Cyclic Slave Axes

A slave axis, whose position setpoints are determined from 

  1. the position setpoints of another axis (master axis) through an affine transformation and
  2. a coupling factor set through the cyclic PLC-NC interface within the PLC cycle,

is called cyclic slave axis. If the coupling factor changes constantly, e.g. because it depends on an external signal, then the slave algorithm is linear in each PLC cycle, i.e. locally linear and globally non-linear.
The following applies: slave set position = coupling factor(PLC) * master set position + offset, where the offset results from the coupling position and the coupling factor is set again and again.
While the coupling of the slave to the master is done offline (master and slave are stationary), the decoupling can be done online: the slave is thereby converted into a master, which continues to move as if it were still a slave, but which can also be stopped independently of the former master.
Each online change of the coupling factor causes a discontinuity in the velocity and thus a load on the dynamics of the axis. In order to avoid excessive strain, the coupling factor arriving via the cyclic interface is therefore smoothed (= filtered).  Smoothing is parameterized by limiting the amount of the slave axis acceleration.

Parameters

The parameter AccBound in mm/s² is the desired acceleration limit of the slave axis. In order to avoid the algorithm becoming instable, a large enough limit must be chosen. Stability is ensured, if AccBound ≥ max(|Cf(t)|) * max(A+,-A-) is selected, where Cf(t) is the coupling factor at time t and A+ and A- are the acceleration limits of the master axis (if the master axis itself is a slave axis, an appropriate calculation must be carried out).

Interfaces

The interfaces consist of the System Manager, PLC blocks and the cyclic NC-PLC axis interface.

Decoupling and new end position

Decoupling is possible in every dynamic state of the master axis - the slave axis is converted into a master axis and continues to travel as if it was still a slave axis, although it can be stopped individually. The coupling flag is reset.
During offline decoupling (decoupling at standstill), the slave axis is converted into a PTP master axis.
When decoupling online (decoupling in motion), the slave axis is converted back into a PTP master axis. A new end position in the direction of movement may be aimed for.