1,720,958 research outputs found
Force-dependent variable impedance controller for contact-rich tasks under reference trajectory uncertainty
No full textIn robotic manipulation, performing force-tracking tasks in an uncertain environment poses the risk of the robot and the environment encountering high contact forces. While learning control methods are used wheninteracting with uncertain environments, the robots generally take some time to learn the correct reference path in such scenarios. During this process, it is important to reduce the contact forces until the environment properties are learned to ensure the safety of the interaction. To this end, this article proposes a force-dependent variable impedance controller (FVIC) that provides compliance in the presence of reference uncertainty and improves the position tracking accuracy as the certainty of the reference position increases. In this FVIC, the stiffness and dampingof the robot are defined as functions of force and force rate, respectively, to ensure compliance and stability. The proposed method is validated via simulations and experiments conducted using the Kinova Gen3 7DOF robot. The results show that, unlike the traditional variable impedance control (VIC) methods, this method ensures stability without compromising the desired impedance characteristics. It is further demonstrated that with this method, the contact forces can be maintained significantly low when there’s a reference uncertainty, thus ensuring safety
Human-robot collaboration for unknown flexible surface exploration and treatment based on mesh iterative learning control
No full textContact tooling operations like sanding and polishing have been high in demand for robotics and automation, as manual operations are labour-intensive with inconsistent quality. However, automating these operations remains a challenge since they are highly dependent on prior knowledge about the geometry of the workpiece. While several methods have been developed in existing research to automate the geometry learning process and adjust the contact force, human supervision is heavily required in the calibration of workpieces and the path planning of robot motion in such methods. Furthermore, the stiffness identification of the workpiece is not considered in most of these methods. This paper presents a human-robot collaboration (HRC) framework, which is able to perform surface exploration on an unknown object combining the operator's flexibility with the control precision of the robot. The operator moves the robot along the surface of the target object, and the robot recognizes the surface geometry and surface stiffness while exerting a desired contact force through control. For this purpose, a mesh iterative learning control (MILC) is developed to learn the surface stiffness, plan the exploration path, and adjust contact force through repetitive online correction based on HRC. The proof of learning convergence and the results of the simulation and experiments performed using a 7-DOF Sawyer robot demonstrate the validity of the proposed controller
Non-repetitive-path iterative learning and control for human-guided robotic operations on unknown surfaces
No full textAutomation of abrasive machining operations has become a challenging aspect in the remanufacturing industry where it is required to conduct operations on a surface of which the exact dimensions are unknown. In such cases, skilled human workers have to step in to perform labor-intensive tasks with inconsistent quality. In existing research work, collaborative robots are used to partially automate such operations under human supervision. However, these methods do not perform learning and control simultaneously and are often affected by the interactions of the human operator. In this article, a novel learning and control scheme is proposed where the robot explores an unknown surface iteratively while achieving the desired contact control performance under supervision and occasional interference from the human operator. The unknown surface is divided into subregions, and the learning and control parameters are updated each time the robot visits each subregion. This method is independent of the path of the robot and, thus, is unaffected by the irregularities introduced by a human operator’s interactions. The proposed method is applied to force control, stiffness learning, and orientation adaptation cases. The validity of this method is shown via simulations as well as experiments conducted using a Kinova Gen3 7-degrees of freedom robot
Modeling of the Haltere-A Natural Micro-Scale Vibratory Gyroscope
Full text linkVibratory gyroscopes have gained immense popularity in the microsystem technology
because of their suitability to planar fabrication techniques. With considerable effort in design and fabrication, MEMS (Micro-electro-mechanical-system) vibratory gyroscopes have started pervading consumer electronics apart from their well known applications in aerospace and defence systems. Vibratory gyroscopes operate on the Coriolis principle for sensing rates of rotation of the r tating body. They typically employ capacitive or piezoresistive sensing for detecting the Coriolis force induced motion which is, in turn, used to determine the impressed rate of rotation. Interestingly, Nature also uses vibratory gyroscopes in its designs. Over several years, it has evolved an incredibly
elegant design for vibratory gyroscopes in the form of dipteran halteres. Dipterans are
known to receive mechanosensory feedback on their aerial rotations from halteres for
their flight navigation. Insect biologists have also studied this sensor and continue to be fascinated by the intricate mechanism employed to sense the rate of rotation.
