Design parametric study based fabrication and evaluation of in-pipe moving mechanism using shape memory alloy actuators

An in-pipe moving mechanism based on design parametric study of dynamic characteristics of clamping or moving module comprising shape memory alloy (SMA) spring actuators has been fabricated and evaluated under in-pipe condition. Conventional in-pipe moving mechanisms for pipe inspection, driven by electromagnetic motors, have large volume and mass. The SMA actuator can be an alternative for a small-sized in-pipe moving mechanism due to its great power-to-weight ratio and simple structure. Therefore, spring type SMA actuators are selected to fabricate an inchworm-like moving mechanism that consists of clamping and moving modules. For selection of proper operating type (a bias type or a differential type) for clamping module and moving module, displacements and dynamic characteristics of each operating type have been investigated. Based on experimental results, we decide some design parameters such as wire diameters, spring diameters and the numbers of turns of SMA spring actuators and fabricate the in-pipe moving mechanism according to the designed results. A moving speed of 34 mm/min and traction force of 0.4 N have been obtained from the driving experiment in a pipe with the diameter of 39 mm.