Programmable Contour Accuracy - Siemens SINUMERIK 840D sl Function Manual

4.3

Programmable contour accuracy

Initial situation
There is always a velocity-dependent difference between setpoint and actual position when
an axis is traversed without feedforward control. This lag results in inaccurate curved
contours.
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
factor (servo gain factor) for the axes concerned and limits the maximum path velocity so 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 precontrol
The function is also active in conjunction with pre-control if:
MD20470 $MC_MC_CPREC_WITH_FFW (Programmable contour accuracy) = TRUE
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)
Activation
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
Function Manual, 09/2011, 6FC5397-2BP40-2BA0
factor with feedforward control.
V
K6: Contour tunnel monitoring
4.3 Programmable contour accuracy
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