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Complex Batch Recipe State Machine

PLC Structured Text

Goal -- WPM

Ready
Exercise Algorithm Area
1PROGRAM BatchRecipeStateMachine

2

3VAR

4// State Machine Variables

5currentState : INT := 0; // 0: Idle, 1: Initializing, 2: Processing, 3: Paused, 4: Error, 5: Completing, 6: Terminating

6nextState : INT;

7

8// Recipe Parameters

9recipeID : STRING := '';

10batchSize : REAL := 0.0;

11targetTemperature : REAL := 0.0;

12currentTemperature : REAL := 0.0;

13heatingActive : BOOL := FALSE;

14mixingSpeed : INT := 0;

15mixingActive : BOOL := FALSE;

16ingredientA_Added : BOOL := FALSE;

17ingredientB_Added : BOOL := FALSE;

18

19// Timers and Flags

20timer_Init : TON;

21timer_Process : TON;

22timer_Complete : TON;

23errorOccurred : BOOL := FALSE;

24errorMessage : STRING := '';

25recipeStep : INT := 0;

26maxSteps : INT := 10;

27

28// Helper Function Flags

29isInitializingComplete : BOOL := FALSE;

30isProcessingStepComplete : BOOL := FALSE;

31isCompletingComplete : BOOL := FALSE;

32

33END_VAR

34

35// Main State Machine Logic

36CASE currentState OF

370: // Idle State

38IF recipeID <> '' AND batchSize > 0.0 THEN

39nextState := 1; // Transition to Initializing

40END_IF;

41

421: // Initializing State

43// Simulate initialization steps

44IF NOT timer_Init.Q THEN

45timer_Init(IN := TRUE, PT := T#5S);

46ELSE

47// Initialization complete

48isInitializingComplete := TRUE;

49nextState := 2; // Transition to Processing

50END_IF;

51// Handle potential initialization errors

52IF timer_Init.ET > T#10S THEN // Example: Timeout

53errorOccurred := TRUE;

54errorMessage := 'Initialization Timeout';

55nextState := 4; // Transition to Error

56END_IF;

57

582: // Processing State

59// Execute recipe steps sequentially

60IF recipeStep < maxSteps THEN

61// Example step: Heat to target temperature

62IF recipeStep = 0 THEN

63heatingActive := TRUE;

64IF currentTemperature >= targetTemperature THEN

65heatingActive := FALSE;

66isProcessingStepComplete := TRUE;

67END_IF;

68ELSIF recipeStep = 1 THEN

69// Example step: Add Ingredient A

70IF NOT ingredientA_Added THEN

71// Logic to add ingredient A

72ingredientA_Added := TRUE;

73ELSE

74isProcessingStepComplete := TRUE;

75END_IF;

76ELSIF recipeStep = 2 THEN

77// Example step: Start Mixing

78mixingActive := TRUE;

79mixingSpeed := 50;

80timer_Process(IN := TRUE, PT := T#3S);

81IF timer_Process.Q THEN

82mixingActive := FALSE;

83mixingSpeed := 0;

84timer_Process(IN := FALSE);

85isProcessingStepComplete := TRUE;

86END_IF;

87END_IF;

88

89// Advance to next step if current one is complete

90IF isProcessingStepComplete THEN

91recipeStep := recipeStep + 1;

92isProcessingStepComplete := FALSE;

93// Reset timers for next step if needed

94timer_Process(IN := FALSE);

95END_IF;

96

97ELSE

98// All processing steps complete

99nextState := 5; // Transition to Completing

100END_IF;

101// Handle processing errors

102IF errorOccurred THEN

103nextState := 4; // Transition to Error

104END_IF;

105

1063: // Paused State

107// Logic for pausing and resuming

108// For simplicity, this state is not fully implemented in this example

109// In a real system, this would involve stopping actuators and waiting for a resume command.

