4 Data Descriptions
11.03
4.4 System variable
© Siemens AG 2003 All Rights Reserved
4-266
SINUMERIK 840D/SIMODRIVE 611 digital SINUMERIK Safety Integrated (FBSI) - Edition 11.03
4.4.2
Description of the system variables
The safe actual value, used by SI, can be read and further processed from the
NC part program for every axis/spindle.
Example:
When an NC part program is started, Safety Integrated checks whether axis X
would move into the vicinity of shutdown limits as a result of the zero offsets
when a program is processed. The part program can be programmed as
follows, for example:
IF ($VA_IS
[
X
]
<
10000) GOTOF POS_OK
; if actual value too high,
MESG ("Axis has nearly reached limit switch!")
; then message,
POS_OK:
; otherwise, continue here
...
The variable can also be used in synchronous actions in order to reduce the
override when the axis is nearly at the limit switch.
Both variable $VA_IS and variable $AA_IM can be used to read actual values.
Table 4-60
Difference between $VA_IS and $AA_IM
Variable Meaning
$VA_IS
Reads the actual value used by Safety Integrated
$AA_IM
Reads the actual value (setpoint of position closed-loop control) used by
the closed-loop control
References:
/PGA/, Programming Guide, Production Planning
Reading actual value crosswise data comparison errors using system
variables
If a crosswise data comparison between NCK and 611 digital detects errors,
the response is determined by the current operating state:
•
SBH, SG, SE or SN active: After a Stop F, a crosswise data comparison
error leads to a Stop B, which initiates the fastest possible braking of the
axis. Then a Stop A is initiated and the pulse enable is cancelled.
•
SBH and SG are not active and SE/SN are not used or Stop C/D/E has
already been activated: In this case, a Stop F due to a crosswise data
comparison error does not result in any further action – only Alarm 27001
is output that provides information. Processing then continues.
This chain of responses is not altered to ensure personnel safety.
To allow responses to a crosswise data comparison error, a new system
variable $A_XFAULTSI is introduced and indicates that a crosswise data
comparison error has occurred on any of SI axes. Retraction can then be
initiated as a response to this system variable.
An axis-specific system variable $VA_XFAULTSI[<Axis name>] is also
introduced so that, if necessary, axis-specific responses can be configured for
particular applications.
System variable
$VA_IS
Difference between
$VA_IS and $AA_IM
System variables
$A_XFAULTSI and
$VA_XFAULTSI
