Safety brake
Safety brakes have the task of decelerating moving masses or loads while they are moving or keeping them safely at a standstill. In the case of safety brakes, the braking torque or braking force is generated via pretensioned springs . The brakes are released electromagnetically, hydraulically or pneumatically . In the de-energized state they are closed. They thus meet the required safety aspects under all operating conditions including emergency stop and power failure. But even if the brake is damaged, for example due to a break in the power supply line or failure of the solenoid , the braking torque is retained. Fail-safe means that the braking effect is always guaranteed, even under unfavorable conditions and operational disruptions.
Construction / assembly
The most common type of safety brake is the electromagnetic, quiescent current actuated spring pressure brake. It is usually attached to the B-bearing side of electric motors. When not energized, springs press against the armature disk of the brake. The friction linings of the rotor , which is connected to the motor shaft via a toothing , are clamped between this armature disk and the mounting surface (rear of the motor) of the brake. If the coil of the brake is energized, a magnetic field builds up , which attracts the armature disk and thus releases the rotor with the friction linings. The brake is released.
variants
Positioning brake (stop and control brake)
In the past, safety brakes were often used to brake machines or systems from moving and to position them exactly at a defined point. The positioning accuracy is negatively influenced by some parameters. When the friction linings wear out, the working air gap increases, the spring force decreases, and the switching times become longer. Other influencing factors are temperature and humidity. Due to the low accuracy, safety brakes are generally no longer used for positioning today.
Working brake (performance brake)
For example, you have the task of slowing down simple machines with uncontrolled drives from moving. Table saws are a typical application. After switching off the motor, the safety brake must bring the rotating saw blade to a standstill as quickly as possible in order to minimize the risk of injury.
Holding brake
Today, safety brakes are mostly used as holding brakes. The movement is slowed down by a regulated drive, the speed of which is first decelerated to zero before the safety brake closes. In normal operation, you only have to keep the system safe when it is at a standstill. As a rule, however, holding brakes must also be designed for emergency braking in order to bring the moving masses to a standstill quickly in the event of a power failure or actuation of the EMERGENCY OFF switch. Ultimately, safety brakes must protect systems from damage and the operating personnel from injury in all possible operating states.
literature
- H. Wittel, D. Jannasch, J. Voßiek, C. Spura: Roloff / Matek machine elements . 24th edition. Springer Vieweg, Wiesbaden 2019, ISBN 978-3-658-26280-8 .