Installation manual
CNC 8055
CNC 8055i
CONCEPTS
7.
SOFT: V02.2X
·303·
Axes and coordinate systems
Tandem axis control.
The block diagram for the application to control the tandem axis is:
Tandem master motor torque.
Is the percentage (%) of rated torque reflected by the Sercos variable TV2 of the drive that governs
the master axis of the tandem. It is read in every loop.
Tandem slave motor torque.
Is the percentage (%) of rated torque reflected by the Sercos variable TV2 of the drive that governs
the slave axis of the tandem. It is read in every loop.
Torque distribution.
Normalizing gain of the torque generated by the motors in order to distribute the torque in a ratio
other than 1:1.
Pre-load.
Previous torque applied to both tandem axes in opposite direction. This sets a traction between them
in order to eliminate the rack-and-pinion backlash when it is in rest position. It is determined as the
torque difference supplied by each axis.
Pre-load filter.
First-order filter to prevent torque steps from coming in when configuring the preload.
Tandem PI.
PI for making each motor provide its corresponding torque. It increases its velocity command if the
torque being supplied is too low and it decreases it if the torque being supplied is too high.
When defining a tandem axis, at each loop, the CNC reads via Sercos the torque supplied by the
master and the slave axes. This may result in a smaller number of read-write variables in the fast
Sercos channel, through PLC parameters.
Adjusting procedure
This procedure must bear in mind the type of machine. In general, a tandem machine has a low
resonance frequency. Therefore, the CNC must generate position commands without frequency
components higher than resonance frequency.
This situation may generate a "Sercos ring error", even when using the same variables and number
of axes as in a non-tandem configuration. This situation is especially critical for a loop time of 2
milliseconds.
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