Wall-climbing type detection robot for vertical storage tank and ultrasonic detection system

Abstract

The invention provides a wall-climbing type detection robot of a vertical storage tank and an ultrasonic detection system, and relates to the technical field of storage tank detection.The wall-climbing type detection robot comprises a bottom plate, two permanent magnet adsorption bodies are installed above the bottom plate in parallel, yoke magnets are arranged on one sides of the two permanent magnet adsorption bodies, motors are fixed to the four corners of the lower portion of the bottom plate, and the motors are fixed to the bottom of the bottom plate; mecanum wheels are fixed to the output ends of the four motors correspondingly. On the basis of storage tank structure analysis, it is determined that the loading capacity of the detection robot is 10 kg, the maximum moving speed is 2 m / min, the adaptive minimum curvature radius is 10 m, and it can be achieved that no detection omission exists on the tank wall of the storage tank, and the robot moves autonomously; the robot body adopts the scheme of permanent magnet adsorption and Mecanum wheel movement, kinematics analysis, statics analysis and dynamics analysis are conducted on the wall-climbing detection robot according to the structural characteristics and the movement mode of Mecanum wheels, and a driving motor is selected according to the analysis result.

Description

Technical Field

[0001] The present invention relates to the technical field of storage tank detection, and in particular to a wall-climbing detection robot and an ultrasonic detection system for a vertical storage tank. Background Art

[0002] With the increasing demand for energy storage, the number of large steel storage tanks in the fields of petroleum and petrochemicals has increased rapidly. Large steel storage tanks need to undergo quality and safety inspections from manufacturing to service. Once quality problems are found, they must be dealt with in a timely manner to avoid safety accidents. At present, the tank wall inspection of large storage tanks is still mainly based on traditional manual inspection. During the inspection process, scaffolding needs to be built around the storage tank in advance. Inspectors climb on the scaffolding to inspect the storage tank. This inspection method has the following disadvantages: 1) Manual inspection requires a large amount of human resources, including inspectors, safety supervisors, etc., and the economic cost is high. 2) The construction of scaffolding and equipment inspection are high-altitude operations, which are highly dangerous and pose safety hazards. 3) Inspectors carry inspection equipment at high altitudes for inspection, and the inspection efficiency is low. Summary of the invention

[0003] 1. Technical issues to be solved

[0004] In view of the deficiencies in the prior art, the present invention provides a wall-climbing inspection robot and an ultrasonic inspection system for a vertical storage tank, which solves the problem that the inspection of storage tanks is mainly based on manual spot checks, with low work efficiency and high missed detection rate.

[0005] (II) Technical solution

[0006] To achieve the above objectives, the present invention provides the following technical solutions: a wall-climbing inspection robot for a vertical storage tank, comprising a base plate, two permanent magnetic adsorption bodies are installed in parallel on the top of the base plate, a yoke magnet is provided on one side of the two permanent magnetic adsorption bodies, motors are fixed at the four corners below the base plate, and Mecanum wheels are fixed at the output ends of the four motors.

[0007] Preferably, a mounting member is installed on one side of the base plate.

[0008] Preferably, the motor is an MD60 brushed DC reduction motor, and the rated voltage of the motor is 24V, the reduction ratio is 1:18, and the rated speed is 175rpm.

[0009] Preferably, an ultrasonic inspection system for a wall-climbing inspection robot for a vertical storage tank, the wall-climbing robot being equipped with a camera / video camera for image capture and an ultrasonic flaw detector for wall panel inspection;

[0010] The ultrasonic detection system comprises a host computer and a slave computer;

[0011] The host computer includes a PC, a camera / camcorder and a ROS host;

[0012] The lower computer includes a chassis drive chip, a motor driver and a motor.

[0013] Preferably, the ultrasonic detection system uses Jetson Nano 4GB as the ROS host, which is responsible for image processing and command sending;

[0014] The ROS host receives the video image data of the camera for processing, and sends a control signal to the chassis drive chip of the lower computer according to the program processing result;

[0015] The chassis drive chip further controls the motor through the motor driver to achieve weld tracking of the wall-climbing robot;

[0016] The PC and the ROS host are configured in the same local area network. The PC is used to remotely log in to the ROS host and view the running status at the same time, which is convenient for monitoring and debugging.

[0017] Preferably, the ROS host realizes communication between modules through the Publish / Subscribe communication mode;

[0018] In the ROS host, the camera is driven by the / usb_cam node;

[0019] The ultrasonic detection system uses OpenCV to process images, including image filtering, edge detection, and centerline extraction;

[0020] The ROS host calls the image in OpenCV through Cv_bridge, subscribes to the ROS host image message and converts it into OpenCV format for processing, and then converts it into ROS host image message for release after processing.

[0021] (III) Beneficial effects

[0022] The present invention provides a wall-climbing detection robot and an ultrasonic detection system for a vertical storage tank, which have the following beneficial effects:

[0023] 1. Based on the analysis of the tank structure, the invention determines that the load capacity of the detection robot is 10kg, the maximum moving speed is 2m / min, the minimum curvature radius of adaptation is 10m, and the tank wall can be detected without omission and the robot can move autonomously; the robot body adopts the solution of permanent magnetic adsorption and Mecanum wheel movement. According to the structural characteristics and movement mode of the Mecanum wheel, the kinematic analysis, static analysis and dynamic analysis of the wall-climbing detection robot are carried out, and the drive motor is selected according to the analysis results.

