METHOD AND SYSTEM FOR CALIBRATING SENSORS

Abstract

A method (100) for calibrating a plurality of sensors (21-24) each comprising a magnetometer (31), a gyroscope (32) and an accelerometer (33), the method comprising: providing (111) a first device (10) comprising at least one cavity (15-18) adapted for introduction of one or more sensors (21-24); introducing (112) each sensor of the plurality of sensors (21-24) into the first device (10); transmitting (113), from each sensor of the plurality of sensors (21-24) to a computing apparatus (40), a first measure corresponding to the respective magnetometer (31); determining (114), the computing apparatus (40), whether differences between the first measure of each sensor and the first measure of the other sensors of the plurality of sensors (21-24) are lower than a predetermined threshold; and calibrating (115) the plurality of sensors (21-24), if at least one of the differences between the first measures is equal to or greater than the predetermined threshold, by rotating the first device (10) or a second device (10) with the plurality of sensors (21-24) introduced therein, the second device comprising at least one cavity (15-18) adapted for introduction of one or more sensors (21-24). Also, a system (5) for calibrating a plurality of sensors (21-24).

Claims

1. A method (100) for calibrating a plurality of sensors (21-24) each comprising a magnetometer (31), a gyroscope (32) and an accelerometer (33), the method comprising: providing (111) a first device (10) comprising at least one cavity (15-18) adapted for introduction of one or more sensors (21-24), the at least one cavity being dimensioned such that the one or more sensors fit therein when the sensors are introduced with a particular orientation; introducing (112) each sensor of the plurality of sensors (21-24) into the first device (10); transmitting (113), from each sensor of the plurality of sensors (21-24) to a computing apparatus (40), a first measure corresponding to the respective magnetometer (31); determining (114), the computing apparatus (40), whether differences between the first measure of each sensor and the first measure of the other sensors of the plurality of sensors (21-24) are lower than a predetermined threshold; and calibrating (115) the plurality of sensors (21-24), if at least one of the differences between the first measures is equal to or greater than the predetermined threshold, by rotating the first device (10) or a second device (10) with the plurality of sensors (21-24) introduced therein, the second device (10) comprising at least one cavity (15-18) adapted for introduction of one or more sensors (21-24).

2. The method (100) of claim 1, wherein the step of calibrating (115) the plurality of sensors (21-24) by rotating the first device (10) or the second device (10) with the plurality of sensors introduced (21-24) therein comprises: transmitting, from the computing apparatus (40) to each sensor of the plurality of sensors (21-24), a start of calibration instruction; and rotating (115) the first device (10) or the second device (10) with the plurality of sensors (21-24) introduced therein according to a predetermined calibration procedure.

3. The method (100) of claim 1, wherein the step of calibrating (115) the plurality of sensors (21-24), if at least one of the differences between the first measures is equal to or greater than the predetermined threshold, by rotating the first device (10) or the second device (10) with the plurality of sensors (21-24) introduced therein is carried out until the determined differences between second measures corresponding to the magnetometer (31) of each sensor are lower than the predetermined threshold; and wherein the method further comprises: transmitting, from each sensor of the plurality of sensors (21-24) to the computing apparatus (40), the second measure corresponding to the respective magnetometer (31); and determining (115), the computing apparatus (40), whether differences between the second measure of each sensor and the second measure of the other sensors of the plurality of sensors (21-24) are lower than the predetermined threshold.

4. The method (100) of claim 3, wherein the step of calibrating (115) the plurality of sensors (21-24) by rotating the first device (10) or the second device (10) with the plurality of sensors (21-24) introduced therein further comprises repeating the calibrating (115) step if at least one of the differences between the second measures of the plurality of sensors (21-24) is equal to or greater than the predetermined threshold.

5. The method (100) of claim 1, wherein each step of determining (114) whether the differences between a measure corresponding to the respective magnetometer (31) of each sensor and a measure corresponding to the respective magnetometer (31) of the other sensors of the plurality of sensors (21-24) are lower than the predetermined threshold comprises: for each sensor of the plurality of sensors (21-24), projecting (118) an orientation corresponding to the measure of the sensor onto a horizontal plane thereby providing a corresponding vector; computing (119) an angle between each pair of corresponding vectors; and determining (120) that the differences between the measures of the plurality of sensors (21-24) are lower than the predetermined threshold if each computed angle is lower than the predetermined threshold.

