Design and Realization of a Non-Circular Cable Spool to Synthesize a Nonlinear Rotational Spring

In this paper we present a cable mechanism that realizes a nonlinear rotational spring from a linear translational spring. The spring is pulled by a cable wound around a non-circular spool, which is rigidly attached to the joint. The non-circular shape of the spool induces a nonlinear relationship between its angular position and the torque created by the tension of the cable. Depending on the shape of the spool, various torque–angle relationships can be realized. We show that for a given nonlinear torque–angle relationship, there is an explicit expression (closed-form solution) of the shape of the spool that synthesizes this function. First, we present the geometry of the problem. Then, we derive the methodology to calculate the shape of the spool to synthesize a prescribed torque–angle relationship. Finally, we verify the design methodology by experiments with three different spools realizing a constant force spring, an exponential softening spring and a cubic polynomial spring. We discuss the possible sources of errors between the theoretical and experimental results.     

Steady Crawl Gait Generation Algorithm for Quadruped Robots

The capability of stable walking on irregular terrain is the primary advantage of legged robots over wheeled mobile robots. However, the traditional foothold selection-based gait generation algorithms are not suitable at some points for blind robots which cannot obtain the exact terrain information. A velocity-based gait generation algorithm with real-time adaptation rules which are necessary for steady walking is suggested. Particularly, we have developed a steady crawl gait with duty factor β = 0.75. The main feature of the suggested algorithm is that it is not based on foothold selection and it can be used for the walking of blind robots on more realistic irregular terrain. The adaptation rules are the translational velocity modification to satisfy the steady gait requirement and the swing period modification to avoid the kinematic limitation. The suggested gait generation algorithm has been implemented in a simple quadruped robot that has a total of eight actuated joints on the legs. Using PD controllers for each actuated joint for the trajectory following and the adaptation algorithm of gait parameters, the steady periodic crawl gait on irregular terrain has been demonstrated.     

Image-based predictive display for high d.o.f. uncalibrated tele-manipulation using affine and intensity subspace models

The addition of immediate but estimated visual feedback, called predictive display, improves tele-manipulaton performance when the real video feedback is delayed. Current systems typically rely upon a previously calibrated camera and manipulator. We present a method where the motor-visual calibration is estimated on-line from motor commands and returned video images only. Predicted visual feedback is presented in two forms. As soon as a basic model has been estimated, a wire frame drawing of the predicted current pose is overlaid on the delayed video feedback. After some time when a rich model has been estimated, predicted intensity images are synthesized and these replace the delayed real video. In an intermediate situation where blurry synthesized images can be computed, the wireframe is overlaid on the synthesized images to show precisely the pose of the object. Experiments with a Utah/MIT robot hand and PUMA robot arm are shown.     

Formation of zinc oxide nanoparticles by mechanochemical reaction

Abstract

The synthesis of zinc oxide (ZnO) nanocrystallites by mechanochemical reaction of ZnCl₂ and Na₂CO₃ with NaCl as diluent and following thermal treatment was investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Calcination of the as milled powder at 600°C in air and removal of NaCl through washing formed ZnO nanocrystallites with an average crystal size of ~ 21 nm, which increased with increasing thermal treatment temperature. Milling time and NaCl/ZnCl₂ molar ratio exerted prominent effects on the crystal size of the ZnO nanoparticles. The mechanism of nanocrystallite growth is discussed.     

Ultrafine and nanoscaled tungsten carbide synthesis from colloidal carbon coated nano tungsten precursor

Abstract

A new process for synthesising homogeneous ultrafine and nanoscaled tungsten carbide with good stability in air from well dispersed colloidal carbon coated nano tungsten precursor with highly agglomerated nanoscaled tungsten powder as starting material in a cost effective way is introduced. It is shown that hydrogen atmosphere facilitates the carbon and tungsten reaction process. Inheritance character in grain size distribution of tungsten carbide from tungsten starting material with BET calculated grain size of 46·1 nm has been observed. When the carburisation temperature increases from 1000 to 1300°C, the Brunauer–Emmett–Teller calculated grain size of tungsten carbide powder increases from 68·6 nm to 339·4 nm and the oxygen content decreases from 0·44 to 0·10%.     

