Kinematic Design of a 6-DOF Parallel Manipulator with Decoupled Translation and Rotation

A new three-limb, six-degree-of-freedom (DOF) parallel manipulator (PM), termed a selectively actuated PM (SA-PM), is proposed. The end-effector of the manipulator can produce 3-DOF spherical motion, 3-DOF translation, 3-DOF hybrid motion, or complete 6-DOF spatial motion, depending on the types of the actuation (rotary or linear) chosen for the actuators. The manipulator architecture completely decouples translation and rotation of the end-effector for individual control. The structure synthesis of SA-PM is achieved using the line geometry. Singularity analysis shows that the SA-PM is an isotropic translation PM when all the actuators are in linear mode. Because of the decoupled motion structure, a decomposition method is applied for both the displacement analysis and dimension optimization. With the index of maximal workspace satisfying given global conditioning requirements, the geometrical parameters are optimized. As a result, the translational workspace is a cube, and the orientation workspace is nearly unlimited.

Effects of Constraint Errors on Parallel Manipulators with Decoupled Motion

From perspective of structure synthesis, certain special geometric constraints, such as joint axes intersecting at one point or perpendicular to each other, are necessary in realizing the end-effector motion of kinematically decoupled parallel manipulators (PMs) along individual motion axes. These requirements are difficult to achieve in the actual system due to assembly errors and manufacturing tolerances. Those errors that violate the geometric constraint requirements are termed “constraint errors”. The constraint errors usually are more troublesome than other manipulator errors because the decoupled motion characteristics of the manipulator may no longer exist and the decoupled kinematic models will be rendered useless due to these constraint errors. Therefore, identification and prevention of these constraint errors in initial design and manufacturing stage are of great significance. In this article, three basic types of constraint errors are identified, and an approach to evaluate the effects of constraint errors on decoupling characteristics of PMs is proposed. This approach is illustrated by a 6-DOF PM with decoupled translation and rotation. The results show that the proposed evaluation method is effective to guide design and assembly.

Asymmetric rhodium carbene insertion into the Si-H bond: identification of new dirhodium(II) carboxylate catalysts using parallel synthesis techniques

Decomposition of methyl 2-diazophenylacetate in the presence of silanes and a chiral dirhodium(11) catalyst results in Si-H insertion of the intermediate carbenoid with varying degrees of enantioselectivity. New chiral dirhodium(11) carboxylate catalysts were identified using solution phase parallel synthesis techniques. (C) 2003 Elsevier Science Ltd. All rights reserved.

From PASS 1 to YES to AND logic: building parallel processing into molecular logic gates by sequential addition of receptors

The synthesis and photophysical characterization of a novel molecular logic gate 4, operating in water, is demonstrated based on the competition between. fluorescence and photoinduced electron transfer (PET). It is constructed according to a 'fluorophore-spacer-receptor(1)-spacer-receptor(2)' format where anthracene is the. fluorophore, receptor(1) is a tertiary amine and receptor(2) is a phenyliminodiacetate ligand. Using only protons and zinc cations as the chemical inputs and. fluorescence as the output, 4 is demonstrated to be both a two-input AND and INH logic gate. When 4 is examined in context to the YES logic gates 1 and 2, and the two-input AND logic gate 3 and three-input AND logic gate 5, each with one or more of the following receptors including a tertiary amine, phenyliminodiacetate or benzo-15-crown-5 ether, logic gate 4 is the missing link in the homologous series. Collectively, the molecular logic gates 1-5 corroborate the PET 'fluorophore-spacer-receptor' model using chemical inputs and a light-signal output and provide insight into controlling the. fluorescence quantum yield of future PET-based molecular logic gates.

Kinematic modeling of Exechon parallel kinematic machine

The studies on PKMs have attracted a great attention to robotics community. By deploying a parallel kinematic structure, a parallel kinematic machine (PKM) is expected to possess the advantages of heavier working load, higher speed, and higher precision. Hundreds of new PKMs have been proposed. However, due to the considerable gaps between the desired and actual performances, the majorities of the developed PKMs were the prototypes in research laboratories and only a few of them have been practically applied for various applications; among the successful PKMs, the Exechon machine tool is recently developed. The Exechon adopts unique over-constrained structure, and it has been improved based on the success of the Tricept parallel kinematic machine. Note that the quantifiable theoretical studies have yet been conducted to validate its superior performances, and its kinematic model is not publically available. In this paper, the kinematic characteristics of this new machine tool is investigated, the concise models of forward and inverse kinematics have been developed. These models can be used to evaluate the performances of an existing Exechon machine tool and to optimize new structures of an Exechon machine to accomplish some specific tasks.

Behaviour of joints with bonded-in steel bars loaded parallel to the grain of timber elements

Within the sustainability context, this paper is extremely timely and relevant. The research focuses on broadening the use of timber structurally. The insight gained forms the basis for sustainable, fire resistant, economic and aesthetically pleasing moment resistant connections in timber.