Siemens sinumerik 840D sl Function Manual page 211

Function
The "Programmable contour accuracy" function permits the user to specify a maximum error
for the contour in the NC program, which may not be exceeded. The control calculates the
K
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that the contour error resulting from the lag does not exceed the value specified. The
"LookAhead" function then ensures that the velocity necessary for maintaining the required
contour accuracy is not exceeded at any point along the path.
Application
The function ensures a defined contour accuracy in situations where feedforward control
cannot or must not be used.
Positioning axes
The function does not affect the velocities of positioning axes.
Active feedforward control
The function is also operative in conjunction with active feedforward control if the following
machine data is set to TRUE:
MD20470 $MC_MC_CPREC_WITH_FFW (Programmable contour accuracy)
With active feedforward control, the reduction of the path velocity is calculated on the basis
of the effective K
Minimum feed
In order to avoid burn marks, the feed is limited to a minimum value:
SD42460 $SC_MINFEED (Minimum path feed with CPRECON)
Activating
The function can be switched on and off by means of the modal G codes CPRECON and
CPRECOF (Contour Precision On/Off).
The magnitude of the contour accuracy is specified with setting data:
SD42450 $SC_CONTPREC (contour accuracy)
Changes to the setting data become valid during preprocessing.
Special functions: Contour Tunnel Monitoring (K6)
Function Manual, 11/2006, 6FC5397-2BP10-2BA0
factor (servo gain factor) for the axes concerned and limits the maximum path velocity so
factor with feedforward control.
V
Detailed description
2.2 Programmable contour accuracy
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