CN114740900B - Four-rotor unmanned aerial vehicle accurate landing system and method based on fault-tolerant control - Google Patents
Four-rotor unmanned aerial vehicle accurate landing system and method based on fault-tolerant control Download PDFInfo
- Publication number
- CN114740900B CN114740900B CN202210645880.2A CN202210645880A CN114740900B CN 114740900 B CN114740900 B CN 114740900B CN 202210645880 A CN202210645880 A CN 202210645880A CN 114740900 B CN114740900 B CN 114740900B
- Authority
- CN
- China
- Prior art keywords
- fault
- unmanned aerial
- openmv4
- aerial vehicle
- sensor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 238000000034 method Methods 0.000 title claims abstract description 25
- 230000000007 visual effect Effects 0.000 claims abstract description 9
- 230000003287 optical effect Effects 0.000 claims description 17
- 238000001514 detection method Methods 0.000 claims description 13
- 238000005457 optimization Methods 0.000 claims description 9
- 230000005540 biological transmission Effects 0.000 claims description 7
- 238000004364 calculation method Methods 0.000 claims description 6
- 230000008569 process Effects 0.000 claims description 6
- 238000011217 control strategy Methods 0.000 claims description 5
- 102100031629 COP9 signalosome complex subunit 1 Human genes 0.000 claims description 4
- 102100022148 G protein pathway suppressor 2 Human genes 0.000 claims description 4
- 101000940485 Homo sapiens COP9 signalosome complex subunit 1 Proteins 0.000 claims description 4
- 101000900320 Homo sapiens G protein pathway suppressor 2 Proteins 0.000 claims description 4
- 238000006073 displacement reaction Methods 0.000 claims description 4
- 230000000694 effects Effects 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 238000010845 search algorithm Methods 0.000 claims description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims 1
- 230000007547 defect Effects 0.000 abstract description 4
- 238000005286 illumination Methods 0.000 abstract description 3
- RZVHIXYEVGDQDX-UHFFFAOYSA-N 9,10-anthraquinone Chemical compound C1=CC=C2C(=O)C3=CC=CC=C3C(=O)C2=C1 RZVHIXYEVGDQDX-UHFFFAOYSA-N 0.000 abstract description 2
- 239000011159 matrix material Substances 0.000 description 9
- 238000004891 communication Methods 0.000 description 3
- 238000002474 experimental method Methods 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- 238000013519 translation Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000007405 data analysis Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000004069 differentiation Effects 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000013507 mapping Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000010355 oscillation Effects 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000012358 sourcing Methods 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
- G05D1/10—Simultaneous control of position or course in three dimensions
- G05D1/101—Simultaneous control of position or course in three dimensions specially adapted for aircraft
Landscapes
- Engineering & Computer Science (AREA)
- Aviation & Aerospace Engineering (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Position Fixing By Use Of Radio Waves (AREA)
- Control Of Position, Course, Altitude, Or Attitude Of Moving Bodies (AREA)
- Optical Radar Systems And Details Thereof (AREA)
- Traffic Control Systems (AREA)
Abstract
The invention relates to the technical field of unmanned aerial vehicle flight control, in particular to a fault-tolerant control-based precise landing system and a fault-tolerant control-based precise landing method for a quad-rotor unmanned aerial vehicle, wherein the landing system comprises an aircraft, a flight controller, a laser range finder, a visual sensor, a fault-tolerant position controller and a GPS (global positioning system) module, an Openmv4 sensor acquires relative coordinates by identifying landmarks on a landing platform, the landmarks on the landing platform adopt Apriltag identification codes, the flight controller receives the relative coordinates of the landmarks on the landing platform and transmits the relative coordinates to the fault-tolerant position controller, and the fault-tolerant position controller ensures that the aircraft can still land on the landing platform successfully under weak GPS signals. The invention solves the defects that the GPS signal is easy to be interfered, has large error, low visual efficiency and easy to be interfered by illumination.
Description
Technical Field
The invention relates to the technical field of unmanned aerial vehicle flight control, in particular to a four-rotor unmanned aerial vehicle accurate landing system and method based on fault-tolerant control.
Background
In recent years, with the continuous development of unmanned aerial vehicles and related technologies, more and more unmanned aerial vehicles are being used. And the four rotors rely on its small and exquisite flexibility, require advantages such as extremely low by the extensive all aspects of using in the life to take off the place, take photo by plane four rotor unmanned aerial vehicle and electric power patrol and examine four rotor unmanned aerial vehicle etc. in the life. As the most important landing process, the most concerned is always. Therefore, the research on the autonomous landing technology of the quad-rotor unmanned aerial vehicle is particularly important. The automatic landing based on the navigation of the global positioning system is a commonly used method at present, but has certain defects only depending on the GPS to guide the automatic landing. Firstly, the GPS positioning precision without special processing can only reach 10m, and for an area with complex terrain, such as a city with dense building groups, the unmanned aerial vehicle is likely to crash in a low-altitude approaching area due to navigation errors; secondly, the GPS signal is greatly interfered by non-air media, and the error is increased or even the signal is lost in an area with more shelters, such as a forest; professional grade high accuracy GPS equipment is expensive, does not possess economic practicality. The navigation by simply using the vision has the defects of low efficiency and easy illumination interference, so that the design of the accurate landing system based on the satellite navigation system and the vision has deep research value and application prospect.
