Papers by Prabhakar Pagilla
Control Engineering Practice, Aug 1, 2015
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IFAC Proceedings Volumes, 2014
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A computer program for conducting model simulations for zero speed splice unwinds is described in... more A computer program for conducting model simulations for zero speed splice unwinds is described in this paper. A typical unwind system consisting of the unwinding material roll, festoon, dancer, and pull rolls is considered. The developed computer model is general enough to be applicable to a variety of unwinds containing these components. The paper also provides a procedure for determining zero speed splicing parameters when the characteristics of the festoon and the splicer, such as number of carriage rollers, festoon capacity, clamp and dwell time, etc., are given; this method can be employed for the selection of splicing parameters, such as acceleration and deceleration profiles, splice diameter, spindle speed profiles, etc. The computer model can predict the transport behavior of webs through the unwinds; this was verified by comparing data from model simulations and experiments on a production unwind. The computer program can be used to evaluate different scenarios of unwind op...
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2021 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM), 2021
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2021 60th IEEE Conference on Decision and Control (CDC), 2021
We describe a novel path following pose control framework for articulated robots which is needed ... more We describe a novel path following pose control framework for articulated robots which is needed for many material handling and surface finishing where constant speed travel is desirable. Using a rotation minimizing frame (RMF) associated with the geometric path, we develop a path following position control law by projecting the robot translation states onto the RMF and based on an analytical description of the reference orientation dynamics of the RMF, we derive a stabilizing controller for orientation control along the path with the Modified Rodrigues parameters to avoid the unwinding problem encountered when rotations of more than 180 degrees are encountered. The effectiveness of the proposed path following framework is verified via simulations on a torque actuated KUKA iiwa robot using a physics-based simulation engine called Bullet.
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2018 IEEE International Conference on Systems, Man, and Cybernetics (SMC), 2018
Combining the benefits of robust situational awareness of human operators with the efficiency and... more Combining the benefits of robust situational awareness of human operators with the efficiency and precision of automatic control has been an important topic of human-machine shared control. The emphasis is on keeping human operators in the loop while automatic control providing assistance to improve task performance. Given a task with specific subgoals, execution of a task using blended shared control involves predicting the operator’s intent of subgoal transitions and deciding the blending weights for inputs from the human operator and automatic control. In this paper we address the problem of subgoal adjustment in blended shared control which is typically initiated by the operator’s intent and necessary to sustain the shared control performance for changing subgoal conditions. First, we provide a method to predict operator’s intent of visiting a subgoal. Based on intent prediction, we propose a method for subgoal adjustment where the adjustment is encoded by a hyperrectangle. The volume of the hyper-rectangle is obtained by using a hyperbolic slope transition function which is based on the distance between subgoals. The adjustment actions within the hyper-rectangle are facilitated by a skill-weighted action integral that takes into consideration the skill level of the operator. The approach is tested on a scaled hydraulic excavator platform with multiple novice operators and a skilled operator. Experimental results are presented and discussed.
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2017 American Control Conference (ACC), 2017
In this paper, we consider the problem of determining optimal configurations of Roll-to-Roll (R2R... more 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.
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IFAC-PapersOnLine, 2020
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2020 American Control Conference (ACC), 2020
In this paper we describe a novel path following scheme for robot end-effectors that is particula... more In this paper we describe a novel path following scheme for robot end-effectors that is particularly suitable for robotic surface finishing operations where constant velocity of travel on the surface is desirable. The scheme is applicable to general situations where the path is typically given in terms of measured data from a sensor, and also to paths that are specified in terms of analytical curves (circular or ellipsoidal). Considering the given data points as control points, we utilize cubic spline interpolation to generate a closed-form geometric description for the path. Since velocity control is quite common in many industrial robots and most surface finishing tasks require travel with constant velocity along the path, we consider a kinematic model for the end-effector with control inputs as rate of change of orientation and translational velocity. By utilizing a path variable and the tangent vector along the path, we describe the complete path as the path that is taken from the initial robot end-effector point to the desired path and subsequent travel on the desired path. To evaluate the performance of the scheme, we have conducted a number of real-time experiments on an industrial robot for circular paths and for paths generated for gear deburring and chamfering, and results from those experiments will be discussed.
