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A new adaptive time delay estimation technique with sliding mode control method is proposed and investigated in this passage for cable-driven manipulators. Time delay estimation technique is an effective tool to compensate for unmodeled dynamics and unknown disturbance, and adaptive time delay estimation performs better due to its adaptive control gain. The proposed adaptive method is based on the fuzzy logic algorithm which has a great advantage in input–output mapping thank to its flexibility. Tuning procedure is addressed to reveal the implementation of the newly proposed algorithm. Moreover, the desired trajectory is taken as an input of adaptive algorithm and better control performance is obtained through this attempt. The proposed controller is ultimately uniformly bounded and proof using the Lyapunov method is provided. Finally, comparative experiments show the validity and effectiveness of the proposed controller.

In recent years, aerial manipulators consist of unmanned aerial vehicles and robotic manipulators have been widely utilized in aerial operations. The complex dynamic coupling effects between unmanned aerial vehicles and robotic manipulators will bring some issues to the motion control. Therefore, the article proposes a new control scheme for aerial manipulators. The proposed method includes three elements, that is, time-delay estimation, backstepping design, and nonsingular terminal sliding mode. The time-delay estimation technique is adopted to estimate the complex system dynamics and to bring a model-free feature of the system. With the backstepping design, the proposed control strategy can ensure the asymptotic stability of the closed-loop system by recursive procedure. To deal with the unmodelling dynamics and disturbances, and to assure finite-time convergence of the system states, the nonsingular terminal sliding mode is adopted. By combining three elements, the tracking performance of aerial manipulators is improved under unmodelling dynamics and disturbances. Global stability of closed-loop control system is analyzed using Lyapunov stability theory. Finally, comparative simulations are conducted, and the results show that the proposed controller has better performance than a conventional proportional–derivative controller or a nonsingular terminal sliding mode controller.

With the increasing demand for air operations, in this article, a control algorithm is proposed for a novel light cable-driven manipulator developed for aerial robots. On account of the control problem of cable-driven manipulators, we design a time delay estimation–based nonsingular terminal sliding mode controller with a fuzzy logic system to further improve the precision of joint position tracking. First, time delay estimation technique is adopted to estimate unknown dynamics of the manipulator system. And thanks to time delay estimation, accurate dynamic model is not needed and thus the controller is model-free which makes it more practical. The main part of the controller is nonsingular terminal sliding mode which ensures satisfactory tracking precision and good robustness under time delay estimation error and external disturbances. Besides, the boundary layer is introduced for reducing chattering and was regulated by a fuzzy logic system to realize a faster convergence. Global stability and finite time convergence to equilibrium of the closed-loop control system are analyzed using Lyapunov stability theory. Finally, comparative experiments are conducted through a newly designed planar cable-driven manipulator. Experimental results show that the proposed controller has a better performance compared with a conventional nonsingular terminal sliding mode controller while control effort is almost the same.

The joint coupling relationship was studied aiming at the motion coupling among multi cable-driven robot joints. A novel motion-decoupled mechanism is proposed and investigated. Two driving cables of distal joint traverse the modular in a specific routing. As a result, cables will wind and unwind at a certain angular along the groove in the following wheel. This design can effectively compensate the length change of cables during the rotating moving of proximal joint. Afterward, a 2–degree-of-freedom cable-driven manipulator platform using this motion-decoupled modular was set up. The verification experiment has shown a productive performance in realizing motion independence. Then, a new robust controller using time-delay estimation and fuzzy algorithm is proposed for the decoupled cable-driven manipulator. Thanks to time-delay estimation and fuzzy algorithm, the proposed controller is model-free, precise and easy to use under practical applications. Finally, contrast control experiments have been performed, and the result illustrates the superiority of the proposed control strategy.

Improving the control performance of active vibration isolation systems is crucial to provide an ultra-quiet environment for precision instruments. This paper presents a new fractional-order robust model reference adaptive controller for the piezo-actuated active vibration isolation systems with a relative-degree-one model. One advantage of the proposed controller lies in that its controller parameters are adjusted online by fractional proportional–integral-type adaptive laws, which not only speeds up the convergence of the closed-loop system, but also improves the control energy efficiency. Moreover, the proposed controller only uses the measurable input and output of the plant as feedback signals, which is convenient for controller implementation. The stability of the closed-loop system is proved based on the Lyapunov theory in detail. The optimal values of the fractional order and adaptive gains for adaptive laws are determined using the multi-objective genetic algorithm through off-line simulation. Comparative experiments on the piezo-actuated active vibration isolation systems are conducted to verify the effectiveness of the proposed controller. Results show that the proposed controller achieves satisfactory isolation performance in a wider frequency band of 20–500 Hz, and simultaneously reduces the control effort compared with the traditional MRAC methods.

