System and a method for detecting wear of a ball-joint connection device of a rod, a rotor assembly, and an aircraft

Abstract

The present invention relates to a detection system for detecting wear of a ball-joint connection device of a pitch rod. The detection system includes at least one measurement assembly, said at least one measurement assembly having at least one deformation gauge for placing on said pitch rod, said detection system comprising at least one electrical conditioning circuit connected to at least one said deformation gauge and to at least one electrical energy source, said electrical conditioning circuit being configured to generate a measurement signal that varies as a function of deformation of said at least one deformation gauge and as a function of said wear.

Claims

1. A detection system for detecting wear of a ball joint connection device of a pitch rod of a rotor assembly; wherein the detection system includes at least one measurement assembly, the at least one measurement assembly having at least one deformation gauge for placing on the pitch rod, the detection system comprising at least one electrical conditioning circuit connected to at least one of the at least one deformation gauge and to at least one electrical energy source, the electrical conditioning circuit being configured to generate a measurement signal that varies as a function of deformation of the at least one deformation gauge and as a function of the wear, the detection system including a carrier, the carrier being provided with a fastener device for fastening to the pitch rod that is to be monitored, the carrier including an elastically deformable measurement segment carrying the measurement assembly, the measurement segment surrounding a hollow space configured to have the pitch rod passing therethrough without being in contact with the pitch rod, the measurement segment being arranged longitudinally between two rigid segments for fastening to the pitch rod.

2. A detection system according to claim 1; wherein the detection system comprises monitoring calculation means in communication with the at least one electrical conditioning circuit, the monitoring calculation means being configured to process the measurement signal and to determine whether the wear is present to a degree that requires maintenance action on the pitch rod when the measurement signal as processed by the monitoring calculation means presents a predetermined anomaly.

3. A detection system according to claim 2; wherein the detection system includes warning means in communication with the monitoring calculation means, the monitoring calculation means being configured to control the warning means in order to signal the presence of wear when the measurement signal as processed presents the predetermined anomaly.

4. A detection system according to claim 1; wherein the detection system includes at least a first antenna for transmitting away from the rotor assembly either the measurement signal or else a signal emitted by a monitoring calculation means connected to the electrical conditioning circuit, the first antenna being connected to the electrical conditioning circuit or to the monitoring calculation means.

5. A detection system according to claim 1; wherein the two segments comprise a first segment including the at least one electrical energy source and a second segment including the at least one electrical conditioning circuit.

6. A detection system according to claim 1; wherein the measurement segment includes at least one energy source or of an electrical conditioning circuit.

7. A detection system according to claim 1; wherein the detection system comprises a plurality of measurement assemblies, each measurement assembly being connected to a concentrator by a wired or wireless connection, the concentrator comprising at least the electrical conditioning circuit.

8. A detection system according to claim 1; wherein the at least one measurement assembly include at least one traction deformation gauge extending along an axial direction suitable for being parallel to the extension direction (D1) of a pitch rod.

9. A detection system according to claim 1; wherein the at least one measurement assembly include at least two first bending deformation gauges arranged around a direction suitable for coinciding with the extension direction (D1) of a pitch rod.

10. A detection system according to claim 1; wherein the at least one measurement assembly include at least five deformation gauges comprising a traction deformation gauge together with at least two first bending deformation gauges arranged around an axis and at least two second bending deformation gauges arranged around the axis, the two first bending deformation gauges and the two second bending deformation gauges being offset in azimuth around the axis.

11. A rotor assembly provided with a plurality of blades and of pitch rods, each pitch rod extending longitudinally from a first zone to a second zone, at least one of the first and second zones including a ball joint connection device; wherein the rotor assembly includes at least one detection system according to claim 1, with each pitch rod carrying a measurement assembly.

12. An aircraft including a rotor assembly according to claim 11.

13. A detection system according to claim 1; wherein the elastically deformable measurement segment has an inside diameter that surrounds a segment of the pitch rod, the inside diameter of the elastically deformable measurement segment is greater than an outside diameter of the pitch rod.

14. A detection system according to claim 1; wherein the elastically deformable measurement segment comprises an elastomeric ring.

15. A detection system according to claim 14; wherein the elastomeric ring has an inside diameter that surrounds a segment of the pitch rod, the inside diameter of the elastomeric ring is greater than an outside diameter of the pitch rod.

16. A detection system according to claim 1; wherein the fastener device is fastened to the pitch rod that is to be monitored and the two rigid segments are fastened to the pitch rod.