[0024] 2. According to the magnetization direction characteristics of the permanent magnet, the present invention designs an adsorption array based on the Halbach array. According to the simulation analysis results, the arrangement of the permanent magnet with more vertical magnetization is selected, and the concept of magnetic adsorption force per unit volume is proposed to optimize the design of the adsorption device.

[0025] 3. Based on the mathematical model of the DC motor speed regulation system, the present invention selects a better fuzzy PID to control the speed of a single motor through simulation comparison, and synchronously controls the four motors through the parallel closed-loop synchronous control method to ensure the straight-line crawling accuracy of the robot and meet the movement requirements of the robot during detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A perspective view of the present invention;

[0027] Figure 2 Another perspective perspective diagram of the present invention;

[0028] Figure 3 A physical picture of the Mecanum wheel of the present invention;

[0029] Figure 4 A diagram of the wheel axle and roller axle of the Mecanum wheel of the present invention;

[0030] Figure 5 This is a kinematic analysis diagram of the four-wheeled wheat wheel robot in the present invention;

[0031] Figure 6 It is a block diagram of the overall design scheme of the system in the present invention;

[0032] Figure 7 It is a flow chart of the weld tracking system of the system in the present invention;

[0033] Figure 8 It is a flow chart of image message conversion of the system in the present invention;

[0034] Fig. 9 It is a schematic diagram of the detection process of the system in the present invention;

[0035] Fig.10 It is the overall block diagram of the wall panel detection of the system in the present invention;

[0036] Fig.11 Design flow chart of the host computer system of the system in the present invention;

[0037] Fig.12 Design flow chart of the lower computer system of the system in the present invention;

[0038] Fig.13 is a flow chart of motor control of the system in the present invention;

[0039] Fig.14Schematic diagram of the Halbach permanent magnetic adsorbent in the present invention;

[0040] Fig.15 It is a schematic diagram of the permanent magnetic adsorbent in the present invention;

[0041] Fig.16 It is the adsorption model and air domain diagram in the present invention;

[0042] Fig.17 It is the magnetic force line distribution diagram of the yokeless magnet in the present invention;

[0043] Fig.18 The magnetic field line distribution diagram of the yoke magnet in the present invention;

[0044] Fig.19 A comparison diagram of the adsorption forces of two adsorption devices in the present invention;

[0045] Fig. 20 It is a simulation diagram of magnetic induction intensity of two Halbach arrays in the present invention;

[0046] Fig.21 This is a comparison diagram of the adsorption forces of the two arrangement modes in the present invention;

[0047] Fig. 22 It is a diagram of parameter analysis results in the present invention;

[0048] Fig.23 It is a schematic diagram of the motion state of the robot in the present invention;

[0049] Fig.24 It is a structural block diagram of the DC motor speed regulation system in the present invention;

[0050] Fig.25 It is a structural block diagram of the DC motor speed regulation system with speed negative feedback control in the present invention;

[0051] Fig.26 It is the principle diagram of the parallel closed-loop synchronous control in the present invention;

[0052] Fig. 27 It is a slide analysis diagram in the present invention;

[0053] Fig.28 It is the longitudinal tipping diagram in the present invention;

[0054] Fig.29 It is the lateral tipping analysis diagram in the present invention;

[0055] Fig.30 This is a force analysis diagram of vertical upward crawling in the present invention;

[0056] Fig.31 This is a force analysis diagram of the Mecanum wheel steering in the present invention.

[0057] Among them, 1. bottom plate; 2. permanent magnetic adsorbent; 3. Mecanum wheel; 4. motor; 5. mounting part; 6. yoke magnet. DETAILED DESCRIPTION

[0058] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0059] Embodiment 1:

[0060] like Figure 1 , 2 As shown in Figures 14-22, an embodiment of the present invention provides a wall-climbing inspection robot for a vertical storage tank, including a base plate 1, two permanent magnetic adsorption bodies 2 are installed in parallel on the top of the base plate 1, a yoke magnet 6 is provided on one side of the two permanent magnetic adsorption bodies 2, motors 4 are fixed at the four corners below the base plate 1, and Mecanum wheels 3 are fixed to the output ends of the four motors 4.

[0061] A mounting member 5 is installed on one side of the bottom plate 1 , and the mounting member 5 is used for installing an ultrasonic flaw detector.

[0062] Motor 4 uses an MD60 brushed DC reduction motor, and the rated voltage of Motor 4 is 24V, the reduction ratio is 1:18, the rated speed is 175rpm, and Motor 4 has a 500-line high-precision GMR encoder with a rated torque of 5.57N·m.

[0063] The working environment of the wall-climbing detection robot of the present application is a normal pressure vertical storage tank. The storage tank stores flammable and explosive petroleum or petrochemical products, and safety is the primary consideration. The permanent magnetic adsorption body 2 is divided into contact and non-contact types. If the wall-climbing detection robot adopts a contact adsorption method, static electricity sparks may be generated during the crawling process of the robot, which may easily lead to safety accidents. Therefore, the present application adopts a non-contact adsorption method. In order to avoid the concentration of adsorption force, which causes the wall-climbing detection robot to roll over, a permanent magnetic adsorption body 2 is designed on both sides of one side of the robot to ensure the adsorption force while avoiding rollover.

[0064] The permanent magnetic adsorption body 2 of the present application is made of NdFeB N35, which has high magnetic energy product, high coercivity, high stability and good corrosion resistance. The performance is shown in the following table. The adsorption unit (permanent magnetic adsorption body 2) is designed based on NdFeB N35.