Aiming at the requirements of lightweight, low energy consumption and low inertia of the manipulators for autonomous underwater vehicles, this article presents a novel underwater cable-driven manipulator for autonomous underwater vehicles. Thanks to the cable-driven mechanism, the motors are installed remotely from joints, which can reduce the disturbance of the motion of the manipulator to the system and extend the operation time under the premise of limited energy. Cable–sheath mechanism is used to realize the motors to be fixedly mounted on the base (postposition). A prototype named Polaris-II is assembled, and experiments are carried out with the time-delay control scheme. Although the control effect of a single time-delay controller is good, there exist large errors caused by the reversing of joints. Therefore, a fuzzy compensator is designed and added to the time-delay controller to suppress the large errors. The experimental results show that the time-delay controller with a fuzzy compensator has a good inhibitory effect on the large errors while maintaining good control effect.

For the repetitive motion control, inaccurate model, and other issues of industrial robots, this article presents a novel control method that the proportion differentiation-type iterative learning parameters are self-tuning based on artificial bee colony algorithm. Considering the influence of the numerical value of iterative learning parameters on the control system, especially in the early iteration, the control effect is not satisfactory. Thus, the artificial bee colony algorithm is introduced in this article. Using bee colony as search unit, the parameters in iterative learning are optimized through the exchange of information and the survival of fittest between them. And then the optimized results are returned to iterative learning control algorithm. Finally, the digital simulation of a two-degrees-of-freedom manipulator and the experimental verification of a cable-driven robot with its first two joints are carried out. The results show that the iterative learning control based on the artificial bee colony algorithm has faster convergence and better control effect than the iterative learning control with fixed parameters.

A novel wearable vibrotactile system is proposed in this article to enhance the performance of teleoperation robot systems. Using a wearable vibrotactile glove, the proposed system guides the operator in the master–slave control through a vibrotactile-visual guidance method. Based on sensory substitution, the vibrotactile-visual combined guidance method combines vibration stimuli and visual feedback to substitute the virtual guidance force. A vibrotactile potential field is constructed in the workspace of the master-operator to calculate the frequency of the vibration stimulus. To provide vibration stimuli, a novel vibrotactile glove is designed and manufactured based on the layout of the sensitive region of human hand. As the human hand is unable to discriminate vibration stimuli of all frequencies, the vibration stimulus is discretization according to the result of the vibration discriminability experiment. At last, two contrast experiments in obstacle-free and obstacle-existing environments are conducted to verify the feasibility and effectiveness of the wearable vibrotactile system. The results show that this wearable vibrotactile system is an effective solution for guiding the operators in teleoperation and virtual environments.

For the multi-degrees of freedom control problem of underwater hydraulic manipulators with non-ignorable valve deadband and strong lumped nonlinearities and uncertainties, a practical continuous fractional-order nonsingular terminal sliding mode control design together with a deadband compensator is presented and studied. The presented method contains three parts a time delay estimation utilized to nearly estimate and compensate the extremely complicated system dynamics, a continuous fractional-order nonsingular terminal sliding mode used to ensure high control performance against the strong lumped nonlinearities and uncertainties, and a valve deadband compensator used to compensate for the non-ignorable valve deadband. The proposed method is model-free thanks to the time delay estimation, and can ensure satisfactory control performance thanks to the continuous fractional-order nonsingular terminal sliding mode and deadband compensator. Stability of the closed-loop control system including the deadband compensator is proved rigorously. Finally, practical 2-degrees of freedom experiments are performed, and corresponding results effectively demonstrate the superiorities of the newly presented controller with deadband compensator.

