Design characteristics of a pipe crawling robot

This thesis deals with the design characteristics of a pipe crawling vehicle which utilises a unique, innovative and patented drive system. The principle of the drive system is simple. That is, if a brush is inserted into a pipe and its bristles are swept back at an angle, then, it is easier to push the brush forwards through the pipe than it is to pull it backwards. Thus, if two brushes are interconnected by a reciprocating cylinder, then, by cycling the cylinder, it is possible for the vehicle to "crawl" through the pipe. The drive mechanism has two main advantages. The first is the ability of the bristles to deflect over or around obstacles, thus, the vehicles can be used in severely damaged pipes. Secondly, the drive mechanism is able to generate extremely high "grip" forces, thus, the vehicle has a high payload to weight ratio. This "simple" traction mechanism has subsequently been proven to be extremely capable in significantly hostile environments, for example, nuclear plants and sewers. The development of the vehicle has resulted in brushes being considered as "engineering" components. This thesis considers the forces present when a brush moves forward through a pipe, further, it also considers the forces present if the brush is required to grip the walls of the pipe. A "simple" cantilever model has been developed which predicts the force required to push a brush forwards through the pipe. A second model has been developed which predicts the forward to reverse or "slip" to "grip" ratio of a brush, for given functional conditions. This model is deemed satisfactory up to the onset of bristle buckling. The experimental program determined three factors, they were, the force required to load a brush into a pipe, the force required to push a brush forward through a pipe and the reverse force a brush could support prior to failure. It can be concluded that this vehicle, through its tractive capability arid environmental compliance, is able to traverse irregularly shaped pipes. Ultimately, this allows tooling to be transported and used at previously unobtainable positions within such pipes

Autonomous control for on-orbit assembly using artificial potential functions

Current spacecraft mission analysis has highlighted a requirement for the assembly of large structures in Earth Orbit. This thesis investigates an autonomous method of assembly for such large structures. The scheme envisaged is based on Lyapunov's method which is extended to potential function theory. The method forms an analytical solution to the assembly problem by generating high level control commands which are then devolved to individual actuator commands for the assembly vehicles. The application of the method to general assembly problems has allowed the development of a generic global potential function. The application of the global potential function has required the use of a connectivity matrix which contains the information required to assemble the goal structure. Thus, a structure may be modified by altering only the characteristics of the connectivity matrix. The generic assembly method is then applied using a subsumptive type architecture which allows the assembly controller to delegate sub-components of the total structure to secondary controllers. Therefore, the method may then be utilised to construct complex structures, which, when linked to the use of smart components and joints allows the assembly of adaptive structures. These adaptive and variable topology structures which may change their functionality with time may prove useful for future mission applications