class: |
F16B 37/14 20130101;
F16B 31/02 20130101; F16B 1/0071 20130101; G01L 5/0038
20130101 |
Class at
Publication: |
73/761 |
International
Class: |
F16B 31/02 20060101
F16B031/02 |
Claims
1. A bolt tension monitoring system, comprising: a hollow housing
having opposed upper and lower ends, the lower end defining a
recess adapted for being retained on a head of a bolt; a force
transducer having opposed upper and lower faces, the upper face
being adapted for providing a bearing surface for the head of the
bolt, the force transducer being positioned between the head of the
bolt and a workpiece surface in which the bolt is fastened, the
force transducer converting tension between the head of the bolt
and the workpiece surface into a calibrated voltage; a controller
circuit electrically connected to the force transducer for
calculating a difference between the calibrated voltage
corresponding to currently measured tension between the head of the
bolt and the workpiece surface and the calibrated voltage
corresponding to an initial tension measured when the bolt is
installed in the workpiece; a transponder circuit for transmitting
an alert signal when the difference exceeds a pre-defined threshold
value, the transponder circuit being electrically connected to the
controller circuit and mounted in the housing; and a power
harvesting circuit connected to the controller and transponder
circuits for harvesting power from radio frequency electromagnetic
waves, the power harvesting circuit being disposed in the
housing.
2. The bolt tension monitoring system as recited in claim 1,
wherein said force transducer is annular, having a central opening
formed therethrough adapted for inserting a shaft of the bolt
through the opening.
3. The bolt tension monitoring system as recited in claim 2,
further comprising a washer positioned between the lower face of
said force transducer and the workpiece surface.
4. The bolt tension monitoring system as recited in claim 1,
further comprising a battery disposed in the housing, the battery
being connected to the controller circuit and the transponder
circuit.
5. The bolt tension monitoring system as recited in claim 1,
wherein said transponder circuit comprises a wireless
transponder.
6. The bolt tension monitoring system as recited in claim 5,
wherein said transponder circuit further comprises a first antenna
mounted on said housing.
7. The bolt tension monitoring system as recited in claim 6,
further comprising a radio frequency identification tag connected
to the wireless transponder.
8. The bolt tension monitoring system as recited in claim 7,
wherein the alert signal includes identification information
associated with the bolt, the identification information being
stored on the radio frequency identification tag.
9. The bolt tension monitoring system as recited in claim 8,
wherein the identification information includes location
information.
10. The bolt tension monitoring system as recited in claim 9,
wherein said power harvesting circuit further comprises: a second
antenna disposed on said housing; a matching circuit connected to
said second antenna, the matching circuit being an LC circuit tuned
to a desired radio frequency range different from said first
antenna; a bridge rectifier connected to the matching circuit for
converting the received radio frequency signal to a DC voltage; a
voltage regulator connected to the bridge rectifier for regulating
the DC voltage; and a capacitor connected between the voltage
regulator and said controller circuit, the capacitor accumulating a
charge harvested from the radio frequency signal, said controller
circuit being triggered to turn on and calculate the difference
between the currently measured tension between the head of the bolt
and the workpiece surface and the initially measured tension when
the capacitor accumulates sufficient charge.
11. The bolt tension monitoring system as recited in claim 6,
wherein said power harvesting circuit comprises: a matching circuit
connected to said first antenna, the matching circuit being an LC
circuit tuned to a desired radio frequency range; a bridge
rectifier connected to the matching circuit for converting the
received radio frequency signal to a DC voltage; a voltage
regulator connected to the bridge rectifier for regulating the DC
voltage; and a capacitor connected between the voltage regulator
and said controller circuit, the capacitor accumulating a charge
harvested from the radio frequency signal, said controller to
circuit being triggered to turn on and calculate the difference
between the currently measured tension between the head of the bolt
and the workpiece surface and the initially measured tension when
the capacitor accumulates sufficient charge.
12. The bolt tension monitoring system as recited in claim 11,
further comprising a zener diode between said capacitor and said
controller circuit, the zener diode preventing said controller
circuit from being triggered to turn on until the capacitor has
accumulated sufficient charge.
