Stepping Motor with Stator Pole Inclined Against Rotor Pole

Abstract

The motor analyzed in this paper is a kind of the stepping motor used for a slave clock. The structure of this motor is like an inductor motor, but the stator poles and the rotor poles are same in number. Moreover the stator poles fixed are inclined against the rotor poles. By the theoretical and experimental analysis of the motor, the expression of the torque with respect to the angle of the rotation of the rotor θ was given as follows; K_T I・sinθ - Mp・sin 2 ( θ - θ_0 ), where I is the exciting current, K_T the torque constant of the motor, Mp the maximum torque induced by the permanent magnet of the rotor and θ_0 = 0.56√<arctan(28α)> by experimentally, where α is the inclined angle of the stator poles. When the above torque satisfies the condition M_P/KT_I(=ε)<1, the natural f requency ω_n and damping ratio ζ C of the small oscillation about the equilibritum were given respectively, ωn=√<NK_T I/J> and ζ=D/(2√<NIK_T I>), where J is the moment of inertia of the rotor, N the half number of the poles and D the linear viscous damping coefficient. Then the diffential equation described the motion of the motor subjected the above torque was deduced, neglecting the inverse electromotive force by the rotation of the rotor and the solid friction torque. Comparing the integral curve of the equation with an actual motion of the motor, the following facts were clarified that the step responce can be expressed by the parameter ω_n , ζ, ε, α and the time constant of the coil of the motor in the case of the constant voltage drive.