Nonlinear robust control of tendon–driven robot manipulators

This work addresses the position tracking control problem for tendon–driven robotic mechanisms in the presence of parametric uncertainty and additive external disturbances. Specifically, a full state feedback nonlinear robust controller is proposed to tackle the link position tracking problem for tendon–driven robot manipulators with uncertain dynamical system parameters. A robust backstepping approach has been utilized to achieve uniformly ultimately bounded tracking performance despite the lack of exact knowledge of the dynamical parameters and presence of additive but bounded disturbance terms. Stability of the overall system is proven via Lyapunov based arguments. Simulation studies performed on a two link planar robot manipulator driven by a six tendon mechanism are presented to illustrate the effectiveness and viability of the proposed approach.Scientific and Technological Research Council of Turkey (112E561

Structural and magnetic characterization of plasma ion nitrided layer on 316L stainless steel alloy

In this study, an FeCrNi alloy (316L stainless steel disc) was nitrided in a low-pressure R.F. plasma at 430 °C for 72 min under a gas mixture of 60% N2-40% H2. Structural, compositional and magnetic properties of the plasma nitrided layer was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and magnetic force microscopy (MFM). The magnetic behaviour of the nitrided layer was also investigated with a vibrating sample magnetometer (VSM). Combined X-ray diffraction, cross-sectional SEM, AFM and MFM, as well as VSM analyses provide strong evidence for the formation of the γN phase, [γN-(Fe, Cr, Ni)], with mainly ferromagnetic characteristics. The uniform nature of the γN layer is clearly demonstrated by the XRD, cross-sectional SEM and AFM analyses. Based on the AFM and SEM data, the thickness of the γN layer is found to be ∼6 μm. According to the MFM and VSM analyses, ferromagnetism in the γN layer is revealed by the observation of stripe domain structures and the hysteresis loops. The cross-sectional MFM results demonstrate the ferromagnetic γN phase distributed across the plasma nitrided layer. The MFM images show variation in the size and form of the magnetic domains from one grain to another.TÜBİTAK TBAG-244

Nonlinear adaptive partial state feedback trajectory tracking control of tendon driven robot manipulators

2014 IEEE Conference on Control Applications, CCA 2014; Juan Les Antibes; France; 8 October 2014 through 10 October 2014In this work, the link position tracking control problem of a tendon driven robotic system is studied in the presence of parametric uncertainty and lack of velocity measurements both of links and actuators. A partial state feedback nonlinear adaptive controller is proposed to deal with the unmeasurable states and uncertain dynamical system parameters. A backstepping approach has been utilized to develop the control strategy. The proposed nonlinear tracking controller utilizes online update laws to adapt for parametric uncertainties, and requires only link and actuator position measurements and tendon tension measurements. Need for link velocity measurements are eliminated by using a nonlinear filter, and a set of linear filters is designed to estimate the actuator velocities. Lyapunov based arguments have been applied to prove the stability of the closed-loop system and semi-global asymptotic link position tracking is achieved. © 2014 IEEE

CoCrMo alloy treated by floating potential plasma assisted nitriding and plasma based ion implantation: Influence of the hydrogen content and of the ion energy on the nitrogen incorporation

Nitriding was performed on a medical grade CoCrMo alloy at 400°C in N2 or N2-H2 atmosphere at a working pressure of 0.84Pa for 2h. Various surface treatment techniques were used to incorporate nitrogen into the CoCrMo alloy: without any plasma assistance, by floating potential radio-frequency plasma assisted nitriding (FPPAN), by plasma based ion implantation (PBII) with several high voltage accelerations (up to 20kV). Without plasma activation, no nitrogen is incorporated in the CoCrMo. On the contrary, all the plasma or PBII treated samples show the formation of a nitrogen-rich f.c.c. γN phase. The layer nitrided over few microns has a nitrogen composition ranging from 30at.% to about 20at.% near the nitrided layer-substrate interface, with an enhanced surface microhardness. Hydrogen is found to enhance the nitriding efficiency. Without hydrogen, a high voltage polarization provides a supplementary amount of implanted nitrogen available for further diffusion and the sputtering of the surface passive oxide. So, with limited high voltages, thicker layers with higher amounts of nitrogen can be achieved by PBII compared to plasma nitriding. However, with higher voltages, the sputtering becomes too important and the nitride layer is thinner. © 2010 Elsevier B.V

Magnetic layer formation on plasma nitrided CoCrMo alloy

In this study structural and magnetic character of the expanded austenite phase (γN) layer formed on a medical grade CoCrMo alloy by a low-pressure Radio-Frequency plasma nitriding process was investigated. The formation of the expanded austenite phase is facilitated at a substrate temperature near 400°C for 1, 2, 4, 6 and 20h under a gas mixture of 60% N2-40% H2. The magnetic state of the γN layers was determined by a surface sensitive technique, magneto-optic Kerr effect (MOKE), and with a scanning probe microscope in magnetic force mode (MFM). Strong evidence for the ferromagnetic nature of the γN-(Co,Cr,Mo) phase is provided by the observation of stripe domain structures and the hysteresis loops. The ferromagnetic state for the γN phase observed here is mainly linked to large lattice expansions (~10%) due to high N contents (~30at.%). As an interstitial impurity, nitrogen dilates the host lattice i.e. the Co-Co (or Fe-Fe) distance is increased, which strongly influences the magnetic interactions. An analogy between the magnetic properties of the expanded phases, γN-(Fe,Cr,Ni) and γN-(Co,Cr,Mo), formed in austenitic stainless steel alloys and the CoCrMo alloy of this study is made, and it is suggested that the ferromagnetic states for the γN-(Co,Cr,Mo) and γN-(Fe,Cr,Ni) phases may be correlated with the volume dependence of the magnetic properties of fcc-Co/Co4N and fcc-Fe/Fe4N, respectively.Turkish National Science Foundation grant 107M21

