Image Number 5 for United States Patent #5726510.
A hybrid type stepping motor in which torque variation is reduced to as low as possible, torque stiffness is improved, and resonant vibration during the rotating movement is minimized. Each fixed magnetic pole has at least two small teeth arranged at intervals of the same pitch as the teeth of a rotor. The total number (NS) of the small teeth of a stator segment of an asymmetrical form is determined by NS=5.times.(n0+n1), wherein n0 is the number of the small teeth on each of five of the ten fixed magnetic poles and n1 is the number of the small teeth on each of the remaining five fixed magnetic poles. The fixed magnetic poles with the n1 small teeth are arranged alternately with the fixed magnetic poles with the n0 small teeth. The n1 small teeth poles and the n0 small teeth poles are disposed opposite to each other about the axis of a rotary shaft. The relation between the total number (NR) of the teeth of the rotor and the total number (NS) of the small teeth of the stator segment is expressed by NS.gtoreq.0.8NR (NS being greater than or equal to 0.8NR). A difference between NR and NS is calculated from NR-NS=K(S0-S1)+10(S1-1+B) where K is an integer from 2 to 5, S0 and S1 are smallest possible integers or may be equal, and B is a fraction of 1 so that 10B is always an integer. Ten windings on their respective fixed magnetic poles are energized by a power supplying means to produce desired numbers of N and S poles. The full step angle is equal to an electric angle 90.degree.=aH=360.degree./10NR and thus, the half step angle is an electric angle 45.degree.=aH=360.degree./20NR. In magnetization, the energization of the ten windings at each step produces N and S poles of the same number. Also, one or more pairs of adjacent magnetic poles are polarized to S of each step.