Advanced Mechanical Brake Control For Hoisting Applications - Danfoss FC 300 Design Manual

9 Application Examples

9.1.8 Advanced Mechanical Brake Control for Hoisting Applications

1. The vertical movement
In the vertical movement, the key point is that the load must be held, stopped, controlled (raised, lowered) in a perfectly safe mode during the entire
operation.
Because the adjustable frequency drive is not a safety device, the crane/lift designer (OEM) must decide on the type and number of safety devices (e.g.,
speed switch, emergency brakes, etc.) to be used, in order to be able to stop the load in case of emergency or malfunction of the system, according to
relevant national crane/lift regulations.
2. Connecting the mechanical brake to the adjustable frequency drive
9
- The electromagnetic disc brake works by the action of a set of springs and is released when applying voltage to the brake coil.
- This means the motor will brake automatically in case of voltage failure, as a significant safety feature.
- Whenever a mechanical brake is present, it is strongly recommended to use an external contactor to take over switching on/off the brake.
- Because of inverse voltage peaks during switch on/off, it is recommended to use a diode block mounted on the contactor's coil, for protection
of the adjustable frequency drive.
- The contact 01-02 in the adjustable frequency drive stays normally open, so the output is not energized.
- When the START condition comes from the command circuit, the drive closes the 01-02 contact according to the programmed brake logic. The
output is now energized until STOP condition occurs.
- If the adjustable frequency drive is in alarm or fault condition, the output relay immediately cuts in.
3. The control parameters
In open-loop structure, the relevant (active) parameters to controlling the mechanical brake output relay are:
Function Relay
- Par. 5-40
- Par. 2-20 Release Brake Current
motor current), in order to produce enough torque to hold the load during the brake release.
- Par. 2-21 Activate Brake Speed [RPM]
value is ½ of the slip. If the value is too high, the mechanical system will be exposed to shocks at every stop. If the value is too small, the
9-4
On Delay, Relay
or par. 5-41 . Mechanical brake control: activates the output brake relay function
. When the START condition is present, the motor current is increased to the set value (closed to the nominal
. By setting this parameter the mechanical brake will be engaged over a rotating shaft. Recommended
MG.33.BC.22 - VLT ® is a registered Danfoss trademark
FC 300 Design Guide