CH715684A2 - System and method for determining at least one parameter relating to an angular movement of an axis. - Google Patents

Abstract

The system (6) and the method according to the invention are provided for determining an angular movement of an axis secured to a crown of a watch, the axis being able to rotate on itself in a longitudinal direction ( D1). The system comprises a rotary reflector (8) mounted on the axis, and two pairs (10A, 10B) of transmitter-detector arranged on either side of the reflector. Each pair of transmitter-detectors includes a light source (16) to illuminate the reflector, and a light detector (18) to receive the reflected light (24) on the reflector and to generate an electrical signal representative of the reflected light. . The system also includes a processor for processing the electrical signals generated by the detectors, and for determining a parameter relating to the angular movement of the axis. The rotary reflector is in the form of a cylinder of revolution and an arrangement of light absorption points is provided on the circumference of a cylindrical outer surface. The arrangement of the absorption points on the external surface is such that, when the reflector turns on itself regularly and in the same direction of rotation (S1, S2), the representative electrical signal generated by each detector of each pair has a substantially sinusoidal shape.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a system and a method for determining at least one parameter relating to an angular movement of an axis capable of rotating on itself. Such a parameter is for example the angular position, or the speed of rotation, or the direction of rotation of the axis.

[0002] The invention also relates to a timepiece comprising the determination system. The timepiece is for example a quartz watch, the axis then being the axis integral with a time setting crown.

STATE OF THE ART

[0003] It is known practice to provide a watch, for example a quartz watch, with an electronic crown by means of which a user can adjust the time and therefore the position of the hands without contact with the wheel of the watch. To do this, an electronic or optical or electro-optical device is arranged within the watch, which makes it possible to determine one or more parameters relating to the angular movement of the axis integral with the crown, and thus to position the hands at the position desired by the user. More precisely, the action of rotating the crown performed by the user is translated by the device into an electronic pulse to a processor of the watch, in order to communicate to it how many steps and in which direction the hands must be turned. This type of coding can for example be carried out via a galvanic contact, a magnetic coil using the Hall effect, a capacitive device, or even an electro-optical device implementing the emission and detection of light signals.

[0004] Such an electro-optical device, making it possible in particular to determine the angular position and / or the direction of rotation of the axis integral with a watch crown, is for example described in patent document EP 3 015 925 A1. The axis integral with the crown has a reflection surface on its outer periphery. The device comprises a light source intended to illuminate the reflection surface, as well as a light detector intended to receive a beam of reflected light coming from the reflection surface and to generate an electrical signal representative of the beam. The device further comprises a processor configured to form, from the electrical signals received from the detector, at least two patterns of pixels at two different times. The processor is also configured to compare the successive pixel patterns, and to deduce therefrom at least one parameter relating to the angular movement of the axis if an offset has occurred between the pixel patterns.

[0005] However, a drawback of the electro-optical device proposed in patent document EP 3 015 925 A1 is that it generates relatively long processing times for the processor, due to the number of data acquired. Such a solution thus requires providing sufficient power for the processor, which impacts the general size of the latter, as well as the consumption of the device. However, the space and energy available being particularly constrained within a watch, this can prove to be problematic for the general size of the system and its autonomy.

SUMMARY OF THE INVENTION

[0006] The aim of the invention is therefore to provide an electro-optical system for determining at least one parameter relating to an angular movement of an axis capable of rotating on itself, which makes it possible to operate with a number of data acquired limited to reduce the processing power required, while ensuring an accurate and rapid determination of the parameter (s).

[0007] To this end, the invention relates to a system for determining at least one parameter relating to an angular movement of an axis, in particular of an axis integral with a crown of a timepiece, which comprises the characteristics mentioned in independent claim 1.

[0008] Particular forms of the system are defined in dependent claims 2 to 9.

[0009] Thanks to the pattern of absorbing dots produced on the cylindrical surface of the rotary reflector, the light detectors of the system according to the invention each generate a representative electrical signal which has a substantially sinusoidal shape, when the reflector rotates on itself according to same direction of rotation. More precisely, the arrangement of the light absorption points on the exterior surface of the reflector, seen from each pair of emitter-detector, changes as the reflector rotates on itself in a regular manner and in such a way that the representative electrical signal generated by each detector has a substantially sinusoidal shape. Thanks to the substantially sinusoidal shape of the signals generated by the detectors, the processing carried out by the system processor, for determining the parameter (s) relating to the angular movement of the axis, is lightened. This makes it possible to determine the parameter (s) in a precise and reliable manner, and with a limited number of acquired data allowing a fast processing time, a small footprint and a minimum power consumption of the processor.