In unmanned aerial vehicle control, unmanned aerial vehicle communication is an indispensable part, the communication protocol between an unmanned aerial vehicle and a sensor, a ground station and the like which are commonly used at present is a MAVLink (micro Air lover link) protocol, and the MAVLink has the characteristics of being more advanced, wider in coverage range and stronger in data analysis and processing capacity. The MAVlink has a function of standardizing data transmission between the unmanned aerial vehicle and the ground station, and also has a capability of checking and checking data signals.
The AprilTag identification code has the advantages of low complexity, high local accuracy, easy identification and information extraction, algorithm sourcing and the like, and is a novel visual positioning system using a 2D bar code style "tag" developed by April laboratories of Michigan State university. The system is an improvement on ARToolkit, improves the performance of a line detection algorithm and the digital coding capability, and can be identified in scenes such as long distance, poor light, lens distortion and the like. There are several AprilTag species: TAG16H5, TAG25H7, TAG25H9, TAG36H10 and TAG36H11, wherein different kinds of apriltags have different characteristics and different application scenes. For example, TAG16H5 has a valid recognition range of 4x4 square blocks, TAG36H11 has a valid recognition range of 6x6 square blocks, TAG16H5 can be recognized at a longer distance but at the same time has a higher recognition error rate, while TAG36H11 has more complex verification information and a lower recognition error rate. In the naming, the TAG36 represents that the bit number of the label is 36 bits, and the smaller the value of the TAG36, the farther the distance can be identified; h11 represents the minimum Hamming distance of two tags in the class, which can be changed to another Tag by modifying the value. Meanwhile, the recognition confidence coefficient is also related to the calibration information, and the smaller the minimum Hamming distance is, the smaller the capacity reserved for the calibration information is, and the lower the recognition confidence coefficient is.
Disclosure of Invention
The invention provides a fault-tolerant control-based accurate landing system and method for a quad-rotor unmanned aerial vehicle, which are used for realizing the successful landing of the quad-rotor unmanned aerial vehicle on a landing platform under weak GPS signals and solving the problems that the existing landing depending on the GPS signals is easy to interfere, has large error, is low in visual efficiency and is easy to interfere by illumination.
In order to realize the purpose of the invention, the adopted technical scheme is as follows: accurate landing system of four rotor unmanned aerial vehicle based on fault-tolerant control, including the aircraft, flight controller, laser range finder, the vision sensor, fault-tolerant position controller and GPS module, the aircraft carries on flight controller and laser range finder, the vision sensor is Openmv4 sensor, the built-in APM firmware of flight controller, laser range finder provides accurate distance information for flight controller, Openmv4 sensor obtains relative coordinate through the landmark of discernment on the landing platform, the landmark of landing platform adopts Apriltag identification code, flight controller receives the relative coordinate of the landmark on the landing platform, and will relative coordinate transmission to fault-tolerant position controller, fault-tolerant position controller ensures that the GPS module can still successfully land on the landing platform under weak GPS signal.
As an optimization scheme of the invention, the fault-tolerant control-based precise landing system of the quad-rotor unmanned aerial vehicle further comprises WIFI wireless data transmission, and the WIFI wireless data transmission is used for communicating with the ground.
In order to realize the purpose of the invention, the adopted technical scheme is as follows: the method for landing by adopting the fault-tolerant control-based precise landing system of the quad-rotor unmanned aerial vehicle comprises the following steps:
s1, controlling the unmanned aerial vehicle to hover above a landmark on the landing platform, searching the landmark, analyzing the position of the landmark Apriltag by an Openmv4 sensor, analyzing the offset between the landmark and the Openmv4 sensor in a pixel coordinate system after the Openmv4 sensor obtains an image frame, and finally obtaining the coordinate in the unmanned aerial vehicle navigation coordinate system through coordinate conversion; altitude information at search timePos z From laser rangefindersH lid Horizontal position informationPos is based on GPS signal quality and horizontal position errorError x,y Selecting each position information source, horizontal position informationPos being the GPS positionPos GPS Or Openmv4 optical flow location informationPos FLOW ；
S2, automatically switching to a landing mode when the ground is captured by the aircraft, and if the ground is greater than a set time threshold valueT th If the aircraft does not find the landmark, the aircraft enters a fixed point mode;
s3, after entering the falling mode, firstly, according to the horizontal position errorError x,y Obtaining maximum error of horizontal positionError max x,y Switching a fault-tolerant position controller, wherein the fault-tolerant position controller takes the horizontal position offset acquired by an Openmv4 sensor as a control target, or the fault-tolerant position controller takes the horizontal position offset acquired by an Openmv4 sensor and the horizontal position information of a GPS module superposed as the control target; then, the horizontal position control is carried out to keep the horizontal position errorError x,y At a set thresholdPos th Within the range;
s4, controlling the altitude according to the altitude information obtained by the laser range finder, when the altitude of the aircraft is larger than the altitude threshold valueAlt th Then the steps S3 and S4 are continued, when the altitude of the aircraft is lower than the set altitude thresholdAlt th In time, the aircraft shuts off the motor and lands on the landing platform.
