1,080 research outputs found

    A case study in applying discrete control synthesis to excavator operation

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    International audienceRobotic and control systems are ever more complex to design, program, as well as to operate. Existing theoretical work and tool support in discrete control synthesis can be applied to improve task-level robot programming. This requires to determine patterns of tasks and objectives, which are at once domain-specific to robotics, and generic enough to cover a broad class of control systems. We illustrate such a framework by a case study concerning the interactive discrete control of tasks in an excavating syste

    Fuzzy Controlled Hydraulic Excavator with Model Parameter Uncertainty

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    The hydraulic actuated excavator, being a non-linear mobile machine, encounters many uncertainties. There are uncertainties in the hydraulic system in addition to the uncertain nature of the load. The simulation results obtained in this study show that there is a need for intelligent control of such machines and in particular interval type-2 fuzzy controller is most suitable for minimizing the position error of a typical excavator’s bucket under load variations. We consider the model parameter uncertainties such as hydraulic fluid leakage and friction. These are uncertainties which also depend up on the temperature and alter bulk modulus and viscosity of the hydraulic fluid. Such uncertainties together with the load variations cause chattering of the bucket position. The interval type-2 fuzzy controller effectively eliminates the chattering and manages to control the end-effecter (bucket) position with positional error in the order of few millimeters

    Risk Evaluation: Brief Review and Innovation Model Based on Fuzzy Logic and MCDM

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    The risk assessment of engineering systems represents an important part of the quality of service and dependability. The existing methods for risk evaluation use crisp sets for rating partial indicators' proposition and their cumulative products as an overall indicator. In this paper, existing FMEA and FMECA methods have been improved using the fuzzy expert system for calculating the risk priority number. The application of fuzzy logic allows the use of linguistic descriptions for risk analysis. In this way, the state of the system in terms of risks and consequences is better described. The settings of the fuzzy systems are based on the application of two multi-criteria decision-making methods. The AHP method was used to define the mutual relationship of the impact of partial indicators (occurrence, severity, and detectability) on risk. In this way, subjectivity in risk assessment is reduced. In the composition of the fuzzy model, the TOPSIS method is introduced to reduce the dissipation of results, which contributes to the accuracy of the outcome. This contributes to the accuracy of the results. The results were verified through a case study of a complex engineering system-bucket-wheel excavators. The risk was observed from the aspect of the danger of damage and the danger of downtime. The initial information for weak points of ES is defined according to historical damage events and statistics of downtime. Expert knowledge was used for weak points grading in the model. Additional model verification was performed using similar methods, using the same input data. The innovative model, presented in the paper, shows that it is possible to correct different weights of risk indicators. The obtained results show less dispersion compared with other existing methods. Weak points with increased risk have been located, and an algorithm has been proposed for risk-based maintenance application and implementation

    A review of friction models in interacting joints for durability design.

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    This paper presents a comprehensive review of friction modelling to provide an understanding of design for durability within interacting systems. Friction is a complex phenomenon and occurs at the interface of two components in relative motion. Over the last several decades, the effects of friction and its modelling techniques have been of significant interests in terms of industrial applications. There is however a need to develop a unified mathematical model for friction to inform design for durability within the context of varying operational conditions. Classical dynamic mechanisms model for the design of control systems has not incorporated friction phenomena due to non-linearity behaviour. Therefore, the tribological performance concurrently with the joint dynamics of a manipulator joint applied in hazardous environments needs to be fully analysed. Previously the dynamics and impact models used in mechanical joints with clearance have also been examined. The inclusion of reliability and durability during the design phase is very important for manipulators which are deployed in harsh environmental and operational conditions. The revolute joint is susceptible to failures such as in heavy manipulators these revolute joints can be represented by lubricated conformal sliding surfaces. The presence of pollutants such as debris and corrosive constituents has the potential to alter the contacting surfaces, would in turn affect the performance of revolute joints, and puts both reliability and durability of the systems at greater risks of failure. Key literature is identified and a review on the latest developments of the science of friction modelling is presented here. This review is based on a large volume of knowledge. Gaps in the relevant field have been identified to capitalise on for future developments. Therefore, this review will bring significant benefits to researchers, academics and industrial professionals

    Electrified Powertrains for a Sustainable Mobility: Topologies, Design and Integrated Energy Management Strategies

