CN117245911B

CN117245911B - Aerial 3D printing robot and printing method thereof

Info

Publication number: CN117245911B
Application number: CN202311529369.7A
Authority: CN
Inventors: 李勇奇; 曹华姿; 赵世钰
Original assignee: Westlake University
Current assignee: Westlake University
Priority date: 2023-11-16
Filing date: 2023-11-16
Publication date: 2024-02-09
Anticipated expiration: 2043-11-16
Also published as: CN117245911A

Abstract

The invention discloses an aerial 3D printing robot and a printing method thereof, and relates to the technical field of unmanned aerial vehicles and 3D printing. According to the aerial 3D printing robot and the printing method thereof, the unmanned aerial vehicle is used as a carrier, space limitation of 3D printing is eliminated, and a tethered 3D printing device is mounted; the additive manufacturing method can realize additive manufacturing of large objects and building houses, and can be applied to repairing walls and high-altitude objects.

Description

Aerial 3D printing robot and printing method thereof

Technical Field

The invention relates to the technical field of unmanned aerial vehicles and 3D printing, in particular to an aerial 3D printing robot and a printing method thereof.

Background

Conventional 3D printing techniques typically print in a single degree of freedom in a fixed area, which limits the size and complexity of the object. In addition, conventional 3D printing materials are generally relatively thin and suitable for manufacturing precision parts, but are not suitable for manufacturing large objects. With the continued advancement of manufacturing technology, there is a growing need to be able to print in multiple degrees of freedom. For example, in the field of construction, there is a need to be able to print in different directions to enable additive manufacturing of large buildings.

Building additive manufacturing is a technology with great potential, and has attracted wide attention in the building field. However, conventional building processes require a lot of labor and time, and faster, efficient and accurate building manufacturing can be achieved using 3D printing techniques, while reducing waste.

The construction robot carrying the mechanical arm repairing operation mechanism replaces construction workers to finish the work of high-temperature and high-harm environments, so that the accident rate can be greatly reduced, the construction cost is reduced, and the operation efficiency is improved. However, when repairing a building, the following technical difficulties often exist:

(one) downwash effect: in the process of aerial 3D printing by unmanned aerial vehicles, the negative impact of downwash airflow on the printing process is a critical technical challenge. Such downwash is due to the rotating propeller of the unmanned aerial vehicle, which may disturb the surrounding environment, thereby affecting the accurate positioning, adhesion and accuracy of the 3D printed material, ultimately affecting the printing quality and the performance of the final product.

In conventional 3D printing techniques, the printing process is performed in a relatively stable environment, with the material being deposited on a fixed platform, so that positioning and attachment are relatively easy to control. However, aerial 3D printing introduces unmanned aerial vehicle motion and airflow disturbances, making the printing process more complex.

(II) end nozzle collision problem: during aerial 3D printing, control accuracy and errors of the drone may cause the end nozzles to come into contact and collide with the surrounding environment (e.g., walls or floors), which may cause serious problems including nozzle damage, print material damage, and overall print quality degradation.

Disclosure of Invention

The invention aims to provide an aerial 3D printing robot and a printing method thereof, which aim to solve two problems of influence of downwash air flow and collision of tail end nozzles in an aerial 3D printing process. And the unmanned aerial vehicle is used as a carrier, so that the space limitation of 3D printing is eliminated, and the tethered 3D printing device is mounted. The robot can realize additive manufacturing of large objects and building houses, and can be applied to repairing walls and high-altitude objects.

In order to achieve the above purpose, the invention provides an aerial 3D printing robot, which comprises an unmanned aerial vehicle body, a mechanical arm, a 3D printing system and an automatic control system, wherein the mechanical arm is arranged on the lower side of the unmanned aerial vehicle body, and the automatic control system is arranged on the upper side of the unmanned aerial vehicle body;

the 3D printing system comprises a tethered feeding device and a damping printing nozzle, the tethered feeding device comprises a dispensing machine, the dispensing machine is connected with an onboard storage bottle arranged on one side of an unmanned aerial vehicle body through a first feeding hose, a quick connection socket is arranged at the bottom of the onboard storage bottle, the quick connection socket is connected with the damping printing nozzle through a second feeding hose, and the other end of the dispensing machine is connected with the feeding machine through a third feeding hose; the upper part of the machine-mounted storage bottle is sleeved with an upper fixing ring, and the lower part of the machine-mounted storage bottle is sleeved with a lower fixing ring;

the damping printing nozzle comprises a base shell, the upper portion of the base shell is connected with a flange plate, a through hole matched with a second feeding hose is formed in the flange plate, the bottom of the base shell is connected with a funnel-shaped windshield, a shell sealing cover is arranged at the joint of the base shell and the funnel-shaped windshield, a laser ranging sensor is connected to the lower side of the shell sealing cover, a spring is arranged inside the base shell, the spring is sleeved on the nozzle, a quick connector is arranged at the upper end of the nozzle, a film pressure sensor is arranged at the bottom end of the nozzle, the nozzle penetrates through the middle of the shell sealing cover, and the bottom of the nozzle is located at the lower side of the bottom of the windshield.

