Elzbieta Roszkowska

Wroclaw University of Science and Technology | WUT · Electronics Faculty, Department of Cybernetics and Robotics

This paper contributes with a multi-level, hierarchical control system for a fleet of mobile robots sharing a common 2D motion space. The system consists of three levels, with the top level being a supervisor based on a discrete representation of the Multiple Mobile Robot System (MMRS), in which robot motion processes are seen as sequences of stage...

The paper contributes with a hybrid controller for multiple mobile robot systems (MMRS) that ensures the correct accomplishment of its mission by each robot. We capitalize on earlier results concerning the supervision of the robot flow, in particular the concept of partitioning the motion area into cells. Then the system comprises three control lev...

In this paper we consider a system of multiple mobile robots (MMRS) and the process of their concurrent motion in a shared two-dimensional workspace. The goal is to plan the robot movement along given fixed paths so as to minimize the completion time of all the robots while ensuring that they never collide. Thus, the considered problem combines the...

An unknown environment could be mapped more efficiently by a group of robots than a single robot. The time reduction due to parallelization is crucial in complex area mapping. There are two general solutions used in the multi-robot mapping. In the first one, robots exchange raw data from sensors. The second approach assumes that each robot creates...

The paper contributes with a hybrid controller for multiple mobile robot systems (MMRS) that ensures the correct accomplishment of its mission by each robot. We capitalize on earlier results concerning the supervision of the robot flow, in particular the concept of partitioning the motion area into cells. Then the system comprises three control lev...

Title: Application of Bézier curves in the synthesis of supervisor control of a group of mobile robots Under the conditions of flexible use of robotic systems, it is extremely important to automate the synthesis of control models for a given specification of robot tasks. In this paper we consider an event-driven supervisory control model for a gro...

This work continues our study on the control synthesis for multiple mobile robot systems (MMRS). We assume a hybrid approach that comprises the supervisory control level, based on a discrete event model of MMRS, and the robot control level, based on a continuous time model of the robot motion. Our objective is to further develop the control concept...

We consider a Multiple Mobile Robot System (MMRS) viewed as a group of autonomous robots sharing a common 2D motion space. Each robot performs a mission that requires it to travel a number of times along a specific, independently planned closed path. The robots operate asynchronously and are able to control their motion with path-following algorith...

The paper presents a hybrid (discrete-event/continuous-time) control concept for a system of mobile robots sharing a common motion space. The logics underlying its construction formally ensures collision-free and deadlock-free motion of the robots, and the modular structure of the controller allows for its modification and experimental optimization...

Artykuł przedstawia metodę podziału ścieżek robotów mobilnych na maksymalne sektory o stałej relacji konfliktu, będące podstawą syntezy dyskretnego zdarzeniowego modelu koordynacji ruchu robotów we współdzielonej przestrzeni 2D. Opracowany algorytm dotyczy klasy robotów typu samochód Dubinsa, tzn. ma zastosowanie do ścieżek zbudowanych z odcinków o...

This article presents a hybrid control system for a group of mobile robots. The components of this system are the supervisory controller(s), employing a discrete, event-driven model of concurrent robot processes, and robot motion controllers, employing a continuous time model with event-switched modes. The missions of the robots are specified by a...

In the paper new control method of skid steering mobile platforms has been presented. Such platforms are robotic objects with deficit of control inputs in dynamic model, i.e. they are dynamically under-actuated. To compensate lack of controls, it has been assumed that there are additional factitious inputs to dynamics (so-called factitious forces),...

In this work we deal with a system of autonomous mobile vehicles with limited communication range and consider the problem of the formally correct distributed control, i.e., the design of the local control for each particular agent so that it ensures globally correct behavior of the system. A particular problem is the fact that the knowledge about...

This work extends our research on motion coordination of free-range vehicular systems based on concepts and results borrowed from resource allocation systems (RAS) theory, to vehicular systems with limited communication range among the vehicles. Similar to the earlier work, the employed model assumes the tessellation of the motion plane into cells,...