Advantageously, the two pairs of emitter-detector are arranged relative to the rotary reflector so that the two emitters, respectively the two detectors, are arranged head-to-tail with respect to each other. This makes it possible to introduce a phase shift between the signals generated by the two light detectors, when the reflector turns on itself. Such a phase shift allows the computer program implemented in memory means of the system to be able to determine the direction or the speed of rotation of the axis. Furthermore, thanks to this spatial arrangement of the two emitter-detector pairs, none of the light detectors misses the reflected light beam from the reflector.

Advantageously, the two pairs of emitter-detector are arranged on either side of the rotary reflector, on a circle whose center is substantially the center of the rotary reflector, and are offset between them by an angle presenting a distinct value of 180 °. This characteristic makes it possible to introduce a phase shift and / or to accentuate the phase shift existing between the signals generated by the two light detectors, when the reflector turns on itself. In fact, the two emitter-detector pairs then do not see the reflector at the same angle, which introduces a phase shift between the signals generated. Preferably, the total phase shift created between the two signals is at least 25 °, more preferably still substantially equal to 90 °.

[0012] According to a particular technical characteristic of the invention, the rotary reflector is formed from a cylinder of revolution. The arrangement of the absorption points can be achieved by means of laser engraving, or even by depositing black dots (ink) from a digital printer.

To this end, the invention also relates to a timepiece comprising the determination system described above, which comprises the characteristics mentioned in independent claim 10.

[0014] A particular form of the timepiece is defined in dependent claim 11.

[0015] To this end, the invention also relates to a method for determining at least one parameter relating to an angular movement of an axis, in particular of an axis integral with a crown of a timepiece, by means of of the determination system described above, and which comprises the features mentioned in independent claim 12.

[0016] Particular forms of the process are defined in dependent claims 13 to 15.

Advantageously, the method further comprises a step, implemented by the processor, consisting in representing the two electrical signals received as the sine and the cosine of the same function and in calculating a tangent arc function having for variable the ratio between the two signals. This makes it possible to determine the angular position of the axis at any time, and in an unequivocal manner.

Advantageously, the method further comprises a step, implemented by the processor, consisting in determining, as a function of the sign of the slope of the calculated tangent arc function, the direction of rotation of the axis.

Advantageously, the method further comprises a step, implemented by the processor, of controlling the switching on of each of the light sources alternately. This prevents the detector of one of the emitter-detector pairs from being influenced by the light coming from the emitter of the other emitter-detector pair.

To this end, the invention also relates to a computer program comprising program instructions stored in memory means of the determination system described above and which, when executed by the processor of the system, are capable of implementing the determination method as described above, and which comprises the characteristics mentioned in independent claim 16.

BRIEF DESCRIPTION OF THE FIGURES

The aims, advantages and characteristics of the system and of the determination method according to the invention, as well as of the timepiece comprising the system, will appear better in the following description on the basis of at least one form of non-limiting execution illustrated by the drawings in which: <tb> - <SEP> FIG. 1 is a perspective view of a watch provided with a crown for setting the time, and with a system for determining at least one parameter relating to an angular movement of the axis integral with the crown, according to the invention; <tb> - <SEP> Figure 2 is a perspective view of the system of Figure 1, the system comprising a rotating reflector and two emitter-detector pairs; <tb> - <SEP> Figure 3 is a front view of the system of Figure 2; <tb> - <SEP> Figure 4 is a perspective view of the rotating reflector of Figure 2; <tb> - <SEP> FIG. 5 represents a calculation of a matrix of black-white pixels to be engraved or printed on the wall of the reflector in order to modulate the reflectivity of its surface according to a sinusoidal function; <tb> - <SEP> FIG. 6 is a diagram showing the evolution of two electrical signals generated by the detectors of the two pairs of emitter-detector, as a function of the angular position of the rotary reflector; <tb> - <SEP> FIG. 7 is a flowchart representing steps of a method for determining at least one parameter relating to an angular movement of an axis, implemented by the system of FIG. 1; and <tb> - <SEP> FIG. 8 is a diagram representing the evolution of an arc tangent function calculated by a processor of the system of FIG. 2, as a function of the angular position of the rotary reflector.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows part of a watch 1 provided with a crown 2 for setting the time. The crown 2 is secured to an axis 4 which extends partly inside the watch 1, in particular the watch case. Watch 1, which is for example a quartz watch, further comprises a system 6 for determining at least one parameter relating to an angular movement of the axis 4 integral with the crown 2.

