Advancing Control for Shield Tunneling Machine by Backstepping Design with LuGre Friction Model

Shield tunneling machine is widely applied for underground tunnel construction. The shield machine is a complex machine with large momentum and ultralow advancing speed. The working condition underground is rather complicated and unpredictable, and brings big trouble in controlling the advancing speed. This paper focused on the advancing motion control on desired tunnel axis. A three-state dynamic model was established with considering unknown front face earth pressure force and unknown friction force. LuGre friction model was introduced to describe the friction force. Backstepping design was then proposed to make tracking error converge to zero. To have a comparison study, controller without LuGre model was designed. Tracking simulations of speed regulations and simulations when front face earth pressure changed were carried out to show the transient performances of the proposed controller. The results indicated that the controller had good tracking performance even under changing geological conditions. Experiments of speed regulations were carried out to have validations of the controllers

Design, simulation and experimental investigation of a novel reconfigurable assembly fixture for press brakes

A reconfigurable assembly fixture is a major and important component of a reconfigurable assembly system. It isrequired for the assembly of a variety of press brake models inorder to reduce the assembly time and overall production time.The stages and requirements for the design of an assembly fixtureand understanding of the assembly process for press brakemodels were used to design a reconfigurable assembly fixture.A detailed design analysis of parts of the fixture and the hydraulicsystem is considered and presented in this article. The stress anddisplacement analysis of the parts is executed using Solidworksexpress simulation. The parameters of the hydraulic componentswere determined from force requirements, and the hydraulic system was modelled physically using Matlab Simscape hydraulics.The response of the hydraulic system was obtained for eachactuator in the system in order to depict the output of the actuators from the spool displacement of the valves. Stress analysisconducted on parts of the fixture showed that it can withstandmaximum stresses that are lesser than the yield strength of thematerial used for the part. It was also established that synchronization of hydraulic actuators can best be achieved by the use of asine input to the electrohydraulic valve. An experimental investigation was done using FESTO hydraulic test bench in order toobserve the synchronized extension and retraction of the hydraulic actuators. The simulation of the hydraulic system, electricsystem and the programmable logic controller was prepared using automation studio. The design is envisaged to provide the industries with relevant information on accurate location and gripping of press brake frames rather than turning and repositioning of the frame in order to fit other parts during assembly. The article provides relevant information on the design analysis of a reconfigurable assembly fixture for press brakes which is novel because articles on reconfigurable assembly fixtures have not considered its application to press brake assembly

NASA Thesaurus. Volume 2: Access vocabulary

The NASA Thesaurus -- Volume 2, Access Vocabulary -- contains an alphabetical listing of all Thesaurus terms (postable and nonpostable) and permutations of all multiword and pseudo-multiword terms. Also included are Other Words (non-Thesaurus terms) consisting of abbreviations, chemical symbols, etc. The permutations and Other Words provide 'access' to the appropriate postable entries in the Thesaurus

NASA thesaurus. Volume 2: Access vocabulary

The Access Vocabulary, which is essentially a permuted index, provides access to any word or number in authorized postable and nonpostable terms. Additional entries include postable and nonpostable terms, other word entries, and pseudo-multiword terms that are permutations of words that contain words within words. The Access Vocabulary contains 40,738 entries that give increased access to the hierarchies in Volume 1 - Hierarchical Listing

Proceedings: New Technology For Coal Mine Roof Support

Roof falls continue to be the greatest single safety hazard faced by underground coal miners. During 1996-99, 44 coal miners lost their lives in rock falls, and nearly 2,400 were injured. In addition, nearly 6,000 noninjury roof collapses were reported. Roof supports are installed to protect the miners, but support system failures contributed to most of these incidents. Reducing the terrible toll taken by ground falls continues to be a major goal of research by the National Institute for Occupational Safety and Health (NIOSH). The purpose of these proceedings is to provide the mining community with a comprehensive survey of coal mine roof supports. Drawing on many years of research undertaken by the NIOSH Pittsburgh and Spokane Research Laboratories, this volume describes what types of support are available, how they work, and when they should be used. The major subjects covered include roof bolts, standing roof supports, cable supports, and longwall shields. Some special topics are also addressed, including an analysis of roof fall accident statistics, techniques for better skin control, material handling considerations, and longwall mining through recovery rooms. This proceedings volume also contains information on several important new technologies, which are described here for the first time: \ue2\u20ac\ua2Guidelines for selecting roof bolt length, pattern, and capacity that were derived from statistical analysis of the roof fall experience at 37 underground mines; \ue2\u20ac\ua2A new design method for longwall tailgate supports; and \ue2\u20ac\ua2A technique for measuring loads developed within cable bolts. The papers in these proceedings were presented at open industry briefings conducted by NIOSH on New Technology for Coal Mine Roof Support. The briefings were held in Norton, VA, Charleston, WV, Evansville, IN, Tuscaloosa, AL, Price, UT, Glenwood Springs, CO, and Washington, PA. The papers were also presented at the Mine Safety and Health Administration (MSHA) Preventative Roof-Rib Outreach Program (PROP) Seminar, which was held at the National Mine Health and Safety Academy near Beckley, WV

