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CLIMBING ROBOT FOR BOILER TUBE INSPECTION

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During the inspection, a camera is held by the magnetic robot that attaches to the wall to take high-resolution photos of the pipes. In this report, the development of the wall-mounted robot is shown, and the remote inspection technique is discussed in detail.

Introduction

  • General
  • Problem Statement
  • Objectives
  • Research Scope
  • Thesis Structure

With the development of the robot, the cost of inspections and the time that must be spent on regular inspections are reduced. Specifically, in Chapter 1, a brief introduction to the design of the inspection robot and its need was made.

Figure 1.1: Coal Fired Power Station and Boiler
Figure 1.1: Coal Fired Power Station and Boiler

Literature Review

Wall-climbing Robot

The influence of different contours of the suction chamber on the grip strength of the robot was tested by experiments [11]. In addition, suction cups adhere to the wall surface due to vacuum pressure, while soft cylindrical tubes control pneumatic springs.

Boiler Tube Inspection

The magnetic adhesion was obtained by the magnetic wheels and magnetic bars under the robot. The robot carried an electromagnetic acoustic transducer (EMAT) probe and camera to the target position, and inspection tasks were performed.

Non-destructive Testing

  • Visual Testing
  • Ultrasonic Testing (UT)
  • Electromagnetic Acoustic Transducer (EMAT)
  • Eddy Current Sensor
  • Magnetic Flux Leakage Sensor

Therefore, some of the more commonly used nondestructive testing methods are briefly presented below, along with their advantages and limitations. Typically, a visual testing method is used to detect cracks, pits, dents and corrosion on the pipe surface. Ultrasonic testing is a type of non-destructive testing that works by propagating ultrasonic waves in the object of examination [25].

It is also used to measure the wall thickness of the pipes to detect corrosion in the pipes and tubes. To make your choice easy, the main advantages and disadvantages of the testing method are listed below. These waves emit the detection material, reflect and move from the wall to the EMAT coil.

Compared to the ultrasonic testing, no coupling device is needed in the application of EMAT, which is shown in figure 2.4. In the previous part of this chapter, some of the popular non-destructive testing methods are reviewed, and their advantages and disadvantages are given. Therefore, a number of suppliers of the sensors required for non-destructive testing are listed in Appendix F.

Figure 2.2: Ultrasonic Testing
Figure 2.2: Ultrasonic Testing

Design and Development

Engineering Apparatus

  • Adherence and Locomotion Design
  • Visual Inspection

In our design, an LS-Y201 camera and an endoscope camera were used to detect cracks on the pipe surface. In the case of the LS-Y201 camera, using the SD card module with the SD card and Arduino UNO to save the images to the SD card, and the analyzes were done when the robot came back. After obtaining pictures or videos, analyzes are carried out on the integrity of the boiler pipes and the condition of the pipes is assessed based on them.

In our design, the remote control system consists of the Bluetooth module, Arduino UNO and L298N dual motor controller. 3D model of the robot is shown in Figure 3.1, where the tracked motion system and the adhesion source from the permanent magnet are specified. The total mass of the robot (M = 1.3 kg) and the coefficient of friction (0.5), acceleration of gravity (g9.8m/s2) are used to calculate the minimum suction force required.

The camera is mounted in the center of the front of the top cover at a 45 degree angle. At the end of the inspection, we take out the SD card and connect it to the computer with an SD card reader, and we can convert the text format to JPEG format with python codes, and we can do analysis on the images. In the endoscopic camera housing, the camera head is attached to the center of the front of the top cover and is directed towards the front of the robot at a 45 degree angle.

Figure 3.1: magnet and magnet holder
Figure 3.1: magnet and magnet holder

Material Selection

  • Hardware Selection
  • Software Algorithm Development

In our design, the Bluetooth HC-05 is used to control the robot wirelessly with a Smartphone at a range of 100m. Since the robot has to climb vertically and stick to the vertical surface of the wall simultaneously all the time, it has to be light enough as long as it can perform the task well. Since the battery is rechargeable up to 2000 times, it is able to reduce the cost of the project.

Moreover, it can supply a current of 680mAh and a voltage of 9V, which is perfect for the DC motors and Arduino. As mentioned earlier, the robot is equipped with a magnetic bonding mechanism, which keeps the robot in contact with the vertical wall surface or the vertical boiler tubes in our task. Moreover, its total mass is 90 grams, and its configuration specifications can be found in Appendix A.

To fix the necessary components on the top of the robot, a lightweight top cover has been designed and manufactured, and it is made of aluminum of 2 mm in thickness with a total mass of 150g. Since the robot can perform the task automatically, it needs to work on some software codes to control the robot up and down or left or right with the Smartphone which is connected to the Arduino via a Bluetooth module. For the movement mechanism, Arduino codes given in Appendix C are used to control DC motors along with the L298N Dual Motor Control and the Bluetooth module glued to the robot.

