An analytical method for predicting cogging forces in linear induction motors

Cogging in a linear machine can be described as a variation in the magnetic forces as the machine travels along its linear uis. This effect can have a severe impact on the overall precision and even stability of the linear uis. In this paper an analytical method to predict the cogging forces in Linear Induction Moton (LIMs) is presented. An aecurate estimation of cogging is useful during the LIM design stage to help millimize this performance limiting factor. One common method used to predict cogging torques in rotary induction moton is the tooth overlap method. Due to the complexity of slot fringing effects in slotted cores, and the fact that fringing effects significantly influence the accuracy of this method, many researchers alJo use Carter and Green coefficients to increase accuracy. However, this approach does not accurately translate to the linear motor case. In this paper an estimation of the magnetic flux path (based on FEM simulations) is used, along with the gradient ofthe magnetic energy stored in the air gap, to predict the cogging forces in an LIM. The aecuracy of this prediction method is also verified experimentally through a cogging force analysis on a simple one-tooth test-bed.