Design and Development of ROV for Underwater Surveillance

Transcription

1 Journal Of Industrial Engineering Research ISSN Journal home page: (1): 9-16 RSEARCH ARTICLE Design and Development of ROV for Underwater Surveillance 1Luqman Al Hakim, 2 Azli Yahya, 3 Muhammad Arif Abdul Rahim, 4 Sophan Wahyudi Nawawi 1Department of Communication Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310, Johor Bahru, Johor, Malaysia. 2Department of Biotechnology and Medical Engineering, Faculty of Biosciences and Medical Engineering, Universiti Teknologi Malaysia, 81310, Johor Bahru, Johor, Malaysia. 3Department of Electronic and Computer Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310, Johor Bahru, Johor, Malaysia. 4Department of Control and Mechatronic Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310, Johor Bahru, Johor, Malaysia. Address For Correspondence: Luqman Al Hakim, Department of Communication Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310, Johor Bahru, Johor, Malaysia. Received 3 January 2016; accepted 26 April 2016; published 3 May 2016 A B S T R A C T Background: In this paper, an ROV is designed and developed for the purpose of underwater surveillance. The development begins by stipulating the design specification and consideration to narrow down the operating scope of the particular ROV. Four aspects have been considered when designing this ROV; mechanical, frame, actuator and power. The primary task of this ROV is to explore and inspects the underwater structure so, it will be equipped with colour video camera with tilting capability and wide aperture lighting. Additional kits such as sensors are used to detect the position and know the exact location of the ROV. The designed ROV is a class 1 ROV which is pure observation vehicle that has at least 4 DOF for easing the navigation through the rough underwater environment. The design concept of this ROV is split into many parts; structural frame, propulsion system, control system, power system, tether and video. The developed ROV is suitable for inspection of underwater building and bridge platform as well as underwater cabling and piping for oil and gas companies. Key words: ROV, Surveillance, design, marine. INTRODUCTION Underwater exploration is an endless effort made by mankind throughout the world to unravel the nature s treasure that enclose within the vast ocean. With the emergent of robotic technology, human are no longer needed to explore the ocean with their own body instead using unmanned underwater vehicle (UUV) to scour the ocean. Remotely Operated Vehicle (ROV) is one of the UUVs, beside Autonomous Underwater Vehicle (AUV) that is famous among the marine researchers, enthusiasts, engineers, scientists and students to be used as an underwater surveillance vessel because of its versatility and robustness features. Normally, ROVs are design based on its tasks and mode of operations. The features of an ROV are highly influenced by the design specification for it for instance, large and sturdy ROV with manipulator are meant to be for a deep water scavenger that hunts the shipwreck s residues. However, the control systems of ROVs are much likely the same in terms of stability and basic translational motions, unless there are other additional features attached to it such as manipulator or robotic arm because the interaction force between the motions of the manipulators and surrounding force affects the stability and attitude of ROV [3]. Open Access Journal Published BY IWNEST Publication 2016 IWNEST Publisher All rights reserved This work is licensed under the Creative Commons Attribution International License (CC BY). To Cite This Article: Luqman Al Hakim, Azli Yahya, Muhammad Arif Abdul Rahim, Sophan Wahyudi Nawawi, Design and Development of ROV for Underwater Surveillance. Journal of Industrial Engineering Research, 2(1): 9-16, 2016

2 10 Luqman Al Hakim et al, 2016 Stability is one of the major concerns when designing an ROV. When the ROV is in the water, it experienced two types of forces acting upon it; buoyant force and gravitational force. Buoyant force is the force that pushes the ROV upward while gravitational force pulls it downward. Each of the forces has a concentrated point in any object in the water which is called as a Centre of Gravity (COG) and Centre of Buoyancy (COB). The distance between those points which is known as Buoyant Gradient (BG) is the parameter that determines the ROV stability. The greater the distance of COG and COB of an ROV, the more stable it would be which is always remains upright when manoeuvring underwater. Though, there is trade-off of having high BG, the manoeuvrability of the ROV is becoming harder in terms of yaw and pitch movements. Fig. 1 depicts the stability of