Irregular Environment Research Articles

FLEXIBLE ANKLE BASED ON PKM WITH FORCE/TORQUE SENSOR FOR HUMANOID ROBOT

This paper describes the development of a novel humanoid robot ankle based on an orientation Parallel Kinematic Mechanism (PKM) for intelligent and flexible control. With three identical Universal-Prismatic-Spherical prismatic-actuated limbs and a central Universal-Revolute passive limb, the PKM can perform three degrees of freedom rotational motions. In order to enable the humanoid robot safely to walk stably on the irregular environment, the control system should possess intelligence and flexibility. As the force information is one of the most important inputs for the control system, a novel integrated force sensor is designed to measure the action force and moment at the foot when humanoid robot maintains balanced or moves. The design possesses some interesting features such as high stiffness and compactness and is helpful for both reliable architectural design and performance improvement of the humanoid robot foot/ankle.

Synthesis, Crystal Structures and Spectroscopic Properties of RbBaTaS4 and K2BaTa2S11

Single crystals of RbBaTaS4 (1) and K2BaTa2S11 (2) were obtained from the reactions of Ta, with in situ formed fluxes of A2S3 (A = K, Rb), BaS, and S at 500 °C. Compound 1 crystallizes in the orthorhombic space group Pnma with a = 9.3286(5), b = 7.0391(4), c = 12.4365(7) Å, V = 816.6(1) Å3, Z = 4. Compound 2 crystallizes in the monoclinic space group P21/c with a = 14.5280(10), b = 12.6347(7), c = 17.5148(12) Å , β = 94.744(8)°, V = 3203.9(4) Å3, Z = 4. The structure of RbBaTaS4 (1) consists of isolated tetrahedral [TaS4]3− anions and Rb+ and Ba2+ cations. The Ba2+ cations are surrounded by nine sulfur atoms forming distorted tricapped trigonal prisms, whereas the Rb+ cations are in an irregular environment of ten sulfur atoms. The structure of K2BaTa2S11 (2) consists of two different dinuclear [Ta2S11] units which are separated by Ba2+ and K+ cations. The Ta atoms are coordinated by S2 2− and S2− ligands according to the mode [Ta2(μ2-S)(μ2-η2,η1- S2)2(η2-S2)2(S)2]4−. Each Ta atom is surrounded by seven sulfur ions forming strongly distorted pentagonal bipyramids. The two [TaS7] polyhedra share a common face in the [Ta2S11] unit. The K+ and Ba2+ cations are statistically distributed over the crystallographic sites. Compound 2 has also been characterized by UV/Vis diffuse reflectance, IR and Raman spectroscopy

Lithium diaquanickel(II)catena-borodiphosphate(V) monohydrate

The title borophosphate LiNi(H2O)2[BP2O8]·H2O was synthesized under hydro­thermal conditions. The crystal structure is isotypic with the Mg analogue and features helical [BP2O8]3− borophosphate ribbons, constructed by BO4 (2 symmetry) and PO4 tetra­hedra. The borate groups share all their oxygen apices with adjacent phosphate tetra­hedra. The ribbons are connected via Ni2+ cations that are located on twofold rotation axes. The cations have a slightly distorted octa­hedral oxygen coordination by four O atoms from the anion and by two water mol­ecules. The voids within the helices are occupied by Li+ cations, likewise located on twofold rotation axes, in an irregular environment of five O atoms. The structure is stabilized by O—H⋯O hydrogen bonds between coordinated or uncoordinated water mol­ecules and O atoms that are part of the helices.

Running on uneven ground: leg adjustment to vertical steps and self-stability

Human running is characterized by comparably simple whole-body dynamics. These dynamics can be modelled with a point mass bouncing on a spring leg. Theoretical studies using such spring-mass models predict that running can be self-stable. In simulations, this self-stability allows for running on uneven ground without paying attention to the ground irregularities. Whether humans actually use this property of the mechanical system in such an irregular environment is, however, unclear. One way to approach this question is to study how the leg stiffness in stance and the leg orientation in flight are changed in response to ground perturbations. Here, for 11 human subjects we studied two consecutive contacts during running on uneven ground with a force plate of adjustable height (step of +5, +10 and +15 cm). We found that runners adjust their leg stiffness to the height of a vertical step. The adjustment is characterized by a 9% increase in leg stiffness in preparation for the perturbation and by a systematic decrease in proportion to the step height. At the highest vertical step (+15 cm), leg stiffness was reduced by about 26%. We also observed that the angle of attack decreased from 68 deg. to 62 deg. with increasing ground height. These leg adjustments are in accordance with the predictions of a stable spring-mass system. Furthermore, we could describe the identified leg forces and leg compressions with a simple spring-mass simulation for a given body mass, leg stiffness, angle of attack and initial conditions. We compared the experimental findings with the self-stabilizing properties of the spring-mass model, and discuss how humans use a combination of strategies that include purely mechanical self-stabilization and active neuromuscular control. Finally, beyond self-stability, we suggest that control may apply to smooth centre of mass kinematics.

Path Planning for Mobile Robots in Irregular Environment Using Immune Evolutionary Algorithm

The traditional evolution algorithm usually traps into local optimization easily. Aiming to the drawback of evolution algorithm, we propose a novel mobile robot path planning approach of immune evolutionary algorithm in irregular environment. The advantages of this method lie in two aspects. The diversity of antibodies can be maintained. Meanwhile immunity operation and optimizing operator can be used to improve the global search ability. The results of simulation experiment show that immune evolution algorithm is feasible and efficient, because it enhances the performance and quality of mobile robot path planning.

