Active disturbance compensation is crucial for realizing high-precision servo control. However, the suppression of rapidly changing disturbances is still a challenging issue. In this article, observer-based disturbance-rejection control is investigated, and an observer with adaptive switching gain is proposed for improved robustness against changing disturbances. First, a disturbance observer (DOB) is established, based on the tracking differentiator technique. Second, a sliding-mode-assisted observer with an adaptive law is designed to estimate the residual-disturbance estimation error of the DOB. The proposed scheme instantly increases the switching gain when the state deviates from a preset boundary, thus eliminating the tuning time. The switching control action with an immediately large switching gain is robust against suddenly changing disturbances. Moreover, the switching gain then decays to zero, reducing chattering in the steady state. The gain adjustment process is designed to have the same dynamic characteristics as the proposed DOB, which guarantees the convergence of the proposed scheme. This method is not only suitable for linear systems, but also extendable to nonlinear systems. The proposed scheme was evaluated experimentally; the results showed that it improves disturbance rejection and decreases servo error.

This study developed a local fixed-time sliding mode control (FTSMC) method based on a novel adaptive disturbance observer (NADOB) dedicated to motion tracking control for piezo-driven microscanning systems with unmodeled uncertainties and external disturbances. First, the NADOB was developed to precisely approximate and compensate for the lumped disturbance, which includes unmodeled uncertainties and external disturbances. The adaptive law of the NADOB method can estimate the upper-bound information of the lumped disturbance, assuming that it is bounded. Its convergence was strictly proven using the Lyapunov theorem. Subsequently, the local FTSMC method with an improved approach law was developed for the piezo-driven microscanning system to achieve high-precision trajectory tracking control. The stability of the tracking controller was proved using the fixed-time convergence theory. Finally, a series of comparative experiments were conducted on a piezo-driven microscanning experimental setup in the presence of a lumped disturbance, illustrating the robustness of the local FTSMC method with the NADOB. Comparative experimental results revealed that the proposed fixed-time tracking control scheme exhibits stronger robustness and higher tracking accuracy compared with existing sliding mode control methods.

Vascular interventional surgical robots(VISR) assisted doctors in surgery can not only protect doctors from X-ray radiation, but also improve the accuracy of surgery. The catheter and guidewire operating systems with master-slave operation mode play an important role in VISR. In recent years, the operating systems have gradually become a research hotspot. After nearly two decades of development, they have made great progress, but there are still some problems to be solved. This review first introduces the research necessity and development history of these operating systems. Then, we summarize the research direction of operating systems from the perspective of hardware devices and algorithms. In the hardware devices, we analyzed the catheter and guidewire operating mechanisms, contact force detection devices, master operating mechanisms and master force feedback devices. In the algorithm, we introduce the bilateral control methods, security strategies and skill evaluation methods. Next, we discuss the actual performance and shortcomings of the operating systems from the perspective of clinical application. Finally, we summarize the current problems of the operating systems and propose the future development direction. This review is helpful for researchers to understand the current situation, and provides a reference framework of catheter and guidewire operating system.

A switching-channel bilateral control with energy monitor (EM) is newly proposed to realize haptic communication through a wireless network. The varying delay in the communication line and the situation of duplex operation are considered. In such a system, human operators on two sides of the master-slave robots system feel the hardness of the remote environment placed on the contralateral side. The EM approach is presented to judge the role of the robot (manipulated by an operator or contacting an environment), which provides a beacon for the switching algorithm. The position tracking of the system is improved by switching off the channel of force control in the human manipulated robot. The problem of position drift in traditional methods is overcome. Disturbance observer is applied to simplify the design of the bilateral control law, and to guarantee the efficient force switching. Because of improved position tracking and satisfactory force fidelity, the proposed approach achieves more vivid haptic transmission. By experiments, the validity is verified.

In this paper, a discrete second order linear equation with the Krasnosel’skii-Pokrovskii (KP) operator is used to describe the piezoelectric actuated stage. The weights of the KP operators are identified by the gradient descent algorithm. To suppress the hysteresis nonlinearity of the piezoelectric actuated stage, this paper proposes an adaptive tracking control with the hysteresis decomposition on the designed error surface. The proposed adaptive tracking controller dispenses with any form of the feed-forward hysteresis compensation and the unknown parameters of the discrete second order linear equation are adaptively adjusted. Some simulations are implemented to verify the effectiveness of the KP operators, then a series of modeling and control experiments are carried out on the piezoelectric actuated stages experimental systems. The comparative experimental results verify the feasibility of the KP operators modeling method and the adaptive tracking control method.