Measurement cycle pedal

Abstract

Cycle pedal for measuring the forces applied by a cyclist to said pedal when pedaling Cycle pedal for measuring the forces applied by a cyclist to said pedal when pedaling, said pedal comprising: a pedal axle arranged to be connected to a pedal crank, a pedal body rotatably mounted on the pedal axle, a device for measuring forces developed by the cyclist on said pedal, comprising: a plurality of strain gauges each capable of at least partially detecting a force in a plane perpendicular to the pedal axle and of providing a signal depending on said gauge, said gauges being arranged to form at least a first measuring circuit, at least two gauges of said measuring circuit being arranged to measure respective non-collinear forces, a unit for processing the signals provided by said gauges. Figure for abstract: Figure 1

Description

Title of the invention: Measuring cycle pedal Technical field

[0001] The present invention relates to a cycle pedal used to measure the forces applied to the pedal during pedaling. Technological background

[0002] Cycle pedals make it possible to study the different variables of pedaling such as frequency, power, forces applied by the cyclist's lower limbs, efficiency or even mechanical performance.

[0003] Pedals of this type conventionally include a device for measuring the forces exerted by a cyclist on the cycle pedal.

[0004] Devices for measuring the effort of a cyclist use sensors of different types such as extensometers formed by strain gauges. They can be applied to elements of the cycle such as the wheels, the crank arms, the bottom bracket axle and the pedal axles. The signals provided by the sensors are then transmitted to electronic signal processing means to be processed and converted into signals that can be used by a display device to show the values of the efforts detected.

[0005] Generally, the measuring devices comprise one or more Wheatstone bridge electrical measuring circuits. Each circuit conventionally comprises one or two pairs of strain gauges. The gauges of each pair are arranged diametrically opposite each other on the outer peripheral surface of the pedal axle.

[0006] Such an arrangement is described in particular in applications FR2950428 and FR3078158.

[0007] Other arrangements of the gauges are proposed in the prior art. Documents EP2304403B1 and EP3999828B1 describe, for example, measuring devices in which the strain gauges of the same bridge measuring circuit are arranged in the same plane.

[0008] There is a need to further improve cycle pedals, in particular to improve the accuracy of measuring the forces applied to them and to reduce their cost. Summary of the invention

[0009] The invention aims to meet this objective, and has as its subject, a cycle pedal for measuring the forces applied by a cyclist to the pedal when pedaling, said pedal comprising: - a pedal axle arranged to be connected to a pedal crank, - a pedal body rotatably mounted on the pedal axle, - a device for measuring the forces developed by the cyclist on said pedal comprising: • a plurality of strain gauges each capable of at least partially detecting a force in a plane perpendicular to the pedal axis and of providing a signal which is a function of said gauge, said gauges being arranged to form at least one first measuring circuit, at least two gauges of said measuring circuit being arranged to measure respective non-collinear forces, • a unit for processing the signals supplied by said gauges.

[0010] Unlike the measuring pedals of the prior art, the strain gauges of the same measuring circuit according to the invention are not placed diametrically opposite or in the same plane. Consequently, the force applied by the user to the body of the pedal does not cause the resistances of said strain gauges to vary in the same way. Also, such an arrangement of the strain gauges makes it possible to identify the characteristics specific to each gauge used and therefore their individual behavior.

[0011] Knowledge of the individual behavior of the gauges is useful for correcting the measurement of the forces developed on the pedal by taking into account changes in temperature. The calibration of the measuring device can therefore comprise two calculation steps, carried out from data collected using a calibration bench, consisting of: - determine the force experienced by the measuring device based on the electrical signals from the measuring circuits, and - calculate the behavior of each strain gauge in each measuring circuit. This calibration step makes it possible to calculate the measurement errors likely to be introduced, in particular by temperature changes. The measurement of the forces developed on the pedal is thus improved. This second step is made possible thanks to the architecture described in

[00009] .

[0012] In the state of the art, the determination of the influence of temperature variations on the value of the measurement signals is obtained directly by subjecting the device to controlled temperature variations in the laboratory and observing the signal change.

[0013] Several types of strain gauges can be used.

