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A Method for feasible rescheduling which does not assume all the initial conditions are timely updated by an execution system

IP.com Disclosure Number: IPCOM000231144D
Publication Date: 2013-Sep-30
Document File: 5 page(s) / 99K

Publishing Venue

The IP.com Prior Art Database

Abstract

Scheduling in supply chains and in manufacturing systems is often a rolling process, where a new scheduling is initiated while the current schedule is being executed. The generation of a new schedule (rescheduling) should take into account the past and current execution (work-in-progress) in order to make the new schedule executable in field. Scheduling systems usually assume that an execution system provides the timely update of the needed initial conditions as part of the main input for the scheduling system. This disclosure does not assume that and proposes a method to obtain the initial conditions and the constraints to be accounted for in the rescheduling.

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A Method for feasible rescheduling which does not assume all the initial conditions are timely updated by an execution system

This is in the domain of scheduling in supply chain and manufacturing environments. There are two systems that are relevant:


1. Scheduling System

2. Execution System


The above systems are prior art and exist in practice. The main function of the scheduling system is to create a plan or schedule for the activities that are to be executed during a pre-specified planning horizon . The schedule is then communicated to the operations team that executes the activities. While the main functions of the execution system is to monitor and track the execution of the activities on the field, the operations team can modify the schedule manually as per the needs and constraints on the field. Let the schedule that has been released (published) to execution be called as the Execution Schedule.

Scheduling is generally a rolling process, where the planner with the support

of a scheduling system creates a new schedule (rescheduling) at regular intervals (e.g. once a week). At times, rescheduling can be triggered due to unplanned events like machine failure or arrival of an urgent customer order. Re-scheduling

    Whenever there is a need for re-scheduling, the PLANNING HORIZON is defined for which the new schedule has to be determined. For creating the new schedule, the Scheduling System, among others, requires the following input:


I. The Execution Schedule with the definition of a frozen horizon (where the

execution schedule should be kept 'as it is'

II. The status of the various inventories in the system at the start of the time
horizon


III. Constraints on the availability of resources and mandatory activities to be
scheduled in the PLANNING HORIZON.

    Without these, the schedule created by the Scheduling System may not be implementable by the Execution System due to the gaps between the schedule and the real world. The inventory status and, the Schedule part of the frozen horizon is defined as the work-in-progress (WIP). The addresses the method for determining input II and III from WIP.


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The user defines the new time horizon for re-scheduling as shown in Figure 1. The various time instances are described below:

· STATUS TIME: The time at which the last WIP status update and the Execution Schedule were obtained from the Execution System.

· UNKNOWN PAST denotes the time period that elapsed since the last status update. The real execution detail is unknown during this period and all relevant activities are assumed to function as per the Execution Schedule .

·The re-scheduling horizon is from START HORIZON to END HORIZON and consists of the following two non-overlapping horizons.

o FROZEN HORIZON: No new schedules are created during the FROZEN

  HORIZON.
o PLANNING HORIZON: The new schedule is created for the activities to

be executed during this time period.

The Scheduling System computes the new schedule for the PLANNI...