To ensure satisfactory control performance for the underwater vehicle-manipulator systems, a novel continuous nonsingular fast terminal sliding mode controller is proposed and investigated using time delay estimation in this article. Complex lumped unknown dynamics including the strong nonlinear couplings and external disturbance are properly compensated with time delay estimation, which are mainly based on the time-delayed signals of underwater vehicle-manipulator systems and can provide with a fascinating model-free feature. Afterwards, the satisfactory tracking control performance and good robustness under heavy lumped uncertainties are ensured using the continuous nonsingular fast terminal sliding mode term with a fast terminal sliding mode–type reaching law. Therefore, the proposed controller is easy to use thanks to time delay estimation, and can ensure good control performance owing to continuous nonsingular fast terminal sliding mode. Stability of the closed-loop control system is analyzed using Lyapunov stability theory, and theoretical tracking errors are calculated and presented. Finally, the effectiveness and advantages of the proposed controller are demonstrated through comparative 7-degree-of-freedom pool experiments.

A new discrete time delay control design is presented and investigated for the joint-space control of hydraulic manipulators in this article. Thanks to the time delay estimation technique, our new designed controller no longer needs the detailed system model, which is very fascinating for practical applications. Also, the proposed discrete time delay control method requires no acceleration information to be obtained through quadratic differential, which is usually essential for the continuous-time version time delay control method of hydraulic manipulators. This may result in fewer requirements of computational effort or unavailability of sensors for obtaining the acceleration signal. Furthermore, the newly proposed discrete time delay control requires no future predicted values of the desired trajectory or system states compared with the traditional discrete time delay control method, which is more suitable for practical applications. The corresponding stability is analyzed using the bounded input bounded output stability theory. The easiness for actual applications and robustness against disturbance are verified through some 2-degree-of-freedom experiments.

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.

Ring periodic structures are widely spread in engineering applications, where natural frequencies can split due to the deviation from axisymmetry. This work aims at the elimination of the dual-mode natural frequency splitting by using feature shifting. A concept of equivalent feature is introduced based on the grouping idea and an analytical model with discrete features is established. The relationships between the group number, feature number, shifting angle and excited circumferential wavenumber are identified as closed-form expressions. The splitting for structures with unshifted standard features depends on the feature number and wavenumber regardless of the grouping patterns. The equivalence between various groupings is verified. Simple rules governing the dual-mode splitting are elaborated, where one splitting is removed by a combination of equivalent feature number and wavenumber, and the other is eliminated by feature shifting. The rules allow immediate estimation and elimination of the dual-mode splitting where the modified structures still hold symmetry. The results can find application in vibratory structures where the frequency splitting is the key concern. The main results are verified by the Finite Element method.

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.

This work examines the elastic vibration of the ultrasonic stator subjected to piezoelectric bending excitation by focusing on two fundamental issues: general driving rule and vibration distortion. An elastic model of a cylindrical ultrasonic stator is developed by using Hamilton’s principle and solved by analytical approach. The results imply that a desired vibration can be aroused provided that an algebraic relation is satisfied by a suitable parameter combination. Traveling/standing wave is excited by conventional time-spatial voltage ones or even other ones. The relationships between the duty ratio of input voltage and wave distortion are identified as closed-form expression of basic parameters. The excitation’s average creates a stationary deflection but it can be neglected thanks to the sufficiently small amplitude it causes relative to that at the resonance frequency. The rotation reversion is realized by changing the duty ratio or excitation frequency but remarkable distortion and amplitude decrease occur, leading to the asymmetry between the forward and inversion. Main results are validated by the superposition approach and comparisons against the existing ones. Discussions on phasing effect and vibration distortion relative to other symmetric systems are also made. Main contributions are the general driving rule with non-π/2 time-spatial phases and explanations on vibration distortion. These are achieved via the general time-spatial phasing in cyclically symmetric power-transmission systems.

To satisfy the needs of surgeons for judging the contact state of the catheter robot and modify the operation accordingly, a novel contact torque estimation and haptic feedback method is proposed in this article. Using the vibrotactile feedback, the proposed method reminds the surgeon which bending unit of the robot contacts with human tissue and guides him to realize the disengagement. Based on a novel simplification of the driving force of the robot, a quasi-statics model is established to estimate the contact torque. Simulations are conducted based on Finite Element Method (FEM) to verify the accuracy of the quasi-statics model and the estimation method. A robot system composed of a catheter robot, a PC, a master-operator, and a wearable vibration glove is assembled according to this method. To verify the feasibility of this method, a contact torque estimation experiment and a vibrotactile feedback experiment are conducted in this article. The results show that this method is accurate and effective.