WO2019220040A1

WO2019220040A1 - Determining the pedalling cadence of a cyclist

Info

Publication number: WO2019220040A1
Application number: PCT/FR2019/051065
Authority: WO
Inventors: Jérôme LEGENNE; François-Xavier MARMET
Original assignee: Centre National d'Études Spatiales
Priority date: 2018-05-15
Filing date: 2019-05-10
Publication date: 2019-11-21
Also published as: EP3794378A1; FR3081228B1; FR3081228A1

Abstract

The invention is based on the observation that, considering the pedalling movement, the power developed by a cyclist takes the form of a permanent sine curve with a frequency that is double the pedalling frequency. This cyclic power variation results in a small oscillation of the speed of the cyclist, the amplitude of which can be observed through GNSS phase measurements which are more precise by an order of magnitude. A first aspect of the invention relates to a method for determining the pedalling cadence of a cyclist (10) on a cycle (12), wherein the pedalling cadence is extracted from an oscillation of GNSS signal phase measurements (16) taken on the cycle (12) via a GNSS receiver (14) or an oscillation of measurements calculated on the basis of the phase measurements.

Description

Determination of the pedaling rate of a cyclist.

Technical area

In general, the invention relates to a method and a device for determining the pedaling frequency of a cyclist from a GNSS signal (acronym for "Global Navigation Satellite System"). satellite positioning) radiofrequency.

Technological background

The pedaling rate of a cyclist is a key parameter for the performance analysis.

The power developed by a cyclist can be calculated by:

P = T w (Eq. 1) where P is the power, in Watts, T is the pair of forces exerted on the pedals, in Newtons-meters, and w is the angular velocity of the pedals w is itself a measure, normally in rad / s, the cadence of pedaling. The pedaling rate is typically expressed in revolutions per minute ("rpm"), but this is not a requirement but rather a habit (which is not meant to limit the invention). In this case, the rate is

[0004] The forces on the pedals can be measured by sensors (eg strain gauges, eg installed at trays, cranks, hubs or pedals) or estimated indirectly depending on the speed, the slope of the ground, the weight of the cyclist, etc.

Currently, the pedaling rate is measured using sensors which must be arranged in or on the bicycle, eg an accelerometer integrated in one of the cranks or a cadence sensor comprising a magnet attached to a crank and a pulse donor, responsive to the magnet, attached to the frame.

Determining the pace of pedaling therefore requires additional equipment on the bicycle. Technical problem

An object of the present invention is to provide an alternative determination of the pedaling rate.

General description of the invention

The invention is based on the observation that, given the pedaling movement, in stable conditions of effort of the cyclist, wind and slope, the power developed by a cyclist takes (approximately) the form of a sinusoid whose frequency is twice the pedaling frequency. This cyclic variation in power has the effect of a small oscillation of the cyclist's speed whose amplitude (a few centimeters per second) can be observed through GNSS phase measurements which are of a more precise order of magnitude (a few millimeters) .

A first aspect of the invention therefore relates to a method of determining the pedaling rate of a cyclist on a cycle, in which the pedaling rate is extracted from an oscillation of GNSS signal phase measurements performed. on the cycle using a GNSS receiver or an oscillation of measurements calculated on the basis of phase measurements.

The term "cycle" means a vehicle with two or more wheels propelled by the muscular energy of the person or persons on the vehicle (the rider or cyclists), including using pedals or cranks. As part of this document, the term "cycle" can therefore designate a vehicle powered exclusively by muscular energy or an assisted pedal cycle.

