Akos Nagy

Path planning and control of differential and car-like robots in narrow environments

This paper presents a comprehensive solution for path planning and control of two popular types of autonomous wheeled vehicles. Differentially driven and car-like motion systems are the most widespread structures among wheeled mobile robots. The planning algorithm employs a rapidly exploring random tree based global planner (RTR), which generates paths made of straight motion and in place turning primitives. Such paths can be directly followed by a differential drive robot. Carlike robots have a minimum turning radius constraint, hence we present a local steering method (C*CS) which obtains a path consisting circular and straight movements based on the primary RTR-path, without losing the existence of the solution. Additionally, a velocity profile generation algorithm is presented, which is responsible for the distribution of the time parameter along the geometric path, taking the physical limitations of the robot into account. Finally, control algorithms for path following are given for both robot types. Simulations and real experiments show the effectiveness of these methods, even is constrained environments containing narrow corridors and passages.

S-duality in Abelian gauge theory revisited

Abstract Definition of the partition function of U ( 1 ) gauge theory is extended to a class of four-manifolds containing all compact spaces and certain asymptotically locally flat (ALF) ones including the multi-Taub–NUT spaces. The partition function is calculated via zeta-function regularization and heat kernel techniques with special attention to its modular properties. In the compact case, compared with the purely topological result of Witten, we find a non-trivial curvature correction to the modular weights of the partition function. But the S -duality can be restored by adding gravitational counter terms to the Lagrangian in the usual way. In the ALF case however we encounter non-trivial difficulties stemming from original non-compact ALF phenomena. Fortunately our careful definition of the partition function makes it possible to circumnavigate them and conclude that the partition function has the same modular properties as in the compact case.

LP-based velocity profile generation for robotic manipulators

ABSTRACT In this paper we examine the minimum-time velocity profile generation problem which belongs to the second stage of the decoupled robot motion planning. The time-optimal profile generation problem can be translated to a convex optimal control task through a nonlinear change of variables. When the constraints of the problem have special structure, the time-optimal solution can be obtained by linear programming (LP). In this special case, the velocity of the robot along the path is maximised, instead of time minimising. The benefit of the LP solution is the lower computational time. Validation of the LP algorithm is also presented based on simulation results.

Analyzing .NET serialization components

In this paper we present a number of available serialization libraries for the .NET platform, both integrated and 3rd party solutions and we analyze and compare their performance. Through this analysis and comparison we aim to deduct how the process of serialization can be further optimized and which parts of the process act as a bottleneck. The comparison also gives insight into how the data exchange format itself affects the whole process.

Programming language neutral design pattern detection

Object-oriented design patterns offer a structural and behavioral solution for a given problem in a given context using basic building blocks. They are widely used in software engineering as they promote extensibility, testability, maintainability and reusability. However, besides their use, their detection also has a great significance in the industry. This paper first presents a general, programming language neutral model and architecture for automated design pattern detection in object-oriented source code. To validate the recognition-capability of the framework, we implemented a version to recognize design patterns in C#. To our knowledge, this is the first work in the field that examines source code written in C#. We also discuss actual results of running this implementation on a number of class libraries. These results can later be used as reference for other works focusing on the C# programming language.

A Planning Method to Obtain Good Quality Paths for Autonomous Cars

Path planning among obstacles for nonholonomic systems is a widely researched area nowadays, but it is still one of the most challenging problems in autonomous navigation. We have recently presented a rapidly exploring random tree based global planner (RTR) and a steering method (C*CS) for car-like vehicles, which uses circular and straight movements. With the aid of these two methods it is possible to obtain a feasible path, even in narrow spaces and in situations requiring non-trivial maneuvers. This paper presents an improved solution for environments, where not all obstacles are known at the beginning and these are discovered during the motion of the robot. We also introduce an extension to the presented algorithm to achieve paths of better quality, i.e. more similar to a reasonable path generated by a human driver.

Minimum-time path tracking for robots with non-convex constraints

The paper examines the time-optimal path tracking problem which belongs to robot motion planning. The goal is to generate a velocity profile for robotic manipulators taking into account kinematic and dynamic constraints. In some cases, profile generation can be translated to a convex optimisation problem through a non-linear change of variables. However, some constraints cannot be taken into account due they non-convex properties. The paper presents a method to solve the time-optimal problem with these non-convex constraints. The method is based on the branch and bound algorithm, and it provides a global solution in contrast to the existing local approaches. Experimental results with a 3-DoF robotic arm are also presented.

Evaluating performance of cloud computing environments

The emerging technology of cloud computing offers off-premise, reliable solutions for common IT related needs of enterprises, but as different providers often envision these solutions in a different way, architects face a complex problem when trying to decide which provider to choose and compare or estimate the costs of different options. This paper presents a generalized, provider-neutral service and cost model to describe the capabilities of different environments and the prices associated with them. This model can serve as the basis for mathematical optimization algorithms.