In hoisting/lowering applications, it must be possible to
control an electro-mehanical brake.
Step-by-step Description
•
To control the mechanical brake any relay output
or digital output (terminal 27 or 29) can be used.
If necessary use a suitable contactor.
•
Ensure that the output is switched off as long as
the frequency converter is unable to drive the
motor, for example due to the load being too
heavy or due to the fact that the motor has not
been mounted yet.
•
Select [32] Mechanical brake control in parameter
groups 5-4* Relays (or 5-3* Digital Outputs) before
connecting the mechanical brake.
•
The brake is released when the motor current
exceeds the preset value in 2-20 Release Brake
Current.
•
The brake is engaged when the output frequency
is less than the frequency set in 2-21 Activate
Brake Speed [RPM] or 2-22 Activate Brake Speed
[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
case of an emergency or a malfunction of a single part
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”.
3.9.1 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] Hoist
Mech. Brake Rel in 1-72 Start Function. 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 setup is more straightforward
for hoisting applications.
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. 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.
2. 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.
3. 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.
Introduction
VLT
®
AutomationDrive FC 300 Design Guide, 0.25-75 kW
48 MG33BE02 - VLT
®
is a registered Danfoss trademark
3
3
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