Linear permanent magnet brakes, also known as eddy current brakes, are a failsafe, power-free deceleration system that is used in conjunction with a metal reaction plate. Ceramic or rare earth magnets are bonded to a steel back iron plate; no input power is required.

They are used in applications such as baggage handling and people-moving systems, inclined material transfer lines, and amusement park rides to reduce the velocity of the payload to almost zero speed.

Operation

The principal of operation is quite simple. As an electrically conductive reaction plate moves through a permanent magnet field at some velocity, eddy currents are produced in the plate. These eddy currents, in conjunction with the magnetic field, produce a force that opposes the driving force of the plate. The result is a braking action on the conductive plate. The amount of braking is proportional to the velocity — the higher the relative velocity, the greater the breaking force; the lower the velocity, the lower the braking force. The net result of all of this is a very smooth, very controlled deceleration of the payload.

Figure 1. Brake is completely disengaged.
Figure 2. Brake is generating about 30% brake force.
Figure 3. Brake is generating about 70% brake force.
Figure 4. Brake is generating 100% brake force.

If there is no relative velocity between the magnets and the conductive plate, no braking will occur. As a result, the exit velocity will never be zero. Depending on system configuration and total travel, either the conductive plate or the magnet assembly can be mounted to the vehicle or pallet system.

The resulting energy from the braking system produces heat in the reaction plate. At higher velocities, more eddy currents are produced, which results in more heat generation in the reaction plate. Since there is no mechanical contact between the reaction plate and the magnet assembly, there are no wearing parts and as a result, no maintenance is required.

Braking systems can be custom-designed to have whatever exit velocity is desired, all the way down to almost zero speed.

Configurations

The linear magnetic brakes come in two configurations. The single-sided brake is a lower-cost solution but has open, exposed, permanent magnets. If the conductive plate is backed with a steel plate to increase the magnetic field in the gap (which in turn increases the braking), there will be a large magnetic attractive force between the two plates and the magnet assembly.

The double-sided brake allows for a thin, conductive plate or fin to pass through the U-shaped permanent magnet assembly. In this case, there is no magnetic attractive force between the two members. This design offers more flexibility for mounting the brakes and does not have exposed magnets. Figures 1 to 4 illustrate the stages of engagement of a double-sided linear magnetic brake.

Advantages

There are a number of advantages to linear magnetic brakes:

  • Failsafe (no power required)

  • Efficient

  • Custom designs

  • Ceramic or rare earth magnets

  • Maintenance-free

  • No electronics are required for brake operation

Environmental Considerations

If mounted in an environment that is wet or excessively dirty, consult the factory to determine if sealed assembly is required. The magnetic assembly is highly magnetic, so it should not be placed in an area where loose steel particles can be drawn into the magnetic gap. The brakes should not be mounted in an environment with ambient temperatures greater than 50 °C.

Maintenance

Linear magnetic brakes require no maintenance except for the periodic inspection and removal of magnetic particles that may accumulate on the exposed magnet surface.

The linear magnet brakes are custom-designed for each application. They are supplied in modular form, which allows for easy handling and installation.

This article was contributed by H2W Technologies, Santa Clarita, CA. For more information, visit here.