6. The method (100) of claim 1, wherein each step of determining (114) whether the differences between a measure corresponding to the respective magnetometer (31) of each sensor and a measure corresponding to the respective magnetometer (31) of the other sensors of the plurality of sensors (21-24) are lower than the predetermined threshold comprises: for each sensor of the plurality of sensors (21-24), projecting (118) an orientation corresponding to the measure of the sensor onto a horizontal plane thereby providing a corresponding vector; computing (119) an angle between each pair of corresponding vectors; comparing (121) each corresponding vector with other corresponding vectors so as to determine if one or more corresponding vectors have an angle difference greater than 90°; and determining (120) that the differences between the measures of the plurality of sensors (21-24) are lower than the predetermined threshold if: each computed angle having an angle difference lower than or equal to 90° is lower than the predetermined threshold; and for each computed angle having an angle difference greater than 90°, a result of 180° minus the computed angle is lower than the predetermined threshold.

7. The method (100) of claim 1, wherein measures transmitted (113) from each sensor of the plurality of sensors (21-24) to the computing apparatus (40) are three-dimensional magnetic field vectors.

8. The method (100) of claim 7, wherein each step of determining (114) whether the differences between a measure corresponding to the respective magnetometer (31) of each sensor and a measure corresponding to the respective magnetometer (31) of the other sensors of the plurality of sensors (21-24) are lower than the predetermined threshold comprises: computing (125) an angle between each pair of corresponding three-dimensional magnetic field vectors; and determining (126) that the differences between the measures of the plurality of sensors (21-24) are lower than the predetermined threshold if each computed angle is lower than the predetermined threshold.

9. The method (100) of claim 7, wherein each step of determining (114) whether the differences between a measure corresponding to the respective magnetometer (31) of each sensor and a measure corresponding to the respective magnetometer (31) of the other sensors of the plurality of sensors (21-24) are lower than the predetermined threshold comprises: computing (127) a Euclidean distance between each pair of corresponding three-dimensional magnetic field vectors; and determining (128) that the differences between the measures of the plurality of sensors (21-24) are lower than the predetermined threshold if each Euclidean distance is lower than the predetermined threshold.

10. The method (100) of claim 1, wherein measures transmitted (113) from each sensor of the plurality of sensors (21-24) to the computing apparatus (40) are provided by the sensors (21-24) upon combining, with a sensor fusion processing, a magnetic field sensed by the respective magnetometer (31) with at least one or more measures of the respective gyroscope (32) and accelerometer (33).

11. A system (5) for calibrating a plurality of sensors (21-24) each comprising a magnetometer (31), a gyroscope (32) and an accelerometer (33), the system comprising: a device (10) comprising at least one cavity (15-18) adapted for introduction of one or more sensors (21-24); and a computing apparatus (40) comprising at least one processor (42), at least one memory (44) and means (46) for transmitting and receiving data, the computing apparatus (40) being programmed to: receive, from each sensor of the plurality of sensors (21-24), at least one measure corresponding to the respective magnetometer (31); determine (114) whether the at least one measure of each sensor differs from the at least one measure of the other sensors of the plurality of sensors (21-24) by less than a predetermined threshold; and transmit start of calibration instructions to the plurality of sensors (21-24) when a difference between the at least one measure from one of the sensors (21-24) and the at least one measure of at least one other of the sensors (21-24) is equal to or greater than the predetermined threshold.

12. The system (5) of claim 11, wherein the computing apparatus (40) is programmed to determine (114) whether the at least one measure of each sensor differs from the at least one measure of the other sensors of the plurality of sensors (21-24) by less than the predetermined threshold by: projecting (118) orientations corresponding to the at least one measure of each sensor of the plurality of sensors (21-24) onto a horizontal plane thereby providing corresponding vectors; computing (119) an angle between each pair of corresponding vectors; and determining (120) that the differences between the at least one measure of the plurality of sensors (21-24) are lower than the predetermined threshold if each computed angle is lower than the predetermined threshold.

