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BECKHOFF
8.17
Restart lock -AS-
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 swit-
ched off, or another contactor was used to disconnect the motor from the servo amplifier.
The disadvantages of this method are :
The restart lock -AS- 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 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. 73) fulfills safety category 1 (EN 954-1) or category 3 with additional
safety relay (e.g. PNOZ of PILZ company).
Advantages of the restart lock -AS- :
Moving single axis-groups in setting-up operation
In setting-up operation, people will frequently be within the danger zone of the machinery. Axes will
normally be moved under the control of permission switches. An additional switch-off of the unused
axes, by means of the restart lock, increases the safety margin and avoids the repeated switching
of main contactors or motor contactors.
Switching off grouped axes with separate working areas
Even when several AX2040/2070 are operating off a common mains supply and DC bus link, it is
possible to set up groups for separate working areas. These groups can then be switched off sepa-
rately for personnel safety.
8.17.1
Safety instructions
l
l
l
l
AX2040/2070 Product 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.
Observe the chapter "use as directed" for the restart lock -AS- (ð p. 70)
The monitoring contacts (KSO1/2) for each amplifier must be looped into the control
circuit. This is vital, so that a malfunction of the internal safety relay or a cable break
can be recognized.
If the restart lock -AS- is automatically activated by a control system (KSI1/2), then
make sure that the output of the control is monitored for possible malfunction. This
can be used to prevent a faulty output from activating the restart lock -AS- while the
motor is running.
Keep to the following functional sequence when the restart lock -AS- is used :
1.
Brake the drive in a controlled manner (speed setpoint = 0V)
2.
When speed = 0 rpm, disable the servo amplifier (enable = 0V)
3.
If there is a suspended load, block the drive mechanically
4.
Activate the restart lock -AS-
06/2007
Electrical Installation
69
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