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MCFB_StepLimitSwitch

Description

This function block performs a single-axis home to a limit switch. In this case the limit switches (always active once moving part working area has been surpassed) are used for homing procedure.

The following figure shows the function block I/O:

MCFB StepLimitSwitch

Figure 11-211: MCFB StepLimitSwitch

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

Data type

BOOL

Range

[0 , 1]

Unit

n/a

Default

—

LimitSwitchMode

Description

Limit switchSwitch limiting the traverse path of the machine; implemented as n.c. (break) contact 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

—

LimitSwitch

Description

The limit switch input I/O point

Data type

BOOL

Range

[0 , 1]

Unit

n/a

Default

—

BufferMode

Description

Define the homing move start action

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 homing procedure performs a homing function searching for sensorA sensor is a type of transducer that converts one type of energy into another for various purposes including measurement or information transfer using only LimitSwitches. (A LimitSwitch has 1 “Off” (or “On”) area).

Home is commanded by user in the desired homing direction at the selected Velocity.
If LimitSwitch is found ‘On’ on rising ‘Execute’, then the process is started in the opposite direction as specified, LimitSwitch is search for ‘Off’ (or On, depending on LimitSwitchMode setting) Edge (released), and process is restarted again in original direction. This ensures that the end conditions are always the same.
The torque is limited.
The Time and Distance Limits can cause error if exceeded
The Direction changes only when the specified Velocity is reached, this ensures acceleration and deceleration spaces are fixed
This Function BlockA function block groups an algorithm and a set of private data. It has inputs and outputs. doesn’t modify actual position

Related Functions

Example

Structured Text

PositiveDirection :=0;

RisingEdge :=2;

Velocity :=10000.0;

TorqueLimit :=50.0;

TimeLimit :=T#10s;

DistanceLimit :=10000.0;

Inst_MCFB_StepLimitSwitch( True, Axis1, PositiveDirection, RisingEdge, Velocity, 1000, 1000, 0, TorqueLimit, TimeLimit, DistanceLimit, LimitSwitch, 0 );

HomeComplete :=Inst_MCFB_StepLimitSwitch.Done;

HomeBusy :=Inst_MCFB_StepLimitSwitch.Busy;

HomeActive :=Inst_MCFB_StepLimitSwitch.Active;

HomeAborted :=Inst_MCFB_StepLimitSwitch.CommandAborted;

HomeError :=Inst_MCFB_StepLimitSwitch.Error;

HomeErrorID :=Inst_MCFB_StepLimitSwitch.ErrorID;

(* LimitSwitch is a declared I/O point *)