[0014] At least one of the plurality of strain gauges may be a shear gauge.

[0015] At least one of the plurality of strain gauges may be a strain gauge. flexion.

[0016] Preferably, the gauges of the plurality of strain gauges are arranged to form a plurality of separate measuring circuits, at least two gauges of each of said measuring circuits being arranged to measure respective non-collinear forces.

[0017] For example, the gauges of the plurality of gauges are arranged to form two separate measuring circuits as described above.

[0018] Two measuring circuits are considered distinct when they each use a strain gauge different from the other.

[0019] At least two separate measuring circuits of said plurality of measuring circuits may comprise at least one common strain gauge. In other words, at least one strain gauge is common to these two measuring circuits. This may make it possible to obtain a sufficient number of circuits for calculating the aforementioned force by using a reduced number of strain gauges. For example, for a number of measuring circuits similar to that of conventional measuring devices, the number of strain gauges may be smaller. By reducing the number of gauges used, the manufacturing cost of the force-measuring pedal is reduced.

[0020] Conversely, this makes it possible to increase the number of measuring circuits used for an identical number of gauges, or even less than known measuring pedals. The use of several measuring circuits makes it possible to reduce noise, and the measurement of the force is consequently improved.

[0021] At least one measuring circuit is a half-bridge, in particular a wheatstone half-bridge.

[0022] At least one measuring circuit is a full bridge, in particular a wheatstone bridge.

[0023] The plurality of strain gauges may comprise an odd number of strain gauges.

[0024] In embodiments, the gauges of the plurality of gauges are arranged on the pedal axle, said gauges being in particular distributed around the pedal axle.

[0025] Alternatively, the plurality of gauges are disposed within the pedal axle.

[0026] The gauges may be in contact with the outer surface of the pedal axle, in particular fixed to said surface, for example by gluing. Alternatively, the strain gauges are carried by a support itself arranged on the pedal axle.

[0027] In embodiments, the gauges are fixed on a substrate separate from the pedal axle. This substrate can itself be fixed on the external surface of the pedal axle or inserted inside said axle.

[0028] In embodiments, the pedal axle comprises at least one planar portion and a diametrically opposed cylindrical portion, the flat portion being opposite said cylindrical portion relative to the center of the pedal axle.

[0029] For example, the pedal axle comprises three flat portions alternating with three cylindrical portions, each of the flat portions being opposite one of the cylindrical portions relative to the center of the pedal axle.

[0030] Preferably, the strain gauges are each arranged on one of said flat portions.

[0031] The presence of the flat faces allows the use of strain gauges of a larger size than those used in conventional measuring pedals. This makes it possible in particular to increase the accuracy of the measurement.

[0032] The processing unit may comprise electronic processing means grouped on at least one electronic card and receiving the signals from the strain gauges for processing. The processing unit may further comprise a power source such as a battery, in particular a rechargeable battery.

[0033] The measuring device may further comprise a transmission module comprising an antenna capable of transmitting measurement data to a display or recording device with real-time display capability. Preferably, the display device is an on-board display device allowing the cyclist to be informed in real time of the efforts he develops when pedaling.

[0034] The invention also relates to a method for calibrating a measuring pedal according to the invention, in which one or more calibration coefficients are determined for each strain gauge. Brief description of the figures

[0035] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented. In the appended figures:

[0036] [Fig-1] [Fig.l] is an exploded perspective view showing a pedal body, a pedal axle and a cycle crank before assembly;

[0037] [Fig.2A] [Fig.2A] separately illustrates the pedal axle of [Fig.l];

[0038] [Fig.2B] [Fig.2B] is a cross-section of the pedal axle of [Fig.2A];

[0039] [Fig.3] [Fig.3] schematically and partially represents a cross-section of the pedal axle according to the invention;

[0040] [Fig.4A] and [Fig.4B] Figures 4A and 4B are diagrams of measuring circuits of a measuring device according to the invention;

[0041] [Fig.5] [Fig.5] schematically and partially represents a cross-section of the pedal axle according to a second embodiment;

[0042] [Fig.6] [Fig.6] shows diagrams of measuring circuits of a device for measurement according to the second embodiment;

