Synthesis of the forward kinematics problem algebraic modeling for the general parallel manipulator: displacement-based equations

This paper closes a triptic to address the issue of the forward kinematics problem (FKP) aimed at certified solving with an exact algebraic method. This solving method was described in the first article published in Advanced Robotics. The second one investigated the formulation specifically applied to the planar parallel manipulators. This third paper is the logical one in the footsteps of the formersones, since it continues the formulation analyses and brings them to the general spatial parallel manipulator. Hence, this paper focuses on the displacement-based equation systems. This paper is the first one to present a synthesis on forward kinematics modeling focusing on finding an optimal mathematical formulation based on the displacement-based equation systems. The majority of parallel manipulators in applications can be modeled by the 6-6 hexapod or so-called Gough platform which is constituted by a fixed base and a mobile platform attached to six kinematics chains with linear (prismatic) actuators located between two revolute or Cardan joints. Again, in order to implement algebraic methods, the parallel manipulator kinematics shall be formulated as polynomial equations systems where the equation number is at least equal to the unknown numbers. Six geometric formulations were derived. The selected algebraic proven method is implementing Gröbner bases from which it constructs an equivalent univariate polynomial system. The resolution of this last system exactly determines the real solutions which correspond to the manipulator postures. The FKP resolution of the general 6-6 parallel manipulator outputs 40 complex solutions. Several instantiations shall be computed in order to select the model which leads to the FKP resolution with the lowest response times and smaller file sizes. It was possible to reject three modelings leading to bad performances or resolution failure. It was possible to determine one formulation where the solving computations were definitely better than the others.     

Control of the Underactuated Inertia Wheel Inverted Pendulum for Stable Limit Cycle Generation

This paper deals with a control approach dedicated to stable limit cycle generation for underactuated mechanical systems. The proposed approach is based on partial nonlinear feedback linearization and dynamic control for optimal periodic reference trajectories tracking. The computation of the reference trajectories is performed in order to optimize the behavior of the whole dynamics of the system and especially its zero dynamics at the end of each cycle. Simulation results as well as experiments show the performance and the efficiency of the proposed control scheme.     

Enhanced Cell Adhesion to Helium Plasma-Treated Polypropylene

Materials used for biomedical applications are required to have suitable surface properties since they depend more on the surface properties than on the bulk properties. Surface properties greatly influence the cell adhesion and its behavior either directly by guiding cell spreading or indirectly by controlling proteins adsorption and their structural rearrangement on the material. Modulation of physical and chemical properties of polymers by various treatments can render the substrates adhesive for cells in a culture. In the present study, polypropylene surface was modified using helium plasma to enhance cell adhesion to its surface. The experiments were run according to the central composite design of response surface methodology to optimize the process conditions. The effects of the process variables, namely, RF power, pressure, flowrate and treatment time on surface energy and percentage weight loss were studied through central composite design (CCD). A statistical model relating the process variables and the responses was developed. The improved hydrophilicity of polypropylene through helium plasma treatment was observed from its surface energy data. Changes in surface chemistry and surface morphology were studied by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Enhanced cell adhesion to polypropylene treated with helium plasma at the optimum conditions, obtained from the statistical design, was observed from cell adhesion test and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay with L929 mouse fibroblast cells.     

Stochastic Optimisation Methods for Biomolecular Structure Prediction

We discuss the use of stochastic optimization methods for biomolecular structure prediction, particularly applied to protein structure prediction and receptor ligand docking. After a brief introduction we give an overview of the dominating physical effects that are important for protein structure prediction and outline our strategy to address this problem. We discuss the strengths and weaknesses of several possible optimization methods, including the stochastic tunneling method. Finally we give examples of applications of this methodology both for protein structure prediction and receptor ligand docking.     

Selective use of rubber toughening to optimize lap-joint strength

This paper introduces a novel approach to increasing the lap joint strength, different from the traditional methods of either increasing the lap joint area or altering the joint geometry. This is accomplished by the selective use of rubber toughening in epoxy to optimize lap joint strength. This was accomplished in three stages. In the first stage an adduct was prepared, this was used to make bulk tensile specimens to calculate the bulk properties for various concentrations of rubber, i.e. 0, 10, and 20 parts per hundred parts of resin (epoxy). In the second stage finite element models were developed using the bulk properties previously obtained. Interfacial stresses were used to access the trends obtained by the selective use of rubber toughening at different locations of the overlap in different configurations. The modeling of adhesive joints was done using ALGOR 2-D, linear and nonlinear finite element analyses (FEA). In the third stage, tensile shear tests conducted on the lap joints validated the trends from the finite element models. Finite element modeling and meshing of the lap joints having 25.4 and 50.8 mm adhesive overlap lengths were completed. Different configurations of rubber toughened and untoughened adhesive were tried in these two overlaps. The validation was done by lap joint tests conducted on an Instron mechanical tester coupled with an extensometer. Comparable strengths were obtained for completely toughened overlap and the configuration where only the edges of the adhesive overlap were toughened and the region in-between was untoughened. Also, the nonlinear FEA was shown to represent the experimental results more closely than the linear approach.     