110// If resume command received, nextState := 2;

111// If cancel command received, nextState := 6;

112

1134: // Error State

114// Log error, stop processes, await reset or recovery

115heatingActive := FALSE;

116mixingActive := FALSE;

117// Logic for error handling and potential recovery

118// If recovery successful, nextState := 1; // or a specific recovery state

119// If reset requested, nextState := 0;

120

1215: // Completing State

122// Perform final actions, e.g., cooling down, final mixing

123IF NOT timer_Complete.Q THEN

124timer_Complete(IN := TRUE, PT := T#2S);

125ELSE

126isCompletingComplete := TRUE;

127nextState := 6; // Transition to Terminating

128END_IF;

129

1306: // Terminating State

131// Clean up resources, reset variables

132recipeID := '';

133batchSize := 0.0;

134recipeStep := 0;

135errorOccurred := FALSE;

136errorMessage := '';

137isInitializingComplete := FALSE;

138isProcessingStepComplete := FALSE;

139isCompletingComplete := FALSE;

140nextState := 0; // Transition back to Idle

141

142END_CASE;

143

144// Update current state

145currentState := nextState;

146

147// Call helper functions (if any were defined, e.g., for specific step logic)

148// Example: Call_Heating_Logic();

149// Example: Call_Mixing_Logic();

150

151// Timer updates (assuming timers are called elsewhere or implicitly handled by PLC runtime)

152// In a real PLC, TON instances would be called within the main program scan.

153// For this example, assume timer logic is implicitly handled by their instantiation.

154

155END_PROGRAM
Algorithm description viewbox

Complex Batch Recipe State Machine

Algorithm description:

This program implements a state machine for managing a complex batch recipe process in a PLC. It defines distinct states such as Idle, Initializing, Processing, Paused, Error, Completing, and Terminating. The machine transitions between these states based on internal logic and external conditions, simulating steps like heating, adding ingredients, and mixing. This is crucial for automated manufacturing where precise sequencing and error handling are paramount for product quality and safety.

Algorithm explanation:

The algorithm uses a finite state machine (FSM) pattern to control a batch recipe. The `currentState` variable dictates the current phase of the recipe, and transitions to `nextState` are managed within a `CASE` statement. Each state encapsulates specific actions and logic, such as timer-based operations for initialization and processing, and conditional checks for ingredient addition and mixing. Error handling is integrated by transitioning to an 'Error' state upon detecting issues, preventing further incorrect operations. The algorithm's correctness relies on ensuring all possible transitions are defined and that each state performs its intended function without unintended side effects. The time complexity is O(1) per scan cycle as it's a fixed number of states and operations. Space complexity is O(1) as it uses a fixed set of variables regardless of recipe complexity.

Pseudocode:

PROGRAM BatchRecipeStateMachine
VAR
    // State variables
    currentState, nextState : INT
    // Recipe parameters
    recipeID, batchSize, targetTemperature, currentTemperature, heatingActive, mixingSpeed, mixingActive, ingredientA_Added, ingredientB_Added : VARIOUS_TYPES
    // Timers and flags
    timer_Init, timer_Process, timer_Complete : TON
    errorOccurred : BOOL
    errorMessage : STRING
    recipeStep, maxSteps : INT
    isInitializingComplete, isProcessingStepComplete, isCompletingComplete : BOOL
END_VAR

// Main logic loop
CASE currentState OF
    Idle:
        IF recipe conditions met THEN
            nextState := Initializing
        END_IF
    Initializing:
        Start initialization timer
        IF timer done THEN
            isInitializingComplete := TRUE
            nextState := Processing
        END_IF
        IF initialization timeout THEN
            errorOccurred := TRUE
            errorMessage := 'Init Timeout'
            nextState := Error
        END_IF
    Processing:
        IF recipeStep < maxSteps THEN
            Execute current recipe step logic (e.g., heating, adding ingredients, mixing)
            IF current step complete THEN
                recipeStep := recipeStep + 1
                isProcessingStepComplete := FALSE
            END_IF
        ELSE
            nextState := Completing
        END_IF
        IF errorOccurred THEN
            nextState := Error
        END_IF
    Paused:
        // Logic for pause/resume
    Error:
        Stop all processes
        Log error message
        // Await reset or recovery
    Completing:
        Start completion timer
        IF timer done THEN
            isCompletingComplete := TRUE
            nextState := Terminating
        END_IF
    Terminating:
        Reset all variables and parameters
        nextState := Idle
END_CASE

// Update state
currentState := nextState

// Call helper functions if any
END_PROGRAM