High Torque Density PCB Axial Flux Permanent Magnet Motor for Micro Robots

2025-09-27

AI Summary

Conventional small-scale (<20 mm) axial-flux permanent-magnet (AFPM) motors suffer from low copper fill factor in wound stators, high winding resistance, and insufficient continuous torque—limitations that hinder their application in micro-robotic joints requiring low-speed, high-torque, ultra-thin direct-drive actuation. To address this, we propose a miniature AFPM motor leveraging high-density interconnect (HDI) printed circuit board (PCB) technology, featuring a 48-layer stacked PCB stator achieving a record-high 45% copper fill factor. Electromagnetic–thermal coupled simulation guided the optimization of both winding configuration and thermal management. The fabricated prototype measures only 19 mm in outer diameter and 5 mm in axial thickness, yet delivers significantly enhanced continuous torque density within this ultra-compact volume. This HDI-based approach overcomes critical manufacturability bottlenecks inherent in miniaturized AFPM motors and establishes a novel pathway toward high-power-density micro-actuators.

Technology Category

• Machine Learning: Hardware-aware ML
• Intelligent Robots: Motion and Path Planning
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Security and Privacy: Large-scale security measurements

Abstract

Quasi-direct-drive (QDD) actuation is transforming legged and manipulator robots by eliminating high-ratio gearboxes, yet it demands motors that deliver very high torque at low speed within a thin, disc-shaped joint envelope. Axial-flux permanent-magnet (AFPM) machines meet these geometric and torque requirements, but scaling them below a 20mm outer diameter is hampered by poor copper fill in conventional wound stators, inflating resistance and throttling continuous torque. This paper introduces a micro-scale AFPM motor that overcomes these limitations through printed-circuit-board (PCB) windings fabricated with advanced IC-substrate high-density interconnect (HDI) technology. The resulting 48-layer stator-formed by stacking four 12-layer HDI modules-achieves a record 45% copper fill in a package only 5mm thick and 19mm in diameter. We perform comprehensive electromagnetic and thermal analyses to inform the motor design, then fabricate a prototype whose performance characteristics are experimentally verified.

Problem

• Develops micro axial-flux motor for quasi-direct-drive robots
• Overcomes copper fill limitations in miniature motor stators
• Achieves high torque density in thin disc-shaped joints

Innovation

• PCB windings using HDI technology
• 48-layer stator with 45% copper fill
• Electromagnetic and thermal analyses for design