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    This Special Issue was intended to contribute to the sustainable mobility agenda through enhanced scientific and multi-disciplinary knowledge to investigate concerns and real possibilities in the achievement of a greener mobility and to support the debate between industry and academic researchers, providing an interesting overview on new needs and investigation topics required for future developments

    Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 192

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    This bibliography lists 247 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1979

    Diagnosis of dynamic behavior of structures using the distribution of kinetic and potential energy

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    U većini objekata vibracije su nepoželjne. To je zato što vibracije stvaraju dinamičke sile i udarce koji mogu izazvati zamor i otkaz strukture. Odgovor strukture na njenu pobudu zavisi od načina primene i lokacije pobudne sile, kao i dinamičke karakteristike strukture kao što su prirodne frekvencije i nivo prigušenja. Strukturalni odgovor se može poboljšati promenom raspodele masa ili krutosti strukture, pomeranjem izvora pobude na drugu lokaciju , ili povećanjem prigušenja u strukturi. Strukturalna dinamička modifikacija (SDM) je veoma efikasna i pouzdna tehnika koja se intenzivno koristi za poboljšanje dinamičkih karakteristika strukture kao što su prirodne frekvencije, glavnih oblika i funkcija frekventnih odziva ( FRFs ) . Dinamičko ponašanje konstrukcije može se poboljšati čineći modifikacije delova kao što su kruta mesta, masa, prigušenja itd. Mnogo puta se desi da struktura ne ispunjava potrebne ograničenja dizajna i da dizajn mora da bude modifikovan nekoliko puta pre nego što ona ispuni sve uslove projektovanja. Suština poboljšanja dinamičko ponašanje objekta jeste povećanje prirodnih frekvencija i povećanje intervala između susednih prirodnih frekvencija. Ovaj zahtev se može postići promenom dizajna parametara strukture. Procedura koje se koriste u ovom radu jesu analize distribucije potencijalne i kinetičke energije i razlike između njih u elementima strukture. Studija distribucije potencijalne i kinetičke energije na glavnim oblicima oscilacija strukture daje očigledno predviđanje koje elemente i kako treba izmeniti da se postigne najbolje dinamičko ponašanje. Cilj predloženog razvijenog metoda reanalise i dijagnostike ponašanja struktura je da se utvrdi stvarno ponašanje konstrukcije u eksploataciji. Tehnika reanalise strukture se izvodi primenom metode konačnih elemenata (MKE ) . Informacije o strukturi kao materijal, geometrija i granični uslovi treba da budu spremni pre nego što generiše model...In most structures vibration is undesirable. This is because vibration creates dynamic stresses and strains which can cause fatigue and failure of the structure. The response of the structure to excitation depends upon the method of application and the location of the exciting force or motion, and the dynamic characteristics of the structure such as its natural frequencies and inherent damping level. The structural response can be improved by changing the mass or stiffness of the structure, by moving the source of excitation to another location, or by increasing the damping in the structure. Structural Dynamics Modification (SDM) is a very effective and reliable technique which is extensively used to improve structure's dynamic characteristics such as natural frequency, mode shape and frequency response functions (FRFs). The dynamic behavior of the structure can be improved by predicting the modified behavior making some modifications parts like rigid links, beams, lumped masses, dampers etc. Many times it happens that the structure does not meet the required design constraints and the design has to be modified numerous times before it meets all the design constraints. This repeated analysis for each such modification becomes very expensive and time consuming, especially if there are lots of degrees of freedoms. The main point of improving dynamic behavior of a structure is increasing its natural frequencies and maximizing the interval between adjacent natural frequencies. This request can be achieved by changing the design parameters of the structure. The procedures used in this thesis are concerned with the analysis of the distribution of potential and kinetic energy and the differences between them in elements of the structure. Study of distribution of potential and kinetic energy in main oscillation modes of structure gives obvious prediction which elements need some modifications to achieve the best dynamic characteristics. The aim of developed the proposed method of reanalysis and diagnostic of structure behavior is to determine real behavior of the construction in exploitation..

