Journal of Computational and Nonlinear Dynamics, 2022
Neuromuscular electrical stimulation (NMES) is a promising technique to actuate the human musculo... more Neuromuscular electrical stimulation (NMES) is a promising technique to actuate the human musculoskeletal system in the presence of neurological impairments. The closed-loop control of NMES systems is nontrivial due to their inherent uncertain nonlinearity. In this paper, we propose a Nussbaum-type neural network (NN)-based controller for the lower leg limb NMES systems. The control accounts for model uncertainties and external disturbances in the system and, for the first time, provides a solution with rigorous stability analysis to the adaptive NMES tracking problem with input saturation and muscle fatigue. The proposed controller guarantees a uniformly ultimately bounded (UUB) tracking for the knee-joint angular position. To evaluate the control performance, a simulation study is taken, where the performance comparison with a NN controller inspired by Ge et al. (2004, “Adaptive Neural Control of Nonlinear Time-Delay Systems With Unknown Virtual Control Coefficients,” IEEE Trans. ...
Highway work zones are prone to traffic accidents when congestion and queues develop. Vehicle que... more Highway work zones are prone to traffic accidents when congestion and queues develop. Vehicle queues expand at a rate of 1 mile every 2 minutes. Back-of-queue, rear-end crashes are the most common work zone crash, endangering the safety of motorists, passengers, and construction workers. The dynamic nature of queuing in the proximity of highway work zones necessitates traffic management solutions that can monitor and intervene in real time. Fortunately, recent progress in sensor technology, embedded systems, and wireless communication coupled to lower costs are now enabling the development of real-time, automated, "intelligent" traffic management systems that address this problem. The goal of this project was to perform preliminary research and proof of concept development work for the use of UAS in real- time traffic monitoring of highway construction zones in order to create real-time alerts for motorists, construction workers, and first responders. The main tasks of the...
2018 Annual American Control Conference (ACC), 2018
In this work, we present a solution to the distance-based formation maneuvering problem of multip... more In this work, we present a solution to the distance-based formation maneuvering problem of multiple nonholo-nomic unicycle-type robots. The control law is designed at the kinematic level and is based on the rigidity properties of the graph modeling the sensing/control interactions among the robots. A simple input transformation is used to facilitate the control design by converting the nonholonomic model into the single-integrator equation. The resulting control ensures exponential convergence to the desired formation while the formation maneuvers according to a desired, time-varying translational velocity. An experimental implementation of the proposed control law is conducted on the Robotarium testbed.
This dissertation focuses on the development of nonlinear controllers for robot manipulators unde... more This dissertation focuses on the development of nonlinear controllers for robot manipulators under constrained motion, i.e., robotic systems that require the simultaneous control of the robot's end-effector position and interaction force with the environmental constraint. The primary objective was to extend previous nonlinear control design and analysis tools developed for unconstrained robots to constrained robot systems. This extension is not obvious due to the structure of the nonlinear differential-algebraic equations that describe the dynamics of constrained robot systems. Specifically, we develop new nonlinear position/force control algorithms that compensate for parametric uncertainty and/or require minimal number of sensors for implementation. While the compensation of unknown parameters is accomplished by utilizing a Desired Compensation Adaptation Law (DCAL) like control structure, the reduction in the sensor count is achieved by (i) designing a model-based observer or...
2020 IEEE Conference on Control Technology and Applications (CCTA), 2020
In this paper, we propose a novel approach to the problem of augmenting distance-based formation ... more In this paper, we propose a novel approach to the problem of augmenting distance-based formation controllers with a secondary feedback variable for the purpose of preventing formation ambiguities. We introduce two variables that form an orthogonal space and uniquely characterize a triangular formation in two dimensions. We show that the resulting controller ensures the almost-global asymptotic stability of the desired formation for an $n$-agent system without conditions on the triangulations of the desired formation or control gains.
Proceedings of the 2003 American Control Conference, 2003.
