Motion Control & Drives

Electromagnetic brakes for DC motors

May 2022 Motion Control & Drives

Mini motor applications utilise DC motor technology because of compactness, low weight, and reliability. Stopping, slowing or holding the position and load of these motors is crucial for many applications, from controlling robotic joints through to automated window shades. This control is achieved by integrating an electromagnetic brake, accurately specified according to the application requirements and parameters of the DC mini motor. Louis Mongin, BLDC product strategic manager at Portescap, explains the technology behind electromagnetic brakes for DC mini motors.

In miniature DC motor applications, electromagnetic brakes are used to hold, stop or slow down a load. Without a brake, a motor would continue to rotate without control, even after cutting its supply of voltage or current; or it would fail to hold position against a competing power. While alternative torque control devices could be used, electromagnetic brakes can combine precision with a compact, reliable, energy-efficient and cost-effective design.

To hold a DC mini motor in position at a specific stopping point across a variety of industrial and medical applications, the general design includes a fixed field coil that acts as an electromagnet to generate torque to brake or hold the load. The coil’s electromagnetism controls an armature that either engages or disengages with a structure. The design of the brake mechanism features a hollow shaft mounted onto the shaft of the DC motor, which gives compact integration.

Brakes are available in a power-on design, which means that the brake is only engaged when current flows in the field coil. This is acceptable when the brake doesn’t have to hold a high load, or if holding torque isn’t required after power-off. Alternatively, with a power-off brake, the brake remains engaged at all times unless current is flowing in the electromagnet, which creates an inherently safer design for some applications.

Spring-set brakes utilise power-off braking and are used to automatically stop and hold a load in the event of a power failure or emergency stop situation. In this design, braking force is applied through a compression spring, and the brake is usually released by manual control. The advantages include repeated braking cycles from full motor speed with no torque fade, and the designs can be customised in aspects such as voltage rating and dynamic friction material according to the spring force requirement. The disadvantage of a spring brake is that it can present backlash, affecting the precision it can offer for dynamic braking or position holding.

Instead, for applications where dynamic stopping and holding a moving load is required, as well as for high cycle rate stopping, a permanent magnet power-off brake should be used. In this design, brakes are engaged magnetically and disengaged electrically, providing safe load holding in power shut-off. When voltage or current is applied to the brake, the coil becomes an electromagnet and produces magnetic lines of flux counteracting those of the permanent magnet. This action releases the armature, creating an air gap and allowing the load shaft to rotate. Increasing voltage or current also enables braking force to be controlled with precision, as opposed to the spring brake’s on/off functionality.

As the permanent magnet brake design includes no moving parts, the brakes can operate at very high speeds. Unlike spring brakes, they don’t allow backlash, because the design includes a fixed connection between the armature, spring and hub. This allows them to be controlled with precision. As heat is generated during dynamic braking, this means that the brake must be correctly sized to deal with friction, load and torque requirements. Permanent magnet brakes require consistent and specific current, meaning that these brake designs should be carefully considered before using them in conditions that could cause current fluctuations, such as high or changing temperatures.

Thanks to the precision control of a permanent magnet brake, they are well suited to use in robotic arm joints. Their zero-backlash capability means they can precisely hold torque and also provide dynamic stopping. An example of a DC mini motor application that requires safety in holding torque is the control of automated window shades. Providing automatic operation, the power-off brake also allows the motor to hold the shade position when power is removed.

Portescap’s engineers regularly integrate DC mini motor braking solutions into bespoke OEM applications. The team ensures exacting sizing and specification, as well as recommending the most effective technology and features for specific requirements. Design is combined with rapid prototyping and testing to ensure safety and precision, before moving the development to volume production.

For more information contact Nicole Monaco, Portescap, +1 404 877 2534,,

Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

Polymer linear guides adopted worldwide
Motion Control & Drives
The product range of lubrication-free drylin linear guides is based on the principle of ‘gliding instead of rolling’.

ML compensates for ‘cogging’ in high-precision linear motion
Beckhoff Automation Motion Control & Drives
Using recorded data, the servo motor software trains a neural network which is ultimately integrated into the control system for current pre-control.

Drive-based solutions enhance machine efficiency and safety
Bearing Man Group t/a BMG Motion Control & Drives
BMG’s electromechanical specialists are able to extend and adjust NORD drive equipment for drive monitoring, drive control and process control.

New motors for servo drive system
Siemens South Africa Motion Control & Drives
The servo motor thus meets all hygienic conditions and can be used for mixing and stirring, dosing and filling, as well as conveying, packaging and storing a wide variety of end products.       The ...

The demand for higher efficiency motors
Motion Control & Drives
With electricity prices increasing rapidly, the justification for adopting more efficient motors is that much greater. To achieve this improved efficiency, such motors are designed to run cooler, which ...

Compact drive technology mobilises high-tech CT scanner
Beckhoff Automation Editor's Choice Motion Control & Drives
PC- and EtherCAT-based technology from Beckhoff delivers the desired viewing angles and mm-precise alignment of the X-ray source to the patient.

Drive-based predictive maintenance solutions
Bearing Man Group t/a BMG Motion Control & Drives
BMG’s NORD predictive maintenance solutions offer fast, efficient and comprehensive evaluation of analogue and digital data, to enhance the operational efficiency and safety of machines. The intelligent ...

Next-generation motor starters with digital innovation
Schneider Electric South Africa Motion Control & Drives
Schneider Electric has announced the release of the new generation of TeSys Giga series motor starters. The iconic TeSys Giga series has been re-imagined with the latest smart digital innovations to deliver ...

Compact planar scanner with air bearing
Horne Technologies Motion Control & Drives
PIglide positioning systems are ideally suited for high-precision applications such as inspection systems, laser marking, microscopy or scanning.

Match & Tag for high accuracy in paired chain
Bearing Man Group t/a BMG Motion Control & Drives
Modern machinery often requires chains of precisely the same length to be used in pairs or other multiples. For these applications, BMG specialists recommend Tsubaki Match & Tag chains, which guarantee ...