As an optimization of the present invention, in step S1, the height information at the time of searchPos z The expression is:
Pos z = H lid
horizontal position information at the time of searchPos, the expression is:
wherein,H lid for the height measured by the laser rangefinder during the search,Pos GPS for GPS position, G, acquired by the GPS module PDOP And distributing space geometric strength factors for the GPS module according to the satellites.
As an optimization scheme of the present invention, in step S1, the step of performing position resolution on the landmark Apriltag by the Openmv4 sensor is:
1) after the Openmv4 sensor identifies Apriltag, firstly, performing line segment detection, and clustering pixel points with similar gradient intensity and direction in the whole image by using the line segment detection so as to gather the pixel points into line segments;
2) then, quadrangle detection is carried out, after all line segments are detected, grouping is carried out through distance thresholds of two adjacent edges, then all combination groups are traversed in four layers by utilizing a depth optimization search algorithm, and when a fourth layer is traversed, if a loop is detected to be formed by the last edge and the first edge, the path traversed to the node is a quadrangle;
3) the position and attitude of the Openmv4 sensor relative to the Apriltag identification code is extracted via image information after the Apriltag identification code is successfully captured.
As an optimization scheme of the present invention, in step S1, Openmv4 optical flow position informationPos FLOW The displacement of two frames of images is calculated through an Openmv4 sensor, so that the quad-rotor unmanned aerial vehicle is positioned.
As an optimization of the present invention, in step S3, the horizontal position errorError x,y The expression is:
wherein,Pos GPS1 for the unmanned aerial vehicle error calculation period start time GPS signal horizontal position information,Pos GPS2 for the unmanned aerial vehicle error calculation period end time GPS signal horizontal position information,Pos openmv the horizontal position offset of the lens, which is the Openmv4 sensor, with respect to the Apriltag center point.
As an optimization scheme of the invention, a stage control strategy of firstly carrying out horizontal alignment and then carrying out height control is adopted in the landing process of the unmanned aerial vehicle, and a strategy of offsetting ground effect by locking an aerial motor in the final landing stage is adopted.
The invention has the positive effects that: 1) the invention realizes the accurate landing of the aircraft based on the Openmv4 sensor with light weight and low power consumption, and provides an effective application scene for the aircraft with weaker load capacity;
2) the aircraft accurate landing control strategy disclosed by the invention is a scheme with multi-stage and high-precision requirements, avoids the problem that the aircraft cannot be accurately landed on a landing platform due to target loss, aircraft oscillation and external interference in a continuous landing mode, and provides a new scheme for an application scene with strict landing precision requirements;
3) the fault-tolerant position controller disclosed by the invention overcomes the problems of large landing error and aircraft explosion of an aircraft in weak GPS signals;
4) the altitude control strategy disclosed in step S4 of the present invention accounts for errors due to ground effects when the aircraft lands.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a flow chart of the landing method of the present invention;
FIG. 2 is a schematic diagram of the connection between an Openmv4 sensor and a flight controller according to the present invention.
Detailed Description
As shown in fig. 1-2, the invention discloses a fault-tolerant control-based precise landing system of a quad-rotor unmanned aerial vehicle, which comprises an aircraft, a flight controller, a laser range finder, a visual sensor, a fault-tolerant position controller and a GPS module, wherein the aircraft carries the flight controller and the laser range finder, the visual sensor is an Openmv4 sensor, the flight controller is internally provided with APM firmware, the laser range finder provides precise distance information for the flight controller, the Openmv4 sensor acquires relative coordinates by recognizing landmarks on a landing platform, the landmarks on the landing platform adopt Apriltag identification codes, the flight controller receives the relative coordinates of the landmarks on the landing platform and transmits the relative coordinates to the fault-tolerant position controller, and the fault-tolerant position controller ensures that the GPS module can still land on the fault-tolerant platform successfully under weak GPS signals. The flight controller is a Pixhawk1 flight controller, and the APM firmware is a software system carried in the flight controller. The Openmv4 sensor can process images without carrying an additional image processor. The Openmv4 sensor is transmitted to the flight controller through a serial port through a Mallink protocol. The Openmv4 sensor has the advantages of low power consumption and light weight. After receiving Openmv4 and resolving a relative coordinate with a landmark Apriltag, the flight controller transmits the relative coordinate to the fault-tolerant position controller, and the fault-tolerant position controller adopts different control modes according to the set judgment condition, so that the aircraft can still successfully land on a landing platform under weak GPS signals. The communication of the flight controller, the Openmv4 sensor and the ground station adopts the Mavlik protocol. The AprilTag identification code is used as a visual guidance landing landmark to guide the unmanned aerial vehicle to finish autonomous landing. The TAG36H11 with the highest accuracy is adopted to ensure the accuracy of the identification information. Quad-rotor unmanned aerial vehicle is referred to as unmanned aerial vehicle for short.
