A Dynamic Model for a Hybrid Articulated Robot

The dynamic modeling of hybrid systems, consisting of flexible and rigid parts results in large partial differential equation systems (PDE). With the assumption of small deflections and the Ritz expansion the PDE can be approximated by an ordinary differential equation system (ODE) but the number of degrees of freedom is generally high. In this paper a hybrid articulated robot with 2 flexible links and 6 joints is under consideration. The joints are equipped with Harmonic Drive gears with high gear ratio but relative low stiffness. Therefore additionally degrees of freedom are introduced for the elastic deflection of the gears. The links are modeled with flexibility in two bending directions and in torsional sense. To be able to achieve structured equations the projection equation in subsystem representation is used. The projection equation is based on the momentum and the angular momentum equations of each single finite or infinitesimal body which are projected into the space of minimal coordinates and subsequently are summed up. Groups of bodies are collected to the so called subsystems with separated describing velocities. These subsystems are linked together with the kinematical chain. Because the robot is tree structured it is possible to obtain an explicit expression for the second derivatives of the minimal coordinates with a recursive scheme (O(n) efficiency). The robot is controlled with a feed forward controller and a linear PD joint controller. Simulation results and measured data are presented and compared. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measuring the Elastic Properties of Freestanding Thick Films Using a Nanoindenter-Based Bending Test

Films with thickness ranging from 10 to 100 μm are increasingly being used as the structural components of microelectromechanical systems (MEMS). Measuring the mechanical properties of these thick films is essential for enabling the design of MEMS with high performance and sufficient reliability. In this paper, we present a simple and convenient method for measuring the elastic modulus of thick films by loading a clamped circular film using a spherical tip. The test is implemented using a commercial nanoindenter so that the load and displacement can be measured with resolution of micronewtons and nanometers, respectively. Robust protocols have been developed for implementing the test within the constraints imposed by the nanoindenter. A crucial component of these protocols is a method for selecting loads to ensure deformation in the elastic bending regime and to minimize the relative contribution of contact indentation. The accuracy and utility of the nanoindenter-based bending test are discussed using measurements on thick films of aluminum and a standard epoxy.     

Insertion of alkynes into the heterocycle of (η-pentaalkyl-2,3-dihydro-1,3-diborolyl)(η-pentamethylcyclopentadienyl)ruthenium: Formation and characterization of 4-borataborepine ruthenium complexes

The violet ruthenium complex [(η⁵-C₅Me₅)Ru(η⁵-C₃B₂Me₄R¹)] (2a, R¹ = Me) reacts with terminal alkynes R²CCH to give yellow 4-borataborepine compounds [(η⁵-C₅Me₅)Ru{η⁷-(MeC)₃(R¹B)₂(R²C₂H)}] (4c, R¹ = Me, R² = Ph; 4d, R¹ = Me, R² = SiMe₃; 4e, R¹ = Me, R² = H). The insertion of alkynes into the folded C₃B₂ heterocycle of 2a causes some steric hindrance, which yields with elimination of the distant boranediyl group the corresponding boratabenzene complexes 5 as byproducts. The analogous reactions with internal alkynes R²CCR² proceed slowly and afford predominantly the boratabenzene complexes [(η⁵-C₅Me₅)Ru{η⁶-(MeC)₃(MeB)(R²C)₂}] (5f, R² = Et, 5g, R² = p-tolyl), respectively. In the latter case, three byproducts are formed: methylboronic acid and 1,2,3,4-tetra-p-tolyl-1,3-butadiene (9) due to hydrolysis of the postulated 2,3,4,5-tetra-p-tolyl-1-methylborole (10) and unexpectedly, the cationic triple-decker complex [{(η⁵-C₅Me₅)Ru}₂{μ,η⁷-(MeC)₃(MeB)₂(CH)₂}]Cl (11) having two separated CH groups. The new compounds were characterized by NMR, MS, and single-crystal X-ray studies of 4c, 5f, 9 and 11.     

