There is a need for technology to investigate the large space beyond a narrow hole. An example is the exploration of the Main Stream Isolation Valve (MSIV) room at the Fukushima Daiichi Nuclear Power Plant. The authors designed and fabricated a prototype long articulated arm, LIBRA-I, for this exploration. The design requirements were that the robot should be able to pass vertically through a naarrow access hole, transport a measurement device horizontally at right angles to the hole axis, be simple, lightweight, compact, and have low power consumption. To meet these requirements, a robot configuration combining a horizontally extending arm and a 2-degree-of-freedom(DoF) joint, and a variable mass 2-DoF counterweight were adopted. As a result, LIBRA-I has a horizontal reach of 4[m], a passable hole diameter of 300[mm], a mass of 11[kg] for the arm, and 5-DoF. As a motion experiment, LIBRA-I successfully performed a horizontal extension motion from a vertically suspended condition. 3D models of the environment was successfully created by capturing video using a camera on the tip of LIBRA-I. We also measured the power consumption in static and confirmed that it was extremely low, ranging from 15.8[W] to 23.5[W].
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