The landing method of the four-rotor unmanned aerial vehicle accurate landing system based on fault-tolerant control comprises the following steps:
s1, controlling the unmanned aerial vehicle to hover above a landmark on the landing platform, searching the landmark, analyzing the position of the landmark Apriltag by an Openmv4 sensor, analyzing the offset between the landmark and the Openmv4 sensor in a pixel coordinate system after the Openmv4 sensor obtains an image frame, and finally obtaining the coordinate in the unmanned aerial vehicle navigation coordinate system through coordinate conversion; altitude information at search timePos z From laser rangefindersH lid Horizontal position informationPos is based on GPS signal quality and aircraft horizontal position errorError x,y Selecting each position information source, horizontal position informationPos being GPS positionPos GPS Or Openmv4 optical flow location informationPos FLOW (ii) a GPS signal quality and horizontal position errorError x,y The position control of the aircraft is greatly influenced, so that a fault-tolerant position controller is designed based on a PID (proportion integration differentiation) controller, the aircraft is always positioned at high precision, and the GPS positioning information and the Openmv4 optical flow position information are switched according to a set threshold;
altitude information at search timePos z The expression is:
Pos z = H lid
horizontal position information at the time of searchPos, the expression is:
wherein,H lid for the height measured by the laser rangefinder during the search,Pos GPS for GPS position, G, acquired by the GPS module PDOP Distributing spatial geometric intensity factors (G) for GPS modules according to satellites PDOP Characterizing GPS signal quality).
According to G when unmanned aerial vehicle carries GPS module PDOP Judging whether the satellite information is accurately available, and according to the GPS official website information, processing the satellite information to G PDOP Can be normally adopted by unmanned aerial vehicle when being less than 5, and horizontal drift error is 5m when unmanned aerial vehicle carries on the GPS module. So when G is PDOP Less than 5 or horizontal position errorError x,y Less than 5m, horizontal position informationPos employs GPS locationPos GPS Otherwise, the horizontal position information adopts Openmv4 optical flow position informationPos FLOW . The invention discloses a two-part algorithm staggered operation mode, wherein the two-part algorithm staggered operation mode is used for determining a flag bit transmitted to an Openmv4 sensor through a flight controller, and the Openmv4 sensor starts optical flow positioning (namely the Openmv4 optical flow position information when the Openmv4 sensor receives the flag bit '1' transmitted by the flight controller (namely the Openmv4 optical flow position information)Pos FLOW ) Otherwise, the Openmv4 sensor runs Apriltag resolution algorithm all the time, i.e., when G PDOP Greater than 5 or horizontal position errorError x,y When the number of the flag bit is larger than 5m, the flight controller transmits a flag bit '1' to the Openmv4 sensor through a serial port, the Openmv4 sensor enters an optical flow positioning algorithm, a connecting line of the flight controller and the Openmv4 sensor is shown in FIG. 2, tx is a sending port, and rx is a receiving port.
In step S1, the step of the Openmv4 sensor performing position resolution on the landmark Apriltag is:
1) after the Openmv4 sensor identifies Apriltag, firstly, carrying out line segment detection, and clustering pixel points with similar gradient intensity and direction in the whole image by using the line segment detection so as to gather the pixel points into line segments;
the method specifically comprises the following steps: apriltag line segment detection is similar to other two-dimensional code line segment detection principles, and all the detection principles are that pixel points with similar gradient strength and direction in the whole image are clustered, so that the pixel points are aggregated into line segments. The clustering algorithm is a graph-based algorithm, each pixel point in an image is a graph node, two adjacent pixel points have an edge, the weight of the edge represents the difference value of the adjacent pixel points in the gradient direction, and then all the edges are sequenced according to the weight of the edge and are subjected to edge combination.
2) Then, quadrangle detection is carried out, after all line segments are detected, grouping is carried out through distance thresholds of two adjacent edges, then all combination groups are traversed in four layers by utilizing a depth optimization search algorithm, and when a fourth layer is traversed, if a loop is detected to be formed by the last edge and the first edge, the path traversed to the node is a quadrangle;
the method specifically comprises the following steps: after all the line segments are detected, the line segments are grouped, when the distance between the tail end of the previous edge and the start end of the next edge is within a certain threshold value and the direction of the connected line segments is in the counterclockwise direction, the two line segments can be contained as a group, and each group of line segments is a candidate which is possible to form a quadrilateral loop. And when the tree is traversed to the fourth layer, if a loop is formed by the last edge and the first edge, the path traversed to the node is a quadrangle.
