Design and Dynamic Modeling of a Coupled-Drive Flexible Joint for Nursing-Care Robot Arm

Abstract

Abstract Patient transfer is one of the most physically challenging tasks in nursing care, the burden of which can be reduced by introducing nursing-care robots. This study proposes a coupled-drive 2-DOF (degree of freedom) joint for nursing-care robot arms to ensure that the arms have a high load capacity and smooth configuration, which is crucial for safe and comfortable contact with the care receiver. This paper presents the design methodology of the coupled-drive joint by using differential mechanism which can superimposing the torque of two motors to achieve a high load capacity. To make the joint flexible for this purpose, we introduced rubber layers in the connections of the major parts. We expressed the dynamics of the rubber layers using a hyper-viscoelastic model and applied it to the joint dynamics to build a dynamic model of the coupled-drive 2-DOF joint using the Lagrange method. To demonstrate the effectiveness of the arms with coupled-drive joints in patient transfer tasks, we built two arms, integrated them into a robot, and conducted a transfer experiment in which the motions were planned based on the dynamic model. The results showed that the designed joints had both a high load capacity and flexibility for safe and comfortable contact with humans.