Design and control of a pneumatic microrobot for in-pipe inspection of nuclear pipes

Micro Electro Mechanical Systems (MEMS) are integrated in many current products and are not only the concern of military defence or medicine. Nowadays, many different types of microactuators exist which use different types of energy and perform a variety of movements. Several applications require small systems to inspect confined and hostile places. Vapour generators in nuclear plants comprise of 3000 to 5000 vertical pipes of 17 mm diameter. These pipes endure high mechanical constraints and have to be inspected to detect possible cracks. Our study is based on the design, modelling and implementation of a microrobot able to move upwards within and carry sensors into these pipes. It moves as an inchworm and is composed of 2 blocking modules that brace the robot on the pipe sides, and one stretching module that creates a step. This actuator is pneumatic and composed of metal bellows. By this original design, the microrobot has a good power-to-volume ratio and it can carry a load of 600 g. Its good positioning accuracy has been proved over a 90 mm course where the error of positioning is less than 60 μm.