Status signals of a PTP-axis

NcToPlc.nStateDword (DWORD), variable of NcToPlc cyclic axis interface structure, consists of various axis status signal flags. The flags discussed herewith are:

AxisHasJob

AxisIsMoving (AxisIsMovingForward OR AxisIsMovingBackwards)

AxisIsNotMoving

AxisHasBeenStopped

AxisIsAtTargetPosition

AxisInPositionWindow

 NOTE:

Only the flags AxisInPositionWindow and AxisIsAtTargetPosition depend on the actual values (actual position, actual velocity). On the other hand, the rest of the flags discussed here depend on the setpoint values (set position, set velocity, set acceleration).

AxisHasJob gives the correct and accurate indication of the axis command status. A transition of AxisHasJob from FALSE to TRUE indicates that the axis has got a new job and hence new parameters (like target position, velocity, acceleration or jerk). Completion of a command of an axis is indicated by a FALSE status of AxisHasJob flag.

AxisIsMoving goes to TRUE when the motion command reaches the axis and the setpoint generator is active. Normally if the flag AxisIsMoving is TRUE, then the setpoint velocity has a value other than zero. An exception for this case is velocity override 0%, which implies that the axis has job and is logically moving but with a velocity zero (in this case AxisHasJob and AxisIsMoving are both TRUE but setpoint velocity is zero). AxisHasJob additionally includes the communication time for the request and response of the command.

AxisIsNotMoving has an exact opposite status to that of AxisIsMoving. TRUE status of AxisIsNotMoving indicates that the axis is logically (not necessary physical standstill) standstill.

AxisHasBeenStopped indicates the execution of a stop command for the corresponding axis. AxisHasBeenStopped goes TRUE as soon as the stop command is issued and executed and remains TRUE throughout the stopping phase (throughout the time axis stop command is active) and is set to FALSE only when a new command is executed.

AxisIsAtTargetPosition depends on two parameters specified in the Global parameters of the corresponding axis in the TwinCAT System Manager; Target Position Window and Target Position Monitoring Time. AxisIsAtTargetPosition is TRUE when actual position is within the Target Position Window for a minimum of the time mentioned in Target Position Monitoring Time (without oscillating outside the Target Position Window).NOTE:

This flag to use should be enabled in TwinCAT System Manager, in the Global parameters of the corresponding axis under the name Target Position Monitoring.

AxisInPositionWindow depends on the Position Range Window parameter in the Global parameters of the corresponding axis in the TwinCAT System Manager. The flag, AxisInPositionWindow is set TRUE when the actual position is within the value specified in Position Range Window and goes FALSE when the actual position value is outside this window.

NOTE:

This flag in order to use should be enabled in TwinCAT System Manager, in the Global parameters of the corresponding axis under the name Position Range Monitoring.

After positioning, all “MC_Move…” blocks check whether positioning was completed successfully. In the simplest case, the “AxisHasJob” flag of the NC axis is checked, which initially signifies that positioning was logically completed. Depending on the parameterization of the NC axis, further checks (quality criteria) are used: