Publications

2025

1. RA-L2025

   Development of a Wireless Embedded Sensing System With Physics-Based Neural Networks for Simultaneous Displacement and Force Measurements of a Magnetic Leadscrew

   Wenjing Li, Kok-Meng Lee^*, Min-Geun Park, and 1 more author

   IEEE Robotics and Automation Letters, May 2025

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   Lightweight impedance-controllable end-effectors are increasingly important in emerging applications involving physical human-robot interaction. Motivated by this need, this paper presents a method to design a magnetic lead screw (Mag-LS) with a built-in wireless sensing system that utilizes its inherent magnetic field for simultaneous displacement and force measurements. Based on the field/force models derived in closed form, this paper analyzes the uniqueness of the inverse solutions for designing the magnetic sensing system and optimizing its parameters to minimize computational cost for implementation on a standalone microcontroller where sensor noises are filtered. Unmodeled geometrical factors are accounted for using physics-based artificial neural networks (ANNs). A prototype Mag-LS with embedded sensors and testbed have been developed, on which noise and parametric effects on sensing accuracy are experimentally investigated. The results demonstrate the effectiveness of a multi-single-output ANN for simultaneously measuring the displacements/force of a Mag-LS, offering an alternative collocated force and displacement sensing solution for impedance/force control.

2024

1. AIM2024

   Magnetic Stiffness of Soft Continuous Permanent Magnet and its Parametric Effects on a Magnetic Series Elastic Actuator Control System

   Wenjing Li, Kok-Meng Lee^*, Min-Geun Park, and 2 more authors

   In 2024 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), Boston, MA, USA, Jul 2024

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   This paper presents the design concept of a soft continuous permanent magnet (C-PM) and magnetic elasticity for the design and control of a magnetic series elastic actuator (Mag-SEA). Unlike a conventional SEA typically designed by integrating an elastic element into an actuator through a mechanical leadscrew (Mech-LS), there is no physical contact between the rotor and translator of a Mag-SEA where their “gap” plays the role of a noncontact “magnetic spring” as the rotor magnetically drives the translator like a LS through helical PMs. Using a distributed current source method verified with analytical solutions and finite element analyses, the magnetic force vector of a Mag-SEA built with C-PM is derived and evaluated by comparing it with that designed with cylindrical PMs to approximate the helical PMs. With the magnetic elasticity computed using the DCS method and a control-oriented perturbation model, the parametric effects on the dynamics and stability are investigated numerically to gain insights into the plant characteristics of a Mag-SEA.