Single-soldier tractor terrain gradient estimation method based on short-time Fourier transform

Abstract

The invention relates to an individual tractor terrain gradient estimation method based on short-time Fourier transform, belongs to the technical field of terrain estimation, and solves the problem that an existing gradient estimation method is not suitable for individual tractor equipment. The method comprises the following steps: in an upright standing stage after a person wears an individual tractor, performing discrete Fourier transform on a collected inclination angle signal to obtain an initial angle; in the movement process of the person, an inclination angle signal and the pull pressure and the wheel speed between the person and the individual tractor are collected, whether the person is in a stop stage or not is recognized according to the fluctuation of the pull pressure and the wheel speed at the current moment, and if yes, a new initial angle is obtained again; otherwise, the tractor angle at the current moment is obtained through short-time Fourier transform on the collected dip angle signals, and the terrain gradient at the current moment is obtained according to the difference value between the tractor angle at the current moment and the latest initial angle. Therefore, dynamic and real-time terrain gradient estimation is realized when the single-soldier tractor is used for walking.

Description

Technical Field

[0001] This invention relates to the field of terrain estimation technology, and in particular to a method for estimating the terrain slope of a single-soldier tractor based on short-time Fourier transform. Background Technology

[0002] In emergency rescue and forest fire fighting, individual soldiers often carry heavy loads. To improve their carrying capacity, a new type of soldier-assisting device—a soldier-trailer—can be mounted on their waist to provide assistance and conserve energy. Before providing assistance, the tow vehicle must automatically identify the slope of the terrain. In other words, only by accurately estimating the slope can the tow vehicle provide assistance, improving operator comfort. Accurate slope identification also ensures the safety of the tow vehicle during use.

[0003] Currently, there are various methods for extracting road slope in the field of vehicle engineering, mainly divided into two categories. One category is the kinematic method, which uses sensors installed inside the vehicle to collect the vehicle's operating parameters, such as the vehicle's lateral and longitudinal acceleration, angular velocity, rate of change of motor speed, and vehicle pitch angle. These parameters are then input into a slope estimation algorithm to obtain slope information, with the Kalman filter being a commonly used algorithm. The other category is the dynamic method, which involves building models of the vehicle and the road, using the vehicle's dynamic equations and parameters, and then using simulation software to solve the dynamic equations to obtain slope information. In addition, there are also slope information extraction methods that combine kinematics and dynamics.

[0004] In existing technologies, the vehicle operating parameters collected by sensors inside the vehicle are unaffected by the driver's actions and depend only on the inherent characteristics of the road slope. However, for a single-person tractor vehicle coupled with a person, even on a level road, the tractor vehicle will experience significant longitudinal movement as the person's center of gravity shifts up and down while walking. Therefore, the data collected by the in-vehicle sensors cannot accurately reflect slope information due to interference from the person's movements, meaning it is difficult to directly calculate the road slope using sensor values. Similarly, because the tractor vehicle and the person are coupled and influence each other, it is difficult to establish an accurate model, thus making it impossible to use dynamics-based methods to obtain slope information for the tractor vehicle. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform, in order to solve the problem that existing slope estimation methods are not applicable to single-soldier tractor equipment.

[0006] This invention provides a method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform, comprising the following steps:

[0007] After the personnel put on the individual soldier tractor and stood upright, the initial angle was obtained by using discrete Fourier transform on the collected tilt angle signal.

[0008] During personnel movement, tilt angle signals, tension and pressure between personnel and the single-soldier tractor, and wheel speed are collected. Based on the fluctuation of tension and pressure and wheel speed at the current moment, it is determined whether the personnel are in a stationary phase. If so, a new initial angle is obtained. Otherwise, the collected tilt angle signal is processed using a short-time Fourier transform to obtain the current tractor angle. Based on the difference between the current tractor angle and the latest initial angle, the terrain slope at the current moment is obtained.

[0009] Based on further improvements to the above method, the tilt angle signal is acquired by a tilt angle sensor located at the rear of the individual soldier tractor; the tension and compression are acquired by a tension and compression sensor located between the personnel and the individual soldier tractor; and the wheel speed is acquired by a wheel speed sensor built into the wheel hub motor of the individual soldier tractor.

[0010] Further improvements to the above method involve obtaining the initial angle by using Discrete Fourier Transform (DFT) on the acquired tilt signal. This involves acquiring the tilt signal within a specified time period, converting the acquired tilt signal from the time domain to the frequency domain using DFT, and then obtaining the amplitude at a frequency of 0 Hz as the initial angle.

[0011] Based on the further improvement of the above method, the fluctuation of tensile and compressive forces at the current moment is obtained by acquiring the tensile and compressive forces collected at the current moment and the previous moment, and calculating the average difference of the horizontal component force of each two adjacent tensile and compressive forces.

[0012] Based on a further improvement of the above method, the fluctuation of tension and compression at the current moment is calculated using the following formula:

[0013]

[0014] Among them, R F N represents the fluctuation of tension and compression. f This indicates the amount of tensile and compressive forces collected between the current and previous moments. and It represents the horizontal component of two adjacent tensile and compressive forces.

[0015] Based on a further improvement of the above method, the system identifies whether a person is in a stopped phase by analyzing the fluctuations in tension and pressure at the current moment and the wheel speed. The person is in a stopped phase if the fluctuations in tension and pressure at the current moment do not exceed the fluctuation limit value, and the speeds of both the left and right wheels at the current moment are within the speed limit range. Otherwise, the person is in a walking phase.

[0016] Based on further improvements to the above method, the fluctuation limit value is set to 5 Newtons, and the speed limit range is [-0.5m / s, 0.5m / s].

[0017] Based on the further improvement of the above method, a new initial angle is obtained. Starting from the current moment, the tilt angle signal within a specified time period is taken forward, and the amplitude at a frequency of 0Hz is obtained again using the discrete Fourier transform to update the initial angle.

[0018] Based on the further improvement of the above method, the current tractor angle is obtained by using short-time Fourier transform on the acquired tilt angle signal, including:

[0019] Obtain the tilt angle signal collected within a specified time period before the current moment, as the signal to be calculated;

[0020] The signal to be computed is segmented and windowed. A short-time Fourier transform is performed on each windowed signal segment to obtain the spectrum of each windowed signal segment at different frequencies.

[0021] Based on the spectrum of each windowed signal segment at different frequencies, the average amplitude of each spectrum at 0Hz is calculated to obtain the current tractor angle.

[0022] Based on a further improvement of the above method, the current angle of the tractor is obtained using the following formula:

[0023]

[0024] Where, θ v The current tractor angle is represented by k, P represents the number of windows, and k| f＝0 This represents the frequency index corresponding to a frequency f of 0Hz, |X r (k| f＝0 )| represents the amplitude of the spectrum of the r-th windowed signal segment at 0Hz.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: in the process of using equipment such as individual soldier towing vehicles, by using short-time Fourier transform to reduce the impact of gait changes on the tilt angle during the walking process, it can realize dynamic real-time estimation of terrain slope, facilitate the adjustment of the towing vehicle's control strategy, optimize the control effect of the towing vehicle, improve the intelligence of the towing vehicle, and enhance the comfort and safety of the user.

[0026] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 This is a flowchart of a terrain slope estimation method for a single-soldier tractor based on short-time Fourier transform in an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram of personnel wearing individual soldier tractor vehicles in an embodiment of the present invention;

[0030] Figure label:

[0031] 1-Right wheel speed sensor; 2-Tilt sensor; 3-Left wheel speed sensor; 4-Tractor chassis; 5-Folding mechanism; 6-Tension and compression sensor. Detailed Implementation

[0032] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0033] A specific embodiment of the present invention discloses a method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform, such as... Figure 1 As shown, it includes the following steps:

[0034] S1. After the personnel put on the individual soldier tractor and stand upright, the initial angle is obtained by using the discrete Fourier transform of the collected tilt angle signal.

