1 / 29

Scheduling

Scheduling. Definition of scheduling. Establishing the timing of the use of equipment, facilities and human activities in an organization In the decision-making hierarchy, scheduling decisions are the final step in the transformation process before actual output occurs.

randygwilliams
Download Presentation

Scheduling

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Scheduling

  2. Definition of scheduling • Establishing the timing of the use of equipment, facilities and human activities in an organization • In the decision-making hierarchy, scheduling decisions are the final step in the transformation process before actual output occurs. • Effective scheduling can yield • Cost savings • Increases in productivity

  3. Volume • Scheduling tasks are largely a function of the volume of system output. • High-volume systems • Intermediate-volume systems • Low-volume systems

  4. High-Volume Systems • Flow system: High-volume system with Standardized equipment and activities • Flow-shop scheduling: Scheduling for high-volume flow system • Goal: a smooth rate of flow of goods or customers through the system to get a high utilization of workforce and equipment • Highly repetitive nature system leads to: • …the determination of many loading and sequence decisions during the design of the system, • …highly specialized: tools and equipnment, arrangement, division of labour • automatization

  5. Balancing the line • Allocating the required tasks to workstationsso that they satisfy technical (sequencing) constraints and are balanced with respect to equal work times among stations. • Goal: maximum utilization and highest possible output rate

  6. Hindrances of highly specialized jobs • Discontent of workers: • Too simple tasks: monotonous, boring • Give rise to fatigue, absenteeism, turnover • Reduce productivity

  7. High-Volume Success Factors • Process and product design: manufacturability • Preventive maintenance: to minimize disruption of the flow of work • Rapid repair when breakdown occurs • Optimal product mixes: linear programming • Minimization of quality problems: to minimize disruption • Reliability and timing of supplies: to avoid shortages (and high carrying costs)

  8. Intermediate-Volume Systems • Outputs are between standardized high-volume systems and made-to-order job shops • Usually standard outputs • Not continuous but intermittent production (periodical shifts from one job to another) • Run size (large), timing, and sequence of jobs • Economic run size: • MRP approach

  9. Setup costs • Depend on the similarity of products • Complex sequencing problem: different setup costs for every combination • Off-line setups, modular set-ups, flexible equipment

  10. Scheduling in Low-Volume Systems • Products made to order not to inventory • Orders can be very different • Job-shop scheduling: Scheduling for low-volume systems with many variations in requirements • Schedules cannot be made prior to actual job order • Loading - assignment of jobs to process centres and to various machines in the centres • Sequencing - determining the order in which jobs will be processed

  11. Aims of loading • Find arrangement to minimize: • Processing and setup costs • Idle time among work centers and machines • Job completion time

  12. Gantt load charts • Visual aid • Depicts the loading and idle times for a group of machines or departments • Trial-and-error schedule development

  13. Loading • Infinite loading: jobs are assigned without regard to the capacity of work centres. This can lead to over- and underloads. • Finite loading: takes into account the work centre capacity and job processing times. Need frequent updating. • Forward scheduling: scheduling ahead from a point in time. ‘How long will it take to complete this job?’ • Backward scheduling: scheduling backward from due date. ‘When is the latest job can be started?’

  14. Gantt schedule chart • Shows the orders or jobs in progress and whether they are on schedule • horizontal axis: time, • vertical axis: jobs in progress

  15. Sequencing • Sequencing: Determine the order in which jobs at a work centre will be processed (and the order in which jobs are processed at individual workstations within work centres). Crucial if work centres are heavily loaded. • Workstation: An area where one person works, usually with special equipment, on a specialized job.

  16. Sequencing • Priority rules: Simple heuristics used to select the order in which jobs will be processed. • Job time: Time needed for setup and processing of a job.

  17. Top Priority Priority Rules • FCFS - first come, first served • SPT - shortest processing time • EDD - earliest due date • CR - critical ratio • S/O - slack per operation • Rush - emergency

  18. Effectiveness of a given sequence • Job flow time – the length of time a job is at a particular workstation or work center. (it includes not only processing time, but waiting time, transportation time) • Average flow time = total flow time /number of jobs • Job lateness – length of time the job completion date is exceed the date the job was due to promised to the customer • Average tardiness=total lateness/number of products • Makespan – is the total time needed to complete a group of jobs (time between start the first and completion of the last one) • Average number of jobs=total flow time/makespan (it reflects the average work-in-process inventory if the jobs represent equal amount of inventory)

  19. SchedulingSeminar exercises 2010.10.14 Process and Production Management

  20. Assumptions • The set of jobs is known • Setup time is independent of processing sequence • Setup time is deterministic • Process time are deterministic • There will be no interruptions in processing such as machine breakdowns, accidents, or workes illness.

  21. Example 1 • Determine the sequence of jobs/products • Determine average flow time • Determine average tardiness • Determine average number of jobs at the workcenter

  22. ABCDEF FCFS • Aft=120/6=20 days • At=54/6=9 days • M=41  Aj=120/41=2,93 pieces

  23.  ACEBDF SPT • Aft=108/6=18 days • At=40/6=6,67 days • Aj=108/41=2,63 pieces

  24. CAEBDF EDD • Aft=110/6=18,33 days • At=38/6=6,33 days • Aj=110/41=2,68 pieces

  25. CR ??? Remaining time untill due to dat (on the 0th day) 1. 2.

  26. 3. 4. 1. 5. 4. 2.

  27. CRCFAEBD • Aft=133/6=22,16 days • At=58/6=9,66 days • Aj=133/41=3,24 pieces

  28. Sequencing Jobs through two Work Center • Job time is known and constant • Job time is independent of job sequence • All job must follow the same two-step job sequence • Job priorities cannot be used • All units must be completed at the first work center before moving on to the second work center

  29. Thank you for your attention!

More Related