As part of this document, the term "GNSS signal" means a radionavigation signal emitted by the satellites of one or more satellite positioning systems (eg GPS, GALILEO, GLONASS, SBAS, etc. In general, a GNSS signal comprises a radiofrequency carrier modulated by a waveform (called "spreading") containing a pseudo-random code. Because carrier modulation causes spectrum spread around the carrier frequency, GNSS signals are often referred to as "spread spectrum". Each pseudo-random code constitutes an identifier of the signal and its transmitter. Known receivers, the pseudo-random codes allow them a Multiple Access to Code Distribution (CDMA). With the exception of "pilot" GNSS signals, GNSS signals also carry data (eg the navigation message) in the form of a binary sequence (at a significantly lower rate than the pseudo-random code) modulated in addition to the carrier.

The term "GNSS receiver" refers to a radio frequency receiver capable of receiving and processing GNSS signals, eg, to determine its position, speed and time. A GNSS receiver is typically capable of performing code measurements and measurements of the carrier phase ("phase measurements"). The two measurements correspond to the apparent distance between the transmitter and the receiver. Phase measurements are much more accurate than code measurements, but they contain an ambiguity equal to an integer multiple (unknown) of the carrier wavelength. These ambiguities being difficult, if not impossible (on conventional receivers), to be solved consistently for all GNSS signals, most applications can not rely solely on phase measurements but need code measurements. This is not the case in the context of this invention, since it is not necessary to remove the ambiguities of the phase measurements.

Given the observation described above, according to a first embodiment of the method, one can calculate the speed or oscillations of the cycle speed based on the phase observations. "Measurements calculated on the basis of phase measurements" would be in this case the speed or the variations of speed thus calculated. In order to calculate the velocity oscillations due to pedaling, it is not necessary to know the absolute value of the velocity and therefore there is no need to remove the ambiguities on the phase measurements.

It should be noted that it is not necessary in all cases to combine the phase measurements made on the different GNSS signals so as to obtain a magnitude corresponding to the speed, because the small oscillations of the speed of the This cycle is reflected in small oscillations in the raw phase measurements, specifically in the phase measurements of GNSS signals whose propagation direction is not (substantially) orthogonal to the oscillations. At a given moment, the raw phase measurement oscillations are therefore present on most of the GNSS signals coming from the satellites which are above the horizon. Therefore, it is possible to extract the pedaling rate from the raw phase measurements or measurements calculated on the basis of the raw phase measurements.

The measurements calculated on the basis of the phase measurements could comprise Doppler measurements, the speed of the GNSS receiver, the projection of the GNSS receiver speed on a horizontal plane, the GNSS receiver speed standard, the acceleration GNSS receiver, the projection of the GNSS receiver acceleration on a horizontal plane and / or the GNSS receiver acceleration standard. This list is not exhaustive.

The measurements calculated on the basis of the raw phase measurements can be obtained using time differentiated phase measurements ("TDCP measurements" of the time-differenced carrier phase). For example, the Doppler shift TDCP on signal i at time tj, denoted D _{i nes} (tj), could be calculated (approximated) by:

where iit _j -i) designates the phase measurement at instant tj _ _l

that at time t _{J + 1} , and At the difference between two moments of measurement (At = tj - t _J-1 = t _{J + 1} - tj).

According to one embodiment of the first aspect of the invention, the method comprises carrying out inertial measurements using one or more accelerometers and / or one or more gyrometers. Accelerometers and / or gyrometers can be part of an inertial unit or operate individually.

An advantage of having inertial measurements available is that the pedaling rate could be extracted from an oscillation of measurements obtained by hybridization of phase measurements and inertial measurements.

In addition or alternatively, the pedaling rate could be extracted from an oscillation of the inertial measurements (taken individually) or a measurement calculated on the inertial measurements only, when the phase measurements of GNSS signals are temporarily unavailable (eg below a bridge, in a tunnel, etc.) or too noisy. The method according to the first aspect of the invention may comprise the realization of phase measurements of GNSS signals by the GNSS receiver. It should however be noted that the method could also operate remotely, on measurements that are performed by a GNSS receiver on the cycle and transmitted by a telecommunication link to the processor that executes the process. In this case, the pedaling rate could be retransmitted via the same or another telecommunication link in the other direction, or used remotely, eg for delayed performance calculations.

