MLMstAbs

Description

Performs a move to an absolute position. Returns TRUE if the function succeeded.

Arguments

Input

BlockID	Description	ID name of the Master Block
	Data type	DINT
	Range	[-2147483648, 2147483648]
	Unit	n/a
	Default	—
Position	Description	Sets the value of the absolute destination position. When the Modulo is turned on, see more explanations below.
	Data type	LREAL
	Range	—
	Unit	User unit
	Default	—

Position with Modulo On

• 
  
• This information applies to both MLMstAbs and MLAxisAbs. For simplicity, the term Axis Block also refers to Master Block.

When the Modulo is turned on, the Axis Block moves to the targeted position during the corresponding period, calculated as follows:

• If the Position input is between 0 and the Modulo Position, then the Axis Block moves within the current period (no position rollover).
• If the Position input is greater than the Modulo Position, then the Axis Block moves during one of the next period (positive position rollover).

The Axis Block works similarly for negative positions: if the Position input is less than zero, then the Axis Block moves during one of the previous period (negative position rollover).

Forcing the direction of rotation

In some applications, the direction of rotation for the axis is forced in one direction only. As a consequence, the motor movement goes to the next or previous modulo in the following situations:

• If the End Position is less than the Start Position and the direction of rotation for the axis is forced to be clockwise (the red point shows when the modulo position is reached)
  
  (see an example in row#2 of the table below)
• If the End Position is greater than the Start Position and the direction of rotation for the axis is forced to be counter clockwise
  
  (see an example in row#4 of the table below)

Examples

Start Position	End Position	Direction of rotation	Cross Modulo	Position Input to MLAxisAbs (1)	RelativeDistance Moved (2)
60	200	clockwise	No	200	140	(i.e. 200 - 60 + 0)
60	30	clockwise	Yes	390	330	(i.e. 30 - 60 + 360)
60	30	counter clockwise	No	30	-30	(i.e. 30 - 60 - 0)
60	200	counter clockwise	Yes	-160	-220	(i.e. 200 - 60 - 360)

With:

(1) Position Input = End Position ( + Modulo * Direction of rotation)   (2) Relative Distance Moved = End Position - Start Position ( + Modulo * Direction of rotation)

Where:

Direction of rotation = 1 when clockwise and -1 when anti-clockwise

Travel Speed Update with MLAxisAbs

The travel speed of the generator can be updated using the function block MLAxisGenWriteSpd. Depending on the state of the generator, this speed is directly reflected on the current move or a future move.

• If MLAxisAbs is not currently being executed, the new travel speed will be applied for the trajectory calculation for a future MLAxisAbs command.
• If MLAxisAbs is currently being executed and a new MLAxisAbs with the same target position is called, the new travel speed will be taken into account only if the current state of the TMP"Trapezoidal Motion Profile" This pipe block is a source block that frequently serves as a virtual master for a system composed of several pipes. Generally, a trapezoidal motion profile generator is used to generate a flow of values with a first derivative which produces a trapezoidal trajectory profile is the constant velocity or acceleration. If the axis was decelerating to stop at the goal position the new travel speed will not be taken into account.
• If a MLAxisAbs is currently being executed and a new MLAxisAbs with a different target position is called, the new travel speed is taken into account.

Following are several examples.

First MLAxisAbs Second MLAxisAbs Initial Speed New Speed

Figure 7-100: Initial speed is smaller than the new speed

First MLAxisAbs Second MLAxisAbs Initial Speed New Speed

Figure 7-101: Initial speed is bigger than the new speed

Acceleration Constant Velocity Deceleration

Figure 7-102: The speed update is taken into account only if the second MLAxisAbs is triggered during acceleration or constant velocity

Output

Default (.Q)	Description	Returns true when function successfully executes See more details here
	Data type	BOOL
	Unit	n/a

• 
  

• To reduce the load on the CPU, call MLMstAbs only once for each move. This can be achieved by adding a control variable, which is illustrated below.

            // Master: modulo is on and modulo range is 0 - 360 with rollover at 360
            
  If Not MoveStarted Then
       Position := 500;
       MLMstAbs( PipeNetwork.MASTER, Position);
       MovesStarted := TRUE;
  End_if;	

• 
  

• Perform one of the following to prevent undesired axis movement if modulo is turned on.

  • Verify that the Position value is within the modulo range.
  • If the Position value is outside of the modulo range, call MLMstAbs function only once. See the TIP above for an example of how to do this.

Related Functions

MLMstWriteSpeed

MLMstWriteDecel

Examples

Structured Text

//Make an absolute positon move with a Master block called “MASTER” to position 1000.0
MLMstAbs( PipeNetwork.MASTER, 1000.0 );

Ladder Diagram

 

Function Block Diagram

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