A promising mechanical bearing candidate for active operation is the tilting-pad bearing. The act... more A promising mechanical bearing candidate for active operation is the tilting-pad bearing. The active tilting-pad bearing has linear actuators that radially translate each pad/pivot pair. The use of feedback control is determining the actuator forces allows for the automatic, continuous adjustment of the pad position during the operations of the rotating machine. In this paper, we first develop the full-order
Lyapunov-Based Control of Mechanical Systems, 2000
Friction is a natural phenomenon that affects almost all motion. It has been the subject of exten... more Friction is a natural phenomenon that affects almost all motion. It has been the subject of extensive studies for centuries, with the main objectives being the design of effective lubricating processes and the understanding of the mechanisms of wear. Whereas friction effects at moderate velocities are somewhat predictable, it is the effect of friction at low velocities that is very difficult to model. The facts that friction changes sign with velocity, is asymmetric about the velocity axis, has evolutionary characteristics, and exhibits the stick-slip phenomenon, etc., aggravates the problem. Although friction effects have been well understood qualitatively, researchers have often relied on experimental data to formulate various mathematical models. A heuristic model for friction was first proposed by Leonardo da Vinci [11] in 1519; however, the model failed to capture the low-velocity friction effects such as the Stribeck effect, presliding displacement, rising static friction, etc., which play a major role in high-precision position/velocity tracking applications. In recent years, several dynamic models have been introduced to describe this highly nonlinear behavior exhibited by friction. For example, Dahl [12] proposed a dynamic model to capture the spring-like behavior during stiction. Canudas et al. [9] proposed a dynamic state-variable model to capture friction effects such as the Stribeck effect, hysteresis, spring-like behavior of stiction, and varying breakaway force.
In this paper, we present an experimental evaluation of several link position tracking control al... more In this paper, we present an experimental evaluation of several link position tracking control algorithms for rigid-link flexible-joint robot manipulators. To study the performance of the controllers, an IMI 2-link direct-drive planar robot manipulator was modified to approximate linear torsional spring couplings from the actuators to the links. Preliminary experimental results seem to indicate that reduced-order, model-based controllers with an actuator feedback loop provide relatively good link position tracking while a full-order, model-based controller offers some further improvement in link position tracking at the expense of increased computation.
Thispaperconsiderstheproblemofrelativepositioncontrolformultiplespacecraftformatione ying.Specie ... more Thispaperconsiderstheproblemofrelativepositioncontrolformultiplespacecraftformatione ying.Specie cally, the full nonlinear dynamics describing the relative positioning of multiple spacecraft formation e ying are used to develop a Lyapunov-based, nonlinear, adaptive control law that guarantees global asymptotic convergence of the position tracking error in the presence of unknown, constant, or slow-varying spacecraft masses, disturbance forces, and gravity forces. Simulation results are included to illustrate the controller performance. that compensated for unknown, constant disturbances while pro- ducing globally asymptotically decaying position tracking errors. This controller, however, required exact knowledge of the space- craft parameters. In this paper we consider the full nonlinear dynamics describ- ing the relative positioning of MSFF for control design purposes. Using Lyapunov-based control design and stability analysis tech- niques, we develop a nonlinear adaptive control law that guarantees global asymptotic convergence of the spacecraft relative position to any sufe ciently smooth desired trajectory, despite the presence of unknown, constant, or slow-varying spacecraft masses, disturbance forces, and gravity forces. In the case when the parameters are ex- actlyknown,theproposedcontrolstrategyyieldsglobalexponential convergence of the tracking errors. In comparison to the work of Refs. 11 and 12, the proposed controller ensures stronger stability resultsandaccountsforawiderclassofparametricuncertainties.As inRefs.11-13, we will consider in this paper the idealized scenario where the spacecraft actuators are capable of providing continuous- time control efforts, as opposed to being of pulse type. 9 We note that the problem of pulse-type, nonlinear control design for MSFF constitutes an open research problem and is beyond the scope of this paper. The paper is organized as follows. Section II presents the non- linear dynamic model derivation. The control objective is stated in Sec. III. The control design and closed-loop stability analysis are presented in Sec. IV. Simulation results are provided in Sec. V, whereas some concluding remarks are given in Sec. VI.
In this paper, we present an adaptive link position tracking controller for robot manipulators wh... more In this paper, we present an adaptive link position tracking controller for robot manipulators which achieves controller/update law modularity. Specifically, the proposed torque input control law is designed to (i)achieve input-to-state stability with respect to the parameter estimation error, and (ii)guarantee asymptotic link position tracking and boundedness of all closed-loop signals for any adaptive update law that satisfies some generic properties. Simulation and experimental results are included to illustrate the advantages of the proposed adaptive control law. Specifically, the proposed controller with a least-squares estimator is compared to a well-known, gradient update-based, adaptive controller. The results indicate an improvement in the tracking performance with the proposed controller.
IEEE Transactions on Control Systems Technology, 2007
In this paper, we address the problem of controlling a magnetic levitation system with reduced el... more In this paper, we address the problem of controlling a magnetic levitation system with reduced electric power losses. A general control/biasing strategy is proposed which introduces a bias flux in the nonlinear control law, function of the mechanical states. The bias flux ensures the power losses converge to zero as the mechanical states converge to zero and a singularity-free control, without affecting the closed-loop stability. General conditions on the functional form of the bias are provided along with a design example of the control/biasing strategy. An experimental study illustrates that the proposed time-varying-bias controller yields a stabilization performance comparable to the constant-bias version of the controller, but with significantly less ohmic power losses.
