Chee Kian Lim

Electromechanical Modeling of a Permanent-Magnet Spherical Actuator Based on Magnetic-Dipole-Moment Principle

Theoretical modeling in any engineering design is of paramount importance as it establishes the interrelationship between variables being analyzed in a given condition. With regard to the design of a permanent-magnet spherical actuator, electromechanical modeling is crucial as it correlates the input parameters such as current to the output mechanical torque. In this paper, a new approach in electromechanical-torque formulation for this class of spherical actuator employing the magnetic-dipole-moment principle is being discussed. Derivation from first principle and the extension of this novel method in the acquisition of the 3-D resultant torque induced on the rotor are presented. The proposed approach circumvents the need for electromagnetic-energy analysis within the air gap between the rotor and stator poles and, henceforth, providing a direct computation of the resultant torque. The validity of the proposed analytical torque model was verified against numerical and empirical data. Comparisons between the 3-D torque results demonstrate the correctness and soundness of the proposed electromechanical torque model.

Torque Modeling of a Spherical Actuator Based on Lorentz Force Law

An actuator with 3-DOF spherical motion is developed based on layered arrangement of stator coils and rotor poles. Due to the use of air-core coils and permanent magnet poles, the torque model of the actuator cannot be obtained by traditional coenergy approach. This paper describes a generic torque modeling method based on Lorentz force law. The closed-form solution of the torque model is derived from the scalar potentials of the magnetic field. Experimental study on the torque model is carried out. A comparison between the closed-form solution and the experimental result shows that the proposed torque model is valid and can be used for real-time control.

A low cost wearable wireless sensing system for upper limb home rehabilitation

Monitoring and guiding real time body motion permits corrective measures to be implemented for more effective rehabilitation results. Taking the rehabilitation practice at home can help stroke patients with movement disability to regain the motor skill. Existing systems for rehabilitation is either too costly, or complicated and bulky to be efficiently employed for personal use at home. In this current work, an innovative and unobtrusive wearable system for home use is being proposed. This compact and cost effective system effectively captures human joint angles and does that hinder limb motion as commonly encountered in other existing systems. The paper details the design and implementation of the proposed sensor and sensing methodology. The tested wireless sensor is able to detect the posture and movement of the human arm with particular attention to its application in upper limb rehabilitation. Real time experimental data are collected from a subject using a hand exerciser and compared with a commercial motion capture system. The results demonstrate the feasibility and viability of the proposed sensing system in tracking human arm postures and movement.

Analysis of Pole Configurations of Permanent-Magnet Spherical Actuators

This paper presents a generic design concept of three degree-of-freedom (3-DOF) permanent-magnet (PM) spherical actuators. A ball-shaped rotor mounted with multiple layers of PM poles is concentrically housed in a spherical-shell-like stator with multiple layers of air-core coils. This design allows more rotor and stator poles to be incorporated to increase torque output and motion range of the actuator. The magnetic field and torque modeling methods are generalized to multiple layers of poles, which provides a convenient way to analyze field distribution and torque performance of spherical actuators with various pole configurations. The simulation results of flux distribution and torque variation of double-layer configuration are compared with those of single-layer one. It shows that the magnetic field distribution and torque variation for both configurations are coincident with PM-pole arrangement on the rotor surface. The tilting torque of double-layer design is larger than that of single layer, and the torque variation is more uniform. The spinning torque of single layer is relatively large. The proposed analyzing methods of field and torque could be employed for preliminary study of other PM spherical actuators.

Torque Modeling of Spherical Actuators with Double-layer Poles

This paper presents a design concept of spherical actuators including a ball-shaped rotor with two layers of permanent-magnet (PM) poles and a spherical-shell-like stator with two layers of circumferential air-core coils. Corresponding to the poles configuration, the torque model of the spherical actuator has been derived. The magnetic field as well as torque output have been compared with that of spherical actuator with single-layer PM-pole configuration. This generic torque modeling method can be extended for spherical actuators with multi-layer PM&coil poles which can achieve high motion resolution as well as large working range

Experimental Investigation on the Magnetic Field of a Permanent Magnet Spherical Actuator

This paper introduces the experimental study on the magnetic field of a permanent magnet (PM) spherical actuator. A new type of testbed is developed to measure the three-dimensional (3D) magnetic flux density distribution of the rotor consisting of PM poles. The captured data are nondimensionlized and normal- ized so that they could be referred by similar rotor designs without regard to the specific dimensions of the poles. Furthermore, the measured data are presented visually in Cartesian coordinates, which facilitates the analysis of the magnetic field generated by the rotor.

An interactive therapy system for arm and hand rehabilitation

The paper presents results from a virtual reality (VR)-based system for upper limb rehabilitation. The system incorporates a range of interchangeable direction sensing devices (the Optical Linear Encoder (OLE) and the inertial measurement unit (IMU)) that can be adjusted to a large range of different arm and hand sizes, and interactive practice applications designed for motivating and seamlessly driving users to perform the functional and non-functional motor recovery tasks. We describe the kinematic models of both arm and hand, the technical details of two motion track components (the arm suit and the SmartGlove) and the design of the interactive scenarios. The system thus promises to be a valuable complement to conventional therapeutic programs offered in rehabilitation clinics.

Mechanical design & numerical electromagnetic analysis of a DC spherical actuator

The focus of this research is to design and develop a spherical actuator for robotics applications. Unlike prior works, this project proposes a new type of a DC spherical manipulator that operates from the forces generated between pairs of air core electromagnetic coils and permanent magnets. The novelty of the proposed design is demonstrated by utilizing air cores as stator poles. This eliminates the drawbacks of existing spherical electromagnetic device where the performance is significantly hindered due to inherent detent force, hysteresis and saturation issue that arises from the ferromagnetic component. The ability to be able to accurately model the electromechanical phenomenon and predict the output torque is essential for high precision motion control. Numerical analysis of the electromechanical forces is performed using FEM software. Design experience in spherical actuators, unlike that of single DOF electromagnetic motors, has been limited and intricate due to the three dimensional nature of the output motion. This paper aims to present the design methodology and electromechanical analysis in a concise and orderly manner that may serve as a starting point for design optimization and research.

A hybrid approach for magnetic field analysis

A new form of 3-DOF spherical actuator having a rotor mounted with rare-earth-magnet poles is developed. Since the air-core coils are used in this actuator, the magnetic flux distribution is different from that of conventional electromagnetic devices. In this paper, the solution of the Laplace equation is used to derive the general form of the magnetic field, and a curve fitting approach is proposed to obtain the mathematical expression of the magnetic field. This mathematical representation of the 3D magnetic field can be applied to the torque modelling of the 3-DOF spherical actuator. Experimental studies have been conducted to determine the critical parameters and verify the effectiveness of the proposed approach.

Flux distribution and back-iron influence of tubular linear motors

Ferromagnetic material affects the magnetic field of electromagnetic actuators significantly. This paper studies the effect of back iron on magnetic field of linear motors. Designs of linear motors with single-sided, double-sided, and without back irons are analyzed quantitatively. The magnetic field for different structures is formulated analytically based on magnetic vector potential. The simulation result is compared with numerical result from finite element calculation. It shows that the analytical model fits with numerical result closely, and the use of back iron helps to enhance the magnetic field of linear motors.