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MCFB_StepAbsSwitch

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 11-209: MCFB StepAbsSwitch

Arguments

Input

Execute

Description

Request the homing step procedure at rising edgeA 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

—

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

Description

Commanded jerkIn 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 torqueTorque 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):

The homing is commanded in the most likely direction were the sensorA sensor is a type of transducer that converts one type of energy into another for various purposes including measurement or information transfer can be found. In this example (-).
The velocity is defined by the input.
The torque is limited.
Both Time and Distance Limits can cause an error if exceeded
If any LimitSwitch is found during HomingThe Homing procedure allows, based on a position measurement, to set a position offset to the motor in order to ensure it is physically at the home position (any of them), then 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 that the end conditions are always 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 (InVelocity).
This Function BlockA function block groups an algorithm and a set of private data. It has inputs and outputs. doesn’t modify the actual position

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

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 *)