[0023] The axis 4 is able to rotate on itself around a longitudinal direction D1. More precisely, when the crown 2 is rotated by a user for setting the time, the axis 4 is rotated on itself around the direction D1. It should be noted that optionally, the crown 2 can be configured to be able to be pulled and / or pushed by a user, causing the axis 4 in longitudinal translation. When the axis 4 is fitted to a watch 1, as is the case in the illustrative example of FIGS. 1 to 4, the diameter of the axis 4 is typically within a range going from 0.5 to 2 mm.

As illustrated in Figures 2 and 3, the system 6 comprises, besides axis 4, a rotary reflector 8 and two pairs 10A, 10B of light emitter-detector. The system 6 also comprises a processor and memory means, these elements not being shown in the figures for reasons of clarity.

The rotary reflector 8 is mounted on the axis 4, around the latter. The rotary reflector 8 is thus secured to the axis 4. The rotary reflector 8 is for example mounted on an end part of the axis 4, although this particular arrangement of the reflector 8 on the axis 4 is in no way limiting. in the context of the present invention. The reflector 8 and the axis 4 can also form a single one-piece part, not shown.

As shown in Figures 2 to 4, the rotary reflector 8 is preferably formed from a cylinder of revolution. The peripheral surface 12 of the reflector 8 is initially fully polished to have constant light reflectivity like a mirror. This constant reflectivity is given only by the properties of the material and the quality of the surface. This cylindrical reflector 8 may for example have a diameter of 1.3 mm and a length of 0.77 mm. These dimensions are given only as an indication without limitations for other values.

The rotating reflector 8 is for example made of metal. The metal of the reflector 8 is preferably chosen such that the polished surface 12 exhibits good reflection in the wavelengths of the light emitted by the light emitters. For example, for infrared light emitters, the metal chosen for the reflector 8 can be a gold deposit. The choice of metal for the reflector 8 is thus conditioned by the type of light emitter chosen, and can be adjusted according to the constraints of the product.

In a subsequent operation, it is planned to engrave or deposit, in particular by printing, for example an arrangement of absorption points around the entire circumference of the polished surface 12 of the cylinder of revolution. This arrangement of points is not completely shown in Figures 1 to 4 for simplicity, but is shown in Figure 5 as explained below. Thus, before making this arrangement of light absorption points on the polished surface, a pattern of absorption points (black dots) must be generated. This is obtained in the form of a 2D image on a computer for example, and more precisely of a matrix of black-white pixels.

FIG. 5 represents a sinusoidal function of frequency 2 to which an offset of 1 can be added so that the value is always positive. This sinusoidal function oscillates between 1 and 0. The frequency 2 means that over a complete turn of the reflector 8, there is detection of two sine waves complete of light beams reflected by the detectors, that is to say 180 ° for each period of sine wave. The matrix of points to be produced on the polished surface of the cylinder is shown in a 2D image under the graph of the sinusoidal function. This 2D image must be reproduced over the entire circumference of the periphery P of the polished surface of the cylinder of revolution and over a length L of the cylinder.

It is carried out by columns. The points where the function is equal to 1, the reflectivity of the mirror must be maximum. So on this column no absorption pixel (black) will be realized. On the other hand, where the function is equal to 0, the reflectivity must be minimal. So all the pixels in this column will be black in particular.

In terms of pixels, and in the example shown in FIG. 5, a reflectivity 1 means that for example 39 pixels of the column are all white. A reflectivity of 0 means that for example 39 pixels of the column are all black. Intermediate cases are treated as follows. If at some point the function is 0.6, it means that 60% of the pixels must remain white (23 pixels) and 40% of them must be black (16 pixels). In the non-limiting example shown, the cylinder has a periphery circumference P equal to 4 mm and a length L equal to 0.77 mm. The starting image consists of a rectangle of 4 mm by 0.77 mm, so 200 times 39 pixels. These pixels or points in this case are 20 µm by 20 µm.

