Real-Time Implementation of the Prescribed Performance Tracking Control for Magnetic Levitation Systems.

For magnetic levitation systems subject to dynamical uncertainty and exterior perturbations, we implement a real-time Prescribed Performance Control (PPC). A modified function of Global Fast Terminal Sliding Mode Manifold (GFTSMM) based on the transformed error of the novel PPC is introduced; hence, the error variable quickly converges to the equilibrium point with the prescribed performance, which means that maximum overshoot and steady-state of the controlled errors will be in a knowledge-defined boundary. To enhance the performance of Global Fast Terminal Sliding Mode Control (GFTSMC) and to reduce chattering in the control input, a modified third-order sliding mode observer (MTOSMO) is proposed to estimate the whole uncertainty and external disturbance. The combination of the GFTSMC, PPC, and MTOSMO generates a novel solution ensuring a finite-time stable position of the controlled ball and the possibility of performing different orbit tracking missions with an impressive performance in terms of tracking accuracy, fast convergence, stabilization, and chattering reduction. It also possesses a simple design that is suitable for real-time applications. By using the Lyapunov-based method, the stable evidence of the developed method is fully verified. We implement a simulation and an experiment on the laboratory magnetic levitation model to demonstrate the improved performance of the developed control system.

A Novel Prescribed-Performance-Tracking Control System with Finite-Time Convergence Stability for Uncertain Robotic Manipulators.

Through this article, we present an advanced prescribed performance-tracking control system with finite-time convergence stability for uncertain robotic manipulators. It is therefore necessary to define a suitable performance function and error transformation to guarantee a prescribed performance within a finite time. Following the definitions mentioned, a modified integral nonlinear sliding-mode hyperplane is constructed from the transformed errors. By using the designed nonlinear sliding-mode surface and the super-twisting reaching control law, an advanced approach to the prescribed performance control was formed for the trajectory tracking control of uncertain robotic manipulators. The proposed controller exhibits improved properties, including estimated convergence speed and a predefined upper and lower limit for maximum overshoot during transient responses. Furthermore, the maximum allowable size of the control errors at the steady-state can be predefined and these errors will inevitably converge to zero within a finite time, while the proposed controller can provide a smooth control torque without the loss of its robustness. It is shown that the proposed control system is globally stable and convergent over a finite time. A comprehensive analysis of the effectiveness of the proposed control algorithm was already conducted via the simulation of an industrial robot manipulator.

An Adaptive Prescribed Performance Tracking Motion Control Methodology for Robotic Manipulators with Global Finite-Time Stability.

In this paper, the problem of an APPTMC for manipulators is investigated. During the robot's operation, the error states should be kept within an outlined range to ensure a steady-state and dynamic attitude. Firstly, we propose the modified PPFs. Afterward, a series of transformed errors is used to convert "constrained" systems into equivalent "unconstrained" ones, to facilitate control design. The modified PPFs ensure position tracking errors are managed in a pre-designed performance domain. Especially, the SSE boundaries will be symmetrical to zero, so when the transformed error is zero, the tracking error will be as well. Secondly, a modified NISMS based on the transformed errors allows for determining the highest acceptable range of the tracking errors in the steady-state, finite-time convergence index, and singularity elimination. Thirdly, a fixed-time USOSMO is proposed to directly estimate the lumped uncertainty. Fourthly, an ASTwCL is applied to deal with observer output errors and chattering. Finally, an observer-based-control solution is synthesized from the above techniques to achieve PCP in the sense of finite-time Lyapunov stability. In addition, the precision, robustness, as well as harmful chattering reduction of the proposed APPTMC are improved significantly. The Lyapunov theory is used to analyze the stability of closed-loop systems. Throughout simulations, the proposed PPTMC has been shown to perform well and be effective.

A Novel Active Fault-Tolerant Tracking Control for Robot Manipulators with Finite-Time Stability.

