WO2023175046A1

WO2023175046A1 - Device for measuring the torsion torque and thrust to which a rotating shaft is subjected

Info

Publication number: WO2023175046A1
Application number: PCT/EP2023/056676
Authority: WO
Inventors: Rodion DENYSYUK
Original assignee: Eyegauge
Priority date: 2022-03-16
Filing date: 2023-03-15
Publication date: 2023-09-21
Also published as: FR3133671A1

Abstract

The invention relates to a device for measuring the torsion torque and thrust of a rotating shaft (1) subjected to resistance torques, the device comprising: - first and second series (3, 4) of a given number of visual patterns (3i, 4i) arranged around the shaft and being spaced apart by a given length (L); each pattern comprising at least one marker encoding a given absolute rotation angle; - a first and at least a second image capture means (5, 6) delivering images of each pattern of the first and second series (3, 4); - synchronous image processing means (7), which are configured to determine the torsion torque (c) and the thrust (p) based on the patterns of the second series and their positions on one and the same reference line shared with the marker of the first series.

Description

Device for measuring the torque and thrust to which a rotating shaft is subjected

The present invention relates generally to measuring devices and more particularly concerns a device for measuring the torque and thrust to which a rotating shaft is subjected.

Such devices are suitable for measuring the mechanical properties of rotating shafts belonging for example to propulsion systems for ships, energy recovery systems in particular wind turbines, etc. These systems use at least one propeller which, depending on the case, can be a driving or receiving propeller coupled to a motor, or generator, by a shaft.

Such a shaft, also called a power transmission shaft, is generally cylindrical in shape with a circular section. It is therefore defined geometrically by its length and its diameter. We will speak of lateral surface, or cylindrical surface to define the exterior surface of the cylinder which is delimited at its ends by two plane circular bases parallel to each other.

Measuring, in situ, the performance of a propulsion system is only possible by precisely measuring the torque and thrust, or axial force, applied to the shaft mechanically connecting the transmitter (the motor, or generator) to the receiver (the propeller). By “in situ”, we mean measurements which are carried out in the real operating environment of the shaft, that is to say: shaft under load and rotating.

To do this, it is known to use torque sensors which measure the load (resisting torques) applied to the shaft, the thrust exerted on the shaft (strain gauges) or even the displacement by torsional deformation of the shaft. shaft (rotating disks, acoustic strings, optical shifts or magnetic tape). Thrust measurement sensors are less common and are generally integrated into a dynamometer which is based on the same principle (deformation or displacement) but in a longitudinal direction of the shaft.

However, the methods and equipment required for implementing this type of sensor are relatively cumbersome, intrusive and expensive.

The present invention provides a non-invasive, high precision, stable and low cost measurement solution.

By non-invasive solution, we mean a solution which has no or very little impact on the measurement (transparency of the measurement means on the measurement itself) and which generates little or no specific transformation or adaptation of the environment, or site. , measurement. It does not require heavy or complicated equipment to set up to carry out the measurement. By stable measurement, we mean a measurement that remains reliable even in the event of intermittent loss of power to the power device.

To this end, the first object of the present invention is a device for measuring the torsional torque and the thrust of a rotating cylindrical shaft subjected to resistant torques, comprising:

- a first series of a determined number of visual patterns arranged regularly around a first straight section of the tree, on the cylindrical surface of the tree, in a first determined location along the length of the tree; each pattern comprising at least one marker encoding a determined absolute rotation angle x;

- at least a second series of the same determined number of visual patterns, identical to the visual patterns of the first series, arranged regularly around a second straight section of the tree, on the cylindrical surface of the tree, in a second location determined along the length of the shaft and at a determined axial distance from the first location; each pattern comprising at least one marker encoding a determined absolute rotation angle x’ or x’+S;

- a first means of capturing so-called reference digital images, arranged fixedly opposite the first series of visual patterns and delivering digital images of each pattern of the first series;

- at least one second digital image capture means arranged fixedly opposite the second series of visual patterns delivering digital images of each pattern of the second series;

- means for synchronous processing of images captured by the first and second image capture means, configured to identify at least one marker x'+S in a pattern of the second series, in correspondence with a marker x of the first series on, or as close as possible to, at least the same reference line; said processing means being further configured to compare the value of the absolute angle of rotation encoded in the marker x'+S and its position T'+TT, with the value of the absolute angle of rotation encoded in the marker x ' of the second series and its position T', previously recorded in a calibration step in which no resistant torque is applied to the shaft, and deduce the torque from S and the thrust from from TT.

