Papers by Ravinder Venugopal
Advances in industrial control, Dec 13, 2013
In sheet metal forming processes the blank holder force controls the material flow into the die c... more In sheet metal forming processes the blank holder force controls the material flow into the die cavity, which is critical to producing a good part. Process control can be used to adjust the blank holder force in-process based on tracking a reference punch force trajectory to improve part quality and consistency. Key issues in process control include process modeling as well as process controller and reference punch force trajectory design. In this chapter a systematic approach to the design and implementation of a suitable process controller and an optimal reference punch force trajectory is presented. The approach includes the modeling for controller design of the sheet metal forming process, design of the process controller, and determination of the optimal punch force trajectory. Experimental results from U-channel forming on a laboratory forming simulator show that a suitable process controller can be designed through simulation and an optimal reference punch force trajectory can be synthesized through experiments. The proposed development will be useful in designing and implementing process control in sheet metal forming processes as described in subsequent chapters.
With the success of adaptive cancellation methods developed largely within the active noise contr... more With the success of adaptive cancellation methods developed largely within the active noise control community, it is of interest to understand these algorithms within a more traditional feedback control framework. This paper thus has two goals, namely, to systematically describe three such algorithms (two LMS algorithms and the recently developed ARMARKOV/Toeplitz algorithm) in standard feedback control terminology, and to experimentally compare the performance of the algorithms. For experimental purposes, we use an acoustic duct testbed with both tonal and broadband disturbances. 'This research was supported in part by the Air Force Office of Scientific Research under grant F49620-95-1-0019 and the University of Michigan Office of the Vice President for Research.
In 1983 Karplus and Strong proposed a highly success-ful algorithm for digital music synthesis. I... more In 1983 Karplus and Strong proposed a highly success-ful algorithm for digital music synthesis. In this paper we describe this algorithm in terms of a linear trans-fer function. Then we propose several extensions and variations of this transfer function that produce inter- ...
Journal of Dynamic Systems Measurement and Control-transactions of The Asme, Nov 1, 2011
Electrohydraulic servo systems (EHSS) are used for several engineering applications, and in parti... more Electrohydraulic servo systems (EHSS) are used for several engineering applications, and in particular, for efficient handling of heavy loads. These systems are characterized by pronounced nonlinearities and are also subject to parameter variations during operation, friction effects, and variable loads. Several studies have addressed the nonlinear nature of EHSS; however, only a few control schemes explicitly address friction and load disturbance effects along with parameter variations. Fuzzy and/or sliding mode versions of feedback linearizing controllers have been used to compensate for the external loads disturbances in the control of EHSS. However, real-time implementations issues limit the use of these techniques. While adaptive control using a feedback-linearization based controller structure has been shown to be effective in the presence of parameter variations, load and friction effects are typically not considered. In this paper, we present a nonlinear adaptive feedback linearizing position controller for an EHSS, which is robust to parameter uncertainty while achieving load disturbances rejection/attenuation and friction compensation. The adaptation law is derived using a Lyapunov approach. Simulation results using the proposed controller are compared to those using a nonadaptive feedback linearizing controller as well as a proportional-integral-derivative (PID) controller, in the presence of torque load disturbance, friction, and uncertainty in the hydraulic parameters. These results show improved tracking performance with the proposed controller. To address implementation concerns, simulation results with noise effects and valve saturation are also presented.