Journal of Computational and Nonlinear Dynamics, 2022
Neuromuscular electrical stimulation (NMES) is a promising technique to actuate the human musculo... more Neuromuscular electrical stimulation (NMES) is a promising technique to actuate the human musculoskeletal system in the presence of neurological impairments. The closed-loop control of NMES systems is nontrivial due to their inherent uncertain nonlinearity. In this paper, we propose a Nussbaum-type neural network (NN)-based controller for the lower leg limb NMES systems. The control accounts for model uncertainties and external disturbances in the system and, for the first time, provides a solution with rigorous stability analysis to the adaptive NMES tracking problem with input saturation and muscle fatigue. The proposed controller guarantees a uniformly ultimately bounded (UUB) tracking for the knee-joint angular position. To evaluate the control performance, a simulation study is taken, where the performance comparison with a NN controller inspired by Ge et al. (2004, “Adaptive Neural Control of Nonlinear Time-Delay Systems With Unknown Virtual Control Coefficients,” IEEE Trans. ...
Highway work zones are prone to traffic accidents when congestion and queues develop. Vehicle que... more Highway work zones are prone to traffic accidents when congestion and queues develop. Vehicle queues expand at a rate of 1 mile every 2 minutes. Back-of-queue, rear-end crashes are the most common work zone crash, endangering the safety of motorists, passengers, and construction workers. The dynamic nature of queuing in the proximity of highway work zones necessitates traffic management solutions that can monitor and intervene in real time. Fortunately, recent progress in sensor technology, embedded systems, and wireless communication coupled to lower costs are now enabling the development of real-time, automated, "intelligent" traffic management systems that address this problem. The goal of this project was to perform preliminary research and proof of concept development work for the use of UAS in real- time traffic monitoring of highway construction zones in order to create real-time alerts for motorists, construction workers, and first responders. The main tasks of the...
2018 Annual American Control Conference (ACC), 2018
In this work, we present a solution to the distance-based formation maneuvering problem of multip... more In this work, we present a solution to the distance-based formation maneuvering problem of multiple nonholo-nomic unicycle-type robots. The control law is designed at the kinematic level and is based on the rigidity properties of the graph modeling the sensing/control interactions among the robots. A simple input transformation is used to facilitate the control design by converting the nonholonomic model into the single-integrator equation. The resulting control ensures exponential convergence to the desired formation while the formation maneuvers according to a desired, time-varying translational velocity. An experimental implementation of the proposed control law is conducted on the Robotarium testbed.
This dissertation focuses on the development of nonlinear controllers for robot manipulators unde... more This dissertation focuses on the development of nonlinear controllers for robot manipulators under constrained motion, i.e., robotic systems that require the simultaneous control of the robot's end-effector position and interaction force with the environmental constraint. The primary objective was to extend previous nonlinear control design and analysis tools developed for unconstrained robots to constrained robot systems. This extension is not obvious due to the structure of the nonlinear differential-algebraic equations that describe the dynamics of constrained robot systems. Specifically, we develop new nonlinear position/force control algorithms that compensate for parametric uncertainty and/or require minimal number of sensors for implementation. While the compensation of unknown parameters is accomplished by utilizing a Desired Compensation Adaptation Law (DCAL) like control structure, the reduction in the sensor count is achieved by (i) designing a model-based observer or...
2020 IEEE Conference on Control Technology and Applications (CCTA), 2020
In this paper, we propose a novel approach to the problem of augmenting distance-based formation ... more In this paper, we propose a novel approach to the problem of augmenting distance-based formation controllers with a secondary feedback variable for the purpose of preventing formation ambiguities. We introduce two variables that form an orthogonal space and uniquely characterize a triangular formation in two dimensions. We show that the resulting controller ensures the almost-global asymptotic stability of the desired formation for an $n$-agent system without conditions on the triangulations of the desired formation or control gains.
Proceedings of the 2003 American Control Conference, 2003.
A promising mechanical bearing candidate for active operation is the tilting-pad bearing. The act... more A promising mechanical bearing candidate for active operation is the tilting-pad bearing. The active tilting-pad bearing has linear actuators that radially translate each pad/pivot pair. The use of feedback control is determining the actuator forces allows for the automatic, continuous adjustment of the pad position during the operations of the rotating machine. In this paper, we first develop the full-order
Lyapunov-Based Control of Mechanical Systems, 2000
Friction is a natural phenomenon that affects almost all motion. It has been the subject of exten... more Friction is a natural phenomenon that affects almost all motion. It has been the subject of extensive studies for centuries, with the main objectives being the design of effective lubricating processes and the understanding of the mechanisms of wear. Whereas friction effects at moderate velocities are somewhat predictable, it is the effect of friction at low velocities that is very difficult to model. The facts that friction changes sign with velocity, is asymmetric about the velocity axis, has evolutionary characteristics, and exhibits the stick-slip phenomenon, etc., aggravates the problem. Although friction effects have been well understood qualitatively, researchers have often relied on experimental data to formulate various mathematical models. A heuristic model for friction was first proposed by Leonardo da Vinci [11] in 1519; however, the model failed to capture the low-velocity friction effects such as the Stribeck effect, presliding displacement, rising static friction, etc., which play a major role in high-precision position/velocity tracking applications. In recent years, several dynamic models have been introduced to describe this highly nonlinear behavior exhibited by friction. For example, Dahl [12] proposed a dynamic model to capture the spring-like behavior during stiction. Canudas et al. [9] proposed a dynamic state-variable model to capture friction effects such as the Stribeck effect, hysteresis, spring-like behavior of stiction, and varying breakaway force.
