1,720,957 research outputs found
Parallel Kinematics Manipulators for Pick and Place of Moving Objects Using 3D Perception: Development of a Test Bench
No full textInterest in increasing the efficiency of manufacturing processes has led to a wide research effort focused on pick- and-place of moving objects. This topic presents a number of difficulties and consequently areas for research due to the need to integrate and optimize both the visual perception system, the image processing algorithm, and the robot control system. In the literature, many experimental efforts regarding new proposals to improve this process are carried out using anthropomorphic manipulators. The authors’ interest is instead to develop a testbed in order to investigate the various issues concerning dynamic pick-and-place, using a parallel kinematics manipulator. In fact, parallel kinematics manipulators are widely used in industry for high-speed pick-and-place tasks due to their inherent stiffness and dynamic performance. In this paper, a 4-degree-of-freedom 5R parallel kinematics robot will be integrated with a 3D camera for tracking moving objects. The manipulator and 3D camera will be presented, and then the software and hardware architecture of the testbed, resulting from the integration of the two systems, will be described. The object tracking algorithm used will be described, and analysis regarding its computational performance will be shown. Finally, considerations about the feasibility of integrating the two systems for dynamic pick-and-place will be drawn, deriving the future activities that are intended to be done
Experimental Investigation on a Power Supply Control System for Hydraulic Actuators
No full textHydraulics is a technology widely used whenever high power is required with relatively small dimensions of the components. However, despite the high power density that characterizes the hydraulic components, they are intrinsically dissipative due to pressure drops across them. One of the possible adoptable solutions to increase the efficiency of the system is to control the power supply at the aim to tailor the generated power to the load demand. Many of the proposed solutions retrievable in literature lead to significant modifications of the hydraulic circuit, and are not of general validity for other kinds of systems. The present paper focuses exactly on a new kind of power supply control system, with a low impact on a hydraulic plant, and applicable to different kinds of systems. It is based on the regulation of the supply pressure by means of a servo valve. This new power supply control system is analysed through preliminary experimental activities conducted on a test rig, where the pressure of the fluid within a constant volume is controlled. Firstly, the bandwidth of the transfer function between the servo valve command and the supply pressure is evaluated. Secondly, a closed loop control of the supply pressure is realized, considering a pressure set-point drawn from a real case, already studied by the authors in a previous work. The experimental results show that the system is able to follow the set-point with a very small error. At the same time, a system model where the fluid is considered incompressible has been set-up. The relevant transfer function obtained shows remarkable differences with respect to the experimental one. Hence, the model needs to be reviewed including other effects, like fluid's compressibility, at the moment neglected. Besides the model improvement, authors have been planning other experimental activities in different conditions to confirm the preliminary results obtained
Co-simulation of Impedance and Hybrid Motion-Force Control Strategies on a 4-DOF 5R Parallel Manipulator
No full textImpedance and hybrid motion-force control systems allow robots to perform complex manipulation tasks in which both force and position should be simultaneously regulated. In contrast to solutions based on passive compliant elements, active control allows adaptation to varied working conditions, through variations of the control system parameters. The evaluation of force control strategies is typically performed experimentally, due to the difficulty of accurately modelling at once different phenomena like contact dynamics, mechanical compliances, measurement noise and delays that affect the actual performance of controller, whose synthesis is necessarily based on simplifying assumptions. The use of co-simulation techniques constitutes however an alternative to experimental tests, and allow the safe and effective analysis of the effects of non-idealities not foreseen at the design stage. This work, therefore, investigates the feasibility of contour tracking of unknown planar profiles with a 4-DOF parallel manipulator using Simulink and MSC Adams co-simulations. The results allow a first selection of the most effective control strategies, and suggest that, prior to implementation on the physical prototype of the robot, friction contact compensation should be introduced in order to accurately track velocities and forces also in the presence of significant tangential disturbances
Real Time MEMS-Based Joint Friction Identification for Enhanced Dynamic Performance in Robotic Applications
Get PDFThe mechatronic design approach to robotics deploys, inter alia, widely available mechanical design engineering tools that, together with standard production techniques, allow the accurate quantification of the system’s mass properties. While this enables the synthesis of model-based centralized controllers, friction still limits the achievable dynamic performances, as its prediction at the design stage is hampered by complex dependencies on loads, temperature, wear, and lubrication. Further uncertainties affecting mechatronic devices stem from the actuation systems, whose parameters are specified by the manufacturer with relatively loose accuracy. These challenges are addressed here through a method based on MEMS IMUs for the real-time estimation of both friction effects and uncertain actuator parameters. The resulting model, inclusive of the frictionless dynamics, is applied in a closed loop to improve the control performance. An experimental comparison with decentralized and non-adaptive regulators highlights severalfold reductions in tracking errors; the ability to track temperature-dependent friction variations is also shown. From this work, it may be concluded that the use of MEMS sensors, together with identification and adaptive control algorithms, sensibly increases the dynamic performance of robotic systems. The real-time properties of the method also enable future investigations into topics such as MEMS-based diagnostics and predictive maintenance
An Experimental Investigation of the Dynamic Performances of a High Speed 4-DOF 5R Parallel Robot Using Inverse Dynamics Control
Get PDFHigh-speed pick-and-place industrial applications often use parallel kinematic robots due to their high stiffness and dynamic performance; furthermore, the latter not only depends on the mechanical characteristics of the robots but also on the control algorithm. The literature shows several theoretical contributions to such controllers, mainly tested at the simulation level or on simple proof-of-concept laboratory equipment that execute low-speed and simple trajectories. This paper presents an experimental investigation of the dynamic performance of an industrial high-speed 4-DOF 5R parallel robot designed for pick-and-place applications on moving objects. The inverse dynamics control in the task space is used as a control algorithm. The results show the contribution of all the components of the control algorithm to the motor torque, and the inverse dynamics controller performances are discussed also in comparison to those achievable with simpler PD or PID controllers in a joint space. Moreover, the paper shows the controller synthesis from a modern mechatronic point of view, and the effectiveness of the proposed solution for the tracking of complex high-speed trajectories in an industrial application
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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