6 Applications
6.4.12
Triggering the starting process based on several
sources
When connecting the light barrier, it must be ensured that the delay times are as short as
possible. A connection through a PLC does not make any sense in many cases (high
speed, high positioning requirements).
In these cases, the light barrier should be connected directly to the start input of the servo
drive. However, as the PLC must also trigger starting processes, the signals must be
merged in an appropriate manner.
Variant 1:
The signal of the PLC and the signal of the light barrier are both connected to the start
input. Disadvantage: The light barrier may trigger unwanted positioning processes.
Variant 2:
The light barrier is connected to a relay via which the PLC can control the access of the
light barrier.
6.4.13
Position offset due to cycle times
As far as positioning processes are concerned, the servo drive has a cycle time of
approximately 400 µs. The necessary pieces of information (position, speed) are available
in their entirety only at specific points of time and it is only at these points of time that a
synchronisation process can be initiated. The system-inherent inaccuracy (jitter) results in
a position error as follows:
To compensate for this, the sampling function can be used. For this purpose, the light
barrier must be connected to the sample input. When a sampling event occurs, the actual
position is saved together with the synchronisation position. This information is then used
for the subsequent synchronisation process to compensate for the offset which is caused
by the cycle times.
6.4.14
Lead of the actual position when the light barrier is not
located in the range of movement of the drive
Sometimes, a trigger event, which must be used as the basis for a synchronisation,
occurs, but the object to be gripped has not reached the range of motion of the axis yet. To
handle this situation, a lead (menu
Parameters/Positioning/Global positioning settings
)
must be specified together with a delay concerning the sampling process and start of the
position set (
Parameters/Positioning/Destination parameters
,
Experts
tab).
Product manual BL 4000-C
Page 115 of 298
