Consider a two-phase stepper motor with a permanent-magnet rotor such as shown in Figure and whose torque-angle curve is as shown in Figure a. This machine is to be excited by a four-bit digital sequence corresponding to the following winding excitation:

a. Make a table of 4-bit patterns which will produce rotor angular positions of 0, 45? . . . 315?.

b. By sequencing through the bit pattern found in part (a) the motor can be made to rotate. What time interval (in milliseconds) between bit-pattern changes will result in a rotor speed of 1200 r/min?

+180 +270 90 +90 T, torque acting on rotor in + Phase 2 excited direction Phase I excited (a) Rotor: permanent- magnet construction Rotor position for phase I excited bit bit iz i, 3 4 - la -l. 1 OFo