Linyi Gu

Practical Tracking Control of Robot Manipulators With Continuous Fractional-Order Nonsingular Terminal Sliding Mode

This paper studies practical tracking control design of robot manipulators with continuous fractional-order nonsingular terminal sliding mode (CFONTSM) based on time-delay estimation (TDE). The proposed control design requires no detailed information about the robot dynamics, leading to an attractive model-free nature thanks to TDE, and ensures fast convergence and high tracking precision under heavy lumped uncertainties due to the FONTSM surface and fast-TSM-type reaching law. Stability of the closed-loop system and finite-time convergence are analyzed using Lyapunov stability theory. Comparative 2-DOF (degree of freedom) simulation and experiment results show that the proposed control design can ensure higher tracking precision and faster convergence compared with TDE-based continuous integer-order NTSM (CIONTSM) design in a wide range of speed; meanwhile, better performance is also observed compared with TDE-based IONTSM and FONTSM control designs using a boundary layer technique.

Fractional-order nonsingular terminal sliding mode control of hydraulic manipulators using time delay estimation

For the trajectory tracking control problem of rigid hydraulic manipulators under heavy uncertainties and nonlinearities, a novel fractional-order nonsingular terminal sliding mode (FO-NTSM) control method based on time-delay estimation (TDE) is proposed. The proposed control scheme mainly contains two parts: a TDE term and a FO-NTSM term. The TDE term is applied to approximately cancel the complex system dynamics using the intentionally time-delayed information leading to an attractive model-free nature. Meanwhile, the FO-NTSM term, based on a novel fractional-order terminal sliding surface, is designed to stabilize the tracking error to zero in finite time. Stability of the closed-loop control system is analyzed based on the Lyapunov stability theory. Finally, comparative degrees of freedom (2-DOF) practical experiments are performed and the results show that the new proposed method can ensure faster convergence rate and higher tracking precision under heavy lumped uncertainties and nonlinearities compared with its integer-order counterpart.

Experimental studies on the overall efficiency performance of axial piston motor with a laser surface textured valve plate

Experimental studies on the overall efficiency performance of axial piston motor with a laser surface textured valve plate are developed to study the potential use of laser surface texturing in the form of spherical micro-dimples. This study adapts the fiber laser marking machine to machine micro-dimples with different dimensions on the surface of the valve plate for axial piston motor. In addition, these tests of the overall efficiency are given to the axial piston motor fixed to the valve plate with laser micro-dimples in order to find the relationship between the overall efficiency of the axial piston motor and different dimensions of micro-dimples on the surface of the valve plate. The regions of inner dead point and outer dead point of the valve plate are easily erodable because of the pressure pulsation. Therefore, in this study, micro-dimples are machined with different dimensions on the region of the valve plate for the axial piston motor. It is shown that the overall efficiency of the axial piston motor fixed to the valve plate with micro-dimples (area ratio of 5%) can be improved by 2.8%–6.1%, compared to that without micro-dimples; the overall efficiency of axial piston motor fixed to the valve plate with micro-dimples (diameter of 0.1 mm) can be improved by 0.8%–4.9%, compared to that without micro-dimples.

Depth control of ROVs using time delay estimation with nonsingular terminal sliding mode

In this paper, a nonsingular terminal sliding mode (NTSM) control method based on time delay estimation (TDE) is proposed and investigated for the depth control of remotely operated vehicles (ROVs). The complex dynamics is approximately compensated by TDE leading to an attractive model-free nature, which is more suitable for practical applications than other model-based methods. Furthermore, the NTSM manifold based on nonlinear error dynamics can ensure better control performance than the traditional sliding mode (SM) manifold with linear error dynamics. Stability of the closed-loop system is analyzed using Lyapunov theory. Finally, the faster convergence and higher tracking accuracy compared with traditional TDE method with linear error dynamics are verified through simulation.

Output Feedback Fractional-Order Nonsingular Terminal Sliding Mode Control of Underwater Remotely Operated Vehicles

For the 4-DOF (degrees of freedom) trajectory tracking control problem of underwater remotely operated vehicles (ROVs) in the presence of model uncertainties and external disturbances, a novel output feedback fractional-order nonsingular terminal sliding mode control (FO-NTSMC) technique is introduced in light of the equivalent output injection sliding mode observer (SMO) and TSMC principle and fractional calculus technology. The equivalent output injection SMO is applied to reconstruct the full states in finite time. Meanwhile, the FO-NTSMC algorithm, based on a new proposed fractional-order switching manifold, is designed to stabilize the tracking error to equilibrium points in finite time. The corresponding stability analysis of the closed-loop system is presented using the fractional-order version of the Lyapunov stability theory. Comparative numerical simulation results are presented and analyzed to demonstrate the effectiveness of the proposed method. Finally, it is noteworthy that the proposed output feedback FO-NTSMC technique can be used to control a broad range of nonlinear second-order dynamical systems in finite time.

