Motion Control in the PLC project

On this page you will find out how to implement motion control from the PLC project in accordance with PLCopen.

Opening the "Add Library" dialog

In order to be able to use motion control in accordance with PLCopen, you must add a reference to your PLC project.

1. Create a new PLC project.

2. Right-click the References folder [1] in the PLC project to which you wish to add a reference.

A context menu opens.

3. Click the entry Add library… [2] in the context menu.

The Add Library… dialog opens.

Selecting a library

Tc2_MC2 is the default library

for motion control in accordance with PLCopen,
PTP motion (Point to Point Motion) and
axis management.

The Add Library dialog is open.

1. Select the library that you wish to add to the PLC project.

2. To do this, switch the Add Library dialog to the Category View [1] if it is in a different view.

3. Expand the Motion subtree [2].

4. Expand the PTP subtree [3].

5. Select the Tc2_MC2 library [4].

6. Confirm your selection with the OK button [5].

A reference to the Tc2_MC2 library [4] is created in the PLC project to which you wish to add this reference.

MC axis variable

The PLC axis variable MAIN.axis has the data type AXIS_REF.

The data type AXIS_REF:

contains information about an axis,
is an interface between the PLC and the NC and
is given to the MC function blocks as a reference to an axis.

	Refreshing the status data structure in `AXIS_REF` The status data structure `Status` of the type `ST_AxisStatus` contains additional or prepared status and diagnostic information about an axis. The structure is not cyclically refreshed, but has to be updated by the PLC program Calling the `ReadStatus()` action from `AXIS_REF` updates the status data structure and should be done once at the beginning of each PLC cycle. The status information does not change within a PLC cycle. After calling `ReadStatus(),` the current status information can be accessed in `AXIS_REF` within the entire PLC program. The nature of the status data structure is purely informative. Therefore, its use is not mandatory.

PROGRAM MAIN
VAR
    axis: AXIS_REF;
END_VAR

axis.ReadStatus();

Simulation axis

[1]

The local MC axis variable MAIN.axis is connected to the NC axis for movement with MC function blocks.

[2]

The simulation axis Standard (Mapping via Encoder and Drive) is set as the NC axis under Axis Type.

[3]

The entry Link To I/O... remains empty for a simulation axis.

MC_Power

The function block MC_Power switches the software enabling of an axis.

MC_Power: Inputs (excerpt)

Enable: BOOL;

Sets the general software and controller enabling for an axis. Enabled if Enable = TRUE. Corresponds to the Controller checkbox in the Set Enabling dialog. Enabled if the checkbox is checked.

Enable_Positive: BOOL;

Sets the feed enabling for an axis for the positive travel direction. Enabled if Enable_Positive = TRUE. Corresponds to the Feed Fw checkbox in the Set Enabling dialog. Enabled if the checkbox is checked.

Enable_Negative: BOOL;

Sets the feed enabling for an axis for the negative travel direction. Enabled if Enable_Negative = TRUE. Corresponds to the Feed Bw checkbox in the Set Enabling dialog. Enabled if the checkbox is checked.

Override: LREAL;

Influences the velocity of all travel commands as a percentage. It is 0 ≤ Override ≤ 100.0.

MC_MoveAbsolute

The function block MC_MoveAbsolute starts the positioning to an absolute target position and monitors the axis movement over the entire travel path.

MC_MoveAbsolute: Inputs (excerpt)

Execute: BOOL;

A rising edge at this input executes the command.

Position: LREAL;

Absolute target position to be used for positioning.

Velocity: LREAL;

Maximum travel velocity. A positive value.

Sample program for moving to a target position

The MAIN program shows a short example with which a target position is to be moved to.

`PROGRAM MAIN`: Declaration

PROGRAM MAIN
VAR
    axis: AXIS_REF;
    fbAxisPower: MC_Power;
    fbAxisMoveAbsolute: MC_MoveAbsolute;
    bEnable: BOOL := FALSE;
    fOverride: LREAL := 100;
    bMove: BOOL := FALSE;
    fTargetPosition: LREAL := 90;
    fTargetVelocity: LREAL := 5;
END_VAR

`PROGRAM MAIN`: Implementation

axis.ReadStatus();

fbAxisPower(
    Axis:= axis,
    Enable:= bEnable,
    Enable_Positive:= bEnable,
    Enable_Negative:= bEnable,
    Override:= fOverride,
    BufferMode:= ,
    Options:= ,
    Status=> ,
    Busy=> ,
    Active=> ,
    Error=> ,
    ErrorID=> );

fbAxisMoveAbsolute(
    Axis:= axis,
    Execute:= bMove,
    Position:= fTargetPosition,
    Velocity:= fTargetVelocity,
    Acceleration:= ,
    Deceleration:= ,
    Jerk:= ,
    BufferMode:= ,
    Options:= ,
    Done=> ,
    Busy=> ,
    Active=> ,
    CommandAborted=> ,
    Error=> ,
    ErrorID=> );

MAIN: Local variables

axis: AXIS_REF;

Instance of an MC axis. This instance can be linked with an NC axis.

fbAxisPower: MC_Power;

Instance variable of the MC_Power function block.

fbAxisMoveAbsolute: MC_MoveAbsolute;

Instance variable of the MC_MoveAbsolute function block.

bEnable: BOOL := FALSE;

Switches the inputs Enable, Enable_Positive and Enable_Negative of the MC_Power function block.

fOverride: LREAL := 100;

Override value for the Override input of the MC_Power function block.

bMove: BOOL := FALSE;

Positive edge switches the Execute input of the MC_MoveAbsolute function block.

fTargetPosition: LREAL := 90;

Target position value for the Position input of the MC_MoveAbsolute function block.

fTargetVelocity: LREAL := 5;

Target velocity value for the Velocity input of the MC_MoveAbsolute function block.