# Switching Sequence: Full and Half-Step Motors

 Home | Articles | Forum | Glossary | Books

above: Diagram of switching circuits for stepper motor.

 FOUR STEP INPUT SEQUENCE(FULL-STEP MODE) Step SW1 SW2 SW3 SW4 1 ON OFF ON OFF 2 ON OFF OFF ON 3 OFF ON OFF ON 4 OFF ON ON OFF 1 ON OFF ON OFF

above: Switching sequence for a four-step (full-step) switching mode.

The stepper motor described in the previous section uses a four-step switching sequence, also known as a full-step switching sequence. The figure on the left (and the table below) shows a switching diagram which indicates the sequence for the four switches used to control the stepper motor. The diagram shows four switches with four separate amplifiers. The diagram for the motor shows the same four windings that were discussed in the theory of operation the previous section. Each winding is tapped at one end and is connected through a resistor to the negative terminal of the power supply.

The table shows the sequence for energizing the coils. During the first step, switches SW1 and SW3 are on and the other two are off. During the second step, switches SW1 and SW4 are on and the other two are off. During the third step, SW2 and SW4 are on and the other two are off. During the fourth step, SW2 and SW3 are on and the other two are off. This sequence continues through four steps, which are repeated again. These steps allows the motor to rotate one step or tooth on the rotor when a pulse is applied by closing two of the switches. The figure, below left, shows the position of the poles during each step when the motor is in full-step mode.

 above: Diagrams that show the position of each pole while the motor is in full-step mode. Diagrams a, b, c, and d show the movement of the rotor in sequence.

### Half-Step Switching Sequence

Another switching sequence for the stepper motor is called an eight-step or half-step sequence. The switching diagram for the half-step sequence is shown in the figure (below). The main feature of this switching sequence is that one can double the resolution of the stepper motor by allowing the rotor to move half the distance it does when the full-step switching sequence is used. Meaning that a 200-step motor, which has a resolution of 1.8°, will have a resolution of 400 steps and 0.9°. The half-step switching sequence requires a special stepper motor controller, but it can be used with a standard hybrid motor. The manner in which the controller gets the motor to reach the half-step is by energizing both phases at the same time with equal current.

In this sequence the first step has SW1 and SW3 on, and SW2 and SW4 are off. The sequence for the first step is the same as the full-step sequence. The second step has SW1 on and all of the remaining switches are off. This configuration of switches causes the rotor to move an additional half-step. The third step has SW1 and SW4 on, and SW2 and SW3 are off, which is the same as step 2 of the full-step sequence. The sequence continues for eight steps and then repeats. The main difference between this sequence and the full-step sequence is that steps 2, 4, 6, and 8 are added to the full-step sequence to create the half-step moves.

above: A stepper motor with its switches, and the switching sequence for the eight-step input (half-step mode).

 Home  Forum  Books  Glossary  Sitemap