Sinumerik 840D - Siemens SINUMERIK 840D sl Function Manual

3.3

SINUMERIK 840D

Interpolator cycle
The interpolator cycle defines the cycle time in which the setpoint interface to the position
controllers is updated. The interpolator cycle is important for two reasons in normal
processing:
• The product of velocities and interpolator cycles defines the geometry resolution of the
interpolated contour. A long interpolator cycle causes a large path error along curved
contours. This error is, however, reduced in the ratio interpolator / position-control cycle by
cubic fine interpolation MD 33000 $MA_FIPO_TYPE.
• The interpolator cycle determines the possible resolution of the velocity profiles. It must be
adapted to the dynamics of the drives so that the machine axes traverse and accelerate
evenly (i.e. position-control cycle time ≤ interpolator cycle << acceleration time constant).
Position control cycle
The position-control cycle is the time which it takes for the control to calculate the actual value
and transfer a new speed setpoint to the speed controller.
Block cycle time
The block cycle time is the sum of the block change time and block preparation time. It is at
least as big as the cycle in which the position setpoints are assigned to the position
controllers - normally equal to the interpolation cycle.
The block cycle time is a common form of measurement used to judge whether the control is
suitable for traversing contours defined in points (frequent problem with 3 and 5-axis milling).
It determines the maximum possible velocity at which a defined point pattern can be
traversed (max. feedrate = average distance between points/block cycle time).
Setting the IPO cycle and position-control cycle
The interpolator and position-control cycles are set in integer multiples of the system clock
cycle in the following machine data:
MD10060 $MN_POSCTRL_SYSCLOCK_TIME_RATIO (factor for position-control cycle)
MD10070 $MN_IPO_SYSCLOCK_TIME_RATIO (factor for the interpolation cycle)
The smallest possible position-control and interpolator cycle should be aimed for.
Apart from special applications in which MD10060 is set to a value greater than 1, the position
control cycle corresponds to the system clock cycle (MD10060 = 1).
The ratio of interpolator to position-control cycle must be an integer value and greater than or
equal to 1.
Special Functions
Function Manual, 09/2011, 6FC5397-2BP40-2BA0
G3: Cycle times
3.3 SINUMERIK 840D
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