Integrating Elastic Actuation In Humanoid Robotics: From Parallel Manipulator Design To Bipedal Locomotion With A Compliant Ankle

Abstract

This thesis explores the integration of elastic elements into humanoid robotic systems, aiming to enhance adaptability, stability, and energy efficiency. Specifically, it focuses on a novel tendon-driven parallel manipulator for the shoulder joint and a simplified bipedal robot, both incorporating compliant elements to improve performance and reduce mechanical complexity. The shoulder joint design incorporates a central elastic limb made from Thermo Plastic Polyurethane (TPU), integrated into a closed-loop kinematic chain with three rigid outer limbs. This design enables two degrees of rotational freedom, providing the necessary compliance for safe and effective human-robot interaction. The kinematic structure is modeled as a series of links connected by universal joints, and its performance is evaluated through numerical simulations, virtual testing, and physical prototypes. Finite Element Analysis (FEA) optimizes the TPU limb’s geometry to enhance its bending and torsional capabilities. The results demonstrate that the final shoulder joint prototype offers superior vibration damping, energy absorption, and stiffness compared to other designs, making it well-suited for humanoid applications. In the second part of the thesis, the focus shifts to a low-DOF bipedal robot designed to achieve stable, energy-efficient locomotion despite its simplified mechanical structure. This robot incorporates flexible TPU-based ankles and an upper inverted pendulum to support three-dimensional balance, particularly during the single support phase (SSP). The kinematic model is analyzed for momentum balance in both the sagittal and coronal planes, ensuring equilibrium is maintained with minimal actuation. The compliant ankles, optimized through FEA and validated through physical testing, enhance posture control by resisting external bending moments and managing weight distribution. Simulations and real-world experiments validate the robot’s ability to stand on one leg and perform basic walking tasks, demonstrating how integrating elastic elements in both the shoulder and bipedal structures leads to robust and energy-efficient humanoid movement.