Step Motor Excitation Modes

Stepper motor drivers often have different modes of operation. These different modes determine in what sequence the coils are energized to make the motor shaft move appropriately. There are four types of these stepping modes. However, only three of the excitation modes are common in most stepper drivers.

Full-step excitation

In full step operation, the motor step through the normal step angle e.g.200 step/revolution motors take 1.8" steps while in half step operation, 0.9" step are taken. There are two kinds of full-step modes. Single phase full-step excitaion is where the motor is operated with only one phase energized at-a-time. This mode should only be used where torque and speed performance are not important, e.g. where the motor is operated at a fixed speed and load conditions are well defined. Problems with resonance can preclude operation at some speeds. This mode requries the least amount of power from the drive power supply of any of the excitation modes. Dual phase full-step excitation is where the motor is operated with two phases energized at-a-time. This mode provides good torque and speed performance with a minimum of resonance problems. Dual excitation, provides about 30 to 40 percent more torque than single excitation, but does require twice the power from the drive power supply.


Half-step excitation

The Half step mode energizes a single coil then two coils then one again. Alternating between energizing a single phase and both phases together gives the motor its higher resolution. A 200 step Step motor driver operating in half step mode would have 400 positions, twice the normal resolution. However, the torque will vary depending on the step position because at times a single phase will be energizes while at other times both phases will be energized. Higher end drivers compensate by increasing the current through the single coil when a single coil is energized. This makes up for the loss in torque, making the half step mode very stable.

Half step excitation is alternating single and dual phase operation resulting in steps that are half the basic step angle. Due to the smaller step angle, this mode provides twice the resolution and smoother operation. Half stepping produces roughly 15% less torque than dual phase full stepping. Modified half stepping eliminates this torque decrease by increasing the current applied to the motor when a single phase is energized.

Micro-step drive

In the micro-step mode, a motor's natural step angle can be divided into much smaller angles. For example, a standard 1.8" degree motor has 200 steps/revolution. If the motor is micro-stepped with a "divide-by-10"). The micro-steps are produced by proportioning the current in the two windings according to sine and cosine functions. This mode is only used where smoother motion or more resolution is required.

It is important to take into consideration the step modes and how best to utilize them when designing the CNC router drive system. It is also very important when choosing a stepper motor driver. Some drivers will micro-step more smoothly than others. In the next section we will cover the ins and outs of buying a stepper driver and what features to look for.

We Fasttobuy Co.,Ltd is a professional manufacturer of automation control. Currently, our company specialized in the production of linear actuator, hybrid stepper motor, screw and nut.For more details, please feel free to contact us!