Preferably, the mechanical arm comprises a Delta mechanical arm and a triaxial serial mechanical arm, the Delta mechanical arm comprises a top plate connected with an unmanned aerial vehicle body, a steering engine is arranged on the lower side of the top plate, a steering engine shell is arranged on the outer side of the steering engine, an output shaft of the steering engine is connected with the upper end of an upper arm through a shaft column, the lower end of the upper arm is connected with the upper end of a lower arm, and the lower end of the lower arm is connected with an annular chassis;

the triaxial serial mechanical arm comprises a base joint connected with the bottom of the annular chassis, an elbow joint is connected to the lower side of the base joint, and a wrist joint is connected to the lower side of the elbow joint.

Preferably, the upper side of the flange plate is connected with the bottom of the wrist joint.

Preferably, the automatic control system comprises a hardware part, wherein the hardware part comprises an airborne computer NUC, PX4 flight control, an airborne control board and a ground control board, the flight control PX4 is responsible for flight control of the unmanned aerial vehicle, the airborne control board is responsible for control and data processing of the mechanical arm and the damping printing nozzle, the ground control board controls the ground dispensing machine, the flight control PX4 and the airborne control board are in communication with the airborne computer NUC through a USB, and the ground control board is in communication with the airborne computer NUC through a wireless Bluetooth.

Preferably, the side face of the unmanned aerial vehicle body is further provided with a vision camera.

The invention also provides an aerial 3D printing method, which comprises the following steps:

s1, acquiring environment information through a vision camera, wherein the environment information comprises position information of a target printing surface and surrounding barrier information;

s2, calculating a V-shaped area of the downward washing air flow by analyzing the rotating speed of the motor, and controlling the mechanical arm to enable the damping printing nozzle to be positioned in the V-shaped area of the downward washing air flow according to an air flow analysis algorithm;

s3, acquiring the distance between the tail end of the damping printing nozzle and the target printing surface through a laser ranging sensor, and acquiring the pressure between the tail end of the damping printing nozzle and the target printing surface through a film pressure sensor;

s4, according to the 3D model to be printed, comprehensively using the position information acquired by the RTK and the environment information detected by the vision camera, and calculating an optimal printing path suitable for the current environment according to a path planning algorithm by combining the distance information acquired by the laser ranging sensor acquired in the step S3, the pressure information acquired by the film pressure sensor and the V-shaped area position information of the washing air flow acquired in the step S2.

Preferably, the airflow analysis algorithm comprises:

s21, acquiring rotation speed information of a motor of the unmanned aerial vehicle through a flight control system;

s22, calculating the speed of the washing air flow, wherein the calculation formula is as follows:

；

wherein,indicating the velocity of the downwash stream;Nis the rotation speed of the unmanned aerial vehicle motor;ρis the air density in the current environment;cthe method is used for describing the coefficient of performance of the blade when generating air flow, and takes the shape and aerodynamic characteristics of the blade into consideration;Kis a coefficient;

s23, determining the direction of the downward washing air flow according to the position, the direction and the angle of the blade of the unmanned aerial vehicle;

s24, calculating a V-shaped area formed by the washing air flow according to the speed of the washing air flow calculated in the step S22, the direction of the washing air flow calculated in the step S23 and the geometric shape of the motor rotor wing:

；

wherein,h(x)representing the height of the downwash, i.e., the distance from the unmanned aerial vehicle blade to the downwash;Dis the diameter of the motor rotor;xis the distance along the horizontal direction from the center position of the motor rotor;

s25, combining current position and attitude information of the unmanned aerial vehicle, and adjusting the position of the tail end nozzle to the upper part of the V-shaped area of the downward washing airflow by solving the angle of each joint of the mechanical arm, so that the interference of the airflow on materials is reduced.

Preferably, the path planning algorithm comprises:

s31, data acquisition:

(1) Extracting key information from a 3D model to be printed, wherein the key information comprises a starting point, a terminal point and barrier information;

(2) Acquiring position information of the unmanned aerial vehicle by using an RTK system;

(3) The vision camera detects the surrounding environment, including the position and the gesture of the obstacle;

(4) Invoking an airflow analysis algorithm, and calculating the position and the range of a V-shaped optimal printing area formed by the washing airflow;

s32, constructing an environment map by combining data acquired by a vision camera, a laser ranging sensor and a film pressure sensor, and marking obstacles and a safety area;

s33, calculating the space distance from the starting point to the end point through a distance measurement algorithm, and searching a path from the starting point to the end point in an environment map by using an A-path searching algorithm; during the searching process, avoiding the obstacle is considered, and the path is kept in the V-shaped area as much as possible;

distance measurement:

；

wherein,drepresenting the distance; (x_1, y_1, z_1) is the coordinates of the start point; (x_2, y_2, z_2) is the coordinates of the target point;

path search algorithm:

