Definition of axes

It is possible to distinguish between various types of axes in a control system. One practical classification is that into programmable, logical and physical axes.

A physical axis corresponds to a real axis on the machine (translatory or rotary axis). Within a control, a physical axis is represented by software by means of a logical axis (1:1 mapping).

A logical axis is the unit representation of an axis in the axis coordinate system (acs). A logical axis, in the control, provides all relevant information required for the related physical axis. From the point of view of the CNC, each logical axis has its own parameter set and its own interface to the PLC.

A programmable axis is an axis which can be programmed or tasked by the user in the part program or MDI mode. A programmable axis corresponds either to a logical / physical axis directly (1:1 mapping) or is mapped to logical / physical axes by means of a kinematic transformation (1:n mapping).

In the case of multi-channel operation, a logical axis may be swapped between channels (“axis swap“). In this case, the same logical axis may occur in different attributes on the NC channels from the point of the view of the programmer, e.g. as a programmable spindle (speed preset, speed-controlled) on one channel and as a programmable C axis (position preset, position-controlled) on another channel.

Programmable, logical and physical axes are generally identical (1:1 mapping) for simple machines (e.g. a 3-axis milling machine with Cartesian linear axes X, Y and Z). In the case of complex machine kinematics or industrial robots, kinematic transformation of programmed to logical / physical axes is required (1:n mapping).

Axes are programmed in the CNC program and moved by the CNC. Alternatively, specific movements may also be triggered directly by the PLC.

The PLC interface for axes has a similar structure to the interface for channels. M functions configured as axis-specific M functions also appear on the axis-specific interface and must be acknowledged by this interface. Likewise, this interface contains axis enables and status information of this axis.