弹性变形对仿人机器人步态规划的影响分析

仿人机器人行走步态研究的理论、方法及建模均未考虑系统各部件弹性变形的影响，导致行走实验结果与理论步态规划存在较大的差异，制约了步行质量的提高和连续快速稳定步行的实现。本文运用ANSYS有限元软件，针对清华大学研制的THBIP—Ⅰ型仿人机器人样机，建立精确的有限元模型，进行步行运动弹性变形及其对步态规划影响的有限元仿真分析，在此基础上提出了对步态规划进行局部修正完善的方法，步行实验证明该有限元模型及仿真分析结果是有效的。     

Comparison of corrosion-resistance and hydrogen permeation properties of Zn-Ni, Zn-Ni-Cd and Cd coatings on low-carbon steel

Zn-Ni-Cd alloy was electroplated from an alkaline sulfate bath under potentiostatic conditions. The corrosion and hydrogen permeation characteristics of Zn-Ni-Cd alloy coatings electrodeposited from alkaline bath were studied and compared with those of Cd and Zn-Ni coatings obtained using commercial baths. Zn-Ni-Cd alloy was electroplated from an alkaline sulfate bath under potentiostatic conditions. The corrosion potential of this Zn-Ni-Cd coating was −0.62 V vs. SCE, which is still negative potential compared to iron. The corrosion rate of Zn-Ni-Cd coated steel was 0.073 mm y⁻¹, which is estimated in a solution at a pH of 7. This value is much lower than the corrosion rate of Zn-Ni alloy (0.502 mm y⁻¹) and Cd (0.306 mm y⁻¹) coatings deposited from commercial baths. Zn-Ni-Cd alloys are also demonstrated to have superior hydrogen permeation inhibition properties compared to Cd and Zn-Ni coatings. Kinetic parameters of hydrogen permeation such as the transfer coefficient, α, the modified exchange current density, i₀^′, thickness dependent adsorption-absorption rate constant, k^″, recombination rate constant, k₃, surface hydrogen coverage, θ_s, were evaluated by applying a mathematical model to analyze experimental results.     

MAXIMIZING SELECTIVITY OF LIQUID-LIQUID REACTION SYSTEMS. CONTROL OF THE DISPERSION PROCESS

Currently available information on droplet coalescence and break-up rates in turbulent flows in mixing vessels can be used to control drop sizes in dispersed phase equipment. The effect of drop size distributions on the selectivity and productivity in multi-reaction systems is examined in this paper.

The reaction system features the primary desired product (C) as resulting from reaction (in the bulk phase) between a reactant (A) in the drop phase and a second reactant (B) in the bulk phase. An adverse reaction is also envisaged which consumes (C) by further reaction with (B) to form a waste product. While small drops promote conversion because of large interfacial area, larger drops promote selectivity because of the facility of the product to re-enter the drop phase avoiding further reaction (to form waste) in the bulk phase. The effect of the bivariate distribution of drop size and reactant (A) concentration in the feed to a continuous stirred tank reactor on the selectivity and productivity of (C) is investigated within the framework of film theory while neglecting drop dynamics such as coalescence and break-up.

The results show the selectivity can be substantially improved by controlling drop size and distribution of the reactants among the differently sized droplets. Contrary to conventional wisdom which emphasizes creation of interfacial area by promoting very small droplets, it emerges that optimal distributions of drop size and reactant concentration which maximize productivity of the desired product exist. The practical implications are discussed.     

High resolution solid state 13C n.m.r. of butadiene grafted polypropylene

¹H dipolar decoupled ¹³C n.m.r. experiments with the aid of the magic angle spinning technique have been used to determine the graft content and the isomer content of the polybutadiene grafts in a graft copolymer with isotactic polypropylene.     

A minimal kinematic model for serial robot calibration using POE formula

Traditional methods based on the product of exponentials (POE) formula are parametrically continuous and complete for the calibration of the kinematic parameters of serial robots. However, these methods are not minimal due to the constraints of joint twists. This paper puts forward a new POE-based model, whose parameters are totally independent and conform to the formula of minimality. This is the first model that simultaneously satisfies the requirements of parametric continuity, completeness, and minimality with uniform and generic modeling rules. The proposed approach avoids the operations of normalization and orthogonalization which are necessary redundancy elimination steps with the traditional model. Simulations on a SCARA robot and experiments on an ABB IRB 120 robot prove that the new model outperforms in convergence, accuracy, and efficiency.     

Effect of Ratio of Surface Area to Volume on Oxygen Self-Diffusion Coefficients Determined for Crushed MgO-Al2O3 Spinels

Oxygen self-diffusion coefficients for single-crystal MgO-Al₂O₃ spinels previously determined for crushed particles were recalculated using the microscopic suface area of the sample, as was done for alumina. The corrected results agree well with those of Reddy and Cooper .     

