International Journal of Control, Automation and Systems

Gravity is omnipresent for all objects on Earth. However, in an environment of different gravitational stress (e.g., microgravity or partial gravity), cells and organs show different biological responses. So, researchers have attempted to achieve micro- or partial gravity on Earth through various approaches, such as parabolic flight or free fall. However, the duration of such ground experiments is highly limited, making it very difficult to conduct time-consuming tasks, such as cell culture. Thus, a three-dimensional (3D) clinostat is utilized as an alternative for experiments on the International Space Station. It provides time-averaged simulated micro- and partial gravity by using mechanical frames with two rotating actuators. This study proposes novel control algorithms for simulating micro- and partial gravity and validates them by applying it to the control of a manufactured 3D clinostat. First, the novel algorithm for time-averaged simulated microgravity (taSMG) provided a more uniformly distributed gravity field by reducing two poles the gravity-concentrated areas. The taSMG with reduced poles provides isotropic gravitational patterns, from which it is possible to minimize the unnecessary effect due to nonuniformity of the gravity vector direction. Second, the other suggested novel algorithm for time-averaged simulated partial gravity (taSPG) controls the pole sizes asymmetrically to generate the intended size of partial gravity. The suggested algorithms are based on mathematical models rather than totally randomized motions. Therefore, the convergence of gravity values, in the rotating frame over time, can be analytically predicted with improved accuracy compared with previously reported algorithms. The developed 3D clinostat hardware and algorithms will effectively provide well-validated taSMG and taSPG for cell growth experiments in future studies for space medicine.

This paper presents a new direct active and reactive power control (DPC) scheme for a three-phase grid connected voltage source inverter (VSI) based on the passivity viewpoint using the port-controlled Hamiltonian (PCH) system. The proposed controller consists of feedforward and feedback parts. The feedforward part (the reference inputs) is generated through the flatness of the dynamics of the VSI model, which makes the error dynamics in the form of PCH system. The nonlinear feedback part is designed to enhance the damping of the error dynamics by using its Lyapunov function. The proposed control method has an ability of the finite time reaching condition similar to sliding mode control (SMC). Moreover, the exponential stability and uniform performance are guaranteed over all operating points without need for reaching a certain manifold. The proposed method is validated by using an experiment through hardware-in-the-loop system with a digital signal processor. The experimental results for the proposed method are compared with those using SMC-DPC method. The proposed method significantly reduces the total harmonic distortion in the output current without deteriorating the transient response of the active and reactive powers. In addition, it provides robust performance against the line impedance variations and the grid voltage sag.

This paper studies the exponential admissibility and H ∞ control problems for a class of singular systems with time-varying delay in state. Firstly, an exponential admissibility criterion is obtained based on linear matrix inequalities (LMIs). It is worth mentioning that the derivative of the time-varying delay does not need to be smaller than one. Based on the proposed condition, a new delay-dependent H ∞ controller is also given, which guarantees the admissibility and the H ∞ performance γ. Numerical examples are given to illustrate the effectiveness of the proposed method.

In this paper, a data-driven scheme for the robust Fault Isolation of multiple sensor faults is proposed. Robustness to modelling uncertainty and noise is achieved via the optimized design of the processing blocks. The main idea of the study is the introduction of a Pre-Isolation block that selects a restricted set of sensors containing (with high probability) the subset of the faulty sensors; in this phase, robustness is achieved through the datadriven design of a redundant number of Multiple Analytic Redundancy Relations (MARRs) and a voting logic for the ranking of the candidate faulty sensors. Then, robust Faults Isolation (FI) is achieved by means of another large set of specialized ARRs, whose fault signatures are specifically designed to optimize, at the same time, noise immunity while maximizing the decoupling only of the pre-isolated fault directions (Partial-Orthogonality Criteria). The proposed diagnostic system may provide an effective means for early sensor failure isolation, particularly useful for critical applications such as aerospace control systems or energy management systems. To assess the performance of the approach, we performed a comparative study with other State-of-the-Art (SoA) approaches using a well-known benchmark model that emulates faults on six sensors. Results for single and multi-contemporary faults have clearly highlighted the superiority of our method.

This paper studies unknown input observer design for discrete-time Takagi-Sugeno fuzzy systems. The proposed unknown input observer has a new structure that can be applied to Takagi-Sugeno fuzzy systems with nonlinear output equation. We derive the design conditions of the proposed unknown input observer based on Lyapunov function and convert them into a set of linear matrix inequalities. Numerical simulations of a vehicle lateral dynamics are given to illustrate the effectiveness of the proposed method.

This paper investigates the robust tracking control of second-order uncertain nonlinear systems by adopting the function augmented sliding mode control approach. An improved version of this approach is proposed such that the exact information of the initial tracking error is not required when generating the desired trajectory of the tracking error. This evidently enlarges the application scope of the function augmented sliding mode control approach. Performance functions are introduced to form the performance envelopes for the sliding mode variables. A robust sliding mode controller is constructed such that the sliding mode variables are confined within their performance envelopes. This further guarantees that the tracking error converges to the given neighbourhood of zero within the preassigned settling time provided that proper control parameters are selected. An application example on the rendezvous control of spacecraft is also employed to illustrate the effectiveness of the proposed control approach.

Neurogenic bladder is one of the known diseases that affects the Lower Urinary Tract (LUT) leading to a dysfunctional operating pattern. The disease is mainly attributed to disorders in the central nervous system or peripheral nerves which play the major role in controlling the micturition process. This paper suggests a new technique to treat this disease considering robust Model Predictive Control (MPC). The proposed MPC controller proves capability to bring the dysfunctional LUT to its normal operating pattern while satisfying the nerve signal constraints and demonstrates high degree of robustness when severe uncertainties between the model and real patients are considered. In addition, in order to pave the way for applying the proposed controller to real patients, the system resistance to external noise is investigated and an attenuation technique is introduced to reduce the harmful effect of potential noise interference.

In this paper, a semi-automatic knob system for assisting control of flexible endoscope is introduced. For conventional flexible endoscope, the torque to bend the bending part is increased proportionally to the curvature of the insertion tube. As the bending angle increases, the required torque is increased. This characteristic makes a surgeon tired. The proposed semi-automatic knob system consists of a knob controller, a power generation unit, and a bending part. The knob controller includes four FSR (force sensitive resistor) sensors to measure external force applied by the operator. The power generation unit generates the power depending on the signal level of FSR sensors. Using the semi-automatic knob system, a user can control the steering of the flexible endoscope with less power as compared to conventional flexible endoscope. The usefulness of the proposed system is verified through experiments.