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

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 torsional torque and thrust to which a rotating shaft is subjected

[0001] The present invention relates generally to measuring devices and more particularly concerns a device for measuring the torsional torque and thrust to which a rotating shaft is subjected.

[0002] Such devices are suitable for measuring mechanical properties of rotating shafts belonging for example to ship propulsion systems, 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.

[0003] Such a shaft, also called a power transmission shaft, is generally cylindrical in shape with a circular cross-section. It is therefore geometrically defined by its length and diameter. We will speak of lateral surface, or cylindrical surface to define the external surface of the cylinder which is delimited at its ends by two plane circular bases parallel to each other.

[0004] In situ measurement of the performance of a propulsion system is only possible by accurately measuring the torque and thrust, or axial force, applied to the shaft mechanically connecting the transmitter (the engine, or generator) to the receiver (the propeller). By "in situ" we mean measurements that are carried out in the actual operating environment of the shaft, i.e.: shaft under load and rotating.

[0005] To do this, it is known to use torque sensors that measure the load (resistive torques) applied to the shaft, the thrust exerted on the shaft (strain gauges) or even the displacement by torsional deformation of the shaft (rotating discs, acoustic strings, optical shifts or magnetic tape). Thrust measuring 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.

[0006] However, the methods and equipment required to implement this type of sensor are relatively cumbersome, intrusive and expensive.

[0007] The present invention provides a non-invasive, high-precision, stable and low-cost measurement solution.

[0008] A non-invasive solution means a solution that has little or no impact on the measurement (transparency of the measurement means on the measurement itself) and that does not require any specific transformation or adaptation of the environment or site of the measurement. It does not require heavy or complicated equipment to set up to carry out the measurement. A stable measurement means a measurement that remains reliable even in the event of intermittent power loss to the power supply device.

[0009] To this end, the present invention has as its first object, a device for measuring the torsional torque and the thrust of a rotating cylindrical shaft subjected to resistant torques, comprising:

[0010] - a first series of a determined number of visual patterns arranged regularly around a first cross-section of the shaft, on the cylindrical surface of the shaft, at a first determined location along the length of the shaft; each pattern comprising at least one marker encoding a determined absolute rotation angle x;

[0011] - 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 cross-section of the shaft, on the cylindrical surface of the shaft, at a second determined location 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;

[0012] - a first means of capturing digital images called a reference means, arranged fixedly opposite the first series of visual patterns and delivering digital images of each pattern of the first series;

[0013] - 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;

[0014] - means for synchronously processing the images captured by the first and second image capture means, configured to locate 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 one same reference line; said processing means being further configured to compare the value of the absolute rotation angle encoded in the marker x'+S and its position T'+TT, with the value of the absolute rotation angle encoded in the marker x' of the second series and its position T', previously recorded in a calibration step in which no resistive torque is applied to the shaft, and to deduce therefrom the torsion torque from S and the thrust from TT.

[0015] 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.

[0016] According to another feature, a side edge of the images is chosen as the vertical reference edge to determine the position of the marker on, or as close as possible to, the reference line.

[0017] 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.

[0018] According to another characteristic, the shaft being of cylindrical shape with circular section, the first and second image capture means are fixedly arranged in the same plane tangential to the cylindrical surface of the shaft and respectively opposite the first and second series of visual patterns.

[0019] According to another characteristic, the first and second image capture means are high-speed cameras arranged tangentially to the shaft, at a determined distance from the patterns so as to present a focal plane in the tangential plane of the patterns.

[0020] The second subject of the present invention is a measuring method implemented by the measuring device as described above, said method consisting of:

[0021] - 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;

[0022] - 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;

[0023] - searching 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 at least one revolution, without resistive torque applied to the shaft;

[0024] - from the marker x identified in the database, to note the value of the absolute rotation angle encoded by the corresponding marker x' and the corresponding position T';

[0025] - subtracting from the value of the absolute rotation angle encoded in said marker x'+S, the value of the absolute rotation angle encoded in the marker x', taken from the database, to deduce the torsion torque; and

[0026] - to subtract from the position T'+TT of said marker x'+S, the position T' noted in said database to deduce the thrust.