13. The system (5) of claim 11, wherein the at least one measure received at the computing apparatus (40) from each sensor of the plurality of sensors (21-24) is a three-dimensional magnetic field vector; and wherein the computing apparatus (40) is programmed to determine (114) whether the at least one measure of each sensor differs from the at least one measure of the other sensors of the plurality of sensors (21-24) by less than the predetermined threshold by: computing (119) an angle between each pair of corresponding three-dimensional magnetic field vectors; and determining (120) that the differences between the at least one measure of the plurality of sensors (21-24) are lower than the predetermined threshold if each computed angle is lower than the predetermined threshold.

14. The system (5) of claim 11, wherein the at least one measure received at the computing apparatus (40) from each sensor of the plurality of sensors (21-24) is a three-dimensional magnetic field vector; and wherein the computing apparatus (40) is further programmed to determine (114) whether the at least one measure of each sensor differs from the at least one measure of the other sensors of the plurality of sensors (21-24) by less than the predetermined threshold by: computing (119) a Euclidean distance between each pair of corresponding three-dimensional magnetic field vectors; and determining (120) that the differences between the at least one measure of the plurality of sensors (21-24) are lower than the predetermined threshold if each Euclidean distance is lower than the predetermined threshold.

15. The system (5) of claim 11, further comprising the plurality of sensors (21-24), each sensor further comprising at least one processor programmed to apply a sensor fusion processing to a magnetic field sensed by the magnetometer (31) and at least one or more measures of the gyroscope (32) and the accelerometer (33), thereby providing the at least one measure.

16. The system (5) of claim 11, wherein the computing apparatus (40) is programmed to determine (114) whether the at least one measure corresponding to the respective magnetometer (31) of each sensor differs from the at least one measure corresponding to the respective magnetometer (31) of the other sensors of the plurality of sensors (21-24) by less than the predetermined threshold by: projecting (118) orientations corresponding to the at least one measure of each sensor of the plurality of sensors (21-24) onto a horizontal plane thereby providing corresponding vectors; comparing (121) each corresponding vector with other corresponding vectors so as to determine if one or more corresponding vectors have an angle difference greater than 90°; and determining (120) that the differences between the measures of the plurality of sensors (21-24) are lower than the predetermined threshold if: each computed angle having an angle difference lower than or equal to 90° is lower than the predetermined threshold; and for each computed angle having an angle difference greater than 90°, a result of 180° minus the computed angle is lower than the predetermined threshold.

17. The system (5) of claim 11, wherein the at least one cavity is dimensioned such that the one or more sensors fit therein when the sensors are introduced with a particular orientation.

18. The system (5) of claim 11, further comprising the plurality of sensors (21-24).

19. The system (5) of claim 11, wherein the computing apparatus (40) is further programmed to: receive, from each sensor of the plurality of sensors (21-24), at least one second measure corresponding to the respective magnetometer (31) after having transmitted start of calibration instructions; and determine whether differences between the at least one second measure of each sensor and the at least one second measure of the other sensors of the plurality of sensors (21-24) are lower than the predetermined threshold.

20. The system (5) of claim 19, wherein the computing apparatus (40) is further programmed to transmit additional start of calibration instructions to the plurality of sensors (21-24) when it determines that a difference between the at least one second measure from one of the sensors (21-24) and the at least one second measure of at least one other of the sensors (21-24) is equal to or greater than the predetermined threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the invention, which should not be interpreted as restricting the scope of the invention, but just as examples of how the invention can be carried out. The drawings comprise the following figures:

[0071] FIGS. 1A-1B show a device for calibration of sensors.

[0072] FIG. 2 diagrammatically shows a system in accordance with an embodiment.

[0073] FIG. 3 diagrammatically shows a method in accordance with an embodiment.

[0074] FIGS. 4-7 diagrammatically show steps of methods in accordance with embodiments.

[0075] FIGS. 8A-8B and 9 diagrammatically show processing of measures of methods and systems in accordance with embodiments.

[0076] FIG. 10 shows the device of FIGS. 1A-1B being manipulated by a user.

[0077] FIG. 11 diagrammatically shows a method in accordance with an embodiment.

DESCRIPTION OF WAYS OF CARRYING OUT THE INVENTION

[0078] FIGS. 1A-1B show a device 10 for calibration of sensors. In FIG. 1A the device 10 is shown from a top view, and in FIG. 1B the device 10 is shown in perspective with a plurality of sensors 21-24 introduced therein.

[0079] The device 10 comprises a plurality of cavities 15-18 adapted to receive a sensor 21-24.

