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 to 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 to 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 to 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 *)

See Also