Siemens SINUMERIK 840D sl, Function Manual

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Basic logic functions: Axis monitoring, protection zones (A3)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
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Detailed description
2
2.1 Axis monitoring
2.1.1 Contour monitoring
2.1.1.1 Contour error
Contour errors are caused by signal distortions in the position control loop.
Signal distortions can be linear or nonlinear.
Linear signal distortions
Linear signal distortions are 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 gain 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
gain 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.
Nonlinear signal distortions
Nonlinear signal distortions are 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 control 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