In modern industrial assembly and quality control processes, that provide one of the crucial factors for the competitiveness of industry in general, there is a strong need for advanced robot-based object detection and recognition, object grasping and for the capability to perform assembling operations in non-structured environments with randomly positioned objects. Vision-based robotic assembly and quality control systems, that have been a topic of continued research interest for almost four decades, have now matured to a point where they can be effectively applied to advanced robot-based assembly and quality control tasks. This chapter will give an overview of research work related to the field of automated vision systems for assembly and quality control processes.

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Robot Vision in Industrial Assembly and Quality Control Processes

Reversible computation vs. reversibility in Petri nets

Petri nets are a general formal model of concurrent systems which supports both action-based and state-based modelling and reasoning. One of important behavioural properties investigated in the context of Petri nets has been reversibility, understood as the possibility of returning to the initial marking from any reachable net marking. Thus reversibility in Petri nets is a global property. Reversible computation, on the other hand, is typically a local mechanism using which a system can undo some of the executed actions. This paper is concerned with the modelling of reversible computation within Petri nets. A key idea behind the proposed construction is to add ‘reverse’ versions of selected transitions. Since such a modification can severely impact on the behavior of the system, it is crucial, in particular, to be able to determine whether the modified system has a similar set of states as the original one. We first prove that the problem of establishing whether the two nets have the same reachable markings is undecidable even in the restricted case discussed in this paper. We then show that the problem of checking whether the reachability sets of the two nets cover the same markings is decidable.

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Reversible Computation vs. Reversibility in Petri Nets

In Petri nets, computation is performed by executing transitions. An effect-reverse of a given transition b is a transition that, when executed, undoes the effect of b. A transition b is reversible if it is possible to add enough effect-reverses of b so to always being able to undo its effect, without changing the set of reachable markings.

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Reversing Unbounded Petri Nets

This paper presents a formal calculation method of a deadlock prevention supervisor by the use of Petri nets. The proposed algorithm uses reachability tree to detect deadlock state and iterative siphon control method to synthesize the deadlock prevention supervisor. Such supervisor is maximally permissive and consists of minimal number of control places. The algorithm is intended for reversible or partially reversible P-T Petri net, but it can also be applied to Ordinary Petri nets. The calculation of the supervisor is illustrated by two examples. The first example shows the synthesis of deadlock prevention supervisor in a manufacturing system consisting of three conveyors and three robots, where the deadlock can occur due to concurrent requests of the conveyors for the robot engagements and unpredictable duration of those engagements. The second example shows the synthesis of deadlock prevention supervisor in a marine traffic system, where dangerous vessel deadlock situations may occur in case of vessels’ irregular motion through the system. To avoid this, the vessel traffic is supervised and controlled by traffic lights using the deadlock prevention supervisor, which is responsible for vessels’ stopping only in the case of dangerous situation and until this situation elapses.

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An Algorithm for Deadlock Prevention Based on Iterative Siphon Control of Petri Net

This paper deals with the traffic control of vessels moving through the marine system of canals and basins. Dangerous vessel deadlock situations may occur in case of vessels’ irregular moving through the system. To avoid this, the vessel traffic is supervised and controlled by traffic lights. A supervisor is responsible for vessels’ stopping only in the case of dangerous situation and until this situation elapses. This paper shows a formal method of calculating a maximal permissible deadlock prevention supervisor by use of Petri net and iterative siphon control method. The functionality of calculated deadlock prevention supervisor is verified using a computer simulation of vessels’ movements.

A Petri Net Approach of Deadlock Prevention in Marine Traffic System

This paper deals with a deadlock prevention method in manufacturing systems based on Petri nets. The manufacturing system is a discrete event system which has the potential deadlock states. The paper shows how it is possible to model manufacturing system by Petri net and how it is possible to synthesize the Petri net supervisor that will prevent deadlock occurrence. Deadlock prevention algorithm proposed in this paper uses reachability tree to detect deadlock state and iterative siphon control method to synthesize the supervisor. Such deadlock prevention supervisor is maximally permissive and consists of minimal number of control places. The algorithm is usable for reversible or partially reversible P-T Petri net, but it can also be applied to ordinary nets. Finally, illustrative example of deadlock prevention of a flexible assembly cell with three robots and conveyors is presented.

Danko Kezić

Papers

An Algorithm for Deadlock Prevention Based on Iterative Siphon Control of Petri Net

A Petri Net Approach of Deadlock Prevention in Marine Traffic System

Deadlock Prevention in Manufacturing Systems Based on Petri Nets

Wavelet-Based Edge Detection for Robot Vision Applications