[0065]

[0066] Analysis of adsorption unit arrangement: Halbach array is a special permanent magnet structure, which was discovered and perfected by American scholar Kalus Halbach in 1979. Its main feature is that a group of permanent magnets are arranged in a plane according to certain rules, so that a strong magnetic field is generated on one side of the array, and there is almost no magnetic field on the other side.

[0067] Since it is impossible to achieve continuous change of the magnetic flux vector in a single permanent magnet, the ideal Halbach array cannot be made. Usually, a Halbach array is made by artificially assembling multiple individually magnetized permanent magnets. Due to the uneven distribution of the magnetic field in the array, the array will have leakage magnetic flux, which can be reduced by adding yoke magnets. The material of the yoke magnet is Q235 steel.

[0068] Permanent magnetic adsorption device simulation experiment: Based on the Ansys Maxwell platform, a group of Halbach arrays with horizontal magnetization arrangement of permanent magnets were simulated with and without yoke magnets.

[0069] Static electromagnetic field analysis: The Maxwell stress method can calculate the finite element analysis equations and boundary conditions of the three-dimensional static magnetic field. The Maxwell equations are shown below:

[0070]

[0071] in,

[0072]

[0073] Where: Ax, Ay, Az, Bx, By and Bz are the components of magnetic field intensity and magnetic induction intensity in x, y and z respectively. According to Maxwell tension method, when the closed surface S is in a uniform and isotropic medium, the area relationship between the resultant force F acting on the magnet and the tension tensor T is:

[0074]

[0075] In the formula: S is the closed surface of the air medium surrounding the permanent magnet; n is the unit vector in the direction of the outer normal of the area dS; B is the magnetic induction intensity on the closed surface S; μ is the magnetic permeability of the air.

[0076] Adsorption unit (permanent magnetic adsorption body) simulation condition setting: This application assembles 5 permanent magnets into a Halbach array, such as Fig.15 As shown, the length, width and height of the permanent magnet are represented by a, b and h, respectively, and the values ​​are 50mm, 30mm and 10mm. The thickness of the choke magnet is represented by w, and the value is 5mm.

[0077] The model established is as Fig.16As shown in the figure, the three-dimensional rectangular frame is the adsorption device model, and the external three-dimensional rectangle is the air domain. The factors that affect the adsorption force are permanent magnets, air, wall surfaces, and yoke magnets. The thickness of the wall is set to 10 mm, the area is large enough, the relative magnetic permeability μrec is set to 2000, the relative magnetic permeability μrec of air is set to 1.0, the relative magnetic permeability μrec of the permanent magnet is set to 1.06, and the relative magnetic permeability μrec of the yoke magnet is set to 5000.

[0078] Simulation analysis of adsorption device: Fig.17 and Fig.18 By comparison, it can be observed that adding yoke magnets can reduce the magnetic lines of force on both sides and eliminate the magnetic lines of force on the top.

[0079] For a set of Halbach arrays with horizontal magnetization of permanent magnets, the adsorption forces of two adsorption devices with and without yoke magnets are compared. Fig.19 As shown, F1 is the adsorption force of the yoke magnet array, and F2 is the adsorption force of the unyoke magnet array. The adsorption forces of the yoke magnet array and the unyoke magnet array are equal when the air gap is 14 mm. When the air gap is less than 14 mm, the adsorption force of the yoke magnet array is greater than that of the unyoke magnet array.

[0080] The results of comparative simulation show that adding yoke magnets can increase the adsorption force and reduce the magnetic lines of force on both sides and eliminate the magnetic lines of force above, which verifies the necessity of adding yoke magnets.

[0081] A comparative analysis of two different arrangements of Halbach adsorption arrays was conducted. The first arrangement starts with a permanent magnet vertical magnetization arrangement, which is characterized by three strong magnetic fields formed between the bottom of the permanent magnet and the wall, and three permanent magnets are vertically magnetized. The second arrangement starts with a permanent magnet horizontal magnetization arrangement, which is characterized by two strong magnetic fields formed between the bottom of the permanent magnet and the wall, and two permanent magnets are vertically magnetized. When simulating an air gap range of 2mm≤D<18mm, it was found that the adsorption force F1 of the first arrangement is greater than the adsorption force F2 of the second arrangement. When the air gap is greater than or equal to 18mm, F1 and F2 are basically equal.

[0082] In summary, the permanent magnetic adsorbent in this paper selects an arrangement form with more vertical magnetization of permanent magnets, and adds yoke magnets to reduce leakage magnetism.

[0083] Parameter optimization analysis of adsorption unit (permanent magnet adsorption body): In order to explore the influence of the length, width, height and thickness of the permanent magnet and the yoke magnet on the adsorption force and adsorption efficiency, the control variable method is used to analyze a certain dimension without changing other dimensions. The material properties of the simulation analysis are the same as before, and the size of the adsorption device is the initial value. Use the permanent magnet arrangement selected in the previous section. First, define an important physical quantity:

[0084] Define the adsorption force per unit volume Fv:

[0085]

[0086] Where: Fv represents the adsorption force per unit volume, and Fv is proportional to the permanent magnet utilization rate. Fmax is the adsorption force generated by the adsorption unit, and V is the volume of the adsorption unit.

