Stepper Motor

Blog number:-023

Hello everybody,

I hope you all will be fine.

In the last session we discussed about Servo motor. So, today we will discuss one more special type of DC Motor called Stepper Motor. The application of Servo Motor and Stepper Motor is common but the fundamental Principle is Different.

Stepper Motor

          A stepper motor or step motor or stepping motor is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can then be commanded to move and hold at one of these steps without any feedback sensor (an open-loop controller) unlike the Servo motor which use the principle of Closed-loop Controller. 

Or, Stepper motors are DC motors that move in discrete steps. They have multiple coils that are organized in groups called "phases". By energizing each phase in sequence, the motor will rotate, one step at a time.
With a computer controlled stepping you can achieve very precise positioning and/or speed control. For this reason, stepper motors are the motor of choice for many precision motion control applications. 

Fundamentals of Operation

Brushed DC motors rotate continuously when DC voltage is applied to their terminals. The stepper motor is known by its property to convert a train of input pulses (typically square wave pulses) into a precisely defined increment in the shaft position. Each pulse moves the shaft through a fixed angle.

                                 

Stepper motors effectively have multiple "toothed" electromagnets arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external driver circuit or a micro controller. To make the motor shaft turn, first, one electromagnet is given power, which magnetically attracts the gear's teeth. When the gear's teeth are aligned to the first electromagnet, they are slightly offset from the next electromagnet. This means that when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one. From there the process is repeated. Each of those rotations is called a "step", with an integer number of steps making a full rotation. In that way, the motor can be turned by a precise angle. The Stepper Motors therefore are manufactured with steps per revolution of 12, 24, 72, 144, 180, and 200, resulting in stepping angles of 30, 15, 5, 2.5, 2, and 1.8 degrees per step. The stepper motor can be controlled  without feedback.

Generally, stepper motors have an internal rotor with a large number of permanent magnet “teeth” with a number of electromagnet “teeth” mounted on to the stator. The stators electromagnets are polarized and depolarized sequentially, causing the rotor to rotate one “step” at a time.

Applications:

1. Industrial Machines – Stepper motors are used in automotive gauges and machine tooling automated production equipment.
2. Security – new surveillance products for the security industry.
3. Medical – Stepper motors are used inside medical scanners, samplers, and also found inside digital dental photography, fluid pumps, respirators and blood analysis machinery.
4. Consumer Electronics – Stepper motors in cameras for automatic digital camera focus and zoom functions.

Stepper Motor System:

A stepper motor system consists of three basic elements, often combined with some type of user interface (host computer, PLC ):

Indexer

The indexer (or controller) is a microprocessor capable of generating step pulses and direction signals for the driver. 

Drivers

The driver (or amplifier) converts the indexer command signals into the power necessary to energize the motor windings. 

Stepper motors

The stepper motor is an electromagnetic device that converts digital pulses into mechanical shaft rotation.

So that's all for this session. if you have any doubt related to the topic, Please comment.

Thank You.