Special characteristics in hardware end positions

If a SERCOS or SoE drive (e.g. AX50xx) is in a hardware end position (positive or negative), the drive blocks further traversing commands in end position direction and beyond the end position (see also bit 3, drive follows command value, in the SERCOS status word), and is therefore no longer operational from a control system perspective. This means that, without special measures, the axis can often no longer be moved from the end position into the valid traversing range via TwinCAT or the control system. This situation is particularly likely to occur with drives in the velocity interface, because in this case the position control leads to frequent changes in direction in the drive velocity output.

To rectify this special situation, a control bit in the PlcToNc axis interface (see bit 8 called AcceptBlockedDriveSignal in nDeCtrlDWord) can be used to force TwinCAT to accept the AX50xx axis as operational and therefore enable a move from the end position into the valid traversing range.

In the past, in many cases the only alternative was to mechanically move the axis away from the end position.