Returning Motion from the State of Falling Sideways for Articulated Mobile Robot

We developed an inchworm-type mobile robot. It consisted of only six segments connected by four pitch joints and one yaw joint. Although this robot had neither legs nor wheels, it was able to advance by using vertically undulatory motion of whole body. Even if it became upside down, it was able to move just like normal posture. But if it fell sideways, it was not able to move until returning to normal posture. In this study, we proposed a returning method by which the angular moment around roll axis was generated by twisting itself. To analyze this motion, we developed a mathematical model for this returning motion by considering the robot to be an underactuated mechanical system that consisted of a base frame and two link frames. We confirmed this returning motion was able to equate with a falling down motion of an underactuated two-linked system.