No abstract is provided for this article.
In this paper, a flight controller with disturbance observer (DOB) is proposed for high-performance trajectory tracking of a quadrotor. The dynamic model of the quadrotor, considering the external disturbances, model mismatches and input delays, is firstly developed. Subsequently, a DOB-based control strategy is designed with the backstepping (BS) technique. In this control scheme, the DOB serves as a compensator, which can effectively reject model mismatches and external disturbances. In this case, the trajectory tracking controller is designed according to the nominal model. Then, the input-to-state stability (ISS) analyses of the developed controllers are presented, which theoretically guarantees the robustness of the developed controller. Finally, comparative studies are carried out. Three types of disturbances including payloads, rotor failures and wind are chosen to verify the effectiveness of the development. The results from simulations and experiments show that the proposed controller provides better performances than the traditional nonlinear controllers.
Piezo-actuated positioning stages are widely applied in many industrial applications for nanometer or sub-nanometer displacement resolution. However, the non-smooth hysteresis nonlinearity inherent to the piezoelectric material usually degrades the tracking performance of the controlled system. The challenge is that there is no general method to design control laws with general hysteresis models. The control algorithms are always developed based on a specific hysteresis model. In this paper, an ellipse-based hysteresis model is used to describe the hysteresis behaviors observed on the piezo-actuated positioning stages. The benefit for such a model lies on the fact that the expressions of the model are completely analytical and can be determined easily by a set of parameters. It is therefore convenient to fuse this model with the available robust control approach to mitigate the effects of hysteresis. To illustrate this advantage, a discontinue-projection-based robust adaptive controller is specifically designed, which guarantees the global stability of the closed control system and achieves excellent tracking performance within a desired precision. Simulation performed on a piezo-actuated positioning stage validates the effectiveness of the developed control approach.
Dielectric elastomer actuators (DEAs) are known as a type of electric-driven artificial muscle that have shown promising potential in the field of soft robotics. However, the inherent viscoelastic nonlinearity makes the modeling and control of DEAs challenging. In this paper, we propose a new phenomenological modeling approach with the Prandtl–Ishlinskii (P–I) model to characterize the viscoelastic hysteresis nonlinearity of DEAs. Differently from the commonly used physics-based models, the developed phenomenological model, called the modified rate-dependent P–I model (MRPIM), produces behavior similar to that of physics-based models but without necessarily considering physical insight into the modeling problem. In this way, the developed MRPIM can characterize the asymmetric and rate-dependent viscoelastic hysteresis with a relative simple mathematical format using only the experimental data. To validate the development, experimental tests were conducted with seven different frequencies; four were selected to identify the model parameters and the rest of the data were used to further verify the model. Comparisons between the model prediction and experimental data demonstrate that the MRPIM can precisely describe the viscoelastic hysteresis effect of DEAs with a maximum prediction error of 9.03% and root-mean-square prediction error of 4.50%.
In this paper, a general skeleton on modeling, controller design, and applications of the piezoelectric positioning stages is presented. Toward this framework, a general model is first proposed to characterize dynamic behaviors of the stage, including frequency response of the stage, voltage-charge hysteresis and nonlinear electric behavior. To illustrate the validity of the proposed general model, a dynamic backlash-like model is adopted as one of hysteresis models to describe the hysteresis effect, which is confirmed by experimental tests. Thus, the developed model provides a general frame for controller design. As an illustration to this aspect, a robust adaptive controller is developed based on a reduced dynamic model under both unknown hysteresis nonlinearities and parameter uncertainties. The proposed control law ensures the boundedness of the closed-loop signals and desired tracking precision. Finally, experimental tests with different motion trajectories are conducted to verify the proposed general model and the robust control law. Experimental results demonstrate the excellent tracking performance, which validates the feasibility and effectiveness of the proposed approach.
This paper deals with the robust inverse compensation and control for a class of nonlinear systems with unknown asymmetric input backlash. With an analytical expression of the inverse compensation error, a corresponding controller is designed by using the robust adaptive control approach. The developed control law ensures global stability of the whole control system and achieves both stabilization and tracking with desired precision. Simulations performed on an unstable uncertain nonlinear system illustrate and clarify the approach.
No abstract is provided for this article.
The emerging field of soft robotics offers the prospect of applying soft actuators as artificial muscles in the robots, replacing traditional actuators based on hard materials, such as electric motors, piezoceramic actuators, etc. Dielectric elastomers are one class of soft actuators, which can deform in response to voltage and can resemble biological muscles in the aspects of large deformation, high energy density and fast response. Recent research into dielectric elastomers has mainly focused on issues regarding mechanics, physics, material designs and mechanical designs, whereas less importance is given to the control of these soft actuators. Strong nonlinearities due to large deformation and electromechanical coupling make control of the dielectric elastomer actuators challenging. This paper investigates feed-forward control of a dielectric elastomer actuator by using a nonlinear dynamic model. The material and physical parameters in the model are identified by quasi-static and dynamic experiments. A feed-forward controller is developed based on this nonlinear dynamic model. Experimental evidence shows that this controller can control the soft actuator to track the desired trajectories effectively. The present study confirms that dielectric elastomer actuators are capable of being precisely controlled with the nonlinear dynamic model despite the presence of material nonlinearity and electromechanical coupling. It is expected that the reported results can promote the applications of dielectric elastomer actuators to soft robots or biomimetic robots.