3) The position and attitude of the Openmv4 sensor relative to the Apriltag identification code is extracted via image information after the Apriltag identification code is successfully captured.
The method specifically comprises the following steps: the pose calculation is related to the focal length of a camera of an Openmv4 sensor and the actual physical distance of an identification code, the two quantities are usually measured and calibrated before pose estimation, and then a homography matrix is calculated by utilizing Direct Linear Transform (DLT) to obtain the information such as the position and the pose of the unmanned aerial vehicle. A 3 × 3 homography may be represented by the product of a 3 × 4 camera internal reference matrix P and a 4 × 3 external reference matrix E:
in the formula, the homography matrix h is the mapping from the homogeneous coordinates of four corner points in the two-dimensional code coordinate system to the coordinates of the four corner points of the image two-dimensional code,sis a scale factor, and is a function of,f x 、f y is the focal length of the camera head,f x =f y ；R ij is a rotation matrix parameter; t is k For shifting the matrix parameters, T x As a translation matrix parameter in the x-direction, T y As a translation matrix parameter in the y-direction, T z The position and the posture of the camera relative to the Apriltag identification code can be obtained by solving the equation for the translation matrix parameter in the z direction.
In step S1, Openmv4 optical flow position informationPos FLOW The displacement of two frames of images is calculated through an Openmv4 sensor, so that the quad-rotor unmanned aerial vehicle is positioned.
Optical flow positioning (obtaining Openmv4 optical flow position information)Pos FLOW ) The displacement of two frames of images is calculated through an Openmv4 sensor, so that the quad-rotor unmanned aerial vehicle is positioned. In the optical flow theory, the premise is that the following two assumptions are established 1) the gray level of pixels between two frames of images acquired by a camera is unchanged; 2) the adjacent two frame pixels have relative motion. When the unmanned aerial vehicle attitude control method is used, only some points in the image need to be tracked, the optical flow vector can be calculated by adopting the method, the attitude control of the unmanned aerial vehicle can be further optimized according to the obtained optical flow vector, and more accurate control is realized.
S2, automatically switching to a landing mode when the aircraft catches the ground, and if the time is greater than a set time thresholdT th And if the aircraft does not find the landmark, the aircraft enters a fixed point mode to be taken over by the flying hand, namely the unmanned aerial vehicle keeps the current position and height unchanged.
In the invention, when the descending of the landmark aircraft is setThe maximum descending speed is 30cm/s, the initial descending height is set to be 2m according to the set focal length of the Openmv4 sensor, and when the airplane is 1m away from the ground, the laser range finder has good working state and can be switched to a fixed point mode rapidly, so that the time threshold value is setT th Set to 3 s.
S3, after entering the falling mode, firstly, according to the horizontal position errorError x,y Obtaining maximum error of horizontal positionError max x,y Switching a fault-tolerant position controller, wherein the fault-tolerant position controller takes the horizontal position offset acquired by an Openmv4 sensor as a control target, or the fault-tolerant position controller takes the horizontal position offset acquired by an Openmv4 sensor and the horizontal position information of a GPS module superposed as the control target; then, the horizontal position control is carried out to keep the horizontal position errorError x,y At a set thresholdPos th Within the range;
in step S3, horizontal position errorError x,y The expression is:
wherein,Pos GPS1 for the unmanned aerial vehicle error calculation period start time GPS signal horizontal position information,Pos GPS2 calculating GPS signal horizontal position information for the unmanned aerial vehicle error at the end of the period,Pos openmv the horizontal position offset of the lens, which is the Openmv4 sensor, with respect to the Apriltag center point.
The Openmv4 sensor offsets the horizontal position of the lens from the center point of ApriltagPos openmv Transmitted to a flight controller and superposed to the horizontal position information of the current GPS signalPos GPS1 Upper as target positionPos target Then subtract the current GPS positionPos GPS2 Obtaining a horizontal position errorError x,y And transmitting the signal to a PID controller for control. Ensure higher reduction for overcoming the defects of easy interference and large error of a GPS moduleSetting fault-tolerant position controller according to the error of horizontal positionError x,y Obtaining maximum error of horizontal positionError max x,y And switching the fault-tolerant position controller, wherein the fault-tolerant position controller takes the horizontal position offset acquired by an Openmv4 sensor as a control target, or the fault-tolerant position controller takes the horizontal position offset acquired by an Openmv4 sensor and the horizontal position information of the GPS module superposed as the control target. And when the horizontal position error is larger than 50cm, only using the horizontal position offset acquired by the Openmv4 sensor as a control target, otherwise, using the horizontal position offset acquired by the Openmv4 sensor and overlapping the horizontal position information of the GPS module as the control target by adopting a fault-tolerant position controller. Maximum error of horizontal positionError max x,y The focal length of the lens of the Openmv4 sensor used in the invention is 3.2mm, Apriltag is TAG36H11, the frame is 97mm, the Openmv4 sensor is calculated to take the center of a landmark as the origin in the horizontal direction, the distance of Apriltag recognized at the farthest left and right is 50cm, so the maximum error of the horizontal position is calculatedError max x,y Greater than 50cm indicates that the GPS generates drift which is much greater than the relative coordinates solved by the Openmv4 sensor, which will cause the unmanned aerial vehicle to lose landmark, so that the fault-tolerant control will improve the positioning accuracy of the aircraft in weak GPS and GPS drift.