The aim with this arrangement of points on the reflector 8 is to obtain a signal in particular of sinusoidal shape upon detection of light by each detector 18 of the emitter-detector pairs. To do this, the reflector 8 rotates on itself in a regular manner, in particular at an almost constant speed and in the same direction of rotation, and again on the basis of a modulation of light reflectivity.

The image shown in Figure 5 can be engraved or printed on the polished surface of the reflector 8 in the form of a cylinder of revolution. Etching of the absorption points can be obtained for example by a laser beam. If each absorption point (black) is 20 µm by 20 µm in size, the engraving laser beam can be a 20 µm spot by being controlled from the computer by a control unit. This 2D image is loaded into the laser control unit and then engraved on the cylinder wall using a rotary setting synchronized with the laser emission.

It should be noted that it is well known that by the action of a laser beam, one can modify the optical properties of the surface of a material. A laser can therefore be used to locally etch absorption points on the surface of the reflector. The laser parameters are kept constant while machining the part so that each black point absorbs light with uniform efficiency. Under these conditions, the modulation of the reflectivity is due only to the density of black dots as shown in figure 5. As the reflector rotates in front of the light emitter, the density of the absorbing dots varies and this produces a variation of the light reflected and sent to the corresponding detector. As indicated, this variation in reflected light generates a detection signal, which can be sinusoidal according to the arrangement of absorbing points made on the reflector which rotates on itself and in the same direction of rotation. It is also possible to envisage having an absorbent surface, for example using a PVD treatment, the etching of which, for example by laser, reveals points of reflection, and not of absorption.

As shown in Figures 1 to 3 and explained in part above, each pair 10A, 10B of emitter-detector comprises a light source 16 and a light detector 18. The light source 16 typically consists of 'one or more light-emitting diodes, suitable for example to emit infrared light. The light source 16 and the light detector 18 are arranged in a protective housing 20 and are preferably optically isolated from each other, for example by means of a partition wall. Each pair 10A, 10B of emitter-detector forms, for example, a unitary device of the proximity detector type.

The two pairs 10A, 10B of emitter-detector are arranged on either side of the rotary reflector 8, facing the reflector 8. In a preferred embodiment shown in Figure 3, the two pairs 10A, 10B of the emitter-detector are arranged relative to the rotary reflector 8 so that the two emitters 16, respectively the two detectors 18, are arranged head-to-tail with respect to one another. Preferably, as illustrated in FIG. 3, the two pairs of emitter-detector 10A, 10B are placed on a circle whose center is substantially the center 22 of the rotary reflector 8, and are offset from each other by an angle having a distinct value. 180 °.

More preferably, as can be seen in FIG. 3, the two pairs 10A, 10B of emitter-detector and the rotary reflector 8 are arranged so as to define a spatial arrangement substantially in the form of a "y". More precisely, the rotating reflector 8 is arranged in the center of the "y", a first pair 10A of emitter-detector is arranged at the free end of a short branch of the "y", and the other pair 10B of transmitter-detector is placed at the free end of the long branch of the “y”. In other words, as visible in FIG. 3, the two pairs 10A, 10B of emitter-detector are arranged on either side of the rotary reflector 8 and are axially offset from one another.

Each light source 16 is intended to illuminate part of the reflector 8. Each light detector 18 is intended to receive a reflected light beam 24 from the reflector 8 and to generate an electrical signal representative of the beam 24. The signal representative electric generated by each detector 18 has a substantially sinusoidal shape when the reflector 8 rotates on itself in the same direction of rotation S1, S2. Such a signal 26A, 26B is for example visible in FIG. 6.

The processor is configured to process each of the electrical signals 26A, 26B generated by the detectors 18. The processor is further configured to determine, as a function of the result of the processing, at least one parameter relating to the angular movement of the axis 4, as will be detailed later. The determined parameter (s) are for example the angular position, the speed of rotation, or the direction of rotation of axis 4.

In Figure 6 are shown two real signals 26A, 26B from the detectors 18, at different angles corresponding to a rotation on itself of the rotary reflector 8. Each signal 26A, 26B comes from a respective detector 18 d one of the emitter-detector pairs 10A, 10B. Each signal 26A, 26B has a substantially sinusoidal shape. Furthermore, in the illustrative example of FIG. 6, the signals 26A, 26B are out of phase with each other by approximately 25 °. Preferably, the signals 26A, 26B are phase-shifted by at least 25 °, more preferably by substantially 90 °.

