Introduction to Scheduling Chapter 1

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Introduction to SchedulingChapter 1

• Prepared by Dr. Tsung-Nan Tsai

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What is Scheduling?

• Scheduling deals with the allocation of scarce
  resources to tasks over time. It is a
  decision-making process with the goal of
  optimizing one or more objectives.
• Consists of planning and prioritizing activities
  that need to be performed in an orderly sequence
  of operation.
• Scheduling leads to increased efficiency and
  capacity utilization, reducing time required to
  complete jobs and consequently increasing the
  profitability of an organization.
• Resource scheduling, such as machines, labor, and
  material.

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The role of scheduling

• The resources and tasks in an organization has
  many forms, the resources such as
• machines in a workshop, runways at an airport
• crews at a construction site, processing units in
  a computing environment.
• The tasks may be
• operations in a production process, take-offs and
  landing at an airport.
• stages in a construction project, executions of
  computer programs.

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Manufacturing systems information flow
MRP - I
Detailed scheduling
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Service systems information flow
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1.1 Scheduling Examples

• Carton manufacturing operations High mixed
  products and on time delivery.
• Order delay How to minimize the penalties?
• Product similarity How to produce with same
  setup? How to plan the production?
• Industrial lighting equipment With current line
  layout and operators
• How to modify the product or new product by using
  same facility and operators?
• How can the assembly lines be modified for
  production modification or new products.

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1.1 Scheduling Examples

• A machine shop has only stamping machine With
  different dye and a different processing time.
• How to generate weekly schedule to minimize the
  number of late shipments?
• How should these schedules be developed?
• Electronic assembly With burn-in (stress
  screen), reliability test
• How to group the PCBs into batch for testing?
• How to meet the due date?

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1.2 Scheduling on the shop floor

• Scheduling is a timetable for both jobs and
  machines, and play an important role in shop
  floor planning.
• Stocking the raw material before the work-order
  release time will add to the carrying cost.
• If materials are not available at release time,
  the jobs could be delayed and added to the
  operational cost.
• Capacity planning is an integral part of
  scheduling procedures. It refers to how much of a
  machines production time should be allocated to
  each job.
• To calculate the processing time for a job,
  considering setup time, unit processing time,
  machine speed, quality factors, and number of
  units needed.

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Scheduling Algorithm

• Data files for shop floor factors
• Workers shift schedules
• Machines and their characteristics
• Maintenance data
• Progress on processing jobs presently
• Current status of the machines (busy, idle,
  broken, need repair, under repair)
• Customer order data
• Priority setting (based on the production status
  daily)
• Hot, very hot
• Information from MRP system

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Methodology

• Practically, schedules are generated using
  scheduling algorithms or knowledge-based rules
  (If-Then).
• Scheduling algorithms tend to optimize a
  measuring criterion such as the minimizing
  deviations from due dates, tardiness penalty, or
  the maximum delay.
• The rule-, or knowledge-based tries to find a
  feasible solution under the operating
  environment. If machine A and operator X are
  available, Then load job Z

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1.2 Scheduling on the shop floor

• What is responsibility of the department
  production control?
• What is responsibility of the department of
  material control?
• What is the responsibility of process engineer?
• What is the responsibility of the production?
• What is responsibility of the department of
  quality control ?
• What is responsibility of the department of
  purchasing?

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Gantt chart
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1.3 Production planning terminology

• Single machine
• Server only one machine (server) available
• Work arriving jobs (work)
• Constraints each job has a processing time and
  a due date and may have other characteristics
  (priority).
• Penalty function deviating from the due date.
• Objective to sequence jobs on the machine with
  min penalty.

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1.3 Production planning terminology

• Flow Shop
• Server multiple machines in an identical
  sequence
• Work arriving jobs (work)
• Constraints processing time of each job on each
  machine may be different.
• Objective to minimize the time required for
  completion of all jobs, called the makespan.

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1.3 Production planning terminology

• Parallel machines
• Server a number of identical machines available
• Work jobs can be processed any one of the
  available machines.
• Constraints Jobs may have dependency. Next job
  in the sequence may not start until the previous
  job has been completely processed.
• Objective to minimize the makespan.

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1.3 Production planning terminology

• Job Shop
• Server there are different machines available in
  the shop
• Work a job may require some or all of these
  machines in specific sequence.
• Constraints a job can not use the same machine
  more than once.
• Objective may be to minimize the makespan or
  tardiness penalty.

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1.3 Production planning terminology

• Open Shop
• Server there are different machines available in
  the shop
• Work is similar to a job shop except that a job
  processed on the machine in any sequence the job
  needs.
• Constraints there is no operationally dependent
  sequence that a job must follow.
• Objective to minimize the makespan.

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1.3 Production planning terminology

• Dependent Shop
• Server there are different machines available in
  the shop
• Work a job shop environment in which the
  processing order of one or more jobs depends on
  the processing of other jobs.
• Objective to minimize the makespan.

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1.3 Production planning terminology

• Batch Processing
• Server machines with limited capacity
• Work jobs are processed in batches, each batch
  requiring certain processing time, and there may
  be a capacity limitation on how many jobs can be
  processed at one time.
• (such as a baking oven)
• Objective increasing the quantity of a batch and
  reduce the processing time.

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1.3 Production planning terminology

• Sequence-dependent setup times
• Server referred to be batch processing
• Work each job may belong to a type. If jobs of
  the same type are processed one after the other,
  then no additional setup is required. If a
  different type of job is processed, there is a
  setup cost.
• Constraints each job has a due date
• Objective to minimize the total tardiness
  penalty.

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1.3 Production planning terminology

• Assembly line
• Server a certain sequence of operations
• Work each job
• Objective to define workstations and assign
  tasks to these stations to achieve a certain
  production level and efficiency.
• Mixed-mode assembly line
• Server an assembly line
• Work similar product (not identical product)
• Constraints each product is with different task
  requirement and task times.

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Deterministic vs. Stochastic problems

• Deterministic problem All scheduling data are
  known.
• Stochastic problem The data are probabilistic in
  nature (randomness or fuzziness).
• Most scheduling problems are either deterministic
  or can be closely approximately by the
  deterministic models.
• The most common way to convert a stochastic
  problem into a deterministic problem is work with
  the average values.

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1.4 Scheduling Techniques

• Software Lindo, Simple, Arena
• Technique Group technique, Gantt Chart, CPM
• Heuristic approach
• Artificial Intelligence Fuzzy logic, Genetic
  Algorithm, Neural network, Artificial Immune
  System,