Showing papers by "Sumeet S. Aphale published in 2016"

Butterworth Pattern-based Simultaneous Damping and Tracking Controller Designs for Nanopositioning Systems

Abstract: The Butterworth filter is known to have maximally flat response. Incidentally, the same response is desired in precise positioning systems. This paper presents a method for obtaining a closed-loop Butterworth filter pattern using common control schemes for positioning applications, i.e. Integral Resonant Control (IRC), Integral Force Feedback (IFF), Positive Position Feedback (PPF), and Positive Velocity and Position Feedback (PVPF). Simulations show a significant increase in bandwidth over traditional design methods and verify the desired pole placement is achieved. The simulations also show a significant limitation of the achievable bandwidth in the case of IRC, IFF, and PPF. For this reason, only PVPF is considered in experimental analysis. Experiments are performed using a two-axis serial kinematic nanopositioning stage. The results show a significant improvement in bandwidth and increased positioning accuracy, specifically at the turn-around point. This allows a greater portion of the scan to be used and improved positioning accuracy at high scanning speeds.

Severity Analysis of Stick-slip Bifurcation in Drill-string Dynamics under Parameter Variation

Abstract: Bifurcations are an interesting class of dynamic behavior exhibited by many nonlinear systems. Drill string typically employed in underground oil exploration are highly nonlinear systems whose dynamic behavior has generated huge research interest. Though it is well-known that typical drill-strings behave like piecewise smooth systems and the severity of bifurcations they exhibit has not been studied in depth. In this work, a two degree of freedom (2-DOF) model of the drill-string is constructed and its dynamic behavior. In-depth analysis of the effect of parameter variation on the severity of bifurcations is conducted. This can potentially deliver key insights in the design of control strategies aimed at suppressing problematic stick-slip oscillation.

A control system to control precision positioning arrangements

Abstract: The present invention relates to a control system to control precision positioning arrangements, such as disk drives, robotic manipulators, micro-grippers, nanopositioners and the like. The control system comprises an input; an output to control the precision positioning arrangement: and a controller having a control loop operating a tracking stage, a control loop operating a pre-filter stage; and a control loop operating a regulator stage.

A parametric study of positive-feedback pole-placement damping controllers for second-order resonant systems

Abstract: A vast number of technological systems exhibit dynamics similar to a second-order system with a lightly damped resonance mode. A number of closed-loop control strategies have been proposed in the past to damp this resonance mode. Positive-feedback controllers based on the pole-placement technique have emerged as a group of wellperforming, and hence, popular damping controllers in a multitude of applications. Yet, their design is based mostly on trial-and-error, where closed-loop poles are arbitrarily placed away from thejω axis and further into the left-half complex plane resulting in increased damping. In this paper, a full parametric study of the Positive Position and Velocity Feedback (PVPF) is carried out. This leads to two distinct design strategies pertaining to applications in which only damping is required, and those which require both damping and tracking. One axis of a serial-kinematic nanopositioner is used as a representative second-order system with a lightly damped resonance mode to test the performance of the proposed PVPF controllers.

Effect of Feed-through Term and the Synthesis of Multi-mode Integral Resonant Control

Abstract: Most damping controller designs are based on, and aimed at, damping the first dominant resonant mode of the targeted system. The higher-order dynamics of these systems are left unmodeled and an adequate feed-through term is generally added to compensate for model truncation effects. The Integral Resonant Control (IRC) exploited this feed-through term to manipulate the dynamics of resonant colocated systems such that a simple integrator delivered adequate damping to the resonant mode. As an added advantage, IRC also imparted damping to other higher-order modes and was guaranteed stable. Nevertheless, this was still a single-mode based design. In this paper, we formalize the effect of the feed-through term on a typical multimode system and present the design and analysis of a true multi-mode IRC.