Method for measuring power in a bicycle
A method and system for measuring the output power produced in a device having a crankset, includes: measuring the orthogonal force exerted on at least one pedal of the crank; determining the angular velocity of the crank; and deducing the tangential force exerted on the crank and the power, using a pre-established model of the distribution of the force exerted on the actuating member as a function of the angular velocity.
1. A system for measuring an output power developed in a crankset, comprising:
at least one pedal for actuating a crank of the crankset, the pedal having at least one guide rail provided on a lateral surface of the pedal;
a single pressure sensor capable of measuring an orthogonal force exerted by a user on the pedal;
at least one sensor for determining an angular position of the crank around a rotation axis of the crankset different from a rotation axis of the pedal with respect to the crank;
a calculator for determining, by means of a pre-established model of distribution of a force exerted on the pedal according to said angular position, a tangential force exerted on the crank; and
an element for fastening to the pedal, the element having the pressure sensor affixed thereto, and an interface plate capable of transmitting a force exerted by the user to the pressure sensor,
wherein said element is assembled on the pedal via the guide rail provided on the pedal.
2. The system of claim 1 , wherein said pressure sensor faces an axis of fastening of the pedal to the crank.
3. The system of claim 1 , wherein said pressure sensor comprises a strain gauge or a piezoelectric element.
4. The system of claim 1 , further comprising means for determining the angular velocity of the crank.
5. The system of claim 1 , further comprising means for determining the acceleration of the crank.
6. The system of claim 1 , wherein said at least one angular position sensor comprises an accelerometer, a gyroscope, or a magnetic angle sensor.
7. The system of claim 1 , wherein said sensors are capable of communicating with the calculator via a wireless link.
8. A bicycle equipped with the system of claim 1 .
9. The system of claim 1 , wherein:
the pedal has a substantially parallelepipedal external shape comprising two main parallel opposite surfaces and four lateral surfaces of smaller areas;
the element covers one of the main surfaces, and two parallel lateral surfaces of the pedal;
the interface plate covers the second main surface of the pedal; and
the pressure sensor is disposed between the element and the interface plate.
10. The system of claim 9 , wherein the pressure sensor is arranged in a free space of the pedal, between the two main surfaces of the pedal.
11. A system for controlling a pedal-assist motor in a pedal vehicle, comprising:
the system of claim 1 ; and
means for increasing the motor power when the power provided by the user decreases and for decreasing it when the power provided by the user increases.
12. A bicycle equipped with a pedal-assist motor and with the system for controlling this motor of claim 11 .
13. A method for using the system of claim 1 , comprising the steps of:
a) measuring the force exerted by the user orthogonally to the pedal;
b) determining the angular position of the crank around the rotation axis of the crankset; and
c) by means of a pre-established model of distribution of the force exerted on the pedal according to said angular position, deducing the tangential force exerted on the crank.
14. The method of claim 13 , further comprising, before step c), the steps of:
b) determining the angular velocity of the crank around the axis of the crankset; and
e) selecting said model from a list of pre-established models.
15. The method of claim 13 , further comprising the step of:
deducing from said tangential force the developed output power.