the designed ROV. Fig. 1: Centre of gravity and centre of buoyancy of a 4 degree of freedom ROV. In this report, the ROV is developed and designed for the purpose of underwater surveillance as shown in Fig. 2. The development begins by stipulating the design specification and consideration to narrow down the operating scope of the particular ROV. Then, the design concept is realized using the AutoCAD Inventor to create a structural framework for the ROV according to the designed criteria. In the next section, the control system is discussed thoroughly including the thrusters, controller used, stability, and the optimum rated operation of the ROV. Fig. 2: The designed ROV for underwater surveillance Design Consideration: When designing an ROV, the considerations are made based on the task assigned to it. In this case, the ROV is assigned to inspect the underwater structure. Hence, there are four aspects needs to be considered when designing this ROV; one of them is mechanical aspect. According to the task allocated to it, the ROV needs to be passively stable when manoeuvring and has low drag on surge and heave. On top of that, it should have a strong frame and equipped with external shock absorber to increase its robustness. For further enhanced performance, the materials used should be lighter and durable such as acrylic, glass, glass reinforced plastic, aluminium, titanium, steel and synthetic rubber [4]. Table 1 provides information on typical material properties due to external pressure.

3 11 Luqman Al Hakim et al, 2016 Table 1: Typical Material Properties Due to External Pressure [4] Material Density lbs/in³ Modulus of (gm/cm³) Elasticity Mpsi (Gpa) Concrete (2.4) (2.4) Compressive Yield Kpsi (Mpa) 10 (6.9) Specific Strength Mpsi/lb/in³ (Gpa/gm/cm³) 116 (29) Specific Modulus Kpsi/lb/in³ (Mpa/gm/cm³) 40.7 (17) Wood (0.65) 1.7 (11.7) 4 (27) 174 (41.5) 74 (18) Steel HY (7.85) 29 (200) 80 (551) 282 (69) 102 (25.4) Acrylic (1.19) 0.45 (3.1) 15 (103) 349 (86) 10.5 (2.6) Aluminium 6061-T6 0.1 (2.77) 10.3 (71) 40 (276) 400 (100) 103 (25.5) Steel 130 HY (7.86) 29 (200) 130 (896) 458 (114) 102 (25.4) Aluminium 7075-T6 0.1 (2.77) 10.3 (71) 70 (482) 700 (174) 103 (25.5) Titanium 6A14Va 0.16 (4.44) 16.4 (113) 125 (862) 781 (194) 103 (25.5) Steel Maraging 0.29 (8.0) 29 (200) (1644) 822 (205) 100 (36) Glass 0.08 (2.23) 9 (62) 200 (1380) 2500 (618) 113 (27.5) Ceramic Alumina 0.13 (3.70) 44 (303) 350 (2413) 2692 (649) 338 (81) Second aspect is frame; the ROV is like an ordinary robot that requires frequent handling for servicing, maintaining and adjusting. The tendency for the ROV to differ with the original design is also higher due to the improvement made. Thus, it is important to design the ROV with customizable features such as multiple mounting positions and adjustable mounting features so that the modification can be made without damaging the robot frame. On the other hand, the design s COB and COG points have to be consider which depending on the ROV s application because it will determine the ROV s stability by the distance of BG. Third is about actuator; thruster is the movement mechanism for the ROV, as it provides translational motion that depends on the ROV s degree of freedom (DOF) by manipulating the on and off of the thruster. The number and position of thruster plays a major role in determining the ROV s DOF [1]. Still, high DOF will make the ROV hard to control and manoeuvre. Besides, high efficiency thruster is very desirable in this case because the sightseeing ROV needs to operate longer time and requires high degree of manoeuvrability. Fourth is the power; thruster is one of the ROV s components that consumed a lot of power especially when the pressure is higher. This is because; the dc motor will draw more current from the supply at a higher torque due to the pressure. Because of that, suitable tether cable has to be used to support high input voltage to supply adequate current to the thrusters and also the on-board controller inside the ROV. The power loss has a directly proportional relationship with the length of the cable, thus if the length of a cable is longer, the greater would be the power loss. Hence, the supply current should be greater than the normal value to compensate for the loss. Design Specification: The primary mission of this ROV is to explore and inspects the underwater structure. In order to realize the task, it must equipped with colour video camera with tilting capability and wide aperture lighting to give excellent footage during the flight. Additional kits such as sensors are needed to detect the position and know the exact location of the ROV. The particular sensors used are including the Inertial Measurement Unit (IMU), altitude and GPS as shown in Fig. 3.

