Method and apparatus for control and evaluation of pending jobs in a factory

• US 5,721,686 A
• Filed: 10/31/1996
• Issued: 02/24/1998
• Est. Priority Date: 02/05/1993
• Status: Expired due to Term

• Current Assignee: Siemens Corp. (Siemens AG)
• Original Assignee: Siemens Corporate Research Incorporated (Siemens AG)
• Inventors: Shahraray, Maryam S., Hadavi, Khosrow
• Primary Examiner(s): RUGGIERO, JOSEPH F
• Application Number:
  US08/730,630
• Time in Patent Office: 481 Days
• Field of Search: 364/468.06, 364/468.07, 364/468.08, 364/468.03, 364/156, 364/194, 395/207, 395/208, 395/209, 395/210, 395/211
• US Class Current: 700/102
• CPC Class Codes: G05B 19/41865 characterised by job scheduling, process planning, material flow
• CPC Class Codes: G05B 2219/32252 Scheduling production, machining, job shop
• CPC Class Codes: G06Q 10/06 Resources, workflows, human or project management; Enterprise or organisation planning; Enterprise or organisation modelling
• CPC Class Codes: H01L 22/20 Sequence of activities consisting of a plurality of measurements, corrections, marking or sorting steps

Abstract

An improved system and method for scheduling a plurality of orders into a factory for processing by one or more of a plurality of machines located therein, based on the use of a Continuity Index job release strategy. The system and method is particularly addressed to the enhancement of such a job release strategy by introduction of Factory Profile and priority criteria and an algorithm for automatic determination of an optimum job release point based on such criteria. The scheduling methodology is characterized by defining a Continuity Index (CI) for each of the jobs as the ratio of the actual time the job is being processed by such one or more machines to the total time from release of the jobs into a shop wherein such machines are located until the completion of the job, establishing a Factory Profile curve of optimum CI value over time, determining a curve of actual CI for each of the jobs being tested for release beginning from a trial start date and extending through the expected completion of the job, comparing the actual CI curve for each of such jobs with the Factory Profile optimum CI curve and accepting the job for processing by the shop on the trial start date if the actual CI curve closely follows the Factory Profile curve throughout the processing time for the job, and otherwise determining a new curve of actual CI for the job from a new trial start date and repeating the comparison.

Claims

1. A method for controlling the release of jobs from a pool of pending jobs into a factory including a plurality of machines processing jobs-in-process, said method comprising the steps of:

storing data from inputs connected to the machines and other components of the factory relating to an amount of time required to process a Rob in the factory and an amount of time anticipated to complete the lob within the factory including waiting time at the machines;

defining a Continuity Index (CI) for one of said jobs in said pool of pending jobs as the ratio of the processing time required for said job;

establishing a Factory Profile curve of optimum CI value over time;

determining a curve of actual CI for said one of said jobs from a trial start date through the expected completion of said job;

comparing said actual CI curve for said one of said jobs with said Factory Profile optimum CI curve; and

releasing said one of said jobs into said factory for processing by at least one of said machines on said trial start date if said actual CI curve closely follows said Factory Profile curve, within predefined bounds, throughout the processing time for said job, and otherwise determining a new curve of actual CI for said job from a new trial start date and repeating said comparison step.

2. The job scheduling method of claim 1 wherein said step of establishing said Factory Profile curve includes the substep of determining a range enclosing said optimum CI value of said Factory Profile curve and wherein criteria for said releasing step are satisfied if said actual CI curve falls within said range enclosing said optimum CI value.

3. The job scheduling method of claim 2 wherein said step of establishing said Factory Profile curve of optimum CI value over time includes the substep of adjusting said range about said optimum CI value to provide a wider range for jobs having a higher than normal priority.

4. The job scheduling method of claim 2 wherein said comparing step includes an error determination based on a minimum of a first sum of squares and a second sum of squares over said processing time for said job being tested for acceptance, said first sum of squares being determined as the difference between the actual CI for said job at each point in said time and the upper bound of said range of optimum CI and said second sum of squares being determined as the difference between the actual CI for said job at each point in said time and the lower bound of said range of optimum CI.

