Accurate analytical computation of magnetic flux density of spherical permanent magnet arrays

In robotic applications, multiple one-degree of freedom electromagnetic actuators together with gearboxes are used for mimicking the multiple degree of freedom motion profiles of human limbs. However, this results in heavy and bulky robotics. A lighter alternative can be provided by the use of spherical electromagnetic actuators in directly driven human-like joints. These spherical actuators have a relative similarity to human joints and also can provide multiple degrees of freedom motion without gearboxes. Existent spherical actuator prototypes cannot deliver yet the required torques in robotic applications, therefore development of accurate and fast analytical models to replace the time-consuming finite element simulations can be a valuable tool for analysis, design and optimization of spherical actuators. As a first step in development of an analytical model of spherical actuators, this paper presents the analytical model of an array of spherical shaped permanent magnets distributed on a spherical surface. The considered structure represents in fact the rotor of a spherical actuator. It has been shown that the developed analytical model can provide fast and accurate calculation of the magnetic flux density distribution in the whole domain in view of its integration in a complete analytical model of a spherical actuator

3D analytical and numerical modeling of spherical structures

In robotic applications, multiple one-degree of freedom electromagnetic actuators together with gearboxes are used for mimicking the multiple degree of freedom motion profiles of human limbs. However, this results in heavy and bulky robotics. A lighter alternative can be provided by the use of spherical electromagnetic actuators in directly driven human-like joints. These spherical actuators have a relative similarity to human joints and also can provide multiple degrees of freedom motion without gearboxes. Existing spherical actuator prototypes still cannot deliver torques required for applications such as robots. Therefore development of accurate and fast analytical models to replace the time-consuming finite element simulations can be a valuable tool for analysis, design and optimization of spherical actuators. As a first step in development of an analytical model of spherical actuators, this paper presents the analytical model of an array of permanent magnets distributed on a spherical surface. The considered structure represents in fact the rotor of a spherical actuator. It has been shown that the developed analytical model can provide fast and accurate calculation of the magnetic flux density distribution in the whole domain. In the same time the analytical model allows optimization of the array structure in view of its integration in a complete analytical model of a spherical actuator

Modeling of spherical magnets 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 3D 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

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]

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