Abstract: In order to reduce yarn breakage, a three-dimensional graph that shows the relationship between the unbalanced magnetic pull and the eccentricity and electric degree is drawn by using Ansoft electromagnetic calculation and MATLAB; the critical speed of the first two orders of a simplified electric spindle model is calculated by using transfer matrix method; then the theory is applied to an actual electric spindle. By comparison, it draws the conclusion that the influence of radial magnetic pull on second-order critical speed can be ignored.

Key words: critical speed; transfer matrix method; unbalanced magnetic pull; motor vibration