Ahmed Chemori

Global Stabilization With Low Computational Cost of the Discrete-Time Chain of Integrators by Means of Bounded Controls

This note proposes a bounded nonlinear control law composed of saturation functions for the discrete-time chain of integrators. A dynamical adaptation rule of the saturation levels involved in the control law is proposed to improve the closed-loop performances. The note unifies the original work of Yang (1997) with static saturation level and convergence improvements that recently appeared in the continuous time case. The possible ranges for the controllers parameters are extended with respect to existing results

Dual-space adaptive control of redundantly actuated cable-driven parallel robots

Cable-driven parallel robots (CDPR) are efficient manipulators able to carry heavy payloads across large workspaces. Therefore, the dynamic parameters such as the mobile platform mass and center of mass location may considerably vary. Without any adaption, the erroneous parametric estimate results in mismatch terms added to the closed-loop system, which may decrease the robot performances. In this paper, we introduce an adaptive dual-space motion control scheme for CDPR. The proposed method aims at increasing the robot tracking performances, while keeping all the cable tensed despite uncertainties and changes in the robot dynamic parameters. Reel-time experimental tests, performed on a large redundantly actuated CDPR prototype, validate the efficiency of the proposed control scheme. These results are compared to those obtained with a non-adaptive dual-space feedforward control scheme.

Dual-Space Control of Extremely Fast Parallel Manipulators: Payload Changes and the 100G Experiment

In this paper, three control schemes are proposed and experimentally compared on the R4 redundantly actuated parallel manipulator for applications with very high accelerations. First, a proportional-integral-differential (PID) in operational space is proposed to adequately take into consideration the actuation redundancy. Because of its lack of performance, a dual-space feedforward control scheme based on the dynamic model of R4 is proposed. The improvements obtained with this controller allowed the implementation of an experiment, which consisted in the tracking of a trajectory with a maximum acceleration of more than 100G. However, such a controller may have loss of performance in case of any operational change (such as different payloads). Therefore, a dual-space adaptive control scheme is proposed. The stability analysis of the R4 parallel robot when controlled by the proposed dual-space adaptive controller is provided. The objective of this paper is to show that the proposed dual-space adaptive controller not only maintains its good performance independently of the operational conditions but also has a better performance than both the PID and the dual-space feedforward controllers, even when the latter is best configured for the given case (which confirms its applicability in an industrial environment).

From PD to Nonlinear Adaptive Depth-Control of a Tethered Autonomous Underwater Vehicle

This paper deals with an experimental comparison between a proportional derivative (PD) controller and an adaptive nonlinear state feedback one, both applied on a tethered autonomous underwater vehicle. The aim is to show the behavior of the closed loop system in the nominal case for each of these two controllers, and then to test their robustness towards some parameters changes. The PD on one hand has a good performance for systems with an unknown model. The adaptive control law on the other hand is known to adjust the unknown parameters of the plant in order to converge to the desired trajectory. This study shows experimental results performed using each of the above mentioned control laws.

Global discrete-time stabilization of the PVTOL aircraft based on fast predictive control

Abstract This paper deals with stabilization control of a non-minimum phase under-actuated Planar Vertical Take-Off and Landing (PVTOL) aircraft. The proposed control approach, inspired from that proposed in Poulin et al. (2007), is based on a discrete time model of the PVTOL and receding horizon technique to take into account constraints on the control inputs (positivity and boundedness). State constraints can also be handled. The computational cost is reduced by decoupling the optimization problem into two QP problems of reduced dimensions. The minimized cost functions proposed here extends the previous work by allowing state and control weight. The proposed control approach is illustrated through simulation case studies including stabilization and robustness towards parameters uncertainties.

A novel application of multivariable ℒ 1 adaptive control: From design to real-time implementation on an underwater vehicle

This paper presents the design and experimental implementation of an ℒ1 adaptive control on a tethered underwater vehicle. This controller, well known for its fast adaptation and its robustness, is proposed to be applied for the first time in the field of underwater vehicles control. This paper summarizes the implementation and experimental results obtained on a modified version of the AC-ROV underwater vehicle. Various experimental scenarios are presented to illustrate the ability of the ℒ1adaptive law not only to successfully control pitch and depth (even with strong modeling uncertainties), but also to be efficient towards disturbances like waves or buoyancy changes.

Nonlinear model predictive running control of Kangaroo robot: A one-leg planar underactuated hopping robot

The control of dynamically stable hopping robots has made great progress in the last decades. This paper deals with modeling and control of Kangaroo hopping robot. It is a one-leg planar hopping robot which imitates the mode of displacement of kangaroos. Lagrangian dynamic model of the hopping robot is computed on the different phases of the jumping cycle. A new control scheme is proposed to control the leg thrust during stance phase for planar hopping. A nonlinear model predictive control has been combined with Raiberts approach which has improved significantly its performances. A simulator has been developed to simulate the behavior of the controlled robot. The proposed control approach is validated in simulation and is compared with Raiberts approach.

Stable limit cycle generation for underactuated mechanical systems, application: Inertia wheel inverted pendulum

This paper deals with a control approach dedicated to stable limit cycle generation for underactuated mechanical systems. The proposed approach is based on partial nonlinear feedback linearization and dynamic control for optimal periodic reference trajectories tracking. Simulation results and experiments show the efficiency of the proposed approach.

Predictive Control for the Stabilization of a Fast Mechatronic System : From Simulation to Real-Time Experiments

In this paper a Generalized Predictive Control (GPC) scheme is proposed for the stabilization of a fast mechatronic system. Namely the inertia wheel inverted pendulum, which has two degrees of freedom and one actuator. The proposed control approach should be able to stabilize this system around its unstable equilibrium point and maintain it in this state. The efficiency and performance of the proposed control scheme are firstly illustrated through simulation results, then its robustness is shown through real-time experiments on the prototype of the system in question.

Dual-space adaptive control of redundantly actuated parallel manipulators for extremely fast operations with load changes

This paper deals with the dual-space adaptive control of R4 redundantly actuated parallel manipulator for applications with very high accelerations. This controller is compared experimentally with a dual-space feedforward controller (which may have good performances for specific cases, but has crucial losses of performance when there is any operational change (such as a change of load)), for a pick-and-place task with accelerations of 30G (without payload) and 20G (with a payload of 200g). The objective of this paper is to show that the proposed dual-space adaptive controller not only keeps a very good performance independently of the operational case, but also has a better performance than the dual-space feedforward controller even when this last one is best configured to the given case.