Make the aircraft horizontal position error in the descending processError x,y Always kept at the threshold valuePos th In the invention, the optimal threshold value is setPos th 5cm, provided that the horizontal position error is taken into accountError x,y And the next step of height control can be executed within 5cm, so that the landmark is prevented from being separated from the visual field of the unmanned aerial vehicle due to accumulated errors of the horizontal position in the descending process.
S4, controlling the altitude according to the altitude information obtained by the laser range finder, adopting different control strategies according to the altitude of the aircraft, and when the altitude of the aircraft is greater than the altitude threshold valueAlt th Continues to execute steps S3 and S4; when the height of the aircraft is lower than the set height thresholdAlt th In time, the aircraft shuts off the motor and lands on the landing platform.
The step is mainly height control in the process of aircraft landing, and the height controller is combined with the horizontal position controllers in the steps S3 and S4 to cooperatively control the aircraft to land accurately. When the aircraft recognizes a landmark and the height is more than 15cm, the aircraft executes a horizontal position controller to keep the horizontal position error within 5cm, then executes a height PID controller to descend, and the operation is circulated until the height is less than 15cm and the horizontal position error is within 5cm, the aircraft shuts down a motor and lands on a landing platform, and the strategy can solve the problems of position deviation, fuselage bounce and the like caused by ground effect during landing of the aircraft. Height thresholds were set according to the Openmv4 sensor focal length and Apriltag size at the time of the experiments of the present inventionAlt th In 15cm, in one embodiment of the invention, the aircraft loses the landmark after being 12cm away from the landmark, the relative coordinate can be normally calculated at 15cm, and experiments prove that the unmanned aerial vehicle can stably land on the ground without bouncing phenomenon caused by too high height when the unmanned aerial vehicle freely falls to the ground under the condition of turning off the motor below 15cm, so that the height threshold value is setAlt th Is 15 cm.
During specific implementation, hardware comprises a 350mm rack, an Openmv4 sensor, a Beixing luna laser range finder, a WIFI wireless data transmission, an Apriltag 36H11 landmark and the like. The method comprises the steps that firstly, an aircraft flies 2m above a landmark and hovers, the aircraft automatically switches to a landing mode after searching the landmark, and the aircraft lands in stages by adopting a landing method of the four-rotor unmanned aerial vehicle accurate landing system based on fault-tolerant control until the aircraft is lower than 15cm in height and the aircraft is locked in the air motor and freely falls onto the landmark when the horizontal position error is 5 cm. A large number of experiments prove that the system and the method provided by the invention can ensure that the normal falling precision of the aircraft under weak GPS and GPS signals is within 10 cm.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. Accurate descending system of four rotor unmanned aerial vehicle based on fault-tolerant control, its characterized in that: the aircraft carries the flight controller and the laser range finder, the visual sensor is an Openmv4 sensor, APM firmware is arranged in the flight controller, the laser range finder provides accurate distance information for the flight controller, the Openmv4 sensor acquires relative coordinates by identifying landmarks on a landing platform, the landmarks on the landing platform adopt Apriltag identification codes, the flight controller receives the relative coordinates of the landmarks on the landing platform and transmits the relative coordinates to the fault-tolerant position controller, and the fault-tolerant position controller ensures that the GPS module can still land on the landing platform successfully under weak GPS signals; the method for landing the precise landing system of the quad-rotor unmanned aerial vehicle based on fault-tolerant control comprises the following steps:
s1, controlling the unmanned aerial vehicle to hover above a landmark on the landing platform, searching the landmark, analyzing the position of the landmark Apriltag by an Openmv4 sensor, analyzing the offset between the landmark and the Openmv4 sensor in a pixel coordinate system after the Openmv4 sensor obtains an image frame, and finally obtaining the coordinate in the unmanned aerial vehicle navigation coordinate system through coordinate conversion; altitude information at search timePos z From laser rangefindersH lid Horizontal position informationPos is based on GPS signal quality and aircraft horizontal position errorError x,y Selecting each position information source, horizontal position informationPos being the GPS positionPos GPS Or Openmv4 optical flow location informationPos FLOW ；
S2, automatically switching to a landing mode when the ground is captured by the aircraft, and if the ground is greater than a set time threshold valueT th If the aircraft does not find the landmark, the aircraft enters a fixed point mode;
s3, after entering the falling mode, firstly, according to the horizontal position errorError x,y Get horizontalMaximum error of positionError max x,y Switching a fault-tolerant position controller, wherein the fault-tolerant position controller takes the horizontal position offset acquired by an Openmv4 sensor as a control target, or the fault-tolerant position controller takes the horizontal position offset acquired by an Openmv4 sensor and the horizontal position information of a GPS module as the control target; then, the horizontal position control is carried out to keep the horizontal position errorError x,y At a set thresholdPos th Within the range;
s4, controlling the altitude according to the altitude information obtained by the laser range finder, when the altitude of the aircraft is larger than the altitude threshold valueAlt th Continuously executing the steps S3 and S4 when the altitude of the aircraft is lower than the set altitude thresholdAlt th In time, the aircraft shuts off the motor and lands on the landing platform.
