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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Multi-axis industrial robot braking distance measurements : For risk assessments with virtual safety zones on industrial robots

Lindqvist, Björn January 2017 (has links)
Industrial robots are increasingly used within the manufacturing industry, especially in collaborative applications, where robots and operators are intended to work together in certain tasks. This collaboration needs to be safe, to ensure that an operator does not get injured in any way. One of several solutions to this is to use virtual safety zones, which limits the robots working range and area to operate within, and may be more flexible than physical fences. When the robot exceeds the allowed limit of the virtual safety zone, a control system that monitors the robot position, forces to robot to stop. Depending on the current speed and payload of the robot, the initialized stop has a braking distance until the robot has completely stopped. How far the separation distance between human and robot must be, is calculated using ISO-standard guidelines when doing risk assessments. To support affected personnel in their work, an investigation and experimentation of braking distances among several robots has been conducted. These testing experiments have been designed to simulate a collaborative operation which is an excessive risk in a robot cell. The tests have been performed with various speeds and payloads, for comparison between the robot models and for validation against already existing data. The difference with this study compared to existing ones is that several robot axis’ are used simultaneously in the testing movements, which is a benefit since a robot rarely operates with only one axis at a time.  Main results of the performed tests are that the robot doesn’t obtain speeds over 2000 mm/s when axis 1 is not involved, before the virtual safety zone is reached. Axis 1 can generate the highest speeds overall, and is therefore a significant factor of the braking distance. The results and conclusions from this thesis states that these kinds of tests give useful information to the industry when it comes to safety separation distance and risk assessments. When applying the information in a correct way, the benefits are that a shorter safety separation distance can be used without compromising on safety. This leads to great advantages in robot cell design, because space is limited on the factory floor.
2

A Proactive Approach to Train Control

Thurston, David Frank January 2012 (has links)
The main objective in optimizing train control is to eliminate the waste associated with classical design where train separation is determined through the use of "worst case" assumptions to calculate Safe Braking Distances that are invariant to the system. In fact, the worst case approach has been in place since the beginning of train control systems. Worst case takes the most conservative approach to the determination of train stopping distance, which is the basis for design and capacity of all train control systems. This leads to stopping distances that could be far more than actually required under the circumstances at the time the train is attempting to brake. A new train control system is proposed that utilizes information about the train and the conditions ahead to optimize and minimize the Safe Braking Distance. Two methods are proposed to reduce safe braking distance while maintaining an appropriate level of safety for the system. The first introduces a statistical method that quantifies a braking distance with various hazards levels and picks a level that meets the safety criteria of the system. The second method uses train mounted sensors to determine the adhesion level of the wheel and rail to determine the appropriate braking rate for the train under known circumstances. Combining these methods provides significant decreases in Safe Braking Distances for trains. A new train control system is utilized to take advantage of these features to increase overall system capacity. / Electrical and Computer Engineering
3

Vliv hloubky dezénové drážky na dosažitelné zpomalení vozidla / Influence of tread grooves depth on achievable vehicle deceleration

Kejíková, Barbora January 2016 (has links)
This thesis is devoted on passenger car tyres. Theoretical part covers description of production, construction and tyre parameters. Practical part is comprised experimental measurement of influence of tread grooves depth on achievable vehicle deceleration. First, it is focused on preparation conditions of measurement, with subsequent processing and evaluation of the data obtained.
4

Dynamic Braking Control for Accurate Train Braking Distance Estimation under Different Operating Conditions

