Siemens SINUMERIK 840C - Manual (Page 1000)

07.97 12 Functional Descriptions
12.20.7 Retraction
• If the function ”Consider software limit switch with controlled emergency retraction” is
selected, the SW limit switch function has the same effect on emergency retraction as in
the NC channels.
Depending on the setting in machine data 5003, bit 7 ”No deceleration at limit switch”,
either deceleration is performed in the emergency retraction channel or setpoint 0 is
output.
The SW prelimit switch also takes effect. The path velocity in the emergency retraction
channel is set to max. the value of MD 1 ”Velocity behind SW prelimit switch”.
The function ”Consider software limit switch with controlled emergency retraction” is
activated via general machine data MD 5022 bit 5.
Triggering of a retraction as an autonomous drive function (G426) from
the control is prevented as long as a retraction as open-loop control
function (G425) is active or not acknowledged.
Individual reactions:
• Axis/spindle-specific reaction
The bit "Retraction active" in set in the standard interface to the PLC for the axis or the
spindle which initiates the retraction process.
• Reaction specific to channel/mode group
The bit "Retraction active" is set in the standard interface to the PLC for the channel
which initiates the retraction process.
• Set/reset HW outputs
It is possible to define a HW output byte which is switched when retraction takes place.
This byte is selected via MD NC MD 312-317 and the idle state is defined via MD NC MD
5021.
The output bit which must be switched from the idle to the active state in the case of an
error is selected via an axis/spindle/channel-specific MD byte NC-MD 916* 528* 588*
(corresponding to the source).
Mode group reaction:
Possible mode group reactions are:
• Output of an alarm via MD
• Initiation of mode group stop via MD
• Programmed retraction according to part program command:
See Programming Guide
By means of programming measures, it is possible to determine for one/several axes or
one/several spindles whether and how they must execute a retraction. If a retraction condition
is fulfilled and if the appropriate NC-MD bit(s) is (are) set, all programmed retraction motions
are executed when the process has been enabled via the interface signal "Enable retraction"
(safety function). In the event of retraction, grouped axes can be positioned incrementally or
absolutely; endlessly turning rotary axes or spindles can be positioned absolutely.
© Siemens AG 1992 All Rights Reserved 6FC5197- AA50 12–225
SINUMERIK 840C (IA)