A flight control method of a pipeline exploration unmanned aerial vehicle

Abstract

The application discloses a flight control method of a pipeline detection unmanned aerial vehicle, the pipeline detection unmanned aerial vehicle comprises distance measuring sensors in four directions of left, right, top and bottom, and the following flight control method is executed when the unmanned aerial vehicle enters a pipeline: when the sum of the measurement values of the distance measuring sensors in the left and right directions is greater than a centering threshold value and the measurement value of the distance measuring sensor in any one side of the left and right directions is less than an obstacle avoidance threshold value, the unmanned aerial vehicle triggers the obstacle avoidance behavior of the side; when the sum of the measurement values of the distance measuring sensors in the left and right directions is less than or equal to the centering threshold value, the unmanned aerial vehicle is controlled to fly in the center of left and right, so that the measurement values of the distance measuring sensors in the left and right directions are equal. The application does not need GPS and a barometer, and can realize automatic obstacle avoidance forward and backward flight of the unmanned aerial vehicle along a straight pipeline towards a pipeline axis only by cooperation of the distance measuring sensors in the four directions of left, right, top and bottom.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of unmanned aerial vehicle detection, and particularly relates to a flight control method of a pipeline detection unmanned aerial vehicle. BACKGROUND

[0002] Multi-rotor unmanned aerial vehicles have been increasingly widely applied in many fields such as model entertainment, agricultural plant protection, fire rescue, mine surveying and mapping, and the like, due to their strong vertical take-off and landing capability, flexible operation and wide application scenarios.

[0003] However, the flight of the unmanned aerial vehicle for detecting the underground narrow straight pipeline with a caliber of 300-1000 mm is mainly controlled by the operator through manual remote control at present, and the manual control of the unmanned aerial vehicle flying in the narrow pipeline has the following technical problems:

[0004] 1) Although the remote control data can be transmitted to the unmanned aerial vehicle through the increase of the transfer stations at both ends of the pipeline, the GPS will lose the signal and cannot realize the positioning of the unmanned aerial vehicle in the pipeline, which seriously depends on the technology of the unmanned aerial vehicle operator, and the unmanned aerial vehicle will be bumped against the wall if the remote control is slightly oversteered in the narrow pipeline, which affects the smooth flight of the unmanned aerial vehicle. Although the propeller will not stop rotating because of the protective cover, frequent collision can easily cause the attitude of the unmanned aerial vehicle to be disordered and the unmanned aerial vehicle to be crashed.

[0005] 2) Due to the large airflow fluctuation caused by the high-speed rotating propeller of the unmanned aerial vehicle in the pipeline, the barometer data fluctuates greatly and is no longer suitable for being used as the accurate height of the unmanned aerial vehicle in the pipeline, so the laser or ultrasonic ranging sensor must be used for the height measurement in the pipeline. However, the underground pipeline generally has accumulated water at the bottom, and the data of the ranging sensor at the bottom will be invalid and fluctuate, which affects the stability of the height measurement.

[0006] 3) The optical flow sensor can be used to detect the displacement of the unmanned aerial vehicle in the horizontal plane, so that the unmanned aerial vehicle can realize local hovering. However, since the optical flow sensor needs to combine the ranging sensor to measure the distance from the surface opposite to the optical flow lens to obtain the accurate displacement value, in the circular pipeline, the optical flow sensor can only accurately measure the displacement along the axis of the pipeline, and cannot accurately measure the displacement value along the radial direction of the pipeline. Because the optical flow sensor collects the image of the curved surface along the radial direction of the pipeline, the varying ranging value and the curved surface will cause large image distortion, so that the optical flow sensor cannot obtain linear displacement measurement in the radial direction of the pipeline. Therefore, the optical flow sensor cannot realize the accurate positioning and hovering of the unmanned aerial vehicle in the radial direction of the pipeline. If the displacement data of the unmanned aerial vehicle along the radial direction of the pipeline is measured by the optical flow sensor to close-loop control the hovering of the unmanned aerial vehicle, the unmanned aerial vehicle will be bumped against the inner wall of the pipeline. SUMMARY

[0007] The technical problem to be solved by the present application is to overcome the shortcomings of the prior art: to provide a flight control method of a pipeline exploration unmanned aerial vehicle, which does not require GPS and barometer, and can realize automatic obstacle avoidance of the unmanned aerial vehicle along the straight pipeline towards the pipeline axis by cooperation of left, right, upper and lower distance measuring sensors, thereby greatly reducing the technical requirements for remote control of the operator.

