XFC_TouchProbe

The function block XFC_TouchProbe records an axis position at the time of the edge of a digital input signal (measuring probe function).

The digital input signal is recorded with an XFC input terminal (e.g. EL1252) with timestamps for the falling and rising signal edge. The function block determines the axis position at which the edge change occurred and issues it as RecordedPosition.

In contrast to the conventional TouchProbe function MC_TouchProbe the digital input is not directly linked to the drive hardware. The position of each EtherCAT or Sercos axis in the system can be recorded via the timestamp of the input. This axis is exactly synchronized via Dead time compensation.

The function block can be used in free-running or single-shot mode. In free-running mode each edge of the input signal is recorded (maximum one edge per PLC cycle). In single-shot mode the next edge is only recorded once until the function block is triggered again.

The optional window function can be used to ignore signal edges outside the defined position filter.

The sample shows how the function block can be used in free-running (FreeRun = TRUE) or in single-shot mode (FreeRun = FALSE).

Signal curve

Inputs

VAR_INPUT
    Execute       : BOOL;
    WindowOnly    : BOOL;
    FirstPosition : LREAL;
    LastPosition  : LREAL;
    Options       : ST_XfcTouchProbeOptions;
END_VAR

Name	Type	Description
Execute	BOOL	If Execute is active, the axis position is recorded at the defined signal edge of the input signal. A falling edge at Execute terminates the process immediately. Depending on the configuration in TriggerInput.FreeRun the next signal edge is recorded and evaluated once. If FreeRun is TRUE, a new position value is recorded continuously with each defined edge of the input signal, while Execute remains TRUE.
WindowOnly	BOOL	If this option is active, only one position inside the window between FirstPosition and LastPosition is recorded. Positions outside the window are discarded. Only if the recorded position lies inside the window does Done become TRUE. The recording window can be interpreted in terms of absolute or modulo values. In this connection the flag ModuloPositionsin the structure TriggerInputis to be set accordingly. In the case of absolute value positions there is exactly one window. In the case of modulo value positions the window repeats itself within the modulo cycle defined in the axis parameters (e.g. 0 to 360 degrees).
FirstPosition	LREAL	Initial position of the recording window, if WindowOnly is TRUE. This position can be interpreted as an absolute or modulo value. In this connection the flag ModuloPositions is to be set appropriately in the structure TriggerInput (see below).
LastPosition	LREAL	Final position of the recording window, if WindowOnly is TRUE. This position can be interpreted as an absolute or modulo value. In this connection the flag ModuloPositions is to be set appropriately in the structure TriggerInput (see below).
Options	ST_XfcTouchProbeOptions	Optional parameters

/ Inputs/Outputs

VAR_IN_OUT
    Axis         : AXIS_REF; 
    TriggerInput : XFC_TRIGGER_REF;
END_VAR

Name	Type	Description
Axis	AXIS_REF	The axis data structure of type AXIS_REF addresses an axis unambiguously within the system. Among other parameters, it contains the current axis status, including position, velocity or error state.
TriggerInput	XFC_TRIGGER_REF	TriggerInput is a data structure for describing the trigger source and for feeding the state and timestamp of a digital input signal. This data structure is filled by the user.

Outputs

VAR_OUTPUT
    Done             : BOOL;
    Busy             : BOOL;
    Error            : BOOL;
    ErrorID          : UDINT;
    RecordedPosition : LREAL;
END_VAR

Name	Type	Description
Done	BOOL	The value RecordedPosition is valid. If TriggerInput.FreeRun is TRUE, Done only remains TRUE only for one PLC cycle and is then reset automatically, since TouchProbe is automatically reactivated.
Busy	BOOL	Becomes TRUE as soon as the function block is active, and becomes FALSE when it has returned to its initial state. If TriggerInput.FreeRun is TRUE, Busy remains TRUE continuously, even if Done or Error become TRUE, since TouchProbe is automatically reactivated.
Error	BOOL	Becomes TRUE if an error occurs.
ErrorID	UDINT	If the error output is set, this parameter supplies the error number
RecordedPosition	LREAL	Axis position recorded at the point in time of the trigger signal. If TriggerInput.FreeRun is TRUE, the function block operates in free-running mode, so that each valid change in the input signal leads to a new RecordedPosition. The position can be analyzed, if Done becomes TRUE.