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A Compact and Compliant External Pipe-Crawling Robot

TitleA Compact and Compliant External Pipe-Crawling Robot
Publication TypeJournal Article
Year of Publication2013
AuthorsSingh, P, Ananthasuresh, GK
JournalIEEE Transactions on Robotics
Date PublishedFeb
KeywordsActuators, annular space, bias spring, bidirectional linear actuator, circumferential motion, compact external pipe-crawling robot, compliant external pipe-crawling robot, Compliant mechanism, compliant mechanisms, compliant ring actuator, control circuit, Crawlers, crawling speed control, grippers, gripping pads, hazardous areas, hazardous environment, inchworm motion, inspection, insulating rollers, kinematic function, longitudinal axis, Manufacturing processes, mobile robots, outer diameter, pipe crawler, pipe inspection, pipes, Prototypes, radial motion, radial span, radially deployable compliant ring actuator, robot automation, robot fabrication, robot kinematics, robot testing, Robots, service robots, Shape, shape memory alloy (SMA), shape memory alloy wires, shape memory effects, SMA wires, spring-steel compliant mechanism, Springs, springs (mechanical), velocity control, wires

The focus of this paper is on the practical aspects of design, prototyping, and testing of a compact, compliant external pipe-crawling robot that can inspect a closely spaced bundle of pipes in hazardous environments and areas that are inaccessible to humans. The robot consists of two radially deployable compliant ring actuators that are attached to each other along the longitudinal axis of the pipe by a bidirectional linear actuator. The robot imitates the motion of an inchworm. The novel aspect of the compliant ring actuator is a spring-steel compliant mechanism that converts circumferential motion to radial motion of its multiple gripping pads. Circumferential motion to ring actuators is provided by two shape memory alloy (SMA) wires that are guided by insulating rollers. The design of the compliant mechanism is derived from a radially deployable mechanism. A unique feature of the design is that the compliant mechanism provides the necessary kinematic function within the limited annular space around the pipe and serves as the bias spring for the SMA wires. The robot has a control circuit that sequentially activates the SMA wires and the linear actuator; it also controls the crawling speed. The robot has been fabricated, tested, and automated. Its crawling speed is about 45 mm/min, and the weight is about 150 g. It fits within an annular space of a radial span of 15 mm to crawl on a pipe of 60-mm outer diameter.