Patent ID: 6092000
Filing Date: 2000-07-18
Classification: G05B,Y02P

Abstract:
A method for maximizing throughput of a multiple-step workstation in a plant, the workstation having a waiting pool buffer of lots waiting to be processed by the workstation, an nth lot L.sub.n in the waiting pool having a process time PT.sub.n and using a recipe R.sub.n, wherein a delay time DT.sub.n is the time the lot L.sub.n is waiting to be processed due to a preceding lot L.sub.n-1 being processed, the lot L.sub.n not being processed or not being in transit between process steps during the delay time DT.sub.n, n being an integer greater than zero, said method comprising:forming an array of interrecipe delay times having a plurality of delay times for a plurality of lots L.sub.n caused by a plurality of lots L.sub.n-1 ;forming an array of feasible recipe-to-recipe sequences having a plurality of feasible recipe-to-recipe sequences for the plurality of lots L.sub.n and orders O.sub.m of lots, m being an integer greater than zero;forming a lot-recipe mapping array that maps a recipe to be used with an associated lot, wherein each mapping is determined from past processing data;generating an objective function for determining recipe-to-recipe sequences having lots with minimized delay times within an order to be processed;determining a constraint function on the recipe-to-recipe sequences;solving the objective function subject to the constraint function using an integer programming model; andforming a solution set of an optimal process of recipe-to-recipe sequences having lots in orders to be processed, wherein each lot in the optimal process has a minimum delay time for the order to be processed, the optimal process having a minimum total delay time for the orders to be processed.