When you need a motor to stop and you can’t just let it naturally come to rest, then you probably need an electric motor brake. And it’s very important that you get the right motor brake for the job.
What All Motor Brakes Have in Common
While there are several different types of motor brakes, there are certain things they all have in common. First is their purpose: motor brakes are responsible for stopping an electric motor or holding its driven load. Motor brakes accomplish this by using friction between mating surfaces to generate the necessary stopping torque. They are used when stopping needs to occur in a limited amount of time, as opposed to a gradual stop achieved by simply powering down an electric motor.
Types of Electric Motor Brakes
Most motor brakes fall under the category of electromechanical brakes and there are two basic categories: spring set and electrically set.
In a spring set brake, springs actuate the brake so that it applies torque when the power is disconnected. The brake is disengaged through either electromagnetic, hydraulic, or pneumatic actuators. Spring set brakes are well adapted to rapid stop and hold applications and are often used as fail-safe holding brakes. They don’t offer much control over the stopping time, however, unless the actuator is hydraulic or pneumatic.
In an electrically set brake, on the other hand, the brake applies torque along as power is present to provide the actuating force via a magnetic coil. You’ll see these brakes used with high-cycling or soft-release applications.
There are also permanent magnet brakes which use the force of permanent magnets as opposed to springs to apply the necessary pressure to generate stopping torque. To disengage these brakes, a magnetic flux is created by applying enough current to the coil of the break to cancel out the ever present magnetic field created by the permanent magnet. These brakes work well when a highly controlled stop is necessary (e.g., escalator).
Most Commonly Used Motor Brakes
Three of the most commonly used types of brakes are DC brakes, 3 phase brakes, and single phase AC solenoid/linkage brakes, although there are other types available.
DC brakes are an example of a spring-actuated, electromagnetically released motor brake. These brakes use springs to press the armature plate against the brake hub. This, in turn, squeezes the friction disk (lying between the armature plate and the mounting plate) to generate the stopping torque.
The friction disk is free to rotate with the hub when energizing the coil attracts the armature plate back to the magnet, which means torque is applied when the power is removed. DC brakes are known for requiring less maintenance and fewer adjustments than other types of brakes, in part because there are no linkages or solenoids involved. They also offer adjustable torque.
3 Phase Brakes
Three-phase brakes, also known as, phase induction brakes, are another example of a spring-actuated, electromagnetically released motor brake. These induction motor brakes work similarly to a DC brake in that a spring presses the armature plate against the brake hub. They differ that instead of using a magnet they use electric coils to generate an electromagnetic field to draw the armature back.
Note that when the brake is powered, it will pull the armature and brake lining away from the hub so the motor can freely rotate. Note that the torque in a three-phased can be adjusted according to the number of springs used and their response time is not as fast as an equivalent DC brake.
Single Phase AC Solenoid / Linkage brakes
Single-phase AC solenoid / linkage brakes are designed a bit differently from DC brakes and 3 phase brakes. To allow the motor to rotate freely, a linear solenoid pulls on a mechanical linkage that releases two pressure springs that then pull up the pressure plate. Once the pressure plate is pulled up, the friction disk rotates freely with the hub. This type of spring set brake does not support torque adjustment, however.
The drawback of this type of brake is the limited lifespan of the solenoid and/or linkage due to the fact moving parts are prone to wear. These brakes should not be used for applications that involve intensive cycling or exact stopping.
Things to Consider when Selecting a Motor Brake
There are several key considerations when you are selecting a motor brake, with the most obvious ones being torque and RPM. You also need to take into account the expected cycle rate as well as available power supply, space and accessibility constraints, and mounting. In addition, it’s important to keep in mind environmental conditions, constraints such as noise, and any applicable industry standards. Some braking applications may require water or air-cooling.
When shopping for a motor brake, it’s extremely important to research what type of brake is right for your application. For example, a brake for an elevator will have different requirements from a fail-safe brake or a brake for use in a theater where sound is a major concern. If you have questions about what motor brake is right for you, HECO -- we’d be glad to share our expertise with you.
Author & Contact Info: Hunter Shields: 312-415-2096 or firstname.lastname@example.org