CN110937051B

CN110937051B - Method for measuring output power of bicycle rider in real time

Info

Publication number: CN110937051B
Application number: CN201911066653.9A
Authority: CN
Inventors: 蔡涛; 王宇恒; 陈杰
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2019-11-04
Filing date: 2019-11-04
Publication date: 2020-12-15
Anticipated expiration: 2039-11-04
Also published as: CN110937051A

Abstract

The invention discloses a method for measuring the output power of a bicycle rider in real time, which uniformly considers torque measurement and rotating speed measurement, and only utilizes a sensor for measuring the torque, thereby not only measuring the torque applied by the rider and borne by a bicycle crank, but also calculating the rotating speed of the bicycle crank, and further achieving the purpose of measuring the output power of a rider in real time; the power measuring method provided by the invention simplifies the design of the bicycle power meter. Due to the adoption of the single-sensor design, the number of components, the size of a circuit board and the power consumption of the circuit are obviously reduced, and the overall cost is saved.

Description

Method for measuring output power of bicycle rider in real time

Technical Field

The invention belongs to the technical field of sensor signal measurement, and particularly relates to a method for measuring output power of a bicycle rider in real time.

Background

The bicycle dynamometer is an important device for detecting the riding performance of a bicycle athlete, and can also be used for collecting self motion data of a common rider. During the competition of the bicyclists, the competition strategy can be modified and perfected based on the measurement data of the power meter, so that the physical strength is prevented from overdrawing in advance; in daily training, athletes can more scientifically execute training plans.

Bicycle power meters were invented in 1986, and originally were completely mechanical in form, complex in structure and very bulky. The dynamometer measures the torque borne by a bicycle crank through a spring structure, and the compression amount of the spring is increased along with the increase of the treading torque, so that the borne torque can be obtained, and the torque applied by a rider can be obtained.

Currently, bicycle power meters are electromechanical integrated devices that calculate the output power of a rider by measuring the output torque of the rider and the rotational speed of a torque-receiving component, respectively. The torque measuring method is to measure the torque generated by the pedal of the bicycle crank when the pedal is stepped by a rider through sensors such as a strain gauge. There are generally two methods for measuring the rotational speed of a torque-bearing component such as a bicycle crank: the first is to fix a magnetic induction device on the bicycle frame, and fix a magnet on a rotating component, such as a wheel, so that a pulse signal is generated on the magnetic induction device every time the magnet rotates past the magnetic induction device. The rotating speed of the component can be obtained by calculating the time between adjacent pulse signals; the second method for measuring the rotation speed is to mount a geomagnetic sensor on a rotating component, and when the rotating component rotates one cycle, the readings of the geomagnetic sensor generate an inverse number, and the rotation speed of the component can be calculated by calculating the time when the inverse number appears.

It can be seen that the torque and the rotation speed of the above-mentioned measuring method are measured by different sensors, respectively, and although they can perform the power measurement of the bicycle rider, they are not the simplest and most effective method.

Disclosure of Invention

In view of the above, the present invention provides a method for measuring the output power of a bicycle rider in real time, which can measure the torque data of the bicycle rider and calculate the output rotation speed of a crank on the basis of the torque data, thereby realizing the real-time measurement of the power of the bicycle rider.

The technical scheme for realizing the invention is as follows:

a method of measuring bicycle rider output power in real time, comprising the steps of:

firstly, mounting strain gauge sensors at the midpoints of the upper surface and the lower surface of a bicycle crank; measuring the torque applied by the rider to which the crank is subjected;

step two, analyzing the output torque rule of the rider according to the torque measurement data, determining the change period T of the torque, and obtaining the rotating speed of the bicycle crank based on the same periodicity of the rotating speed of the crank and the torque applied by the crank;

and step three, obtaining the real-time power output by the bicycle rider by using the torque and the bicycle crank rotating speed.

Further, T is obtained by measuring the time when the single-side crank torque value is not zero in the change cycle, namely T/2.

Has the advantages that:

the bicycle rider power measuring method provided by the invention uniformly considers torque measurement and rotating speed measurement, and only utilizes a sensor for measuring the torque to measure torque information and calculate the rotating speed of a bicycle crank, thereby achieving the purpose of measuring the output power of a rider in real time.

The power measuring method provided by the invention simplifies the design of the bicycle power meter. Due to the adoption of the single-sensor design, the number of components, the size of a circuit board and the power consumption of the circuit are obviously reduced, and the overall cost is saved.

Drawings

FIG. 1 is a force analysis of a bicycle crank.

Fig. 2 is a crank torque vs. rotational angle curve.

FIG. 3 is a block diagram of an algorithm implementation of the present invention.

Fig. 4 is a torque measurement true curve.

FIG. 5 is a comparison of the measurement results of the present invention and the measurement results of the geomagnetic rotation speed sensor.