4 12 Luqman Al Hakim et al, 2016 Fig. 3: 5 DOF IMU and GPS sensor In this paper, the designed ROV is a class 1 ROV which is pure observation vehicle should has 4 DOF for easing the navigation through the rough underwater environment. To have that feature, the minimum number of thruster to mount on the ROV is at least three or more despite where it is located because the 4 DOF will cater the ROV motion of surge, yaw, heave and pitch. The design vessel has to be working at the depth ranging up to 50m to be able to get a clear picture of the environment. In Table 2, the summarized design specifications were tabulated in details according to the designed ROV in which is going to be discussed in this paper. Table 2: Design Specification Description Specification Dimension 360mm x 381mm x 165mm Camera Colour HD camera (1280 x 720p) Viewing angle 78⁰ (Horizontal) 180⁰ (Vertical) Lighting Bright LED Operating time 2 hours (minimum) Working depth 50m (maximum) Tether/Umbilical cable 100m Pilot control Gamepad, Joystick, Keyboard Navigation sensor IMU, Altitude, GPS On-board controller Arduino Uno Power supply Surface-supplied, on deck Propulsion 3x Thrusters Speed 3 Knots (maximum) Weight 10Kg (maximum) Design Concept: a) Structural Frame: The frame is comprised of two sections; viewing deck and support frame. The viewing deck is a dry compartment of the ROV that holds the electronic system inside it as well as camera and lighting. It is made from a transparent acrylic cylinder with a cap and flange to give clear viewing angle for the camera. The cylindrical shape of the viewing deck, minimizes the pressure exerted to it and create hydrodynamic that will reduce the drag resistance [1]. On top of that, the flange is attached to the cap to prevent the water from leaking but it will cause lower pressure inside the deck because when the ROV dived deeper into the ocean, the high pressure outside will make the air inside to be compressed or low pressure and try to push the tube outward. The combine forces exerted from both pressure will break the tube if the ROV is going deeper. To maintain the pressure inside the tube, there is a designated hole made at the cap that will be filled with enclosure vent to allow the air to sip through it. The support frame was made to be strong, durable and easy to manufacture. It resembles skeleton frame like ROV as it has bare frame without cover. The idea behind this design is for the ROV to have the customizable feature so that when there is a need to modify it, the other designs or features will not get affected. The frame has mounting feature that can hold 1 vertical thruster and 2 horizontal thrusters. The function of vertical thruster is to provide the ROV s ascent and descent translation while the horizontal thrusters provide sideways translation. The viewing deck and the support frame were intended to be attachable and detachable for easing the maintaining and servicing process as well as the thruster s holding cover. Other unnecessary material was removed from the frame to reduce the drag and prevent them from affecting the ROV s hydrodynamic and thruster s propulsive efficiency during ROV flight [2]. On other issue, the stability is not an important criterion for this type of application because it requires high degree of maneuverability to maneuver through the rough underwater environment. In this design, the ROV s BG is quite small because COB point s distance from COG point is short thus; the probability for the ROV to turn over is fairly high.