Research on a Nonlinear Robust Adaptive Control Method of the Elbow Joint of a Seven-Function Hydraulic Manipulator Based on Double-Screw-Pair Transmission

A robust adaptive control method with full-state feedback is proposed based on the fact that the elbow joint of a seven-function hydraulic manipulator with double-screw-pair transmission features the following control characteristics: a strongly nonlinear hydraulic system, parameter uncertainties susceptible to temperature and pressure changes of the external environment, and unknown outer disturbances. Combined with the design method of the back-stepping controller, the asymptotic stability of the control system in the presence of disturbances from uncertain systematic parameters and unknown external disturbances was demonstrated using Lyapunov stability theory. Based on the elbow joint of the seven-function master-slave hydraulic manipulator for the 4500 m Deep-Sea Working System as the research subject, a comparative study was conducted using the control method presented in this paper for unknown external disturbances. Simulations and experiments of different unknown outer disturbances showed that (1) the proposed controller could robustly track the desired reference trajectory with satisfactory dynamic performance and steady accuracy and that (2) the modified parameter adaptive laws could also guarantee that the estimated parameters are bounded.

Research on the Stability of a Hydraulic Propulsion System Controlled by Proportional Pressure Reducing Valves

The hydraulic propulsion system is widely used in underwater vehicles due to its high power density and good control performance. In this paper, a torque-controlled hydraulic propulsion system which consists of a pump, a couple of proportional pressure reducing valves and a thruster driven by a hydraulic motor is presented. It has a much lower cost and a higher efficiency compared with servo valve control systems. And its response is still quick enough to control the underwater vehicles’ attitude compared with secondary regulation systems. However, while the propeller is running at a low shaft speed, its load characteristics may lead to instability due to its low load stiffness at low speed, low friction and small internal leakage inside the hydraulic motor.In this paper, all these hydraulic parameters, even the fluid viscosity and the effective bulk modulus, which may influence its stability, are all analyzed and simulated. Based on this, a drive-pressure and back-pressure independent regulation control method is proposed. Pool experiments shows that this double pressure regulated hydraulic propulsion system is quite stable and reliable at low shaft speed.Copyright

Stability analysis of virtual passive actuator with time delay and parameter uncertainties

The purpose of this paper is to present a virtual passive actuator which enables the manipulator joint to behave as a desired spring-damper system. When the manipulator interacts with an unknown environment or human operator, huge contact force will be generated with a high-stiffness trajectory tracking controller: to avoid violent collisions, the virtual passive actuator is proposed to diminish the interaction force, and adjust the system stiffness to adapt to the environment. With the mathematical model of the virtual passive actuator, the system’s stable region is determined based on the Routh–Hurwitz criterion. The influence of operation time delay, filter and model uncertainty is taken into consideration. Finally, the virtual passive actuator is incorporated into a manipulator, and validity is verified through a set of experiments. Experiment results show that, with the proposed controller, virtual passive actuator joint deformation is proportional to the external torque, and the proportional ratio is close to the stiffness setting: it can perform dynamic behavior just like a spring-damper system when subject to step external torque.

The adaptive robust tracking control of deep-sea hydraulic manipulator based on backstepping design

In this paper, design and experiments of the 4500m deep-sea manipulator are introduced. With the extreme working condition, the deep-sea manipulator is more complex and the study is more challenging. The design highlight is stressed, including the double screw pairs elbow joint which could transmit large torque with a compact size, principle of pressure compensator which could balance the water pressure and so on. To achieve high tracking performance, the adaptive robust tracking control based on backstepping algorithm is proposed. The unknown parameters are estimated to enhance the tracking precision. Simulations and experiments based on this algorithm has been performed to verify the controller, the results show that the joint tracking control is fast and smooth, the overshot is small.

The observer-based neural network adaptive robust control of underwater hydraulic manipulator

Hydraulic system is widely used in industry where large actuation forces are needed such as electro-hydraulic positioning system, active suspension control, and so on. One of the main problem in hydraulic system is the nontriviality, for instance, the deadbands in valve operation, frictions of links, saturations, pressure dynamics, etc. both system unknown nonlinearities and external disturbances should be considered in controller design. For underwater hydraulic manipulator, because of the environment of sea and the large nonlinearities of the hydraulic manipulator system, both system unknown nonlinearities and external disturbances should be considered in controller design. A lot of control methods have been proposed to solve the problem properly, such as sliding mode control, adaptive control, fuzzy adaptive control, adaptive robust control, ect. However, due to limited knowledge about hydraulic manipulator system, it is hard to precisely estimate the nonlinearities for a possible higher performance. In this paper, a neural network adaptive robust control method is proposed to help control an underwater hydraulic manipulator. In order to achieve better performance using adaptive robust control strategy, unknown nonlinearities in the system are approximated by the outputs of radial basis function neural network (RBFNNs). A projection law has been used to bound the NN weights when they are tuning on-line to avoid possible adaptive divergence, and the tracking transient performance is guaranteed by robust control law. Simulation results illustrate that manipulator has a good tracking performance.