MCFB_StepAbsSwitch

PLCopen motion icon

Function Block - Homing to a home switch.

Inputs

Input	Data Type	Range	Unit	Default	Description
Execute	BOOL	FALSE, TRUE	N/A	No default	Request the homing step procedure at the rising edge. Outputs are reset when execute input is FALSE.
AxisID	AXIS_REF	1 to 256	N/A	No default	Name of a declared instance of the AXIS_REF library function. See AXIS_REF Structure.
Direction	DINT	0, 3	N/A	No default	Defines the axis homing direction. 0 (zero) = Clockwise rotation. 1 = Counterclockwise rotation. 2 = Clockwise if AbsoluteSwitch starts Off and negative if switch starts On. 3 = Counter-clockwise if AbsoluteSwitch starts On and positive if switch starts Off.
SwitchMode	DINT	0, 3	N/A	No default	Switch state to complete homing. 0 (zero) = Switch is on. 1 = Switch is off. 2 = Rising edge of switch. 3 = Falling edge of switch.
Velocity	LREAL	No range	User unit/sec	No default	Commanded velocity for the homing move.
Acceleration	LREAL	No range	User unit/sec²	No default	Commanded acceleration for the homing move.
Deceleration	LREAL	No range	User unit/sec²	No default	Commanded deceleration for the homing move.
Jerk	LREAL	No range	User unit/sec³	No default	Commanded jerk for the homing move. If 0 (zero), trapezoidal acc/dec is used.
TorqueLimit	LREAL	No range	User units	No default	Maximum torque applied for the homing move. Entered in thousandths of maximum torque. Example: 250 is 250/1000, or 25%.
TimeLimit	TIME	No range	Sec	No default	Maximum time for homing move to complete. If exceeded, the homing procedure errors out. 0 (zero) = no time limit.
DistanceLimit	LREAL	No range	User units	No default	Maximum distance for homing move to complete. If exceeded, the homing procedure errors out. 0 (zero) = no distance limit.
AbsoluteSwitch	BOOL	FALSE, TRUE	N/A	No default	The absolute switch input I/O point.
PosLimitSwitch	BOOL	FALSE, TRUE	N/A	No default	The positive direction limit switch input I/O point.
NegLimitSwitch	BOOL	FALSE, TRUE	N/A	No default	The negative direction limit switch input I/O point.
SwitchMode	SINT	0, 5	N/A	No default	Switch state to complete homing. 0 = Abort. 1 = Buffer. 2 = Blend to active. 3 = Blend to next. 4 = Blend to low velocity. 5 = Blend to high velocity. See Buffer Modes for detailed information.

Outputs

Output

Data Type

Range

Unit

Description

Done

BOOL

FALSE, TRUE

N/A

Indicates the move completed successfully.
The Command Position has reached the endpoint.

Busy

BOOL

FALSE, TRUE

N/A

High from the moment the Execute input goes high until the time the move is ended.

Active

BOOL

FALSE, TRUE

N/A

Indicates this move is the Active move.

CommandAborted

BOOL

FALSE, TRUE

N/A

Indicates the move was aborted.

Error

BOOL

FALSE, TRUE

N/A

Indicates either:

An invalid input was specified.
The move was terminated due to an error.

ErrorID

INT

Enumerated

N/A

Indicates the error if the Error output is set to TRUE.

Error identifier:

ErrorID	Description
1	TimeLimit exceeded.
2	DistanceLimit exceeded.
3	TorqueLimit exceeded.
4	Axis error stop state.
5	Axis not enabled.
6	Invalid inputs for Velocity-Acceleration-Deceleration.

Remarks

Performs a homing function by searching for an absolute positioned external physical switch.
An Absolute Switch has two Off (or On) areas.

This image shows the function or function block I/O.

Figure 1: MCFB_StepAbsSwitch

Usage

This physical layout has the risk that homing is started in the wrong direction (escaping the switch).

To support such case, it implements a special behavior when Limit Switches are found (or the AbsSwitch itself is On at Execute).

This function block does not modify the actual position.
The homing is commanded in the most likely direction where the sensor can be found.
The Velocity is defined by the input.
The Torque is limited.
Time and Distance Limits can cause an error if exceeded.
If any LimitSwitch is found during Homing (any of them), a special process is started in the opposite direction.
- The AbsSwitch is searched to switch Off (or On, depending on SwitchMode setting).
The Edge (passed by) and homing process is restarted in the original direction and with the same conditions.
- This ensures the end conditions are always the same.
If the SwitchMode is either MC_SwitchNegative or MC_SwitchPositive, then the special process is also started in opposite direction depending from the switch state at Execute.
The direction changes only when the specified Velocity is reached.

Figure 2: MCFB_StepAbsSwitch Usage 1

Figure 3: MCFB_StepAbsSwitch Usage 2

Figure 4: MCFB_StepAbsSwitch Usage 3

An overlapping switch configuration is also possible.

This has same the behavior as working on the limit switches:

Figure 5: MCFB_StepAbsSwitch Usage 4

If the input Direction is set to a fixed direction (MC_Positive or MC_Negative), then the initial switch state is ignored.

Used for example in rotary axis where only one sense of rotation is allowed:

Figure 6: MCFB_StepAbsSwitch Usage 5

FBD Language Example

FFLD Language Example

IL Language Example

Not available.

ST Language Example

NegativeDirection :=1;
RisingEdge :=2;
Velocity :=10000.0;
TorqueLimit :=50.0;
TimeLimit :=T#10s;
DistanceLimit :=10000.0;

Inst_MCFB_StepAbsSwitch( True, Axis1, NegativeDirection, RisingEdge, Velocity, 1000, 1000, 0, TorqueLimit, TimeLimit, DistanceLimit, AbsoluteSwitch, PosLimitSwitch, NegLimitSwitch, 0 );

HomeComplete :=Inst_MCFB_StepAbsSwitch.Done;
HomeBusy :=Inst_MCFB_StepAbsSwitch.Busy;
HomeActive :=Inst_MCFB_StepAbsSwitch.Active;
HomeAborted :=Inst_MCFB_StepAbsSwitch.CommandAborted;
HomeError :=Inst_MCFB_StepAbsSwitch.Error;
HomeErrorID :=Inst_MCFB_StepAbsSwitch.ErrorID;
(* AbsoluteSwitch, PosLimitSwitch, NegLimitSwitch are declared I/O points *)