Property:Abstract
From Murray Wiki
Jump to navigationJump to search
This is a property of type Text.
T
This paper gives a survey of current and emerging techniques for motion control of
nonlinear mechanical systems, motivated by applications in robotic locomotion. For this
class of systems, internal changes of shape and/or application of body fixed forces are
the mechanism by which the robot mov es in its environment and the geometric mechanical
properties of the system are crucial in understanding how specific gaits for generating
motion can be obtained. +
G
This paper gives a survey of some recent results on control of systems with magnitude
and rate limits, motivated by problems in real-time trajectory generation and tracking for
unmanned aerial vehicles. Two problems are considered: stabilization using ``nonlinear
wrappers'' to rescale a given control law and real-time trajectory generation using
differential flatness. For both problems, simplified versions of the general problem are
studied using tools from differential geometry and nonlinear control to give insights into
the limitations imposed by magnitude and rate limits and provide insights into
constructive solutions to the trajectory generation and tracking problems. +
U
This paper introduces a new computationally
inexpensive approach to perception and modeling of the
environment that allows fusion of sensory range data of
various types and fidelities while explicitly taking into account
a complete description of uncertainty of the range measurements.
This approach makes use of known sensor uncertainty
models to create a single 2.5D digital elevation map whose
accuracy is robust to sensor noise and spurious data. This
approach is particularly suitable for real-time application in
high speed and highly unstructured outdoor environments
for which reasonably accurate and timely vehicle state estimates
are available. Experimental results are presented in
which LADAR range measurements and state estimates are
combined according to this approach. We provide qualitative
comparison to other classes of environment modeling. +
O
This paper introduces the concept of outer flatness,
a derivative of differential flatness.
Outer flatness describes a
system that can be split
in 2 subsytems, a non-flat inner system and a flat outer system.
The outputs of the outer system are the tracking outputs of interest.
The inputs of the outer system are the outputs of the inner system,
and not subject to our direct control.
The inputs of the inner system are the real actuator inputs.
This system structure is also present in backstepping and dynamic
inversion.
We present two theorems on exponential and bounded tracking for
outer flat systems, based on Lyapunoff arguments.
We validate the approach with simulations and experiments
on a model helicopter.
<p> +
S
This paper investigates the results of distributing the delay of a single feedback system. To distribute the delayed feedback, the single delay is replaced by the sum of two distinct delays with the same effective delay. The statistical properties of the new distribution function in the feedback, namely the sum of two delta functions, are used to quantify the effectiveness of delay distribution. We show that the distribution is effective in reducing the magnitude of the open loop transfer function, thereby, decreasing the gain-crossover frequency and improving the phase margin. Finally, inspired by Orosz et al., we demonstrate an example of how these results can be used to design a controller using delays. +
This paper investigates the stability of linear systems with stochastic delay in discrete time. Stability of the mean and second moment of the non-deterministic system is determined by a set of deterministic discrete time equations with distributed delay. A theorem is provided that guarantees convergence of the state with convergence of the second moment, assuming the delays are identically independently distributed. The theorems are applied to a scalar equation where the stability of the equilibrium is determined. +
R
This paper investigates the use of efficient computational algorithms for the
computation of a nominal trajectory for fast transition between flight modes. We use
differential flatness of an approximate model of the longitudinal dynamics of a thrust
vectored aircraft to achieve fast switching between flight modes. We investigate some
methods to compensate for the discrepancy between the full aerodynamic model and the
approximate flat model, and analyze their performance. Simulations and experimental data
for a thrust vectored flight control experiment at Caltech are provided to validate the
approach. +
This paper is a very brief outline of an invited poster session giving a
first-year progress report on a research program with the above title being
carried out in the Control and Dynamical Systems (CDS) department at Caltech.
