Maximizing Cogging Torque in a Radial-Flux Motor: Toward a Novel Cogging-Torque Actuator

• Main Author: Aman, Jacob Lucas Barlow
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Electrical engineering; Electromagnetics
• ISBN: 9798209908531

The electric motor is the essential component of most robotic actuators. Each attachment connected to the robot actuator is designed to adapt the electric motor’s motion to the intended output. Despite their popularity, these electric motors have a number of shortcomings for use in agile robots. Some of their deficiencies include the following: (1) Motors are designed to rotate efficiently at high speeds, and must typically be geared down to achieve velocities typical of robot applications. (2) Direct-drive motors are easy to model and control as torque sources, but they are weak for their size. (3) In order to hold a position under load, direct-drive and lightly geared motors must either continuously supply electrical power to the motor or use a brake. (4) Heavily geared motors are inefficient, and are designed with no inherent compliance or backdrivability. Redesigning the electric motor is key to designing better robotic actuators. This thesis addresses the design of a new type of electric motor called the cogging-torque actuator. The cogging-torque actuator is an electrical motor with a passive magnetic torsional spring that results from the inherent cogging torque. The design of this novel actuator is motivated by promising applications in robotics, which have currently been addressed by series elastic actuators using mechanical components, such as springs for compliance, and brakes for holding passive loads. The cogging-torque actuator has the potential to be a simpler and more compact solution for use in robotic systems than traditional series elastic actuators. This thesis focuses on maximizing cogging torque and developing methods for designable compliance. The contributions include a nondimensional method for scaling cogging torque based on all parameters defining the cogging torque, a maximum-cogging-torque geometry, and a nondimensional method to scale the combined electromagnetic torque and cogging torque. Finally, the maximum-cogging-torque actuator is evaluated to determine if it can be electrically actuated.