Hoist Mechanical Brake - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide
Step-by-step Description
•
•
•
•
•

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 setup 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.
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.
Mechanical brake control
Select
mechanical brake.
The brake is released when the motor current exceeds the preset value in par. 2-20.
The brake is engaged when the output frequency is less than the frequency set in par.
2-21 or 2-22 and only if the frequency converter carries out a stop command.
NB!
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.
NB!
For hoisting applications make sure that the torque limits in par. 4-16 and 4-17 are
set lower than the current limit in par. 4-18. Also it is recommendable to set par.
Trip Delay at Torque Limit
14-25,
"0" and par. 14-10, Mains Failure
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.B9.02 - VLT ® is a registered Danfoss trademark
[32] in par. 5-4* (or in par. 5-3*) before connecting the
Trip Delay at Inverter Fault
to "0", par. 14-26,
to "[3], Coasting ".
Torque Ref
determines the delay before the load is
3. Introduction to FC 300
to
, the brake is released.
47
3