138 Industrial Robotics Fundamentals Copyright Goodheart-Willcox Co., Inc. Operation of a stepping motor is achieved using a four-step switching sequence. Any of the four combinations of switches 1 or 2 will produce an appro- priate rotor position. The switching cycle then repeats itself. Each switching com- bination causes the motor to move one-fourth step. The rotor in the circuit illustrated in Figure 6-21 permits four steps per tooth, or 200 steps per revolution. The amount of linear displacement, or step angle, is determined by the number of teeth on the rotor and the switching sequence. A stepping motor that takes 200 steps to produce one revolution moves 360°/200 or ° 1.8° per step. It is not unusual for stepping motors to require eight switching com- binations to achieve one step. 6.4.4 Rotary Electric Actuators Robots require rotary electric actuators to produce rotary motion different from that produced by an electric motor. This type of rotary motion controls the angu- lar position of a shaft. Using rotary electric actuators, rotary motion is transmitted between locations without direct mechanical linkage. Servomotors and synchro- nous motors are types of rotary actuators. For these applications, computer sig- nals are applied to the actuators and translated into precise amounts of rotary motion. The electrical signals are applied to the motor, causing mechanical (rotary) movement. Motor DC source + – Switch 1 R Switch 2 3 5 2 1 Phase A Phase B 4 Step 1 Switch #1 Switching Sequence* Switch #2 2 3 4 1 1 1 3 3 1 5 4 4 5 5 *To reverse direction, read chart from bottom to top. Stator windings (Phase A) Stator windings (Phase B) Superior Electric Co. Figure 6-21. This dc stepping motor is similar in construction to an ac synchronous motor.