On the contact dynamics and adaptive fuzzy sliding mode impedance control for 4-PS parallel mechanism with model uncertainties and external disturbances

Distributed collaborative control to pose tracking for six-DOF parallel mechanism under multi-cylinder communication.

Parallel manipulation mechanisms are multiloop systems in which the parallel arrangement of the kinematic chains allows for the load capacity to be increased, the size and weight of every component to be reduced, and the movable links to be relieved of the gravity force of the actuators by locating them on a fixed base. In this article, the synthesis of a new parallel mechanism with an increased number of parallel loops for transmitting the power from the actuators to the output link is considered. A workspace has been constructed for the mock-up of the mechanism developed equipped with actuators of the translational and rotational movements of the output link. Dynamic analysis of the parallel mechanism with three kinematic chains has been performed considering the weights of the intermediate links.

This paper designed a trajectory tracking controller for an underwater vehicle considering model uncertainties and external force disturbances using the Port-Hamiltonian (PH) control theory. Firstly, the mathematical model of the underwater vehicle is established and expressed under the PH framework. However, the hydrodynamic force coefficients inside the mathematical model are hard to obtain accurately without detailed towing tank experiments. To address this, we will propose a parameter observer to estimate the unknown parameters caused by model uncertainties. Meanwhile, the vehicle inevitably suffers from external unknown force disturbances driven by current and wind. So another observer based on passivity theory is proposed to address the unknown fore disturbance. The control law is derived from reshaping kinetic energy and injecting damping terms via the interconnection and damping assignment passivity-based control method. This proposed controller has a physical interpretation. Moreover, it has been proved that the proposed controller can enable vehicles to track the desired trajectory and minimize the tracking errors exponentially. Numerical simulations and comparisons illustrate the stability and effectiveness of the proposed controller to model uncertainties and unknown external disturbances.KeywordsUnmanned underwater vehiclePort-controlled Hamiltonian systemTrajectory tracking control

This paper first investigates the force tracking performance by impedance control subjecting to model uncertainties and random external disturbances. A simple joint impedance/direct control structure is then proposed. The resulted controller has higher robustness to the environment and model uncertainties, and external disturbances. Furthermore, it does not require to switch the control modes for all task executions. Therefore, the proposed control structure combines the advantages of both the hybrid position/force control and the impedance control. Computer simulations are performed to verify the analysis of the impedance control and the effectiveness of the proposed control structure

Decoupled 2-dof spherical parallel mechanism is an important valued spherical parallel mechanism. It is one of the preferred solutions in the field of large-angle spherical workspaces. By studying the configuration of the exiting kinematic decoupled spherical parallel mechanism, it is found that the key issues that it cannot achieve a fully spherical workspace is that the output angle range of the “linear input – rotation output” kinematic chain cannot reach 180°. Based on the input and output characteristics of the double rocker mechanism, two new ideas for constructing the configuration of the “linear input – rotation output” kinematic chain are presented. The output angle range of the new “linear input – rotation output” kinematic chain can reach 180°. Based on the new design idea for “linear input – rotation output” kinematic chain, two new kinematic chains are designed: P5R and PRR. Based on the above kinematic chains, two 2-dof decoupled parallel mechanism with a fully spherical workspace are designed, i.e. RR&P5R parallel mechanism and RR&PRR parallel mechanism.

This paper presents a position-based impedance control scheme for force tracking of a wall-cleaning unit installed on the wallclimbing mobile platform ROPE RIDE. It is important to maintain a contact force between the wall-cleaning unit and various types of walls in order to guarantee good cleaning performance. For this purpose, the target stiffness of impedance model as well as the reference position command for the wall-cleaning unit are tactfully adjusted according to the force tracing error between the real and reference contact forces. In comparison with existing impedance control methods, the proposed impedance control scheme is not only simple to implement but also robust against external disturbances such as varying trajectory or stiffness of walls as well as model uncertainties of cleaning unit. As a result, the proposed impedance control scheme can promise acceptable force tracking error in the steady state even for various trajectories of wall and varying reference forces. The stability and performance of proposed impedance control scheme are theoretically examined and the extensive experiments using the wall-cleaning unit are carried out to prove the force tracking capability of the proposed impedance control scheme.

A helicopter is a highly nonlinear system. Its mathematical model is difficult to establish accurately, especially the complicated flapping dynamics. In addition, the forces and moments exerted on the fuselage are very vulnerable to external disturbances like wind gust when flying in the outdoor environment. This paper proposes a composite control scheme which consists of a nonlinear backstepping controller and an extended state observer (ESO) to handle the above problems. The stability of the closed-loop system can be guaranteed based on Lyapunov theory. The external disturbances and model nonlinearities are treated as a lumped disturbance. Meanwhile, the ESO is employed to compensate the influence by estimating the lumped disturbance in real-time. Numerical simulation results are presented to demonstrate that the algorithm can achieve accurate and agile attitude tracking under the external wind gust disturbances even with model uncertainties. When coming to the flight test, a block dropping device was designed to generate a quantifiable and replicable disturbance, and the experimental results indicate that the algorithm introduced above can reject the external disturbance rapidly and track the given attitude command precisely.

