An improved design procedure for hybrid stepper motors

A design methodology for hybrid stepper motors is presented. It takes into account the saturation throughout the motor, allows for variations in magnet working point, and enables the designer to optimize the balance of coil and magnet MMFS (magnetomotive forces) to achieve a specified holding torque. The procedure is based on the use of the finite-element technique to generate permeance curves for the complex tooth/airgap region of the motor, accounting for localized saturation effects in the teeth. The curves are then used in a nonlinear lumped parameter network of the entire motor. The network models the motor´s 3-D nature and may include other saturating elements as well as leakage permeances. By applying the virtual-work technique, the lumped parameter network is used to calculate torque/displacement characteristics as well as the winding inductance and back-EMF (electromotive force) constants. The technique has been used in the design and analysis of several industrial stepper motors utilizing high-energy rare-earth magnets