Spring-applied brake and permanent magnet brake in comparison

Both spring-loaded brakes and permanent magnet brakes have their place. But which one is the right one for the respective application? Since very different aspects have to be taken into account when making the selection, the user should rely on competent advice. Then it is of course an advantage if the brake manufacturer providing advice has both operating principles in its program and advises without any self-interest. The contribution from the manufacturer of clutches and brakes Kendrion shows that not all brakes are the same.

Contents

• Distinction between holding brake and working brake
• Two principles of action - different properties
  • Permanent magnet brake
  • Allrounder spring pressure brake
• New spring-loaded brake with reduced air gap – video statement
• Frequently asked questions

Distinction between holding brake and working brake

Depending on the operating conditions, a distinction is made between holding and working brakes. The Holding brake has the task of keeping loads at a standstill. The braking of the movement is carried out by the drive. Only in the event of an error, e.g. B. during an emergency stop, the holding brake performs braking work to bring the system to a standstill and then keep it at rest.

In contrast, the Working brake the task of destroying the kinetic energy and then keeping the system at rest when it is at a standstill. Typical areas of application for holding and working brakes can be found in elevators, overhead conveyors and wind turbines as well as in robotics and mechanical engineering.

The use of work brakes is becoming more and more in the background as modern ones Drives and Controllers cope with the braking task safely and also wear-free can work. Applications in which work brakes are used are served by spring-applied brakes because the organic friction systems used there - similar to the brake pads in cars - are well suited to providing a high level of overall work over the service life.

Both permanent magnet and spring-applied brakes are used for the vast majority of holding brake applications. The user is spoiled for choice here, as in so many other areas. He has to decide which one Operating Principle is best suited for its application. Both have characteristic properties that make them ideal for different areas of application.

Two principles of action - different properties

Both types of brakes are closed when de-energized. It is a matter of Safety brakes: In the event of a power outage or failure of the energy supply, such as a line break, the system is safely maintained. However, there are fundamental differences beyond that. With the spring-applied brake, which is usually installed on the B bearing side of an electric motor, springs press against the armature disk of the brake when de-energized.

The Friction linings of the rotor, which is connected to the motor shaft via a toothing, is clamped between this armature disk and the mounting surface of the brake on the rear of the motor. When the brake coil is energized, a magnetic field is created that attracts the armature disk and thus releases the rotor with the friction linings. The brake releases.

When it comes to the active principle permanent magnet On the other hand, in the de-energized state, the armature or rotor is pulled against the stator or the excitation system by the permanent magnetic field. When energized, an electromagnetic field is created that cancels out the attractive force of the permanent magnets and thus releases the armature from the excitation system through the tensile force of the springs between the armature and the flange hub. The brake releases.

The force-fitting connection The permanent magnet brake is free of play between the armature, hub and shafts. However, defined installation conditions must be adhered to in order to ensure a defined air gap in the motors.

Permanent magnet brake

From these two active principles with their different Friction pairings, steel/steel in the permanent magnet brake and organic friction linings/steel in the spring-applied brake result in defined, essential properties that result in typical fields of application for both types of brakes:

Permanent magnet brakes (PE) are well suited for servomotors, for example in handling technology and Robotic. Here they are particularly impressive due to their compact dimensions and their comparatively low weight. Thanks to the permanent magnets, the power density is twice as high as usual with spring-applied brakes (FD). But there are also other reasons why people tend to prefer lightweight, dynamic and almost abrasion-free brakes in robotics.

The freedom from abrasion of the PE brake is ensured by this mode of action the brake is ensured. The anchor is completely released by the spring. With the FD brake, start-up wear occurs because when the speed increases, an air cushion must first build up between the pad and the friction surfaces. This wear can occur due to acceleration of the friction disk, e.g. B. the acceleration due to gravity when the drive is arranged vertically or due to centrifugal forces when the rotor blades of a wind turbine rotate. Usually only one friction lining is affected.