Modeling of Reconfigurable Modular Redundant Robotic Systems

This paper deals with the dynamical modeling and control of modular redundant robots. The robots under consideration consist of modular actuators (brushless DC motors with Harmonic Drive gears) connected by rigid links. Different configurations can be designed by rearranging these subsystems. In order to fulfill the requirement for an efficient dynamical modeling, the Projection Equation in subsystem representation is used. The subsystems are connected via the kinematical chain. The Projection Equation offers the possibility to calculate the minimal accelerations recursively, leading to an O(n) computational effectiveness. To validate the proposed method, the model of an articulated robot arm with seven joints is considered. Simulation results are compared to measurements. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Lightweight Robot ElRob: Interesting Aspects in Modeling and Control

The articulated robot ElRob, consisting of flexible links and joints, is considered in several publications. Recent developments are presented in this work. The overall goal of the research is to decrease the effects of structural elasticities in lightweight robots. For this purpose model-based control concepts are investigated and very accurate and efficient kinematic and dynamic models are necessary. The robot is split into groups of bodies, the so called subsystems, with separated describing velocities and coordinate systems. To obtain structured equations of motion the Projection Equation is used. The beams are modelled using the floating frame of reference formulation and a Ritz-approach. Because of its flexibility, the examined robot is an underactuated system leading to special difficulties. As an example is it not possible to compute the desired joint angles with respect to a reference path in task space for the flexible system (inverse kinematic problem). Different methods to solve this drawback and other problems resulting from flexibility are discussed with special focus on feed forward control and different feedback control concepts. The resulting end point error, the necessary control input and other interesting results for the laboratory experiment are presented and compared. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A golden age of general relativity? Some remarks on the history of general relativity

This article deals with the concepts “renaissance” and “low water mark between 1925 and 1955” of general relativity suggested in the literature. By empirical data, it is shown that no such period did exist. Research on general relativity continued continuously since the 1920s interrupted only by the second world war. On a broad scale, research on general relativity started only after 1945.     

2-Dimensional porphyrin self-assemblies at molecular interfaces

The heterodimer formed by electrostatic association of zinc(II) meso-tetrakis(N-methylpyridyl)porphyrin (ZnTMPyP) and zinc(II) meso-tetrakis(p-sulfonatophenyl)porphyrin (ZnTPPS) exhibits a strong affinity for the interface between water and 1,2-dichloroethane (DCE). Surface tension measurements using the quasi-elastic light scattering (QELS) technique reveal that the heterodimer adsorption can be described in terms of a Langmuir isotherm with standard Gibbs energy of adsorption of -45.5 kJ mol(-1). The orientation of the heterodimer transition dipole moment, as estimated from light polarization modulated reflectance (LPMR), shows a marked dependence on the bulk concentration of heterodimer. On the other hand, changes in the Galvani potential difference between the two phases have little effect on the heterodimer organization at the water/1,2-dichloroethane interface when the surface coverage is close to maximum. This behavior suggests that the ZnTPPS-ZnTMPyP heterodimer forms an adsorbed layer of aggregated molecules which affects the physical properties of the interface. Indeed, capacitance and surface tension measurements reveal that the dielectric properties of the water/DCE interface are significantly altered in the presence of heterodimer species.     

Aryldithioethyloxycarbonyl (Ardec): a new family of amine protecting groups removable under mild reducing conditions and their applications to peptide synthesis

The development of phenyldithioethyloxycarbonyl (Phdec) and 2-pyridyldithioethyloxycarbonyl (Pydec) protecting groups, which are thiol-labile urethanes, is described. These new disulfide-based protecting groups were introduced onto the epsilon-amino group of L-lysine; the resulting amino acid derivatives were easily converted into N alpha-Fmoc building blocks suitable for both solid- and solution-phase peptide synthesis. Model dipeptide(Ardec)s were prepared by using classical peptide couplings followed by standard deprotection protocols. They were used to optimize the conditions for complete thiolytic removal of the Ardec groups both in aqueous and organic media. Phdec and Pydec were found to be cleaved within 15 to 30 min under mild reducing conditions: i) by treatment with dithiothreitol or beta-mercaptoethanol in Tris.HCl buffer (pH 8.5-9.0) for deprotection in water and ii) by treatment with beta-mercaptoethanol and 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU) in N-methylpyrrolidinone for deprotection in an organic medium. Successful solid-phase synthesis of hexapeptides Ac-Lys-Asp-Glu-Val-Asp-Lys(Ardec)-NH2 has clearly demonstrated the full orthogonality of these new amino protecting groups with Fmoc and Boc protections. The utility of the Ardec orthogonal deprotection strategy for site-specific chemical modification of peptides bearing several amino groups was illustrated firstly by the preparation of a fluorogenic substrate for caspase-3 protease containing the cyanine dyes Cy 3.0 and Cy 5.0 as FRET donor/acceptor pair, and by solid-phase synthesis of an hexapeptide bearing a single biotin reporter group.