5 13 Luqman Al Hakim et al, 2016 Fig. 4: Support frame and viewing deck of the designed ROV b) Propulsion System: The most important part of class 1 ROV is its propulsion system. This is where the performance of ROV is measured and analyzed because nearly 80% or more of overall power is consumed by the propulsion system. The reliability and efficiency of the system is depending solely on the thruster. Thruster is consisting of 2 parts; motor and propeller. For this design, bilge pump is used as the dc motor of the thruster and the RC boat propeller is used for the propeller of the thruster as shown in Fig. 5 and Fig. 6 respectively. They were connected by a coupler 3.2 mm to 4 mm by connecting the 3.2 mm input to motor shaft and 4 mm output to propeller shaft. The pump is capable of pumping maximum 1100 gallon of water per hour at 13.6 Volt by drawing 5 Ampere of current. The chosen propeller for this design is 2 blade 4.5 cm diameter rake type propeller that capable of achieving higher top end speed and better ventilation when cutting the water [5]. The combination of both chosen motor and propeller at maximum power will produce approximately ROV s top speed of 1.5 m/s or 3 Knot. At deeper depth, the ROV s propulsion system efficiency will reduce slightly due to the high current demands from the thruster to overcome the pressure. In this situation, the current drawn will be limited to 2A maximum by motor driver to maximize the efficiency. In terms of translation motion, to improve the system s efficiency, only particular thruster will operates corresponding to the desired direction while others are turn off. Fig. 5: Bilge pump as a thruster Fig. 6: Rake type propeller [5] On the same issue, swirl loss is an unavoidable loss that is developed when the thruster produces the thrust force at the propeller. The swirling motion will makes a fluid flow recirculate back behind the ROV which is called wake to create a vortex that reduces the pressure within itself. Low pressure within the wake induces the suction force that will pull the ROV and increase the drag. From this effect, the propulsion efficiency is dropped to almost 40 to 50 percent. Fortunately there is a way to minimize this effect which is by adding opposite rotating propeller at the thruster. In other word, the thruster will have 2 propellers in order to improve the

6 14 Luqman Al Hakim et al, 2016 efficiency. The second propeller will rotate together with the primary propeller to cancel out the swirling effect induced. However, in this design, the second propeller is not implemented due to the budget restriction. c) Control System: The main control system is divided into two parts. Fig. 7 indicates that the first part is the user control system which is based on Arduino IDE and Processing IDE applications running on a laptop. The application is highly flexible and simple to use which makes it a suitable platform for user to design the robot s control system. The second part is the robot control system which is driven by Arduino Uno microcontroller through RS-232 serial communication. The Arduino Uno microcontroller communicates with the user control system via the tether or umbilical cable. The serial commands that were sent from the laptop were actually the commands directly from gamepad through the Processing application and the signal is sent to the microcontroller to drive the thrusters. The controller actuates the corresponding thrusters according to the user command sent signal by sending pulse width modulation (PWM) signal that has specific duty cycle to the dual full-bridge motor driver (L298). It also sends PWM signal to servo motor that holding the camera for tilting. The camera signal is not connected to the controller but it is connected directly to the user control system or laptop. The Processing application will amalgamate the signals from camera and gamepad to display one viewing window on laptop for facilitating the monitoring process. Fig. 7: Control System process flow of the designed ROV Apart from that, the navigating sensors which are IMU, altitude and GPS were controlled and monitored through the controller by collecting and converting the analogue signals that is produced from those sensors to digital form [9][13]. The signals then were analysed and compared with the desired set points and the results obtained were sent to the user control system for decision making [13]. The designed ROV does not need to have an on-board decision making actuator because it is remote controlled robot that needs user to control it. Though, it is realizable if the designer wants to add that feature but it will makes the control system more complex and difficult to troubleshoot. The response time of the ROV is quite delayed due the propagation time, noise and processing delay plus it will deteriorates significantly when the depth is deeper [11]. There are many ways to improve this performance, in this design the ROV s sensitivity setting was tuned according to the pilot s customize control [10]. The setting was manipulated through the Arduino IDE software by adjusting the PWM signal s duty cycle [10]. However, the method is not improving much of the system response time but it is acceptable for this design because the effect is not too noticeable. An effective way of improving this performance is by applying the proportional integrated derivative (PID) controller to improve the design s system transient response and reduce the steady state error [6]. The controller can be designed using electronic circuit for example, if a Darlington pair transistor is placed in front of the motor driver, the output response which drives the thruster will be faster because the transistor has a high current gain thus, increasing the system s sensitivity [14]. The analysis of this procedure is not discussed in this paper.