Synthesis and crystal structures of two mixed-ligand Cu(II) complexes of tripyridyldiamine

Two novel Cu(II) complexes, [Cu(H2tpda)(acac)](ClO4)0.5Cl0.5 · H2O, [Cu(H2tpda)(NO3)]ClO4 (2) (H2tpda = tripyridyldiamine) have been synthesized, and characterized by X-ray analyses, elemental analyses, IR, UV and ESR spectra. Single crystal X-ray diffraction revealed that the Cu atom in complex 1 is coordinated to three N atoms from H2tpda and two oxygen atoms from acac with an approximately trigonal bipyramidal geometry. The molecules are assembled through intermolecular hydrogen bonds and π–π stacking, affording a two dimensional network. In complex 2, the Cu atom is coordinated with three N atoms from H2tpda and two oxygen atoms from in addition to a weak coordination with one oxygen from , resulting in an irregular octahedral environment, and the molecules are also connected by intermolecular hydrogen bonding and π–π stacking, affording a one dimensional structure.

Quasi-Static Analysis of a Novel Crawler-Driven Robot Motion

The novel crawler-driven robot we designed used a planetary gear reducer as the major power transmission device and provides two types of output in different form using one actuator. The crawler mechanism switches between two outputs autonomously based on the terrain. Using this feature, the crawler-driven robot is expected to perform adaptably and effectively in irregular environments. We conducted 2-dimensional quasi-static analysis to explain the condition under which the robot performs some locomotion modes in an irregular environment. Experimental results showed that the crawler-driven robot moves over even ground and uses efficient locomotion modes or postures to adapt autonomously to irregular environments.

Refinement of Phase Formation in the Na2MoO4-Hf(MoO4)2 System. Crystal Structure of the New Binary Molybdate Na8Hf(MoO4)6

Phase equilibria in the subsolidus region of the Na2MoO4-Hf(MoO4)2 system have been investigated. The existence of Na2Hf(MoO4)3 was confirmed, and a new binary molybdate, Na8Hf(MoO4)6, has been found, whose crystal structure with dimensions a = 20.661(3) A, b = 9.816(1) A, c = 13.796(3) A, β = 113.47(1)°, Z = 4, space group C2/c, R = 0.023 is similar to that of K8Hf(MoO4)6. In the structure, each HfO6 octahedron is linked (through common vertices) to six MoO4 tetrahedra, forming [Hf(MoO4)6]8− cluster groups. Between the groups are Na+ ions having considerably distorted tetragonal pyramidal or octahedral oxygen surroundings; c.n. of sodium here is 5 or 6 versus c.n. = 7–9 of potassium in K8Hf(MoO4)6. The open irregular environment of sodium and the continuous three-dimensional openwork of oxygen polyhedra around sodium suggest that Na8Hf(MoO4)6 or its analogs may be good ion conductors.

Fractal concepts in studies of soil fauna

Despite the fact that their objects of study live in a highly complex and irregular environment, soil zoologists have not yet made use of the advantage of fractal geometry in their work. Less than 1% of papers published during the last 3 years that dealt with fractal applications in the field of biological and environmental sciences were directed at studies of soil fauna. This paper tries to initiate a more intensive use of fractals in soil zoology and outlines their potential for different aspects of research. It reviews a fractal approach to describe soil nematode movement patterns in an artificial two-dimensional soil matrix and presents original work on the impact of habitat complexity on the abundance:body size distribution of soil microarthropods and on the potential of detecting scaling regions of microarthropod aggregations by identifying scale-dependent changes of a fractal exponent.

Further studies on the saline lakes of the eastern Paroo, inland New South Wales, Australia

Continuing studies of 25 shallow lakes in the semi-desert of northwestern New South Wales during drier years revealed greater physicochemical extremes than previously recorded and wider fluctuations in salinity, even in less saline lakes. Earlier data on species composition and species richness were confirmed, with a few new species reported from either further field collections or the hatching of dried lake muds. A summer filling as against almost regular previous autumn-winter fillings made only a minor difference in faunas, though insects and phyllopods, for different reasons, were less prevalent in the drier years. The fauna of these inland saline lakes is not only biogeographically different from those in southern Australia, but is adapted to a more extreme and irregular environment.

Controlling chaos in a temporally irregular environment

In this paper we examine the problem of controlling a chaotic system embedded in a time varying environment, where the environmental variation may be of relatively large amplitude, and may have a fairly irregular nature. Our results show that a previous method of controlling chaos, which selects and stabilizes unstable steady states or unstable periodic orbits, can be adapted to this time irregular situation, provided that one can make on-line, short-term predictions of the future evolution of the environment. We demonstrate this by using an example in which a ship is impacted by ocean waves on its side. The goal of control here is to prevent capsizing from taking place.

A modified adaptive Kalman filter for real-time applications

A modified adaptive Kalman filtering algorithm is derived for the standard linear problem under an irregular environment where all variances of the zero-mean Gaussian white (system and observation) noises are unknown a priori. This algorithm has certain merits over various existing adaptive schemes in that it is simple, efficient, and suitable for real-time applications. An illustrative numerical example is presented. >

Arrangements of ligands giving low electric field gradients

The rules for predicting arrangements of point charges which give zero electric field gradient at a point are summarized. It is then shown that in an axially symmetric group of charges, it is quite a straightforward matter to calculate the position of the zero-EFG point and that the tetrahedron and octahedron are only special cases of an infinite set of possibilities. These concepts are applied to a number of molecules which contain a quadrupolar nucleus in an apparently irregular environment but which give a narrow nuclear resonance, and it is shown that in such cases it may be possible to place quite strict limits upon the directions in which the electronic charge is concentrated and which portion of the bond is effective in generating field gradients. The results obtained support Gordy's contention that only the electronic density near the nucleus in question is effective.