Ahmad, Husain Abdulrahman 28 March 2013 (has links)
The application of Model Reference Adaptive Control (MRAC) for train dynamic braking is investigated in order to control dynamic braking forces while remaining within the allowable adhesion and coupler forces.  This control method can accurately determine the train braking distance.  One of the critical factors in Positive Train Control (PTC) is accurately estimating train braking distance under different operating conditions.  Accurate estimation of the braking distance will allow trains to be spaced closer together, with reasonable confidence that they will stop without causing a collision.  This study develops a dynamic model of a train consist based on a multibody formulation of railcars, trucks (bogies), and suspensions.   The study includes the derivation of the mathematical model and the results of a numerical study in Matlab.  A three-railcar model is used for performing a parametric study to evaluate how various elements will affect the train stopping distance from an initial speed.  Parameters that can be varied in the model include initial train speed, railcar weight, wheel-rail interface condition, and dynamic braking force.  Other parameters included in the model are aerodynamic drag forces and air brake forces. An MRAC system is developed to control the amount of current through traction motors under various wheel/rail adhesion conditions while braking.  Minimizing the braking distance of a train requires the dynamic braking forces to be maximized within the available wheel/rail adhesion.  Excessively large dynamic braking can cause wheel lockup that can damage the wheels and rail.  Excessive braking forces can also cause large buff loads at the couplers.  For DC traction motors, an MRAC system is used to control the current supplied to the traction motors.  This motor current is directly proportional to the dynamic braking force.  In addition, the MRAC system is also used to control the train speed by controlling the synchronous speed of the AC traction motors.  The goal of both control systems for DC and AC traction motors is to apply maximum available dynamic braking while avoiding wheel lockup and high coupler forces.  The results of the study indicate that the MRAC system significantly improves braking distance while maintaining better wheel/rail adhesion and coupler dynamics during braking.  Furthermore, according to this study, the braking distance can be accurately estimated when MRAC is used.  The robustness of the MRAC system with respect to different parameters is investigated, and the results show an acceptable robust response behavior. / Ph. D.
5

Konceptstudie för att korta bromssträckan hos personbilar i nödsituationer / Concept study on reducing the braking distance of passenger cars in emergency situations