7 15 Luqman Al Hakim et al, 2016 d) Power System: The ROV s power is supplied by a Lead Acid rechargeable battery at the surface and also on-board (Fig. 8). The battery is capable of providing 7 Ampere hour (Ah) of power at 12 Volt. When operated, the main power drawn by the ROV is on the surface while the on-board power is just used for backup power in case of emergency. The power is solely supplied to the thrusters for this design because the microcontroller and the camera get their power directly from the laptop through RS-232. By doing this, the operating time of the ROV can be increased as well as the battery lifespan. From the design specification, the ROV should operate at least 2 hours and the rated current allowed by the motor driver at maximum is 2A at 12V. Meanwhile, the battery capacity is 7Ah at 12 so, what is the suitable operating time for the ROV so that it can prolong the battery lifespan. The answer is by discharging the battery at most 50% of its total capacity. This can be done by reducing the operating time of the ROV. By considering all of the concern parameters, the operating time of the ROV can be calculated for instance in this case, to obtain the power; the voltage 12V is times with the rated current 2A and times 2 to discharge the battery at half of its capacity which gives 48 Watt. The result is then divided by the voltage 12V to get the current drawn which is 4A. By neglecting the loss, the battery capacity is divided by the current drawn to obtain the operating time. From the calculation, the rated operating time for this ROV is 2 hours and 15 minutes which fulfil the specification. Fig. 8: 12V 7Ah rechargeable Lead-Acid battery e) Tether: Tether cable for this ROV is 12 core screened copper cable that has outer diameter of 6mm (Fig. 9). The cable can be extended to 100 meter long that is connected from the laptop to the ROV. At the laptop, RS-232 will acts as an interface for each camera and microcontroller cable to boost the signal [3]. In the cable, there is an aluminium sheet that screened the copper from the clad to minimize the noise effect throughout the cable. This means that the information signals will be less distorted during a mission and capable of producing high quality video from the camera especially [8]. With the small outer diameter, the tether has negligible drag and light so, it will not affecting the vehicle dynamics. Still, the cable needs to be monitored carefully to prevent it from tangling and bending due to the way of handling and also because of rough underwater environment in which if it is not care enough, it might breaks and lose the communication. Fig. 9: 12 core screened cable f) Video: The ROV is equipped with a digital high definition colour camera that capable of displaying the image up to 1280x720 pixels. It has automatic light correction system to adjust the image quality due to the poor lighting condition inside the ROV. For the outside vision, the bright LEDs were added on the ROV to light up the path with minimum power consumption so that the visibility can be extended further. Besides that, the camera is mounted on the servo motor to provide the tilting angle up to 180 degree vertical. It is controlled using the same controller used for the ROV s translation motion. The footage is controlled and sent to the user control system for further process.