Due to the character of the original source materials and the nature of batch digitization, quali... more Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references.Recent advances in aviation technology have led to fundamental changes in aircraft flight control systems. The increasing popularity of fly-by-wire systems necessitates an investigation into the design of the interface between the pilot and the flight control computers that drive the actuators of the control surfaces. Maintaining the basic cockpit configuration alleviates problems of transition, however, the control input devices should ensure that the benefits of the new system are well utilized. A control stick that converts pilot control actions into representative electrical signals for input to the on-board computers is a valid choice in this context. This choice presents the design options of either using the force applied on the control stick, or its angular displacement, or both, as bases for the electrical input signals. In this study, a force side-stick and a displacement center-stick are designed and installed on a fixed-base simulator and a preliminary evaluation of both devices is conducted. There are four stages of development in this project. The first is the modification of the existing Texas A&M University Flight Mechanics Laboratory flight simulator to upgrade it to a level at which the force and displacement devices can be compared. This phase involves design and fabrication of mechanical and electronic hardware, and software development. The second stage is the design and installation of the two types of control input devices. The third is the evaluation test design. The fourth and last stage is the conduct of these tests and the analysis of the results. The preliminary evaluation by eight test subjects, six of whom have prior flying experience, validates the design concepts and provides direction for further improvement of the devices. The results of the comparative tests indicate that preferences for either of the devices are aircraft type and task specific. The force stick is preferred for the more aggressive maneuvers of high performance fighter type aircraft while the displacement stick performs better for maneuvers in general aviation class aircraft. The force stick is very sensitive and enables quick response while the displacement stick provides feedback in the form of positional cues to the pilot, though it is not as sensitive. The primary drawback with the force stick is that it does not cue the pilot about the control input that the system receives, while that of the displacement stick is biasing due to friction. The force/response gradient for the force stick and the displacement/response gradient for the displacement stick are slightly high in the opinion of experienced test subjects. Suggestions for modifications of the control sticks and the test design are listed for a more detailed and conclusive study. These include providing an armrest for the force-stick and centering detents for both devices. Revisions in experimental method include using more test subjects (approximately 20)with more learning time to enable consistent performance of tasks
Advances in industrial control, Dec 13, 2013
This section describes the design and implementation of automatic controller tuning and model ref... more This section describes the design and implementation of automatic controller tuning and model reference adaptive control (MRAC) to improve part quality in stamping and extends previous work on a manually-tuned fixed-gain process controller. Automatic tuning is described with a discussion of implementation issues in the presence of plant disturbances. Design of a direct MRAC, whose controller gains are continuously adjusted to accommodate changes in process dynamics and disturbances, is investigated, including simulation-based robustness analysis of the adaptation law and a consideration of constrained estimation in the recursive least squares algorithm to address practical implementation issues. The performance of the MRAC process controller designed through simulation is experimentally validated. Good tracking of the reference process variable (i.e., punch force), and significant part quality improvement in the presence of disturbances, is achieved.
IEEE Transactions on Control Systems and Technology, 2001
In this paper we present a numerical and experimental investigation of the properties of the ARMA... more In this paper we present a numerical and experimental investigation of the properties of the ARMARKOV adaptive control (AAC) algorithm with simultaneous identification. This algorithm requires a model of only the secondary path (control input to performance variable) transfer function which is identified online using the time-domain ARMARKOV/Toeplitz identification technique. For a 5-mode acoustic duct model, we present numerical as well as experimental results for single-tone, dual-tone, and broadband disturbance rejection. In the simulations and experiments we assume no knowledge of the disturbance signal.
IEEE Transactions on Control Systems and Technology, May 1, 1996
Although active noise control has been a subject of interest for over 50 years, it has become fea... more Although active noise control has been a subject of interest for over 50 years, it has become feasible only with recent technological advances. This paper formulates the problem of noise control in a one-dimensional acoustic duct in a form that lends itself to the application of feedback control theory. In contrast to most of the literature on the subject which uses feedforward techniques, a feedback approach is used. Inconsistencies that appear in previous feedback control models are rectified, controllers are designed using precompensated linear quadratic Gaussian (LQG) synthesis, and experimental verification of the control designs is presented. The experimental results show a reduction of about 5-12 dB over a frequency range from 150-350 Hz.
IEEE Control Systems Magazine, Dec 1, 2007
ABSTRACT Real-time simulation and its use in Hardware in the Loop and Power Hardware in the Loop ... more ABSTRACT Real-time simulation and its use in Hardware in the Loop and Power Hardware in the Loop testing may not be realized with one single hardware platform. Instead, multiple systems are needed to realistically address the analysis and testing needs of the smart grid. This is particularly the case when the target system is the future electrical distribution grid, with its multi-physic, hybrid nature, its pervasive power electronics and communication. The approach adopted at the authors' laboratory is presented to exemplify the interface and integration challenges when such platform is extended to realize relevant scenarios.
International Journal of Control, May 10, 2004
The problem of discrete-time and continuous-time adaptive stabilization under full-state feedback... more The problem of discrete-time and continuous-time adaptive stabilization under full-state feedback control is considered. In the discrete-time case the main result is based on a gain update law involving a step-size function. The formulation generalizes and unifies prior results based on quadratic and logarithmic Lyapunov functions. In the continuous-time case adaptive stabilization under full-state feedback using a normalized gradient algorithm is considered and Lyapunov stability is demonstrated.