13. A bolt tension monitoring system, comprising: a hollow housing
having opposed upper and lower ends, the lower end thereof defining
a recess adapted for receiving an external face of a head of a
bolt; a force transducer having opposed upper and lower faces, the
upper face thereof being adapted for contacting an internal face of
the head of the bolt, the force transducer being positioned between
the head of the bolt and a surface in which the bolt is embedded,
wherein the force transducer measures tension between the head of
the bolt and the surface; a controller circuit electrically
connected to the force transducer for calculating a difference
between the calibrated voltage corresponding to currently measured
tension between the head of the bolt and the workpiece surface and
the calibrated voltage corresponding to an initial tension measured
when the bolt is installed in the workpiece; a wireless transponder
circuit for transmitting an alert signal when the difference
exceeds a pre-defined threshold value, the transponder circuit
being electrically connected to the controller circuit and mounted
in the housing; and a power harvesting circuit connected to the
controller for harvesting power from radio frequency
electromagnetic waves, the power harvesting circuit being disposed
in the housing.
14. The bolt tension monitoring system as recited in claim 13,
wherein said force transducer is annular, having a central opening
formed therethrough adapted for inserting a shaft of the bolt
through the opening.
15. The bolt tension monitoring system as recited in claim 14,
further comprising a washer positioned between the lower face of
said force transducer and the workpiece surface.
16. The bolt tension monitoring system as recited in claim 13,
further comprising a battery connected to the controller circuit
and the wireless transponder circuit.
17. The bolt tension monitoring system as recited in claim 13,
wherein said wireless transponder circuit comprises: a wireless
transponder; and a first antenna mounted on said housing.
18. The bolt tension monitoring system as recited in claim 17,
further comprising a radio frequency identification tag in
communication with the wireless transponder.
19. The bolt tension monitoring system as recited in claim 17,
wherein the signal includes identification information associated
with the bolt, wherein said identification information includes
location information.
20. The bolt tension monitoring system as recited in claim 17,
wherein said means for harvesting power from a transmitted radio
frequency signal comprises: a second antenna disposed on said
housing; a matching circuit connected to the second antenna, the
matching circuit being an LC circuit tuned to a desired radio
frequency range different from said first antenna; a bridge
rectifier connected to the matching circuit for converting the
received radio frequency signal to a DC voltage; a voltage
regulator connected to the bridge rectifier for regulating the DC
voltage; a capacitor connected between the voltage regulator and
said controller circuit, the capacitor accumulating a charge
harvested from the radio frequency signal, said controller circuit
being triggered to turn on and calculate the difference between the
currently measured tension between the head of the bolt and the
workpiece surface and the initially measured tension when the
capacitor accumulates sufficient charge; and a zener diode
connected between the capacitor and said controller circuit for
preventing said controller circuit from being triggered to turn on
until the capacitor has accumulated sufficient charge.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to mechanical fasteners and to
electronic sensors for detecting failure of mechanical components,
and particularly to a bolt tension monitoring system for
transmitting signals identifying measured tension, power for and
actuation of the system being provided through radio frequency
power harvesting.
[0003] 2. Description of the Related Art
[0004] Bolted joints are found in a wide range of structures and
machines, and improperly tightened bolts, or loosened bolts, may
severely compromise the safety and structural integrity of a joint.
Insufficient pre-loading tension is a common cause of bolted joint
failure. Similarly, due to the stresses a structure or machine
undergoes in its lifetime, bolts can easily become loosened over
time. Insufficient tension in the bolt, even if it was properly
tightened at the time of construction, can also cause joint
failure.
[0005] Given that most structures and machines use hundreds or
thousands of bolts in their construction, it is impractical to
regularly manually test the tension of each bolt. Bolts are often
hidden from view or are otherwise inaccessible once a structure or
machine is fully constructed. Thus, it would be desirable to
provide a remote monitoring system that could measure the tension
in a bolt, throughout its lifetime, and also provide accurate
identification and location information for that bolt if a loss of
tension is detected.
