Overview
TwinCAT NC combines function groups that serve to control and regulate axes or synchronized axis groups. An NC task consists of one or more channels of type PTP channel, FIFO channel or NCI channel, and their subsidiary parts. Immediately after start-up the NC axes generally find themselves in one or more PTP channels. If necessary they are then moved to a different channel through a process of reconfiguration.
Safety functions
You should make yourself aware of the TwinCAT safety functions before commissioning any axes.
See: Safety functions
Interfaces: System Manager and PLC
The insertion of an NC task, the configuration of the NC channels and the axes, and the use of most of the functionalities is described in the NC section of the System Manager, and in the following libraries: the NC Configuration Library, the NC Library and the NCI Interpreter Library.
NC-PLC-Interface
The NC-PLC interface is a cyclic interface, with which on the one hand the PLC channel and axis data can be read and on the other hand the NC channel and axis parameters can be set.
Axes
TwinCAT supports a variety of axis types: servo axes, rapid/creep axes, stepper motor axes, "low-cost" stepper motor axes, encoder axes and simulation axes.
Axis components
Each axis consists of various elements, depending on the axis type. These elements include the encoder, the drive, the controller and the setpoint generator, along with the PLC interface. There are also more complex axes consisting of a number of encoders, switchable controllers or changing setpoint generators.
Axis commissioning
Axis commissioning includes knowledge and use of the NC safety functions, application of the necessary safety precautions, observation of a specific sequence of commissioning steps for the axis elements (encoder, drive and controller) and setting the axis parameters.
See:
PTP
PTP (Point To Point) axis functionality is a control process for one-dimensional positioning of axes, in particular of servo axes. One-dimensional does not necessarily mean linear. It simply means that one component is interpolated in some specified coordinate system (Cartesian coordinates, polar coordinates).
PTP forms the basis of the whole of TwinCAT NC, because at system startup the axes are normally in PTP mode, and are thus position controlled. The extended TwinCAT NC functionalities are achieved on the basis of the PTP modes by reconfiguration (FIFO, NCI) or by coupling (all slave types).
Slave axes
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 position setpoints - 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 synchronization with the master axis. The master axis can itself 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.
FIFO
The TwinCAT NC FIFO group provides the facility of supplying externally generated setpoints to a group of axes via the NC, and thus of driving them synchronously. The position setpoints of the axes corresponding to a fixed, although selectable, time period (the FIFO cycle time) are present in the form of a FIFO which is kept topped up by the PLC. The FIFO allows the position of a group of axes to be handled synchronously with reference to time. The FIFO contains a fixed number of specified interpolation points between which the NC position is interpolated and from which the velocity is determined. The axis positions of the FIFO are either read out from a large table calculated off-line in the PLC or generated by a function in the PLC and permanently passed on to the FIFO of the NC by a PLC program in the PLC cycle.
NCI
TwinCAT NC I is the function group for controlling specified synchronized axis movements in three dimensions, according to the conventions of DIN 66025 and various extensions. It consists of interpreter/PLC function blocks, set preparation task, look ahead, set execution task, cyclic channel interface and cyclic axis interface. On-line access is possible to all levels (interpreter stop, programmed halt, override). See: TwinCAT NCI documentation.