According to one characteristic, the images are generally rectangular in shape; the reference line corresponding to the horizontal center line passing through the center of the images.

According to another characteristic, a lateral edge of the images is chosen as a vertical reference edge to determine the position of the marker on, or as close as possible, to the reference line.

According to another characteristic, the position of the marker in the image corresponds to a determined number of pixels between the reference line and a first pixel of the marker.

According to another characteristic, the shaft being of cylindrical shape with circular section, the first and second image capture means are arranged fixedly in the same plane tangential to the cylindrical surface of the shaft and respectively facing the first and second series of visual patterns.

According to another characteristic, the first and second image capture means are high-speed cameras arranged tangentially to the tree, at a determined distance from the patterns so as to present a focal plane in the tangential plane of the patterns.

The second object of the present invention is a measurement method implemented by the measuring device as described above, said method consisting of:

- to identify, in the image captured by the second image capture means, on or as close as possible to a horizontal reference line, at least one marker x'+S encoding a determined absolute rotation angle, and its position T'+TT relative to a vertical reference edge of the image;

- to identify, in the image captured by the first image capture means, on or as close as possible to the same horizontal line, the corresponding marker x, encoding a determined absolute rotation angle, and its position T;

- to search for said marker x in a database containing the markers of the first series and their position T in the first series and the corresponding markers x’ of the second series, and their position T’; the values of the absolute rotation angles encoded by said markers x, x' and their positions T, T' having been previously recorded in the database during a preliminary calibration phase consisting of rotating the shaft d 'at least one revolution, with no resistive torque applied to the shaft;

- from the marker x identified in the database, to note the value of the absolute rotation angle encoded by the corresponding marker x’ and of the corresponding position T’;

- to subtract from the value of the absolute angle of rotation encoded in said marker x'+S, the value of the absolute angle of rotation encoded in the marker x', recorded in the database, to deduce the torque twisting; And

- to subtract from the position T’+TT of said marker x’+S, the position T’ recorded in said database to deduce the thrust.

Finally, the fourth object of the present invention is a propulsion system comprising a propeller mechanically coupled to a motor by a shaft; said system comprising a measuring device as described above.

Other advantages and characteristics may emerge more clearly from the description which follows, given solely by way of non-limiting example and made with reference to the drawings in which:

illustrates a block diagram of a measuring device according to the invention;

graphically illustrates the measurement method implemented by the measuring device according to the invention; And

illustrates an example of coding band used by the measurement method implemented by the measuring device according to the invention.

The present invention proposes a device for precise, real-time and simultaneous measurement of the torsional torque and the thrust of a rotating and loaded shaft (in the presence of resistant torques), using imaging means, or vision. , industrial. This measurement can be carried out occasionally at regular intervals or continuously for continuous monitoring of the performance of the propulsion system.

The thrust to which a loaded shaft is subjected, at one end of the shaft, has the effect of compressing the shaft in its longitudinal direction. The tree therefore undergoes deformation or displacement in this direction.

The torsional torque to which a shaft is subjected under load and which is maximum during the start-up phase of the rotation of the shaft, has the effect of deforming the cylindrical surface of the shaft in a direction of torsion.

The device according to the invention uses these two types of deformation to measure “visually” and simultaneously the torsional torque and the thrust.

We consider, below, that the tree is a tree used for the propulsion of ships. In the example described, it is cylindrical in shape with a constant circular section of radius R and determined length. Its diameter (2xR) is between 200 mm and 1000 mm. The rotation speed of the shaft is between 100 and 1000 rpm.

There schematically illustrates an embodiment of a measuring device according to the invention.

In this figure, a shaft 1 belonging to propulsion system 2, object of the measurement, is represented with its longitudinal axis AA' extending horizontally along X.

Shaft 1 transmits the power generated by an MOT motor, or generator, to a HEL load, notably a propeller.

The thrust exerted on shaft 1, from left to right in the figure, is represented by an arrow P in the axial direction X. The direction of rotation of the shaft is shown in the figure by the arrow ROT.