[0043] [Fig.7] [Fig.7] is a perspective view of a pedal axle along a third embodiment;

[0044] [Fig.8A] and [Fig.8B] Figures 8A and 8B are cross-sections of the axis of pedal of [Fig.7];

[0045] [Fig.9] [Fig.9] represents another variant of the pedal axle according to the invention;

[0046] [Fig.lOA], [Fig.lOB] Figures 10A-B are cross-sections of the pedal axle of [Fig.9];

[0047] [Fig. 11] [Fig. 11] shows circuit diagrams of the measuring device measurement according to [Fig.9];

[0048] [Fig. 12] [Fig. 12] shows, in cross-section, another variant of an axis of pedal according to the invention; and

[0049] [Fig. 13] [Fig. 13] shows circuit diagrams of the measuring device measurement according to [Fig.7]. Description of embodiment(s)

[0050] In the figures, and unless otherwise provided, identical elements will bear the same reference signs.

[0051] [Fig.l] illustrates a measuring pedal 1 according to the invention. The pedal 1 comprises a pedal body 10 intended to be mounted on a pedal axle 12. As illustrated, the pedal axle 12 extends along an elongation axis A and is provided at one of its ends with a first thread 13 adapted to cooperate with a tapping provided in a through-hole 3 for fixing at the free end of a pedal crank 2. The other crank is not shown in the figures, but it is identical to that shown, while it extends in the opposite direction.

[0052] The pedal body 10 is, in a conventional manner, rotatably mounted on the pedal axle 12 using a needle roller 19 and a bearing arranged in a hollow transverse part 11 of the pedal body 10.

[0053] To finalize the assembly, a screw 17 is screwed into a thread provided at the corresponding end of the pedal axle 12 to limit the longitudinal movement of the body 10 on the axle 12. A plug 14 is arranged outside the screw 17 to close the end of the hollow transverse part 11 of the pedal body 10.

[0054] The measuring pedal 1 further comprises a measuring device 20 making it possible to measure the force F developed by a cyclist on the measuring pedal 1 when pedaling.

[0055] The measuring device comprises a plurality of strain gauges 24 arranged capable of detecting at least partially the force F directed perpendicular to the pedal axis 12 and of providing a signal depending on the detected force. The measuring device 20 further comprises a unit for processing the received signals. As illustrated, the processing unit comprises electronic processing means grouped on at least an electronic card 26 and receiving the signals from the strain gauges 24 for processing. The processing unit further comprises a power source 27 which is a battery, in particular rechargeable, in the example illustrated.

[0056] Regarding the strain gauges 24, as shown, the strain gauges 24 are deposited on the external surface of the pedal shaft 12, but may be arranged otherwise, for example, inside the pedal shaft 12. In the example illustrated, surfaces for receiving the strain gauges are provided on the pedal shaft 12. The measuring device 20 further comprises a connector 16 between the strain gauges 24.

[0057] The strain gauges 24 are arranged so as to form one or more measuring circuits. Each measuring circuit 30 delivers information relating to the force F applied to the measuring pedal 1. In the example illustrated, at least two measuring circuits are used to calculate the force F.

[0058] As illustrated schematically in [Fig. 3], the strain gauges 24a-d of each measuring circuit are distributed around the pedal axis 12 without specific position so that the force F applied to the pedal axis 12 does not stress the strain gauges 24a-d of the same measuring circuit in the same way.

[0059] The arrangement of the strain gauges 24a-d can be carried out in several ways. For example, adjacent strain gauges 24 can be connected in the same measuring circuit or one strain gauge 24 out of two can be connected in the same measuring circuit.

[0060] In the example illustrated in [Fig.4A], the adjacent strain gauges 24a and 24b form a first measuring circuit W1 and the adjacent strain gauges 24c and 24d form a second measuring circuit W2.

[0061] In the example of [Fig.4B], a first measuring circuit W'1 comprises the strain gauges 24a and 24c and a second measuring circuit W'2 comprises the strain gauges 24b and 24d.