[0008] The technical solution of the present application is as follows: a flight control method of a pipeline exploration unmanned aerial vehicle, the pipeline exploration unmanned aerial vehicle comprising left, right, upper and lower distance measuring sensors, when the unmanned aerial vehicle enters the pipeline, the following flight control method is executed: when the sum of the left and right distance measuring sensor measurement values is greater than the centering threshold value and the measurement value of any one of the left and right distance measuring sensors is less than the obstacle avoidance threshold value, the unmanned aerial vehicle triggers the obstacle avoidance behavior of the side; when the sum of the left and right distance measuring sensor measurement values is less than or equal to the centering threshold value, the unmanned aerial vehicle is controlled to fly centrally left and right, so that the left and right distance measuring sensor measurement values are equal.

[0009] As an optimization, when the sum of the upper and lower distance measuring sensor measurement values is greater than the centering threshold value and the measurement value of one of the upper and lower distance measuring sensors is less than the obstacle avoidance threshold value, the unmanned aerial vehicle triggers the obstacle avoidance behavior of the direction; when the sum of the upper and lower distance measuring sensor measurement values is less than or equal to the centering threshold value, the unmanned aerial vehicle is controlled to fly centrally up and down, so that the upper and lower distance measuring sensor measurement values are equal.

[0010] As an optimization, the pipeline exploration unmanned aerial vehicle comprises left, right, upper and lower distance measuring sensors, and their distance measurement values are respectively denoted as D left , D right , D up , D down ; when the unmanned aerial vehicle enters the pipeline, the following flight control method is executed:

[0011] In the left and right directions, when (D left +D right )>S LR , if the left D left or the right D right is less than the threshold value S MIN , the measurement value of the side is taken as the distance feedback value of the control algorithm to close-loop control the unmanned aerial vehicle to fly in the left and right directions, so that the target distance D LRset of the unmanned aerial vehicle to the obstacle of the side is equal to S MIN ; when (D left +D right )≤S LR , the left D left or the right D rightThe measurement value is used as the distance feedback value of the control algorithm to close-loop control the UAV to fly in the left or right direction, so that the target distance D LRset of the UAV to the obstacle on the side is equal to (D left +D right ) / 2; wherein S LR is the left and right side center threshold, and S MIN is the threshold for triggering obstacle avoidance.

[0012] As an optimization, in the up and down direction, when (D up +D down )>S UD , if the up D up or the down D down is less than the threshold S MIN , the measurement value is used as the distance feedback value of the control algorithm to close-loop control the UAV to fly in the up and down direction, so that the target distance D UDset of the UAV to the obstacle on the side is equal to S MIN ; when (D up +D down )≤S UD , the up D up or the down D down measurement value is used as the distance feedback value of the control algorithm to close-loop control the UAV to fly in the up and down direction, so that the target distance D UDset of the UAV to the obstacle on the side is equal to (D up +D down ) / 2; wherein S UD is the up and down direction center threshold, and S MIN is the threshold for triggering obstacle avoidance.

[0013] As an optimization, the size of S UD and S LR is 300-1000mm, the size of S MIN is 100-500mm, and S UD and S LR are both greater than S MIN .

[0014] As an optimization, the sliding window method is used to calculate the variance of D left and D right , when (D left +D right )≤S LR , the measurement value with smaller variance is selected from the left D left and the right D right measurement value as the distance feedback value of the control algorithm to close-loop control the UAV to fly in the left or right direction, and in the control process, D left and D right are used to calculate the variance.Real-time switching of variance magnitude comparison D left Or D right As a feedback value.