2. The fault tolerant control based quad-rotor unmanned aerial vehicle precision landing system of claim 1, wherein: accurate descending system of four rotor unmanned aerial vehicle based on fault-tolerant control still includes the wireless data transmission of WIFI, and the wireless data transmission of WIFI is used for communicating with ground.
3. The four-rotor unmanned aerial vehicle precise landing system based on fault-tolerant control of claim 1, wherein: in step S1, height information at the time of searchPos z The expression is:
Pos z = H lid
horizontal position information at the time of searchPos, the expression is:
wherein,H lid for the height measured by the laser rangefinder during the search,Pos GPS for GPS position, G, acquired by the GPS module PDOP And distributing space geometric intensity factors for the GPS module according to the satellites.
4. The four-rotor unmanned aerial vehicle precise landing system based on fault-tolerant control of claim 3, wherein: in step S1, the step of the Openmv4 sensor performing position analysis on the landmark Apriltag is:
1) after the Openmv4 sensor identifies Apriltag, firstly, carrying out line segment detection, and clustering pixel points with similar gradient intensity and direction in the whole image by using the line segment detection so as to gather the pixel points into line segments;
2) then, quadrangle detection is carried out, after all line segments are detected, grouping is carried out through distance thresholds of two adjacent edges, then all combination groups are traversed in four layers by utilizing a depth optimization search algorithm, and when a fourth layer is traversed, if a loop is detected to be formed by the last edge and the first edge, the path traversed to the node is a quadrangle;
3) the position and attitude of the Openmv4 sensor relative to the Apriltag identification code is extracted via image information after the Apriltag identification code is successfully captured.
5. The fault-tolerant control-based precision landing system for quad-rotor unmanned aerial vehicles according to claim 4, wherein: in step S1, Openmv4 optical flow position informationPos FLOW The displacement of two frames of images is calculated through an Openmv4 sensor, so that the quad-rotor unmanned aerial vehicle is positioned.
6. The fault-tolerant control-based precision landing system for quad-rotor unmanned aerial vehicles according to claim 5, wherein: in step S3, horizontal position errorError x,y The expression is:
wherein,Pos GPS1 for the unmanned aerial vehicle error calculation period start time GPS signal horizontal position information,Pos GPS2 GPS signal water for unmanned aerial vehicle error calculation period end timeThe information of the horizontal position is displayed on the display,Pos openmv the horizontal position offset of the lens, which is the Openmv4 sensor, with respect to the Apriltag center point.
7. The fault-tolerant control-based precision landing system for quad-rotor unmanned aerial vehicles according to claim 6, wherein: in the landing process of the unmanned aerial vehicle, a stage control strategy of firstly carrying out horizontal alignment and then carrying out height control is adopted, and a strategy of offsetting ground effect by locking an aerial motor is adopted in the final landing stage.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210645880.2A CN114740900B (en) | 2022-06-09 | 2022-06-09 | Four-rotor unmanned aerial vehicle accurate landing system and method based on fault-tolerant control |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210645880.2A CN114740900B (en) | 2022-06-09 | 2022-06-09 | Four-rotor unmanned aerial vehicle accurate landing system and method based on fault-tolerant control |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN114740900A CN114740900A (en) | 2022-07-12 |
| CN114740900B true CN114740900B (en) | 2022-09-06 |
Family
ID=82287406
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202210645880.2A Active CN114740900B (en) | 2022-06-09 | 2022-06-09 | Four-rotor unmanned aerial vehicle accurate landing system and method based on fault-tolerant control |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN114740900B (en) |
Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103226356A (en) * | 2013-02-27 | 2013-07-31 | 广东工业大学 | Image-processing-based unmanned plane accurate position landing method |
| CN104166854A (en) * | 2014-08-03 | 2014-11-26 | 浙江大学 | Vision grading landmark locating and identifying method for autonomous landing of small unmanned aerial vehicle |
| CN106054931A (en) * | 2016-07-29 | 2016-10-26 | 北方工业大学 | Unmanned aerial vehicle fixed-point flight control system based on visual positioning |
