Siemens SINUMERIK 840Di Function Manual page 21

Note
When the servo enable is set, if the part program is active, the last programmed position is
approached internally in the NC (REPOSA: Approach along line on all axes). In all other
cases, all subsequent movements start at the current actual position.
During "follow-up", clamping or zero-speed monitoring are not active.
Function: Hold
The hold function does not correct the setpoint position of the machine axis to the actual
position. If the machine axis moves away from the setpoint position, a following error
(difference between setpoint and actual position) is generated. This error is corrected
"suddenly" when the servo enable is set by the position controller, without observing the
axial acceleration characteristic.
The following interface signals have to be set for the hold function:
DB31, ... DBX2.1 = 0 (servo enable)
DB31, ... DBX1.4 = 0 (follow-up mode)
Checkback signal
DB31, ... DBX61.3 = 0 (follow-up mode active)
During "hold", clamping or zero-speed monitoring are active.
Notice
With the "hold" function, once the servo enable has been set, the setpoint/actual-value
difference is corrected directly by the position controller, i.e., without following the axial
acceleration characteristic.
Application example
Positioning response of machine axis Y following clamping when "servo enable" set.
Clamping pushed the machine axis from the actual position Y
Various NC/PLC Interface Signals and Functions (A2)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
Detailed Description
2.1 NC/PLC interface signals
to the clamping position Y
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