FIG. 6 is a flow chart of the method of the present invention.

Detailed Description

The invention is described in detail below by way of example with reference to the accompanying drawings.

The invention provides a method for measuring the output power of a bicycle rider in real time, which is characterized in that torque measurement and rotating speed measurement are considered uniformly, and only a sensor for measuring the torque is utilized, so that the torque applied by the rider and borne by a bicycle crank is measured, and the rotating speed of the bicycle crank can be calculated according to the change rule of the torque, thereby achieving the purpose of measuring the output power of a rider in real time.

1. Torque measurement

Since the torque generated by the pedaling force of the bicycle rider is directly applied to the bicycle crank, the applied torque can be measured by measuring the strain generated by the bicycle crank.

Firstly, force analysis is carried out on a bicycle crank, as shown in fig. 1, wherein A is a crank force bearing point, alpha is a crank rotating angle, p is a treading concentrated load, and l is a length of a treading force arm. Because the pedals are basically kept parallel to the ground during riding, the pedaling force of the rider is vertical downwards, and the p direction is vertical to the ground.

Let the torque borne by the crank be T_qThe calculation formula is as follows:

T_q＝p×l×cosα

because the rotation center of the crank is fixed, the crank is equivalent to a cantilever beam structure, when the crank bears torque around the rotation center, the crank generates strain due to stress, and the strain of the crank can be measured through the adhered strain gauge. The strain is in direct proportion to the treading force, so that the treading force p of the bicycle rider can be measured. Since the moment arm length l is an accurate value, the torque can be measured.

2. Rotational speed measurement

From the above equation, when p and l are constant values, the torque T_qThe magnitude of (a) and the rotation angle alpha are in a trigonometric function relationship. The magnitude of the torque measured under ideal conditions should therefore be a sinusoidal curve. In the actual riding process, the curve is close to a sine curve, the period of the curve is the time for the crank to rotate for one circle, namely the change period of the torque is the time for the crank to rotate for one circle, and the crank rotating speed can be calculated according to the principle.

However, in the actual pedaling process of the rider, the crank receives a pedaling torque T when the angle alpha is 0 DEG_qMaximum, torque T with increasing angle α_qGradually decreases to zero at around 90 deg.. Then the treading force born by the other crank is gradually increased from zero, the chain wheel of the bicycle is driven by the crank to continue rotating until the alpha angle is about 270 degrees, and the torque T born by the first crank is_qGradually increasing from zero until the angle alpha again becomes 0 deg., reaches a maximum value, exhibiting a periodic waveform, as shown in fig. 2.

When the rotation speed of the crank changes, the time when the torque applied to the crank is not zero also changes correspondingly. Therefore, the rotation speed of the crank during pedaling can be calculated by accurately measuring the time (i.e. half of the crank rotation period) when the torque value is not zero in each period in fig. 2. A block diagram of the programming that runs within the embedded processor is shown in fig. 3. The idea is as follows: using a timer of the processor, when the measured value is larger than the threshold value, the timer interrupts the counting variable a to add 1 from 0, and adds the result of the measurement to the sum c of the previous measurement (the initial value of c is set to 0), and then collects the next data; when the collected data is smaller than the threshold value, the rotating speed measuring module outputs the value of the counting variable a (namely, the time period when the measured value is larger than the threshold value) and the average measured value (corresponding to the average torque) in the period. And then returning to the beginning of the program and continuing to circulate.

The counting variable a is in a linear relation with the time of one cycle of crank rotation and in an inverse proportional function relation with the crank rotation speed, and the crank rotation speed can be calculated after algebraic transformation.

Experimental verification

First, the torque value of the bicycle crank over a period of time is measured and plotted as a curve, as shown in FIG. 4, which is similar to the waveform of FIG. 2.

The existing bicycle speed sensor on the market and the torque sensor of the invention are installed on the bicycle crank at the same time, and the speed measurement curve is obtained by comparison, as shown in fig. 5. As can be seen from the figure, the rotating speed measured by the invention is very close to the measured value of the existing rotating speed sensor on the market, and the requirement of measuring the rotating speed of the bicycle crank can be met, so that the real-time measurement of the output power applied to the crank by a bicycle rider is completed.

In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method of measuring bicycle rider output power in real time, comprising the steps of:

the method specifically comprises the following steps: crank armSubjected to a torque of T_q，T_qWhere p × l × cos α, l is the length of the treading arm, p is the treading force of the rider, and when p and l are constant values, the torque T is set_qThe magnitude of the torque and the angle alpha of the crank rotation are in a trigonometric function relationship, and the change period of the torque is the time taken by the crank to rotate for one circle;

2. The method of claim 1, wherein T is obtained by measuring the time during which the one-sided crank torque value is not zero during its cycle of variation, i.e., T/2.