| CN106970651A (en) * | 2017-06-06 | 2017-07-21 | 南京理工大学泰州科技学院 | A kind of the autonomous flight system and control method of four rotor wing unmanned aerial vehicles of view-based access control model navigation |
| CN110595476A (en) * | 2019-08-30 | 2019-12-20 | 天津航天中为数据***科技有限公司 | Unmanned aerial vehicle landing navigation method and device based on GPS and image visual fusion |
| CN111003192A (en) * | 2019-12-30 | 2020-04-14 | 南京信息工程大学 | Unmanned aerial vehicle autonomous landing system and landing method based on GPS and vision |
| CN113973606A (en) * | 2021-10-28 | 2022-01-28 | 塔里木大学 | Intelligent control system and method for cotton topping unmanned aerial vehicle |
-
2022
- 2022-06-09 CN CN202210645880.2A patent/CN114740900B/en active Active
Patent Citations (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103226356A (en) * | 2013-02-27 | 2013-07-31 | 广东工业大学 | Image-processing-based unmanned plane accurate position landing method |
| CN104166854A (en) * | 2014-08-03 | 2014-11-26 | 浙江大学 | Vision grading landmark locating and identifying method for autonomous landing of small unmanned aerial vehicle |
| CN106054931A (en) * | 2016-07-29 | 2016-10-26 | 北方工业大学 | Unmanned aerial vehicle fixed-point flight control system based on visual positioning |
| CN106970651A (en) * | 2017-06-06 | 2017-07-21 | 南京理工大学泰州科技学院 | A kind of the autonomous flight system and control method of four rotor wing unmanned aerial vehicles of view-based access control model navigation |
| CN110595476A (en) * | 2019-08-30 | 2019-12-20 | 天津航天中为数据***科技有限公司 | Unmanned aerial vehicle landing navigation method and device based on GPS and image visual fusion |
| CN111003192A (en) * | 2019-12-30 | 2020-04-14 | 南京信息工程大学 | Unmanned aerial vehicle autonomous landing system and landing method based on GPS and vision |
| CN113973606A (en) * | 2021-10-28 | 2022-01-28 | 塔里木大学 | Intelligent control system and method for cotton topping unmanned aerial vehicle |
Also Published As
| Publication number | Publication date |
|---|---|
| CN114740900A (en) | 2022-07-12 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP7141403B2 (en) | Laser scanner with real-time online self-motion estimation | |
| CN113359810B (en) | Unmanned aerial vehicle landing area identification method based on multiple sensors | |
| US20200344464A1 (en) | Systems and Methods for Improving Performance of a Robotic Vehicle by Managing On-board Camera Defects | |
| Krajník et al. | A practical multirobot localization system | |
| US11019322B2 (en) | Estimation system and automobile | |
| Heng et al. | Autonomous visual mapping and exploration with a micro aerial vehicle | |
| Merino et al. | Vision-based multi-UAV position estimation | |
| Martínez et al. | On-board and ground visual pose estimation techniques for UAV control | |
| CN102967305B (en) | Multi-rotor unmanned aerial vehicle pose acquisition method based on markers in shape of large and small square | |
| CN109270953A (en) | A kind of multi-rotor unmanned aerial vehicle Autonomous landing method based on concentric circles visual cues | |
| US20190243376A1 (en) | Actively Complementing Exposure Settings for Autonomous Navigation | |
| CN109212545A (en) | Multiple source target following measuring system and tracking based on active vision | |
| Li et al. | UAV autonomous landing technology based on AprilTags vision positioning algorithm | |
| Haala et al. | Dense multiple stereo matching of highly overlapping UAV imagery | |
| US10642272B1 (en) | Vehicle navigation with image-aided global positioning system | |
| KR102289752B1 (en) | A drone for performring route flight in gps blocked area and methed therefor | |
| EP3989034B1 (en) | Automatic safe-landing-site selection for unmanned aerial systems | |
| US20200167953A1 (en) | Image Sensor Initialization in a Robotic Vehicle | |
| CN114815871A (en) | Vision-based autonomous landing method for vertical take-off and landing unmanned mobile platform | |
| CN116578035A (en) | Rotor unmanned aerial vehicle autonomous landing control system based on digital twin technology | |
| CN109764864B (en) | Color identification-based indoor unmanned aerial vehicle pose acquisition method and system | |
| CN114740900B (en) | Four-rotor unmanned aerial vehicle accurate landing system and method based on fault-tolerant control | |
| Chen et al. | Robust autonomous landing of UAVs in non-cooperative environments based on comprehensive terrain understanding | |
| Stathoulopoulos et al. | Redundant and Loosely Coupled LiDAR-Wi-Fi Integration for Robust Global Localization in Autonomous Mobile Robotics | |
| US20220413519A1 (en) | Light emitting device positional tracking for mobile platforms |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |