Motor removal on the vertical axis

Brake technology has come a long way in the last half-century. The introduction of new materials, both for the braking surface and the structure, along with changes in mechanical design and electronic systems, have all contributed to significant changes in conventional brakes.

Brakes retard the rotation of a shaft, either to reduce rotational speed (dynamic brake) or to hold it stationary (holding or parking brake). Of course, dynamic brakes must be considerably larger than a parking or holding brake, which need only to be large enough to hold the weight of the rotating load when at rest.

A major progression has been the move to electronic braking systems. With a Variable Frequency Drive (VFD), the frequency and voltage applied to the motor are ramped down at a controlled rate. When the frequency approaches zero, the motor is shut off. A small amount of braking torque is used to help decelerate the load a little faster than it would stop if the motor were simply switched off and allowed to coast. Additional braking torque can also be obtained by adding a braking circuit to dissipate braking energy.

Reduced wear & tear

In many arrangements, a mechanical brake is still required, but now it can be smaller, and the drive takes control of the load when releasing the brake during any move command. This also significantly reduces wear and tear on the mechanical brake.

Currently, the global market penetration for all applications for variable speed drives (VFDs) is still relatively small. In mining, for example, due to cost, it is still cheaper to use a traditional motor/gearbox/brake combination. But mining equipment is getting bigger and the introduction of VFD drives has changed the duty of the brake.

The brake would traditionally perform inching/positioning duties, but now this can be done accurately by a VFD driving the motor.

A holding brake integrated in a motor adapter is an electrically operated spring-applied failsafe brake which is actuated automatically in a voltage drop or emergency stop situation in the de-energised state. The brake is released before the motor is switched on by an electro-magnetic direct-current coil.

Suitable for all common makes of motor, Stober's ServoStop MB integrated brake module for gear units will secure the axis while the motor is removed. Using this, it is safe to remove or replace the motor without any extra precautions on a vertical axis, such as a rack and pinion drive. A plug connector enables easy removal of the motor with the braked axis in any position (known as crash protection).

However, installation with vertical motor mounting position (motor down) is not permitted when the brake which is integrated in the motor adapter is part of a redundant braking system and the second brake is installed in the motor. Also, gear units with a motor adapter integrated brake module are not suitable for operation in explosion-proof areas (ATEX).

There are various time parameters which relate to the operation of the device: the switch-on, or release, time, which is the time until the armature disk releases from the axial brake disk and is magnetically held in place on the stator body. The brake is released in this state and the clutch hub can rotate.

When the motor and brake are switched off, the retentive magnet flux of the iron particles (armature and stator body) must be reduced and the time unt11 that this takes up until torque begins to be generated is defined as the trigger delay during linking. The linking time is the time until the braking torque has become the nominal braking torque.