；

wherein,h(node)is a heuristic function for estimating slave nodesnodeCost to the target location;xtarget、 ytargetandztargetis the coordinates of the target location;xnode、ynodeandznodeis a nodenodeCoordinates of (c);

s34, according to an objective function, comprehensively considering the length of the path, the distance between the path and an obstacle, the distance between the end nozzle and the pressure data, and evaluating and sequencing the searched path;

；

wherein,F(path)an objective function for evaluating the comprehensive performance of the path;w ₁ 、w ₂ 、w ₃ 、w ₄ is a weight coefficient;obstacle_avoidanceis associated withA measure of avoidance obstacle correlation;nozzle_distancerepresenting the distance of the end nozzle from the target print surface;pressure_datadata representing the pressure applied by the end nozzle;length(path)representing the path length;

s35, if the evaluation finds a better path, path optimization is carried out, and the path is smoothed through an interpolation method;

s36, in the printing process, monitoring data of a laser ranging sensor and a film pressure sensor in real time, and if the data exceeds a threshold value, adjusting the gesture of the mechanical arm, adjusting the tail end position of the damping printing nozzle, wherein the tail end adjusting formula of the damping printing nozzle is as follows:

；

wherein,new_positionrepresenting the new position of the damping print nozzle after adjustment;current_positionrepresenting the current position of the damping print nozzle;Δpositionindicating the amount of change in position that the damping print nozzle needs to adjust.

Therefore, the invention adopts the aerial 3D printing robot and the printing method thereof, and has the following technical effects:

(1) The problem that the downward washing air flow influences printing is solved. The operation of the 3D printing robot needs to be close to a target operation area, and the materials can be blown away by the downward air flow blown out by the unmanned aerial vehicle blade, and meanwhile, the ground effect can be caused in the process of flying close to the ground. The funnel-shaped wind shield is additionally arranged at the tail end of the nozzle, and the blown air flow is guided to the periphery, so that a stable air flow environment is formed below the wind shield. The mechanical arm is controlled to enable the tail end nozzle to be positioned in a V-shaped area with weak washing air flow through an aerial 3D printing method, and the two are combined to prevent the washing air flow and ground effect caused by blade rotation from blowing off 3D printing materials, so that the normal operation of 3D printing is protected;

(2) The problem of collision between the tail end of the nozzle and the target surface is solved. The damping printing nozzle is arranged, the nozzle at the tail end adopts a spring damping design, the nozzle is very close to the ground in the printing process, errors exist in control of the robot, and the damping design can play a role in protection when the nozzle impacts the ground; in the 3D printing process, a laser ranging sensor measures the distance between the bottom of a nozzle and a target printing surface, and is used for inputting data of a printing control algorithm and an anti-collision algorithm: the film pressure sensor measures the contact pressure at the bottom of the nozzle, and the data input for an anti-collision algorithm is used for preventing the collision between the terminal nozzle and the target surface through an aerial 3D printing method;

(3) The design of the quick-inserting interface has the advantage of easy disassembly, and the storage tube can be replaced conveniently;

(4) The problems of 3D printing material endurance and power source can be solved by using a tethered extrusion mode, and the scheme of an onboard motor is adopted, so that the pressure is too small and the motor is too heavy;

(5) The 3D printing material is a special configuration material, and the solidification time of the 3D printing material can be adjusted according to the proportion;

(6) Through the aerial 3D printing method, the problems that materials are blown away by the downward gas washing flow and the tail end of the nozzle collides with the target surface in the printing process are solved, the unmanned aerial vehicle can replace workers to finish high-risk environmental operation, high-altitude accidents are avoided, and the working efficiency is improved.

The technical scheme of the invention is further described in detail through the drawings and the embodiments.

Drawings

Fig. 1 is a schematic diagram of an aerial 3D printing robot;

FIG. 2 is a partial front view of the aerial 3D printing robot;

FIG. 3 is a cross-sectional view of a damping nozzle;

FIG. 4 is a flow chart of an aerial 3D printing method;

FIG. 5 is a diagram of a membrane pressure sensor algorithm;

FIG. 6 is a graph of an airflow analysis algorithm;

fig. 7 is a path planning algorithm diagram.

Reference numerals

1. An unmanned aerial vehicle body;

2. a mechanical arm; 21. delta mechanical arm; 211. a top plate; 212. steering engine; 213. steering engine shell; 214. an upper arm; 215. a lower arm; 216. an annular chassis; 22. the three shafts are connected in series with the mechanical arm; 221. a base joint; 222. an elbow joint; 223. a wrist joint;

3. a 3D printing system; 31. mooring the feeding device; 311. a dispensing machine; 312. a first feeding hose; 313. an onboard storage bottle; 314. a second feeding hose; 315. a third feeding hose; 316. a feeder; 317. a fixing ring at the upper part; 318. a lower fixing ring; 32. damping the printing nozzle; 321. a base housing; 322. a flange plate; 323. a funnel-shaped windshield; 324. a housing cover; 325. a laser ranging sensor; 326. a spring, 327, nozzle; 328. a membrane pressure sensor;

4. an automatic control system; 401. airborne computer NUC; 402. PX4 flight control; 403. an onboard control board; 404. and a ground control board.

