Fastener tightening control system in an assembly and method for controlling the tightening of a fastener in an assembly

1 . A control system for controlling the tightening of a fastener in an assembly, said fastener comprising a rod and an assembly member, the control system comprising:

a first measuring device, the first measuring device being suitable for measuring a first parameter representative of a temporal response of the rod to ultrasonic excitation,

a second measuring device, the second measuring device being suitable for measuring a second parameter representative of a frequency response of the rod to ultrasonic excitation, and

a calculator, the calculator being suitable for determining a value of the rod tightening as a function of at least said first parameter and said second parameter.

2 . The control system according to claim 1 , wherein the first parameter is a time of flight of a longitudinal or transverse ultrasonic wave in the rod.

3 . The control system according to claim 1 , wherein the second parameter is a frequency interval between two resonant frequencies of the rod.

4 . The control system according to claim 1 , wherein the calculator is suitable for determining the value of the rod tightening also as a function of a parameter (κ) relating to the rod.

5 . The control system according to claim 4 , wherein the calculator is suitable for calculating a value F of the rod tightening by applying the following formula:

F

=

1

κ

⁢

1

-

t

σ

·

⁢

f

σ

1

where:

κ is the rod parameter,

t σ is a time of flight of an ultrasonic excitation in the rod, and

f

σ

1

is a frequency interval between two resonant frequencies of the rod.

6 . The control system according to claim 1 , wherein the first measuring device comprises:

a first ultrasonic probe arranged to generate an ultrasonic excitation of the rod and collect a rod response signal to the generated excitation, and

a first acquisition device, the first acquisition device being suitable for controlling the first ultrasonic probe according to a first control law and receiving the response signal, the first control law being an impulse law,

wherein the response signal is processed to extract the first parameter.

7 . The control system according to claim 6 , wherein a principal axis for the rod is defined, wherein the first ultrasonic probe is arranged to generate an ultrasonic excitation propagating along the principal axis of the rod.

8 . The control system according to claim 1 , wherein the second measuring device comprises:

a second ultrasonic probe arranged to generate an ultrasonic excitation of the rod and collect a plurality of rod response signals to the generated excitation, and

a second acquisition device, the second acquisition device being suitable for controlling the second ultrasonic probe according to a second control law and for receiving the plurality of response signals, the second control law comprising a pulse train at different frequencies,

wherein the plurality of response signals are processed to extract the second parameter.

9 . The control system according to claim 8 , wherein a frequency analysis of the plurality of response signals is performed to extract the second parameter.

10 . The control system according to claim 1 , wherein

the first measuring device comprises

a first ultrasonic probe arranged to generate an ultrasonic excitation of the rod and collect a rod response signal to the generated excitation, and

a first acquisition device, the first acquisition device being suitable for controlling the first ultrasonic probe according to a first control law and receiving the response signal, the first control law being an impulse law,

wherein the response signal is processed to extract the first parameter;

the second measuring device comprises

a second ultrasonic probe arranged to generate an ultrasonic excitation of the rod and collect a plurality of rod response signals to the generated excitation, and

a second acquisition device, the second acquisition device being suitable for controlling the second ultrasonic probe according to a second control law and for receiving the plurality of response signals, the second control law comprising a pulse train at different frequencies,

wherein the plurality of response signals are processed to extract the second parameter; and

the first ultrasonic probe and the second ultrasonic probe are merged and comprise an ultrasonic transducer made of lead titano-zirconates.