| Abstract: | A series‐universal motor is usually used in hand‐held electrical tools, such as cutting or grinding machines. The corresponding two carbon brushes are preloaded by springs to maintain a proper contact necessary to reduce their wear and erosion. The oscillations of carbon brushes are coupled with the rotor motion. A model including carbon brushes and the main parts of tool rotor is described. By using the method of multibody systems the equations of motion are derived. The one‐sided contact forces and the electrical forces between commutator and brushes are mainly responsible for the nonlinear oscillations of brushes. The contour of contact surface is one of the major parameters of contact force. There exist periods where the brushes are separated from the commutator, i.e. a free flight motion of carbon brush occurs. The measured and simulated results show that a large spring preload and a small brush mass improve the contact and result in reduced free flight periods. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) |