8 16 Luqman Al Hakim et al, 2016 Conclusion: In this paper, the designed ROV for underwater surveillance has been elucidated thoroughly. The process began by considering the design consideration as the first step before proceeding to the design specification. It emphasizes more on the external aspects such as frame and thruster which is based on the main task designates to the design ROV. On the next part, the design specification is developed based on the consideration made on the design ROV according to the financial support allocated. In this part, the specific parameters and material used are specified precisely to provide the reference points for the next section. The last part is where the ROV is realized conferring to the prior processes. Each subsystem is explained in details about the system used on the designed ROV by discussing and analysing the pros and cons and methods on how to improve the ROV s performances. By reviewing the designed ROV s concepts and capabilities, the vehicle is able to adapt and withstand the harsh underwater environment condition for a longer period. Due to that, it is suitable to be used as a thorough inspection tool for underwater piping and cabling. Oil and Gas Company such as Petronas and Shell might want to consider employing this vessel in the future because of its credibility as a meticulous low cost inspection robot that has incredible robustness feature and very reliable in the ocean. ACKNOWLEDGEMENT The author would like to thank RMC-UTM for providing financial support through grant FRGS- R.J F394. REFERENCES [1] Roslan, S., M. F. M Said, S.A.A. Bakar, Conceptual Design of Remotely Operated Underwater Vehicle, Journal of Transport System Engineering, 1(2): [2] Martins, J.B., Sousa, F.L. Pereira, A New ROV Design: Issues on Low Drag and Mechanical Symmetry, Journal of Oceans, 3(19): [3] Brundage, H.M., L. Cooney, E. Huo, H. Lichter, 0. Oyebode, P. Sinha, M.J. Stanway, T. Stefanov-Wagner, K. Stiehl, D.Walker, Design of an ROV to Compete in the 5th Annual MATE ROV Competition and Beyond, in MATE ROV Competition, Massachusetts, USA, pp: [4] Stachiw, P.E., Acrylic Plastic as Structural Material for Underwater Vehicles, IEEE Trans., 1(4): [5] ROV, Program Team Manual Underwater Robotics for High School Students, Eastern Edge Robotics, pp: [6] Nise, N.S., Control System Engineering, in Design Via Root Locus, 6th ed., New Jersey: John Wiley & Sons. [7] Bruno, F., M. Muzzupappa, A. Gallo, L. Barbieri, F. Spadafora, D. Galati, B.D. Petriaggi, R. Petriaggi, Electromechanical devices for supporting the restoration of underwater archaeological artefacts, in MTS/IEEE OCEANS 15 Conference, Genova, Italy, pp: [8] Webster, S., The development of excavation technology for remotely operated vehicles, Archaeological Oceanography, pp: [9] Corke, P., C. Detweiker, M. Dunbabin, M. Hamilton, D. Rus, I. Vasilescu, Experiments with Underwater Robot Localization and Tracking, 2007 IEEE International Conference on Robotics and Automation, , Roma, Italy, pp: [10] Hanai, H.T., Choi, S.K. Choi and J. Yuh, Experimental study on fine motion control of underwater robot, Advanced Robotics, 18(10): [11] Azis, F.A., M.S.M. Aras, S.S. Abdullah, M.Z.A. Rashid, M.N. Othman, Problem Identification for Underwater Remotely Operated Vehicle (ROV), A Case Study. Procedia Engineeringm, 41: [12] Aras, M.S.M., F.A. Azis, M.N. Othman, S.S. Abdullah, A Low Cost 4 DOF Remotely Operated Underwater Vehicle Integrated With IMU and Pressure Sensor, In 4 th International Conference on Underwater System Technology: Theory and Applications 2012 (USYS'12), pp: [13] Aras, M., M. Shahrieel, M. Farriz, Md Basar, A. Azis, Fadilah, F. Ashikin, Ali, Analysis Movement of Unmanned Underwater Vehicle using the Inertial Measurement Unit, International Journal of Emerging Science and Engineering (IJESE), 1(10): [14] Teck, L.W., M. Shahrieel, M. Aras, Fadilah, A. Azis, A. Syahida, H. Norhaslinda, Comparison of Depth Control from Surface And Bottom Set Point of an Unmanned Underwater Remotely Operated Vehicle using PID Controller, International Conference on Underwater System Technology: Theory and Applications.