[0015] As an optimization, the sliding window method is used to statistically analyze D. up and D down The variance, when (D up +D down )≤S UD At that time, above D up and below D down The measured values ​​with smaller variance are selected as the distance feedback values ​​for the control algorithm. This closed-loop control propels the UAV vertically, and during the control process, the distance is determined based on D... up and D down Real-time switching of variance magnitude comparison D up Or D down As a feedback value.

[0016] As an optimization, the window size of the sliding window method is 50-100.

[0017] As an optimization, the control algorithm is specifically a PID control algorithm.

[0018] As an optimization, the pipeline inspection drone also includes an optical flow sensor located at the bottom or top. When the drone enters a straight pipeline and flies back and forth in the direction of the pipeline axis, the forward and backward displacement measurement value of the optical flow sensor is used as the feedback value of the control algorithm to control the drone to navigate to a fixed point along the direction of the pipeline axis in a closed loop.

[0019] The beneficial effects of this invention are:

[0020] 1) This invention does not require GPS or barometers. It only relies on the cooperation of range sensors in four directions: left, right, top, and bottom to enable the drone to automatically avoid obstacles and fly forward and backward along the axis of the straight pipe. This greatly reduces the requirements for the operator's remote control skills. The operator only needs to control the drone's yaw angle and forward and backward movement according to the image transmission of the drone's camera to pass smoothly in the pipe.

[0021] 2) The flight control algorithm of this invention combines symmetrical ranging sensors (top, bottom, left, and right). Even if water accumulation at the bottom of an underground pipe causes data fluctuations in the bottom ranging sensor, the algorithm can automatically switch to the opposite ranging sensor while maintaining centered flight, achieving stable flight. If a single ranging sensor is consistently used as the control algorithm's feedback value, interference to that sensor will cause the drone to sway and vibrate. The feedback value switching mechanism of this invention greatly enhances robustness.

[0022] 3) The application utilizes the linear displacement measurement data of the optical flow sensor along the pipeline axis direction alone, and also realizes the stopping of the unmanned aerial vehicle in the front-back direction, solves the problem of positioning and hovering of the unmanned aerial vehicle in the front-back direction, and in combination with the center positioning of the up-down and left-right ranging sensors in a narrow area, the hovering of the unmanned aerial vehicle in the pipeline can be realized, and the local stopping and detection of the unmanned aerial vehicle in the pipeline is facilitated. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The structure schematic diagram of the pipeline detection unmanned aerial vehicle in example 1-2.

[0024] Figure 2 The flight schematic diagram of the pipeline detection unmanned aerial vehicle in example 1 in the pipeline.

[0025] Figure 3 The flight schematic diagram of the pipeline detection unmanned aerial vehicle in example 2 in the pipeline.

[0026] In the figure: 1, left ranging sensor; 2, right ranging sensor; 3, upper ranging sensor; 4, lower ranging sensor; 5, camera; 6, optical flow sensor. DETAILED DESCRIPTION

[0027] The embodiments of the application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only for illustration of the application and should not be regarded as limiting the scope of the application. If the specific conditions are not specified in the examples, the conventional conditions are used.

[0028] Example 1

[0029] In combination Figures 1-3 As shown in the figure, the pipeline detection unmanned aerial vehicle of the present embodiment is a four-rotor unmanned aerial vehicle with length x width x height = 10 cm x 10 cm x 6 cm, which is provided with a main controller STM32F411CEU6, including left ranging sensor 1, right ranging sensor 2, upper ranging sensor 3 and lower ranging sensor 4 connected with the main controller through IIC serial communication, and inertial measurement unit MPU6500, the four ranging sensors are VI5300, the unmanned aerial vehicle is provided with a camera 5 facing forward, a lighting lamp, the video data collected by the camera 5 is wirelessly forwarded to the monitoring screen or the flight glasses of the unmanned aerial vehicle operator through the picture transmission system, and the propeller is provided with a propeller protection cover; as Figure 2As shown, the flight control method of the embodiment realizes collision-free obstacle avoidance flight of the UAV in the multi-inner-diameter straight pipeline with the front section pipeline inner diameter of 600 mm and the rear section pipeline inner diameter of 300 mm, and the UAV flies towards the pipeline axis without collision. The operator only needs to fly into the pipeline and control the UAV head to be roughly oriented towards the pipeline axis according to the image transmission picture, and then only needs to remotely control the UAV to advance and retreat, so as to realize that the UAV automatically avoids the inner wall of the pipeline and smoothly enters and exits the pipeline along the pipeline axis, and the auxiliary camera detects and collects images in the pipeline.

