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Scheduling Chapter 19

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Learning Objectives Know what a Manufacturing Execution System production activity control is. Understand typical priority scheduling rules and the impact they have on scheduling performance measures. Recognize a simple job allocation procedure. Explain the issues considered in employee scheduling.

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**Manufacturing Execution Systems**

Manufacturing execution system (MES): an information system that schedules, dispatches, tracks, monitors, and controls production Real-time linkage to: MRP Product and process planning Systems that extend beyond the factory Service execution system (SES): an information system that links schedules, dispatches, tracks, monitors, and controls the customer’s encounters with the service organization LO 1

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Work Center A work center is an area in a business in which productive resources are organized and work is completed Can be a single machine, a group of machines, or an area where a particular type of work is done 3

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Loading Infinite loading: work is assigned to a work center based on what is needed No consideration to capacity Finite loading: schedules each resource using the setup and run time required for each order Determines exactly what will be done by each resource at every moment during the day LO 1

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Scheduling Forward scheduling: the system takes an order and schedules each operation that must be completed forward in time Can tell the earliest date an order can be completed Backward scheduling: starts with due date and schedules the required operations in reverse sequence Can tell when an order must be started in order to be done by a specific date LO 2

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**Typical Scheduling and Control Functions**

Allocating orders, equipment, and personnel Determining the sequence of order performance Initiating performance of the scheduled work Shop-floor control LO 2 5

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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 6

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Job Sequencing Sequencing: the process of determining the job order on machines or work centers Also known as priority sequencing Priority rules: the rules used in obtaining a job sequence Can be simple or complex Can use one or more pieces of information Common rules shown on next slide LO 2

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**Priority Rules for Job Sequencing**

1. First-come, first-served (FCFS) 2. Shortest operating time (SOT) 3. Earliest due date first (DDate) 4. Slack time remaining (STR) first 7

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**Priority Rules for Job Sequencing (Continued)**

5. Critical ratio (CR) 8

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**Example of Job Sequencing: First-Come First-Served**

Suppose you have the four jobs to the right arrive for processing on one machine What is the FCFS schedule? Do all the jobs get done on time? Answer: FCFS Schedule No, Jobs B, C, and D are going to be late 10

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**Example of Job Sequencing: Shortest Operating Time**

Suppose you have the four jobs to the right arrive for processing on one machine What is the SOT schedule? Do all the jobs get done on time? Answer: Shortest Operating Time Schedule No, Jobs A and B are going to be late 11

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**Example of Job Sequencing: Earliest Due Date First**

Suppose you have the four jobs to the right arrive for processing on one machine What is the earliest due date first schedule? Do all the jobs get done on time? Answer: Earliest Due Date First No, Jobs C and B are going to be late 13

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**Example of Job Sequencing: Critical Ratio Method**

Suppose you have the four jobs to the right arrive for processing on one machine What is the CR schedule? Do all the jobs get done on time? In order to do this schedule the CR’s have be calculated for each job. If we let today be Day 1 and allow a total of 15 days to do the work. The resulting CR’s and order schedule are: CR(A)=(5-4)/15=0.06 (Do this job last) CR(B)=(10-7)/15=0.20 (Do this job first, tied with C and D) CR(C)=(6-3)/15=0.20 (Do this job first, tied with B and D) CR(D)=(4-1)/15=0.20 (Do this job first, tied with B and C) No, but since there is a three-way tie, only the first job or two will be on time 13

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**Scheduling n Jobs on Two Machines**

Two or more jobs must be processed on two machines in a common sequence Wish to minimize the flow time from the beginning of the first job to the finish of the last job Use Johnson’s rule LO 2

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**Steps to Johnson’s Rule**

List the operation time for each job Select the shortest operation time If the shortest time is on the first machine, do first If the shortest time is on the second machine, do the job last For ties, do first Repeat 2-3 for each remaining job LO 2

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**Example of Job Sequencing: Johnson’s Rule**

Suppose you have the following five jobs with time requirements in two stages of production. What is the job sequence using Johnson’s Rule? Time in Hours Jobs Stage 1 Stage 2 A B C D 13

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**Scheduling a Set Number of Jobs on the Same Number of Machines**

Some work centers have enough machines to start all the jobs Here the issue is the particular assignment of individual jobs to individual machines Assignment method: a special case of the transportation method of linear programming There are n things to be distributed to n destinations Each thing assigned to one and only one destination Only one criterion can be used LO 2

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**Example : Assignment Method**

Assignment Matrix Showing Machine Processing Costs for Each Job LO 2

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**Example Step 1: Row Reduction**

LO 2

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**Example Step 2: Column Reduction**

LO 2

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**Example Step 3: Apply Line Test**

LO 2

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**Example Step 4: Additional Reduction**

LO 2

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**Example Optimal Solution**

LO 2

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**Example Optimal Assignment and Their Costs**

Job I to Machine E $3 Job II to Machine B 4 Job III to Machine C 2 Job IV to Machine D 5 Job V to Machine A 3 Total Cost $17 LO 2

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**Personnel Scheduling in Services**

Scheduling consecutive days off Scheduling daily work times Scheduling hourly work times LO 4 21

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Any Questions? Scheduling

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