# Basic Operating Principles of Stepping Motors

2022.09.21

・In a two-phase bipolar stepping motor, when coils are excited in order one phase at a time, the motor rotates.

・If excitation occurs in the opposite order, motor rotation in the opposite direction is possible.

In succession to “Structure of Stepping Motors”, basic operating principles are explained.

## Basic Operating Principles of Stepping Motors (Single-phase excitation)

The basic operating principles of stepping motors are explained using the diagrams below. In this example, the two-phase bipolar type coils shown in “Structure of Stepping Motors” of the previous article are excited one phase (one set of coils) at a time. The diagrams presuppose that the state changes from ① to ④. The coils 1 and coils 2 each form a coil set. The orange arrows indicate the direction of current flow.

• ・Current is caused to flow into coils 1 from the left and flow out of coils 1 from the right.
• ・No current is made to flow in coils 2.
• ・At this time, the inside of coil 1 on the left is the N pole, and the inside of coil 1 on the right is the S pole.
• ・Hence the permanent magnet in the center is attracted by the magnetic field of coils 1 such that the S pole is on the left and the N pole is on the right, and the magnet stops.
• ・The current in coils 1 is stopped, and current is caused to flow into coils 2 from above and to flow out from below.
• ・The inside of the upper coil 2 is the N pole, and the inside of the lower coil 2 is the S pole.
• ・The permanent magnet is attracted by the magnetic field to rotate clockwise 90°, and then stops.
• ・The current in coils 2 is stopped, and current is caused to flow into coils 1 from the right and to flow out from the left.
• ・The inside of coil 1 on the left is the S pole, and the inside of coil 1 on the right is the N pole.
• ・The permanent magnet is attracted by the magnetic field to rotate clockwise another 90°, and then stops.
• ・The current in coils 1 is stopped, and current is caused to flow into coils 2 from below and to flow out from above.
• ・The inside of the upper coil 2 is the S pole, and the inside of the lower coil 2 is the N pole.
• ・The permanent magnet is attracted by the magnetic field to rotate clockwise another 90°, and then stops.

In this way, by using an electronic circuit to switch the current flowing in the coils in the order ① to ④, the motor can be made to rotate. In this example, the motor is rotated through 90° with each switch in current. Further, if current flow in a certain coil set is continued, the stopped state is maintained, and a holding torque can be provided. It should also be noted that if the order of the states of current flow in the coils is reversed, the motor can be rotated in the opposite direction.