[0087] According to Fig. 22 (a) The simulation results shown, under the given parameter conditions (b = 30 mm, h = 10 mm, w = 5 mm, air gap 10 mm), the relationship between the permanent magnet adsorption force F and the adsorption force per unit volume Fv with the change of the a value was studied. The permanent magnet adsorption force F increases with the increase of the a value and shows an approximately linear relationship. This means that increasing the length of the permanent magnet can significantly improve the magnetic adsorption force. The adsorption force per unit volume Fv increases with the increase of the permanent magnet length, but the growth rate gradually slows down. When 0 ≤ a ≤ 35 mm, Fv increases rapidly with the increase of the permanent magnet length, and at this time the permanent magnet utilization rate increases greatly; while when 35 < a ≤ 50 mm, the growth rate of the permanent magnet utilization rate slows down, which means that increasing the permanent magnet length within this range mainly brings an increase in the permanent magnet volume, and the permanent magnet utilization rate increases little.

[0088] According to Fig. 22 (b) The simulation results shown, under the given parameter conditions (a = 50 mm, h = 10 mm, w = 5 mm, air gap 10 mm), the relationship between the permanent magnet adsorption force F and the adsorption force per unit volume Fv with the change of the b value was studied. The permanent magnet adsorption force F shows a linear increasing trend with the increase of the permanent magnet width b, that is, with the increase of the b value, the increase amount of the adsorption force also increases accordingly. The adsorption force per unit volume Fv increases with the increase of the permanent magnet width b, but when the b value is about 30 mm, the growth rate begins to slow down.

[0089] According to Fig. 22 (c) The simulation results, under the given parameter conditions (a = 50 mm, b = 30 mm, w = 5 mm, air gap 10 mm), the relationship between the permanent magnet adsorption force F and the adsorption force per unit volume Fv with the change of the permanent magnet height h was studied. The permanent magnet adsorption force F increases with the increase of the permanent magnet height h and shows a linear increasing trend with the increase of h. This shows that increasing the height of the permanent magnet can significantly improve the magnetic adsorption force. The adsorption force per unit volume Fv shows a trend of increasing first and then decreasing with the increase of the permanent magnet height h. When h = 12 mm, the value of Fv reaches the maximum of 4.46 N / cm3. Then with the further increase of h, Fv begins to decrease slowly.

[0090] According to Fig. 22The simulation results in (d) study the relationship between the permanent magnetic adsorption force F and the unit volume adsorption force Fv as the yoke magnet thickness w changes under given parameter conditions (a = 50mm, b = 30mm, h = 10mm, air gap 10mm). When the yoke magnet thickness w reaches 1mm, the adsorption force gradually stabilizes at around 350N, and the unit volume adsorption force value stabilizes at about 4.6N / cm 3 When the thickness of the yoke magnet continues to increase, the adsorption force F and the unit volume adsorption force Fv remain basically unchanged.

[0091] According to the above analysis results, the adsorption performance of the adsorption device is affected by multiple parameters, and the correlations between them are complex. Although the influence of a certain parameter on the adsorption performance can be studied by changing other parameters and keeping them unchanged, it is difficult to find the optimal parameter value when all parameters are changed together. Considering the initial value of the adsorption device size and the air gap thickness of 10 mm, it is found that the change of the size parameters b and h has little effect on the permanent magnet utilization rate, while the change of the parameters a and w has a greater impact on the permanent magnet utilization rate, so it is chosen to keep the initial size of b and h unchanged and only optimize a and w. In addition, adding a yoke magnet can increase the adsorption force of the adsorption device, because the magnetic concentration effect of the yoke magnet enhances the magnetic field strength between the adsorption device and the wall plate, thereby improving the adsorption force of the adsorption device. It should be noted that the addition of the yoke magnet will not affect the inherent magnetic field performance of the Halbach array, and there is no interference between the parameters a and w. Therefore, when optimizing the performance of the adsorption device, b and h can be kept unchanged, a and w can be adjusted, and the addition of a yoke magnet can be considered to enhance the adsorption force to achieve the best adsorption effect.

[0092] The optimized adsorption device dimensions a, b, and h are 35 mm, 30 mm, and 10 mm respectively, and the thickness w of the yoke magnet is 1 mm. The optimized adsorption force per unit volume is 4.28 N / cm 3 It increased to 5.19N / cm3, with an increase rate of 21.2%, and the magnetic adsorption efficiency was improved.

[0093] The two sets of permanent magnetic adsorption bodies on the robot have an optimized adsorption force of 604.27N, which is greater than 560N and meets the adsorption force requirements of the wall-climbing robot when working normally.

[0094] In summary, the Ansys Maxwell software was used to simulate and analyze the permanent magnet adsorption body of the wall-climbing robot, which verified the necessity of adding yoke magnets, optimized the adsorption body based on Halbach array, and proposed the concept of adsorption force per unit volume. Through simulation comparative tests, the length, width and height of a single permanent magnet were finally optimized to be 35mm, 30mm, and 10mm respectively. When the air gap was 10mm, the combined adsorption force of the two sets of adsorption devices was 604.27N, which met the adsorption force requirements of the wall-climbing robot during normal operation.