[0080] The cavities 15-18 are dimensioned such that the sensors 21-24 may be introduced with a particular orientation thereof. The sensors 21-24 may fit tightly or with some play, in which case the rotation of the device 10 for calibrating the sensors 21-24 may require covering the sensors with the hand so that they do not fall off from the device 10, as shown in FIG. 10.

[0081] FIG. 2 diagrammatically shows a system 5 in accordance with an embodiment.

[0082] The system 5 comprises the device 10, a computing apparatus 40, and a plurality of sensors 21-23. In some embodiments, the sensors 21-23 are not part of the system.

[0083] The computing apparatus 40 comprises at least one processor 42, at least one memory 44, and means 46 for transmitting and receiving data. The computing apparatus 40 may be a computer, a wireless electronic device such as a mobile phone or a tablet, a single-board computer, a microcontroller, etc.

[0084] Each sensor 21-23 at least comprises a magnetometer 31, a gyroscope 32, an accelerometer 33, and means 35 for transmitting and receiving data. In some examples, the sensors 21-23 also comprise at least one processor (not illustrated) that may be configured to run a sensor fusion algorithm with at least the values sensed by the magnetometer and the values sensed by the gyroscope and/or the accelerometer. In the example illustrated in FIG. 2, the sensors 21-23 are MARG sensors.

[0085] The measures resulting from the sensing of the magnetometers 31 are sent to the computing apparatus 40 using the means 35 for transmitting and receiving data (preferably the transmission is carried out wirelessly, for example via Bluetooth, WLAN, or cellular communications, but could also be carried out via a wired connection). The computing apparatus 40 receives the measures through its means 46 for transmitting and receiving data, and the at least one processor 42 determines the differences between each pair of measures and commands the calibration thereof if at least one difference exceeds a predetermined threshold.

[0086] In this embodiment there are three sensors 21-23, however in other embodiments there may be two, four, five or even more than five sensors.

[0087] In some embodiments, the computing apparatus 40 further comprises a display, or notification LEDs, or a combination thereof, that may be used for indicating to a user how to calibrate the sensors 21-23 and what is the calibration status thereof. In some embodiments, the computing apparatus 40 uses the means 46 for transmitting and receiving data to send information regarding the calibration to another device, that may be remote from the computing apparatus 40, which in turn displays said information.

[0088] FIG. 3 diagrammatically shows a method 100 in accordance with an embodiment.

[0089] The method 100 comprises a step of providing 111 a device (for example the device 10 of FIGS. 1A-1B and 2) with at least one cavity adapted for introduction of one or more sensors (for example the sensors 21-24 of FIG. 1B or the sensors 21-23 of FIG. 2).

[0090] The method 100 further comprises a step of introducing 112 the sensors into the device, particularly into one of the at least one cavity.

[0091] The method 100 further comprises a step of transmitting 113, from each sensor to a computing apparatus (for example the computing apparatus 40 of FIG. 2), one or more first measures corresponding to the magnetometer of the sensors that are introduced into the device. In this respect, the computing apparatus receives said one or more first measures.

[0092] The method 100 further comprises a step of determining 114 whether the biases between a measure corresponding to the magnetometer of each sensor and a measure corresponding to the magnetometer of the other sensors of the plurality of sensors are lower than a predetermined threshold. To this end, at least one processor (for example the at least one processor 42 of FIG. 2) of the computing apparatus is configured to carry out this determining 114 step together with at least one memory thereof (for example the at least one memory 44 of FIG. 2).

[0093] The method 100 further comprises a step of calibrating 115 the sensors introduced in the device if in the determining 114 step it was determined that at least one bias of the measure of a sensor, relative to the measure of another sensor, is equal to or greater than the predetermined threshold. For calibrating 115 the sensors, the device is rotated according to a magnetometer calibration procedure or pattern (i.e. the way in which the sensors have to be rotated) known in the art until the biases of all the sensors are lower than the predetermined threshold according to further measure(s) (corresponding to the magnetometers) provided by them. The calibration procedure or pattern itself is not within the scope of the present disclosure. Therefore, the method 100 may repeat the determining 114 and calibrating 115 steps in order to achieve such biases.

[0094] FIG. 4 diagrammatically shows a determining 114 step of methods in accordance with embodiments.

[0095] The determining 114 step comprises a step of projecting 118 one or more orientation(s) corresponding to measures, which correspond to the magnetometer of each sensor, onto a horizontal plane so as to provide a vector of each orientation.

[0096] The determining 114 step further comprises a step of computing 119 an angle between each pair of vectors provided in the projecting 118 step.

[0097] The determining 114 step further comprises a step of determining 120 whether the sensors introduced into the device provide measures with biases (relative to the measures of the other sensors) that are lower than the predetermined threshold. In order to determine 120 that the biases are lower than the predetermined threshold, each angle of the computing 119 step must be lower than the predetermined threshold.

[0098] In some embodiments, prior to the step of determining 120 whether the sensors provide measures with biases lower than the predetermined threshold, a step of comparing each corresponding vector with other corresponding vectors is conducted in order to determine if one or more corresponding vectors have an angle difference greater than 90°. In these embodiments, in the step of determining 120 whether the sensors provide measures with biases lower than the predetermined threshold, each angle of the computing 119 step which does not have an angle difference greater than 90° (according to the comparing step) must be lower than the predetermined threshold, whereas each angle of the computing 119 step which has an angle difference greater than 90° (according to the comparing step), a result of 180° minus the angle computed 119 must be lower than the predetermined threshold.

[0099] The at least one processor of the computing apparatus is configured, together with the at least one memory, to carry out each of the projecting 118, computing 119 and determining 120 steps.

[0100] FIG. 5 diagrammatically shows a determining 114 step of methods in accordance with embodiments.

[0101] The determining 114 step comprises the step of projecting 118 the one or more orientation(s) onto the horizontal plane.

[0102] The determining 114 step further comprises a step of comparing 121 each vector of the projecting 118 step with other vectors of the projecting step 118 so as to determine if one or more vectors have an angle difference greater than 90°.

[0103] The determining 114 step further comprises a step of rotating 122 180° each vector whose angle difference, according to the comparing 121 step, is greater than 90° with respect to other vectors.

[0104] The determining 114 step further comprises the step of computing 119 the angle between each pair of vectors (once any rotation 122 necessary has been carried out), and the step of determining 120 whether the sensors introduced in the device provide measures with biases (relative to the measures of the other sensors) that are lower than the predetermined threshold.

[0105] The at least one processor of the computing apparatus is further configured, together with the at least one memory, to carry out each of the comparing 121 and rotating 122 steps.

[0106] FIG. 6 diagrammatically shows a determining 114 step of methods in accordance with embodiments.

[0107] The determining 114 step comprises a step of computing 125 an angle between each pair of measures provided by the sensors, the measuring corresponding to three-dimensional magnetic field vectors.

[0108] The determining 114 step further comprises a step of determining 126 that the differences between the measures of the sensors are lower than the predetermined threshold if each angle of the computing 125 step is lower than the predetermined threshold.

[0109] FIG. 7 diagrammatically shows a determining 114 step of methods in accordance with embodiments.

[0110] The determining 114 step comprises a step of computing 127 a Euclidean distance between each pair of measures provided by the sensors, the measuring corresponding to three-dimensional magnetic field vectors.

[0111] The determining 114 step further comprises a step of determining 128 that the differences between the measures of the sensors are lower than the predetermined threshold if each Euclidean distance of the computing 127 step is lower than the predetermined threshold.

[0112] The at least one processor of the computing apparatus is further configured, together with the at least one memory, to carry out each of the computing 125, 127 and determining 126, 128 steps.

[0113] FIGS. 8A-8B diagrammatically show processing of orientations of methods and systems in accordance with embodiments. FIG. 8A shows, in a 3D view, the processing, whereas FIG. 8B shows the same processing from a top view.

[0114] Each sensor 21-23 provides a measure of a magnetic field, owing to the magnetometer thereof, in the form of orientations 81, 82a, 83, respectively, in an Earth's reference frame. The orientations 81, 82a, 83 may be provided, for example, in the form of 3D vectors as illustrated in FIG. 8A.