MODIFIED GENETIC ALGORITHM APPLIED TO SOLVE PRODUCT FAMILY OPTIMIZATION PROBLEM

The product family design problem solved by evolutionary algorithms is discussed.A successful product family design method should achieve an optimal tradeoff among a set of compet- ing objectives,which involves maximizing commonality across the family of products and optimizing the performances of each product in the family.A 2-level chromosome structured genetic algorithm (2LCGA)is proposed to solve this class of problems and its performance is analyzed in comparing its results with those obtained with other methods.By interpreting the chromosome as a 2-level linear structure,the variable commonality genetic algorithm(GA)is constructed to vary the amount of plat- form commonality and automatically searches across varying levels of commonality for the platform while trying to resolve the tradeoff between commonality and individual product performance within the product family during optimization process.By incorporating a commonality assessing index to the problem formulation,the 2LCGA optimize the product platform and its corresponding family of products in a single stage,which can yield improvements in the overall performance of the product family compared with two-stage approaches(the first stage involves determining the best settings for the platform variables and values of unique variables are found for each product in the second stage). The scope of the algorithm is also expanded by introducing a classification mechanism to allow mul- tiple platforms to be considered during product family optimization,offering opportunities for supe- rior overall design by more efficacious tradeoffs between commonality and performance.The effec- tiveness of 2LCGA is demonstrated through the design of a family of universal electric motors and comparison against previous results.     

HYDROSTATIC PRESSURE CALCULATION AND OPTIMIZATION FOR DESIGN OF BEAM ＆ SLIDE-REST GUIDEWAYS IN HEAVY DUTY CNC VERTICAL TURNING MILL

Aiming at the approximate error of commonly used methods on calculation of hydrostatic pressures of closed hydrostatic guideways with multiple pockets, a more accurate solution is proposed. Taking design of beam & slide-rest guideways for a heavy duty CNC vertical turning mill as an example, under an assumption that stiffnesses of guideways and their jointing structure are sufficiently large, the pressures of the pockets can be attained by adding a co-planarity equation that con strains pocket centers. Then, an optimization model is built to minimize the highest pocket pressure under additional constraints that are posed on the highest seal margin pressure, the highest levitating pressure of the pockets, and the maximum deformation of the guideways. The optimization problem is solved sequentially by using the methods of design of experiments and adaptive simulated annealing on iSIGHT software platform. The results show significant improvements to the original design. Optimized maximum hydrostatic pressure meets the requirement of hydraulic system.     

Parallel Programming and Performance Evaluation with the URSA Tool Family

This paper contributes to the solution of several open problems with parallel programming tools and their integration with performance evaluation environments. First, we propose interactive compilation scenarios instead of the usual black-box-oriented use of compiler tools. In such scenarios, information gathered by the compiler and the compiler's reasoning are presented to the user in meaningful ways and on-demand. Second, a tight integration of compilation and performance analysis tools is advocated. M any of the existing, advanced instruments for gathering performance results are being used in the presented environment and their results are combined in integrated views with compiler information and data from other tools. Initial instruments that assist users in data mining this information are presented and the need for much stronger facilities is explained. The URSA Family provides two tools addressing these issues. URSA MINOR supports a group of users at a specific site, such as a research or development project. URSA MAJOR complements this tool by making available the gathered results to the user community at large via the World-wide Web. This paper presents objectives, functionality, experience, and next development steps of the URSA tool family. Two case studies are presented that illustrate the use of the tools for developing and studying parallel applications and for evaluating parallelizing compilers.     

The Forcer Concept and Express Route Planning in Mesh-Survivable Networks

To date, mesh network design theory has beendeveloped for the case where working and protectioncapacity is terminated at every node. It is recognizedthat express routes, which bypass some nodes en-route, would decrease the total DCS port costs but ithas been unclear how to incorporate bypass planning inthe optimal spare capacity design for a mesh-restorablenetwork. An important issue is whether the introduction of nodal bypass will increase the total sparecapacity needed for restorability, due to a reduction ofrestoration re-routing flexibility. To address thesequestions, we introduce the forcer concept for analysis of the relationship between workingand spare capacity in a mesh-restorable network. Weapply the forcer concept to show theoretically whybypass in fact need never require an increase in sparing and may actually permit a decrease in somecases. In tests to validate and exploit these findings,an average reduction of 12% in total spare capacity and16% in DCS port count totals were obtainedsimultaneously with an Integer Programming optimization. Thesesavings are relative to an already optimized fullyterminated network design. The work thus contributes togreater theoretical understanding and designcost-effectiveness for mesh-based restorable networks.