We propose a novel paradigm for conflict resolution in multivehicle traffic systems, where a number of mobile agents move freely in a finite area, with each agent following a prespecified-motion profile. The key idea behind the proposed method is the tessellation of the underlying motion area in a number of cells and the treatment of these cells as...

The establishment of collision-free and live vehicle motion is a prominent problem for many traffic systems. Past work studying this problem in the context of guidepath-based and free-range vehicular systems has implicitly assumed that its resolution through maximally permissive supervision is NP-hard, and therefore, it has typically pursued subopt...

The safety problem in multi-vehicle systems seeks to establish collision-free and live vehicle motion, and it is a prominent problem for many configurations of these environments. Past work studying this problem in the context of free-range vehicular systems through abstractions based on Resource Allocation System (RAS) theory, has implicitly assum...

Generalized algebraic deadlock avoidance policies (DAPs) for sequential resource allocation systems (RASs) have recently been proposed as an interesting extension of the class of algebraic DAPs, that maintains the analytical representation and computational simplicity of the latter, while it guarantees completeness with respect to the maximally per...

This paper describes a problem of designing control laws preserving a motion along desired path for doubly nonholonomic mobile manipulators. The doubly nonholonomic mobile manipulator is composed of a mobile platform moving without slipping effect between wheels and the surface (i.e. nonholonomic platform) and an onboard manipulator equipped with s...

Coordination of the motions of multiple mobile robots as they perform their task in a shared workspace is an important capability and a problem widely studied in robotics. The theoretical studies in this area have mostly concentrated on motion planning with respect to collision avoidance and performance optimization [1]. The realization of motion p...

This paper proposes a novel paradigm for conflict resolution in multi-vehicle traffic systems where a number of mobile agents move freely in a finite area, each agent following a motion profile designated to it. The key idea underlying the proposed method is the tesselation of the underlying motion area in a number of cells of a certain shape and s...

Zone-controlled, guidepath-based, dynamically routed, closed traffic systems constitute the modelling abstraction for a large set of industrial and public transport systems. An important requirement for the traffic flow of these systems is that the vehicles maintain their ability to access every location in the underlying guidepath-network, through...

In this work we deal with a group of heterogeneous robots that cooperatively accomplish a task in a common area. For such a system, we develop a distributed control mechanism that ensures the correct coordination of their concurrent motion in the shared workspace. The concept assumes an additional level of robot motion control, that enforces tempor...

Currently, one of the most actively researched approaches regarding the design of deadlock avoidance policies for sequential resource allocation systems is based on concepts and techniques provided by the, so called, theory of regions, that addresses the broader problem of synthesizing PN models with prespecified behaviors. However, one limitation...

Generalized algebraic deadlock avoidance policies (DAPs) for sequential resource allocation systems (RAS) have recently been proposed as an interesting extension of the class of algebraic DAPs, that maintains the analytical representation and computational simplicity of the latter, while it guarantees completeness with respect to the maximally perm...

Currently, one of the most actively researched approaches regarding the design of deadlock avoidance policies for sequential resource allocation systems is based on concepts and techniques provided by the, so called, theory of regions, that addresses the broader problem of synthesizing PN models with pre-specified behaviors. However, one limitation...

This paper presents a rigorous approach to the coordination of space-sharing mobile robots, based on the Discrete-Event-System (DES) formalism. The proposed solution provides a closed-loop, scalable control model, ensuring in a provable manner the correct concurrent robot movement. The control logics guarantee the occurrence of no collisions or dea...

The paper presents a DES-based controller for an emerging, important class of industrial and public transport media - guidepath-based, zone-controlled, closed traffic systems. We build upon and extend our earlier results concerning the formal methods of control synthesis. An essential requirement for the traffic flow in these systems is that the ve...

This paper presents a Petri net-based method for deadlock control in flexible assembly systems (FAS). Instead of a process-oriented modeling method, a resource-oriented Petri net modeling method is used. A new control policy is thus formulated and proved to outperform the existing one in the literature. The deadlock problem in FAS is often more dif...

