Pan Donghua

Magnetic Field of a Tubular Linear Motor With Special Permanent Magnet

This paper describes a tubular linear motor with special permanent magnet. Then, two kinds of permanent magnet magnetization directions for this motor are proposed, and the air-gap magnetic field is calculated and researched based on a finite-element method. Moreover, the magnetic field of the slotless tubular linear motor is contrasted with that of the traditional interior axially magnetized permanent magnet tubular linear motors. Finally, the advantages of the motor are analyzed and pointed out.

Eddy Current Damping Suppression of Air-Core Monopole Linear Motor for Nanopositioning System

In the nanopositioning system, a damping force is generated by eddy current in the cooling plate and it is a disturbing force for this system. In this paper, a new method is introduced to suppress eddy current by offsetting back EMF. In order to offset back EMF, several slits have been incorporated in the cooling plate, which can help with regulating the series order in every region. Based on the electromagnetic theory, the analytical model of new cooling plate is established. The analytical model and eddy current suppression effect of the new cooling plate are proven by experiment: 17% reduction in the damping force significantly help with reducing the thrust fluctuation, with less than 4% analytical error.

An Approach to Analyzing Magnetically Shielded Room Comprising Discontinuous Layers Considering Permeability in Low Magnetic Field

To enable the realization of weak magnetic field at the level of several nanotesla, a magnetically shielded room (MSR) is required to create a space with residual magnetic field below 1 nT. Since the magnetic field shielded by inner shielding shells is very low, the permeability of shielding materials in this range is measured. As the gaps between ferromagnetic material strips in shielding wall lead to considerable reduction of shielding factor, a new numerical model to evaluate the equivalent permeability of discontinuous shielding layers is proposed and demonstrated experimentally. Based on the equivalent magnetic property in lower and normal magnetic field range, the improved approach to predicting the performance of MSR is obtained.

Analysis of a Short-Stroke DC Linear Motor for nanopositioning

The analysis of a Short-Stroke DC Linear Motor (DCLM) with Halbach array structure is described. The motor is applied for nanopositioning system. The method of images is adopted to predict the distributions of global and local magnetic field for obtaining precise calculations. The derivation of flux density formulae are shown in this paper. The method of images and testing curves are coincident, at different position, demonstrates the analytically predicted distributions of air-gap flux density is exact. Then the thrusts of DCLM have been predicted by the method of image at different positions.

Analysis of eddy current damping for short-stroke DC linear motor

Eddy currents induced in a conductor in a changing magnetic field produce a damping force proportional to the heat generated in the conductive material. In the DC linear motor system, the conductive plate is added under coils for damping force to improve motors dynamic response. In the preliminary work, the formula of magnetic field distribution is obtained by the method of images, so the eddy current inducted in the conductor is calculated. Then the damping force is obtained after the equivalent resistance and inductance of conductance place are calculated. The design of eddy current damping for short-stroke DC linear motor is optimized by the formula of damping force, and obtains the speed of mover when maximal damping force is induced.