Detailed Description

The technical scheme of the invention is further described below through the attached drawings and the embodiments.

Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.

Example 1

As shown in fig. 1, an aerial 3D printing robot includes an unmanned aerial vehicle body 1, a robot arm 2, a 3D printing device 3, and an automatic control system 4. In the embodiment, the four-rotor unmanned aerial vehicle is used as a carrier to realize an aerial 3D printing task. The lateral surface of the unmanned aerial vehicle body is also provided with a visual camera (not shown in the figure), and the visual camera is used for acquiring surrounding environment information.

As shown in fig. 2, the mechanical arm 2 is composed of a Delta mechanical arm 21 and a triaxial serial mechanical arm 22, and forms a six-degree-of-freedom control platform. The Delta mechanical arm 21 and the triaxial serial mechanical arm 22 form a pose moving unit, the top end of the Delta mechanical arm 21 is connected with the unmanned aerial vehicle body 1, and the bottom end of the Delta mechanical arm is connected with the triaxial serial mechanical arm 22; the mechanical arm unit is provided with a driving steering engine for driving the mechanical arm unit to move. Both the two mechanical arm structures belong to common technical means in the field, and the control method is optimized through research aiming at a 3D printing scene.

The design structure of the Delta mechanical arm 21 comprises a top plate 211, a steering engine shell 213, a steering engine 212, an upper arm 214, a lower arm 215 and an annular chassis 216. The top plate 211 is used as a base of the Delta mechanical arm 21 and is fixedly connected with the bottom of the unmanned aerial vehicle body 1 through a nylon stud, and the top plate 211 provides a stable support and a stable connection platform for the Delta mechanical arm 21.

Delta arm is provided with three, and three steering wheel shell 213 are fixed respectively on roof 211, and steering wheel shell 213 internally mounted has steering wheel 212, and steering wheel shell 213 is used for bearing and fixing steering wheel 212, ensures the accuracy of arm motion. Each steering engine 212 is connected with an upper arm 214 through an output shaft thereof, the upper arm 214 is connected with a steering engine output shaft through an aluminum alloy shaft post, a lower arm 215 is connected with the upper arm 214 through a ball hinge, an annular chassis 216 is positioned at the bottom of the Delta mechanical arm 21, and is connected with the lower end of the lower arm 215 through a ball hinge.

The three-axis serial robot arm 22 has a configuration with three rotational joints, a base joint 221, an elbow joint 222, and a wrist joint 223, respectively. These joints cooperate to achieve complex positioning and movement. The base joint 221 (first axis) is located on the bottom surface of the annular chassis 216 and is connected to the fixed base of the mechanical arm. It allows the robot arm to rotate about a vertical axis in a horizontal plane for controlling the direction of rotation of the robot arm. An elbow joint 222 (second axis) is connected to the end of the base joint 221 to rotate the robot arm in a plane perpendicular to the base joint 221. This joint enables the robotic arm to be raised and lowered in a vertical direction. A wrist joint 223 (third axis) is connected to the end of the elbow joint 222, allowing the robot arm to rotate in a plane perpendicular to the elbow joint 222. Wrist joint 223 controls the positioning and orientation of the end effector of the robotic arm.

Six-degree-of-freedom control of the pose moving unit is achieved by a combination of a Delta mechanical arm 21 and a triaxial serial mechanical arm 22. The Delta robot 21 is responsible for the movement at X, Y, Z and the tri-axial serial robot 22 is responsible for the pitch, roll, yaw angle movement. The combination can simultaneously improve the stability of terminal printing, meets the printing requirements under different angle scenes, and is particularly suitable for solving the problem that the wall surface has different inclination angles.

In unmanned aerial vehicle organism design, selected four rotor unmanned aerial vehicle as carrier platform, this is the advanced technique of this field wide application. The core of the unmanned aerial vehicle carrier is an onboard computer NUC401 and a PX4 flight control 402. The onboard computer NUC401 takes on the computational tasks of upper layer applications, communications, planning and sensing algorithms, which provides a solid foundation for the intelligence and efficiency of the system. The PX4 flight control 402 is dedicated to calculating a control algorithm of the unmanned aerial vehicle to ensure the safety and stability of the flight.

The on-board computer NUC401 and the PX4 flight control 402 are directly connected through USB and realize efficient communication through a mavlink protocol. In addition, 10000mAh6S batteries are selected as energy sources for supply, and a power source mooring technology can be adopted according to requirements so as to meet the power requirements of different flight tasks.

The unmanned aerial vehicle's selection has brought the flexibility of multidimension for aerial 3D printing robot. The vertical take-off, landing and hovering functions enable the aircraft to fly freely in three-dimensional space, so that the aircraft can easily reach different heights and positions. This feature strongly overcomes the space limitations of conventional 3D printing machines, providing convenience for achieving a wider print job.

The 3D printing system 3 is a key component comprising a tethered feed device 31 and a dampened printing nozzle 32, aimed at achieving accurate feeding and fine ejection of material.

