LocalControl - Control of Discrete Event Systems Control...

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Control of Discrete Event Systems Control refers to the process of forcing the system into certain states. Since the states of a discrete event system consists of the initiation or completion of tasks, control then refers to the issuing of command to the system to command it do perform certain tasks. For example, in an automated manufacturing cell, the primary controller sends commands to each machine to perform certain tasks upon given jobs. In making this assignment, the primary controller must also coordinate the movement of a job to the machine where the execution of the task has been assigned. In this case, the controller sends a command to the material handling system (MHS) to pick up a job at its current location and deliver it to the allocated machine. Once the job is delivered, the controller then tells the machine to unload the job from the MHS and perform a set of prescribed tasks upon it. In the control of automated systems, the executive function provides some additional features that allow us to use the model to control the real system. Computer code is inserted into the model at the appropriate locations to execute software related to the control of the system. This code is generally some kind of communication to the physical system. The executive function has a means to manage the execution of events based of the event list, then waiting action list and now additionally on the input communication it received from the hardware. In the general case, the model consists of many actions corresponding to events that occur during execution of the system. Each action sends the appropriate message to the hardware. The controller manages the messages that are sent to the system by managing the actions to perform. The engineer builds the model by inserting code to send the messages appropriate to the situation that exits when that action gets executed. The simulation / control tool must also receive a function that handles the communication between the controller and the hardware. This function is created and sent to the tool just as the model function is. Additional data structures The following is an additional data structure that must be added to the executive object, in order for the model to possess the capability for controlling a system. The prior data structures employed for a standard simulation are used as well. The pending event list object The pending event list is an unordered list of events that are pending responses from the hardware before they can occur. There is no time associated with a pending event. The pending event list object manages this list. The same data structure that was previously employed for the event list is also used for the pending event list, but with the key data fields used instead of the time field. When the hardware finishes a task, it responds to the controller with a message. A communication function, which must be supplied by the modeler, usually retrieves a key from the hardware message. This key is then sent to the
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This note was uploaded on 09/13/2011 for the course EEL 5937 taught by Professor Staff during the Spring '08 term at University of Central Florida.

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LocalControl - Control of Discrete Event Systems Control...

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