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Knowledge-Based Dynamic Scheduler in Distributed Computer Control

IP.com Disclosure Number: IPCOM000100781D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 5 page(s) / 196K

Publishing Venue

IBM

Related People

Shah, MJ: AUTHOR

Abstract

This article describes a rule-based programming system for dynamic scheduling of shared transporters moving components processed at sequential stations, where each processing step may have critical timing and processing requirements. This scheduling problem arises in many manufacturing environments where assembly line operations take place at many sequential processing stations. In our scheme the transporters are reserved, moved to required stations to pick up the component(s) being processed and move to the next sequential station in such a way that time-critical processing requirements are met while maintaining the optimum throughput of production through the manufacturing line.

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Knowledge-Based Dynamic Scheduler in Distributed Computer Control

       This article describes a rule-based programming system
for dynamic scheduling of shared transporters moving components
processed at sequential stations, where each processing step may have
critical timing and  processing  requirements. This scheduling
problem arises in many manufacturing environments where assembly line
operations take place at many sequential processing stations.  In our
scheme the transporters are reserved, moved to required stations to
pick up the component(s) being processed and move to the next
sequential station in such a way that time-critical processing
requirements are met while maintaining the optimum throughput of
production through the manufacturing line.  Our programming system
uses a rule-based approach together with a real-time interface of the
IBM KnowledgeTool* Program, allowing dynamic decisions to
continuously modify the strategies when station failures (such as
machine breakdown) occur or one or more processing equipments are
temporarily removed for maintenance.  The real-time interface of the
Knowledge Tool Program is used to send the rule-based program
decisions for transporter movement to the micro controllers or
programmable logic controllers.

      The process in our case is controlled by a hierarchical
computer system (1) where the knowledge-based system resides at a
supervisory level computer performing the transporter movement
decisions, whereas monitoring and control of the stations are
performed by microprocessors and control computers at a lower level.
As an example, the processing stations may be tanks performing
chemical processing of semiconductor components. Each tank is
monitored and controlled for maintaining temperatures, flows and
chemical composition using cell level computers, which also send the
process and transporter status information to the upper level.  The
transporter scheduling is performed at the upper level where
supervisory decisions and operator interfaces take place.  This
technique combines the microcontroller high speed (milliseconds)
response (for single loop controllers) with real-time knowledge-based
systems at supervisory level where operator interfaces reside.

      The Application The manufacturing process for the example,
shown in the figure, is used for chemical treatment of semiconductor
component substrates in a series  of wet tanks. The residence time
for the component batch in each tank is a function of the stage of
the wet process and in some cases is critical in that the component
batch must be removed and sent to the next stage immediately on
completion of the processing time.  The component batches arrive
continuously and are processed in gangs of parallel tanks.   To
maximize the throughput in this section of the plant, two or more
batches may be in process in each line, depending upon the number of
sequential process tanks required and a reasonable safety...