Construção de um robô trepador com locomoção através de rodas e adesão através de meios magnéticos

Mestrado em Engenharia Electrotécnica e de ComputadoresO interesse no desenvolvimento de robôs do tipo trepador tem vindo a crescer rapidamente nos últimos anos. Os robôs trepadores são equipamentos úteis que podem ser adoptados numa variedade de aplicações, tais como na manutenção, na construção, na inspecção e na segurança, em indústrias de processo e da construção civil. Estes sistemas são essencialmente adoptados em locais onde o acesso directo por um operador humano é demasiado caro, devido à necessidade de montagem de andaimes, ou muito perigoso, devido à presença de um ambiente hostil. As principais motivações para a sua utilização prendem-se com o aumento da necessidade de maior eficiência nas operações a realizar, através da eliminação da montagem de andaimes, ou com a necessidade de protecção da integridade física dos trabalhadores humanos na realização de tarefas consideradas perigosas. Vários robôs trepadores foram já desenvolvidos, e outros encontram-se em desenvolvimento, para aplicações que vão desde a limpeza até à inspecção de construções de difícil acesso. Um robô trepador deve, não só, ser leve mas também apresentar uma elevada capacidade de carga, de forma a reduzir as forças de adesão necessárias e conseguir transportar equipamentos e instrumentos durante a sua navegação. Estas máquinas devem ser capazes de se movimentarem em diferentes tipos de superfícies, com diferentes inclinações, e de passarem de umas superfícies para as outras. Para além disso, devem ser capazes de se adaptarem a diferentes condições ambientais e de se reconfigurarem. Até à data, já foi dedicado um esforço significativo de investigação ao desenvolvimento destas máquinas e já foram propostos diferentes tipos de modelos experimentais. Os dois aspectos principais a considerar no desenvolvimento de robôs trepadores são os seus métodos de locomoção e adesão. Relativamente ao tipo de locomoção, são geralmente considerados três tipos de robôs: com segmentos deslizantes, com rodas e com pernas. Quanto ao princípio de adesão às superfícies, os robôs devem ser capazes de produzir uma força elevada utilizando um mecanismo relativamente leve. De acordo com o método de adesão utilizado, estes tipos de equipamentos são geralmente classificados em quatro grupos: por vácuo ou sucção, os magnéticos, por preensão à superfície e através de propulsão. Recentemente têm vindo a ser propostos novos métodos para assegurar a adesão, baseados em princípios de inspiração biológica. Este trabalho apresenta um tipo específico de robô trepador, que possui rodas para locomoção e pertence ao grupo dos robôs trepadores magnéticos, relativamente ao princípio de adesão adoptado. A sua diferenciação está associada ao mecanismo utilizado para controlar o sistema magnético de adesão, cujo principal objectivo é optimizar a produção de forças elevadas, e equilibradas, sobre a superfície e minimizar os atritos, independentemente das irregularidades que as superfícies a explorar apresentem. A sua principal aplicação será a utilização com o objectivo de inspeccionar diferentes tipos de estruturas ferromagnéticas para, por exemplo, detectar fragilidades devidas à corrosão, nomeadamente em depósitos de combustível, cascos de navios, etc. O robô terá um comportamento semi-autónomo, permitindo um processo de inspecção controlado à distância por um técnico especializado, reduzindo os riscos associados às inspecções em altura e em outros locais onde existem características associadas perigosas para a inspecção directa por humanos.The interest in the development of climbing robots is growing rapidly. Climbing robots are useful devices that can be adopted in a variety of applications like maintenance, building, inspection and safety in the process and construction industries. These systems are mainly adopted in places where direct access by a human operator is very expensive, because of the need for scaffolding, or very dangerous, due to the presence of an hostile environment. The main motivations are to increase the operation efficiency, by eliminating the costly assembly of scaffolding, or to protect human health and safety in hazardous tasks. Climbing robots have already been developed, and are being developed, for applications ranging from cleaning to inspection of difficult to reach constructions. A wall climbing robot should not only be light but also have large payload, so that it may reduce excessive adhesion forces and carry instrumentations during navigation. These machines should be capable of travelling over different types of surfaces, with different inclinations, such as floors, walls, ceilings, and to walk between such surfaces. Furthermore, they should be able of adapting and reconfiguring for various environment conditions and to be self-contained. Up to now, considerable research has been devoted to these machines and various types of experimental models have already been proposed. The major two issues in the design of wall climbing robots are their locomotion and adhesion methods. With respect to the locomotion type, three types are often considered: the frame walking, the wheeled and the legged types. Regarding the adhesion to the surface, the robots should be able to produce a secure gripping force using a light-weight mechanism. According to the adhesion method, these robots are generally classified into four groups: vacuum or suction cups, magnetic, gripping to the surface and propulsion type. Recently, new methods for assuring the adhesion, based in biological findings, have been proposed. This thesis presents a specific type of climbing robot, which has wheels for locomotion, and belongs to the magnetic climbers robots, based on the principle of adhesion adopted. Its differentiation is associated with the mechanism used to control the magnetic adhesion system, whose main objective is to optimize the production of high and balanced forces on the surface and minimize friction, regardless of the irregularities that the areas to explore present. Its primary application will be to inspect different types of ferromagnetic structures to, for example, detect weakness due to corrosion, particularly in fuel tanks, ship hulls, etc. The robot will have a semi-autonomous behavior, allowing an inspection process controlled remotely by a technician, reducing the risks associated with direct inspections in height and other characteristics associated with sites where there are hazardous to humans

