How to Calculate Stepper Motor Steps per Revolution

Stepper motors are widely used in various industries and applications, from robotics to 3D printing. These motors provide precise control and accuracy, making them ideal for positioning and motion control systems. One essential parameter of a stepper motor is its steps per revolution. In this article, we will explore how to calculate the steps per revolution for a stepper motor and understand its significance in motor control.

Understanding Stepper Motors

Stepper motors are electromechanical devices that convert electrical pulses into precise mechanical movements. Unlike conventional motors, stepper motors move in discrete steps or increments at a time. These steps are controlled by the number of pulses sent to the motor. Each pulse corresponds to a step rotation, allowing for precise position control.

The Importance of Steps per Revolution

The steps per revolution (SPR) value determines the number of steps required to complete one full revolution of the stepper motor shaft. It defines the motor's resolution or the smallest increment of movement it can achieve. By knowing the SPR value, engineers can calculate distances, angles, or any other unit of displacement with high accuracy.

Calculating the Steps per Revolution

To calculate the steps per revolution for a stepper motor, we need to consider the motor's construction and specifications. The most crucial parameters are the number of stator teeth, rotor teeth, and the type of stepper motor (unipolar or bipolar).

1. Determine the Stator and Rotor Teeth

Begin by counting the number of stator teeth (NS) and rotor teeth (NR) of the stepper motor. Stator teeth are found on the stationary part, while rotor teeth are located on the rotating part of the motor. These teeth help in the precise movement of the motor.

2. Determine the Type of Stepper Motor

Next, identify whether the stepper motor is unipolar or bipolar. Unipolar stepper motors have one winding per phase, while bipolar stepper motors have two windings per phase. This distinction affects the motor's steps per revolution calculation.

3. Calculate the Steps per Revolution for a Unipolar Motor

For unipolar stepper motors, the steps per revolution can be calculated using the formula:

SPR = NS x NR x u

Here, u represents the motor's stepping rate, which is typically given in degrees per step or steps per revolution. In the case of degrees per step, the SPR value reflects the motor's angular resolution.

4. Calculate the Steps per Revolution for a Bipolar Motor

For bipolar stepper motors, the steps per revolution calculation is slightly different. The formula becomes:

SPR = NS x NR x b x 2

In this formula, b represents the number of phases, generally denoted as 2 because bipolar motors have two windings per phase.

Let's consider an example to further clarify the steps per revolution calculation process.

Example:

Suppose we have a unipolar stepper motor with 12 stator teeth and 8 rotor teeth. The motor has a stepping rate of 1.8 degrees per step.

SPR = 12 x 8 x 1.8

SPR = 172.8 steps per revolution

In this case, the stepper motor requires 172.8 steps to complete one full revolution.

Applications of Steps per Revolution

Understanding the steps per revolution is vital for several reasons. Firstly, it helps in accurately controlling the motor's position, enabling precise movements in various applications such as CNC machines, 3D printers, and automated manufacturing systems. Secondly, it allows for calculating linear displacement or angles based on the stepper motor's movements, which is essential in many positioning systems.

Controlling Stepper Motors

To effectively control a stepper motor, the number of steps and the sequence of pulses sent to the motor should be considered. By varying the pulse sequence and frequency, precise movements can be achieved.

Microstepping is another technique used to further refine the motor's movement. It involves applying smaller subdivisions within each step, resulting in smoother motion and increased resolution. Microstepping reduces the chances of the motor skipping steps and improves overall accuracy.

Conclusion

Stepper motors provide exceptional precision and control in various applications. Understanding the steps per revolution is crucial for achieving accurate position control. By knowing the number of steps required for one full rotation, engineers can accurately calculate distances, angles, or any other displacement unit. This knowledge is essential in applications that require precise movements, such as robotics, automation, and 3D printing.