This 5-year grant funded by the AFOSR Partnership for Research Excellence
Transition (PRET) Program has a special emphasis on transitioning new methods
to industrial practice and thus involves a high level of industrial
participation. The focus of our program is fundamental research in general
methods of analysis and design of complex uncertain nonlinear systems, from
creating new mathematical theory to working to make that theory help engineers
solve a variety of real industrial problems. Caltech's Control and Dynamical
Systems department was created with precisely this goal, which is shared by our
industrial collaborators, led by Honeywell. Further details will be available
at the poster session. +
O
This paper is concerned with the distributed averaging problem subject to a quantization constraint. Given a group of agents associated with scalar numbers, it is assumed that each pair of agents can communicate with each other with a prescribed probability, and that the data being exchanged between them is quantized. In this part of the paper, it is proved that the stochastic gossip algorithm proposed in a recent paper leads to reaching the quantized consensus. Some important properties of the system in the steady-state (after reaching the consensus) are also derived. The results developed here hold true for any arbitrary quantization, provided the tuning parameter of the gossip algorithm is chosen properly. The expected value of the convergence time bounded in the second part of the paper. +
Q
This paper is concerned with the distributed averaging problem over a given undirected graph. To enable every vertex to compute the average of the initial numbers sitting on the vertices of the graph, the policy is to pick an edge at random and update the values on its ending vertices based on some rules, but only in terms of the quantized data being exchanged between them. Our recent paper showed that the quantized consensus is reached under a simple updating protocol which deploys a fixed tuning factor. The current paper allows the tuning factor to be time-dependent in order to achieve two goals. First, this makes it possible to study the numerical stability of the protocol with a fixed tuning factor under a small perturbation of this parameter. Furthermore, exploiting a time-varying tuning factor facilitates the implementation of the consensus protocol and pushes the steady state of the system towards an equilibrium point, as opposed to making it oscillatory. The current paper is an important extension of our recent work, which generalizes a finite-dimensional problem toan infinite-dimensional one that is more challenging in nature. +
T
This paper presents a general framework for the control of mechanical
systems with as many inputs as degrees of freedom. The notes of error
functions and transport map are introduced to properly define a configuration
and velocity error. These are the crucial ingredients in designing a
proportional derivative feedback and feedforward control. The proposed
approach includes various results on control of manipulators, autonomous
vehicles and pointing devices. +
A
This paper presents a mathematical model for a synthetic transcriptional regulatory network in vitro. This circuit design resembles one of the well-known network motifs, the inco- herent feed-forward loop, in which an activator regulates both a gene and a repressor of the gene. Through mathematical analysis, we show how the circuit can be controlled to demonstrate exact adaptation to input signals. +
C
This paper presents a method for optimal trajectory generation for discrete-time nonlinear systems with linear temporal logic (LTL) task specifications. Our approach is based on recent advances in stochastic optimization algorithms for optimal trajectory generation. These methods rely on estimation of the rare event of sampling optimal trajectories, which is achieved by incrementally improving a sampling distribution so as to minimize the cross-entropy. A key component of these stochastic optimization algorithms is determining whether or not a trajectory is collision-free. We generalize this collision checking to e�ciently verify whether or not a trajectory satisfies a LTL formula. Interestingly, this verification can be done in time polynomial in the length of the LTL formula and the trajectory. We also propose a method for e�ciently re-using parts of trajectories that only partially satisfy the specification, instead of simply discarding the entire sample. Our approach is demonstrated through numerical experiments involving Dubins car and a generic point-mass model subject to complex temporal logic task specifications. +
S
Synthesis of Control Protocols for Switched Electrical Power Systems for Commercial Applications with Safety Specifications +
This paper presents a method for synthesizing fault tolerant control protocols for a deterministic discrete event system subject to safety specifications. The system discussed in the paper is modeled as a finite state machine (FSM) and Behavior Tree (BT). The synthesis procedure involves formulating the policy problem as a shortest path dynamic programming problem, and performing a backward search from the desire sates or behavior to the initial configuration. The search is performed over all possible states when applied to the FSM, or over all possible actions when applied to the BT. The resulting strategy minimizes the number of actions performed to meet operational objectives without violating safety conditions. The effectiveness of the procedure on FSMs and BTs is demonstrated through three examples of switched electrical power systems for commercial applications. +
