Stepper Motor and its Types
Updated: Dec 5, 2020
#Stepper motor is widely used in today's world due to its accurate and durable characteristics, let us see in this article characteristics, types, and application of stepper motor.
Stepper motor is a synchronous brushless motor that converts digital input pulses into mechanical shaft rotation.
The Stepper motor needs a pulse for every single step. It takes one step at a time and the duration of the steps is the same.
The step movement changes into the continuous rotation as the frequency of the digital pulses, hence we can say that frequency of pulses is directly proportional to the speed of rotation of the motor.
Stepper motors are reliable, low cost, rigid which produce high torque at low speeds that's why they are in both industrial as well as commercial usage. Let us throw some light on the types of Stepper motor based on types of modes and construction of Stepper Motor.
Working of Stepper motor
Stepper motor is a Dc brushless #motor which represents an open-loop controller as it rotates in steps. It does not need a feedback sensor which leads to its position more precise. The Stepper motor consists of a rotor as a permanent magnet which is surrounded by a stator that has windings on it.
On the stator, there are teeth on which coil is wounded where the rotor is a permanent magnet or either a variable reluctance iron core.
The basic principle of the stepper motor is by energizing the stator phases a magnetic field will generate due to stator windings, due to which rotor will get aligns or energized with the field by energizing different phases in sequence the rotor gets rotated in a specific position as a step.
Types of stepper motor using Driving modes
Based on the driving modes there are several different types of stepper motor lets check one by one,
Wave Drive or Single-coil Extraction, In this mode only one coil is activated or energized at a time, lets take a 4 coil motor as an example then it will perform 4 steps at a time.
Full Step drive mode, in this type of driving mode 2 coils are activated or energized at a time. Because of 2 coils, the torque produce is higher at the output.
Half Step drive mode, in order to increase resolution Half Step drive mode is used. In this mode when one coil is activated it is followed by 2 coils those who are also activated. This mode is basically a combination of the first two modes, which results in double resolution while using the same construction which results in 8 steps in one full cycle.
Microstepping mode, in this mode a variable, a controlled current is provided to the coils in a form of a sine wave, which results in a smooth motion of rotor, accuracy, and reduces the stress of the motor. Due to such characteristics, it is used more nowadays for controlling stepper motors.
Types of Stepper Motor based on Rotor construction
In a Permanent magnet Rotor, the rotor is a permanent magnet that gets energized with the magnet field generated by the stator circuit, which results in good and detent torque. The main drawback of this type of motor is that it has lower speed and also lower motor resolution as compared to that of others. The diagram below is the construction of a permanent magnet stepper motor.
Variable reluctance Rotor, in this type of rotor the rotor is made up of an iron core which gets aligns with the magnetic field generated by the stator. The construction of the variable reluctance Rotor is shown in the diagram below. In this type of rotor, it is quite easy to reach higher speeds and gain higher resolution, although it does not develop higher or detent torque. Below is the construction of a Variable Reluctance Rotor.
In Hybrid Rotor as the name states, it is a hybrid or combination of permanent magnet rotor and variable reluctance. The basic construction of the Hybrid Rotor is given below.
The rotor has two caps which has alternating teeth and it is magnetized axially. As it is a hybrid motor it has a combination of advantages of both permanent as well as variable reluctance rotor, which mainly consists of high speed, resolution, and torque. Due to its hybrid nature, its costs and construction are more complex. In real motors have more complex construction also has a higher number of teeth, which allows the motor to gain more small step size. The schematic diagram of the Hybrid stepper motor is shown in the diagram alongside, where supply to motor through phases are shown.
Stepper Motor Advantages and Disadvantages
Due to the internal structure of the stepper motor, it does not require any external sensor to detect the position.
Stepper motor control is pretty simple, motor does not require any driver also doesn't require any calculations or tuning for working.
Stepper motors are good for torque at lower speeds, holding the position of the motor, and better for long life.
Higher rotational speed as speed is proportional to the input pulses.
If the load on the motor is too high then the motor can skip a step.
The efficiency of the motor can be low as it overheats due to draining maximum current even at a standstill position.
Has low torque which may make the motor pretty noisy.
Has low power density and low torque-to-inertia ratio.
Due to its holding torque and high-resolution properties stepper motors are used in many applications in today's world some of them are,
Used in cameras for focus regulation in lenses.
In printers, in printer heads, paper feeds, scan bar, etc.
Also in video cameras in Tilt, focus, and zoom applications.
In robotics applications, actuators, and effectors.
ATM machines in the cash tray and tray elevators.