Hoist Mechanical Brake - Danfoss FC 300 Design Manual

FC 300 Design Guide

3.8.2. Hoist Mechanical Brake

The VLT Automation Drive FC 300 features a mechanical brake control specifically designed for
hoisting applications. The hoist mechanical brake is activated by choice [6] in par. 1-72. The main
difference compared to the regular mechanical brake control, where a relay function monitoring
the output current is used, is that the hoist mechanical brake function has direct control over the
brake relay. This means that instead of setting a current for release of the brake, the torque
applied against the closed brake before release is defined. Because the torque is defined directly
the set-up is more straightforward for hoisting applications.
By using the Proportional Gain Boost (par. 2-28), a quicker control when releasing the brake can
be obtained. The hoist mechanical brake strategy is based on a 3-step sequence, where motor
control and brake release are synchronized in order to obtain the smoothest possible brake re-
lease.
3-step sequence
1.
2.
3.
3.4: Brake release sequence for hoist mechanical brake control
3.8.3. Cabling
EMC (twisted cables/shielding)
Pre-magnetize the motor
In order to ensure that there is a hold on the motor, and to verify that it is mounted
correctly, the motor is first pre-magnetized.
Apply torque against the closed brake
When the load is held by the mechanical brake, its size cannot be determined, only its
direction. The moment the brake opens, the load must be taken over by the motor. To
facilitate the takeover, a user defined torque, set in par. 2-26, is applied in hoisting di-
rection. This will be used to initialize the speed controller that will finally take over the
load. In order to reduce wear on the gearbox due to backlash, the torque is ramped up.
Release brake
When the torque reaches the value set in par. 2-26
Brake Release Time
The value set in par. 2-25
released. In order to react as quickly as possible on the load-step that follows upon brake
release, the speed-PID control can be boosted by increasing the proportional gain.
MG.33.B9.22 - VLT ® is a registered Danfoss trademark.
3. Introduction to FC 300
Torque Ref , the brake is released.
determines the delay before the load is
3
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