Development of a Wall Climbing Robot and Ground Penetrating Radar System for NonDestructive Testing of Vertical Safety Critical Concrete Structures

This research aims to develop a unique adhesion mechanism for wall climbing robot to automate the technology of non-destructive testing (NDT) of large safety critical reinforced concrete structures such as nuclear power plants, bridge columns, dams etc. This research work investigates the effect of key design parameters involved in optimizing the adhesion force achieved from rare earth neodymium magnets. In order to penetrate a nominal concrete cover to achieve magnetic coupling with buried rebar and generate high enough adhesion force by using minimum number of permanent magnets, criteria such as distance between multiple magnets, thickness of flux concentrator are evaluated by implementing finite element analysis (FEA). The proposed adhesion module consists of three N42 grade neodymium magnets arranged in a unique arrangement on a flux concentrator called yoke. The preliminary FEA results suggest that, using two yoke modules with minimum distance between them generate 82 N higher adhesion force compared to a single module system with higher forceto-weight ratio of 4.36. Presence of multiple rebars in a dense mesh setting can assist the adhesion module to concentrate the magnetic flux along separate rebars. This extended concentration area has led to higher adhesion force of 135.73 N as well as enabling the robot to take turns. Results suggest that, having a 50×50 mm rebar meshing can sustain steep robot rotational movement along it’s centre of gravity where the adhesion force can fall as low as 150 N. A small, mobile prototype robot with on-board force sensor is built that exhibited 3600 of manoeuvrability on a 50×50 mm meshed rebars test rig with maximum adhesion force of 108 N at 35 mm air gap. Both experiment and simulationresults prove that the magnetic adhesion mechanism can generate efficient adhesion force for the climbing robot to operate on vertical reinforced concrete structures. In terms of the NDT sensor, an in-depth analysis of the ground penetrating radar (GPR) is carried out to develop a low cost operational laboratory prototype. A one-dimensional numerical framework based on finite difference time domain (FDTD) method is developed to model response behaviour of a GPR. The effects of electrical properties such as dielectric constant, conductivity of the media are evaluated. A Gaussian shaped pulse is used as source which propagates through the 1D array grid, and the pulse interactions at different media interfaces are investigated. A real life application of GPR to detect a buried steel bar in 1 m thick concrete block is modelled, and the results present 100% accurate detection of the steel bar along with measured depth of the concrete cover. The developed framework could be implemented to model multi-layer dielectric blocks with detection capability of various buried objects. Experimental models are built by utilizing a proposed antenna miniaturization technique of dipole antenna with additional radiating arms. The resultant reflection coefficient values indicate a reduction of 55% and 44% in length reduction compared to a conventional 100 MHz and 200 MHz dipole antenna respectively. The GPR transmitting pulse generator features an enhanced tuneable feature to make the GPR system more adaptable to various environmental conditions. The prototype pulse generator circuit can produce pulses with variable width from 750 ps to 10 ns. The final assembled robotic GPR system’s performance is validated by its capability of detecting and localizing an aluminium sheet and a rebar of 12 mm diameter buried under a test rig built of wood to mimic the concrete structure environment. The final calculations reveal a depth error of +0.1 m. However, the key focus of this work is to prove the design concept and the error in measurement can be addressed by utilizing narrower bandwidth pulse that the proposed pulse generator is capable of generating. In general, the proposed robotic GPR system developed in this research proves the concept of feasibility of undertaking inspection procedure on large concrete structures in hazardous environments that may not be accessible to human inspector