Shulou(Shulou.com)11/24 Report--

In addition to binge eating pagoda food (learning fractal)

The editor is still exercising.

However, the editor of the daily work

How can you just run honestly?

Continue to adhere to the previous idea of "thinking hard can also burn calories"

The editor has found a new "heat gap".

For the success of "painless removal of whole body fat cover"

The editor keeps running for 5 km every day.

The setting speed of the treadmill also gradually increased from 9 km / h.

However, at the speed of 10.5 km / h,

The editor is suddenly curious.

What is the difference between using a mobile phone to record and a treadmill record?

The result is that you don't try and don't know.

I was startled when I tried.

Treadmill speed 10.5 km / h cumulative running 5 km

It takes a total of 28 hours and 34 hours.

If you convert it to speed per kilometer, it will be...

From km / h to min / km

True primary school mathematics

So, have you figured it out yet?

The treadmill data is 5.71428 per kilometer. Min

It takes about 5: 43 miles per kilometer.

And the result of the cell phone record is...

A total of 28'47 'running distances of 6.55 km

(there is a slight delay in ending the record)

This pace, this distance.

The editor eats whales after watching it.

So here's the problem--

How much did I run?

Where do such record differences come from?

Gorgeous counterattack treadmill treadmill as a common indoor fitness equipment, we will naturally think that its role is to help people strengthen their bodies and provide convenience for indoor sports.

Photo Source | pixabay however, I never expected that the treadmill had an inspirational story about counterattacking from torture to fitness equipment.

The corresponding English word for treadmill is Treadmill, and the earliest use is closer to "treadmill", that is, human-driven power machinery.

In the 19th century, the "treadmill" was transformed into a "treadmill" and became a torture tool for punishing prisoners. Prisoners need to trample on spokes to drive huge paddle wheels to pump water, crush grain or drive mills.

[1] prisoners are often forced to step on the mill for more than six hours a day, which is equivalent to climbing a mountain of 1500 to 4300 meters a day.

After a series of development, the treadmill has evolved from human-driven to electric-driven, and has gradually become a popular indoor fitness equipment.

From the above story, we can know that from the mechanical structure classification, the treadmill is mainly divided into mechanical treadmill and electric treadmill.

Mechanical treadmill mainly through the friction between the runner and the running belt, driving the running belt to follow the footsteps of the athlete, that is, "human drive".

It is also easy to experience a mechanical treadmill. When the treadmill is off, the process of driving the running belt on the treadmill is similar to the working principle of the mechanical treadmill. (but who would want to do that? )

Now, the electric treadmill has become the mainstream, and its mode of operation is to drive the running belt to rotate through the motor, so as to drive the athlete to follow its rotation speed. The runners on the treadmill have also changed from "active" to "passive".

In addition to being unaffected by the weather, the treadmill conveyor belt has a shock absorber function, which can reduce the knee and back injury caused by running to a certain extent.

So how does the treadmill record the running distance and speed?

At present, the acceleration and deceleration of the electric treadmill is controlled by manual buttons, and we can independently set the desired speed for running.

In other words, through the speed set by the user, the control system of the treadmill and the motor work together to ensure that the running belt rotates at a fixed speed (that is, set speed).

In this working mode, you only need to record the runner's running speed and time, and then you can get the running distance:

Take the running situation of the editor as an example, if the running speed is 10.5km / h and the running time is 28:34, you can get the running distance of 5 km.

Treadmill: counterattack is not enough, I can be better, but this control mode restricts the freedom of fitness people to change speed, and has a lot of adverse effects on the development of electric treadmill applications.

Therefore, more and more new treadmill speed tracking control methods have been proposed, hoping to make everyone exercise more scientific and comfortable.

In order to make the treadmill speed control more convenient, the simplest idea is to establish a set of automatic speed tracking control method.

To put it simply, a feedback loop is introduced into the treadmill control system so that the control system can automatically adjust according to the actual running conditions of the runners.