This paper introduces and advocates a new approach to the coordination of the motion of multiple mobile robots. In contrast to the current literature solutions, based on the execution of off-line generated plans, this work develops a state-based, closed-loop control mechanism ensuring in a provable manner the correct concurrent robot movement. The...

The paper concerns AGV systems (automated guided vehicle systems or AGVS) with bidirectional guide path network, unidirectional vehicles, zone control for avoiding collisions, and dynamic route planning. An AGVS is represented with a DES that models the feasible system dynamics. We study the liveness problem of the system and associate this propert...

The liveness of a closed AGV system is understood as the constant potential of each vehicle to attain any given zone in the guide path network. Based on the DES model of AGVS and the liveness condition proposed in our earlier work, we conduct a further analysis of the system behavior. The result is a general, algorithmically defined supervisor for...

Most of the research devoted to the supervisory control for deadlock avoidance in automated manufacturing systems has employed various models that represent concurrent sequential processes. In this paper, we address this problem for compound processes, that is, sequences of operations related in the fork/join manner and interacting as consumers/pro...

The paper concerns closed AGV systems with bidirectional guidepath network, unidirectional vehicles, zone control for avoiding collisions, and dynamic route planning. An AGVS is represented as a DES (Discrete Event System) that models the feasible system dynamics. We study the problem of the system liveness and associate this property with the perm...

Proposes a control architecture for a multiple mobile robot system, and within this framework concentrates on the robot motion coordination problem. A DES-based supervisory control is developed that formally ensures collision and deadlock avoidance between a group of robots concurrently accomplishing their missions in a common 2D space.

This paper presents closed AGV systems with bidirectional guide path networks, zone control for avoiding collisions, and dynamic route planning. An AGV system is represented as a colored Petri net with undirected arcs and directed tokens, which substantially reduces the number of net components and simplifies the insight into the model. We study th...

The paper is twofold. First we introduce a new concept-a partially directed graph, in which an edge can be undirected or have one of the two possible directions-and examine some of its structural properties. Then we assume that the edge attribute is variable and employ the concept to build a general, discrete event model of a system of vehicles mov...

We build a discrete-event model of concurrent FMS processes and consider the problem of its safe and maximally flexible behavior. To reduce the complexity of the problem we bound the class of systems addressed by the model with the requirement that the capacity of some selected resources be greater than one. The constraint prevents the occurrence t...

In the paper we develop a discrete dynamic model of concurrent cyclic processes and state two formal decision problems concerning testing the realizability of such system at its design phase and testing the safety (with respect to deadlocks) of control decisions undertaken on-line. We prove the NP-completeness of the problems and point out that suc...

In the paper we consider a manufacturing cell in which two robots cyclically move along well-defined paths of the workspace area. The concurrent motion of the robots in the common workspace must comply with the physical motion constraints. This implies a necessity of delays which are difficult to predict because the robots progress independently wi...

A general model of concurrent, asynchronous process flow in flexible assembly systems (FASs) is considered. It allows all feasible (with respect to the physical constraints of the system operation) process realizations, hence also the realizations leading to a deadlock. The main investigations are focused on the problems of process realizability, i...

A fault-tolerant resource allocation procedure aimed at automatic modification of Petri net-based control models is presented. The recovery scheme is based on the assumption that some of the system shared resources may be replaced by others, e.g. in case of their malfunctioning. The method encompasses a new deadlock avoidance algorithm which guaran...

A general approach to automatic synthesis of FMS-dynamics models is presented. The problems that require analytical solution are discussed. An illustration of the approach with respect to a certain class of manufacturing processes and using Petri nets as a modelling formalism is given. Application of the synthesis method is indicated.

Due to the high capital involvement in a Flexible Manufacturing System (FMS), the maximisation of its efficiency is of particular importance. This results in the following optimisation problems of FMSs: FMS design (selection and layout of the FMS conmponent), production planning, process planning, and real-time control and management.

The problem concerns an automatic synthesis of P/T systems modelling all feasible realizations of concurrent pipeline processes occurring in FMSs. First we define a P/T system Σ(A), with A the specification of a manufacturing process, as a parameter, providing the model respecting the resources constraints and parts routing requirements. Then we in...