[0030] The flight control method is as follows: the distance measurement values of the left distance sensor 1, the right distance sensor 2, the upper distance sensor 3 and the lower distance sensor 4 are respectively denoted as D left , D right , D up and D down ; the variances of D left , D right , D up and D down are counted by using the sliding window method, the size of the window is 100, and the sampling interval of each data is 10 ms; when the UAV enters the pipeline, the following flight control method is executed:

[0031] In the left-right direction, when (D left +D right )>500 mm, it is generally set to 5 times the width of the UAV, if the left D left or the right D right is less than the threshold value 100 mm, the measurement value of the side is taken as the distance feedback value of the PID control algorithm to close-loop control the UAV to fly in the left-right direction, so that the target distance D LRset of the UAV to the side obstacle is equal to 100 mm, at this time, the remote control can also manually adjust the size of the target distance D LRset to control the UAV to move away from the side obstacle; for example, when the UAV flies to the left D left is less than the threshold value 100 mm, the left D left is taken as the distance feedback value of the PID control algorithm to close-loop control the UAV so that the measurement value of the left D left reaches the target distance D LRset =100 mm, at this time, the operator can also manually adjust the size of the target distance D LRset to close-loop control the UAV to move away from the left obstacle.

[0032] When (D left +D right )≤500 mm, in the left D left and the right D rightThe measured values ​​with the smallest variance obtained from the current sliding window method are selected as the distance feedback value for the PID control algorithm. This closed-loop control directs the drone to fly left or right, ensuring the drone's distance D from the obstacle on that side is controlled. LRset equals (D) left +D right ) / 2; and in the control process according to D left and D right Real-time switching of variance magnitude comparison D left Or D right As a feedback value. For example, the left-hand side D of the current sliding window method statistics. left The variance is less than the right-hand side D right The variance of the measured values, then let D on the left side... left The measured value is used as the distance feedback value in the PID control algorithm to control the drone's left and right flight to the left (D). left The measured value reaches the target distance D LRset =(D left +D right ) / 2; and in the control process according to D left and D right Real-time switching between D with smaller variance and variance conditions. left Or D right As the distance feedback value for the PID control algorithm: First, the D value, which is statistically obtained using the sliding window method, is... left D right The variance is compared with the normal variance threshold VarN of the VI5300 data. The normal variance threshold VarN is obtained from the sensor manual or data under good measurement conditions. When the sliding window method is used to statistically analyze D... left D right The variances are all less than 3-5 times the normal variance threshold VarN and (D left variance-D right The D with smaller variance is switched only when the absolute value of the variance is greater than the normal variance threshold VarN. left Or D right As the distance feedback value of the PID control algorithm, it is necessary to reset all variables of the PID control algorithm before switching to avoid instability caused by frequent switching when the data on both sides are roughly bad or roughly good.

[0033] In the up-down direction, when (D up +D down When )>500mm, if the upper D up Or below D down If the distance is less than the threshold of 100mm, the measured value in that direction is used as the distance feedback value for the PID control algorithm to control the drone to fly vertically, so that the drone is at a target distance D from the obstacle in that direction. UDsetequal to 100mm, at this time the remote control can also be manually adjusted target distance D UDset the size to control the UAV away from the direction of the obstacle;

[0034] When (D up +D down )≤500mm, in the upper D up and lower D down measurement value, select the smaller variance measurement as the distance feedback value of PID control algorithm closed loop control UAV to fly in the up and down direction, so that the target distance D UDset of the UAV to the obstacle in this direction is equal to (D up +D down ) / 2; and in the control process according to D up and D down variance size comparison real-time switching D up or D down as the feedback value. The obstacle avoidance and feedback value switching logic in the up and down direction is similar to the left and right direction, which is not expanded here.

