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BECKHOFF
6
Expansions / Accessories
6.1
Option -AS-, restart lock for personal safety
6.1.1
Advantages of the -AS- option
A frequently required application task is the protection of personnel against the restarting of drives.
This can not be achieved by an electronic inhibit, but must be implemented with mechanical ele-
ments (positively driven relay contacts).
To get round this problem, up to now either the main contactor in the mains supply line was
switched off, or another contactor was used to disconnect the motor from the servo amplifier.
The disadvantages of this method are :
The -AS- option avoids these disadvantages. A safety relay in the servo amplifier is activated either
by the PLC or manually. Positively driven contacts provide a safe disconnection of the servo ampli-
fier, the setpoint input of the servo amplifier is inhibited, and a signal is sent to the safety circuit.
The suggested circuits (ð p. 68) fulfills safety category 1 (EN 954-1). You can fulfill safety category
3, if you use a mains contactor with suited supervision.
Advantages of the -AS- option :
6.1.2
Functional description
An additional connector (X10) is mounted on the front panel of the AX2000. The coil connections
and a make (n.o.) contact of a safety relay are made available through 4 terminals on this connec-
tor.
The 24VDC safety relay in the servo amplifier (approved) is controlled externally. All the relay con-
tacts have positive action.
Two contacts switch off the driver supply of the output stage in the servo amplifier, and short the
internal setpoint signal to AGND (0 V).
The make (n.o.) contact used for monitoring is looped into the control circuit.
If the safety relay is not energized, then the monitoring contact is open and the servo amplifier is
ready for operation.
If the drive is electronically braked, the servo amplifier is disabled and the motor-holding brake is
on, then the safety relay is energized (manually or by the controls).
The supply voltage for the driver circuit of the output stage is switched off in a safe manner, the
internal setpoint is shorted to 0V, and the monitoring contact bridges the safety logic in the control
circuit of the system (monitoring of protective doors etc.)
Even if the output stage or driver is destroyed, it is impossible to start the motor.
If the safety relay itself is faulty, then the monitoring contact cannot bridge the safety logic of the
system. Opening the protective devices will then switch off the system.
AX2000 Installation manual
—
the DC bus link has to be charged up again at restart
—
wear on the contacts of the contactors, caused by switching under load
—
extensive wiring required, with additional switching components
—
the DC bus link remains charged up, since the mains supply line remains active
—
only low voltages are switched, so there is no contact wear
—
very little wiring is required
—
the functionality and the personnel safety when using the circuit recommendations
in this documentation have been approved by the Trade Liability Association.
Expansions / Accessories
02/06
65
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