Adaptive sliding mode enhanced disturbance observer-based control of surgical device

Global fast non-singular terminal sliding-mode control for high-speed nanopositioning

This paper presents a new Global Fast Non-singular Terminal Sliding Mode Controller (GFNTSMC) that delivers high-precision tracking of high-frequency trajectories when applied to a piezo-driven nanopositioner. The control scheme is realized by combing inverse hysteresis model and global fast non-singular terminal sliding mode compensation. The inverse Bouc-Wen hysteresis model is used to calculate the required hysteresis-compensating feedforward control voltage according to the reference signal. The key uniqueness of the proposed control strategy is it's red global fast convergence, achieved with high accuracy and high bandwidth. The stability of the reported GFNTSMC controller is proved with the Lyapunov theory. Its performance is verified through experimentally recorded tracking results, and its superiority over three benchmark control approaches, namely the Proportional-Integral-Derivative (PID), the Positive Position Feedback with integral action (PPF+I) and the conventional linear high-order sliding mode controller (LHOSMC) is demonstrated through comparative tracking error analysis. Its wide-band stability as well as its significant robustness to parameter uncertainty is also showcased.

Nominal-Model-Based Sliding-Mode Control for Traveling-Wave Ultrasonic Motor

Traveling-wave ultrasonic motors (TWUSMs) have strong nonlinearity and uncertainty, which are sensitive to the environment, disturbances, and load changes. Thus, precision control of TWUSMs is hard to achieve with traditional methods for complex driving mechanisms. A nominal-model-based sliding-mode control strategy with strong robustness is proposed to achieve accurate speed control of TWUSMs. Firstly, a second-order nominal model of the speed difference and output torque was deduced to construct a nonlinear sliding-mode surface; then, a nonlinear sliding-mode controller was designed with the collaborative regulation of frequency and the amplitude of two-phase control voltages. The global asymptotic stability of the controller was proved under bounded disturbances and parameter uncertainty. Finally, the effectiveness and accurate control were testified to and verified by the simulations and experiments, which showed good robustness and a disturbance rejection of the strategy for TWUSMs, with strong nonlinearity and uncertainty.

Finite-time adaptive sliding mode control for high-precision tracking of piezo-actuated stages

Piezo-actuated stages are widely used in nanopositioning applications. However, they not only have inherent static hysteresis characteristics but also have dynamic rate-dependent hysteresis nonlinearity. Therefore, to address dynamic hysteresis nonlinearity and uncertainty in the model parameters, an adaptive switching-gain sliding mode controller with a proportional-integral-derivative surface is designed. In particular, the combination of Bouc-Wen model and second-order linear system is used to describe the dynamic hysteresis process. To improve the robustness and reduce chattering in the sliding mode control method, an adaptive switching-gain is added to the controller without knowing in advance the upper bound of uncertainties. Finite-time convergence conditions of the closed-loop system are also analyzed. Finally, the proposed control method is implemented in real time on an ARM experimental platform. Comparative experimental results demonstrate excellent tracking performance and robustness. The dynamic hysteresis characteristics are suppressed effectively, and this result provides a powerful reference for engineering applications.

A Low-Voltage Cylindrical Traveling Wave Ultrasonic Motor Incorporating Multilayered Piezoelectric Ceramics

In-plane bending traveling wave ultrasonic motors (USM), which are compact in structure and flexible in design, have been widely applied in biological engineering, optical engineering, and aerospace engineering. However, the high driving voltage and complicated driving circuit of this kind of USM restrict their further miniaturization and electromechanical integration in these applications and bring some potential safety hazards. To solve this problem, a low-voltage-driving traveling wave USM incorporating cofired multilayer piezoelectric ceramics was proposed in this work. Four cofired piezoelectric ceramics were strategically designed to excite two orthogonal third-order in-plane bending modes with the same frequency of the USM. The principles of traveling wave synthesis and low-voltage-driving of the USM were deduced, and the stator dynamic design and transient dynamic simulation were carried out by finite-element method. The microproperties of cofired piezoelectric multilayer ceramics, the vibration characteristics of the stator, and the mechanical output performance of the USM were tested by experiments. The results indicated that the motor can work as low as 5 [Formula: see text]. A long stroke with a maximum forward and reverse rotational speeds of 187.7 and 176.6 r/min were obtained, respectively, and a maximum stalling torque of 4.8 mN · m at 47.3 kHz under 15 [Formula: see text] was achieved. The results showed that the proposed USM is small, low in driving voltage, and high in torque output, which has promising applications in aerospace, biomedicine, and other fields that require a lightweight and integration of driving devices.

Adaptive nonsingular fixed-time sliding mode control for uncertain robotic manipulators under actuator saturation

This paper describes an adaptive nonsingular fixed-time sliding mode control (ANFSMC) scheme under actuator saturation that can track the trajectory of a robotic manipulator under external disturbances and inertia uncertainties. First, a novel NFSMC that offers rapid convergence and avoids singularities is proposed for ensuring robotic manipulators global approximate fixed-time convergence. An ANFSMC is then developed for which the bound of the coupling uncertainty is not necessary to know in advance. The controller exhibits small absolute tracking errors and consumes little energy. An actuator saturation compensator is designed and shown to minimize the chattering of the system while accelerating the trajectory tracking. The proposed schemes are analyzed using Lyapunov stability theory, and their effectiveness and superiority are demonstrated through numerical simulations.

Adaptive robust controller using intelligent uncertainty observer for mechanical systems under non-holonomic reference trajectories

Non-holonomic reference trajectories and uncertainties are typically encountered in a class of mechanical systems. For such systems, this paper investigates the development of a novel explicit adaptive robust controller. By employing the structure of the Udwadia controller, the designed controller can deal with holonomic and non-holonomic reference trajectories in a unified manner. To avoid degradation of performance due to uncertainties, an observer is proposed to identify the uncertainties; the observer is designed using a fuzzy cerebellar model articulation controller neural network. A robust term is designed to restrain the initial deviations and to enhance the robustness of systems. Moreover, a compensatory term is designed to compensate for the residual errors resulted from the uncertainty observer. Rigorous theoretical analysis of the proposed controller is verified via the Lyapunov stability method, and an illustrative example is presented to demonstrate the effectiveness of the designed controller.

Finite-time sliding mode controller for perturbed second-order systems

This paper presents a novel finite-time sliding mode controller applied to perturbed second order systems. The proposed scheme employs a disturbance observer that can identify growing in time disturbances. Then, the observer is combined with a sliding mode controller to achieve finite-time stabilization of the second-order system. The convergence of the observer as well as the finite-time stability of the closed-loop system is theoretically demonstrated. Besides, it is also shown that the finite-time convergence properties of a given controller can be enhanced when using a compensation term based on the disturbance observer. The proposed controller is compared with a twisting algorithm and a finite-time sliding mode controller with disturbance estimation. Also, a conventional proportional integral derivative (PID) controller is combined with the proposed disturbance observer in a trajectory tracking task. Numerical simulations indicate that the proposed controller attains finite-time stabilization of the second order system by requiring a less amount of power than that demanded by the other control schemes and without being affected by the peaking phenomenon. Besides, the performance of the PID technique is enhanced by applying the proposed control methodology.