[0006] Thus, a bolt tension monitoring system solving the
aforementioned problems is desired.
SUMMARY OF THE INVENTION
[0007] The bolt tension monitoring system provides remote
monitoring of the tension of a bolt, thus allowing for remote
monitoring of general structural health and integrity. The bolt
tension monitoring system includes a cap or housing having opposed
upper and lower ends, the lower end defining a recess adapted for
being retained on a head of a bolt to be monitored. The system
further includes a force transducer having opposed upper and lower
faces, the head of the bolt bearing on the upper face of the force
transducer when the bolt is fastened to a workpiece. The force
transducer is positioned between the head of the bolt and a surface
in which the bolt is embedded and measures tension between the head
of the bolt and the workpiece surface.
[0008] A controller circuit disposed in the housing calculates the
difference between a currently measured tension between the head of
the bolt and the workpiece surface and an initially measured
tension. A wireless transponder mounted in the housing transmits an
alert signal if the calculated difference exceeds a pre-defined
threshold value. A radio frequency identification tag is also
mounted in the housing, and is in communication with the wireless
transponder. The radio frequency identification tag has
identification information associated with the bolt stored therein,
and the alert signal includes the identification information.
[0009] Actuation and power are provided through radio frequency
power harvesting. Upon receiving an actuating signal within a
specific frequency range, power is provided to the system through
power harvesting, and the signal also serves to "wake up" or
actuate the system. The system may send the alert signal, as
described above, if the tension is found to be outside of the
desired range, or, alternatively, a signal containing the measured
tension can be transmitted at the time of actuation.
[0010] These and other features of the present invention will
become readily apparent upon further review of the following
specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is an environmental, side view of a bolt tension
monitoring system according to the present invention, the housing
or cap and the printed circuit board housed therein being shown in
section.
[0012] FIG. 2 is a block diagram illustrating system components of
the bolt tension monitoring system according to the present
invention.
[0013] FIG. 3 is a flowchart illustrating operation of the bolt
tension monitoring system according to the present invention.
[0014] FIG. 4 is a schematic drawing of a controller circuit for an
alternative embodiment of the bolt tension monitoring system.
[0015] Similar reference characters denote corresponding features
consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] The bolt tension monitoring system 10 provides remote
monitoring of the tension of a bolt B, thus allowing for remote
monitoring of general structural health and integrity of the
fastener. The bolt tension monitoring system 10 includes a hollow
cap or housing 12 having opposed upper and lower ends 16, 18,
respectively, the lower end 18 defining a recess 20 adapted for
receiving the outer face 82 of a head H of a bolt B to be
monitored. Preferably, the head H of the bolt B is snugly received
within the recess 20. It should be understood that the housing 12
may be dimensioned and configured to form a snap fit or pressure
fit with the size and shape of the particular type of bolt B to
which the housing 12 is applied.
[0017] The system 10 further includes a force transducer 32 having
opposed upper and lower faces 86, 88, respectively, the head H of
the bolt B having an inner or lower face bearing against the
transducer 32 when the bolt B is fastened to a workpiece. The force
transducer 32 is positioned between the head H of bolt B and a
workpiece surface 80 in which the bolt B is fastened and measures
tension between the head H and the workpiece surface 80. The force
transducer 32 is preferably annular, having a central aperture or
opening thereof receiving the shaft ST of the bolt B. A washer 34
may be provided, the lower face 88 of the force transducer 32
contacting the washer 34, which is positioned between the lower
face 88 and the workpiece surface 80. The shaft ST of the bolt B
passes through the central opening of the washer 34.
[0018] In operation, the system 10 is ordinarily in a sleep, or low
power, mode. Upon receiving a polling or activation signal from a
remote station 36, the system 10 actuates. Upon actuation,
depending upon the particular programming of system 10, either a
direct measurement of tension is made by the transducer 32, and
this tension measurement is transmitted to the remote station 36,
or alternatively, a controller circuit 24 mounted on a printed
circuit board (PCB) in the housing 12 calculates the difference
between a currently measured tension between the head H of bolt B
and the workpiece surface 80 and an initially measured tension. A
transmission is only made if the currently measured tension is
outside of a preferred range or threshold, as will be described in
detail below.
