Stepper motors and brushless dc motors are two very widely used drive motors, the structure, field, drive characteristics of the two are obviously different, the following details the difference between stepper motors and brushless dc motors, will be introduced from the drive principle, characteristics, application scenarios.
What is a stepper motor?
Stepper motor, also known as pulse motor, is based on the most basic electromagnet principle, which is a kind of electromagnet that can be freely rotated, and its action principle relies on the change of air gap magnetic permeability to generate electromagnetic torque.
A stepper motor is a motor that converts electrical pulse signals into corresponding angular or linear displacements. The output angular displacement or linear displacement is proportional to the number of pulses input, and the speed is proportional to the pulse frequency. Therefore, stepper motor is also called pulse motor.
Usually the rotor of the motor is a permanent magnet, and when the current flows through the stator winding, the stator winding produces a vector magnetic field. This magnetic field drives the rotor to rotate at an angle so that the direction of the rotor’s pair of magnetic fields coincides with that of the stator’s field.
When the stator’s vector magnetic field rotates by an angle. The rotor also rotates at an angle with the magnetic field. Stepper motors are characterized by smooth operation, low noise, fast response, long service life, and high output torque.
What are the applications of stepper motors?
Stepper motors are used in intelligent robot drive, lift table lift, electric sofa telescoping, ATM machine, airbrush, lettering machine, photo machine, spraying equipment, medical instruments and equipment, industrial automation equipment, small power tools, precision instruments, industrial control system, office automation, robots and other fields.
Principle of brushless dc motor
Brushless DC motor uses semiconductor switching device to realize electronic commutation, i.e., electronic switching device instead of traditional contact commutator and brush. It has the advantages of high reliability, no commutation spark, low mechanical noise, etc. It is widely used in high-grade recording docks, video recorders, electronic instruments and automatic office equipment.
Brushless DC motor consists of permanent magnet rotor, multi-pole winding stator, position sensor, etc.
The position sensing switches the current of the stator winding along a certain sequence according to the change of rotor position (i.e. detects the position of the rotor pole relative to the stator winding and generates a position sensing signal at the determined position, which is processed by the signal conversion circuit to control the power switching circuit to switch the winding current according to a certain logic relationship).
The operating voltage of the stator winding is provided by the electronic switching circuit controlled by the position sensor output.
Brushless dc motor advantages
Brushless dc motor, low interference, low noise, smooth operation, long life, low maintenance costs, etc.
Brushless dc motor uses
Small power, small brushless motors need to be used together with gearboxes, widely used in smart car drive, robot drive, smart home drive, home appliance drive, consumer electronics drive, communication equipment drive, medical equipment drive, electronic lock drive and other industries and equipment.
The main difference between stepper motor and brushless motor
Fundamentally, both are basically the same. However, they differ in the intended application. Stepper motors should run gradually. Brushless dc motors are intended to provide smooth motion.
Since stepper motors are used for motion control, repeatable steps are required. That is, if you start with one step and then go to another and then back to the first step, it should ideally return to exactly where it was before.
A variety of things can confuse things. Brushless dc motors are optimized for smooth torque between steps, not repeatability.
Stepper motors are designed to maximize holding torque, the ability of a stepper to hold a mechanical load at a certain level. This can be achieved by keeping the winding current high even if the rotor is aligned with the stator.
This wastes a lot of energy because it does not generate torque unless the load tries to deviate from its position, but it does avoid the need for any feedback mechanism.
On the other hand, Brushless dc motors typically operate with the rotor lagging behind the stator, so the applied current will always produce the maximum torque, which is what a brushed motor would produce.
If less torque is required, the current is reduced. This is more efficient, but the position of the load must be sensed to know how much torque to apply. As a result, stepping motor are usually larger to accommodate the additional heat generated by running the motor at maximum current at all times.
Again, for most applications, one expects the stepper to perform small steps for precise motion control. This means a large number of magnetic poles. A stepper motor typically has hundreds of steps per revolution.
Brushless dc motors will typically have much less. For example, I was recently using a brushless dc motors from a hard disk drive that had four “steps” per revolution.
Hybrid stepper motors are usually designed for maximum holding torque first, then second speed. This usually means that the windings are very large and each unit of current produces a stronger magnetic field, which produces more torque.
However, this comes at the cost of increased counter-electromotive force, which reduces speed per unit voltage.
Similarly, stepper motors are usually driven by two phases 90 degrees apart, while bldc motor usually have three phases (120 degrees apart) (although there are exceptions in both cases).
