140 research outputs found
The International Journal of Robotics Research - Special Issue on the Mechanics and Design of Robotic Hands
No full textThis special issue consists of nine papers from
researchers around the globe. The scope of the papers spans
a wide spectrum of approaches, from underactuated hands
with a single or small number of actuators, to fully actuated
hands with nearly human-like controllable degrees of
freedom. A number of the hands incorporate some novel
design feature that has yet to be examined in the context
of robotic hands, including electrostatic clutches, twistedstring
actuators, or novel underactuated mechanisms. Two
of the hands present modular designs, with multiple uses of
the same actuation module, and thre
Scaling hard vertical surfaces with compliant microspine arrays
No full textA new approach for climbing hard vertical surfaces has been developed that allows a robot to scale concrete, stucco, brick and masonry walls without using suction or adhesives. The approach is inspired by the mechanisms observed in some climbing insects and spiders and involves arrays of microspines that catch on surface asperities. The arrays are located on the toes of the robot and consist of a tuned, multi-link compliant suspension. In this paper we discuss the fundamental issues of spine allometric scaling versus surface roughness and the suspension needed to maximize the probability that each spine will find a useable surface irregularity and to distribute climbing tensile and shear loads among many spines. The principles are demonstrated with a new climbing robot that can scale a wide range of exterior walls
Vanishing of differentials along ideals and non-archimedean approximation
No full textOne of the major new developments in commutative algebra over the last decade or so was the introduction of the theory of tight closure of an ideal by Hochster and Huneke. It proved to be an extremely useful technique to study ideals, and it also turned out to be closely related to many geometric questions. Fedder [F] used derivations in positive characteristic to obtain characterizations of two-dimensional graded rational singularities in terms of F-purity and F-injectivity. In an attempt to generalize these techniques and to relate rational singularities with F-rationaIity, Craig Huneke raised the following problem (cf. [FHH]): Let R be a regular local ring, containing a perfect field k, over which R is essentially of finite type, and let C(R/k) be the subring of derivationally constant elements of R/k (i.e. C(R/k) = (x is an element of R : delta(x) = 0 for all delta is an element of Der(k)(R))). Then Huneke asked: (1) If subset of or equal to R is an ideal, does there exist a constant l = l(R, I) is an element of N with the following property: If x is an element of R with delta (x) is an element of In+l then there exists a c is an element of C(R/k) with x - c is an element of I-n. (2) If an l as in (1) exists, is it possible to bound it in a way useful for reduction mod p techniques, i.e. if char(k) = 0, does there exist a model R/A,L subset of or equal to R of R/k, I with A/Z of finite type and a constant I (L) such that l(R/mR, L + m/m) less than or equal to l(L) for all m is an element of Max(A)
The development of the SPRING Hand: a Self-adaptive hand Prosthesis for Restoring Natural Grasping, Journal of Autonomous Robots
No full textApproximating gecko setae via direct laser lithography
No full textThe biomimetic replication of dry adhesion present in the gecko's foot has attracted great interest in recent years. All the microfabrication techniques used so far were not able to faithfully reproduce the hierarchical and complex three-dimensional geometry of the gecko's setae, with features at the micro- and nano-scale, thus reducing the effectiveness that such conformal morphology could provide. By means of direct laser lithography we fabricated artificial hairs that faithfully reproduce the natural model. This technique allows the fabrication of three-dimensional microstructures with outstanding results in terms of reproducibility and resolution at the micro- and nano-scale. It was possible to get very close to the morphology of the natural gecko setae, especially concerning the hierarchical shape. We designed several morphologies for the setae and studied the effects in terms of adhesion and friction performances compared to the natural counterpart, showing the interplay between morphology, dimensional scaling and materials. Direct laser lithography promises great applications in the biomimetics field, paving the way to the implementation of the concept of hierarchical bioinspired dry adhesives
Dry adhesion of artificial gecko setae fabricated via direct laser lithography
No full textBiomimetics has introduced a new paradigm: by constructing structures with engineered materials and geometries, innovative devices may be fabricated. According to this paradigm, both shape and material properties are equally important to determine functional performance. This idea has been applied also in the field of the microfabrication of smart surfaces, exploiting properties already worked out by nature, like in the case of self-cleaning, drag reduction, structural coloration, and dry adhesion. Regarding dry adhesive properties, geckos represent a good example from which we take inspiration, since they have the extraordinary ability to climb almost every type of surface, even smooth ones, thanks to the hierarchical conformation of the fibrillary setae in their toe pads. Due to this design, they can increase the area of contact with a surface and thus the amount of attractive van der Waals forces. While reproducing with artificial materials the same functional morphology of gecko’s pads is typically not achievable with traditional microfabrication techniques, recently Direct Laser Litography offered new opportunities to fabrication of complex three-dimensional structures in the microscale with nanometric resolution. Using direct laser lithography, we have fabricated artificial gecko setae, reproducing with unprecedented faithfulness the natural morphology in the same dimensional scale. Adhesion force of artificial setae toward different surfaces have been tested in dry condition by means of a dedicated setup and compared with natural ones
Semigroups of valuations on local rings, II
No full textGiven a noetherian local domain and a valuation of its field of fractions which is non negative on , we derive some very general bounds on the growth of the number of distinct valuation ideals of corresponding to values lying in certain parts of the value group of . We show that this growth condition imposes restrictions on the semigroups for noetherian which are stronger that those resulting from the previous paper \cite{C2} of the first author. Given an ordered embedding , where is the rank of , we also study the shape in of the parts of which appear naturally in this study. We give examples which show that this shape can be quite wild in a way which does not depend on the embedding and suggest that it is a good indicator of the complexity of the semigroup
The Rees algebra and analytic spread of a divisorial filtration
No full textIn this paper we investigate some properties of Rees algebras of divisorial
filtrations and their analytic spread. A classical theorem of McAdam shows that
the analytic spread of an ideal in a formally equidimensional local ring is
equal to the dimension of the ring if and only if the maximal ideal is an
associated prime of for some . We show in Theorem 1.6
that McAdam's theorem holds for -divisorial filtrations in an
equidimensional local ring which is essentially of finite type over a field.
This generalizes an earlier result for -divisorial filtrations in an
equicharacteristic zero excellent local domain by the author. This theorem does
not hold for more general filtrations.
We consider the question of the asymptotic behavior of the function for a -divisorial filtration
of -primary ideals on a -dimensional normal excellent local ring. It is
known from earlier work of the author that the multiplicity can be irrational. We
show in Lemma 4.1 that the limsup of the first difference function is always
finite for a -divisorial filtration. We then give an example in
Section 4 showing that this limsup may not exist as a limit.
In the final section, we give an example of a symbolic filtration
of a prime ideal in a normal two dimensional excellent local
ring which has the property that the set of Rees valuations of all the symbolic
powers of is infinite.Comment: 25 page
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