[0062] In order to reduce costs and / or improve the accuracy of the measurement of the force F, the measuring circuits may comprise a common strain gauge 24. Also, with the arrangement of the strain gauges of [Fig. 3], it is possible to obtain six separate measuring circuits using only the four strain gauges 22a-d illustrated. Preferably, two measuring circuits are used to measure the force F and the remaining four measuring circuits are used to improve accuracy.

[0063] In the embodiment illustrated in Figures 5 and 6, the measuring device 20 comprises an odd number of strain gauges 24a-c, three in number in this example. These strain gauges 24a-c are arranged to form three circuits separate measuring circuits W” 1 to W”3. The strain gauges 24a and 24b form a first measuring circuit W” 1, the strain gauges 24a and 24c form a second measuring circuit W”2 and the strain gauges 24b and 24c form a third measuring circuit W”3.

[0064] As shown in [Fig.2A], in particular, the pedal shaft 12 comprises a plurality of planar portions 15a on which the strain gauges 24. The presence of such planar portions makes it possible to use larger strain gauges. This makes it possible in particular to improve the precision. The planar portions 15a alternate with cylindrical portions 15b, as can be seen in [Fig.2B]. Each planar portion 15a is opposite a cylindrical portion 15b relative to the center of the pedal shaft O.

[0065] As can be seen, such a shape of the pedal axle makes it possible to obtain a quasi-constant diameter regardless of the orientation of the axle. This makes it possible to standardize the deformation under load.

[0066] In the examples which have just been described, the measuring circuits correspond to Wheatstone half-bridges.

[0067] Alternatively, the measuring circuits are complete Wheatstone bridges.

[0068] Figures 7, 8A and 8B show an embodiment in which bridges complete are used. The measuring device 20 comprises 6 strain gauges 24 ai ciet 24a2_c2 arranged to form three separate measuring circuits W*i, W*2 and W*3. The measuring circuits are full bridges.

[0069] As illustrated, the first measuring circuit W*i comprises the strain gauges 24ab 24cb 24a2 and 24c2. The second measuring circuit W*2 comprises the strain gauges 24ab 24bb 24^ and 24b2. The third measuring circuit W*3 comprises the strain gauges 24bb 24cb 24b2 and 24c2. As can be seen in particular in FIGS. 8A and 8B, the strain gauges or the same bridge are not mounted in opposition, nor on the same plane.

[0070] The receiving area 15 may have a shape different from that of [Fig. 7]. For example, the receiving area of the gauges has a rectangular section, as illustrated in Figures 9 to 11.

[0071] In this example, the measuring device 20 comprises eight strain gauges 24 ai diet 24a2 d2 arranged to form two separate measuring circuits W**i and W**2. The two measuring circuits are complete bridges.

[0072] As illustrated, the strain gauges 24abdi form a first measuring circuit W**b. The strain gauges 24a2d2 form a second measuring circuit W**2. As can be seen in [Fig.9] to 11, the strain gauges 24abdi or 24a2 d2 of the same bridge W**i or W**2 are not mounted in opposition, nor on the same plane.

[0073] As mentioned above, the strain gauges 24 of the same measuring circuit according to the invention are not placed diametrically opposite or in the same plane. Also, the force applied by the cyclist to the pedal body does not cause the resistances of said strain gauges to vary in the same way. Also, such an arrangement of the strain gauges makes it possible to identify the characteristics specific to each gauge used as well as its individual behavior.

[0074] We will describe in the following a method of calibrating a measuring pedal according to the invention.

[0075] The method comprises a step of identifying the characteristics and / or individual behavior of the strain gauges. This calibration according to the invention is an additional step compared to the state of the art. This calibration according to the invention does not require heating or cooling the pedal to determine the K coefficients. This calibration according to the invention is done with the same data as for the calibration according to the state of the art.

[0076] This step is carried out in the laboratory and involves determining an individual correction coefficient for each strain gauge. The set of individual correction coefficients of the strain gauges makes it possible to predict the evolution of the value of the signals of the measuring circuits when the temperature changes. This makes it possible to reduce the measurement errors linked to the change in temperature in proportions equivalent to the state of the art when a calibration as described in

[00075] is used. This makes it possible to reduce the measurement errors linked to the change in temperature in proportions greater than the state of the art when the calibration

[00075] is not carried out. The correction of the signals to compensate for a shift of the zero due to the temperature can then be carried out in real time and accurately.