Picture source | pixabay so, which information is suitable to be added to the feedback loop? Heart rate and the location of the runner seem to be good choices.

Let's first learn some knowledge about sensors.

Sensor technology refers to the ability to sense the surrounding environment and special substances, analyze the collected environmental or material information, and convert the analog signals that identify substances into digital signals.

Therefore, the sensor can determine the quantity and quality of the data information obtained.

The treadmill speed automatic tracking method mentioned above refers to the integration of heart rate sensing technology and position sensing technology, which can track the heart rate state and position state of the athlete in real time.

The principle of its automatic control flow is shown in the following figure:

Automatic tracking control method of treadmill speed based on sensor technology flow chart [3] in order to ensure the safety of the athlete, the optical heart rate sensor will provide the heart rate information of the athlete at all times.

When the athlete's heart rate exceeds the set threshold, the runner will automatically slow down, making the athlete's heart rate gradually return to the normal value.

Photo Source | pixabay if the heart rate of the athlete is not relieved, the treadmill will automatically stop to maximize the safety of the athlete.

On the other hand, when the athlete is in the middle of the running belt, he or she is in the best state of motion from the point of view of balance.

Therefore, the position sensor can determine the position of the athlete on the running belt at all times, and the feedback loop will also adjust if the athlete deviates from the central position of the treadmill. Return the athlete to the central position by fine-tuning the speed of the running belt.

However, this way of adjustment also has some shortcomings, for example, the same position deviation may be caused by far and near, or near and far, and it is easy to misjudge when carrying out speed compensation. on the contrary, it makes the athlete deviate more from the central position.

In addition, during the normal operation of the treadmill, people running on the running belt can be approximately regarded as pulse load.

The pulse load has obvious periodicity, the action time of loading and unloading is short, and the motor may change speed at any time of the foot touch plate, which will cause acceleration and deceleration shock and bring bad experience.

Picture source | pixabay in addition to considering the heart rate and the runner's position, footwork can also be used as important information in the feedback loop.

Footwork information refers to the force signal between the sole of the foot and the treadmill during exercise, which can be obtained by installing a pressure sensor under the running belt of the electric treadmill.

By analyzing the footwork information during exercise, the movement trend of the athlete can be distinguished. The vertical Z direction generated by the person collected by the pressure sensor during movement is as follows:

The position information of the athlete at any time can be obtained from the moment balance equation:

As a result, the real-time curves of F (t), X (t) and Y (t) can be obtained, and each stage of the runner's gait cycle can be divided by analysis.

The footwork information (F (t), X (t), Y (t), etc.) is taken as the important discriminant factor of the feedback loop, and then the acceleration or deceleration of the motor is controlled, so that the speed of the treadmill changes with the change of the human body speed. The treadmill speed follow control can be realized in a certain range, and the performance of the treadmill can be improved.

One step, two steps, three steps, four steps. How do you count it? The previous detailed introduction of treadmill pedometer and performance optimization related knowledge, let's go on to understand the principle of mobile phone recording running distance and speed, to see why the two recording methods are so different?

First of all, we start with a simple pedometer, which can record the number of walking steps, walking distance, walking speed and walking time, and on this basis, calculate the calorie or thermal energy consumption of the athlete in a certain period of time. Mainly used to calculate the amount of exercise.

Electronic pedometer | Picture Source at present, common pedometers are divided into mechanical pedometer, electronic pedometer based on special pedometer chip, smart bracelet and pedometer software developed based on smart phone built-in sensors.

Picture source | pixabay take the electronic pedometer as an example. In order to achieve the function of pedometer, it is necessary to accurately record the periodic physical quantities when walking and running.

When people are walking or running, the change of acceleration is the most obvious, which can be divided into forward, longitudinal and lateral variables.

During walking and running, the acceleration changes periodically with our pace.

The action of our walking is divided, in which, in the action of closing the foot, because the center of gravity is upward and one foot touches the ground, the acceleration in the vertical direction shows a positive increasing trend; when stepping forward, the center of gravity moves down and touches the ground, and the acceleration shows a reverse decreasing trend; while the horizontal acceleration decreases at the end of the foot and increases during the step.

