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A newly designed small sized inspection robot consisting of two modules, such as a locomotion module and a diagnostic module, has capabilities of moving along the inside of pipelines the internal diameter of which is about fifty mm, and freely passing through an L-joint by rotating its head in the direction to be turned by sensing and recognizing the L-joint with four infrared ray proximity sensors in front. This inspection robot equiped with a diagnosis sensor can detect flaws on the inside surface at the time of inspection when moving along the inside of pipelines. Diagnosis sensor outputs have been analized statistically in order to discriminate small flaws from disturbances caused by the robots movement, and fluctuations of the inside surface of pipelines.
Fukuda et al. (1986) studied this question.