Many terminal sliding mode controllers (TSMCs) have been suggested to obtain exact tracking control of robotic manipulators in finite time. The ordinary method is based on TSMCs that secure trajectory tracking under the assumptions such as the known robot dynamic model and the determined upper boundary of uncertain components. Despite tracking errors that tend to zero in finite time, the weakness of TSMCs is chattering, slow convergence speed, and the need for the exact robot dynamic model. Few studies are handling the weakness of TSMCs by using the combination between TSMCs and finite-time observers. In this paper, we present a novel finite-time fault tolerance control (FTC) method for robotic manipulators. A finite-time fault detection observer (FTFDO) is proposed to estimate all uncertainties, external disturbances, and faults accurately and on time. From the estimated information of FTFDO, a novel finite-time FTC method is developed based on a new finite-time terminal sliding surface and a new finite-time reaching control law. Thanks to this approach, the proposed FTC method provides a fast convergence speed for both observation error and control error in finite time. The operation of the robot system is guaranteed with expected performance even in case of faults, including high tracking accuracy, small chattering behavior in control input signals, and fast transient response with the variation of disturbances, uncertainties, or faults. The stability and finite-time convergence of the proposed control system are verified that they are strictly guaranteed by Lyapunov theory and finite-time control theory. The simulation performance for a FARA robotic manipulator proves the proposed control theory's correctness and effectiveness.

A Robust Observer-Based Control Strategy for n-DOF Uncertain Robot Manipulators with Fixed-Time Stability.

In this paper, a robust observer-based control strategy for n-DOF uncertain robot manipulators with fixed-time stability was developed. The novel fixed-time nonsingular sliding mode surface enables control errors to converge to the equilibrium point quickly within fixed time without singularity. The development of the novel fixed-time disturbance observer based on a uniform robust exact differentiator also allows uncertain terms and exterior disturbances to be proactively addressed. The designed observer can accurately approximate uncertain terms within a fixed time and contribute to significant chattering reduction in the traditional sliding mode control. A robust observer-based control strategy was formulated, according to a combination of the fixed-time nonsingular terminal sliding mode control method and the designed observer, to yield global fixed time stability for n-DOF uncertain robot manipulators. The proposed controller proved definitively that it was able to obtain global stabilization in fixed time. The approximation capability of the proposed observer, the convergence of the proposed sliding surface, and the effectiveness of the proposed control strategy in fixed time were fully confirmed by simulation performance on an industrial robot manipulator.

Minimally Invasive Mitral Valve Surgery for Rheumatic Valve Disease.

BACKGROUND: The development of minimally invasive mitral valve surgery has created the motivation for using this approach in young patients with chronic rheumatic valve disease. We report our recent experience with patients undergoing minimally mitral valve surgery in this group of patients. METHODS: Between July 2014 and June 2018, 142 patients with rheumatic mitral valve dysfunction underwent minimally invasive surgery through a right thoracotomy approach at the University Medical Center of Ho Chi Minh City in Vietnam. Diagnosis was confirmed with transthoracic and transesophageal echocardiography (TTE and TEE). We analyzed the in-hospital and midterm follow-up outcomes of this group. RESULTS: The mean age was 42.6 ± 9.6 years. Sixty patients (42.3%) were male. Sixty-three patients were diagnosed with functional severe tricuspid regurgitation, 29 patients were identified with moderate tricuspid regurgitation, and tricuspid annulus was more than 21 mm/m²). Mitral valve repair was performed in 16 patients (11.3%), and 126 patients underwent mitral valve replacement. Mitral valve repair techniques included annuloplasty, leaflet peeling, and commissurotomy. Thirty-day mortality was 0.7%. Two patients had to be converted to conventional sternotomy, due to left atrial appendage laceration and mitral annular rupture. The overall survival rate was 98.6%. Freedom from reoperation was 97.1%. CONCLUSIONS: In patients with rheumatic valve disease, minimally invasive mitral surgery safely and effectively can be performed with few perioperative complications and good midterm results.

A model-free terminal sliding mode control for robots: Achieving fixed-time prescribed performance and convergence.

This paper introduces a new control strategy for robot manipulators, specifically designed to tackle the challenges associated with traditional model-based sliding mode (SM) controller design. These challenges include the need for accurately computed system models, knowledge of disturbance upper bounds, fixed-time convergence, prescribed performance, and the generation of chattering. To overcome these obstacles, we propose the incorporation of a neural network (NN) that effectively addresses these issues by removing the constraint of a precise system model. Additionally, we introduce a novel fixed-time prescribed performance control (PPC) to enhance response performance and position-tracking accuracy, while effectively limiting overshoot and maintaining steady-state error within the predefined range. To expedite the convergence of the SM surface to its equilibrium point, we introduce a faster terminal sliding mode (TSM) surface and a novel fixed-time reaching control algorithm (RCA) with adaptable factors. By integrating these approaches, we develop a novel control strategy that successfully achieves the desired goals for robot manipulators. The effectiveness and stability of the proposed approach are validated through extensive simulations on a 3-DOF SAMSUNG FARA-AT2 robot manipulator, utilizing both Lyapunov criteria and performance evaluations. The results demonstrate improved convergence rate and tracking accuracy, reduced chattering, and enhanced controller robustness.

