Stepper Motors

Summary

What is Stepper Motor?

Isn’t it intriguing how a Robotic arm in a Factory successfully repeats its activity again and again without any mistakes also how can a Milling machine move with such precision? It is all because of a Stepper Motor. A Stepper Motor is a simple, accurate, and open-loop system that can control the Angular Position of the Rotor. But how does it achieve to move precisely in discrete steps? Let us look at its working Principle.

Stepper Motor Working Principle

Three main things are involved with the working of the Stepper motor

1. Stator
2. Rotor
3. Stator Winding

The stator has teeth on which a wire is a coil and the rotor is either some metallic substance or a permanent magnet. The Motor is made functional by supplying electricity to specific coils on the stator and this rotates the rotor and brings it to a specific position, this process is repeated until the desired position is achieved by the rotor.

ref:MonolithicPower . com

The above figure shows the basic functioning of the stepper motor, in the leftmost diagram you can see that when A rotor tooth is charged, the rotor aligns it towards it, and then B is activated and A is Deactivated the rotor then moves by certain degrees and align itself the way it does as in the middle figure and then when C is Charged, the rightmost figure illustrates the action of the stepper motor accordingly

The running properties and the Torque of the motor are controlled by three Stepper Drives or Excitation levels on which the Steeper motor Operates.

These three Drives are Full Stepping, Half Step, and Micro stepping.

As we already know that an electric pulse to the stator coil converts the electronic signal or pulse to the mechanical movement of the Rotor.

Full Stepping

The Full step Excitation Mode is of two types

1. One phase-on Full step

2. Two Phase-on Full Step

1.In One Phase-On Full Step Mode, as the name suggests, only one Stator Tooth is activated ie the coil of only one stator is activated or energized at a time this places the rotor as shown in fig

2.Whereas in Two Phase-On full step mode two adjacent stator teeth are energized, this places the rotor in between those stators, giving more fine and small rotor movement as shown in fig II

This provides Maximum Torque but low Angular Resolution

ref:Design Spark

Half Step

A more precise and finer resolution of rotor angle is achieved in Half stepping mode of the stepper motor which is the combination of the two modes of the Full step excitation mode.

This provides a better Angular Resolution than Full Step

ref:Design Spark

Microstepping:

This Excitation mode gives even finer resolution, as the rotor now moves with very small angles.

In here the Current in Coil A is maximum and in Coil B is Zero, now as the current is decreased in Coil A the same amount of current is increased in Coil B until the situation is reversed as it was initially, this moves the rotor in smaller and finer angles.

This Mode provides low torque but extremely high angular resolution.

Different Types of Stepper Motors

Things to Keep in mind when choosing a motor

1. Know your load requirements: You should know the load type whether it is Inertial or Frictional Load.
2. Choose a Stepper motor with twice as much as required torque and then run the motor with 1/4th supply voltage.
3. Never take a High-Speed motor for a Low-Speed Application, as you may waste a lot of power and the motor might stall.

Stepper with a MicroController

1.Using Arduino Uno: While using an Arduino Uno, interfacing a stepper Motor is comparatively easy.

Here we are using a unipolar Stepper Motor that has 6 wires, out of which 4 wires need to be connected to the Motor Driver and the other two are connected to the 5v supply, the driver four input pins are connected to the 4 pins of the UNO.

Ref: Electronic Wings

You can write a code according to your requirement of direction and speed of the rotor.

You can use many different kinds of Microcontrollers whose I/O pins need to be connected to that of the driver and the driver and motor connections as done in the above example.

Apart from the different kinds of Microcontroller, there are a plethora of Stepper Motor Drivers that can be used when interfacing a Stepper motor with a Microcontroller.

Stepper Motor Drivers:

Applications where Stepper Motors are used.

1.Robotic Arms

2.Printing Presses

3.3D Printing Equipment

4.Welding types of equipment

5.Machines that do Medical Imaging