Developing a Sewer Inspection Robot through a Mechatronics Approach

Transcription

1 Developing a Sewer Inspection Robot through a Mechatronics Approach Alireza. Hadi, Gholamhossein. Mohammadi Abstract Sewerage is a harsh environment which requires periodically inspection. The inspection should be done duo to the unanticipated problems that may occur in the sewer networks. Entrance of objects like roots, corrosion and deformation of pipe are some usual problems occur in the network. As a result, monitoring the pipe interior is necessary for managing the sewer system. Sewer inspection robots as a kind of mobile robots are specially developed to inspect the pipe interior. At first, the robot should move through the pipe and provide pictures and video from the inside of pipe. In addition, producing sensory data from the pipe interior would be very valuable. The progress of technology in the field of mechatronics provided more opportunities for improving the inspection robots capabilities. In this paper, an improved version of sewer inspection robot is developed. The main concept in the hardware development of the system in mechanical and electrical is considered from the beginning of the design. Further, through the developments in the software of the robot, the output of the system is more attractive for the waste water companies and produced a more acceptable product. Application of robot in live sewer networks show reasonable results and verifies the system application. T Keywords Inspection, Robot, Sewer. I. INTRODUCTION HE ability to monitor and evaluate the pipe s interior is an important requirement of maintaining of pipelines. Visual confirmation is desired before performing corrective actions and/or expanding capital costs. Sewer pipelines in Iran are usually existed from 200 to 2000 mm in diameter for sewer transmission from houses to refineries. In the past, pipes were manufactured from concrete but recently the polyethylene type is more usual in the new networks. However, the material of the pipes affect the kind of problems occurred in the system. Some of the problems may happen in sewer network are: Entrance of roots of trees and lateral branches to the pipe Settling of materials in a single place which cause obstruction Corrosion of pipe surface Distraction of pipes in joints Deformation of pipe and change of cross section Unwanted variation of pipe slope Alireza. Hadi is with the Islamic Azad University-Roudehen Branch, Roudehen, Tehran, Iran (phone: ; fax: ; e- mail: arhadi@riau.ac.ir). Gholamhossein. Mohammadi is with the Kavosh Mechanizeh Fanavar Co., Tehran, Iran ( mohammadi@kavoshmech.com). The mentioned problems increase the motivation for inspecting the interior of the sewer pipelines periodically. In addition to this, existence of small diameter pipes, unsuitable environment of sewer pipes and the necessity of inspecting live networks, force the application of a robot for this mission. In this way no human need to exist in pipes and the monitoring of the pipes status being done through a remotely controllable mobile robot. Furthermore, the classic robots conclude some sensors for better evaluating the pipe status. However, the technology progress provided more facilities for improving the inspection capabilities. This work deals with the design and prototyping of an apparatus that traverses through pipes for inspection, cleaning and/or examining of the piping system known as a pipe crawler in the industry. Pipe crawlers are frequently used to deploy monitoring equipments including sensors and/or cameras to monitor the pipe integrity and to help diagnose needed repair or maintenance [1 6]. Typically, such devices include testing probes, sensors, or cameras. While existing pipe crawlers are advantageous in that they allow for the in situ cleaning, examination, inspection of piping systems, each has its own difficulties passing through pipes. The simple mechanisms permit movement only in horizontal pipes [1 2]. Although they have the difficulty of producing necessary friction force to continue moving in far distances to pull extensive lengths of their power and signal cables, the traversing mechanism is are much simpler. However, many original locomotion concepts have been proposed to solve the numerous technical difficulties associated with the changes in the pipe diameters, presence of vertical pipes, various elbow and providing the necessary energy supply [4 6]. Walking mechanisms offer complex discrete, rather than simple continuous pipe wall contact for movement. Consequently these mechanisms have not been used in the pipe inspection industry. Based on the authors experiences [7] and utilizing a mechatronics approach, in this paper, an inspection robot is proposed which has the ability of traversing through horizontal sewer pipes. The robot is a four wheel drive mobile robot and is remotely controllable by an operator. The rest of the paper is organized as follows. Section 2 presents the design of the system hardware. Although designing the mechanical and electrical parts of the system is done simultaneously through the mechatronics approach, the mechanical and electrical designs are presented in two subsections. Section 3 describes the software of the system. Section 4 introduces the experiments done with the developed 187