5. The job scheduling method of claim 2 wherein said new trial start date for acceptance by said comparing step is automatically computed, as by a digital computer, using a BestStartDate algorithm:

space="preserve" listing-type="tabular">______________________________________ Let Ethmax be maximum Threshold Error Let Ethmin (E = Error) be minimum Threshold Error Emin <

- Eth Emax <

- 0 is the max error without going over the threshold value Sd <

- Desired.sub.-- Sd (desired start date), SDc <

- Sd, i.e. current Sd is originaliy set to the Desired.sub.-- Sd Nr, N1 no of right shifts and left shifts allowed Nr is a function of order priority, i.e. as order priority increases then Nr becomes smaller;

N1 is a management- determined finished good inventory function, stating how early, in the worst case, completion of the order will be acceptable. Note that these two parameters decide on the boundaries of the search space. They can be either predefined or can be decided at the time of order entry. n is shift counter;

+ve for right shifts &

-ve for left shifts;

n <

- 0 Wc is the current window.sub.-- no w <

- Wc Allocate;

Set t <

- end.sub.-- of(w) /* t is the max time unit in w, e.g., last day of week w */ Allocate until t OR all steps done otherwise EXIT Evaluate e(t), where t is the end of current window If e(t) >

Ethmin THEN BEGIN if e(t) <

Emin THEN BestSD <

- SDc, Emin <

-e(t);

/*else the previous SD was better*/ find.sub.-- a.sub.-- better.sub.-- sd;

auto allocate i END-begin ELSE /* error term is still smaller than threshold */ BEGIN w <

- w+1 Emax <

- e(t) GOTO allocate END-begin;

If e(t) >

Ethmax THEN warning;

Promised due date is too good for this priority class;

print(BestSD, Emin, Emax);

END BestStartDate. PROCEDURE find.sub.-- a.sub.-- better.sub.-- sd;

If n=<

0 &

n>

N1 THEN shiftleftORright(-) /* note that N1 is a -ve number */ Else IF n<

Nr THEN shiftleftORright(+);

ELSE /*UNSUCCESSFUL release */ DO ONE OF THE FOLLOWING Increase job'"'"'s priority;

not recommended if done too often;

Decrease job'"'"'s priority, i.e., increasing Nr the search space this is relaxing constraints;

Decrease(make more negative) N1, this is also relaxing WIP constraint;

Suspend release until a later time;

Other alternatives are changing Eth and CI* etc but these are not recommended since they would have a global effect. END-else;

END.sub.-- find.sub.-- a.sub.-- better sd. PROCEDURE shiftleftORright (.sup.˜

);

/* .sup.˜

is - if shiftleft and + if shiftright */ n <

- n.sup.˜

1 w <

- w.sup.˜

1 Wc <

- w SDc <

- max(starttime(w), Today) END shiftORright. ______________________________________

6. A system for controlling the release of jobs from a pool of pending jobs into a factory including a plurality of machines processing jobs-in-progress, comprising:

scheduling means for controlling release of a job from the pool of pending jobs into the factory, said scheduling means having inputs connected to the machines and other components of the factory relating to an amount of time required to process a job in the factory and an amount of time anticipated to complete the job within the factory including waiting time at the machines;

means for defining a Continuity Index (CI) for one of said jobs as the ratio of the processing time required for said one of said jobs in said pool of pending jobs to the total time from release of said job into the factory until the completion of said job and output thereof from said factory;

means for establishing a Factory Profile curve of optimum CI value over time for the factory;

means for determining a curve of actual CI for said one of said jobs from a trial start date through the expected completion of said job in said factory;

means for comparing said actual CI curve for said one of said jobs with said Factory Profile optimum CI curve;

means for operating said scheduling means for releasing said one of said jobs into said factory for processing by at least one of said machines on said trial start date if said actual CI curve closely follows said Factory Profile curve, within predefined bounds, throughout the processing time for said job, and otherwise determining a new curve of actual CI for said job from a new trial start date with said new curve being compared by said means for comparing to establish a new job release.

7. The job scheduling system of claim 6 wherein said means for establishing said Factory Profile curve includes a further means for determining a range enclosing said optimum CI value of said Factory Profile curve and wherein said criteria for releasing said one of said jobs into said factory for processing by at least one of said machines on said trial start date are satisfied if said actual CI curve falls within said range enclosing said optimum CI value.

8. The job scheduling system of claim 7 wherein said means for establishing an optimum CI curve for said shop/includes a further means for adjusting said range about said optimum CI value to provide a wider range for jobs having a higher than normal priority.

9. The job scheduling system of claim 7 wherein said comparison means further includes an error determination means enabled to compute a minimum of a first sum of squares and a second sum of squares over said processing time for said job being tested for acceptance, said first sum of squares being determined as the difference between the actual CI for said job at each point in said time and the upper bound of said range of optimum CI and said second sum of squares being determined as the difference between the actual CI for said job at each point in said time and the lower bound of said range of optimum CI.

10. The job scheduling system of claim 7 further including a computational means for computing said start date for acceptance by said comparison means using a BestStartDate algorithm