TwinCAT Slave Axes
Definition
Axes whose set values (position, velocity, acceleration) are generated in functional dependency on the set values of other axes (master axes, virtual axes, slave axes, simulation axes) - in particular on their set position values - are called slave axes. Apart from the coupling and uncoupling, these axes do not generally have any functionality of their own (in particular they do not have start or stop functions) and operate under linear path control in synchronisation with the master axis (which itself can in turn be a slave axis).
When a master axis (which is to become a slave axis) is coupled to another master axis, the slave axis retains its own position control.
Slave topologies
The permitted slave topologies (link options) are star and cascade.
Star, i.e. all slaves are linked directly to a master axis (virtual master axis).
Cascade, i.e. all slaves are linked consecutively through a chain, and the first slave axis is linked to a master axis (virtual master axis).
The cascade may be set up in any order.
Uncoupling within a cascade may occur in any order.
Slave types
Depending on the type of set value generation, a distinction is made between the following types:
- linear slave axis,
- flying saw,
- camshaft axis,
- multi-table axis,
These will now be explained briefly.
Linear slave axis
A slave axis whose position setpoints are determined from the position setpoints of another axis by an affine transformation is called Linear slave axis.
The following applies: slave set position = coupling factor × master set position + offset, whereby the offset results from the coupling position and the coupling factor is determined during coupling. The coupling factor can be changed online.
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 that continues to operate as if it were still a slave, but that can also be stopped independently of the former master.
Cyclic slave axis
A slave axis, whose position set values are determined from
- the position set value of another axis (master axis) through an affine transformation and
- a coupling factor set through the cyclic PLC-NC interface within the PLC cycle,
is called cyclic slave axis.