Design characteristics of a pipe crawling robot

Abstract

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.