349 research outputs found
Prehensile Pushing: In-hand Manipulation with Push-Primitives
No full textThis paper explores the manipulation of a grasped object by pushing it against its environment. Relying on precise arm motions and detailed models of frictional contact, prehensile pushing enables dexterous manipulation with simple manipulators, such as those currently available in industrial settings, and those likely affordable by service and field robots. This paper is concerned with the mechanics of the forceful interaction between a gripper, a grasped object, and its environment. In particular, we describe the quasi-dynamic motion of an object held by a set of point, line, or planar rigid frictional contacts and forced by an external pusher (the environment). Our model predicts the force required by the external pusher to “break” the equilibrium of the grasp and estimates the instantaneous motion of the object in the grasp. It also captures interesting behaviors such as the constraining effect of line or planar contacts and the guiding effect of the pusher’s motion on the objects’s motion. We evaluate the algorithm with three primitive prehensile pushing actions—straight sliding, pivoting, and rolling—with the potential to combine into a broader in-hand manipulation capability.National Science Foundation (U.S.). National Robotics Initiative (Award NSF-IIS-1427050)Karl Chang Innovation Fund Awar
Dexterous manipulation with simple grippers
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2020Cataloged from the official PDF of thesis.Includes bibliographical references (pages 117-124).This thesis focuses on enabling robots, specially those with simple grippers, to dexterously manipulate an object in a grasp. The dexterity of a robot is not limited to the intrinsic capability of a gripper. The robot can roll the object in the gripper using gravity, or adjust the object's pose by pressing it against a surface, or it can even toss the object in the air and catch it in a different pose. All these techniques rely on resources extrinsic to the hand, either gravity, external contacts or dynamic arm motions. We refer to such techniques collectively as "extrinsic dexterity". We focus on empowering robots to autonomously reason about using extrinsic dexterity, particularly, pushes against external contacts. We develop mechanics and algorithms for simulating, planning, and controlling motions of an object pushed in a grasp. We show that the force-motion relationship at contacts can be captured well with complementarity constraints and the mechanics of prehensile pushing in a general setting can be formulated as a mixed nonlinear complementarity problem. For computational efficiency, we derive the abstraction of the mechanics in the form of motion cones. A motion cone defines the set of object motions a pusher can induce using frictional contact. Building upon these mechanics models, we develop a sampling-based planner and an MPC-based controller for in-hand manipulation. The planner generates a series of pushes, possibly from different sides of the object, to move the object to a desired grasp. The controller generates local corrective pushes to keep the object close to the planned pushing strategy. With a variety of regrasp examples, we demonstrate that our planner-controller framework allows the robot to handle uncertainty in physical parameters and external disturbances during manipulation to successfully move the object to a desired grasp.by Nikhil Chavan-Dafle.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineerin
Experimental Validation of Contact Dynamics for In-Hand Manipulation
No full textThis paper evaluates state-of-the-art contact models at predicting the motions and forces involved in simple in-hand robotic manipulations. In particular it focuses on three primitive actions—linear sliding, pivoting, and rolling—that involve contacts between a gripper, a rigid object, and their environment. The evaluation is done through thousands of controlled experiments designed to capture the motion of object and gripper, and all contact forces and torques at 250 Hz. We demonstrate that a contact modeling approach based on Coulomb’s friction law and maximum energy principle is effective at reasoning about interaction to first order, but limited for making accurate predictions. We attribute the major limitations to (1) the non-uniqueness of force resolution inherent to grasps with multiple hard contacts of complex geometries, (2) unmodeled dynamics due to contact compliance, and (3) unmodeled geometries due to manufacturing defects.
Keywords: Contact Force, Contact Model, Grasp Object, Contact Compliance, Grip Force Increas
A two-phase gripper to reorient and grasp
No full textThis paper introduces the design of novel two-phase fingers to passively reorient objects while picking them up. Two-phase refers to a change in the finger-object contact geometry, from a free spinning point contact to a firm multipoint contact, as the gripping force increases. We exploit the two phases to passively reorient prismatic objects from a horizontal resting pose to an upright secure grasp. This problem is particularly relevant to industrial assembly applications where parts often are presented lying on trays or conveyor belts and need to be assembled vertically. Each two-phase finger is composed of a small hard contact point attached to an elastic strip mounted over a V-groove cavity. When grasped between two parallel fingers with low gripping force, the object pivots about the axis between the contact points on the strips, and aligns upright with gravity. A subsequent increase in the gripping force makes the elastic strips recede into the cavities letting the part seat in the V-grooves to secure the grasp. The design is compatible with any type of parallel-jaw gripper, and can be reconfigured to specific objects by changing the geometry of the cavity. The two-phase gripper provides robots with the capability to accurately position and manipulate parts, reducing the need for dedicated part feeders or time-demanding regrasp procedures.National Science Foundation (U.S.). National Robotics Initiative (NSF-IIS-1427050
Corrigendum to "Familial determinants of bone health parameters - a dual X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT)-based parent and offspring study in rural Indian children" [Bone (2026), volume 202, article 117685].