[0019] The controller circuit 24 may include any suitable type of
controller, such as a microprocessor, a programmable logic
controller, or the like. A wireless transponder 40 mounted in the
housing 12 transmits an alert signal S if the calculated difference
exceeds a pre-defined threshold value. A first antenna 28 is
preferably mounted on the housing 12 and is in communication with
the controller circuit 24 and the transponder circuit 40 via a
wired connection.
[0020] It should be understood that the wireless transponder
circuit 40 may comprise any suitable type of wireless transponder,
and may be provided as a separate component or integrated into the
controller circuit 24. The wireless transponder 40 may be a
ZigBee.RTM. transponder, for example. A radio frequency
identification tag (RFID) 50 is also mounted in the housing 12 and
is in communication with the wireless transponder 40. The radio
frequency identification tag 50 has identification information
associated with the bolt stored therein, so that the alert signal S
may include the identification information from the RFID tag
50.
[0021] The initially measured tension when the bolt B is first
installed may be stored in memory 90, which may be any suitable
type of computer readable storage medium, or a desired initial
tension may be recorded in the RFID tag 50. The RFID tag 50
preferably includes a particular identifier associated with a
particular bolt, location information for the bolt (included in the
transmitted identification information) and, as noted above, may
also include the desired initial tension. A battery 22 is
preferably provided within housing 12 for powering the controller
circuit 24, the transponder circuit 40, and the other system
components, the battery 22 being connected to the PCB and the
circuits mounted thereon by a spacer containing internal wiring. It
should be understood that any suitable type of power source may be
utilized. Preferably, power harvesting from transmitted signal S,
from remote station 36, may be used in combination with, or to
replace, the battery 22.
[0022] The actuation signal from the remote station 36 not only
"wakes up" or actuates the system 10, but the particular radio
frequency used is collected by a second antenna 29, processed
through an RF power module 31 to generate usable electricity, and
is in communication with battery 22 via line 33. RF power
harvesting, similar to solar power, is known in the art. One such
system is shown in U.S. patent publication no. US 2009/0303076 A1,
which is herein incorporated by reference in its entirety. It
should be understood that any suitable type of RF or
electromagnetic power harvesting or conversion system, or
rectifier, may be utilized. As an alternative, the second antenna
29 may be removed, and the first antenna 28 may be used for both
communication and power harvesting from the transmitted RF
signal.
[0023] As shown in FIG. 1, the force transducer 32 communicates
with the controller circuit 24 via wired connection 30. The
transducer 32 may be any suitable type of force, tension or torque
transducer. The transducer 32 is preferably a relatively
low-voltage transducer with calibrated readings on the order of a
few Volts. Such transducers are well known in the art and
commercially available, and need not be described further herein.
Torque applied to the bolt B is measured as tension between bolt
head H and surface 80. This tension must be maintained at a
constant level for structural safety and integrity.
[0024] As shown in FIG. 3, the initially measured tension (set at
the time of bolt tightening) occurs in step 100 and is recorded in
memory 90. Alternatively, RFID tag 50 may have a desired initial
tension stored therein. The transducer 32 measures currently
applied tension, either continuously or at regular intervals, as
indicated in step 102. The controller circuit 24 calculates the
difference value between the currently measured tension and the
stored initial tension. At step 104, the controller circuit 24
determines if the calculated difference exceeds a pre-defined
threshold. If not, then the flow returns to step 102, and the
system 10 continues to monitor the tension, either continuously or
at regular intervals. If the difference exceeds the pre-defined
tension, then the flow proceeds to step 106, at which point the
wireless transponder 40 transmits an alert signal S to a remote
monitoring station 36. As noted above, the alert signal S includes
identification information regarding the particular bolt, including
the bolt's location, so that appropriate repair and maintenance can
be performed by responding personnel.