[0035] S2. During personnel movement, collect tilt angle signals, tension and pressure between personnel and the single-soldier tractor, and wheel speed. Based on the fluctuation of tension and pressure and wheel speed at the current moment, identify whether the personnel are in a stationary phase. If so, reacquire a new initial angle; otherwise, use short-time Fourier transform on the collected tilt angle signals to obtain the current tractor angle. Based on the difference between the current tractor angle and the latest initial angle, obtain the current terrain slope.

[0036] During implementation, the effect of personnel wearing individual soldier tractor vehicles is as follows: Figure 2 As shown, in Figure 2In this embodiment, the turning mechanism 5 of the single-soldier tractor is used to adjust the length of the tractor body; the tilt sensor 2 is arranged at the rear of the tractor to measure the change of the tractor tilt angle with the terrain; the wheel speed sensor 1 of the right wheel and the wheel speed sensor 3 of the left wheel are respectively built into the corresponding tractor wheel hub motor to measure the corresponding wheel speed; the tension and compression sensor 6 is arranged between the personnel and the tractor to measure the magnitude of the tension and compression between the personnel and the tractor; the module corresponding to the slope estimation method in this embodiment is placed in the chassis 4 of the tractor.

[0037] Because of differences in height among personnel, the initial angle of the towing vehicle will vary after the personnel are equipped with it. Therefore, the initial angle needs to be estimated based on the collected tilt angle signal. In step S1, after the personnel are equipped with the individual towing vehicle and stand upright, the tilt angle sensor adjusts its angle based on its sampling frequency f. angel The tilt angle signal is collected within a specified time period. Since personnel movement is a key piece of information in the application scenario of this embodiment, according to Shannon's sampling theorem, the sampling frequency f of the tilt angle sensor is... angel f should be satisfied angel ≥2·f h , where f h For the frequency of personnel movement, preferably, the sampling frequency of the tilt sensor is 200Hz.

[0038] Furthermore, the acquired tilt angle signal is transformed from the time domain to the frequency domain using the discrete Fourier transform to obtain the spectrum of the tilt angle signal at different frequencies, as shown in the following formula:

[0039]

[0040] Where X(k) represents the spectrum at the k-th frequency, N represents the length of the tilt signal, x[n] represents the n-th sample point of the tilt time-domain signal, and j represents the imaginary unit. This represents a complex exponential function used for conversion from the time domain to the frequency domain.

[0041] The spectrum calculated according to formula (1) is a complex number, which includes the amplitude spectrum and the phase spectrum. The amplitude spectrum is obtained by calculating the magnitude (absolute value) of the spectrum. Therefore, the amplitude at a frequency of 0 Hz in the spectrum is taken as the initial angle of the tilt. It should be noted that the amplitude corresponding to the 0 Hz frequency is a constant value. In this way, the interference of personnel shaking or other high-frequency interference signals on the initial tilt angle is effectively reduced.

[0042] Since the height of the personnel and the adjustment capability of the turning mechanism are both within a certain range, the initial angle of the tractor's tilt angle is... Should meet In this embodiment, θ is taken. refmin 25°, θ refmaxThe initial angle is 35°. If the calculated result is outside this range, the tractor will sound an alarm to alert the user and recalculate the initial angle.

[0043] During the personnel movement process in step S2, the terrain slope at each moment is fed back in real time based on the difference between the tractor angle and the initial angle. Since the personnel movement process includes two stages: personnel walking and personnel stopping, and the turning mechanism 5 may be adjusted during the personnel stopping stage, affecting the initial angle of the tractor tilt calculated in step S1, step S2 includes the identification of the personnel movement stage and the updating of the initial angle.

[0044] Specifically, the system identifies whether a person is in a stopped phase based on the fluctuations in tension and compression and wheel speed at the current moment. A person is in a stopped phase if the fluctuations in tension and compression do not exceed the fluctuation limit, and both the left and right wheel speeds are within the speed limit range. Otherwise, they are in a walking phase. It should be noted that the time here is determined by the frequency of real-time slope information feedback. The tilt sensor and tension / compression sensor sample at their respective frequencies.

