Stepper Motor – Types, Advantages & Applications

A stepper motor is an electromechanical device it converts electrical power into mechanical power. Also it is a brushless, synchronous electric motor that can divide a full rotation into an expansive number of steps. The motor’s position can be controlled accurately without any feedback mechanism, as long as the motor is carefully sized to the application. Stepper motors are similar to switched reluctance motors.

The stepper motor uses the theory of operation for magnets to make the motor shaft turn a precise distance when a pulse of electricity is provided. The stator has eight poles, and the rotor has six poles. The rotor will require 24 pulses of electricity to move the 24 steps to make one complete revolution. Another way to say this is that the rotor will move precisely 15° for each pulse of electricity that the motor receives.

Stepper Motor
Stepper Motor

Types of Stepper Motor:

There are three main types of stepper motors, they are:

  1. Permanent magnet stepper
  2. Hybrid synchronous stepper
  3. Variable reluctance stepper

Permanent Magnet Stepper Motor: Permanent magnet motors use a permanent magnet (PM) in the rotor and operate on the attraction or repulsion between the rotor PM and the stator electromagnets.

Variable Reluctance Stepper Motor: Variable reluctance (VR) motors have a plain iron rotor and operate based on the principle that minimum reluctance occurs with minimum gap, hence the rotor points are attracted toward the stator magnet poles.

Hybrid Synchronous Stepper Motor: Hybrid stepper motors are named because they use a combination of permanent magnet (PM) and variable reluctance (VR) techniques to achieve maximum power in a small package size.

Advantages of Stepper Motor:

  1. The rotation angle of the motor is proportional to the input pulse.
  2. The motor has full torque at standstill.
  3. Precise positioning and repeatability of movement since good stepper motors have an accuracy of 3 – 5% of a step and this error is non cumulative from one step to the next.
  4. Excellent response to starting, stopping and reversing.
  5. Very reliable since there are no contact brushes in the motor. Therefore the life of the motor is simply dependant on the life of the bearing.
  6. The motors response to digital input pulses provides open-loop control, making the motor simpler and less costly to control.
  7. It is possible to achieve very low speed synchronous rotation with a load that is directly coupled to the shaft.
  8. A wide range of rotational speeds can be realized as the speed is proportional to the frequency of the input pulses.

Applications:

  1. Industrial Machines – Stepper motors are used in automotive gauges and machine tooling automated production equipments.
  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.

And also have business machines applications, computer peripherals applications.

Operation of Stepper Motor:

Stepper motors operate differently from DC brush motors, which rotate when voltage is applied to their terminals. Stepper motors, on the other hand, effectively have multiple toothed electromagnets arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external control circuit, for example a microcontroller.

Stepper Motor Circuit
Stepper Motor Circuit

To make the motor shaft turn, first one electromagnet is given power, which makes the gear’s teeth magnetically attracted to the electromagnet’s teeth. The point when the gear’s teeth are thus aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when the next electromagnet is turned ON and the first is turned OFF, the gear rotates slightly to align with the next one and from there the process is repeated. Each of those slight 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. Stepper motor doesn’t rotate continuously, they rotate in steps. There are 4 coils with 90o angle between each other fixed on the stator. The stepper motor connections are determined by the way the coils are interconnected.In stepper motor, the coils are not connected together. The motor has 90o rotation step with the coils being energized in a cyclic order, determining the shaft rotation direction. The working of this motor is shown by operating the switch. The coils are activated in series in 1 sec intervals. The shaft rotates 90o each time the next coil is activated. Its low speed torque will vary directly with current.

Stepper Motor Control by Varying Clock Pulses

Stepper motor control circuit is a simple and low-cost circuit, mainly used in low power applications. The circuit is shown in figure, which consist 555 timers IC as stable multi-vibrator. The frequency is calculated by using below given relationship:

Frequency = 1/T = 1.45/(RA + 2RB)C Where RA = RB = R2 = R3 = 4.7 kilo-ohm and C = C2 = 100 µF.

Stepper Motor Control by Varying Clock Pulses
Stepper Motor Control by Varying Clock Pulses

The output of timer is used as clock for two 7474 dual ‘D’ flip-flops (U4 and U3) configured as a ring counter. When power is initially switched on, only the first flip-flop is set (i.e. Q output at pin 5 of U3 will be at logic ‘1’) and the other three flip-flops are reset (i.e. output of Q is at logic 0). On receipt of a clock pulse, the logic ‘1’ output of the first flip-flop gets shifted to the second flip-flop (pin 9 of U3). Thus logic 1 output keeps shifting in a circular manner with every clock pulse. Q outputs of all the four flip-flops are amplified by Darling-ton transistor arrays inside ULN2003 (U2) and connected to the stepper motor windings orange ,brown, yellow, black to 16, 15 ,14, 13 of ULN2003 and the red to +ve supply.

The common point of the winding is connected to +12V DC supply, which is also connected to pin 9 of ULN2003. The color code used for the windings is may vary form make to make. When the power is switched on, the control signal connected to SET pin of the first flip-flop and CLR pins of the other three flip-flops goes active ‘low’ (because of the power-on-reset circuit formed by R1-C1 combination) to set the first flip-flop and reset the remaining three flip-flops. On reset, Q1 of IC3 goes ‘high’ while all other Q outputs go ‘low’. External reset can be activated by pressing the reset switch. By pressing the reset switch, you can stop the stepper motor. The motor again starts rotating in the same direction by releasing the reset switch.

Now you have got an idea about the types of super motors and its applications if you have any queries on this topic or on the electrical and electronic projects leave the comments below.

Photo Credit:

  • Stepper Motor by cst

6 Comments

  1. Please, add the release date of this article

  2. It’s useful to students and it has full information about electrical

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  3. Sir very knowledgeable description, i wanna get the circuit diagram which you made understand

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