Dynamics and iterative learning control of robots with parallel kinematical structures / Bodo Heimann and Houssem Abdellatif

The paper deals with model-based control of robots with parallel kinematical structure (PKM). At first, an approach for the identification of friction and rigid-body dynamics of complex parallel kinematical structures is presented. The approach is based on optimal excitation trajectories. The trajectories are bounded, such they are easy to befit into the small and hard constraint workspace of PKM. Secondly, some results are presented using feedforward control in order to compensate nonlinear dynamical influences. Thirdly, Iterative Learning Control (ILC) is proposed in this paper for tracking accuracy enhancement of a parallel direct driven manipulator. It is shown both by means of simulation study and experimental results that linear ILC is appropriate for application to the considered high nonlinear and coupled systems

Hybrid Approach for the Maintenance of Materialized Webviews

In this paper, we have developed an approach to specify when updating materialized webviews. A webview is a web page that is automatically constructed from a structured database. We have introduced a new update policy called “early ondemand” update which is based on the user preferences. Then we have combines this policy with the on-demand one to update the materialized webviews. Our experiments showed that the proposed hybrid approach guarantees strong consistency of data and allows reducing latency of updating webviews. In addition, they prove that our solution decreases the server overload (access+ update cost) significantly better that the on-demand and the immediate policies

A novel multiple-heuristic approach for singularity-free motion planning of spatial parallel manipulators

The issue of motion planning for closed-loop mechanisms, such as parallel manipulators or robots, is still an open question. This paper proposes a novel approach for motion planning of spatial parallel robots. The framework for the geometric modeling is based on the visibility graph methodology. It is opted for a multiple-heuristics approach, where different influences are integrated in a multiplicative way within the heuristic cost function. Since the issue of singularities is a fundamental one for parallel robots, it is emphasized on the avoidance of such configurations. To include singularity-free planning within the heuristic approach, two heuristic functions are proposed, the inverse local dexterity as well as a novel defined "next-singularity" function, in such a way, well conditioned motions can be provided by a single planning procedure. The success of the method is illustrated by some examples. © 2008 Cambridge University Press

Practical Model-based and Robust Control of Parallel Manipulators Using Passivity and Sliding Mode Theory

This chapter provides a practical strategy to realize accurate and robust control for 6 DOFs (degrees of freedom) parallel robots. The presented approach consists in two parts. The first basic part is based on the the compensation of the desired dynamics in combination with controller/observer for the single actuators. The passivity formalism offers an excellent framework to design and to tune the closed-loop dynamics, such that the desired behavior is obtained. The basic algorithm is proved to be locally robust towards uncertainties. The second part of the control strategy consists in a sliding mode controller. To keep the practical and computational efficient implementation, the proposed switching control considers explicitly only the friction model. Here we opt for the so called model-decomposition paradigm and we use additional integral action to improve robustness. The proposed approach is substantiated with experimental results demonstrating the effectiveness and success of the strategy that keeps control setup simple and intuitive. Keywords parallel manipulators, robust control, passivity formalism, sliding mode control, desired dynamics compensation, velocity observe

Soave transanal one-stage endorectal pull-through in the treatment of Hirschsprung′s disease of the child above two-year-old: A report of 20 cases

Background: The definitive treatment of Hirschsprung′s disease is the removal of the aganglionic bowel by a pull-through surgery. In most cases, this surgery is performed in infancy or in the neonatal period as presentation in older children and adulthood is uncommon. Materials and Methods: It is a retrospective study of 20 patients above two-year-old who underwent a transanal Soave one-stage endorectal pull-through procedure for Hirschsprung′s disease between January 2002 and December 2010. Results: Twenty patients were recruited in this study. Fourteen were males and six were females. Patient ages ranged from 2 to 14 years (median age: five years and three months). All patients presented with persistent constipation and abdominal distension. Two of them had an intestinal obstruction that required colostomy. Ten patients (50%) had a recto-sigmoid Hirschsprung′s disease. All patients were operated on using a Soave one-stage endorectal pull-through procedure. The laparoscopy was necessary during the pull-through in three cases. The average duration of the intervention was 240 minutes. That represents almost the double of the duration of the same procedure in newborns and infants in our department (130 minutes). Early postoperative complications included one case of anastomosis leakage and one case of intussusception. Late postoperative complications were perineum irritation in five cases (25%), anal stenosis in four cases (20%) and enterocolitis in one case (5%). None of our patients developed fecal incontinence. Soiling was reported in four cases (20%). There was no death. Conclusion: Soave transanal one-stage endorectal pull-through is safely feasible in children of more than two years of age. Laparoscopy may be necessary whenever there are difficulties in the pull-through

Detection of CTX-M-15 harboring Escherichia coli isolated from wild birds in Tunisia

Abstract Background The spreading of antibiotic resistant bacteria is becoming nowadays an alarming threat to human and animal health. There is increasing evidence showing that wild birds could significantly contribute to the transmission and spreading of drug-resistant bacteria. However, data for antimicrobial resistance in wild birds remain scarce, especially throughout Africa. The aims of this investigation were to analyze the prevalence of ESBL-producing E. coli in faecal samples of wild birds in Tunisia and to characterize the recovered isolates. Results One hundred and eleven samples were inoculated on MacConkey agar plates supplemented with cefotaxime (2 μg/ml). ESBL-producing E. coli isolates were detected in 12 of 111 faecal samples (10.81%) and one isolate per sample was further characterized. β-lactamase detected genes were as follows: bla CTX-M-15 (8 isolates), bla CTX-M-15 + bla TEM-1b (4 isolates). The ISEcp1 and orf477 sequences were found respectively in the regions upstream and downstream of all bla CTX-M-15 genes. Seven different plasmid profiles were observed among the isolates. IncF (FII, FIA, FIB) and IncW replicons were identified in 11 CTX-M-15 producing isolates, and mostly, other replicons were also identified: IncHI2, IncA/C, IncP, IncI1 and IncX. All ESBL-producing E. coli isolates were integron positive and possessed “empty” integron structures with no inserted region of DNA. The following detected virulence genes were: (number of isolates in parentheses): fimA (ten); papC (seven); aer (five); eae (one); and papGIII, hly, cnf, and bfp (none). Molecular typing using pulsed-field gel electrophoresis and multilocus sequence typing showed a low genetic heterogeneity among the 12 ESBL-producing strains with five unrelated PFGE types and five different sequence types (STs) respectively. CTX-M-15-producing isolates were ascribed to phylogroup A (eleven isolates) and B2 (one isolate). Conclusion To our knowledge, this study provides the first insight into the contribution of wild birds to the dynamics of ESBL-producing E. coli in Tunisia