The tethered feed device 31 includes a feeder 316, a dispenser 311, a first feed hose 312, a second feed hose 314, a third feed hose 315, and an on-board storage bottle 313, which cooperate closely to ensure the accuracy and stability of the material supply. The feeder 316 and the dispenser 311 are powered by a 220V power supply and placed on the ground, the feeder 316 and the dispenser 311 are connected through a third feeding hose 315, the feeder 316 is responsible for providing required pressure, and the dispenser 311 can control the pressure and the extrusion switch. Both are tethered to an on-board storage bottle 313 on the unmanned aerial vehicle body 1 by a feeding hose so that material flows from the on-board storage bottle 313 to the damping print nozzle 32.

The on-board storage bottle 313 is a cylindrical container, the upper end of which is equipped with screw threads, and may be fitted with a cap. The lower end is conical, and a small outlet is formed in the tail end, so that the second feeding hose 314 can be connected with the damping printing nozzle 32 below through a quick inserting port of the outlet. The airborne storage bottle 313 is fixed in the side of unmanned aerial vehicle organism through the retainer plate of two 3D prints. The upper fixing ring 317 is slightly larger than the outer diameter of the on-board storage bottle 313, and the on-board storage bottle 313 passes through the upper fixing ring 317 from bottom to top, thereby preventing toppling. The lower fixing ring 318 is slightly smaller than the outer diameter of the onboard storage bottle 313, and supports the bottom of the onboard storage bottle 313 to keep stable. The top cover of the onboard storage bottle 313 has a quick-connect interface that can be connected to the floor dispenser 311 via a second feeding hose 314. The operation of the printing device buffers the materials in the material supply process so as to ensure that the materials can flow uniformly when being extruded from the printing nozzle, thereby ensuring the printing quality.

The ground control board 404 is electrically connected with the feeder 316 through a relay. The ground control board 404 can control the switch of the feeder and the pressure of the dispenser 311. The control board also communicates wirelessly with the onboard computer NUC401 in the automatic control system via bluetooth, thereby realizing remote control. In this way, after receiving the control instruction of the airborne computer NUC401, the singlechip can control the on-off of the relay, thereby controlling the switch of the feeder 316 and realizing the real-time remote control of the operation of the 3D printing device.

Damping print nozzle 32 is a critical component in a 3D printing system. As shown in fig. 3, the damped print nozzle 32 includes a base housing 321, a flange 322, a housing cover 324, a nozzle 327, a spring 326, a funnel-shaped windshield 323, a quick-connect fitting, a film pressure sensor 328, and a laser ranging sensor 325. The base housing 321 is a damped print body structure that dampens the print nozzles 32, and has a number of important functions. The top is provided with a flange 322 for connecting the damping print nozzle 32 with a triaxial serial mechanical arm assembly for accurate positioning. A small hole is provided in the middle for the feed hose to pass through to introduce printing material into the nozzle 327. Below the flange 322 is a cylindrical housing body of 70mm length and 19mm inner diameter, with a matching hollow housing cover 324 at the bottom to secure the overall nozzle structure closed.

The nozzle 327 is positioned in the base shell 321, the tail end just passes through the cover of the hollow shell, the top of the nozzle 327 is provided with a quick-inserting port for inserting a feeding hose, the main body part of the nozzle 327 is in a conical design, the inner diameter of the discharging port is smaller than that of the feeding port, the design is favorable for guiding flow, and the material flows out better, so that uniform spraying is ensured. The spring 326 is positioned within the base housing 321 and is sleeved on top of the nozzle 327, with its upper end in contact with the base housing 321 and its lower end in contact with the outer ring of the nozzle 327. The presence of the spring 326 effectively reduces nozzle vibration and improves print stability. The length of the spring 326 plus the length of the outer ring of the nozzle 327 makes it slightly longer than the base housing, thereby creating a damping effect that slows down the up and down movement of the nozzle. The inner diameter of the cylindrical housing is slightly larger than the outer diameter of the nozzle outer ring, and the hollow housing cover 324 forms a limit, so that the nozzle 327 can just move up and down in the base housing 321, and the nozzle 327 is prevented from contacting the ground during printing, thereby damaging the device. The funnel-shaped windshield 323 is positioned at the bottom of the nozzle and has a diameter of 120mm, so that the sprayed material is protected from the interference of the motor washing air flow and the ground effect, and the printing stability is ensured.

A film pressure sensor 328 is mounted at the end of the nozzle 327 for monitoring the contact pressure at the bottom of the nozzle 327 to adjust the position of the spray head and protect the spray head when needed. A laser ranging sensor 325 is mounted beside the nozzle 327 for measuring the distance between the nozzle 327 and the printing surface, thereby achieving precise control of the printing height and position. The two sensors are connected to an on-board control board 403 to achieve real-time acquisition of sensor measurement data, thereby ensuring stability and accuracy during printing.

The 3D printing material adopts a mixture of polydimethylsiloxanes 1700 and 184, the viscosity and plasticity of which can be adjusted by changing the ratio according to 4:1 is suitable for the 4mm feed hose used in this example.

