text: <user>
  Create a function block for motion control in TwinCAT Structured Text that implements a multi-axis controller for a CNC sheet cutting machine. Include functionality for homing, velocity control, and emergency stop.<|endoftext|>
  <assistant>
  FUNCTION_BLOCK FB_SheetCuttingController
  VAR_INPUT
      bEnable         : BOOL;    // Enable controller
      bHomeAll        : BOOL;    // Home all axes
      bEmergencyStop  : BOOL;    // Emergency stop signal
      fVelocityX      : LREAL;   // Velocity for X-axis
      fVelocityY      : LREAL;   // Velocity for Y-axis
  END_VAR
  
  VAR_OUTPUT
      bReady          : BOOL;    // Controller ready
      bError          : BOOL;    // Error flag
      nErrorID        : UDINT;   // Error ID
      bHomed          : BOOL;    // All axes homed
  END_VAR
  
  VAR
      // Axis references
      axisX           : AXIS_REF;
      axisY           : AXIS_REF;
      
      // Motion function blocks
      fbPowerX        : MC_Power;
      fbPowerY        : MC_Power;
      fbHomeX         : MC_Home;
      fbHomeY         : MC_Home;
      fbMoveX         : MC_MoveVelocity;
      fbMoveY         : MC_MoveVelocity;
      fbStopX         : MC_Stop;
      fbStopY         : MC_Stop;
      
      // Internal variables
      bInitialized    : BOOL := FALSE;
      bHomingInProgress : BOOL := FALSE;
  END_VAR
  
  // Initialize the controller
  METHOD Init
      IF NOT bInitialized THEN
          // Link axis references
          axisX.ReadStatus();
          axisY.ReadStatus();
          
          // Initialize power function blocks
          fbPowerX(Axis := axisX, Enable_Positive := TRUE, Enable_Negative := TRUE);
          fbPowerY(Axis := axisY, Enable_Positive := TRUE, Enable_Negative := TRUE);
          
          bInitialized := TRUE;
      END_IF
  END_METHOD
  
  // Main cycle
  METHOD CyclicUpdate
      // Check for emergency stop
      IF bEmergencyStop THEN
          EmergencyStop();
          RETURN;
      END_IF
      
      // Enable axes
      fbPowerX(Enable := bEnable);
      fbPowerY(Enable := bEnable);
      
      // Perform homing if requested
      IF bHomeAll AND NOT bHomingInProgress THEN
          StartHoming();
      ELSIF bHomingInProgress THEN
          CheckHomingStatus();
      END_IF
      
      // Move axes if homed and not in error
      IF bHomed AND NOT bError THEN
          MoveAxes();
      END_IF
      
      // Update status
      bReady := bHomed AND NOT bError AND fbPowerX.Status AND fbPowerY.Status;
  END_METHOD
  
  // Start homing procedure
  METHOD StartHoming
      bHomingInProgress := TRUE;
      fbHomeX(Axis := axisX, Execute := TRUE);
      fbHomeY(Axis := axisY, Execute := TRUE);
  END_METHOD
  
  // Check homing status
  METHOD CheckHomingStatus
      IF fbHomeX.Done AND fbHomeY.Done THEN
          bHomingInProgress := FALSE;
          bHomed := TRUE;
          fbHomeX(Execute := FALSE);
          fbHomeY(Execute := FALSE);
      ELSIF fbHomeX.Error OR fbHomeY.Error THEN
          bError := TRUE;
          nErrorID := SEL(fbHomeX.Error, fbHomeY.ErrorID, fbHomeX.ErrorID);
          bHomingInProgress := FALSE;
      END_IF
  END_METHOD
  
  // Move axes based on velocity inputs
  METHOD MoveAxes
      fbMoveX(Axis := axisX, Execute := TRUE, Velocity := fVelocityX);
      fbMoveY(Axis := axisY, Execute := TRUE, Velocity := fVelocityY);
      
      IF fbMoveX.Error OR fbMoveY.Error THEN
          bError := TRUE;
          nErrorID := SEL(fbMoveX.Error, fbMoveY.ErrorID, fbMoveX.ErrorID);
      END_IF
  END_METHOD
  
  // Emergency stop procedure
  METHOD EmergencyStop
      fbStopX(Axis := axisX, Execute := TRUE);
      fbStopY(Axis := axisY, Execute := TRUE);
      bHomed := FALSE;
      bError := TRUE;
      nErrorID := 16#8000; // Custom error ID for emergency stop
  END_METHOD
  
  // Implementation explanation:
  // This function block implements a multi-axis controller for a CNC sheet cutting machine using TwinCAT 3 Structured Text.
  // It provides functionality for enabling the controller, homing all axes, velocity control, and emergency stop.
  // The controller uses separate function blocks for each axis to handle power, homing, movement, and stopping.
  // Error handling is implemented throughout to ensure safe operation.
  
  // Suggested TwinCAT 3 features to enhance this implementation:
  // 1. Use of TcCOM objects for more efficient axis control
  // 2. Implementation of a state machine using TwinCAT's State Machine Framework
  // 3. Integration with TwinCAT HMI for operator interface and visualization<|endoftext|>
  