A method according to the invention for determining at least one parameter relating to an angular movement of the axis 4, implemented by the processor of the system 6, will now be described with reference to FIGS. 7 and 8. It is assumed that initially a user manipulates the axis 4 so as to make it rotate on itself around the longitudinal direction D1, for example by manipulating the crown 2 for setting the time of a watch 1. This rotation of the axis 4 causes a rotation of the rotary reflector 8 around the longitudinal direction D1.

Preferably, the method comprises an initial step 30 during which the processor controls the switching on of each of the light sources 16 alternately.

During an initial or next step 32, the processor receives two electrical signals 26A, 26B from the two light detectors 18. Each of the electrical signals 26A, 26B is representative of a reflected light beam 24 from the reflector 8, and has a substantially sinusoidal shape.

During a next step 34, the processor determines the frequency of each of the two sinusoidal signals 26A, 26B received.

During a following step 36, the processor determines the speed of rotation of axis 4, by comparison between the frequency determined during step 34 and a correspondence table pre-recorded in the memory means of the system.

Preferably, the method comprises a parallel or following step 38, during which the processor represents the two electrical signals 26A, 26B received as the sine and the cosine of the same function, then calculates an arc function tangent whose variable is the ratio between the two signals. The result of this calculation is shown in FIG. 8, for the particular embodiment of the signals 26A, 26B represented in FIG. 6. It is noted that over a half period of revolution of the rotary reflector 8, corresponding to 180 °, the curve obtained 39 is a straight line. This thus allows the processor, by having access to a given value of the calculated tangent arc function, to deduce therefrom the angular position of the axis 4, in an unequivocal manner. In addition, the sign of the slope of the line obtained is a function of the direction of rotation of axis 4. Thus, the method can include a parallel or following step 40 during which the processor determines, as a function of the sign of the axis. slope of the line obtained, the direction of rotation of axis 4.

It should be noted that, to obtain the shape of the curve 39 as shown in FIG. 8, it is necessary that the signals 26A, 26B are out of phase, preferably by at least 25 °. Such a phase shift is obtained by the head-to-tail arrangement of the pairs 10A, 10B of emitter-detector, as previously described, and / or by the non-symmetrical arrangement of the two pairs 10A, 10B of emitter-detector on each side and the other of the rotary reflector 8, as described above. Thus, the resulting phase shift between the signals 26A, 26B makes it possible to obtain the shape of the curve 39 as shown in FIG. 8, and consequently allows the processor to be able to precisely determine the angular position and the direction of rotation of the axis 4.

The memory means store a computer program product comprising program instructions which, when executed by the processor of the system 6, are able to implement the method as described above.

It should also be noted that the algorithm described above for the generation of the reflectivity image remains of general validity also when the pattern on the cylindrical reflector is produced with techniques other than the laser. For example the black pixels could be produced using black ink ejected by a digital printer.

It should also be noted that the same algorithm can be used to achieve other shapes of reflectivity and generate other signals in the detector such as a square wave or a ramp. However, it is more difficult to easily determine the speed of rotation of the axis or rod secured to the crown.

Claims (16)