17. A detection system according to claim 16; wherein the pitch rod is connected to a ball-joint.

18. A detection method for detecting wear of a ball-joint connection device of a pitch rod of a rotor assembly of the aircraft, the rotor assembly being provided with a plurality of blades and of pitch rods, each pitch rod extending longitudinally from a first zone to a second zone, at least one of the first and second zones comprising a ball-joint connection device, the rotor assembly including at least one detection system including at least one measurement assembly having at least one deformation gauge for placing on the pitch rod, the detection system including at least one electrical conditioning circuit connected to at least one of the at least one deformation gauge and to at least one electrical energy source, the electrical conditioning circuit being configured to generate a measurement signal that varies as a function of deformation of the at least one deformation gauge and as a function of the wear; wherein at least one deformation gauge is a traction deformation gauge arranged to measure deformation along the extension direction of the pitch rod and the method comprises the following steps: establishing a time-varying traction measurement signal by measuring deformation of the pitch rod with the traction deformation gauge; evaluating a current stage of flight of the aircraft; and while the aircraft is flying in a level stage of flight, detecting wear to a degree that requires replacement of the ball-joint connection device when the time-varying traction measurement signal presents an erroneous amplitude, and/or while the aircraft is in an approach stage of flight, establishing a processed measurement signal at least by performing a Fourier transform on the time-varying traction measurement signal and detecting a degree of wear that requires replacement of the ball-joint connection device when the processed measurement signal presents, at a predetermined frequency or in a predetermined range of frequencies, at least one frequency component that has an amplitude that drops below a traction threshold during an approach.

19. A detection method for detecting wear of a ball-joint connection device of a pitch rod of a rotor assembly of the aircraft, the rotor assembly being provided with a plurality of blades and of pitch rods, each pitch rod extending longitudinally from a first zone to a second zone, at least one of the first and second zones comprising a ball-joint connection device, the rotor assembly including at least one detection system including at least one measurement assembly having at least one deformation gauge for placing on the pitch rod, the detection system including at least one electrical conditioning circuit connected to at least one of the at least one deformation gauge and to at least one electrical energy source, the electrical conditioning circuit being configured to generate a measurement signal that varies as a function of deformation of the deformation gauge(s) and as a function of the wear; wherein at least one deformation gauge is a bending deformation gauge arranged to measure bending deformation of the pitch rod, and the method comprises the following steps: establishing a time-varying bending measurement signal by measuring deformation of the pitch rod with the bending deformation gauge; and establishing a processed measurement signal at least by performing a Fourier transform on the time-varying bending measurement signal, and detecting a degree of wear that requires replacement of the ball-joint connection device when the processed measurement signal presents, at a predetermined frequency or in a predetermined range of frequencies, at least one frequency component that has an amplitude that becomes greater than a bending threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail in the context of the following description of embodiments given by way of illustration and with reference to the accompanying figures, in which:

(2) FIG. 1 is a diagrammatic view of a rotor assembly provided with a detection system of the invention;

(3) FIG. 2 is a view of a pitch rod fitted with a detection system of the invention;

(4) FIG. 3 is a view of a pitch rod fitted with a carrier of the invention;

(5) FIG. 4 is a diagram showing an example of a carrier of the invention;

(6) FIG. 5 is a diagrammatic plan view showing a carrier of the invention;

(7) FIG. 6 is a diagrammatic plan view showing a carrier of the invention;

(8) FIG. 7 is a fragmentary view of a rotary assembly provided with detection system carriers;

(9) FIG. 8 is a graph showing a time-varying measurement signal emitted during a stage of level flight from a traction deformation gauge arranged on a pitch rod that presents a ball-joint connection device with no wear;

(10) FIG. 9 is a graph showing a time-varying measurement signal emitted during a stage of level flight from a traction deformation gauge arranged on a pitch rod that presents a ball-joint connection device with medium wear;

(11) FIG. 10 is a graph showing a time-varying measurement signal emitted during a stage of level flight from a traction deformation gauge arranged on a pitch rod that presents a ball-joint connection device that is very worn and that is to be removed;

(12) FIG. 11 is a graph showing a time-varying measurement signal emitted during an approach stage from a traction deformation gauge arranged on a pitch rod that presents a ball-joint connection device with no wear;

(13) FIG. 12 is a graph showing a time-varying measurement signal emitted during an approach stage from a traction deformation gauge arranged on a pitch rod that presents a ball-joint connection device with medium wear;

