Function Block MCFB_StepAbsSwitchPLCopen motion icon

Description

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

The following figure shows the function block I/O:

MCFB StepAbsSwitch

Figure 7-247: MCFB StepAbsSwitch

Arguments

Input

Execute

Description

Request the homing step procedure at rising edgeClosedA rising edge is the transition of a digital signal from low to high. It is also called positive edge. Outputs are reset when execute input is false.

 

Data type

BOOL

 

Range

[0 , 1]

 

Unit

N/A

 

Default

AxisID

Description

Name of a declared instance of the AXIS_REF library function

 

Data type

AXIS_REF

 

Range

[1 , 256]

 

Unit

N/A

 

Default

Direction

Description

Define the axis homing direction

Value

Description

0

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

 

Data type

DINT

 

Range

[0 , 3]

 

Unit

N/A

 

Default

SwitchMode

Description

Switch state to complete homing

Value

Description

0

switch is on

1

switch if off

2

rising edge of switch

3

falling edge of switch

 

Data type

DINT

 

Range

[0 , 3]

 

Unit

N/A

 

Default

Velocity

Description

Commanded velocity for the homing move

 

Data type

LREAL

 

Range

 

Unit

User unit/sec

 

Default

Acceleration

Description

Commanded acceleration for the homing move

 

Data type

LREAL

 

Range

 

Unit

User unit/sec2

 

Default

Deceleration

Description

Commanded deceleration for the homing move

 

Data type

LREAL

 

Range

 

Unit

User unit/sec2

 

Default

JerkClosedIn physics, jerk is the rate of change of acceleration; more precisely, the derivative of acceleration with respect to time

Description

Commanded jerkClosedIn physics, jerk is the rate of change of acceleration; more precisely, the derivative of acceleration with respect to time for the homing move (if zero, then trapezoidal acc/dec is used)

 

Data type

LREAL

 

Range

 

Unit

User unit/sec3

 

Default

TorqueLimit

Description

Maximum torqueClosedTorque is the tendency of a force to rotate an object about an axis. Just as a force is a push or a pull, a torque can be thought of as a twist applied for the homing move entered in thousandths of maximum torque, e.g. "250" is 250/1000, or 25%.

 

Data type

LREAL

 

Range

 

Unit

User unit

 

Default

TimeLimit

Description

Maximum time for homing move to complete. If exceeded the homing procedure will error out. 0= no time limit

 

Data type

TIME

 

Range

 

Unit

sec

 

Default

DistanceLimit

Description

Maximum distance for homing move to complete. If exceeded the homing procedure will error out. 0= no distance limit

 

Data type

LREAL

 

Range

 

Unit

User unit

 

Default

AbsoluteSwitch

Description

The absolute switch input I/O point

 

Data type

BOOL

 

Range

[0 , 1]

 

Unit

N/A

 

Default

PosLimitSwitch

Description

The positive direction limit switch input I/O point

 

Data type

BOOL

 

Range

[0 , 1]

 

Unit

N/A

 

Default

NegLimitSwitch

Description

The negative direction limit switch input I/O point

 

Data type

BOOL

 

Range

[0 , 1]

 

Unit

N/A

 

Default

SwitchMode

Description

Switch state to complete homing

Value

Description

0

abort

1

buffer

2

Blend to active

3

blend to next

4

blend to low velocity

5

blend to high velocity

See table in Buffer Modes

 

Data type

SINT

 

Range

[0 , 5]

 

Unit

N/A

 

Default

Output

Done

Description

Indicates the move completed successfully.

The Command Position has reached the endpoint

 

Data type

BOOL

 

Unit

N/A

Busy

Description

High from the moment the Execute input is one-shot to the time the move is ended

 

Data type

BOOL

 

Unit

N/A

Active

Description

Indicates this move is the active move

 

Data type

BOOL

 

Unit

N/A

CommandAborted

Description

Indicates the move was aborted

 

Data type

BOOL

 

Unit

N/A

Error

Description

Indicates an invalid input was specified or the move was terminated due to an error

 

Data type

BOOL

 

Unit

N/A

ErrorID

Description

Indicates the error if Error output is set to TRUE

Value 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
 

Data type

INT

 

Unit

N/A

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):

 

 

 

An overlapping switch configuration is also possible. This has same the behavior as working on the limit switches:

 

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):

Related Functions

MCFB_StepAbsolute

MCFB_StepRefPulse

MCFB_StepBlock

MCFB_StepLimitSwitch

Example

Structured Text

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 *)

Ladder Diagram

UDFB StepAbsSwitch: LD example

 

Function Block Diagram

UDFB StepAbsSwitch: FBD example

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