The method according to the invention could be implemented on any mobile device comprising or being connected to a GNSS receiver, eg on a multifunction mobile (in English: "smartphone"), a connected watch (or watch intelligent, "smart watch"), a GNSS receiver, etc. Some mobile terminals incorporating a GNSS receiver are configured to operate in a static or adaptive "duty cycling" mode. If "duty cycling" is enabled, the GNSS receiver operates in a mode that alternates between activity and inactivity intervals, which in particular reduces the power consumption of the GNSS receiver and thus increases the power consumption of the GNSS receiver. autonomy of the mobile terminal. The disadvantage of the "duty cycling" mode is that it involves interruptions of the measurements. For phase measurements, this may mean an arbitrary phase jump after each restart and thus make it impossible to detect phase oscillations in the range of pedaling rates. To overcome this problem, the method could include detecting whether the GNSS receiver is operating in a mode that alternates between activity and inactivity intervals ("duty cycling" mode) and, where appropriate, (a) activation. a mode in which the GNSS receiver remains permanently active or (b) the adaptation of the length of the activity and inactivity intervals according to the needs of the determination of the pedaling rate.

Preferably, the extraction of the cadence of the oscillation of the phase measurements or measurements calculated on the basis of the phase measurements comprises a frequency analysis in the range of 1 to 6 Hz, corresponding to a cadence. pedaling between 30 and 180 rpm. Frequency (spectral) analysis could be done using a Fourier transform (normal or fast) and a peak detection (s) in the indicated range. The frequency range can be fixed or be dynamically adapted according to the speed, position and / or geographical information concerning the position of the cyclist. This would reduce the search for cadence to a reduced range, including the most likely range under the circumstances.

To validate the cadence of pedaling, an analysis, based on the speed of the cyclist, the plausibility of the pedaling rate determined could be achieved. This plausibility analysis will preferably take into account that jumps in the determined rate may occur if the cyclist changes gear ratio. This may, for example, be done using the known cycle speed ratios (plateaux and gears).

A second aspect of the invention relates to a method of evaluating the performance of a cyclist which comprises calculating the performance on the basis of the cyclist's pedaling rate determined by the method according to the first aspect of the invention. invention.

A third aspect of the invention relates to a computer program, eg mobile application or web application, comprising program code instructions for performing the steps of the method when the program is run on a computer. . According to one embodiment, the program is recorded on a computer medium (eg a memory, a storage medium, etc.), and is preferably accessible to a processor to be loaded into the RAM of that for the execution of the program.

A fourth aspect of the invention relates to a mobile terminal, such as, for example, a multifunction mobile, a GNSS receiver, a connected watch, configured (eg using a computer program). for the implementation of the method according to the first and / or second aspect of the invention.

Brief description of the drawings

Other features and characteristics of the invention will become apparent from the detailed description of certain advantageous embodiments presented below, by way of illustration, with reference to the accompanying drawings which show: FIG. 1: a schematic view of a cycle equipped with a GNSS receiver to perform carrier phase measurements; Fig. 2: a graph illustrating the oscillations of the speed of a cycle due to pedaling.

Detailed description of an embodiment of the invention

[0028] Figure 2 illustrates the pedaling effect of a cyclist on his speed. It is observed that the speed as a function of time has the form of a sinusoid with an amplitude of a few cm / s. The illustrated case is based on a simulation based on the following parameters:

o cadence of pedaling: 60 rpm

o minimum power transmitted to the pedals (in neutral): 20 W

o maximum power transmitted to the pedals: 480 W

o average power: 250 W

o mass of the cyclist and the bike: 80 kg.

The oscillations obtained correspond to a rolling situation on the flat in steady state. Gravity forces, air resistance, rolling resistance and friction force have been taken into account. It can be seen that the amplitude (peak-to-peak) is about 4 to 5 cm / s. For a rolling situation on a 5 ° slope with otherwise the same assumptions as above, the amplitude (peak to peak) would be about 14 cm / s.

These oscillations of the speed of the cyclist relative to the ground have the effect that in the repository of a GNSS receiver mounted on the cycle, an oscillatory movement is superimposed on non-oscillatory movement and trajectories GNSS satellites. Since the accuracy of the carrier phase measurements is of the order of a few millimeters (for example, on the L1 frequency of the GPS, a measurement noise of 2 to 3 mm is observed), it will be possible to measure the oscillations of the speed. through these measures.

[0031] FIG. 1 schematically shows a cyclist 10 on his bicycle 12. The cyclist has mounted a mobile terminal 14 (eg a GNSS receiver or a multifunctional mobile) on the cycle (for example on the handlebars) by means of a fixation. The mobile terminal 14 comprises an integrated GNSS receiver, capable of receiving and processing the GNSS signals 16 which are broadcast by the satellites 18 of one or more GNSS constellations. It should be noted that it is not essential for the invention that the mobile terminal is attached to the cycle. Indeed, the cyclist could also wear the terminal on his body (eg attached to the arm) or in a pocket.

In the example illustrated, the multifunction mobile 14 is equipped with a mobile application that has access to the raw measurements made by the GNSS receiver and which is configured to execute a method according to the invention, in particular to extract the oscillations of phase measurements that are due to pedaling.

A possibility to measure small oscillations is indicated, by way of example, in the following. The Doppler shift D _£ is due to the relative movement between the satellite i and the GNSS receiver (RX) and is given by the formula:

where ÎRX, _Î is the frequency of the carrier of the signal i in the receiver's reference frame, ίtc, ί the frequency of the carrier of the signal i in the reference frame of the satellite i which transmits it (equal to the nominal frequency / of the carrier after compensation for the effects of drift of satellite clock), c the speed of light, v _t the speed of satellite i, v _RX actuator speed, r _£ i the position of the satellite, the position of r _RX receiver, "" the dot product and "|| - || The Euclidean norm. The velocity and position vectors are indicated with respect to a common reference frame, eg a terrestrial reference frame. For

r -r _RX

facilitate the notation, we define d = _£ the unit vector pointing from the receiver to

\\ ri-f _R x \\

satellite i.

The observed carrier frequency (and thus the observed Doppler shift) by the receiver includes a systematic error due to the drift of the receiver clock δh _RX and noise e. After correction of the drift of the satellite clock, we obtain the equation for the rate of variation of pseudo-range _£ (in English "pseudo-range rate"):

Note that this expression depends on the position of the receiver. An estimate of the position is therefore necessary to obtain v _RX . [0036] D _{i my} can be estimated using TDCP measures. The Doppler shift observed on the signal i at time tj is approximated by:

where (i itj-i) designates the phase measurement at time t, · _ _1;

The speed v _t and position r _e of the satellites can be calculated by the receiver using the GNSS ephemerides diffused in the navigation message contained in the GNSS signals or made available to the users by another means (Internet, GNSS helpdesk, etc.)

The GNSS receiver can calculate its position in a conventional manner, using the code measurements. The positioning accuracy thus obtained is sufficient in this context.

The measurements D _{i rnes} , velocities and positions of the satellites as well as the estimate of the position of the receiver are combined by means of the Eq. 4. The system of equations can be solved for _RX by the least squares method, a Kalman filter, or any other suitable method.

To determine the oscillations, the receiver records the indeterminate values for a certain time and performs a frequency analysis in the range of 1 to 6 Hz. Such a frequency analysis may include a Fourier transform and a peak detection. Instead of carrying out this analysis on the components of v _RX in an individual way, it is possible to realize it on the norm of the velocity vector \\ v _RX \\, on the projection of v _RX on a horizontal plane, on the projection of v _RX on the ground plane, on the projection of v _RX on the longitudinal axis of the cycle, etc. The frequency of the oscillations of the speed being twice the cadence of the pedaling the frequency found by the spectral analysis is divided by 2. If necessary, a conversion in revolutions / minute is realized.

The Eqs. 4 and 5 show that velocity oscillations have a direct impact on the carrier phase measurements if the vector v _RX is not orthogonal to d _.. Another possibility to determine the pedaling rate is therefore to submit (all) the raw phase measurements to a spectral analysis. So Alternatively, the terminal could be configured to first determine which satellites are best positioned (in terms of _RX at _t ), taking into account its current position and speed, and then detect the characteristic peaks of pedaling. in the spectrum of gross phase measurements for these satellites.

While particular embodiments have just been described in detail, those skilled in the art will appreciate that various modifications and alternatives thereto can be developed in light of the overall teaching provided by the present disclosure of the present invention. the invention. Therefore, the specific arrangements and / or methods described herein are intended to be given by way of illustration only, with no intention of limiting the scope of the invention.

Claims

claims

A method of determining the pedaling rate of a cyclist (10) on a cycle (12), characterized in that the pedaling rate is extracted from an oscillation of phase measurements of GNSS signals (16) performed on the cycle (12) using a GNSS receiver (14) or measurements calculated on the basis of the phase measurements.

Method according to claim 1, characterized in that the measurements calculated on the basis of the phase measurements comprise Doppler measurements, the speed of the GNSS receiver, the projection of the speed of the GNSS receiver on a horizontal plane, the standard of the GNSS receiver speed, receiver acceleration

GNSS, the projection of GNSS receiver acceleration on a horizontal plane and / or the GNSS receiver acceleration standard.

Method according to claim 1 or 2, characterized in that the measurements calculated on the basis of the phase measurements are obtained by means of time-differentiated phase measurements.

4. Method according to any one of claims 1 to 3, characterized in that it comprises the realization of inertial measurements using one or more accelerometers and / or one or more gyrometers.

5. Method according to claim 4, characterized in that the cadence rate is extracted from an oscillation of measurements obtained by hybridization of phase measurements and inertial measurements.

6. Method according to claim 4 or 5, characterized in that the pedaling rate is extracted from an oscillation of the inertial measurements when the phase measurements of GNSS signals are temporarily unavailable or too noisy.

7. Method according to any one of claims 1 to 6, characterized in that it comprises the realization of phase measurements of GNSS signals by the GNSS receiver.

8. Process according to claim 7, characterized in that it comprises

o detection if the GNSS receiver operates in a mode alternating between activity and inactivity intervals, o and, if applicable, the activation of a mode in which the GNSS receiver remains permanently active or the adaptation of the length of the activity and inactivity intervals according to the needs of the determination of the rate of pedaling.

9. Method according to any one of claims 1 to 8, characterized in that the extraction of the pedaling cadence of the oscillation of the phase measurements or measurements calculated on the basis of the phase measurements comprises a frequency analysis in the range of 1 to 6 Hz., corresponding to a cadence of pedaling between 30 and 180 revolutions / minute.

10. Method according to any one of claims 1 to 9, characterized in that the extraction of the pedaling cadence of the oscillation of the phase measurements or measurements calculated on the basis of the phase measurements comprises a frequency analysis in a frequency range that is dynamically adapted according to the speed, position and / or geographical information concerning the cyclist's position.

11. Method according to any one of claims 1 to 10, characterized by an analysis of the plausibility of the pedaling rate determined on the basis of the speed of the cyclist.

A method of evaluating the performance of a cyclist (10), comprising calculating the performance based on the cyclist's cadence determined by the method of any one of claims 1 to 11.

Computer program, eg mobile application or web application, comprising program code instructions for performing the steps of the method according to any one of claims 1 to 12 when said program is executed on a computer .

14. Mobile terminal (14), eg multifunctional mobile, GNSS receiver, connected watch, configured for the implementation of the method according to any one of claims 1 to 12.