The measuring device according to the invention implements first and second visual coding bands 3 and 4 respectively supporting first and second series of visual patterns 3i and 4i. The first and second bands 3 and 4 are fixedly attached to the cylindrical surface SC of the shaft 1, respectively around the first and second straight sections of the shaft 1, by gluing or other very slightly intrusive fixing process. When they are attached to shaft 1, bands 3 and 4 are in the form of rings of negligible thickness. As a variant, the patterns 3i, 4i can be directly printed on the surface SC of the shaft 1 by a laser marking, screen printing or other process. The two bands 3 and 4 are identical: same width (along X) and same visual patterns 3i and 4i arranged in the same way on their respective bands 3 and 4. The first and second bands 3 and 4 are arranged on the tree 1 respectively, in the vicinity of the HEL propeller (represented on the left in the figure) and the MOT motor (represented on the right in the figure), being spaced axially (along X) by a determined length L.

Each pattern 3i, 4i contains at least one marker encoding an absolute rotation angle, arranged so as to obtain a resolution of at least 1 degree when measuring the torque. Patterns 3i and 4i are of identical height and can be contiguous or evenly spaced from each other. Patterns can represent alphanumeric characters, geometric shapes, etc.

As indicated above, the thrust P has the effect of deforming the shaft 1 in its axial direction the first coding band 3. This movement, symbolized by the arrow p, is quantified by a distance TT.

As also indicated above, the twisting torque which is applied to the shaft 1 has the effect of deforming the cylindrical surface SC of the shaft 1 in a twisting direction. This deformation, symbolized by the arrow c , results in an angular displacement φ of the surface SC of the shaft 1, a displacement which is undergone by the second coding strip 4 which is arranged on the MOT motor side. This angular displacement (torsion angle) φ is quantified by a distance S (length of the arc).

The movement of the second band 4, symbolized by the arrow c , introduces an offset S of the patterns 4i of the second coding band 4 relative to the patterns 3i of the first coding band 3.

Taking as an example a shaft 1 of 500 mm in diameter (2xR), made of steel (rigidity modulus G = 79 GPa) with a torque C = 500 KNm (equivalent to 2600 kW of power), the twist angle φ of the tree 1 considered between two points on the surface of the tree 1 spaced by a length L = 5 m, will be φ = 0.3 degrees which is equivalent, in arc length, to S = 15 .5mm.

φ is obtained from the following formula: where J ₀ corresponds to the polar moment of inertia of a section of shaft 1.

The measuring device according to the invention, and in the embodiment described, further comprises two digital image capture means 5 and 6 arranged respectively opposite the two coding bands 3 and 4.

The image capture means 5 and 6 are preferably high-speed cameras (speeds greater than 60 images/second) which are cameras generally used in industry for part inspection and/or process control. industrial. Each camera 5 and 6 is arranged fixedly and at a determined distance from the coding bands 3 and 4 so as to present a focal plane (plane of sharpness or focusing plane) in the same plane tangential to each of the coding bands 3 and 4. Each camera 5 or 6 is preferably equipped with a lighting source in the visual or infrared spectrum, IR (InfraRed), not shown. By convention, we define the first camera 5, the one closest to the HEL propeller, as the reference camera also called “master” camera. The second camera 6 is therefore designated as a “slave” camera.

The two cameras 5 and 6 are thus capable of capturing images of each of the patterns 3i and 4i of the two coding bands 3 and 4 during the rotation of the shaft 1. The two cameras 5 and 6 are synchronized by a synchronizer 10, so as to deliver their “synchronous” images to processing means 7 comprising image analysis means 8. A database 9 hosted in a memory or storage server is coupled to the processing means 7. This database 9 contains measurement data from a calibration phase described below.

The synchronous processing means 7 reconstruct plane images of rectangular shape of the visual patterns 3i and 4i from the image sequences captured by the two cameras 5 and 6 during the rotation of the shaft 1 using the means (one or more calculators) for image analysis 8.

The image analysis method implemented by the analysis means 8 is described below with reference to Figures 2 and 3.

We represented on the same , the images IMG1-IMG4 captured by the first and second cameras 5 and 6 in a preliminary calibration phase (IMG1 and IMG2) and in an operating phase (IMG3 and IMG4) of the shaft 1 in a real operating configuration : shaft 1 rotating and under load. The IMG1-IMG4 images are generally rectangular in shape.

The analysis method considers a horizontal MED midline as the horizontal reference line in the IMG1-IMG4 images. This horizontal reference line MED extends in the axial direction along X of shaft 1. It is used as a “reading cursor” of the absolute angle of rotation.