1. System for determining (6) at least one parameter relating to an angular movement of an axis (4), in particular of an axis (4) integral with a crown (2) of a timepiece (1). ), the system (6) comprising: - an axis (4) configured so as to be able to rotate on itself around a longitudinal direction (D1), - a rotating reflector (8) mounted on the axis (4), around said axis (4), - two pairs (10A, 10B) of emitter-detector, the two pairs (10A, 10B) being arranged on either side of the rotating reflector (8), facing the reflector (8), each pair (10A, 10B) of an emitter-detector comprising a light source (16) intended to illuminate a part of the reflector (8), and a light detector (18) intended to receive a beam of reflected light (24) from the reflector (8) ) and generating an electrical signal (26A, 26B) representative of said beam (24), and - a processor configured to process each of the electrical signals generated by the detectors (18), and to determine, as a function of the result of the processing, said at least one parameter relating to the angular movement of the axis (4), characterized in that the rotating reflector (8) is in the form of a cylinder of revolution, and an arrangement of light absorbing points is made around the entire circumference of a reflective outer surface (12) of the cylinder of revolution , the arrangement of the absorption points on the outer surface (12) being such that, when the reflector (8) rotates on itself regularly and in the same direction of rotation (S1, S2), the electrical signal representative (26A, 26B) generated by each detector (18) of each pair (10A, 10B) has a substantially sinusoidal shape. 2. Determination system (6) according to claim 1, characterized in that the two pairs (10A, 10B) of emitter-detector are arranged relative to the rotary reflector (8) so that the two emitters (16 ), respectively the two detectors (18), are arranged head-to-tail with respect to each other. 3. Determination system (6) according to claim 1 or 2, characterized in that the two pairs (10A, 10B) of emitter-detector are arranged on either side of the rotary reflector (8), on a circle. the center of which is substantially a center (22) of the rotary reflector (8), and are offset from each other by an angle having a distinct value of 180 °. 4. Determination system (6) according to claim 3, characterized in that the two pairs (10A, 10B) of emitter-detector and the rotary reflector (8) are arranged so as to define a spatial arrangement substantially in the form of. "Y", the rotating reflector (8) being arranged in the center of the "y", one of the emitter-detector pairs (10A) being arranged at the free end of a short branch of the "y", the other pair of transmitter-detector (10B) being arranged at the free end of the long leg of the “y”. 5. Determination system (6) according to any one of the preceding claims, characterized in that, in each pair (10A, 10B) of emitter-detector, the emitter (16) and the detector (18) are isolated. optically from each other. 6. Determination system (6) according to claim 1, characterized in that the rotating reflector (8) is made of metal, the outer surface (12) of the metal reflector being polished. 7. Determination system (6) according to claim 1, characterized in that the points of the arrangement of light absorption points on the entire circumference of the outer surface (12) of the cylinder of revolution are obtained by etching. by means of a laser controlled on the basis of a determined image defining a matrix of points or pixels, where the density of the absorbing points varies sinusoidally. 8. Determination system (6) according to claim 1, characterized in that the points of the arrangement of light absorption points on the entire circumference of the outer surface (12) of the cylinder of revolution, are obtained by deposition. of ink black dots coming from a digital printer on the basis of a determined image defining a matrix of dots or pixels, where the density of the absorbing dots varies sinusoidally. 9. Determination system (6) according to claim 7 or 8, characterized in that the density of absorbent points engraved or printed on the entire circumference of the outer surface varies according to two sinusoidal wave periods. 10. Timepiece (1) comprising a determination system (6) of at least one parameter relating to an angular movement of an axis (4), characterized in that the determination system (6) conforms to any one of the preceding claims. 11. Timepiece (1) according to claim 10, characterized in that the timepiece (1) is a quartz watch provided with a crown (2) for setting the time, said axis (4). ) being the axis (4) integral with the crown (2). 12. Method for determining at least one parameter relating to an angular movement of an axis (4), in particular of an axis (4) integral with a crown (2) of a timepiece (1), at the means of a determination system (6) according to any one of claims 1 to 8, the method comprising the following steps, implemented by the processor: - receive (32) two electrical signals (26A, 26B) from the two light detectors (18), each of the electrical signals (26A, 26B) being representative of a reflected light beam (24) from the reflector (8) , each of the electrical signals (26A, 26B) having a substantially sinusoidal shape, - determining (34) the frequency of each of the two electrical signals received (26A, 26B), - determining (36), by comparison between the frequency determined by the processor and a correspondence table pre-recorded in memory means of the system (6), the speed of rotation of the axis (4). 13. The determination method according to claim 12 when the determination system (6) depends on claim 3, characterized in that it further comprises a step (38), implemented by the processor, consisting in representing the two electrical signals (26A, 26B) received as the sine and cosine of the same function and to calculate a tangent arc function (39) having as a variable the ratio between the two signals. 14. Determination method according to claim 13, characterized in that it further comprises a step (40), implemented by the processor, consisting in determining, as a function of the sign of the slope of the tangent arc function. (39) calculated, the direction of rotation of the axis (4). 15. Determination method according to one of claims 12 to 14, characterized in that it further comprises a step (30), implemented by the processor, consisting in controlling the switching on of each of the light sources ( 16) alternately. 16. Computer program product comprising program instructions stored in memory means of a determination system (6) according to one of claims 1 to 8 and which, when executed by the processor of the determination system (6) ), are able to implement the method according to one of claims 12 to 15, for determining at least one parameter relating to an angular movement of an axis (4).