8 Application examples 11.03
8.6 Direction detection when retracting from SE
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8-466 SINUMERIK 840D/SIMODRIVE 611 digital SINUMERIK Safety Integrated (FBSI) - Edition 11.03
8.6 Direction detection when retracting from SE
When SE responds, there is no SGA signal to indicate which SE was exceeded
or not reached. In order to only allow retraction from the safe limit position in
the specified direction, it is necessary to develop a retraction logic in the PLC
program. A possible solution is outlined below.
The axis in which the SE has responded is moved into a range in which the
monitoring system no longer responds. This is achieved by canceling the user
enable (the SE monitoring system is then no longer active) or by changing over
to another SE (with a longer traversing range).
The error message output when the safe limit position is exceeded must be
acknowledged in accordance with the configured stop response.
If SE responds, traversing motion in the minus direction must be inhibited; if
SE+ responds, traversing motion in the plus direction must be inhibited. This
prevents damage to the mechanical system and simplifies operation at this
point.
The "safe cam” SI function is used for the solution. A detailed description of this
function is given in Chapter 3.7. The section below only describes how the
function is used.
The retraction logic is based on the following considerations:
1. SI function "Safe cam": The SGA signal assigned to the safe cam is only
used on the PLC side (it is not necessary to configure the machine data).
This meets the needs of the application in question because a fail-safe
function is not required and the traversing inhibit can only be initiated
through one channel.
The following interface signals are relevant in the axis DB
SN1- DBX.109.0 SN1+ DBX.109.1
SN2- DBX.109.2 SN2+ DBX.109.3
SN3- DBX.109.4 SN3+ DBX.109.4
SN4-
DBX.109.6
SN4+
DBX.109.7
2. Interface signals for the hardware limit switch function
The following interface signals in the axis DB are relevant
(see Description of Functions /A3/ "Axis Monitoring, Protection Zones")
Hardware limit switch-
DBX12.0
Hardware limit switch+ DBX12.1
If the signal is detected as being set, Alarm 21614 "Hardware limit switch +
or –” is output and the axis is immediately braked (this is not necessary
based on the configured stop response). Further traversing motion is only
permitted in the appropriate retraction direction.
Description
Acknowledge and
retract
refer to Chapter 3.6.1
Conditions for
retraction
Development of
retraction logic
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