Linear permanent magnet brakes, also known as eddy current brakes, are a fail safe, 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.
They do not require any input power to operate and as a result they are fail-safe.
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.
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 resultant 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.
Linear magnetic brakes can be used as a passive braking/decelerator system where a multi permanent magnet assembly interacts with a conductive plate to decelerate a moving vehicle. Please note that our permanent magnet brakes are actually decelerators; they will reduce the speed of a payload, but they will not completely bring the velocity to zero. The deceleration force is proportional to velocity.
A linear induction motor could potentially be used as an active braking system where the linear motor generates a force in opposition to the moving vehicle. A linear induction motor generates a force that can be controlled by varying both the input voltage and frequency to the motor. The induction motor would interact with the conductive plate on the track. For both cases above, they would both be mounted on the moving vehicle.
H2W has a number of off-the-shelf permanent magnetic brakes, a listing of these can be found under the brushless linear motor magnet tracks. A general deceleration force number for a double sided permanent magnetic “D” sized brake/decelerator is 30 N/m/sec for a 1.2” (30 mm) long decelerator. Our brake/decelerators come in a range of standard sizes from approximately 4” (100 mm) to 48” (1200 mm) in length. These can be arranged in series to achieve your desired length. We can also offer you a custom length. You would need to perform your own calculations to determine the volume of brake that is needed for your application.
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 2 plates and the magnet assembly.
The double-sided brake allows for a thin conductive plate or fin to pass thru the “U” shaped permanent magnet assembly. In this case, there is no magnetic attractive force between the 2 members. This design offers more flexibility for mounting the brakes and does not have exposed magnets.
Linear Magnetic Brake Advantages
- Fail Safe (no power required)
- Custom Designs
- Ceramic or Rare Earth Magnets
- Maintenance free
No Electronics are required for brake operation
If mounted in an environment that is wet or excessively dirty, consult factory to determine if sealed assembly is required. The magnetic assembly is highly magnetic, 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 high ambient temperatures (>50ºC).
The linear magnetic brakes requires no maintenance except for the periodic inspection and removal of magnetic particles that may accumulate on the the exposed magnet surface.
The linear magnet brakes are custom designed for each application. They are supplied in modular form, which allow for easy handling and installation. Consult factory for size and part numbers.
For More Information
And a better visual representation of how a linear magnetic brake functions, click on one of the links below: