What’s the difference?
A closed loop stepper motor, by its definition, has a sensor in the motor that feeds information to the driver, allowing the driver to know exactly what position the motor is in and at what speed it is operating. They are able to complete accurate positioning faster and more accurately than any servo motor, do not require tuning and can be manufactured at reduced cost. Some have high-speed and highly accurate return-to-home and thanks to a mechanical absolute encoder, eliminates the need for a battery backup, meaning less maintenance and easier shipping. They fit perfectly with the rationale of Industry 4.0 as they support various industry comms systems and protocols, have intelligent drivers and allow for remote control and monitoring.
When might a closed loop stepper motor be used?
These motors are incredibly versatile. As previously mentioned, they can often be used in place of servo motors and are particularly effective for rapid indexing and applications with complex motion profiles. Some of the many other uses include robotics, testing and inspection systems plus applications that require smooth operation, short settling times and precision across many positions.
Brushless DC Motors
Brushed motors have been in use since the late 1800s and show Faraday’s Law in action: electromagnetic induction. They rely on a brush inside the motor to deliver current to the motor windings through rotary switches, so powering the motor. Their long use in motorised applications indicate their wide-ranging capabilities. However, as advancements in technology have gathered pace, we see the emergence of the brushless DC motor - BLDC. They work in the same way as brushed motors – but without the brush. The windings in a brushless DC motor are within the case of the motor, but separate to the stator, in the same manner as a servo motor is built. This eliminates the need for brushes.
What’s the difference?
If the brush motor has been around for so long, why the shift? The driving force and their primary feature is efficiency – think 85-90% efficient compared to 75-80% efficiency of brushed DC motors. More of the power used by the motor results in rotational force and less is lost as heat. Their speed ratio can be as great as 1:50. The brush is the weak point of a DC motor as they wear out or need replacing – without that they are more or less maintenance-free and create little noise or heat variations because of the lack of friction from the brush. The permanent magnet employed allows for great and very accurate speed as well as and torque control and stability. Cost-wise, they are significantly less to manufacture than a servo.
When might a brushless DC motor be used?
The BLDC is perfect for any application that requires a motor to rotate at a stable speed, from low to high, even when the load fluctuates. Ideal applications include more advanced conveyor systems, checkweigher systems, AVGs, certain axis on factory automation machinery as well as tensioning and winding applications. As a compact motor, a BLDC can help in downsizing equipment and saving energy. They significantly reduce power consumption as the use of permanent magnets in the rotor portion prevents secondary loss from the rotor.
There is an enormous variety of motor options available for an enormous variety of applications. Industry 4.0 has enabled us to reconsider what we use where and to look at options that will save time, cost and materials. The motor sector is moving at as fast a pace as the rest of the electro mechanical industry andexciting times definitely lie ahead in terms of advancements in technology.