Multi-degree-of-freedom electromagnetic actuator implemented as a spinal segment

Aadnesgaard, Sigrid

Multi-degree-of-freedom electromagnetic actuator implemented as a spinal segment

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Electrical Engineering

Faculty

Faculty of Engineering and the Built Environment

Abstract

Quadruped and humanoid robots are increasingly integrated into daily life, contributing to applications ranging from hazardous exploration to manufacturing and domestic assistance. While advancements in agility, efficiency, and adaptability have been achieved, the flexibility of robotic spines remains a significant limitation. The inclusion of flexibility in robotic spines is a feature that is often overlooked, resulting in robots with rigid structures, limited degrees of freedom (DOF), and complex control mechanisms. Traditional actuation methods in quadruped and humanoid spines rely on bulky, redundant systems with multiple motors and tendons, where actuator design and optimisation are rarely prioritised. This thesis explores multi-degree-of-freedom (MDOF) actuators, focusing on their application in an electromagnetic spinal segment. Electromagnetic actuators offer a promising alternative to traditional actuators as they enable bidirectional movement directly on the end effector, reducing the number of required actuators and removing the need for wires and tendons. A novel Double Helix (DH) actuator is proposed to facilitate MDOFs from a single structure. Despite the DH achieving two DOFs, its integration into a spinal actuator was replaced by a linear solenoid electromagnetic plunger that offers a quick response, high force, ease of control, and configurable stroke lengths. This thesis details the design and optimisation methodology for the linear solenoid plunger, highlighting its potential for more efficient actuation. The system achieves enhanced stability and increased DOF by combining the linear actuators into a parallel configuration. The resulting spinal segment is a compliant six-legged parallel actuator capable of six DOF. The parallel system demonstrates its feasibility and potential for enhancing robotic movement by reducing actuators and tendons, improving flexibility and eliminating complex control methods. The thesis highlights the importance of the design methodology of electromagnetic robots and robots alike, reducing their complexity and improving their adaptability and modularity. The resulting structure achieves six DOF in the form of a parallel manipulator, with potential applications as a spinal segment in both quadruped and humanoid robots.

Keywords

robots, actuator design

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