[0095] Embodiment 2:

[0096] like Figure 23-26 The embodiment of the present invention provides a linear motion control method for a wall-climbing robot: the wall-climbing detection robot moves on the wall of a large steel storage tank in two states. The first state is to crawl linearly on the tank wall for detection. Fig.23 (a) is shown. The second method is to track along the weld and start the inspection when it reaches the designated wall panel, as shown in Fig.23 (b) is shown. In the first motion state, the wall-climbing robot is required to crawl in a straight line to ensure that the wall panels are not missed. As can be seen from the above, the wall-climbing inspection robot is driven by four motors. When performing linear inspection, as long as the speed of the motors on both sides of the wall-climbing robot is controlled to be equal, linear motion can be achieved. Therefore, the linear crawling problem of the wall-climbing inspection robot is essentially a problem of controlling the motor speed.

[0097] Mathematical model of the speed control system: The Mecanum wheel is driven by four DC motors. According to the principle of motor rotation, the speed formula is:

[0098]

[0099] Where: U represents the armature voltage, I is the armature current, R is the total armature resistance, and the electromotive force constant is K e , the excitation flux is Φ. According to the formula, the motor speed can be adjusted by changing the armature voltage. The controller ensures precise control by sending a pulse width modulation (PWM) signal. PWM is a pulse voltage with a fixed frequency and adjustable width. The PWM signal is converted into a voltage across the motor, which can be expressed as:

[0100]

[0101] Where: T S Expressed as delay time, K S It is expressed as the voltage magnification. PWM signal is a high-frequency signal, and the high-order terms can be ignored. The above formula can be replaced by a first-order inertia link.

[0102]

[0103] The motor dynamic equations are:

[0104]

[0105] Where: U d is the voltage across the DC motor, R is the resistance, I d is the current, L is the armature inductance, and E is the DC motor armature back electromotive force. The relationship between the driving torque and current is:

[0106] M e =C m I d (5)

[0107] Where: M e is the driving torque, C m Torque coefficient

[0108] The dynamic equation of the motor shaft is:

[0109]

[0110] Where: M L is the load moment, GD 2 Total moment of inertia

[0111] Load torque and load current I dL The relationship is:

[0112]

[0113] The relationship between back EMF and motor speed is:

[0114] E=C e n (8)

[0115] Where: E is the back electromotive force, C e Electromotive force coefficient

[0116] Electromagnetic time constant T l and T m The motor time constant is:

[0117]

[0118] The above equations (4) and (9) can be simplified to:

[0119]

[0120] Under zero initial conditions, Laplace transform of equations (11) and (12) above yields:

[0121]

[0122] Considering the relationship between back electromotive force and motor speed from equations (13) and (14), we can get the DC motor speed control system structure diagram, as shown in Fig.24 As shown:

[0123] Adjustable pulse width signal U g , it will go through the first-order inertia link of the PWM converter, and then go through the second-order linear link from voltage to speed, and finally get the speed n, whose transfer function is:

[0124]

[0125] This application can obtain the following by querying the parameters of the MD60 DC motor and the parameters of the PWM signal conversion circuit: s =0.0182s, K S =4.2, T m =0.0819s, T l =0.0182s.

[0126] The motor encoder will rotate with the motor and output a square wave. The motor speed can be obtained by reading the square wave. The transfer function of the encoder speed and output signal is:

[0127]

[0128] Combining (15) and (16), we can get the block diagram of the DC motor speed regulation system with speed negative feedback control, as shown in Fig.25 shown.

[0129] Straight-line crawling control method of wall-climbing robot: To ensure that the wall-climbing robot does not miss any rectangular wall panels when inspecting, straight-line crawling is the basic crawling function of the wall-climbing robot when performing inspections. In the control system of the four drive motors of the wall-climbing robot, if the same control current is input to the four motors without external interference, theoretically the motors will output the same speed. However, due to the processing precision and the incomplete symmetry of the wall-climbing robot, the center of mass position is not centered, etc., which results in differences in speed and causes the wall-climbing robot to deviate.

[0130] Fuzzy PID control is used to control a single motor of the wall-climbing robot to ensure the stable output of a single motor. In order to make the four motors coordinated, this application adopts parallel closed-loop synchronous control. The control principle is as follows Fig.26 In the parallel closed-loop synchronous control process, each motor is controlled independently and each motor will not affect each other.

[0131] In the parallel closed-loop synchronous control system, at about 0.55s, the speed of the four drive motors reaches the rated speed of 175rpm and tends to be stable. The four drive motors have good synchronization. The synchronous operation of the four motors can ensure that the wall-climbing robot crawls in a straight line.

[0132] Embodiment three:

[0133] like Figure 6-13 As shown, an embodiment of the present invention provides an ultrasonic detection system of a wall-climbing detection robot for a vertical storage tank, wherein the wall-climbing robot is equipped with a camera / video camera for image capture and an ultrasonic flaw detector for wall panel detection;

[0134] Ultrasonic testing system, including a host computer and a slave computer;

[0135] Host computer, including PC, camera / camcorder and ROS host;

[0136] The system design process of the host computer is as follows Fig.11 As shown. After initialization, the upper computer first determines whether the communication between the upper and lower computers is normal. If the communication is normal, it waits for instructions and sends the instructions to the lower computer. After receiving the control instruction, the lower computer will send back a feedback signal and start to perform the detection task. If an exit instruction is received, the lower computer will shut down the entire system. After receiving the feedback signal, the upper computer will continue to wait and read instructions. If the communication is not normal, the upper computer will wait and continue to detect the communication system.

[0137] The lower computer includes a chassis drive chip, a motor driver and a motor (4).

