Prabhakar R. Pagilla

Intent aware shared control in off-nominal situations

We propose a new shared control technique that takes into account the operators intent to quickly relinquish control to the operator in off-nominal conditions. Human-machine shared control is an emerging area of research in which the autonomous control is utilized to augment the operators performance. Existing work has established that shared control can improve cycle times in nominal conditions, that is, when the operating environment satisfies the assumptions made in the design of the optimal augmenting controller. However, these methods can be too slow to relinquish control in off-nominal cases, when the operator needs to deviate from the nominally optimal trajectory due to unforeseen obstacles or other uncertainties. In this paper, we attempt to address this gap by mathematically quantifying operator intent. The resulting technique provides autonomous control augmentation to the operator when they are attempting to drive the system along the suggested optimal trajectory, but offers little hindrance to the operator when they are attempting to deal with off-nominal conditions. Theoretical results show that the performance of the presented intent aware shared control technique is at least as good as existing techniques, and that it results in improved obstacle reaction time. Human interaction experiments on the Zermelos navigation problem in the presence of a random pop-up obstacle show a significant reduction in obstacle collision with our method when compared to existing work.

Optimal velocity profile design for transport of viscoelastic webs in roll-to-roll manufacturing

In this paper, we consider the problem of optimal velocity profile design to minimize transverse vibrations (web flutter) for moving viscoelastic webs. The web is modeled as a membrane considering the viscoelastic behavior of web materials. Governing equations for the in-plane and out-of-plane motions are derived using extended Hamiltons principle and the Galerkin method is employed to obtain numerical solutions for the equations of motion. An optimal control problem is utilized to obtain the desired web velocity profile that minimizes the transverse vibration energy. Numerical simulation results of the approach show that the new velocity profile achieves suppression of transverse vibrations. The proposed velocity profile is compared with the conventional velocity profile which is implemented in many industrial roll-to-roll machines. Comparative results are presented and discussed in the paper in addition to the development of governing equations of motion for viscoelastic webs.

Design of a model-based observer for estimation of steel strip tension in continuous galvanizing/annealing lines

Continuous Galvanizing Lines (CGL) and Continuous Annealing Lines (CAL) are productive manufacturing machines used by steel making companies for the manufacture of thin steel sheet products. In these lines, an annealing furnace is employed to continuously heat and cool a moving steel strip to impart certain mechanical properties to the strip. Although rotational speeds of driven rollers in the furnace are measured, tension measurement is spatially intermittent and located between any two heat transfer sections because of the inability to reliablymeasure tension within each heat transfer section due to harsh conditions.We consider a dynamicmodel of the strip transport behavior consisting of nonlinear governing equations for strip tension and speed. Since strip strain and elastic modulus are functions of the moving strip temperature distribution, the dynamic model contains temperature-dependent parameters. Based on this dynamic model, we design an adaptive nonlinear observer to estimate span tensions within each heating/cooling section. First, we design an observer for estimating strip tension in a single span assuming measurement of tension in adjacent spans using Lyapunovs second method. Then, we extend this to the multiple span case for each heating or cooling section by assuming measurement of tension in the entry and exit spans of the section. In both cases we show stable convergence of the tension observation error to zero and provide conditions on the observer gains. To illustrate the effectiveness of the proposed observer, we present numerical simulation results for a four span case with values for system parameters and reference of transport variables that mimic industrial CGL/CAL.

Spatially Dependent Transfer Functions for Web Lateral Dynamics in Roll-to-Roll Manufacturing

In this paper we derive spatially dependent transfer functions for web span lateral dynamics which provide web lateral position and slope as outputs at any location in the span; the inputs are guide roller displacement, web lateral position disturbances from upstream spans, and disturbances due to misaligned rollers. This is in sharp contrast to the existing approach where only web lateral position response is available on the rollers. We describe the inherent drawbacks of the existing approach and how the new approach overcomes them. The new approach relies on taking the 1D Laplace transform with respect to the temporal variable of both the web governing equation and the boundary conditions. One can also obtain the web slope at any location within the web span with the proposed approach. A general span lateral transfer function, which is an explicit function of the spatial position along the span, is obtained first followed by its application to different intermediate guide configurations.

Effects of V2V communication on time headway for autonomous vehicles

In this paper, we investigate the benefits of Vehicle-to-Vehicle (V2V) communication for autonomous vehicles employing a Constant Time Headway Policy (CTHP). It is known that ACC equipped vehicles employing a CTHP must maintain a time headway that is lower bounded by 2τ<inf>0</inf> for string stability, where τ<inf>0</inf> is the maximum value of parasitic actuation lag. We show the following: (1) if acceleration of preceding vehicle (obtained via V2V communication) were also to be used, then the minimum employable time headway can be reduced to τ<inf>0</inf> (2) if the position and velocity information of r immediately preceding vehicles ahead were to be used, then the minimum employable time headway can be reduced to 4τ<inf>0</inf>/(1 + r); and (3) furthermore, if the acceleration of ‘r’ immediately preceding vehicle is used, then the minimum employable headway can be reduced to 2τ<inf>0</inf>/(1 + r).

Optimal configurations to minimize disturbance propagation in manufacturing networks

In this paper, we consider the problem of determining optimal configurations of Roll-to-Roll (R2R) process machines which consist of many interconnected dynamic elements to transport flexible materials (webs) on rollers. The problem is to optimally locate the controlled dynamic elements within the R2R machine so as to minimize the effect of disturbances propagated by the transported web. Typical disturbances on R2R machines include misalignment and out-of-roundness of rollers which cause web wrinkles and registration errors if unattenuated. The central contribution of this paper is to pose the combinatorial problem of determining the optimal configuration for a R2R machine as a Mixed-Integer Semi-Definite Program (MISDP) and provide an algorithm to efficiently compute feasible configurations and bounds on their sub-optimality. The proposed algorithm is based on tools such as McCormick relaxations, outer-approximation via eigenvalue cuts, and bound tightening procedures. We provide numerical results for representative R2R systems to show the efficiency of the proposed algorithm.

Reconfiguration of a vehicle formation with ring communication structure

In multiple vehicle formations, there is often a need to reconfigure communication graphs to accommodate (1) for addition or removal of vehicles or (2) for change in positions of the vehicles within a given formation. This problem is commonly referred to as the topology or graph reconfiguration problem. In this paper, we will study the reconfiguration problem from the point of view of increasing the size of the formation. We first discuss the suitability of the ring structure to add vehicles into the formation followed by ways to reconfigure the communication structure when adding vehicles. We will show that the directed ring graph is well suited for adding vehicles from the point of view of scalability of the existing controller and the ease with which the existing ring structure will be able to handle the increase in the formation size. The algorithm for obtaining the ring structure is formulated as a specific instance of the Traveling Salesman Problem, where constraints may be included to model the communication sensing range; in addition, we use the nearest neighbor search to include new vehicles into the perimeter of the formation.

A governing equation for moving web temperature heated by radiative panels

In this paper we consider modeling of temperature distribution in moving webs due to heating by radiation panels. We develop a web heat transfer model by considering radiation from the heating panels and convection on the surface of moving webs. We address the issue of convection coefficient changes with web temperature. Using this model, one can predict the web temperature in the moving web at different speeds. The model development and analysis is dimensionless, so it can be applicable to a variety of web materials and heating panel locations. The modeling is motivated by R2R ALD/MLD application and an experimental platform designed to conduct ALD/MLD is employed to validate the model for different scenarios. Comparative results from experiments and model simulations for varying speeds and different operating conditions are provided to validate the model.