MC_TouchProbe

Description

This function block arms a Fast Input The inputs are taken into account at each cycle depending on the system periodicity (for example each millisecond). Under certain circumstances this can be insufficient when more accuracy is needed, or if a quick response is required from the system. To fill the gap, a drive may have some Fast Input connections (generally one or two). When an event happens that triggers a Fast Input (e.g. when a sensor sends a rising edge), the detection of a signal occurs faster (which can be 1000 times more accurate than the system periodicity). Then the timestamp associated with this input can be provided to the IPC to take corrective action and returns the latched position when the Fast Input event occurs. This function block causes no motion.

When the Execute input transitions from low to high, the control requests the drive to arm its Fast Input to latch the axis position when a Fast Input occurs. The Axis input specifies which axis's position to latch and the TriggerInput input specifies which Fast Input to use and whether to trigger on the rising or falling edge of the Fast Input. When the Fast Input event occurs, the drive latches the axis's position. This function block then returns the latched position at the RecordedPosition output and set the Done output high. This process can be canceled with the AbortTrigger function block.

If the WindowOnly input is high, the FirstPosition input and the LastPosition input define a window in which a Fast Input is accepted. Any Fast Input events that occur outside the window is ignored.

If First Position ≤ LastPosition, the window in which a Fast Input is accepted is:

FastInputPosition ≥ FirstPosition AND FastInputPosition ≤ LastPosition.

If First Position > LastPosition, the window in which a Fast Input is accepted is:

FastInputPosition >= FirstPosition OR FastInputPosition <= LastPosition.

The following figure shows the ladder diagram view of the MC_TouchProbe function block:

Figure 7-129: MC_TouchProbe

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• The accuracy of captured position data depends on the travel velocity. Please see the article MC_TouchProbe and Time-Based Capture on KDN for more information and how to correct for timing.

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• This function block starts a motion-related action and therefore stores data for calculations and error checking. Please see Calling Function Blocks Multiple Times in the Same Cycle if you are using a dual-core controller.

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• There are some differences in how MC_TouchProbe interacts with AKD and AKD2G drives. Please refer to the following topics for some drive-specific information.
  • AKD Support With MC_TouchProbe
  • AKD2G Support With MC_TouchProbe

Arguments

For more detail on how inputs and outputs work, refer to PLCopen Function Blocks - General Rules

Input

Execute	Description	Enables execution
	Data type	BOOL
	Range	0, 1
	Unit	N/A
	Default	—
Axis	Description	Selects the axis for which the position is latched
	Data type	AXIS_REF
	Range	[1,256]
	Unit	N/A
	Default	—
TriggerInput	Description	Sets up the mechanism on the controller for the capture input signal.
	Data type	TRIGGER_REF - an instance of the TRIGGER_REF reference function must first be setup in the Project Dictionary, as seen here.
	Elements	Capture Engine (drive capture engine to be used) INT TriggerInput.InputID 0 = Touch Probe 1 / Capture Engine 0 1 = Touch Probe 2 / Capture Engine 1 Range is [0,1]   Trigger Direction (input signal’s edge to capture) INT TriggerInput.Direction 1 = rising edge A rising edge is the transition of a digital signal from low to high. It is also called positive edge 2 = falling edge Range is [1,2] Trigger Direction is also sent to the servo drive A servo drive is a special electric amplifier used to power electric servo motors. It monitors feedback signals from the motor and continually adjusts for deviation from expected behavior and is shown in the WorkBench Position Capture screen Edge setup. Axis Number (where input comes from) INT TriggerInput.TrigID 0 = trigger axis is to be the same as Axis.AXIS_NUM. Range is [0,256]   Trigger Mode (capture method) INT TriggerInput.TrigMode 0 = time based capture 1 = position based capture. For position based capture the TrigID must be the same as the Axis_Ref. Range is [0,1] The Mode (either Position or Time) must be configured the same in the servo drive. This can be done either:  in COE Init commands and executed when the EtherCAT ***EtherCAT is an open, high-performance Ethernet-based fieldbus system. The development goal of EtherCAT was to apply Ethernet to automation applications which require short data update times (also called cycle times) with low communication jitter (for synchronization purposes) and low hardware costs network is initialized (0x3460, subindex 3 and 4) in the WorkBench Positon Capture screen (see image above).
	Unit	N/A
	Default	—
WindowOnly	Description	Enables a position latching window. When this input is set, a window is defined by the FirstPosition and LastPosition inputs. Any Fast Input event that occurs outside the window is ignored. The first Fast Input event that occurs within the window latches the axis position
	Data type	BOOL
	Range	—
	Unit	N/A
	Default	—
FirstPosition	Description	See the function block Description above for an explanation of how this input and the LastPosition input define the window. This input is only applicable when the WindowOnly input is high. If the WindowOnly input is low, this input is ignored
	Data type	LREAL
	Range	—
	Unit	User unit
	Default	—
LastPosition	Description	See the function block Description above for an explanation of how this input and the FirstPosition input define the window. This input is only applicable when the WindowOnly input is high. If the WindowOnly input is low, this input is ignored
	Data type	LREAL
	Range	—
	Unit	User unit
	Default	—

Output

Usage

This function block can be used to:

• Perform registration
• Determine the position of a product
• Measure product length

Limitations

• Both high speed inputs cannot be used at the same time.
• The TrigMode option is only used by MC_TouchProbe.

Related Functions

MC_AbortTrigger

See Also

• Fast Inputs with Pipe Network Motion
• Fast Inputs with PLCOpen
• Fast Homing Example with the Pipe Network Motion Engine Axis Pipe Block
• Fast Homing Example with the PLCopen Motion Engine
• Pipe Network Registration and Fast Homing
• Registration Position Capture Example with Pipe Network Trigger Block

Example

Structured Text

(* MC_TouchProbe ST example *)
TriggerInputRef.InputID := 1;    //configure InputID
TriggerInputRef.Direction := 1;  //configure Direction
TriggerInputRef.TrigID := 0;     //configure TrigID
TriggerInputRef.TrigMode := 0;     //Capture trigger based on distributed clock time
Inst_MC_TouchProbe( ArmProbe, Axis1, TriggerInputRef, FALSE,0.0, 0.0 );
//Inst_MC_TouchProbe is an instance of MC_TouchProbe function block
ProbeIsDone := Inst_MC_TouchProbe.Done;            //store Done output into a user defined variable
ProbeValue := Inst_MC_TouchProbe.RecordedPosition; //store RecordedPosition output into a user defined variable

Ladder Diagram

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