[0027] Finally, the present invention has as its fourth object, a propulsion system comprising a propeller mechanically coupled to a motor by a shaft; said system comprising a measuring device as described above.

[0028] 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:

[0029] illustrates a block diagram of a measuring device according to the invention;

[0030] graphically illustrates the measuring method implemented by the measuring device according to the invention; and

[0031] illustrates an example of a coding strip used by the measuring method implemented by the measuring device according to the invention.

[0032] The present invention proposes a device for precise, real-time and simultaneous measurement of the torsional torque and thrust of a rotating and loaded shaft (in the presence of resistive torques), using industrial imaging or vision means. This measurement can be carried out punctually at regular intervals or continuously for continuous monitoring of the performance of the propulsion system.

[0033] 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 shaft therefore undergoes deformation or displacement in this direction.

[0034] The torsional torque to which a loaded shaft is subjected, which is maximum in the start-up phase of the shaft's rotation, has the effect of deforming the cylindrical surface of the shaft in a torsional direction.

[0035] The device according to the invention uses these two types of deformation to “visually” and simultaneously measure the torsional torque and the thrust.

[0036] The shaft is considered below to be a shaft used for ship propulsion. In the example described, it is cylindrical in shape with a constant circular section of radius R and a determined length. Its diameter (2xR) is between 200 mm and 1000 mm. The shaft rotation speed is between 100 and 1000 rpm.

[0037] Diagrammatically illustrates an embodiment of a measuring device according to the invention.

[0038] In this figure, a shaft 1 belonging to propulsion system 2, the object of the measurement, is represented with its longitudinal axis AA' extending horizontally along X.

[0039] Shaft 1 transmits the power generated by an MOT engine, or generator, to a HEL load, notably a propeller.

[0040] 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.

[0041] The measuring device according to the invention uses first and second visual coding strips 3 and 4 respectively supporting first and second series of visual patterns 3i and 4i. The first and second strips 3 and 4 are fixedly attached to the cylindrical surface SC of the shaft 1, respectively around first and second straight sections of the shaft 1, by gluing or other very minimally intrusive attachment method. When they are attached to the shaft 1, the strips 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 strips 3 and 4 are identical: same width (along X) and same visual patterns 3i and 4i arranged in the same way on their respective strips 3 and 4.The first and second bands 3 and 4 are arranged on the shaft 1 respectively, in the vicinity of the propeller HEL (shown on the left in the figure) and the motor MOT (shown on the right in the figure), being spaced axially (along X) by a determined length L.

[0042] Each 3i, 4i pattern contains at least one marker encoding an absolute rotation angle, arranged to achieve a resolution of at least 1 degree when measuring torque. The 3i and 4i patterns are of identical height and may be contiguous or regularly spaced from each other. The patterns may represent alphanumeric characters, geometric shapes, etc.

[0043] As indicated above, the thrust P has the effect of deforming the shaft 1 in its axial direction X. This deformation results in a displacement of the surface SC of the shaft 1 in this direction, a displacement which is therefore undergone by the first coding strip 3. This displacement, symbolized by the arrow p, is quantified by a distance TT.

[0044] As also indicated above, the torsional torque which is applied to the shaft 1 has the effect of deforming the cylindrical surface SC of the shaft 1 in a torsional 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 engine side MOT. This angular displacement (torsion angle) φ is quantified by a distance S (arc length).

[0045] The displacement 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.

[0046] Taking as an example a shaft 1 of 500 mm diameter (2xR), made of steel (modulus of rigidity G = 79 GPa) with a torque C = 500 KNm (equivalent to 2600 kW of power), the torsion angle φ of shaft 1 considered between two points on the surface of shaft 1 spaced by a length L = 5 m, will be φ = 0.3 degrees which is equivalent, in length of arc of circle, to S = 15.5 mm.

[0047] φ is obtained from the following formula: where J0corresponds to the polar moment of inertia of a section of shaft 1.

[0048] 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 strips 3 and 4.

[0049] 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 the inspection of parts and / or the control of industrial processes. Each camera 5 and 6 is arranged fixedly and at a determined distance from the coding strips 3 and 4 so as to present a focal plane (sharpness plane or focusing plane) in the same plane tangential to each of the coding strips 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, the first camera 5, the one closest to the helix HEL, is defined as the reference camera, also called the “master” camera. The second camera 6 is therefore designated as the “slave” camera.

[0050] The two cameras 5 and 6 are thus able to capture images of each of the patterns 3i and 4i of the two coding strips 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.

[0051] The synchronous processing means 7 reconstruct rectangular-shaped plane images 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 image analysis means (one or more computers) 8.

[0052] The image analysis method implemented by the analysis means 8 is described below with reference to Figures 2 and 3.

[0053] The same image shows 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 images IMG1-IMG4 are generally rectangular in shape.

[0054] The analysis method considers a horizontal centerline MED as a horizontal reference line in images IMG1-IMG4. This horizontal reference line MED extends along the axial direction along X of shaft 1. It is used as a "reading cursor" of the absolute rotation angle.

[0055] The left lateral edge EDG of the images IMG1-IMG4 is chosen as the vertical reference line. It extends perpendicular to the horizontal reference line MED in the Y direction. The axial position along X of a coding strip 3 or 4 is calculated by the distance between the lateral edge (in the described embodiment: the left lateral edge) of the strip 3,4 and the lateral edge (in the described embodiment: the left lateral edge) of the image.

[0056] It is previously considered that each pattern 3i of the first coding band 3 corresponds to a single and same pattern 4i of the second coding band 4.

[0057] Each pattern 3i, 4i has 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 of the absolute rotation angles, encoded by the markers x, x' and x'+S, increments positively in the direction of rotation ROT of the 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 markers x, 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.

[0058] The calibration phase, graphically illustrated by images IMG1 and IMG2, is performed during the installation of the measuring device. This calibration consists in 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 strips 3 and 4 with respect to the vertical reference line EDG, by rotating the shaft 1 at least one complete revolution in the direction of rotation ROT, without any load (no resistive torque) applied to the shaft 1. The values ​​of the absolute rotation angles x' and the positions T' measured, are recorded in a database 9, in correspondence with the values ​​of the absolute rotation angles x and the respective positions T.These records will be used by the processing means 7 during the measurement in real operating conditions, as reference values, to calculate the thrust and the torsional torque applied to the shaft 1. In the real operating phase, the torsional torque is obtained by calculating the difference S between the reading of the actual 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 marker x. The thrust is obtained by calculating the position difference TT (displacement) between the actual reading of the position T'+TT of the marker x'+S and the corresponding position T', pre-recorded in the database 9.

[0059] In Figures 2 and 3, images IMG3 and IMG4 correspond to the images captured respectively by cameras 5 and 6 after starting the MOT engine under real operating conditions (shaft 1 under load).

[0060] 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.

[0061] The slave camera 6 renders an image IMG4 in which the pattern 4i which shares the horizontal reference line MED with the pattern 3i of the image IMG3, supports a marker x'+S encoding the absolute rotation angle taking into account the angular offset S induced by the torsion torque applied to the shaft 1.

[0062] The analysis of the images is carried out by the analysis means 8 from the images restored by the cameras 5 and 6 with the reference frame as defined above: left lateral edge EDG, horizontal median line MED. The analysis method consists of locating the markers in the image using one or more image recognition algorithms.

[0063] 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 to increase the recognition resolution and therefore the measurement accuracy. The dimensions (or size) of a given marker can therefore be expressed in number of pixels in the image.

[0064] A marker is a characteristic visual element belonging to a 3i or 4i pattern. There is at least one marker per 3i, 4i pattern. Each marker has a determined known shape and physical dimensions (or actual size). The markers are regularly spaced apart 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 rotation angle of the corresponding strip 3, 4.

[0065] For some types of patterns, the accuracy of the absolute rotation angle calculation is increased by calculating the distance (calculating the number of pixels) between the horizontal reference line MED and the start of the marker and since 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 image pixels on the surface of the strip.

