Primitive Contact Research Articles

Examining the Frictional Behavior of Primitive Contact Geometries for use as Robotic Finger Pads

Prosthetic and robotic grippers rely on soft finger pads to better acquire objects of varying size, shape and surface. However, the frictional behavior of soft finger pads of different designs and geometries have yet to be quantitatively compared, in large part due to the difficulty in modeling soft contact mechanics. In this letter, we experimentally examine the frictional behavior of several common primitive contact geometries in terms of their performance under shear loads that would tend to cause the contact to slip and the grasp to potentially fail. The effective static and kinetic coefficients of friction were recorded for each finger pad under a range of common grasping loads. The results show that the variance in contact curvature, contact patch geometry and pressure distribution have influences on key parameters for grasping at low forces. The advantages and disadvantages of these simple geometries are discussed for design of single finger, multi-finger and manipulation-based robotic hands.

History, Time, and Lived Experience in Toni Morrison’s Beloved (1987), Jazz (1992), and Paradise (1997)

Abstract My essay interprets Toni Morrison’s works as ‘timeless,’ not so much from the perspective of their presumable universal appeal, but from that of their narrative composition, which denies established forms of temporal arrangement and facilitates new ways of textual experience. Focusing on Morrison’s Trilogy (Beloved, Jazz, and Paradise), I will argue that the three novels challenge conventional ideas of history and time to create a narrative space situated in the living present. While filled with numerous references to concrete timelines, Morrison’s writings also insist on a quasi-universal ‘truth’ that takes the reader beyond the boundaries of objective history. Beloved first limits the narrative perspective to the year 1873, but then invites its readers to embark on a virtual ‘time travel’ through various periods of the protagonist’s life. Memories and subjective lapses back into the past dominate the narration, thus focusing on experience and imaginary time. Jazz and Paradise both situate literary ‘truth’ in the sentient dynamic of the reading experience. Following the claim of phenomenological theory that perception is always a kind of action in which the world appears “afresh from the perspective of […] ‘lived’ experience” (Chaplin, A.D. [2002]. “Phenomenology: Merleau-Ponty and Sartre.” B. Gaut and D.M. Lopes, eds. The Routledge Companion to Aesthetics. London and New York, NY: Routledge, 159), I will examine Morrison’s novels as ‘living events’ that reconstruct the narrated occurrences as haptic experiences. Through mnemonic elements within the esthetics of her texts, Morrison transforms the novels’ story time into a very subjective discourse time that engages readers immediately. In the phenomenological sense, these strategies enable us to lose ourselves in Morrison’s novels and, instead of perceiving them as mere textual constructions, indulge in the illusion of “re-achieving a direct and primitive contact with the world” (Merleau-Ponty, Maurice (1996 [1945]). Phenomenology of Perception. Trans. Colin Smith. London and New York, NY: Routledge, vii).

On Computing Reliable Optimal Grasping Forces

This paper presents algorithms for optimal grasping forces. The previous work reveals that contact forces with minimal sum or maximum of normal force components can be written as positive combinations of primitive contact forces, to which the corresponding primitive contact wrenches express the required resultant wrench as their positive combination with minimum coefficients in terms of the L1 or L∞ metric. On this basis, we first propose an algorithm to compute such a set of primitive contact forces and the minimum contact forces. Moreover, considering the uncertainty in the actual friction coefficient, we develop another algorithm to determine the minimum required friction coefficient and the corresponding minimum contact forces within a given limit on their magnitude so that such contact forces are more reliable in practice. As our algorithms do not rely on any general optimization technique, they are very efficient and easy to implement. These algorithms can also be used in grasp quality evaluation and optimal grasp planning.

Wittgenstein's Builders and Perry's Objection to Sentence Priority

In the first section of this paper I present a view of linguistic meaning that I label 'Sentence Priority' (SP): the position that semantically primitive language-world contact is made at the level of complete sentences (rather than the level of sentence parts). Then, in the main part of the paper, I consider and reject an objection against Sentence Priority raised by John Perry, an objection that appeals to Wittgenstein's builders parable. Perry argues that the builder's utterances ('Slab', 'Pillar', etc.) are utterances of self-standing nouns, and that therefore they constitute a counter-example to SP. A sound assessment of Perry's argument, however, depends on a clear distinction between two cases: one in which the four expressions mentioned in Wittgenstein's example exhaust the builders' expressive powers, and one in which they do not. Once these cases are distinguished it can be seen that in neither does Perry's argument go through.

Qualitative test and force optimization of 3-D frictional form-closure grasps using linear programming

This paper formalizes qualitative test of 3D frictional form-closure grasps of n robotic fingers as a problem of linear programming (LP). It is well-known that a sufficient and necessary condition for form-closure grasps is that the origin of the wrench space lies inside the convex hull of primitive contact wrenches. We demonstrate that the problem of querying whether the origin lies inside the convex hull is equivalent to a ray-shooting problem, which is dual to a LP problem based on the duality between convex hulls and convex polytopes. Furthermore, this paper addresses a problem of minimizing the L/sub 1/ norm of the grasp forces balancing an external wrench, which can be also transformed to a ray-shooting problem. We have implemented the algorithms and confirmed their real-time efficiency for qualitative test and grasp force optimization.

The lorisiform wrist joint and the evolution of “brachiating” adaptations in the hominoidea

In lorisines (Loris, Nycticebus, Perodicticus, Arctocebus), the tip of the ulna is reduced to the dimensions of a styloid process, a new and more proximal ulnar head is developed, and the pisiform is displaced distally away from its primitive contact with the ulna. In some Nycticebus, intra-articular tissues separate the ulna from the triquetrum. These traits are not seen in other quadrupedal primates, but they are characteristic of extant hominoids. Among hominoids, these features have been interpreted as adaptations to arm-swinging locomotion. Since hominoid-like features of the wrist joint are found in lorisines, but not in New World monkeys that practice arm-swinging locomotion, these features may have been evolved in both lorisines and large hominoids to enhance wrist mobility for cautious arboreal locomotion involving little or no leaping. Most of the other morphological traits characteristic of modern hominoids can be explained as adaptations to cautious quadrupedalism as well as to brachiation, and may have developed for different reasons in different lineages descended from an unspecialized cautious quadruped resembling Alouatta.

XXI. The Eight Immortals

One of the subjects beloved of Chinese artists is a venerable figure in an attitude of profound reverie shown as part of a wild and romantic scene of forest, crag, and torrent. Sometimes below his rocky hermitage there stretches a plain with far-off shadowy outlines of ordinary mortal habitations, of which the faint remoteness suggests the gulf separating him from mundane cares and vanities. Looking at such a one, instinct tells us that he feels, to use the words of Shelley, “as if his nature were resolved into the surrounding universe, or as if the surrounding universe were resolved into his being.” He belongs to a strange race, variously named by Western writers Fairies, Immortals, Genii, Rishi. And here may it be remarked in parenthesis that neither “fairy” nor “immortal” is a term that exactly fits them; nor, indeed, does Arabic jinn or Sanskrit ṛishi. They are a race peculiarly Chinese and apart. Hence it would seem most appropriate to call them by their native name hsien, now commonly written , a pictogram representing perfectly the essence of their cult—the primitive contact of man with Nature typified by the mountains. Hsien, therefore, they will be termed in these pages.