Synthesized articulated behavior using space-temporal on-line principal component analysis

This paper presents a new framework to synthesize humanoid behavior by learning and imitating the behavior of an articulated body using motion capture. The video-based motion capturing method has been developed mainly for analysis of human movement, but is very rarely used to teach or imitate the behavior of an articulated body to a virtual agent in an on-line manner. Using our proposed applications, new behaviors of one agent can be simultaneously analyzed and used to train or imitate another with a novel visual learning methodology. In the on-line learning phase, we propose a new way of synthesizing humanoid behavior based on on-line learning of principal component analysis (PCA) bases of the behavior. Although there are many existing studies which utilize PCA for object/behavior representation, this paper introduces two criteria to determine if the dimension of the subspace is to be expanded or not and applies a Fisher criterion to synthesize new behaviors. The proposed methodology is well-matched to both behavioral training and synthesis, since it is automatically carried out as an on-line long-term learning of humanoid behaviors without the overhead of an expanding learning space. The final outcome of these methodologies is to synthesize multiple humanoid behaviors for the generation of arbitrary behaviors. The experimental results using a humanoid figure and a virtual robot demonstrate the feasibility and merits of this method.     

Synthesis and characterisation of gelatin–nano hydroxyapatite composite scaffolds for bone tissue engineering

Abstract

Gelatin–hydroxyapatite (HAp) nanocomposites have been prepared by particulate leaching technique using glutaraldehyde (GTA) as cross-linking agent for polymer. The porosity in the scaffolds was controlled using sodium chloride as porogen agent. Microstructural investigation by scanning electron microscopy (SEM), revealed the formation of a well interconnected porous scaffold with pore size in the range of 100–200 μm. X-ray diffraction and Fourier transform infrared spectroscopy were used to confirm the formation of crystalline HAp as well the presence of both constituents in the composite samples. The bioactivity of the samples was evaluated by conducting MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay and cell adhesion tests. The results suggest that the use of GTA in excess of 0˙25% can be detrimental to cell survival. Cell attachment on the nanocomposite scaffold was verified by microscopic analysis.     

Sol–gel derived nanostructure hydroxyapatite powder and coating: aging time optimisation

Abstract

The aim of this work was to evaluate the effect of aging time on the formation and phase purity of nanostructure hydroxyapatite powder and coating. Hydroxyapatite powder and coating were prepared by sol–gel method using calcium nitrate and phosphorous pentoxide as starting materials. Precursor sols were dip coated onto the pure titanium substrates. The coated plates were aged in different aging times and dried. Finally, samples were calcinated at 600 and 700°C. Thermal behaviour, phase formation, surface morphology and interfacial coherency were investigated by thermogravitometry analysis, X-ray diffraction and scanning electron microscope. Results showed that a solution aging time of at least 24 h was required to achieve monophasic nanostructure hydroxyapatite powder and coating. Hydroxyapatite structure of coating was obtained at 600°C, and a β-tricalcium phosphate phase was formed at 700°C. The effect of sintering temperatures on crystallite size of the coatings was not significant.     

The meaning of action: a review on action recognition and mapping

In this paper, we analyze the different approaches taken to date within the computer vision, robotics and artificial intelligence communities for the representation, recognition, synthesis and understanding of action. We deal with action at different levels of complexity and provide the reader with the necessary related literature references. We put the literature references further into context and outline a possible interpretation of action by taking into account the different aspects of action recognition, action synthesis and task-level planning.     

Consolidation of diamond tools using Cu–Co–Fe based alloys as metallic binders

Abstract

The present work reports the results obtained on the evaluation of both the response of commercially available Cu–Fe–Co pre-alloyed powders during processing for the consolidation of diamond tools under several fabrication routes, and the performance of the tools during in field cutting operations. The new metallic binders look attractive since they combine good sinterability with adequate values of hardness and wear resistance, as observed from the cutting tests carried out on granite and marble. The consolidation routes under research were conventional hot pressing, pressureless sintering, and hipping after sintering. The amount of copper contained in these alloys leads to fully dense parts by hot pressing at temperatures approximately 150°C lower than those used for cobalt. Pressureless sintering experiments showed that full densification requires the application of hipping post-sintering treatments. During processing under non-reducing atmospheres, the presence of metallic oxides contained in the powder was observed to exert a direct influence on the degradation of the diamond grits.