Relationship Single Axis and Group State Diagrams

Example of the relationship between three single axes combined in an axes group.

Relationship single axis and group state diagrams

When a number of axes are grouped, and a single axis command, like MC_MoveAbsolute, is issued to an axis in this group, there are basically three options:

• Not allowed. Issuing a single axis command is not accepted and not performed: it signals this by setting the er-ror output of the applicable (issued) single axis Function Block. There is no change to the group, and as such continues their movements.
• Aborting the current group command(s), as well as following group commands, and continue with the single axis command only. The remaining axes of the group move to the state StandStill (via an implicit MC_Halt per axis). The original trajectory will not be finalized.
• Superimpose the single axis commands to the group commands.

This specification does not restrict to any of these options. This means that different implementations of this behavior will exists, and the supplier of the system has to specify what their system does support.

General rules for the interaction between a single axis towards its groups (for all 3 options above):

• If at least one axis in the group is moved by a command then the group is in the state GroupMoving.
• If all axes are in StandStill, the group can be in the state GroupStandby, GroupDisabled or GroupErrorStop.
• If one axis in a group is in ErrorStop, the whole group is in GroupErrorStop.
• If a single axis MC_Home is issued the group is in state GroupMoving.
• If a single axis MC_Stop is issued the group is in state GroupMoving.
• If supported by the system, it is allowed to disable a single axis of the axis group without influencing the axes group state. This can be useful to save energy or to apply a mechanical brake for a single axis not involved in the on-going motion.

General rules for the interaction between a group and the single axis in it (for all 3 options above):

• If the group is commanded by a group moving command, all the single axes in the group are in the state Synchronized Motion.
• If the group is in the state GroupStandby, the states of the single axes do not have to be all in StandStill.
• If the group is in the state GroupErrorStop the state of the single axis is not affected.

Overview of the influence of group motion commands on a single axis state

Command	Group State	Axis State
MC_MoveLinearXxx MC_MoveCircularXxx MC_MoveDirectXxx MC_MovePath MC_GroupHalt MC_TrackConveyorBelt MC_TrackRotaryTable	GroupMoving	Synchronized Motion
MC_GroupStop	GroupStopping / GroupStandby	Synchronized Motion / StandStill
MC_GroupReset	GroupErrorStop / GroupStandby	Not relevant for Axis
MC_GroupHome	GroupHoming	Synchronized Motion

Explanation: A stopping group leaves the single axis in Synchronized Motion as none of the single axis performs a single axis stop.