A Time-delayed Control Scheme with a Sliding Mode Controller for a Robot Manipulator

In this paper, a high accuracy linear positioning system with linear force actuator and magnetic levitation is proposed. By locating a permanently magnetized rod inside a current-carrying solenoid, the axial force is achieved by boundary effect of magnet poles and utilized to power the linear motion. While the force for levitation is governed by Ampere's law supplied with the same solenoid. With the levitation in radial direction, there is hardly any friction between the rod and the solenoid. The high speed motion can hence be achieved. Besides, the axial force act on the rod is a smooth function of rod position, so the system can provide nanometer resolution linear positioning to the molecule size. Since the force-position relation is highly nonlinear, and mathematical model is derived according to some assumptions, such as equivalent solenoid of the permanently magnetized rod, so there exists unknown dynamics in practical application. Thus robustness is an important issue in controller design. Meanwhile the load effect reacts directly on the servo system without transmission elements, so the capability of rejection is also required. With above consideration, a time-delay control scheme is chosen and applied. By comparing the input-output relation and the mathematical model, the time-delay controller calculates an estimation of unmodelled dynamics and disturbance then composes the desired compensation into the system. Effectiveness of the linear positioning system and control scheme are illustrated with simulation results.

A finite time synergetic control scheme for robot manipulators

A sliding mode control based on motor angular speed control has been presented for a robot manipulator grasping a payload with mass variation. In order to guarantee the continuity of the control signals applied to the actuators of the robot manipulator, a sliding mode control with integral compensation is adopted. Improvement of robustness of the control system against payload mass variation is obtained by introducing a sliding mode feedforward signal. The control scheme is applied to a three joint robot manipulator, control performance both with payload torque compensation and without payload torque compensation are investigated. Simulation results show that the control scheme presented, is robust against payload mass variation and has satisfactory control performance.

Throttle actuator control system for vehicle traction control

In many industrial applications, the end-effectors of robotic manipulators are required to move from one place to the other and follow some desired trajectories accurately. This paper proposes the nonlinear backstepping design with sliding mode control (SMC) scheme for the trajectory tracking of a robotic manipulator. The main control objective here is not only to track the desired trajectory, but also to cope with the system uncertainty. For realization, the motor dynamics would be considered in our system model. In general, the backstepping with SMC controller can be successfully developed to achieve our control goals for the robot arm system with N links. In addition, an adaptive backstepping design method is proposed to deal with the system uncertainty for the position tracking control of this robotic manipulator. Finally, some comparative simulations are given to illustrate the good performance of the proposed control schemes applied to a two-link robot arm.

Uncertainty and disturbance are common in a planar snake robot model due to its structural complexity and variation in system parameters. To achieve efficient head angle and velocity tracking with least computational complexity and unknown uncertainty bounds, a time-delayed control (TDC) scheme has been presented in this paper. A Serpenoid gait function is being tracked by the joint angles utilizing virtual holonomic constraints (VHCs) method. The first layer of TDC has been proposed for stabilizing the VHC dynamics to the origin. Once the VHCs are satisfied, the system is said to be on the constraint manifold. The second layer of TDC has been applied to an output system defined over the reduced order dynamics on the constrained manifold. To establish the robustness of the control approach through simulation, uncertainty in the friction coefficients is considered to be time-varying emulating change in the ground conditions. Simulation results and Lyapunov stability analysis affirm the uniformly ultimately bounded stability of the robot employing the proposed approach.

The Time Delay Control with Switching Action (TDCSA) method, which consists of Time Delay Control (TDC) and a switching action of sliding mode control (SMC), has been proposed as a promising technique in the robust control area where the plant has an unknown dynamics with parameter variations and substantial disturbances are preset. When TDCSA is applied to the plant with saturation nonlinearity, however, the so-called windup phenomenon is observed to arise, causing excessive overshoot and instability. The integral element of TDCSA and the saturation element of a plant cause the windup phenomenon. There are two integral effects in TDCSA. One is the integral effect caused by time delay estimation of TDC. The other is the integral term of an integral sliding surface. To solve this problem, we have proposed an anti-windup scheme method for TDCSA. The stability of the overall system has been proved for a class of nonlinear system. Experimental results show that the proposed method overcomes the windup problem of the TDCSA.

We investigate the possibility to suppress noise-induced intensity pulsations (relaxation oscillations) in semiconductor lasers by means of a time-delayed feedback control scheme. This idea is first studied in a generic normal-form model, where we derive an analytic expression for the mean amplitude of the oscillations and demonstrate that it can be strongly modulated by varying the delay time. We then investigate the control scheme analytically and numerically in a laser model of Lang-Kobayashi type and show that relaxation oscillations excited by noise can be very efficiently suppressed via feedback from a Fabry-Perot resonator.

