Lecture on High Performance Robotic Actuation

Speaker: Nikola Zlatkov Georgiev

Institution: California Institute of Technology

Topic: Thesis Defense on High Performance Robotic Actuation

Abstract

• Objective: Development of high-performance actuation for robots (legged, limbed, mobile).
• Requirements: Actuators need to be lightweight, compact, efficient, shock tolerant, and backdrivable.
• Impact: Actuator design affects robot dynamics sensitivity.

Key Areas of Focus:

• Outer rotor motors with concentrated windings
• Bearingless planetary gearbox
• Rotary planar springs

Contributions:

1. Motor Design:

   • Application-specific design for electric vehicles, drones, and robotic joints.
   • Trade-offs in design for copper loss, core loss, and mass.

2. Gearbox Design:

   • Introduction of Bearingless Planetary Gearbox with high reduction ratios.
   • Advantages: improved robustness, load distribution, and manufacturability.

3. Spring Design:

   • Analysis and prototyping of rotary planar springs for elastic actuators.
   • Optimization and mass reduction techniques.

Published Content and Contributions

• Various studies and papers co-authored by Nikola Georgiev on topics such as planar rotary springs and bearingless planetary gearboxes.

Contents Overview

1. Introduction
2. Robot Dynamics Sensitivity
3. Brushless-DC Outer Rotor Motors
4. Bearingless Planetary Gearbox Design
5. Planar Rotary Spring Design
6. Actuator Prototypes
7. Conclusion and Future Work

Detailed Notes

Chapter 1: Introduction

• Electric motors dominate robotic actuation.
• High power density can be achieved at high speeds; however, torque density is low.
• High reduction gearboxes increase actuator shock tolerance.
• Series Elastic Actuators (SEA) introduced for shock tolerance; however, intrinsic limitations exist.
• Alternative approach: Low to mid reduction ratio gearboxes with large torque-optimized motors.

Chapter 2: Robot Dynamics Sensitivity

• Focus: Sensitivity of multi-limbed robots to actuator design.
• Reflected inertia of actuators affects mass matrix condition number.
• SEAs eliminate actuator dynamics influence on robot dynamics.
• Methods to improve dynamics include actuator inertia optimization and robot design adjustments.

Chapter 3: Motor Design

• Objective: Design high torque density outer rotor motors.
• Considerations:
  • Motor losses in relation to load and speed.
  • Application-specific designs: EVs, drones, robotics.
• Advantages: Outer rotor motors with high pole counts for high torque density.
• Challenges: Managing core and copper losses, especially at high speeds.
• Verification: Analytic models verified with FEA.

Chapter 4: Bearingless Planetary Gearbox

• Purpose: Improve gearbox torque density and robustness.
• Design: Removes carrier, introduces secondary sun gear.
• Benefits: Floating gears improve load distribution.
• Challenges: Managing unbalanced loads and noise.

Chapter 5: Planar Rotary Springs

• Goal: Optimize rotary springs for SEAs.
• Methods: Spring modeling, composite materials, cutouts for mass reduction.
• Analysis: Arm contacts and optimization techniques for improved torque density.

Chapter 6: Actuator Prototypes

• Description of prototypes integrating motor, gearbox, and spring designs.
• Examples include low reduction actuators and bearingless SEAs.

Chapter 7: Conclusion and Future Work

• Achievements: Developed methods to optimize robotic actuation.
• Future Directions: Focus on actuator design for improved dynamics, high torque density motors, and innovative gearboxes.

Appendices and References

• Detailed list of figures, tables, and nomenclature.
• Comprehensive bibliography documenting prior research and studies cited throughout the thesis.