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:

Figure 7-249: MCFB StepAbsSwitch

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 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	—
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	—
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 sensor A 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 Homing The 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 Block A 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

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

 

Function Block Diagram

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