The left lateral edge EDG of the IMG1-IMG4 images is chosen as the vertical reference line. It extends perpendicular to the horizontal reference line MED in the direction Y. The axial position along X of a coding strip 3 or 4 is calculated by the distance between the lateral edge (in the embodiment described: the left side edge) of the strip 3,4 and the side edge (in the embodiment described: left side edge) of the image.

We consider beforehand that each pattern 3i of the first coding band 3 corresponds to one and the same pattern 4i of the second coding band 4.

Each pattern 3i, 4i includes at least one marker, here, a marker x, x’, x’+S encoding an absolute rotation angle. By convention, the patterns 3i, respectively 4i, are ordered vertically (along Y) on their respective bands 3 and 4. The patterns 3i, 4i extend horizontally (along X) across their respective bands 3 and 4. The value absolute rotation angles, encoded by the markers x, x' and x'+S, increment positively in the direction of rotation ROT of shaft 1 (direction along Y) from the reference line MED: x , x+1, x+2, x+3, … for the first coding band 3 (IMG1 and IMG3), x', x'+1, x'+2, x'+3, … (IMG2) and x'+S, x'+S+1, x'+S+2, x'+S+3… (IMG4) for the second coding band 4. The value of the absolute rotation angles, encoded by the x markers , x' and x'+S, increments negatively in the opposite direction of rotation ROT of shaft 1 from the reference line MED: x, x-1, x-2, x-3, … for the first coding band 3 (IMG1 and IMG3), x', x'-1, x'-2, x'-3, …, (IMG2) and x'+S, x'+S-1, x' +S-2, x'+S-3, … (IMG4) for the second coding band 4.

The calibration phase, graphically illustrated by images IMG1 and IMG2, is carried out during installation of the measuring device. This calibration consists of synchronously recording the values of the absolute rotation angles (markers: x, x') for each pattern 3i and its corresponding pattern 4i as well as the axial positions T and T' (along X) of the left lateral edges of the bands 3 and 4 relative to the vertical reference line EDG, by rotating shaft 1 at least one complete turn in the direction of rotation ROT, without any load (no resisting torque) applied to shaft 1. The values of the measured absolute angles of rotation x' and positions T' are recorded in a database 9, in correspondence with the values of the absolute angles of rotation x and the respective positions T. These recordings will be used by the processing means 7 during the measurement in real operating conditions, as reference values, to calculate the thrust and the torque applied to the shaft 1. In the real operating phase, the torque of torsion is obtained by calculating the difference S between the reading of the real value of the absolute rotation angle x'+S and the corresponding absolute rotation angle x', pre-recorded in the database 9 in correspondence with the value of the absolute rotation angle encoded in the x marker. The thrust is obtained by calculating the difference in position TT (displacement) between the actual reading of the position T'+TT of the marker x'+S and the corresponding position T', pre-recorded in database 9.

In Figures 2 and 3, images IMG3 and IMG4 correspond to the images captured respectively by cameras 5 and 6 after starting the MOT motor in real operating conditions (shaft 1 under load).

In real measurement conditions (IMG3 and IMG4), the first camera 5, considered as the reference (or master) camera, is used as a “reading key” for the measurement. The absolute rotation angle encoded by the marker x (IMG3) and read by the master camera 5, is used to search in the database 9 for the corresponding values of absolute rotation angle x' and position T', pre-recorded from the slave camera 6 during the calibration phase.

The slave camera 6 renders an IMG4 image in which the pattern 4i which shares the horizontal reference line MED with the pattern 3i of the IMG3 image, supports a marker x'+S encoding the absolute rotation angle taking into account the angular offset S induced by the torque applied to shaft 1.

The analysis of the images is carried out by the analysis means 8 from the images rendered by the cameras 5 and 6 with the reference frame as defined above: left lateral edge EDG, horizontal center line MED. The analysis process consists of locating markers in the image using one or more image recognition algorithms.

A point of interest such as a marker can be represented by one or more pixels, or even less than one pixel, by sub-pixel interpolation from neighboring pixels making it possible to increase the resolution of the recognition and therefore the precision of the measurement. The dimensions (or size) of a specific marker can therefore be expressed in number of pixels in the image.

A marker is a characteristic visual element belonging to a 3i or 4i pattern. There is at least one marker per pattern 3i, 4i. Each marker has a specific known shape and physical dimensions (or actual size). The markers are regularly spaced apart from each other by a determined distance and arranged at a determined distance from the lateral edges of their respective coding strips 3, 4. The analysis means 8 are therefore able to identify the markers as pixels of the image and to locate them to the nearest millimeter on the surface of their respective coding strips 3, 4. Each marker encodes a determined absolute angle of rotation of the corresponding strip 3, 4.