Figure 3.6: Arduino UNO with description
Figure 3.6: Arduino UNO with description

Final Prototype

During the inspection process, the images of the surface conditions can be automatically recorded with the LS-Y201 camera and saved to the SD card via the Arduino and the SD card module. Nevertheless, as mentioned earlier, the captured images are saved in text format, which must be converted to the JPEG format using the software codes in Appendix D.2. A camera is attached to the robot that detects the cracks in the outer surface of the pipes and tubes.

It is the second version of a wall-climbing robot with a belt-shaped wheel driven by two DC motors, the first version is designed based on a pneumatic adhesion mechanism [30], together with a 3D model.

Experimental Results and Analyses

Climbing Performance

  • Trials and Errors
  • Experiment Results

After assembly, it was determined that the design was unable to provide sufficient suction force to hold the robot on the wall surface without sliding down. Finally, the result showed that the robot was able to stand still on the surface of the wall. While the robot was able to climb the wall surface without slipping, to make it move up, down, left or right, a DC motor with the desired maximum torque must be selected.

When the robot was tested with the provided motors, the results came out as predicted. Since the climbing mechanism task was completed, the robot was tested on several climbing tasks. First, a flat metal wall surface was selected for testing the robot's climbing performance, which was shown in Figure 4.4.

As the pipe surface was rough and sloping, the robot could climb up relatively easily. And the robot could solve the task satisfactorily with a speed of almost 0.02 m/s, and it is shown in figure 4.6. Finally, the signal was transmitted successfully and the robot could be controlled with the APP on the smartphone.

Figure 4.1: Conventional magnet and two other small neodymium magnets
Figure 4.1: Conventional magnet and two other small neodymium magnets

Inspection Task with LS-Y201 Camera

In all cases, the robot was controlled by a remote control application installed on the smartphone, while a 9V adapter was used for the power supply instead of the battery in the case of the vertical flat surface test. What's more, initially, during the electrical connection process for locomotion, the Bluetooth module and the Arduino are connected by connecting TX to TX and RX to RX. Although Bluetooth could be connectable, no signal was received or transmitted between the Bluetooth module and the Arduino UNO.

One of the images captured by the camera on the robot is shown in Figure 4.7, which was converted from the text format stored on the SD card. Since the location was too close, the captured images were not very clear, but the robot can still inspect the pipes and find cracks on the outer surface. However, images can only give information about the condition of the outer surface of the pipe.

Regarding the inner surface, the robot must move through the inner surface to inspect the inner surface of a pipe or tube. Normally, the outer surface inspection gives an overall idea about the structural health of the pipes and tubes, although extensive and comprehensive inspection is always preferable and reliable, as some cracks may occur from the inside which are invisible from the outer surface. To get the pipes and tubes thoroughly evaluated, other professional non-destructive testing methods should be considered.

Figure 4.7: One of the images taken by the robot
Figure 4.7: One of the images taken by the robot

Inspection with Endoscope Camera

In comparison, the endoscope camera showed stronger capability and professionalism to inspect for cracks on the outer surfaces than the case of LS-Y201 camera. Nevertheless, as mentioned in the previous parts, other non-destructive testing methods are always preferable for thorough inspection of pipes and tubes, since these sensors manage to detect both internal and external cracks and other fatigues instead of only inspecting the external surfaces as in our design.

Figure 4.9: Images taken by the endoscope camera while the robot is climbing
Figure 4.9: Images taken by the endoscope camera while the robot is climbing

Conclusions and Possible

Conclusions

Possible Future Works

NDE technologies for the inspection of heat exchangers and boiler tubes - Principles, advantages and limitations. Development of mobile robotic systems for automatic diagnostics of boiler tubes in fossil fuel power plants and large pipelines. Modeling and experimental analysis of the suction pressure generated by a wall-climbing robot based on an active suction chamber with a novel bottom limiter.

IEEE International Conference on Cyber ​​Technology in Automation, Control and Intelligent Systems (CYBER) 2015, Shenyang, 2015, p. 19] XueqinL., RongfuQ., GangL. and FuzhenH. Design of an inspection robot for inspecting boiler tubes. Proceedings of the 2014 3rd International Conference on Applied Robotics for the Power Industry, Foz do Iguassu, 2014, pp.

Development of mobile robotic systems for automatic diagnosis of boiler tubes, fossil power plants and large pipelines.

Figure A.1 3D Model of Magnet Holder
Figure A.1 3D Model of Magnet Holder

Сурет

Figure 1.1: Coal Fired Power Station and Boiler
Figure 2.1: Boiler Tube Water Wall and Particular Tube Failures
Figure 2.2: Ultrasonic Testing
Figure 2.3: EMAT and EMAT SET
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