Wenle Zhang

Evaluating order of circuits for deadlock avoidance in a flexible manufacturing system

Circuits and knots in the diagraph model of a manufacturing system are the rudimentary causes of deadlocks - a type of deadlock that is difficult to detect. A new deadlock avoidance algorithm that dynamically evaluates the order of circuits is presented. The algorithm is highly permissive since the order evaluation captures more parts flow dynamics, especially when there exist multiple knots in the diagraph model. It also runs in polynomial time once the set of circuits of the diagraph is given. Simulation results are provided to illustrate the application of the algorithm.

Deadlock avoidance algorithm for flexible manufacturing systems by calculating effective free space of circuits

Modern flexible manufacturing systems (FMS) are highly automated and flexible in which raw parts of various types are processed concurrently. Deadlock issue arises easily in these systems due to shared equipment usage and high production flexibility. This paper presents a deadlock avoidance algorithm for FMS with free choices in part routing by calculation of effective free space of circuits of the digraph model. The algorithm is highly permissive since the effective free space calculation captures more parts flow dynamics, especially when there exist multiple knots in the digraph model. It runs in polynomial time once the set of circuits is computed offline. Simulation results are provided.

Deadlock avoidance in manufacturing systems with non-deterministic part routings

A deadlock avoidance algorithm for flexible manufacturing systems containing both multiple capacity resources and mixed choices in part routing is presented. The method determines whether moving a part to its next step is safe, unsafe, or undetermined. That classification is linear in complexity. Undetermined part movements are further analyzed using another procedure, which attempts to empty the system virtually to determine whether the move is safe or not. It is polynomial in complexity. An example is provided to illustrate how the method can be applied.

A scalable deadlock avoidance algorithm for flexible manufacturing systems with free choice in part routing

A new deadlock avoidance algorithm for flexible manufacturing systems that contain both multiple capacity resources and free choice in part routing is presented. The method determines whether moving a part to its next step is safe, unsafe, or undetermined. This classification is linear in complexity. Part movements that are classified as undetermined are further analyzed using another procedure, which attempts to empty the system to determine whether the move is safe or not. It is polynomial in complexity. By adjusting a simple tuning parameter, the size of the set of possible undetermined classifications returned can be made arbitrarily small at the cost of increasing the order of the algorithm. An example showing the application of the method is provided.

Classification of part movements for deadlock avoidance in manufacturing systems

A method that classifies part movements to avoid deadlock in manufacturing systems which contain single capacity resources is presented. The proposed method determines whether a particular part movement is safe, unsafe, or undetermined. This classification is linear in complexity. Part movements that are classified as undetermined are analyzed using another procedure. This alternative procedure attempts to empty the system to determine whether the move is safe, unsafe, or undetermined. It is polynomial in complexity. By adjusting a simple parameter, the size of the set of possible undetermined classifications returned can be made arbitrarily small by increasing the order of the algorithm. Examples showing the application of the method are provided.

Deadlock avoidance in manufacturing systems with a multiple resource request model

A deadlock avoidance method for flexible manufacturing systems with both free choices and multiple resource requests allowed in part routing is presented. Based on a digraph model of the system, the method classifies whether moving a part to its next step is safe, unsafe, or undetermined. An undetermined part movement is further analyzed using a very efficient system simulation, which attempts to empty the system virtually to determine whether the move is safe. This classification algorithm is shown to be polynomial in complexity. To avoid deadlocks, only safe part movements should be allowed to proceed. An example is provided to illustrate how the method can be applied.