Siemens SINUMERIK 840Di Function Manual page 73

Detailed Description
2.1 Motion monitoring functions
2.1
2.1.1 Contour monitoring
Contour error
Contour errors are caused by signal distortions in the position control loop.
A distinction is made between:
• Linear signal distortions
• Nonlinear signal distortions
Axis Monitoring, Protection Zones (A3)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
This is caused by:
– Speed and position controller not being set optimally
– Different servo gain factors of the feed axes involved in creating the path
With the same servo factor for two linear-interpolated axes, the actual position follows
the set position along the same path but with a time delay. With different servo factors,
a parallel offset arises between the set and actual path.
– Unequal dynamic response of the feed drives
Unequal drive dynamic responses lead to path deviations especially on contour
changes. Circles are distorted into ellipses by unequal dynamic responses of the two
feed drives.
This is caused by:
– Activation of the current limitation within the machining area
– Activation of the limitation of the set speed
– Backlash within and/or outside the position control loop.
When traversing a circular path, contour errors occur primarily due to the reversal
error and friction.
During movement along straight lines, a contour error arises due to a reversal error
outside the position feedback loop, e.g. due to a tilting milling spindle. This causes a
parallel offset between the actual and the set contour. The shallower the gradient of
the straight line, the larger the offset.
– Nonlinear friction behavior of slide guides.
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