(14) FIG. 13 is a graph showing a time-varying measurement signal emitted from a traction deformation gauge arranged on a pitch rod that presents a ball-joint connection device that is very worn and that is to be removed;

(15) FIG. 14 is a graph showing a processed measurement signal obtained from a signal emitted during an approach stage from a traction deformation gauge arranged on a pitch rod that presents a ball-joint connection device with no wear;

(16) FIG. 15 is a graph showing a processed measurement signal obtained from a signal emitted during an approach stage from a traction deformation gauge arranged on a pitch rod that presents a ball-joint connection device that is worn and that is to be removed; and

(17) FIG. 16 is a graph showing both a processed measurement signal obtained from a measurement signal emitted from a bending deformation gauge arranged on a pitch rod presenting a healthy ball joint and also a processed measurement signal obtained from a measurement signal emitted from a bending deformation gauge arranged on a pitch rod presenting a ball-joint connection device that is worn and that is to be removed.

DETAILED DESCRIPTION

(18) FIG. 1 shows an embodiment of a detection system 30 of the invention seeking to detect wear of a ball-joint connection device, referred to more simply as a “ball joint”.

(19) By way of example, such a detection system 30 may be arranged on a rotor assembly 5, and in particular on a rotor assembly 5 of an aircraft 1, in order to detect wear of a ball-joint connection device 25 of a pitch rod 20.

(20) Specifically, such a rotor assembly 5 may include a plurality of blades 10. Each blade 10 is carried by a rotor head not shown, possibly via a cuff 11 and/or via hinge and retaining devices. Certain blades may include cuffs that are integrated therein.

(21) The rotor assembly 5 also includes multiple pitch rods, and in FIG. 1 it includes one pitch rod 20 for each blade 10 in order to connect each blade 10 to flight controls. Each pitch rod 20 extends longitudinally along its extension direction D1 from a first zone 21 to a second zone 22, the first zone 21 and/or the second zone 22 including a ball-joint connection device 25. For example, the first zone 21 is hinged to a rotary swashplate 8 of a set of swashplates 6, optionally via a first ball-joint connection device 26, and the second zone 22 is hinged to a pitch lever 9, optionally via a second ball-joint connection device 27. The non-rotary swashplate 7 is then controlled by flight controls, e.g. via servocontrols or via other pitch rods.

(22) The rotor assembly 5 then has at least one detection system 30 of the invention for detecting wear of at least one ball-joint connection device 25 of at least one pitch rod 20.

(23) FIGS. 1 to 7 show various non-restrictive embodiments of a detection system 30 of the invention, and FIGS. 8 to 16 comprise graphs showing a method of detecting wear of a ball-joint connection device 25 by means of such a detection system.

(24) Independently of the embodiment, a detection system 30 includes at least one measurement assembly 31, and for example it may include one measurement assembly 31 for each blade. Such a measurement assembly 31 is provided with at least one measurement subassembly including at least one deformation gauge for placing on a pitch rod 20 that is to be monitored.

(25) A measurement assembly 31 may include a traction-measurement subassembly 32. The traction-measurement subassembly 32 comprises at least one traction deformation gauge 33. The traction deformation gauge 33 may extend along an axial direction, optionally suitable for being parallel to the extension direction D1 of a pitch rod 20 so as to deform when the pitch rod 20 is stretched or compressed. For example, where appropriate, such an extension direction D1 passes through the centers both of a first ball-joint connection device 26 and also of a second ball-joint connection device 27 of the pitch rod 28.

(26) A measurement assembly 31 may include at least one first bending measurement subassembly 34. For example, the first bending measurement subassembly 34 may include at least two first bending deformation gauges 35 and 36 arranged around a direction optionally suitable for coinciding with the extension direction D1.

(27) A measurement assembly 31 may include at least one second bending measurement subassembly 37. For example, the second bending measurement subassembly 37 may include at least two second bending deformation gauges 38 and 39 that are arranged around the extension direction D1 and that are offset in azimuth relative to the first deformation gauges 35 and 36.

(28) In the example shown, a measurement assembly 31 may thus comprise in particular one traction deformation gauge 33 together with two first bending deformation gauges 35 and 36, and two second bending deformation gauges 38 and 39.