For some pattern types, the accuracy of absolute rotation angle calculation is increased by calculating the distance (pixel count calculation) between the horizontal reference line MED and the start of the marker and as the physical dimensions of the marker ( actual size of the markers) are known, the distance between the start of this marker and the edge of the coding strip is deduced by simple translation of the pixels of the image on the surface of the strip.

To limit reading errors and therefore robusten the calculation of the absolute rotation angle, it is possible to use several horizontal MED reference lines in the same image. The use of cameras as measuring means offers the advantage of having a two-dimensional reading medium: image (2D), unlike a sensor delivering a signal in only one dimension (1D).

In summary, the measurement method implemented by the measuring device according to the invention consists of:

- to identify, in the IMG4 image captured by the second camera (slave camera) 6, on or as close as possible to the horizontal reference line MED, at least one marker x'+S encoding a determined absolute rotation angle, and its position T'+TT relative to the vertical reference edge EDG of the IMG4 image;

- to identify, in the IMG3 image captured by the first camera (master camera) 5, on or as close as possible to the same horizontal line MED, the corresponding marker x, encoding a determined absolute rotation angle, and its position T;

- to search for said marker x in a database 9 containing the markers of the first band 3 and their position T in the first band 3 and the corresponding markers x’ of the second band 4, and their position T’; the values of the absolute rotation angles encoded by said markers x, x' and their positions T, T' having been previously recorded in the database 9 during a preliminary calibration phase consisting of rotating the shaft 1 at least one revolution, without resistive torque applied to shaft 1;

- from the marker x identified in the database 9, to note the value of the absolute angle of rotation encoded by the corresponding marker x’ and of the corresponding position T’;

- to subtract from the value of the absolute angle of rotation encoded in said marker x'+S, the value of the absolute angle of rotation encoded in the marker x', recorded in the database 9, to deduce the torque twisting; And

- to subtract from the position T’+TT of said marker x’+S, the position T’ recorded in said database 9 to deduce the thrust.

There illustrates an example of patterns of a coding strip 3, 4 having the appearance of a ruler graduated in centimeters (cm). The patterns 3i and 4i, respectively x-1, x, x+1 and x'-1, x' and x'+1, correspond to 2 cm, 3 cm and 4 cm (IMG3) and 4 cm, 5 cm and 6 cm (IMG4). The marker here corresponds to a millimeter (mm) which is an element of the pattern 3i and 4i (the centimeter). Thus, the reading of the marker, encoding the absolute angle of rotation, is interpreted by the position of the marker (the millimeter) inside the pattern (the centimeter) and closest to the center line MED which acts as a cursor reading. The precision of the measurement is therefore given by the interval between two successive markers, here the millimeter. The value of the code seen by the first camera 5 and interpreted by the analysis means 8 is here 2.8 cm. The torque applied to the shaft 1 induced an angular shift (absolute rotation angle) which is directly interpreted by the processing means 7 from the images (IMG4) captured by the camera 6. The new value of the corresponding marker to the pattern x', is here 5.7 cm. This offset, reduced to the length of an arc of a circle, is equivalent to a distance S = 2.9 cm.

With this type of coding (absolute angular position), the measurement remains reliable even in the event of intermittent loss of power to the measuring device, reading errors for example due to degradation of the markers, etc.

Other types of patterns and markers can be used by the device according to the invention and in particular patterns in the form of a sequence of bar codes, of identical size, and aligned, vertically (along Y).

The use of this data can then make it possible to precisely determine the performance of the propulsion system and its changes over time (aging due to wear, the external environment, load, etc.), thus making it possible to anticipate future changes. possible damage or even breakage of the shaft which could lead to the immobilization of the vessel.

Multiple “slave” cameras can be used by being arranged at different locations along the tree, always facing their respective coding strips and synchronized to the “master” camera. In which case, the processing means 7 average the thrust and torque values obtained by each of the “slave” cameras.