Endovascular treatment for life-threatening hemoptysis due to rupture of descending thoracic aortic aneurysm: A case series.

INTRODUCTION AND IMPORTANCE: Aortic aneurysm is an uncommon but life-threatening cause of hemoptysis. Treatments include surgery and/or endovascular intervention, each with its own advantages and disadvantages. Endovascular intervention is associated with good early and medium-term outcomes. CASE PRESENTATIONS: We report three cases of hemoptysis due to ruptured thoracic aortic aneurysm who underwent endovascular intervention. In all three cases, endovascular grafts were placed in the descending thoracic aorta, the number of grafts used was 1, the average time to stop hemoptysis was 4 to 5 days, and the length of hospital stay was between 6 and 8 days. No intravascular fistula, renal failure, prolonged mechanical ventilation and other major cardiovascular events were reported. CLINICAL DISCUSSION: Endovascular treatment for descending TAA has been demonstrated to be safe and effective, particularly in emergencies in which patients presented with life-threatening hemoptysis, due to its rapid access to the aorta. In our experience at a tertiary hospital in southern Vietnam, the procedural time for a thoracic endovascular aortic repair is relatively brief and can last between 15 and 30 min. Thus, endovascular treatment for ruptured TAA can substantially improve patient prognosis, reduce mortality and complications. CONCLUSION: The implementation of endovascular intervention can help improve prognosis, reduce mortality and complications in patients with hemoptysis due to ruptured thoracic aortic aneurysm.

Aortic prosthetic size predictor in aortic valve replacement.

BACKGROUND: Patient-prosthesis mismatch (PPM) is a major concern in aortic valve replacement (AVR) and leads to perioperative morbidity and rehospitalization. Predicting aortic annulus diameter pre-procedurally is crucial to managing patients with high-risk of PPM. OBJECTIVES: To compare preoperative measurements of aortic annulus from echocardiography and CT scan with surgical sizing and develop an imaging-based algorithm to predict PPM. METHODS: From January 2017 to December 2020, patients underwent AVR at a teaching hospital were examined. The relationship between imaging measurements with operative values was assesed using scatter plots and Pearson's correlation coefficient. Univariable linear regression was then used to build the predictive model. RESULTS: A total of 144 patients underwent AVR during the study period. Suture types and surgical approaches were not significantly associated with prosthesis size. CT scan-based measurements showed strong correlation with prosthesis size: mean diameter (R = 0.79), perimeter-derived diameter (R = 0.76), and area-derived diameter (R = 0.75). Mechanical valve and tissue valve shared similar correlation coefficients. Prosthesis size predictive models based on CT scan were 12.89 + 0.335 × d for mean diameter, 13.275 + 0.315 × d for perimeter-derived diameter and 13.626 + 0.309 × d for area-derived diameter. CONCLUSIONS: Preoperative CT scan measurements are a reliable predictor of aortic prosthesis size. Transthoracic echocardiography is a possible alternative, though it is highly performer-dependent and unable to represent the aortic annulus fully. Together, these two imaging modalities can be used to quantitatively anticipate PPM preoperatively.

Long-Term Outcome of Thrombolytic Therapy for Massive Pulmonary Embolism in Pregnancy.

A 25-year-old pregnant woman presented at 12 weeks of gestation with syncope and shortness of breath caused by massive pulmonary embolism. Due to persistent shock, fibrinolytic therapy with rtPA was administered. After fibrinolysis, clinical and hemodynamic response was excellent. No bleeding and fetal complications were recorded.

Conservative Treatment of Postinfarction Left Ventricular Free Wall Rupture.

Left ventricular free wall rupture is a fatal complication of acute myocardial infarction. Emergency surgical repair is usually indicated to treat this condition. However, in very high surgical risk cohort, conservative treatment can also be considered. We report a case of left ventricle pseudoaneurysm that was successfully treated conservatively in a 4-year period.