[0138] The lower computer is initialized first, and checks whether the communication is normal like the upper computer. If the communication is normal, it will wait to read the control command of the upper computer. The command is divided into motion command, and the lower computer controls the drive motor to start rotating, so that the robot can crawl in a straight line. If it is an exit command, the lower computer will shut down the entire motion control system. The overall control process is as follows Fig.12 shown.

[0139] The ultrasonic detection system uses Jetson Nano 4GB as the ROS host, which is responsible for image processing and command sending;

[0140] The ROS host receives the video image data from the camera for processing, and sends a control signal to the chassis driver chip of the lower computer according to the program processing results;

[0141] The chassis drive chip further controls the motor (4) through the motor driver to achieve weld tracking of the wall-climbing robot;

[0142] The PC and ROS host are configured in the same LAN. Use the PC to remotely log in to the ROS host and view the running status at the same time, which is convenient for monitoring and debugging.

[0143] The ROS host uses the Publish / Subscribe communication mode to achieve communication between modules;

[0144] In the ROS host, the camera is driven through the / usb_cam node;

[0145] The ultrasonic detection system uses OpenCV to process images, including image filtering, edge detection, and centerline extraction;

[0146] The ROS host calls the image in OpenCV through Cv_bridge, subscribes to the ROS host image message and converts it into OpenCV format for processing. After processing, it is converted into ROS host image message for publication. In this mode, a module (node) can publish a message to a topic, and other modules (nodes) can subscribe to this topic to receive messages. This article uses the ROS Kinetic version on the Ubuntu16.04 system to implement the program design and development of the host computer.

[0147] First, the robot is placed on the tank wall, and the image of the weld is transmitted to the ROS host. The ROS host uses the computer vision algorithm in OpenCV to grayscale, filter, binarize, detect edges, and extract the centerline of the image. The obtained centerline is used as the robot's crawling path, and the offset (offset distance and deflection angle) between the wall-climbing robot and the centerline is calculated. According to the robot's differential motion model and deviation correction algorithm, instructions are issued to the lower computer driver chip to correct the robot's deviation and realize the wall-climbing robot tracking along the weld.

[0148] After the wall-climbing robot finishes tracking the weld, it arrives at the designated inspection point and begins inspecting the target wall panel. Turn on the ultrasonic flaw detector, which is connected to the ultrasonic probe on the robot mounting part via a cable. The ultrasonic flaw detector has a saving function. When the wall-climbing robot inspects the entire wall panel, the detected data is analyzed and saved. The forward movement of the wall-climbing robot is controlled through the control interface. When the robot reaches the end of the wall panel, the inspector controls the wall-climbing robot to move laterally to the left or right (this application selects Mecanum wheels as the moving wheels. According to the characteristics of the Mecanum wheels, the robot's posture will not change during lateral movement, avoiding the problem of the robot needing to adjust its direction due to turning), and then moves in the opposite direction until the entire wall panel is inspected. The process is as follows: Fig. 9 shown.

[0149] The motion state control process is as follows: the control terminal transmits the control command to the robot end through the WIFI module. The main control chip STM32 of the robot end uses the wall-climbing robot motion model in Chapter 2 of this design to calculate the speed and forward and reverse direction of each wheel. The STM32 chip will transmit the calculation results to the motor driver. The motor driver controls each Mecanum wheel. Each motor uses fuzzy PID control. The four motors use parallel closed-loop synchronous control to ensure the synchronization of the motor speed. Finally, the motor will transmit the speed to the corresponding Mecanum wheel through the reducer to realize the predetermined motion of the mobile platform. The control block diagram is as follows Fig.10 shown.

[0150] To ensure the synchronization of the four drive wheels, the robot adopts parallel closed-loop synchronous control, and each motor uses fuzzy PID independent control. The control process is as follows: Fig.13 shown.

[0151] Embodiment 4:

[0152] like Figure 3-5 As shown, the embodiment of the present invention provides a kinematic analysis of a wall-climbing robot: the Mecanum wheel is composed of a wheel hub and a roller on the periphery, the angle between the wheel axle and the roller axle is 45°, and the surface of the wheel is provided with rollers at a certain angle, so that the wheel generates a lateral propulsion force when rotating, thereby achieving lateral movement. Mecanum wheels are generally used in pairs, a pair of left-handed wheels and a pair of right-handed wheels, and the wheels rotating in the same direction are diagonally distributed. The kinematic analysis of the Mecanum wheel is performed.

[0153] Attached Figure 5 In the figure, W represents the distance between the left and right wheels, H represents the distance between the front and rear wheels, and V represents the distance between the left and right wheels. x Represents the front-to-back displacement velocity, V y Represents the left and right displacement speed, V z Indicates the robot rotation speed, V A轮 、V B轮 、V C轮 、V D轮 Respectively represent the linear speed of wheels A, B, C, and D. C辊 V represents the roller linear velocity when the center of mass of wheel C contacts the ground. Z-c V is the linear velocity of the center of mass of wheel C rotating around point O. C-x V represents the forward and backward moving speed of the center of mass of wheel C. C-y Indicates the left and right moving speed of the center of mass of wheel C, α c It represents the angle between the line connecting the wheel and point O and the forward direction, and β represents the angle between the wheel axle and the roller axle.