[0066] To limit reading errors and thus robustify the calculation of the absolute rotation angle, it is possible to use several MED horizontal reference lines in the same image. Using cameras as measuring means offers the advantage of having a two-dimensional reading medium: image (2D), unlike a sensor delivering a single-dimensional signal (1D).

[0067] In summary, the measuring method implemented by the measuring device according to the invention consists of:

[0068] - to identify, in the image IMG4 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 image IMG4;

[0069] - to identify, in the image IMG3 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;

[0070] - searching 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 the shaft 1;

[0071] - from the marker x identified in the database 9, to note the value of the absolute rotation angle encoded by the corresponding marker x' and the corresponding position T';

[0072] - subtracting from the value of the absolute rotation angle encoded in said marker x'+S, the value of the absolute rotation angle encoded in the marker x', taken from the database 9, to deduce the torsion torque; and

[0073] - to subtract from the position T'+TT of said marker x'+S, the position T' noted in said database 9 to deduce the thrust.

[0074] The illustration is 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 rotation angle, is interpreted by the position of the marker (the millimeter) inside the pattern (the centimeter) and as close as possible to the median line MED which acts as a reading cursor. 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 shaft 1 has induced an angular shift (absolute rotation angle) which is directly interpreted by the processing means 7 from the images (IMG4) captured by camera 6. The new value of the marker corresponding to the pattern x' is here 5.7 cm. This shift, reduced to the length of a circular arc, is equivalent to a distance S = 2.9 cm.

[0075] With this type of coding (absolute angular position), the measurement remains reliable even in the event of intermittent power loss to the measuring device, reading errors for example due to degradation of the markers, etc.

[0076] 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).

[0077] 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 possible deterioration or even breakage of the shaft which could lead to the immobilization of the vessel.

[0078] Several “slave” cameras can be used by being arranged at different locations along the shaft, always facing their respective coding strips and synchronized with the “master” camera. In which case, the processing means 7 average the thrust and torque values ​​obtained by each of the “slave” cameras.

Claims

A device for measuring the torque and thrust of a rotating cylindrical shaft (1) subjected to resisting torques, comprising: - a first series (3) of a determined number of visual patterns (3i) arranged regularly around a first cross-section of the shaft (1), at a first location determined on the length of the shaft (1); each pattern (3i) having at least one marker encoding a determined absolute angle of rotation 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 cross-section of the shaft (1) at a second location determined on the length of the shaft (1) and at a determined axial distance (L) from the first location; each pattern (4i) having at least one marker encoding a determined absolute angle of rotation x' or x'+S;- a first measurement means (5) called the reference means, fixedly arranged 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 a second measurement means (6) fixedly arranged 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 measurement means (5 and 6), configured to identify at least one marker x'+S in a pattern of the second series (4), corresponding to a marker x of the first series (3) on or as close as possible to at least one same reference line (MED);said processing means (7) being further configured to compare the value of the absolute rotation angle encoded in the marker x'+S and its position T'+TT, with the value of the absolute rotation angle encoded in the marker x' of the second series (4) and its position T', previously recorded in a calibration step in which no resisting torque is applied to the shaft (1), and to deduce the torsional torque 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 actual size is represented by a determined number of pixels and its position in the image corresponds to a determined number of pixels separating the beginning of the pattern (3i, 4i) from the reference line (MED) and the reference edge (EDG). Device according to the preceding claim wherein 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, wherein the tree (1) being cylindrical in shape with a circular cross-section, the first and second image capture means (5 and 6) are fixedly arranged 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, wherein 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). Measurement method implemented by the measuring device according to the preceding claims, said method consisting of: - identifying, 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); - identifying, 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 a determined absolute rotation angle, and its position T; - searching 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 shaft (1) by at least one revolution, without resisting torque applied to the shaft (1); - from the marker x identified in the database (9), to record the value of the absolute rotation angle encoded by the corresponding marker x' and the corresponding position T'; - to subtract from the value of the absolute rotation angle encoded in said marker x'+S, the value of the absolute rotation angle encoded in the marker x', recorded in the database (9), to deduce the torsional 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 program containing instructions for executing the steps of the process 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 any one of claims 1 to 5.

Images