No full textThe affiliation of the second author, Dr. Nikhil Shah, was listed incorrectly. His correct affiliations are “a” (Hirabai Cowasji Jehangir Medical Research Institute, Jehangir Hospital, Pune, India) and “d” (Department of Pediatric Endocrinology, MRR Children's Hospital, Mumbai)
EXTERNAL PHOTOEVAPORATION OF THE SOLAR NEBULA: JUPITER's NOBLE GAS ENRICHMENTS
No full textabstract: We present a model explaining the elemental enrichments in Jupiter's atmosphere, particularly the noble gases Ar, Kr, and Xe. While He, Ne, and O are depleted, seven other elements show similar enrichments (~3 times solar, relative to H). Being volatile, Ar is difficult to fractionate from H[subscript 2]. We argue that external photoevaporation by far-ultraviolet (FUV) radiation from nearby massive stars removed H[subscript 2], He, and Ne from the solar nebula, but Ar and other species were retained because photoevaporation occurred at large heliocentric distances where temperatures were cold enough (lesssim 30 K) to trap them in amorphous water ice. As the solar nebula lost H, it became relatively and uniformly enriched in other species. Our model improves on the similar model of Guillot & Hueso. We recognize that cold temperatures alone do not trap volatiles; continuous water vapor production is also necessary. We demonstrate that FUV fluxes that photoevaporated the disk generated sufficient water vapor in regions [< over ~]30 K to trap gas-phase species in amorphous water ice in solar proportions. We find more efficient chemical fractionation in the outer disk: whereas the model of Guillot & Hueso predicts a factor of three enrichment when only <2% of the disk mass remains, we find the same enrichments when 30% of the disk mass remains. Finally, we predict the presence of ~0.1 M [subscript ⊕] of water vapor in the outer solar nebula and protoplanetary disks in H II regions.Copyright IOP Publishing. This is the authors' final, peer-reviewed manuscript. Monga, Nikhil, & Desch, Steven (2015). EXTERNAL PHOTOEVAPORATION OF THE SOLAR NEBULA: JUPITER's NOBLE GAS ENRICHMENTS. ASTROPHYSICAL JOURNAL, 798(1), 0-0. http://dx.doi.org/10.1088/0004-637X/798/1/9. The final version as published can be viewed online at http://dx.doi.org/10.1088/0004-637X/798/1/
Detection results of NMC particles in composite battery cathodes
No full textThis dataset shows more examples of the NMC particles detection overlayed with the original images in composite battery cathodes.
@journal{li2022networkevolution,
title={Dynamics of particle network in composite battery cathodes},
author={Li, Jizhou and Sharma, Nikhil and Jiang, Zhisen and Yang, Yang and Monaco, Federico and Xu, Zhengrui and Hou, Dong and Ratner, Daniel and Pianetta, Piero and Cloetens, Peter and Lin, Feng and Zhao, Kejie and Liu, Yijin},
year={2022},
journal={Science}
Pattern Discovery of Sequential Symbolic Data using Automata with an application to Author Identification
No full textAuthor Identification is the process of identifying a piece of text to ascertain if it has an inherent writing style or pattern based on a certain author. Almost all literary books can be accredited to a certain author since it has been signed. However, there also exist a plethora of unfinished books or manuscripts that could be attributed to a range of possible authors. For example, William Shakespeare has written many plays that have not been signed by him. In order to assess the importance of such texts that do not bear the authors signature, it could be vital to know who was the writer. I plan to solve this dilemma using the characteristics of finite state automata coupled with the ALERGIA algorithm
Dynamics of particle network in composite battery cathodes
No full textThis repository contains the source codes for the study of active particle-network evolution in Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC) composite battery cathodes, as described in the following paper:
@journal{li2021networkevolution,
title={Dynamics of particle network in composite battery cathodes},
author={Li, Jizhou and Sharma, Nikhil and Jiang, Zhisen and Yang, Yang and Monaco, Federico and Xu, Zhengrui and Hou, Dong and Ratner, Daniel and Pianetta, Piero and Cloetens, Peter and Lin, Feng and Zhao, Kejie and Liu, Yijin},
year={2022},
journal={Science}
Extrinsic Dexterity: In-Hand Manipulation with External Forces
No full textAbstract — “In-hand manipulation ” is the ability to reposition an object in the hand, for example when adjusting the grasp of a hammer before hammering a nail. The common approach to in-hand manipulation with robotic hands, known as dexterous manipulation [1], is to hold an object within the fingertips of the hand and wiggle the fingers, or walk them along the object’s surface. Dexterous manipulation, however, is just one of the many techniques available to the robot. The robot can also roll the object in the hand by using gravity, or adjust the object’s pose by pressing it against a surface, or if fast enough, it can even toss the object in the air and catch it in a different pose. All these techniques have one thing in common: they rely on resources extrinsic to the hand, either gravity, external contacts or dynamic arm motions. We refer to them as “extrinsic dexterity”. In this paper we study extrinsic dexterity in the context of regrasp operations, for example when switching from a power to a precision grasp, and we demonstrate that even simple grippers are capable of ample in-hand manipulation. We develop twelve regrasp actions, all open-loop and handscripted, and evaluate their effectiveness with over 1200 trials of regrasps and sequences of regrasps, for three different objects (see video [2]). The long-term goal of this work is to develop a general repertoire of these behaviors, and to understand how such a repertoire might eventually constitute a general-purpose in-hand manipulation capability. I
- …