In this paper, we present an experimental evaluation of several link position tracking control al... more In this paper, we present an experimental evaluation of several link position tracking control algorithms for rigid-link flexible-joint robot manipulators. To study the performance of the controllers, an IMI 2-link direct-drive planar robot manipulator was modified to approximate linear torsional spring couplings from the actuators to the links. Preliminary experimental results seem to indicate that reduced-order, model-based controllers with an actuator feedback loop provide relatively good link position tracking while a full-order, model-based controller offers some further improvement in link position tracking at the expense of increased computation.
Thispaperconsiderstheproblemofrelativepositioncontrolformultiplespacecraftformatione ying.Specie ... more Thispaperconsiderstheproblemofrelativepositioncontrolformultiplespacecraftformatione ying.Specie cally, the full nonlinear dynamics describing the relative positioning of multiple spacecraft formation e ying are used to develop a Lyapunov-based, nonlinear, adaptive control law that guarantees global asymptotic convergence of the position tracking error in the presence of unknown, constant, or slow-varying spacecraft masses, disturbance forces, and gravity forces. Simulation results are included to illustrate the controller performance. that compensated for unknown, constant disturbances while pro- ducing globally asymptotically decaying position tracking errors. This controller, however, required exact knowledge of the space- craft parameters. In this paper we consider the full nonlinear dynamics describ- ing the relative positioning of MSFF for control design purposes. Using Lyapunov-based control design and stability analysis tech- niques, we develop a nonlinear adaptive control law that guarantees global asymptotic convergence of the spacecraft relative position to any sufe ciently smooth desired trajectory, despite the presence of unknown, constant, or slow-varying spacecraft masses, disturbance forces, and gravity forces. In the case when the parameters are ex- actlyknown,theproposedcontrolstrategyyieldsglobalexponential convergence of the tracking errors. In comparison to the work of Refs. 11 and 12, the proposed controller ensures stronger stability resultsandaccountsforawiderclassofparametricuncertainties.As inRefs.11-13, we will consider in this paper the idealized scenario where the spacecraft actuators are capable of providing continuous- time control efforts, as opposed to being of pulse type. 9 We note that the problem of pulse-type, nonlinear control design for MSFF constitutes an open research problem and is beyond the scope of this paper. The paper is organized as follows. Section II presents the non- linear dynamic model derivation. The control objective is stated in Sec. III. The control design and closed-loop stability analysis are presented in Sec. IV. Simulation results are provided in Sec. V, whereas some concluding remarks are given in Sec. VI.
In this paper, we present an adaptive link position tracking controller for robot manipulators wh... more In this paper, we present an adaptive link position tracking controller for robot manipulators which achieves controller/update law modularity. Specifically, the proposed torque input control law is designed to (i)achieve input-to-state stability with respect to the parameter estimation error, and (ii)guarantee asymptotic link position tracking and boundedness of all closed-loop signals for any adaptive update law that satisfies some generic properties. Simulation and experimental results are included to illustrate the advantages of the proposed adaptive control law. Specifically, the proposed controller with a least-squares estimator is compared to a well-known, gradient update-based, adaptive controller. The results indicate an improvement in the tracking performance with the proposed controller.
IEEE Transactions on Control Systems Technology, 2007
In this paper, we address the problem of controlling a magnetic levitation system with reduced el... more In this paper, we address the problem of controlling a magnetic levitation system with reduced electric power losses. A general control/biasing strategy is proposed which introduces a bias flux in the nonlinear control law, function of the mechanical states. The bias flux ensures the power losses converge to zero as the mechanical states converge to zero and a singularity-free control, without affecting the closed-loop stability. General conditions on the functional form of the bias are provided along with a design example of the control/biasing strategy. An experimental study illustrates that the proposed time-varying-bias controller yields a stabilization performance comparable to the constant-bias version of the controller, but with significantly less ohmic power losses.
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Papers by Marcio de Queiroz