Cogging Force Research Articles

Design of permanent magnet flat linear motors for standstill applications

The authors examine planar linear permanent magnet motors and consider their operation at standstill. A method of finite element analysis (FEA) is used in which the use of several space phase-shifted force profiles accounts for the machine skew. The origin of the cogging forces, namely tooth and finite stator length effects, is explained. Results are given from a large experiment rig. It is shown that both cogging and electromagnetic forces compare well with the FEA. The authors conclude with a design survey using simple magnetic circuit theory considering the application of both NdFeB and ferrite magnets. Points on the graphs are validated by the FEA. >

Dynamic performance of a brushless DC tubular drive system

The authors describe the computer-aided analysis of the dynamic performance of a tubular linear machine system with permanent magnetic cogging forces. These forces include not only the conventional tooth cogging force apparent in both linear and rotary machines but also a force unique to permanent magnet linear machines that is due to the finite length of the stator. System equations which describe both the machine and the inverter supply are solved by a step-to-step numerical method to find the dynamic performance of the machine in an oscillator mode. The work is verified by experimental results obtained for a practical model. >