[0115] The computing apparatus projects the orientations 81, 82a, 83 onto a horizontal plane 80 (i.e. a plane that, in a Cartesian coordinate system, extends in X and Y dimensions and is defined by a constant height, that is a constant Z dimension), thereby providing respective vectors 91, 92a, 93. In FIG. 8B, the vectors 91, 92a, 93 match the orientations 81, 82a, 83 because the projection onto the horizontal plane 80 relates to the Z dimension. In the example of FIGS. 8A-8B, the orientations 81 and 82a are directed towards the positive Z dimension whereas the orientation 83 is directed towards the negative Z dimension.

[0116] FIG. 9 diagrammatically shows processing of the vectors 91, 92a, 93 of FIGS. 8A-8B, from a top view of the horizontal plane 80.

[0117] In this example, the vectors 91, 92a, 93 are compared one to each other so as to determine whether any of the sensors 21-23 was introduced into the device rotated 180° with respect to the other sensors. By comparing the angles between each pair of vectors 91, 92a, 93 it is determined that the sensor 22 was introduced flipped into the device with respect to the other sensors as the angle difference of the vector 92a thereof relative to the other vectors 91 and 93 is greater than 90°. Accordingly, the vector 92a may be rotated 180° so as to provide a further vector 92b, even though in some embodiments the vector is not rotated but the predetermined threshold is compared to the result of 180° minus the difference in angle between said vector and another vector.

[0118] The vectors 91, 92b, 93 are then compared to determine whether the biases between them, that is the angle differences between these vectors, are lower than the predetermined threshold, e.g. angles of 3°, 5°, 8°, etc. First, second and third angles 96-98 are computed (resulting from each possible pair of vectors 91, 92b, 93), and then compared with the predetermined threshold. If all the angles 96-98 are less than the predetermined threshold, it is determined that the sensors 21-23 have an acceptable bias, otherwise at least one has an excessive bias, therefore the sensors must be calibrated.

[0119] FIG. 10 shows the device 10 of FIGS. 1A-1B being manipulated by a user.

[0120] The plurality of cavities 15-18 of the device 10 are dimensioned such that the sensors 21-24 are introduced therein with some play. Therefore, the user in order to perform the rotation of the device 10 to calibrate the sensors 21-24 covers the sensors with his/her hand 150 so that the sensors do not fall off.

[0121] FIG. 11 diagrammatically shows a method 101 in accordance with an embodiment.

[0122] The method 101 is similar to the method 100 of FIG. 3 but involving the use of two devices. A first part of the method 101 is conducted with a first device and a second part of the method 101 is conducted with a second device. The first device may be used for verifying that a magnetic field measure of the sensors does not differ from the magnetic field measure of the other sensors by more than a certain value, and also for storing the sensors while they are not in use. The second device may be used for calibrating the sensors and for conducting a similar verification while the sensors are being subjected to the calibration procedure.

[0123] The first device with at least one cavity adapted for introduction of one or more sensors is provided 111. The sensors are introduced 112 into the first device. Each sensor transmits 113, to the computing apparatus, one or more first measures corresponding to the magnetometer of the sensors that are introduced into the first device. The computing apparatus determines 114 whether the biases between a measure corresponding to the magnetometer of each sensor and a measure corresponding to the magnetometer of the other sensors of the plurality of sensors are lower than a predetermined threshold.

[0124] The method 101 further comprises a step of providing 131 the second device with at least one cavity adapted for introduction of one or more sensors (for example the device 10 of FIGS. 1A-1B and 2).

[0125] The method 101 further comprises a step of introducing 132 the sensors into the second device.

[0126] The method 101 further comprises calibrating 133 the sensors by rotating the second device with the sensors introduced therein according to a magnetometer calibration procedure or pattern if it was determined 114 that at least one bias of the measure of a sensor, relative to the measure of another sensor, is equal to or greater than the predetermined threshold.

[0127] The method 101 further comprises determining 134, the computing apparatus, whether the biases between a measure corresponding to the magnetometer of each sensor and a measure corresponding to the magnetometer of the other sensors of the plurality of sensors are lower than the predetermined threshold; these measures are transmitted while the calibration 133 procedure is under way or after the same has ended, thus they are transmitted while the sensors are introduced in the second device. If at least one bias is greater than the predetermined threshold, both the calibration 133 and the determination 134 steps may be further carried out one or more times.

[0128] The second determining 134 step is based on a same processing as the first determining 114 step, thus the processing described with reference to any of FIGS. 4-9 applies to this second determining 134 step as well.

[0129] In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0130] On the other hand, the invention is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.