Ekermann, Sara January 2012 (has links)
Utifrån en problemställning formulerad av Trafikverkets skyltfond har produktutvecklingsföretaget Prodelox drivit ett projekt med syfte att testa kreativa idéer för att minska bromssträckan för personbilar i nödsituationer. Som en del i projektet har ett examensarbete genomförts vilket resulterat i denna rapport. Examensarbetet ämnar sammanställa en mängd idéer på alternativa metoder att bromsa bilar, för att sedan välja ut tre av dessa för praktiska tester. Idén med att korta bromssträckan grundar sig i trafiksäkerhetsarbetet i kombination med introduktionen av nya tekniska system som kan förutspå kollisioner. Om en kollision kan förutses är det av största intresse att kunna bromsa in bilen så mycket som möjligt innan detta sker för att minska skadorna och rädda liv. Ur ett förutsättningslöst perspektiv har kreativa idéer tagits fram. Rapporten tar dessutom upp och sammanfattar friktionsteorier och fordonsdynamiska aspekter att ta hänsyn till vid utvecklingsarbetet. Projektet följer en produktutvecklingsmetodik presenterad av Ulrich och Eppinger (2008) och omfattningen är utvecklingsfasens tidiga steg. Genom två iterationer utvecklas koncept genom framtagande av kravspecifikation, konceptgenerering, och konceptval. Idéer testas löpande genom fysiska såväl som virtuella prototyper under hela processen. Den första utvecklingsiterationen resulterar i 17 konceptidéer innefattande olika typer av bromsmetoder. Koncepten delas in i kategorierna ökad friktion, ökad normalkraft, spjärn mot asfalten, aerodynamik och magnetism. Tre koncept väljs ut och utvecklas vidare: Koncept Ankare, Gummiplatta och Avverkan. Utvecklingen av koncept Ankare resulterar i ett koncept där en infästning i asfalten sker i farten under bilen med hjälp av krutdrivna spikpistoler. Fästet förbinds med bilen med ett textilband kallat Tear Webbing. Det är två sydda remmar som producerar en konstant kraft då remmarna slits isär och sömmarna rivs upp. Bandet testas praktiskt och ger en bromseffekt på uppemot 1,5 g-krafter, medan de krutdrivna spikpistolerna inte kan testas i farten inom ramen för detta projekt. Koncept Gummiplatta bygger på att en stor gummiyta placerad under bilen trycks ner i marken och lyfter framvagnen på bilen. Olika gummibelägg testas med förhoppningen att hitta ett gummibelägg med goda friktionsegenskaper. Ökad area och optimerade materialegenskaper kan i teorin leda till bättre friktion. Konceptet testas på både vått och torrt väglag genom en konstruktion under testbilens framvagn. Fyra olika gummiprover jämförs med bilens vanliga bromsar. Endast ett gummi, naturgummi, presterar bättre än referensen i tester från 50 km/h, medan resten resulterar i längre bromssträcka. Vid tester från 100 km/h presterar samtliga gummiprover sämre än referensbromsningarna. Koncept Avverkan baseras på idén att en större kraft än friktionskraften kan fås ut om ett hårt material trycks ner i asfaltens yta och river upp densamma. Deformationerna av asfalten åstadkommer den bromsande kraften. I test av konceptet höll inte konstruktionen, men retardationen som utvecklades innan konstruktionen gav vika kom upp i 1,2 g-krafter, något som visar på att konceptet har kapacitet att korta bromssträckan. Som fortsättning på detta projekt föreslås flera vägar att gå. Koncepten Ankare och Avverkan visar på stor potential att korta bromssträckan och nya projekt med syfte att fortsatt utveckla och testa dessa koncept föreslås. Även andra projekt som ligger utanför syftet av denna rapport, så som en idé för att minska dubbdäcksanvändningen, föreslås för utredning i framtida studier. / At the request of the Swedish Transport Administration the product development company Prodelox has initiated a project aiming to test creative ideas on reducing the braking distance for passenger cars in emergency situations. As a part of this project a master thesis has been conducted resulting in this report. The thesis aims to compile ideas on alternative methods for braking cars, and thereafter choosing three of them for practical testing. In combination with introduction of new technical innovations that predict collisions, an alternative braking system that could brake more than standard brakes are of great interest. By reducing the braking distance deaths and serious injuries in traffic can be reduced. From this perspective ideas have been impartially generated. The report includes friction theory and vehicle dynamics to consider in the development. The project is following a product development process presented by Ulrich and Eppinger (2008) and focuses on the early stages of the process. In two iterations concepts are developed through the phases target specification, concept generation and concept selection. Ideas are concurrently tested through physical as well as virtual prototypes. The first development iteration resulted in 17 concepts including different kinds of braking methods. The concepts are divided into five categories; increased friction, increased normal load, grabbing of the asphalt, aerodynamics, and magnetism. Three concepts are chosen for further development; concept Anchor, Rubber plate, and Rip up. The development of concept Anchor results in a concept for which an attachment is made in the asphalt on the fly by use of cartridge actuated fastening machine. The attachment is connected to the car by a textile webbing, called Tear Webbing. It consists of two sewn straps that produce a constant force when torn apart. In practical tests, the concept generate a breaking effect of 1.5 g-forces, while the cartridge actuated fastening cannot be tested on the fly within this project. The development of concept Anchor results in a concept for which an attachment is made in the asphalt on the fly by use of cartridge actuated fastening machine. The attachment is connected to the car by a textile webbing, called Tear Webbing. It consists of two sewn straps that produce a constant force when torn apart. In practical tests, the concept generate a breaking effect of 1.5 g-forces, while the cartridge actuated fastening cannot be tested on the fly within this project. Concept Rip up is based on idea that a bigger force than the frictional force can be achieved by pressing a hard material into the surface of the asphalt road and tearing up the same. The deformations of the asphalt generate the braking force. While testing the concept the structure holding the horns broke, but the force achieved before time of collapse was corresponding to a deceleration of 1.2 g-forces. This shows that the concept has potential to reduce the braking distance. To conclude this project several new projects are suggested. The concepts Anchor and Rip up show great potential to reduce the braking distance and new projects aiming to further develop and test these concepts are recommended. Also other further studies outside the frame of this report are suggested, for example an idea on how to reduce the usage of studded tires.
6

Stabdomų lengvųjų automobilių judėjimo parametrų tyrimas / Research of movement parameters of motorcars in braking

Nagurnas, Saulius 23 June 2005 (has links)
Research of movement parameters of motorcars in braking.
7

Stabdomų lengvųjų automobilių judėjimo parametrų tyrimas / Research of movement parameters of motorcars in braking

Nagurnas, Saulius 27 June 2005 (has links)
Research of movement parameters of motorcars in braking.
8

Analýza brzdění vozidla s nestandardním zásahem do brzdové soustavy / Analysis of Non-Standard Braking Intervention into the Brake System

Kortán, Daniel January 2017 (has links)
This master’s thesis focused on the issue of the possible conversion of liquid brake systems, in the form of replacement of wheel brakes. The first part focused on the function and description of the construction of different types of brakes. The second part is focused on description the types of brake system testing and the regulations regarding brake systems. The last part focused on the measurement of both vehicles and comparison of the results with the calculations.

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