When used, the PE brake behaves as a pure holding brake Emergency stop function different from the FD brake. Due to its design, the PE brake is free of residual torque. There is only abrasion during the emergency stops. When actuated, the armature is completely released by the spring. In contrast, the FD brake has a starting torque, which leads to a certain amount of wear with every start. The above-mentioned wear and tear caused by acceleration forces makes things even more difficult. Often this additional wear cannot be determined precisely because usually only one side of the friction disk is affected.

Whisper-quiet elevator brake secures elevators and escalators

Another difference lies in the behavior Temperature range. PE brakes are very temperature stable and have a guaranteed high torque over the entire temperature range. Things are different with FD brakes. Here, the temperature stability is essentially influenced by the composition of the organic friction lining. You can compare this to a car tire, which is also developed for different operating conditions. Just as a Formula 1 tire cannot be used in winter, some organic friction linings cannot be used in brakes.

With a high coefficient of friction, the covering has good adhesion high torques, but the covering wears out very quickly. For pads in FD brakes this means: pads with high coefficients of friction show a greater drop over the entire temperature range and sometimes only have half the torque at 120° or -40°C. In general, it can be said that FD brakes either achieve very good torque, but are not as temperature-stable or that the coefficient of friction is comparatively lower with a temperature-stable pad. However, it should be emphasized that within a given temperature range, the torque of the FD brake can be adjusted very precisely to the torque specified by the customer in the design process.

Allrounder spring pressure brake

Lifting and travel drives with high braking energies and defined braking torque, i.e. controlled deceleration during an emergency stop, cannot be operated by PE. In addition, there are numerous applications where high dynamics and power density are not required. Cranes, overhead conveyors and roller doors provide typical examples of this.

The brake must brake if the worst comes to the worst Emergency stop If necessary, deliver high deceleration values ​​per braking and reliably maintain the weight. The switching time and power density only play a minor role. High braking work is no problem for the organic friction linings of the spring-applied brakes and they can also be used as a working brake if necessary.

Besides, that is moment of inertia Due to the comparatively low weight of the friction disc, it is lower than with permanent magnet brakes. In addition, these applications usually use IEC standard motors on which spring-applied brakes can be easily and quickly installed. The brake, whose structure is less complex than permanent magnet brakes, usually remains easily accessible.

Anyone who has a cost-effective solution in an application Standard standard motor can therefore normally use a spring-applied brake. For the respective area of ​​application, e.g. B. for a specific operating temperature range, a friction lining optimized for the application can be selected.

The FD brake With the correct selection of the organic friction lining and the design of the springs, it can be easily adjusted to a desired torque with a relatively small tolerance. If the temperature range is still comparatively small, the torque can be maintained well within this range. In addition, development has not stopped when it comes to spring-applied brakes: With the new Kobra brakes from Kendrion, 80% more torque or three times the service life can be achieved compared to previously available solutions on the market. By reducing the control power, power consumption is reduced by a third. Less heat is generated, which reduces component aging.

New spring-applied brake with reduced air gap

05.02.2014 | Jörg Heilmann, Head of Sales, Kendrion GmbH, Villingen Schwenningen, presents a new spring-loaded brake at the trade press days in Karlsruhe. The air gap was reduced to 0,02 mm.

Frequently asked questions

What is the difference between spring-applied brakes and spring-applied brakes?

Although they sound similar and can often be confused, spring-applied brakes and spring-applied brakes are not the same. With the spring-applied brake, the spring provides a braking effect when de-energized, while with the spring-applied brake, the spring keeps the brake open when de-energized and energy is required to close the brake or described in more detail as follows:

• Spring brake: With a spring-applied brake, the braking force is generated by the spring, which presses the brake pads against the element to be braked. This type of brake is usually a "fail-safe" brake, meaning it activates when de-energized. This means that the brake automatically switches to the braking state in the event of a power failure or an interruption in the energy supply.
• Spring pressure brake: A spring-applied brake works exactly the opposite of a spring-applied brake. This brake uses spring force to pull the brake pads away from the brake disc or brake element, allowing movement. The brake is activated by applying energy, i.e. it is opened when there is no power.