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 frequency converter 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 frequency converter

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

frequency converter.

The contact 01-02 in the frequency converter 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 frequency converter 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:

Par. E-24 Function Relay and par. E-26 On Delay, Relay. Mechanical brake control: activates the output brake relay function

Par. B-20 Release Brake Current. When the START condition is present, the motor current is increased to the set value (closed to the nominal motor

current), in order to produce enough torque to hold the load during the brake release.

Par. B-21 Activate Brake Speed [RPM]. By setting this parameter the mechanical brake will be engaged over a rotating shaft. Recommended 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 torque (current) might be

insufficient to holding the load at zero speed. When STOP condition is present, the motor is decelling to zero speed (mechanical brake is still open), and

at the set value (rpm) engages (closes down) the mechanical brake.

Par. B-22 Activate Brake Speed [Hz]. Linked to par. B-21 Activate Brake Speed [RPM]. Automatically adjusted according to the par. B-21 value.

Par. B-23 Activate Brake Delay. The shaft is held at zero speed with full holding torque. This function ensures that the mechanical brake has locked the

load before the motor enters coast mode.

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AF-650 GP Design Guide

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