Anomalous left coronary artery from the pulmonary artery (ALCAPA) as a concealed cause of severe mitral regurgitation in children and adults: Case reports.

INTRODUCTION: Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) is a rare congenital coronary artery anomaly and is a concealed cause of mitral regurgitation. PRESENTATION OF CASE: We reported two cases of severe mitral regurgitation in whom the presence of ALCAPA was overlooked in the first cardiac surgery. In the first case, ALCAPA was diagnosed one year after the mitral annuloplasty and the surgical reimplantation was successfully performed. In the second case, ALCAPA was incidentally detected on multislice computerized tomography during preoperative workup for the second surgery to replace the dehiscent mitral prosthesis. DISCUSSION: The clinical presentation of ALCAPA varies highly. It is not difficult to diagnose an ALCAPA in newborns and infants. Contrarily, ALCAPA in children and adults can be overlooked. CONCLUSION: Physicians should always look for the presence of ALCAPA in patients who present with unexplained mitral regurgitation. The surgical strategy in patients with ALCAPA should be carefully individualised to achieve an optimal outcome and alleviate complications.

Learning curve in minimally invasive mitral valve surgery: a single-center experience.

BACKGROUND: Minimally invasive mitral valve surgery is becoming a gold standard and provides many advantages for patients. A learning curve is required for a surgeon to become proficient, and the exact number to overcome this curve is controversial. Our study aimed to define this number for mitral valve surgery in general, for replacement and repair separately. METHODS: A total of 204 mitral valve surgeries were performed via the right minithoracotomy approach from October 2014 to January 2019 by a single surgeon who isexperienced in conventional mitral valve surgery. Learning curves were analysed based on the trend of important variables (cross-clamp time, CPB time, ventilation time, ICU time, composite technical failure) over time, and the number of operations required was calculated by CUSUM method. RESULTS: MIMVS provided an excellent outcome in the carefully selected patients, with low mortality of 0.5% and low rate of complications. The decreasing trend of the important variables were observed over the years and as the cumulative number of procedures increased. The number of operations required to overcome the learning curve was 75 to 100 cases. When considered separately, the quantity for mitral valve replacement was 60 cases, whereas valve repair necessitated at least 90 cases to have an acceptable technical complication rate. CONCLUSION: MIMVS is an excellent choice for mitral valve surgery. However, this approach required a long learning curve for a surgeon who is experienced in conventional mitral valve surgery. TRIAL REGISTRATION: The research was registered and approved by the ethical board of the University of Medicine and Pharmacy at Ho Chi Minh City, number 141/DHYD-HDDD, on April 11th 2018.

Left isomerism syndrome with total anomalous systemic connection.

We present a case of left isomerism with total anomalous systemic venous connection where the inferior vena cava was absent and all other systemic veins connected abnormally to the left atrium. The right atrium was hypoplastic with an intact atrial septum. Blood flow to the lungs was through a large ventricular septal defect. The diagnosis was made with echocardiography, angiography, and computed tomography. Complete repair was performed successfully, and the 7-year-old patient had an uneventful recovery.

Ministernotomy for correction of ventricular septal defect.

BACKGROUND: The development of minimally invasive surgery in the adult has created motivation for similar approaches in the congenital heart domain. Over the past 20 years, this type of surgery has been advocated in an effort to reduce costs related to hospital stay, and to improve the cosmetic results. We report our experience with ventricular septal defect repair utilizing a ministernotomy incision. METHODS: From August 2014 to August 2015, 26 patients underwent ministernotomy for correction of ventricular septal defect at our center. All patients were between the ages of 14 months-old to 24 years-old with weight ranged from 7.5 to 54 kg (median weight 12 kg). Diagnoses were confirmed with echocardiography. We analysed in-hospital and 6 months follow-up outcomes of the group. RESULTS: All defects were corrected successfully with satisfactory exposure. The median cardiopulmonary bypass time was 64 min, and median cross clamp time was 42 min. The intensive care unit stay ranged from 1 day to 3 days (median ICU stay, 1.5 days) and the hospital stay ranged from 4 to 13 days (median hospital stay, 5 days). There were no deaths during the operation or severe postoperative complications. No residual shunts were observed. CONCLUSION: Our results demonstrated the safety and efficacy of ministernotomy for the correction of ventricular septal defect with improved cosmetic results in patients greater than 7.5 kg. This aprroach can be used in either the transatrial or transarterial approach, and in smaller weight infants.