In most Diptera, including the soldier fly, Hermetia illucens, the halteres are simple
cantilever like structures with an end mass that probably evolved from the hind wings of
the ancestral four-winged insect form. The halteres along with their connecting joint with the fly’s body constitute a mechanism that is used for muscle-actuated oscillations of the halteres along the actuation direction. These oscillations occur in the actuation plane such that any rotation of the insect body, induces Coriolis force on the halteres causing their plane of vibration to shift laterally by a small degree. This induced deflection along the sensing plane (out of the haltere’s actuation plane) results in strain variation at the
base of the haltere shaft, which is sensed by the campaniform sensilla. The goal of the
current study is to understand the strain sensing mechanism of the haltere, the nature
of boundary attachments of the haltere with the fly’s body, the reasons of asymmetrical
geometry of the haltere, and the interaction between both wings and the contralateral
wing and haltere.
In order to understand the haltere’s strain sensing mechanism, we estimate the strain
pattern at the haltere base induced due to rotations about the body’s pitch, roll, and yaw axes. We model the haltere as a cantilever structure (cylindrical stalk with a spherical end knob) with experimentally determined material properties from nanoindentation and carry out analytical and numerical (finite element) analysis to estimate strains in the haltere
due to Coriolis forces and inertia forces resulting from various body rotations. From
the strain pattern, we establish a correlation between the location of maximum strain and the position of the campaniform sensilla and propose strain sensing mechanisms.
The haltere is connected to the meta thoracic region of the fly’s body by a complicated
hinge mechanism that actuates the haltere into angular oscillations with a large
amplitude of 170 ◦ in the actuation plane and very small oscillation in the sensing plane.
We aim to understand the reason behind the dissimilar boundary attachments along
the two directions. We carry out bending experiments using micro Newton force sensor
and estimate the stiffness along the actuation and sensing directions. We observe that the haltere behaves as a rigid body in the actuation direction and a flexible body in the sensing direction. We find the haltere to be a resonating structure with two different kinds of boundary attachments in the actuation and sensing directions. We create a finite element model of the haltere joint based on the optical and scanning microscope images, approximate material properties, and stiffness properties obtained from the bending experiments. We subsequently validate the model with experimental results.
The haltere geometry has asymmetry along the length and the cross-section. This
specific design of the haltere is in contrast to the the existing MEMS vibratory gyroscope,
where the elastic beams supporting the proof mass are typically designed with symmetric
cross-sections so that there is a mode matching between the actuation and the sensing vibrations. The mode matching provides high sensitivity and low bandwidth. Hence, we are interested in understanding the mechanical significance of the haltere’s asymmetry.
First, we estimate the location of the maximum stress by using the actual geometry of the haltere. Next, by using the stiffness determined from bending experiments and mass
properties from the geometric model, we find the natural frequencies along both actuation
and sensing directions. We compare these findings with existing MEMS vibratory
gyroscopes.
The dipteran halteres always vibrate at the wing beat frequency. Each wing maintains
180 ◦ phase difference with its contralateral haltere and the opposite wing. Both
wings and the contralateral wing-haltere mechanism exhibit coupled oscillatory motion
through passive linkages. These linkages modulate the frequency and maintain the out- of-phase relationship. We explore the dynamics behind the out-of-phase behaviour and the frequency modulation of the wing-wing and wing-haltere coupled oscillatory motion.
We observe that the linear coupled oscillatory model can explain the out-of-phase relationship between the two wings. However, a nonlinear coupled oscillator model is required to explain both frequency synchronization and frequency modulation of the wing with the haltere. We also carry out a finite element analysis of the wing-haltere
mechanism and show that the out-of-phase motion between the wing and the haltere is
due to the passive mechanical linkage of finite strength and high actuation force.
The results of this study reveal the mechanics of the haltere as a rate sensing gyroscope and show the basis of the Nature’s design of this elegant sensor. This study brings out two specific features— the large amplitude actuated oscillations and the asymmetric geometry of the haltere structure— that are not found in current vibratory gyroscope designs. We hope that our findings inspire new designs of MEMS gyroscopes that have elegance and simplicity of the haltere along with the desired performance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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