Drug Interaction Between Valproic Acid and Meropenem: A Case Report

To report a probable interaction between meropenem and antiepileptic drugs that resulted in poor control of epileptic seizures. A previously healthy 21 years old woman admitted to emergency department with fever and stiff neck. Her Glasgow Coma Scale score was E3M5V4. Physical examination revealed conscious to tend to fall asleep, closed eyes and normal-sized and reactive pupils. Meropenem and vancomycin were initiated for the suspicion of menengitis. On the 3rd day of the antibiotic therapy generalized tonic clonic seizures were observed. Phenytoin and intravenous (IV) thiopental were initiated. The patient was intubated and mechanically ventilated. EEG revealed generalized epileptiform activity. In the following days, seizure activity continued. Levetirasetam, carbamazepine and VPA were added for treatment respectively, but seizures were continued. On the 20th day of meropenem therapy, interaction of carbapenems and anti-epileptic agents was suspected. Antibiotherapy was discontinued. Serum concentrations of VPA increased over the next days and achieved therapeutic levels. On day 21 she was extubated, no seizures occurred over the following 48 hours. She was discharged from the ICU, with blood anti epileptic concentrations within the therapeutic range. Carbapenems have a potential effect of inducing seizures and may also lower serum levels of antiepileptic drugs. Clinicians should be aware of this potential interaction that may be associated with serious adverse effects. Status epilepticus is one of the most important neurologic emergencies, and therapeutic control becomes more difficult as its duration becomes longer. Patients receiving antiepileptics and carbapenem group antibiotics concominantly should be closely monitored due to possible drug interaction between these agents

Electrical and mechanical properties of superconducting MgB2/Mg metal matrix composites

MgB2/Mg composites were prepared using a metal matrix composite fabrication method that offers the potential to produce superconducting wires as an alternative approach to the powder in tube process. To obtain composites, MgB2 and Mg powders were mixed at different weight fractions and uniaxially pressed in a cylindrical die under the pressure of 0.5 and 1.0GPa for two hours at various temperatures. The x-ray diffraction technique was used for phase identification. Temperature dependence of resistivity and magnetization measurements were carried out to determine superconducting properties. The effects of composite fabrication temperature and the addition of the Mg on the mechanical properties of MgB2/Mg composites were investigated. For this purpose, the compressive mechanical testing was performed to measure the elastic modulus and fracture strength values of the composites. It was found that the relative weight fraction of the Mg and the fabrication conditions of the composites have considerable effect on the superconducting and mechanical properties of the composites.TÜBİTAK: TBAG-2031 and LO/TUBA-GEBIP/2002-1-1

Colonic replacement of esophagus in children

Purpose: The purpose of this study was to evaluate the indications and results of colonic replacement in children. Methods: During the last 18 years (1977-1995) 27 colonic transpositions have been carried out on 25 children due to esophageal pathologies. Their medical records have been analyzed retrospectively. Results: The major indication for esophageal replacement was caustic stricture. The procedure of choice was retrosternal without thoracotomy in 23 children, and intrathoracic with left thoracotomy in 2. The right colon was transposed in 21 patients, but in 2 of them the left colon was also used due to the flap necrosis of the right colon. Left colonic flap necrosis had also developed in one and gastric transposition was the choice of treatment as the last stage. The left colon was used primarily in 4 patients. Wound infection (11/27), cervical anastomotic leakage (8/27), cervical anastomotic stricture (7/27), mediastinitis (4/27), flap necrosis (4/27), and cologastric anastomotic strictures (2/27) were the complications. There were 5 deaths. Medium-term results were assessed as excellent in 10, good in 7 children. Two patients still require cervical anastomotic dilatations. One patient whose right colon is sitting in retrosternal area needs an oropharyngoplasty due to severe oropharyngeal stenosis. Conclusions: Colonic interposition is an operation of considerable magnitude and should be undertaken only after appropriate indications. Before operating for corrosive strictures every attempt should be made to establish patency and function of the patient's native esophagus

Structural and low-field magnetic characterization of superconducting MgB2 wires

Superconducting MgB2 composite wires were prepared by packing blend of MgB2 inside of Cu tubes using powder in tube (PIT) method. The produced samples of the wires were then characterised by using SEM, XRD and AC susceptibility measurements, The measured fundamental susceptibility is compared with Bean model. We have obtained an empirical functions for the penetration field Hp = Hα(1-t)β, where t is the reduced temperature. In addition, ac losses were calculated at the same fixed temperatures to compare theoretical solutions. There is a qualitative agreement between the experimental results and theory.DPT 2002-K-120130-5 and TÜBİTAK (Scientific and Technical Research Council of Turkey) TBAG-221