New technology for coal mine roof support

"Roof falls continue to be the greatest single safety hazard faced by underground coal miners. During 1996-99, 44 coal miners lost their lives in rock falls, and nearly 2,400 were injured. In addition, nearly 6,000 noninjury roof collapses were reported. Roof supports are installed to protect the miners, but support system failures contributed to most of these incidents. Reducing the terrible toll taken by ground falls continues to be a major goal of research by the National Institute for Occupational Safety and Health (NIOSH). The purpose of these proceedings is to provide the mining community with a comprehensive survey of coal mine roof supports. Drawing on many years of research undertaken by the NIOSH Pittsburgh and Spokane Research Laboratories, this volume describes what types of support are available, how they work, and when they should be used. The major subjects covered include roof bolts, standing roof supports, cable supports, and longwall shields. Some special topics are also addressed, including an analysis of roof fall accident statistics, techniques for better skin control, materials handling considerations, and longwall mining through recovery rooms. This proceedings volume also contains information on several important new technologies, which are described here for the first time: - Guidelines for selecting roof bolt length, pattern, and capacity that were derived from statistical analysis of the roof fall experience at 37 underground mines; - A new design method for longwall tailgate supports; and - A technique for measuring loads developed within cable bolts. http://www.cdc.gov/niosh/mining/pubs/pdfs/2000-151-errata.pdf " - NIOSHTIC-2edited by Christopher Mark, Dennis R. Dolinar, Robert J. Tuchman, Thomas M. Barczak, Stephen P. Signer and Priscilla F. Wopat.NIOSHTIC no 20000874Includes bibliographical references

NASA thesaurus. Volume 2: Access vocabulary

The access vocabulary, which is essentially a permuted index, provides access to any word or number in authorized postable and nonpostable terms. Additional entries include postable and nonpostable terms, other word entries and pseudo-multiword terms that are permutations of words that contain words within words. The access vocabulary contains almost 42,000 entries that give increased access to the hierarchies in Volume 1 - Hierarchical Listing

NASA Thesaurus. Volume 1: Hierarchical listing

There are 16,713 postable terms and 3,716 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary

NASA thesaurus. Volume 1: Hierarchical Listing

There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions

Вдосконалення процесу синхронізації руху гідравлічних двигунів

Синхронізація роботи декількох робочих органів для забезпечення точного переміщення одного робочого елемента (застосування багатодвигунних гідравлічних агрегатів) є актуальною проблемою в багатьох галузях промисловості: обладнання для пресування і кування, підйомно-транспортні пристрої, пристрої для створення вібрації, землерийні машини тощо. Ефективність використання сучасного технологічного обладнання, яке представляє собою складні автоматизовані комплекси з великою кількістю виконавчих органів, в значній мірі залежить від можливості прогнозування характеристик силових приводів, які в ньому застосовуються. Виконано аналіз схем синхронізації гідродвигунів, розглянуто фактори, які впливають на узгодження руху вихідних ланок двигунів (штоків гідроциліндрів, роторів гідромоторів). Розглянуті схеми синхронізації гідравлічних двигунів характеризуються сталою похибкою швидкості руху гідравлічних двигунів в усталеному режимі. Встановлено, що при несиметричному навантаженні похибка синхронізації за положенням вихідної ланки гідравлічного двигуна пропорційна величині переміщення (часу руху). За результатами аналізу поставлені задачі по вдосконаленню процесу синхронізації руху гідравлічних двигунів у багатодвигунному гідравлічному агрегаті. Досліджено гідравлічний привід з двома гідравлічними циліндрами, синхронізація швидкості руху штоків яких здійснюється дільником потоку робочої рідини. На основі розробленої математичної моделі проведено розрахунок роботи синхронізованих гідроциліндрів в неусталеному режимі при раптовій зміні навантаження на одному з гідроциліндрів. Визначено швидкості руху штоків гідроциліндрів і тиск в міждросельних камерах дільника потоку. Встановлено, що при перехідних режимах роботи приводу, обумовлених раптовою зміною навантаження гідроциліндрів, виникають коливання тиску в міждросельних камерах дільника потоку і, в результаті цього, похибка синхронізації швидкості руху штоків гідроциліндрів на початковому етапі. Відносний перепад тисків в міждросельних камерах досягає 1, а відносна різниця швидкостей руху – до 0.43. Для підвищення точності синхронізації руху гідравлічних двигунів запропонований дільник потоку, в якому додано додатковий зворотний зв'язок по перепаду тиску в міждросельних камерах дільника. Додатковий зворотний зв'язок реалізований за рахунок застосування двохщілинного дроселюючого розподільника золотникового типу. Виходячи з умов забезпечення мінімальної похибки синхронізації, визначена необхідна залежність зміни площі робочої щілини регульованих дроселів та наведено рекомендації щодо профілізації робочих щілин золотникового дроселя. Встановлено розрахунковим шляхом і підтверджено в експерименті, що застосування регульованих дроселів зменшує похибку синхронізації швидкості руху штоків гідроциліндрів до 0.27, а перепад тисків в міждросельних камерах дільника потоку – до 0.53. В перехідному процесі для швидкості і тиску виникли гармоніки вищого порядку, зумовлені рухом золотника двохщілинного розподільника. Наявність гармоніки вищого порядку в коливаннях тиску і швидкості несуттєво впливає на роботу гідравлічних двигунів, оскільки амплітуда коливань незначна. Підвищення точності синхронізації швидкості зумовлено одночасною зміною площі дроселя, який стабілізує перепад тиску та площі регульованого дроселя.Synchronization of several working bodies operation to ensure the precise movement of one working element (the implementation of multi-engine hydraulic units) is an urgent problem in many industries: pressing and forging equipment, hoist and transport devices, vibration generators, earth-moving machines etc. The efficiency to use the modern technological equipment including complex automated aggregates with a large number of executive bodies greately depends on the ability to predict the properties of the power drivers used in it. The schemes of the hydraulic engines synchronization are analyzed, the factors that influence the motion coordination of the output units in the engines (rods of hydraulic cylinders, rotors of hydraulic engines) are considered. The schemes of hydraulic engines synchronization are characterized by a constant error of the hydraulic engines motion velocity in the steady mode. It is established that at the asymmetrical loading the synchronization error by the position of the output link of the hydraulic engine is proportional to the amount of movement (motion time). According to the results of the analysis, tasks to improve the synchronization process regarding the movement of the hydraulic engines in a multi-engine hydraulic unit are set. The hydraulic drive with two hydraulic cylinders is investigated, the motion velocity of rods is synchronized by the divider of the working fluid flow. Based on the investigated mathematical model, the operation of synchronized hydraulic cylinders in unsteady mode with a sudden change of load on one of the hydraulic cylinders is calculated. The motion velocities of the rods of the hydraulic cylinders and the pressure in the inter-throttle chambers of the flow divider are determined. It is established that during transient operation modes of the drive, caused by a sudden change in the load of the hydraulic cylinders, there are oscillations of pressure in the inter-throttle chambers of the flow divider and, as a result, the synchronization error of the motion velocity of the cylinders rods at the initial stage. The relative pressure drop in the inter-throttle chambers reaches 1, and the relative difference of motion velocities - up to 0.43. In order to improve the accuracy of the hydraulic engines synchronization, a flow divider is proposed, which added extra feedback regarding the pressure drop in the inter-throttle chambers of the divider. Additional feedback is realized through the use of a double-slotted spool-type throttle valve. Based on the conditions of minimum synchronization error, the necessary dependence to change the working gap of the regulated throttles is determined and the recommendations on the profiling of the working gaps of the spool-type throttle are given. It is established through calculation and confirmed in the experiment that the use of adjustable throttles reduces the error regarding the synchronization of movement velocity of the cylinders rods to 0.27, and the pressure drop in the inter-throttle chambers of the flow divider - to 0.53. In the transition process for the velocity and pressure, there are higher-order harmonics, caused by the movement of the spool valve of the double-slot distributor. The presence of higher-order harmonics in pressure and velocity oscillations does not significantly affect the hydraulic motors operation, since the amplitude of oscillations is negligible. The reduction of the velocity synchronization error is due to the simultaneous change of the throttle area, which stabilizes the pressure drop and the adjustable throttle area