Development of the multi-segment lumbar spine for humanoid robots

Abstract

The paper presents the development of the multi-segment lumbar structure based on the human spine. The research is performed within the project based on the development of socially acceptable robot named "SARA". Two approaches for the spine realization of humanoids exist: multi-joint viscoelastic structures (5-10 joints) that have variable flexibility, and structures that consist of one joint-torso/waist joint, which has low elasticity and high stiffness. We propose multi-joint flexible structure with stiff, low backlash and self-locking mechanisms that require small actuators. Based on kinematic-dynamic requirements, the dynami-cal model of the robot is formed. Dynamical simulation is performed for several postures of the robot and the driving torques of lumbar structure is determined. During the development of the lumbar structure, 16 variant solutions are consid-ered. Developed lumbar structure consists of three equal segments, it has 6 DOF (2 DOF per segment) and allows movements of lateral flexion â±30° and torsion â±45°, as well as the combination of these two movements. In the development phase, the movements of flexion/extension are excluded, for the bending of the body forward to an angle of 45° is achieved by rotation in the hip joints. Pro-posed solution of the lumbar structure is characterized by the self-locking of mechanisms (if for any reason actuators stop working, lumbar structure retains in the current posture), low backlash (high positioning accuracy and repeatabil-ity of movements), compactness, high carrying capacity, and small dimensions.