TwinCAT NC Master Axes
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 co-ordinate 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 advanced TwinCAT NC functionalities are achieved on the basis of the PTP modes by reconfiguration (FIFO, NCI) or by coupling (all slave types).
Axis start
At the axis start, a jerk-limited dynamic profile is generated via the global dynamic parameters (acceleration, deceleration, jerk) and the start parameters (set velocity and target position), and stored in form of a table (run time table), which is then used for the generation of the set values within the block execution task.
Override and Stop
The override is used to change the target velocity of the axis online in the quickest possible way. The request 'Override on x%' causes a new runtime table to be calculated and activated, if the axis was started and no stop is active and the brake phase has not yet been reached. In case of failure, the function is not called again automatically.
Stop is realized via override 0.0 and has - provided the brake phase has not yet been reached - priority over all other functions.
New end position
The function 'New target position' is used to change the target position of the axis online in the quickest possible way. If the axis was started and no stop is active, the request 'new target position' causes a query to ascertain whether
- the axis has exceeded the new target or whether
- the axis cannot be stopped before the new target.
In these cases, the axis is stopped internally via a stop and must automatically be moved back to the new target via a new start. Otherwise a new runtime table is calculated and activated.
New velocity and new end position
The function 'New velocity and new end position' is used for instantly changing the target position and - after an activation position APos has been crossed - for (later) changing the target velocity of the axis. The specified velocity NewV in mm/s must be genuinely larger than 0.0, and the new end position EPos must be within the software limit switches. The function 'New velocity and new end position' cannot be activated during position compensation.
Position compensation
Sometimes it is desirable for an axis to carry out additional positioning by a preset distance (compensation difference D - may also be negative) within a certain distance (compensation length L) compared with the positioning resulting from the runtime table. This procedure is usually used for spatial synchronization with other axes and can be activated on any axis (master, slave).
If position compensation cannot be achieved with the specified compensation parameters, the maximum possible compensation is automatically carried out.
Position compensation may be aborted via a compensation stop (continuous).