53,147 research outputs found
Safety Verification of Fault Tolerant Goal-based Control Programs with Estimation Uncertainty
Fault tolerance and safety verification of control systems that have state variable estimation uncertainty are essential for the success of autonomous robotic systems. A software control architecture called mission data system, developed at the Jet Propulsion Laboratory, uses goal networks as the control program for autonomous systems. Certain types of goal networks can be converted into linear hybrid systems and verified for safety using existing symbolic model checking software. A process for calculating the probability of failure of certain classes of verifiable goal networks due to state estimation uncertainty is presented. A verifiable example task is presented and the failure probability of the control program based on estimation uncertainty is found
Conversion and verification procedure for goal-based control programs
Fault tolerance and safety verification of control systems are essential for the success of autonomous robotic systems. A control architecture called Mission Data System, developed at the Jet Propulsion Laboratory, takes a goal-based control approach. In this paper, a method for converting goal network control programs into linear hybrid systems is developed. The linear hybrid system can then be verified for safety in the presence of failures using existing symbolic model checkers. An example task is developed and successfully verified using HyTech, a symbolic model checking software for linear hybrid systems
Distributed Receding Horizon Control with Application to Multi-Vehicle Formation Stabilization
We consider the control of interacting subsystems whose dynamics and constraints are uncoupled, but whose state vectors are coupled non-separably in a single centralized cost function of a finite horizon optimal control problem. For a given centralized cost structure, we generate distributed optimal control problems for each subsystem and establish that the distributed receding horizon implementation is asymptotically stabilizing. The communication requirements between subsystems with coupling in the cost function are that each subsystem obtain the previous optimal control trajectory of those subsystems at each receding horizon update. The key requirements for stability are that each distributed optimal control not deviate too far from the previous optimal control, and that the receding horizon updates happen sufficiently fast. The theory is applied in simulation for stabilization of a formation of vehicles
Model-based estimation of off-highway road geometry using single-axis LADAR and inertial sensing
This paper applies some previously studied extended
Kalman filter techniques for planar road geometry estimation
to the domain of autonomous navigation of off-highway
vehicles. In this work, a clothoid model of the road geometry is
constructed and estimated recursively based on road features
extracted from single-axis LADAR range measurements. We
present a method for feature extraction of the road centerline
in the image plane, and describe its application to recursive
estimation of the road geometry. We analyze the performance of
our method against simulated motion of varied road geometries
and against closed-loop detection, tracking and following of
desert roads. Our method accomodates full 6 DOF motion of
the vehicle as it navigates, constructs consistent estimates of the
road geometry with respect to a fixed global reference frame,
and requires an estimate of the sensor pose for each range
measurement
Space photography and the exploration of Mars
A general exposition of the scientific potentialities and analytic framework of space photography is presented using the photography of Mars from flybys and orbiters as the principal example. Space photography is treated here as a communication process in which planetary scene information is communicated to the eye-brain receiver of earth-based interpreters. The salient parameters of this process are: (1) total information returned, (2) surface resolution, and (3) a priori knowledge regarding the planetary surface observed
Dynamical Self-assembly during Colloidal Droplet Evaporation Studied by in situ Small Angle X-ray Scattering
The nucleation and growth kinetics of highly ordered nanocrystal
superlattices during the evaporation of nanocrystal colloidal droplets was
elucidated by in situ time resolved small-angle x-ray scattering. We
demonstrated for the first time that evaporation kinetics can affect the
dimensionality of the superlattices. The formation of two-dimensional
nanocrystal superlattices at the liquid-air interface of the droplet has an
exponential growth kinetics that originates from interface "crushing".Comment: 4 pages, 4 figure
Safety verification of a fault tolerant reconfigurable autonomous goal-based robotic control system
Fault tolerance and safety verification of control
systems are essential for the success of autonomous robotic
systems. A control architecture called Mission Data System
(MDS), developed at the Jet Propulsion Laboratory, takes
a goal-based control approach. In this paper, a method for
converting goal network control programs into linear hybrid
systems is developed. The linear hybrid system can then be
verified for safety in the presence of failures using existing
symbolic model checkers. An example task is simulated in
MDS and successfully verified using HyTech, a symbolic model
checking software for linear hybrid systems
DNA nano-mechanics: how proteins deform the double helix
It is a standard exercise in mechanical engineering to infer the external
forces and torques on a body from its static shape and known elastic
properties. Here we apply this kind of analysis to distorted double-helical DNA
in complexes with proteins. We extract the local mean forces and torques acting
on each base-pair of bound DNA from high-resolution complex structures. Our
method relies on known elastic potentials and a careful choice of coordinates
of the well-established rigid base-pair model of DNA. The results are robust
with respect to parameter and conformation uncertainty. They reveal the complex
nano-mechanical patterns of interaction between proteins and DNA. Being
non-trivially and non-locally related to observed DNA conformations, base-pair
forces and torques provide a new view on DNA-protein binding that complements
structural analysis.Comment: accepted for publication in JCP; some minor changes in response to
review 18 pages, 5 figure + supplement: 4 pages, 3 figure
A new approach to teaching feedback
The Control and Dynamical Systems (CDS) Department at the California Institute of Technology (Caltech) has revised its entry-level curriculum in dynamics, feedback, and control with the goals of updating the subject matter to include modern tools and making control tools accessible to a nontraditional audience. One of the approaches made was to divide the introductory control theory class into two tracks, with a conceptual track geared toward students who need only a conceptual overview of control tools and an analytical track providing a more detailed mathematical treatment of feedback. The conceptual track, CDS 101, which is mainly discussed in the paper, is intended for advanced students in science and engineering who can benefit from an overview of control techniques but who might not have the need for the mathematical depth underlying the material. Special attention is paid to ensuring that the course is accessible to students from biological, physical, and information sciences, using examples from these domains to illustrate concepts. The goal of the course is to enable students to use the principles and tools of feedback in their research activities
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