This article proposes an enhanced adaptive time delay controller (ATDC) for robot manipulators subjected to external disturbances. This approach is model-free and uses time delay estimation (TDE) to estimate complex and unknown robot dynamics. First, to remove the reaching phase and improve the robustness of the control, an integral sliding surface (ISS) is used. Second, to speed up the convergence and compensate for the TDE errors and external disturbances, the gains of time delay control and the sliding mode have been made adaptive. In this article, we clearly point out using the Lyapunov method that the position and velocity tracking errors are guaranteed to be uniformly ultimately bounded (UUB). The effectiveness and the robustness of the designed controller over existing methods are experimentally verified on a parallel Delta robot. The novel model-free proposed control is robust and highly accurate, which is appropriate and recommended for industrial robotic applications.

This article presents an original motion control strategy for robot manipulators based on the coupling of the inverse dynamics method with the so-called second-order sliding mode control approach. Using this method, in principle, all the coupling non-linearities in the dynamical model of the manipulator are compensated, transforming the multi-input non-linear system into a linear and decoupled one. Actually, since the inverse dynamics relies on an identified model, some residual uncertain terms remain and perturb the linear and decoupled system. This motivates the use of a robust control design approach to complete the control scheme. In this article the sliding mode control methodology is adopted. Sliding mode control has many appreciable features, such as design simplicity and robustness versus a wide class of uncertainties and disturbances. Yet conventional sliding mode control seems inappropriate to be applied in robotics since it can generate the so-called chattering effect, which can be destructive for the controlled robot. In this article, this problem is suitably circumvented by designing a second-order sliding mode controller capable of generating a continuous control law making the proposed sliding mode controller actually applicable to industrial robots. To build the inverse dynamics part of the proposed controller, a suitable dynamical model of the system has been formulated, and its parameters have been accurately identified relying on a practical MIMO identification procedure recently devised. The proposed inverse dynamics-based second-order sliding mode controller has been experimentally tested on a COMAU SMART3-S2 industrial manipulator, demonstrating the tracking properties and the good performances of the controlled system.

The following topics are dealt with: renewable energy sources; energy conservation; computer aided engineering; thermal power stations; solar power stations; solar absorber-convertors; distributed power generation; photovoltaic power systems; domestic appliances; humidity.

In dealing with the trajectory tracking control of robotic manipulator many scholars have had to work in a sliding mode controller. However, SMC has two major limitations one is chattering the other is asymptotical convergence. The chattering problem occurs in traditional SMC due to the switching function of the discontinuous controller and the constant gain parameter of K. Though in this study a Fuzzy Gain Scheduling Terminal Sliding Mode (FGSTSM) controller with a hyperbolic tangent function instead of signum function, is proposed and applied for tracking control of the UR5 robot manipulator. Moreover, the mathematical model of the UR5 robot manipulator using the Newton-Euler algorithm was developed on Maple software of version Maple 18.2. Hence the trajectory tracking control of the UR5 robot manipulator simulation was conducted on MATLAB/SIMULINK of version Matlab R2016a. Then for simulation purposes, a curve (arc) was taken as the desired trajectory for the robot manipulator to track and finally the result is compared with the conventional SMC controller.

This paper deals with the interaction control of robot manipulators. The ideal goal is to control the manipulator so that its end‐effector reaches a desired position in the operative space. The attainment of this goal can be prevented by the fact that during its motion the end‐effector can interact with the environment. So, a realistic goal is regarded as control objective in the paper, that of asymptotically reaching an equilibrium position jointly determined by the choice of the ideal desired position, and by the presence of the environment. The model of the manipulator is supposed to be affected by uncertainties, so that a classical impedance control scheme cannot be adopted. The approach proposed in this paper relies on the theory of sliding mode control. In general, this methodology is deemed nonappropriate to control mechanical systems like robot manipulators, since it introduces the so‐called chattering phenomenon, which produces undesired wear and vibrations. Yet, the final control solution proposed in this paper is based on the generation of sliding modes of the second order, which practically reduces the degradation of performances, and the mechanical stress due to the chattering effect. Indeed, the proposed second‐order sliding mode control scheme relies on the use of a continuous control law, in contrast to conventional sliding mode control schemes. Copyright © 2007 John Wiley & Sons, Ltd.

Chattering-free higher order sliding mode controller with a high-gain observer for the load following of a pressurized water reactor

This article presents a novel reinforcement learning (RL)-based control scheme for trajectory tracking of robot manipulators, incorporating an uncertainty estimator and an optimal tracking controller. A momentum observer (MO) is implemented in conjunction with an integral sliding mode control (ISMC) to facilitate uncertainty estimation for compensation. A proportional-derivative-like (PD-like) control plus an actor-critic neural network (NN)-based feedforward control is utilized for trajectory tracking. An NN parameter selection scheme is adopted to circumvent the time-consuming adjustments of its activation functions and initial weights, thereby ensuring the admissibility of the initial control policy and improving its efficiency. Lyapunov function analysis demonstrates stability of the closed-loop system, in which all error signals are shown to remain bounded and eventually settle into a small residual set. The proposed control scheme is compared with a conventional PD approach consisting of a feedforward controller and an NN controller with adaptive radial basis functions (RBFs). Comparison is also made with a recent approach featuring a feedforward super-twisting sliding mode control (FSTSMC). Simulation and experimental results show superior tracking performance of the presented control scheme against the comparative counterparts, validating the new approach and further supporting its effectiveness and feasibility.