**6. Conclusions**

Herein, we introduced our researched and developed in-pipe inspection robots and their shadow-based operation assistant system (orientation adjustment). The key point to designing such robot for various pipelines available is downsizing and simplification by the functional complex. Our approach for this functional complex included a differential mechanism, arrangement of multiple DoFs on a common axis, and usage of a camera not only for inspection but also for the operation assistant system. At the present stage, we are testing such approach in simulated pipelines installed in our laboratory. Nonetheless, we will continue to improve the development while collaborating with the user company and are planning to carry out experiments on the actual site.