This paper presents a new singular perturbation approach for analysing
flexibility in manipulators. This approach does not treat the flexible
manipulator as a perturbation of the rigid manipulator, and therefore,
allows for significant amounts of flexibility (beyond the linear
range). Analysis based on this approach leads to some provably stable
control schemes for the position and force control of flexible-link
manipulators. Simulation results are presented for a single flexible
manipulator pushing against a wall. +
R
This paper presents a survey of recent research in cooperative control of multivehicle systems, using a common mathematical framework to allow different methods to be described in a unified way. The survey has three primary parts: an overview of current applications of cooperative control, a summary of some of the key technical approaches that have been explored, and a description of some possible future directions for research. Specific technical areas that are discussed include formation control, cooperative tasking, spatiotemporal planning, and consensus. +
D
Dynamic Separation Control in a Low-Speed Asymmetric Diffuser with Varying Downstream Boundary Condition +
This paper presents an experimental investigation
into the effect of a varying downstream boundary
condition on dynamic separation control in a twodimensional
low-speed asymmetric diffuser. The potential
for coupling between the downstream boundary
condition and the separation dynamics is relevant,
for example, in using separation control to enable
more aggressive serpentine aircraft inlets, where
the compressor may be close to the separation point.
Separation control in the experiment is obtained using
spanwise unsteady forcing from a single tangential
actuator located directly upstream of the separation
point. The downstream boundary condition
simulates the dominant quasi-steady and reflection
characteristics of a compressor. Although the
boundary condition affects the uncontrolled pressure
recovery, the optimal forcing frequency is shown to
depend only on the mass flow rate and not on either
the presence, impedance, or location of the downstream
boundary condition. At the conditions tested
herein, we therefore conclude that the mechanism
underlying dynamic separation control is local in nature,
and is not influenced by global system dynamics. +
E
Experimental Evaluation of Air Injection for Actuation of Rotating Stall in a Low Speed, Axial Fan +
This paper presents an experimental investigation of the effects of
air injection on the rotating stall instability in a low speed axial
compressor. Two experiments concerning air injection were tried. The
first experiment used a continuous forcing perpendicular to the flow
in the same or opposite direction of the tip velocity. The results
show a dramatic difference between the two directions, with opposite
direction forcing causing a significant increase in performance, and
same direction forcing causing a significant decrease in performance.
This result contradicts the Emmons stall propagation model. The
second experiment investigated the differences with respect to
different frequencies of air injection, with the injector pointed at
the fan, parallel to the flow. We found that the change in the
compressor characteristic in the unstalled region was highly dependent
upon the forcing frequency with the maximum change occurring near the
frequency of stall. +
A
This paper presents an optimization framework for broadcast power-control, specifically addressed
at wireless networking issues arising in implementing information flows for multi-vehicle
systems. We formulate an optimization problem for the minimization of an aggregate cost subject
to a constraint on a quantity we call the geometric connection robustness, which is a locally
computable numerical assessment of the robustness of the an information flow to perturbations
in position. Our main result is a location-aided distributed power-control algorithm based on
a gradient-like optimization scheme. We also use geometric connection robustness to develop a
cheap distributed heuristic for the construction of sparse connected information flow. +
Active Control of Rotating Stall Using Pulsed Air Injection: A Parametric Study on a Low-Speed, Axial Flow Compressor +
This paper presents preliminary results on the use of low flow, high
momentum, pulsed air injectors to control the onset of stall in a
low-speed, axial flow compressor. By measuring the unsteady pressures
in front of the rotor, the controller determines the magnitude and
phase of a stall cell and controls the injection of air in front of
the rotor face. Initial experimental results have verified that
controller slightly extends the stall point of the compressor and
virtually eliminates the hysteresis loop normally associated with
stall. An explanation of this effect is proposed based on the
quasi-steady effects of air injection on the compressor characteristic
curve. +
