B. van Ninhuijs

Modeling of Spherical Magnet Arrays Using the Magnetic Charge Model

This paper presents an analytical method for evaluating the magnetic flux density produced by spherical permanent magnet arrays used in spherical actuators. To investigate the performances of magnetic arrays, analytical models are used due to their lower computational time compared to 3-D finite element analysis. This paper presents an analytical model for the calculation of the magnetic field produced by a spherical permanent magnet array using magnetic charge modeling. To obtain the total magnetic field solution, first the magnetic field produced by a single spherical tile is considered. By means of superposition, the magnetic field produced by the array is obtained. Two magnet array topologies are modeled and the analytical results are validated using finite element analysis.

Topology Comparison of Slotless Permanent Magnet Semispherical Actuators

This paper presents a comparison of several three-degrees-of-freedom (DoFs) semispherical actuator topologies, which can mimic a shoulder joint of an actuated support system. A semianalytical model is applied to determine the torque performance as function of the position. Hence, the current distribution through the coils with minimized ohmic losses can be determined. The performed topology comparison is based on the average power dissipation and on a set of torque and range of motion requirements.

Multi-degree-of-freedom spherical permanent-magnet gravity compensator for mobile arm support systems

This paper presents a magnetic gravity compensator which is able to provide compensation around two axis of rotation for mobile arm support systems. Because of the compensation around two axes it provides more flexibility than the existing mechanical gravity compensators. This flexibility is achieved by using two semispherical permanent magnets, where the inner semisphere can rotate around the x, y and, z axis with respect to the outer semisphere. Several magnetization topologies, evaluated using 2D finite element analysis, are investigated and the most suitable topology is optimized in 2D finite element analysis. The optimization results are verified with 3D finite element analysis.

Multi-degree-of-freedom spherical permanent magnet gravity compensator for mobile arm support systems

This paper presents a magnetic gravity compensator, which is able to provide compensation about two axes of rotation for mobile arm support systems. Because of the compensation about two axes, it provides more flexibility than the existing mechanical gravity compensators. This flexibility is achieved by using two semispherical permanent magnets, where the inner semisphere can rotate about the x-, y-, and z-axis with respect to the outer semisphere. Several magnetization topologies, which are evaluated using 2-D finite-element analysis (FEA), are investigated, and the most suitable topology is optimized in 2-D FEA. The optimization results are verified with 3-D FEA.

Harmonic and magnetic charge model comparison of spherical permanent magnet structures considering a neumann boundary

The rapid advances in assistive devices brought out the desire of spherical actuators because of their multiple degrees of freedom and similarity to ball and socket joints [1]. For this application a high torque density is beneficial for the volume of these devices. Due to the typical structure of slotted spherical actuators, designs have to be modeled in 3-D to gain accurate results. As commercially available modeling tools, such as FEA (finite element analysis), are very time consuming, semi-analytical models are needed to optimize a design. A slotted topology can be evaluated by including a Neumann boundary, representing material with a high permeability and a surface current density sheet distribution to model the coils [2]. Two semi-analytical models exists for obtaining the magnetic flux density generated by a spherical permanent magnet array namely, harmonic model [3] and magnetic charge model [4].

Comparison of Harmonic and Magnetic Charge Model for Spherical Magnetic Structures With a Neumann Boundary

This paper includes the Neumann boundary conditions in the magnetic charge modeling method for spherical magnetic structures. In the spherical coordinate system, the geometry and the magnetic properties of the imaged magnetic structure are obtained with the method of inversion. This method is applied to a spherical permanent magnet array, and the results are compared with the harmonic modeling and finite-element analysis. In addition to this validation, the modeling methods are compared on their limitations and accuracy.