[0035] This embodiment does not need GPS and barometer, only relies on left, right, top and bottom four direction ranging sensor to realize the UAV automatic obstacle avoidance in the straight pipe along the pipe axis, greatly reduces the technical requirements of the operator remote control, when entering the narrow area, the UAV can automatically fly up and down and left and right, and fly stably under the PID closed loop control without up and down and left and right overshoot swing.

[0036] This embodiment flight control algorithm combines the up and down and left and right symmetrical ranging sensor to execute the feedback value switching logic, even if there is water on the bottom of the underground pipeline, which causes the bottom ranging sensor data to fail and fluctuate, resulting in large variance, which can automatically switch to the opposite ranging sensor while flying in the center, realizing stable flight.

[0037] Embodiment 2

[0038] As Figure 1 shown, different from embodiment 1, the UAV of this embodiment further comprises a light flow sensor 6 of PMW3901 type arranged on the top towards the upper, and a light supplementing lamp arranged upwards for light supplementing illumination of the light flow sensor. The light flow sensor 6 is arranged on the top because the probability of water accumulation on the bottom of the pipeline is larger, and the water accumulation will affect the data stability of the light flow sensor 6.

[0039] As Figure 3As shown, because the optical flow sensor 6 acquires images of an arc-shaped surface along the radial direction of the pipe, the changing ranging values ​​and the curved surface cause significant image distortion. This results in the optical flow sensor 6 being unable to obtain linear displacement measurements in the radial direction of the pipe. The optical flow sensor 6 calculates the displacement change by capturing and comparing the displacement of feature pixels in two consecutive frames of images, and then combining this with the distance from the lens to the upper surface of the pipe measured by the ranging sensor 3 above. Figure 3 As can be seen, moving along the radial direction of the pipe causes rapid changes in the measurement value of the ranging sensor 3 and distortion of the pipe wall surface texture image. Therefore, the displacement measurement value of the optical flow sensor 6 in the pipe diameter direction cannot accurately reflect the displacement change of the UAV, and thus cannot be directly used for [further analysis]. Figure 3 The drone needs to hover in the left and right directions to avoid crashing into the pipe wall. However, this embodiment ignores the data from the optical flow sensor 6 moving along the pipe diameter, and only uses the displacement measurement value of the optical flow sensor 6 along the pipe axis as the displacement feedback value for the PID control algorithm to control the drone to hover at a fixed point along the pipe axis.

[0040] This embodiment uses the measurement data of the one-dimensional optical flow sensor 6 along the pipe axis direction combined with the four-way ranging sensor of Embodiment 1 for collaborative positioning. The linear displacement measurement data of the optical flow sensor 6 along the pipe axis direction is used alone to realize the drone's hovering in the forward and backward directions, which solves the problem of drone positioning and hovering in the forward and backward directions. In narrow areas, the combination of center positioning with the up, down, left and right ranging sensors can enable the drone to hover in the pipe, which is convenient for the drone to hover and detect in local areas in the pipe.

[0041] When a hovering function is required, the following flight control method is executed when the drone enters a straight pipe and flies forward and backward along the pipe axis: The forward and backward displacement measurement value of the optical flow sensor 6 is used as the feedback value of the PID control algorithm to control the drone to fly along the pipe axis in a closed loop. If hovering at the current position is required, the current displacement value of the optical flow sensor 6 is read as the PID displacement target value. The PID control algorithm outputs a control quantity based on the deviation between the current real-time measurement value and the target value to control the drone to position itself at the target displacement and achieve hovering. Remotely adjusting the magnitude of this target displacement value can also achieve closed-loop control of the drone's forward and backward movement. The PID control algorithm is existing technology, mainly using the deviation between the measured feedback value and the target value as the PID input to perform proportional-integral-derivative output control of the drone's closed-loop flight.