[0045] Furthermore, the fluctuation of tensile and compressive forces at the current moment is obtained by acquiring the tensile and compressive forces collected at the current moment and the previous moment, and calculating the average difference of the horizontal components of each two adjacent tensile and compressive forces, as shown in the following formula:

[0046]

[0047] Among them, R F N represents the fluctuation of tension and compression. f This indicates the amount of tensile and compressive forces collected between the current and previous moments. and It represents the horizontal component of two adjacent tensile and compressive forces.

[0048] In this embodiment, the fluctuation limit value is set to 5 Newtons, and the speed limit range for the left wheel speed and the right wheel speed is [-0.5m / s, 0.5m / s].

[0049] When it is identified that the person is in a stationary phase, the tilt angle signal within a specified time period is taken from the current moment, and the amplitude at the frequency of 0Hz is obtained again using the Discrete Fourier Transform, thus updating the initial angle. When calculating the terrain slope at each moment in the subsequent travel phase, the difference between the real-time tractor angle and the new initial angle is calculated based on the new initial angle.

[0050] When it is identified that the person is in the walking phase, the short-time Fourier transform is used to obtain the current angle of the tractor unit from the collected tilt angle signal, including:

[0051] ① Obtain the tilt angle signal collected within a specified time period before the current moment, and use it as the signal to be calculated.

[0052] ② Perform segmented windowing on the signal to be calculated at the current time, and perform short-time Fourier transform on each windowed signal segment to obtain the spectrum of each windowed signal segment at different frequencies.

[0053] Specifically, the signal x[n] to be calculated at the current time has a length of N, a window length of M, and a step size of h. The signal is divided into multiple segments of length M based on the step size. A window function H[n] is applied to each segment of the signal. The window function can be a Hanning window, a Hamming window, a Gaussian window, etc. Then, the signal x[n] of the r-th segment after windowing at the current time... r,ω [n], n=0,1,…,M-1, is obtained through the following formula:

[0054] x r,k [n]=x[(r-1)·h+n]·H[n] Formula (3)

[0055] Where r represents the window index and k represents the frequency index.

[0056] It should be noted that in this embodiment, the characteristics of low-frequency signals are of significantly higher concern than those of high-frequency signals. Therefore, the window length M should be increased as much as possible to improve the frequency resolution and facilitate more accurate differentiation of very close low-frequency signals.

[0057] Furthermore, by performing a short-time Fourier transform on each windowed signal segment using the following formula, the spectrum of each windowed signal segment at different frequencies is obtained:

[0058]

[0059] Among them, X r (k) represents the spectrum of the signal segment at the k-th frequency after the r-th windowing at the current time.

[0060] ③ Based on the spectrum of each windowed signal segment at different frequencies, calculate the average amplitude of each spectrum at 0Hz to obtain the current tractor angle:

[0061]

[0062] Where, θ v The current tractor angle is represented by k, P represents the number of windows, and k| f＝0 This represents the frequency index corresponding to a frequency f of 0Hz, |X r (k| f＝0 )| represents the amplitude of the spectrum of the r-th windowed signal segment at 0Hz.

[0063] It should be noted that this embodiment obtains the tractor angle at each moment by analyzing the tilt angle signal. The key to analyzing the tilt angle signal lies in separating the interference of personnel walking and terrain conditions on the tilt angle signal. Since the interference of personnel walking on the tilt angle signal is chaotic, but when the slope change is not significant in different time periods, the interference of terrain conditions on the tilt angle signal is constant. Therefore, the tractor angle is obtained by aggregating the amplitude at 0Hz based on the result of short-time Fourier transform during the walking phase. This method can significantly reduce the impact of gait changes on the tilt angle during personnel walking compared to the result obtained by direct measurement by sensors.

[0064] The current tractor angle θ is obtained. v Then, the terrain slope θ at the current moment is obtained using the following formula:

[0065]

[0066] in, This indicates the latest initial angle.