[0154] The main body of the wall-climbing robot and the center of mass of the Mecanum wheel can be regarded as a rigid body, and the velocity can be decomposed to obtain:

[0155]

[0156] V C辊 Indicates the relative sliding speed between the McReel C and the ground. When V C辊 When rotating, the torque generated by the motor drives the wheel hub and the roller at the same time, V C_x and V C_y It can be expressed as:

[0157] V C_x =V C轮 +V C辊 ×sinβ (3)

[0158] V C_y =-V C辊 ×cosβ (4)

[0159] Combining equations (1), (2), (3) and (4) above, we can obtain:

[0160]

[0161] Formula (6) can be transformed into:

[0162]

[0163] Substitute formula (7) into (5), let We can get:

[0164] V C轮 -V y -V Z ×L×cosα C ×tanβ=V x +V Z ×L×sinα C (8)

[0165] V C轮 =V x +V y +V Z ×L×(sinα C +cosα C ×tanβ) (9)

[0166] β=45°, then:

[0167] V C轮 =V x +V y +V Z ×L×(sinα C +cosα C )(10)

[0168] again but,

[0169]

[0170] Similarly, V A 、V B 、V C With V x 、V y 、V z relationship,

[0171] V A_y =-V A辊 ×cosβ(12)

[0172] V B_y =V B辊 ×cosβ(13)

[0173] V D_y =V D辊 ×cosβ(14)

[0174] The target speeds of the four wheels are obtained by using the inverse kinematics formula of the robot:

[0175]

[0176] By combining formulas (15), (16), (17), and (18), we can calculate the kinematic formula of the wall-climbing robot. The real-time speed of the three axes can be calculated from the real-time speed of the four wheels:

[0177]

[0178] Embodiment five:

[0179] like Figure 27-31 As shown, the embodiment of the present invention provides static analysis and dynamic analysis of the wall-climbing robot: In order to ensure reliable adsorption and flexible crawling of the wall-climbing inspection robot on the wall of a large steel structure tank, the adsorption device needs to meet the minimum adsorption force and the drive motor needs to meet the minimum torque. Therefore, static and dynamic analysis are performed to match the adsorption force of the robot's adsorption device, the motor torque, and the deadweight of the wall-climbing robot.

[0180] 1. Statics analysis:

[0181] The wall-climbing detection robot works on the outer wall of a large steel storage tank, so the angle between the wall and the vertical surface is 90°. Fig. 27 (a) When the robot works on the outer wall of a large steel tank, it may fail in the following ways: sliding down, longitudinal overturning, lateral overturning, etc.

[0182] Slide analysis: When the robot is stationary on the wall and slides down, the force analysis is as follows: Fig. 27 (b) a1、F a2 is the adsorption force of the magnet on the wall panel, F n1 、F n2 、F n3 、F n4 The support force of the wall panel on the car, F f1 、F f2 、F f3 、F f4 is the friction force of the wall panel on the McDonnell Douglas wheel, G is the overall gravity of the robot (robot's own weight and load), which is 20kg, L is the distance between the center of mass of the front and rear McDonnell Douglas wheels, which is 300mm, and D is the distance between the wall panel and the center of gravity of the trolley, which is 125mm.

[0183] According to the force balance principle:

[0184]

[0185] It can be deduced that:

[0186]

[0187] μ is the friction coefficient, which is taken as 0.5, and k is the safety factor, which is taken as 1.4. It can be deduced that the minimum adsorption force of the magnet on the wall panel is 560N.

[0188] Longitudinal rollover: When the robot is attached to the wall panel, it will be affected by the overturning moment and will roll over. The rollover around the y-axis is called longitudinal rollover, and the rollover along the x-axis is called lateral rollover. Fig.28 This is a schematic diagram of a longitudinal rollover. The robot rolls over along the line connecting O1 and O2. At this time, the support force between the wheel and the wall panel at O3 O1 of the machine is zero.

[0189] ΣM 纵向 =0

[0190] (F a2 -F n3 -F n4 )L-GD=0

[0191] When longitudinal rollover occurs, F n3 and F n4 is 0, so F a2 84N,F a2 With F a1 The minimum adsorption force is 168N.

[0192] Lateral tipping: Fig.29 This is a schematic diagram of a lateral rollover, which occurs around the X-axis, that is, it rolls along the line connecting O1 and O3. At this time, the support force between the robot O4 O2 wheels and the wall panel is zero.

[0193] ΠM 横向 =0

[0194]

[0195] W is the distance between the center of mass of the left and right wheels, which is 350 mm. The minimum adsorption force is 171 N. In the static analysis, the robot's sliding, longitudinal tipping, and horizontal tipping are considered. It is found that when the robot slides, the maximum adsorption force is required, and the adsorption value is 560 N.

[0196] 2. Kinetic analysis:

[0197] In order to calculate the minimum torque of the motor when the wall-climbing inspection robot walks flexibly on the wall of a large steel tank, it is necessary to conduct a dynamic analysis of the robot mechanism. The wall-climbing robot designed in this paper adopts four-wheel drive and uses Mecanum wheels to move. When the wall-climbing robot climbs vertically upward, gravity needs to be calculated, but when it crawls downward, gravity does not need to be calculated; when the wall-climbing robot climbs obliquely, the component of gravity needs to be calculated; when the wall-climbing robot turns, the sliding friction of the Mecanum wheel needs to be calculated. Therefore, the dynamic analysis only needs to analyze the force analysis of the two situations of vertical climbing and turning. Based on the adsorption force value of the adsorption device calculated above, the force analysis of the two situations of vertical climbing and turning of the wall-climbing robot is carried out, so that the adsorption force of the robot's adsorption device, the motor torque, and the deadweight of the wall-climbing robot match each other.