Claims

Device for measuring the torsional torque and the thrust of a cylindrical shaft (1) in rotation subjected to resistant torques, comprising:
- a first series (3) of a determined number of visual patterns (3i) arranged regularly around a first straight section of the tree (1), in a first determined location along the length of the tree (1) ; each pattern (3i) comprising at least one marker encoding a determined absolute rotation angle x;
- at least a second series (4) of the same determined number of visual patterns (4i), identical to the visual patterns (3i) of the first series (3), arranged regularly around a second straight section of the tree (1 ) at a second location determined along the length of the shaft (1) and at a determined axial distance (L) from the first location; each pattern (4i) comprising at least one marker encoding a determined absolute rotation angle x' or x'+S;
- a first measuring means (5) called reference, arranged fixedly opposite the first series (3) of visual patterns (3i) and delivering a signal (IMG1, IMG3) of each pattern (3i) of the first series ( 3);
- at least one second measuring means (6) arranged fixedly opposite the second series (4) of visual patterns (4i) delivering a signal (IMG2, IMG4) of each pattern (4i) of the second series (4);
- synchronous processing means (7) of the signals measured by the first and second measuring means (5 and 6), configured to identify at least one marker x'+S in a pattern of the second series (4), in correspondence with a marker x of the first series (3) on or closest to at least the same reference line (MED); said processing means (7) being further configured to compare the value of the absolute angle of rotation encoded in the marker x'+S and its position T'+TT, with the value of the absolute angle of rotation encoded in the marker x' of the second series (4) and its position T', previously recorded in a calibration step in which no resistant torque is applied to the shaft (1), and deduce the torsion torque therefrom from S and the thrust from TT,
characterized in that the visual patterns (3i, 4i) of the first and second series (3, 4) are arranged on the cylindrical surface (SC) of the shaft (1), in that the first and second measuring means ( 5, 6) are digital image capture means delivering digital images (IMG1-IMG4) of generally rectangular shape; the reference line (MED) corresponding to the horizontal median line passing through the center of the images (IMG1-IMG4), and in that a lateral edge of the images (IMG1-IMG4) is chosen as the vertical reference edge (EDG) to determine the position (T', T'+TT) of the marker on, or as close as possible, to the reference line (MED).
Device according to the preceding claim in which a marker of known real size is represented by a determined number of pixels and its position in the image corresponds to a determined number of pixels separating the start of the pattern (3i, 4i) from the line of reference (MED) and reference edge (EDG).
Device according to the preceding claim in which the position of the marker in the image corresponds to a determined number of pixels between the reference line (MED) and a first pixel of the marker.
Device according to the preceding claim, in which the shaft (1) being of cylindrical shape with circular section, the first and second image capture means (5 and 6) are arranged fixedly in the same plane tangential to the cylindrical surface of the tree (1) and respectively opposite the first and second series (3, 4) of visual patterns (3i, 4i).
Device according to the preceding claim, in which the first and second image capture means (5 and 6) are high-speed cameras arranged tangentially to the shaft (1), at a determined distance from the patterns (3i, 4i) so as to present a focal plane in the tangential plane of the patterns (3i, 4i).
Measuring method implemented by the measuring device according to the preceding claims, said method consisting of:
- to identify, in the image (IMG4) captured by the second image capture means (6), on or as close as possible to a horizontal reference line (MED), at least one marker x'+S encoding a determined absolute rotation angle, and its position T'+TT relative to a vertical reference edge (EDG) of the image (IMG4);
- to identify, in the image (IMG3) captured by the first image capture means (5), on or as close as possible to the same horizontal line (MED), the corresponding marker x, encoding an absolute rotation angle determined, and its position T;
- to search for said marker x in a database (9) containing the markers of the first series (3) and their position T in the first series (3) and the corresponding markers x' of the second series (4), and their position T'; the values of the absolute rotation angles encoded by said markers x, x' and their positions T, T' having been previously recorded in the database (9) during a preliminary calibration phase consisting of rotating the the shaft (1) of at least one turn, without resisting torque applied to the shaft (1);
- from the marker x identified in the database (9), to note the value of the absolute angle of rotation encoded by the corresponding marker x' and of the corresponding position T';
- to subtract from the value of the absolute angle of rotation encoded in said marker x'+S, the value of the absolute angle of rotation encoded in the marker x', recorded in the database (9), to deduce the torque; And
- to subtract from the position T'+TT of said marker x'+S, the position T' recorded in said database (9) to deduce the thrust.
Computer produced program comprising instructions for carrying out the steps of the method according to claim 6.
Propulsion system (2) comprising a propeller (HEL) mechanically coupled to a motor (MOT) by a shaft (1); said system (2) comprising a measuring device according to one of claims 1 to 5.