Showing papers by "Richard H. Middleton published in 2006"

Output feedback stabilisation over bandwidth limited, signal to noise ratio constrained communication channels

Abstract: Stabilisability of an open loop unstable plant is studied under the presence of a bandwidth limited additive coloured noise communication channel with constrained signal to noise ratio. The problem is addressed through the use of an LTI filter explicitly modelling the bandwidth limitation, and another LTI filter to model the additive coloured noise. Results in this paper show that a bandwidth limitation increases the minimum value of signal to noise ratio required for stabilisability, in comparison to the infinite bandwidth, white noise case. Examples are used to illustrate the results in the continuous and discrete framework.

The minimal signal-to-noise ratio required to stabilize over a noisy channel

Abstract: We consider the problem of stabilizing a discrete-time plant over a noisy channel that is subject to a signal-to-noise ratio (SNR) constraint. It has previously been shown that a necessary condition for stabilization with linear time-invariant state feedback is that the SNR satisfy a lower bound whose value depends solely upon the unstable plant poles. The same lower bound is also necessary for stabilization using linear time invariant output feedback for a minimum phase plant with relative degree one. Following Nair and Evans, we use the concept of entropy power to show that the same bound is also necessary when nonlinear time-varying control laws are applied. Another previous result is that the aforementioned bound on the SNR is also sufficient for stabilization. We apply the concept of entropy rate to provide an alternate proof of this result that also demonstrates an intimate connection between the discrete Bode sensitivity integral and the problem of disturbance-free estimation.

Rolling Shutter Image Compensation

Abstract: This paper describes corrections to image distortion found on the Sony AIBO ERS-7 robots. When obtaining an image the camera captures each pixel in series, that is there is effectively a 'rolling shutter'. This results in a delay between the capture of the first and last pixel. When combined with movement of the camera the image produced will be distorted. The sensor values from the robot, coupled with knowledge of the camera's timing, are used to calculate the effect of the robots movement on the image. This information can then be used to remove much of the distortion from the image. The correction improves the effectiveness of shape recognition and bearing-to-object accuracy.

Fundamental limitations in self-sensing magnetic bearings when modeled as linear periodic systems

Abstract: In "Magnetic bearing measurement configurations and associated robustness and performance limitations", Thibeault and Smith demonstrate that self-sensing magnetic bearings are impractical due to fundamental limitations in the achievable closed-loop robustness. Due to experimental data which appeared to contradict these results, Maslen, Montie, and Iwasaki showed that significantly better robustness is achievable in "Robustness limitations in self-sensing magnetic bearings" if the magnetic bearing is modeled as a linear periodic (LP) system rather than the linear time invariant (LTI) system used by Thibeault and Smith. The present paper explores why modeling the self-sensing magnetic bearing as a LP system improves the achievable robustness. This is accomplished by utilizing lifting to analyze the LP model as a MIMO discrete LTI system.

Optimal Signal to Noise Ratio in Feedback over Communication Channels with Memory

Abstract: Communication channels impose a number of obstacles to feedback control, such as delay, noise, and constraints in communication data-rate. One alternate line of recent work considers the problem of feedback stabilization subject to a constraint in the signal-to-noise ratio (SNR). It has been shown for continuous-time systems that the optimal control problem arising in achieving minimal SNR can be formulated as a linear quadratic Gaussian (LQG) control problem with weights chosen as in the loop transfer recovery (LTR) technique. The present paper extends such LQG/LTR formulation to discrete-time systems with feedback over channels with memory. By using such formulation, we derive exact expressions for the LTI controller and loop sensitivity functions that achieve minimal SNR under the effect of time-delay, non minimum phase zeros and colored additive noise. For the minimum-phase case with white noise and no time delay, we show that the optimal feedback loop obtained after applying LTR has a structure equivalent to that of a communication channel with feedback from the output to the input.

On Limitations to the Achievable Path Tracking Performance for Linear Multivariable Plants

Abstract: In this paper we consider a problem termed "path tracking". This differs from the common problem of reference tracking, in that here we can adjust the speed at which we traverse the reference trajectory. We are interested in ascertaining the degree to which we can track a given trajectory, and in characterizing the class of paths for which we can generate an appropriate temporal specification so that the path can be tracked arbitrarily well in an L2 sense.

Proposal of a kit-style robot as the new standard platform for the four-legged league

Abstract: In 2006 the Sony Corporation announced that production of the Aibo robot, which is the standard robot platform of the four-legged league of RoboCup, would be discontinued. This paper describes a prototype robot kit which could lead to a new standard platform for the four-legged league. The aims for development of the new platform can be summarized as follows: 1.) Continue and improve the concepts behind the Sony Aibo robot. 2.) Allow research into sophisticated quadruped soccer skills. 3.) Build an open systems robot to advance low level features and to support high level strategy planning and learning. 4.) Achieve faster and more exciting soccer games. 5.) Contribute to progress of the four-legged league, which to date has been a very successful league. 6.) Determine kit style hardware for year to year upgrades of selected modules. The robot kit allows for substantial new flexibility in hardware design in associated scientific challenges and research projects. The present paper addresses two possible versions of the proposed kit: terrier and bear.

Fairness and Convergence Results for Additive-Increase Multiplicative-Decrease Multiple-Bottleneck Networks

Abstract: We examine the behavior of the Additive-Increase Multiplicative-Decrease (AIMD) congestion control algorithm. We present a variant of a recently proposed matrix model that allows us to obtain previous results for competition via a single bottleneck link. We then extend these results to the case of multiple bottleneck links paying particular attention to some aspects of fairness and convergence properties for multiple bottleneck systems. We examine both the synchronous (deterministic) and asynchronous (stochastic) cases. A simple simulation example illustrates the results.

Feedback Medicine: Control Systems Concepts in Personalised, Predictive Medicine and Combinatorial Intervention

Abstract: In its broadest definition, systems biology is the application of a `systems' way of thinking about and doing cell biology. By implication, this also invites us to consider a systems approach in the context of medicine and the treatment of disease. In particular, the idea that systems biology can form the basis of a personalised, predictive medicine will require that much closer attention is paid to the analytic properties of the feedback loops which will be set up by a personalised approach to healthcare. To emphasize the role that feedback theory will play in understanding personalised medicine, we use the term feedback medicine to describe the issues this http URL these notes we consider feedback and control systems concepts applied to two important themes in medical systems biology - personalised medicine and combinatorial intervention. In particular, we formulate a feedback control interpretation for the administration of medicine, and relate them to various forms of medical treatment.