Operation
05/06 AWB2724-1584GB
42
Referencing:
In many positioning controllers, a reference point is approached at
the start of positioning. For example, a tool slide is moved to its
home position. In this position, a “reference switch” is closed,
thus sending a signal to input I4. This can also be done by the
“SetRefWindow” signal which can be activated in the user
program. The “RefActive” signal is set as a feedback signal. An
incremental encoder connected to the slide generates a reference
pulse to specify the tool position exactly. This is detected at input
I3 if the reference switch is closed and the reference window is
opened. The reference pulse causes the counter to be overwritten
with the reference value that you have defined in the PLC
configuration. “RefActive” is reset and “RefDone” is set until the
reference window is opened again.
System events
System events are:
You can react to system events of the controller by creating
program routines (POUs) that are run once if an event occurs.
The execution time is monitored. The value set as the maximum
permissible cycle time is used as a basis.
START, COLD START, WARM START, STOP
If an event occurs, such as a warm start of the controller, an
interrupt is generated (a page 45) that calls up the program
routine assigned to it. This assignment is carried out in the task
configuration.
h
Set the reference window large enough for the reference
signal to be present once and still be evaluated reliably.
Figure 37: Relationship between reference signal and reference
window
T1 Pulse repetition time of two successive reference pulses with one
rotation of the incremental encoder
T2 Maximum permissible duration of the reference window. Must be
shorter enough than T1 to ensure that a second reference pulse is not
detected.
T3 must be long enough to ensure that the L/H edge of the reference
pulse is reliably detected.
T2 and T3 depend on the frequency of the reference pulse and must be
determined for each application by trial and error.
T1
T2
T3
Reference Signal
Reference Window
START START: User program start (cold and warm start)
COLDSTART Cold start of the user program
WARMSTART Warm start of the user program
STOP
User program stop (does not apply to cycle time
timeout or hardware watchdogs)
IO-Interrupt 1, 2,
3, 4
Voltage change at inputs I1, I2, I3, I4
Counter-Interrupt1 Act = Preset on 16-bit counter 0
Counter-Interrupt2
Act = Preset on 16-bit counter 1 or 32-bit
counter
TIMER-INTERRUPT A timer set by the user triggers an interrupt.
Figure 38: System events
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