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Research Papers

J. Dyn. Sys., Meas., Control. 2019;141(9):091001-091001-10. doi:10.1115/1.4043053.

The design of a trajectory tracking controller for a general class of n-link type (m,s) electrically driven wheeled mobile manipulators has been addressed in this paper. In order to achieve a high level of the tracking performance, an adaptive robust proportional-integral-derivative (PID) controller is proposed which only requires position measurements by designing a velocity observer. Integral actions are incorporated into the design of both controller and observer to reduce the steady-state error as much as possible. The dynamic surface control approach is also applied to reduce the design complexity at the actuator level. Lyapunov's direct method is used to guarantee that tracking and observation errors are semiglobally uniformly ultimately bounded. Simulation results are presented to illustrate the effectiveness of the proposed controller for a group of mobile manipulators.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2019;141(9):091002-091002-10. doi:10.1115/1.4043227.

Quadrotors have been used in many areas such as cargo transportation, agriculture, and search and rescue. The low energy density of power sources and the low energy efficiency of quadrotors have prevented quadrotors from a wider range of applications where a large payload has to be carried or long flight time is required. This paper optimizes the energy efficiency of a quadrotor via rotating its arms to proper positions calculated based on the dynamics model of the quadrotor and the power–thrust curve of rotors. The conditions that a quadrotor in steady-state can achieve the optimal energy efficiency are mathematically derived and the energy efficiency of a quadrotor in various scenarios is analyzed. Based on the analysis, an arm-rotation approach is proposed to optimize the energy efficiency of a quadrotor with a center-of-gravity offset in steady hovering. It is shown with simulation that an example quadrotor with rotatable arms can save up to 13% of energy. Experiments show that the same example quadrotor can save even more energy in practice, owing to the byproduct of the arm-rotation approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2019;141(9):091003-091003-7. doi:10.1115/1.4043154.

This paper studies control problems of underactuated mechanical systems with model uncertainties. The control is designed with the method of backstepping. The first-order low-pass filters are used to estimate the unknown quantities and to avoid the “explosion of terms.” A novel method is also proposed to implement the control without the knowledge of the control coefficient, which makes the whole process of backstepping control data-driven. The stability of the proposed control in the Lyapunov sense is studied. It is numerically and experimentally validated, and compared with the well-known model-based linear quadratic regulator (LQR) control. The data-driven backstepping control is found to provide comparable performances to that of the LQR control with the advantage of being model-free and robust.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Dyn. Sys., Meas., Control. 2019;141(9):094501-094501-8. doi:10.1115/1.4043025.

In this work, we establish a new estimate result for fractional differential inequality, and this inequality is used to derive a robust sliding mode control law for the fractional-order (FO) dynamic systems. The sliding mode control law is provided to make the states of the system asymptotically stable. Some examples are given to illustrate the results.

Commentary by Dr. Valentin Fuster

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