Scheduling

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Scheduling
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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

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Volume

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

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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

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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

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Hindrances of highly specialized jobs

• Discontent of workers
• Too simple tasks monotonous, boring
• Give rise to atigue, absenteesm, turnover
• Reduce productivity

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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 (a and high carrying costs)

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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

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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

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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

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Aims of loading

• Find arrangement to minimize
• Processing and setup costs
• Idle time among work centres and machines
• Job completition time

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Gantt load charts

• Visual aid
• Depicts the loading and iddle times for a group
  of machines or departments
• Trial-and-error schedule development

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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
  center 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?

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Gantt schedule chart

• Shows the orders or jobs in progress and whether
  they are on schedule
• horizontal axis time,
• vertical axis jobs in progress

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Sequencing

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

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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.

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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

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Effectiveness of a given sequence

• Job flow time the length of time a job is at a
  particular workstation or work center.Processing
  time waiting
• Job lateness the length of time the job
  completition date is expected to eyceed the date
  the job was due or promised to a customer.Actual
  completition time due date
• Makespan total time needed to complete a group
  of jobs from the beginning of the first job to
  the completition of the last job
• Average number of jobstotal flow time /
  makespan

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Thank you for your attention!