Julia Braman's Research

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My research involves the verification of fault-tolerant control systems. One way to include fault tolerance in a control architecture is to allow the control program to reconfigure as faults occur. A goal-based control architecture, called Mission Data System (MDS), which was developed at the Jet Propulsion Laboratory (JPL), allows goals to elaborate and re-elaborate different tactics upon goal failure. Tactics are sets of goals that ensure the success of the parent goal. If there is more than one way for the parent goal to succeed, it may have more than one tactic that it can elaborate.

There is a way to verify these goal-based control programs by converting them to linear hybrid systems and then using existing symbolic model checking software such as PHAVer to verify the hybrid automata. The conversion and verification procedure for certain types of goal networks has been developed in the following papers:

  • Braman, J.M.B., M.D. Ingham, and R.M. Murray. "Verification Procedure for Generalized Goal-based Control Programs." AIAA Infotech@Aerospace, May 2007. <pdf>
  • Braman, J.M.B., R.M. Murray and D.A. Wagner. "Safety Verification of a Fault Tolerant Reconfigurable Autonomous Goal-Based Robotic Control System." To appear IROS 2007. <pdf>

The verification procedure described in the papers above all assume that every state variable that is used to condition transitions between tactics are known exactly. Because of the special structure of the hybrid systems created from the goal networks in the above procedure, it is possible to calculate the probability of failure of a verifiable goal network due to state variable estimation uncertainty in some cases. This verification procedure for goal networks with state variable uncertainty is described in the following paper:

  • Braman, J.M.B. and R.M. Murray. "Safety Verification of Fault Tolerant Goal-based Control Programs with Estimation Uncertainty." Submitted, American Control Conference, 2008. <pdf>
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