Picture source | pixabay therefore, no matter where the pedometer is placed, the acceleration amplitude in at least one direction will have a significant periodic change, thus achieving the purpose of accurate pedometer.

Smart phones: n methods of calculation in smartphones, a variety of sensors work together to support our needs-light sensors, distance sensors, gravity acceleration sensors, magnetic sensors, heart rate sensors, vibration sensors …

Similar to the electronic pedometer, the smartphone can also collect the acceleration signal of the human body when it is moving, and the cyclic characteristics of the acceleration during walking can be seen in the picture below.

The magnitude of acceleration produced during continuous walking [6] based on the cyclic characteristics of acceleration, the step calculation algorithm of autocorrelation coefficient determines whether pedestrians walk or not by calculating the correlation of the overall acceleration in two adjacent walking cycles. The higher the correlation, the greater the probability of accurate step counting.

Another smart phone step counting method is frequency domain step counting, which collects sensor data from discrete time series and performs short-time Fourier transform (Short Term Fourier Transform,STFT) or fast Fourier transform (Fast Fourier Transform,FFT).

After the data collected by the sensor is converted to the frequency domain, some signal features which are not obvious in the time domain can be amplified.

Gyroscopes, which we are very familiar with, also play an important role in the pedometer function of smartphones. The main function of the gyroscope is to detect angular momentum.

Taking the FFT step calculation method as an example, the coordinate axis of the maximum angular velocity collected by the gyroscope is taken as the sensitive axis, then the diagonal velocity data are processed by FFT, and the time domain angular velocity data are converted into frequency domain data.

Finally, it is determined whether the data is within the typical walking frequency range and exceeds the preset amplitude threshold, and if the above conditions are met, one step is counted.

Compared with the time-domain step-counting method, the frequency-domain step-counting method will be more accurate, but it also brings more energy consumption.

The following table gives a brief summary of the current step counting methods:

Comparison of the advantages and disadvantages of various step counting algorithms [7] through the understanding of treadmill and smartphone pedometer, we can know that the treadmill records the distance through the speed and time set by the athlete.

On the other hand, the step counting methods of smart phones are relatively more diverse, but their commonness is through the analysis of different algorithms for the data obtained by the sensor.

In this way, the posture, step length and frequency of our running on the treadmill will all lead to differences in the accuracy of smartphone measurements, resulting in a huge difference in the running distance recorded by the editor on the treadmill at 5 km, while the smartphone record is 6.55 km.

So think about it... Could it be that the short legs of the editor led to the high step frequency, so the result of mobile phone recording was falsely high?

Let's take a look at the differences between different recording methods.

reference

[1] Zhihu | how did the treadmill turn from torture to mass fitness equipment?

Chu Junying, Guo Bin, Sun Tong. Automatic tracking control method of treadmill speed based on sensing technology [J]. Automation and instrumentation, 2020 (07): 38-41.DOI:10.14016 / j.cnki.1001-9227.2020.07.038.

Cheng Longle, Xu Jinlin, et al. research on Speed Adaptive Technology of treadmill based on Image processing [J]. Computer Technology and Development, 2016, (10): 92mur94.

Liu Yang, Zhou Xu, Sun Yining, Liu Yao, Ma Shufang. Treadmill speed tracking control method based on footwork [J]. Journal of Sensing Technology, 2015. 28 (02): 217-220.

[5] Wang Pan. Design of intelligent pedometer based on single chip microcomputer [J]. Instrument Technology, 2021 (06): 23-25+45.DOI:10.19432 / j.cnki.issn1006-2394.2021.06.006.

[6] Yang Runze. Research and application of an energy-saving step counting algorithm for smart phone [D]. Inner Mongolia University, 2019.

Wang Ji. Research on indoor smart phone location method based on pedestrian track inference [D]. Shandong University of Science and Technology, 2020.

The emojis pictures that are not marked in the article all come from the network.

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Norma

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