2 system. Section 5 summarizes the contributions and results of the paper. II. MECHANICAL DESIGN The hardware of system consists of mechanical and electrical parts. Through the properties of the system which guided this paper to develop it through a mechatronics concept, the hardware design of the two parts is done simultaneously from the beginning. However, for more clarification, the design is presented in mechanical and electrical parts. In the mechanical design, some reservations duo to the goals of the system should be considered carefully. A. Size The robot body should be small enough to be able to move toward 200 mm diameter pipes. On the other hand, it should have enough power to move into the harsh environment of sewerage. An inspection robot may be used in different sizes of pipes. So, the robot should be extended in size to be able to inspect the harsh environment of sewerage. All the mechanical and electrical elements should be mounted in the robot in a talent manner. The actuators, sensors, power transmission parts, electronic boards and others should be managed to be placed in the robot. The size of sewer transmission lines are more than 200 mm. so, the robot is designed to effectively traverse 200 mm and more pipes. B. Traversing mechanism Sewer network is usually straight pipes from one manhole to another. So, steering is not necessary for the robot and a forward and backward move may handle traversing requirements. To optimize the number of actuators, only a motor is used for robot navigation. In the harsh and slippery environment of sewer a 4 wheels drive mechanism would be more effective and provide better traction in experiment. So, in the power transmission system of the robot, the output shaft of the gearbox is coupled with the four wheels through a right angle gearbox and a chain. Another important factor which improves the mobility of the robot is the distance between bottom of the robot and the ground. Increasing the distance, results in passing through bigger obstacles and more mobility. This parameter is increased in the new version. First version of the robot Second version of the robot Fig. 1 A modular concept in developing the robot C. Modularity The variety of demands in inspection, has guided the designers to make a modular design for proving services to different requests. In this approach, the base unit is a platform providing suitable traction requirements. This approach may also provide other benefits in extending the robot application Firstly, in maintenance; the module could be replaced with the same one. This decrease the maintenance time very much. In addition, changing the robot mission may be easily provided. D. Camera head One of the most important capabilities of a sewer robot is providing a qualified image from the pipe interior. Angle of view in cameras is limited, so fixing them in the axis of the pipe although provide a general illustration, could not describe the details properly. Rotation of camera toward robot sides provides more complete images. Pan and tilt mechanisms provide this facility as well. This pan-tilt mechanism of robot is shown in Fig.? The pan-tilt mechanism is developed as a separate module mounted in the front of the robot. Usually the pan-tilts include both pan and tilt actuators but in this paper, the pan actuator is embedded in the main platform. This helps minimizing the pan-tilt mechanism as a changeable unit. E. Sealing Many electrical devices are embedded in the robot body which should be protected against water entrance when the robot is submerged. Sealing of the robot may divided in two parts, static and dynamic. Static seal means sealing the parts with no movement toward each other while in dynamic seal the parts move rather to each other. Static seals would be implemented easier by some standard elements like o-ring or washer. As the o-rings are more reliable elements, they are used as static sealants in this work. For dynamic sealing, packing, o-ring and lip seal are suitable candidates. The active shafts come out the robot require dynamic seal. In cases that small space is required, such as pan-tilt shafts, o-rings are applied and in cases that larger space is provided, such as main deriving shaft, packing is used. A strategy for checking the robot sealing status is injection of a gas like air into the robot and monitoring its pressure. The ability of robot in keeping the pressure shows the sealing status. This would be also used for explosion protection of robot. When a natural gas like N 2 is injected, there is no opportunity for explosion. Monitoring the gas pressure inside the robot help in checking the robot sealing and keeping it explosion proof. F. Accessibility of devices The robot concludes some devices such as electrical boards and sensors. The electrical devices should be embedded in robot skillfully in order to consume lower spaces as possible. In addition, they should be replaced quickly to decrease the maintenance time. In inspection of different sizes of pipes, keeping the camera in the center of pipe makes the inspection easier. However, the mechanism of changing the camera height increases the robot 188

3 complexity. Further, the inspection could be implemented without this mechanism. As illustrated in fig.?, the first version of this robot was equipped with this option but the recent version do not contain that. G. Cable reel Power, control signals and video signal is transmitted through the cable. In addition to safe communication through the cable, it is an instrument for moving the robot outside the pipe when it is stopped in the sewerage. So, the tensile strength and the jacket resistance of it are important. III. ELECTRICAL DESIGN The electrical design of robot which is progressed beside the mechanical design is presented in this part. In the following, the conceptual design of the system is developed through the mechatronic concept. Afterward, more details about the specification of electrical hardware are presented. A. Conceptive design The robot should be operated remotely outside the pipe. So, a command unit is necessary for communication of operator and the robot. Fig. 2 illustrates a block diagram of the hardware of the system. Fig. 2 General block diagram of the station hardware The electrical hardware is separated into a robot part which is placed on the robot and an operating and power system placed outside the pipe in the navigation station. A safe communication for a few hundred meters of cable is serial RS485 protocol. B. Electrical parts details From the industrial actuators such as electrical, pneumatic and hydraulic, the electrical actuators are the best candidate for applying in a sewer inspection robot. Because utilizing, deriving and control is very simple. Among the electrical actuators, DC gear motors could better support the above properties. In inspections, operator manages the robot through a command unit. This unit which is illustrated in Fig. 3 includes the electronic boards of the station for deriving the main traversing motor, power distributers, keyboard and a local LCD. Fig. 3 The robot command unit The images provided through a high quality camera. Some important parameters in visual inspection as zoom, focus and iris are controlled through a standard protocol. The sensory system of the inspection robot shows its property. Slope and ovality of pipe are two major requests of inspection. Further, the distance of pipe joints and cracks is required. Some of the parameters should be straightly provided through sensors and some could be measured by image processing. Analyzing the qualified images of the robot and extracting more information would not increase the hardware cost and easily done through the software. In this paper, the robot includes an inclination sensor to measure the tilt. Also to providing the exact profile of the pipe cross section, a laser range finder sensor is mounted on the pan-tilt mechanism. By rotation the pan in the pipe, the sensor measure the distance of sensor to the pipe and extract the profile of the pipe. The other parameters such as pipe joints distance, size of cracks and so on calculated by image processing. Lightning in the pipe is necessary to produce images. It is provided by a group of high power leds mounted on the pantilt mechanism and derived by the electronic boards of the robot. Another important strategy applied in robot system, is synchronizing the cable reel velocity with the robot movement. In forward traversing of robot, the cable real is free and robot could easily go forward. In backward movement, the cable reel collects the cable. The velocity of cable drum should be synchronized with the robot velocity. The strategy for reaching to this goal is driving the cable reel with a arbitrary velocity and using the cable velocity as a setpoint for robot to reach. An encoder, measures the cable velocity. This sensor is also useful for estimating the robot position into the pipe. IV. SOFTWARE The software has a special role in a mechatronics system in increasing the system efficiency. The operator manages the inspection through the software. As the main goal of sewer inspection is providing images from the pipe interior, in the main window a good view of the pipe is presented. The provided pictures may be recorded as a video file. A snap shot may also be taken from defects. Further, the various defects may be described in detail through a standard classification. EN13508 standard of sewer inspection classification is implemented in the software for classification of observed defects. The online video, snap shot images and the assigned defects in addition to all the sensory data are presented in the software in separate windows. Fig. 4.a presents the main 189