Miscibility and morphology in crystalline/amorphous blends of poly(caprolactone)/poly(4-vinylphenol) as studied by DSC, FTIR, and C solid state NMR

The miscibility and morphology of poly(caprolactone) (PCL) and poly (4-vinylphenol) (PVPh) blends were investigated by using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and ¹³C solid state nuclear magnetic resonance (NMR) spectroscopy. The DSC results indicate that PCL is miscible with PVPh. FTIR studies reveal that hydrogen bonding exists between the hydroxyl groups of PVPh and the carbonyl groups of PCL. ¹³C cross polarization (CP)/magic angle spinning (MAS)/dipolar decoupling (DD) spectra of the blends show a 1 ppm downfield shifting of ¹³C resonance of PVPh hydroxyl-substituted carbons and PCL carbonyl carbons with increasing PCL content. Both FTIR and NMR give evidence of inter-molecular hydrogen bonding within the blends. The proton spin-lattice relaxation in the laboratory frame, T₁(H), and in the rotating frame, T_1ρ(H), were studied as a function of the blend composition. The T₁(H) results are in good agreement with thermal analysis; i.e. the blends are completely homogeneous on the scale of 50-80 nm. The T_1ρ(H) results indicate that PCL in the blends has both crystalline and amorphous phases. The amorphous PCL phase is miscible with PVPh, but the PCL crystal domain size is probably larger than the spin-diffusion path length within the T_1ρ(H) time-frame, i.e. larger than 2-4 nm. The mobility differences between the crystalline and amorphous phases of PCL are clearly visible from the T_1ρ(H) data.     

Studies on miscibility in homopolymer/ random copolymer blends by equation of state theory

The miscibility of poly(methyl methacrylate) (PMMA) and styrene-acrylonitrile random copolymers (SAN) blends was investigated on the basis of the Flory—Orwoll—Vrij equation of state theory. To obtain the equation of state parameters (P*, V*_sp, T*: characteristic parameters), the pressure—volume—temperature (PVT) behaviour was measured for PMMA and a series of SANs with various acrylonitrile contents. The exchange energy parameter X_ij was also calculated by fitting the theory to some phase diagrams of PMMA/SAN blends. The Flory—Huggins interaction parameter χ was separated into two contributions based on the equation of state theory for mixtures: the exchange energy term χ_inter and the free volume term χ_free. Both the temperature and copolymer composition dependences of χ_inter and χ_free were estimated by calculations using the equation of state parameters. There exists a region in which χ_inter is negative, leading to a miscibility window in PMMA/SAN blends. However, the immiscibility at high temperatures in the blends cannot be explained only by χ_inter; it is caused by the free volume contribution, χ_free. The miscibility window behaviour in PMMA/SAN blends may be explained within the framework of the equation of state theory.     

Composition of mixed octadecadienoates via ozonolysis,chromatography and computer solution of linear equations

An approach to the analysis of 55 possible nonconjugated positional isomers of octadecadienoic acid is described and tested with mixtures of individual synthetic methyl esters. In the first example, by ozonolysis a sevencomponent mixture consisting ofcis,cis 5,12-, 6,10-, 6,11-, 6,12-, 7,12-, 8,12-, and 9,12-octadecadienoates was converted to aldehydes, aldehyde-esters and dialdehydes. These fragments were separated on a 50 m×0.2 mm free fatty acid phase (FFAP) vitreous silica capillary column. Equations for an arbitrarily restricted 12×15 matrix of linear simultaneous equations and a computer solution of the matrix provided the composition of the initial methyl octadecadienoate mixture. The power and significance of this method became apparent with the observation that only two of the seven isomers in the known mixture were resolved as single peaks by state-of-the-art capillary gas chromatography, but all seven were identified and estimated with acceptable error by the ozonolysis-capillary gas chromatography-computer procedure. In a generalized approach to the analysis of the 55 possible nonconjugated isomers, a computer program selects the appropriate matrix of linear simultaneous equations based on the aldehyde data supplied by the analyst. Twenty of 21 combinations of seven isomeric esters taken five at a time have been analyzed to assess the efficiency of the method. To illustrate applicability at this stage of development, the method has been used to analyze the diene products of the hydrazine reduction of γ-linolenic acid and the diene products from the biological desaturation of isomeric monoenes. The possibility of distinguishing geometric and positional isomers of 18∶2 has been opened by the observed separation ofcis-andtrans-unsaturated aldehydes and aldehyde-esters. Presented in part at the 16th World Congress of the International Society for Fat Research, October 4–7, 1983, in Budapest, Hungary, and at the American Oil Chemists' Society Meeting, May 15, 1986, in Honolulu, Hawaii.     

Designing amino acid sequences to fold with good hydrophobic cores

We present two methods for designing amino acid sequences ofproteins that will fold to have good hydrophobic cores. Giventhe coordinates of the desired target protein or polymer structure,the methods generate sequences of hydrophobic (H) and polar(P) monomers that are intended to fold to these structures.One method designs hydrophobic inside, polar outside; the otherminimizes an energy function in a sequence evolution process.The sequences generated by these methods agree at the levelof 60–80% of the sequence positions in 20 proteins inthe Protein Data Bank. A major challenge in protein design isto create sequences that can fold uniquely, i.e. to a singleconformation rather than to many. While an earlier lattice-basedsequence evolution method was shown not to design unique folders,our method generates unique folders in lattice model tests.These methods may also be useful in designing other types offoldable polymer not based on amino acids