    Towards Smart Earthwork Sites Using Location-based Guidance and Multi-agent Systems

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    The growing complexity and scope of construction projects is making the coordination and safety of earthwork of a great concern for project and site managers. The difficulty of safeguarding the construction workers is mainly commensurate with the type, scale, and location of the project. In construction operations, where heavy machines are used, various safety and risk issues put the timely completion of a project at stake. Additionally, the construction working environment is heavily susceptible to unforeseen changes and circumstances that could impact the project, both cost and schedule wise. As a response to the looming safety threats or unforeseen changes of working conditions, re-planning is almost always required, in both proactive (preemptive) or reactive (corrective) fashion. In order for re-planning to yield the optimum results, real-time information gathering and processing is a must. Global Positioning System (GPS) and other Real-time Location Systems (RTLSs) have been used for the purpose of real-time data gathering and decision-making in recent years. Similarly, Location-based Guidance Systems (LGSs), e.g., Automated Machine Control/Guidance (AMC/G), have been recently introduced and employed, mainly for the purpose of high-precision earthwork operations. However, currently the application of available LGSs (i.e., AMC/G) is restricted to the machine-level task control and improvement. Also, the high cost of procuring available LGSs, which cost approximately $80,000 for every new piece of equipment, limits the availability of LGSs for small and medium size contractors. Furthermore, the valuable real-time data gathered from various pieces of equipment on site are not effectively utilized to continuously update the simulation models developed at the design phase so that a more realistic view of project progress is available in the execution phase. Finally, despite the growing availability of LGSs, their application for safety is limited to real-time proximity-based object detection and warnings. In view of the ability to control the finest motion of LGS-enabled earthwork equipment, there is a great potential to boost their level of application to the project level, where decisions about the equipment control are made based on the global consideration of a fleet rather that a local view of one single equipment. To the best of the author’s knowledge, a generic methodology that combines real-time data-gathering technologies, LGS and intelligent decision making tools, particularly Multi-agent Systems (MASs), and addresses the safety-sensitive re-planning, is missing. On this premise, this research pursues a methodology which addresses the issue of coordination and safety improvement through the integration of LGSs and MASs. In a nutshell, this research is dedicated to the pursuit of the following objectives: (1) to enable the project-level coordination, monitoring and control through the integration of a MAS architecture and a LGS to help better resolve operational and managerial conflicts; (2) to provide a method for improving the performance of pose estimation based on affordable RTLSs so that LGSs can be applied to a wider scope of older earthwork equipment; (3) to devise a generic framework for Near Real-Time Simulation (NRTS) based on data from LGSs; and (4) to develop a mechanism for improving the safety of earthwork operations using the capabilities of the LGS, NRTS, and MAS. In the proposed framework, every staff member of the project is represented by an exclusive agent in the MASs. More affordable positioning technologies, such as Ultra-Wideband (UWB), are utilized to provide accurate real-time data about the location of machines and workers. An optimization-based method is proposed to consider a set of geometric and operational constraints that govern the behavior of the Data Collectors (DCs) attached to the equipment to improve the equipment pose estimation accuracy. NRTS is used to keep track of the progress of the project and fine-tune the schedule based on the data captured from the site. The agents observe the progress of work executed by their associated equipment, and if any anomalies are detected, viable corrective measures are devised and executed. The inputs to this system are: (a) a stream of real-time data, e.g., location data, flowing from the site, (b) the project design data, and (c) the project progress data and the schedule. Furthermore, a two-layer safety mechanism monitors the safe operation of different pieces of equipment. The first layer of this mechanism enables the equipment to plan a collision-free path considering the predicted movement of all other pieces of equipment. The second layer is acting as a last line of defense in view of possible discrepancies between the predicted paths and actual paths undertaken by the operators. Several prototypes and case studies are developed to demonstrate and verify the feasibility of the proposed framework. It is found that the proposed optimization-based method has a very strong potential to improve the pose estimation using redundancy of more affordable RTLS DCs. Also, the proposed overarching NRTS approach provides a tracking-technology-independent method for processing, analyzing, filtering and visualizing the equipment states that can work with various types of RTLS technologies and under the availability of different levels of sensory data. The proposed safety system is found to provide a balance between economic use of space and the ability to warn against potential collisions in an effective manner using the pose, state, geometry, and speed characteristics of the equipment. Additionally, the safety system demonstrates the ability to provide a reliable basis for the generation of the risk maps of earthwork equipment, using the expected pose and state, and considering the proximity-based and visibility-based risks. The MAS-based framework helps expand the effective domain of LGSs from machine-level guidance to fleet-level coordination. In the view of the presented case studies, the MAS structure is found to be effective in assigning different operations and tasks of a project to the specific agents that will be responsible for their realization. Using a combination of strategic and tactical planning methods, the MAS is able to effectively provide readily executable guidance/control for equipment operators considering a variety of safety issues
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