[0198] The robot crawls vertically upward: When the robot starts to move upward, there is acceleration. Fig.30 The symbols are consistent with those in statics, and a is the acceleration of the robot's upward movement.

[0199] d is the diameter of the wheel, which is 100mm. T1 and T2 are the torques of the two rear wheels, and T3 and T4 are the torques of the two front wheels. T1, T2, T3, and T4 are equal. According to the principle of moment balance, we get:

[0200]

[0201] According to static analysis, the following formula is obtained:

[0202]

[0203] Assume that the forces on the four wheels are equal, that is, F f1 =F f2 =F f3 =F f4 , we can deduce that:

[0204]

[0205] In the formula, K is the safety factor, which is 1.4 here, and the acceleration a is 0.5m / s 2 , g is the acceleration due to gravity, take 10m / s 2, and T is 3.675N·m. When the robot crawls down the wall, gravity can provide power for the wall-climbing robot. If the wall-climbing robot meets the upward crawling condition, it can also meet the downward crawling condition.

[0206] Robot steering force analysis: Each wheel of the robot uses an independent DC motor. Assume that the driving force of each wheel is the same, set as P, the distance between the center of mass of the left and right wheels is W, and the distance between the center of mass of the wheels on the same side is H. Fig.31 shown.

[0207] The driving force provided by a single motor when the robot turns:

[0208] Mi=P×R

[0209] The single motor driving force required for the robot to turn:

[0210] M0=P×W

[0211] When the wall-climbing robot turns, the center of mass does not change, so the rolling resistance caused by the overall gravity is not considered, and the friction torque generated is:

[0212] M fi =μN i l i

[0213] Ni is the support force of the wall on a single wheel, μ is the friction coefficient, and Li is the distance from the McNamee wheel to the center of mass of the robot. For a wall-climbing robot to achieve steering, the following conditions must be met:

[0214]

[0215] Right now:

[0216]

[0217] F ni In practice, they are equal, F n1 =F n2 =F n3 =F n4 , the driving torque required by a single motor is derived as:

[0218]

[0219] Among them, μ = 0.4, R = 50mm, H = 300mm, W = 350mm, G = 200N, Fn = 560N. According to the calculation, the minimum torque output of the motor is 4.73N·m. This application uses the MD60 DC brush motor, adds a reducer, the reduction ratio is 1:18, the rated torque is 5.57N·m, and the rated speed is 175rpm, which meets the requirements.

[0220] In summary, the permanent magnetic adsorption and wheeled mobility schemes of the wall-climbing detection robot were determined by comparison. The advantages and disadvantages of the Mecanum wheel and the ordinary mobile wheel were compared. Combined with the actual detection scenario requirements of the wall-climbing detection robot, the Mecanum wheel, a special wheel, was selected as the mobile wheel. The kinematic analysis of the wall-climbing robot was carried out, and the speed control model of the robot was established. Finally, through static and dynamic calculations, it was found that the minimum adsorption force of the wall-climbing robot was 560N, and the minimum torque of the motor was 4.73N.

[0221] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A wall-climbing inspection robot for a vertical storage tank, comprising a bottom plate (1), characterized in that: Two permanent magnetic adsorption bodies (2) are installed in parallel above the bottom plate (1), and a yoke magnet (6) is provided on one side of each of the two permanent magnetic adsorption bodies (2). Motors (4) are fixed at the four corners below the bottom plate (1), and Mecanum wheels (3) are fixed at the output ends of the four motors (4).

2. A wall-climbing inspection robot for a vertical storage tank according to claim 1, characterized in that: A mounting member (5) is mounted on one side of the base plate (1).

3. The wall-climbing inspection robot for a vertical storage tank according to claim 1, characterized in that: The motor (4) is an MD60 brushed DC reduction motor, and the rated voltage of the motor (4) is 24V, the reduction ratio is 1:18, and the rated speed is 175rpm.

4. An ultrasonic detection system for a wall-climbing detection robot of a vertical storage tank, characterized in that: The wall-climbing robot is equipped with a camera / video camera for image capture and an ultrasonic flaw detector for wall panel inspection; The ultrasonic detection system comprises a host computer and a slave computer; The host computer includes a PC, a camera / camcorder and a ROS host; The lower computer comprises a chassis drive chip, a motor driver and a motor (4).

5. The ultrasonic detection system of a wall-climbing detection robot for a vertical storage tank according to claim 4 is characterized in that: The ultrasonic detection system uses Jetson Nano 4GB as the ROS host, which is responsible for image processing and command sending; The ROS host receives the video image data of the camera for processing, and sends a control signal to the chassis drive chip of the lower computer according to the program processing result; The chassis drive chip further controls the motor (4) through the motor driver to achieve weld seam tracking of the wall-climbing robot; The PC and the ROS host are configured in the same local area network. The PC is used to remotely log in to the ROS host and view the running status at the same time, which is convenient for monitoring and debugging.

6. The ultrasonic detection system of a wall-climbing detection robot for a vertical storage tank according to claim 4, characterized in that: The ROS host realizes communication between modules through the Publish / Subscribe communication mode; In the ROS host, the camera is driven by the / usb_cam node; The ultrasonic detection system uses OpenCV to process images, including image filtering, edge detection, and centerline extraction; The ROS host calls the image in OpenCV through Cv_bridge, subscribes to the ROS host image message and converts it into OpenCV format for processing, and then converts it into ROS host image message for release after processing.

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