Stepper Motors – Functions and Advantages
Published on : Saturday 30-09-2023
What is a stepper motor? Their functioning, advantages and applications...
A stepper motor is a type of DC motor that works in discrete steps. It is a synchronous brushless motor where a full rotation is divided into a number of steps. The two main components of a stepper motor are the rotor and the stator. The rotor is the rotating shaft and the stator consists of electromagnets that form the stationary part of the motor. When a discrete DC voltage is applied, the stepper motor rotates in a particular angle called the step angle and it can be operated with or without a feedback control.
A stepper motor is a particular type of DC motor that does not rotate continuously. Instead, a full rotation is divided into a number of equal steps. A stepper motor consists of phases, which are multiple coils that are organised into groups. By applying the energy from the input voltage to each phase in a sequence, the stepper motor rotates by taking one step at a time. Thus a stepper motor converts electrical energy or an input digital pulse into mechanical shaft rotation.
Functioning of a stepper motor
Stepper motor can offer the precision they do, without any sensors or a feedback sensing mechanism. They are different from Brushless DC motors. They comprise a rotor and a stator. The rotor is a permanent magnet, while the stator has windings that cover the rotor. These windings are activated in a certain order to facilitate the flow of current through them.
This magnetises the stator to form two electromagnetic poles and propel the motor.
There are various driving modes used to drive a stepper motor:
i. Wave drive or single motor excitation: In this mode, the rotor completes one full cycle in a certain number of steps depending on the number of coils. For instance, if the motor has four coils, one cycle will be completed in four steps by the rotor. We need to activate one coil at a time.
ii. Full step drive: In this mode, the torque is much higher than the previous mode as there are two coils activated at any given point of time. In spite of this, the rotor takes four steps to complete one cycle, so there is not much difference in the resolution.
iii. Half step drive mode: This mode is a combination of full step drive mode and wave drive mode. This is basically devised to improve the resolution of the stepper. So, in this mode, we have an alternating sequence of one active coil followed by two active coils again followed by one active coil. This sequence is repeated, which helps the rotor complete one full cycle in eight steps. So, with the same setup, the resolution is doubled.
iv. Micro stepping: This is the most widely used method of driving a stepper motor. In this mode, a variable controlled current flows through the coils in the form of a sine wave. This enables a smooth rotor motion and increased accuracy of the stepper motor. It reduces stress on the parts. In a bid to increase the resolution, the number of poles on the rotor and stator are increased.
Advantages of the stepper motor
1. Life of the stepper motor: If we examine the construction of the stepper motor, we will see that there is no friction in the moving parts except this bearing, so this is the reason the stepper motor survives for a long time. But again, motor use matters. The life of any motor depends on how we use the motor. More rigorous use of the motor can affect the life of the motor.
2. Holding torque of the stepper motor: Holding Torque of any motor is a really important parameter. It should be as high as possible. Holding Torque is the motor's ability to maintain its original position after energising the motor windings, even when a large amount of force is applied to the shaft of the motor. It is also known as the stand stall torque of the motor. On top of this, the stepper motor has another capability that keeps the rotor in the same position when no current flows through the winding and this is called the Detent Torque of the motor.
3. Maintenance cost of the stepper motor: Unlike other motors, this type of motor will not increase your expenses on maintenance costs and the reason for this is that the stepper motor is a brushless type of motor. Unlike other motors, in this motor, you do not need to change the brush repeatedly; and so we can say that this type of motor has a low maintenance cost.
4. Repeatability of the stepper motor: This is one of the best features of the stepper motor. The stepper motor has the ability to return to its original position after completing a full detour. This feature of this type of motors makes them more accurate and most useful motors in applications where precise speed is the priority.
5. Excellent low speed torque: Stepper motors produce high torque at low speed. This makes it more suitable for applications where high torque is required with high precision.
6. Cost and complexity of the stepper motor: If you are looking for a motor that controls the object more accurately then this is the best option for you. As we discussed, the stepper motor operates on an open-loop system, which means, unlike other motors, the stepper motor does not require an encoder and this makes the stepper motor less complex and inexpensive than other motors.
Applications of stepper motors
Consumer Electronics – Stepper motors in cameras for automatic digital camera focus and zoom functions. Stepper motors as actuators for mobile phones camera modules.
Automotive and Aircraft – Stepper motors help enable cars, SUVs and RVs to receive telecommunication signals. Stepper motors are also used for cruise control, military antenna positioners, automated sensing devices, and automated cameras. In aircrafts, stepper motors are used in aircraft instruments, sensing devices, antennas, scanning equipment.
Office Equipment – Stepper motors are incorporated inside PC based scanning equipment, data storage tape drives, optical disk drive head driving mechanism, printers, bar-code printers, scanners.
Medical – Step motors are used inside medical scanners, multi-axis stepper motor microscopic or nanosomic motion control of automated devices, dispensing pumps, samplers, and chromatograph auto-injectors. Also found inside digital dental photography, fluid pumps, respirators, and blood analysis machinery.
Industrial machines – Stepper motors are used in automotive gauges, machine tooling automated production equipment (single/multi axis stepper motor controllers) and also in retrofit kits [stepper motor controllers and motors] for CNC machine control.
Scientific Instrumentation – Scientific Equipment Spectrograph’s, observatory telescope positioning.
Chemical – Mixing and sampling devices utilising stepper motor controllers and single/multi axis stepper motor controlled environmental testing equipment.
Security – New surveillance products for the security industry.
Gaming industry – Stepper motors are used in the motors that power slot machines, wheel spinners and card shufflers.
Durga Mechatronics can provide Minebea make stepper motors.