Design and Basic Control of Extra Robotic Legs for Dynamic Walking Assistance This paper presents an Extra Robotic Legs (XRL) system which is designed to assist in the human walking with carrying loads. The design and basic control of the XRL system are proposed, and performances of the system are verified by primary experiments. The main aim of the design is to enable the XRL system to generate enough power for assistance during the natural human walking with low selfweight. Two robotic legs are designed for the XRL system, and each leg has three degrees of freedom (DOFs): two rotational DOFs intersecting at one point on its basis, and one prismatic one along its length generating assistant forces. The prismatic DOF is driven by synchronous belts along a linear slider, and has a high linear velocity for dynamic walking assistance. A force control method is used to generate assistant forces. The final weight of our autonomous XRL system is 8.3 kg, lower than other relative autonomous systems in present. Primary experiments verify the functional performances of the XRL system. This work may inspire other XRL designs and can expand the applications of wearable robots in daily life.

Performance Analysis of Torquesensorless Assist Control of a Powered Exoskeleton Using Highly Backdrivable Actuators For human motion support, there is an active focus on research and development of powered exoskeletons. A powered exoskeleton is directly fitted to the human body; thus, it is necessary to consider the safety of the humanrobot interaction, including improving the backdrivability. Toward this problem, a powered exoskeleton that uses a highly backdrivable reduction gearbox even at a high reduction ratio is proposed, and a userxe2x80x99s external force can be estimated without using a torque sensor even though the system has very high total gear ratio of 408.57:1. This paper investigated the apparent mechanical impedance of an exoskeleton during assist control execution and examined the performance and operability of the assist control. Finally, a questionnaire of participants was conducted and the mechanical impedance that resulted in a high operability was examined by implementing admittance control.