There are two types of electromagnetic power-off brakes. They are spring applied brakes and permanent magnet brakes. Ogura offers both types. Both have their pros and cons, but one thing that stands out is torque control on a permanent magnet brake. These brakes are used on medical equipment, parking brakes on AGV's and other wheeled vehicles, robotics equipment, and more.

A permanent magnet brake has permanent magnets mounted inside of the coil assembly of the brake. The magnets offer constant electromagnetic flux. That flux attracts the armature towards the coil body. When the armature contacts the coil body, the friction provides the braking force.

The permanent magnet brake releases when electric current is applied to the brake coil. The electromagnetic flux from the coil is directional and purposely opposite of the direction of the permanent magnets' flux direction. When full power is applied, both lines of flux cancel each other out and the shaft is free to rotate since the armature is no longer held to the coil body.

The nice thing about these types of brakes is that you can vary the power that you apply to the coil and that will vary the amount of electromagnetic flux that gets cancelled out from the permanent magnets. This helps to control the torque. If you reverse the polarization of the electrical connection, the brake will theoretically provide 2x the rated brake torque.

It should be noted that when brakes are used dynamically, they burnish. Burnishing is a wearing-in of the clutch surfaces. Since the surfaces change under dynamic stopping conditions, the torque will not always be exactly the same when compared to previous stops, even under the same power conditions. In other words, torque control is a relative to the condition of the brake surfaces, but still applicable in many applications that don't need precision control.

PMB series brakes for stopping or holding are rated up to 120 Nm / 90 lb-ft static torque. Custom designs and sizes are available. They have zero backlash and higher torque than an equivalent sized spring set brake.

Benefits you will see using permanent magnet brakes:

• Brakes provide holding power when voltage is released
• Standard voltages are 24 and 90, but other coil voltages are possible
• Controlled torque
• Compact size
• Zero backlash

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