[0025] As shown in FIG. 2, an analog front-end (AFE) circuit 42 is
also preferably provided for conditioning the signal generated by
the force transducer 32 prior to measurement and analysis by the
controller circuit 24. The AFE circuit 42 may be a stand-alone
conditioning circuit, or may be integrated into the controller
circuit 24. Additionally, it should be understood that power-saving
circuitry or programming may be utilized, allowing the system 10 to
enter a power saving or "sleep" mode when not in use. Further, the
AFE circuit 42 preferably communicates with at least one
analog-to-digital converter for converting analog signals generated
by the transducer 32 into digital data for processing by controller
24. The analog-to-digital converter may be integrated into the
controller 24 or into the transducer 32.
[0026] In addition to measuring force or tension of bolt B, it
should be understood that additional types of sensors may be
integrated into system 10. For example, local temperature and/or
humidity sensors may also provide environmental condition
information to further be transmitted in signal S. Further, the
controller circuit 24 may be programmed to monitor tension
continuously or at pre-set intervals, or the wireless transponder
40 may be used to receive an actuation signal from the remote
station 36, with monitoring occurring only when an actuation signal
is received by the wireless transponder 40.
[0027] It should be understood that the system 10 may be used to
communicate with other neighboring bolts equipped with similar
systems, each individual system 10 forming a single node in a
monitoring network. Each system in the network can send out a
polling signal, including location/identification information, and
a power reading from the on-board battery 22. A cluster head may be
elected based upon the residual power measurements and centralized
location.
[0028] In the embodiment illustrated in FIG. 4, the controller
circuit 200 includes a microcontroller 224, similar to controller
circuit 24, a first antenna 228, similar to first antenna 28, and a
second antenna 229, similar to antenna 29. The second antenna 229
is in communication with a matching circuit 202, which is an LC
circuit tuned to a specific frequency range, such as the 900 MHz
range, which is frequently used for RFID signals. The output of the
matching circuit 202 is fed to a rectifying bridge of diodes 204
(in this case, a full wave bridge rectifier, which rectifies the
signal from a sinusoidal AC signal to an almost continuous DC
voltage. This DC voltage is fed to a voltage regulator 206, which
charges a capacitor 208. The capacitor 208 is connected to the
power pin (indicated as V+ in FIG. 4) of microcontroller 224
through a Zener diode 210.
[0029] As in the previous embodiment, the microcontroller 224
either has its own RF transceiver module built in, or is in
communication with a separate RF transceiver module. Preferably,
the RF transceiver operates at a higher frequency than the
frequency range of second antenna 229 for transmitting signals
through first antenna 228 to the remote station. The range of the
first antenna 228 may be, for example, in the 2.4 GHz range. The
separate frequency ranges are used to avoid interference.
[0030] When the remote station transmits the lower frequency, which
is received by second antenna 229, the controller 224 is "woken up"
or actuated. This occurs via the above process, so that power is
fed into the power pin of microcontroller 224 from capacitor 208.
Once actuated, the microcontroller 224 performs the tasks described
above, such as taking measurements, analyzing the measurements, and
transmitting signal S, if necessary.
[0031] In a networked scenario, if several such systems 200 are
woken up simultaneously, each will eventually attempt to
communicate with the remote station, which will result in
communication collisions and increases in the number of
communication attempts. The uptime required in such a case becomes
higher than expected, which requires more power. In order to avoid
such a problem, the microcontroller 224 may continuously switch
between on "on" state and an "off" state in order to save power and
allow the energy harvesting module to charge the capacitor 206.
[0032] The controller 224 will then operate in a very limited time
period, performing a very simple task and then saving its context
to non-volatile memory (such as memory 90 or RFID tag 50 of the
previous embodiment), preparing for the next uptime. The controller
224 will then switch to sleep mode, waiting for the power to go off
The uptime is computed according to the amount of power that is
saved in the capacitor 208. The Zener diode 210 functions to make
sure that the supply voltage is not delivered (through the Zener
diode 210) to the microcontroller 224 until the voltage level at
the capacitor 208 is above the Zener diode's threshold.
[0033] It is to be understood that the present invention is not
limited to the embodiments described above, but encompasses any and
all embodiments within the scope of the following claims.
* * * * *