(29) In another aspect, the detection system 30 comprises at least one electrical conditioning circuit 40 connected to at least one deformation gauge 33, 35, 36, 38, 39, and for example comprises one electrical conditioning circuit 40 for each measurement subassembly 32, 34, 37. The electrical conditioning circuit(s) 40 may be carried by a pitch rod 20 or may be arranged within a concentrator 90 arranged on the rotor head.

(30) Furthermore, a detection system 30 includes at least one electrical energy source 50, and for example may include an electrical energy source 15 for each measurement subassembly 32, 34, 37. The electrical energy source(s) 50 may be carried by a pitch rod 20 or may be arranged within a concentrator 90.

(31) Under such circumstances, each electrical conditioning circuit 40 receives electrical energy in order to prepare a measurement signal that varies as a function of the deformation of a deformation gauge 33, 35, 36, 38, 39 and as a function of said wear. For example, an electrical conditioning circuit 40 may comprise a Wheatstone bridge circuit including each deformation gauge 33, 35, 36, 38, 39 of a measurement subassembly. Furthermore, the electrical conditioning circuit 40 may include a voltmeter or the equivalent that emits a time-varying measurement signal relating to a potential difference that varies over time as a function of the deformation of the deformation gauges, which deformation varies as a function of the wear of a ball-joint connection device 25. Also, and by way of example, an electrical conditioning circuit 40 may include a memory for storing the emitted measurement signal.

(32) Furthermore, a detection system 30 may include monitoring calculation means 60 that are connected by a wired or wireless connection to at least one electrical conditioning circuit 40. For example, a detection system 30 may comprise monitoring calculation means 60 connected to a single electrical conditioning circuit 40 and optionally carried by a pitch rod 20, or it may comprise respective monitoring calculation means 60 connected to each of the electrical conditioning circuits 40 of a pitch rod 20 and optionally carried by that pitch rod, or indeed it may comprise monitoring calculation means 60 arranged in a concentrator 90 and connected to at least one electrical conditioning circuit 40. Optionally shared calculation means 60 may also be arranged away from the rotor assembly 5.

(33) By way of example, each monitoring calculation means 60 may comprise at least one processor or the equivalent, at least one memory, at least one integrated circuit, at least one programmable system, and/or at least one logic circuit, these examples not limiting the scope to be given to the term “monitoring calculation means”.

(34) Each monitoring calculation means 60 is configured to process at least one measurement signal emitted by an electrical conditioning circuit 40 in order to determine the presence of wear to a degree that requires maintenance action on the pitch rod 20 if the measurement signal processed by the monitoring calculation means 60 presents a predetermined anomaly.

(35) Optionally, a detection system 30 may include warning means 70 in wired or wireless connection with at least one monitoring calculation means 60. The monitoring calculation means 60 transmit a signal to the warning means 70 that generate, where appropriate, a warning when a processed measurement signal presents a predetermined anomaly.

(36) Furthermore, the detection system 30 may include one or more antennas for providing wireless connections.

(37) For example, at least one first antenna 75 is used for transmitting a signal away from the rotor assembly 5. Thus, a first antenna 75 may be connected to an electrical conditioning circuit 40 in order to transmit a measurement signal to monitoring calculation means 60 present away from the rotor assembly 50. In another example, at least one first antenna 75 may be connected to monitoring calculation means 60 in order to transmit a signal, e.g. to warning means 70. The monitoring calculation means 60 may communicate with other monitoring calculation means 60, likewise via antennas.

(38) FIG. 2 shows an embodiment. In this embodiment, the measurement assembly 31 is carried directly by the pitch rod 20, e.g. being fastened thereto by attachment means. By way of example, each deformation gauge 33, 35, 36, 38, 39 is adhesively bonded on the pitch rod 20 between the first zone 21 and the second zone 22 of the pitch rod.

(39) In this embodiment, each measurement subassembly 32, 34, 37 is connected by a wired connection to a respective electrical conditioning circuit 40. By way of example, the electrical conditioning circuit 40 is likewise adhesively bonded on the pitch rod 20. Alternatively, it may be arranged in a concentrator that is constrained to rotate with the rotor assembly 5.

(40) In this embodiment, each electrical conditioning circuit 40 is connected to one or more sources of electrical energy, optionally adhesively bonded on the pitch rod 20 or else arranged in a concentrator 90 that is constrained to rotate with the rotor assembly 5.

(41) FIG. 3 shows another embodiment.