The automatic control system 4 incorporates a plurality of hardware and software components to enable autonomous control and operation of the drone and 3D printing device, the hardware portions of the system including on-board computer NUCs 401, PX4 flight controls 402, on-board control boards 403, and ground control boards 404, and the software portions of the system including communication, control, application, planning, and sensing algorithms. The on-board computer NUC401 is responsible for high-level mission planning, sensing algorithms and application execution, which is the core decision unit of the system, and will implement autonomous decisions and control based on sensor data and external instructions. PX4 flight control 402 is responsible for flight control and attitude adjustment of the drone, which is a critical component in ensuring stable flight of the drone, receives data from sensors and controls motors to maintain the desired flight conditions. The onboard control board 403 takes over the control and data processing tasks of the robotic arm and the spray head, including the movement of the robotic arm, the control of the spray head, and the acquisition and processing of sensor data. The ground control board 404 controls the operation of the ground feeder and dispenser, starting and stopping the dispenser, and adjusting the relevant parameters.

Example two

As shown in fig. 4, the air 3D printing method can solve two problems of material blowing by a downward washing air flow and collision between the tail end of a nozzle and a target surface in the printing process. According to the method, the mechanical arm is controlled to enable the tail end nozzle to be located in a V-shaped area with weak washing air flow, the distance between the tail end nozzle and the target printing surface is measured through the laser ranging sensor, the tail end nozzle pressure data measured through the film pressure sensor are used for preventing the tail end nozzle from colliding with the target surface, the target information is recognized through the vision camera to plan a printing path, the position of the tail end nozzle is finally controlled, and the aerial 3D printing work is completed.

The aerial 3D printing method comprises the following specific steps:

s1, environment sensing and analysis: the surrounding environment is sensed comprehensively by using a series of environment sensors including laser ranging sensors, thin film pressure sensors, and visual sensing systems. The laser ranging sensor is used for measuring the distance between the tail end nozzle and the target printing surface, and the film pressure sensor is used for measuring the pressure exerted by the tail end nozzle on the target surface. At the same time, the vision camera can recognize the target printing position and surrounding obstacles. The data acquired by these sensors may be processed and analyzed by specific algorithms to provide accurate information of the environmental conditions.

S2, airflow analysis: the intensity and direction of the downwash stream were carefully analyzed. Because the position, the direction and the angle of the unmanned aerial vehicle blade are fixed, and the motor rotating speed and the air flow intensity show clear corresponding relation, the downward washing air flow can form a conical outward expansion pattern downwards from the motor rotor wing. In this configuration, the intersection of the two streams creates a V-shaped region, which is the most suitable region for operation. By analyzing the motor speed in detail, the V-shaped area of the downwash air flow is determined, and the tail end nozzle is arranged in the area, so that the interference of the downwash air flow to materials is effectively reduced.

S3, collision protection: and (3) monitoring the distance between the tail end nozzle and the target printing surface in real time by adopting distance data obtained by a laser ranging sensor. In the printing process, fine adjustment of the position of the tail end nozzle is realized through accurate mechanical arm control, so that the printing distance is accurately controlled, and the safe distance between the printing distance and the target surface is ensured. By the method, collision between the tail end nozzle and the target surface is effectively prevented, and stable printing process is guaranteed.

S4, path planning: according to the 3D model to be printed, position information acquired by RTK and environment information detected by a vision camera are comprehensively used, and the laser ranging sensor distance information, the pressure information of a film pressure sensor and the position information of a V-shaped area with weaker downwash air flow acquired by the steps are combined, so that an optimal printing path suitable for the current environment is calculated by a path planning algorithm, and the safety and stability of the printing path are ensured.

S5, real-time control and adjustment: the sensor data and the visual perception information are continuously monitored for changes throughout the printing process. And flexibly adjusting the gesture of the mechanical arm and the position of the tail end nozzle according to a preset algorithm decision. Such real-time adjustment not only ensures maintenance of print quality, but also effectively avoids potential collision risk, so that the entire printing process remains in a safe and high quality state.

The specific processes of the film pressure sensor, the airflow analysis algorithm and the path planning algorithm are as follows:

fitting algorithm of film pressure sensor

As shown in fig. 5, a film pressure sensor algorithm is shown.

And (3) data acquisition: first, a series of different force values known to be applied to the membrane pressure sensor are collected and the corresponding sensor output values are recorded. These data will be used to train the algorithm.

Data preprocessing: preprocessing the acquired data, including noise removal, normalization and smoothing. This will help to improve the accuracy and stability of the fitting algorithm.

Fitting model selection: a mathematical model of the relationship between the unitary linear model membrane pressure sensor output and the actual applied force is selected.

；

Wherein:yis a dependent variable (predicted value);xis an argument (input feature);mis a slope (coefficient) representing the degree of influence of the independent variable on the dependent variable;bis the intercept, representing the value of the argument at 0.

