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:

Figure 7-251: MCFB StepLimitSwitch

Arguments

Input

Execute	Description	Request the homing step procedure at rising edge A 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 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	—
Jerk In physics, jerk is the rate of change of acceleration; more precisely, the derivative of acceleration with respect to time	Description	Commanded jerk In 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 torque Torque 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 sensor A 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 Block A function block groups an algorithm and a set of private data. It has inputs and outputs. doesn’t modify actual position

Related Functions

MCFB_StepAbsolute

MCFB_StepRefPulse

MCFB_StepBlock

MCFB_StepAbsSwitch

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 *)

Ladder Diagram

Function Block Diagram

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