4 windows of the software and Fig. 4.b show the sensory data window in detail. Fig. 5 a) The inspection system place on a van, b. Robot cable reel Fig. 4 a) The main window of software b) window of sensory data V. EXPERIMENTS Some experiments are done by the robot in the real and live sewer networks in Tehran. The 4 wheel drive traction of the robot was experienced in concrete and polyethylene pipes. The robot could successfully traverse different pipe diameters with less than 40 % of sewerage. However, using wheels with more friction increases the contact force and robot efficiency in traction. High quality images provided by the camera, in addition to satisfying visual inspection requirements, provide a platform for image processing. The inclination sensor of the robot provides accurate data verified by straight measuring methods. Also, the laser sensor produces the exact profile of the pipe cross section. An illustration of inspection system mounted on a van is presented in Fig. 5.a. Some other helpful instruments like generator, larger pipes wheels and maintenance tools are mounted on the van. Also Fig. 5.b presents the automatic cable reel developed for the robot. In front of the cable reel, a crane mechanism is added for vertical movement of the robot in the manhole. Fig. 6 The variation of sensory data generated by the software and robot a) pipe slope and b) height VI. CONCLUSION In this paper, a robot for inspecting sewer pipeline was presented. The system in this paper is considered as a mechatronics system. Because of that, mechanical, electrical, software and control challenges are related to each other from the beginning of the design. In the presented system of this paper which the previous experience of the authors was applied in developing that, the robot application in real environment was verified in experiment. Application of robot in sewer network for a few months shows the progress of system rather than the previous version. 190

5 Good sealing, suitable traction and accurate sensory data could be seen in real. However some improvements would increase the system efficiency. Using wheels with more friction may increase the robot traction. Also adding a mechanism for pushing the robot to the pipe surface improves this capability. ACKNOWLEDGMENT The authors may appreciate Kavosh Mechanizeh Fanavar Company which provided the support for developing this project. REFERENCES [1] A. Casals, C. Riba, and V. Minguillon, Sric: A mobile vehicle for pipes inspection and maintenance, ICAR1995. [2] Y. Kawaguchi, I. Yoshida, H. Kurumatani, T. Kikuta, and Y. Yamada, Internal pipe inspection robot, Proc. of IEEE International Conference on Robotics and Automation, pp , [3] H. Roth, K. Schiling, S. Futterknecht, U. Weigele, M. Risch, Inspection and repair robots for waste water pipes, a challenge to sensories and locomotion, Proc. of IEEE International Conference on Robotics and Automation, pp , [4] K. Suzumori, T. Miyagawa, M. Kimura, and Y. Hasegawa, Micro Inspection Robot for 1-in Pipes, IEEE/ASME transactions on mechatronics, Vol. 4, No. 3, [5] S.G. Roh, S.M. Ryew, J.H. Yang, H.R. Choi, Actively steerable in pipe inspection robots for underground urban gas pipelines, Proceedings of the IEEE International Conference on Robotics & Automation, Korea, [6] W. Ilg, K. Berns, S. Cordes, M. Eberl, R. Dillmann, A wheeled multijoint robot for autonomous sewer inspection, Proceedings of the IEEE international conference on robotics & automation, pp , [7] M. Moghaddam, A. Hadi, T. Abbasian, Design and Manufacturing SEWBOT: a Sewer Inspection Robot, 1st International Conference on Technical Inspection and NDT, October 2007, Tehran, Iran. 191