Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1999-03-22
2002-03-05
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S099000
Reexamination Certificate
active
06353769
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to allocation of priority of lots of work to processing in a factory and more particularly to ranking of lots to determine their priority.
2. Description of Related Art
U.S. Pat. No. 5,319,544 of Schmerer et al. for “Computerized Inventory Monitoring and Verification System and Method”; U.S. Pat. No. 5,128,861 of Kagami et al. for “Inventory Control Method and System”; and U.S. Pat. No. 5,396,432 of Saka et al. for “Versatile Production System and Method of Operating Same” show production systems.
U.S. Pat. No. 5,446,671 of Weaver et al. for “Look-Ahead Method for Maintaining Optimum Queued Quantities of In-Process Parts at a Manufacturing Bottleneck” shows a production system.
U.S. Pat. No. 5,546,326 of Tai et al. for “Dynamic Dispatching Rule that Uses Long Term Due Date and Short Term Queue Time to Improve Delivery Performance”; U.S. Pat. No. 5,612,866 of Weng for “Method and System for Dynamic Dispatching in Semiconductor Manufacturing Plants”; and U.S. Pat. No. 5,721,686 of Shahraray et al. for “Method and Apparatus for Control and Evaluation of Jobs in a Factory” show scheduling systems.
SUMMARY OF THE INVENTION
GLOSSARY
Budget_Q . . . Budget Queue Time or BQT
BR . . . Base Rate
Critical Ratio.C/R: Critical Ratio Degree of Customer Dissatisfaction
C
tR
. . . BT (Budget Time) according to Required Date of lot
C
tD
. . . BT (Budget Time) by the Due Date of lot
C
tqR
. . . Budget_Q (BQT) according to Required Date of lot
C
tqD
. . . Budget_Q (BQT) by Due Date of lot
C
tI
. . . Step Budget_Q (BQT) for Lot Lm, Ln, etc.
CT . . . Cycle Time
Due_Date . . . Scheduled Due Date from MPS, i.e. date when processing of a lot must be finished for an order placed on MPS.
Due_Date_Now . . . Current Scheduled Due Date
FAB . . . Fabrication plant
FFOT . . . Forecast_FAB_Out_Time
Finished out . . . Completed the manufacturing process
MTD . . . Month To Date
MTD_OUT . . . Month To Date wafers OUT of FAB
MPS . . . Master Production Schedule
OTD . . . On-Time-Delivery
P . . . Temporary priority (P value) according to BQT
RP . . . Remaining Theoretical Recipe Processing Time
RD . . . (Required Date) Date when a lot must be finished out according to start date and average past cycle time data.
SLACK . . . Due_Date_Now—FFOT
Least SLACK . . . Lot with least amount of SLACK
t
p
. . . time from current step to finished step
t
sp
. . . Process time from step s from to p (process): Recipe time (process time) by step by product
&Sgr;t
sp
. . . Remaining theoretical process time equal to sum of t
p
from current step to finished step.
T . . . Time
WIP . . . Work in Process
X . . . Index for Week when lot must be Delivered i.e. Lot is Required to be out of FAB
The required cycle time is based on PC Lot's RD definition based on the FIFO principle.
PROBLEM SOLVED BY INVENTION
Two of the indices most commonly used for setting lot priorities are least SLACK and the critical ratio (C/R). These two indices are used to dispatch with the aim of meeting or improving OTD. However, the values of SLACK or C/R sometimes cannot reflect the actual urgent status of a lot due to the variances of the uncontrollable portion of the remaining Cycle Time (CT), i.e. the remaining recipe processing time between different products. Thus, only after the processing time is deducted while calculating the remaining time, is it possible to define the urgency or the priority of lots clearly. There are two kinds of dates/times when a lot should have completed processing, which are the Required Date (RD) and the Due_Date. The RD denotes the delivery requirement and the Due_Date indicates the shorter cycle time deviation. In practice, the two values, i.e. (the RD and the Due_Date) can be combined together and integrated into a date for calculating the remaining CT. While the combination of the two dates is a convenience; it can lead an operator to be confused by the two different concepts of delivery time and CT variance when evaluating the priority to be assigned to a given lot.
Problems solved and improvements obtained by this invention include the features as follows:
1. With the index of X, the lots are pushed more correctly for delivery especially for the back end stages.
2. With the index of P, the lots are moved according to the remaining Budget Queue Time. This makes lots finished out with little variance.
3. With the distinguishability between delivery and cycle time variance of lots by two parameters of (X,P), the analysis of delivery and variance of the whole line is made easily. Production planners benefit greatly as they are able to make scheduling decisions resolving conflicts arising upon conflicting customer requirements.
The concept of Budget Queue Time is used to define the priority of lots while distinguishing clearly between the controllable an uncontrollable portions of the remaining production time needed and to make the priority setting further meet the actual status. Two indices X and P are used concurrently to define the priority of a lot. X is the index of the delivery week which indicates the week in which the lot must be out of the fabrication process and P denotes the temporary priority according to the Budget Queue Time, but X is the dominant one of the two indices X and P. Use is made of the concept of remaining Budget Queue Time instead of traditional queue time of current stage for dispatching to reduce the variance of cycle time variance.
REFERENCES:
patent: 5128861 (1992-07-01), Kagami et al.
patent: 5319544 (1994-06-01), Schmerer et al.
patent: 5396432 (1995-03-01), Saka et al.
patent: 5446671 (1995-08-01), Weaver et al.
patent: 5546326 (1996-08-01), Tai et al.
patent: 5612886 (1997-03-01), Weng
patent: 5721686 (1998-02-01), Shahraray et al.
patent: 5751580 (1998-05-01), Chi
patent: 5818716 (1998-10-01), Chin et al.
Ackerman Stephen B.
Garland Steven R.
Grant William
Jones II Graham S.
Saile George O.
LandOfFree
Method for allocating lot priority by ranking lots as a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for allocating lot priority by ranking lots as a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for allocating lot priority by ranking lots as a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2843340