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DOM 102:DOM 102: Principles of Operations ManagementPrinciples of Operations Management
Operations SchedulingOperations Scheduling
Irwin/McGraw-Hill
© The McGraw-Hill Companies, Inc., 1998
©The McGraw-Hill Companies, Inc., 1998
Irwin/McGraw-Hill
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Operations Scheduling
Ordering the sequence of workflow through a system to achieve a given objective(s)
Will depend on the type of workflow involved thus;
– Job/Batch shop
– Flow shop
– Project
** Job systems are complex because
High variety, skilled manpower, random arrival of orders & use of process technology
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Work Center
Area in a business in which productive resources are organized and work is completed.
May be a single machine, a group of machines, or an area where a particular type of work is done. – Job shop (by function)– Flow (product)– Assembly line– GT cell
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Capacity and Scheduling
Infinite loading – work is assigned to a center based on what is needed over time
Finite loading – schedules in detail each resource using the setup and run time required for each order.
Forward scheduling Backward scheduling
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Typical Scheduling and Control Functions
Allocating orders, equipment, and personnel - Loading
Determining the sequence of order performance - Sequencing
Initiating performance of the scheduled work – Dispatching
Shop-floor control- reviewing status, controlling & expediting late & critical orders
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Work-Center Scheduling Objectives
Meet due dates
Minimize lead time
Minimize setup time or cost
Minimize work-in-process inventory
Maximize machine utilization
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Priority Rules for Job Sequencing
1. First-come, first-served (FCFS)
2. Shortest operating time
3. Earliest due date first
4. Earliest start date first (due date-lead time)
5. Least slack time remaining first
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Priority Rules for Job Sequencing
6. Least slack time remaining (per operation as opposed to per job) first
7. Smallest critical ratio first(due date-current date)/(number of days remaining)
8. Smallest queue ratio first(slack time remaining in schedule)/(planned remaining queue time)
9. Last come, first served
10. Random order
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Schedule Performance Measures
Meeting due dates of customers or downstream operations.
Minimizing the flow time (the time a job spends in the process).
Minimizing work-in-process inventory.
Minimizing idle time of machines or workers.
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Job Sequencing ExampleFirst-Come First-Served
Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)
A 4 5 4B 7 10 11C 3 6 14D 1 4 15
FCFS Schedule
Late?On-Time?
Orders submittedat beginning of week
Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)
A 4 5B 7 10C 3 6D 1 4 n-jobs on one machine
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Job Sequencing ExampleShortest Operating Time
Orders submittedat beginning of week
Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)
A 4 5B 7 10C 3 6D 1 4
Shortest Operating Time Schedule
Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)
D 1 4 1C 3 6 4A 4 5 8B 7 10 15
Late?On-Time?
n-jobs on one machine
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Job Sequencing ExampleLast-Come First-Served
Orders submittedat beginning of week
Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)
A 4 5B 7 10C 3 6D 1 4 n-jobs on one machine
Last-Come First-Served ScheduleJobs (in order Processing Due Date Flow Time
of arrival) Time (days) (days hence) (days)D 1 4 1C 3 6 4B 7 10 11A 4 5 15
Late?On-Time?
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Job Sequencing ExampleEarliest Due Date First
Orders submittedat beginning of week
Jobs (in order Processing Due Dateof arrival) Time (days) (days hence)
A 4 5B 7 10C 3 6D 1 4
Earliest Due Date First
Jobs (in order Processing Due Date Flow Timeof arrival) Time (days) (days hence) (days)
D 1 4 1A 4 5 5C 3 6 8B 7 10 15
Late?On-Time?
n-jobs on one machine
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Other Scheduling Techniques
1. Johnsons Rule – many jobs Vs Two machines sequentially. Shortest time for first machine do job first otherwise do the job last.
2. The Assignment Method – same No. of Jobs & machines. Make use of the Assignment Algorithm or Hungarian Method
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Shop-Floor ControlMajor Functions
1. Assigning priority of each shop order
2. Maintaining work-in-process quantity information
3. Conveying shop-order status information to the office
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Shop-Floor ControlMajor Functions
4. Providing actual output data for capacity control purposes
5. Providing quantity by location by shop order for WIP inventory and accounting purposes
6. Providing measurement of efficiency, utilization, and productivity of manpower and machines
Capacityrequirements
planning
Routingsand
work centers
Shop-floor
dispatching
Work-in-process
control
Input/output
analysis
Prioritizedqueuelists
Standardproduction
costs
Labor andequipment
requirements
Work orders
Work orderscheduling
Work ordertracking
Hewlett-Packard’sShop-Floor ControlSystem
16©The McGraw-Hill Companies, Inc., 1998
Irwin/McGraw-Hill
©The McGraw-Hill Companies, Inc., 1998
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Input/Output Control
Input Output
Planned input should never exceed planned output
Focuses attention on bottleneck work centers
WorkCenter
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Principles of Work-Center Scheduling
1. There is a direct equivalence between work flow and cash flow.
2. The effectiveness of any job shop should be measured by speed of flow through the shop.
3. Schedule jobs as a string, with process steps back to back.
4. A job once started should not be interrupted.
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Principles of Job Shop Scheduling
5. Speed of flow is most efficiently achieved by focusing on bottleneck work centers and jobs.
6. Reschedule every day.
7. Obtain feedback each day on jobs that are not completed at each work center.
8. Match work center input information to what the worker can actually do.
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Principles of Job Shop Scheduling
9. When seeking improvement in output, look for incompatibility between engineering design and process execution.
10. Certainty of standards, routings, and so forth is not possible in a job shop, but always work towards achieving it.
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Personnel Scheduling in Services
Scheduling consecutive days off
Scheduling daily work times
Scheduling hourly work times
