Practical Tracking Control Under Actuator Saturation for a Class of Flexible-Joint Robotic Manipulators Driven by DC Motors

This paper is devoted to the practical tracking control for a class of flexible-joint robotic manipulators driven by DC motors. Different from the related literature where control constraint is neglected and the disturbances are excluded or only exist in one subsystem, actuator saturation is considered in this paper while the disturbances are present in all the three subsystems. This leads to the incapability of the traditional schemes on this topic. For this, a novel control design scheme is proposed by skillfully incorporating adaptive dynamic compensation technique, constructive methods of command filters and an auxiliary system for the actuator saturation into the backstepping framework, and in turn to design a practical tracking controller which ensures that all the states of the resulting closed-loop system are bounded and the system output practically tracks the reference signal. It is worthwhile strengthening that a more wider class of reference signals can be tracked since they are only first order continuously differentiable but twice or more in the related literature. Finally, a numerical example is provided to validate the effectiveness of the proposed theoretical results.

A Hierarchical Structure Control Strategy Based on MPC for a Six-DOF Flexible Joint Manipulator

The six-degree-of-freedom flexible joint manipulator is a complex system that suffers from the problem that the trajectory planning results are inconsistent with the control results. To keep the planned trajectory within the control range of the manipulator, a hierarchical structure control strategy is designed, which consists of a trajectory planning layer, a model predictive control layer, and a bottom control layer. Specifically, first, the target joint angles are obtained by a time-optimal trajectory planning algorithm based on a genetic algorithm in the trajectory planning layer. Second, in the model predictive control layer, considering the system physical constraints, the model predictive controller is adopted to provide the set points for the Proportion-Differentiation (PD) controllers. Finally, in the bottom control layer, the manipulator moves along the target trajectory under the PD controllers with the feedback control law. The simulation results show that, compared with the PD control strategy, the hierarchical structure control strategy can achieve better control performance and reduce the tracking error of the terminal trajectory by 33.70%.

Investigation on Orbital EDM for Double-Hole Thin Wall of Integrated Flexible Joint

The thin neck structure of integrated flexible joint is the key factor to realize high-precision navigation in dynamically tuned gyroscope. The thin neck structure is composed of two adjacent circular holes and the thin wall between the two holes. The thin wall is easy to deform under the external force and vibration exerted by the tool when using traditional machining methods such as drilling and boring, and the cutting tools are easily to be damaged for the machining of small holes in superhard materials, inducing high processing cost. Aiming at these problems, the machining method of double-hole thin wall in the step-by-step orbital electrical discharge machining (EDM) with a high rotation speed electrode is proposed. The procedure for EDM of double-hole flexible thin wall is designed, and the process parameters of each step machining are optimized using orthogonal experiment and signal-to-noise ratio analysis. The machining experiments of double-hole thin wall of 3J33B material are proceed using the optimized parameters. The results show that the hole diameter of the double-hole flexible thin wall is 2 mm, the hole depth is 8mm, and the average thickness of the thin wall is about 46.5 μm. The thickness range between the measured point and the average is 1.55 μm, that compared with average thickness of 46.5 μm, the error is less than 3%, the overall thickness is uniform relatively.

Investigating the Deformation and Failure Mechanism of a Submarine Tunnel with Flexible Joints Subjected to Strike-Slip Faults

Knowledge from historical earthquake events indicates that a submarine tunnel crossing active strike-slip faults is prone to be damaged in an earthquake. Previous studies have demonstrated that the flexible joints are an effective measure for a submarine tunnel crossing a strike-slip fault. The background project of this paper is the second submarine tunnel of Jiaozhou bay. In this work, model tests and numerical simulations are conducted to investigate the deformation and failure mechanism of a submarine tunnel with flexible joints under a strike-slip fault dislocation. The influence of strike-slip faults on a tunnel with flexible joints has been investigated by examining the deformation of rock mass surface, analyzing lining stains, and crack propagation from model tests. Numerical simulations are conducted to study the effects of the design parameters of a tunnel with flexible joints on the mechanical response of the lining. The results showed that the ‘articulated design’ measure can improve the ability of the tunnel to resist the strike-slip faults. In terms of the mechanism of design parameters of a tunnel with flexible joints, this paper finds that increasing the lining thickness, decreasing the lining segment length, and decreasing the tunnel diameter to a reasonable extent could effectively improve the performance of this faulting resistance measure for a tunnel under the strike-slip fault zone dislocation. Compared with the horseshoe tunnel cross-section, the circular tunnel cross-section can improve the ability of the faulting resistance of a tunnel with flexible joints, while the optimal angle of the tunnel crossing the fault zone is 90º. It is concluded that the wider fault zone, smaller flexible joint width, and less stiffness of the flexible joint could make lining safer under a strike-slip fault dislocation. The above research results can serve as a necessary theoretical reference and technical support for the design of reinforcement measures for a submarine tunnel with flexible joints under strike-slip fault dislocation.

Chattering-Suppressed Sliding Mode Control for Flexible-Joint Robot Manipulators

In this paper, sliding mode tracking control and its chattering suppression method are investigated for flexible-joint robot manipulators with only state measurements of joint actuators. First, within the framework of singular perturbation theory, the control objective of the system is decoupled into two typical tracking aims of a slow subsystem and a fast subsystem. Then, considering lumped uncertainties (including dynamics uncertainties and external disturbances), a composite chattering-suppressed sliding mode controller is proposed, where a smooth-saturation-function-contained reaching law with adjustable saturation factor is designed to alleviate the inherent chattering phenomenon, and a radial basis function neural network (RBFNN)-based soft computing strategy is applied to avoid the high switching gain that leads to chattering amplification. Simultaneously, an efficient extended Kalman filter (EKF) with respect to a new state variable is presented to enable the closed-loop tracking control with neither position nor velocity measurements of links. In addition, an overall analysis on the asymptotic stability of the whole control system is given. Finally, numerical examples verify the superiority of the dynamic performance of the proposed control approach, which is well qualified to suppress the chattering and can effectively eliminate the undesirable effects of the lumped uncertainties with a smaller switching gain reduced by 80% in comparison to that in the controller without RBFNN. The computational efficiency of the proposed EKF increased by about 26%.