[0067] Compared with existing technologies, this embodiment provides a method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform. By utilizing short-time Fourier transform during the use of equipment such as single-soldier tractors, the method reduces the impact of gait changes on the tilt angle during walking, thereby achieving dynamic real-time estimation of terrain slope. This facilitates adjustment of the tractor's control strategy, optimizes the tractor's control effect, improves the tractor's intelligence, and enhances the comfort and safety of the user.

[0068] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0069] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform, characterized in that, Includes the following steps: After the personnel put on the individual soldier tractor and stood upright, the initial angle was obtained by using discrete Fourier transform on the collected tilt angle signal. During personnel movement, tilt angle signals, tension and pressure between personnel and the single-soldier tractor, and wheel speed are collected. Based on the fluctuation of tension and pressure and wheel speed at the current moment, it is determined whether the personnel are in a stationary phase. If so, a new initial angle is obtained. Otherwise, the collected tilt angle signal is processed using a short-time Fourier transform to obtain the current tractor angle. Based on the difference between the current tractor angle and the latest initial angle, the terrain slope at the current moment is obtained.

2. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 1, characterized in that, The tilt angle signal is acquired by a tilt angle sensor located at the rear of the individual soldier tractor; the tension and compression are acquired by a tension and compression sensor located between the personnel and the individual soldier tractor; and the wheel speed is acquired by a wheel speed sensor built into the wheel hub motor of the individual soldier tractor.

3. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 1, characterized in that, The process of obtaining the initial angle by using Discrete Fourier Transform (DFT) on the acquired tilt angle signal involves acquiring the tilt angle signal within a specified time period, converting the acquired tilt angle signal from the time domain to the frequency domain using DFT, and then obtaining the amplitude at a frequency of 0 Hz as the initial angle.

4. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 2, characterized in that, The fluctuation of the tensile and compressive forces at the current moment is obtained by acquiring the tensile and compressive forces collected at the current moment and the previous moment, and calculating the average difference of the horizontal component force of each two adjacent tensile and compressive forces.

5. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 4, characterized in that, The fluctuation of tension and pressure at the current moment can be calculated using the following formula: Among them, R F N represents the fluctuation of tension and compression. f This indicates the amount of tensile and compressive forces collected between the current and previous moments. and It represents the horizontal component of two adjacent tensile and compressive forces.

6. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 2, characterized in that, The method of identifying whether a person is in a stopped phase based on the fluctuation of tension and pressure at the current moment and the wheel speed is as follows: if the fluctuation of tension and pressure at the current moment does not exceed the fluctuation limit value, and the speeds of both the left and right wheels at the current moment are within the speed limit range, then the person is in a stopped phase; otherwise, the person is in a walking phase.

7. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 6, characterized in that, The fluctuation limit value is set to 5 Newtons, and the speed limit range is [-0.5m / s, 0.5m / s].

8. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 2, characterized in that, The process involves re-acquiring a new initial angle by taking the tilt angle signal over a specified time period starting from the current moment, and then using the Discrete Fourier Transform to obtain the amplitude at a frequency of 0Hz, thereby updating the initial angle.

9. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 2, characterized in that, The process of obtaining the current tractor angle using a short-time Fourier transform of the acquired tilt angle signal includes: Obtain the tilt angle signal collected within a specified time period before the current moment, as the signal to be calculated; The signal to be computed is segmented and windowed. A short-time Fourier transform is performed on each windowed signal segment to obtain the spectrum of each windowed signal segment at different frequencies. Based on the spectrum of each windowed signal segment at different frequencies, the average amplitude of each spectrum at 0Hz is calculated to obtain the current tractor angle.

10. The method for estimating terrain slope of a single-soldier tractor based on short-time Fourier transform according to claim 9, characterized in that, The current angle of the tractor unit can be obtained using the following formula: Where, θ v The current tractor angle is represented by k, P represents the number of windows, and k| f＝0 This represents the frequency index corresponding to a frequency f of 0Hz, |X r (k| f＝0 )| represents the amplitude of the spectrum of the r-th windowed signal segment at 0Hz.

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