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IFAC-PapersOnLine, 2020
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Journal of Manufacturing Science and Engineering, 2020
Smart manufacturing concepts are being integrated into all areas of manufacturing industries, fro... more Smart manufacturing concepts are being integrated into all areas of manufacturing industries, from the device level (e.g., intelligent sensors) to the efficient coordination of business units. Vital components of any manufacturing enterprise are the processes that transform raw materials into components, assemblies, and finally products. It is the manufacturing process where smart manufacturing is poised to make substantial impact through process control, i.e., the intelligent manipulation of process variables to increase operation productivity and part quality. This article discusses three areas of manufacturing process control: control-oriented modeling, sensing and monitoring, and the design and construction of controllers. The discussion will center around the following manufacturing processes: machining, grinding, forming, joining, and additive. While many other important processes exist, the discussions of control of these mechanical manufacturing processes will form a framewo...
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Robotics and Computer-Integrated Manufacturing, 2021
Abstract This paper describes a novel method for robotic gear chamfering called dual-edge chamfer... more Abstract This paper describes a novel method for robotic gear chamfering called dual-edge chamfering which can facilitate simultaneous chamfering of the two edges of adjacent gear teeth and overcome typical registration errors arising due to the placement of the workpiece in the robot workspace. Deviations of the robot end-effector trajectory when compared to the nominal trajectory due to registration errors are discussed first; such trajectory deviations caused by typical registration errors due to gear center translation and rotation are quantified. Dual-edge chamfering process is described and an efficient trajectory design strategy is developed by considering the kinematic constraints imposed by the profiles of the gear edge and the abrasive tool. The dual-edge chamfering robot trajectory is facilitated by a simple procedure for identifying the gear and gear root centers by employing the robot. To execute the dual-edge chamfering trajectory, an efficient motion/force control strategy that includes active compliance from the tool mounted on the robot is proposed. A number of real-time experiments are conducted to evaluate the proposed method by employing a commercial six degree-of-freedom robot. Two types of large cylindrical metal gears are utilized for testing, an external gear with teeth on the outside and an internal gear with teeth on the inside. In addition to these, two different robotic compliant tools with axial and radial compliance are tested. A representative sample of the experimental results are presented and discussed.
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IEEE Transactions on Intelligent Transportation Systems, 2018
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IFAC Proceedings Volumes, 2004
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Journal of Dynamic Systems, Measurement, and Control, 2017
In this paper, we study vehicle formations employing ring-structured communication strategies and... more In this paper, we study vehicle formations employing ring-structured communication strategies and propose a combinatorial approach for developing ring graphs for vehicle formations. In vehicle platoons, a ring graph is formed when each vehicle receives information from its predecessor, and the lead vehicle receives information from the last vehicle, thus forming a ring in its basic form. In such basic form, the communication distance between the first and the last vehicle increases with the platoon size, which creates implementation issues due to sensing range limitations. If one were to employ a communication protocol such as the token ring protocol, the delay in updating information and communication arises from the need for the token to travel across the entire graph. To overcome this limitation, alternative ring graphs which are formed by smaller communication distances between vehicles are proposed in this paper. For a given formation and a constraint on the maximum communicati...
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2016 IEEE 55th Conference on Decision and Control (CDC), 2016
We propose a new shared control technique that takes into account the operator's intent to qu... more We propose a new shared control technique that takes into account the operator's 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 operator's 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 Zermelo's 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.
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ISA Transactions, 2016
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Volume 3: Multiagent Network Systems; Natural Gas and Heat Exchangers; Path Planning and Motion Control; Powertrain Systems; Rehab Robotics; Robot Manipulators; Rollover Prevention (AVS); Sensors and Actuators; Time Delay Systems; Tracking Control Systems; Uncertain Systems and Robustness; Unmann..., 2015
In this paper, we focus on the problem of controlling the load speed of a mechanical transmission... more In this paper, we focus on the problem of controlling the load speed of a mechanical transmission system consisting of a belt-pulley and a gear-pair. We consider two inertias (motor and load) system connected by a compliant transmission. Because of the transmission dynamics, regulation of motor shaft speed may not translate to regulation of load speed. Further, determination of whether to use of motor speed or load speed feedback or a combination of both that would facilitate control of load speed is of importance. In this paper we investigate both the motor and load speed feedback options by considering transmission compliance and utilizing the singular perturbation method. We propose a two degree of freedom control system that utilizes both motor and load speed feedback and an adaptive feedforward scheme to reject torque disturbances on the load. Experiments conducted on a typical industrial transmission system that is commonly employed in roll-to-roll manufacturing are discussed,. A representation sample of the experimental results are presented and discussed.Copyright © 2015 by ASME
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Proceedings of the 48h IEEE Conference on Decision and Control (CDC) held jointly with 2009 28th Chinese Control Conference, 2009
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Papers by Prabhakar Pagilla