[0042] Preferably, the data from the optical flow sensor and the ranging sensor can be fused with the IMU accelerometer data using existing sensor fusion algorithms to obtain more accurate fused values ​​as displacement and distance measurements, thereby improving the accuracy of the measurements.

[0043] The above merely illustrates the embodiments of the present application, and does not constitute any limitation on the protection scope of the present application. Any technical scheme formed by equivalent exchange or equivalent replacement falls within the protection scope of the present application.

Claims

1. A flight control method of a pipeline exploration drone, characterized by, The pipeline exploration unmanned aerial vehicle comprises distance measuring sensors in left, right, upper and lower directions, and the distance measurement values of the distance measuring sensors are respectively recorded as D left , D right , D up , D down ; when the unmanned aerial vehicle enters the pipeline, the following flight control method is executed: In the left-right direction, when (D left +D right )>S LR , if the left D left or the right D right is less than the threshold S MIN , the measurement value of the side is taken as the distance feedback value of the control algorithm to close-loop control the UAV to fly in the left-right direction, so that the target distance D LRset of the UAV to the obstacle on the side equals S MIN ; when (D left +D right )≤S LR , the left D left or the right D right measurement value is taken as the distance feedback value of the control algorithm to close-loop control the UAV to fly in the left-right direction, so that the target distance D LRset of the UAV to the obstacle on the side equals (D left +D right ) / 2; wherein S LR is the left-right centering threshold, and S MIN is the threshold for triggering obstacle avoidance. The variance of D left and D right is calculated by using the sliding window method, when (D left +D right )≤S LR , the measurement value with smaller variance is selected from the left D left and the right D right as the distance feedback value of the control algorithm, the unmanned aerial vehicle is controlled to fly in the left and right directions, and the D left or D right is switched as the feedback value according to the variance comparison of D left and D right in real time during the control process.

2. The flight control method of a pipe exploration drone according to claim 1, wherein, In the up-down direction, when (D up +D down )>S UD , if the up D up or the down D down is less than the threshold S MIN , the direction measurement value is taken as the distance feedback value of the control algorithm to close-loop control the UAV to fly in the up-down direction, so that the target distance D UDset of the UAV to the obstacle in the direction equals S MIN ; when (D up +D down )≤S UD , the up D up or the down D down measurement value is taken as the distance feedback value of the control algorithm to close-loop control the UAV to fly in the up-down direction, so that the target distance D UDset of the UAV to the obstacle in the direction equals (D up +D down ) / 2; wherein S UD is the up-down direction centering threshold, and S MIN is the threshold triggering obstacle avoidance. 3.The flight control method of a pipe exploration drone according to claim 2, wherein, S UD and S LR have a size of 300-1000 mm, S MIN has a size of 100-500 mm and S UD and S LR are both larger than S MIN .

4. The flight control method of a pipe exploration drone according to claim 2, wherein, The variance of D up and D down is calculated by using the sliding window method, when (D up +D down )≤S UD , the measurement value with smaller variance is selected from the upper D up and the lower D down as the distance feedback value of the control algorithm, the unmanned aerial vehicle is controlled to fly in the upward and downward directions, and during the control process, the feedback value is switched to D up or D down according to the comparison of the variance of D up and D down .

5. The flight control method of a pipe exploration drone according to claim 4, wherein, The size of the window of the sliding window method is 50-100. 6.The flight control method of the pipeline exploration drone according to claim 5, wherein, The control algorithm is specifically a PID control algorithm.

7. The flight control method of a pipe exploration drone according to claim 1 or 2, wherein, The pipeline detection unmanned aerial vehicle further comprises an optical flow sensor arranged on the bottom or the top, and when the unmanned aerial vehicle flies forward and backward along the straight pipeline towards the pipeline axis direction, the forward and backward displacement measurement values of the optical flow sensor are used as feedback values of a control algorithm to close-loop control the unmanned aerial vehicle to fly along the pipeline axis direction.

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