Fitting algorithm: the preprocessed data is fitted using a mathematical model. The best fit parameters are found using regression analysis methods so that the model can accurately predict the relationship between the sensor output and the actual applied force:

；

wherein:yis a dependent variable (predicted value);xis an argument (input feature);β ₀ is the intercept, representing the value of the argument at 0;β ₁ is a slope, representing the degree of influence of the independent variable on the dependent variable;εis an error term representing a random error that the model cannot fully interpret;

model verification: model verification is performed using a portion of the data that was not used in training. And (3) evaluating the accuracy and generalization capability of the fitting algorithm by comparing the sensor output predicted by the model with the actual measured value.

And (3) adjusting and optimizing: if the verification result is not ideal enough, the selection of the fitting model or the algorithm parameters can be adjusted, and the training and verification can be retrained to obtain better performance.

Real-time application: and embedding the fitted algorithm into a data processing flow of the film pressure sensor. In practical application, the output measured by the sensor is converted into an actually applied force value through the algorithm, and the obtained force value is finally input into an aerial 3D printing method.

(II) airflow analysis algorithm

As shown in fig. 6, which is a flow analysis algorithm diagram, a specific analysis process is as follows:

firstly, acquiring motor rotation speed information: the rotating speed information of the unmanned aerial vehicle motor can be obtained through a flight control system or a sensor.

Calculating the washing air flow speed: and calculating the strength of the washing air flow according to the formula of the rotating speed of the motor and the property of the related air flow. This may involve factors such as air density, blade shape, etc.

；

Wherein,indicating the velocity of the downwash stream;Nis the rotation speed of the unmanned aerial vehicle motor;ρthe air density in the current environment is influenced by factors such as temperature, air pressure and the like;cis a description of the coefficient of performance of the blade in generating the airflow, taking into account the shape and aerodynamic characteristics of the blade.KIs a coefficient.

Analyzing the direction of the air flow: and determining the main direction of the downwash air flow according to the position, the direction and the angle of the blade of the unmanned aerial vehicle.

Determining a V-shaped area: and determining a V-shaped area formed by the downwash air flow through a mathematical model and geometric calculation according to the calculated air flow intensity and direction and the geometric shape of the motor rotor wing.

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Wherein,h(x)representing the height of the downwash, i.e., the distance from the unmanned aerial vehicle blade to the downwash;Dis the diameter of the motor rotor;xis the distance in the horizontal direction from the center position of the motor rotor.

Adjusting the position of the nozzle: and combining the current position and the gesture information of the unmanned aerial vehicle, and adjusting the position of the tail end nozzle to the upper part of the V-shaped area of the downward washing airflow by solving the angle of each joint of the mechanical arm so as to reduce the interference of the airflow on materials.

(III) Path planning Algorithm

A path planning algorithm is shown in fig. 7.

And (3) data acquisition:

key information such as start point, end point and obstacle information is extracted from the 3D model to be printed.

An RTK system is used to obtain accurate positional information of the drone.

The visual perception system detects the surrounding environment, including the position and pose of the obstacle.

And (3) the position and the range of the V-shaped optimal printing area formed by the washing air flow are calculated by calling the air flow analysis algorithm.

Environmental analysis: and constructing an environment map by combining the data of the visual perception system and the data of the environment sensor, and identifying the obstacle and the safety area.

And (3) path searching: calculating the space distance from the starting point to the end point through a distance measurement algorithm, and searching a path from the starting point to the end point in an environment map by using an A-path searching algorithm. During the search, avoidance of obstacles is considered, and the path is kept as much as possible within the V-shaped region.

Distance measurement:

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path search algorithm:

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path evaluation: and according to the objective function, comprehensively considering the length of the path, the distance from the obstacle, the distance of the tail end nozzle, pressure data and the like, and evaluating and sequencing the searched path.

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Wherein,F(path)representing an objective function for evaluating the overall performance of the path;length(path)representing the path length;w ₁ 、w ₂ 、w ₃ 、w ₄ is a weight coefficient;obstacle_avoidanceis a measure related to avoidance of an obstacle;nozzle_ distancerepresenting the distance of the end nozzle from the target print surface;pressure_datapressure data applied by the tip nozzle is represented for preventing collision of the tip nozzle with the target surface. The smaller the pressure data, the safer the representation.

Path optimization: if the evaluation finds a better path, path optimization can be performed, and the path is smoothed by interpolation and other methods, so that acute angles and unstable conditions are avoided.

And (3) real-time adjustment: during the printing process, the data of the laser ranging sensor and the film pressure sensor are monitored in real time. If the data exceeds the threshold value, namely the distance between the tail end nozzles is too close or the pressure is too high, the gesture of the mechanical arm is adjusted immediately, and the position of the tail end nozzles is adjusted so as to avoid collision and maintain a stable printing process.

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Wherein,new_positionrepresenting the adjusted new position;current_positionis the current end nozzle position;Δpositionis the amount of change in position that needs to be adjusted.

In addition, the aerial 3D printing method comprises the following specific processes:

file sending and starting: the user sends the object file to be printed to the airborne computer NUC, and then starts the unmanned aerial vehicle, the feeder, the dispenser and the ground control panel. These devices are a critical part in achieving aerial 3D printing.