[0077] For example, a zero measurement is carried out indoors which gives the value: ZI = (xl, yl). Then, when the pedal is used outdoors at a different temperature, a zero recalibration is carried out: Z2 = (xl+Kl*AT, yl+K2*AT), AT being the temperature difference between the second and first calibrations and Kl; K2 being the calibration coefficients.

[0078] The calculation of the force F applied by the cyclist on the pedal axle can be determined as a function of the signals, in particular corrected using the individual coefficients of the strain gauges.

[0079] Of course, the invention is not limited to the examples illustrated and described, but can be the subject of many variants within the reach of those skilled in the art without departing from the scope of the invention.

[0080] For example, the strain gauges 24 may be placed inside the pedal axle.

[0081] The number of strain gauges used may be different.

Claims

Claims

1. Cycle pedal (1) for measuring the forces applied by a cyclist to said pedal when pedaling, said pedal comprising: - a pedal axle (12) arranged to be connected to a pedal crank, - a pedal body (10) rotatably mounted on the pedal axle, - a device for measuring forces (2) developed by the cyclist on said pedal, comprising: • a plurality of strain gauges (24; 24a-d) each capable of detecting at least partially a force (F) in a plane perpendicular to the pedal axle (12) and of providing a signal which is a function of said gauge, said gauges (24; 24a-d) being arranged to form at least one first measuring circuit (W1; W2; W'1; W'2; W'3; W”l; W”2; W”3; W*l; W*2; W**l; W**2), at least two gauges of said circuit measuring gauges being arranged to measure respective non-collinear forces, • a unit for processing the signals supplied by said gauges.

2. A pedal according to claim 1, the plurality of gauges (24; 24a-d) being arranged to form a plurality of separate measuring circuits (Wl-2; W'l-3; W”l-3; W*l-2; W**l-2), at least two gauges of each measuring circuit being arranged to measure respective non-collinear forces.

3. Pedal according to the preceding claim, at least two measuring circuits (W”l; W”2; W”3) of said plurality of measuring circuits comprising at least one common strain gauge.

4. A pedal according to any one of the preceding claims, at least one measuring circuit (W'1; W'2) of the plurality of measuring circuits being a half-bridge, in particular a wheatstone half-bridge.

5. A pedal according to any one of the preceding claims, at least one measuring circuit (W*i; W*2; W*3) of the plurality of measuring circuits being a full bridge, in particular a wheatstone bridge.

6. A pedal according to any preceding claim, the plurality of strain gauges (24a-c) comprising an odd number of strain gauges.

7. A pedal according to any preceding claim, wherein the plurality of gauges are disposed on the pedal axle.

8. A pedal according to any one of claims 1 to 6, wherein the plurality of gauges are disposed within the pedal axle.

9. Pedal according to any one of the preceding claims, the pedal shaft (12) comprising at least one flat portion (15a), in particular arranged to receive a strain gauge and a diametrically opposed cylindrical portion (15b), the flat portion (15a) being opposite said cylindrical portion (15b) relative to the center of the pedal shaft (0), for example, the pedal shaft (12) comprising three flat portions (15a) alternating with three cylindrical portions (15b), each of the flat portions (15a) being opposite one of the cylindrical portions (15b) relative to the center (0) of the pedal shaft (12).

10. A pedal according to any preceding claim, at least one of the plurality of strain gauges being a shear gauge.

11. A pedal according to any preceding claim, wherein at least one of the plurality of strain gauges is a bending gauge.

12. Pedal according to any one of the preceding claims, the gauges being in contact with the outer surface of the pedal axle, in particular fixed to said surface, for example by gluing.

13. A pedal according to any one of claims 1 to 11, the gauges being fixed on a substrate separate from the pedal axle, said substrate itself being fixed on the outer surface of the pedal axle or inserted inside said pedal axle.

14. Method for calibrating a measuring pedal according to any one of the preceding claims, the method comprising a step of determining one or more calibration coefficients for each strain gauge.

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