A novel bilateral model reference adaptive impedance controller is proposed to achieve the force and position coordinated synchronization of dual manipulator under the conditions of manipulator model parameter uncertainty and external unknown disturbance. In order to compensate the uncertain errors of the desired impedance model and the dual manipulator model, two robust adaptive controllers with two reference desired impedance model based on sliding mode function are designed. In the robust adaptive controller process, the adaptive law is utilized to appraise the upper bound of the external uncertain disturbance, which makes sure that the closed-loop dynamic of the dual manipulators are consistent with the new desired impedance mode respectively. The Lyapunov-based stability proof is implemented to prove the tracking performance and global stability. On the MATLAB/Simulink platform two degrees of freedom teleoperation simulation with the robust adaptive controllers is achieved, and the force-position tracking asymptotic convergence ability is verified. The novel controller is experimentally investigated to guarantee the asymptotic convergence. The results show that the proposed controller has good performance of force-position tracking ability under the influences of model parameter uncertainty and unknown external disturbances and the overall system has a good stability and strong robustness.KeywordsTeleoperationDesired impedance modelForce-position trackingLyapunov-based stabilityAdaptive control

Two-level variable impedance control for internal/External forces tracking of dual-arm manipulators under uncertainties.

For the robot force control system, affected by the uncertainty of system modeling, unknown environmental parameters, nonlinear time lag and unknown external disturbances, classic force control schemes such as: hybrid force/position control, impedance control are suppressing transient forces the overshoot and steady-state force tracking phases cannot achieve good results. Therefore, this paper proposes an adaptive switching update rate impedance control scheme (SAHI) based on the above control algorithm. The algorithm dynamically changes the damping parameters in the impedance model and adjusts the adaptive update rate appropriately to compensate for environmental parameter errors. The force tracking error caused by the robot system model error not only solves the transient force overshoot problem in the case of discontinuous force tracking, but also guarantees the steady-state force tracking accuracy. And based on the Routh criterion, the stability analysis of the system ensures that all parameters and states of the entire closed-loop system are consistent and ultimately bounded. The simulation part compares the dynamic performance of different stages of hybrid impedance control (HI), adaptive hybrid impedance control (AHI), and adaptive switching update rate impedance control (SAHI), which verifies the effectiveness of the research scheme.

Sum-of-squares-based robust H∞ controller design for discrete-time polynomial fuzzy systems

In this paper, a steering robust control method based on professional driver behavior with modeling uncertainties and external disturbance is proposed for an unmanned driving robotic vehicle, to realize the accurate and stable steering control like a professional human driver. An unmanned driving robotic vehicle nonlinear dynamics model considering modeling uncertainties and external disturbance is established. A driver behavior model composed of an adaptive preview model, a driver path planning model, and a driver desired yaw rate model is established, with the influences on preview time and driver path planning strategy, respectively. On the basis of this, a robust steering controller based on professional driver behavior is presented, by taking road information, driver reaction delay time, and vehicle driving status as inputs and the servo motor rotation angle of the steering mechanical arm as output. The stability of the control system with modeling uncertainties and external disturbance is proved. A comparison of the analysis results of simulation and experiment among the proposed control method, other existing control methods, and professional human driver demonstrates the effectiveness of the proposed method.

Learning‐based robust control methodologies under information constraints

Neural network-based variable stiffness impedance control for internal/external forces tracking of dual-arm manipulators under uncertainties

Parallel mechanisms (PMs) having the same motion characteristic with a UP kinematic chain (U denotes a universal joint, and P denotes a prismatic joint) are called UP-equivalent PMs. They can be used in many applications, such as machining and milling. However, the existing UP-equivalent PMs suffer from the disadvantages of strict assembly requirements and limited rotational capability. Type synthesis of UP-equivalent PMs with high rotational capability is presented. The special 2R1T motion is briefly discussed and the fact that the parallel module of the Exechon robot is not a UP-equivalent PM is disclosed. Using the Lie group theory, the kinematic bonds of limb chains and their mechanical generators are presented. Structural conditions for constructing such UP-equivalent PMs are proposed, which results in numerous new architectures of UP-equivalent PMs. The high rotational capability of the synthesized mechanisms is illustrated by an example. The advantages of no strict assembly requirements and high rotational capability of the newly developed PMs will facilitate their applications in the manufacturing industry.