(II) printing path planning: and the airborne computer NUC calculates according to the incoming article file, plans a printing path and determines the motion trail of the 3D printing robot in the air.

And (III) flight control and positioning: the on-board computer NUC sends an instruction to the PX4 for flight control, and the unmanned aerial vehicle flies above the target printing area through technologies such as visual perception and the like, so that accurate positioning and flight control are ensured.

(IV) mechanical arm adjustment: and the airborne computer NUC sends an instruction to the airborne control board to control the steering engine of the delta mechanical arm to rotate so as to adjust the position of the mechanical arm with the tail end connected in series, so that the nozzle is close to the construction area. The direction of the nozzle is adjusted by controlling the rotation of the motors of the serial mechanical arms, so that the nozzle is ensured to be positioned on the normal line of the plane of the required repair area.

And (V) extruding printing materials: the on-board computer NUC sends an instruction to the ground control board, and the feeder and the glue dispenser are started. Through the buffering of storage bottle, 3D printing material is evenly extruded from the nozzle, realizes the layer by layer printing of object.

And (six) finishing printing: under the synergistic effect of the unmanned aerial vehicle, the mechanical arm, the 3D printing system and the automatic control system, the whole 3D printing process is completed layer by layer according to the planned path.

Therefore, the aerial 3D printing robot and the printing method thereof are adopted, the unmanned aerial vehicle is used as a carrier, the space limitation of 3D printing is eliminated, and a tethered 3D printing device is mounted; the robot can realize additive manufacturing of large objects and building houses, and can be applied to repairing walls and high-altitude objects.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention and not for limiting it, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that: the technical scheme of the invention can be modified or replaced by the same, and the modified technical scheme cannot deviate from the spirit and scope of the technical scheme of the invention.

Claims

1. The aerial 3D printing robot is characterized by comprising an unmanned aerial vehicle body, a mechanical arm, a 3D printing system and an automatic control system, wherein the mechanical arm is arranged on the lower side of the unmanned aerial vehicle body, and the automatic control system is arranged on the upper side of the unmanned aerial vehicle body;

the damping printing nozzle comprises a base shell, wherein the upper part of the base shell is connected with a flange plate, a through hole matched with a second feeding hose is formed in the flange plate, the bottom of the base shell is connected with a funnel-shaped windshield, a shell sealing cover is arranged at the joint of the base shell and the funnel-shaped windshield, a laser ranging sensor is connected to the lower side of the shell sealing cover, a spring is arranged in the base shell, the spring is sleeved on the nozzle, a quick connector is arranged at the upper end of the nozzle, a film pressure sensor is arranged at the bottom end of the nozzle, the nozzle penetrates through the middle of the shell sealing cover, and the bottom of the nozzle is positioned at the lower side of the bottom of the windshield;

the mechanical arm comprises a Delta mechanical arm and a triaxial serial mechanical arm, the Delta mechanical arm comprises a top plate connected with an unmanned aerial vehicle body, a steering engine is arranged on the lower side of the top plate, a steering engine shell is arranged on the outer side of the steering engine, an output shaft of the steering engine is connected with the upper end of an upper arm through a shaft column, the lower end of the upper arm is connected with the upper end of a lower arm, and the lower end of the lower arm is connected with an annular chassis;

the triaxial serial mechanical arm comprises a base joint connected with the bottom of the annular chassis, an elbow joint is connected to the lower side of the base joint, and a wrist joint is connected to the lower side of the elbow joint;

the upper side of the flange plate is connected with the bottom of the wrist joint;

the automatic control system comprises a hardware part, wherein the hardware part comprises an airborne computer NUC, PX4 flight control, an airborne control board and a ground control board, the flight control PX4 is responsible for flight control of the unmanned aerial vehicle, the airborne control board is responsible for control and data processing of the mechanical arm and the damping printing nozzle, the ground control board controls the ground dispenser, the flight control PX4 and the airborne control board are communicated with the airborne computer NUC through USB connection, and the ground control board is communicated with the airborne computer NUC through wireless Bluetooth connection;

the side face of the unmanned aerial vehicle body is also provided with a visual camera;

the method comprises the following steps:

s4, according to the 3D model to be printed, comprehensively using the position information acquired by the RTK and the environment information detected by the vision camera, and calculating an optimal printing path suitable for the current environment according to a path planning algorithm by combining the distance information acquired by the laser ranging sensor acquired in the step S3, the pressure information acquired by the film pressure sensor and the V-shaped area position information of the washing air flow acquired in the step S2;

the airflow analysis algorithm includes:

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2. An aerial 3D printing robot as defined in claim 1, wherein the path planning algorithm comprises:

s31, data acquisition:

distance measurement:

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path search algorithm:

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wherein,F(path)an objective function for evaluating the comprehensive performance of the path;w ₁ 、w ₂ 、w ₃ 、w ₄ is a weight coefficient;obstacle_ avoidanceis a measure related to avoidance of an obstacle;nozzle_distancerepresenting the distance of the end nozzle from the target print surface;pressure_datadata representing the pressure applied by the end nozzle;length(path)representing the path length;

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