Test a Chart with Fault Detection and Redundant Logic

An operating point is a snapshot of the state of a Simulink^® model at a specific time during simulation. For a Stateflow^® chart, an operating point includes:

Activity of chart states
Values of chart local data
Values of chart output data
Values of persistent data in MATLAB^® functions and Truth Table blocks

For more information, see Using Operating Points in Stateflow.

Goal of the Tutorial

Suppose that you want to test the response of the sf_aircraft model to one or more actuator failures in an elevator system. For details of how this model works, see Detect Faults in Aircraft Elevator Control System.

The Mode Logic chart monitors the status of actuators for two elevators. Each elevator has an outer (primary) actuator and an inner (secondary) actuator. In normal operation, the outer actuators are active and the inner actuators are on standby.

When the four actuators are working correctly, the left and right elevators reach steady-state positions in 3 seconds.

Suppose that you want to see what happens at t = 3 when at least one actuator fails. You can simulate the model, save the operating point at t = 3, load and modify the operating point, and then simulate again between t = 3 and 10.

Step	Task	Reference
1	Define the operating point for your chart.	Define the Operating Point
2	Load the operating point and modify values for one actuator failure.	Modify Operating Point Values for One Actuator Failure
3	Test the modified operating point by running the model.	Test the Operating Point for One Failure
4	Modify operating point values for two actuator failures.	Modify Operating Point Values for Two Actuator Failures
5	Test the modified operating point by running the model again.	Test the Operating Point for Two Failures

Define the Operating Point

Open the sf_aircraft model.

openExample("stateflow/FaultDetectionControlLogicInAnAircraftControlSystemExample")

Open the Configuration Parameters dialog box.
Enable saving of an operating point. In the Data Import/Export pane:
1. Select Final states.
2. Enter a name, such as xFinal.
3. Select Save final operating point.
Programmatic equivalent
You can programmatically enable saving of an operating point:
set_param("sf_aircraft",SaveFinalState="on", ... FinalStateName="xFinal", ... SaveOperatingPoint="on");
For more information, see Set Configuration Parameters Programmatically.
Define the stop time for this simulation segment. In the Solver pane, set Stop time to 3.
Programmatic equivalent
You can programmatically set the stop time:
set_param("sf_aircraft",StopTime="3");
Click OK.
Start the simulation.
When you simulate the model, you save the complete operating point at t = 3 in the variable xFinal in the MATLAB base workspace.
Disable saving of an operating point. In the Configuration Parameters dialog box, in the Data Import/Export pane, clear the Save final operating point and Final states parameters and click OK.
This step prevents you from overwriting the operating point you saved in the previous step.
Programmatic equivalent
You can programmatically disable saving of an operating point:
set_param("sf_aircraft", ... SaveOperatingPoint="off", ... SaveFinalState="off");

Modify Operating Point Values for One Actuator Failure

Enable loading of an operating point. In the Configuration Parameters dialog box, in the Data Import/Export pane, select Initial state and enter the variable that contains the operating point of your chart: xFinal.
Programmatic equivalent
You can programmatically enable loading of an operating point:
set_param("sf_aircraft", ... LoadInitialState="on", ... InitialState="xFinal");
Define an object handle for the operating point values of the Mode Logic chart.
At the command prompt, type:
```
blockpath = "sf_aircraft/Mode Logic";
c = xFinal.get(blockpath);
```
Tip
If the chart appears highlighted in the model window, you can specify the block path using gcb (Simulink):
c = xFinal.get(gcb);
Use the get method for Operating Points
The get method:
- Makes a copy of the operating point of your chart, which is stored in the final state data of the model.
- Provides a root-level handle or reference to the copy of the operating point, which is a hierarchical tree of graphical and nongraphical chart objects.
  Each node in this tree is also a handle to a state, data, or other chart object.
Note
Because the entire tree consists of object handles, the following assignment statements do not work:
- stateCopy = c.state
- dataCopy = c.data
- operatingPointCopy = c
These assignments create copies of the object handles, not operating point values. The only way to copy operating point values is to use the clone method. For details, see Methods for Interacting with the Operating Point of a Chart and Guidelines for Using the Operating Point of a Chart.

Look at the contents of the operating point.

c = 

  Block:    "Mode Logic"    (handle)    (active)
  Path:     sf_aircraft/Mode Logic

  Contains:

    + Actuators          "State (OR)"          (active)
    + LI_act             "Function"
    + LO_act             "Function"
    + L_switch           "Function"
    + RI_act             "Function"
    + RO_act             "Function"
    + R_switch           "Function"
    + LI_mode            "State output data"		sf_aircraft_ModeType [1,1]
    + LO_mode            "State output data"		sf_aircraft_ModeType [1,1]
    + RI_mode            "State output data"		sf_aircraft_ModeType [1,1]
    + RO_mode            "State output data"		sf_aircraft_ModeType [1,1]

The operating point of your chart contains a list of states, functions, and data in hierarchical order.

Highlight the states that are active in your chart at t = 3.
At the command prompt, type:
```
c.highlightActiveStates;
```
Active states appear highlighted. By default, the two outer actuators are active and the two inner actuators are on standby.
Tip
To check if a single state is active, you can use the isActive method. For example, type:
c.Actuators.LI.L1.Standby.isActive
This command returns true (1) when a state is active and false (0) otherwise. For information on other methods, see Methods for Interacting with the Operating Point of a Chart.
Change the state activity in the chart to reflect one actuator failure.
Assume that the left outer (LO) actuator fails. To change the state, use this command:
```
c.Actuators.LO.Isolated.setActive;
```
The newly active substate appears highlighted in the chart.
The setActive method ensures that the chart exits and enters the appropriate states to maintain state consistency. However, the method does not perform entry actions for the newly active substate. Similarly, the method does not perform exit actions for the previously active substate.
Save the modified operating point by using this command:
```
xFinal = xFinal.set(blockpath,c);
```

Test the Operating Point for One Failure

Define the new stop time for the simulation segment to test. In the Configuration Parameters dialog box, in the Solver pane, set Stop time to 10.
You do not need to enter a new start time because the simulation continues from where it left off.
Programmatic equivalent
You can programmatically set the stop time:
set_param("sf_aircraft",StopTime="10");

Start simulation.

Chart animation shows that the other three actuators react appropriately to the failure of the left outer (LO) actuator.

This actuator...	Switches from...	Because...
Left inner (LI)	Standby to active	The left elevator must compensate for the left outer (LO) actuator failure.
Right inner (RI)	Standby to active	The same hydraulic line connects to both inner actuators.
Right outer (RO)	Active to standby	Only one actuator per elevator can be active.

Both elevators continue to maintain steady-state positions.

Modify Operating Point Values for Two Actuator Failures

Change the state activity in the chart to reflect two actuator failures.
Assume that the left inner (LI) actuator also fails. To change the state, use this command:
```
c.Actuators.LI.Isolated.setActive;
```
Save the modified operating point by using this command:
```
xFinal = xFinal.set(blockpath,c);
```

Test the Operating Point for Two Failures

Open the Configuration Parameters dialog box and, in the Solver pane, verify that Stop time is 10.
Restart the simulation.
Because of failures in both actuators, the left elevator stops working. The right elevator maintains a steady-state position.

If you modify the operating point of your chart to test the response of the right elevator to actuator failures, you get similar results.