Hoist Mechanical Brake - Danfoss VLT AutomationDrive Design Manual

Introduction to FC 300
[Hz] and only if the frequency converter carries
out a stop command.
NOTE
For vertical lifting or hoisting applications it is strongly
recommended to ensure that the load can be stopped in
3 3
case of an emergency or a malfunction of a single t such
as a contactor, etc.
If the frequency converter is in alarm mode or in an over
voltage situation, the mechanical brake cuts in.
NOTE
For hoisting applications make sure that the torque limits
in 4-16 Torque Limit Motor Mode and 4-17 Torque Limit
Generator Mode are set lower than the current limit in
4-18 Current Limit. Also it is recommendable to set
14-25 Trip Delay at Torque Limit to "0", 14-26 Trip Delay at
Inverter Fault to "0" and 14-10 Mains Failure to "[3],
Coasting".

3.9.2 Hoist Mechanical Brake

The VLT AutomationDrive features a mechanical brake
control specifically designed for hoisting applications. The
hoist mechanical brake is activated by choice [6] in
1-72 Start Function. The main difference comed 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 setup is more straightforward for
hoisting applications.
46
FC 300 Design Guide
By using 2-28 Gain Boost Factor 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 release.
3-step sequence
1.
2.
3.
®
MG.33.BD.02 - VLT is a registered Danfoss trademark
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
2-26 Torque Ref, is applied in hoisting direction.
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
2-26 Torque Ref the brake is released. The value
set in 2-25 Brake Release Time determines the
delay before the load is 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.