(42) In this embodiment, a detector system 30 includes at least one carrier 80, and by way of example one carrier 80 for each pitch rod. The carrier 80 is hollow in its center so as to surround a segment of the pitch rod 20. The carrier 80 may be threaded onto the pitch rod 20 or it may comprise elements for fastening together, e.g. such as two half-shells for screwing together.

(43) The carrier 80 may be provided with a fastener device 85 to enable it to be fastened to the pitch rod 20 that is to be monitored. Such a fastener device 85 may include high and low abutments for switching between two nuts 23 and 24 of the pitch rod, nut-and-bolt systems, . . . .

(44) Furthermore, the carrier 80 possesses a measurement segment 81 that is elastically deformable, optionally for amplifying deformation of the pitch rod. For example, the measurement segment 81 may comprise an elastomer ring. The measurement segment 81 carries a measurement assembly 31, with each deformation gauge of the measurement assembly 31 being adjacent to the measurement segment or else embedded in the measurement segment 81, for example.

(45) With reference to FIG. 4, the measurement segment 81 need not be in contact with the pitch rod 20, at least when at rest, i.e. when there is no deformation of the pitch rod. By way of example, the measurement segment 81 surrounds a hollow space 84 through which the pitch rod 28 passes, and without coming into contact with the pitch rod 20. In the embodiment shown, the measurement segment 81 presents an inside diameter 100 that is greater than the outside diameter of a segment of the pitch rod 20 that is surrounded by the measurement segment 81.

(46) Optionally, the measurement segment 81 is arranged longitudinally, i.e. along the longitudinal extension direction D1 of the pitch rod 20 between two rigid segments 82 and 83 that are for fastening to the pitch rod 20.

(47) For example, the carrier 80 may have a segment fitted with at least one electrical energy source 50 in order to have its own energy supply, and/or at least one electrical conditioning circuit 40, and/or at least one monitoring calculation means 60, and/or at least one antenna 75. In an example, such a segment may be the measurement segment.

(48) In the embodiment shown, a first segment 82 carries a respective electrical energy source 50 for each measurement subassembly. Furthermore, a second segment 83 carries at least one electrical conditioning circuit 40, and/or at least one monitoring calculation means 60, and/or at least one antenna 75, the measurement segment 81 being arranged between the first segment 82 and the second segment 83.

(49) In this embodiment, the carrier 80 includes in particular one electronics card 41 for each measurement subassembly, i.e. three electronics cards 41 respectively for a single traction measurement subassembly 32, for the first bending measurement subassembly 34, and for the second bending measurement subassembly 37.

(50) Under such circumstances, each electronics card 41 comprises an electrical conditioning circuit 40 connected by a wired connection to each deformation gauge of the associated measurement subassembly, and also to an energy source 50. Furthermore, the electronics card 41 may carry respective monitoring calculation means 60 connected to the electrical conditioning circuit 40 by a wired connection.

(51) Also, the monitoring calculation means 60 may be connected to a common first antenna 75 and/or to respective antennas.

(52) With reference to FIGS. 5 and 6, the electrical energy sources 50 and the electronics cards may be positioned so as to balance the carrier 80 in order to ensure that the carrier 80 does not interfere with the design of the pitch rod 20.

(53) FIG. 7 shows a rotor assembly 5 including pitch rods 20 provided with carriers 80. Optionally, the carriers 80 need not include monitoring calculation means, the various electrical conditioning circuits 40 being connected by wired or wireless connections to at least one monitoring calculation means of a concentrator 90. Optionally, the carriers 80 need not include electrical energy sources, the various electrical conditioning circuits 40 being connected by wired connections to electrical energy sources 50 of a concentrator 90.

(54) FIGS. 8 to 16 comprise various graphs for showing methods implemented by a detection system of the invention.

(55) In particular, FIGS. 8 to 10 show wear of a ball-joint connection device 25 being detected by means of a time-varying measurement signal emitted by an electrical conditioning circuit 40 from a traction deformation gauge 33.

(56) In this method, the electrical conditioning circuit normally emits an electrical signal in the form of a time-varying signal measuring traction that varies over time as a function of the deformation in traction and/or compression of the traction deformation gauge 33.

(57) This time-varying measurement signal may optionally be processed by conventional sampling methods or by averaging over a predetermined number of revolutions of the rotor assembly 5.

(58) Furthermore, the current stage of flight of the aircraft 1 is determined by conventional instruments.

(59) The current stage of flight and the time-varying measurement signal may optionally be stored in a memory or they may be processed by monitoring calculation means 60.

(60) FIG. 8 shows the time-varying measurement signal obtained for one revolution during a stage of level flight with a pitch rod that is healthy. FIG. 9 shows the time-varying measurement signal obtained over one revolution during a stage of level flight with a pitch rod that presents a ball-joint connection device with a degree of wear that is acceptable. FIG. 10 shows the time-varying measurement signal obtained over one revolution during a stage of level flight with a pitch rod that presents a ball-joint connection device with a degree of wear that requires maintenance action. FIGS. 8 to 10 thus comprise graphs, each plotting time along an abscissa axis and a potential difference up an ordinate axis, each curve showing a measurement signal that presents a potential difference that varies as a function of time.

(61) An operator can perceive a defect visually by observing the maximum amplitude 110 of the time-varying measurement signal. The greater the amount of wear of a ball-joint connection device, the higher this maximum amplitude 110. It is thus possible to establish a threshold that is the image of a degree of wear requiring maintenance action.

(62) Thus, while the aircraft 1 is in a stage of level flight, the method may comprise a step of detecting wear requires the ball-joint connection device 25 to be replaced once the time-varying traction measurement signal presents an erroneous amplitude, e.g. an amplitude greater than or equal to a threshold or that is different from the amplitudes of measurement signals coming from other pitch rods. This analysis may be performed visually by an operator or automatically by the monitoring calculation means.

(63) FIG. 11 shows the time-varying measurement signal obtained over one revolution during an approach stage from a traction deformation gauge on a pitch rod that is healthy. FIG. 12 shows the time-varying measurement signal obtained over one revolution during an approach stage from a traction deformation gauge on a pitch rod presenting a ball-joint connection device having a degree of wear that is acceptable. FIG. 13 shows the time-varying measurement signal obtained over one revolution during an approach stage from a traction deformation gauge on a pitch rod presenting a ball-joint connection device having a degree of wear that requires a maintenance action.

(64) An operator can perceive a defect visually by observing the appearance of the time-varying measurement signal. The greater the amount of wear of a ball-joint connection device, the greater the extent to which the signal is “smoothed”, as can be seen by looking at the segments 120 of the signals visible in FIGS. 11 to 13. Specifically, any clearance that is present in a ball-joint connection device has the effect of filtering out some fraction of the vibration in a pitch rod as induced by the resonant modes of vibration in the blade connected to the pitch rod and in lower dynamic assemblies.

(65) In order to perform automatic processing, while the aircraft 1 is in an approach stage, the monitoring calculation means can process the time-varying traction measurement signal at least by performing a Fourier transform in order to obtain a processed measurement signal.

(66) FIGS. 14 and 15 show such a processed measurement signal. FIG. 15 thus presents a graph having frequencies plotted along the abscissa axis and energy plotted up the ordinate axis. Frequency components of the processed measurement signal present attitudes the decrease in FIG. 15 when at least one ball-joint connection device presents wear that requires maintenance action.

(67) Under such circumstances, the monitoring calculation means can detect wear that requires the ball-joint connection device 25 to be replaced when the processed signal presents, at a predetermined frequency or in a predetermined range of frequencies, one or more frequency components of amplitude dropping below a traction threshold during an approach or during level flight.

(68) When at least one deformation gauge is a bending deformation gauge 35, 36, 38, 39, the electrical conditioning circuit emits in normal manner an electrical signal in the form of a time-varying bending measurement signal that varies as a function of the deformation of the deformation gauge.

(69) This time-varying measurement signal may optionally be processed by conventional sampling methods or by averaging over a predetermined number of revolutions of the rotor assembly 5.

(70) The time-varying measurement signal may optionally be stored in a memory.

(71) Thereafter, monitoring calculation means can process the time-varying bending measurement signal at least by performing a Fourier transform in order to obtain a processed bending measurement signal.

(72) FIG. 16 plots a first curve C1 that shows such a processed bending measurement signal emitted from a pitch rod that is healthy and a second curve C2 that shows such a processed bending measurement signal emitted from a pitch rod having a ball-joint connection device that is worn. In the presence of wear, numerous frequency components present increased amplitude.

(73) Under such circumstances, the monitoring calculation means can detect wear that requires the ball-joint connection device 25 to be replaced when the processed signal presents, at a predetermined frequency or in a predetermined range of frequencies, one or more frequency components of amplitude rising above a bending threshold.

(74) Naturally, the present invention may be subjected to numerous variations as to its implementation. Although several embodiments are described, it should readily be understood that it is not conceivable to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.