ABSTRACT This paper develops an adaptive algorithm for position control of electrohydraulic servo... more ABSTRACT This paper develops an adaptive algorithm for position control of electrohydraulic servo systems (EHS), with the objective of addressing variations in supply pressure. Most approaches for control of EHS assume constant supply pressures, which in practical terms require the use of additional components such as accumulators. In this article, we consider a nonlinear model of an electrohydraulic system, establish a controller structure using feedback linearization (model inversion) and then derive an adaptive control law for position control with unknown supply pressure. A function of the unknown parameter is estimated using a gradient method based on an augmented error. Closed-loop stability is established using a Lyapunov approach and the tracking-error between a desired model-reference output and the system output is shown to asymptotically go to zero. Finally, simulation results pertaining to implementation issues are presented.
An adaptive disturbance rejection algorithm is developed for the standard control problem. The mu... more An adaptive disturbance rejection algorithm is developed for the standard control problem. The multiple input-multiple output (MIMO) system and controller are represented as AR-MARKOV/Toeplitz models, and the parameter matrix of the compensator is updated on-line by means of a gradient algorithm. The algorithm requires minimal knowledge of the plant, specifically, the numerator of the ARMARKOV model of the transfer function from the control inputs to the performance variables is required. No knowledge about the spectrum of the disturbance is needed. Experimental results demonstrating tonal and broadband disturbance rejection in an acoustic duct are presented. Index Terms-Active noise and vibration control, adaptive control, discrete-time systems, disturbance rejection. NOMENCLATURE zero matrix. identity matrix. ones matrix.. Euclidean vector norm. Frobenius matrix norm.
IEEE Transactions on Control Systems and Technology, Jul 1, 2012
ABSTRACT Electrohydraulic servo systems (EHSS) are used for several engineering applications, and... more ABSTRACT Electrohydraulic servo systems (EHSS) are used for several engineering applications, and in particular, for efficient handling of heavy loads. proportional-integral-differential (PID) control is used extensively to control EHSS, but the closed-loop performance is limited using this approach, due to the nonlinear dynamics that characterize these systems. Recent studies have shown that feedback linearization is a viable control design technique that addresses the nonlinear dynamics of EHSS; however, it is important to establish the robustness of this method, given that hydraulic system parameters can vary significantly during operation. In this study, we focus on supply pressure variations in a rotational electrohydraulic drive. The supply pressure appears in a square-root term in the system model, and thus, standard adaptive techniques that require uncertain parameters to appear linearly in the system equations, cannot be used. A Lyapunov approach is used to derive an enhanced feedback-linearization-based control law that accounts for supply pressure changes. Simulation results indicate that standard feedback-linearization based control is robust to EHSS parameter variations, providing significant improvement over PID control, and that the performance can be further improved using the proposed control law.
2022 IEEE 13th International Symposium on Power Electronics for Distributed Generation Systems (PEDG), Jun 26, 2022
2022 IEEE 13th International Symposium on Power Electronics for Distributed Generation Systems (PEDG)
Management of transmission and distribution of electrical power has become an increasingly comple... more Management of transmission and distribution of electrical power has become an increasingly complex task with the large-scale induction of renewable sources with unsteady production levels, FACTS and HVDC networks, as well as active network control for grid stability and transmission efficiency. Complex power electronic systems are the basis for achieving optimal management of the grid, but deploying, tuning and monitoring these systems is a task that can only be achieved in a secure and efficient manner through the use of simulation. This paper aims to provide an overview of commercially available solutions that allow Real Time Simulation of the complex modern-day power grids.
Springer eBooks, Dec 13, 2013
This chapter presents a review of research on control of the sheet metal stamping process, and it... more This chapter presents a review of research on control of the sheet metal stamping process, and its effect on the quality of stamped parts. First the evolution of control strategies for the forming process is presented. Next the different types of active blank holder force systems from previous research are described. Finally, a review of in-process sensor technologies to monitor the process variables used in process controllers for sheet metal stamping is given.
Uploads
Papers by Ravinder Venugopal